403,741 research outputs found
Relativistic Coulomb Green's function in -dimensions
Using the operator method, the Green's functions of the Dirac and
Klein-Gordon equations in the Coulomb potential are derived for
the arbitrary space dimensionality . Nonrelativistic and quasiclassical
asymptotics of these Green's functions are considered in detail.Comment: 9 page
Some aspects of geological information contained in LANDSAT images
The characteristics of MSS images and methods of interpretation are analyzed from a geological point of view. The supportive role of LANDSAT data are illustrated in several examples of surface expressions of geological features, such as synclines and anticlines, spectral characteristics of lithologic units, and circular impact structures
Mechanisms limiting the coherence time of spontaneous magnetic oscillations driven by DC spin-polarized currents
The spin-transfer torque from a DC spin-polarized current can generate
highly-coherent magnetic precession in nanoscale magnetic-multilayer devices.
By measuring linewidths of spectra from the resulting resistance oscillations,
we argue that the coherence time can be limited at low temperature by thermal
deflections about the equilibrium magnetic trajectory, and at high temperature
by thermally-activated transitions between dynamical modes. Surprisingly, the
coherence time can be longer than predicted by simple macrospin simulations.Comment: 12 pages, 4 figure
A Maximally Symmetric Vector Propagator
We derive the propagator for a massive vector field on a de Sitter background
of arbitrary dimension. This propagator is de Sitter invariant and possesses
the proper flat spacetime and massless limits. Moreover, the retarded Green's
function inferred from it produces the correct classical response to a test
source. Our result is expressed in a tensor basis which is convenient for
performing quantum field theory computations using dimensional regularization.Comment: 21 pages, no figures, uses LaTeX 2 epsilon, version 2 has an error in
eqn (86) corrected and an updated reference lis
Vortex Viscosity in Magnetic Superconductors Due to Radiation of Spin Waves
In type-II superconductors that contain a lattice of magnetic moments,
vortices polarize the magnetic system inducing additional contributions to the
vortex mass, vortex viscosity, and vortex-vortex interaction. Extra magnetic
viscosity is caused by radiation of spin waves by a moving vortex. Like in the
case of Cherenkov radiation, this effect has a characteristic threshold
behavior and the resulting vortex viscosity may be comparable to the well-known
Bardeen-Stephen contribution. The threshold behavior leads to an anomaly in the
current-voltage characteristics, and a drop in dissipation for a current
interval that is determined by the magnetic excitation spectrum.Comment: 4 pages, 1 figur
Advection-dominated Inflow/Outflows from Evaporating Accretion Disks
In this Letter we investigate the properties of advection-dominated accretion
flows (ADAFs) fed by the evaporation of a Shakura-Sunyaev accretion disk (SSD).
In our picture the ADAF fills the central cavity evacuated by the SSD and
extends beyond the transition radius into a coronal region. We find that,
because of global angular momentum conservation, a significant fraction of the
hot gas flows away from the black hole forming a transsonic wind, unless the
injection rate depends only weakly on radius (if , ). The Bernoulli number of the inflowing gas is negative
if the transition radius is Schwarzschild radii, so matter
falling into the hole is gravitationally bound. The ratio of inflowing to
outflowing mass is , so in these solutions the accretion rate is
of the same order as in standard ADAFs and much larger than in
advection-dominated inflow/outflow models (ADIOS). The possible relevance of
evaporation-fed solutions to accretion flows in black hole X-ray binaries is
briefly discussed.Comment: 5 pages Latex with 2 ps figures. Accepted for publication in ApJ
Letter
Bose-Einstein-condensed gases in arbitrarily strong random potentials
Bose-Einstein-condensed gases in external spatially random potentials are
considered in the frame of a stochastic self-consistent mean-field approach.
This method permits the treatment of the system properties for the whole range
of the interaction strength, from zero to infinity, as well as for arbitrarily
strong disorder. Besides a condensate and superfluid density, a glassy number
density due to a spatially inhomogeneous component of the condensate occurs.
For very weak interactions and sufficiently strong disorder, the superfluid
fraction can become smaller than the condensate fraction, while at relatively
strong interactions, the superfluid fraction is larger than the condensate
fraction for any strength of disorder. The condensate and superfluid fractions,
and the glassy fraction always coexist, being together either nonzero or zero.
In the presence of disorder, the condensate fraction becomes a nonmonotonic
function of the interaction strength, displaying an antidepletion effect caused
by the competition between the stabilizing role of the atomic interaction and
the destabilizing role of the disorder. With increasing disorder, the
condensate and superfluid fractions jump to zero at a critical value of the
disorder parameter by a first-order phase transition
Triplectic Quantization of W2 gravity
The role of one loop order corrections in the triplectic quantization is
discussed in the case of W2 theory. This model illustrates the presence of
anomalies and Wess Zumino terms in this quantization scheme where extended BRST
invariance is represented in a completely anticanonical form.Comment: 10 pages, no figure
Non-Ground-State Bose-Einstein Condensates of Trapped Atoms
The possibility of creating a Bose condensate of trapped atoms in a
non-ground state is suggested. Such a nonequilibrium Bose condensate can be
formed if one, first, obtains the conventional Bose condensate in the ground
state and then transfers the condensed atoms to a non-ground state by means of
a resonance pumping. The properties of ground and non-ground states are
compared and plausible applications of such nonequilibrium condensates are
discussed.Comment: 1 file, 16 pages, RevTe
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