27,970 research outputs found
Universality class of criticality in the restricted primitive model electrolyte
The 1:1 equisized hard-sphere electrolyte or restricted primitive model has
been simulated via grand-canonical fine-discretization Monte Carlo. Newly
devised unbiased finite-size extrapolation methods using temperature-density,
(T, rho), loci of inflections, Q = ^2/ maxima, canonical and C_V
criticality, yield estimates of (T_c, rho_c) to +- (0.04, 3)%. Extrapolated
exponents and Q-ratio are (gamma, nu, Q_c) = [1.24(3), 0.63(3); 0.624(2)] which
support Ising (n = 1) behavior with (1.23_9, 0.630_3; 0.623_6), but exclude
classical, XY (n = 2), SAW (n = 0), and n = 1 criticality with potentials
phi(r)>Phi/r^{4.9} when r \to \infty
Critical Casimir force in He films: confirmation of finite-size scaling
We present new capacitance measurements of critical Casimir force-induced
thinning of He films near the superfluid/normal transition, focused on the
region below where the effect is the greatest. He films of
238, 285, and 340 \AA thickness are adsorbed on N-doped silicon substrates with
roughness . The Casimir force scaling function ,
deduced from the thinning of these three films, collapses onto a single
universal curve, attaining a minimum at
. The collapse confirms the finite-size
scaling origin of the dip in the film thickness. Separately, we also confirm
the presence down to of the Goldstone/surface fluctuation force, which
makes the superfluid film thinner than the normal film.Comment: 4 pages, 3 figures, submitted to PR
An extended scaling analysis of the S=1/2 Ising ferromagnet on the simple cubic lattice
It is often assumed that for treating numerical (or experimental) data on
continuous transitions the formal analysis derived from the Renormalization
Group Theory can only be applied over a narrow temperature range, the "critical
region"; outside this region correction terms proliferate rendering attempts to
apply the formalism hopeless. This pessimistic conclusion follows largely from
a choice of scaling variables and scaling expressions which is traditional but
which is very inefficient for data covering wide temperature ranges. An
alternative "extended caling" approach can be made where the choice of scaling
variables and scaling expressions is rationalized in the light of well
established high temperature series expansion developments. We present the
extended scaling approach in detail, and outline the numerical technique used
to study the 3d Ising model. After a discussion of the exact expressions for
the historic 1d Ising spin chain model as an illustration, an exhaustive
analysis of high quality numerical data on the canonical simple cubic lattice
3d Ising model is given. It is shown that in both models, with appropriate
scaling variables and scaling expressions (in which leading correction terms
are taken into account where necessary), critical behavior extends from Tc up
to infinite temperature.Comment: 16 pages, 17 figure
The Bispectrum of IRAS Galaxies
We compute the bispectrum for the galaxy distribution in the IRAS QDOT, 2Jy,
and 1.2Jy redshift catalogs for wavenumbers 0.05<k<0.2 h/Mpc and compare the
results with predictions from gravitational instability in perturbation theory.
Taking into account redshift space distortions, nonlinear evolution, the survey
selection function, and discreteness and finite volume effects, all three
catalogs show evidence for the dependence of the bispectrum on configuration
shape predicted by gravitational instability. Assuming Gaussian initial
conditions and local biasing parametrized by linear and non-linear bias
parameters b_1 and b_2, a likelihood analysis yields 1/b_1 =
1.32^{+0.36}_{-0.58}, 1.15^{+0.39}_{-0.39} and b_2/b_1^2=-0.57^{+0.45}_{-0.30},
-0.50^{+0.31}_{-0.51}, for the for the 2Jy and 1.2Jy samples, respectively.
