5,639 research outputs found
The Search for AGN in Distant Galaxy Clusters
We are undertaking the first systematic study of the prevalence of AGN
activity in a large sample of high redshift galaxy clusters. Local clusters
contain mainly red elliptical galaxies, and have little or no luminous AGN
activity. However, recent studies of some moderate to high redshift clusters
have revealed significant numbers of luminous AGN within the cluster. This
effect may parallel the Butcher-Oemler effect - the increase in the fraction of
blue galaxies in distant clusters compared to local clusters. Our aim is to
verify and quantify recent evidence that AGN activity in dense environments
increases with redshift, and to evaluate the significance of this effect. As
cluster AGN are far less prevalent than field sources, a large sample of over
120 cluster fields at z > 0.1 has been selected from the Chandra archives and
is being analysed for excess point sources. The size of the excess, the radial
distribution and flux of the sources and the dependence of these on cluster
redshift and luminosity will reveal important information about the triggering
and fueling of AGN.Comment: 2 pages, to appear in proceedings of 'Multi-wavelength AGN surveys',
Cozumel, 200
HgSe, a highly electronegative stable metallic contact for semiconductor devices
Schottky barriers formed by the highly electronegative substance HgSe on n-ZnS and on n-ZnSe have been characterized by capacitance-voltage and photoresponse measurements. The barriers are about 0.5 eV greater than Au barriers on these n-type substrates. HgSe contacts are stable under ambient conditions and are easily fabricated, making them attractive for device use
A short survey on nonlinear models of the classic Costas loop: rigorous derivation and limitations of the classic analysis
Rigorous nonlinear analysis of the physical model of Costas loop --- a
classic phase-locked loop (PLL) based circuit for carrier recovery, is a
challenging task. Thus for its analysis, simplified mathematical models and
numerical simulation are widely used. In this work a short survey on nonlinear
models of the BPSK Costas loop, used for pre-design and post-design analysis,
is presented. Their rigorous derivation and limitations of classic analysis are
discussed. It is shown that the use of simplified mathematical models, and the
application of non rigorous methods of analysis (e.g., simulation and
linearization) may lead to wrong conclusions concerning the performance of the
Costas loop physical model.Comment: Accepted to American Control Conference (ACC) 2015 (Chicago, USA
Environmental dependence of AGN activity in the supercluster A901/2
We present XMM data for the supercluster A901/2, at z ~ 0.17, which is
combined with deep imaging and 17-band photometric redshifts (from the COMBO-17
survey), 2dF spectra and Spitzer 24um data, to identify AGN in the
supercluster. The 90ksec XMM image contains 139 point sources, of which 11 are
identified as supercluster AGN with L_X(0.5-7.5keV) > 1.7x10^41 erg/cm2/s. The
host galaxies have M_R < -20 and only 2 of 8 sources with spectra could have
been identified as AGN by the detected optical emission lines. Using a large
sample of 795 supercluster galaxies we define control samples of massive
galaxies with no detected AGN. The local environments of the AGN and control
samples differ at >98 per cent significance. The AGN host galaxies lie
predominantly in areas of moderate projected galaxy density and with more local
blue galaxies than the control sample, with the exception of one very bright
Type I AGN very near the centre of a cluster. These environments are similar
to, but not limited to, cluster outskirts and blue groups. Despite the large
number of potential host galaxies, no AGN are found in regions with the highest
galaxy density (excluding some cluster cores where emission from the ICM
obscures moderate luminosity AGN). AGN are also absent from the areas with
lowest galaxy density. We conclude that the prevalence of cluster AGN is linked
to their environment.Comment: 20 pages, 15 figures. MNRAS accepted. Version with full resolution
figures, including Figure 14, is available at
http://www.sc.eso.org/~rgilmour
Pedagogy, Protests, and Moving Toward Progress
Our world is in constant flux and educators are at the ship’s helm steering toward what former U.S. Representative John Lewis called “good trouble.” However, in many cases, educators lack the training required to be most effective in doing so. As instructors face student demands to address topics on race and social justice, many educators are unsure about how to respond appropriately to the chants of “No Justice, No Peace!” Thus, this essay explores humanistic and pragmatic approaches for doing so in terms of fostering cultural communication competence when incorporating topics on race and social justice issues in the classroom
Decentralised Monte Carlo Tree Search for Active Perception
We propose a decentralised variant of Monte Carlo tree search (MCTS) that is suitable for a variety of tasks in multi-robot active perception. Our algorithm allows each robot to optimise its own individual action space by maintaining a probability distribution over plans in the joint-action space. Robots periodically communicate a compressed form of these search trees, which are used to update the locally-stored joint distributions using an optimisation approach inspired by variational methods. Our method admits any objective function defined over robot actions, assumes intermittent communication, and is anytime. We extend the analysis of the standard MCTS for our algorithm and characterise asymptotic convergence under reasonable assumptions. We evaluate the practical performance of our method for generalised team orienteering and active object recognition using real data, and show that it compares favourably to centralised MCTS even with severely degraded communication. These examples support the relevance of our algorithm for real-world active perception with multi-robot systems
Effect of low-intensity long-duration ultrasound on the symptomatic relief of knee osteoarthritis: a randomized, placebo-controlled double-blind study
Background: Wearable long-duration low-intensity ultrasound is an emerging non-invasive and non-narcotic therapy for the daily treatment of musculoskeletal pain. The aim of this randomized, double-blind, placebo-controlled study was to examine whether long-duration low-intensity ultrasound was effective in treating pain and improving function in patients with knee osteoarthritis. Methods: Ninety patients with moderate to severe knee pain and radiographically confirmed knee osteoarthritis (Kellgren-Lawrence grade I/II) were randomized for treatment with active (n = 55) or placebo (n = 35) devices applied daily to the treated knee. Investigators and subjects were blinded to treatment groups. Ultrasound (3 MHz, 0.132 W/cm2, 1.3 W) was applied with a wearable device for 4 h daily for 6 weeks, delivering 18,720 J per treatment. The primary outcome was change in pain intensity (numeric rating scale) assessed prior to intervention (baseline) and after 6 weeks. Secondary outcomes of functional change were measured at baseline and after 6 weeks using the Western Ontario McMaster Osteoarthritis Questionnaire (n = 84), along with range of motion (flexion, extension) and isometric muscle strength (flexion, extension and rotation) tests on the injured knee in a small pilot subset (n =17). Results: The study had a 93% retention rate, and there were no significant differences between the groups regarding demographic variables or baseline outcome measures. Patients treated with active therapy observed a significant mean NRS pain reduction over the 6-week study of 1.96 points for active (p \u3c 0.0001), compared with a 0.85 points reduction for placebo (p = 0.13). The functional score was also significantly improved by 505 points for the active group over the 311-point improvement for placebo group compared to baseline (p = 0.02). In the pilot subset evaluated, rotational strength increased from baseline to 6 weeks (3.2 N, p = 0.03); however, no other measures were significant. Conclusions: Long-duration low-intensity ultrasound significantly reduced pain and improved joint function in patients with moderate to severe osteoarthritis knee pain. The clinical findings suggest that ultrasound may be used as a conservative non-pharmaceutical and non-invasive treatment option for patients with knee osteoarthritis. Additional research is warranted on non-weight bearing joints of the musculoskeletal system as well as extended treatment time frames and follow-up. Trial registration: NCT02083861, registered 11 March 2014, https://clinicaltrials.gov/ct2/show/results/NCT0208386
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