6,645 research outputs found
Finite-size-scaling analysis of the XY universality class between two and three dimensions: An application of Novotny's transfer-matrix method
Based on Novotny's transfer-matrix method, we simulated the (stacked)
triangular Ising antiferromagnet embedded in the space with the dimensions
variable in the range 2 \le d \le 3. Our aim is to investigate the criticality
of the XY universality class for 2 \le d \le 3. For that purpose, we employed
an extended version of the finite-size-scaling analysis developed by Novotny,
who utilized this scheme to survey the Ising criticality (ferromagnet) for 1
\le d \le 3. Diagonalizing the transfer matrix for the system sizes N up to
N=17, we calculated the -dependent correlation-length critical exponent
\nu(d). Our simulation result \nu(d) appears to interpolate smoothly the known
two limiting cases, namely, the KT and d=3 XY universality classes, and the
intermediate behavior bears close resemblance to that of the analytical formula
via the 1/N-expansion technique. Methodological details including the
modifications specific to the present model are reported
Comment on ``Density Matrix Renormalization Group Study of the Haldane Phase in Random One-Dimensional Antiferromagnets"
In a recent Letter (PRL 83, 3297 (1999)), Hida presented numerical results
indicating that the Haldane phase of the Heisenberg antiferromagnetic spin-1
chain is stable against bond randomness, for box distributions of the bond
strength, even when the box distribution stretches to zero bond strength. The
author thus concluded that the Haldane phase is stable against bond randomness
for any distribution of the bond strength, no matter how broad. In this
Comment, we (i) point out that the randomness distributions studied in this
Letter do not represent the broadest possible distributions, and therefore
these numerical results do not lead to the conclusion that the Haldane phase is
stable against any randomness; and (ii) provide a semiquantitative estimate of
the critical randomness beyond which the Haldane phase yields to the Random
Singlet phase, in a specific class of random distribution functions for the
bond strength.Comment: A comment on PRL 83, 3297 (1999). One pag
Direct observation of the effective bending moduli of a fluid membrane: Free-energy cost due to the reference-plane deformations
Effective bending moduli of a fluid membrane are investigated by means of the
transfer-matrix method developed in our preceding paper. This method allows us
to survey various statistical measures for the partition sum. The role of the
statistical measures is arousing much attention, since Pinnow and Helfrich
claimed that under a suitable statistical measure, that is, the local mean
curvature, the fluid membranes are stiffened, rather than softened, by thermal
undulations. In this paper, we propose an efficient method to observe the
effective bending moduli directly: We subjected a fluid membrane to a curved
reference plane, and from the free-energy cost due to the reference-plane
deformations, we read off the effective bending moduli. Accepting the
mean-curvature measure, we found that the effective bending rigidity gains even
in the case of very flexible membrane (small bare rigidity); it has been rather
controversial that for such non-perturbative regime, the analytical prediction
does apply. We also incorporate the Gaussian-curvature modulus, and calculated
its effective rigidity. Thereby, we found that the effective Gaussian-curvature
modulus stays almost scale-invariant. All these features are contrasted with
the results under the normal-displacement measure
Time Dependent Pairing Equations for Seniority One Nuclear Systems
When the time dependent Hartree-Fock-Bogoliubov intrinsic equations of motion
are solved in the case of seniority one nuclear systems, the unpaired nucleon
remains on the same orbital. The blocking effect hinders the possibility to
skip from one orbital to another. This unpleasant feature is by-passed with a
new set of pairing time dependent equations that allows the possibility that
the unpaired nucleon changes its single-particle level. These equations
generalize the time dependent Hartree-Fock-Bogoliubov equations of motion by
including the Landau-Zener effect. The derivation of these new equations is
presented in details. These equations are applied in the case of a
superasymmetric fission process, that is, in order to explain the fine
structure the 14C emission from 233Ra. A new version of the Woods-Saxon model
extended for two-center potentials is used in this context.Comment: 12 pages, 6 figure
