The Universidad Nacional Autónoma de México is a public research university in Mexico City, Mexico that is the largest university in Latin America. UNAM was founded, in its modern form, on 22 September 1910 by Justo Sierra as a liberal alternative to its preceding institution the Royal and Pontifical University of Mexico . To this date, the National Autonomous University of Mexico owns and uses for academic activities the old buildings located in downtown Mexico City that once belonged to the old Royal and Pontifical University of Mexico UNAM's autonomy, granted in 1929, has given it the freedom to define its own curriculum and manage its own budget without interference from the government. This has had a profound effect on academic life at the university, which some claim boosts academic freedom and independence.The UNAM generates a number of different publications in diverse areas, such as mathematics, physics and history. It is also the only university in Mexico with Nobel Prize laureates among its alumni: Alfonso García Robles , Octavio Paz , and Mario Molina .Besides being the most recognized university in Latin America, its campus is one of the largest and most artistically detailed. It is a World Heritage site that was designed by some of Mexico's best-known architects of the 20th century. Murals in the main campus were painted by some of the most recognized artists in Mexican history such as Diego Rivera and David Alfaro Siqueiros. The UNAM is widely regarded by many university world rankings as the leading university of the Spanish-speaking world. Wikipedia.
National Autonomous University of Mexico | Date: 2015-09-25
The present invention provides osteogenic peptides derived from the Cementum-derived attachment protein (HACD1/CAP) and another derived from the Cementum Protein 1 (CEMP1) and pharmaceutical compositions of these peptides for the prevention and treatment of osteopenia and osteoporosis. These peptides increase bone mineral density in an osteoporotic model and without in vivo side effects, demonstrating clinical effectiveness in the prevention and treatment of osteopenia and osteoporosis in vivo as well as bone repair and/or regeneration.
Drescher J.,New York Medical College |
Drescher J.,New York University |
Cohen-Kettenis P.T.,VU University Amsterdam |
Reed G.M.,National Autonomous University of Mexico
The Lancet Psychiatry | Year: 2016
As part of the development of the eleventh revision of the International Classification of Diseases (ICD-11), WHO appointed a Working Group on Sexual Disorders and Sexual Health to recommend changes necessary in the classification of mental and behavioural disorders in ICD-10 that are related to sexuality and gender identity. This Personal View focuses on the Working Group's proposals to include the diagnosis gender incongruence of childhood in ICD-11 and to move gender incongruence of childhood out of the mental and behavioural disorders chapter of ICD-11. We outline the history of ICD and DSM child gender diagnoses, expert consensus, knowledge gaps, and controversies related to the diagnosis and treatment of extremely gender-variant children. We argue that retaining the gender incongruence of childhood category is justified as a basis to structure clinical care and to ensure access to appropriate services for this vulnerable population, which provides opportunities for education and informed consent, the development of standards and pathways of care to help guide clinicians and family members, and a basis for future research efforts. © 2016 Elsevier Ltd.
Valiente-Banuet A.,National Autonomous University of Mexico
Oikos | Year: 2011
The structure of the real ecological networks is determined by multiple factors including neutral processes, the relative abundances of species, and the phylogenetic relationships of the interacting species. Previous efforts directed to analyze the relative contribution of these factors to network structure have not been able to fully incorporate the phylogenetic relationships between the interacting species. This limitation stems from the difficulty of predicting interaction probabilities based on the independent phylogenies of interacting species (e.g. plants and animals). This is not the case for plant facilitation networks, where nurse and facilitated species evolve in a common phylogeny (e.g. spermatophyte phylogeny). Facilitation networks are characterized by both high nestedness and interactions tending to occur between distantly related nurse and facilitated species. We evaluate the relative contribution of phylogeny and species abundance to explain both the frequency of observed interactions as well as the network structure in a real plant facilitation network at Tehuacán Valley (central Mexico). Our results show that the combined effects of phylogeny and species abundance were, by far, the best predictors of both the frequency of the interactions observed in this community and the parameters (nestedness and connectance) defining the network structure. This finding indicates that species interact proportionally to both their phylogenetic distances and abundances simultaneously. In short, the phylogenetic history of species, acting together with other ecological factors, has a pervasive influence in the structure of ecological networks. © 2011 The Authors. Oikos © 2011 Nordic Society Oikos.
Melo F.P.L.,Federal University of Pernambuco |
Arroyo-Rodriguez V.,National Autonomous University of Mexico |
Fahrig L.,Carleton University |
Martinez-Ramos M.,National Autonomous University of Mexico |
Tabarelli M.,Federal University of Pernambuco
Trends in Ecology and Evolution | Year: 2013
With the decreasing affordability of protecting large blocks of pristine tropical forests, ecologists have staked their hopes on the management of human-modified landscapes (HMLs) to conserve tropical biodiversity. Here, we examine key forces affecting the dynamics of HMLs, and propose a framework connecting human disturbances, land use, and prospects for both tropical biodiversity and ecosystem services. We question the forest transition as a worldwide source of new secondary forest; the role played by regenerating (secondary) forest for biodiversity conservation, and the resilience of HMLs. We then offer a conceptual model describing potential successional trajectories among four major landscape types (natural, conservation, functional, and degraded) and highlight the potential implications of our model in terms of research agendas and conservation planning. © 2013 Elsevier Ltd.
Erler J.,National Autonomous University of Mexico |
Langacker P.,Institute for Advanced Study
Physical Review Letters | Year: 2010
There has been recent renewed interest in the possibility of additional fermion generations. At the same time there have been significant changes in the relevant electroweak precision constraints, in particular, in the interpretation of several of the low energy experiments. We summarize the various motivations for extra families and analyze them in view of the latest electroweak precision data. © 2010 The American Physical Society.
Burton A.,University of Strasbourg |
Muller J.,Agency for Science, Technology and Research Singapore |
Tu S.,Howard Hughes Medical Institute |
Padilla-Longoria P.,National Autonomous University of Mexico |
And 3 more authors.
Cell Reports | Year: 2013
Cell plasticity or potency is necessary for the formation of multiple cell types. The mechanisms underlying this plasticity are largely unknown. Preimplantation mouse embryos undergo drastic changes in cellular potency, starting with the totipotent zygote through to the formation of the pluripotent inner cell mass (ICM) and differentiated trophectoderm in the blastocyst. Here, we set out to identify and functionally characterize chromatin modifiers that define the transitions of potency and cell fate in the mouse embryo. Using a quantitative microfluidics approach in single cells, we show that developmental transitions are marked by distinctive combinatorial profiles of epigenetic modifiers. Pluripotent cells of the ICM are distinct from their differentiated trophectoderm counterparts. We show that PRDM14 is heterogeneously expressed in 4-cell-stage embryos. Forced expression of PRDM14 at the 2-cell stage leads to increased H3R26me2 and can induce a pluripotent ICM fate. Our results shed light on the epigenetic networks that govern cellular potency and identity invivo
Znidaric M.,National Autonomous University of Mexico |
Znidaric M.,University of Ljubljana
Physical Review Letters | Year: 2011
We analytically and numerically study spin transport in a one-dimensional Heisenberg model in linear-response regime at infinite temperature. It is shown that as the anisotropy parameter Δ is varied spin transport changes from ballistic for Δ<1 to anomalous at the isotropic point Δ=1, to diffusive for finite Δ>1, ending up as a perfect isolator in the Ising limit of infinite Δ. Using perturbation theory for large Δ a quantitative prediction is made for the dependence of diffusion constant on Δ. © 2011 American Physical Society.
Gomez-Aparicio L.,CSIC - Institute of Natural Resources and Agriculture Biology of Seville |
Valiente-Banuet A.,National Autonomous University of Mexico
Proceedings of the Royal Society B: Biological Sciences | Year: 2012
Biotic interactions assembling plant communities can be positive (facilitation) or negative (competition) and operate simultaneously. Facilitative interactions and posterior competition are among the mechanisms triggering succession, thus representing a good scenario for ecological restoration. As distantly related species tend to have different phenotypes, and therefore different ecological requirements, they can coexist, maximizing facilitation and minimizing competition. We suggest including phylogenetic relatedness together with phenotypic information as a predictor for the net effects of the balance between facilitation and competition in nurse-based restoration experiments. We quantify, by means of a Bayesian meta-analysis of nurse-based restoration experiments performed worldwide, the importance of phylogenetic relatedness and life-form disparity in the survival, growth and density of facilitated plants. We find that the more similar the life forms of neighbouring plants are the greater the positive effect of phylogenetic distance is on survival and density. This result suggests that other characteristics beyond life form are also contained in the phylogeny, and the larger the phylogenetic distance, the less is the niche overlap, and therefore the less is the competition. As a general rule, we can maximize the success of the nurse-based practices by increasing life-form disparity and phylogenetic distances between the neighbour and the facilitated plant. © 2012 The Royal Society.
Znidaric M.,National Autonomous University of Mexico |
Znidaric M.,University of Ljubljana |
Pineda C.,National Autonomous University of Mexico |
Garcia-Mata I.,CONICET |
Garcia-Mata I.,Laboratory TANDAR
Physical Review Letters | Year: 2011
The channel induced by a complex system interacting strongly with a qubit is calculated exactly under the assumption of randomness of its eigenvectors. The resulting channel is represented as an isotropic time-dependent oscillation of the Bloch ball, leading to non-Markovian behavior, even in the limit of infinite environments. Two contributions are identified: one due to the density of states and the other due to correlations in the spectrum. Prototype examples, one for chaotic and the other for regular dynamics are explored. © 2011 American Physical Society.
Valiente-Banuet A.,National Autonomous University of Mexico
Annals of Botany | Year: 2012
BackgroundPlant facilitation occurs when the presence of a plant (i.e. a nurse plant) modifies the environment, making it more favourable for the establishment and survival of other species (i.e. facilitated plants), which can germinate and grow nearby. Facilitative associations can be maintained or turned into competition as the facilitated seedling grows. According to the competition-relatedness hypothesis that suggests that closely related species tend to compete more, facilitation turns into competition between phylogenetically close species. However, some examples of facilitation between congeneric species, which are supposed to be closely related species, have been found in nature.ScopeIn this work, some examples of congeneric facilitation and subsequent coexistence are reviewed and an attempt is made to explain those exceptions to the competition-relatedness hypothesis.ConclusionsTwo mechanisms are proposed that can switch the facilitation-competition balance: trait divergence and indirect interactions. When traits have diverged within the genus, the niche overlap is reduced and competition relaxed, thus allowing the coexistence of congeneric species. The presence of third interplayers (mycorrhizal fungi, seed dispersers, pollinators or pathogens) participating in the interaction between plants can alleviate the competition or enhance the reproduction and allow the coexistence of species that could not coexist in their absence. © 2012 The Author. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved.
Bravo A.,National Autonomous University of Mexico |
Likitvivatanavong S.,University of California at Riverside |
Gill S.S.,University of California at Riverside |
Soberon M.,National Autonomous University of Mexico
Insect Biochemistry and Molecular Biology | Year: 2011
Bacillus thuringiensis (Bt) bacteria are insect pathogens that rely on insecticidal pore forming proteins known as Cry and Cyt toxins to kill their insect larval hosts. At least four different non-structurally related families of proteins form the Cry toxin group of toxins. The expression of certain Cry toxins in transgenic crops has contributed to an efficient control of insect pests resulting in a significant reduction in chemical insecticide use. The mode of action of the three domain Cry toxin family involves sequential interaction of these toxins with several insect midgut proteins facilitating the formation of a pre-pore oligomer structure and subsequent membrane insertion that leads to the killing of midgut insect cells by osmotic shock. In this manuscript we review recent progress in understanding the mode of action of this family of proteins in lepidopteran, dipteran and coleopteran insects. Interestingly, similar Cry-binding proteins have been identified in the three insect orders, as cadherin, aminopeptidase-N and alkaline phosphatase suggesting a conserved mode of action. Also, recent data on insect responses to Cry toxin attack is discussed. Finally, we review the different Bt based products, including transgenic crops, that are currently used in agriculture. © 2011 Elsevier Ltd.
Palomar M.,National Autonomous University of Mexico |
Covarrubias A.A.,National Autonomous University of Mexico
Scientific Reports | Year: 2013
The declining water availability for agriculture is becoming problematic for many countries. Therefore the study of plants under water restriction is acquiring extraordinary importance. Botanists currently follow the dehydration of plants comparing the fresh and dry weight of excised organs, or measuring their osmotic or water potentials; these are destructive methods inappropriate for in-vivo determination of plants' hydration dynamics. Water is opaque in the terahertz band, while dehydrated biological tissues are partially transparent. We used terahertz spectroscopy to study the water dynamics of Arabidopsis thaliana by comparing the dehydration kinetics of leaves from plants under well-irrigated and water deficit conditions. We also present measurements of the effect of dark-light cycles and abscisic acid on its water dynamics. The measurements we present provide a new perspective on the water dynamics of plants under different external stimuli and confirm that terahertz can be an excellent non-contact probe of in-vivo tissue hydration.
Merchant H.,National Autonomous University of Mexico |
Kikuchi Y.,Northumbria University |
Hattori Y.,Kyoto University |
ten Cate C.,Leiden University
Philosophical Transactions of the Royal Society B: Biological Sciences | Year: 2015
In the introduction to this theme issue, Honing et al. suggest that the origins of musicality—the capacity that makes it possible for us to perceive, appreciate and produce music—can be pursued productively by searching for components of musicality in other species. Recent studies have highlighted that the behavioural relevance of stimuli to animals and the relation of experimental procedures to their natural behaviour can have a large impact on the type of results that can be obtained for a given species. Through reviewing laboratory findings on animal auditory perception and behaviour, as well as relevant findings on natural behaviour, we provide evidence that both traditional laboratory studies and studies relating to natural behaviour are needed to answer the problem of musicality. Traditional laboratory studies use synthetic stimuli that provide more control than more naturalistic studies, and are in many ways suitable to test the perceptual abilities of animals. However, naturalistic studies are essential to inform us as to what might constitute relevant stimuli and parameters to test with laboratory studies, or why we may or may not expect certain stimulus manipulations to be relevant. These two approaches are both vital in the comparative study of musicality. © 2015 The Authors.
Valiente-Banuet A.,National Autonomous University of Mexico
Frontiers in Ecology and the Environment | Year: 2013
Highly biodiverse ecosystems worldwide are rapidly losing species diversity as a result of human overexploitation of natural resources. However, it is not known whether there is a critical threshold of species loss at which an ecosystem fails to recover, leading to its collapse. By combining multiple ecological networks (including facilitation, pollination, and seed dispersal) into a realistic scenario, we document how an ecosystem may collapse through synergistic disruptions to those networks. Although the interdependence of different ecological networks is indicative of ecosystem fragility and low resilience, our findings may improve environmental remediation efforts, thereby helping to bridge the gap between the disciplines of ecology and conservation biology. © The Ecological Society of America.
Moreno J.A.,National Autonomous University of Mexico |
Fridman L.,National Autonomous University of Mexico
Automatica | Year: 2013
An arbitrary order differentiator that, in the absence of noise, converges to the true derivatives of the signal after a finite time independent of the initial differentiator error is presented. The only assumption on a signal to be differentiated (n - 1) times is that its n-th derivative is uniformly bounded by a known constant. The proposed differentiator switches from a newly designed uniform differentiator to the classical High-Order Sliding Mode (HOSM) differentiator. The Uniform part drives the differentiation error trajectories into a compact neighborhood of the origin in a time that is independent of the initial differentiation error. Then, the HOSM differentiator is used to bring the differentiation error to zero in finite-time. © 2013 Elsevier Ltd. All rights reserved.
Fridman L.,National Autonomous University of Mexico |
Moreno J.A.,National Autonomous University of Mexico
Automatica | Year: 2013
A novel methodology for designing multivariable High-Order Sliding-Mode (HOSM) controllers for disturbed feedback linearizable nonlinear systems is introduced. It provides for the finite-time stabilization of the origin of the state-space by using output feedback. Only the additional assumptions of algebraic strong observability and smooth enough matched disturbances are required. The control problem is solved in two consecutive steps: firstly, designing an observer based on the measured output and, secondly, designing of a full-state controller computed from a new virtual output with vector relative degree. The introduced notion of algebraic strong observability allows recovering the state of the system using the measured output and its derivatives. By estimating the required derivatives through the HOSM differentiator, a finite-time convergent observer is constructed. © 2013 Elsevier Ltd. All rights reserved.
Tye Pettaya D.,Pennsylvania State University |
Tye Pettaya D.,University of Delaware |
Whama D.C.,Pennsylvania State University |
Smith R.T.,National Autonomous University of Mexico |
And 3 more authors.
Proceedings of the National Academy of Sciences of the United States of America | Year: 2015
Human-induced environmental changes have ushered in the rapid decline of coral reef ecosystems, particularly by disrupting the symbioses between reef-building corals and their photosymbionts. However, escalating stressful conditions enable some symbionts to thrive as opportunists. We present evidence that a stress-tolerant "zooxanthella" from the Indo-Pacific Ocean, Symbiodinium trenchii, has rapidly spread to coral communities across the Greater Caribbean. In marked contrast to populations from the Indo-Pacific, Atlantic populations of S. trenchii contained exceptionally low genetic diversity, including several widespread and genetically similar clones. Colonies with this symbiont tolerate temperatures 1-2 ° C higher than other host-symbiont combinations; however, calcification by hosts harboring S. trenchii is reduced by nearly half, compared with those harboring natives, and suggests that these new symbioses are maladapted. Unforeseen opportunism and geographical expansion by invasive mutualistic microbes could profoundly influence the response of reef coral symbioses to major environmental perturbations but may ultimately compromise ecosystem stability and function. © 2015, National Academy of Sciences. All rights reserved.
Pacheco-Alvarez D.,Panamerican University of Mexico |
Gamba G.,National Autonomous University of Mexico
Cellular Physiology and Biochemistry | Year: 2011
The with-no-lysine kinase 3 (WNK3) is a serine/threonine kinase that modulates the activity of the electroneutral cation-coupled chloride cotransporters (CCC). Using the Xenopus laevis oocyte heterologous expression system, it has been shown that WNK3 activates the Na +-coupled chloride cotransporters NKCC1, NKCC2, and NCC and inhibits the K +-coupled chloride cotransporters KCC1 through KCC4. Interestingly, the effect of catalytically inactive WNK3 is opposite to that of wild type WNK3: inactive WNK3 inhibits NKCCs and activates KCCs. In doing so, wild type and catalytically inactive WNK3 bypass the tonicity requirement for activation/inhibition of the cotransporter. Thus, WNK3 modulation of the electroneutral cotransporters promotes Cl - influx and prevents Cl - efflux, thus fitting the profile for a putative "Cl --sensing kinase". Other kinases that potentially have these properties are the Ste20-type kinases, SPAK/OSR1, which become phosphorylated in response to reductions in intracellular chloride concentration and regulate the activity of NKCC1. It has been demonstrated that WNKs lie upstream of SPAK/OSR1 and that the activity of these kinases is activated by phosphorylation of threonines in the T-loop by WNKs. It is possible that a protein phosphatase is also involved in the WNK3 effects on its associated cotransporters because activation of KCCs and inhibition of NKCCs by inactive WNK3 can be prevented by known inhibitors of protein phosphatases, such as calyculin A and cyclosporine, suggesting that a protein phosphatase is also involved in the protein complex. Copyright © 2011 S. Karger AG, Basel.
Rosales R.,Virolab |
Rosales C.,National Autonomous University of Mexico
World Journal of Clinical Oncology | Year: 2014
Human papillomaviruses (HPVs) are a large family of double strand DNA viruses comprising more than 180 types. Infection with HPV is very common and it is associated with benign and malignant proliferation of skin and squamous mucosae. Many HPVs, considered lowrisk such as HPV 6 and 11, produce warts; while highrisk viruses, such as HPVs 16, 18, 31, 33, 35, 39, 45, 51, 52, 56, and 58, induce tumors. About 5% of all cancers in men and women are associated with HPV infection. Because there are not antiviral drugs for HPV infection, current therapies for low-risk HPV infections involve physical removal of the lesion by cryotherapy, trichloracetic acid, laser, or surgical removal. Surgical procedures are effective in the treatment of precancerous lesions, however after these procedures, many recurrences appear due to new re-infections, or to failure of the procedure to eliminate the HPV. In addition, HPV can inhibit recognition of malignant cells by the immune system, leading to the development of cancer lesions. When this occurs, radiotherapy and chemotherapy are then used. Unfortunately, about 50% of the HPV-cancer patients still die. In the past decade, a better knowledge of the natural history of the virushost interaction and of the immune response against this viral infection has brought new therapeutic strategies geared to modulate the immune system to generate an efficient virus-specific cytotoxic response. Novel HPV protein-expressing vaccines have shown some significant clinical efficacy and systemic HPV-specific cytotoxic T cell responses. This review will describe the current status of the several therapeutic strategies used to treat HPV-induced lesions, and discuss the various new therapies now being tested. © 2014 Baishideng Publishing Group Inc. All rights reserved.
Jesenko S.,University of Ljubljana |
Znidaric M.,University of Ljubljana |
Znidaric M.,National Autonomous University of Mexico
Physical Review B - Condensed Matter and Materials Physics | Year: 2011
We study finite-temperature magnetization transport in a one-dimensional anisotropic Heisenberg model, focusing in particular on the gapped phase. Using numerical simulations by two different methods, a propagation of localized wave packets and a study of nonequilibrium steady states of a master equation in a linear-response regime, we conclude that the transport at finite temperatures is diffusive. With decreasing temperature the diffusion constant increases, possibly exponentially fast. This means that at low temperatures the transition from ballistic to asymptotic diffusive behavior happens at very long times. We also study dynamics of initial domain-wall-like states, showing that on the attainable time scales they remain localized. © 2011 American Physical Society.
Valiente-Banuet A.,National Autonomous University of Mexico
New Phytologist | Year: 2012
• Ecological network theory predicts that in mutualistic systems specialists tend to interact with a subset of species with which generalists interact (i.e. nestedness). Approaching plant-arbuscular mycorrhizal fungi (AMF) association using network analyses will allow the generality of this pattern to be expanded to the ubiquitous plant-AMF mutualism. • Based on certain plant-AMF specificity recently suggested, networks are expected to be nested as a result of their mutualistic nature, and modular, with certain species interacting more tightly than others. Network analyses were used to test for nestedness and modularity and to compare the different contribution of plant and AMF to the overall nestedness. • Plant-AMF networks share general network properties with other mutualisms. Plant species with few AMFs in their roots tend to associate with those AMFs recorded in most plant species. AMFs present in a few plant species occur in plant species sheltering most AMF (i.e. nestedness). This plant-AMF network presents weakly interlinked subsets of species, strongly connected internally (i.e. modularity). Both plants and AMF show a nested structure, although AMFs have lower nestedness than plants. • The plant-AMF interaction pattern is interpreted in the context of how plant-AMF associations can be underlying mechanisms shaping plant community assemblages. © 2012 The Authors. New Phytologist © 2012 New Phytologist Trust.
Znidaric M.,National Autonomous University of Mexico |
Znidaric M.,University of Ljubljana
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2011
We study a one-dimensional XX chain under nonequilibrium driving and local dephasing described by the Lindblad master equation. The analytical solution for the nonequilibrium steady state found for particular parameters in a previous study is extended to arbitrary coupling constants, driving, and a homogeneous magnetic field. All one-, two-, and three-point correlation functions are explicitly evaluated. It is shown that the nonequilibrium stationary state is not Gaussian. Nevertheless, in the thermodynamic and weak-driving limit it is only weakly correlated and can be described by a matrix product operator ansatz with matrices of fixed dimension 4. A nonequilibrium phase transition at zero dephasing is also discussed. It is suggested that the scaling of the relaxation time with the system size can serve as a signature of a nonequilibrium phase transition. © 2011 American Physical Society.
Lee W.H.,National Autonomous University of Mexico |
Ramirez-Ruiz E.,University of California at Santa Cruz |
De Van Ven G.,Max Planck Institute for Astronomy |
De Van Ven G.,Institute for Advanced Study
Astrophysical Journal | Year: 2010
We present a detailed assessment of the various dynamical pathways leading to the coalescence of compact objects in globular clusters (GCs) and Short Gamma-ray Burst (SGRB) production. We consider primordial binaries, dynamically formed binaries (through tidal two-body and three-body exchange interactions), and direct impacts of compact objects (WD/NS/BH). Here, we show that if the primordial binary fraction is small, close encounters dominate the production rate of coalescing compact systems. We find that the two dominant channels are the interaction of field neutron stars (NSs) with dynamically formed binaries and two-body encounters. Under such conditions, we estimate the redshift distribution and host galaxy demographics of SGRB progenitors, and find that GCs can provide a significant contribution to the overall observed rate. Regarding the newly identified channel of close stellar encounters involving WD/NS/BH, we have carried out precise modeling of the hydrodynamical evolution, giving us a detailed description of the resulting merged system. Our calculations show that there is in principle no problem in accounting for the global energy budget of a typical SGRB. The particulars of each encounter, however, are variable in several aspects and can lead to interesting diversity. First and most importantly, the characteristics of the encounter are highly dependent on the impact parameter. This is in contrast to the merger scenario, where the masses of the compact objects dictate a typical length and luminosity scale for SGRB activity. Second, the nature of the compact star itself can produce very different outcomes. Finally, the presence of tidal tails in which material will fall back onto the central object at a later time is a robust feature of the present set of calculations. The mass involved in these structures is considerably larger than for binary mergers. It is thus possible to account generically in this scenario for a prompt episode of energy release, as well as for activity many dynamical time scales later. © 2010. The American Astronomical Society. All rights reserved. Printed in the U.S.A.
Drigo R.,Localita Collina 5 |
Ghilardi A.,National Autonomous University of Mexico |
Masera O.,National Autonomous University of Mexico
Nature Climate Change | Year: 2015
Over half of all wood harvested worldwide is used as fuel, supplying ∼9% of global primary energy. By depleting stocks of woody biomass, unsustainable harvesting can contribute to forest degradation, deforestation and climate change. However, past efforts to quantify woodfuel sustainability failed to provide credible results. We present a spatially explicit assessment of pan-tropical woodfuel supply and demand, calculate the degree to which woodfuel demand exceeds regrowth, and estimate woodfuel-related greenhouse-gas emissions for the year 2009. We estimate 27-34% of woodfuel harvested was unsustainable, with large geographic variations. Our estimates are lower than estimates from carbon offset projects, which are probably overstating the climate benefits of improved stoves. Approximately 275 million people live in woodfuel depletion 'hotspots' - concentrated in South Asia and East Africa - where most demand is unsustainable. Emissions from woodfuels are 1.0-1.2 Gt CO2e yr- (1.9-2.3% of global emissions). Successful deployment and utilization of 100 million improved stoves could reduce this by 11-17%. At US$11 per tCO2e, these reductions would be worth over US$1 billion yr - in avoided greenhouse-gas emissions if black carbon were integrated into carbon markets. By identifying potential areas of woodfuel-driven degradation or deforestation, we inform the ongoing discussion about REDD-based approaches to climate change mitigation.
Agency: Cordis | Branch: FP7 | Program: CP-FP | Phase: NMP.2010.1.2-4 | Award Amount: 5.34M | Year: 2010
The aim of the present project is to explore the properties and possible applications of bismuth and bismuth based compounds when they are synthesized at the nanometric scale. This approach is motivated by the uncommon but advantageous properties of bismuth which, in part, have been exploited for many years. However, there are many unexplored possibilities and with the advent of nanotechnology new prospectives may be expected. We believe this approach will lead to new and high-tech applications of bismuth based materials, adding new value to one of the major mining products of Mexico (second most important world production) and boost the related economic benefits which at present are low. In the project, we have integrated complementary research groups from Mexico and Europe covering interdisciplinary fields. In the thematic work-packages, research groups working on the synthesis of the nanostructured materials will collaborate with others doing the physical-chemical materials characterization and the application development. The materials include Bi, Bi2O3 and Bi2S3 nanostructures, Bismuth metal oxide nanostructured ceramics and thin films, bismuth-based nanocomposites where Bi constitutes the nanoscale inclusion and the matrices varied from ceramics, polymers or glasses, and finally Bi superconductors. Extensive chemical and structural characterization will be required to correlate the synthesis parameters with the physical properties. Finally, the project includes the physical evaluation focused on the optical, electrical, magnetic, ferroelectric, etc. properties, according to the proposed applications. The time scale of the project is sufficient for the preparation of masters degree students and the initial years of doctorate students. These students will work in a very academic-rich environment and at the same time have contact with the industrial partners in the project, some of which are leaders in the development of Bi-based commercial products.
Agency: Cordis | Branch: FP7 | Program: CSA | Phase: INFRA-2007-1.2.3;INFRA-2007-1.2-03 | Award Amount: 5.11M | Year: 2008
EELA-2 aims to build, on the current EELA e-Infrastructure, a high capacity, production-quality, scalable Grid Facility providing round-the-clock, worldwide access to distributed computing, storage and network resources for a wide spectrum of applications from European and Latin American scientific communities. The project will provide an empowered Grid Facility with versatile services fulfilling application requirements and ensure the long-term sustainability of the e-Infrastructure beyond the term of the project. The specific EELA-2 objectives are: - Build a Grid Facility by: Expanding the current EELA e-Infrastructure to consist of more production sites mobilising more computing nodes and more storage space, at start of the project and to further grow storage over the duration of the project; Providing, in collaboration with related projects (e.g. EGEE), the full set of Grid Services needed by all types of scientific applications; Supporting applications various types (from classical off-line data processing up to control and data acquisition of scientific instruments), selected against well defined criteria (including grid added value, suitability for Grid deployment, outreach/potential impact); - Ensure the Grid Facility sustainability: Through the already established and new contacts with policy/decision makers, collaborating with RedCLARA and NRENs and supporting the ongoing creation of e-Science Initiatives and/or National Grid initiatives (NGI). Building the support of the e-Infrastructure to provide a complete set of Global Services from a Central Operation Centre and to pave the way for the creation of Regional Operation Centres in Latin America: Attracting new applications; Making available knowledge of EELA-2 Grid Facility to all potential users, developers, and decision makers through an extensive Training and Dissemination program; Creating knowledge repositories federated with the EGEE ones.
Agency: Cordis | Branch: FP7 | Program: CSA-CA | Phase: KBBE.2010.4-04 | Award Amount: 1.15M | Year: 2011
The main objective of BIO CIRCLE 2 is to foster the knowledge base about FP7 FAFB & the networking capacities of Third Country researchers in order to reinforce their participation in FP7 projects. 3 project goals are distinguished: 1.Disseminate information effectively to Third Country researchers; 2.Organise information days and training for Third Country researchers; 3.Provide Third Country researchers with efficient networking opportunities. 5 European plus 16 Third Country partners (International Cooperation Partner Countries ICPC and Industrialised Countries) will all be involved in the activities. Apart from Kazakhstan and Thailand all involved countries (and the African continent represented by FARA) have signed a bilateral S&T agreement with the EU. The expected impacts are supported by various activities: Enhanced awareness of the Third Country researchers on the FP7 FAFB: WP2 will develop the regional strategies for the Third Country partners. Increased Third Country researchers participation in EU projects: WP3 will organise at least 2 trainings for Third Country researchers at national and regional level, 3 trainings of Third Country BIO NCPs and the organisation of 1 Regional Event per World Region. Strengthened collaborations with Third Countries signatories of bilateral S&T agreements with the EU: WP4 will implement networking activities for Third Country researchers, including brokerage events and working visits of Third Country researchers to EU research institutes and vice versa. Finally WP5 on dissemination activities will increase the awareness of European researchers about the international cooperation in FP7 FAFB. The impact of the activities will be further maximised by: 1.involving other countries that are not partners through a regional approach; 2.linking the BIO CIRCLE 2 activities to the activities of related INCO projects; 3.involving industrialised countries that are global S&T leaders in FAFB related research.
Agency: Cordis | Branch: FP7 | Program: CPCSA | Phase: INFRA-2010-1.2.3 | Award Amount: 2.76M | Year: 2010
The GISELA objective is to guarantee the long-term sustainability of the European Latin American e-Infrastructure and thus ensure the continuity and enhancement of the Virtual Research Communities (VRC) using it. The project will focus on:\n\tImplementing the Latin American Grid Initiative (LGI) sustainability model rooted on National Grid Initiatives (NGI) or Equivalent Domestic Grid Structures (EDGS), in association with CLARA and collaborating with EGI;\n\tProviding VRCs with the e-Infrastructure and Application-related Services required to improve the effectiveness of their research, addressing both:\no\tCurrent EELA-2 small User Communities;\no\tLarger VRCs through Specialised Support Centres (SSCs).\nThe GISELA mission is twofold:\n- Ensure the sustainability of the EU-LA e-Infrastructure\nThe sustainability of the EU part of the e-Infrastructure being cared of by EGI, GISELA will concentrate on its LA component. The tasks, at each level of the e-Infrastructure are:\n\tInstitution: Get all Services fully operational in the Resource Centre (RC);\n\tCountry: Implement all Grid Operation Centre (GOC) Services;\n\tContinent: Implement all Grid & Network Support Centres (GSC, NSC) Services;\n\tSupport a catchall GOC.\n- Support Virtual Research Communities\nThe support will encompass:\n\tUser Support:\no\tProvide access to the EU-LA Infrastructure to VOs represented in GISELA (HEP, Life Sciences, Earth Sciences, etc.);\no\tPublicise and support the GISELA e-Infrastructure and Application Services;\no\tCollaborate with VRCs or SSCs to the development of integrated services (e.g. gateways).\n\tTraining & Dissemination activities\no\tOrganisation of tutorials for single users and VRCs;\no\tCoordinate dissemination actions, workshops, Conferences;\no\tProduce dissemination material.\nGrid Services for VRCs will be provided by CLARA on the basis of a business plan using a Life Cycle Product Management (LCPM) approach.
Agency: Cordis | Branch: H2020 | Program: RIA | Phase: INT-12-2015 | Award Amount: 2.60M | Year: 2016
EULAC Focus addresses the whole set of topics included in the Call. It delivers a significant contribution to the improvement of EUCELAC relations through a better understanding of the three dimensions selected by the call: cultural, scientific and social. The main objective is that of giving focus to these three dimensions of EUCELAC relations, with a view to determining synergies and cross-fertilization, as well as identifying asymmetries in bi-lateral and bi-regional relations. Research is focused on areas crucial to explain the current state of relations between EU and LAC, and will be pursued at two levels: a) research activities; b) strategic set of recommendations. In order to guarantee high impact, the research is pursued in six interdisciplinary WPs, organized matricially. Three are horizontal : Cross-cutting pathways, Towards a common vision for EUCELAC and Dissemination and outreach. The other three are thematic/vertical: Cultural, Scientific and Social Dimension, and not only intersect the horizontal WPs but also interact between them. To achieve the objectives, the project is organized by the multidisciplinary and well balanced consortium of19 members from 15 counties. The consortium represents a unique group of highly competent and experienced institutions, composed specifically for the purpose of this project,comprising, in both regions, Gov Research Agencies, Research institutes, Universities, University Association, and two International European LA Organizations active in analytical and policy oriented research and dissemination. EULAC Focus builds upon the outcomes of prior mapping conducted at the bi-regional level and will facilitate access to end-users, as well as feeding into the work of the EU-LAC Foundation and informing bi-regional networking activities of the JIRI and T-APs work. The number of partners has been carefully defined to ensure project goals and proper diversity, while allowing for efficient project management.
Agency: Cordis | Branch: H2020 | Program: RIA | Phase: LCE-11-2015 | Award Amount: 6.00M | Year: 2016
The business model currently under development for second generation ethanol is a replication of the model used for first generation which is plants with massive annual production capacities. Such high production rates require high capital investment and huge amounts of biomasses (250-350,000 tons per year) concentrated in small radius catchment areas to afford transportation costs (50 km). Under such conditions, opportunities for installing plants in most rural areas in Europe and worldwide are scarce. The objective of the project is to develop an alternative solution for the production of 2G ethanol, competitive at smaller industrial scale and therefore applicable to a large amount of countries, rural areas and feedstocks. The target is to reach technical, environmental and economical viabilities in production units processing at least 30,000 tons equivalent dry biomass per year. This approach will definitely enlarge the scope of biomass feedstocks exploitable for the production of biofuel and create better conditions for the deployment of production sites, to the benefit of rural areas in Europe and worldwide. The main concept underpinning the project relies on a new biomass conversion process able to run all the steps from the pretreatment of the raw material to the enzymatic pre-hydrolysis in one-stage-reactor under mild operating conditions. This new process recently developed to TRL 4, offers the most integrated and compact solution for the conversion of lignocellulosic biomass for the production of ethanol developed so far, and it will lead to reduced capital and operation expenditures. The new process will be developed to TRL 5 in the project with the goal of achieving satisfactory technical, environmental and economical performances in relevant operation environment. The project will investigate and select business cases for installations of demonstration/first-of-a-kind small-scale industrial plants in different European and Latino American countries.
National Polytechnic Institute of Toulouse and National Autonomous University of Mexico | Date: 2013-06-07
A method of treating a solid lignocellulosic material (10) in which the solid lignocellulosic material (10) is subjected to a treatment, called a mechano-chemical treatment (1), of mixing and chemical degradation of the solid lignocellulosic material (10) so as to form an intermediate composition having a hydrated lignocellulosic material whose enzymatic digestibility is increased relative to the digestibility of the solid lignocellulosic starting material (10), then; the hydrated lignocellulosic material is subjected to a treatment, called a mechano-chemical treatment (2), in which a dispersion is formed, called an aqueous dispersion, of the hydrated lignocellulosic material (10) in an aqueous composition, the aqueous dispersion including at least one enzyme for degrading the hydrated lignocellulosic material (10).
Castillo J.P.,National Autonomous University of Mexico |
Valiente-Banuet A.,National Autonomous University of Mexico
Ecology | Year: 2010
Facilitation and competition are ecological interactions that are crucial for the organization of plant communities. Facilitative interactions tend to occur among distantly related species, while the strength of competition tends to decrease with phylogenetic distance. The balance between both types of interactions will ultimately determine the specific composition of multispecies associations. Although multispecies patches are the arena in which coexistence develops among different phylogenetic groups within communities, the specific processes that occur across life stages have not been explored. Here we study how different species, in composing discrete patches in central Mexico, exert competitive or facilitative effects on seeds and seedlings. We relate these interactions to phylogenetic relationships among nurse species and beneficiary species, and among members of the patches. Survivorship and growth rates of the columnar cactus Neobuxbaumia mezcalaensis were highly positively related to increasing phylogenetic distance to different nurse species, to the presence of related species in patches, and to mean phylogenetic distances to the rest of the species in the patch. Each of these three elements influenced N. mezcalaensis differently, with different nurse species varying substantially in their early effects on emergence, and the nearest relatives and species composition of patches varying in their late effects on survival and growth. Our results emphasize that evolutionary relationships among co-occurring species in vegetation clumps exert direct and indirect effects on plants, affecting individual performance and species coexistence. © 2010 by the Ecological Society of America.
Agency: Cordis | Branch: FP7 | Program: CSA-SA | Phase: KBBE-2008-4-01 | Award Amount: 1.64M | Year: 2008
BIO CIRCLE will extend the network of National Contact Points for the FP7 theme Food, Agriculture and Fisheries and Biotechnology (BIO NCP) to National Information Points (NIP) from Third Countries over a two year period. The European Commission needs to implement the bilateral Scientific & Technological Agreements signed with Third Countries (TC), for increasing their participation in FAFB FP7 and strengthening the collaboration between European and TC researchers. The main focus of the project will be on identifying, sharing and implementing good practices between NCPs and NIPs. The expected results of BIO CIRCLE are: 1. Capacities built for Third Country BIO NIPs (through SWOT analysis, training of NIPs and twinning); 2. Strengthened consortium building in FAFB international cooperation projects (through mapping of Third Country research potential and the organisation of 2 international Brokerage Events); 3. Capacities built for Third Country Researchers to participate in FP7 (through preparation of specific training materials, training and networking with EU researchers); 4. Strengthened identification, development and sharing of Good Practices to enhance cooperation between the NCP and NIP networks (through 5 Regional Benchmarking Workshops, a Common Benchmarking Workshop and the design of a Good Practices Guide). The 6% of budget is foreseen to grant researchers from TCs to attend the 2 International Brokerage Events. The 5 BIO NCP partners of BIO CIRCLE led by APRE will assure the successful implementation of the project. The 18 NIPs partners of BIO CIRCLE will be embraced in this circle of activities aimed at ensuring quality and dynamism in implementing the Scientific & Technological Agreements between the EU and Third Countries. BIO CIRCLE will work in synergy with and be closely linked to the BIO-NET project, the complete NCP FAFB network.
Agency: Cordis | Branch: FP7 | Program: CSA-SA | Phase: ENERGY-2007-3.2-07 | Award Amount: 1.29M | Year: 2008
The overall objective of the BioTop proposal is to identify technical opportunities and research needs for Latin America and to create and support specific RTD cooperation activities between Latin America and the European Union in order to maximize synergies in the biofuels sectors. Specific objectives are: - to provide a broad overview of the existing biofuel sectors in all Latin American countries. - to identify priorities, needs and opportunities in the field of RTD for sustainable biofuel production and biomass conversion technologies in Latin America; - to inform European and Latin American actors in the biofuel sector about opportunities for collaboration and partnerships; - to harmonize the agenda between Latin America and the EU on sustainable biofuel production; - to facilitate and advance mutual knowledge and technology transfer between biofuel stakeholders in LA and the EU; - to make recommendations on RTD and policies for the production and utilization of biomass conversion technologies. The BioTop project will provide a broad overview of the existing biofuels sector in Latin American counties, with focus on countries with special EU S&T agreements (Argentina, Brazil, Chile, and Mexico). Key focus of the project will be the identification and assessment of improved 1st and 2nd generation biofuel conversion technologies. Sustainability, standardization and trade aspects of future large-scale biofuel production will be addressed, and RTD scenarios, roadmaps and recommendations will be developed. Exchanges between stakeholders active in research and development of biofuel conversion technologies will be promoted and BioTop activities will be effectively linked with existing networks and a large variety of stakeholders, target groups and key actors. Outcome of the BioTop project will be increased awareness about EU-LA opportunities for collaboration in the area of biofuels and the identification of suitable areas for biofuels RTD cooperation.
Agency: Cordis | Branch: FP7 | Program: CP-IP-SICA | Phase: ENV.2009.2.2.1.5 | Award Amount: 8.58M | Year: 2010
The Future of Reefs in a Changing Environment (FORCE) Project partners a multi-disciplinary team of researchers from Europe and the Caribbean to enhance the scientific basis for managing coral reefs in an era of rapid climate change and unprecedented human pressure on coastal resources. The overall aim is to provide coral reef managers with a toolbox of sustainable management practices that minimise the loss of coral reef health and biodiversity. An ecosystem approach is taken that explicitly links the health of the ecosystem with the livelihoods of dependent communities, and identifies the governance structures needed to implement sustainable development. Project outcomes are reached in four steps. First, a series of experimental, observational and modelling studies are carried out to understand both the ultimate and proximate drivers of reef health and therefore identify the chief causes of reef degradation. Second, the project assembles a toolbox of management measures and extends their scope where new research can significantly improve their efficacy. Examples include the first coral-friendly fisheries policies that balance herbivore extraction against the needs of the ecosystem, the incorporation of coral bleaching into marine reserve design, and creation of livelihood enhancement and diversification strategies to reduce fisheries capacity. Third, focus groups and ecological models are used to determine the efficacy of management tools and the governance constraints to their implementation. This step impacts practical reef management by identifying the tools most suited to solving a particular management problem but also benefits high-level policy-makers by highlighting the governance reform needed to implement such tools effectively. Lastly, the exploitation and dissemination of results benefits from continual engagement with practitioners. The project will play an important and measurable role in helping communities adapt to climate change in the Caribbean.
Agency: Cordis | Branch: FP7 | Program: CP-CSA | Phase: ENERGY.2013.10.1.10 | Award Amount: 21.20M | Year: 2014
Concentrating Solar Thermal Energy encompasses Solar Thermal Electricity (STE), Solar Fuels, Solar Process Heat and Solar Desalination that are called to play a major role in attaining energy sustainability in our modern societies due to their unique features: 1) Solar energy offers the highest renewable energy potential to our planet; 2) STE can provide dispatchable power in a technically and economically viable way, by means of thermal energy storage and/or hybridization, e.g. with biomass. However, significant research efforts are needed to achieve this goal. This Integrated Research Programme (IRP) engages all major European research institutes, with relevant and recognized activities on STE and related technologies, in an integrated research structure to successfully accomplish the following general objectives: a) Convert the consortium into a reference institution for concentrating solar energy research in Europe, creating a new entity with effective governance structure; b) Enhance the cooperation between EU research institutions participating in the IRP to create EU added value; c) Synchronize the different national research programs to avoid duplication and to achieve better and faster results; d) Accelerate the transfer of knowledge to industry in order to maintain and strengthen the existing European industrial leadership in STE; e) Expand joint activities among research centres by offering researchers and industry a comprehensive portfolio of research capabilities, bringing added value to innovation and industry-driven technology; f) Establish the European reference association for promoting and coordinating international cooperation in concentrating solar energy research. To that end, this IRP promotes Coordination and Support Actions (CSA) and, in parallel, performs Coordinated Projects (CP) covering the full spectrum of current concentrating solar energy research topics, selected to provide the highest EU added value and filling the gaps among national programs.
Agency: Cordis | Branch: FP7 | Program: CP-FP-SICA | Phase: ENV.2011.1.3.3-1 | Award Amount: 4.57M | Year: 2011
Our knowledge of the causative links between subsurface processes, resulting unrest signals and imminent eruption is, today, wholly inadequate to deal effectively with crises of volcanic unrest. The VUELCO project consortium has come together for a multi-disciplinary attack on the origin, nature and significance of volcanic unrest from the scientific contributions generated by collaboration of ten partners in Europe and Latin America. Dissecting the science of monitoring data from unrest periods at six type volcanoes in Italy, Spain, the West Indies, Mexico and Ecuador the consortium will create global strategies for 1) enhanced monitoring capacity and value, 2) mechanistic data interpretation and 3) identification of reliable eruption precursors; all from the geophysical, geochemical and geodetic fingerprints of unrest episodes. Experiments will establish a mechanistic understanding of subsurface processes capable of inducing unrest and aid in identifying key volcano monitoring parameters indicative of the nature of unrest processes. Numerical models will help establish a link between the processes and volcano monitoring data to inform on the causes of unrest and its short-term evolution. Using uncertainty assessment and new short-term probabilistic hazard forecasting tools the scientific knowledge base will provide the crucial parameters for a comprehensive and best-practice approach to 1) risk mitigation, 2) communication, 3) decision-making and 4) crisis management during unrest periods. The VUELCO project consortium efforts will generate guidance in the definition and implementation of strategic options for effective risk mitigation, management and governance during unrest episodes. Such a mechanistic platform of understanding, impacting on the synergy of scientists, policy-makers, civil protection authorities, decision-makers, and the public, will place volcanic unrest management on a wholly new basis, with European expertise at its peak.
Agency: Cordis | Branch: FP7 | Program: CP-IP-SICA | Phase: ENV.2011.2.1.4-1 | Award Amount: 9.01M | Year: 2011
To realise the full potential of tropical forests in climate change mitigation (CCM) & the provision of other ecosystem services in the face of ongoing global change we must improve our understanding of the relationships between biodiversity (BD) and the socio-ecological processes through which we respond & adapt to change. ROBIN will provide information for policy & resource use options under scenarios of socio-economic & climate change to: quantify interactions between terrestrial BD, land use & CCM potential in tropical Latin America; develop scenarios for CCM options by evaluating their effectiveness, unintended effects on other ecosystem services (e.g. disease mitigation) and their socio-ecological consequences. We will achieve this by combining new techniques (including remote sensing) for BD assessments in complex multi-functional landscapes, data-based analyses, integrated modelling & participatory-driven approaches at local & regional scales. Case studies along a gradient of sites in Mesoamerica and Amazonia will be used to develop understanding of the relationships between BD & CCM options & feed policy development. These studies will improve understanding of the options favourable to stakeholders & barriers & drivers affecting adoption of resource management strategies. Key deliverables will be: improved understanding of the role of BD in climate change; participatory-driven strategies & tools for CCM; assessments of the risks & uncertainties associated with CCM options. The main impact of the work will be improved outcomes from CCM & BD protection measures by providing natural resource managers in Latin America with guidance on how BD & ecosystems can be used in CCM without creating new problems. We will provide improved indicators for BD relevant to the Convention on Biological Diversity & the design & implementation of REDD\/\\ schemes, to ensure increased storage of carbon in forests & multi-functional landscapes & decreased rates of BD loss.
Agency: Cordis | Branch: FP7 | Program: CP-IP | Phase: ENV.2009.3.1.6.1 | Award Amount: 8.53M | Year: 2009
Coastal areas are vital economic hubs in terms of settlement, industry, agriculture, trade and tourism to mention some key sectors. There are already many coastal problems including erosion, flood risk and long-term habitat deterioration. As economies continue to develop the asset base at risk will grow, while accelerating climate change will increase the likelihood of damaging extreme events, as well as accelerate habitat decline. Existing coastal management and defence approaches are not well tuned to these challenges as they assume a static situation. THESEUS will develop a systematic approach to delivering both a low-risk coast for human use and healthy habitats for evolving coastal zones subject to multiple change factors. The innovative combined mitigation and adaptation technologies to be considered will include ecologically-based mitigation measures (such as restoration and/or creation of habitats), hydro-morphodynamic techniques (such as wave energy converters, sediment reservoirs, multi-purpose structures, overtop resistant dikes), actions to reduce the impact on society and economy (such as promotion of risk awareness or spatial planning) and GIS-based software to support defence planning. To integrate the best of these technical measures in a strategic policy context we will develop overarching THESEUS guidelines which will considers the environmental, social and economic issues raised in any coastal area. It is in this spirit that THESEUS will advance European and international experience in applying innovative technologies to reducing coastal risks. THESEUS activities will be carried out within a multidisciplinary framework using 8 study sites across Europe, with specific attention to the most vulnerable coastal environments such as deltas, estuaries and wetlands, where many large cities and industrial areas are located.
