一类Lorenz 型超混沌系统的Zero⁃Zero⁃Hopf 分岔及共存吸引子研究

针对一类四维Lorenz型超混沌系统,首先,在局部动力学方面,基于平均化理论方法,研究了该系统在原点平衡点处发生的Zero-Zero-Hopf分岔行为,得到了系统在原点发生Zero-Zero-Hopf分岔的参数条件,证明了两条周期轨的存在性,并且给出了它们的稳定性条件.除此之外,借助数值模拟,发现该系统在某些特定参数下存在不同吸引子之间的共存现象,比如超混沌吸引子与周期吸引子共存,不同周期吸引子之间的共存.     

一个粘弹性振子的动力学与控制

本文详细分析了一个具有粘弹性项的非线性振子的动力学与控制.首先研究了系统平衡点的稳定性,表明系统存在复杂的无界动力学行为.然后引入时滞速度反馈对这个不稳定系统进行控制.研究结果表明速度反馈控制能镇定此不稳定的粘弹性系统.适当的选择控制增益和控制时滞,控制系统有稳定的平衡点,由Hopf分岔产生的周期解,拟周期解,并能展现出复杂的混沌解.数值模拟验证了结论的正确性.     

具有共存吸引子的混沌系统及其分数阶系统的镇定

研究一个具有共存吸引子的混沌系统及对应分数阶系统的镇定问题.提出了一个新的具有双翼与四翼吸引子共存的混沌系统,利用Lyapunov指数谱和分岔图对系统的性质进行了分析.借助于拓扑马蹄理论和数值计算,找到了系统的拓扑马蹄,并获得了拓扑熵.构造了相应的分数阶混沌系统,此系统亦存在两个孤立的双翼吸引子以及四翼吸引子且共存的双翼吸引子之间没有重叠.设计了线性反馈标量控制器,此控制器用于分数阶混沌系统的镇定.在控制过程中并未删除系统的非线性项,理论分析与仿真计算表明了该方法的有效性.     

Newton-Leipnik系统的多种吸引子及其形成机制

研究了Newton-Leipnik混沌系统的各种动力学行为,从中发现了新的双体双核混沌吸引子,发现了混沌吸引子与小周期吸引子、大周期吸引子并存于同一相空间的各种情况,发现了趋于周期吸引子的暂态混沌运动。这些特性是由五个平衡点的属性所确定的。每个平衡点邻域的状态轨线沿某方向发散而沿某方向收敛,这导致了系统复杂的动力学行为发生。     

新混沌系统及其分数阶系统的自适应同步控制

研究一个存在共存吸引子的混沌系统及相应的分数阶系统的自适应同步问题.首先,提出了一个新的具有双翼和四翼吸引子共存的混沌系统,对系统的动力学特性进行了分析,找到了系统的拓扑马蹄和拓扑熵,从而验证了系统具有混沌特性;然后,根据该系统构建了一个亦存在两个孤立的双翼吸引子以及四翼吸引子的分数阶系统.最后,采用分数阶Lyapunov稳定性理论以及自适应控制方法,对分数阶系统的自适应同步问题进行了研究.仿真结果表明,控制参数k越大,系统同步速度越快;控制参数λ越大,系统参数识别的速度越快.     

五平衡点非线性系统的多核混沌运动分析

研究了外力矩作用下刚体转动动力学系统存在的混沌吸引子类型、数量和特性,分析了5个平衡点的属性。系统状态在5个平衡点邻域沿某方向的收敛和沿某方向的发散,可以形成各种各样的周期吸引子,单核、双核、三核、连体四核、单体四核混沌吸引子。该系统中包含的各类混沌运动形式复杂,吸引子种类繁多。     

一个新超混沌系统及其线性反馈控制

为提高混沌吸引子的拓扑结构的复杂性,构造了一个新的四维超混沌系统.用数值模拟的方法研究了该系统的超混沌吸引子的相图、系统的分岔图、Lyapunov指数谱图和Lyapunov维数等.分析结果表明,新的四维系统当参数满足一定条件时,具有两个正的Lyapunov指数,是一个超混沌系统,系统的分岔图与Lyapunov指数谱是完全吻合的,随着参数变化呈现周期、混沌及超混沌动力学行为.利用线性反馈控制法镇定了超混沌系统的不稳定平衡点,数值模拟结果表明该方法的可行性和有效性.     

