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Search Results: 1 - 10 of 193130 matches for " G. Ortega-Zarzosa "
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Coercivity Values Enhancement by Incorporation of Magnetic Powders in Inorganic Matrix Hosts  [PDF]
J. R. Martínez, J. Román de Alba, I. G. Blanco-Esqueda, A. Guerrero-Serrano, G. Ortega-Zarzosa
New Journal of Glass and Ceramics (NJGC) , 2013, DOI: 10.4236/njgc.2013.31001
Abstract: Enhancement in coercivity values of precursor powders of cobalt ferrite embedded in silica xerogel as well as polyaniline was observed using vibrating sample magnetometry. We compared the magnetic properties of pure precursor powders of ferrite cobalt prepared by coprecipitation method and those embedded in xerogel and polyaniline matrix, prepared by sol-gel and by a conventional in situ chemical oxidation polymerization, respectively. The main magnetic effect is the altered coercivity value growing two magnitude orders for the precursor powders of cobalt ferrite embedded in silica xerogel and in polyaniline. The value goes from 52 Oe to 2200 Oe and 1054 Oe for pure coprecipitated precursor powder and embedded in silica xerogel, and embedded in polyaniline, respectively, without any heat-treatment.
Effect of Aging in the Structure of Silica Xerogels with Incorporation of Extract’s Leaves  [PDF]
José R. Martínez, Erika Espericueta, Gerardo Ortega-Zarzosa
New Journal of Glass and Ceramics (NJGC) , 2011, DOI: 10.4236/njgc.2011.11002
Abstract: The spectral fluorescence characteristics of extracts leaves embedded in silica xerogel matrix promoted by aged time was studied. We obtain a higher PSII stability for extract of leaves embedded in xerogel matrix, with concentration of 8 g / 20 ml and water to TEOS molar ratio of 11, which remain bioactive over a very long period of time, whereas for a water to TEOS molar ratio of 5 a blue-shift fluorescence is observed indicating the PSII denaturizing and formation of fluorescing aggregates associated with the activation of carotenoids radicals.
Análisis del grado de conocimiento declarativo y procedural de estudiantes en cursos de física universitaria
J. R. Martínez,C. Araujo-Andrade,S. A. Palomares-Sánchez,G. Ortega-Zarzosa
Revista mexicana de física , 2006,
Abstract: Se analiza el grado de retención de conocimiento del alumno después de haber pasado por un curso de física universitaria y la habilidad para enfrentar problemas abiertos que poseen, como la mayoría de los problemas académicos, una solución conocida por anticipado. El análisis se enfoca al grado de conocimiento declarativo y de procedimiento, este último utilizando el grado de categorización basado en valoraciones de las resoluciones en un estudio semicuantitativo con base en etapas dise adas para el análisis de respuestas escritas y cerradas de acuerdo con metodologías estándar. De los resultados inferimos que el proceso de aprendizaje al que fueron sometidos los alumnos en cuestión provocó solamente una memoria semántica rutinaria sin llegar a producir conocimientos semánticos significativos, debido a la ausencia de trabajo de procedimiento, que propicia un alejamiento de la ense anza científica.
Modelo de predicción basado en análisis multivariante para la determinación de concentración de azúcar en solución
C. Araujo-Andrade,I. Campos-Cantón,J. R. Martínez,G. Ortega-Zarzosa
Revista mexicana de física , 2005,
Abstract: La medición de la actividad óptica utilizando el principio de polarización es un método comúnmente usado para determinar la cantidad del contenido de azúcares en soluciones. El método de polarización es regularmente utilizado en la industria alimentaria. A fin de mostrar la importancia de los métodos estadísticos para el análisis de soluciones complejas, utilizamos un modelo de predicción basado en el análisis multivariante para la determinación del contenido de azúcar en soluciones medidas por técnicas espectroscópicas. Específicamente, medimos espectros en el cercano infrarrojo de soluciones con diferente concentración de azúcar, como base para la determinación de concentraciones desconocidas de azúcares. En particular, estimamos la concentración de azúcar en bebidas gaseosas comerciales, obteniendo resultados satisfactorios.
Coesite Formation at Ambient Pressure and Low Temperatures
J. R. Martínez,A. Vázquez-Durán,G. Martínez-Casta ón,G. Ortega-Zarzosa,S. A. Palomares-Sánchez,Facundo Ruiz
Advances in Materials Science and Engineering , 2008, DOI: 10.1155/2008/406067
Abstract: Partial crystallization of silica xerogel in the form of coesite has been obtained at low-pressure conditions and temperatures of ~565°C, in samples containing chlorophyll aggregates dispersed in amorphous silica. Silica xerogel samples were prepared by the sol-gel method using an ethanol:H2O:TEOS molar ratio of 4:11.6:1 and loaded with extracts from frozen spinach leaves. The silica xerogel microstructure of the powders was studied as a function of annealing temperature. It was found that partial crystallization of the glass matrix in the form of coestite was obtained at lower pressure than those specified by the phase diagram. Chlorophyll aggregates were added to the starting solutions which, upon thermal treatments, form small colloidal particles in the glass matrix. The presence of coesite is corroborated by the Rietveld refinement method.
