Time filter

Source Type

Mexico City, Mexico

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.

Efimov D.V.,University of Bordeaux 1 | Fridman L.,National Autonomous University of Mexico
IEEE Transactions on Automatic Control | Year: 2011

A variant of super-twisting differentiator is proposed. Lyapunov function is designed and an estimate on finite time of derivatives estimation is given. The differentiator is equipped with hybrid adaptation algorithm that ensures global differentiation ability independently on amplitude of the differentiated signal and measurement noise. © 2011 IEEE. Source

Moreno Mendez E.,National Autonomous University of Mexico | Moreno Mendez E.,University of Bonn
Astrophysical Journal | Year: 2014

Using binary evolution with Case-C mass transfer, the spins of several black holes (BHs) in X-ray binaries (XBs) have been predicted and confirmed (three cases) by observations. The rotational energy of these BHs is sufficient to power up long gamma-ray bursts (GRBs) and hypernovae (HNe) and still leave a Kerr BH behind. However, strong magnetic fields and/or dynamo effects in the interior of such stars deplete their cores from angular momentum preventing the formation of collapsars. Thus, even though binaries can produce Kerr BHs, most of their rotation is acquired from the stellar mantle, with a long delay between BH formation and spin up. Such binaries would not form GRBs. We study whether the conditions required to produce GRBs can be met by the progenitors of such BHs. Tidal-synchronization and Alfvén timescales are compared for magnetic fields of different intensities threading He stars. A search is made for a magnetic field range that allows tidal spin up all the way in to the stellar core but prevents its slow down during differential rotation phases. The energetics for producing a strong magnetic field during core collapse, which may allow for a GRB central engine, are also estimated. An observationally reasonable choice of parameters is found (B ≲ 102 G threading a slowly rotating He star) that allows Fe cores to retain substantial angular momentum. Thus, the Case-C mass-transfer binary channel is capable of explaining long GRBs. However, the progenitors must have low initial spin and low internal magnetic field throughout their H-burning and He-burning phases. © 2014. The American Astronomical Society. All rights reserved. Source

Buijs R.M.,National Autonomous University of Mexico
Handbook of Clinical Neurology | Year: 2013

The overarching theme of the present chapter is the importance of the interaction between brain and body in order to maintain homeostasis - an interaction, rather than a mere top-down or reflex regulation, as signals from the organs may influence the functioning of the brain. For example, the reflex regulation of blood pressure and heart rate is not only subject to modulation by ascending information from the body, but also by descending information from several areas in hypothalamus and cortex. The central nervous system (CNS) has the capacity to control its output via the autonomic nervous system (ANS) using an amazing differentiation. For example, not only do the biological clock and prefrontal cortex contain neurons which influence the parasympathetic or sympathetic motor neurons, they also contain different neurons that project to diverse body compartments. In the end this leads to integrated responses whereby visceral sensory information reaches higher centers in the CNS via vagal or spinal sensory pathways, causing a reaction which takes into account factors such as the time of day, the season, the reproductive status, mood. Based on all this information, the brain sets the balance of the different parts of the ANS, causing its output to change its emphasis according to the situation. A disturbed balance, either as a result of behavior or of disease of any of the organs, may lead to pathology affecting the functioning of the entire individual. © 2013 Elsevier B.V.. Source

Valdez-Mondragon A.,National Autonomous University of Mexico
Journal of Arachnology | Year: 2013

With 30 species and a natural distribution in North America, 28 confined to Mexico, Physocyclus Simon 1893 is the most diverse genus within the pholcid spider subfamily Arteminae. This paper provides the first phylogenetic test of the genus's monophyly through a cladistic analysis of 54 morphological characters using equal and implied weighting. The equally weighted analysis found 12 most parsimonious trees, whereas the analysis with implied weights varying the concavity values (K = 6-10) found five or six most parsimonious trees. The monophyly of the genus Physocyclus is supported by three synaphomorphies: 1) the paired ventral apophysis on the anterior part of the epigynum; 2) the lateral constraints in the middle part of the epigynum; and 3) the arc of the uterus, with a single sclerotized projection on the anterior part. The genus Physocyclus contains two clades treated as species groups: The globosus group, with 11 species, and the dugesi group with 19 species. The species relationships within the globosus group were better resolved than those in the dugesi group. The globosus group has a biogeographical distribution pattern in the Mesoamerican and Mexican Mountain biotic components, whereas the dugesi group has a distribution pattern in the Mesoamerican and Continental Nearctic biotic components. Given the complex biogeography in Mexico, apparently a large-scale vicariant event separated the two major clades within the genus Physocyclus. © 2013 The American Arachnological Society. Source

Pina E.,National Autonomous University of Mexico | Reaven G.M.,Stanford University
Journal of Lipid Research | Year: 2013

Studies in mature adults suggest that the plasma concentration ratio of triglyceride (TG)/HDL-cholesterol (HDL-C) provides a simple way to identify apparently healthy individuals who are insulin resistant (IR) and at increased cardiometabolic risk. This study extends these observations by examining the clinical utility of the TG/HDL-C ratio and the metabolic syndrome (MetS) in 2,244 healthy college students (17-24 years old) of Mexican Mestizo ancestry. The TG/HDL-C ratio separating the 25% with the highest value was used to identify IR and increased cardiometabolic risk. Cardiometabolic risk factors were more adverse in men and women whose TG/HDL-C ratios exceeded 3.5 and 2.5, respectively, and approximately one third were identified as being IR. The MetS identified fewer individuals as being IR, but their risk profile was accentuated. In conclusion, both a higher TG/HDL-C ratio and a diagnosis of the MetS identify young IR individuals with an increased cardiometabolic risk profile. The TG/HDL-C ratio identified a somewhat greater number of "high risk" subjects, whereas the MetS found a group whose risk profile was somewhat magnified. These findings suggest that the TG/ HDL-C ratio may serve as a simple and clinically useful approach to identify apparently healthy, young individuals who are IR and at increased cardiometabolic risk. Copyright © 2013 by the American Society for Biochemistry and Molecular Biology, Inc. Source

Gutierrez-Garica T.A.,Posgrado en Ciencias Biologicas | Vazquez-Dominguez E.,National Autonomous University of Mexico
BioScience | Year: 2011

Comparative phylogeography (CP) can be defined as the study of the effects of evolutionary history and biogeography on the distribution of genetic variation of codistributed species. CP studies have intensified in recent years, which is a natural progression from an extensive history of intraspecific phylogeography research. On the basis of a thorough review of published studies that specifically deal with CP, our objective in the present review is to provide a comprehensive guide to the discipline that will help those wishing to develop a CP project. We describe the characteristics that shape a CP study and summarize the field's prime theoretical, methodological, and analytical requirements; frequent hypotheses tested; and current achievements and limitations, including a variety of illustrative examples throughout. We finally highlight some new approaches in CP and briefly discuss future directions for the field. © 2011 by American Institute of Biological Sciences. All rights reserved. Source

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. Source

Gomez-Lagunas F.,National Autonomous University of Mexico
Journal of Physiology | Year: 2010

Quinidine is a commonly used antiarrhythmic agent and a tool to study ion channels. Here it is reported that quinidine equilibrates within seconds across the Sf9 plasma membrane, blocking the open pore of Shab channels from the intracellular side of the membrane in a voltage-dependentmanner with 1:1 stoichiometry. On binding to the channels, quinidine interacts with pore K + ions in a mutually destabilizing manner. As a result, when the channels are blocked by quinidine with the cell bathed in an external medium lacking K +, the Shab conductance G K collapses irreversibly, despite the presence of a physiological [K +] in the intracellular solution. The quinidine-promoted collapse of Shab G K resembles the collapse of Shaker G K observed with 0 K + solutions on both sides of the membrane: thus the extent of G K drop depends on the number of activating pulses applied in the presence of quinidine, but is independent of the pulse duration. Taken together the observations indicate that, as in Shaker, the quinidine-promoted collapse of Shab G K occurs during deactivation of the channels, at the end of each activating pulse, with a probability of 0.1 per pulse at -80 mV. It appears that when Shab channels are open, the pore conformation able to conduct is stable in the absence of K +, but on deactivation this conformation collapses irreversibly. © 2010 The Authors. Journal compilation © 2010 The Physiological Society. Source

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. Source

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. Source

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) [3] 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) [15]. © 2015 Elsevier B.V. All rights reserved. Source

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. Source

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. Source

Carrillo J.,University Militar Nueva Granada | Alcocer S.M.,National Autonomous University of Mexico
Engineering Structures | Year: 2013

As it is widely recognized, seismic design parameters used in most current codes are mainly intended for designing concrete walls in medium- or high-rise buildings. In low-rise concrete housing, thin walls with low concrete strength, web steel ratio smaller than the minimum ratio prescribed by codes, and in many cases, shear web reinforcement made of welded wire meshes are commonly used. In this paper, a simplified equation for estimating the period of vibration of low-rise concrete housing is proposed. The equation is based on response measured during shaking table tests of solid walls and walls with openings, on the results derived from conventional spectral analysis of ambient vibration tests, as well as on results obtained from mathematical models using the wide-column analogy and the finite element method. Statistical analysis of the ratios of predicted-to-measured periods demonstrated that predicted periods were very similar to those observed, and the scatter is also lower than in existing equations. The proposed equation is useful for seismic design, as well as for assessing the adequacy of available equations in current codes. © 2013 Elsevier Ltd. Source

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. Source

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. Source

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. Source

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. Source

Cadenas E.,Universidad Michoacana de San Nicolas 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. Source

Aldana-Bobadilla E.,National Autonomous University of Mexico | Kuri-Morales A.,Autonomus Institute of Technology of Mexico
Entropy | Year: 2015

Clustering is an unsupervised process to determine which unlabeled objects in a set share interesting properties. The objects are grouped into k subsets (clusters) whose elements optimize a proximity measure. Methods based on information theory have proven to be feasible alternatives. They are based on the assumption that a cluster is one subset with the minimal possible degree of "disorder". They attempt to minimize the entropy of each cluster. We propose a clustering method based on the maximum entropy principle. Such a method explores the space of all possible probability distributions of the data to find one that maximizes the entropy subject to extra conditions based on prior information about the clusters. The prior information is based on the assumption that the elements of a cluster are "similar" to each other in accordance with some statistical measure. As a consequence of such a principle, those distributions of high entropy that satisfy the conditions are favored over others. Searching the space to find the optimal distribution of object in the clusters represents a hard combinatorial problem, which disallows the use of traditional optimization techniques. Genetic algorithms are a good alternative to solve this problem. We benchmark our method relative to the best theoretical performance, which is given by the Bayes classifier when data are normally distributed, and a multilayer perceptron network, which offers the best practical performance when data are not normal. In general, a supervised classification method will outperform a non-supervised one, since, in the first case, the elements of the classes are known a priori. In what follows, we show that our method's effectiveness is comparable to a supervised one. This clearly exhibits the superiority of our method. © 2015 by the authors. Source

Guzman F.S.,Universidad Michoacana de San Nicolas 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. Source

Skutsch M.M.,National Autonomous University of Mexico | Ba L.,Programme Energie
Forest Policy and Economics | Year: 2010

Policy on Reduced Emissions from Deforestation and Degradation in Developing Countries (REDD) is currently being debated under the auspices of the UNFCCC. The paper reviews developments in this, particularly as regards potential crediting for reduced forest degradation in places such as the Sahel, given that degradation in the tropical dry forests and savanna woodlands is a considerable source of carbon dioxide emissions. It then presents field data from sites in Guinea Bissau, Mali and Senegal where the Kyoto: Think Global Act Local project has been working for a number of years. In these sites, the local communities had been managing their forests under a variety of different programmes before KTGAL started. The purpose of KTGAL was to record the carbon outcomes of typical community forest management regimes, and to assess whether local communities were capable of making carbon stock measurements themselves. The results indicate that carbon savings range from 5 to 14 tons carbon dioxide per hectare, if both avoided degradation and increased biomass due to forest enhancement are included. They also show that communities can be trained relatively easily to make stock (and thus carbon) assessments, at a much lower cost than employing professional forest surveyors. It is not clear yet whether both reduced degradation and enhanced stock will be rewarded under REDD, nor is it sure how much of the financial reward might potentially be claimed by the communities, but even if only 10% of the financial value of the carbon were to filter back to the communities, this would still represent a considerable incentive for participation. © 2009 Elsevier B.V. All rights reserved. Source

Gazol A.,National Autonomous University of Mexico
Astrophysical Journal | Year: 2014

We numerically study the thermal pressure distribution in a gas with thermal properties similar to those of the cold neutral interstellar gas by analyzing three-dimensional hydrodynamic models in boxes with sides of 100 pc with turbulent compressible forcing at 50 pc and different Mach numbers. We find that at high pressures and for large Mach numbers, both the volume-weighted and the density-weighted distributions can be appropriately described by a log-normal distribution, whereas for small Mach numbers they are better described by a power law. Thermal pressure distributions resulting from similar simulations but with self-gravity differ only for low Mach numbers; in this case, they develop a high pressure tail. © 2014. The American Astronomical Society. All rights reserved. Source

Perez-Garcia I.,National Autonomous University of Mexico
Atmosfera | Year: 2014

This study explores the zonal flow in the form of Legendre polynomials. The basic flow is divided into a zonally symmetric flow and a Rossby-Haurwitz (RH) wave. Several features of this (more realistic) zonal flow make it particularly interesting, such as the midlatitude westerly jet streams and an easterly wind around the equator, which closely resembles the mean horizontal flow at 200 mb of the December-February period. The zonal flow is combined with the RH wave, in order to test the blocking formation mechanism on early stages for the northeastern Pacific. A numerical simulation has been performed using a linear barotropic model with tropical forcing and damping to check the extra-tropical response of the mechanism of eddies reinforcement of the ridge along the western coast of North America. Source

Franklin K.,University of Arizona | Molina-Freaner F.,National Autonomous University of Mexico
Conservation Biology | Year: 2010

In large parts of northern Mexico native plant communities are being converted to non-native buffelgrass (Pennisetum ciliare) pastures, and this conversion could fundamentally alter primary productivity and species richness. In Sonora, Mexico land conversion is occurring at a regional scale along a rainfall-driven gradient of primary productivity, across which native plant communities transition from desert scrub to thorn scrub. We used a paired sampling design to compare a satellite-derived index of primary productivity, richness of perennial plant species, and canopy-height profiles of native plant communities with buffelgrass pastures. We sampled species richness across a gradient of primary productivity in desert scrub and thorn scrub vegetation to examine the influence of site productivity on the outcomes of land conversion. We also examined the influence of pasture age on species richness of perennial plants. Index values of primary productivity were lower in buffelgrass pastures than in native vegetation, which suggests a reduction in primary productivity. Land conversion reduced species richness by approximately 50% at local and regional scales, reduced tree and shrub cover by 78%, and reduced canopy height. Land conversion disproportionately reduced shrub species richness, which reflects the common practice among Sonoran ranchers of conserving certain tree and cactus species. Site productivity did not affect the outcomes of land conversion. The age of a buffelgrass pasture was unrelated to species richness within the pasture, which suggests that passive recovery of species richness to preconversion levels is unlikely. Our findings demonstrate that land conversion can result in large losses of plant species richness at local and regional scales and in substantial changes to primary productivity and vegetation structure, which casts doubt on the feasibility of restoring native plant communities without active intervention on the part of land managers. © 2010 Society for Conservation Biology. Source

Bejarano F.J.,National Autonomous University of Mexico | Pisano A.,University of Cagliari
IEEE Transactions on Automatic Control | Year: 2011

Two state observers are designed for some classes of switched linear systems with unknown inputs. The design of the proposed observers assumes that all switching subsystems fulfill a property of "strong detectability" that allows to implement suitable reduced-order unknown-input switched observers. The synthesis of the observers is based on the feasibility of a certain system of LMIs. Two main schemes are presented. For the case when the set of possible unknown-input distribution matrices are linearly dependent, an observer is suggested that guarantees the asymptotic state reconstruction without imposing any slow-switching dwell-time constraint about the sequence of the switching times. For the general case, the existence of a minimal average dwell-time for every switching sequence is assumed. By appropriate Lyapunov analysis, the convergence of the state estimate is proven to be exponential in both cases. Simulation results confirm the predicted performance. © 2006 IEEE. Source

Efimov D.,University of Bordeaux 1 | Fridman L.,National Autonomous University of Mexico
Automatica | Year: 2011

A state observer design procedure is proposed for nonlinear locally Lipschitz systems with high relative degree from the available for measurements output to the nonlinearity. The possible presence of disturbances is taken into account. The solution is based on logic-based control and the high order super-twisting observer. The approach is applicable to nonlinear systems with bounded solutions. © 2010 Elsevier Ltd. All rights reserved. Source

It is accepted that sensory experience instructs the remodelling of neuronal circuits during postnatal development, after their specification has occurred. The story is less clear with regard to the role of experience during the initial formation of neuronal circuits, whether prenatal or postnatal, since this process is now supposed to be primarily influenced by genetic determinants and spontaneous neuronal firing. Here we evaluated this last issue by examining the effect that postnatal chronic exposure to cognate odorants has on the formation of I7 and M72 glomeruli, iterated olfactory circuits that are formed before and after birth, respectively. We took advantage of double knock-in mice whose I7 and M72 primary afferents express green fluorescent protein and β-galactosidase, correspondingly. Our results revealed that postnatal odorant chronic exposure led to the formation of permanent supernumerary I7 and M72 glomeruli in a dose and time dependent manner. Glomeruli in exposed mice were formed within the same regions of olfactory bulb and occupy small space volumes compared to the corresponding single circuits in non-exposed mice. We suggest that local reorganization of the primary afferents could participate in the process of formation of supernumerary glomeruli. Overall, our results support that sensory experience indeed instructs the permanent formation of specific glomeruli in the mouse olfactory bulb by means of constructivist processes. Source

Bejarano F.J.,National Autonomous University of Mexico | Pisano A.,University of Cagliari | Usai E.,University of Cagliari
Nonlinear Analysis: Hybrid Systems | Year: 2011

This work addresses the state observation problem for a class of switched linear systems with unknown inputs. The proposed high-order sliding-mode observer provides a finite-time converging estimate of the continuous system's state vector in spite of the presence of unknown inputs. The design procedure, which assumes knowledge of the discrete state of the switched system, is based on the principles of disturbance decoupling and hierarchical observer output injection. In order to cope with the switching nature of the plant under observation, jumps in the observer state space are enforced intentionally. The implementation of an additional observer allows for the reconstruction of the unknown inputs, which may be important in the framework of fault detection. Numerical examples illustrate the effectiveness of the suggested technique. © 2010 Elsevier Ltd. Source

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 Source

Fraija N.,National Autonomous University of Mexico
Astrophysical Journal | Year: 2014

The spectral energy distribution of giant lobes shows one main peak detected by the Wilkinson Microwave Anisotropy Probe at the low energy of 10-5 eV and a faint γ-ray flux imaged by the Fermi Large Area Telescope at an energy of ≥100 MeV. On the other hand, the Pierre Auger Observatory associated some ultra-high-energy cosmic rays with the direction of Centaurus A and IceCube reported 28 neutrino-induced events in a TeV-PeV energy range, although none of them related with this direction. In this work, we describe the spectra for each of the lobes, the main peak with synchrotron radiation, and the high-energy emission with p-p interactions. After obtaining a good description of the main peak, we deduce the magnetic fields, electron densities, and the age of the lobes. Successfully describing the γ-ray emission by p-p interactions and considering thermal particles in the lobes with density in the range 10-10-10-4 cm-3 as targets, we calculate the number of ultra-high-energy cosmic rays. Although the γ-spectrum is well described with any density in the range, only when 10-4 cm-3 is considered are the expected number of events very similar to that observed by the Pierre Auger Observatory, otherwise we obtain an excessive luminosity. In addition, correlating the γ-ray and neutrino fluxes through p-p interactions, we calculate the number of high-energy neutrinos expected in IceCube. Our analysis indicates that neutrinos above 1 TeV cannot be produced in the lobes of Centaurus A, which is consistent with the results recently published by the IceCube Collaboration. © 2014. The American Astronomical Society. All rights reserved.. Source

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. Source

Herold M.,Wageningen University | Skutsch M.,National Autonomous University of Mexico
Environmental Research Letters | Year: 2011

Different options have been suggested by Parties to the UNFCCC (United Framework Convention on Climate Change) for inclusion in national approaches to REDD and REDD + (reduced deforestation, reduced degradation, enhancement of forest carbon stocks, sustainable management of forest, and conservation of forest carbon stocks). This paper proposes that from the practical and technical points of view of designing action for REDD and REDD + at local and sub-national level, as well as from the point of view of the necessary MRV (monitoring, reporting and verification), these should be grouped into three categories: conservation, which is rewarded on the basis of no changes in forest stock, reduced deforestation, in which lowered rates of forest area loss are rewarded, and positive impacts on carbon stock changes in forests remaining forest, which includes reduced degradation, sustainable management of forest of various kinds, and forest enhancement. Thus we have moved degradation, which conventionally is grouped with deforestation, into the forest management group reported as areas remaining forest land, with which it has, in reality, and particularly as regards MRV, much more in common. Secondly, in the context of the fact that REDD/REDD + is to take the form of a national or near-national approach, we argue that while systematic national monitoring is important, it may not be necessary for REDD/REDD + activities, or for national MRV, to be started at equal levels of intensity all over the country. Rather, areas where interventions seem easiest to start may be targeted, and here data measurements may be more rigorous (Tier 3), for example based on stakeholder self-monitoring with independent verification, while in other, untreated areas, a lower level of monitoring may be pursued, at least in the first instance. Treated areas may be targeted for any of the three groups of activities (conservation, reduced deforestation, and positive impact on carbon stock increases in forest remaining forest). © 2011 IOP Publishing Ltd. Source

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. Source

Lopez-Martinez R.,National Autonomous University of Mexico | Mendez-Tovar L.J.,Laboratory of Dermatology and Medical Mycology Research
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. Source

Ramirez-Bermudez J.,National Autonomous University of Mexico
Archives of Medical Research | Year: 2012

