Realization and identification of autonomous linear periodically time-varying systems

The subsampling of a linear periodically time-varying system results in a collection of linear time-invariant systems with common poles. This key fact, known as “lifting”, is used in a two-step realization method. The first step is the realization of the time-invariant dynamics (the lifted system). Computationally, this step is a rank-revealing factorization of a block-Hankel matrix. The second step derives a state space representation of the periodic time-varying system. It is shown that no extra computations are required in the second step. The computational complexity of the overall method is therefore equal to the complexity for the realization of the lifted system. A modification of the realization method is proposed, which makes the complexity independent of the parameter variation period. Replacing the rank-revealing factorization in the realization algorithm by structured low-rank approximation yields a maximum likelihood identification method. Existing methods for structured low-rank approximation are used to identify efficiently a linear periodically time-varying system. These methods can deal with missing data.     

动态调整步长的参数曲线生成算法

本文提出一种在图形显示设备上生成参数曲线的通用算法 ,使生成的曲线精确到象素级 (即以象素逼近曲线上的点 ) .本算法采用在曲线生成过程中动态调整步长的方法 ,调整步长的方法简便 ,无需增加太多的计算量 .应用算法的结果表明 ,生成的曲线既可达到所要求的精确度又可大大地避免点的重复计算 .除了精确到象素级外 ,该算法也适用于其它精确度要求 ,如用折线逼近曲线时 ,相邻两点之间的距离小于给定值等 .而且该算法适用于一切多项式的、有理的或其它形式的参数曲线 ,不受曲线表示形式和曲线次数的限制 .     

For real! XCS with continuous-valued inputs

Many real-world problems are not conveniently expressed using the ternary representation typically used by Learning Classifier Systems and for such problems an interval-based representation is preferable. We analyse two interval-based representations recently proposed for XCS, together with their associated operators and find evidence of considerable representational and operator bias. We propose a new interval-based representation that is more straightforward than the previous ones and analyse its bias. The representations presented and their analysis are also applicable to other Learning Classifier System architectures. We discuss limitations of the real multiplexer problem, a benchmark problem used for Learning Classifier Systems that have a continuous-valued representation, and propose a new test problem, the checkerboard problem, that matches many classes of real-world problem more closely than the real multiplexer. Representations and operators are compared using both the real multiplexer and checkerboard problems and we find that representational, operator and sampling bias all affect the performance of XCS in continuous-valued environments.     

基于双参数的几何细分法

提出一种基于两个参数的几何细分方法。首先,借助于标准型的二次有理Bézier 曲 线公式,以相邻的两个初始控制点及其切向量所在直线的交点作为该二次有理Bézier 曲线的控制 顶点;同时,选取分点参数值t  0.5,并以该曲线的权因子作为控制顶点的参数λ,计算新增控 制顶点。其次,定义每个顶点的临时切向量,以每点及其相邻两点确定该点的圆切向;引入切向 量的控制参数,从而确定该顶点新切向量的计算公式。然后,从理论上证明了该方法的保凸性 与收敛性。取定切向量参数=0,重新定义每步的权因子参数λ,其极限曲线是C1连续的分段二 次有理Bézier 曲线;令=1,在每一步骤中采用不同的权因子参数λ 求新增点,具有保圆性。最 后,通过一些实例说明了该方法的有效性。     

Synthesis of slow‐wave structures based on capacitive‐loaded lines through aggressive space mapping (ASM)

This article is focused on the automated synthesis of slow‐wave structures based on microstrip lines loaded with patch capacitors. Thanks to the presence of the shunt capacitors, the effective capacitance of the line is enhanced, and the phase velocity of the structure can be made significantly smaller than the one of the unloaded line. The target is to achieve the layout of the slow‐wave structure able to provide the required slow‐wave ratio, characteristic (Bloch) impedance and electrical length (i.e., the usual specifications in the design of slow‐wave transmission lines). To this end, a two‐step synthesis method, based on the aggressive space mapping (ASM) algorithm, is proposed for the first time. Through the first ASM algorithm, the circuit schematic providing the target specifications is determined. Then, the second ASM optimizer is used to generate the layout of the structure. To illustrate the potential of the proposed synthesis method, three application examples are successfully reported. The two‐step ASM algorithm is able to provide the layout of the considered structures from the required specifications, without the need of an external aid in the process. © 2015 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:629–638, 2015.     

