5,720 research outputs found
Clinical surveillance of thrombotic microangiopathies in Scotland, 2003-2005
The prevalence, incidence and outcomes of haemolytic uraemic syndrome (HUS) and thrombotic thrombocytopaenic purpura (TTP) are not well established in adults or children from prospective studies. We sought to identify both outcomes and current management strategies using prospective, national surveillance of HUS and TTP, from 2003 to 2005 inclusive. We also investigated the links between these disorders and factors implicated in the aetiology of HUS and TTP including infections, chemotherapy, and immunosuppression. Most cases of HUS were caused by verocytotoxin-producing Escherichia coli (VTEC), of which serotype O157 predominated, although other serotypes were identified. The list of predisposing factors for TTP was more varied although use of immunosuppressive agents and severe sepsis, were the most frequent precipitants. The study demonstrates that while differentiating between HUS and TTP is sometimes difficult, in most cases the two syndromes have quite different predisposing factors and clinical parameters, enabling clinical and epidemiological profiling for these disorders
Graviton n-point functions for UV-complete theories in Anti-de Sitter space
We calculate graviton n-point functions in an anti-de Sitter black brane
background for effective gravity theories whose linearized equations of motion
have at most two time derivatives. We compare the n-point functions in Einstein
gravity to those in theories whose leading correction is quadratic in the
Riemann tensor. The comparison is made for any number of gravitons and for all
physical graviton modes in a kinematic region for which the leading correction
can significantly modify the Einstein result. We find that the n-point
functions of Einstein gravity depend on at most a single angle, whereas those
of the corrected theories may depend on two angles. For the four-point
functions, Einstein gravity exhibits linear dependence on the Mandelstam
variable s versus a quadratic dependence on s for the corrected theory.Comment: 29 page
The EXOSAT medium-energy slew survey catalog
We present a catalog of X-ray sources observed during slew maneuvers by the
Medium Energy Detector Array onboard the EXOSAT Observatory. The EXOSAT Medium
Energy slew-survey catalog (EXMS) provides a unique record of the 1--8 keV
X-ray sky between 1983 and 1986. 98% of the sky was observed, with 85%
receiving an exposure of >60 s. 1210 sources were detected. By comparing these
source positions with other catalogs, identifications are given for 992
detections (82% of the sample). These identifications consist of 250 distinct
objects, including 95 different X-ray binary systems, and 14 different AGN. A
further 58 detections have multiple candidates, while 160 detections remain
unidentified. Collimator transmission corrected 1-8 keV count rates are given
for the identified sources, together with raw count rates for the other
detections. The construction of the EXMS and the checks performed to ensure the
validity of the derived source properties are discussed. A publically available
version of this catalog is maintained on the EXOSAT database and archive system
(telnet://[email protected]).Comment: 52 pages. 22 Figures. To be published in A&AS. For more information,
see http://astro.estec.esa.nl/SA-general/Projects/Exosat/exmsintro.htm
The XMM-Newton EPIC X-ray Light Curve Analysis of WR 6
We obtained four pointings of over 100 ks each of the well-studied Wolf-Rayet
star WR 6 with the XMM-Newton satellite. With a first paper emphasizing the
results of spectral analysis, this follow-up highlights the X-ray variability
clearly detected in all four pointings. However, phased light curves fail to
confirm obvious cyclic behavior on the well-established 3.766 d period widely
found at longer wavelengths. The data are of such quality that we were able to
conduct a search for "event clustering" in the arrival times of X-ray photons.
