Browsing by Author "Dhurandhar, S.V."

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Algorithm for optimally distributing quantized load on transputers with unequal speed: An application to the detection of gravitational wave signals from coalescing binaries
(2015-01-13) Pitre, Sangita. N.; Dhurandhar, S.V.
In a parallel computing system, we work with a network of a large number of processors wherein the performance characteristics each processer may have are different. This leads to a situation that when there is equal load on all the processer, some complete the job before the others. To make the optimum use of the available computing facility and optimise on time, it is necessary to balance the load on the processers according to there characteristics like speed etc. Here we present an algorithm to optimse to on ‘ time ‘ when difference processer have difference speed and the load is quantised in integral multiples of a given unit of load. The algorithm distribute the load in such a manner that all the processer work optimally and the processing time is minimal. The optimal distribution of the load is achived by employing the well known bisection technique for finding the rots of an equation. We discuss this algorithm in the context of our application for filtering the coalescing binary gravitational wave signals. Numerical result are finally discussed for the 64 transputer machine ( PARAM ) .
Choice of filters for the detection of gravitational waves from coalescing binaries II: detection in coloured noise
(2014-11-25) Dhurandhar, S.V.; Sathyaprakash, B.S.
We discuss the problem of detecting gravitational waves signals embedded in coloured noise from coalescing binary systems. The signal is assumed to be Newtonian and matched filtering techniques are employed to filter out the signal. The problem is discussed at first for a general power spectral density of the noise and then specific numerical results are obtained for the standard recycling case. Since the signal parameters are unknown, a bank of filters is needed to carry out the signal detection. The number of filters in a bank , the spacing between filter etc. is obainted for different values of minimum strength of the signal relative to the threshold. We also present an approximate analytical formula which relates the spacing between filter to the minimum strength. Finally we discuss the problem of detection probabilities given a data train.
Coincidence detection of broadband signals by networks of the planned interferometric gravitational wave detectors
(2015-01-25) Bhawal, Biplab; Dhurandhar, S.V.
We describe how the six planned detectors (2 LIGOs, VIRGO, GEO, AIGO, TAMA) can be used to perform coincidence experiments for the detection of broadband signals from either coalescing compact binaries or burst sources. We make comparisons of the achievable sensitivities of these detectors under different optical configurations and find that a meaningful coincidence experiment for the detection of coalescing binary signals can only be performed by a network where the LIGOs and VIRGO are operated in power recycling mode and other medium scale detectors are operated in dual recycling mode. For the model of burst waveform considered by us (i.e. uniform power upto 2000Hz), we find that the relative sensitivity of the power-recycled VIRGO is quite high as compared to others with their present design parameters and thus coincidence experiment performed by including VIRGO in the network would not be a meaningful one. We also calculate optimized values for the time-delay window sizes for different possible networks. The effect of filtering on the calculation of thresholds has also been discussed. We set the thresholds for different detectors and find out the volume of sky that can be covered by different possible networks and the corresponding rate of detection of coalescing binaries in the beginning of the next century. We note that a coincidence experiment of power-recycled LIGOs and VIRGO and dual-recycled GEO and AIGO can increase the volume of the sky covered by 3.2 times as compared with only the power-recycled LIGO detectors and by 1.7 times the sky covered by the power-recycled LIGO-VIRGO network. These values are far less than the range that can be covered by only the LIGO-VIRGO network with dual recycling operation at a later stage, but the accuracy in the determination of direction, distance and other source parameters will be much better in a coincidence experiment in which other detectors and especially AIGO take part.
Detection of gravitational waves using a network of detectors
(2015-03-01) Bose, Sukanta; Dhurandhar, S.V.; Pai, Archana
We formulate the data analysis problem for the detection of the Newtonian coalescing-binary signal by a network of laser interferometric gravitational wave detectors that have arbitrary orientations, but are located at the same site. We use the maximum likelihood method for optimizing the detection problem. We show that for networks comprising of up to three detectors, the optimal statistic is just the matched network-filter. Alternatively, it is simply a linear combination of the signal-to-noise ratios of the individual detectors. This statistic, therefore, can be interpreted as the signal-to-noise ratio of the network. The overall sensitivity of the network is shown to increase roughly as the square-root of the number of detectors in the network. We further show that these results continue to hold even for the restricted post Newtonian filters. Finally, our formalism is general enough to be extended, in a straightforward way, to address the problem of detection of such waves from other sources by some other types of detectors, eg., bars or spheres, or even by networks of spatially well-separated detectors.
Estimation of parameters of gravitational waves from coalescing binaries
(2015-01-25) Balasubramanian, R.; Sathyaprakash, B.S.; Dhurandhar, S.V.
Hierarchial search strategy for inspiraling compact binaries
(2015-03-11) Dhurandhar, S.V.
Losses in pendular suspension due to centrifugal coupling
(2014-11-25) Pitre, Sangita. N.; Dhurandhar, S.V.; Blair, D.G.; Li, Ju
We present an analysis of the centrifugal coupling of simple pendulum to a dissipative support. We show that such a coupling leads to an amplitude dependent quality factor. For amplitudes which could be present in laser interferometer gravitational wave detector suspension, this mechanism could limit the quality factor of the test mass suspension significantly to 1010 and should be considered in the design of advanced LIGO type detectors.
Numerical simulation of time delay interferometry for LISA with the simplification or having only one interferometer
(2012-08) Dhurandhar, S.V.; Ni, W.-T.; Wang, G.
A parallel algorithm for filtering gravitational waves from coalescing binaries
(2014-11-23) Sathyaprakash, B.S.; Dhurandhar, S.V.
