Luisa Rojas de Astudillo

PASCUAL-LEONE AND BADDELEY'S MODELS OF INFORMATION PROCESSING AS PREDICTORS OF ACADEMIC PERFORMANCE

The main purpose was to compare whether Pascual-Leone and Baddeleys models of information processing can explain performance of 83 Venezuelan freshman students in subjects such as chemistry, physics, mathematics, and language (Spanish). All students were tested on (a) Working Memory Span based on an adaptation of the Daneman and Carpenter task by Baddeley and colleagues, (b) Structural Mental Capacity based on Pascual-Leones Figural Intersection Test with no time limit, (c) Pascual-Leones Functional mental capacity based on the Figural Intersection Test with a time limit, (d) Witkins field dependence/independence based on the Group Embedded Figures Test, and (e) formal operational reasoning based on the Group Assessment of Logical Thinking. Multiple regression analyses showed that compared to scores on Working Memory Span, scores on both the Group Assessment of Logical Thinking and Structural Mental Capacity are better predictors of performance in science courses. Scores on Working Memory Span, however, are better predictors in the language course. Simultaneous processing of a large number of bits of information (Pascual-Leones Structural Mental Capacity) may be a more important constraint on performance in science courses than a model that postulates the storage and processing of information at the same time (Baddeleys working memory).

Distribution of Total and Organic Mercury in Superficial Soils in the Upper Manzanares River Watershed, Sucre State, Venezuela

Total and organic mercury contents were determined from samples of surface soils (0-5 cm), sieved at ≤63 μm. collected from 10 different locations in the upper Manzanares River watershed, using cold vapor atomic absorption spectroscopy. Methylmercury was determined using a HPLC-UV detector. The mean total mercury concentration was 1.3 μg. g-1, a value permitted by the Canadian environment quality guidelines for farming soils, but high for European standards. Using certified reference materials, we verified that a modification of the method described by Qian et al. (2000) was effective for organic mercury extraction, with a recovery of 92.17% for DORM-2 and 92.11% for TORT-2. This modified method was applied to soil samples, obtaining concentrations of 0.5-1.0 μg.g-1 of organic mercury. The parameters for determining methylmercury using HPLC-UV were optimized; the best results were obtained with a 4.6 mm × 25 cm Zorbax CN– column, with a mobile phase of 70/30 V/V of methanol: ammonium acetate 0.05 mol.l-1, with a flow rate of 0.5 ml.min-1; the methylmercury was detected at 4.99 min retention time. Methylmercury was not found in the soil samples. Using the certified reference material we proved that the method used produced reliable results. The analysis confirmed the existence of mercury in this farming area.

SÍNTESIS DE CARBÓN ACTIVADO A PARTIR DE EPICARPIO DE Attalea macrolepis Y SU APLICACIÓN EN LA REMOCIÓN DE Pb2+ EN SOLUCIONES ACUOSAS

En este trabajo se sintetizo carbon activado a partir del epicarpio de Attalea macrolepis y se evaluo como adsorbente para la remocion de iones Pb 2+ . El pH, la masa del adsorbente, el tiempo y la concentracion inicial de plomo se evaluaron como parametros influyentes en el proceso de adsorcion. Por otro lado, se evaluo el mecanismo de adsorcion de los iones de plomo sobre el carbon activado usando los modelos de Langmuir, Freundlich y Dubinin-Radushkevich. Mediante espectroscopia infrarroja con transformada de Fourier en el material adsorbente se identificaron los grupos funcionales hidroxilos, carboxilatos, olefinas y anillos bencenicos. Por medio de microscopia electronica de transmision se evidencio una matriz de particulas aglomeradas heterogeneas de tamano comprendido entre 149 a 185 nm. Las condiciones optimas obtenidas para la remocion de 70 % de iones Pb 2+ (5 mg/L) fueron a pH 5, una masa de adsorbente de 150 mg, un tiempo de contacto de una hora, una agitacion de 1500 rpm y un volumen de 25 mL. A partir de las isotermas se obtuvo una capacidad maxima de adsorcion de 0.500 mg/g. La energia de adsorcion calculada a partir del modelo de Dubinin-Radushkevich fue de 10.42 KJ/mol, este valor energetico permite inferir que en el sistema carbon activado-iones Pb 2+ ocurre una adsorcion quimica. Los resultados demuestran que el carbon activado producido con el epicarpio de Attalea macrolepis es un adsorbente alternativo de bajo costo y amigable con el ambiente para remover Pb 2+ de sistemas acuosos.