1,723 research outputs found
Neutrino emission rates in highly magnetized neutron stars revisited
Magnetars are a subclass of neutron stars whose intense soft-gamma-ray bursts
and quiescent X-ray emission are believed to be powered by the decay of a
strong internal magnetic field. We reanalyze neutrino emission in such stars in
the plausibly relevant regime in which the Landau band spacing of both protons
and electrons is much larger than kT (where k is the Boltzmann constant and T
is the temperature), but still much smaller than the Fermi energies. Focusing
on the direct Urca process, we find that the emissivity oscillates as a
function of density or magnetic field, peaking when the Fermi level of the
protons or electrons lies about 3kT above the bottom of any of their Landau
bands. The oscillation amplitude is comparable to the average emissivity when
the Landau band spacing mentioned above is roughly the geometric mean of kT and
the Fermi energy (excluding mass), i. e., at fields much weaker than required
to confine all particles to the lowest Landau band. Since the density and
magnetic field strength vary continuously inside the neutron star, there will
be alternating surfaces of high and low emissivity. Globally, these
oscillations tend to average out, making it unclear whether there will be any
observable effects.Comment: 7 pages, 2 figures; accepted for publication in Astronomy &
Astrophysic
Red Noise in Anomalous X-ray Pulsar Timing Residuals
Anomalous X-ray Pulsars (AXPs), thought to be magnetars, exhibit poorly
understood deviations from a simple spin-down called "timing noise". AXP timing
noise has strong low-frequency components which pose significant challenges for
quantification. We describe a procedure for extracting two quantities of
interest, the intensity and power spectral index of timing noise. We apply this
procedure to timing data from three sources: a monitoring campaign of five
AXPs, observations of five young pulsars, and the stable rotator PSR B1937+21.Comment: submitted to the proceedings of the "40 Years of Pulsars" conferenc
Reactivity of OH and CH3OH between 22 and 64 K: Modelling the gas phase production of CH3O in Barnard 1b
In the last years, ultra-low temperature chemical kinetic experiments have
demonstrated that some gas-phase reactions are much faster than previously
thought. One example is the reaction between OH and CH3OH, which has been
recently found to be accelerated at low temperatures yielding CH3O as main
product. This finding opened the question of whether the CH3O observed in the
dense core Barnard 1b could be formed by the gas-phase reaction of CH3OH and
OH. Several chemical models including this reaction and grain-surface processes
have been developed to explain the observed abundance of CHO with little
success. Here we report for the first time rate coefficients for the gas-phase
reaction of OH and CH3OH down to a temperature of 22 K, very close to those in
cold interstellar clouds. Two independent experimental set-ups based on the
supersonic gas expansion technique coupled to the pulsed laser photolysis-laser
induced fluorescence technique were used to determine rate coefficients in the
temperature range 22-64 K. The temperature dependence obtained in this work can
be expressed as k(22-64 K) = (3.6+/-0.1)e-12 (T/ 300)^(-1.0+/-0.2) cm3
molecule-1 s-1. Implementing this expression in a chemical model of a cold
dense cloud results in CH3O/CH3OH abundance ratios similar or slightly lower
than the value of 3e-3 observed in Barnard 1b. This finding confirms that the
gas-phase reaction between OH and CH3OH is an important contributor to the
formation of interstellar CH3O. The role of grain-surface processes in the
formation of CH3O, although it cannot be fully neglected, remains
controversial.Comment: Accepted for publication in The Astrophysical Journa
Hadronic structure aspects of decays
As is known from previous studies the lepton number violating decays have good prospects to probe new physics beyond the
Standard Model and provide valuable information on neutrino masses and mixing.
