On parallel machine replacement problems with general replacement cost functions and stochastic deterioration

The parallel machine replacement problem consists of finding a minimum cost replacement policy for a finite population of economically interdependent machines. In this paper, we formulate a stochastic version of the problem and analyze the structure of optimal policies under general classes of replacement cost functions. We prove that for problems with arbitrary cost functions, there can be optimal policies where a machine is replaced only if all machines in worse states are replaced (Worse Cluster Replacement Rule). We then show that, for problems with replacement cost functions exhibiting nonincreasing marginal costs, there are optimal policies such that, in any stage, machines in the same state are either all kept or all replaced (No‐Splitting Rule). We also present an example that shows that economies of scale in replacement costs do not guarantee optimal policies that satisfy the No‐Splitting Rule. These results lead to the fundamental insight that replacement decisions are driven by marginal costs, and not by economies of scale as suggested in the literature. Finally, we describe how the optimal policy structure, i.e., the No‐Splitting and Worse Cluster Replacement Rules, can be used to reduce the computational effort required to obtain optimal replacement policies. © 2005 Wiley Periodicals, Inc. Naval Research Logistics, 2005     

A generalization of the weighted set covering problem

We study a generalization of the weighted set covering problem where every element needs to be covered multiple times. When no set contains more than two elements, we can solve the problem in polynomial time by solving a corresponding weighted perfect b‐matching problem. In general, we may use a polynomial‐time greedy heuristic similar to the one for the classical weighted set covering problem studied by D.S. Johnson [Approximation algorithms for combinatorial problems, J Comput Syst Sci 9 (1974), 256–278], L. Lovasz [On the ratio of optimal integral and fractional covers, Discrete Math 13 (1975), 383–390], and V. Chvatal [A greedy heuristic for the set‐covering problem, Math Oper Res 4(3) (1979), 233–235] to get an approximate solution for the problem. We find a worst‐case bound for the heuristic similar to that for the classical problem. In addition, we introduce a general type of probability distribution for the population of the problem instances and prove that the greedy heuristic is asymptotically optimal for instances drawn from such a distribution. We also conduct computational studies to compare solutions resulting from running the heuristic and from running the commercial integer programming solver CPLEX on problem instances drawn from a more specific type of distribution. The results clearly exemplify benefits of using the greedy heuristic when problem instances are large. © 2003 Wiley Periodicals, Inc. Naval Research Logistics, 2005     

多维TCM的编码符号同步方法

针对多维TCM译码中的编码符号同步问题,提出了两种同步方法:累计度量和同步法、回溯初始状态比较同步法。其中累计度量和同步法适用于非完全透明的编码,而回溯初始状态比较同步法对完全透明的编码和非完全透明的编码都适用。它们都直接利用Viterbi译码器的中间结果,计算量少,简单有效。     

Spark-05加速器真空界面设计

为了驱动中高阻抗的高功率微波源,建造了油介质Blumlein型加速器Spark-05,其真空绝缘子界面为设计的难点之一。为了减小体积和结构简单,确定了真空界面采用径向绝缘结构,利用静电场有限元程序计算了界面上的电场分布,通过调整均压环和屏蔽环的形状使电场分布更加均匀,真空界面上沿面场强和三结合点处场强均得到了有效的控制,在1MV实验中工作稳定。     

在Vs．net集成环境下创建带卸载的安装程序

创建安装程序是一件很简单的事,Vs.net提供了创建安装程序的向导,开发人员能够轻松地创建一个便于用户使用的安装程序。而按向导创建的安装程序没有为用户提供相应的卸载程序或快捷方式,为用户带来许多不便。以示例的形式详细介绍如何在Vs.net集成环境下创建带卸载的安装程序。     

非局部薄板动力学特性分析的广义有限积分变换方法

基于应力梯度非局部薄板理论模型,推导了非局部薄板动力学特性求解的广义有限积分变换方法.通过选取适应边界条件的积分核函数并构建广义积分变换对,应用积分变换将非局部薄板的高阶偏微分方程变换成线性方程组,直接求解得到固有频率.将广义有限积分变换方法的计算结果和有限元法及已有文献的结果进行对比,验证了本文方法的正确性.在此基础...     

语篇分析与大学英语词汇教学

“语篇分析”在大学英语教学中具有重要作用。通过语篇分析,可以使学生对篇章的内容有初步的了解,增加感性认识,从而使学生在大学英语词汇学习的过程中有所突破和提高。     

抢险救援社会化进程中加减乘除法则探析

以抢险救援过程中面临的各种问题为出发点,以部分国家的抢险救援体系为参照,就增强战斗力、减少盲目性、整合各方资源、完善法制保障等四方面提出了应对和改进措施。     

电晕放电辐射信号分析的小波基函数选取

研究电晕放电辐射信号既有利于消除其危害又有助于加强对其利用。针对小波变换提出在不同情况下对不同类型的电晕放电进行分析时,选取小波基函数的方法,理论上可以通过信号与小波波形的匹配或者通过计算信号与小波相关系数的方法来确定,而在不确定放电类型时可进行实际分析。     

基于中间层驱动程序构建广域网环境下分布仿真联邦

从数据包的截获、解析、封装及解封等方面讨论了分布仿真中间层驱动程序的实现。通过该中间层驱动程序对多播数据的封装处理,使多播数据在广域网上以单播数据进行传输,从而实现跨路由的目的,完成分布仿真联邦的构建。