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Search Results: 1 - 10 of 565721 matches for " Sánchez Francisco J. "
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Perspectivas para la producción de alquilato
Sánchez C. Francisco J.,Oviedo Alfredo
Ingeniería e Investigación , 1998,
Abstract: Para disminuir la polución causada por la combustión de las gasolinas en automotores, se requiere la producción de gasolinas reformuladas en el país. Esto implica eliminar algunos componentes de las gasolinas corrientes e incorporar alquilato, isómeros y compuestos oxigenados, para mantener el número de octano y favorecer una combustión limpia. El proceso de alquilación actual emplea catalizadores ácidos líquidos como el H2S04, HF y H3PO4 que presentan problemas en la salud de los operarios, son altamente corrosivos y causan contaminación ambiental por su disposición final. Actualmente, la investigación se orienta a encontrar procesos heterogéneos con catalizadores ácidos sólidos, eficientes, que eviten los problemas anteriores.
Transient Cholesterol Effects on Nicotinic Acetylcholine Receptor Cell-Surface Mobility
Gonzalo Almarza, Francisco Sánchez, Francisco J. Barrantes
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0100346
Abstract: To what extent do cholesterol-rich lipid platforms modulate the supramolecular organization of the nicotinic acetylcholine receptor (AChR)? To address this question, the dynamics of AChR particles at high density and its cholesterol dependence at the surface of mammalian cells were studied by combining total internal reflection fluorescence microscopy and single-particle tracking. AChR particles tagged with a monovalent ligand, fluorescent α-bungarotoxin (αBTX), exhibited two mobile pools: i) a highly mobile one undergoing simple Brownian motion (16%) and ii) one with restricted motion (~50%), the rest being relatively immobile (~44%). Depletion of membrane cholesterol by methyl-α-cyclodextrin increased the fraction of the first pool to 22% and 33% after 15 and 40 min, respectively; the pool undergoing restricted motion diminished from 50% to 44% and 37%, respectively. Monoclonal antibody binding results in AChR crosslinking-internalization after 2 h; here, antibody binding immobilized within minutes ~20% of the totally mobile AChR. This proportion dramatically increased upon cholesterol depletion, especially during the initial 10 min (83.3%). Thus, antibody crosslinking and cholesterol depletion exhibited a mutually synergistic effect, increasing the average lifetime of cell-surface AChRs~10 s to ~20 s. The instantaneous (microscopic) diffusion coefficient D2–4 of the AChR obtained from the MSD analysis diminished from ~0.001 μm2 s?1 to ~0.0001–0.00033 μm2 s?1 upon cholesterol depletion, ~30% of all particles falling into the stationary mode. Thus, muscle-type AChR exhibits heterogeneous motional regimes at the cell surface, modulated by the combination of intrinsic (its supramolecular organization) and extrinsic (membrane cholesterol content) factors.
Increased Cortical Thickness in Male-to-Female Transsexualism  [PDF]
Eileen Luders, Francisco J. Sánchez, Duygu Tosun, David W. Shattuck, Christian Gaser, Eric Vilain, Arthur W. Toga
Journal of Behavioral and Brain Science (JBBS) , 2012, DOI: 10.4236/jbbs.2012.23040
Abstract: Background: The degree to which one identifies as male or female has a profound impact on one’s life. Yet, there is a limited understanding of what contributes to this important characteristic termed gender identity. In order to reveal factors influencing gender identity, studies have focused on people who report strong feelings of being the opposite sex, such as male-to-female (MTF) transsexuals. Method: To investigate potential neuroanatomical variations associated with transsexualism, we compared the regional thickness of the cerebral cortex between 24 MTF transsexuals who had not yet been treated with cross-sex hormones and 24 age-matched control males. Results: Results revealed thicker cortices in MTF transsexuals, both within regions of the left hemisphere (i.e., frontal and orbito-frontal cortex, central sulcus, perisylvian regions, paracentral gyrus) and right hemisphere (i.e., pre-/post-central gyrus, parietal cortex, temporal cortex, precuneus, fusiform, lingual, and orbito-frontal gyrus). Conclusion: These findings provide further evidence that brain anatomy is associated with gender identity, where measures in MTF transsexuals appear to be shifted away from gender-congruent men.
Estudio cinético para la oxidación selectiva de etanol a acetaldehido
Sánchez C. Francisco j.,Carballo S. Luis M.
