The fast matched filter for gravitational-wave data analysis: Characteristics and applications

We report on the application of a matched filter to the data of two-mode resonant gravitational-wave antennas for the detection of burst signals, with reference to data obtained by direct acquisition, i.e. without going through lock-in amplifiers, sampled at relatively high speed. After a review of the basic model of resonant detectors, that includes a discussion of the signal and of the noise, we present a detailed mathematical derivation of the optimum filter matched to an input burst. We then analyze and discuss the performance of the matched filter as regards both the improvement of the signal-to-noise ratio and the observation bandwidth, also considering the adaptive realization of the filter, based on the actual spectrum of the noise as estimated from the data. The discussion that follows is centered on various aspects concerning the practical application of the matched filter as well as the loss of performance due both to uncertainties on the parameters used for building the filter and to various discretization effects, both in the time and frequency domains. Finally, we consider some experimental results obtained by applying the matched filter to the data of the Explorer detector, also providing a comparison with what we obtained by applying an optimum filter to data processed by lock-in amplifiers, sampled at lower speed

An Advanced Colour Calibration Method for Fish Freshness Assessment: a Comparison Between Standard and Passive Refrigeration Modalities

Freshness represents a pivotal aspect in fish product for both security and quality. Its evaluation still represents the key factor driving the consumer' choices. Fish appearance is affected by many different factors that demand the contribution of different disciplines to be understood: from the physical and optical properties to the slaughtering and post-slaughtering conditions. An innovative preservation system is represented by the Passive Refrigeration PRS (TM) developed for the preservation and transport of perishable food products. Scientific methods for product freshness evaluation may be conveniently divided into two categories: sensorial and instrumental. In this study, an instrumental method of colour calibration and discrimination is proposed at pilot scale for automatic evaluation of gilthead seabream (Sparus aurata) freshness. We propose a non-destructive method based on the colorimetric imaging of the whole external body of seabreams to evaluate through multivariate partial least squares which approach the differences in the freshness preservation under four refrigeration modalities. The matrix of the independent variables is represented by RGB values for each pixel belonging to an extracted region of interest (129,633 values). The dependent variable is composed by two dummy variable corresponding to fresh (T-0) or non-fresh (T-2) individuals. T-1 individuals were used as external test. The results quantified significant colorimetric differences between fresh and non-fresh fish. All fish used to create the model (T-0 and T-2) were correctly classified as fresh or non-fresh, while external test individuals (T-1) were all classified as fresh. The proposed imaging method merges different image analysis techniques: (a) colorimetric calibration, (b) morphometric superimposition and (c) partial least square discriminant analysis modelling. This innovative and non-destructive approach allows the automatic assessment of fish freshness

Dark Matter searches using gravitational wave bar detectors: quark nuggets and newtorites

Many experiments have searched for supersymmetric WIMP dark matter, with null results. This may suggest to look for more exotic possibilities, for example compact ultra-dense quark nuggets, widely discussed in literature with several different names. Nuclearites are an example of candidate compact objects with atomic size cross section. After a short discussion on nuclearites, the result of a nuclearite search with the gravitational wave bar detectors Nautilus and Explorer is reported. The geometrical acceptance of the bar detectors is 19.5 $\rm m^2$ sr, that is smaller than that of other detectors used for similar searches. However, the detection mechanism is completely different and is more straightforward than in other detectors. The experimental limits we obtain are of interest because, for nuclearites of mass less than $10^{-5}$ g, we find a flux smaller than that one predicted considering nuclearites as dark matter candidates. Particles with gravitational only interactions (newtorites) are another example. In this case the sensitivity is quite poor and a short discussion is reported on possible improvements.Comment: published on Astroparticle Physics Sept 25th 2016 replaced fig 1

Increasing the bandwidth of resonant gravitational antennas: The case of Explorer

Resonant gravitational wave detectors with an observation bandwidth of tens of hertz are a reality: the antenna Explorer, operated at CERN by the ROG collaboration, has been upgraded with a new read-out. In this new configuration, it exhibits an unprecedented useful bandwidth: in over 55 Hz about its frequency of operation of 919 Hz the spectral sensitivity is better than 10^{-20} /sqrt(Hz) . We describe the detector and its sensitivity and discuss the foreseable upgrades to even larger bandwidths.Comment: 4 pages- 4 figures Acceted for publication on Physical Review Letter

