Three-Dimensional Multi-mesh Material Point Method for Solving Collision Problems

A new multi-mesh contact algorithm for three-dimensional material point method is presented. The contact algorithm faithfully recovers the opposite acting forces between colliding bodies. Collision procedures between regular bodies and/or rigid bodies are treated within the same framework. Multi-value of momentum and mass are defined on every node to describe the contact/sliding/separation procedure. Both normal and tangential velocities of each particle at the contact surface are calculated in respective individual mesh. A Coulomb friction is applied to describe the sliding or slipping between the contacting bodies. The efficiency of the contact algorithm is linearly related to the number of the contacting bodies because the overlapped nodes are labeled by sweeping the material particles of all bodies when the nodal momentum and mass are formed at every time step. Numerical simulation shows that our contact algorithm possesses high accuracy and low numerical energy dissipation, which is very important for solving collision problems.     

Method for Solving Physical Problems Described by Linear Differential Equations

Russian Physics Journal - A method for solving physical problems is suggested in which the general solution of a differential equation in partial derivatives is written in the form of decomposition...     

基于验前试验信息熵的测试性验证试验方案

产品在研制阶段存在大量的试验数据,为有效利用验前数据,降低测试性验证试验样本量,提出一种基于验前试验信息熵的测试性验证试验方案。该方案利用信息熵来度量研制阶段多次验前试验数据对测试性验证试验所起的作用,依据平均互信息熵和信息总量相等的原则,将多次验前试验数据等效成一次成败型数据。在此基础上,通过相容性检验方法确定验前数据与试验数据的相容性水平,并以Beta分布为验前分布,利用加权混合贝叶斯理论建立混合验后分布,之后,基于贝叶斯平均风险理论求解满足双方风险要求的试验方案。最后,以某型雷达发射分机为例,对其进行测试性验证试验研究,研究结果验证了该方案的有效性。     

基于加权暗通道的图像去雾方法

传统基于暗通道图像去雾中仅考虑初始透射图对于透射图优化的影响,而未充分考虑深度信息对于透射图优化贡献不同的特点,造成去雾结果在深度不连续处出现"晕"且离视点较远区域的去雾效果有明显下降.针对上述问题,本文提出一种基于边缘特征的加权暗通道先验去雾算法.该方法根据边缘特征的位置估计深度信息的连续性,将边缘点及非边缘点赋予不同权值,对加权透射图优化求解.仿真实验表明,新的去雾算法在恢复图像细节的基础上能够有效抑制"晕"的产生,证实了本文方法的可行性和有效性.     

Mie散射激光雷达回波信号小波去噪方法

针对强背景光下,Mie散射激光雷达回波信号所含噪声的特点,提出小波滤波消噪方法.该方法通过小波变换分离出背景光的直流部分,并利用小波软阈值消除来自背景光的白噪声和探测系统的电噪声.为了验证该方法的有效性,提取并反演了Mie散射激光雷达系统实际探测得到的大气回波信号.反演结果显示有效探测距离从2.5km提高到5km,表明该方法能够在白天背景下有效降低Mie散射激光雷达回波信号中的电噪声和背景光的噪声污染.     

A Hybrid Method of Solving the Electromagnetic Inverse Scattering Problem in Lossy Medium

A hybrid method of solving the electromagnetic inverse scattering problem in a lossy medium is proposed. The gradient search method is first used to determine the spatial distribution of the target, then the Monte Carlo method is selected to calculate the conductivity and permittivity of the scatterer. The results of numerical experiments verify that the hybrid method of combining the two ways is high-precision, efficient, and suited to global optimization.     

Method for Solving Nonstationary Electrodynamic Problems in Dielectric Media with Time Dispersion

Radiophysics and Quantum Electronics - We consider three-dimensional singular integral equations with time delay that describe three-dimensional problems of interaction of a nonstationary...     

