1,720,997 research outputs found
Self-constrained inversion of potential fields through a 3D depth weighting
No full textA new method for inversion of potential fields is developedusing a depth-weighting function specifically designed forfields related to complex source distributions. Such a weight-ing function is determined from an analysis of the field thatprecedes the inversion itself. The algorithm is self-consistent,meaning that the weighting used in the inversion is directlydeduced from the scaling properties of the field. Hence, thealgorithm is based on two steps: (1) estimation of the locallyhomogeneous degree of the field in a 3D domain of the har-monic region and (2) inversion of the data using a specificweighting function with a 3D variable exponent. A multiscaledata set is first formed by upward continuation of the originaldata. Local homogeneity and a multihomogeneous model arethen assumed, and a system built on the scaling function issolved at each point of the multiscale data set, yielding amultiscale set of local-homogeneity degrees of the field.Then, the estimated homogeneity degree is associated to themodel weighting function in the source volume. Tests on syn-thetic data show that the generalization of the depth weightingto a 3D function and the proposed two-step algorithm hasgreat potential to improve the quality of the solution. Thegravity field of a polyhedron is inverted yielding a realisticreconstruction of the whole body, including the bottom sur-face. The inversion of the aeromagnetic real data set, from theMt. Vulture area, also yields a good and geologically consis-tent reconstruction of the complex source distribution
Inversion of potential fields with an inhomogeneous depth weighting function
No full textThe purpose of this work is to introduce a new inversion method of potential field, based on a 3D model weighting function. For gravity and magnetic inversion, the model weighting function is normally assumed as a power law of the depth, with a constant exponent. Our approach is to consider a 3D varying exponent. Such inhomogeneous approach is built in two steps: a) each block is assigned an exponent β equal to the homogeneity degree of the potential field, estimated at different vertical and horizontal positions in the source-free (harmonic) region; b) the source model is computed by any inverse algorithms using a model weighting function. Here we perform step a) based on the scaling function method (Fedi and Florio, 2006) and step b) using the classical algorithm by Li and Oldenburg (1996) for magnetic data. We demonstrate the effectiveness of this method by application to a synthetic and a real case scenario
Unsupervised Boundary Analysis of potential field data: a machine learning method
No full textWe propose a boundary analysis method, called Unsupervised Boundary Analysis, based on machine learning algorithms applied to potential fields. Its main purpose is to create a data-driven process yielding a good estimate of the source position and extension, which does not depend on choices or assumptions typically made by expert interpreters, such as a low-pass filtering or weights in the Enhanced Horizontal Derivative case. We first tested the simple synthetic case of two vertical faults, to understand the robustness of the method. We recognized three classes on the basis of their centroids and found that the sources edges could be detected at the transition between two of them. Subsequently, we applied the Unsupervised Boundary Analysis to the real magnetometric data of the archaeological site of Torre Galli (Calabria, Italy). We compared the results with those from two different boundary analysis techniques, the Enhanced Horizontal Derivative and the Tilt Derivative. The main sources were well recognized by our approach, in good agreement with the Enhanced Horizontal Derivative results, but the Unsupervised Boundary Analysis led us to have a more complete description of the lineaments and to retrieve further features of archaeologic interest in the area. Instead, the Tilt Derivative features were affected by noise, which made interpretation more complicated
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
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