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Drijvende krachten achter de beweging en deformatie van het Euraziatische continent
No full textDat mantelconvectie aan de basis staat van de beweging van de tektonische platen, is een vaststaand
gegeven. Maar hoe mantelconvectie de beweging van platen beïnvloedt en, andersom, wat de invloed
is van een onderschuivende plaat op de mantel zijn vragen waarover nog veel onduidelijkheid bestaat.
Karin Warners-Ruckstuhl (Universiteit Utrecht) promoveerde op 24 februari j.l. op de vraag welke
krachten verantwoordelijk zijn voor de beweging van de Euraziatische plaat en zorgen voor de
spanningen die aan de basis staan van tal van aardbevinge
Lithosphere-mantle coupling and the dynamics of the Eurasian Plate
No full textMechanical equilibrium of tectonic plates implies that lithospheric edge and body forces are balanced by forces arising from interaction with the underlying mantle. We use this quantitative physical relation to integrate existing modelling approaches of lithosphere dynamics and mantle flow into a new combined approach applied to the Eurasian Plate. By combining a thorough analysis of lithospheric forces with the requirement of torque balance we constrain the orientation of the torque on Eurasia arising from mantle tractions. We use this constraint to evaluate convective mantle flow models driven by tomographic or subduction history model anomalies and observed plate motion. Mantle forcing is considered through both shear at the bottom of the plate and induced dynamic topography. We find that instantaneous semi-analytic flow models without lateral viscosity variations generate tractions that meet the constraint from Eurasian lithosphere dynamics, but only for specific ranges of mantle flow parameters. Of the explored set of mantle anomaly models, only mantle flow models based on S-wave tomography anomalies can balance Eurasia for realistic viscosity profiles and velocity–density scaling. Choices in mantle density forcing and viscosity are crucial in that they govern the relative magnitude of tractions due to convective mantle flow (‘active tractions’) and resistive tractions due to plate motion (‘passive tractions’). We find mechanical balance is only achieved for similar torque magnitudes of active and passive shear. The two shear contributions do however in no case balance each other and a considerable, dominant, net torque from edge forces is required to balance total mantle tractions and lithospheric body forces (LBFs). Our analysis provides a range of mechanically consistent total force sets acting on the Eurasian Plate. Using this result we find that mantle buoyancy forces and LBFs acting on Eurasia itself are important driving forces but do not drive Eurasia in the observed direction. Continental collision at Eurasia’s southern boundary significantly deviates Eurasia northwards. Our combined torque balance approach, in which mantle tractions from convective mantle flow modelling are combined with explicitly applied edge forces, thus emphasizes the role of plate interactions to the dynamics of tectonic plate
Tethyan collision forces and the stress field of the Eurasian plate
No full textResistive forces along convergent plate boundaries have a major impact on surface deformation, most visibly at collisional plate boundaries. Although quantification of these forces is key to understanding the evolution and present state of mountain belts, they remain highly uncertain due to the complexity of plate boundary structures and rheologies. In previous studies of the Eurasian Plate, we have analysed the balance of plate boundary forces, tractions resulting from lithosphere–mantle coupling, and intraplate variations in topography and density structure. This yielded a range of acceptable force distributions. In this study, we investigate to which extent the observed present-day stress field provides further constraints on the distribution of forces.
We address the dynamics of the Eurasian Plate as a whole. This enables us to base our analysis on mechanical equilibrium of a tectonic plate and to evaluate all forces as part of an internally consistent set of forces driving and deforming Eurasia. We incorporate tractions from convective mantle flow modelling in a lithospheric model in which edge and lithospheric body forces are modelled explicitly and compute resulting stresses in a homogeneous elastic thin shell. Intraplate stress observations used are from the World Stress Map project. Eurasia's stress field turns out to be particularly sensitive to the distribution of collision forces on the plate's southern margin and, to a much lesser extent, to lithospheric density structure and tractions from mantle flow. Stress observations require collision forces on the India–Eurasia boundary of 7.0–10.5 TN m−1 and on the Arabia–Eurasia boundary of 1.3–2.7 TN m−1. Implication of mechanical equilibrium of the plate is that forces on the contacts with the African and Australian plates amount to 1.0–2.5 and 0–1.3 TN m−1, respectively. We use our results to assess the validity of the classical view that the mean elevation of an orogenic plateau can be taken as a measure of the magnitude of the compressive (in this case: collision-related) forces involved. For both the Tibetan and the Iranian plateaus, two plateaus with significantly different average elevations, we find that the horizontal force derived from the excess gravitational potential energy (collapse force) is in balance with the collision force
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
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
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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