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Search Results: 1 - 10 of 207569 matches for " P.;Perez-Alvarez "
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Symmetries and General Principies in the Multiband Effective Mass Theory: A Transfer Matrix Study
L. Diago-Cisneros,H. Rodriguez-Coppola,R. Perez-Alvarez,P. Pereyra
Physics , 2004,
Abstract: We study the time reversal and space inversion symmetry properties of those transfer matrices mostly used in the calculation of energy spectra and transport-process. We study the time reversal and space inversion symmetry properties of those transfer matrices mostly used in the calculation of energy spectra and transport-process quantities. We determine the unitary transformation relating transfer matrices. We consider the Kohn-Luttinger model for a quasi-2D system and show that even though the system studied in the (4 x 4) scheme satisfies all the symmetry requirements, the (2 x 2)subspaces do not fulfill such constrains, except in the Gamma point of the Brillouin Zone. We find new exchange properties between the (2\times 2)subspace quantities.
Interesting coupling phenomena of heavy and light holes in a (GaAs/AlAs) superlattice
L. Diago-Cisneros,H. Rodriguez-Coppola,R. Perez-Alvarez,P. Pereyra
Physics , 2004,
Abstract: An appropriate combination of the scattering theory and the transfer matrix formalism, for the solution of a (4 x 4) Kohn-Luttinger model, allow us to study the multichannel-multiband transmission process of heavy and light holes through a (GaAs/AlAs) superlattice. Appealing effects and interesting channel coupling phenomena, mediated by quasi-bond states, are clearly foreseen.
A Better Look at Learning: How Does the Brain Express the Mind?  [PDF]
Frederic Perez-Alvarez, Alexandra Perez-Serra, Carme Timoneda-Gallart
Psychology (PSYCH) , 2013, DOI: 10.4236/psych.2013.410108

Learning problems in the light of PASS assessment and intervention were studied. Data for 248 subjects with specific learning impairment (SLI), dyslexia, dyscalculia, and non-defined learning difficulty were studied. Hierarchical cluster analysis of PASS scores at baseline was performed. PASS re-assessment was carried out at 6 and 12 months after 6-month period of intervention. Four statistically different cluster groups were identified. All groups, except one, showed cognitive weakness. Planning weakness, associated with other weakness, appears involved in all groups except two where isolated planning and successive weaknesses were identified, respectively. SLI, dyslexia, and dyscalculia are not homogenous entities. A kind of dyslexia is clearly linked to isolated successive weakness. SLI-expressive (SLIe) and a minority of both dyslexia and dyscalculia appear linked to successive weakness although associated with planning and additionally with attention in the case of SLIe. SLI-expressive-receptive (SLIe-r) and Dyscalculia appear linked to simultaneous weakness, although associated with planning weakness. Other kind of SLIe-r appears linked to isolated planning weakness. Other types of SLIe-r and Dyscalculia appear liked to combined planning + successive + attention weakness. Isolated dysfunctional attention does not appear in any case. After 6 months of intervention, planning improves statistically in all cases. Attention improves in few cases. Successive and simultaneous do not improve. The best result is in dyslexia, SLIe and a minority of Dyscalculia. The worst result is in those without cognitive deficiency. The effect of intervention at 6 months remains with minor changes at 12 months after 6 months without intervention.

The methyl ester of rosuvastatin elicited an endothelium-independent and 3-hydroxy-3-methylglutaryl coenzyme A reductase-independent relaxant effect in rat aorta
López-Canales, J.S.;López-Sanchez, P.;Perez-Alvarez, V.M.;Wens-Flores, I.;Polanco, A.C.;Castillo-Henkel, E.;Castillo-Henkel, C.;
Brazilian Journal of Medical and Biological Research , 2011, DOI: 10.1590/S0100-879X2011007500032
Abstract: the relaxant effect of the methyl ester of rosuvastatin was evaluated on aortic rings from male wistar rats (250-300 g, 6 rats for each experimental group) with and without endothelium precontracted with 1.0 μm phenylephrine. the methyl ester presented a slightly greater potency than rosuvastatin in relaxing aortic rings, with log ic50 values of -6.88 and -6.07 m, respectively. unlike rosuvastatin, the effect of its methyl ester was endothelium-independent. pretreatment with 10 μm indomethacin did not inhibit, and pretreatment with 1 mm mevalonate only modestly inhibited the relaxant effect of the methyl ester. nω-nitro-l-arginine methyl ester (l-name, 10 μm), the selective nitric oxide-2 (no-2) inhibitor 1400 w (10 μm), tetraethylammonium (tea, 10 mm), and cycloheximide (10 μm) partially inhibited the relaxant effect of the methyl ester on endothelium-denuded aortic rings. however, the combination of tea plus either l-name or cycloheximide completely inhibited the relaxant effect. inducible no synthase (nos-2) was only present in endothelium-denuded aortic rings, as demonstrated by immunoblot with methyl ester-treated rings. in conclusion, whereas rosuvastatin was associated with a relaxant effect dependent on endothelium and hydroxymethylglutaryl coenzyme a reductase in rat aorta, the methyl ester of rosuvastatin exhibited an endothelium-independent and only slightly hydroxymethylglutaryl coenzyme a reductase-dependent relaxant effect. both no produced by nos-2 and k+ channels are involved in the relaxant effect of the methyl ester of rosuvastatin.
