2,030 research outputs found
Gravitational-wave data analysis using binary black-hole waveforms
Coalescing binary black-hole systems are among the most promising sources of
gravitational waves for ground-based interferometers. While the \emph{inspiral}
and \emph{ring-down} stages of the binary black-hole coalescence are
well-modelled by analytical approximation methods in general relativity, the
recent progress in numerical relativity has enabled us to compute accurate
waveforms from the \emph{merger} stage also. This has an important impact on
the search for gravitational waves from binary black holes. In particular,
while the current gravitational-wave searches look for each stage of the
coalescence separately, combining the results from analytical and numerical
relativity enables us to \emph{coherently} search for all three stages using a
single template family. `Complete' binary black-hole waveforms can now be
produced by matching post-Newtonian waveforms with those computed by numerical
relativity. These waveforms can be parametrised to produce analytical waveform
templates. The `complete' waveforms can also be used to estimate the efficiency
of different search methods aiming to detect signals from black-hole
coalescences. This paper summarises some recent efforts in this direction.Comment: Minor modifications in the text, added table of phenomenological
coefficient
Tracking the precession of compact binaries from their gravitational-wave signal
We present a simple method to track the precession of a black-hole-binary
system, using only information from the gravitational-wave (GW) signal. Our
method consists of locating the frame from which the magnitude of the
modes is maximized, which we denote the "quadrupole-aligned"
frame. We demonstrate the efficacy of this method when applied to waveforms
from numerical simulations. In the test case of an equal-mass nonspinning
binary, our method locates the direction of the orbital angular momentum to
within . We then
apply the method to a binary that exhibits significant
precession. In general a spinning binary's orbital angular momentum
is \emph{not} orthogonal to the orbital plane. Evidence that our
method locates the direction of rather than the normal of the
orbital plane is provided by comparison with post-Newtonian (PN) results. Also,
we observe that it accurately reproduces similar higher-mode amplitudes to a
comparable non-spinning (and therefore non-precessing) binary, and that the
frequency of the modes is consistent with the "total
frequency" of the binary's motion. The simple form of the quadrupole-aligned
waveform will be useful in attempts to analytically model the
inspiral-merger-ringdown (IMR) signal of precessing binaries, and in
standardizing the representation of waveforms for studies of accuracy and
consistency of source modelling efforts, both numerical and analytical.Comment: 11 pages, 12 figures, 1 tabl
Length requirements for numerical-relativity waveforms
One way to produce complete inspiral-merger-ringdown gravitational waveforms
from black-hole-binary systems is to connect post-Newtonian (PN) and
numerical-relativity (NR) results to create "hybrid" waveforms. Hybrid
waveforms are central to the construction of some phenomenological models for
GW search templates, and for tests of GW search pipelines. The dominant error
source in hybrid waveforms arises from the PN contribution, and can be reduced
by increasing the number of NR GW cycles that are included in the hybrid.
Hybrid waveforms are considered sufficiently accurate for GW detection if their
mismatch error is below 3% (i.e., a fitting factor about 0.97). We address the
question of the length requirements of NR waveforms such that the final hybrid
waveforms meet this requirement, considering nonspinning binaries with q =
M_2/M_1 \in [1,4] and equal-mass binaries with \chi = S_i/M_i^2 \in [-0.5,0.5].
We conclude that for the cases we study simulations must contain between three
(in the equal-mass nonspinning case) and ten (the \chi = 0.5 case) orbits
before merger, but there is also evidence that these are the regions of
parameter space for which the least number of cycles will be needed.Comment: Corrected some typo
Yelling Fire and Hacking: Why the First Amendment Does Not Permit Distributing DVD Decryption Technology?