均匀参与介质的渲染方法研究

参与介质在现实世界中广泛存在,光线在参与介质中的传播过程比在表面上的传播过程更加复杂,比如在高度散射参与介质中会发生成千上万次反射、在低散射参与介质中由于表面聚集出现体焦散效果,从而使得光线的模拟过程非常耗时。目前常用的方法包括点、光束和路径统一模型法（unifying points,beams and paths,UPBP）以及流型探索梅特罗波利斯光线传递方法（manifold exploration Metropolis light transport,MEMLT）等,这些方法在一定程度上改进了原有方法,但是在一些特殊情况下仍然需要很长时间才能收敛。本文介绍几种针对均匀参与介质的高效渲染方法。1）基于点的参与介质渲染方法,主要通过在参与介质内分布一些点来分别加速单次、二次和多次散射的计算,在GPU （graphics processing unit）实现的基础上,最终达到可交互的效率,并且支持对任意的均匀参与介质的编辑。2）基于多次反射的预计算模型,预计算出无限参与介质中的多次散射分布,通过分析光照分布的对称性,将该分布的维度从4维减低为3维,并且将该分布应用到多种蒙特卡洛渲染方法中,比如MEMLT、UPBP等,从而提高效率。3）参与介质中的路径指导方法,通过学习光线在参与介质中的分布,该分布用SD-tree （spatial-directional tree）来表示,与相位函数进行重采样来产生出射方向。以上3种方法分别从不同角度加快了参与介质的渲染效率。     

Application of singular value decomposition for integral equation procedures in MIMICAD

An efficient moment method procedure which utilizes a point matching scheme together with a generalized inverse is formulated and implemented with the use of the singular value decomposition. The integral representation of Green's functions and a combination of semi-infinite and subdomain expansion functions are used to formulate the numerical technique required to solve for the scattering parameters of planar microstrip multiports. Scattering parameters of typical microstrip discontinuities computed by utilizing this procedure are presented and compared with known published results. © 1992 John Wiley & Sons, Inc.     

Electromagnetic scattering by arbitrarily shaped stratified anisotropic media using the equivalent dipole moment method

The equivalent dipole moment method, which was used to model the isotropic media, is extended and applied to the analysis of the electromagnetic scattering characteristics of arbitrarily shaped multilayer electric anisotropic media in this work. The initial motivation to put forward this method is based on the intrinsic physical properties of the electric anisotropic media whose constitutive parameter permittivity is a tensor matrix that can be modeled as equivalent electric dipole moment. This method employs the method of moments to solve the electric field volume integral equation (VIE) formulated by discretizing the scattering body into tetrahedral volume elements, in which the electrical parameters are assumed constant in each element. Then the VIE is solved directly to obtain the scattered field. Numerical results are given to validate the accuracy and efficiency of this method. © 2010 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2010.     

Optimal tuning of PI coefficients by using fuzzy-genetic for V/f controlled induction motor

This paper presents a novel speed control scheme of an induction motor using genetic-fuzzy logic. The aim of this paper is to improve a new method of the optimal tuning of proportional integral controller coefficients in the off-line control of a induction motor.

The V/f control, which realizes a low cost and simple design, is advantageous in the middle to high-speed range. Its torque response depends on the electrical time constant of the motor and adjustments of the control parameters are not need. Therefore, V/f control of induction motor is carried out. Space vector pulse width modulation with V/f is used for controlling the motor. Because, it includes minimum harmonics according to the other PWM techniques. In this paper, the first step is the identification of the system via fuzzy logic, using performance value (1/(1 + maximum overshoot and settling time)) obtained from the application circuit for different K_p–K_i pairs. In the second step, the purpose is to find the optimum controller coefficients using the fuzzy model as the objective function via genetic algorithms. A digital signal processor controller (dsPIC30F6010) was used to carry out control applications. Then, the proposed method is compared with Ziegler–Nichols method.     

