575 research outputs found
X-ray Spectra of the RIXOS source sample
We present results of an extensive study of the X-ray spectral properties of
sources detected in the RIXOS survey, that is nearly complete down to a flux
limit of 3e-14 cgs (0.5-2 keV). We show that for X-ray surveys containing
sources with low count rate spectral slopes estimated using simple hardness
ratios in the ROSAT band can be biased. Instead we analyse three-colour X-ray
data using statistical techniques appropriate to the Poisson regime which
removes the effects of this bias. We have then applied this technique to the
RIXOS survey to study the spectral properties of the sample. For the AGN we
find an average energy index of 1.05+-0.05 with no evidence for spectral
evolution with redshift. Individual AGN are shown to have a range of properties
including soft X-ray excesses and intrinsic absorption. Narrow Emission Line
Galaxies also seem to fit to a power-law spectrum, which may indicate a
non-thermal origin for their X-ray emission. We infer that most of the clusters
in the sample have a bremsstrahlung temperature >3 keV, although some show
evidence for a cooling flow. The stars deviate strongly from a power-law model
but fit to a thermal model. Finally, we have analysed the whole RIXOS sample
containing 1762 sources. We find that the mean spectral slope of the sources
hardens at lower fluxes in agreement with results from other samples. However,
a study of the individual sources demonstrates that the hardening of the mean
is caused by the appearance of a population of very hard sources at the lowest
fluxes. This has implications for the nature of the soft X-ray background.Comment: 31,LaTeX file, 2 PS files with Table 2 and 22 PS figures. MNRAS in
pres
Supersoft X-ray sources identified with Be binaries in the Magellanic Clouds
We investigated four luminous supersoft X-ray sources (SSS) in the Magellanic
Clouds suspected to have optical counterparts of Be spectral type. If the
origin of the X-rays is in a very hot atmosphere heated by hydrogen burning in
accreted envelopes of white dwarfs (WDs), like in the majority of SSS, these
objects are close binaries, with very massive WD primaries. Using the South
African Large Telescope (SALT), we obtained the first optical spectra of the
proposed optical counterparts of two candidate Be stars associated with SUZAKU
J0105-72 and XMMU J010147.5-715550, respectively a transient and a recurrent
SSS, and confirmed the proposed Be classification and Small Magellanic Clouds
membership. We also obtained new optical spectra of two other Be stars proposed
as optical counterparts of the transient SSS XMMU J052016.0-692505 and
MAXI-J0158-744. The optical spectra with double peaked emission line profiles,
are typical of Be stars and present characteristics similar to many high mass
X-ray binaries with excretion disks, truncated by the tidal interaction with a
compact object. The presence of a massive WD that sporadically ignites nuclear
burning, accreting only at certain orbital or evolutionary phases, explains the
supersoft X-ray flares. We measured equivalent widths and distances between
lines' peaks, and investigated the variability of the prominent emission lines'
profiles. The excretion disks seem to be small in size, and are likely to be
differentially rotating. We discuss possible future observations and the
relevance of these objects as a new class of type Ia supernovae progenitors.Comment: Accepted for publication in teh Astrophysical Journa
Lung cancer in HIV-infected patients
Purpose: Several studies have shown that HIV patients are at higher risk of lung cancer. Our aim is to analyse the prevalence and features of lung cancer in HIV-infected patients. Methods: The clinical charts of 4,721 HIV-infected patients seen in three hospitals of southeast Spain (study period 1992–2012) were reviewed, and all patients with a lung cancer were analysed. Results: There were 61 lung cancers, giving a prevalence of 1.2%. There was a predominance of men (82.0%), and smokers (96.6%; mean pack-years 35.2), with a median age of 48.0 (41.7–52.9) years, and their distribution according to risk group for HIV was: intravenous drug use 58.3%, homosexual 20.0%, and heterosexual 16.7%. Thirty-four (56.7%) patients were Aids cases, and 29 (47.5%) had prior pulmonar events: tuberculosis 16, bacterial pneumonia 9, and P. jiroveci pneumonia 4. The median nadir CD4 count was 149/mm3 (42–232), the median CD4 count at the time of diagnosis of the lung cancer was 237/mm3 (85–397), and 66.1%<350/mm3. 66.7% were on ART, and 70% of them had undetectable HIV viral load. The most common histological types of lung cancer were adenocarcinoma and epidermoid, with 24 (40.0%) and 23 (38.3%) cases, respectively. There were 49 (80.3%) cases with advanced stages (III and IV) at diagnosis. The distribution of treatments was: only palliative 23 (39.7%), chemotherapy 14 (24.1%), surgery and chemotherapy 8 (13.8%), radiotherapy 7 (12.1%), surgery 4 (6.9%), and other combined treatments 2 (3.4%). Forty-six (76.7%) patients died, with a median survival time of 3 months. The Kaplan-Meier survival rate at 6 months was 42.7% (at 12 months 28.5%). Conclusions: The prevalence of lung cancer in this cohort of HIV-patients is high. People affected are mainly men, smokers, with transmission of HIV by intravenous drug use, and around half of them with prior opportunistic pulmonary events. Most patients had low nadir CD4 count, and were immunosuppressed at the time of diagnosis. Adenocarcinoma is the most frequent histological type. The diagnosis is usually made at advanced stages of the neoplasm, and mortality is high
A Medium Survey of the Hard X-Ray Sky with ASCA. II.: The Source's Broad Band X-Ray Spectral Properties
A complete sample of 60 serendipitous hard X-ray sources with flux in the
range \ecs to \ecs (2 - 10
keV), detected in 87 ASCA GIS2 images, was recently presented in literature.
