12,554 research outputs found
Quark core impact on hybrid star cooling
In this paper we investigate the thermal evolution of hybrid stars, objects
composed of a quark matter core, enveloped by ordinary hadronic matter. Our
purpose is to investigate how important are the microscopic properties of the
quark core to the thermal evolution of the star. In order to do that we use a
simple MIT bag model for the quark core, and a relativistic mean field model
for the hadronic envelope. By choosing different values for the microscopic
parameters (bag constant, strange quark mass, strong coupling constant) we
obtain hybrid stars with different quark core properties. We also consider the
possibility of color superconductivity in the quark core. With this simple
approach, we have found a set of microscopic parameters that lead to a good
agreement with observed cooling neutron stars. Our results can be used to
obtain clues regarding the properties of the quark core in hybrid stars, and
can be used to refine more sophisticated models for the equation of state of
quark matter.Comment: 8 pages, 10 figures. Accepted for publication in Physical Review
Evolution of the local superconducting density of states in ErRhB close to the ferromagnetic transition
We present local tunneling spectroscopy experiments in the superconducting
and ferromagnetic phases of the reentrant superconductor ErRhB. The
tunneling conductance curves jump from showing normal to superconducting
features within a few mK close to the ferromagnetic transition temperature,
with a clear hysteretic behavior. Within the ferromagnetic phase, we do not
detect any superconducting correlations. Within the superconducting phase we
find a peculiar V-shaped density of states at low energies, which is produced
by the magnetically modulated phase that coexists with superconductivity just
before ferromagnetism sets in.Comment: 5 pages, 4 figure
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Guttate leukoderma and acrokeratosis verruciformis of Hopf: a rare combination in Darier disease
A distinct Darier phenotype presenting with confetti-like hypopigmented macules was first described in 1965. Designated as "guttate leukoderma," this skin finding is a rarely-reported presentation of Darier disease. It has been theorized that the mutation in ATP2A2 causes defective E-cadherin, which in turn disrupts the adhesion of melanocytes to keratinocytes, thus leading to impaired dendrite formation, hindered melanin transfer, and ultimately to melanocyte apoptosis. Herein, we contribute a case of a 56-year old woman who presented with the rarely-described guttate leukoderma of Darier disease and acrokeratosis verruciformis of Hopf
Electrically Charged Strange Quark Stars
The possible existence of compact stars made of absolutely stable strange
quark matter--referred to as strange stars--was pointed out by E. Witten almost
a quarter of a century ago. One of the most amazing features of such objects
concerns the possible existence of ultra-strong electric fields on their
surfaces, which, for ordinary strange matter, is around V/cm. If
strange matter forms a color superconductor, as expected for such matter, the
strength of the electric field may increase to values that exceed
V/cm. The energy density associated with such huge electric fields is on the
same order of magnitude as the energy density of strange matter itself, which,
as shown in this paper, alters the masses and radii of strange quark stars at
the 15% and 5% level, respectively. Such mass increases facilitate the
interpretation of massive compact stars, with masses of around , as
strange quark stars.Comment: Revised version, references added, 6 pages, 4 figures, accepted for
publication in Physical Review
AAT/WFI observations of the Extragalactic H I Cloud HIPASS J1712-64
AAT/WFI optical images of a candidate extragalactic HI cloud, HIPASS
J1712-64, are presented. The g and r-band CCD mosaic camera frames were
processed using a new data pipeline recently installed at the AAO. The
resultant stacked images reach significantly deeper levels than those of
previous published optical imaging of this candidate, providing a detection
limit M_g -7 at a distance of 3Mpc, the inferred distance to HIPASS J1712-64.
However, detailed analysis of the images fails to uncover any stellar
population associated with the HI emission. If this system is a member of the
Local Group then it is pathologically different to other members. Hence, our
observations reinforce earlier suggestions that this HI cloud is most likely
Galactic in origin and not a Local Volume dwarf galaxy.Comment: 8 pages, accepted for publication in PASA (Figures reduced in
resolution, please contact gfl if you wish the higher resolution versions
Impurity assisted nanoscale localization of plasmonic excitations in graphene
The plasmon modes of pristine and impurity doped graphene are calculated,
using a real-space theory which determines the non-local dielectric response
within the random phase approximation. A full diagonalization of the
polarization operator is performed, allowing the extraction of all its poles.
It is demonstrated how impurities induce the formation of localized modes which
are absent in pristine graphene. The dependence of the spatial modulations over
few lattice sites and frequencies of the localized plasmons on the electronic
filling and impurity strength is discussed. Furthermore, it is shown that the
chemical potential and impurity strength can be tuned to control target
features of the localized modes. These predictions can be tested by scanning
tunneling microscopy experiments.Comment: 5 pages, 4 figure
Cosmology on a Mesh
An adaptive multi grid approach to simulating the formation of structure from
collisionless dark matter is described. MLAPM (Multi-Level Adaptive Particle
Mesh) is one of the most efficient serial codes available on the cosmological
'market' today. As part of Swinburne University's role in the development of
the Square Kilometer Array, we are implementing hydrodynamics, feedback, and
radiative transfer within the MLAPM adaptive mesh, in order to simulate
baryonic processes relevant to the interstellar and intergalactic media at high
redshift. We will outline our progress to date in applying the existing MLAPM
to a study of the decay of satellite galaxies within massive host potentials.Comment: 3 pages, 2 figures, to appear in the proceedings of "The IGM/Galaxy
Connection - The Distribution of Baryons at z=0", ed. M. Putman & J.
Rosenber
The Stellar Halo Metallicity - Luminosity Relationship for Spiral Galaxies
The stellar halos of spiral galaxies bear important chemo-dynamical
signatures of galaxy formation. We present here the analysis of 89
semi-cosmological spiral galaxy simulations, spanning ~ 4 magnitudes in total
galactic luminosity. These simulations sample a wide variety of merging
histories and show significant dispersion in halo metallicity at a given total
luminosity - more than a factor of ten in metallicity. Our preliminary analysis
suggests that galaxies with a more extended merging history possess halos which
have younger and more metal rich stellar populations than the stellar halos
associated with galaxies with a more abbreviated assembly. A correlation
between halo metallicity and its surface brightness has also been found,
reflecting the correlation between halo metallicity and its stellar mass. Our
simulations are compared with recent Hubble Space Telescope observations of
resolved stellar halos in nearby spirals.Comment: 5 pages, 4 figures. MNRAS Letters, in pres
Quantitative Proteomics and Phosphoproteomics Reveal TNF-α-Mediated Protein Functions in Hepatocytes
Increased secretion of proinflammatory cytokines, such as tumor necrosis factor-alpha (TNFα), is often associated with adipose tissue dysregulation, which often accompanies obesity. High levels of TNFα have been linked to the development of insulin resistance in several tissues and organs, including skeletal muscle and the liver. In this study, we examined the complex regulatory roles of TNFα in murine hepatocytes utilizing a combination of global proteomic and phosphoproteomic analyses. Our results show that TNFα promotes extensive changes not only of protein levels, but also the dynamics of their downstream phosphorylation signaling. We provide evidence that TNFα induces DNA replication and promotes G1/S transition through activation of the MAPK pathway. Our data also highlight several other novel proteins, many of which are regulated by phosphorylation and play a role in the progression and development of insulin resistance in hepatocytes
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