杠杆平衡条件探究仪

杠杆平衡条件探究仪采用了互变杠杆,既可以探究直杠杆的平衡条件,又可以探究曲杠杆的平衡条件,较易得出较为普遍的结论.该仪器设计了限位器,保证了仪器的稳定性;设计平衡指针和平衡角度盘,直观地显示杠杆平衡时的偏转角度;同时通过力臂标尺可准确地测出动力臂和阻力臂.     

实验仪器几问

1为什么说电子天平不是称质量的仪器 我们最常用的天平、杆秤、台秤、磅秤、地中衡都是利用杠杆平衡条件制造出的测量工具，在称量物体时，都需要移动秤砣、游码或添加砝码使其平衡，平衡后，根据杠杆平衡条件有     

汽液界面动力学行为与热力学性质的分子动力学研究

本文采用分子动力学方法研究了热平衡条件下的汽液界面的动力学行为和热力学性质。统计获得了界面区的密度、压力张量及温度的分布,并且从分子层次观察分析了界面结构和动力学特性。研究表明汽液界面是一个随时间起伏涨落的曲面,界面层的分子并不是处于液相和蒸汽相之间的一种过渡状态,从汽相到液相密度的连续变化是长时间的统计结果,汽渡过渡区的厚度与汽液界面区的密度涨落的范围是一致的。对于平衡条件下的汽液界面,由于汽液相变的影响,在紧贴界面处存在一个分子平均动能非平衡分布的区域。此非平衡区域的存在与汽液两相的宏观热平衡并不矛盾,但可能对蒸发／凝结流率的估计有不可忽略的影响。     

关于平面力系平衡条件和平衡方程的教学探讨

从平面力系简化,分析平面力系平衡条件、平衡方程的实质和三种形式适用条件及其等价性。平面力系平衡方程的实质是对任意点的主矢等于零和主矩等于零,其形式由三个独立的力平衡方程或力矩平衡方程构成。有利于学生对平面力系平衡方程三种形式等价性的理解。     

快速调节交流电桥的平衡

本介绍交流电桥平衡条件和一种快速调节交流电桥平衡的方法，对初学大有益处。     

水蒸气对声致发光单气泡稳定性的影响

在考虑水蒸气凝结与水的蒸发过程的基础上，推导了球形气泡形状稳定性方程-利用这个方程以及气泡运动时的气体扩散平衡条件，分别研究了环境水温217℃时声驱动频率为206kHz（溶于水中的氩气含量是其饱和度的14％）、环境水温0℃时声驱动频率为319kHz（溶于水中的氮气分压为20kPa，其中含1％氩气），以及环境水温20℃时声驱动频率为338kHz（溶于水中的氮气分压为20kPa，其中含1％氩气）可控制条件下气泡稳定性问题-理论计算结果与前人的实验数据比较，发现考虑水蒸气以后比忽略水蒸气对单气泡稳定区域 关键词： 声致发光 水蒸气 形状不稳定性 扩散平衡     

对一个静电平衡问题的分析

本文通过一个典型静电平衡问题的分析，指出在电磁学教材中作为静电平衡条件提出的“导体在静电平衡时体内电场强度处处为零”实际是静电动平衡的结果，不能机械地用来分析一个导体是否会产生新的静电平衡过程；介绍了导体电位情况的分析在导体静电平衡现象讨论中的意义。     

交流电桥实验的计算机辅助分析

交流电桥实验的计算机辅助分析倪新蕾，潘元胜（南京大学物理系．２１０００８）交流电桥是测量交流元件的常用仪器，图１是测量电路，Ｚｘ为待测电抗元件的复阻抗，其平衡条件为：图１交流电桥众所周知，在交流电桥实验中，要使电桥完全调平衡是十分困难的，一般在平衡指...     

