1,738 research outputs found
The (Re-)Discovery of G350.1-0.3: A Young, Luminous Supernova Remnant and Its Neutron Star
We present an XMM-Newton observation of the long-overlooked radio source
G350.1-0.3. The X-ray spectrum of G350.1-0.3 can be fit by a shocked plasma
with two components: a high-temperature (1.5 keV) region with a low ionization
time scale and enhanced abundances, plus a cooler (0.36 keV) component in
ionization equilibrium and with solar abundances. The X-ray spectrum and the
presence of non-thermal, polarized, radio emission together demonstrate that
G350.1-0.3 is a young, luminous supernova remnant (SNR), for which archival HI
and 12-CO data indicate a distance of 4.5 kpc. The diameter of the source then
implies an age of only ~900 years. The SNR's distorted appearance, small size
and the presence of 12-CO emission along the SNR's eastern edge all indicate
that the source is interacting with a complicated distribution of dense ambient
material. An unresolved X-ray source, XMMU J172054.5-372652, is detected a few
arcminutes west of the brightest SNR emission. The thermal X-ray spectrum and
lack of any multi-wavelength counterpart suggest that this source is a neutron
star associated with G350.1-0.3, most likely a "central compact object", as
seen coincident with other young SNRs such as Cassiopeia A.Comment: 6 pages, uses emulateapj. One B/W figure, one color figure. Minor
text changes and update to Fig 2 following referee's report. ApJ Letters, in
pres
An XMM-Newton Study of the Bright, Nearby Supernova Remnant G296.1-0.5
We present a detailed study of the supernova remnant G296.1-0.5, performed
using observations with the EPIC and RGS instruments of the XMM-Newton
satellite. G296.1-0.5 is a bright remnant that displays an incomplete
multiple-shell morphology in both its radio and X-ray images. We use a set of
observations towards G296.1-0.5, from three distinct pointings of EPIC, in
order to perform a thorough spatial and spectral analysis of this remnant, and
hence determine what type of progenitor gave rise to the supernova explosion,
and describe the evolutionary state of the SNR. Our XMM-Newton observations
establish that the spectral characteristics are consistent across the X-ray
bright regions of the object, and are best described by a model of the emission
from a nonequilibrium ionization collisional plasma. The study reveals that the
emission from the shell is characterized by an excess of N and an
underabundance of O, which is typical of wind material from red supergiant
(RSG) and Wolf-Rayet (WR) stars. Additionally, we have detected transient X-ray
source 2XMMi J115004.8-622442 at the edge of the SNR whose properties suggest
that it is the result of stellar flare, and we discuss its nature in more
detail.Comment: 10 pages, 7 figures, 3 tables. Accepted for publication in Ap
Recommended from our members
Evaluation of critical congenital heart defects screening using pulse oximetry in the neonatal intensive care unit.
ObjectiveTo evaluate the implementation of early screening for critical congenital heart defects (CCHDs) in the neonatal intensive care unit (NICU) and potential exclusion of sub-populations from universal screening.Study designProspective evaluation of CCHD screening at multiple time intervals was conducted in 21 NICUs across five states (n=4556 infants).ResultsOf the 4120 infants with complete screens, 92% did not have prenatal CHD diagnosis or echocardiography before screening, 72% were not receiving oxygen at 24 to 48 h and 56% were born ⩾2500 g. Thirty-seven infants failed screening (0.9%); none with an unsuspected CCHD. False positive rates were low for infants not receiving oxygen (0.5%) and those screened after weaning (0.6%), yet higher among infants born at <28 weeks (3.8%). Unnecessary echocardiograms were minimal (0.2%).ConclusionGiven the majority of NICU infants were ⩾2500 g, not on oxygen and not preidentified for CCHD, systematic screening at 24 to 48 h may be of benefit for early detection of CCHD with minimal burden
Pharmacokinetic and safety profile of raltegravir and ribavirin, when dosed separately and together, in healthy volunteers
Results: No statistically significant differences in PK parameters were observed for raltegravir between phases 2 and 3. A statistically significant decrease in maximum plasma concentration (Cmax) and an increase in time to maximum plasma concentration (Tmax) were observed for ribavirin in phase 3 compared with phase 1 [GMR (95% confidence interval) 0.79 (0.62 –1.00) and 1.39 (1.08 –1.78), respectively], whereas no significant differences in other ribavirin PK parameters were observed between study phases. No clinically significant safety concerns were reported. Conclusions: The PK profile of ribavirin is altered when administered with raltegravir (reduced Cmax and increased Tmax), with no safety concerns identified. This is unlikely to be of clinical significance or have an impact on the antiviral effects of ribavirin in HIV-1- and HCV-co-infected subjects
Predicting spontaneous clearance of acute hepatitis C virus in a large cohort of HIV-1-infected men
