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Search Results: 1 - 10 of 519705 matches for " Carlos A. Fernández "
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Molecular Dynamics of Free and Graphite-Supported Pt-Pd Nanoparticles  [PDF]
Carlos Fernández-Navarro, Sergio Mejía-Rosales
Advances in Nanoparticles (ANP) , 2013, DOI: 10.4236/anp.2013.24044
Abstract:

The thermal characteristics of bimetallic Pt-Pd nanoparticles, both free and graphite-supported, were investigated through molecular dynamics simulations using quantum Sutton-Chen many-body potentials for the metal-metal interactions. The graphite substrate was represented as layers of fixed carbons sites and modeled with the Lennard-Jones potential model. The melting temperatures for bimetallic nanoparticles were estimated based on variations in thermodynamic properties such as potential energy and heat capacity. Melting temperatures of the nanoparticles were found to be considerably lower than those of bulk Pt and Pd. The Pt-Pd clusters exhibited a two-stage melting, where surface melting of the external atoms is followed by homogeneous melting of the internal atoms. The melting transition temperature was found to increase when the particle is on the graphite support, with an increase at least 180 K higher than that of the same-sized free nanoparticle. The results of the density distributions perpendicular to the surface indicate that the Pd atoms have a tendency to remain at the surface, and the Pd atoms wet the graphite surface more than the Pt atoms, while root mean squares suggest that surface melting starts from the cluster surface, and surface melting was seen in both free and graphite-supported nanoparticles. Structural changes accompanying the thermal evolution were studied by the bond-orientational order parameter method.

Efecto residual de la roca fosfórica de riecito modificada por calcinación o acidulación sobre plantas de maíz en suelos con nivel variable de calcio
Fernández,Shirley M; Meza,Carlos A;
Bioagro , 2004,
Abstract: with the purpose of evaluating the residual effect of phosphoric rock from riecito (venezuela) treated with vinaza or high temperatures, three successive crops of corn, used as indicative plant, were grown in an acid soil (ph 3.7) whitewashed up to ph 5.7 and 6.8. the treatments consisted in the use of: a) rock of riecito natural (rfn), b) rock burnt at 900 oc for 7 hours (rfc), c) acidulated rock with vinaza in proportion 1/1 (rfv), d) amoniacal phosphate (fma), and e) a control without phosphorus (te). the dose of phosphorus applied was 300 mg·kg-1. the plants were harvested 30 days after planting to determine their dry biomass. for the acid soil, in the first crop, the treatment rfv produced values of dry biomass comparable to the fma, in the second crop the treatments rfv, rfc and rfn presented a similar behavior to the fma; for the third crop the rfc was able to overcome the fma. the control always showed the lowest values. in the soil with ph 5.7 the sources rfv, rfc and rfn showed an inferior residual effect to the one found in the soil ph with 3.7. in the soil ph with 6.8 the fma overcame all the other sources. the results suggest that the acidification of the phosphoric rock with vinaza or burning at high temperatures increases its solubility, when the soil ph is less than 5.7.
Efecto residual de la roca fosfórica de riecito modificada por calcinación o acidulación sobre plantas de maíz en suelos con nivel variable de calcio Residual effect of acidulated or burnt Riecito phosphoric rock on maize grown in soils with variable levels of calcium
Shirley M Fernández,Carlos A Meza
Bioagro , 2004,
Abstract: Con la finalidad de evaluar el efecto residual de la roca fosfórica proveniente de Riecito (Venezuela) tratada con vinaza y altas temperaturas, se realizaron tres cosechas sucesivas de maíz, el cual fue usado como planta indicadora en un suelo ácido (pH 3,7) encalado hasta pH 5,7 y 6,8. Los tratamientos fueron el uso de: a) roca de Riecito natural (RFN), b) roca calcinada a 900 oC por 7 horas (RFC), c) roca acidulada con vinaza en proporción 1/1 (RFV), d) fosfato monoamónico (FMA), y e) testigo sin fósforo (Te). La dosis de fósforo empleada fue 300 mg·kg-1. Las plantas se colectaron a los 30 días de la siembra para determinar la biomasa seca. Para el suelo de pH 3,7 en la primera cosecha, el tratamiento RFV produjo valores de biomasa seca comparables al FMA; para la segunda cosecha las fuentes RFV, RFC y RFN presentaron un comportamiento similar al FMA, e incluso, para la tercera cosecha la RFC logró superar al FMA. El testigo presentó siempre los menores