数字图像的两类非线性变换及其周期性

研究了Fibonacci-Q变换及其逆变换的周期性,并证明了Fibonacci变换周期与Arnold变换周期的关系式,利用Fibonacci-Q变换Arnold变换之间的内在关系,定义了一种新的非线性变换－A－F变换,同时对其变换周期及其逆变换周期进行了研究,也给出了这两类变换周期的简洁算法。由于A－F变换和Fibonacci-Q变换与Arnold变换的周期性大相径庭,在实际应用中可达到更加安全保密的效果。     

基于DST的实值离散Gabor变换

Gabor变换已被公认为是通信和信号处理中信号与图像表示的最好的方法之一,一直以来对Gabor变换的研究和应用实际上是基于Fourier变换的复值Gabor变换,因此这里对实值Gabor变换进行了研究.采用双正交分析方法,定义了一种基于离散正弦变换(DST)的实值离散Gabor变换(RDGT),该变换不仅适用于临界抽样条件而且适用于过抽样条件,并证明了变换的完备性条件(即该变换中综合窗与分析窗的双正交条件),该实验结果也验证了变换的完备性.针对实值信号,该变换由于仅涉及实值运算,并可利用快速DST、IDST算法来加速变换,因此比传统复值离散Gabor变换在计算、实现方面更为简单.在实际应用中,将更方便于软件和硬件的实现.     

矩阵的秩变换、相似变换与合同变换的联系

本文应用理论研究的方法,将矩阵的秩变换、相似变换以及合同变换转换到线性变换当中去,讨论了矩阵的这三种变换之间的联系与区别,并给出证明,对矩阵的秩变换、相似变换以及合同变换的异同点做出一个综述性的描述。     

基于DST的实值离散Gabor变换

Gabor变换已被公认为是通信和信号处理中信号与图像表示的最好的方法之一,一直以来对Gabor变换的研究和应用实际上是基于Fourier变换的复值Gabor变换,因此这里对实值Gabor变换进行了研究。采用双正交分析方法,定义了一种基于离散正弦变换(DST)的实值离散Gabor变换(RDGT),该变换不仅适用于临界抽样条件而且适用于过抽样条件,并证明了变换的完备性条件(即该变换中综合窗与分析窗的双正交条件),该实验结果也验证了变换的完备性。针对实值信号,该变换由于仅涉及实值运算,并可利用快速DSTI、DST算法来加速变换,因此比传统复值离散Gabor变换在计算、实现方面更为简单。在实际应用中,将更方便于软件和硬件的实现。     

微扰Kepler系统的守恒量与对称性

用直接积分法和Noether法研究微扰Kepler系统的守恒量,都得到了一个不同于Hamilton函数的守恒量,此守恒量与Runge—Lenz矢量有相同的量纲,可以称其为“类Runge-Lenz矢量守恒量”．文中还讨论了守恒量的Noether对称性、Lie对称性与Mei对称性,结果表明：与守恒量相应的无限小变换同时是Noether对称变换、Lie对称变换和Mei对称变换．     

数字通信信号小波变换尺度选取问题研究

利用小波变换检测信号奇异性时,往往选择特定的尺度因子来进行,但是目前对于尺度因子选取问题研究的很少。文章以经均方根升余弦脉冲成形的ASK信号提取瞬时包络为例,对小波变换尺度选择问题进行了研究。首先利用Haar小波变换系数的模来提取ASK信号瞬时包络,并与传统的基于Hilbert变换提取法进行了比较;然后重点对小波变换的尺度因子选取问题进行了研究,从改善信噪比的角度对最佳尺度因子选取进行了推导,并通过仿真验证了算法的可行性。     

时间序列相似性定义延拓

时间序列相似性定义没有一个明确的、统一的表述方法,造成了研究上的困难。将研究序列分解为多个与参照序列等维的子序列,把问题转化为研究子序列与参照序列的相似性。选择满足保范同构的线性变换算子对子序列和参照序列进行变换,以降低直接计算的复杂度。利用集合理论对相似关系进行了宏观描述,用子序列与参照序列变换前后向量差的范数定义序列相似性度量函数,将相似性度量进行了统一。研究结果为基于傅立叶变换和小波变换研究时间序列的相似性提供了理论依据。     

图像采集中基于小波变换阈值去噪算法研究

阐述了基于小波变换阈值去噪算法的相关概念与优点,介绍了小波变换基本原理,对基于小波阈值的图像去噪方法进行了深入探讨研究,并给出了仿真结果。     

基于非抽样Contourlet变换的最佳软阈值图像去噪

研究了小波变换在图像处理中的缺陷,以及Contourlet变换在图像处理中产生伪Gibbs失真的原因.为了在多尺度分析框架下改进图像去噪的效果,提出了一种基于非抽样Contourlet变换的图像去噪算法,利用非抽样Contourlet变换的多尺度多方向性以及平移不变性,对加噪图像进行非抽样Contourlet变换得到变换系数,然后对变换系数采用分层最佳软阈值处理,最后将其反变换得到去噪后的图像.实验结果表明,与Contourlet变换图像去噪算法相比,该算法可以达到更好的效果.     

