Avendano C.G.,Autonomous University of Mexico City |
Reyes A.,National Autonomous University of Mexico
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2017
We theoretically study the dispersion relation for axially propagating electromagnetic waves throughout a one-dimensional helical structure whose pitch and dielectric and magnetic properties are spatial random functions with specific statistical characteristics. In the system of coordinates rotating with the helix, by using a matrix formalism, we write the set of differential equations that governs the expected value of the electromagnetic field amplitudes and we obtain the corresponding dispersion relation. We show that the dispersion relation depends strongly on the noise intensity introduced in the system and the autocorrelation length. When the autocorrelation length increases at fixed fluctuation and when the fluctuation augments at fixed autocorrelation length, the band gap widens and the attenuation coefficient of electromagnetic waves propagating in the random medium gets larger. By virtue of the degeneracy in the imaginary part of the eigenvalues associated with the propagating modes, the random medium acts as a filter for circularly polarized electromagnetic waves, in which only the propagating backward circularly polarized wave can propagate with no attenuation. Our results are valid for any kind of dielectric and magnetic structures which possess a helical-like symmetry such as cholesteric and chiral smectic-C liquid crystals, structurally chiral materials, and stressed cholesteric elastomers. © 2017 American Physical Society.
Ponsich A.,Autonomous University of Mexico City |
Jaimes A.L.,Mexican Center for Research and Advanced Studies |
Coello C.A.C.,Mexican Center for Research and Advanced Studies
IEEE Transactions on Evolutionary Computation | Year: 2013
The coinciding development of multiobjective evolutionary algorithms (MOEAs) and the emergence of complex problem formulation in the finance and economics areas has led to a mutual interest from both research communities. Since the 1990s, an increasing number of works have thus proposed the application of MOEAs to solve complex financial and economic problems, involving multiple objectives. This paper provides a survey on the state-of-the-art of research, reported in the specialized literature to date, related to this framework. The taxonomy chosen here makes a distinction between the (widely covered) portfolio optimization problem and the other applications in the field. In addition, potential paths for future research within this area are identified. © 1997-2012 IEEE.
Alfonso L.,Autonomous University of Mexico City |
Raga G.B.,National Autonomous University of Mexico
Atmospheric Chemistry and Physics | Year: 2017
The impact of stochastic fluctuations in cloud droplet growth is a matter of broad interest, since stochastic effects are one of the possible explanations of how cloud droplets cross the size gap and form the raindrop embryos that trigger warm rain development in cumulus clouds. Most theoretical studies on this topic rely on the use of the kinetic collection equation, or the Gillespie stochastic simulation algorithm. However, the kinetic collection equation is a deterministic equation with no stochastic fluctuations. Moreover, the traditional calculations using the kinetic collection equation are not valid when the system undergoes a transition from a continuous distribution to a distribution plus a runaway raindrop embryo (known as the sol-gel transition). On the other hand, the stochastic simulation algorithm, although intrinsically stochastic, fails to adequately reproduce the large end of the droplet size distribution due to the huge number of realizations required. Therefore, the full stochastic description of cloud droplet growth must be obtained from the solution of the master equation for stochastic coalescence. In this study the master equation is used to calculate the evolution of the droplet size distribution after the sol-gel transition. These calculations show that after the formation of the raindrop embryo, the expected droplet mass distribution strongly differs from the results obtained with the kinetic collection equation. Furthermore, the low-mass bins and bins from the gel fraction are strongly anticorrelated in the vicinity of the critical time, this being one of the possible explanations for the differences between the kinetic and stochastic approaches after the sol-gel transition. Calculations performed within the stochastic framework provide insight into the inability of explicit microphysics cloud models to explain the droplet spectral broadening observed in small, warm clouds. © Author(s) 2017.
