基于QoS的网格服务选择优化机制

在网格服务发现和选择过程中，如何根据请求方（用户）对服务质量的需求，以及网格QoS的动态变化选择网格服务是一个重要问题。该文基于请求方（用户）对不同网格服务QoS赋予的权重不同以及容忍度不同，提出了网格服务选择算法，从而使得请求方（用户）获得的网格服务的性价比最高。     

DoS拒绝服务

目前的Ｉｎｔｅｒｎｅｔ网络对拒绝服务（Ｄｅｎｉａｌ ｏｆＳｅｒｖｉｃｅ, ＤＯＳ）攻击的抵抗力很有限,这种攻击将使合法的用户无法正常使用网络和服务,这种威胁甚至影响到了Ｉｎｔｅｒｎｅｔ的发展。拒绝服务有三种常见的攻击方式,它们是：服务过载、消息流和信号接地。此外还有两种方式但不常见,一种通常称它为“粘住”,另一种是ＳＹＮ－Ｆｌｏｏｄｉｎｇ（请求泛滥）。下面将详细地讲述这些攻击方法以及防范的措施。服务过载 ＞攻击＜ 当大量的服务请求发向一台计算机中的服务守护进程时,就会发生服务过载。这些请求可以通过许…     

点击IT术语

翻阅IT报刊杂志，经常碰到IRQ、DMA、I/O这些术语，它们究竟是什么含义呢？1.IRQ（Interrupt ReQuest）中断请求为了使计算机对随机事件能及时响应并妥善处理，以及有效解决低速外设和高速主机之间的性能差异等问题，人们发明了中断系统。所谓“中断”，通俗讲就是一个“过程”，该“过程”由计算机内、外部硬件或软中断指令（又称为中断源）触发，即由它们发出服务请求，CPU接受请求后，可暂时中止现行程序的执行，转去执行请求服务的那个外设或事件的服务（中断）处理程序，待处理完毕后再返回到被中止程序的断点处继续执行原来的…     

一种多参数的Web服务选择方法

随着服务计算的快速发展，如何快速而准确地找到最优的Web服务组合是众多挑战中最重要的一项。提出了一种基于二阶隐马尔可夫模型（HMM）的服务选择方法。该方法使用服务质量（QoS）参数去区分具有相同功能的Web服务，并且选择一组最优的Web服务来执行用户请求。通过考虑两个QoS参数-吞吐量和响应时间，该方法能够解决根据设定的阈值来衡量Web服务质量的问题。通过构建的模型和算法，方法能够选择出最优的Web服务以满足用户的需求。仿真实验验证了所提出的方法是有效的。     

动态服务组合中资源选择的研究与实现

在面向服务的网格中，需要按用户请求动态地根据当前系统中服务的状况，组合出满足用户请求的服务组合。目前，当存在多个服务提供者提供相同功能的服务时，如何动态选择合适的服务却很少被论述，而且真实网格环境中的不确定性（如Cpu、网络的负载）也很少考虑。如何选择最合适的服务所在的资源，是服务组合中必须要考虑的。在分析动态服务组合的基础上，设计了一种动态选择资源的方法。并利用GT4中工厂设计模式给出其实现方式。该设计考虑了网格环境中资源的安全性和不确定性因素，比如资源经常失败，以及Cpu和网络的负载等，从而最大程度地提高服务执行的可靠性和高效性以及均衡系统负载。     

看清Windows系统服务中的隐患

什么是系统服务　在Windows 2000/XP/2003系统中,服务是指执行指定系统功能的程序、例程或进程,以便支持其他程序,尤其是低层（接近硬件）程序。通过网络提供服务时。服务可以在Active Directory（活动目录）中发布，从而促进了以服务为中心的管理和使用。     

如何选择Modem

要到Internet上“深洒走一回”，Medem（调制解调器）可是必不可少的设备。Modem的种类很多，但是现在绝大多数用户都是在公用电话网上使用模拟调制解调器通过ISP连接到Inter－net的，我们下面讨论的也就是这种Modem。单就这种Modem而言，目前国内市场上的品牌和种类也真不少，到底应该怎样选择呢？下面就是笔者的一些建议。门）购买速度不低于28．SKbpo（数据位／秒）数据传输率的Modem，无论14．4KbpsModem的价格多么便宜都不应该去购买。不知道什么时候开始有一种说法，即国内的电话线路质量如何差或者ISP的带宽如何低，两者限制…     

