Multiport analysis of arbitrary circular-rod insets in rectangularwaveguide by the generalized admittance matrix

An original generalized-admittance-matrix (GAM) approach for the analysis of multiport junctions in rectangular waveguide having an arbitrary circular-rod inset is presented in this paper. The method is based on an efficient computation of the GAM for the blocks that compose the structure. The efficiency is due to the fact that, for each block, the full three-dimensional GAM is obtained by solving a set of uncoupled two-dimensional problems. The accuracy and efficiency of the method developed have been assessed by comparing the results obtained with some measured data and with data obtained by the finite-element method     

An iterative FEM for scattering by a 3-D cavity-backed aperture

A finite-element method (FEM)-based hybrid method (or iterative FEM) is successfully applied to a three-dimensional (3-D) scattering problem without the effect of internal resonance. With only a small number of meshes around a 3-D scatterer, this FEM is shown to give an accurate result through several iterative updates of the boundary conditions. To confirm the efficiency of this method, scattering from a 3-D cavity-backed aperture is analyzed and the results obtained are compared with the same obtained by another conventional method     

AWG中阵列波导耦合系数的计算

针对阵列波导光栅（AWG）中阵列波导耦合系数的计算问题，提出了基于光束传播方法（BPM）的叠加积分方法的修正方法。将修正前、后的结果与简单叠加积分方法的结果作了分析比较，从而验证了修正方法的正确性。分析了阵列波导之间的耦合对耦合系数的影响，阵列波导间距越小，影响越大。     

对称非线性包层平板多量子阱波导TE模的传播特性

分别用精确计算和方均根近似方法得到了包层及衬底均为非线性Ｋｅｒｒ型介质、芯区为多量子阱的对称平板波导中ＴＥ模的传播特性。数值计算表明,当芯区多量子阱的层数较多时,方均根近似方法得到的结果与用精确方法得到的结果一致,此时多量子阱波导可以等效为均匀介质。对于自聚焦情况,在合适的光功率下,当分界面处包层（及衬底）的有效折射率与芯区折射率相等时,芯区的场分布呈均匀分布而两侧的场呈指数式衰减;功率继续增大时,场分布的极值进入芯区两侧,而芯区场分布呈下凹形。对于自散焦情况,波导对导波场有较强干线性波导的束缚作用,且随光功率的增大而增强。     

Research on the Radiation Characteristics of Patched Leaky Coaxial Cable by FDTD Method and Mode Expansion Method

Patched leaky coaxial cable (PLCX) is proposed as an alternative to the conventional leaky cable for wireless links in a complex environment. It is expected to have the capability of adjusting the coupling between the cable and the environment and give smoother electric field coverage. In this paper, the radiation characteristics of the PLCX with general inclined patches are studied by a hybrid method that involves the finite-difference time-domain (FDTD) method for the near-field computation and the mode expansion method for the transformation of near field to far field. In the method, the space around the patched leaky cable is divided into two regions by an artificial closed cylindrical surface that is incorporated with the FDTD lattice surface when implementing the FDTD iteration. The field distribution on the artificial surface is obtained after the implementation of the FDTD method. Meanwhile, the field outside the artificial boundary is expanded in terms of the Floquet modes with coefficients to be determined. By matching the field expressed by modes and the field obtained from the FDTD method at the artificial boundary, a matrix equation with unknown coefficients is obtained. Solving this matrix equation, the expansion coefficients are known, and the field outside the artificial boundary is ready to be obtained.     

Extraction of left ventricular contours from left ventriculograms by means of a neural edge detector

We propose a method for extracting the left ventricular (LV) contours from left ventriculograms by means of a neural edge detector (NED) in order to extract the contours which accord with those traced by a cardiologist. The NED is a supervised edge detector based on a modified multilayer neural network, and is trained by use of a modified back-propagation algorithm. The NED can acquire the function of a desired edge detector through training with a set of input images and the desired edges obtained from the contours traced by a cardiologist. The proposed contour-extraction method consists of 1) detection of "subjective edges" by use of the NED; 2) extraction of rough contours by use of low-pass filtering and edge enhancement; and 3) a contour-tracing method based on the contour candidates synthesized from the edges detected by the NED and the rough contours. Through experiments, it was shown that the proposed method was able to extract the contours in agreement with those traced by an experienced cardiologist, i.e., we achieved an average contour error of 6.2% for left ventriculograms at end-diastole and an average difference between the ejection fractions obtained from the manually traced contours and those obtained from the computer-extracted contours of 4.1%.     

