偶偶核基带的量子群Uqp(u2)模型的理论分析

通过对锕系和稀土偶偶核基带转动谱实验数据的拟合和Mallmann图的研究,系统地分析了量子群U_qp(u₂)模型对原子核转动谱的适用性.结果表明,U_qp(u₂)模型的理论值与实验值比较接近,明显优于单参数形变量子代数SU_q(2)模型.此外,还建立了U_qp(u₂)的形变参量q、p与核软度的关系.     

用于电压基准的Nb/NbxSi1-x/Nb约瑟夫森单结的研制

现代可编程约瑟夫森电压基准的核心器件是约瑟夫森结阵.目前最具有优势的约瑟夫森结阵是 Nb/Nb_xSi_1-x/Nb材料的结阵. Nb/Nb_xSi_1-x/Nb材料的约瑟夫森结 具有三层薄膜的制作过程简便, Nb和Nb_xSi_1-x刻蚀工艺相同以及Nb_xSi_1-x 势垒层成分可调等优点.中国计量科学研究院设计制作了Nb/Nb_xSi_1-x/Nb约瑟夫森单结. 通过在4.2 K低温下对所做单结进行直流电流-电压特性测量,观测到了清晰的超导隧穿电流和 从零电压态向电压态的跳变,最后就测量结果进行了分析讨论.此项工作属于国内首个开展 Nb/Nb_xSi_1-x/Nb材料约瑟夫森单结研究的工作.     

流体静压力对锗隧道二极管伏安特性的影响

本文报导了在流体静压力18000kg/cm²的范围内,锗隧道二极管伏安特性随压力变化的实验结果。测量了十六只锗隧道二极管的峯值电流I_P、峯值电压V_P、谷值电流I_V、谷值电压V_V、指数过剩电流I_X和反向隧道电流等参数与流体静压力的关系。结果表明:峯值电流I_P相对于压力的半对数作图为斜率不同的二段下降直线,在5000—9000kg/cm²范围内有转折点;峯值电压随压力改变较小;在误差范围内谷值电压不随压力而改变。对于大部分被测管子,谷值电流与压力的关系类似于峯值电流与压力的关系;随着压力的增加,指数过剩电流区向高偏压方向移动。讨论了峯值电流及指数过剩电流随压力变化的规律和其他结果。认为转折点的存在是表明隧道跃迁机构的改变;由指数过剩电流区固定电流值测偏压随压力改变,求得禁带宽度的压力系数与其他方法获得的结果很好符合。     

单相三电平H桥逆变器分岔现象的研究

三电平逆变器相较于传统的两电平逆变器具有输出电压谐波畸变率小、开关管电压应力小等优点,因而在大功率场合受到了越来越多的关注. 本文针对一种复合式单相三电平逆变器,对其中的分岔和混沌现象进行了深入的研究,建立了电流闭环比例控制下的一阶离散模型,得到了不同时间段内的频闪映射模型. 以比例系数k,负载电阻R,负载电感L及输入电压E为变化参数,研究了三电平逆变器的分岔现象：通过分岔图和李雅普诺夫指数谱分析了慢变尺度下比例系数、负载电感、负载电阻和输入电压对系统动态性能的影响;通过折叠图直观地观测到了快变尺度下不同比例系数、负载电感所导致的分岔过程. 最后搭建了Matlab/Simulink仿真模型,得到了电流闭环比例控制时电流i的时域波形,仿真结果与理论分析相一致. 研究表明,正确选择单相三电平逆变器的电路参数对于其稳定运行具有重要意义. 关键词： 三电平逆变器 频闪映射 分岔 混沌     

不稳定局域模及其对杂质中心吸收带宽的影响

本文运用羣论方法,把不稳定局域模和含杂晶格的带内本征矢的散射部分都按格位羣的不可约表示分了类。具体地讨论了最近邻相互作用的简单立方晶格的情况,计算结果表明:可。能产生同P(=γ′/γ)和(=m′/m)有关的T_1u型不稳定局域模和仅与P有关的简并的A_1g,E_g,T_1g,T_2g和简并的T_1u,T_2u型不稳定局域模,以及只有同一类型的对称性驻波才能为杂质所散射。这里m′和m分别为杂质原子和基质原子的质量;γ′和γ分别为杂质与近邻之间和一般近邻之间的力常数。以同样的模型计算了各种类型声子对杂质中心吸收带宽的贡献。指出,宽度很窄的g型不稳定局域模对带宽的贡献可能变得很大,而超过其余声子的总贡献。最后讨论了单有效频率近似可能有的微观理论基础的问题。     

