2,012 research outputs found
The cooling, mass and radius of the neutron star in EXO 0748-676 in quiescence with XMM-Newton
We analyse four XMM-Newton observations of the neutron-star low-mass X-ray
binary EXO 0748676 in quiescence. We fit the spectra with an absorbed
neutron-star atmosphere model, without the need for a high-energy (power-law)
component; with a 95 per cent confidence the power-law contributes less than 1
per cent to the total flux of the source in keV. The fits show
significant residuals at around 0.5 keV which can be explained by either a hot
gas component around the neutron star or a moderately broad emission line from
a residual accretion disc. The temperature of the neutron-star has decreased
significantly compared to the previous observation, from 124 eV to 105 eV, with
the cooling curve being consistent with either an exponential decay plus a
constant or a (broken) power law. The best-fitting neutron-star mass and radius
can be better constrained if we extend the fits down to the lowest possible
energy available. For an assumed distance of 7.1 kpc, the best-fitting
neutron-star mass and radius are and
km if we fit the spectrum over the keV range, but
and km if we restrict the
fits to the keV range. We finally discuss the effect of the assumed
distance to the source upon the best-fitting neutron-star mass and radius. As
systematic uncertainties in the deduced mass and radius depending on the
distance are much larger than the statistical errors, it would be disingenuous
to take these results at face value.Comment: 12 pages, 6 figure
Monodisperse cluster crystals: classical and quantum dynamics
We study the phases and dynamics of a gas of monodisperse particles
interacting via soft-core potentials in two spatial dimensions, which is of
interest for soft-matter colloidal systems and quantum atomic gases. Using
exact theoretical methods, we demonstrate that the equilibrium low-temperature
classical phase simultaneously breaks continuous translational symmetry and
dynamic space-time homogeneity, whose absence is usually associated with
out-of-equilibrium glassy phenomena. This results in an exotic self-assembled
cluster crystal with coexisting liquid-like long-time dynamical properties,
which corresponds to a classical analog of supersolid behavior. We demonstrate
that the effects of quantum fluctuations and bosonic statistics on
cluster-glassy crystals are separate and competing: zero-point motion tends to
destabilize crystalline order, which can be restored by bosonic statistics.Comment: 8 pages, 7 figure
Location and Shape Reconstruction of 2D Dielectric Objects by Means of a Closed-Form Method: Preliminary Experimental Results
An analytical approach to location and shape reconstruction of dielectric scatterers, that was recently proposed, is tested against experimental data. Since the cross-sections of the scatterers do not depend on the z coordinate, a 2D problem can be formulated. A closed-form singular value decomposition of the scattering integral operator is derived and is used to determine the radiating components of the equivalent source density. This is a preliminary step toward a more complete solution, which will take into account the incident field inside the investigation domain in order to provide the dielectric features of the scatterer and also the nonradiating sources. Reconstructions of the equivalent sources, performed on some scattering data belonging to the Fresnel database, show the capabilities of the method and, thanks to the closed-form solution, results are obtained in a very short computation time
Amyand’s hernia: a case report and review of the literature
Amyand´s hernia represents an unusual cause of hernia. It has an incidence of 1% of all inguinal hernias. The clinical presentation depends on the involvement of the hernial sac and the inflammatory state of the appendix. Due to the low frequency of presentation of Amyand's hernia, there is no protocolized treatment. Authors present the case of a 70-year-old patient with the presence of surgically resolved Amyand´s hernia
Anderson Localization Phenomenon in One-dimensional Elastic Systems
The phenomenon of Anderson localization of waves in elastic systems is
studied. We analyze this phenomenon in two different set of systems: disordered
linear chains of harmonic oscillators and disordered rods which oscillate with
torsional waves. The first set is analyzed numerically whereas the second one
is studied both experimentally and theoretically. In particular, we discuss the
localization properties of the waves as a function of the frequency. In doing
that we have used the inverse participation ratio, which is related to the
localization length. We find that the normal modes localize exponentially
according to Anderson theory. In the elastic systems, the localization length
decreases with frequency. This behavior is in contrast with what happens in
analogous quantum mechanical systems, for which the localization length grows
with energy. This difference is explained by means of the properties of the re
ection coefficient of a single scatterer in each case.Comment: 15 pages, 10 figure
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