多径衰落信道的分数布朗运动模型

本文旨在将分形理论引入多径衰落信道的研究,从非线性科学的角度出发建立了多径信道的分数布朗运动模型.通过探讨多径信号的增量统计分布、统计自相似性、广义功率谱和分形维数,揭示了多径衰落与分数布朗运动间的内在联系;指出信号的分维是描述无线信道传播特性的重要参数;在分形模型的基础上,对多径信号进行了重构.实验结果表明,无线信道的分数布朗运动模型比传统的随机模型能更有效地刻划和描述多径衰落的行为.     

漫射光自相关测组织微循环血流模型

提出了一种用漫射光自相关方法无损测量组织微循环血流速度的模型 ,理论分析了散射粒子的布朗运动和微循环血流对漫射光自相关函数的影响。理论计算和蒙特卡罗 (MonteCarlo)法模拟结果表明 ,随着微循环血流均方速率的增大 ,特征相关时间呈负指数规律减小     

产生相关时间序列的布朗桥方法及其应用

在对无线信道的仿真分析中,需要构造出具有一定统计特性和相关关系的时间序列。针对电磁波在无线信道中的传播特点,使用布朗桥过程产生相关时间序列,构造出建模相关散射无线信道特征参量的基本随机变量。对布朗桥过程产生时间序列的相关特性进行仿真分析,发现调整布朗桥过程中布朗运动的方差,可以改变该时间序列的相关特性。分别研究了由自由布朗桥过程和有约束布朗桥过程的时间序列产生基本随机变量的统计特性。结果表明,有约束布朗桥过程产生的随机变量的统计特性,与相应的约束条件密切相关;低跳跃次数基本随机变量的概率密度分布,显示出明显的局部偏好性。     

业界快讯

斯坦福大学设计出捕捉纳米粒子的DNA分子陷阱溶液中的微粒由于受到周围液体分子的胡乱冲撞而使科研人员对它们的观察变得非常困难。目前,科学家采用激光手段(如“光镊”)控制这些粒子,但必须将小于200nm的分子附着在更大的微粒上,才能用光镊夹住它们并对其进行研究,结果很可能导致分子变形。斯坦福大学的化学家W.E.Moerner和研究生Adam Cohen介绍了一种捕获装置,能够对抗溶液中5～200nm粒子的布朗运动。这种抗布朗运动电泳(ABEL)陷阱能够捕获水中小到5nm的单个荧光(或荧光标记)粒子。这种方法十分温和,可以在几分钟内抓住并控制单个DN…     

基于分形布朗运动的无线信道研究

介绍了分形布朗运动与无线信道中信号的关系,并运用分形布朗运动模型,基于MATLAB仿真工具,对分形布朗信道下的无线信号功率谱进行仿真分析。结果证明了分数布朗运动建模无线信道的可行性,并表明了对于不同的无线信道,可以利用检测功率方法估计其分形维数。     

基于分数布朗特征的低分辨雷达目标分类

低分辨雷达目标的JEM效应不仅体现在对目标回波的频率调制上,还体现在幅度调制上,以上2种调试特征是互补的关系,综合运用2种调制特征将会改善低分辨雷达对飞机目标的分类与识别能力。分数布朗运动模型是一种可以用来描述自然界中随机分形的统计模型,文中提出将分数布朗运动模型用于反映回波幅度的不规则程度或起伏程度,以及回波幅度起伏的快慢,分别提取回波时域和频域的分数布朗分形维,再采用支持向量机分类器进行分类,很好地将直升机与民航机2类目标区分开来。实测数据表明,综合分类正确率大于85!。     

基于序贯重点采样粒子滤波的分布估计算法

 连续域分布估计算法一般假设数据服从高斯分布,而且大多采用了单峰的概率模型,但是对于一些复杂的优化问题,单峰的高斯分布模型不能有效地描述解在空间的分布.本文提出一种基于序贯重点采样粒子滤波的分布估计算法,采用带权粒子描述优选集样本服从的概率分布并从中采样得到下一代种群,不需要假设样本服从高斯分布,并且算法采用的概率模型是多峰的.仿真实验结果验证了本文方法的正确性和有效性.     

