一种分布式存储系统用户磁盘配额的实现

用户磁盘配额可实现集群系统中分布式文件系统资源的管理和控制.在分布式文件系统中常使用多数据服务器来扩充文件系统的存储空间、提高并行数据IO的能力.结合NFS,Lustre中分布式配额实现方式,提出了一种适合对等存储模式下的用户磁盘配额策略.该策略使用静态设置和动态调整相结合的方式,能够很好地解决多数据服务器用户配额使用空间不均匀的问题;它可以运行在全局文件系统的所有客户端,避免了单客户端节点失效的问题,且对文件系统性能影响较小.     

移动实时事务预留广播空间的验证协议

在无线数据广播环境中,从移动客户机到服务器的上行带宽非常有限,传统的并发控制协议不适合这种不对称通信环境.本文提出一种可变乐观并发控制协议,服务器周期性向移动客户机广播数据对象,同时把一个广播周期分成若干个子周期,在两个连续的子周期间,一个保留空间被预留来存放服务器更新事务在第一个子周期开始后修改的所有数据对象,移动只读事务通过比较服务器更新事务提交的写集合和自己读集合来自主进行一致性验证,如果只读事务不能通过部分验证,它不会被草率地夭折并重新启动,相反,应用一个改进的向前验证策略,帮助移动只读事务争取更多提交机会.最后,本文进行充分的实验对提出的算法性能进行了评价.     

面向对象存储的文件系统Lustre

针对Lustre文件系统主要运用在高性能计算集群系统上的情况,分析Lustre文件系统的系统结构及其内部实现机制,测试系统在不同参数影响下的性能,认为Lustre可以运用在高性能集群系统上,也能运用在由普通计算机和 TCP／IP网络构建的集群系统上。实验结果表明,在TCP／IP协议和千兆交换机下, Lustre的并发性很难发挥,但设置合适的客户端数和系统参数可以优化其性能,相对本地磁盘系统, Lustre系统仍有较大的性能提高和实用价值。     

实时Client/Server数据库并发控制和恢复机制研究

该文提出了实时Client／Server数据库系统多版本两阶段封锁并发控制协议和有效的恢复机制。协议区分只读事务和更新事务。只读事务在执行读操作时遵从多版本时间排序协议,更新事务执行强两阶段封锁协议,即持有全部锁直到事务结束。只读事务读请求从不失败,不必等待等特性。在典型数据库系统中,读操作比写操作频繁。这个特性对于实践来说至关重要。为了提高只读事务的响应时间,协议让每个客户端与一个一致数据库影子相联,只读事务在客户端处理。更新事务提交到服务端运行。服务端每个事务Ti在提交时系统必须向所有客户端广播信息。客户端根据得到的广播信息自动构造一致数据库影子。一致数据库影子还将用于系统恢复。通过仿真模拟。与2V2PL和OCC-TI-WAIT-50协议进行比较,结果表明：该并发控制协议不仅能有效降低事务延误截止时间率和重起动率,而且能改善只读事务的响应时间,减少优先级高事务的锁等待时间。协议性能优于2V2PL协议和OCC-TI-WAIT-50协议。     

基于对象存储文件系统的协作式缓存一致性策略

基于对象存储文件系统引入了客户端缓存机制以加快文件访问速度,由此也带来了缓存数据一致性问题。针对多客户端访问共享文件时缓存更新策略存在的延时、网络和服务器负载过大及网络消耗大等问题,基于Lustre对象存储文件系统实现了一种改进的协作式缓存一致性策略。实验结果表明,改进后的缓存更新策略,不仅可以保证缓存数据的一致性,而且减少了客户端与服务器交互次数,降低了访问延迟,提高了系统I/O性能。     

