基于细观方向平均模型的颗粒材料宏观Cosserat连续体本构关系

提出了基于细观微-方向模型（Micro—Directional Model）的宏观Cosserat连续体本构关系。在细观尺度上考虑颗粒旋转自由度及接触力矩,微结构的影响通过接触分布函数体现。给出均质各向同性Cosserat连续体模型弹性常数的细观参数表达式,并建议了二维情况下内尺度参数的细观力学表达式。对颗粒材料宏观行...     

The two-dimensional beta binomial distribution

We introduce the two-dimensional beta binomial distribution to describe correlated counts data. Properties of the distribution are explored and in an example the distribution is used to describe a set of orthodontic data.     

细菌模型的非协调有限元分析

将非协调元应用于描述细菌传播的反应扩散方程组的初边值问题.借助单元的一些特性和非协调误差估计技巧,分别在半离散和全离散有限元格式下,研究了其数值解与精确解的误差估计,得到了最优的误差估计以及超逼近结果.     

随机利率下相依索赔的离散风险模型的分红问题

本文考虑随机利率下相依索赔的离散风险模型,模型中假设每次主索赔可能引起一次副索赔,而每次副索赔有可能延迟发生,当资产盈余达到边界b时,公司给投保者分发一定红利;考虑预期红利的现值时,假设利率服从一有限状态空间的马尔可夫链,我们得到了破产前预期累积分红所满足的差分方程及特殊索赔情形下预期累积分红现值的精确解析式,并结合实例进行了数值模拟.     

New second order nonconforming triangular element for planar elasticity problems

In the use of finite element methods to the planar elasticity problems,one diffculty is to overcome locking when elasticity constant λ→∞.In the case of traction boundary condition,another diffculty is to make the discrete Korn’s second inequality valid.In this paper,a triangular element is presented.We prove that this element is locking-free,the discrete Korn’s second inequality holds and the convergence order is two.     

基于时频分析的成像小弱运动目标检测方法

 针对传统空时域滤波器难以剔除杂波(尤其是杂波边缘)的缺点,提出了一种基于时频分析的弱小运动目标检测方法。理论分析表明,目标经过处的时频是一个小波包,波包的幅度与目标的幅度一致,而宽度则与目标速度成反比关系;杂波边缘经过处的时频则是一个上坡或者下坡。采用两级滤波方法检测运动目标,即首先采用恒虚警率准则过滤噪声,然后再利用目标出现处存在的波包,分别统计主瓣与旁瓣能量及其能量比,去除杂波,检测出运动目标。云背景下弱小目标检测试验结果证明了该方法的有效性。     

Sato-theoretic construction of solutions to noncommutative integrable systems

Solutions to noncommutative version of KP and discrete KP equations are given by Sato-theoretic construction, which utilizes operator factorization. Noncommutative generalization of discrete KdV and two-dimensional Toda equations are also given.     

二维抛物线离散映射的动力学研究

由两个一维抛物线离散映射作推广并非线性耦合,实现了一个新的二维抛物线离散映射.利用不动点稳定性分析和映射分岔分析,研究了所提出的二维离散映射的复杂动力学行为及其吸引子的演变过程,阐述了它所特有的共存分岔模式和快慢周期振荡效应等动力学特性.研究结果表明:二维抛物线离散映射具有动力学特性调节和动态幅度调节的两个功能不同的控制参数,存在Hopf分岔、分岔模式共存、锁频和周期振荡快慢效应等非线性物理现象.并基于微控制器实现的数字电路验证了相应的理论分析和数值仿真结果. 关键词： 二维离散映射 分岔 吸引子 参数     

Theoretical analysis on the structure of Nb‐doped SrBi4Ti4O15

The structure of niobium‐doped SrBi₄Ti₄O₁₅ was calculated by using density function and discrete variation method (DFT–DVM). By comparing the total energy of different doping sites, the total energy is found to be lower when Nb ion was substituted into the Ti site in the upper perovskite layer, which is far from the two bismuth (Bi) ions in the perovskite layer. The bonding strength of Nb (3)‐O increases and the electronic conductivity of the SBT decreases after Nb doping. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Nonequilibrium effects of reactive flow based on gas kinetic theory

How to accurately probe chemically reactive flows with essential thermodynamic nonequilibrium effects is an open issue. Via the Chapman–Enskog analysis, the local nonequilibrium particle velocity distribution function is derived from the gas kinetic theory. It is demonstrated theoretically and numerically that the distribution function depends on the physical quantities and derivatives, and is independent of the chemical reactions directly as the chemical time scale is longer than the molecular relaxation time. Based on the simulation results of the discrete Boltzmann model, the departure between equilibrium and nonequilibrium distribution functions is obtained and analyzed around the detonation wave. In addition, it has been verified for the first time that the kinetic moments calculated by summations of the discrete distribution functions are close to those calculated by integrals of their original forms.