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1.
Douglas Henderson Stefan Sokolowski Darsh Wasan 《Journal of statistical physics》1997,89(1-2):233-247
A fluid of hard spheres confined between two hard walls and in equilibrium with a bulk hard-sphere fluid is studied using
a second-order Percus-Yevick approximation. We refer to this approximation as second-order because the correlations that are
calculated depend upon the position of two hard spheres in the confined fluid. However, because the correlation functions
depend upon the positions of four particles (two hard spheres and two walls treated as giant hard spheres), this is the most
demanding application of the second-order theory that has been attempted. When the two walls are far apart, this calculation
reduces to our earlier second-order approximation calculations of the properties of hard spheres near a single hard wall.
Our earlier calculations showed this approach to be accurate for the single-wall case. In this work we calculate the density
profiles and the pressure of the hard-sphere fluid on the walls. We find, by comparison with grand canonical Monte Carlo results,
that the second-order approximation is very accurate, even when the two walls have a small separation. We compare with a singlet
approximation (in the sense that correlation functions that depend on the position of only one hard sphere are considered).
The singlet approach is fairly satisfactory when the two walls are far apart but becomes unsatisfactory when the two walls
have a small separation. We also examine a simple theory of the pressure of the confined hard spheres, based on the usual
Percus-Yevick theory of hard-sphere mixtures. Given the simplicity of the latter approach the results of this simple (and
explicit) theory are surprisingly good. 相似文献
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A. I. Grigor’ev 《Technical Physics》2011,56(6):776-781
A liquid layer resting on a hard bottom and bounded by hard walls is considered. Analysis of the dispersion relation shows that both slowly decaying solitary waves and rapidly decaying periodic waves may arise inside the layer at the interface between stratified ~100-nm-thick near-surface regions of low-viscous liquids. Stratification is due to the orienting influence of the hard bottom and to fluctuation forces. The dispersion laws for the waves are characteristic of purely capillary waves in both a deep and shallow liquid. 相似文献
5.
We investigate stationary nonequilibrium states of systems of particles moving according to Hamiltonian dynamics with specified potentials. The systems are driven away from equilibrium by Maxwell-demon reflection rules at the walls. These deterministic rules conserve energy but not phase space volume, and the resulting global dynamics may or may not be time reversible (or even invertible). Using rules designed to simulate moving walls, we can obtain a stationary shear flow. Assuming that for macroscopic systems this flow satisfies the Navier-Stokes equations, we compare the hydrodynamic entropy production with the average rate of phase-space volume compression. We find that they are equalwhen the velocity distribution of particles incident on the walls is a local Maxwellian. An argument for a general equality of this kind, based on the assumption of local thermodynamic equilibrium, is given. Molecular dynamic simulations of hard disks in a channel produce a steady shear flow with the predicted behavior. 相似文献
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We propose a general formalism to study the static properties of a system composed of particles with nearest neighbor interactions that are located on the sites of a one-dimensional lattice confined by walls (confined Takahashi lattice gas). Linear recursion relations for generalized partition functions are derived, from which thermodynamic quantities, as well as density distributions and correlation functions of arbitrary order can be determined in the presence of an external potential. Explicit results for density profiles and pair correlations near a wall are presented for various situations. As a special case of the Takahashi model we consider in particular the hard rod lattice gas, for which a system of nonlinear coupled difference equations for the occupation probabilities has been presented by Robledo and Varea. A solution of these equations is given in terms of the solution of a system of independent linear equations. Moreover, for zero external potential in the hard-rod system we specify various central regions between the confining walls, where the occupation probabilities are constant and the correlation functions are translationally invariant in the canonical ensemble. In the grand canonical ensemble such regions do not exist. 相似文献
8.
Robin J. Speedy 《Physica A》1994,210(3-4):341-351
Exact analytical expressions are derived for the thermodynamic properties of two discs in square and rhomboidal boxes with hard walls, and in a square cell with periodic boundaries. With periodic boundaries the equation of state has a van der Waals loop and a second order cusp. In a box with hard walls there is a third order “glass transition” which seems to capture the essence of the glass transition observed in systems of a few hundred hard spheres. 相似文献
9.
We obtain the grand potential and the associated distribution functions for a system of hard rods on a line of finite length. These functions are shown to be related to those of a semi-infinite system bounded by one hard wall. It follows that the contact values of the density and distribution functions at the walls of the finite system are related to those at the wall of the semi-infinite system, and that the force on the walls is the density at contact. We obtain also the density and distribution functions for a system with repeating boundary conditions, which are also expressible in terms of those of the finite and semi-infinite systems. 相似文献
10.
Shiqi Zhou 《The European physical journal. E, Soft matter》2000,3(4):343-353
A density functional theory is proposed for nonuniform freely jointed tangential hard sphere polymer melts in which the bonding
interaction is treated on the basis of the properties of the Dirac δ-function, thus avoiding the use of the single chain simulation
in the theory. The excess free energy is treated by making use of the universality of the free energy density functional and
the Verlet-modified (VM) bridge function. To proceed numerically, one of the input parameters, the second-order direct correlation
function of a uniform polymer melt is obtained by solving numerically the Polymer-RISM integral equation with the Percus-Yevick
(PY) closure. The predictions of the present theory for the site density distribution, the partition coefficient and the adsorption
isotherm, near a hard wall or between two hard walls are compared with computer simulation results and with those of previous
theories. Comparison indicates that the present approach is more accurate than the previous integral equation theory and the
most accurate Monte Carlo density functional theories. The predicted oscillations of the medium-induced force between two
hard walls immersed in polymer melts are consistent with the experimental results available in the literature.
