原子核形变中的动力学效应I.172Os核高自旋态的形变

利用我们最近提出的Hill-Wheeler方程的一种数值解法,考虑动力学效应计算了¹⁷²Os核转晕态的形状随转动频率的变化.所得结果比通常的总罗斯量面(TRS)计算的形变值更符合于实验测量值.这表明,至少对于像¹⁷²Os这样的过渡核,核形变的动力学效应是不能忽略的.     

环形Josephson结中圆对称孤子解的微扰分析

本文用微扰方法,研究环形Josephson结中有扰动情形下sine-Gordon方程的圆对称孤子解,得到孤子的动力学方程的解析形式。所得的I—V曲线(第一零场台阶)与数值计算结果符合得很好。 关键词：     

核力短程部分与长程部份的统一描述

采用相对论性的多体理论方法,在介子云口袋模型^[1]的基础上,统一计算了夸克间交换胶子与π介子所给出的核子间相互作用的短程与长程部份.短程部份在扣除了两个核子相对运动动能之后,得到了300MeV左右的"软"排斥心.长程部份得到与单π介子交换位势(OPEP)相同的解析形式,基强度由介子云口袋模型的参数决定.如果取f=93MeV,其强度大约比OPEP低30%.     

锰酸钇薄膜中Mn3+离子d-d跃迁的超快光谱学研究

本文利用时间分辨光谱技术,系统研究了飞秒激光诱导YMnO₃薄膜中Mn³⁺离子3d轨道跃迁的 载流子动力学过程.当抽运光子能量为1.7 eV,对应于Mn³⁺离子的3d轨道跃迁, 抽运-探测零延迟时间处的透射率变化随着温度的降低逐渐减小. 这起源于低温下短程反铁磁有序诱导Mn³⁺离子d-d能级发生"蓝移". 载流子弛豫过程由快、慢两个过程组成,分别对应于电子-声子相互作用和自旋-声子相互作用. 实验发现,当温度低于80 K,电子-声子热化时间显著增加,表明低温下电子-声子的 耦合强度受长程反铁磁有序的影响.     

二维合金系统的有序动力学研究

采用主方程方法在对概率近似下对三元fcc结构晶体在(001)方向的一个层面的有序无序动力学过程进行了研究.计算了长程序参量(LRO)和短程序参量(SRO)随时间的演化过程.在系统从完全无序态弛豫到平衡态的过程中存在各种瞬态有序相.瞬态相有着不同的特点,如序参量(LRO,SRO)瞬态相曲线形状不同等.产生它们的原因有不同的原子特征迁移时间、原子间最近邻和次近邻相互作用差异、短程相关性和长程相关性的差异对弛豫过程的影响. 关键词： 对概率近似 瞬态有序相 长程序参量(LRO) 长程相关性     

煤的热天平燃烧反应动力学特性的研究

采用热天平获得同一种煤在不同升温速率下的TG、DTG曲线,可求出燃烧速率、燃烧温度随燃烬度的变化曲线,根据两个不同升温速率下的数据,可计算出化学动力学参数活化能和指前因子随燃烬度的变化曲线。根据实验数据计算得到四个煤种的反应动力学参数随燃烬度变化的曲线,并预测其中一种煤在第三个升温速率下的燃烧速率随燃烬度的变化曲线,计算结果与实验结果符合较好。用此模型预测了在不同的恒定温度下试验煤种的煤粉燃烧速率随燃烬度的变化趋势。     

基于最新势能面的C(1D)+H2反应的环聚合分子动力学研究

本文利用环聚合分子动力学方法对C(¹D)+H₂反应开展了详细的理论研究. 计算中使用了最近构建的Zhang-Ma-Bian(ZMB)从头算势能面,该势能面对锥形交叉附近区域以及范德华区域均有精确的描述. 环聚合分子动力学计算得到的热反应速率常数与最新实验值吻合很好. 与前人计算结果比较,发现在?¹A′电子基态的ZMB-a势能面上获得的反应速率常数远大于前人构建的RKHS势能面上的结果,这是由于ZMB势能面上的范德华鞍具有与之前势能面上的范德华阱完全不同的动态学作用,表明环聚合分子动力学方法能够处理范德华作用引起的势能面拓扑结构所导致的动态学效应. 本文还揭示了b¹A′′电子激发态ZMB-b势能面以及量子效应对反应的重要性.     

