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Search Results: 1 - 10 of 297838 matches for " José Luis Herrera-Pérez "
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Negative thermal diffusivity enhancement in semiconductor nanofluids  [PDF]
Martha Patricia González-Araoz, José Francisco Sánchez-Ramírez, José Luis Jiménez-Pérez, Ernesto Chigo-Anota, José Luis Herrera-Pérez, Julio Gregorio Mendoza-álvarez
Natural Science (NS) , 2012, DOI: 10.4236/ns.2012.412131
Abstract: Colloidal suspensions of semiconductor InP@ZnS nanoparticles were prepared using single-step procedure without precursor injection. Thermal properties of toluene containing InP@ZnS semiconductor with different sizes (3.1, 4.2, and 4.6 nm) were measured by mode mismatched dualbeam thermal lens technique. This was done in order to measure the effect of the presence of semiconductor nanoparticles and size on the nanofluids thermal diffusivity. The characteristic time constant of the transient thermal lens was estimated by fitting the experimental data to the theoretical expression for transient thermal lens. The thermal diffusivity of the nanofluids (toluene, containing InP@ZnS semiconductor nanoparticles) it seems to be strongly dependent on the presence of semiconductor nanoparticles and particles size. For the case of nanofluids consisting of InP@ZnS nanoparticles dispersed in toluene, it was observed a decrease in the thermal diffusivity. Such behavior differs from other nanofluids, in the sense that they had shown positive thermal diffusivity enhancement. The minimum diffusivity was achieved for the nanoparticles with lowest size. Plausible explanation for such nanofluids low thermal diffusivity with semiconductor nanoparticles is given. UV-Vis spectroscopy, TEM and high-resolution electron microscopy (HRTEM), and energy dispersive spectroscopy (EDS) techniques were used to characterize the InP@ZnS nanoparticles.
Melatonin Inhibits GnRH-1, GnRH-3 and GnRH Receptor Expression in the Brain of the European Sea Bass, Dicentrarchus labrax
Arianna Servili,Patricia Herrera-Pérez,María del Carmen Rendón,José Antonio Mu?oz-Cueto
International Journal of Molecular Sciences , 2013, DOI: 10.3390/ijms14047603
Abstract: Several evidences supported the existence of melatonin effects on reproductive system in fish. In order to investigate whether melatonin is involved in the modulation of GnRH systems in the European sea bass, we have injected melatonin (0.5 μg/g body mass) in male specimens. The brain mRNA transcript levels of the three GnRH forms and the five GnRH receptors present in this species were determined by real time quantitative PCR. Our findings revealed day–night variations in the brain expression of GnRH-1, GnRH-3 and several GnRH receptors (dlGnRHR-II-1c, -2a), which exhibited higher transcript levels at mid-light compared to mid-dark phase of the photocycle. Moreover, an inhibitory effect of melatonin on the nocturnal expression of GnRH-1, GnRH-3, and GnRH receptors subtypes 1c, 2a and 2b was also demonstrated. Interestingly, the inhibitory effect of melatonin affected the expression of hypophysiotrophic GnRH forms and GnRH receptors that exhibit day–night fluctuations, suggesting that exogenous melatonin reinforce physiological mechanisms already established. These interactions between melatoninergic and GnRH systems could be mediating photoperiod effects on reproductive and other rhythmic physiological events in the European sea bass.
Participación de las hormonas gonadales en el efecto de los fármacos antidepresivos en la rata macho
Lucía Martínez-Mota,José Jaime Herrera-Pérez,Maribel Olivares Nazario,Alonso Fernández-Guasti
Salud mental , 2012,
Abstract: Se ha propuesto que las hormonas gonadales participan en la regulación del estado de ánimo en los varones, y en el efecto de los fármacos psicoactivos, tales como los antidepresivos. Sin embargo, la evaluación de este tipo de interacciones ha sido estudiada escasamente. El objetivo del presente trabajo fue determinar el papel que cumplen las hormonas testosterona (T) y 17β-estradiol (E2), uno de sus principales metabolitos, en el efecto de dos fármacos antidepresivos utilizados en la práctica clínica, desipramina y fluoxetina. El primero es un tricíclico con acciones sobre el sistema noradrenérgico, mientras que la fluoxetina es un inhibidor selectivo de la recaptura de serotonina. Las evaluaciones se llevaron a cabo utilizando ratas macho adultas jóvenes, gonadalmente intactas u orquidectomizadas (Orx), bajo tratamiento con T (0-1 mg/rata), E2 (0-40 μg/rata), desipramina (0-20 mg/kg), fluoxetina (0-20 mg/kg) y sus respectivas combinaciones. Se utilizó la prueba de nado forzado (PNF) para detectar las acciones antidepresivas de los tratamientos. Encontramos que desipramina y fluoxetina redujeron la conducta de depresión en los machos gonadalmente intactos; sin embargo, el efecto de ambos tratamientos fue abolido por la orquidectomía. El tratamiento de restitución hormonal con E2, pero no con T, indujo acciones antidepresivas en los machos Orx. A su vez, cuando los animales Orx recibieron la restitución con T se produjo la recuperación del efecto antidepresivo de la desipramina, mientras que el E2 restableció las acciones antidepresivas de ambos fármacos. En conclusión, el principal andrógeno de origen testicular, la T, participa en la expresión del efecto de los fármacos antidepresivos explorados en el presente estudio, principalmente a través de su metabolito estrogénico, el E2. Estos resultados apoyan la idea de que una terapia adjunta de tratamientos hormonales y antidepresivos sería de beneficio para varones hipogonadales que cursen con depresión resistente a los fármacos antidepresivos convencionales.