News Article | March 17, 2016
The star and its disk were studied in 2014 with the Atacama Large Millimeter/submillimeter Array (ALMA), which produced what astronomers then called the best image ever of planet formation in progress. The ALMA image showed gaps in the disk, presumably caused by planet-like bodies sweeping out the dust along their orbits. This image, showing in real life what theorists had proposed for years, was surprising, however, because the star, called HL Tau, is only about a million years old—very young by stellar standards. The ALMA image showed details of the system in the outer portions of the disk, but in the inner portions of the disk, nearest to the young star, the thicker dust is opaque to the short radio wavelengths received by ALMA. To study this region, astronomers turned to the VLA, which receives longer wavelengths. Their VLA images show that region better than any previous studies. The new VLA images revealed a distinct clump of dust in the inner region of the disk. The clump, the scientists said, contains roughly 3 to 8 times the mass of the Earth. "We believe this clump of dust represents the earliest stage in the formation of protoplanets, and this is the first time we've seen that stage," said Thomas Henning, of the Max Planck Institute for Astronomy (MPIA). "This is an important discovery, because we have not yet been able to observe most stages in the process of planet formation," said Carlos Carrasco-Gonzalez from the Institute of Radio Astronomy and Astrophysics (IRyA) of the National Autonomous University of Mexico (UNAM). "This is quite different from the case of star formation, where, in different objects, we have seen stars in different stages of their life cycle. With planets, we haven't been so fortunate, so getting a look at this very early stage in planet formation is extremely valuable," he added. Analysis of the VLA data indicates that the inner region of the disk contains grains as large as one centimeter in diameter. This region, the scientists said, is presumably where Earth-like planets would form, as clumps of dust grow by pulling in material from their surroundings. Eventually, the clumps would gather enough mass to form solid bodies that would continue to grow into planets. The VLA observations, made in 2014 and 2015, received radio waves with a wavelength of 7 millimeters. The earlier ALMA observations of HL Tau were made at a wavelength of 1 millimeter. The VLA images showed a similar level of detail as the ALMA images. "These VLA observations are the most sensitive and show the most detail of any yet made of HL Tau's disk at these longer wavelengths," said Claire Chandler, of the National Radio Astronomy Observatory (NRAO). "The VLA's ability to produce such high-quality images in this region is very important to advancing our understanding of these initial stages of planet formation," Chandler added. The scientists are reporting their findings in the Astrophysical Journal Letters. Explore further: VLA images 18 years apart show dramatic difference in young stellar system
News Article | December 2, 2016
Seagrass pollen swirls around on currents and tides, but it turns out that the grains can also hitch a ride on tiny marine creatures. Underwater invertebrates can ferry pollen between flowers, in the same way that bees and other animals pollinate plants on land. Seagrasses provide food and a habitat for everything from microscopic crustaceans to manatees, and stabilise coasts by anchoring sediment with their roots. They can propagate by cloning, or by sexual reproduction through the transfer of pollen from male to female flowers. Until recently, scientists thought that their pollen was conveyed from bloom to bloom by water alone, without the help of pollinators, says Brigitta van Tussenbroek at the National Autonomous University of Mexico’s marine science institute in Puerto Morelos. So van Tussenbroek and her colleagues were surprised when underwater video footage of a turtle-grass bed revealed hundreds of invertebrates, mostly small crustaceans, visiting flowers. “We saw all of these animals coming in, and then we saw some of them carrying pollen,” says van Tussenbroek (see video below). To see if the creatures could act as pollinators, the team added crustacean-containing seawater to laboratory aquariums containing male and female turtle-grass flowers, some of which already sported pollen grains. Within 15 minutes, several extra grains appeared on the female blooms, whereas flowers in control tanks without invertebrates did not gain any pollen. In the absence of water movement, grain germination that would indicate successful pollination was frequent when marine invertebrates were present, but rare or non-existent without them. Pollinators are probably attracted to the tasty, gooey pollen masses that the male flowers produce. While the invertebrates chow down, some pollen probably sticks to their bodies and is then deposited when they later visit a female flower. “That pollination by animals can occur adds an entirely new level of complexity to the system, and describes a very interesting plant-animal interaction that hasn’t really fully been described before,” says Kelly Darnell at The Water Institute of the Gulf, a non-profit research group in Baton Rouge, Louisiana. So far, underwater pollinators have only been seen visiting turtle-grass, which has relatively large flowers. It would be interesting to see whether, for example, other plants with much smaller flowers can also be pollinated in this way, says Darnell. It’s not clear how important invertebrate pollinators might be for other seagrass species. Nevertheless, expanding our basic knowledge of their biology is crucial in the face of a drastic worldwide decline in seagrasses, says Darnell. “It’s important that we understand all aspects of the seagrass life cycle, including reproduction,” she says.
News Article | November 8, 2016
A new study challenges the tenet of herpes viruses being strictly host-specific. Scientists from the Leibniz Institute for Zoo and Wildlife Research (IZW) in Germany have discovered that gammaherpesviruses switch their hosts more frequently than previously thought. In fact, bats and primates appear to be responsible for the transfer of these viruses to other mammals in many cases. The findings were published in the scientific journal mBio. For herpes, it has generally been thought that every animal has its own specific viruses and that virus and host species have co-evolved. Now, an international team of scientists led by the Leibniz-IZW discovered that herpesviruses may not conform to this commonly held view. Surprisingly, while studying a group of herpesviruses called gammaherpesviruses, the researchers demonstrated that the herpes viruses found in common vampire bats (Desmodus rotundus) and hairy-legged vampire bats (Diphylla ecaudata) were similar to those previously found in cattle. While it is known that vampire bats exclusively feed on animal blood, preferring domestic swine and cattle, since they represent an easily accessible food source, the result was somewhat unusual. Were bats being infected by viruses from their food source? To answer this question, researchers from the Leibniz-IZW worked together with the Centro Nacional de Investigación Disciplinaria en Microbiología Animal -- INIFAP; the Facultad de Medicina Veterinaria y Zootecnia of the Universidad Veracruzana; the Instituto de Biotecnología of the National Autonomous University of Mexico, the SUNY Downstate Medical Center in the USA, and the Freie Universität Berlin in Germany. Following up on the results from vampire bats, the researchers compiled the largest dataset of gammaherpesvirus sequences to date from their own sequencing data and publicly available data, including viruses from many bat species, and performed extensive analyses to determine the relationships of the viruses to one another and to their hosts. This shows that herpesviruses have frequently switched between species in the past, rather than being host specific. Most switches derived from bats, with primates being the second most common source of switches. "We speculate that bat-specific traits such as their ability to fly and a wide geographical range might have been important in promoting a virus spillover from bats to other animal groups," says Dr Marina Escalera-Zamudio, scientist at the Leibniz-IZW. After switching, herpesviruses may have adapted to their new hosts, creating the impression of host specificity. So the vampire bats were not likely infected by their food but more likely infected by other mammals in the past. Also surprisingly, vampire bats were not more prone among bats to transfer viruses, as many viruses from non-blood feeding bats also appear to have jumped. Since many viruses that cause disease in humans belong to the herpes virus family, it is important to understand their evolutionary development. "Herpes viruses establish latent life-long infections. Although they generally cause disease only in immunosuppressed individuals, they can survive largely below the radar even after infection," Escalera-Zamudio adds. Therefore, there may be even more species switches to uncover. However, only further sampling across a larger diversity of hosts will help determine the full scale of such switches. Future efforts should concentrate on clarifying the role of bats and primates for spreading these viruses.
News Article | March 18, 2016
New images of a young star made with the Karl G. Jansky Very Large Array (VLA) reveal what scientists think may be the very earliest stages in the formation of planets. The scientists used the VLA to see unprecedented detail of the inner portion of a dusty disk surrounding the star, some 450 light-years from Earth. The star and its disk were studied in 2014 with the Atacama Large Millimeter/submillimeter Array (ALMA), which produced what astronomers then called the best image ever of planet formation in progress. The ALMA image showed gaps in the disk, presumably caused by planet-like bodies sweeping out the dust along their orbits. This image, showing in real life what theorists had proposed for years, was surprising, however, because the star, called HL Tau, is only about a million years old—very young by stellar standards. The ALMA image showed details of the system in the outer portions of the disk, but in the inner portions of the disk, nearest to the young star, the thicker dust is opaque to the short radio wavelengths received by ALMA. To study this region, astronomers turned to the VLA, which receives longer wavelengths. Their VLA images show that region better than any previous studies. The new VLA images revealed a distinct clump of dust in the inner region of the disk. The clump, the scientists said, contains roughly 3 to 8 times the mass of the Earth. "We believe this clump of dust represents the earliest stage in the formation of protoplanets, and this is the first time we've seen that stage," said Thomas Henning, of the Max Planck Institute for Astronomy (MPIA). "This is an important discovery, because we have not yet been able to observe most stages in the process of planet formation," said Carlos Carrasco-Gonzalez from the Institute of Radio Astronomy and Astrophysics (IRyA) of the National Autonomous University of Mexico (UNAM). "This is quite different from the case of star formation, where, in different objects, we have seen stars in different stages of their life cycle. With planets, we haven't been so fortunate, so getting a look at this very early stage in planet formation is extremely valuable," he added. Analysis of the VLA data indicates that the inner region of the disk contains grains as large as one centimeter in diameter. This region, the scientists said, is presumably where Earth-like planets would form, as clumps of dust grow by pulling in material from their surroundings. Eventually, the clumps would gather enough mass to form solid bodies that would continue to grow into planets. The VLA observations, made in 2014 and 2015, received radio waves with a wavelength of 7 millimeters. The earlier ALMA observations of HL Tau were made at a wavelength of 1 millimeter. The VLA images showed a similar level of detail as the ALMA images. "These VLA observations are the most sensitive and show the most detail of any yet made of HL Tau's disk at these longer wavelengths," said Claire Chandler, of the National Radio Astronomy Observatory (NRAO). "The VLA's ability to produce such high-quality images in this region is very important to advancing our understanding of these initial stages of planet formation," Chandler added. The VLA study of HL Tau was an international collaboration, involving the UNAM, the MPIA, the NRAO, and the Spanish Consejo Superior de Investigaciones Cientificas (CSIC). The project leaders were Carlos Carrasco Gonzalez (UNAM) and Thomas Henning (MPIA). The scientists are reporting their findings in the Astrophysical Journal Letters. The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.
News Article | November 8, 2016
A new study challenges the tenet of herpes viruses being strictly host-specific. Scientists from the Leibniz Institute for Zoo and Wildlife Research (IZW) in Germany have discovered that gammaherpesviruses switch their hosts more frequently than previously thought. In fact, bats and primates appear to be responsible for the transfer of these viruses to other mammals in many cases. The findings were published in the scientific journal "mBio". For herpes, it has generally been thought that every animal has its own specific viruses and that virus and host species have co-evolved. Now, an international team of scientists led by the Leibniz-IZW discovered that herpesviruses may not conform to this commonly held view. Surprisingly, while studying a group of herpesviruses called gammaherpesviruses, the researchers demonstrated that the herpes viruses found in common vampire bats (Desmodus rotundus) and hairy-legged vampire bats (Diphylla ecaudata) were similar to those previously found in cattle. While it is known that vampire bats exclusively feed on animal blood, preferring domestic swine and cattle, since they represent an easily accessible food source, the result was somewhat unusual. Were bats being infected by viruses from their food source? To answer this question, researchers from the Leibniz-IZW worked together with the Centro Nacional de Investigación Disciplinaria en Microbiología Animal - INIFAP; the Facultad de Medicina Veterinaria y Zootecnia of the Universidad Veracruzana; the Instituto de Biotecnología of the National Autonomous University of Mexico, the SUNY Downstate Medical Center in the USA, and the Freie Universität Berlin in Germany. Following up on the results from vampire bats, the researchers compiled the largest dataset of gammaherpesvirus sequences to date from their own sequencing data and publicly available data, including viruses from many bat species, and performed extensive analyses to determine the relationships of the viruses to one another and to their hosts. This shows that herpesviruses have frequently switched between species in the past, rather than being host specific. Most switches derived from bats, with primates being the second most common source of switches. "We speculate that bat-specific traits such as their ability to fly and a wide geographical range might have been important in promoting a virus spillover from bats to other animal groups," says Dr Marina Escalera-Zamudio, scientist at the Leibniz-IZW. After switching, herpesviruses may have adapted to their new hosts, creating the impression of host specificity. So the vampire bats were not likely infected by their food but more likely infected by other mammals in the past. Also surprisingly, vampire bats were not more prone among bats to transfer viruses, as many viruses from non-blood feeding bats also appear to have jumped. Since many viruses that cause disease in humans belong to the herpes virus family, it is important to understand their evolutionary development. "Herpes viruses establish latent life-long infections. Although they generally cause disease only in immunosuppressed individuals, they can survive largely below the radar even after infection," Escalera-Zamudio adds. Therefore, there may be even more species switches to uncover. However, only further sampling across a larger diversity of hosts will help determine the full scale of such switches. Future efforts should concentrate on clarifying the role of bats and primates for spreading these viruses. Explore further: Virus in bats homologous to retroviruses in rodents and primates More information: Escalera-Zamudio M, et al. (2016): Bats, primates, and the evolutionary origins and diversification of mammalian gammaherpesviruses. mBio, DOI: 10.1128/mBio.01425-16
News Article | January 18, 2017
More than half of the world’s apes, monkeys, lemurs and lorises are now threatened with extinction as agriculture and industrial activities destroy forest habitats and the animals’ populations are hit by hunting and trade. In the most bleak assessment of primates to date, conservationists found that 60% of the wild species are on course to die out, with three quarters already in steady decline. The report casts doubt on the future of about 300 primate species, including gorillas, chimps, gibbons, marmosets, tarsiers, lemurs and lorises. Anthony Rylands, a senior research scientist at Conservation International who helped to compile the report, said he was “horrified” at the grim picture revealed in the review which drew on the International Union for the Conservation of Nature (IUCN) red list, peer-reviewed science reports and UN databases. “The scale of this is massive,” Rylands told the Guardian. “Considering the large number of species currently threatened and experiencing population declines, the world will soon be facing a major extinction event if effective action is not implemented immediately,” he writes in the journal Science Advances, with colleagues at the University of Illinois and the National Autonomous University of Mexico. The most dramatic impact on primates has come from agricultural growth. From 1990 to 2010 it has claimed 1.5 million square kilometres of primate habitats, an area three times the size of France. In Sumatra and Borneo, the destruction of forests for oil palm plantations has driven severe declines in orangutan populations. In China, the expansion of rubber plantations has led to the near extinction of the northern white-cheeked crested gibbon and the Hainan gibbon, of which only about 30 or animals survive. More rubber plantations in India have hit the Bengal slow loris, the western hoolock gibbon and Phayre’s leaf monkey. Primates are spread throughout 90 countries, but two thirds of the species live in just four: Brazil, Madagascar, Indonesia and the Democratic Republic of the Congo (DRC). In Madagascar, 87% of primate species face extinction, along with 73% in Asia, the report states. It adds that humans have “one last opportunity” to reduce or remove the threats facing the animals, to build conservation efforts, and raise worldwide awareness of their predicament. The market for tropical timber has driven up industrial logging and damaged forest areas in Asia, Africa and the neotropics. Mining for minerals and diamonds have also taken a toll. On Dinagat island in the Philippines, gold, nickel and copper mining endanger the Philippine tarsier. In the DRC, hunters working around the tin, gold and diamond mine industry are the greatest threat to the region’s Grauer’s gorilla. The industries at work in tropical forest areas are expected to be served by an extra 25m km of roads by 2050, further fragmenting the primates’ habitats. While some species are resilient and adapt to the loss of traditional habitats, survival in patches of forest and urban areas is unlikely to be sustainable, the authors write. One of the more unusual threats facing lemurs and chimps who come into contact with humans is infection with diarrhoea-causing bugs. Another major force driving primates to extinction is commercialised bushmeat hunting, which has expanded to provide food to the growing human population. The report cites accounts that claim 150,000 primates from 16 species are traded each year in Nigeria and Cameroon. In Borneo, between 2,000 and 3,000 orangutans are killed for food each year, a rate that is far from sustainable. Russell Mittermeier, another Conservation International scientist and co-author of the study, said that it was crucial to target conservation on the most threatened forests and species. “Clearly we need to deal with the drivers of extinction, from commercial agriculture to mining and logging. But if we focus all of our efforts on that, by the time we have had an impact, there won’t be anything left. So we must first protect the last remaining pieces of habitat and if no protected areas exist, we must create them. “I’m an optimist and I believe we can come up with solutions, but we have to be very targeted now to make sure we don’t lose anything,” he said. Writing in the journal, the authors add: “Despite the impending extinction facing many of the world’s primates, we remain adamant that primate conservation is not yet a lost cause.”
King Jr. T.E.,University of California at San Francisco |
Pardo A.,National Autonomous University of Mexico |
Selman M.,Instituto Nacional Of Enfermedades Respiratorias
The Lancet | Year: 2011
Idiopathic pulmonary fibrosis is a devastating, age-related lung disease of unknown cause that has few treatment options. This disease was once thought to be a chronic inflammatory process, but current evidence indicates that the fibrotic response is driven by abnormally activated alveolar epithelial cells (AECs). These cells produce mediators that induce the formation of fibroblast and myofibroblast foci through the proliferation of resident mesenchymal cells, attraction of circulating fibrocytes, and stimulation of the epithelial to mesenchymal transition. The fibroblast and myofibroblast foci secrete excessive amounts of extracellular matrix, mainly collagens, resulting in scarring and destruction of the lung architecture. The mechanisms that link idiopathic pulmonary fibrosis with ageing and aberrant epithelial activation are unknown; evidence suggests that the abnormal recapitulation of developmental pathways and epigenetic changes have a role. In this Seminar, we review recent data on the clinical course, therapeutic options, and underlying mechanisms thought to be involved in the pathogenesis of idiopathic pulmonary fibrosis. © 2011 Elsevier Ltd.
Sanchez S.,National Autonomous University of Mexico |
Demain A.L.,Drew University
Organic Process Research and Development | Year: 2011
Enzymes are an important part of industry due to their many favorable properties. The development of industrial enzymes has depended heavily on the use of microbial sources. Microbes are useful because they can be produced economically in short fermentations and inexpensive media. Screening is simple, and strain improvement for increased production has been very successful. In the 1980s and 1990s, microbial enzymes replaced many plant and animal enzymes. They have found use in many industries including food, detergents, textiles, leather, pulp and paper, diagnostics, and therapy. The development of recombinant DNA technology had a major effect on production levels of enzymes as their genes were transferred from native species into industrial strains. Over 50% of the enzyme market is provided by recombinant enzymes. In many cases, enzymes have also been used to carry out conversions that were synthetic in previous years. Accompanying this trend is the use of whole cells to carry out bioconversions. Bioconversions have become very important to industry especially because of the demand for single isomer intermediates. © 2010 American Chemical Society.
Prince M.J.,King's College London |
Wu F.,Shanghai Institutes of Preventative Medicine |
Guo Y.,U.S. Center for Disease Control and Prevention |
Gutierrez Robledo L.M.,National Autonomous University of Mexico |
And 3 more authors.
The Lancet | Year: 2015
23% of the total global burden of disease is attributable to disorders in people aged 60 years and older. Although the proportion of the burden arising from older people (≤60 years) is highest in high-income regions, disability-adjusted life years (DALYs) per head are 40% higher in low-income and middle-income regions, accounted for by the increased burden per head of population arising from cardiovascular diseases, and sensory, respiratory, and infectious disorders. The leading contributors to disease burden in older people are cardiovascular diseases (30·3% of the total burden in people aged 60 years and older), malignant neoplasms (15·1%), chronic respiratory diseases (9·5%), musculoskeletal diseases (7·5%), and neurological and mental disorders (6·6%). A substantial and increased proportion of morbidity and mortality due to chronic disease occurs in older people. Primary prevention in adults aged younger than 60 years will improve health in successive cohorts of older people, but much of the potential to reduce disease burden will come from more effective primary, secondary, and tertiary prevention targeting older people. Obstacles include misplaced global health priorities, ageism, the poor preparedness of health systems to deliver age-appropriate care for chronic diseases, and the complexity of integrating care for complex multimorbidities. Although population ageing is driving the worldwide epidemic of chronic diseases, substantial untapped potential exists to modify the relation between chronological age and health. This objective is especially important for the most age-dependent disorders (ie, dementia, stroke, chronic obstructive pulmonary disease, and vision impairment), for which the burden of disease arises more from disability than from mortality, and for which long-term care costs outweigh health expenditure. The societal cost of these disorders is enormous. © 2015 Elsevier Ltd.
Sussman R.A.,National Autonomous University of Mexico |
Izquierdo G.,University of Burgundy
Classical and Quantum Gravity | Year: 2011
We consider spherically symmetric inhomogeneous dust models with a positive cosmological constant, Λ, given by the Lemaître-Tolman-Bondi metric. These configurations provide a simple but useful generalization of the Λ-CDM model describing cold dark matter (CDM) and a Λ term, which seems to fit current cosmological observations. The dynamics of these models can be fully described by scalar evolution equations that can be given in the form of a proper dynamical system associated with a four-dimensional phase space whose critical points and invariant subspaces are examined and classified. The phase space evolution of various configurations is studied in detail by means of two two-dimensional subspaces: a projection into the invariant homogeneous subspace associated with Λ-CDM solutions with FLRW metric, and a projection into a subspace generated by suitably defined fluctuations that convey the effects of inhomogeneity. We look at cases with perpetual expansion, bouncing and loitering behavior, as well as configurations with 'mixed' kinematic patters, such as a collapsing region in an expanding background. In all cases, phase space trajectories emerge from and converge to stable past and future attractors in a qualitatively analogous way as in the case of the FLRW limit. However, we can identify in both projections of the phase space various qualitative features absent in the FLRW limit that can be useful in the construction of toy models of astrophysical and cosmological inhomogeneities. © 2011 IOP Publishing Ltd.
Spiller D.G.,Crown Bioscience |
Wood C.D.,National Autonomous University of Mexico |
Rand D.A.,University of Warwick |
White M.R.H.,Crown Bioscience
Nature | Year: 2010
Populations of cells are almost always heterogeneous in function and fate. To understand the plasticity of cells, it is vital to measure quantitatively and dynamically the molecular processes that underlie cell-fate decisions in single cells. Early events in cell signalling often occur within seconds of the stimulus, whereas intracellular signalling processes and transcriptional changes can take minutes or hours. By contrast, cell-fate decisions, such as whether a cell divides, differentiates or dies, can take many hours or days. Multiparameter experimental and computational methods that integrate quantitative measurement and mathematical simulation of these noisy and complex processes are required to understand the highly dynamic mechanisms that control cell plasticity and fate. © 2010 Macmillan Publishers Limited. All rights reserved.
Roig P.,National Autonomous University of Mexico |
Sanz Cillero J.J.,Autonomous University of Madrid
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2014
The anomalous V V P Green function and related form-factors (π0→γ *γ * and τ -→X - ντ vector form-factors, with X - = (K Kπ) -, φ -γ, (φV) -) are analyzed in this letter in the large-N C limit. Within the single (vector and pseudoscalar) resonance approximation and the context of Resonance Chiral Theory, we show that all these observables overdetermine in a consistent way a unique set of compatible high-energy constraints for the resonance couplings. This result is in agreement with analogous relations found in the even intrinsic-parity sector of QCD like, e.g., FV2=3F2. The antisymmetric tensor formalism is considered for the spin-one resonance fields. Finally, we have also worked out and provide here the relation between the two bases of odd intrinsic-parity Lagrangian operators commonly employed in the literature. © 2014 The Authors.
Selman M.,Instituto Nacional Of Enfermedades Respiratorias |
Pardo A.,National Autonomous University of Mexico |
King Jr. T.E.,University of California at San Francisco
American Journal of Respiratory and Critical Care Medicine | Year: 2012
Hypersensitivity pneumonitis (HP) is a complex syndrome resulting from repeated exposure to a variety of organic particles. HP may present as acute, subacute, or chronic clinical forms but with frequent overlap of these various forms. An intriguing question is why only few of the exposed individuals develop the disease. According to a two-hit model, antigen exposure associated with genetic or environmental promoting factors provokes an immunopathological response. This response is mediated by immune complexes in the acute form and by Th1 and likely Th17 T cells in subacute/chronic cases. Pathologically, HP is characterized by a bronchiolocentric granulomatous lymphocytic alveolitis, which evolves to fibrosis in chronic advanced cases. On high-resolution computed tomography scan, ground-glass and poorly defined nodules, with patchy areas of air trapping, are seen in acute/ subacute cases, whereas reticular opacities, volume loss, and traction bronchiectasis superimposed on subacute changes are observed in chronic cases. Importantly, subacute and chronic HP may mimic several interstitial lung diseases, including nonspecific interstitial pneumonia and usual interstitial pneumonia, making diagnosis extremely difficult. Thus, the diagnosis of HP requires a high index of suspicion and should be considered in any patient presenting with clinical evidence of interstitial lung disease. The definitive diagnosis requires exposure to known antigen, and the assemblage of clinical, radiologic, laboratory, and pathologic findings. Early diagnosis and avoidance of further exposure are keys in management of the disease. Corticosteroids are generally used, although their long-term efficacy has not been proved in prospective clinical trials. Lung transplantation should be recommended in cases of progressive end-stage illness. Copyright © 2012 by the American Thoracic Society.
Lazarian A.,University of Wisconsin - Madison |
Esquivel A.,National Autonomous University of Mexico |
Crutcher R.,University of Illinois at Urbana - Champaign
Astrophysical Journal | Year: 2012
Recent observational results for magnetic fields in molecular clouds reviewed by Crutcher seem to be inconsistent with the predictions of the ambipolar diffusion theory of star formation. These include the measured decrease in mass to flux ratio between envelopes and cores, the failure to detect any self-gravitating magnetically subcritical clouds, the determination of the flat probability distribution function (PDF) of the total magnetic field strengths implying that there are many clouds with very weak magnetic fields, and the observed scaling Bρ2/3 that implies gravitational contraction with weak magnetic fields. We consider the problem of magnetic field evolution in turbulent molecular clouds and discuss the process of magnetic field diffusion mediated by magnetic reconnection. For this process that we termed "reconnection diffusion," we provide a simple physical model and explain that this process is inevitable in view of the present-day understanding of MHD turbulence. We address the issue of the expected magnetization of cores and envelopes in the process of star formation and show that reconnection diffusion provides an efficient removal of magnetic flux that depends only on the properties of MHD turbulence in the core and the envelope. We show that as the amplitude of turbulence as well as the scale of turbulent motions decrease from the envelope to the core of the cloud, the diffusion of the magnetic field is faster in the envelope. As a result, the magnetic flux trapped during the collapse in the envelope is being released faster than the flux trapped in the core, resulting in much weaker fields in envelopes than in cores, as observed. We provide simple semi-analytical model calculations which support this conclusion and qualitatively agree with the observational results. Magnetic reconnection is also consistent with the lack of subcritical self-gravitating clouds, with the observed flat PDF of field strengths, and with the scaling of field strength with density. In addition, we demonstrate that the reconnection diffusion process can account for the empirical Larson relations and list a few other implications of the reconnection diffusion concept. We argue that magnetic reconnection provides a solution to the magnetic flux problem of star formation that agrees better with observations than the long-standing ambipolar diffusion paradigm. Due to the illustrative nature of our simplified model we do not seek quantitative agreement, but discuss the complementary nature of our approach to the three-dimensional MHD numerical simulations. © 2012. The American Astronomical Society. All rights reserved.
Villaver E.,Autonomous University of Madrid |
Manchado A.,Institute of Astrophysics of Canarias |
Garcia-Segura G.,National Autonomous University of Mexico
Astrophysical Journal | Year: 2012
We study the hydrodynamical behavior of the gas expelled by moving asymptotic giant branch stars interacting with the interstellar medium (ISM). Our models follow the wind modulations prescribed by stellar evolution calculations, and we cover a range of expected relative velocities (10-100kms-1), ISM densities (between 0.01 and 1 cm-3), and stellar progenitor masses (1 and 3.5 M ). We show how and when bow shocks and cometary-like structures form, and in which regime the shells are subject to instabilities. Finally, we analyze the results of the simulations in terms of the different kinematical stellar populations expected in the Galaxy. © 2012. The American Astronomical Society. All rights reserved..
Valiente-Banuet A.,Institute Ecologia |
Valiente-Banuet A.,National Autonomous University of Mexico |
Verdu M.,University of Valencia
Annual Review of Ecology, Evolution, and Systematics | Year: 2013
The relationship between facilitation and evolutionary ecology is poorly understood. We review five issues elucidating how the phylogenetic relatedness of species provides insight into the role of facilitation in community assembly: (a) Are the facilitative interactions more common between species that differ in a regeneration niche? (b) Are facilitative interactions more common between distantly related species? (c) Do communities governed by facilitation (rather than competition) have higher phylogenetic diversity? (d) As facilitated juvenile plants mature, do they compete with their nurses more often if they are closely related to them? (e) How does the phylogenetic signature in a community reveal ecological processes, such as succession, regeneration dynamics, indirect interactions, and coextinction cascades? The evolutionary history of lineages explains the regeneration niche of species, which ultimately determines the facilitation-competition balance and therefore community assembly and dynamics. We apply this framework to the conservation of biodiversity and propose future research avenues. © Copyright ©2013 by Annual Reviews. All rights reserved.
Palacios D.,Complutense University of Madrid |
de Marcos J.,Complutense University of Madrid |
Vazquez-Selem L.,National Autonomous University of Mexico
Quaternary International | Year: 2011
The study area is located in the Sierra de Gredos, a portion of the Sistema Central range of central Spain, specifically in the Gredos Gorge, on the north side of Pico Almanzor (2596 masl), where glacial forms are present down to an altitude of 1410 m, 10 km from the headwall. This paper presents cosmogenic 36Cl surface exposure dates of four closely spaced lateral moraine ridges within the area of maximum advance of the ancient glacier, 8 km from the headwall; and two glacially polished bedrock thresholds 3 and 5 km from the headwall. The dates are overall coherent and indicate a maximum advance at 26-24 ka. Subsequently the glacier front stabilized around its maximum position for ∼3 ka, with small scale fluctuations resulting in small, closely spaced moraines ridges. Glacier recession began after 21 ka, accelerating sharply by ∼16 ka. The glacier had probably disappeared from the Gredos Gorge by 15 ka. There are no traces of older or more recent moraines than those dated in this study. These results are in agreement with the well known late Pleistocene climatic evolution of the Northern Atlantic and with the glacial chronology of the Alps and other Mediterranean mountains. However, the Gredos Gorge has no geomorphic evidence of the Younger Dryas cold event, probably because of the low altitude and southern character of these mountains. © 2010 Elsevier Ltd and INQUA.
Honey-Roses J.,University of Illinois at Urbana - Champaign |
Baylis K.,University of Illinois at Urbana - Champaign |
Ramirez M.I.,National Autonomous University of Mexico
Conservation Biology | Year: 2011
With the potential expansion of forest conservation programs spurred by climate-change agreements, there is a need to measure the extent to which such programs achieve their intended results. Conventional methods for evaluating conservation impact tend to be biased because they do not compare like areas or account for spatial relations. We assessed the effect of a conservation initiative that combined designation of protected areas with payments for environmental services to conserve over wintering habitat for the monarch butterfly (Danaus plexippus) in Mexico. To do so, we used a spatial-matching estimator that matches covariates among polygons and their neighbors. We measured avoided forest loss (avoided disturbance and deforestation) by comparing forest cover on protected and unprotected lands that were similar in terms of accessibility, governance, and forest type. Whereas conventional estimates of avoided forest loss suggest that conservation initiatives did not protect forest cover, we found evidence that the conservation measures are preserving forest cover. We found that the conservation measures protected between 200 ha and 710 ha (3-16%) of forest that is high-quality habitat for monarch butterflies, but had a smaller effect on total forest cover, preserving between 0 ha and 200 ha (0-2.5%) of forest with canopy cover >70%. We suggest that future estimates of avoided forest loss be analyzed spatially to account for how forest loss occurs across the landscape. Given the forthcoming demand from donors and carbon financiers for estimates of avoided forest loss, we anticipate our methods and results will contribute to future studies that estimate the outcome of conservation efforts. © 2011 Society for Conservation Biology.
Fucikova K.,University of Connecticut |
Lewis P.O.,University of Connecticut |
Gonzalez-Halphen D.,National Autonomous University of Mexico |
Lewis L.A.,University of Connecticut
Genome biology and evolution | Year: 2014
The majority of our knowledge about mitochondrial genomes of Viridiplantae comes from land plants, but much less is known about their green algal relatives. In the green algal order Sphaeropleales (Chlorophyta), only one representative mitochondrial genome is currently available-that of Acutodesmus obliquus. Our study adds nine completely sequenced and three partially sequenced mitochondrial genomes spanning the phylogenetic diversity of Sphaeropleales. We show not only a size range of 25-53 kb and variation in intron content (0-11) and gene order but also conservation of 13 core respiratory genes and fragmented ribosomal RNA genes. We also report an unusual case of gene arrangement convergence in Neochloris aquatica, where the two rns fragments were secondarily placed in close proximity. Finally, we report the unprecedented usage of UCG as stop codon in Pseudomuriella schumacherensis. In addition, phylogenetic analyses of the mitochondrial protein-coding genes yield a fully resolved, well-supported phylogeny, showing promise for addressing systematic challenges in green algae. © The Author(s) 2014. Published by Oxford University Press on behalf of the Society for Molecular Biology and Evolution.
Agency: Cordis | Branch: FP7 | Program: CSA-SA | Phase: SSH.2012.8.8-2 | Award Amount: 1.20M | Year: 2013
NET4SOCIETY3 is the continuation of the international network of National Contact Points for Socio-economic Sciences and Humanities (SSH NCPs). NCPs are set up to guide researchers in their quest for securing EU funding. NET4SOCIETY was established in 2008 and includes almost 60 SSH NCPs from Europe and beyond. Facing the transition from FP7 to Horizon 2020, NET4SOCIETY3 will help researchers prepare for new funding schemes and structures, and will ensure that all SSH NCPs have the relevant knowledge and skills for this task. All nominated SSH NCPs, even if not beneficiaries of the project itself, will have access to information and capacity building tools such as workshops, NCP Info days, trainings and an online Virtual Helpdesk. The project website will address NCPs and researchers alike, and include first-hand information on FP7 and Horizon 2020, an SSH event calendar and a repository of relevant publications. NET4SOCIETY3 will support researchers to connect into all Societal challenges of Horizon 2020. Its aim is to increase the visibility of SSH research to policy makers and other research areas in order to ensure that SSH aspects are integrated into all Societal challenges. The integration of SSH aspects in the Societal Challenges, other ERA-Initiatives and SSH Infrastructures will be monitored and analysed. Established services of NET4SOCIETY, such as the Research Directory, will be continued and improved. A dedicated task addressing EU12 issues will analyse the reasons for low participation and success rates of these countries. It will identify recommendations on how to overcome existing barriers. A large information event targeting 250-300 participants will be organised in spring 2014, coinciding with the launch of Horizon 2020. It will inform about Horizon 2020 and connect researchers and policy makers. Various promotion activities enhancing the visibility of the SSH programme and Best Practice in SSH research will underline these efforts.
Agency: Cordis | Branch: FP7 | Program: CP-SICA | Phase: ENERGY.2008.3.2.1 | Award Amount: 4.39M | Year: 2009
Today, USA and Brazil have massively invested in ethanol mono-production, taking advantage of their respective native crops, intensive culture practices and large availability of land. These renewable biofuel production models cannot be applied to most of the industrial and emerging countries. For these countries with limited land use, one of the best solutions to comply with their objectives of renewable biofuel and avoid food/fuel competition is the production of ethanol from diversified lignocellulosic residues. Yet, more research efforts are necessary to reach this objective. The BABETHANOL project proposes solutions for a more sustainable approach of 2nd generation renewable ethanol, based on a moderate, environmental-friendly and integrated transformation process that should be applicable to an expanded range of lignocellulosic feedstocks. The new process, called CES - Combined Extrusion-Saccharification, will be an alternative to the costly processes of the current state-of-the-art, notably the pre-treatment requiring much energy, water, chemical products, detoxification and waste water treatment. CES will be developed and tested from laboratory up to semi-industrial pilot scale with different new feedstock: Blue Agave Bagass, Palm Oil Empty Fruit Bunches and Olive oil Milled Husks. A Europe-Latin America lignocellullosic biomass catalogue will also be developed as a further contribution to the expansion of feedstocks. The success of the new project much relies on the well-balanced consortium with 7 European partners, 8 Latin American partners, the multidisciplinary expertise with agriculture/agronomy, chemical/catalysis, microbial systems engineering, industrial plant design and the integration of SMEs.
Agency: Cordis | Branch: FP7 | Program: CSA-CA | Phase: SSH-2007-8.0-02 | Award Amount: 3.10M | Year: 2008
A strong and efficient Network of National Contacts Points (NCP) is not only elementary to the success of the Seventh EU Framework Programme but also to the realization of the European Research Area. The trans-national project NET4SOCIETY will strive to achieve this declared goal. For its proposed duration of three years, NET4SOCIETY will support the creation and establishment of a functional Network of Socioeconomic Sciences and the Humanities (SSH)-NCPs. NET4SOCIETY will offer specific high quality training sessions (based on a questionnaire that will be sent to all SSH-NCPs), dedicated workshops, and mentoring and brokerage events. The project will provide targeted tools such as a best practice handbook and a database for the specific area of Socioeconomics and the Humanities, including a refined partner-search tool. These tools will be published on the projects dedicated Internet site (www.net4scociety.eu). Through the project NET4SOCIETY the first network of SSH-NCPs will be created. The Network consists of a total of 38 beneficiaries, including NCPs from International Cooperation Partner Countries (ICPCs). A core group of Work Packages leaders, including the Third Country Task Force Leader, will work closely together with the Co-ordinator to implement the projects objectives. All beneficiaries and natural members will be involved in the surveys, which build the foundation of several Network activities, will have access to all Network events and tools. NET4SOCIETY is opened to all SSH-NCPs, including those who have declined their official participation. All network beneficiaries and natural members will be informed on a regular basis; they will have the possibility to contribute to the projects objectives, participate in the network events and benefit fully from the projects results.
Caballero-Lopez R.A.,National Autonomous University of Mexico |
Moraal H.,North West University South Africa
Journal of Geophysical Research: Space Physics | Year: 2012
Since the middle 1950s, neutron monitors have provided a continuous record of the intensity of secondary atmospheric particles produced by the primary cosmic radiation above the atmosphere. The number of counts due to these secondary particles is related to the primary spectrum above the atmosphere through the so-called atmospheric yield function. This yield function includes the secondary particles produced in the atmosphere, as well as inside the particular detector. In this paper the primary focus is to recalculate the yield function for neutron monitors. The motivation for this study is that the quality of the experimental observations has increased to such an extent that it has become possible to reduce uncertainties in the yield function down to approximately 10%. It thus becomes possible to refine our knowledge of the atmospheric cascade process considerably. We parameterize the yield functions in a simple way; we also make reference to the yield and response functions of muon, Cherenkov and stratospheric balloon detectors, and we compare their response to that of the neutron monitors. © 2012. American Geophysical Union. All Rights Reserved.
Greene D.F.,Environment Canada |
Quesada M.,National Autonomous University of Mexico
Functional Ecology | Year: 2011
While it is well known that many plant species enhance the dispersal of seeds by wind via traits such as lift-promoting wings and drag-producing fibres, we hypothesized that natural selection would also increase dispersal capacity through the evolution of mechanisms that promoted abscission by updrafts rather than downdrafts. An experiment with the cosmopolitan weed, Tragopogon dubius, showed that a combination of simple morphological traits and achene orientation made updrafts from three to five times more likely than downdrafts to abscise a seed over the vertical wind speed range of 0·2-0·5ms-1. (Abscission will not occur at speeds lower than about 0·2ms-1 while vertical speeds >0·5ms-1 near ground level would be extremely rare.) Horizontal winds were even more effective than updrafts at abscising seeds at any wind speed. We speculate that mechanisms causing an updraft abscission bias are quite common and will eventually be seen as a crucial component of long distance seed movement for almost all wind-dispersed species. © 2010 The Authors. Functional Ecology © 2010 British Ecological Society.
News Article | December 22, 2016
The International Association of HealthCare Professionals is pleased to welcome Jose Tellez-Zenteno, MD, PhD, FRCP, CNSC (EEG), to their prestigious organization with his upcoming publication in The Leading Physicians of the World. He is a highly trained and qualified Neurologist with an extensive expertise in all facets of his work, especially Epilepsy and general neurology. Dr. Jose Tellez-Zenteno has been in practice for more than 20 years and is currently serving patients within Royal University Hospital in Saskatoon, Saskatchewan, Canada. Dr. Jose Tellez-Zenteno’s career in medicine began in 1996 when he graduated with his Medical Degree from the National Autonomous University of Mexico in Mexico City. Following his graduation, residencies in Internal Medicine and Neurology were then completed at the National Institute of Medical Sciences and Nutrition, before Dr. Tellez-Zenteno moved to Canada and completed two clinical fellowships in Epilepsy-EEG at the epilepsy program of the London Health Sciences Center, followed by an additional fellowship at the Foothills Medical Center in Calgary, Alberta. Dr. Tellez-Zenteno keeps up to date with the latest advances in his field by maintaining a professional membership with the American Epilepsy Society, Canadian League Against Epilepsy, Canadian Society of Clinical Neurophysiology. He has earned the coveted title of Fellow of the Royal College of Physicians, and has published more than 120 peer reviewed articles and publications. In addition to his practice, Dr. Tellez-Zenteno teaches Neurology to medical students. He attributes his success to his love for his work, as well as is passion for clinical research. When Dr. Tellez-Zenteno is not assisting patients, he enjoys soccer. Learn more about Dr. Tellez-Zenteno by reading his upcoming publication in The Leading Physicians of the World. FindaTopDoc.com is a hub for all things medicine, featuring detailed descriptions of medical professionals across all areas of expertise, and information on thousands of healthcare topics. Each month, millions of patients use FindaTopDoc to find a doctor nearby and instantly book an appointment online or create a review. FindaTopDoc.com features each doctor’s full professional biography highlighting their achievements, experience, patient reviews and areas of expertise. A leading provider of valuable health information that helps empower patient and doctor alike, FindaTopDoc enables readers to live a happier and healthier life. For more information about FindaTopDoc, visit http://www.findatopdoc.com
News Article | December 22, 2015
An amazing bird once viewed as a sacred symbol by the Maya and Aztecs now faces an uncertain future due to habitat loss, population fragmentation and illegal trafficking. The resplendent quetzal, a breathtakingly beautiful bird with tail feathers in males nearly twice the length of their bodies, once roamed through much of Southern Mexico and six other countries. That’s no longer the case. “All of these seven countries have serious problems of habitat loss and fragmentation,” says one of the few researchers to study the species, Sofia Solorzano of National Autonomous University of Mexico. “I feel that if the habitat loss and fragmentation are not stopped the future for remnant populations is genetic isolation, reduction of population sizes and, consequently, rapid local extinctions.” In fact, she has already documented some local extirpations as well as degraded forests that each hold just a handful of remaining birds. Compounding the problem is that Solorzano’s previous research indicated that resplendent quetzals are actually two species, not the single species with two subspecies currently recognized by the conservation community. A genetic and morphological study she published in 2010 found that the birds in Mexico and Nicaragua are one species, Pharomachrus mocinno, while the birds in the more southern countries are a second species, P. costaricensis. This means that each species has a more limited population and range and is more threatened than previously realized. Both quetzal species are specialized fruit eaters and rely on large dead or dying trees with soft wood, in which they carve their nests. Those food supplies and trees are now in short supply. Solorzano says many of the birds’ forest habitats have been chopped down to make way for coffee plantations, livestock pastures or other farming. She has documented what she described as “drastic fragmentation” of quetzal habitat in southern Mexico. The establishment of some protected areas has helped, but she says is hasn’t been enough. Of course, habitat loss is not the quetzals’ only threat. The species also have several natural predators, including toucan birds and squirrels that eat their eggs or small chicks. Larger birds of prey such as owls, falcons and hawks also kill the adult quetzals. Meanwhile, humans have been known to hunt them for their feathers—something that would have been forbidden during the days of the Maya and Aztec—or for the illegal pet trade, even though there is no history of the birds surviving in captivity. Unfortunately, there do not appear to be any dedicated quetzal conservation efforts, despite the birds’ historical and cultural significance and the fact that they are the central image of the Guatemalan flag. “I think it is time to seriously protect this bird and its breeding and migratory habitats,” Solorzano says. She calls the resplendent quetzal a “resilient” bird and predicted that it could return to its previous habitats if they are protected. “We will have quetzals if the deforestation is stopped,” she said. Photo 1 © Fulvio Eccardi, courtesy of National Autonomous University of Mexico. Photo 2 by Frank Vassen. Used under Creative Commons license
News Article | December 15, 2016
DENVER, COLORADO--(Marketwired - Dec. 15, 2016) - TrackX Holdings Inc. (TSX VENTURE:TKX) ("TrackX" or the "Company"), a global leader in providing cloud-based, asset tracking solutions for supply chain and logistics-intensive businesses, is pleased to announce that Monica Kimbrough has joined the Company as a strategic advisor. In this role, Kimbrough will assist TrackX with their expansion of strategic partnerships and capabilities within the Industrial Internet of Things. Kimbrough is a highly experienced technology executive, having held senior technology leadership roles with Global 100 companies such as Costco, Motorola, Best Buy, Teradata, Wells Fargo, and Deutsche Telekom. Kimbrough also has served as Chief Enterprise Architect for Salesforce and supported the COO Lead Transformation Office at Cisco Systems. "Monica's wealth of experience and substantial business relationships will be a tremendous asset to TrackX as we continue to carve out our niche within the Industrial Internet of Things," said TrackX President and CEO, Tim Harvie. "In addition, we will utilize Monica's deep expertise in developing partnerships within Latin America. This will provide TrackX with the means to respond to several large opportunities in those countries, and service existing customers with Latin American operations." On joining TrackX, Kimbrough said, "TrackX represents a very exciting industrial software opportunity that has provided tremendous value throughout its customer base. We will continue to differentiate TrackX's unique and powerful enterprise asset tracking offerings as a pillar of our customer's operations within the rapidly emerging Industrial Internet of Things." Kimbrough received her MBA from the University of Dallas and BS in mechanical and electrical engineering from the National Autonomous University of Mexico - the largest university in Latin America. TrackX is a global leader in providing cloud-based, asset tracking solutions for supply chain and logistics-intensive businesses. Headquartered in Denver, Colorado, TrackX's patented platform combines support for multiple auto-ID technologies, workflow, event management, alert notifications, and analytics, to deliver significant value its customers. TrackX solutions include high-value asset tracking, yard management, returnable asset management, and mobile inventory management solutions. TrackX delivers value to Fortune 500 customers in a variety of industries, including transportation, beverage, brewery, healthcare, hi-tech, hospitality, mining, agriculture, horticulture, manufacturing, and government. Neither TSX Venture Exchange nor its Regulations Services Provider (as that term is defined in the policies of the TSX Venture Exchange) accepts responsibility for the adequacy or accuracy of this release.
News Article | February 22, 2017
One of the worst epidemics in human history, a sixteenth-century pestilence that devastated Mexico’s native population, may have been caused by a deadly form of salmonella from Europe, a pair of studies suggest. In one study, researchers say they have recovered DNA of the stomach bacterium from burials in Mexico linked to a 1540s epidemic that killed up to 80% of the country's native inhabitants. The team reports its findings in a preprint posted on the bioRxiv server on 8 February1. This is potentially the first genetic evidence of the pathogen that caused the massive decline in native populations after European colonization, says Hannes Schroeder, an ancient-DNA researcher at the Natural History Museum of Denmark in Copenhagen who was not involved in the work. “It’s a super-cool study.” In 1519, when forces led by Spanish conquistador Hernando Cortés arrived in Mexico, the native population was estimated at about 25 million. A century later, after a Spanish victory and a series of epidemics, numbers had plunged to around 1 million. The largest of these disease outbreaks were known as cocoliztli (from the word for ‘pestilence’ in Nahuatl, the Aztec language). Two major cocoliztli, beginning in 1545 and 1576, killed an estimated 7 million to 18 million people living in Mexico’s highland regions. “In the cities and large towns, big ditches were dug, and from morning to sunset the priests did nothing else but carry the dead bodies and throw them into the ditches,” noted a Franciscan historian who witnessed the 1576 outbreak. There has been little consensus on the cause of cocoliztli — although measles, smallpox and typhus have all been mooted. In 2002, researchers at the National Autonomous University of Mexico (UNAM) in Mexico City proposed that a viral haemorrhagic fever, exacerbated by a catastrophic drought, was behind the carnage2. They compared the magnitude of the 1545 outbreak to that of the Black Death in fourteenth-century Europe. In an attempt to settle the question, a team led by evolutionary geneticist Johannes Krause at the Max Planck Institute for the Science of Human History in Jena, Germany, extracted and sequenced DNA from the teeth of 29 people buried in the Oaxacan highlands of southern Mexico. All but five were linked to a cocoliztli that researchers think ran from 1545 to 1550. Ancient bacterial DNA recovered from several of the people matched that of Salmonella, based on comparisons with a database of more than 2,700 modern bacterial genomes. Further sequencing of short, damaged DNA fragments from the remains allowed the team to reconstruct two genomes of a Salmonella enterica strain known as Paratyphi C. Today, this bacterium causes enteric fever, a typhus-like illness, that occurs mostly in developing countries. If left untreated, it kills 10–15% of infected people. It’s perfectly reasonable that the bacterium could have caused this epidemic, says Schroeder. “They make a really good case.” But María Ávila-Arcos, an evolutionary geneticist at UNAM, isn't convinced. She notes that some people suggest that a virus caused the cocoliztli, and that wouldn't have been picked up by the team’s method. Krause and his colleagues’ proposal is helped by another study posted on bioRxiv last week, which raises the possibility that Salmonella Paratyphi C arrived in Mexico from Europe3. A team led by Mark Achtman, a microbiologist at the University of Warwick in Coventry, UK, collected and sequenced the genome of the bacterial strain from the remains of a young woman buried around 1200 in a cemetery in Trondheim, Norway. It is the earliest evidence for the now-rare Salmonella strain, and proof that it was circulating in Europe, according to the study. (Both teams declined to comment on their research because their papers have been submitted to a peer-reviewed journal.) “Really, what we’d like to do is look at both strains together,” says Hendrik Poinar, an evolutionary biologist at McMaster University in Hamilton, Canada. And if more ancient genomes can be collected from Europe and the Americas, it should be possible to find out more conclusively whether deadly pathogens such as Salmonella arrived in the New World from Europe. The existence of Salmonella Paratyphi C in Norway 300 years before it appeared in Mexico doesn’t prove that Europeans spread enteric fever to native Mexicans, says Schroeder, but that hypothesis is reasonable. A small percentage of people infected with Salmonella Paratyphi C carry the bacterium without falling ill, so apparently healthy Spaniards could have infected Mexicans who lacked natural resistance. Paratyphi C is transmitted through faecal material, and a collapse of social order during the Spanish conquest might have led to the poor sanitary conditions that are ripe for Salmonella spread, Krause and his team note in the paper. Krause’s study offers a blueprint for identifying the pathogens behind ancient outbreaks, says Schroeder. His own team plans to look for ancient pathogens in Caribbean burial sites that seem to be linked to catastrophic outbreaks, and that were established after the Europeans arrived. “The idea that some of them might have been caused by Salmonella is now a distinct possibility,” he says.
