Simón Bolívar University

About: Simón Bolívar University is a education organization based out in Caracas, Venezuela. It is known for research contribution in the topics: Population & Crystallization. The organization has 5912 authors who have published 8294 publications receiving 126152 citations.

Dietary nitrogen as a limiting nutrient in frugivorous birds

Abstract: La pulpa de las frutas es considerada un alimento inadecuado para las aves frugivoras debido a su bajo contenido de proteina. Por lo tanto, se espera que los frugivoros minimicen sus perdidas de nitrogeno como una adaptacion a la frugivoria. En esta revision examinamos las propiedades de las frutas y los rasgos fisiologicos de los frugivoros que afectan su capacidad para subsistir en base a una dieta de frutas. La mayoria de las frutas tropicales y templadas parecen contener suficiente nitrogeno para satisfacer los requerimientos de los pajaros, si su ingesta de alimento estuviera ajustada para compensar el gasto energetico. Los requerimientos, sin embargo, dependen del tamano corporal. Las aves mas grandes deberian requerir alimentos con una relacion de nitrogeno a energia mas elevada que las aves pequenas. No obstante, el nitrogeno digerible puede de hecho ser limitante ya que las pulpas de las frutas parecen contener cantidades considerables de nitrogeno no-proteico y una composicion de aminoacidos diferente a la requerida por las aves. Ambas caracteristicas de las frutas conducen a un aumento de las perdidas de nitrogeno en aves frugivoras al consumir dietas naturales. En terminos de sus adaptaciones fisiologicas, esperariamos que los frugivoros posean una elevada capacidad de extraccion de nitrogeno de la dieta y esbozamos la posibilidad de que las bajas perdidas urinarias de nitrogeno de los frugivoros pudieran estar relacionadas con una baja tasa metabolica. La minimizacion de las perdidas endogenas fecales podria ser la adaptacion mas importante de los frugivoros para subsistir con base en dietas pobres en nitrogeno. No es evidente como los frugivoros especializados pueden tener requerimientos de nitrogeno mas bajos que los esperados en comparacion a aves de otros grupos dietarios. Finalmente, sugerimos varios topicos de investigacion que conducirian a mejorar nuestra comprension de las complejas interacciones involucradas en la regulacion de las necesidades proteicas de las aves frugivoras

Internal modes of sine-Gordon solitons in the presence of spatiotemporal perturbations.

Abstract: We investigate the dynamics of the sine-Gordon solitons perturbed by spatiotemporal external forces. We prove the existence of internal (shape) modes of sine-Gordon solitons when they are in the presence of inhomogeneous space-dependent external forces, provided some conditions (for these forces) hold. Additional periodic time-dependent forces can sustain oscillations of the soliton width. We show that, in some cases, the internal mode even can become unstable, causing the soliton to decay into an antisoliton and two solitons. In general, in the presence of spatiotemporal forces the soliton behaves as a deformable (nonrigid) object. A soliton moving in an array of inhomogeneities can also present sustained oscillations of its width. There are very important phenomena (like the soliton-antisoliton collisions) where the existence of internal modes plays a crucial role.

Accessing marine protists from the anoxic Cariaco Basin.

Abstract: The earliest microbial cells evolved in an anoxic ocean (Martin and Muller, 1998), and many argue that the earliest Eukarya arose in the absence of oxygen as well. The microbe-mediated biogeochemical processes taking place below oxic/anoxic interfaces are of undeniable importance and interest, and the Cariaco Basin off the coast of Venezuela is a superb model ecosystem in this regard. It is the world’s largest body of truly marine anoxic waters and has been almost continuously anoxic for at least the last 2M years (Schubert, 1982). Consequently, the Basin became the site of many investigations, including a long-term biogeochemical time series initiated in 1995 (Muller-Karger et al., 2001; Taylor et al., 2001) and an NSF-funded Microbial Observatory established in 2004. This Observatory was a multi-year, multi-investigator international effort. Its principal goals were: to combine molecular and cell-based approaches to survey microbial Eukarya among geochemically diverse habitats in the Basin; to analyze the community structure and its dynamics across time and space; to discover novel organisms, and to gain insights into what governs their distribution dispersal and biogeography.

La cáscara de cacao (Theobroma cacao L.): una posible fuente comercial de pectinas

Abstract: Commercial exploitation of cocoa (Theobroma cacao L.) generates a volume of hulls that could be used in the production of pectins on an industrial scale. Therefore, pectins from cocoa hulls were extracted at different pH and temperature conditions, and their main chemical characteristics were evaluated. EDTA at 0.5% was used for the extraction at pHs 3, 4 and 5 and temperatures of 60, 75 and 90 degrees C, under a 3 2 factorial design. The response variables were yield, content of anhydrous galacturonic acid (AGA), content of metoxil, degree of esterification and equivalent weight of the pectins extracted. The strength of the pectic gel was determined with a TA-XT2 texturometer. Strawberry jam was made with the pectin extracted, and its acceptability was determined using a 7-point hedonic scale. The results obtained were as follows: an extraction yield from 2.64 to 4.69 g/100 g; an AGA content between 49.8 and 64.06 g/100 g; a content of metoxil between 4.72 and 7.18 g/100 g; a degree of esterification between 37.94 and 52.20%; an equivalent weight from 385.47 to 464.61 g/equivalent of H+, and a degree of gelation between 28.64 and 806.03 g force. The pectin extracted at pH 4 and 90 degrees C showed a gelation power of 422.16 g force, purity 62.26 g/100 g of AGA, and a yield of extraction of 3.89 g/100 g and allowed to prepare ajam with an average level of liking of "like moderately". Pectins from cocoa hulls show potential application in the food industry, but it is necessary to optimize the extraction parameters to increase its yield.