基于向量空间不同访问群体的门限方案

针对具有不同访问权限的群体的秘密共享是难于处理的问题,在有限域上引入内积向量空间的概念,研究子空间的直和及其正交补结构中基向量的组成形式;利用Gram-Schmidt算法和最近向量定理设计了一个基于向量空间的（s+r, m+n）门限方案,并将此方案推广到有限多个不同访问群体的情形。结果表明,基于向量空间的不同访问群体的门限方案满足秘密共享的重构和安全性要求,是一个完备的秘密共享方案。     

Threshold voltage of narrow channel field effect transistors

A new effect associated with Metal-Oxide-Silicon Field-Effect-Transistors (MOS-FET's) is presented in this paper. MOS-FET's show an increase of threshold voltage with decreasing ratio of channel width to gate depletion width. This narrow channel effect is explained by means of geometrical edge effects. With decreasing channel width the transition from the field oxide depletion region to the gate oxide depletion region becomes comparable to the gate width and cannot be neglected in the derivation of the threshold voltage equation.A theoretical model is given to explain the influence of decreasing channel width on the threshold voltage as well as on other electrical parameters. This theoretical model is in good agreement with experimental results given in this paper.     

Detecting boundaries in a vector field

A vector gradient approach is proposed to detect boundaries in multidimensional data with multiple attributes (a vector field). It is used to extend a gradient edge detector to color images. The statistical effects of noise on the distribution of the amplitudes and directions of the vector gradient are characterized. The noise behavior of the L ₂ norm of the scalar gradients is also characterized for comparison. When the attribute components are highly correlated, as is often the case in color images, use of the vector gradient shows a small gain in signal-to-noise ratio over that of the L₂ norm of the scalar gradients. This small gain may or may not be significant, depending on other measures an edge detector uses to deal with noise     

Matched direction detectors and estimators for array processing with subspace steering vector uncertainties

In this paper, we consider the problem of estimating and detecting a signal whose associated spatial signature is known to lie in a given linear subspace but whose coordinates in this subspace are otherwise unknown, in the presence of subspace interference and broad-band noise. This situation arises when, on one hand, there exist uncertainties about the steering vector but, on the other hand, some knowledge about the steering vector errors is available. First, we derive the maximum-likelihood estimator (MLE) for the problem and compute the corresponding Crame/spl acute/r-Rao bound. Next, the maximum-likelihood estimates are used to derive a generalized likelihood ratio test (GLRT). The GLRT is compared and contrasted with the standard matched subspace detectors. The performances of the estimators and detectors are illustrated by means of numerical simulations.     

Threshold variability in fibers with field stimulation of excitablemembranes

The central focus of this report is the evolution of transmembrane potentials following initiation of a point-source field stimulus, particularly when the stimulus is short and the stimulating electrode is close to the fiber. The transmembrane voltage threshold in response to a point-source field stimulus was determined in a numerical model of a single unmyelinated fiber. Both nerve (Hodgkin-Huxley [1952]) and cardiac (Ebihara-Johnson [1980]) models of the fiber membrane were evaluated. A central question is whether it is possible to know in advance whether a stimulus of specific magnitude, duration, and location will result in a subsequent action potential. Such determination can be based on the membrane's “voltage threshold”. In contrast to the commonly held view, the voltage threshold was found to vary markedly depending on the duration and location of the field stimulus. Voltage thresholds ranged from about 8 mV above baseline to more than 100 mV above baseline, the higher thresholds occurring with shorter stimuli and electrode locations closer to the membrane. A related question is whether the passive membrane response can be used as a tool in determining whether a subsequent action potential is elicited. If the answer is affirmative, this finding can be very useful, since passive properties are linear and thereby much simpler to evaluate than active ones. The results show that the passive response tracks active responses long enough to be a good estimator of subsequent action potential development. Examples show that the evaluation of V_m at 0.2-0.5 msec after stimulus initiation, times chosen on the basis of membrane characteristics, was a better predictor of subsequent excitation than was either initial transmembrane current or V_m at the time when the stimulus ends. Most of the circumstances analyzed here with electric field stimulation also appear likely to be valid with magnetic field stimulation     

