Flavio Vetrano

Measurement of the VIRGO superattenuator performance for seismic noise suppression

Below a few tens of hertz interferometric detection of gravitational waves is masked by seismic vibrations of the optical components. In order to isolate the mirrors of the VIRGO interferometer, a sophisticated suspension system, called superattenuator, has been developed. Its working principle is based on a multistage pendulum acting on seismic vibrations as a chain of second order mechanical low-pass filters. A complete superattenuator has been built and tested. This apparatus allows extending the VIRGO detection band down to a few Hz. A detailed description of the attenuation system and its performance are presented in this article.

Senescence delay and change of antioxidant enzyme levels in Cucumis sativus L. etiolated seedlings by ELF magnetic fields

We exposed cucumber Cucumis sativus L. etiolated seedlings to a 50 Hz, 1-Gauss magnetic field (MF) 24 h per day for 2 weeks in the dark, starting from complete divarication of cotyledons and observed quickened growth and prolonged life of EMF-exposed seedlings compared to the controls. Since this phenomenon may be due to MF-induced delay in the senescence process which, in turn, is believed to be dependent on the potency of the seedling oxidative defense system, we assayed some related enzymes and found that the combined action of higher levels of superoxide dismutase (SOD), catalase (CAT) and glutathione reductase (GR) in MF-exposed seedlings may promote their survival and delay the appearance of signs of decay.

The linear variable differential transformer (LVDT) position sensor for gravitational wave interferometer low-frequency controls

Low-power, ultra-high-vacuum compatible, non-contacting position sensors with nanometer resolution and centimeter dynamic range have been developed, built and tested. They have been designed at Virgo as the sensors for low-frequency modal damping of Seismic Attenuation System chains in Gravitational Wave interferometers and sub-micron absolute mirror positioning. One type of these linear variable differential transformers (LVDTs) has been designed to be also insensitive to transversal displacement thus allowing 3D movement of the sensor head while still precisely reading its position along the sensitivity axis. A second LVDT geometry has been designed to measure the displacement of the vertical seismic attenuation filters from their nominal position. Unlike the commercial LVDTs, mostly based on magnetic cores, the LVDTs described here exert no force on the measured structure.

In vitro effects of 50 Hz magnetic fields on oxidatively damaged rabbit red blood cells

The aim of this study was to investigate the effects of 50 Hz magnetic fields (0.2-0.5 mT) on rabbit red blood cells (RBCs) that were exposed simultaneously to the action of an oxygen radical-generating system, Fe(II)/ascorbate. Previous data obtained in our laboratory showed at the exposure of rabbit erythrocytes or reticulocytes to Fe(II)/ascorbate hexokinase inactivation, whereas the other glycolytic enzymes do not show any decay. We also observed depletion of reduced glutathione (GSH) content with a concomitant intracellular and extracellular increase in oxidized glutathione (GSSG) and a decrease in energy charge. In this work we investigated whether 50 Hz magnetic fields could influence the intracellular impairments that occur when erythrocytes or reticulocytes are exposed to this oxidant system, namely, inactivation of hexokinase activity, GSH depletion, a change in energy charge, and hemoglobin oxidation. The results obtained indicate the a 0.5 mT magnetic field had no effect on intact RBCs, whereas it increased the damage with Fe(II)/ascorbate to a 0.5 mT magnetic field induced a significant further decay in hexokinase activity (about 20%) as well as a twofold increase in methemoglobin production compared with RBCs that were exposed to the oxidant system alone. Although further studies will be needed to determine the physiological implications of these data, the results reported in this study demonstrate that the effects of the magnetic fields investigated are able to potentiate the cellular damage induced in vitro by oxidizing agents.

Antibacterial effect of a magnetic field on Serratia marcescens and related virulence to Hordeum vulgare and Rubus fruticosus callus cells

The exposure to a static magnetic field of 80+/-20 Gauss (8+/-2 mT) resulted in the inhibition of Serratia marcescens growth. Callus cell suspensions from Hordeum vulgare and Rubus fruticosus were also examined and only the former was found to be affected by the magnetic field, which induced a decreased viability. S. marcescens was shown to be virulent only toward H. vulgare and this virulence was reduced by the presence of the magnetic field. The modification of glutathione peroxidase activity under the different experimental conditions allowed us to speculate on the possibility of an oxidative-stress response of H. vulgare both to S. marcescens infection and magnetic field exposure. Since the control of microbial growth by physical agents is of interest for agriculture, medicine and food sciences, the investigation presented herein could serve as a starting point for future studies on the efficacy of static magnetic field as low-cost/easy-handling preservative agent.