Coalescing binary stars are perhaps the most promising sources for the observation of gravitational waves with laser interferometric gravity wave detectors. The waveform from these sources can be predicted with sufficient accuracy for matched filtering techniques to be applied. In this paper we present a parallel algorithm for detecting signals from coalescing compact binaries by the method of matched filtering. We also report the details of its implementation on a 256-node connection machine consisting of a network of transputers. The results of our analysis indicate that parallel processing is a promising approach to on-line analysis of data from gravitational wave detectors to filter out coalescing binary signals. The algorithm described is quite general in that the kernel of the algorithm is applicable to any set of matched filters.
Performance of Newtonian filters in the detection of gravitational radiation from coalescing binaries
(2015-01-13) Balasubramanian, R.; Dhurandhar, S.V.
Post – Newtonian corrections to the gravitational waveform emitted by coalescing binaries have been found to lead to a secular phase accumulation error as compared with the signals calculated in the Newtonian approximation. The matched filtering process which relies on the correlation between the correlation between the signal and the filter is extremely sensitive to errors in phase. We explore the possibility of compensating for the phase difference caused by the post-Newtonian terms by allowing for a shift in the Newtonian filter parameters. We find that, on the average, we lose by about 30% in the correlation.
Radiation pressure induced instabilities in laser interferometric detectors of gravitational waves
(2015-03-13) Pai, A.; Dhurandhar, S.V.; Hello, P.; Vinet, J.Y.
The large scale interferometric gravitational wave detectors consist of Fabry-Perot cavities operating at very high powers ranging from tens of kW to MW. The high powers may result in several nonlinear effects which would affect the performance of the detector. In this paper, we investigate the effects of radiation pressure, which tend to displace the mirrors from their resonant position resulting in the detuning of the cavity. We observe a remarkable effect, namely, that the freely hanging mirrors gain energy continuously and swing with increasing amplitude. It is found that the 'time delay', that is, the time taken for the field to adjust to its instantaneous equilibrium value, when the mirrors are in motion, is responsible for this effect. This effect is likely to be important in the optimal functioning of the full-scale interferometers such as the VIRGO and LIGO.
Response of the interferometric antenna to gravitational radiation from pulsars
(2015-01-13) Jotania, Kanti; Dhurandhar, S.V.
We present here a full calculation of the response of a laser interferometric gravitational wave detector on which gravitational radiation from a continuous source is incident. The observation time is taken to be of the order of few months. The long observation time implies that the motion of the detector is important and must be included in the response as a modulation effect. For simplicity we consider only two motions of the Earth , namely the rotation of the Earth about axis and the orbital motions about the sun. The orbit is assumed to be circular. We consider the detector to be situated and oriented arbitrarily on the Earth, except that we assume the arms of the detector must lie in the tangent plane to the Earth at the point where the detector is situated. The gravitational wave incident on the detector is assumed to be a plane wave having arbitrary direction and polarization. We also present here the computation of the quadrupole wave form of a typical continuous source – a pulsar-which is modelled as an almost spherical object of uniform density, spinning about an arbitrary axis with uniform angular velocity. We use techniques of spherical tensors and Gel’fandfunction developed in the literature to compute the waveform
Search for continuous gravitational wave signals from sources in binary system
(2015-03-01) Dhurandhar, S.V.; Vecchio, Albert
We analyze the computational costs of searches for continuous monochromatic gravitational waves emitted by rotating neutron stars orbiting a companion object. As a function of the relevant orbital parameters, we address the computational load involved in targeted searches, where the position of the source is known; the results are applied to known binary radio pulsars and Sco-Xl.
The search for gravitational waves
(2014-11-26) Dhurandhar, S.V.
The direct detection of gravitational waves is one of the most challenging problems in experimental physics today. Sustained efforts have led to impressive advances on both theoretical and experimental fronts. This article first deals with the theoretical aspects of gravitational waves and then continues on to describe the detectors in vogue, the present status and various gravitational waves sources.
Search for gravitational waves from the millisecond pulsar PSR 0437-471
(2015-03-11) Mohanty, S.D.; Heng, I.S.; Blair, D.G; Dhurandhar, S.V.; Tobar, M.; Ivanov, E.
A search for gravitational waves from the millisecond pulsar PSR 0437-471has been initiated using the bar detector NIOBE which is located at the University of Western Australia. This search involves a very long coherent integration of the bar output which may stretch over a few years. We present a detailed report on the data analysis algorithm, called phase plane rotation,which will be used in this search. A discussion of the actual implementation of the algorithm is presented.
Signal analysis of the gravitational waveform of pulsars
(2015-01-17) Jotania, Kanti; Dhurandhar, S.V.; Valluri, S.R.
The thermo-optical coupling in optical resonators
(2015-02-07) Dhurandhar, S.V.; Hello, P.; Sathyaprakash, B.S.
Interferometric detectors of gravitational waves employ long baseline FabryPerot cavities with stored power of the order of 10 kW. The mirrors have a high reflectivity with absorption coefficient of a few parts in a million. The laser beam therefore acts as a source of heat creating a thermal gradient in the substrate and the consequent deformation in the mirror which in turn modifies the intra-cavity light field. The problem is thus coupled and nonlinear. Though the effect is expected to be negligible in the case of initial interferometers future interferometers are expected to employ much higher powers and it is necessary to ascertain thermo-elastic deformations and their effect on the stability of the laser field in the cavity. In this paper, which is first in a series to study instabilities in giant high power laser cavities, we have analytically solved the coupled problem of thermo-elastic deformations and their effect on the laser field, perturbatively and we show that within the realm of our (physically reasonable) assumptions there are no instabilities in the frequency range of 1 Hz-1 kHz.