Interface analysis of Si-C-O fibre/magnesium aluminosilicate matrix composites

Interface characteristics of Si-C-O (Nicalon^R) fibre-reinforced glass ceramic matrix composites were studied using scanning Auger microscopy (SAM). Composites with and without the cation additions of Ba, Nb, Zr, Li and Li-Zr-Nb to the magnesium aluminosilicate (MAS) matrix were fracturedin situ under ultrahigh vacuum. SAM depth profiles and flexural strength results showed the compositional effects of the additives in the fibre-matrix interface region.     

Effects of administration of the chemoprotective agent oltipraz on CYP1A and CYP2B in rat liver and rat hepatocytes in culture

The success of oltipraz (OPZ) [5-(2-pyrazinyl)-4-methyl-1,2-dithiole-3-thione] as a chemoprotective agent against aflatoxin B1 (AFB1)-induced hepatocarcinogenesis in the rat is thought to depend principally on its ability to enhance detoxication by inducing phase II enzymes, especially glutathione transferases. However, in primary cultures of human hepatocytes, we recently demonstrated that OPZ also has an important inhibitory effect on the major cytochromes P450 (CYPs) of human hepatic AFB1 metabolism. This has prompted a detailed study of the effect of OPZ on some CYPs involved in metabolism of AFB1 in the rat. Primary cultures of rat hepatocytes behaved similarly to human hepatocytes and responded to OPZ by inhibition of ethoxyresorufin-O-deethylase (EROD) and pentoxyresorufin-O-depentylase (PROD) activities mainly associated, respectively, with CYP1A and CYP2B. A time-course shows that this inhibition is largely reversible, with EROD and PROD activities reaching a minimum at 12 h and tending towards control values within 24 h. As is to be expected, the incubation of isolated microsomes with OPZ also inhibits CYP1A and 2B. The effect of OPZ on CYP1A is not a phenomenon limited to cells in culture, but also occurs in vivo. Using the whole animal, we were able to demonstrate that OPZ also transiently inhibited CYP1A activity in a rat given caffeine, by measuring the amounts of methylxanthines found in the serum. However, microsomes isolated from rats, that had been treated with OPZ in vivo, show no such inhibition, presumably because, since OPZ is a reversible inhibitor, it dissociates and is lost during the course of conventional procedures of microsomal preparation. This explains some earlier failures in studies of isolated microsomes to observe the inhibition of CYPs by OPZ. In addition to inhibiting their enzymatic activity, OPZ is also an inducer of CYP1A and 2B as shown by the increased levels of their mRNAs and of caffeine metabolism in vivo after 24 h or more. It is concluded that the mechanism of chemoprotection by OPZ, of toxic chemical metabolism in the rat, is complex and involves competitive inhibition of activation succeeded by induction of the enzymes of both activation and detoxication.     

The effect of physical vapor deposition parameters on the thermoelectric power of thin film molybdenum-nickel junctions

The effect of various physical vapor deposition parameters on the thermoelectric power of thin film (10 000 Å) Mo-Ni junctions deposited by electron beam evaporation was investigated in this study. The deposition parameters of interest were the substrate temperature, the deposition rate and the vapor source purity. The thermoelectric power of the thin film Mo-Ni junctions was dependent on the structure of the Mo thermoelectric element of the couple, the characteristics of which were significantly altered by varying the deposition parameters. Varying the deposition parameters caused a change in lattice imperfections in the metal, which changed the mean free path of the conduction electrons and the thermoelectric power of the couple. The parameters having the greatest effect on the thermoelectric power were the deposition rate and the substrate temperature. Couples deposited at a high deposition rate (10 000 Å min^-1) and a high substrate temperature (? 300 °C) demonstrated e.m.f. characteristics closest to bulk values.     

Fractionation with condensation and evaporation in wetted-wall columns

A model is presented to describe the behavior of falling film fractionators with evaporation or condensation. Experimental measurements of vapor composition, vapor temperature and wall temperature profiles were made. Close agreement suggests that the model is applicable to both adiabatic and nonadiabatic conditions.     

Observability and redundancy classification in process networks: Theorems and algorithms

The utility of observability and redundancy in characterizing the performance of process data estimators was established in previous studies [10]. In this paper two classification algorithms for determining local and global observability and redundancy for individual variables and measurements are presented. The concepts of biconnected components, perturbation subgraphs and feasible unmeasurable perturbations are introduced, and their properties are developed and used to effect classification, simplification and dimensional reduction. Step-by-step application of these algorithms is illustrated by examples.     

Effects of thermophysical property estimation on process design

This paper demonstrates the importance of relating thermophysical data estimation procedures to the design application of the information so generated. Examples are given of the utility of vapor-liquid equilibrium and solubility data in distillation and extractive distillation. Computer-aided design techniques were employed to generate the property estimates and to evaluate their effects on distillation column designs. Specific guidelines are developed on screening of data sources, determination of data requirements and verification of correlations.     

A Newton type linearization method for solution of nonlinear equations

Convergence properties of a new iterative method for solution of non-linear equations are investigated. It is shown that for a system of equations which contain mixed linear equations and homogeneous functions of degree n, the convergence of this method is equivalent to the convergence of Newton's method. In contrast to the latter, this new method does not require evaluation of the vector of function values at every iteration.