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.

Responses to simulated herbivory and water stress in two tropical C4 grasses

Abstract: The African grass Hyparrhenia rufa has established itself successfully in South American savannas (Llanos) and displaced dominant native grasses such as Trachypogon plumosus from the wetter and more fertile habitats. Several ecophysiological traits have been related to the higher competitive capacity of H. rufa. To further analyze the behavior of both species, their growth, biomass allocation, physiological and architectural responses to defoliation and water stress were compared under controlled conditions. Although total, aerial and underground biomass decreased under defoliation in both grasses, increases in clipped-leaf biomass and area compensated for defoliation in H. rufa but not in T. plumosus. This difference was due mainly to a higher proportion of assimilates being directed to leaf and tiller production and a higher leaf growth rate in the African grass as compared to T. plumosus, which showed incrased senescence under frequent defoliation. In both species, water stress ameliorated the effects of defoliation. The ability to compensate for defoliated biomass in H. rufa is possibly related to its long coevolution with large herbivores in its original African habitat and is apparently one of the causes of its success in Neotropical savannas.

Socioeconomic impact on device-associated infections in pediatric intensive care units of 16 limited-resource countries: International Nosocomial Infection Control Consortium findings*

Abstract: Objectives: We report the results of the International Nosocomial Infection Control Consortium prospective surveillance study from January 2004 to December 2009 in 33 pediatric intensive care units of 16 countries and the impact of being in a private vs. public hospital and the income country level on device-associated health care-associated infection rates. Additionally, we aim to compare these findings with the results of the Centers for Disease Control and Prevention National Healthcare Safety Network annual report to show the differences between developed and developing countries regarding device-associated health care-associated infection rates. Patients: A prospective cohort, active device-associated health care-associated infection surveillance study was conducted on 23,700 patients in International Nosocomial Infection Control Consortium pediatric intensive care units. Methods: The protocol and methodology implemented were developed by International Nosocomial Infection Control Consortium. Data collection was performed in the participating intensive care units. Data uploading and analyses were conducted at International Nosocomial Infection Control Consortium headquarters on proprietary software. Device-associated health care-associated infection rates were recorded by applying Centers for Disease Control and Prevention National Healthcare Safety Network device-associated infection definitions, and the impact of being in a private vs. public hospital and the income country level on device-associated infection risk was evaluated. Interventions: None. Measurements and Main Results: Central line-associated bloodstream infection rates were similar in private, public, or academic hospitals (7.3 vs. 8.4 central line-associated bloodstream infection per 1,000 catheter-days [p < .35 vs. 8.2; p < .42]). Central line-associated bloodstream infection rates in lower middle-income countries were higher than low-income countries or upper middle-income countries (12.2 vs. 5.5 central line-associated bloodstream infections per 1,000 catheter-days [p < .02 vs. 7.0; p < .001]). Catheter-associated urinary tract infection rates were similar in academic, public and private hospitals: (4.2 vs. 5.2 catheter-associated urinary tract infection per 1,000 catheter-days [p = .41 vs. 3.0; p = .195]). Catheter-associated urinary tract infection rates were higher in lower middle-income countries than low-income countries or upper middle-income countries (5.9 vs. 0.6 catheter-associated urinary tract infection per 1,000 catheter-days [p < .004 vs. 3.7; p < .01]). Ventilator-associated pneumonia rates in academic hospitals were higher than private or public hospitals: (8.3 vs. 3.5 ventilator-associated pneumonias per 1,000 ventilator-days [p < .001 vs. 4.7; p < .001]). Lower middle-income countries had higher ventilator-associated pneumonia rates than low-income countries or upper middle-income countries: (9.0 vs. 0.5 per 1,000 ventilator-days [p < .001 vs. 5.4; p < .001]). Hand hygiene compliance rates were higher in public than academic or private hospitals (65.2% vs. 54.8% [p < .001 vs. 13.3%; p < .01]). Conclusions: Country socioeconomic level influence deviceassociated infection rates in developing countries and need to be considered when comparing device-associated infections from one country to another. (Pediatr Crit Care Med 2012; 13:399–406)

High Speed SSA Thermal Fractionation and Limitations to the Determination of Lamellar Sizes and Their Distributions

Abstract: Summary: The technique of successive self-nucleation and annealing (SSA) has been applied using differential scanning calorimetry (DSC) to a model hydrogenated polybutadiene prepared by anionic polymerization and to a commercial Ziegler-Natta ethylene/1-butene copolymer. Here, it is shown that the use of high scanning rates (50 °C · min−1) in the SSA protocol can reduce the thermal fractionation time to only 78 min in length (if 6 fractions are produced with a fractionation window of 5 °C), taking into consideration the need to compensate the increment in heating rates by reducing the sample mass. This time is much shorter than those previously achieved by thermal fractionation in the literature, where fractionation times of 12 or 24 h are common. Potentially, much higher rates could be employed by further reducing the fractionation times by SSA. For the first time, a distribution of lamellar thicknesses has been obtained by transmission electron microscopy after SSA fractionation and compared to distributions calculated by the Thomson-Gibbs equation. It is shown that the results are highly dependent on the equilibrium melting temperatures employed in the calculations, and it is recommended that the values of lamellar thicknesses obtained are checked by comparing with methylene sequence lengths derived from calibration measurements available in the literature. The Thomson-Gibbs equation is useful for comparing lamellar thickness distributions obtained by SSA with different polymers only on a semi-quantitative basis. Rate and mass compensation as a way to reduce fractionation time employing SSA.

Support for Augmented Reality Simulation Systems: The Effects of Scaffolding on Learning Outcomes and Behavior Patterns

Abstract: An AR-based simulation system that integrates background knowledge and experimental support (AR-SaBEr) was designed as a learning tool for teaching basic principles of electricity to ninth-grade students. The aim of this study was to investigate how supporting the learner focus on meaningful activities affects behavior and learning performance. The sample was 82 students, who were randomly assigned to two groups. The control group used AR-SaBEr with no support for recommending activities. The experimental group had personalized extra support designed to help learners focus on the subject matters that they did not master. The study found that learners from the experimental group showed better learning achievements than those who participated in the control group. Furthermore, learners’ behavioral patterns were dependent upon the support received. Learners from the control group were more willing to browse information about activities than to read about the subject before experimenting. Learners from the experimental group browsed information about prior to carrying them out and read about the subject matter prior to experimentation. The observed behavioral patterns and learning achievements suggest that in augmented reality based simulation environments, it is worth providing mechanisms to focus the attention of students on the most relevant topics for them.