15,289 research outputs found
The Exact Ground State of the Frenkel-Kontorova Model with Repeated Parabolic Potential: II. Numerical Treatment
A procedure is described for efficiently finding the ground state energy and
configuration for a Frenkel-Kontorova model in a periodic potential, consisting
of N parabolic segments of identical curvature in each period, through a
numerical solution of the convex minimization problem described in the
preceding paper. The key elements are the use of subdifferentials to describe
the structure of the minimization problem; an intuitive picture of how to solve
it, based on motion of quasiparticles; and a fast linear optimization method
with a reduced memory requirement. The procedure has been tested for N up to
200.Comment: 9 RevTeX pages, using AMS-Fonts (amssym.tex,amssym.def), 3 Postscript
figures, accepted by Phys.Rev.B to be published together with
cond-mat/970722
Full Sky Study of Diffuse Galactic Emission at Decimeter Wavelengths
A detailed knowledge of the Galactic radio continuum is of high interest for
studies of the dynamics and structure of the Galaxy as well as for the problem
of foreground removal in Cosmic Microwave Background measurements. In this work
we present a full-sky study of the diffuse Galactic emission at frequencies of
few GHz, where synchrotron radiation is by far the dominant component. We
perform a detailed combined analysis of the extended surveys at 408, 1420 and
2326 MHz (by Haslam et al. 1982, Reich 1982, Reich & Reich, 1986 and Jonas et
al. 1998, respectively). Using the technique applied by Schlegel et al. (1998)
to the IRAS data, we produce destriped versions of the three maps. This allows
us to construct a nearly-full-sky map of the spectral index and of the
normalization factor with sub-degree angular resolution. The resulting
distribution of the spectral indices has an average of beta = 2.695 and
dispersion sigma_{beta} = 0.120. This is representative for the Galactic
diffuse synchrotron emission, with only minor effects from free-free emission
and point sources.Comment: 10 pages, 16 jpeg figures, accepted to Astronomy & Astrophysics,
Comments and figure adde
A Compact Linear Programming Relaxation for Binary Sub-modular MRF
We propose a novel compact linear programming (LP) relaxation for binary
sub-modular MRF in the context of object segmentation. Our model is obtained by
linearizing an -norm derived from the quadratic programming (QP) form of
the MRF energy. The resultant LP model contains significantly fewer variables
and constraints compared to the conventional LP relaxation of the MRF energy.
In addition, unlike QP which can produce ambiguous labels, our model can be
viewed as a quasi-total-variation minimization problem, and it can therefore
preserve the discontinuities in the labels. We further establish a relaxation
bound between our LP model and the conventional LP model. In the experiments,
we demonstrate our method for the task of interactive object segmentation. Our
LP model outperforms QP when converting the continuous labels to binary labels
using different threshold values on the entire Oxford interactive segmentation
dataset. The computational complexity of our LP is of the same order as that of
the QP, and it is significantly lower than the conventional LP relaxation
Isotropic inverse-problem approach for two-dimensional phase unwrapping
In this paper, we propose a new technique for two-dimensional phase
unwrapping. The unwrapped phase is found as the solution of an inverse problem
that consists in the minimization of an energy functional. The latter includes
a weighted data-fidelity term that favors sparsity in the error between the
true and wrapped phase differences, as well as a regularizer based on
higher-order total-variation. One desirable feature of our method is its
rotation invariance, which allows it to unwrap a much larger class of images
compared to the state of the art. We demonstrate the effectiveness of our
method through several experiments on simulated and real data obtained through
the tomographic phase microscope. The proposed method can enhance the
applicability and outreach of techniques that rely on quantitative phase
evaluation
An hybrid Tykhonov method for neutron spectrum unfolding
An hybrid iterative Tykhonov regularization approach with an accelerating
algorithm is considered. This method is illustrated by two neutron spectrum
unfoldings measured with a Bonner Sphere system.Comment: 19 pages, work done at IRS
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