基于分层动态规划的红外弱小目标检测

为了检测低信噪比下的红外弱小目标,本文将方向中值滤波与分层动态规划算法相结合进行检测前跟踪。利用背景杂波在局部空间上的相关性,提取目标在四个方向的中值进行自适应加权滤波,抑制结构性杂波分量,改善信噪比。针对分割后的备选目标点,为了减少跟踪检测的计算量,根据真实目标运动轨迹的连续性与光滑性,利用分层动态规划算法进行多帧检测,进而对多层检测结果进行配准并做出决策。仿真实验表明方向中值滤波有效的提高了信噪比,分层动态规划算法进一步降低了虚警概率,同时大大提升了计算速度。     

基于自适应能量聚集和动态规划的体视算法

为了得到准确、稠密的视差图,提出了一种利用自适应能量聚集和动态规划的立体匹配算法.该算法首先根据颜色相似性和空间距离计算窗口内所有像素的视差支持权值,并利用自适应能量聚集方法得到视差空间图;然后引入一种加强顺序约束和遮挡约束的动态规划的方法,求得参考图像中所有扫描线上的最优路径并处理遮挡问题;最后使用一些国际标准立体图像进行了实验.结果表明,与传统的动态规划算法相比,本算法可以减少典型的条纹状瑕眦,同时保持目标边缘的清晰,在视差不连续区域和大的无纹理区域均能取得很好的效果.     

基于视差区域分割的动态规划立体匹配算法改进

基于动态规划的立体匹配算法在较低的硬件条件下,也可以满足实时性的要求,因此,可以在基于立体视觉的机器人导航避障系统中应用。但传统动态规划算法存在匹配精度不高、易出现分散畸变点等问题,因此,论文对动态规划算法初始匹配代价求取、路径寻径及回溯等加以改进。在初始代价求取阶段,提出了一种变窗口能量聚集法,通过获取场景的视差变化区域与视差连续区域的位置信息,从而使像素点在能量聚合时能够根据视差变化自适应地调整聚合窗口的大小,使能量聚合方式更加合理,提高了初始视差的准确性;在路径寻径及回溯阶段,使用多路径寻径回溯法,保留更多的可靠点,减少了误匹配现象的发生。因此,提高了立体匹配的匹配精度,并具有较好的实时性。     

基于卡尔曼滤波的光纤压力信号解调方法

针对光纤法布里-珀罗传感系统长时间运行时,数据采集等电路部分热噪声过大,造成压力信号相位解调误差过大的问题,建立了基于卡尔曼滤波算法的压力解调算法模型,使用卡尔曼滤波算法对光纤压力信号进行去噪处理.经过计算,当信噪比为15 dB的情况下相位解调误差低于0.1 rad,标准差缩小1 000倍,不同信噪比下,滤波后的相位解调标准差稳定在0.012~0.026 rad之间,绝对相位拟合直线的截距稳定在75.8~76.7.实验结果表明,经过降噪滤波处理的信号解调出的结果精度明显改善,提高了系统在噪声条件下的解调精度和整体稳定性.     

基于F-P标准具和Music算法的FBG动态应变传感系统

提出了基于可调光纤环形激光器结构,并采用F-P标准具解调的光纤布拉格光栅(FBG)动态应变传感系统,具有高达60 dB的光学信噪比.F-P标准具用来作为一个边缘滤波器探测FBG波长的漂移,这样的解调方式具有稳定性高的优点.为了提高动态应变测量系统的分辨率,采用了Music算法进行频谱分析.实验结果显示,在700Hz时的动态应变分辨率达到了0.1με/Hz~(1/2),是传统FFT算法的10倍.     

用高阶累积量投影法检测红外弱小目标

为检测弱小红外运动目标,提出了一种基于高阶累积量投影的检测算法.红外图像序列经背景抑制后,首先计算时域数据的归一化三阶累积量,并将其投影到二维空间,然后在二维空间内对目标轨迹进行统计判决,以实现目标检测.推导出了目标和噪声在二维投影空间中的分布公式.通过与相关算法对比分析,该算法计算量小,检测率随目标信噪比增长较快.利用实际录制的图像序列进行了仿真实验,成功检测到了信噪比不小于2、像面运动速度为2帧/像素的目标,验证了算法的有效性.     

