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The capacity of direct-sequence code-division multiple-access (DS/CDMA) systems is co-channel severely limited by multiple access interference (MAI) produced by the other users. To improve the capacity, joint-detection receivers and MAI cancellation techniques have been proposed. This paper presents an adaptive neural network-based receiver that has the capacity of combating the 'near-far' problem and rejecting the multi-user interference in a multipath channel. A comparative performance analysis of the conventional receiver and the adaptive neural network receiver is camel out using a Monte Carlo simulation. It is found that the new receiver performs extremely well in multipath and multiple access channels with a significant 'near-far' effect.
산업기술정보원이 자체 개발한 사내 정보관리시스템인 TIMS의 구성과 주요특징, 제공기능 등에 대하여 설명하고, TIMS를 활용한 기업의 정보관리모델을 제시함으로써 기업의 정보관리 활동에 도움을 주고자 하였다. It is purposed to give an explanation of the constitution, major distinction and providing function of TIMS(Technology Information Management System) developed by KINITI(Korea INstitute of Industry and Technology Information). And, it is intended to help companies to manage information effectively by providing the model of information management of company.
The effect of Mn alloying on the growth rate and oxidation resistance of MoSi2 coatings formed by pack siliconizing process, (Mo-Mn)Si₂ coatings formed by single-step pack process (codeposition of Si and Mn), and two-step pack process (manganizing+siliconizing), respectively, was investigated at 1373K and 1573K. The growth rate of MoSi₂ coatings was fast in order of two-step pack process, single-step pack process and pack siliconizing process at 1373K because the increase of Mn concentration on MoSi₂ coating surface resulted in the increase of mass balance condition of silicon for MoSi₂ growth. The static and cyclic oxidation resistance decreased in order of two-step pack process, single-step pack process, and pack siliconizing process in air at 1573K because higher levels of Mn tended to retard the growth rate of Mo_5Si₃ diffusion layer and rapid oxidation at the edge of MoSi₂ coatings was prevented by the formation of thick Mn-Si-O complex oxides and decrease of the formation frequency of microcracks within MoSi₂ coatings.
The effect of inert fillers and Si contents on pack siliconizing kinetics of pure molybdenum was investigated in the range of 1273K-1473K. Si contents were varied from 1wt%Si to 40wt.%Si. Al₂O₃, and SiC powders were used as inert fillers. Similar coating microstructures were obtained and the growth rate of MoSi₂ coatings was observed to be proportional to the square root of time regardless of whether inert filler was Al₂O₃, or SiC. The dependence of parabolic growth rate constant of MoSi₂ coatings on the square root of Si contents was changed at the standard of 10wt.%Si. Apparent activation energy for the growth of MoSi₂ coatings was obtained to be 193 KJ/mole. Under the quasi steady state assumption, if the transport rate of Si containing gases in the pack is varied with Si contents and inert fillers, the surface composition of coatings tends to shift to another value which will re-satisfy the requirement of zero Si transport rate difference between gas diffusion and solid diffusion on the coating surface Therefore, pack siliconizing kinetics of pure molybdenum was controlled by a self-adjusted mechanism which combined the Si transport capability of gas diffusion in the pack and solid diffusion in the Mo substrate.
Thermodynamic and kinetics of pack siliconizing on pure molybdenum were investigated in the range of 1273K-1473K. Siliconizing was carried out in a hydrogen atmosphere using 40wt.%Si-5wt.%NaF-55wt.%Al₂O₃ packs. The growth rate of MoSi₂ coating was observed to be proportional to the square root of time. Apparent activation energy for growth of the MoSi₂ coating was obtained between that for gas diffusion through Si depleted zone and that for solid diffusion of Si in MoSi₂. The rate limiting step for pack siliconizing process was subject to theoretical considerations. Three models such as a gas diffusion model from the pack to substrate surface, a solid diffusion model in MoSi₂, and an equilibrium model of gas diffusion and solid diffusion were evaluated, Theoretically predicted results based on the quasi steady state parabolic kinetic theory induced from an equilibrium model and experimentally obtained results for pack siliconizing on pure molybdenum were found to be good argeement. The Si halide vapors contributed to growth of the MoSi₂ wating were SiF₂, SiF₃, SiF₄, SiH₃F, SiH₂F₂, SiH₃F and the deposition of Si from Si halide vapors on the molybdenum substrate may occur by reactions involving hydrogen reduction, disproportionation, or a Na vapor species.