1,720,958 research outputs found
EXPERIMENTAL STUDY OF INTERCONNECTIVITY AND GRAIN BOUNDARY WETNESS OF HYDROUS CARBONATITIC LIQUIDS IN MANTLE PERIDOTITE
Full text linkCarbon-bearing solids, fluids, and melts in the Earth's deep interior play an important role in the
long-term carbon cycle. Carbonatite magmas have been suggested as important agents of mantle
metasomatism and yet, their physical features are expected to control the mobility from the
source region to shallow Earth. Carbonatites are known to form at relatively low temperatures
and are very mobile, as controlled by their low viscosities and their ability to form an
interconnected grain-edge melt at low melt fraction. The factors promoting migration and
infiltration are the minimization of interfacial energy, the density and chemical gradients, the
thermal diffusion. However, the mobility and infiltration rates of carbonatitic melts, together
with their influence on the annealing of mantle peridotites are poorly constrained processes.
Although natural carbonatitic melts are complex chemical systems with C-O-H species as a
major component, previous work has been performed in anhydrous model systems.
Here we present a quantitative laboratory simulation of variables and processes controlling the
ascent, mobility and connectivity of carbonatites in a model mantle material investigating the
dihedral angle of hydrous carbonatitic liquids. We aim at comparing the texturally equilibrated
volume proportions of volatile-rich carbonatitic melts with silicate melts in a partially molten
peridotite, and and we examine whether carbonatitic liquids are always more wetting than
silicate melts.
The percolation of carbonatitic liquids and the interconnectivity of melt pockets are investigated
by placing a cylindrical dunite rod against a liquid reservoir. As peridotitic matrix we used a
synthetic dunite starting from natural San Carlos olivine powder. Sintering has been performed
in a single stage piston-cylinder apparatus at 0.8 GPa and 1200°C P-T conditions. The liquid
reservoir has a dolomitic composition (Ca0.541, Mg0.389, Fe0.069) CO3 and uses free water as
hydrous source (5 wt.% and 30% of the starting material). Time resolved infiltration experiments
were performed employing an end loaded piston-cylinder apparatus, at T= 1200°C and P = 2.5
GPa. In order to account for the different roles of gravity, chemical diffusion and Ludwig-Soret
diffusion we used two opposite capsule geometries.
Hydrous carbonatitic melt pockets were found along olivine grain boundaries; image analysis on
electron back scattered and X-ray maps allow us quantifying the apparent dihedral angles
between the liquid and olivine and to calculate the grain boundary wetness. Experiments performed at 5 wt. % of water content and 3, 30 and 300 hours of run durations
result in dihedral angles evolving from ∼ 31° for 3 hours run, to ∼ 41° for 300 hours run through
∼ 34° for 30 hours run. The volume of liquid fraction infiltrated provides values of 10 vol.%, 8
vol.% and 2 vol.% for short, medium and long run duration experiments respectively.
Experiments carried out at 30 wt. % of water content and 48 hours of durations show a dihedral
angle values of almost 50° with a range of volume infiltrated melts between 4 to 9 vol. %. The
experimental results indicate that dihedral angles progressively increase with increasing water
dissolved from 25°-28° in anhydrous carbonatitic liquids up to 50° in water-rich carbonatitic
liquids, and, as expected, the volume of interstitial liquid decreases with water increasing.
The increase of wetting angles is representative of a sintering process of the solid matrix, which
evolves with time in the development of channels of pores, as highlighted relating the grain
boundary wetness with fraction of liquid infiltrated. We suggest that the low grain boundary
wetness measured may be due to a relatively low liquid-solid interfaces which develop with
channelized liquid, and that channelization is promoted by chemical gradient, as established by a
carbonatitic segregate in the silicate matrix.
If H2O is available, we expect that H2O strongly partitions into carbonatitic liquids. As a result,
their dihedral angle may evolve up to 50°, a value which is significantly higher than that
characterizing silicate melts at similar mantle conditions
Wetting angles of hydrous carbonatitic liquids and reversal in wettability for silicate and carbonatitic magmas in the mantle
No full textCarbon-bearing solids, fluids, and melts in the Earth’s deep interior play an important role in the long-term carbon cycle. Carbonatite magmas have been suggested as important agents of mantle metasomatism and yet, their physical features are expected to control the mobility from the source region to shallow Earth. The mobility and infiltration rates of carbonatitic melts, together with their influence on the annealing of mantle peridotites are poorly constrained processes. Although natural carbonatitic melts are complex chemical systems with C-O-H species as a major component, previous work has been performed in anhydrous model systems. Here we present a quantitative laboratory simulation of variables and processes controlling the ascent, mobility and connectivity of carbonatites in a model mantle material investigating the dihedral angle of hydrous carbonatitic liquids. We aim at comparing the texturally equilibrated volume proportions of volatile-rich carbonatitic melts with silicate melts in a partially molten peridotite, and we examine whether carbonatitic liquids are always more wetting than silicate melts. The infiltration experiments were performed employing an end loaded piston-cylinder apparatus, at T= 1200°C and P = 2.5 GPa to investigate the percolation of carbonatitic liquids and interconnectivity of melt pockets in a peridotitic matrix. Hydrous carbonatitic melt pockets were found along olivine grain boundaries; image analysis on electron back scattered and X-ray maps allow us quantifying the apparent dihedral angles between the liquid and olivine and to calculate the grain boundary wetness. Experiments performed at 5 wt.% of water contents result in dihedral angles evolving from ~31° to ~41° with a volume of liquids from 2 to 10 vol.%, while experiments carried out at 30wt. % of water content show a dihedral angle values of almost 50° with a range of volume infiltrated melts between 4 to 9vol.%. These results indicate that dihedral angles progressively increase with increasing water dissolved from 25°-28° in anhydrous carbonatitic liquids up to 50° in water-rich carbonatitic liquids, and, as expected, the volume of interstitial liquid decreases with water increasing. The increase of wetting angles is representative of a sintering process of the solid matrix, which evolves with time in the development of channels of pores, as highlighted relating the grain boundary wetness with fraction of liquid infiltrated. We suggest that the low grain boundary wetness measured may be due to a relatively low melt-rock interfaces which develop with channelized liquid, and that channelization is promoted by chemical gradient, as established by a carbonatitic segregate in the silicate matrix. If H2O is available, we expect that H2O strongly partitions into carbonatitic liquids. As a result, their dihedral angle may evolve up to 50°, a value which is significantly higher than that characterizing silicate melts at similar mantle conditions
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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