valores. En el suelo de pH 5,7 las fuentes RFV, RFC y RFN evidenciaron un efecto residual inferior al presentado en el suelo de pH 3,7. En el suelo de pH 6,8 el FMA superó todas las otras fuentes. Los resultados sugieren que la roca fosfórica de Riecito calcinada o acidulada con vinaza incrementan la solubilidad del P cuando el pH del suelo es inferior a 5,7. With the purpose of evaluating the residual effect of phosphoric rock from Riecito (Venezuela) treated with vinaza or high temperatures, three successive crops of corn, used as indicative plant, were grown in an acid soil (pH 3.7) whitewashed up to pH 5.7 and 6.8. The treatments consisted in the use of: a) rock of Riecito natural (RFN), b) rock burnt at 900 oC for 7 hours (RFC), c) acidulated rock with vinaza in proportion 1/1 (RFV), d) amoniacal phosphate (FMA), and e) a control without phosphorus (Te). The dose of phosphorus applied was 300 mg·kg-1. The plants were harvested 30 days after planting to determine their dry biomass. For the acid soil, in the first crop, the treatment RFV produced values of dry biomass comparable to the FMA, in the second crop the treatments RFV, RFC and RFN presented a similar behavior to the FMA; for the third crop the RFC was able to overcome the FMA. The control always showed the lowest values. In the soil with pH 5.7 the sources RFV, RFC and RFN showed an inferior residual effect to the one found in the soil pH with 3.7. In the soil pH with 6.8 the FMA overcame all the other sources. The results suggest that the acidification of the phosphoric rock with vinaza or burning at high temperatures increases its solubi
Water as a Source of Conflicts: A Review of the Focal Points for Conflicts in the World
Carlos A. Fernández-Jáuregui
Revista CIDOB d'Afers Internacionals , 1999,
Abstract: Since time immemorial, the access to water has been the source of power or become the apple of discord that has originated great conflicts. Today, thanks to the development of understanding in the area of water sciences, one may observe with greater clarity whichcontinents are more at risk to possible conflicts because of their elevated populations and availability of water resources.This article reviews the management of the supply and demand of the hydrological resource and analyzes its evolution from the 1980s to the present. It utilizes a mathematical model for generating future scenarios that enables experts to situate themselves, before avision of the state of water, in the year 2025. Seeing as today, countries, most of them in the Middle East, are already in conflict over water, this article goes on to outline the new sources for global conflicts due to the scarcity of this vital resource. Presented are possible measures to be taken to resolve conflicts by using muliticriteria-based tools of decisionmaking, and put forth, too, are other monitoring mechanisms that would address possiblenew conflicts.
Notas para una filosofía de la educación intercultural abiayalense.
Carlos María Pagano Fernández
Cultura-Hombre-Sociedad , 2009, DOI: 10.7770/cuhso-v17n1-art291
Abstract: La educación intercultural se convierte en un imperativo global. Hasta las empresas multinacionales hablan de la necesidad de contar con personal capacitado interculturalmente. El continente Abia Yala no está ajeno a esta atmósfera. Por su parte, la filosofía, como cuestionadora permanente de todo statu quo en aras a crear las condiciones para hacer realidad una humanización solidaria más plena, debe hacerse cargo de esa función crítica, no siempre cómoda, con el fin de que lo reconocido como necesario y que va configurando una atmósfera mundial en las propuestas educativas, mantenga su creativa vigilia frente a las instrumentaciones que pueden desvirtuar el propósito educativo intercultural. La filosofía debe realizar el primer cuestionamiento frente a sí misma y sus modos de educar filosóficamente, puesto que el eurocentrismo interiorizado de la educación filosófica académica asegura la hegemonía cultural gnoseológica en la que hace pie el monótono ritmo del tiempo y del espacio sancionado por el mercado como única posibilidad cultural pedagógica y civilizatoria mundial. La filosofía intercultural no se queda en sí misma, cómplice del proyecto mercantil neoliberal; debe formular sus propuestas para mantener la guardia a fin de que la educación intercultural no se convierta en fachada que esconde su asimilación sistémica deshumanizante y depredadora de culturas, del mismo modo que el mercado procede con el medio ambiente, pues con ello no pasaría de una nueva herramienta neocolonial depredadora de la vida natural y humana.
