反向传播神经网络的太平洋海域温跃层反演*

温跃层是反映海洋温度场的重要指标,针对太平洋中东部海域复杂多变的水文情况以及传统温跃层分析模式的局限性,本文基于BOA_Argo历史网格,通过BP神经网络,建立温度剖面的经验正交系数与海面遥感数据、少量深度处海水温度之间的非线性映射关系,实现海洋垂向温度剖面的实时反演,最后利用垂向梯度法获得海洋温跃层的相关参数。实验结果表明,相比于传统方法,该方法反演得到的跃层深度与测量值更加吻合,其中上层深度平均反演误差从10.3m下降到5.7m,下层深度平均反演误差从16.8m下降到8.8m。     

组合利用统计和结构信息的道路提取算法

提出了一种组合利用统计和结构信息从遥感图像中提取道路的算法,这个算法包括三个处理步骤,利用道路的多种局部统计特性获得道路基元与道路段,以及利用能量函数提取道路边沿,在检测道路基元时,用统计分析来表达道路的结构信息,避免了提取线段来表达,增强了抗噪性与稳健性;在检测和拟合道路边沿时,能量函数中的参数由前面的运算结果确定,使算法具有自适应能力。     

零件矩形边界框区域自动提取算法及应用

为了提高图像处理速度,提出了基于机器视觉的目标图像矩形边界框区域提取算法。分析了图像在含有孤立点噪声的情况下该算法的可靠性以及阈值选取对实验结果的影响;设计出了针对齿形链板和自动扶梯用链板图像的抗噪模板;利用最小二乘法和最小区域法确定链板圆孔几何参数,并从目标与背景之比和算法复杂度两个方面分析了该算法对处理速度的贡献能力。实验表明,该算法对于孤立点噪声具有良好的抑制作用,可快速、准确地找出包含目标图像的矩形区域。     

一种基于蚁群算法的边缘提取算法

提出一种基于梯度定义和蚁群算法的边缘提取算法.根据梯度在边缘处的直观响应,提出自适应的边缘特征定义,并结合蚁群算法的特性,令蚂蚁遗留不同等级的信息素.根据搜索权值矩阵得到尽量平滑的边缘,最终的边缘通过自动阈值进行提取.实验表明:该算法的性能在同样的智能算法和经典的边缘检测算子中表现良好,并对噪音不敏感.     

一类带组合边界的变物性耦合场问题

在正交各向同性体框架内，讨论了在热冲击作用下，具耦合效应的变物性热弹性方程的求解问题，它是近几年来关于热冲击下常物性耦合场讨论的继续 。     

一种基于蚁群算法的边缘提取算法

提出一种基于梯度定义和蚁群算法的边缘提取算法.根据梯度在边缘处的直观响应,提出自适应的边缘特征定义,并结合蚁群算法的特性,令蚂蚁遗留不同等级的信息素.根据搜索权值矩阵得到尽量平滑的边缘,最终的边缘通过自动阈值进行提取.实验表明：该算法的性能在同样的智能算法和经典的边缘检测算子中表现良好,并对噪音不敏感.     

截断阶梯Legendre函数加权阵列恒定束宽波束特性分析*

连续Legendre函数加权的恒定束宽换能器(CBT)阵列可以在一定频率范围内采用与频率无关的简单阵元权重实现恒定束宽的波束特性。然而常规CBT阵列需要为每个阵元配置相应的阵元权重,当阵元数量较大时会增加复杂度。该文分析了截断阶梯Legendre函数加权的面阵列,包括球面阵、柱面阵和平面阵,并且分别分析了Legendre函数球面加权方法和Legendre函数柱面加权方法应用于上述阵列的性能。结果表明,截断阶梯Legendre函数加权对波束方向的影响可以忽略,而主要影响波束宽度。对于面阵列,当采样阶梯不大于3 dB,截断点不大于-21 dB时,截断阶梯Legendre函数加权能很好近似连续Legendre函数加权。因此截断阶梯Legendre函数加权可以在保证CBT阵列性能的前提下有效减少阵元加权系数的数量。     