We analyze these processes with an emphasis on their hadronic structure
aspects applying relativistic constituent quark model. We conclude that the
previously ignored contribution associated with the t-channel Majorana neutrino
exchange is comparable with the s-channel one in a wide range of neutrino
masses. We also estimated model independent absolute upper bounds on neutrino
contribution to these decays.Comment: 15 pages, 1 figure. Version to appear in PRD, normalization factor in
Eq. (25) is correcte
The Long-term Radiative Evolution of Anomalous X-ray Pulsar 1E 2259+586 after its 2002 Outburst
We present an analysis of five X-ray Multi-Mirror Mission (XMM) observations
of the anomalous X-ray pulsar (AXP) 1E 2259+586 taken in 2004 and 2005 during
its relaxation following its 2002 outburst. We compare these data with those of
five previous XMM observations taken in 2002 and 2003, and find the observed
flux decay is well described by a power-law of index -0.69+/-0.03. As of
mid-2005, the source may still have been brighter than preoutburst, and was
certainly hotter. We find a strong correlation between hardness and flux, as
seen in other AXP outbursts. We discuss the implications of these results for
the magnetar model.Comment: 23 Pages, 4 figures, 3 tables, published on Ap
Lipome geant parapharynge
L’espace parapharyngé est une région anatomique complexe. Seulement 0,5% des tumeurs de la tête et cou se localisent à ce niveau. elles sont essentiellement représentées par les tumeurs nerveuses, salivaires et vasculaires, les lipomes ont été exceptionnellement décrits. Notre observation a un double intérêt : documenter cette rareté et faire une mise au point sur l’abord chirurgical de cette région.Mots clés :Lipome, espace parapharyngé, chirurgi
A protosolar nebula origin for the ices agglomerated by Comet 67P/Churyumov-Gerasimenko
The nature of the icy material accreted by comets during their formation in
the outer regions of the protosolar nebula is a major open question in
planetary science. Some scenarios of comet formation predict that these bodies
agglomerated from crystalline ices condensed in the protosolar nebula.
Concurrently, alternative scenarios suggest that comets accreted amorphous ice
originating from the interstellar cloud or from the very distant regions of the
protosolar nebula. On the basis of existing laboratory and modeling data, we
find that the N/CO and Ar/CO ratios measured in the coma of the Jupiter
family comet 67P/Churyumov-Gerasimenko by the ROSINA instrument aboard the
European Space Agency's Rosetta spacecraft match those predicted for gases
trapped in clathrates. If these measurements are representative of the bulk
N/CO and Ar/CO ratios in 67P/Churyumov-Gerasimenko, it implies that the
ices accreted by the comet formed in the nebula and do not originate from the
interstellar medium, supporting the idea that the building blocks of outer
solar system bodies have been formed from clathrates and possibly from pure
crystalline ices. Moreover, because 67P/Churyumov-Gerasimenko is impoverished
in Ar and N, the volatile enrichments observed in Jupiter's atmosphere
cannot be explained solely via the accretion of building blocks with similar
compositions and require an additional delivery source. A potential source may
be the accretion of gas from the nebula that has been progressively enriched in
heavy elements due to photoevaporation.Comment: The Astrophysical Journal Letters, in pres
Numerical study of the effect of the structural disorder on the electronic properties in disordered solids
During the last few years, it became clear that the characterization of the nature of electron states in disordered systems is one of the fundamental topics in condensed matter physics. Along these lines, our present work consists of the study of the effect of the structural disorder on a wide range of electronic properties (density of electron states, participation ratio of electron states and distribution of energy levels). For this, we generate the structural disorder according to three different models: a model named "Shaken lattice’’, a model simulated by molecular dynamics and the model of the random triangles. Concerning the Hamiltonian model, we use a Tight-Binding model with explicit S-type orbitals for the first two structures and a clean Tight-Binding model for the model of the random triangles. Our results show that electron states are localized or delocalized depending on the type of the structural disorder used to generate a particular topologically disordered system.During the last few years, it became clear that the characterization of