1,720,968 research outputs found
Ray tracing in elliptical anisotropic media using Linear Traveltime Interpolation (LTI) method applied to traveltime seismic tomography
No full textTracciamento di raggi sismici in un mezzo trasversalmente isotropo nel caso di tomografia a geometria complessa
No full textHybrid approach for travel time seismic tomography in elliptical anysotropic media
Full text linkHybrid approach for seismic travel time tomography is proposed in the case of elliptical anisotropic media. A sequential scheme is presented that combines Simulating Annealing with Linearized Least Squares inversion: at first, Simulated Annealing is implemented to obtain a velocity model that can be used as initial guess for successive Linearized Least Square inversion; in the meantime Linear Traveltime Interpolation is diffusely used to trace raypaths and calculate traveltimes. The procedure was tested both for a synthetic model and a field study. Since the field study come from a previous study, uniquely solved by Linearized Least Squares inversion without suggestions for initial guess of the velocity model, we were interested in evaluating upgrades from hybrid approach compared with solutions coming from a single technique. We found hybrid approach able to individuate a better velocity model with respect to a ”single technique” approach but, as the improvement was slight despite of the big amount of computation time needed by simulated annealing, we had also an indirect validation of the previous results of the field study
Electrical resistivity and seismic refraction tomography to detect buryed cavity
No full textNear-surface cavities can pose serious hazards to human safety, especially in highly urbanized town centres. The location of subsurface voids, the estimation of their size and the evaluation of the overburden thickness are necessary to assess the risk of collapse. In this study, electrical resistivity tomography (ERT) and seismic refraction tomography data are integrated in a joint interpretation process for cavity location in the city of Rome. ERT is a well established and widely employed method for cavity detection. However, additional information provided by seismic refraction tomography is capable of eliminating some potential pitfalls in resistivity data interpretation. We propose that the structure of the cavities defined by ERT can be used as a base to optimize seismic refraction tomography investigations within the framework of a joint interpretation process. Data integration and the insertion of a priori information are key issues for reducing the uncertainties associated with the inversion process and for optimizing both acquisition procedures and computation time. Herein, the two geophysical methods are tested on both synthetic and real data and the integration of the results is found to be successful in detecting isolated cavities and in assessing their geometrical characteristics. The cavity location inferred by geophysical non-invasive methods has been subsequently confirmed by direct inspection
Staggered grids as a tool to improve the model resolution in seismic tomography for elliptical anisotropic media
No full textIn this study we present the use of staggered grid as a tool to improve the resolution of inverse model in seismic tomography in the case of elliptical anisotropic media. We analyze two synthetic models, both showing elliptical anisotropic characteristics, with different complexity: the first consists of a body with rectangular shape having inside an anomaly with higher velocity and the second one is characterized by morphological variation to simulate a watershed. This second case is studied for both cross-hole and high ray coverage configuration. Successively, a previous field survey is analyzed introducing staggered grids and the results are compared with the old ones, solved using a constant cells’ size model. Staggered grid give enhanced results in terms of the velocity model and can be used as a tool to improve the knowledge of the studied domain by determining cells with variable shape and size, useful to infer a good initial model for a further inversion. This conclusion applies also to isotropic media
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
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