2,904 research outputs found
Convergence of adaptive and interacting Markov chain Monte Carlo algorithms
Adaptive and interacting Markov chain Monte Carlo algorithms (MCMC) have been
recently introduced in the literature. These novel simulation algorithms are
designed to increase the simulation efficiency to sample complex distributions.
Motivated by some recently introduced algorithms (such as the adaptive
Metropolis algorithm and the interacting tempering algorithm), we develop a
general methodological and theoretical framework to establish both the
convergence of the marginal distribution and a strong law of large numbers.
This framework weakens the conditions introduced in the pioneering paper by
Roberts and Rosenthal [J. Appl. Probab. 44 (2007) 458--475]. It also covers the
case when the target distribution is sampled by using Markov transition
kernels with a stationary distribution that differs from .Comment: Published in at http://dx.doi.org/10.1214/11-AOS938 the Annals of
Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical
Statistics (http://www.imstat.org
Quantum Global Strings and Their Correlation Functions
A full quantum description of global vortex strings is presented in the
framework of a pure Higgs system with a broken global U(1) symmetry in 3+1D. An
explicit expression for the string creation operator is obtained, both in terms
of the Higgs field and in the dual formulation where a Kalb-Ramond
antisymmetric tensor gauge field is employed as the basic field. The quantum
string correlation function is evaluated and from this, the string energy
density is obtained. Potential application in cosmology (cosmic strings) and
condensed matter (vortices in superfluids) are discussed.Comment: 14 pages, latex, no figure
Efficiency of the Wang-Landau algorithm: a simple test case
We analyze the efficiency of the Wang-Landau algorithm to sample a multimodal
distribution on a prototypical simple test case. We show that the exit time
from a metastable state is much smaller for the Wang Landau dynamics than for
the original standard Metropolis-Hastings algorithm, in some asymptotic regime.
Our results are confirmed by numerical experiments on a more realistic test
case
Dipolar interaction and incoherent quantum tunneling: a Monte Carlo study of magnetic relaxation
We study the magnetic relaxation of a system of localized spins interacting
through weak dipole interactions, at a temperature large with respect to the
ordering temperature but low with respect to the crystal field level splitting.
The relaxation results from quantum spin tunneling but is only allowed on sites
where the dipole field is very small. At low times, the magnetization decrease
is proportional to as predicted by Prokofiev and Stamp, and at long
times the relaxation can be described as an extension of a relaxed zone. The
results can be directly compared with very recent experimental data on Fe_8
molecular clusters.Comment: 9 pages, 11 figures; accepted for publication on Eur. Phys. J.
Test of Information Theory on the Boltzmann Equation
We examine information theory using the steady-state Boltzmann equation. In a
nonequilibrium steady-state system under steady heat conduction, the
thermodynamic quantities from information theory are calculated and compared
with those from the steady-state Boltzmann equation. We have found that
information theory is inconsistent with the steady-state Boltzmann equation.Comment: 12 page
Reduction of tilt rotor download using circulation control
The effect of boundary layer control blowing on the download of a wing in the wake of a hovering rotor was measured in a small scale experiment. The objective was to evaluate the potential of boundary layer control blowing for reducing tilt rotor download. Variations were made in rotor thrust coefficient, blowing pressure ratio, and blowing slot height. The effect of these parameter variations on the wing download and wing surface pressures is presented. The boundary layer control blowing caused reductions in the wing download of 25 to 55 percent
Gravitational Lensing & Stellar Dynamics
Strong gravitational lensing and stellar dynamics provide two complementary
and orthogonal constraints on the density profiles of galaxies. Based on
spherically symmetric, scale-free, mass models, it is shown that the
combination of both techniques is powerful in breaking the mass-sheet and
mass-anisotropy degeneracies. Second, observational results are presented from
the Lenses Structure & Dynamics (LSD) Survey and the Sloan Lens ACS (SLACS)
Survey collaborations to illustrate this new methodology in constraining the
dark and stellar density profiles, and mass structure, of early-type galaxies
to redshifts of unity.Comment: 6 pages, 2 figures; Invited contribution in the Proceedings of XXIst
IAP Colloquium, "Mass Profiles & Shapes of Cosmological Structures" (Paris,
4-9 July 2005), eds G. A. Mamon, F. Combes, C. Deffayet, B. Fort (Paris: EDP
Sciences
The New Laches: Creating Title Where None Existed
Article published in the George Mason Law Review
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