Heat Production Partition in Sheep Fed above Maintenance from Indirect Calorimetry Data  [PDF]
Patricia Criscioni, María del Carmen López, Victor Zena, Carlos Fernández
Open Journal of Animal Sciences (OJAS) , 2015, DOI: 10.4236/ojas.2015.52011
Abstract: The objective of this study is to compare the partition of heat energy (HE) in two sheep breeds by indirect calorimetry and integral calculus. An experiment was conducted with two Spanish native sheep breeds (dry and non-pregnant) which were fed with pelleted mixed diets above maintenance. Six Guirras and six Manchegas breed sheep were selected (58.8 ± 3.1 and 60.2 ± 3.2 kg body weight, respectively). All sheep were fed with the same concentrate mixed ration (0.300 kg cereal straw as forage and 0.700 kg concentrate) in two meals. Half the daily ration was offered at 800 h and another half at 1600 h. The sheep had free access to water. Sheep were allocated in metabolic cages; energy balance and gas exchange were assessed in each sheep. The statistical analyses included the fixed effect of breed and random effect of sheep. The metabolic energy (ME) for maintenance represented 69% of the total ME intake and the average was 354 kJ per kg of metabolic body weight (kg0.75 BW) on average. The basal metabolism (HeE) was greater (P < 0.05) in Guirra than Manchega breed (270 ± 18 vs. 247 ± 15 kJ/kg0.75 BW and day). As sheep were fed with above maintenance, the retained energy in the body accounted for 22% of the ME intake and 77% of the ME intake was lost as heat. 51% of the MEI was converted to HeE; 5% was lost as physical activity of standing and lying down (HjE), and 13% was associated with the process of feeding and work of digestion and metabolism (HdE). Within HdE, 47% represented the cost of intake and feeding and 54% the cost of digestion and metabolism. No differences in HE partition between breeds were found, although Guirra breed showed less efficiency of energy retention than Manchega breed. Therefore, this study demonstrated a tentative approach of partitioning HE, combining indirect calorimetry and integral calculus.
Incidencia de las comisiones de nombramientos y retribuciones sobre las remuneraciones de los consejeros ejecutivos
Carlos Fernándezndez,Rubén Arrondo García,Enrique Fernández Rodríguez
Cuadernos de Economía y Dirección de la Empresa , 2012,
Abstract: Este trabajo estudia el papel desempe ado por las comisiones de nombramientos y retribuciones (CNR) en el dise o de las políticas retributivas de los consejeros ejecutivos de las empresas espa nolas cotizadas. Se analiza si la independencia y la relevancia de las CNR afectan a las remuneraciones percibidas por los consejeros ejecutivos. Los resultados obtenidos, contrariamente a lo esperado, ofrecen indicios de que tanto la independencia como la relevancia de las CNR, aproximada esta última a través de la participación accionarial de sus miembros y de su tama no en términos relativos al del consejo, incrementan el volumen retributivo asociado a los ejecutivos. Igualmente, se han identificado el tama o, el riesgo empresarial y la existencia de oportunidades de inversión como factores determinantes de estas retribuciones.
Replacement of Cereal with Low Starch Fibrous By-Products on Nutrients Utilization and Methane Emissions in Dairy Goats  [PDF]
Carla Ibá?ez, Vicente Javier Moya, Haritz Arriaga, Diana María López, Pilar Merino, Carlos Fernández
Open Journal of Animal Sciences (OJAS) , 2015, DOI: 10.4236/ojas.2015.52022
Abstract: Feeding systems for dairy ruminants need to ensure high intake of energy to achieve maximum milk production potential. This might be accomplished by raising the dietary concentration of cereal grain. Increasing the concentration of starch in diets can lead to undesirable ruminal fermentation, and to prevent it, the partial replacement of cereal grain with low starch by-product feeds is recommended. The purpose of the present study was to compare the effect of fed two mixed diets to dairy goats differing in the type of carbohydrate (starch vs. easily degradable fiber). Energy and nitrogen balance, short chain fatty acids in rumen liquor and milk performance in dairy goats during mid lactation were determined. Enteric methane (CH4) emissions and CH4 production from manure were determined as well. Ten multiparous Muciano-Granadina goats were assigned to two isoenergetic and isoproteic diets (19.1 MJ/kg dry matter (DM) and 18.1% of CP, DM basis) in a crossover design. One group was fed a mixed ration with 21.9% of starch (HS diet) and the other (LS diet) with 7.0% of starch. HS diet had 36% of barley (as source of starch) and it was replaced with soy hulls and corn gluten feed in LS diet (as potentially digestible fiber). No differences were observed for dry matter intake in both diets (2.05 kg/d, on average). A significant increase of ruminal acetic acid was found for low starch diet (66.4 and 56.6 mol/100 mol for LS and HS diet, respectively). No significant effect was found among diets for enteric CH4 emissions (28.5 g/d, on average). Manure derived maximum potential yield was (Bo) higher in HS diet, with 5.9 L CH4/kg OM vs. 0.28 L CH4/kg OM for LS diet, probably associated with the low ADF digestibility. Differences among diets were found for milk production (2.4 vs. 2.2 kg/d for HS and LS, respectively), and greater milk fat was observed with LS diet compared with HS (6.4% vs. 5.5%, respectively).
