可信安全计算平台的一种实现

依据TCPA所提出的可信计算平台的原理给出了可信安全计算平台的一种具体实现——JETWAY安全计算机，其系统结构和所采用的主要技术路线与TCPA PC规范相一致，并有独特的智能卡开机身份认证和设备安全控制功能，最后给出了JETWAY安全计算机在证券网络远程交易系统中的一个应用实例．     

短焦数字投影镜头的光学设计

为了满足短焦投影市场的需求,利用ZEMAX光学软件开发设计出了一款适用于0.8英寸单片数字光处理投影机的短焦数字投影镜头,该镜头总长172.6 mm,全口径70 mm,采用反远距结构,由6组7片透镜组成,其中包括6片玻璃透镜和1片塑料透镜(两个偶次非球面).镜头全视场达到80°,相对孔径为1/2.1,反远比(工作距离/...     

玻色-爱因斯坦凝聚特性及其应用

本文介绍了北京大学建立的玻色-爱因斯坦凝聚实验平台，实现了玻色-爱因斯坦凝聚（图1），获得了原子数为五十万个，温度为50纳开尔文的玻色凝聚体。在此基础上我们精密测量了玻色-爱因斯坦凝聚的相变温度，还利用玻色-爱因斯坦凝聚实验平台通过马越让那跃迁获得了可控的多量子态玻色爱因斯坦凝聚体。并利用四种方法获得了原子激光（图2），其中有三种方法是国际上第一次使用。另外，我们提出了将玻色一爱因斯坦凝聚转入Magic光晶格阱，实现精度优于10^-17的新型原子钟的设想。     

Study on surface acoustic wave rotary motors

On the surface of 128° yx-LiNbO3 substrate, two pairs of Inter-Digital Transducers (IDTs) are parallelly arranged in the propagation direction, which is a stator of surface acoustic wave (SAW) rotary motors. A plastic disk with small balls distributed around the circumference is a rotor. When a high frequency voltage is inputted to two IDTs, two Rayleigh wave beams are generated and are propagating on the substrate in opposite directions with each other. The resulting local relative motion between the particles of the stator and the balls produces two inverse frictional forces to form a moment to drive the rotor. The experimental results and theoretical analysis and calculation for two operating frequencies are accomplished and discussed.     

电子学实验平台研制——兼谈加强应用物理专业电子学技术的教学

本文报导了为加强我系学生电子学能力而研制的电子学实验平台，该平台可以提供十多个高等电子这实验，配套设备只需要一台２０ＭＨＺ双线示波器和一台万用表，若有一台函数发生器则更好，教学实践效果良好，达到了少花线，多开实验，开好实验的目的。     

A Novel Method for Multi-Pumped Fibre Raman Amplifier Gain Adjustment

A novel method for gain adjustment of multi-pumped fibre Raman amplifiers is proposed and numerically demonstrated. The method uses the areas under the curves of the pump power evolution along the gain fibre and the Newton-Raphson method to find an appropriate power combination of the pumps to realize the desired gain profile. Compared with the previously proposed methods, our method has two advantages: first, it can maintain the gain profile while changing the gain magnitude to the desired value; second, it is independent of the actual pumping scheme of the amplifier, i.e. it can be used for fibre Raman amplifiers with all kinds of pumping schemes including co-, counter-, or hi-directional pumping. Numerical simulations are provided to verify the proposed method and to demonstrate its effectiveness.     

Beam divergence effects on high power optical parametric oscillation

The beam divergence effects of the input pump laser on a high power nanosecond optical parametric oscillator （OPO） have been numerically simulated. The OPO conversion efficiency is affected due to the angular deviation of real laser beams from ideal phase matching conditions. Our theoretical model is based on the decomposition of the Gaussian beam and assumes each component has a single deviation angle and thus a particular wave vector mismatch. We take into account the variable intensity profile in the spatial and temporal domains of the Gaussian beam, the pump depletion effects for large-signal processes as well as the oscillatory effects of the three waves. Two nonlinear crystals β-BaB2O4 （BBO） and LiB305 （LBO） have been investigated in detail. The results indicate that the degree of beam divergence strongly influences the maximum pump intensity, optimum crystal length and OPO conversion efficiency. The impact of beam divergence is much more severe in the case of critical phase-matching for BBO than in the case of non-critical phase-matching for LBO. The results provide a way to choose the optimum parameters for a high power ns OPO such as the nonlinear material, the crystal length and the pump intensity, etc. Good agreement is obtained with our experimental results.     

Quantitative measurement of displacement and strain by the numerical moire method

The numerical moire method with sensitivity as high as 0.03 nm has been presented. A quantitative displacement and strain analysis program has been proposed by using this method. It is applied to an edge dislocation and a stacking fault in aluminum. The measured strain of edge dislocation is compared with theoretical prediction given by Peierls-Nabarro dislocation model. The displacement of stacking fault is also obtained.     

光互连网络中的光学比较交换实现方法

本文提出了一种全混洗交换光互连网络中对两个数字光信号进行比较交换的新方法。用液晶光调制器和光导开关构成数字光信号交换控制单元,自动完成两列数字光信号大小的并行比较和交换     

传票算、帐表算综合练习题的设计方案

传票算虽一册在手，却以数字众多，拟题灵活，答案千变万化的优势，是练习加算的极好习题，深受珠算爱好者喜受．一般的拟题方法是；每20页为一笔，每次只连加每页中的某行，求出和数．以32开纸单面而言，每张纸能拟题40道。