1,721,832 research outputs found
Parametric Spectral Estimation and Data Whitening
No full textThe knowledge of the noise Power Spectral Density is fundamental in signal processing for the detection algorithms and for the analysis of the data. In this lecture we address both the problem of identifying the noise Power Spectral Density of physical system using parametric techniques and the problem of the whitening procedure of the sequence of data in time domain
Enhancing gravitational-wave science with machine learning
No full textMachine learning has emerged as a popular and powerful approach for solving problems in astrophysics. We review applications of machine learning techniques for the analysis of ground-based gravitational-wave (GW) detector data. Examples include techniques for improving the sensitivity of Advanced Laser Interferometer GW Observatory and Advanced Virgo GW searches, methods for fast measurements of the astrophysical parameters of GW sources, and algorithms for reduction and characterization of non-astrophysical detector noise. These applications demonstrate how machine learning techniques may be harnessed to enhance the science that is possible with current and future GW detectors
The VIRGO experiment
No full textThe status of the VIRGO experiment, as of summer 2000 is presented: we report on the progress in the construction and the next steps are briefly illustrated
The inertial damping of the VIRGO superattenuator and the residual motion of the mirror
No full textThe VIRGO superattenuator (SA) is effective in suppressing seismic noise below the expected thermal noise level above 4 Hz. However, the residual mirror motion associated with the SA normal modes can saturate the interferometer control system. This motion is reduced by implementing a wideband (DC-5 Hz) multidimensional active control (the so-called inertial damping) which makes use of both accelerometers and position sensors and of a digital signal processing (DSP) system. Feedback forces are exerted by coil-magnet actuators on the top of an inverted pendulum pre-isolator stage. The residual root mean square motion of the mirror in 10 s is less than 0.1 mum
Hydrogeochemical dynamics affecting steam-heated pools at El Chichon Crater (Chiapas - Mexico)
No full textEl Chichón is an active volcano located in the north-western Chiapas, southern Mexico. The crater hosts a lake, a spring, named Soap Pool, emerging from the underlying volcanic aquifer and several mud pools/hot springs on the internal flanks of the crater which strongly interact with the current fumarolic system (steam-heated pools). Some of these pools, the crater lake and a cold spring emerging from the 1982 pumice deposits, have been sampled and analysed. Water-volcanic gas interactions determine the heating (43-99°C) and acidification (pH 2-4) of the springs, mainly by H2S oxidation. Significantly, in the study area, a significant NH3 partial pressure has been also detected. Such a geochemically aggressive environment enhances alteration of the rock in situ and strongly increases the mineralization of the waters (and therefore their electrical conductivity). Two different mineralization systems were detected for the crater waters: the soap pool-lake (Na+/Cl- = 0.4, Na/Mg>10) and the crater mud pools (Na+/Cl- > 10, Na/Mg < 4). A deep boiling, Na+-K+-Cl--rich water reservoir generally influences the Soap Pool-lake, while the mud pool is mainly dominated by water-gas-rock interactions. In the latter case, conductivity of sampled water is directly proportional to the presence of reactive gases in solution. Therefore, chemical evolution proceeds through neutralization due to both rock alteration and bacterial oxidation of ammonium to nitrate. The chemical compositions show that El Chichón aqueous fluids, within the crater, interact with gases fed by a geothermal reservoir, without clear additions of deep magmatic fluids. This new geochemical dataset, together with previously published data, can be used as a base line with which to follow-up the activity of this deadly volcano. © 2013 John Wiley & Sons Ltd
The VIRGO suspensions
No full textThe VIRGO suspensions are chains of passive mechanical filters designed to isolate the interferometer mirrors from seismic noise starting from a few Hz. In order to reduce the low-frequency swing of the mirror along the beam, an active control system, acting at the level of the suspension point, damps the main resonant modes of the system (all below 2.5 Hz). Another control loop, at the level of the optical payload, makes use of a digital camera monitoring the mirror position in all six degrees of freedom. Its main goal is to decrease the rms angular displacements of the mirror, on a time scale of several minutes, down to less than I murad. All the seven suspensions of the VIRGO central interferometer are presently in operation, while the assembly of the last two, for the terminal mirrors, is in progress, The design and performance of the system are described in this paper
A gravitational wave detector: The virgo interferometer
No full textGravitational waves were predicted in 1916 by Einstein as a conse- quence of the theory of General Relativity: accelerated masses can produce ripples propagating at the speed of light, which perturb the space-time metric. Thanks to the extremely weak coupling with matter, gravitational waves can cross the universe undisturbed and, hence, are a probe of the regions where they are produced which is not accessible by the eventual electromagnetic counterpart. The gravitational waves sources of detectable amplitudes are expected to be compact astrophysical sources such as the coalescence of binaries formed by black holes and neutron stars, the collapses of stellar cores, or the rotation of non-axis-symmetric neutron stars. For more than 40 years the search for gravitational waves has been pursued with resonant detectors made of metallic bars. The development of gravitational wave detectors based on laser interferometers started in the early seventies. After more than two decades of development, the construction of the first interferometers with kilometer scale arms started in the nineties. The sensitivity of such detectors is fun- damentally proportional to its length, and with its 3 kilometer long arms Virgo is the largest gravitational wave detector in Europe, and the third largest in the world. It is located at the European Gravitational Observatory (EGO), close to Pisa, and it is designed to detect gravitational waves emitted by astrophysical sources in the frequency range between 10Hz and a few kHz. Among the other current ground- based gravitational wave detectors, Virgo is the one having the best sensitivity at low frequency, thanks to the particular seismic attenuators, from which the mirrors are suspended. Construction started in 1996 and ended in July 2003. After a very intense commissioning phase, the performances of the detector are now very close to the design ones, and the detector is entering the operation phase. In parallel, the design phase of the second generation of interferometers should be finalized this year with a construction planned to start in 2011. Also, the conceptual design is under study for a third generation. The corresponding European project is called the "Einstein Telescope". ©2010 by Società Italiana di Fisica
The VIRGO suspensions: Design and recent performance measurements
No full textThe success of the VIRGO interferometer to detect gravitational waves, starting from a few Hz, depends on the ability of its suspension systems to isolate the test masses from seismic noise and to maintain them actively at a working position with relative displacement of ∼ 10-12 m rms on a time scale of several hours. For this purpose, considerable development effort has been dedicated to realize a multi-stage vibration isolator to suspend the test masses: the SuperAttenuator (SA). It has been designed to provide an attenuation of more than 10 orders of magnitude starting from about 4 Hz. Hierarchical control forces, exerted via coil-magnet actuators placed at three different stages of the SA, damp the fundamental mechanical modes of the system (all below 2 Hz) and maintain the relative orientation and position of the test mass for interferometer alignment and locking. In this Letter a description of the SA is given and recent experimental results are presented. © 2003 Elsevier B.V. All rights reserved
Performance of a 'generalized delta-filter' for the detection of burst events
No full textIn this work we report on the performance of a complete implementation of the generalized delta filter detector for burst events, tested against simulated data. We measure the receiver operating characteristics in the case of noise having the expected spectral density of the Virgo interferometer, injecting test signals taken from the Zwerger–Müller library of simulated events, predicted to result from the collapse of type II supernovae, for different levels of signal to noise ratio
- …
