7,160 research outputs found
Reversibility Violation in the Hybrid Monte Carlo Algorithm
We investigate reversibility violations in the Hybrid Monte Carlo algorithm.
Those violations are inevitable when computers with finite numerical precision
are being used. In SU(2) gauge theory, we study the dependence of observables
on the size of the reversibility violations. While we cannot find any
statistically significant deviation in observables related to the simulated
physical model, algorithmic specific observables signal an upper bound for
reversibility violations below which simulations appear unproblematic. This
empirically derived condition is independent of problem size and parameter
values, at least in the range of parameters studied here.Comment: 17 pages, 5 figures, typos corrected, comment added, matches
published versio
Two-dimensional melting far from equilibrium in a granular monolayer
We report an experimental investigation of the transition from a hexagonally
ordered solid phase to a disordered liquid in a monolayer of vibrated spheres.
The transition occurs as the intensity of the vibration amplitude is increased.
Measurements of the density of dislocations and the positional and
orientational correlation functions show evidence for a dislocation-mediated
continuous transition from a solid phase with long-range order to a liquid with
only short-range order. The results show a strong similarity to simulations of
melting of hard disks in equilibrium, despite the fact that the granular
monolayer is far from equilibrium due to the effects of interparticle
dissipation and the vibrational forcing.Comment: 4 pages, 4 figure
Flavor-singlet meson decay constants from twisted mass lattice QCD
We present an improved analysis of our lattice data for the --
system, including a correction of the relevant correlation functions for
residual topological finite size effects and employing consistent chiral and
continuum fits. From this analysis we update our physical results for the
masses and
, as well
as the mixing angle in the quark flavor basis
in excellent
agreement with other results from phenomenology. Similarly, we include an
analysis for the decay constant parameters, leading to
and
. The second error
reflects the uncertainty related to the chiral extrapolation. The data used for
this study has been generated on gauge ensembles provided by the European
Twisted Mass Collaboration with dynamical flavors of Wilson twisted
mass fermions. These ensembles cover a range of pion masses from
to and three values of the lattice
spacing. Combining our data with a prediction from chiral perturbation theory,
we give an estimate for the physical
decay widths and the singly-virtual
transition form factors in the limit of large momentum transfer.Comment: 22 pages, 8 figures, 12 tables; matching version accepted for
publicatio
Effect of inelasticity on the phase transitions of a thin vibrated granular layer
We describe an experimental and computational investigation of the ordered
and disordered phases of a vibrating thin, dense granular layer composed of
identical metal spheres. We compare the results from spheres with different
amounts of inelasticity and show that inelasticity has a strong effect on the
phase diagram. We also report the melting of an ordered phase to a homogeneous
disordered liquid phase at high vibration amplitude or at large inelasticities.
Our results show that dissipation has a strong effect on ordering and that in
this system ordered phases are absent entirely in highly inelastic materials.Comment: 5 pages, 5 figures, published in Physical Review E. Title of first
version slightly change
Retrieving the Size of Deep-subwavelength Objects via Tunable Optical Spin-Orbit Coupling
We propose a scheme to retrieve the size parameters of a nano-particle on a
glass substrate at a scale much smaller than the wavelength. This is achieved
by illuminating the particle using two plane waves to create rich and
non-trivial local polarization distributions, and observing the far-field
scattering pattern into the substrate. A simple dipole model which exploits
tunneling effect of evanescent field into regions beyond the critical angle, as
well as directional scattering due to spin-orbit coupling is developed, to
relate the particle's shape, size and position to the far-field scattering with
remarkable sensitivity. Our method brings about a far-field super-resolution
imaging scheme based on the interaction of vectorial light with nanoparticles
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