Application of Romero García method to the degradation process of DGEBA/ETDA filled with ultra fine metallic copper

Summary The thermal properties of an epoxy resin (diglycidyl ether Bisphenol A, DGEBA) cured with a primary amine (ethylenediamine, ETDA) and filled with 10, 20 and 30 wt. % of ultra fine copper particles were analyzed. The thermal results were evaluated by means of the Romero-Garcia method, which allowed to obtain the resin degradation kinetic parameters, as well as the possible decomposition mechanism. From the obtained results is possible to infer that higger copper content strongly affects the degradation process of the epoxy resin, which causes a drop off on the composites thermal stability. This behavior could be attributed to water presence, being this effect less pronounced for the resin with 10 wt. % copper and unfilled resin. Regarding to decomposition mechanism, three way transport showed the best correlation for all samples.     

Effective parameters of static coupled physicomechanical field in matrix composites

Conclusions It is shown that the problem of evaluating the effective parameters of composites for a wide range of stationary coupled fields is reduced to examining uncoupled fields.The multiparticle method of the effective field was generalized with special reference to the problems of examining the static coupled physicomechanical fields in composites.Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 27, No. 4, pp. 105–111, July–August, 1991.     

MODELING WATER LOSS DURING FRYING OF POTATO STRIPS: EFFECT OF SOLUTE IMPREGNATION

The effect of solute impregnation on water loss and oil uptake during potato strip frying was studied. Blanched potato strips were impregnated at 25°C by soaking in a solution of sucrose-NaCl-water, 20-5-75% by weight. After rinsing and air drying, strips were deep fried in sunflower oil at 160, 170 and 180°C. A control treatment, consisting of potato strips blanched but not soaked and later air dried was also conducted. Solute impregnation provided a decrease of the oil uptake. Two models, based on Fick's law were used to describe water loss during frying. The first one is the classic model with an effective moisture diffusion coefficient assumed a constant value. The second model considers that diffusion coefficient varies during the frying process. For a given frying temperature, constant diffusion coefficient for control potatoes resulted in lower values than the impregnated ones. The variable diffusivity model showed a two-stage behavior: during the first stage of frying, diffusion coefficient increased with frying temperatures, but from a given time on an inverse behavior began. This last fact was found to be related to an increase of the measured peak force needed to penetrate the potato crust.     

Spectral predictions for pulse interval and width modulation

An expression for the frequency spectrum of pulse interval and width modulation (PIWM) is presented. Experimental results obtained have shown close agreement with spectral predictions from the formula. Performance figures are also included from a practical PIWM optical-fibre transmission system intended for use with TV and video signals.<>     

职工持股计划在中国:理论上可行,实践上慎行

在对中美两国的职工持股计划进行分析后,本文认为职工持股计划在中国,理论上可行,但在实践中 需要谨慎行事。