the nature of electron states in disordered systems is one of the fundamental topics in condensed matter physics. Along these lines, our present work consists of the study of the effect of the structural disorder on a wide range of electronic properties (density of electron states, participation ratio of electron states and distribution of energy levels). For this, we generate the structural disorder according to three different models: a model named "Shaken lattice’’, a model simulated by molecular dynamics and the model of the random triangles. Concerning the Hamiltonian model, we use a Tight-Binding model with explicit S-type orbitals for the first two structures and a clean Tight-Binding model for the model of the random triangles. Our results show that electron states are localized or delocalized depending on the type of the structural disorder used to generate a particular topologically disordered system
NGC 7538 : Multiwavelength Study of Stellar Cluster Regions associated with IRS 1-3 and IRS 9 sources
We present deep and high-resolution (FWHM ~ 0.4 arcsec) near-infrared (NIR)
imaging observations of the NGC 7538 IRS 1-3 region (in JHK bands), and IRS 9
region (in HK bands) using the 8.2m Subaru telescope. The NIR analysis is
complemented with GMRT low-frequency observations at 325, 610, and 1280 MHz,
molecular line observations of H13CO+ (J=1-0), and archival Chandra X-ray
observations. Using the 'J-H/H-K' diagram, 144 Class II and 24 Class I young
stellar object (YSO) candidates are identified in the IRS 1-3 region. Further
analysis using 'K/H-K' diagram yields 145 and 96 red sources in the IRS 1-3 and
IRS 9 regions, respectively. A total of 27 sources are found to have X-ray
counterparts. The YSO mass function (MF), constructed using a theoretical
mass-luminosity relation, shows peaks at substellar (~0.08-0.18 Msolar) and
intermediate (~1-1.78 Msolar) mass ranges for the IRS 1-3 region. The MF can be
fitted by a power law in the low mass regime with a slope of Gamma ~ 0.54-0.75,
which is much shallower than the Salpeter value of 1.35. An upper limit of 10.2
is obtained for the star to brown dwarf ratio in the IRS 1-3 region. GMRT maps
show a compact HII region associated with the IRS 1-3 sources, whose spectral
index of 0.87+-0.11 suggests optical thickness. This compact region is resolved
into three separate peaks in higher resolution 1280 MHz map, and the 'East'
sub-peak coincides with the IRS 2 source. H13CO+ (J=1-0) emission reveals peaks
in both IRS 1-3 and IRS 9 regions, none of which are coincident with visible
nebular emission, suggesting the presence of dense cloud nearby. The virial
masses are approximately of the order of 1000 Msolar and 500 Msolar for the
clumps in IRS 1-3 and IRS 9 regions, respectively.Comment: 27 pages, 18 figures, 5 tables. Accepted for publication in MNRA
Maladie de kimura: À propos d’un cas
Introduction : Mots-clés : Maladie de Kimura, parotide, chirurgie.La maladie de Kimura ou lymphogranulome éosinophile est une pathologie inflammatoire chronique très rare, d’étiologie inconnue. Nous rapportons un cas de maladie de Kimura à localisation parotidienne et à travers une revue de la littérature, rappelons les principales caractéristiques cliniques, paracliniques, thérapeutiques et évolutives de cette pathologie. Matériel et méthodes : Patient de 17 ans qui a consulté devant l’apparition d’une tuméfaction de la région parotidienne gauche évoluant depuis un an et sans paralysie faciale. Résultats : L’échographie cervico-parotidienne a révélé une parotide gauche hypertrophiée siège de multiples nodules hypoéchogènes. La tomodensitométrie cervico-faciale a mis en évidence une glande parotide gauche augmentée de taille et de structure hétérogène nodulaire sans adénopathies cervicales. La cytopontion était non concluante. Le patient a bénéficié d’une parotidectomie exofaciale gauche et l’étude anatomopathologique de la pièce opératoire revenue en faveur de la maladie de Kimura. Les suites opératoires étaient simples. Le recul est d’un an sans récidive. Discussion : La Maladie de Kimura se caractérise cliniquement par des nodules sous cutanés de localisation cervicofaciale, une augmentation du volume des glandes salivaires et des adénopathies satellites. Son diagnostic est histologique reposant sur l’identification d’une hyperplasie follicullaire avec des abcès à polynucléaires éosinophiles. Le traitement est chirurgical le plus souvent mais dans certains cas la corticothérapie est proposée. Ce diagnostic doit cependant rester à l’esprit devant toute masse cervico-faciale
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