Resolution and contrast enhancement in optical sub-traction microscopy with annular aperture

A method for improving lateral resolution and reducing imaging distortion of optical subtraction microscopy is proposed. First, an azimuthally polarized (AP) light is modulated by an annular aperture. Then, an image with higher lateral resolu-tion is obtained by subtracting an image obtained by an annular AP beam from an image obtained by a radially polarized beam. The simulation results demonstrate that compared with the case without the annular aperture, negative side-lobes in the effective point spread function are effectively suppressed, and the imaging quality of subtraction microscopy is obvi-ously enhanced.     

Regularized Estimation of Retinal Vascular Oxygen Tension From Phosphorescence Images

The level of retinal oxygenation is potentially an important cue to the onset or presence of some common retinal diseases. An improved method for assessing oxygen tension in retinal blood vessels from phosphorescence lifetime imaging data is reported in this paper. The optimum estimate for phosphorescence lifetime and oxygen tension is obtained by regularizing the least-squares (LS) method. The estimation method is implemented with an iterative algorithm to minimize a regularized LS cost function. The effectiveness of the proposed method is demonstrated by applying it to simulated data as well as image data acquired from rat retinas. The method is shown to yield estimates that are robust to noise and whose variance is lower than that obtained with the classical LS method.     

On the Design of Nearly-PR and PR FIR Cosine Modulated Filter Banks Having Approximate Cosine-Rolloff Transition Band

This paper proposes an efficient method for designing nearly perfect reconstruction (NPR) and perfect reconstruction (PR) cosine modulated filter banks (CMFBs) with prototype filters having an approximate cosine-rolloff (CR) transition band. It is shown that the flatness condition required for an NPR CMFB can be automatically satisfied by using a prototype filter with a CR transition band. The design problem is then formulated as a convex minimax optimization problem, and it can be solved by second-order cone programming (SOCP). By using the NPR CMFB so obtained as an initial guess to nonlinear optimizers such as Fmincon in Matlab, high-quality PR CMFBs can be obtained. The advantages of the proposed method are that it does not require a user-supplied initial guess of the prototype filter and bumps in the passband of the analysis filters can be effectively suppressed.     

Indoor field strength prediction based on FMM

1 Introduction With the popularization of personal communication service (PCS), indoor radio propagation has attracted more attention, especially for ultra-wideband (UWB) signals. Ultra-wideband communication systems have very high data rates (at least 10…     

Image restoration in computed tomography: the spatially invariant point spread function

Image restoration to deblur smoothing caused by the finite-size X-ray beam profile for a simulated computed tomography (CT) system is presented. Three simple image restoration methods are compared when the point-spread-function (PSF) is spatially invariant. In the first restoration method, an iterative least squares solution, regularized with the image norm and constrained by the boundary of the object, is obtained from the projection data. In the second method, a Wiener filter, designed using the power spectrum of CT noise, is applied to the reconstructed CT image. The third method obtains a weighted least-squares solution, by iteration, from the reconstructed CT image; the solution is regularized with the weighted image norm. Restored images were compared with the image obtained using filtered backprojection method. Differences between these images were evaluated qualitatively.     

Forward-backward method for scattering from dielectric rough surfaces

The iterative forward-backward (FB) method is a recently proposed efficient technique for numerical evaluation of scattering from perfectly conducting rough surfaces. Extension of the method to include scattering from imperfect conducting surfaces, with a high imaginary part of the complex dielectric constant, has also been proposed. The FB method is further generalized to analyze scattering from dielectric rough surfaces with arbitrary complex dielectric constant. Electric and magnetic equivalent surface currents are split into forward and backward components and equations governing these current components are obtained. As a solution, an iterative scheme is proposed and its convergence rate is analyzed. Finally, the effectiveness of the method is assessed by comparing the obtained scattering results with "exact" ones, computed by employing the usual method of moments (MoM).     

An AR spectral analysis of non-stationary signals

A method of estimating an adaptive spectral density is described. At each time-sample of the signal an autoregressive (AR) filter is calculated by a covariance method. The length of the memory is adapted to the stationarity of the signal by a minimum prediction error power criterion. Advantages of a pole trajectories representation in the time frequency domain are illustrated. The evolution of the prediction error power and of the length of the memory versus time gives information about the stationarity of the signal. Resolution and precision obtained by this AR method are better than those obtained by a Fourier Transform method.     

