1,585 research outputs found
Charged-current neutrino interactions in core-collapse supernovae in a virial expansion
Core-collapse supernovae may depend sensitively on charged-current neutrino interactions in warm, low-density, neutron-rich matter. A proton in neutron-rich matter is more tightly bound than is a neutron. This energy shift ΔU increases the electron energy in ν_e + n → p + e, increasing the available phase space and absorption cross section. Likewise ΔU decreases the positron energy in ν̅_ e + p → n + e+, decreasing the phase space and cross section. We have calculated ΔU using a model-independent virial expansion and we find that ΔU is much larger, at low densities, than the predictions of many mean-field models. Therefore ΔU could have a significant impact on charged-current neutrino interactions in supernovae. Preliminary simulations of the accretion phase of core-collapse supernovae find that ΔU increases ν̅ _e energies and decreases the ν_e luminosity
Chaotic, staggered and polarized dynamics in opinion forming: the contrarian effect
We revisit the no tie breaking 2-state Galam contrarian model of opinion
dynamics for update groups of size 3. While the initial model assumes a
constant density of contrarians a for both opinions, it now depends for each
opinion on its global support. Proportionate contrarians are thus found to
indeed preserve the former case main results. However, restricting the
contrarian behavior to only the current collective majority, makes the dynamics
more complex with novel features. For a density a<a_c=1/9 of one-sided
contrarians, a chaotic basin is found in the fifty-fifty region separated from
two majority-minority point attractors, one on each side. For 1/9<a< 0.301 only
the chaotic basin survives. In the range a>0.301 the chaotic basin disappears
and the majority starts to alternate between the two opinions with a staggered
flow towards two point attractors. We then study the effect of both, decoupling
the local update time sequence from the contrarian behavior activation, and a
smoothing of the majority rule. A status quo driven bias for contrarian
activation is also considered. Introduction of unsettled agents driven in the
debate on a contrarian basis is shown to only shrink the chaotic basin. The
model may shed light to recent apparent contradictory elections with on the one
hand very tied results like in US in 2000 and in Germany in 2002 and 2005, and
on the other hand, a huge majority like in France in 2002.Comment: 17 pages, 10 figure
Random fluctuation leads to forbidden escape of particles
A great number of physical processes are described within the context of
Hamiltonian scattering. Previous studies have rather been focused on
trajectories starting outside invariant structures, since the ones starting
inside are expected to stay trapped there forever. This is true though only for
the deterministic case. We show however that, under finitely small random
fluctuations of the field, trajectories starting inside Arnold-Kolmogorov-Moser
(KAM) islands escape within finite time. The non-hyperbolic dynamics gains then
hyperbolic characteristics due to the effect of the random perturbed field. As
a consequence, trajectories which are started inside KAM curves escape with
hyperbolic-like time decay distribution, and the fractal dimension of a set of
particles that remain in the scattering region approaches that for hyperbolic
systems. We show a universal quadratic power law relating the exponential decay
to the amplitude of noise. We present a random walk model to relate this
distribution to the amplitude of noise, and investigate this phenomena with a
numerical study applying random maps.Comment: 6 pages, 6 figures - Up to date with corrections suggested by
referee
A New Open-Source Code for Spherically-Symmetric Stellar Collapse to Neutron Stars and Black Holes
We present the new open-source spherically-symmetric general-relativistic
(GR) hydrodynamics code GR1D. It is based on the Eulerian formulation of GR
hydrodynamics (GRHD) put forth by Romero-Ibanez-Gourgoulhon and employs
radial-gauge, polar-slicing coordinates in which the 3+1 equations simplify
substantially. We discretize the GRHD equations with a finite-volume scheme,
employing piecewise-parabolic reconstruction and an approximate Riemann solver.
