基于Gabor滤波系数高阶矩的图像检索

在分析Gabor滤波器进行图像纹理特征提取的基础上,提出了利用多尺度和多方向Gabor滤波系数的高阶矩提取图像特征进行CBIR的方法,利用滤波系数的方差给出了基于Gabor滤波组提取的图像纹理特征的平滑度和纹理一致性算法,并采用四个尺度和六个方向的滤波系数的能量、方差、峰态、平滑度和一致性组成了CBIR特征向量.采用Brodatz纹理库和Corel图像库中的典型图像进行了对比实验.实验证明,提出的方法比传统的Gabor滤波进行CBIR具有更高的查准率.     

基于多尺度Kalman数据融合滤波

本文通过分析基于小波变换的动态系统模型,提出一种基于小波多尺度的Kalman数据滤波方法,本文利用小波的多尺度特点,把初始估计序列多尺度分解,并在不同尺度层上进行Kalman滤波估计,再利用小波重构来融合各层的估计信息,把标准Kalman滤波只在单一尺度和时间轴上对状态估计值和误差协方差进行数据更新,改进为基于小波变换的尺度轴和时间轴上的双向数据更新,该算法将小波多尺度分解去噪和Kalman滤波相结合,对实际中含较强噪声的动态系统的状态估计效果较好.算法也可用于多分辨率多传感器数据融合.     

一种基于印刷图像处理技术的模糊图像复原方法

根据印刷图像处理技术的基本原理,针对印前的电子出版图像处理中存在的原稿图像运动模糊现象,介绍了约束最小二乘方滤波复原技术消除图像模糊方法.阐述了运动模糊图像的退化模型和复原模型,利用二值图的信息来估计模糊方向,通过对二值图的矩阵变换来估计模糊尺度,再利用约束最小二乘方滤波的方法复原图像.实验表明,该方法行之有效.     

基于ADCP测量的海浪方向谱研究

海洋方向谱的研究对于海洋预报、海上建设等人类海洋活动有重要的意义。介绍了一种利用声学多普勒流速剖面仪(Acoustic Doppler Current Profiler, ADCP)测量海浪方向谱的方法。通过计算ADCP测量的流速之间的交叉谱,利用最大似然算法可以得到海浪的方向谱。给出了利用 ADCP 估计方向谱的算法流程,进行了仿真,结果表明所提出的方法可以较准确地估计海浪方向谱。     

基于曲率尺度空间的轮廓角点检测

在曲率尺度空间和多尺度曲率积的基础上,提出了一种基于多尺度曲率多项式的角点检测算法.首先基于曲率尺度空间检测不同尺度下的角点,然后利用多尺度曲率积或曲率和对检测到的角点进行增强处理,该方法可有效抑制噪声影响,防止高尺度下对一些角点平滑;另外,根据多尺度曲率多项式结果的符号还可有效的判别所检测角点的凹凸性.采用不同的评价准则及实例图像进行测试,实验结果证明该角点检测器是非常有效的,优于文中其它两种检测算法.     

阵列天线CDMA系统用户相干多径信号波达方向估计

提出了一种适用于阵列天线CDMA系统用户相干多径信号波达方向(DOA)估计的有效算法.该算法巧妙利用CDMA系统用户扩频序列的先验知识和特性,对用户相干多径信号进行解扩和匹配滤波处理,实现了对用户多径信号的有效分离和对多址干扰的抑制,对解扩后的用户多径信号采用DOA估计的综合方法进行波达方向的估计,对N元阵列,可同时估计出任一用户2N/3个相干多径信号的DOA.仿真结果表明该算法十分适合应用于CDMA类移动通信系统用户相干多径信号的波达方向估计.     

基于曲率估计的运动平滑性度量算法

研究了用运动平滑性量化度量和评价康复程度的方法。针对现有运动平滑性检测算法缺乏一致性、灵敏性和鲁棒性的问题,通过对康复运动平滑性的分析,提出了一种新的基于曲率估计的运动平滑性度量算法。该算法的核心是利用速度曲线局部结构的协方差矩阵特征根估计曲率,并基于估计的曲率实现对运动平滑性的量化度量。用该算法,实现了对根据康复过程中各种情况生成的模拟曲线和实际病人康复训练的运动曲线的平滑性度量,并与现有的6种平滑性度量方法进行了对比。试验结果表明,该算法与已有算法的度量结果具有一致性,并且在灵敏性和抗干扰方面表现出了较好的性能。     

基于正交匹配追踪算法的虚拟内插空间平滑DOA估计

针对正交匹配追踪(Orthogonal Matching Pursuit, OMP)算法在实际的波达方向(Direction of Arrival, DOA)估计应用中,测向分辨率较低且在相干信号环境下估计性能较差的问题,提出了一种虚拟阵列空间平滑DOA估计算法.以互质阵列为模型,通过在正交匹配追踪算法重构信号的基础上,使用虚拟内插的方法,构造均匀虚拟阵列,能够提高波达方向的估计精度,加入空间平滑算法,可以分辨相干信号.仿真结果表明,使用虚拟内插算法之后,空间谱图波峰更尖锐,且在信噪比为0 dB时,最高探测精度提高到2°,测向分辨率明显有所提升,同时加入空间平滑算法,可以有效地分辨相干信号,且在信噪比为0 dB时,最高探测精度提高为4.7°,验证了本文方法的有效性.     