News Article | November 21, 2016
Last month, researchers from the National Autonomous University of Mexico hoped to reach the top of Popocatépetl, a 5400-meter-tall volcano near Mexico City, to install monitoring equipment at its summit crater. But El Popo, as locals call it, rebuffed them with ash and belches of acrid gas—precisely what the scientists wanted to measure. They settled for installing the sensor lower down the mountain, and hope to move it higher next year. The goal is to measure just what—and how much—El Popo has been smoking, because the fumes may hold a promising way to forecast eruptions. A growing body of monitoring data suggests that a sharp jump in the ratio of carbon to sulfur gases emanating from a volcano can provide days to weeks of warning before an impending outburst. The latest evidence comes from three recent studies, focusing on volcanoes monitored as part of the Volcano Deep Earth Carbon Degassing (DECADE) initiative. They offer hope that geochemical monitoring of gases could someday join the two geophysical mainstays of forecasting: tracking the swelling of Earth’s surface and the rise in earthquakes that typically precede eruptions. “It’s statistically robust as a forecasting tool,” says Tobias Fischer, a volcanologist at the University of New Mexico in Albuquerque, and chair of the DECADE project. The idea of sniffing out restlessness in volcanic fumes has been around for decades. For instance, a sharp rise in sulfur emissions helped scientists anticipate the 1991 eruption of Mount Pinatubo in the Philippines. Scientists have also keyed in on the carbon-to-sulfur (C-S) ratio in volcanic gases as a particularly helpful metric. In principle, it can signal when a fresh injection of magma is rising from deep in the crust—a prelude to an eruption. The ratio changes because carbon dioxide (CO ) dissolved in rising magma bubbles out at depths of 10 kilometers or more, as the pressure drops. Sulfur-rich gases, in contrast, stay in solution up to shallower depths. A spike in the ratio can thus provide warning that a new batch of magma has risen above a deep threshold. A subsequent drop in the C-S ratio could indicate that the magma has climbed further, to depths where sulfur gases are released, but Fischer says this hasn’t been observed enough to be reliable. Despite the simple mechanism, establishing a clear link between the ratios and eruptions requires constant monitoring. Historically, researchers just bottled a few gas samples during a visit to a volcano or used airplanes or remote-sensing tools to watch a volcano for several days or weeks, says Christoph Kern, a physicist with the U.S. Geological Survey in Vancouver, Washington. Either way, Kern says, it was hard to catch an eruption in the act. But that changed in the early 2000s, when scientists began to develop new devices that could be left on volcanoes to make continuous measurements and transmit the data to researchers. They were solar powered, hardy enough to survive the elements, and cheap enough to risk sacrificing in an eruption. “They’re essentially expendable,” says Marie Edmonds, a volcanologist at the University of Cambridge in the United Kingdom. Italian scientists were the first to deploy these instruments at volcanoes like Etna and Stromboli, and they began to notice changes in the C-S ratio in the days and hours prior to eruptions. Since then, U.S. and Japanese geologists have installed instruments at a handful of volcanoes in those countries, and the DECADE project has added them at nine more around the world, including El Popo. Overall, changes in C-S gas ratios seem to be a powerful portent, Fischer says. “Now, we’re seeing it at many different volcanoes.” Perhaps the clearest illustration comes from Turrialba in Costa Rica, a volcano that poses a threat to the city of San José, 30 kilometers to the west. Maarten de Moor, a researcher at the Volcanic and Seismic Observatory of Costa Rica, helped install gas sensors on Turrialba in early 2014, just in time for the volcano to start erupting. He led a study, published in the in August, reporting sharp increases in the C-S ratio of gases a few weeks before each outburst over two eruption cycles (see chart, above). “What we’ve seen is quite mind-blowing,” he says. “These signals are eye-opening.” But for monitoring gas ratios to become a widely used forecasting tool, researchers will need to understand many complicating factors, says Clive Oppenheimer, a volcanologist at the University of Cambridge. “The interpretation of gas chemistry, particularly for the purposes of forecasting, is not an exact science,” he says. “Very far from it.” At Turrialba, for instance, there were different sulfur gases in the mix. Sulfur dioxide (SO ) gas from the magma interacted with underground water to produce hydrogen sulfide during the first eruptive episode, but not the second. De Moor says these observations could indicate that the water eventually boiled off, or that new volcanic conduits formed, bypassing the water reservoirs. At Poás, another Costa Rican volcano, the summit crater contains an acid lake that normally absorbs the SO percolating through it but allows the CO to pass through unimpeded—keeping the C-S ratio relatively high even when an eruption isn’t imminent. But DECADE’s monitoring efforts have revealed that, in the days before an eruption at Poás, the emissions of sulfur gases spike, exceeding the lake’s ability to scrub out the sulfur and causing the C-S ratio to plummet. It’s the opposite signal from the one seen at places like Etna and Turrialba, but it’s equally reliable, Fischer says. Satellites could theoretically help researchers monitor many of the world’s 550 historically active volcanoes from orbit. Instruments aboard NASA’s Terra satellite, for instance, can already measure volcanic sulfur emissions reasonably well. But researchers are still working to measure SO and CO at the same time, and measuring point sources of CO is challenging because of high background levels in the atmosphere. Even a big CO burp from a volcano only increases the concentration measured by satellites by less than a percent, says Florian Schwandner, a geochemist at NASA’s Jet Propulsion Lab in Pasadena, California. For now, the scientists who want to explore the forecasting power of the C-S ratio must wait for ground-based monitors to capture more eruptions. And maintaining these sensors can be a hassle, De Moor says. Even small dustings of ash can cover up solar panels or damage electronics. That’s what caused a sensor on Turrialba to stop transmitting data in May, forcing De Moor to visit once a week to download it in person—sometimes in dangerous conditions. But he says he’s always careful, and tries to remember a bit of wisdom passed down from Fischer, his Ph.D. supervisor, about taking risks in the name of science. “You are going to make more contributions if you actually survive this.” *Correction, 23 November, 4:17 p.m.: A previous version of the story incorrectly stated that the Carnegie Institutions for Science manages DECADE. In fact, DECADE is a program run by the Deep Carbon Observatory, an international effort led by Carnegie.
Nissen P.E.,University of Aarhus |
Schuster W.J.,National Autonomous University of Mexico
Astronomy and Astrophysics | Year: 2010
Aims: Precise abundance ratios are determined for 94 dwarf stars with 5200 < T eff < 6300K, -1.6 < [Fe/H] < -0.4, and distances D ≲ 335 pc. Most of them have halo kinematics, but 16 thick-disk stars are included. Methods: Equivalent widths of atomic lines are measured from VLT/UVES and NOT/FIES spectra with resolutions R ≃ 55 000 and R ≃ 40 000, respectively. An LTE abundance analysis based on MARCS models is applied to derive precise differential abundance ratios of Na, Mg, Si, Ca, Ti, Cr, and Ni with respect to Fe. Results: The halo stars fall into two populations, clearly separated in [α/Fe], where α refers to the average abundance of Mg, Si, Ca, and Ti. Differences in [Na/Fe] and [Ni/Fe] are also present with a remarkably clear correlation between these two abundance ratios. Conclusions: The "high-α" stars may be ancient disk or bulge stars "heated" to halo kinematics by merging satellite galaxies or they could have formed as the first stars during the collapse of a proto-Galactic gas cloud. The kinematics of the "low-α" stars suggest that they have been accreted from dwarf galaxies, and that some of them may originate from the ωCen progenitor galaxy. © 2010 ESO.
Nissen P.E.,University of Aarhus |
Schuster W.J.,National Autonomous University of Mexico
Astronomy and Astrophysics | Year: 2012
Context. A previous study of F and G main-sequence stars in the solar neighborhood has revealed the existence of two distinct halo populations with a clear separation in [α/Fe] for the metallicity range-1.4 < [Fe/H] <-0.7. Taking into account the kinematics and ages of the stars, some Galactic formation models suggest that the "high-alpha" halo stars were formed in situ, whereas the "low-alpha" stars have been accreted from satellite galaxies. Aims. In this paper we investigate if there is a systematic difference in the lithium abundances of stars belonging to the high-and low-alpha halo populations. Methods. Equivalent widths of the Li i 6707.8Å resonance line are measured from high resolution VLT/UVES and NOT/FIES spectra and used to derive Li abundances on the basis of MARCS model atmospheres. Furthermore, masses of the stars are determined from the log T eff-log g diagram by interpolating between evolutionary tracks based on Yonsei-Yale models. Results. There is no significant systematic difference in the lithium abundances of high-and low-alpha stars. For the large majority of stars with masses 0.7 < M/M · < 0.9 and heavy-element mass fractions 0.001 Z < 0.006, the lithium abundance is well fitted by a relation A(Li) = a 0 + a 1 M + a 2 Z + a 3 M Z, where a 0, a 1, a 2, and a 3 are constants. Extrapolating this relation to Z = 0 leads to a lithium abundance close to the primordial value predicted from standard Big Bang nucleosynthesis calculations and the WMAP baryon density. The relation, however, does not apply to stars with metallicities below [Fe/H]-1.5. Conclusions. We suggest that metal-rich halo stars were formed with a lithium abundance close to the primordial value, and that lithium in their atmospheres has been depleted in time with an approximately linear dependence on stellar mass and Z. The lack of a systematic difference in the Li abundances of high-and low-alpha stars indicates that an environmental effect is not important for the destruction of lithium. © 2012 ESO.
Potekhin A.Y.,Saint Petersburg State University |
Pons J.A.,University of Alicante |
Page D.,National Autonomous University of Mexico
Space Science Reviews | Year: 2015
Observations of thermal radiation from neutron stars can potentially provide information about the states of supranuclear matter in the interiors of these stars with the aid of the theory of neutron-star thermal evolution. We review the basics of this theory for isolated neutron stars with strong magnetic fields, including most relevant thermodynamic and kinetic properties in the stellar core, crust, and blanketing envelopes. © 2015, Springer Science+Business Media Dordrecht.
Saldana-Meyer R.,National Autonomous University of Mexico |
Saldana-Meyer R.,Howard Hughes Medical Institute |
Gonzalez-Buendia E.,National Autonomous University of Mexico |
Guerrero G.,National Autonomous University of Mexico |
And 5 more authors.
Genes and Development | Year: 2014
The multifunctional CCCTC-binding factor (CTCF) protein exhibits a broad range of functions, including that of insulator and higher-order chromatin organizer. We found that CTCF comprises a previously unrecognized region that is necessary and sufficient to bind RNA (RNA-binding region [RBR]) and is distinct from its DNA-binding domain. Depletion of cellular CTCF led to a decrease in not only levels of p53 mRNA, as expected, but also those of Wrap53 RNA, an antisense transcript originated from the p53 locus. PAR-CLIP-seq (photoactivatable ribonucleoside-enhanced cross-linking and immunoprecipitation [PAR-CLIP] combined with deep sequencing) analyses indicate that CTCF binds a multitude of transcripts genome-wide as well as to Wrap53 RNA. Apart from its established role at the p53 promoter, CTCF regulates p53 expression through its physical interaction with Wrap53 RNA. Cells harboring a CTCF mutant in its RBR exhibit a defective p53 response to DNA damage. Moreover, the RBR facilitates CTCF multimerization in an RNA-dependent manner, which may bear directly on its role in establishing higher-order chromatin structures in vivo. © 2014 Saldaña-Meyer et al.
Altieri M.A.,University of California |
Toledo V.M.,National Autonomous University of Mexico
Journal of Peasant Studies | Year: 2011
This paper provides an overview of what we call 'agroecological revolution' in Latin America. As the expansion of agroexports and biofuels continues unfolding in Latin America and warming the planet, the concepts of food sovereignty and agroecology-based agricultural production gain increasing attention. New approaches and technologies involving the application of blended agroecological science and indigenous knowledge systems are being spearheaded by a significant number of peasants, NGOs and some government and academic institutions, and they are proving to enhance food security while conserving natural resources, and empowering local, regional and national peasant organizations and movements. An assessment of various grassroots initiatives in Latin America reveals that the application of the agroecological paradigm can bring significant environmental, economic and political benefits to small farmers and rural communities as well as urban populations in the region. The trajectory of the agroecological movements in Brazil, the Andean region, Mexico, Central America and Cuba and their potential to promote broad-based and sustainable agrarian and social change is briefly presented and examined. We argue that an emerging threefold 'agroecological revolution', namely, epistemological, technical and social, is creating new and unexpected changes directed at restoring local self-reliance, conserving and regenerating natural resource agrobiodiversity, producing healthy foods with low inputs, and empowering peasant organizations. These changes directly challenge neoliberal modernization policies based on agribusiness and agroexports while opening new political roads for Latin American agrarian societies. © 2011 Taylor & Francis.
Meier K.,University of Marburg |
Meier K.,National Autonomous University of Mexico |
Brehm A.,University of Marburg
Epigenetics | Year: 2014
Gene transcription is tightly regulated at different levels to ensure that the transcriptome of the cell is appropriate for developmental stage and cell type. The chromatin state in which a gene is embedded determines its expression level to a large extent. Activation or repression of transcription is typically accomplished by the recruitment of chromatin-associated multisubunit protein complexes that combine several molecular tools, such as histone-binding and chromatin-modifying activities. Recent biochemical purifications of such complexes have revealed a substantial diversity. On the one hand, complexes that were thought to be unique have been revealed to be part of large complex families. On the other hand, protein subunits that were thought to only exist in separate complexes have been shown to coexist in novel assemblies. In this review we discuss our current knowledge of repressor complexes that contain MBT domain proteins and/or the CoREST co-repressor and use them as a paradigm to illustrate the unexpected heterogeneity and tool sharing of chromatin regulating protein complexes. These recent insights also challenge the ways we define and think about protein complexes in general. © 2014 Taylor & Francis Group, LLC.
Nissen P.E.,University of Aarhus |
Schuster W.J.,National Autonomous University of Mexico
Astronomy and Astrophysics | Year: 2011
Context. Current models of galaxy formation predict that the Galactic halo was assembled hierarchically. By measuring abundance ratios in stars it may be possible to identify substructures in the halo resulting from this process. Aims. A previous study of 94 dwarf stars with -1.6 < [Fe/H] < -0.4 in the solar neighborhood has revealed the existence of two distinct halo populations with a systematic difference in [α/Fe] at a given metallicity. In continuation of that work, abundances of Mn, Cu, Zn, Y, and Ba are determined for the same sample of stars. Methods. Equivalent widths of atomic lines are measured from high resolution VLT/UVES and NOT/FIES spectra and used to derive abundance ratios from an LTE analysis based on MARCS model atmospheres. The analysis is made relative to two thick-disk stars, HD 22879 and HD 76932, such that very precise differential values are obtained. Results. Systematic differences between the high-α and low-α halo populations are found for [Cu/Fe], [Zn/Fe], and [Ba/Y], whereas there is no significant difference in the case of [Mn/Fe]. At a given metallicity, [Cu/Fe] shows a large scatter that is closely correlated with a corresponding scatter in [Na/Fe] and [Ni/Fe]. Conclusions. The metallicity trends of [Cu/Fe], [Zn/Fe], and [Ba/Y] can be explained from existing nucleosynthesis calculations if the high-α stars formed in regions with such a high star formation rate that only massive stars and type II supernovae contributed to the chemical enrichment. The low-α stars, on the other hand, most likely originate from systems with a slower chemical evolution, characterized by additional enrichment from type Ia supernovae and low-mass AGB stars. © 2011 ESO.
Heinze J.,Albert Ludwigs University of Freiburg |
Frontana-Uribe B.A.,Autonomous University of Mexico State |
Frontana-Uribe B.A.,National Autonomous University of Mexico |
Ludwigs S.,Albert Ludwigs University of Freiburg
Chemical Reviews | Year: 2010
A study on electrochemistry of conducting polymers (CP), their persistent models and new concepts was reported. A central point of electrochemical research is the analysis of the doping process, which corresponds to redox reactions in the polymer matrix. Starting with the electrochemical formation mechanism of CPs, it has been clarified that oligomerization occurs in solution in front of the electrode and is preferably based on succeeding dimerization steps of ionic (radicalic) species. Deposition of the oligomers involves nucleation, growth, and solid state coupling processes. The results of the oligomer approach prove that the redox charging of conjugated systems is due to potential-dependent successive redox steps, which may overlap, causing a faradaic plateau current. Conceivable applications such as electrocatalysis, electronic devices, solar cells, or electrochromic windows are just a few challenges which have motivated researchers to refine strategies in preparing materials with tailor-made properties.
News Article | February 18, 2017
"[It] fills me with pride to be able to carry the flag of Mexico on such an important mission." NASA’s youngest researcher Yair Israel Piña López, 20, might be on his way to Mars. According to Remezcla, the National Autonomous University of Mexico student is among six crew members en route to Utah’s Mars Desert Research Station. Through intricate astronaut cosplay and individual research, the physics major is an essential part of making an eventual mission to the Red Planet possible. “I’m very proud,” he said of his selection in a statement. “Now in Mexico we need to support each other to get ahead, and it fills me with pride to be able to carry the flag of Mexico on such an important mission, and make the first mission to Mars a real possibility.” This post NASA’s Youngest Researcher Poised To Be First Mexican On Mars first appeared on Vibe.
News Article | November 18, 2016
The ancient Temple of Kukulkan, dedicated to its namesake—the feathered serpent god K'uk'ulkan, or Quetzalcoatl—has been slowly revealing its secrets for more than a century. During excavations in the 1930s, a second, hidden pyramid containing an embellished red jaguar-shaped throne was discovered inside of the structure. Years later, in 2015, it was revealed that an enormous underground cavern, or "cenote," lead to a subterranean river system beneath Kukulkan, and possibly held sacred significance to the early Mayans who worshipped there. Now, archaeologists believe they've found the temple's original structure: another smaller pyramid "encapsulated underneath the visible temple" that was built somewhere between 500 and 800 CE, according to the Associated Press. This third pyramid could represent the "pure Maya" style, which bears no stylistic influence from outside civilizations, such as the Toltec peoples who originated from modern Hidalgo, Mexico, and are said to have conquered the city of Chich'en Itza. "If this could be investigated in the future, this structure would be significant because it would speak to the first few periods of habitation of the site and would provide information about how the settlement developed," archaeologist Denisse Lorenia Argote told CNN. "With the discovery of this structure we're talking about something from the pure Mayans. A lot has been excavated, and there is a lot of information on the transitional periods [of the Mayas] and there is a Mexican style at the site, but there is little information on the original site," Argote added. Researchers identified the 33-foot by 66-foot-tall structure using tri-dimensional electric resistivity tomography (ERT-3D), a 3D surveying technique that allows archaeologists to illuminate areas below the surface. The same imaging technique was also used to investigate buried tunnel chambers at Kukulkan that lay concealed within its limestone features. The team of scientists confirmed the existence of a small ramp or stairway, along with portions of a religious altar. According to Rene Chavez Segura, a scientist at the National Autonomous University of Mexico, this new structure is close to the underground cenote, which could mean that Mayans purposefully built around the cavern. Separate excavations at Chich'en Itza have uncovered human bones, likely the victims of ritualistic sacrifice, that had been ceremonially tossed into the cenote. However, not everyone buys into the theory that this discovery is a new one. Geoffrey Braswell, an anthropology professor at the University of California, San Diego who was not involved with the project, suspects the structure was actually found in the 1940s, when an archaeologist supposedly hit a third layer of the pyramid while digging near the second formation. Braswell compared Kukulkan's layout to that of a Russian nesting doll, with several smaller compartments "rattling around inside the same shell." "The tunnel was unstable, so we know very little about this platform. It appears to be much smaller than the outer two pyramids, and is not perfectly aligned within them," Braswell added. Nestled in plain sight in Mexico's Yucatán Peninsula, Kukulkan is one of several monuments that still stand at the Mayan complex of Chich'en Itza. It was likely founded sometime around the 6th century, with Toltec invaders later constructing the visible portion of Kukulkan, which was given the alternate name, "El Castillo," by Spanish Conquistadors. The Temple of Kukulkan is nearly 100-feet-tall, and boasts 91 steps on each of its four faces. Legend has it that Quetzalcoatl returns to Earth twice a year before making its passage into the underworld. A precise knowledge of time and mathematics went into the pyramid's construction, and it's said to be a manifestation of the 365-day Mayan Calendar. For the two days when Quetzalcoatl is present in Chich'en Itza, shadows of a giant serpent can be seen descending the corners of the temple. For 1,000 years, a diverse lineage of Mesoamerican peoples lived, worshipped, and built a mind-bending array of architectural masterpieces within the urban center. Chich'en Itza has since been designated as a UNESCO World Heritage Site, and sees an estimated 1.4 million tourists every year.
News Article | October 26, 2016
Martin Tingley was coming undone. It was late autumn 2014, just over a year into his assistant-professor job at Pennsylvania State University in State College, and he was on an eight-hour drive home after visiting his wife in Boston. He was stressed, exhausted and close to tears. As the traffic zipped past in the dark hours of the early morning, the headlights gave him the surreal feeling that he was inside a video game. Usually, Tingley thought of himself as a “pretty stoic guy” — and on paper, his career was going well. He’d completed a master’s degree in statistics and a PhD in Earth science, both at Harvard University. With these, and four years of postdoctoral experience, he had landed a rare tenure-track faculty position. He thought he would soon be successfully combining statistics and climate science to produce the type of interdisciplinary research that funding agencies say they want. In fact, scientific life was proving tough. He found himself working 60–80 hours per week doing teaching and research. His start-up funding had run out, he had yet to secure a major grant and, according to a practice common in US academia, he would not be paid by his university for three summer months. His wife had not been able to move with him, so he was making tiring weekend commutes. It seemed that the pressures had reached unsustainable levels. Something had to give. Tingley is one of many young scientists who are deeply frustrated with life in research. In September, Nature put a post on Facebook asking scientists who were starting their first independent position to tell us about the challenges that they faced. What followed was a major outpouring of grief. Within a week, nearly 300 scientists from around the world had responded with a candid catalogue of concerns. “I see many colleagues divorcing, getting burnt out, moving out of science, and I am so tired now,” wrote one biomedical researcher from Belgium (see ‘Suffering in science’). Nature selected three young investigators who voiced the most common frustrations; here, we tell their stories. But are young scientists whining — or drowning? Our interviewees acknowledge that they are extremely fortunate to have an opportunity to direct their own creative, stimulating careers, and they are hardly the only professionals who are expected to work hard. It’s easy for each generation to imagine that things are more difficult for them than they were in the past. But some data and anecdotal evidence suggest that scientists do face more hurdles in starting research groups now than did many of their senior colleagues 20–30 years ago. Chief among those challenges is the unprecedented number competing for funding pools that have remained stagnant or shrunk in the past decade. “The number of people is at an all-time high, but the number of awards hasn’t changed,” says Jon Lorsch, director of the US National Institute of General Medical Sciences (NIGMS) in Bethesda, Maryland. “A lot of people with influence on the system recognize this is a serious problem and are trying to fix it.” Young scientists and senior scientists alike feel an acute pressure to publish and are weighed down by a growing bureaucratic burden, with little administrative support. They are largely judged on their record of publishing and of winning grants — but without clear targets, they find themselves endlessly churning out paper after paper. The crucial question is whether this is harming science and scientists. Bruce Alberts, a prominent biochemist at the University of California, San Francisco, and former president of the US National Academy of Sciences, says that it is. The current hyper-competitive atmosphere is stifling creativity and pushing scientists “to do mediocre science”, he says — work that is safe and uninteresting. “We’ve got to reward people who do something differently.” Our informal survey suggests that the situation is already making research an unwelcoming career. “Frankly, the job of being a principal investigator and running a lab just looks horrible,” wrote one neuroscientist from the United States. Tingley wouldn’t disagree. Tingley has always had broad interests. At university in Canada, he switched from art history to physics. For his graduate studies, he was drawn to the vibrant research environment at Harvard, in Cambridge, Massachusetts, where he built statistical methods that helped to make sense of data on past climate gathered from sources such as tree rings and ice cores. By the time he was searching for academic positions, he was already working 60-hour weeks, he says: he would be at work by 8 a.m., go home for dinner, and then pull out his laptop again at night. But by 2013, his research was hitting a high: he had published a statistical analysis in Nature1 and, after applying for jobs worldwide, was offered a joint appointment in meteorology and statistics at Penn State. By this point, his wife, Gabrielle, ran the communications programme for Harvard’s Research Computing centre in Cambridge. Positions offered to her at Penn State fell far short of her qualifications, and she opted to stay where she was. They were facing the ‘two-body problem’ — a long-standing stress point for scientists. Like many first-year assistant professors, Tingley immediately felt pressure to publish in top journals, attract funding and students, and innovate in the classroom. He also knew that his roughly US$200,000 in start-up funding from the university — to cover his summer salary, computing access and more — wouldn’t last long, and he applied to the US National Science Foundation for grants. That process was “heartbreaking”, he says. In one instance, he put in a proposal with his collaborator, organic geochemist Jessica Tierney at the University of Arizona in Tucson, for work on proxies for past sea surface temperatures. On the first round of review, the application got two scores of “excellent” and two of “very good”, yet it still fell short of being funded. The two were encouraged to resubmit, which they did. On the next round, the proposal scored worse. “Part of it is on me, I was unsuccessful,” Tingley says — but the anecdote shows the frustration that young scientists face when trying to get a research programme off the ground. “The funding cycle is brutal.” In the meantime, the pair published the initial stages of the work2 in an article that has been cited 40 times. The views of scientists who responded to Nature revealed a generational divide: many feel that today’s senior investigators experienced a more comfortable trajectory in science and now have a competitive advantage. The ‘baby boom’ scientists, who have longer track records and well-established labs, are in a stronger position to win funds. (In September, Nature asked on Twitter: “What are the challenges facing young scientists?” “Old scientists,” one respondent shot right back.) In December 2014, shortly after his low point in the car, Tingley and his wife took a month-long trip to Australia and Indonesia for some much-needed time together. The next month, Tingley returned to the winter chill at State College and walked across campus feeling as if his head was scraping against the low-hanging clouds. He knew that much of his time was about to be sucked up teaching two advanced courses, leaving little time for research, and he would be back to the tiring commute to see his wife at the weekends. If he didn’t get a grant soon, he would have no summer salary. “My wife and I knew this wasn’t a sustainable way for us to live our lives.” Tingley started googling around late at night, and in March, he spied the perfect job posting. Insurance Australia Group in Sydney was looking for someone with experience in meteorology, statistics and climate. He started there two months later, and his wife easily found a position in communications with the University of New South Wales. Now a senior research analyst, Tingley models and quantifies risks from bush fires, cyclones and other storms. The transcontinental move was not without its difficulties, of course — and as a young researcher moving to the private sector, he’s had to prove himself all over again. Tingley now advises others to recognize that there are various paths to a successful career. “It’s perfectly legitimate to use your training and skill set in the private sector.” He isn’t missing the stress and high expectations placed on young investigators’ shoulders, he says. On a sunny spring Saturday in September, he and his wife head out for a walk on their neighbourhood beach. “It turns out that weekends are fantastic,” he says. Sometimes, pressures come not from chasing funding or tenure, but from chasing an ideal of what makes a good scientist. Young researchers from all disciplines told Nature that they wrestle with the lack of clear expectations for success — and materials scientist Eddie López-Honorato is one. He grew up in Mexico City and studied chemistry there, at the National Autonomous University of Mexico, but for his PhD, he struck out for the University of Manchester, UK. He worked at night and at weekends to complete his experiments, he says, which became more difficult after his son was born. He found it stressful, but his time at Manchester gave him high working standards that he now tries to emulate. Next, he did a postdoctoral fellowship at the Institute for Transuranium Elements in Karlsruhe, Germany, where he worked on developing safer coatings for nuclear fuels used in reactors. At the end of his postdoc, he had the opportunity to return to the United Kingdom as a lecturer at the University of Sheffield, but he and his wife, Paola, yearned to go back to Mexico. They weighed up the pros and cons. López-Honorato knew that he would need to build up his professional reputation in Mexico and that the science infrastructure there was less developed than in Europe. But he thought that working in the United Kingdom would be harder for his family, because they faced constant changes in language and culture. The family chose Mexico. In March 2012, López-Honorato started at the Center for Research and Advanced Studies of the National Polytechnic Institute (CINVESTAV) in Ramos Arizpe. He felt an amazing sense of independence and potential on standing in front of his brand new empty lab space. “You know that you have to get some students and money fast, really fast, and that’s when the urge to work kicks in,” he says. Although the government paid his and his students’ salaries, he still needed to secure funds to support his research. He sent out a flurry of grant proposals for government funding, without success. López-Honorato spent 2012 travelling around Mexico and the United States to build collaborations. He cold e-mailed other scientists to explain his work. The grants started trickling in. By 2014, he had secured enough to cover most of his research expenses and had established a second arm to his lab’s work: developing adsorptive materials to remove arsenic from drinking water, a problem that affected nearly half of all wells in certain parts of Mexico3. Since starting at CINVESTAV, he has published 20 research papers and has built up a lab group of 15 people. Like many of those interviewed, he says that the work to sustain funding is as tough as winning the first grants. Even though his position is secure, he feels the pressure of maintaining his research projects and launching the careers of younger scientists. “It’s stressful when you don’t have money, and stressful when you do have money, because then you have to deliver. It’s my fault if anything goes wrong.” He points to a recent eight-month bureaucratic delay in purchasing a coating machine that is essential to his nuclear-fuel work; it put the project a year behind schedule, and he feels that he is to blame. Many scientists, like other professionals, say that there aren’t enough hours in the day. (“My cohort, we feel exhausted,” said one Generation X scientist, who asked to remain anonymous to protect his career.) In the past two months, López-Honorato says, he has averaged four hours of sleep per night. He and other early-career researchers are “in a stage where our kids and partners need us the most at home”, he says. His second son is now eight months old. He wrestles with whether he has valid reasons to complain, and knows the pressures are largely self-generated. “It’s a problem of saying, ‘That’s enough’,” he says. It’s an issue that many young investigators struggle with — when you’re the one setting the goals, when do you have enough money, students or publications? Philip Guo, a cognitive scientist at the University of California, San Diego, described in a 2014 blogpost how academics often feel as if they are on an accelerating treadmill. In his previous work as a software engineer at Google, Guo wrote, he had “tremendous clarity about what and how much I was expected to do”. Academics, however, have obligations to teach, advise, do research, write grants and support departments, universities and the academic community — and “none of these sources of work know of or care about one another”. Alberts highlights the young investigators who need two major grants, one to supply their salary and one for their research programme. “It’s horrible pressure on young people. How are they going to be excellent at anything? The incentives are all wrong.” This year, López-Honorato is trying to lower his own expectations, applying for only one industry grant — compared with the seven he applied for in 2012 — in the hope that he’ll get home in time to play with his boys. But that internal pressure is hardest to quell. “We want to be the best — that’s how we got to the job we have right now. It’s a personal pressure. But that’s even more difficult to get rid of.” Computing always attracted Felienne Hermans, who taught herself programming at age 10. She specialized in computer science at university and pursued a PhD at Delft University of Technology in the Netherlands. There, she applied methods of software engineering to spreadsheets, so that end users such as accountants or biologists would have better ways of maintaining and annotating their data4. The creative work won her top conference papers, which are key for advancement in this field. When a tenure-track position opened up in her research group of four professors, she asked whether she could apply. She beat internal and external candidates and started as an independent professor in March 2013, at the age of just 28. Two years into the position, Hermans was feeling overwhelmed. She was grappling with the responsibilities of managing her two graduate students and one postdoc, prepping for teaching courses, and what felt like endless ‘service’ requests to review papers for journals and colleagues. The spreadsheet work had in some ways run its course, and she wanted to pivot to a more stimulating research area. But the pressure to publish continuously and copiously dogged her. Her job is formally split between 40% teaching, 40% research and 20% academic service, but the message is that research should trump everything else. “Four papers are better than three. And five are better than four,” she says. Like Alberts, she says the idea that research output is now synonymous with publication quashes all creativity. “Papers are just one form of communicating ideas and experiments.” She yearns “for an afternoon of looking out the window and thinking, ‘What will I do next?’”. Another barrier has been constant throughout her career: being a woman in an overwhelmingly male-dominated field. In 2014, she attended the Code Generation hands-on programming conference in Cambridge, UK, and found herself 1 of only 2 women among roughly 100 attendees. She spent the three days speaking to colleagues about this sad statistic, rather than about her programming, as she would have preferred. “It drags you down and drains your energies,” she says. In the survey, Nature received roughly a dozen comments from young scientists who indicated that sexism, gender bias or lack of support for women held back their careers. Hermans eventually developed a fresh research focus through her Saturday volunteer work at a community centre, where she taught programming to inner-city kids. She and a colleague began thinking about how best to teach the children. Rather than just explaining how to make a robot move forward, say, they wanted to communicate how to maintain code quality through properly naming program features and avoiding ‘code smells’, or poorly designed program sections. The pivot wasn’t totally smooth — her first conference paper about a generic theory for code smells was rejected for not having enough supporting evidence, but now she is hitting her stride. Looking back, Hermans says that she probably should have ignored the pressure to publish, and ruminated more. “But I was new in the tenure track and super scared about not being able to pay my mortgage in two years.” Now, she keeps more careful track of her time. If a colleague knocks on her door for help with a student’s paper, she can turn them down: “I’ve already done my 20% to service.” She’s rearranged her week, cramming teaching, grant writing and service into Monday to Thursday so that she can spend Fridays with her lab group, which now comprises six people. There are more-organized moves to help young investigators — to win grants, for example. Alberts says that “there has to be a shift of resources to the younger people”. He points to the European Research Council grant programme that divides applicants into three career stages — Starter (2–7 years post-PhD), Consolidator (7–12 years post-PhD) and Advanced (more than 12 years post-PhD) — so that applicants from each career stage compete with their peers. In the same vein, this year the NIGMS piloted a grant called Maximizing Investigators’ Research Award, which separates early-stage investigators from established ones, and offers five years of guaranteed funding. That’s an innovation in the US funding system, says Lorsch, because it means no longer “comparing apples and oranges”. And Lorsch says that older investigators should be encouraged to move into alternative stages of their career — working in teaching, mentoring and science advocacy — that don’t require research funds. This could help younger researchers to break in. Other scientists vehemently oppose such ideas. And Alberts, like many senior scientists, doesn’t see the problem as solely based on age. “It’s not about fairness. It’s about how to get the best science for the dollar. We’ll get much better science by funding young or old people to do innovative things.” Hermans is acutely aware that the grumbles of young scientists can be brushed away. “If people are complaining about an injustice, it’s easy to say they are just moaning,” she says. “But these are not imaginary problems.” She feels it’s her duty to be vocal about the challenges facing young investigators. “Experienced researchers should be observing if a young scientist is failing and asking, ‘Are you overwhelmed? Why aren’t you inspired?’” Lorsch says that he knows first-hand that Generation X scientists are not whiners: “I do not hear complaining from the people who are trying to get their first grant or renew their first grant, the people trying to get a lab running,” he says. “It’s the really well-funded people who’ve lost one of their grants — that’s who call me and scream.”
News Article | November 16, 2016
All Rodrigo Medellín wanted was a nap. A biologist at the National Autonomous University of Mexico in Mexico City, he had been trapping bats for several nights in a row in the Lacandon rainforest near Guatemala, and was exhausted. “So I lay on the ground,” he says, and blithely fell asleep. Forty winks later, he awoke uneasily. One of the deadliest snakes in Mexico, a tawny fer-de-lance, was slithering by his head, 30 centimeters away. “I did not move and let her pass,” he recalls. Even after the coast cleared and he set about his bat hunt again, fear wouldn’t loosen its grip on his sleep-deprived mind. That entire night, “I kept hallucinating more snakes,” he says. Every twitching shadow concealed another serpent, every rustling leaf had fangs. Although a veteran of the night shift, Medellín greeted that dawn frazzled. Working nights is unavoidable, or at least commonplace, in certain scientific fields. If you want to study bat behavior or stellar nebulae or sleep physiology, you may have to become half-nocturnal yourself, and scientists who sign up for the night shift encounter problems that just don’t arise during the day. They tumble down embankments in the pitch black, nod off midexperiment, and grow paranoid in the witching hours. It’s a tough gig, and for these and other reasons psychologists and sleep experts take a dim view of night work, which can disrupt sleep, throw hormones out of whack, and make you measurably dumber. “Human beings are meant to be regulated by light,” says Candice Alfano, a psychologist at the University of Houston in Texas who’s leading a study for NASA that includes a focus on circadian rhythm disruptions. “We still have that biology, even though our social culture has changed dramatically.” And yet, few of the nocturnal researchers Science talked to would give up their work. Amid the misery and exhaustion, science after hours can still produce moments of serenity, even euphoria. “Either you’re getting to know more about the natural world, or you’re getting to know more about yourself,” Medellín says. “It’s always a source of happiness to me.” The challenges faced by researchers on the night shift vary significantly by discipline. Biologists, for instance, sometimes upend their whole lives to match the nondiurnal schedules of certain plants and animals. Nicky Creux, a postdoc at the University of California (UC), Davis, studies sunflowers, whose buds open up just before dawn. That means getting up at 3:30 a.m. for weeklong stretches to set up cameras and dissecting equipment, in order to track the minute-by-minute emergence and growth of anthers and styles, plant reproductive organs. Although she’s naturally a morning lark, “Cycling out to the fields in the dark is pretty miserable,” she laughs. At the end of one recent 6-day stretch, her fine motor skills basically broke down from exhaustion: She kept dropping the tiny flower parts and losing them in the grass. She’s hoping the lost data won’t submarine the whole week. Creux’s social life suffered as well, because she essentially lived those weeks in a different time zone from everyone around her. “Friends want to go to dinner and I can’t,” she says. “I have to be in bed by 8 p.m.” She also found it hard to abandon the lab to rest while others nearby were still hard at work. “As a scientist, you’re used to working 12-hour shifts, and staying until 7 p.m. I had to get my head around the fact that it’s okay to go home at 3.” Alfano says that like traditional night workers, such as hospital staff, janitors, and truckers, scientists can feel tempted to “cheat” and attend daytime events with friends and family. That can compromise an already spotty sleep schedule. “At some point, you’re really pushing the limit of what your sleep-wake system can do,” she says. Beyond the strange hours, nocturnal biologists often work in environments that can prove dangerous to human beings, who lack the dim light vision and sharp senses of smell or hearing that most night-adapted species rely on. Hong Young Yan, a fish and frog biologist at the Taiwan National Academy of Science in Taipei, was tramping along a dark trail at night once when a colleague went tumbling down a 30-meter embankment. “Suddenly, he just disappeared,” Yan says. The colleague lived, but sprained an ankle and cried with pain as he limped back to camp. Another time, Yan walked smack into a beehive in the dark, and the colony erupted. “We had to run and jump into a stream” to dodge the swarm, he says. To help his students overcome their fear of the dark, Medellín performs a little hazing ritual, which involves creeping up behind them in a jaguar mask. He gets a lot of screams. “Some might call it a bit of abuse,” Medellín says, but he argues that maintaining a calm demeanor is essential when you dwell among the bats or other nocturnal animals: “The dark is much more comfortable, if you accept it.” Unlike biologists, astronomers usually moonlight indoors, in relative comfort. But being sedentary has its own downside: drowsiness. Brent Miszalski, an astronomer in Cape Town who observes at the South African Astronomical Observatory in Sutherland, recalled one night during a multiweek telescope run when he helped clean up after a pipe burst. “I didn’t do anything particularly strenuous,” he says, “but the physical work, combined with the exhaustion, meant that when I had to start observing again, I fell asleep in the chair.” He’s far from alone. Drowsiness hits regulars on the night shift for two reasons. First, night work violates our body’s expectations about when to sleep and when to remain alert. Second, compensatory daytime sleep usually stinks. Exposure to sunlight prevents the brain from producing melatonin and other natural soporifics. As a result, people sleep fewer hours, and less deeply, during the day. Alfano likens the overall feeling to chronic jet lag. The poor sleep experienced by night workers also has knock-on effects. It can raise blood pressure and alter levels of hormones, such as ghrelin and leptin, that affect appetite and satiety. As a result, “People tend to snack through night shifts instead of sitting down to eat meals, and those snacks are often quite unhealthy,” says Philip Tucker, a psychologist at Swansea University in the United Kingdom who studies shift workers. Not surprisingly, longtime night shift workers suffer from obesity and other conditions such as cardiovascular disease at rates up to double that of daytime workers. No studies specifically examine whether scientists on the night shift suffer those problems. And most researchers don’t work at night for months or years at a stretch. Indeed, there’s a trend nowadays toward less night work. Computer technology has automated many tasks, and many observatories and particle accelerators have dedicated technicians to run the complex instruments. Astronomers, for example, can observe the sky remotely by requesting a series of observations and simply waiting for the results, without having to travel and turn their daily routine upside down. Still, night shifts remain a tradition and even a badge of honor in many fields, and the on/off schedules at such facilities—at Miszalski’s observatory, most astronomers work a “night week” each month—can be physically grueling. “It’s the worst of both worlds,” Tucker says. “A week [at night] definitely disrupts the body clock. But by the time you get to the end, and are approaching adjustment, you go back” to daytime hours, wiping you out all over again. In order to minimize such disruptions, Miszalski prefers working 2-week-long observation shifts every few months. The toll on the body can impair the mind as well. Night work may slow down mental processing, shorten attention span, and leave people feeling unmotivated. NASA scientist-astronaut Tracy Caldwell Dyson, who studied gas chemistry in orbit, had to endure several “slam-shifts” during her two tours on the International Space Station. These consisted of a full day’s work, a “silly 2-hour nap,” she says, and another immediate shift, usually to coordinate with ground crews in Russia. During such shifts, Dyson and other astronauts occasionally took computer tests to measure mental sharpness—matching patterns, or adding up strings of small numbers. The results were clear, she says: “We’re kidding ourselves to think we’re at our best when sleep is compromised.” Astronomer Vivian U, a postdoc at UC Riverside, once tried writing a paper overnight at the United Kingdom Infrared Telescope on Mauna Kea in Hawaii, where the 4267-meter elevation can exacerbate the mental loopiness caused by an extended stint of night work. Feeling inspired, she crafted a brilliant analogy about the similarities between the formation of galaxies and apples falling from trees. The next morning she realized it was gibberish. All joking aside, night shift–induced mental fogginess does increase the odds of mishaps. Overnight workers contributed in small but significant ways to the accidents at Three Mile Island in Pennsylvania and Chernobyl in Ukraine as well as the Challenger space shuttle explosion. Several studies have found that medical staff working daylong, or longer, shifts make more errors (e.g., misreading electrocardiogram outputs, giving the wrong medication) when chronically deprived of sleep. Nor does the danger stop at work. Studies of doctors and nurses on night shifts found them twice as likely to get in wrecks or nod off behind the wheel on the drive home. Some facilities have informal rules to save scientists from somnolent stupidity. “I was told to never send an email from the control room at night,” says Lizette Guzman-Ramirez, an astronomer at Leiden Observatory in the Netherlands. “You get up and read it the next morning, and it doesn’t make any sense.” Similarly, some nocturnal scientists have developed tricks to stay alert at 3 a.m. Miszalski and his co-workers have “nonsense conversations” or even “make animal noises” to perk up. When Guzman-Ramirez worked a few 14-hour nights by herself at a telescope in South Africa, she belted out pop songs at the top of her lungs. “I remember singing a lot of ‘Torn,’ by Natalie Imbruglia,” she says. “It was my go-to karaoke song, and I perfected it.” If 14-hour overnight shifts sound bad, then pity poor polar scientists. During the polar winter they often endure several months without sunlight—the ultimate night shift. Not surprisingly, polar stations attract night owls. “I’ve always had this loathing for sunrise, because I knew I should be in bed already,” says Mack van Rossem, a physicist at the IceCube Neutrino Observatory at the South Pole. But without a sunrise to cap his all-nighters during the winter, Van Rossem found himself drifting through 32-hour “days,” where he’d sleep for 10 hours at once and work for 22. Now that the sun has risen for the year—it poked its head over the horizon in mid-September and won’t set again for months—he’s had trouble sleeping, logging 6 hours a night at most. “It definitely takes me a few hours to get going now,” he says. Polar scientists also struggle with another facet of winter life. Many outdoor polar experiments require absolute darkness, and residents at the bases must cover their windows to prevent light from leaking out. “So you’re in a box all the time,” Van Rossem says. “I really missed being able to look out the window.” John Parker, a medical doctor at the Australian Antarctic base at Davis, agrees. “When you’re not looking out the window, your perspective of life changes,” he says. “Small things become much larger.” He called it mental “myopia,” and in a detail worthy of Edgar Allan Poe, even found himself growing paranoid in the endless nighttime: “I’d lose something and think, ‘Someone’s taken it!’ A bit of suspicion comes in.” Other scientists who worked overnight shifts elsewhere reported similar, if subtler, mood swings, growing more irritable and snappy with colleagues. Despite these rough patches, Parker appreciated his months-long night shift in Antarctica, calling it an adventure. Activities like dart nights and costume parties helped defuse tension, and the 16-person team held a barbecue in September to welcome the sun back. “It was cloudy, so we didn’t see anything,” he laughs, “but it was a special event.” He’d definitely overwinter there again—following a suitable break. “Maybe after having some fresh fruit.” Many scientists who work at night share Parker’s sentiments: It was miserable, and I loved it. Some savored the profound quiet, or a perfect sunrise, or shimmering green aurorae on white snow. Some learned to appreciate different tenors of darkness—the relatively bright desert sky at night versus caves and undercanopies so black that opening or closing your eyes makes no difference. If nothing else, some enjoyed binge-watching movies or catching up on neglected work. This past winter in Antarctica, Parker completed a memoir about several humanitarian medical missions he’s served on. “And I can say I wrote my book in 1 night,” he adds. As they age, many nocturnal scientists find that their capacity for night work has diminished. Yet they still relish the chance to connect more deeply with some beloved species or natural wonder, and somehow the sacrifice and discomfort of night work makes it all the more special. Sergio Speziale, a mineral physicist at the German Research Centre for Geosciences in Potsdam, has pulled many a long night at synchrotrons and other particle accelerators around the world, and his time served has left him feeling philosophical.“Repeated night shifts tend to amplify the effect of whatever happens,” he says. “If things are really cool and interesting, there’s a more euphoric approach to discovery. When things fall apart, the sadness is amplified, too. Working nights will always remain in my mind. It’s sometimes good to experience that in life.” If you're interested in learning more about circadian rhythms then listen to our podcast interview with author Sam Kean and check out related research.
News Article | November 17, 2016
Scientists studying the Chicxulub crater have shown how large asteroid impacts deform rocks in a way that may produce habitats for early life. Scientists studying the Chicxulub crater have shown how large asteroid impacts deform rocks in a way that may produce habitats for early life. Around 65 million years ago a massive asteroid crashed into the Gulf of Mexico causing an impact so huge that the blast and subsequent knock-on effects wiped out around 75 per cent of all life on Earth, including most of the dinosaurs. This is known as the Chicxulub impact. In April and May 2016, an international team of scientists undertook an offshore expedition and drilled into part of the Chicxulub impact crater. Their mission was to retrieve samples from the rocky inner ridges of the crater - known as the 'peak ring' - drilling 506 to 1335 metres below the modern day sea floor to understand more about the ancient cataclysmic event. Now, the researchers have carried out the first analysis of the core samples. They found that the impact millions of years ago deformed the peak ring rocks in such a way that it made them more porous, and less dense, than any models had previously predicted. Porous rocks provide niches for simple organisms to take hold, and there would also be nutrients available in the pores, from circulating water that would have been heated inside the Earth's crust. Early Earth was constantly bombarded by asteroids, and the team have inferred that this bombardment must have also created other rocks with similar physical properties. This may partly explain how life took hold on Earth. The study, which is published today in the journal Science, also confirmed a model for how peak rings were formed in the Chicxulub crater, and how peak rings may be formed in craters on other planetary bodies. The team's new work has confirmed that the asteroid, which created the Chicxulub crater, hit the Earth's surface with such a force that it pushed rocks, which at that time were ten kilometres beneath the surface, farther downwards and then outwards. These rocks then moved inwards again towards the impact zone and then up to the surface, before collapsing downwards and outwards again to form the peak ring. In total they moved an approximate total distance of 30 kilometres in a matter of a few minutes. Professor Joanna Morgan, lead author of the study from the Department of Earth Science and Engineering, said: "It is hard to believe that the same forces that destroyed the dinosaurs may have also played a part, much earlier on in Earth's history, in providing the first refuges for early life on the planet. We are hoping that further analyses of the core samples will provide more insights into how life can exist in these subterranean environments." The next steps will see the team acquiring a suite of detailed measurements from the recovered core samples to refine their numerical simulations. Ultimately, the team are looking for evidence of modern and ancient life in the peak-ring rocks. They also want to learn more about the first sediments that were deposited on top of the peak ring, which could tell the researchers if they were deposited by a giant tsunami, and provide them with insights into how life recovered, and when life actually returned to this sterilised zone after the impact. "The formation of peak rings in large impact craters", published Thursday 17 November in the journal Science. See paper for full list of authors. Imperial College London is one of the world's leading universities. The College's 16,000 students and 8,000 staff are expanding the frontiers of knowledge in science, medicine, engineering and business, and translating their discoveries into benefits for society. Founded in 1907, Imperial builds on a distinguished past - having pioneered penicillin, holography and fibre optics - to shape the future. Imperial researchers work across disciplines to improve health and wellbeing, understand the natural world, engineer novel solutions and lead the data revolution. This blend of academic excellence and its real-world application feeds into Imperial's exceptional learning environment, where students participate in research to push the limits of their degrees. Imperial collaborates widely to achieve greater impact. It works with the NHS to improve healthcare in west London, is a leading partner in research and education within the European Union, and is the UK's number one research collaborator with China. Imperial has nine London campuses, including its White City Campus: a research and innovation centre that is in its initial stages of development in west London. At White City, researchers, businesses and higher education partners will co-locate to create value from ideas on a global scale. http://www. Imperial College London academic experts are available for interview via broadcast quality Globelynx TV facilities and an ISDN line for radio at our South Kensington Campus. To request an interview, please contact a member of the communications team http://www. The expedition was conducted by the European Consortium for Ocean Research Drilling (ECORD) as part of the International Ocean Discovery Program (IODP). The expedition is also supported by the International Continental Scientific Drilling Programme (ICDP). The expedition would not have been possible without the support and assistance of the Yucatán Government, Mexican federal government agencies and scientists from the National Autonomous University of Mexico (UNAM) and the Centro de Investigación Científica de Yucatán (CICY).
Schmulson M.,National Autonomous University of Mexico |
Chang L.,University of California at Los Angeles
Alimentary Pharmacology and Therapeutics | Year: 2011
Aliment Pharmacol Ther 2011; 33: 1071-1086 Summary Background Abdominal bloating and distension are common symptoms in patients with functional gastrointestinal disorders (FGIDs), however, relatively little is known about their treatment. Aim To review the treatment trials for abdominal bloating and distension. Methods A literature review in Medline for English-language publications through February 2010 of randomised, controlled treatment trials in adults. Study quality was assessed according to Jadad's score. Results Of the 89 studies reviewed, 18% evaluated patients with functional dyspepsia, 61% with irritable bowel syndrome (IBS), 10% with chronic constipation and 10% with other FGIDs. No studies were conducted in patients diagnosed with functional abdominal bloating. The majority of trials investigated the efficacy of prokinetics or probiotics, although studies are heterogeneous with respect to diagnostic criteria and outcome measures. In general, bloating and/or distension were evaluated as secondary endpoints or as individual symptoms as part of a composite score rather than as primary endpoints. A greater proportion of IBS patients with constipation reported improvement in bloating with tegaserod vs. placebo (51% vs. 40%, P < 0.0001) and lubiprostone (P < 0.001). A greater proportion of nonconstipating IBS patients reported adequate relief of bloating with rifaximin vs. placebo (40% vs. 30%, P < 0.001). Bloating was significantly reduced with the probiotics, Bifidobacterium infantis 35624 (1 à- 10 8 dose vs. placebo: -0.71 vs. -0.44, P < 0.05) and B. animalis (live vs. heat-killed: -0.56 ± 1.01 vs. -0.31 ± 0.87, P = 0.03). Conclusions Prokinetics, lubiprostone, antibiotics and probiotics demonstrate efficacy for the treatment of bloating and/or distension in certain FGIDs, but other agents have either not been studied adequately or have shown conflicting results. © 2011 Blackwell Publishing Ltd.
