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.

Water Absorption Effect on the Dynamic Properties of Nylon-6 by Dielectric Spectroscopy

Abstract: New results of dielectric spectroscopy in semicrystalline nylon-6 samples with different moisture contents are presented by using a wide frequency (10-2−3 × 106 Hz) and temperature range (133−433 K). The dielectric absorption spectra in frequency domain are decomposed in Cole−Cole distributions corresponding to the local γ and β modes, two segmental α modes, and a high-intensity Maxwell−Wagner−Sillars relaxation. The presence of two segmental relaxations in the isothermal runs, attributed to the plasticized and the unplasticized α mode, is interpreted as the manifestation of two different length and time scales of cooperative motions. A quantitative comparison between the results obtained for the wet and dry samples, such as relaxation times variation, activation energies, Vogel−Tammann−Fulcher parameters, dielectric increments, and distribution widths, is presented for each mode and shows how the progressive drying of the sample during the experiment affects all these quantities.

Salinity effect on plant growth and leaf demography of the mangrove, Avicennia germinans L.

Abstract: We assessed the effect of salinity on plant growth and leaf expansion rates, as well as the leaf life span and the dynamics of leaf production and mortality in seedlings of Avicennia germinans L. grown at 0, 170, 430, 680, and 940 mol m−3 NaCl. The relative growth rates (RGR) after 27 weeks reached a maximum (10.4 mg g−1 d−1) in 170 mol m−3 NaCl and decreased by 47 and 44% in plants grown at 680 and 940 mol m−3 NaCl. The relative leaf expansion rate (RLER) was maximal at 170 mol m−3 NaCl (120 cm m−2 d−1) and decreased by 57 and 52% in plants grown at 680 and 940 mol m−3 NaCl, respectively. In the same manner as RGR and RLER, the leaf production (P) and leaf death (D) decreased in 81 and 67% when salinity increased from 170 to 940 mol m−3 NaCl, respectively. Since the decrease in P with salinity was more pronounced than the decrease in D, the net accumulation of leaves per plant decreased with salinity. Additionally, an evident increase in annual mortality rates (λ) and death probability was observed with salinity. Leaf half-life (t0.5) was 425 days in plants grown at 0 mol m−3 NaCl, and decreased to 75 days at 940 mol m−3 NaCl. Thus, increasing salinity caused an increase in mortality rate whereas production of new leaves and leaf longevity decreased and, finally, the leaf area was reduced.

Abbreviated Measures of Food Sufficiency Validly Estimate the Food Security Level of Poor Households: Measuring Household Food Security

Abstract: This study was designed to develop an abbreviated method that captures both the qualitative and quantitative dimensions of household food security (HFS). Women in poor and very poor households (n = 238) in a peri-urban barrio in Caracas, Venezuela, provided data on food availability and their perception of food resource constraints and hunger experiences within the home. Socioeconomic data and food-related behavior that may predict HFS levels were gathered. On average, the top 12 food contributors of energy provided 81% and predicted more than 90% of the variation in households' total energy availability using stepwise regression analysis. On the other hand, a 4-point 12-item scale was shown to have face, content and construct validity with reiterative testing, factor analysis and a Chronbach's alpha coefficient of 0.92. Assessing predictors of energy availability together with a self-perceived HFS scale may provide a valid and reliable method for identifying and monitoring food security levels among poor urban households.

Predictors of perceived barriers to physical activity in the general adult population: a cross-sectional study.

Abstract: Background The perception of personal barriers to physical activity varies according to the sociodemographic characteristics of individuals. Objective To determine the predictors of the perception of barriers to physical activity in the adult population. Method A cross-sectional study with 1066 adult women and 1036 adult men. The sociodemographic variables (age, gender, marital status, socioeconomic level, level of education), the perception of barriers that do not allow performance of physical activity (i.e. lack of time, social support, energy, motivation, skill, resources, and fear of injury during practice); and the level of physical activity through the International Physical Activity Questionnaire in its short-form version were evaluated. Results Individuals from low socioeconomic level (1 and 2) have higher risks of perceiving barriers such as lack of motivation [OR 1.76 (95% CI (1.4–2.1))] and lack of resources [OR 1.37 (95% CI (1.1–1.6))]; individuals with partners did not perceive the lack of social support [OR 0.29 (95% CI (0.2–0.4))] and lack of motivation [OR 0.54 (95% CI (0.4–0.7))] as barriers to physical activity. Individuals with low schooling perceived lack of social support [OR 3.81 (95% CI (3–4.7))], lack of resources [OR 2.78 (95% CI (2.2–3.3))], and fear of injury [OR 2.70 (95% CI (2.2–3.3))] as barrier to physical activity. Conclusion Factors such as socioeconomic level, marital status, level of education, and self-perception of health are predictors of barriers to physical activity.