1,720,977 research outputs found
Reconstruction of convex lattice sets from tomographic projections in quartic time
No full textFilling operations are procedures which are used in Discrete Tomography for the reconstruction of lattice sets having some convexity constraints. Many algorithms have been published giving fast implementations of these operations, and the best running time [S. Brunetti, A. Daurat, A. Kuba, Fast filling operations used in the reconstruction of convex lattice sets, in: Proc. of DGCI 2006, in: Lecture Notes in Comp. Sci., vol. 4245, 2006, pp. 98–109] is O(N2logN) time, where N is the size of projections. In this paper we improve this result by providing an implementation of the filling operations in O(N2). As a consequence, we reduce the time-complexity of the reconstruction algorithms for many classes of lattice sets having some convexity properties. In particular, the reconstruction of convex lattice sets satisfying the conditions of Gardner–Gritzmann [R.J. Gardner, P. Gritzmann, Discrete tomography: Determination of finite sets by X-rays, Trans. Amer. Math. Soc. 349 (1997) 2271–2295] can be performed in O(N4)-time
Determination of Q-convex bodies by X-rays
No full textThe class of Q-convex bodies is defined, and the uniqueness result proved by Gardner and McMullen in 1980 for planar convex bodies is extended to this new class
Reconstruction of Discrete Sets From Two or More Projections in any Direction
No full textWe study the problem of reconstructing discrete sets satisfying properties of connectivity and convexity by projections taken along many directions. The members of the class we consider are called Q-convexes. We design a polynomial time reconstruction algorithm for this class
Reconstruction of Q-convex lattice sets
No full textWe present a class od lattice sets for which there are unique determination and a polynomial time reconstruction algorithm by X-rays in suitable directions. Moreover many reconstructions of different classes of lattice sets having convexity/connnectivity constrains can be seen as particular cases of the former case
Fast filling operations used in the reconstruction of convex lattice sets
No full textFilling operations are procedures which are used in Discrete Tomography for the reconstruction of lattice sets having some convexity constraints. In [1], an algorithm which performs four of these filling operations has a time complexity of O(N2 log N), where N is the size of projections, and leads to a reconstruction algorithm for convex polyominoes running in O(N 6 log N)-time. In this paper we first improve the implementation of these four filling operations to a time complexity of O(N2), and additionally we provide an implementation of a fifth filling operation (introduced in [2]) in O(N2 log N) that permits to decrease the overall time-complexity of the reconstruction algorithm to O(N4 log N). More generally, the reconstruction of Q-convex sets and convex lattice sets (intersection of a convex polygon with Z2) can be done in O(N4 log N)-time. © Springer-Verlag Berlin Heidelberg 2006
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
An Algorithm for Reconstructing Special Lattice Sets from Their Approximate X-rays
No full textWe study the problem of reconstructing finite subsets of the integer lattice Z2 from their approximate X-rays in a finite number of prescribed lattice directions. We provide a polynomial-time algorithm for reconstructing Q-convex sets from their “approximate” X-rays. A Qconvex set is a special subset of Z2 having some convexity properties. This algorithm can be used for reconstructing convex subsets of Z2 from their exact X-rays in some sets of four prescribed lattice directions, or in any set of seven prescribed mutually nonparallel lattice directions
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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