Rodriguez A.H.,National Autonomous University of Mexico |
Moreno Y.,University of Zaragoza
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2010
The use of dyadic interaction between agents, in combination with homophily (the principle that "likes attract") in the Axelrod model for the study of cultural dissemination, has two important problems: the prediction of monoculture in large societies and an extremely narrow window of noise levels in which diversity with local convergence is obtained. Recently, the inclusion of social influence has proven to overcome them. Here, we extend the Axelrod model with social influence interaction for the study of mass media effects through the inclusion of a superagent which acts over the whole system and has non-null overlap with each agent of the society. The dependence with different parameters as the initial social diversity, size effects, mass media strength, and noise is outlined. Our results might be relevant in several socioeconomic contexts and for the study of the emergence of collective behavior in complex social systems. © 2010 The American Physical Society.
Ochoa T.J.,Cayetano Heredia Peruvian University |
Ochoa T.J.,University of Houston |
Contreras C.A.,Cayetano Heredia Peruvian University |
Contreras C.A.,National Autonomous University of Mexico
Current Opinion in Infectious Diseases | Year: 2011
Purpose of Review: Enteropathogenic Escherichia coli (EPEC) is an important diarrheal pathogen of young children. As the diagnosis of EPEC is now based mainly on molecular criteria, there has been an important change in its prevalence. The purpose of this study is to review the current epidemiology of EPEC infection and the new insights into its physiopathology. Recent Findings: Recent epidemiological studies indicate that atypical EPEC (aEPEC) is more prevalent than typical EPEC (tEPEC) in both developed and developing countries, and that aEPEC is important in both pediatric endemic diarrhea and diarrhea outbreaks. Therefore, it is important to further characterize the pathogenicity of these emerging strains. The virulence mechanisms and physiopathology of the attaching and effacing lesion (A/E) and the type three secretion-system (T3SS) are complex but well studied. A/E strains use their pool of locus of enterocyte effacement (LEE)-encoded and non-LEE-encoded effector proteins to subvert and modulate cellular and barrier properties of the host. However, the exact mechanisms of diarrhea in EPEC infection are not completely understood. Summary: Remarkable progress has been made to identify virulence determinants required to mediate the pathogenesis of EPEC. However, fast, easy, and inexpensive diagnostic methods are needed in order to define optimal treatment and prevention for children in endemic areas. © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins.
Trillmich F.,Bielefeld University |
Hudson R.,National Autonomous University of Mexico
Developmental Psychobiology | Year: 2011
Interest has been growing among behavioral biologists in individual differences in animal behavior of the kind that can be considered to reflect differences in personality. Once considered the exclusive domain of human psychology, biologists have found evidence for personality across a wide range of species, while behavioral ecologist and theoretical biologists recognize the likely evolutionary origins and contribution to fitness of such. However, until recently most work has concentrated on ultimate questions of fitness and thus on adult animals, with little attention given to proximate, developmental origins. This is now changing, as approaches to studying animal personality broaden and methodologies are developed enabling this to be studied across periods of near continuous and often rapid ontogenetic change. Debate continues, however, about the right methodologies to characterize the phenomenon and attempt to do so in a comparable manner across taxa that differ as widely in the expression of "personality" as insects and mammals. This makes it necessary to discuss this field in an interdisciplinary context among psychologists and biologists, and was the rational for a meeting on "The Emergence of Personality in Animals" held in May 2010 at the Center for Interdisciplinary Research (Zentrum für Interdisziplinäre Forschung; ZiF), Bielefeld, Germany. The diversity of topics, viewpoints and organisms covered and the excitement created by the ensuing discussions is reflected in the resulting collection of papers forming this special issue. © 2011 Wiley Periodicals, Inc.
Martinez-Ortiz J.,National Autonomous University of Mexico |
Flores R.,Electric Research Institute of Mexico |
Vazquez-Duhalt R.,National Autonomous University of Mexico
Biosensors and Bioelectronics | Year: 2011
In order to improve the direct electron transfer in enzymatic biofuel cells, a rational design of a laccase electrode is presented. Graphite electrodes were functionalized with 4-[2-aminoethyl] benzoic acid hydrochloride (AEBA). The benzoic acid moiety of AEBA interacts with the laccase T1 site as ligand with an association constant (KA) of 6.6×10-6M. The rational of this work was to orientate the covalent coupling of laccase molecule with the electrode surface through the T1 site and thus induce the direct electron transfer between the T1 site and the graphite electrode surface. Direct electron transfer of laccase was successfully achieved, and the semi-enzymatic fuel cell Zn-AEBA laccase showed a current density of 2977μAcm-2 and a power density of 1190μWcm-2 at 0.41V. The molecular oriented laccase cathode showed 37% higher power density and 43% higher current density than randomly bound laccase cathode. Chronoaperometric measurements of the Zn-AEBA fuel cell showed functionality on 6h. Thus, the orientation of the enzyme molecules improves the electron transfer and optimizes enzyme-based fuel cells efficiency. © 2010 Elsevier B.V.
Velasco-Velazquez M.,National Autonomous University of Mexico |
Pestell R.G.,Thomas Jefferson University
OncoImmunology | Year: 2013
Recently, we have shown that the CCL5/CCR5 axis is active in patients affected by an aggressive basal subtype of breast cancer. Using preclinical models, we have demonstrated that CCR5 promotes breast cancer invasiveness and metastatic potential, while CCR5 inhibition abrogates them. Thus, CCR5 antagonists may constitute an alternative therapeutic approach for patients affected by metastatic basal breast cancer. © 2013 Landes Bioscience. © 2013 Landes Bioscience.
Piekarewicz J.,Florida State University |
Sanchez G.T.,National Autonomous University of Mexico
Physical Review C - Nuclear Physics | Year: 2012
Monte Carlo simulations of neutron-rich matter of relevance to the inner neutron-star crust are performed for a system of A=5000 nucleons. To determine the proton fraction in the inner crust, numerical simulations are carried out for a variety of densities and proton fractions. We conclude-as others have before us using different techniques-that the proton fraction in the inner stellar crust is very small. Given that the purported nuclear pasta phase in stellar crusts develops as a consequence of the long-range Coulomb interaction among protons, we question whether pasta formation is possible in such proton-poor environments. To answer this question, we search for physical observables sensitive to the transition between spherical nuclei and exotic pasta structures. Of particular relevance is the static structure factor S(k)-an observable sensitive to density fluctuations. However, no dramatic behavior was observed in S(k). We regard the identification of physical observables sensitive to the existence-or lack thereof-of a pasta phase in proton-poor environments as an open problem of critical importance. © 2012 American Physical Society.
De La Torre L.,National Autonomous University of Mexico |
Langer J.C.,Hospital for Sick Children
Seminars in Pediatric Surgery | Year: 2010
The transanal endorectal pull-through emerged in the late 1990s as the most recent step in the evolution of the surgical correction of Hirschsprung disease. This operation provides the advantages of a minimal access approach with shorter hospital stay, shorter time to full feeding, less pain, and improved cosmesis with excellent outcomes. This article will review the technical principles of the transanal endorectal pull-through, and will address ongoing controversies in the application of this technique. We will also discuss an organized approach to the problem of obstructive symptoms that may affect a subgroup of patients after the transanal pull-through. © 2010 Elsevier Inc.
Munguia-Rosas M.A.,Autonomous University of Yucatán |
Munguia-Rosas M.A.,University of Northampton |
Ollerton J.,University of Northampton |
Parra-Tabla V.,Autonomous University of Yucatán |
De-Nova J.A.,National Autonomous University of Mexico
Ecology Letters | Year: 2011
Flowering times of plants are important life-history components and it has previously been hypothesized that flowering phenologies may be currently subject to natural selection or be selectively neutral. In this study we reviewed the evidence for phenotypic selection acting on flowering phenology using ordinary and phylogenetic meta-analysis. Phenotypic selection exists when a phenotypic trait co-varies with fitness; therefore, we looked for studies reporting an association between two components of flowering phenology (flowering time or flowering synchrony) with fitness. Data sets comprising 87 and 18 plant species were then used to assess the incidence and strength of phenotypic selection on flowering time and flowering synchrony, respectively. The influence of dependence on pollinators, the duration of the reproductive event, latitude and plant longevity as moderators of selection were also explored. Our results suggest that selection favours early flowering plants, but the strength of selection is influenced by latitude, with selection being stronger in temperate environments. However, there is no consistent pattern of selection on flowering synchrony. Our study demonstrates that phenotypic selection on flowering time is consistent and relatively strong, in contrast to previous hypotheses of selective neutrality, and has implications for the evolution of temperate floras under global climate change. © 2011 Blackwell Publishing Ltd/CNRS.
Soldevila G.,National Autonomous University of Mexico |
Raman C.,University of Alabama at Birmingham |
Lozano F.,University of Barcelona
Current Opinion in Immunology | Year: 2011
CD5 is a scavenger-like receptor expressed in association with the antigen-specific receptors on T and B-1a lymphocytes. Recent studies reveal a broader biology for CD5 that includes its role as regulator of cell death and as a receptor for pathogen-associated molecular patterns, in addition to its previously described function as an inhibitory receptor. These findings shed new light into the mechanistic role of CD5 in leukemias and effector cells to exogenous (infectious) or endogenous (autoimmune, tumoral) antigens. The newly identified properties make this receptor a potential candidate to be targeted for therapeutic intervention as well as immune modulation. This review describes the current knowledge on the function of CD5 as an immunomodulatory receptor both in health and in disease. © 2011 Elsevier Ltd.
Tocilizumab inhibits structural joint damage in rheumatoid arthritis patients with inadequate responses to methotrexate: Results from the double-blind treatment phase of a randomized placebo-controlled trial of tocilizumab safety and prevention of structural joint damage at one year
Kremer J.M.,Albany Medical College |
Blanco R.,Hospital Marques Of Valdecilla |
Brzosko M.,Pomeranian Medical University |
Burgos-Vargas R.,National Autonomous University of Mexico |
And 2 more authors.
Arthritis and Rheumatism | Year: 2011
Objective. To assess the efficacy and safety o tocilizumab plus methotrexate (MTX) versus MTX alone in preventing structural joint damage and improving physical function and disease activity in patient with moderate-to-severe rheumatoid arthritis and inadequate responses to MTX. Methods. A total of 1,196 patients were enrolled in a 2-year, randomized, double-blind, placebo-controlled trial. Patients received tocilizumab (8 mg/kg or 4 mg/kg) or placebo every 4 weeks plus MTX. Rescue treatment was available from week 16. Results from year 1 are presented. Results. Mean change in the total Genantmodified Sharp score was 0.29 and 0.34 with tocilizumab 8 mg/kg plus MTX and 4 mg/kg plus MTX, respectively, versus 1.13 with placebo plus MTX (P < 0.0001 for both comparisons). Analysis of variance of the area under the curve for change from baseline in the disability index of the Health Assessment Questionnaire showed greater decreases with tocilizumab 8 mg/kg and 4 mg/kg (-144.1 and-128.4 units, respectively) than with placebo (-58.1 units; P < 0.0001 for both comparisons). Proportions of patients with American College of Rheumatology 20%, 50%, and 70% improvement and with Disease Activity Score in 28 joints remission were higher in those receiving 8 mg/kg tocilizumab than in those receiving placebo (P < 0.0001 for all comparisons). The safety profile of tocilizumab was consistent with the profiles in previous studies. Infections were the most common adverse and serious adverse events. Conclusion. The findings of this study show that tocilizumab plus MTX results in greater inhibition of joint damage and improvement in physical function than does MTX alone. Tocilizumab has a wellcharacterized safety profile. © 2011, American College of Rheumatology.
Casimiro M.C.,Thomas Jefferson University |
Velasco-Velazquez M.,National Autonomous University of Mexico |
Aguirre-Alvarado C.,National Autonomous University of Mexico |
Pestell R.G.,Thomas Jefferson University
Expert Opinion on Investigational Drugs | Year: 2014
Introduction: Intensive efforts, over the last decade, have been made to inhibit the kinase activity of cyclins that act as mediators during cell-cycle progression. Activation of the cyclin D1 oncogene, often by amplification or rearrangement, is a major driver of multiple types of human tumors including breast and squamous cell cancers, B-cell lymphoma, myeloma and parathyroid adenoma. Areas covered: In this review, the authors summarize the activity of cyclins and cyclin-dependent kinases in cell-cycle progression and transcription. They focus on cyclin D1/CDK4/CDK6, a central mediator in the transition from G1 to S phase. Furthermore, the authors discuss the first generation of pan-cyclin-dependent kinase inhibitors that failed to meet expectation and discuss, in detail, the second generation of highly specific cyclin D1/CDK4/CDK6 inhibitors that are proving to be more efficacious. Expert opinion: The mechanism by which cyclin D1 drives tumorigenesis may be dependent on kinase and kinase-independent functions. Further evidence is necessary to delineate the roles of cyclin D1 in early pre-neoplastic lesions where its overexpression may promote genomic instability in a kinase-independent manner. © 2014 Informa UK, Ltd.
Cejnar P.,Charles University |
Stransky P.,National Autonomous University of Mexico
AIP Conference Proceedings | Year: 2014
We use two models of nuclear collective dynamics-the geometric collective model and the interacting boson model-to illustrate principles of classical and quantum chaos. We propose these models as a suitable testing ground for further elaborations of the general theory of chaos in both classical and quantum domains. © 2014 AIP Publishing LLC.
Bryan S.E.,Queensland University of Technology |
Ferrari L.,National Autonomous University of Mexico
Bulletin of the Geological Society of America | Year: 2013
Large igneous provinces are exceptional intraplate igneous events throughout Earth's history. Their significance and potential global impact are related to the total volume of magma intruded and released during these geologically brief events (peak eruptions are often within 1-5 m.y. in duration) where millions to tens of millions of cubic kilometers of magma are produced. In some cases, at least 1% of Earth's surface has been directly covered in volcanic rock, being equivalent to the size of small continents with comparable crustal thicknesses. Large igneous provinces thus represent important, albeit episodic, periods of new crust addition. However, most magmatism is basaltic, so that contributions to crustal growth will not always be picked up in zircon geochronology studies, which better trace major episodes of extension-related silicic magmatism and the silicic large igneous provinces. Much headway has been made in our understanding of these anomalous igneous events over the past 25 yr, driving many new ideas and models. (1) The global spatial and temporal distribution of large igneous provinces has a long-term average of one event approximately every 20 m.y., but there is a clear clustering of events at times of super continent breakup, and they are thus an integral part of the Wilson cycle and are becoming an increasingly important tool in reconnecting dispersed continental fragments. (2) Their compositional diversity in part reflects their crustal setting, such as ocean basins and continental interiors and margins, where, in the latter setting, large igneous province magmatism can be dominated by silicic products. (3) Mineral and energy resources, with major platinum group elements (PGEs) and precious metal resources, are hosted in these provinces, as well as magmatism impacting on the hydro carbon potential of volcanic basins and rifted margins through enhancing source-rock maturation, providing fluid migration pathways, and initiating trap formation. (4) Biospheric, hydro spheric, and atmospheric impacts of large igneous provinces are now widely regarded as key trigger mechanisms for mass extinctions, although the exact kill mechanism(s) are still being resolved. (5) Their role in mantle geodynamics and thermal evolution of Earth as large igneous provinces potentially record the transport of material from the lower mantle or core-mantle boundary to the Earth's surface and are a fundamental component in whole mantle convection models. (6) Recognition of large igneous provinces on the inner planets, with their planetary antiquity and lack of plate tectonics and erosional processes, means that the very earliest record of large igneous province events during planetary evolution may be better preserved there than on Earth. © 2013 Geological Society of America.
Agency: Cordis | Branch: FP7 | Program: BSG-CSO | Phase: ENV.2011.4.2.3-1 | Award Amount: 2.47M | Year: 2012
Current development models are leading to unprecedented environmental challenges, chief amongst them, climate change. How to respond to these challenges are key research questions. Although they are global problems, their effects are felt locally, especially by the communities that traditionally base their livelihoods in those natural resources. The relevance of these problems at global level has driven different initiatives to increase public awareness and to put in practice measures to improve them. However, many good conservation and management practices are done at local level. Research is needed to better understand local capabilities and to encourage and support potential locally-owned solutions. COMET-LAs objective is to identify sustainable community-based governance models for the management of natural resources that could be used in different social-ecological systems in a context of climate change and increasing competition for the use of these resources. A civil society-scientific partnership has been created to develop the project. Three Latin American civil society organizations, a global CSO and 7 research institutions (3 Latin American and 4 European) comprise this partnership. COMET-LA will create a space of interaction for CSOs, policy makers and research organizations, sharing local and scientific knowledge and contributing to a better knowledge of problems and potential solutions for current and future sustainable management of natural resources. Three different case studies will be analyzed: water and biodiversity systems in Colombia, forest systems in Mexico and marine and coastal areas in Argentina. Similar methods will be used to characterize the current and future ecosystem states, sustainable governance models and locally-tailored scenarios for future changes and challenges. The outcomes will be synthesized and up-scaled to deliver a potentially useful tool to other local communities facing current environmental challenges.
News Article | December 26, 2016
« Toyota reports Intelligent Clearance Sonar has significantly reduced pedal misapplication & vehicle reversing accidents | Main | Materials science as key enabler for clean energy transition » Scientists at Stanford University and the Department of Energy’s SLAC National Accelerator Laboratory have discovered a one-pot synthesis process using diamondoids—the smallest possible bits of diamond—to assemble atoms into hybrid metal–organic chalcogenide nanowires with solid inorganic cores having three-atom cross-sections, representing the smallest possible nanowires. By grabbing various types of atoms and putting them together LEGO-style, the new technique could potentially be used to build tiny wires for a wide range of applications, including fabrics that generate electricity, optoelectronic devices that employ both electricity and light, and superconducting materials that conduct electricity without any loss. The scientists reported their results in Nature Materials. What we have shown here is that we can make tiny, conductive wires of the smallest possible size that essentially assemble themselves. The process is a simple, one-pot synthesis. You dump the ingredients together and you can get results in half an hour. It’s almost as if the diamondoids know where they want to go. —Hao Yan, a Stanford postdoctoral researcher and lead author of the paper Although there are other ways to get materials to self-assemble, this is the first one shown to make a nanowire with a solid, crystalline core that has good electronic properties, said study co-author Nicholas Melosh, an associate professor at SLAC and Stanford and investigator with SIMES, the Stanford Institute for Materials and Energy Sciences at SLAC. The needle-like wires have a semiconducting core—a combination of copper and sulfur known as a chalcogenide—surrounded by the attached diamondoids, which form an insulating shell. Their minuscule size is important, Melosh said, because a material that exists in just one or two dimensions—as atomic-scale dots, wires or sheets—can have very different, extraordinary properties compared to the same material made in bulk. The new method allows researchers to assemble those materials with atom-by-atom precision and control. The diamondoids they used as assembly tools are tiny, interlocking cages of carbon and hydrogen. Found naturally in petroleum fluids, they are extracted and separated by size and geometry in a SLAC laboratory. Over the past decade, a SIMES research program led by Melosh and SLAC/Stanford Professor Zhi-Xun Shen has found a number of potential uses for the little diamonds, including improving electron microscope images and making tiny electronic gadgets. For this study, the research team took advantage of the fact that diamondoids are strongly attracted to each other through van der Waals forces. (This attraction is what makes the microscopic diamondoids clump together into sugar-like crystals, which is the only reason you can see them with the naked eye.) They started with the smallest possible diamondoids—single cages that contain just 10 carbon atoms—and attached a sulfur atom to each. Floating in a solution, each sulfur atom bonded with a single copper ion. This created the basic nanowire building block. The building blocks then drifted toward each other, drawn by the van der Waals attraction between the diamondoids, and attached to the growing tip of the nanowire. The team has already used diamondoids to make one-dimensional nanowires based on cadmium, zinc, iron and silver, including some that grew long enough to see without a microscope, and they have experimented with carrying out the reactions in different solvents and with other types of rigid, cage-like molecules, such as carboranes. The cadmium-based wires are similar to materials used in optoelectronics, such as light-emitting diodes (LEDs), and the zinc-based ones are like those used in solar applications and in piezoelectric energy generators, which convert motion into electricity. Theorists led by SIMES Director Thomas Devereaux modeled and predicted the electronic properties of the nanowires, which were examined with X-rays at SLAC’s Stanford Synchrotron Radiation Lightsource, a DOE Office of Science User Facility, to determine their structure and other characteristics. The team also included researchers from the Stanford Department of Materials Science and Engineering, Lawrence Berkeley National Laboratory, the National Autonomous University of Mexico (UNAM) and Justus-Liebig University in Germany. Parts of the research were carried out at Berkeley Lab’s Advanced Light Source (ALS) and National Energy Research Scientific Computing Center (NERSC), both DOE Office of Science User Facilities. The work was funded by the DOE Office of Science and the German Research Foundation.
News Article | December 26, 2016
Menlo Park, Calif. -- Scientists at Stanford University and the Department of Energy's SLAC National Accelerator Laboratory have discovered a way to use diamondoids - the smallest possible bits of diamond - to assemble atoms into the thinnest possible electrical wires, just three atoms wide. By grabbing various types of atoms and putting them together LEGO-style, the new technique could potentially be used to build tiny wires for a wide range of applications, including fabrics that generate electricity, optoelectronic devices that employ both electricity and light, and superconducting materials that conduct electricity without any loss. The scientists reported their results today in Nature Materials. "What we have shown here is that we can make tiny, conductive wires of the smallest possible size that essentially assemble themselves," said Hao Yan, a Stanford postdoctoral researcher and lead author of the paper. "The process is a simple, one-pot synthesis. You dump the ingredients together and you can get results in half an hour. It's almost as if the diamondoids know where they want to go." Although there are other ways to get materials to self-assemble, this is the first one shown to make a nanowire with a solid, crystalline core that has good electronic properties, said study co-author Nicholas Melosh, an associate professor at SLAC and Stanford and investigator with SIMES, the Stanford Institute for Materials and Energy Sciences at SLAC. The needle-like wires have a semiconducting core - a combination of copper and sulfur known as a chalcogenide - surrounded by the attached diamondoids, which form an insulating shell. Their minuscule size is important, Melosh said, because a material that exists in just one or two dimensions - as atomic-scale dots, wires or sheets - can have very different, extraordinary properties compared to the same material made in bulk. The new method allows researchers to assemble those materials with atom-by-atom precision and control. The diamondoids they used as assembly tools are tiny, interlocking cages of carbon and hydrogen. Found naturally in petroleum fluids, they are extracted and separated by size and geometry in a SLAC laboratory. Over the past decade, a SIMES research program led by Melosh and SLAC/Stanford Professor Zhi-Xun Shen has found a number of potential uses for the little diamonds, including improving electron microscope images and making tiny electronic gadgets. For this study, the research team took advantage of the fact that diamondoids are strongly attracted to each other, through what are known as van der Waals forces. (This attraction is what makes the microscopic diamondoids clump together into sugar-like crystals, which is the only reason you can see them with the naked eye.) They started with the smallest possible diamondoids - single cages that contain just 10 carbon atoms - and attached a sulfur atom to each. Floating in a solution, each sulfur atom bonded with a single copper ion. This created the basic nanowire building block. The building blocks then drifted toward each other, drawn by the van der Waals attraction between the diamondoids, and attached to the growing tip of the nanowire. "Much like LEGO blocks, they only fit together in certain ways that are determined by their size and shape," said Stanford graduate student Fei Hua Li, who played a critical role in synthesizing the tiny wires and figuring out how they grew. "The copper and sulfur atoms of each building block wound up in the middle, forming the conductive core of the wire, and the bulkier diamondoids wound up on the outside, forming the insulating shell." The team has already used diamondoids to make one-dimensional nanowires based on cadmium, zinc, iron and silver, including some that grew long enough to see without a microscope, and they have experimented with carrying out the reactions in different solvents and with other types of rigid, cage-like molecules, such as carboranes. The cadmium-based wires are similar to materials used in optoelectronics, such as light-emitting diodes (LEDs), and the zinc-based ones are like those used in solar applications and in piezoelectric energy generators, which convert motion into electricity. "You can imagine weaving those into fabrics to generate energy," Melosh said. "This method gives us a versatile toolkit where we can tinker with a number of ingredients and experimental conditions to create new materials with finely tuned electronic properties and interesting physics." Theorists led by SIMES Director Thomas Devereaux modeled and predicted the electronic properties of the nanowires, which were examined with X-rays at SLAC's Stanford Synchrotron Radiation Lightsource, a DOE Office of Science User Facility, to determine their structure and other characteristics. The team also included researchers from the Stanford Department of Materials Science and Engineering, Lawrence Berkeley National Laboratory, the National Autonomous University of Mexico (UNAM) and Justus-Liebig University in Germany. Parts of the research were carried out at Berkeley Lab's Advanced Light Source (ALS) and National Energy Research Scientific Computing Center (NERSC), both DOE Office of Science User Facilities. The work was funded by the DOE Office of Science and the German Research Foundation. SLAC is a multi-program laboratory exploring frontier questions in photon science, astrophysics, particle physics and accelerator research. Located in Menlo Park, California, SLAC is operated by Stanford University for the U.S. Department of Energy Office of Science. To learn more, please visit http://www. . SLAC National Accelerator Laboratory is supported by the Office of Science of the U.S. Department of Energy. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.
News Article | December 28, 2016
Scientists at Stanford University and the Department of Energy’s SLAC National Accelerator Laboratory have discovered a way to use diamondoids – the smallest possible bits of diamond – to assemble atoms into the thinnest possible electrical wires, just three atoms wide. By grabbing various types of atoms and putting them together LEGO-style, the new technique could potentially be used to build tiny wires for a wide range of applications, including fabrics that generate electricity, optoelectronic devices that employ both electricity and light, and superconducting materials that conduct electricity without any loss. The scientists reported their results today in Nature Materials. “What we have shown here is that we can make tiny, conductive wires of the smallest possible size that essentially assemble themselves,” said Hao Yan, a Stanford postdoctoral researcher and lead author of the paper. “The process is a simple, one-pot synthesis. You dump the ingredients together and you can get results in half an hour. It’s almost as if the diamondoids know where they want to go.” The Smaller the Better Although there are other ways to get materials to self-assemble, this is the first one shown to make a nanowire with a solid, crystalline core that has good electronic properties, said study co-author Nicholas Melosh, an associate professor at SLAC and Stanford and investigator with SIMES, the Stanford Institute for Materials and Energy Sciences at SLAC. The needle-like wires have a semiconducting core – a combination of copper and sulfur known as a chalcogenide – surrounded by the attached diamondoids, which form an insulating shell. Their minuscule size is important, Melosh said, because a material that exists in just one or two dimensions – as atomic-scale dots, wires or sheets – can have very different, extraordinary properties compared to the same material made in bulk. The new method allows researchers to assemble those materials with atom-by-atom precision and control. The diamondoids they used as assembly tools are tiny, interlocking cages of carbon and hydrogen. Found naturally in petroleum fluids, they are extracted and separated by size and geometry in a SLAC laboratory. Over the past decade, a SIMES research program led by Melosh and SLAC/Stanford Professor Zhi-Xun Shen has found a number of potential uses for the little diamonds, including improving electron microscope images and making tiny electronic gadgets. For this study, the research team took advantage of the fact that diamondoids are strongly attracted to each other, through what are known as van der Waals forces. (This attraction is what makes the microscopic diamondoids clump together into sugar-like crystals, which is the only reason you can see them with the naked eye.) They started with the smallest possible diamondoids – single cages that contain just 10 carbon atoms – and attached a sulfur atom to each. Floating in a solution, each sulfur atom bonded with a single copper ion. This created the basic nanowire building block. The building blocks then drifted toward each other, drawn by the van der Waals attraction between the diamondoids, and attached to the growing tip of the nanowire. “Much like LEGO blocks, they only fit together in certain ways that are determined by their size and shape,” said Stanford graduate student Fei Hua Li, who played a critical role in synthesizing the tiny wires and figuring out how they grew. “The copper and sulfur atoms of each building block wound up in the middle, forming the conductive core of the wire, and the bulkier diamondoids wound up on the outside, forming the insulating shell.” The team has already used diamondoids to make one-dimensional nanowires based on cadmium, zinc, iron and silver, including some that grew long enough to see without a microscope, and they have experimented with carrying out the reactions in different solvents and with other types of rigid, cage-like molecules, such as carboranes. The cadmium-based wires are similar to materials used in optoelectronics, such as light-emitting diodes (LEDs), and the zinc-based ones are like those used in solar applications and in piezoelectric energy generators, which convert motion into electricity. “You can imagine weaving those into fabrics to generate energy,” Melosh said. “This method gives us a versatile toolkit where we can tinker with a number of ingredients and experimental conditions to create new materials with finely tuned electronic properties and interesting physics.” Theorists led by SIMES Director Thomas Devereaux modeled and predicted the electronic properties of the nanowires, which were examined with X-rays at SLAC’s Stanford Synchrotron Radiation Lightsource, a DOE Office of Science User Facility, to determine their structure and other characteristics. The team also included researchers from the Stanford Department of Materials Science and Engineering, Lawrence Berkeley National Laboratory, the National Autonomous University of Mexico (UNAM) and Justus-Liebig University in Germany. Parts of the research were carried out at Berkeley Lab’s Advanced Light Source (ALS) and National Energy Research Scientific Computing Center (NERSC), both DOE Office of Science User Facilities. The work was funded by the DOE Office of Science and the German Research Foundation.
News Article | December 21, 2016
Physics is a diverse subject that should in principle be open to all types of people from all types of background. In reality, however, there are often biases – be they conscious or unconscious – that can prevent access and stifle career progression based on irrelevant factors such as gender, race or physical ability. While these issues require cultural and organisational change, we believe that quality journalism can add to the debate and influence the direction of travel. We can contribute to this by profiling the many faces of physics – in terms of the diversity of science and the diversity of people involved. Within our journalist toolkit, podcasts and videos can tell compelling stories from the world of physics in personal and engaging ways. Here is a selection of some of the audio and visual highlights from Physics World in 2016. In January, we published the final instalment from our "Light in Our Lives" series, which we commissioned as an official media partner with the Internal Year of Light (IYL 2015). Each film in the series told a local story involving light and its applications and how they can affect people's lives. Transforming Light is a film about the 2015 Day of the Dead celebrations in Mexico City and how a multimedia lightshow blended old traditions with new technologies to spectacular effect. The film was produced by Jorge Benjamín Ruiz Gutiérrez and his team of film-makers at the National Autonomous University of Mexico (UNAM). Following on from the Light in Our Lives series, we decided to commission another film series for 2016 – this time related to diversity within physics. "Faces of Physics" reveals the working lives of people involved in physics, focusing on the day-to-day activities as much as the applications of their work. Inspiring the Next Generation (above) offers a profile of Ghada Nehmeh, a physics teacher who has brought about innovative changes at the Bronx High School of Science in New York. By creating an interactive environment in her classroom, Nehmeh has significantly boosted the number of female students taking Advanced Placement (AP) physics. The other films published in this series to date are: Working in Green Energy about renewable energy engineer Samantha Carter; and A HAWC Eye on the Sky about Adiv González Muñoz – an astronomer and timelapse photographer at High-Altitude Water Cherenkov (HAWC) gamma-ray observatory in Mexico. For more stories and analysis about diversity issues in physics take a look at the March special issue of Physics World, which is introduced in this blog post by Physics World editor Matin Durrani. I mentioned at the start of this article that physics is a diverse subject spanning a range of areas. A good example of this was the July episode of the Physics World podcast, which brought together the unlikely mix of particle physics, Native American storytelling and the evolution of audio recording media. "Bringing Native American voices back to life" profiled a project to restore early 20th century recordings of Native Americans performing songs and stories. The method, based on imaging technologies at particle accelerators, has been developed by Carl Haber of the Lawrence Berkeley National Laboratory (LBNL). Listen to the podcast to hear rare recordings of myths told by Ishi – the last surviving member of the Yahi people of the central Sierra Nevada mountain range in northern California. Theoretical physics can seem abstract at times and about as far removed from everyday life as one could imagine. But it is also an intellectual pursuit like any other, carried out by people with personalities, opinions and beliefs – people who don't always agree with each other. The sociological dimensions of theoretical physics were particularly apparent in the so-called "string wars" – a vitriolic debate played out in the 2000s about the scientific validity of string theory. A key player in the string wars was mathematical physicist Peter Woit whose 2006 book Not Even Wrong took string theory's supposed inadequacies to task. In the September podcast, Peter Woit is in conversation with Physics World reporter Tushna Commissariat 10 years since the book's release. Woit speaks about controversy sparked by his book and what he thinks needs to happen now in mathematical physics to propel it into the future. If the complex mathematics of physics is hard to get your head around sometimes, then imagine trying to do it without the ability to see the equations. That is the reality for Aqil Sajjad, a particle physicist at Harvard University in the US, who lost his sight to retina detachments in both eyes when he was a teenager in Pakistan. Sajjad tells his story in the November episode of the Physics World podcast produced by journalist Lucina Melesio. You will hear how Sajjad accesses maths and science concepts using speech-to-text software. When not pondering the nature of the universe, Sajjad is also a keen baseball player and often travels to other US cities with his team the Boston Renegades. Though – as Sajjad explains in the podcast – at heart he prefers cricket. Finally, in this collection of stories celebrating the social aspects of physics, we'd like to draw your attention to the various short videos we've been producing for our social media channels. With the proliferation of smart phones and other mobile devices, we know that your viewing habits are changing and that you want to get your physics stories on the go. So we have been producing a number of short videos for our Facebook page, Twitter feed and YouTube channel. They can be enjoyed with or without sound. For instance, the video above provides a guide to NASA's Juno mission, which arrived at Jupiter in July where it is now investigating this planet from orbit. One of the major scientific goals of the mission is to better understand the origins of this giant planet, providing key information about the origins of the entire Solar System. Watch out for much more multimedia – including social videos – in 2017.
Toala J.A.,Institute Astrofisica Of Andalucia |
Arthur S.J.,National Autonomous University of Mexico
Monthly Notices of the Royal Astronomical Society | Year: 2014
We carry out high-resolution two-dimensional radiation-hydrodynamic numerical simulations to study the formation and evolution of hot bubbles inside planetary nebulae. We take into account the evolution of the stellar parameters, wind velocity and mass-loss rate from the final thermal pulses during the asymptotic giant branch (AGB) through to the post-AGB stage for a range of initial stellarmasses. The instabilities that form at the interface between the hot bubble and the swept-up AGB wind shell lead to hydrodynamical interactions, photoevaporation flows and opacity variations.We explore the effects of hydrodynamical mixing combined with thermal conduction at this interface on the dynamics, photoionization, and emissivity of our models.We find that even models without thermal conduction mix significant amounts of mass into the hot bubble. When thermal conduction is not included, hot gas can leak through the gaps between clumps and filaments in the broken swept-up AGB shell and this depressurises the bubble. The inclusion of thermal conduction evaporates and heats material from the clumpy shell, which expands to seal the gaps, preventing a loss in bubble pressure. The dynamics of bubbles without conduction is dominated by the thermal pressure of the thick photoionized shell, while for bubbles with thermal conduction it is dominated by the hot, shocked wind. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.
De Diego J.A.,National Autonomous University of Mexico |
De Diego J.A.,Institute of Astrophysics of Canarias
Astronomical Journal | Year: 2014
Microvariations probe the physics and internal structure of quasars. Unpredictability and small flux variations make this phenomenon elusive and difficult to detect. Variance-based probes such as the C and F tests, or a combination of both, are popular methods to compare the light curves of the quasar and a comparison star. Recently, detection claims in some studies have depended on the agreement of the results of the C and F tests, or of two instances of the F-test, for rejecting the non-variation null hypothesis. However, the C-test is a non-reliable statistical procedure, the F-test is not robust, and the combination of tests with concurrent results is anything but a straightforward methodology. A priori power analysis calculations and post hoc analysis of Monte Carlo simulations show excellent agreement for the analysis of variance test to detect microvariations as well as the limitations of the F-test. Additionally, the combined tests yield correlated probabilities that make the assessment of statistical significance unworkable. However, it is possible to include data from several field stars to enhance the power in a single F-test, increasing the reliability of the statistical analysis. This would be the preferred methodology when several comparison stars are available. An example using two stars and the enhanced F-test is presented. These results show the importance of using adequate methodologies and avoiding inappropriate procedures that can jeopardize microvariability detections. Power analysis and Monte Carlo simulations are useful tools for research planning, as they can demonstrate the robustness and reliability of different research approaches. © 2014. The American Astronomical Society. All rights reserved.
Santopinto E.,National Institute of Nuclear Physics, Italy |
Bijker R.,National Autonomous University of Mexico
Physical Review C - Nuclear Physics | Year: 2010
The flavor asymmetry of the nucleon sea is studied in the framework of the unquenched quark model in which the effects of quark-antiquark pairs (uu, dd̄, and ss̄) are taken into account via a microscopic, QCD-inspired, quark-antiquark creation mechanism. The inclusion of the qq̄ pairs leads to an excess of d̄ over ū, in agreement with the experimental data for the proton. In addition, the results for the flavor asymmetry of all ground-state octet and decuplet baryons are presented. The isospin symmetry leads to simple relations among the flavor asymmetries of octet and decuplet baryons. The flavor asymmetry of the Σ⊃+ hyperon is predicted to be very similar to that of the proton and much larger than that for the Ξ0 hyperon. A comparison with other approaches shows large differences in the predictions for the flavor asymmetries of the hyperons. © 2010 The American Physical Society.
Verma S.P.,National Autonomous University of Mexico |
Diaz-Gonzalez L.,Autonomous University Of Estado Of Morelos
International Geology Review | Year: 2012
Basically, two main types of statistical methods - robust and outlier-based - are available for handling experimental data; we document here the application of the outlier-based method. Due to the unavailability of a suitable software system for statistically correct application of the outlier-based method, a new computer program, DODESSYS (Discordant Outlier DEtection and Separation SYStem), was written for the application of 33 discordancy test variants to experimental data, constituting contaminated or uncontaminated normal statistical samples. We illustrate the application of the discordant outlier-based scheme by five specific examples; three include univariate data for which this procedure was specifically designed and two are for bivariate data for which this methodology can be easily adopted. We thus report new statistical information on two reference materials (granite G-2 and sediment IAEA-417), bryozoan species from eastern Oman, a new improved Na/K geothermometric equation, and a more significant correlation with water depth of the abundance of meiofauna from the Gulf of Mexico. Recently, two sets of multi-dimensional discrimination diagrams for basic as well as acid rocks have been proposed from statistically correct methodology of natural logarithm-transformation of element ratios; the diagrams also require that these ratios should be normally distributed. We present numerous examples of application of these new diagrams for inferring tectonic setting of Archaean to Recent rocks, both before and after testing the datasets for discordant outliers. We recommend that outlying observations should always be evaluated for their discordancy. © 2012 Taylor & Francis.
Page D.,National Autonomous University of Mexico |
Prakash M.,Ohio University |
Lattimer J.M.,State University of New York at Stony Brook |
Steiner A.W.,Michigan State University
Physical Review Letters | Year: 2011
We propose that the observed cooling of the neutron star in Cassiopeia A is due to enhanced neutrino emission from the recent onset of the breaking and formation of neutron Cooper pairs in the P23 channel. We find that the critical temperature for this superfluid transition is 0.5×109K. The observed rapidity of the cooling implies that protons were already in a superconducting state with a larger critical temperature. This is the first direct evidence that superfluidity and superconductivity occur at supranuclear densities within neutron stars. Our prediction that this cooling will continue for several decades at the present rate can be tested by continuous monitoring of this neutron star. © 2011 American Physical Society.
Naumis G.G.,National Autonomous University of Mexico |
Phillips J.C.,Rutgers University
Journal of Non-Crystalline Solids | Year: 2012
Measured exponents associated with stretched exponential relaxation (SER) are widely scattered in microscopically heterogeneous glasses, but accurately bifurcate into two "magic" values, 3/5 and 3/7, in a wide variety of microscopically homogeneous glasses. These bifurcated values are derived here from a statistical product model that involves diffusion of excitations to native traps in the presence of short-range forces only, or combined short- and long-range forces, respectively. Bifurcated SER can be used to monitor sample homogeneity. It explains a wide range of experimental data, and even includes multiple aspects of the citation distributions of 20th century science, involving 25 million papers and 600 million citations, and why these changed radically in 1960. It also shows that the distribution of country population sizes has compacted glassy character, and is strongly influenced by migration. © 2012 Elsevier B.V. All rights reserved.
Turbiner A.V.,National Autonomous University of Mexico |
Turbiner A.V.,State University of New York at Stony Brook
Physics Reports | Year: 2016
Quasi-Exactly Solvable Schrödinger Equations occupy an intermediate place between exactly-solvable (e.g. the harmonic oscillator and Coulomb problems, etc.) and non-solvable ones. Mainly, they were discovered in the 1980s. Their major property is an explicit knowledge of several eigenstates while the remaining ones are unknown. Many of these problems are of the anharmonic oscillator type with a special type of anharmonicity. The Hamiltonians of quasi-exactly-solvable problems are characterized by the existence of a hidden algebraic structure but do not have any hidden symmetry properties. In particular, all known one-dimensional (quasi)-exactly-solvable problems possess a hidden sl(2,R)-Lie algebra. They are equivalent to the sl(2,R) Euler-Arnold quantum top in a constant magnetic field.Quasi-Exactly Solvable problems are highly non-trivial, they shed light on the delicate analytic properties of the Schrödinger Equations in coupling constant, they lead to a non-trivial class of potentials with the property of Energy-Reflection Symmetry. The Lie-algebraic formalism allows us to make a link between the Schrödinger Equations and finite-difference equations on uniform and/or exponential lattices, it implies that the spectra is preserved. This link takes the form of quantum canonical transformation. The corresponding isospectral problems for finite-difference operators are described. The underlying Fock space formalism giving rise to this correspondence is uncovered. For a quite general class of perturbations of unperturbed problems with the hidden Lie algebra property we can construct an algebraic perturbation theory, where the wavefunction corrections are of polynomial nature, thus, can be found by algebraic means.In general, Quasi-Exact-Solvability points to the existence of a hidden algebra formalism which ranges from quantum mechanics to 2-dimensional conformal field theories. © 2016 Elsevier B.V.
Gruber C.,Free University of Berlin |
Luongo O.,University of Naples Federico II |
Luongo O.,National Institute of Nuclear Physics, Italy |
Luongo O.,National Autonomous University of Mexico
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2014
Cosmography is used in cosmological data processing in order to constrain the kinematics of the universe in a model-independent way, providing an objective means to evaluate the agreement of a model with observations. In this paper, we extend the conventional methodology of cosmography employing Taylor expansions of observables by an alternative approach using Padé approximations. Due to the superior convergence properties of Padé expansions, it is possible to improve the fitting analysis to obtain numerical values for the parameters of the cosmographic series. From the results, we can derive the equation of state parameter of the universe and its first derivative and thus acquire information about the thermodynamic state of the universe. We carry out statistical analyses using observations of the distance modulus of type 1a supernovae, provided by the union 2.1 compilation of the supernova cosmology project, employing a Markov chain Monte Carlo approach with an implemented Metropolis algorithm. We compare the results of the original Taylor approach to the newly introduced Padé formalism. The analyses show that experimental data constrain the observable universe well, finding an accelerating universe and a positive jerk parameter. We demonstrate that the Padé convergence radii are greater than standard Taylor convergence radii, and infer a lower limit on the acceleration of the universe solely by requiring the positivity of the Padé expansion. We obtain fairly good agreement with the Planck results, confirming the ΛCDM model at small redshifts, although we cannot exclude a dark energy density varying in time with negligible speed of sound. © 2014 American Physical Society.
Bonder Y.,Indiana University Bloomington |
Bonder Y.,National Autonomous University of Mexico
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2015
Lorentz violation is a candidate quantum-gravity signal, and the Standard-Model Extension (SME) is a widely used parametrization of such a violation. In the gravitational SME sector, there is an elusive coefficient for which no effects have been found. This is known as the t puzzle and, to date, it has no compelling explanation. This paper analyzes whether there is a fundamental explanation for the t puzzle. To tackle this question, several approaches are followed. Mainly, redefinitions of the dynamical fields are studied, showing that other SME coefficients can be moved to nongravitational sectors. It is also found that the gravity SME sector can be consistently treated à la Palatini, and that, in the presence of spacetime boundaries, it is possible to correct its action to get the desired equations of motion. Moreover, through a reformulation as a Lanczos-type tensor, some problematic features of the t term, which should arise at the phenomenological level, are revealed. The most important conclusion of the paper is that there is no evidence of a fundamental explanation for the t puzzle, suggesting that it may be linked to the approximations taken at the phenomenological level. © 2015 American Physical Society.
Sussman R.A.,National Autonomous University of Mexico |
Delgado Gaspar I.,Autonomous University of the State of Morelos
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2015
We examine the spatial extrema (local maxima, minima and saddle points) of the covariant scalars (density, Hubble expansion, spatial curvature and eigenvalues of the shear and electric Weyl tensors) of the quasispherical Szekeres dust models. Sufficient conditions are obtained for the existence of distributions of multiple extrema in spatial comoving locations that can be prescribed through initial conditions. These distributions evolve without shell crossing singularities at least for ever expanding models (with or without cosmological constant) in the full evolution range where the models are valid. By considering the local maxima and minima of the density, our results allow for setting up elaborated networks of "pancake" shaped evolving cold dark matter overdensities and density voids whose spatial distribution and amplitudes can be controlled from initial data compatible with standard early Universe initial conditions. We believe that these results have an enormous range of potential application by providing a fully relativistic nonperturbative coarse grained modeling of cosmic structure at all scales. © 2015 American Physical Society.
Wences A.H.,Simons Center for Quantitative Biology |
Wences A.H.,National Autonomous University of Mexico |
Schatz M.C.,Simons Center for Quantitative Biology
Genome Biology | Year: 2015
Genome assembly projects typically run multiple algorithms in an attempt to find the single best assembly, although those assemblies often have complementary, if untapped, strengths and weaknesses. We present our metassembler algorithm that merges multiple assemblies of a genome into a single superior sequence. We apply it to the four genomes from the Assemblathon competitions and show it consistently and substantially improves the contiguity and quality of each assembly. We also develop guidelines for meta-assembly by systematically evaluating 120 permutations of merging the top 5 assemblies of the first Assemblathon competition. The software is open-source at http://metassembler.sourceforge.net. © 2015 Wences and Schatz.
Bijker R.,National Autonomous University of Mexico |
Ferretti J.,National Institute of Nuclear Physics, Italy |
Santopinto E.,National Institute of Nuclear Physics, Italy
Physical Review C - Nuclear Physics | Year: 2012
We present an unquenched quark model calculation of the ss̄ sea pairs' contribution to the magnetic moment of the proton (the strange magnetic moment) and its charge radius (the strange radius). In our approach the effects of the ss̄ pairs are taken explicitly into account through a microscopic, QCD-inspired, quark-antiquark pair creation mechanism. Our results for the two "strangeness" observables are compatible with the latest experimental results and recent lattice calculations. © 2012 American Physical Society.
Discovery and development of DNA methyltransferase inhibitors using in silico approaches This paper is dedicated to the memory of Dr Eugene Athanas Bratoeff Titeff honoring his many contributions to drug discovery.
Medina-Franco J.L.,National Autonomous University of Mexico |
Mendez-Lucio O.,University of Cambridge |
Duenas-Gonzalez A.,National Autonomous University of Mexico |
Yoo J.,Daewoong Pharmaceutical Co.
Drug Discovery Today | Year: 2015
Multiple strategies have evolved during the past few years to advance epigenetic compounds targeting DNA methyltransferases (DNMTs). Significant progress has been made in HTS, lead optimization and determination of 3D structures of DNMTs. In light of the emerging concept of epi-informatics, computational approaches are employed to accelerate the development of DNMT inhibitors helping to screen chemical databases, mine the DNMT-relevant chemical space, uncover SAR and design focused libraries. Computational methods also synergize with natural-product-based drug discovery and drug repurposing. Herein, we survey the latest developments of in silico approaches to advance epigenetic drug and probe discovery targeting DNMTs. © 2014 Elsevier Ltd.
Flores-Ruiz H.M.,National Autonomous University of Mexico |
Naumis G.G.,National Autonomous University of Mexico |
Phillips J.C.,Rutgers University
Physical Review B - Condensed Matter and Materials Physics | Year: 2010
Using molecular dynamics, we study the relationship between the excess of low-frequency vibrational modes (Boson peak, BP) and the glass transition for a bidispersive glass interacting through a truncated Lennard-Jones potential. The evolution of the BP with increasing temperature is correlated with the average coordination, as predicted by rigidity theory. This is due to a lack of atomic "contacts," as is confirmed by taking a crystal with broken bonds. We show how the quadratic mean displacement (u2) is enhanced by the BP. When u2 is obtained on short time scales or measured on inherent structures, the glass transition temperature Tg is determined by the position and height of the BP. Between the melting temperature Tm and Tg, the nature of the relaxation processes exhibit phase separation, where the backbone increases its rigidity while the smaller atoms diffuse away to form separate crystals. © 2010 The American Physical Society.
Agency: Cordis | Branch: FP7 | Program: CP-FP-SICA | Phase: KBBE.2010.2.5-02 | Award Amount: 3.74M | Year: 2011
According to bilateral Eu-Latin America cooperation agreements, there is a mutual interest in developing strategies to tackle Latin American eco-challenges by promoting social cohesion, economic development, and improving food SMEs markets access. SALSA defines an integrated strategy for reducing negative socio-economic and environmental impact of soya bean and beef chains. The rationale is that these productions influence Latin America eco-challenges, reduction in food security and exclusion of SMEs and smaller farmers from market. SALSA belief is that sustainable competitiveness derives from multi-facet determinants that need to be jointly considered to reach a grass root development. The adoption of guidelines for sustainable agro-food productions is constrained by the lack of: i) technical and managerial solutions able to lower costs and cultural barriers for small farmers and SMEs; ii) research and training supporting new knowledge transfer among the food chain stakeholders and research institutions; iii) consumers and policy makers awareness. SALSA aims at developing monitoring tools based on a Life Cycle thinking approach suitable for integrating ethical, environmental and socio-economical impacts in one consistent model. SALSA provides sustainable solutions (strategies and processes) suitable to support farmers and SMEs relations within entire food chains. Shared benefits for end-users will derive from an increased efficiency of knowledge-based sustainable food production and management: fairer food chain relations, higher incomes, safer and better quality food, reduced environmental burden. SALSA added value relies on strengthening the EU- Latin America cooperation between leading institutions and industries; a joint EU-Latin America Industrial Platform will exploit the results. Guidelines will be produced for the benefits of food chain stakeholders and policy makers to improve food production sustainability and EU-Latin America trade relations.
