分布式系统死锁的Petri网分析

阐述了分布式系统中的死锁问题,采用Petri网对分布式系统中的死锁进行分析,给出了几种解决死锁的模型,并分析了这些模型的优缺点,指出了分析和解决死锁的一般方法.     

分布式系统死锁的预防、避免和检测

分布式系统涉及到资源和数据的高度共享,从而可能引发死锁。分布式系统的死锁是由于资源和通讯产生的。从分布式系统死锁产生的条件,解决策略,以及分布式系统中死锁预防、避免和检测的各种算法进行了具体阐述。     

分布式锁的Petri网建模及死锁检测

分布式锁管理DLM细化了锁模式的粒度,使得分布式系统具有更高的并发性,但死锁检测等锁的管理过程却更加复杂了,Petri网的应用能很好地解决该问题。为分布式锁建立Petri网模型,通过化简和合成建立系统的Petri网模型,借助Petri网的可达标识图实时检测出分布式系统的死锁状态,并查找死锁进程。     

基于Petri网的分布式系统并发进程的死锁检测

分布式系统中的并发进程具有明显的并发、异步及分布性,而Petri网是模拟与分析并发、异步、分布式系统的有效工具.为此通过引入Petri网,给出了分布式系统局部并发进程等待的Petri网模型及死锁检测方法,提出了全链路合成的概念,利用全链路合成技术组装了全局并发进程等待的Petri网模型,给出了判断整个系统是否出现死锁的充分必要条件.     

选举策略在分布式系统死锁避免中的应用

将单机系统或集中式系统中的死锁避免策略移植到分布式需要面临并发性和冲突问题的解决。本文通过分析二阶段锁的机制,引入了一种应用选举策略来幽雅地解决分布式系统中死锁避免所碰到问题的算法。     

并发操作系统中基于有色Petri网的死锁检测与避免

1.引言系统的并发性与资源的共享性是并发操作系统的主要特征,其目的是最大限度地提高计算机资源的利用率。死锁是并发操作系统必须解决的一个重要问题。人们试图用不同的方法来解决死锁问题。如Dijkstra提出的有名的死锁避免的“银行家算法”,Coffman等人给出的死锁检测算法。 Petri网模型作为模拟与分析并发、异步、分布式系统的一种有效工具,已被用于解决操作系统中的许多问题。如进程通讯中的生产者/消费者问题、哲学家用餐问题,资源竞     

N个有限状态机的死锁和死环回避算法

死锁和死环是分布式系统或计算机网络中进程间通信时经常发生的逻辑错误，它们往往造成分布式系统中的部分主机或整个系统瘫痪，本文提出两个回避死锁和死环的算法，这些算法可被用来设计分布式系统的通信协议，从而提高分布式系统的可靠性和减少协议开发成本。     

分布式死锁检测算法中伪死锁率的研究和改进

死锁处理是分布式系统中的关键问题,其中处理死锁最主要的手段为死锁检测。在评价死锁检测算法性能时伪死锁率被视为一项重要指标,故降低伪死锁率对提高算法性能有着促进作用,而目前大多数算法改进对伪死锁率关注较少。本文阐述了伪死锁研究的意义,并对若干种死锁检测算法的伪死锁率进行研究和模拟实验,认为现有的死锁算法可分为两类:环内检测和环无关检测。并分别通过减少冗余消息和本地死锁解决两种改进方法来降低目前算法的伪死锁率,最终实验表明算法性能获得较大提高。     

一个两段加锁不死锁的充分条件

两段加锁是分布式系统中最广泛使用的并发控制算法。该算法除实现较为复杂外，其致命弱点是容易产生死锁。本文在分析两段加锁产生死锁原因的基础上，给出了一个不会产生死锁的两段加锁方法的充分条件和构造性定理以及实现的方法。     

容错的分布式系统通用死锁模型检测解除算法

分布式系统技术为采用低成本购建高性能系统提供了有效的途径,但是由于资源的分配与需求可能产生冲突,造成系统中发生死锁,导致系统运行陷入停滞.在不可靠的分布式系统中,故障会干扰正常的死锁检测,但现有的死锁检测算法不具有容错功能.对失效形式进行了归类,提出一个容错的死锁检测解除算法.算法建立在通用的AND-OR模型基础上,采用扩散计算和集中规约方式,不仅能够检测到死锁,而且能给出死锁环的全部成员.若死锁拓扑处于静态且为环状,算法的消息复杂度的上限为e n-1,时间复杂度为d,其中e为死锁等待图中边的个数,n和d为构成死锁环的节点的个数,分析表明算法性能等于或优于同类算法.     

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.