用基于厚度估计的卷积算法校正X线图像散射的方法

在数字X线摄影中,散射-眩光造成了图像对比度的下降,为了提高数字X线图像的质量,本方法使用曝光参数和图像灰阶值对图像中的每个像素确定等价的有机玻璃厚度,然后在像素-像素的基础上使用厚度信息估计散射-眩光强度。这里我们把60kV和80kV两种参考状态进行线性组合求校正系数,避免了片面性。为了测试本方法估计散射-眩光强度的能力,把它应用在对志愿者胸部所拍摄的图像中,并获得了一定的结果。本方法为解决数字X线图像中的散射校正问题提供了一种有效的手段。     

A Noteworthy Trap in Using the EDC Method for Solving Dielectric Waveguide Problems

EDC method is probably the simplest method to obtain a good approximation for the propagation constant of a dielectric waveguide. It is well know that there are two ways to perform the EDC procedure: one is to treat the LSE mode first then the LSM mode and the other is just reverse. It is true that the difference between the results got from the two ways is usually rather small and thus both of them are good approximations. In this paper, we show that in some cases the two ways will lead to much different results; one is still a good approximation while the other is completely unacceptable. The theoretical analysis tells us that if performing the LSM mode first then with the LSE mode will usually get a good result.     

有耗半空间上方导体目标电磁散射的多层快速多极子算法

提出基于高阶拟合的多层快速多极子算法,用于分析有耗半空间上方导体目标的电磁散射.采用高阶拟合方法将远区相互作用单元的半空间空域格林函数用级数表示,对高阶拟合项作加法定理展开,进而应用多层快速多极子算法.该方法具有分组小,内存需求低,易于实现的优点.用数值算例验证其正确性与有效性.     

A Boundary Meshless Method for Solving Heat Transfer Problems Using the Fourier Transform

Fourier transform is applied to remove the time-dependent variable in the diffusion equation. Under non-harmonic initial conditions this gives rise to a non-homogeneous Helmholtz equation, which is solved by the method of fundamental solutions and the method of particular solutions. The particular solution of Helmholtz equation is available as shown in [4, 15]. The approximate solution in frequency domain is then inverted numerically using the inverse Fourier transform algorithm. Complex frequencies are used in order to avoid aliasing phenomena and to allow the computation of the static response. Two numerical examples are given to illustrate the effectiveness of the proposed approach for solving 2-D diffusion equations.     

The Method of Fundamental Solutions for Solving Exterior Axisymmetric Helmholtz Problems with High Wave-Number

In this paper, we investigate the method of fundamental solutions (MFS) for solving exterior Helmholtz problems with high wave-number in axisymmetric domains. Since the coefficient matrix in the linear system resulting from the MFS approximation has a block circulant structure, it can be solved by the matrix decomposition algorithm and fast Fourier transform for the fast computation of large-scale problems and meanwhile saving computer memory space. Several numerical examples are provided to demonstrate its applicability and efficacy in two and three dimensional domains.     

大角度蚀刻衍射光栅的模拟

研究了平面波导密集波分复用器件中很有发展潜力的蚀刻衍射光栅(EDG).小角度范围光栅的模拟通常采用高斯近似的输入光场,由于近轴的高斯光场接近实际光场,所以模拟结果很准确.但这种方法应用于大角度范围的光栅则有偏差.本文提出了大角度蚀刻衍射光栅的模拟方法,分析了这种偏差并给出了模拟结果.事实上这种方法也适合于实际任意输入光场的模拟.     

基于表面光散射法的聚乙二醇水溶液表面张力实验研究

基于表面波散射原理,本文研制了表面光散射法表面张力实验系统。利用标准参考物质纯水和乙醇对实验系统的可靠性进行了检验,并标定了散射角度。结果表明:新系统测量的两种物质的表面张力实验结果与标准数据的偏差为0.1mN·m~(-1),散射角度约为0.2°。利用新的表面光散射法表面张力实验系统,对质量分数为4%~16%的PEG1000、PEG2000、PEG4000、PEG6000、PEG8000水溶液的表面张力进行了实验研究,结果表明:PEG水溶液的表面张力随着PEG质量分数的增大有减小趋势,且PEG水溶液的表面张力与PEG本身的聚合度无关;PEG4000和PEG6000水溶液具有较大的表面张力,可以作为潜在的诱导蛋白质结晶的沉淀剂。     