GR1D is intended for the simulation of stellar collapse to neutron stars and
black holes and will also serve as a testbed for modeling technology to be
incorporated in multi-D GR codes. Its GRHD part is coupled to various
finite-temperature microphysical equations of state in tabulated form that we
make available with GR1D. An approximate deleptonization scheme for the
collapse phase and a neutrino-leakage/heating scheme for the postbounce epoch
are included and described. We also derive the equations for effective rotation
in 1D and implement them in GR1D. We present an array of standard test
calculations and also show how simple analytic equations of state in
combination with presupernova models from stellar evolutionary calculations can
be used to study qualitative aspects of black hole formation in failing
rotating core-collapse supernovae. In addition, we present a simulation with
microphysical EOS and neutrino leakage/heating of a failing core-collapse
supernova and black hole formation in a presupernova model of a 40 solar mass
zero-age main-sequence star. We find good agreement on the time of black hole
formation (within 20%) and last stable protoneutron star mass (within 10%) with
predictions from simulations with full Boltzmann neutrino radiation
hydrodynamics.Comment: 25 pages, 6 figures, 2 appendices. Accepted for publication to the
Classical and Quantum Gravity special issue for MICRA2009. Code may be
downloaded from http://www.stellarcollapse.org Update: corrected title, small
modifications suggested by the referees, added source term derivation in
appendix
GRHydro: a new open-source general-relativistic magnetohydrodynamics code for the Einstein toolkit
We present the new general-relativistic magnetohydrodynamics (GRMHD) capabilities of the Einstein toolkit, an open-source community-driven numerical relativity and computational relativistic astrophysics code. The GRMHD extension of the toolkit builds upon previous releases and implements the evolution of relativistic magnetized fluids in the ideal MHD limit in fully dynamical spacetimes using the same shock-capturing techniques previously applied to hydrodynamical evolution. In order to maintain the divergence-free character of the magnetic field, the code implements both constrained transport and hyperbolic divergence cleaning schemes. We present test results for a number of MHD tests in Minkowski and curved spacetimes. Minkowski tests include aligned and oblique planar shocks, cylindrical explosions, magnetic rotors, Alfvén waves and advected loops, as well as a set of tests designed to study the response of the divergence cleaning scheme to numerically generated monopoles. We study the code's performance in curved spacetimes with spherical accretion onto a black hole on a fixed background spacetime and in fully dynamical spacetimes by evolutions of a magnetized polytropic neutron star and of the collapse of a magnetized stellar core. Our results agree well with exact solutions where these are available and we demonstrate convergence. All code and input files used to generate the results are available on http://einsteintoolkit.org. This makes our work fully reproducible and provides new users with an introduction to applications of the code
Maximum Entropy for Gravitational Wave Data Analysis: Inferring the Physical Parameters of Core-Collapse Supernovae
The gravitational wave signal arising from the collapsing iron core of a Type
II supernova progenitor star carries with it the imprint of the progenitor's
mass, rotation rate, degree of differential rotation, and the bounce depth.
Here, we show how to infer the gravitational radiation waveform of a core
collapse event from noisy observations in a network of two or more LIGO-like
gravitational wave detectors and, from the recovered signal, constrain these
source properties. Using these techniques, predictions from recent core
collapse modeling efforts, and the LIGO performance during its S4 science run,
we also show that gravitational wave observations by LIGO might have been
sufficient to provide reasonable estimates of the progenitor mass, angular
momentum and differential angular momentum, and depth of the core at bounce,
for a rotating core collapse event at a distance of a few kpc.Comment: 44 pages, 12 figures; accepted version scheduled to appear in Ap J 1
April 200
Gravitational Waves from Axisymmetric, Rotational Stellar Core Collapse
We have carried out an extensive set of two-dimensional, axisymmetric,
purely-hydrodynamic calculations of rotational stellar core collapse with a
realistic, finite-temperature nuclear equation of state and realistic massive
star progenitor models. For each of the total number of 72 different
simulations we performed, the gravitational wave signature was extracted via
the quadrupole formula in the slow-motion, weak-field approximation. We
investigate the consequences of variation in the initial ratio of rotational
kinetic energy to gravitational potential energy and in the initial degree of
differential rotation. Furthermore, we include in our model suite progenitors
from recent evolutionary calculations that take into account the effects of
rotation and magnetic torques. For each model, we calculate gravitational
radiation wave forms, characteristic wave strain spectra, energy spectra, final
rotational profiles, and total radiated energy. In addition, we compare our
model signals with the anticipated sensitivities of the 1st- and 2nd-generation
LIGO detectors coming on line. We find that most of our models are detectable
by LIGO from anywhere in the Milky Way.Comment: 13 pages, 22 figures, accepted for publication in ApJ (v600, Jan.
