Analysis of inhomogeneously dielectric filled cavities coupled to dielectric-loaded waveguides: application to the study of NRD-guide components

In this paper, we present two contributions. First, we develop a computationally efficient technique for the full-wave characterization of inhomogeneously dielectric-filled cavities connected to inhomogeneously dielectric-loaded waveguides. This method is based on the expansion of the electromagnetic field within the cavity in terms of their solenoidal and irrotational modes. The presented formulation allows the treatment of hybrid modes in the waveguide ports, where the definition of a characteristic modal impedance or admittance is not possible. The multimode scattering matrix of the structure is computed throughout an efficient implementation of the orthonormal-basis method for the calculation of the cavity modes. Secondly, we have employed the present technique for the analysis and design of nonradiative dielectric (NRD) guide components and discontinuities. Moreover, the application of the bi-orthonormal-basis method for the calculation of the full-spectrum of NRD guides is demonstrated as being a very efficient approach for the rigorous treatment of such guides. Next, an efficient computer-aided design tool has been developed for the analysis of complex NRD-guide circuits. We have compared our simulations with theoretical and experimental results available in the technical literature, fully validating our software. This code has been employed for the specific analysis of a linear continuous taper to match two NRD guides with different widths, demonstrating a considerable reduction of the return losses over a wide frequency band. Finally, stopband and bandpass NRD-guide filters based on an electromagnetic-bandgap concept are presented.     

Orthonormal-basis partitioning and time-frequency representation of cardiac rhythm dynamics

Although a number of time-frequency representations have been proposed for the estimation of time-dependent spectra, the time-frequency analysis of multicomponent physiological signals, such as beat-to-beat variations of cardiac rhythm or heart rate variability (HRV), is difficult. We thus propose a simple method for 1) detecting both abrupt and slow changes in the structure of the HRV signal, 2) segmenting the nonstationary signal into the less nonstationary portions, and 3) exposing characteristic patterns of the changes in the time-frequency plane. The method, referred to as orthonormal-basis partitioning and time-frequency representation (OPTR), is validated using simulated signals and actual HRV data. Here we show that OPTR can be applied to long multicomponent ambulatory signals to obtain the signal representation along with its time-varying spectrum.     

Two-dimensional representations of axisymmetric fields for computer calculations

An accurate representation of axisymmetric fields has been devised by extending the method of ideal current loops to off-axis fields. It is assumed that the data to be simulated are available through measurements or through a solution of a boundary value problem. The method provides an algebraic expression for the fields throughout a two-dimensional region of interest and eliminates the need for the axial expansion formula in approximating off-axis fields. The use of Gaussian and other functions as alternatives to the coil function is proposed. Examples of the technique in simulating a periodic permanent magnet (PPM) focusing field are presented and compared with a Fourier analysis of the problem.     

p=5的AST随机数产生法

The standard method to construct a finite field requires a primitive irreducible polynomial of a given degree. Therefore, it is difficult to apply for the construction of huge finite fields. To avoid this problem, we propose a new method to construct huge finite fields with the characteristic p = 5 by using an Artin-Schreier tower. Utilizing the recursive basis of the Artin-Schreier tower, we define a multiplication algorithm. The algorithm can explicitly calculate the multiplication of two elements on the top finite field of this tower, without any primitive element. We also define a linear recurrence equation as an application, which produces a sequence of numbers, and call the new pseudorandom number generator Abstract Syntax Tree (AST) for p= 5. The experimental results show that our new pseudorandom number generator can produce a sequence of numbers with a long period.     

A Convex Optimization Approach for Depth Estimation Under Illumination Variation

Illumination changes cause serious problems in many computer vision applications. We present a new method for addressing robust depth estimation from a stereo pair under varying illumination conditions. First, a spatially varying multiplicative model is developed to account for brightness changes induced between left and right views. The depth estimation problem, based on this model, is then formulated as a constrained optimization problem in which an appropriate convex objective function is minimized under various convex constraints modelling prior knowledge and observed information. The resulting multiconstrained optimization problem is finally solved via a parallel block iterative algorithm which offers great flexibility in the incorporation of several constraints. Experimental results on both synthetic and real stereo pairs demonstrate the good performance of our method to efficiently recover depth and illumination variation fields, simultaneously.      

