1,721,058 research outputs found
Long gamma-ray bursts as binary-driven hypernovae - analysis within the induced gravitational collapse paradigm
Full text linkThe central engine of long gamma-ray bursts (GRBs) is still under debate. The (currently) prevailing theoretical understanding is referred to as the standard fireball model. Here, the prompt emission is attributed to the internal shocks and the afterglow emission is attributed to the external shocks. The GRB outflow contains a wide range of bulk Lorentz factors. When a fast-moving portion overtakes the slower one, an internal shock is generated. On the other hand, the external shocks are caused by the interaction between the outflow and the circum-burst medium. However, data that was accumulated in the last 25 years challenges the overall picture. Some of the observed properties can not be explained within the standard framework. For example, the immense isotropic energy requirements of GRBs can be considerably reduced if one assumes the outflow is collimated. As a consequence, an achromatic break should appear in the afterglow light-curves. However, for the majority of GRBs the break is not achromatic, if present at all. In addition, the model itself does not deal with the exact mechanism of this initial energy release, but only its consequences.
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One of the alternatives to the fireball model is the fireshell model. Its origins can be traced back to the idea which revolves around the energy extraction from a charged black hole. During the years, with the implementation of new available data, the fireshell model evolved into the induced gravitational collapse (IGC) paradigm. This theory emphasizes the importance of binary system interaction for the GRB production mechanism, offering additional channels to study the role these systems have in GRB formation. In it, all GRBs originate from binary systems. Different observational properties are a direct consequence of a wide spectrum of acceptable binary system parameters. According to these observational properties, long and short GRBs are divided into nine different sub-classes. GRBs belonging to the type-I binary driven hypernova (BdHNe-I) class are of main interest in this thesis. The name is referring to GRBs with energies above that originate from a collapse of a neutron star into a black hole. This collapse is initiated by the supernova explosion of its binary companion.
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In the work presented here, the theoretical framework of the IGC paradigm was tested on twelve GRBs. From these, only GRB 160829A is a member of the short GRB class. The remaining ones are long bursts, classified as BdHNe-I on the account of their energetics and GeV emission. Two main tools were put to use in order to analyze and interpret the data: the erb|rmfit| software and the simulation of the fireshell propagation that is available on our group's server. All of the GRBs were detected with the GBM detector onboard the extit{Fermi} satellite. Time-integrated and time-resolved analysis was carried out for each GRB in order to determine their isotropic equivalent energy and to possibly identify the P-GRB signature. The latter is expected to occur in the beginning of the prompt emission and to have a spectrum that shows a presence of thermal signatures. From 11 BdHNe-I, five had an identified P-GRB associated emission: GRB 100728A, GRB151027A, GRB 090618, GRB 110731A and GRB 141028A. A black body component was found in six GRBs. For three of them, the component did not exhibit the expected P-GRB spectral and temporal properties and it was therefore rejected as a possible P-GRB. GRB 110731A, GRB151027A and GRB 090618 were further interpreted within the fireshell model. Average values of circum-burst medium density inferred from the simulations are , and , respectively. Therefore, these bursts occurred in different environments. The averaged value of this sample, 1 baryon per , is consistent with previous findings. Baryon load and the relativistic Lorentz gamma factor at transparency point were also consistent with long GRBs, although we find that GRB 110731A shared some of these values with short bursts. In the case of short GRB 160829A, the fireshell simulation up to the transparency point was used in order to evaluate the redshift. Poor S/N ratio constrained its redshift to z<5. This is not particularly helpful considering it is true for all of the short GRBs observed so far. That is, if one does not take into account GRB 080913 at , which was observed to last longer than due to its high redshift, but it may be intrinsically short. The difficulties encountered during the analyses played a role in the further development of the IGC paradigm. The ongoing work is also discussed. It was devised with a goal to enable a more consistent and faster analysis. Then, a more complete BdHNe-I catalog with all of the fireshell parameters included would be easier to produce
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
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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