1,913 research outputs found
Universal Dynamics of Independent Critical Relaxation Modes
Scaling behavior is studied of several dominant eigenvalues of spectra of
Markov matrices and the associated correlation times governing critical slowing
down in models in the universality class of the two-dimensional Ising model. A
scheme is developed to optimize variational approximants of progressively
rapid, independent relaxation modes. These approximants are used to reduce the
variance of results obtained by means of an adaptation of a quantum Monte Carlo
method to compute eigenvalues subject to errors predominantly of statistical
nature. The resulting spectra and correlation times are found to be universal
up to a single, non-universal time scale for each model
Monte Carlo computation of correlation times of independent relaxation modes at criticality
We investigate aspects of universality of Glauber critical dynamics in two
dimensions. We compute the critical exponent and numerically corroborate
its universality for three different models in the static Ising universality
class and for five independent relaxation modes. We also present evidence for
universality of amplitude ratios, which shows that, as far as dynamic behavior
is concerned, each model in a given universality class is characterized by a
single non-universal metric factor which determines the overall time scale.
This paper also discusses in detail the variational and projection methods that
are used to compute relaxation times with high accuracy
Finite temperature results on the 2d Ising model with mixed perturbation
A numerical study of finite temperature features of thermodynamical
observables is performed for the lattice 2d Ising model. Our results support
the conjecture that the Finite Size Scaling analysis employed in the study of
integrable perturbation of Conformal Field Theory is still valid in the present
case, where a non-integrable perturbation is considered.Comment: 9 pages, Latex, added references and improved introductio
Death is not a success: reflections on business exit
This article is a critical evaluation of claims that business exits should not be seen as failures, on the grounds that may constitute voluntary liquidation, or because they are learning opportunities. This can be seen as further evidence of bias affecting entrepreneurship research, where failures are repackaged as successes. This article reiterates that the majority of business exits are unsuccessful. Drawing on ideas from the organisational life course, it is suggested that business âdeathâ is a suitable term for describing business closure. Even cases of voluntary âharvest liquidationâ such as retirement can be meaningfully described as business deaths
Critical line of an n-component cubic model
We consider a special case of the n-component cubic model on the square
lattice, for which an expansion exists in Ising-like graphs. We construct a
transfer matrix and perform a finite-size-scaling analysis to determine the
critical points for several values of n. Furthermore we determine several
universal quantities, including three critical exponents. For n<2, these
results agree well with the theoretical predictions for the critical O(n)
branch. This model is also a special case of the () model of
Domany and Riedel. It appears that the self-dual plane of the latter model
contains the exactly known critical points of the n=1 and 2 cubic models. For
this reason we have checked whether this is also the case for 1<n<2. However,
this possibility is excluded by our numerical results
Comment on "Two Phase Transitions in the Fully frustrated XY Model"
The conclusions of a recent paper by Olsson (Phys. Rev. Lett. 75, 2758
(1995), cond-mat/9506082) about the fully frustrated XY model in two dimensions
are questioned. In particular, the evidence presented for having two separate
chiral and U(1) phase transitions are critically considered.Comment: One page one table, to Appear in Physical Review Letter
The Dynamic Exponent of the Two-Dimensional Ising Model and Monte Carlo Computation of the Sub-Dominant Eigenvalue of the Stochastic Matrix
We introduce a novel variance-reducing Monte Carlo algorithm for accurate
determination of autocorrelation times. We apply this method to two-dimensional
Ising systems with sizes up to , using single-spin flip dynamics,
random site selection and transition probabilities according to the heat-bath
method. From a finite-size scaling analysis of these autocorrelation times, the
dynamical critical exponent is determined as (12)
Magnetization reversal times in the 2D Ising model
We present a theoretical framework which is generally applicable to the study
of time scales of activated processes in systems with Brownian type dynamics.
This framework is applied to a prototype system: magnetization reversal times
in the 2D Ising model. Direct simulation results for the magnetization reversal
times, spanning more than five orders of magnitude, are compared with
theoretical predictions; the two agree in most cases within 20%.Comment: 9 pages, 8 figure
High precision Monte Carlo study of the 3D XY-universality class
We present a Monte Carlo study of the two-component model on the
simple cubic lattice in three dimensions. By suitable tuning of the coupling
constant we eliminate leading order corrections to scaling. High
statistics simulations using finite size scaling techniques yield
and , where the statistical and
systematical errors are given in the first and second bracket, respectively.
These results are more precise than any previous theoretical estimate of the
critical exponents for the 3D XY universality class.Comment: 13 page
Finite-size scaling corrections in two-dimensional Ising and Potts ferromagnets
Finite-size corrections to scaling of critical correlation lengths and free
energies of Ising and three-state Potts ferromagnets are analysed by numerical
methods, on strips of width sites of square, triangular and honeycomb
lattices. Strong evidence is given that the amplitudes of the ``analytical''
correction terms, , are identically zero for triangular-- and honeycomb
Ising systems. For Potts spins, our results are broadly consistent with this
lattice-dependent pattern of cancellations, though for correlation lengths
non-vanishing (albeit rather small) amplitudes cannot be entirely ruled out.Comment: 11 pages, LaTeX with Institute of Physics macros, 2 EPS figures; to
appear in Journal of Physics
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