1,137 research outputs found
Reverberation Mapping of High-Luminosity Quasars: First Results
Reverberation mapping of nearby active galactic nuclei has led to estimates
of broad-line-region (BLR) sizes and central-object masses for some 37 objects
to date. However, successful reverberation mapping has yet to be performed for
quasars of either high luminosity (above L_opt~10^{46} erg/s) or high redshift
(z>0.3). Over the past six years, we have carried out, at the Hobby-Eberly
Telescope, rest-frame-ultraviolet spectrophotometric monitoring of a sample of
six quasars at redshifts z=2.2--3.2, with luminosities of
L_opt~10^{46.4}--10^{47.6} erg/s, an order of magnitude greater than those of
previously mapped quasars. The six quasars, together with an additional five
having similar redshift and luminosity properties, were monitored
photometrically at the Wise Observatory during the past decade. All 11 quasars
monitored show significant continuum variations of order 10%--70%. This is
about a factor of two smaller variability than for lower luminosity quasars
monitored over the same rest-frame period. In the six objects which have been
spectrophotometrically monitored, significant variability is detected in the
CIV1550 broad emission line. In several cases the variations track the
continuum variations in the same quasar, with amplitudes comparable to, or even
greater than, those of the corresponding continua. In contrast, no significant
Ly\alpha variability is detected in any of the four objects in which it was
observed. Thus, UV lines may have different variability trends in
high-luminosity and low-luminosity AGNs. For one quasar, S5~0836+71 at z=2.172,
we measure a tentative delay of 595 days between CIV and UV-continuum
variations, corresponding to a rest-frame delay of 188 days and a central
black-hole mass of 2.6\times10^9 M_\odot.Comment: 11 pages, 6 figures, emulateapj, accepted for publication in The
Astrophysical Journa
Exploratory X-ray Monitoring of Luminous Radio-Quiet Quasars at High Redshift: No Evidence for Evolution in X-ray Variability
We report on the second installment of an X-ray monitoring project of seven
luminous radio-quiet quasars (RQQs). New {\sl Chandra} observations of four of
these, at , yield a total of six X-ray epochs, per source,
with temporal baselines of days in the rest frame. These data
provide the best X-ray light curves for RQQs at , to date, enabling
qualitative investigations of the X-ray variability behavior of such sources
for the first time. On average, these sources follow the trend of decreasing
variability amplitude with increasing luminosity, and there is no evidence for
X-ray variability increasing toward higher redshifts, in contrast with earlier
predictions of potential evolutionary scenarios. An ensemble variability
structure function reveals that their variability level remains relatively flat
across days in the rest frame and it is generally lower than
that of three similarly luminous RQQs at over the same
temporal range. We discuss possible explanations for the increased variability
of the lower-redshift subsample and, in particular, whether higher accretion
rates play a leading role. Near-simultaneous optical monitoring of the sources
at indicates that none is variable on -day
timescales, although flux variations of up to \% are observed on
-day timescales, typical of RQQs at similar redshifts. Significant
optical-X-ray spectral slope variations observed in two of these sources are
consistent with the levels observed in luminous RQQs and are dominated by X-ray
variations.Comment: 11 pages (emulateapj), 4 figures. Accepted for publication in Ap
From non-Brownian Functionals to a Fractional Schr\"odinger Equation
We derive backward and forward fractional Schr\"odinger type of equations for
the distribution of functionals of the path of a particle undergoing anomalous
diffusion. Fractional substantial derivatives introduced by Friedrich and
co-workers [PRL {\bf 96}, 230601 (2006)] provide the correct fractional
framework for the problem at hand. In the limit of normal diffusion we recover
the Feynman-Kac treatment of Brownian functionals. For applications, we
calculate the distribution of occupation times in half space and show how
statistics of anomalous functionals is related to weak ergodicity breaking.Comment: 5 page
Gender-based violence and the need for evidence-based primary prevention in South Africa
Gender-based violence is a significant problem globally and in South Africa. The public and political discourse has been dominated by calls for increased penalties and convictions for perpetrators of various types of gender-based violence. However, these responses are unlikely to prevent such violence from occurring in the first place. Primary prevention strategies should address the underlying causes and drivers of gender-based violence in order to prevent violence and promote safer, respectful, happy relations between men and women. Through rigorous research, these factors have been identified and specific strategies based on these findings include: (a) building gender equality and challenging hegemonic masculinities; (b) challenging the widespread acceptance of violence; (c) improving conflict resolution and communication skills; (d) developing relationship-building skills; (e) reducing substance abuse; and (f) improved gun control. Each of these strategies and the evidence-base for the recommendations is discussed. Interventions that combine these strategies and are informed by research evidence during development are most likely to be effective in preventing gender-based violence on a large scale.Keywords: gender equality, masculinities, primary prevention, gender-based violence, South Afric