Cosmic-ray spectra near the LISA orbit

Cosmic-ray particles traverse the LISA apparatus charging the proof masses. This process causes spurious Coulomb forces between the test masses and the surrounding conducting surfaces mimicking gravitational wave signals. Approximately 13 g cm−2 of matter overlies the proof masses. The nucleonic component of cosmic rays (about 99% of the total) below 100 MeV/n stops inside the spacecraft without reaching the masses. It is of major importance to determine the primary and solar cosmic-ray particle fluxes above this energy near the LISA orbit in order to predict the effect on the apparatus.

On-line power spectra identification and whitening for the noise in interferometric gravitational wave detectors

The knowledge of the noise power spectral density of an interferometric detector of gravitational waves is fundamental for detection algorithms and for the analysis of the data. In this paper we address both the problem of identifying the noise power spectral density of interferometric detectors by parametric techniques and the problem of the whitening procedure of the sequence of data. We will concentrate the study on a power spectral density like that of the Italian–French detector VIRGO and we show that with a reasonable number of parameters we succeed in modelling a spectrum like the theoretical one of VIRGO, reproducing all of its features. We also propose the use of adaptive techniques to identify and to whiten the data of interferometric detectors on-line. We analyse the behaviour of the adaptive techniques in the field of stochastic gradient and in the least-squares filters. As a result, we find that the least-squares lattice filter is the best among those we have analysed. It succeeds optimally in following all the peaks of the noise power spectrum, and one of its outputs is the whitened part of the spectrum. Besides, the fast convergence of this algorithm, it lets us follow the slow non-stationarity of the noise. These procedures could be used to whiten the overall power spectrum or only some region of it. The advantage of the techniques we propose is that they do not require a priori knowledge of the noise power spectrum to be analysed. Moreover, the adaptive techniques let us identify and remove the spectral line, without building any physical model of the source that produced it.

Noise parametric identification and whitening for LIGO 40-m interferometer data

One of the goals of gravitational data wave analysis is the knowledge and accurate estimation of the noise power spectral density of the data taken by the detector, this being necessary in the detection algorithms. In this paper we show how it is possible to estimate the noise power spectral density of gravitational wave detectors using modern parametric techniques and how it is possible to whiten the noise data before they pass to the algorithms for gravitational wave detection. We report the analysis we made of data taken by the Caltech 40-m prototype interferometer to identify the noise power spectral density and to whiten the sequence of noise. We concentrate our study on data taken in November 1994; in particular, we analyze two frames of data: the 18nov94.2.frame and the 19nov94.2.frame. We show that it is possible to whiten these data, to a good degree of whiteness, using a high order whitening filter. Moreover, we can choose to whiten only a restricted band of frequencies around the region we are interested in, obtaining a higher level of whiteness.

Simulation of the charging process of the LISA test masses due to solar particles

Cosmic-ray and solar particles above 100 MeV penetrate the LISA experiment test masses. Consequently, electric charges accumulating there generate spurious Coulomb forces between the masses and the surrounding electrodes. This process increments the noise level of the experiment. We have estimated the amount of charge deposited per second on the LISA test masses by primary cosmic-ray protons at solar minimum and solar maximum and by solar energetic particle (SEP) events. This simulation has been carried out with the Fluka Monte Carlo program. A simplified geometry for the experiment has been considered. We have found an effective charge rate of 110 e s−1 for primary protons at solar maximum and 150 e s−1 at solar minimum between 0.1 and 1000 GeV. The amount of charge released by a medium intensity gradual event (7 May 1978) varies from 206 e s−1 in the first few minutes to 4575 e s−1 at the peak of the event. At the occurrence of medium or strong solar events, the LISA sensitivity curve at frequencies lower than 3 × 10−4 Hz is dominated by the noise due to the test-mass charging process.

Monocrystalline fibres for low thermal noise suspension in advanced gravitational wave detectors

Thermal noise in mirror suspension will be the most severe fundamental limit to the low-frequency sensitivity of future interferometric gravitational wave detectors. We propose a new type of materials to realize low thermal noise suspension in such detectors. Monocrystalline suspension fibres are good candidates both for cryogenic and for ambient temperature interferometers. Material characteristics and a production facility are described in this paper.