10,727 research outputs found
A dimension-breaking phenomenon for water waves with weak surface tension
It is well known that the water-wave problem with weak surface tension has
small-amplitude line solitary-wave solutions which to leading order are
described by the nonlinear Schr\"odinger equation. The present paper contains
an existence theory for three-dimensional periodically modulated solitary-wave
solutions which have a solitary-wave profile in the direction of propagation
and are periodic in the transverse direction; they emanate from the line
solitary waves in a dimension-breaking bifurcation. In addition, it is shown
that the line solitary waves are linearly unstable to long-wavelength
transverse perturbations. The key to these results is a formulation of the
water wave problem as an evolutionary system in which the transverse horizontal
variable plays the role of time, a careful study of the purely imaginary
spectrum of the operator obtained by linearising the evolutionary system at a
line solitary wave, and an application of an infinite-dimensional version of
the classical Lyapunov centre theorem.Comment: The final publication is available at Springer via
http://dx.doi.org/10.1007/s00205-015-0941-
Quantum theory of resonantly enhanced four-wave mixing: mean-field and exact numerical solutions
We present a full quantum analysis of resonant forward four-wave mixing based
on electromagnetically induced transparency (EIT). In particular, we study the
regime of efficient nonlinear conversion with low-intensity fields that has
been predicted from a semiclassical analysis. We derive an effective nonlinear
interaction Hamiltonian in the adiabatic limit. In contrast to conventional
nonlinear optics this Hamiltonian does not have a power expansion in the fields
and the conversion length increases with the input power. We analyze the
stationary wave-mixing process in the forward scattering configuration using an
exact numerical analysis for up to input photons and compare the results
with a mean-field approach. Due to quantum effects, complete conversion from
the two pump fields into the signal and idler modes is achieved only
asymptotically for large coherent pump intensities or for pump fields in
few-photon Fock states. The signal and idler fields are perfectly quantum
correlated which has potential applications in quantum communication schemes.
We also discuss the implementation of a single-photon phase gate for continuous
quantum computation.Comment: 10 pages, 11 figure
Automatic annotation of bioinformatics workflows with biomedical ontologies
Legacy scientific workflows, and the services within them, often present
scarce and unstructured (i.e. textual) descriptions. This makes it difficult to
find, share and reuse them, thus dramatically reducing their value to the
community. This paper presents an approach to annotating workflows and their
subcomponents with ontology terms, in an attempt to describe these artifacts in
a structured way. Despite a dearth of even textual descriptions, we
automatically annotated 530 myExperiment bioinformatics-related workflows,
including more than 2600 workflow-associated services, with relevant
ontological terms. Quantitative evaluation of the Information Content of these
terms suggests that, in cases where annotation was possible at all, the
annotation quality was comparable to manually curated bioinformatics resources.Comment: 6th International Symposium on Leveraging Applications (ISoLA 2014
conference), 15 pages, 4 figure
Large deviations for many Brownian bridges with symmetrised initial-terminal condition
Consider a large system of Brownian motions in with some
non-degenerate initial measure on some fixed time interval with
symmetrised initial-terminal condition. That is, for any , the terminal
location of the -th motion is affixed to the initial point of the
-th motion, where is a uniformly distributed random
permutation of . Such systems play an important role in quantum
physics in the description of Boson systems at positive temperature .
In this paper, we describe the large-N behaviour of the empirical path
measure (the mean of the Dirac measures in the paths) and of the mean of
the normalised occupation measures of the motions in terms of large
deviations principles. The rate functions are given as variational formulas
involving certain entropies and Fenchel-Legendre transforms. Consequences are
drawn for asymptotic independence statements and laws of large numbers.
