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Caracas, Venezuela

The Central University of Venezuela is a premier public University of Venezuela located in Caracas. Founded in 1721, it is the oldest university in Venezuela and one of the oldest in the Western Hemisphere .The main university campus, Ciudad Universitaria de Caracas, was designed by architect Carlos Raúl Villanueva and it is considered a masterpiece of urban planning and was declared a World Heritage Site by UNESCO in 2000. Wikipedia.

This work presents a study of the molecular composition of the saturated and aromatic hydrocarbon fractions of crude oils from the Orinoco Oil Belt (Junín area) in the Eastern Venezuelan Basin, with the purpose of classifying these samples following two distinct biodegradation assessment schemes: the PM scale [Peters, K.E., Moldowan, J.M., 1993. The Biomarker Guide: Interpreting Molecular Fossils in Petroleum and Ancient Sediments. Prentice Hall, Englewood Cliffs, New Jersey, p. 363] and the Manco scale [Larter, S., Huang, H., Adams, J., Bennett, B., Snowdon, L.R., 2012. A practical biodegradation scale for use in reservoir geochemical studies of biodegraded oils. Organic Geochemistry 45, 66-76]. Both scales agree on the presence of different levels of biodegradation for the analyzed oils, although they are based on different groups of compounds. The PM scale uses mainly compounds from the saturated hydrocarbon fractions (e.g., n-alkanes, acyclic isoprenoids, terpanes and steranes) as well as aromatic steroids. On the other hand, the Manco scale considers other compounds (e.g., alkyltoluenes, naphthalene, methylnaphthalene, phenanthrene, alkylphenanthrenes and methyldibenzothiophenes) not included in the PM biodegradation scale. Thus, the combined use of these two scales allows the determination of the level of biodegradation of both saturated and aromatic compound classes. Dibenzothiophene (DBT), which was not included for the Manco score determination, also shows variations in peak intensity when compared to C4-alkylnaphthalenes, presumably associated with the process of biological alteration. The differences in the biodegradation levels observed in the present study may be attributed to variations in parameters that control biodegradation rates laterally across the study area or the existence of varying communities of microorganisms, among other possible factors. © 2013 Elsevier Ltd. Source

Herrera A.,Central University of Venezuela
Frontiers in Plant Science | Year: 2013

This review summarizes the research on physiological responses to flooding of trees in the seasonal black-water wetland of the Mapire River in Venezuela. Inter-annual variability was found during 8 years of sampling, in spite of which a general picture emerged of increased stomatal conductance (gs and photosynthetic rate (PN during the flooded period to values as high as or higher than in plants in drained wet soil. Models explaining the initial inhibitory responses and the acclimation to flooding are proposed. In the inhibitory phase of flooding, hypoxia generated by flooding causes a decrease in root water absorption and stomatal closure. An increase with flooding in xylem water potential (ψ) suggests that flooding does not cause water deficit. The PN decreases due to changes in relative stomatal and non-stomatal limitations to photosynthesis; an increase in the latter is due to reduced chlorophyll and total soluble protein content. Total non-structural carbohydrates (TNC accumulate in leaves but their content begins to decrease during the acclimatized phase at full flooding, coinciding with the resumption of high gs and PN. The reversal of the diminution in gs is associated, in some but not all species, to the growth of adventitious roots. The occurrence of morpho-anatomical and biochemical adaptations which improve oxygen supply would cause the acclimation, including increased water absorption by the roots, increased rubisco and chlorophyll contents and ultimately increased PN. Therefore, trees would perform as if flooding did not signify a stress to their physiology. © 2013 Herrera. Source

Homicides occur the world over, but they are not homogeneously distributed by geographical areas (continents, countries, regions), either over long or short periods of time, or in social groups, namely age, gender, social class or ethnicity. Why are there more homicides in some countries than in others? Why do killings increase in some countries, while they decrease in others? There are two fundamental schools of thought for social explanations of crime and violence: those attributing its origins to poverty and inequality and those blaming institutionalization or social norms. To discuss these theories, this paper analyzes and compares the changes in Colombia, Venezuela and Brazil in the first decade of the twenty-first century, where the homicide rate has decreased, increased and remained the same, respectively. Using the measurement of six variables (poverty, inequality, unemployment, national wealth, human development and the rule of law) and the technique of trajectory analysis, the results revealed that institutionalization is more to blame for the change than poverty and inequality. The text concludes that poverty and inequality affect crime and homicides, although not directly, but mediated by the institutions instead. Source

Encinas-Viso F.,University of Groningen | Revilla T.A.,Central University of Venezuela | Revilla T.A.,French National Center for Scientific Research | Etienne R.S.,University of Groningen
Ecology Letters | Year: 2012

Several network properties have been identified as determinants of the stability and complexity of mutualistic networks. However, it is unclear which mechanisms give rise to these network properties. Phenology seems important, because it shapes the topology of mutualistic networks, but its effects on the dynamics of mutualistic networks have scarcely been studied. Here, we study these effects with a general dynamical model of mutualistic and competitive interactions where the interaction strength depends on the temporal overlap between species resulting from their phenologies. We find a negative complexity-stability relationship, where phenologies maximising mutualistic interactions and minimising intraguild competitive interactions generate speciose, nested and poorly connected networks with moderate asymmetry and low resilience. Moreover, lengthening the season increases diversity and resilience. This highlights the fragility of real mutualistic communities with short seasons (e.g. Arctic environments) to drastic environmental changes. © 2012 Blackwell Publishing Ltd/CNRS. Source

Longo C.,Central University of Venezuela
Coordination Chemistry Reviews | Year: 2010

The present review describes several examples of the use of soluble and immobilized complexes of rhodium with pyridine ligands as catalysts. Examples include the water-gas shift reaction, the carbonylation of methanol, the reduction of nitroarenes, the hydrocarboxylation and oligomerization of CO/ethylene, the hydrocarbonylation of 1-hexene, the hydroesterification and hydroformylation-acetalization of 1-hexene, the hydrodechlorination of dichloroethane, the carbonylation of naphtha and the hydrogenation and hydroformylation of alkenes. © 2009 Elsevier B.V. All rights reserved. Source

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