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.

Relaciones entre estrés académico, apoyo social, salud mental y rendimiento académico en estudiantes universitarios venezolanos

Abstract: El objetivo de la presente investigacion fue evaluar el estres academico, el apoyo social y su relacion con la salud mental y el rendimiento academico en estudiantes universitarios. Trescientos veintiun estudiantes de carreras tecnicas en Caracas, Venezuela, diligenciaron, durante el periodo academico de mayor tension, instrumentos sobre estres academico, apoyo social y salud mental. Los resultados indican que las condiciones favorables de salud mental estan asociadas con un mayor apoyo social y un menor estres academico. En las mujeres, la mayor intensidad del estres se asocio al menor apoyo social de los amigos, mientras que en los hombres se relaciono con un menor apoyo social por parte de personas cercanas, y un menor apoyo en general. Ambos presentaron mejor rendimiento cuando el estres academico percibido fue mayor y el apoyo social de las personas cercanas fue moderado. Los resultados se discuten en funcion de las implicaciones en la salud mental y el rendimiento academico de los estudiantes universitarios.

Investigation of the Early Flame Development in Spark Assisted HCCI Combustion Using High Speed Chemiluminescence Imaging

Abstract: Auto-ignition with SI-compression ratio can be achieved by replacing some of the fresh charge by hot residuals. In this work an engine is run with a negative valve overlap (NVO) trapping hot residuals. By increasing the NVO, thus raising the initial charge temperature it is possible to investigate the intermediate zone between SI and HCCI as the amount of residuals is increased. Recent research has shown the potential of using spark assistance to aid gasoline HCCI combustion at some operating conditions, and even extend the operating regime into regions where unsupported HCCI combustion is impossible. In this work the influence of the spark is studied in a single cylinder operated engine with optical access. Combustion is monitored by in-cylinder pressure and simultaneous high speed chemiluminescence imaging. It is seen that even for large NVO and thus high residual fractions it is a growing SI flame that interacts with, and governs the subsequent HCCI combustion. Using the spark timing it is possible to phase the combustion timing even when the major part of the released heat is from HCCI combustion. The flame expansion speed is decreases for higher NVO, but prevails also for high residual fractions. A higher spark advance is found to compensate for the slower flame expansion up to a point. The auto-ignition process is found to be stratified for both spark assisted HCCI as well as for pure HCCI. For pure HCCI the initial front spreading velocity is found to be in the same order of magnitude as for the expansion speed of the SI flame. Calculations to estimate the crank angle of auto-ignition are performed based on cylinder pressure information providing good statistics on how the proportion of SI to HCCI behaves for different operating conditions.

Scale of fluctuation of rainfall models

Abstract: The role of scale in the rainfall characterizations resulting from different rainfall models is the main issue under study. Three different types of models are analyzed: temporal rainfall models at a point, areal storm rainfall models, and space-time rainfall representations. The perspective is taken that precipitation models need mainly to incorporate those features of the process which lead to an adequate representation under some amount of local averaging either in time or in space or in space and time. Thus the characteristics of the averaged rainfall process resulting from the different models are analyzed with a special emphasis on the role of the scale of fluctuation of the process in these characteristics.

Validation of a Rapid and Reliable Test for Diagnosis of Chagas' Disease by Detection of Trypanosoma cruzi-Specific Antibodies in Blood of Donors and Patients in Central America

Abstract: In this study we compared the performance of the Chagas Stat-Pak rapid immunochromatographic test with a standard enzyme-linked immunosorbent assay (ELISA) in the serodiagnosis of Chagas' disease in Central America. Out of 3,400 blood donor samples, 156 (4.6%) were positive in both assays. Three sera out of 2,084 samples from reference laboratories were negative with the rapid test but positive with the ELISA (99.8% agreement). Agreement of 100% between the two tests was observed with 339 additional sera from patients with cardiopathies and 175 sera from potential blood donors in emergency surgical cases occurring on weekends or at night. In conclusion, Chagas Stat-Pak showed 99.6% and 99.9% sensitivity and specificity, respectively, when assayed with 5,998 serum samples. It is a sensitive and specific alternative to the ELISA, as required in medical emergencies and blood screenings in Central America.