Fundamental solutions for plane problem of piezoelectric materials

Based on the basic equations of two-dimensional, transversely isotropic, piezoelectric elasticity, a group of general solutions for body force problem is obtained. And by utilizing this group of general solutions and employing the body potential theory and the integral method, the closed-form solutions of displacements and electric potential for an infinite piezoelectric plane loaded by point forces and point charge are acquired. Therefore, the fundamental solutions, which are very important and useful in the boundary element method (BEM), are presented.     

伪币鉴定问题的一个改进算法

本文研究如下的伪币鉴定问题：设有ｎ枚硬币，其中隐藏着若干枚伪币．真币具有相同重量，伪币也具有相同重量，但真币与伪币重量不同．问题要求利用一台没有法码的天平，在最少或尽可能少次数的测试后将真伪币一一区分出来．Ｘ．Ｄ．Ｈｕ和Ｆ．Ｋ．Ｈｗａｎｇ［１］［２］等人研究了这一问题，提出了一些两分算法．本文基于一种新的逐次成倍扩展搜索技巧，构造了一个改进算法．根据测试次数分析，即使在最不顺利的情况下，我们的算法也能使用更少的测试次数，从而大大节省了测试的时间与经费．     

用边界元法计算轴对称弹性体内部点位移、应力和边界应力

采用边界元法推导出了具有轴对称问题的弹性体内部点位移、应力和边界应力的计算公式，并且给出了算例。     

集合覆盖问题的启发函数算法

本文给出了求解NP困难问题的完备策略的概念,在此基础上提出了一个求解集合覆盖问题的启发函数算法SCHF(set-covering heuristic function),文中对该算法的合理性、时间复杂性以及解的精度进行了分析,本文的主要创新点是用已知的完备策略建立启发函数,并用该启发函数进行空间搜索求出优化解.该方法具有一定的普遍性,可以应用到其它的NP困难问题.它为求解NP困难问题的近似解提供了一种行之有效的方法.在规则学习中的应用结果表明,本文给出的SCHF算法是非常有效的.     

The Complete Solution of the Competitive Rank Selection Problem

Two decision-makers A and B observe sequentially a given permutation of n uniquely rankable options. A and B have one choice each (without recall) and both must make a choice. At each step only the relative ranks are known, and A has the priority of choice. At the end the (absolute) ranks are compared and the winner is the one who has chosen the better rank. Extending results by Enns and Ferenstein [6] and Berry et al. [1] this article gives, for both A and B , the optimal strategy and the corresponding winning probabilities. We show in particular that the limiting winning probabilities for A and B do exist, which closes a most important gap in the work of previous authors. This also provides an algorithm for numerically computing the limiting value of these probabilities. Although our proof is analytic in a strong sense, it is interesting to see that it would have been very hard to assemble it without the help of computer algebra. The reason is that the functions we have to investigate display subranges of indices which contrast considerably with respect to error terms when certain terms are replaced by approximations, and that computations were very helpful to locate those ranges where a particularly fine tuning of error estimates turned out to be indispensable. Received October 1997; revised March 15, 1998.     

A Tractable Class of Maximal Hedging Policies in Multi-Part Manufacturing Systems

The flow control problem in multi-part failure prone manufacturing systems is considered. While computationnaly attractive, the near optimal controllers of Caramanis and Sharifnia, suffer from the drawback that the production capacity set must be approximated via a very restricted set of inscribed hypercubes, namely those for which a componentwise feasibility requirement is satisfied. Also, due to the completely decoupled nature of production along each component, utilization of the restricted capacity set is suboptimal. A class of capacity set incribed hypercube policies called simple maximal hedging (SMH) policies is introduced. In SMH policies production levels along the various components of the capacity set are coupled, the componentwise feasibility requirement is lifted, and there is no underutilization of production capacity if needed. In a p part types manufacturing system, for partwise additive cost functionals, it is shown that performance evaluation of a given SMH policy reduces to the analysis of p decoupled (fictitious) semi-Markovian machines. The machines are Markovianized via first passage-time analysis and a Padé approximants technique. Numerical optimization over the class of SMH policies in a sample manufacturing system indicates that their performance can come close to that of the optimal control.     