Structural Effects of Heat-Treated Silica Xerogel Induced by Incorporation of Chlorophyll Species
J. R. Martínez,G. Martínez-Casta ón,G. Ortega-Zarzosa,J. A. de la Cruz-Mendoza,S. A. Palomares-Sánchez,Facundo Ruiz
Advances in Materials Science and Engineering , 2007, DOI: 10.1155/2007/23018
Abstract: Composites containing chlorophyll aggregates dispersed in amorphous silica are of interest because of their optical attractive properties. The silica powders added with chlorophyll species, prepared by the sol-gel method, were studied using X-ray diffraction, IR spectroscopy and differential temperature analysis. Silica xerogel samples were prepared using an ethanol/H2O/TEOS molar ratio of 4:11.6:1 and loaded with extracts from frozen spinach leaves. The silica xerogel microstructure of the powders was studied as a function of the annealing temperature. We found in our samples partial crystallization of the glass matrix in form of tridymite and cristobalite phases and quenching centers or nonfluorescing aggregates due to denaturation of photosystem promoted by chlorophyll decomposition after 400∘C.
Preparation and characterization of nanostructured powders of hydroxyapatite
Martínez-Casta?ón, G. A.;Loyola-Rodríguez, J. P.;Zavala-Alonso, N. V.;Hernández-Martínez, S. E.;Ni?o-Martínez, N.;Ortega-Zarzosa, G.;Ruiz, F.;
Superficies y vacío , 2012,
Abstract: in this work, hydroxyapatite nanostructured powders were prepared with different crystallinity degree, crystal size and morphology using a simple aqueous precipitation method varying the ph and temperature parameters. we found that at higher ph values the crystal size grows and crystallinity was improved; at higher temperatures there is also a crystal size growth and crystallinity improving but this change is more significant, a change in the morphology of the nanopowders was also observed. using xrd patterns and rietveld analysis we found that the crystal size change from 9.15 to 26.4 nm. the prepared powders are highly agglomerated with a pseudo-spherical and rod-like morphology.
Thermo-Stability of Natural Products Based on Chlorophyll Species Embedded in Silica Xerogel  [PDF]
José Martínez-Mendoza, Erika Espericueta-González, Diana Espericueta González, Gerardo Ortega-Zarzosa, Azdrubal Lobo Guerrero
American Journal of Analytical Chemistry (AJAC) , 2016, DOI: 10.4236/ajac.2016.74034
Abstract: This work studied the thermostability and the biostability of chlorophyll species obtained from an extract of spinach leaves embedded in a silica xerogel matrix. The analysis was done by monitoring the photosystem II (PSII) using fluorescence spectroscopy. Samples were prepared using the sol gel method with a molar ratio of ethanol/H2O/TEOS of 4:11.6:1. Then, silica xerogel matrix was loaded with an extract of spinach leaves, obtained in dark conditions. The measurement of the fluorescence spectra was done at selected temperatures to the corresponding non-physiological regimen. Results indicate that the PSII band position remains unchanged when heat treatment temperature increases up 200°C. For temperatures above 100?C, the fluorescence intensity diminishes linearly when the temperature increases. The photosystem II embedded in silica xerogel matrix is decomposed at temperatures above 200°C.
Structural Comportment of Extract of Bougainvillea xbuttiana Flower Incorporated in Silica Xerogel Matrix  [PDF]
José Martínez-Mendoza, Erika Espericueta-González, Diana Espericueta-González, Gerardo Ortega-Zarzosa, Azdrubal Lobo Guerrero
American Journal of Plant Sciences (AJPS) , 2016, DOI: 10.4236/ajps.2016.76078
Abstract: Measurement of the fluorescence comportment of Bougainvillea xbuttiana flowers embedded in silica xerogels matrix prepared with two different water to tetraethyl-orthosilicate [Si(OC2H5)4] ratio molar of 11 and 5, without heat-treatment, we report the grade of biostability of compound. The structural comportment for the PSI and PSII present in Bougainvillea flower is similar to the structural comportment for these photosystems present in leaves when they are incorporated on inorganic matrix such as silica xerogels. The contribution of the natural pigment of this kind of flower such as betalains which consist of betaxanthins and betacyanins, determines their colors contributed in the range of wavelength from about 550 nm to 660 nm.
Programa de cómputo para el desarrollo de lectura estratégica a nivel universitario
Luis G. Zarzosa Escobedo
Universidades , 2004,
Abstract:
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