1,721,346 research outputs found
Quantum noise reduction in Advanced Virgo
No full textIn order to detect the small distance variations induced by gravitational waves, very sensitive devices must be used. Gravitational wave detectors are sophisticated interferometers sensitive even to vacuum fluctuations. These latter are responsible for quantum noise. Due to the frequency-dependent response of gravitational wave interferometers, quantum noise manifests itself as radiation pressure noise for frequencies below 100 Hz, while as shot noise for higher frequencies. The solution that has been adopted in order to reduce quantum noise is the injection, through the interferometer output port, of vacuum states, called squeezed, whose amplitude and phase uncertainties are correlated. A frequency-independent squeezing technique, as a method for the reduction of the quantum noise, has been already demonstrated in long-arm interferometers. Radiation pressure noise does not limit the sensitivity of the present interferometers, being this completely covered by other noises. But, in the near future, these noises will be reduced and also this quantum noise component will be relevant. The adopted solution to have a broad-band quantum noise reduction is a frequency-dependent squeezing technique. In this paper the results obtained in Advanced Virgo using the frequency-independent squeezing technique will be shown. Moreover the conceptual design for the implementation of the frequency-dependent squeezing will be presented
Development of a squeezed light source for the gravitational wave detector Advanced Virgo
No full textThis work of thesis deals with the design and the first steps toward the realization of a squeezed light source for the Gravitational Wave interferometric detector Advanced Virgo, located in Cascina (PI). The final goal of this new generation interferometer is to achieve an improvement in the sensitivity by a factor of 10 with respect to the first generation detectors. One of the most important noise sources in these advanced detectors, dominating at higher frequencies of the detection band (10 Hz- 10 kHz), is the shot noise. This noise is due to the vacuum fluctuations entering the interferometer through its output port; to reduce it, in Advanced Virgo a very high power laser will be employed (up to 125 W), but such a high circulating power into the interferometer can increase thermal effects. The injection of phase-squeezed vacuum states, into the output port of the interferometer makes it possible to reduce shot noise, without the need of higher power and thus the reduction of the related risks. Squeezed vacuum is produced by a below threshold nonlinear process (down-conversion) inside an Optical Parametric Oscillator (OPO). In common squeezing experiments, vacuum squeezed light at MHz frequency band is produced. For a gravitational wave detector the challenge consists in the production of squeezed light in the audio-frequency band.
A first sensitivity enhancement of gravitational waves detectors by means of squeezed vacuum was already demonstrated by the British-German GEO interferometer and, in the next few years, it is planned to be finally integrated, for continuous runs, also in the in the American LIGO Scientific Collaboration. This same approach is now being pursued by the Virgo Collaboration, with the goal to inject squeezing states of light also in Advanced Virgo
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
No full text“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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