3,181 research outputs found
Discovery of a tight correlation between pulse lag/luminosity and jet-break times: a connection between gamma-ray burst and afterglow properties
A correlation is presented between the pulse lag and the jet-break time for
seven BATSE gamma-ray bursts with known redshifts. This is, to our best
knowledge, the first known direct tight correlation between a property of the
gamma-ray burst phase (the pulse lag) and the afterglow phase (the jet-break
time). As pulse lag and luminosity have been found to be correlated this also
represents a correlation between peak luminosity and jet-break time. Observed
timescales (variability or spectral lags) as well as peak luminosity naturally
have a strong dependence on the Lorentz factor of the outflow and so we propose
that much of the variety among GRBs has a purely kinematic origin (the speed or
direction of the outflow).
We explore a model in which the variation among GRBs is due to a variation in
jet-opening angles, and find that the narrowest jets have the fastest outflows.
We also explore models in which the jets have similar morphology and size, and
the variation among bursts is caused by variation in viewing angle and/or due
to a velocity profile. The relations between luminosity, variability, spectral
lag and jet-break time can be qualitatively understood from models in which the
Lorentz factor decreases as a function of angle from the jet axis. One expects
to see high luminosities, short pulse lags and high variability as well as an
early jet-break time for bursts viewed on axis, while higher viewing
inclinations will yield lower luminosities, longer pulse lags, smoother bursts
and later jet-break times.Comment: 10 pages, 3 figures, accepted to ApJ (new version contains minor
changes
Reaction rate calculation by parallel path swapping
The efficiency of path sampling simulations can be improved considerably
using the approach of path swapping. For this purpose, we have devised a new
algorithmic procedure based on the transition interface sampling technique. In
the same spirit of parallel tempering, paths between different ensembles are
swapped, but the role of temperature is here played by the interface position.
We have tested the method on the denaturation transition of DNA using the
Peyrard-Bishop-Dauxois model. We find that the new algorithm gives a reduction
of the computational cost by a factor 20.Comment: 5 pages, 3 figure
The crystal and molecular structure of Hydridotetrakis(diethyl phenylphosphonite)cobalt(I)
An X-ray structure determination of the title compound shows that the co-ordination about the cobalt atom is approximately trigonal bipyramidal; n.m.r. data indicate that the complex is non-rigid in solution
Multi-camera Realtime 3D Tracking of Multiple Flying Animals
Automated tracking of animal movement allows analyses that would not
otherwise be possible by providing great quantities of data. The additional
capability of tracking in realtime - with minimal latency - opens up the
experimental possibility of manipulating sensory feedback, thus allowing
detailed explorations of the neural basis for control of behavior. Here we
describe a new system capable of tracking the position and body orientation of
animals such as flies and birds. The system operates with less than 40 msec
latency and can track multiple animals simultaneously. To achieve these
results, a multi target tracking algorithm was developed based on the Extended
Kalman Filter and the Nearest Neighbor Standard Filter data association
algorithm. In one implementation, an eleven camera system is capable of
tracking three flies simultaneously at 60 frames per second using a gigabit
network of nine standard Intel Pentium 4 and Core 2 Duo computers. This
manuscript presents the rationale and details of the algorithms employed and
shows three implementations of the system. An experiment was performed using
the tracking system to measure the effect of visual contrast on the flight
speed of Drosophila melanogaster. At low contrasts, speed is more variable and
faster on average than at high contrasts. Thus, the system is already a useful
tool to study the neurobiology and behavior of freely flying animals. If
combined with other techniques, such as `virtual reality'-type computer
graphics or genetic manipulation, the tracking system would offer a powerful
new way to investigate the biology of flying animals.Comment: pdfTeX using libpoppler 3.141592-1.40.3-2.2 (Web2C 7.5.6), 18 pages
with 9 figure
DEVELOPMENT OF BASIC FORMULA PRICE POLICY: IMPLICATIONS FOR U.S.-CANADIAN TRADE ISSUES
Agricultural and Food Policy, International Relations/Trade,
Dynamics of a two-level system coupled with a quantum oscillator in the very strong coupling limit
The time-dependent behavior of a two-level system interacting with a quantum
oscillator system is analyzed in the case of a coupling larger than both the
energy separation between the two levels and the energy of quantum oscillator
(, where is the frequency of the
transition between the two levels, is the frequency of the
oscillator, and is the coupling between the two-level system and the
oscillator). Our calculations show that the amplitude of the expectation value
of the oscillator coordinate decreases as the two-level system undergoes the
transition from one level to the other, while the transfer probability between
the levels is staircase-like. This behavior is explained by the interplay
between the adiabatic and the non-adiabatic regimes encountered during the
dynamics with the system acting as a quantum counterpart of the Landau-Zener
model. The transition between the two levels occurs as long as the expectation
value of the oscillator coordinate is driven close to zero. On the contrary, if
the initial conditions are set such that the expectation values of the
oscillator coordinate are far from zero, the system will remain locked on one
level.Comment: 4 pages, 4 figures, to be published in Physical Review
EVALUATION OF "FINAL" FOUR BASIC FORMULA PRICE OPTIONS
Demand and Price Analysis,
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