保留边界特征的深度图像增强算法研究

针对现有深度图像增强算法存在边界保留特性差的问题,提出梯度掩模导向联合滤波(gradient mask guided joint filter, GMGJF)算法。利用深度图像进行Sobel梯度变换获取边界方向信息,利用深度图像空洞区域生成空洞掩模,再以边界方向和空洞掩模为导向联合彩色图像对深度图像进行迭代高斯滤波和空洞填充。实验结果表明,GMGJF算法的PSNR(peak signal to noise ratio)、SSIM(structural similarity index measure)比IMF(iterative median filter)、GF(guided filter)、JBF(joint bilateral filter)算法的PSNR、SSIM至少提高了3.50%和1.07%,不仅去噪能力、空洞填充能力最强,而且边界特征保持最好,有利于深度图像的特征提取与目标识别。     

高精度激光告警参数提取算法

激光告警系统通过提取来袭激光的相关参数进行告警定位,其角度定位精度直接与战场生存能力相关。为了有效提高激光告警系统的角度定位精度,基于光栅衍射型激光告警原理,提出一种高精度测量来袭激光参数的算法。对激光告警系统进行标定,用高斯拟合法精确提取出衍射光斑标定图片的0级光斑中心,将来袭激光角度与对应角度的光斑中心进行拟合,根据拟合结果确定任意角度的光斑衍射图像对应的来袭激光角度参数。实验结果表明,方位角测量误差优于0.29°,俯仰角测量误差优于0.38°。该算法有效提高了激光告警系统的测算精度。     

基于累积梯度的裂缝提取算法

受光照条件和噪声影响, 采用摄像方法检测裂缝时, 常用的边缘提取算法适用性较差。为此, 提出累积梯度算法用于计算裂缝边界。首先采用自适应二值化方法和图像形态学操作得到掩模图像。将掩模图像作用于原始图像, 得到扩充的裂缝区域图像。对该图像进行迭代膨胀, 对图像灰度值相加得到累积灰度值, 再用膨胀前后2幅图像的累积灰度值相减其差值最大时为累积梯度, 并将膨胀前的图像作为提取的裂缝。实验结果表明该方法能够在复杂背景下提取得到裂缝。     

Ocean circumstance effects on the sound scattering of thermocline

I.IntroductionTheformationofoccanthermoc1ineistheresultfromasea-atmosphereintcraction,whichdependsonvariousintensitiesanddepthsofthethermocline,andthedynamictransactionofthermoenergybetweenlayers.Thercfore,thetcmporalandspacialchangcofthethcrmoc1inebecomesanimportantparameterforrcsearchonuppcrboundary1ayerofsea.Thetempera-tUre,salinityandprcssurevarywithdcpth,whichhasformedthcvcrticalprofileofsoundvclooityintheuppcrboundarylaycrsofsca.A1ongthcshallowwatcrareaofChina,thereareobvi-ousnon-unifo…     

An experimental study of acoustic scattering from thermocline in shallow sea

I.IntroductionThetemperature,salinityandstaticprcssureofscawaterchangewithdepth,whichformsthcsoundvelocityvertica1distributioninthesea.Duringsummcrscason,thercaren0n-uniformthermoclinelaycrsinthedepths0fshallowseaal0ngChinacoast.Wearenowabletodeducctheimpedanccproflle(pc)byechoesofacousticwavesfr0mvarioustherm0c1ine1ayers.Thewaterdcnsityvaricsonlyslight1y,hencetheac0usticve1ocityde-Pendsmainlyonthetemperatureofseawatcr,andthercfore,itispossiblctorecordthcdepthofthermoclinelaycrsbyusingacoust…     

