1,721,006 research outputs found
The galactic very metal-poor stars : from La Silla to Paranal
No full textThe search for the most galactic metal-poor stars began soon after the publication of the fundamental paper of Burbidge et al. (1957): the elements are synthesised little by little in the stars, and thus the most metal-poor galactic stars are (at least in a first approximation) the oldest ones.
The abundances of the elements tell us the story of the evolution of our Galaxy. I will try to recall the contribution of the La Silla instruments to the detection and the study of the primitive metal-poor stars, and I will rapidly review what we know today about the early phases of the Galactic evolution
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
Étoiles particulières pauvres en métaux à l’époque de Gaia
No full textComme on ne peut observer directement l’Univers lorsque les toutes premières étoiles se sont formées, (environ 1 Gyr après le Big Bang), une des méthodes pour approfondir notre connaissance de l’ Univers primitif consiste à étudier les propriétés chimiques et cinématiques des étoiles de petite masse, pauvres en métaux, formées à cette période, et qui brillent toujours aujourd’hui. Les étoiles pauvres en métaux ne sont pas très fréquentes dans notre Galaxie, et différentes techniques de détection ont été utilisées dans le passé : exploitation de bases de données photométriques ou spectroscopiques, et aussi sélection d’étoiles à grande vitesse. Une fois les bonnes candidats sélectionnés et observés à grande résolution, les spectres doivent être analysés. Grâce à la “Gaia Data Release 2” et “l’Early Data Release 3”, les paramètres principaux de l’atmosphère de ces étoiles ont pu être déterminés avec une très bonne précision. Cette thèse présente une analyse chimique et dynamique de trois échantillons d’étoiles. (1) Un échantillon d’étoiles naines sélectionnées dans la base de données spectroscopique Hambourg-ESO et HK afin de comprendre si les étoiles extrêmement pauvres en métaux et de plus, pauvres en Li, présentent une quelconque autre anomalie d’abondance ou une anomalie cinématique.(2) Deux étoiles sélectionnées pour leur très grande vitesse par rapport au soleil pour rechercher une éventuelle particularité chimique.(3) Un échantillon d’étoiles sélectionnés d’après la photométrie á bande étroite du relevé Pristine associée à de la photométrie à bande large (SDSS), afin de valider la calibration enmétallicité de ce relevé.- Dans le premier échantillon aucune anomalie chimique ou cinématique n’a pu être mise en évidence dans les étoiles extrêmement pauvres en métaux dont l’abondance en Li est inférieure à celle du “Spite plateau”. Ces étoiles sont comparables en tout point à celles dont l’abondance en Li est compatible avec le plateau. - Les deux étoiles à très grande vitesse ne présentent non plus aucune anomalie. Ellessont comparables aux étoiles de la littérature ayant les mêmes paramètres atmosphériques.- Du troisième échantillon (Pristine), nous avons pu conclure que l’utilisation de la bande étroite de Pristine associée à l’utilisation de la bande photométrique large de Gaia et de la parallaxe de l’étoile, permet une amélioration décisive de la détermination de la métallicité pour, en particulier, les étoiles évoluées.Comme toutes les spectres analysés dans ces trois échantillons étaient disponibles dès le début de ce projet de thèse, une double campagne d’observation a été conduite dans le cadre du projet MINCENot having the chance to directly observe the young Universe at a time when the first stellar generations formed (less than a Gyr after the Big Bang), we can deepen our knowledge on the early universe, by studying low mass metal-poor stars formed at that far away time, investigating their chemical pattern and their kinematic properties. Metal-poor stars are not common in the Milky Way, so to find them several techniques have been used in the past years, such as exploitation of low resolution spectroscopic or photometric databases, or selection of stars with high-speed. Once the good metal-poor candidates are selected and the high-resolution observations secured, the spectra have to be analysed. The access to the Gaia Data Release 2 and Early Data Release 3 provided the possibility to use Gaia photometry and parallaxes to select the stars and determine the parameters of their atmosphere with a very good precision. This thesis presents the chemo-dynamical investigation of three samples of metal-poor stars. (1) A sample of dwarf stars selected from the low resolution Hamburg-ESO and HK spectroscopic databases to understand if the extremely metal-poor and moreover Li-poor, stars show, apart from Li, any chemical or kinematical anomaly. (2) Two stars selected from their high-speed with respect to the Sun, to see if they have any chemical peculiarity. (3) A stellar sample selected by combining the wide-band (SDSS) and the Pristine narrow-band photometry to validate the photometric selection. - The search for chemical or kinematical anomalies in the first sample of stars was negative. The metal-poor stars below the Spite plateau are comparable to the star on the plateau. - The two high-speed stars also do not show anomalies, they are chemically similar to stars form the literature of comparable stellar parameters.- From the third sample (Pristine), we could conclude that in the selection of the metalpoor candidates by using Pristine as the narrow-band photometry, the use of Gaia as wideband photometry accompanied by the Gaia parallax provides a decisive improvement for the evolved stars. All the data analysed were already available at the beginning of the project. An observing campaign, with two observing runs, was done in the context of the MINC
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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