1,721,026 research outputs found
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Uniform tightness for time-inhomogeneous particle systems and for conditional distributions of time-inhomogeneous diffusion processes
No full text20 pagesInternational audienceIn this article, we consider time-inhomogeneous diffusive particle systems, whose particles jump from the boundary of a bounded open subset of , . We give a sufficient criterion for the family of empirical distributions of such systems to be uniformly tight, independently of the jump location of the particles. As an application, we show that the conditional distribution of a family of time-inhomogeneous and environment-dependent diffusions conditioned not to hit the boundary of a bounded open subset of is uniformly tight
Quasi-compactness for dominated kernels with application to quasi-stationary distribution theory
No full textWe establish a domination principle for positive operators, yielding a upper bound on the essential spectral radius and a practical quasi-compactness criterion on weighted supremum spaces. We then apply these results to absorbed Markov processes and show that quasi-compactness of the transition kernel ensures existence and convergence to quasi-stationary distributions in broadly reducible settings, without regularity requirements. In continuous time, we show that measurability plus quasi-compactness at a single time propagates to all times, rules out periodic behavior, and yields convergence to quasi-stationary distributions. Two illustrative cases demonstrate the scope and simplicity of the criteria.</div
Variations on the Author
Full text link“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
Full text linkWe 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
Approximation of quasi-stationary distributions for 1-dimensional killed diffusions with unbounded drifts
No full textThe long time behavior of an absorbed Markov process is well described by the limiting distribution of the process conditioned to not be killed when it is observed. Our aim is to give an approximation's method of this limit, when the process is a -dimensional Itô diffusion whose drift is allowed to explode at the boundary. In a first step, we show how to restrict the study to the case of a diffusion with values in a bounded interval and whose drift is bounded. In a second step, we show an approximation method of the limiting conditional distribution of such diffusions, based on a Fleming-Viot type interacting particle system. We end the paper with two numerical applications : to the logistic Feller diffusion and to the Wright-Fisher diffusion with values in conditioned to be killed at
Distributions quasi-stationnaires et méthodes particulaires pour l'approximation de processus conditionnés
No full textMy PhD thesis focuses on the study of the distributions of stochastic processes with absorption and their approximation. This processes are commonly used in a large area of applications in ecology, finance or reliability studies. In particular, we study the long term evolution of the distribution of Markov processes with absorption. Non-trivial behaviors, like mortality plateaus, can be described and explained by the limiting distribution of a process conditioned not to be absorbed when it is observed. When such a limiting distribution exists, it is called a quasi-stationary distribution. In the first chapter, we recall and prove in all generality some specific properties of these distributions. In the following chapters, we prove in a great generality an approximation method based on particle systems in order to approximate the distribution of conditioned Markov processes and their quasi-stationary distributions. Programs written in C++ during my thesis allow us to present a numerical implementation of this approximation method for biological models, like the Wright-Fisher diffusion process or the Lotka-Volterra diffusion processes. The approximation method proved in this thesis associated with coupling technics allows us to obtain new results of existence and uniqueness of quasi-stationnary distributions. Moreover, we show some mixing properties for diffusion processes conditioned to remain in a bounded open subset.Ma thèse porte sur l'étude de la distribution de processus stochastiques avec absorption et leur approximation. Ces processus trouvent des applications dans de nombreux domaines, tels que l'écologie, la finance ou les études de fiabilité. Nous étudions en particulier l'évolution en temps long de la distribution de processus de Markov avec absorption. La distribution limite d'un processus conditionné à ne pas être éteint au moment où on l'observe permet de décrire et d'expliquer des comportements non-triviaux, comme les plateaux de mortalité. Lorsqu'une telle distribution existe, elle est appelée distribution quasi-stationnaire. Dans le premier chapitre, nous rappelons et démontrons en toute généralités des propriétés propres à ces distributions. Dans les chapitres suivants, nous démontrons dans une grande généralité une méthode particulaire d'approximation des distributions de processus de Markov conditionnés à ne pas être absorbés et de leur limite distribution quasi-stationnaire. Des programmes en C++ ont été écrits afin d'implémenter numériquement l'approximation particulaire de distribution quasi-stationnaires de processus provenant de modèles biologiques, tels que les diffusions de Wright-Fisher et les diffusions de Lotka-Volterra. La méthode d'approximation démontrée dans cette thèse associée à des méthodes de couplage nous permet également d'obtenir des nouveaux résultats d'existence et d'unicité de distributions quasi-stationnaires, ainsi que de démontrer des propriétés de mélanges nouvelles pour les diffusions conditionnées à ne pas sortir d'un ouvert borné
Approximation of quasi-stationary distributions for 1-dimensional killed diffusions with unbounded drifts
No full textThe long time behavior of an absorbed Markov process is well described by the limiting distribution of the process conditioned to not be killed when it is observed. Our aim is to give an approximation's method of this limit, when the process is a -dimensional Itô diffusion whose drift is allowed to explode at the boundary. In a first step, we show how to restrict the study to the case of a diffusion with values in a bounded interval and whose drift is bounded. In a second step, we show an approximation method of the limiting conditional distribution of such diffusions, based on a Fleming-Viot type interacting particle system. We end the paper with two numerical applications : to the logistic Feller diffusion and to the Wright-Fisher diffusion with values in conditioned to be killed at
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