16,408 research outputs found
Monte Carlo simulations of the classical two-dimensional discrete frustrated model
The classical two-dimensional discrete frustrated model is studied
by Monte Carlo simulations. The correlation function is obtained for two values
of a parameter that determines the frustration in the model. The ground
state is a ferro-phase for and a commensurate phase with period N=6
for . Mean field predicts that at higher temperature the system enters
a para-phase via an incommensurate state, in both cases. Monte Carlo data for
show two phase transitions with a floating-incommensurate phase
between them. The phase transition at higher temperature is of the
Kosterlitz-Thouless type. Analysis of the data for shows only a
single phase transition between the floating-fluid phase and the ferro-phase
within the numerical error.Comment: 5 figures, submitted to the European Physical Journal
Dutch listeners' use of suprasegmental cues to English stress
Dutch listeners outperform native listeners in identifying syllable stress in English. This is because lexical stress is more useful in recognition of spoken words of Dutch than of English, so that Dutch listeners pay greater attention to stress in general. We examined Dutch listeners’ use of the acoustic correlates of English stress. Primary- and secondary-stressed syllables differ significantly on acoustic measures, and some differences, in F0 especially, correlate with data of earlier listening experiments. The correlations found in the Dutch responses were not paralleled in data from native listeners. Thus the acoustic cues which distinguish English primary versus secondary stress are better exploited by Dutch than by native listeners
Towards a Community Framework for Agent-Based Modelling
Agent-based modelling has become an increasingly important tool for scholars studying social and social-ecological systems, but there are no community standards on describing, implementing, testing and teaching these tools. This paper reports on the establishment of the Open Agent-Based Modelling Consortium, www.openabm.org, a community effort to foster the agent-based modelling development, communication, and dissemination for research, practice and education.Replication, Documentation Protocol, Software Development, Standardization, Test Beds, Education, Primitives
Effects of Turbulent Mixing on the Critical Behavior
Effects of strongly anisotropic turbulent mixing on the critical behavior are
studied by means of the renormalization group. Two models are considered: the
equilibrium model A, which describes purely relaxational dynamics of a
nonconserved scalar order parameter, and the Gribov model, which describes the
nonequilibrium phase transition between the absorbing and fluctuating states in
a reaction-diffusion system. The velocity is modelled by the d-dimensional
generalization of the random shear flow introduced by Avellaneda and Majda
within the context of passive scalar advection. Existence of new nonequilibrium
types of critical regimes (universality classes) is established.Comment: Talk given in the International Bogolyubov Conference "Problems of
Theoretical and Mathematical Physics" (Moscow-Dubna, 21-27 August 2009
Obesity Prevalence in the Long-Term Future in 18 European Countries and in the USA
Introduction: Obesity constitutes a major public health problem in Europe, but how the obesity epidemic in European countries will evolve remains unknown. Most previous obesity projections considered the short-term future only, focused on single non-European countries, and projected ongoing increases foremost. We comparatively project obesity prevalence into the long-term future for 18 European countries and the USA. Data: We used national age-specific (20–84 years) and sex-specific obesity prevalence estimates (1975–2016) from the NCD Risk Factor Collaboration (NCD-RisC) 2017 study, which are based on available measured height and weight data, supplemented with estimates from a Bayesian hierarchical model. Methods: We projected age- and sex-specific obesity prevalence up to the year 2100 by integrating the notion of a wave-shaped obesity epidemic into conventional age-period projections. Results: In 1990–2016, the increasing trends in obesity prevalence were decelerating. Obesity is expected to reach maximum levels between 2030 and 2052 among men, and between 2026 and 2054 among women. The maximum levels will likely be reached first in The Netherlands, USA, and UK, and last in Switzerland; and are expected to be highest in the USA and UK, and lowest in The Netherlands for men and Denmark for women. In 2060, obesity prevalence is expected to be lowest among Dutch men and highest among Swiss men. The projected age-specific obesity prevalence levels have an inverse U-shape, peaking at around the age of 60–69 years. Discussion: Applying our novel approach to the NCD-RisC 2017 data, obesity prevalence is expected to reach maximum levels between 2026 and 2054, with the USA and UK reaching the highest maximum levels first, followed by other European countries
Persistence of Manifolds in Nonequilibrium Critical Dynamics
We study the persistence P(t) of the magnetization of a d' dimensional
manifold (i.e., the probability that the manifold magnetization does not flip
up to time t, starting from a random initial condition) in a d-dimensional spin
system at its critical point. We show analytically that there are three
distinct late time decay forms for P(t) : exponential, stretched exponential
and power law, depending on a single parameter \zeta=(D-2+\eta)/z where D=d-d'
and \eta, z are standard critical exponents. In particular, our theory predicts
that the persistence of a line magnetization decays as a power law in the d=2
Ising model at its critical point. For the d=3 critical Ising model, the
persistence of the plane magnetization decays as a power law, while that of a
line magnetization decays as a stretched exponential. Numerical results are
consistent with these analytical predictions.Comment: 4 pages revtex, 1 eps figure include
Short-time Critical Dynamics of the 3-Dimensional Ising Model
Comprehensive Monte Carlo simulations of the short-time dynamic behaviour are
reported for the three-dimensional Ising model at criticality. Besides the
exponent of the critical initial increase and the dynamic exponent
, the static critical exponents and as well as the critical
temperature are determined from the power-law scaling behaviour of observables
at the beginning of the time evolution. States of very high temperature as well
as of zero temperature are used as initial states for the simulations.Comment: 8 pages with 7 figure
Vacuum properties of nonsymmetric gravity in de Sitter space
We consider quantum effects of a massive antisymmetric tensor field on the
dynamics of de Sitter space-time. Our starting point is the most general,
stable, linearized Lagrangian arising in nonsymmetric gravitational theories
(NGTs), where part of the antisymmetric field mass is generated by the
cosmological term. We construct a renormalization group (RG) improved effective
action by integrating out one loop vacuum fluctuations of the antisymmetric
tensor field and show that, in the limit when the RG scale goes to zero, the
Hubble parameter -- and thus the effective cosmological constant -- relaxes
rapidly to zero. We thus conclude that quantum loop effects in de Sitter space
can dramatically change the infrared sector of the on-shell gravity, making the
expansion rate insensitive to the original (bare) cosmological constant.Comment: 32 pages, 2 eps figure
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