<b>Objective</b> An epidemic of acute hepatitis C virus (HCV) infection in HIV-positive men-who-have-sex-with-men (MSM) is emerging in Europe, Australia and the USA. The aim of this study was to characterise the natural history of primary HCV in this setting and to assess host and viral factors which predict spontaneous clearance.<p></p>
<b>Methods</b> This prospective longitudinal cohort study was carried out in 112 HIV-positive patients who were followed in a single centre (the St Mary's Acute HCV Cohort). Plasma and peripheral blood mononuclear cells (PBMCs) were obtained at monthly intervals for 3 months and at 3-monthly intervals thereafter for a median of 45 months (IQR=29–69 months). The primary end point was spontaneous clearance of HCV. Cox regression was used to assess the impact of clinical and virological variables on outcome, including liver function, CD4 count, rate of HCV RNA decline, T cell response and clonal sequence evolution within the HCV E2 envelope gene.<p></p>
<b>Results</b> 15% of patients cleared HCV spontaneously, while 85% progressed towards chronicity. The latter group included a significant proportion of ‘fluctuating’ progressors (37.5%), in whom a fall followed by a rise (>1 log10) in viraemia was observed. This was associated with superinfection with new HCV strains and partially effective T cell responses. Spontaneous clearance was strongly associated with a 2.2 log10 viral load drop within 100 days of infection (HR=1.78; p<0.0001), elevated bilirubin (≥40 μmol/l; HR=5.04; p=0.006), elevated alanine aminotransferase (ALT; ≥1000 IU/ml; HR=2.62; p=0.048) and baseline CD4 count ≥650×106/l (HR=2.66; p=0.045), and only occurred in patients with genotype 1 infection. Evolution to spontaneous clearance occurred in patients with low viral diversity in the presence of an early multispecific T cell response.<p></p>
<b>Conclusions</b> Spontaneous clearance of acute HCV in HIV-positive men can be predicted by a rapid decline in viral load, high CD4 count, elevated bilirubin and ALT, and is associated with low viral diversity and strong T cell responses
Magnetically Dominated Strands of Cold Hydrogen in the Riegel-Crutcher Cloud
We present new high resolution (100 arcsec) neutral hydrogen (H I)
self-absorption images of the Riegel-Crutcher cloud obtained with the Australia
Telescope Compact Array and the Parkes Radio Telescope. The Riegel-Crutcher
cloud lies in the direction of the Galactic center at a distance of 125 +/- 25
pc. Our observations resolve the very large, nearby sheet of cold hydrogen into
a spectacular network of dozens of hair-like filaments. Individual filaments
are remarkably elongated, being up to 17 pc long with widths of less than ~0.1
pc. The strands are reasonably cold, with spin temperatures of 40 K and in many
places appearing to have optical depths larger than one. Comparing the H I
images with observations of stellar polarization we show that the filaments are
very well aligned with the ambient magnetic field. We argue that the structure
of the cloud has been determined by its magnetic field. In order for the cloud
to be magnetically dominated the magnetic field strength must be > 30
microGauss.Comment: To appear in the Astrophysical Journal. 26 pages, 6 figures. Full
resolution version available at
ftp://ftp.atnf.csiro.au/pub/people/nmcclure/papers/rc_cloud.pd
Tilted-Cone Induced Cusps and Nonmonotonic Structures in Dynamical Polarization Function of Massless Dirac Fermions
The polarization function of electrons with the tilted Dirac cone found in
organic conductors is studied using the tilted Weyl equation. The dynamical
property is explored based on the analytical treatment of the particle-hole
excitation. It is shown that the polarization function as the function of both
the frequency and the momentum exhibits cusps and nonmonotonic structures. The
polarization function depends not only on the magnitude but also the direction
of the external momentum. These properties are characteristic of the tilted
Dirac cone, and are contrast to the isotropic case of grapheme. Further, the
results are applied to calculate the optical conductivity, the plasma frequency
and the screening of Coulomb interaction, which are also strongly influenced by
the tilted cone.Comment: 28 pages, 12 figures, to be published in Journal of the Physical
Society of Japan Vol. 79 (2010) No. 1
Discovery of novel alphacoronaviruses in European rodents and shrews
Eight hundred and thirteen European rodents and shrews encompassing seven different species were screened for alphacoronaviruses using PCR detection. Novel alphacoronaviruses were detected in the species Rattus norvegicus, Microtus agrestis, Sorex araneus and Myodes glareolus. These, together with the recently described Lucheng virus found in China, form a distinct rodent/shrew-specific clade within the coronavirus phylogeny. Across a highly conserved region of the viral polymerase gene, the new members of this clade were up to 22% dissimilar at the nucleotide level to the previously described Lucheng virus. As such they might represent distinct species of alphacoronaviruses. These data greatly extend our knowledge of wildlife reservoirs of alphacoronaviruses
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