1,721,018 research outputs found
Runaway stars and the Galactic supernova remnant landscape: non-thermal emission and observational evidence
No full textContext. A significant fraction (~30%) of massive stars in our Galaxy are moving supersonically through the interstellar medium, which strongly governs their location at the time they end their lives, e.g. die as a supernova and give birth to a supernova remnant (SNR). These dead stellar environments accelerate particles, emitting by non-thermal mechanisms up to the TeV range, and they are considered as a major contributor to the very-high-energy band of the local cosmic-ray spectrum.
Aims. This study investigates the effect of the runaway motion of supernova progenitors on the spatial distribution of SNRs in the Milky Way and how this influences the deduced properties of the population.
Methods. We construct Galactic populations of SNRs by Monte Carlo simulation, taking into account the bulk motion and the evolution history of their progenitor stars once ejected from their parent clusters. The gamma-ray domain emission of each population is then calculated, to be compared with the High Energy Stereoscopic System (H.E.S.S.) Galactic Plane Survey.
Results. We find that including the runaway motion of supernova progenitors strongly modifies the detectability of the simulated emission of their remnants in the very-high-energy band. Particularly, our best fit model using a Reid Milky Way model for core-collapse supernova progenitors requires 33% of massive runaway stars, which is close to the known fraction of runaway high-mass stars, to be in accordance with the H.E.S.S. Galactic Plane Survey data.
Conclusions. Our results show that the runaway nature of supernova progenitors must be taken into account in the study of the Galactic population of SNRs within the H.E.S.S. Galactic Plane Survey and the forthcoming Galactic Plane Survey of the Cherenkov Telescope Array Observatory, as it is a governing factor of the detectability of non-thermal emission of their subsequent SNRs.The authors would like to give the referee a big thank-you, their suggestions and comments significantly improved the work. The authors are grateful for the computing time on the high-performance computer “Lise” at the NHR Center NHR@ZIB, jointly supported by the Federal Ministry of Education and Research and the state governments participating in the NHR (https://www.nhr-verein.de/unsere-partner). This work is funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) with the grant 500120112 and supported by the grant PID2021-124581OB-I00 funded by MCIN/AEI/10.13039/501100011033 and 2021SGR00426 of the Generalitat de Catalunya. This work is also supported by the Spanish program Unidad de Excelencia María de Maeztu CEX2020-001058-M. This work is also supported by MCIN with funding from European Union NextGeneration EU (PRTR-C17.I1).With funding from the Spanish government through the "María de Maeztu Unit of Excellence" accreditation (CEX2020-001058-M)Peer reviewe
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
Estimating the performance gain achievable by the H. E. S. S. I camera upgrade
No full textThe High Energy Stereoscopic System (H.E.S.S.) is an array of four 12-m and one 28-m Imaging Atmospheric Cherenkov Telescopes (IACT) that is used to study the emission of cosmic gamma-rays at very-high energies (100 GeV − 100 TeV). In 2015/2016 the H. E. S. S. collaboration undertook an upgrade of the more than 10-year-old cameras of the four 12-m-telescopes. The upgrade aims for an increase of the rate of gamma-ray events that are observed by more than one telescope (stereo events) by reducing the dead time of the telescopes. Especially at low energies, where currently most gamma-ray events are recorded only by the 28-m-telescope (mono events), the more accurate reconstruction of stereo events will improve the performance of the system.In the course of this thesis Monte Carlo simulations are used to estimate the performance gain that can be achieved with the camera upgrade. The standard simulation chain has been adjusted for this purpose. The adjustments include the implementation of the effect of the dead time of the cameras, the reduction of the pixel trigger threshold and the read-out of additional information related to the signal timing in each pixel. Based on the signal timing a new image cleaning approach is introduced.An optimisation of analysis parameters is performed in order to yield the maximal perfor- mance for the upgraded system. The performance of a Hillas-based stereo event analysis of simulated data for the upgraded cameras, using the optimised parameters, is compared to the performance of the original cameras with the standard analysis parameters being applied. Furthermore, the performance of a mono event analysis is compared to the stereo event anal- yses. The comparison reveals that the camera upgrade can reduce the energy threshold for a Hillas-based stereo event analysis by 25 % down to 100 GeV. For the same analysis param- eters the reduction of the dead time improves the sensitivity by a factor of 30 % in the core energy range around 1TeV. It is also shown that stereo event analyses with the upgraded cameras provide a higher angular resolution, a more accurate energy reconstruction and a better sensitivity than a mono event analysis.The new image cleaning approach is demonstrated to be able to reduce the impact of elec- tronic noise and the night sky background in event images notably when low pixel intensity thresholds are applied for the cleaning. Since applying low pixel intensity thresholds could ad- ditionally reduce the energy threshold of the system, further investigations are recommended to test whether this method can be optimised to yield an improved image quality compared to a standard cleaning with high pixel intensity thresholds.Finally, this work proves that the camera upgrade enhances the performance of H. E. S. S. sig- nificantly, which will allow for more precise analyses of cosmic gamma-ray source at very-high energies
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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