基于梯度离散化改进的DG_CENTRIST行人检测

针对复杂背景下的行人检测,从边缘信息入手,提出了一种新的基于梯度离散化的改进的中心对称统计变换(DG_CENTRIST)的行人检测方法。首先根据原始图像的梯度方向的分布,离散地形成多张梯度图;然后进行中心变换(CT)获得改进的DG_CENTRIST特征,最后提出的新的计算方法,结合线性和HIK-SVM,通过级联方式实现实时的行人检测。实验结果表明,该算法取得了较高的检测精度。     

Three-dimensional analysis of electromagnetic fields in rectangularwaveguides by the boundary integral equation method

A rapidly convergent expression of electromagnetic fields in rectangular waveguides is proposed for three-dimensional electromagnetic field analysis by using the integral equation method. The new method is an improved image expansion method utilizing the rapid convergence of the orthogonal expansion method. By this new method, the slow convergence of the orthogonal method with currents near an observation point can be removed completely. In order to investigate the adequacy of the new expression, the fields produced by the line electric and magnetic current segments are calculated and compared with the values obtained by the orthogonal expansion method. This confirms that the new expression gives accurate numerical values with a short computing time. Electromagnetic fields in a rectangular waveguide with circular metallic and dielectric posts are analyzed by using the new expression. From computed values, equivalent circuits of the metallic and dielectric post are obtained and compared with values obtained by N. Marcuvitz (1951). Reasonably good agreement is obtained     

一种基于空间光调制器的微透镜阵列制备技术

提出了一种基于空间光调制器的并行光刻制备微透镜阵列的技术。采用数字微反射镜器件输入光刻图形,结合热回流技术,制作任意结构和排布的微透镜阵列。无限远校正显微微缩光学系统的长焦深保证了深纹光刻的实现,热回流法提供了良好的表面光滑度。与传统逐层并行光刻和掩模曝光技术相比,提出的技术方案更加便捷灵活,特别适合制作特征尺寸在数微米至百微米的微透镜阵列器件。得到的微透镜阵列模版经过电铸转移为金属模具,利用紫外卷对卷纳米压印技术在柔性基底上制备微透镜阵列器件,在超薄液晶显示、有机发光二极管(OLED)照明等领域有广泛应用。     

Linearized method: A new approach for kinetic analysis of central dopamine D(2) receptor specific binding

We proposed a new method (;linearized method') to analyze neuroleptic ligand-receptor specific binding in a human brain using positron emission tomography (PET). We derived the linear equation to solve four rate constants, k(3), k(4), k(5), k(6) from PET data. This method does not demand a radioactivity curve in plasma as an input function to the brain, and can perform fast calculations in order to determine rate constants. We also tested the nonlinearized method including nonlinear equations which is a conventional analysis using plasma radioactivity corrected for ligand metabolites as an input function. We applied these methods to evaluate dopamine D(2) receptor specific binding of [(11)C] YM-09151-2. The value of B(max)/K(d)=k(3)/k (4) obtained by the linearized method was 5.72+/-3.1 which was consistent with the value of 5.78+/-3.4 obtained by the nonlinearized method.     

A local interpolatory cardinal spline method for the determinationof eigenstates in quantum-well structures with arbitrary potentialprofiles

A numerical method based on a variational approach and local interpolatory cardinal spline (LICS) functions is developed to compute the eigenstates of a quantum well with an arbitrary potential profile. The formulation of this method is straightforward, while the numerical solution is more accurate than results obtained by using other methods in the published literature     

工艺随机扰动下非均匀RLC互连线串扰的谱域方法分析

 考虑工艺随机扰动对互连线传输性能的影响,建立了互连线随机扰动模型,提出了一种基于谱域随机方法的互连线串扰分析新方法.该方法将具有随机扰动的耦合互连线模型在线元分析阶段进行解耦,分别采用随机伽辽金方法(SGM)和随机点匹配方法(SCM)进行串扰分析.最后,利用复逼近给出工艺随机扰动下互连线串扰噪声的解析表达式.实验结果表明本文方法不仅可以对工艺随机扰动下的非均匀耦合互连线串扰进行有效估计,相较于SPICE仿真还具有更高的计算效率.     

抗反射膜对衍射光学元件衍射效率的影响分析

针对抗反射膜引入的附加位相,分析了衍射光学元件的衍射效率,提出了含有抗反射膜的衍射光学元件的优化设计方法。以工作在可见光波段的衍射光学元件为例,对比分析了采用传统方法和优化方法设计的衍射光学元件的衍射效率。结果表明:抗反射膜对衍射光学元件的衍射效率和带宽积分平均衍射效率的影响是不可忽略的。针对正入射和30°斜入射两种工作状态,采用优化设计方法得到的衍射光学元件的带宽积分平均衍射效率高于94%。