在电子-质子碰撞中识别瞬子末态方法的蒙特卡罗研究

在e⁺p深度非弹性散射的光子胶子融合过程中有可能出现瞬子. 这是 一类特殊的事件, 称为瞬子参与的深度非弹性散射事件. 本文用蒙特卡罗事件产生器QCDINS讨论了在瞬子参与的深度非弹性散射事件中识别瞬子末态和流喷注的方法. 对各种不同方法作了对比研究. 找到了一种能使重建得到的喷注能量、瞬子能量、瞬子质量与强子化前的取值均比较接近的最佳方法.     

e-A深度非弹性散射中胶子辐射振幅的新计算方法

在e-A深度非弹性散射过程中, 喷注穿过冷核介质时, 多重散射诱导胶子辐射会导致对碎裂函数的修正及喷注的能量损失.前期研究中关于计算e-A深度非弹性散射中胶子辐射振幅的两种方法: 螺旋振幅近似和微扰QCD严格计算都异常繁杂. 本文发展了一种新的方法, 可以方便计算出多重散射导致胶子辐射的振幅, 得到的碎裂函数的修正以及能量损失与严格计算的结果一致.     

改进Q￣2-重标度模型与部分子分布函数的核效应

针对原有的Ｑ￣２－重标度模型中存在的问题，提出了改进的Ｑ￣２－重标度模型，利用核动量守恒条件，采取对价夸克、海夸克、胶子进行不同的Ｑ￣２－重标度来描述束缚核子内部分子动量分布。利用改进的Ｑ￣２－重标度模型所得到的束缚核子内部分子分布函数，对轻子－核深度非弹性散射过程，核Ｄｒｅｌｌ－Ｙａｎ过程及Ｊ／ψ光生过程均给出较满意的解释     

改进Q2–重标度模型与部分子分布函数的核效应

针对原有的Q²-重标度模型中存在的问题,提出了改进的Q²-重标度模型,利用核动量守恒条件,采取对价夸克、海夸克、胶子进行不同的Q²-重标度来描述束缚核子内部分子动量分布. 利用改进的Q²-重标度模型所得到的束缚核子内部分子分布函数,对轻子-核深度非弹性散射过程,核Drell-Yan过程及J/ψ光生过程均给出较满意的解释.     

氮化铀热中子截面的第一性原理计算

氮化铀（UN）因其较好的热物性和耐事故容错性成为先进动力堆的候选燃料,但目前热能区缺少可靠的UN热中子截面数据,这对于热中子反应堆物理计算是很不利的.本文基于量子力学的第一性原理,利用VASP/PHONON软件模拟计算了UN的声子态密度,以此为积分得到UN的定容比热容,并基于新制作的声子态密度,采用核截面处理程序NJOY/LEAPR,利用热中子散射理论,得到UN的S（α,β）数据,进而研究UN的热中子散射截面,并与传统压水堆的二氧化铀（UO₂）进行对比.结果表明：优化的晶格参数与数据库符合较好,UN声子态密度的声子项和光子项较UO₂的分隔更加明显,定容比热容计算结果与实验值一致,基于该声子态密度计算得到的UN中²³⁸U的非弹性散射和弹性散射截面比相同温度下UO₂中²³⁸U小,UN中N仅考虑了非相干散射部分,随着温度升高,UN弹性散射截面变小,非弹性散射变大,并在高能段趋于自由核散射截面.本文的研究结果填补了UN热中子截面数据的缺失,为下一步系统研究UN燃料在轻水堆中的中子学性能奠定了基础.     

相对论重离子碰撞中的软探针和硬探针

简要回顾了高能核碰撞中夸克胶子等离子体的软探针和硬探针的一些最新进展,主要内容集中在相对论重离子对撞机和大型强子对撞机实验中各向异性集体流和喷注淬火的理论和唯象研究,对小系统中集体流的来源也做了简要的讨论。对于软探针,讨论了初态三维涨落和碰撞几何各向异性、相对论流体力学演化、末态各向异性集体流以及集体流的涨落、关联和纵向去关联等。通过与实验数据作系统的比较,可以探测重离子碰撞中夸克胶子等离子体的动力演化和各种输运性质。对于硬探针,集中讨论了部分子能量损失和喷注淬火对部分子味道的依赖性、重味夸克在夸克胶子等离子体中的强子化、整体喷注在核介质中的演化以及核介质对喷注的响应等。细致分析相关的观测量,可以帮助我们更全面地了解相对论核碰撞中喷注与核介质的相互作用以及重味粒子的生成。对于小系统,讨论初态和末态效应在解释小系统中轻强子和重味强子的集体流方面的贡献,这有助于我们理解大碰撞系统中集体流的起源成因。     