An efficient shooting algorithm for Evans function calculations in large systems

In Evans function computations of the spectra of asymptotically constant-coefficient linear operators, a basic issue is the efficient and numerically stable computation of subspaces evolving according to the associated eigenvalue ODE. For small systems, a fast, shooting algorithm may be obtained by representing subspaces as single exterior products [J.C. Alexander, R. Sachs, Linear instability of solitary waves of a Boussinesq-type equation: A computer assisted computation, Nonlinear World 2 (4) (1995) 471–507; L.Q. Brin, Numerical testing of the stability of viscous shock waves, Ph.D. Thesis, Indiana University, Bloomington, 1998; L.Q. Brin, Numerical testing of the stability of viscous shock waves, Math. Comp. 70 (235) (2001) 1071–1088; L.Q. Brin, K. Zumbrun, Analytically varying eigenvectors and the stability of viscous shock waves, in: Seventh Workshop on Partial Differential Equations, Part I, 2001, Rio de Janeiro, Mat. Contemp. 22 (2002) 19–32; T.J. Bridges, G. Derks, G. Gottwald, Stability and instability of solitary waves of the fifth-order KdV equation: A numerical framework, Physica D 172 (1–4) (2002) 190–216]. For large systems, however, the dimension of the exterior-product space quickly becomes prohibitive, growing as , where n is the dimension of the system written as a first-order ODE and k (typically n/2) is the dimension of the subspace. We resolve this difficulty by the introduction of a simple polar coordinate algorithm representing “pure” (monomial) products as scalar multiples of orthonormal bases, for which the angular equation is a numerically optimized version of the continuous orthogonalization method of Drury–Davey [A. Davey, An automatic orthonormalization method for solving stiff boundary value problems, J. Comput. Phys. 51 (2) (1983) 343–356; L.O. Drury, Numerical solution of Orr-Sommerfeld-type equations, J. Comput. Phys. 37 (1) (1980) 133–139] and the radial equation is evaluable by quadrature. Notably, the polar-coordinate method preserves the important property of analyticity with respect to parameters.     

Computable upper bounds for the adiabatic approximation errors

For a given Hermitian Hamiltonian H(s)(s∈[0,1])with eigenvalues Ek(s)and the corresponding eigenstates|Ek(s)(1 k N),adiabatic evolution described by the dilated Hamiltonian HT(t):=H(t/T)(t∈[0,T])starting from any fixed eigenstate|En(0)is discussed in this paper.Under the gap-condition that|Ek(s)-En(s)|λ0 for all s∈[0,1]and all k n,computable upper bounds for the adiabatic approximation errors between the exact solution|ψT(t)and the adiabatic approximation solution|ψadi T(t)to the Schr¨odinger equation i|˙ψT(t)=HT(t)|ψT(t)with the initial condition|ψT(0)=|En(0)are given in terms of fidelity and distance,respectively.As an application,it is proved that when the total evolving time T goes to infinity,|ψT(t)-|ψadi T(t)converges uniformly to zero,which implies that|ψT(t)≈|ψadi T(t)for all t∈[0,T]provided that T is large enough.     

A new real-space algorithm for realistic density functional calculations

We present the implementation of a fast real-space algorithm for density functional calculations for atomic nanoclusters. The numerical method is based on a fourth-order operator splitting technique for the solution of the Kohn-Sham equation [1]. The convergence of the procedure is about one order of magnitude better than that of previously used second-order operator factorizations. The method has now been extended to deal with non-local pseudopotentials of the Kleinman-Bylander [2] type, permitting calculations for realistic systems, without significantly degrading the convergence rate. We demonstrate the convergence of the method for the examples C and C₆₀ and present examples of structure calculations of Na and Mg clusters.     