一种基于复合问题的双重认证存取控制方案

本文基于复合问题针对信息保密系统提出了一种双重认证的存取控制方案。该方案与已有类似方案相比要更安全。要攻破该方案，攻击者得同时具有攻破ＲＳＡ方案和ＥＬＧａｍａｌ方案的能力。在该方案中，用户认证信息不仅用来计算对所需访问文件的存取权，也用于认证需访问保密文件的请求用户的合法性。此外，该方案还能够在动态环境中执行像改变存取权和插入／删除用户或文件这样的存取控制操作，而不影响任何用户的认证信息。     

适应超级节点SPP体系结构的并行程序设计语言研究

在国际超级计算机领域，并行机的体系结构和相应的并行程序设计语言一直是前沿课题和难点，而且体系结构的变化必将带来程序设计语言的改进和发展。本文基于一个带有超级节点的ＳＰＰ体系结构，对该结构下的控制（任务）并行、数据分布和同步问题分别从语言一级进行了探讨。     

控制能量有界的时不变系统线性二次型最优控制*

本文通过新的途径讨论控制能量有界的时不变系统一二次型最优控制问题，文中通过“不亏损的Ｓ－过程”方法将该问题转化成无约束的时不变性二次理优控制问题，从而利用后者的基本结果给出本文问题的最优控制的最优结构造，结果表明此时最优控制仍由一线性状态反馈控制器确定，但其增益矩阵的选择是与初始状态有关的，并且对某些安始状态还可能出现奇异情况。     

On a batch arrival Poisson queue with a random setup time and vacation period

The single server queue with vacation has been extended to include several types of extensions and generalisations, to which attention has been paid by several researchers (e.g. see Doshi, B. T., Single server queues with vacations — a servey. Queueing Systems, 1986, 1, 29–66; Takagi, H., Queueing Analysis: A Foundation of Performance evaluation, Vol. 1, Vacation and Priority systems, Part. 1. North Holland, Amsterdam, 1991; Medhi, J., Extensions and generalizations of the classical single server queueing system with Poisson input. J. Ass. Sci. Soc., 1994, 36, 35–41, etc.). The interest in such types of queues have been further enhanced in resent years because of their theoretical structures as well as their application in many real life situations such as computer, telecommunication, airline scheduling as well as production/inventory systems. This paper concerns the model building of such a production/inventory system, where machine undergoes extra operation (such as machine repair, preventive maintenance, gearing up machinery, etc.) before the processing of raw material is to be started. To be realistic, we also assume that raw materials arrive in batch. This production system can be formulated as an M^x/M/1 queues with a setup time. Further, from the utility point of view of idle time this model can also be formulated as a case of multiple vacation model, where vacation begins at the end of each busy period. Besides, the production/inventory systems, such a model is generally fitted to airline scheduling problems also. In this paper an attempt has been made to study the steady state behavior of such an M^x/M/1 queueing system with a view to provide some system performance measures, which lead to remarkable simplification when solving other similar types of queueing models.This paper deals with the steady state behaviour of a single server batch arrival Poisson queue with a random setup time and a vacation period. The service of the first customer in each busy period is preceded by a random setup period, on completion of which service starts. As soon as the system becomes empty the server goes on vacation for a random length of time. On return from vacation, if he finds customer(s) waiting, the server starts servicing the first customer in the queue. Otherwise it takes another vacation and so on. We study the steady state behaviour of the queue size distribution at random (stationary) point of time as well as at departure point of time and try to show that departure point queue size distribution can be decomposed into three independent random variables, one of which is the queue size of the standard M^x/M/1 queue. The interpretation of the other two random variables will also be provided. Further, we derive analytically explicit expressions for the system state (number of customers in the system) probabilities and provide their appropriate interpretations. Also, we derive some system performance measures. Finally, we develop a procedure to find mean waiting time of an arbitrary customer.