5,441 research outputs found
Non-localities in nucleon-nucleus potentials
Two causes of non-locality inherent in nucleon-nucleus scattering are
considered. They are the results of two-nucleon antisymmetry of the projectile
with each nucleon in the nucleus and the dynamic polarization potential
representation of channel coupling. For energies MeV, a
g-folding model of the optical potential is used to show the influence of the
knock-out process that is a result of the two-nucleon antisymmetry. To explore
the dynamic polarization potential caused by channel coupling, a multichannel
algebraic scattering model has been used for low-energy scattering.Comment: 12 pages, 11 figures, submitted to EPJ
Transport of magnetic vortices by surface acoustic waves
In a thin film of superconducting YBCO the impact of surface acoustic waves
(SAWs) traveling on the piezoelectric substrate is investigated. A pronounced
interaction between the ultrasonic waves and the vortex system in the type II
superconductor is observed. The occurrence of a SAW-induced dc voltage
perpendicular to the sound path is interpreted as {\em dynamic pinning} of
vortices by the piezoacoustic SAW, which acts as a conveyor for the fluxquanta.
Its antisymmetry with respect to the magnetic field directly evidences the
induced, directed flux motion.This dynamic manipulation of vortices can be seen
as an important step towards flux-based electronic devices.Comment: submitte
Symmetries in Images on Ancient Seals
We discuss the presence of symmetries in images engraved on ancient seals, in
particular on stamp seals. Used to stamp decorations, to secure the containers
from tampering and for owner's identification, we can find seals that can be
dated from Neolithic times. Earliest seals were engraved with lines, dots and
spirals. Nevertheless, these very ancient stamp seals, in the small circular or
ovoid space of their bases, possess bilateral and rotational symmetries. The
shape of the base seems to determine the symmetries of images engraved on it.
We will also discuss what could be the meaning of antisymmetry and broken
symmetry for images on seals.Comment: CogPrints, University of Southampton, ID6221, 16 October 200
A class of random walks in reversible dynamic environment: antisymmetry and applications to the East model
We introduce via perturbation a class of random walks in reversible dynamic
environments having a spectral gap. In this setting one can apply the
mathematical results derived in http://arxiv.org/abs/1602.06322. As first
results, we show that the asymptotic velocity is antisymmetric in the
perturbative parameter and, for a subclass of random walks, we characterize the
velocity and a stationary distribution of the environment seen from the walker
as suitable series in the perturbative parameter. We then consider as a special
case a random walk on the East model that tends to follow dynamical interfaces
between empty and occupied regions. We study the asymptotic velocity and
density profile for the environment seen from the walker. In particular, we
determine the sign of the velocity when the density of the underlying East
process is not 1/2, and we discuss the appearance of a drift in the balanced
setting given by density 1/2
Correlations in self-bound systems of identical fermions
A method for the calculation of translationally invariant wave functions for
systems of identical fermions with arbitrary potential of pair interaction is
developed. It is based on the well-known result that the essential dynamic part
of the Hamiltonian for the system of identical particles is the Reduced
Hamiltonian operator describing relative movement of two particles inside the
system. The eigenfunctions of this operator take into account all correlations
caused by interaction. These eigenfunctions are basic for the construction of
the components (i.e. the functions with a lower degree of antisymmetry) of the
system wave functions. The main problem of this approach appears to be
antisymmetrization of the components. The developed universal algorithm for
antisymmetrization gives a possibility to perform this operation in a simple
way and keep numerical approximations under control.Comment: 20 pages REVTeX, submitted to Lithuanian J. Phy
The Structure of High Strehl Ratio Point-Spread Functions
We describe the symmetries present in the point-spread function (PSF) of an
optical system either located in space or corrected by an adaptive o to Strehl
ratios of about 70% and higher. We present a formalism for expanding the PSF to
arbitrary order in terms of powers of the Fourier transform of the residual
phase error, over an arbitrarily shaped and apodized entrance aperture. For
traditional unapodized apertures at high Strehl ratios, bright speckles pinned
to the bright Airy rings are part of an antisymmetric perturbation of the
perfect PSF, arising from the term that is first order in the residual phase
error. There are two symmetric second degree terms. One is negative at the
center, and, like the first order term, is modulated by the perfect image's
field strength -- it reduces to the Marechal approximation at the center of the
PSF. The other is non-negative everywhere, zero at the image center, and can be
responsible for an extended halo -- which limits the dynamic range of faint
companion detection in the darkest portions of the image. In regimes where one
or the other term dominates the speckles in an image, the symmetry of the
dominant term can be exploited to reduce the effect of those speckles,
potentially by an order of magnitude or more. We demonstrate the effects of
both secondary obscuration and pupil apodization on the structure of residual
speckles, and discuss how these symmetries can be exploited by appropriate
telescope and instrument design, observing strategies, and filter bandwidths to
improve the dynamic range of high dynamic range AO and space-based
observations. Finally, we show that our analysis is relevant to high dynamic
range coronagraphy.Comment: Accepted for publication in ApJ; 20 pages, 4 figure
Towards a Generic Trace for Rule Based Constraint Reasoning
CHR is a very versatile programming language that allows programmers to
declaratively specify constraint solvers. An important part of the development
of such solvers is in their testing and debugging phases. Current CHR
implementations support those phases by offering tracing facilities with
limited information. In this report, we propose a new trace for CHR which
contains enough information to analyze any aspects of \CHRv\ execution at some
useful abstract level, common to several implementations. %a large family of
rule based solvers. This approach is based on the idea of generic trace. Such a
trace is formally defined as an extension of the semantics of
CHR. We show that it can be derived form the SWI Prolog CHR trace
Partitioning strategy for efficient nonlinear finite element dynamic analysis on multiprocessor computers
A computational procedure is presented for the nonlinear dynamic analysis of unsymmetric structures on vector multiprocessor systems. The procedure is based on a novel hierarchical partitioning strategy in which the response of the unsymmetric and antisymmetric response vectors (modes), each obtained by using only a fraction of the degrees of freedom of the original finite element model. The three key elements of the procedure which result in high degree of concurrency throughout the solution process are: (1) mixed (or primitive variable) formulation with independent shape functions for the different fields; (2) operator splitting or restructuring of the discrete equations at each time step to delineate the symmetric and antisymmetric vectors constituting the response; and (3) two level iterative process for generating the response of the structure. An assessment is made of the effectiveness of the procedure on the CRAY X-MP/4 computers
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