A novel method of structural shape optimization coupling BEM with an optimization method based on biological growth

Local stress peaks are the main reason for fatigue failure of structures, and therefore many researchers make every effort to search for effective methods of structural shape optimization. Mattheck and Burkhard (1990) have developed a method by simulating the self-optimization mechanism of biological growth, using FEM. BEM is a very effective method in which only the boundary is divided into elements, and particularly, accurate results at the boundary can be obtained. It is obvious that BEM is a more suitable analysis method for structural shape optimization than FEM. Coupling BEM of three-dimensional thermoelasticity problems with an optimization method based on biological growth, a novel method of structural shape optimization is successfully developed by the authors. Several examples are used to demonstrate that the method is successful and efficient.     

宽带网满负荷试验对于UniLINK协议的验证

ＵｎｉＬＩＮＫ是一种基于现存有线电视网的介质访问控制层（ＭＡＣ）协议。该协议的设计适用于树型拓扑结构的宽带网络，且支持的距离从主控端到客户端可达１６０公里。ＵｎｉＬＩＮＫ协议基于一种改进的时分多路控制（ＴＤＭ）协议，支持固定、和保留三三种带宽分配策略，且会依据不同的网络负担动态地在三种策略中进行选择。目前，基于该协议的ＬＡＮＣｉｔｙ系列产品在上海有线电视台和上海交大的互联试验中被使用。基于该测试的     

单片机控制的PWM调速装置的研究

与交流电动机相比,直流电动机结构复杂,成本高,运行维护困难。但是直流电动机具有良好的调速性能、较大的起动转矩和过载能力强等许多优点,因此在许多行业中仍得到了广泛的应用。文章介绍了一种利用单片机控制的PWM调速装置实现小功率直流电动机调速的方法,具体详述了电路的设计思想、电路的组成以及工作原理。     

汽包水位保护逻辑改造在三河发电厂的应用

原汽包水位保护系统为三取中逻辑,不能准确判断汽包水位变送器的质量。根据国家电力公司颁布的《防止电力生产重大事故二十五项重点要求》,将汽包水位保护系统进行了改造,引入分散控制系统(DCS),实现了三取二逻辑控制,并能够实现当1个变送器退出时自动转为二取一,当2个变送器退出时自动转为一取一的逻辑转换,提高了判断汽包水位变送器运行情况的质量,有效地防止了水位保护的拒动和误动。     

欺骗网络体系框架研究

本文提出了一种基于信息欺骗的信息防护框架。从欺骗网络的交互程度,拓扑和技术三个方面对该框架进行了论述。     

我国钢铁产业组织结构浅析

从产业组织的角度看，我国钢铁产业在蓬勃快速发展的背后，其产业组织结构存在着严重的不合理状况，主要表现在产业集中度低，规模经济性差，进入壁垒低等方面，使得产业的市场绩效低下，其反作用又促使产业结构矛盾加剧。这种相互作用的结果，已成为影响我国钢铁产业持续健康发展的主要原因。因此，必须从市场和产业组织政策两方面着手加以解决。     

烧结机点火炉设计浅谈

点火炉是烧结机的重要组成部分，虽然其结构“简单”，但点火炉运行的好坏真接影响烧结机的正常工况，作为设计者应掌握点火炉的结构。笔者较详细的介绍了点火炉的结构、设计要点及发展趋势，尤其在点火炉单位燃料消耗量的确定上引入了全新的计算概念，具有较强的指导性。     

无线环境下一种新的证书状态查询方案

分析有线环境现有证书状态查询方案的基础上,提出了一种对传统的 O C S P进行了改进的方案-用户端部分缓存的ocsp方案,并将其与其他证书状态查询方案进行了比较。该方案借鉴了哈希链的思想,具有很高的安全性,可以有效减少用户端及服务器端的运算量,降低带宽负荷,适合用作无线环境下的证书状态查询方案。     

用FPGA实现线阵红外探测器的奇偶校正

法国Sofradir公司生产的288×4红外焦平面阵列(IRFPA)具有很高的探测灵敏度,是军用红外系统的理想器件。由于器件本身的结构特点,在使用时需要进行奇偶校正。该电路的控制逻辑比较复杂,实现的方法有三种:用传统的中小规模集成电路实现,这种实现方法难度比较大;用CPLD或FPGA做逻辑,其它部分用中小规模集成电路,这种实现方法布线比较困难;所有电路全部用FPGA实现,这种实现方法布线简单,电路集成度高,体积小,功耗低,可靠性好,是最佳实现方案。文中就是用这种方案实现了该探测器的奇偶校正电路。     

Maintaining mobile transactional consistency in hybrid broadcast environments

Recently there have been attempts in several research areas at efficiently utilizing the resources of mobile computers. Considering the properties in mobile computing environments, push-based data dissemination systems have lately attracted considerable attention. However, skewed access patterns among mobile clients makes response time worse, and they prefer to send data requests to the server explicitly through an uplink channel. A broadcast supporting an uplink channel is called a hybrid broadcast. In this paper, we devise new transaction processing algorithms for hybrid broadcasts. It is assumed that data objects that the server maintains are divided into Push_Data for periodic broadcasting and Pull_Data for on-demand service. That is, clients have to explicitly request data objects in Pull_Data. Maintaining transactional consistency in this environment without much additional cost is our main concern. Finally, we evaluate performance behavior through simulation study.Received: 15 November 2002, Published online: 5 August 2004This work was done as part of the Information & Communication Fundamental Technology Research Program, supported by the Ministry of Information & Communication in the Republic of Korea.