1,720,976 research outputs found
Chaotic orbit determination in the context of the JUICE mission
No full textTidal dissipation within Io and Jupiter leads to a migration of the Galilean satellites. In fact, the resonant interaction between Io, Europa and Ganymede spreads the dissipative effects from Io to the orbits of the other moons. The amount of the loss of energy and the consequent rate of the orbital evolution was determined in (Lainey et al., 2009), along with the dissipative parameters k2/Q of Io and Jupiter. Although this could be considered the most reliable result in literature, there are other articles with different solutions of the moons migration. In this context, the future ESA space mission JUICE can play a key role: during its flybys tour of the Galilean satellites and an orbiting phase around Ganymede, it will provide new extremely accurate observations of the Jovian system, with which it will be possible to constrain moons’ physical properties and orbits. In particular, in this study we investigate the possibility of performing an independent estimation of the k2/Q parameters using JUICE data. However, the multiple flybys trajectory is well known to be chaotic, raising critical issues both in the design of the mission and in the orbit determination experiments. In this article we present the results of simulations using JUICE data from two different experiments (3GM and PRIDE). Differently from (Dirkx et al., 2017), we perform a simultaneous estimation of the spacecraft and Galilean satellites’ orbits, along with some dynamical parameters of interest. We will show that adopting the constrained multi-arc strategy during the chaotic phase, we manage to improve the determination of the dissipative parameters, as expected by (Serra et al., 2018). Although a complete estimation of all the relevant parameters will be addressed in future works, in this preliminary study we find a formal uncertainty of the two k2/Q of the same order of (Lainey et al., 2009). This implies that the content of information provided by JUICE is similar to the one hundred years astrometric observations used in the same article. Therefore, with JUICE data we will be able to check results and theories of previous studies about the dissipation in the Jovian system, and once added to the other available data sets, we could get a more accurate solution, covering a time span greater than the 4 years of the mission
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
Orbit determination methods for interplanetary missions: development and use of the Orbit14 software
No full textIn the last years, a new generation of interplanetary space missions have been designed for the exploration of the solar system. At the same time, radio-science instrumentation has reached an unprecedented level of accuracy, leading to a significant improvement of our knowledge of celestial bodies. Along with this hardware upgrade, software products for interplanetary missions have been greatly refined. In this context, we introduce Orbit14, a precise orbit determination software developed at the University of Pisa for processing the radio-science data of the BepiColombo and Juno missions. Along the years, many tools have been implemented into the software and Orbit14 capitalized the experience coming from simulations and treatment of real data. In this paper, we present a review of orbit determination methods developed at the University of Pisa for radio-science experiments of interplanetary missions. We describe the basic theory of the process of parameters estimation and refined methods necessary to have full control on experiments involving spacecraft orbiting millions of kilometers far from the Earth. Our aim is to give both an extensive description of the treatment of radio-science experiments and step-to-step instructions for those who are approaching the field of orbit determination in the context of space missions. We show also the work conducted on the Juno and BepiColombo missions by means of the Orbit14 software. In particular, we summarize the recent results obtained with the gravity experiment of Juno and the simulations performed so far for the gravimetry-rotation and relativity experiments of BepiColombo
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
The past and future obliquity of Saturn as Titan migrates
No full textContext. Giant planets are expected to form with near-zero obliquities. It has recently been shown that the fast migration of Titan could be responsible for the current 26.7◦ -tilt of Saturn’s spin axis.
Aims. We aim to quantify the level of generality of this result by measuring the range of parameters allowing for this scenario to happen. Since Titan continues to migrate today, we also aim to determine the obliquity that Saturn will reach in the future.
Methods. For a large variety of migration rates for Titan, we numerically propagated the orientation of Saturn’s spin axis both backwards and forwards in time. We explored a broad range of initial conditions after the late planetary migration, including both small and large obliquity values.
Results. In the adiabatic regime, the likelihood of reproducing Saturn’s current spin-axis orientation is maximised for primordial obliquities between about 2◦ and 7◦ . For a slightly faster migration than expected from radio-science experiments, non-adiabatic effects even allow for exactly null primordial obliquities. Starting from such small tilts, Saturn’s spin axis can evolve up to its current state provided that: (i) the semi-major axis of Titan changed by more than 5% of its current value since the late planetary migration, and (ii) its migration rate does not exceed ten times the nominal measured rate. In comparison, observational data suggest that the increase in Titan’s semi-major axis exceeded 50% over 4 Gyr, and error bars imply that the current migration rate is unlikely to be larger than 1.5 times its nominal value.
Conclusions. If Titan did migrate substantially before today, tilting Saturn from a small obliquity is not only possible, but it is the most likely scenario. Saturn’s obliquity is still expected to be increasing today and could exceed 65◦ in the future. Maximising the likelihood would also put strict constraints on Saturn’s polar moment of inertia. However, the possibility remains that Saturn’s primordial obliquity was already large, for instance as a result of a massive collision. The unambiguous distinction between these two scenarios would be given by a precise measure of Saturn’s polar moment of inertia
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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