Far field in transient two-dimensional scattering

A heuristic definition of far field is given for time-domain two-dimensional scattering that simplifies the expression of the scattered far field as an integral over the sources. The meaning of this definition and of the ensuing simplifications is clarified by Fourier transforming the approximate time-domain result to compare it with well-known frequency-domain expressions in the Fresnel and Fraunhofer approximations.     

A strong version of the redundancy-capacity theorem of universalcoding

The capacity of the channel induced by a given class of sources is well known to be an attainable lower bound on the redundancy of universal codes with respect to this class, both in the minimax sense and in the Bayesian (maximin) sense. We show that this capacity is essentially a lower bound also in a stronger sense, that is, for “most” sources in the class. This result extends Rissanen's (1984, 1986) lower bound for parametric families. We demonstrate the applicability of this result in several examples, e.g., parametric families with growing dimensionality, piecewise-fixed sources, arbitrarily varying sources, and noisy samples of learnable functions. Finally, we discuss implications of our results to statistical inference     

理疗产品中LED辐射源有效波长的研究

用不同波长的LED辐射源照射离体组织标本,然后通过光谱仪接收其透过光线。比较了LED光透射组织后的波形和波长分布,分析了不同频率的光透过同一组织标本后的频谱,最终得出了LED光透射组织时的最佳波长范围。该结果可以对LED辐射源在理疗产品中的应用起到一定的指导作用。     

Minimax universal noiseless coding for unifilar and Markov sources (Corresp.)

Constructive upper bounds are presented for minimax universal noiseless coding of unifilar sources without any ergodicity assumptionS. These bounds are obtained by quantizing the estimated probability distribution of source letters with respect to the relative entropy. They apply both to fixed-length to variable-length (FV) and variable-length to fixed-length (VF) codes. Unifilar sources are a generalization of the usual definition of Markov sources, so these results apply to Markov sources as well. These upper bounds agree asymptotically with the lower bounds given by Davisson for FV coding of stationary ergodic Markov sources.     

一种新的红外焦平面阵列盲元检测算法

受材料、制造工艺等因素的影响,红外焦平面阵列探测器均存在一定数量的盲元。在分析探测单元响应特性的基础上,提出一种双参考辐射源+定义检测算法。实验结果表明,该算法具有盲元误检率低,查找快速等优点。     

Increase of accuracy of definition of coordinates by multi-position passive complexes on a basis of difference-distance measuring method and the problem solution in redundancy conditions

It is proposed a method of definition of coordinates of radiation sources (RS) using difference-distance measuring method and the problem solution in condition of redundant information about target space location. It is considered mathematical tool for the problem solution in condition of redundancy, it is represented a validation of considered method of RS coordinates definition. It is carried out simulation of RS coordinates definition, and on a basis of statistic characteristics of simulation results it is shown increase of the accuracy of RS coordinates in case of application of given method in the system of passive radio location.     

基于克隆选择和多重空间构造的彩色图像分割

该文提出一种基于克隆选择和多重空间构造的彩色图像分割方法。该方法首先将一些常见的颜色分量分为亮度成分、单频光谱成分、双频光谱成分、多频光谱成分,利用主分量分析技术(PCA)分别对其进行计算,得到最具有识别能力的颜色分量来构造多重颜色空间;然后利用克隆选择算法对样本进行自学习,得到全局最优的聚类中心;最后用得到的聚类中心对图像进行分割。由于该文的方法结合了克隆选择算法的非线性分类能力,通过对彩色图像自适应的构造最佳多重空间,能够快速准确地得到分割结果,克服了传统分割方法使用固定颜色空间以及容易陷入局部最优的缺点。通过实验表明,该方法对彩色图像同质区的分割均匀,边缘保持度好。此外,新方法对彩色图像的亮度和纹理变化不敏感,鲁棒性较强。     

Complexity of strings in the class of Markov sources

Shannon's self-information of a string is generalized to its complexity relative to the class of finite-state-machine (FSM) defined sources. Unlike an earlier generalization, the new one is valid for both short and long strings. The definition is justified in part by a theorem stating that, asymptotically, the mean complexity provides a tight lower bound for the mean length of all so-called regular codes. This also generalizes Shannon's noiseless coding theorem. For a large subclass of FSM sources a simple algorithm is described for computing the complexity.     

