An equivalent electric field source for wideband FDTD simulations of waveguide discontinuities

Transparent sources are often used in wideband finite-difference time-domain (FDTD) simulations of waveguide discontinuity problems. Direct implementations of transparent sources may not correspond to the original hard source spectrum, or else require auxiliary simulation steps for correction purposes. In this letter, we propose a more direct approach to construct FDTD transparent electric field source-models for waveguides. We also provide an explanation for a "spectrum distortion" phenomenon recently reported for FDTD sources in waveguide problems . The main findings are illustrated by means of FDTD simulations of waveguides operating at Ku-band.     

Bayesian approach with hidden Markov modeling and mean field approximation for hyperspectral data analysis

The main problems in hyperspectral image analysis are spectral classification, segmentation, and data reduction. In this paper, we propose a Bayesian estimation approach which gives a joint solution for these problems. The problem is modeled as a blind sources separation (BSS). The data are M hyperspectral images and the sources are K < M images which are composed of compact homogeneous regions and have mutually disjoint supports. The set of all these regions cover the total surface of the observed scene. To insure these properties, we propose a hierarchical Markov model for the sources with a common hidden classification field which is modeled via a Potts-Markov field. The joint Bayesian estimation of the hidden variable, sources, and the mixing matrix of the BSS gives a solution for all three problems: spectra classification, segmentation, and data reduction of hyperspectral images. The mean field approximation (MFA) algorithm for the posterior laws is proposed for the effective Bayesian computation. Finally, some results of the application of the proposed methods on simulated and real data are given to illustrate the performance of the proposed method compared to other classical methods, such as PCA and ICA.     

Applications for incomplete Lipschitz-Hankel integrals inelectromagnetics

Incomplete Lipschitz-Hankel integrals (ILHIs) are a class of special functions that appear in the analytical solutions for numerous canonical problems in electromagnetics. The reason that they appear so often in electromagnetics is because they provide solutions to the wave equation. The intent of the article is to provide an overview of the research that has been carried out in this area. After providing a brief introduction to the theory of ILHIs, applications for these special functions in problems involving diffraction, dispersion, sources radiating in layered media, and traveling-wave sources radiating in a homogeneous space, are discussed     

Diffraction Tomography with Arrays of Discrete Sources and Receivers

We present both theory and numerical simulations of diffraction tomography for arrays of line sources. The approach taken is applicable to a wide range of imaging problems where discrete sources and receivers are located near the object to be imaged rather than in its far field. As such, these new results tie into the vast body of research on inverse scattering, which to date is based largely on planewave sources. Our derivation implicitly includes a method for synthesizing plane waves; this method leads to inversion formulas based on the generalized projection-slice theorem. Although related techniues for synthesizing plane waves from discrete arrays are known, it is helpful to have available a theory that incorporates the synthesis directly into the scattering theory. The formulation is presented for propagating fields satisfying the Born and Rytov approximations in weakly inhomogeneous media and provides a convenient means for treating both forward and inverse scattering problems. Through a numerical example, we illustrate two important features of diffraction tomography inversion, i. e., 1) the effects of limited view and 2) results of probing with different signal frequencies. The example utilizes data generated by an exact forward modeling technique thus providing strong evidence supporting the usefulness of weak scattering approximations for inversion problems.     

Spherical Wave Diffraction by a Slit in an Impedance Screen

An exact solution is developed for the problem of diffraction of an E-polarized and an H-polarized spherical waves by a slit in an impedance screen. This consideration is important in the sense that point sources are regarded as better substitutes for real sources than line sources/plane waves. The two independent problems are solved using the Fourier transform, the Wiener-Hopf technique and asymptotic approximations.     

Domain-decomposed MEI method for field computation in single andmultiple regions

The domain-decomposed measured equation of invariance (DDMEI) method is proposed for field computation in single and multiple regions. The whole computing domain is partitioned into a cluster of subdomains. For single region problems, this partition splits the computing domain into many subdomains artificially. For multiple regions problems, these subdomains can be taken as those regions separated geometrically. The contribution of sources residing in a subdomain is approximated by a set of sources selected out of these original sources with greatly reduced amounts. The approximation is implemented numerically by the MEI method. The resultant MEI matrices are blocked matrices and each submatrix is highly sparse. Approaches and numerical results are given respectively for the applications of the DDMEI to the scattering of single conducting cylinders, radiation of wire arrays, and capacitance matrix computation for multiconductor transmission lines. The DDMEI proposed in this paper is an improved version of the surface current MEI method (SCMEI). Compared with the SCMEI, the DDMEI improves the sparsity of the MEI matrices and the feasibility of measuring out the MEI coefficients. Furthermore, the DDMEI makes it possible to apply the kind of on-surface MEI methods (OSMEI) to multiple region problems for the first time     

