高压下Ni_3Al热力学性质的第一性原理研究北大核心CSCD

运用第一性原理方法结合准谐Debye-Grüneisen模型研究了高压下Ni3Al的热力学性质,拟合了Ni3Al的状态方程,计算了不同压强下Ni3Al的弹性模量及吉布斯自由能等热力学性质随温度的变化关系.计算结果表明:采用七阶Birch-Murnaghan方程拟合的晶格常数与实验测量结果吻合较好;零压下弹性模量、吉布斯自由能、焓、熵、热容和体膨胀系数随温度的变化与实验值符合较好;在特定压强下,Ni3Al的弹性模量和吉布斯自由能随温度升高而减小,焓、熵随温度升高而增加;预测的德拜温度约为500K,与实验值符合较好.     

高压下Ni3Al热力学性质的第一性原理研究

运用第一性原理方法结合准谐Debye-Grüneisen模型研究了高压下Ni3Al的热力学性质,拟合了Ni3Al的状态方程,计算了不同压强下Ni3Al的弹性模量及吉布斯自由能等热力学性质随温度的变化关系. 计算结果表明：采用七阶Birch-Murnaghan方程拟合的晶格常数与实验测量结果吻合较好;零压下弹性模量、吉布斯自由能、焓、熵、热容和体膨胀系数随温度的变化与实验值符合较好;在特定压强下,Ni3Al的弹性模量和吉布斯自由能随温度升高而减小,焓、熵随温度升高而增加;预测的德拜温度约为500K,与实验值符合较好.     

第一性原理研究Ni_3Al_(1-x)V_x(x=0-0.4)的力学和热力学性质

采用第一性原理方法研究了Ni_3Al_(1-x)V_x(x=0-0.4)的力学性质,发现当V含量为0.1时,Ni_3Al_(1-x)V_x的块体模量、剪切模量、杨氏模量和硬度都出现极大值,因此V掺杂对于Ni_3Al力学性能的提升具有重要作用.另外,还研究了不同压强下Ni_3Al_(0.9)V_(0.1)的吉布斯自由能、焓、熵、热容等热力学性质随温度的变化关系,结果表明:在高温高压条件下,Ni_3Al_(0.9)V_(0.1)的吉布斯自由能、焓、熵、定压热容都出现明显变化.通过计算Ni_3Al_(0.9)V_(0.1)的体膨胀系数,发现压强对于Ni_3Al_(0.9)V_(0.1)的体膨胀效应具有明显的抑制作用.     

环面黑洞的热力学函数

本文把宇宙学常数看成与压强相当的动力学变量,研究了环面黑洞的热力学函数.计算得到环面黑洞的状态方程,环面黑洞的Smarr关系.然后通过计算其欧氏作用量得到了吉布斯函数,并进一步求得环面黑洞的自由能、内能和热力学焓,以及环面黑洞的定压热容和定容热容.结果表明:环面黑洞没有范德瓦耳斯型的相变.环面黑洞的定压热容大于零,定容热容等于零,故是一个稳定的热力学系统.     

高锰酸钾测定痕量亚硝酸根的热动力学微量热法研究

用微热量计对高锰酸钾测定痕量亚硝酸根在水中的液液反应进行了热动力学研究。通过实验和计算得出该反应的热力学参数(活化焓、活化熵及活化自由能)、速率常数和动力学参数(活化能、指前因子及反应级数)。结合实验数据讨论了反应的条件。     

Berthelot流体的热力学性质和参数解

研究了Berthelot流体的热力学性质.导出了单原子Berthelot流体Helmholtz自由能、熵、吉布斯函数、内能和焓;求得了Berthelot流体两相共存的的参数解,并用参数解讨论了Berthelot流体的相图和热力学量在临界点的行为及其相关性质.本文的研究为符合Berthelot流体的物质提供了热力学及其相变的解析理论.     