Uso rutinario del balón de contra-pulsación aórtica preoperatorio en pacientes con enfermedad del tronco común izquierdo sometidos a cirugía de revascularización coronaria
Fernández,Andrés; Uribe,Carlos; Villegas,Francisco A; Fernández,Darío; Porras,álvaro;
Revista Colombiana de Cardiología , 2008,
Abstract: background: left main coronary artery disease as the only criterion for intra-aortic balloon counterpulsation implantation is an indication which evidence is limited to experts? recommendations; therefore, studies that may give a higher level of evidence are required. for this reason, we developed in our institution a study that evaluated the experience in the use of iabp in patients with left main coronary artery disease undergoing coronary revascularization surgery. objective: describe mortality, length of stay and percentage of infections and sepsis in the intensive care unit, as well as the mechanical ventilation duration in patients undergoing an elective coronary revascularization surgery with or without the use of preoperative intra-aortic balloon counterpulsation. methods: descriptive retrospective study performed in the santa maría cardiovascular clinic in patients undergoing elective coronary revascularization surgery with or without the use of preoperative intra-aortic balloon counterpulsation between 1999 and 2003. postoperative behaviour in patients with severe left main disease (stenosis > 50%) submitted to this surgery was observed. results: a total of 79 patients submitted to elective surgical revascularization were analyzed. 46 underwent preoperative balloon implantation and 33 underwent surgery without previous balloon implantation. mean age was 62 years. 67.4% of patients were 60 years or older. main pathologies previous to surgery were arterial hypertension in 67% of the patients, and ancient acute myocardial infarction in 59%. 87% of the patients with balloon and 45.5% of those without it had severe angina (class iii) before surgery. in the intensive care unit 6.5% patients with balloon were infected as well as 3% of the group without balloon (p=0,49) and sepsis was found in 4,3% of the balloon group and none in the non-balloon group (p=0,23). mortality in the intensive care unit was 2.2% in the balloon group and 3% in the non-balloon group (p=0
Uso rutinario del balón de contra-pulsación aórtica preoperatorio en pacientes con enfermedad del tronco común izquierdo sometidos a cirugía de revascularización coronaria Routine use of preoperative intra-aortic balloon pump counterpulsation (IABP) implantation in patients with left main coronary artery disease undergoing coronary revascularization surgery
Andrés Fernández,Carlos Uribe,Francisco A Villegas,Darío Fernández
Revista Colombiana de Cardiología , 2008,
Abstract: Generalidades: la enfermedad del tronco común izquierdo como único criterio para la colocación de balón de contra-pulsación aórtica, es una indicación cuya evidencia se limita a la recomendación de expertos y, por lo tanto, se requieren estudios que puedan aportar mayor nivel de evidencia al respecto. Por este motivo, en nuestra institución se desarrolló un estudio que evaluó la experiencia del uso de balón de contra-pulsación aórtica preoperatorio, en pacientes sometidos a cirugía de revascularización cardiaca electiva, con enfermedad del tronco común izquierdo. Objetivo: describir la letalidad, el tiempo de estancia y el porcentaje de infecciones y sepsis en la unidad de cuidados intensivos, así como el tiempo de ventilación mecánica, en los pacientes sometidos a cirugía de revascularización coronaria electiva con y sin el uso preoperatorio de balón de contra pulsación aórtica. Métodos: estudio descriptivo retrospectivo, que se llevó a cabo en la Clínica Cardiovascular Santa María, con los pacientes que se sometieron a revascularización coronaria quirúrgica electiva acompa ados o no de balón de contra-pulsación aórtica preoperatorio entre 1999 y 2003, y en el que se observó el comportamiento post-operatorio de los pacientes con enfermedad severa del tronco común izquierdo (entendida como estenosis mayor de 50%) sometidos a dicha intervención. Resultados: se analizaron en total 79 pacientes sometidos a revascularización quirúrgica electiva, a 46 de los cuales se les implantó balón preoperatorio y a 33 se les practicó intervención quirúrgica sin balón. El promedio de edad fue de 62 a os. El 67,4% de los pacientes tenía 60 a os o más. Las principales patologías previas a la cirugía fueron hipertensión arterial (67%) e infarto agudo del miocardio antiguo, (59%). 87% de los pacientes con balón y 45,5% de aquellos sin éste, tenían angina severa (clase III) antes de la cirugía. En la unidad de cuidados intensivos se infectaron 6,5% de los pacientes con balón y 3% del grupo sin balón (p=0,49) y hubo sepsis en 4,3% del grupo con balón y en ninguno del grupo restante (p=0,23). La letalidad en la unidad de cuidados intensivos se presentó en 2,2% del grupo de balón y en 3% del otro grupo (p=0,06). No ocurrió mortalidad intrahospitalaria fuera de la unidad de cuidados intensivos como tampoco mortalidad a 30 días después del alta. El tiempo de estancia en la misma unidad fue de 4,13 días en el grupo de balón y 2,7 días en el grupo sin balón, sin diferencia estadísticamente significativa entre éstos (p=0,154). El tiempo de ventilación mecánica en el grupo de balón fu
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