Castro-Villarreal P.,Autonomous University of Chiapas |
Ruiz-Sanchez R.,Chiapas Polytechnic University
Physical Review B - Condensed Matter and Materials Physics | Year: 2017
The general covariance of the Dirac equation is exploited in order to explore the curvature effects appearing in the electronic properties of graphene. Two physical situations are then considered: the weak curvature regime, with R<1/L2, and the strong curvature regime, with 1/L2 R<1/d2, where R is the scalar curvature, L is a typical size of a sample of graphene, and d is a typical size of a local domain where the curvature is pronounced. In the first scenario, we found that the curvature transforms the conical nature of the dispersion relation due to a shift in the momentum space of the Dirac cone. In the second scenario, the curvature in the local domain affects the charge carriers in such a manner that bound states emerge; these states are declared to be pseudo-Landau states because of the analogy with the well known Landau problem; here the curvature emulates the role of the magnetic field. Seeking more tangible curvature effects we calculate, e.g., the electronic internal energy of graphene in the small curvature regime and give an expression for the ground state energy in the strong curvature regime. © 2017 American Physical Society.
Ruiz-Perez V.I.,Autonomous University of Chiapas |
Guzman-Sepulveda J.R.,University of Central Florida
Optics Express | Year: 2017
In this paper we demonstrate the passive, material-based athermalization of all-fiber architectures by cascading multimode interference (MMI) devices. In-line thermal compensation is achieved by including a liquid-core multimode section of variable length that allows ensuring temperature-independent operation while preserving the inherent filter-like spectral response of the MMI devices. The design of the temperature compensation unit is straightforward and its fabrication is simple. The applicability of our approach is experimentally verified by fabricating a wavelength-locked MMI laser with sensitivity of only -0.1 pm/°C, which is at least one order of magnitude lower than that achieved with other fiber optics devices. © 2017 Optical Society of America.
Castellanos E.,Autonomous University of Chiapas |
Rivas J.I.,Metropolitan Autonomous University
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2015
We analyze the possible effects arising from the Planck scale regime upon the interference pattern of two noninteracting Bose-Einstein condensates. We start with the analysis of the free expansion of a condensate, and have taken into account the effects produced by a deformed dispersion relation, suggested in several quantum-gravity models. The analysis of the condensate free expansion, in particular, the modified free velocity expansion, suggests in a natural way, a modified uncertainty principle that could lead to new phenomenological implications related to the quantum structure of space-time. Finally, we analyze the corresponding separation between the interference fringes after the two condensates overlap, in order to explore the sensitivity of the system to possible signals caused by the Planck scale regime. © 2015 American Physical Society.
Imberton G.,Autonomous University of Chiapas
Culture, Medicine and Psychiatry | Year: 2012
According to ethnographic material collected since 2003, the Chol Mayan indigenous people in southern Mexico have different causal explanations for suicide. It can be attributed to witchcraft that forces victims to take their lives against their own will, to excessive drinking, or to fate determined by God. However, it can also be conceived of as a conscious decision made by a person overwhelmed by daily problems. Drawing from the theoretical framework developed by Laura M. Ahearn, inspired by practice theory, the paper contends that these different explanations operate within two different logics or understandings of human agency. The first logic attributes responsibility to supernatural causes such as witchcraft or divine destiny, and reflects Chol notions of personhood. The second logic accepts personal responsibility for suicide, and is related to processes of social change such as the introduction of wage labor, education and a market economy. The contemporary Chol resort to both logics to make sense of the human drama of suicide. © 2012 Springer Science+Business Media, LLC.
Linares R.,Metropolitan Autonomous University |
Morales-Tecotl H.A.,Metropolitan Autonomous University |
Pedraza O.,Autonomous University of Chiapas
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2010
Casimir force encodes the structure of the field modes as vacuum fluctuations and so it is sensitive to the extra dimensions of brane worlds. Now, in flat spacetimes of arbitrary dimension the two standard approaches to the Casimir force, Green's function, and zeta function yield the same result, but for brane world models this was only assumed. In this work we show that both approaches yield the same Casimir force in the case of universal extra dimensions and Randall-Sundrum scenarios with one and two branes added by p compact dimensions. Essentially, the details of the mode eigenfunctions that enter the Casimir force in the Green's function approach get removed due to their orthogonality relations with a measure involving the right hypervolume of the plates, and this leaves just the contribution coming from the zeta function approach. The present analysis corrects previous results showing a difference between the two approaches for the single brane Randall-Sundrum; this was due to an erroneous hypervolume of the plates introduced by the authors when using the Green's function. For all the models we discuss here, the resulting Casimir force can be neatly expressed in terms of two four-dimensional Casimir force contributions: one for the massless mode and the other for a tower of massive modes associated with the extra dimensions. © 2010 The American Physical Society.