基于泊松过程的半导体激光器空间辐射效应研究

针对始终处于加电状态工作模式的半导体激光器,通过分析单个粒子对器件的辐射过程,将空间辐射效应离散的描述为所有单粒子造成辐射效应的累积。考虑到粒子到达服从泊松过程的特点,建立了半导体激光器空间辐射效应性能退化模型。推导了器件可靠度函数以及平均故障前时间的表达式。对InGaAs多量子阱激光二极管在高轨空间辐射环境中的性能退化过程进行了仿真,得到了器件的光功率退化曲线。结果表明光功率退化量与辐射时间近似成正比例关系。由此提出了同时考虑辐射与退火效应条件下,器件的光功率退化速率,通过拟合得出该速率与空间辐射平均剂量率成正比。获得了半导体激光器的可靠度曲线,进而计算了器件的平均故障前时间。     

PC型HgCdTe探测器的反常效应

在中波和长波PC型HgCdTe红外探测器中发现了与正常光响应规律完全不同的反常效应。文中通过对该效应大量的实验研究,确定了反常效应产生的条件和反常效应的特点。最后,对反常效应产生的机制进行了探讨。此效应的发现为物质结构更深层次的认识以及激光与物质相互作用新机制的探究和应用提供了新的线索和实验支持。     

双光镊测量胶体微粒间相互作用势

分析了两个存在相互作用势的胶体微粒的布朗运动,讨论了通过微粒布朗运动的显微观测来测量胶体微粒间相互作用势的实验方法。将双光镊系统与同步斩光器相结合,建立了相应的测量系统。对1μm直径的聚苯乙烯球悬浮液中两个小球之间的静电相互作用势进行了实验研究。实验结果和DLVO(Derjagin-Landau-Verwey-Overbeek)理论符合较好,为DLVO理论提供了直接的微观实验依据。对决定实验精度和效率的一些实验因素,包括测量过程中光镊的开关切换时间、光镊打开和关闭的持续时间、样品离样品池底面高度和实验测量区间划分精度等进行了具体讨论。所建立的实验装置和方法可用于测量不同类型胶体粒子间的相互作用势,这为深入研究决定分散体系宏观性质的微观基础提供了一种有效的手段。     

基于动态粒子流场的视频异常行为自动识别

为了有效实现视频异常 行为的自动识别,基于动态粒子流场,将视频运动对象的运 动行为,映射为有效 反映其运动变化状态的动态粒子流,同时提取度量不同场景内容下的运动方式各异的异常行 为的显著性运动特 征,进行异常行为的分类与识别。对来自不同场景并具有不同运动行为方式的公开视频 测试序列的实验表明,本文方法无需跟踪运动对象,也无需预先采集 异常行为样本进行学习与训 练,可在多种条件下实现视频运动对象异常行为的有效自动识别。     

Probabilistic potential theory applied to electrical engineering problems

The mathematical equivalence between a potential satisfying a deterministic Laplace-type equation within a closed region and a certain probability associated with a particle exercising Brownian motion is described. Two methods are outlined for obtaining a potential by Brownian motion, the usual Monte Carlo method and a "number-diffusion" process. Two probabilistic solutions of Poisson's equation are described. The number-diffusion process with complex diffusion coefficients is applied to a lumped linear electrical network under sinusoidal excitation, for computation of complex voltages. The node equations of a general network are interpreted probabilistically for transient behavior, and computations for a particular case verify the theory. The computation efficiencies (as measured by computing time) of both Monte Carlo and number-diffusion calculations of a potential are compared to the efficiency of matrix manipulation. It is shown how the probabilistic computations at sparse space-time points on a grid of a large number of points in two or three space dimensions may require orders of magnitude less time than for matrix solution, as well as less storage space. Probabilistic solutions of the wave equation for a finite lossy transmission line sinusoidally excited are shown to converge accurately only if |1 + ½(γΔx)²| > 1 (exp ± γx spacial variation of the natural waves). Then the numerical convergence of the number-diffusion algorithm is examined for various equations and sufficient conditions derived for that convergence.     

The first passage time distribution of brownian motion and its applications

This paper traces the development of the first passage time distribution of Brownian motion (inverse Gaussian) together with its various applications in inventory problems, usage and storage times, detection theory, labor turnover, money supply, purchasing models, hospital inpatient stay times, strikes duration, biology, … etc. Besides, since the inverse Gaussian distribution arises as the distribution of first passage time of Brownian motion, its applicability to lifetime modeling is a natural consequence. The general characteristics of the inverse Gaussian model which make it attractive for various applications are also identified.     

