多体关联Green函数动力学Ⅲ截断近似

从多体关联Green函数的基本动力学方程组出发,通过对多体关联Green函数作低阶截断近似,得到了通常Green函数理论中所有主要的非微扰结果.而且二体关联Green函数动力学把梯形图对应的短程关联与环形图对应的长程关联统一在同一个动力学方程组中,这是通常的Green函数理论所没有得到的新结果.     

海森伯铁磁系统的总能量

对于海森伯铁磁系统,利用多体格林函数方法,在无规相近似下,并且考虑到关联函数〈S⁺S^-〉时,得到对于任意自旋S普遍适用的总能量的表达式.对于三维和二维的情况给出了计算结果.得到的总能量的数值低于没有考虑关联函数时的数值. 关键词： 海森伯模型 铁磁系统 总能量 关联函数     

多体关联Green函数动力学Ⅰ多体关联Green函数的运动方程

从多体系统的哈密顿量及海森堡方程出发,通过引进非线性变换,完成了体系的多体Green函数的关联分离,并建立起非相对论性的多体关联Green函数的动力学方程组.这个方程组为描述多体系统提供了一种完整的、系统的非微扰计算方法.     

多体关联Green函数动力学——Ⅲ.截断近似

从多体关联Green函数的基本动力学方程组出发,通过对多体关联Green函数作低阶截断近似,得到了通常Green函数理论中所有主要的非微扰结果。而且二体关联Green函数动力学把梯形图对应的短程关联与环形图对应的长程关联统一在同一个动力学方程组中,这是通常的Green函数理论所没有得到的新结果。     

正则形式的SU(N)规范理论的约束关联动力学(Ⅲ)等时关联Green函数的运动方程与二体关联近似

把多时关联Green函数的运动方程转变成等时关联Green函数的运动方程,其中包括夸克和胶子的密度矩阵的运动方程以及顶角函数的运动方程.在二体关联截断近似下,给出运动方程、高斯定律和Ward恒等式的明显表达式.     

三体关联与次近邻两体关联下的渗流

本文用实空间重正群(RSRG)方法对二维三角格子的淬火体系,处理其在三体关联及最近邻与次近邻关联下的渗流问题。对于格点多体关联函数采用叠加近似,对于格点-空位多体关联是由几率守恒求出的。结果表明,引入三体关联或次近邻关联后,都并不改变临界现象的普适律。 关键词：     

二模非线性增光子热态的非经典特性

本文从非线性囚禁离子Jaynes-Cummings模型出发,研究了非线性参数对囚禁离子沿两个正交方向的振动模式之间的互相关函数的影响.采用理论分析和数值计算相结合的方法,分析了二维非线性增光子热态的互相关函数.结果表明,在低温下,二维非线性增光子热态呈现关联效应.随着温度的增加和非线性参数的增大,两模式之间的关联效应减弱.当温度大于时,两模式之间呈现反关联效应.     

正则形式的QED约束关联动力学(Ⅱ)等时关联格林函数的运动方程与二体关联近似

本文把多时关联格林函数的运动方程转变成等时关联格林函数的运动方程,包括电子和光子的密度矩阵的运动方程以及等时顶点的运动方程,在二体关联截断近似下,给出运动方程,高斯定律及Ward恒等式的明显表达式.     

二维电子体系的关联和多体波函数

本文利用二维电子气的集体振荡行为和静态结构因子确定了体系的多体波函数,同时在坐标空间中建立了关联函数g(R)的积分方程,从而给出了一种计算二维电子气的多体波函数、关联函数和关联能的新方法。本方法可保证对任意的r_s关联函数恒为正,避免了其他方法中在r_s较大时出现g(0)<0的不合理结果,并为研究低温下二维电子体系的特殊性质提供了一个合理基础。     

电子关联与二维晶格的不稳定性

本文从电子相互作用的屏蔽库仑势出发,构造了Wannier函数来计算二维不稳定晶格的能带及电子波函数,用相关基函数理论计算了二维非均匀体系的电子关联函数,由此研究了电子关联对二维晶格不稳定性的影响。结果表明,二维体系与一维体系不同,电子相互作用使晶格二聚化减弱。 关键词：     

Fluids of pseudo-hard bodies: the direct correlation function

A new series of computer simulations on a fluid of pseudo-hard bodies has been conducted in order to find a closed analytical expression for the direct correlation function as a function of the intermolecular distance and fluid density, in analogy with a similar expression for the fluid of hard spheres. A pseudo-hard body resulting from the extended primitive model of water has been considered. The accuracy of the expression has been tested against computer simulation results for pair correlation function and pressure of the system and turned out to be fairly high. The direct correlation function is important for the construction of weighted density functionals, and consequently any other theoretical study of the properties of inhomogeneous systems containing associating component.     

