Generalized Virial Theorem for Mixed State When Hamiltonians Include Coordinate-Momentum Couplings

The generalized Virial theorem for mixed state, derived from the generalized Hellmann Feynman theorem, only applies to Hamiltonians in which potential of coordinates is separate from momentum energy term. In this paper we discuss Virial theorem for mixed state for some Hamiltonians with coordinate-momentum couplings in order to know their contributions to internal energy.     

平面团簇稳定结构的蒙特卡罗树搜索

以平面团簇为例提出了一种结合结构识别和蒙特卡罗树技术搜索稳定结构的新方法.体系原子之间的相互作用由两类模型势能函数来描述:Lennard-Jones二体势函数与基于Lennard-Jones势的三体势函数.考虑可能的三角晶格碎片作为候选结构,引入编号策略对结构进行快速识别,并运用蒙特卡罗树搜索研究稳定结构随着原子数增大的演化过程;对于能量较低的候选结构,进一步采取局域优化来获得对应体系的稳定结构.计算表明,Lennard-Jones二体势函数对应的三角晶格团簇更稳定;在特定的参数下,三体势函数对应的六角晶格团簇更稳定.结合结构识别和蒙特卡罗树搜索可以对候选结构空间进行高效扫描,在较短时间内更容易搜索到稳定的团簇结构,并可以与第一原理计算结合实现材料的结构预测.     

He和类He离子基态能量与波函数的变分计算

在研究Pekeris模型的基础上,提出了一种包含坐标张弛系数的试探波函数,同时利用Matlab(或者Mathematica)语言,开发了一个运用变分法对三体问题进行计算的软件程序.在此基础上对He原子和类He离子的基态能量和解析波函数进行了变分计算,得到了比较理想的结果.这表明,采用Matlab或Mathematica设计的软件,在处理变分法问题时,在运算功能、数据的可靠性和准确度方面都是很具潜力的.     

Monte-Carlo simulation of heavy-ion collisions

We present Monte-Carlo simulations for heavy-ion collisions combining PYTHIA and the McGill-AMY formalism to describe the evolution of hard partons in a soft background, modelled using hydrodynamic simulations. MARTINI generates full event configurations in the high p_T region that take into account thermal QCD and QED effects as well as effects of the evolving medium. This way it is possible to perform detailed quantitative comparisons with experimental observables.     

用多群蒙特卡罗方法计算快中子核临界keff和通量密度

 用多群蒙特卡罗方法对快中子核裂变系统进行了临界计算。有效增殖因子keff的计算值与实验结果符合。计算所得中子通量密度的空间分布在球形裂变系统中随半径增大单调下降。中子通量密度的能量分布在由高浓缩铀组成的活性区内呈单一能量极大值,其对应能量对于裸球核裂变系统和具有反射层裂变系统分别为0.35MeV和0.25MeV,而在由天然铀组成的反射层中在0.1MeV附近出现能量双峰。由通量密度所得中子能谱在无反射层球形裂变系统中随半径增加变硬,在有反射层球形裂变系统中随半径增加变软。     

蒙特卡洛模拟中伪随机数的STTDMR检验

伪随机数发生器(PNG)是蒙特卡洛法概率模拟中的基本工具,但它也成为影响蒙特卡洛法精确度的最大误差源.提出了一种检验方法——二维介质辐射对称性检验法STTDMR,它可在不同条件下对各种伪随机数程序进行无限制的检验,在更精细的层次上区分伪随机数发生器的优劣.STTDMR不仅可检验伪随机数的特性,还可检验概率模型是否正确.利用STTDMR分析了多种典型的伪随机数产生法,获得一个性能上较优越的组合伪随机数ZH产生程序.     

投篮概率的蒙特卡罗数值计算分析

建立理想的投篮模型,运用蒙特卡罗数值计算方法得出给定点的空心中框概率,并由此得到最佳投篮速度、最佳投篮角度和截止投篮速度.根据中框投篮角分析了不同投篮速度区间对应的投篮弧线,还对空心中框率和投篮距离及投篮点高度间的关系作了讨论.     