基于尺度、方向和距离约束的改进SIFT配准方法

针对SIFT算法在图像配准过程中存在遗漏掉大量的正确匹配对且产生误匹配对等问题,本文提出一种基于尺度、方向和距离约束的改进SIFT配准方法(SODC-SIFT).首先用SIFT算法对图像进行初匹配,利用特征点的尺度和主方向的差异剔除误匹配对;然后用最小二乘法求出两幅图像的几何关系;最后利用距离约束,迭代求解,找出正确匹配对,从而实现图像的精确配准.实验结果表明,本文方法与SIFT算法相比具有较强的鲁棒性,能够提升正确匹配对的数量并提高图像的正确匹配率,增强了算法匹配的精确性.     

分形信号的小波分析

本文提出了分形信号的小波分解与重构的一种快速算法。针对分形信号的自相似和长时相关的特点,采取离散小波变换（ＤＷＴ）对分形信号进行多尺度分解,使其成为各尺度上的近似平稳信号,从而可利用通常的Ｗｉｅｎｅｒ滤波＾［５］或Ｋａｌｍａｎ滤波＾［７］方法进行估计,然后再由ＤＷＴ进行多尺度重构,估计出被噪声污染了的原始信号。本文重点对分形信号的ＤＷＴ进行算法设计,并估计了计算复杂度。     

基于区域平滑约束的光流场估计方法

从光流的基本约束方程出发，提出了一种基于区域平滑约束的光流场估计方法。     

Noise-resilient estimation of optical flow by use of overlapped basis functions

Conventional techniques for the computation of optical flow from image gradients are used to formulate the problem as a nonlinear optimization that comprises a gradient constraint term and a field smoothness factor. The results of these techniques are often erroneous, highly sensitive to noise and numerical precision, determined sparsely, and computationally expensive. We regularize the gradient constraint equation by modeling optical flow as a linear combination of a set of overlapped basis functions. We develop a theory for estimating model parameters robustly and reliably. We prove that the extended-least-squares solution proposed here is unbiased and robust to small perturbations in the gradient estimates and to mild deviations from the gradient constraint. Our solution is obtained with a numerically stable sparse matrix inversion, which gives a reliable flow-field estimate over the entire frame. To validate our claims, we perform a series of experiments on standard benchmark data sets at a range of noise levels. Overall, our algorithm outperforms by a wide margin the others considered in the comparison. We demonstrate the applicability of our algorithm to image mosaicking and to motion superresolution through experiments on noisy compressed sequences. We conclude that our flow-field model offers greater accuracy and robustness than conventional optical flow techniques in a variety of situations and permits real-time operation.     

A Comparative Study of Near-Limit Flame Spread Over a Thick Solid in Space- and Ground-Based Experiments

Microgravity experiments have been performed aboard the SJ-10 satellite of China to investigate flame spread behaviors over a thick PMMA in low-velocity opposed flow. Two variables are considered: opposed-flow velocity in a range of 0 to 9 cm/s, and ambient oxygen concentration in a range of 25% to 50%. It is found that, when the flow velocity is reduced, the initial extended flame may breaks into separate flamelets after a dynamic transition process. This is the first observation of the flamelets spreading over a thick solid fuel in microgravity. Flame and flamelet propagate with a steady spread rate, which increases with the increasing flow velocity and oxygen concentration. A flammability map using oxygen concentration and flow velocity as coordinates is established, which delineates the uniform regime, the flamelet regime, and extinguished regime. The flammability boundary was extended to lower oxygen concentrations and lower flow velocities by the flamelet regime. The microgravity results are compared with the counterparts in ground-based narrow channel apparatus (NCA) experiments. Results showed that although the NCA tests overestimate the flame spread rate and flammable area, also exhibit differences in detailed flamelet formation process, flame and flamelet behaviors agree well with that in microgravity in a qualitative manner.     

High-frequency surface acoustic waves excited on thin-oriented LiNbO3 single-crystal layers transferred onto silicon

The need for high-frequency, wide-band filters has instigated many developments based on combining thin piezoelectric films and high acoustic velocity materials (sapphire, diamond-like carbon, silicon, etc.) to ease the manufacture of devices operating above 2 GHz. In the present work, a technological process has been developed to achieve thin-oriented, single-crystal lithium niobate (LiNbO3) layers deposited on (100) silicon wafers for the fabrication of radio-frequency (RF) surface acoustic wave (SAW) devices. The use of such oriented thin films is expected to favor large coupling coefficients together with a good control of the layer properties, enabling one to chose the best combination of layer orientation to optimize the device. A theoretical analysis of the elastic wave assumed to propagate on such a combination of material is first exposed. Technological aspects then are described briefly. Experimental results are presented and compared to the state of art.     

