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Institution

Simón Bolívar University

EducationCaracas, Venezuela
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.


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Journal ArticleDOI
23 Sep 2010-PLOS ONE
TL;DR: It is found that most environmental variables contributed to explain a large and significant proportion of variation of the intercontinental submodel both for genera and families, and these variables should be preferably considered when forecasting large-scale spatial patterns of polychaete assemblages in relation to ongoing or predicted changes in environmental conditions.
Abstract: This study examined spatial relationships between rocky shore polychaete assemblages and environmental variables over broad geographical scales, using a database compiled within the Census of Marine Life NaGISA (Natural Geography In Shore Areas) research program. The database consisted of abundance measures of polychaetes classified at the genus and family levels for 74 and 93 sites, respectively, from nine geographic regions. We tested the general hypothesis that the set of environmental variables emerging as potentially important drivers of variation in polychaete assemblages depend on the spatial scale considered. Through Moran’s eigenvector maps we indentified three submodels reflecting spatial relationships among sampling sites at intercontinental (.10000 km), continental (1000–5000 km) and regional (20–500 km) scales. Using redundancy analysis we found that most environmental variables contributed to explain a large and significant proportion of variation of the intercontinental submodel both for genera and families (54% and 53%, respectively). A subset of these variables, organic pollution, inorganic pollution, primary productivity and nutrient contamination was also significantly related to spatial variation at the continental scale, explaining 25% and 32% of the variance at the genus and family levels, respectively. These variables should therefore be preferably considered when forecasting large-scale spatial patterns of polychaete assemblages in relation to ongoing or predicted changes in environmental conditions. None of the variables considered in this study were significantly related to the regional submodel.

36 citations

Journal ArticleDOI
TL;DR: A group of optimization models for real-time operation of a hydropower system of reservoirs is presented in this paper, where the dimensionality problems usually found in dynamic programming formulations are solved by a space-time aggregation/disaggregation procedure that combines stochastic dynamic programming and linear programming techniques.
Abstract: A group of optimization models for the real-time operation of a hydropower system of reservoirs is presented in this paper. The dimensionality problems usually found in dynamic programming formulations are solved by a space-time aggregation/disaggregation procedure that combines stochastic dynamic programming and linear programming techniques. The reservoirs in a hydropower system are aggregated in power units rather than in water units, and an optimal operating policy for the equivalent aggregated reservoir is found in the first part of this work. The objective function in this first part is to minimize the total cost or energy production for a hydrothermal system. The aggregated policy obtained is used in the real-time operation of the system to determine the recommended daily releases and power production from each reservoir of the system. The proposed methodology is applied to a case study, the Lower Caroni system in Venezuela, which is composed of four reservoirs in series and a total installed capacity of 17,000 MW, with satisfactory results.

36 citations

Journal ArticleDOI
TL;DR: The high variability between tissue mortality values among coral colonies also suggests that overall host health-status may alter susceptibility to BBD infections, and that nutrient enrichment of the local waters by upwelling counteracts the expected reductions of the disease prevalence and virulence due to the lower temperature.
Abstract: Temporal variability of Black Band Disease (BBD) prevalence, incidence, recurrence, recovery and virulence was estimated in a Diploria strigosa population from an upwelling zone of Venezuela, for 1 year between August 2004 and August 2005. The sampling spanned both upwelling and non-upwelling seasons, and included three samplings, roughly 60 days apart, within each season. The negative effects of BBD epizootiology in the sampling population (El Mercado reef) were positively correlated with sea surface temperature (taken as an upwelling estimator). Disease prevalence, incidence and recurrence decreased significantly during upwelling, and the recovery rate increased. Contrary to expectations, tissue mortality did not decrease significantly during the upwelling season, remaining at 1.2 ± 0.7 mm day−1. BBD prevalence, and the ensuing rates of tissue mortality were higher than values previously reported for other Caribbean reefs, even during upwelling episodes, suggesting that nutrient enrichment of the local waters by upwelling counteracts the expected reductions of the disease prevalence and virulence due to the lower temperature. Colonies which had previously been infected with BBD were up to six times more susceptible to new infections than those which were not infected during the preceding 7 months, suggesting that the infected colonies never healed completely. The high variability between tissue mortality values among coral colonies also suggests that overall host health-status may alter susceptibility to BBD infections.