A MEMS Brownian ratchet

A Brownian ratchet is a device that can rectify the random Brownian motion of particles to yield a directed steady-state flow. We can imagine a thermofluid field of particles, which interact with the ratchet. The laws of thermodynamics imply that the ratchet must use energy from some other source.The dynamics of continuous-time Brownian ratchets are determined by a stochastic partial differential equation. We have used a simplified discrete-time model of a Brownian ratchet called ‘Parrondo's games’, which are governed by a difference equation. In their original form, Parrondo's games are a finite set of simple games of chance. An indefinite pure sequence of any single game is neutral or even losing. A periodic or randomised sequence of mixed games can be winning. There is a steady state flow of probability in the preferred direction.We have been able to design a feasible and consistent device, by mapping the conservation law of total probability onto the law of conservation of charge. This device can absorb energy from a mechanical field to produce a directed flow of charge. The fundamental architecture is based on a ‘bucket-brigade’ device. The capacitors are 2-port MEMS devices. We use CMOS transmission gates to connect the capacitors in the required topology.We present an analysis and simulation of the MEMS Brownian ratchet and suggest some possible applications.     

On a class of signals and matrices giving very fast algorithms for linear problems

In this paper is presented a class of stochastic signals and of correlation matrices introducing very fast algorithms for solving linear problems. These signals are derived from white noise by using three kinds of operations combined in various orders: summation, difference and instantaneous modulation. The discrete time Brownian motion is a particular example of such signals.     

一种利用MAP估计的双目运动体视算法

本文提出一种融合运动和体视信息的运动与结构参数的鲁棒估计算法，算法首先通过计算瞬时ＦＯＥ，实现对每个像素处位移的ＭＡＰ估计，并计算关联的置信度；然后利用位移估计，从两图像序列之一计算相对深度，导出能用于匹配两体视图像序列的视差先验概率分布，使体视对的两帧图像匹配，确定３Ｄ景物深度，算法可方便地估计每个像素处的视差，不需对表面作平滑假设。     

Effects of heat and electron irradiation on the melting behavior of Al-Si alloy particles and motion of the Al nanosphere within

In situ heating and electron-beam irradiation in the transmission electron microscope were performed to study melting of Al-11.6 at.% Si alloy submicron particles supported on an amorphous-C thin film. It was found that electron irradiation could be used to melt the particles, even when the hot-stage specimen holder was kept at a much lower temperature than the bulk melting point (i.e. the eutectic temperature) of the particles. The critical current densities required to achieve partial melting increased linearly with the incident electron-beam energy for a given temperature. Comparison between this behavior and analytical calculations indicates that melting under electron-beam irradiation is caused by a temperature rise due to electron thermal spikes in the particles and poor thermal conduction away from the particles. The motion of the crystalline Al nanosphere inside the partially molten particles was also investigated, using the electron beam to both stimulate and observe the motion of the nanosphere. The irregular motion observed was quantified as antipersistent fractional Brownian motion. Analysis of possible phenomena contributing to the motion demonstrates that the incident electrons provide the fractional force that moves the Al nanosphere, and that gravity and the oxide shell on the partially molten particle cause the antipersistent behavior. Another interesting phenomenon observed in this study was that the crystalline Al nanosphere inside the partially molten Al-Si alloy particle followed a focused electron beam as it was moved about on the partially molten particle. This observation suggests that it may be possible to manipulate metallic nanospheres inside opaque liquids using an electron beam.     

一种基于运动相似熵的人群异常行为检测

实现对人群异常事件的检测是图形处理在智能视频监控领域的重要研究内容.提出了一种基于运动相似性熵(EMS)的人群异常行为检测算法.该算法在对视频图像进行光流计算的基础上,以底层光流块为基本单位获取场景运动信息,根据社会网络模型的概念,提出构建场景的运动网络模型(MNM),完成对场景粒子运动相似性的划分,并在时间域上计算MNM的粒子分布熵值EMS,最后将得到的图像熵与设置合理的阈值相比,判断异常行为是否发生.实验证明,该算法可有效检测异常行为,与其他经典检测算法相比有较大优势.     

基于观测迭代的插值粒子滤波算法

基于序贯重要性抽样(SIS)及贝叶斯理论的粒子滤波能够很好地处理非线性及非高斯问题。如何选取重要密度函数以减小粒子退化影响提高粒子滤波精度是粒子滤波的主要问题之一。传统粒子滤波器以高斯分布作为参考分布。由于没有利用新的观测,通常需要大量的粒子才能准确表达状态后验分布。本文采用基于观测迭代的插值参考分布提高重要密度函数估计精度,减少了后验概率密度估计误差,同时结合观测系统的最近一次的量测,更好的匹配后验概率密度。 仿真结果显示该滤波器要优于其他粒子滤波器。