Brain SERT Expression of Male Rats Is Reduced by Aging and Increased by Testosterone Restitution
José Jaime Herrera-Pérez,Alonso Fernández-Guasti,Lucía Martínez-Mota
Neuroscience Journal , 2013, DOI: 10.1155/2013/201909
Abstract: In preclinical and clinical studies aging has been associated with a deteriorated response to antidepressant treatment. We hypothesize that such impairment is explained by an age-related decrease in brain serotonin transporter (SERT) expression associated with low testosterone (T) levels. The objectives of this study were to establish (1) if brain SERT expression is reduced by aging and (2) if the SERT expression in middle-aged rats is increased by T-restitution. Intact young rats (3–5 months) and gonad-intact middle-aged rats with or without T-restitution were used. The identification of the brain SERT expression was done by immunofluorescence in prefrontal cortex, lateral septum, hippocampus, and raphe nuclei. An age-dependent reduction of SERT expression was observed in all brain regions examined, while T-restitution recovered the SERT expression only in the dorsal raphe of middle-aged rats. This last action seems relevant since dorsal raphe plays an important role in the antidepressant action of selective serotonin reuptake inhibitors. All data suggest that this mechanism accounts for the T-replacement usefulness to improve the response to antidepressants in the aged population. 1. Introduction Clinical studies propose a delayed response of aged patients to antidepressants as compared to young ones [1, 2]. Accordingly, we recently found in the chronic mild stress paradigm that middle-aged male rats (MA, 13–15 months) responded slower than young adults to the antidepressant treatment with citalopram (a selective serotonin reuptake inhibitor—SSRI—) [3]. The serotonin transporter (SERT) is the primary target of SSRIs and has a polymorphism in the promoter region of its gene with two variants: long (l) and short (s), interestingly, the s-variant has been associated to a reduced SERT expression and low serotonin uptake [4–7]. Patients carrying the s-variant (associated to low SERT expression) displayed a retarded response to SSRIs [8–10], suggesting a relationship between therapeutic response and number of SERTs [9, 11, 12]. On the other hand, it has been shown that in aged subjects there is deterioration of serotoninergic fibers in the rat forebrain [13] and reduced binding of [11C](+)McN5652 to SERT in several brain areas of Rhesus monkey, such as prefrontal cortex and hippocampus [14], a structure involved in the response to antidepressants [15]. On these bases we hypothesize that the impaired antidepressant-like response of MA rats to citalopram [3] is associated with an age-related reduction of brain SERT expression. The mechanisms underlying the
Study of the electronic structure of transition metal compounds by absorption and emission of X-rays
J. Jiménez-Mier,G. Herrera-Pérez,P. Olalde-Velasco,E. Chavira
Revista mexicana de física , 2007,
Abstract: Se presentan resultados de espectroscopias de absorci′on y emisi′on de rayos x de ′oxidos y fluoruros de metales de transici′on. Se estudia la absorci′on en la cercan′ a de la orilla L de absorci′on del metal de transici′on. Para algunos valores de la eneg′ a de excitaci′on tambi′en se muestran espectros de emisi′on. Los datos se interpretan en t′erminos de la estructura de multiplete del ion del metal de transici ′on en un campo cristalino, considerando tambi′en efectos de interacci′on de configuraciones en el s′olido, como es la transferencia de carga. Se comparan los datos con resultados de un c′alculo para ion libre que permite una interpretaci′on directa de los espectros de absorci′on. Los c′alculos para iones libres tambi′en indican que algunos de los picos de emisi′on m′as importantes corresponden a la producci′on de excitadiones d a d en el compuesto, con picos de emisi′on a m′as altas energ′ as de p′erdida debidos a estados de transferencia de carga.
Electron dynamics of transition metal compounds studied with resonant soft x-ray scattering
J. Jiménez-Mier,G. Herrera-Pérez,P. Olalde-Velasco,G. Carabalí
Revista mexicana de física , 2011,
Abstract: Se presentan datos experimentales para el esparcimiento resonante de rayos x en compuestos de metales de transición. Los compuestos estudiados son los difluoruros de metales de transición que son iónicos, ortovanadatos iónicos y covalentes, y varios miembros de la familia de Perovskitas La1-xSr xCoO3. En todos los compuestos estudiamos la orilla L2,3 del metal de transición y la orilla K del ligando (oxígeno o fluor). Para los compuestos iónicos los datos del metal de transición están en buen acuerdo con cálculos de multiplete atómico con campo ligante que incluyen transferencia de carga. Cálculos que emplean funcionales de densidad dan información muy útil para interpretar los datos de emisión de rayos x en la orilla del ligando. Los datos de emisión Lα muestran que la region entre las bandas de valencia y conducción en los difluoruros tiene estados excitados d. En la orilla L2 de los ortovanadatos ionicos encontramos características de un proceso Coster-Kronig de decaimiento que da lugar a un pico de emision muy localizado. En las orillas L2,3 del metal y K de oxígeno se observaron cambios en el estado de oxidación en los compuestos La1-xSr xCoO3.