四方、单斜和正交Ge3N4的结构、电子结构和热力学性质

数值计算了四方、单斜和正交结构Ge₃N₄的点阵常数、晶胞体积、弹性模量、维氏硬度和态密度.计算结果与已有的实验数据和理论值符合得很好.形成焓为负、晶格形变和晶胞体积随压强呈线性变化,表明三种相在0~20 GPa压强范围内可以保持结构稳定.态密度研究表明三种氮化锗内部存在强烈的s-p杂化.三种相都属于脆性半导体材料,具备各向异性且硬度适中.采用包含原子振动和非谐效应的准谐波近似方案,研究材料的热力学性质,发现压强对赫姆霍兹自由能和内能有显著影响.结果为进一步理解氮化锗三种新结构的电子结构和热力学性质提供初步的物理图像.     

均匀物质热力学关系记忆法

均匀物质的热力学关系是研究其热力学性质的基本方程.但是这些用全微分和偏微商表示的关系形式相近,极易错乱.为了准确记忆,曾提出过不少办法[1],现经加工提炼,介绍如下. 一、热力学函数和“魔句” “Good Physicists Have Studied UnderVery Fine Teachers.”(杰出的物理学家都受到过极为优秀教师的教诲.)按照精心设计的这一句英语的词首字母,把八个热力学函数排列成G(古布斯函数),P(压强),H(焓), S(熵), U(内能), V(体积), F(自由能),T(温度),并用方框从顶角开始顺时针安置如图1.这是记忆法的基础. 二、全微分公式记忆法 图一顶角…     

四方、单斜和正交Ge_3N_4的结构、电子结构和热力学性质（英文）

数值计算了四方、单斜和正交结构Ge_3N_4的点阵常数、晶胞体积、弹性模量、维氏硬度和态密度.计算结果与已有的实验数据和理论值符合得很好.形成焓为负、晶格形变和晶胞体积随压强呈线性变化,表明三种相在0~20 GPa压强范围内可以保持结构稳定.态密度研究表明三种氮化锗内部存在强烈的s-p杂化.三种相都属于脆性半导体材料,具备各向异性且硬度适中.采用包含原子振动和非谐效应的准谐波近似方案,研究材料的热力学性质,发现压强对赫姆霍兹自由能和内能有显著影响.结果为进一步理解氮化锗三种新结构的电子结构和热力学性质提供初步的物理图像.     

金属纳米晶体的界面热力学特性

根据准协德拜近似从理论上计算了金属纳米晶体的界面热力学特性,包括界面过剩能、过剩焓、过剩熵、过剩Gibbs自由能等,着重讨论了界面过剩热力学参量与界面过剩体积和温度的关系.一些实验测量结果表明,理论计算与实验结果基本相符. 关键词：     

Thermodynamic and Transport Properties of Ablated Vapors of PTFE, Alumina, Perspex, and PVC in the Temperature Range 5000-30 000 K

Values of density, specific heat, enthalpy, sonic velocity, viscosity, thermal, and electrical conductivities have been calculated for the plasmas of PTFE, alumina, Perspex, and PVC for temperatures from 5000 to 30 000 K. Equilibrium particle concentrations and degrees of ionization are calculated using the minimization of Gibbs free energy, and transport properties are calculated using the Chapman-Enskog approximations.     

Nonlocal fluid density distribution in the vicinity of the critical point

The differential equation for the component local density of a binary fluid was obtained as a result of an isoperimetric problem of the system free energy minimization under condition of particle number stability. The obtained expression can be used in the calculation of liquid's profiles as well as in the investigation of thermodynamic properties in the vicinity of the critical point. An isoperimetric problem solution for the model binary fluid of the system free energy minimization under condition of particle number stability was obtained in different cases: fluid within flat parallel layer under a gravitational field, under a gravitational field and wall potential as well as under a wall potential for another equation of state.     

