289 research outputs found
ASCA observations of type-2 Seyfert Galaxies. III. Orientation and X-ray Absorption
We discuss the spectral properties of a sample of type-2 Seyfert galaxies
based upon the analysis of \asca data. In this paper we consider the sources
for which the X-ray spectra appear to be dominated by the nuclear continuum,
transmitted through a large column of absorbing material. We find that both
Seyfert-2 galaxies and NELGs show iron K line profiles indicative of
reprocessing of nuclear X-rays in a face-on accretion disk. Such line profiles
are also observed in Seyfert-1 galaxies. This result is contrary to unification
models, which would predict the inner regions of Seyfert-2 galaxies to be
observed edge-on. This raises some questions as to the orientation of the
circumnuclear absorber. If the observed differences between Seyfert type-1 and
type-2 galaxies, and NELGs are not due to differences in the orientation of the
absorbing material, then we suggest that differences in dust composition and
grain size, and in the density of the circumnuclear gas could be of primary
importance.Comment: 28 pages, 3 figures. LaTeX with encapsulated postscript. To appear in
the Astrophysical Journa
High-Energy Spectral Complexity from Thermal Gradients in Black Hole Atmospheres
We show that Compton scattering of soft photons with energies near 100 eV in
thermally stratified black-hole accretion plasmas with temperatures in the
range 100 keV - 1 MeV can give rise to an X-ray spectral hardening near 10 keV.
This could produce the hardening observed in the X-ray spectra of black holes,
which is generally attributed to reflection or partial covering of the incident
continuum source by cold optically thick matter. In addition, we show that the
presence of very hot (kT=1 MeV) cores in plasmas leads to spectra exibiting
high energy tails similar to those observed from Galactic black-hole
candidates.Comment: 11 pages, uuencoded gziped postscript, ApJ Letters in pres
Origin of Magnetic Fields in the Universe Due to Nonminimal Gravitational-Electromagnetic Coupling
Basically the only existing theories for the creation of a magnetic field B
in the Universe are the creation of a seed field of order 10^{-20} G in spiral
galaxy which is subsequently supposedly amplified up to the observed 10^{-6} -
10^{-5} G by a dynamo process or a seed intergalactic field of magnitude
10^{-12} - 10^{-10} G which is amplified by collapse and differential rotation.
No satisfactory dynamo theory, however, exists today. We show that a 10^{-6} -
10^{-5} G magnetic field in spiral galaxies is directly obtained from a
nonminimal gravitational-electromagnetic coupling, without the need of
significant dynamo amplification.Comment: 5 pages, Latex (Revtex), no figures, To appear in PR
X-ray Absorption and Reflection in Active Galactic Nuclei
X-ray spectroscopy offers an opportunity to study the complex mixture of
emitting and absorbing components in the circumnuclear regions of active
galactic nuclei, and to learn about the accretion process that fuels AGN and
the feedback of material to their host galaxies. We describe the spectral
signatures that may be studied and review the X-ray spectra and spectral
variability of active galaxies, concentrating on progress from recent Chandra,
XMM-Newton and Suzaku data for local type 1 AGN. We describe the evidence for
absorption covering a wide range of column densities, ionization and dynamics,
and discuss the growing evidence for partial-covering absorption from data at
energies > 10 keV. Such absorption can also explain the observed X-ray spectral
curvature and variability in AGN at lower energies and is likely an important
factor in shaping the observed properties of this class of source.
