激光辐照使滇三角大香糯产生变异的机理研究

从2001年开始,连续两年用激光辐照加电场、磁场激发对滇“三角大香糯”进行了育种研究和各生育期的田间试验观测,并得到了一些有较优变异的稻种。用喇曼光谱分析和量子力学方法对稻种的变异机制进行了研究。     

CO2激光诱变滇糯稻诱变剂量的筛选及其效应研究

我们在进行了连续两年激光诱变滇“三角大香糯”水稻育种的研究基础上,采用CO2激光诱变剂量筛选,田间栽种试验的方法进行探索,其样品发生明显的正向变异,表明水稻种子对激光的吸收阈值确实存在。     

激光加电磁场诱变滇稻“三角大香糯”的育种初探

用He-Ne激光(1.5 mW,632.8 nm)辐照加电场磁场(电场强度1.2×106 m/V,2.0×106 m/V;磁感应强度4.8 T)激发处理了云南姚安三角大香糯稻种.通过育种和田间试验发现,多数处理种子仅产生非基因变异的表型变化,仅有5株发生性状变异.     

激光诱变滇糯稻机理分析及遗传稳定性研究

我们采用He-Ne、CO2激光对滇糯稻--云南姚安三角大香糯水稻品种进行诱变育种改良,其目的是要在保持原品种良好特性的前提下,降低植株高度,缩短生育期,提高产量,并扩大种植适应区域.经过连续六年的探索研究和试验,其样品在试验地及原产地都出现了较好宏观表现,并具有基本稳定的遗传.结合实验室和田间试验表现,对激光诱变水稻的作用机理及遗传稳定性进行了分析研究.     

激光辐照加电场激发对滇稻的育种研究

我们用激光辐照加电场激发处理了滇稻种子，通过室内育秧和田间试验，发现在出苗率，有效分蘖和结实率等方面均优于单纯激光处理的稻种。     

"国家点火装置"前景难测

启动聚变反应最容易的途径是用原子弹 ,但是美国政府已于 1 992年保证不进行核武器试验 ,这就使科学家得寻找其他途径以产生和研究聚变反应。“国家点火装置”是劳伦斯·里弗莫尔国家实验室在建的超级激光器 ,其设计目标是用激光而不是用核爆炸产生聚变反应 ,以解决上述问题。该装置的估计费用近 40亿美元 ,这是能源部研究计划耗资最巨的单一项目。但是“国家点火装置”预算超支 ,进度滞后。能源部官员原来估计该项目 1 993年批准 ,拟于 2 0 0 2年完工 ,耗资约 2 0亿美元 ,但在 1 999年 6月该装置靶室的剪彩仪式上 ,能源部长 Bill Rachards…     

CO2激光治疗耳廓囊肿45例

耳廓囊肿临床上较常见 ,大部分因外伤引起 ,少数原因不明。我科自 1 994年 8月至今采用CO2 激光治疗 45例效果满意。一般资料 :本组 45例 ,男性 3 0例 ,女性 1 5例 ,年龄 2 0 -6 0岁 ,病程 5 -3 0天 ,3 0例位于耳甲腔 ,4例位于舟状窝 ,6例位于三角窝 ,另外 5例囊肿较大 ,贯穿舟     

"掠夺者"无人驾驶作战飞机将进行实弹发射试验

据《Flight International》 2 0 0 1年 2月 6日～ 1 2日报道 ,RQ- 1 A“掠夺者”无人战机将在 2 0 0 1年 2月进行实弹试验。据称 ,2 0 0 1年 2月 1 2日和 1 6日计划在尼尔森空军基地进行两次这样的试验。 2 0 0 1年 1月 2 3日 ,RQ- 1 A在海军空中武器中心的中国湖靶场进行的导弹地面发射成功 ,命中了静态目标。在首次利用瞄准线进行的射击中 ,计划在 6 0 0 m高空发射并自指示 AGM- 1 1 4海尔法激光制导导弹射击静目标。随后 ,将高度提升到 45 0 0 m进行非瞄准线发射对付动目标。美空军计划用尚在研制中的微型弹药装备无人机来打击对时…     

