The gravitational wave detector VIRGO aims at extending the detection band down to a few Hertz by isolating the mirrors of the interferometer from seismic noise. This result is achieved by hanging ...each mirror through an elastic suspension (Superattenuator), designed to filter mechanical vibrations in all the degrees of freedom. An experimental upper limit of the mirror residual seismic noise at a few Hertz is provided in this paper. This is lower than the thermal noise floor, expected to limit the antenna sensitivity in the low frequency range.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Animal mitochondrial DNA is characterized by a remarkably high level of within-species homoplasy, that is, phylogenetic incongruence between sites of the molecule. Several investigators have invoked ...recombination to explain it, challenging the dogma of maternal, clonal mitochondrial inheritance in animals. Alternatively, a high level of homoplasy could be explained by the existence of mutation hot spots. By using an exhaustive mammalian data set, we test the hot spot hypothesis by comparing patterns of site-specific polymorphism and divergence in several groups of closely related species, including hominids. We detect significant co-occurrence of synonymous polymorphisms among closely related species in various mammalian groups, and a correlation between the site-specific levels of variability within humans (on one hand) and between Hominoidea species (on the other hand), indicating that mutation hot spots actually exist in mammalian mitochondrial coding regions. The whole data, however, cannot be explained by a simple mutation hot spots model. Rather, we show that the site-specific mutation rate quickly varies in time, so that the same sites are not hypermutable in distinct lineages. This study provides a plausible mutation model that potentially accounts for the peculiar distribution of mitochondrial sequence variation in mammals without the need for invoking recombination. It also gives hints about the proximal causes of mitochondrial site-specific hypermutability in humans.
This paper presents a complete description of Virgo, the French-Italian gravitational wave detector. The detector, built at Cascina, near Pisa (Italy), is a very large Michelson interferometer, with ...3 km-long arms. In this paper, following a presentation of the physics requirements, leading to the specifications for the construction of the detector, a detailed description of all its different elements is given. These include civil engineering infrastructures, a huge ultra-high vacuum (UHV) chamber (about 6000 cubic metres), all of the optical components, including high quality mirrors and their seismic isolating suspensions, all of the electronics required to control the interferometer and for signal detection. The expected performances of these different elements are given, leading to an overall sensitivity curve as a function of the incoming gravitational wave frequency. This description represents the detector as built and used in the first data-taking runs. Improvements in different parts have been and continue to be performed, leading to better sensitivities. These will be detailed in a forthcoming paper.
Virgo is a laser Michelson interferometer with 3-km long Fabry-Perot in the arms, aiming at the detection of gravitational waves emitted by astrophysical sources in the frequency band from 10 Hz to ...few kHz. The core of the detector, the central interferometer, was installed first. It is a recycled Michelson interferometer, with 6-m long arms, obtained by replacing the 3-km long Fabry- Perot cavities with high reflectivity mirrors and using the same components designed for Virgo. In particular all the mirrors of the interferometer are suspended from the seismic isolators that represent the main unique characteristic of the Virgo detector. The interferometer has been controlled by means of a fully digital control system, capable of monitoring and controlling the relative position of the mirrors with an accuracy of 10 exp -12 m. The best displacement sensitivity was 10 exp -13 m/sq rt Hz at 10 Hz and 8 x 10 exp -17 m/sq rt Hz above 1 kHz. This article describes the detector configuration, the tests performed in view of commissioning the full detector and the main results obtained.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The mirrors of interferometric detectors of gravitational waves (GW) are suspended in order to be isolated from external disturbances. A local control system able to keep them correctly aligned and ...to damp the angular modes of the suspension is necessary. In this paper we present the solution adopted for Virgo based on a CCD camera sensor and on digital controls. With this solution the mirrors are kept aligned at the level of less than 1 μrad
rms, enough to lock the interferometer and start the automatic alignment system.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
10.
The Virgo status Amico, P; Alshourbagy, M; Aoudia, S ...
Classical and Quantum Gravity,
10/2006, Volume:
23, Issue:
19
Journal Article, Conference Proceeding
Peer reviewed
We report on the status of the Virgo detector, under commissioning. We will focus on the last year's activity. The two commissioning runs performed during 2005 allowed us to reach a sensitivity of
h
...∼ 6 × 10
−22
. The data obtained during the runs were used to test a few data analysis algorithms, namely coalescing binaries and burst searches. The main improvements made on the detector during this year will be described, as well as the plans and activities foreseen in the coming years.
PDF
