561 research outputs found
Singularities of the renormalization group flow for random elastic manifolds
We consider the singularities of the zero temperature renormalization group
flow for random elastic manifolds. When starting from small scales, this flow
goes through two particular points and , where the average value
of the random squared potential turnes negative ($l^{*}$) and where
the fourth derivative of the potential correlator becomes infinite at the
origin ($l_{c}$). The latter point sets the scale where simple perturbation
theory breaks down as a consequence of the competition between many metastable
states. We show that under physically well defined circumstances $l_{c} to negative values does not
take place.Comment: RevTeX, 3 page
Marginal Pinning of Quenched Random Polymers
An elastic string embedded in 3D space and subject to a short-range
correlated random potential exhibits marginal pinning at high temperatures,
with the pinning length becoming exponentially sensitive to
temperature. Using a functional renormalization group (FRG) approach we find
, with the
depinning temperature. A slow decay of disorder correlations as it appears in
the problem of flux line pinning in superconductors modifies this result, .Comment: 4 pages, RevTeX, 1 figure inserte
A condition for first order phase transitions in quantum mechanical tunneling models
A criterion is derived for the determination of parameter domains of first
order phase transitions in quantum mechanical tunneling models. The criterion
is tested by application to various models, in particular to some which have
been used recently to explore spin tunneling in macroscopic particles. In each
case agreement is found with previously heuristically determined domains.Comment: 13 pages, 5 figure
Metastability of (d+n)-dimensional elastic manifolds
We investigate the depinning of a massive elastic manifold with internal
dimensions, embedded in a -dimensional space, and subject to an
isotropic pinning potential The tunneling process is
driven by a small external force We find the zero temperature and
high temperature instantons and show that for the case the
problem exhibits a sharp transition from quantum to classical behavior: At low
temperatures the Euclidean action is constant up to exponentially
small corrections, while for The results are universal and do not depend on the detailed shape
of the trapping potential . Possible applications of the problem to
the depinning of vortices in high- superconductors and nucleation in
-dimensional phase transitions are discussed. In addition, we determine the
high-temperature asymptotics of the preexponential factor for the
-dimensional problem.Comment: RevTeX, 10 pages, 3 figures inserte
A description of a system of programs for mathematically processing on unified series (YeS) computers photographic images of the Earth taken from spacecraft
A description of a batch of programs for the YeS-1040 computer combined into an automated system for processing photo (and video) images of the Earth's surface, taken from spacecraft, is presented. Individual programs with the detailed discussion of the algorithmic and programmatic facilities needed by the user are presented. The basic principles for assembling the system, and the control programs are included. The exchange format within whose framework the cataloging of any programs recommended for the system of processing will be activated in the future is displayed
Free-energy distribution functions for the randomly forced directed polymer
We study the -dimensional random directed polymer problem, i.e., an
elastic string subject to a Gaussian random potential and
confined within a plane. We mainly concentrate on the short-scale and
finite-temperature behavior of this problem described by a short- but
finite-ranged disorder correlator and introduce two types of
approximations amenable to exact solutions. Expanding the disorder potential
at short distances, we study the
random force (or Larkin) problem with as well as the shifted
random force problem including the random offset ; as such, these
models remain well defined at all scales. Alternatively, we analyze the
harmonic approximation to the correlator in a consistent manner.
Using direct averaging as well as the replica technique, we derive the
distribution functions and of free energies
of a polymer of length for both fixed () and free boundary
conditions on the displacement field and determine the mean
displacement correlators on the distance . The inconsistencies encountered
in the analysis of the harmonic approximation to the correlator are traced back
to its non-spectral correlator; we discuss how to implement this approximation
in a proper way and present a general criterion for physically admissible
disorder correlators .Comment: 16 pages, 5 figure
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