News Article | December 12, 2016
On 18 July 2011, Celia García Velázquez’s son Alfredo disappeared. The 33-year-old lived in a town called Chiconquiaco in the Mexican state of Veracruz, and at the time of his disappearance he was running for president of his municipality against a candidate supported by the country’s most powerful political party. “Everybody knew him,” says García Velázquez, a stout woman with hair the color of a lion’s mane and a blast of bright pink lipstick. One day Alfredo went to Xalapa, the capital of Veracruz state, to sort out the paperwork for a car he’d bought. Like so many young men in Veracruz these days—more than 700 since 2006—he never made it home. “I need to know what happened,” García Velázquez says to 15 people gathered in a classroom overlooking the courtyard of a church in this port city. Her voice breaking, she says, “How is it possible that someone can disappear like that, as if he never existed?” The group nods. They, too, have family members who have disappeared. Many here are mothers looking for their sons. Others are searching for brothers or cousins; one woman seeks six loved ones. They are part of the Solecito collective, a group of more than 100 people searching for the disappeared. And they are getting help from a new source: forensic anthropologists. Veracruz, like many states in Mexico, is experiencing an epidemic of disappearances. Since the beginning of the drug war in 2006, more than 28,000 people have gone missing across the country, according to Mexico’s National Registry of Missing or Disappeared Persons. (That is likely an underestimate, as many disappearances go unreported because families fear retaliation.) Some are kidnapped by drug cartels and either killed or forced into labor or human trafficking. Human Rights Watch, a nonprofit based in New York City, says that many others are abducted by the police and military, and that the government does little to investigate. The 15 people in the classroom this weekend have come for help searching for their disappeared. At the front of the classroom is anthropologist Roxana Enríquez Farias, who in 2013 founded a nonprofit organization called the Mexican Forensic Anthropology Team (EMAF) based in Mexico City. EMAF anthropologists often serve as expert witnesses, evaluating state investigations of disappearances. But on this November weekend, Enríquez Farias is explaining to the families themselves the steps of a search for the disappeared, and how to use their amateur searches to pressure the authorities into action. “We want to build the base [of knowledge] that will support their right to truth and justice,” Enríquez Farias explains. “Until a few years ago, we scientists didn’t think about the families [of victims],” says Lorena Valencia Caballero, a forensic anthropologist at the National Autonomous University of Mexico in Mexico City who is not part of the group. But as the disappearances mounted into a humanitarian crisis, EMAF’s work became “exceedingly necessary,” she says. “It now falls to anthropologists to help the families understand how we determine age, what are the stage[s] of decomposition, how do organized crime groups behave—a thousand things they should never have had to learn.” “It’s a brilliant strategy” when authorities are not sensitive to families’ needs, says forensic anthropologist Nicholas Márquez-Grant of Cranfield University in the United Kingdom. When he met families of the disappeared in Mexico this fall, “I could see that many relatives were completely lost.” He hopes EMAF’s model can be replicated in other countries, such as Iraq, where families are left by the wayside in disappearance investigations. On Mother's Day this year, Solecito organized a rally to bring attention to the disappearances and protest government inaction. As the group listened to a prayer, young men moved into the crowd and discreetly slipped folded papers to several Solecito members. They were photocopies of a hand-drawn map of a Veracruz neighborhood called Colinas de Santa Fe, with crudely drawn directions to an empty field. There, someone had drawn a cluster of crosses labeled cuerpos—“bodies.” The members of Solecito weren’t sure what to do with the information. Where had it come from? What could grieving civilians do about a potential mass grave? After weeks of deliberation, they decided to start digging. So they contacted Enríquez Farias. Enríquez Farias had come face-to-face with Mexico’s disappearance problem while working as a forensic archaeologist in the prosecutor’s office of Ciudad Juárez, the border city across the Rio Grande River from El Paso, Texas. From 2008 to 2012, when the city had the highest murder rate in the world, she excavated clandestine graves to help identify victims. She began to see how her scientific expertise could help bring justice to victims. That inspired her to found EMAF, which now employs seven scientists and two student volunteers and is funded by grants from international agencies. Before Solecito went out to dig up graves this summer, Enríquez Farias came here and gave the group a workshop on forensic anthropology. “They were preparing themselves for what they would find,” she says. She explained how archaeologists examine and remove the layers of earth deposited over a grave, how physical anthropologists measure bones to determine the gender of a skeleton, and which family members can provide the most useful samples for DNA identifications. But she steered clear of giving the searchers explicit instructions. “We don’t teach them techniques. We teach fundamentals,” she says. Once families understand the principles, “they can evaluate the techniques,” including those they see the police using, and judge whether evidence is being lost. That approach wins approval from forensic bioarchaeologist Derek Congram of the University of Toronto in Canada. Trying to turn families into practicing scientists overnight would be impossible as well as “irresponsible,” he says. In August, Solecito began to dig, under the watchful eye of the local police and prosecutor’s office. “We use rudimentary methods, but they’re effective,” says Lucy Díaz, one of Solecito’s founders. Searchers look for places where the earth has a different texture or color than the surrounding ground, or where plants have been cleared. Then they plunge a 2-meter-long metal rod into the earth, bring it up, and sniff the tip for the stench of decomposition. If they smell death, they dig. Since August, the group has uncovered 107 graves, containing 124 skulls and myriad other remains, all in the area indicated by the map. It is the largest mass grave discovered in Mexico so far. “It’s not a clandestine grave. It’s a clandestine cemetery,” Díaz said at a scientific meeting in October. The graves, she says, are at least 1.6 meters deep, and most of the bodies are buried in garbage bags. The majority are men, many still blindfolded. A few show gunshot wounds. Such burials are sensitive because state agents might have been involved in some disappearances. Human Rights Watch documented 249 disappearances between 2007 and 2013, and found that the Mexican police or military were involved in 149 of them. But Solecito’s initiative spurred the government to send forensic investigators from Mexico’s federal police force, known as the Scientific Police, to the cemetery. Solecito locates the bodies, but once a grave is found, the investigators document everything in and around it—clothing, bandages, and even the occasional work identification card, Díaz says—and remove the remains for lab analysis. It’s slow going: So far, 52 of 107 graves have been fully processed. Solecito expects an update from the Scientific Police in January 2017, perhaps including the first identifications. (The National Security Commission, which oversees the Scientific Police, did not respond to interview requests.) After searching for her son independently for 5 years, García Velázquez joined Solecito in August, when she heard about the cemetery. She hopes Alfredo isn’t there, that he’s still alive somewhere—perhaps held by his political rivals, or forced to work for a drug cartel. But she knows that even if her son isn’t buried in Colinas de Santa Fe, someone else’s son is. She helps excavate in the cemetery twice a week. “It’s horrible. It hurts your heart,” she says. But she believes that if she and other family members don’t take action, the bodies will stay in the ground, lost and unidentified, forever. Enríquez Farias admires the bravery of the searchers but worries their work won’t result in justice. The problem, she says, is that local prosecutors aren’t doing the basic investigation of cases that could lead to hypotheses about who is likely to be buried at Colinas de Santa Fe. That means authorities can’t efficiently compare DNA from the remains to probable family members, or even use basic investigative strategies like matching the clothes a missing person was last seen wearing to clothes found in the cemetery. “The investigation isn’t just going and looking for bodies. There are steps before that,” Enríquez Farias says. Congram sees a parallel in Spain, where families in recent years have pushed investigators like him to search for loved ones who disappeared during the country’s civil war in the 1930s. “There was a rush to go out and dig up bodies,” he says, but it hasn’t provided much closure. “A lot of bodies were coming up without background research being done.” One site where he worked yielded more than 400 bodies, but so far, “not one of them is identified.” Everybody in the classroom that November day has notified prosecutors by filing missing person reports, sometimes against the wishes of other family members, who fear becoming targets themselves. Most have also provided a description of the disappeared, plus a list of their friends. Some have given blood and hair samples for DNA analysis. But no one is sure what investigators did with that information, if anything. So in this latest workshop, Enríquez Farias shows families how to pressure prosecutors to tackle their cases. She invites Ibette Estrada Gazga, a lawyer with the Institute for Security and Democracy, a nonprofit in Mexico City, to the front. Prosecutors “have a constitutional obligation to investigate,” Estrada Gazga explains. Families can check progress by requesting a copy of the prosecutor’s case file, she tells the group. If the file shows that nothing has happened, a judge can order the prosecutor to return to the case. Later, Enríquez Farias says she’s surprised at the direction her work has taken. “At first we thought that just doing exhumations or DNA analyses would be enough.” She sighs. “It’s always so much more complicated.” For example, in one of EMAF’s cases in another state, they eventually won the right to exhume a body to confirm a DNA identification. But the cemetery is in such disarray—one private grave held three extra bodies—that after three attempts, EMAF has yet to locate the body in question. Then there are the legal issues: EMAF anthropologists don’t excavate unofficially with Solecito, because their opinion might then be seen as biased and be discredited in a trial, Enríquez Farias says. “If the legal context doesn’t exist, the anthropology goes down the drain,” she says. Instead, families must request EMAF’s services as expert witnesses. She hopes that together, families and EMAF can prod the state into investigating. “Our mission is to build a different kind of country.” Congram agrees that “families bringing up the dead can be a way of shaming the government to fulfill its obligations.” But he thinks EMAF anthropologists could go into the field independently, as has happened in other countries. For example, a nonprofit foundation in Guatemala independently identified bodies of people who disappeared during the country’s civil war. Its analyses ultimately were accepted in court. As the workshop draws to a close, Liliana González, an anthropology student volunteering with EMAF, writes in big letters at the front of the classroom, “What is science?” People call out: “Chemistry!” “Physics!” “Anthropology!” And what are scientists looking for? “Knowledge!” That’s right, Enríquez Farias says. “Science is a search for knowledge. But not just any knowledge. It has to be the truth.” García Velázquez leaves the church that weekend more determined than ever to discover her piece of that truth, starting with obtaining a copy of her case file. “The workshop was excellent,” she says. The next time the state throws up an obstacle, “we’ll remember what they taught us.” And no matter what, she’ll keep digging.
News Article | February 15, 2017
A dark plume leapt into the sky over southern Mexico. Below, waves of hot gas and rock screamed down volcanic slopes, stripping the mountain and surrounding area of vegetation, killing any living thing in their path. It mixed with rivers to create torrents of water, mud and other material as thick as wet concrete. For days afterward the air was choked with ash—microscopic shards of glass—that sickened survivors who inhaled it. It fell like snow onto the surrounding landscape, jamming rivers to create massive floods that wreaked havoc on agriculture. It was A.D. 540, and El Chichón—a small and previously unremarkable volcano—had plunged Maya civilization into darkness and chaos. At least that is the story according to a new paper published in the February Geology, jumping into the long-running archaeological debate about what drove Maya civilization—one of the most sophisticated of its time—into a century-long “dark age.” The Maya, who thrived from A.D. 250 to 900, are widely considered the most advanced civilization in the pre-Columbian Americas. They developed a writing system, precise calendars, new mathematics and magnificent cities with pyramids that still cast their shadows today. But a major mystery remains. In 1938 an archaeologist noticed a strange gap in dated Maya monuments. For more than 100 years the Maya inexplicably halted construction projects, seemingly deserted some areas and engaged in warfare. And in the 75 years since the discovery archaeologists have failed to find an explanation—although they have come up with a lot of hypotheses. Some have speculated an earthquake or hurricane struck the area. Others think trade routes might have collapsed. An early hint that an ancient volcanic eruption might be the culprit came far from the Maya lowlands, in Greenland and Antarctica. A volcano can send a large amount of sulfur particles rocketing into the stratosphere, where they can easily spread across the globe. Once they reach the area over the poles they fasten to snow crystals and eventually become trapped in the ice sheets below, leaving a precise record for scientists to uncover centuries later. That is how Michael Sigl, a chemist from the Paul Scherrer Institute in Switzerland, deduced that a massive eruption must have happened somewhere in the world in A.D. 540—right at the start of the mysterious Maya “dark age.” Tree ring records indicate that sunlight-reflecting sulfur particles high in the atmosphere caused the global temperature to plummet by 1.5 to 2 degrees Celsius at the same time. A volcanic eruption had clearly rocked the world. But could scientists pinpoint its location? The answer came at a chance meeting. Sigl encountered Kees Nooren, a PhD student from Utrecht University in the Netherlands, when the two were presenting side-by-side research posters at a conference. Nooren had been studying lake sediments in a delta just west of the Términos Lagoon along the Gulf of Mexico near the Yucatan Peninsula, when he unearthed a few shiny layers of volcanic ash. He analyzed individual shards of volcanic glass in the sediment and traced them back to El Chichón, then used carbon dating to pin the layers to A.D. 540, give or take 16 years. So when Nooren saw the sulfur spike at 540 on Sigl’s poster, he turned to him and said: “Hey, I might have a candidate for that.” The resulting study clearly shows El Chichón erupted around the same time that sulfur particles got into the ice sheets, and that the Maya “dark age” began. Still, scientists disagree on what the eruption’s exact effect on the Maya might have been. If this eruption was the major event that lofted sulfur particles halfway across the world, it would not have only caused harsher winters (as seen from tree ring records), but also regional droughts. This is what Payson Sheets, an archaeologist at the University of Colorado Boulder who was not involved in the study, thinks interrupted Maya civilization. When Tikal—a powerful Maya city that dominated much of the region—was especially devastated by the ensuing drought, it was attacked by other Maya cities that fared better, causing a temporary collapse, Sheets believes. He also thinks drought affected other civilizations across the world, from the Wei Dynasty in northern China to the pre-Columbian city of Teotihuacán in the Mexican highlands (both civilizations are believed to have revolted against their rulers after poor harvests in the mid-6th century A.D.). But it is also possible that El Chichón did not cause these global changes and that the true culprit has yet to be detected. “The equatorial Pacific is really a hotspot for these big eruptions,” says Matthew Toohey, a climate scientist from the Helmholtz Center for Ocean Research Kiel in Germany, who was not involved in the latest study. “But it’s also a blind spot, and there could be a different eruption there that we just don’t have any records of at the moment.” A number of studies have tried to link other tropical volcanoes to the sulfur spike, albeit with dates that are less certain. Discovering ash in the ice cores (along with the previously detected sulfur) would give scientists a smoking gun, allowing them to trace that ash to a specific volcano. But none has been discovered yet. Nor can researchers be sure El Chichón’s A.D. 540 eruption was massive enough for its effects to span the entire globe. Nooren’s team assumes it was as large as the devastating event that occurred in 1982, when the mountain released huge amounts of sulfur dioxide gas, buried nine villages and killed 2,000 people. Juan Espindola, a volcanologist at the National Autonomous University of Mexico who was not involved in the study, agrees with this assessment given the large distance between the deposited ash that Nooren’s team studied in the Mexican Delta and El Chichón itself. Only a massive eruption would blow ash more than 100 kilometers, he thinks. Volcanologists will have to search for other ash deposits in order to really measure the event’s magnitude. However, even if the eruption was too small to have global effects, its proximity could have helped it play a role in the Maya “dark age.” Nooren and his colleagues think ash and pyroclastic flows from El Chichón could have easily thrown nearby cities into chaos. Other archaeologists who were not part of this research agree the Maya hiatus was likely caused by the volcano—but they think it is because the eruption was beneficial, not disastrous. “Human societies are amazingly resilient and adaptable to natural disasters,” says Robin Torrence, an archaeologist from the Australian Museum. “People can often pick themselves up, dust themselves off and in many cases take advantage of new opportunities.” Those opportunities could have included the volcanic ash itself; in small amounts it can be a great fertilizer. Kenneth Tankersley, an archaeologist from the University of Cincinnati, thinks the Maya might have deserted some areas after the eruption to move closer to the beneficial ash. He goes so far as to suggest they depended on the fertilizing ash so much that a dearth of major volcanism at the end of the eighth century might have led to their civilization’s ultimate collapse—another mystery waiting to be solved. Large or small, El Chichón likely played a role in the Maya’s mysterious dark age. It is no wonder that Sheets thinks this era could easily be turned into a screenplay. “This is great drama,” he says, “and it’s based in reality.”
News Article | November 11, 2016
Like every other industry in the region, Latin America’s fast-growing wind and solar sectors are holding their breath to see what a Donald Trump presidency means for them – and there is plenty to gain or lose. They shouldn’t expect any early answers, warned Ramón Fiestas, head of the Latin American arm of the Global Wind Energy Council (GWEC), who said it would take at least three months after Trump is sworn in to "see what is his real political project". If events play out in a certain direction, Trump could actually spell good tidings for growth prospects in Latin America’s solar and wind industries, which will suddenly assume a greater significance in the global clean-energy push. That could happen, for example, if a decisively anti-renewables Trump prompts more US businesses to look south for opportunities, potentially boosting competition in Latin American markets. Whether because of increased long-term uncertainty in the US’s domestic renewables market or through the effects of a weaker US economy – and consequently the US dollar in relation to other currencies – Latin American countries are expected to continue, and even strengthen, their renewables policies, mostly based on competitive tenders and long-term PPAs. “Geopolitical instability is one of biggest allies of renewable energy, because by relying on their own energy resources countries can increase supply security,” Fiestas pointed out. Argentina, Brazil, Chile, Mexico, Peru, Uruguay and several smaller Central American nations have in the past few years implemented policies to reduce dependence on fossil fuels and drought-ridden hydroelectric dams through an increase in solar and wind capacity. According to the International Renewable Energy Association (Irena), installed renewable energy capacity topped 35GW in 2015 up from under 15GW in 2010, and the trend is due to continue as nations look to cut power prices and create jobs. But with his divisive approach Trump is by no means a welcome presence in Latin America, and there is considerable regional trepidation over potential downsides. “Whatever policies he pursues, the election of Trump is likely to sour relations with virtually every country in Latin America, where he is widely disliked,” wrote Peter Hakim, president-emeritus of the US-based US-Latam relations think-tank Latin America Dialogue, just before the elections. Mexico is in the front line of Trump’s anti-LatAm rhetoric, and the US’s southern neighbour has already been the worst affected, especially due to the Republican President-elect’s recent comments on trade. With the Mexican Peso’s plunging against the US dollar, local central bank authorities were quick to call a press conference to appease markets the day after the election. “Trump has directly expressed doubts vis-a-vis NAFTA, the Trans-Pacific Partnership and explicitly against firms such as Ford and others investing outside of the US and concretely in Mexico. I expect at least some negotiation of NAFTA from Trump’s perspective and this, without a question, would generate a lot of uncertainty in Mexico,” Enrique Dussel Peters, a foreign policy specialist at the National Autonomous University of Mexico, told Recharge. With many of the winners of the country’s recent renewable energy tenders relying on US imports for equipment, especially solar, uncertainty is sure to affect strategies. By 2018 no less than 5GW of wind and solar needs to be built. “If there is a real risk of trade barriers, then the import of US products to the Mexico projects will accelerate [before the 2018 deadline],” Josefin Berg, senior global solar demand analyst at IHS Markit told Recharge. Bets are on over whether some of the worst of Trump’s comments against renewables, free trade and relations with Latin America will be enacted, or were just campaign bravado. “Trump is a businessman and as a businessman he understands economics and how companies work, so I don’t think he will move to cause harm to business,” says GWEC’s Fiestas. But if the new Trump administration really does disrupt the rhythm of the US’s domestic renewables market, the news could be even better for Latin America. That could mean US companies, or the US units of global solar and wind equipment makers, focusing on the growing demand in the region, therefore increasing competition with European and Chinese suppliers who currently have the upper hand in Latin America. In the sights of US companies would be the annual 1GW-plus renewable energy tenders in each of Argentina, Brazil, Chile and Mexico, as well the expected entrance of Colombia, which is preparing new legislation to open up its renewables market over the next two years. “The solar industry in Latin America has its own drivers and Trump threatens [commercial, investment and immigration] flows going into the US, not the flows towards other countries,” said Manam Parikh senior Latin America analyst at GTM Research. “If there is a downturn in the local renewables market in the US, companies will look for business down south, as they are already doing. Mexico, being so close, could benefit.” Except for Brazil, most of Latin America has set up tender policies looking at importing equipment and quickly attracting investment through US dollar-denominated PPAs, and lower import taxes on solar and wind equipment. Brazil could see its fledgling renewables supply chain in the firing line if US renewable players are really forced increase their activities abroad. It is the only big player to have local-currency PPAs and a 3GW-a-year local wind turbine assembly park, which is not yet competitive enough to face any kind of imports. Still, as Brazil completes its transition from local-currency, public bank financing to a more international-reliant capital structure, it has room to remodel its relations with the rest of the world, including in its sights Trump’s new inward looking policies. Until the dust settles, Latin American nations will be doing their sums to see whether Trump’s ascent to power will be better served by keeping current pro-renewables policies or bolstering them. Clean energy supporters worldwide will be hoping Latin America’s renewables markets have the strength to brush off Trump’s anti-globalisation rhetoric.
Mireles F.,University of Regensburg |
Mireles F.,National Autonomous University of Mexico |
Schliemann J.,University of Regensburg
New Journal of Physics | Year: 2012
We present a theoretical study of the band structure and Landau levels in bilayer graphene at low energies in the presence of a transverse magnetic field and Rashba spin-orbit interaction in the regime of negligible trigonal distortion. Within an effective low-energy approach the (Löwdin partitioning theory), we derive an effective Hamiltonian for bilayer graphene that incorporates the influence of the Zeeman effect, the Rashba spin-orbit interaction and, inclusively, the role of the intrinsic spin-orbit interaction on the same footing. Particular attention is paid to the energy spectrum and Landau levels. Our modeling unveils the strong influence of the Rashba coupling λ R in the spin splitting of the electron and hole bands. Graphene bilayers with weak Rashba spin-orbit interaction show a spin splitting linear in momentum and proportional to λ R, but scaling inversely proportional to the interlayer hopping energy λ 1. However, at robust spin-orbit coupling λ R, the energy spectrum shows a strong warping behavior near the Dirac points. We find that the bias-induced gap in bilayer graphene decreases with increasing Rashba coupling, a behavior resembling a topological insulator transition. We further predict an unexpected asymmetric spin splitting and crossings of the Landau levels due to the interplay between the Rashba interaction and the external bias voltage. Our results are of relevance for interpreting magnetotransport and infrared cyclotron resonance measurements, including situations of comparatively weak spin-orbit coupling. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.
Sandoval A.,National Autonomous University of Mexico |
Louis C.,University Pierre and Marie Curie |
Zanella R.,National Autonomous University of Mexico
Applied Catalysis B: Environmental | Year: 2013
Au-Cu bimetallic catalysts supported on TiO2 were prepared for the first time by sequential deposition-precipitation with the urea method, copper first then gold. Au-Cu catalysts with four different Au:Cu atomic ratios were synthesized (1:0.4 to 1:1.2). This method allowed quantitative deposition of both copper and gold and the formation of small metal particles. Characterization by TPR and by DRIFTS coupled with CO adsorption showed that when the samples were activated in air at 300°C gold was present in metallic form, copper in the form of an oxide, and Au and Cu were in interaction, probably forming a Au/CuO/TiO2 system. When the catalysts were activated in hydrogen at 300°C, the metal particles were smaller (2nm) and bimetallic. The activation of Au-Cu catalysts in air at 300°C produced more active catalysts than the activation under hydrogen at the same temperature. However, whatever the activation procedure, the highest catalytic activity in CO oxidation was obtained for the catalyst with an Au:Cu ratio of 1:0.9. This calcined catalyst also presented a TOF almost 3 times higher and a better temporal stability than monometallic gold catalysts in the reaction of CO oxidation at 20°C. Compared to monometallic catalysts, the better catalytic results obtained with calcined Au-Cu/TiO2 indicate a promoting effect between gold and copper oxide in the reaction of CO oxidation. © 2013 Elsevier B.V.
De La Mora E.,National Autonomous University of Mexico |
Lovett J.E.,University of Oxford |
Blanford C.F.,University of Oxford |
Blanford C.F.,University of Manchester |
And 3 more authors.
Acta Crystallographica Section D: Biological Crystallography | Year: 2012
X-ray radiation induces two main effects at metal centres contained in protein crystals: radiation-induced reduction and radiolysis and a resulting decrease in metal occupancy. In blue multicopper oxidases (BMCOs), the geometry of the active centres and the metal-to-ligand distances change depending on the oxidation states of the Cu atoms, suggesting that these alterations are catalytically relevant to the binding, activation and reduction of O2. In this work, the X-ray-determined three-dimensional structure of laccase from the basidiomycete Coriolopsis gallica (Cg L), a high catalytic potential BMCO, is described. By combining spectroscopic techniques (UV-Vis, EPR and XAS) and X-ray crystallography, structural changes at and around the active copper centres were related to pH and absorbed X - ray dose (energy deposited per unit mass). Depletion of two of the four active Cu atoms as well as low occupancies of the remaining Cu atoms, together with different conformations of the metal centres, were observed at both acidic pH and high absorbed dose, correlating with more reduced states of the active coppers. These observations provide additional evidence to support the role of flexibility of copper sites during O2 reduction. This study supports previous observations indicating that interpretations regarding redox state and metal coordination need to take radiation effects explicitly into account. © 2012 International Union of Crystallography Printed in Singapore - all rights reserved.
Medina-Franco J.L.,National Autonomous University of Mexico |
Yoo J.,Ewha Womans University
Molecular Diversity | Year: 2013
Inhibitors of DNA methyltransferase (DNMT) are attractive compounds not only as potential therapeutic agents for the treatment of cancer and other diseases, but also as research tools to investigate the role of DNMTs in epigenetic events. Recent advances in high-throughput screening (HTS) for epigenetic targets and the availability of the first crystallographic structure of human DNMT1 encourage the integration of research strategies to uncover and optimize the activity of DNMT inhibitors. Herein, we present a binding model of a novel small-molecule DNMT1 inhibitor obtained by HTS, recently released in a public database. The docking model is in agreement with key interactions previously identified for established inhibitors using extensive computational studies including molecular dynamics and structure-based pharmacophore modeling. Based on the chemical structure of the novel inhibitor, a sequential computational screening of five chemical databases was performed to identify candidate compounds for testing. Similarity searching followed by molecular docking of chemical databases such as approved drugs, natural products, a DNMT-focused library, and a general screening collection, identified at least 108 molecules with promising DNMT inhibitory activity. The chemical structures of all hit compounds are disclosed to encourage the research community working on epigenetics to test experimentally the enzymatic and demethylating activity in vivo. Five candidate hits are drugs approved for other indications and represent potential starting points of a drug repurposing strategy. © 2013 Springer Science+Business Media Dordrecht.
Yoo J.,Ewha Womans University |
Choi S.,Ewha Womans University |
Medina-Franco J.L.,National Autonomous University of Mexico
PLoS ONE | Year: 2013
DNA methylation is an epigenetic modification that regulates gene expression by DNA methyltransferases (DNMTs). Inhibition of DNMTs is a promising approach for cancer therapy. Recently, novel classes of the quinolone-based compound, SGI-1027, and RG108-procainamide conjugates, CBC12, have been identified as potent DNMT inhibitors. In this work, we report comprehensive studies using induced-fit docking of SGI-1027 and CBC12 with human DNMT1 and DNMT3A. The docking was performed in the C-terminal MTase catalytic domain, which contains the substrate and cofactor binding sites, in the presence and absence of other domains. Induced-fit docking predicts possible binding modes of the ligands through the appropriate structural changes in the receptor. This work suggests a hypothesis of the inhibitory mechanisms of the new inhibitors which is in agreement with the reported autoinhibitory mechanism. The insights obtained in this work can be used to design DNMT inhibitors with novel scaffolds. © 2013 Yoo et al.
Lopez-Moreno S.,National Autonomous University of Mexico |
Errandonea D.,University of Valencia
Physical Review B - Condensed Matter and Materials Physics | Year: 2012
In this work we present a theoretical study of structural stability of CrVO 4-type orthophosphates InPO 4 and TiPO 4 at ambient and high pressures. Total energy calculations and lattice dynamics were used to obtain structural and vibrational properties of these compounds. Also, we have studied at ambient pressure the orthophosphates TlPO 4 and VPO 4 in order to compare their structural and vibrational properties with InPO 4 and TiPO 4. Here we analyze the variation of the Raman and IR frequencies as functions of the reduced mass. Using the phonon dispersion relations we have calculated the Gibbs free energy and evaluated the phase transitions at 300 K, at which most experimental measurements are performed. By taking into consideration the Bastide's diagram and previous theoretical and experimental studies in APO 4 compounds, we have considered 12 candidate structures for the high-pressure regime. We found the following sequence for pressure-driven structural transition: CrVO 4 type → zircon → scheelite → wolframite, for InPO 4 and TiPO 4. The equations of state, phonon frequencies, and their behavior with pressure of the most stable polymorphs are also reported. We also included the phonon spectrum and the projected phonon density of states of each phase for both compounds. Finally, calculation of the evolution of magnetic moment is reported for TiPO 4. © 2012 American Physical Society.
Bonilla C.,University of Valencia |
Morisi S.,German Electron Synchrotron |
Peinado E.,National Autonomous University of Mexico |
Valle J.W.F.,University of Valencia
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2015
In this letter we present a model for quarks and leptons based on T7 as flavour symmetry, predicting a canonical mass relation between charged leptons and down-type quarks proposed earlier. Neutrino masses are generated through a Type-I seesaw mechanism, with predicted correlations between the atmospheric mixing angle and neutrino masses. Compatibility with oscillation results leads to lower bounds for the lightest neutrino mass as well as for the neutrinoless double beta decay rates, even for normal neutrino mass hierarchy. © 2015.
Higgins D.C.,University of Waterloo |
Meza D.,University of Waterloo |
Meza D.,National Autonomous University of Mexico |
Chen Z.,University of Waterloo
Journal of Physical Chemistry C | Year: 2010
Nitrogen-doped carbon nanotubes (N-CNTs) were utilized as platinum nanoparticle support materials, with the significant effect of the nitrogen precursor solution utilized N-CNT growth elucidated. N-CNTs synthesized from a nitrogen-rich ethylenediamine (ED) precursor solution (ED-CNTs) were found to have superior catalytic activity toward the oxygen reduction reaction (ORR) compared with N-CNTs grown from a precursor solution with relatively low nitrogen content pyridine (Py-CNTs). Significant increase in the nitrogen incorporation and edge plane exposure was observed for ED-CNTs. When utilized as platinum nanoparticle supports, Pt/ED-CNTs displayed significantly enhanced electrocatalytic activity toward the ORR when compared with Pt/Py-CNTs and nitrogen free Pt/CNTs, with the increase in performance being attributed to the distinct structural and electronic enhancements resulting from heterogeneous nitrogen doping. The performance of Pt/ED-CNTs as a cathodic catalyst for proton exchange membrane fuel cell operation was found to be significantly higher than that of Pt/CNT. © 2010 American Chemical Society.
Pacheco-Lopez G.,ETH Zurich |
Bermudez-Rattoni F.,National Autonomous University of Mexico
Philosophical Transactions of the Royal Society B: Biological Sciences | Year: 2011
Neuro-immune interactions are widely manifested in animal physiology. Since immunity competes for energy with other physiological functions, it is subject to a circadian trade-off between other energy-demanding processes, such as neural activity, locomotion and thermoregulation. When immunity is challenged, this trade-off is tilted to an adaptive energy protecting and reallocation strategy that is identified as 'sickness behaviour'. We review diverse disease-avoidant behaviours in the context of ingestion, indicating that several adaptive advantages have been acquired by animals (including humans) during phylogenetic evolution and by ontogenetic experiences: (i) preventing waste of energy by reducing appetite and consequently foraging/hunting (illness anor-exia), (ii) avozding unnecessary danger by promoting safe environments (preventing disease encounter by olfactory cues and illness potentiation neophobia), (iii) help fighting against pathogenic threats (hyperthermia/somnolence), and (iv) by associative learning evading specific foods or environments signalling danger (conditioned taste avoidance/aversion) and/or at the same time preparing the body to counteract by anticipatory immune responses (conditioning immunomodula-tion). The neurobiology behind disease-avoidant ingestive behaviours is reviewed with special emphasis on the body energy balance (intake versus expenditure) and an evolutionary psychology perspective. © 2011 The Royal Society.
Zapata A.,National Autonomous University of Mexico |
Herrera G.,University of Valencia
Ceramics International | Year: 2013
Mn3Zn polycrystalline ferrites with Mn1-xZnxFe 2O4 stoichiometry (x=0.59, 0.61, 0.65) were prepared by solid state reaction. These ferrites were heated at different temperatures. The cubic structure with space group Fd3m (Oh 7) No. 227 was confirmed by the refinement of x-ray diffraction (XRD) powders through Rietveld́s method using fullprof. Scanning electron microscopy (SEM) results revealed for all compounds a non-homogeneous grain size and shape distribution, with a mean grain size of 9 μm. The Curie temperature T c was found to decrease as the Zn concentration increases. The magnetic domain relaxation was investigated by inductance spectroscopy (IS). The relaxation frequency fr shows an increase with the increase of the grain size while the initial permeability μi decreased. We propose an RpLp parallel arm equivalent circuit to model the IS results. The theoretical approximation is in agreement with the experimental results. We found that Mn-Zn ferrites with zinc concentration at x=0.59 and heated to 1300° C during 6 h show a slight improvement of the homogeneous microstructure and a relatively higher relaxation frequency without the abrupt degradation of their permeability. This result suggests that ferrites treated in the manner presented in this paper are good candidates for high frequency applications. © 2013 Elsevier Ltd and Techna Group S.r.l.
News Article | March 30, 2016
Astronomers have captured images of a young star system in the earliest stages of planet formation. Researchers in 2014 used the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile to image the star HL Tau and its dusty disk, some 138 parsecs (450 light years) from Earth. They found distinct gaps in the disk, where developing planets were thought to be collecting material along their orbits as they grew. To study the system further, Carlos Carrasco-González of the National Autonomous University of Mexico in Morelia and his colleagues used the Very Large Array in New Mexico, which is more sensitive to the disk's inner region than ALMA. It revealed that part of the innermost ring of dust seems to be clumping together into a planet that is 3–8 times the mass of Earth, suggesting that planets are forming in the rings rather than in the gaps. This is the first time that planetary formation has been observed at such an early stage, the authors say. Astrophys. J. Lett. in the press; preprint at http://arxiv.org/abs/1603.03731 (2016)
News Article | March 18, 2016
Karl G. Jansky Very Large Array (VLA) was able to snap the galactic drama of a planet being born some 450 light-years away from the Earth. The images captured are believed to showcase the earliest stages of planet formation, presenting specific details of the core of the dusty disk surrounding the star. "This is an important discovery, because we have not yet been able to observe most stages in the process of planet formation," says Carlos Carrasco-Gonzalez from the National Autonomous University of Mexico. In 2014, the said star and its disk called the HL Tau were observed using the Atacama Large Millimeter/submillimeter Array (ALMA). During that time, astronomers said that ALMA was able to capture the best image ever of planet formation. The said image exhibited disk gaps, believed to be due to planet-like materials that brushed off the dust along the orbits. While the image was able to show the outer areas of the disk, the inner regions, which are closest to the young star, were enveloped in thick dust that is opaque to the short radio wavelengths collected by ALMA. To get a more vivid picture of the inner portions of the disk, experts used the VLA, which are able to obtain longer wavelengths. Such observatory was able to present the inner regions better than any other previous attempts. For comparison, the VLA was able to receive radio waves that are seven millimeters in diameter, while the ALMA was able to receive a mere one millimeter. As per detail, both observatories were able to present fairly similar information. VLA was specifically able to show a definite blob of dust in the inner part of the disk. As per scientists, this blob holds about three to eight times more mass than the Earth. Thomas Henning from the Max Planck Institute for Astronomy says the team believes that the blob of dust depicts the earliest phases of protoplanet formation, which is something that they have never observed before. For Carrasco-Gonzalez, such discovery is different from formation of any other stars, which life stages have already been observed by experts. The case now is unique because astronomers are quite unfortunate at getting a closer look at early planet formation. More Information About HL Tau Via VLA With the VLA images, experts are able to gain more information about the HL Tau. First, they learned that the inner region has very large grains that measure about one centimeter in diameter. Astronomers presume that this is where Earth-like planets would be produced, as blobs of dust grow by attracting surrounding objects. Subsequently, the clump would become so big that the solid bodies would continue to form planets. VLA is truly valuable in the quest for more data about planet formation. Claire Chandler from the National Radio Astronomy Observatory says the images of HL Tau collated by VLA is by far the most sensitive and detailed picture of the disk at longer wavelengths. The study was published in the Astrophysical Journal Letters.
News Article | December 20, 2016
Competitive sports and games are all about the performance of players and teams, which results in performance-based hierarchies. Because such performance is measurable and is the result of varied rules, sports and games are considered a suitable model to help understand unrelated social or economic systems characterised by similar rules-based complexity. Now, a team of Mexican scientists have used the performance of national teams in tennis, chess, golf, poker and football as a test-bed for identifying universal features in the creation of hierarchies - such as the stratified structure found in the global hierarchical distribution of wealth. José Morales from the National Autonomous University of Mexico and his colleagues found they could, in principle, predict changes in rank occupancy over the course of a contender's lifetime, regardless of the particularities of the sports or activity. These findings, published in EPJ Data Science, enhance our ability to forecast how stratification occurs in competitive activities. The authors set out to determine the path to establishing complex hierarchies, like sports teams' performance rankings. Their objective was to detect statistical regularities that indicate how competition shapes the hierarchies of players and teams. In particular, the team analysed how the performance rankings of players and teams for several sports and specific games evolved over time - referred to as rank diversity, a concept previously used to study how vocabulary changes in time in the context of linguistics. They found that ranking hierarchies may be driven by the same underlying generic mechanisms as rank formation, regardless of the nature of the teams' or players' characteristics. This means that the measure of the number of elements occupying a given performance rank over a length of time has the same functional form in sports and games as in languages; another system where competition is determined by the use or disuse of grammatical structures instead of sports rules. More information: José A Morales et al, Generic temporal features of performance rankings in sports and games, EPJ Data Science (2016). DOI: 10.1140/epjds/s13688-016-0096-y
News Article | December 20, 2016
Competitive sports and games are all about the performance of players and teams, which results in performance-based hierarchies. Because such performance is measurable and is the result of varied rules, sports and games are considered a suitable model to help understand unrelated social or economic systems characterised by similar rules-based complexity. Now, a team of Mexican scientists have used the performance of national teams in tennis, chess, golf, poker and football as a test-bed for identifying universal features in the creation of hierarchies - such as the stratified structure found in the global hierarchical distribution of wealth. José Morales from the National Autonomous University of Mexico and his colleagues found they could, in principle, predict changes in rank occupancy over the course of a contender's lifetime, regardless of the particularities of the sports or activity. These findings, published in EPJ Data Science, enhance our ability to forecast how stratification occurs in competitive activities. The authors set out to determine the path to establishing complex hierarchies, like sports teams' performance rankings. Their objective was to detect statistical regularities that indicate how competition shapes the hierarchies of players and teams. In particular, the team analysed how the performance rankings of players and teams for several sports and specific games evolved over time - referred to as rank diversity, a concept previously used to study how vocabulary changes in time in the context of linguistics. They found that ranking hierarchies may be driven by the same underlying generic mechanisms as rank formation, regardless of the nature of the teams' or players' characteristics. This means that the measure of the number of elements occupying a given performance rank over a length of time has the same functional form in sports and games as in languages; another system where competition is determined by the use or disuse of grammatical structures instead of sports rules. References: José A. Morales, Sergio Sánchez, Jorge Flores, Carlos Pineda, Carlos Gershenson, Germinal Cocho, Jerónimo Zizumbo, Rosalío F. Rodríguez and Gerardo Iñiguez (2016), Generic temporal features of performance rankings in sports and games, EPJ Data Science, 5:33, DOI 10.1140/epjds/s13688-016-0096-y
News Article | August 31, 2016
Abdulsalam Nasidi's phone rang shortly after midnight: Nigeria's health minister was on the line. Nasidi, who worked at the country's Federal Ministry of Health, learnt that he was needed urgently in the Benue valley to investigate a cluster of dying patients. People were bleeding out of their noses, their mouths, their eyes. Names of spine-chilling viruses such as Ebola, Lassa and Marburg raced through Nasidi's mind. When he arrived in Benue, he found people splayed on the ground and tents serving as makeshift hospital wards and morgues. But Nasidi quickly realized that the cause of the mystery illness was millions of times larger than any virus. The onset of the rainy season had brought the start of spring planting for farmers in the valley, and flooding had disturbed the resident carpet vipers (Echis ocellatus). Many farmers were simply too poor to buy boots — and their exposed feet became targets for the highly venomous snakes. Nasidi wanted to help, but he found himself with limited tools. He had only a small amount of antivenom with which to neutralize the toxin — and it quickly ran out. Once the hospital exhausted its supply, people stopped coming. No one knows how many people were killed. In an average year, hundreds of Nigerians die from snakebite, and that rainy season, which started in 2012, was far from average. Snakebites are a growing public-health crisis. According to the World Health Organization, around 5 million people worldwide are bitten by snakes each year; more than 100,000 of them die and as many as 400,000 endure amputations and permanent disfigurement. Some estimates point to a higher toll: one systematic survey concluded that in India alone, more than 45,000 people died in 2005 from snakebite1 — around one-quarter the number that died from HIV/AIDS (see 'The toll of snakebite'). “It's the most neglected of the world's neglected tropical diseases,” says David Williams, a toxinologist and herpetologist at the University of Melbourne, Australia, and chief executive of the non-profit organization Global Snakebite Initiative in Herston. Many of those bites are treatable with existing antivenoms, but there are not enough to go around. This long-standing problem became international news in September 2015, when Médecins Sans Frontières (MSF, also known as Doctors Without Borders) announced that the last remaining vials of the antivenom Fav-Afrique, used to treat bites from several of Africa's deadliest snakes, were about to expire. The French pharma giant Sanofi Pasteur in Lyons had decided to cease production in 2014. MSF estimates that this could cause an extra 10,000 deaths in Africa each year — an “Ebola-scale disaster”, according to Julien Potet, a policy adviser for MSF in Paris. Yet, because most of those affected by snakebites are in the poorest regions of the world, the issue has been largely ignored. In May, however, the crisis was discussed for the first time at the annual World Heath Assembly meeting in Geneva, Switzerland. The world's handful of snakebite specialists gathered in a small conference room in the Palais des Nations — although they shared concern over the problem, they were split about how to solve it. Many want to use synthetic biology and other high-tech tools to develop a new generation of broad-spectrum antivenoms. Others argue that existing antivenoms are safe, effective and low cost, and that the focus should be on improving their production, price and use. “From the physician perspective, patient care and public health comes before anything new,” says Leslie Boyer, who directs an institute dedicated to antivenom study at the University of Arizona, Tucson. The debate mirrors those around many other developing-world challenges, from improving agriculture to providing clean drinking water. Do people need high-tech solutions, or can cheaper, lower-tech remedies do the job? The answer is simple to Jean-Philippe Chippaux, a physician working on snakebite for the French Institute of Research for Development in Cotonou, Benin. “We have the ability to fix this problem now. We just lack the will to do it,” he says. Every December, Williams sees snakebite victims flood into the Port Moresby General Hospital in Papua New Guinea. Nearly all of them were bitten by the taipan (Oxyuranus scutellatus), one of the world's deadliest snakes, which emerges at the start of the rainy season. The venom stops a victim's blood from clotting, paralyses muscles and leads to a slow, agonizing death. It seems a far cry from Australia, where Williams is based. “There's this incredible suffering just 90 minutes away from the modern world,” he says. Yet Williams knows that these people are the lucky ones. The hospital ward, which might be treating as many as eight taipan victims at any time, is often the only place in the country with antivenom drugs. Without them, some 10–15% of all snakebite victims die; with them, just 0.5% do. The situation is reflected around the world. “Many countries don't want to admit that they have such a primeval-sounding problem,” Chippaux says. The method used to make antivenom has changed little since French physician Albert Calmette developed it in the 1890s. Researchers inject minuscule amounts of venom, milked from snakes, into animals such as horses or sheep to stimulate the production of antibodies that bind to the toxins and neutralize them. They gradually increase doses of venom until the animal is pumping out huge amounts of neutralizing antibodies, which are purified from the blood and administered to snakebite victims. Across much of Latin America, government-funded labs typically produce antivenoms and distribute them free of charge. But in other areas, especially sub-Saharan Africa, these life-saving medications are too often out of reach. Many governments lack the infrastructure or political will to purchase and distribute antivenom. Bribery and corruption often jack up the price of an otherwise inexpensive drug from a typical wholesale cost of US$18 to $200 per vial to a retail cost between $40 and $24,000 for a complete treatment, according to a 2012 analysis2. Not all hospitals and clinics can afford the antivenom, and some won't risk buying it because their patients either can't pay for it or won't, because they doubt that it really works. With no reliable market for the medicines, some pharmaceutical companies have halted production. Sanofi Pasteur stopped making Fav-Afrique because, at an average retail price of around $120 per vial, it just couldn't sell enough to make production worthwhile. A total of 35 government or commercial manufacturers produce antivenom for distribution around the world, but only 5 now make the drugs for sub-Saharan Africa. In the absence of medicines, snakebite victims have been known to drink petrol, electrocute themselves or apply a poultice of cow dung and water to the bite, says Tim Reed, executive director of Health Action International in Amsterdam. But there are also problems with the drugs themselves, says Robert Harrison, head of the Alistair Reid Venom Research Unit at the Liverpool School of Tropical Medicine, UK. They often have a limited shelf life and require continuous refrigeration, which is a problem in remote areas without electricity. And many are effective against just one species of snake, so clinics need an array of medicines constantly on hand. (A few, such as Fav-Afrique, combine antibodies to create a broad-spectrum product.) Venoms from spiders and scorpions typically have only one or two toxic proteins; snake venoms can have more than ten times that amount. They are a “pandemonium of molecules”, says Alejandro Alagón, a toxinologist at the National Autonomous University of Mexico in Mexico City. Researchers do not always know which proteins in this toxic soup are the damaging ones — which is why some think that smarter biology could help. Ten years ago, teams led by Harrison and José María Gutiérrez, a toxinologist at the University of Costa Rica in San José, began parallel efforts to create a universal antivenom for sub-Saharan Africa using 'venomics' and 'antivenomics'. The aim is to identify destructive proteins in venoms using an array of techniques, ranging from genome sequencing to mass spectrometry, and then find the specific parts, known as epitopes, that provoke an immunological response and are neutralized by the antibodies in antivenom drugs. The ultimate goal is to use the epitopes to produce antibodies synthetically, using cells rather than animals, and develop antivenoms that are effective against a wide range of snake species in one part of the world. The scientists have made slow but steady progress. Last year, Gutiérrez and his colleagues separated and identified the most toxic proteins from a family of venomous snakes known as elapids (Elapidae). By combining information about the abundance of each protein and how lethal it is to mice, the team created a toxicity score to indicate how important it was to neutralize a protein with antivenom, a first step towards making the treatment3. In March this year, a Brazilian team reported that they had gone further, designing short pieces of DNA that encode key toxic epitopes in the venom of the coral snake (Micrurus corallinus), a member of the elapid family4. Mice were injected with the DNA using a technique that enabled some to generate antibodies against coral-snake venom, and the group enhanced the mice's immune responses by injecting them with synthetic antibodies manufactured in bacterial cells. These and other advances led Harrison to estimate that the first trials of new antivenoms in humans could be just three or four years away. But with so few researchers working on the problem, a paucity of funding and the biological complexity of snake venoms, he and others admit that this is an optimistic prediction. Despite the growing literature on antivenomics, Alagón and Chippaux aren't convinced that the approach will help. Alagón estimates that newly developed antivenoms would need to be priced at tens of thousands of dollars per dose to be financially viable to produce, and that no biotech or pharma company would manufacture one without substantial government subsidies. Compare that, he says, to the rock-bottom price of many existing antivenoms. “You can't get cheaper than that,” he says. “We can make an entire lot of antivenoms in one day using technology that's been available for 80 years.” Finding someone to produce new medications might be a greater challenge than actually developing them, Williams acknowledges: governments or non-governmental organizations (NGOs) will almost certainly have to step in to help to defray the development costs. But he argues that now is the time to research alternative approaches. These could “revolutionize the treatment of snakebite envenoming in the next 10–15 years”, Williams says. All these tensions, brewing for nearly a decade, came to a head at the Geneva meeting in May. Around 75 scientists, public-health experts and health-assembly delegates crowded around three long tables in a third-floor conference room at the United Nations Headquarters. Spring rain pelted the tall windows. Lights were dimmed, and then the screams of a toddler filled the room. A short documentary co-produced by the Global Snakebite Initiative told the story of a girl bitten by a cobra whose parents carried her for days over rocky roads in Africa to find antivenom. They arrived in time — the girl survived — but she lost the use of her arm. Her sister had already died after a bite from the same snake. Convincing attendees of the scale of the problem was the meeting's primary goal; how to solve it came next. For 90 minutes, scientists and NGOs made short, impassioned speeches laying out the scope of the issue and the variety of problems that they faced. At the centre of each presentation was the same message: we need more antivenom. But the meeting was strained. Chippaux and representatives of the African Society of Venomology were disappointed and angry that so few Africans had been invited to speak, even though the continent is where antivenom shortages are most acute. “Our voice, our issues, were completely overlooked,” Chippaux says. Seated at the front of the room, group members whispered and gestured frantically to each other, and Chippaux barely managed to keep them from storming out. They argue that the current antivenom shortage stems from Africa's reliance on foreign companies and governments for its drugs, and that the only solution lies in building up infrastructure in Africa to produce its own high-quality antivenom. Alagón views antivenomics as a dangerous diversion. “It's distracting many brilliant minds and resources from improving antivenoms using existing technology,” he says. “Perhaps by 2050 this will be the standard technique, but the problem is now.” Williams and Gutiérrez take a middle ground. They feel that the problem requires attacks on all fronts. As well as innovation, Gutiérrez calls for existing manufacturers to step up the production of current drugs. There are signs of this happening already. Latin America has a long history of producing antivenoms both for its own needs and for those of countries around the world, and even before Sanofi Pasteur announced that it would cease production of Fav-Afrique, Costa Rica, Brazil and Mexico were testing antivenoms for different parts of Africa. One product, EchiTAb-Plus-ICB, is produced by Costa Rica and effective against a range of African viper species; it completed clinical trials in 2014 and is now available for use. Several other antivenoms are expected to be ready in the next two years. The drugs should be affordable: government labs in Costa Rica have already indicated that they will not seek to make money from the antivenoms, just recoup their expenditures. But beyond that, the way forward remains murky. Williams knows that the World Heath Assembly meeting was just a start. Inevitably, more meetings will be needed to produce a concrete action plan. But the discussion still gave him and some others a renewed sense of hope that the international community is beginning to take snakebite seriously — momentum they hope to build on by banging away at the topic at conferences and in the media. Boyer says that whatever solution the snakebite field decides on, the most important thing is to “break the cycle of antivenom failure in Africa”. Doing that requires building trust from governments, health-care workers and the public that the drugs are safe and effective, that clinics will have antivenom on hand, and that people will be able to afford treatment. “Without that, you've got nothing,” Boyer says. Educating local clinics on how to care for snakebite victims and administer treatments in a timely manner would also go a long way towards preventing deaths. Speaking of the devastation he saw in Benue, Nasidi says that something as simple as providing boots for poor farmers would have helped to prevent much of the suffering and death that he witnessed. It's perhaps the ultimate in low-tech methods in snakebite protection: shielding vulnerable human skin.”
