9,343 research outputs found
Properties of Gamma-Ray Burst Progenitor Stars
We determine some basic properties of stars that produce spectacular
gamma-ray bursts at the end of their life. We assume that accretion of the
outer portion of the stellar core by a central black hole fuels the prompt
emission, and that fall-back and accretion of the stellar envelope later
produces the plateau in the X-ray light curve seen in some bursts. Using X-ray
data for three bursts we estimate the radius of the stellar core to be ~ 1-3 x
10^10 cm, and that of the stellar envelope to be ~ 1-2 x 10^11 cm. The density
profile in the envelope is fairly shallow, with \rho ~ r^-2. The rotation
speeds of the core and envelope are ~ 0.05 and ~ 0.2 of the local Keplerian
speed, respectively.Comment: Science in pres
A genotyping protocol for multiple tissue types from the polyploid tree species Sequoia sempervirens (Cupressaceae).
Premise of the studyIdentifying clonal lineages in asexually reproducing plants using microsatellite markers is complicated by the possibility of nonidentical genotypes from the same clonal lineage due to somatic mutations, null alleles, and scoring errors. We developed and tested a clonal identification protocol that is robust to these issues for the asexually reproducing hexaploid tree species coast redwood (Sequoia sempervirens).MethodsMicrosatellite data from four previously published and two newly developed primers were scored using a modified protocol, and clones were identified using Bruvo genetic distances. The effectiveness of this clonal identification protocol was assessed using simulations and by genotyping a test set of paired samples of different tissue types from the same trees.ResultsData from simulations showed that our protocol allowed us to accurately identify clonal lineages. Multiple test samples from the same trees were identified correctly, although certain tissue type pairs had larger genetic distances on average.DiscussionThe methods described in this paper will allow for the accurate identification of coast redwood clones, facilitating future studies of the reproductive ecology of this species. The techniques used in this paper can be applied to studies of other clonal organisms as well
One pion events by atmospheric neutrinos: A three flavor analysis
We study the one-pion events produced via neutral current (NC) and charged
current (CC) interactions by the atmospheric neutrinos. We analyze the ratios
of these events in the framework of oscillations between three neutrino
flavors. The ratios of the CC events induced by to that of the NC
events and a similar ratio defined with help us in distinguishing the
different regions of the neutrino parameter space.Comment: 14 pages, 4 figures (separate postscript files
Advanced ablation strategies for management of post-surgical atrial arrhythmias.
Post-surgical arrhythmias include a wide range of arrhythmias occurring late after cardiac surgery and represent a complex substrate for catheter ablation either because of extended scar and remodeling or because of limited access to the area of interest. Novel image integration and ablation tools have made the catheter ablation in this population both feasible and successful. We review a structured approach to catheter ablation of post-surgical atrial arrhythmias in various patient cohorts including the most common congenital heart defects
Determining the sign of at long baseline neutrino experiments
Recently it is advocated that high intensity and low energy neutrino beams should be built to probe the mixing angle to
a level of a few parts in . Experiments using such beams will have better
signal to background ratio in searches for oscillations. We
propose that such experiments can also determine the sign of even
if the beam consists of {\it neutrinos} only. By measuring the transitions in two different energy ranges, the effects due to
propagation of neutrinos through earth's crust can be isolated and the sign of
can be determined. If the sensitivity of an experiment to
is , then the same experiment is automatically sensitive to matter
effects and the sign of for values of .Comment: Title changed and paper rewritten. 4 pages, 1 figure, revte
Spin-s wavefunctions with algebraic order
We generalize the Gutzwiller wavefunction for s = 1/2 spin chains to
construct a family of wavefunctions for all s > 1/2. Through numerical
simulations, we demonstrate that the spin spin correlation functions for all s
decay as a power law with logarithmic corrections. This is done by mapping the
model to a classical statistical mechanical model, which has coupled Ising spin
chains with long range interactions. The power law exponents are those of the
Wess Zumino Witten models with k = 2s. Thus these simple wavefunctions
reproduce the spin correlations of the family of Hamiltonians obtained by the
Algebraic Bethe Ansatz.Comment: 10 pages, 7 figure
Probing the matter term at long baseline experiments
We consider (\nu_\mu --> \nu_e) oscillations in long baseline experiments
within a three flavor framework. A non-zero measurement of this oscillation
probability implies that the (13) mixing angle `phi' is non-zero. We consider
the effect of neutrino propagation through the matter of earth's crust and show
that, given the constraints from solar neutrino and CHOOZ data, matter effects
enhance the mixing for neutrinos rather than for anti-neutrinos. We need data
from two different experiments with different baseline lengths (such as K2K and
MINOS) to distinguish matter effects unambiguously.Comment: 9 pages including three figure
Vertical distribution of stars and gas in a galactic disk
We study the vertical density distribution of stars and gas (HI and H_2) in a
galactic disk which is embedded in a dark matter halo. The new feature of this
work is the inclusion of gas, and the gravitational coupling between stars and
gas, which has led to a more realistic treatment of a multi-component galactic
disk. The gas gravity is shown to be crucially important despite the low gas
mass fraction. This approach physically explains the observed scaleheight
distribution of all the three disk components, including the long-standing
puzzle (Oort 1962) of a constant HI scaleheight observed in the inner Galaxy.
The above model is applied to two external galaxies: NGC 891 and NGC 4565, and
the stellar disk is shown to be not strictly flat as was long believed but
rather it shows a moderate flaring of a factor of about 2 within the optical
radius.Comment: 4 pages, 2 figures; to appear in the Proceedings of "Island
Universes: Structure and evolution of disk galaxies" (Terschelling, The
Netherlands, July 2005), ed. R. de Jon
Radio light curves during the passage of cloud G2 near Sgr A*
We calculate radio light curves produced by the bow shock that is likely to
form in front of the G2 cloud when it penetrates the accretion disk of Sgr A*.
The shock acceleration of the radio-emitting electrons is captured
self-consistently by means of first-principles particle-in-cell simulations. We
show that the radio luminosity is expected to reach maximum in early 2013,
roughly a month after the bow shock crosses the orbit pericenter. We estimate
the peak radio flux at 1.4 GHz to be 1.4 - 22 Jy depending on the assumed orbit
orientation and parameters. We show that the most promising frequencies for
radio observations are in the 0.1<nu<1 GHz range, for which the bow shock
emission will be much stronger than the intrinsic radio flux for all the models
considered.Comment: 15 pages, 10 figures, accepted for publication in MNRA
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