Petri网在可靠性分析中的研究综述

可靠性的相关研究在安全关键系统中具有重要意义,利用Petri网可以实现对可靠性的形式化建模以及动态行为的描述。首先对基于Petri网的可靠性分析与研究的基本方法进行分类。其次,着重分析了利用随机Petri网求解系统可靠性的基本方法和步骤,针对等价于Markov过程和非Markov过程的两类系统,重点讨论了基于随机Petri网的系统可靠性分析方法,并指出各类分析研究方法的优缺点。进一步,分析和比较了其他各种类型Petri网在可靠性分析中的应用方法及其优缺点。最后,总结了一些常见的Petri网计算机仿真软件,并针对基于Petri网的可靠性研究展望了几个有价值的研究方向。     

基于Petri网的作战单元任务可靠性仿真

现代战争要求充分发挥武器系统的整体作战效能,任务可靠性为武器系统作战效能的评估提供了依据。本文在分析作战单元任务可靠性仿真重要性以及Petri网技术优点的基础上,描述了作战单元复杂任务的构成及特点,建立了作战单元任务可靠性理论模型并明确仿真思路,利用Petri网技术,在ExSpect仿真环境下逐层构建了作战单元复杂任务可靠性仿真模型,最后针对具体实例进行仿真分析。实例结果表明,此模型可以有效的对作战单元任务可靠性进行仿真,对增强部队综合保障能力具有积极的意义。     

基于Petri网的通信网络可靠性评估建模仿真

该文重点研究基于Petri网的建模仿真方法在通信网络可靠性评估中的应用。首先对Petri网和通信网络可靠性进行概述，并在分析通信网络体系结构和失效模式的基础上，引入了基于Petri网建模仿真的递增建模方法；最后将该方法用于通信网络可靠性评估研究，采用不同的模型，评估得到不同的指标值。结果表明该方法在通信网络可靠性分析与评估方面具有一定的可操作性。     

采用随机Petri网的嵌入式机载软件可靠性检测

针对嵌入式机载软件设计中存在的典型缺陷问题，结合嵌入式机载软件任务调度特性，提出采用随机Petri网对嵌入式机载软件设计进行仿真验证的可靠性检测方法，以提高嵌入式机载软件设计的可靠性。该方法采用随机Petri网对嵌入式机载软件系统行为建模，并给出典型缺陷的检测策略和判定准则，然后通过对Petri网模型进行仿真验证，检测系统是否存在此类设计缺陷；并给出了软件设计的运行流程的仿真验证算法，以支持对相应设计的可靠性检测。通过与其他可靠性检测方法的比较，表明了该方法的有效性。     

模糊时间Petri网及扩展的模糊时间Petri网

网络实时系统对时间和QoS有严格要求,因此对设计、实现和测试的技术和工具都有很高的要求。模糊时间Petri网是将模糊集合理论用于不确定的或主观的时间信息的表示,在每个变迁上添加时间间隔约束对模糊时间Petri网进行扩展得到扩展的模糊时间Petri网,它是一种对网络实时系统进行建模和分析的形式化模型,Petri网数学理论基础能保证并发系统的可靠性和正确性。本文详细地介绍了模糊时间Petri网及可扩展的时间Petri网,可扩展的时间Petri网的网精简方法,使用design／CPN仿真,及使用EFTN对多媒体同步建模,并探讨了进一步研究的方向。     

基于非马尔可夫随机Petri网的软件再生建模与分析

软件老化是影响软件系统可靠性的重要潜在因素,软件再生作为一种主动预防性的软件容错技术是解决软件老化问题的主要手段.以往的随机Petri网再生模型假定所有变迁的实施时间服从指数分布.针对变迁的实施时间服从确定性分布或一般性分布的情况,文中提出了一种用非马尔可夫随机Petri网建立软件再生模型的方法.该方法采用马尔可夫再生理论对模型进行分析,并给出模型的瞬态解和稳态解.仿真实验表明:选择合适的软件再生周期,可以有效地降低存在老化的软件系统的平均宕机成本,提高系统的可用性和可靠性.     

Petri网在C3I系统仿真建模中的应用

建模仿真技术是C^3I系统性能评估、C^3I系统仿真分析与设计的一个重要方法。该文介绍了Petri网的基本概念,说明了Petri网建模的特征;给出了一种应用于C^3I系统仿真研究的建模方法：应用Petri网对C^3I系统进行分析与设计,实现从C^3I系统的组织框图到Petri网数学模型的转换;指出了Petrl网在C^3I系统仿真建模方面的不足和改进方向。最后,该文给出了用Petri网建模的一个简单应用实例。     

Petri网仿真模型改造为HLA邦元的理论和方法

该文从改造建立在其他平台 (如OPMSE)上的Petri网仿真模型为HLA邦元的意义入手 ,给出了改造的可行性、理论和方法。通过对Petri网仿真模型和HLA邦元运行机制的比较 ,采用模型代理的思想解决原模型与外界交互的封装 ,从而实现Petri网仿真模型和RTI运行支撑环境的无缝连接。同时在此基础上 ,探讨了开发基于RTI环境下Petri网仿真模型的集成环境的理论和方法     

