1,720,982 research outputs found
Localized Inverse Design in Conservation Laws and Hamilton-Jacobi Equations
Get PDFInternational audienceConsider the inverse design problem for a scalar conservation law, i.e., the problem of finding initial data evolving into a given profile at a given time. The solution we present below takes into account localizations both in the final interval where the profile is assigned and in the initial interval where the datum is sought, as well as additional a priori constraints on the datum’s range provided by the model. These results are motivated and can be applied to data assimilation procedures in traffic modeling and accidents localization
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
Local and asymptotic analysis for some longwave approximations of fluid dynamics equations
No full textCette thèse est composée de deux parties indépendantes. Dans la première partie, nous étudions la stabilité orbitale et asymptotique de certaines ondes solitaires pointues (appelées peakons) de l'équation de Novikov. Dans la seconde partie, nous étudions le caractère bien posé local et global pour certaines équations de type Korteweg-de Vries en dimension un et deux, lorsqu'on pose le problème autour d'une fonction bornée sans décroissance spatiale particulière.L'équation de Novikov est une généralisation d'ordre supérieur de l'équation de Camassa-Holm. Elle possède une non-linéarité cubique, est complètement intégrable et conserve toutes les propriétés intéressantes (physiquement pertinentes) de l'équation de Camassa-Holm. Pour cette équation nous commençons par revisiter les résultats déjà connus de stabilité orbitale des peakons et nous établissons celle des multi-peakons. Puis, motivé par l'approche développée pour l'équation de Camassa-Holm, nous montrons la stabilité asymptotique des peakons et des multi-peakons de l'équation de Novikov. Pour cela nous introduisons en particulier une nouvelle fonctionnelle de Lyapunov qui peut être adaptée à un grand nombre de généralisations de Camassa-Holm d'ordre supérieur.Les équations Korteweg-de Vries généralisées et l'équation de Zakharov-Kuznetsov sont des modèles asymptotiques classiques respectivement uni et bi-dimensionels pour la propagation d'ondes longues dans un milieu dispersif ayant une réponse non linéaire.Nous étudions le caractère bien posé local et global dans ''l'espace d'énergie" de ces équations dans un contexte assez général, où nous permettons à la solution d'évoluer autour d'une fonction bornée ��. Cela nous permet de fournir un cadre afin étudier l'évolution temporelle des perturbations localisées de kinks, ainsi que des perturbations localisées des solutions périodiques de chacune de ces équations. Les approches classiques basées sur une utilisation du théorème du point fixe de Banach ne peuvent pas aboutir dans cette configuration du fait de la perte d'une dérivée due à l'introduction de la fonction ��. Nous sommes donc amenés à nous tourner vers des raffinements de la méthode d'énergie. Nous utilisons deux approches différentes selon la dimension. La première approche repose sur une méthode introduite par Molinet-Vento qui utilise le caractàre fortement non résonant de l'équation de Korteweg-de Vries classique. Elle est de ce fait moins bien adaptée aux dimensions supérieures mais à l'avantage de donner en plus l'unicité inconditionnelle (unicité des solutions faibles). La deuxième approche repose sur l'utilisation des espaces Bourgain en temps courts, développée en particulier par Ionescu, Kenig et Tataru. Ici un choix approprié du rapport entre la longueur des petits intervalles de temps et l'inverse de la fréquence spatiale permet entre autre de rattraper la perte de dérivée.This thesis is composed of two independent parts. In the first part, we study the orbital and asymptotic stability of certain peaked solitary waves (peakons) of the Novikov equation. In the second part, we study the local and global well-posedness for certain Korteweg-de Vries type equations in dimensions one and two, when the problem is posed in the background of a bounded function without any particular spatial decay.The Novikov equation is a higher-order generalization of the Camassa-Holm equation. It has a cubic nonlinearity, is completely integrable, and keeps all the interesting (physically relevant) properties of the Camassa-Holm equation. For this equation, we start by revisiting the already known orbital stability results for peakons, and we establish the corresponding result for multi-peakons. Then, motivated by the approach developed for the Camassa-Holm equation, we show the asymptotic stability of peakons and multi-peakons of the Novikov equation. With this aim, we introduce in particular a new Lyapunov functional, which can be adapted to a large number of higher-order generalizations of the Camassa-Holm equation.The generalized Korteweg-de Vries equations and the Zakharov-Kuznetsov equation are classical asymptotic models, in dimensions one and two respectively, for the propagation of long waves in a dispersive medium with a nonlinear response. We study the local and global well-posedness of these equations in the "energy space", in a rather general context, where we allow the solution to evolve in the background of a bounded function ��. These results provide a framework for studying the time evolution of localized perturbations of Kinks, as well as localized non-periodic perturbations of periodic solutions for each of these equations. Classical approaches based on the use of Banach's fixed point theorem cannot succeed in the present configuration due to the loss of a derivative due to the introduction of the non-integrable background function ��. Thus, we are led to turn to refinements of the energy method. We use two different approaches depending on whether we are on the one- or two-dimensional case. The first approach is based on a method introduced by Molinet-Vento which uses the strongly non-resonant character of the classical Korteweg-de Vries equation. This method is not well suited to higher dimensional problems but has the advantage of providing, in addition, the unconditional uniqueness of solutions (uniqueness of weak solutions). The second approach is based on the use of short-time Bourgain spaces, introduced for the first time by Ionescu, Kenig, and Tataru. Here, an appropriate choice of the relationship between the length of the time intervals and the inverse of the spatial frequency allows us, among other things, to recover the derivative loss
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
Exact Controllability of Scalar Conservation Laws with an Additional Control in the Context of Entropy Solutions
No full textInternational audienceIn this paper, we study the exact controllability problem for nonlinear scalar con-servation laws on a compact interval, with a regular convex flux and in the framework of entropy solutions. With the boundary data and a source term depending only on the time as controls, we provide sufficient conditions for a state to be reachable in arbitrary small time. To do so we introduce a slightly modified wave-front tracking algorithm
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