1,721,023 research outputs found
Ambiguity and Depth Resolution in Potential Field Inversion
No full textWe study the inversion of potential fields and evaluate
the degree of depth resolution achievable for a given
problem. To this end, we introduce a powerful new tool:
the depth-resolution plot (DRP). The DRP allows a
theoretical study of how much the depth resolution in
a potential-field inversion is influenced by the way the
problem is discretized and regularized. The DRP also
allows a careful study of the influence of various kinds
of ambiguities, such as those from data errors or of a
purely algebraic nature. The achievable depth resolution
is related to the given discretization, regularization,
and data noise level. We compute DRP by means of
singular-value decomposition (SVD) or its generalization
(GSVD), depending on the particular regularization
method chosen.
To illustrate the use of the DRP, we assume a source
volume of specified depth and horizontal extent in
which the solution is piecewise constant within a 3D
grid of blocks. We consider various linear regularization
terms in a Tikhonov (damped least-squares) formulation,
some based on using higher-order derivatives
in the objective function. DRPs are illustrated for
both synthetic and real data. Our analysis shows that if
the algebraic ambiguity is not too large and a suitable
smoothing norm is used, some depth resolution can be
obtained without resorting to any subjective choice of
depth weighting
IR Tools: a MATLAB package of iterative regularization methods and large-scale test problems
No full text
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
A tool for analysing depth resolution in potential-field inversion: application to the Neapolitan Volcanic Area
No full textA careful management of the data errors in potential field inversion is crucial for obtaining reliable information about the source distribution with respect to depth. The Depth Resolution Plot introduced by Fedi, Hansen and Paoletti provides a convenient tool for this analysis: it allows a computational/visual analysis of how much the depth resolution in a potential-field inversion problem is influenced by the way the problem is discretized and regularized. Here we present a variant of the Depth Resolution Plot, called Approx Depth Resolution Plot, which is better suited for large-scale problems, and we employ it to study the retrievable depth resolution in the inversion of the gravity field of the Neapolitan Volcanic Area
A tool for analysing depth resolution in potential-field inversion
No full textA careful management of the ambiguities and errors in potential field inversion is crucial for obtaining
reliable information about the source distribution with respect to depth. In this paper we introduce a tool,
the ApproxDRP, which is based on an approximation of the singular vectors obtained by the iterative
Lanczos bidiagonalization algorithm. This tool allows a computational/visual analysis of how much the
depth resolution in a potential-field inversion problem is influenced by the way the problem is discretized
and regularized. Since the ApproxDRP is based on an iterative method, it is suitable for large-scale
problems. We show that when used in combination with a plot of the approximate SVD quantities, the
ApproxDRP may successfully show the limitations of depth resolution resulting from noise in the data.
This allows a reliable analysis of the retrievable depth information and effectively guides the user in
choosing the optimal number of iterations, for a given problem
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
- …
