1,720,964 research outputs found
Approche photométrique et spectroscopique de la pulsation des étoiles céphéides
No full textCe travail de thèse est une étude observationnelle des étoiles Céphéides. Ce sont plus de 1100 mesures photométriques dans le système de Genève et 1600 mesures de vitesse radiale (CORAVEL) qui forment le matériau de base de ce travail.
Les mesures de photométrie ont permis d'obtenir une nouvelle échelle de rougissement. La procédure adoptée permet de calculer l'excès de couleur de n'importe quelle Céphéide.
A partir des mesures de vitesse radiale, on a pu déterminer la vitesse de microturbulence au cours du cycle de pulsation pour chaque Céphéide. Ceci a permis de faire usage de modèles d'atmosphères (calculés par d'autres auteurs) pour déterminer la température effective, la gravité et la correction bolométrique.
Les températures effectives qu'on en déduit sont, pour la première fois, indépendantes de la microturbulence.</p
Variabilité, sismologie et paramètres physiques stellaires
No full textAfin de comprendre ce qui se passe au cœur des étoiles et d'obtenir des informations sur l'évolution et la structure stellaire, il est nécessaire d'observer des étoiles variables qui, par leurs variations photométriques ou spectroscopiques, nous renseignent sur leurs secrets les plus intimes.
Dans le cadre de ce travail, des variations stellaires de types différents ont été suivies et analysées:
- Les variations apériodiques parmi les étoiles Be sont révélatrices des processus d'éjection de matière, de rotation de leur disque de poussières et peuvent nous aider à comprendre leur formation
- L'analyse simultanée des courbes de lumière et vélocimétrique de systèmes de type Algol permet de déterminer très précisément les paramètres physiques de ces objets
- Le taux de binaires parmi les étoiles chimiquement particulières, étant semblable à celui des étoiles normales A, cela laisse envisager que les particularités de cette classe d'étoiles proviennent d'autres phénomènes
- L'astérosismologie, l'étude des pulsations, permet de connaître les paramètres physiques internes des étoiles en n'observant que la surface de celles-ci.</p
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
Résonances et multipériodicité des céphéides et des hypergéantes
No full textL'étude des oscillations stellaires fournit des tests observationnels importants dans des domaines très divers de l'astrophysique. Les oscillations d'étoiles de type solaire permettent de connaître en détail la structure interne de ces objets, alors que les fortes pulsations des étoiles de type céphéide fournissent un outil pour mesurer les distances cosmologiques. Cette thèse aborde divers aspects concernant la pulsation des céphéides. Nous montrerons à l'aide de modèles comment la composition chimique, variable d'une galaxie à l'autre, influence la pulsation de ces étoiles et quel en est l'effet sur les grandeurs observées. Les résonances entre les modes propres d'oscillations de l'étoile sont primordiales dans les céphéides. Nous montrerons comment les utiliser pour obtenir de nouvelles contraintes sur les paramètres stellaires. Enfin, nous aborderons le problème des oscillations multipériodiques dans les céphéides à l'aide de modèles hydrodynamiques et nous étudierons en détail l'instabilité quasipériodique d'une hypergéante galactique
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
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