一种新的混沌伪随机序列生成方法*

针对单混沌系统因计算机有限精度效应产生的混沌退化问题,提出了一种多级混沌映射交替变参数的伪随机序列产生方法。该方法基于一维Logistic映射和二维Henon映射,用交错变参的Logistic映射的混沌迭代值的汉明重量来控制Henon映射输出的混沌迭代分量。生成序列通过仿真表明,符合Golomb三个随机性公设要求及局部随机性统计检验要求,可作为密钥流序列应用到加密体制中。     

基于时空混沌的伪随机序列发生器设计与分析

提出了一种基于耦合帐篷映像格子模型的改进型时空混沌模型,基于此模型设计了一种快速产生多维混沌伪随机序列的伪随机序列发生器。改进的耦合帐篷映像格子模型继承了耦合帐篷映像格子系统在空间上的并行迭代特征和时间上的耦合扩散机理,格点间采用猫映射作为耦合方式,使不同序列之间的互信息趋近于零。基于此模型设计的伪随机序列发生器能快速并行产生多维混沌伪随机序列,多维序列具有均匀分布及相互独立两个特征,从而克服了混沌伪随机序列发生器设计中存在的根本性缺陷。     

一类数字混沌系统的有限精度实现

1 引言混沌现象作为一种类随机现象在20世纪60年代首先被气象学家Lorenz发现,此后用非线性差分方程映射产生的混沌数字序列在物理学、密码学以及信息安全等领域的应用都有大量报导,混沌的应用研究已受到广大学者的重视。混沌由于对初始条件的极端敏感性而具有高度的随机性,可作为产生密钥流的伪随机序列发生器,优点是统计性能好、实现简单且码源丰富。理想的混沌系统其状态是无限不重复的,但作工程     

基于线性同余比较器和混沌系统的伪随机序列生成方法

本文基于线性同余原理,设计一种线性同余比较器。该同余比较器将两个独立的线性同余生成器结合起来,用一个比较器来控制输出。将输出序列作为扰动信号,以异或函数叠加到混沌轨道来改善混沌系统生成序列的随机性。分析攻击者通过线性同余比较器生成序列来破解种子密钥的计算复杂度,及加入随机扰动后的混沌序列的平衡度、相关性及初值敏感性,结果表明,计算复杂度是呈指数幂增长的,线性同余比较器生成序列具有前向和后向不可预测性,并且该密钥流生成器具有较大的密钥空间,可以生成具有良好随机性的序列,可以有效地克服混沌序列在有限精度实现时出现的短周期问题。     

计算机迭代下混沌序列的周期研究

研究了计算机迭代下基于浮点格式的混沌序列周期及其分布规律。通过构造与标准浮点格式匹配的非标准浮点格式,统计测算了六种常见混沌系统在不同浮点精度下退化的混沌序列周期及其分布,采用线性拟合方法获得了混沌序列周期随计算精度变化的分布关系,纠正了多年来基于定点格式的相应分布关系,为后续的混沌抗退化机制研究提供了一个合理的可用于实验测试的参考标准,也表明对于混沌序列而言,基于定点格式的结论不能简单随意推广到浮点格式。     

混沌伪随机序列发生器的FPGA设计与实现

基于简化Lorenz系统,提出混沌伪随机序列发生器的一种设计方法。根据IEEE-754浮点运算标准,按照模块化设计理念,设计混沌方程所需的浮点运算模块,并在FPGA(Field Programmable Gate Array)上实现了简化Lorenz混沌系统。设计混沌伪随机序列量化算法,对生成的混沌伪随机序列进行复杂度分析。分析结果表明,量化算法显著提高了序列复杂度。使用NIST标准进行伪随机序列性能测试,测试结果表明,序列具有良好的随机特性,可直接用于实际加密应用。为连续混沌系统FPGA实现和混沌伪随机序列在信息安全中的应用奠定了基础。     

基于混沌神经网络的伪随机序列性能分析

伪随机序列在保密通信、航空航天、测距、密码学、自动控制等领域具有重要作用。本文结合神经网络和混沌映射的特点，提出了一种基于混沌神经网络和混沌映射混沌伪随机序列的设计方法，该方法可以克服有限精度效应对混沌系统的影响。从而改善混沌序列特性，用理论与计算机仿真实验相结合的方法对混沌序列的随机性、平衡性、相关性和线性复杂度等特性进行了系统的分析。分析结果表明，基于混沌神经网络和混沌映射的混沌伪随机序列具有十分理想的随机特性和相关特性，为在低成本下得到比较实用的序列密码提供了一种新的思路。     

混沌伪随机序列发生器设计与分析

对区间数目参数化分段线性混沌映射（SNP-PLCM）的密码学特性进行详细分析,并以此为基础,提出了一种基于区间数目参数化分段线性混沌映射的伪随机序列发生器。该发生器同时利用控制参数扰动策略和输出序列扰动策略避免数字化混沌系统的动力学特性退化。理论分析和仿真实验结果表明,该算法产生的伪随机序列具有理想的性能。     

混沌伪随机序列复杂性的一种量度方法

基于序列生成过程及特征序列等概念,定义了序列的原生系数来度量混沌伪随机序列的复杂性。仿真结果表明这种量度方法十分有效。利用分岔图和近似熵论证了新量度方法的优点,相对于近似熵,原生系数更能有效地反映序列复杂度。     