X光导管传输特性的蒙特卡罗模拟

 X光在导管中的传输性能是设计X光透镜的基础。在研究X光导管传输理论基础上，建立了X光在导管中传输的射线跟踪方法，编制了蒙特卡罗模拟计算程序。对具体的模型，计算给出了导管的传输效率随X光源与导管入口面的距离、导管直径和曲率半径的变化关系。模拟表明：直圆柱导管的传输效率随导管直径增大而减小，随Ｘ光源所在平面与导管入口面之间的距离增大而增大；弯曲圆柱导管的传输效率随其曲率半径的增大而增大，当曲率半径趋向无穷大时，X光在弯圆柱导管的传输效率趋向于直圆柱导管的传输效率。利用编制程序计算得到的传输效率与实验结果符合较好。     

Monte-Carlo analysis of centroid detected accuracy for wavefront sensor

By utilizing Monte-Carlo simulation technology, the centroid algorithms have been compared in detail. The factors such as the detected window size, threshold and weighting power factor, which affect the detected accuracy of the wavefront sensor, have been studied and the optimal parameters for each algorithm have been found. The numerical results will be helpful for further improving the measurement accuracy of the wavefront sensor.     

Monte-Carlo simulation of light scattering in fractal porous media

Monte-Carlo simulation of light propagation in a porous medium with a mass fractal morphology was carried out. It was shown that the simulation results can be used to analyze experimental data on light scattering and to study the porous medium structure. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 2, pp. 193–196, March–April, 2008.     

Coordinate representation of the McWeeny-Coulson wave function for the helium atom

The coordinate representation of the McWeeny-Coulson wave function for the helium atom is obtained in the form of an expansion in scalar tripolar spherical harmonics. The coefficients of the expansion, which are functions of the interparticle coordinates, are represented as a sum of terms admitting separation of variables. Analysis of the expansion constructed substantiates the presence of the Huelten correlation factor in the wave function as well as the appearance of Huelten orbitals.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 37–43, August, 1985.     

微波器件微放电阈值计算的蒙特卡罗方法研究

为了精准快速地计算微波器件中微放电效应的阈值,在传统蒙特卡罗方法的基础上,提出了三种不同的蒙特卡罗方法,分别对二次电子的初始能量、出射角度和初始相位等参数进行随机,结合四阶龙格-库塔法和Furman模型计算电子的运动轨迹和单次碰撞产生的二次电子发射系数,然后应用不同的方法计算有效二次电子发射系数作为微放电效应的判据.以平板传输线TEM模式为研究对象,采用四种不同的蒙特卡罗方法计算微放电阈值,并与统计模型结果进行对比.结果表明单电子-多碰撞蒙特卡罗方法误差最小,而且稳定性最好.     

Monte-Carlo Simulation of Energy Migration in Uniaxially Oriented Polymer Films

Nonradiative electronic energy migration between identical fluorophores is studied numerically in uniaxially oriented polymer films. The reorientation effect of dipole moments induced by film stretching leads to extremely different concentration- and time-courses of emission anisotropy compared to those in disordered system. In particular, the effect of a much weaker concentration depolarization of fluorescence is due to the fact that not only primarily excited molecules contribute to emission anisotropy in oriented films.     

Auxiliary field quantum Monte-Carlo simulation of interacting electrons in quantum dots

Accurate auxiliary field quantum Monte-Carlo (AFQMC) simulations of interacting electrons in quantum dots are reported. Two different formulations of this approach are presented both of which have been designed specifically for application to quantum dots. A deflation technique for calculation of anti-symmetrized traces is introduced. The auxiliary field is sampled with a hybrid algorithm and the artificial dynamics needed for use with the present formulation of AFQMC is described. The constrained path approximation is used to control the sign problem. Results for the ground state energy of two spin-polarised, interacting electrons are presented and are found to agree well with exact diagonalization results for a wide range of screening lengths. The sign problem does not appear in the regime of small screening length.     

