1,720,955 research outputs found
On the Backus average of a layered medium with elasticity tensors in random orientations
No full textAs shown by Backus (J Geophys Res 67(11):4427-4440, 1962), the average of a stack of isotropic layers results in a transversely isotropic medium. Herein, we consider a stack of layers consisting of randomly oriented anisotropic elasticity tensors, whichone might reasonably expectwould result in an isotropic medium. However, we showby means of a fundamental symmetry of the Backus averagethat the corresponding Backus average is only transversely isotropic and not, in general, isotropic. In the process, we formulate, and use, an analogy between the Backus and Gazis et al. (Acta Crystallogr 16(9):917-922, 1963) averages
On mathematical modelling and parameter estimation of seismic media
No full textWithin the multidisciplinary field of geophysics, seismology is a branch that
accounts for the generation and propagation of vibrations within the Earth,
otherwise referred to as seismic waves. To study the mechanical properties of these
waves, seismologists model the Earth’s subsurface as a continuous elastic medium.
Such an approximation facilitates the interpretation of physical observations within
a mathematical framework, which can be approached either as forward or inverse
problem. To that end, this dissertation is comprised of two forward problems and
one inverse problem.
From a forward perspective, theoretical models are proposed based on a priori
assumptions of mechanical properties of the subsurface, which can be quantified as
changes in velocity with location (inhomogeneity) or direction (anisotropy). Two
chapters of this dissertation reside within this context and are applied to
homogeneous anisotropic media. In the first of these chapter, we determine the
conditions for elliptical roots of the Christo!el equation in media that are the result
of the Backus average. Within these conditions, we demonstrate that the slowness
surfaces are nondetached. In the second chapter, we present a novel formulation for
the purpose of forward modelling traveltimes. Through the Taylor expansion along
vertical rays in a horizontally stratified Earth model, we obtain a homogeneous
transversely isotropic medium within which the traveltimes are similar to the
Fermat traveltimes of its constituent layers.
From an inverse perspective, the parameters of the theoretical models are estimated
so as to provide an agreement with physical observations. In this dissertation, one
chapter resides within this context, where we perform an inversion on traveltime
measurements acquired from a vertical seismic profile, otherwise referred to as field
data. We implement a derivative-free approach to minimize the residual sum of
squares between the measurements and the model. Since field data are not
necessarily complete and can be subject to measurement errors, we conduct a
simulation study on synthetically generated traveltimes to assess the accuracy of our
estimates. Then, we apply our approach to the field data to estimate the
inhomogeneity and anisotropy of the subsurface.Includes bibliographical references (pages 138-145
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
- …