Consideration of self-consistent models for local AGN indicates that X-ray
spectra likely comprise a combination of absorption and reflection effects from
material originating within a few light days of the black hole as well as on
larger scales. It is likely that AGN X-ray spectra may be strongly affected by
the presence of disk-wind outflows that are expected in systems with high
accretion rates, and we describe models that attempt to predict the effects of
radiative transfer through such winds, and discuss the prospects for new data
to test and address these ideas.Comment: Accepted for publication in the Astronomy and Astrophysics Review. 58
pages, 9 figures. V2 has fixed an error in footnote
Idiopathic pulmonary fibrosis
Idiopathic pulmonary fibrosis (IPF) is a non-neoplastic pulmonary disease that is characterized by the formation of scar tissue within the lungs in the absence of any known provocation. IPF is a rare disease which affects approximately 5 million persons worldwide. The prevalence is estimated to be slightly greater in men (20.2/100,000) than in women (13.2/100,000). The mean age at presentation is 66 years. IPF initially manifests with symptoms of exercise-induced breathless and dry coughing. Auscultation of the lungs reveals early inspiratory crackles, predominantly located in the lower posterior lung zones upon physical exam. Clubbing is found in approximately 50% of IPF patients. Cor pulmonale develops in association with end-stage disease. In that case, classic signs of right heart failure may be present. Etiology remains incompletely understood. Some environmental factors may be associated with IPF (cigarette smoking, exposure to silica and livestock). IPF is recognized on high-resolution computed tomography by peripheral, subpleural lower lobe reticular opacities in association with subpleural honeycomb changes. IPF is associated with a pathological lesion known as usual interstitial pneumonia (UIP). The UIP pattern consists of normal lung alternating with patches of dense fibrosis, taking the form of collagen sheets. The diagnosis of IPF requires correlation of the clinical setting with radiographic images and a lung biopsy. In the absence of lung biopsy, the diagnosis of IPF can be made by defined clinical criteria that were published in guidelines endorsed by several professional societies. Differential diagnosis includes other idiopathic interstitial pneumonia, connective tissue diseases (systemic sclerosis, polymyositis, rheumatoid arthritis), forme fruste of autoimmune disorders, chronic hypersensitivity pneumonitis and other environmental (sometimes occupational) exposures. IPF is typically progressive and leads to significant disability. The median survival is 2 to 5 years from the time of diagnosis. Medical therapy is ineffective in the treatment of IPF. New molecular therapeutic targets have been identified and several clinical trials are investigating the efficacy of novel medication. Meanwhile, pulmonary transplantation remains a viable option for patients with IPF. It is expected that, during the next decade, considerable progress will be made toward the understanding and treatment of this devastating illness
Genome-wide analysis of ivermectin response by Onchocerca volvulus reveals that genetic drift and soft selective sweeps contribute to loss of drug sensitivity
Treatment of onchocerciasis using mass ivermectin administration has reduced morbidity and transmission throughout Africa and Central/South America. Mass drug administration is likely to exert selection pressure on parasites, and phenotypic and genetic changes in several Onchocerca volvulus populations from Cameroon and Ghana-exposed to more than a decade of regular ivermectin treatment-have raised concern that sub-optimal responses to ivermectin's anti-fecundity effect are becoming more frequent and may spread.Pooled next generation sequencing (Pool-seq) was used to characterise genetic diversity within and between 108 adult female worms differing in ivermectin treatment history and response. Genome-wide analyses revealed genetic variation that significantly differentiated good responder (GR) and sub-optimal responder (SOR) parasites. These variants were not randomly distributed but clustered in ~31 quantitative trait loci (QTLs), with little overlap in putative QTL position and gene content between the two countries. Published candidate ivermectin SOR genes were largely absent in these regions; QTLs differentiating GR and SOR worms were enriched for genes in molecular pathways associated with neurotransmission, development, and stress responses. Finally, single worm genotyping demonstrated that geographic isolation and genetic change over time (in the presence of drug exposure) had a significantly greater role in shaping genetic diversity than the evolution of SOR.This study is one of the first genome-wide association analyses in a parasitic nematode, and provides insight into the genomics of ivermectin response and population structure of O. volvulus. We argue that ivermectin response is a polygenically-determined quantitative trait (QT) whereby identical or related molecular pathways but not necessarily individual genes are likely to determine the extent of ivermectin response in different parasite populations. Furthermore, we propose that genetic drift rather than genetic selection of SOR is the underlying driver of population differentiation, which has significant implications for the emergence and potential spread of SOR within and between these parasite populations