It is generally accepted that Alois Alzheimer, the German neuropathologist and clinician, discovered the disease that carries his name, after the clinicopathological study of a 51-year-old woman named Auguste D. who presented a dementia syndrome. The pathological study of the brain revealed the presence of neurofibrillary tangles and senile plaques. Emil Kraepelin coined the eponym Alzheimer's disease in the 8th edition of his textbook Clinical Psychiatry. However, several critical aspects of this history have been pointed out by historians of psychiatry. This article provides a narrative of the best-known facts leading to the formation of the original concept but also presents an informed discussion of the main critical points: 1. The descriptions of senile plaques and neurofibrillary tangles in the context of dementia before Alzheimer's report. 2. The presence or absence of arteriosclerotic changes in the brain of Auguste D. 3. The presence of noncognitive symptoms in August D. 4. The influence of social, political and economic issues in the formation and selection of medical concepts. © 2012 IMSS. Source

Huang Y.,La Jolla Institute for Allergy and Immunology | Pastor W.A.,La Jolla Institute for Allergy and Immunology | Zepeda-Martinez J.A.,National Autonomous University of Mexico | Rao A.,La Jolla Institute for Allergy and Immunology
Nature Protocols | Year: 2012

5-hydroxymethylcytosine (5hmC) is a recently discovered base in the mammalian genome, produced upon oxidation of 5-methylcytosine (5mC) in a process catalyzed by TET proteins. The biological functions of 5hmC and further oxidation products of 5mC are under intense investigation, as they are likely intermediates in DNA demethylation pathways. Here we describe a novel protocol to profile 5hmC at a genome-wide scale. This approach is based on sodium bisulfite-mediated conversion of 5hmC to cytosine-5-methylenesulfonate (CMS); CMS-containing DNA fragments are then immunoprecipitated using a CMS-specific antiserum. The anti-CMS technique is highly specific with a low background, and is much less dependent on 5hmC density than anti-5hmC immunoprecipitation (IP). Moreover, it does not enrich for CA and CT repeats, as noted for 5hmC DNA IP using antibodies to 5hmC. The anti-CMS protocol takes 3 d to complete. © 2012 Nature America, Inc. All rights reserved. Source

Prendini L.,American Museum of Natural History | Francke O.F.,National Autonomous University of Mexico | Vignoli V.,University of Siena
Cladistics | Year: 2010

The scorpion family Typhlochactidae Mitchell, 1971 is endemic to eastern Mexico and exclusively troglomorphic. Six of the nine species in the family are hypogean (troglobitic), morphologically specialized for life in the cave environment, whereas three are endogean (humicolous) and comparably less specialized. The family therefore provides a model for testing the hypotheses that ecological specialists (stenotopes) evolve from generalist ancestors (eurytopes) and that specialization (in this case to the cavernicolous habitat) is an irreversible, evolutionary dead-end that ultimately leads to extinction. Due to their cryptic ecology, inaccessible habitat, and apparently low population density, Typhlochactidae are very poorly known. The monophyly of these troglomorphic scorpions has never been rigorously tested, nor has their phylogeny been investigated in a quantitative analysis. We test and confirm their monophyly with a cladistic analysis of 195 morphological characters (142 phylogenetically informative), the first for a group of scorpions in which primary homology of pedipalp trichobothria was determined strictly according to topographical identity (the " placeholder approach" ). The phylogeny of Typhlochactidae challenges the conventional wisdom that ecological specialization (stenotopy) is unidirectional and irreversible, falsifying Cope's Law of the unspecialized and Dollo's Law of evolutionary irreversibility. Troglobitism is not an evolutionary dead-end: endogean scorpions evolved from hypogean ancestors on more than one occasion.© The Willi Hennig Society 2009. © The Willi Hennig Society 2009. Source

Broom D.M.,National Autonomous University of Mexico
Proceedings. Biological sciences / The Royal Society | Year: 2013

What is the future for livestock agriculture in the world? Consumers have concerns about sustainability but many widely used livestock production methods do not satisfy consumers' requirements for a sustainable system. However, production can be sustainable, occurring in environments that: supply the needs of the animals resulting in good welfare, allow coexistence with a wide diversity of organisms native to the area, minimize carbon footprint and provide a fair lifestyle for the people working there. Conservation need not just involve tiny islands of natural vegetation in a barren world of agriculture, as there can be great increases in biodiversity in farmed areas. Herbivores, especially ruminants that consume materials inedible by humans, are important for human food in the future. However, their diet should not be just ground-level plants. Silvopastoral systems, pastures with shrubs and trees as well as herbage, are described which are normally more productive than pasture alone. When compared with widely used livestock production systems, silvopastoral systems can provide efficient feed conversion, higher biodiversity, enhanced connectivity between habitat patches and better animal welfare, so they can replace existing systems in many parts of the world and should be further developed. Source

Szulagyi J.,University of Nice Sophia Antipolis | Morbidelli A.,University of Nice Sophia Antipolis | Crida A.,University of Nice Sophia Antipolis | Masset F.,National Autonomous University of Mexico
Astrophysical Journal | Year: 2014

In the core-accretion model, the nominal runaway gas-accretion phase brings most planets to multiple Jupiter masses. However, known giant planets are predominantly Jupiter mass bodies. Obtaining longer timescales for gas accretion may require using realistic equations of states, or accounting for the dynamics of the circumplanetary disk (CPD) in the low-viscosity regime, or both. Here we explore the second way by using global, three-dimensional isothermal hydrodynamical simulations with eight levels of nested grids around the planet. In our simulations, the vertical inflow from the circumstellar disk (CSD) to the CPD determines the shape of the CPD and its accretion rate. Even without a prescribed viscosity, Jupiter's mass-doubling time is 104 yr, assuming the planet at 5.2 AU and a Minimum Mass Solar Nebula. However, we show that this high accretion rate is due to resolution-dependent numerical viscosity. Furthermore, we consider the scenario of a layered CSD, viscous only in its surface layer, and an inviscid CPD. We identify two planet-accretion mechanisms that are independent of the viscosity in the CPD: (1) the polar inflow - defined as a part of the vertical inflow with a centrifugal radius smaller than two Jupiter radii and (2) the torque exerted by the star on the CPD. In the limit of zero effective viscosity, these two mechanisms would produce an accretion rate 40 times smaller than in the simulation. © 2014. The American Astronomical Society. All rights reserved.© 2014. The American Astronomical Society. All rights reserved. Printed in the U.S.A. Source

Morales-Sanchez A.,National Autonomous University of Mexico
Viruses | Year: 2014

The first human tumor virus was discovered in the middle of the last century by Anthony Epstein, Bert Achong and Yvonne Barr in African pediatric patients with Burkitt’s lymphoma. To date, seven viruses-EBV, KSHV, high-risk HPV, MCPV, HBV, HCV and HTLV1-have been consistently linked to different types of human cancer, and infections are estimated to account for up to 20% of all cancer cases worldwide. Viral oncogenic mechanisms generally include: generation of genomic instability, increase in the rate of cell proliferation, resistance to apoptosis, alterations in DNA repair mechanisms and cell polarity changes, which often coexist with evasion mechanisms of the antiviral immune response. Viral agents also indirectly contribute to the development of cancer mainly through immunosuppression or chronic inflammation, but also through chronic antigenic stimulation. There is also evidence that viruses can modulate the malignant properties of an established tumor. In the present work, causation criteria for viruses and cancer will be described, as well as the viral agents that comply with these criteria in human tumors, their epidemiological and biological characteristics, the molecular mechanisms by which they induce cellular transformation and their associated cancers. © 2014 by the authors; licensee MDPI, Basel, Switzerland. Source

Sussman R.A.,National Autonomous University of Mexico
Astronomische Nachrichten | Year: 2014

We apply a recent proposal to define "gravitational entropy" to the expansion of cosmic voids within the framework of nonperturbative General Relativity. By considering CDM void configurations compatible with basic observational constraints, we show that this entropy grows from post-inflationary conditions towards a final asymptotic value in a late time fully nonlinear regime described by the Lemaître-Tolman-Bondi (LTB) dust models. A qualitatively analogous behavior occurs if we assume a positive cosmological constant consistent with a Λ-CDM background model. However, the Λ term introduces a significant suppression of entropy growth with the terminal equilibrium value reached at a much faster rate. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

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. Source

Pandarinath K.,National Autonomous University of Mexico
Turkish Journal of Earth Sciences | Year: 2014

Recently developed multidimensional tectonomagmatic discrimination diagrams based on log-ratio variables of chemical elements, discordant outlier-free databases, and probability-based boundaries have been shown to work better than the earlier diagrams. Hydrothermally altered drilled well rock cuttings obtained from different depths of geothermal fields were used to test these diagrams to compare the inferred tectonic setting with the expected one. In spite of the hydrothermal alteration effects, these diagrams provided the following expected tectonic settings: (1) an arc setting for Ahuachapán and Berlin geothermal fields, El Salvador; (2) a rift setting for Cerro Prieto geothermal field, Mexico, and Tendaho geothermal field, Afar region; (3) a MORB setting for Reykjanes geothermal field, Iceland; (4) a transitional arc and collision setting for Roman volcanic provenance, Italy; and (5) an arc setting for Tongonan geothermal field, Philippines. The present study indicates that the recently developed multielement discriminant function based diagrams may be successfully applied to infer the original tectonic setting of hydrothermally altered rock samples and thus confirms the robustness of these diagrams. © Tübi̇tak. Source

The formal description of new species has been the basic method, during 250 years, ofdocumenting the Planet's biodiversity. Analysis of species description patterns identifyiestrends and gaps in taxonomic knowledge. Here, I present an analysis of Colombian newspecies described during 2000-2009. I constructed a dataset by bibliographic databasesearching with specific key words, and then classified each record where a new specieswas described for Colombia. I compared my results against information for the entirePlanet. During the years 2000-2009, 1272 new species where described for Colombia,which represents 0.72 % of the new species for the Planet. Some taxa as Ascomycota andProteobacteria where poorly represented for Colombia representing less than 0.14 %of the new species for those taxa in the planet; while new plant and vertebrate speciesdescribed for the country comprised between 1.2 and 10 % of the new species in thesegroups. Because Colombia is a megadiverse country, the discovery and description ofits unknown species would have a great effect at the global biodiversity knowledge.However, it is necessary more support for taxonomic research and strengthening thetaxonomic work in some groups (e.g., Insecta). Source

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. Source

Galano A.,Metropolitan Autonomous University | Martinez A.,National Autonomous University of Mexico
Journal of Physical Chemistry B | Year: 2012

The free radical scavenging activity of capsaicin (CAP), which is the pungent component of hot chili peppers, has been studied in aqueous and lipid solutions, using the density functional theory. Different mechanisms of reaction have been considered: single electron transfer (SET), hydrogen transfer (HT), and radical adduct formation (RAF). Rate constants and branching ratios of the different channels of reaction are provided, as well as an interpretation of the UV-vis spectra. CAP is predicted to react faster in aqueous solution than in nonpolar media with oxygenated free radicals, and it was found to be a more efficient scavenger than melatonin and caffeine. It was also found that while SET does not contribute to the overall reactivity of CAP toward •OOH, •OOCH3, and •OCH3 radicals, it might be important for the reactions with more electrophilic radicals such as •OH, •OCCl3, and •OOCCl3. The main process, responsible for the peroxyl scavenging activity of CAP, was found to be the HT from the OH phenolic group. For the reaction with •OCH3, on the other hand, the HT from allylic sites are predicted to be the main channels of reaction. In this particular case a wider product distribution is predicted. This supports the role of the reacting free radical on the preponderant mechanism of action of free radical scavengers. © 2011 American Chemical Society. Source

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. Source

Baruteau C.,University of Cambridge | Ramirez-Ruiz E.,University of California at Santa Cruz | Masset F.,National Autonomous University of Mexico
Monthly Notices of the Royal Astronomical Society: Letters | Year: 2012

We present 2D hydrodynamical simulations of the tidal interaction between a supermassive black hole binary with moderate mass ratio and the fossil gas disc where it is embedded. Our study extends previous 1D height-integrated disc models, which predicted that the density of the gas disc between the primary and the secondary black holes should rise significantly during the ultimate stages of the binary's hardening driven by the gravitational radiation torque. This snowplough mechanism, as we call it, would lead to an increase in the bolometric luminosity of the system prior to the binary merger, which could be detected in conjunction with the gravitational wave signal. We argue here that the snowplough mechanism is unlikely to occur. In 2D, when the binary's hardening time-scale driven by gravitational radiation becomes shorter than the disc's viscous drift time-scale, fluid elements in the inner disc get funnelled to the outer disc through horseshoe trajectories with respect to the secondary. Mass leakage across the secondary's gap is thus found to be effective and, as a result, the predicted accretion disc luminosity will remain at roughly the same level prior to merger. © 2012 The Authors. Monthly Notices of the Royal Astronomical Society. © 2012 RAS. Source

Alduncin G.,National Autonomous University of Mexico
Nonlinear Analysis: Hybrid Systems | Year: 2011

Composition duality methods for dual quasistatic evolution elastoviscoplastic variational problems are studied. Dual evolution mixed analysis is performed, as well as corresponding primal static mixed analysis. For multi-constitutive modeling and parallel computing, macro-hybrid variational formulations are further considered at the continuous level. © 2010 Elsevier Ltd. Source

Flores-Morales A.,Technological Institute of Tlaxcala Plateau | Jimenez-Estrada M.,National Autonomous University of Mexico | Mora-Escobedo R.,Escuela Nacional de Ciencias Biologicas
Carbohydrate Polymers | Year: 2012

The nixtamalization, production and storage of tortillas in refrigeration cause several changes on the starch structure, resulting in an increased crystallinity and therefore a higher content of resistant starch. The IR analysis for resistant starch (RS) showed a band at 1047 cm-1 associated to the retrogradation process; this band was due to the weakening of the intermolecular H-bonds. These associated together to form ordered regions. The Raman analysis shows a characteristic band at 856 cm-1 corresponding to C-C skeletal modes of glucose of α-1,4 glycosidic linkage starches, and a band at 480 cm-1 attributed to skeletal vibrations of the pyranose ring in the glucose unit of starches. These changes may be related to the polymerization degree of the starch molecules, as well as to the retrogradation of amylose and amylopectin. The spectrum of 13C CP-MAS/NMR for RS3 supports the results obtained by IR and Raman. Lipidic and proteic groups were observed which may be in the form of complexes with amylose. One can proclaim that the existence of the salt form is induced and stabilized by the interactions dominating the V amylose structure in the solid state. © 2011 Elsevier Ltd. All Rights Reserved. Source

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. Source

Esquivel-Sirvent R.,National Autonomous University of Mexico | Schatz G.C.,Northwestern University
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2011

The Casimir-Lifshitz force is calculated between two inhomogeneous composite slabs, each made of a homogeneous matrix with spherical metallic inclusions. The effective dielectric function of the slabs is calculated using several effective medium approximations and we compare the resulting forces as a function of slab separation and filling fraction. We show that the choice of effective medium approximation is critical in making precise comparisons between theory and experiment. The role that the spectral representation of the effective medium plays in making a Wick rotation to the complex frequency axis is also discussed. © 2011 American Physical Society. Source

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. Source

Loa Zavala N.,National Autonomous University of Mexico
International Journal of Psychoanalysis | Year: 2010

The formal study of hysteria started with psychoanalysis, which opened paths to studying the unconscious. However, we have found no psychoanalytic or psychiatric studies in the literature reporting epidemics of hysteria in hundreds of adolescent girls affected for several months like the one we describe. This epidemic occurred in a religious boarding-school in a rural area of Mexico. Our study aimed to determine psychoanalytic and sociocultural elements contributing to explain a behavioural epidemic outbreak during which young girls were unable to walk normally and which led to a temporary cessation of routine activities at the boarding-school. Key informers were interviewed, including the first cases of affected adolescent girls and the nuns. Interviews included questions concerning informers' life history and their life at the boarding-school before and during the epidemic. We found that this boarding-school functioned as a large family affected by a psychotic episode which resulted from modes of communication of its members. This article describes the phenomenon and emphasizes perceived communication among members of the boarding-school and visitors at the time of the outbreak. Copyright © 2010 Institute of Psychoanalysis. Source

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. Source

Wijnands R.,University of Amsterdam | Degenaar N.,University of Michigan | Page D.,National Autonomous University of Mexico
Monthly Notices of the Royal Astronomical Society | Year: 2013

It is assumed that accreting neutron stars in low-mass X-ray binaries are heated due to the compression of the existing crust by the freshly accreted matter which gives rise to a variety of nuclear reactions in the crust. It has been shown that most of the energy is released deep in the crust by pycnonuclear reactions involving low-Z elements (the deep-crustal heating scenario). In this paper we discuss if neutron stars in the so-called very-faint X-ray transients (VFXTs; those transients have outburst peak 2-10 keV X-ray luminosities <1 × 1036 erg s-1) can be used to test this deep-crustal heatingmodel.We demonstrate that such systemswould indeed be very interesting objects to test the deep-crustal heating model with, but that the interpretation of the results might be challenging because of the large uncertainties in our estimates of the accretion rate history of those VFXTs, both the short-term (less than a few tens of thousands of years) and the one throughout their lifetime. The latter is particularly important because it can be so low that the neutron stars might not have accreted enough matter to become massive enough that enhanced core cooling processes become active. Therefore, they could be relatively warm compared to other systems for which such enhanced cooling processes have been inferred. However, the amount of matter can also not be too low because then the crust might not have been replaced significantly by accreted matter and thus a hybrid crust of partly accreted and partly original, albeit further compressed matter, might be present. This would inhibit the full range of pycnonuclear reactions to occur and therefore possibly decrease the amount of heat deposited in the crust. More detailed calculations of the heating and cooling properties of such hybrid crusts have to be performed to be conclusive. Furthermore, better understanding is needed about how a hybrid crust affects other properties such as the thermal conductivity. A potentially interesting way to observe the effects of a hybrid crust on the heating and cooling of an accreting neutron star is to observe the crust cooling of such a neutron star after a prolonged (years to decades) accretion episode and compare the results with similar studies performed for neutron stars with a fully accreted crust. We also show that some individual neutron-star low-mass X-ray binaries might have hybrid crusts as well as possibly many of the neutron stars in high-mass X-ray binaries. This has to be taken into account when studying the cooling properties of those systems when they are in quiescence. In addition, we show that the VFXTs are likely not the dominate transients that are associated with the brightest (~1033 erg s-1) low-luminosity X-ray sources in globular clusters as was previously hypothesized. © 2013 The Author. Published by Oxford University Press on behalf of the Royal Astronomical Society. Source

Garduno E.,National Autonomous University of Mexico | Herman G.T.,New York University
IEEE Transactions on Nuclear Science | Year: 2014

A reconstructed image in positron emission tomography (PET) should be such that its likelihood, assuming a Poisson model, is high given the observed detector readings. The expectation maximization (EM) methodology leads to an iterative algorithm, called ML-EM, that converges in the limit to an image that maximizes this likelihood. An undesirable property of the algorithm is that it produces images with irregular high amplitude patterns as the number of iterations increases. One approach to alleviate these high amplitude patterns is to use a stopping rule that terminates the process before the appearance of the undesirable high amplitude patterns; one recently-proposed stopping rule results in the method called MLEM-STOP. This paper takes a different approach by applying the recently developed superiorization methodology to ML-EM. Superiorization is an automated procedure for turning an iterative algorithm for producing images that satisfy a primary criterion (in our case that of having a high likelihood given the observed detector readings) into its superiorized version that will be as good as the original algorithm according to the primary criterion, but will in addition produce images that are also good according to a secondary criterion. The approach is demonstrated for two secondary criteria, one provided by an assumed Gaussian prior distribution and the other based on total variation minimization. It is demonstrated that the superiorization methodology achieves its aim for both these criteria. It is further shown by a study, using statistical hypothesis testing on simulated collection of PET data from the human head, that for either secondary criterion the superiorized version of ML-EM outperforms MLEM-STOP for the task of estimating activity within neuroanatomical structures. © 2013 IEEE. Source

Guevara N.L.,Kansas State University | Turbiner A.V.,National Autonomous University of Mexico
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2011

In nonrelativistic quantum mechanics we study the Coulomb systems of infinitely massive center of charge Z and two-three electrons: (Z,e,e) and (Z,e,e,e). It is shown that in both cases the total energy curve in Z is smooth, without any visible irregularities. Thus, for both systems the physical integer charges Z=1,2,... do not play a distinguished role as would be associated with charge quantization. By definition, a critical charge Z cr is a charge which separates a domain of the existence of bound states from a domain of unbound ones (continuum). For both systems the critical charges are found, Z cr,2e=0.910850 and Z cr,3e=2.0090, respectively. Based on numerical analysis, the Puiseux expansion in fractional powers of (Z-Z cr) is constructed for both systems. Our results indicate the existence of a square-root branch point singularity at Z cr with exponent 3/2. A connection between the critical charge and the radius of convergence of 1/Z expansion is briefly discussed. © 2011 American Physical Society. Source

Garcia-Calderon G.,National Autonomous University of Mexico
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2011

An analytical solution for the time evolution of decay of two identical noninteracting quantum particles seated initially within a potential of finite range is derived using the formalism of resonant states. It is shown that the wave function, and hence also the survival and nonescape probabilities, for factorized symmetric and entangled symmetric or antisymmetric initial states evolve in a distinctive form along the exponentially decaying and nonexponential regimes. Our findings show the influence of the Pauli exclusion principle on decay. We exemplify our results by solving exactly the s-wave δ shell potential model. © 2011 American Physical Society. Source

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. Source

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. Source

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. Source

Nilles H.P.,University of Bonn | Ramos-Sanchez S.,National Autonomous University of Mexico | Ratz M.,TU Munich | Vaudrevange P.K.S.,German Electron Synchrotron
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2013

We re-derive the R symmetries for the Z6-II orbifold with non-trivial Wilson lines and find expressions for the R charges which differ from those in the literature. © 2013 Elsevier B.V. Source

Esposito M.,National Autonomous University of Mexico
Theory in Biosciences | Year: 2013

In 1930, while R.A. Fisher, J.B.S. Haldane, E.B. Ford and S.G. Wright were laying the foundations of what a decade later J.S. Huxley dubbed "Modern Synthesis", E.S. Russell published a groundbreaking work, The Interpretation of Development and Heredity. In this book Russell not only condemned Mendelian genetics and neo-Darwinism, but also proposed an alternative synthesis unifying heredity, development, and evolution. The book did not represent the work of a mind operating in isolation. Rather, it was a synthetic work connecting ideas and doctrines of many influential scientists working in Europe and the USA. Through the analysis of archival documents and rarely or never mentioned sources, this article provides an unconventional picture of Russell's theoretical biology. It will be shown that Russell was an international celebrity; he was at the centre of a large network of scholars who shared his ideas and insights. He was one of several biologists arguing for a different synthesis; a synthesis perhaps less visible, less institutionalised, and less 'modern', nevertheless with its influential advocates and international support. Finally, this study shows that Russell's synthesis was not rooted in the classic pantheon of towering figures in the history of biology, i.e. Darwin, Wallace, and Mendel, but was based on the teachings of Kant, Goethe, Cuvier, von Baer, and Müller. © 2013 Springer-Verlag Berlin Heidelberg. Source