Quasi-ray Gaussian beam algorithm for short-pulse two-dimensional scattering by moderately rough dielectric interfaces

We consider short-pulse (SP) time-domain (TD) two-dimensional (2-D) scattering by moderately rough interfaces, which separate free space from a slightly lossy dielectric half-space, and are excited by one-dimensional (1-D) SP-TD aperture field distributions. This study extends to the SP-TD in our previous investigation of time-harmonic high frequency 2-D scattering of Gabor-based quasi-ray Gaussian beam fields excited by 1-D aperture field distributions in the presence of moderately rough dielectric interfaces (Galdi et al.). The proposed approach is based on the Kirchhoff physical optics (PO) approximation in conjunction with the Gabor-based quasi-ray narrow-waisted Gaussian pulsed-beam (PB) discretization (Galdi et al.), which is applied to the SP-induced equivalent magnetic surface currents on the interface that establish the TD reflected/transmitted fields. We show that, for well-collimated truncated SP incident fields, the PO-PB synthesis of the reflected/transmitted fields yields an approximate explicit physically appealing, numerically efficient asymptotic algorithm, with well-defined domains of validity based on the problem parameters. An extensive series of numerical experiments verifies the accuracy of our method by comparison with a rigorously-based numerical reference solution, and assesses its computational utility. The algorithm is intended for use as a rapid forward solver in SP-TD inverse scattering and imaging scenarios in the presence of moderately rough dielectric interfaces.     

Binary random fields, random closed sets, and morphologicalsampling

We theoretically formulate the problem of processing continuous-space binary random fields by means of mathematical morphology. This may allow us to employ mathematical morphology to develop new statistical techniques for the analysis of binary random images. Since morphological transformations of continuous-space binary random fields are not measurable in general, we are naturally forced to employ intermediate steps that require generation of an equivalent random closed set. The relationship between continuous-space binary random fields and random closed sets is thoroughly investigated. As a byproduct of this investigation, a number of useful new results, regarding separability of random closed sets, are presented. Our plan, however, suffers from a few technical problems that are prominent in the continuous case. As an alternative, we suggest morphological discretization of binary random fields, random closed sets, and morphological operators, thereby effectively implementing our problem in the discrete domain.     

直扩灵巧干扰技术的理论分析

直扩技术是一种在通信领域获得广泛应用的主要通信抗干扰技术。由于扩频原理的作用．常规的非相关压制干扰方法往往效果不佳。而自相关干扰方法难以解决干扰信号和通信信号在通信接收点的同步问题。文章提出了可实现的新型灵巧相关干扰方法，并进行了理论分析。仿真和实验结果证明了该方法的有效性，能够极大地降低所需的干扰功率。     

Moment method analysis of the magnetic shielding factor of aconducting TM shield at ELF

This paper presents an integral equation and method of moments (MoM) solution to the problem of TM transmission by a metallic conducting shield at extremely low frequencies (ELF). In order to accurately compute the total fields interior to the shield, equivalent problems are formulated which avoid the numerically difficult problem of computing the total fields as the sum of the incident plus scattered fields. In particular, the total electric field on the interior surface of the shield is obtained by a volume current equivalent problem, and then the total magnetic field interior to the shield is formulated in terms of equivalent magnetic surface currents flowing on the interior surface of the shield replaced by a perfect conductor     

Radiation from dielectric-loaded arrays of parallel-plate waveguides

The problem of calculating the reflected and transmitted fields as a function of scan angle in an infinite phased array of parallel-plate waveguides is studied on an analytical basis. Two infinite sets of simultaneous linear equations are derived for the scattered fields internal and external to the waveguides. These sets of equations are attacked by a newly developed modified residue calculus method. Application of the results to the problem of designing rectangular waveguide arrays with improved impedance performance over a wide range ofH-plane scan angles is discussed. It is indicated that the present analysis may serve as a first step toward investigating the more general problem of phased arrays scanning at an arbitrary angle.     

Realisation of cutset matrices into graphs

Realisation of cutset matrices into graphs is an important problem having applications in many fields of electrical engineering. Recently, many solutions have been offered to this problem. Nevertheless, these solutions are too complicated to be useful in practice. The present method offers an easier solution and can be carried out even by an unskilled person.     

On the radiation field from an electric dipole in an anisotropic and compressible plasma medium

The radiation fields from an electric dipole in a homogeneous, anisotropic, and compressible plasma are considered. Using the Fourier transform method, the problem is formulated in terms of three scalar functions, each of which satisfies the two-dimensional inhomogeneous wave equation. Asymptotic expressions of the radiation fields are obtained for the integrals by the saddle point method of integration.     

High-field electronic conduction in insulators

The quantum theory of electronic transport phenomena in large electric fields in highly dissipative media is critically examined. Serious conceptual problems and computational difficulties arise because neither the field nor the dissipation can be treated as a perturbation. We review a decade-old calculation of the velocity acquired by an electron in a finite electric field in a polar crystal and subsequent work which expanded our understanding of our method and results. A key feature of the earlier work was that in a single curve of electric field vs velocity, all the expected phenomena appeared, including a threshold field for producing hot electrons, in quantitative agreement with experiment, and a decreasing rate of energy loss with velocity for very fast electrons. A more recently studied problem, that of electron acceleration below the threshold field will be discussed. This problem is very important since such acceleration is the necessary precursor of ionization and breakdown. The physical significance of dissipation processes far from thermal equilibrium will also be mentioned.     