Spatial resolution improvement of SSM/I data with image restorationtechniques

A space variant image restoration algorithm has been developed with the aim of improving the spatial resolution of SSM/I (Special Sensor Microwave/Imager) passive microwave imagery. Due to the conical scanning of the instrument the relative geometry of the data samples changes over the scan. This change is accounted for by using a space variant point-spread-function in the restoration algorithm. Application of this algorithm to a scene from the Weddell Sea results in an image with enhanced ice edge and coast definition. As a result ice concentration estimates near the edge agree more closely with higher resolution (optical) data from AVHRR     

Representation of electromagnetic fields over arbitrary surfaces bya finite and nonredundant number of samples

It is shown that the electromagnetic (EM) field, radiated or scattered by bounded sources, can be accurately represented over a substantially arbitrary surface by a finite number of samples even when the observation domain is unbounded. The number of required samples is nonredundant and essentially coincident with the number of degrees of freedom of the field. This result relies on the extraction of a proper phase factor from the field expression and on the use of appropriate coordinates to parameterize the domain. It is demonstrated that the number of degrees of freedom is independent of the observation domain and depends only on the source geometry. The case of spheroidal sources and observation domains with rotational symmetry is analyzed in detail and the particular cases of spherical and planar sources are explicitly considered. For these geometries, precise and fast sampling algorithms of central type are presented, which allow an efficient recovery of EM fields from a nonredundant finite number of samples. Such algorithms are stable with respect to random errors affecting the data     

Multisources actives annular slot antenna

This analysis of multisources annular slot antennas includes the study of the influence of the real spatial extension of the excitation sources and of the lumped elements inserted in the slot to conform the radiation pattern or to perform the power matching of the sources. The definition of a reference excitation source insures a field formulation consistent with the electrical circuits definitions taking into account the real spatial extension of the sources. Owing to the introduction of a surface impedance operator in the boundary conditions, the integral formulation also describes the lumped elements whatever the domain of definition of the expansion functions is. The analysis of rotation invariant configurations is also carried out.     

Analysis and Optimization Issues for Superposition Modulation in Cooperative Networks

This paper deals with superposition modulation for a three-node system (two sources, one destination) in a cooperative ad hoc configuration. An information-theoretic achievable capacity region is given for both amplify-and-forward (AF) and decode-and-forward (DF) superposition schemes, and it is shown that it is dependent on the frame length. To simplify the analysis of the superposition modulation, an approximation of the achievable capacity region is proposed. This approximation uses only two well-defined time slots with appropriate capacity constraints and efficiently approaches the true capacity region for large frame lengths. Another issue that is discussed in this paper is the definition of the optimal superposition weight factor. In contrast with previously reported studies, which were based on simulation results, a theoretical framework that provides the optimal weight factor is also investigated. The proposed algorithm uses simplified outage probabilities of the system model, and the result only depends on the required spectral efficiency. Analytical results and simulation studies show the gains of the proposed schemes.      