Technical Considerations for Establishing Requirements Pertaining to Broad-Band EMI from Data-Processing Equipment and Office Machines

This paper extends the scope of earlier narrow-band work to include control of broad-band emission sources which can exist independently of, or in conjunction with, narrow-band sources in electronic data-processing (EDP) and office-machine (OM) equipment (products). While both narrow-band and broad-band noise sources have the potential for RF interference with communication services, our experience with broad-band problems has shown this class of sources to be much less significant than the low incidence of actual narrow-band component EDP interference problems examined in the initial paper [1]. Limits are discussed considering the empirical data base and need for international harmonization of interference requirements     

The reliability functions of the general source with fixed-lengthcoding

The reliability function problems with fixed-length source coding for the general source are studied for all rates R. Our fundamental philosophy in doing so is to convert all of the reliability function problems to the pertinent computation problems in the large derivation-probability theory. It turns out that this kind of new methodology, which was previously developed by Han (see ibid., vol.43, p.1145-64, 1997), enables us to establish quite compact general formulas of the reliability function for general sources including all nonstationary and/or nonergodic sources with countably infinite alphabet. Such general formulas are presented from the information-spectrum point of view     

On the Distributed Compression of Quantum Information

The problem of distributed compression for correlated quantum sources is considered. The classical version of this problem was solved by Slepian and Wolf, who showed that distributed compression could take full advantage of redundancy in the local sources created by the presence of correlations. Here it is shown that, in general, this is not the case for quantum sources, by proving a lower bound on the rate sum for irreducible sources of product states which is stronger than the one given by a naive application of Slepian-Wolf. Nonetheless, strategies taking advantage of correlation do exist for some special classes of quantum sources. For example, Devetak and Winter demonstrated the existence of such a strategy when one of the sources is classical. Optimal nontrivial strategies for a different extreme, sources of Bell states, are presented here. In addition, it is explained how distributed compression is connected to other problems in quantum information theory, including information-disturbance questions, entanglement distillation and quantum error correction     

Hypothesis testing with the general source

The asymptotically optimal hypothesis testing problem, with general sources as the null and alternative hypotheses, is studied under exponential-type error constraints on the first kind of error probability. Our fundamental philosophy is to convert all of the hypothesis testing problems to the pertinent computation problems in the large deviation-probability theory. This methodologically new approach enables us to establish compact general formulas of the optimal exponents of the second kind of error and correct testing probabilities for the general sources including all nonstationary and/or nonergodic sources with arbitrary abstract alphabet (countable or uncountable). These general formulas are presented from the information-spectrum point of view     

Conception approach of access control in heterogeneous information systems using UML

The development of the information systems should answer more and more to the problems of federated data sources and the problems with the heterogeneous distributed information systems. The assurance of data access security realized in the cooperative information systems with loose connection among local data sources is hard to achieve mainly for two reasons: the local data sources are heterogeneous (i.e. data, models, access security models, semantics, etc.) and the local autonomy of systems does not allow to create a global integrated security schema. The paper proposes to use one common set of access control concepts to support the access control management in security of heterogeneous information systems. The UML (Unified Modeling Language) concepts can be used to define and implement the most popular access control models, such as DAC, MAC or RBAC. Next, the concepts derived from different models can be joined to use one common approach comprehensible for each administrator of each cooperative information system in the federation.     

基于双平行线阵的相干分布源二维DOA估计

针对现有相干分布源二维波达方向(DOA)估计算法存在的一些问题,基于双平行均匀线阵提出了一种相干分布源二维DOA估计新算法。利用旋转不变的思想并结合传播算子法来估计相干分布源的二维中心DOA。无需谱搜索和对样本协方差矩阵做特征分解,和传统算法相比,其计算复杂度更低。此外,还给出了详细的参数配对过程,因而能够应用于多源场合。算法在小角度扩展条件下估计性能良好,其性能甚至接近于一维交替搜索算法。算法还是一种对角分布先验知识盲的估计。仿真结果证实了算法的有效性。     

Faraday chiral media revisited. I. Fields and sources

Faraday chiral media, previously conceptualized as chiroplasmas or chiroferrites, are envisioned to combine the effects of Faraday rotation and chirality. Electromagnetic field representations for arbitrary sources are derived after the previous correct characterization of the constitutive relations of such media. The scalar Hertz potential (SHP) technique is employed and its applicability is thoroughly investigated. In particular, it is shown that all field components can be derived from one scalar Green function (plus so-called auxiliary source potentials) in source problems, whereas one scalar superpotential suffices for source-free problems. Expressions pertaining to radiation from electric and magnetic dipole sources are presented in a simple and compact form. Further generalizations of the results and the actual realizability of Faraday chiral media are discussed     