Morales I.O.,French Atomic Energy Commission | Frank A.,National Autonomous University of Mexico
Physical Review C - Nuclear Physics | Year: 2011

We describe a procedure to improve the nuclear mass predictions obtained by means of the Garvey-Kelson iterative process. This is achieved by reducing the degrees of freedom involved in the process, expressing the Garvey-Kelson relations in terms of one-neutron and one-proton separation energies, and using a theoretical estimation for them. This approach has the effect that the intrinsic error associated with the iterative process grows significantly more slowly. This leads to a better quality of nuclear mass predictions and therefore extends the range for which the predictions are accurate. We test these ideas using different mass models. © 2011 American Physical Society. Source

Garcia C.M.,National Autonomous University of Mexico
Proceedings. Biological sciences / The Royal Society | Year: 2012

Male ornaments can evolve through the exploitation of female perceptual biases such as those involved in responding to cues from food. This type of sensory exploitation may lead to confusion between the male signals and the cues that females use to find/recognize food. Such interference would be costly to females and may be one reason why females evolve resistance to the male ornaments. Using a group of species of viviparous fish where resistance to a sensory trap has evolved, we demonstrate that females exposed to an ornament that resembles food have a diminished foraging efficiency, that this effect is apparent when foraging on a food item with which the ornament shares visual attributes, and that not all species are equally affected by such confusion. Our results lend support to the model of ornamental evolution through chase-away sexual conflict. Source

Rendon-Huerta E.P.,National Autonomous University of Mexico
Annals of hepatology | Year: 2013

Hepatitis C virus (HCV) infection usually results in long-term viremia. Entry of HCV into the hepatocyte requires claudin-1, -6, -9 and occludin. The efficacy of Pegylated interferon-α (PEG-IFN) treatment against HCV infection increased when ribavirin (RBV) was added to the therapeutic scheme. Our aim was to investigate if PEG-IFN plus RBV regulate claudin expression. HepG2, Huh-7 and Huh-7.5 cells were treated with PEG-IFN-α2a or α2b and/or RBV at different times before obtaining the cytosolic, membrane and cytoskeletal fractions. Claudin-1, 3, 4, 6, and 9, E-cadherin and occludin expression was evaluated by Western blot analysis. Transepithelial electrical resistance (TER) was also determined. Claudin-1, 3, 4, 6, E-cadherin and occludin are constitutively expressed mainly in HepG2 cell membrane. Claudin-1 and E-cadherin cell membrane expression diminished after exposure to PEGIFNα2b (50 ng) + RBV(50 μg); the maximal decrease was observed with 200 ng of PEG-IFNα2b + 200 μg of RBV. The effect was less intense with PEG-IFNα2a. The inhibition of claudin-1 and E-cadherin expression in Huh-7 and Huh-7.5 cells was only observed with 200 ng of PEG-IFNα2b + 200 μg of RBV. TER diminished marginally in the HCV containing hepatoma cells with 200 ng of PEG-IFNα2b + 200 μg of RBV. Claudin-1 mRNA expression level was not affected by the combined treatment. The increased therapeutic efficacy of the PEG-IFNα2b plus RBV treatment could be secondary to the inhibition of claudin-1 and E-cadherin cell membrane expression. Source

Bello M.,National Polytechnic Institute of Mexico | Garcia-Hernandez E.,National Autonomous University of Mexico
Biopolymers | Year: 2014

Although the thermodynamic principles that control the binding of drug molecules to their protein targets are well understood, the detailed process of how a ligand reaches a protein binding site has been an intriguing question over decades. The short time interval between the encounter between a ligand and its receptor to the formation of the stable complex has prevented experimental observations. Bovine β-lactoglobulin (βlg) is a lipocalin member that carries fatty acids (FAs) and other lipids in the cellular environment. Βlg accommodates a FA molecule in its highly hydrophobic cavity and exhibits the capability of recognizing a wide variety of hydrophobic ligands. To elucidate the ligand entry process on βlg, we report molecular dynamics simulations of the encounter between palmitate (PA) or laurate (LA) and βlg. Our results show that residues localized in loops at the cavity entrance play an important role in the ligand penetration process. Analysis of the short-term interaction energies show that the forces operating on the systems lead to average conformations very close to the crystallographic holo-forms. Whereas the binding free energy analysis using the molecular mechanics Generalized Born surface area method shows that these conformations were thermodynamically favorable. © 2013 Wiley Periodicals, Inc. Source

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. Source

Avendano-Alejo M.,National Autonomous University of Mexico
Journal of the Optical Society of America A: Optics and Image Science, and Vision | Year: 2013

We study the formation of caustic surfaces formed in both convex-plano and plano-convex aspheric lenses by considering a plane wave incident on the lens along the optical axis. Using the caustic formulas and a paraxial approximation we derive expressions to evaluate the spherical aberration at third-order and also provide a formula to reduce it, where the first-order aspheric term is given in a simply analytic equation. Furthermore, we redefine the method to evaluate the circle of least confusion for a positive lens as a function of all parameters involved in the process of refraction through the aspheric lenses. © 2013 Optical Society of America. Source

Esquivel A.,National Autonomous University of Mexico | Lazarian A.,University of Wisconsin - Madison
Astrophysical Journal | Year: 2011

We use a set of magnetohydrodynamic simulations of fully developed (driven) turbulence to study the anisotropy in the velocity field that is induced by the presence of the magnetic field. In our models, we study turbulence characterized by sonic Mach numbers Ms from 0.7 to 7.5 and Alfvén Mach numbers from 0.4 to 7.7. These are used to produce synthetic observations (centroid maps) that are then analyzed. To study the effect of large-scale density fluctuations and of white noise, we have modified the density fields and obtained new centroid maps, which are analyzed. We show that restricting the range of scales at which the anisotropy is measured makes the method robust against such fluctuations. We show that the anisotropy in the structure function of the maps reveals the direction of the magnetic field for MA ≲ 1.5, regardless of the sonic Mach number. We find that the degree of anisotropy can be used to determine the degree of magnetization (i.e., MA ) for MA ≲ 1.5. To do this, one needs an additional measure of the sonic Mach number and an estimate of the line of sight magnetic field, both feasible by other techniques, offering a new opportunity to study the magnetization state of the interstellar medium. © 2011. The American Astronomical Society. All rights reserved. Source

Loske A.M.,National Autonomous University of Mexico
Ultrasonics | Year: 2010

Today a high percentage of urinary stones are successfully treated by extracorporeal shockwave lithotripsy (SWL); however, misconceptions regarding fragmentation mechanisms, as well as treatment parameters like dose, applied energy and focal area are still common. A main stone comminution mechanism during SWL is acoustic cavitation. The objective of this study was to analyze the influence of cavitation and energy density on stone fragmentation. A research lithotripter was used to expose a large set of artificial kidney stones to shock waves varying different parameters. Hundreds of pressure records were used to calculate the energy density of the lithotripter at different settings. Results indicate that energy density is a crucial parameter and that better SWL treatment outcomes could be obtained placing the calculus at a prefocal position. © 2009 Elsevier B.V. All rights reserved. Source

Fridman L.,National Autonomous University of Mexico | Davila J.,National Polytechnic Institute of Mexico | Levant A.,Tel Aviv University
Nonlinear Analysis: Hybrid Systems | Year: 2011

A high-order sliding-mode observer is designed for linear systems with unknown inputs. The concepts of strong observability and strong detectability are studied and their relation with the relative degree of a plant is established. High-order sliding-mode-based observers for linear time-invariant systems with unknown inputs satisfying the condition of strong observability or strong detectability are developed. © 2010 Elsevier Ltd. Source

Tobin J.J.,University of Michigan | Hartmann L.,University of Michigan | Loinard L.,National Autonomous University of Mexico
Astrophysical Journal Letters | Year: 2010

We present high-resolution L′-band imaging of the inner scattered light structure of Class 0 protostar L1527 IRS (IRAS 04368+2557) taken with the Gemini North telescope. The central point-source-like feature seen in Spitzer Space Telescope IRAC images is resolved in the Gemini image into a compact bipolar structure with a narrow dark lane in the center. Two scattered light lobes are extended ∼1. ″8 (200 AU) perpendicular to the direction of the outflow and ∼2.″5 (350 AU) along the outflow axis; the narrow dark lane between the scattered light lobes is ∼0. ∼0.″45 (60 AU) thick. The observations are consistent with our initial modeling of a bright inner cavity separated by a dark lane due to extinction along the line of sight of the central protostar by the disk. The bright, compact scattered light might be due to complex inner structure generated by the outflow, as suggested in our first paper, or it may more likely be the upper layers of the disk forming from infalling matter. © 2010 The American Astronomical Society. All rights reserved. Source

Arita H.T.,National Autonomous University of Mexico | Christen A.,Research Center en Matematicas | Rodriguez P.,Comision Nacional para el Conocimiento y Uso de la Biodiversidad | Soberon J.,University of Kansas
Global Ecology and Biogeography | Year: 2012

Aim A great deal of information on distribution and diversity can be extracted from presence-absence matrices (PAMs), the basic analytical tool of many biogeographic studies. This paper presents numerical procedures that allow the analysis of such information by taking advantage of mathematical relationships within PAMs. In particular, we show how range-diversity (RD) plots summarize much of the information contained in the matrices by the simultaneous depiction of data on distribution and diversity. Innovation We use matrix algebra to extract and process data from PAMs. Information on the distribution of species and on species richness of sites is computed using the traditional R (by rows) and Q (by columns) procedures, as well as the new Rq (by rows, considering the structure of columns) and Qr (by columns, considering the structure by rows) methods. Matrix notation is particularly suitable for summarizing complex calculations using PAMs, and the associated algebra allows the implementation of efficient computational programs. We show how information on distribution and species richness can be depicted simultaneously in RD plots, allowing a direct examination of the relationship between those two aspects of diversity. We explore the properties of RD plots with a simple example, and use null models to show that while parameters of central tendency are not affected by randomization, the dispersion of points in RD plots does change, showing the significance of patterns of co-occurrence of species and of similarity among sites. Main conclusion Species richness and range size are both valid measures of diversity that can be analysed simultaneously with RD plots. A full analysis of a system requires measures of central tendency and dispersion for both distribution and species richness. © 2011 Blackwell Publishing Ltd. Source

Limon-Pacheco J.H.,National Autonomous University of Mexico
Central nervous system agents in medicinal chemistry | Year: 2010

The glutathione system includes reduced (GSH) and oxidized (GSSG) forms of glutathione; the enzymes required for its synthesis and recycling, such as gamma-glutamate cysteine ligase (γ-GCL), glutathione synthetase (GS), glutathione reductase (GSR) and gamma glutamyl transpeptidase (γ-GGT); and the enzymes required for its use in metabolism and in mechanisms of defense against free radical-induced oxidative damage, such as glutathione s-transferases (GSTs) and glutathione peroxidases (GPxs). Glutathione functions in the central nervous system (CNS) include maintenance of neurotransmitters, membrane protection, detoxification, metabolic regulation, and modulation of signal transduction. A common pathological hallmark in various neurodegenerative disorders, such as amyotrophic lateral sclerosis and Alzheimer's and Parkinson's diseases is the increase in oxidative stress and the failure of antioxidant systems, such as the decrease in the GSH content. The administration of exogenous neurohormone melatonin at pharmacological doses has been shown not only to be an effective scavenger of reactive oxygen and nitrogen species but also to enhance the levels of GSH and the expression and activities of the GSH-related enzymes including γ-GCL, GPxs, and GSR. The exact mechanisms by which melatonin regulates the glutathione system are not fully understood. The main purpose of this short review is to discuss evidence relating to the potential common modulation signals between the glutathione system and melatonin in the CNS. The potential regulatory mechanisms and interactions between neurons and non-neuronal cells are also discussed. Source

Liew T.C.H.,Nanyang Technological University | Rubo Y.G.,National Autonomous University of Mexico | Kavokin A.V.,University of Southampton
Physical Review B - Condensed Matter and Materials Physics | Year: 2014

We introduce and model spin-Rabi oscillations based on exciton-polaritons in semiconductor microcavities. The phase and polarization of oscillations can be controlled by resonant coherent pulses and the propagation of oscillating domains gives rise to phase-dependent interference patterns in real space. We show that interbranch polariton-polariton scattering controls the propagation of oscillating domains, which can be used to realize logic gates based on an analog variable phase. © 2014 American Physical Society. Source

Paredes R.G.,National Autonomous University of Mexico
Vitamins and hormones | Year: 2010

There are different physiological processes that influence behavior. One of this processes that produces approach behavior to a stimuli that induces a positive affective (PA) state, commonly known as reward, plays an important role in modulating behavior. There is an extensive literature in which the rewarding effects of drugs have been investigated. Less research has been devoted to the study of naturally occurring behaviors that produce a PA or reward state. Hormones modulate different behaviors, including sex. However, little attention has been devoted to study the possible role of hormones in reward states. One of the methods most frequently used to study reward or PA states is the conditioned place preference (CPP) paradigm. Hopefully this review will encourage researchers to directly address the effects of hormones on reward, research that is much needed. Copyright 2010 Elsevier Inc. All rights reserved. Source

Vaca L.,National Autonomous University of Mexico
Cell Calcium | Year: 2010

Depletion of intracellular calcium stores via activation of G-protein-coupled receptors associated to the inositol trisphosphate cascade, or by the blockade of the endoplasmic reticulum calcium APTase (SERCA) results in the activation of calcium influx via the so-called store-operated channels (SOCs). The recent identification of STIM1 as the putative sensing molecule responsible for communicating the depleted state of intracellular calcium stores to the plasma membrane channel highlights the relevance of protein complexes in calcium signaling. Further developments in this area identify Orai as part of the store-operated channel complex. Upon depletion of intracellular calcium stores, STIM1 (at the ER) and Orai (at the plasma membrane) aggregate into macromolecular complexes. This molecular aggregation appears to be necessary to induce activation of calcium influx. Several studies have identified novel members from what I would like to define here as the store-operated calcium influx complex (SOCIC), such as the TRPC1 channel, SERCA and the microtubule end tracking protein, EB1. An orchestrated series of events involving the association and dissociation of several protein complexes culminate with the activation of calcium influx upon depletion of the ER. There are other likely players in this sophisticated signaling mechanism, waiting to be uncovered. The SOCIC assembly does not appear to occur in random areas of the plasma membrane, but rather in highly specialized areas known as lipid raft domains. These results strongly suggest that not only proteins but lipids also may be part or active players in the modulation of the store-operated calcium entry (SOCE). In this review we will analyze the evidence supporting macromolecular complex assembly as a prerequisite for SOC activation. We will highlight the evidence showing novel members from SOCIC and speculate about possible yet undiscovered members and players in this highly regulated calcium signaling mechanism. Finally we will discuss about the role of lipid raft domains in controlling store- and agonist-activated calcium influx. © 2010 Elsevier Ltd. All rights reserved. Source

Yatsimirsky A.K.,National Autonomous University of Mexico
Natural Product Communications | Year: 2012

Binding of alkaloids by different hosts (native and modified cyclodextrins, cucurbiturils, calixarenes, and metal complexes of porphyrin and Salphen-type ligands), as well as receptor properties of alkaloid based hosts are reviewed. With alkaloids as guests, the largest binding constants and most significant spectral changes, in particular strong fluorescence enhancements induced by complexation with isoquinoline alkaloids, are observed with cucurbituril hosts. Cyclodextrins are successfully employed for improvement of solubility and for chiral separation of alkaloids of different types. Receptor properties of native and modified cinchona and bisbenzylisoquinoline alkaloids have attracted considerable attention for development of chiral selectors for analysis and separation. Source

Corichi A.,National Autonomous University of Mexico | Sloan D.,University of Cambridge
Classical and Quantum Gravity | Year: 2014

Several recent misconceptions about the measure problem in inflation and the nature of inflationary attractors are addressed. We clarify some issues regarding the Hamiltonian dynamics of a flat Friedmann-Lemaître-Robertson- Walker cosmology coupled to a massive scalar field. In particular we show that the focusing of the Liouville measure on attractor solutions is recovered by properly dealing with a gauge degree of freedom related to the rescaling of the spatial volume. Furthermore, we show how the Liouville measure formulated on a surface of constant Hubble rate, together with the assumption of constant a priory probability, induces a non-uniform probability distribution function on any other surfaces of other Hubble rates. The attractor behaviour is seen through the focusing of this function on a narrow range of physical observables. This qualitative behaviour is robust under change of potential and underlying measure. One can then conclude that standard techniques from Hamiltonian dynamics suffice to provide a satisfactory description of attractor solutions and the measure problem for inflationary dynamics. © 2014 IOP Publishing Ltd. Source

Boege K.,National Autonomous University of Mexico
Ecology | Year: 2010

Herbivory and competition are two of the most common biotic stressors for plants. When occurring simultaneously, responses to one interaction can constrain the induction of responses to the other interaction due to resource limitation and other interactive effects. Thus, to maximize fitness when interacting with competitors and herbivores, plants are likely to express particular combinations of plastic responses. This study reports the interactive effects of herbivory and competition on responses induced in Tithonia tubaeformis plants and describes how natural selection acts on particular plastic responses and on their different combinations. Competition induced a stem elongation response, expressed through an increase in height and mean internode length, together with a decrease in basal diameter. Interestingly, realized, resistance increased in both competition and herbivory treatments, suggesting a plastic response in both constitutive and induced resistance traits. Particular combinations of plastic responses defined three plant phenotypes: vigorous, elongated, and resistant plants. The ecological context in which plants grew modified the traits and the particular combinations of plastic responses that were favored by selection. Vigorous plants were favored by selection in all environments, except when they were damaged by herbivores in the absence of neighbors. The combination of responses defining an elongated plant phenotype was favored by selection in crowded conditions. Resistance was negatively selected in the absence of competition and herbivory but favored in the presence of both interactions. In addition, contextual analyses detected that population structure in heterogeneous environments can also influence the outcomes of selection. These findings suggest that natural selection can act on particular combinations of plastic responses, which may allow plants to adjust their phenotypes to those that promote greater fitness under particular ecological conditions. © 2010 by the Ecological society of America. Source

Bruni M.,University of Portsmouth | Hidalgo J.C.,University of Portsmouth | Hidalgo J.C.,National Autonomous University of Mexico | Wands D.,University of Portsmouth
Astrophysical Journal Letters | Year: 2014

We show how the nonlinearity of general relativity generates a characteristic nonGaussian signal in cosmological large-scale structure that we calculate at all perturbative orders in a large-scale limit. Newtonian gravity and general relativity provide complementary theoretical frameworks for modeling large-scale structure in ΛCDM cosmology; a relativistic approach is essential to determine initial conditions, which can then be used in Newtonian simulations studying the nonlinear evolution of the matter density. Most inflationary models in the very early universe predict an almost Gaussian distribution for the primordial metric perturbation, ζ. However, we argue that it is the Ricci curvature of comoving-orthogonal spatial hypersurfaces, R, that drives structure formation at large scales. We show how the nonlinear relation between the spatial curvature, R, and the metric perturbation, ζ, translates into a specific nonGaussian contribution to the initial comoving matter density that we calculate for the simple case of an initially Gaussian ζ. Our analysis shows the nonlinear signature of Einstein's gravity in large-scale structure. © 2014. The American Astronomical Society. All rights reserved. Source

Briscese F.,National Autonomous University of Mexico
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2011

We study the viability of a complex scalar field χ with self-interacting potential V=m0 χ/2|χ|2+h|χ|4 as dark matter. The scalar field is produced at reheating through the decay of the inflaton field and then, due to the self-interaction, a Bose-Einstein condensate of χ particles forms. The condensate represents dark matter in that model. We analyze the cosmological evolution of the model, stressing how, due to the presence of the self-interaction, the model naturally admits dark matter domination at late times, thus avoiding any fine tuning on the energy density of the scalar field at early times. Finally we give a lower bound for the size of dark matter halos at present time and we show that our model is compatible with dark matter halos greater than 0.1 kpc and with BBN and CMB bounds on the effective number of extra neutrinos Δν eff. Therefore, the model is viable and for hb≃10-4-10-12 one obtains a mass mχb≃m0χb≃1-10-2 eV for dark matter particles from radiation-matter equality epoch to present time, but at temperatures Tγ≫10 eV, where Tγ is the photons temperature, thermal corrections to m0 χ due to the self-coupling h are dominant. © 2011 Elsevier B.V. Source

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. Source

Hacyan S.,National Autonomous University of Mexico
Annals of Physics | Year: 2011

The algebraic structures of a general electromagnetic field and its energy-momentum tensor in a stationary space-time are analyzed. The explicit form of the reference frame in which the energy of the field appears at rest is obtained in terms of the eigenvectors of the electromagnetic tensor and the existing Killing vector. The case of a stationary electromagnetic field is also studied and a comparison is made with the standard short-wave approximation. The results can be applied to the general case of a structured light beams, in flat or curved spaces. Bessel beams are worked out as example. © 2011 Elsevier Inc. Source

Rodriguez M. M.A.,Institute Ecologia | Rodriguez M. M.A.,Grupo Mexico | Herrera M. L.G.,National Autonomous University of Mexico
Oecologia | Year: 2013

Caution for the indiscriminate conversion of the isotopic niche into ecologic niche was recently advised. We tested the utility of the isotopic niche to answer ecological questions on oceanic islands. We compared the isotopic niches of black rats (Rattus rattus) on two islands in the Gulf of California, Mexico: Farrallón de San Ignacio (FSI) and San Pedro Mártir (SPM). Both islands maintained several species of marine birds, but FSI is devoid of terrestrial vegetation and SPM has several species of terrestrial plants. We tested the hypothesis that rats on FSI have a narrower trophic niche due to its lower diversity of food items. We predicted a smaller variance in δ13C and δ15N values of rat muscle on FSI, and a lower use of marine birds as food on SPM. We also examined stomach contents of rats on both islands to validate the isotopic information. Variances in δ13C and δ15N values of black rats were lower on FSI, and the contribution of marine birds to the diet of rats was smaller on SPM. Stomachs in most rats collected on FSI contained only one or two types of food items, mostly marine birds and terrestrial invertebrates. In contrast, stomachs with only one type of food item were rare on SPM, and in most cases they contained three or more food types. Our findings showed that isotopic variance is a good approximation for trophic niche when comparing populations with access to an assemblage of preys with contrasting biological and isotopic diversity. © 2012 Springer-Verlag. Source