In the special case related to quantum physics, our rate function for the
occupation measures turns out to be equal to the well-known Donsker-Varadhan
rate function for the occupation measures of one motion in the limit of
diverging time. This enables us to prove a simple formula for the large-N
asymptotic of the symmetrised trace of , where
is an -particle Hamilton operator in a trap
Full quantum solutions to the resonant four-wave mixing of two single-photon wave packets
We analyze both analytically and numerically the resonant four-wave mixing of
two co-propagating single-photon wave packets. We present analytic expressions
for the two-photon wave function and show that soliton-type quantum solutions
exist which display a shape-preserving oscillatory exchange of excitations
between the modes. Potential applications including quantum information
processing are discussed.Comment: 7 pages, 3 figure
Astrophysics from data analysis of spherical gravitational wave detectors
The direct detection of gravitational waves will provide valuable
astrophysical information about many celestial objects. Also, it will be an
important test to general relativity and other theories of gravitation. The
gravitational wave detector SCHENBERG has recently undergone its first test
run. It is expected to have its first scientific run soon. In this work the
data analysis system of this spherical, resonant mass detector is tested
through the simulation of the detection of gravitational waves generated during
the inspiralling phase of a binary system. It is shown from the simulated data
that it is not necessary to have all six transducers operational in order to
determine the source's direction and the wave's amplitudes.Comment: 8 pages and 3 figure
Annealed lower tails for the energy of a polymer
We consider the energy of a randomly charged polymer. We assume that only
charges on the same site interact pairwise. We study the lower tails of the
energy, when averaged over both randomness, in dimension three or more. As a
corollary, we obtain the correct temperature-scale for the Gibbs measure.Comment: 27 page
Quality of Life and Clinical Outcomes in Elderly Patients Treated with Ventricular Pacing as Compared with Dual-Chamber Pacing
ABSTRACT
Background Standard clinical practice permits the use of either single-chamber ventricular pacemakers or dual-chamber pacemakers for most patients who require cardiac pacing. Ventricular pacemakers are less expensive, but dual-chamber pacemakers are believed to be more physiologic. However, it is not known whether either type of pacemaker results in superior clinical outcomes.
Methods The Pacemaker Selection in the Elderly study was a 30-month, single-blind, randomized, controlled comparison of ventricular pacing and dualchamber pacing in 407 patients 65 years of age or older in 29 centers. Patients received a dual-chamber pacemaker that had been randomly programmed to either ventricular pacing or dual-chamber pacing. The primary end point was health-related quality of life as measured by the 36-item Medical Outcomes Study Short-Form General Health Survey.
Results The average age of the patients was 76 years (range, 65 to 96), and 60 percent were men. Quality of life improved significantly after pacemaker implantation (P0.001), but there were no differences between the two pacing modes in either the quality of life or prespecified clinical outcomes (including cardiovascular events or death). However, 53 patients assigned to ventricular pacing (26 percent) were crossed over to dual-chamber pacing because of symptoms related to the pacemaker syndrome. Patients with sinus-node dysfunction, but not those with atrioventricular block, had moderately better quality of life and cardiovascular functional status with dual-chamber pacing than with ventricular pacing. Trends of borderline statistical significance in clinical end points favoring dual-chamber pacing were observed in patients with sinus-node dysfunction, but not in those with atrioventricular block.
Conclusions The implantation of a permanent pacemaker improves health-related quality of life. The quality-of-life benefits associated with dualchamber pacing as compared with ventricular pacing are observed principally in the subgroup of patients with sinus-node dysfunction. (N Engl J Med 1998;338:1097-104.
Fermi super-Tonks-Girardeau state for attractive Fermi gases in an optical lattice
We demonstrate that a kind of highly excited state of strongly attractive
Hubbard model, named of Fermi super-Tonks-Girardeau state, can be realized in
the spin-1/2 Fermi optical lattice system by a sudden switch of interaction
from the strongly repulsive regime to the strongly attractive regime. In
contrast to the ground state of the attractive Hubbard model, such a state is
the lowest scattering state with no pairing between attractive fermions. With
the aid of Bethe-ansatz method, we calculate energies of both the Fermi
Tonks-Girardeau gas and the Fermi super-Tonks-Girardeau state of spin-1/2
ultracold fermions and show that both energies approach to the same limit as
the strength of the interaction goes to infinity. By exactly solving the quench
dynamics of the Hubbard model, we demonstrate that the Fermi
super-Tonks-Girardeau state can be transferred from the initial repulsive
ground state very efficiently. This allows the experimental study of properties
of Fermi super-Tonks-Girardeau gas in optical lattices.Comment: 7 pages, 7 figure
Heat bounds and the blowtorch theorem
We study driven systems with possible population inversion and we give
optimal bounds on the relative occupations in terms of released heat. A precise
meaning to Landauer's blowtorch theorem (1975) is obtained stating that
nonequilibrium occupations are essentially modified by kinetic effects. Towards
very low temperatures we apply a Freidlin-Wentzel type analysis for continuous
time Markov jump processes. It leads to a definition of dominant states in
terms of both heat and escape rates.Comment: 11 pages; v2: minor changes, 1 reference adde
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