1,294 research outputs found
Mass Measurements of AGN from Multi-Lorentzian Models of X-ray Variability. I. Sampling Effects in Theoretical Models of the rms^2-M_BH Correlation
Recent X-ray variability studies suggest that the log of the square of the
fractional rms variability amplitude, rms^2, seems to correlate with the log of
the AGN black-hole mass, M_BH, with larger black holes being less variable for
a fixed time interval. This has motivated the theoretical modeling of the
rms^2-M_BH correlation with the aim of constraining AGN masses based on X-ray
variability. A viable approach to addressing this problem is to assume an
underlying power spectral density with a suitable mass dependence, derive the
functional form of the rms^2-M_BH correlation for a given sampling pattern, and
investigate whether the result is consistent with the observations. For
simplicity, previous studies, inspired by the similarities shared by the timing
properties of AGN and X-ray binaries, have explored model power spectral
densities characterized by broken power laws. and ignored, in general, the
distorting effects that the particular sampling pattern imprints in the
observed power spectral density. Motivated by the latest timing results from
X-ray binaries, obtained with RXTE, we propose that AGN broad-band noise
spectra consist of a small number of Lorentzian components. This assumption
allows, for the first time, to fully account for sampling effects in
theoretical models of X-ray variability in an analytic manner. We show that,
neglecting sampling effects when deriving the fractional rms from the model
power spectral density can lead to underestimating it by a factor of up to 80%
with respect to its true value for the typical sampling patterns used to
monitor AGN. We discuss the implications of our results for the derivation of
AGN masses using theoretical models of the rms^2-M_BH correlation. (Abridged)Comment: The Astrophysical Journal, in press, 11 pages, 6 figure
A variability study of the Seyfert 2 galaxy NGC 6300 with XMM-Newton
We present the results of timing analysis of the XMM-Newton observation of
the Seyfert 2 galaxy NGC 6300. The hard X-ray spectrum above 2 keV consists of
a Compton-thin-absorbed power law, as is often seen in Seyfert 2 galaxies. We
clearly detected rapid time variability on a time scale of about 1000 s from
the light curve above 2 keV. The excess variance of the time variability
(sigma2_RMS) is calculated to be ~0.12, and the periodogram of the light curve
is well represented by a power law function with a slope of 1.75. In contrast
with previous results from Seyfert 2 nuclei, these variability characteristics
are consistent with those of Seyfert 1 galaxies. This consistency suggests that
NGC 6300 has a similar black hole mass and accretion properties as Seyfert 1
galaxies. Using the relation between time variability and central black hole
mass by Hayashida et al. (1998), the black hole mass of NGC 6300 is estimated
to be ~2.8x10^5 Mo. Taking uncertainty of this method into account, the black
hole mass is less than 10^7 Mo. Taking the bolometric luminosity of 3.3x10^43
erg/s into consideration, this yields an accretion rate of > 0.03 of the
Eddington value, and comparable with estimates from Seyfert 1 galaxies using
this method. The time variability analysis suggests that NGC 6300 actually has
a Seyfert 1 nucleus obscured by a thick matter, and more generally provides a
new pillar of support for the unified model of Seyfert galaxies based on
obscuration.Comment: 11 pages, 6 figures, accepted for publication in Ap
Talking quiescence: a rigorous theory that supports parallel composition, action hiding and determinisation
The notion of quiescence - the absence of outputs - is vital in both
behavioural modelling and testing theory. Although the need for quiescence was
already recognised in the 90s, it has only been treated as a second-class
citizen thus far. This paper moves quiescence into the foreground and
introduces the notion of quiescent transition systems (QTSs): an extension of
regular input-output transition systems (IOTSs) in which quiescence is
represented explicitly, via quiescent transitions. Four carefully crafted rules
on the use of quiescent transitions ensure that our QTSs naturally capture
quiescent behaviour.
We present the building blocks for a comprehensive theory on QTSs supporting
parallel composition, action hiding and determinisation. In particular, we
prove that these operations preserve all the aforementioned rules.
Additionally, we provide a way to transform existing IOTSs into QTSs, allowing
even IOTSs as input that already contain some quiescent transitions. As an
important application, we show how our QTS framework simplifies the fundamental
model-based testing theory formalised around ioco.Comment: In Proceedings MBT 2012, arXiv:1202.582
Diagnostics of Neutron Star and Black Hole X-Ray Binaries with X-Ray Shot Widths
A statistic w, the differential coefficient of the mean absolute difference
of an observed lightcurve, is proposed for timescale analysis of shot widths.
