1,721,674 research outputs found
Dehydration reactions and micro-nanostructures in experimentally deformed serpentinites
No full textHigh-T torsion experiments on lizardite + chrysotile serpentinites produced mineralogical and micro/nanostructural changes, with important implications in rheological properties. High-resolution TEM showed that specimens underwent ductile [by microkinking and (001) interlayer glide] and brittle deformation (by microfracturing), together with dehydration and break-down reactions. Lizardite is affected by polytypic disorder and microkinking [kink axial planes at high angle with respect to (001) planes], that were not present in the initial ordered 1T-lizardite. Chrysotile fibres are deformed, resulting in elliptical cross-sections, with strong loss of interlayer cohesion. Both lizardite and chrysotile break down to a fine intergrowth of olivine (up to 200 nm), talc (up to 30 nm) and poorly-crystalline material. Lizardite-out reaction preferentially occurs at kink axial planes, representing sites of preferential strain and enhanced reactivity; conversely, chrysotile break-down is a bulk process, resulting in large healed olivine aggregates, up to micrometric in size. Overall observations suggest that dehydration and break-down reactions are more advanced in chrysotile than in lizardite. © Springer-Verlag 2008
Thermal decomposition of serpentine during coseismic faulting: nanostructures and mineral reactions
No full textThis paper reports a detailed characterization of an antigorite-bearing serpentinite, deformed at seismic
slip-rate (1.1 m/s) in a high-velocity friction apparatus. Micro/nanostructural investigation of the slip
zone (200 mm thick) revealed a zonal arrangement, with a close juxtaposition of horizons with significantly
different strength, respectively consisting of amorphous to poorly-crystalline phases (with bulk
anhydrous composition close to starting antigorite) and of highly-crystalline assemblages of forsterite
and disordered enstatite (200 nm in size and in polygonal-like nanotextures). The slip zone also hosts
micro/nanometre sized Cr-magnetite grains, aligned at low angle with respect to the slipping surface and
inherited from the host serpentinite.
Overall observations suggest that frictional heating at asperities on the slipping surface induced
a temperature increase up to 820e1200 C (in agreement with flash temperature theory), responsible for
serpentine complete dehydration and amorphization, followed by crystallization of forsterite and
enstatite (under post-deformation, static conditions). The results of this study may provide important
keys for the full comprehension of the mechanical behaviour and of the possible geodynamical role of
serpentinite-hosted faults through the seismic cycle
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
Evidence of thermal pressurization in high-velocity friction experiments on smectite-rich gouges
No full textThermal pressurization of pore fluid is one of the possible mechanisms responsible for dynamic weakening in landslides and earthquakes, but, to date, has not been reproduced in the laboratory. Here, we report high-velocity experiments performed in a rotary shear friction apparatus on smectite-rich gouges from the 1963 Vaiont landslide (Italy). The gouges were slid under 1 MPa normal stress, for displacements up to 30 m and a slip rate of 1.31 m s-1 under room-humidity and water-saturated conditions. Sample dilatancy was observed in room-humidity runs after similar to 3-4 m of slip, concomitant with an increase in normal stress and a decrease in shear stress. Mineralogical and microstructural investigations suggest that dilatancy resulted from expansion of the H(2)O released by the collapse of the smectite structure due to frictional heating of the slipping zone at T > 200 degrees C. We conclude that sample dilatancy is due to thermal pressurization of the clay-rich gouge
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