Quark nuggets search using 2350 Kg gravitational waves aluminum bar detectors

The gravitational wave resonant detectors can be used as detectors of quark nuggets, like nuclearites (nuclear matter with a strange quark). This search has been carried out using data from two 2350 Kg, 2 K cooled, aluminum bar detectors: NAUTILUS, located in Frascati (Italy), and EXPLORER, that was located in CERN Geneva (CH). Both antennas are equipped with cosmic ray shower detectors: signals in the bar due to showers are continuously detected and used to characterize the antenna performances. The bar excitation mechanism is based on the so called thermo-acoustic effect, studied on dedicated experiments that use particle beams. This mechanism predicts that vibrations of bars are induced by the heat deposited in the bar from the particle. The geometrical acceptance of the bar detectors is 19.5 $\rm m^2$ sr, that is smaller than that of other detectors used for similar searches. However, the detection mechanism is completely different and is more straightforward than in other detectors. We will show the results of ten years of data from NAUTILUS (2003-2012) and 7 years from EXPLORER (2003-2009). The experimental limits we obtain are of interest because, for nuclearites of mass less than $10^{-4}$ grams, we find a flux smaller than that one predicted considering nuclearites as dark matter candidates.Comment: presented to the 33rd International Cosmic Ray Conference Rio de Janeiro 201

Search for Periodic Gravitational Wave Sources with the Explorer Detector

We have developped a procedure for the search of periodic signals in the data of gravitational wave detectors. We report here the analysis of one year of data from the resonant detector Explorer, searching for pulsars located in the Galactic Center (GC). No signals with amplitude greater than $\bar{h}= 2.9~10^{-24}$, in the range 921.32-921.38 Hz, were observed using data collected over a time period of 95.7 days, for a source located at $\alpha=17.70 \pm 0.01$ hours and $\delta=-29.00 \pm 0.05$ degrees. Our procedure can be extended for any assumed position in the sky and for a more general all-sky search, even with a frequency correction at the source due to the spin-down and Doppler effects.Comment: One zipped file (Latex+eps figures). 33 pages, 14 figures. This and related material also at http://grwav3.roma1.infn.it

Analysis of 3 years of data from the gravitational wave detectors EXPLORER and NAUTILUS

We performed a search for short gravitational wave bursts using about 3 years of data of the resonant bar detectors Nautilus and Explorer. Two types of analysis were performed: a search for coincidences with a low background of accidentals (0.1 over the entire period), and the calculation of upper limits on the rate of gravitational wave bursts. Here we give a detailed account of the methodology and we report the results: a null search for coincident events and an upper limit that improves over all previous limits from resonant antennas, and is competitive, in the range h_rss ~1E-19, with limits from interferometric detectors. Some new methodological features are introduced that have proven successful in the upper limits evaluation.Comment: 12 pages, 12 figure

Particle acoustic detection in gravitational wave aluminum resonant antennas

The results on cosmic rays detected by the gravitational antenna NAUTILUS have motivated an experiment (RAP) based on a suspended cylindrical bar, which is made of the same aluminum alloy as NAUTILUS and is exposed to a high energy electron beam. Mechanical vibrations originate from the local thermal expansion caused by warming up due to the energy lost by particles crossing the material. The aim of the experiment is to measure the amplitude of the fundamental longitudinal vibration at different temperatures. We report on the results obtained down to a temperature of about 4 K, which agree at the level of about 10% with the predictions of the model describing the underlying physical process.Comment: RAP experiment, 16 pages, 7 figure

Study of the coincidences between the gravitational wave detectors EXPLORER and NAUTILUS in 2001

We report the result from a search for bursts of gravitational waves using data collected by the cryogenic resonant detectors EXPLORER and NAUTILUS during the year 2001, for a total measuring time of 90 days. With these data we repeated the coincidence search performed on the 1998 data (which showed a small coincidence excess) applying data analysis algorithms based on known physical characteristics of the detectors. With the 2001 data a new interesting coincidence excess is found when the detectors are favorably oriented with respect to the Galactic Disk

All-sky upper limit for gravitational radiation from spinning neutron stars

We present results of the all-sky search for gravitational-wave signals from spinning neutron stars in the data of the EXPLORER resonant bar detector. Our data analysis technique was based on the maximum likelihood detection method. We briefly describe the theoretical methods that we used in our search. The main result of our analysis is an upper limit of ${\bf 2\times10^{-23}}$ for the dimensionless amplitude of the continuous gravitational-wave signals coming from any direction in the sky and in the narrow frequency band from 921.00 Hz to 921.76 Hz.Comment: 12 pages, 4 figures, submitted to Proceedings of 7th Gravitational Wave Data Analysis Workshop, December 17-19, 2002, Kyoto, Japa