1,720,981 research outputs found
On the dynamical evolution of a young planetary system
Full text linkThe dynamical evolution of planetary and protoplanetary structures represents one of the major challenges for the modern Computational Astrophysics. The focus of our investigation is to study the dynamical evolution of a young planetary system both in isolation as well as embedded in a typical stellar open cluster. We simulate the whole system using the code GASPH (Pinto, Capuzzo-Dolcetta & Magni, 2019), an optimized SPH (Smoothed Particle Hydrodynamics) code which deals with self-gravity by mean of a tree-based scheme. Our young planetary system is composed by a central, solar like, star surrounded by a gaseous disk containing a fully formed Jovian planet. The disk is assumed as a marginally self-gravitating, ideal, gas and, to study its evolutionary properties, it is parameterized as an ensemble of SPH particles with an initial mass of 0.01 solar masses, essentially the value of the so called minimum solar mass nebula. We set our young planetary system in a typical open star cluster in order to study the gravitational perturbations induced by stellar flybys at varying the mass of the stellar perturber from 0.5 to 8 solar masses. We change the perturber periastron in the range of 100 - 500 AU and ,in order to investigate prograde and retrograde configurations, we vary its orbital inclination from 0 to 180 degrees. We followed the evolution of orbital planetary parameters like the semi-major axis and eccentricity. In addition, we investigated the accretion mass rate of the planet inside the disk, both during the stellar flyby and in the case without any external perturbation. In this frame, the dynamical evolution of the disk is quantified by the analysis of its Lagrangian radii. We confirmed the relevant role of the disk to catalyze the gravitational perturbation from the stellar perturber to the Jovian planet, converting the impulsive action of the stellar flyby to a softer long-time planet-disk interaction. We show the different role of retrograde and prograde perturber orbits for the dynamical evolution of a young planetary system in a stellar environment. Finally, our theoretical, simulative, study could be a support for exploratory astrophysics surveys in stellar clusters, aiming to the search of new young exoplanetary systems in such environments
Dynamical evolution of a young planetary system: stellar flybys in co-planar orbital configuration
No full textStellar flybys in star clusters may perturb the evolution of young planetary systems in terms of disk truncation, planetary migration and planetary mass accretion. We
investigate the feedback of a young planetary system during a single close stellar encounter in a typical open young stellar cluster. We consider 5 masses for the stellar perturbers:
0.5, 0.8, 1, 3 and 8 M, in coplanar, prograde and retrograde orbits respect to the planetary disk, varying the perturberhost star orbital periastron from 100 au to 500 au. We have
made 3D modelizations with the smooth particle hydrodynamics code GaSPH of a system composed by a solar type star surrounded by a low density disk where a giant planet is
embedded in. We focus on the dynamical evolution of global parameters characterizing the disk and the planet, like the
Lagrangian radius containing the 63.2% of the mass of the disk, the distance of the planet to its host star, the planet orbital eccentricity and the planetary mass accretion. We find
that the most part of the simulated systems show a significant disk truncation after a single close encounter, a final orbital distance of the Jovian, from the central star, lower
than the unperturbed case and, finally, the perturbed systems show a final mass accretion of the Jovian planet larger than the non-perturbed case. Therefore, stellar flybys significantly perturb the dynamics of a young planetary system, regardless the orbital configuration of the stellar perturber.
In such experiments, the final disk radius and the orbital parameters of the Jovian planet are considerably affected by the stellar close encounter
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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