On the Convergence of Kikuchi’s Natural Iteration Method

In this article we investigate on the convergence of the natural iteration method, a numerical procedure widely employed in the statistical mechanics of lattice systems, to minimize Kikuchi’s cluster variational free energies. We discuss a sufficient condition for the convergence, based on the coefficients of the cluster entropy expansion, depending on the lattice geometry. We also show that such a condition is satisfied for many lattices usually studied in applications. Finally, we consider a recently proposed class of methods for the minimization of Kikuchi functionals, showing that the natural iteration method turns out as a particular instance of that class.     

小功率等离子体射流的流特性

采用焓探针对小功率(5kW)热喷涂等离子体射流的焓、温度和速度进行了测量和计算。研究了气体成分、流量、电弧电压和电流对等离子流体的焓、温度和速度分布的影响。结果表明，对于单一氩气等离子体，当使用新喷嘴时，增大氩气流量能够使喷嘴内部电弧弧根向出口方向移动，从而增加等离子体射流的焓、温度和速度。对于Ar-N2等离子体，增加气体中氮气的含量，会提高等离子电弧电压，在同样的输入功率下，改变等离子电流和电压对等离子体的焓、温度和速度影响较小。对于Ar-N2等离子体，增加氢气含量会明显地提高等离子射流的速度和热传递。     

Surface free enthalpy in multilayer surface descriptions

The surface free enthalpy is shown to have layer contributions on the basis of the additivity of the free enthalpy function. The contribution of the topmost layer is shown to be the largest by theoretical considerations. Numerical calculations on real binary alloys show that only about 0.01–0.10% is associated with the layers under the topmost one.     

Markov entropy decomposition: a variational dual for quantum belief propagation

We present a lower bound for the free energy of a quantum many-body system at finite temperature. This lower bound is expressed as a convex optimization problem with linear constraints, and is derived using strong subadditivity of von Neumann entropy and a relaxation of the consistency condition of local density operators. The dual to this minimization problem leads to a set of quantum belief propagation equations, thus providing a firm theoretical foundation to that approach. The minimization problem is numerically tractable, and we find good agreement with quantum Monte Carlo calculations for spin-1/2 Heisenberg antiferromagnet in two dimensions. This lower bound complements other variational upper bounds. We discuss applications to Hamiltonian complexity theory and give a generalization of the structure theorem of [P. Hayden et al., Commun. Math. Phys. 246, 359 (2004).] to trees in an appendix.     

高焓膨胀管风洞性能调试试验研究

为评估新建成的高焓膨胀管风洞的设备性能,开展了风洞调试试验.通过测量激波速度、静压及Pitot压力等流场参数,结合考虑高温热化学效应的理论计算方法,对设备在常规氦气驱动模式及自由活塞驱动模式、低焓到高焓的运行状态进行了调试与分析.调试试验表明风洞最高气流速度达到11.5 km/s,最高焓值达到71.7 MJ/kg,高焓...     

Self-consistent modelling of hot plasmas within non-extensive Tsallis’ thermostatistics

A study of the effects of non-extensivity on the modelling of atomic physics in hot dense plasmas is proposed within Tsallis’ statistics. The electronic structure of the plasma is calculated through an average-atom model based on the minimization of the non-extensive free energy.     

Atomistic study on the activation enthalpies for interface mobility and boundary diffusion in an interface-controlled phase transformation

A multi-lattice kinetic Monte Carlo atomistic simulation method has been used to simulate the austenite to ferrite interface-controlled transformation in pure iron. By performing simulations with different amounts of “free volume” at the interface, quantitative relations between the activation energies for interface mobility, boundary self diffusion and bulk self diffusion were investigated. The effect of different interface orientations on the distribution of free volume over the interface, as determined by interface crystallography, and its consequences for interface mobility activation energy was also evaluated. The essential role of thermal fluctuations in free volume distribution at the interface has been shown. The activation enthalpy for boundary diffusion is shown to be larger than the interface mobility activation enthalpy.