1,721,014 research outputs found
The explosion of massive stars and their compact remnant
Full text linkMassive stars (M ≥ 8Ms) end their life exploding as Core Collapse Supernovae (CCSN). As a result of such a kind of explosions, a very dense and compact remnant, either a Neutron Star (NS) or a Black Hole (BH), is left. The understanding of how the remnant is formed and how its mass is linked with the properties of both the progenitor star (initial mass and initial metallicity) and the explosion (explosion energy, light curve and spectra) is fundamental in several astrophysical areas: for example, the formation of high massive remnants (1) limits the ejection of the heavy elements produced during either the hydrostatic and explosive nucleosynthesis and therefore this may have a significant impact on the chemical evolution of the galaxies as well as on the behavior of the light curve and spectra; (2) contributes significantly to the population of high mass compact objects, and (3) constitutes potential sources of gravitational waves (GWs) through BH-BH or NS-BH mergers. Unfortunately, at present, there is no self consistent hydrodynamic model for CCSN in which the explosion is obtained naturally and systematically. Even in those few cases where the explosion is successful, the results are not fully compatible with the observations (e.g., the energy of the explosion in these cases is a factor of 3 to 10 lower than that usually observed). In addition, these sophisticated 3D hydro simulations cannot predict with certainty of precision the mass of the remnant. The reason is that the fallback occurs on timescales (few hours) much longer than the typical timescales followed by the hydro calculations (few seconds). For all these reasons, at present, the systematic simulations of CCSNe are are still based on artificially induced explosions. In these calculations an arbitrary amount of energy is injected in the presupernova model (typically close to the edge of the iron core) and the shock wave that is generated in this way is followed during its propagation within the exploding mantle. In this context we substantially improved the 1D hydrodynamic code (HYPERION), extensively used for the explosive nucleosynthesis calculations, mainly with the inclusion of the radiative transport in the flux limited diffusion approximation and with a better treatment of the inner boundary conditions. By means of this new version of the code we computed the explosions, and the associated bolometric light curves, remnant masses and explosive nucleosynthesis, of a subset of red super giant presupernova models extracted from the database published by Limongi and Chieffi in 2018. In total 203 explosions have been computed, for different values of the explosion energy. In this way we were able to study the dependence of the light curve behavior (the maximum luminosity, the luminosity at 50 days, the plateau duration, the radioactive tail) and the mass of the remnant on the properties of the progenitor star (mass, metallicity) and on the explosion energy. Such a theoretical predictions constitute a fundamental reference framework for the interpretation of a number of astrophysical topical subjects among which the gravitational waves and their sources
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
Advances in Computational Astrophsyics: Methods, Tools and Outcomes
No full textIt was an international Conference cofunded by European Scinece Foundatio
Advances in Computational Astrophysics: Methods, Tools, and Outcome
No full textThis book contains the proceedings of a conference, held on 13-17 June 2011 in Cefalu' (Sicily, Italy) to discuss the recent progress in the application of modern numerical tools to the solution of open problems in astrophysics, from star formation up to the large scale structure of the universe.
This conference was the sixth in a series of Astronomy and Astrophysics workshops and conferences held in Cefalu' in the past years, and devoted to hot topics over the whole fields of modern Astrophysics.
This conference was a little different from many others where the
accent was put on the computational part of scientific work related to astrophysics.
Actually, more than dealing with deep numerical and computational aspects in a specific subfield of astrophysics or cosmology, we intended to gather scientists who are contemporarily at top of their fields on both the scientific side and that of numerical and computational methods, techniques, showing also expertise in the use of modern hardware and software resources.
The content of the book is divided into various Parts, from I to X, any of them referring to a specific topic of astrophysics where important achievements are presented after some introduction to the topic.
In particular, Parts V and X are specifically devoted to Advanced tools in computational astrophysics and to New Technologies in computational astrophysics, respectively.
A total of about 65 articles are presented here, with a length ranging from the 4 pages of the normal contributed papers to the 8 pages of the invited talks and the 10 pages of the introductory reviews.
The eleventh Part is dedicated to the summaries of the many poster contributions presented at the conference.
The conference resulted as a success, thanks to the high level of the oral and poster presentations and to the huge number of participants from many countries. In particular, we cite the vast participation of graduate students and young post docs, who contributed to the meeting also thanks to their ample participation to the debate after each talk
Influence of the 12C(α,γ)16O reaction rate on the evolution of a 15MO star. Nuclear Physics A688(2001)249
No full textVariations 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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