Proposal and testing for a fiber-optic-based measurement of flow vorticity

A fiber-optic arrangement is devised to measure the velocity difference, deltav(l), down to small separation l. With two sets of optical fibers and couplers the new technique becomes capable of measuring one component of the time- and space-resolved vorticity vector omega(r, t). The technique is tested in a steady laminar flow, in which the velocity gradient (or flow vorticity) is known. The experiment verifies the working principle of the technique and demonstrates its applications. It is found that the new technique measures the velocity difference (and hence the velocity gradient when l is known) with the same high accuracy and high sampling rate as laser Doppler velocimetry does for the local velocity measurement. It is nonintrusive and capable of measuring the velocity gradient with a spatial resolution as low as ~50 mum. The successful test of the fiber-optic technique in the laminar flow with one optical channel is an important first step for the development of a two-channel fiber-optic vorticity probe, which has wide use in the general area of fluid dynamics, especially in the study of turbulent flows.     

Stabilized finite element method for viscoplastic flow: formulation with state variable evolution

A stabilized, mixed finite element formulation for modelling viscoplastic flow, which can be used to model approximately steady‐state metal‐forming processes, is presented. The mixed formulation is expressed in terms of the velocity, pressure and state variable fields, where the state variable is used to describe the evolution of the material's resistance to plastic flow. The resulting system of equations has two sources of well‐known instabilities, one due to the incompressibility constraint and one due to the convection‐type state variable equation. Both of these instabilities are handled by adding mesh‐dependent stabilization terms, which are functions of the Euler–Lagrange equations, to the usual Galerkin method. Linearization of the weak form is derived to enable a Newton–Raphson implementation into an object‐oriented finite element framework. A progressive solution strategy is used for improving convergence for highly non‐linear material behaviour, typical for metals. Numerical experiments using the stabilization method with hierarchic shape functions for the velocity, pressure and state variable fields in viscoplastic flow and metal‐forming problems show that the stabilized finite element method is effective and efficient for non‐linear steady forming problems. Finally, the results are discussed and conclusions are inferred. Copyright © 2002 John Wiley & Sons, Ltd.     

基于子空间约束的面部特征点跟踪算法

为克服纹理不丰富和非刚性形变等因素引起的面部特征点跟踪困难,提出了一种基于子空间约束的面部特征点跟踪算法。针对人脸运动特点,将面部特征点分为具有复杂运动模式和简单运动模式的特征点集。用通过样例学习得到的特定描述模型准确刻画了具有复杂运动模式的特征点集的变化,保证了子空间约束的有效性。对运动模式简单的特征点集的跟踪则采用基于光流的算法,以提高算法的效率,也为基于特定描述模型的跟踪算法提供了更准确的起始搜索位置。对跟踪结果进一步应用子空间约束解决跟踪中的开孔问题和消除跟踪误差。实验结果表明,在存在较大验部变形和部分特征点纹理不丰富的情况下,该方法可以有效地跟踪较密集的面部特征点。     

Velocity field measurement of a round jet using quantitative schlieren

This paper utilizes the background oriented schlieren (BOS) technique to measure the velocity field of a variable density round jet. The density field of the jet is computed based on the light deflection created during the passage of light through the understudy jet. The deflection vector estimation was carried out using phase-based optical flow algorithms. The density field is further exploited to extract the axial and radial velocity vectors with the aid of continuity and energy equations. The experiment is conducted at six different jet-exit temperature values. Additional turbulence parameters, such as velocity variance and power spectral density of the vector field, are also computed. Finally, the measured velocity parameters are compared with the hot wire anemometer measurements and their correlation is displayed.     

On some similarity solutions to shear flows of non-Newtonian power law fluids

Summary The nonlinear rheological effects of non-Newtonian power law fluids on some shear flows are addressed. Exact similarity solutions to Stokes' first problem for unsteady flow generated by the vertical motion of a slender cylinder in an unbounded fluid are presented. The nonlinear effects on the velocity and shear stress distributions are shown and discussed. These reveal the existence of traveling wave characteristics for a shear thickening fluid, which determine a moving shear front for which the shear disturbances propagate with a finite velocity.     

改进的光流法及其在云爆弹研究中的应用

在Hom-Schunck和N．Ohta的传统光流法的基础上，提出了用于抑制光线影响的改进的光流法，并将其用在云爆弹的爆炸过程分析研究中，得到云爆弹爆炸云雾扩散速度这一重要参数指标。改进的方法运用自适应高斯核平滑滤波器，对所拍摄的图像序列进行平滑滤波处理，以平滑图像和降低随机噪声对图像处理的干扰。利用脚彩色模型在白光照射下的不变性原理，将传统彩色图像光流法中的RGB彩色模型转换为rgb彩色模型，得到了一种新的可抑制光线变化影响光流场算法，以减少因光线变化而造成对目标的误检测的影响。以云爆弹为研究实例，采用改进的方法计算云爆弹爆炸云雾图片中各点光流，并提取了扩散云雾平均速度信息。实验所得图片中平均光流大小约2．5pixel／ms，经过参数换算得出云雾扩散速度为109．78m／s，取得了良好的效果。