Study of semileptonic decays Bs→Ds1(2536)lν and Bs→Ds2(2573) lν in the CQM model

Based on the assumption that D_s1(2536) and D_s2(2573) belong to T doublet (1⁺,2⁺), we calculate the semileptonic decays of B_s to D_s1(2536) and D_s2(2573) in terms of the Constituent Quark Meson (CQM) model. For B_s→D_s1(2536)+lν and B_s→D_s2(2573)+lν, the order of magnitude of the obtained branching ratios is 10^－3. Our numerical results of the semileptonic decays of B_s to D_s1(2536) and D_s2(2573) are large, which implies that two semileptonic decays should be seen     

A new model analysis of the third harmonic voltage in inductive measurement for critical current density of superconducting films

The critical current density J c is one of the most important parameters of high temperature superconducting films in superconducting applications,such as superconducting filter and superconducting Josephson devices.This paper presents a new model to describe inhomogeneous current distribution throughout the thickness of superconducting films applying magnetic field by solving the differential equation derived from Maxwell equation and the second London equation.Using this model,it accurately calculates the inductive third-harmonic voltage when the film applying magnetic field with the inductive measurement for J c.The theoretic curve is consistent with the experimental results about measuring superconducting film,especially when the third-harmonic voltage just exceeds zero.The J c value of superconducting films determined by the inductive method is also compared with results measured by four-probe transport method.The agreements between inductive method and transport method are very good.     

基于多时相航空高光谱遥感影像的冬小麦长势空间变异研究

精准农业技术是基于农田信息在空间和时间上存在的差异而实施的变量管理技术,本研究以2001年～2002年度在国家精准农业研究示范基地开展的冬小麦变量施肥对比试验为基础,获取冬小麦拔节期、灌浆初期及乳熟期的推扫式成像光谱仪(pushbroom hyperspectral imager, PHI)航空高光谱影像数据,提取反映冬小麦长势光谱参数,进行变量施肥处理区与常规处理区冬小麦长势空间变异的对比。研究发现,变量区与对照区光谱反射率分散度最大的区域主要集中在红边及近红外反射平台的附近, 其中,乳熟期冬小麦光谱分散度最大,其次为拔节期和灌浆期。通过对比不同时相冬小麦长势信息,发现拔节期变量区作物长势空间变异程度要高于对照区,经过变量施肥处理后,灌浆期和乳熟期变量施肥区冬小麦长势空间变异程度低于对照区;对冬小麦产量的分析发现,变量区产量的总体空间变异小于对照区,但变量区总体产量略低于对照区。研究表明,利用遥感影像数据,可以及时获取作物长势的空间变异情况,为农业管理的生产、决策及时提供信息。     

Growth of TlBa_2Ca_2Cu_3O_9 Epitaxial Thin Films by Two-Step Method in Argon

TlBa_2 Ca_2 Cu_3 O_9(Tl-1223) films have promising applications due to their high critical temperature and strong magnetic flux pinning. Nevertheless, the preparation of pure phase Tl-1223 film is still a challenge. We successfully fabricate Tl-1223 thin films on LaAlO_3(001) substrates using dc magnetic sputtering and a post annealing two-step method in argon atmosphere. The crystallization temperature of Tl-1223 films in argon is reduced by 100℃ compared to that in oxygen. This greatly reduces the volatilization of Tl and improves the surface morphology of films. The lower annealing temperature can effectively improve the repeatability of the Tl-1223 film preparation. In addition, pure Tl-1223 phase can be obtained in a broad temperature zone,from 790℃ to 830℃. In our study, the films show homogenous and dense surface morphology using the presented method. The best critical temperature of Tl-1223 films is characterized to be 110 K, and the critical current J_c(77 K, 0 T) is up to 2.13 × 106 A/cm~2.     

