Structural properties of liquidN,N-dimethylformamide

Monte-Carlo simulation of liquidN,N-dimethylformamide was performed. The influence or electrostatic and van der Waals interactions on regularities of the mutual molecular arrangement was investigated. The spatial structure of liquid DMF is determined by the type of molecular packing and steric factors and is close to a random closely packed system of soft spheres. The electrostatic interactions only affect the mutual orientation of the molecular Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 21–27, January, 1998.     

Analytic and numerical evidence from quantum field theory for the hyperscaling relation dv = 2Δ−γ in the d=3 ising model

The hyperscaling relationdv = 2 - (d=3) for the Ising model has been shown to follow from a constructive approach proposed by one of the authors (R.S.) of a relativistic theory of self-interacting Bosons in d space-time dimensions. We present evidence that the two assumptions made in this approach are valid: On a finite Euclidean (hyper-) cubical lattice in d dimensions the renormalization map from the bare to the renormalized parameters should have nonvanishing Jacobian everywhere. We show this analytically and numerically on the boundary set of the parameters. The numerical analysis involves Monte Carlo calculations in the region where the bare coupling constantg ₀ is infinite, giving the Ising model. The linear sizen of the lattice (with periodic boundary conditions) was taken to be 5, 6, and 10. There we also checked the second assumption saying that the correlation length for the Ising model is a monotonic function of the temperature. We also comment on the possible numbers of zeros of the Callan-Symanzik function of this theory.     

Studying a kind of portable ultra-bright microfocus x-raysource

This paper studies the properties of a kind of portable ultra-bright microfocus x-ray source with the Monte-Carlo method in detail. The new x-ray source consists of an electron-emission system, an electrostatic focusing system and a metal target. A crystal Lanthanum Hexaboride cathode, a Wehnelt grid and an extracted electrode compose the triode electrode electron-gun system. Two equal radius cylinder electrodes form the focusing system. The key factors determining the focus properties of the electron beam such as the ratio D_w/H, grid bias V_g, and the properties of the extracted electrode are numerically studied. The calculated results reveal that when D_w/H, V_g, the length of the extracted electrode, and the distance between the grid and the extracted electrode equals 5, --0.6~kV, 10~mm, and 8~mm respectively, the electron beam focal spot can be concentrated down to 9~μm in radius and a reasonable focal length about 72.5~mm can be achieved, at the same time, the cathode emission currents can be as high as 30~mA.     

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。     

The development of a high-power bremsstrahlung radiator for the production of monochromatic X-rays

An experimental set-up for the production of monochromatic X-ray beams tuneable in the energy region between 40 and 700 keV was built at our facility. This paper describes the design of a bremsstrahlung radiator to create a suitable photon field for monochromatisation by Laue diffraction on a curved single-crystal.     

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.     

An Ergodic Sampling Scheme for Constrained Hamiltonian Systems with Applications to Molecular Dynamics

This article addresses the problem of computing the Gibbs distribution of a Hamiltonian system that is subject to holonomic constraints. In doing so, we extend recent ideas of Cancès et al. (M2AN 41(2), 351–389, 2007) who could prove a Law of Large Numbers for unconstrained molecular systems with a separable Hamiltonian employing a discrete version of Hamilton’s principle. Studying ergodicity for constrained Hamiltonian systems, we specifically focus on the numerical discretization error: even if the continuous system is perfectly ergodic this property is typically not preserved by the numerical discretization. The discretization error is taken care of by means of a hybrid Monte-Carlo algorithm that allows for sampling bias-free expectation values with respect to the Gibbs measure independently of the (stable) step-size. We give a demonstration of the sampling algorithm by calculating the free energy profile of a small peptide.     

Research of diffusing plates for LCD backlights

With requests for large backlight more and more strictly, direct backlights will be used popularly for large backlight. A diffuser is necessarily in need for a backlight, so the relation between diffusing plates and luminance uniformity of backlights and the relation between diffusing plates and color uniformity of backlights are studied on the basis of Mie scattering theory and Monte-Carlo simulation. And the effect on energy by diffusing plates will be researched.     

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.     

激光加速电子束放射照相的模拟研究

激光加速产生高能量电子束具有源尺寸小、准单能、脉宽窄等特征.通过蒙特卡罗程序模拟研究了高能电子束的放射照相.模拟了200 MeV准直电子束照射台阶靶、厚铁靶,11 MeV点源电子束照射惯性约束聚变模型靶,以及70 MeV点源电子束在激光等离子体磁场下的偏转.结果表明激光加速电子束在探伤厚材料内部、确认薄材料界面、测量电磁场等诊断中具有高时空分辨、灵敏等能力.