1,720,970 research outputs found
Complete characterization of the regions of C2 and C3 convergence of combined ternary 4-point subdivision schemes
No full textWe present a 3-parameter combined ternary 4-point subdivision scheme that provides a unifying framework for several independent proposals appeared in the literature. For such a scheme we completely characterize the regions of C2 and C3 convergence, that is the sets of parameters that fulfill the necessary and sufficient conditions for C2 and C3 convergence, respectively. The identified region of C2 convergence improves a recent result obtained by other authors by considering only sufficient conditions for C2 convergenc
On extraordinary rules of quad-based interpolatory subdivision schemes
No full textThis article deals with interpolatory subdivision schemes generalizing the tensor-product version of the Dubuc-Deslauriers 4-point scheme to quadrilateral meshes of arbitrary manifold topology. In particular, we focus our attention on an extension of the C1 regular stencils that respectively exploits (N+2)-point and (2N+8)-point stencils for the computation of an edge-point and a face-point in the vicinity of an extraordinary vertex of valence N≠4 not lying on a boundary. The aim of our work consists in identifying which constraints are required to be respected by the weights appearing in the above stencils in order to get closed limit surfaces that are C1-continuous at extraordinary points, have both principal curvatures bounded and at least one of them nonzero. The obtained constraints are used to easily check these features in the limit surfaces resulting from the application of special extraordinary rules proposed in the literature by different authors. Moreover, the conditions derived on the stencil weights are exploited to design new extraordinary rules that can produce closed limit surfaces of the same quality as the existing proposals, but at a reduced computational cos
On the interpolating 5-point ternary subdivision scheme: A revised proof of convexity-preservation and an application-oriented extension
No full textIn this paper we provide the conditions that the free parameter of the interpolating 5-point ternary subdivision scheme and the vertices of a strictly convex initial polygon have to satisfy to guarantee the convexity preservation of the limit curve. Furthermore, we propose an application-oriented extension of the interpolating 5-point ternary subdivision scheme which allows one to construct . C2 limit curves where locally convex segments as well as conic pieces can be incorporated simultaneously. The resulting subdivision scheme generalizes the non-stationary ternary interpolatory 4-point scheme and improves the quality of its limit curves by raising the smoothness order from . 1 to . 2 and by introducing the additional property of convexity preservatio
Building blocks for designing arbitrarily smooth subdivision schemes with conic precision
No full textSince subdivision schemes featured by high smoothness and conic precision are strongly required in many application contexts, in this work we define the building blocks to obtain new families of non-stationary subdivision schemes enjoying such properties. To this purpose, we firstly derive a non-stationary extension of the Lane-Riesenfeld algorithm, and we exploit the resulting class of schemes to design a non-stationary family of alternating primal/dual subdivision schemes, all featured by reproduction of 1, x, e^tx, e^-tx, t in [0, π) ∪ iR+. Then, we focus our attention on interpolatory subdivision schemes with conic precision, that can be obtained as a byproduct of the above classes. In particular, we present a novel construction of a family of non-stationary interpolatory 2n-point schemes which generalizes the well-known Dubuc-Deslauriers family in such a way the nth (n ≥ 2) family member reproduces Π_2n-3 ∪ e^tx, e^-tx, t in [0, π) ∪ iR+, and keeps the original smoothness of its stationary counterpart unchanged
Improving smoothness and accuracy of Modified Butterfly subdivision scheme
No full textMotivated by the increasing request of surface representation techniques suitable for biomedical imaging applications, we construct a non-stationary subdivision scheme for regular 3-directional grids, which enjoys the following properties: (i) interpolation, (ii) affine invariance, (iii) C2 smoothness, (iv) approximation order 6 and (v) the capability of reproducing several trigonometric surfaces, especially ellipsoids. To study the smoothness properties of this new scheme via existing analysis tools, we also construct an auxiliary stationary subdivision scheme enjoying properties (i)-(iv). Taking into account that, when applied on regular 3-directional grids, the Modified Butterfly scheme is C1 and has approximation order 4, the subdivision schemes derived in this paper can be considered improved variants of the Modified Butterfly schem
Convergence and Normal Continuity Analysis of Nonstationary Subdivision Schemes Near Extraordinary Vertices and Faces
Full text linkConvergence and normal continuity analysis of a bivariate nonstationary (level-dependent) subdivision scheme for 2-manifold meshes with arbitrary topology is still an open issue. Exploiting ideas from the theory of asymptotically equivalent subdivision schemes, in this paper we derive new sufficient conditions for establishing convergence and normal continuity of any rotationally symmetric, nonstationary subdivision scheme near an extraordinary vertex/face
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
- …
