97,548 research outputs found
Measurement of the Entropy and Critical Temperature of a Strongly Interacting Fermi Gas
We report a model-independent measurement of the entropy, energy, and
critical temperature of a degenerate, strongly interacting Fermi gas of atoms.
The total energy is determined from the mean square cloud size in the strongly
interacting regime, where the gas exhibits universal behavior. The entropy is
measured by sweeping a bias magnetic field to adiabatically tune the gas from
the strongly interacting regime to a weakly interacting regime, where the
entropy is known from the cloud size after the sweep. The dependence of the
entropy on the total energy quantitatively tests predictions of the
finite-temperature thermodynamics.Comment: 16 pages, 3 figure
Limits on [OIII] 5007 emission from NGC4472's globular clusters: constraints on planetary nebulae and ultraluminous black hole X-ray binaries in globular clusters
We have searched for [OIII] 5007 emission in high resolution spectroscopic
data from Flames/Giraffe VLT observations of 174 massive globular clusters
(GCs) in NGC4472. No planetary nebulae (PNe) are observed in these clusters,
constraining the number of PNe per bolometric luminosity,
\alpha<0.8*10^{-7}PN/L_{\odot}. This is significantly lower than the rate
predicted from stellar evolution, if all stars produce PNe. Comparing our
results to populations of PNe in galaxies, we find most galaxies have a higher
\alpha than these GCs (more PNe per bolometric luminosity - though some massive
early-type galaxies do have similarly low \alpha). The low \alpha required in
these GCs suggests that the number of PNe per bolometric luminosity does not
increase strongly with decreasing mass or metallicity of the stellar
population. We find no evidence for correlations between the presence of known
GC PNe and either the presence of low mass X-ray binaries (LMXBs) or the
stellar interaction rates in the GCs. This, and the low \alpha observed,
suggests that the formation of PNe may not be enhanced in tight binary systems.
These data do identify one [OIII] emission feature, this is the (previously
published) broad [OIII] emission from the cluster RZ 2109. This emission is
thought to originate from the LMXB in this cluster, which is accreting at
super-Eddington rates. The absence of any similar [OIII] emission from the
other clusters favors the hypothesis that this source is a black hole LMXB,
rather than a neutron star LMXB with significant geometric beaming of its X-ray
emission.Comment: 10 pages, 3 figures, accepted for publication in Ap
Keck IR Spectroscopy of WZ Sge: Detection of Molecular Emission from the Accretion Disk
Time-resolved IR spectroscopy of WZ Sge was obtained using NIRSPEC on Keck
II. We detect CO and H emission from the accretion disk placing WZ
Sge into a rarefied class of astronomical objects including YSOs and high
luminosity early-type stars. During the eclipse phase, the molecular emission
greatly weakens but no firm evidence for the secondary star is seen allowing
new limits on its luminosity to be determined. The detection of molecular
emission provides physical properties within the outer disk of T=3000K and
N cm. Such a cool, dense region, not associated with areas
of H I and He I emission, provides the first observational confirmation of
predictions made by accretion disk models.Comment: 10 pages, 3 figures. Accepted for publication in ApJ Letter
Photodynamic Therapy of Necrobiosis Lipoidica - A Multicenter Study of 18 Patients
Background: Necrobiosis lipoidica (NL) is a granulomatous skin disease of unknown origin, and no reliably effective treatment option exists to handle this often disfiguring disease. Recently, a patient with long-lasting NL was reported to be cured by topical photodynamic therapy (PDT). Objective: To evaluate the overall potential of PDT in the treatment of NL on the lower legs. Methods: Retrospective study of 18 patients (aged 16 - 62 years) from 3 European university departments of dermatology treated with PDT for NL. Methyl aminolevulinate or 5-aminolevulinic acid were used as topically applied photosensitizers. Illumination followed with red light-emitting diode light. Results: Complete response was seen in 1/18 patients after 9 PDT cycles, and partial response in 6/18 patients (2 - 14 PDT cycles) giving an overall response rate of 39% (7/18). Conclusion: Although almost 40% of the cases showed some degree of response, PDT cannot currently be recommended as first-line therapy of NL. Subpopulations of therapy-resistant NL patients may, however, benefit from PDT. Copyright (C) 2008 S. Karger AG, Base
Efficient multiple time scale molecular dynamics: using colored noise thermostats to stabilize resonances
Multiple time scale molecular dynamics enhances computational efficiency by
updating slow motions less frequently than fast motions. However, in practice
the largest outer time step possible is limited not by the physical forces but
by resonances between the fast and slow modes. In this paper we show that this
problem can be alleviated by using a simple colored noise thermostatting scheme
which selectively targets the high frequency modes in the system. For two
sample problems, flexible water and solvated alanine dipeptide, we demonstrate
that this allows the use of large outer time steps while still obtaining
accurate sampling and minimizing the perturbation of the dynamics. Furthermore,
this approach is shown to be comparable to constraining fast motions, thus
providing an alternative to molecular dynamics with constraints.Comment: accepted for publication by the Journal of Chemical Physic
Electron transport through antidot superlattices in heterostructures: new magnetoresistance resonances in lattices with large diameter antidots
In the present work we have investigated the transport properties in a number
of Si/SiGe samples with square antidot lattices of different periods. In
samples with lattice periods equal to 700 nm and 850 nm we have observed the
conventional low-field commensurability magnetoresistance peaks consistent with
the previous observations in GaAs/AlGaAs and Si/SiGe samples with antidot
lattices. In samples with a 600 nm lattice period a new series of
well-developed magnetoresistance oscillations has been found beyond the last
commensurability peak which are supposed to originate from periodic skipping
orbits encircling an antidot with a particular number of bounds.Comment: To appear in EuroPhys. Let
- …