Liquid immersion cooling of small electronic devices

The primary purpose of this investigation was to examine liquid immersion techniques for cooling minute heat sources. The study demonstrated that nucleate boiling is an effective means of cooling larger heat sources. However, for heat sources with surface areas less than 0·01 sq. cm, nucleate boiling was found to offer very little improvement in convective heat transfer over free convection with the same liquid. In addition, nucleate boiling may introduce mechanical stresses, contamination and physical design problems. For these reasons, two alternatives to boiling (forced convection and bubble induced mixing) were also investigated which reduced (or bypassed) some of these problems.In the forced convection study, boundary layer analysis showed the convective heat transfer coefficient would increase significantly as the heat source size decreased. This was verified experimentally with two different liquids. The experiments found the convection coefficient increased by a factor of 15 when the source size was decreased from 2·00 to 0·01 sq. cm. A similar increase was noted in the free convection and bubble induced mixing experiments. In addition, with small sources both bubble induced mixing and forced convection gave significantly larger heat transfer coefficients than were practical with boiling.     

Nonradiating and minimum energy sources and their fields:generalized source inversion theory and applications

A new general framework for characterizing scalar and electromagnetic (EM) nonradiating (NR) and minimum energy (ME) sources and their fields is developed that is of interest for both radiation and source reconstruction problems. NR sources are characterized in connection with the concept of reciprocity as nonreceptors. Localized ME sources are shown to be free fields truncated within the source's support. A new source analysis tool is developed that is based on the decomposition of a source and its field into their radiating and NR components. The individual radiating and reactive energy roles of the radiating and NR parts of a source are characterized. The general theory is illustrated with a time-harmonic EM example     

On the Cramer- Rao bound for time delay and Doppler estimation (Corresp.)

Using a theorem due to Whittle, simple derivations of the Cramer-Rao lower bound are presented for some delay estimation problems related to a single source, multiple sources, and multipath. The problem of Doppler estimation is briefly discussed.     

Bayesian solutions and performance analysis in bioelectric inverse problems

In bioelectric inverse problems, one seeks to recover bioelectric sources from remote measurements using a mathematical model that relates the sources to the measurements. Due to attenuation and spatial smoothing in the medium between the sources and the measurements, bioelectric inverse problems are generally ill-posed. Bayesian methodology has received increasing attention recently to combat this ill-posedness, since it offers a general formulation of regularization constraints and additionally provides statistical performance analysis tools. These tools include the estimation error covariance and the marginal probability density of the measurements (known as the "evidence") that allow one to predictively quantify and compare experimental designs. These performance analysis tools have been previously applied in inverse electroencephalography and magnetoencephalography, but only in relatively simple scenarios. The main motivation here was to extend the utility of Bayesian estimation techniques and performance analysis tools in bioelectric inverse problems, with a particular focus on electrocardiography. In a simulation study we first investigated whether Bayesian error covariance, computed without knowledge of the true sources and based on instead statistical assumptions, accurately predicted the actual reconstruction error. Our study showed that error variance was a reasonably reliable qualitative and quantitative predictor of estimation performance even when there was error in the prior model. We also examined whether the evidence statistic accurately predicted relative estimation performance when distinct priors were used. In a simple scenario our results support the hypothesis that the prior model that maximizes the evidence is a good choice for inverse reconstructions.     

New source number estimation algorithm based on l 1 sparse regularization

In view of the problems of inefficient in low SNR and less snapshots when using existing sources number estimation related algorithms,a new algorithm based on e₁sparse regularization under space stationary noise was proposed to estimate the number of signal sources.The algorithm estimated the sources number by using the sparse representation of eigenvalues vectors with the suitable regularization parameter.Theoretical analysis and simulation results show that the algorithm can realize an accurate sources number estimation in low SNR and less snapshots.     

液晶投影光源技术分析

根据主流液晶微显投影系统的技术特征，分析阐述了液晶投影光源的基本特点，并就现代液晶投影光源的技术特性和相关问题进行讨论，对液晶投影光源的进一步发展提出观点。     

Transparent boundary conditions for parabolic equation solutions ofradiowave propagation problems

Perfectly transparent boundary conditions are derived for truncating the integration domain when solving radiowave propagation problems with a parabolic equation (PE) method. The boundary conditions are nonlocal: they are expressed as a convolution integral involving the field at all previous ranges. The convolution kernel is matched to the refractive index vertical gradient at the boundary. The boundary conditions include an incoming energy term which can model an arbitrary incident field. In particular, they may be used with plane-wave incidence, or with a point-source located below or above the domain boundary. If required, the solution can be extended to heights above the boundary with a generalized horizontal PE method. Closed-form solutions for the incoming energy term are given for plane-wave incidence and for Gaussian sources when the refractive index above the boundary is constant or linear. The resulting finite-difference algorithms provide efficient solutions to problems involving airborne sources. Numerical examples are given, showing excellent agreement with a pure split-step/Fourier PE algorithm