This implies that IRAS galaxies trace dark matter increasingly weakly as the
density contrast increases, consistent with their being under-represented in
clusters. In a model with chi^2 non-Gaussian initial conditions, the bispectrum
displays an amplitude and scale dependence different than that found in the
Gaussian case; if IRAS galaxies do not have bias b_1> 1 at large scales, \chi^2
non-Gaussian initial conditions are ruled out at the 95% confidence level. The
IRAS data do not distinguish between Lagrangian or Eulerian local bias.Comment: 30 pages, 11 figure
Ionic fluids: charge and density correlations near gas-liquid criticality
The correlation functions of an ionic fluid with charge and size asymmetry
are studied within the framework of the random phase approximation. The results
obtained for the charge-charge correlation function demonstrate that the
second-moment Stillinger-Lovett (SL) rule is satisfied away from the gas-liquid
critical point (CP) but not, in general, at the CP. However in the special case
of a model without size assymetry the SL rules are satisfied even at the CP.
The expressions for the density-density and charge-density correlation
functions valid far and close to the CP are obtained explicitely
A Monte Carlo study of leading order scaling corrections of phi^4 theory on a three dimensional lattice
We present a Monte Carlo study of the one-component model on the
cubic lattice in three dimensions. Leading order scaling corrections are
studied using the finite size scaling method. We compute the corrections to
scaling exponent with high precision. We determine the value of the
coupling at which leading order corrections to scaling vanish. Using
this result we obtain estimates for critical exponents that are more precise
than those obtained with field theoretic methods.Comment: 20 pages, two figures; numbers cited from ref. 23 corrected, few
typos correcte
Use of ERTS-1 data in identification, classification, and mapping of salt-affected soils in California
There are no author-identified significant results in this report
Expansion of the Gibbs potential for quantum many-body systems: General formalism with applications to the spin glass and the weakly non-ideal Bose gas
For general quantum systems the power expansion of the Gibbs potential and
consequently the power expansion of the self energy is derived in terms of the
interaction strength. Employing a generalization of the projector technique a
compact representation of the general terms of the expansion results. The
general aspects of the approach are discussed with special emphasis on the
effects characteristic for quantum systems. The expansion is systematic and
leads directly to contributions beyond mean-field of all thermodynamic
quantities. These features are explicitly demonstrated and illustrated for two
non-trivial systems, the infinite range quantum spin glass and the weakly
interacting Bose gas. The Onsager terms of both systems are calculated, which
represent the first beyond mean-field contributions. For the spin glass new
TAP-like equations are presented and discussed in the paramagnetic region. The
investigation of the Bose gas leads to a beyond mean-field thermodynamic
description. At the Bose-Einstein condensation temperature complete agreement
is found with the results presented recently by alternative techniques.Comment: 17 pages, 0 figures; revised version accepted by Phys Rev
Fluctuation dissipation ratio in an aging Lennard-Jones glass
By using extensive Molecular Dynamics simulations, we have determined the
violation of the fluctuation-dissipation theorem in a Lennard-Jones liquid
quenched to low temperatures. For this we have calculated , the ratio
between a one particle time-correlation function and the associated
response function. Our results are best fitted by assuming that is a
discontinuous, piecewise constant function. This is similar to what is found in
spin systems with one step replica symmetry breaking. This strengthen the
conjecture of a similarity between the phase space structure of structural
glasses and such spin systems.Comment: improved data and metho
Classical dimers on the triangular lattice
We study the classical hard-core dimer model on the triangular lattice.
Following Kasteleyn's fundamental theorem on planar graphs, this problem is
soluble by Pfaffians. This model is particularly interesting for, unlike the
dimer problems on the bipartite square and hexagonal lattices, its correlations
are short ranged with a correlation length of less than one lattice constant.
We compute the dimer-dimer and monomer-monomer correlators, and find that the
model is deconfining: the monomer-monomer correlator falls off exponentially to
a constant value sin(pi/12)/sqrt(3) = .1494..., only slightly below the
nearest-neighbor value of 1/6. We also consider the anisotropic triangular
lattice model in which the square lattice is perturbed by diagonal bonds of one
orientation and small fugacity. We show that the model becomes non-critical
immediately and that this perturbation is equivalent to adding a mass term to
each of two Majorana fermions that are present in the long wavelength limit of
the square-lattice problem.Comment: 15 pages, 5 figures. v2: includes analytic value of monomer-monomer
correlator, changes titl
- …