7,629 research outputs found
Spectral Evolution of Two High-Energy Gamma-Ray Bursts
The prompt emission of the gamma-ray bursts is found to be very energetic,
releasing ~10^51 ergs in a flash. However, their emission mechanism remains
unclear and understanding their spectra is a key to determining the emission
mechanism. Many GRB spectra have been analyzed in the sub-MeV energy band, and
are usually well described with a smoothly broken power-law model. We present a
spectral analysis of two bright bursts (GRB910503 and GRB930506), using BATSE
and EGRET spectra that cover more than four decades of energy (30 keV - 200
MeV). Our results show time evolutions of spectral parameters (low-energy &
high-energy photon indices and break energy) that are difficult to reconcile
with a simple shock-acceleration model.Comment: 8 pages, 2 figures, to appear in the proceedings of "Astrophysical
Particle Acceleration in Geospace and Beyond", Chattanooga, 2002, AGU
monograp
Subtraction of Bright Point Sources from Synthesis Images of the Epoch of Reionization
Bright point sources associated with extragalactic AGN and radio galaxies are
an important foreground for low frequency radio experiments aimed at detecting
the redshifted 21cm emission from neutral hydrogen during the epoch of
reionization. The frequency dependence of the synthesized beam implies that the
sidelobes of these sources will move across the field of view as a function of
observing frequency, hence frustrating line-of-sight foreground subtraction
techniques. We describe a method for subtracting these point sources from dirty
maps produced by an instrument such as the MWA. This technique combines matched
filters with an iterative centroiding scheme to locate and characterize point
sources in the presence of a diffuse background. Simulations show that this
technique can improve the dynamic range of EOR maps by 2-3 orders of magnitude.Comment: 11 pages, 8 figures, 1 table, submitted to PAS
Exact semi-relativistic model for ionization of atomic hydrogen by electron impact
We present a semi-relativistic model for the description of the ionization
process of atomic hydrogen by electron impact in the first Born approximation
by using the Darwin wave function to describe the bound state of atomic
hydrogen and the Sommerfeld-Maue wave function to describe the ejected
electron. This model, accurate to first order in in the relativistic
correction, shows that, even at low kinetic energies of the incident electron,
spin effects are small but not negligible. These effects become noticeable with
increasing incident electron energies. All analytical calculations are exact
and our semi-relativistic results are compared with the results obtained in the
non relativistic Coulomb Born Approximation both for the coplanar asymmetric
and the binary coplanar geometries.Comment: 8 pages, 6 figures, Revte
Persoonia mollis R.Br. subsp. Mollis
https://thekeep.eiu.edu/herbarium_specimens_byname/20802/thumbnail.jp
The cessation in pregnancy incentives trial (CPIT): study protocol for a randomized controlled trial
Background: Seventy percent of women in Scotland have at least one baby, making pregnancy an opportunity to help most young women quit smoking before their own health is irreparably compromised. By quitting during pregnancy their infants will be protected from miscarriage and still birth as well as low birth weight, asthma, attention deficit disorder and adult cardiovascular disease. In the UK, the NICE guidelines: 'How to stop smoking in pregnancy and following childbirth' (June 2010) highlighted that little evidence exists in the literature to confirm the efficacy of financial incentives to help pregnant smokers to quit. Its first research recommendation was to determine: Within a UK context, are incentives an acceptable, effective and cost-effective way to help pregnant women who smoke to quit?
<p/>Design and Methods: This study is a phase II exploratory individually randomised controlled trial comparing standard care for pregnant smokers with standard care plus the additional offer of financial voucher incentives to engage with specialist cessation services and/or to quit smoking during pregnancy. Participants (n=600) will be pregnant smokers identified at maternity booking who when contacted by specialist cessation services agree to having their details passed to the NHS Smokefree Pregnancy Study Helpline to discuss the trial. The NHS Smokefree Pregnancy Study Helpline will be responsible for telephone consent and follow-up in late pregnancy. The primary outcome will be self reported smoking in late pregnancy verified by cotinine measurement. An economic evaluation will refine cost data collection and assess potential cost-effectiveness while qualitative research interviews with clients and health professionals will assess the level of acceptance of this form of incentive payment. Research questions What is the likely therapeutic efficacy? Are incentives potentially cost-effective? Is individual randomisation an efficient trial design without introducing outcome bias? Can incentives be introduced in a way that is feasible and acceptable?
<p/>Discussion: This phase II trial will establish a workable design to reduce the risks associated with a future definitive phase III multicentre randomised controlled trial and establish a framework to assess the costs and benefits of financial incentives to help pregnant smokers to quit
BATSE Gamma-Ray Burst Line Search: IV. Line Candidates from the Visual Search
We evaluate the significance of the line candidates identified by a visual
search of burst spectra from BATSE's Spectroscopy Detectors. None of the
candidates satisfy our detection criteria: an F-test probability less than
10^-4 for a feature in one detector and consistency among the detectors which
viewed the burst. Most of the candidates are not very significant, and are
likely to be fluctuations. Because of the expectation of finding absorption
lines, the search was biased towards absorption features. We do not have a
quantitative measure of the completeness of the search which would enable a
comparison with previous missions. Therefore a more objective computerized
search has begun.Comment: 18 pages AASTEX 4.0; 4 POSTSCRIPT figures on request from
[email protected]
A study of logarithmic corrections and universal amplitude ratios in the two-dimensional 4-state Potts model
Monte Carlo (MC) and series expansion (SE) data for the energy, specific
heat, magnetization and susceptibility of the two-dimensional 4-state Potts
model in the vicinity of the critical point are analysed. The role of
logarithmic corrections is discussed and an approach is proposed in order to
account numerically for these corrections in the determination of critical
amplitudes. Accurate estimates of universal amplitude ratios ,
, and are given, which arouse
new questions with respect to previous works
High cooperativity coupling of electron-spin ensembles to superconducting cavities
Electron spins in solids are promising candidates for quantum memories for
superconducting qubits because they can have long coherence times, large
collective couplings, and many quantum bits can be encoded into the spin-waves
of a single ensemble. We demonstrate the coupling of electron spin ensembles to
a superconducting transmission-line resonator at coupling strengths greatly
exceeding the cavity decay rate and comparable to spin linewidth. We also use
the enhanced coupling afforded by the small cross-section of the transmission
line to perform broadband spectroscopy of ruby at millikelvin temperatures at
low powers. In addition, we observe hyperfine structure in diamond P1 centers
and time domain saturation-relaxation of the spins.Comment: 4pgs, 4 figure
Improving coastal livelihoods through sustainable aquaculture practices - a report to the collaborative APEC Grouper Research and Development Network
Wild-harvest fisheries for live reef fish are largely over-exploited or unsustainable because of over-fishing and the widespread use of destructive fishing practices such as blast and cyanide fishing. Sustainable aquaculture – such as that of groupers – is one option for meeting the
strong demand for reef fish, as well as potentially maintaining or improving the livelihoods of coastal communities. This report from a short study by the STREAM Initiative draws on secondary literature, media sources and four diverse case studies from at-risk reef fisheries, to frame a strategy for encouraging sustainable aquaculture as an alternative to destructive fishing practices. It was undertaken as a component of the APEC-funded project Collaborative Grouper Research and Development Network (FWG/01/2001) to better understand how recent technical advances in grouper culture and other complementary work – including that of the Asia-Pacific Marine Finfish Aquaculture Network (APMFAN) hosted by NACA – could better support the livelihoods of poor coastal communities. (PDF contains 49 pages
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