The shortest width of random shots can be measured by the position of the lower
cut-off in the timescale spectrum of w. We use the statistic to analyze X-ray
lightcurves from a sample of neutron star and black hole binaries and the
results show that the timescale analysis can help us distinguish between
neutron star binaries and black hole binaries. The analysis can further reveal
the structure and dynamics of accretion disks around black holes.Comment: 17 pages, 6 figures, accepted by Ap
Triple Therapy Protocol for Primary and Secondary Auricular Keloids:A Prospective Outcome Evaluation
BACKGROUND:Ear keloid lesions present a significant challenge to the aesthetic surgeon. Keloids are known to recur and can cause severe cosmetic, functional, and psychological impairments. Several adjuvants to surgical removal have been promoted, with varying recurrence rates. OBJECTIVE: To evaluate the effectiveness of triple therapy to treat secondary (and large primary) auricular keloids.Ā MATERIALS AND METHODS:Ā Patients with secondary or large primary auricular keloids undergoing triple therapy were prospectively studied. Keloids were excised intramarginally under magnification and repeated triamcinolone acetonide 40 mg/mL injections were administered, followed by the application of a custom-made acrylate pressure device. Recurrent keloid formation and adverse events were monitored during a minimum of 6 months of follow-up.Ā RESULTS:Ā Sixteen auricular keloid lesions (3 large primary and 13 secondary) were subjected to the proposed technique with a mean follow-up of 28 months. All cases that adhered to the protocol were free of keloid after triple therapy. Side effects were limited to 1 case of lobular atrophy and slight hypopigmentation. All patients were satisfied with the results.Ā CONCLUSION:Ā The triple therapy protocol is highly effective in primary and secondary auricular keloid as long as patients remain compliant.</p
Have Gender Gaps in Math Closed? Achievement, Teacher Perceptions, and Learning Behaviors Across Two ECLS-K Cohorts
Studies using data from the Early Childhood Longitudinal StudyāKindergarten Class of 1998ā1999 (ECLS-K:1999) revealed gender gaps in mathematics achievement and teacher perceptions. However, recent evidence suggests that gender gaps have closed on state tests, raising the question of whether such gaps are absent in the ECLS-K:2011 cohort. Extending earlier analyses, this study compares the two ECLS-K cohorts, exploring gaps throughout the achievement distribution and examining whether learning behaviors might differentially explain gaps more at the bottom than the top of the distribution. Overall, this study reveals remarkable consistency across both ECLS-K cohorts, with the gender gap developing early among high achievers and spreading quickly throughout the distribution. Teachers consistently rate girlsā mathematical proficiency lower than that of boys with similar achievement and learning behaviors. Gender differences in learning approaches appear to be fairly consistent across the achievement distribution, but girlsā more studious approaches appear to have more payoff at the bottom of the distribution than at the top. Questions remain regarding why boys outperform girls at the top of the distribution, and several hypotheses are discussed. Overall, the persistent ECLS-K patterns make clear that girlsā early mathematics learning experiences merit further attention
Gamification of health professions education:a systematic review
Gamification refers to using game attributes in a non-gaming context. Health professions educators increasingly turn to gamification to optimize students' learning outcomes. However, little is known about the concept of gamification and its possible working mechanisms. This review focused on empirical evidence for the effectiveness of gamification approaches and theoretical rationales for applying the chosen game attributes. We systematically searched multiple databases, and included all empirical studies evaluating the use of game attributes in health professions education. Of 5044 articles initially identified, 44 met the inclusion criteria. Negative outcomes for using gamification were not reported. Almost all studies included assessment attributes (n = 40), mostly in combination with conflict/challenge attributes (n = 27). Eight studies revealed that this specific combination had increased the use of the learning material, sometimes leading to improved learning outcomes. A relatively small number of studies was performed to explain mechanisms underlying the use of game attributes (n = 7). Our findings suggest that it is possible to improve learning outcomes in health professions education by using gamification, especially when employing game attributes that improve learning behaviours and attitudes towards learning. However, most studies lacked well-defined control groups and did not apply and/or report theory to understand underlying processes. Future research should clarify mechanisms underlying gamified educational interventions and explore theories that could explain the effects of these interventions on learning outcomes, using well-defined control groups, in a longitudinal way. In doing so, we can build on existing theories and gain a practical and comprehensive understanding of how to select the right game elements for the right educational context and the right type of student
A near-IR variability study of the Galactic black hole: a red noise source with no detected periodicity
We present the results of near-infrared (2 and 3 microns) monitoring of Sgr
A*-IR with 1 min time sampling using the natural and laser guide star adaptive
optics (LGS AO) system at the Keck II telescope. Sgr A*-IR was observed
continuously for up to three hours on each of seven nights, between 2005 July
and 2007 August. Sgr A*-IR is detected at all times and is continuously
variable, with a median observed 2 micron flux density of 0.192 mJy,
corresponding to 16.3 magnitude at K'. These observations allow us to
investigate Nyquist sampled periods ranging from about 2 minutes to an hour.
