1,721,150 research outputs found
Capture of Trojan's by growing proto-Jupiter
No full textWe have studied the capture of planetesimals in Trojan orbits by a growing proto-Jupiter by integrating numerically the equations of motion of planetesimals in a four-body problem Sun-Jupiter-Saturn-planetesimal. The masses of Jupiter and Saturn increase exponentially with time. Nebular gas drag on small planetesimals is taken into account. We show that a fraction of the planetesimals near Jupiter's orbit and almost all planetesimals originally in horseshoe orbits are trapped into stable Trojan orbits. This mechanism was probably an important factor together with collisional diffusion, for delivering a large amount of planetesimals into Trojan orbits during the final growth of Jupiter by gas in-fall. We find also that the libration amplitude of trapped Trojans is damped by the increase of Jupiter's mass reinforcing the stability of the resonance lock. For planetesimals small enough to be perturbed by nebular gas drag, we find an asymmetry between the trapping rate in L5 compared to L4. Peale (1993, Icarus 106, 308-322) noted also that the stability of the L4 resonant region is reduced in presence of an intense frictional drag. We present here a simple semi-analytical explanation for the trapping asymmetry based on the evolution of the angular difference between the planetesimal's and proto-Jupiter's longitude of perihelion. The asymmetry between L4 and L5 could have led to the capture of a larger number of small planetesimals in L5. This may have favored a higher degree of collisional activity in L5 and might explain an alleged asymmetry in the size distribution of the two swarms
Stability of Jupiter Trojans investigated using frequency map analysis: the MATROS project
No full textUsing the frequency map analysis (FMA) method we investigate the stability properties of Trojan-type orbits in the proximity of the L4 and L5 Lagrangian points of Jupiter. This study is part of the MATROS project. The orbits of about 2 × 104 virtual Trojans with random initial conditions have been computed numerically and for each body the diffusion rate in frequency space has been determined by spectral analysis. The diffusion portraits show where stable orbits are located in the space of proper elements for different values of inclination. For low inclined orbits we reproduce the stability region outlined by Levison, Shoemaker & Shoemaker and, due to our fast sampling capability, we find additional resonant features in the libration amplitude versus proper eccentricity space. At higher inclinations, the stability region gradually shrinks and it disappears for inclinations of about 40°. The maximal Lyapunov characteristic exponent is computed for a limited number of Trojan orbits in our sample and the predictions concerning the chaotic behaviour of each orbit are compared with those given by the FMA method. A good agreement is obtained and the value of the Lyapunov exponent may be used to tune the results of the FMA analysis. A synthetic secular theory for the proper frequencies of Jupiter Trojans is obtained by numerically fitting the outcome of th
Collision rates and impact velocities in the Trojan asteroids swarms
No full textCollision rates and impact velocities for Trojan asteroids have been estimated by a robust numerical approach, based on a parallel computation of orbits over time spans of ~10^4 year and the subsequent statistical analysis of the resulting close encounter data bases. The average intrinsic collision probabilities for the two Trojan swarms are 6.46 x 10^-18 km^-2 year^-1 (L_4) and 5.30 x 10^-18 km^-2 year^-1 (L_5), namely about twice the corresponding value for the main asteroid belt. Collision speeds range from ~1 to 14 km/sec, with a mean value close to 5 km/sec. These findings suggest that the intensity of the collisional process is about the same in the Trojan swarms as in the main belt, and are consistent with the detection of dynamical families among Trojans. The collisional flux in the Trojan regions is very anisotropic, with a dominant component perpendicular to the invariable plane. Subtle dynamical mechanisms are likely to somewhat affect the Trojan collision rates, but their understanding requires further work on the very long-term evolution of Trojan orbits
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
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