10,352 research outputs found
Reply to "Comment on Evidence for the droplet picture of spin glasses"
Using Monte Carlo simulations (MCS) and the Migdal-Kadanoff approximation
(MKA), Marinari et al. study in their comment on our paper the link overlap
between two replicas of a three-dimensional Ising spin glass in the presence of
a coupling between the replicas. They claim that the results of the MCS
indicate replica symmetry breaking (RSB), while those of the MKA are trivial,
and that moderate size lattices display the true low temperature behavior. Here
we show that these claims are incorrect, and that the results of MCS and MKA
both can be explained within the droplet picture.Comment: 1 page, 1 figur
Phase Ordering Dynamics of the O(n) Model - Exact Predictions and Numerical Results
We consider the pair correlation functions of both the order parameter field
and its square for phase ordering in the model with nonconserved order
parameter, in spatial dimension and spin dimension .
We calculate, in the scaling limit, the exact short-distance singularities of
these correlation functions and compare these predictions to numerical
simulations. Our results suggest that the scaling hypothesis does not hold for
the model. Figures (23) are available on request - email
[email protected]: 23 pages, Plain LaTeX, M/C.TH.93/2
Drowsy Cheetah Hunting Antelopes: A Diffusing Predator Seeking Fleeing Prey
We consider a system of three random walkers (a `cheetah' surrounded by two
`antelopes') diffusing in one dimension. The cheetah and the antelopes diffuse,
but the antelopes experience in addition a deterministic relative drift
velocity, away from the cheetah, proportional to their distance from the
cheetah, such that they tend to move away from the cheetah with increasing
time. Using the backward Fokker-Planck equation we calculate, as a function of
their initial separations, the probability that the cheetah has caught neither
antelope after infinite time.Comment: 5 page
Comment on "General Method to Determine Replica Symmetry Breaking Transitions"
In a recent letter Marinari et al [Phys. Rev. Lett. 81, 1698 (1998)]
introduced a new method to study spin glass transitions and argued that by
probing replica symmetry (RS) as opposed to time reversal symmetry (TRS), their
method unambiguously shows that replica symmetry breaking (RSB) occurs in
short-range spin glasses. In this comment we show that while the new method is
indeed useful for studying transitions in systems where TRS is absent (such as
the p-spin model studied by them), the conclusion that it shows the existence
of RSB in short-range spin glasses is wrong.Comment: 1 page, RevTe
The de Almeida-Thouless line in vector spin glasses
We consider the infinite-range spin glass in which the spins have m > 1
components (a vector spin glass). Applying a magnetic field which is random in
direction, there is an Almeida Thouless (AT) line below which the "replica
symmetric" solution is unstable, just as for the Ising (m=1) case. We calculate
the location of this AT line for Gaussian random fields for arbitrary m, and
verify our results by numerical simulations for m = 3$.Comment: 19 pages, 4 eps figure
Stress-free Spatial Anisotropy in Phase-Ordering
We find spatial anisotropy in the asymptotic correlations of two-dimensional
Ising models under non-equilibrium phase-ordering. Anisotropy is seen for
critical and off-critical quenches and both conserved and non-conserved
dynamics. We argue that spatial anisotropy is generic for scalar systems
(including Potts models) with an anisotropic surface tension. Correlation
functions will not be universal in these systems since anisotropy will depend
on, e.g., temperature, microscopic interactions and dynamics, disorder, and
frustration.Comment: 4 pages, 4 figures include
Evidence for the droplet/scaling picture of spin glasses
We have studied the Parisi overlap distribution for the three dimensional
Ising spin glass in the Migdal-Kadanoff approximation. For temperatures T
around 0.7Tc and system sizes upto L=32, we found a P(q) as expected for the
full Parisi replica symmetry breaking, just as was also observed in recent
Monte Carlo simulations on a cubic lattice. However, for lower temperatures our
data agree with predictions from the droplet or scaling picture. The failure to
see droplet model behaviour in Monte Carlo simulations is due to the fact that
all existing simulations have been done at temperatures too close to the
transition temperature so that sytem sizes larger than the correlation length
have not been achieved.Comment: 4 pages, 6 figure
Is the droplet theory for the Ising spin glass inconsistent with replica field theory?
Symmetry arguments are used to derive a set of exact identities between
irreducible vertex functions for the replica symmetric field theory of the
Ising spin glass in zero magnetic field. Their range of applicability spans
from mean field to short ranged systems in physical dimensions. The replica
symmetric theory is unstable for d>8, just like in mean field theory. For 6<d<8
and d<6 the resummation of an infinite number of terms is necessary to settle
the problem. When d<8, these Ward-like identities must be used to distinguish
an Almeida-Thouless line from the replica symmetric droplet phase.Comment: 4 pages. Accepted for publication in J.Phys.A. This is the accepted
version with the following minor changes: one extra sentence in the abstract;
footnote 2 slightly extended; last paragraph somewhat reformulate
Sex distribution of offspring-parents obesity: Angel's hypothesis revisited
This study, which is based on two cross sectional surveys' data, aims to establish any effect of parental obesity sex distribution of offspring and to replicate the results that led to the hypothesis that obesity may be associated with sex-linked recessive lethal gene. A representative sample of 4,064 couples living in Renfrew/Paisley, Scotland was surveyed 1972-1976. A total of 2,338 offspring from 1,477 of the couples screened in 1972-1976, living in Paisley, were surveyed in 1996. In this study, males represented 47.7% among the total offspring of the couples screened in 1972-1976. In the first survey there was a higher male proportion of offspring (53%, p < 0.05) from parents who were both obese, yet this was not significant after adjustment for age of parents. Also, there were no other significant differences in sex distribution of offspring according to body mass index, age, or social class of parents. The conditions of the original 1949 study of Angel (1949) (which proposed a sex-linked lethal recessive gene) were simulated by selecting couples with at least one obese daughter. In this subset, (n = 409), obesity in fathers and mothers was associated with 26% of offspring being male compared with 19% of offspring from a non-obese father and obese mother. Finally we conclude that families with an obese father have a higher proportion of male offspring. These results do not support the long-established hypotheses of a sex-linked recessive lethal gene in the etiology of obesity
Correlated random fields in dielectric and spin glasses
Both orientational glasses and dipolar glasses possess an intrinsic random
field, coming from the volume difference between impurity and host ions. We
show this suppresses the glass transition, causing instead a crossover to the
low phase. Moreover the random field is correlated with the inter-impurity
interactions, and has a broad distribution. This leads to a peculiar variant of
the Imry-Ma mechanism, with 'domains' of impurities oriented by a few frozen
pairs. These domains are small: predictions of domain size are given for
specific systems, and their possible experimental verification is outlined. In
magnetic glasses in zero field the glass transition survives, because the
random fields are disallowed by time-reversal symmetry; applying a magnetic
field then generates random fields, and suppresses the spin glass transition.Comment: minor modifications, final versio
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