Ingeniería e Investigación , 1991,
Abstract: Se explica una metodología para efectuar el Desarrollo del Catalizador. Se hace una revisión bibliográfica, análisis termodinámico, patrones de actividad de catalizadores, pruebas preliminares. Con base en los resultados experimentales se plantea un mecanismo de reacción y una expresión cinética para esta reacción. Se demuestra que bajo las condiciones experimentales ensayadas los efectos de Transferencia de masa y calor, no influyen en la cinética encontrada, por tal razón esta cinética corresponde a la cinética intrínseca. MARCO DE REFERENCIA: Esta investigación hace parte del programa ALCOHOLQUIMICA del Departamento de Ingeniería Química. Como primer objetivo busca formar un grupo de Investigadores y adquirir conocimiento y destreza en la preparación de catalizadores, estudios cinéticos. Dise o, construcción, simulación y manejo de reactores catalíticos heterogéneos. Como segundo objetivo, el desarrollo de tecnología para la producción de materias primas Químicas actualmente inportadas al país, a partir de materias primas disponibles en Colombia. Los materiales para la preparación de los catalizadores y la tecnología desarrollada, han de poder conseguirse e implementarse en nuestro medio.
Empleo de una sonda infrarroja in situ para monitorear reacciones de esterificación
Sánchez C.,Francisco J.; Cesteros,Carlos; Katime,Issa A.;
Ingeniería e Investigación , 2006,
Abstract: a batch reactor was employed having ph meter, ir probe and continuous operation detectors so that it could work as a cstr reactor. as esterification advanced, then ir bands corresponding to the carboxyl acid cooh group and the alcohol c-oh group decreased whilst a parallel increase was presented in the ester -coor group band which was forming. reaction progress could be observed by continuous ir spectrum registration. the ir band for hoh (water) could not be studied because it needed a completely anhydrous medium for doing so. standard solutions could be prepared for quantifying ir band peak intensity, according to a component?s composition in the mixture. however, when phase changes occurred in the reaction mixture, this method could not be employed for following the course of a particular reaction because random variation was detected in band intensity.
Lipid metabolism in experimental animals
Sánchez-Mu?iz, Francisco J.,Cuesta, Carmen
Grasas y Aceites , 1998,
Abstract: Publications are scarce in the way in chich metabolic processes are affected by the ingestion of heated fats used to prepare food. Similarly studies measuring metabolic effects of the consumption on fried food are poorly known. The purpose of this presentation is to summarize information on frying fats and frying foods upon lipid metabolism in experimental animals. Food consumption is equivalent or even higher when oils or the fat content of frying foods are poorly alterated decreasing their acceptability when their alteration degree increase. After 4hr. experiment the digestibility and absorption coefficients of a single dosis of thermooxidized oils were significantly decreased in rats, however the digestive utilization of frying thermooxidized oils included in diets showed very little change in comparison with unused oils by feeding trials on rats. Feeding rats different frying fats induced a slight hypercholesterolemic effect being the magnitude of this effect related to the linoleic decrease in diet produced by frying. However HDL, the main rat-cholesterol carrier, also increased, thus the serum cholesterol/HDL-cholesterol ratio did not change. Results suggest that rats fed frying fats adapt their lipoprotein metabolism increasing the number of HDL particles. Deep fat frying deeply changed the fatty acid composition of foods, being possible to increase their n-9 or n-6 fatty acid and to decrease the saturated fatty acid contents by frying. When olive oil-and sunflower oil-fried sardines were used as the only protein and fat sources of rats-diets in order to prevent the dietary hypercholesterolemia it was provided that both fried-sardine diets showed a powerful check effect on the cholesterol raising effect induced by dietary cholesterol. The negative effect of feeding rats cholesterol plus bovine bile to induce hypercholesterolemia on some cell-damage markers such as lactate dehydrogenase, transaminases, alkaline phosphatase, was significantly check when olive oil- or sunflower oil-fired sardines were used in rats. However, gamma-glutamyltransferase increased when diets containing fried sardines from oils used several times for frying were consumed. In conclusion frying appears to be an useful tool to modify the fatty acid composition of food and the lipoprotein metabolism of consumers, however this culinary procedure has to be gently done to avoid high level of potential toxic compounds.
