1,721,019 research outputs found
Improving arctic sea ice thickness estimates from satellite altimetry
No full textLes observations spatiales d'extension de glace de mer montrent que la banquise arctique a fortement réduit au cours des 40 dernières années, avec une nette tendance à l'accélération depuis la fin des années 1990. Bien que les processus expliquant cette fonte accélérée soient en partie compris, les modèles de banquise ne reproduisent pas clairement les variations d'extension observées. Cette mauvaise représentation des modèles est généralement attribuée à une méconnaissance des rétroactions climatiques. Parmi ces rétroactions, nous souhaitons nous intéresser à l'une d'entre elles en particulier: l'amincissement de la glace de mer. Cet amincissement est généralement associé à une fonte plus précoce et à une accélération de l'export de glace. L'amélioration de la représentation de l'épaisseur de banquise est donc nécessaire pour mieux comprendre les variations d'extension de banquise observées au cours des dernières décennies. Contrairement aux données d'extension de banquise, il n'existe pas à l'heure actuelle de données d'épaisseur de glace à l'échelle du Bassin Arctique couvrant une longue période (> 20 ans). En revanche, de multiples études ont montré qu'il était possible d'estimer l'épaisseur de glace à l'échelle du Bassin Arctique à partir de l'altimétrie spatiale. Pour mesurer l'épaisseur de glace par altimétrie, on emploie généralement la technique du "franc-bord". Cette méthode consiste à estimer par altimétrie spatiale l'épaisseur de glace émergée (le franc-bord) et à convertir cette mesure en épaisseur totale en résolvant l'équation d'hydrostatique qui existe entre la glace recouverte de neige et l'océan. La méthode du franc-bord a été appliquée à diverses missions altimétriques (ERS-2, Envisat et CryoSat-2) depuis 1995 et devrait ainsi pouvoir fournir une série temporelle d'épaisseur de glace de plus de 20 ans. Cela dit, il n'existe à ce jour aucune série temporelle d'épaisseur de glace couvrant plus de 6 années. Cette absence d'une longue série temporelle est principalement due à un manque de continuité de la mesure du franc-bord liée à l'évolution des techniques radar (altimétrie conventionnelle/altimétrie SAR) ainsi qu'aux incertitudes liées à la conversion du franc-bord en épaisseur de glace. Dans ce contexte, cette thèse a pour objectifs d'analyser les biais inter-missions de franc-bord et d'améliorer la conversion du franc-bord en épaisseur de glace en exploitant au mieux la mesure altimétrique. Pour remplir ces objectifs, un travail de fond est réalisé sur l'interaction de la mesure radar avec l'environnement de la banquise (neige, rugosité, etc). Les résultats de l'analyse de la mesure radar sur la banquise permettent d'établir la plus longue série temporelle d'épaisseur de glace de mer disponible à ce jour (2002-2016). L'analyse de cette série temporelle montre que la banquise s'est amincie en moyenne de 0.013(± 0.09) m/an au cours de la période 2002-2016. Cet amincissement est principalement attribué à la réduction de surface de glace pérenne ayant eu lieu au cours de la même période. La forte incertitude associée à cette tendance est quant à elle attribuée à l'importante variabilité inter-annuelle de l'épaisseur de banquise arctique.Satellite observations have shown that the arctic sea ice extent has strongly decreased during the last 40 years, with a clear increase of the shrinking since the 90's. While the mechanisms responsible for this accelerated shrinking are relatively well known, sea ice models do not clearly reproduce the observed extent variations. This inaccurate representation is generally attributed to a misunderstanding of the arctic system climate feedbacks. Among these feedbacks, we seek to study one of them in particular: the sea ice thinning. Sea ice thinning is generally associated with an earlier seasonal melt as well as an increase in sea ice export; both tend to accelerate the sea ice retreat. A good representation of sea ice thickness is therefore necessary to improve our understanding of the arctic sea ice extent variations observed during the last decades. Unlike sea ice extent data, there are currently no pan-Arctic sea ice thickness observations covering a large period (> 20 years). However, several studies have demonstrated the potential of satellite altimetry to retrieve sea ice thickness at a basin scale. To measure sea ice thickness from radar altimetry, the "freeboard" technique is generally employed. This methodology consists of estimating the thickness of the emerged sea ice (freeboard) from radar altimetry and then converting this measurement to sea ice thickness, using an equation for the hydrostatic equilibrium that exists between the snow covered sea ice and the ocean. The freeboard methodology has been applied to diverse altimetric missions (ERS-2, Envisat and CryoSat-2) since 1995 and should allow the retrieval of more than 20 years of pan-Arctic ice thickness. However, the previous estimates of sea ice thickness are data shorter than 6 years in duration. This absence of a long ice thickness time series is mostly due to the difficulty in providing continuity between the different altimetric missions (conventional altimetry/SAR altimetry) as well as to the uncertainties related to the freeboard-to-thickness conversion. In this context, this thesis makes an analysis of the freeboard inter-mission biases and improves the freeboard-to-thickness conversion in order to produce long term ice thickness estimates. To achieve these goals, a thorough analysis of the interaction between the radar signal and the sea ice parameters (snow, roughness, etc) is performed. The analysis of the radar signal physics over sea ice allows to derive the longest time series of arctic sea ice thickness ever established to this day (2002-2016). The analysis of this time series shows that sea ice has thinned from 0.013(± 0.09) m/year in average during the 2002-2016 period. The ice thinning is mainly attributed to the loss of perennial sea ice that occurred during the same period while the high uncertainty associated with this trend is associated to the important inter-annual variability of arctic sea ice thickness
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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
Author Under Sail The Imagination of Jack London, 1893-1902
No full textIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Intro -- Title Page -- Copyright Page -- Dedication -- Contents -- Acknowledgments -- Introduction -- 1. Spirit Truth -- 2. From Absorption to Theatricality and Back Again -- 3. "I Will Build a New Present" -- 4. Sons as Authors -- 5. Fathers as Publishers -- 6. The Daughter as Author -- 7. Lovers as Authors -- 8. At Sea with the Family -- 9. Yellow News, Yellow Stories -- 10. The Return Home -- Notes -- Bibliography -- Index -- About Jay WilliamsIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Description based on publisher supplied metadata and other sources.Electronic reproduction. Ann Arbor, Michigan : ProQuest Ebook Central, YYYY. Available via World Wide Web. Access may be limited to ProQuest Ebook Central affiliated libraries
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