在193 nm关于Si2分子的离子解离动力学的成像研究

在193 nm的单色激光实验中,本文利用时间切片离子速度成像技术,研究了经193 nm双光子电离得到的Si₂⁺的解离反应动力学过程. 根据实验得到的Si⁺离子的速度成像,观测到了两种离子直接解离通道：Si(³P_g)+Si⁺(²P_u)和Si(¹D₂)+Si⁺(²P_u). 电子基态的Si₂分子处于v=0∽5的振动态上,其经过双光子电离后激发到Si₂⁺离子的多个电子激发态势能面,生成主要通道Si(³P_g)+Si⁺(²P_u),其中v=1的解离信号最强. 此外,由于势能曲线2²Π_g与3²Π_g相同对称性引起的避免性势能面交叉,生成次要反应通道Si(¹D₂)+Si⁺(²P_u). 通道Si(¹D₂)+Si⁺(²P_u)的产物亦可以由生成的基态Si₂⁺(X⁴Σ_g^-)吸收一个193 nm光子后解离得到,其对应产物则具有更大的动能.     

流体静压力对高简并砷化镓P-N结某些参数的影响

本文报导了在流体静压力18000kg/cm²范围内,高简并砷化镓P-N结峯值电流l_p,谷值电流l_v,峯值电压V_p,谷值电压V_v,指数过剩电流I_x等参数随压力变化的实验结果。分析了峯值电压V_p随压力P的增加按指数规律显著减小,以及指数过剩电流I_x的斜率S=(dlnI_x)/dV随压力P的增加而增加等实验结果。分析的     

几种纤锌矿相硫族和磷族半金属铁磁体磁电性能的第一性原理

采用基于密度泛函理论中的广义梯度近似的第一性原理研究, 优化了纤锌矿结构化合物CrX(X=As、Sb、O、Se和Te)的几何结构, 并详细计算了它们的磁电性能． 结果表明, 这些磷族或硫族化合物在费米面处的自旋极化率均为100%, 分子磁矩分别为整数3.00和4.00 μB; 分子磁矩主要来自于Cr离子; 磷族和硫族化合物中存在亚铁磁性耦合; 它们的居里温度均较高; 磷族和硫族化合物中Cr离子的电子结构分别为a²_1g↑↓t⁴_1u↑↓t¹_1u↑e²_g↑和a²_1g↑↓t⁴_1u↑↓t¹_1u↑t³_2g↑.     

Cs2 23△1g态碰撞线归属和超精细结构解释

根据最新的Cs₂分子中间态A¹∑⁺_u -b³Πu全局解微扰获得的能级数据, 归属了通过微扰增强红外-红外光学双共振中间态A¹∑⁺_u 到上态2³△_1g的140条碰撞线, 包含之前实验观测到的221条2³△_1g←A¹∑⁺_u← X¹∑⁺_g 双共振跃迁[J. Chem. Phys. 128, 204313 (2008)], 重新计算了2³△_1g态的分子常数和势能曲线(排除54个微扰能级). 本次拟合得到的离心畸变常数和从经验公式计算得到的值相符合. 在亚多普勒激发光谱中,没有分辨出2³△_1g态的超精细结构. 对2³△_1g态的超精细结构进行初步计算,比较实验结果给出解释和说明.     

CO2激光成像雷达距离分辨率测距精度的分析与实验研究

分析了脉冲外差体制CO₂激光成像雷达系统的目标距离分辨率、测距精度和误差的主要来源.对于单个光脉冲测距来讲,信噪比(SNR)起伏引起的探测误差、脉冲前沿触发等概率分布以及脉冲建立时间的随机性等是激光脉冲外差测距的主要随机误差,其它随机误差在数量级上可忽略不计.同时利用现有的CO₂激光脉冲外差探测系统,进行了远目标测距对比实验,观测到了2355 m目标脉冲回波信号,并精确测量出CO₂光脉冲飞行的往返时间,该实验数据可用做系统误差的校正和补偿.     

Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide

Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.     

Hybrid Wavelength and Code Division Multiple Access in Optical Networks

A review of schemes for multiple access in fiber optic networks shows that a hybrid of wavelength and code division multiple access (WCDMA) combines the best features of both. In particular, the hybrid scheme retains the large information carrying capacity of wavelength division multiple access (WDMA) and flexibility of code division multiple access (CDMA). In this paper WDMA, optical CDMA (OCDMA), and WCDMA networks are discussed. In OCDMA networks, concept of incoherent and coherent coding including inverse decoding and matched filter is introduced. The delay performance of both WDMA and WCDMA networks, under the simple suboptimum access protocols based on cyclic search, is computed. It has been shown quantitatively that tuning delay significantly affects the delay performance of both WDMA and WCDMA networks. Futhermore, delay performance of WCDMA networks is always better than the WDMA networks for the same tuning delay, load, and number of users.     

