1,721,022 research outputs found
COMPUTATION OF TRANSIT ORBITS IN THE THREE-BODY-PROBLEM WITH FAST LYAPUNOV INDICATORS
No full textWe describe in this paper how to compute special orbits of the three-body-problem which transit from a region which is internal to the secondary mass to the region which is external to the binary system, by using a recent variant of the Fast Lyapunov Indicator method. The orbits are obtained by slightly changing the initial conditions of orbits which are heteroclinic to Lyapunov orbits of the Lagrangian equilibrium points L1 and L2 of the restricted three-body-problem
Theory and applications of fast Lyapunov indicators to model problems of celestial mechanics
No full textIn the last decades, we have seen a rapid increment in the use of finite-time chaos indicators in celestial mechanics. They have been used to analyze the complex dynamics of planetary systems, of minor planets and of space debris. In fact, theoretical studies on fundamental dynamical models have revealed that, computed on short time intervals, they allow to efficiently detect resonances, represent the phase portraits of complex dynamics, compute center-stable-unstable manifolds as well as Lagrangian coherent structures. In this paper, we focus on applications of the fast Lyapunov indicator (FLI) and review through examples why its computation is particularly powerful for those systems whose solutions may have an
asymptotic behavior very different from the short-term one, as it is the case of sequences of close encounters in gravitational systems and the advection of particles in aperiodic flows. The main case study here considered is the computation of the manifold tubes and the related transit orbits in the restricted three-body problem. We also provide a new application of the FLI to
a complex problem of planetary hydrodynamics, such as the detection of the stable and unstable manifolds guiding the motions of particles advected by the gas of a protoplanetary nebula
Scenarios for the dynamics of comet 67P/Churyumov-Gerasimenko over the past 500 kyr
No full textThe complex dynamics of 67P has the typical uncertainties of the Jupiter-family comets. The
Rosetta mission provided a unique opportunity to dissipate them with fresh experimental data.
We aim to constrain the residence time of the comet in a dynamics dominated by Jupiter and
Saturn by comparing statistics of large sets of numerical integrations with assumptions on
the erosion experienced by the comet. We integrated backward for 150 kyr 2000 clones of
67P selected from preliminary integrations of 500 000 clones. We find that the clones that
did not arrive from hyperbolic/parabolic orbits have been mostly in the region dominated by
Jupiter and Saturn in the last 150 kyr; they transit easily between dynamics dominated by
Jupiter, dynamics also dominated by Saturn and, with smaller probability, by Saturn alone.
Many clones were injected in the Jupiter family from hyperbolic orbits and orbits of large
periods P > 500 yr, but none of the clones was injected from a Uranus-dominated dynamics
through sequences of planetary scatterings, while 5 per cent of the clones were injected on this
route in 500 kyr. 60 per cent of the clones had already been in an orbit with q < 1.5 au before
1959. Compatible with the uncertainties on the long-term model of non-gravitational forces,
we conclude that 67P was injected from a cometary reservoir into a dynamics dominated by
Jupiter and Saturn at an epoch that we estimate as being in between 30 and 150 kyr ago; this
interval should be extended by considering periods of dormancies
From Discrete to Continuous Dynamical Systems and Vice-versa. Application to a Neo-Austrian Representation of the Production Process.
No full textThis paper deals with the relations between the solution of dynamical systems whose equations, either discrete or continuous originate from the same model. We introduce the problem for a simple physical model : the pendulum. We discuss then a neo-Austrian representation of the production process. Finally we present a general numerical method which allows to transform a continuous problem into a discrete one.Cet article traite des relations entre les solutions d'un système dynamique dont les équations, discrètes ou continues, concernent le même modèle. Nous avons introduit le problème pour un simple cas physique : le pendule. Nous avons, par la suite, discuté la représentation néo-autrichienne du processus de production. On présente enfin une méthode numérique générale pour la transformation d'un problème continu dans un problème discret.Froeschle Claude, Lega Elena. From Discrete to Continuous Dynamical Systems and Vice-versa. Application to a Neo-Austrian Representation of the Production Process. In: Revue économique, volume 46, n°6, 1995. pp. 1511-1526
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
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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