Growth and characterization of GaAs films deposited on Ge/Si composite substrates by metalorganic chemical vapor deposition

We report the results of studies which have been made on heteroepitaxial layers of GaAs and AlGaAs grown by metalorganic chemical vapor deposition on composite substrates that consist of four different types of heteroepitaxial layered structures of Ge and Ge-Si grown by molecular beam epitaxy on (100)-oriented Si substrates. It is found that of the four structures studied, the preferred composite substrate is a single layer of Ge ∼1 μm thick grown directly on a Si buffer layer. The double-crystal X-ray rocking curves of 2 μm thick GaAs films grown on such substrates have FWHM values as small as 168 arc sec. Transmission electron micrographs of these Ge/Si composite substrates has shown that the number of dislocations in the Ge heteroepitaxial layer can be greatly reduced by an anneal at about 750° C for 30 min which is simultaneously carried out during the growth of the GaAs layer. The quality of the GaAs layers grown on these composite substrates can be greatly improved by the use of a five-period GaAs-GaAsP strained-layer superlattice (SLS). Using the results of these studies, low-threshold optically pumped AlGaAs-GaAs DH laser structures have been grown by MOCVD on MBE Ge/Si composite substrates.     

A REVIEW OF TEXTURAL DEFECTS IN COOKED RECONSTITUTED LEGUMES —THE INFLUENCE OF STRUCTURE AND COMPOSITION

Legumes provide an important part of the world's protein requirements, as well as other nutrients, but they are underutilized as food. A major factor limiting expanded consumption is storage induced textural defects that prolong cooking time and demand correspondingly higher energy requirements for preparation. These defects, including the hard-to-cook phenomenon and hardshell, are initiated by structural and compositional factors but can be at least partially controlled by storage and processing conditions. Structural components implicated include seed coat, cell walls, middle lamella, starch granules and membranes while, compositionally, proteins, carbohydrates, phytate, polyphenols and lignin may also be important. Methods of texture measurement of legumes, including mechanical, physical and sensory properties are reviewed. The most commonly held hypothesis for the mechanism of the hard-to-cook defect states that beans fail to soften after exposure to high temperature and humidity storage because the increased water activity potentiates phytase which hydrolyzes phytate, rendering it no longer capable of chelating the Ca⁺⁺ and Mg⁺⁺ ions of the middle lamella and, hence, undissoluble. More recent evidence, however, provides potential roles for lignification, starch gelatinization and perhaps other mechanisms depending upon conditions. The possibility of a nonenzymatic as well as an enzymatic route is raised and thoughts presented on a course of action for future research.     

Ghana

A strategic task for building research in the Ghanaian context should be to give new life to well-tried methods and to develop the local resources of labour and materials, writes the director of the Building and Road Research Institute at Kumasi. The reasons are not only economic - saving scarce foreign exchange - but social, by creating viable local industries. This article concentrates on the housing-related studies and reports a few projects which have tried to apply the concepts in a practical way.     

Cognition must be computational.

Reviews the book, Computation and Cognition: Toward A Foundation for Cognitive Science by Z. W. Pylyshyn (see record 1986-97211-000). The history of science provides many demonstrations of our intellectual debt to our tools: from Descartes forward, psychological theory has depended on metaphors based on the technology of the day. Computers are the currently exciting technology, and, from that fact alone, one might expect a book with the title Computation and Cognition to invite us to reshape psychological theory in image of the digital computer. That message is not what Pylyshyn has to sell. Instead, he examines computation at a theoretical level and shows that it involves three distinct levels of analysis: a physical, a symbolic, and a semantic level. He argues that to understand mental processes, one needs exactly the same three-level analysis, that is, cognition is computational. In spite of the book's faults, my opinion remains firmly positive: Computation and Cognition is an instant classic. It is a book which deserves to have a major influence on the shape of future work. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dynamics of nanosecond laser annealing of silicon

On the basis of a numerical solution of the Stefan problem, the dynamics of nanosecond laser annealing of silicon is investigated.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 48, No. 2, pp. 306–312, February, 1985.     

Analysis and Design of Robust Controllers Using the Interval Diophantine Equation

In this paper the design of pole placement feedback controllers for interval plants is addressed within an Interval Analysis framework. Three main topics connected by the concept of interval Diophantine equation are treated: a relatively straightforward investigation about robust coprimeness of interval polynomials, a reliable computing approach for the design of pole placement controllers in the presence of inaccuracies of interval type, and the design of robust controllers with regional pole placement specifications. After explicitly characterizing a convex subset of robust controllers, the problem of designing non-fragile controllers is formulated as a design centering problem, which is then solved by a global optimization algorithm. Numerical examples illustrate the main characteristics of the approach proposed.This paper has been partially supported by grants from Conselho Nacional de Desenvolvimento Científico e Tecnológico–Brazil.