小心！上网卡也有陷阱

可能是被智商越来越高的“木马”（能窃取用户密码）吓怕了，也可能是“网费恐惧症”已成为大多数网民的通病，所以市场上那些廉价、安全的上网卡成为许多网民的首选。然而令人眼花缭乱、名目繁多的上网卡却成了一些JS敛财的又一法宝。第一招：指鹿为马你可能看到市场上有许多公司的包月卡（也就是月租费固定、不限制时间的上网卡）。但是你知道包月卡有两种类型吗？一种上网卡的包月费中已经包含了电话费和网络费。这种卡往往比较昂贵；另一种卡的包月费中只包含网络费，而电话费仍然按实际使用计算。这种卡相对比较便宜。于是一些上网卡…     

自组织网络有效的组合服务执行路径发现方法

无线自组织网络中的服务组合是指通过将几个简单的服务即原子服务组合成一个功能更强大的服务,来满足用户提出的复杂的请求。在无线自组织网络中,组合服务的执行首先要找到能够实现服务组合的执行路径,即确定网络中能够实现组合服务的合成方案及提供各原子服务的节点。已有工作提出的服务组合执行路径的发现方法并没有考虑所发现执行路径需要的开销和服务的执行情况。文章在保证组合服务执行路径发现成功率的前提下,提出了两种限制跳数的组合服务执行路径发现方法,通过限制组合服务执行路径请求包广播的跳数来减少网络中请求包转发的数量,避免无用的传输消耗。实验证明提出的方法有效地减少了网络中执行路径请求包的转发量,降低了网络的负载。     

集中与分散——全面接触电话自动银行业务系统

越来越多的电话已经开始通过人工提示来开展业务了，“电话自动银行业务系统”即是其中的一种。电话自动银行业务系统是指通过自动语音交互系统(IVR)拨打特定的接入号码，并按照自动语音菜单的导航和业务提示．按下特定的电话键来实现用户请求业务的执行和受理，而鉴于现有的银行业务的数据模式，在构建自动电活银行的组刚方案上也可以有集中方式的组网方案、分散方式的组网方案或二者结合形式。     

煤矿井下安全监控分站的设计及其仿真实现

为了设计一种具有低成本、低功耗、易操作、功能强且可靠性高的煤矿井下安全分站,针对煤矿安全生产实际,文章提出了采用MCS-51系列单片机为核心、具有CAN总线通信接口的煤矿井下安全监控分站的设计方案;首先给出煤矿井下安全监控分站的整体构架设计,然后着重阐述模拟量输入信号处理系统的设计过程,最后说明单片机最小系统及其键盘、显示、报警、通信等各个组成部分的设计;为验证设计方案的可行性与有效性,使用Proteus软件对设计内容进行仿真验证,设计的煤矿井下安全监控分站具有瓦斯、温度等模拟量参数超标报警功能和电机开停、风门开闭等开关量指示功能;仿真结果表明:设计的煤矿井下安全监控分站具有一定的实际应用价值.     

Only connect: teaching, technology and telesis

Abstract This paper describes an approach to the design of interactive multimedia materials being developed in a European Community project. The developmental process is seen as a dialogue between technologists and teachers. This dialogue is often problematic because of the differences in training, experience and culture between them. Conditions needed for fruitful dialogue are described and the generic model for learning design used in the project is explained.     

View-based model-driven architecture for enhancing maintainability of data access services

In modern service-oriented architectures, database access is done by a special type of services, the so-called data access services (DAS). Though, particularly in data-intensive applications, using and developing DAS are very common today, the link between the DAS and their implementation, e.g. a layer of data access objects (DAOs) encapsulating the database queries, still is not sufficiently elaborated, yet. As a result, as the number of DAS grows, finding the desired DAS for reuse and/or associated documentation can become an impossible task. In this paper we focus on bridging this gap between the DAS and their implementation by presenting a view-based, model-driven data access architecture (VMDA) managing models of the DAS, DAOs and database queries in a queryable manner. Our models support tailored views of different stakeholders and are scalable with all types of DAS implementations. In this paper we show that our view-based and model driven architecture approach can enhance software development productivity and maintainability by improving DAS documentation. Moreover, our VMDA opens a wide range of applications such as evaluating DAS usage for DAS performance optimization. Furthermore, we provide tool support and illustrate the applicability of our VMDA in a large-scale case study. Finally, we quantitatively prove that our approach performs with acceptable response times.     