Castro-Villarreal P.,Autonomous University of Chiapas
Journal of Statistical Mechanics: Theory and Experiment | Year: 2014
Based upon the Smoluchowski equation on curved manifolds, three physical observables are considered for Brownian displacement, namely geodesic displacement s, Euclidean displacement δR, and projected displacement δR⊥. The Weingarten-Gauss equations are used to calculate the mean-square Euclidean displacements in the short-time regime. Our findings show that from an extrinsic point of view the geometry of the space affects the Brownian motion in such a way that the particle's diffusion is decelerated, contrasting with the intrinsic point of view where dynamics is controlled by the sign of the Gaussian curvature (Castro-Villarreal, 2010 J. Stat. Mech. P08006). Furthermore, it is possible to give exact formulas for δR and δR2 on spheres and minimal surfaces, which are valid for all values of time. In the latter case, surprisingly, Brownian motion corresponds to the usual diffusion in flat geometries, albeit minimal surfaces have non-zero Gaussian curvature. Finally, the two-dimensional case is emphasized due to its close relation to surface self-diffusion in fluid membranes. © 2014 IOP Publishing Ltd and SISSA Medialab srl.
Castro-Villarreal P.,Autonomous University of Chiapas
Journal of Statistical Mechanics: Theory and Experiment | Year: 2010
The general covariance of the diffusion equation is exploited in order to explore the curvature effects appearing in Brownian motion over a ddimensional curved manifold. We use the local frame defined by the so-called Riemann normal coordinates to derive a general formula for the mean-square geodesic distance (MSD) at the short-time regime. This formula is written in terms of O(d) invariants that depend on the Riemann curvature tensor. We study the n-dimensional sphere case to validate these results. We also show that the diffusion for positive constant curvature is slower than the diffusion in a plane space, while the diffusion for negative constant curvature turns out to be faster. Finally the two-dimensional case is emphasized, as it is relevant for single-particle diffusion on biomembranes. © 2010 IOP Publishing Ltd and SISSA.
Grajales F.O.,Autonomous University of Chiapas
Boletin Academico | Year: 2016
Aalto was in México in 1963 during the International Symposium of Architecture of the UIA. A concise review in a magazine records that only visit to Aztec lands. Neither his participation in an exhibition in this country, nor the fact of being awarded with a local distinction had an impact in media. Besides that, Göran Schildt did not of er a wide coverage to the trip, limiting itself to tell an irrelevant anecdote. Surprisingly, Aalto did not make drawings during his stay in Mexico. Based in this context, the present work offers a route across some of the Mexican publications in order to present a follow-up to the presence that the most famous Finnish architect of the twentieth century has had in printed media.
Cifuentes-Goches J.C.,Autonomous University of Chiapas
Revista médica del Instituto Mexicano del Seguro Social | Year: 2012
to determine the impact of lipid serum abnormalities and the prevalence of metabolic syndrome (MS) in healthy adults. a cross-sectional, prospective and observational study in apparently healthy adults aged 20 to 60 years who had at least three of the following criteria: abdominal obesity (waist circumference > 102 cm in men and > 88 cm in women), triglycerides ≥ 150 mg/dL, HDL cholesterol < 40 mg/dL in men and < 50 mg/dL in women, blood pressure ≥ 130/85 mmHg and fasting glucose ≥ 110 mg/dL). the prevalence of MS was 20 %, being higher in women (67.7 %) than men (32.3 %). However, no dependence was found with gender (χ(2)= 2.059, p = 0.151). The age range with a higher prevalence of was 45-49 years. Low HDL cholesterol [HR = 11,059 (3.559, 34.610) p < 0.01], was present in 67.9 % of women and hypertriglyceridemia [HR = 15.53 (4.975, 48.513) p < 0.01] was present in 60.5 % of men. the results suggested that hypertriglyceridemia and hypoalphalipoproteinemia are high impact factors for MS in adults.
Fu-Espinosa M.,Autonomous University of Chiapas
Revista médica del Instituto Mexicano del Seguro Social | Year: 2013
Diabetes mellitus type 2 (DM2) is the leading cause of death in people from 15 to 64 years in Mexico, and other regions in the world. For the chronic nature of diabetes and complications caused by inadequate metabolic control, patients may have mood disorders such as depression. Several studies have demonstrated higher prevalence of depression in diabetic patients than in general population. Our objective: is to determine prevalence and factors associated with depressive disorder in patients with type 2 diabetes mellitus enrolled in DiabetIMSS during 2010. Analytical study with random probability sampling. The analysis included prevalence, odds ratios with 95% confidence intervals. The Center Epidemiological Studies Depression Instrument was used. Prevalence of depression was 32.7% at 95% CI = 26.4-38.9%), 67.3% for women, 32.7 % for men; good metabolic control was 51.9%, CI = 95% (45.13-58.66%). We found a higher prevalence of depressive disorders than in the general population, no statistical association with glycemic control, keeping a greater proportion of women as well as the main aspect of depression associated with the perception of emotional support. We discuss DiabetIMSS program effectiveness.