1,721,135 research outputs found
Investigating the neutral sodium emissions observed at comets
Full text linkNeutral sodium emission is typically very easy to detect in comets, and has been seen to form a distinct neutral sodium tail at some comets. If the source of neutral cometary sodium could be determined, it would shed light on the composition of the comet, therefore allowing deeper understanding of the conditions present in the early solar system. Detection of neutral sodium emission at other solar system objects has also been used to infer chemical and physical processes that are difficult to measure directly. Neutral cometary sodium tails were first studied in depth at comet Hale-Bopp, but to date the source of neutral sodium in comets has not been determined. Many authors considered that orbital motion may be a significant factor in conclusively identifying the source of neutral sodium, so in this work details of the development of the first fully heliocentric distance and velocity dependent orbital model, known as COMPASS, are presented. COMPASS is then applied to a range of neutral sodium observations, including spectroscopic measurements at comet Hale-Bopp, wide field images of comet Hale-Bopp, and SOHO/LASCO observations of neutral sodium tails at near-Sun comets. The author finds that COMPASS is relatively successful at reproducing the morphology of the neutral sodium tails seen in wide field images, and to a lesser extent the intensity profiles produced by spectroscopic measurements. The success of COMPASS indicates that the current understanding of the physics of the production and evolution of neutral cometary sodium is broadly accurate. Using a simplistic dust tail source the author also finds that a source of neutral sodium within the dust tail is likely to result in a secondary neutral sodium tail feature, that has not yet been observed to the best of their knowledge
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
Cassini observations of ionospheric plasma sources and plasma distribution in Saturn’s magnetosphere
Full text linkThis thesis utilises data from the Cassini spacecraft in the analysis of the Saturnian system focusing on two areas of research. The first is estimating the impact of the ionosphere as a plasma source in the system, from a case study that uses data from the thermal plasma spectrometer, the UV imager, the energetic particle detectors, and radio and plasma wave detector, when the spacecraft was located at ~ 2200 hours Saturn local time at 36 RS in Saturns magnetotail, and the second consists in a survey of the bulk plasma composition using time-of-flight data from CAPS/IMS, from 2004 to 2013, that is, at the moment, the most extensive survey conducted on TOF/IMS data. We find the first evidence of polar ionospheric outflow from Saturn. During several entries into the magnetotail lobe, cold ions (mainly H+ and (m/q=2)), and electrons, dispersed in energy, were observed directly adjacent to the plasma sheet and, apparently, extending into the lobe. Moreover, ions were flowing downtail. The unique nature of this event led to two survey studies, with different resolutions and coordinate systems, to investigate typical and atypical characteristics in bulk plasma composition and its relations to Enceladus, Dione, Rhea, and Titan. We studied [(m/q=2)]/[H+], [W+]/[H+], and [O+, OH+, H2O+, H3O+]/[W+] ratios, where we indicate with W+ ions produced from water, as a function of position in the magnetosphere, radial distance and local time, and distance from the planet and longitude in respect to the moons. We found that the plasma composition in Saturn’s magnetosphere presents significant local time asymmetries and variability. Some evidence of displacement of the stagnation point towards earlier local times (~ 1900 LT) compared to Cowley et al. [2004]’s plasma circulation model, suggests that the solar wind has greater influence on Saturn’s magnetosphere
Comets as natural laboratories: Interpretations of the structure of the inner heliosphere
Full text linkComets can be considered to be natural laboratories of the inner heliosphere, as their ion tails trace the solar wind flow. Much has been learnt about the heliosphere’s structure from in situ solar wind spacecraft observations. Their coverage is however limited in time and space. This thesis proposes to address these constraints and ascertain the validity of analysing comets’ ion tails as complementary sources of information on dynamical heliospheric phenomena and the underlying continuous solar wind. Solar wind conditions influence comets’ induced magnetotails, formed through the draping of the heliospheric magnetic field by the velocity shear in the mass-loaded solar wind. I present a novel imaging technique and software to exploit the vast catalogues of amateur and professional images of comet ion tails. My projection technique uses the comet’s orbital plane to sample its ion tail as a proxy for determining radial solar wind velocities in each comet’s vicinity. Making full use of many observing stations from astrophotography hobbyists to professional observatories and spacecraft, this approach is applied to several comets observed in recent years. Complementary velocities, derived from folding ion rays and a velocity profile map built from consecutive images, are provided as an alternative means of quantifying the solar wind-cometary ionosphere interaction. I review the validity of these techniques by comparing near-Earth comets to solar wind models in the inner heliosphere and extrapolated measurements by ACE to a near-Earth comet’s orbit. My radial velocities are mapped back to the solar wind source surface to identify sources of the quiescent solar wind and heliospheric current sheet crossings. Comets are found to be good indicators of solar wind structure, but the quality of results is strongly dependent on the observing geometry. Many ion tails also show a constant curvature, so far unexplained, which further complicates the interpretation of tails’ orientations
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