Received 18 April 2000 相似文献
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Németh ZT Löwen H 《Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics》1999,59(6):6824-6829
Dynamical and static properties of N=13-4000 hard spheres in spherical cavities with smooth and rough walls have been calculated by molecular-dynamics computer simulations. We use a dynamical criterion to distinguish between fluidlike and solidlike states. The associated crossover densities show a strong dependence both on the system size and on the surface roughness. For large N, these crossover densities tend to the bulk glass transition density for rough walls and to the bulk crystallization density for smooth walls. The crossover densities for finite N are found to be significantly smaller than the corresponding bulk densities. A detailed examination of the layer-resolved radial- and tangential mean-square displacements reveals qualitatively different dynamics for smooth and rough cavities. 相似文献
13.
Two numerical procedures for finding the acoustic eigenvalues in the rectangular room with arbitrary (uniform) wall impedances are developed. One numerical procedure applies Newton's method. Here, starting with soft walls, the eigenvalues are found by increasing the impedances of each wall pair in small increments up to the terminal impedances. Another procedure poses the eigenvalue problem as one of homotopic continuation from a non-physical reference configuration in which all eigenvalues are known and obvious. The continuation is performed by the numerical integration of two differential equations. The latter procedure was found to be faster and finds all possible solutions. The set of eigenvalues allowed the room modal natural frequencies and damping constants to be obtained. From sound decays measured in a hard-walled rectangular room, and from the collective-modal-decay curve, the impedances of the hard walls are estimated. These are then used to find the reverberation times of the modes in the room with the floor lined with sound absorbing material of known acoustic impedance. It was found that a single reverberation time, for all modes, is only supported in the rectangular room with hard walls and at the higher frequency bands, consistent with Sabine's theory, which assumes a diffuse sound field. In the rectangular room with hard walls and at the lower frequency bands, and in the rectangular room with the floor lined with sound absorbing material and for all frequency bands, modes with rather distinctive reverberation times may produce sound decays not always consistent with Sabine's prediction. 相似文献
14.
Single two dimensional polymers confined to a strip are studied by Monte Carlo simulations. They are described by N-step self-avoiding random walks on a square lattice between two parallel hard walls with distance
(
is the Flory exponent). For the simulations we employ the pruned-enriched-Rosenbluth method (PERM) with Markovian anticipation. We measure the densities of monomers and of end points as functions of the distance from the walls, the longitudinal extent of the chain, and the forces exerted on the walls. Their scaling with D and the universal ratio between force and monomer density at the wall are compared to theoretical predictions.Received: 14 August 2003, Published online: 8 December 2003PACS:
61.25.Hq Macromolecular and polymer solutions; polymer melts; swelling - 07.05.Tp Computer modeling and simulation - 61.41. + e Polymers, elastomers, and plastics 相似文献
15.
The structural and thermodynamic properties of a confined hard ellipse fluid are studied using Monte Carlo simulation. The angular, average number densities and order parameters of hard ellipses confined between hard parallel walls are obtained for various bulk densities, aspect ratios and wall separations. The results show that the effect of the existence of the wall on the molecular fluid structure, either on their directions or their locations, with respect to the bulk, especially close to the walls, is significant. For this system the pressure is also obtained and it is shown that the average density at the wall is proportional to the pressure, βP=〈ρw〉. Our simulation results show that the order parameters depend on the number of the particles in the box unless it exceeds thousand. 相似文献
16.
J. K. Percus 《Journal of statistical physics》1980,23(6):657-699
We investigate lower order distribution functions in classical fluids in the presence of large-scale inhomogeneities, in particular those imposed by wall contacts. The consequences of the effective shielding of a wall by the nearest particle of the set being considered are determined in the context of two distribution function hierarchies, kinematic and dynamic in origin. The effects of both flat and spherical, hard and soft walls are considered, as well as those of curved and double walls. A few correction sequences to the basic shielding approximation are discussed.Supported in part by the Department of Energy under contract DE-AC02-76 ERO 3077. 相似文献
17.
Acoustical Physics - The paper considers the problem of sound absorption by a Helmholtz resonator in a room with perfectly hard walls. The resonator parameters are determined that yield the maximum... 相似文献
18.
Vortex domain walls (DWs) are characterized by their chirality, an important property that needs to be controlled for the use of such walls in potential technological applications. In this work we explore a wire-ring structure in which we have alternate hard and soft magnetic materials. Our results evidence that, depending on the materials, it is possible to control the DW chirality when it goes through the ring section. Therefore, this system can be used as a device that controls domain wall chirality. 相似文献
19.
应用微通道板通道玻璃表面对大角入射的X射线吸收和小角入射的X射线全反射的特性,讨论适用于硬X射线和软X射线准直的两种类型微通道板,分析影响准直性能的因素。最后,对硬X射线微通道板准直器的辐射通量与通用准直器的进行比较。 相似文献