Jalbout A.F.,National Autonomous University of Mexico
International Journal of Modern Physics B | Year: 2011

The present study is geared towards investigating methods to increase the tendency of fullerene structures to aggregate with biological systems. To accomplish this task, the encapsulation of metals inside a fullerene structure was performed. The calculations performed demonstrate that the Ca@C 60 structure leads to stronger interactions with amino acids at the DFT-BLYP/DND level of theory. Correlations of the dissociation energies, HOMO/LUMO band gaps and hardness are discussed. © 2011 World Scientific Publishing Company. Source

Sussman R.A.,National Autonomous University of Mexico
Classical and Quantum Gravity | Year: 2011

We provide a thorough examination of the conditions for the existence of back-reaction and an effective acceleration (in the context of Bucherts averaging formalism) in regular generic spherically symmetric LematreTolmanBondi (LTB) dust models. By considering arbitrary spherical comoving domains,we verify rigorously the fulfillment of these conditions expressed in terms of suitable scalar variables that are evaluated at the boundary of every domain. Effective deceleration necessarily occurs in all domains in (a) the asymptotic radial range of models converging to a FLRW background (b) the asymptotic time range of non-vacuum hyperbolic models (c) LTB self-similar solutions and (d) near a simultaneous big bang. Accelerating domains are proven to exist in the following scenarios: (i) central vacuum regions(ii) central (non-vacuum) density voids (iii) the intermediate radial range of models converging to a FLRW background (iv) the asymptotic radial range of models converging to a Minkowski vacuum and (v) domains near and or intersecting a non-simultaneous big bang. All these scenarios occur in hyperbolic models with negative averaged and local spatial curvature though scenarios (iv) and (v) are also possible in low density regions of a class of elliptic models in which the local spatial curvature is negative but its average is positive. Rough numerical estimates between 0.003 and 0.5 were found for the effective deceleration parameter. While the existence of accelerating domains cannot be ruled out in models converging to an Einsteinde Sitter background and in domains undergoing gravitational collapse the conditions for this are very restrictive. The results obtained may provide important theoretical clues on the effects of back-reaction and averaging in more general non-spherical models. Communicated by L Andersson © 2011 IOP Publishing Ltd. Source

Mwampamba T.H.,National Autonomous University of Mexico | Schwartz M.W.,University of California at Davis
Forest Ecology and Management | Year: 2011

Using fallows under shifting cultivation systems as a case study, we examined the effects of landuse history (cultivation duration and cropping strategies) on rate and extent of forest recovery. Cultivation duration and five cropping strategies were investigated post facto, indirectly, and with regards to their effect on the structure (basal area, BA and stand complexity, CHCI) and diversity (Fisher's α) of forests in fallows. Data were generated from vegetation surveys conducted in the Nguru Mountain block of the Eastern Arc Mountains, Tanzania. The surveys were conducted in primary forests, ongoing farms, and fallows that had been out of production for 1-31 years (N=109, plot size=0.1ha). Recovery patterns between lowland (300-800m) and submontane (800-1600m) elevations varied substantially. BA and CHCI recovery levels were consistently higher in submontane fallows. None of the fallows had attained BA and CHCI levels equivalent to those of primary forests; α in lowland fallows, however, was 124% of primary forest levels. Forest recovery was limited to fallows whose cultivation period was ≤16 years. Recovery was fastest and highest in fallows located within a dense primary/old growth forest matrix. The findings provide a more thorough understanding of how local farming practices affect forest recovery. Improving the recovery outcomes of fallows that are located outside the old growth forest matrix will require (a) more strategic inclusion of remnant trees, (b) drastically shorter cultivation periods, and (c) human intervention through assisted regeneration. © 2010 Elsevier B.V. Source

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. Source

Suarez-Diaz E.,National Autonomous University of Mexico
Studies in History and Philosophy of Science Part C :Studies in History and Philosophy of Biological and Biomedical Sciences | Year: 2014

Ruben Lisker's research on the genetic hematological traits of Mexican indigenous populations illustrates the intersection of international health policies and the local modernizing nationalism of the Mexican post-revolution period. Lisker's surveys of blood group types, and of G6PD (glucose-6-phosphodehydrogenase) and hemoglobin variants in indigenous populations, incorporated linguistic criteria in the sampling methods, and historical and cultural anthropological accounts in the interpretation of results. In doing so, Lisker heavily relied on the discourse and the infrastructure created by the indigenista program and its institutions. Simultaneously, Lisker's research was thoroughly supported by international and bilateral agencies and programs, including the malaria eradication campaign of the 1950s and 1960s. As a member of the scientific elite he was able to make original contributions to the postwar field of human population genetics. His systematic research illustrates the complex entanglement of local and international contexts that explains the co-construction of global knowledge on human variation after WWII.11James V. © 2014 Elsevier Ltd. Source

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. Source

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. Source

Schmulson M.,National Autonomous University of Mexico | Chey W.D.,University of Michigan
American Journal of Gastroenterology | Year: 2012

Evidences suggest that there is low-grade inflammation in the colonic mucosa and/or a state of immune activation in patients with irritable bowel syndrome (IBS). Results from available studies are inconsistent mainly because of differences in measures, methodologies and study populations. In this issue, Chang et al. evaluated a comprehensive set of cytokines, immune markers and immune-related cells in patients with non post infectious IBS (non PI-IBS) and controls. The main finding was a lower expression of the mRNA of the anti-inflammatory IL-10 cytokine in the colonic mucosa of women with non PI-IBS without any differences in the cell counts. These results suggest that in non PI-IBS, there is altered immune regulation/activation without evidence of low-grade mucosal inflammation. Further, PI and non PI-IBS may be associated with different alterations in immune function/activation. © 2012 by the American College of Gastroenterology. Source

Lazcano A.,National Autonomous University of Mexico
PLoS ONE | Year: 2011

The discussion on the existence of prokaryotic species is reviewed. The demonstration that several different mechanisms of genetic exchange and recombination exist has led some to a radical rejection of the possibility of bacterial species and, in general, the applicability of traditional classification categories to the prokaryotic domains. However, in spite of intense gene traffic, prokaryotic groups are not continuously variable but form discrete clusters of phenotypically coherent, well-defined, diagnosable groups of individual organisms. Molecularization of life sciences has led to biased approaches to the issue of the origins of biodiversity, which has resulted in the increasingly extended tendency to emphasize genes and sequences and not give proper attention to organismal biology. As argued here, molecular and organismal approaches that should be seen as complementary and not opposed views of biology. © 2011 Antonio Lazcano. Source

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. Source

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. Source

Bruce N.C.,National Autonomous University of Mexico
Waves in Random and Complex Media | Year: 2013

A recently developed numerical method is used to calculate the single- and double-scattered Mueller matrices for scattering of vector-electromagnetic waves from rough surfaces. Calculations are performed for the case of a single groove and a single rib on a silicon surface and results are compared to the published experimental results. The calculated results show good agreement with the experimental results for the groove case and poorer agreement with the rib case, probably due to errors in the experimental construction of the rib. It is found that, for the cases studied here, variations of the sign with scatter angle in individual Mueller matrix elements are associated with the presence of double- (or multiple-)scattered light, as has been found previously for scalar diffraction calculations in Gaussian randomly rough surfaces. © 2013 Copyright Taylor and Francis Group, LLC. Source

Hahn F.,National Autonomous University of Mexico
Computers and Electronics in Agriculture | Year: 2011

Sunlight heats the greenhouse air temperature during the day and can encourage tomato cracking and decrease marketable product. A fuzzy controller was designed to control greenhouse climate to reduce tomato cracking using as variables solar radiation, substrate temperature and canopy temperature. A movable shade screen reduced incoming radiation during warm and sunny conditions; meanwhile irrigation was controlled according to canopy and substrate temperature. The shade screen was opened or closed with a gear motor driven by a photovoltaic system. The motor controlled by a pulse width modulated inverter started softly decreasing its starting current. The fuzzy system injected additional water and nutrients between 12:00 and 15:00. h; irrigation cycles were removed during very cloudy days. Tomato cracking decreased from 52% to 17% using the fuzzy controller and canopy temperature never exceeded 30. °C. © 2011 Elsevier B.V. Source

Wolf K.B.,National Autonomous University of Mexico
Journal of Physics A: Mathematical and Theoretical | Year: 2013

The Euclidean group contains two models of free Hamiltonian evolution: one has a continuous configuration space in which the wavefunctions obey the Helmholtz equation, and require two initial conditions: initial values and initial velocities; the other is based on a discrete position space where the wavefunctions obey a difference equation, and its evolution requires only initial values. Yet the two models are unitarily equivalent. We find that the two initial conditions of the former correspond, according to their parity, with the initial condition of the latter at alternate points, either even or odd. © 2013 IOP Publishing Ltd. Source

Blanchon P.,National Autonomous University of Mexico
Coral Reefs | Year: 2010

The elevation of reefs and coastal deposits during the last Interglaciation (MIS-5e) indicates that sea level reached a highstand of as much as 6 m above the present, but it is uncertain how rapidly this level was attained and how it impacted reef development. To investigate this problem, I made a detailed sedimentological analysis of a well-dated reef from the northeast coast of the stable Yucatan Peninsula. Two linear reef tracts were delineated which are offset and at different elevations. The lower reef tract crops out along northern shore for 575 m and extends from below present mean sea level to +3 m. The reef crest facies consists of large Acropora palmata colonies dispersed within a coral boulder-gravel and is flanked by an A. cervicornis-dominated reef-front and a large area of lagoonal framework formed by coalesced patches of A. cervicornis and Montastraea spp. Constituents in the upper centimetre of the lower tract are heavily encrusted by a cap of crustose corallines and, in places, are levelled by a discontinuous marine-erosion surface. The upper reef tract crops out ~150 m inland up to an elevation of +5.8 m and parallels the southern section of shore for ~400 m. It also consist of an A. palmata-dominated crest facies flanked by reef-front, back-reef and lagoonal frameworks. In this case, however, lagoonal frameworks are dominated by a sediment-tolerant assemblage of branching coralline algae. Also different is the lack of encrustation by corallines, and the infiltration of upper tract facies by beach-derived shell-gravels from regressive shoreface deposits above. These results indicate that the lower reef tract and lagoonal patch-reefs formed at a sea level of +3 m. Final capping by crustose corallines and discontinuous marine erosion indicates that the lower tract was terminated by the complete demise of corals on the crest but only patchy demise in the lagoon. Areas of continuous framework accretion between the lagoonal patch reefs and the upper reef-tract, however, require that the demise of this reef was ecologically synchronous with initiation of the upper reef-tract, which had back-stepped 100 m into the lagoon. In this new position, the upper tract developed a reef crest that corresponded to a final sea-level position of +6 m. Reef flat development at +5 m and large in-place colonies of A. palmata at the base of the crest unit indicate, however, that sea level must have risen rapidly from +3 to more than +5 m to accommodate back-stepping. This sea-level jump created a higher energy wave field that mobilized back-reef and lagoonal sediments, and the resulting high sediment flux eroded lagoonal framework and prevented the recovery of the submerged lower reef crest. So this single jump in sea level was responsible not only for reef demise and back-stepping but also for marine erosion and suppression of subsequent reef development-features that elsewhere have been used to support multiple sea-level excursions during the last interglacial. © Springer-Verlag 2010. Source

Morrone J.J.,National Autonomous University of Mexico
Ecography | Year: 2010

Transition zones, located at the boundaries between biogeographic regions, represent events of biotic hybridization, promoted by historical and ecological changes. They deserve special attention, because they represent areas of intense biotic interaction. In its more general sense, the Mexican Transition Zone is a complex and varied area where Neotropical and Nearctic biotas overlap, from southwestern USA to Mexico and part of Central America, extending south to the Nicaraguan lowlands. In recent years, panbiogeographic analyses have led to restriction of the Mexican Transition Zone to the montane areas of Mexico and to recognize five smaller biotic components within it. A cladistic biogeographic analysis challenged the hypothesis that this transition zone is biogeographically divided along a north-south axis at the Transmexican Volcanic Belt, as the two major clades found divided Mexico in an east-west axis. This implies that early Tertiary geological events leading to the convergence of Neotropical and Nearctic elements may be younger (Miocene) than those that led to the east-west pattern (Paleocene). The Mexican Transition Zone consists of five biogeographic provinces: Sierra Madre Occidental, Sierra Madre Oriental, Transmexican Volcanic Belt, Sierra Madre del Sur, and Chiapas. Within this transition zone, at least four cenocrons have been identified: Paleoamerican, Nearctic, Montane Mesoamerican, and Tropical Mesoamerican. Future studies should continue refining the identification of cenocrons and the reconstruction of a geobiotic scenario, as well as integrating ecological biogeographic studies, to allow a more complete understanding of the patterns and processes that have caused the biotic complexity of this transition zone. © 2010 The Authors. Journal compilation © 2010 Ecography. Source

Ivanov V.B.,RAS Timiryazev Institute of Plant Physiology | Dubrovsky J.G.,National Autonomous University of Mexico
Trends in Plant Science | Year: 2013

Despite the relative simplicity of Arabidopsis root organization, there is no general agreement regarding the terminology used to describe the longitudinal zonation pattern (LZP) of this model system. In this opinion article, we examine inconsistencies in the terminology and provide a conceptual framework for the LZP that may be applied to all angiosperms. We propose that the root apical meristem (RAM) consists of the cell-proliferation domain where cells maintain a high probability to divide and the transition domain with a low probability of cell division; in both domains cells grow at the same, relatively low, rate. Owing to stochastic termination of cell proliferation in the RAM, the border between the domains is 'fuzzy'. Molecular markers analyzed together with quantitative growth and cell analyses could help to identify developmental zones along the root and lead to a better understanding of the LZP in angiosperms. © 2012 Elsevier Ltd. Source

Garcia-Guzman G.,National Autonomous University of Mexico | Heil M.,CINVESTAV
New Phytologist | Year: 2014

Plant pathogens affect the fitness of their hosts and maintain biodiversity. However, we lack theories to predict the type and intensity of infections in wild plants. Here we demonstrate using fungal pathogens of tropical plants that an examination of the life histories of hosts and pathogens can reveal general patterns in their interactions. Fungal infections were more commonly reported for light-demanding than for shade-tolerant species and for evergreen rather than for deciduous hosts. Both patterns are consistent with classical defence theory, which predicts lower resistance in fast-growing species and suggests that the deciduous habit can reduce enemy populations. In our literature survey, necrotrophs were found mainly to infect shade-tolerant woody species whereas biotrophs dominated in light-demanding herbaceous hosts. Far-red signalling and its inhibitory effects on jasmonic acid signalling are likely to explain this phenomenon. Multiple changes between the necrotrophic and the symptomless endophytic lifestyle at the ecological and evolutionary scale indicate that endophytes should be considered when trying to understand large-scale patterns in the fungal infections of plants. Combining knowledge about the molecular mechanisms of pathogen resistance with classical defence theory enables the formulation of testable predictions concerning general patterns in the infections of wild plants by fungal pathogens. © 2013 New Phytologist Trust. Source

Larriva-Sahd J.A.,National Autonomous University of Mexico
Frontiers in Neuroanatomy | Year: 2014

Rafael Lorente de Nó, the youngest of Santiago Ramon y Cajal disciples, was one of the last Century’s more influential researches in neuroscience. This assay highlights two fundamental contributions of Rafael Lorente de Nó to neurobiology: the intrinsic organization of the mammalian cerebral cortex and the basic physiology of the neuron processes. © 2014 Larriva-Sahd. Source

Perez M.C.,National Autonomous University of Mexico
Journal of integrative bioinformatics | Year: 2013

Many complex systems cannot be analyzed using traditional mathematical tools, due to their irreducible nature. This makes it necessary to develop models that can be implemented computationally to simulate their evolution. Examples of these models are cellular automata, evolutionary algorithms, complex networks, agent-based models, symbolic dynamics and dynamical systems techniques. We review some representative approaches to model the stem cell niche in Arabidopsis thaliana and the basic biological mechanisms that underlie its formation and maintenance. We propose a mathematical model based on cellular automata for describing the space-time dynamics of the stem cell niche in the root. By making minimal assumptions on the cell communication process documented in experiments, we classify the basic developmental features of the stem-cell niche, including the basic structural architecture, and suggest that they could be understood as the result of generic mechanisms given by short and long range signals. This could be a first step in understanding why different stem cell niches share similar topologies, not only in plants. Also the fact that this organization is a robust consequence of the way information is being processed by the cells and to some extent independent of the detailed features of the signaling mechanism. Source

Vega G.,National Autonomous University of Mexico
IEEE Transactions on Information Theory | Year: 2012

A class of two-weight non-irreducible cyclic codes was recently presented by Ma. This class of codes generalizes and extends some of the codes presented in papers by Wolfmann in 2005 and Vega and Wolfman in 2007. The aim of this note is to show that the class of codes presented by Ma is properly contained in a superclass of two-weight cyclic codes that was introduced by Vega in 2008. © 2006 IEEE. Source

Lemus R.,National Autonomous University of Mexico
Symmetry | Year: 2012

The eigenfunction approach used for discrete symmetries is deduced from the concept of quantum numbers. We show that the irreducible representations (irreps) associated with the eigenfunctions are indeed a shorthand notation for the set of eigenvalues of the class operators (character table). The need of a canonical chain of groups to establish a complete set of commuting operators is emphasized. This analysis allows us to establish in natural form the connection between the quantum numbers and the eigenfunction method proposed by J.Q. Chen to obtain symmetry adapted functions. We then proceed to present a friendly version of the eigenfunction method to project functions. © 2012 by the author. Source

Since its introduction in the early 1990s, diffusion-weighted magnetic resonance imaging (MRI) has played a crucial role in the non-invasive evaluation of tissue microstructure of brain parenchyma in vivo. Diffusion anisotropy, in particular, has been extensively used to infer histological changes due to brain maturation and pathology, as it shows a clear dependence on tissue architecture. Although the resolution used in most studies lies in the macroscopic range, the information provided originates at the microscopic level and, as such, diffusion MRI serves as a microscope that can reveal profound details of tissue with direct clinical and research applications. The interpretation of diffusion parameters of white matter rests on what is known to drive diffusion anisotropy, namely axonal membranes, density and coherence, as well as myelin sheaths. However, these factors interact to modulate anisotropy, making interpretations potentially difficult. While there are numerous publications that report diffusion changes in response to particular, histologically confirmed tissue abnormalities in animal models of disease, the microscopic correlates of altered diffusion parameters due to neurological disorders in humans have been difficult to characterize. Animal models may provide insight into the mechanisms involved, but do not necessarily provide accurate representations of the human condition, making human diffusion MRI studies with direct histological confirmation crucial for our understanding of tissue changes secondary to neurodevelopment and disease. This work provides a synopsis of tissue characteristics that give rise to highly informative, specific diffusion patterns, and also of how methodological and artifactual aspects can provide erroneous diffusion measurements that do not accurately reflect tissue and may lead to misinterpretation of results. Examples of diffusion changes due to human conditions are provided to illustrate the wealth of applications of diffusion MRI in clinical and research fields. © 2013 IBRO. Source

Turbiner A.V.,National Autonomous University of Mexico
Journal of Physics A: Mathematical and Theoretical | Year: 2013

A notion of a particular integrability is introduced when two operators commute on a subspace of the space where they act. Particular integrals for one-dimensional (quasi)-exactly-solvable Schrödinger operators and Calogero-Sutherland Hamiltonians for all roots are found. In the classical case some special trajectories for which the corresponding particular constants of motion appear are indicated. Particular integrability manifests the existence of super-integrable substructures in an integrable system. © 2013 IOP Publishing Ltd. Source

Martinez A.,National Autonomous University of Mexico
Journal of Physical Chemistry C | Year: 2010

The main goal of this investigation is to analyze the electron donor-acceptor properties of planar and three-dimensional gold clusters (Au N (with N = 2-20), and for this purpose, a new simple model based on density functional theory is used. Calculations at the B3LYP level permit us to determine the electrodonating (χ-) and electroaccepting (χ+) electronegativity of AuN. On the basis of this analysis, it is possible to conclude that gold clusters with an odd number of atoms are better electron acceptors and better electron donors than clusters with an even number of atoms. Likewise, planar clusters are better electron acceptors than three-dimensional ones. These parameters are used to explain previous results concerning the reactivity of neutral clusters with O2 and CO. The interaction of these neutral gold clusters with adenine-uracil (AU) and guanine-cytosine (GC) base pairs is also described. A rather particular correlation was found between χ+ or χ- and the binding energies, which indicates the usefulness of this simple model to anticipate the direction of the charge transfer process and to estimate the magnitude order of the binding energies. The relevance of being planar with reference to these results is also analyzed. © 2010 American Chemical Society. Source

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. Source

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. Source

Reyes J.L.,National Autonomous University of Mexico
Methods in molecular biology (Clifton, N.J.) | Year: 2010

In plants, small RNA (microRNAs and other endogenous small RNAs)-guided target gene expression is vital for a wide variety of biological processes including adaptation to stress conditions. Identification of stress-regulated microRNAs or other classes of endogenous small RNAs advances our understanding of post-transcriptional gene regulation important for plant stress tolerance. This chapter describes a detailed step-by-step protocol for cloning of small RNAs. Following 5' and 3' adapter ligation to the purified small RNAs, cDNA will be synthesized using reverse transcription, which will be further amplified using a polymerase chain reaction. The resulting small DNA fragments can be either cloned and sequenced using traditional sequencing method or subjected to direct high-throughput pyrosequencing or sequencing-by-synthesis technology. Source

Arroyo D.,Metropolitan Autonomous University | Ordaz M.,National Autonomous University of Mexico
Bulletin of the Seismological Society of America | Year: 2010

An application of a linear multivariate Bayesian regression model to compute pseudoacceleration (SA) ground-motion prediction equations (GMPEs) is presented. The model is able to include the correlation between observations for a given earthquake, the correlation between SA ordinates at different periods, and the correlation between regression coefficients of the ground-motion prediction model. We evaluate the advantages of the Bayesian approach over the traditional regression methods, and we discuss the differences between univariate and multivariate analyses. Because the application of the Bayesian method is in general complex and implies an increase in the numerical effort with respect to the traditional methods, our computer code to perform linear Bayesian analyses is freely available on request. Source

