基于通用带权分布式哈希表的数据放置算法研究

研究了动态网络环境下基于网络的存储系统的数据放置算法,分析了现有的数据放置算法,提出了通用带权分布式哈希表算法.与相容哈希算法和对数算法定义的评判函数相比,考虑了各个节点的存储空间、数据分发节点与数据存储节点之间的物理距离、网络带宽等的限制.仿真结果表明,该算法能够实现数据的公平分发.     

面向海量非结构化数据的非关系型存储管理机制

针对传统的关系数据存储系统性能不足、容错性差,无法适应海量非结构化数据管理的问题,提出一种高性能、高可用非关系型存储管理机制。首先,设计了良好的用户访问服务接口,通过高效的一致性哈希算法支持数据分发到多个存储节点;其次,采用可配置的数据副本机制改善存储系统的可用性;最后,提出查询故障处理机制,用以提升存储系统的容错性,避免节点失效导致服务中断问题。实验结果表明,在不同规模用户负载下,新的存储系统的并发访问请求能力和传统的文件系统、关系数据库相比,分别提升了30%和50%;同时,在合理响应时间内,故障状态下的存储系统的可用性损失小于14%。因此,该机制适用于海量非结构化数据的高效存储管理。     

可验证布隆过滤器:加速区块链中的不存在查询与证明

传统基于区块链的“真实存储”系统在过滤“无效查询请求”时忽略了提供“不存在证明”,恶意节点可以随时对指定用户发动拒绝服务攻击.本文提出了可验证布隆过滤器的一种构建方式,基于布隆过滤器快速过滤无效查询请求的同时能有效提供证据证明数据不存在;此外,针对证明过程中可能造成的隐私泄露问题,本文提出了“隐秘的可验证布隆过滤器”和“数据混淆”两种方式,前者确保每个“不存在证明”只会泄露布隆过滤器的一位置零位,减少了数据泄露量;后者则是在前者的基础上进一步降低用户从泄露的布隆过滤器中推测出真实内容准确率.实验数据表明,当无效查询请求量占比为35%时,读取性能提升大约30%;当无效查询请求量占比为95%时,读取性能可提升十倍以上.     

基于混合计数布隆过滤器的高效数据名查找方法

数据名查找是信息中心网络、内容分发网络、5G核心网中基础功能组件的关键操作，需要面向大规模规则表进行最长前缀匹配，在查找速度、更新开销和存储开销等方面面临严峻挑战.首先设计了混合计数布隆过滤器（HyCBF），将数据名前缀和前缀标记维护在同一个计数布隆过滤器中同时保持二者的逻辑独立性.这样可在不增加额外存储开销和时间开销的情况下提供更丰富的指示信息.基于此，提出HyCBF辅助的二分数据名查找（HyBS）方法以实现高效查找.进一步，为缓解二分查找过程中因回溯导致的性能损失，为HyCBF中每个条目关联一个特征比特位图以降低其假阳性率.实验表明，HyBS相比现有方法在查找性能和更新速度方面具有明显优势，存储效率也有一定提升.此外，将HyBS集成到向量化数据包处理（VPP）框架中进行系统性能评估，结果表明HyBS可用于构建高通量可扩展的数据名查找引擎.     

合作性DTN的基于系统效益的内容分发

近年来在时延容忍网络(delay tolerant network,DTN)中的数据分发成为研究热点.由于DTN节点之间不存在持续的端到端连接,节点通常采用"存储-搬运-转发"的方式进行数据递交.当两个节点相接触时,节点如何为空间有限的缓存选择存储内容是一个关键问题,这关系到整个DTN网络的分发性能.但在分布式动态的DTN环境下,每个节点难以找到全局最优的存储选择.基于这个原因,全局效益最大化问题被转变为每次接触时的效益增益最大化问题,然后将转化后的问题形式化为0-1背包问题,并设计了一种启发式贪婪算法来进行求解,使得每个节点在与其他节点发生接触时,能够依据自身维护的局部网络信息来选取转发内容,从而最大化系统分发效益的增益.此外进一步详细分析了节点维护的网络信息的范围与节点对转发内容选择之间的关系.基于Trace的仿真结果表明,与SocialCast算法相比,启发式算法可以有效地提高节点对订阅内容的接收率和降低接收时延,并且随着节点维护的网络信息范围的增大系统效益也不断增大.     

基于对象分组的集群存储系统可靠性分析模型

可靠性问题是研究大规模集群存储系统的一个重要方面。借鉴RAID的方法,提出基于对象分组在算法一级实现数据冗余分布的高可靠数据对象布局算法。在数据对象和存储节点失效时,利用冗余数据重构数据对象和存储节点,有效保证存储系统的高可用性。采用马尔可夫激励模型对存储系统进行定量的可用性分析,计算结果表明该方法是有效的。     

海量存储系统的数据分布策略研究

针对海量存储系统中数据分布存在可扩展性以及灵活性的问题,提出一种高效的数据分布算法。该算法采用一致性哈希的存储思想,利用“二分”的映射方式映射物理存储节点,摒弃了Chord算法中每台节点对路由表维护的做法,实现O（1）时间内直接路由。该算法还采用了“微分逼近”的思想,实现数据的均匀分布性。实验结果证明, TTD算法具备数据分布无关性的特点,且当物理节点逼近2^N （N〉0）时,数据分布就会越均匀。反之,可以通过虚拟节点的引入,确保数据的均匀分布。算法改进了海量存储系统中数据分布的均匀程度,有效优化了系统的整体性能。     

P2P分布式存储系统

设计了一个基于P2P的分布式存储系统.该存储系统采用高可扩展的P2P体系结构,将大量分散的节点组织成一个逻辑网络,充分利用原先被忽视的端系统资源,构建大规模分布式存储系统.该存储系统采用高效的结构化P2P路由机制、动态自适应的副本管理、信任机制和激励机制为用户提供高效、可靠的分布式存储服务.     

基于智能网络磁盘的安全存储系统研究与设计

针对海量数据存储安全问题,提出并设计了一种基于智能网络磁盘的安全存储系统。介绍了该存储系统的硬件和软件构成以及体系结构,分别从数据编码、数据分发以及数据恢复3个方面详细阐述了基于纠删码的数据安全存储机制的设计思路,对系统的安全可靠性进行了分析。分析结果表明,提出的安全存储机制具有较高的安全可靠性和良好的整体性能,对系统的时间开销影响较小。     

MANET中基于动态地址的机会路由算法

机会路由过程中分发矩阵的计算量太大,随着网络规模的增大,分发矩阵的计算严重影响路由性能。针对该问题,提出基于动态地址的机会路由算法。该算法将分发矩阵的计算量从整个网络降低到一跳邻居节点之间,根据反映网络节点相对物理位置的动态地址,简化分发矩阵的计算。在大规模网络中,该路由算法的平均跳数减少了5%~10%,吞吐量提高了7%~26%。     

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.