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.

Nitrous oxide and methane fluxes from soils of the Orinoco savanna under different land uses

Abstract: The study investigates the effect of land-use change on nitrous oxide (N2O) and methane (CH4) fluxes from soil, in savanna ecosystems of the Orinoco region (Venezuela). Gas fluxes were measured by closed static chambers, in the wet and dry season, in representative systems of land management of the region: a cultivated pasture, an herbaceous savanna, a tree savanna and a woodland (control site). Higher N2O emissions were observed in the cultivated pasture and in the herbaceous savanna compared with the tree savanna and the woodland, and differences were mainly related to fine soil particle content and soil volumetric water content measured in the studied sites. Overall N2O emissions were quite low in all sites (0‐1.58mgN2O-Nm � 2 day � 1 ). The cultivated pasture and the woodland savanna were on average weak CH4 sinks (� 0.05 � 0.07 and � 0.08 � 0.05mgCH4m � 2 day � 1 , respectively), whereas the herbaceous savanna and the tree savanna showed net CH4 production (0.23 � 0.05 and 0.19 � 0.05mgCH4m � 2 day � 1 , respectively). Variations of CH4 fluxes were mainly driven by variation of soil waterfilled pore space (WFPS), and a shift from net CH4 consumption to net CH4 production was observed at around 30% WFPS. Overall, the data suggest that conversion of woodland savanna to managed landscape could alter both CH4 and N2O fluxes; however, the magnitude of such variation depends on the soil characteristics and on the type of land management before conversion.

Moisture Sorption Characteristics of Starchy Products: Oat Flour and Rice Flour

Abstract: Moisture sorption isotherms for oat flour and rice flour were determined at 5, 23, and 45 °C using a gravimetric technique in an aw range of 0.08–0.98. The results obtained showed that, for aw values lower than around 0.75, in both flours, the sorption capacity decreased with increasing temperature, while the opposite behavior was observed at aw greater than this value. It was found that the experimental data in the water activity range considered were better represented by the four-parameter Peleg equation. The monolayer water contents for both materials were determined by the BET and GAB models. The net isosteric heats of sorption were estimated using the Clausius–Clapeyron equation. For both materials, the monolayer water content and the isosteric heat of sorption were found to decrease with increasing temperature and increasing moisture content, respectively.

First report of folliculinid ciliates affecting Caribbean scleractinian corals

Abstract: This is the first report of a ciliate of the genus Halofolliculina infecting hard coral species of six families (Acroporidae, Agaricidae, Astrocoeniidae, Faviidae, Meandrinidae and Poritidae) and milleporids in the Caribbean. Surveys conducted during 2004–2005 in Venezuela, Panama and Mexico confirmed that this ciliate affects up to 25 scleractinian species. The prevalence of this ciliate at the coral community level was variable across sites, being most commonly found at Los Roques, Venezuela, and at Bocas del Toro, Panama (prevalence 0.2–2.5%), but rarely observed in the Mexican Caribbean. Ciliates were more prevalent within populations of acroporids (Acropora palmata, Acropora cervicornis and Acropora prolifera) in Los Roques. Recent observations also corroborate the presence of these ciliates in Curacao and Puerto Rico. Our observations indicate that ciliates affecting corals have a wider distribution than previously thought, and are no longer exclusively found in the Indo-Pacific and Red Sea.

Flow of polymer solutions through porous media

Abstract: The molecular mechanism for viscosity enhancement during the flow of poly(ethylene oxide) solutions through porous media has been investigated. Random packed beds of uniform-size spheres have been used as porous media. Experiments were conducted for one-dimensional (uniform) flow, as well as for a particular three-dimensional (nonuniform) flow situation. A substantial increase in flow resistance with respect to that exhibited by Newtonian fluids has been observed in both cases. The results obtained suggest that, under the conditions employed in the present work, the mechanism that causes the increased flow resistance is related to the formation of transient networks of polymer molecules in the flow field. The nonuniform flow results indicate that the presence of the polymer induces a change in the macroscopic flow distribution within the porous medium.