1,720,960 research outputs found
Characterising the variations in volcanism across the Afar region
No full textContinental
rifting and mantle upwellings are key components in our understanding of plate
tectonics and the asthenospheric mantle. While volcanism is common as rifts
mature from continental rifting to ocean-spreading, our current understanding
of how volcanism changes during rift evolution is limited. The Afar triangle,
in East Africa, is a rift-rift-rift system that meets in a triple junction and
has been proposed to be underlain by a mantle plume. Given that Afar has
already undergone extensive rifting, yet remains subaerial, the region presents
a unique opportunity to investigate the physical and chemical characteristics
of volcanism associated with a proto-oceanic rift. Here, the volcanic
evolution of three volcanoes, Alu, Dalafilla and Borale, are characterised
through a combination of detailed remote-sensing mapping, petrology, major
element, trace element and radiogenic isotope geochemistry. The approximate
eruptive frequency and style is constrained as well as highlighting the changes
in melt production and storage over the recorded eruptive history of the
volcanoes. The results show that each of the volcanoes has a compositional
cyclicity (basalt-trachy-andesite/rhyolite), which is likely controlled by the
time required for fractional crystallisation to occur in an interconnected
stacked-sill system (∼1-4 km depth). The variation in the melting extent and
depth among the basalts can be attributed to potential variations in the
rifting rate throughout the evolution of the volcanoes. Following this,
an integrated approach combining geochemistry (>100 new observations),
geophysics (shear wave velocities and Moho depth) and statistical modelling is
applied to investigate the melt production beneath the region, assessing the
spatial and chemical characteristics of mantle upwelling across the region. The
statistical modelling shows the favoured predictive model to explain melt
characteristics observed is a single heterogeneous plume, which is asymmetric
around the triple junction. This, combined with results from K-means cluster
analysis, indicate that different spreading rates across each rift arm may be
the cause of the plume’s asymmetry. </p
Characterising the wind-advected medial fall deposit from fissure 8 fountaining during the 2018 lower East Rift Zone eruption, Kīlauea
No full textThe 2018 eruption on the lower East Rift Zone, Hawaii, involved the opening of 24 fissures before the eruption focussed on a single point source, fissure 8 (F8). This study characterises the preserved medial F8 tephra deposit using an isopach map, maximum clast size data, and total grain size distribution analysis, shedding light on the tephra transport and dispersal mechanisms beyond the F8 cone occurring during the fountaining. The medial sheet-like deposit covers approximately 0.22 km2, best fit by a Power-Law thinning rate. The TephraFits model estimated the corresponding volume of the continuous medial tephra blanket to be ~ 2 × 104 m3, just 0.02% of the total volume erupted from fissure 8. Samples from the preserved medial deposit have grain size modes of − 3.5 to − 4 Φ, compatible with Voronoi tessellation calculations. Maximum clast size did not show a ‘typical’ fining relationship with distance from the vent; instead, it shows no clear pattern. One factor was that the extremely low clast density, a function of a secondary vesiculation event, enabled the pyroclasts to be re-entrained, often repeatedly, by large eddies downwind of the vent. This should be considered in future studies of prolonged fountaining episodes as the clasts involved in the medial fall are rarely well preserved in the geologic record due to their fragile nature but their presence adds complexity to the inferred eruption dynamics.</p
Melt generation and evolution in the Adda’do rift segment of the Afar rift from trace elements and petrography
No full textAlong-rift variations in the stage of continental separation are observed in the northern East African Rift System (EARS), from magma-assisted continental rifting in the Main Ethiopian Rift (MER) to nascent oceanic spreading in Afar. However, the implications on spatial and temporal changes in mantle melting and melt evolution remain poorly understood. Given that the EARS is the longest and best-exposed example of continental rifting in the world, the MER and Afar are an ideal place to investigate magmatism and volcanism in late-stage continental rifts. Here, we focus on the Adda’do Magmatic Segment (AMS) in the northernmost sector of the MER, that has experienced the most prolonged lithospheric thinning. We present new trace element data and petrographic observations from around 50 samples, and combine these with geochemical modelling to investigate depth of melt origin and melt evolution, in the AMS. Using mixing modelling of garnet lherzolite and spinel lherzolite mantle peridotite sources, we show that the AMS magmas are produced from a relatively deep source with 10%–60% garnet lherzolite, corresponding to depths of around 85 km, and generated by approximately 4%–9.5% partial melting of the mantle. We find no significant variation of these characteristics with either sample age or sample location at the AMS, suggesting no systematic temporal variations occurred in either the depth or the degree of melting within a single magmatic segment. However, on a regional scale, depth of melting is between that interpreted for the MER and northern Afar, implicating the stage of rift evolution and consequent degree of lithospheric thinning as a major control. MELTS modelling of the samples indicates that the observed variations in sample compositions in the AMS can be explained predominantly by fractional crystallisation, with negligible crustal contamination in the basaltic samples. Crustal contamination may play a greater role in the composition of intermediate and evolved samples in the AMS.</p
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
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