Ligand field and interference effects in L-edge x-ray raman scattering of MnF2 and CoF2
J. Jiménez-Mier,G.M. Herrera-Pérez,P. Olalde-Velasco,D.L. Ederer
Revista mexicana de física , 2008,
Abstract: Presentamos resultados experimentales para absorción y emisión resonante de rayos x en la orilla L del metal de transici′on en MnF2 y CoF2. Los datos de emisión se presentan corregidos por autoabsorción. Los datos se comparan con cálculos en la aproximación de ión libre y con el efecto de un campo ligante de simetría D4h incluido. Los resultados del cálculo toman en cuenta los términos de interferencia en la expresión de Kramers-Heisenberg. Se encuentra muy buen acuerdo entre el experimento y la teoría en los dos compuestos. La inclusión del campo ligante es muy importante para alcanzar dicho acuerdo. Sin embargo, los resultados del cálculo que no incluyen los términos de interferencia están en mejor acuerdo con el experimento, indicando que el modelo empleado probablemente sobre-estima la importancia de los términos de interferencia
Ligand field and interference effects in L-edge x-ray Raman scattering of MnF2 and CoF2
J. Jiménez-Mier,G.M. Herrera-Pérez,P. Olalde-Velasco,D.L. Ederer
Revista mexicana de física , 2008,
Abstract: We present experimental results for x-ray absorption and resonant emission at the L-edge of the transition metal in MnF2 and CoF2. The emission data are corrected for self-absorption. The data are compared with calculations in both the free-ion approximation and with the effect of the ligand field of D4h symmetry included. The results of the calculations take into account interference terms in the Kramers- Heisenberg expression. We obtain very good agreement between experiment and theory for both x-ray absorption and resonant emission in the two compounds. The inclusion of the ligand field is important to achieve such agreement. However, the results of the calculation that does not take into account the interference terms are in better agreement with experiment, indicating that the model used probably overestimates the importance of interference effects.
Analysis of DC Electrical Conductivity Models of Carbon Nanotube-Polymer Composites with Potential Application to Nanometric Electronic Devices
Rafael Vargas-Bernal,Gabriel Herrera-Pérez,Ma. Elena Calixto-Olalde,Margarita Tecpoyotl-Torres
Journal of Electrical and Computer Engineering , 2013, DOI: 10.1155/2013/179538
Abstract:
Analysis of DC Electrical Conductivity Models of Carbon Nanotube-Polymer Composites with Potential Application to Nanometric Electronic Devices
Rafael Vargas-Bernal,Gabriel Herrera-Pérez,Ma. Elena Calixto-Olalde,Margarita Tecpoyotl-Torres
Journal of Electrical and Computer Engineering , 2013, DOI: 10.1155/2013/179538
Abstract: The design of nanometric electronic devices requires novel materials for improving their electrical performance from stages of design until their fabrication. Until now, several DC electrical conductivity models for composite materials have been proposed. However, these models must be valued to identify main design parameters that more efficiently control the electrical properties of the materials to be developed. In this paper, four different models used for modeling DC electrical conductivity of carbon nanotube-polymer composites are studied with the aim of obtaining a complete list of design parameters that allow guarantying to the designer an increase in electrical properties of the composite by means of carbon nanotubes. 1. Introduction In the nanometer era, VLSI circuits must be simulated by novel models that allow us to predict and estimate the electrical behavior waited from their phase of design and during their performance. With the introduction of the nanomaterials as an alternative to silicon, numerous research groups around the world have been developing models to simulate electrical properties of such materials. Within this class of nanomaterials, carbon nanotube-polymer nanocomposites are offering improved electrical properties thanks to inherent electrical properties of the carbon nanotubes either semiconducting or conducting. Previous studies of these materials have predicted successful technological applications [1–3]. However, their design must overcome important barriers involved with the control of phenomena between their interfaces and fabrication methods with the aim of achieving repetitive results. Electrical properties of materials are determined through four fundamental parameters called dielectric constant, tangent of dielectric loss angle, dielectric breakdown, and electrical conductivity. Most polymers exhibit a highly insulating dielectric behavior and a very high electrical resistivity. Thus, it is required adding an electrically conductive filler to polymers for changing their electrical properties. The resulting nanocomposite of such combination can give place to a semiconducting or conducting behavior. Electrical fillers can be ceramic materials, metals, and/or carbon nanotubes. In particular, carbon nanotubes form composite materials which can be applied in gas sensors, biosensors, electromagnetic shielding, antistatic coatings, high-strength low-density corrosion-resistant components, and lightweight energy storage. The use of these nanocomposites will be extended to VLSI circuit design when a complete domain of
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