1,720,962 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
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
Rational cross-sections, bounded generation and orders on groups
Get PDFWe provide new examples of groups without rational cross-sections (also
called regular normal forms), using connections with bounded generation and
rational orders on groups. Specifically, our examples are extensions of
infinite torsion groups, groups of Grigorchuk type, wreath products similar to
and , a group of permutations of
, and a finitely presented HNN extension of the first Grigorchuk
group. This last group is the first example of finitely presented group with
solvable word problem and without rational cross-sections. It is also not
autostackable, and has no left-regular complete rewriting system.Comment: Fixed a mistake in the proof of Proposition 7.4, and other minors
change
A virtually nilpotent group with non D-finite Green series
Get PDFWe provide an example of a virtually -step nilpotent group, and a specific generating set, for which the Green series (sometimes called cogrowth series) is not D-finite. The proof relies on an arithmetical miracle, and the study of the subword complexity of a multiplicative sequence coming out of it.11 pages, 2 figures. Comments are welcom
Intermediate geodesic growth in virtually nilpotent groups
Get PDFWe give a criterion on pairs - where is a virtually -step
nilpotent group and is a finite generating set - saying whether the
geodesic growth is exponential or strictly sub-exponential. Whenever ,
this goes further and we prove the geodesic growth is either exponential or
polynomial. For however, intermediate growth is possible. We provide
an example of virtually -step nilpotent group for which
. This
is the first known example of group with intermediate geodesic growth. Along
the way, we prove results on the geometry of virtually nilpotent groups,
including asymptotics with error terms for their volume growth.Comment: 24 pages, 11 figures. Comments welcome
Geometric and algorithmic aspects of nilpotent groups
No full textEn théorie géométrique des groupes, les groupes nilpotents font partie des classes les mieux comprises. Dans cette thèse, nous montrerons qu'ils se comportement de manière surprenante en plus d'un sens.
Tout d'abord, on montre que la croissance du nombre de géodésiques dans certains groupes virtuellement nilpotents est intermédiaire, ce sont les premiers exemples de la sorte. On étudie ensuite le bord des horofonctions de certains groupes, exhibant ainsi des différences importantes entre les groupes nilpotents de classe 2 et 3, que ce soit au niveau de l'action du groupe sur son bord, ou du nombre de points de Busemann. La suite prend une direction plus algorithmique, on étudie les problèmes d'appartenance aux sous-monoïdes et sous-ensembles rationnels. On montre que ces deux problèmes ne sont pas équivalents, et on résout le second problème dans le groupe de Heisenberg. Dans les deux derniers chapitres, on étudie les séries de croissance complètes et de Green.In geometric group theory, nilpotent groups are among the better understood classes of groups. In this thesis, we will show that nilpotent groups behave in surprising ways.
First, we prove that the growth of the number of geodesics in some virtually nilpotent groups is intermediate, these are the the first examples of this type. Next, we study the horofunction boundary of some groups, highlighting important differences between nilpotent groups of class 2 and 3, both regarding the action of a group on its boundary, or the number of Busemann points. From this point on, we take an algorithmic direction, studying the membership problems to submonoids and rational subsets. We show that these two problems are not equivalent, and solve the second problem in the Heisenberg group. In the last two chapters, we study complete growth series and Green series.</p
Membership problems in nilpotent groups
Get PDFWe study both the Submonoid Membership problem and the Rational Subset
Membership problem in finitely generated nilpotent groups. We give two
reductions with important applications. First, Submonoid Membership in any
nilpotent group can be reduced to Rational Subset Membership in smaller groups.
As a corollary, we prove the existence of a group with decidable Submonoid
Membership and undecidable Rational Subset Membership, confirming a conjecture
of Lohrey and Steinberg. Second, the Rational Subset Membership problem in
can be reduced to the Knapsack problem in the same group, and
is therefore decidable. Combining both results, we deduce that the filiform
-step nilpotent group has decidable Submonoid Membership.Comment: v2. 26 pages, 5 figures. Added references, a new result on solving
equations under rational constraint, and a discussion of possible extension
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
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