2,047 research outputs found
A Clumpy Stellar Wind and Luminosity-Dependent Cyclotron Line Revealed by The First Suzaku Observation of the High-Mass X-ray Binary 4U 1538-522
We present results from the first Suzaku observation of the high-mass X-ray
binary 4U 1538-522. The broad-band spectral coverage of Suzaku allows for a
detailed spectral analysis, characterizing the cyclotron resonance scattering
feature at keV and the iron K line at
keV, as well as placing limits on the strengths of the iron K line and
the iron K edge. We track the evolution of the spectral parameters both in time
and in luminosity, notably finding a significant positive correlation between
cyclotron line energy and luminosity. A dip and spike in the lightcurve is
shown to be associated with an order-of-magnitude increase in column density
along the line of sight, as well as significant variation in the underlying
continuum, implying the accretion of a overdense region of a clumpy stellar
wind. We also present a phase-resolved analysis, with most spectral parameters
of interest showing significant variation with phase. Notably, both the
cyclotron line energy and the iron K line intensity vary significantly
with phase, with the iron line intensity significantly out-of-phase with the
pulse profile. We discuss the implications of these findings in the context of
recent work in the areas of accretion column physics and cyclotron resonance
scattering feature formation.Comment: 15 pages, 8 figures. Accepted to ApJ on 2 July 201
X-ray Spectral Variability and Rapid Variability of the Soft X-ray Spectrum Seyfert 1 Galaxies Ark 564 and Ton S180
The bright, soft X-ray spectrum Seyfert 1 galaxies Ark 564 and Ton S180 were
monitored for 35 days and 12 days with ASCA and RXTE (and EUVE for Ton S180).
The short time scale (hours-days) variability patterns were very similar across
energy bands, with no evidence of lags between any of the energy bands studied.
The fractional variability amplitude was almost independent of energy band. It
is difficult to simultaneously explain soft Seyferts stronger variability,
softer spectra, and weaker energy-dependence of the variability relative to
hard Seyferts. The soft and hard band light curves diverged on the longest time
scales probed, consistent with the fluctuation power density spectra that
showed relatively greater power on long time scales in the softest bands. The
simplest explanation is that a relatively hard, rapidly-variable component
dominates the total X-ray spectrum and a slowly-variable soft excess is present
in the lowest energy channels of ASCA. Although it would be natural to identify
the latter with an accretion disk and the former with a corona surrounding it,
a standard thin disk could not get hot enough to radiate significantly in the
ASCA band, and the observed variability time scales are much too short. The
hard component may have a more complex shape than a pure power-law. The most
rapid factor of 2 flares and dips occurred within ~1000 sec in Ark 564 and a
bit more slowly in Ton S180. The speed of the luminosity changes rules out
viscous or thermal processes and limits the size of the individual emission
regions to <~15 Schwarzschild radii (and probably much less), that is, to
either the inner disk or small regions in a corona
Human SHPRH suppresses genomic instability through proliferating cell nuclear antigen polyubiquitination
Differential modifications of proliferating cell nuclear antigen (PCNA) determine DNA repair pathways at stalled replication forks. In yeast, PCNA monoubiquitination by the ubiquitin ligase (E3) yRad18 promotes translesion synthesis (TLS), whereas the lysine-63–linked polyubiquitination of PCNA by yRad5 (E3) promotes the error-free mode of bypass. The yRad5-dependent pathway is important to prevent genomic instability during replication, although its exact molecular mechanism is poorly understood. This mechanism has remained totally elusive in mammals because of the lack of apparent RAD5 homologues. We report that a putative tumor suppressor gene, SHPRH, is a human orthologue of yeast RAD5. SHPRH associates with PCNA, RAD18, and the ubiquitin-conjugating enzyme UBC13 (E2) and promotes methyl methanesulfonate (MMS)–induced PCNA polyubiquitination. The reduction of SHPRH by stable short hairpin RNA increases sensitivity to MMS and enhances genomic instability. Therefore, the yRad5/SHPRH-dependent pathway is a conserved and fundamental DNA repair mechanism that protects the genome from genotoxic stress
An X-ray Bright Nucleus in the Low Surface Brightness Galaxy UGC 6614
We report a study of the X-ray emission from the nuclear region of the low
surface brightness (LSB) galaxy UGC 6614. Very little is known about the
central objects in LSB galaxies especially their X-ray properties and X-ray
spectra. In this study we have used XMM-Newton archival data to study the
characteristics of the X-ray spectrum and the X-ray flux variability of the AGN
in the LSB galaxy UGC 6614. The nucleus of UGC 6614 is very bright in X-ray
emission with an absorption corrected 0.2-10.0 keV luminosity of ~1.1 x 10^{42}
erg s^{-1}. The X-ray spectrum is found to be power-law type with a moderate
column density. A short time scale of intensity variation and large X-ray flux
is indicative of the presence of a black hole at the centre of this galaxy.
