186 research outputs found
Estimating parameters of binary black holes from gravitational-wave observations of their inspiral, merger and ringdown
No full textWe characterize the expected statistical errors with which the parameters of
black-hole binaries can be measured from gravitational-wave (GW) observations
of their inspiral, merger and ringdown by a network of second-generation
ground-based GW observatories. We simulate a population of black-hole binaries
with uniform distribution of component masses in the interval ,
distributed uniformly in comoving volume, with isotropic orientations. From
signals producing signal-to-noise ratio in at least two detectors, we
estimate the posterior distributions of the binary parameters using the
Bayesian parameter estimation code LALInference. The GW signals will be
redshifted due to the cosmological expansion and we measure only the
"redshifted" masses. By assuming a cosmology, it is possible to estimate the
gravitational masses by inferring the redshift from the measured posterior of
the luminosity distance. We find that the measurement of the gravitational
masses will be in general dominated by the error in measuring the luminosity
distance. In spite of this, the component masses of more than of the
population can be measured with accuracy better than using the
Advanced LIGO-Virgo network. Additionally, the mass of the final black hole can
be measured with median accuracy . Spin of the final black hole can
be measured with median accuracy for binaries with
non-spinning (aligned-spin) black holes. Additional detectors in Japan and
India significantly improve the accuracy of sky localization, and moderately
improve the estimation of luminosity distance, and hence, that of all mass
parameters. We discuss the implication of these results on the observational
evidence of intermediate-mass black holes and the estimation of cosmological
parameters using GW observations
Review of the book Critiquing Brahmanism: A collection of essays, by K. Murali (Ajith)
No full textDr. Devin Zane Shaw (Douglas College) reviews the book Critiquing Brahmanism: A collection of essays, by K. Murali (Ajith) (2020).Final article published
Constraining black hole mimickers with gravitational wave observations
No full textLIGO and Virgo have recently observed a number of gravitational wave (GW) signals that are fully consistent with being emitted by binary black holes described by general relativity. However, there are theoretical proposals of exotic objects that can be massive and compact enough to be easily confused with black holes. Nevertheless, these objects differ from black holes in having nonzero tidal deformabilities, which can allow one to distinguish binaries containing such objects from binary black holes using GW observations. Using full Bayesian parameter estimation, we investigate the possibility of constraining the parameter space of such "black hole mimickers" with upcoming GW observations. Employing perfect fluid stars with a polytropic equation of state as a simple model that can encompass a variety of possible black hole mimickers, we show how the observed masses and tidal deformabilities of a binary constrain the equation of state. We also show how such constraints can be used to rule out some simple models of boson stars
Gravitational waves from binary neutron stars systems
No full textThe first observation of gravitational waves from a merger of binary neutron stars (BNS) along with measurements of electromagnetic counterpart has led the beginning of multi-messenger gravitational wave astronomy. In this thesis, we investigate various gravitational waveform models. These models are employed for extracting source properties from the gravitational wave signal from the BNS merger. We perform parameter estimation studies in order to deduce the systematics among these models. We employ different injection scenarios to understand the biases that occur due to differences in the physics included in different waveform models. We present the construction of hybrid waveforms and discuss their applications as a full waveform, e.g., for validation of other waveform models and to check the performance of the models by performing mismatch calculations and parameter estimation studies where hybrid waveforms used as a substitute for a real signal. Based on the systematics study, we show a few of the waveform models give biased esti- mates of the parameters for specific injection scenarios. We improve those models and present the results of the improved models. In the context of having an accurate yet fast-to-evaluate waveform model, we review reduced-order-modeling techniques and present its application for the multipolar TEOBResum model. Furthermore, to validate and tune analytical models, and to investigate the last few orbits near the merger and after the merger, numerical simulations are inevitable. We evaluate the performance of an initial data generating code, called new SGRID code for BNS systems. With the upcoming advance detectors, it is highly likely that events with extreme source properties will get observed. Therefore, in this thesis, we show preliminary results for numerical simulations of BNS mergers with high spins. We vary equation-of-states (EOSs) and spins to investigate the effects of spin and EOS on the dynamics and gravitational waves
On aspects of gravitational-wave detection: detector characterisation, data analysis and source modelling for ground-based detectors
No full text[no abstract
Gravitational-wave data analysis using binary black-hole waveforms
No full textCoalescing 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
Ultrasonic time-of-flight shift measurements in carbon composite laminates containing matrix microcracks
No full textTime-of-flight (TOF) shifts are calculated from the fundamental A0 Lamb mode using air-coupled ultrasound. The technique is applied to carbon/bismaleimide samples containing varying microcrack density along the length of the sample. The phase and group velocity reduction is inferred from the TOF shift data. The relation between group velocity and crack density is presented. Approximate microcrack densities over several segments of the sample are calculated using a simple constant thresholding algorithm applied to X-ray MicroCT data.This proceeding may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing.
