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Field-oriented control of permanent magnet synchronous motor fed by matrix converter is designed. By introducing space vector modulation for inverter, AC-AC matrix converter is equivalent to AC-DC-AC substitution. Then, perfect PWM technology is adopted for virtual rectifier and virtual inverter of substitution whose modulating schedule and model are analyzed and deduced. of field-oriented control for matrix converter fed permanent magnet synchronous motor is built up. Finally, simulations are carried out, and simulating results show that the proposed system is feasible and valid, which provides theoretical foundations for experimentation.

AbstractThe design of distributed systems can be based on exercising either centralized or decentralized control mechanisms as per the application requirements. In this paper, for a centralized controlled distributed system, we design a dynamic object allocation and replication algorithm that adapts to the arriving requests patterns. We propose a mathematical cost model that considers the costs involved in servicing a request, such as I/O cost and communication cost, and design a dynamic algorithm, referred to as dynamic window mechanism (DWM). Our objective is to minimize the total servicing cost of all the arriving requests. We use competitive analysis to quantify the performance of DWM algorithm in the stationary computing environment (SCE) and extend our analytical study to the mobile computing environment (MCE).

Casein kinase II is a heterotetrameric protein kinase with an α₂β₂ composition; the subunits can be separated only under harsh denaturing conditions. In this study, the optimal conditions for renaturation of denatured casein kinase II have been established. Purified casein kinase II from rabbit reticulocytes was denatured with 8 M urea and 0.1 M dithiothreitol at 25°C. Various parameters, including arginine, oxidized glutathione/dithiothreitol, substrate, and temperature were optimized for renaturation. Under optimal conditions, the denatured protein kinase was successfully renatured with a recovery of 75% activity and eluted around 160,000 Da upon gel filtration, indicating the tetrameric structure. When the α (catalytic) and β (regulatory) subunits of casein kinase II from Drosophila were cloned and overexpressed with the pET3a vector in Eseherichia coli, the majority of the subunits were in an insoluble form. The optimal conditions for denaturation/renaturation of the recombinant casein kinase II from Drosophila were identical to those developed for the holoenzyme, except for the redox state and temperature. When the a subunit was solubilized and renatured in an approximate 1:1 ratio with the β subunit, the catalytic activity was stimulated fourfold over that of the α subunit alone. The reconstituted enzyme was purified to apparent homogeneity in one step by chromatography on heparin-TSK. Gel filtration indicated the formation of an α₂β₂ tetramer. The reconstituted recombinant casein kinase II exhibited characteristics of the native holoenzyme in subunit composition, inhibition by heparin, stimulation by basic compounds, and the KC1 concentration required for optimal activity. The conditions described herein for the reconstitution of casein kinase II will enable investigation of the enzymatic properties of casein kinase II through recombinant DNA techniques.Copyright 1993, 1999 Academic Press

An improved slot etch technique based on an Si planar doped layer has been applied to gate recessing in the fabrication of AlGaAs/InGaAs/GaAs pseudomorphic high electron mobility transistors (HEMTs). The devices exhibited comparable gm with much better breakdown and leakage behaviour than conventional pseudomorphic HEMT devices.

Au/AuBe and Au/AuBe/Cr contacts have been deposited onto the surface of p-ZnTe. It was found that with a proper choice of Cr thickness, a low specific contact resistance of 2.0 × 10-6 Ωcm2 can be achieved for Au/AuBe/Cr on p-ZnTe. It was also found that Zn outdiffusion will significantly degrade the electrical properties of the Au/AuBe contact on p-ZnTe when annealing temperature is above 300°C. Conversely, Au/AuBe/Cr contact is more thermally reliable. Such a property makes Au/AuBe/Cr attractive in device application.

Ohmic contacts of AuBe to p-ZnTe show a minimum specific contact resistance of 3.0 × 10–6 Ω cm2 for a p-doping level of 1.6 × 1019 cm–3 and at an annealing temperature of 200°C. The beryllium is very effective at improving the electrical properties of p-type contacts to ZnTe.

A porous-SiC thin-film photodetector with a pn junction structure has been successfully fabricated on an Si substrate. The developed device exhibits a high responsivity of 0.4 A/W at 25°C for 650 nm irradiation. In particular, the device has a responsivity of 0.35 A/W and a photo/dark current ratio larger than 100 at 200°C, indicating its potential capability for high-temperature operation.

The letter describes the use of LPE in the preparation of CuInS2 epitaxial layers. Both the tipping and sliding boat methods were adopted for the LPE growth, the latter being found more suitable.