周期驱动的二能级系统中的准宇称-时间对称动力学

本文研究了一个周期驱动的非宇称-时间对称二能级量子系统的非厄米动力学.通过经典相空间分析方法,解出了该非厄米系统的Floquet态和准能谱,并解析构造了由该非厄米哈密顿量支配下的量子态的非幺正时间演化算符,给出了不同参数区域的量子态演化.本文数值和分析证明,该非宇称-时间对称二能级Floquet系统,类似于宇称-时间对称系统,存在一个准能谱从实数谱到复数谱的相变.本文还揭示了在量子态的动态演化中存在一种准宇称-时间对称动力学,即,该系统的粒子布居概率演化完全满足时间空间对称(宇称-时间对称),但是由于相位演化违反了宇称-时间对称性的要求,因此包含相位信息的量子态演化不满足时间空间对称(宇称-时间对称).这些结果加深了对非厄米物理的理解,拓展和推广了传统的宇称-时间对称概念.     

An Experimental Observation of Axial Variation of Average Size of Methane Clusters in a Gas Jet

Axial variation of average size of methane clusters in a gas jet produced by supersonic expansion of methane through a cylindrical nozzle of 0.8 mm in diameter is observed using a Rayleigh scattering method. The scattered light intensity exhibits a power scaling on the backing pressure ranging from 16 to 50bar, and the power is strongly Z dependent varying from 8.4 （Z = 3mm） to 5.4 （Z = 11mm）, which is much larger than that of the argon cluster. The scattered light intensity versus axial position shows that the position of 5mm has the maximum signal intensity. The estimation of the average cluster size on axial position Z indicates that the cluster growth process goes forward until the maximum average cluster size is reached at Z - 9 mm, and the average cluster size will decrease gradually for Z 〉 9 mm.     

用于NPA标定系统的高频离子源研制

研制了一台用于Neutral Particle Analyzer(NPA)标定系统的高频离子源,对其性能参数进行了实验测量,得到引出束流与高频振荡器板压、引出电压及放电气压之间的特性曲线,对影响引出束流稳定性的原因进行了分析.结果表明:当工作气体为氢气,在板压580 V、引出电压1600 V、聚焦电压1550 V和气压9.5×10~(-4) Pa时,能引出66μA的离子流;在41μA束流条件下,4小时内的束流稳定性优于2.6%,影响束流稳定性的主要因素是放电管内工作气体气压的波动和等离子体温度的升高.此结果可以满足HL-2A/M上NPA系统的标定对离子源的要求.     

铀氧化物中238U含量的定量研究

准确定量铀氧化物样品中238U的含量对于裂变产额测量等工作具有重要意义,其定量方法的研究对于涉及238U的绝对测量的诸多实验都具有参考价值。利用四川大学2.5 MeV质子静电加速器产生的准单能中子对八氧化三铀样品进行中子活化,用高纯锗探测器测量活化产物的β衰变子体239Np的277.6 keV特征γ射线,利用已知的活化截面,算出样品中238U的质量占比为79.1%,不确定度为6.2%。利用电感耦合等离子体质谱法对样品中238U的含量进行了测量,其质量占比为59.2%。此外,基于EA3000元素分析仪、卡尔费休电位滴定仪和TGA-DSC2同步热分析质谱联用仪,测知样品中不含N元素,含水量在2.2%以下。并利用PIXE方法排除了样品中含有Al元素以上杂质,利用EPBS方法测知样品中U/O原子数比为1:3.6,误差约2%,推知样品中238U质量占比为80%,验证了活化法测得的238U含量。最终测得样品中238U的质量占比为79.1%,不确定度6.2%。对照按U3O8分子式折算的84.5%,考虑到水分含量等,此结果合理。The accurate quantification of 238U in uranium oxides is of great importance for measurements of fission yield. The study for the method of 238U quantification has significance to lots of experiments involving absolute measurement of 238U. The reaction (n, γ) in the triuranium octoxide samples was induced by T(p,n)3He quasi-monoenergetic neutrons provided by the 2.5 MeV proton electrostatic accelerator in Sichuan University. The 277.6 keV characteristic γ ray of 239Np that comes from β-decay of the activation product 239U was detected by a HPGe detector. With the known (n, γ) cross section, the mass percentage of 238U in samples was determined to be 79.1%, with the uncertainty of 6.2%. ICP-MS was also used in the quantification of 238U in samples, its result was 59.2%. Meanwhile, the samples were analyzed by other several methods and the results showed that less than 2.2% H₂O, no nitrogen, and no other impurity elements above Al were contained in the samples. EPBS was used to measure the atomic ratio of U and O and it was found that the mass percentage of 238U in samples was about 80%, verifying the result 79.1% of INAA.     