基于矢量场卷积的虹膜定位

为了提高虹膜定位的精度和准确性,从而进一步提高虹膜识别系统的识别率,提出了一种基于矢量场卷积(Vector Field Convolution,VFC)的虹膜定位算法,用于精确定位虹膜内边界。首先利用最小灰度平均值法自动确定VFC模型的初始化轮廓,在活动轮廓内外力作用下实现虹膜内边界定位;然后对于虹膜外边界,采用改进的Daugman算法进行定位。利用多个虹膜图库进行了大量实验,并与几种常见的虹膜定位算法进行了比较,实验结果表明:该方法定位准确度更高,虹膜内边界定位更接近真实边界,定位结果有明显改善。     

Stability issues in vector electric field propagation

Demonstrates that although standard paraxial and wide-angle vector field propagation techniques lead to divergences for sufficiently small grid-point spacings and large refractive index differences, stability may be restored through either certain Pade approximates to the propagation operator or suitable boundary conditions. The authors also introduce a novel alternating directional implicit method applicable to less divergent discretizations of the vector wave equation     

雷达图像运动矢量场计算

多普勒天气雷达是强对流天气监测和预警的主要工具。基于能够达到准确预报天气的目的,需要计算雷达图像的运动矢量场,因此在全局约束光流算法和L-K算法的基础上,本文提出了一种计算雷达图像运动矢量场的详细算法,这种算法能有效加快运算时间,同时又能保证运算结果的有效性。其中包括图像预处理方面的内容,并给出了处理过程中所需的较好的参数。并通过天津地区雷达图像数据的大量实验,确定此算法能够较为准确的计算出雷达图像的矢量场,从而可用于天气预报的过程之中。     

A recursive nonstationary MAP displacement vector field estimationalgorithm

A recursive model-based algorithm for obtaining the maximum a posteriori (MAP) estimate of the displacement vector field (DVF) from successive image frames of an image sequence is presented. To model the DVF, we develop a nonstationary vector field model called the vector coupled Gauss-Markov (VCGM) model. The VCGM model consists of two levels: an upper level, which is made up of several submodels with various characteristics, and a lower level or line process, which governs the transitions between the submodels. A detailed line process is proposed. The VCGM model is well suited for estimating the DVF since the resulting estimates preserve the boundaries between the differently moving areas in an image sequence. A Kalman type estimator results, followed by a decision criterion for choosing the appropriate line process. Several experiments demonstrate the superior performance of the proposed algorithm with respect to prediction error, interpolation error, and robustness to noise.     

基于场效应晶体管的太赫兹探测器中天线设计的一种有效方法

在场效应晶体管太赫兹探测器中,合理的天线设计可以增强晶体管和太赫兹波之间的耦合效率,从而提高太赫兹探测器的响应度.提出一种基于晶体管栅极边缘沟道电场的仿真来设计平面天线的方法.这种方法尤其适用于太赫兹波段晶体管输入阻抗不容易得到的情况.通过流片完成的基于氮化镓高电子迁移率晶体管的太赫兹探测器的响应度测试证实了这种方法的有效性.集成碟形天线和双偶极子天线的太赫兹探测器最大响应度分别在170.7 GHz(1568.4 V/W)和124.3 GHz(1047.2 V/W)频点处测得,这个测试结果接近基于晶体管栅极边缘沟道电场的仿真结果.     

Near field vector beam measurements at 1 THz

We have performed near-field vector beam measurements at 1.03 THz to characterize and align the receiver optics of a superconducting receiver. The signal source is a harmonic generator mounted on an X-Y translation stage. We model the measured two-dimensional complex beam pattern by a fundamental Gaussian mode, from which we derive the position of the beam center, the beam radius and the direction of propagation. By performing scans in the planes separated by 400 mm, we have confirmed that our beam pattern measurements are highly reliable.     

