1,720,959 research outputs found
Invariance Rules in the Regularized Inversion of Gravity and Magnetic Fields and their Derivatives
No full textIn potential field inversion problems we usually solve underdetermined systems and this leads to a very shallow solution, typically known as minimum length solution. This may be avoided introducing a depth weighting function in the objective function (Li and Oldenburg, 1996). In this paper we derive invariance rules for either the minimum norm minimization and for the regularized inversion with depth weighting and positivity constraints. For a given source class, corresponding to a specific structural index N, the invariance rule assures that the same solution is obtained inverting the magnetic (or gravity) field or any of its nth order vertical derivatives. Although we demonstrate mathematically this invariance rule for the minimum norm minimization only, it is shown to occur also for the regularized inversion with depth weighting and positivity constraints. In this case, a source-class invariant form of depth weighting is derived, referring to that of the magnetic field, in the magnetic case, and to the 1st derivative of the gravity field, in the gravity case. We also illustrate how the combined effect of regularization parameter and depth weighting influences the estimated source model depth in the regularized inversion with depth weighting and positivity constraints
Large-scale 3D gravity data space inversion in hydrocarbon exploration
No full textGravity data inversion is a fundamental tool for geological exploration. A large amount of algorithms have been developed in the past, with different approaches.
The choice of the inversion algorithm depends, mainly, on the geological contest, the kind of solution desired, its resolution at the end of the process, the availability of a priori information and on how they can be included in the inversion algorithm.
A priori information has, often, a key-role in the inversion process. However, in case of reconstruction of salt and sub-salt structures, seismic information may be poor and unfeasible. So we need to constrain the model with other kind of information. In this work, we present a part of recent Eni R&D activity focused on gravity data inversion. The shown results are mainly based on the Data Space Inversion algorithm (Pilkington 2009), originally presented for the magnetic case, and here extended to the gravity problem.
We also putted a strong effort on the computational side of the problem, taking advantage from our experience in HPC (High Performance Computing), in order to speed up the inversion process and so enable its use at industrial level.
In this paper we present and discuss some results regarding the application of the methodology to the SEAM (SEG Advance Modeling, 2007) demonstrating that the algorithm allows a consistent depth and density model
Volume upward continuation of potential fields from the minimum-length solution: an optimal tool for continuation through general surfaces
No full textAlterazione di rocce tonalitiche nel deposito a Zn-Pb di Yanque (Cuzco, Peru): geologia e geomagnetismo.
No full textSelf-constrained inversion of microgravity data along a segment of the Irpinia fault
No full textA microgravity survey was completed to precisely locate and better characterize the near-surface geometry of a
recent fault with small throw in a mountainous area in the Southern Apennines (Italy). The site is on a segment of
the Irpinia fault,which is the source of theM6.9 1980 earthquake. This fault cuts a few meter of Mesozoic carbonate
bedrock and its younger,mostly Holocene continental deposits cover. The amplitude of the complete Bouguer
anomaly along two profiles across the fault is about 50 μGal. The data were analyzed and interpreted according to
a self-constrained strategy, where some rapid estimation of source parameters was later used as constraint for
the inversion. The fault has been clearly identified and localized in its horizontal position and depth. Interesting
features in the overburden have been identified and their interpretation has allowed us to estimate the fault slip rate,
which is consistent with independent geological estimates
Alteration of tonalite bodies at Yanque Zn-Pb deposit (Cuzco, Peru): geology and geomagnetism.
No full text
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
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