1,721,002 research outputs found
Surface Reconstruction From Point Cloud using a Semi-Lagrangian Scheme with Local Interpolator
No full textWe propose a level set method to reconstruct unknown surfaces from point clouds, without assuming that the connections between points are known. We consider a variational formulation with a curvature constraint that minimizes the surface area weighted by the distance of the surface from the point cloud. More precisely we solve an equivalent advection–diffusion equation that governs the evolution of an initial surface described implicitly by a level set function. Among all the possible representations, we aim to compute the signed distance function at least in the vicinity of the reconstructed surface. The numerical method for the approximation of the solution is based on a semi-Lagrangian scheme coupled with a local interpolator. In particular, we resort to a multi-linear interpolator and to a Weighted Essentially Non-oscillatory one, to improve the accuracy of the reconstruction. An analysis of the parameters employed in the model is given, focusing in particular on the effect of the curvature regularization, and on the presence of noisy data. Special attention has been paid to the localization of the method and to the development of fast algorithms that run in parallel, resulting in faster reconstruction and thus the opportunity to easily improve the resolution. Numerical tests in two and three dimensions are presented to evaluate the quality of the reconstruction and the efficiency of the algorithm in terms of computational time
L'impatto della Direttiva Eurosim sulla struttura e sul funzionamento del mercato mobiliare italiano
No full textIn Collana"Direttiva Eurosim,la borsa e le banche" - Bancaria Editrice, Rom
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
A CWENO Large Time-Step Scheme for Hamilton-Jacobi Equations
No full textWe propose a high-order numerical scheme for time-dependent first-order Hamilton-Jacobi-Bellman (HJB) equations. In particular, we propose to combine a semi-Lagrangian (SL) scheme with a Central Weighted Essentially Non-Oscillatory (CWENO) reconstruction. The CWENO method provides a non-oscillatory, high-order reconstruction polynomial that allows efficient evaluations at multiple reconstruction points, while the SL method ensures stability without any time-step restrictions. Together, they form a particularly effective framework for solving HJB equations. We prove a convergence result in the case of state- and time-independent Hamiltonians. Numerical simulations are presented in space dimensions one and two, also for more general state- and time-dependent Hamiltonians, demonstrating superior performance in terms of CPU time gain compared with a semi-Lagrangian scheme coupled with Weighted Non-Oscillatory reconstructions
From Point Clouds to 3D Simulations of Marble Sulfation
No full textIn this chapter we present a complete workflow for the prediction of the marble sulfation of a work of art. The computations are based on a mathematical model of the physical-chemical phenomenon of penetration of a pollutant gas in the pores of the stone, its reaction with the pristine material and the consequent change of porosity and speed of diffusion of the gas. The computations are performed in three space dimensions and the geometry of the object is described by a levelset function, which in turn is computed from a cloud of points belonging to the surface of the object, without using any information on the connectivity among the points. We consider a synthetic and a real object. On the first an exact levelset is also known and we study the convergence of the levelset algorithms and compare the solutions computed on the exact and on the approximated geometry. The second one is a point cloud acquired by laser scanning a real stone object representing a frog
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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