一种新的类Lorenz系统的混沌行为与形成机制

提出一种新的类Lorenz系统,它具有三维二次型的自治常微分方程组形式．理论分析中,应用Lyapunov判定方法研究了系统平衡点的稳定性．在此基础之上,数值仿真表明,文中所考查的动力学系统具有极其丰富的动力学现象．包括混沌和多种形式的周期运动形式．文中还分析了两个重要参数对系统稳定性的影响,并通过构建一个受控系统分析了系统混沌吸引子的形成机制．     

混沌在密码学中的应用

混沌是确定性非线性动力系统内在随机性的表现。混沌吸引子具有周期无穷长的特征,混沌解的这种特征为在密码技术中应用提供了可能。论文探讨了混沌吸引子在密码系统分析中应用的可行性,这将是一种加密技术的新方法。     

非线性增益下半导体激光方程的动力学行为分析

分析了在非线性增益下各种因素对Lang-Kobayashi模型动力学行为的影响．由于时滞反馈的作用,系统中存在着不同的ECM解,Hopf分岔是这些ECM解失稳的主要原因,进而演化为各种形式的混沌解,不同吸引子之间的相互作用会引发混沌结构的突变,表现为混沌吸引子在空间尺寸上的明显变化,随着时滞量的变化,这些演化模式会重复出现．值得指出的是,在一定条件下,不同频率的两个ECM共存,其中之一会由Hopf分岔失稳,并由倍周期分岔进入混沌,最终通过混沌危机回到另一个稳定的ECM上．另外,随着非线性增益系数的变化,在极坐标下系统的概周期运动的两个频率相差很大,激光器呈现出明显的快慢效应．     

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。     

煤矿井下安全监控分站的设计及其仿真实现

为了设计一种具有低成本、低功耗、易操作、功能强且可靠性高的煤矿井下安全分站,针对煤矿安全生产实际,文章提出了采用MCS-51系列单片机为核心、具有CAN总线通信接口的煤矿井下安全监控分站的设计方案;首先给出煤矿井下安全监控分站的整体构架设计,然后着重阐述模拟量输入信号处理系统的设计过程,最后说明单片机最小系统及其键盘、显示、报警、通信等各个组成部分的设计;为验证设计方案的可行性与有效性,使用Proteus软件对设计内容进行仿真验证,设计的煤矿井下安全监控分站具有瓦斯、温度等模拟量参数超标报警功能和电机开停、风门开闭等开关量指示功能;仿真结果表明:设计的煤矿井下安全监控分站具有一定的实际应用价值.     

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.     

View-based model-driven architecture for enhancing maintainability of data access services

In modern service-oriented architectures, database access is done by a special type of services, the so-called data access services (DAS). Though, particularly in data-intensive applications, using and developing DAS are very common today, the link between the DAS and their implementation, e.g. a layer of data access objects (DAOs) encapsulating the database queries, still is not sufficiently elaborated, yet. As a result, as the number of DAS grows, finding the desired DAS for reuse and/or associated documentation can become an impossible task. In this paper we focus on bridging this gap between the DAS and their implementation by presenting a view-based, model-driven data access architecture (VMDA) managing models of the DAS, DAOs and database queries in a queryable manner. Our models support tailored views of different stakeholders and are scalable with all types of DAS implementations. In this paper we show that our view-based and model driven architecture approach can enhance software development productivity and maintainability by improving DAS documentation. Moreover, our VMDA opens a wide range of applications such as evaluating DAS usage for DAS performance optimization. Furthermore, we provide tool support and illustrate the applicability of our VMDA in a large-scale case study. Finally, we quantitatively prove that our approach performs with acceptable response times.