A PHASE TRANSITION MODEL WITH PERPETUAL ORDER

A simple model is given to show there exists a kind of phase transition for which the order parameter never vanishes; its characteristic is the second derivative of the order parameter rather than the order parameter itself, and its critical behavior satisfies the scaling.     

混合自旋模型的动力学相变

考察了混合自旋模型的两种组态按Metropolis动力学随时间的演化,并分析了其在平方格子上的Darnage。计算结果表明存在有一高温相和一低温相,与平衡相变符合。     

STUDY ON ONE-DIMENSIONAL CI PHASE TRANSITION WITH TRIPLE-WELL INTERACTIONS

To study modulated structures and commensurate-incommensurate (CI) transitions, we generalize the Frenkel-Kontorova model to the Frenkel-Kontorova-Devonshire model where the interparticle interactions are the triple-well potential. By use of the so called effective potential method, numerical solutions of the eigenvalue problem are used to work out the exact phase diagrams of W, a triple-well potential. According to the winding number Ω and the rotation number ω, we analyze the periodicity of the phase diagram and find some complex but regular phase structures. These new structures result from the triple-well interatomic interactions. A series of new transition behaviors enrich the traditional understanding on the periodicity of CI transitions.     

非平衡相变的临界标度理论及普适性

综述了作者近年来在非平衡相变临界（ Ｎ Ｐ Ｃ） 标度理论及普适性研究的进展。主要包括一般 Ｎ Ｐ Ｃ 系统规格化模型,局域序参量的概率分布,广义势的临界渐近形式,空时有关函数及其临界奇异行为。论证了 Ｎ Ｐ Ｃ 系统的临界可标度性,导出了一组普适的 Ｎ Ｐ Ｃ 标度关系,由之计算出的４ 种 Ｎ Ｐ Ｃ 普适类的临界指数与目前已知的实验及理论结果吻合得非常好。此外,还讨论了非平衡相变临界标度理论的普适性,将平衡相变临界标度理论作为一种特殊极限情况含于同一理论体系中。     

PHASE TRANSITION FOR A NOISE-DRIVEN MODEL COUPLED BY A MEAN FIELD

We report a new model for infinite interacting noise driven subsystems which are coupled by a mean field and study its nonequilibrium phase transitions. In this model, under some circumstances the phase transition is between the state with zero mean field and the state with non zero mean field, and has a breaking of symmetry, which is similar to that reported by Van den Broeck, Parrondo, Toral, and Armcro [Phys. Rev. Lett.,73(1994),3395; Phys. Rev., E49(1994),2639], by Pikovsky, Rateitschak, and Kurths [Z.Phys.,B95(1994),541], and by other authors. We style this nonequi librium phase transition the symmetry breaking mean field. However, under other circumstances, the nonequilibrium phase transition of our model is not of the symme try breaking mean field type, which is a new phenomenon that has not been reported before.     

PHASE TRANSITION PROPERTY OF THE BOSONIZED HUBBARD MODEL

Using the bosonization method of one-dimensional fermion system, we discussed the bosonized Hamiltonian of the half-filling Hubbard model, and investigated the ground state and phase transition properties with the gaussian effective potential method of sine-Gordon field.     

过冷态超流氦浴中的二步相变传热研究

本文提出了考虑过冷态超流氦传热中的He／Hell、GHe／Hel的二步相变传热模型,该模型与实验结果符合得很好。     

A FINITE TEMPERATURE λφ4 MODEL AND DE SITTER-FRIEDMANN PHASE TRANSITION IN THE EARLY UNIVERSE

In this paper, we propose a simple finite temperature λφ⁴ cosmological model to show that a new type singularity free cosmological model could be established by taing a series of impoftant quantum and statistical effects into consideration such as spontaneoui rymetry breaking, trace anomaly and pirtide creation, symmetry restoration at hish temperature through.phase transition and others. To begin with, the state of the universe would be a cold singu1arity.free and horizon free Beltrami-Anti de Sitter one rather than a hot one. Then associated with the,particle creatipl, the temperature would, become higher and higher and as soon. as the temperature reached a critical value, T_c a second-order phase transition would take place and the universe would transfer to a hot radiation dominated Friedmann state.     

粗糙微通道内气体流动的分子动力学研究

为研究粗糙度对微通道内气体流动及其边界滑移性质的影响,采用分子动力学模拟方法研究了氩气在0.1 μm铂通道内的流动,通道表面粗糙度由三角粗糙元阵列构成。气体流动的边界条件决定于2个准则数: A/λ和Kn=λ/L(其中A为壁面粗糙度、λ为气体分子的平均自由程、L为流动系统的尺度)。Maxwell基于Kn的滑移模型当A/λ<0.25时适用;A/λ<1时,气体流动存在边界速度滑移,体现出稀薄效应,A/λ≈1时为无滑移,A/λ>1时为等效负滑移.     

DYNAMICS IN A DRIVEN DISORDERED VORTEX LATTICE: A NUMERICAL STUDY

Using a repulsive vortex-vortex interaction model, we numerically investigate the dynamics of vortices in a driven disordered two-dimensional superconductor. At low driving forces and temperatures, we have seen the evidence of plastic and filamentary flow. At high driving forces and very low temperatures, the evidence of an ordering of the moving vortices is seen in the flux flow regime. Our results are in agreement with the previous simulation results and recent experiments.     