Verma S.P.,National Autonomous University of Mexico |
Agrawal S.,University of Rajasthan
Revista Mexicana de Ciencias Geologicas | Year: 2011
The statistically correct handling of compositional data requires log-ratio transformation whereas the multivariate technique of linear discriminant analysis (LDA) assumes a normal distribution of the transformed variables. In addition to other requirements, both these aspects were considered for proposing five new discriminant function diagrams based on log-ratios of five high-field strength elements - (TiO2)adj, Nb, V, Y, and Zr. A representative world database of 1877 analyses of basic and ultrabasic magmas from four tectonic settings of island arc, continental rift, ocean-island, and mid-ocean ridge, was used. After identifying discordant outliers in log-transformed ratios using single outlier tests, 1793 analyses proved to be normally distributed in terms of the following four variables: ln(Nb/(TiO2)adj), ln(V/(TiO2)adj), ln(Y/(TiO2)adj), and ln(Zr/(TiO2)adj). Use of LDA of the complete dataset of 1877 analyses divided into 1477 analyses for training set and 400 for testing set provided high success rates of 78.5-92.2% and 81.7-93.0% for the discrimination of the four tectonic settings based on the training and testing sets, respectively. However, using LDA of the normally distributed 1793 analyses divided into 1393 for training set and 400 for testing set, we obtained new diagrams that showed still higher success rates of 80.2-93.5% and 84.0-94.0%, respectively. The advantage of fulfilling the requirement of normal distributions of log-ratio variables resides in the observation that an overall net gain in success rates of 0.5-3.3% was achieved when the LDA was correctly applied to discordant-outlier-free log-transformed ratios (1793 analyses) than to the complete data set (1877 analyses). The application of these discrimination diagrams to ophiolites from Taitao Peninsula (southern Chile), Gabal Gerf complex (northeastern Africa), Jormua (northeastern Finland) and Macquarie Island (southwest Pacific) indicated tectonic setting of mid-ocean ridge, transitional between island arc and mid-ocean ridge, mid-ocean ridge and continental rift, respectively. Although only a few rock samples from a study of south-central Sweden could be identified as mafic, the present diagrams indicated an arc setting for this area. The application to three case studies from Turkey, being a country with highly complex geological history, suggested continental rift setting for Kula Quaternary basic volcanic rocks, inconclusive evidence for Jurassic volcanic rocks from eastern Pontides, arc setting for Tauride belt ophiolite, and continental rift setting for East Anatolian and Dead Sea fault zones, the latter application being based on probability calculations for each sample without any need to plot the samples in the discrimination diagrams. The use of normal discordant outlier-free samples of log-transformed ratios from each area in our new discrimination diagrams reinforced these conclusions for all areas, providing somewhat better discrimination in those cases in which such discordant observations were observed. We suggest that the new diagrams be used for tectonic discrimination of basic and ultrabasic rock samples that are confirmed to have discordant outlier-free normally distributed log-transformed variables. Basic and ultrabasic character of the rock samples could be determined from computer program SINCLAS and the discordant outliers of logtransformed variables identified from DODESSYS, whereas the use of new diagrams proposed during 2004-2011 would be facilitated from program TecD.
Bryson Jr. R.W.,University of Nevada, Las Vegas |
Garcia-Vazquez U.O.,National Autonomous University of Mexico |
Riddle B.R.,University of Nevada, Las Vegas
Journal of Biogeography | Year: 2011
Aim We used inferences of phylogeographical structure and estimates of divergence times for three species of gophersnakes (Colubridae: Pituophis) distributed across the Mexican Transition Zone (MTZ) to evaluate the postulated association of three Neogene geological events (marine seaway inundation of the Isthmus of Tehuantepec, formation of the Transvolcanic Belt across central Mexico, and secondary uplifting of the Sierra Madre Occidental) and of Pleistocene climate change with inter- and intraspecific diversification. Location Mexico, Guatemala, and the western United States. Methods We combined range-wide sampling (67 individuals representing three putative species distributed across northern Middle America and western North America) and phylogenetic analyses of 1637base pairs of mitochondrial DNA to estimate genealogical relationships and divergence times. The hypothesized concordance of inferred gene trees with geological histories was assessed using topology tests. Results We identified three major lineages of Middle American gophersnakes, and strong phylogeographical structure within each lineage. Gene trees were statistically congruent with hypothesized geological histories for two of the three postulated geological events. Estimated divergence dates and the geographical distribution of genetic variation further support mixed responses to these geological events. Considerable phylogeographical structure appears to have been generated during the Pleistocene. Main conclusions Phylogenetic and phylogeographical structure in gophersnakes distributed across northern Middle America and western North America highlights the influence of both Neogene vicariance events and Pleistocene climate change in shaping genetic diversity in this region. Despite the presence of two major geographical barriers in southern Mexico, extreme geological and environmental heterogeneity in this area may have differentially structured genetic diversity in highland taxa. To the north, co-distributed taxa may display a more predictable pattern of diversification across the warm desert regions. Future studies should incorporate nuclear data to disentangle inferred lineage boundaries and further elucidate patterns of mitochondrial introgression. © 2011 Blackwell Publishing Ltd.
Noriega-Crespo A.,California Institute of Technology |
Raga A.C.,National Autonomous University of Mexico
Astrophysical Journal | Year: 2012
We present unpublished Spitzer IRAC observations of the HH 1/2 young stellar outflow processed with a high angular resolution deconvolution algorithm that produces subarcsecond (∼0″.6-0″.8) images. In the resulting mid-infrared images, the optically invisible counterjet is detected for the first time. The counterjet is approximately half as bright as the jet at 4.5μm (the IRAC band that best traces young stellar outflows) and has a length of ∼10″. The NW optical jet itself can be followed back in the mid-IR to the position of the exciting VLA 1 source. An analysis of the IRAC colors indicates that the jet/counterjet emission is dominated by collisionally excited H2 pure rotational lines arising from a medium with a neutral hydrogen gas density of ∼1000-2000cm-3 and a temperature of ∼1500 K. The observed jet/counterjet brightness asymmetry is consistent with an intrinsically symmetric outflow with extinction from a dense, circumstellar structure of ∼6″ size (along the outflow axis), and with a mean visual extinction, AV ∼ 11 mag. © 2012. The American Astronomical Society. All rights reserved.
Bryson R.W.,University of Nevada, Las Vegas |
Garcia-Vazquez U.O.,National Autonomous University of Mexico |
Riddle B.R.,University of Nevada, Las Vegas
Molecular Phylogenetics and Evolution | Year: 2012
Neogene vicariance during the Miocene and Pliocene and Quaternary climate change have synergistically driven diversification in Mexican highland taxa. We investigated the impacts of these processes on genetic diversification in the widely distributed bunchgrass lizards in the Sceloporus scalaris group. We searched for correlations between timing in diversification and timing of (1) a period of marked volcanism across the Trans-Mexican Volcanic Belt in central Mexico 3-7.5. million years ago (Ma) and (2) a transition to larger glacial-interglacial cycles during the mid-Pleistocene. From our phylogenetic analyses of mitochondrial DNA we identified two major clades that contained 13 strongly supported lineages. One clade contained lineages from the two northern sierras of Mexico, and the other clade included lineages associated with the Trans-Mexican Volcanic Belt and Central Mexican Plateau. Results provided support for Neogene divergences within the S. scalaris group in response to uplift of the Trans-Mexican Volcanic Belt, a pattern observed in several co-distributed taxa, and suggested that Quaternary climate change likely had little effect on diversification between lineages. Uplift of the Trans-Mexican Volcanic Belt during specific time periods appears to have strongly impacted diversification in Mexican highland taxa. © 2011 Elsevier Inc.
Serkin V.N.,Institute Ciencias |
Belyaeva T.L.,National Autonomous University of Mexico
Journal of Modern Optics | Year: 2010
The fundamental concept of colored nonautonomous solitons in nonlinear and dispersive nonautonomous physical systems is introduced. Novel soliton solutions for the nonautonomous nonlinear Schrodinger equation models with linear and harmonic oscillator potentials substantially extend the concept of classical solitons and generalize it to the plethora of nonautonomous solitons that interact elastically and generally move with varying amplitudes, speeds and spectra adapted both to the external potentials and to the dispersion and nonlinearity variations. The parallels between nonlinear guided wave phenomena in optics and nonlinear guided wave phenomena in Bose condensates are clearly demonstrated by considering optical and matter wave soliton dynamics in the framework of nonautonomous evolution equations. The exact analytical solutions and numerical experiments reveal many specific features of nonautonomous solitons. Fundamental laws of the soliton adaptation to the external potentials are derived. Bound states of colored nonautonomous solitons are studied in detail and a comparison of the canonical Satsuma-Yajima breather dynamics with a nonautonomous 'agitated' breather is presented. The nonautonomous soliton concept can be applied to different physical systems, from hydrodynamics and plasma physics to nonlinear optics and matter waves, and offer many opportunities for further scientific studies © 2010 Taylor & Francis.
Imine H.,Laboratory for Road Operation |
Fridman L.M.,National Autonomous University of Mexico |
Madani T.,Laboratoire Dingenierie Des Systemes Of Versailles
IEEE Transactions on Vehicular Technology | Year: 2012
The aim of this paper is to develop an active steering assistance system to avoid the rollover of heavy vehicles (HV). The proposed approach is applied on a single body model of HV presented in this paper. An estimator based on the high-order sliding mode observer is developed to estimate the vehicle dynamics, such as lateral acceleration limit and center height of gravity. Lateral position and lateral speed are controlled using a twisting algorithm to ensure the stability of the vehicle and avoid accidents. At the same time, the identification of unsprung masses and suspension stiffness parameters of the model have been computed to increase the robustness of the method. Some simulation and experimental results are given to show the quality of the proposed concept. © 2012 IEEE.
Sahu S.,National Autonomous University of Mexico |
Zhang B.,University of Nevada, Las Vegas |
Fraija N.,National Autonomous University of Mexico
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2012
Centaurus A (Cen A) is the nearest radio-loud AGN and is detected from radio to very high-energy gamma rays. Its nuclear spectral energy distribution (SED) shows a double-peak feature, which is well explained by the leptonic synchrotron+synchrotron self-Compton model. This model however cannot account for the observed high energy photons in the TeV range, which display a distinct component. Here, we show that ∼TeV photons can be well interpreted as the π0 decay products from pγ interactions of Fermi-accelerated high-energy protons in the jet with the seed photons around the second SED peak at ∼170keV. Extrapolating the inferred proton spectrum to high energies, we find that this same model is consistent with the detection of two ultra-high-energy cosmic ray events detected by Pierre Auger Observatory from the direction of Cen A. We also estimate the GeV neutrino flux from the same process, and find that it is too faint to be detected by current high-energy neutrino detectors. © 2012 American Physical Society.
Keppie D.F.,Natural Resources Canada |
Keppie J.D.,National Autonomous University of Mexico
International Geology Review | Year: 2012
Understanding Pangea breakup requires a robust reconstruction, and this article focuses on the Middle America sector of the supercontinent. Although most Pangean reconstructions locate the Yucatan Block along the southern USA, the Chortis Block is generally placed off southern Mexico (Pacific model), undergoing sinistral relative motion during the Mesozoic and Cenozoic. However, the Pacific model is inconsistent with the absence of a Cenozoic fault linking the Cayman transforms and the Middle America Trench. We present an alternative Pangean reconstruction, where both the Yucatan and Chortis Blocks are placed in the future Gulf of Mexico, moving Mexico westwards along the Mojave-Sonora megashear to accommodate overlap with South America. Subsequent Mesozoic and Cenozoic evolution is inferred to have occurred in two stages: (i) Jurassic clockwise rotation along the Mojave-Sonora and West Florida megashears, followed by (ii) Cenozoic anticlockwise rotation along the Sierra Madre Oriental and East Yucatan megashears. The first stage is linked to the breakup of Pangea where the Gulf of Mexico formed as a pull-apart basin. The second stage is related to the evolution of the Caribbean where the Chortis and Yucatan Blocks rotated into the trailing side of the Caribbean Plate (pirate model). The new reconstruction is consistent with major parameters, such as (i) gravity, magnetic, and palaeomagnetic data; (ii) the westward continuation of the Cayman transform faults through the Chiapas foldbelt and along the N-S front of the Sierra Madre Oriental foldbelt; (iii) the 27-19 Ma removal of the southern Mexican forearc; (iv) offset of the Cretaceous volcanic arc (Guerrero-Suina); (v) the deflection of the Laramide orogen (Sierra Madre Oriental-Zongolica- Colon); and (vi) the continuity of Cretaceous platformal carbonates containing Caribbean fauna across Middle America. In this latter context, the Motagua high-pressure belt is interpreted as a Cretaceous extrusion zone into the upper plate above a subduction zone rather than as an oceanic suture. © 2012 Taylor & Francis.
Tovar-y-Romo L.B.,Johns Hopkins University |
Tovar-y-Romo L.B.,National Autonomous University of Mexico
ASN Neuro | Year: 2012
VEGF (vascular endothelial growth factor) prevents neuronal death in different models of ALS (amyotrophic lateral sclerosis), but few studies have addressed the efficacy of VEGF to protect motor neurons after the onset of symptoms, a critical point when considering VEGF as a potential therapeutic target for ALS. We studied the capability of VEGF to protect motor neurons after an excitotoxic challenge in two models of spinal neurodegeneration in rats induced by AMPA (α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid) administered either chronically with osmotic minipumps or acutely by microdialysis. VEGF was administered through osmotic minipumps in the chronic model or injected intracerebroventricularly in the acute model, and its effects were assessed by immunohistochemical and histological analyses and motor performance tests. In the chronic model, VEGF stopped the progression of the paralysis and protected motor neurons when administered after AMPA before the onset of the motor symptoms, whereas no protection was observed when administered after the onset. VEGF was also protective in the acute model, but with a short time window, since the protection was effective when administered 1 h but not 2 h after AMPA. Our results indicate that while VEGF has an indubitable neuroprotective effect, its therapeutic potential for halting or delaying the progression of motor neuron loss in ALS would likely have a short effective time frame. © 2012 The Author(s).
Valbuena A.,University of Salamanca |
Castro-Obregon S.,National Autonomous University of Mexico |
Lazo P.A.,University of Salamanca
PLoS ONE | Year: 2011
Human VRK1 induces a stabilization and accumulation of p53 by specific phosphorylation in Thr18. This p53 accumulation is reversed by its downregulation mediated by Hdm2, requiring a dephosphorylated p53 and therefore also needs the removal of VRK1 as stabilizer. This process requires export of VRK1 to the cytosol and is inhibited by leptomycin B. We have identified that downregulation of VRK1 protein levels requires DRAM expression, a p53-induced gene. DRAM is located in the endosomal-lysosomal compartment. Induction of DNA damage by UV, IR, etoposide and doxorubicin stabilizes p53 and induces DRAM expression, followed by VRK1 downregulation and a reduction in p53 Thr18 phosphorylation. DRAM expression is induced by wild-type p53, but not by common human p53 mutants, R175H, R248W and R273H. Overexpression of DRAM induces VRK1 downregulation and the opposite effect was observed by its knockdown. LC3 and p62 were also downregulated, like VRK1, in response to UV-induced DNA damage. The implication of the autophagic pathway was confirmed by its requirement for Beclin1. We propose a model with a double regulatory loop in response to DNA damage, the accumulated p53 is removed by induction of Hdm2 and degradation in the proteasome, and the p53-stabilizer VRK1 is eliminated by the induction of DRAM that leads to its lysosomal degradation in the autophagic pathway, and thus permitting p53 degradation by Hdm2. This VRK1 downregulation is necessary to modulate the block in cell cycle progression induced by p53 as part of its DNA damage response. © 2011 Valbuena et al.
Pineda-Garcia F.,National Autonomous University of Mexico |
Paz H.,National Autonomous University of Mexico |
Paz H.,U.S. Department of Agriculture |
Meinzer F.C.,U.S. Department of Agriculture
Plant, Cell and Environment | Year: 2013
The mechanisms of drought resistance that allow plants to successfully establish at different stages of secondary succession in tropical dry forests are not well understood. We characterized mechanisms of drought resistance in early and late-successional species and tested whether risk of drought differs across sites at different successional stages, and whether early and late-successional species differ in resistance to experimentally imposed soil drought. The microenvironment in early successional sites was warmer and drier than in mature forest. Nevertheless, successional groups did not differ in resistance to soil drought. Late-successional species resisted drought through two independent mechanisms: high resistance of xylem to embolism, or reliance on high stem water storage capacity. High sapwood water reserves delayed the effects of soil drying by transiently decoupling plant and soil water status. Resistance to soil drought resulted from the interplay between variations in xylem vulnerability to embolism, reliance on sapwood water reserves and leaf area reduction, leading to a tradeoff of avoidance against tolerance of soil drought, along which successional groups were not differentiated. Overall, our data suggest that ranking species' performance under soil drought based solely on xylem resistance to embolism may be misleading, especially for species with high sapwood water storage capacity. © 2012 Blackwell Publishing Ltd.
Fraija N.,National Autonomous University of Mexico |
Marinelli A.,University of Pisa
Astroparticle Physics | Year: 2015
Long TeV γ-ray campaigns have been carried out to study the spectrum, variability and duty cycle of the BL Lac object Markarian 421. These campaigns have given some evidence of the presence of protons in the jet: (i) Its spectral energy distribution which shows two main peaks; one at low energies (∼1 keV) and the other at high energies (hundreds of GeV), has been described by using synchrotron proton blazar model. (ii) The study of the variability at GeV γ-rays and X-rays has indicated no significant correlation. (iii) TeV γ-ray detections without activity in X-rays, called "orphan flares" have been observed in this object. Recently, The Telescope Array Collaboration reported the arrival of 72 ultra-high-energy cosmic rays with some of them possibly related to the direction of Markarian 421. The IceCube Collaboration reported the detection of 37 extraterrestrial neutrinos in the TeV-PeV energy range collected during three consecutive years. In particular, no neutrino track events were associated with this source. In this paper, we consider the proton-photon interactions to correlate the TeV γ-ray fluxes reported by long campaigns with the neutrino and ultra-high-energy cosmic ray observations around this blazar. Considering the results reported by The IceCube and Telescope Array Collaborations, we found that only from ∼25% to 70% of TeV fluxes described with a power law function with exponential cutoff can come from the proton-photon interactions. © 2015 Elsevier B.V. All rights reserved.
Carballido A.,National Autonomous University of Mexico |
Bai X.-N.,Princeton University |
Monthly Notices of the Royal Astronomical Society | Year: 2011
We study the turbulent diffusion of solids in a protoplanetary disc, in order to discriminate between two existing analytical models of the turbulent diffusion process. These two models predict the same radial turbulent diffusion coefficient D p, x for small particles (τ s≪ 1), but differ in the value of D p, x for large particles (τ s≫ 1, where τ s is the dimensionless particle stopping time, closely related to particle radius). The model given by Youdin & Lithwick (YL) takes into account orbital oscillations of the solids, while the other model given by Cuzzi, Dobrovolskis & Champney (CDC) does not. The CDC model predicts for τ s≫ 1, but the YL model gives. To investigate, we perform 3D, magnetohydrodynamic (MHD) numerical simulations. Turbulence in the disc is generated by the magnetorotational instability. The athena code is used to solve the equations of ideal MHD in the shearing-box approximation, which allows us to model a local region of the disc with the relevant orbital dynamics. Solids are represented by Lagrangian particles that interact with the gas through drag, and are also subject to orbital forces. The aerodynamic coupling of particles to the gas is parametrized by τ s. In one set of simulations, particle displacements along the radial direction are measured in a shearing box without vertical stratification of the gas density. In another simulation, the vertical component of stellar gravity is included, with a Gaussian gas density vertical profile, but the particle motion is restricted to fixed planes of constant height z. In both cases, the radial diffusion coefficient as a function of stopping time τ s is in very good agreement with the YL model. To study particle vertical diffusion, we use the unstratified shearing box, in which we allow the effects of vertical gravity and turbulence on the particles to balance out, resulting in particle layers whose scaleheight varies approximately as. Based on this result and YL, we calculate a vertical diffusion coefficient D p, z that, in the limit τ s≫ 1, varies as τ -2 s, similarly to radial diffusivity. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.
Species identification in the taxonomically neglected, highly diverse, neotropical parasitoid wasp genus Notiospathius (Braconidae: Doryctinae) based on an integrative molecular and morphological approach
Ceccarelli F.S.,National Autonomous University of Mexico |
Sharkey M.J.,University of Kentucky |
Zaldivar-Riveron A.,National Autonomous University of Mexico
Molecular Phylogenetics and Evolution | Year: 2012
Various DNA sequence-based methods for species delineation have recently been developed to assess the species-richness of highly diverse, neglected invertebrate taxa. These methods, however, need to be tested under a variety of conditions, including the use of different markers and parameters. Here, we explored the species diversity of a species-rich group of braconid parasitoid wasps, the Neotropical genus Notiospathius, including 233 specimens from 10 different countries. We examined sequences of two mitochondrial (mt) (COI, cyt b) and one nuclear (wg) gene fragments. We analysed them separately as well as concatenating the mt data with the general mixed Yule-coalescent (GMYC) model for species delineation using different tree-building methods and parameters for reconstructing ultrametric trees. We evaluated the performance of GMYC analyses by comparing their species delineations with our morphospecies identifications. Reconstructing ultrametric trees with a relaxed lognormal clock rate using the program BEAST gave the most congruent results with morphology for the two mt markers. A tree obtained with wg using the programs MrBayes + Pathd8 had the fewest cases of incongruence with morphology, though the performance of this nuclear marker was considerably lower than that of COI and cyt b. Species delimitation using the coalescent prior to obtain ultrametric trees was morphologically more congruent with COI, whereas the Yule prior was more congruent with cyt b. The analyses concatenating the mt datasets failed to recover some species supported both by morphology and the separate analyses of the mt markers. The highest morphological congruence was obtained with the GMYC analysis on an ultrametric tree reconstructed with cyt b using the relaxed lognormal clock rate and the Yule prior, thus supporting the importance of using alternative markers when the information of the barcoding locus (COI) is not concordant with morphological evidence. Seventy-one species were delimited based on the congruence found among COI, cyt b and morphology. Both mt markers also revealed the existence of seven potential cryptic species. This high species richness from a scattered geographical sampling indicates that there is a remarkable number of Notiospathius species that remains undiscovered. © 2011 Elsevier Inc.
Gonzalez-Olvera M.A.,Autonomous University of Mexico City |
Tang Y.,National Autonomous University of Mexico
IEEE Transactions on Neural Networks | Year: 2010
This brief presents a structure for black-box identification based on continuous-time recurrent neurofuzzy networks for a class of dynamic nonlinear systems. The proposed network catches the dynamics of a system by generating its own states, using only input and output measurements of the system. The training algorithm is based on adaptive observer theory, the stability of the network, the convergence of the training algorithm, and the ultimate bound on the identification error as well as the parameter error are established. Experimental results are included to illustrate the effectiveness of the proposed method. © 2006 IEEE.
Trueta C.,Instituto Nacional Of Psiquiatria Ramon Of La Fuente Muniz |
De-Miguel F.F.,National Autonomous University of Mexico
Frontiers in Physiology | Year: 2012
We review the evidence of exocytosis from extrasynaptic sites in the soma, dendrites, and axonal varicosities of central and peripheral neurons of vertebrates and invertebrates, with emphasis on somatic exocytosis, and how it contributes to signaling in the nervous system. The finding of secretory vesicles in extrasynaptic sites of neurons, the presence of signaling molecules (namely transmitters or peptides) in the extracellular space outside synaptic clefts, and the mismatch between exocytosis sites and the location of receptors for these molecules in neurons and glial cells, have long suggested that in addition to synaptic communication, transmitters are released, and act extrasynaptically. The catalog of these molecules includes low molecular weight transmitters such as monoamines, acetylcholine, glutamate, gama-aminobutiric acid (GABA), adenosine-5-triphosphate (ATP), and a list of peptides including substance P, brain-derived neurotrophic factor (BDNF), and oxytocin. By comparing the mechanisms of extrasynaptic exocytosis of different signaling molecules by various neuron types we show that it is a widespread mechanism for communication in the nervous system that uses certain common mechanisms, which are different from those of synaptic exocytosis but similar to those of exocytosis from excitable endocrine cells. Somatic exocytosis has been measured directly in different neuron types. It starts after high-frequency electrical activity or long experimental depolarizations and may continue for several minutes after the end of stimulation. Activation of L-type calcium channels, calcium release from intracellular stores and vesicle transport towards the plasma membrane couple excitation and exocytosis from small clear or large dense core vesicles in release sites lacking postsynaptic counterparts. The presence of synaptic and extrasynaptic exocytosis endows individual neurons with a wide variety of timeand space-dependent communication possibilities. Extrasynaptic exocytosis may be the major source of signaling molecules producing volume transmission and by doing so may be part of a long duration signaling mode in the nervous system. © 2012 Trueta and De- Miguel.
Herlihy M.,Brown University |
Rajsbaum S.,National Autonomous University of Mexico
Proceedings of the Annual ACM Symposium on Principles of Distributed Computing | Year: 2010
Failure patterns in modern parallel and distributed systems are not necessarily uniform. The notion of an adversary scheduler is a natural way to extend the classical wait-free and t-faulty models of computation. A well-established way to characterize an adversary is by its set of cores, where a core is any minimal set of processes that cannot all fail in any execution. We show that the protocol complex associated with an adversary is (c - 2)-connected, where c is the size of the adversary's smallest core. This implies, among other results, that such an adversary can solve c-set agreement, but not (c - 1)-set agreement. The proofs are combinatorial, relying on a novel application of the Nerve Theorem of modern combinatorial topology. Copyright 2010 ACM.
Herlihy M.,Brown University |
Rajsbaum S.,National Autonomous University of Mexico
Proceedings of the Annual ACM Symposium on Principles of Distributed Computing | Year: 2012
If one model of computation can simulate another, then the existence (or non-existence) of an algorithm in the simulated model reduces to a related question about the simulating model. The BG-simulation algorithm uses this approach to prove that k-set agreement cannot be solved when t processes can crash, 1 ≤ t ≤ k, by reduction to the wait-free case, where it is known that n+1 processes cannot solve n-set agreement, and similarly for any other colorless task. We give a definition, expressed in the language of combinatorial topology, for what it means for one model of distributed computation to simulate another with respect to the ability to solve colorless tasks. This definition is not linked to specific models or specific protocols. We show how to exploit elementary topological arguments to show when a simulation exists, without the need for an explicit construction. We use this approach to generalize the BG-simulation and to unify a number of simulation relations linking various models, some previously known, some not. © 2012 ACM.
Tian C.,Perlegen Sciences |
Stokowski R.P.,Perlegen Sciences |
Kershenobich D.,National Autonomous University of Mexico |
Ballinger D.G.,Perlegen Sciences |
And 2 more authors.
Nature Genetics | Year: 2010
Two genome-wide association studies (GWAS) have described associations of variants in PNPLA3 with nonalcoholic fatty liver and plasma liver enzyme levels. We investigated the contributions of these variants to liver disease in Mestizo subjects with a history of alcohol dependence. We found that rs738409 in PNPLA3 is strongly associated with alcoholic liver disease and clinically evident alcoholic cirrhosis (unadjusted OR= 2.25, P=1.7 × 10-10 ancestry-adjusted OR=1.79, P=1.9 × 10 -5). © 2010 Nature America, Inc. All rights reserved.
Modak S.K.,National Autonomous University of Mexico |
Singleton D.,California State University, Fresno
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2014
The Comment [J.T. Firouzjaee, preceding Comment, Phys. Rev. D 89, 068301 (2014)] raises two points in regard to our paper [S.K. Modak and D. Singleton, Phys. Rev. D 86, 123515 (2012)]. The first is that one cannot use the tunneling picture to obtain the temperature and particle production rate in the Friedman-Robertson-Walker space-time. The second comment raised by Firouzjaee is that the Hawking-like radiation model for inflation presented in [Modak and Singleton; S.K. Modak and D. Singleton, Int. J. Mod. Phys. D 21, 1242020 (2012)] is inconsistent with the observed scalar and tensor perturbation spectrum. We show that the first comment is beside the point - we do not use the tunneling method in our papers [Modak and Singleton; Modak and Singleton]. The second criticism by Firouzjaee comes from the author evaluating quantities at different times - he evaluates the parameters of our model at the beginning of inflation and then compares this with the scalar and tensor perturbations evaluated at the horizon exit point. © 2014 American Physical Society.
Ramos-Caro J.,University of Campinas |
Agon C.A.,National Autonomous University of Mexico |
Pedraza J.F.,University of Texas at Austin
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2012
In this paper we study the kinetic theory of many-particle astrophysical systems imposing axial symmetry and extending our previous analysis in Phys. Rev. DPRVDAQ1550-7998 83, 123007 (2011).10.1103/PhysRevD.83.123007 Starting from a Newtonian model describing a collisionless self-gravitating gas, we develop a framework to include systematically the first general relativistic corrections to the matter distribution and gravitational potentials for general stationary systems. Then, we use our method to obtain particular solutions for the case of the Morgan and Morgan disks. The models obtained are fully analytical and correspond to the post-Newtonian generalizations of classical ones. We explore some properties of the models in order to estimate the importance of post-Newtonian corrections and we find that, contrary to the expectations, the main modifications appear far from the galaxy cores. As a by-product of this investigation we derive the corrected version of the tensor virial theorem. For stationary systems we recover the same result as in the Newtonian theory. However, for time dependent backgrounds we find that there is an extra piece that contributes to the variation of the inertia tensor. © 2012 American Physical Society.
Merchant H.,National Autonomous University of Mexico |
Grahn J.,University of Western Ontario |
Trainor L.,McMaster University |
Rohrmeier M.,Massachusetts Institute of Technology |
And 2 more authors.
Philosophical Transactions of the Royal Society B: Biological Sciences | Year: 2015
Humans possess an ability to perceive and synchronize movements to the beat in music (‘beat perception and synchronization’), and recent neuroscientific data have offered new insights into this beat-finding capacity at multiple neural levels. Here, we review and compare behavioural and neural data on temporal and sequential processing during beat perception and entrainment tasks in macaques (including direct neural recording and local field potential (LFP)) and humans (including fMRI, EEG and MEG). These abilities rest upon a distributed set of circuits that include the motor cortico-basal- ganglia- thalamo-cortical (mCBGT) circuit, where the supplementary motor cortex (SMA) and the putamen are critical cortical and subcortical nodes, respectively. In addition, a cortical loop between motor and auditory areas, connected through delta and beta oscillatory activity, is deeply involved in these behaviours, with motor regions providing the predictive timing needed for the perception of, and entrainment to, musical rhythms. The neural discharge rate and the LFP oscillatory activity in the gamma- and beta-bands in the putamen and SMA of monkeys are tuned to the duration of intervals produced during a beat synchronization-continuation task (SCT). Hence, the tempo during beat synchronization is represented by different interval-tuned cells that are activated depending on the produced interval. In addition, cells in these areas are tuned to the serial-order elements of the SCT. Thus, the underpinnings of beat synchronization are intrinsically linked to the dynamics of cell populations tuned for duration and serial order throughout the mCBGT. We suggest that a cross-species comparison of behaviours and the neural circuits supporting them sets the stage for a new generation of neurally grounded computational models for beat perception and synchronization. ©2015 The Author(s) Published by the Royal Society. All rights reserved.
Guijosa A.,National Autonomous University of Mexico |
Pedraza J.F.,University of Texas at Austin
Journal of High Energy Physics | Year: 2011
We carry out an analytic study of the early-time motion of a quark in a strongly-coupled maximally-supersymmetric Yang-Mills plasma, using the AdS/CFT correspondence. Our approach extracts the first thermal effects as a small perturbation of the known quark dynamics in vacuum, using a double expansion that is valid for early times and for (moderately) ultrarelativistic quark velocities. The quark is found to lose energy at a rate that differs significantly from the previously derived stationary/late-time result: it scales like T4 instead of T2, and is associated with a friction coefficient that is not independent of the quark momentum. Under conditions representative of the quark-gluon plasma as obtained at RHIC, the early energy loss rate is a few times smaller than its late-time counterpart. Our analysis additionally leads to thermally-corrected expressions for the intrinsic energy and momentum of the quark, in which the previously discovered limiting velocity of the quark is found to appear naturally. © SISSA 2011.
Koning N.,University of Calgary |
Kwok S.,University of Hong Kong |
Steffen W.,National Autonomous University of Mexico
Astrophysical Journal | Year: 2013
A model for post asymptotic giant branch bipolar reflection nebulae has been constructed based on a pair of evacuated cavities in a spherical dust envelope. Many of the observed features of bipolar nebulae, including filled bipolar lobes, an equatorial torus, searchlight beams, and a bright central light source, can be reproduced. The effects on orientation and dust densities are studied and comparisons with some observed examples are offered. We suggest that many observed properties of bipolar nebulae are the result of optical effects and any physical modeling of these nebulae has to take these factors into consideration. © 2013. The American Astronomical Society. All rights reserved.
Herlihy M.,Brown University |
Rajsbaum S.,National Autonomous University of Mexico
Distributed Computing | Year: 2013
Roughly speaking, a simplicial complex is shellable if it can be constructed by gluing a sequence of n-simplexes to one another along (n-1) (n - 1) -faces only. Shellable complexes have been widely studied because they have nice combinatorial properties. It turns out that several standard models of concurrent computation can be constructed from shellable complexes. We consider adversarial schedulers in the synchronous, asynchronous, and semi-synchronous message-passing models, as well as asynchronous shared memory. We show how to exploit their common shellability structure to derive new and remarkably succinct tight (or nearly so) lower bounds on connectivity of protocol complexes and hence on solutions to the k k -set agreement task in these models. Earlier versions of material in this article appeared in the 2010 ACM Symposium on Principles of Distributed Computing (Herlihy and Rajsbaum 2010), and the International Conference on Distributed Computing (Herlihy and Rajsbaum 2010, doi: 10.1145/1835698.1835724). © 2013 Springer-Verlag Berlin Heidelberg.
Chernicoff M.,University of Cambridge |
Guijosa A.,National Autonomous University of Mexico |
Pedraza J.F.,University of Texas at Austin
Journal of High Energy Physics | Year: 2013
As evidence for the ER=EPR conjecture, it has recently been observed that the string that is holographically dual to an entangled quark-antiquark pair separating with (asymptotically) uniform acceleration has a wormhole on its worldsheet. We point out that a two-sided horizon and a wormhole actually appear for much more generic quarkantiquark trajectories, which is consistent with the fact that the members of an EPR pair need not be permanently out of causal contact. The feature that determines whether the causal structure of the string worldsheet is trivial or not turns out to be the emission of gluonic radiation by the dual quark and antiquark. In the strongly-coupled gauge theory, it is only when radiation is emitted that one obtains an unambiguous separation of the pair into entangled subsystems, and this is what is reflected on the gravity side by the existence of the worldsheet horizon. © SISSA 2013.
Cortez J.,National Autonomous University of Mexico |
Mena Marugan G.A.,CSIC - Institute for the Structure of Matter |
Velhinho J.M.,University of Beira Interior
Annals of Physics | Year: 2015
We address the question of unitary implementation of the dynamics for scalar fields in cosmological scenarios. Together with invariance under spatial isometries, the requirement of a unitary evolution singles out a rescaling of the scalar field and a unitary equivalence class of Fock representations for the associated canonical commutation relations. Moreover, this criterion provides as well a privileged quantization for the unscaled field, even though the associated dynamics is not unitarily implementable in that case. We discuss the relation between the initial data that determine the Fock representations in the rescaled and unscaled descriptions, and clarify that the S-matrix is well defined in both cases. In our discussion, we also comment on a recently proposed generalized notion of unitary implementation of the dynamics, making clear the difference with the standard unitarity criterion and showing that the two approaches are not equivalent. © 2015 Elsevier Inc.
Delgado-Inglada G.,National Institute of Astrophysics, Optics and Electronics |
Delgado-Inglada G.,National Autonomous University of Mexico |
Rodriguez M.,National Institute of Astrophysics, Optics and Electronics
Astrophysical Journal | Year: 2014
We study the dust present in 56 Galactic planetary nebulae (PNe) through their iron depletion factors, their C/O abundance ratios (in 51 objects), and the dust features that appear in their infrared spectra (for 33 objects). Our sample objects have deep optical spectra of good quality, and most of them also have ultraviolet observations. We use these observations to derive the iron abundances and the C/O abundance ratios in a homogeneous way for all the objects. We compile detections of infrared dust features from the literature and we analyze the available Spitzer/IRS spectra. Most of the PNe have C/O ratios below one and show crystalline silicates in their infrared spectra. The PNe with silicates have C/O <1, with the exception of Cn 1-5. Most of the PNe with dust features related to C-rich environments (SiC or the 30 μm feature usually associated to MgS) have C/O ≳ 0.8. Polycyclic aromatic hydrocarbons are detected over the full range of C/O values, including 6 objects that also show silicates. Iron abundances are low in all the objects, implying that more than 90% of their iron atoms are deposited into dust grains. The range of iron depletions in the sample covers about two orders of magnitude, and we find that the highest depletion factors are found in C-rich objects with SiC or the 30 μm feature in their infrared spectra, whereas some of the O-rich objects with silicates show the lowest depletion factors. © 2014. The American Astronomical Society. All rights reserved..
Olson M.E.,National Autonomous University of Mexico |
Rosell J.A.,Macquarie University
New Phytologist | Year: 2013
Variation in angiosperm vessel diameter is of major functional significance. In the light of recent models predicting optimal vessel taper given resistance imposed by conductive path length, we tested the prediction that plant size should predict vessel diameter, with dryland plants having narrower vessels for their stem sizes. We assembled a comparative dataset including vessel and stem diameter measurements from 237 species from over 40 angiosperm orders across a wide range of habits and habitats. Stem diameter predicted vessel diameter across self-supporting plants (slope 0.36, 95% CI 0.32-0.39). Samples from 142 species from five communities of differing water availability showed no tendency for dryland plants to have narrower vessels. Predictable relationships between vessel diameter and stem diameter mirrored predictable relationships between stem length and diameter across self-supporting species. That vessels are proportional to stem diameter and stem diameter is proportional to stem length suggests that taper in relation to conductive path length gives rise to the vessel diameter-stem diameter relationship. In turn, plant size is related to climate, leading indirectly to the vessel-climate relationship: vessels are likely narrower in drier communities because dryland plants are on average smaller, not because they have narrow vessels for their stem sizes. © 2012 The Authors. New Phytologist © 2012 New Phytologist Trust.
McClure B.,University of Missouri |
Cruz-Garcia F.,National Autonomous University of Mexico |
Romero C.,Instituto Valenciano Of Investigaciones Agrarias Ivia
Annals of Botany | Year: 2011
Background S-RNase-based self-incompatibility (SI) occurs in the Solanaceae, Rosaceae and Plantaginaceae. In all three families, compatibility is controlled by a polymorphic S-locus encoding at least two genes. S-RNases determine the specificity of pollen rejection in the pistil, and S-locus F-box proteins fulfill this function in pollen. S-RNases are thought to function as S-specific cytotoxins as well as recognition proteins. Thus, incompatibility results from the cytotoxic activity of S-RNase, while compatible pollen tubes evade S-RNase cytotoxicity. ScopeThe S-specificity determinants are known, but many questions remain. In this review, the genetics of SI are introduced and the characteristics of S-RNases and pollen F-box proteins are briefly described. A variety of modifier genes also required for SI are also reviewed. Mutations affecting compatibility in pollen are especially important for defining models of compatibility and incompatibility. In Solanaceae, pollen-side mutations causing breakdown in SI have been attributed to the heteroallelic pollen effect, but a mutation in Solanum chacoense may be an exception. This has been interpreted to mean that pollen incompatibility is the default condition unless the S-locus F-box protein confers resistance to S-RNase. In Prunus, however, S-locus F-box protein gene mutations clearly cause compatibility. ConclusionsTwo alternative mechanisms have been proposed to explain compatibility and incompatibility: compatibility is explained either as a result of either degradation of non-self S-RNase or by its compartmentalization so that it does not have access to the pollen tube cytoplasm. These models are not necessarily mutually exclusive, but each makes different predictions about whether pollen compatibility or incompatibility is the default. As more factors required for SI are identified and characterized, it will be possible to determine the role each process plays in S-RNase-based SI. © The Author 2011. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved.
Gutierrez-Aguilar M.,University of Missouri |
Uribe-Carvajal S.,National Autonomous University of Mexico
Mitochondrion | Year: 2015
Opening of the mitochondrial permeability transition (MPT) pore mediates the increase in the unselective permeability to ions and small molecules across the inner mitochondrial membrane. MPT results from the opening of channels of unknown identity in mitochondria from plants, animals and yeast. However, the effectors and conditions required for MPT to occur in different species are remarkably disparate. Here we critically review previous and recent findings concerning the mitochondrial unselective channel of the yeast Saccharomyces cerevisiae to determine if it can be considered a counterpart of the mammalian MPT pore. © 2015 Elsevier B.V. and Mitochondria Research Society.
Martinez-Garcia E.E.,National Institute of Astrophysics, Optics and Electronics |
Martinez-Garcia E.E.,National Autonomous University of Mexico |
Gonzalez-Lopezlira R.A.,National Autonomous University of Mexico
Astrophysical Journal | Year: 2013
Azimuthal age/color gradients across spiral arms are a signature of long-lived spirals. From a sample of 19 normal (or weakly barred) spirals where we have previously found azimuthal age/color gradient candidates, 13 objects were further selected if a two-armed grand-design pattern survived in a surface density stellar mass map. Mass maps were obtained from optical and near-infrared imaging, by comparison with a Monte Carlo library of stellar population synthesis models that allowed us to obtain the mass-to-light ratio in the J band, (M/L) J , as a function of (g-i) versus (i-J) color. The selected spirals were analyzed with Fourier methods in search of other signatures of long-lived modes related to the gradients, such as the gradient divergence toward corotation, and the behavior of the phase angle of the two-armed spiral in different wavebands, as expected from theory. The results show additional signatures of long-lived spirals in at least 50% of the objects. © 2013. The American Astronomical Society. All rights reserved.
Calderoni G.,Italian National Institute of Geophysics and Volcanology |
Rovelli A.,Italian National Institute of Geophysics and Volcanology |
Singh S.K.,National Autonomous University of Mexico
Geophysical Journal International | Year: 2013
The empirical Green's function (EGF) technique is applied in the frequency domain to 962 broad-band seismograms (3.3 ≤ MW ≤ 6.1) to determine stress drop and source scaling of the 2009 April L'Aquila earthquakes. The station distance varies in the range 100-250 km from the source. Ground motions of several L'Aquila earthquakes are characterized by large azimuthal variations due to source directivity, even at low magnitudes. Thus, the individual-station stress-drop estimates are significantly biased when source directivity is not taken into account properly. To reduce the bias, we use single-station spectral ratios with pairs of earthquakes showing a similar degree of source directivity. The superiority of constant versus varying stress-drop models is assessed through minimization of misfit in a least-mean-square sense. For this analysis, seismograms of 26 earthquakes occurring within 10 km from the hypocentres of the three strongest shocks are used.We find that a source model where stress drop increases with the earthquake size has the minimum misfit: as compared to the best constant stress-drop model the improvement in the fit is of the order of 40 per cent.We also estimate the stress-drop scaling on a larger data set of 64 earthquakes, all of them having an independent estimate of seismic moment and consistent focal mechanism. An earthquake which shows no directivity is chosen as EGF event. This analysis confirms the former trend and yields individual-event stress drops very close to 10 MPa at magnitudes MW > 4.5 that decrease to 1 MPa, on the average, at the smallest magnitudes. A varying stress-drop scaling of L'Aquila earthquakes is consistent with results from other studies using EGF techniques but contrasts with results of authors that used inversion techniques to separate source from site and propagation effects. We find that there is a systematic difference for small events between the results of the two methods, with lower and less scattered values of stress drop resulting from the EGF approach. © The Authors 2012. Published by Oxford University Press on behalf of The Royal Astronomical Society.
News Article | December 7, 2016
Fabián Díaz achieved a milestone last year when he derived the first human embryonic stem-cell line from cells of Mexican origin. Biologists across Mexico now use the stem cells, which Díaz — a researcher at the National Institute of Perinatology in Mexico City — created using embryos discarded by a fertility clinic. But in recent months, Díaz has put his stem-cell research on hold. He is waiting to see whether Mexico’s legislature will approve an amendment to the national health law that would ban experiments with human embryos. The proposal is winding its way through the legislature’s lower house, the Chamber of Deputies. To become law, it would have to be approved by the legislature and by Mexico’s president, Enrique Peña Nieto. “They want to eliminate an entire area of research in Mexico,” says René Drucker-Colín, a neurobiologist at the National Autonomous University of Mexico (UNAM) in Mexico City who hopes to use embryonic tissue as a treatment for people with Parkinson’s disease. The amendment is intended to regulate assisted reproduction, including the payment of surrogate mothers, donations to egg and sperm banks and the fertilization of more than three eggs at a time. But it would also ban the creation of human embryos for any purpose except reproduction and any research with existing human embryos. Such restrictions are intended to address Mexico’s thriving reproductive tourism industry, which has few protections for surrogate mothers. But the proposed amendment would have prohibited a scientific world first that took place in Mexico: the conception of a baby with DNA from three people. The child was born in April. His parents, who are from Jordan, used the treatment to prevent their baby from inheriting a disease that would otherwise be passed down through his mother’s mitochondrial DNA. The proposed changes to Mexico’s health law have the backing of the National Action Party (PAN) and Peña Nieto’s Institutional Revolutionary Party (PRI), but researchers worry that they are too broad. “We’re not against the regulation,” says Diana Escalante, a neurodevelopmental biologist at UNAM. “But the way in which they are doing it is just forbidding everything.” The amendment would prevent the creation of new embryonic stem-cell lines, she says, as well as a standard way to test whether the cells can develop into any cell type in the body. The penalties for violating the restrictions would include heavy fines and imprisonment. Human-rights groups have joined scientists in opposing the proposed amendment, which would restrict artificial reproduction to heterosexual couples. Only Mexican-national couples would be able to use surrogate mothers, who would be limited to their relatives. Opponents of the plan say that it discriminates against same-sex couples and people without family members of reproductive age. But Rosa Velez, a spokesperson for Sylvana Beltrones, the legislator who authored the amendment, says that the restrictions would protect human dignity and the legal rights of children who are created using fertility techniques and their parents. She adds that scientists would be able to study stem cells obtained from adults. Researchers have protested against the plan. On 24 October, more than 60 Mexican scientists sent a letter to the newspaper El Universal critizing the proposed amendment. Drucker-Colín says that he has also asked Mexico’s National Academy of Sciences to intercede with the politicians. The amendment would make it harder for scientists to study the earliest stages of human development, says Iván Velasco, a neurodevelopmental biologist at UNAM and president of the Mexican Society for Stem Cell Research. “It’s possible people will train abroad, but if they want to come back they won’t be able to do it here,” he says. Yet Velasco thinks that his own work, which uses existing human embryonic stem-cell lines, would be permitted. Others are worried about how a ban on the use of embryonic stem cells would affect clinical research. “We are close to beginning working with [embryonic stem] cells, and these laws are going to trash everything,” says Raymundo Cañales de la Fuente, a research gynaecologist at the Hospital Angeles Pedregal in Mexico City whose group looks for ways to improve the efficacy of assisted reproductive techniques. The amendment would limit the use of routine techniques used in fertility clinics, including a method used to screen embryos for genetic mutations before they are implanted into the mother. Such screening can prevent the transmission of severe genetic diseases, and help some infertile couples to understand why they are having trouble conceiving. If the technique is banned, researchers would need to rely on older, less precise methods to determine whether embryos are likely to survive implantation, says Patricia Grether, a geneticist at the National Institute of Perinatology. Clinicians could also send patients to the United States for treatment, but that is too expensive for many Mexicans. Velez says that the intent of the proposed amendment is to improve assisted reproduction, not to ban it. But Cañales de la Fuente says that the proposal would prevent many reputable clinics from offering such services. Clinicians would be limited to fertilizing three eggs at a time, reducing their success rates. They would also have to verify that a couple is not storing fertilized eggs at another clinic. With more than 100 such clinics in Mexico City alone, there is no practical way to do this. “We need to make a new law,” Cañales de la Fuente says. “Completely different from this one, with a scientific basis and a medical basis to be practical — and from the ministry of health, not from the congressmen.”
Ullrich B.,National Autonomous University of Mexico |
Wang J.S.,Air Force Research Lab
Applied Physics Letters | Year: 2013
The Stokes shift of colloidal 4.7 nm PbS quantum dots was measured between 5 and 300 K at incrementally increasing continuous laser intensities. The results demonstrate Stokes shift tuning by optical means only at stable given temperatures due to optically enforced electronic state alteration in the quantum dots. The tuning phenomenon is perfectly fit by a semi-empirical model, which provides a design tool for the chromaticity of quantum dots at different optical pump intensities. © 2013 American Institute of Physics.
Norini G.,National Autonomous University of Mexico |
Norini G.,University of Milan Bicocca |
Acocella V.,Third University of Rome
Journal of Geophysical Research: Solid Earth | Year: 2011
Mount Etna is characterized by significant flank instability, whose triggering factors are still a matter of debate. We use analog models to investigate the role of different factors. In the models, a cone and base of granular material simulate the volcanic edifice and its basement. The asymmetric geometry of the basement simulates the topographic gradient around the volcano. Injections of silicone (sets A and B) and low-viscosity vegetable oil (set C) simulate the pressurization of plutonic complex, deep reservoirs, and the emplacement of dikes, respectively. Other experiments (set D) reproduce regional extensional tectonics in the last 105 years, within layers with different cohesion simulating strength differences in the basement. Laser scanner and control points allow the tracking of surface deformation with submillimeter precision. The asymmetric topography enhances flank instability on the side with the weakest confinement (i.e., seaside), providing the preparing factor for instability. In sets A and B, any type of pressurized reservoir enhances, up to 10 times, the amount of flank instability toward the seaside with respect to the other flanks of the volcano. In set C, dike emplacement enhances seaside flank instability up to 8 times. Regional tectonics and crustal layering in set D enhance flank instability up to 2 and 1.3 times, respectively. Considering the duration and frequency of the simulated processes in nature, we propose a semiquantitative evaluation and hierarchy of the factors controlling flank instability at Etna. Magmatic activity (point-like source inflation and dike emplacement) provides the most important triggering factor. Extensional tectonics, in the last 105 years, and crustal layering are more than 10 times less effective. This study shows the importance of differential buttressing at the volcano base for flank instability. This condition is an important indication to expect asymmetric activity in any volcano (flank eruptions and deformation). Copyright © 2011 by the American Geophysical Union.
