1,721,076 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
Some applications of harmonic analysis to control theory
No full textCette thèse explore des questions fondamentales en théorie du contrôle et en analyse de l’observabilité des équations aux dérivées partielles, en se concentrant sur deux thèmes interconnectés : la null-contrôlabilité des systèmes paraboliques via des inégalités spectrales, et l’observabilité des équations dispersives par des méthodes d’analyse harmonique. Le premier thème porte sur les inégalités spectrales et leur rôle dans la null-contrôlabilité des équations de type chaleur. Pour des opérateurs de Schrödinger unidimensionnels, nous établissons de nouvelles inégalités spectrales sur des ensembles épais à densité décroissante, en exploitant les propriétés de propagation de la petitesse pour les solutions d’équations elliptiques dans le plan. Ces inégalités permettent de déduire directement des résultats de null-contrôlabilité via la méthode de Lebeau-Robbiano. De plus, nous analysons les opérateurs de Baouendi–Grushin en construisant des inégalités spectrales dépendant explicitement des paramètres des potentiels. Cela conduit à des preuves de null-contrôlabilité pour des équations de type chaleur de Baouendi–Grushin posées sur des bandes verticales équidistribuées, élargissant ainsi les résultats antérieurs sur les opérateurs hypoelliptiques. Le second thème étudie des estimations de normes L2 et L1 pour des polynômes trigonométriques non harmoniques à fréquences éparses, ainsi que leurs applications à l’observabilité dans les équations dispersives. Pour des équations dispersives linéaires sur le tore, nous relions l’inégalité d’Ingham à des critères d’observabilité pour des segments de ligne définis par leur pente. Nous prouvons également des bornes inférieures pour les normes L1 de polynômes trigonométriques non harmoniques, résultats applicables à l’établissement d’estimées d’observabilité en L1 pour des équations aux dérivées partielles telles que l’équation de Schrödinger libre.This thesis investigates fundamental questions in the control theory and observability analysis of partial differential equations, focusing on two interconnected themes: nullcontrollability of parabolic systems via spectral inequalities, and observability of dispersive equations through harmonic analytic methods. The first theme centers on spectral inequalities and their role in the null-controllability of heat-like equations. For one-dimensional Schrödinger operators, we derive new spectral inequalities on thick sets with decaying density by leveraging propagation of smallness properties for solutions of elliptic equations in the plane. These inequalities enable us to deduce null-controllability results directly via the Lebeau-Robbiano method. Additionally, we analyze Baouendi–Grushin operators by constructing spectral inequalities with explicit dependence on potential parameters. This leads to null-controllability for Baouendi–Grushin heat-like equations posed on equidistributed vertical strips, expanding prior results on hypoelliptic operators. The second theme investigates L2- and L1-norm estimates for nonharmonic trigonometric polynomials with sparse frequencies and their applications to observability in dispersive equations. For linear dispersive equations on the torus, we link Ingham’s inequality to observability criteria for line segments defined by their slopes. We also establish lower bounds for L1-norms of nonharmonic trigonometric polynomials. This can be applied to establish L1-observability estimates for PDEs such as the free Schrödinger equation
The phase retrieval problem for the Radar Ambiguity Function and vice versa
No full textInternational audienceThe first part of this note is based on a joint paper with A. Bonami and G. Garrigós [3] in which the phase retrieval problem for the Radar Ambiguity Function (i.e. the Radar Ambiguity Problem) has been tackled. In particular it was shown that for wide classes of signals, the radar ambiguity problem has a unique solution, up to trivial transformations. In the second part of this note, we report on ongoing work by the author where the radar ambiguity function is used as a tool to solve other phase retrieval problems
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
The Littlewood problem and non-harmonic Fourier series
No full textNous étudions les polynômes trigonométriques à la fois dans le cadre harmonique et non-harmonique (non-périodique). Plus précisément, nous nous intéressons aux bornes inférieures au sens de la norme L1 et de la norme B1 (de Besicovitch) de ces polynômes. D’abord, nous considérons les polynômes trigonométriques avec des fréquences quadratiques et des coefficients complexes. Nous étendons ainsi les résultats précédents sur les polynômes ayant seulement zéro ou un comme coefficients. Pour les polynômes à coefficients monotones et uniformément bornés, nous obtenons une minoration de la norme L1 par la racine du nombre de termes. Ensuite, nous donnons aussi des bornes inférieures explicites pour les normes L1 et B1 de tels polynômes. Lorsque les polynômes n’ont que zéro ou un comme coefficients, nous en déduisons une minoration de la norme L1 ou B1 par le logarithme du nombre de termes. Nous nous intéressons aussi aux polynômes trigonométriques non-harmoniques tels que les différences successives entre les fréquences tendent vers l’infini. Nous donnons des minorations de la norme L1 pour de tels polynômes. Enfin, nous étudions deux types de polynômes trigonométriques. D’une part ceux dont les fréquences sont lacunaires et d’autre part, ceux dont les fréquences ayant une structure multidimensionnelle. Nous étendons plusieurs résultats du cas entier au cas non-entier. Nous obtenons des bornes inférieures pour la norme B1 pour de tels polynômes.We investigate trigonometric polynomials both in the harmonic and the nonharmonic (non-periodic) case. More precisely, we are interested in lower bounds for L1- norms or B1-norms (Besicovitch-norms) of such polynomials. We study harmonic trigonometric polynomials with quadratic frequencies. We extend previous results for polynomials having only zero or one as coefficients to polynomials with complex coefficients. Furthermore, we obtain that up to a multiplicative constant, the square root is a lower bound for the L1-norms of polynomials with monotone and uniformly bounded coefficients. Next, we give explicit lower bounds for L1 and B1-norms of non-harmonic trigonometric polynomials. If the polynomials have only zero or one as coefficients, we deduce a logarithmic lower bound for its L1 or B1-norms with respect to the number of terms. Afterwards, we look at non-harmonic trigonometric polynomials with gaps (between the frequencies) going to infinity. We give lower bounds for the L1-norm of such polynomials. Finally, we investigate two particular trigonometric polynomials: Lacunary and polynomials with frequencies having multidimensional structure. We extend multiple results from the integer to non-integer case. We obtain lower bounds for B1-norms of such polynomials
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe 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
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
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