Effect ofγ-radiation on the spectral luminescence characteristics of impure cadmium tungstate crystals

Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation (5.5·10⁴ Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure crystals is analyzed (preliminarily). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997.     

Femtosecond Transform-Limited Pulse Generation by Compensating for the Linear Chirp of SPM Spectra in Dispersion Shifted Fibers

A simple technique of pulse compression, based on the linear chirp compensation of self-phase modulation (SPM) spectra in dispersion shifted fibers, is demonstrated. The optimization procedure is carried out, for a short span of a single-mode fiber, using a parabolic law, which describes the behavior of the squared output pulse width versus the pump peak power in the case of Gaussian pulses. The experimental results give a minimum pulse duration of 233 fs, which is in good agreement with the model. Shorter and coherent pulses, down to 90 fs, have been obtained by inserting an interference filter at the optical output.     

Sorting of bending magnets for the SSRF booster

The Shanghai Synchrotron Radiation Facility(SSRF)booster ring,a full energy injector for the storage ring,is deigned to accelerate the electron beam energy from 150MeV to 3.5GeV that demands high extraction efficiency at the extraction energy with low beam loss rate when electrons are ramping.Closed orbit distortion(COD)caused by bending magnet field uniformity errors which affects the machine performance harmfully could be effectively reduced by bending magnet location sorting.Considering the affections of random errors in measurement,both ideal sorting and realistic sorting are studied based on measured bending magnet field uniformity errors and one reasonable combination of bending magnets which can reduce the horizontal COD by a factor of 5is given as the final installation sequence of the booster bending magnets in this paper.     

Measurement of nonlinear coefficient of optical fiber based on small chirped soliton transmission

We measure the waveform and phase curves of short optical pulses before and after transmission over different lengths of fibers by use of the pulse analyzer with the frequency-resolved optical gating (FROG),and numerically simulate pulse evolution under the experimental conditions.The nonlinear coefficient of the fiber is given by comparing the experimental results with the numerical ones.Difference between the experiment and numerical simulation is analyzed.     

Resonance scattering of canonical elastic shells in absorbing fluid medium

Resonance scattering of elastic spherical shell and cylindrical shell while the surrounding fluid medium has absorption is studied. The normal mode solution derived using exact elastic theory and the separation of variables is still applicable. However, the scattering form function has to be modified for the absorbing medium, otherwise the unreasonable result would be obtained. The backscattering form function in the absorbing medium is redefined, and the form function of elastic spherical and cylindrical shell with vacuum or solid matter filled is calculated in various absorption conditions. The results show that the absorption of surrounding fluid leads to notable attenuation of the coincidence resonances in the mid-frequency, but it has a little influence on the low-frequency resonance scattering induced by the filler inside the shell.     

Single-beam self-referenced phase-sensitive surface plasmon resonance sensor with high detection resolution

A versatile and low-cost single-beam self-referenced phase-sensitive surface plasmon resonance(SPR)sensing system with ultra-high resolution performance is presented.The system exhibits a root-mean-square phase fluctuation of ±0.0028.over a period of 45 min.i.e.a resolution of±5.2×10-9 refractive index units.The enhanced performance has been achieved through the incorporation of three design elements:a true single-beam configuration enabling complete self-referencing so that only the phase change associated with SPR gets detected,a differential measurement scheme to eliminate spurious signals not related to the sensor response,and the elimination of retardation drifts by incorporating temperature stabilization in the liquid crystal phase modulato .Our design should bring the detection sensitivity of non-labeling SPR biosensing closer to that achievable by conventional fluorescence-based techniques.     

Influences of SiO2 protective layers and annealing on the laser-induced damage threshold of Ta2O5 films

Ta2O5 films are prepared on BK7 substrates with conventional electron beam evaporation deposition.The effects of SiO2 protective layers and annealing on the laser-induced damage threshold (LIDT) of the films are investigated.The results show that SiO2 protective layers exert little influence on the electric field intensity(EFI)distribution,microstructure and microdefect density but increase the absorption slightly.Annealing iS effective on decreasing the microdefect density and the absorption of the films.Both SiO2 protective layers and annealing are beneficial to the damage resistance of the films and the latter is more effective to improve the LIDT.Moreover,the maximal LIDT of Ta2O5 films is achieved by the combination of SiO2 protective layers and annealing.