Lustre文件系统I/O锁的应用与优化

分布式文件系统需要有一种机制对来自各个客户端的并发访问进行控制,维护文件数据的一致性。锁是实现并发控制最流行的机制。研究了Lustre文件系统的分布式I/O范围锁的模型,并对它的各种应用进行了优化。介绍了Lustre分布式锁的基本概念,对基于锁实现数据客户端写回缓冲以及多写者文件大小的动态获取的算法进行了分析;提出自适应I/O锁策略,基于区间树的范围锁冲突检测优化策略以及客户端锁淘汰策略来增强Lustre锁服务的性能和扩展性。     

工程数据库管理系统OSCAR的页面服务器

为了适应工程应用的特点，工程数据库管理系统OSCAR采用了页面服务器体系结构．OSCAR的页面服务器集中实现了数据库管理系统核心的事务管理，即并发控制和恢复功能．它向客户端提供支持多用户共享的、可靠的数据页面服务，客户端模块在此基础上构建一个功能完备的工程数据库管理系统．介绍了设计与实现OSCAR页面服务器过程中碰到的问题及其解决方法，包括OSCAR页面服务器的功能在物理层、缓冲层和事务层的分配，客户／服务器环境中ARIES恢复策略的改进以及先写日志文件原则的实现方案。     

LVS负载均衡调度算法的改进及实现

采用服务器集群架构提供服务成为互联网服务业中普遍采用的策略,目前使用得比较广泛的网络负载均衡集群是Linux虚拟服务器集群。优秀的负载均衡算法可以将用户请求合理地分配到集群中的真实服务器中．提高集群中服务器的利用率和集群系统的吞吐量。针对LVS默认算法WLC算法的不足之处,对WLC算法进行改进．设计并实现一种基于反馈式的负载均衡算法。实验证明,改进算法能够增大集群的吞吐量,提升集群的整体性能。     

基于MMORPG的网络同步问题的研究与实现

结合多人在线角色扮演游戏系统,根据网络同步问题产生的原因,分别从客户端到服务器同步、服务器广播、客户端到客户端同步三个方面对解决同步问题进行探讨分析,从而得到一个改进的综合解决方案系统采用IOCP、线程池技术、被动检测算法,给予客户端一定决策权,并对Time Warp算法和Dead Reckoning算法进行改进。系统在校园网内进行实验,测试数据表明该方案能较好地解决MMORPG中的同步问题。     

Web服务器集群的负载均衡中遗传算子的设计

应用遗传算法进行作业调度已被越来越多的学者关注。在Web服务器集群环境中,对于客户端的Web请求分配问题,采用常规的遗传算法进行负载均衡并不总是有效的,好的遗传算子对算法收敛性及收敛到最优解非常重要。基于集群环境中Web请求分配的特点,设计了有针对性的遗传算子,即改进的内外结合交叉算子和主动变异算子。模拟实验结果与分析表明这些算子对Web集群的请求分配是有效的。     

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.     

European Community policy and the market

Abstract This paper starts with some reflections on the policy considerations and priorities which are shaping European Commission (EC) research programmes. Then it attempts to position the current projects which seek to capitalise on information and communications technologies for learning in relation to these priorities and the apparent realities of the marketplace. It concludes that while there are grounds to be optimistic about the contribution EC programmes can make to the efficiency and standard of education and training, they are still too technology driven.     

一种自适应子融合集成多分类器方法

融合集成方法已经广泛应用在模式识别领域,然而一些基分类器实时性能稳定性较差,导致多分类器融合性能差,针对上述问题本文提出了一种新的基于多分类器的子融合集成分类器系统。该方法考虑在度量层融合层次之上通过对各类基多分类器进行动态选择,票数最多的类别作为融合系统中对特征向量识别的类别,构成一种新的自适应子融合集成分类器方法。实验表明,该方法比传统的分类器以及分类融合方法识别准确率明显更高,具有更好的鲁棒性。     

Avoiding semantic and temporal gaps in developing software intensive systems

Development of software intensive systems (systems) in practice involves a series of self-contained phases for the lifecycle of a system. Semantic and temporal gaps, which occur among phases and among developer disciplines within and across phases, hinder the ongoing development of a system because of the interdependencies among phases and among disciplines. Such gaps are magnified among systems that are developed at different times by different development teams, which may limit reuse of artifacts of systems development and interoperability among the systems. This article discusses such gaps and a systems development process for avoiding them.     