2004). Revised version: Corrected typos and minor mistakes in text and
references. Minor additions to the text according to the referee's
suggestions, conclusions unchange
Expression of ISG15, UBE1L and MX2 in white blood cells of early pregnant and bred-nonpregnant dairy cows
Abstract only availableIdentifying pregnant and nonpregnant cows shortly after insemination can improve reproductive efficiency in dairy cows if resynchronization is practiced on nonpregnant cows. Bovine Interferon Stimulated Gene Product 15 (ISG15), Bovine Ubiquitin-Activating E1-Like (UBE1L) Enzyme and MX2 are produced in response to conceptus-dervied interferon-Ï„. The objective was to determine the level of these mRNA in pregnant and bred-nonpregnant Holstein cows (n=14). We hypothesized that the amount of ISG15, UBE1L and MX2 mRNA would increase between d 14 to 20 in pregnant cows but not increase in bred-nonpregnant cows. Cows were synchronized to estrus and inseminated (d 0). Blood samples were collected on d 14, 16, 18 and 20 following insemination. Pregnancy status was determined at approximately 30 and 60 d after insemination. RNA was isolated, reverse transcribed into cDNA and amplified using quantitative RTPCR. Six cows were nonpregnant (open) and eight cows were pregnant on d 30. On d 60, four of the pregnant cows remained pregnant (pregnant-pregnant) and four were found open (aborted; pregnant-open). mRNA data were expressed as fold increase above control and relative to cyclophilin. A status by day interaction was detected for ISG15 (P<.001) and MX2 (P<.02). The interaction was not significant for UBE1L. Mean ISG15 and mean MX2 remained low for open cows, but increased markedly on d 18 and 20 in pregnant-pregnant cows. Pregnant-open cows either had low levels of ISG15 and MX2 or underwent an increase in ISG15 and MX2 on d 18 and 20. We conclude that ISG15, UBE1L and MX2 are differentially regulated in dairy cows during pregnancy recognition. ISG15 and MX2 mRNA expression could be used as an indicator of early pregnancy. Cows that abort their pregnancy after d 28 (pregnant-open) have abnormal ISG15 and MX2 mRNA expression between d 14 to 20.F.B. Miller Undergraduate Research Program in Animal Science
Notes on the integration of numerical relativity waveforms
A primary goal of numerical relativity is to provide estimates of the wave
strain, , from strong gravitational wave sources, to be used in detector
templates. The simulations, however, typically measure waves in terms of the
Weyl curvature component, . Assuming Bondi gauge, transforming to the
strain reduces to integration of twice in time. Integrations
performed in either the time or frequency domain, however, lead to secular
non-linear drifts in the resulting strain . These non-linear drifts are not
explained by the two unknown integration constants which can at most result in
linear drifts. We identify a number of fundamental difficulties which can arise
from integrating finite length, discretely sampled and noisy data streams.
These issues are an artifact of post-processing data. They are independent of
the characteristics of the original simulation, such as gauge or numerical
method used. We suggest, however, a simple procedure for integrating numerical
waveforms in the frequency domain, which is effective at strongly reducing
spurious secular non-linear drifts in the resulting strain.Comment: 23 pages, 10 figures, matches final published versio
- …