发射机音频信号数字化处理问题

DX 2 0 0全固态数字化广播发射机是近年来我国广播系统引进美国哈里斯 (HARRIS)公司 80年代末发明并生产的新式广播发射机。其工程原理是对音频输入信号进行数字化处理 ,然后用数字化音频信号去控制射频功率放大器模块 (2 2 0块 )的导通数目多少 ,实现调频发射。因此 ,DX 2 0 0发射机对音频信号的数字化处理至关重要 ,而该机音频数字化处理中超音频三角波叠加和可编程只读存储器编码 ,对发射机的工作状态、技术指标起到重要的作用 ,下面我们只讨论该发射机这两部分的内容。1超音频三角波的叠加DX 2 0 0发射机三角波信号叠加在已被模拟…     

意大利工业激光器

意大利 CO2 工业激光源的研究比其它欧洲国家开始得早。 1 976年 ,信息试验研究中心和 Valfivre协作生产 5 0 0 W慢流 CO2激光源 ,由 Valfivre销售。用冲压结构开发的第一台激光切割系统于 1 979年在米兰展示。与使用相干通用公司 CO2 激光源的 Behrens和 Trumpf同步 ,Salvagnini系统安装了Valfivre激光器。这些研究由意大利国家研究委员会的专门课题“高功率激光”扩展 ,其目的是支持已有的菲亚特研究中心、RTM,信息试验研究中心和激光中心等 ,并在信息试验研究中心发展 1 0 k W CO2 激光源。 1 980年 ,菲亚特在全球汽车制造商中率…     

强激光武器技术最新发展评述

在过去三年里,高能激光武器技术取得了巨大的发展,第一代实用的武器系统即将实现。本文中首先评述了美国的高能激光武器计划和最新的发展。然后分析和评述了各种武器技术取得的重大进展。最后简要地介绍了最近进行的激光射击卫星试验。     

毛细管快放电激励X光激光实验设计

近年来,有关利用毛细管放电激励产生X光激光的研究十分活跃,国际上已经取得了许多显著的成果,并且正向实现实用化Table-top Laser发展.作者首先介绍了毛细管放电激励X光方案的原理及国内外的重要进展,在对两种典型机制的分析的同时,也阐述了对该方案的发展方向及需要克服难点的看法.     

数字电路测试生成的基本算法

计算机辅助测试（CAT）工具有助于数字电路测试的自动化，这主要是由于使用了有效的算法和相应的软件结构。文章主要介绍了测试生成领域有重大影响的基本要领和算法。     

Transport of photocarriers in CdxHg1−xTe graded-gap structures

A theoretical and experimental study has been made on the transport of light injected excess charge carriers in Cd_xHg_1−xTe variable band gap materials. A theoretical analysis is given of the ambipolar motion of the charge carriers in terms of diffusion and drift in the electric fields associated with the gradients of the band gap, lifetime, effective masses and doping level. The photoelectromagnetic effect (P.E.M.) has been calculated for two limiting cases: when the electric field is predominantly associated with a gradient of band gap (ideal case), and when the net electric field is zero (pseudohomogeneous case). It is shown that the two situations can be distinguished by analysing the variation of the P.E.M. effect in a magnetic field. Two different experimental studies have been made: a study of the optical transmission spectra which leads to the determination of the profiles of the structures and the spatial distribution of the absorbed photons, and a study of the P.E.M. effect and the photoconductivity as a function of several parameters: magnetic field, wavelength and temperature. The interpretation of these results shows that the structures studied can be characterized as pseudohomogeneous and an estimation of the variation of the diffusion length (1·5–18·5 μ) and the lifetime (5·10⁻¹¹–2·10⁻⁸ sec) of the electrons in the composition range 0·15 < x < 0·25 has been made.     

Optimum Noise Measure of IMPATT Diodes

An attempt is made to determine some of the factors responsible for the noise performance of avalanche diodes. In particular we are interested whether there are any lower lids in the noise measure. We derive a theorem which shows that there is a lower limit M/sub opt/ = 1/2 q/ /spl alpha'/kT for an IMPATT diode which has a constant value of a', where M/sub opt/ is the optimum noise measure, q is the electronic charge, a' is the derivative with respect to the electric field of the carrier generation rate, k is Boltzmann's constant, and T is the standard absolute temperature. Even though the optimum noise measure is derived for a diode with constant a' in extensive numerical calculations of structures with sections of different a', we never found cases where the overall diode noise figure was lower than calculated by the above formula using the largest value of a'. Detailed calculations show that the lowest noise measure is achieved for carrier transit angles near 2/spl pi/. The negative real part of the impedance becomes rather small when both the transit angle is near 2/spl pi/ and when a' is made large. In practical cases it is therefore often not possible to reach noise measures close to M/sub opt/. The paper also investigates how the amplifier noise determines amplitude and frequency noise of the corresponding avalanche oscillators.     