钍基碳化物ThC的高压结构稳定性研究

钍基碳化物ThC是重要的核材料,基于第一性原理计算,我们研究了ThC的结构稳定性及相变.声子色散曲线表明基态结构的晶格能够稳定到42 GPa附近,当压力继续升高时虚频的出现表明了动力学的不稳定.经比较基态Fm-3m及高压相Pnma结构的自由能,发现零温下,相变压力为22.4 GPa,符合声子色散曲线的结果,同时预测了两种结构的相变边界.     

锗红外干涉仪

本文叙述了一个锗制的红外干涉仪,它可供在2—11微米的红外区域内测定有机液体色散曲线之用。用此干涉仪测量了液体苯及氯仿在2—6微米区域内的色散曲线,所得结果与前人数据相比,符合良好。     

关于Pb208附近原子核的能谱(Ⅰ)——Pb205和Pb204

利用独立粒子模型的观点、用分波的方法,将两体相互作用当作微扰来处理。并且认为在计算能谱中,三体以上核子之间的相互关连不重要,对Pb²⁰⁵及Pb²⁰⁴两个原子核的能级进行了计算。所得结果与实验符合得很好。     

Ordering mechanisms in epitaxial SiGe nanoislands

We investigate and elucidate the surprising observation of atomically ordered domains in dome-shaped SiGe nanoislands. We show, through atomistic Monte Carlo simulations, that this ordering is a surface-related phenomenon, and that is driven by surface equilibrium rather than by surface kinetics. The ordering depends on facet orientation. The main source of ordering is the {15 3 23} facet, while the {105} and {113} facets contribute less. Subsurface ordered configurations self-organize under this facet and are frozen-in and buried during island growth, giving rise to the ordered domains. Ordering mechanisms based on constrained surface kinetics, requiring step-mediated segregation at the island facets, are shown to be much less likely.     

First-principles thermodynamics of coherent interfaces in samarium-doped ceria nanoscale superlattices

Nanoscale superlattices of samarium-doped ceria layers with varying doping levels have been recently proposed as a novel fuel cell electrolyte. We calculate the equilibrium composition profile across the coherent {100} interfaces present in this system using lattice-gas Monte Carlo simulations with long-range interactions determined from electrostatics and short-range interactions obtained from ab initio calculations. These simulations reveal the formation of a diffuse, nonmonotonic, and surprisingly wide (11 nm at 400 K) interface composition profile, despite the absence of space charge regions.     

Magnetism and giant magnetocaloric effect in rare-earth-based compounds R_3BWO_9(R = Gd,Dy, Ho)

The magnetism and magnetocaloric effect(MCE) of rare-earth-based tungstate compounds R_3 BWO_9(R=Gd,Dy,Ho) have been studied by magnetic susceptibility,isothermal magnetization,and specific heat measurements.No obvious long-range magnetic ordering can be found down to 2 K.The Curie-Weiss fitting and magnetic susceptibilities under different applied fields reveal the existence of weak short-range antiferromagnetic couplings at low temperature in these systems.The calculations of isothermal magnetization exhibit a giant MCE with the maximum changes of magnetic entropy being 54.80 J/kg-K at 2 K for Gd_3 BWO_9,28.5 J/kg-K at 6 K for Dy_3 BWO_9,and 29.76 J/kg-K at 4 K for Ho_3 BWO_9,respectively,under a field change of 0-7 T.Especially for Gd_3 BWO_9,the maximum value of magnetic entropy change(-ΔS_M~(max)) and adiabatic temperature change(-ΔT_(ad)~(max)) are 36.75 J/kg·K and 5.56 K for a low field change of 0-3 T,indicating a promising application for low temperature magnetic refrigeration.     

