Pressure infiltration of Al and Al-12 wt% Si alloy into compacts of SiC and oxidized SiC particles

Oxidizing SiC particles is a common practice in the fabrication of SiC/Al composites through direct mixing of the liquid metal and the ceramic particles. This practice is addressed to reduce the reaction between the two materials. In a previous work it was concluded that oxidizing SiC particles scarcely affected the threshold pressure for infiltration of pure Al into compacts made of those particles. In this work we present a detailed study of this problem for infiltration of pure Al and the eutectic Al-Si alloy. Our results indicate that oxidizing of SiC particles does not affect significantly either the threshold pressure or the infiltration kinetics. This conclusion is equally valid for both pure Al and the eutectic alloy.     

PERFORMANCE-DRIVEN AUTONOMOUS DESIGN OF PATTERN-RECOGNITION SYSTEMS

The closed-loop design experiment described in this paper demonstrates a three-phase automated design approach to pattern recognition. The experiment generates morphological feature detectors and then uses a novel application of genetic algorithms to select cooperative sets of features to pass to a neural net classifier. The self-organizing hybrid learning approach embodied in this closed-loop design methodology is complementary to conventional artificial intelligence (AI) expert systems that utilize rule-based approaches and a specific set of design elements. This experiment is part of a study directed to emulating the nondirected processes of biological evolution. The approach we discuss is semiautomatic in that initialization of computer programs requires human experience and expertise to select representations, develop search strategies, choose performance measures, and devise resource-allocation strategies. The hope is that these tasks will become easier with experience and will provide the means to exploit parallel processing without the need to analyze or program an entire design solution.     

Case-based reasoning assisted explanation of genetic algorithm results

Abstract

This paper describes a system for explaining solutions generated by genetic algorithms (GAs) using tools developed for case-based reasoning (CBR). In addition, this work empirically supports the building block hypothesis (BBH) which states that genetic algorithms work by combining good sub-solutions called building blocks into complete solutions. Since the space of possible building blocks and their combinations is extremely large, solutions found by GAs are often opaque and cannot be easily explained. Ironically, much of the knowledge required to explain such solutions is implicit in the processing done by the GA. Our system extracts and processes historical information from the GA by using knowledge acquisition and analysis tools developed for case-based reasoning. If properly analysed, the resulting knowledge base can be used: to shed light on the nature of the search space; to explain how a solution evolved; to discover its building blocks; and to justify why it works. Such knowledge about the search space can be used to tune the GA in various ways. As well as being a useful explanatory tool for GA researchers, our system serves as an empirical test of the building block hypothesis. The fact that it works so well lends credence to the theory that GAs work by exploiting common genetic building blocks.     

Series Solutions of Poisson Equations and Space Charge Theory†

An inverse power aeries solution, dealing with a wide variety of space charge problems, which has been proposed previously, suffers from one drawback. The first coefficient in the expansion is given as the solution of an infinite polynomial and all other coefficients depend on the first one. In this paper we describe a method of obtaining the first coefficient directly from a Poisson Equation of the form ü=g(u) for the case where ∫g(u) du is readily obtainable. That this is often the case physically is shown by applying the theory to several junction and blocking electrode problems both with and without traps.     

THE SLIDEX RT CODE

Abstract

In this article, we describe the five block cipher modes of operation that have been approved by the National Institute of Standards and Technology (NIST) for confidentiality. Each mode specifies an algorithm for encrypting/decrypting data sequences that are longer than a single block.     

REVIEW OF THINGS CRYPTOLOGIC

Abstract

Sets out, with comments, an account by A. G. Denniston (the operational head of the British Government Code and Cypher School in 1939) of the meeting near Pyry, Poland, in July 1939, when Polish cryptanalysts revealed how they broke Enigma, and a letter by Dillwyn Knox on the meeting's outcome.     

Hydration behaviour of synthetic saponite at variable relative humidity

Hydration behaviour of synthetic saponite was examined by X-ray powder diffraction simulation at various relative humidities (RH). The basal spacing of the Ca-saponite increased stepwise with increase in RH. The (00l) reflections observed reflect single or dual hydration states of smectite. Quasi-rational, intermediate, or asymmetrical reflections were observed for all XRD patterns and reflecting heterogeneity of the samples, especially along the transition between two hydration states.