Transfer Matrices and Green Functions for the study of elementary excitations in multilayered heterostructures
R. Perez-Alvarez,F. Garcia-Moliner
Physics , 2004,
Abstract: This article is concerned with a mathematical tool, the Associated Transfer Matrix T, which proves useful in the study of a wide class of physical problems involving multilayer heterostructures. General properties of linear, second order differential matrix Sturm Liouville operators are discussed as a basis for establishing general properties of T, which is also generally related to the Green function G. Some identities satisfied by T are derived, which prove useful in practice to monitor the numerical quality of computational processes.
The Electrostatic Potential Associated to Interface Phonon Modes in Nitride Single Heterostructures
Miguel Eduardo Mora-Ramos;Rolando Perez-Alvarez;Victor R. Velasco
PIER Letters , 2008, DOI: 10.2528/PIERL07111806
Abstract: The electrostatic potential associated to the interface oscillation modes in nitride-based heterostructure is calculated with the use of a complete phenomenological electroelastic continuum approach for the long wave optical oscillations, and the Surface Green Function Matching technique. The crystalline symmetries of zincblende and - isotropically averaged - wurtzite are both considered in the sets of input bulk frequencies and dielectric constants.
Transmittance and Fractality in a Cantor-Like Multibarrier System
Dan S. Diaz-Guerrero;Fernando Montoya;Luis Manuel Gaggero-Sager;Rolando Perez-Alvarez
PIER Letters , 2008, DOI: 10.2528/PIERL07122804
Abstract: The transmittance is studied for a Cantor-like multibarrier system. The calculation are made in the framework of effective mass theory. Some typical values of effective masses and potentials are used in order to have an experimental reference. The techniques of Transfer Matrix are used to calculate the transmittance of the entire structure having some dozens of layers. The results display a complex structure of peaks and valleys. The set of maxima is studied with the tool of the q-dependent dimension D(q). The set of transmittance maxima exhibits a fractal structure, or more exactly, a multifractal structure, i.e., a q-dependent dimension, characterized as usually with limit one when q parameter tends to -∞ but witha limit between 0 and 1 when tends to +∞. This numerical experiment demonstrate that spatially bounded potential may exhibit spectrum with fractal character.
