1,720,965 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
Dinâmica pullback de equações da onda supercríticas em variedades Riemannianas compactas
No full textThis thesis is concerned with large-time dynamics of non-autonomous wave equations defined on compact Riemannian manifolds with boundary. It contains three main contributions. First, we give a detailed proof of well-posedness for the wave equation with supercritical nonlinearities and time-dependent external forces, on the energy space. It is a slight generalization of known results for autonomous problems. However our arguments are different. Thus, the wave problem can be studied as a non-autonomous dynamical system since its finite energy solution flows define a continuous evolution process. Next, we establish the existence of pullback exponential attractors to this non-autonomous system, such that any section have finite fractal dimensions on the natural energy space. Finally, in the case of external force is dependent on a parameter, we study the continuity of pullback attractors with respect to it.A presente tese é dedicada ao estudo da dinâmica a longo-prazo de equações de ondas definidas em variedades Riemannianas compactas com bordo. Apresentamos três resultados principais. Primeiramente, estudamos a boa colocação do problema com não linearidades supercríticas e forças dependente do tempo. O resultado é uma extensão dos trabalhos anteriores para o caso autônomo. Entretanto a nossa abordagem é diferente. Assim, nosso problema gera um processo de evolução e pode ser estudado como um sistema dinâmico não autônomo. Em seguida, mostramos a existência de atratores pullback exponencial, o qual toda seção possui dimensão fractal finita no espaço de energia. Por fim, no caso em que a força externa depende de um parâmetro, estudamos a continuidade dos atratores em relação ao parâmetro
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
Attractors for non-autonomous wave equations with acoustic boundary condition
No full textEsta tese é dedicada ao estudo de uma classe de equações de ondas com condições de fronteira da acústica. Investigamos a dinâmica assintótica de tais equações no caso em que o sistema está sujeito à ação de uma força externa não autônoma. Nessa situação, adicionando uma dissipação fraca, provamos que o problema gera um processo de evolução dissipativo. O nosso objetivo é então o estudo da existência de atratores não autônomos. Num primeiro momento estabelecemos a existência de um atrator do tipo \\pullback\", minimal, dentro de um universo de conjuntos temperados. Também estudamos a semicontinuidade superior dos atratores quando a perturbação não autônoma tende para zero. Nosso resultado permite considerar forcas externas não limitadas e perturbações não lineares com crescimento crítico (de Sobolev). Num segundo momento, fazemos um estudo sobre a existência de atratores uniformes. Em vista de resultados recentes de Zelik (2015), consideramos forcas externas mais gerais do que a dita classe das forcas compactas por translação (translation-compact). Parte desta tese foi aceita para publicação na revista \\Differential and Integral Equations\" sob o ttulo \\Pullback dynamics of non-autonomous wave equations with acoustic boundary condition\".This thesis is concerned with the study of a class of wave equations with acoustic boundary conditions. We investigate the long-time dynamics of such equations in the case where the system is subject to a non-autonomous external force. In this situation, by adding a weak dissipation, we prove that the problem generates a dissipative evolution process. Our goal is then the existence of non-autonomous attractors. In this direction, we first establishes the existence of a minimal pullback attractor within a universe of tempered sets. We also studied the upper semi-continuity of attractors when the non-autonomous perturbation tends to zero. Our result allows to consider unbounded external forces and nonlinear perturbation with critical (Sobolev) growth. Secondly, we establish the existence of uniform attractors, as well. In view of recent results Zelik (2015) we consider more general external forces than the so called class of translation-compact forces. Part of this thesis was accepted for publication in the journal \\Differential and Integral Equations\" under the title \\Pullback dynamics of non-autonomous wave equations with acoustic boundary condition\"
Global attractors for a viscoelastic equation nonlinear with history
No full textNeste trabalho estudamos uma classe de equações de ondas da forma ∣∂tu∣p ∂ ttu - Δ∂ttu - αu + ∫∞0µ(s)Δu(t - s)ds +F(u) = h, definida num domínio limitado de R3, com condição de fronteira de Dirichlet e parâmetros α, ρ >0. Tais equações modelam problemas de viscoelasticidade não linear e têm sido estudados por diversos autores. Aqui, apresentamos um teorema de existência, unicidade e dependência contínua em relação aos dados iniciais, para soluções fracas, como discutido por Conti, Marchini & Pata (2014). Em seguida provamos um teorema novo sobre a existência de atratores globais para o sistema dinâmico associado ao problema, explorando tão somente a dissipação dada pelo termo de memória. Tal resultado generaliza substancialmente o trabalho pioneiro de Araújo, Ma & Qin (2013).In this work we study a class of wave equations of the form ∣∂tu∣p ∂ ttu - αΔu + ∫∞0µ(s)Δu(t - s)ds +f(u) = h, defined in a bounded domain of R3, with Dirichlet boundary condition and parameters α, ρ > 0. Such equations model problems from nonlinear visco-elasticity and have been considered by several authors. Here, we prove the well-posedness of the problem, as discussed by Conti, Marchini & Pata (2014). Next, we prove a new result on the existence of global attractors for the dynamical system generated by the problem, by exploring the dissipation the memory term only. The result extends substantially the pioneering work by Araújo, Ma & Qin (2013)
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
Dinâmica assintótica de equações de onda sobre variedades Riemannianas compactas: dissipação localizada ótima e forças supercríticas
No full textThe present thesis is concerned with long-time dynamics of wave equations, defined on compact Riemannian manifolds, with boundary, and featuring localized damping and nonlinear forcing terms with supercritical Sobolev growth. The main objective is to construct optimal damping regions with arbitrarily small summed interior/boundary measure that imply the existence of a regular finite-dimensional global attractor. To this end, among other results, we prove a supercritical extension of a unique continuation theorem of Triggiani and Yao (2002).A presente tese é dedicada ao estudo da dinfimica a longo prazo de equaqées de ondas definidas sobre variedades Riemannianas compactas, com bordo, que possuam dissipagfio localizada e forgas corn crescimento Sobolev supercrltico. O objetivo principal é construir regiées de dissipagao com medida total (interior c fronteira) arbitrariamente pcquena, de forma a garantir a existéncia de atratores globais regulates dc dimensao finita. Entre outros resultados, provaremos uma versfio supercritica de um teorema de continuagao finica de Triggiani and Yao (2002
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
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