Designing economic np control charts: A programmed simulation approach

This paper presents control charts models and the necessary simulation software for the location of economic values of the control parameters. The simulation program is written in FORTRAN, requires only 10K of main storage, and can run on most mini and micro computers. Two models are presented - one describes the process when it is operating at full capacity and the other when the process is operating under capacity. The models allow the product quality to deteriorate to a further level before an existing out-of-control state is detected, and they can also be used in situations where no prior knowledge exists of the out-of-control causes and the resulting proportion defectives.     

The development of robot art

Going through a few examples of robot artists who are recognized worldwide, we try to analyze the deepest meaning of what is called “robot art” and the related art field definition. We also try to highlight its well-marked borders, such as kinetic sculptures, kinetic art, cyber art, and cyberpunk. A brief excursion into the importance of the context, the message, and its semiotics is also provided, case by case, together with a few hints on the history of this discipline in the light of an artistic perspective. Therefore, the aim of this article is to try to summarize the main characteristics that might classify robot art as a unique and innovative discipline, and to track down some of the principles by which a robotic artifact can or cannot be considered an art piece in terms of social, cultural, and strictly artistic interest. This work was presented in part at the 13th International Symposium on Artificial Life and Robotics, Oita, Japan, January 31–February 2, 2008     

Explanation and prediction: an architecture for default and abductive reasoning

Although there are many arguments that logic is an appropriate tool for artificial intelligence, there has been a perceived problem with the monotonicity of classical logic. This paper elaborates on the idea that reasoning should be viewed as theory formation where logic tells us the consequences of our assumptions. The two activities of predicting what is expected to be true and explaining observations are considered in a simple theory formation framework. Properties of each activity are discussed, along with a number of proposals as to what should be predicted or accepted as reasonable explanations. An architecture is proposed to combine explanation and prediction into one coherent framework. Algorithms used to implement the system as well as examples from a running implementation are given.     

Three Process Perspectives: Organizations, Teams, and People

This paper provides the author's personal views and perspectives on software process improvement. Starting with his first work on technology assessment in IBM over 20 years ago, Watts Humphrey describes the process improvement work he has been directly involved in. This includes the development of the early process assessment methods, the original design of the CMM, and the introduction of the Personal Software Process (PSP)^SM and Team Software Process (TSP){^SM}. In addition to describing the original motivation for this work, the author also reviews many of the problems he and his associates encountered and why they solved them the way they did. He also comments on the outstanding issues and likely directions for future work. Finally, this work has built on the experiences and contributions of many people. Mr. Humphrey only describes work that he was personally involved in and he names many of the key contributors. However, so many people have been involved in this work that a full list of the important participants would be impractical.     

基于复小波噪声方差显著修正的SAR图像去噪

提出了一种基于复小波域统计建模与噪声方差估计显著性修正相结合的合成孔径雷达(Synthetic Aperture Radar,SAR)图像斑点噪声滤波方法。该方法首先通过对数变换将乘性噪声模型转化为加性噪声模型,然后对变换后的图像进行双树复小波变换(Dualtree Complex Wavelet Transform,DCWT),并对复数小波系数的统计分布进行建模。在此先验分布的基础上,通过运用贝叶斯估计方法从含噪系数中恢复原始系数,达到滤除噪声的目的。实验结果表明该方法在去除噪声的同时保留了图像的细节信息,取得了很好的降噪效果。     

How do children do mathematics with LOGO?

Abstract  This paper considers some results of a study designed to investigate the kinds of mathematical activity undertaken by children (aged between 8 and 11) as they learned to program in LOGO. A model of learning modes is proposed, which attempts to describe the ways in which children used and acquired understanding of the programming/mathematical concepts involved. The remainder of the paper is concerned with discussing the validity and limitations of the model, and its implications for further research and curriculum development.