36 citations

Journal ArticleDOI
TL;DR: This sample exhibited a unique surface morphology with long range ordered domains of edge-on PLLA lamellae that can promote "cell contact guidance" and play a major role in determining cell preference toward a specific surface for the materials employed in this work.
Abstract: An evaluation of cell proliferation and adhesion on biocompatible film supports was performed. A series of films were compression molded from commercially available poly (L-lactide), PLLA, and poly(epsilon-caprolactone), PCL, and from their melt mixed blends (PLLA/PCL blends). These were compared with compression molded films of PLLA-b-PCL model diblock copolymers. The samples were analyzed by differential scanning calorimetry (DSC), contact angle measurements, and scanning force microscopy (SFM). Cell adhesion and proliferation were performed with monkey derived fibroblasts (VERO) and with osteoblastic cells obtained either enzymatically or from explants cultures of Sprague-Dawley rat calvaria. Migration studies were performed with bone explants of the same origin. The results obtained indicate that although all materials tested were suitable for the support of cellular growth, a PLLA-b-PCL diblock copolymer sample with 93% PLLA was significantly more efficient. This sample exhibited a unique surface morphology with long range ordered domains (of the order of 2-3 mum) of edge-on PLLA lamellae that can promote "cell contact guidance." The influence of other factors such as chemical composition, degree of crystallinity, and surface roughness did not play a major role in determining cell preference toward a specific surface for the materials employed in this work.

36 citations

Journal ArticleDOI
TL;DR: In this article, an enhanced strategy for direct torque control (DTC) combining artificial intelligent (AI) and predictive algorithms was proposed, where fuzzy logic control with dynamic rules based on the P-DTC law's was introduced to reduce the parameter dependency and improve the performance of DTC.
Abstract: This paper proposes an enhanced strategy for direct torque control (DTC) combining artificial intelligent (AI) and predictive algorithms. The advantages of this merge are in the solution of closed-loop controlled induction machine (IM) problems. Predictive DTC (P-DTC) methods reduce the high torque ripple and improve the performance at both starting condition and low mechanical speed operation. However, P-DTC depends on the IM parameter's knowledge. The approach here is the introduction of fuzzy logic control with dynamic rules based on the P-DTC law's to reduce the parameter dependency and improve the performance of P-DPC. Additional comparative performance study of eight modulation strategies under the proposed fuzzy-predictive DTC (FP-DTC) is conducted. It results that the space-vector modulation (SVM) is the most suitable scheme with the best combination of criteria such stator current total harmonic distortion, switching losses and dynamic behavior. The parameter dependency of the FP-DTC is tested by a sensitivity analysis which corroborates the robustness of the proposed control. For verification purposes, simulations of the DTC, P-DTC, and FP-DTC were conducted and compared. Experimental results for the three controllers and two modulations (pulse width modulation and SVM) confirm the expected performance of the proposed control algorithm and modulation assessment study.

36 citations


Authors

Showing all 5925 results

NameH-indexPapersCitations
Franco Nori114111763808
Ignacio Rodriguez-Iturbe9633432283
Ian W. Hamley7846925800
Francisco Zaera7343219907
Thomas G. Habetler7339520725
Douglas L. Jones7051221596
I. Taboada6634613528
Enrique Herrero6424211653
Rudi Studer6026819876
Alejandro J. Müller5842012410
David Padua5824311155
Rudolf Jaffé5818210268
Luis Balicas5732814114
Volker Abetz5538611583
Ananias A. Escalante511608866
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Performance
Metrics
No. of papers from the Institution in previous years
YearPapers
20232
202220
2021286
2020384
2019340
2018312