Enhancement of electrical conductivity by Al-doped ZnO ceramic varistors

Zn_1−xAl_xO ceramic samples with various x values (0.00≤x≤0.20) are sintered in air at temperatures of 850 °C for 10 h and then quenched to room temperature. Structural, surface morphology and I-V characteristics of the samples are investigated using X-ray diffractometer (XRD), scanning electron microscope (SEM) and dc electrical measurements. It is found that addition of Al up to 0.05 does not influence the well-known peaks related to wurtzite structure of ZnO ceramics, and other unknown peaks could be formed above 0.05 of Al. The cell parameters of Al-doped samples are a little shorter than the undoped ZnO, and also the shape and size of grains are clearly affected. Average crystalline diameters, deduced from XRD analysis, are between 39.90 and 47.18 nm, which are 25 times lower than those obtained from SEM micrographs. Although breakdown field, nonlinear coefficient and barrier height are generally decreased by Al addition, the electrical conductivity is improved. These results are discussed in terms of the interaction mechanism between atoms of Al and Zn in both under and over-doped regions.     

负电子亲和势光电阴极量子效率公式的修正

量子效率是表征负电子亲和势（NEA）光电阴极发射性能的最重要的特性参数,准确建立量子效率公式为揭示各个阴极参量对整体性能的影响以及NEA光电阴极的优化设计提供了重要的理论指导.在对NEA光电阴极体内及表面光电发射过程的分析基础上,考虑入射光子能量、表面能带弯曲区以及表面势垒对电子发射的影响,对表面逸出概率和电子衰减长度进行了修正,并利用积分法推导了NEA光电阴极的量子效率公式,其理论预测曲线与实验曲线基本一致,从而验证了修正公式的实用性.为NEA光电阴极的研究提供了有效的理论参考依据. 关键词： 负电子亲和势光电阴极 量子效率 能带弯曲区 衰减长度     

基于区域增长的图像跟踪算法的研究

为了提高序列图像的跟踪精度,提出了基于区域增长的特征量提取方法。这种方法可捕获图像中所有单连通域,并能准确地提取其特征量,然后依据所提取的特征量设计分类器,实现对图像中所有单连通域进行分类识别并加以跟踪的目的。此算法有效地解决了一般传统识别算法难以区分目标和其近邻区域的干扰,而导致跟踪目标特征量提取不准确的问题。在目标特征提取识别算法的基础上,还提出了阈值预测分割算法,并应用在序列图像的跟踪中,取得了较好效果。     

一种LD泵浦双向输出固体环形激光器

提出了一种用于激光陀螺仪的LD泵浦Nd∶YVO4双向输出固体环形激光器。计算了谐振腔的环绕矩阵,分析了曲面镜焦距和放置距离对谐振腔稳定性的影响。得出了构成环形腔的稳定条件,光腰最大化条件,以及光束特性。并对所设计的环形腔进行了实验,获得了双向、多纵模基横模连续输出。     

带有锥形增益区14xxnm量子阱激光器的研制

利用MOCVD生长了14xxnm AlGaInAs/AlInAs/InP应变量子阱外延片.采用带有锥形增益区脊型波导结构和普通条形脊型波导结构在相同的实验条件下制作800 μm腔长激光器管芯,在相同的驱动电流下前者可以获得更高的输出光功率,而且P-Ⅰ曲线线性度较好、饱和电流高. 1200 μm腔长带有锥形增益区脊型波导结构管芯功率达到500 mW,饱和电流3 A以上,峰值波长1460 nm,远场发散角为39°×11°.     

高压VDMOS器件的SPICE模型研究

基于高压VDM O S器件的物理机理和特殊结构,对非均匀掺杂沟道、漂移区非线性电阻及非线性寄生电容效应进行分析,用多维非线性方程组描述了器件特性与各参数之间的关系,建立了精确的高压六角型元胞VDM O S器件三维物理模型,并用数值方法求解。基于该物理模型提出的等效电路,在SP ICE中准确地模拟了高压VDM O S的特性,包括准饱和特性和瞬态特性。在全电压范围内(0~100 V),直流特性与测试结果、瞬态特性(频率≤5 MH z)与M ED IC I模拟结果相差均在5%以内,能够满足HV IC CAD设计的需要。     

Computation of the scattering amplitude for a scattering wave produced by a disc — Approach by a fundamental solution method

Our fundamental solution method gives an analytic representation of the approximate solution for the reduced wave problem in the exterior region of a disc. The asymptotic behavior of this representation yields an approximate formula for the scattering amplitude. An error estimate for this formula is given. We add two numerical tests: the numerical estimate of errors; and profiles of scattering cross sections and the far-field coefficient. Both tests include cases of high wave numbers.     

A nonmonotone conic trust region method based on line search for solving unconstrained optimization

In this paper, we present a nonmonotone conic trust region method based on line search technique for unconstrained optimization. The new algorithm can be regarded as a combination of nonmonotone technique, line search technique and conic trust region method. When a trial step is not accepted, the method does not resolve the trust region subproblem but generates an iterative point whose steplength satisfies some line search condition. The function value can only be allowed to increase when trial steps are not accepted in close succession of iterations. The local and global convergence properties are proved under reasonable assumptions. Numerical experiments are conducted to compare this method with the existing methods.     

Interaction of three and four rarefaction waves of the pressure-gradient system

We study the two-dimensional pressure-gradient system, a subsystem of the two-dimensional compressible Euler system. We consider the problem of interaction of four rarefaction waves which is one case of two-dimensional Riemann problems. It is known that, when two planar waves interact, there exists a smooth solution in the interaction region. In this paper, we establish the existence of a smooth solution in the hyperbolic domain of determinacy, in which we encounter the interaction of simple and planar waves and shock prevention in simple waves.     

A fast subspace method for image deblurring

Image deblurring problems appear frequently in astronomical image analysis. For image deblurring problems, it is reasonable to add a non-negativity constraint because of the physical meaning of the image. Previous research works are mainly full-space methods, i.e., solving a regularized optimization problem in a full space. To solve the problem more efficiently, we propose a subspace method. We first formulate the problem from full space to subspace and then use an interior-point trust-region method to solve it. The numerical experiments show that this method is suitable for ill-posed image deblurring problems.