La1．48Nd0．4Sr0．12CuO4的结构相变研究

用高分辨电镜观察了室温下La1．48Nd0．4Sr0．12CuO4和La1.88Sr0.12CuO4样品的原子结构像，观察到了其中的La2O2层和CuO2层沿c轴方向交叉堆砌．这两个样品的微结构非常相似，说明Nd掺杂没有造成周期性的调制结构．用变温X射线研究了La1．48Nd0．4Sr0．12CuO4样品中低温正交（LTO）到低温四方（LTT）结构相变，给出了晶格常数随温度的演化过程．     

La1.48Nd0.4Sr0.12CuO4的结构相变研究

用高分辨电镜观察了室温下La1.48Nd0.4Sr0.12CuO4和La1.88Sr0.12CuO4样品的原子结构像,观察到了其中的La2O2层和CuO2层沿c轴方向交叉堆砌.这两个样品的微结构非常相似,说明Nd掺杂没有造成周期性的调制结构.用变温X射线研究了La1.48Nd0.4Sr0.12CuO4样品中低温正交(LTO)到低温四方(LTT)结构相变,给出了晶格常数随温度的演化过程.     

相分离液体在玻璃转变过程中的动力学性质

近年来,相分离动力学一直受到大家的关注,人们从技术和理论角度进行了研究.一个二元系统从混溶温度开始进行快速冷却,这个过程驱使两个相的形成和生长.这种自发生长过程遵从幂规律R(t)∝t~n,R(t)是在t时刻的相分离域尺寸大小,增长指数n是一个重要的量,有效的反映了相分离域的增长机制.但是对于相分离液体的玻璃转变过程的研究相对较少.本文采用分子动力学(MD)模拟方法,提出了一个新的模型——相分离液体来研究玻璃转变过程.相分离在玻璃转变过程中,过冷液体分离为两个相.我们主要研究了体系的动力学不均匀性.发现两个相的动力学性质是不均匀的,两个相的玻璃转变温度是不一样的.分析得出,相分离液体在玻璃转变过程中存在着一个动力学奇异点.说明相分离可能是引起玻璃转变系统动力学奇异性的一个原因.     

双球近似和速度空间的非平衡相变

本文在双球近似下,用边界层近似解法求解了磁化等离子体中的反应——扩散方程。结果表明,由扩散项的非线性正反馈同样能导致非平衡相变,而且环流器中的磁面可以不是等电位面。     

过冷熔体中枝晶生长的相场模拟

本文利用相场方法对过冷镍熔体中枝晶生长过程进行了模拟,发现在过冷度低于 200 K时,生长速度与过冷度之间近似呈幂函数关系,当过冷度高于 200 K时,生长速度与过冷度之间基本呈线性关系。伴随着速度/过冷度之间关系的变化,枝晶尖端半径/过冷度的关系则呈现先减小后增加的趋势,并在 200 K时达到最小。本文还将模拟结果与实验值和经典LKT理论进行了比较,对上述关系转变的物理机制进行了分析。     

玻色弦耦合的两维引力模型的数值研究

给出了Riemann-Cartan空间上玻色弦耦合两维引力模型的运动方程,应用数值积分方法得到其数值解,并给出相应的运动曲线图。     

磁场对水系统内能影响的MC计算机模拟方法研究

用Monte-Carlo计算机模拟方法,通过对一个含有64个水分子的三维体系在磁场作用时内能变化的计算,定量评估了磁场强度及温度对磁处理效应的影响。研究发现:水的内能与外加磁场强度的关系曲线是一条多极值曲线;水-水径向分布函数伴峰的高度与磁感应强度也具有多极值特征;计算机模拟结果与实验结果基本一致,计算机模拟确实是从分子水平研究磁处理机理的有效方法。     

一种新的k方程转捩湍流模型

本文在分析了针对充分发展湍流模型建立的k方程湍流模型模拟转捩流动的能力之后，构筑了一种新的Fμ函数及相应的k方程湍流模型．将该模型应用于数值求解NS方程，模拟了中等来流湍流度下零压力梯度平板捩报流动，并将部分计算结果与实验结果及经验关系进行了比较．     

La0.95K0.05MnO3的低频内耗研究

本文研究了样品La0.95K0.05MnO3的内耗、直流电阻、交流磁化率.发现在20～275K的温度范围内,在0.3T的磁场下有明显的磁阻(MR)效应,温度为259K时MR效应达到极大值26%.在直流电阻测量中发现267K时出现很尖锐的电阻峰;在220K附近出现"肩峰".内耗温度曲线在210K～250K的温度范围有一个很宽的内耗峰;在268K有一个很明显的内耗蜂同时伴随着模量软化,并且由Kissinger关系求出顺磁-铁磁转变的表观激活能Eap=0.53eV(请说明通过什么公式求出什么东西的活化能).     

Ag/Si（111）超薄膜光学二次谐波强度变化与结构相变研究

在130-830K温度范围内,系统研究了Si（111）-√3×√3-Ag和Si（111）-3×1-Ag超薄膜重构表面的光学二次谐波的温度依赖性,分析了信号强度的变化和表面结构之间的关联.结果表明,对于Si（111）-3×3-Ag结构薄膜表面而言,在130K到320 K的温度范围内,表面光学二次谐波信号强度的变化中没有出...