The distribution of an electric field in p-n junctions of silicon edgeless detectors

Development of silicon edgeless detectors started in 2004 and was motivated by preparations for the total elastic and diffractive cross-section measurement (TOTEM) experiment at the Large Hadron Collider (LHC) at CERN. In the context of this experiment, it would be necessary to detect protons scattered at ultimately small angles with respect to the LHC proton beam, which brings about a limitation imposed on the maximum distance between the beam and the sensitive region of the detector. In order to solve this problem, a new type of silicon detector (edgeless detectors) was developed; these detectors have the structure, which controls the distribution of the current near the edge of the p-n junction. In this paper we report the results of studying the distribution of the potential and an electric field in the region of the cut edge in the silicon edgeless detectors; the models, which account for the obtained results, as well as their consistency with current-voltage characteristics of silicon edgeless detectors developed for the TOTEM experiment, are discussed.     

Effect of magnetic field on the performance of millimeter-wave detectors using bulk InSb

The performance of microwave-biased millimeter-wave detectors using bulk InSb in the presence of a magnetic field is described. Broad-band transitions between the impurity and conduction bands together with free-carrier absorption are responsible for the detection mechanism. The performance of the device is examined as a function of the magnetic field, millimeter-wave signal, and microwave bias levels. The results show that the performance can be improved by proper choice of the magnetic field.     

基于向量场距离函数的网孔模型修复

提出了一种基于向量场距离函数的网孔模型修复算法,用于修复各种多边形网孔模型。可用于激光三维建模等应用中,作为一种体修复算法,其鲁棒性好,对于任意带缺陷的输入网孔模型,经修复后均能得到无缺陷的封闭且法向一致的三角形网孔输出。修复过程中,体模型用向量场距离函数表征,该表征方法比传统的标量场距离函数更能保留模型的原始特征。此外,在提取输出表面轮廓时,对传统MC算法中求取立方体网格与形面交点的插补算法作了改进。理论和实践证明,改进后插补点的位置更接近网格与形面交点的实际位置,因而提取出来的网孔模型更为精确,比传统方法精确约16.8%。     

径向矢量光场在双延迟器作用下的偏振演化

延迟器作为改变光信号偏振态的一种重要光学器件,具有高偏振变换精度、低成本、算法简单等特点,利用一个1/4波片和一个1/2波片组合可实现对径向矢量光场偏振调制的新方法,采用Jones矩阵算法分析了双波片的调制机理,将光场的偏振演化规律在庞加莱球上表示,并通过实验验证理论分析的正确性,研究结果表明:双延迟器结构可实现对径向矢量光场的复杂偏振调控,并获得光强均匀分布、偏振态有规律分布的矢量光束。     

Threshold voltage, field effect mobility, and gate-to-channelcapacitance in polysilicon TFTs

Based on experimental and theoretical studies of n- and p-channel polysilicon thin film transistors with gate W/L ratios from 0.3 to 3.3, we have demonstrated that the threshold voltage extracted from gate to channel capacitance data results in field effect mobility parameters which are independent of device geometry. The parameters extracted using this V_t allow us to reproduce the I-V characteristics of the n- and p channel TFTs over wide ranges of bias voltages and gate sizes. The C_gc-V_GS characteristics of polysilicon TFTs are strongly affected by the trapping and de-trapping of carriers. As a result, the measured C_gc characteristic is a function of measurement frequency and gate length. However, we demonstrate that to the first order, the frequency dispersion of the C_gc curve can be related to the effective carrier transit time determined using the V_GS dependent field effect mobility     

关于标量场高斯光束成为矢量场的分析

本文阐述了标量场高斯光学理论是一种近似的实质。阐述了以高斯光束为基础,要使它成为电磁场的矢量解的一般原理,提出并简化,统一使之矢量化必须配置的极经矢量场Ａ（ｘ）的满足的基本方程,讨论了间化求解的方程,为高斯光束传输的应用及研究中,涉及必须考虑矢量场（极化类型）的领域,指明了理论的局限,并提供了使之矢量化的理论分析一种途径和基础。     

在真空中电磁场的梯度矢势

人们对于电磁场的认识已经很深入了,已经认识到电磁场是物质存在的一种形式,电磁场的传播可以由麦克斯韦(Maxwell)方程完全确定。 由麦克斯韦方程可以引出电磁场的连续性方程如下:     

Size detectors

An edge separation method of detecting one-dimensional objects in a given size range is described, and its capabilities contrasted with those of the conventional linear matched filter approach to object detection.