1,721,127 research outputs found
Search for ultra-high energy photons with the Pierre Auger Observatory
No full textThe Pierre Auger Observatory has an unprecedented sensitivity to photons at energies above 10^18 eV.
Particularly the combination of ground array and fluorescence detection techniques offers a unique power to discriminate the primary particles based on different observables. Implications of photon searches extend from astrophysics to fundamental and particle physics. Current results and future prospects are reported
Search for primary photons and neutrinos in the ultra-high energy cosmic rays with the Pierre Auger Observatory
No full textAlong with primary protons and nuclei most of the scenarios of the origin of cosmic rays predict fluxes of photons and neutrinos at the highest energies. Thanks to the huge collection area and the hybrid design, combining ground array and fluorescence detection techniques, the Pierre Auger Observatory is a unique tool to search for primary photons and neutrinos in ultra-high energy cosmic rays. Implications of these searches extend from astrophysics to fundamental and particle physics. Current results and future perspectives are reported
Use of star tracks to determine photocathode anisotropy of PMTs and absolute pointing of the Pierre Auger fluorescence detector telescopes
No full textThe fluorescence detector (FD) of the Southern Pierre Auger Observatory consists of four groups of six telescopes, concentrated in four different buildings at the periphery of the 3000 km^2 observatory site. Each telescope consists of a 3.5x3.5 m^2 mirror of 3.4-m radius, an aperture of 2.2 m diameter covered by a UV filter, a corrector ring in its periphery, and an array of PMTs, disposed as a matrix of 20 columns by 22 rows in its focal surface. The pointing accuracy should be verified regularly during the whole life of the experiment, estimated to be about 20 years.
Recording background-light tracks left by stars gives important information for this scope. In addition, the response along known
tracks of many PMTs can be mapped by averaging the signals left by the same star in different nights. During the engineering array phase of the experiment, all PMTs have been equipped with the optically-coupled current-mirror, a novel optoelectronic system
developed to perform a highly sensitive measurement of the dc or slowly varying component of the anode current, despite the
fact that the PMT is biased with cathode grounded. We proved that the FD telescopes are extremely sensitive, even to 5.4 visual
magnitude stars that could be clearly recorded despite the fact that a UV filter was present at the telescope aperture
Tracking stars with the fluorescence detector of the Pierre Auger observatory
No full textRecording tracks of stars traversing the field of view of the Auger's fluorescence detector (FD) is a powerful tool to
monitor various FD parameters. Regular control of these tracks would allow checking the telescope's stability during
the whole life of the experiment, estimated to be about 20 years. The prototypes used during the engineering array phase
have been equipped with a novel optoelectronic system that measured the DC anode current. Dim stars were clearly
recorded. We report the results of a reconstruction performed to determine the pointing of a telescope as well as
comparisons of a PMT's response to shower and star signals
Galvanically isolated and linear transmission of analog current-signals using the optically coupled current–mirror architecture
No full textWe describe a novel circuit architecture, the optically coupled current-mirror (OCCM), that allows linear transmission of analog current signals over optical fibers. The OCCM ensures Galvanic isolation between the detector where the current-signals flow, and ground. A remarkable difference compared to other methods used so far for the analog transmission of signals via optical means, is that the input stage of the OCCM, the only one that remains at the detector side, is passive; therefore, it does not require to be powered. This is the most distinctive feature of the OCCM, which opens new opportunities for the realization of multichannel analog links for particle physics experiments and other applications requiring Galvanic isolation and linear transmission with a dynamic range of at least two orders of magnitude. In addition, operation at LAr or LXe temperatures improves the loop-gain by a factor 2: The signal bandwidth, at present about 5 MHz; is expected to increase by at least the same factor by optimizing the gain-bandwidth product of the open-loop amplifier
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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