11,978 research outputs found
Constraints on Association of Single-pulse Gamma-ray Bursts and Supernovae
We explore the hypothesis, similar to one recently suggested by Bloom and
colleagues, that some nearby supernovae are associated with smooth,
single-pulse gamma-ray bursts, possibly having no emission above ~ 300 keV. We
examine BATSE bursts with durations longer than 2 s, fitting those which can be
visually characterized as single-pulse events with a lognormal pulse model. The
fraction of events that can be reliably ascertained to be temporally and
spectrally similar to the exemplar, GRB 980425 - possibly associated with SN
1998bw - is 4/1573 or 0.25%. This fraction could be as high as 8/1573 (0.5%) if
the dimmest bursts are included. Approximately 2% of bursts are morphologically
similar to GRB 980425 but have emission above ~ 300 keV. A search of supernova
catalogs containing 630 detections during BATSE's lifetime reveals only one
burst (GRB 980425) within a 3-month time window and within the total 3-sigma
BATSE error radius that could be associated with a type Ib/c supernova. There
is no tendency for any subset of single-pulse GRBs to fall near the
Supergalactic Plane, whereas SNe of type Ib/c do show this tendency. Economy of
hypotheses leads us to conclude that nearby supernovae generally are not
related to smooth, single-pulse gamma-ray bursts.Comment: 25 pages, 5 figure
The Negativity Bias Predicts Response Rate To Behavioral Activation For Depression
Background and Objectives: This treatment study investigated the extent to which asymmetric dimensions of affective responding, specifically the positivity offset and the negativity bias, at pretreatment altered the rate of response to Behavioral Activation treatment for depression. Method: Forty-one depressed participants were enrolled into 16 weekly sessions of BA. An additional 36 lifetime healthy participants were evaluated prospectively for 16 weeks to compare affective responding between healthy and remitted patients at post-treatment. All participants were assessed at Weeks 0, 8 and 16 using repeated measures, involving a structured clinical interview for DSM-IV Axis I disorders, questionnaires, and a computerized task designed to measure affective responses to unpleasant, neutral, and pleasant images. Results: The negativity bias at pre-treatment predicted the rate of response to BA, while the positivity offset did not. Limitations: Only one treatment condition was used in this study and untreated depressed participants were not enrolled, limiting our ability to compare the effect of BA. Conclusions: Baseline negativity bias may serve as a signal for patients to engage in and benefit from the goal-directed BA strategies, thereby accelerating rate of response
Overlay copy technique to provide high-contrast electron micrographs for automatic metallographic analysis
Overlay copy technique to provide high-contrast electron micrographs for automatically determining quantitative microstructure of multiphase specimen
Atom detection in a two-mode optical cavity with intermediate coupling: Autocorrelation studies
We use an optical cavity in the regime of intermediate coupling between atom
and cavity mode to detect single moving atoms. Degenerate polarization modes
allow excitation of the atoms in one mode and collection of spontaneous
emission in the other, while keeping separate the two sources of light; we
obtain a higher confidence and efficiency of detection by adding
cavity-enhanced Faraday rotation. Both methods greatly benefit from coincidence
detection of photons, attaining fidelities in excess of 99% in less than 1
microsecond. Detailed studies of the second-order intensity autocorrelation
function of light from the signal mode reveal evidence of antibunched photon
emissions and the dynamics of single-atom transits.Comment: 10 pages, 10 figures, to be published in Phys. Rev.
Comment on "Self-Purification in Semiconductor Nanocrystals"
In a recent Letter [PRL 96, 226802 (2006)], Dalpian and Chelikowsky claimed
that formation energies of Mn impurities in CdSe nanocrystals increase as the
size of the nanocrystal decreases, and argued that this size dependence leads
to "self-purification" of small nanocrystals. They presented
density-functional-theory (DFT) calculations showing a strong size dependence
for Mn impurity formation energies, and proposed a general explanation. In this
Comment we show that several different DFT codes, pseudopotentials, and
exchange-correlation functionals give a markedly different result: We find no
such size dependence. More generally, we argue that formation energies are not
relevant to substitutional doping in most colloidally grown nanocrystals.Comment: 1 page, 1 figur
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A tale of one city: intra-institutional variations in migrating VLE platform
City University London committed in 2009 to make Moodle the Virtual Learning Environment (VLE) at the core of a new Strategic Learning Environment (SLE) comprised of VLE, externally facing website and related systems such as video streaming and virtual classrooms. Previously, the WebCT VLE had been separate from most of the other systems at the institution with very limited connections to other tools. Each of the schools within the institution was able to pursue their own strategy and timeframe for the migration and embedding of Moodle within their subject areas, within an absolute limit of 2 years. This paper outlines the approaches taken by the various schools, highlighting similarities and differences, and draws out common aspects from the project to make recommendations for institutions seeking to undertake similar migrations
Compact Radio Cores in Seyfert Galaxies
We have observed a sample of 157 Seyfert galaxies with a 275 km baseline
radio interferometer to search for compact, high brightness temperature radio
emission from the active nucleus. We obtain the surprising result that compact
radio cores are much more common in Seyfert 2 than in Seyfert 1 galaxies, which
at first seems to be inconsistent with orientation unification schemes. We
propose a model, involving optical depth effects in the narrow-line region,
which can reconcile our result with the standard unified scheme. (Accepted for
publication in ApJ 1994 Sep 10)Comment: 21 pages and 7 figures, uuencoded tar-compressed postscript files,
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