一种非标定的快速星图识别方法

大多数现有算法在星敏感器光学系统参数标定不准确时,识别率显著降低。针对这种情况提出了一种无需标定参数的识别算法。该算法引入比例距离作为径向特征,角度作为环向特征。这两种特征不依赖焦距、主点等任何光学系统参数,仅和图像平面上的星点位置有关。识别时首先按照特征量进行初始匹配,然后利用FOV(Field of View)约束筛选待选星进行精确匹配。为了加快速度,精确匹配时引入了快速分组方法。仿真实验表明,该方法具有较快的识别速度,在没有光学系统参数的情况下,识别率可以达到97%。     

应用改进的特征基函数法和自适应交叉近似算法快速分析导体目标电磁散射特性

特征基函数的构造是特征基函数法的关键步骤之一, 传统方法在构造特征基函数时, 需要在每个子域设置足够多的入射波激励, 生成的特征基函数个数较多, 奇异值分解时间较长. 为了加快特征基函数的构造, 本文提出了一种改进的特征基函数法. 该方法充分考虑每个子域之间的耦合作用, 求出每个子域的次要特征基函数, 从而降低入射波激励的个数, 大大减少了特征基函数的个数; 并且结合自适应交叉近似算法加速阻抗矩阵元素的计算, 提高了次要特征基函数求解和缩减矩阵构建过程中的矩阵矢量相乘的速度. 数值结果证明了本文方法的精确性和高效性. 关键词： 电磁散射 矩量法 特征基函数法 自适应交叉近似     

三维随机粗糙面上导体目标散射的解析-数值混合算法

提出三维导体目标与导体粗糙面复合散射的解析-数值混合迭代算法,推导出三维目标与粗糙面的耦合积分方程,以及粗糙面散射的Kirchhoff近似(KA)计算式.粗糙面的KA解析计算大大降低了粗糙面求解的复杂度,与目标矩量法的混合迭代保证了计算结果的精度,使得三维体-面目标复合散射计算变得可行.由于体-面两者的高阶耦合作用明显减小,保证了该混合迭代算法的收敛性.与镜像Green函数方法的比较表明该混合算法的有效性,并讨论了粗糙面长度选择对计算结果的影响.结合Monte-Carlo方法,数值分析了理想导体Gauss 关键词： 复合散射 Kirchhoff近似 共轭梯度法 互耦迭代     

基于lucidshape的投影型前照灯的曲面设计

投影型前照灯是自适应前照灯AFS系统的硬件基础,利用逐次逼近法求解非球面透镜母线二元高次方程,建立非球面透镜数学模型,解决非球面曲面的母线方程求解复杂,不能显化反映非球面透镜已知参数间关系的问题;利用轴长渐变法实现双焦点多椭圆反射曲面从水平面到垂直面的光滑过渡,建立双焦点多椭圆反射面曲面方程,完成投影型前照灯反射镜面的设计。利用lucidshape软件建立投影型前照灯光学模型,并进行仿真实验,实验结果表明:利用逐次逼近法设计非球面透镜和轴长渐变法设计双焦点多椭圆反射镜面方法可行,设计出的投影型前照灯满足GB4599-2007及ECE R112法规的配光要求,提高了前照灯的照明质量,并降低了炫目效果。     

A novel, fast entropy-minimization algorithm for bias field correction in MR images

A novel, fast entropy-minimization algorithm for bias field correction in magnetic resonance (MR) images is suggested to correct the intensity inhomogeneity degradation of MR images that has become an increasing problem with the use of phased-array coils. Four important modifications were made to the conventional algorithm: (a) implementation of a modified two-step sampling strategy for stacked 2D image data sets, which included reducing the size of the measured image on each slice with a simple averaging method without changing the number of slices and then using a binary mask generated by a histogram threshold method to define the sampled voxels in the reduced image; (b) improvement of the efficiency of the correction function by using a Legendre polynomial as an orthogonal base function polynomial; (c) use of a nonparametric Parzen window estimator with a Gaussian kernel to calculate the probability density function and Shannon entropy directly from the image data; and (d) performing entropy minimization with a conjugate gradient method. Results showed that this algorithm could correct different types of MR images from different types of coils acquired at different field strengths very efficiently and with decreased computational load.