高能非线性现象研究的新进展

经典色动力学有混沌解,但是量子混沌是一个困难的理论问题,因而高能物理中的非线性目前还只能用唯象方法进行研究.80年代末,实验观察到多粒子未态相空间中有局域大起伏,激发了对高能非线性现象——间歇与分形研究的热潮.实验发现,一维阶乘矩有饱和现象,这被解释为高维间歇投影到低维的结果;但是,三维阶乘矩也并没有严格的反常标度性.这一困难在一段时间里曾使得间歇(分形)的研究陷于停顿.以后发现,其原因在于高能多粒子未态相空问高度各向异性,因而相应的分形是自仿射分形.只有对相空间进行正确的各向异性分割,才能观察到反常标度性.这一预言已在NA22和NA27的实验数据中得到证实,成功地观察到了反常标度性,从而使高能非线性的研究取得突破性进展.本文介绍这一进展,并作一些讨论.     

Z0能区正负电子湮没强子多重数分布的近泊松形式与肩状结构

对Z⁰能区91.2GeV正负电子湮没产生强子末态的事例,分别针对全喷注和双喷注在不同快度窗口的单、双半球空间内进行多重数分布的泊松拟合.根据/D参量及拟合度得到近泊松形式,与有关理论模型进行了比较,并讨论了与KNO无标度性的关系.分析了偏离泊松形式的有关参数与非独立粒子发射及关联强度之间的联系.利用JADE喷注分析法讨论了中心快度区的“肩状结构”.     

基于纳米点嵌入的界面导热性能优化

调节界面热导(ITC)是纳米电子器件热管理的关键任务.本文采用非平衡态分子动力学方法研究了在界面处嵌入锡(Sn)纳米点对硅锗(Si/Ge) ITC的影响.研究发现,在声子弹性和非弹性两种竞争机制下ITC随Sn纳米点的数量的增加先升后降,在嵌入4个Sn纳米点时达到顶峰,ITC是完美界面(无纳米点嵌入)时的1.92倍.通过计算声子透射函数和态密度可以知道,ITC增加的原因是声子的非弹性散射得到加强,增强的非弹性声子散射为界面声子输运打开了新的通道.随着纳米点数量增加到一定值时,声子的弹性散射逐渐占据主导地位,ITC开始降低.     

高能电子-正电子碰撞中产生喷注的标度

对高能电子-正电子对撞产生实验上可以直接观察的可视喷注的标度进行了仔细研究.根据在s=17—30Gev的电子-正电子对撞实验中最先观察到三喷注这一历史事实,论证了可视喷注的相对横动量kt.在5—10GeV/c的范围.并通过一个具体例子说明,只有k_t在这一范围时才能正确地判定事件中的喷注数.仔细比较了由不同k_t得到的喷注内部的动力学起伏,发现只有k_t在5—10GeV/c范围时,喷注内部系统才有最好的反常标度性.从而得到,可视喷注的标度是k_t～5—10GeV/c.讨论了这一标度和微扰QCD的标度1—2GeV之间的关系.     

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.     

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.     

A stereo matching algorithm using multi-peak candidate matches and geometric constraints

Gray cross correlation matching technique is adopted to extract candidate matches with gray cross correla- tion coefficients less than some certain range of maximal correlation coefficient called multi-peak candidate matches. Multi-peak candidates are extracted corresponding to three closest feature points at first. The corresponding multi-peak candidate matches are used to construct the model polygon. Correspondence is determined based on the local geometric relations between the three feature points and the multi-peak candidates. The disparity test and the global consistency checkout are applied to eliminate the remaining ambiguous matches that are not removed by the local geometric relational test. Experimental results show that the proposed algorithm is feasible and accurate.