Modelling in relation to cation ordering

We review the methodology of using computer models to obtain quantitative information about cation ordering. Empirical interatomic potentials or ab initio electronic structure calculations are used to generate the energies for many configurations containing disordered arrangements of cations, and the parameters in model Hamiltonians can be determined from these energies. Monte Carlo simulations are then used to generate ensemble averages as functions of temperature or chemical composition. Analysis of the Monte Carlo ensembles directly yields the temperature dependence of long-range and short-range order, and thermodynamic quantities such as energy and heat capacity. Use of thermodynamic integration allows for the calculation of entropy and free energy. The methods are illustrated by examples showing long-range order/disorder phase transitions (feldspars), short-range order in solid solutions (pyrope-grossular), and non-convergent ordering (magnesium aluminate spinel); where comparisons with experimental data are possible, the model calculations are seen to give results that are reasonably accurate. The example in which ab initio electronic structure calculations are used show that it is now possible to extract accurate thermodynamic data for ordering processes using models that require no prior experimental data.     

Vortex mass in a superfluid at low frequencies

An inertial mass of a vortex can be calculated by driving it around in a circle with a steadily revolving pinning potential. We show that in the low-frequency limit this gives precisely the same formula that was used by Baym and Chandler, but find that the result is not unique and depends on the force field used to cause the acceleration. We apply this method to the Gross-Pitaevskii model, and derive a simple formula for the vortex mass. We study both the long-range and short-range properties of the solution. We agree with earlier results that the nonzero compressibility leads to a divergent mass. From the short-range behavior of the solution we find that the mass is sensitive to the form of the pinning potential, and diverges logarithmically when the radius of this potential tends to zero.     

淬入空位在AuCu有序化过程中的作用

本文通过电阻测量研究了淬火和退火温度对AuCu合金有序化过程的影响,结果表明:1.AuCu合金的有序化过程可分为两个阶段:1)局部有序或有序相成核阶段,电阻上升;2)有序相(或畴)长大阶段,电阻下降。2.淬火后低温退火时,AuCu有序化主要是通过过饱和的淬入空位在金属中的移动而实现的。有序化的速度正比于淬入空位的浓度和移动率。3.通过有序化速度随淬火温度和退火温度的变化,测得AuCu中空位的形成能E_f和移动激活能E_m相应为0.95eV和0.81eV。4.在等温退     

Analysis of the results of investigation of the kinetics of ordering in alloys of different systems by the methods of formal chemical kinetics

Several different alloy systems are used as examples to show that the experimental dependences of the degree of long-range order on the time of isothermal annealing can be approximated by the equations of formal chemical kinetics. It was found that there are functions-linear for actual processes-which can conditionally be used as a criterion of the accuracy of models of processes. The results obtained regarding the kinetics of the alloy Ni₂Cr are compared with calculations based on an ordering model in terms of the theory of absolute reaction rates.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 55–60, June, 1988.     

Nuclear Short range correlations in finite nuclei

The short-range correlations between nucleons in finite nuclei are investigated in the framework of Glauber multiple scattering theory without any free parameters. The effects on proton-nucleus and nucleus - nucleus interactions such as p - {4}He$ and {4}He- {12}C elastic scattering, and in particular the proton elastic scattering off hallo-like nuclei, {6,8}He, are estimated. Our calculations show that the short-range correlations play an important role in reproducing experimental data and could be also thought of as being the origin and nature of halo-like phenomena in the nuclear structure. More accurate calculations along this line are needed.     

Internal energy and parameters of the order-disorder phase transition in titanium monoxide TiO y

Quantum-mechanical ab initio calculations are used to simulate the free energy functions for titanium monoxide TiO _y . The effect of the long-range order of the Ti₅O₅ type superstructure on the internal energy of the compound is studied by the supercell method. The dependences of the configuration entropy and free energy on the long-range order parameter are determined. It is found that the order-disorder phase transition in titanium monoxide must occur in accordance with the mechanism of the first-order phase transition with a critical value of the long-range order parameter of 0.971. The calculated parameters of the phase transition are compared with the experimental data and the results obtained using the model of point charges and by calculating the Madelung energy. It is concluded that the short-range order and the phonon entropy must be taken into account in calculating the equilibrium phase diagrams for strongly nonstoichiometric compounds.