535 research outputs found
Minimal Delaunay Triangulations of Hyperbolic Surfaces
Get PDFMotivated by recent work on Delaunay triangulations of hyperbolic surfaces, we consider the minimal number of vertices of such triangulations. First, we show that every hyperbolic surface of genus g has a simplicial Delaunay triangulation with O(g) vertices, where edges are given by distance paths. Then, we construct a class of hyperbolic surfaces for which the order of this bound is optimal. Finally, to give a general lower bound, we show that the Ω(√g) lower bound for the number of vertices of a simplicial triangulation of a topological surface of genus g is tight for hyperbolic surfaces as well
Algorithms for Length Spectra of Combinatorial Tori
Get PDFConsider a weighted, undirected graph cellularly embedded on a topological
surface. The function assigning to each free homotopy class of closed curves
the length of a shortest cycle within this homotopy class is called the marked
length spectrum. The (unmarked) length spectrum is obtained by just listing the
length values of the marked length spectrum in increasing order.
In this paper, we describe algorithms for computing the (un)marked length
spectra of graphs embedded on the torus. More specifically, we preprocess a
weighted graph of complexity in time so that, given a
cycle with edges representing a free homotopy class, the length of a
shortest homotopic cycle can be computed in time. Moreover,
given any positive integer , the first values of its unmarked length
spectrum can be computed in time .
Our algorithms are based on a correspondence between weighted graphs on the
torus and polyhedral norms. In particular, we give a weight independent bound
on the complexity of the unit ball of such norms. As an immediate consequence
we can decide if two embedded weighted graphs have the same marked spectrum in
polynomial time. We also consider the problem of comparing the unmarked spectra
and provide a polynomial time algorithm in the unweighted case and a randomized
polynomial time algorithm otherwise.Comment: 33 pages, 16 figure
Societal need for multifunctional flood defenses: Introduction
No full textProf.dr.ir. Matthijs Kok is Professor of Flood Risk at the Faculty of Civil Engineering and Geosciences at TU Delft; he was Program leader of the ‘Integral and Sustainable Design of Multifunctional Flood Defenses’ research program, funded by the Dutch Science and Technology Foundation STW. Presently, he is Program leader of the STW-Perspectief research program ‘All RISK’, which will study the implementation of new risk standards in the Dutch national flood protection program (2017-2022). Hydraulic Structures and Flood Ris
Delaunay triangulations of hyperbolic surfaces
Get PDFTriangulations are among the most important and well-studied objects in computational geometry. A triangulation is a subdivision of a surface into triangles. This allows the use of computer algorithms to analyze the geometry of the surface or perform simulations. A Delaunay triangulation is a particular kind of triangulation that is often used because of its favorable properties. In this thesis we studied Delaunay triangulations of hyperbolic surfaces. Hyperbolic surfaces are surfaces with a constant negative curvature and can be used to model shapes or structures that, intuitively speaking, cannot be "flattened" in the Euclidean plane. In the thesis we describe the properties of a specific class of hyperbolic surfaces that allow a well-known algorithm for computing Delaunay triangulations to be generalized to these surfaces. In particular, we compute the systole of these surfaces, which is an important parameter in the algorithm. Moreover, we provide upper and lower bounds for the minimal number of vertices of Delaunay triangulations of hyperbolic surfaces and show that these bounds are asymptotically optimal
On curves with constant curvatures
Get PDFOne of the fields of research of Computer Aided Geometric Design is approximating complex curves by simpler curves. Curves with constant curvatures are useful tools for these purposes. However, parametrizations of such curves are not always easily given. In this paper we will derive several necessary and sufficient geometric conditions for a curve to have constant curvatures, both in Euclidean geometry and in affine geometry
Correction to: CT angiography vs echocardiography for detection of cardiac thrombi in ischemic stroke: a systematic review and meta-analysis (Journal of Neurology, (2020), 267, 6, (1793-1801), 10.1007/s00415-020-09766-8)
No full textThe original version of this article unfortunately contained a mistake. In the author list, the first and last names of two authors, S. Matthijs Boekholdt and R. Nils Planken, were tagged incorrectly. Therefore, author names are abbreviated wrongly in Springerlink. The first and last names should be as follows: First name: S. Matthijs Last name: Boekholdt First name: R. Nils Last name: Planken
"What drives ability peer effects?" Replication Datasets
No full textData repository for replication datasets of "What drives ability peer effects?", Max Coveney and Matthijs Oosterveen, European Economic Review.The archived datasets contain all variables that were available to the researchers and allows for complete replication. Separate datasets are used for the different types of analyses (student level, student-course level, student-pair level). The student and group IDs are anonymized to prevent identification of individuals. Access to the data can be granted by submitting a research request to the corresponding author ([email protected]).The full paper can be found at: https://doi.org/10.1016/j.euroecorev.2021.103763</div
Computing the second and third systoles of a combinatorial surface
Get PDFGiven a weighted, undirected graph cellularly embedded on a topological
surface , we describe algorithms to compute the second shortest and third
shortest closed walks of that are homotopically non-trivial in . Our
algorithms run in time for the second shortest walk and in
time for the third shortest walk. We also show how to reduce the
running time for the second shortest homotopically non-trivial closed walk to
when both the genus and the number of boundaries are fixed.
Our algorithms rely on a careful analysis of the configurations of the first
three shortest homotopically non-trivial curves in . As an intermediate
step, we also describe how to compute a shortest essential arc between
\emph{one} pair of vertices or between \emph{all} pairs of vertices of a given
boundary component of in time or time, respectively.Comment: 29 pages, 6 figure
Computing the second and third systoles of a combinatorial surface
No full text29 pages, 6 figuresGiven a weighted, undirected graph cellularly embedded on a topological surface , we describe algorithms to compute the second shortest and third shortest closed walks of that are homotopically non-trivial in . Our algorithms run in time for the second shortest walk and in time for the third shortest walk. We also show how to reduce the running time for the second shortest homotopically non-trivial closed walk to when both the genus and the number of boundaries are fixed. Our algorithms rely on a careful analysis of the configurations of the first three shortest homotopically non-trivial curves in . As an intermediate step, we also describe how to compute a shortest essential arc between \emph{one} pair of vertices or between \emph{all} pairs of vertices of a given boundary component of in time or time, respectively
Corrigendum to “The right hemisphere is dominant in organization of visual search—A study in stroke patients” [Behav. Brain Res. 304 (2016) 71–79]((S0166432816300626)(10.1016/j.bbr.2016.02.004))
No full textThe authors regret as the name of the second author was published incorrectly. The correct surname is ‘Biesbroek’ and the correct first names are “J. Matthijs”. The authors would like to apologise for any inconvenience caused
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