1,720,973 research outputs found
Rigid and strongly rigid relations on small domains
Get PDFLes relations fortement rigides jouent un rôle important dans l’étude de la complexité
des problèmes de satisfaction de contraintes (CSPs) (Feder et Vardi [22], Schaefer [9],
Jeavons [23], Bulatov, Jeavons et Krokhin [24], Larose et Tesson [34], Larose [31],
Barto et Kozik [36], et Bulatov, Jeavons et Krokhin [27]) qui font l’objet de recherches
intenses à la fois en intelligence artificielle et en recherche opérationnelle (Russell et
Norvig [19]). Une relation n-aire r sur un ensemble U est rigide si elle n’admet aucun
automorphisme non-trivial ; elle est fortement rigide si elle n’est préservée que par les
projections. De plus r est dite projective si les seules opérations idempotentes qui la
préservent sont les projections.
Rosenberg (1973) a caracterisé toutes les relations fortement rigides sur un ensemble
à deux éléments, et a construit une relation binaire fortement rigide sur tout ensemble de
plus de deux éléments. Larose et Tardif (2001) ont étudié les graphes projectifs et fortement
rigides, et ont construit de grandes familles de graphes fortement rigides. Łuczak
et Nešetˇril (2004) ont démontré une conjecture de Larose and Tardif qui prévoyait que
la plupart des graphes avec suffisamment de sommets sont projectifs, et ont caractérisé
tous les graphes homogènes qui sont projectifs. Łuczak et Nešetˇril (2006) ont ensuite
confirmé une conjecture de Rosenberg qui prédisait que la plupart des relations sur un
ensemble suffisamment grand sont fortement rigides.
Le premier résultat principal de cette thése est une caractérisation des relations fortement
rigides sur un ensemble d’au moins 3 éléments, résolvant ainsi un problème ouvert
de Rosenberg (Rosenberg [7], Problème 6 de [13]). Ensuite nous montrons qu’à isomorphisme
près, il n’existe que 4 relations binaires rigides sur un ensemble à trois éléments,
parmi lesquelles deux seulement sont fortement rigides. De plus, nous déterminons, à
isomorphisme près, les 40 relations binaires rigides sur un univers à quatre éléments, et
montrons que 25 d’entre elles sont fortement rigides (Exemple 5.4 et Exemple 6.1 dans
Sun [41]). Nous généralisons une de ces relations pour construire une nouvelle relation
binaire fortement rigide sur tout ensemble d’au moins 4 éléments (Sun [43]), et décrivons
de plus une relation ternaire fortement rigide sur tout ensemble fini avec au moins 2 éléments
et conjecturons une relation k-aire fortement rigide sur tout domaine fini (Sun [42]).Strongly rigid relations play an important role in the study of the complexity of
Constraint Satisfaction Problems (CSPs) (Feder and Vardi [22], Schaefer [9], Jeavons
[23], Bulatov, Jeavons and Krokhin [24], Larose and Tesson [34], Larose [31], Barto
and Kozik [36], and Bulatov, Jeavons and Krokhin [27]) which are the subject of intense
research in both artificial intelligence and operations research (Russell and Norvig [19]).
An n-ary relation r on a set U is strongly rigid if it is preserved only by trivial operations.
It is projective if the only idempotent operations in Polr are projections.
Rosenberg (1973) characterized all strongly rigid relations on a set with two elements
and found a strongly rigid binary relation on every domain U of at least 3 elements.
Larose and Tardif (2001) studied the projective and strongly rigid graphs, and
constructed large families of strongly rigid graphs. Łuczak and Nešetˇril (2004) settled
in the affirmative a conjecture of Larose and Tardif that most graphs on a large set are
projective, and characterized all homogenous graphs that are projective. Łuczak and
Nešetˇril (2006) confirmed a conjecture of Rosenberg that most relations on a big set are
strongly rigid.
In this thesis we characterize all strongly rigid relations on a set with at least three
elements to answer an open question by Rosenberg (1973) (Rosenberg [7], Problem 6 in
Rosenberg [13]). We classify the binary relations on the 3-element domain and demonstrate
that there are merely 4 pairwise nonisomorphic rigid binary relations on the same
domain (among them 2 are pairwise nonisomorphic strongly rigid), and we classify the
binary relations on the 4-element domain and show that there are merely 40 pairwise
nonisomorphic rigid binary relations on the same domain (among them 25 are pairwise
nonisomorphic strongly rigid) (Example 5.4 and Example 6.1 in Sun [41]). We extend
a strongly rigid relation on a 4-element domain to any finite domain (Sun [43]). Finally,
we give a strongly rigid ternary relation on any finite domain and conjecture a strongly
rigid k-ary relation on any finite domain (Sun [42])
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
Complexité des homomorphismes de graphes avec listes
Get PDFLes problèmes de satisfaction de contraintes, qui consistent à attribuer des valeurs à des variables en respectant un ensemble de contraintes, constituent une large classe de problèmes naturels. Pour étudier la complexité de ces problèmes, il est commode de les voir comme des problèmes d'homomorphismes vers des structures relationnelles. Un axe de recherche actuel est la caractérisation des classes de complexité auxquelles appartient le problème d'homomorphisme, ceci dans la perspective de confirmer des conjectures reliant les propriétés algébriques des structures relationelles à la complexité du problème d'homomorphisme.
Cette thèse propose dans un premier temps la caractérisation des digraphes pour lesquels le problème d'homomorphisme avec listes appartient à FO. On montre également que dans le cas du problèmes d'homomorphisme avec listes sur les digraphes télescopiques, les conjectures reliant algèbre et complexité sont confirmées.
Dans un deuxième temps, on caractérise les graphes pour lesquels le problème d'homomorphisme avec listes est résoluble par cohérence d'arc. On introduit la notion de polymorphisme monochromatique et on propose un algorithme simple qui résoud le problème d'homomorphisme avec listes si le graphe cible admet un polymorphisme monochromatique TSI d'arité k pour tout k ≥ 2.Constraint satisfaction problems, consisting in assigning values to variables while respecting a set of constraints, form a large class of natural problems. In order to study the complexity of these problems, it is convenient to see them as homomorphism problems on relational structures. One current research topic is to characterise complexity classes where the homomorphism problem belongs. The ultimate goal is to confirm conjectures that bind together algebraic properties of the relationnal structure and complexity of the homomorphism problem.
At first, the thesis characterizes digraphs which generate FO list-homomorphism problems. It is shown that in the particular case of telescopic digraphs, conjectures binding together algebra and complexity are confirmed.
Subsequently, we characterize graphs which generate arc-consistency solvable list-homomorphism problems. We introduce the notion of monochromatic polymorphism and we propose a simple algorithm which solves the list-homomorphism problem if the target graph admits a monochromatic TSI polymorphism of arity k for every k ≥ 2
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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