Lopez-Camarillo C.,Autonomous University of Mexico City |
Lopez-Rosas I.,Autonomous University of Mexico City |
Ospina-Villa J.D.,Polytechnic School of Algiers |
Marchat L.A.,Polytechnic School of Algiers
Wiley Interdisciplinary Reviews: RNA | Year: 2014
Although extraordinary rapid advance has been made in the knowledge of mechanisms regulating messenger RNA (mRNA) metabolism in mammals and yeast, little information is known in deep-branching eukaryotes. The complete genome sequence of Entamoeba histolytica, the protozoan parasite responsible for human amoebiasis, provided a lot of information for the identification and comparison of regulatory sequences and proteins potentially involved in mRNA synthesis, processing, and degradation. Here, we review the current knowledge of mRNA metabolism in this human pathogen. Several DNA motifs in promoter and nuclear factors involved in transcription, as well as conserved polyadenylation sequences in mRNA 3′-untranslated region and possible cleavage and polyadenylation factors, are described. In addition, we present recent data about proteins involved in mRNA decay with a special focus on the recently reported P-bodies in amoeba. Models for mechanisms of decapping and deadenylation-dependent pathways are discussed. We also review RNA-based gene silencing mechanisms and describe the DEAD/DExH box RNA helicases that are molecular players in all mRNA metabolism reactions. The functional characterization of selected proteins allows us to define a general framework to describe how mRNA synthesis, processing, and decay may occur in E. histolytica. Taken altogether, studies of mRNA metabolism in this single-celled eukaryotic model suggest the conservation of specific gene expression regulatory events through evolution. © 2013 John Wiley & Sons, Ltd.
Voutssas J.,Autonomous University of Mexico City
Aslib Proceedings: New Information Perspectives | Year: 2012
Purpose: The purpose of this paper is to summarize the current situation of digital preservation and describe the additional main challenges and issues faced in Latin American countries within the framework of the factors of digital preservation. Design/methodology/approach: This paper reviews the literature on existing digital information preservation around the world, and then focuses on Latin American countries. It proposes a framework in which to analyze the situation in developing countries, particularly in Latin America, and summarizes the issues in six preservation factors and seven principles of preservation. Findings: The amount of digital information has increased geometrically without proper knowledge, theories, strategies, policies and proceedings to preserve it. Developed countries and regions have started to create this knowledge and know-how, as well as setting the basis to manage their digital collections within libraries, archives, and other organizations with the aim to preserve them in the long-term. The situation is radically different in Latin America where we found limited research and projects on digital preservation. Practical implications: The problem of the long-term authentic preservation of digital document collections is not a simple technology problem; it is a much more complex one. This paper summarizes the approaches to understand it but further study is required in order to develop a practical strategy and/or plan. It also highlights the importance of raising awareness of digital preservation in Latin America in order to ensure availability in the future. Social implications: Research, planning, initiatives and proper execution in regard to digital collections preservation is extremely limited in Latin American developing countries, thus endangering vast amounts of digital information. There is a serious risk that valuable digital information will not be preserved adequately for future generations. Originality/value: This paper reviews the main challenges for libraries and archives to preserve digital information over the long term and summarizes the main issues to understand and to thwart this problem. It also highlights the often overlooked problem of digital preservation in developing countries, in particular Latin America. © Emerald Group Publishing Limited.
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.
Raya-Rivera A.M.,Autonomous University of Mexico City |
Esquiliano D.,Autonomous University of Mexico City |
Fierro-Pastrana R.,Autonomous University of Mexico City |
Lopez-Bayghen E.,Autonomous University of Mexico City |
And 5 more authors.
The Lancet | Year: 2014
Background Several disorders might require vaginal reconstruction, such as congenital abnormalities, injury, or cancer. Reconstructive techniques for which non-vaginal tissue is used can be associated with complications. We assessed the use of engineered vaginal organs in four patients with vaginal aplasia caused by Mayer-Rokitansky-Küster-Hauser syndrome (MRKHS). Methods We invited to participate four consecutive patients who presented over a 3-year period with congenital vaginal aplasia due to MRKHS. Patients were aged 13-18 years. We obtained a vulvar biopsy of autologous tissue from every patient. We cultured, expanded, and seeded epithelial and muscle cells onto biodegradable scaff olds. The organs were constructed and allowed to mature in an incubator in a facility approved for human-tissue manufacturing. We used a perineal approach to surgically implant these organs. We recorded history, physical examination, vaginoscopy, serial tissue biopsies, MRIs, and self-administered Female Sexual Function Index questionnaire results for all patients, with a follow-up of up to 8 years. Findings We noted no long-term postoperative surgical complications. Yearly serial biopsies showed a tri-layered structure, consisting of an epithelial cell-lined lumen surrounded by matrix and muscle, with expected components of vaginal tissue present. Immunohistochemical analysis confi rmed the presence of phenotypically normal smooth muscle and epithelia. The MRIs, which showed the extent of the vaginal aplasia before surgery, showed the engineered organs and the absence of abnormalities after surgery, which was confi rmed with yearly vaginoscopy. A validated selfadministered Female Sexual Function Index questionnaire showed variables in the normal range in all areas tested, such as desire, arousal, lubrication, orgasm, satisfaction, and painless intercourse. Interpretation Vaginal organs, engineered from the patient's own cells and implanted, showed normal structural and functional variables with a follow-up of up to 8 years. These technologies could be useful in patients requiring vaginal reconstruction. Funding Wake Forest University and Hospital Infantil de México Federico Gómez.
