1,720,983 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
Concentration and compression over infinite alphabets, mixing times of random walks on random graphs
No full textCe 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.This 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
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
Le phénomène de Cutoff pour quelques systèmes de particules en interaction
No full textSur un espace d’états fini, une chaîne de Markov irréductible à temps continu converge vers sa mesure stationnaire unique, ou en d’autres termes, se mélange. La convergence est mesurée par rapport à la distance en variation totale. Dans la théorie moderne des chaînes de Markov, nous nous intéressons aux chaînes où l’espace d’états devient grand. En étudiant certains modèles de mélange de cartes, Aldous, Diaconis et Shashahani ont découvert le phénomène remarquable maintenant connu sous le nom de cutoff : lorsque l’espace d’états devient grand, la distance entre la chaîne et l’équilibre reste proche de sa valeur maximale pendant une longue période, puis chute soudainement vers zéro sur une échelle de temps beaucoup plus courte. Depuis, le phénomène de cutoff a été observé dans de nombreux contextes différents, tels que les chaînes de naissance et de mort, les systèmes de spin à haute température, les systèmes de particules en interaction, etc. Malgré l’accumulation de modèles, il n’existe pas encore de théorie générale permettant de prédire efficacement cutoff. Au lieu de cela, le cutoff est montré modèle par modèle. Dans cette thèse, nous étudions trois systèmes de particules en interaction: le processus d’exclusion unidimensionnel avec réservoirs, le processus de Glauber-Exclusion dans le régime à haut température, et le processus de Zero-Range à champ-moyen avec potentiel croissant sous-linéairement. Pour chaque modèle, nous établissons cutoff et fournissons une estimation fine pour le trou spectral. Nous nous concentrons particulièrement sur le cadre de la percolation de l’information introduit par Lubetzky et Sly, qui nous permet de montrer le cutoff même sans connaître la formule explicite de la mesure invariante.On a finite state space, an irreducible continuous-time Markov chain converges to its unique stationary measure, or in other words, mixes. The convergence is often measured by the total variation distance. In the modern theory of Markov Chains, we are interested in the case where the state space becomes large. When studying some models of card shuffling, Aldous, Diaconis, and Shashahani discovered a remarkable phenomenon now known as cutoff: as the state space becomes large, the distance between the chain and equilibrium stays close to its maximal value for a long time and then suddenly drops to near zero in a much shorter time scale. Since then, the cutoff phenomenon has been observed in many different contexts, such as birth and death chains, high-temperature spin systems, interacting particle systems, etc. Despite the accumulation of models, there is not yet a general theory to effectively predict cutoff. Instead, cutoff is proved model by model.In this thesis, we study three models : the one-dimensional Exclusion process with reservoirs, the Glauber-Exclusion process in the high-temperature regime, and the mean-field Zero-Range process with increasing sublinear potential. These three models all fall under the category of interacting particle systems. For each model, we establish cutoff and provide a sharp estimate on the spectral gap. We particularly focus on the information percolation framework introduced by Lubetzky and Sly, which allows us to show cutoff even without knowing the explicit formula of the invariant measure
High eigenvalues of sparse random graphs
No full textUne matrice aléatoire n x n est diluée lorsque le nombre d'entrées non nulles est d'ordre n ; les matrices d'adjacence de graphes d-réguliers ou les graphes d'Erdös-Rényi de degré moyen d fixé sont dilués. Dans le premier chapitre, je démontre une borne supérieure sur la deuxième valeur propre de la matrice de transition sur certains graphes dilués, les graphes de configuration dirigés, dans lesquels on a spécifié le degré (entrant et sortant) de chaque sommet. On obtient aussi une généralisation importante du théorème de Friedman : la seconde valeur propre de la matrice d'adjacence d'un graphe d-régulier dirigé est inférieure à racine carrée de d+o(1). Dans le second chapitre, issu d'une collaboration avec Charles Bordenave, on donne une généralisation du théorème d'Erdös-Gallai. Le troisième chapitre, issu d'une collaboration avec Justin Salez, résout un problème posé en 2004 par Bauer et Golinelli : l'existence ou non d'états étendus dans le spectre limite des graphes d'Erdös-Rényi de paramètre d/n. On y démontre l'absence d'états étendus en zéro lorsque d e. Nos résultats s'étendent aux arbres de Galton-Watson unimodulaires. Je démontre également l'absence d'états étendus en zéro dans le spectre de l'arbre squelette d'Aldous. Le dernier chapitre est issu d'une collaboration avec Charles Bordenave et Raj Rao Nadakuditi. On y étudie les valeurs propres de la matrice d'adjacence A d'un graphe d'Erdös-Rényi de paramètre d/n, dans lequel les arêtes sont pondérées par les entrées d'une matrice symétrique P. On montre une transition de phase spectaculaire : il existe un seuil Thêta dépendant de P et de d tel que les plus grandes valeurs propres de (n/d)A convergent vers les valeurs propres de P plus grandes que Thêta, et tel que les vecteurs propres de A associés sont alignés avec ceux de P.A random n x n matrix is diluted when the number of non-zero entries is of order n; adjacency matrices of d-regular graphs or adjacency matrices of Erdös-Rényi graphs with fixed average degree d are diluted. This dissertation is about the spectrum of diluted random matrices. In the first chapter I show an upper bound on the second eigenvalue of the transition matrix on a diluted directed graph model, the directed configuration model, in which the degree (in and out) of each vertex is specified. We also get an important generalization of Friedman's theorem: the second eigenvalue of the adjacency matrix of a directed d-regular graph is less than square root of d+o(1). A second short chapter, from a collaboration with Charles Bordenave, gives a generalization of the Erdös-Gallai theorem. The third chapter, a collaboration with Justin Salez, solves a problem raised in 2004 by Bauer and Golinelli: the existence (or not) of extended states in the limiting spectrum of Erdös-Rényi graphs with parameter d/n. We show the absence of extended states at zero when d e. Our results extend to the spectra of unimodular Galton-Watson tree. I also prove the absence of extended states at zero in the spectrum of the skeleton tree. The last chapter is a collaboration with Charles Bordenave and Raj Rao Nadakuditi. We study the eigenvalues of the adjacency matrix A of a directed Erdös-Rényi graph with parameter d/n, in which the edges are weighted by the entries of a symmetric matrix P. We show a spectacular phase transition: there is a threshold Theta depending on P and d such that the largest eigenvalues of (n/d)A converge to the eigenvalues of P which are greater than Theta. The associated eigenvectors of A are aligned with those of P
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
- …