紧凑针孔中性粒子分析器标定系统的设计和研制

介绍了紧凑针孔中性粒子分析器(CP-NPA)标定系统,包括一套高能量、小流强的中性粒子束线源和一个配套旋转平台.束线源由高频离子源、电单透镜、速度选择器、加速管、电四极透镜和中性化室组成.高频离子源已经完成研制,并顺利建立起等离子体.单透镜已经完成仿真、制造和测试.实验中引出电压为1.0kV时,调整单透镜聚焦电压最高可...     

加速可靠性试验中LED寿命的快速评估

对于大功率LED产品而言,由于其寿命较长,采用传统的方法测定其寿命需花很长时间,一般采用加速可靠性实验来对LED产品寿命进行测试推断。目前的LED加速寿命测试多采用离线的方法,存在数据样本少、不能准确地反映真实衰减情况的问题.本文提出了一种在线测试的方法,并利用此方法对LED模块的加速寿命进行了推断.实验结果证明,采用在线测试方法可以有效地减少实验时间,达到快速评估高温加速可靠性试验中LED寿命的目的.     

基于量子点测量LED芯片表面温度的实验研究

本文围绕CdSe/ZnS量子点发光光谱与温度的依赖关系,对LED芯片表面温度进行实验研究。CdSe/ZnS量子点作为温度传感器对GaN LED芯片表面温度进行测量,量子点的掺入导致光谱中引入量子点发射谱,测得不同温度下的光致发光谱,通过红外热像仪对LED芯片表面温度进行定标,就可以获得LED芯片表面温度和量子点光谱峰值波长的曲线,最后利用该方法测得LED芯片在不同电流下和不同通电时间的表面温度。实验结果表明在25~85℃温度范围内,CdSe/ZnS量子点温度灵敏度为0.11 nm/℃,测温精度为±3℃。     

大功率LED荧光粉硅胶点涂工艺的三维格子Boltzmann模拟

为实现蓝光LED(light emitting diode)芯片向白光LED照明的转化,大功率LED封装工艺流程中存在一个关键的环节——荧光粉涂覆,即通过点涂方式将荧光粉硅胶涂覆于LED芯片周围.荧光粉硅胶涂覆工艺是一个两相流动过程,它直接决定了荧光粉硅胶层的几何形貌及物理特性,并影响LED最终的光学和热学性能;因此对其中流动过程物理机制的理解有利于提升荧光粉涂覆质量,实现高性能LED产品.基于格子Boltzmann方法,建立荧光粉硅胶流动模型,并应用该模型研究了在平坦表面和方形凸起结构两种封装形式上的荧光粉硅胶点涂成形流动过程.结果表明:格子Boltzmann方法能够准确地模拟荧光粉点涂流动过程;在平坦表面上荧光粉硅胶液滴接触线与液滴直径之比(dL/D)和相对时间(t/T)成幂函数关系.     

Ionization for Hf- and W-L-shell by electron impact

Electron-induced Hf-, W-L-shell partial, total production cross sections, mean ionization cross sections and Hf-L_3-shell ionization cross sections (at two energies) have been measured as functions of electron energies (from near threshold to 36keV). The influence of electrons reflected from the backing of the thin targets on measured results was corrected using a model to relate to the electron transport process. The mean paths of electron multi-scattered in the target itself (including forward and backward scattering) were calculated by means of Monte Carlo program (EGS4) and they were used to correct measured results. A comparison with both theoretical predictions was given.     

Suppression of Chaos in a Bose-Einstein Condensate Loaded into a Moving Optical Superlattice Potential

We have shown that the application of modulating the secondary lattice is an efficient route to suppressing the generation of chaotic traveling waves of a Bose-Einstein Condensate with attractive interatomic interaction loaded into a moving optical superlattiee consisting of two lattices. With the Melnikov method, we obtain the optimal value of the relative phase between the two lattice harmonics for the control of chaos. We also find that the regularization route as the potential depth of the secondary lattice is varied and fairly rich, including the period-doubling bifurcations.