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Percolation de dernier passage sur les graphes acycliques orientés complets
No full textThis thesis focuses on last-passage percolation on complete directed acyclic graphs. We study the maximal weight of a path in a complete graph where the edges are assigned random weights, and where the weight of a path is the sum of the weights of its edges. More precisely, we study the "time constant", which asymptotically represents the maximal weight of a path divided by the number of vertices in the graph, when the number of vertices goes to infinity. We will explore various properties of this time constant seen as a function of the distribution of the edges weights, such as strict monotonicity, continuity, and analyticity. A notable case is when the edge weights are either equal to 1 or m with respective probabilities p and 1-p. For m>0, the time constant is a rational fraction of p. For m=0, it corresponds to the inverse of a Ramanujan theta function. For negative m, there is no known closed formula, but we will provide an analytical formula in this specific case. For m=-∞, we will disprove a conjecture by Mallein and Ramassamy regarding the Taylor series expansion of this time constant. When m=-∞, last-passage percolation is equivalent to the infinite bin model, a model introduced by Foss and Konstantopoulos. In the last chapter, we will study a hydrodynamic limit of the infinite bin model. For this deterministic hydrodynamic limit, the time constant is explicit. We will show that the parameter space of the model is divided into regions indexed by combinatorial objects. On each region, the time constant is a rational function of the model parameters.Cette thèse porte sur la percolation de dernier passage sur des graphes complets acycliques orientés. Ce problème consiste en l'étude du poids maximal d'un chemin dans un graphe complet où les arêtes sont pondérées par des poids aléatoires, et où le poids d'un chemin consiste en la somme des poids de ses arêtes. Notre travail porte sur la "constante de temps", représentant asymptotiquement le poids maximal d'un chemin divisé par le nombre de sommets du graphe, lorsque le nombre de sommets dans le graphe est grand. Nous étudierons différentes propriétés de cette constante de temps vue en tant que fonction de la distribution des poids des arêtes, telles que la stricte monotonie, la continuité et l'analyticité. Un cas notable est lorsque les poids des arêtes valent soit 1 ou m avec probabilités respectives p et 1-p. Pour m>0, la constante de temps est une fonction rationnelle de p. Pour m=0, elle correspond à l'inverse d'une fonction thêta de Ramanujan. Il n'existe pas de formule close connue pour m<0, mais nous donnerons une formule analytique dans ce cas précis. Dans le cas m=-∞, on réfutera une conjecture de Mallein et Ramassamy concernant le développement de Taylor de cette constante de temps. Enfin, nous étudierons une limite hydrodynamique de l'infinite bin model, un modèle introduit par Foss et Konstantopoulos qui est équivalent à la percolation de dernier passage pour m=-∞. Pour cette limite hydrodynamique déterministe, la constante de temps est explicite. On montrera que l'espace des paramètres du modèle se divise en régions indexées par des objets combinatoires. Sur chaque région, la constante de temps est une fonction rationnelle des paramètres du modèle
Last passage percolation on complete directed acyclic graphs
No full textCette thèse porte sur la percolation de dernier passage sur des graphes complets acycliques orientés. Ce problème consiste en l'étude du poids maximal d'un chemin dans un graphe complet où les arêtes sont pondérées par des poids aléatoires, et où le poids d'un chemin consiste en la somme des poids de ses arêtes. Notre travail porte sur la "constante de temps", représentant asymptotiquement le poids maximal d'un chemin divisé par le nombre de sommets du graphe, lorsque le nombre de sommets dans le graphe est grand. Nous étudierons différentes propriétés de cette constante de temps vue en tant que fonction de la distribution des poids des arêtes, telles que la stricte monotonie, la continuité et l'analyticité. Un cas notable est lorsque les poids des arêtes valent soit 1 ou m avec probabilités respectives p et 1-p. Pour m>0, la constante de temps est une fonction rationnelle de p. Pour m=0, elle correspond à l'inverse d'une fonction thêta de Ramanujan. Il n'existe pas de formule close connue pour m0, the time constant is a rational fraction of p. For m=0, it corresponds to the inverse of a Ramanujan theta function. For negative m, there is no known closed formula, but we will provide an analytical formula in this specific case. For m=-∞, we will disprove a conjecture by Mallein and Ramassamy regarding the Taylor series expansion of this time constant. When m=-∞, last-passage percolation is equivalent to the infinite bin model, a model introduced by Foss and Konstantopoulos. In the last chapter, we will study a hydrodynamic limit of the infinite bin model. For this deterministic hydrodynamic limit, the time constant is explicit. We will show that the parameter space of the model is divided into regions indexed by combinatorial objects. On each region, the time constant is a rational function of the model parameters