基于混沌系统的伪随机序列生成方法

给出了一种循环迭代结构的伪随机序列生成方法。选择函数根据LFSR的计算结果进行取值,确定当前迭代计算使用的混沌系统,通过迭代计算产生相应的混沌序列,然后将生成的混沌序列进行相应的数制转换,将得到的二进制值序列作为产生的伪随机序列输出,同时将其作为反馈值与LFSR的反馈值进行相应的运算,运算结果作为LFSR的最终反馈值,实现对LFSR生成序列的随机扰动。通过实验对生成的伪随机序列进行了分析,结果表明,产生的序列具有良好的随机性和安全性。     

时空混沌二值化方法研究

针对耦合映像格子模型产生的时空混沌序列的特点,在符号函数二值化法的基础上,给出了一种新的二值化方法。随机性能和相关性检验的结果表明按这种方法得到的二值序列具有优良的伪随机性能及相关特性,说明提出的方法是有效的,而且简单实用。     

Intelligent finite element mesh generation

A knowledge-based and automatic finite element mesh generator (INTELMESH) for two-dimensional linear elasticity problems is presented. Unlike other approaches, the proposed technique incorporates the information about the object geometry as well as the boundary and loading conditions to generate an a priori finite element mesh which is more refined around the critical regions of the problem domain. INTELMESH uses a blackboard architecture expert system and the new concept of substracting to locate the critical regions in the domain and to assign priority and mesh size to them. This involves the decomposition of the original structure into substructures (or primitives) for which an initial and approximate analysis can be performed by using analytical solutions and heuristics. It then uses the concept of wave propagation to generate graded nodes in the whole domain with proper density distribution. INTELMESH is fully automatic and allows the user to define the problem domain with minimum amount of input such as object geometry and boundary and loading conditions. Once nodes have been generated for the entire domain, they are automatically connected to form well-shaped triangular elements ensuring the Delaunay property. Several examples are presented and discussed. When incorporated into and compared with the traditional approach to the adaptive finite element analysis, it is expected that the proposed approach, which starts the process with near optimal initial meshes, will be more accurate and efficient.     

Automatic generation of finite element meshes

This paper describes a new algorithm for the automatic generation of finite element meshes of arbitrary multiply connected domains. The strategy is based upon the construction of a mapping from the generated mesh into a regular one. The scheme is designed for maximum flexibility and is able to generate meshes of triangular or quadrilateral curved elements. Several examples are presented to illustrate the applicability of the algorithm.     

Semantics of roundoff error propagation in finite precision calculations

We introduce a concrete semantics for floating-point operations which describes the propagation of roundoff errors throughout a calculation. This semantics is used to assert the correctness of a static analysis which can be straightforwardly derived from it. In our model, every elementary operation introduces a new first order error term, which is later propagated and combined with other error terms, yielding higher order error terms. The semantics is parameterized by the maximal order of error to be examined and verifies whether higher order errors actually are negligible. We consider also coarser semantics computing the contribution, to the final error, of the errors due to some intermediate computations. As a result, we obtain a family of semantics and we show that the less precise ones are abstractions of the more precise ones.     

扫掠法有限元网格生成方法

为了提高有限元网格的生成质量,扫掠法生成六面体网格过程中内部节点定位成为关键一步,在研究复杂扫掠体六面体有限元网格生成算法过程中,提出了一种基于扫掠法的六面体网格生成算法,算法利用源曲面已经划分好的网格和连接曲面的结构化网格,用仿射映射逐层投影,生成目标曲面,提出基于Roca算法的内部节点定位的新算法,运用由外向内推进的波前法思想,生成全部的六面体网格。通过实例表明,该算法快速,稳定,可靠,可处理大量复杂2.5维实体六面体网格生成问题。     

Uniform finite generation of compact Lie groups

Consider a compact connected Lie group G and the corresponding Lie algebra . Let {X₁,…,X_m} be a set of generators for the Lie algebra . We prove that G is uniformly finitely generated by {X₁,…,X_m}. This means that every element KG can be expressed as K=e^Xt₁e^Xt₂···e^Xt_l, where the indeterminates X are in the set {X₁,…,X_m}, , and the number l is uniformly bounded. This extends a previous result by F. Lowenthal in that we do not require the connected one dimensional Lie subgroups corresponding to the X_i, i=1,…,m, to be compact. We link the results to the existence of universal logic gates in quantum computing and discuss the impact on bang bang control algorithms for quantum mechanical systems.     

Automatic mesh generation for finite element analysis

The finite element analysis in engineering applications comprises three phases: domain discretization, equation solving and error analysis. The domain discretization or mesh generation is the pre-processing phase which plays an important role in the achievement of accurate solutions. In this paper, the improvement of one particularly promising technique for generating two-dimensional meshes is presented. Our technique shows advantages and efficiency over some currently available mesh generators.     

A high precision triangular laminated anisotropic cylindrical shell finite element

The stiffness matrix for a high precision triangular laminated anisotropic cylindrical shell finite element has been formulated and coded into a composite structural analysis program. The versatility of the element's formulation enables its use in the analysis of multilayered composite plate and cylindrical shell type structures taking into account actual lamination parameters. The example applications presented demonstrated that accurate predictions of stresses as well as displacements are obtained with modest number of elements.     

一种高精度超声波测距系统研究

介绍了一种以单片机AT89S52为核心,同时用74LS04驱动超声波发射探头,用CX20106A对接收信号进行放大、滤波、检波并输出负脉冲的低成本、高精度超声波测距系统的硬件和软件设计方法。实验证明,这套超声波测距系统软硬件设计合理、抗干扰能力强、实时性好。