Galindo-Murillo R.,University of Utah |
Garcia-Ramos J.C.,National Autonomous University of Mexico |
Ruiz-Azuara L.,National Autonomous University of Mexico |
Cheatham T.E.,University of Utah |
Cortes-Guzman F.,National Autonomous University of Mexico
Nucleic Acids Research | Year: 2015
The family of anticancer complexes that include the transition metal copper known as Casiopeínas® shows promising results. Two of these complexes are currently in clinical trials. The interaction of these compounds with DNA has been observed experimentally and several hypotheses regarding the mechanism of action have been developed, and these include the generation of reactive oxygen species, phosphate hydrolysis and/or base-pair intercalation. To advance in the understanding on how these ligands interact with DNA, we present a molecular dynamics study of 21 Casiopeínas with a DNA dodecamer using 10 μs of simulation time for each compound. All the complexes were manually inserted into the minor groove as the starting point of the simulations. The binding energy of each complex and the observed representative type of interaction between the ligand and the DNA is reported. With this extended sampling time, we found that four of the compounds spontaneously flipped open a base pair and moved inside the resulting cavity and four compounds formed stacking interactions with the terminal base pairs. The complexes that formed the intercalation pocket led to more stable interactions. © 2015 The Author(s) 2015. Published by Oxford University Press on behalf of Nucleic Acids Research.
Sahu S.,National Autonomous University of Mexico |
Oliveros A.F.O.,University of Los Andes, Colombia |
Sanabria J.C.,University of Los Andes, Colombia
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2013
The 1ES 1959+650 is a high-peaked BL Lacertae object. On the 4th of June, 2002, it exhibited a strong TeV flare without any low energy counterpart, providing for the first time an example of an orphan flare from a blazar. Observation of this orphan flare is in striking disagreement with the predictions of the leptonic models thus challenging the conventional synchrotron self-Compton interpretation of the TeV emission. Here we propose that the low energy tail of the synchrotron self-Compton photons in the blazar jet serve as the target for the Fermi-accelerated high energy protons of energy 100 TeV within the jet to produce the TeV photons through the decay of neutral pions from the delta resonance. Our model explains very nicely the observed TeV flux from this orphan flare and we also estimate the high energy neutrino flux from this flaring event. © 2013 American Physical Society.
Alvarado-Tenorio B.,National Autonomous University of Mexico |
Romo-Uribe A.,National Autonomous University of Mexico |
Mather P.T.,Syracuse Biomaterials Institute
Macromolecules | Year: 2011
This contribution concerns the microstructure of POSS-based networks previously reported for their shape memory properties [LeeMacromolecules 2008, 41, 4730-4738]. Simultaneous wide-angle and small-angle X-ray scattering (WAXS/SAXS) analysis has revealed highly ordered nanoscale structures in polyhedral silsesquioxane-poly(ε-caprolactone) (POSS-PCL) semicrystalline cross-linked nanocomposites. Architecturally, the oligomers used for network formation resemble a highly asymmetrical triblock copolymer featuring a single POSS moiety centered between two PCL chains, yielding two short tethers for a total molecular weight of 2600 g/mol. WAXS patterns of the diol-terminated POSS-PCL sample showed the existence of both crystalline reflections of the PCL orthorhombic phase and crystalline reflections of the POSS rhombohedral phase, indicating microphase separation that allows independent crystallization. Accordingly, two endothermic thermal transitions associated with the melting of each crystal phase were exhibited by the material. Strikingly, SAXS revealed two long period spacings: one associated with the POSS nanobuilding blocks (long period of 66 Å) and the other associated with PCL lamellar nanophase (long period of 151 Å). Surprisingly, end-capping of the PCL alcohol groups with acrylate groups (needed for cross-linking) greatly reduced the crystalline order of POSS nanocages, whereas the orthorhombic phase of PCL remained unchanged. The acrylate groups also produced a significant reduction of melting transition temperature of POSS crystals. Moreover, SAXS showed only one long period (117 Å) associated with PCL crystalline nanostructure. Macromolecular end-linked networks exhibiting shape memory behavior were obtained by photocuring the acrylate-terminated nanocomposites utilizing a tetrathiol cross-linker. Despite the architectural constraints of cross-links, POSS-PCL networks also featured the POSS rhombohedral crystalline phase. However, PCL crystallization was suppressed, resulting in an amorphous PCL phase. DSC analysis of the POSS-PCL networks showed only one endothermic transition. SAXS showed the existence of long-range order in the cross-linked material with the intensity maxima indexed to a cubic lattice with parameter a = 13 nm. That is, a superstructure is present in the cross-linked networks, and the cubic superstructure is attributed to crystalline clusters formed by POSS molecules. To our knowledge, this is the first evidence for such a nanoscale superstructure in a polymer network. © 2011 American Chemical Society.
Perusquia M.,National Autonomous University of Mexico |
Perusquia M.,Texas A&M University |
Stallone J.N.,Texas A&M University
American Journal of Physiology - Heart and Circulatory Physiology | Year: 2010
The marked sexual dimorphism that exists in human cardiovascular diseases has led to the dogmatic concept that testosterone (Tes) has deleterious effects and exacerbates the development of cardiovascular disease in males. While some animal studies suggest that Tes does exert deleterious effects by enhancing vascular tone through acute or chronic mechanisms, accumulating evidence suggests that Tes and other androgens exert beneficial effects by inducing rapid vasorelaxation of vascular smooth muscle through nongenomic mechanisms. While this effect frequently has been observed in large arteries at micromolar concentrations, more recent studies have reported vasorelaxation of smaller resistance arteries at nanomolar (physiological) concentrations. The key mechanism underlying Tes-induced vasorelaxation appears to be the modulation of vascular smooth muscle ion channel function, particularly the inactivation of L-type voltage-operated Ca2+ channels and/or the activation of voltage-operated and Ca2+-activated K+ channels. Studies employing Tes analogs and metabolites reveal that androgen-induced vasodilation is a structurally specific nongenomic effect that is fundamentally different than the genomic effects on reproductive targets. For example, 5α-dihydrotestosterone exhibits potent genomic-androgenic effects but only moderate vasorelaxing activity, whereas its isomer 5β-dihydrotestosterone is devoid of androgenic effects but is a highly efficacious vasodilator. These findings suggest that the dihydro-metabolites of Tes or other androgen analogs devoid of androgenic or estrogenic effects could have useful therapeutic roles in hypertension, erectile dysfunction, prostatic ischemia, or other vascular dysfunctions. Copyright © 2010 the American Physiological Society.
Chavez-Baeza C.,Benito Juarez University |
Sheinbaum-Pardo C.,National Autonomous University of Mexico
Energy | Year: 2014
This paper presents passenger road transport scenarios that may assist the MCMA (Mexico City Metropolitan Area) in achieving lower emissions in both criteria air pollutants (CO, NOx, NMVOC (non-methane volatile organic compounds), and PM10) and GHG (greenhouse gas) (CH4, N2O and CO2), while also promoting better mobility and quality of life in this region. We developed a bottom-up model to estimate the historical trends of energy demand, criteria air pollutants and GHG emissions caused by passenger vehicles circulating in the Mexico City Metropolitan Area (MCMA) in order to construct a baseline scenario and two mitigation scenarios that project their impact to 2028. Mitigation scenario "eff" considers increasing fuel efficiencies and introducing new technologies for vehicle emission controls. Mitigation scenario "BRT" considers a modal shift from private car trips to a Bus Rapid Transport system. Our results show significant reductions in air pollutants and GHG emissions. Incentives and environmental regulations are needed to enable these scenarios. © 2013 Elsevier Ltd.
Assanto G.,Third University of Rome |
Minzoni A.A.,National Autonomous University of Mexico |
Smyth N.F.,Third University of Rome
Optics Letters | Year: 2014
We investigate the routing of vortex beams in nonlocal media by means of coaxial, co-propagating spatial optical solitons. By introducing a refractive index perturbation in the form of a localized defect or a dielectric interface, the soliton waveguide can be curved and, therefore, can deviate the collinear vortex, effectively routing it, while preventing its destabilization and breakup. © 2014 Optical Society of America.
Martin N.,National Autonomous University of Mexico |
Martin N.,IMDEA Madrid Institute for Advanced Studies
Angewandte Chemie - International Edition | Year: 2011
In a stable condition: The first example of a non-IPR hollow fullerene that is more stable than the IPR isomer has been reported for the C 2v-C72 fullerene (see picture). This molecule has been trapped by the exohedral chlorination reaction that affords the #11188C72Cl4 molecule, the structure of which has been unambiguously determined by X-ray analyses. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Bradler K.,McGill University |
Jauregui R.,National Autonomous University of Mexico
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2012
In this Comment we show that the ambiguity of entropic quantities calculated by Montero and Martín-Martínez for fermionic fields in the context of the Unruh effect is not related to the properties of anticommuting fields, as claimed therein, but rather to wrong mathematical manipulations with them and not taking into account a fundamental superselection rule of quantum field theory. © 2012 American Physical Society.
Vidal O.,World Wildlife Fund |
Lopez-Garcia J.,National Autonomous University of Mexico |
Rendon-Salinas E.,World Wildlife Fund
Conservation Biology | Year: 2014
We used aerial photographs, satellite images, and field surveys to monitor forest cover in the core zones of the Monarch Butterfly Biosphere Reserve in Mexico from 2001 to 2012. We used our data to assess the effectiveness of conservation actions that involved local, state, and federal authorities and community members (e.g., local landowners and private and civil organizations) in one of the world's most iconic protected areas. From 2001 through 2012, 1254 ha were deforested (i.e., cleared areas had <10% canopy cover), 925 ha were degraded (i.e., areas for which canopy forest decreased), and 122 ha were affected by climatic conditions. Of the total 2179 ha of affected area, 2057 ha were affected by illegal logging: 1503 ha by large-scale logging and 554 ha by small-scale logging. Mexican authorities effectively enforced efforts to protect the monarch reserve, particularly from 2007 to 2012. Those efforts, together with the decade-long financial support from Mexican and international philanthropists and businesses to create local alternative-income generation and employment, resulted in the decrease of large-scale illegal logging from 731 ha affected in 2005-2007 to none affected in 2012, although small-scale logging is of growing concern. However, dire regional social and economic problems remain, and they must be addressed to ensure the reserve's long-term conservation. The monarch butterfly (Danaus plexippus) overwintering colonies in Mexico-which engage in one of the longest known insect migrations-are threatened by deforestation, and a multistakeholder, regional, sustainable-development strategy is needed to protect the reserve. © 2013 Society for Conservation Biology.
Mwampamba T.H.,National Autonomous University of Mexico |
Owen M.,Chardust Ltd. |
Pigaht M.,MARGE Consulting
Energy for Sustainable Development | Year: 2013
Charcoal briquettes are solid fuel made from carbonized biomass, or densified biomass that is subsequently carbonized. In spite of clear advantages of charcoal briquettes that include price, burn time, environmental sustainability and potential for product standardization, their uptake as a substitute for wood charcoal in Sub-Saharan Africa (SSA) remains very limited. By analyzing the experiences of pioneer charcoal briquette producers in Kenya, Rwanda, Uganda, and Tanzania, we identify factors limiting the growth of the industry in the region and make recommendations for how to address these challenges. Our analysis shows that widespread adoption of charcoal briquettes is unlikely to have a significant effect on demand for wood charcoal within SSA, as has been the case in many Asian countries. To date, the availability of charcoal briquettes has displaced only small volumes of charcoal demand and has increased the energy options for limited consumer groups within niche markets. Limiting factors for the industry include prevailing low prices of wood charcoal, punitive legal and fiscal requirements for briquette producers, and supply-driven (versus market-led) approaches to industry development. Policy, technical and marketing interventions are proposed to address these barriers and stimulate more widespread production and use of charcoal briquettes in the region. Our recommendations include marketing studies to better understand consumer preferences in fuel and stove attributes, better enforcement of existing forestry and charcoal regulations, reduced regulatory hurdles for registering new briquette businesses, targeted tax exemptions, and expansion of consumption to new industrial and other consumers. © 2012 Elsevier Ltd.
Research Center Y Of Estudios Avanzados Del Instituto Polytechnic Aacion, National Autonomous University of Mexico and University Autonoma Del Estado Demorlos | Date: 2011-12-16
The present invention relates to polyene macrolide derivatives according to the formula: wherein M is a macrocyclic lactone ring; N is a polyene sugar, substituted or unsubstituted; X is independently selected from O, S, N or NH; R is independently selected from an alkyl, cycloalkyl, heterocycloalkyl aryl, heteroaryl, arylalkyl, and heteroaryalkyl group; and i is an integer from 1 to 3, with the condition that it has a negative charge or the zwitterions character is restored; or a pharmaceutically acceptable salt thereof useful as antibiotics.
Castanos F.,McGill University |
Fridman L.,CINVESTAV |
Fridman L.,National Autonomous University of Mexico
Automatica | Year: 2011
The robustness properties of sliding-mode and H∞ controllers are exploited to produce a dynamic output feedback controller that is insensitive to matched perturbations and attenuates the unmatched ones. The assumptions on the plant differ from the standard assumptions of the Riccati state-space approach to H∞ control. The sliding-mode controller drives the state into a reduced-order manifold for which the equivalent system does satisfy the standard assumptions and hence the standard theory can be applied. The resulting Riccati equations are of reduced order. © 2011 Elsevier Ltd. All rights reserved.
Zelenski M.,Institute of Experimental Mineralogy |
Taran Y.,National Autonomous University of Mexico
Bulletin of Volcanology | Year: 2011
We report chemical compositions (major and trace components including light hydrocarbons), hydrogen, oxygen, helium and nitrogen isotope ratios of volcanic and geothermal fluids of Mutnovsky volcano, Kamchatka. Several aspects of the geochemistry of fluids are discussed: chemical equilibria, mixing of fluids from different sources, evaluation of the parent magmatic gas composition and contributions to magmatic vapors of fluids from different reservoirs of the Kamchatkan subduction zone. Among reactive species, hydrogen and carbon monoxide in volcanic vapors are chemically equilibrated at temperatures <300°C with the SO2-H2S redox-pair. A metastable equilibrium between saturated and unsaturated light hydrocarbons is attained at close to discharge temperatures. Methane is disequilibrated. Three different sources of fluids from three fumarolic fields in the Mutnovsky craters can be distinguished: (1) magmatic gas from a large convecting magma body discharging through Active Funnel, a young crater with the hottest fumaroles (up to 620°C) contributing ~80% to the total volcanic gas output; (2) volcanic fluid from a separate shallow magma body beneath the Bottom Field of the main crater (96-280°C fumaroles); and (3) hydrothermal fluid with a high relative and absolute concentrations of CH4 from the Upper Field in the main crater (96-285°C fumaroles). The composition of the parent magmatic gas is estimated using water isotopes and correlations between He and other components in the Active Funnel gases. The He-Ar-N2 systematics of volcanic and hydrothermal fluids of Mutnovsky are consistent with a large slab-derived sedimentary nitrogen input for the nitrogen inventory, and we calculate that only ~1% of the magmatic N2 has a mantle origin and <<1% is derived from the arc crust. © 2011 Springer-Verlag.
Ullrich B.,National Autonomous University of Mexico |
Xi H.,Bowling Green State University
Optics Letters | Year: 2013
Square root photocurrent dependences of nanowires on light intensity were reported in the literature without clarification of the limiting effect. In this Letter, we derived a relation excellently fitting the observed nonlinearities and, intensifying the significance of the result, we demonstrated that the fit parameters involved can be employed to determine the impurity concentration and electronic response time of nano-sized semiconductors. © 2013 Optical Society of America.
News Article | April 13, 2016
MEXICO CITY - Scientists have begun drilling for core samples, nearly 5,000 feet below the seabed, of a prehistoric crater caused by an asteroid collision that is linked to the extinction of dinosaurs. Some scientists believe the asteroid, and perhaps other factors, may have led to the end of dinosaurs. The theory that their demise 66 million years ago was linked to the asteroid impact was first proposed in 1980. The biggest piece of evidence is the 110-mile (180-km) crater near Chicxulub in Mexico. During the two-month expedition the international team of scientists will look for clues about how life recovered after the impact and whether the crater could have been a home for microbial life. "The impact caused the extinction of some 75 percent of species that existed in that period," said Dr Jaime Urrutia-Fucugauchi, of the Institute of Geophysics at the National Autonomous University of Mexico. "It marks the transition of what colloquially, we know as the era of the dinosaurs to the era of the mammals."
Mendoza C.,National Autonomous University of Mexico |
Hartzell S.,U.S. Geological Survey
Bulletin of the Seismological Society of America | Year: 2013
We examine the ability of teleseismic P waves to provide a timely image of the rupture history for large earthquakes using a simple, 2D finite-fault source parameterization. We analyze the broadband displacement waveforms recorded for the 2010 Mw ~ 7 Darfield (New Zealand) and El Mayor-Cucapah (Baja California) earthquakes using a single planar fault with a fixed rake. Both of these earthquakes were observed to have complicated fault geometries following detailed source studies conducted by other investigators using various data types. Our kinematic, finite-fault analysis of the events yields rupture models that similarly identify the principal areas of large coseismic slip along the fault. The results also indicate that the amount of stabilization required to spatially smooth the slip across the fault and minimize the seismic moment is related to the amplitudes of the observed P waveforms and can be estimated from the absolute values of the elements of the coefficient matrix. This empirical relationship persists for earthquakes of different magnitudes and is consistent with the stabilization constraint obtained from the L-curve in Tikhonov regularization. We use the relation to estimate the smoothing parameters for the 2011 Mw 7.1 East Turkey, 2012 Mw 8.6 Northern Sumatra, and 2011 Mw 9.0 Tohoku, Japan, earthquakes and invert the teleseismic P waves in a single step to recover timely, preliminary slip models that identify the principal source features observed in finite-fault solutions obtained by the U.S. Geological Survey National Earthquake Information Center (USGS/NEIC) from the analysis of body- and surface-wave data. These results indicate that smoothing constraints can be estimated a priori to derive a preliminary, first-order image of the coseismic slip using teleseismic records.
Villabona-Monsalve J.P.,National Autonomous University of Mexico |
Noria R.,National Autonomous University of Mexico |
Matsika S.,Temple University |
Peon J.,National Autonomous University of Mexico
Journal of the American Chemical Society | Year: 2012
The dynamics following electronic excitation of hypoxanthine and its nucleoside inosine were studied by femtosecond fluorescence up-conversion. Our objective was to explore variants of the purinic DNA bases in order to determine the molecular parameters that increase or reduce the accessibility to ground state conical intersections. From experiments in water and methanol solution we conclude that both dominant neutral tautomers of hypoxanthine exhibit ultrashort excited state lifetimes (τ < 0.2 ps), which are significantly shorter than in the related nucleobase guanine. This points to a more accessible conical intersection for the fluorescent state upon removal of the amino group, present in guanine but absent in hypoxanthine. The excited state dynamics of singly protonated hypoxanthine were also studied, showing biexponential decays with a 1.1 ps component (5%) besides a sub-0.2 ps ultrafast component. On the other hand, the S 1 lifetimes of the singly deprotonated forms of hypoxanthine and inosine show drastic differences, where the latter remains ultrafast but the singly deprotonated hypoxanthine shows a much longer lifetime of 19 ps. This significant variation is related to the different deprotonation sites in hypoxanthine versus inosine, which gives rise to significantly different resonance structures. In our study we also include multireference perturbation theory (MRMP2) excited state calculations in order to determine the nature of the initial electronic excitation in our experiments and clarify the ordering of the states in the singlet manifold at the ground state geometry. In addition, we performed multireference configuration interaction calculations (MR-CIS) that identify the presence of low-lying conical intersections for both prominent neutral tautomers of hypoxanthine. In both cases, the surface crossings occur at geometries reached by out of plane opposite motions of C2 and N3. The study of this simpler purine gives several insights into how small structural modifications, including amino substitution and protonation site and state, determine the accessibility to conical intersections in this kind of heterocycles. © 2012 American Chemical Society.
Carmona D.,National Autonomous University of Mexico |
Lajeunesse M.J.,National Evolutionary Synthesis Center |
Johnson M.T.,North Carolina State University
Functional Ecology | Year: 2011
1. Although secondary metabolites are recognized as fundamental to the defence of plants against insect and mammalian herbivores, their relative importance compared to other potential defensive plant traits (e.g. physical resistance, gross morphology, life-history, primary chemistry and physiology) are not well understood. 2.We conducted a meta-analysis to answer the question: What types of genetically variable plant traits most strongly predict resistance against herbivores? We performed a comprehensive literature search and obtained 499 separate measurements of the strength of covariation (measured as genetic correlations) between plant traits and herbivore susceptibility - these were extracted from 72 studies involving 19 plant families. 3.Surprisingly, we found no overall association between the concentrations of secondary metabolites and herbivore susceptibility - plant traits other than secondary metabolites most strongly predicted herbivore susceptibility. Specifically, genetic variation in life-history traits (e.g. flowering time, growth rate) consistently exhibited the strongest genetic correlations with susceptibility. Genetic variation in gross morphological traits (e.g. no. branches, plant size) and physical resistance traits (e.g. latex, trichomes) were also frequently correlated with variation in herbivore susceptibility, but these relationships depended on attributes of the herbivores (e.g. feeding guild) and plants (e.g. longevity). 4.These results call into question the conventional wisdom that secondary metabolites are the most important anti-herbivore defence of plants. We propose the hypothesis that herbivores select most strongly on genetic variation in life-history, morphological and physical resistance traits, but the greater pleiotropic effects of genes controlling these traits impose strong constraints on their evolution. Meanwhile, secondary metabolites could have evolved to be important defensive mechanisms not because they have the largest effect on herbivores, but because the constraints on their evolution are the weakest. © 2010 The Authors. Journal compilation © 2010 British Ecological Society.
Jara-Oseguera A.,National Autonomous University of Mexico |
Jara-Oseguera A.,U.S. National Institutes of Health |
Islas L.D.,National Autonomous University of Mexico
Biophysical Journal | Year: 2013
Thermo-transient receptor potential channels display outstanding temperature sensitivity and can be directly gated by low or high temperature, giving rise to cold- and heat-activated currents. These constitute the molecular basis for the detection of changes in ambient temperature by sensory neurons in animals. The mechanism that underlies the temperature sensitivity in thermo-transient receptor potential channels remains unknown, but has been associated with large changes in standard-state enthalpy (ΔHo) and entropy (ΔSo) upon channel gating. The magnitude, sign, and temperature dependence of ΔHo and ΔSo, the last given by an associated change in heat capacity (ΔCp), can determine a channel's temperature sensitivity and whether it is activated by cooling, heating, or both, if ΔCp makes an important contribution. We show that in the presence of allosteric gating, other parameters, besides ΔHo and ΔSo, including the gating equilibrium constant, the strength- and temperature dependence of the coupling between gating and the temperature-sensitive transitions, as well as the ΔHo/ΔSo ratio associated with them, can also determine a channel's temperature-dependent activity, and even give rise to channels that respond to both cooling and heating in a ΔC p-independent manner. © 2013 Biophysical Society.
Bengochea G.R.,CONICET |
Canate P.,National Autonomous University of Mexico |
Sudarsky D.,National Autonomous University of Mexico
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2015
In this work, we consider the problem of the emergence of seeds of cosmic structure in the framework of the non-inflationary model proposed by Hollands and Wald. In particular, we consider a modification to that proposal designed to account for breaking the symmetries of the initial quantum state, leading to the generation of the primordial inhomogeneities. This new ingredient is described in terms of a spontaneous reduction of the wave function. We investigate under which conditions one can recover an essentially scale free spectrum of primordial inhomogeneities, and which are the dominant deviations that arise in the model as a consequence of the introduction of the collapse of the quantum state into that scenario. © 2015 The Authors.
Hartzell S.,U.S. Geological Survey |
Mendoza C.,National Autonomous University of Mexico |
Zeng Y.,U.S. Geological Survey
Geophysical Research Letters | Year: 2013
We independently invert teleseismic P waveforms and regional crustal phases to examine the finite fault slip model for the 2011 Mw 5.8 Mineral, Virginia, earthquake. Theoretical and empirical Green's functions are used for the teleseismic and regional models, respectively. Both solutions show two distinct sources each about 2 km across and separated by 2.5 km. The source at the hypocenter is more localized in the regional model leading to a higher peak slip of 130 cm and higher average stress drop of 250 bars compared with 86 cm and 150 bars for the same source in the teleseismic model. Both sources are centered at approximately 8 km depth in the regional model, largely below the aftershock distribution. In the teleseismic model, the sources extend updip to approximately 6 km depth, into the depth range of the aftershocks. The rupture velocity is not well resolved but appears to be near 2.7 km/s. Key Points Two main sources separated by 2 km and rupture velocity of 2.7 km/sec Teleseismic and regional data provide independent imaging of finite slip model The average stress drop is estimated by finite fault analysis to be 200 bars ©2013. American Geophysical Union. All Rights Reserved.
Cruz-Zavala E.,National Autonomous University of Mexico |
Moreno J.A.,National Autonomous University of Mexico |
Fridman L.M.,CINVESTAVIPN |
Fridman L.M.,National Autonomous University of Mexico
IEEE Transactions on Automatic Control | Year: 2011
The differentiators based on the Super-Twisting Algorithm (STA) yield finite-time and theoretically exact convergence to the derivative of the input signal, whenever this derivative is Lipschitz. However, the convergence time grows unboundedly when the initial conditions of the differentiation error grow. In this technical note a Uniform Robust Exact Differentiator (URED) is introduced. The URED is based on a STA modification and includes high-degree terms providing finite-time, and exact convergence to the derivative of the input signal, with a convergence time that is bounded by some constant independent of the initial conditions of the differentiation error. Strong Lyapunov functions are used to prove the convergence of the URED. © 2011 IEEE.
Lopez-Martinez R.,National Autonomous University of Mexico |
Mendez-Tovar L.J.,Hospital Of Especialidades
Clinics in Dermatology | Year: 2012
Blastomycosis is a systemic mycosis with a high prevalence in the Midwest of the United States. The fungus inhabits soil, and human infection occurs through inhalation. Its asexual phase is called Blastomyces dermatitidis and its sexual phase, Ajellomyces dermatitidis. It is more common in men. Signs and symptoms are usually severe, starting with an infection resembling pneumonia that later disseminates to the skin, bones, and central nervous system. Infection in dogs is common in endemic areas. The diagnosis can be achieved by identifying the organism with direct microscopy, culture, histopathology, serologic tests, and molecular techniques, although these are still in trial phase. The treatments of choice are azoles (itraconazole, fluconazole, and posaconazole), and in severe cases, amphotericin B. © 2012.
Bastarrachea-Magnani M.A.,National Autonomous University of Mexico |
Lerma-Hernandez S.,University of Xalapas |
Hirsch J.G.,National Autonomous University of Mexico
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2014
The nonintegrable Dicke model and its integrable approximation, the Tavis-Cummings model, are studied as functions of both the coupling constant and the excitation energy. The present contribution extends the analysis presented in the previous paper by focusing on the statistical properties of the quantum fluctuations in the energy spectrum and their relation with the excited-state quantum phase transitions. These properties are compared with the dynamics observed in the semiclassical versions of the models. The presence of chaos for different energies and coupling constants is exhibited, employing Poincaré sections and Peres lattices in the classical and quantum versions, respectively. A clear correspondence between the classical and quantum result is found for systems containing between N=80 and 200 atoms. A measure of the Wigner character of the energy spectrum for different couplings and energy intervals is also presented employing the statistical Anderson-Darling test. It is found that in the Dicke model, for any coupling, a low-energy regime with regular states is always present. The richness of the onset of chaos is discussed both for finite quantum systems and for the semiclassical limit, which is exact when the number of atoms in the system tends to infinite. © 2014 American Physical Society.
Bastarrachea-Magnani M.A.,National Autonomous University of Mexico |
Lerma-Hernandez S.,University of Xalapas |
Hirsch J.G.,National Autonomous University of Mexico
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2014
We study the nonintegrable Dicke model and its integrable approximation, the Tavis-Cummings model, as functions of both the coupling constant and the excitation energy. Excited-state quantum phase transitions (ESQPT) are found analyzing the density of states in the semiclassical limit and comparing it with numerical results for the quantum case in large Hilbert spaces, taking advantage of efficient methods recently developed. Two different ESQPTs are identified in both models, which are signaled as singularities in the semiclassical density of states; one static ESQPT occurs for any coupling, whereas a dynamic ESQPT is observed only in the superradiant phase. The role of the unstable fixed points of the Hamiltonian semiclassical flux in the occurrence of the ESQPTs is discussed and determined. Numerical evidence is provided that shows that the semiclassical results describe very well the tendency of the quantum energy spectrum for any coupling in both models. Therefore, the semiclassical density of states can be used to study the statistical properties of the fluctuation in the spectra, a study that is presented in a companion paper. © 2014 American Physical Society.
Campos-Navarro R.,National Autonomous University of Mexico |
Journal of Ethnopharmacology | Year: 2013
Ethnopharmacological relevance Empacho is one of the most recognized cultural-bound syndromes in Argentina. It is a digestive disorder with many causes, being excessive food intake the most frequent. It is easily diagnosed in household medicine and there are different treatments applied for releasing the obstruction of the gastrointestinal tract. Therapeutics includes the use of medicinal plants and abdominal maneuvers, as well as rituals of magical and/or religious nature. The aim of this work is to analyze the compiled literature, considering documents from the XVIIIth century up to present, related to the employed plant species for the treatment of empacho. Material and methods The bibliographic and journal collections of several Argentinean and foreign libraries and bookstores were consulted, in addition to the comprehensive review of the specific information found online. Results Ninety (90) primary sources, spanning three hundred years (from 1710 to 2010) were found; most of them included ethnobotanical studies besides others of medical botany, pharmacobotanical and anthropological origin. A total of 152 plant species used to treat empacho were found in 360 total quotations, being Dysphania ambrosioides (L.) Mosyakin and Clemants; Alternanthera pungens Kunth; Ruta chalepensis L.; Clinopodium gilliesii (Benth.) Kuntze; Aloysia polystachya (Griseb.) Moldenke; Lippia turbinata Griseb., and Pluchea sagittalis (Lam.) Cabrera, the most frequently mentioned. The main therapeutic properties of the medicinal plants cited against empacho are stomachic, purgative, antispasmodic, bitter-tonic, carminative, and cholagogue-choleretic. Conclusions The variety of regions - spanning most of the country - from which the information comes, as well as the great variety of therapeutic strategies used, diversity of plant species and knowledge related to the treatment of empacho, is directly associated with the great significance that this disorder has within the system of medical-nosologic representations of the Argentinean popular medicine. © 2013 Elsevier Ireland Ltd. All rights reserved.
Lanterna A.E.,CONICET |
Coronado E.A.,National Autonomous University of Mexico |
Journal of Physical Chemistry C | Year: 2012
The degree of surface functionalization of colloidal dispersions of Au nanoparticles (AuNPs) by sulfur heterocyclic compounds is determined using localized surface plasmon resonance spectroscopy (LSPRS), morphological characterization, and electrodynamic modeling. We demonstrate that AuNP surface coverage is the result of the interplay between the molecular geometry of ligands and the Au nanoparticle diameter. For the same ligand, it is found that the surface density of molecules (σ) is almost constant or slightly decreases as the Au nanoparticle diameter increases, while for the same NP size the degree of surface coverage increases as the length of the molecule increases. The chemical interaction between the ligand molecules and the AuNP surface is demonstrated using surface enhanced Raman scattering (SERS) and 1H NMR. For the same average AuNP size, the full width at half maximum (fwhm) of the LSPR is significantly greater for derivatized AuNPs, a feature that shows the important role played by chemical interface damping in NP surface functionalization. The strong chemical stability of the modified AuNPs is further probed against KCN etching, indicating that there is a close correspondence between σ and the slow kinetics of the decay of the LSPR peak. © 2012 American Chemical Society.
McDougall K.,U.S. Geological Survey |
Martinez A.Y.M.,National Autonomous University of Mexico
Geosphere | Year: 2014
Foraminiferal assemblages in the stratigraphically lower part of the Bouse Formation in the Blythe basin (lower Colorado River corridor, western USA) indicate marine conditions, whereas assemblages in the upper part of the Bouse Formation indicate lacustrine conditions and suggest the presence of a saline lake. Benthic foraminiferal assemblages in the lower part of the Bouse Formation are similar to lagoonal and inner neritic biofacies of the modern Gulf of California. Evidence suggesting a change from marine to lacustrine conditions includes the highest occurrence of planktic foraminifers at an elevation of 123 m above sea level (asl), the change from low diversity to monospecific foraminiferal assemblages composed only of Ammonia beccarii (between 110 and 126 m asl), an increase in abundance of A. beccarii specimens (above ~110 m asl), increased number of deformed tests (above ~123 m asl), first appearance of Chara (at ~85 m asl), lowest occurrence of reworked Cretaceous coccoliths (at ~110 m), a decrease in strontium isotopic values (between 70 and 120 m), and δ18O and δ13C values similar to seawater (between 70 and 100 m asl). Planktic foraminifers indicate a late Miocene age between 8.1 and 5.3 Ma for the oldest part of the Bouse Formation in the southern part of the Blythe basin. Benthic and planktic foraminifers correlate with other late Miocene sections in the proto-Gulf of California and suggest that the basal Bouse Formation in the Blythe basin was deposited at the northern end of this proto-gulf. After the marine connection was restricted or eliminated, the Colorado River flowed into the Blythe basin, forming a saline lake. This lake supported a monospecific foraminiferal assemblage of A. beccarii until the lake spilled into the Salton Trough and the Colorado River became a through-flowing river. © 2014 Geological ociety of America.
Delgado-Olguin P.,Gladstone |
Recillas-Targa F.,National Autonomous University of Mexico
Briefings in Functional Genomics | Year: 2011
Pluripotent embryonic stem (ES) cells are specialized cells with a dynamic chromatin structure, which is intimately connected with their pluripotency and physiology. In recent years somatic cells have been reprogrammed to a pluri-potent state through over-expression of a defined set of transcription factors. These cells, known as induced pluripotent stem (iPS) cells, recapitulate ES cell properties and can be differentiated to apparently all cell lineages, making iPS cells a suitable replacement for ES cells in future regenerative medicine. Chromatin modifiers play a key function in establishing and maintaining pluripotency, therefore, elucidating the mechanisms controlling chromatin structure in both ES and iPS cells is of utmost importance to understanding their properties and harnessing their therapeutic potential. In this review, we discuss recent studies that provide a genome-wide view of the chromatin structure signature in ES cells and iPS cells and that highlight the central role of histone modifiers and chromatin remodelers in pluripotency maintenance and induction. © The Author 2011. Published by Oxford University Press. All rights reserved.
Evangelista C.,CONICET |
Puleston P.,CONICET |
Valenciaga F.,CONICET |
Fridman L.M.,National Autonomous University of Mexico
IEEE Transactions on Industrial Electronics | Year: 2013
This work explores an adaptive second-order sliding mode control strategy to maximize the energy production of a wind energy conversion system (WECS) simultaneously reducing the mechanical stress on the shaft. Such strategy successfully deals with the random nature of wind speed, the intrinsic nonlinear behavior of the WECS, and the presence of model uncertainties and external perturbations acting on the system. The synthesized adaptive controller is designed from a modified version of the super-twisting (ST) algorithm with variable gains. The suitability of the proposed strategy is proved by extensive computer-aided simulations employing a comprehensive model of the system emulating realistic conditions of operation, i.e., considering variations in the parameters and including external disturbances. Additionally, a second controller based on the traditional ST algorithm is also designed and simulated. Results are presented and discussed in order to establish a comparison framework. © 2012 IEEE.
Arciniega-Ceballos A.,National Autonomous University of Mexico |
Dawson P.,U.S. Geological Survey |
Chouet B.A.,U.S. Geological Survey
Geophysical Research Letters | Year: 2012
The seismicity of Popocatépetl is dominated by long-period and very-long period signals associated with hydrothermal processes and magmatic degassing. We model the source mechanism of repetitive long-period signals in the 0.4-2s band from a 15-station broadband network by stacking long-period events with similar waveforms to improve the signal-to-noise ratio. The data are well fitted by a point source located within the summit crater ∼250 m below the crater floor and ∼200 m from the inferred magma conduit. The inferred source includes a volumetric component that can be modeled as resonance of a horizontal steam-filled crack and a vertical single force component. The long-period events are thought to be related to the interaction between the magmatic system and a perched hydrothermal system. Repetitive injection of fluid into the horizontal fracture and subsequent sudden discharge when a critical pressure threshold is met provides a non-destructive source process. © 2012. American Geophysical Union. All Rights Reserved.
Guha R.,U.S. National Institutes of Health |
Medina-Franco J.L.,National Autonomous University of Mexico
Journal of Cheminformatics | Year: 2014
Background: Most work on the topic of activity landscapes has focused on their quantitative description and visual representation, with the aim of aiding navigation of SAR. Recent developments have addressed applications such as quantifying the proportion of activity cliffs, investigating the predictive abilities of activity landscape methods and so on. However, all these publications have worked under the assumption that the activity landscape models are "real" (i.e., statistically significant). Results: The current study addresses for the first time, in a quantitative manner, the significance of a landscape or individual cliffs in the landscape. In particular, we question whether the activity landscape derived from observed (experimental) activity data is different from a randomly generated landscape. To address this we used the SALI measure with six different data sets tested against one or more molecular targets. We also assessed the significance of the landscapes for single and multiple representations. Conclusions: We find that non-random landscapes are data set and molecular representation dependent. For the data sets and representations used in this work, our results suggest that not all representations lead to non-random landscapes. This indicates that not all molecular representations should be used to a) interpret the SAR and b) combined to generate consensus models. Our results suggest that significance testing of activity landscape models and in particular, activity cliffs, is key, prior to the use of such models. © 2014 Guha and Medina-Franco; licensee Chemistry Central Ltd.
News Article | November 30, 2016
What do a Russian nesting doll and a Mayan pyramid have in common? Archaeologists have confirmed that the iconic Pyramid of El Castillo in eastern Mexico is actually a pyramid within a pyramid within a pyramid. In the 1930s, the first hidden pyramid was revealed within the Kukulkan tomb at Chichén Itzá in Mexico, which researchers estimate was built between about A.D. 850 and A.D. 900. Now, scientists have found an even smaller pyramid inside that one that may have been constructed between A.D. 600 and A.D. 800. Although the last construction of El Castillo occurred around A.D. 950 to 1000 and combined elements of Mayan and central Mexico cultures, the interior pyramids are "more purely Mayan" because they were constructed earlier, the archaeologists said. [Photos: First Glimpse into a Mayan Tomb] There has been some controversy surrounding the chronology of Chichén Itzá, according to Denisse Argote, an archaeologist and geophysicist at Mexico’s National Institute of Anthropology and History. Argote said that although the dating of the structures is not fully proven, the pyramid's interior structure could add to the establishedchronology and understanding of the Mayan culture's early stages. "Now the second substructure, more ancient than the ones known, would be of a pure Mayan style," Argote said in a statement. "The study of this substructure could tell us a lot about the beginning of the settlement in the site and its cultural influences." The researchers used a technique called electrical resistivity tomography (ERT), which involves deploying hundreds of electrodes on the surface of the pyramid and into the ground. Without disturbing the archaeological site, ERT injects a direct current and relays any changes in electrical properties, highlighting structural differences inside the monument. Using this technique, the researchers acquired more than 45,000 observations that helped detail the interior of the Pyramid of El Castillo. The ERT technique confirmed the 2014 discovery of a partially water-filled sinkhole beneath the pyramid, as well as the previous pyramid discovery and the finding of the new structure, the archaeologists said. "The results indicate the existence of two pyramids inside the main Mayan building," said coordinating researcher René Chávez, a geophysicist at the National Autonomous University of Mexico. Chávez added that although Mexican researchers discovered one of the interior pyramids in the 1930s, "the second substructure was just a hypothesis in some archaeologists’ minds." The new discoveries will be detailed in a poster presentation Dec. 14 at the American Geophysical Union's fall meeting in San Francisco.
Suter M.,National Autonomous University of Mexico
Bulletin of the Seismological Society of America | Year: 2016
The Trans-Mexican volcanic belt is an active volcanic arc being deformed by an intra-arc extensional fault network. The Morelia fault, with a length of 14 km and a maximum throw of 260 m, is a major normal fault in the central part of this volcanic arc and forms part of a 36-km-long fault array. Slickenlines measured on the primary fault surface indicate north–south extensional dip slip with a minor left-lateral component. In a well-exposed cross section in the hanging wall of the Morelia fault, some few meters from the master fault trace, two buried soil layers, containing ceramic shards and stone tools, yielded radiocarbon ages of A.D. 420–660 (prehispanic classic period, Chupícuaro culture) and A.D. 1290–1435 (postclassic period), respectively. The underlying bedrock (Atécuaro ignimbrite) is cut in a staircase pattern by three synthetic secondary normal faults that delimit two colluvial wedges. Three slip events, with displacements ranging between 46 and 185 cm (average 109 cm), can be inferred from this section. The latest of these events must have occurred after A.D. 1290–1435, during the postclassic period or possibly during early novohispanic times. The Morelia fault, which is capable of generating Mw 6–7 earthquakes, poses a major seismic ground-shaking hazard and locally a surface fault-rupture hazard within the metropolitan Morelia region with a population of more than 900,000 habitants. The foci of a sequence of seven small 2007 earthquakes on the Morelia fault were located below the center of town, at a depth of 11 km, and the fault trace crosses urban residential areas. Moreover, the town repeatedly experienced severe ground shaking during historical earthquakes. The best documented is the 19 June 1858 earthquake, which caused Morelia extensive damage corresponding to a macroseismic intensity of VIII–IX on the modified Mercalli scale. © 2016 Seismological Society of America. All rights reserved.
Bartolo R.,National Autonomous University of Mexico |
Merchant H.,National Autonomous University of Mexico
Journal of Neuroscience | Year: 2015
oscillations in the basal ganglia have been associated with interval timing. Werecorded the putaminal local field potentials (LFPs) from monkeys performing a synchronization-continuation task (SCT) and a serial reaction-time task (RTT), where the animals produced regularly and irregularly paced tapping sequences, respectively. We compared the activation profile of β oscillations between tasks and found transient bursts of β activity in both the RTT and SCT. During the RTT, β power was higher at the beginning of the task, especially when LFPs were aligned to the stimuli. During the SCT, β was higher during the internally driven continuation phase, especially for tap-aligned LFPs. Interestingly, a set of LFPs showed an initial burst of β at the beginning of the SCT, similar to the RTT, followed by a decrease in β oscillations during the synchronization phase, to finally rebound during the continuation phase. The rebound during the continuation phase of the SCT suggests that the corticostriatal circuit is involved in the control of internally driven motor sequences. In turn, the transient bursts of β activity at the beginning of both tasks suggest that the basal ganglia produce a general initiation signal that engages the motor system in different sequential behaviors. © 2015 the authors.
Tlahuice A.,National Autonomous University of Mexico |
Garzon I.L.,National Autonomous University of Mexico
Physical Chemistry Chemical Physics | Year: 2012
First principles calculations are used for a systematic search of the lowest-energy (most-stable) structure of the recently synthesized Au 18(SR) 14 cluster. A comparison of the calculated optical absorption and electronic circular dichroism spectra, which are highly sensitive to the cluster structure and chirality, with the experimental spectra of the glutathione-protected gold cluster, Au 18(SG) 14, is used to discriminate between low-energy isomers of the Au 18(SR) 14 (R = CH 3) cluster. From the good agreement between calculated and measured spectra, it is predicted that the structure of the Au 18(SR) 14 cluster consists of a prolate Au 8 core covered with two dimer (SR-Au-SR-Au-SR) and two trimer (SR-Au-SR-Au-SR-Au-SR) motifs. These results provide additional evidence on the existence of longer trimer motifs as protecting units of small thiolated gold clusters. © 2011 The Owner Societies.
Galano A.,Metropolitan Autonomous University |
Alvarez-Idaboy J.R.,National Autonomous University of Mexico
Physical Chemistry Chemical Physics | Year: 2012
Different deprotonation paths of the radical cation formed by one-electron oxidation of 2′-deoxyguanosine (2dG) sites in DNA have been studied using Density Functional Theory (M05-2X/6-31+G(d,p)) and ONIOM methodology (M05-2X/6-31+G(d,p):PM6) in conjunction with the SMD model to include the solvent effects. Models of increased complexity have been used ranging from the isolated nucleoside to a three unit double-stranded oligomer including the sugar units, the base pairing with cytidine, and the phosphate linkage. The reported results correspond to aqueous solution, at room temperature, and pH = 7.4. Under such conditions it was found that the proton transfer (PT) within the base pair is a minor path compared to the PT between the base pair and the surrounding water. It was also found that the deprotonation of ground-state 2dG+ sites mainly yields C centered radicals in the sugar unit, with the largest populations corresponding to C4′ and C5′, followed by C3′. The different aspects of the presented theoretical study have been validated with experimental results. This journal is © the Owner Societies 2012.
Hernandez-Lucas I.,National Autonomous University of Mexico |
Calva E.,National Autonomous University of Mexico
Molecular Microbiology | Year: 2012
LeuO is a quiescent genetic regulator present in many bacteria, which forms part of the H-NS regulon. LeuO in turn has been proposed to activate a subset of genes of the regulon by antagonizing H-NS. In the paper by Dillon etal., binding of LeuO to the S. Typhimurium genome was observed by ChIP-chip to some of the previously described LeuO-regulated genes, upon growth under stress conditions. However, studies at a higher LeuO concentration from a cloned inducible promoter rendered many more binding sites, pointing towards the importance of the abundance of the regulator in the cell, in a given moment. Binding of LeuO was observed not only to intergenic sequences, but in the majority of cases to intragenic sequences, and co-binding was observed with H-NS in many sites and with RNA polymerase to the majority of sites. The authors define a binding motif that allowed the detection of several other LeuO-regulated genes that were not detected by ChIP-chip, which were possibly missed because LeuO binds and bridges distal sites, in those instances. The observations reported open new questions regarding the mode of action for LeuO. © 2012 Blackwell Publishing Ltd.
Tlahuice A.,National Autonomous University of Mexico |
Garzon I.L.,National Autonomous University of Mexico
Physical Chemistry Chemical Physics | Year: 2012
We report results of a theoretical study, based on density functional theory (DFT), on the structural, electronic, optical, and chiroptical properties of small thiolated gold clusters, [Au n(SR) m (n = 12-15, 16-20; m = 9-12, 12-16)]. Some of these clusters correspond to those recently synthesized with the surfactant-free method. To study the cluster physical properties, we consider two cluster families with Au 6 and Au 8 cores, respectively, covered with dimer [Au 2(SR) 3] and trimer [Au 3(SR) 4] (CH 3 being the R group) motifs or their combinations. Our DFT calculations show, by comparing the relaxed structures of the [Au 6[Au 2(SR) 3] 3] +, [Au 6[Au 2(SR) 3] 2[Au 3(SR) 4]] +, [Au 6[Au 2(SR) 3][Au 3(SR) 4] 2] +, and [Au 6[Au 3(SR) 4] 3] + cationic clusters, that there is an increasing distortion in the Au 6 core as each dimer is replaced by a longer trimer motif. For the clusters in the second family, Au 8[Au 3(SR) 4] 4, Au 8[Au 2(SR) 3][Au 3(SR) 4] 3, Au 8[Au 2(SR) 3] 2[Au 3(SR) 4] 2, Au 8[Au 2(SR) 3] 3[Au 3(SR) 4], and Au 8[Au 2(SR) 3] 4, a smaller distortion of the Au 8 core is observed as dimer motifs are substituted by trimer ones. An interesting trend emerging from the present calculations shows that as the number of trimer motifs increases in the protecting layer of both Au 6 and Au 8 cores, the average of the interatomic Au(core)-S distances reduces. This shrinkage in the Au(core)-S distances is correlated with an increase of the cluster HOMO-LUMO (H-L) gap. From these results, it is predicted that a larger number of trimer motifs in the cluster protecting layer would induce larger H-L gaps. By analyzing the electronic transitions that characterize the optical absorption and circular dichroism spectra of the clusters under study, it is observed that the molecular orbitals involved are composed of comparable proportions of orbitals corresponding to atoms forming the cluster core and the protecting dimer and trimer motifs. © 2012 the Owner Societies.
Perez-Vega A.,University of Guanajuato |
Mas J.-F.,National Autonomous University of Mexico |
Ligmann-Zielinska A.,Michigan State University
Environmental Modelling and Software | Year: 2012
Land use/cover change (LUCC) modeling is an important approach to evaluating global biodiversity loss and is the topic of a wide range of research in ecology, geography and environmental social science. This paper reports on development and assessment of maps of change potential produced by two spatially explicit models and applied to a Tropical Deciduous Forest in western Mexico. The first model, DINAMICA EGO, uses the weights of evidence method which generates a map of change potential based on a set of explanatory variables and past trends involving some degree of expert knowledge. The second model, Land Change Modeler (LCM), is based upon neural networks. Both models were assessed through Relative Operating Characteristic and Difference in Potential. At the per transition level, we obtained better results using DINAMICA. However, when the per transition susceptibilities are combined to compose an overall change potential map, the map generated using LCM is more accurate because neural networks outputs are able to express the simultaneous change potential to various land cover types more adequately than individual probabilities obtained through the weights of evidence method. An analysis of the change potential obtained from both models, compared with observed deforestation and selected biodiversity indices (species richness, rarity, and biological value) showed that the prospective LUCC maps tended to identify locations with higher biodiversity levels as the most threatened areas as opposed to areas that had actually undergone deforestation. Overall however, the approximate assessment of biodiversity given by both models was more accurate than a random model. © 2011 Elsevier Ltd.
Lacerna I.,University of Santiago de Chile |
Lacerna I.,National Autonomous University of Mexico |
Padilla N.,University of Santiago de Chile
Monthly Notices of the Royal Astronomical Society: Letters | Year: 2012
We study an assembly-type bias parametrized by the dimensionless spin parameter that affects massive structures. In numerical simulations, higher spin haloes are more strongly clustered than lower spin haloes of equal mass. We detect a difference of over 30 per cent in the clustering strength for dark matter haloes of 1013-1014 h-1 M⊙, which is similar to the result of Bett et al. We explore whether the dependence of clustering strength on halo spin is removed if we apply the redefinition of overdensity peak height proposed by Lacerna & Padilla (Paper I) obtained using assembly ages. We find that this is not the case due to two reasons. First, only a few objects of low virial mass are moved into the mass range where the spin introduces an assembly-type bias after using this redefinition. Secondly, this formalism does not alter the mass of massive objects. In other words, the sample of haloes with redefined mass M in the high-mass regime is practically the same as before the redefinition of peak height, and thus the clustering behaviour is the same. We then repeat the process of finding the redefined peak height of Paper I but using the spin. In this case, the new masses show no spin-related assembly bias but they introduce a previously absent assembly bias with respect to relative age. From this result, we conclude that the assembly-type bias with respect to the halo spin has a different origin from that with respect to the assembly age. The former may be due to the material from filaments, which is accreted by massive haloes, and enhanced in highdensity environments, thus causing more extreme spin values without significantly changing the formation age of the halo. In addition, the estimates of the mass of collapsed structures in numerical simulations could be lower than the true mass, even in cluster-size haloes. Highmass objects may correspond, in some cases, to a different peak height from that suggested by their virial mass, providing a possible explanation for the assembly-type bias with respect to the spin. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.