Construction of an isotropic cellular automaton for a reaction-diffusion equation by means of a random walk
We propose a new method to construct an isotropic cellular automaton
corresponding to a reaction-diffusion equation. The method consists of
replacing the diffusion term and the reaction term of the reaction-diffusion
equation with a random walk of microscopic particles and a discrete vector
field which defines the time evolution of the particles. The cellular automaton
thus obtained can retain isotropy and therefore reproduces the patterns found
in the numerical solutions of the reaction-diffusion equation. As a specific
example, we apply the method to the Belousov-Zhabotinsky reaction in excitable
media
Transfer-matrix approach to the three-dimensional bond percolation: An application of Novotny's formalism
A transfer-matrix simulation scheme for the three-dimensional (d=3) bond
percolation is presented. Our scheme is based on Novotny's transfer-matrix
formalism, which enables us to consider arbitrary (integral) number of sites N
constituting a unit of the transfer-matrix slice even for d=3. Such an
arbitrariness allows us to perform systematic finite-size-scaling analysis of
the criticality at the percolation threshold. Diagonalizing the transfer matrix
for N =4,5,...,10, we obtain an estimate for the correlation-length critical
exponent nu = 0.81(5)
High resolution observations of Cen A: Yellow and red supergiants in a region of jet-induced star formation?
We present the analysis of near infrared (NIR), adaptive optics (AO) Subaru
and archived HST imaging data of a region near the northern middle lobe (NML)
of the Centaurus A (Cen A) jet, at a distance of kpc north-east (NE)
from the center of NGC5128. Low-pass filtering of the NIR images reveals strong
-- above the background mean -- signal at the expected position of
the brightest star in the equivalent HST field. Statistical analysis of the NIR
background noise suggests that the probability to observe signal at
the same position, in three independent measurements due to stochastic
background fluctuations alone is negligible () and, therefore,
that this signal should reflect the detection of the NIR counterparts of the
brightest HST star. An extensive photometric analysis of this star yields
, visual-NIR, and NIR colors expected from a yellow supergiant (YSG) with
an estimated age Myr. Furthermore, the second and third
brighter HST stars are, likely, also supergiants in Cen A, with estimated ages
Myr and Myr, respectively. The ages of
these three supergiants are in good agreement with the ages of the young
massive stars that were previously found in the vicinity and are thought to
have formed during the later phases of the jet-HI cloud interaction that
appears to drive the star formation (SF) in the region for the past
Myr.Comment: 11 pages, 6 figures, 2 tables, accepted for publication in Ap
Scaling Theory of Antiferromagnetic Heisenberg Ladder Models
The antiferromagnetic Heisenberg model on multi-leg ladders is
investigated. Criticality of the ground-state transition is explored by means
of finite-size scaling. The ladders with an even number of legs and those with
an odd number of legs are distinguished clearly. In the former, the energy gap
opens up as , where is the strength of the
antiferromagnetic inter-chain coupling. In the latter, the critical phase with
the central charge extends over the whole region of .Comment: 12 pages with 9 Postscript figures. To appear in J. Phys. A: Math.
Ge
Ricardian Equivalence Under Asymmetric Information
Several empirical studies have found that extended household units do not appear to be highly altruistically linked, thereby violating the very premise of the Ricardian Equivalence Hypothesis (REH). This finding has a very strong implication for the effectiveness of fiscal policies that change the allocation of resources between generations. We build a two-sided altruistic-linkage model in which private transfers are made in the presence of two types of shocks: an “observable” shock that is public information (for example, a public redistribution like debt or pay-as-you-go social security) and an “unobservable” shock that is private information (for example, individual wage innovations). Parents and children observe each other’s total income but not each other’s effort level. In the second-best solution, unobservable shocks are only partially shared, whereas, for any utility function satisfying a condition derived herein, observable shocks are fully shared. The model, therefore, can generate the low degree of risk sharing found in previous empirical studies, but REH still holds
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