126 research outputs found
Second post-Newtonian gravitational radiation reaction for two-body systems: Nonspinning bodies
Starting from the recently obtained 2PN accurate forms of the energy and
angular momentum fluxes from inspiralling compact binaries, we deduce the
gravitational radiation reaction to 2PN order beyond the quadrupole
approximation - 4.5PN terms in the equation of motion - using the refined
balance method proposed by Iyer and Will. We explore critically the features of
their construction and illustrate them by contrast to other possible variants.
The equations of motion are valid for general binary orbits and for a class of
coordinate gauges. The limiting cases of circular orbits and radial infall are
also discussed.Comment: 38 pages, REVTeX, no figures, to appear in Phys. Rev.
Eccentricity content of binary black hole initial data
Using a post-Newtonian diagnostic tool developed by Mora and Will, we examine
numerically generated quasiequilibrium initial data sets that have been used in
recently successful numerical evolutions of binary black holes through plunge,
merger and ringdown. We show that a small but significant orbital eccentricity
is required to match post-Newtonian and quasiequilibrium calculations. If this
proves to be a real eccentricity, it could affect the fine details of the
subsequent numerical evolutions and the predicted gravitational waveforms.Comment: 5 pages, 5 figures, clarifications and minor corrections; version
submitted to Phys. Rev.
Cumulative Dragging - An Intrinsic Characteristic of Stationary Axisymmetric Spacetime
The Cumulative Drag Index defined recently by Prasanna has been generalised
to include the centrifugal acceleration. We have studied the behaviour of the
drag index for the Kerr metric and the Neugebauer-Meinel metric representing a
self-gravitating rotating disk and their Newtonian approximations. The
similarity of the behaviour of the index for a given set of parameters both in
the full and approximated forms, suggests that the index characterises an
intrinsic property of spacetime with rotation. Analysing the index for a given
set of parameters shows possible constraints on them.Comment: Discussion of Neugebauer-Meinel rotating disk and clarifications
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A post-Newtonian diagnosis of quasiequilibrium configurations of neutron star-neutron star and neutron star-black hole binaries
We use a post-Newtonian diagnostic tool to examine numerically generated
quasiequilibrium initial data sets for non-spinning double neutron star and
neutron star-black hole binary systems. The PN equations include the effects of
tidal interactions, parametrized by the compactness of the neutron stars and by
suitable values of ``apsidal'' constants, which measure the degree of
distortion of stars subjected to tidal forces. We find that the post-Newtonian
diagnostic agrees well with the double neutron star initial data, typically to
better than half a percent except where tidal distortions are becoming extreme.
We show that the differences could be interpreted as representing small
residual eccentricity in the initial orbits. In comparing the diagnostic with
preliminary numerical data on neutron star-black hole binaries, we find less
agreement.Comment: 17 pages, 6 tables, 8 figure
Centrifugal Force and Ellipticity behaviour of a slowly rotating ultra compact object
Using the optical reference geometry approach, we have derived in the
following, a general expression for the ellipticity of a slowly rotating fluid
configuration using Newtonian force balance equation in the conformally
projected absolute 3-space, in the realm of general relativity. Further with
the help of Hartle-Thorne (H-T) metric for a slowly rotating compact object, we
have evaluated the centrifugal force acting on a fluid element and also
evaluated the ellipticity and found that the centrifugal reversal occurs at
around , and the ellipticity maximum at around . The result has been compared with that of Chandrasekhar and
Miller which was obtained in the full 4-spacetime formalism
SPEAR : Semi-supervised Data Programming in Python
We present SPEAR, an open-source python library for data programming with
semi supervision. The package implements several recent data programming
approaches including facility to programmatically label and build training
data. SPEAR facilitates weak supervision in the form of heuristics (or rules)
and association of noisy labels to the training dataset. These noisy labels are
aggregated to assign labels to the unlabeled data for downstream tasks. We have
implemented several label aggregation approaches that aggregate the noisy
labels and then train using the noisily labeled set in a cascaded manner. Our
implementation also includes other approaches that jointly aggregate and train
the model for text classification tasks. Thus, in our python package, we
integrate several cascade and joint data-programming approaches while also
providing the facility of data programming by letting the user define labeling
functions or rules. The code and tutorial notebooks are available at
https://github.com/decile-team/spear. Further, extensive documentation can be
found at https://spear-decile.readthedocs.io/. Video tutorials demonstrating
the usage of our package are available here. We also present some real-world
use cases of SPEAR.Comment: EMNLP Demonstrations - 202
Computational Relativistic Astrophysics With Adaptive Mesh Refinement: Testbeds
We have carried out numerical simulations of strongly gravitating systems
based on the Einstein equations coupled to the relativistic hydrodynamic
equations using adaptive mesh refinement (AMR) techniques. We show AMR
simulations of NS binary inspiral and coalescence carried out on a workstation
having an accuracy equivalent to that of a regular unigrid simulation,
which is, to the best of our knowledge, larger than all previous simulations of
similar NS systems on supercomputers. We believe the capability opens new
possibilities in general relativistic simulations.Comment: 7 pages, 16 figure
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