51 research outputs found
Effects of weak surface fields on the density profiles and adsorption of a confined fluid near bulk criticality
The density profile and Gibbs adsorption of a near-critical fluid confined
between two identical planar walls is studied by means of
Monte Carlo simulation and by density functional theory for a Lennard-Jones
fluid. By reducing the strength of wall-fluid interactions relative to
fluid-fluid interactions we observe a crossover from behaviour characteristic
of the normal surface universality class, strong critical adsorption, to
behaviour characteristic of a 'neutral' wall. The crossover is reminiscent of
that which occurs near the ordinary surface transition in Ising films subject
to vanishing surface fields. For the 'neutral' wall the density profile, away
from the walls, is almost constant throughout the slit capillary and gives rise
to an adsorption that is constant along the critical isochore. The same
'neutral' wall yields a line of capillary coexistence that is almost identical
to the bulk coexistence line. In the crossover regime we observe features in
the density profile similar to those found in the magnetisation profile of the
critical Ising film subject to weak surface fields, namely two smooth maxima,
located away from the walls, which merge into a single maximum at midpoint as
the strength of the wall-fluid interaction is reduced or as the distance
between walls is decreased. We discuss similarities and differences between the
surface critical behaviour of fluids and of Ising magnets.Comment: 34 pages, 10 figures, submitted to the Journ. Chem. Phy
Surface Incommensurate Structure in an Anisotropic Model with competing interactions on Semiinfinite Triangular Lattice
An anisotropic spin model on a triangular semiinfinite lattice with
ferromagnetic nearest-neighbour interactions and one antiferromagnetic
next-nearest-neighbour interaction is investigated by the cluster
transfer-matrix method. A phase diagram with antiphase, ferromagnetic,
incommensurate, and disordered phase is obtained. The bulk uniaxial
incommensurate structure modulated in the direction of the competing
interactions is found between the antiphase and the disordered phase. The
incommensurate structure near the surface with free and boundary condition
is studied at different temperatures. Paramagnetic damping at the surface and
enhancement of the incommensurate structure in the subsurface region at high
temperatures and a new subsurface incommensurate structure modulated in two
directions at low temperatures are found.Comment: 13 pages, plainTex, 11 figures, paper submitted to J. Phys.
X-Ray Scattering at FeCo(001) Surfaces and the Crossover between Ordinary and Normal Transitions
In a recent experiment by Krimmel et al. [PRL 78, 3880 (1997)], the critical
behavior of FeCo near a (001) surface was studied by x-ray scattering. Here the
experimental data are reanalyzed, taking into account recent theoretical
results on order-parameter profiles in the crossover regime between ordinary
and normal transitions. Excellent agreement between theoretical expectations
and the experimental results is found.Comment: 9 pages, Latex, 1 PostScript figure, to be published in Phys.Rev.
Microscopic Non-Universality versus Macroscopic Universality in Algorithms for Critical Dynamics
We study relaxation processes in spin systems near criticality after a quench
from a high-temperature initial state. Special attention is paid to the stage
where universal behavior, with increasing order parameter emerges from an early
non-universal period. We compare various algorithms, lattice types, and
updating schemes and find in each case the same universal behavior at
macroscopic times, despite of surprising differences during the early
non-universal stages.Comment: 9 pages, 3 figures, RevTeX, submitted to Phys. Rev. Let
An assessment of the potential of continuous-wave ranging for measuring the distance to a highly reflective, infinite sheet
The feasibility of a continuous-wave, distance-measuring technique for measuring the distance from a spacecraft antenna to a highly ionized plasma surface is examined. The reflection coefficient angle is computed for several aperture models. It is concluded that aperture size and the presence of a nonablating dielectric cover over the antenna are critical factors
Dynamic SU(2) Lattice Gauge Theory at Finite Temperature
The dynamic relaxation process for the (2+1)--dimensional SU(2) lattice gauge
theory at critical temperature is investigated with Monte Carlo methods. The
critical initial increase of the Polyakov loop is observed. The dynamic
exponents and as well as the static critical exponent
are determined from the power law behaviour of the Polyakov loop, the
auto-correlation and the second moment at the early stage of the time
evolution. The results are well consistent and universal short-time scaling
behaviour of the dynamic system is confirmed. The values of the exponents show
that the dynamic SU(2) lattice gauge theory is in the same dynamic universality
class as the dynamic Ising model.Comment: 10 pages with 2 figure
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