光学扩散特征的生鲜肉细菌总数的无损检测方法

细菌总数是生鲜肉的最主要安全参数之一,肉品的光学扩散特征反映其细菌总数。对高光谱扩散数据利用不同的拟合算法处理与分析,并比对生鲜猪肉细菌总数建模的相关性差异,确定了用于最终建模的最佳扩散特征参数,为后续的装置开发提供建模依据。冰箱调至4℃恒温,在里面放置63个分割好的猪肉样品,每天间隔固定时间从里面随机取出4~5块样品,获取猪肉表面的400~1 100nm波长范围内高光谱散射图像,从高光谱图像中提取猪肉的扩散光谱曲线,利用Lorentz函数和Gompertz函数以及修正后的函数,拟合处理与分析扩散数据,拟合后的不同参数可以代表样品的特征光谱,细菌总数的标准值用平板计数法获得,然后单独用各单个参数、多个参数结合的方式,多元线性回归的统计方法,与细菌总数分别建立模型。实验结果表明,Lorentz三参数结合,Lorentz四参数结合,Gompertz四参数拟合的模型相关系数较高,其校正集和预测集相关系数分别为0.93,0.96,0.96和0.90,0.90,0.92,标准偏差分别为0.47,0.44,0.39和0.56,0.46,0.42,其中,相关性最好的是Gompertz四参数结合,在装置的开发中可以优选相关性和稳定性最好的模型导入装置系统中。     

基于表面生成法的粗糙基底上半透明涂层的光散射特性

针对光在半透明涂层和粗糙基底构成的两层粗糙面的散射过程,采用表面生成法,考虑入射遮蔽以及多次散射效应,构建表面散射的蒙特卡罗模型,得到粗糙基底上半透明涂层的反射光的能量分布,研究涂层厚度、表面粗糙度、入射光波长等对双向反射分布函数(Bidirectional Reflectance Distribution Function,BRDF)的影响.结果表明,BRDF受表面的粗糙程度影响较大,其峰值随表面均方根斜率的增加线性递减;半透明涂层厚度影响BRDF峰值的大小,厚度为十分之一波长时,BRDF达最小值;近红外光入射时镜反射方向附近BRDF的局部分布曲线相对于可见光入射时有展宽趋势,且方向半球反射率相对于可见光入射时更大.     

结合光场深度估计和大气散射模型的图像去雾方法

目前大部分基于物理模型的图像去雾算法存在复原图像色彩失真和天空边界区域出现光晕效应的问题.为了解决这些问题,本文提出了一种将光场深度计算与大气散射模型相结合的图像去雾方法.该方法通过光场极平面图像计算得到场景深度,将场景深度信息计算所得的透射率与暗通道透射率融合得到最终透射率.同时利用场景深度对天空边界进行判定,单独对天空区域进行处理.在合成雾天图像和真实雾天图像上的实验结果表明,与现有的单幅图像去雾算法相比,本文提出的方法在峰值信噪比以及结构相似性上均有提升.同时对去雾之后的图像的色彩保真度以及光晕效应的抑制方面都取得了较好的结果 .     

基于共振瑞利散射法的人血清蛋白浓度的研究

文章针对人标准血清总蛋白浓度的定量测定, 建立了以四羧基金属酞菁锌为光谱探针检测蛋白质的共振光散射的新方法。该方法的实质是将人标准血清总蛋白和酞菁锌溶液混合, 当光源照射到样品池中的混合液时, 将激发出强烈的共振瑞利散射荧光信号, 根据信号强度的强弱, 计算血清蛋白浓度的大小。自行设计的测试装置采用了薄壁试管的样品皿, 减小了激光光波穿过溶液时的光程, 可得到更强的探测信号。测试结果表明: 根据数字示波器显示的探测器信号, 可得出电压的峰峰值, 体现了荧光的大小, 从而可以进一步计算出血清蛋白的浓度。     

基于Mie散射理论的紫外光散射相函数研究

本文根据Mie散射理论,研究了四种典型大气条件下紫外光在大气传输中的散射相函数,并与常用的用于非紫外光散射相函数的三类经验公式进行了比较。研究结果表明:三种经验公式用于紫外光大气传输模拟存在一定的局限性。     

LCOS大屏幕薄型背投电视广角投影物镜的设计

为了满足67英寸大屏幕LCOS背投电视的需要,设计了一款广角投影物镜.此广角投影镜头采用远心反远距结构,通过合理选用非球面和光学材料,设计的镜头具有视场大、投影距离短、工作距离长、相对孔径大、无渐晕、辐照度均匀等优点.在LCOS芯片奈奎斯特空间频率处的调制传递函数值高于0.5,色差仅约1/4像元,畸变低于5‰.