53,928 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
Child Poverty in Rural America
This report explores the well-being of the 14 million children who live in rural America. Rural families represent a significant share of our total population and they are disproportionately poor, less educated, and underemployed. Yet poor children and the unique challenges they face are often overlooked by policymakers. Poor children living in rural America face significant educational, social, and economic challenges just as their urban counterparts do, but many of these problems are exacerbated by the isolation and limited access to support services common in rural areas
A Target Restricted Assembly Method (TRAM) for Phylogenomics
While next generation sequencing technology can produce sequences covering the entire genome, assembly and annotation are still prohibitive steps for many phylogenomics applications. Here we describe a method of Target Restricted Assembly (TRAM) of a single lane of Illumina sequences for genes of relevance to phylogeny reconstruction, i.e. single copy protein-coding genes. This method has the potential to produce a data set of hundreds of genes using only one Illumina lane per taxon
Adiabatic self-tuning in a silicon microdisk optical resonator
We demonstrate a method for adiabatically self-tuning a silicon microdisk resonator. This mechanism is not only able to sensitively probe the fast nonlinear cavity dynamics, but also provides various optical functionalities like pulse compression, shaping, and tunable time delay
Velocity correlations in dense granular flows
Velocity fluctuations of grains flowing down a rough inclined plane are
experimentally studied. The grains at the free surface exhibit fluctuating
motions, which are correlated over few grains diameters. The characteristic
correlation length is shown to depend on the inclination of the plane and not
on the thickness of the flowing layer. This result strongly supports the idea
that dense granular flows are controlled by a characteristic length larger than
the particle diameter
Open-mindedness can decrease persuasion amongst adolescents: The role of self-affirmation
Objectives
Self-affirmation (e.g., by reflecting on important personal values) has been found to promote more open-minded appraisal of threatening health messages in at-risk adults. However, it is unclear how self-affirmation affects adolescents and whether it has differential effects on the impact of these messages amongst those at relatively lower and higher risk. The current study explored moderation by risk.
Design
Participants were randomly assigned to either a self-affirmation or a control condition before receiving a health message concerning physical activity.
Methods
Older adolescents (N = 125) completed a self-affirmation or control writing task before reading about the health consequences of not meeting recommendations to be physically active for at least 60 min daily. Most of the sample did not achieve these levels of activity (98%, N = 123). Consequently, the message informed these participants that – unless they changed their behaviour – they would be at higher risk of heart disease. Participants completed measures of responses to the message and behaviour-specific cognitions (e.g., self-efficacy) for meeting the recommendations.
Results
For relatively inactive participants, self-affirmation was associated with increased persuasion. However, for those who were moderately active (but not meeting recommendations), those in the self-affirmation condition were less persuaded by the message.
Conclusions
Whilst self-affirmation can increase message acceptance, there are circumstances when the open-mindedness it induces may decrease persuasion. The evidence provided in this study suggests that caution may be needed when recommendations are challenging and it could be considered reasonable to be sceptical about the need to change behaviour
An optical fiber-taper probe for wafer-scale microphotonic device characterization
A small depression is created in a straight optical fiber taper to form a
local probe suitable for studying closely spaced, planar microphotonic devices.
The tension of the "dimpled" taper controls the probe-sample interaction length
and the level of noise present during coupling measurements. Practical
demonstrations with high-Q silicon microcavities include testing a dense array
of undercut microdisks (maximum Q = 3.3x10^6) and a planar microring (Q =
4.8x10^6).Comment: 8 pages, 5 figures, for high-res version see
http://copilot.caltech.edu/publications/index.ht
A proposal for highly tunable optical parametric oscillation in silicon micro-resonators
We propose a novel scheme for continuous-wave pumped optical parametric oscillation (OPO) inside silicon micro-resonators. The proposed scheme not only requires a relative low lasing threshold, but also exhibits extremely broad tunability extending from the telecom band to mid infrared
Helicity supersymmetry of dyons
The 'dyon' system of D'Hoker and Vinet consisting of a spin 1/2 particle with
anomalous gyromagnetic ratio 4 in the combined field of a Dirac monopole plus a
Coulomb plus a suitable potential (which arises in the long-range limit
of a self-dual monopole) is studied following Biedenharn's approach to the
Dirac-Coulomb problem: the explicit solution is obtained using the
`Biedenharn-Temple operator', , and the extra two-fold degeneracy is
explained by the subtle supersymmetry generated by the 'Dyon Helicity' or
generalized `Biedenharn-Johnson-Lippmann' operator . The new SUSY
anticommutes with the chiral SUSY discussed previously.Comment: 14 pages, 2 figure
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