1,721,111 research outputs found
Modelling optical emission of Ultra-luminous X-ray Sources accreting above the Eddington limit
No full textRoche-lobe overflow systems powered by black holes in young star clusters: The importance of dynamical exchanges
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Quantum Astronomy at the University and INAF Astronomical Observatory of Padova, Italy
Full text linkTwenty years ago, we started to apply quantum optics to the astronomical research carried
out inside the Department of Physics and Astronomy and the INAF Astronomical Observatory
in Padova, Italy. The initial activities were stimulated by the project of the European Southern
Observatory (ESO) to build a 100 m diameter telescope, the Overwhelmingly Large (OWL) telescope.
The enormous photon flux expected from such an aperture suggested that quantum optics concepts
be utilized in order to obtain novel astrophysical results. Following initial successful attempts to
utilize the orbital angular momentum of the light beam to enhance the visibility of faint companions
to bright stars, the Padova team concentrated its efforts on very high time resolution, in order to
measure and store the arrival time of celestial photons to better than one nanosecond. To obtain
observational results, we built two photon counting photometers (AquEye and IquEye) to be used
with our telescopes of the Asiago Observatory and with 4 m class telescopes such as the ESO New
Technology Telescope (NTT) in Chile. This paper firstly describes these two instruments and then
expounds the results obtained on pulsar light curves, lunar occultations and the first photon counting
intensity interferometry measurements of the bright star Vega. Indeed, the correlation of photon
arrival times on two or more apertures can lead to extremely high angular resolutions, as shown
around 1970 by Hanbury Brown and Twiss. Prospects for quantum intensity interferometry with
arrays of Cherenkov light telescopes will also be described
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
Iqueye at the NTT : The best light curves of the optical pulsars in the Crab, LMC B0540-69 and Vela supernova remnants
Full text linkThe Iqueye single-photon ultrafast photometer was mounted at the NTT for three runs, two in 2009 (January and December) and one in 2010 (July). Several objects with fast variability were observed. Here we focus on the light curves of the optical pulsars in Crab, Vela, and 0540-69 supernova remnants. The quality of the Iqueye light curves and accuracy of pulse phases allowed us to obtain the best light curves of these three pulsars and were instrumental to compare the optical profiles and timing with those determined at radio frequency, in the UV and at X/gamma-ray energies, and to study the emission geometry
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