统一混沌系统的混合同步在图像加密中的应用

研究参数已知的统一混沌系统的混合同步现象,在这种同步模式中,系统的一部分状态正相同步,而其它状态反相同步,设计了一个简单的单向线性反馈控制器,提出实现混合同步的充分条件.采用近似熵算法对耦合的混沌同步系统的复杂性研究结果表明,与单一混沌系统相比,本文实现的同步系统具有较高的复杂度.最后,基于该同步系统实现了一个图像加密方案,加密方案采用典型的图像加密框架,混乱阶段采用2D标准映射方案,扩散阶段采用像素的位置信息进行像素值替换,仿真实验结果与安全性分析表明,该算法加密效果良好,安全性较高.     

Ectopic beats in approximate entropy and sample entropy-based HRV assessment

Approximate entropy (ApEn) and sample entropy (SampEn) are the promising techniques for extracting complex characteristics of cardiovascular variability. Ectopic beats, originating from other than the normal site, are the artefacts contributing a serious limitation to heart rate variability (HRV) analysis. The approaches like deletion and interpolation are currently in use to eliminate the bias produced by ectopic beats. In this study, normal R–R interval time series of 10 healthy and 10 acute myocardial infarction (AMI) patients were analysed by inserting artificial ectopic beats. Then the effects of ectopic beats editing by deletion, degree-zero and degree-one interpolation on ApEn and SampEn have been assessed. Ectopic beats addition (even 2%) led to reduced complexity, resulting in decreased ApEn and SampEn of both healthy and AMI patient data. This reduction has been found to be dependent on level of ectopic beats. Editing of ectopic beats by interpolation degree-one method is found to be superior to other methods.     

Approximate controllability of linear retarded systems in Hilbert spaces

The object of this paper is to construct some results on the control problems for retarded functional differential equations of parabolic type with unbounded principal operators in Hilbert spaces. In order to establish relations between controllability of the given equation and observability of the adjoint system, we investigate the equivalent relation for the completeness of generalised eigenspaces of the infinitesimal generators. Finally, when the control space is a finite-dimensional space, a necessary and sufficient condition for the approximate controllability of retarded equations is given by the so-called rank condition.     

Approximate controllability of partial neutral functional differential systems of fractional order with state-dependent delay

We prove the approximate controllability of control systems governed by a class of partial neutral functional differential systems of fractional order with state-dependent delay in an abstract space. Sufficient conditions for approximate controllability of the control systems are established provided the approximate controllability of the corresponding linear control systems. The results are obtained by using the Krasnoselskii–Schaefer type fixed point theorem with the fractional power of operators. An example is provided to illustrate the main results.     

Approximate controllability of nonlinear stochastic impulsive systems with control acting on the nonlinear terms

This paper is concerned with the approximate controllability of the stochastic impulsive system with control acting on the nonlinear terms. In the case that the nonlinear terms are dependent on the control, the control cannot be expressed explicitly and analysed. In this situation, we generate the control sequence by the approximate equations and give the properties of the control sequence and the driven solution sets. Some discussions on the assumptions are given to impose on the system. The Hausdorff measure is adopted to relax the requirement of the compactness condition. It is also shown that under some sufficient conditions the stochastic impulsive system is approximately controllable without the requirement of the controllability of the associated linear system. The results of this paper can be degraded into special cases and coincide with some existing ones.     

无线传感器网络中基于模型拟合的可信近似查询处理算法

无线传感器网络的一个重要应用是可信地查询网络中所有节点的监测数据.目前,多数研究主要集中在如何利用节点之间的时空相关性,节省能量地查询感知数据.但是这些方法的查询结果不能满足某些应用对数据的高可信要求,也不能适用于节点之间不存在空间相关性或空间相关性不稳定的情况.针对这一问题,提出了基于模型拟合的可信近似查询处理方法.该方法在感知数据集合上寻找具有最小数据传输比的拟合模型,通过传输模型及其参数来代替传输实际的监测数据.理论分析和实验结果证明,基于模型拟合的可信近似查询处理方法不仅能够节省大量能源而且能够返回满足用户精度要求的可信查询结果.     

一种改进的语音端点检测方法研究

为了提高语音信号端点检测的准确率,提出了改进的端点检测方法。该方法在传统基于能量和过零率的端点检测方法基础上,加入第三道门限——近似熵,对信号进行三级门限检测。仿真实验表明,该方法比传统方法更有效、更优越．能够比较准确的检测语音信号。     

分数阶单自由度间隙振子的受迫振动

研究了含有分数阶微分项的单自由度间隙振子的受迫振动,利用KBM渐近法获得了系统的近似解析解。分析了分段线性系统的主共振,得到了分数阶阶次在0～2时分数阶项的统一表达式;发现分数阶微分项在分段系统中以等效线性阻尼和等效线性刚度的形式影响着系统的动力学特性,而间隙以等效非线性刚度的形式影响着系统的动力学特性。获得了主共振幅频响应的表达式,并得到了系统的稳定性条件;比较了系统主共振幅频响应的近似解析解和数值解,发现两者符合程度较高,验证了近似解析解的正确性;详细分析了分数阶项和间隙对系统主共振幅频响应的影响。研究表明KBM渐近法是分析分数阶分段光滑系统动力学的有效方法。     

光纤光阱力计算的近似条件及误差分析

光纤光镊技术利用光纤出射的光束捕获和操控粒子,其飞速发展对光阱力的理论研究提出了更高的要求。采用射线光学模型对光纤光阱中的米氏微球所受到的光阱力进行数值模拟,讨论了光阱力计算中可采用的近似条件及其应用范围,比较了在近似条件下与直接计算情况下结果的差异,分析了微球与光纤端面之间的距离对近似计算的影响。理论分析和模拟计算表明,当微球与光纤端面之间的距离大于临界值时,可对计算模型中光束在微球表面的入射角、入射点的方位角等角度参量作近似处理,该结论为简化光纤光阱力计算提供了理论依据。     

基于稀疏重构的跳频信号时频分析方法

针对现有时频分析方法存在噪声抑制能力弱、时频聚集性不强的缺点,提出了一种基于稀疏重构的跳频信号时频分析方法来获取清晰的、高聚集度的时频图。首先根据惩罚函数的思想建立了跳频信号无约束的稀疏重构模型;然后理论分析了罚函数因子的取值标准;最后用近似l0范数算法求解得出跳频信号的时频图。仿真结果表明该算法能够有效地获取跳频信号的时频图。