Quintero C.,University of Colorado at Boulder | Barton K.E.,University of Hawaii at Manoa | Boege K.,National Autonomous University of Mexico
Perspectives in Plant Ecology, Evolution and Systematics | Year: 2013

Plants frequently attract natural enemies of their herbivores, resulting in a reduction in tissue damage and often in enhanced plant fitness. While such indirect defenses can dramatically change as plants develop, only recently have ecologists begun to explore such changes and evaluate their role in mediating plant-herbivore-natural enemy interactions. Here we review the literature documenting ontogenetic patterns in plant rewards (i.e. extrafloral nectaries (EFNs), food bodies (FBs) and domatia) and volatile organic compounds (VOCs), and identify links between ontogenetic patterns in such traits and the attraction of natural enemies (ants). In the case of reward traits we concentrate in ant-plant studies, which are the most numerous. We report that all indirect defensive traits commonly vary with plant age but ontogenetic trajectories differ among them. Myrmecophytic species, which provide both food and shelter to their defenders, do not produce rewarding traits until a minimum size is reached. Then, a pronounced increase in the abundance of food rewards and domatia often occurs as plants develop, which explains the temporal succession or colony size increase of mutualistic ant species and, in some cases, leads to a reduction in herbivore damage and enhanced fitness as plants age. In contrast, ontogenetic patterns were less consistent in plant species that rely on VOC emissions to attract natural enemies or those that provide only food rewards (EFNs) but not nesting sites to their associated ants, showing an overall decline or lack of trend with plant development, respectively. Future research should focus on uncovering: (i) the costs and mechanisms underlying ontogenetic variation in indirect defenses, (ii) the relative importance of environmental and genetic components shaping these ontogenetic trajectories, and (iii) the consequences of these ontogenetic trajectories on plant fitness. Advances in this area will shed light on the context dependency of bottom-up and top-down controls of herbivore populations and on how natural selection actually shapes the ontogenetic trajectories of these traits. © 2013 Perspectives in Plant Ecology, Evolution and Systematics. Source

Rosell J.A.,National Autonomous University of Mexico
New Phytologist | Year: 2016

Global variation in total bark thickness (TBT) is traditionally attributed to fire. However, bark is multifunctional, as reflected by its inner living and outer dead regions, meaning that, in addition to fire protection, other factors probably contribute to TBT variation. To address how fire, climate, and plant size contribute to variation in TBT, inner bark thickness (IBT) and outer bark thickness (OBT), I sampled 640 species spanning all major angiosperm clades and 18 sites with contrasting precipitation, temperature, and fire regime. Stem size was by far the main driver of variation in thickness, with environment being less important. IBT was closely correlated with stem diameter, probably for metabolic reasons, and, controlling for size, was thicker in drier and hotter environments, even fire-free ones, probably reflecting its water and photosynthate storage role. OBT was less closely correlated with size, and was thicker in drier, seasonal sites experiencing frequent fires. IBT and OBT covaried loosely and both contributed to overall TBT variation. Thickness variation was higher within than across sites and was evolutionarily labile. Given high within-site diversity and the multiple selective factors acting on TBT, continued study of the different drivers of variation in bark thickness is crucial to understand bark ecology. © 2016 New Phytologist Trust. Source

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. Source

Sussman R.A.,National Autonomous University of Mexico
General Relativity and Gravitation | Year: 2010

We examine the radial asymptotic behavior of spherically symmetric Lemaître-Tolman-Bondi dust models by looking at their covariant scalars along radial rays, which are spacelike geodesics parametrized by proper length ℓ, orthogonal to the 4-velocity and to the orbits of SO(3). By introducing quasi-local scalars defined as integral functions along the rays, we obtain a complete and covariant representation of the models, leading to an initial value parametrization in which all scalars can be given by scaling laws depending on two metric scale factors and two basic initial value functions. Considering regular "open" LTB models whose space slices allow for a diverging ℓ, we provide the conditions on the radial coordinate so that its asymptotic limit corresponds to the limit as ℓ → ∞. The "asymptotic state" is then defined as this limit, together with asymptotic series expansion around it, evaluated for all metric functions, covariant scalars (local and quasi-local) and their fluctuations. By looking at different sets of initial conditions, we examine and classify the asymptotic states of parabolic, hyperbolic and open elliptic models admitting a symmetry center. We show that in the radial direction the models can be asymptotic to any one of the following spacetimes: FLRW dust cosmologies with zero or negative spatial curvature, sections of Minkowski flat space (including Milne's space), sections of the Schwarzschild-Kruskal manifold or self-similar dust solutions. © 2010 Springer Science+Business Media, LLC. Source

Lehnert R.,National Autonomous University of Mexico
Revista Mexicana de Fisica | Year: 2010

The Chern-Simons-type term in the photon sector of the Lorentz- and CPT-breaking minimal Standard-Model Extension (mSME) is considered. It is argued that under certain circumstances this term can be removed from the mSME. In particular, it is demonstrated that for lightlike Lorentz violation a field redefinition exists that maps the on-shell free Chern-Simons model to conventional on-shell free electrodynamics. A compact explicit expression for an operator implementing such a mapping is constructed. This expression establishes that the field redefinition is non-local. Source

Larriva-Sahd J.A.,National Autonomous University of Mexico
Frontiers in Neuroanatomy | Year: 2010

The structure of two neuron types native to the adult mouse piriform cortex (PC) is described. The first cell, termed an interfascicular neuron (IFN), lies between the axon fascicles of layer I. The IFN axon divides dichotomously and daughter fibrils run horizontally in the domain of layer Ia. The frequent apposition of the IFN axon to distal dendrites of the underlying pyramidal cells suggests an en passage synaptic interaction with them. A second neuron observed in layer II, or less frequently in layer III, matched in most respects the structure of the chandelier cell (CC) described elsewhere in the neo- and archi-cortex. In the PC, chandelier cells (PC-CC) display the following peculiarities. First, the PC-CC axonal field distributes in the neuropil of layers II and III and candlesticks are in close apposition to the initial axonal segment of the pyramidal cell, although somatic interactions cannot be rule out. Second, the PC-CC ascending dendrites pierce layer I, receiving short collaterals and boutons en passage from the olfactory axons therein. The possible role of IFN's and PC-CC and their interactions with the adjacent cells is discussed in the broad context of the cellular organization of the PC. © 2010 Larriva-Sahd. Source

Bunge C.F.,National Autonomous University of Mexico
Theoretical Chemistry Accounts | Year: 2010

A set of 432 energy-optimized Slater-type radial orbitals together with spherical harmonics up to ℓ = 30 is used to approximate the corresponding full configuration interaction (CI) expansion for Be ground state. An analysis of radial and angular patterns of convergence for the energy yields a basis set incompleteness error of 8.7 μhartree of which 85% comes from radial basis truncations for ℓ ≤ 30. Select-divide-and-conquer CI (Bunge in J Chem Phys 125:014107, 2006; Bunge and Carbó-Dorca in J Chem Phys 125:014108, 2006) produces an energy upper bound 0.02(1) μhartree above the full CI limit. The energy upper bound E = -14.6673473 corrected with these two truncation energy errors yields E = -14.6673560 a.u. (Be) in fair agreement with the latest explicitly correlated Gaussian results of E = -14.66735646 a.u. (Be). The new methods employed are discussed. It is acknowledged that at this level of accuracy traditional atomic CI has reached a point of diminishing returns. Modifications of conventional (orbital) CI to seek for significantly higher accuracy without altering a strict one-electron orbital formalism are proposed. © 2009 Springer-Verlag. Source

Orozco-Ramirez Q.,National Autonomous University of Mexico
Heredity | Year: 2016

While prevailing theories of crop evolution suggest that crop diversity and cultural diversity should be linked, empirical evidence for such a link remains inconclusive. In particular, few studies have investigated such patterns on a local scale. Here, we address this issue by examining the determinants of maize diversity in a local region of high cultural and biological richness in Southern Mexico. We collected maize samples from villages at low and middle elevations in two adjacent municipalities of differing ethnicity: Mixtec or Chatino. Although morphological traits show few patterns of population structure, we see clear genetic differentiation among villages, with municipality explaining a larger proportion of the differentiation than altitude. Consistent with an important role of social origin in patterning seed exchange, metapopulation model-based estimates of differentiation match the genetic data within village and ethnically distinct municipalities, but underestimate differentiation when all four villages are taken together. Our research provides insights about the importance of social origin in structuring maize diversity at the local scale.Heredity advance online publication, 24 February 2016; doi:10.1038/hdy.2016.10. © 2016 The Genetics Society Source

Luna-Ulloa L.B.,National Autonomous University of Mexico
IUBMB life | Year: 2011

Although it is well known that Wnt and protein kinase C (PKC) signaling pathways are both involved in carcinogenesis and tumor progression, their synergistic contribution to these processes or the crosstalk between them has just recently been approached. The Wnt and PKC signaling are involved in many cellular functions including proliferation, differentiation, survival, apoptosis, cytoskeletal remodeling, and cell motility. Canonical Wnt signaling has been well characterized as one of the most important contributors to tumorigenesis, and it has been implicated in many types of solid tumors. PKC is one of the key targets of noncanonical Wnt signaling, particularly in the Wnt/Ca(2+) pathway. Recently, data have implicated components of noncanonical Wnt/Ca(2+) and Wnt/planar cell polarity signaling in directly promoting the invasiveness and malignant progression of diverse forms of human cancer. But, unlike the canonical pathway, defining the roles of noncanonical Wnt signaling in human cancer is in its infancy. In this review, we provide a concise description of the current knowledge of the interaction between PKC and Wnt pathways and discuss the role of this crosstalk in cancer initiation and progression. Copyright © 2011 Wiley Periodicals, Inc. Source

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. Source

Schouwenaars R.,National Autonomous University of Mexico
Philosophical Magazine | Year: 2014

Eighty years since G.I. Taylor presented the first empirical explanation for the yield stress and strain hardening of metals, generally accepted formalisms to explain strain hardening have been established. The most important of these empirical laws have eluded full mathematical analysis until now. The Taylor equation provides a relationship between yield stress and strain. The semi-empirical Kocks-Mecking model provides a description of the physical phenomena of dislocation storage and annihilation, but lacks information on the formation of substructure and its effects. Here, a recently developed mathematical analysis of the corresponding phenomena is presented, which reproduces the essential equations in strain hardening. The first important result is the proof that the Taylor equation is the unique solution of a fundamental evolution equation for dislocation density. The second one demonstrates that dislocation storage and annihilation are exactly additive. The latter conclusion is independent of substructure, explaining the success of the Kocks-Mecking model during stages II and III. © 2014 © 2014 Taylor & Francis. Source

Alvarez-Idaboy J.R.,National Autonomous University of Mexico | Galano A.,Metropolitan Autonomous University
Theoretical Chemistry Accounts | Year: 2010

The effect of the inclusion of counterpoise corrections (CP) on the accuracy of interaction energies has been studied for different systems accounting for (1) intermolecular interactions, (2) intramolecular interactions and (3) chemical reactions. To minimize the error associated with the method of choice, the energy calculations were performed using CCSD(T) in all the cases. The values obtained using aug-cc-pVXZ basis sets are compared to CBS-extrapolated values. It has been concluded that at least for the tested systems CP corrections systematically leads to results that differ from the CBS-extrapolated ones to a larger extension than the uncorrected ones. Accordingly, from a practical point of view, we do not recommend the inclusion of such corrections in the calculation of interaction energies, except for CBS extrapolations. The best way of dealing with basis set superposition error (BSSE) is not to use CP corrections, but to make a computational effort for increasing the basis set. This approach does not eliminate BSSE but significantly decreases it, and more importantly it proportionally decreases all the errors arising from the basis set truncation. © 2009 Springer-Verlag. Source

Mendoza S.,National Autonomous University of Mexico
Canadian Journal of Physics | Year: 2014

This review describes why the geometric nature of space-time, the Einstein equivalence principle, and the geodesic motion of particles show the possibility of building an extended relativistic theory of gravity on regions where the Tully-Fisher law is valid. It is also shown how a metric construction of gravity can have a modified Newtonian dynamics behaviour compatible with the Tully-Fisher law and the bending of light observed in individual, groups, and clusters of galaxies. It is also reviewed how this metric theory of gravity fits reasonably well on cosmological scales explaining the current acceleration of the universe. © 2015 Published by NRC Research Press. Source

Morrone J.J.,National Autonomous University of Mexico
Journal of Biogeography | Year: 2015

Aim: Panbiogeography, as originally formulated by Léon Croizat, assumed that vicariance and range expansion are the only biogeographical processes needed to explain general biotic distributions. This was in opposition to the prevailing paradigm at the time, known as dispersalism, which postulates that organisms evolve in 'centres of origin' from pre-existing species and then randomly cross barriers to occupy new areas, where they adapt and evolve into new species. The panbiogeographic approach is implemented through track analysis, which consists of three basic steps: constructing individual tracks for two or more different taxa, obtaining generalized tracks where two or more different individual tracks coincide, and identifying nodes in the areas where two or more generalized tracks intersect. In this synthesis I discuss some criticisms that have been directed at panbiogeography and track analysis. Location: Global. Methods: I evaluated the papers with track analyses that have been published in the last few decades and the critiques provided by several authors. Results: Most of the critiques have been directed at the original panbiogeographic approach, with its complete or almost complete reliance on vicariance explanations. Track analyses published in the 1980s and 1990s usually applied a strict vicariance explanation; however, most of the analyses published in the last 10 years or so consider both vicariance and dispersal to explain the observed patterns. Main conclusions: Although Croizat's metaphor 'Earth and life evolve together' may be a useful guide to understanding broad, general patterns, the relationships between Earth history and life are more complex because biotic history is reticulate. To reduce our explanations exclusively to vicariance or dispersal is misguided. We should integrate both processes into a dispersal-vicariance model that allows us to understand the evolution of biotic distributions, incorporating the dating of the lineages and the identification of the cenocrons (sets of taxa that share the same biogeographical history) that coexist within biotas. In the framework of this model, panbiogeographic track analysis is a useful method for identifying biotas, and may constitute the first step of an evolutionary biogeographical analysis. © 2015 John Wiley & Sons Ltd. Source

de la Cruz-Reyna S.,National Autonomous University of Mexico
Geofisica Internacional | Year: 2011

In contrast with polygenetic volcanoes, eruptions giving birth to monogenetic volcanoes are much less frequent and thus more difficult to observe and study. Only a few events of this type have occurred worldwide in historical times. Among these, Jorullo (1759~1766), Paricutin (1943~1952), Ukinrek maar (1977), and the East-Izu activity in Japan (1930~1989) are among the events that were studied and reported according to the scientific level of each period. The first two eruptions lasted for several years and were actual births of cinder cones and large lava flows. The maar resulted from a series of phreatomagmatic explosions, with relatively small basaltic magma production, and East-Izu caused earthquake swarms intermittently since 1930 ending with a small submarine eruption in 1989, not large enough to form a scoria cone. Here, we discuss the physical processes that originated those monogenetic volcanoes, mostly from the available seismological data and other reported parameters that reveal similarities and differences among those eruptions. Notwithstanding the common features of monogenetic activity, different types of volcanoes may thus be recognized. The main common feature for all types is a deep seated primary magma source, below the crust. Depending on the ascending capacity of magma derived from the excess pressure at the source and on its buoyancy, the surface activity may range from long-duration, high magma productivity eruptions forming cinder cones and extensive lava fields, to short-duration, low productivity eruptions related to similar sources but with a lower magma ascent capacity, that tends to stall within the crust. End members of the latter type may be limited to phreatic activity related to conducted heat phenomena or to local swarm seismicity. Sharing characteristics of those volcano types, but in a different spatial scale and with a shallower magma source, we recognize another type of monogenetic volcanism, namely the parasitic cones associated to polygenetic volcanoes that seem to result from the balance between the magmatic pressure and the mechanical strength of the polygenetic volcanic edifice. Source

Vega G.,National Autonomous University of Mexico
IEEE Transactions on Information Theory | Year: 2012

The weight distribution of a class of nonirreducible cyclic codes was given by Ma . By imposing a special set of conditions on this class of codes, it was recently shown that the resulting codes, for this class, can be obtained as elements in a family of codes introduced by Vega in . Now, by using a different set of conditions, the aim of this paper is to present an extended version for the class of codes studied by Ma © 2012 IEEE. Source

Guzman-Speziale M.,National Autonomous University of Mexico
Tectonophysics | Year: 2010

I investigate the role of two strike-slip faults in the tectonics of the western North America-Caribbean plate margin. The Ixcan fault, located in Guatemala north of the Polochic fault, is seismically active, with earthquakes of magnitude up to 5.7 reported recently. Fault-plane solutions along this curvilinear but generally E-W trending fault indicate left-lateral, strike-slip displacement. Several historic earthquakes appear to have taken place along the Ixcan fault since 1728, the largest one being the 1816 event (M= 7.5). The NW-SE trending Concordia fault in southeastern Mexico appears to be the site of the great (M= 7.6) earthquake of 1902. Isoseismals for this event suggest shallow, left-lateral strike-slip faulting. I propose a seismotectonic model in which both faults are part of the deformation associated to the North America-Caribbean plate boundary zone. Transpressive structures are found in the fault steps between strike-slip fault systems. © 2010 Elsevier B.V. Source

The present study deals with the morphologic variability of eight Clathria species from the southern Gulf of Mexico and Mexican Caribbean. Clathria (Clathria) foliacea, C. (C.) carteri, C. (Microciona) calla, C. (M.) echinata, C. (M.) spinosa, C. (Thalysias.) venosa, and C. (T.) virgultosa were collected by scuba diving and dredging from the southern Gulf of Mexico (Veracruz, Campeche Bank, Yucatan) to the Caribbean coast (Quintana Roo) from shoreline to 120 m depth. The population of Clathria seems to be neither abundant nor diverse in the studied area. However, the seven species considered here are presumed to have a slight morphologic variability, and the interspecific relationships had not been fully resolved. The present study focuses on their differentiation through comparison of external morphology, skeletal architecture, spiculation and measurements of characters as well as scanning electronic microscopy. Comparisons were made among intra- and interspecific material and with the available type material. In particular, C. carteri Topsent (1889), previously synonymized with C. foliacea, is resurrected by establishing a neotype from material from the type locality, Campeche Bank; this has not been studied since its original description and is here redescribed for the first time. Another neotype is assigned for C. foliacea from Campeche also, since the original material is no longer available, and this species is redescribed also. Significant differences in spiculation between C. foliacea and C. carteri were found by one-way ANOVA. Although C. (T.) venosa resembles C. (T.) raraechelae in spiculation, these two species differ in measurements and skeletal organization. C. (T.) virgultosa is typified by a peculiar acanthostyle that is markedly spined on distal parts of the shaft, and by two types of tiny microscleres. This study has extended the known geographic distribution of each of these Clathria spp. within the lower Gulf of Mexico. © Copyright 2014 Magnolia Press. Source

Arzate-Mejia R.G.,National Autonomous University of Mexico
IUBMB life | Year: 2011

Cells must be able to respond rapidly and precisely not only to changes in their external environment but also to developmental and differentiation cues to determine when to divide, die, or acquire a particular cell fate. Signal transduction pathways are responsible for the integration and interpretation of most of such signals into specific transcriptional states. Those states are achieved by the modulation of chromatin structure that activates or represses transcription at particular loci. Although a large variety of signal transduction pathways have already been described, much less is known about the crosstalk between signal transduction and its consequent changes in chromatin structure and, therefore, gene expression. Here we present some examples of the relationship between chromatin-associated proteins and important signal transduction pathways during critical processes like development, differentiation, and disease. There is a great diversity of epigenetic mechanisms that have unexpected interactions with signaling pathways to establish transcriptional programs. Moreover, there are also particular cases where signaling pathways directly affect important components of the epigenetic machinery. Based on such examples, we further propose future research directions linking cell signaling and epigenetics. It is foreseeable that analyzing the relationship between cell signaling and epigenetics will be a huge area for future development that will help us understand the complex process by which a cell is able to induce transcriptional changes in response to external and internal signals. Copyright © 2011 Wiley Periodicals, Inc. Source

Chimal-Monroy J.,National Autonomous University of Mexico
IUBMB life | Year: 2011

During the hand plate development, the processes of cell differentiation and control of cell death are relevant to ensure a correct shape of the limb. The progenitor cell pool that later will differentiate into cartilage to form the digits arises from undifferentiated mesenchymal cells beneath the apical ectodermal ridge (AER). Once these cells abandon the area of influence of signals from AER and ectoderm, some cells are committed to chondrocyte lineage forming the digital rays. However, if the cells are not committed to chondrocyte lineage, they will form the prospective interdigits that in species with free digits will subsequently die. In this work, we provide the overview of the molecular interactions between different signaling pathways responsible for the formation of digit and interdigit regions. In addition, we briefly describe some experiments concerning the most important signals responsible for promoting cell death. Finally, on the basis that the interdigital tissue has chondrogenic potential, we discuss the hypothesis that apoptotic-promoting signals might also act as antichondrogenic factors and chondrogenic factors might operate as anti-apoptotic factors. Copyright © 2011 Wiley Periodicals, Inc. Source

Arroyo D.,Metropolitan Autonomous University | Ordaz M.,National Autonomous University of Mexico
Bulletin of the Seismological Society of America | Year: 2010

An application of a linear multivariate Bayesian regression model, described in a companion article, to obtain a ground-motion prediction equation (GMPE) using a set of actual ground-motion records and a realistic functional form is presented. Based on seismological grounds and on an adopted functional form,we include a sound discussion about how the prior information required for the model can be defined. For the regression analyses we use two subsets of ground-motion records from the Next Generation of Ground-Motion Attenuation Models (NGA) database. We compare the results obtained with the Bayesian model with those obtained through the one-stage maximum-likelihood and the constrained maximum-likelihood methods. The advantages of the Bayesian approach over traditional regression techniques are discussed. Source

Flisser A.,National Autonomous University of Mexico
Korean Journal of Parasitology | Year: 2013

Three species of tapeworms infect humans in their adult stage (Taenia solium, Taenia saginata and Taenia asiatica). The 3 are fat, opaque white or yellowish, and exceptional long segmented parasites, measuring 1 to 12 m in their adult stage. In this review, the development of the knowledge regarding the first species, mainly focused on understanding how the larval stage or cysticercus is transmitted to humans, is described. The second species is a cosmopolitan parasite that only causes taeniosis and not cysticercosis; therefore, it will not be included. Information on the third species, which is presently being produced, since this species was recognized as such only at the end of the 20th century, will be discussed at the end of this review. © 2013, Korean Society for Parasitology and Tropical Medicine. Source

