Difusion

The moisture accumulation within clothing is a serious problem for sportswear and clothing in cold climate. There are several experimental methods available to measure moisture build up in insulate materials. However, information on parameters such as temperature, relative humidity and vapor pressure can be obtained through simulation using a predictive mathematical model. The focus of this study is the development of a mathematical model to simulate heat and moisture transfer in a sample of fabric, coated to provide insulation, which is in contact with human skin on one side and with the external environment on the other. To numerically simulate the mathematical model the finite volume method is used and a computational procedure for the solution of the model is designed. The simulation results are analyzed to verify whether they are consistent with the physical reality.

Este libro brinda una introducción a la electrónica en semiconductores -también llamada de estado
sólido- para carreras de ingeniería en electrónica, electricidad, computadoras, comunicaciones, control y sistemas. Provee una explicación de los mecanismos de conducción eléctrica en Silicio,
que luego se utiliza para el desarrollo de cuatro dispositivos fundamentales de la electrónica actual: el diodo de juntura, el capacitor Metal-Oxido-Semiconductor (MOS), el transistor MOS, y el transistor bipolar de juntura. El libro conduce al estudiante a que entienda el funcionamiento de cada dispositivo, partiendo de sus principios fundamentales, y que a partir de allí, comprenda en profundidad los diferentes modelos eléctricos que puede utilizar para representarlo, sus alcances y limitaciones. El objetivo último es que el estudiante conozca y sepa utilizar los distintos modelos de los dispositivos electrónicos, de acuerdo al rango de amplitud y frecuencia, para su utilización futura en el diseño y análisis de circuitos.

Adsorption of methylene blue from aqueous solutionsonto unexpanded and expanded perlite samples activatedby H2SO4 and NaCl solutions has beeninvestigated, to assess the possibility of usingperlite for removing cationic dyes from aqueoussolutions. The effects of pH and temperature of dyesolution on the adsorption capacities have beenevaluated. The experimental data were correlatedreasonably well by the Langmuir adsorption isothermand the isotherm parameters (Q m and K) have beencalculated. The removal efficiency (P) anddimensionless separation factor (R) have shown thatperlite can be used for removal of methylene blue fromaqueous solutions, but unexpanded perlite is more effective.

This paper proposes a study of different cation exchange resins, used as catalysts for the synthesis of peroxypropionic acid (PPA) from propionic acid and hydrogen peroxide at 40 °C, equimolar concentration of reactants and an apparent Brønsted concentration of 0.2 M. The catalytic activities of the resins are on the same scale as sulfuric acid at comparable concentration level and decrease in the order: Dowex 50Wx2 > Smopex-101 > Dowex 50Wx8 ≈ Amberlite IR-120 > Amberlyst 15. The influence of external and internal mass transfer limitation was evaluated. The experiments also demonstrated that a gelular resin with a degree of cross-linking equal to 8% and a particle size of more than 0.1 mm showed a stronger resistance to deactivation.