1,721,014 research outputs found
The extreme blazar phenomenon in a multi-messenger context
Get PDFThis Thesis illustrates the activities and the results that I have obtained during my three-year PhD course at the University of Padova.
My work was mainly based on the study of the extreme blazars, or better “extreme high-energy peaked BL Lac objects” (generally referred to as EHBLs). EHBLs are an emerging class of blazars with exceptional spectral properties, presenting a spectral energy distribution peaking with the synchrotron emission in hard X-rays and a high-energy emission in TeV gamma rays. The hard-TeV spectrum of EHBLs is important also for the implications on the indirect estimations of the extragalactic background light and of the intergalactic magnetic fields. The emission processes producing such extremely-high photon energies are currently not completely understood, and may represent a challenge for the standard modelling of these sources. In fact, the standard models are generally able to fit the experimental spectral data, but the parameters they assume are unusual compared to the standard blazar modelling currently available in literature. More complex models, assuming – for example – multiple emission zones or hadronic contributions, may provide more relaxed parameter spaces. In particular, the presence of hadronic processes in the blazar emission might make the EHBLs producers of extragalactic high-energy neutrinos.The number of EHBL objects is currently very limited. Thanks to recent observations, new sources have been classified as candidate EHBLs. Their spectral properties reveal new features that enrich the properties of this class of objects. In this framework, my research work started with the search for new EHBL candidates on the basis of all-sky surveys in hard X-rays. This new method allowed me to select the most promising extreme blazars relying on their X-ray to high-energy gamma-ray flux ratio. The analysis of the spectral properties of this new sample revealed interesting spectral features and systematic differences that are emerging in the EHBL class, especially in TeV gamma rays. This suggests the possible emergence of a sub-classification, and a new population of EHBLs may be unveiled. One specific aspect of my analysis was to predict the feasibility of observations of these objects with the current and next generation of Cherenkov telescopes. In the MAGIC Collaboration, I had the opportunity to propose a list of EHBL candidates for observations. Among them, a source named PGC 2402248 was observed and finally detected in TeV gamma rays, and several others are now being observed with the MAGIC telescopes. These results have been published together with a detailed discussion on the comparison between several theoretical models proposing different interpretations of the spectral properties of these sources. During my PhD, I had the opportunity to contribute to several other projects that complemented my preparation in this field. In the MAGIC Collaboration, I was involved in projects related to the detection of new EHBLs in TeV gamma rays and in the study of interesting blazars like PG 1553+113. I was also involved in two analyses on the relation between extreme blazars and extragalactic background light, and on the selection of extreme blazar candidates from a sample of faint sources in the high-energy gamma-ray band. Finally, an important part of my PhD activity within the MAGIC Collaboration was devoted to a contribution to the discovery of the first association between a high-energy neutrino, the so-called IceCube EHE-170922A event, and the blazar TXS 0506+056. During the analysis of this event, registered on September 2017, I was main analyser of the MAGIC data. Considering the importance of the discovery – with implications about the origin of the very-high-energy cosmic rays – and the intense multi-collaboration work, it was really a unique opportunity for me to gain new experience in this field and to further motivate my interest in the multi-messenger astrophysics
A new hard X-ray selected sample of extreme high-energy peaked BL Lac objects and their TeV gamma-ray properties
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Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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