Boundary knot method for 2D and 3D Helmholtz and convection–diffusion problems under complicated geometry

The boundary knot method (BKM) of very recent origin is an inherently meshless, integration‐free, boundary‐type, radial basis function collocation technique for the numerical discretization of general partial differential equation systems. Unlike the method of fundamental solutions, the use of non‐singular general solution in the BKM avoids the unnecessary requirement of constructing a controversial artificial boundary outside the physical domain. The purpose of this paper is to extend the BKM to solve 2D Helmholtz and convection–diffusion problems under rather complicated irregular geometry. The method is also first applied to 3D problems. Numerical experiments validate that the BKM can produce highly accurate solutions using a relatively small number of knots. For inhomogeneous cases, some inner knots are found necessary to guarantee accuracy and stability. The stability and convergence of the BKM are numerically illustrated and the completeness issue is also discussed. Copyright © 2003 John Wiley & Sons, Ltd.     

Analysis and Optimization of Noise in Bipolar RF Harmonic Mixers

A noise analysis of bipolar harmonic mixers (BHM) used for direct-conversion receivers is presented in this paper. Analytical and simulated results for the transfer function of the mixer are presented. Simple analytical expressions describing noise contribution from all sources are derived. Estimation of flicker noise quite agrees with harmonic-balance simulation results. Based on the derived expressions, total time average noise power spectral density (PSD) at the output is compared with simulation results. For the recommended regions of operation, error is less than 20%. The overall BHM noise figure (NF) is calculated and optimized based on a simple extracted formula. Errors introduced by analysis remain within a 1.5-dB margin with respect to simulation results. The validity of analysis for high frequencies is justified. The effect of flicker noise coefficient on the overall mixer NF is compared for different available processes.     

无磷洗涤剂的现状及存在问题

含磷洗涤剂中含的“磷”主要是STPP，作用很大但对环境的危害也很大，它是造成地表水体出现富营养化的重要原因之一，所以许多地方政府都在实行“禁磷”——禁止销售、使用含磷洗涤剂。现在我国使用的无磷洗涤剂中代磷助剂主要有3种，其中4A沸石用量最大，但它会对环境带来新的问题。主要介绍了含磷洗涤剂的危害及无磷洗涤剂的应用现状，指出了我国禁磷后将面临的问题。     

光电双基区晶体管(PDUBAT)的器件模型

本文在考虑了晶体管的小注入效应和大注入效应以及基区宽变效应等因素后,首次用近似和简化的数学表示式和相应的等效电路,描述了光电双基区晶体管(PDUBAT)负阻形成的机理并使负阻区和谷值区的理论计算和实验结果一致性很好.     

基于面像识别技术的公安网上追逃系统

研究了公安网上追逃系统的体系结构和系统的程序流程，阐述了ASP COM 后台比对服务的3层B／S模式面像网上比对的实现方法，最后给出系统的性能指标和特点。     

生产装置在线模拟与优化技术的应用

概述了以通用软件为基础开发化工生产装置严格在线模拟与优化系统的过程，介绍了在线模型的５个层次及其特点，以合成氨为例说明了在线模型的运行和应用情况。     

酸性盐水及其配套装置的应用与运行

介绍了对进槽盐水由酸碱性改为微酸性的技术改造，减少了副反应的发生，从而提高了电解槽的电流效率。     

The State of the Art in Text Filtering

This paper develops a conceptual framework for text filtering practice and research, and reviews present practice in the field. Text filtering is an information seeking process in which documents are selected from a dynamic text stream to satisfy a relatively stable and specific information need. A model of the information seeking process is introduced and specialized to define text filtering. The historical development of text filtering is then reviewed and case studies of recent work are used to highlight important design characteristics of modern text filtering systems. User modeling techniques drawn from information retrieval, recommender systems, machine learning and other fields are described. The paper concludes with observations on the present state of the art and implications for future research on text filtering. This revised version was published online in July 2006 with corrections to the Cover Date.     

On the Realization of Current－Mode Continuous－Time Operational Transconductance Capacitance Filter

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开关电流技术：一种新的模拟抽样数据处理方法

开关电流（ＳＩ）技术是一种新的模拟抽样数据处理技术，介绍了开关电流电路的基本单元结构，讨论了目前开关电流技术中存在的问题及其解决方法。对开关电流技术与开关电容技术的一些基本特征进行了比较，ＳＩ技术不仅结构简单，而且与标准ＣＭＯＳ工艺兼容，可望替代开关电容电路。