Relation between the expansions of the correlation function at the object and image planes for partially coherent illumination

By using an expansion of the correlation function of partially coherent fields, the relation between the coherent components at the object and image planes has been analyzed. Also, in order to establish a one-to-one correspondence between these coherent components at both planes, a new expansion of the correlation function of the source at the object plane has been obtained.     

载体姿态对海底混响时空相关特性的影响

讨论了载体姿态对海底混响时空相关特性的影响.考虑载体姿态对相关声呐信号发射的影响,推导理论时空相关函数,得到了时空相关特性与载体姿态之间的关系:载体在某一方向上的摇动越大,在该方向上的相关系数下降越快.将理论推导与仿真结果进行比较,发现在海底不存在大尺度起伏、表面粗糙度各向同性的情况下,二者的时空相关函数吻合得较好。实际海底通常具有大尺度起伏和各向异性的粗糙度,时空相关函数的形状不能由载体姿态和海底大尺度起伏完全确定,但海试数据证明了二者的联合影响。此外,讨论了载体姿态对载体垂向速度测量的影响。      

Effect of an external action on a pair distribution function in a steady state

An external action that reduces a two-component equilibrium thermodynamic system to a nonequilibrium steady state with scalar fluxes has been studied. A system of integrodifferential equations for pair correlation functions has been obtained. These equations coincide with the second equations of the Bogoliubov-Born-Green-Kirkwood-Yvon hierarchy, but with different effective temperatures. Thus, ordinary integrodifferential equations for a pair correlation function with effective temperatures expressed in terms of the perturbed (nonequilibrium) Maxwellian momentum distribution function can be used to calculate the structural and thermodynamic properties of such a system.     

Calculation of the viscosity of SU(2) gluodynamics with the lattice simulation

The viscosity of SU(2) gluodynamics within the simulation of the lattice quantum chromodynamics at a temperature of T/T _c = 1.2 has been calculated with the Kubo formula relating the viscosity to the spectral function of the correlation function of the energy-momentum tensor. The correlation function of the energy-momentum tensor has been calculated using the numerical simulation of the lattice SU(2) gluodynamics on supercomputers.     

Motional narrowing under diffusion of two spin sub-lattices in LiNaSO4

An expression for the dipolar correlation function characterizing the fluctuations of the Hamiltonian under uncorrelated diffusion of two cationic sub-lattices in a solid has been obtained. A corresponding formula, which can be used for fitting the two-step temperature dependencies of the NMR line width, has been deduced. We also considered the case of a distribution of correlation times and deduced a corresponding analytical fitting function. Elaborated expressions have been applied to the NMR line width analysis of LiNaSO₄ in the temperature range 295–788 K.     

Sphaleron Transition Rate in Lattice Gluodynamics

The sphaleron transition rate in gluodynamics at the temperature T /T_c = 1.24 has been calculated by lattice simulation. The calculations involve the Kubo formula, which relates the sphaleron transition rate to the correlation function of the topological charge density. The gradient flow method has been used to calculate the correlation function of the topological charge density. The Kubo formula has been inverted by the Backus–Gilbert method. The results have been compared to those obtained by other methods.     

Structure and phase transition of a two—dimensional dusty plasma

The structure and phase transition of a two-dimensional (2D) dusty plasma have been investigated in detail bymolecular dynamics simulation. Pair correlation function, static structure factor, mean square displacement, and bondangle correlation function have been calculated to characterize the structural properties. The variation of internalenergy, shear modulus, particle trajectories and structural properties with temperature has been monitored to studythe phase transition of the 2D dusty plasma system. The simulation results are in favour of a two-step continuoustransition for this kind of plasma.     

Quantum statistical properties of photon-added spin coherent states

The photon-added spin coherent state as a new kind of coherent state has been defined by iterated actions of the proper raising operator on the ordinary spin coherent state. In this paper, the quantum statistical properties of photon-added spin coherent states such as photon number distribution, second-order correlation function and Wigner function are studied. It is found that the Wigner function shows the negativity in some regions and the second-order correlation function is less than unity. Therefore, the photon-added spin coherent state is a nonclassical state.     

On the acoustic wave attenuation in a turbulent medium

The equation for the mean acoustic field has been obtained for a random turbulent medium using the Green function approach. The correlation function was described by the Karman distribution with the index n=2 approximately≃11/6. Applying Bourret's approximation, the exact expression for the mass operator has been calculated analytically. The frequency dependence of the scattering coefficient of the mean field has been derived. Conditions of Cherenkov radiation are discussed.