稀释晶场对纳米管上Blume-Capel模型磁化性质的研究

利用有效场理论研究了纳米管上稀释晶场中Blume-Capel模型格点的磁化强度、内能、比热和自由能,得到了系统格点的磁化强度、内能、比热和自由能与温度和稀释晶场的关系.结果表明:稀释晶场取值概率和晶场强度等诸多因素相互竞争,使系统表现出比含恒定晶场作用的Blume-Capel模型更为丰富的磁学特性;稀释晶场会抑制系统格点的磁化强度,导致其基态饱和值小于1;温度较低时,系统格点的磁化强度表现出复杂性;晶场较强时,系统的内能、比热和自由能也呈现出不同的磁学性质.     

用独立元格等效作用量研究三维U(1)格点规范理论的相结构

在格点规范理论中,应用变分累积展开方法,引入独立元格等效作用量,研究了三维U(1)格点规范理论的元格内能,得到连续的内能曲线,与Monte Carlo(MC)数据相符,表明理论是禁闭的.     

SU(3)格点规范理论两种新作用量的Monte Carlo研究

我们对SU(3)格点规范理论的两种新作用量进行了Monte Carlo模拟, 计算了元格平均内能和比热. 内能曲线都趋向共同的弱耦合极限, 比热都有峰. 我们观察到了由于格点间隔α的高次幂项不同引起的比热峰明显漂移的现象.     

外磁场对纳米管上Blume-Capel模型磁热性能的研究

利用有效场理论研究了纳米管上外磁场中Blume-Capel模型格点的磁化强度、磁化率、内能、比热和自由能,得到了系统格点的磁化强度、磁化率、内能、比热和自由能与外磁场和晶场的关系.结果表明:外磁场强度、交换相互作用和晶场强度等诸多因素相互竞争,使系统表现出比没有外磁场作用的Blume-Capel模型更为丰富的磁学特性;外磁场能够增大系统格点的磁化强度,导致系统的二级相变消失;负晶场作用系统时,系统会发生一级相变;晶场强度、外磁场强度不同时,系统的磁化率、内能、比热和自由能也呈现出复杂性.     

精确到累积展开三级贡献的U_1及SU_2平均元格内能的解析结果

我们在格点规范理论中应用累积展开的方法,在4维和5维时空解析地计算了精确到累积展开三级贡献的U_1和SU_2群元格平均内能,计算结果和MonteCarlo数据自洽。本文并对在格点规范理论中使用累积展开方法作了讨论。     

最近邻原子间交换相互作用对纳米管上Blume-Capel模型磁热性质的影响

利用有效场理论研究了纳米管上最近邻原子间交换相互作用对Blume-Capel模型格点的磁化强度、内能、比热和自由能的影响,得到了系统格点的磁化强度、内能、比热和自由能与交换相互作用和晶场强度的关系.结果表明:最近邻交换相互作用和晶场强度等诸多因素相互竞争,使系统表现出丰富的磁学特性;正晶场对系统磁化强度具有促进作用;负晶场对系统磁化强度具有抑制作用;负晶场作用下,系统发生一级相变;晶场强度参数和交换相互作用不同时,系统的内能、比热和自由能也呈现出奇异性.     

SU(2)格点规范理论一种新作用量的弦张力的Monte Carlo计算

在10⁴格点上我们对作用量为S_p=sin1-sin(1/2)TrU_p的SU(2)格点规范系统进行了Monte Carlo模拟,计算了弦张力σ和标度常数Δ₀²之比。计算还表明,元格的平均内能和比热峰对于格点体积的变化来说是稳定的。 关键词：     

精确到累积展开三级贡献的U1及SU2平均元格内能的解析结果

我们在格点规范理论中应用累积展开的方法, 在4维和5维时空解析地计算了精确到累积展开三级贡献的U₁和SU₂群元格平均内能, 计算结果和Monte Carlo数据自洽. 本文并对在格点规范理论中使用累积展开方法作了讨论.     

2维O(3)非线性σ模型的解析研究

在格点规范理论中应用变分累积展开方法,解析计算了2维O(3)非线性σ模型的内能和比热,并将计算结果和Monte Carlo数据进行了比较.     

一个基于Hlder积分不等式的格点规范场论变分方法

用Hlder积分不等式使出现在格点模型配分函数中的高重群积分退耦,并以不等式中的任意参数作为变分参数,可以求出体系元格自由能的下限。我们计算了Wilson作用量的四维Z_2,U(1)、SU(2)纯规范格点模型的内能曲线,Z_2的一级相变点在β=0.4—0.45处是非常明显的。但不能发现U(1),SU(2)、的高于一级的相变点。     

一种具有铁磁与反铁磁相互作用Ising模型的热力学性质

对最近邻自旋间具有反铁磁相互作用Ｊ_s，相隔偶数个自旋间又具有指数型长程铁磁相互作用Ｊ₁的一维Ｉｓｉｎｇ模型，利用积分方程的方法得出内能和比热的解析表达式。在Ｊ₁＝１，Ｊ_s分别为０．０５，０．１和０．３的条件下，作出零场时的内能和比热随温度参量变化的图形，并指出其相变临界点。在Ｊ₁＝１，Ｊ_s＝０．１的条件下，作出外磁场变化对内能和比热的影响图。鉴于系统在低温、零场或弱场以及较弱 关键词：     