Using this sample it was possible to extend the description of the 2-10 keV
LogN(>S)-LogS down to a flux limit of \ecs (the
faintest detectable flux), resolving about a quarter of the Cosmic X-ray
Background. In this paper we have combined the ASCA GIS2 and GIS3 data of these
sources to investigate their X-ray spectral properties using the "hardness"
ratios and the "stacked" spectra method. Because of the sample statistical
representativeness, the results presented here, that refer to the faintest hard
X-ray sources that can be studied with the current instrumentation, are
relevant to the understanding of the CXB and of the AGN unification scheme.Comment: 28 pages plus 6 figures, LaTex manuscript, Accepted for publication
in the Astrophysical Journal, Figure 5 can retrieved via anonymous ftp at
ftp://ftp.brera.mi.astro.it/pub/ASCA/paper2/fig5.ps.g
Glassy Dynamics of Protein Folding
A coarse grained model of a random polypeptide chain, with only discrete
torsional degrees of freedom and Hookean springs connecting pairs of
hydrophobic residues is shown to display stretched exponential relaxation under
Metropolis dynamics at low temperatures with the exponent , in
agreement with the best experimental results. The time dependent correlation
functions for fluctuations about the native state, computed in the Gaussian
approximation for real proteins, have also been found to have the same
functional form. Our results indicate that the energy landscape exhibits
universal features over a very large range of energies and is relatively
independent of the specific dynamics.Comment: RevTeX, 4 pages, multicolumn, including 5 figures; larger
computations performed, error bars improve
Evidence of a Critical time in Constrained Kinetic Ising models
We study the relaxational dynamics of the one-spin facilitated Ising model
introduced by Fredrickson and Andersen. We show the existence of a critical
time which separates an initial regime in which the relaxation is exponentially
fast and aging is absent from a regime in which relaxation becomes slow and
aging effects are present. The presence of this fast exponential process and
its associated critical time is in agreement with some recent experimental
results on fragile glasses.Comment: 20 Pages + 7 Figures, Revte
Повседневность первобытного человека
Seven samples of Siluro-Devonian sedimentary rocks from the Cantabrian and Central Iberian zones of the Iberian
Variscan belt have been investigated for provenance and contain four main age populations in variable relative proportion:
Ediacaran–Cryogenian (c. 0.55–0.8Ga), Tonian–Stenian (0.85–1.2Ga), Palaeoproterozoic (c. 1.8–2.2Ga) and Archaean (c.
2.5–3.3Ga). Five samples contain very minor Palaeozoic (Cambrian) zircons and six samples contain minor but significant
zircons of Middle and Early Mesoproterozoic (Ectasian–Calymmian, 1.6–1.8) age. These data highlight the transition from
an arc environment to a stable platform following the opening of the Rheic Ocean. Variations in detrital zircon populations
in Middle–Late Devonian times reflect the onset of Variscan convergence between Laurussia and Gondwana. The presence
of a high proportion of zircons of Tonian–Stenian age in Devonian sedimentary rocks may be interpreted as (1) the existence
of a large Tonian–Stenian arc terrane exposed in the NE African realm (in or around the Arabian–Nubian Shield), (2) the
participation, from the Ordovician time, of a more easterly alongshore provenance of Tonian–Stenian zircons, and (3) an
increase in the relative proportion of Tonian–Stenian zircons with respect to the Ediacaran–Cryogenian population owing to
the drift of the Avalonian–Cadomian ribbon continent, or the progressive burial of Ediacaran–Cryogenian rocks coeval with
the denudation of older source rocks from the craton interior
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