Using Monte Carlo simulations, we find that the variability of Sgr A* in this
data set is consistent with models based on correlated noise with power spectra
having frequency dependent power law slopes between 2.0 to 3.0, consistent with
those reported for AGN light curves. Of particular interest are periods of ~20
min, corresponding to a quasi-periodic signal claimed based upon previous
near-infrared observations and interpreted as the orbit of a 'hot spot' at or
near the last stable orbit of a spinning black hole. We find no significant
periodicity at any time scale probed in these new observations for periodic
signals. This study is sensitive to periodic signals with amplitudes greater
than 20% of the maximum amplitude of the underlying red noise component for
light curves with duration greater than ~2 hours at a 98% confidence limit.Comment: 37 pages, 2 tables, 17 figures, accepted by Ap
Determinants of female sexual function in inflammatory bowel disease: a survey based cross-sectional analysis
<p>Abstract</p> <p>Background</p> <p>Sexual function is impaired in women with inflammatory bowel disease (IBD) as compared to normal controls. We examined disease specific determinants of different aspects of low sexual function.</p> <p>Methods</p> <p>Women with IBD aged 18 to 65 presenting to the university departments of internal medicine and surgery were included. In addition, a random sample from the national patients organization was used (separate analyses). Sexual function was assessed by the Brief Index of Sexual Function in Women, comprising seven different domains of sexuality. Function was considered impaired if subscores were < -1 on a z-normalized scale. Results are presented as age adjusted odds ratios with 95% CI based on multiple logistic regression.</p> <p>Results</p> <p>336 questionnaires were included (219 Crohn's disease, 117 ulcerative colitis). Most women reported low sexual activity (63%; 17% none at all, 20% moderate or high activity). Partnership satisfaction was high in spite of low sexual interest in this group. Depressed mood was the strongest predictor of low sexual function scores in all domains. Urban residency and higher socioecomic status had a protective effect. Disease activity was moderately associated with low desire (OR 1.8, 95% CI 1.0 to 3.2). Severity of the disease course impacted most on intercourse frequency (OR 2.3, 95% CI 1.4 to 4.7). Lubrication problems were more common in smokers (OR 2.5, 95% CI 1.3 to 5.1).</p> <p>Conclusion</p> <p>Mood disturbances and social environment impacted more on sexual function in women with IBD than disease specific factors. Smoking is associated with lubrication problems.</p
X-ray Fluctuation Power Spectral Densities of Seyfert 1 Galaxies
By combining complementary monitoring observations spanning long, medium and
short time scales, we have constructed power spectral densities (PSDs) of six
Seyfert~1 galaxies. These PSDs span 4 orders of magnitude in temporal
frequency, sampling variations on time scales ranging from tens of minutes to
over a year. In at least four cases, the PSD shows a "break," a significant
departure from a power law, typically on time scales of order a few days. This
is similar to the behavior of Galactic X-ray binaries (XRBs), lower mass
compact systems with breaks on time scales of seconds. NGC 3783 shows tentative
evidence for a doubly-broken power law, a feature that until now has only been
seen in the (much better-defined) PSDs of low-state XRBs. It is also
interesting that (when one previously-observed object is added to make a small
sample of seven), an apparently significant correlation is seen between the
break time scale and the putative black hole mass , while none
is seen between break time scale and luminosity. The data are consistent with
the linear relation T = M_{\rm BH}/10^{6.5} \Msun; extrapolation over 6--7
orders of magnitude is in reasonable agreement with XRBs. All of this
strengthens the case for a physical similarity between Seyfert~1s and XRBs.Comment: 27 pages, 13 figures. Accepted for publication in ApJ. Typo correcte
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