2,544 research outputs found
An interferometric seismic sensor: theoretical model and experimental performances
Laser Optical Interferometry has been introduced in different fields of research for applications requiring very high precision displacement measurements. We have applied optical interferometry for the solving the problem of amplitude and direction measurement of seismic waves. In particular we propose a Michelson Interferometer as a velocimeter with optical readout.
In this work we demostrate that a simple array of two Michelson interferometer can be used as an effective seismic sensor to measure the velocity of ground motion. The sensitivity of such device should be delimited only by the enviromental parameter that can be monitored and controlled. A preliminary experimental test on this technique confirms the theoretical results: in fact there is a good agreement with a standard accelerometer for seismic application
A chi-squared time-frequency discriminator for gravitational wave detection
Searches for known waveforms in gravitational wave detector data are often
done using matched filtering. When used on real instrumental data, matched
filtering often does not perform as well as might be expected, because
non-stationary and non-Gaussian detector noise produces large spurious filter
outputs (events). This paper describes a chi-squared time-frequency test which
is one way to discriminate such spurious events from the events that would be
produced by genuine signals. The method works well only for broad-band signals.
The case where the filter template does not exactly match the signal waveform
is also considered, and upper bounds are found for the expected value of
chi-squared.Comment: 18 pages, five figures, RevTex
IIR Adaptive Filters for Detection of Gravitational Waves from Coalescing Binaries
In this paper we propose a new strategy for gravitational waves detection
from coalescing binaries, using IIR Adaptive Line Enhancer (ALE) filters. This
strategy is a classical hierarchical strategy in which the ALE filters have the
role of triggers, used to select data chunks which may contain gravitational
events, to be further analyzed with more refined optimal techniques, like the
the classical Matched Filter Technique. After a direct comparison of the
performances of ALE filters with the Wiener-Komolgoroff optimum filters
(matched filters), necessary to discuss their performance and to evaluate the
statistical limitation in their use as triggers, we performed a series of
tests, demonstrating that these filters are quite promising both for the
relatively small computational power needed and for the robustness of the
algorithms used. The performed tests have shown a weak point of ALE filters,
that we fixed by introducing a further strategy, based on a dynamic bank of ALE
filters, running simultaneously, but started after fixed delay times. The
results of this global trigger strategy seems to be very promising, and can be
already used in the present interferometers, since it has the great advantage
of requiring a quite small computational power and can easily run in real-time,
in parallel with other data analysis algorithms.Comment: Accepted at SPIE: "Astronomical Telescopes and Instrumentation". 9
pages, 3 figure
A solution of linearized Einstein field equations in vacuum used for the detection of the stochastic background of gravitational waves
A solution of linearized Einstein field equations in vacuum is given and
discussed. First it is shown that, computing from our particular metric the
linearized connections, the linearized Riemann tensor and the linearized Ricci
tensor, the linearized Ricci tensor results equal to zero. Then the effect on
test masses of our solution, which is a gravitational wave, is discussed. In
our solution test masses have an apparent motion in the direction of
propagation of the wave, while in the transverse direction they appear at rest.
In this way it is possible to think that gravitational waves would be
longitudinal waves, but, from careful investigation of this solution, it is
shown that the tidal forces associated with gravitational waves act along the
directions orthogonal to the direction of propagation of waves. The computation
is first made in the long wavelengths approximation (wavelength much larger
than the linear distances between test masses), then the analysis is
generalized to all gravitational waves.
