466 research outputs found
Vapour-liquid coexistence in many-body dissipative particle dynamics
Many-body dissipative particle dynamics is constructed to exhibit
vapour-liquid coexistence, with a sharp interface, and a vapour phase of
vanishingly small density. In this form, the model is an unusual example of a
soft-sphere liquid with a potential energy built out of local-density dependent
one-particle self energies. The application to fluid mechanics problems
involving free surfaces is illustrated by simulation of a pendant drop.Comment: 8 pages, 6 figures, revtex
Polyhedral vesicles
Polyhedral vesicles with a large bending modulus of the membrane such as the
gel phase lipid membrane were studied using a Brownian dynamics simulation. The
vesicles exhibit various polyhedral morphologies such as tetrahedron and cube
shapes. We clarified two types of line defects on the edges of the polyhedrons:
cracks of both monolayers at the spontaneous curvature of monolayer , and a crack of the inner monolayer at . Around the
latter defect, the inner monolayer curves positively. Our results suggested
that the polyhedral morphology is controlled by .Comment: 4 pages, 5 figure
The liquid-vapor interface of an ionic fluid
We investigate the liquid-vapor interface of the restricted primitive model
(RPM) for an ionic fluid using a density-functional approximation based on
correlation functions of the homogeneous fluid as obtained from the
mean-spherical approximation (MSA). In the limit of a homogeneous fluid our
approach yields the well-known MSA (energy) equation of state. The ionic
interfacial density profiles, which for the RPM are identical for both species,
have a shape similar to those of simple atomic fluids in that the decay towards
the bulk values is more rapid on the vapor side than on the liquid side. This
is the opposite asymmetry of the decay to that found in earlier calculations
for the RPM based on a square-gradient theory. The width of the interface is,
for a wide range of temperatures, approximately four times the second moment
correlation length of the liquid phase. We discuss the magnitude and
temperature dependence of the surface tension, and argue that for temperatures
near the triple point the ratio of the dimensionless surface tension and
critical temperature is much smaller for the RPM than for simple atomic fluids.Comment: 6 postscript figures, submitted to Phys. Rev.
Phase-field-crystal models for condensed matter dynamics on atomic length and diffusive time scales: an overview
Here, we review the basic concepts and applications of the
phase-field-crystal (PFC) method, which is one of the latest simulation
methodologies in materials science for problems, where atomic- and microscales
are tightly coupled. The PFC method operates on atomic length and diffusive
time scales, and thus constitutes a computationally efficient alternative to
molecular simulation methods. Its intense development in materials science
started fairly recently following the work by Elder et al. [Phys. Rev. Lett. 88
(2002), p. 245701]. Since these initial studies, dynamical density functional
theory and thermodynamic concepts have been linked to the PFC approach to serve
as further theoretical fundaments for the latter. In this review, we summarize
these methodological development steps as well as the most important
applications of the PFC method with a special focus on the interaction of
development steps taken in hard and soft matter physics, respectively. Doing
so, we hope to present today's state of the art in PFC modelling as well as the
potential, which might still arise from this method in physics and materials
science in the nearby future.Comment: 95 pages, 48 figure
Anomalous Effects of "Guest" Charges Immersed in Electrolyte: Exact 2D Results
We study physical situations when one or two "guest" arbitrarily-charged
particles are immersed in the bulk of a classical electrolyte modelled by a
Coulomb gas of positive/negative unit point-like charges, the whole system
being in thermal equilibrium. The models are treated as two-dimensional with
logarithmic pairwise interactions among charged constituents; the
(dimensionless) inverse temperature is considered to be smaller than 2
in order to ensure the stability of the electrolyte against the collapse of
positive-negative pairs of charges. Based on recent progress in the integrable
(1+1)-dimensional sine-Gordon theory, exact formulas are derived for the
chemical potential of one guest charge and for the asymptotic large-distance
behavior of the effective interaction between two guest charges. The exact
results imply, under certain circumstances, anomalous effects such as an
effective attraction (repulsion) between like-charged (oppositely-charged)
guest particles and the charge inversion in the electrolyte vicinity of a
highly-charged guest particle. The adequacy of the concept of renormalized
charge is confirmed in the whole stability region of inverse temperatures and
the related saturation phenomenon is revised.Comment: 21 pages, 1 figur
Multipolar Reactive DPD: A Novel Tool for Spatially Resolved Systems Biology
This article reports about a novel extension of dissipative particle dynamics
(DPD) that allows the study of the collective dynamics of complex chemical and
structural systems in a spatially resolved manner with a combinatorially
complex variety of different system constituents. We show that introducing
multipolar interactions between particles leads to extended membrane structures
emerging in a self-organized manner and exhibiting both the necessary
mechanical stability for transport and fluidity so as to provide a
two-dimensional self-organizing dynamic reaction environment for kinetic
studies in the context of cell biology. We further show that the emergent
dynamics of extended membrane bound objects is in accordance with scaling laws
imposed by physics.Comment: submitted to CMSB 0
On the nature of the so-called generic instabilities in dissipative relativistic hydrodynamics
It is shown that the so-called generic instabilities that appear in the
framework of relativistic linear irreversible thermodynamics, describing the
fluctuations of a simple fluid close to equilibrium, arise due to the coupling
of heat with hydrodynamic acceleration which appears in Eckart's formalism of
relativistic irreversible thermodynamics. Further, we emphasize that such
behavior should be interpreted as a contradiction to the postulates of linear
irreversible thermodynamics (LIT), namely a violation of Onsager's hypothesis
on the regression of fluctuations, and not as fluid instabilities. Such
contradictions can be avoided within a relativistic linear framework if a
Meixner-like approach to the phenomenological equations is employed.Comment: 13 pages, no figures. Accepted for publication in GR
Hard pomeron enhancement of ultrahigh-energy neutrino-nucleon cross-sections
An unknown small-x behavior of nucleon structure functions gives appreciable
uncertainties to high-energy neutrino-nucleon cross-sections. We construct
structure functions using at small x Regge inspired description by A. Donnachie
and P. V. Landshoff with soft and hard pomerons, and employing at larger x the
perturbative QCD expressions. The smooth interpolation between two regimes for
each Q^2 is provided with the help of simple polynomial functions. To obtain
low-x neutrino-nucleon structure functions and
singlet part of from Donnachie-Landshoff
function , we use the Q^2-dependent ratios R_2(Q^2) and
R_3(Q^2) derived from perturbative QCD calculations. Non-singlet part of F_3 at
low x, which is very small, is taken as power-law extrapolation of perturbative
function at larger x. This procedure gives a full set of smooth
neutrino-nucleon structure functions in the whole range of x and Q^2 at
interest.
Using these structure functions, we have calculated the neutrino-nucleon
cross-sections and compared them with some other cross-sections known in
literature. Our cross-sections turn out to be the highest among them at the
highest energies, which is explained by contribution of the hard pomeron.Comment: Final revised version, accepted by Phys. Rev. D; 18 pages, 7 figure
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