Munoz-Villers L.E.,National Autonomous University of Mexico | McDonnell J.J.,University of Saskatchewan | McDonnell J.J.,University of Aberdeen
Hydrology and Earth System Sciences | Year: 2013

While tropical montane cloud forests (TMCF) provide critical hydrological services to downstream regions throughout much of the humid tropics, catchment hydrology and impacts associated with forest conversion in these ecosystems remain poorly understood. Here, we compare the annual, seasonal and event-scale streamflow patterns and runoff generation processes of three neighbouring headwater catchments in central Veracruz (eastern Mexico) with similar pedological and geological characteristics, but different land cover: old-growth TMCF, 20 yr-old naturally regenerating TMCF and a heavily grazed pasture. We used a 2 yr record of high resolution rainfall and stream flow data (2008-2010) in combination with stable isotope and chemical tracer data collected for a series of storms during a 6-week period of increasing antecedent wetness (wetting-up cycle). Our results showed that annual and seasonal streamflow patterns in the mature and secondary forest were similar. In contrast, the pasture showed a 10% higher mean annual streamflow, most likely because of a lower rainfall interception. During the wetting-up cycle, storm runoff ratios increased at all three catchments (from 11 to 54% for the mature forest, 7 to 52% for the secondary forest and 3 to 59% for the pasture). With the increasing antecedent wetness, hydrograph separation analysis showed progressive increases of pre-event water contributions to total stormflow (from 35 to 99% in the mature forest, 26 to 92% in the secondary forest and 64 to 97% in the pasture). At all three sites, rainfall-runoff responses were dominated by subsurface flow generation processes for the majority of storms. However, for the largest and most intense storm (typically occurring once every 2 yr), sampled under wet antecedent conditions, the event water contribution in the pasture (34% on average) was much higher than in the forests (5% on average), indicating that rainfall infiltration capacity of the pasture was exceeded. This result suggests that despite the high permeability of the volcanic soils and underlying substrate in this TMCF environment, the conversion of forest to pasture may lead to important changes in runoff generation processes during large and high intensity storms. On the other hand, our results also showed that 20 yr of natural regeneration may be enough to largely restore the original hydrological conditions of this TMCF. © Author(s) 2013. CC Attribution 3.0 License. Source

Gazol A.,National Autonomous University of Mexico | Kim J.,Korea Astronomy and Space Science Institute
Astrophysical Journal | Year: 2010

In this paper, we numerically study the behavior of the density power spectrum in turbulent thermally bistable flows. We analyze a set of five three-dimensional simulations where turbulence is randomly driven in Fourier space at a fixed wavenumber and with different Mach numbers M (with respect to the warm medium) ranging from 0.2 to 4.5. The density power spectrum becomes shallower as M increases and the same is true for the column density power spectrum. This trend is interpreted as a consequence of the simultaneous turbulent compressions, thermal instability generated density fluctuations, and theweakening of thermal pressure force in diffuse gas. This behavior is consistent with the fact that observationally determined spectra exhibit different slopes in different regions. The values of the spectral indices resulting from our simulations are consistent with observational values.We also explore the behavior of the velocity power spectrum, which becomes steeper as M increases. The spectral index goes from a value much shallower than the Kolmogorov one for M = 0.2 to a value steeper than the Kolmogorov one for M = 4.5. © 2010. The American Astronomical Society. Source

Islas-Flores T.,National Autonomous University of Mexico
Plant signaling & behavior | Year: 2012

RACK1 is a scaffold protein with the ability to interact in a regulated manner with a diverse number of ligands from distinct signal-transduction pathways. This assessment allowed us to infer that it may be involved in different processes such as nodulation. In a recent study we showed by silencing, that PvRACK1 has a pivotal role in cell expansion and in symbiosome and bacteroid integrity during nodule development in Phaseolus vulgaris. On the other hand, we have also observed that its over-expression provokes a dramatic phenotype in: (a) seedlings that have been exposed to heat, in which systemic necrosis is induced; and (b) in Agrobacterium rhizogenes-transformed roots, where nodulation is strongly inhibited and nodules show early senescent symptoms. These findings indicate that PvRACK1 may be an integrator of diverse signal-transduction pathways in processes as varied as nodulation, cell expansion, heat stress responses, and systemic activation of necrosis.  Source

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. Source

Avila Acevedo J.G.,National Autonomous University of Mexico
BMC complementary and alternative medicine | Year: 2014

In recent years, there has been considerable interest in using botanical agents to prevent skin damage resulting from solar UV-irradiation. Buddleja cordata is a plant that is known as "tepozan". Some people in Mexico use the leaves of this plant to treat tumours, abscesses, sores and burns. The purpose of this study is to investigate the photoprotective properties of Buddleja cordata methanolic extract (BCME) against UVB-induced skin damage in SKH-1 hairless mice at the macroscopic and histological levels. BCME was characterised to determine its spectroscopic, chromatographic and antioxidant (DPPH, superoxide and hydroxyl radicals) properties. To conduct the photoprotection studies, BCME was applied topically to the skin of SKH-1 mice before acute exposure to UVB for 10 minutes. The murine skin samples were used for macroscopic and histological studies to assess tissue damage. Penetration of active components of BCME into stratum corneum on the dorsal area of mice was investigated in vivo by the tape stripping method. Moreover, genotoxicity of BCME was evaluated in a Vicia faba cell root micronucleus model. BCME displayed absorbance over the entire UVB spectrum, and its principal components included verbascoside and linarin. BCME exhibited antioxidant activity and significantly scavenged hydroxyl radicals. BCME reduced erythema, sunburn cell production, vessel congestion and epidermal thickening of UVB irradiated mouse skin. BCME penetrate the skin of mice. BCME did not exhibit genotoxic activity in the micronucleus test. The topical administration of BCME protected against acute UVB-induced damage in mouse SKH-1 skin, and our results suggest that BCME may potentially prevent photodamage. Source

Iturraran-Viveros U.,National Autonomous University of Mexico
Journal of Applied Geophysics | Year: 2012

Data mining is very important to characterize complex geological structures, where a large variety of geophysical and petrophysical variables are typically involved and interrelated. In this paper we apply smooth regression for data analysis, by means of the Gamma test (a revolutionary estimator of the noise in a data set) to aid in the construction of Artificial Neural Network (ANN) models to predict effective porosity (φ e) using seismic attributes. As a result, we obtain the best combination of seismic attributes to estimate φ e. We briefly describe the Gamma test, its benefits in model identification and model building. The first validation of the Neural Network based on leave-one-out was poor. Therefore, we generate a complementary set of synthetic data (from the original well-log data), varying the effective porosity and applying the Gassmann's equation for fluid substitution to obtain resulting velocities and densities. The complete procedure is repeated including the new synthetic well-logs and the best suited selection of seismic attributes is used to train a new ANN producing a better validation and more accurate results. The advantage of smooth regression over other techniques is that it tells us how well we can predict φ e using any model. This information saves time during training of the ANN and also sets a lower bound for the mean squared error to prevent over-training. © 2011 Elsevier B.V. Source

Selman M.,Instituto Nacional Of Enfermedades Respiratorias Ismael Cosio Villegas | Pardo A.,National Autonomous University of Mexico
American Journal of Respiratory and Critical Care Medicine | Year: 2014

A growing body of evidence indicates that aberrant activation of alveolar epithelial cells and fibroblasts in an aging lung plays a critical role in the pathogenesis of idiopathic pulmonary fibrosis (IPF). However, the biopathological processes linking aging with IPF and the mechanisms responsible for the abnormal activation of epithelial cells and fibroblasts have not been elucidated. Many of the hallmarks of aging (e.g., genomic instability, telomere attrition, epigenetic alterations, mitochondrial dysfunction, and cellular senescence) have been proposed as essential mechanisms for the development of IPF; however, these disturbances are not restricted to IPF and also occur in other aging-related lung disorders, primarily chronic obstructive pulmonary disease (COPD). Therefore, an unanswered question is why a current/former smoker of about 60 years of age with shorter telomeres, alveolar epithelial senescence, excessive oxidative stress, and mitochondrial dysfunction develops IPF and not COPD; in other words, what makes old lungs specifically susceptible to develop IPF? In this Perspective, we propose an integral model in which the combination of some gene variants and/or gene expression in the aging lung results in the loss of epithelial integrity and consequently in the failure of the alveoli to correctly respond to injury and to face the stress associated with mechanical stretch. Afterward, a distinctive epigenetic "reprogramming" that affects both epithelial cells and fibroblasts provokes, among others, the recapitulation of developmental pathways and the aberrant activation and miscommunication between both cell types, resulting in the exaggerated production and accumulation of extracellular matrix and the subsequent destruction of the lung architecture. Copyright © 2014 by the American Thoracic Society. Source

Yamamoto-Kimura L.,National Autonomous University of Mexico
Archivos de Cardiologia de Mexico | Year: 2010

Aim: To know the metabolic syndrome and its components prevalence in Mexico City adolescents sample. Design: A cross-sectional survey was conducted in 772 men and 1078 women, 12 to 16 years old, from 8 randomly selected public junior high schools in Mexico City. Methods: Anthropometric variables, lipids, lipoproteins, Apo Al and B, glucose and insulin were determined. Results: Prevalence of metabolic syndrome was 12.5%, 11.15% in men and 13.5% en women (p ns). The most frequently metabolic syndrome component found in México City adolescents was low HDL-C levels (38%), followed by hypertriglyceridemia (25.5%), hypertension (19.2%), central obesity (11.8%) and elevated fasting glucose (1.7). Except by the hypertriglyceridemia, higher in woman than in men, 28.2% vs. 21.6%, p < 0.001, the prevalence of metabolic syndrome components was similar between males and females. Conclusions: The high prevalence of biochemical and physiological factors of metabolic syndrome, associated with overweight and obesity in Mexico City adolescents, increases the risk of premature development of coronary atherosclerosis and diabetes mellitus in this population. © 2010 Instituto Nacional de Cardiología Ignacio Chávez. Publicado por Elsevier. Source

Jung-Cook H.,National Autonomous University of Mexico
Expert Review of Clinical Pharmacology | Year: 2012

Human neurocysticercosis is a severe disease caused by the installation of Taenia solium larvae in the CNS. A wide variety of clinical manifestations are related to neurocysticercosis. These are determined by a number of important factors, including the number and location of the cysts, the stage of cystercerci and the host response to the infection. Epilepsy, focal neurological signs and increased intracranial pressure are the most common clinical manifestations of the disease. Neurocysticercosis is still deeply rooted in Latin America, Africa and Asia. Albendazole and praziquantel are the drugs used in the treatment of cysticercosis. Both drugs have limited solubility and extensive metabolism, and thus great interindividual variability in plasma levels is found. This article focuses on current knowledge of the pharmacokinetics and the drug interactions of the anthelmintic drugs and the perspectives in the treatment of this parasitic disease. © 2012 Expert Reviews Ltd. Source

Trevino C.,National Autonomous University of Mexico
International Journal of Hydrogen Energy | Year: 2011

This paper deals with transient ignition of very lean hydrogen/air mixtures by thin catalytic wire in a natural convection environment. Modeling is accomplished via a reduced set of heterogeneous kinetic processes which include dissociative adsorption and desorption of both reactants, three fast surface reactions of the Langmiur-Hinshelwood type and the desorption reaction of the adsorbed product. For equivalence ratios smaller than a critical value (which in this case is 0.22), the ignition process shows a dual character, depending on the initial conditions for the surface coverages at the wire. Besides the classical thermal ignition mechanism, there is another branch called in this paper the equi-adsorption regime (EAR), characterized by equal adsorption rates of both reactants. In this regime, the overall reaction rates are very much higher than in the thermal regime, producing the combustion process at relatively low temperatures, even at room temperatures. A closed form solution for the overall reaction rate has obtained in this regime. This mechanism is appropriate to remove even traces of hydrogen in critical environments. © 2011 Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. Source

Morrone J.J.,National Autonomous University of Mexico
Zootaxa | Year: 2014

A biogeographic regionalisation of the Neotropical region is proposed as a hierarchical classification of sub-regions, dominions, provinces and districts. This regionalisation is based on biogeographic analyses of terrestrial plant and animal taxa, and seeks to provide universality, objectivity and stability, such that it can be applied when describing distributional areas of particular taxa or comparing different biogeographic analyses. The Neotropical region is currently comprised of three sub-regions (Antillean, Brazilian and Chacoan), two transition zones (Mexican and South American), seven dominions (Mesoamerican, Pacific, Boreal Brazilian, Southwestern Amazonian, Southeastern Amazonian, Chacoan and Parana) and 53 provinces. For some of the latter, sub-provinces and districts are recognized. Complete synonymies and brief descriptions of the areas are provided, as well as the endemic taxa that diagnose the different provinces. © 2014 Magnolia Press. Source

Galata G.,University of Genoa | Galata G.,National Autonomous University of Mexico | Santopinto E.,University of Genoa
Physical Review C - Nuclear Physics | Year: 2012

A simple hybrid quark-diquark model for the baryons is constructed as a partial solution to the well-known "missing resonances" problem. In this model, the quark-diquark approach is merged with the usual constituent three-quark model. The underlying idea is that the quark-diquark approach describes the excited states while the three-quark model the ground states. The spectrum is calculated through a mass formula, a generalization of the Gürsey-Radicati formula, built to reproduce the rotational and vibrational Regge trajectories. Using the quark-diquark scheme, we were also able to describe the spin-flavor degrees of freedom in the framework of an algebraic model. Moreover, we have constructed a complete classifications of the possible quark-diquark states only based on group theory and thus it can be useful both for other model builders and for experimentalists. © 2012 American Physical Society. Source

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. Source

Iturraran-Viveros U.,National Autonomous University of Mexico | Parra J.O.,Southwest Research Institute
Journal of Applied Geophysics | Year: 2014

Permeability and porosity are two fundamental reservoir properties which relate to the amount of fluid contained in a reservoir and its ability to flow. The intrinsic attenuation is another important parameter since it is related to porosity, permeability, oil and gas saturation and these parameters significantly affect the seismic signature of a reservoir. We apply Artificial Neural Network (ANN) models to predict permeability (k) and porosity (φ) for a carbonate aquifer in southeastern Florida and to predict intrinsic attenuation (1/. Q) for a sand-shale oil reservoir in northeast Texas. In this study, the Gamma test (a revolutionary estimator of the noise in a data set) has been used as a mathematically non-parametric nonlinear smooth modeling tool to choose the best input combination of seismic attributes to estimate k and φ, and the best combination of well-logs to estimate 1/. Q. This saves time during the construction and training of ANN models and also sets a lower bound for the mean squared error to prevent over-training. The Neural Network method successfully delineates a highly permeable zone that corresponds to a high water production in the aquifer. The Gamma test found nonlinear relations that were not visible to linear regression allowing us to generalize the ANN estimations of k, φ and 1/. Q for their respective sets of patterns that were not used during the learning phase. © 2014 Elsevier B.V. Source

Coello P.,National Autonomous University of Mexico | Hey S.J.,Rothamsted Research | Halford N.G.,Rothamsted Research
Journal of Experimental Botany | Year: 2011

Sucrose non-fermenting-1 (SNF1)-related protein kinases (SnRKs) take their name from their fungal homologue, SNF1, a global regulator of carbon metabolism. The plant family has burgeoned to comprise 38 members which can be subdivided into three sub-families: SnRK1, SnRK2, and SnRK3. There is now good evidence that this has occurred to allow plants to link metabolic and stress signalling in a way that does not occur in other organisms. The role of SnRKs, focusing in particular on abscisic acid-induced signalling pathways, salinity tolerance, responses to nutritional stress and disease, and the regulation of carbon metabolism and, therefore, yield, is reviewed here. The key role that SnRKs play at the interface between metabolic and stress signalling make them potential candidates for manipulation to improve crop performance in extreme environments. © 2010 The Author(s). Source

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. Source

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. Source

De La Luz V.,National Autonomous University of Mexico
Astrophysical Journal | Year: 2016

Observations of the emission at radio, millimeter, sub-millimeter, and infrared wavelengths in the center of the solar disk validate the autoconsistence of semi-empirical models of the chromosphere. Theoretically, these models must reproduce the emission at the solar limb. In this work, we tested both the VALC and C7 semi-empirical models by computing their emission spectrum in the frequency range from 2 GHz to 10 THz at solar limb altitudes. We calculate the Sun's theoretical radii as well as their limb brightening. Non-local thermodynamic equilibrium was computed for hydrogen, electron density, and H-. In order to solve the radiative transfer equation, a three-dimensional (3D) geometry was employed to determine the ray paths, and Bremsstrahlung, H-, and inverse Bremsstrahlung opacity sources were integrated in the optical depth. We compared the computed solar radii with high-resolution observations at the limb obtained by Clark. We found that there are differences between the observed and computed solar radii of 12,000 km at 20 GHz, 5000 km at 100 GHz, and 1000 km at 3 THz for both semi-empirical models. A difference of 8000 km in the solar radii was found when comparing our results against the heights obtained from Hα observations of spicules-off at the solar limb. We conclude that the solar radii cannot be reproduced by VALC and C7 semi-empirical models at radio - infrared wavelengths. Therefore, the structures in the high chromosphere provide a better measurement of the solar radii and their limb brightening as shown in previous investigations. © 2016. The American Astronomical Society. All rights reserved. Source

Chamel N.,Free University of Colombia | Page D.,National Autonomous University of Mexico | Reddy S.,University of Washington
Physical Review C - Nuclear Physics | Year: 2013

We study the low-energy collective excitations in the inner crust of the neutron star, where a neutron superfluid coexists with a Coulomb lattice of nuclei. The dispersion relation of the modes is calculated systematically from a microscopic theory including neutron band structure effects. These effects are shown to lead to a strong mixing between the Bogoliubov-Anderson bosons of the neutron superfluid and the longitudinal crystal lattice phonons. In addition, the speed of the transverse shear mode is greatly reduced as a large fraction of superfluid neutrons are entrained by nuclei. Not only does the much smaller velocity of the transverse mode increase the specific heat of the inner crust, it also decreases its electron thermal conductivity. These results may impact our interpretation of the thermal relaxation in accreting neutron stars. Due to strong mixing, the mean free path of the superfluid mode is found to be greatly reduced. Our results for the collective mode dispersion relations and their damping may also have implications for neutron star seismology. © 2013 American Physical Society. Source

Hacyan S.,National Autonomous University of Mexico
Journal of Optics | Year: 2011

The general form of the exact solutions of Maxwell's equations in Rindler coordinates is obtained. These solutions represent electromagnetic waves that preserve their shapes in a relativistic uniformly accelerating frame. In the non-relativistic limit, the Airy beam turns out to be an exceptional solution with physically realizable parameters. A similarity with Bessel beams is pointed out. © 2011 IOP Publishing Ltd. Source

Gonzalez A.L.,Autonomous University of Puebla | Noguez C.,National Autonomous University of Mexico | Barnard A.S.,CSIRO
Journal of Physical Chemistry C | Year: 2012

The remarkable relationship among the size, shape, and optical properties of gold nanoparticles is proving to be very useful in a range of high-performance applications. Considerable effort and investment is focused on delivering gold nanoparticles with precise morphologies. However, the reliability of these particles is contingent upon the morphological stability, particularly against variations in the thermodynamic environment, such as changes in temperature. Presented here are results from a combination of computational and theoretical techniques showing how the optical properties of gold nanoparticles respond to changes in the size, shape, or temperature, obtained by sampling the optical spectrum over large configuration space, in accordance with the nanoscale phase diagram. We find that spectrum from morphologies expected at small sizes is robust against temperature fluctuations, unless the concentration is very high. At larger sizes, the color will likely change with temperature, due to the accompanying change in particle shape, and this change will be noticeable when the concentration is low. © 2012 American Chemical Society. Source

MacIas-Ruvalcaba N.A.,National Autonomous University of Mexico | Evans D.H.,Purdue University
Journal of Physical Chemistry C | Year: 2010

The electrochemical reduction of nine quinones has been studied in acetonitrile and, in one case, in dimethyl sulfoxide. Included are seven hydroxyquinones plus 1,4-naphthoquinone, 8, and 9,10-anthraquinone, 9. Each quinone is reduced in two steps, first to the anion radical and then, at more negative potentials, to the dianion. However, digital simulations show that the voltammetric data cannot be explained by these two reactions alone. For three of the hydroxyquinones, 2-4, plus 8 and 9, the fast disproportionation/ comproportionation reaction connecting the neutral, anion radical, and dianion must be included along with a diffusion coefficient of the anion radical that is smaller than that of the neutral quinone and a still smaller diffusion coefficient for the dianion. Three other hydroxyquinones, 5-7, require, in addition, the formation of a neutral-anion radical complex. Finally, 5-hydroxy-1,4-naphthoquinone, 1, in acetonitrile involves both σ- and π-dimerization of the anion radical with subsequent reduction of the π-complex, whereas in dimethyl sulfoxide the σ-dimer is replaced by the aforementioned formation of the neutral-anion radical complex. The differences in behavior are discussed in terms of distribution of spin density in the anion radicals and intermolecular and intramolecular hydrogen bonding. © 2010 American Chemical Society. Source

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. Source

Becerra-Diaz M.,National Autonomous University of Mexico
International journal of biological sciences | Year: 2011

Helminth parasites are a diverse group of multicellular organisms. Despite their heterogeneity, helminths share many common characteristics, such as the modulation of the immune system of their hosts towards a permissive state that favors their development. They induce strong Th2-like responses with high levels of IL-4, IL-5 and IL-13 cytokines, and decreased production of proinflammatory cytokines such as IFN-γ. IL-4, IFN-γ and other cytokines bind with their specific cytokine receptors to trigger an immediate signaling pathway in which different tyrosine kinases (e.g. Janus kinases) are involved. Furthermore, a seven-member family of transcription factors named Signal Transducers and Activators of Transcription (STAT) that initiate the transcriptional activation of different genes are also involved and regulate downstream the JAK/STAT signaling pathway. However, how helminths avoid and modulate immune responses remains unclear; moreover, information concerning STAT-mediated immune regulation during helminth infections is scarce. Here, we review the research on mice deficient in STAT molecules, highlighting the importance of the JAK/STAT signaling pathway in regulating susceptibility and/or resistance in these infections. Source

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. Source

Kaikina E.I.,National Autonomous University of Mexico
Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences | Year: 2013