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
Percolation de dernier passage sur les graphes acycliques orientés complets
No full textThis thesis focuses on last-passage percolation on complete directed acyclic graphs. We study the maximal weight of a path in a complete graph where the edges are assigned random weights, and where the weight of a path is the sum of the weights of its edges. More precisely, we study the "time constant", which asymptotically represents the maximal weight of a path divided by the number of vertices in the graph, when the number of vertices goes to infinity. We will explore various properties of this time constant seen as a function of the distribution of the edges weights, such as strict monotonicity, continuity, and analyticity. A notable case is when the edge weights are either equal to 1 or m with respective probabilities p and 1-p. For m>0, the time constant is a rational fraction of p. For m=0, it corresponds to the inverse of a Ramanujan theta function. For negative m, there is no known closed formula, but we will provide an analytical formula in this specific case. For m=-∞, we will disprove a conjecture by Mallein and Ramassamy regarding the Taylor series expansion of this time constant. When m=-∞, last-passage percolation is equivalent to the infinite bin model, a model introduced by Foss and Konstantopoulos. In the last chapter, we will study a hydrodynamic limit of the infinite bin model. For this deterministic hydrodynamic limit, the time constant is explicit. We will show that the parameter space of the model is divided into regions indexed by combinatorial objects. On each region, the time constant is a rational function of the model parameters.Cette thèse porte sur la percolation de dernier passage sur des graphes complets acycliques orientés. Ce problème consiste en l'étude du poids maximal d'un chemin dans un graphe complet où les arêtes sont pondérées par des poids aléatoires, et où le poids d'un chemin consiste en la somme des poids de ses arêtes. Notre travail porte sur la "constante de temps", représentant asymptotiquement le poids maximal d'un chemin divisé par le nombre de sommets du graphe, lorsque le nombre de sommets dans le graphe est grand. Nous étudierons différentes propriétés de cette constante de temps vue en tant que fonction de la distribution des poids des arêtes, telles que la stricte monotonie, la continuité et l'analyticité. Un cas notable est lorsque les poids des arêtes valent soit 1 ou m avec probabilités respectives p et 1-p. Pour m>0, la constante de temps est une fonction rationnelle de p. Pour m=0, elle correspond à l'inverse d'une fonction thêta de Ramanujan. Il n'existe pas de formule close connue pour m<0, mais nous donnerons une formule analytique dans ce cas précis. Dans le cas m=-∞, on réfutera une conjecture de Mallein et Ramassamy concernant le développement de Taylor de cette constante de temps. Enfin, nous étudierons une limite hydrodynamique de l'infinite bin model, un modèle introduit par Foss et Konstantopoulos qui est équivalent à la percolation de dernier passage pour m=-∞. Pour cette limite hydrodynamique déterministe, la constante de temps est explicite. On montrera que l'espace des paramètres du modèle se divise en régions indexées par des objets combinatoires. Sur chaque région, la constante de temps est une fonction rationnelle des paramètres du modèle
Regularity of the time constant for last passage percolation on complete directed acyclic graphs
No full textWe study the time constant C(ν) of last passage percolation on the complete directed acyclic graph on the set of non-negative integers, where edges have i.i.d. weights with distribution ν with support included in {−∞} ∪ R. We show that ν → C(ν) is strictly increasing in ν. We also prove that C(ν) is continuous in ν for a large set of measures ν. Furthermore, when ν is purely atomic, we show that C(ν) is analytic with respect to the weights of the atoms. In the special case of two positive atoms, it is an explicit rational function of these weights
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
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