在固液混合相区物质剪切模量的讨论

 从实验和理论两个方面对处于固液相变平衡条件下物质在固液混合相区的剪切模量进行了讨论，认为物质的剪切模量在开始熔化时并不等于零。采用逾渗理论对物质在固液混合相区的固相连通性进行了计算，得到物质整体剪切模量消失的临界熔化质量分数为0.687左右。所给出的物质的熔化失稳因子F(p)能够定性的描述处于固液相变平衡条件下物质固液混合相区内相关物理参量的变化。     

复相系的热力学稳定性条件

导出在有广义功存在情况下多元复相系的热力学稳定性条件，并进行了讨论。     

The critical state and its thermodynamic stability

The Gibbs approach to study of the critical state is expanded. It is noted that the well known critical state condition D=0 was obtained by Gibbs as a necessary condition for a non-zero solution of a system of homogeneous linear equations and defines a line of spinoidal solutions. To determine the critical point on this line the explicit form of solutions of a system of homogeneous equations is considered and their relationship to the slope of the phase equilibrium line is established. For the condition D=0 four possible cases of critical system thermodynamic behavior are considered. The relationship between each of these cases and the slope of the phase equilibrium line at the critical point is established. General thermodynamic stability conditions for the critical point are considered as a function of the type of critical behavior at the point. It is shown that one of the consequences of critical point stability is a merger of the binodal line with the spinodal at the critical point.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 93–98, June, 1988.     

Anomaly in the stability limit of liquid 3He

We propose that the liquid-gas spinodal line of 3He reaches a minimum at 0.4 K. This feature is supported by our cavitation measurements. We also show that it is consistent with extrapolations of sound-velocity measurements. Speedy [J. Phys. Chem. 86, 3002 (1982)] previously proposed this peculiar behavior for the spinodal of water and related it to a change in sign of the expansion coefficient alpha, i.e., a line of density maxima. 3He exhibits such a line at positive pressure. We consider its extrapolation to negative pressure. Our discussion raises fundamental questions about the sign of alpha in a Fermi liquid along its spinodal.     

Entropy of a Two-phase Mixture

The isentropic expansion of a blob of nuclear matter towards the two-phase instability region is studied by considering two extreme conditions: the instantaneous development of the phase transition and the spinodal decomposition. We show that the experimentally observed entropy values of light clusters give evidence for the onset of a liquid-gas phase transition in heavy ion and proton induced reactions, but to be more conclusive the disassembly of relatively cold nuclear systems has experimentally to be investigated in more detail.     

On the theory of spinodal decomposition in solid and liquid binary mixtures

The kinetics of phase separation is discussed with emphasis on the transition between spinodal decomposition and nucleation. A reanalysis of the theory of Langer, Baron and Miller shows that it exhibits a spinodal line somewhat closer to the coexistence curve than the meanfield spinodal. There the same (as we think unphysical) critical singularities occur as in Cahn-Hilliard theory. The precise location of this spinodal line depends on the cell size of the coarse graining. For concentrations less than the spinodal one the structure factorS(k, t) converges then towards the structure factor of the metastable onephase state, implying an infinite lifetime of the latter.In order to include the effects of nucleation and growth we hence present an alternative treatment, extending our previous work on cluster dynamics. From a simple approximation for the radial concentration distribution function of clustersS(k, t) is computed numerically. Even at rather low concentrations the time evolution ofS(k, t) is then similar to what Langer et al. find at high concentrations, implying a very gradual transition from nucleation and growth to spinodal decomposition, at least for parameter values appropriate to the Ising model. This treatment, which is consistent with Lifshitz-Slyozov's coarsening law at late times, is extended to the early stages of phase separation in liquid mixtures.     

Constant chemical potential,pressure and temperature profiles in liquid–vapour equilibrium obtained by spinodal decomposition

Constant chemical potential, pressure and temperature profiles across a slab of liquid in equilibrium with its vapour confirm that, the spinodal decomposition procedure carried on the NVT ensemble simulated via molecular dynamics produce an equilibrium system. An initial homogeneous crystalline configuration of fluid is kept in a cell with a parallelepiped shape at a density near the critical density and a temperature between the triple and critical temperatures, form a slab of liquid in equilibrium with its vapour by the spinodal decomposition phenomenon if the simulation is performed in the NVT ensemble. An elongated box favours the formation of two planar parallel surfaces along the largest side of the box. We show in this paper that the ‘three conditions’ for thermodynamic equilibrium: constant temperature, constant pressure and constant chemical potential are met for such a system.     

Statistical thermodynamics of bulk and surface properties of polymer mixtures

A generalized version of the lattice fluid theory of solutions is considered. Necessary and sufficient conditions for phase stability in a binary mixture are defined by a spinodal inequality. From the general properties of the spinodal, the necessary conditions for polymer/polymer miscibility and bimodal behavior of the spinodal are defined. A general theory of interfacial tension in phase separated multi-component mixtures is formulated. The interfacial tension theory can be combined with lattice fluid theory to obtain a unified theory of bulk and interfacial properties.     