The past, present, and the future of underwater acoustic signalprocessing

This is a collection of articles written by members of the Underwater Acoustic Signal Processing (UASP) Technical Committee. The first article, by D. W. Tufts, deals with the history of UASP prior to 1980. In this period, initial mathematical models were developed and the first experimental investigations of underwater acoustic propagation were performed. It was also recognized during this time that there are many similarities between radar and sonar signal processing. The article by J.P. Ianniello deals with research in passive and active sonar from 1980 to the present. Work in this period included experimental verification of algorithms that had been developed in the 1960s and 1970s (e.g. for adaptive beamforming), as well as the development of new approaches, which include acoustic propagation modeling in the design of signal processing algorithms. Such processing is referred to as matched field processing. A common task in passive sonar systems is to estimate the difference in times at which different sensors receive the same signal. Time-delay estimation is a first stage that feeds into subsequent processing blocks. I. Lourtie provides a concise review of work in this field. The article by J.C. Preisig deals with underwater acoustic communications. The underwater channel has several features that make reliable communication a challenging problem. Nevertheless, progress is being made by combining results from ocean acoustic modeling, communication theory, and signal processing. The final article, by J.M.F. Moura, deals with the future of signal processing in the ocean. In addition to considering advances in detection and localization, he deals with new applications such as acoustic tomography, physical oceanography, and synthetic aperture sonar     

激光光束质量因子的研究进展

本文详细分析了各种光场下光束质量M2因子。在不同的场中,A.E.Siegman当初所定义的M2因子,已经有了很大的变化,因而M2因子的特性也与当初不同,不仅M2因子可以大于等于1,而且可以小于1,甚至小于0。其反映的物理意义,也从经典场中的衍射极限倍数,变化为非经典场中的准直性量度以及对空间相干性的某些反映。此外还列举并分析了几种特殊的光束质量因子,最后讨论了M2因子应用的问题并指出了其局限性。     

CMR锰氧化物在激光及光探测方面的应用进展

混合价态钙钛矿锰氧化物在外界温度变化和磁场作用下表现出巨大的磁电阻 (Colossalmagnetoresistance ,简称CMR)效应 ,引起了人们的广泛关注。由于CMR材料在传感器、探测器以及硬盘读出磁头等应用器件研发上极具潜力 ,科学家们对其进行了大量研究。本文在简单介绍CMR材料结构和机理的基础上 ,着重报道了我们利用CMR薄膜的激光感生热电电势 (LITV)制备激光功率 能量探测器和利用电阻在室温附近的巨大变化研制的光热辐射探测器 (Bolometer)方面的新进展     

方正新一代藏文电子出版系统的设计与实现

20世纪90年代初随着我国第一代藏文电子出版系统的普及和推广,使得我国藏文出版印刷＂告别了铅与火,迎来了光与电＂.以后的十多年间,无论是信息技术还是电子出版技术都发生了巨大的变化,第一代藏文电子出版系统迫切需要更新换代.详细阐述了方正新一代藏文电子出版系统建设的基本思路、框架以及具体实现方法.     

Resonant modes of GaAs junction lasers--III: Propagation characteristics of laser beams with rectangular symmetry

In Parts I and II of this work [1], [2], the resonant modes of GaAs lasers, as predicted from a proposed model, are found to be in very good agreement with experimental results that emphasize the frequency domain. This paper, Part III, supplements the previous work by investigating the spatial field distributions of junction-laser beams. For the first time, the propagation characteristics of the beams are described mathematically in a manner that is consistent with detailed beamwidth measurements in the Fresnel and Fraunhofer regions of the diffraction field. This correlation between theory and experiment is made possible by the use of a lens-slit combination that ensures the generation of reproducible beams with rectangular symmetry. The astigmatic beam solutions describing the propagation characteristics beyond the slit include beam-broadening effects produced both by the lens and by phase variations at the laser mirror, along the junction plane. These latter variations have not been previously reported. Their existence is deduced from our measurements beyond the slit, which show a greater beam expansion along the junction plane than can be theoretically accounted for by the lens system alone. Near threshold, at a distance of one beamwidth from the center of the mirror illumination, the phase lag is found to have a current-dependent magnitude of a few degrees.