203 research outputs found
The nature of X-ray spectral variability in Seyfert Galaxies
We use a model-independent technique to investigate the nature of the 2-15
keV X-ray spectral variability in four Seyfert galaxies and distinguish between
spectral pivoting and the two-component model for spectral variability. Our
analysis reveals conclusively that the softening of the X-ray continuum with
increasing flux in MCG -6-30-15 and NGC 3516 is a result of summing two
spectral components: a soft varying component (SVC) with spectral shape
independent of flux and a constant hard component (HCC). In contrast, the
spectral variability in NGC 4051 can be well described by simple pivoting of
one component, together with an additional hard constant component. The
spectral variability model for NGC 5506 is ambiguous, due to the smaller range
of fluxes sampled by the data. We investigate the shape of the hard spectral
component in MCG -6-30-15 and find that it appears similar to a pure reflection
spectrum, but requires a large reflected fraction (R>3). We briefly discuss
physical interpretations of the different modes of spectral variability.Comment: Accepted for publication in MNRAS letter
Very fast X-ray spectral variability in Cygnus X-1: Origin of the hard and soft-state emission components
The way in which the X-ray photon index, {\Gamma}, varies as a function of
count rate is a strong diagnostic of the emission processes and emission
geometry around accreting compact objects. Here we present the results from a
study using a new, and simple, method designed to improve sensitivity to the
measurement of the variability of {\Gamma} on very short time-scales.
We have measured {\Gamma} in ~2 million spectra, extracted from observations
with a variety of different accretion rates and spectral states, on time-scales
as short as 16 ms for the high mass X-ray binary Cygnus X-1, and have
cross-correlated these measurements with the source count rate. In the
soft-state cross-correlation functions (CCFs) we find a positive peak at zero
lag, stronger and narrower in the softer observations. Assuming that the X-rays
are produced by Compton scattering of soft seed photons by high energy
electrons in a corona, these results are consistent with Compton cooling of the
corona by seed photons from the inner edge of the accretion disc, the
truncation radius of which increases with increasing hardness ratio.
The CCFs produced from the hard-state observations, however, show an
anti-correlation which is most easily explained by variation in the energy of
the electrons in the corona rather than in variation of the seed photon flux.
The hard-state CCFs can be decomposed into a narrow anti-correlation at zero
lag, which we tentatively associate with the effects of self-Comptonisation of
cyclo-synchrotron seed photons in either a hot, optically thin accretion flow
or the base of the jet, and a second, asymmetric component which we suggest is
produced as a consequence of a lag between the soft and hard X-ray emission.
The lag may be caused by a radial temperature/energy gradient in the
Comptonising electrons combined with the inward propagation of accretion rate
perturbations.Comment: 12 pages, 14 figures; accepted for publication in Monthly Notices of
the Royal Astronomical Society, 2013 June
HST emission-line images of nearby 3CR radio galaxies: two photoionization, accretion and feedback modes
We present HST/ACS narrow-band images of a low-z sample of 19 3C radio
galaxies to study the H and [OIII] emissions from the narrow-line
region (NLR). Based on nuclear emission line ratios, we divide the sample into
High and Low Excitation Galaxies (HEGs and LEGs). We observe different line
morphologies, extended line emission on kpc scale, large [OIII]/H
scatter across the galaxies, and a radio-line alignment. In general, HEGs show
more prominent emission line properties than LEGs: larger, more disturbed, more
luminous, and more massive regions of ionized gas with slightly larger covering
factors. We find evidence of correlations between line luminosities and (radio
and X-ray) nuclear luminosities. All these results point to a main common
origin, the active nucleus, which ionize the surrounding gas. However, the
contribution of additional photoionization mechanism (jet shocks and star
formation) are needed to account for the different line properties of the two
classes. A relationship between the accretion, photoionization and feedback
modes emerges from this study. For LEGs (hot-gas accretors), the synchrotron
emission from the jet represents the main source of ionizing photons. The lack
of cold gas and star formation in their hosts accounts for the moderate
ionized-gas masses and sizes. For HEGs (cold-gas accretors), an ionizing
continuum from a standard disk and shocks from the powerful jets are the main
sources of photoionization, with the contribution from star formation. These
components, combined with the large reservoir of cold/dust gas brought from a
recent merger, account for the properties of their extended emission-line
regions.Comment: accepted for publication on ApJ (22 pages, 12 figures
A jet-dominated model for a broad-band spectral energy distribution of the nearby low-luminosity active galactic nucleus in M94
We have compiled a new multiwavelength spectral energy distribution (SED) for
the closest obscured low-ionization emission-line region active galactic
nucleus (AGN), NGC 4736, also known as M94. The SED comprises mainly
high-resolution (mostly sub-arcsecond, or, at the distance to M94, <23 pc from
the nucleus) observations from the literature, archival data, as well as
previously unpublished sub-millimetre data from the Plateau de Bure
Interferometer (PdBI) and the Combined Array for Research in Millimeter-wave
Astronomy, in conjunction with new electronic MultiElement Radio
Interferometric Network (e-MERLIN) L-band (1.5 GHz) observations. Thanks to the
e-MERLIN resolution and sensitivity, we resolve for the first time a double
structure composed of two radio sources separated by ~1 arcsec, previously
observed only at higher frequency. We explore this data set, which further
includes non-simultaneous data from the Very Large Array, the Gemini telescope,
the Hubble Space Telescope and the Chandra X-ray observatory, in terms of an
outflow-dominated model. We compare our results with previous trends found for
other AGN using the same model (NGC 4051, M81*, M87 and Sgr A*), as well as
hard- and quiescent-state X-ray binaries. We find that the nuclear broad-band
spectrum of M94 is consistent with a relativistic outflow of low inclination.
