1,720,954 research outputs found
The long-term evolution of Montserrat volcanism
No full textThis thesis investigates the long-term geochemical trends of volcanism on Montserrat and Guadeloupe, islands in the northern Lesser Antilles arc, through both their terrestrial and marine (from International Ocean Discovery Program core U1396C) records, to examine the processes driving geochemical evolution in island arcs.Detailed mapping of the Silver Hills, the least studied volcanic centre on Montserrat, reveals activity was dominated by andesite dome growth and collapse. New 40Ar/39Ar ages from terrestrial samples, combined with new palaeomagnetic and biostratigraphic ages of tephra layers from marine sediment core U1396C, reveal the previously unrecognised overlap in volcanic activity between the Silver and Centre Hills, and Centre and Soufrière Hills.Pb-Nd-Sr isotope and major and trace element data for the Silver Hills show that lavas fall into two compositional groups; ‘normal’ lavas and ‘low Al2O3-high Fe2O3’ lavas. The latter group formed from parental magmas which experienced up to 25% greater plagioclase fractionation compared to the parent magmas of the normal lavas, likely as a result of lower magmatic H2O content. There is no systematic geochemical variation between lava domes of the Silver Hills, but there is an observed systematic shift in 143Nd/144Nd to progressively less radiogenic values with time, which is inferred to result from mantle heterogeneity.Tephra layers from core U1396C have been analysed for Pb-Nd-Sr isotope and major and trace element data, which provide a record of the geochemical evolution of volcanism on Montserrat and Guadeloupe over the past ~4.5 Ma; 2.3 and 1.7 Ma longer than their respective terrestrial records. The main geochemical change for the Montserrat source region occurred ~4.5–3.9 Ma, resulting from an increase in slab sediment contribution to the mantle wedge via an aqueous fluid. Tephra layers from Guadeloupe display greater temporal geochemical variation, driven by crustal assimilation of mid-ocean ridge basalt.Componentry, grain size and grain morphology analyses of the thickest tephra layer in core U1396C derived from Guadeloupe, T2.36, reveal it was formed by deposition from fallout from an eruption column, followed by a co-ignimbrite ash cloud from the same eruption. Eruption reconstructions suggest that this deposit likely formed from a VEI 6 eruption
Emplacement of the Cabezo Maria lamproite volcano (Miocene, SE Spain)
No full textLamproite volcanoes are uncommon in the geological record but are exceptionally well preserved in the Betic Cordilleras of SE Spain, where they erupted during the Late Miocene (Tortonian to Messinian stages). The parent melts are thought to have been channelled through major lithospheric faults to erupt at or near the faulted margins of Neogene sedimentary basins. Lamproite magmas are thought to be relatively CO2-poor (<1 wt %) and are typically characterised by an effusive eruption style and the development of lava lakes and scoria cones. Cabezo María is a relatively small (∼550 m diameter) lamproite volcano that was emplaced within the shallow-water marine-influenced Vera Basin. The lamproites are compositionally similar to those of the Roman Province and generally less potassic (K2O<5 wt%) than other (ultra-) potassic rocks in SE Spain (e.g. Cancarix, Fortuna). The initial eruption stages were dominated by explosive magma-water interactions and the formation of peperites. These are characterised by angular fragments of glassy lamproite lavas (and isolated lobes) incorporated in sediments, locally showing the effects of thermal metamorphism. Further, elutriation pipes and ‘jigsaw-fit’ textures are observed in the peperites. The lavas and peperites are overlain by outward-dipping well-stratified scoria deposits defining part of a cinder cone, which is inferred to have emerged above sea level. Steep internal contacts with inward-dipping, structureless breccias likely represent the inner wall deposits of a central conduit. The deposits are cross-cut by late-stage dykes, which supplied fissure eruptions of geochemically similar lavas capping the scoria cone. The transition from explosive to effusive behaviour may reflect the decreased availability of water, possibly due to downward migration of the feeder conduit below the level of water-saturated sediments
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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