1,721,029 research outputs found
Role of iron-spin transition in ferropericlase on seismic interpretation: A broad thermochemical transition in the mid mantle?
No full textModelling Earth's surface topography: Decomposition of the static and dynamic components
No full textContrasting results on the magnitude of the dynamic component of topography motivate us to analyse the sources of uncertainties affecting long wavelength topography modelling. We obtain a range of mantle density structures from thermo-chemical interpretation of available seismic tomography models. We account for pressure, temperature and compositional effects as inferred by mineral physics to relate seismic velocity with density. Mantle density models are coupled to crustal density distributions obtained with a similar methodology. We compute isostatic topography and associated residual topography maps and perform instantaneous mantle flow modelling to calculate the dynamic topography. We explore the effects of proposed mantle 1-D viscosities and also test a 3D pressure- and temperature-dependent viscosity model. We find that the patterns of residual and dynamic topography are robust, with an average correlation coefficient (r) of respectively ∼0.74 and ∼0.71, upper-lower quartile ranges of 0.86–0.65 for residual topography and 0.83–0.62 for dynamic topography maps. The amplitudes are, on the contrary, poorly constrained. For the static component, the inferred density models of lithospheric mantle give an interquartile range of isostatic topography that is always higher than 100 m, reaching 1.7 km in some locations, and averaging ∼720 m. Crustal density models satisfying the same compressional velocity structure lead to variations in isostatic topography averaging 350 m, with peaks of 1 km in thick crustal regions, and always higher than 100 m. The uncertainties on isostatic topography are strong enough to mask, if present, the contribution of mantle convection to surface topography. For the dynamic component, we obtain a peak-to-peak dynamic topography amplitude exceeding 3 km for all our mantle density and viscosity models. These extremely high values would be associated with a magnitude of geoid undulations that is not in agreement with observations. Considering chemical heterogeneities in correspondence with the lower mantle Large Low Shear wave Velocity Provinces (LLSVPs) helps to decrease the peak-to-peak amplitudes of dynamic topography and geoid, but significantly reduces the correlation between synthetic and observed geoid. The correlation coefficients between all our residual and dynamic topography maps (a total of 220 and 198, respectively) is <0.55 (average = ∼0.19). The correlation slightly improves when considering only the very long-wavelength components of the maps (average = ∼0.23). We therefore conclude that a robust determination of dynamic topography is not feasible since current uncertainties affecting crustal density, mantle density and mantle viscosity are still too large. A truly interdisciplinary approach, combining constraints from the geological record with a multi-methodological interpretation of geophysical observations, is required to tackle the challenging task of linking the surface topography to deep processes
Large Scale Three-dimensional Boundary Element Simulation of Subduction
No full textWe present a novel approach for modeling subduction using a Multipole-accelerated Boundary Element Method (BEM). The present approach allows large-scale modeling with a reduced number of elements and scales linearly with the problem size. For the first time the BEM has been applied to a subduction model in a spherical planet with an upper-lower mantle discontinuity, in conjunction with a free-surface mesh algorith
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
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