310 research outputs found
Self-pulsing effect in chaotic scattering
We study the quantum and classical scattering of Hamiltonian systems whose
chaotic saddle is described by binary or ternary horseshoes. We are interested
in parameters of the system for which a stable island, associated with the
inner fundamental periodic orbit of the system exists and is large, but chaos
around this island is well developed. In this situation, in classical systems,
decay from the interaction region is algebraic, while in quantum systems it is
exponential due to tunneling. In both cases, the most surprising effect is a
periodic response to an incoming wave packet. The period of this self-pulsing
effect or scattering echoes coincides with the mean period, by which the
scattering trajectories rotate around the stable orbit. This period of rotation
is directly related to the development stage of the underlying horseshoe.
Therefore the predicted echoes will provide experimental access to topological
information. We numerically test these results in kicked one dimensional models
and in open billiards.Comment: Submitted to New Journal of Physics. Two movies (not included) and
full-resolution figures are available at http://www.cicc.unam.mx/~mejia
Electron microscope evaluation of irreversible electroporation on the liver in a porcine model
From thermal rectifiers to thermoelectric devices
We discuss thermal rectification and thermoelectric energy conversion from
the perspective of nonequilibrium statistical mechanics and dynamical systems
theory. After preliminary considerations on the dynamical foundations of the
phenomenological Fourier law in classical and quantum mechanics, we illustrate
ways to control the phononic heat flow and design thermal diodes. Finally, we
consider the coupled transport of heat and charge and discuss several general
mechanisms for optimizing the figure of merit of thermoelectric efficiency.Comment: 42 pages, 22 figures, review paper, to appear in the Springer Lecture
Notes in Physics volume "Thermal transport in low dimensions: from
statistical physics to nanoscale heat transfer" (S. Lepri ed.
Performance of the 2007 WHO Algorithm to diagnose Smear-negative Pulmonary Tuberculosis in a HIV prevalent setting
The 2007 WHO algorithm for diagnosis of smear-negative pulmonary tuberculosis (PTB) including Mycobacterium tuberculosis (MTB) culture was evaluated in a HIV prevalent area of Kenya
Correlación genotipo-fenotipo cardiovascular de la dopamina β-hidroxilasa (DβH)
Al convertir dopamina en norepinefrina la dopamina β-hidroxilasa (DβH) regula el tono dopaminérgico y adrenérgico. Los alelos rs1989787, rs1611115 y rs1108580 del gen DβH se asocian con actividad deficiente de la enzima y por eso evaluamos sus influencias sobre variables cardiovasculares clínicas, bioquímicas y farmacológicas.Métodos. A 44 voluntarios sanos con los haplotipos triple homocigoto nativo (CC/CC/AA), triple heterocigoto (CT/CT/AG), doble homocigoto mutado (TT/CC/GG) y homocigoto mutado para el rs1611115 (CC/TT/AA) les medimos presión arterial sistólica (PAS), presión arterial diastólica (PAD) y frecuencia cardíaca (FC) en posición decúbito, sentado, de pie, bajo estímulo de frío, con la maniobra de Valsalva y post ingestión de clonidina; adicionalmente medimos actividad enzimática por espectrofotometría y concentraciones séricas de dopamina y norepinefrina por ELISA
Academic student satisfaction and perceived performance in the e-learning environment during the COVID-19 pandemic: Evidence across ten countries
The outbreak of the COVID-19 pandemic has dramatically shaped higher education and seen the distinct rise of e-learning as a compulsory element of the modern educational landscape. Accordingly, this study highlights the factors which have influenced how students perceive their academic performance during this emergency changeover to e-learning. The empirical analysis is performed on a sample of 10,092 higher education students from 10 countries across 4 continents during the pandemic’s first wave through an online survey. A structural equation model revealed the quality of e-learning was mainly derived from service quality, the teacher’s active role in the process of online education, and the overall system quality, while the students’ digital competencies and online interactions with their colleagues and teachers were considered to be slightly less important factors. The impact of e-learning quality on the students’ performance was strongly mediated by their satisfaction with e-learning. In general, the model gave quite consistent results across countries, gender, study fields, and levels of study. The findings provide a basis for policy recommendations to support decision-makers incorporate e-learning issues in the current and any new similar circumstances.info:eu-repo/semantics/publishedVersio
Teratogenic processes in an embryo without gills and low yolk absorption of Zapteryx brevirostris (Elasmobranchii: Rhinobatidae)
Correlation between HIV viral load and aminotransferases as liver damage markers in HIV infected naive patients: a concordance cross-sectional study
Abnormalities in liver function tests could be produced exclusively by direct inflammation in hepatocytes, caused by the human immunodeficiency virus (HIV). Mechanisms by which HIV causes hepatic damage are still unknown. Our aim was to determine the correlation between HIV viral load, and serum levels of aspartate aminotransferase (AST) and alanine aminotransferase (ALT) as markers of hepatic damage in HIV naive infected patients
Higher education students’ achievement emotions and their antecedents in e-learning amid COVID-19 pandemic: A multi-country survey
The outbreak of the COVID-19 pandemic has had a wide range of negative consequences for higher education students. We explored the generalizability of the control-value theory of achievement emotions for e-learning, focusing on their antecedents. We involved 17019 higher education students from 13 countries, who completed an online survey during the first wave of the pandemic. A structural equation model revealed that proximal antecedents (e-learning self-efficacy, computer self-efficacy) mediated the relation between environmental antecedents (cognitive and motivational quality of the task) and positive and negative achievement emotions, with some exceptions. The model was invariant across country, area of study, and gender. The rates of achievement emotions varied according to these same factors. Beyond their theoretical relevance, these findings could be the basis for policy recommendations to support stakeholders in coping with the challenges of e-learning and the current and future sequelae of the pandemic.info:eu-repo/semantics/publishedVersio
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