复杂环境下基于目标指引的RRT*路径规划算法

机器人路径规划算法需应对运动过程中遇到的各种复杂环境。针对快速扩展随机树(RRT)算法规划时间长、产生新节点随机性大、盲目性强的缺点,提出基于目标指引的RRT*路径规划算法。该算法在障碍物和目标点处分别产生虚拟势场,引入引力函数和斥力函数使得生成的随机点具有目标性,随机点朝向目标点方向产生,降低盲目性和随机性;回归策略和动态自适应步长策略减少规划时间和产生冗余点的数量。当环境复杂时,提出带有预测机制的模糊推理策略,以解决机器人在U型陷阱下易产生的局部死锁现象。在动态环境下,提出重规划策略使机器人拥有动态避障能力。最后,在树莓派智能小车上进行了实验测试,结果验证了该算法的有效性。     

认知无线电系统的动态双门限协作能量检测算法

认知无线电系统中,认知用户间协作检测有利于提高频谱检测的准确性。基于OR(或)协作方式和多门限能量检测算法,提出了一种动态双门限协作能量检测算法,并根据认知用户接收到的主用户信噪比确定检测门限。理论分析和仿真结果表明,该算法可以有效提高频谱检测概率,降低系统漏检概率。     

一种改进的稳健高分辨力DOA估计算法

介绍了一种基于最大后验概率准则的约束最优空间处理(Spatial Processing-Optimized and Constrained,SPOC)DOA算法。这种算法将阵列接收到的空间能量近似为来自远场的密集分布的独立信号源发出的信号,在极限情况下,这些点源是连续分布的。算法应用最大后验概率准则,在满足接收信号能量不变的情况下,使得接收到的总功率最小,通过估计每个点源的能量完成对来波方位的估计。算法只针对单快拍数据进行处理,因此避免了目标运动以及环境非平稳性带来的影响。针对算法在低信噪比下不稳定的缺点,使用对角加载技术(diagonal loading)进行了改进,增强了算法的稳健性。使用单个发射换能器和接收水听器进行了水池实验,实验显示DL-SPOC算法相比于MVDR、CBF等算法拥有更高的角度分辨力。     

基于均值移动确定性漂移的改进CONDENSATION人脸跟踪

针对视频序列目标跟踪粒子滤波经典CONDENSATION算法用先验转移概率,即采用一阶或二阶AR模型难以有效进行粒子传播的问题,提出了一种改进的CONDENSATION人脸跟踪算法.首先利用高效的均值移动跟踪器以低廉的计算成本初步进行人脸目标跟踪定位,并用此初步跟踪结果来确定CONDENSATION粒子动态传播模型中的确定性漂移部分,然后只需加入一个较小的随机扩散噪声来完成粒子的传播.由于这样所得的粒子点能较为集中地分布在状态的真实区域附近,因而大大提高了粒子的利用效率.人脸跟踪实验表明,该改进算法的性能明显优于原CONDENSATION方法.     

Dielectric spectroscopy — an analytical tool for monitoring the deterioration due to high energy radiation in ethylene propylene diene terpolymer (EPDM) vulcanizates

This paper demonstrates the use of a dielectric spectroscopy technique for monitoring the high energy radiation ageing and stabilization of ethylene propylene diene terpolymer vulcanizates. The measurement of dielectric constants and dielectric losses in the frequency domain help to quantify the physico-chemical changes in the bulk due to high energy irradiation. It is found that the relaxation time calculated using an empirical approach is exponentially related to the total exposed dose. A quantitative comparison of different antirads with a control vulcanizate has been demonstrated by using parameters defined as relative efficiency indices (REI) and relative stability indices (RSI). Three types of REI parameters are defined and computed from dielectric measurements after irradiation over a period of time at a fixed frequency. These REI values are a good estimate of antirad efficiency for energy scavenging and transient charge scavenging. Two types of RSI parameters are defined and computed from the frequency scans of dielectric properties for a material exposed to various doses of γ irradiation. These RSI values provide a good estimate of the rate and extent of changes in the physico-chemical structure due to irradiation. A third type of RSI, computed from equilibrium swelling measurements, closely matches that obtained from dielectric data. It is concluded that the deterioration is predominantly created by a cross-linking reaction even after the addition of antirads. It is observed that polymeric antirads provide the highest efficiency stability. This revised version was published online in November 2006 with corrections to the Cover Date.     