进路建立过程的时间有色petri网建模与仿真

计算机联锁软件作为计算机联锁系统的核心主控软件,可靠性和安全性需建立在好的安全模型之上,提出了采用时间有色Petri网对进路建立的具体过程进行形式化建模,时间戳可以得知联锁设备的精确动作时刻以及操作持续时间,通过CPN Tools进行编辑和仿真,以VC++6.0为开发环境完成代码编写进行验证,体现时间有色Petri网描述联锁系统逻辑和性能特性的特点,以便在软件开发初期尽早发现系统的设计错误或缺陷,突出采用时间有色Petri网建模的可靠性和安全性。     

网络安全组件组合强度研究

介绍了安全组件组合安全强度分析的现实意义,对现有方法进行研究,重点探讨了安全边界已知情况下安全组件组合的安全特性。研究段云所副教授所提出的理论,并以其方法为基础,提出了一种基于Petri网的网络系统安全组件组合强度分析方法,进一步研究了Petri网模型的构造,并利用Petri网仿真工具ExSpect对所提出方法的正确性进行仿真验证。     

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。     

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.     

Editorial: Special issue on recent advances in hybrid control theory and applications

正The demands of a rapidly advancing technology for faster and more accurate controllers have always had a strong influence on the progress of automatic control theory.In recent years control problems have been arising with increasing frequency in widely different areas,which cannot be addressed using conventional control techniques.The principal reason for this is the fact that a highly competitive economy is forcing systems to operate in regimes where     

Information for Authors

正Aim The Journals of Zhejiang University-SCIENCE(A/B/C)areedited by the international board of distinguished Chinese andforeign scientists,and are aimed to present the latest devel-opments and achievements in scientific research in China andoverseas to the world’s scientific circles,especially to stimulateand promote academic exchange between Chinese and for-eign scientists everywhere.     

Enhancing a leaf radiative transfer model to estimate concentrations and in vivo specific absorption coefficients of total carotenoids and chlorophylls a and b from single-needle reflectance and transmittance

The relative concentrations of different pigments within a leaf have significant physiological and spectral consequences. Photosynthesis, light use efficiency, mass and energy exchange, and stress response are dependent on relationships among an ensemble of pigments. This ensemble also determines the visible characteristics of a leaf, which can be measured remotely and used to quantify leaf biochemistry and structure. But current remote sensing approaches are limited in their ability to resolve individual pigments. This paper focuses on the incorporation of three pigments—chlorophyll a, chlorophyll b, and total carotenoids—into the LIBERTY leaf radiative transfer model to better understand relationships between leaf biochemical, biophysical, and spectral properties.Pinus ponderosa and Pinus jeffreyi needles were collected from three sites in the California Sierra Nevada. Hemispheric single-leaf visible reflectance and transmittance and concentrations of chlorophylls a and b and total carotenoids of fresh needles were measured. These data were input to the enhanced LIBERTY model to estimate optical and biochemical properties of pine needles. The enhanced model successfully estimated reflectance (RMSE = 0.0255, BIAS = 0.00477, RMS%E = 16.7%), had variable success estimating transmittance (RMSE = 0.0442, BIAS = 0.0294, RMS%E = 181%), and generated very good estimates of carotenoid concentrations (RMSE = 2.48 µg/cm², BIAS = 0.143 µg/cm², RMS%E = 20.4%), good estimates of chlorophyll a concentrations (RMSE = 10.7 µg/cm², BIAS = − 0.992 µg/cm², RMS%E = 21.1%), and fair estimates of chlorophyll b concentrations (RMSE = 7.49 µg/cm², BIAS = − 2.12 µg/cm², RMS%E = 43.7%). Overall root mean squared errors of reflectance, transmittance, and pigment concentration estimates were lower for the three-pigment model than for the single-pigment model. The algorithm to estimate three in vivo specific absorption coefficients is robust, although estimated values are distorted by inconsistencies in model biophysics. The capacity to invert the model from single-leaf reflectance and transmittance was added to the model so it could be coupled with vegetation canopy models to estimate canopy biochemistry from remotely sensed data.     

Mr. Twinn’s bombes

This article discusses the history and design of the special versions of the bombe key-finding machines used by Britain’s Government Code & Cypher School (GC&CS) during World War II to attack the Enigma traffic of the Abwehr (the German military intelligence service). These special bombes were based on the design of their more numerous counterparts used against the traffic of the German armed services, but differed from them in important ways that highlight the adaptability of the British bombe design, and the power and flexibility of the diagonal board. Also discussed are the changes in the Abwehr indicating system that drove the development of these machines, the ingenious ways in which they were used, and some related developments involving the bombes used by the U.S. Navy’s cryptanalytic unit (OP-20-G).