1,720,984 research outputs found
Seismic properties of the upper crust in the central Friuli area (northeastern Italy) based on petrophysical data
No full textThe compressional and shear wave velocities have been measured at room temperature and pressure up to 450 Mpa on 5 sedimentary rock samples, representative of the most common lithologies of the upper crust in the central Friuli area (northeastern Italy). At 400 MPa confining pressure the Triassic dolomitic rock shows the highest velocities (Vp similar to 7 km/s, Vs similar to 3.6 km/s), the Jurassic and Triassic limestones samples intermediate velocities (Vp similar to 6.3 km/s, Vs similar to 3.5 km/s) and the Cenozoic and Paleozoic sandstones the lowest velocities (Vp similar to 6.15 km/s, Vs similar to 3.35 km/s). The Paleozoic sandstone sample is characterized by the strongest anisotropy (10%) and significant bireffingence (0.2 km/s) is found only on the Cenozoic sandstone sample. We elaborated the synthetic profiles of seismic velocities, density, elastic parameters and reflection coefficient, related to 4 one-dimensional geological models extended up to 22 kin depth. The synthetic profiles evidence high rheological contrasts between Triassic dolomitic rocks and the soft sandstones and the Jurassic limestones. The Vp profiles obtained from laboratory measurements match very well the in-situ Vp profile measured by sonic log for the limestones and dolomitic rocks, supporting our one-dimensional modelling of the calcareous-carbonatic stratigraphic series. The Vp and Vs values of the synthetic profiles are compared with the corresponding ones obtained from the 3-D tomographic inversion of local earthquakes. The laboratory Vp are generally higher than the tomographic ones with major discrepancies for the dolomitic lithology. The comparison with the depth location of seismicity reveals that the seismic energy is mainly released in correspondence of high-contrast theological boundaries. (c) 2007 Elsevier B.V All rights reserved
Deep slab hydration induced by bending-related variations in tectonic pressure
No full textBending of oceanic plates at subduction zones results in extension and widespread normal faulting(1) in the upper, brittle part of the slab(2,3). Detailed seismic surveys at trenches reveal that this part of the oceanic plate could be pervasively hydrated for several kilometres below the crust-mantle boundary(4-7). Similarly, heat-flow surveys indicate active fluid circulation within the slab(8). Yet, the mechanisms that enable fluids to percolate to such depths in spite of their natural buoyancy remain unclear. Here we use two-dimensional numerical experiments to show that stress changes induced by the bending oceanic plate produce subhydrostatic or even negative pressure gradients along normal faults, favouring downward pumping of fluids. The fluids then react with the crust and mantle surrounding the faults and are stored in the form of hydrous minerals. We suggest that this process is the dominant mechanism of deep slab hydration, although it may be locally aided by the enhancement in porosity due to prefailure dilatancy(9), pre-existing cracks(10) and migrating fluid-filled cracks(11). Our results have implications for the transport of water into the deeper parts of the mantle(12), and for further clarifying the seismic anisotropy of slabs(13)
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Large strain shearing of halite: Experimental and theoretical evidence for dynamic texture changes
No full textWe report results from torsion experiments on polycrystalline halite (NaCl) to shear strains γ=8 and observe a very complex texture evolution. The same behavior was reproduced with polycrystal plasticity simulations, suggesting that we capture the underlying mechanisms. While crystal shapes gradually rotate into the shear plane, crystal orientations change continuously and dynamic texture patterns evolve with increasing shear. This is highly significant for ultra-large deformation, as for example implied from geodynamic modeling for the deep earth, where seismic anisotropy patterns may develop and locally disappear again as material is deformed during convection. The study also suggests that caution is required when interpreting deformation mechanisms from simple shear preferred orientation patterns
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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
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