Stabilized finite elements for time-harmonic waves in incompressible and nearly incompressible elastic solids

The propagation of waves in elastic solids at or near the incompressible limit is of interest in many current and emerging applications. Standard low-order Galerkin finite element discretization struggles with both incompressibility and wave dispersion. Galerkin least squares stabilization is known to improve computational performance of each of these ingredients separately. A novel approach of combined pressure-curl stabilization is presented, facilitating the use of continuous, equal-order interpolation of displacements and pressure. The pressure stabilization parameter is determined by stability considerations, while the curl stabilization parameter is determined by dispersion considerations. The proposed pressure-curl–stabilized scheme provides stable and accurate results on a variety of numerical tests for incompressible and nearly incompressible elastic waves computed with linear elements.     

Mean‐strain eight‐node hexahedron with optimized energy‐sampling stabilization for large‐strain deformation

A method for stabilizing the mean‐strain hexahedron for applications to anisotropic elasticity was described by Krysl (2015). The technique relied on a sampling of the stabilization energy using the mean‐strain quadrature and the full Gaussian integration rule. This combination was shown to guarantee consistency and stability. The stabilization energy was expressed in terms of input parameters of the real material, and the value of the stabilization parameter was fixed in a quasi‐optimal manner by linking the stabilization to the bending behavior of the hexahedral element (Krysl, submitted). Here, the formulation is extended to large‐strain hyperelasticity (as an example, the formulation allows for inelastic behavior to be modeled). The stabilization energy is expressed through a stored‐energy function, and contact with input parameters in the small‐strain regime is made. As for small‐strain elasticity, the stabilization parameter is determined to optimize bending performance. The accuracy and convergence characteristics of the present formulations for both solid and thin‐walled structures (shells) compare favorably with the capabilities of mean‐strain and other high‐performance hexahedral elements described in the open literature and also with a number of successful shell elements. Copyright © 2015 John Wiley & Sons, Ltd.     

A strategy for designing stable nanocrystalline alloys by thermo-kinetic synergy

Aiming to design stable nanocrystalline(NC) materials, so far, it has been proposed to construct nanostructure stability maps in terms of thermodynamic parameters, while kinetic stabilization has seldom been considered, despite the synergy of thermodynamics and kinetics. Consequently, the thermodynamically stabilized NC materials may be easily subjected to grain growth at high temperatures due to the weakly kinetic stabilization. Starting from the thermo-kinetic synergy, a stabilization criterion is proposed as a function of intrinsic solute parameters(e.g. the activation energy for bulk diffusion and the segregation enthalpy), intrinsic solvent parameters(e.g. the intrinsic activation energy for GB migration and the GB energy) and processing parameters(e.g. the grain size, the temperature and the solute concentration). Using first-principles calculations for a series of combinations between fifty-one substitutional alloying atoms as solute atoms and Fe atom as fixed solvent atom, it is shown that the thermal stability neither simply increases with increasing the segregation enthalpy as expected by thermodynamic stabilization, nor monotonically increases with increasing the activation energy for bulk diffusion as described by kinetic stabilization. By combination of thermodynamic and kinetic contributions, the current stabilization criterion evaluates quantitatively the thermal stability, thus permitting convenient comparisons among NC materials involved by various combinations of the solute atoms, the solvent atoms, or the processing conditions. Validity of this thermo-kinetic stabilization criterion has been tested by current experiment results of Fe-Y alloy and previously published data of Fe-Ni, Fe-Cr, Fe-Zr and Fe-Ag alloys,etc., which opens a new window for designing NC materials with sufficiently high thermal stability and sufficiently small grain size.     

纳米粉体在液相中的分散和稳定

从理论上分析了纳米粉体在液相中的分散过程和稳定机理,将获得稳定纳米粉体分散液分为分散和稳定2个过程,重点考虑纳米颗粒的表面自由能对纳米粉体分散的影响以及纳米颗粒之间的相互作用能对分散液稳定所起的作用.在此基础上,研究了提高分散液稳定性的条件和措施.     

