1,720,958 research outputs found
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
Il Problema Inverso di Galois
No full textIl Problema Inverso di Galois consiste nel chiedersi se, dato un gruppo finito qualsiasi, esista una estensione di Galois di un campo fissato avente quale gruppo di Galois proprio il gruppo assegnato, a meno di isomorfismo. Verranno presentate le tecniche di approccio al problema storicamente più rilevanti: programma di Noether, tecnica della Rigidità, Problemi di Immersione, presentando alcuni esempi di applicazione pratica: i gruppi simmetrici, alterni, PSL(2,p) per p primo non congruo a 1 o -1 mod(24), condizioni sulle estensioni di quarto grado affinchè siano cicliche e il gruppo delle unità dei quaternioni
Lower bound estimates on canonical heights and Manin-Mumford conjecture
No full textLe travail est constitué de deux chapitres qui ne sont pas liés entre eux. Dans le premier chapitre nous proposons une minoration de la hauteur canonique pour une certaine classe de modules de Drinfeld à caractéristique 0 exprimée en fonction de la dimension sur le corps de définition de ce module, des points algébriques (dans une opportune cloture algébrique) qui ne sont pas de torsion, en dévéloppant ainsi une étude du problème de Lehmer au cas des modules de Drinfeld. Dans le deuxième chapitre nous proposons une stratégie d’attaque à la conjecture de Manin-Mumford au cas des T-modules abéliens et uniformisables basée sur la méthode introduite par J. Pila et U.Zannier au cas des variétés abéliennes définies sur un corps de nombres. Nous proposons en particulier un premier pas dans une telle direction qui consiste à reprendre les travaux de J. Pila et J. Wilkie pour parvenir à une majoration du nombre des points de torsion d’un T-module qui respecte nos hypothèses, et qui puisse constituer un fondament essentiel au dévéloppement de cette méthode comme dans le cas classique.We divide this work in two different chapters having no relation between them. In the first chapter we propose a lower bound estimate of the canonical height on a certain family of Drinfeld modules having characteristic 0, depending by the dimension of these Drinfeld module algebraic points on the base function field (into a well-chosen algebraic closure). This will take us to deeply analyze the Lehmer problem on Drinfeld modules. In the second chapter we propose a strategy to approach the Manin-Mumford conjecture on uniformizable abelian T-modules, based on the new techniques introduced by J. Pila and U. Zannier for abelian varieties defined on a number field. We propose in particular a first step in such a direction by a new interpretation of the J. Pila and J. Wilkie’s work in order to obtain an higher bound estimate on the number of torsion points of a such T-module. This would be an important basis to a future development of this method, as in the classic case
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
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
Minoration de hauteurs canoniques et conjecture de Manin-Mumford
No full textLe travail est constitué de deux chapitres qui ne sont pas liés entre eux. Dans le premier chapitre nous proposons une minoration de la hauteur canonique pour une certaine classe de modules de Drinfeld à caractéristique 0 exprimée en fonction de la dimension sur le corps de définition de ce module, des points algébriques (dans une opportune cloture algébrique) qui ne sont pas de torsion, en dévéloppant ainsi une étude du problème de Lehmer au cas des modules de Drinfeld. Dans le deuxième chapitre nous proposons une stratégie d attaque à la conjecture de Manin-Mumford au cas des T-modules abéliens et uniformisables basée sur la méthode introduite par J. Pila et U.Zannier au cas des variétés abéliennes définies sur un corps de nombres. Nous proposons en particulier un premier pas dans une telle direction qui consiste à reprendre les travaux de J. Pila et J. Wilkie pour parvenir à une majoration du nombre des points de torsion d un T-module qui respecte nos hypothèses, et qui puisse constituer un fondament essentiel au dévéloppement de cette méthode comme dans le cas classique.We divide this work in two different chapters having no relation between them. In the first chapter we propose a lower bound estimate of the canonical height on a certain family of Drinfeld modules having characteristic 0, depending by the dimension of these Drinfeld module algebraic points on the base function field (into a well-chosen algebraic closure). This will take us to deeply analyze the Lehmer problem on Drinfeld modules. In the second chapter we propose a strategy to approach the Manin-Mumford conjecture on uniformizable abelian T-modules, based on the new techniques introduced by J. Pila and U. Zannier for abelian varieties defined on a number field. We propose in particular a first step in such a direction by a new interpretation of the J. Pila and J. Wilkie s work in order to obtain an higher bound estimate on the number of torsion points of a such T-module. This would be an important basis to a future development of this method, as in the classic case.LILLE1-Bib. Electronique (590099901) / SudocSudocFranceF
Densities on Dedekind domains, completions and Haar measure
Get PDFLet be the ring of -integers in a global field and its
profinite completion. We discuss the relation between density in and the
Haar measure of : in particular, we ask when the density of a subset
of is equal to the Haar measure of its closure in . In order
to have a precise statement, we give a general definition of density which
encompasses the most commonly used ones. Using it we provide a necessary and
sufficient condition for the equality between density and measure which
subsumes a criterion due to Poonen and Stoll. In another direction, we extend
the Davenport-Erd\H{o}s theorem to every as above and offer a new
interpretation of it as a "density=measure" result. Our point of view also
provides a simple proof that in any the set of elements divisible by at
most distinct primes has density 0 for any natural number . Finally, we
show that the closure of the set of prime elements of is the union of the
group of units of with a negligible part.Comment: 41 pages, no figures. Final version, accepted in Mathematische
Zeitschrif
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