A pragmatic multi-method investigation of discrepant technological events: Coping,attributions, and ‘accidental’ learning

Discrepant technological events or situations that entail a problem, a misunderstanding or a difficulty with the Information Technology (IT) being employed, are common in the workplace, and can lead to frustration and avoidance behaviors. Little is known, however, about how individuals cope with these events. This paper examines these events by using a multi-method pragmatic approach informed by coping theory. The results of two studies – a critical incident study and an experiment – serve to build and test, respectively, a theoretical model that posits that individuals use a variety of strategies when dealing with these events: they experience negative emotions, make external attributions, and adopt engagement coping strategies directed at solving the event, eventually switching to a disengagement coping strategy when they feel they have no control over the situation. Furthermore, users’ efforts may result in ‘accidental’ learning as they try to overcome the discrepant IT events through engagement coping. The paper ends with a discussion of the results in light of existing literature, future opportunities for research, and implications for practice.     

The Distributed Time-Triggered Simulation Scheme: Core Principles and Supporting Execution Engine

Distributed real-time simulation is a young technology field but its practice is under increasing demands. In recent years the author and his collaborators have been establishing a new approach called the distributed time-triggered simulation (DTS) scheme which is conceptually simple and easy to use but widely applicable. The concept was initiated in the course of developing a new-generation object-oriented real-time programming scheme called the time-triggered message-triggered object (TMO) programming scheme. Some fundamental issues inherent in distributed real-time simulation that were learned during recent experimental studies are discussed along with some approaches for resolving the issues. An execution engine developed to support both the TMOs engaged in control computation and the TMOs engaged in DTS is also discussed along with its possible extensions that will enable significantly larger-scale DTSs.     

Software-Konfigurationsmanagement in großen Softwareprojekten

Zusammenfassung Mit zunehmender Größe der Softwaresysteme verschärfen sich die für die Software-Herstellung typischen Probleme: Beherrschen großer Objektmengen, Erhalten der Systemkonsistenz, Kontrolle der ständigen Änderungseinflüsse und Gewährleisten einer langen Lebensdauer. Die Disziplin Konfigurationsmanagement bildet den methodischen Ansatz, diese Probleme besser zu beherrschen. Software-Konfigurationsmanagement faßt die Herstellung von Softwaresystemen als eine Abfolge von kontrollierten Änderungen an gesicherten Zwischen- und Endergebnissen auf. Dargestellt werden die Objekte und Funktionen des Software-Konfigurationsmanagements sowie die hierfür in großen Software-Projekten benötigten Methoden, Instanzen und Hilfsmittel.     

Call for Papers The 6^th International Conference on Grid and Cooperative Computing

Recent years have seen rapid advances in various grid-related technologies, middleware, and applications. The GCC conference has become one of the largest scientific events worldwide in grid and cooperative computing. The 6th international conference on grid and cooperative computing (GCC2007) Sponsored by China Computer Federation (CCF),Institute of Computing Technology, Chinese Academy of Sciences (ICT) and Xinjiang University ,and in Cooperation with IEEE Computer Soceity ,is to be held from August 16 to 18, 2007 in Urumchi, Xinjiang, China.     

Information for Authors

正http://www.zju.edu.cn/jzus http://www.springerlink.com Aim The Journals of Zhejiang University-SCIENCE(A/B/C)are edited by the international board of distinguished Chinese and foreign scientists,and are aimed to present the latest developments and achievements in scientific research in China and     

Editorial:Brain-machine interface(BMI) and cyborg intelligence

正Brain-machine interfaces(BMIs)aim at building a direct communication pathway between the brain and an external device,and represent an area of research where significant progress has been made during the past decade.Based on BMIs,mind information can be read out by neural signals to control     

Information for Authors

正http://www.zju.edu.cn/jzus http://www.springerlink.com Aim The Journals of Zhejiang University-SCIENCE(A/B/C)are edited by the international board of distinguished Chinese and foreign scientists,and are aimed to present the latest developments and achievements in scientific research in China and overseas to the world’s scientific circles,especially to stimulate