Incremental variations of image moments for nonlinear image registration

In this paper, we use image moments to solve the problem of estimating deformation fields given a pair of images as input. We use a single family of polynomials to parameterize the deformation field and to define image moments. In this way, variations in image moments can be represented by a set of linear equations. We solve these equations iteratively for the deformation parameters between two shapes. Our approach improves existing moment-based registration methods in both robustness to noise and convergence rate. In addition, our method does not rely on solving the correspondence problem. We have extensively tested our new method on both synthetically deformed MPEG-7 shapes and real-world biomedical images.     

NUMERICAL SIMULATION OF ANNULAR PHASED ARRAY OF DIPOLE ANTENNAS USING THE FD-TD METHOD

The problem for calculating near fields of EM radiation systems by using the finitedifference time domain(FD-TD)method are discussed and the annular phased array of dipoleantennas has been simulated numerically by use of the FD-TD method.For a test run thenear field and current distribution of the single dipole antenna are calculated.The near fieldsof the annular phased array of dipole antennas in central region filled with deionized water arecomputed and the interaction of near fields with an anatomically-based inhomogeneous model ofhuman torso is considered as well.     

基于正则化高斯场模型的低光图像增强

利用交替方向优化技术的Retinex分解是一种有效的低光图像增强解决思路。但是由于反射层和照度层的联立估计通常被视为一个多块凸优化问题,这导致算法结构复杂,优化效率低。本文将Retinex分解扩展到高斯场中,提出了一种基于正则化高斯场(Regularized Gaussian Fields,RGF)模型的低光图像增强方法。通过建立基于RGF的目标函数,将反射层和照度层的联立估计表述为一个无约束优化问题。该目标函数是可微的,因此可以通过标准的梯度优化技术进行解优化,同时解出反射层和照度层。然后,利用高斯核权重对求解出的反射层进行校正,以避免过度曝光而导致的细节丢失。经过大量的定性和定量对比实验,结果说明了与目前公认效果较好的方法相比,本文方法在增强效率和质量方面都具有一定优势。     

A Scheme for Analyzing the RCS of a Scale Model Beyond the Size Measureable in the Range of Millimeter-Wave

The problem of obtaining the radar cross section (RCS) of a scale model too large to measure in the range of millimeter-wave by measurement is investigated. This topic, to the best of our knowledge, has been little investigated due to its complexity. A scheme named RCS part measurement and synthesis to this problem is developed in this paper. This method combines measurement with theoretical calculation. The first step in using the method is that a scale model is partitioned into several parts measurable. Then the contributions of the sections and shadow region shadowed by all other parts are removed from the measured RCS data of every part. Finally, the scattered fields of all the parts are synthesized to obtain the total RCS of the scale model by means of the technique of relative phase synthesis. A result is presented to illustrate the utility of this scheme.     

The Application of the Discrete Mode Matching Method to Noncircular Dielectric Waveguides

This letter presents an extension of the discrete mode matching method to the analysis of dielectric waveguides with noncircular cross sections. The problem is analyzed in cylindrical coordinates expanding the fields in terms of Bessel functions. Matching of the fields tangential to the interfaces between different dielectric layers is ensured by applying the proper boundary conditions. The mathematical formulation is given in this letter, followed by its application to compute the propagation constants in elliptical dielectric waveguides.     

An inverse problem for line and strip sources of electromagnetic field above an imperfectly conducting ground plane

An analytic method of solving the inverse problem of determining the optimal excitation of line and strip sources of electromagnetic fields generating given directional functions above an imperfectly conducting ground plane is presented. The method used is based upon algebraization of the problem. The overdetermined system of equations obtained is solved by the method of generalized matrix inverse and the method of regularization of Tikhonov. An error estimate, criteria for the choice of parameters, and an experimental procedure are given. Numerical examples related to airborne radionavigation illustrate the application of the theory.     

A hybrid finite-element method for axisymmetric waveguide-fed horns

A new method for finding radiation patterns and the reflection coefficients associated with an axisymmetric waveguide fed horn is presented. The approach is based on a hybrid finite element method (FEM) wherein the electromagnetic fields in the FEM region are coupled to the fields outside by two surface integral equations. Because of the local nature of the FEM, this formalism allows for the presence of inhomogeneities to be included in the problem domain. The matrix equation which results from the application of this method is shown to be complex-symmetric. Comparisons of calculated and measured data for two different horns show good agreement