Pharmacological Characterization of the Mechanisms Involved in Delayed Calcium Deregulation in SH-SY5Y Cells Challenged with Methadone
Sergio Perez-Alvarez,Maria E. Solesio,Maria D. Cuenca-Lopez,Raquel M. Melero-Fernández de Mera,Carlos Villalobos,Hanna Kmita,Maria F. Galindo,Joaquin Jordán
International Journal of Cell Biology , 2012, DOI: 10.1155/2012/642482
Abstract: Previously, we have shown that SH-SY5Y cells exposed to high concentrations of methadone died due to a necrotic-like cell death mechanism related to delayed calcium deregulation (DCD). In this study, we show that, in terms of their Ca2+ responses to 0.5?mM methadone, SH-SY5Y cells can be pooled into four different groups. In a broad pharmacological survey, the relevance of different Ca2+-related mechanisms on methadone-induced DCD was investigated including extracellular calcium, L-type Ca2+ channels, -opioid receptor, mitochondrial inner membrane potential, mitochondrial ATP synthesis, mitochondrial Ca2+/2Na+-exchanger, reactive oxygen species, and mitochondrial permeability transition. Only those compounds targeting mitochondria such as oligomycin, FCCP, CGP 37157, and cyclosporine A were able to amend methadone-induced Ca2+ dyshomeostasis suggesting that methadone induces DCD by modulating the ability of mitochondria to handle Ca2+. Consistently, mitochondria became dramatically shorter and rounder in the presence of methadone. Furthermore, analysis of oxygen uptake by isolated rat liver mitochondria suggested that methadone affected mitochondrial Ca2+ uptake in a respiratory substrate-dependent way. We conclude that methadone causes failure of intracellular Ca2+ homeostasis, and this effect is associated with morphological and functional changes of mitochondria. Likely, this mechanism contributes to degenerative side effects associated with methadone treatment. 1. Introduction Methadone (D,L-methadone hydrochloride) is frequently used in different therapies including opioid addiction [1], long-lasting analgesics in cancer and neuropathic pain syndromes [1–3]. However, numerous reports indicate a negative impact on human cognition by chronic exposure to opioid drugs. Patients subjected to methadone maintenance programs show impaired cognitive abilities in aspects such as psychomotor performance, information processing, attention, problem solving, memory, decision making, reaction time, and emotional facial expression recognition [4–10]. Changes in the cytosolic free-calcium concentration ([Ca2+]cyt) are involved in control of a large number of cellular and physiological processes including neuronal excitability, synaptic plasticity, and gene transcription [11, 12]. However, the physiological Ca2+ signal can switch to a death signal when the [Ca2+]cyt??increases dramatically. For example, excitotoxic high glutamate concentrations result in an initial transient increase in [Ca2+]cyt??that is followed by a delayed, irreversible rise in [Ca2+]cyt??known
Time of Progression to Osteopenia/Osteoporosis in Chronically HIV-Infected Patients: Screening DXA Scan
Eugenia Negredo, Anna Bonjoch, Moisés Gómez-Mateu, Carla Estany, Jordi Puig, Nuria Perez-Alvarez, Joaquin Rosales, Silvana di Gregorio, Luis del Rio, Guadalupe Gómez, Bonaventura Clotet
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0046031
Abstract: Background Algorithms for bone mineral density (BMD) management in HIV-infected patients are lacking. Our objective was to assess how often a dual-energy x-ray absorptiometry (DXA) scan should be performed by assessing time of progression to osteopenia/osteoporosis. Methods All DXA scans performed between 2000 and 2009 from HIV-infected patients with at least two DXA were included. Time to an event (osteopenia and osteoporosis) was assessed using the Kaplan–Meier method. Strata (tertiles) were defined using baseline minimum T scores. Differences between strata in time to an event were compared with the log-rank test. Results Of 391 patients (1,639 DXAs), 49.6% had osteopenia and 21.7% osteoporosis at their first DXA scan. Of the 112 (28.6%) with normal BMD, 35.7% progressed to osteopenia; median progression time was 6.7 years. These patients were stratified: “low-risk" (baseline minimum T score >?0.2 SD), “middle-risk" (between ?0.2 and ?0.6 SD), and “high-risk" (from ?0.6 to ?1 SD); median progression time to osteopenia was 8.7, >7.2, and 1.7 years, respectively (p<0.0001). Of patients with osteopenia, 23.7% progressed to osteoporosis; median progression time was >8.5 years. Progression time was >8.2 years in “low-risk" tertile (T score between ?1.1 and ?1.6 SD), >8.5 years in “middle-risk" (between ?1.6 and ?2), and 3.2 years in “high-risk" (from ?2 to ?2.4) (p<0.0001). Conclusions Our results may help to define the BMD testing interval. The lowest T score tertiles would suggest recommending a subsequent DXA in 1–2 years; in the highest tertiles, ≥6 years. Early intervention in patients with bone demineralization could reduce fracture–related morbidity/mortality.
Hopf Bifurcation Control in a Lorenz Type System  [PDF]
P. E. Calderon-Saavedra, E. Munoz-Aguirre, J. Alvarez-Mena, S. Gomez-Perez
Journal of Applied Mathematics and Physics (JAMP) , 2018, DOI: 10.4236/jamp.2018.68146
Abstract: In this paper Hopf bifurcation control is implemented in order to change the bifurcation from supercritical to subcritical in a differential equations system of Lorenz type. To achieve this purpose: first, a region of parameters is identified where the system has a supercritical Hopf bifurcation; second, a class of non-linear feedback control laws is proposed; finally, it is shown that there are control laws which the disturbed system undergoes subcritical Hopf bifurcation.
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