SUPERCONDUCTING PROPERTIES AND STRUCTURAL PERFECTION OF EPITAXIAL YBa2Cu3O7-x THIN FILMS

High quality epitaxial YBa₂Cu₃O_7-x thin films have been succcessfully prepared by dc magnetron sputtering deposition, on (100) and (110) aligned SrTiO₃, LaAlO₃ and yttria-stabilized zirconia (YSZ) substrates. The films showed zero resistance around 90 K and had a J_c (at 77 K, H=0) over 10⁶A/cm². It was found that superconducting properties and structures of the films were strongly dependent on oxygen pressure and substrate temperature. The epitaxial structure of the films have been studied by X-ray diffraction. Rutherford backscattering and channeling spectroscopy, X-ray double-crystal diffraction and transmission election microscopy. The experimental results demonstrated that the epitaxial YBa₂Cu₃O_7-x films had excellent superconducting properties and quite perfect structure.     

高延时分辨低抖动同步时序信号产生技术

针对大型激光装置中广空间分布的甚多路高精度(一是长时间时间抖动小于5 ps,二是时间延迟微步进分辨率小于15 ps)同步触发信号的需求,设计了一种“数据流编解码光传输+高速串行收发器粗延时+宽带微带线微步进延时”的同步时序产生方案。通过数据流编解码光传输架构实现了广空间范围内时序的对齐;高速串行收发器粗延时和微带线微步进延时技术解决了同步触发信号低时间抖动和高延迟分辨的问题。通过对系统的时序逻辑和电路板的关键线路进行仿真,完成了整个系统的设计与研制,并开展了实验测试。测试结果表明:该系统可以实现广空间范围内的同步时序信号产生,同步触发信号的时间抖动精度优于3.76 ps(均方根值,8 h),39.6 ps(峰峰值,8 h),时间延迟分辨率优于15 ps;若应用于小空间范围,同步触发信号的时间精度可优于1.27 ps(均方根值,8 h),12.4 ps(峰峰值,8 h)。     

SUPERCONDUCTING PROPERTIES AND STRUCTURAL PERFECTION OF EPITAXIAL YBa2Cu3O7-x THIN FILMS

The photoconductivity spectra of semimagnetic semiconductor Cd_0.7Mn_0.3Se have been measured at 50-300 K and in the wavelength range of 5500? to 8000?. It is found that the energy gap of Cd_0.7Mn_0.3Se changes with the temperature linearly, and the temperature coefficient (dE_g/dT) is about -7×10^-4 eV/K. A photoconductivity peak which is related to Mn²⁺ is also found. This peak is located around 1.85 eV, nearly unshifted with variation of the temperature. The possible transition mechanisms in Cd_1-xMn_xSe have been discussed in the light of group theory and crystal field theory, and the results are in good agreement with experiments.     

从吴大猷科普奖看海峡两岸文化差异

本文是甘子钊先生在海峡两岸科普论坛上的讲话。他从吴大猷基金会举办的三届海峡两岸科普图书评奖活动,分析海峡两岸在科普图书以及科普工作上的优势,以促进两岸科普工作者的相互交流和学习。     

SrTiO3同质外延过程中的反射高能电子衍射图案分析

在激光分子束外延实验中,用RHEED原位监测了SrTiO3基片初始、退火以及同质外延过程中的表面形态.通过对RHEED图案分析,获取了表面面内的晶格常数振荡与衍射条纹的半高宽振荡现象,前者是由退火重构表面与薄膜之间的界面造成的,后者与二维岛边界的弛豫相关.另外还观察到了等离子体对入射电子束的影响而导致的RHEED强度振荡行为的相位移现象. 关键词： 反射高能电子衍射 SrTiO3 表面晶格常数及衍射强度振荡     

都是“物流”惹的“祸”

物流对于每一个组织的成功都是至关重要的。过去只是把物流看做一种重要的幕后活动，而现在认识到物流也是一种创造顾客价值和忠诚度的战略工具。像沃尔玛、可口可乐、耐克等大公司都把成功归因于他们全球化的物流系统。他们已经认识到，整合组织内的各种活动、与供应商建立稳固的关系、与物流服务提供者的合作，这些对于通过物流来建立竞争优势都是至关重要的。     

Rotation invariant pattern recognition with a volume holographic wavelet correlation processor

A volume holographic wavelet correlation processor for performing rotation invariant Pattern recognitionis suggested.It uses wavelet transform to get the digital edge extraction of the original object and a singlecircular harmonic component iS used as the matched filter to get good rotation invariance.The new filterused in this method is called wavelet circular harmonic component fllter (WCHCF).Simulation resultsvalidate the theory and the experiment to recognize human faces with any rotation angle shows the utilityof the newly proposed method.     

杰出的固体物理学家──黄昆教授

1989年9月 2日是著名物理学家黄昆教授的70寿辰,为了庆贺他50年来从事教学和科研活动所取得的卓越成就,1990年 1月 4日在北京大学举行了“黄昆教授七十寿辰学术报告会”.北京大学校长吴树青教授和中国科学院院长周光召教授致词祝贺,著名华裔物理学家杨振宁教授专程来京参加会议并作了学术报告.来自中国科学院、机械电子工业部所属研究所和19所高等院校等单位的170多名专家、教授参加了会议,他们之中有黄昆教授的朋友、同事,但绝大多数是黄昆教授的学生.会上宣读了10篇论文,这些论文反映出了我国近年来在半导体物理、晶格动力学方面的研究成…     

锗中隧道电流过程的理论(Ⅱ)——声子隧道电流

本文是对锗中声子散时引起的隧道电流的理论分析。指出这过程主要是二级过程,由导带底进入禁带的电子,被声子散射到联系着导带(0,0,0)谷的状态,再在结势垒场的作用下跃迁到价带。对这过程起主要作用的是在结势垒区中一定区域(大致是20?厚)的晶体原子振动。这过程的几率几乎是各向同性的。从对称性的一般考虑,说明锗中纵声学支格波对隧道过程的贡献是最强的。 关键词：