基于非抽样Contourlet变换的最佳软阈值图像去噪

研究了小波变换在图像处理中的缺陷,以及Contourlet变换在图像处理中产生伪Gibbs失真的原因。为了在多尺度分析框架下改进图像去噪的效果,提出了一种基于非抽样Contourlet变换的图像去噪算法,利用非抽样Contourlet变换的多尺度多方向性以及平移不变性,对加噪图像进行非抽样Contourlet变换得到变换系数,然后对变换系数采用分层最佳软阈值处理,最后将其反变换得到去噪后的图像。实验结果表明,与Contourlet变换图像去噪算法相比,该算法可以达到更好的效果。     

Positive invariance, monotonicity and comparison of nonlinear systems

In this paper, the interrelation between positive invariance, monotonicity and comparison of iterated nonlinear systems defined in partially ordered sets is studied. First, necessary and sufficient conditions guaranteeing the positive invariance of sets defined by relations of the form v(x)≤w with respect to nonlinear systems are established. Then, various characterizations of monotone nonlinear systems are developed and a connection between positive invariance and monotonicity is established. Finally, necessary and sufficient conditions for a, not necessarily monotone, nonlinear system to be a comparison system are established. No specific algebraic structure is necessary for developing the main results of this work. Numerical examples illustrating the applicability of all these results to the case of discrete-time dynamical systems are also given.     

On controllability,near-controllability,controllable subspaces,and nearly-controllable subspaces of a class of discrete-time multi-input bilinear systems

This paper considers a class of discrete-time multi-input inhomogeneous bilinear systems. The structure of such systems is most close to linear time-invariant systems’ but they own a strong property. That is, if the systems are uncontrollable, they can still be nearly controllable. Necessary and sufficient conditions for controllability and near-controllability of the systems are established by using a classical decomposition. Furthermore, a geometric characterization is given for the systems such that controllable subspaces and nearly-controllable subspaces are derived and characterized. Similar results on controllability are also obtained for the continuous-time counterparts of the systems. Finally, examples are provided to demonstrate the conceptions and results of this paper.     

Information systems practice, education and research

Abstract. The launch of a new journal in information systems prompts thought and debate concerning the state of the subject area and some contemplation on its past and future. This introductory paper reflects the views of the editors, views which will not be shared by all. We find a wide spectrum of interpretations and experiences concerning the nature of information systems and this wide range of views is both a strength and a weakness. It is a weakness in the sense that it is very difficult to put boundaries around the area and establish common definitions and accepted norms. The latter are usually associated with more stable and established disciplines that have accepted underlying theories. It is a strength in the sense that the wide variety of views, experiences and background subjects adds richness to the discipline. From the point of view of the Journal of Information Systems this should mean a wide variety of interesting topics from which we can draw. Our paper begins with an introduction to the debate about the nature of information systems, a debate which is continued in the following paper. We also give an overview of practice, education and research in information systems. In order to keep the paper to a reasonable length, this overview will necessarily be selective and will probably be Anglocentric.     

2-D常系数线性离散系统可分性判定

针对二维常系数线性离散系统一般状态空间模型(2-DGM)的可分性判定问题进行 探讨,给出了系统可分的若干判定法则,这些法则有助于进一步完善2-D系统现有的理论体 系.     

Matching, linear systems, and the ball and beam

A recent approach to the control of underactuated systems is to look for control laws which will induce some specified structure on the closed loop system. In this paper, we describe one matching condition and an approach for finding all control laws that fit the condition. After an analysis of the resulting control laws for linear systems, we present the results from an experiment on a nonlinear ball and beam system.     

基于脉冲微分系统模型的有损网络控制系统研究

针对闭环网络控制系统,在考虑网络数据传输可能发生丢包的情况下,提出了一类切换系统模型,并在此基础上导出了一类脉冲微分系统模型.从数学上严格分析了该模型的合理性,并利用驻留时间的概念得到了此系统模型的稳定性条件,进一步研究了能够忍受一定程度的数据丢包的稳定化控制器设计问题.最后给出了一个具体示例.     

Reflections on information systems practice, education and research: 10 years of the Information Systems Journal

This paper celebrates the 10‐year anniversary of the Information Systems Journal (ISJ) and the Editors reflect on the papers that have been published over that period and the changes that have occurred in the discipline of information systems. In the opening paper of ISJ, we suggested that the ‘launch of a new journal in information systems prompts thought and debate concerning the state of the subject area and some contemplation of its past and future’. We discussed three areas of this ‘not‐yet‐established discipline’: practice, education and research. In this follow‐up paper, we forgo our convention of ISJ editors not publishing in the Journal. We examine the issues raised in the first paper and consider what has happened in the intervening years as charted in the ISJ. The overview is necessarily selective, probably Anglocentric (with, perhaps, a slight Francophile tinge), sometimes downright opinionated, as well as over‐estimating, perhaps, the contribution of one particular IS journal.     

Frequency domain identification of continuous-time output error models, Part I: Uniformly sampled data and frequency function approximation

This paper treats several aspects relevant to identification of continuous-time output error (OE) models based on sampled data. The exact method for doing this is well known both for data given in the time and frequency domains. This approach becomes somewhat complex, especially for non-uniformly sampled data. We study various ways to approximate the exact method for reasonably fast sampling. While an objective is to gain insights into the non-uniform sampling case, this paper only gives explicit results for uniform sampling.     

Nonlinear stochastic passivity,feedback equivalence and global stabilization

This paper addresses several important issues including stochastic passivity, feedback equivalence and global stabilization for a class of nonlinear stochastic systems. Based on a nonlinear stochastic Kalman–Yacubovitch–Popov (KYP) lemma, we investigate the relationship between a stochastic passive system and the corresponding zero‐output system. Different from the deterministic case, it is shown for the first time that feedback equivalence to a stochastic passive system requires a strong minimum‐phase condition, not the minimum‐phase one. Following the stochastic passivity theory, global stabilization results are established for a class of nonlinear stochastic systems with relative degree 1≤r<n. An example is presented to illustrate the effectiveness of our results. Copyright © 2011 John Wiley & Sons, Ltd.     

非线性广义系统的右可逆性

研究了广义非线性系统的右可逆性,给出构造性的求逆算法以克服以往结果中需求解 非线性方程组的困难,从而使得求逆算法对任意足够光滑的非线性广义系统皆为可行.