Detrusor response to outlet obstruction
Bladder responses to outlet obstruction are thought to involve muscular hyperplasia, increased pressure, and finally, decompensation. While these things probably do occur, the process of bladder response to obstruction also includes loss of reflex control and deposition of collagen.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47058/1/345_2004_Article_BF00327002.pd
ASCA observations of Seyfert 1 galaxies: I. Data Analysis, Imaging and Timing
We present the first in a series of papers describing the X-ray properties of
a sample of 18 Seyfert 1 galaxies, using data obtained by \asca. The imaging
data reveal a number of serendipitous hard X-ray sources in some source fields,
but none contribute significantly to the hard X-ray flux of the AGN. All but
one of the Seyferts show evidence for variability on timescales of
minutes-hours, with the amplitude anti-correlated with the source luminosity,
confirming previous results. In at least 8 sources, there is evidence that the
variability amplitude below 2 keV is greater than that in the hard X-ray band,
perhaps indicating variable components other than the power-law in the soft
band. Ultra-rapid variability, implying significant power at frequencies ~Hz is detected in at least 5 sources, but is difficult to detect in
most cases, due to the sampling and signal-to-noise ratio. In Mrk 766 and
MCG-6-30-15 there is also an indication that the high--frequency power--spectra
are variable in shape and/or intensity. There is similar evidence in NGC 4151,
but on longer time scales.Comment: 30 pages, 5 figures. LaTeX with encapsulated postscript. To appear in
the Astrophysical Journal. Also available via
http://lheawww.gsfc.nasa.gov/~nandra/pubs/paper1/abstract.htm
Non-specific interstitial pneumonia in cigarette smokers: a CT study
The goal of this study was to seek indirect evidence that smoking is an aetiological factor in some patients with non-specific interstitial pneumonia (NSIP). Ten current and eight ex-smokers with NSIP were compared to controls including 137 current smokers with no known interstitial lung disease and 11 non-smokers with NSIP. Prevalence and extent of emphysema in 18 smokers with NSIP were compared with subjects meeting GOLD criteria for chronic obstructive pulmonary disease (COPD; group A; n = 34) and healthy smokers (normal FEV1; group B; n = 103), respectively. Emphysema was present in 14/18 (77.8%) smokers with NSIP. Emphysema did not differ in prevalence between NSIP patients and group A controls (25/34, 73.5%), but was strikingly more prevalent in NSIP patients than in group B controls (18/103, 17.5%, P < 0.0005). On multiple logistic regression, the likelihood of emphysema increased when NSIP was present (OR = 18.8; 95% CI = 5.3–66.3; P < 0.0005) and with increasing age (OR = 1.04; 95% CI = 0.99–1.11; P = 0.08). Emphysema is as prevalent in smokers with NSIP as in smokers with COPD, and is strikingly more prevalent in these two groups than in healthy smoking controls. The association between NSIP and emphysema provides indirect support for a smoking pathogenesis hypothesis in some NSIP patients
The XMM-Newton Serendipitous Survey. V. The Second XMM-Newton Serendipitous Source Catalogue
Aims: Pointed observations with XMM-Newton provide the basis for creating
catalogues of X-ray sources detected serendipitously in each field. This paper
describes the creation and characteristics of the 2XMM catalogue. Methods: The
2XMM catalogue has been compiled from a new processing of the XMM-Newton EPIC
camera data. The main features of the processing pipeline are described in
detail. Results: The catalogue, the largest ever made at X-ray wavelengths,
contains 246,897 detections drawn from 3491 public XMM-Newton observations over
a 7-year interval, which relate to 191,870 unique sources. The catalogue fields
cover a sky area of more than 500 sq.deg. The non-overlapping sky area is ~360
sq.deg. (~1% of the sky) as many regions of the sky are observed more than once
by XMM-Newton. The catalogue probes a large sky area at the flux limit where
the bulk of the objects that contribute to the X-ray background lie and
provides a major resource for generating large, well-defined X-ray selected
source samples, studying the X-ray source population and identifying rare
object types. The main characteristics of the catalogue are presented,
including its photometric and astrometric properties .Comment: 27 pages (plus 8 pages appendices), 15 figures. Minor changes
following referee's comments; now accepted for publication in A & A. Note
that this paper "V", not paper "VI" in the series. Previous posting was
incorrect in this regar
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