57,878 research outputs found
How `sticky' are short-range square-well fluids?
The aim of this work is to investigate to what extent the structural
properties of a short-range square-well (SW) fluid of range at a
given packing fraction and reduced temperature can be represented by those of a
sticky-hard-sphere (SHS) fluid at the same packing fraction and an effective
stickiness parameter . Such an equivalence cannot hold for the radial
distribution function since this function has a delta singularity at contact in
the SHS case, while it has a jump discontinuity at in the SW case.
Therefore, the equivalence is explored with the cavity function .
Optimization of the agreement between y_{\sw} and y_{\shs} to first order
in density suggests the choice for . We have performed Monte Carlo (MC)
simulations of the SW fluid for , 1.02, and 1.01 at several
densities and temperatures such that , 0.2, and 0.5. The
resulting cavity functions have been compared with MC data of SHS fluids
obtained by Miller and Frenkel [J. Phys: Cond. Matter 16, S4901 (2004)].
Although, at given values of and , some local discrepancies
between y_{\sw} and y_{\shs} exist (especially for ), the SW
data converge smoothly toward the SHS values as decreases. The
approximate mapping y_{\sw}\to y_{\shs} is exploited to estimate the internal
energy and structure factor of the SW fluid from those of the SHS fluid. Taking
for y_{\shs} the solution of the Percus--Yevick equation as well as the
rational-function approximation, the radial distribution function of the
SW fluid is theoretically estimated and a good agreement with our MC
simulations is found. Finally, a similar study is carried out for short-range
SW fluid mixtures.Comment: 14 pages, including 3 tables and 14 figures; v2: typo in Eq. (5.1)
corrected, Fig. 14 redone, to be published in JC
A rotating cylinder in an asymptotically locally anti-de Sitter background
A family of exact solutions is presented which represents a rigidly rotating
cylinder of dust in a background with a negative cosmological constant. The
interior of the infinite cylinder is described by the Godel solution. An exact
solution for the exterior solution is found which depends both on the rotation
of the interior and on its radius. For values of these parameters less than a
certain limit, the exterior solution is shown to be locally isomorphic to the
Linet-Tian solution. For values larger than another limit, it is shown that the
exterior solution extends into a region which contains closed timelike curves.
At large distances from the source, the space-time is shown to be asymptotic
locally to anti-de Sitter space.Comment: To appear in Classical and Quantum Gravit
Contact values of the radial distribution functions of additive hard-sphere mixtures in d dimensions: A new proposal
The contact values of the radial distribution functions
of a -dimensional mixture of (additive) hard spheres are considered. A
`universality' assumption is put forward, according to which
, where is a common function for all
the mixtures of the same dimensionality, regardless of the number of
components, is the packing fraction of the mixture, and is a
dimensionless parameter that depends on the size distribution and the diameters
of spheres and . For , this universality assumption holds for the
contact values of the Percus--Yevick approximation, the Scaled Particle Theory,
and, consequently, the Boublik--Grundke--Henderson--Lee--Levesque
approximation. Known exact consistency conditions are used to express
, , and in terms of the radial distribution
at contact of the one-component system. Two specific proposals consistent with
the above conditions (a quadratic form and a rational form) are made for the
-dependence of . For one-dimensional systems, the proposals for
the contact values reduce to the exact result. Good agreement between the
predictions of the proposals and available numerical results is found for
, 3, 4, and 5.Comment: 10 pages, 11 figures; Figure 1 changed; Figure 5 is new; New
references added; accepted for publication in J. Chem. Phy
Fourth virial coefficients of asymmetric nonadditive hard-disc mixtures
The fourth virial coefficient of asymmetric nonadditive binary mixtures of
hard disks is computed with a standard Monte Carlo method. Wide ranges of size
ratio () and nonadditivity () are
covered. A comparison is made between the numerical results and those that
follow from some theoretical developments. The possible use of these data in
the derivation of new equations of state for these mixtures is illustrated by
considering a rescaled virial expansion truncated to fourth order. The
numerical results obtained using this equation of state are compared with Monte
Carlo simulation data in the case of a size ratio and two
nonadditivities .Comment: 9 pages, 7 figures; v2: section on equation of state added; tables
moved to supplementary material
(http://jcp.aip.org/resource/1/jcpsa6/v136/i18/p184505_s1#artObjSF
Pair correlation function of short-ranged square-well fluids
We have performed extensive Monte Carlo simulations in the canonical (NVT)
ensemble of the pair correlation function for square-well fluids with well
widths ranging from 0.1 to 1.0, in units of the diameter
of the particles. For each one of these widths, several densities and
temperatures in the ranges and
, where is the
critical temperature, have been considered. The simulation data are used to
examine the performance of two analytical theories in predicting the structure
of these fluids: the perturbation theory proposed by Tang and Lu [Y. Tang and
B. C.-Y. Lu, J. Chem. Phys. {\bf 100}, 3079, 6665 (1994)] and the
non-perturbative model proposed by two of us [S. B. Yuste and A. Santos, J.
Chem. Phys. {\bf 101}, 2355 (1994)]. It is observed that both theories
complement each other, as the latter theory works well for short ranges and/or
moderate densities, while the former theory does for long ranges and high
densities.Comment: 10 pages, 10 figure
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