In the last sections of this paper it is shown that the frequency dependent
angular pattern of interferometers can be obtained from our solution and the
total signal seen from an interferometer for the stochastic background of
gravitational waves is computed.Comment: Definitive version published in Astroparticle Physic
Calibration of advanced Virgo and reconstruction of the gravitational wave signal h(t) during the observing run O2
In August 2017, advanced Virgo joined advanced LIGO for the end of the O2 run, leading to the first gravitational waves detections with the three-detector network. This paper describes the advanced Virgo calibration and the gravitational wave strain h(t) reconstruction during O2. The methods are the same as the ones developed for the initial Virgo detector and have already been described in previous publications; this paper summarizes the differences and emphasis is put on estimating systematic uncertainties. Three versions of the h(t) signal have been computed for the Virgo O2 run, an online version and two post-run reprocessed versions with improved detector calibration and reconstruction algorithm. A photon calibrator has been used to establish the sign of h(t) and to make an independent partial cross-check of the systematic uncertainties. The uncertainties reached for the latest h(t) version are 5.1% in amplitude, 40 mrad in phase and 20 ÎŒs in timing
Thermal noise from optical coatings in gravitational wave detectors
Gravitational waves are a prediction of Einstein's general theory of relativity. These waves are created by massive objects, like neutron stars or black holes, oscillating at speeds appreciable to the speed of light. The detectable effect on the Earth of these waves is extremely small, however, creating strains of the order of 10â21. There are a number of basic physics experiments around the world designed to detect these waves by using interferometers with very long arms, up to 4 km in length. The next-generation interferometers are currently being designed, and the thermal noise in the mirrors will set the sensitivity over much of the usable bandwidth. Thermal noise arising from mechanical loss in the optical coatings put on the mirrors will be a significant source of noise. Achieving higher sensitivity through lower mechanical loss coatings, while preserving the crucial optical and thermal properties, is an area of active research right now
A new numerical method to construct binary neutron star initial data
We present a new numerical method for the generation of binary neutron star
initial data using a method along the lines of the the Wilson-Mathews or the
closely related conformal thin sandwich approach. Our method uses six different
computational domains, which include spatial infinity. Each domain has its own
coordinates which are chosen such that the star surfaces always coincide with
domain boundaries. These properties facilitate the imposition of boundary
conditions. Since all our fields are smooth inside each domain, we are able to
use an efficient pseudospectral method to solve the elliptic equations
associated with the conformal thin sandwich approach. Currently we have
implemented corotating configurations with arbitrary mass ratios, but an
extension to arbitrary spins is possible. The main purpose of this paper is to
introduce our new method and to test our code for several different
configurations.Comment: 18 pages, 8 figures, 1 tabl
Binary Neutron Stars in Quasi-equilibrium
Quasi-equilibrium sequences of binary neutron stars are constructed for a
variety of equations of state in general relativity. Einstein's constraint
equations in the Isenberg-Wilson-Mathews approximation are solved together with
the relativistic equations of hydrostationary equilibrium under the assumption
of irrotational flow. We focus on unequal-mass sequences as well as equal-mass
sequences, and compare those results. We investigate the behavior of the
binding energy and total angular momentum along a quasi-equilibrium sequence,
the endpoint of sequences, and the orbital angular velocity as a function of
time, changing the mass ratio, the total mass of the binary system, and the
equation of state of a neutron star. It is found that the orbital angular
velocity at the mass-shedding limit can be determined by an empirical formula
derived from an analytic estimation. We also provide tables for 160 sequences
which will be useful as a guideline of numerical simulations for the inspiral
and merger performed in the near future.Comment: 66 pages, 26 figures, 6 tables, aaste
Performance of the WaveBurst algorithm on LIGO data
In this paper we describe the performance of the WaveBurst algorithm which
was designed for detection of gravitational wave bursts in interferometric
data. The performance of the algorithm was evaluated on the test data set
collected during the second LIGO Scientific run. We have measured the false
alarm rate of the algorithm as a function of the threshold and estimated its
detection efficiency for simulated burst waveforms.Comment: proceedings of GWDAW, 2003 conference, 13 pages, 6 figure
Relic gravitons and viscous cosmologies
Previously it was shown that there exists a class of viscous cosmological
models which violate the dominant energy condition for a limited amount of time
after which they are smoothly connected to the ordinary radiation era (which
preserves the dominant energy conditions). This violation of the dominant
energy condition at an early cosmological epoch may influence the slopes of
energy spectra of relic gravitons that might be of experimental relevance.
However, the bulk viscosity coefficient of these cosmologies became negative
during the ordinary radiation era, and then the entropy of the sources driving
the geometry decreases with time.
We show that in the presence of viscous sources with a linear barotropic
equation of state we get viscous cosmological models with
positive bulk viscous stress during all their evolution, and hence the matter
entropy increases with the expansion time. In other words, in the framework of
viscous cosmologies, there exist isotropic models compatible with the standard
second law of thermodynamics which also may influence the slopes of energy
spectra of relic gravitons.Comment: 5 pages, 4 figure
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