The thermodynamic characteristics of multicomponent reaction mixtures in the sub- and supercritical states

The paper presents mathematical models and calculation methods for solving particular research problems related to the thermodynamic characteristics of multicomponent and multiphase mixtures. The special features of chemical and phase equilibria in such mixtures are considered in the ideal gas approximation and taking nonideality into account. The conditions of equilibrium phase stability are studied for multiphase systems. The results of calculations of characteristic phase diagrams and binodal and spinodal are given for model systems with a fixed chemical composition, and a new interpretation of the mathematical model for localizing the critical point of a multicomponent mixture with a given composition is presented. A new interpretation of the well-known classic homotopy method is suggested for solving complex nonlinear systems of equations. Some anomalies of phase portraits and critical curves that are necessary to take into account in selecting (planning) experimental conditions and calculating chemical processes and reaction parameters are considered separately. The possibility of calculating thermodynamic and thermophysical properties (entropy, enthalpy, heat capacity, heat effects of reactions, and adiabatic heating) is demonstrated for the example of particular multicomponent nonideal mixtures. The conclusion is drawn that cubic equations of state can be used for predicting the deviations of these properties from the ideal gas state and their anomalies in the vicinity of the critical points of mixtures.     

Stability analysis of nonlinear Roesser-type two-dimensional systems via a homogenous polynomial technique

<正>This paper is concerned with the problem of stability analysis of nonlinear Roesser-type two-dimensional(2D) systems.Firstly,the fuzzy modeling method for the usual one-dimensional(1D) systems is extended to the 2D case so that the underlying nonlinear 2D system can be represented by the 2D Takagi-Sugeno(TS) fuzzy model,which is convenient for implementing the stability analysis.Secondly,a new kind of fuzzy Lyapunov function,which is a homogeneous polynomially parameter dependent on fuzzy membership functions,is developed to conceive less conservative stability conditions for the TS Roesser-type 2D system.In the process of stability analysis,the obtained stability conditions approach exactness in the sense of convergence by applying some novel relaxed techniques.Moreover,the obtained result is formulated in the form of linear matrix inequalities,which can be easily solved via standard numerical software.Finally,a numerical example is also given to demonstrate the effectiveness of the proposed approach.     

Analytical solutions describing the phase separation driven by a free energy functional containing a long-range interaction term

We are primarily concerned with the variational problem with long-range interaction. This functional represents the Gibbs free energy of the microphase separation of diblock copolymer melts. The critical points of this variational problem can be regarded as the thermodynamic equilibrium state of the phase separation phenomenon. Experimentally it is well-known in the diblock copolymer problem that the final equilibrium state prefers periodic structures such as lamellar, column, spherical, double-diamond geometries and so on. We are interested in the characterization of the periodic structure of the global minimizer of the functional (corresponding to the strong segregation limit). In this paper we completely determine the principal part of the asymptotic expansion of the period with respect to epsilon (interfacial thickness), namely, we estimate the higher order error term of the period with respect to epsilon in a mathematically rigorous way in one space dimension. Moreover, we decide clearly the dependency of the constant of proportion upon the ratio of the length of two homopolymers and upon the quench depth. In the last section, we study the time evolution of the system. We first study the linear stability of spatially homogeneous steady state and derive the most unstable wavelength, if it is unstable. This is related to spinodal decomposition. Then, we numerically investigate the time evolution equation (the gradient flow of the free energy), and see that the free energy has many local minimizers and the system have some kind of sensitivity about initial data. (c) 1999 American Institute of Physics.     

Molecular dynamics simulations of surface-controlled phase separation of binary fluid mixtures confined in slit pores - Online only

When binary mixtures are confined into nanoscopic slit pores, an intricate interplay between surface enrichment (wetting) of one component and lateral phase separation occurs. After a brief review of the static equilibrium phase diagram of such systems, a discussion of the kinetics of phase separation is given. Considering quenches from an initially homogeneous distribution of the two species in the slit, it is shown by molecular dynamics simulation that typically in the initial stages a stratified structure develops, with enrichment layers of the preferred component at the walls of the slit pore. Then this laterally homogeneous structure breaks up into domains, which coarsen with time according to a power law with a 2/3 exponent. This growth law must be attributed to a hydrodynamic mechanism, since corresponding simulations of a diffusive Ginzburg-Landau model yield an exponent of 1/3 only. The relation to spinodal decomposition in d=2 space dimensions is briefly discussed.