Alvarez-Idaboy J.R.,National Autonomous University of Mexico |
Galano A.,Metropolitan Autonomous University
Journal of Physical Chemistry B | Year: 2012
The chemical repair of radical-damaged DNA by glutathione in aqueous solution has been studied using density functional theory. Two main mechanisms were investigated: the single electron transfer (SET) and the hydrogen transfer (HT). Glutathione was found to repair radical damaged DNA by HT from the thiol group with rate constants that are close to the diffusion-limited regime, which means that the process is fast enough for repairing the damage before replication and therefore for preventing permanent DNA damage. The SET mechanism was found to be of minor importance for the activity of glutathione. In addition while SET can be essential for other compounds when repairing radical cation species, repairing the C′-centered guanosyl radicals via SET is not a viable mechanism, due to the very low electron affinity of these species. The importance of considering pH-related physiological conditions and using complex enough models, including the ribose moiety and the H bonding between base pairs, to study this kind of systems is discussed. © 2012 American Chemical Society.
Galano A.,Metropolitan Autonomous University |
Leon-Carmona J.R.,Metropolitan Autonomous University |
Alvarez-Idaboy J.R.,National Autonomous University of Mexico
Journal of Physical Chemistry B | Year: 2012
The peroxyl radical scavenging activity of five guaiacol derivatives (GD) has been studied in nonpolar and aqueous solutions, using the density functional theory. The studied GD are guaiacol, vanillin, vanillic alcohol, vanillic acid, and eugenol. It was found that the environment plays an important role in the peroxyl scavenging activity of these compounds. They were all found to react faster in aqueous solution than in nonpolar media. The order of reactivity in nonpolar environments was found to be vanillic alcohol > eugenol > guaiacol > vanillin > vanillic acid, while, in aqueous solution, at physiological pH, it becomes vanillic acid > vanillic alcohol > guaiacol ≈ eugenol > vanillin. It was also found that in aqueous solution as the pH increases so does the reactivity of GD toward peroxyl radicals. The environment also has important effects on the relative importance of the hydrogen transfer (HT) and the sequential proton electron transfer (SPET) mechanisms, which are the ones relevant to the peroxyl radical scavenging activity of GD. The HT from the phenolic OH was identified as the main scavenging process in nonpolar media, and in aqueous solution at pH ≥ 4. On the other hand, SPET is proposed to be the one contributing the most to the overall peroxyl scavenging activity of GD in aqueous solution at pH ≥ 6. © 2012 American Chemical Society.
Magallon S.,National Autonomous University of Mexico |
Hilu K.W.,Virginia Polytechnic Institute and State University |
Quandt D.,University of Bonn
American Journal of Botany | Year: 2013
Premise of the study: Land plants play an essential role in the evolution of terrestrial life. Their time of origin and diversification is fundamental to understanding the evolution of life on land. We investigated the timing and the rate of molecular evolution of land plants, evaluating the effects of different types of molecular data, including temporal information from fossils, and using different molecular clock methods. Methods: Ages and absolute rates were estimated independently with two substitutionally different data sets: a highly conserved 4-gene data set and matK, a fast-evolving gene. The vascular plant backbone and the crown nodes of all major lineages were calibrated with fossil-derived ages. Dates and absolute rates were estimated while including or excluding the calibrations and using two relaxed clocks that differ in their implementation of temporal autocorrelation. Key results: Land plants diverged from streptophyte alga 912 (870-962) million years ago (Mya) but diversified into living lineages 475 (471-480) Mya. Ages estimated for all major land-plant lineages agree with their fossil record, except for angiosperms. Different genes estimated very similar ages and correlated absolute rates across the tree. Excluding calibrations resulted in the greatest age differences. Different relaxed clocks provided similar ages, but different and uncorrelated absolute rates. Conclusions: Whole-genome rate accelerations or decelerations may underlie the similar ages and correlated absolute rates estimated with different genes. We suggest that pronounced substitution rate changes around the angiosperm crown node may represent a challenge for relaxed clocks to model adequately. © 2013 Botanical Society of America.
Oswald Spring U.,National Autonomous University of Mexico
Current Opinion in Environmental Sustainability | Year: 2011
In megacities water quantity and quality are threatened by complex and interrelated processes caused by population growth, land use change, unsustainable agricultural practices, deforestation, erosion, destruction of ecosystems, lack of planning, laissez-faire policies, unsustainable water management, political conflicts, and increasingly also by the impacts of climate change. In the Metropolitan Valley of Mexico City (MVMC) located in the high plateau of Mexico City and on former lakes, the dry out policies during the last 300 years have been counterproductive, causing scarcity, pollution, health and environmental problems, subsidence and water conflicts, particularly affecting social vulnerable people. Megacities require an integrated management of water and aquatic systems. - integral water resource management, rainwater harvesting, maintenance and replacement of infrastructure, restoration of ecosystems and urban planning. This implies investments and a water culture including a transparent administration and peaceful negotiation of conflicts regarding concessions, access, and reuse of water allocation. Socio-political and environmental processes are complex; besides technical factors and ecosystem recovery, socio-cultural changes must transform human settlements and power structures. © 2011 Elsevier B.V.
Hernandez-Marin E.,National Autonomous University of Mexico |
Martinez A.,National Autonomous University of Mexico
Journal of Physical Chemistry B | Year: 2012
A density functional theory (DFT) study on the free radical (OH • and OOH•) scavenging properties of some mono- and polysaccharides is presented. Two mechanisms, single electron transfer (SET) and hydrogen atom transfer (HAT), are considered. The former mechanism is studied by making use of the vertical ionization energy and vertical electron affinity of the radicals and carbohydrates. It is confirmed that the SET mechanism is not plausible to occur. With respect to the HAT, not only does the OH• radical react preferably with one hydrogen atom bonded to one carbon atom, but also the reaction with a hydrogen atom bonded to an oxygen is possible. Finally, it is suggested that the carbohydrates are not able to directly scavenge OOH•. © 2012 American Chemical Society.
Bello-Bedoy R.,National Autonomous University of Mexico |
Nunez-Farfan J.,National Autonomous University of Mexico
Journal of Evolutionary Biology | Year: 2011
The ability of plants to respond to natural enemies might depend on the availability of genetic variation for the optimal phenotypic expression of defence. Selfing can affect the distribution of genetic variability of plant fitness, resistance and tolerance to herbivores and pathogens. The hypothesis of inbreeding depression influencing plant defence predicts that inbreeding would reduce resistance and tolerance to damage by natural enemies relative to outcrossing. In a field experiment entailing experimentally produced inbred and outcrossed progenies, we assessed the effects of one generation of selfing on Datura stramonium resistance and tolerance to three types of natural enemies, herbivores, weevils and a virus. We also examined the effect of damage on relative growth rate (RGR), flower, fruit, and seed production in inbred and outcrossed plants. Inbreeding significantly reduced plant defence to natural enemies with an increase of 4% in herbivore damage and 8% in viral infection. These results indicate inbreeding depression in total resistance. Herbivory increased 10% inbreeding depression in seed number, but viral damage caused inbred and outcrossed plants to have similar seed production. Inbreeding and outcrossing effects on fitness components were highly variable among families, implying that different types or numbers of recessive deleterious alleles segregate following inbreeding in D. stramonium. Although inbreeding did not equally alter all the interactions, our findings indicate that inbreeding reduced plant defence to herbivores and pathogens in D. stramonium. © 2010 The Authors. Journal of Evolutionary Biology © 2010 European Society For Evolutionary Biology.
Arenas I.,National Autonomous University of Mexico |
Bravo A.,National Autonomous University of Mexico |
Soberon M.,National Autonomous University of Mexico |
Gomez I.,National Autonomous University of Mexico
Journal of Biological Chemistry | Year: 2010
Cry toxins produced by Bacillus thuringiensis have been recognized as pore-forming toxins whose primary action is to lyse midgut epithelial cells in their target insect. In the case of the Cry1A toxins, a prepore oligomeric intermediate is formed after interaction with cadherin receptor. The Cry1A oligomer then interacts with glycosylphosphatidylinositol-anchored receptors. Two Manduca sexta glycosylphosphatidylinositol-anchored proteins, aminopeptidase (APN) and alkaline phosphatase (ALP), have been shown to bind Cry1Ab, although their role in toxicity remains to be determined. Detection of Cry1Ab binding proteins by ligand blot assay revealed that ALP is preferentially expressed earlier during insect development, because it was found in the first larval instars, whereas APN is induced later after the third larval instar. The binding of Cry1Ab oligomer to pure preparations of APN and ALP showed that this toxin structure interacts with both receptors with high affinity (apparent K d = 0.6 nM), whereas the monomer showed weaker binding (apparent Kd = 101.6 and 267.3 nM for APN and ALP, respectively). Several Cry1Ab nontoxic mutants located in the exposed loop 2 of domain II or in β-16 of domain III were affected in binding to APN and ALP, depending on their oligomeric state. In particular monomers of the nontoxic domain III, the L511A mutant did not bind ALP but retained APN binding, suggesting that initial interaction with ALP is critical for toxicity. Our data suggest that APN and ALP fulfill two roles. First APN and ALP are initial receptors promoting the localization of toxin monomers in the midgut microvilli before interaction with cadherin. Then APN and ALP function as secondary receptors mediating oligomer insertion into the membrane. However, the expression pattern of these receptors and the phenotype of L511A mutant suggest that ALP may have a predominant role in toxin action because Cry toxins are highly effective against the neonate larvae that is the target for pest control programs. © 2010 by The American Society for Biochemistry and Molecular Biology, Inc.
Pimentel-Dominguez R.,National Autonomous University of Mexico |
Hernandez-Cordero J.,National Autonomous University of Mexico |
Zenit R.,National Autonomous University of Mexico
Optics Express | Year: 2012
We show that fiber optic tips can be used as microbubble generators in liquid media. Using standard single-mode silica fibers incorporating nanoparticles (carbon nanoparticles and metallic powders), bubbles can be generated with low optical powers owing to the enhanced photothermal effects of the coating materials. We provide details about the hydrodynamic effects generated in the vicinity of the fiber tip during the coating process, bubble generation and growth. Flow visualization techniques show that thermal effects lead to bubble formation on the tip of the fibers, and coating optimization is crucial for optimal performance of the probes. © 2012 Optical Society of America.
Bolejko K.,National Autonomous University of Mexico |
Bolejko K.,University of Oxford |
Sussman R.A.,National Autonomous University of Mexico
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2011
Inhomogeneous cosmological models are able to fit cosmological observations without dark energy under the assumption that we live close to the "center" of a very large-scale under-dense region. Most studies fitting observations by means of inhomogeneities also assume spherical symmetry, and thus being at (or very near) the center may imply being located at a very special and unlikely observation point. We argue that such spherical voids should be treated only as a gross first approximation to configurations that follow from a suitable smoothing out of the non-spherical part of the inhomogeneities on angular scales. In this Letter we present a toy construction that supports the above statement. The construction uses parts of the Szekeres model, which is inhomogeneous and anisotropic thus it also addresses the limitations of spherical inhomogeneities. By using the thin-shell approximation (which means that the Israel-Darmois continuity conditions are not fulfilled between the shells) we construct a model of evolving cosmic structures, containing several elongated supercluster-like structures with underdense regions between them, which altogether provides a reasonable coarse-grained description of cosmic structures. While this configuration is not spherically symmetric, its proper volume average yields a spherical void profile of 250 Mpc that roughly agrees with observations. Also, by considering a non-spherical inhomogeneity, the definition of a "center" location becomes more nuanced, and thus the constraints placed by fitting observations on our position with respect to this location become less restrictive. © 2011.
Zelenski M.,Russian Academy of Sciences |
Taran Y.,National Autonomous University of Mexico
Geochimica et Cosmochimica Acta | Year: 2012
Up to 60ppmv (180mg/m 3) of Cl 2 together with 40-80ppmv HCl were measured in gas emissions from the Tolbachik scoria cones, Kamchatka, which are still hot after the 1975-1976 eruption. Other gas components were atmospheric air (94-99vol %), water vapour (1-6vol %) and other acid species (HF, CO 2 and H 2SO 4, total less than 0.1vol %). Two different processes can account for the existence of Cl 2 in the Tolbachik emissions. The catalytic oxidation of volcanic HCl by oxygen is probably the main source of Cl 2. Fine crystals of Fe 2O 3, and oxides and chlorides of other transition metals on the surface of altered basalt can serve as catalysts. The oxidative decomposition of Na, K and Mg chloroferrates formed as a result of basalt acid leaching, can also create high concentrations of molecular chlorine in volcanic gases. The processes described represent a previously unknown case of abiogenic heterogeneous catalysis in nature and examples of gas-rock interactions that affect the composition of volcanic gases. © 2012 Elsevier Ltd.
Palomares L.A.,National Autonomous University of Mexico |
Mena J.A.,National Autonomous University of Mexico |
Ramirez O.T.,National Autonomous University of Mexico
Methods | Year: 2012
The insect cell-baculovirus system (IC-BEVS) is widely used for the production of recombinant viral proteins for vaccine applications. It is especially suitable for the production of virus-like particles, which often require the simultaneous production of several recombinant proteins. Here, the available tools and process requirements for the simultaneous production of several recombinant proteins using the IC-BEVS are discussed. The production of double-layered rotavirus like particles is used as a specific example for the simultaneous production of two recombinant proteins. Methods to quantify VLP in small samples are described. The multiplicity and time of infection are presented as tools to manipulate protein concentration, and the effect on protein concentration ratios on the assembly efficiency of double-layered rotavirus like particles is discussed. It was found that not only the ratio between the recombinant proteins is determinant of VLP assembly efficiency, but also that assembly efficiency is related to the characteristics of the assembled proteins. This is the first time that kinetics of VLP production are followed during cultures, and that the assembly efficiency is quantitatively determined. © 2012 Elsevier Inc..
Fanjul-Moles M.L.,National Autonomous University of Mexico
Frontiers in Bioscience | Year: 2013
This work reviews concepts regarding the endogenous circadian clock and the relationship between oxidative stress (OS), light and entrainment in different organisms including crustaceans, particularly crayfish. In the first section, the molecular control of circadian rhythms in invertebrates, particularly in Drosophila, is reviewed, and this model is contrasted with recent reports on the circadian genes and proteins in crayfish. Second, the redox mechanisms and signaling pathways that participate in the entrainment of the circadian clock in different organisms are reviewed. Finally, the light signals and transduction pathways involved in the entrainment of the circadian clock, specifically in relation to cryptochromes (CRYs) and their dual role in the circadian clock of different animal groups and their possible relationship to the circadian clock and redox mechanisms in crustaceans is discussed. The relationship between metabolism, ROS signals and transcription factors, such as HIF-1 alpha in crayfish, as well as the possibility that HIF-1 alpha participates in the regulation of circadian control genes (ccgs) in crustaceans is discussed.
Lopez-Diaz D.,National Autonomous University of Mexico |
Castillo R.,National Autonomous University of Mexico
Soft Matter | Year: 2011
A family of methods uses colloidal particles as a mechanical probe for deforming the medium in conjunction with a procedure to trace the movement of the particles to get rheological information in a very wide frequency range. All of them are under the heading of microrheology. In the last decade, they have been developed up to the point of being a useful tool for understanding the structure and the dynamics of solutions with embedded thread-like supramolecular structures. This is the case of wormlike micellar solutions, which is the main interest of the paper. Here the impact of microrheology has been essential, providing structural information not easily obtained by other methods. Microrheology has also made an important contribution to the understanding of other threadlike system, as in the case of F-actin or fd virus solutions; they will also be discussed. © The Royal Society of Chemistry 2011.
Munoz-Gutierrez I.,National Autonomous University of Mexico |
Martinez A.,National Autonomous University of Mexico
Journal of Industrial Microbiology and Biotechnology | Year: 2013
Escherichia coli can ferment a broad range of sugars, including pentoses, hexoses, uronic acids, and polyols. These features make E. coli a suitable microorganism for the development of biocatalysts to be used in the production of biocommodities and biofuels by metabolic engineering. E. coli cannot directly ferment polysaccharides because it does not produce and secrete the necessary saccharolytic enzymes; however, there are many genetic tools that can be used to confer this ability on this prokaryote. The construction of saccharolytic E. coli strains will reduce costs and simplify the production process because the saccharification and fermentation can be conducted in a single reactor with a reduced concentration or absence of additional external saccharolytic enzymes. Recent advances in metabolic engineering, surface display, and excretion of hydrolytic enzymes provide a framework for developing E. coli strains for the so-called consolidated bioprocessing. This review presents the different strategies toward the development of E. coli strains that have the ability to display and secrete saccharolytic enzymes to hydrolyze different sugar-polymeric substrates and reduce the loading of saccharolytic enzymes. © 2013 Society for Industrial Microbiology and Biotechnology.
Ceccarelli F.S.,National Autonomous University of Mexico |
Zaldivar-Riveron A.,National Autonomous University of Mexico
Molecular Phylogenetics and Evolution | Year: 2013
Morphological convergence is a frequently observed pattern that occurs in species with similar environments, trophic niches, and/or life history strategies. In particular, adaptive morphological convergence is common in small, highly diverse invertebrate taxa sharing similar life history strategies such as parasitoidism. The genus Notiospathius is a braconid parasitoid wasp group with a vast, undetermined number of species distributed throughout the Neotropics. Members of this genus possess a considerably elongated, petiolate first metasomal tergite. This structure, however, also occurs in species of other doryctine genera, both closely and distantly related, probably due to adaptation for attacking wood and bark boring coleopteran larvae. Here we investigated the phylogenetic relationships among 117 species assigned to Notiospathius, including species of its closely related genera Masonius and Tarasco, as well as members of a number of other doryctine genera in order to test its monophyly. Separate and concatenated Bayesian partitioned analyses were carried out using two mitochondrial and three nuclear gene markers. The influence of each gene on the overall topology was verified using a cross-validation analysis for each marker with a "leave-one-out" approach. Moreover, the historical biogeography of Notiospathius was assessed calculating divergence time estimates of clades with BEAST and performing ancestral area reconstruction analyses both with RASP (Bayesian and S-DIVA) and Lagrange (DEC). All analyses recovered a polyphyletic Notiospathius consisting of three separate clades that were more related to other doryctine genera than to each other. The relationships reconstructed could not be used to confidently establish the limits of Notiospathius with respect to its closely related genera Tarasco and Masonius, and thus the generic status of the latter two taxa is maintained. Our divergence time estimates and ancestral area reconstructions indicate that the most recent common ancestor of Notiospathius sensu stricto originated in the Caribbean subregion during the Oligocene-Miocene boundary, and subsequently diversified during the mid- to late Miocene, radiating throughout the Neotropics. © 2013 Elsevier Inc.
Garcia F.,National Autonomous University of Mexico |
Sanchez L.,National Autonomous University of Mexico
Chemistry - A European Journal | Year: 2010
Triangular-shaped oligo(phenylene ethynylene) amphiphiles 1a and 1 b decorated in their periphery with two- and four-branched hydrophilic triethyleneglycol dendron wedges, have been synthesized and their self-assembling properties in solution and onto surfaces investigated. The steric demand produced by the dendritic substituents induces a face-to-face rotated φ stacking of the aromatic moieties. Studies on the concentration and temperature dependence confirm this mechanism and provide binding constants of 1.2 xl05 and 1.7 x105 M1 in acetonitrile for 1a and 1b, respectively. Dynamic and static light scattering measurements complement the study of the self-assembly in solution and demonstrate the formation of rod-like supramolecular structures in aqueous solution. The nanofibers formed in solution can be efficiently transferred onto surfaces. Thus, TEM images reveal the presence of strands of various thickness, with the most common being several micrometers long and with diameters of around 70 nm. Some of these nanofibers present folded edges that are indicative of their ribbon-like nature. Interestingly, compound 1b can also form thick filaments with a rope-like appearance, which points to a chiral arrangement of the fibers. AFM images under highly diluted conditions also reveal long fibers with height profiles that fit well with the molecular dimensions calculated for both amphiphiles. Finally, we have demonstrated the intercalation of the hydrophobic dye Disperse Orange 3 within the filaments and its subsequent release upon increasing the temperature. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA.
Leon-Carmona J.R.,Metropolitan Autonomous University |
Alvarez-Idaboy J.R.,National Autonomous University of Mexico |
Galano A.,Metropolitan Autonomous University
Physical Chemistry Chemical Physics | Year: 2012
The peroxyl radical scavenging activity of four hydroxycinnamic acid derivatives (HCAD) has been studied in non-polar and aqueous solutions, using the density functional theory. The studied HCAD are: ferulic acid (4-hydroxy-3-methoxycinnamic acid), p-coumaric acid (trans-4-hydroxycinnamic acid), caffeic acid (3,4-dihydroxycinnamic acid), and dihydrocaffeic acid (3-(3,4-dihydroxyphenyl)-2-propionic acid). It was found that the polarity of the environment plays an important role in the relative efficiency of these compounds as peroxyl scavengers. It was also found that in aqueous solution the pH is a key factor for the overall reactivity of HCAD towards peroxyl radicals, for their relative antioxidant capacity, and for the relative importance of the different mechanisms of reaction. The H transfer from the phenolic OH has been identified as the main mechanism of reaction in non-polar media and in aqueous solution at acid pHs. On the other hand, the single electron transfer mechanism from the phenoxide anion is proposed to be the one contributing the most to the overall peroxyl scavenging activity of HCAD in aqueous solution at physiological pH (7.4). This process is also predicted to be a key factor in the reactivity of these compounds towards a large variety of free radicals. This journal is © the Owner Societies 2012.
Estrada A.,National Autonomous University of Mexico
American Journal of Primatology | Year: 2013
Recent assessments by the International Union for Conservation of Nature (IUCN) indicate the existence of about 612 recognized primate species and subspecies (IUCN RedList, 2012), but close to 50% of these taxa are at risk of extinction as a result of human action. In this article, I call attention to underlying regional and global socioeconomic contexts of primate conservation. Using information from FAO and UN databases and other sources, I examine, for the Neotropics, sub-Saharan Africa, and Southeast Asia, trends in forest loss and human demographics and social condition, discuss the impact of global market pressures upon primate habitats, and examine land-use patterns that may favor primate conservation. Between 1990 and 2010, an estimated 149 million ha of forest were lost in the three regions and additional losses are expected in the future. Global human population will increase from 7 billion in 2012 to 9 billion in 2050. Currently, 2 billion people live in the three primate range regions under high levels of poverty. Large-scale deforestation is related to global market demands, especially from developed and developing nations, for food (e.g., cattle), domestic animal feed (e.g., soybeans), biofuel-based crops (e.g., oil palm), and industrial round wood. The growth of protected areas in the three regions has been steady for several decades, but it is not enough to ensure long-term conservation of many primate taxa. Other conservations tools involving sustainable land use and biodiversity conservation corridors are required at the landscape level. The above assessment can easily be applied at the local level by primatologists, giving more precision to conservation initiatives. © 2012 Wiley Periodicals, Inc.
Parrales A.,National Autonomous University of Mexico |
Lopez E.,National Autonomous University of Mexico |
Lopez-Colome A.M.,National Autonomous University of Mexico
Biochimica et Biophysica Acta - Molecular Cell Research | Year: 2011
The retinal pigment epithelium (RPE) plays an essential role in the survival and function of the neural retina. RPE uncontrolled proliferation leads to the development of proliferative ocular pathologies, among which proliferative vitreoretinopathy (PVR) is the main cause of retinal surgery failure. Upon the breakdown of the BRB due to trauma or metabolic imbalance the contact of RPE with serum-contained thrombin has been shown to stimulate the proliferation of otherwise quiescent RPE cells. Although the molecular mechanisms involved in this effect are still undetermined, thrombin proteolytic activation of protease-activated G protein coupled receptor-1 (PAR-1) activates PI3K and Akt, known to play an essential role in proliferation. The present study demonstrates that: 1) thrombin stimulates Ser 473 Akt phosphorylation without affecting Thr 308 basal phosphorylation in RPE cells; 2) thrombin-induced Akt stimulation promotes cyclin D1 accumulation through the phosphorylation/ inhibition of GSK-3β, thus preventing Thr 286 cyclin D1 phosphorylation, nuclear export and degradation; 3) Akt signaling requires the upstream activation of PI3K and PLC. Since the pharmacological inhibition of these pathways or the silencing of cyclin expression prevent thrombin-induced RPE cell proliferation, these results contribute relevant evidence for establishing the mechanism involved in the development of proliferative eye diseases. © 2011 Elsevier B.V.
Merchant-Larios H.,National Autonomous University of Mexico
Sexual development : genetics, molecular biology, evolution, endocrinology, embryology, and pathology of sex determination and differentiation | Year: 2013
Temperature-dependent sex determination (TSD) was first discovered in reptiles. Since then, a great diversity of sex-determining responses to temperature has been reported. Higher temperatures can produce either males or females, and the temperature ranges and lengths of exposure that influence TSD are remarkably variable among species. In addition, transitory gene regulatory networks leading to gonadal TSD have evolved. Although most genes involved in gonadal development are conserved in vertebrates, including TSD species, temporal and spatial gene expression patterns vary among species. Despite variation in TSD pattern and gene expression heterochrony, the structural framework, the medullary cords, and cortex of the bipotential gonad have been strongly conserved. Aromatase (CYP19), which regulates gonadal estrogen levels, is proposed to be the main target of a putative thermosensitive factor for TSD. However, manipulation of estrogen levels rarely mimics the precise timing of temperature effects on expression of gonadal genes, as occurs with TSD. Estrogen levels may influence sex determination or gonad differentiation depending on the species. Furthermore, the process leading to sex determination under the influence of temperature poses problems that are not encountered by species with genetic sex determination. Yolk steroids of maternal origin and steroids produced by the embryonic nervous system should also be considered as sources of hormones that may play a role in TSD. Copyright © 2012 S. Karger AG, Basel.
Arce E.,National Autonomous University of Mexico |
Alcaraz G.,National Autonomous University of Mexico
Marine Biology | Year: 2012
The preference of the hermit crab, Calcinus californiensis, among six species of shells, was tested by two different experiments. The first experiment used pair-wise trials, analyzing the preference by Chi-square tests using two different constructions of the null hypothesis. One hypothesis was based on a no-preference among shell species, the second on comparing the number of crabs changing for a particular shell species when two options were given versus the changing when no options were offered. The second experiment was a multiple-alternative test based on a rank ordering of the shell preference. This method has both statistical and resource-saving advantages over the traditional pair-wise comparisons. The sequence of shell preference was similarly independent of the procedure used. The preferred shell species are heavy and might be associated with hydrodynamic advantages and with the protection against predation. The shell preference matches with the pattern of shell occupancy indicating that the shell use in nature is determined by the crab's preference. The information generated may be used for further research on shell preference as a methodological alternative. © 2012 Springer-Verlag.
Castro-Longoria E.,CICESE |
Vilchis-Nestor A.R.,National Autonomous University of Mexico |
Avalos-Borja M.,National Autonomous University of Mexico
Colloids and Surfaces B: Biointerfaces | Year: 2011
The development of production processes that can reduce the environmental impact, offer waste reduction and increase energy efficiency is an important step in the field of application of nanotechnology. In this work the filamentous fungus Neurospora crassa was screened and found to be successful for the production of mono and bimetallic Au/Ag nanoparticles (NPs). Analysis by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and transmission electron microscopy (TEM) confirmed the biosynthesis of NPs by the fungus. The shape of NPs was found to be mainly spherical with average diameter of 11nm for silver and 32nm for gold, when the fungus was exposed to the aqueous solutions of 10-3M of AgNO3 and HAuCl4, respectively. EDS analysis also confirmed the formation of alloy-type Au/Ag bimetallic NPs when three different ratios of AgNO3/HAuCl4 were used. TEM images of thin sections of N. crassa cells confirmed the intracellular formation of silver and gold NPs. The results obtained indicate that N. crassa can be a potential " nanofactory" for the synthesis of metallic NPs. The use of this organism will offer several advantages since it is considered as a non-pathogenic organism, has a fast growth rate, rapid capacity of metallic ions reduction, NPs stabilization and facile and economical biomass handling. © 2010 Elsevier B.V.
Larriva-Sahd J.,National Autonomous University of Mexico
Frontiers in Neuroanatomy | Year: 2012
This study describes the microscopic organization of a wedge-shaped area at the intersection of the main (MOB) and accessory olfactory bulbs (AOBs), or olfactory limbus (OL), and an additional component of the anterior olfactory nucleus or alpha AON that lies underneath of the AOB. The OL consists of a modified bulbar cortex bounded anteriorly by the MOB and posteriorly by the AOB. In Nissl-stained specimens the OL differs from the MOB by a progressive, antero-posterior decrease in thickness or absence of the external plexiform, mitral/tufted cell, and granule cell layers. On cytoarchitectual grounds the OL is divided from rostral to caudal into three distinct components: a stripe of glomerular-free cortex or preolfactory area (PA), a second or necklace glomerular area, and a wedge-shaped or interstitial area (INA) crowned by the so-called modified glomeruli that appear to belong to the anterior AOB. The strategic location and interactions with the main and AOBs, together with the previously noted functional and connectional evidence, suggest that the OL may be related to both sensory modalities. The alpha component of the anterior olfactory nucleus, a slender cellular cluster (i.e., 650 × 150 μm) paralleling the base of the AOB, contains two neuron types: a pyramidal-like neuron and an interneuron. Dendrites of pyramidal-like cells (P-L) organize into a single bundle that ascends avoiding the AOB to resolve in a trigone bounded by the edge of the OL, the AOB and the dorsal part of the anterior olfactory nucleus. Utrastructurally, the neuropil of the alpha component contains three types of synaptic terminals; one of them immunoreactive to the enzyme glutamate decarboxylase, isoform 67. © 2012 Larriva-Sahd.
Servin-Garciduenas L.E.,National Autonomous University of Mexico |
Martinez-Romero E.,National Autonomous University of Mexico
Eukaryotic Cell | Year: 2012
We report the complete organelle genome sequences of Trebouxiophyceae sp. strain MX-AZ01, an acidophilic green microalga isolated from a geothermal field in Mexico. This eukaryote has the remarkable ability to thrive in a particular shallow lake with emerging hot springs at the bottom, extremely low pH, and toxic heavy metal concentrations. Trebouxiophyceae sp. MX-AZ01 represents one of few described photosynthetic eukaryotes living in such a hostile environment. The organelle genomes of Trebouxiophyceae sp. MX-AZ01 are remarkable. The plastid genome sequence currently presents the highest G+C content for a trebouxiophyte. The mitochondrial genome sequence is the largest reported to date for the Trebouxiophyceae class of green algae. The analysis of the genome sequences presented here provides insight into the evolution of organelle genomes of trebouxiophytes and green algae. © 2012, American Society for Microbiology. All Rights Reserved.
Delgado-Inglada G.,National Autonomous University of Mexico |
Morisset C.,National Autonomous University of Mexico |
Stasinska G.,University Paris Diderot
Monthly Notices of the Royal Astronomical Society | Year: 2014
We compute a large grid of photoionization models that covers a wide range of physical parameters and is representative of most of the observed planetary nebulae (PNe). Using this grid, we derive new formulae for the ionization correction factors (ICFs) of He, O, N, Ne, S, Ar, Cl, and C. Analytical expressions to estimate the uncertainties arising from our ICFs are also provided. This should be useful since these uncertainties are usually not considered when estimating the error bars in element abundances. Our ICFs are valid over a variety of assumptions such as the input metallicities, the spectral energy distribution of the ionizing source, the gas distribution, or the presence of dust grains. Besides, the ICFs are adequate both for large aperture observations and for pencil-beam observations in the central zones of the nebulae.We test our ICFs on a large sample of observed PNe that extends as far as possible in ionization, central star temperature, and metallicity, by checking that the Ne/O, S/O, Ar/O, and Cl/O ratios showno trend with the degree of ionization. Our ICFs lead to significant differences in the derived abundance ratios as compared with previous determinations, especially for N/O, Ne/O, and Ar/O. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.
Esquivel-Sirvent R.,National Autonomous University of Mexico |
Schatz G.C.,Northwestern University
Journal of Physical Chemistry C | Year: 2012
We study the effects of spatial dispersion or nonlocality in the calculation of the Hamaker coefficient. Using a hydrodynamic model to describe the dielectric function of the materials, we show that at small separations, less that 10 nm, the Hamaker coefficient decreases significantly when a nonlocal dielectric is used. As a case study we compute the van der Waals interaction between two Au nanospheres and between two Au parallel nanorods. In both cases, the interaction energy shows variations of up to 2 orders of magnitude between the local and nonlocal cases. We show that at the nanoscale the usual approach to the calculation of the Hamaker coefficients has to be modified to properly take into account the dielectric properties of the nanoparticles. © 2011 American Chemical Society.
Fraija N.,National Autonomous University of Mexico |
Bernal C.G.,National Autonomous University of Mexico |
Hidalgo-Gamez A.M.,National Polytechnic Institute of Mexico
Monthly Notices of the Royal Astronomical Society | Year: 2014
The neutrino signal from SN1987A confirmed the core-collapse scenario and the possible formation of a neutron star. Although this compact object has eluded all observations, theoretical and numerical developments have allowed a glimpse of the fate of it. In particular, a hypercritical accretion model has been proposed to forecast the accretion of ∼0.15M⊙ in two hours and the subsequent submergence of the magnetic field in the newborn neutron star. In this paper, we revisit Chevalier's model in a numerical framework, focusing on the neutrino cooling effect on the supernova fall-back dynamics. For that, using a customized version of the FLASH code, we carry out numerical simulations of the accretion of matter on to the newborn neutron star in order to estimate the size of the neutrino-sphere, the emissivity and luminosity of neutrinos. As a signature of this phase, we estimate the neutrinos expected on SK neutrino experiment and their flavour ratios. This is academically important because, although currently it was very difficult to detect 1.46 thermal neutrinos and their oscillations, these fingerprints are the only viable and reliable way to confirm the hypercritical phase. Perhaps new techniques for detecting neutrino oscillations will arise in the near future allowing us to confirm our estimates. © 2014 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.
Fraija N.,National Autonomous University of Mexico
Monthly Notices of the Royal Astronomical Society | Year: 2014
Long gamma-ray bursts have been widely associated with collapsing massive stars in the framework of collapsar model. High-energy neutrinos and photons can be produced in the internal shocks of middle relativistic jets from core-collapse supernova. Although photons can hardly escape, high-energy neutrinos could be the only signature when the jets are hidden. We show that using suitable parameters, high-energy neutrinos in GeV-PeV range can be produced in the hidden jet inside the collapsar, thus demonstrating that these objects are candidates to produce neutrinos with energies between 1 and 10 PeV which were observed with IceCube. On the other hand, due to matter effects, high-energy neutrinos may oscillate resonantly from one flavour to another before leaving the star. Using two- (solar, atmospheric and accelerator parameters) and three-neutrino mixing, we study the possibility of resonant oscillation for these neutrinos created in internal shocks. Also we compute the probabilities of neutrino oscillations in the matter at different distances along the jet (before leaving the star) and after in vacuum, on their path to Earth. Finally, neutrino flavour ratios on Earth are estimated. © 2013 The Author. Published by Oxford University Press on behalf of the Royal Astronomical Society.
Olivares Pilon H.,Metropolitan Autonomous University |
Turbiner A.V.,National Autonomous University of Mexico
Physics Letters, Section A: General, Atomic and Solid State Physics | Year: 2015
The Schrödinger equation for two electrons in the field of a charged fixed center Z is solved with the Lagrange mesh method for charges close to the critical charge Zcr. We confirm the value of the nuclear critical charge Zcr recently calculated by Estienne et al. (2014)  to 11 decimal digits using an inhomogeneous (non-uniform) three-dimensional lattice of size 70×70×20. We show that the ground state energy for H- is accurate to 14 decimals on the lattice 50×50×40 in comparison with the highly accurate result by Nakashima and Nakatsuji (2007) . © 2015 Elsevier B.V. All rights reserved.
Cadenas E.,Universidad Michoacana de San Nicolás de Hidalgo |
Rivera W.,National Autonomous University of Mexico
Renewable Energy | Year: 2010
In this paper the wind speed forecasting in the Isla de Cedros in Baja California, in the Cerro de la Virgen in Zacatecas and in Holbox in Quintana Roo is presented. The time series utilized are average hourly wind speed data obtained directly from the measurements realized in the different sites during about one month. In order to do wind speed forecasting Hybrid models consisting of Autoregressive Integrated Moving Average (ARIMA) models and Artificial Neural Network (ANN) models were developed. The ARIMA models were first used to do the wind speed forecasting of the time series and then with the obtained errors ANN were built taking into account the nonlinear tendencies that the ARIMA technique could not identify, reducing with this the final errors. Once the Hybrid models were developed 48 data out of sample for each one of the sites were used to do the wind speed forecasting and the results were compared with the ARIMA and the ANN models working separately. Statistical error measures such as the mean error (ME), the mean square error (MSE) and the mean absolute error (MAE) were calculated to compare the three methods. The results showed that the Hybrid models predict the wind velocities with a higher accuracy than the ARIMA and ANN models in the three examined sites. © 2010 Elsevier Ltd.
Fraija N.,National Autonomous University of Mexico
Astroparticle Physics | Year: 2015
Abstract TeV γ-ray detections in flaring states without activity in X-rays from blazars have attracted much attention due to the irregularity of these "orphan" flares. Although the synchrotron self-Compton model has been very successful in explaining the spectral energy distribution and spectral variability of these sources, it has not been able to describe these atypical flaring events. On the other hand, an electron-positron pair plasma at the base of the AGN jet was proposed as the mechanism of bulk acceleration of relativistic outflows. This plasma in quasi-thermal equilibrium called Wein fireball emits radiation at MeV-peak energies serving as target of accelerated protons. In this work we describe the "orphan" TeV flares presented in blazars 1ES 1959+650 and Mrk 421 assuming geometrical considerations in the jet and evoking the interactions of Fermi-accelerated protons and MeV-peak target photons coming from the Wein fireball. After describing successfully these "orphan" TeV flares, we correlate the TeV γ-ray, neutrino and UHECR fluxes through pγ interactions and calculate the number of high-energy neutrinos and UHECRs expected in IceCube/AMANDA and TA experiment, respectively. In addition, thermal MeV neutrinos produced mainly through electron-positron annihilation at the Wein fireball will be able to propagate through it. By considering two- (solar, atmospheric and accelerator parameters) and three-neutrino mixing, we study the resonant oscillations and estimate the neutrino flavor ratios as well as the number of thermal neutrinos expected on Earth. © 2015 Elsevier B.V.
Davalos-Orozco L.A.,National Autonomous University of Mexico
Physics Letters, Section A: General, Atomic and Solid State Physics | Year: 2015
The flow of a thin film down a vertical cold thick wall with finite thermal conductivity is investigated under the lubrication approximation. It is shown that, despite the cooling from the wall, it is possible to find a new flow instability. That is, the free surface response to the wall deformation increases its amplitude with the negative Marangoni number. This amplitude growth is independent from the evolution of the time-dependent perturbations imposed on the free surface which, in contrast, are stabilized by cooling from the wall. However it is demonstrated that, even in this case, spatial resonance (see Dávalos-Orozco, 2007, 2008) is more effective to stabilize the time-dependent perturbations. From the results it is evident that these effects are possible only when the magnitudes of the thicknesses ratio and the thermal conductivities ratio are small. © 2015 Elsevier B.V. All rights reserved.
Leon G.,University of Buenos Aires |
Sudarsky D.,National Autonomous University of Mexico
Journal of Cosmology and Astroparticle Physics | Year: 2015
The statistical properties of the primordial density perturbations has been considered in the past decade as a powerful probe of the physical processes taking place in the early universe. Within the inflationary paradigm, the properties of the bispectrum are one of the keys that serves to discriminate among competing scenarios concerning the details of the origin of cosmological perturbations. However, all of the scenarios, based on the conventional approach to the so-called ''quantum-to-classical transition'' during inflation, lack the ability to point out the precise physical mechanism responsible for generating the inhomogeneity and anisotropy of our universe starting from and exactly homogeneous and isotropic vacuum state associated with the early inflationary regime. In past works, we have shown that the proposals involving a spontaneous dynamical reduction of the quantum state provide plausible explanations for the birth of said primordial inhomogeneities and anisotropies. In the present manuscript we show that, when considering within the context of such proposals, the characterization of the spectrum and bispectrum turn out to be quite different from those found in the traditional approach, and in particular, some of the statistical features, must be treated in a different way leading to some rather different conclusions. © 2015 IOP Publishing Ltd and Sissa Medialab srl .
Gutierrez-Preciado A.,National Autonomous University of Mexico |
Merino E.,National Autonomous University of Mexico
Clinical Microbiology and Infection | Year: 2012
In the current post-genomic era, only 3% of all genes have been annotated based on experimental evidence. Even though functions can readily be predicted for many genes, 25% of these are likely to be wrong. The most widely used methods for function prediction rely on sequence similarity, which might be misleading in many cases. Other methods such as genomic context or phylogenetic profiles have been developed to increase gene annotation accuracy; nevertheless these are only efficient when complete genome sequences are available. Here we propose a new approach based on riboswitch identification. Riboswitches are highly conserved regulators of gene expression located in the 5′ untranslated region of certain genes. When transcribed they adopt three-dimensional structures that recognize their ligands with great affinity and specificity. This specificity is a key issue for our method, allowing functional assignment with great accuracy. © 2012 The Authors. Clinical Microbiology and Infection © 2012 European Society of Clinical Microbiology and Infectious Diseases.
Sussman R.A.,National Autonomous University of Mexico |
Larena J.,Rhodes University
Classical and Quantum Gravity | Year: 2015
We undertake a non-perturbative study of the evolution of the 'gravitational entropy' proposed by Clifton, Ellis and Tavakol (CET) on local expanding cosmic CDM voids of ∼50-100 Mpc size described as spherical under-dense regions with negative spatial curvature, whose dynamics is determined by Lemaître-Tolman-Bondi (LTB) dust models asymptotic to three different types of FLRW background: ΛCDM, Einstein-de Sitter and 'open' FLRW with and negative spatial curvature. By assuming generic nearly spatially flat and linear initial conditions at the last scattering time, we examine analytically and numerically the CET entropy evolution into a fully nonlinear regime in our present cosmic time and beyond. Both analytic and numerical analysis reveal that the late time CET entropy growth is determined by the amplitude of initial fluctuations of spatial curvature at the last scattering time. This entropy growth decays to zero in the late asymptotic time range for all voids, but at a faster rate in voids with ΛCDM and open FLRW backgrounds. However, only for voids in a ΛCDM background is this suppression sufficiently rapid for the CET entropy itself to reach a terminal equilibrium (or 'saturation') value. The CET gravitational temperature vanishes asymptotically if and becomes asymptotically proportional to Λ for voids in a ΛCDM background. In the linear regime of the LTB evolution our results coincide, qualitatively and quantitatively, with previous results based on linear perturbation theory. © 2015 IOP Publishing Ltd.
Escobar-Ruiz M.A.,National Autonomous University of Mexico |
Turbiner A.V.,National Autonomous University of Mexico
Annals of Physics | Year: 2015
The moving neutral system of two Coulomb charges on a plane subject to a constant magnetic field B perpendicular to the plane is considered. It is shown that the composite system of finite total mass is bound for any center-of-mass momentum P and magnetic field strength; the energy of the ground state is calculated accurately using a variational approach. Its accuracy is cross-checked in a Lagrange-mesh method for B= 1 a.u. and in a perturbation theory at small B and P. The constructed trial function has the property of being a uniform approximation of the exact eigenfunction. For a Hydrogen atom and a Positronium a double perturbation theory in B and P is developed and the first corrections are found algebraically. A phenomenon of a sharp change of energy behavior for a certain center-of-mass momentum and a fixed magnetic field is indicated. © 2014 Elsevier Inc.
Boyer D.,National Autonomous University of Mexico |
Solis-Salas C.,National Autonomous University of Mexico
Physical Review Letters | Year: 2014
Strongly non-Markovian random walks offer a promising modeling framework for understanding animal and human mobility, yet, few analytical results are available for these processes. Here we solve exactly a model with long range memory where a random walker intermittently revisits previously visited sites according to a reinforced rule. The emergence of frequently visited locations generates very slow diffusion, logarithmic in time, whereas the walker probability density tends to a Gaussian. This scaling form does not emerge from the central limit theorem but from an unusual balance between random and long-range memory steps. In single trajectories, occupation patterns are heterogeneous and have a scale-free structure. The model exhibits good agreement with data of free-ranging capuchin monkeys. © 2014 American Physical Society.
Castillo M.,National Autonomous University of Mexico |
Bishop P.,University of Glasgow |
Jansen J.D.,University of Stockholm
Geomorphology | Year: 2013
A sudden drop in river base-level can trigger a knickpoint that propagates throughout the fluvial network causing a transient state in the landscape. Knickpoint retreat has been confirmed in large fluvial settings (drainage areas >100km2) and field data suggest that the same applies to the case of small bedrock river catchments (drainage areas <100km2). Nevertheless, knickpoint recession on resistant lithologies with structure that potentially affects the retreat rate needs to be confirmed with field-based data. Moreover, it remains unclear whether small bedrock rivers can absorb base-level fall via knickpoint retreat. Here we evaluate the response of small bedrock rivers to base-level fall on the isle of Jura in western Scotland (UK), where rivers incise into dipping quartzite. The mapping of raised beach deposits and strath terraces, and the analysis of stream long profiles, were used to identify knickpoints that had been triggered by base-level fall. Our results indicate that the distance of knickpoint retreat scales to the drainage area in a power law function irrespective of structural setting. On the other hand, local channel slope and basin size influence the vertical distribution of knickpoints. As well, at low drainage areas (~4km2) rivers are unable to absorb the full amount of base-level fall and channel reach morphology downstream of the knickpoint tends towards convexity. The results obtained here confirm that knickpoint retreat is mostly controlled by stream discharge, as has been observed for other transient landscapes. Local controls, reflecting basin size and channel slope, have an effect on the vertical distribution of knickpoints; such controls are also related to the ability of rivers to absorb the base-level fall. © 2012 Elsevier B.V.
Estrada A.,National Autonomous University of Mexico |
Fridman L.M.,National Autonomous University of Mexico
IEEE Transactions on Automatic Control | Year: 2010
The present technical note studies a class of nonlinear systems with unmatched perturbations. The combination of integral high-order sliding modes with the hierarchical quasi-continuous controller is proposed allowing finite-time exact compensation of unmatched perturbations with semiglobal convergence features for both regulation and tracking. © 2006 IEEE.
Avila-Becerril S.,National Autonomous University of Mexico |
Espinosa-Perez G.,National Autonomous University of Mexico
Proceedings of the American Control Conference | Year: 2012
Synchronization of networks composed by fully-actuated Lagrangian systems has received a lot of attention from the control theory community. Unfortunately, the case of networks composed by under-actuated systems of the same kind has not been deeply studied and the related literature is very reduced. The aim of this paper is to contribute towards the establishment of a control scheme for this class of networks by solving the particular case of a network composed by agents defined by Flexible-joint robots. The proposed schemes consider the presence of unknown delays in the communication channels. The usefulness of the controllers is validated through numerical simulations. © 2012 AACC American Automatic Control Council).
Moreno J.A.,National Autonomous University of Mexico
Proceedings of the IEEE Conference on Decision and Control | Year: 2012
In this paper we obtain a homogeneous, continuous, quadratic and strict Lyapunov function for Levant's Second Order Differentiator. Since its derivative is a non quadratic, discontinuous, homogeneous form its negative definiteness is determined using some new inequalities, providing coarser bounds than Young's inequalities. © 2012 IEEE.
Sheinbaum-Pardo C.,National Autonomous University of Mexico
Applied Energy | Year: 2016
According to the Fifth Assessment Report of the Intergovernmental Panel of Climate Change, several mitigation strategies for the industrial sector are needed to achieve global mitigation scenarios that include: carbon intensity, energy intensity, material intensity, product-service intensity, and the global demand for services. Under this contextual, this paper presents a decomposition analysis of energy related carbon dioxide emissions from the steel produced to manufacture new automobiles. The novelty of this analysis is that it links energy related carbon dioxide emissions from service demand to material production, breaking changes in demand for services measured as passenger-kilometers driven by new automobiles either for replacement or for new demand; steel content in new automobiles (material intensity); production process (structure); final energy intensity; and carbon intensity. The study boundaries include direct and indirect steel imports (contained in automobile imports). This analysis is applied to the Mexican case from 1993 to 2011. The results show that an increase in the pass-km followed by the growth in the vehicle size is the most important factors influencing carbon dioxide emissions. The rise of fuels with higher carbon contents in countries that export vehicles and steel to Mexico is also an important variable that had increased emissions. A projection for CO2 emissions for 2025 was developed to understand the significance of the different variables in the reduction of CO2 emissions related to the steel production for new automobiles. © 2016.
Bernal-Gamboa R.,National Autonomous University of Mexico |
Rosas J.M.,University of Jaén |
Callejas-Aguilera J.E.,University of Jaén
Psychonomic Bulletin and Review | Year: 2014
In two experiments with rats, we analyzed the effect of experiencing extinction in one task on the context specificity of a new association learned within a different task. Rats were trained to run in a runway for water in Task 1, and received taste aversion conditioning in Task 2 (the tasks were reversed in Exp. 2). Half of the rats received conditioning and extinction of Task 1 in Context A, whereas the other half received no extinction. Then all animals received training in the alternate task in Context B, prior to testing in Context C. When they were tested in Context C, Task 2 performance was attenuated if Task 1 had been extinguished prior to Task 2. These results are similar to those we have reported in humans, and consistent with the idea that extinction prompts attention to contexts, regardless of whether or not the contexts were involved in extinction. © 2013 Psychonomic Society, Inc.
Guzman F.S.,Universidad Michoacana de San Nicolás de Hidalgo |
Lora-Clavijo F.D.,National Autonomous University of Mexico
General Relativity and Gravitation | Year: 2015
We study the rotation curves of ultralight BEC dark matter halos. These halos are long lived solutions of initially rotating BEC fluctuations. In order to study the implications of the rotation characterizing these long-lived configurations we consider the particular case of a boson mass m=10-23, eV/c2 and no self-interaction. We find that these halos successfully fit samples of rotation curves of LSB galaxies. © 2015, Springer Science+Business Media New York.
Ortiz Velasquez A.,National Autonomous University of Mexico
Nuclear Physics A | Year: 2015
In this work, a study of the average transverse momentum (pT) as a function of the mid-rapidity charged hadron multiplicity (Nch) and hadron mass (m) in p-Pb and Pb-Pb collisions at LHC energies is presented. For the events producing low Nch, the average pT is found to scale with the reduced hadron mass, i.e., mass divided by the number of quark constituents (m/nq), this scaling also holds for inelastic pp collisions at RHIC and LHC energies. The scaling is broken in high multiplicity p-Pb and Pb-Pb collisions, where, for 〈dNch/dη〉<~60 the average pT is higher for baryons than that for mesons, though they increase linearly with m/nq. This behavior is qualitatively well reproduced by Pythia 8, but not by hydro calculations, where an universal scaling with the hadron mass (and not with m/nq) is predicted for all the multiplicity event classes. Only the central (0-60%) Pb-Pb collisions behave as expected from hydro. © 2015 Elsevier B.V.
Ormeno-Orrillo E.,National Autonomous University of Mexico |
Martinez-Romero E.,National Autonomous University of Mexico
Systematic and Applied Microbiology | Year: 2013
Rhizobia seem to have large degradative and metabolic capabilities that allow them to grow on diverse soil and rhizospheric substances, many of which are still unknown. Rhizobial genome sequences encode numerous transporters for unknown substrates, and transcriptomic studies have revealed genes with unknown functions that are highly expressed in roots or rhizospheres. It is proposed here that some of these unknown-fun