Uncertain variables and learning algorithms in knowledge-based control systems

This paper concerns a class of knowledge-based control systems with unknown parameters in the knowledge representation describing a plant. For the deterministic case, the logic-algebraic method of determination of the control decisions has been developed. The purpose of this paper is to present an extension of this method for the case with unknown parameters. In the first part, an approach based on uncertain variables is presented. In the second part, the method and algorithms of current knowledge updating in the learning system are proposed. The main idea of this approach consists of a step-by-step estimation of the unknown parameters in the knowledge representation using the successive values of the control decisions and their results. This concept may be considered as an extension of the known ideas of identification and adaptation for the traditional case. This work was presented, in part, at the Third International Symposium on Artificial Life and Robotics, Oita, Japan, January 19–21, 1998     

Three dimensional reconstruction of coronary arteries from two views

Geometric representation and measurements of localized lumen stenosis of coronary arteries are important considerations in the diagnosis of cardiovascular diseases. This discrete narrowing of the arteries typically impairs blood flow in regions of the heart, and can be present along the entire length of the artery. Three-dimensional (3-D) reconstruction of coronary arterial tree allows clinician to visualize vascular geometry. Three-dimensional representation of tree topology facilitates calculation of hemodynamic measurements to study myocardial infarction and stenosis. The 3-D arterial tree, computed from two views, can provide more information about the tree geometry than individual views. In this paper, a 3-step algorithm for 3-D reconstruction of arterial tree using two standard views is presented. The first step is a multi-resolution segmentation of the coronary vessels followed by medial-axis detection along the entire arterial tree for both views. In the second step, arterial trees from the two views are registered using medial-axis representation at the coarsest resolution level to obtain an initial 3-D reconstruction. This initial reconstruction at the coarsest level is then modified using 3-D geometrical a priori information. In the third step, the modified reconstruction is projected on the next higher-resolution segmented medial-axis representation and an updated reconstruction is obtained at the higher resolution. The process is iterated until the final 3-D reconstruction is obtained at the finest resolution level. Linear programming based constrained optimization method is used for registering two views at the coarse resolution. This is followed by a Tree-Search method for registering detailed branches at higher resolutions. The automated 3-D reconstruction method was evaluated on computer-simulated as well as human angiogram data. Results show that the automated 3-D reconstruction method provided good registration of computer-simulated data. On human angiogram data, the computed 3-D reconstruction matched well with manual registration.     

Rational Beta-splines for representing curves and surfaces

The rational Beta-spline representation, which offers the features of the rational form as well as those of the Beta-spline, is discussed. The rational form provides a unified representation for conventional free-form curves and surfaces along with conic sections and quadratic surfaces, is invariant under projective transformation, and possesses weights, which can be used to control shape in a manner similar to shape parameters. Shape parameters are an inherent property of the Beta-spline and provide intuitive and natural control over shape. The Beta-spline is based on geometric continuity, which provides an appropriate measure of smoothness in computer-aided geometric design. The Beta-spline has local control with respect to vertex movement, is affine invariant, and satisfies the convex hull property. The rational Beta-spline enjoys the benefit of all these attributes. The result is a general, flexible representation, which is amenable to implementation in modern geometric modeling systems     

关键点图对比图像分类方法

深度学习是目前图像分类的主流方法之一,其重视感受野内的局部信息,却忽略了类别的先验拓扑结构信息。本文提出了一种新的图像分类方法,即Key-D-Graph,这是基于关键点的图对比网络方法,在识别图像类别时可以显式地考虑拓扑先验结构。具体地,图像分类需要2个步骤,第一步是基于关键点构建图像的图表达,即采用深度学习方法识别图像中目标类别的可能关键点,并采用关键点坐标生成图像的拓扑图表达;第二步基于关键点的图像图表达建立图对比网络,以估计待识别图与目标类别之间的结构差异,实现类别判断,该步骤利用了物体的拓扑先验结构信息,实现了基于图像全局结构信息的物体识别。特别的,Key-D-Graph的中间输出结果为类别关键点,具有语义可解释性,便于在实际应用中对算法逐步分析调试。实验结果表明,提出的方法可在效率和精度上超过主流方法,且通过消融实验分析验证了拓扑结构在分类中的作用机制和有效性。     

The Bézier Tangential Surface System: a Robust Dual Representation of Tangent Space

This paper develops a robust dual representation for the tangent space of a rational surface. This dual representation of tangent space is a very useful tool for visibility analysis. Visibility constructs that are directly derivable from the dual representation of this paper include silhouettes, bitangent developables and kernels. It is known that the tangent space of a surface can be represented by a surface in dual space, which we call a tangential surface. Unfortunately, a tangential surface is usually infinite. Therefore, for robust computation, the points at infinity must be clipped from a tangential surface. This clipping requires two complementary refinements, the first to allow clipping and the second to do the clipping. First, three cooperating tangential surfaces are used to model the entire tangent space robustly, each defined within a box. Second, the points at infinity on each tangential surface are clipped away while preserving everything that lies within the box. This clipping only involves subdivision along isoparametric curves, a considerably simpler process than exact trimming to the box. The isoparametric values for this clipping are computed as local extrema from an analysis using Sederbergs piecewise algebraic curves. A construction of the tangential surface of a parametric surface is outlined, and it is shown how the tangential surface of a Bézier surface can be expressed as a rational Bézier surface.     

