1,721,060 research outputs found
Hierarchical bases preconditioners for a conformingly discretized combined field integral equation operator
No full textIt is shown how hierarchical bases preconditioners constructed for stabilizing the electric field integral equation (EFIE) operator can be used for stabilizing the combined field integral equation (CFIE) operator. Since the CFIE operator consists of the EFIE and magnetic field integral equation (MFIE) operator, also the CFIE operator is affected by the low-frequency and the dense-discretization breakdown of the EFIE operator. We show that the hierarchical basis preconditioner for the EFIE operator must not directly be applied to the CFIE operator, since this would introduce a new ill-conditioning. Instead, Helmholtz projectors are used in a left-preconditioning scheme for implicitly regularizing the solenoidal Helmholtz subspace of the CFIE operator, while the hierarchical stars are used for the regularization of the non-solenoidal Helmholtz subspace. Numerical results corroborate the presented theory
A hierarchical preconditioner for the electric field integral equation on unstructured meshes based on primal and dual Haar bases
No full textLow-Frequency-Stabilized Electric Field Integral Equation on Topologically Non-Trivial Geometries for Arbitrary Excitations
No full textThe low-frequency preconditioned electric field integral equation (EFIE) based on quasi-Helmholtz decompositions is widely used to determine the radiated or scattered field by a given structure over a wide frequency range. However, if the excitation source is not a plane wave but, for instance, a line current, the standard preconditioners cannot recover all current components required to accurately obtain the fields. In this work, we propose an adaptive frequency normalization scheme of the discretized system that overcomes this problem irrespective of the specific excitation and irrespective of the underlying topology of the structure. To this end, the appropriate scaling factors are derived solely based on the norms of the right-hand side (RHS) components. Numerical results demonstrate the importance of our approach to obtain accurate results
Towards Accurate Discretization of Arbitrary Right-Hand Side Excitations on Multiply-Connected Geometries
No full textFor the computation of the field scattered by an object, integral equation formulations such as the electric field integral equation (EFIE), the magnetic field integral equation (MFIE), and the combined field integral equation (CFIE) are well-established techniques. They are flexible, accurate, and computationally efficient. They suffer, however, from different issues when the frequency becomes low: The EFIE and the CFIE become ill-conditioned. Furthermore, for the MFIE significant round-off errors prevent an accurate solution. As a remedy, a quasi¬Helmholtz decomposition of the surface current density into a loop-star or a loop-tree basis can be leveraged [1]. Even more suitable are quasi-Helmholtz projectors derived from the loop-star basis [2]. They avoid the introduction of a dense-discretization breakdown such that in combination with Calderon preconditioning a stable system matrix is obtained
Hierarchical basis preconditioners and their application to the PMWCHT integral equation
No full textWe present an analysis of the application of (general) hierarchical basis preconditioners developed for preconditioning the electric field integral equation (EFIE) to the Poggio-Miller-Chang-Harrington-Wu-Tsai (PMCHWT) integral equation on simply and multiply-connected geometries. First, we discuss the correct choice of the rescaling factors for the solenoidal and non-solenoidal hierarchical bases. Then we consider the harmonic subspace that appears on multiply-connected domains: it turns out that differently from the combined field integral equation (CFIE), the global loops must not be rescaled in frequency. The numerical results confirm the theoretically predicted results
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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