Using the method of excess variance, we have determined the black hole mass to
be ~0.12 x 10^{6} solar mass. The X-ray spectral properties are similar to that
of the Seyfert I type AGNs. Our study thus demonstrates that although LSB
galaxies are poor in star formation, they may harbour AGNs with X-ray
properties comparable to that seen in more luminous spiral galaxies.Comment: 5 pages, 4 figures, Accepted for publication in MNRA
Absence of HIV-1 Evolution in the Gut-Associated Lymphoid Tissue from Patients on Combination Antiviral Therapy Initiated during Primary Infection
Mucosal mononuclear (MMC) CCR5+CD4+ T cells of the gastrointestinal (GI) tract are selectively infected and depleted during acute HIV-1 infection. Despite early initiation of combination antiretroviral therapy (cART), gut-associated lymphoid tissue (GALT) CD4+ T cell depletion and activation persist in the majority of HIV-1 positive individuals studied. This may result from ongoing HIV-1 replication and T-cell activation despite effective cART. We hypothesized that ongoing viral replication in the GI tract during cART would result in measurable viral evolution, with divergent populations emerging over time. Subjects treated during early HIV-1 infection underwent phlebotomy and flexible sigmoidoscopy with biopsies prior to and 15–24 months post initiation of cART. At the 2nd biopsy, three GALT phenotypes were noted, characterized by high, intermediate and low levels of immune activation. A representative case from each phenotype was analyzed. Each subject had plasma HIV-1 RNA levels <50 copies/ml at 2nd GI biopsy and CD4+ T cell reconstitution in the peripheral blood. Single genome amplification of full-length HIV-1 envelope was performed for each subject pre- and post-initiation of cART in GALT and PBMC. A total of 280 confirmed single genome sequences (SGS) were analyzed for experimental cases. For each subject, maximum likelihood phylogenetic trees derived from molecular sequence data showed no evidence of evolved forms in the GALT over the study period. During treatment, HIV-1 envelope diversity in GALT-derived SGS did not increase and post-treatment GALT-derived SGS showed no substantial genetic divergence from pre-treatment sequences within transmitted groups. Similar results were obtained from PBMC-derived SGS. Our results reveal that initiation of cART during acute/early HIV-1 infection can result in the interruption of measurable viral evolution in the GALT, suggesting the absence of de-novo rounds of HIV-1 replication in this compartment during suppressive cART
Observations of the High-mass X-Ray Binary A 0535+26 in Quiescence
We have analyzed three observations of the high-mass X-ray binary A 0535+26 performed by the Rossi X-Ray Timing Explorer (RXTE) three, five, and six months after the last outburst in 2011 February. We detect pulsations only in the second observation. The 3-20 keV spectra can be fit equally well with either an absorbed power law or absorbed thermal bremsstrahlung model. Reanalysis of two earlier RXTE observations made 4 yr after the 1994 outburst, original BeppoSAX observations 2 yr later, reanalysis of four EXOSAT observations made 2 yr after the last 1984 outburst, and a recent XMM-Newton observation in 2012 reveal a stacked, quiescent flux level decreasing from ~2 to <1 × 10^(–11) erg cm^(–2) s^(–1) over 6.5 yr after outburst. The detection of pulsations during half of the quiescent observations would imply that accretion onto the magnetic poles of the neutron star continues despite the fact that the circumstellar disk may no longer be present. The accretion could come from material built up at the corotation radius or from an isotropic stellar wind
Searching for the Kuhnian moment : the Black-Scholes-Merton formula and the evolution of modern finance theory
The Black-Scholes-Merton formula has been put to widespread use by options traders because it provides a means of calculating the theoretically 'correct' price of stock options. Traders can therefore see whether the market price of stock options undervalues or overvalues them compared with their hypothetical Black-Scholes-Merton price, before choosing to buy or sell options accordingly. As a consequence of this close relationship between options pricing theory and options pricing practice, a strong performativity loop was activated, whereby market prices quickly converged on the hypothetical Black-Scholes-Merton prices following the dissemination of the formula. The theory has therefore had significant real-world effects, but how should we characterize the initial instinct to derive the theory from a philosophy of science perspective? The two books under review suggest that a Kuhnian reading of the advancement of scientific knowledge might well be the most appropriate. But, on closer inspection, it becomes clear that the publication of the Black-Scholes-Merton formula should not be seen as a Kuhnian moment with paradigm-shaping attributes. It is shown that, at most, the formula acts as an important exemplar which, via its use in the training of options pricing theorists and options pricing practitioners, reinforces the entrenchment of finance theory within the orthodox economics worldview
Compassion fade and the challenge of environmental conservation
Compassion shown towards victims often decreases as the number of individuals in need of aid increases, identifiability of the victims decreases, and the proportion of victims helped shrinks. Such “compassion fade” may hamper individual-level and collective responses to pressing large-scale crises. To date, research on compassion fade has focused on humanitarian challenges; thus, it remains unknown whether and to what extent compassion fade emerges when victims are non-human others. Here we show that compassion fade occurs in the environmental domain, but only among non-environmentalists. These findings suggest that compassion fade may challenge our collective ability and willingness to confront the major environmental problems we face, including climate change. The observed moderation effect of environmental identity further indicates that compassion fade may present a significant psychological barrier to building broad public support for addressing these problems. Our results highlight the importance of bringing findings from the field of judgment and decision making to bear on pressing societal issues
Should Psychotherapy be taught to Psychiatric Residents? A Debate.
Much of this discussion was inspired by a debate held at the 1984 APA Annual Meeting, entitled Does Psychodynamic Theory Have Little Relevance to Contemporary Psychiatric Care? We saw the need for a debate, resident generated, that would address a corollary issue in residency training.
Our program will include an introduction, a debate involving statements for the affirmative, that is, that psychotherapy should be taught to psychiatric residents, and two statements for the negative, that psychotherapy should not be taught to psychiatric residents. Concluding remarks will follow.
If our title is provocative , if what we have to say inspires you to participate in this critical discussion, either by way of pleasing, stimulating, or offending you, then we have served our purpose well
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