A characterization of s-languages

We show that a language L is an s-language if and only if the set of the quotients of L (i.e., the set of the states of its minimal deterministic automaton seen as languages) is a subset of a free monoid generated by a finite set of prefix codes. We demonstrate through examples how to use this result for deciding whether a given language is an s-language.     

微观移动协议仿真和评估

1.介绍 Internet的无线访问(即IP指出主机的移动)是目前计算机网络研究的一个热点,目前所提出的Mobile IP是为支持主机移动而提出的。它提出了一种简单的,可扩充性很强并且与现有的网络有很强兼容性的框架,但是它的提出是单纯从计算机网络的角度去看主机的移动,并没有考虑到下层电信网络和移动主机的特点等方面的因素,因此Mobile IP存     

细胞自动机函数优化算法

细胞自动机广泛用于仿真、建模，提出用细胞自动机进行函数优化。该思想与演化算子结合的算法CAMGA在试验中取得了很好的效果。其中对BUMP问题的求解优于现今已经发表的结果。     

元胞自动机模型在五道口交通流中的应用

应用元胞自动机模型对较为复杂的五道口交通流进行研究，通过分析道路因素、车辆因素和车辆运行规则建立五道口交通模型。四道口通常分东-西、南-北两个相位即可，五道口需增加一个相位，构成三相位控制。每一相分为6个车道，对车道进行编号以确定车辆具体位置；所有车辆均按一定系数转化成小型车以简化仿真模型，各相位上的车分为绿灯和红灯两种时步分析。仿真设计平台采用VC++，使用3个定时器产生五道口交通模型的动态画面。所建模型可对流量和配时参数进行动态设置，模拟复杂的实际交通流，具有良好的可重复性。     

基于元胞自动机法的晶粒长大模拟

采用元胞自动机（Cellular Automata，简称CA）法对晶粒长大过程进行了计算机模拟和分析．模拟结果表明，CA法能够较好地模拟晶粒长大过程，所反映的晶界迁移规律及其拓扑特征符合晶粒长大的物理机制，是一种简便、有效的模拟方法．     

Structure and Mechanical Properties of AFS Sandwiches Studied by in‐situ Compression Tests in X‐ray Microtomography

Al foam core / Al alloy skins sandwiches have potential for application in light weight structures. Recently, the foaming processes have improved and large, thick and 3D‐shape panels can be produced using the precursor technology. The microstructure of an AFS sandwich is analysed in this paper at a microscale and a mesoscale using X‐ray tomography and conventional SEM analysis. The main deformation mechanism of the core under compression is also studied thanks to in situ test. It is shown that the foam first present plastic buckling and then walls rupture. This is well correlated to the microstructure of the constitutive material of the core.     

人工生命及其基本原理

该文总结了人工生命的产生和发展状况，介绍了人工生命的研究对象和实现技术，讨论了人工生命和人工智能的关系。通过若干典型人工生命研究实例，分析了人工生命技术的基本原理，并用计算机程序模拟自然生态系统对人工生命的理论方法和实现技术进行了探讨。程序模拟方法在基因的遗传与优选方面有着相当的实际意义，用类似方法对各种自然生物的生命状态、生活习性进行模拟，可在较短的时间内模拟自然生命需要几千乃至上万年的进化历程。     

A speed-adaptive strategy for location management cost reduction in cellular networks

A speed adaptive location management scheme will greatly reduce the cost of tracking mobile stations, because mobile stations can travel at a wide range of speeds. Recently, an elegant distance- and time-based scheme has been proposed. The scheme uses a look-up table which describes the relationship between the distance and the time: the distance decreases while the time increases. In the scheme, the paging area for a mobile station will be automatically reduced if the mobile station does not update its location over a certain time period. Therefore, the scheme performs well when a mobile station travels at a low speed. However, it does not perform well when the incoming call arrival rate is high or when the speed of a mobile station is high. To overcome those drawbacks, a novel speed-adaptive scheme is proposed in this paper. The proposed scheme uses an enhanced look-up table that consists of two parts: the distance in the first part increases while the time increases; in the second part, the distance decreases with the increasing time. By introducing the first part, the proposed scheme reduces the paging cost for a call arriving shortly after a location update, and adapts to the speed range of a mobile station. To reduce the paging cost further, a paging angle is introduced for high-speed mobile stations. Numerical simulations using various activity-based models and random walk models show that the proposed scheme performs well for mobile stations traveling at both high and low speeds. Zhijun Wang is a Ph.D. candidate in the Department of Computer Science at the University of Alabama. He received his M.S. in computer science from the University of Alabama in 2002. He also had a formal training in physics and obtained his B.S. in physics from Tianjin University in 1993 and his M.S. in physics from Yale University in 1998. His current research interests include location management in cellular networks and routing in ad hoc networks. Jingyuan Zhang received the bachelor’s degree from Shandong University in 1984, the master’s degree from Zhejiang University in 1987, and the doctoral degree from Old Dominion University in 1992, all in computer science. He is currently an assistant professor with the Department of Computer Science at the University of Alabama. Prior to joining the University of Alabama, he was an instructor with Ningbo University, an assistant professor with Elizabeth City State University, and a principal computer scientist with ECI Systems and Engineering. Dr. Zhang’s current research interests include wireless networks and mobile computing, single display groupware, graphics, and parallel processing. He is a member of the IEEE.     

物理细胞自动机在模拟混凝土破坏过程的应用

根据混凝土的结构与破坏特征,建立了一种细胞自动机———二维物理细胞自动机(PCA)的基本模型.该模型考虑了混凝土材料的非均质性、非连续性和各向异性等特征,可以更有效地模拟混凝土的破坏过程.该模型对进一步研究混凝土的非线性特征具有重要的应用价值.     

Kelvin结构多孔材料弹性模量分析

Kelvin模型是由六个正四边形和八个正六边形组成的十四面体结构，可与在金属中观察到的晶粒和在一些生物组织中观察到的细胞形状相媲美。本文根据线弹性均匀化理论，结合有限元方法给出了三维周期性Kelvin结构的均匀化有限元列式。并利用ANSYS平台和二次开发工具，建立了Kelvin结构实体表示和有限元计算模型，预测出不同相对密度下规则闭孔Kelvin结构的等效弹性系数E1111^H,E1122^H，E1212^H和等效泊松比μ12^H。计算结果表明，Kelvin结构的刚度一质量比随着相对密度增大而增大，剪切刚度一质量比在相对密度3％左右出现极小值点。