We consider the initial-boundary-value problem for the cubic nonlinear Schrödinger equation, formulated on a half-line with inhomogeneous Robin boundary data. We study traditionally important problems of the theory of nonlinear partial differential equations, such as the global-in-time existence of solutions to the initial-boundary-value problem and the asymptotic behaviour of solutions for large time. © 2013 The Author(s) Published by the Royal Society. All rights reserved. Source

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. Source

Castanos L.O.,National Autonomous University of Mexico
Quantum Information and Computation | Year: 2012

We consider two two-level atoms fixed at different positions, driven by a resonant monochromatic laser field, and interacting collectively with the quantum electromagnetic field. A Born-Markov-secular master equation is used to describe the dynamics of the two atoms and the steady-state is obtained analytically for a configuration of the atoms. The steady-state populations of the energy levels of the free atoms, entanglement, quantum and geometric discords and degree of mixedness are calculated analytically as a function of the laser field intensity and the distance between the two atoms. It is found that there is a possibility of considerable steady-state entanglement and left/right quantum discord and that these can be controlled either by increasing/decreasing the intensity of the laser field or by increasing/decreasing the distance between atoms. It is shown that the system of two atoms can be prepared in a separable mixed state with non-zero quantum discord that turns into an X-state for high laser field intensities. The behavior and relationships between the different correlations are studied and several limiting cases are investigated. © Rinton Press. Source

Garcia-Islas J.M.,National Autonomous University of Mexico
Classical and Quantum Gravity | Year: 2010

Recently an idea for computing the entropy of black holes in the spin foam formalism has been introduced. Particularly complete calculations for the three-dimensional Euclidean BTZ black hole were performed. The whole calculation is based on observables living at the horizon of the black hole universe. Departing from this idea of observables living at the horizon, we now go further and compute the entropy of the BTZ black hole in the spirit of statistical mechanics. We compare both calculations and show that they are very interrelated and equally valid. This latter behaviour is certainly due to the importance of the observables. © 2010 IOP Publishing Ltd. Source

Stoks R.,Catholic University of Leuven | Crdoba-Aguilar A.,National Autonomous University of Mexico
Annual Review of Entomology | Year: 2012

Most insects have a complex life cycle with ecologically different larval and adult stages. We present an ontogenetic perspective to analyze and summarize the complex life cycle of Odonata within an evolutionary ecology framework. Morphological, physiological, and behavioral pathways that generate carry-over effects across the aquatic egg and larval stages and the terrestrial adult stage are identified. We also highlight several mechanisms that can decouple life stages including compensatory mechanisms at the larval and adult stages, stressful and stochastic events during metamorphosis, and stressful environmental conditions at the adult stage that may overrule effects of environmental conditions in the preceding stage. We consider the implications of these findings for the evolution, selection, and fitness of odonates; underline the role of the identified numerical and carry-over effects in shaping population and metapopulation dynamics and the community structure across habitat boundaries; and discuss implications for applied conservation issues. © 2012 by Annual Reviews. All rights reserved. Source

Fornoni J.,National Autonomous University of Mexico
Functional Ecology | Year: 2011

1. Plant tolerance to herbivory has been accepted as a mechanism of defense that can be expressed jointly with resistance. Recent advances have partially validated previous theoretical predictions and improved our understanding of tolerance. Here, I highlight the necessity of integrating tolerance into ecological and co-evolutionary theory to better understand the biology of this defensive mechanism. 2.Existing work has been biased toward understanding the adaptive nature and constraints acting on tolerance rather than its ecological implications. Increasing consensus that tolerance may alter the classical antagonistic dynamic between plants and herbivores suggests possible avenues to explore its population and community consequences. 3.In this review, I summarize previous advances in the ecology and evolution of tolerance to herbivory. I also discuss recent evidence that improves our understanding of unresolved issues such as the specificity of tolerance in response to herbivory, its role as an agent of selection on herbivores, and its ecological and evolutionary consequences which include a role of tolerance during biological invasions. 4.Although there is good support for an adaptive role of tolerance in response to herbivory damage, tolerance can itself impose selection on herbivores. Furthermore, tolerance can influence herbivore population dynamics and coexistence, as recent studies show that tolerance responses increase diversity of the associated herbivore communities on individual host plants. 5.Future studies that take into account the role of herbivores on the expression of tolerance will provide novel insight that will help disentangle the mechanisms of tolerance and its ecological and evolutionary implications. © 2010 The Author. Functional Ecology © 2010 British Ecological Society. Source

Bernal J.P.,National Autonomous University of Mexico
American Mineralogist | Year: 2015

In-situ U-Th dating is among the most challenging analytical techniques, requiring extreme sensitivity to quantify the low-abundance 230Th. Consequently, not all mineral phases are suitable for this technique. In this issue, Wu et al. have demonstrated that baddeleyite in basic rocks can provide meaningful U-Th ages when analyzed using secondary ionization mass spectrometry. © 2015 by Walter de Gruyter Berlin/Boston. Source

de la Macorra A.,National Autonomous University of Mexico
Astroparticle Physics | Year: 2010

We present a new dark matter model BDM which is an hybrid between hot dark matter HDM and cold dark matter CDM, in which the BDM particles behave as HDM above the energy scale Ec and as CDM below this scale. Evolution of structure formation is similar to that of CDM model but BDM predicts a nonvanishing free streaming λfs scale and a inner galaxy core radius rcore, both quantities determined in terms of a single parameter Ec, which corresponds to the phase transition energy scale of the subjacent elementary particle model. For energies above Ec or for a scale factor a smaller then ac, with a < ac < aeq, the particles are massless and ρ redshifts as radiation. However, once the energy becomes E ≤ Ec or a > ac then the BDM particles acquire a large mass through a non-perturbative mechanism, as baryons do, and ρ redshifts as matter with the particles having a vanishing velocity. Typical energies are Ec = O (10 s(-) 100) eV giving a λfs ∝ Ec - 4 / 3 ≲ Mpc and Mfs ∝ Ec - 4 ≲ 109 M ȯ. A λfs ≠ 0, rcore ≠ 0 help to resolve some of the shortcomings of CDM such as over-abundance substructure in CDM halos and numerical fit to rotation curves in dwarf spheroidal and LSB galaxies. Finally, our BDM model and the phase transition scale Ec can be derived from particle physics. © 2010 Elsevier B.V. All rights reserved. Source

Garcia-Segura G.,National Autonomous University of Mexico
Astronomy and Astrophysics | Year: 2010

Aims. We explore the effects of photodissociation at the stages of post-asymptotic giant branch stars to find a mechanism able to produce multi-polar shapes. Methods. We perform two-dimensional gasdynamical simulations to model the effects of photodissociation in proto-planetary nebulae. Results. We find that post-asymptotic giant branch stars with ~7000 K or hotter are able to photodissociate a large amount of the circumstellar gas. We compute several solutions for nebulae with low-velocity multi-lobes. We find that the early expansion of a dissociation front is crucial to understand the number of lobes in proto-planetary nebulae. Conclusions. A dynamical instability appears when cooling is included in the swept-up molecular shell. This instability is similar to the one found in photoionization fronts, and it is associated with the thin-shell Vishniac instability. The dissociation front exacerbates the growth of the thin-shell instability, creating a fast fragmentation in shells expanding into media with power-law density distributions such as r-2. © 2010 ESO. Source

Fraija N.,National Autonomous University of Mexico
Astrophysical Journal | Year: 2015

One of the most energetic gamma-ray bursts, GRB 110731A, was observed from an optical to GeV energy range. Previous analysis of the prompt phase revealed similarities between the Large Area Telescope (LAT) bursts observed by Fermi: (1) a delayed onset of the high-energy emission (> 100 MeV), (2) a short-lasting bright peak at later times, and (3) a temporally extended component from this phase, lasting hundreds of seconds. Additionally to the prompt phase, multiwavelength observations over different epochs showed that the spectral energy distribution was better fitted by a wind afterglow model. We present a leptonic model based on an early afterglow that evolves in a stellar wind of its progenitor. We apply this model to interpret the temporally extended LAT emission and the brightest LAT peak exhibited by the prompt phase of GRB 110731A. Additionally, using the same set of parameters, we describe the multiwavelength afterglow observations. The origin of the temporally extended LAT, X-ray, and optical flux is explained through synchrotron radiation from the forward shock (FS) and the brightest LAT peak is described, evoking the synchrotron self-Compton emission from the reverse shock (RS). The bulk Lorentz factor required in this model (Γ ≃ 520) lies in the range of values demanded for most LAT-detected GRBs. We show that the strength of the magnetic field in the RS region is ∼50 times stronger than that in the FS region. This result suggests that, for GRB 110731A, the central engine is likely entrained with strong magnetic fields. © 2015. The American Astronomical Society. All rights reserved. Source

Nunez-Perez R.,National Autonomous University of Mexico
Journal of Zoology | Year: 2011

Reliable data on jaguar population densities are needed to propose appropriate conservation and management strategies, and camera trapping may be effective for estimating the population density of secretive large cats. I determined the population density of jaguars in the Chamela-Cuixmala Biosphere Reserve along the coast of Jalisco, Mexico, through camera trapping and capture-recapture analysis during the dry season of March to June 2008. I applied the half mean maximum distance moved (1/2MMDM) to calculate the radius of the effectively sampled area, and compared this with estimates of the effectively sampled area based on existing data on mean home range of jaguars at the study site. I found that both methods of calculating the effectively sampled area produced similar population density estimates. The widely used 1/2MMDM based on camera-trapping data produced a population density of 5.3jaguars/100km2, while calculation of the effectively sampled area based on mean home range produced a population density of 5jaguars/100km2. Despite the small size of the 131-km2 Chamela-Cuixmala Biosphere Reserve, jaguar population density was relatively high, suggesting that small, well-protected reserves can be important refuges for jaguars. © 2011 The Authors. Journal of Zoology © 2011 The Zoological Society of London. Source

Contreras-Ramos A.,National Autonomous University of Mexico
Zootaxa | Year: 2011

Phylogenetic relationships of the World genera of dobsonflies, subfamily Corydalinae, are reappraised, as well as those of species of the New World genus Corydalus, both on the basis of morphological characters. Previous phylogenetic hypotheses of dobsonfly genera by Glorioso, Penny, and Contreras-Ramos, respectively, are re-evaluated, and a fourth revised phylogeny is presented. Ninety-five characters of 10 taxa, one outgroup and nine ingroup taxa, were used in the updated analysis of Corydalinae. It recognizes four lineages, with Chloroniella as sister to the other three, of which the Nevromus lineage (Acanthacorydalis + Nevromus + Neoneuromus) is sister to the Corydalus lineage (Chloronia + Platyneuromus + Corydalus), and both as a group are sister to the Protohermes lineage (Protohermes + Neurhermes). The main changes in the updated Corydalinae phylogeny are the placement of Chloroniella as sister to all other dobsonfly genera, and the placement of Acanthacorydalis as a member of the Nevromus lineage. Previously, Penny had proposed Chloroniella as sister to all dobsonfly genera except the Protohermes lineage, and both Glorioso and Penny, respectively, placed Acanthacorydalis as sister to the Corydalus lineage. About Corydalus, its species phylogeny is herein updated, as four species from Venezuela were added to the genus after its taxonomic revision. For the new phylogeny, 120 characters of 35 taxa, two outgroup and 33 ingroup taxa, were used. It produced a strict consensus of two trees, better resolved than the previous one. The C. arpi species group is moved to sister of all other species except the C. cephalotes species pair, while the C. batesii species group is conserved, being the only unresolved group within the phylogeny. Two of the species added, C. hayashii and C. mayri, belong to the well defined C. arpi species group, of Guayana Shield affinity, whereas C. crossi is sister to a large and widespread group beginning with the C. nubilus species group, and C. clavijoi is sister to C. tesselatus within the latter group. Copyright © 2011 · Magnolia Press. Source

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. Source

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. Source

Krongold Y.,National Autonomous University of Mexico | Prochaska J.X.,University of California at Santa Cruz
Astrophysical Journal | Year: 2013

We study the ≳ 10 ratios in the X-ray to optical column densities inferred from afterglow spectra of gamma ray bursts (GRBs) due to gas surrounding their progenitors. We present time-evolving photoionization calculations for these afterglows and explore different conditions of their environment. We find that homogenous models of the environment (constant density) predict X-ray columns similar to those found in the optical spectra, with the bulk of the opacity being produced by neutral material at large distances from the burst. This result is independent of gas density or metallicity. Only models assuming a progenitor immersed in a dense (∼10 2-4 cm-3) cloud of gas (with radius ∼10 pc), with a strong, declining gradient of density for the surrounding interstellar medium (ISM) are able to account for the large X-ray to optical column density ratios. However, to avoid an unphysical correlation between the size of this cloud and the size of the ionization front produced by the GRB, the models also require that the circumburst medium is already ionized prior to the burst. The inferred cloud masses are ≲ 106 M , even if low metallicities in the medium are assumed (Z ∼ 0.1 Z ). These cloud properties are consistent with those found in giant molecular clouds and our results support a scenario in which the progenitors reside within intense star formation regions of galaxies. Finally, we show that modeling over large samples of GRB afterglows may offer strong constraints on the range of properties in these clouds, and the host galaxy ISM. © 2013. The American Astronomical Society. All rights reserved. Source

Heras J.A.,National Autonomous University of Mexico
European Journal of Physics | Year: 2014

In their recent paper, Barbieri et al (2013 Eur. J. Phys. 34 1209) proposed an educational path for the magnetic vector potential. In this comment I point out that this educational path involves several inconsistencies and is therefore unattractive from a pedagogical point of view. © 2014 IOP Publishing Ltd. Source

Tanner M.,National Autonomous University of Mexico
Journal of Analytical Atomic Spectrometry | Year: 2010

Signal to noise ratios of transient signals depend on the signal duration and are usually better for shorter signals. Poisson distribution is the dominating noise source for mass spectrometers at low count numbers. The IUPAC concept of 'detection limit' is used as a measure of the noise level and three different ways of detection limit calculations are compared and discussed. Assumption of Normal distribution leads to underestimation of the detection limit compared to exact Poisson based calculations. A simple formula given by IUPAC bases detection limit on the standard deviation of the blank but introduces a term to correct for the difference between Normal and Poisson distributions. Results of this formula are comparable to exact Poisson calculations. Signal to noise in transient signals was evaluated. It was found that an optimum duration for transient signals exists and that it depends on the level of the instrument background. © 2010 The Royal Society of Chemistry. Source

Ortiz Velasquez A.,National Autonomous University of Mexico
Nuclear and Particle Physics Proceedings | Year: 2015

The ALICE detector was designed to study the physics of matter under extreme conditions of high energy density. Different results were reported by the experiment using data from the successful run I of the LHC. The goal of the present work is to present an overview of recent ALICE results. This comprises selected results from several analyses of pp, p-Pb and Pb-Pb data at the LHC energies. © 2015 Elsevier B.V. Source

Moreno J.A.,National Autonomous University of Mexico | Osorio M.,Pontifical Bolivarian University
IEEE Transactions on Automatic Control | Year: 2012

A method to construct a family of strict Lyapunov functions, i.e., with negative definite derivative, for the super-twisting algorithm, without or with perturbations, is provided. This second order sliding modes algorithm is widely used to design controllers, observers and exact differentiators. The proposed Lyapunov functions ascertain finite time convergence, provide an estimate of the convergence time, and ensure the robustness of the finite-time or ultimate boundedness for a class of perturbations wider than the classical ones for this algorithm. Since the Lyapunov functions and their derivatives are quadratic forms, the operation with them is as simple as for linear time invariant systems. © 2011 IEEE. Source

Gaona-Narvaez T.,Florida International University | Maurrasse F.J.-M.R.,Florida International University | Moreno-Bedmar J.A.,National Autonomous University of Mexico
Cretaceous Research | Year: 2013

Detailed stable carbon-isotope and biostratigraphic data based on ammonites allow us to reinterpret the timing of the different units of the Madotz section (62 m thick) in Navarra, northern Spain, relative to OAE-1a. We also infer bulk sedimentary rates and the duration of the intervals that include facies indicative of oxygen depletion. The lowermost part of the sequence includes the predominately clastic unit 1 (3 m) overlain in ascending order by subunits 2a (20 m), 2b (24.4 m) and 2c (basal 15 m studied) of the "Madotz Limestone". Subunits 2a and 2c consist of Urgonian-type pure carbonate rocks. In contrast, subunit 2b consists of mixed carbonate-clastic facies (24.4 m thick) including beds of claystone and clay/shale with dispersed pyrite and scarce or no benthic foraminifera suggestive of oxygen-depleted conditions, and intermittent orbitolinid-rich intervals. δ13Corg data within subunit 2b, between 26.6 and 49.2 m show two excursions of 4.21 and 3.34‰, separated by a central segment with more uniform values around 22.56%. Compared to the high-resolution δ13C stratigraphy of the Early Aptian of the Alpine Tethys, these two positive excursions correlate with segments C4 and C6 of OAE-1a, whereas the central segment correlates with segment C5. New ammonite findings include Deshayesites cf. forbesi Casey and Pseudohaploceras? sp. in the uppermost part of unit 1, and D. cf. forbesi Casey, Pseudosaynella bicurvata (Michelin) and P. raresulcata (d'Orbigny) in the middle part of subunit 2b. The presence of D. cf. forbesi in unit 1 (0-37.7 m) and subunit 2b (lower 14.7 m), the first appearance datum of Pseudosaynella in subunit 2b, and the high relative abundance of Pseudosaynella specimens, support a stratigraphic position correlative with at least the upper part of the D. forbesi Zone (formerly D. weissi Zone). Such an ammonite faunal assemblage implies a lower stratigraphic position in the Lower Aptian (Bedoulian) than previously assigned to the section. Segments C4 and most of C5 comprise the lower part of subunit 2b and correspond to the upper part of the D. forbesi Zone. Based on chemostratigraphic correlations with published Spanish sections (Barranco de las Calzadas, Cap de Vinyet and Cau) in which calibrations of δ13Ccarb stages with ammonite zones was possible, we infer that the interval of the Madotz section between 37.7 and 53.1 m, or the upper part of subunit 2b and the basal part of subunit 2c, whose δ13Corg signal is indicative of stages C5, C6, and perhaps the beginning of stage C7, also correlates with the D. forbesi Zone. Average bulk sedimentation rate for C-isotope stages C4-C6 of OAE-1a ranges from 1.8 to 2.09 cm/kyr in the Madotz section. Facies indicative of oxygen deficiency are restricted to C-isotope stage C4 and part of C5 of OAE-1a. Hypoxic conditions lasted about 95.23-120 kyr and are coeval with deposition of the most prominent claystone and shale layers (1.8 m thick), which display the lowest TIC values (8.16-18.93 weight% CaCO3) and the highest TOC in the section (0.4-0.97%). © 2012. Source

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. Source

Verma S.P.,National Autonomous University of Mexico | Verma S.K.,University of Campinas | Oliveira E.P.,University of Campinas
International Geology Review | Year: 2015

Fifty-five new multi-dimensional diagrams, mostly based on log-ratio transformations, were used to decipher tectonic settings for 17 cases of Precambrian belts in Canada, the USA, Poland, Finland, Jordan, Democratic Republic of Congo and Zambia, China, and India. The results of different sets of diagrams for basic-ultrabasic, intermediate, and acid magmas were generally internally consistent. Possible reasons for some inconsistencies may be related to the use of a sample group of mixed ages because of their uncertainties, extreme element mobility caused by metamorphism especially of high-grade type, analytical data quality, different petrogenetic processes for basic to acid magmas such as mantle versus crustal origin, and some deficiencies that still exist in the multi-dimensional diagrams. To partly overcome the last problem, one new multi-dimensional diagram is proposed and used to discriminate mid-ocean ridge and oceanic plateau settings. © 2014 © 2014 Taylor & Francis. Source

Perez-Castorena A.-L.,National Autonomous University of Mexico
Journal of the Mexican Chemical Society | Year: 2014

The chemical study of the leaves and stems of Tibouchina urvilleana afforded triterpenes of different types: four oleanane, four ursane, one glutinane, and one taraxerane. Also, two flavonoids and two sterols were isolated. Additionally, the toxicity and topical antiinflammation activity of the extracts were tested. © 2014, Sociedad Química de México. Source

Two discriminant-function-based multidimensional major-element diagrams for the tectonic discrimination of siliciclastic sediments were recently published from a coherent statistical methodology of loge-ratio transformation and linear discriminant analysis. These diagrams were constructed based on worldwide examples of Neogene-Quaternary siliciclastic sediments from known tectonic settings. In this work, these two tectonic discrimination diagrams were first successfully tested from Holocene (<0.0117-0 Ma) beach and deep-sea sediments from the Gulf of Mexico. These diagrams were used to decipher tectonic settings of 11 case studies of the Precambrian clastic sedimentary rocks (~512-2800 Ma) from Argentina, USA, Ghana, Spain, Norway, India, China, and Australia. The test and application results obtained from these discrimination diagrams were generally consistent with the geology of the Precambrian source areas. Therefore, the two multidimensional diagrams can be considered as a useful tool for successfully discriminating the tectonic setting of older sedimentary basins, which may consist of one or more tectonic assemblages. Comparison of results of this study with the previously published tectonic discrimination diagrams is illustrated and the probable reasons for some inconsistent inferences were also discussed. © 2014 © 2014 Taylor & Francis. Source

Epidemiological studies worldwide have shown that A. fumigatus exhibits important phenotypic and genotypic diversity, and these findings have been of great importance in improving the diagnosis and treatment of diseases caused by this fungus. However, few studies have been carried out related to the epidemiology of this fungus in Latin America. This study's aim is to report on the epidemiology of the fungus by analyzing the phenotypic variability of Aspergillus section Fumigati isolates from different Latin American countries and the relationship between this variability, the geographical origin and genotypic characteristics. We analyzed the phenotypic characteristics (macro- and micromorphology, conidial size, vesicles size, antifungal susceptibility and thermotolerance at 28, 37 and 48°C) of A. section Fumigati isolates from Mexico (MX), Argentina (AR), Peru (PE) and France (FR). The results were analyzed using analysis of variance (ANOVA) and Tukey's multiple comparison test to detect significant differences. Two dendrograms among isolates were obtained with UPGMA using the Euclidean distance index. One was drawn for phenotypic data, and the other for phenotypic and genotypic data. A PCoA was done for shown isolates in a space of reduced dimensionality. In order to determine the degree of association between the phenotypic and genotypic characteristics AFLP, we calculated the correlation between parwise Euclidean distance matrices of both data sets with the nonparametric Mantel test. No variability was found in the macromorphology of the studied isolates; however, the micromorphology and growth rate showed that the PE isolates grew at a faster rate and exhibited the widest vesicles in comparison to the isolates from MX, AR and FR. The dendrogram constructed with phenotypic data showed three distinct groups. The group I and II were formed with isolates from PE and FR, respectively, while group III was formed with isolates from MX and AR. The dendrogram with phenotypic and genotypic data showed the same cluster, except for an isolate from FR that formed a separate cluster. This cluster was confirmed using PCoA. The correlation between the phenotypic and genotypic data of the isolates revealed a statistically significant association between these characteristics. The PE isolates showed specific phenotypic characteristics that clearly differentiate them from the rest of the isolates, which matches the genotypic data. The correlation between the phenotypic and genotypic characteristics showed a statistically significant association. In conclusion, phenotypic and genotypic methods together increase the power of correlation between isolates. Source