数字视频上变换器及其应用

针对当前HDTV高清数字视频节目源的不足,介绍一种基于自主设计的视频格式转换芯片而开发的数字视频上变换器(SD—HD)系统。通过视频格式转换,将SD—SDI或BT656输入接口的标准清晰度格式的视频数据转换为满足SMPTE292标准的高清晰度的数字串行视频输出数据。该串行数字高清视频信号将作为高清编码器的输入源,可以用于完成高清数字视频节目的制作。     

基于云模型的基本概率赋值生成方法及应用

针对证据理论应用中基本概率赋值(BPA)生成模型难以确定问题,该文提出一种基于云模型的BPA生成方法。首先基于样本属性的正态云模型构建单子集命题的BPA模型函数,并将复合子集的模型函数表示为高斯函数乘积融合。其次提出一种根据测试样本动态度量属性权重的方法来兼顾信息源的可靠性。最后,用属性权重修正模型函数输出的结果得到BPA。鸢尾花等数据集分类识别实验表明,该方法识别准确性高,且适用于样本较少的情况。     

Potential of Image Forces in a Dielectric Film

The potential of image forces for the charge in a three-layer medium (a dielectric film between two dielectrics) is considered in terms of electric fields (by definition) rather than potentials. It is demonstrated that the result differs from the usual result by a constant. Related issues are discussed.     

Process definitions of distortion-rate functions and source coding theorems

The standard definition of the distortion-rate function involves a limit of information-tbeoretic minimizations over distributions of random vectors. Several alternative definitions, each involving a single minimization over random processes, are presented here and verified. These definitions parallel Khinchine's process definition of channel capacity, provide a new interpretation of block and nonblock source coding (with a fidelity criterion) theorems in terms of optimal stochastic codes, and provide a comparison between the optimal performance theoretically attainable (OPTA) using block and nonblock source codes. Coupling the process definitions with recently developed bounding techniques provides a new and simple proof of the block source coding theorem for ergodic sources.     

Analysis of output slave clock stability in SDH systems in terms of percentile MRTIE(τ)

The ‘maximum (relative) time interval error’ (MRTIE(τ)) is one of the parameters most used by international standardization bodies to characterize the stability of the clocks in modern SDH synchronization networks. Besides the original definition of MRTIE(τ), ITU-T has introduced a new MRTIE(τ) definition of percentile character. This new definition allows linking of the MRTIE(τ) parameter to the stochastic noise processes affecting the clocks in synchronization networks. In this paper, after a brief discussion about the original and percentile definitions of MRTIE(τ), the study focuses on the output stability of a slave clock based on a phase-locked loop (PLL) system. A PLL with internal phase noise sources and fixed bandwidth value is considered. The output slave clock stability is studied when there is a step change in the phase of the PLL reference signal. The need to consider the MRTIE(τ) parameter not only as a simple measure of wander (slow phase fluctuations) but also as a measure of fast phase fluctuations (jitter) on the clocks is emphasized, in spite of the latest ITU-T recommendations and ETSI standards. © 1998 John Wiley & Sons, Ltd.     

模糊函数的快速计算

模糊函数是研究雷达信号的主要数学工具,在有些情况下,由于信号序列比较长,此时如果直接按照定义计算信号的模糊函数,计算量太大,无法达到实时性要求。本文在其正型定义的基础上,提出了两种利用快速傅里叶变换的快速计算模糊函数的方法,分析了它们的计算量,并与按照定义直接计算的计算量进行了比较。理论和仿真结果均表明,本文的方法在处理大量数据的时候能大幅减少计算量。     

An iterative method using conditional second-order statistics applied to the blind source separation problem

This paper is concerned with the problem of blind separation of an instantaneous mixture of sources (BSS), which has been addressed in many ways. When power spectral densities of the sources are different, methods using second-order statistics are sufficient to solve this problem. Otherwise, these methods fail and others (higher order statistics, etc.) must be used. In this paper, we propose an iterative method to process the case of sources with the same power spectral density. This method is based on an evaluation of conditional first and second-order statistics only. Restrictions on characteristics of sources are given to reach a solution, and proofs of convergence of the algorithm are provided for particular cases of probability density functions. Robustness of this algorithm with respect to the number of sources is shown through computer simulations. A particular case of sources that have a probability density function with unbounded domain of definition is described; here, the algorithm does not lead directly to a separation state but to an a priori known mixture state. Finally, prospects of links with contrast functions are mentioned, with a possible generalization of them based on results obtained with particular sources.