A comparative study of group delay equalizers for satellite communications

This article presents a comparative study of four different group delay (GD) equalizers with a narrow band filter used as input multiplexer for a Ku‐band satellite transponder. A dual mode cylindrical filter with 36 MHz bandwidth is designed and fabricated. The filter GD is measured and two types of group‐delay equalizers are designed to fulfill the requirements of the transponder's GD mask. Two rectangular and two cylindrical equalizers are designed and their performance parameters, such as insertion loss and equalized bandwidth, are compared. In addition, a comparison between the designed first order (C‐section) and second order (D‐section) GD equalizers is done.     

基于FPGA和LVDS的AOS高速合路器/分路器研究

在对AOS进行功能划分的基础上,介绍了一种基于FPGA和LVDS的高速合路器/分路器,它是空间数据传输标准AOS(高级在轨系统)的仿真和验证系统中一个非常关键的组成部分。该方案采用FPGA对多路信号进行并行处理和调度,并且通过LVDS在合路器、分路器、链路控制器等高速设备之间交换数据。试验结果表明采用该合路器/分路器的系统较好地实现了高速环境下AOS的数据传输,并具有很大的灵活性。     

Bidirectional representation for face recognition across pose

Conventional representation methods try to express the test sample as a weighting sum of training samples and exploit the deviation between the test sample and the weighting sum of the training samples from each class (also referred to as deviation between the test sample and each class) to classify the test sample. In particular, the methods assign the test sample to the class that has the smallest deviation among all the classes. This paper analyzes the relationship between face images under different poses and, for the first time, devises a bidirectional representation method-based pattern classification (BRBPC) method for face recognition across pose. BRBPC includes the following three steps: the first step uses the procedure of conventional representation methods to express the test sample and calculates the deviation between the test sample and each class. The second step first expresses the training sample of a class as a weighting sum of the test sample and the training samples from all the other classes and then obtains the corresponding deviation (referred to as complementary deviation). The third step uses the score-level fusion to integrate the scores, that is, deviations generated from the first and second steps for final classification. The experimental results show that BRBPC classifies more accurately than conventional representation methods.     

基于腿部三角特征的贝叶斯步态识别方法

提出了一种基于步态序列中腿部三角特征的步态表示方法,在这种特征上用改进的朴素贝叶斯分类方法进行步态识别。选取步幅最大、最小两种情况下的姿态作为关键帧,用三角型模拟其腿部特征,提取三角型模型参数作为步态特征,识别时先分别用KNN和一种改进的N-best取得属性值在训练数据中的对应数值,然后用贝叶斯分类方法识别。在NLPR数据库上使用留一校验方法进行算法验证,实验证明该方法简单快速,而且取得了比较理想的识别效果。     

ARMA model parameter estimation based on the equivalent MA approach

The paper investigates the relation between the parameters of an autoregressive moving average (ARMA) model and its equivalent moving average (EMA) model. On the basis of this relation, a new method is proposed for determining the ARMA model parameters from the coefficients of a finite-order EMA model. This method is a three-step approach: in the first step, a simple recursion relating the EMA model parameters and the cepstral coefficients of an ARMA process is derived to estimate the EMA model parameters; in the second step, the AR parameters are estimated by solving the linear equation set composed of EMA parameters; then, the MA parameters are obtained via simple computations using the estimated EMA and AR parameters. Simulations including both low- and high-order ARMA processes are given to demonstrate the performance of the new method. The end results are compared with the existing method in the literature over some performance criteria. It is observed from the simulations that our new algorithm produces the satisfactory and acceptable results.     

基因序列图形表达及聚类分析应用研究

在基因序列图形表达模型研究的基础上，提出了一种新的非退化的基因图形三维表示方法。该表达方法不仅避免了图形的重叠和交叉，同时还保留了序列的生物学特征。利用该表达方法对H5N1病毒基因序列进行数字特征的提取并引入基于多维PFS判别函数进行模糊聚类分析应用。在聚类分析过程中直接利用数字特征矩阵作为分析数据，分析结果表明：利用文中所给图形表达建立基因序列数字特征矩阵进行的聚类分析具有一定的合理性。