220,785 research outputs found
Solid weak BCC-algebras
We characterize weak BCC-algebras in which the identity is
satisfied only in the case when elements belong to the same branch
Off-Axis Afterglow Light Curves from High-Resolution Hydrodynamical Jet Simulations
Numerical jet simulations serve a valuable role in calculating gamma-ray
burst afterglow emission beyond analytical approximations. Here we present the
results of high resolution 2D simulations of decelerating relativistic jets
performed using the RAM adaptive mesh refinement relativistic hydrodynamics
code. We have applied a separate synchrotron radiation code to the simulation
results in order to calculate light curves at frequencies varying from radio to
X-ray for observers at various angles from the jet axis. We provide a
confirmation from radio light curves from simulations rather than from a
simplified jet model for earlier results in the literature finding that only a
very small number of local Ibc supernovae can possibly harbor an orphan
afterglow.
Also, recent studies have noted an unexpected lack of observed jet breaks in
the Swift sample. Using a jet simulation with physical parameters
representative for an average Swift sample burst, such as a jet half opening
angle of 0.1 rad and a source redshift of z = 2.23, we have created synthetic
light curves at 1.5 keV with artificial errors while accounting for Swift
instrument biases as well. A large set of these light curves have been
generated and analyzed using a Monte Carlo approach. Single and broken power
law fits are compared. We find that for increasing observer angle, the jet
break quickly becomes hard to detect. This holds true even when the observer
remains well within the jet opening angle. We find that the odds that a Swift
light curve from a randomly oriented 0.1 radians jet at z = 2.23 will exhibit a
jet break at the 3 sigma level are only 12 percent. The observer angle
therefore provides a natural explanation for the lack of perceived jet breaks
in the Swift sample.Comment: 4 pages, 3 figures. First of two contributions to proceedings GRB2010
Maryland conference. Editors: McEnery, Racusin and Gehrels. The data from
this paper is publicly available from http://cosmo.nyu.edu/afterglowlibrary
An on-line library of afterglow light curves
Numerical studies of gamma-ray burst afterglow jets reveal significant
qualitative differences with simplified analytical models. We present an
on-line library of synthetic afterglow light curves and broadband spectra for
use in interpreting observational data. Light curves have been calculated for
various physics settings such as explosion energy and circumburst structure, as
well as differing jet parameters and observer angle and redshift. Calculations
gave been done for observer frequencies ranging from low radio to X-ray and for
observer times from hours to decades after the burst. The light curves have
been calculated from high-resolution 2D hydrodynamical simulations performed
with the RAM adaptive-mesh refinement code and a detailed synchrotron radiation
code.
The library will contain both generic afterglow simulations as well as
specific case studies and will be freely accessible at
http://cosmo.nyu.edu/afterglowlibrary . The synthetic light curves can be used
as a check on the accuracy of physical parameters derived from analytical model
fits to afterglow data, to quantitatively explore the consequences of varying
parameters such as observer angle and for accurate predictions of future
telescope data.Comment: 4 pages, 2 figures. Second of two contributions to proceedings
GRB2010 Maryland conference. Editors: McEnery, Racusin and Gehrels. The data
from this paper is publicly available from
http://cosmo.nyu.edu/afterglowlibrary
Domain Walls in Superfluid 3He-B
We consider domain walls between regions of superfluid 3He-B in which one
component of the order parameter has the opposite sign in the two regions far
from one another. We report calculations of the order parameter profile and the
free energy for two types of domain wall, and discuss how these structures are
relevant to superfluid 3He confined between two surfaces.Comment: 6 pages with 3 figures. Conference proceedings of QSF 2004, Trento,
Ital
Universal Properties of the Ultra-Cold Fermi Gas
We present some general considerations on the properties of a two-component
ultra-cold Fermi gas along the BEC-BCS crossover. It is shown that the
interaction energy and the ground state energy can be written in terms of a
single dimensionless function , where and
. The function incorporates all the many-body physics
and naturally occurs in other physical quantities as well. In particular, we
show that the RF-spectroscopy shift \bar{\d\o}(\xi,\tau) and the molecular
fraction in the closed channel can be expressed in terms of
and thus have identical temperature dependence. The conclusions
should have testable consequences in future experiments
Effective nucleon-nucleon interactions and nuclear matter equation of state
Nuclear matter equations of state based on Skyrme, Myers-Swiatecki and
Tondeur interactions are written as polynomials of the cubic root of density,
with coefficients that are functions of the relative neutron excess .
In the extrapolation toward states far away from the standard one, it is shown
that the asymmetry dependence of the critical point ()
depends on the model used. However, when the equations of state are fitted to
the same standard state, the value of is almost the same in Skyrme
and in Myers-Swiatecki interactions, while is much lower in Tondeur
interaction. Furthermore, does not depend sensitively on the choice
of the parameter in Skyrme interaction.Comment: 15 pages, 9 figure
Nuclear matter properties and relativistic mean-field theory
Nuclear matter properties are calculated in the relativistic mean field
theory by using a number of different parameter sets. The result shows that the
volume energy and the symmetry energy are around the acceptable
values 16MeV and 30MeV respectively; the incompressibility is
unacceptably high in the linear model, but assumes reasonable value if
nonlinear terms are included; the density symmetry is around for
most parameter sets, and the symmetry incompressibility has positive sign
which is opposite to expectations based on the nonrelativistic model. In almost
all parameter sets there exists a critical point , where
the minimum and the maximum of the equation of state are coincident and the
incompressibility equals zero, falling into ranges
0.014fmfm and ; for a few
parameter sets there is no critical point and the pure neutron matter is
predicted to be bound. The maximum mass of neutron stars is predicted
in the range 2.45MM, the corresponding
neutron star radius is in the range 12.2kmkm.Comment: 10 pages, 5 figure
Quantum quench dynamics of the Bose-Hubbard model at finite temperatures
We study quench dynamics of the Bose-Hubbard model by exact diagonalization.
Initially the system is at thermal equilibrium and of a finite temperature. The
system is then quenched by changing the on-site interaction strength
suddenly. Both the single-quench and double-quench scenarios are considered. In
the former case, the time-averaged density matrix and the real-time evolution
are investigated. It is found that though the system thermalizes only in a very
narrow range of the quenched value of , it does equilibrate or relax well in
a much larger range. Most importantly, it is proven that this is guaranteed for
some typical observables in the thermodynamic limit. In order to test whether
it is possible to distinguish the unitarily evolving density matrix from the
time-averaged (thus time-independent), fully decoherenced density matrix, a
second quench is considered. It turns out that the answer is affirmative or
negative according to the intermediate value of is zero or not.Comment: preprint, 20 pages, 7 figure
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