1,721,004 research outputs found
Traces of the oxygen isotope composition of ancient air in fossilized cosmic dust
Full text linkAs a sub-type of micrometeorites, I-type cosmic spherules form by complete melting and oxidation of extraterrestrial Fe, Ni metal particles during their atmospheric entry. All oxygen in the resulting Fe, Ni oxides sources from the Earth’s atmosphere and hence makes them probes for the composition of atmospheric oxygen. When recovered from sedimentary rocks, they allow the reconstruction of the triple oxygen isotope composition of past atmospheric O2, providing quantitative constraints on past CO2 levels or global primary production. Here we establish using fossil I-type cosmic spherules as an archive of Earth’s atmospheric composition with the potential for a unique record of paleo-atmospheric conditions dating back billions of years. We present combined triple oxygen and iron isotope compositions of a collection of fossil I-type cosmic spherules recovered from Phanerozoic sediments. We reconstruct the triple oxygen isotope anomalies of past atmospheric O2 and quantify moderate ancient CO2 levels during the Miocene (~8.5 million years) and late Cretaceous (~87 million years). We also demonstrate this method’s competitive precision for paleo-CO2 determination, despite challenges in finding micrometer-sized unaltered fossil I-type cosmic spherules. Our work indicates that morphologically intact spherules can be isotopically altered by terrestrial processes, underscoring the need for rigorous sample screening
Multi-collector 40Ar/39Ar dating of microtektites from Transantarctic Mountains (Antarctica): A definitive link with the Australasian tektite/microtektite strewn field
No full textMicrotektites represent high-velocity/distal meteorite impact ejecta. Demonstrating that microtektites found at several locations throughout East-Antarctica consist of a homogeneous class of geological objects belonging to the Australasian tek- tite/microtektite strewn field is fundamental to define the actual extent of the largest and youngest known tektite field on Earth produced by an asteroidal impact 4 times a previous fission track date, thus providing conclusive evidence that microtektites found throughout the Transantarctic Mountains of Antarc- tica belong to a single source – the Australasian field. This study strengthens the southward extension of the Australasian field ($4,000 km southward with respect to Australasian microtektites recovered at lower latitudes from deep sea sediments), thus implying a launch distance of nearly 12,000 km from the putative impact location in Indochina. From a broad perspective, results also reveal a contrasting behavior between microtektites from the Transantarctic Mountains, highly contaminated by extraneous Ar, and Australasian macroscopic tektites, weakly or negligibly contaminated. Although future dedicated exper- imental work, aimed at the definition of physical homogeneity of microtektites at the submicroscale and at the understanding of the true intra-particle spatial distribution of Ar isotopes are necessary, we speculatively hypothesize that the contrasting behavior between tektites and microtektites may reflect displacement in different environments
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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