Effects of Solid-State Reaction Synthesis Processing Parameters on Thermoelectric Properties of MgaSi

The Mg2 Si-matrix thermoelectric material was stnthesized by low temperature solid-state renc-tion.This paper studies the effects of holding time and reaction temperatare on the particle size and the properties of the material, and also studies effects of doping elemental Sb, Te and their doping seqence on the properties of the materiol. The result shows that excessirely high temperature and elongated holding time of solid-state reaction are harmful, there is a range of partiele size to ensure optimum properties and the doping sequence of Sb or Te without influencing the properties.     

现场砼检测中"行标"和"地标"的差异

现场砼回弹法测强中,国家行业标准和江苏省地方标准存有不同,故而分析了地标在应用中的不足之处,并建议"地标"在修订时,对均方差规定一个限值,以便公正、合理地推定砼强度。     

试论WTO与我国高等教育的发展观

加入WTO后,中国高等教育面临更加复杂的环境,机遇多于挑战。面对中外不同办学思想和模式的冲突及教育服务贸易竞争日益激烈的形势,必须树立科学的发展观,不断调整应对策略,使WTO中的中国高等教育与时俱进,为科教兴国战略的实施作出应有的贡献。     

周铣加工表面形貌仿真新算法

考虑主轴偏心，基于周铣过程中刀具切削刃上任意点与工件相对运动的轨迹方程和周铣过程几何特征，构造出可以求解周铣加工表面上任意一点形貌高度值的三维表面形貌仿真算法，并给出了相应的仿真算例。该算法无需对刀齿进行微段离散，并且不依赖于工件网格划分，加工表面上任意一点形貌高度值的计算次数等于刀具齿数，具有通用性好、运算速度快、结果准确度高的特点。     

Percolation threshold and morphology of composites of conducting carbon black/polypropylene/EVA

Conducting carbon black (CB), one of the intrinsic semi-conductors, was added into matrix polypropylene (PP) to prepare conducting composites by means of the melt processing method. Another component EVA was mixed into the composites in order to lower the percolation threshold. The percolation threshold of the ternary CB/PP/EVA composites was merely 3.8 vol%, while it was up to 7.8 vol% for the binary CB/PP composites without EVA. The conductivity of the ternary CB/PP/EVA composites was up to 10^–2 S/cm when the CB percentage was 5 vol%, while that of the binary CB/PP was lower than 10^–2 S/cm when the CB percentage was up to 10 vol%. DSC thermograms of the CB/PP/EVA composites showed that the melting peak shifted to low temperature with increasing CB content. The addition of CB and EVA resulted in the decrease of the crystallinity of PP in the ternary composites. The mechanical properties are also discussed. SEM and TEM were employed to study the morphology of the blend system. The results indicated that CB existed in the form of aggregations in the blend system. The smallest unit that formed a percolation network was grape-like aggregates with some small branches, which consisted of some CB particles, rather than the individual particles. This distribution was very valuable for forming conducting paths and for lowering the percolation value.     

Producing a compact long-lived plasma formation

A method of producing compact long-lived plasma formations (plasmoids) is described. The method is based on the effect of capture of a high-current relativistic electron beam under conditions of significant overcompensation of space charge of the beam by positive background ions. Requirements are formulated which are placed on the parameters of a plasma-beam system for the realization of this method, and numerical estimates are given of the overall electric charge and energy content of the electron component of a plasmoid. The dynamics of forming a plasmoid are investigated experimentally.Translated from Teplofizika Vysokikh Temperatur, Vol. 42, No. 6, 2004, pp. 843–849.Original Russian Text Copyright © 2004 by B. V. Alekhin, A. E. Dubinov, V. S. Zhdanov, V. G Kornilov, K. E. Mikheev, V. D. Selemir, N. V. Stepanov, V. I. Chelpanov, and O. A. Shamro.     

Optimal design of unit hydrographs using probability distribution and genetic algorithms

A nonlinear optimization model is developed to transmute a unit hydrograph into a probability distribution function (PDF). The objective function is to minimize the sum of the square of the deviation between predicted and actual direct runoff hydrograph of a watershed. The predicted runoff hydrograph is estimated by using a PDF. In a unit hydrograph, the depth of rainfall excess must be unity and the ordinates must be positive. Incorporation of a PDF ensures that the depth of rainfall excess for the unit hydrograph is unity, and the ordinates are also positive. Unit hydrograph ordinates are in terms of intensity of rainfall excess on a discharge per unit catchment area basis, the unit area thus representing the unit rainfall excess. The proposed method does not have any constraint. The nonlinear optimization formulation is solved using binary-coded genetic algorithms. The number of variables to be estimated by optimization is the same as the number of probability distribution parameters; gamma and log-normal probability distributions are used. The existing nonlinear programming model for obtaining optimal unit hydrograph has also been solved using genetic algorithms, where the constrained nonlinear optimization problem is converted to an unconstrained problem using penalty parameter approach. The results obtained are compared with those obtained by the earlier LP model and are fairly similar.     

基于UA302H数采器的虚拟测试系统设计

本文针对计算机辅助测试问题,阐述了集成测试和虚拟仪器的巨大优势,重点介绍了一套以UA302H数据采集器为A/D转换装置的虚拟测试系统的设计与应用情况,为普通用户自行开发虚拟测试系统提供了思路.