One of the consequences of the black-hole "no-hair" theorem in general relativity (GR) is that gravitational radiation (quasi-normal modes) from a perturbed Kerr black hole is uniquely determined by its mass and spin. Thus, the spectrum of quasi-normal mode frequencies have to be all consistent with the same value of the mass and spin. Similarly, the gravitational radiation from a coalescing binary black hole system is uniquely determined by a small number of parameters (masses and spins of the black holes and orbital parameters). Thus, consistency between different spherical harmonic modes of the radiation is a powerful test that the observed system is a binary black hole predicted by GR. We formulate such a test, develop a Bayesian implementation, demonstrate its performance on simulated data and investigate the possibility of performing such a test using previous and upcoming gravitational wave observations
Using the null-stream of GEO600 to veto transient events in the detector output
A network of gravitational wave detectors is currently being commissioned around the world. Each of these detectors will search for gravitational waves from various astronomical sources. One of the main searches underway is for un-modelled, transient gravitational wave events. The nature of these signals is such that it will be difficult to distinguish them from bursts of instrumental noise that originate in or around the detector and which then couple to the main detector output. One way to deal with this is to look for events that are coincident in more than one gravitational wave detector. However, with very large event lists (potentially thousands of events per day per detector), the number of events that pass this test due to random chance can still be large. At each detector site, various methods are being developed to veto instrumental bursts from lists of candidate events from that particular detector. This reduces the size of the event lists of each detector, and hopefully the final coincident event list, to a more manageable level. This paper presents one such veto method that can be used to veto certain classes of transient events detected in the output data stream of GEO 600. The method uses events detected in the null-stream output of GEO 600 (which contains, in principle, no gravitational wave signal) with a threshold to veto events detected in the main strain output. We show that, for the certain types of signals tested, the method is very robust, delivering high efficiency for a very low false-veto rate. In particular, it is shown that when applied to real detector data, the method is able to strongly veto a certain type of events which appear around 370 Hz in the detector output
An effectual template bank for the detection of gravitational waves from inspiralling compact binaries with generic spins
We report the construction of a three-dimensional template bank for the
search for gravitational waves from inspiralling binaries consisting of
spinning compact objects. The parameter space consists of two dimensions
describing the mass parameters and one "reduced-spin" parameter, which
describes the secular (non-precessing) spin effects in the waveform. The
template placement is based on an efficient stochastic algorithm and makes use
of the semi-analytical computation of a metric in the parameter space. We
demonstrate that for "low-mass" () binaries,
this template bank achieves effective fitting factors --
towards signals from generic spinning binaries in the advanced detector era
over the entire parameter space of interest (including binary neutron stars,
binary black holes, and black hole-neutron star binaries). This provides a
powerful and viable method for searching for gravitational waves from generic
spinning low-mass compact binaries. Under the assumption that spin magnitudes
of black-holes [neutron-stars] are uniformly distributed between 0--0.98 [0 --
0.4] and spin angles are isotropically distributed, the expected improvement in
the average detection volume (at a fixed signal-to-noise-ratio threshold) of a
search using this reduced-spin bank is , as compared to a search
using a non-spinning bank.Comment: Minor changes, version appeared in Phys. Rev.
IN VITRO HEPATOPROTECTIVE ACTIVITY OF YELLOW LEAF EXTRACTS OF THESPESIA POPULNEA AGAINST CARBON TETRACHLORIDE INDUCED TOXICITY
Objective: The study was aimed to evaluate in vitro hepatoprotective activity of yellow leaf extracts of Thespesiapopulnea.
Methods: Hepatoprotective activity is studied by carbon tetrachloride-induced hepato-toxicity in isolated rat hepatocytes. The biochemical parameters observed in serum were serum glutamate oxaloacetate transaminase (SGOT/AST), serum glutamate pyruvate transaminase (SGPT/ALT) levels. The extracts exhibited a dose-dependent reduction in AST, ALT levels.
Results: Methanolic extract was found to exhibit higher hepatoprotection. T. populnea extract was found to be antihepatotoxic at a concentration of 125 mcg with a significant decrease in ALT (P<0.001) and AST (P<0.0001).
Conclusion: The results suggest that the methanolic extract has produced significant (p<0.001) hepatoprotection by decreasing the activity of serum enzymes which is comparable to that of standard drug silymarin
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