Angular Distributions for φ＇ Sequential Decays into 2（π^＋π^-）pp^-γ via XCJ

Amplitudes for φ（2S） sequential decays into 2（π^＋π^-）pp^-γ via XCJ are constructed in effective coupling scheme. A Mote-Carlo simulation is carried out to study angular distributions of the decayed particles in laboratory system. The results can be taken as a reference for measuring the decay of XCJ into at BESⅡ/BEPC in the near future.     

Pitman-Yor process mixture model for community structure exploration considering latent interaction patterns

The statistical model for community detection is a promising research area in network analysis. Most existing statistical models of community detection are designed for networks with a known type of community structure, but in many practical situations, the types of community structures are unknown. To cope with unknown community structures, diverse types should be considered in one model. We propose a model that incorporates the latent interaction pattern, which is regarded as the basis of constructions of diverse community structures by us. The interaction pattern can parameterize various types of community structures in one model. A collapsed Gibbs sampling inference is proposed to estimate the community assignments and other hyper-parameters. With the Pitman-Yor process as a prior, our model can automatically detect the numbers and sizes of communities without a known type of community structure beforehand. Via Bayesian inference, our model can detect some hidden interaction patterns that offer extra information for network analysis. Experiments on networks with diverse community structures demonstrate that our model outperforms four state-of-the-art models.     

Monte-Carlo estimation of time-dependent statistical characteristics of random dynamical systems

The problem of estimating the time-dependent statistical characteristics of a random dynamical system is studied under two different settings. In the first, the system dynamics is governed by a differential equation parameterized by a random parameter, while in the second, this is governed by a differential equation with an underlying parameter sequence characterized by a continuous time Markov chain. We propose, for the first time in the literature, stochastic approximation algorithms for estimating various time-dependent process characteristics of the system. In particular, we provide efficient estimators for quantities such as the mean, variance and distribution of the process at any given time as well as the joint distribution and the autocorrelation coefficient at different times.     

Formation of short-range order in Al–Ge–Fe melts: influence of composition

ABSTRACT

The short-range order in Al–Ge–Fe melts has been studied by X-ray diffraction and reverse Monte Carlo simulations in wide concentration range. Influence of the replacement of one component by another while the content of third component is constant on the formation of a local structure of ternary melts has been discussed. It has been shown that at Ge content less than 30 аt. % Ge atoms are uniformly distributed in the volume of the Al–Ge–Fe melts and atomic clusters with structure similar to the liquid germanium are formed at content more than 30 аt. % Ge. The addition of the third component (Ge or Al) to the binary Al–Fe or Fe–Ge melts, correspondingly, results in competition between Al and Ge atoms in formation of the local structure around Fe atoms. The obtained concentration dependences of the nearest neighbour distances point out that the ternary interactions take place in the Al–Fe–Ge melts.     

具有随机参数的盾构管片弹性密封垫防水性能优化分析

盾构管片接缝弹性密封垫断面的几何尺寸极易受生产工艺的影响而呈现出随机性,从而对盾构管片弹性密封垫的防水性能产生影响.该文选取密封垫的孔洞圆心坐标、孔径、断面宽度、断面高度等参数作为随机输入变量,运用ANSYS-PDS模块得出了各随机参数对密封垫防水性能的灵敏度数值,结果显示圆孔孔径对闭合压力及接触应力的影响较其他几何尺寸更大;圆孔垂向位置改变对闭合压力及接触应力的影响较横向位置更大.在此基础上,应用ANSYS优化设计模块,选取密封垫闭合压力和下表面平均接触应力作为状态变量,以在闭合压力不超过某一定值的条件下接触应力最大为目标函数,对密封垫进行几何参数优化分析,得出了某盾构隧道弹性密封垫优化断面,试验结果很好地验证了优化计算结果的可靠性.     

Ge/Pb/Si(111)生长中Ge原子沿团簇边缘扩散的三维Monte-Carlo模拟

用动态Monte-Carlo方法对Ge在单层表面活性剂Pb覆盖的Si(111)表面上沿团簇边缘扩散进行三维模拟.重点讨论Ge原子是否沿团簇边缘扩散,沿边缘扩散时的最大扩散步数及最近邻原子数对三维生长的影响,并计算薄膜表面粗糙度研究三维生长模式.模拟表明Ge沿团簇边缘扩散的行为对薄膜生长模式的影响很大,同时讨论了ES势对三维生长模式的影响.     

BC537探测器中γ射线的响应函数测量与蒙特卡罗模拟

为了将氘化液闪探测器(BC537)测量的反冲电子谱转换为γ射线能谱,利用标准γ点源对BC537探测器的响应进行了测量并运用基于蒙特卡罗方法的Geant4程序计算了BC537探测器探测γ射线的响应函数。讨论了探测器建模中有无铝壳和入射γ射线束流半径对探测效率和响应函数的影响。对比模拟和实验测量的反冲电子谱,两者符合较好。利用模拟的响应函数和实验测量标准γ源Cs-137和Co-60以及AmBe源在BC537探测器中的反冲电子谱,经迭代法解谱得到了对应的标准γ射线能谱,验证了模拟参数的合理性以及该响应函数的实用性。     

蒙特卡罗模拟LED并联电路电流降额特性

利用蒙特卡罗方法对LED并联电路的电流降额特性进行了模拟,假设分档后的大功率白光LED的正向电压(VF)分布符合正态分布,研究了1×n(2≤n≤15)系列LED并联电路电流降额量(IP)的概率(P)分布。模拟结果表明,IP的概率分布函数偏离了正态分布,密度函数曲线最高值点的两侧不对称,左侧较右侧陡峭;随着LED并联数(n)的增加,概率密度函数沿IP增大的方向移动,并且越来越趋近于正态分布。当n一定时,IP随电路中出现LED承载电流超过其额定电流的概率增大而降低,降低的速度由快转慢;当P为0.01%～1%时,IP大约为20%～30%。当P一定时,IP随n的增加而增大;当n6时,IP的增大速度变缓。模拟结果可以推广到m×n阵列化互连大功率LED模组。     

Density functional theory-based cluster expansion to simulate thermal annealing in FeCrW alloys

Abstract

In this work, we develop a rigid lattice cluster expansion as an ultimate goal to track the micro-structural evolution of Eurofer steel under neutron irradiation. The fact that all (defect) structures are mapped upon a rigid lattice allows a simplified computation and fitting procedure, thus enabling alloys of large chemical complexity to be modelled. As a first step towards the chemical complexity of Eurofer steels, we develop a cluster expansion (CE) for the FeCrW-vacancy system based on density functional theory (DFT) calculations in the dilute alloy limit. The DFT calculations suggest that only CrW clusters containing vacancies are stabilised. The cluster expansion was used to simulate thermal annealing in Fe–20Cr–xW alloys at 773 K. It is found that the addition of W to the alloy results in a non-linear decrease in the precipitation kinetics. The CE was found suitable to describe the energetics of the FeCrW-vacancy system in the Fe-rich limit.