Aplicación de un test colorimétrico al estudio del rendimiento y vida útil en fritura de alimentos precocinados y frescos de aceite de oliva, aceite de girasol y su mezcla
Bastida, Sara,Sánchez-Muniz, Francisco J.,Trigueros, Gemma
Grasas y Aceites , 2003,
Abstract: The frying-life of olive oil, sunflower oil and a their homogeneous blend used in 40 repeated and discontinuous frying of different food, mostly precooked and frozen foods, were comparatively determined by using the qualitative color test a Fritesta and color developed at 500 nm using this test (A500). These measurements were significantly correlated (p< 0.001) to polar material, oligomer content and other thermaloxidation parameters The color selected to discard the oil -3 crosses- corresponds to A500 of 0.35 and to 25 % polar material and 10-15 % of oligomers. The shelf life (< 3 crosses or A500< 0.35) was 32 frying for olive oil, 22 fryings for sunflower oil, and 26 for their blend. The oil efficiency was assessed taking into account the weight decrease of foods, the oil loss, and the amount of food fried (kg food/L oil used) before oil discarding taking into account A500< 0,35 o A500< 0,4 cut-points. Olive oil presented a better efficiency (3.1 kg/L) than the sunflower oil and the blend (2.23 and 2.64 kg/L, respectively). Results suggest (i) the validity of the a Fritesta for a rapid evaluation of the alterations of different oils; (ii) the better efficiency and the longer shelf-life of olive oil than sunflower oil and the blend when frying different foods mostly pre-cooked and frozen foods. Se compara la vida útil de aceite de oliva, aceite de girasol y una mezcla de ambos utilizados en 40 frituras repetidas de alimentos, la mayoría precocinados y congelados, mediante el test cualitativo colorimétrico a Fritesta y la determinación del color desarrollado por dicho test a 500 nm. (A500) correlaciona muy significativamente (p< 0.001) con el material polar, contenido de oligómeros y otros parámetros de la alteración termoxidativa estudiados. El color para el cual debía eliminarse un aceite -3 cruces- se correspondió con una A500 de 0,35 y con 25% de material polar y con 12-15% de oligómeros. La vida útil de los aceites (< 3 cruces o A500< 0,35) fue de 32 frituras para el aceite de oliva, 22 para el de girasol y 26 para la mezcla. El rendimiento de los aceites se valoró en términos de merma ponderal de alimento, gasto de aceite y cantidad de alimento que pudo ser frito por litro de aceite antes de ser desechado atendiendo A500< 0,35 o A500< 0,4. El aceite de oliva presentó un rendimiento superior (3,1 kg de alimento/L de aceite) al de girasol y mezcla de aceites (2,23 y 2,64 kg/L, respectivamente). Estos resultados se alan (i) la validez del a Fritesta para la evaluación rápida de la vida útil de aceites de fritura y (ii) el mayor rendimient
Síntesis de mono y diitaconatos de alquilo y arilo
Sánchez Francisco J.,Katime Issa A.,Meaurio Emilio
Ingeniería e Investigación , 1997,
Abstract: Se presenta una técnica para la síntesis en laboratorio de mono y diitaconatos y la separación de los mismos por extracción selectiva con solventes orgánicos. La pureza de los productos se determina por cromatografía en capa fina y por espectroscopia infrarroja.
Esterificación
Sánchez C. Francisco J.,Rodríguez N. Gerardo
Ingeniería e Investigación , 1996,
Abstract: Los conceptos básicos en una reacción de esterificación ácido-alcohol, se plantean de una forma clara y concreta, incluyendo mecanismo de la reacción, efecto del alcohol y del ácido, tipos de catalizador, proporciones y forma de operación todo lo cual redunda en un buen dise o en un proceso de esterificación. Todos estos conceptos muy conocidos, son actualmente aplicados minuciosa y detalladamente en los procesos de esterificación, algunos de ellos en investigación y otros cubiertos por el velo de patentes recientes.
CóMO MEJORAR LA TASA DE RESPUESTA EN ENCUESTAS ON LINE?
Juan Sánchez Fernández,Francisco Mu?oz Leiva,Francisco J. Montoro Ríos
Revista de Estudios Empresariales. Segunda época , 2009,
Abstract: Most studies of the effect of contributing factors on response rates have attempted to extrapolate to Internet the already existing broad knowledge base of methodologies for personal surveys by telephone and post. However, such knowledge about existing methods is not directly applicable to the Internet-based interviews. This paper therefore examines the manner in which different combinations of incentives, the personalization of mails and a lower periodicity of reminder message (weekly versus semimonthly) can affect response to a survey on Internet.The results prove an effective way to improve the response and retention rate consists in the mailing of invitations weekly. Furthermore it is shown the personalization of the mails allows basically having the individuals' attention and reaches them the end of the questionnaire (retention rate). A surprising result is that the joint use of the contributing factors (weekly mails, pre-incentive and personalized call) significantly improves response and retention rates.
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