有机金属卤化物钙钛矿薄膜中的光诱导载流子动力学和动态带重整效应

近年来有机-无机金属卤化物钙钛矿太阳能电池因具有光电能量转换效率高、制备工艺简单等优点,引起了学术界和产业界的广泛关注,其优异的光电特性逐渐在能源领域展现出独特的优越特性.在短短几年内,有机-无机混合物钙钛矿太阳能电池的能量转换效率已经高达23%,发展速度逐步赶上甚至超越了成熟的硅太阳能电池.本文利用飞秒瞬态吸收光谱,对二步法制备的(5-AVA)_(0.05)(MA)_(0.95)PbI_3和(5-AVA)_(0.05)(MA)_(0.95)PbI_3/Spiro-OMeTAD有机-无机卤化物钙钛矿薄膜材料的激发态动力学进行了对比研究,详细讨论了两种薄膜样品中的电荷载流子产生与复合机制.通过紫外-可见吸收光谱测得钙钛矿薄膜(5-AVA)_(0.05)(MA)_(0.95)PbI_3和(5-AVA)_(0.05)(MA)_(0.95)PbI_3/Spiro-OMeTAD的吸收光谱与CH_3NH_3PbI_3钙钛矿薄膜材料的双价带结构相对应.从瞬态吸收光谱中,观察到760 nm附近的光致漂白信号,此时的载流子复合过程符合二阶动力学过程,而在约550—700 nm光谱范围内则是光诱导激发态吸收信号.实验结果表明,(5-AVA)_(0.05)(MA)_(0.95)PbI_3钙钛矿薄膜样品中光生载流子主要的弛豫途径是自由电子和空穴的复合.抽运光激发样品使价带中的电子跃迁到导带,随着延迟时间的增加,电子和空穴复合,光谱发生红移现象.所观察到的带重整效应可以根据Moss-Burstein效应解释.相比较而言,(5-AVA)_(0.05)(MA)_(0.95)PbI_3/Spiro-OMeTAD钙钛矿薄膜样品在光激发后电子和空穴分离,空穴迅速转移到空穴传输层,这将导致样品吸收度增加,漂白信号快速恢复,电子-空穴的复合不再对漂白信号的弛豫动力学起主导作用,同时也削弱了带重整现象.本文的实验结果对半导体有机-无机金属卤化物钙钛矿薄膜在光伏领域的应用具有重要意义,为今后高效、稳定的钙钛矿太阳电池的研究提供了参考.     

Access Grid网格环境下的可视化群组协同工作环境

Access Grid通常被称作访问网格，它是一种以开放网格服务体系结构(OGSA)为基础的，结合视频会议技术、网络技术和网格技术、建立起来的群组可视化交流环境。文章首先介绍了Access Grid系统的现状、体系结构、设计实现及其关键技术，然后以中科院网络中心(CNIC)的Access Grid结点建设为例，来阐述Access Grid群组协同工作环境的工作过程。最后，介绍了Access Grid与相关技术的结合和应用前景。     

量热法在表面活性剂溶液中的应用

近年来,表面活性剂在生产应用中带来的经济效益以及它的广泛使用前景使科研工作者对它的研究兴趣剧增,发表文献以惊人的数字增加。尽管如此,表面活性剂溶液的研究还很不充分,缺乏系统性,且多以相行为的研究为主。胶束热,转移焓、溶解热或稀释热等重要的热力学性质用其它方法无法涉足,然而却是全     

印刷体汉字文本的微型计算机自动识别

本文提出一个微机印刷体汉字文本识别系统。该系统是基于汉字识别特征点方法实现的,是一个包括版面分析、文本识别和编改处理的完整的系统。该系统在实用中,经过约200万字的识别得出:对中等印刷质量的书刊、文件,在纯软件条件下,达到20字/s的识别速度(20MC386微机)和95％以上的识则率。     

红外导引头光学系统的低温补偿

红外导引头光学系统的低温补偿是解决光学系统和导引头的低温性能的一种有效方法。从红外导引头研制到设计定型,光学系统的低温一直是个突出的问题,也是导引头技术中的关键问题。随着科研的深入发展和当今武器系统的必需,导引头进入设计定型阶段提出了-40℃的低温要求,然而,由于光学系统在-40℃时散焦量很