1,721,083 research outputs found
On a connection between KAM and Nekhoroshev's theorem
No full textUsing the iteration of Nekhoroshev's theorem as a basic tool, we point out the existence of a hierarchic structure of nested domains underlying the phenomenon of diffusion. At each level we find that the diffusions speed is exponentially small with respect to the previous level. The set of KAM tori is the domain characterized by a zero diffusion speed
Superexponential stability of KAM tori
No full textWe study the dynamics in the neighborhood of an invariant torus of a nearly integrable system. We provide an upper bound to the diffusion speed, which turns out to be of superexponentially small size exp[-exp(1/σ)], σ being the distance from the invariant torus. We also discuss the connection of this result with the existence of many invariant tori close to the considered one
Invariant KAM tori and global stability for Hamiltonian systems
No full textWe point out a deep connection between KAM theorem and Nekhoroshev's theorem. Precisely, we reformulated the construction by Arnold of the set of invariant tori using Nekhoroshev's theorem as a basic tool. We prove in this way the existence of a hierarchic structure of nested domains characterized by a diffusion speed exponentially decreasing at each step. The set of KAM tori appears as the domain characterized by vanishing diffusion speed
On the role of high order resonances in normal forms and in separatrix splitting
No full textWe discuss the role of high order resonances in the construction of normal forms for ε-close to integrable Hamiltonian systems. By heuristic considerations based on standard estimates, we show that the remainder of normal forms is dominated by the terms corresponding to the main high order resonances, and we provide a general argument to show that the size of such leading terms is exponentially small in 1/ε. We apply this method to the problem of estimating the splitting of separatrices in resonant perturbed systems
Quantitative perturbation theory by successive eliminations of harmonics
No full textWe revisit some results of perturbation theories by a method of successive elimination of harmonics inspired by some ideas of Delaunay. On the one hand, we give a connection between the KAM theorem and the Nekhoroshev theorem. On the other hand, we support in a quantitative fashion a semi-numerical method of analysis of a perturbed system recently introduced by one of the authors
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Book Review: The Solar System Beyond Neptune, M. A. Barucci, H. Boehnhardt, D. P. Cruikshank, A. Morbidelli (Eds.)
No full textBook Review: The Solar System Beyond Neptune, M. A. Barucci, H. Boehnhardt, D. P. Cruikshank, A. Morbidelli (Eds.). Tucson, Arizona: The University of Arizona Press (2008).The Meteoritics & Planetary Science archives are made available by the Meteoritical Society and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform February 202
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
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
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