相对论重离子碰撞中逐事件横动量起伏的蒙特卡洛研究

用蒙特卡罗模型研究了相对论重离子碰撞中逐事件横动量起伏与多重数的关联, 发现蒙特卡罗产生器,HIJING,不能描述实验现象. 提出了一个简单的蒙特卡罗模型, 可以与实验一致, 有助于理解逐事件横动量起伏与多重数关联的动力学起源.     

浅表组织后向散射检测中偏振门的蒙特卡罗研究

已有实验表明偏振门和斜入射技术能有效地抑止深层散射光子,实现浅表组织光学特性的检测。采用蒙特卡罗方法,分析了斜入射、偏振门的特性,研究了组织光学参量和入射角等参量对平均探测深度的影响。结果表明,组织的各向异性因子和入射角对平均探测深度影响较大。当各向异性因子较小(小于0.8)或者入射角较大(大于1.4 rad)时,组织的平均探测深度能满足小于2倍平均自由程的要求。偏振门和斜入射技术均可使探测光子经历的散射次数和探测深度有明显减小,因此,结合偏振门和斜入射技术能够更有效地分辨来自浅层的信号光,抑止来自深层的背景光。     

Polarization imaging of multiply-scattered radiation based on integral-vector Monte Carlo method

A new integral-vector Monte Carlo method (IVMCM) is developed to analyze the transfer of polarized radiation in 3D multiple scattering particle-laden media. The method is based on a “successive order of scattering series” expression of the integral formulation of the vector radiative transfer equation (VRTE) for application of efficient statistical tools to improve convergence of Monte Carlo calculations of integrals. After validation against reference results in plane-parallel layer backscattering configurations, the model is applied to a cubic container filled with uniformly distributed monodispersed particles and irradiated by a monochromatic narrow collimated beam. 2D lateral images of effective Mueller matrix elements are calculated in the case of spherical and fractal aggregate particles. Detailed analysis of multiple scattering regimes, which are very similar for unpolarized radiation transfer, allows identifying the sensitivity of polarization imaging to size and morphology.     

Monte Carlo Study on Singly Tagged D Mesons at BES-III

We present Monte Carlo studies on the singly tagged D mesons, which are crucial in the absolute measurements of D meson decays, based on a full Monte Carlo simulation for the BES-III detector, with the BES-III Offline Software System. The expected detection efficiencies and mass resolutions of the tagged D mesons are well estimated.     

A Quantum Monte Carlo Study on Mixed-Spin Chains of

The ground-state and thermodynamic properties of quantum mixed-spin chains of1/2-1/2-1-1and 3/2-3/2-1-1are investigated by a quantum Monte Carlo simulation with the loop-cluster algorithm. For 1/2-1/2-1-1 chain, we find it has two phases separated by an energy-gap vanishing point in the ground-state. For 3/2-3/2-1-1 chain, the numerical results show two energy-gap vanishing points isolated by different phases in its ground-state. Our calculations indicate that all these ground state phases can be understood by means of valence-bond-solid picture, and the thermodynamic behavior at finite temperatures is continuous as a function of parameterα=J2/J1.     

Monte Carlo simulation of polymers at interfaces

Polymers at interfaces pose challenging problems to statistical physics because their configurations often differ greatly from the bulk. Computer simulation of coarse-grained models then gives valuable insight and allows stringent tests of various theoretical predictions. Three examples are briefly treated: chain configurations of B-chains in the surface-enriched B-rich layer of an (AB) binary polymer mixture; “frustrated” lamellar ordering in ultra-thin block-copolymer films; and the collapse of polymer brushes in bad solvents.     

A Monte Carlo Study of the Half-Filled Two-Dimensional Hubbard Model

Using the path integral representation,bulk thermodynamic properties of the two-dimensional Hubbard model on a square lattice are studied numerically using the hybrid Monte Carlo simulation algorithm.Results for averaged energy,spin-spin correlation functions and Cooper pair correlation functions are presented.All these results suggest that the system exhibits an anti-ferromagnetic correlation at half-filling for a wide range of temperature.``     

A Monte Carlo Study of the Half-Filled Two-Dimensional Hubbard Model

Using the path integral representation,bulk thermodynamic properties of the two-dimensional Hubbard model on a square lattice are studied numerically using the hybrid Monte Carlo simulation algorithm.Results for averaged energy,spin-spin correlation functions and Cooper pair correlation functions are presented.All these results suggest that the system exhibits an anti-ferromagnetic correlation at half-filling for a wide range of temperature.     

A Study of Nanoparticle Aerosol Charging by Monte Carlo Simulations

A Direct Simulation Monte Carlo (DSMC) technique is applied for describing the dynamics of aerosol charging. The method is based on the transformation of known combination coefficients into charging probabilities. Changes in the particle charge distribution are computed as a stochastic game, calculating the time-step after each event. The simulations are validated by comparison with analytical solutions for unipolar aerosol diffusion charging and aerosol photocharging. The advantage of the DSMC method lies in the uncomplicated simulation of multi-dimensional systems that would result in very elaborate population balances. The DSMC method is used for simulation of the photocharging of moderately concentrated bicomponent polydisperse aerosols. By means of this method, the influence of the particle parameters (size, material) on the dynamics of the charge distribution in different size and material fractions has been studied. It is shown that charge separation between size or material fractions can be achieved for aerosol components with dissimilar work functions, while the total aerosol charge is zero.     