Sanchez-Salcedo F.J.,National Autonomous University of Mexico
Astrophysical Journal | Year: 2012

The dynamical friction force experienced by a massive gravitating body moving through a gaseous medium is modified by sufficiently strong large-scale magnetic fields. Using linear perturbation theory, we calculate the structure of the wake generated by, and the gravitational drag force on, a body traveling in a straight-line trajectory in a uniformly magnetized medium. The functional form of the drag force as a function of the Mach number (≡ V 0/cs, where V 0 is the velocity of the body and cs is the sound speed) depends on the strength of the magnetic field and on the angle between the velocity of the perturber and the direction of the magnetic field. In particular, the peak value of the drag force is not near Mach number ∼ 1 for a perturber moving in a sufficiently magnetized medium. As a rule of thumb, we may state that for supersonic motion, magnetic fields act to suppress dynamical friction; for subsonic motion, they tend to enhance dynamical friction. For perturbers moving along the magnetic field lines, the drag force at some subsonic Mach numbers may be stronger than at supersonic velocities. We also mention the relevance of our findings to black hole coalescence in galactic nuclei. © 2012. The American Astronomical Society. All rights reserved. Source

Martinez-Garcia E.E.,National Autonomous University of Mexico
Astrophysical Journal | Year: 2012

According to one version of the recently proposed "manifold" theory that explains the origin of spirals and rings in relation to chaotic orbits, galaxies with stronger bars should have a higher spiral arms pitch angle when compared to galaxies with weaker bars. A subsample of barred-spiral galaxies in the Ohio State University Bright Galaxy Survey was used to analyze the spiral arms pitch angle. These were compared with bar strengths taken from the literature. It was found that the galaxies in which the spiral arms maintain a logarithmic shape for more than 70° seem to corroborate the predicted trend. © 2012. The American Astronomical Society. All rights reserved. Source

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. Source

Ibanez G.,University of Arts and Science of Chiapas | Cuevas S.,National Autonomous University of Mexico
Energy | Year: 2010

The dissipative processes that arise in a microchannel flow subjected to electromagnetic interactions, as occurs in a MHD (magnetohydrodynamic) micropump, are analyzed. The entropy generation rate is used as a tool for the assessment of the intrinsic irreversibilities present in the microchannel owing to viscous friction, heat flow and electric conduction. The flow in a parallel plate microchannel produced by a Lorentz force created by a transverse magnetic field and an injected electric current is considered assuming a thermally fully developed flow and conducting walls of finite thickness. The conjugate heat transfer problem in the fluid and solid walls is solved analytically using thermal boundary conditions of the third kind at the outer surfaces of the walls and continuity of temperature and heat flux across the fluid-wall interfaces. Velocity, temperature and current density fields in the fluid and walls are used to calculate the global entropy generation rate. Conditions under which this quantity is minimized are determined for specific values of the geometrical and physical parameters of the system. The Nusselt number is also calculated and explored for different conditions. Results can be used to determine optimized conditions that lead to a minimum dissipation consistent with the physical constraints demanded by the microdevice. © 2010 Elsevier Ltd. Source

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. Source

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. Source

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. Source

Garcia-Valladares O.,National Autonomous University of Mexico
Applied Thermal Engineering | Year: 2015

A stepped capillary tube is a new design proposed by Zhao et al. that consist of two serial-connected capillary tubes with different diameter as an alternative in order to reduce the manufacturing cost of the typical assembly of two capillary tubes and a by-pass check valve widely used to achieve different mass flow rates in residential heat pump systems. In previous works, one-dimensional numerical modeling of fluid-flow inside capillary tubes and short tube orifices were performed, and successfully validated against a wide range of mass flow rate measurements reported for different refrigerant and mixtures. In this article, the model is applied to stepped capillary tubes (expansion devices). Governing equations (continuity, momentum, energy, and entropy) for describing the fluid flow have been solved by using a fully implicit step-by-step method. A numerical treatment has been codified for considering thermodynamic and flow transitions (subcooled liquid region, metastable liquid region, metastable two-phase region and equilibrium two-phase region). Sudden contraction and enlargement were also considered. A comparison and validation analyses of the simulation results were carried out by using mass flow rate experimental data (No = 30), which have been recently reported in the literature for R-22. Linear relationships between mass flow rate (predicted) and experimental mass flow rate data were statistically demonstrated. Average deviation error of ±3.2% was consistently computed between numerical model and experimental data, which demonstrates the good capability of the model developed for predicting the fluid flow processes. These results demonstrate a new and robust application of the model developed to predict reliably the mass flow rate through stepped capillary tubes, which enable this tool to be reliably used for the design of this kind of systems. © 2015 Elsevier Ltd, All rights reserved. Source

Campion R.,National Autonomous University of Mexico
Geophysical Research Letters | Year: 2014

We report recent satellite measurements of the SO2 emissions from the Virunga Volcanic Group (VVG), which comprises the very active Nyamuragira and Nyiragongo volcanoes. Combining high time resolution data from the UV-operating OMI (Ozone Monitoring Instrument) with high ground resolution data from the IR-operating ASTER (Advanced Spaceborne Thermal Emission and Reflection radiometer), we show that (1) the SO2 emissions from the VVG have increased severalfold since the end of the last eruption of Nyamuragira. (2) Nyamuragira, which used to have very low intereruptive emissions of SO2 before this eruption, is now contributing to 60 to 90% of the combined emissions measured by OMI. Considering the eruptive history of Nyamuragira, the evidence from previous research for the existence of a shallow magma chamber, and the detection of isolated thermal anomalies since April 2014, we conclude that a deep-seated lava lake has formed in the N pit of Nyamuragira's caldera. Key Points We measured SO2 fluxes from Virunga volcanoes using spaceborne sensorsCombining ASTER and OMI to resolve temporally and spatially the emission sourcesHigh gas fluxes and thermal anomalies prove a lava lake formed at Nyamuragira ©2014. American Geophysical Union. All Rights Reserved. Source

Alvarez A.F.,National Autonomous University of Mexico
Methods in enzymology | Year: 2010

The Arc (anoxic redox control) two-component system (TCS) is a complex signal transduction system that plays an important role in regulating energy metabolism at the level of transcription in bacteria. This system comprises the ArcB protein, a hybrid membrane-associated sensor kinase, and the ArcA protein, a typical response regulator. Under anoxic growth conditions, ArcB autophosphorylates and transphosphorylates ArcA via a His→Asp→His→Asp phosphorelay. Under aerobic conditions, the ArcB kinase activity is silenced by the oxidation of two cytosol-located redox-active cysteine residues that participate in intermolecular disulfide bond formation. Under such conditions, ArcB acts as a phosphatase that catalyzes the dephosphorylation of ArcA-P and thereby releasing its transcriptional regulation. This chapter describes general in vitro and in vivo assays and strategies that have been used to characterize the ArcB/A two-component signal transduction system, which could, also, be applied to most other TCS. Copyright © 2010 Elsevier Inc. All rights reserved. Source

Within the social sciences, the standardized notion of representation refers to knowledge expressed through language and sourced from supra-individual thought processes. This notion underscores the social foundation of knowledge while minimizing its inherent material and symbolic foundations, without which it cannot be wholly understood. The article argues that the circulation of heterogeneous inscriptions underpins the elaboration of representations. To demonstrate this, I analyze practices intended to improve a therapeutic treatment for kidney stones and show how scientists place a series of objects, animals, models, texts, and so on in circulation, eventually transformed into the mathematic representation of a treatment. Source

Dorazco-Gonzalez A.,National Autonomous University of Mexico
Organometallics | Year: 2014

The new luminescent platinum(II) pincer complex [Pt(NCN)(S)]TfO (I; NCN = 1,3-bis(2-N-phenylbenzimidazolyl)benzene, S = solvent, and TfO- = triflate anion) was synthesized and studied as a chemosensor for chloride in aqueous media. In 50 vol % aqueous DMF or CH3CN chloride quenches the fluorescence with association constants of 1.2 × 103 and 81 M-1, respectively. On the other hand, in the micellar medium of cetyltrimethylammonium hydrogensulfate at pH 7.0 additions of inorganic anions to I enhance the fluorescence with a pronounced selectivity toward chloride, which shows also much tighter binding to the receptor with association constant 7.9 × 104 M-1 in comparison to that in mixed organic solvents. On basis of 1H NMR titration experiments and the crystal structure of the neutral chloro complex of I the binding mode of chloride is proposed involving the coordination of chloride to the Pt(II) atom with simultaneous formation of intramolecular short C-H···Cl-Pt contacts. The combination of the cyclometalated platinum complex I with a cationic surfactant allows for the detection of chloride in the micromolar concentration range in samples of bottled mineral water. © 2014 American Chemical Society. Source

This text looks at the difference between sociology in medicine (collaborator of health institutions) and the sociology of medicine (independent of health institutions). If consistent, sociology in medicine should become a sociology of medicine. As an example, it is shown how the study of the social determinants of health and illness begins by assuming non-problematically the ontological reality of health and illness, but ends up problematizing the very concept of health-disease, demonstrating that the study of health determinants also requires the study of the determinants of the social construction of disease. The urgent necessity of objectifying collective health itself is argued. By applying sociological tools we can examine the so-called objective factors in the determination of health and disease, the socially constructed nature of these categories of knowledge, and the struggles and power relations that determine whether or not such categories are viable. Source

Kershenobich D.,National Autonomous University of Mexico
Annals of Hepatology | Year: 2010

Hepatitis C signifies a highly prevalent infection in patients with end stage renal disease. Most frequently it is associated to glomerulonephritis, patients on hemodyalisis and renal transplants. The prevalence of HCV antibodies in hemodialysis patients varies between 5-70% depending on the geographical location of the patients. Factors associated with the prevalence of anti HCV in patients with hemodialysis include: age, blood transfusions, tattoos, use of illegal drugs, time in hemodialysis, more than two hospitalizations, treatment in multiple hemodialysis units or a kidney transplant. In some of the reported outbreaks of hepatitis in hemodialysis units, the phylogenetic analysis indicate that the transmission of HCV could relate to failures or breaches in general precautions in the management of these type of patients resulting in nosocomial transmission owed to sharing equipment or instruments employed in the hemodialysis or by transmission from professional members of the hemodialysis units. Antiviral treatment may be affected by a number of co-factors and co-morbidities, it consist mainly of non pegylated interferon or pegylated interferon. The treatment with interferon after a renal transplant is associated with an increase in the number of rejections; reason enough to recommended that treatment should be administered before the transplant. Source

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. Source

Bruni M.,University of Portsmouth | Hidalgo J.C.,University of Portsmouth | Hidalgo J.C.,National Autonomous University of Mexico | Meures N.,University of Portsmouth | Wands D.,University of Portsmouth
Astrophysical Journal | Year: 2014

The goal of the present paper is to set initial conditions for structure formation at nonlinear order, consistent with general relativity, while also allowing for primordial non-Gaussianity. We use the nonlinear continuity and Raychaudhuri equations, which together with the nonlinear energy constraint, determine the evolution of the matter density fluctuation in general relativity. We solve this equations at first and second order in a perturbative expansion, recovering and extending previous results derived in the matter-dominated limit and in the Newtonian regime. We present a second-order solution for the comoving density contrast in a ΛCDM universe, identifying nonlinear contributions coming from the Newtonian growing mode, primordial non-Gaussianity and intrinsic non-Gaussianity, due to the essential nonlinearity of the relativistic constraint equations. We discuss the application of these results to initial conditions in N-body simulations, showing that relativistic corrections mimic a non-zero nonlinear parameter f NL. © 2014. The American Astronomical Society. All rights reserved.. Source

Prince M.J.,Kings 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. Source

Martinez A.,National Autonomous University of Mexico | Galano A.,Metropolitan Autonomous University | Vargas R.,Metropolitan Autonomous University
Journal of Physical Chemistry B | Year: 2011

Mangosteen is a tropical fruit that presents beneficial effects on human health since it is rich in anthocyanins and xanthones, which are considered bioactive compounds that have been described as good free radical scavengers. One of its most active compounds is α-mangostin. In this report, a theoretical study on the free radical scavenger capacity of α-mangostin and its monoanion is analyzed using the density functional theory approximation. Two well-known reaction mechanisms are investigated: the hydrogen atom transfer (HAT) and the radical adduct formation (RAF). Two other mechanisms are also considered: sequential electron proton Transfer (SEPT) and proton coupled electron transfer (PCET). According to thermodynamics and kinetics, α-mangostin and its deprotonated form are good free radical scavenger through the HAT mechanism, with the anionic (deprotonated) form being more reactive than the neutral one. Their capacity to scavenge OOH free radical is similar to that of carotenes, higher than that of allicin, much higher than that of melatonin and N-acetylcysteine amide, and about 15 times lower than that of 2-propenesulfenic acid. © 2011 American Chemical Society. Source

Dominguez H.,National Autonomous University of Mexico
Journal of Physical Chemistry B | Year: 2011

Molecular dynamics simulations were used to investigate aggregation of surfactants at the solid-liquid interface at different surfactant concentrations. For these studies simulations of the sodium dodecyl sulfate (SDS) surfactant with a graphite surface were carried out. At low concentrations the SDS molecules aggregated in slices of cylinders attached to the solid surface, whereas at slightly higher concentrations the structures showed irregular shapes. When the concentration was again increased to a higher value, the molecules aggregated in a more complex structure, an irregular aggregate on the top of a semicylinder adsorbed on the graphite surface. From the present results more insights about the internal structure of the aggregates were observed than in actual experiments, e.g., it was found that the SDS tails arrayed in well-defined layers close to the graphite surface. More over, from the internal structure it was possible to show a structural transition driven by an increment in the surfactant concentration which, to the best of our knowledge, has not been studied from a molecular point of view. Therefore the transition was studied in terms of the height of the structures. Along with these studies adsorption of the aggregates, by calculating contact angles, and adsorption isotherms were also analyzed. Finally, investigations of the surface coverage with the concentration showed that this quantity did not change considerably with the concentration. © 2011 American Chemical Society. Source

Bribiesca E.,National Autonomous University of Mexico
Pattern Recognition | Year: 2013

A measure of tortuosity for 2D curves is presented. Tortuosity is a very important property of curves and has many applications, such as: how to measure the tortuosity of retinal blood vessels, intracerebral vasculature, aluminum foams, etc. The measure of tortuosity proposed here is based on a chain code called Slope Chain Code (SCC). The SCC uses some ideas which were described in [A geometric structure for 2D shapes and 3D surfaces, Pattern Recognition 25 (1992) 483-496]. The SCC of a curve is obtained by placing straight-line segments of constant length around the curve (the endpoints of the straight-line segments always touching the curve), and calculating the slope changes between contiguous straight-line segments scaled to a continuous range from -1 to 1. The SCC of a curve is independent of translation, rotation, and optionally, of scaling, which is an important advantage for computing tortuosity. Also, the minimum and maximum values of tortuosity for curves and a measure of normalized tortuosity are described. Finally, an application of the proposed measure of tortuosity is presented which corresponds to the computation of retinal blood vessel tortuosity. © 2012 Elsevier Ltd. Source

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. Source

Bizarro M.,National Autonomous University of Mexico
Applied Catalysis B: Environmental | Year: 2010

Zinc oxide and aluminum doped zinc oxide films were produced using the spray pyrolysis technique. The substrate temperature and the solution flow rate were varied to optimize the surface morphology of the films. Different concentrations of aluminum were added to the precursor solution in Al/Zn = 0.05, 0.10, 0.25, and 0.50 to study the effect on the photocatalytic activity of ZnO. The films were characterized by profilometry, scanning electron microscopy (SEM), X-ray diffraction (XRD) and the photocatalytic activity was tested by the decomposition of methyl orange dye under UV illumination. The addition of aluminum did not change the ZnO crystalline structure, but changed the surface morphology and increased the photocatalytic activity of ZnO films reducing the time taken to degrade an 80% of the dye from 4 to only 1.25 h. © 2010 Elsevier B.V. All rights reserved. Source

Argatov I.I.,University of Oulu | Sabina F.J.,National Autonomous University of Mexico
International Journal of Engineering Science | Year: 2014

Frictionless indentation of an elastic layer attached to an elastic half-space is considered in the small-scale contact range. Based on the first-order asymptotic solution, a simple analytical approximation is suggested for the indentation scaling factor that takes into account the elastic layer's finite thickness as well as the effect of the elastic substrate. The influence of both Poisson's ratios on the substrate effect is studied in detail, and the error of the 1/10 rule of Buckle is estimated for a relatively large range of the elastic moduli mismatch. © 2014 Elsevier Ltd. All rights reserved. Source

Bijker R.,National Autonomous University of Mexico | Iachello F.,Yale University
Physical Review Letters | Year: 2014

We derive the rotation-vibration spectrum of a 4α configuration with tetrahedral symmetry Td and show evidence for the occurrence of this symmetry in the low-lying spectrum of O16. All vibrational states with A, E, and F symmetry appear to have been observed as well as the rotational bands with LP=0+, 3-, 4+, 6+ on the A states and part of the rotational bands built on the E, F states. We derive analytic expressions for the form factors and B(EL) values of the ground-state rotational band and show that the measured values support the tetrahedral symmetry of this band. © 2014 American Physical Society. Source

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.. Source

Page D.,National Autonomous University of Mexico | Reddy S.,University of Washington
Physical Review Letters | Year: 2013

It is now possible to model thermal relaxation of neutron stars after bouts of accretion during which the star is heated out of equilibrium by nuclear reactions in its crust. Major uncertainties in these models can be encapsulated in modest variations of a handful of control parameters that change the fiducial crustal thermal conductivity, specific heat, and heating rates. Observations of thermal relaxation constrain these parameters and allow us to predict longer term variability in terms of the neutron star core temperature. We demonstrate this explicitly by modeling ongoing thermal relaxation in the neutron star XTE J1701-462. Its future cooling, over the next 5 to 30 years, is strongly constrained and depends mostly on its core temperature, uncertainties in crust physics having essentially been pinned down by fitting to the first three years of observations. © 2013 American Physical Society. Source

Vazquez R.,National Autonomous University of Mexico
Astrophysical Journal | Year: 2012

High-resolution Hubble Space Telescope archive imaging and high-dispersion spectroscopy are used to study the complex morphological and kinematical structure of the planetary nebula, NGC2818. We analyze narrowband Hα, [O III], [N II], [S II], and He II images, addressing important morphological features. Ground-based long-slit echelle spectra were obtained crossing NGC2818 at five different positions to precisely determine kinematical features in the structure of the nebula. A distance of 2.5kpc was used to determine physical scales. Constructing models to fit the data with modern computational tools, we find NGC2818 is composed of (1) a non-uniform bipolar structure with a semimajor axis of 0.92pc (75″), possibly deformed by the stellar wind, (2) a 0.17pc (14″) diameter central region, which is potentially the remnant of an equatorial enhancement, and (3) a great number of cometary knots. These knots are preferentially located inside a radius of 0.24pc (20″) around the central star. The major axis of the main structure is oriented at i ≃ 60° with respect to the line of sight and at P.A. = +89° on the plane of the sky. Expansion velocities of this nebula are V pol = 105 km s-1 and V eq = 20 km s-1, which lead to our estimate of the kinematical age of τk ≃ 8400 ± 3400yr (assuming homologous expansion). Our observations do not support the idea that high-velocity collimated ejections are responsible for the formation of microstructures inside the nebula. We determine the systemic velocity of NGC2818 to be V HEL = +26 ± 2 km s-1. © 2012. The American Astronomical Society. All rights reserved.. Source

Morrone J.J.,National Autonomous University of Mexico
Systematics and Biodiversity | Year: 2014

Biogeographers working under different approaches have proposed several terms to refer to biotas, e.g. The flora and fauna of a region, and to name subsets of taxa within such biotas. It is not clear whether they refer exactly to the same entities and which is the most adequate term to refer to them. Ten concepts refer to the set of taxa that inhabit an area at a single temporal plane (concrete biota, chronofauna, area of endemism, nuclear area, phytocorion, centre of endemism, generalized track, biogeographical assemblage, taxonomic assemblage, and species assemblage), whereas another nine concepts refer to subsets of taxa within a biota (biotic element, historical source, historical component, faunal element, cenocron, dispersal pattern, distributional pattern, lineage, and historical biota). Three concepts can be ascribed to both groups, depending on the author considered (horofauna, chorotype and biotic component). I propose to use the terms biota and cenocron as general terms, within a framework of integrative pluralism. Biotas can be considered individuals, for which the terms area of endemism, generalized track or chorotype can be preferred for specific analyses. Cenocrons incorporate a temporal dimension when implying explicitly or implicitly a different time of their incorporation to the biota. © 2014 The Trustees of the Natural History Museum, London. Source

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. Source

Martinez-Calvillo S.,National Autonomous University of Mexico
Journal of biomedicine & biotechnology | Year: 2010

The parasites Leishmania spp., Trypanosoma brucei, and Trypanosoma cruzi are the trypanosomatid protozoa that cause the deadly human diseases leishmaniasis, African sleeping sickness, and Chagas disease, respectively. These organisms possess unique mechanisms for gene expression such as constitutive polycistronic transcription of protein-coding genes and trans-splicing. Little is known about either the DNA sequences or the proteins that are involved in the initiation and termination of transcription in trypanosomatids. In silico analyses of the genome databases of these parasites led to the identification of a small number of proteins involved in gene expression. However, functional studies have revealed that trypanosomatids have more general transcription factors than originally estimated. Many posttranslational histone modifications, histone variants, and chromatin modifying enzymes have been identified in trypanosomatids, and recent genome-wide studies showed that epigenetic regulation might play a very important role in gene expression in this group of parasites. Here, we review and comment on the most recent findings related to transcription initiation and termination in trypanosomatid protozoa. Source

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. Source