Dieleman H.,Autonomous University of Mexico City
Journal of Cleaner Production | Year: 2013
This article is about cities and climate change, and about ways to make cities more resilient to the effects of climate change. It presents the two dominant strategies of mitigation and adaptation, and goes on to present a systems view on the city in which resilience is the key response to climate change. The article argues that resilience depends on three dimensions or areas: a city's physical form, infrastructure and technology, its people and particular multilevel governance, levels of human connectedness and communal self-reliance, and the innovative capacity as well as the level of inclusion of marginalized groups within the economy. Teaching and training is seen as an important element in strengthening resilience, and the article presents a number of case studies showing the relevance of learning processes as conditions to work successfully in urban networks in the areas mentioned. The article takes organizational learning as its main orientation and presents important concepts such as "reflective action", "learning by doing", "mental maps", the "experiential learning cycle" and the "5 disciplines of the learning organization". This forms the base for the design of concrete educational material. This material is centered on a number of eco-cultural innovations: concrete ideas, technologies, systems or activities that focus on neighborhood-based activities that reinforce the local economy or introduce small-scale technology for water, renewable energy or waste. © 2013 Elsevier Ltd. All rights reserved.
Alfonso L.,Autonomous University of Mexico City
Atmospheric Chemistry and Physics | Year: 2015
In cloud modeling studies, the time evolution of droplet size distributions due to collision-coalescence events is usually modeled with the Smoluchowski coagulation equation, also known as the kinetic collection equation (KCE). However, the KCE is a deterministic equation with no stochastic fluctuations or correlations. Therefore, the full stochastic description of cloud droplet growth in a coalescing system must be obtained from the solution of the multivariate master equation, which models the evolution of the state vector for the number of droplets of a given mass. Unfortunately, due to its complexity, only limited results were obtained for certain types of kernels and monodisperse initial conditions. In this work, a novel numerical algorithm for the solution of the multivariate master equation for stochastic coalescence that works for any type of kernels, multivariate initial conditions and small system sizes is introduced. The performance of the method was seen by comparing the numerically calculated particle mass spectrum with analytical solutions of the master equation obtained for the constant and sum kernels. Correlation coefficients were calculated for the turbulent hydrodynamic kernel, and true stochastic averages were compared with numerical solutions of the kinetic collection equation for that case. The results for collection kernels depending on droplet mass demonstrates that the magnitudes of correlations are significant and must be taken into account when modeling the evolution of a finite volume coalescing system. © 2015 Author(s).
Dieleman H.,Autonomous University of Mexico City
Journal of Cleaner Production | Year: 2016
The article presents urban agriculture as a practice that is gaining attention in many cities worldwide, and focuses in particular on the experiences in Mexico City. It first gives a general description of urban agriculture, introduces some conceptual dimensions and presents a policy framework to stimulate agriculture in cities worldwide. It then discusses current practices in the periurban, suburban and interurban parts of Mexico City, and analyses them in terms of their economic, ecological, social and symbolic dimension. The article shows that Mexico City produces some 20% of its own food, but that its importance in economic terms - seen as employment and income generation - is still limited. Its contribution to the ecological infrastructure of the city equally is limited but has potential, as recent policies firmly integrate urban agriculture in environmental policies of the city. An important challenge is to expand urban agriculture to the 22,000 m2 of green roof gardens recently created in the city. In terms of the social dimension, it is observed that Mexico City clearly follows international policy recommendations, invests in capacity building and has policies to help vulnerable groups and women. Finally it addresses the symbolic dimension and observes that this is very important in Mexico City, as urban agriculture is seen as a way to restore some of the pre-Hispanic practices of the Aztecs especially the Floating gardens or Chinampas that have largely been lost due to colonization. Its final conclusion is that a policy to balance the economic, ecological, social and symbolic dimensions of urban agriculture is missing, and that such a policy is important, especially for the periurban zone of the city, where most of the food is produced. © 2016 Elsevier Ltd.