Gabriel Wittum

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In this paper, the algorithms of the automatic mesh generator NETGEN are described. The domain is provided by a Constructive Solid Geometry (CSG). The whole task of 3D mesh generation splits into four subproblems of special point calculation, edge following, surface meshing and finally volume mesh generation. Surface and volume mesh generation are based on(More)
Time plays an important role in medical and neuropsychological diagnosis and research. In the field of Electroand MagnetoEncephaloGraphy (EEG/MEG) source localization, a current distribution in the human brain is reconstructed noninvasively by means of measured fields outside the head. High resolution finite element modeling for the field computation leads(More)
Acknowledgements This thesis has been prepared during my work at the Interdisciplinary Center for Scientiic Computing (IWR) of the Ruprecht-Karls-Universitt at Heidelberg. I would like to thank Prof. H.G. Bock for providing a very creative and inspiring atmosphere within his research group, of which I am lucky enough to be a member. I am indebted to him and(More)
The shape of neuronal cells strongly resembles botanical trees or roots of plants. To analyze and compare these complex three-dimensional structures it is important to develop suitable methods. We review the so called tree-edit-distance known from theoretical computer science and use this distance to define dissimilarity measures for neuronal cells. This(More)
Mathematical modeling of skin transport is considered a valuable alternative of in-vitro and in-vivo investigations especially considering ethical and economical questions. Mechanistic diffusion models describe skin transport by solving Fick's 2nd law of diffusion in time and space; however models relying entirely on a consistent experimental data set are(More)
Synaptic activity initiates many adaptive responses in neurons. Here we report a novel form of structural plasticity in dissociated hippocampal cultures and slice preparations. Using a recently developed algorithm for three-dimensional image reconstruction and quantitative measurements of cell organelles, we found that many nuclei from hippocampal neurons(More)
Partial differential operators in finance often originate in bounded linear stochastic processes. As a consequence, diffusion over these boundaries is zero and the corresponding coefficients vanish. The choice of parameters and stretched grids lead to additional anisotropies in the discrete equations or inequalities. In this study various block smoothers(More)
A class of a posteriori estimators is studied for the error in the maximum-norm of the gradient on single elements when the finite element method is used to approximate solutions of second order elliptic problems. The meshes are unstructured and, in particular, it is not assumed that there are any known superconvergent points. The estimators are based on(More)
In this paper we study the convergence of a multigrid method for the solution of a two-dimensional linear second order elliptic equation, discretized by discontinuous Galerkin (DG) methods. For the Baumann–Oden and for the symmetric DG method, we give a detailed analysis of the convergence for celland point-wise block-relaxation strategies. We show that,(More)