1,720,961 research outputs found
Low degree melting under the Southwest Indian Ridge: the roles of mantle temperature, conductive cooling and wet melting
No full textBoth low mantle temperatures and conductive cooling have been suggested as the cause of the atypically thin oceanic crust and the incompatible element enrichment characteristic of very slow-spreading ridges. Here we present a model of melting under the Southwest Indian Ridge, which takes into account mantle temperature, conductive cooling, source composition and wet melting. The model parameters are constrained by oceanic crustal thickness, lava chemistry and isotopic composition and water content. The results suggest that conductive cooling to a depth of around 20 km, expected in areas with a full spreading rate of 15 mm/yr, is necessary to generate the Southwest Indian Ridge lava chemistry, but not that from faster spreading rate ridges at 23°N on the Mid Atlantic Ridge or 45°N on the Juan de Fuca Ridge. The mantle potential temperatures of ~1280°C, estimated for the Southwest Indian Ridge lavas are close to the global average of the upper mantle. Mantle water contents of 150-300 ppm can explain the observed melt water contents and allow sufficient melting at depth to explain the observed heavy rare earth element depletions in the melts
Time-and temperature-dependent conduit wall porosity: A key control on degassing and explosivity at Tarawera volcano, New Zealand
No full textThe permeability of volcanic conduit walls and overlying plug can govern the degassing and explosivity of eruptions. At volcanoes characterized by a protracted history of episodic volcanism, conduit walls are commonly constructed of quenched magma. During each successive eruptive phase, reheating by ascending magma can modify the porosity, permeability and H 2O content of the conduit wall rocks and overlying plug. We investigate whether the unusual explosivity of the 1886 basaltic eruption at Tarawera volcano is related to the heating and degassing of the AD1314 Kaharoa rhyolitic rocks, through which it erupted. We heat cores of perlitic Tarawera dome rhyolite to 300 °C–1200 °C for 30 min to 3 days at atmospheric pressure. We characterize time ( t)- and temperature ( T)-dependent variations in porosity, volatile content and texture through SEM image analyses. We also directly measure pre- and post-experimental connected and isolated porosity and water content. We identify four textural/outgassing regimes: Regime 1 ( T ≤ 800 °C, t ≤ 2 h), with negligible textural changes and a significant loss of meteoric water (1.4–0.72 wt.% H 2O); Regime 2 (800 ≤ T ≤ 1100 °C, t ≤ 6 h), with cracking and vesicle growth and a 5–10% increase in connected porosity; Regime 3 (800 ≤ T ≤ 1200 °C, t ≥ 30 min), with healed cracks, coalesced and collapsed vesicles, and overall reduced porosity; and Regime 4 ( T ≥ 1200 °C, t > 30 min), with a collapse of all connected porosity. These regimes are governed by the temperature of the event ( T) relative to the glass transition temperature ( T g ) and the time scale of the event ( t) relative to a critical relaxation time for structural failure of the melt (τ r ) . We identify a quantitative transition from predominantly brittle behavior such as cracking, which enhances connected porosity and permeability, to viscous processes including crack healing and vesicle collapse, which act to reduce connected porosity. Applied to the 1886 basalt eruption at Tarawera, we show that progressive heat transfer ultimately reduced the open porosity and permeability of the conduit walls, thereby partially sealing the conduit and reducing volatile loss. We argue that this mechanism was an underlying reason for the exceptional explosivity of the 1886 eruption. We further suggest that textural changes associated with reheating could explain some of the cyclic deformation and degassing observed at many lava domes preceding explosive eruptions.Peer reviewedFinal article publishedlava domeexplosivemagmaconduitdegassingVolcan
Is Iceland a wet spot?
No full textSIGLEAvailable from British Library Document Supply Centre-DSC:DXN037598 / BLDSC - British Library Document Supply CentreGBUnited Kingdo
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
- …