Repeatability of nerve conduction measurements derived entirely by computer methods
<p>Abstract</p> <p>Background</p> <p>Nerve conduction studies are an objective, quantitative, and reproducible measure of peripheral nerve function and are widely used in the diagnosis of neuropathies. The purpose of this study is to determine the reliability of nerve conduction parameters derived entirely from computer based data acquisition and waveform cursor assignments and to quantify the relative contributions of test variability sources.</p> <p>Methods</p> <p>Thirty volunteers, some with symptoms suggestive of neuropathies; of these, 29 completed the study. The median, ulnar, deep peroneal, posterior tibial, and sural nerves were evaluated bilaterally at two test sessions 3-7 days apart. Within each session, nerves were tested twice within 10 minutes. The analyzed nerve conduction parameters include motor latencies, motor conduction velocity (CV), compound muscle action potential (CMAP) amplitude, F-wave latencies (minimum, mean and maximum), sensory peak latency (DSL), sensory CV, and sensory nerve action potential (SNAP) amplitude. The primary outcome measure is variance component analysis and the corresponding coefficient of variation (CoV). The between-session-test variance is the sum of within-session variance and between-session variance, quantifying the total variation between test sessions. Additional statistical measures include the intraclass correlation coefficient (ICC) and relative interval variation (RIV).</p> <p>Results</p> <p>Motor and sensory latencies, CV and F-wave latency parameters have low between-session-test CoVs, ranging from 4.2% to 9.8%. Amplitude parameters have a higher between-session-test CoVs in the range of 15.6--19.8%. Between-test CoVs are about 30--80% lower than between-session CoVs with the exception of F-wave latency parameters. Between-test ICC values are 0.96 or above for all parameters. Between-session ICC ranges from 0.98 for F-wave latency to 0.77 for sural sensory CV. All latency-related between-session ICCs have a value 0.83 or above. The RIVs are the tightest for F-wave latency parameters and widest for CMAP amplitude parameters. Repeatability in a sub-group of subjects with more severe symptom grades follows the same trend as the overall study population without substantial quantitative differences.</p> <p>Conclusion</p> <p>The study demonstrates the high repeatability of nerve conduction parameters acquired by modern electrodiagnostic instruments using computer based waveform cursor assignment. The reliability is comparable to benchmark studies in which the nerve conduction measurements were performed manually in controlled multi-center clinical trials. Furthermore, the ranking of reliability, whereby F-wave latencies have the best reproducibility and amplitudes the worst, is also consistent with the benchmark studies.</p
The Hard X-ray Spectral Slope as an Accretion-Rate Indicator in Radio-Quiet Active Galactic Nuclei
We present new XMM-Newton observations of two luminous and high
accretion-rate radio-quiet active galactic nuclei (AGNs) at z~2. Together with
archival X-ray and rest-frame optical spectra of three sources with similar
properties as well as 25 moderate-luminosity radio-quiet AGNs at z<0.5, we
investigate, for the first time, the dependence of the hard (>~2 keV) X-ray
power-law photon index on the broad H_beta emission-line width and on the
accretion rate across ~3 orders of magnitude in AGN luminosity. Provided the
accretion rates of the five luminous sources can be estimated by extrapolating
the well-known broad-line region size-luminosity relation to high luminosities,
we find that the photon indices of these sources, while consistent with those
expected from their accretion rates, are significantly higher than expected
from the widths of their H_beta lines. We argue that, within the limits of our
sample, the hard-X-ray photon index depends primarily on the accretion rate.Comment: 4 pages (emulateapj), 2 figures. Accepted for publication in ApJ
Letter
Continuous input nonlocal games
We present a family of nonlocal games in which the inputs the players receive
are continuous. We study three representative members of the family. For the
first two a team sharing quantum correlations (entanglement) has an advantage
over any team restricted to classical correlations. We conjecture that this is
true for the third member of the family as well.Comment: Journal version, slight modification
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