广义Cholesky分解乘法扰动分析

0引言关于实对称矩阵的广义Cholesky分解和扰动问题是矩阵计算的重要问题,可参考文献[1-2].本文首先介绍已有的采用加法扰动的角度得到的广义Cholesky分解的一阶相对     

一种基于手机令牌和NFC技术的身份认证系统

针对目前Web站点的身份认证安全问题,提出了一种基于手机令牌和近距离无线通信(NFC,near field communication)技术的身份认证方法,并在Android平台上实现了该系统.该系统利用手机使用手机令牌实现了USBKey的主要功能,当用户访问站点进行注册时,将获得惟一的手机令牌并存于带有加解密功能的手机中.在下次访问站点进行身份认证时,用户可通过手机直接在Web站点进行身份认证,也可通过NFC技术将手机令牌传于PC机,使得用户可在PC机上利用手机进行身份认证.该系统将手机作为类USBKey设备,在增强Web站点身份认证安全的同时,省去了为用户颁发USBKey的流程和成本,具有较强的实用价值.     

Study on Preferential Solvation of Water by Electrochemical Method

The preferential solvation of water plays an important role in ferrocene research which is a subject of current interest. Voltammetric investigations were carried out for Au electrode in acetonitrile/water, showing preferential solvation of water. In our work, the preferential solvation of water in acetonitrile/water was studied by electrochemical methods including cyclic volitammetry, electrochemical impedance spectra and double‐step chronoamperometry. Ferrocenemethanol (FcCH₂OH) molecules as a solute spontaneously adsorb on the electrode surface in anhydrous acetonitrile, resulting from acetonitrile molecules tend to form an acetonitrile solvent layer on the surface of the electrode and acetonitrile solvent layer has a lower energy barrier than the aqueous solvent layer, which has been obtained by modeling solvation. The solvent strongly influences electrochemical behavior of solute. Once there is an amount of water in acetonitrile solvent, FcCH₂OH that adsorbed on the electrode surface desorb. This is because water preferentially solvate with FcCH₂OH in term of intermolecular forces between solvent and solute. Moreover, hydrogen bond between water molecules and FcCH₂OH molecules is stronger than dipole‐dipole interaction between acetonitrile molecules and FcCH₂OH molecules in solvation effect. Through electrochemical behavior of FcCH₂OH changing, preferential solvation of water is analyzed by electrochemical methods.     

横截面上光强的精确表述

在考虑了时间平均能流密度的矢量特性的情况下，对光强的概念进行了推广－定义为单位时间单位面积内所流过的能量的时间平均值，从而使其中适用于任何一个连续的曲面，也能与光强子的实际测量值取得一致，这个推广的定义式表明，曲面上任一点处的光强值都不仅与该处理振幅有关，而且还和该处的时间平均能流密度与面元方向的夹角有关，作为一个重要的特例情况，文中还给横截面（垂直于光束传输方向）上的光强公式，这个结果可用来对非     

Propagation of Flattened Hermite-GaussBeams Around a Thin Lens

SupportedbytheNationalNaturalScienceFoundationofChina.1.IntrodtlctionInourprcviOLISbaper[1J,x\'ehavcstLldicdthepropagati0n0ff1attencdHermite}Gaussbeams(FGHlls)infreespace,bytakingthcmasc0hercntsuperimpositi0nofHermite-Gaussbcamsofevcndrder.Inpracticaluse,suchbcamsareusualIyf0cuscdbyalens.'Sincetrans-formation0fhighordcrHermite-Gaussbcamsbythin]enscanbestudicdana1yticalIy,wecandcscribetheficlddistributions0fFGHllsafterathinlensalongpropagati0naxikexp1icitly,andwriteouttheirbeamspotsiz…     

Nd：YLF单纵模调Q激光器腔内脉冲稳幅的实验研究

报道用超快ＧａＡｓ光电导开关为基础的光电反馈网络对ＮＤ：ＹＬＦ单纵模调Ｑ脉冲激光器的腔内光强度成功地进行了负反馈控制，输出的调Ｑ激光脉冲幅度稳定性得到提高，不稳定度＜±３％。     

超短电子脉冲的时空转换测量方法理论研究

分析了超快电子枪处于扫描状态下电子束的传输特性,对飞秒量级的超短电子束脉冲通过偏转扫描系统时的偏转距离等物理量进行了数值计算。计算结果显示：为确保电子束能够顺利通过偏转扫描系统并最后轰击直径为30 mm的荧光屏,必须加一个700~1400 V的初始电压,以便抵消负斜坡扫描电压的作用;700~1400 V的初始电压和负斜坡扫描电压的共同作用,是扫描实验成功的一个前提。扫描实验成功的另一个前提是激发光电阴极的光路和控制扫描的电路之间的同步。讨论了前提一带给同步实验的巨大困难,并设计了一个可以在扫描实验中以较高效率调节光路延时的实验系统,该系统可解决脉宽测量实验中扫描斜坡电压信号和超快电子脉冲的同步难题。     

LD泵浦的Nd∶YAG微片激光器实验研究

详细讨论了激光二极管泵浦的Ｎｄ∶ＹＡＧ微片激光器输出的纵、横模特性．当泵浦功率小于７４０ｍＷ时，输出为单纵模、基横模，线宽达到仪器分辨极限２５ＭＨｚ．     

Colliding pulse mode-locked Nd: YLF laser with negative feedback control by GaAs Photoconductive switch

A picosecond colliding pulse mode-locked Nd: YLF laser with negative feedback provided by GaAs photoconductive switch was described. Optical pulse with～4ps duration, 10μJ energy and about 7μs long pulse train were generated.