1,721,063 research outputs found
Beam-forming and matched filter techniques for the underwater acoustic detection of UHE neutrino
No full textThe search for UHE neutrinos is one of the most promising fields in astroparticle physics. The experimental techniques proposed to identify cosmic neutrino signatures are mainly three: the detection of Cherenkov blue light originated by charged leptons (electrons, positrons, muons and tauons) from neutrino interaction in water or ice; the detection of acoustic waves produced by neutrino energy deposition in water, ice or salt; the detection of radio pulses following neutrino interaction in ice or salt. Due to the expected neutrino fluxes (approximate to 10(-8) E(2) Gev/cm(2) s sr) and due to their extremely low interaction cross-section (approximate to 10(-32) cm(2) at 10(20) eV). huge target volumes (approximate to km(3)) are required to detect them. Acoustic detection of neutrino is a very suitable technique since the sound attenuation length, at the frequency of interest, is of the order of km. Due to the small amplitude of the expected neutrino bipolar signal (approximate to 10 mPa), it is mandatory to develop an effective algorithm that increases the signal to noise ratio (SNR). In the present work a combination of matched filter, applied to each single hydrophone, and a beam-forming technique applied to a small array of hydrophones is proposed. The matched filter is a well-known technique of signal processing that maximizes the SNR in the presence of white noise. Beam forming is a signal-processing technique used in sensor arrays for directional analysis; the signals from different sensors are combined in such a way that pressure waves arriving from a specific direction are coherently summed. Preliminary results on simulated data will be shown. (C) 2009 Elsevier B.V. All rights reserved
Acoustic detection of UHE neutrinos: Status and perspective
Full text linkIn recent years the astro-particle community is involved in the realization of experimental apparatuses for the detection of high-energy neutrinos originated in cosmic sources or produced in the interaction of cosmic rays with the cosmic microwave background. For neutrino energies in the TeV-PeV range, the underwater optical Cherenkov technique is considered optimal. For higher energies, three experimental techniques are under study: the detection of radio pulses produced by showers following a neutrino interaction, the detection of air showers initiated by neutrinos interacting with rocks or deep Earth's atmosphere and the detection of acoustic waves produced by deposition of energy in the interaction of neutrinos in acoustically transparent mediums. The acoustic detection technique is based on the thermo-acoustic effect, first proposed by Askaryan in 1957. The deposit of the cascade energy in a small volume of suitable medium such as ice, water or salt, cylindrical in shape with a length of few tens of metres and a few centimetres in radius, turns out in heating of the medium, therefore in its expansion. The quasi-instantaneous expansion of the medium results in a coherent production of a collimated mechanical wave propagating, in a homogeneous medium, perpendicularly to the shower axis. Different groups are conducting studies to characterize acoustic properties of different mediums and developing the technologies required for future large-scale acoustic arrays. Test experiments were carried out using military arrays of hydrophones or available scientific infrastructures and first searches for neutrino signals were performed. Though the studies on this technique are still in an early stage, its potential use to build very large neutrino detectors is appealing, thanks to the optimal properties of mediums such as water, ice or salt as sound propagator. The status of simulation work, medium studies, sensor developments and first results from test experimental setups will be discussed. © Società Italiana di Fisica
Acoustic detection of UHE neutrinos in the Mediterranean sea: status and perspective
Full text linkIn recent years the astro-particle community is involved in the realization of experimental apparatuses for the detection of high energy neutrinos originated in cosmic sources or produced in the interaction of Cosmic Rays with the Cosmic Microwave Background. For neutrino energies in the TeV-PeV range, optical Cherenkov detectors, that have been so far positively exploited by Baikal[1], IceCube[2] and ANTARES[3], are considered optimal. For higher energies, three different experimental techniques are under study: the detection of radio pulses produced by showers induced by a neutrino interaction, the detection of air showers initiated by neutrinos interacting with rocks or deep Earth’s atmosphere and the detection of acoustic waves produced by deposition of energy following the interaction of neutrinos in an acoustically transparent medium. The potential of the acoustic detection technique, first proposed by Askaryan[4], to build very large neutrino detectors is appealing, thanks to the optimal properties of media such as water or ice as sound propagator. Though the studies on this technique are still in an early stage, acoustic positioning systems used to locate the optical modules in underwater Cherenkov neutrino detectors, give the possibility to study the ambient noise and provide important information for the future analysis of acoustic data
Data taking system for the NEMO experiment
No full textA four-floors prototype of the Nemo towers has been successfully deployed off the Sicily coast in December 2006. The detector is working and data acquisition is going on since then. The aim of this contribution is to give an overview of the NEMO electronic system and to explain the different stages of data acquisition and transport. The underwater electronics sample signals from photomultipliers and acquire slow-control data both from oceanographic instruments and dedicated sensors, allowing to monitor the operational conditions of the apparatus. The whole data are sent to laboratory through a fully bidirectional fiber optic link. On shore the data are received by dedicated boards that distribute them to first level-trigger and to the slow-control system. The NEMO data acquisition/transmission electronic system will be described, properties of acquired signals and of data flow will be discussed
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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