However, we fail to detect any such clustering. One possibility is that X-rays
are generated in a stationary shock structure. In this context we favor a
co-rotating interaction region (CIR) and present a phenomenological model for
X-rays from a CIR structure. We show that a CIR has the potential to account
simultaneously for the X-ray variability and constraints provided by the
spectral analysis. Ultimately, the viability of the CIR model will require both
intermittent long-term X-ray monitoring of WR 6 and better physical models of
CIR X-ray production at large radii in stellar winds.Comment: to appear in Ap
Search for periodicities near 59 s in the COS-B gamma-ray data of 2CG195+04 (Geminga)
The COS-B data relating to five observations in the general direction of Geminga, spanning 6.7 years, were searched for pulsation near 59 s. The SAS-2 indication is not confirmed. An indication of a 59 s pulsation in the gamma ray emission from 2CG195+04 (Geminga) was reported. Early analysis of COS-B data supported the result while later improved statistics did not confirm it. Subsequently, detection of a 59 s pulsation in the emission from the direction of Geminga at ultra high gamma and X-rays was reported. Geminga was identified with the X-ray source 1E0630+128. The final COS-B data on Geminga which was observed five times for a total of 214 days are reported
Probing Wolf-Rayet Winds: Chandra/HETG X-Ray Spectra of WR 6
With a deep Chandra/HETGS exposure of WR 6, we have resolved emission lines
whose profiles show that the X-rays originate from a uniformly expanding
spherical wind of high X-ray-continuum optical depth. The presence of strong
helium-like forbidden lines places the source of X-ray emission at tens to
hundreds of stellar radii from the photosphere. Variability was present in
X-rays and simultaneous optical photometry, but neither were correlated with
the known period of the system or with each other. An enhanced abundance of
sodium revealed nuclear processed material, a quantity related to the
evolutionary state of the star. The characterization of the extent and nature
of the hot plasma in WR 6 will help to pave the way to a more fundamental
theoretical understanding of the winds and evolution of massive stars.Comment: Accepted by the Astrophysical Journa
Cyg X-3: Not seen in high-energy gamma rays by COS-B
COS-B had Cyg X-3 within its field of view during 7 observation periods between 1975 and 1982 for in total approximately 300 days. In the skymaps (70 meV E 5000 meV) of the Cyg-X region produced for each of these observations and in the summed map, a broad complex structure is visible in the region 72 deg approximately less than 1 approximately less than 85 deg, approximately less than 5 deg. No resolved source structure is visible at the position of Cyg X-3, but a weak signal from Cyg X-3 could be hidden in the structured gamma-ray background. Therefore, the data has been searched for a 4.8 h timing signature, as well as for a source signal in the sky map in addition to the diffuse background structure as estimated from tracers of atomic and molecular gas
Parity violating elastic electron scattering and neutron density distributions in the Relativistic Hartree-Bogoliubov model
Parity violating elastic electron scattering on neutron-rich nuclei is
described in the framework of relativistic mean-field theory. Self-consistent
ground state density distributions of Ne, Na, Ni and Sn isotopes are calculated
with the relativistic Hartree- Bogoliubov model, and the resulting neutron
radii are compared with available experimental data. For the elastic scattering
of 850 MeV electrons on these nuclei, the parity-violating asymmetry parameters
are calculated using a relativistic optical model with inclusion of Coulomb
distortion effects. The asymmetry parameters for chains of isotopes are
compared, and their relation to the Fourier transforms of neutron densities is
studied. It is shown that parity-violating asymmetries are sensitive not only
to the formation of the neutron skin, but also to the shell effects of the
neutron density distribution.Comment: RevTeX 17 pages, 18 eps figs, submitted to Phys. Rev.
The thermodynamic evolution of the cosmological event horizon
By manipulating the integral expression for the proper radius of the
cosmological event horizon (CEH) in a Friedmann-Robertson-Walker (FRW)
universe, we obtain an analytical expression for the change \dd R_e in
response to a uniform fluctuation \dd\rho in the average cosmic background
density . We stipulate that the fluctuation arises within a vanishing
interval of proper time, during which the CEH is approximately stationary, and
evolves subsequently such that \dd\rho/\rho is constant. The respective
variations 2\pi R_e \dd R_e and \dd E_e in the horizon entropy and
enclosed energy should be therefore related through the cosmological
Clausius relation. In that manner we find that the temperature of the CEH
at an arbitrary time in a flat FRW universe is , which recovers
asymptotically the usual static de Sitter temperature. Furthermore, it is
proven that during radiation-dominance and in late times the CEH conforms to
the fully dynamical First Law T_e \drv S_e = P\drv V_e - \drv E_e, where
is the enclosed volume and is the average cosmic pressure.Comment: 6 page
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