70,882 research outputs found
A fundamental measure theory for the sticky hard sphere fluid
We construct a density functional theory (DFT) for the sticky hard sphere
(SHS) fluid which, like Rosenfeld's fundamental measure theory (FMT) for the
hard sphere fluid [Phys. Rev. Lett. {\bf 63}, 980 (1989)], is based on a set of
weighted densities and an exact result from scaled particle theory (SPT). It is
demonstrated that the excess free energy density of the inhomogeneous SHS fluid
is uniquely defined when (a) it is solely a function of the
weighted densities from Kierlik and Rosinberg's version of FMT [Phys. Rev. A
{\bf 42}, 3382 (1990)], (b) it satisfies the SPT differential equation, and (c)
it yields any given direct correlation function (DCF) from the class of
generalized Percus-Yevick closures introduced by Gazzillo and Giacometti [J.
Chem. Phys. {\bf 120}, 4742 (2004)]. The resulting DFT is shown to be in very
good agreement with simulation data. In particular, this FMT yields the correct
contact value of the density profiles with no adjustable parameters. Rather
than requiring higher order DCFs, such as perturbative DFTs, our SHS FMT
produces them. Interestingly, although equivalent to Kierlik and Rosinberg's
FMT in the case of hard spheres, the set of weighted densities used for
Rosenfeld's original FMT is insufficient for constructing a DFT which yields
the SHS DCF.Comment: 11 pages, 3 figure
On the nonlocal viscosity kernel of mixtures
In this report we investigate the multiscale hydrodynamical response of a
liquid as a function of mixture composition. This is done via a series of
molecular dynamics simulations where the wave vector dependent viscosity kernel
is computed for three mixtures each with 7-15 different compositions. We
observe that the nonlocal viscosity kernel is dependent on composition for
simple atomic mixtures for all the wave vectors studied here, however, for a
model polymer melt mixture the kernel is independent of composition for large
wave vectors. The deviation from ideal mixing is also studied. Here it is shown
that a Lennard-Jones mixture follows the ideal mixing rule surprisingly well
for a large range of wave vectors, whereas for both the Kob-Andersen mixture
and the polymer melt large deviations are found. Furthermore, for the polymer
melt the deviation is wave vector dependent such that there exists a critical
length scale at which the ideal mixing goes from under-estimating to
over-estimating the viscosity
Self-consistent Ornstein-Zernike approximation for molecules with soft cores
The Self-Consistent Ornstein-Zernike Approximation (SCOZA) is an accurate
liquid state theory. So far it has been tied to interactions composed of hard
core repulsion and long-range attraction, whereas real molecules have soft core
repulsion at short distances. In the present work, this is taken into account
through the introduction of an effective hard core with a diameter that depends
upon temperature only. It is found that the contribution to the configurational
internal energy due to the repulsive reference fluid is of prime importance and
must be included in the thermodynamic self-consistency requirement on which
SCOZA is based. An approximate but accurate evaluation of this contribution
relies on the virial theorem to gauge the amplitude of the pair distribution
function close to the molecular surface. Finally, the SCOZA equation is
transformed by which the problem is reformulated in terms of the usual SCOZA
with fixed hard core reference system and temperature-dependent interaction
Entropy scaling laws for diffusion
Comment to the letter of Samanta et al., Phys. Rev. Lett. 92, 145901 (2004).Comment: 2 pages, 1 figur
Feasibility study of an Integrated Program for Aerospace vehicle Design (IPAD) Volume 7: IPAD benefits and impact
The potential benefits, impact and spinoff of IPAD technology are described. The benefits are projected from a flowtime and labor cost analysis of the design process and a study of the flowtime and labor cost savings being experienced with existing integrated systems. Benefits in terms of designer productivity, company effectiveness, and IPAD as a national resource are developed. A description is given of the potential impact of information handling as an IPAD technology, upon task and organization structure and people who use IPAD. Spinoff of IPAD technology to nonaerospace industries is discussed. The results of a personal survey made of aerospace, nonaerospace, government and university sources are given
Hydrophobic interactions with coarse-grained model for water
Integral equation theory is applied to a coarse-grained model of water to
study potential of mean force between hydrophobic solutes. Theory is shown to
be in good agreement with the available simulation data for methane-methane and
fullerene-fullerene potential of mean force in water; the potential of mean
force is also decomposed into its entropic and enthalpic contributions. Mode
coupling theory is employed to compute self-diffusion coefficient of water, as
well as diffusion coefficient of a dilute hydrophobic solute; good agreement
with molecular dynamics simulation results is found
A universal velocity distribution of relaxed collisionless structures
Several general trends have been identified for equilibrated,
self-gravitating collisionless systems, such as density or anisotropy profiles.
These are integrated quantities which naturally depend on the underlying
velocity distribution function (VDF) of the system. We study this VDF through a
set of numerical simulations, which allow us to extract both the radial and the
tangential VDF. We find that the shape of the VDF is universal, in the sense
that it depends only on two things namely the dispersion (radial or tangential)
and the local slope of the density. Both the radial and the tangential VDF's
are universal for a collection of simulations, including controlled collisions
with very different initial conditions, radial infall simulation, and
structures formed in cosmological simulations.Comment: 13 pages, 6 figures; oversimplified analysis corrected; changed
abstract and conclusions; significantly extended discussio
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