1,721,073 research outputs found
Atmospheric precipitation analysis in desert area using both disdrometers and satellite data
No full textInvariant KAM Tori: From Theory to Applications to Exoplanetary Systems
No full textWe consider the classical problem of the construction of invariant tori exploiting suitable Hamiltonian normal forms. This kind of approach can be translated by means of the Lie series method into explicit computational algorithms, which are particularly suitable for applications in the field of Celestial Mechanics. First, the algorithm constructing the Kolmogorov normal form is described in detail. Then, the extension to lower-dimensional elliptic tori is provided. We adopt the same formalism and notations in both cases, with the aim of making the latter easier to understand. Finally, they are both used in a combined way in order to approximate carefully the secular dynamics of the extrasolar system hosting two planets orbiting around the HD 4732 star
A numerical criterion evaluating the robustness of planetary architectures; applications to the υ Andromedæ system
Full text linkWe revisit the problem of the existence of KAM tori in extrasolar planetary systems. Specifically, we consider the υ Andromedæ system, by modelling it with a three-body problem. This preliminary study allows us to introduce a natural way to evaluate the robustness of the planetary orbits, which can be very easily implemented in numerical explorations. We apply our criterion to the problem of the choice of a suitable orbital configuration which exhibits strong stability properties and is compatible with the observational data that are available for the υ Andromedæ system itself
Thesaurus Maintenance, Alignment and Publication as Linked Data: The AGROVOC Use Case
Full text linkThe AGROVOC multilingual thesaurus maintained by the Food and Agriculture Organization of the United Nations (FAO) is now published as linked data. In order to reach this goal AGROVOC was expressed in Simple Knowledge Organization System (SKOS), and its concepts provided with dereferenceable URIs. AGROVOC is now aligned with ten other multilingual knowledge organization systems related to agriculture, using the SKOS properties exact match and close match. Alignments were automatically produced in Eclipse using a custom-designed tool and then validated by a domain expert. The resulting data is publicly available to both humans and machines using a SPARQL endpoint together with a modified version of Pubby, a lightweight front-end tool for publishing linked data. This paper describes the process that led to the current linked data AGROVOC and discusses current and future applications and directions
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
Elliptic tori in FPU non-linear chains with a small number of nodes
Full text linkWe revisit an algorithm constructing elliptic tori, that was originally designed for applications to planetary hamiltonian systems. The scheme is adapted to properly work with models of chains of N + 1 particles interacting via anharmonic potentials, thus covering also the case of FPU chains. After having preliminarily settled the Hamiltonian in a suitable way, we perform a sequence of canonical transformations removing the undesired perturbative terms by an iterative procedure. This is done by using the Lie series approach, that is explicitly implemented in a programming code with the help of a software package, which is especially designed for computer algebra manipulations. In the cases of FPU chains with N = 4 , 8 , we successfully apply our new algorithm to the construction of elliptic tori for wide sets of the parameter ruling the size of the perturbation, i.e., the total energy of the system. Moreover, we explore the stability regions surrounding 1D elliptic tori. We compare our semi-analytical results with those provided by numerical explorations of the FPU-model dynamics, where the latter ones are obtained by using techniques based on the so called frequency analysis. We find that our procedure works up to values of the total energy that are of the same order of magnitude with respect to the maximal ones, for which elliptic tori are detected by numerical methods. ? 2021 Elsevier B.V. All rights reserved
Computer-assisted estimates for birkhoff normal forms
Full text linkBirkhoff normal forms are commonly used in order to ensure the
so called “effective stability” in the neighborhood of elliptic equilibrium points
for Hamiltonian systems. From a theoretical point of view, this means that
the eventual diffusion can be bounded for time intervals that are exponen-
tially large with respect to the inverse of the distance of the initial conditions
from such equilibrium points. Here, we focus on an approach that is suitable
for practical applications: we extend a rather classical scheme of estimates
for both the Birkhoff normal forms to any finite order and their remainders.
This is made for providing explicit lower bounds of the stability time (that
are valid for initial conditions in a fixed open ball), by using a fully rigorous
computer-assisted procedure. We apply our approach in two simple contexts
that are widely studied in Celestial Mechanics: the Hénon-Heiles model and
the Circular Planar Restricted Three-Body Problem. In the latter case, we
adapt our scheme of estimates for covering also the case of resonant Birkhoff
normal forms and, in some concrete models about the motion of the Trojan
asteroids, we show that it can be more advantageous with respect to the usual
non-resonant ones
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