The findings in this work add to the growing body of evidence that the physics
of weakly accreting black holes scales with mass in a rather straightforward
fashion.Comment: 18 pages, 7 figure
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Coccidioidomycosis Complement Fixation Titer Trends in the Age of Antifungals.
Coccidioidomycosis is associated with a broad spectrum of illness severity, ranging from asymptomatic or self-limited pulmonary infection to life-threatening manifestations of disseminated disease. Serologic studies before the widespread availability of antifungals established current understanding of serologic kinetics and dynamics. Chart histories and complement fixation (CF) titer trends were analyzed for 434 antifungal-treated coccidioidomycosis patients, who were classified by three infectious disease physicians as having either pulmonary uncomplicated coccidioidomycosis (PUC) (n = 248), pulmonary chronic coccidioidomycosis (PCC) (n = 64), disseminated coccidioidomycosis (DC) not including meningitis (n = 86), or coccidioidal meningitis (CM) (n = 36). The median maximal CF titers were 1:4 for PUC patients, 1:24 for PCC patients, 1:128 for DC patients, and 1:32 for CM patients. Approximately 25.4% of PUC patients, 6.2% of PCC patients, 2.3% of DC patients, and 8.3% of CM patients did not develop detectable titers during the study period. Maximal titers developed a mean of 31 days (95% confidence interval [CI], 13 to 50 days) after initial serologic positivity, with no significant differences between groups. Serologic recurrence occurred in 9% of PUC patients, 36% of PCC patients, 50% of DC patients, and 52% of CM patients. Median titer improvement rates were 91 days/dilution for PUC patients, 112 days/dilution for PCC patients, 136 days/dilution for DC patients, and 146 days/dilution for CM patients. Receiver operating characteristic (ROC) analysis revealed that CF testing retains moderate classification value for disseminated infections (area under the curve [AUC], 0.82 [95% CI, 0.78 to 0.87]) and complicated infections (AUC, 0.82 [95% CI, 0.77 to 0.86]). A suitable cutoff value for complicated infections is ≥1:32. Findings update serologic parameters that are relevant for clinical assessment of coccidioidomycosis patients in the triazole era
Tax Optimization in Change of Legal Form from a Sole Entrepreneur to a Limited Company
Diplomová práce se zabývá analýzou změny právní formy podnikání z fyzické osoby na právnickou, konkrétně na společnost s ručením omezeným. Práce je zaměřená na způsob zdanění fyzických a právnických osob, na jednotlivé možnosti přechodu mezi těmito právními formami a zhodnocení záporů a kladů jednotlivých forem podnikání. Cílem práce je sdělit podnikateli výhody a nevýhody zdanění jednotlivých forem podnikání, navrhnout podnikateli změnu právní formy a seznámit ho s jednotlivými kroky, které jsou potřeba při změně právní formy udělat.This thesis analyzes the changes in the legal form of business from individuals to corporate, namely the limited liability company. The work is focused on the method of taxation of natural and legal persons, individual ability to switch between these legal forms and evaluate the pros and cons of various forms of business. The aim is to communicate the business advantages and disadvantages of different forms of taxation of business, entrepreneurs propose a change of legal form and to acquaint him with the steps that are needed to change the legal form to do.
DNA builds and strengthens the extracellular matrix in Myxococcus xanthus biofilms by interacting with exopolysaccharides.
One intriguing discovery in modern microbiology is the extensive presence of extracellular DNA (eDNA) within biofilms of various bacterial species. Although several biological functions have been suggested for eDNA, including involvement in biofilm formation, the detailed mechanism of eDNA integration into biofilm architecture is still poorly understood. In the biofilms formed by Myxococcus xanthus, a Gram-negative soil bacterium with complex morphogenesis and social behaviors, DNA was found within both extracted and native extracellular matrices (ECM). Further examination revealed that these eDNA molecules formed well organized structures that were similar in appearance to the organization of exopolysaccharides (EPS) in ECM. Biochemical and image analyses confirmed that eDNA bound to and colocalized with EPS within the ECM of starvation biofilms and fruiting bodies. In addition, ECM containing eDNA exhibited greater physical strength and biological stress resistance compared to DNase I treated ECM. Taken together, these findings demonstrate that DNA interacts with EPS and strengthens biofilm structures in M. xanthus
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