Accurate Expansions of Internal Energy and Specific Heat of Critical Two-Dimensional Ising Model with Free Boundaries

The bond-propagation algorithm for the specific heat of the two dimensional Ising model is developed and that for the internal energy is completed. Using these algorithms, we study the critical internal energy and specific heat of the model on the square lattice and triangular lattice with free boundaries. Comparing with previous works (Phys Rev E 86:041149, 2012; Phys Rev E 87:022124, 2013), we reach much higher accuracy ( $10^{-28}$ ) of the internal energy and specific heat, compared to the accuracy $10^{-11}$ of the internal energy and $10^{-9}$ of the specific heat reached in the previous works. This leads to much more accurate estimations of the edge and corner terms. The exact values of all edge and corner terms are therefore conjectured. The accurate forms of finite-size scaling for the internal energy and specific heat are determined for the rectangle-shaped square lattice with various aspect ratios and various shaped triangular lattice. For the rectangle-shaped square and triangular lattices and the triangle-shaped triangular lattice, there is no logarithmic correction terms of order higher than $1/S$ , with $S$ the area of the system. For the triangular lattice in rhombus, trapezoid and hexagonal shapes, there exist logarithmic correction terms of order higher than $1/S$ for the internal energy, and logarithmic correction terms of all orders for the specific heat.     

用格子Boltzmann模型模拟可压缩完全气体流动

采用一种新的格子Boltzmann模型模拟超音速流动。在这种模型中,粒子的速度不受限制,可以取得很广。而平衡分布函数的支集却相对集中,使模型得以简化。粒子速度的这种自适应特性允许流体以较高的马赫数流动。通过引入粒子的势能使得该模型适用于具有任意比热比的完全气体。利用Chapman-Enskog方法,从BGK型Boltzmann方程推导出Navier-Stokes方程。在六边形网格上模拟了马赫数为3的前台阶绕流,得到了合理的结果。     

Lattice dynamical properties of ScB2, TiB2, and V B2 compounds

We have investigated the structural and lattice dynamical properties of XB₂(X=Sc,V,Ti) by using first-principles total energy calculations. Specifically, the lattice parameters (a, c) of the stable phase, the bond lengths of X–B and B–B atoms, phonon dispersion curves and the corresponding density of states, and some thermodynamical quantities such as internal energy, entropy, heat capacity, and their temperature-dependent behaviours, are presented. The obtained results for structural parameters are in good agreement with the available experimental and other theoretical studies.     

Universal scaling in BCS superconductivity in three dimensions in non-s waves

The solutions of a renormalized BCS equation are studied in three space dimensions in s, p and d waves for finite-range separable potentials in the weak to medium coupling region. In the weak-coupling limit, the present BCS model yields a small coherence length and a large critical temperature, , appropriate for some high- materials. The BCS gap, , and specific heat as a function of zero-temperature condensation energy are found to exhibit potential-independent universal scalings. The entropy, specific heat, spin susceptibility and penetration depth as a function of temperature exhibit universal scaling below in p and d waves. Received: 18 July 1997 / Revised: 8 September 1997 / Accepted: 29 September 1997     

金刚石膜的厚度及背表面过渡层对热导率的影响

 采用微波等离子体化学气相沉积（MWPCVD）方法制备金刚石膜，研究了金刚石膜的厚度以及生长初期的SiC过渡层对其热导率的影响，给出了膜厚和背表面SiC过渡层减薄厚度与金刚石膜热导率的关系。     

Phase diagram of the one-state potts model on the Cayley tree

The phase diagram of the one-state Potts model on the closed asymmetric Cayley tree with branching ratior=2 is obtained from the Bethe-Peierls map. The route to chaos, via the period doubling cascade, is obtained by considering the antiferromagnetic coupling limit. The connection of the Potts model with the percolation problem is shown by calculating the order parameter, its susceptibility, the internal energy, and the specific heat as well as their asymptotic behavior at the paramagnetic-ferromagnetic critical point. Due to the type of the lattice and to the polynomial character of the map, this is the simplest known example of a McKay-Berker-Kirkpatrick spin-glass.     

Thermodynamical Properties of Spin-3/2 Ising Model in a Longitudinal Random Field with Crystal Field

A theoretical study of a spin-3/2 Ising model in a longitudinal random field with crystal field is studied by using of the effective-field theory with correlations. The phase diagrams and the behavior of the tricritical point are investigated numerically for the honeycomb lattice when the random field is bimodal. In particular, the specific heat and the internal energy are examined in detail for the system with a crystal-field constant in the critical region where the ground-state configuration may change from the spin-3/2 state to the spin-1/2 state. We find many interesting phenomena in the system.