A Monte Carlo simulation of coagulation

A Monte Carlo simulation technique is described for the study of the coagulation of suspended particles. The method is computationally efficient since the particle trajectories are not used to determine coagulations. Instead, pairs of particles are assigned probabilities to coagulate and the evolution is computed as a stochastic Markov game. We also describe a simple analytic method to obtain the stationary distribution of sizes for the various mechanisms of relative particle motion. It is demonstrated that the simulation yields the correct stationary size distribution independent of initial condition.     

Monte Carlo Simulation on Glueball Search at BESIII

The J/ψ radiative decays are suggested as promising modes for glueball search. A full Monte Carlo simulation of J/ψ →γηη and γηη, based on the design of BESIII detector, is performed to study the sensitivity of searching for a possible tensor glueball at BESIII.     

闪烁光纤时间特性的蒙特卡罗模拟

用蒙特卡罗模拟的方法，研究了影响闪烁光纤时间分辨的物理因素，包括光子在光纤中的发射，传输，吸收和最后在光电倍增管输出端形成电泳冲等过程，并和实验结果进行了比较。     

The Role of One Single Lambda Hyperon on Binding Energy Difference of Hypernuclear Mirror Pair

Investigation on isospin symmetry in light Lambda hypernuclei is one of the most important issues in hypernuclear physics. In order to know the influences introduced by a single Lambda hyperon, we study the binding energy difference of mirror hypernuclear pair with mass A=16, 18, 28, 40, and 42 using a time-odd triaxial relativistic mean field theory. Effects as the spin-orbit interaction, the time-odd component of vector fields, the core polarization, the proton-neutron mass difference, and the center-of-mass energy correction are self-consistently considered. Compared to the reported results of ordinary nuclei, the binding energy difference of mirror hypernuclei shows trivial change. With core polarization modified by an impurity hyperon, the isospin nonconserving effect between proton and neutron is hardly reduced for nuclei in study.     

A second-quantized few-fermion Monte Carlo scheme

We propose a new Monte Carlo algorithm for the solution of the few-fermion Schrödinger equation. Antisymmetry is maintained by working in the space of N-fermion determinants for an N-fermion system. This does not solve the problem of cancelling positive and negative contributions to the wave function. The problem appears in a different form, however, due to negative signs introduced by dynamic correlations instead of statistics and appears also for boson systems in this approach. Since the determinants are constructed from plane-wave states use may be made of the long range of nuclear forces in momentum space to cancel negative and positive contributions more efficiently. Incorporation of non-radial interactions, i.e. interactions with spin dependence and tensor forces, reduces the problem to a quantitative problem.     

Monte Carlo simulation of carbon fragmentation at high energies

The dominating decay channels of fragmenting carbon nuclei in high-energy proton-carbon collisions were studied by means of a Monte Carlo simulation. We study the influence of the Coulomb interaction on the energy spectra and two-fragment (energy and angular) correlations between the various fragments in the context of a statistical model. We show that the Coulomb interaction between the fragments strongly affects their energy and angular correlation functions. Qualitative predictions for the exclusive analysis of the various final states are given. Comparison with experiments of this type should soon be possible.     

Monte Carlo studies of finite-size effects at first-order transitions

First-order phase transitions are ubiquitous in nature but their presence is often uncertain because of the effects which finite size has on all transitions. In this article we consider a general treatment of size effects on lattice systems with discrete degrees of freedom and which undergo a first-order transition in the thermodynamic limit. We review recent work involving studies of the distribution functions of the magnetization and energy at a first-order transition in a finite sample of size N connected to a bath of size N′. Two cases: N′ = ∞ and N′ = finite are considered. In the former (canonical ensemble) case, the distributions are approximated by a superposition of Gaussians corresponding to the different phases; all finite-size effects then vary as N or 1/N. The latter case involves the Gaussian ensemble where the entropy of the bath has a convenient form; for small N′, first-order transitions are characterized by van der Waals' loops in (for example) the energy vs. temperature curves. Results from extensive Monte Carlo simulations of Ising and Potts models in d = 2 are presented to confirm the predictions. Comparison is made with data from second-order transitions to show that the order of a transition can be distinguished through such studies, although problems still occur for first-order transitions very close to critical points.     

不同温度下团簇生长的Monte Carlo模拟

引入基底表面束缚能、最近邻粒子间的耦合能以及应力场,对粒子扩散势垒进行修正,采用Monte Carlo方法对不同温度下薄膜生长过程进行模拟研究.结果表明,当400 K≤T ≤ 480 K,所得团簇的平均分支宽度基本保持不变,其值近似为单粒子直径.当500 K≤T ≤ 680 K,团簇分支宽度随着温度的升高而逐渐增大至约4个粒子.随着温度的继续升高,由于粒子较高的活跃性而无法凝聚形成大团簇,团簇包含粒子数的平均值小于2.还研究了不同温度下团簇在生长过程中的形貌演化过程以及团簇数变化规律.     

Monte Carlo study of three-dimensional QCD at finite temperature

Three-dimensional QCD at finite temperature is analyzed using Monte Carlo calculations. It is shown that confinement at low temperature is lost through a second-order phase transition. At high temperature, static quarks are liberated and screened and it is argued that timelike (A₀) gluons are liberated. Just above the critical temperature electric correlation functions seem to be dominated by a resonance of two timelike gluons, whose existence is suggested by perturbation theory. The influence of an external magnetic field close to the critical point is considered.