1,720,964 research outputs found
Experimental studies of the differentiation process and pre-eruptive conditions in the magmatic system of Phlegreans Fields (Naples, Italy)
No full textPhase relations of two samples of the Breccia Museo Eruption (BME), BME is an explosive event that took place (about 20 ky ago) during the caldera-forming phase of the Ignimbrite Campana eruption, have been determined experimentally as a function of temperature (700 to 885 °C), pressure (50 to 200 MPa) and water content of the melt. The crystallization experiments were carried out at fO2 = NNO + 1 log unit. Melt water content ranged from 3.4 to 8 wt.% (H2O saturation). The synthetic products are compared to the natural phases to constrain the pre-eruptive conditions of trachytic magma in the presence of an H2O-rich fluid. The major phases occurring in the BME have been reproduced. The stability of biotite is favoured at pressures higher than 135 MPa. Phase equilibria at 200 MPa reproduce the phase assemblage of the magma only at temperatures below 775 °C. Phase abundances and melt fractions indicate that the eruption tapped a magma body that was at a temperature of 780 °C and a pressure in the range 200-140 MPa. The observed major element variations are fully consistent with a fractional crystallization of a sanidine-dominated assemblage starting from the least differentiated trachytes. The compositions of the experimental products are compatible with the progressive tapping of a shallow magma chamber that was chemically zoned. These results suggest that after an early eruptive phase during which the upper, most differentiated level of the magma chamber was tapped, the sudden collapse of the roof of the reservoir triggered drainage of the less evolved remaining magma. © 2007 Elsevier B.V. All rights reserved
New experimental data on biotite + magnetite + sanidine saturated phonolitic melts and application to the estimation of magmatic water fugacity
No full textNew experimental data are presented that allows the biotitemagnetitesanidine equilibrium to be
used for estimating water fugacity (H2O) in hydrous phonolitic magmas. It is also demonstrated that
the partly ionic model gives the best estimate for the annite activity (aannite). Crystallization experiments
were carried out on a representative sample of peralkaline, phonolitic obsidian of Montaña
Blanca (MB) pumice deposit, Tenerife, Canary Islands. Experiments were performed from 720810
°C and 50250 MPa. Redox conditions were varied between NNO (nickel + nickel oxide) + 1 (±0.2)
and FMQ (fayalite + magnetite + quartz). The majority of the experiments were done under H2O
saturation conditions (Pwater = Ptotal). Several experiments were done using a mixed H2O-CO2 ß uid
phase whereas in other experiments 10 or 20 wt% powdered alkali feldspar was added to the starting
material. The pre-eruptive H2O of the Montaña Blanca magma is estimated at 676 ± 200 bars. The
pre-eruptive H2O for the Fish Canyon tuff (7532978 bars) and Bishop tuff rhyolite (10652440 bars)
were also calculated, as well as H2O for metamorphic biotite from Au Sable Forks (≈ 130 bars). The
results of this study suggest that this geohygrometer can be used in any magmatic system in which
biotitemagnetitesanidine is a stable assemblage.
Keywords: Crystallization experiments, geohygrometer, phonolitic magmas, water fugacit
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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