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Concentration et compression sur alphabets infinis, temps de mélange de marches aléatoires sur des graphes aléatoires
No full textThis document presents the problems I have been interested in during my PhD thesis. I begin with a concise presentation of the main results, followed by three relatively independent parts. In the first part, I consider statistical inference problems on an i.i.d. sample from an unknown distribution over a countable alphabet. The first chapter is devoted to the concentration properties of the sample's profile and of the missing mass. This is a joint work with Stéphane Boucheron and Mesrob Ohannessian. After obtaining bounds on variances, we establish Bernstein-type concentration inequalities and exhibit a vast domain of sampling distributions for which the variance factor in these inequalities is tight. The second chapter presents a work in progress with Stéphane Boucheron and Elisabeth Gassiat, on the problem of universal adaptive compression over countable alphabets. We give bounds on the minimax redundancy of envelope classes, and construct a quasi-adaptive code on the collection of classes defined by a regularly varying envelope. In the second part, I consider random walks on random graphs with prescribed degrees. I first present a result obtained with Justin Salez, establishing the cutoff phenomenon for non-backtracking random walks. Under certain degree assumptions, we precisely determine the mixing time, the cutoff window, and show that the profile of the distance to equilibrium converges to the Gaussian tail function. Then I consider the problem of comparing the mixing times of the simple and non-backtracking random walks. The third part is devoted to the concentration properties of weighted sampling without replacement and corresponds to a joint work with Yuval Peres and Justin Salez.Ce document rassemble les travaux effectués durant mes années de thèse. Je commence par une présentation concise des résultats principaux, puis viennent trois parties relativement indépendantes.Dans la première partie, je considère des problèmes d'inférence statistique sur un échantillon i.i.d. issu d'une loi inconnue à support dénombrable. Le premier chapitre est consacré aux propriétés de concentration du profil de l'échantillon et de la masse manquante. Il s'agit d'un travail commun avec Stéphane Boucheron et Mesrob Ohannessian. Après avoir obtenu des bornes sur les variances, nous établissons des inégalités de concentration de type Bernstein, et exhibons un vaste domaine de lois pour lesquelles le facteur de variance dans ces inégalités est tendu. Le deuxième chapitre présente un travail en cours avec Stéphane Boucheron et Elisabeth Gassiat, concernant le problème de la compression universelle adaptative d'un tel échantillon. Nous établissons des bornes sur la redondance minimax des classes enveloppes, et construisons un code quasi-adaptatif sur la collection des classes définies par une enveloppe à variation régulière. Dans la deuxième partie, je m'intéresse à des marches aléatoires sur des graphes aléatoires à degrés precrits. Je présente d'abord un résultat obtenu avec Justin Salez, établissant le phénomène de cutoff pour la marche sans rebroussement. Sous certaines hypothèses sur les degrés, nous déterminons précisément le temps de mélange, la fenêtre du cutoff, et montrons que le profil de la distance à l'équilibre converge vers la fonction de queue gaussienne. Puis je m'intéresse à la comparaison des temps de mélange de la marche simple et de la marche sans rebroussement. Enfin, la troisième partie est consacrée aux propriétés de concentration de tirages pondérés sans remise et correspond à un travail commun avec Yuval Peres et Justin Salez
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
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
Graphes aléatoires peu denses : de spécifications locales vers desphénomènes globaux
No full textThis thesis is devoted to the study of different random graphs, defined by local properties (suchas the distribution of the degrees of the vertices, or the probability that two given vertices sharean edge). We investigate some of their global characteristics, in particular their geometry andthe behaviour of random walks. It consists of three independent parts. In each of them, thelocal limit of the random graph is a tree, and a fine comparison between the tree and the graphallows to implement properties of the former on the latter.• The first part (Chapter 2) is about the scaling limit of a critical random graph, more pre-cisely a configuration model with independent and identically distributed degrees havingpower-law heavy tail behaviour: there is a variance, but no third moment. It was knownthat the largest connected components of this graph scale like Θ(n a ) if the graph is on nvertices, for some model-dependent constant a. We prove that their structure convergesto a biased version of a particular random R-tree, the stable tree, to which one adds afinite number of cycles.• The second part (Chapter 3) is devoted to the Gaussian free field on random d-regulargraphs. We study its percolation above a fixed level. If this level is below a certain criticalthreshold, we establish the emergence with high probability of a unique giant componentcontaining a positive proportion of the vertices, surrounded by islets of logarithmic size,while only the latter survive above the critical threshold. We show that this big continentshares remarkable similarities with the giant component of a famous random graph, theErdős-Rényi model.• The third part (Chapter 4) deals with random walks on random lifts of an arbitraryfinite base graph. Random lifts are sparse graphs with good connectivity properties anda regular structure, the associated tree being periodic. We prove that the random walkon these graphs admits a cutoff, i.e. there is a brutal transition between the time when itis still localized around its starting point, and the time when we have completely lost itstrack.The last two parts have been realized in Paris under the supervision of Justin Salez, between2017 and 2021. The first part stems from a collaboration with Christina Goldschmidt (OxfordStatistics), started in 2016 during a research internship and continued until 2020.Cette thèse est consacrée à l’étude de différents graphes aléatoires, définis par des propriétéslocales (comme la distribution des degrés des sommets ou la probabilité que deux sommetsdonnés soient reliés par une arête), et dont on cherche à déterminer des caractéristiques globales,notamment leur géométrie et le comportement de marches aléatoires. Elle se compose de troisparties indépendantes. À chaque fois, le graphe aléatoire étudié admet un arbre comme limitelocale, et une comparaison fine entre l’arbre et le graphe permet de transposer des propriétésdu premier au second.• La première partie (Chapitre 2) porte sur la limite d’échelle d’un graphe aléatoire critique,un modèle de configuration avec des degrés indépendants et distribués selon une mêmeloi de puissance à queue lourde : elle a une variance, mais pas de troisième moment. Ilétait connu que les plus grandes composantes connexes de ce graphe ont une taille Θ(n a )pour un graphe à n sommets, le paramère a dépendant du modèle. On montre que leurstructure converge vers une version biaisée d’un arbre aléatoire continu particulier, l’arbrestable, auquel on rajoute un nombre fini de cycles.• La seconde partie (Chapitre 3) est consacrée au champ libre gaussien sur des graphesaléatoires d-réguliers. On étudie la percolation du champ libre au-dessus d’un niveau fixé.Si on baisse ce niveau en-dessous d’un certain seuil critique, on établit l’émergence avecgrande probabilité d’une unique composante connexe géante englobant une proportionpositive des sommets, entourée d’ilôts de taille logarithmique, tandis que seuls ces dernierssurvivent au-dessus du seuil critique. On montre alors que ce grand continent admetde remarquables similitudes avec la composante géante d’un graphe aléatoire célèbre, lemodèle d’Erdős-Rényi.• La troisième partie (Chapitre 4) traite de marches aléatoires sur des relèvements aléatoires(”random lifts”) d’un graphe fini quelconque donné. Ces relèvements sont des graphes peudenses mais avec de bonnes propriétés de connectivité et une structure assez régulière,l’arbre associé étant périodique. On prouve que la marche aléatoire sur ces graphes admetun cutoff, c’est-à-dire qu’il y a une transition brusque entre le moment où le marcheurest encore localisé autour de son point de départ, et celui où on a définitivement perdu satrace.Les deux dernières parties ont été réalisées à Paris sous la direction de Justin Salez entre 2017 et2021. La première est issue d’une collaboration avec Christina Goldschmidt (Oxford Statistics),initiée en 2016 lors d’un stage de recherche et poursuivie jusqu’en 2020
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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