透射式碲铯(Cs2Te)光阴极厚度不均匀现象消除方法的研究

为解决透射式Cs₂Te光阴极厚度不均匀问题,通过理论和实验研究,分析了产生此问题的机理及其影响因素。这些因素包括：蒸发源发生器形状及其与阴极基底之间的相对位置;Cs/Te原子在阴极基底表面上完成化学反应所需的结合能以及制作阴极前基底表面所能达到的温度均匀性水平等。实验证明,上述最后一个因素是影响Cs₂Te光阴极厚度不均匀的主要原因。通过改变加温程序,优化保温时间,均衡阴极基底与阴极托盘温度梯度等途径,使得制作的透射式Cs₂Te光阴极厚度不均匀性由原来的76.4%,改善为＜10%。     

基于多视点视频编码宏块模式选择的快速算法

为降低多视点视频编码中宏块模式选择带来的编码复杂度,提出了一种新的宏块模式选择快速算法.首先分析了最优模式选择的统计特征,接着根据宏块的亮度信息对图像进行区域划分,进而对不同区域选择不同的模式,以达到快速找到最优模式的目,最后提出了一种基于宏块亮度绝对均值差的宏块模式选择的快速算法.实验结果表明:提出的快速算法在保持率失真性能基本不变的情况下,编码速度比多视点视频编码校验模型JMVM提高4.14~9.83倍.     

天空背景辐射亮度测量与研究

天空背景辐射亮度在空间目标探测与识别中有着重要作用,为了对其进行研究,介绍了天空背景辐射参数测量系统,与法国CIMEL公司研制的CE318太阳辐射计进行对比实验,取得了较好的一致性。利用天空背景辐射参数测量系统,在空间某目标过境时段,对其运行轨道上的天空背景辐射亮度参数进行了测量,通过对数据分析与研究,初步得出了该空间目标过境时段轨道上的天空背景辐射亮度参数变化特征,为应用研究提供了重要信息。     

积分球辐射光源照度均匀性研究

针对CCD等焦面阵列光电器件常被置于积分球辐射光源出口平面进行测试的误区,研究了积分球辐射光源照度分布的均匀性,得到了合理使用积分球光源测试光电器件的依据。基于数值解析方法和蒙特卡罗方法,建立了理想积分球辐射光源照度均匀性数学模型和非理想积分球辐射光源照度均匀性仿真模型,分析了与积分球光源出口不同距离处光电器件受光面上照度分布情况,并实验测试了两套积分球辐射光源照度分布情况,得到了与积分球辐射光源不同距离处光电器件受光面上照度均匀性分布规律。研究表明:当光电器件受光面直径小于积分球光源出口直径一半、光电器件和积分球出口之间的距离与积分球出口直径的比值在3至5之间时,可在光电器件受光面上获得均匀性优于99%的照度场。     

100MeV质子双环双散射体扩束方案设计

为满足质子单粒子效应实验对大面积、均匀化质子束流的需求,针对中国原子能科学研究院100 MeV质子回旋加速器提供的100 MeV质子进行了双环双散射体扩束方案设计.Geant4模拟表明该方案可在2.4 m位置产生一个均匀性为±1.89%、半径为8 cm的照射野,在5 m位置产生一个均匀性为±5.32%、半径为20 cm的照射野.此外,利用Geant4对双环双散射体扩束方法的基本原理进行了进一步探索,并对第二散射体后加速器管道、初始束斑尺寸、照射野形成距离、改变入射质子能量等实际中各种可能因素对该方案扩束效果的影响进行了讨论.     

Modelling of rapid thermal processing

An overview is given of modelling issues in rapid thermal processing. Firstly, the influence of surface and bulk properties on wafer emissivity is discussed. Secondly, the influence of back-side layers, wafer transparency and back-side roughness on temperature measurement is discussed. Thirdly, several causes of temperature non-uniformity are mentioned.     

Asymptotic bounds for estimators without limit distribution

Let be a general family of probability measures,κ : a functional, and the optimal limit distribution for regular estimator sequences of κ. On intervals symmetric about 0, the concentration of this optimal limit distribution can be surpassed by the asymptotic concentration of an arbitrary estimator sequence only forP in a “small” subset of . For asymptotically median unbiased estimator sequences the same is true for arbitrary intervals containing 0. The emphasis of the paper is on “pointwise” conditions for , as opposed to conditions on shrinking neighbourhoods, and on “general” rather than parametric families.     

Theoretical considerations in growing uniform epilayers

We briefly describe, theoretical considerations in the quest to grow crystalline films with perfection in uniformity of thickness. The endeavor of perfect crystallinity is best served by growing epitaxially. Thickness uniformity is facilitated by growing in a monolayer-by-monolayer mode-so called Frank-van der Merwe (FM) mode. The island (Volmer-Weber=VW) mode is undesirable; it promotes roughening and the creation of crystalline imperfections. Equilibrium criteria, proposed by Bauer, on the basis of shape equilibrium, predict that FM growth is favored by strong substrate bonding. The dependence of shape equilibration on adatom migration barriers, substrate temperature, and deposition rate is discussed. Modification of the system to improve adverse conditions by intermixing, alloying, and the use of surfactants is outlined. VW growth may also commence after completion of one or a few monolayers (MLs) in FM mode. This form of island growth, also known as Stranski-Krastanov (SK) growth, is mainly due to electronic effects, but may also be triggered by epitaxial strain relief. The tailoring of growth into FM-like growth, when VW or SK conditions exist-by an appropriate increase of supersaturation usually effected by controlling the substrate temperature and deposition rate, is briefly discussed.     

Effect of Spatial Frequency on Equal-Luminance Point for the Mechanism of Shape from Shading

We examined 1) whether the perception of shape from shading is based on luminance or brightness by testing the additivity law, and 2) whether the spatial frequency contents in the stimulus affect on the spectral sensitivity. We measured the relative radiance at which shading disappeared in a simple shading figure. Results showed that 1) the additivity law holds for shading disappearance settings and that 2) the sensitivity for green to white decreased as higher spatial frequencies in the figure decreases. These results suggest that the perception of shape from shading is based on a luminance type additive mechanism and that the spectral sensitivity of the mechanism varies depending on spatial frequency.Presented at the International Commission of Optics Topical Meeting, Kyoto, 1994.     

用正交光楔列阵获得连续可调的均匀方形光斑

提出用两组相互正交的光楔列阵系统获得方形光斑，其特点是光斑尺寸在一定范围内连续可调，形状不受入射光截面形状影响，光斑强度空间分布均匀性好，且受入射光强度分布的影响很小。对该系统作了详细的理论分析和数值计算。