并行虚拟文件系统客户端缓存技术研究与实现

缓存技术是一种提高文件系统性能的关键性技术．在并行文件系统中实现客户端缓存，既能够减轻集群服务器系统的通信负载，又能有效地提高文件系统的性能．对PVFS并行文件系统进行了分析，建立了客户端缓存模型，就客户端缓存实现的一些关键性问题，如一致性、查找、替换等进行了研究，给出了解决方案，并在此基础上实现了一个客户端缓存的原型系统．测试结果表明，加入缓存后，PVFS整体性能有明显的提高．     

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。     

并行网络文件系统PNFS性能评测与分析

传统的网络文件系统难以满足高性能计算系统的I/O 需求,并行网络文件系统——PNFS可以有效地解决传统网络文件系统在可扩展性、可用性和性能上存在的问题。首先对PNFS的体系结构进行了设计,实现了元数据服务器与存储服务器的分离,消除了由于集中服务器结构引发的I/O瓶颈问题。然后,对PNFS的原型系统进行了性能测试,并与相同环境下NFS的测试结果进行比较与分析,结果表明PNFS能够为客户端提供并行访问文件数据的能力,有着较高的I/O读写带宽和较低的访问延迟,同时实现了客户端I/O带宽与存储服务器规模之间的线性可扩展关系,能较好地满足高性能计算中的I/O需求。     

高性能集群文件系统的研究

集群系统提供了强大的批处理和并行计算的能力,具有高性能、高可扩展性、高吞吐量和易用性等特点,但是I／O性能和处理器性能的不匹配使得I／O成为许多应用的瓶颈,特别是处理大量数据的应用就更是如此。针对集群系统当前的现状,克服该瓶颈的常用方法就是采用一种并行虚拟文件系统（PVFS）技术。随着Linux群集系统性能的持续提高,高速并行文件已成为并行计算的一个必备部分。并行虚拟文件系统（PVFS）为高性能计算（HPC）群集和大型I／O密集并行应用提供了这样一个文件系统。首先介绍了PVFS的结构;然后研究了PVFS的存取和管理机制;最后分析,PVFS的工作原理。     

PVFS元数据服务器的并行化设计与实现

PVFS并行文件系统采用集中式的元数据服务器,这使得元数据服务器在大量的文件操作情况下成为I／O瓶颈。该文通过增强PVFS的客户端和元数据服务器的相关功能,使得客户的文件请求按照文件名的Hash变换转向不同的元数据服务器,在保留原来的用户访问方式和系统配置不变的情况下实现元数据服务器的并行化,达到明显提高元数据服务器的总吞吐量和可扩展性。     

海量小文件系统的可移植操作系统接口兼容技术

基于Hadoop分布式文件系统（HDFS）研发的海量小文件系统（SMDFS）遗留了HDFS不兼容可移植操作系统接口（POSIX）约束的问题,为解决SMDFS的这一问题,提出基于本地缓存的POSIX兼容技术和基于数据暂存区的元数据高效管理技术。首先,通过设置数据暂存区来实现读写模式文件流的重定向,然后建立异步线程池模型,实现数据暂存区镜像文件的同步,从而完成用户层到存储层的所有POSIX相关的文件操作。此外,借助跳表结构的元数据缓存实现List目录等元数据操作效率优化。测试表明,相较于HDFS的Linux客户端,基于技术成果实现的SMDFS3.0的随机读性能有10倍以上的性能提升,顺序读和顺序写性能有约3~4倍的提升,随机写性能可以达到本地文件系统的20%,基于目录的元数据缓存的设计使目录的List操作效率提升近10倍。但是,由于用户空间文件系统（FUSE）挂载的客户端会引入额外的内核态和用户态切换等带来的开销,因此SMDFS3.0的Linux客户端相对于系统的Java接口会有大约50%的性能损耗。     

基于代理的并行文件系统元数据优化与实现

在高性能计算环境中,并行文件系统面临百万量级的客户端,这些客户端往往在同一时间段内发出大量并发I/O请求,使元数据服务器承载巨大的压力.另一方面,这些客户端发出的并发读写请求往往指向同一目录,导致很难将元数据负载调度到多个服务器上.为此,提出在并行文件系统的客户端和元数据服务器之间增加一级代理(proxy),并给出相应的优化措施降低元数据服务器的负载.在元数据代理上实现2方面的优化:1)由于高性能计算程序往往并发访问大量的文件,可以考虑通过元数据聚合将大量请求合并成1个请求发送到元数据服务器上,降低元数据服务器的负载;2)高性能计算程序的并发I/O往往指向同一目录,而传统的元数据负载均衡机制一般采用子树划分的方法将元数据负载调度到多个元数据服务器上,无法实现针对同一目录元数据操作的负载均衡,通过代理将针对同一目录的元数据操作调度到多个元数据服务器上,实现细粒度的负载均衡.     

Grid VFS中代理管理客户端磁盘缓存的设计与实现

设计并实现了在网格虚拟文件系统Grid VFS客户端采用代理管理磁盘缓存来隐藏网络延迟，提高网格数据利用率。此方法扩展了虚拟化分布式文件系统，提高了对网格资源有效完整的数据访问。在Grid VFS中，客户端代理动态地产生和管理磁盘缓存，每一个未修改的应用程序和OS都能应用，支持write-back策略、文件系统之间缓存的共享以及磁盘缓存的多级化，通过用户级VFS可以完整的集成到网格应用程序和资源中，从而提高了网格数据的访问性能。     

并行文件系统管理工具的设计与实现

通过对常用并行文件系统体系结构的分析，提出了一种适用于某一大类并行文件系统的管理框架。以该管理框架为基础，实现了PVFS并行文件系统的管理工具，并为用户提供了单一映像的管理控制台。功能测试结果表明，该管理工具的引入降低了并行文件系统管理的复杂性。     

SNFS并行文件系统负载均衡技术的研究与实现

在大规模集群系统的并行运算环境中,I/O效率一直是影响系统整体性能的关键因素,并行文件系统技术是目前解决I/O性能瓶颈的有效途径之一。介绍当前并行文件系统的发展现状以及并行文件系统的类型,阐述SNFS并行文件系统的架构以及负载均衡DLC(分布式LAN客户端)技术的实现原理,并给出大规模集群系统环境中SNFS文件系统负载均衡技术的实现方法,最后,通过实际应用分析说明该技术在提升I/O性能上的优势。     

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.