1,721,018 research outputs found
Analisi quantitativa delle tessiture di metadioriti, deformate durante la subduzione alpina: Falda Languard-Campo – Austroalpino, Alpi Centrali.
No full textThe grid-work texture of authigenic microcrystalline quartz in siliceous crust-type (SCT) mineralized horizons
No full textSiliceous crust-type (SCT) formations are pervasive silicified horizons associated with fluorite-barite-polymetallic sulfide mineralization in carbonate rocks. They almost invariably show a peculiar grid-work texture formed by microcrystalline quartz. The mineralogical and textural features of several SCT samples from Italy, Spain, France, China, and Brazil were investigated by optical and electron microscopy and X-ray and neutron powder diffraction. The resulting 10011 pole figures exhibit two main components of orientation of the crystallographic c axis with respect to the normal to the sample surface, one located at about 35degrees and the other in the range 60-85degrees. The observed textural features are seen in all samples and they appear to be independent of the age and geographical location of the SCT formation. The observed grid-work texture is tentatively interpreted as forming by nucleation of quartz seeds on specific faces of surrounding crystals. The observed morphology and the regularly oriented populations of crystals are consistent with simultaneous growth of quartz crystals having well-defined reciprocal orientations. The grid-work texture of quartz in SCT horizons is similar to the type reported for Magadi-type cherts, which are commonly interpreted as formed by magadiite-mediated silica precipitation processes. Since the genesis of SCT deposits is totally unrelated to alkaline-take genetic processes, it is concluded that cherts showing strongly textured patterns of microcrystalline quartz may have a different origin than Mapdi-type deposits
The 3D quantitative lattice and shape preferred orientation of a mylonitised metagranite from Monte Rosa (Western Alps): Combining neutron diffraction texture analysis and synchrotron X-ray microtomography
Full text linkTwo complementary 3D techniques, neutron diffraction and synchrotron X-ray microtomography (SXR-μCT), were used to compare the Shape and Lattice Preferred Orientations of a mylonitised metagranite from the Monte Rosa unit (Western Alps, Italy). The goal of using these techniques was to obtain two different orientation distribution functions. Although the two functions describe relatively independent characteristics of the rock fabric, nonetheless they also exhibit close relationships to macroscopic fabrics and may be complementarily used to quantify rock fabrics and microstructures, thereby highlighting 3D features that cannot be obtained with either technique, if used independently. We describe an approach that can be potentially useful in various disciplines, e.g., structural geology, rock mechanics, tectonics and geophysics, when a complete data set of preferred orientations and size distribution is needed.Micas display a strong orthorhombic symmetry between mesoscopic lineation and microscopic SPO and LPO, whereas quartz and feldspars are characterised by a monoclinic symmetry between mesoscopic lineation and LPO. These observations suggest a rheological decoupling between the weak phase mica layers and the stronger quartz+feldspar layers. This mechanical decoupling occurred during the Alpine subduction-collision, when the Monte Rosa unit was part of the Insubric Line system and accommodated large vertical strain
Brittle plus plastic deformation of gypsum aggregates experimentally deformed in torsion to high strains: Quantitative microstructural and texture analysis from optical and diffraction data
No full textThis contribution presents a quantitative microstructural analysis of a polycrystalline aggregate of gypsum, deformed in torsion (T = 70-90 °C) at γ (shear strain) ranging from 0 to 4.82. Quantitative microstructural analysis is used to compare the evolution of microstructures observed by optical microscope with those obtained from analysis of X-ray and neutron diffraction data. This analysis shows that during experimental deformation, gypsum accommodated strain by brittle and plastic deformation mechanisms, developing Riedel-like microfaults with plastic foliations and crystallographic preferred orientation (CPO). The relations of microstructures show that with increasing strain, the Riedel systems start from R planes with an angle of ≈30° to the Imposed Shear Plane. This angle decreases (5°-15°) when strain increases, and Y planes develop. Quantitative texture analysis (QTA) shows that S-foliations start developing at low γ and maintain their orientation up to high y, and that the most active slip system is the (010) along normal to (100) and the [001]-axis. Shape preferred orientation (SPO) of gypsum does not coincide with the theoretical orientation as it does not decrease with increasing strain. This discrepancy is explained by the role of the brittle shear planes that impose a back rotation to gypsum. No brittle to plastic transition occurs. But both plastic and brittle structures contemporaneously accommodate and localize strain
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
Opening kinematics of the Auletta and Vallo di Diano basins, southern Italy : constraints from structural analysis, paleomagnetism, and neutron texture analysis
No full textVariations 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
X-ray Techniques for Advanced Materials, Nanostructures and Thin Films: from Laboratory Sources to Synchrotron Radiation - Proceedings of the EMRS 2009 Spring Meeting - Symposium R, held in Strasbourg in June 2009.
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