35,413 research outputs found
Keldysh action for disordered superconductors
Keldysh representation of the functional integral for the interacting
electron system with disorder is used to derive microscopically an effective
action for dirty superconductors. In the most general case this action is a
functional of the 8 x 8 matrix Q(t,t') which depends on two time variables, and
on the fluctuating order parameter field and electric potential. We show that
this approach reproduces, without the use of the replica trick, the well-known
result for the Coulomb-induced renormalization of the electron-electron
coupling constant in the Cooper channel. Turning to the new results, we
calculate the effects of the Coulomb interaction upon: i) the subgap Andreev
conductance between superconductor and 2D dirty normal metal, and ii) the
Josephson proximity coupling between superconductive islands via such a metal.
These quantities are shown to be strongly suppressed by the Coulomb interaction
at sufficiently low temperatures due to both zero-bias anomaly in the density
of states and disorder-enhanced repulsion in the Cooper channel.Comment: RevTeX; 39 pages + 10 EPS figure
Design and Performance of the Wide-Field X-Ray Monitor on Board the High-Energy Transient Explorer 2
The Wide-field X-ray Monitor (WXM) is one of the scientific instruments
carried on the High Energy Transient Explorer 2 (HETE-2) satellite launched on
2000 October 9. HETE-2 is an international mission consisting of a small
satellite dedicated to provide broad-band observations and accurate
localizations of gamma-ray bursts (GRBs). A unique feature of this mission is
its capability to determine and transmit GRB coordinates in almost real-time
through the burst alert network. The WXM consists of three elements: four
identical Xe-filled one-dimensional position-sensitive proportional counters,
two sets of one-dimensional coded apertures, and the main electronics. The WXM
counters are sensitive to X-rays between 2 keV and 25 keV within a
field-of-view of about 1.5 sr, with a total detector area of about 350 cm.
The in-flight triggering and localization capability can produce a real-time
GRB location of several to 30 arcmin accuracy, with a limiting sensitivity of
erg cm. In this report, the details of the mechanical
structure, electronics, on-board software, ground and in-flight calibration,
and in-flight performance of the WXM are discussed.Comment: 28 pages, 24 figure
Quasiclassical theory of charge transport in disordered interacting electron systems
We consider the corrections to the Boltzmann theory of electrical transport
arising from the Coulomb interaction in disordered conductors. In this article
the theory is formulated in terms of quasiclassical Green's functions. We
demonstrate that the formalism is equivalent to the conventional diagrammatic
technique by deriving the well-known Altshuler-Aronov corrections to the
conductivity. Compared to the conventional approach, the quasiclassical theory
has the advantage of being closer to the Boltzmann theory, and also allows
description of interaction effects in the transport across interfaces, as well
as non-equilibrium phenomena in the same theoretical framework. As an example,
by applying the Zaitsev boundary conditions which were originally developed for
superconductors, we obtain the -theory of the Coulomb blockade in tunnel
junctions. Furthermore we summarize recent results obtained for the
non-equilibrium transport in thin films, wires and fully coherent conductors.Comment: 46 pages; review articl
Localization properties of the anomalous diffusion phase in the directed trap model and in the Sinai diffusion with bias
We study the anomalous diffusion phase with which
exists both in the Sinai diffusion at small bias, and in the related directed
trap model presenting a large distribution of trapping time . Our starting point is the Real Space Renormalization method in
which the whole thermal packet is considered to be in the same renormalized
valley at large time : this assumption is exact only in the limit
and corresponds to the Golosov localization. For finite , we thus
generalize the usual RSRG method to allow for the spreading of the thermal
packet over many renormalized valleys. Our construction allows to compute exact
series expansions in of all observables : at order , it is
sufficient to consider a spreading of the thermal packet onto at most
traps in each sample, and to average with the appropriate measure over the
samples. For the directed trap model, we show explicitly up to order
how to recover the diffusion front, the thermal width, and the localization
parameter . We moreover compute the localization parameters for
arbitrary
, the correlation function of two particles, and the generating function
of thermal cumulants. We then explain how these results apply to the Sinai
diffusion with bias, by deriving the quantitative mapping between the
large-scale renormalized descriptions of the two models.Comment: 33 pages, 3 eps figure
On-Manifold Preintegration for Real-Time Visual-Inertial Odometry
Current approaches for visual-inertial odometry (VIO) are able to attain
highly accurate state estimation via nonlinear optimization. However, real-time
optimization quickly becomes infeasible as the trajectory grows over time, this
problem is further emphasized by the fact that inertial measurements come at
high rate, hence leading to fast growth of the number of variables in the
optimization. In this paper, we address this issue by preintegrating inertial
measurements between selected keyframes into single relative motion
constraints. Our first contribution is a \emph{preintegration theory} that
properly addresses the manifold structure of the rotation group. We formally
discuss the generative measurement model as well as the nature of the rotation
noise and derive the expression for the \emph{maximum a posteriori} state
estimator. Our theoretical development enables the computation of all necessary
Jacobians for the optimization and a-posteriori bias correction in analytic
form. The second contribution is to show that the preintegrated IMU model can
be seamlessly integrated into a visual-inertial pipeline under the unifying
framework of factor graphs. This enables the application of
incremental-smoothing algorithms and the use of a \emph{structureless} model
for visual measurements, which avoids optimizing over the 3D points, further
accelerating the computation. We perform an extensive evaluation of our
monocular \VIO pipeline on real and simulated datasets. The results confirm
that our modelling effort leads to accurate state estimation in real-time,
outperforming state-of-the-art approaches.Comment: 20 pages, 24 figures, accepted for publication in IEEE Transactions
on Robotics (TRO) 201
Non-Hermitian Localization and Population Biology
The time evolution of spatial fluctuations in inhomogeneous d-dimensional
biological systems is analyzed. A single species continuous growth model, in
which the population disperses via diffusion and convection is considered.
Time-independent environmental heterogeneities, such as a random distribution
of nutrients or sunlight are modeled by quenched disorder in the growth rate.
Linearization of this model of population dynamics shows that the fastest
growing localized state dominates in a time proportional to a power of the
logarithm of the system size. Using an analogy with a Schrodinger equation
subject to a constant imaginary vector potential, we propose a delocalization
transition for the steady state of the nonlinear problem at a critical
convection threshold separating localized and extended states. In the limit of
high convection velocity, the linearized growth problem in dimensions
exhibits singular scaling behavior described by a (d-1)-dimensional
generalization of the noisy Burgers' equation, with universal singularities in
the density of states associated with disorder averaged eigenvalues near the
band edge in the complex plane. The Burgers mapping leads to unusual transverse
spreading of convecting delocalized populations.Comment: 22 pages, 11 figure
Finite Size Effects in Vortex Localization
The equilibrium properties of flux lines pinned by columnar disorder are
studied, using the analogy with the time evolution of a diffusing scalar
density in a randomly amplifying medium. Near H_{c1}, the physical features of
the vortices in the localized phase are shown to be determined by the density
of states near the band edge. As a result, H_{c1} is inversely proportional to
the logarithm of the sample size, and the screening length of the perpendicular
magnetic field decreases with temperature. For large tilt the extended ground
state turns out to wander in the plane perpendicular to the defects with
exponents corresponding to a directed polymer in a random medium, and the
energy difference between two competing metastable states in this case is
extensive. The divergence of the effective potential associated with strong
pinning centers as the tilt approaches its critical value is discussed as well.Comment: 10 pages, 2 figure
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