1,720,954 research outputs found
Space weathering and tidal effects among near-Earth objects
No full textThe spectral slope of sunlight reflected by an asteroid surface may change with time due to several physical processes acting on the surface (``space weathering''). We present a general and significant relation between the spectral slope of silicate--rich near-Earth and Main Belt asteroids and the "exposure" to space weathering. We find strong evidences that the Sun-related processes dominate the space weathering. Moreover, by using a large data set of spectroscopic observations of planet--crossing asteroids (near--Earth objects and Mars--crossers), we found a statistically significant correlation between their spectral slope and the perihelion distance. The correlation could be due to tidal effects: during a close encounter with a terrestrial planets tides may partially, or even completely, remove the old and the weathering process. The effects have to be combined to understand the evolution of optical properties of NEAs with time
A spectral slope versus perihelion distance correlation for planet-crossing asteroids
No full textThe spectral slope of sunlight reflected by an asteroid surface may change with time as a result of several physical processes acting on the surface layer known as `space weathering'. The effects of space weathering are important for asteroid studies because they may help us to explain the paucity of spectroscopic analogues of ordinary chondrites (OCs) among the main belt asteroids.
In this Letter we report a new result that may be used to understand better how asteroid surfaces evolve with time. Using a large data set of spectroscopic observations of planet-crossing asteroids (near-Earth objects and Mars-crossers), we have found a statistically significant correlation between their spectral slope and the perihelion distance. We have also determined that the Q- and Sq-type planet-crossing asteroids are more abundant (relative to more space-weathered S-type asteroids) at small perihelion distances that characterize dynamically evolved orbits.
We take these results as evidence for some (so far neglected) process that modifies surfaces of planet-crossing asteroids. As originally proposed by Nesvorný et al., the close encounters of these objects with the terrestrial planets may produce tidal perturbations to their surfaces that may partially, or even completely, remove the old and weathered layers and expose non-weathered OC-like material. Our findings may provide new evidence for this process because standard models for the dynamical evolution of asteroids show that planet-crossing asteroids with small perihelion distances have undergone more frequent planetary encounters than those residing in more distant orbits. Therefore, if planetary encounters are important, the distribution of Q-type asteroids in the planet-crossing space should show a correlation with the perihelion distance, exactly as we have found here
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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