3,228 research outputs found
On asymptotic stability of the Skyrmion
We study the asymptotic behavior of spherically symmetric solutions in the
Skyrme model. We show that the relaxation to the degree-one soliton (called the
Skyrmion) has a universal form of a superposition of two effects: exponentially
damped oscillations (the quasinormal ringing) and a power law decay (the tail).
The quasinormal ringing, which dominates the dynamics for intermediate times,
is a linear resonance effect. In contrast, the polynomial tail, which becomes
uncovered at late times, is shown to be a \emph{nonlinear} phenomenon.Comment: 4 pages, 4 figures, minor changes to match the PRD versio
Structure of solutions of the Skyrme model on three-sphere. Numerical results
The hedgehog Skyrme model on three-sphere admits very rich spectrum of
solitonic solutions which can be encompassed by a strikingly simple scheme. The
main result of this paper is the statement of the tripartite structure of
solutions of the model and the discovery in what configurations these solutions
appear. The model contains features of more complicated models in General
Relativity and as such can give insight into them.Comment: 20 pages, 13 figures in, with emai
Asymptotics of self-similar solutions to coagulation equations with product kernel
We consider mass-conserving self-similar solutions for Smoluchowski's
coagulation equation with kernel with
. It is known that such self-similar solutions
satisfy that is bounded above and below as . In
this paper we describe in detail via formal asymptotics the qualitative
behavior of a suitably rescaled function in the limit . It turns out that as . As becomes larger
develops peaks of height that are separated by large regions
where is small. Finally, converges to zero exponentially fast as . Our analysis is based on different approximations of a nonlocal
operator, that reduces the original equation in certain regimes to a system of
ODE
Infrared nano-spectroscopy and imaging of collective superfluid excitations in conventional and high-temperature superconductors
We investigate near-field infrared spectroscopy and superfluid polariton
imaging experiments on conventional and unconventional superconductors. Our
modeling shows that near-field spectroscopy can measure the magnitude of the
superconducting energy gap in Bardeen-Cooper-Schrieffer-like superconductors
with nanoscale spatial resolution. We demonstrate how the same technique can
measure the c-axis plasma frequency, and thus the c-axis superfluid density, of
layered unconventional superconductors with a similar spatial resolution. Our
modeling also shows that near-field techniques can image superfluid surface
mode interference patterns near physical and electronic boundaries. We describe
how these images can be used to extract the collective mode dispersion of
anisotropic superconductors with sub-diffractional spatial resolution.Comment: 11 pages, 8 figure
The FIRST-Optical-VLA Survey for Lensed Radio Lobes
We present results from a survey for gravitationally lensed radio lobes.
Lensed lobes are a potentially richer source of information about galaxy mass
distributions than lensed point sources, which have been the exclusive focus of
other recent surveys. Our approach is to identify radio lobes in the FIRST
catalog and then search optical catalogs for coincident foreground galaxies,
which are candidate lensing galaxies. We then obtain higher-resolution images
of these targets at both optical and radio wavelengths, and obtain optical
spectra for the most promising candidates. We present maps of several radio
lobes that are nearly coincident with galaxies. We have not found any new and
unambiguous cases of gravitational lensing. One radio lobe in particular, FOV
J0743+1553, has two hot spots that could be multiple images produced by a
z=0.19 spiral galaxy, but the lensing interpretation is problematic.Comment: 38 pages, 18 figures, aastex, accepted to A
A Comprehensive Archival Search for Counterparts to Ultra-Compact High Velocity Clouds: Five Local Volume Dwarf Galaxies
We report five Local Volume dwarf galaxies (two of which are presented here
for the first time) uncovered during a comprehensive archival search for
optical counterparts to ultra-compact high velocity clouds (UCHVCs). The UCHVC
population of HI clouds are thought to be candidate gas-rich, low mass halos at
the edge of the Local Group and beyond, but no comprehensive search for stellar
counterparts to these systems has been presented. Careful visual inspection of
all publicly available optical and ultraviolet imaging at the position of the
UCHVCs revealed six blue, diffuse counterparts with a morphology consistent
with a faint dwarf galaxy beyond the Local Group. Optical spectroscopy of all
six candidate dwarf counterparts show that five have an H-derived
velocity consistent with the coincident HI cloud, confirming their association,
the sixth diffuse counterpart is likely a background object. The size and
luminosity of the UCHVC dwarfs is consistent with other known Local Volume
dwarf irregular galaxies. The gas fraction () of the five
dwarfs are generally consistent with that of dwarf irregular galaxies in the
Local Volume, although ALFALFA-Dw1 (associated with ALFALFA UCHVC
HVC274.68+74.70123) has a very high 40. Despite the
heterogenous nature of our search, we demonstrate that the current dwarf
companions to UCHVCs are at the edge of detectability due to their low surface
brightness, and that deeper searches are likely to find more stellar systems.
If more sensitive searches do not reveal further stellar counterparts to
UCHVCs, then the dearth of such systems around the Local Group may be in
conflict with CDM simulations.Comment: 18 pages, 4 tables, 4 figures, ApJ Accepte
The provision of adult intensive care in Northern Ireland with reference to the role of high dependency care.
In 1991 an audit of Intensive Care Services was carried out by the Northern Ireland Intensive Care Group. In conjunction with this regional overview, all patients in the Regional Intensive Care Unit, (RICU) in the Royal Victoria Hospital were assessed daily, over a 10 month period in 1990-91 and classified as conforming to either intensive care or high dependency status. These data were then used to compare adult intensive care service in Northern Ireland with recent national and international recommendations on intensive care. Ten units in Northern Ireland were surveyed. In regard to national or international guidelines, all ten were deficient to some degree. Four units had significant deficiencies; small patient numbers, lack of 'dedicated' 24 hr medical cover and or deficiencies in the provision of appropriate monitoring and or equipment. There was a large diversity in casemix among the ten units surveyed which suggested differing admission criteria. The bed occupancy of RICU was 100%. Refused admissions constituted a further 13% of unresourced workload. The lack of physically separate, dedicated high dependency unit facilities meant that 26% of bed days were devoted to HDU care (usually for "improved" intensive care unit patients not yet ready for discharge to a general ward. Achieving nationally recommended intensive care standards (on a regional basis) is probably only possible if a number of the smaller intensive care units are redesignated as high dependency units, and patients requiring intensive care are concentrated in a smaller number of larger ICUs. This will increase the frequency of interhospital transfer of critically ill patients
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