Modification of the quadratic 10‐node tetrahedron for thin structures and stiff materials under large‐strain hyperelastic deformation

The concept of energy‐sampling stabilization is used to develop a mean‐strain quadratic 10‐node tetrahedral element for the solution of geometrically nonlinear solid mechanics problems. The development parallels recent developments of a “composite” uniform‐strain 10‐node tetrahedron for applications to linear elasticity and nonlinear deformation. The technique relies on stabilization by energy sampling with a mean‐strain quadrature and proposes to choose the stabilization parameters as a quasi‐optimal solution to a set of linear elastic benchmark problems. The accuracy and convergence characteristics of the present formulation are tested on linear and nonlinear benchmarks and compare favorably with the capabilities of other mean‐strain and high‐performance tetrahedral and hexahedral elements for solids, thin‐walled structures (shells), and nearly incompressible structures.     

Stabilization of the zero-energy modes of under-integrated isoparametric finite elements

The coefficient matrices of isoparametrically distorted finite elements are frequently computed by numerical integration formulas with a lower degree of exactness than required by the degree of the integrand. This may result in a rank deficiency of the element matrices which causes an oscillatory instability in the solution. To avoid this effect the element matrices may be stabilised, i. e. their rank may be raised artificially. A new approach is suggested which approximates exact integration without the computational expense usually connected with it. For this purpose, a new family of integration formulas is introduced which is based on the standard Gauss product formulas extended by derivatives of the integrand. For the stabilization, these derivatives can be approximated very easily. The procedure generates a stabilization matrix which, when added to the under-integrated matrix, produces the correct rank. If e. g. shear locking is a problem, the stabilization matrix may be scaled down. Two- and three-dimensional Lagrange elements in second and fourth order problems and Mindlin plate elements are presented together with the results of computations and numerical experiments.     

Temporal stabilization of the node-based smoothed finite element method and solution bound of linear elastostatics and vibration problems

A stabilization procedure for curing temporal instability of node-based smoothed finite element method (NS-FEM) is proposed for dynamic problems using linear triangular element. A stabilization term is added into the smoothed potential energy functional of the original NS-FEM, consisting of squared-residual of equilibrium equation. A gradient smoothing operation on second order derivatives is applied to relax the requirement of shape function, so that the squared-residual can be evaluated using linear elements. Numerical examples demonstrate that stabilization parameter can “tune” NS-FEM from being “overly soft” to “overly stiff”, so that eigenvalue solutions can be stabilized. Numerical tests provide an empirical value range of stabilization parameter, within which the stabilized NS-FEM can still produce upper bound solutions in strain energy to the exact solution of force-driven elastostatics problems, as well as lower bound natural frequencies for free vibration problems.     

Mean‐strain 10‐node tetrahedron with energy‐sampling stabilization

In this study, a new mean‐strain 10‐node tetrahedral element is developed using energy‐sampling stabilization. The proposed 10‐node tetrahedron is composed of several four‐node linear tetrahedral elements, four tetrahedra in the corners and four tetrahedra that tile the central octahedron in three possible sets of four‐node linear tetrahedra, corresponding to three different choices for the internal diagonal. The assumed strains are calculated from mean ‘basis function gradients.’ The energy‐sampling technique introduced previously for removing zero‐energy modes in the mean‐strain hexahedron is adapted for the present element: the stabilization energy is evaluated on the four‐corner tetrahedra. The proposed element naturally leads to a lumped‐mass matrix and does not have unphysical low‐energy vibration modes. For simplicity, we limit our developments to linear elasticity with compressible and nearly incompressible material. The numerical tests demonstrate that the present element performs well compared with the classical 10‐node tetrahedral elements for shell and plate structures, and nearly incompressible materials. Copyright © 2016 John Wiley & Sons, Ltd.     

A uniform nodal strain tetrahedron with isochoric stabilization

A stabilized node‐based uniform strain tetrahedral element is presented and analyzed for finite deformation elasticity. The element is based on linear interpolation of a classical displacement‐based tetrahedral element formulation but applies nodal averaging of the deformation gradient to improve mechanical behavior, especially in the regime of near‐incompressibility where classical linear tetrahedral elements perform very poorly. This uniform strain approach adopted here exhibits spurious modes as has been previously reported in the literature. We present a new type of stabilization exploiting the circumstance that the instability in the formulation is related to the isochoric strain energy contribution only and we therefore present a stabilization based on an isochoric–volumetric splitting of the stress tensor. We demonstrate that by stabilizing the isochoric energy contributions only, reintroduction of volumetric locking through the stabilization can be avoided. The isochoric–volumetric splitting can be applied for all types of materials with only minor restrictions and leads to a formulation that demonstrates impressive performance in examples provided. Copyright © 2008 John Wiley & Sons, Ltd.