289 research outputs found
The magnetar emission in the IR band: the role of magnetospheric currents
There is a general consensus about the fact that the magnetar scenario
provides a convincing explanation for several of the observed properties of the
Anomalous X-ray Pulsars and the Soft Gamma Repeaters. However, the origin of
the emission observed at low energies is still an open issue. We present a
quantitative model for the emission in the optical/infrared band produced by
curvature radiation from magnetospheric charges, and compare results with
current magnetars observations.Comment: 6 Pages, 2 Figures. Astrophysics and Space Science, in press.
Proceedings of the ICREA Workshop on The High-Energy Emission from Pulsars
and their Systems, Sant Cugat, April 12-16 201
Analysis of Parametric Oscillatory Instability in Power Recycled LIGO Interferometer
We present the analysis of a nonlinear effect of parametric oscillatory
instability in power recycled LIGO interferometer with the Fabry-Perot (FP)
cavities in the arms. The basis for this effect is the excitation of the
additional (Stokes) optical mode and the mirror elastic mode, when the optical
energy stored in the main FP cavity main mode exceeds the certain threshold and
the frequencies are related so that sum of frequencies of Stokes and elastic
modes are approximately equal to frequencyof main mode. The presence of
anti-Stokes modes (with frequency approximately equal to sum of frequencies of
main and elastic modes) can depress parametric instability. However, it is very
likely that the anti-Stokes modes will not compensate the parametric
instability completely.Comment: 9 pages, 2 figures. submitted to Physics Letters
Eccrine porocarcinoma of the head: An important differential diagnosis in the elderly patient
Background: Eccrine porocarcinoma is a rare malignant tumor of the sweat gland, characterized by a broad spectrum of clinicopathologic presentations. Surprisingly, unlike its benign counterpart eccrine poroma, eccrine porocarcinoma is seldom found in areas with a high density of eccrine sweat glands, like the palms or soles. Instead, eccrine porocarcinoma frequently occurs on the lower extremities, trunk and abdomen, but also on the head, resembling various other skin tumors, as illustrated in the patients described herein. Observations: We report 5 cases of eccrine porocarcinoma of the head. All patients were initially diagnosed as having epidermal or melanocytic skin tumors. Only after histopathologic examination were they classified as eccrine porocarcinoma, showing features of epithelial tumors with abortive ductal differentiation. Characteristic clinical, histopathologic and immunohistochemical findings of eccrine porocarcinomas are illustrated. Conclusion: Eccrine porocarcinomas are potentially fatal adnexal malignancies, in which extensive metastatic dissemination may occur. Porocarcinomas are commonly overlooked, or misinterpreted as squamous or basal cell carcinomas as well as other common malignant and even benign skin tumors. Knowledge of the clinical pattern and histologic findings, therefore, is crucial for an early therapeutic intervention, which can reduce the risk of tumor recurrence and serious complications. Copyright (c) 2008 S. Karger AG, Basel
A Relativistic Type Ibc Supernova Without a Detected Gamma-ray Burst
Long duration gamma-ray bursts (GRBs) mark the explosive death of some
massive stars and are a rare sub-class of Type Ibc supernovae (SNe Ibc). They
are distinguished by the production of an energetic and collimated relativistic
outflow powered by a central engine (an accreting black hole or neutron star).
Observationally, this outflow is manifested in the pulse of gamma-rays and a
long-lived radio afterglow. To date, central engine-driven SNe have been
discovered exclusively through their gamma-ray emission, yet it is expected
that a larger population goes undetected due to limited satellite sensitivity
or beaming of the collimated emission away from our line-of-sight. In this
framework, the recovery of undetected GRBs may be possible through radio
searches for SNe Ibc with relativistic outflows. Here we report the discovery
of luminous radio emission from the seemingly ordinary Type Ibc SN 2009bb,
which requires a substantial relativistic outflow powered by a central engine.
The lack of a coincident GRB makes SN 2009bb the first engine-driven SN
discovered without a detected gamma-ray signal. A comparison with our extensive
radio survey of SNe Ibc reveals that the fraction harboring central engines is
low, ~1 percent, measured independently from, but consistent with, the inferred
rate of nearby GRBs. Our study demonstrates that upcoming optical and radio
surveys will soon rival gamma-ray satellites in pinpointing the nearest
engine-driven SNe. A similar result for a different supernova is reported
independently.Comment: To appear in Nature on Jan 28 2010. Embargoed for discussion in the
press until 13:00 US Eastern Time on Jan 27 (Accepted version, 27 pages,
Manuscript and Suppl. Info.
Vitamin D status of inmates. The experience of penitentiaries prisons in the province of Salerno in Southern Italy
Introduction: Prisoners are at risk of developing vitamin D deficiency due to their lacking exposure to sunlight. So far, there are no published studies evaluating blood levels of vitamin D in relation to the health status of inmates and the quality of the Italian prison system.
Aim: To investigate vitamin D status and its determinants in a cohort of prisoners.
Subject and methods: One hundred and seventy-two (172) pri-son inmates (males, n=159, age 47± 11.3 years; females, n=13, age 43.91±12.18 years) of three penitentiaries in the province of Salerno. Vitamin D deficiency, insufficiency and sufficiency were respectively defined as a 25(OH)D level <20 ng/mL; from 20 to 30 ng/mL, >30 ng/mL.
Results: In our group, Vitamin D deficiency occurs in 77.32% of the prisoners with 32.55% of the cases having severe insufficiency. Prisoners with higher BMI show lower circulating vitamin D levels (p<0.001). No significant relationship was found with the duration of detention (Pearson R: 0.01).
Conclusion: In this cohort of inmates the vitamin D status is determined by BMI, but not by the duration of the detention
Activated Magnetospheres of Magnetars
Like the solar corona, the external magnetic field of magnetars is twisted by
surface motions of the star. The twist energy is dissipated over time. We
discuss the theory of this activity and its observational status. (1) Theory
predicts that the magnetosphere tends to untwist in a peculiar way: a bundle of
electric currents (the "j-bundle") is formed with a sharp boundary, which
shrinks toward the magnetic dipole axis. Recent observations of shrinking hot
spots on magnetars are consistent with this behavior. (2) Continual discharge
fills the j-bundle with electron-positron plasma, maintaining a nonthermal
corona around the neutron star. The corona outside a few stellar radii strongly
interacts with the stellar radiation and forms a "radiatively locked" outflow
with a high e+- multiplicity. The locked plasma annihilates near the apexes of
the closed magnetic field lines. (3) New radiative-transfer simulations suggest
a simple mechanism that shapes the observed X-ray spectrum from 0.1 keV to 1
MeV: part of the thermal X-rays emitted by the neutron star are reflected from
the outer corona and then upscattered by the inner relativistic outflow in the
j-bundle, producing a beam of hard X-rays.Comment: 23 pages, 7 figures; review chapter in the proceedings of ICREA
Workshop on the High-Energy Emission from Pulsars and Their Systems, Sant
Cugat, Spain, April 201
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