547 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
High-field (40 T) magnetization studies of linear Heisenberg chains with alternating exchange
Metals in Catalysis, Biomimetics & Inorganic Material
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.
The Gamma Ray Bursts GRB970228 and GRB970508: What Have We Learnt?
We examine what we regard as key observational results on GRB 970228 and GRB
970508 and show that the accumulated evidence strongly suggests that gamma-ray
bursts (GRBs) are cosmological fireballs.
We further show that the observations suggest that GRBs are not associated
with the nuclear activity of active galactic nuclei, and that late-type
galaxies are more prolific producers of GRBs.
We suggest that GRBs can be used to trace the cosmic history of the
star-formation rate. Finally, we show that the GRB locations with respect to
the star-forming regions in their host galaxies and the total burst energies
can be used to distinguish between different theoretical models for GRBs.Comment: 7 pages (with 2 embedded figures), to be published in the Proceedings
of the Fourth Huntsville Gamma-Ray Burst Symposium, held Sep 15-20, 1997,
Huntsville, Alabam
Three-body interactions in colloidal systems
We present the first direct measurement of three-body interactions in a
colloidal system comprised of three charged colloidal particles. Two of the
particles have been confined by means of a scanned laser tweezers to a
line-shaped optical trap where they diffused due to thermal fluctuations. Upon
the approach of a third particle, attractive three-body interactions have been
observed. The results are in qualitative agreement with additionally performed
nonlinear Poissson-Boltzmann calculations, which also allow us to investigate
the microionic density distributions in the neighborhood of the interacting
colloidal particles
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
Foundations of Dissipative Particle Dynamics
We derive a mesoscopic modeling and simulation technique that is very close
to the technique known as dissipative particle dynamics. The model is derived
from molecular dynamics by means of a systematic coarse-graining procedure.
Thus the rules governing our new form of dissipative particle dynamics reflect
the underlying molecular dynamics; in particular all the underlying
conservation laws carry over from the microscopic to the mesoscopic
descriptions. Whereas previously the dissipative particles were spheres of
fixed size and mass, now they are defined as cells on a Voronoi lattice with
variable masses and sizes. This Voronoi lattice arises naturally from the
coarse-graining procedure which may be applied iteratively and thus represents
a form of renormalisation-group mapping. It enables us to select any desired
local scale for the mesoscopic description of a given problem. Indeed, the
method may be used to deal with situations in which several different length
scales are simultaneously present. Simulations carried out with the present
scheme show good agreement with theoretical predictions for the equilibrium
behavior.Comment: 18 pages, 7 figure
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