This proceeding appeared in Subramanian, Ajith, Vinay Dayal, and Daniel J. Barnard. "Ultrasonic time-of-flight shift measurements in carbon composite laminates containing matrix microcracks." In AIP Conference Proceedings, vol. 1581, no. 1, pp. 1098-1105. American Institute of Physics, 2014, and may be found at
DOI: 10.1063/1.4864943.
Copyright 2014 AIP Publishing LLC.
Posted with permission
Listening to black holes
No full textThe recent discovery of gravitational waves not only confirms Albert Einstein’s century old prediction, but also opens up a completely new way of observing the Universe. This article describes the exciting story of this discovery, what went behind it, and what lies ahea
Do sphenoidal electrodes aid in surgical decision making in drug resistant temporal lobe epilepsy?
No full textObjective: The utility of sphenoidal electrodes (SPh) in analyzing interictal epileptiform discharges (IEDs) and ictal electrography remains controversial, despite its widespread use.Methods: One hundred and twenty-two consecutive patients with presumed temporal lobe epilepsy (TLE) who underwent presurgical evaluation were prospectively studied. SPh and Silverman's electrodes were placed, in addition to routine electrodes in 10-20 international system. IEDs and ictal electroencephalography (EEG) were analyzed separately in bipolar and referential montages. The proportion of patients selected for surgery after adjusting for SPh placement based on the earlier ictal onset and IEDs were analyzed.Results: Of the 8701 IEDs in SPh, only 65% were seen over the scalp bipolar montage; 1392 (16%) IEDs were confined to SPh electrodes, and were not seen at scalp bipolar montage (p < 0.001). Spike amplitudes were highest at SPh (p < 0.001). Of the 592 seizures analyzed, 62 (61%) had simultaneous SPh and scalp onset, while in 26 (25%) SPh onset preceded the scalp.Conclusions: Out of the 35 patients with unilateral mesial temporal sclerosis (MTS) with additional neocortical changes and/or non-lateralized bitemporal IEDs and/or diffuse ictal onset (group 1), 27 were selected for surgery (77%). About 7% was selected for surgery in this group by SPh placement. Also, in patients with bilateral MTS (group 2), 25% (5/20) were chosen for anterior temporal lobectomy, SPh provided an additional benefit in 11% (p < 0.001). Patients with normal magnetic resonance imaging (group 3) and temporal plus epilepsy (group 4) had a lower surgical yield, only 12% and 9.5% could undergo surgery. They were denied surgical candidacy with SPh (p < 0.001). Significance: One-third of patients after SPh placement were selected for resective surgery obviating the need for invasive monitoring. The maximum yield was noted in unilateral MTS (associated with additional neocortical features or non-lateralized bilateral temporal interictal IEDs or diffuse ictal onset in scalp EEG) and in bilateral MTS. Those with normal MRI/temporal plus epilepsy could be excluded from direct resective surgery. (C) 2011 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved
Addressing the spin question in gravitational-wave searches: Waveform templates for inspiralling compact binaries with nonprecessing spins
No full textThis paper presents a post-Newtonian (PN) template family of gravitational waveforms from inspiralling compact binaries with nonprecessing spins, where the spin effects are described by a single “reduced-spin” parameter. This template family, which reparametrizes all the spin-dependent PN terms in terms of the leading-order (1.5PN) spin-orbit coupling term in an approximate way, has very high overlaps (fitting factor >0.99) with nonprecessing binaries with arbitrary mass ratios and spins. We also show that this template family is “effectual” for the detection of a significant fraction of generic spinning binaries in the comparable-mass regime (m_2/m_1≲10), providing an attractive and feasible way of searching for gravitational waves from spinning low-mass binaries. We also show that the secular (nonoscillatory) spin-dependent effects in the phase evolution (which are taken into account by the nonprecessing templates) are more important than the oscillatory effects of precession in the comparable-mass (m_1≃m_2) regime. Hence the effectualness of nonspinning templates is particularly poor in this case, as compared to non-precessing-spin templates. For the case of binary neutron stars observable by Advanced LIGO, even moderate spins (L̂_N·S/m^2≃0.015–0.1) will cause considerable mismatches (~3%–25%) with nonspinning templates. This is contrary to the expectation that neutron-star spins may not be relevant for gravitational wave detection
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