1,720,977 research outputs found
From Kolmogorov's Normalization Algorithm to the Orbits in the Three-Body Planetary Problem
No full text
Sulla stabilità del problema planetario dei tre corpi
Full text linkSi discute se il celebre teorema di Kolmogorov sulla persistenza di moti quasi periodici si applichi al sistema solare, prendendo a modello il problema dei tre corpi nel caso in cui le masse ed i parametri orbitali siano quelli di Sole, Giove e Saturno. Facendo ricorso a metodi di manipolazione algebrica al calcolatore si mostra per la prima volta che almeno in questo caso il teorema si puo' applicare, e dunque che le orbite dei due pianeti maggiori, almeno nell'approssimazione del problema dei tre corpi, giacciono in prossimita' di tori invarianti di Kolmogorov. Si discutono poi brevemente le possibili estensioni di questo lavoro accennando alla possibilita' di affrontare il problema classico della stabilita' del sistema solare alla luce della teoria della stabilita' esponenziale alla Nekhoroshev
On classical series expansions for quasi-periodic motions
No full textWe reconsider the problem of convergence of classical
expansions in a parameter for quasiperiodic motions on
invariant tori in nearly integrable Hamiltonian systems. Using a
reformulation of the algorithm proposed by Kolmogorov, we show that if
the frequencies satisfy the nonresonance condition proposed by Bruno,
then one can construct a normal form such that the coefficient of
is a sum of terms each of which is bounded by
. This allows us to produce a direct proof of the classical
expansions. We also discuss some relations between our
expansions and the Lindstedt's ones
Invariant tori in the Sun-Jupiter Saturn system
No full textWe discuss the applicability of Kolmogorov’s theorem on existence of invariant tori to the real Sun–Jupiter–Saturn system. Using computer algebra, we construct a Kolmogorov’s normal form defined in a neighborhood of the actual orbit in the phase space, giving a sharp evidence of the convergence of the algorithm. If not a rigorous proof, we consider our calculation as a strong indication that Kolmogorov’s theorem applies to the motion of the two biggest planets of our solar system
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
Kolmogorov theorem and classical perturbation theory
No full textWe reconsider the original proof of Kolmogorov's theorem in
the light of classical perturbation methods based on expansions in some
parameter. With a careful analysis of the accumulation of small divisors
we prove that their effect is bounded by a geometrically increasing
numerical sequence. This allows us to achieve the proof without using
the so called quadratic method.
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
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
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