蒙特卡罗法在高功率激光系统输出能量稳定性研究中的应用

以"四程 助推"放大系统为例,运用蒙特卡罗(Monte-Carlo)法计算分析了放大过程中注入能量、放大增益及损耗单独存在随机变化和以上因素共同作用时对系统输出能量稳定性的影响.计算结果表明,系统输出能量稳定性对四程小信号增益系数和腔内光学元件透过率的随机变化相当敏感;小信号增益随机变化明显大于注入能量对输出能量稳定性的影响.同时,也说明应用蒙特卡罗方法解决随机性问题的有效性和简洁性.     

固体金属二次电子发射的Monte-Carlo模拟

二次电子的发射在生产实践中有着广泛的应用,但其相关测量结果受实验环境和实验仪器的影响很大．在实验中难以精确测量．所以本文建立了一个包含二次电子激发、在固体内部传输和最后逸出固体表面的二次电子系统模型．采用Monte-Carlo的模拟方法仿真二次电子运动轨迹,定量分析二次电子的发射系数和能谱分布．并探讨它们与一次电子的入射角度和入射能量的关系．仿真结果表明：本文建立的二次电子系统模型能较好地反映实际情况．通过该模型仿真,可以定量得到二次电子发射系数和能谱分布与一次电子的入射能量和入射角度的关系．     

采用光纤和YAP晶体的小型γ相机的蒙特卡罗模拟

基于波长位移光纤(WSF)耦合YAP晶体中的光子传输特性,用GEANT4软件包建立了一个蒙特卡罗模拟程序.对采用波长位移光纤耦合平板式YAP晶体的小型单管γ相机的性能进行了计算机模拟.采用波长位移光纤耦合光电倍增管光阴极面的读出方式,和晶体直接耦合光电倍增管光阴极面相比,在相同的晶体面积大小条件下,PSPMT光阴极面积可大大缩小,使费用降低.模拟结果表明：γ射线与晶体发生作用的地方所对应的光纤输出的平均光子数最少为15个,位置灵敏光电倍增管完全可以探测到.说明采用闪烁晶体－WSF－位置灵敏光电倍增管的读出方式是可行的;在用硅油耦合波长位移光纤和YAP晶体的情况下,获得的空间分辨率为1.28 mm(FWHM).模拟结果也说明了增加平均光子数对提高空间分辨率的重要性.     

蒙特卡罗采样法辐射温度测量不确定度分析

确定了影响辐射温度测量的软X光能谱仪各种光学元件、电子器件的不确定度及还原算法等不确定度来源。建立了基于蒙特卡罗随机采样的不确定度分析方法,获得了各种不确定度综合影响下的辐射温度不确定度。通过单独对谱仪各个探测通道时间对齐进行的分析,显示这一因素对辐射温度不确定度有较大影响。     

A simple and accurate equation of state for hard-disk fluids

A long-standing problem for hard-disk fluids is to find a simple and accurate equation of state. By observing the known updated virial coefficients from up to , we obtain an accurate empirical formula, with errors less than 0.5%. We further assume that the empirical formula is valid for all the virial coefficients. Using this assumption, we obtain a simple and accurate equation of state. In the density range 0<ρa²≤0.83, the predicted pressures are in good agreement with the simulation results. For 0<ρa²≤0.70, the errors are less than 0.007%. Even at ρa²=0.83, the error is only 0.5%.     

氢硼聚变三体级联衰变连续能谱的Monte-Carlo模拟与分析

¹¹B(p,α1)⁸Be^*(1)(2α)三体级联衰变中居间核8Be⁽¹⁾衰变成两个α粒子的连续能谱呈马鞍形分布.编写了模拟三体级联衰变连续能谱的Monte-Carlo程序,计算结果表明:沿居间核8Be⁽¹⁾运动方向α发射强度增强的各向异性分布,能较好地解释实验结果,揭示p+¹¹B核反应中⁸Be⁽¹⁾核α衰变各向异性发射.