@incollection{PoethkowHege2012, author = {P{\"o}thkow, Kai and Hege, Hans-Christian}, title = {Uncertainty Propagation in DT-MRI Anisotropy Isosurface Extraction}, series = {New Developments in the Visualization and Processing of Tensor Fields}, booktitle = {New Developments in the Visualization and Processing of Tensor Fields}, editor = {Laidlaw, David and Vilanova, Anna}, publisher = {Springer}, address = {Berlin}, pages = {209 -- 225}, year = {2012}, language = {en} } @article{PoethkowWeberHege2011, author = {P{\"o}thkow, Kai and Weber, Britta and Hege, Hans-Christian}, title = {Probabilistic Marching Cubes}, series = {Computer Graphics Forum}, volume = {30}, journal = {Computer Graphics Forum}, number = {3}, doi = {10.1111/j.1467-8659.2011.01942.x}, pages = {931 -- 940}, year = {2011}, language = {en} } @article{PoethkowHege2013, author = {P{\"o}thkow, Kai and Hege, Hans-Christian}, title = {Nonparametric Models for Uncertainty Visualization}, series = {Computer Graphics Forum}, volume = {32}, journal = {Computer Graphics Forum}, number = {3}, doi = {10.1111/cgf.12100 target}, pages = {131 -- 140}, year = {2013}, language = {en} } @article{PoethkowPetzHege2013, author = {P{\"o}thkow, Kai and Petz, Christoph and Hege, Hans-Christian}, title = {Approximate Level-Crossing Probabilities for Interactive Visualization of Uncertain Isocontours}, series = {International Journal for Uncertainty Quantification}, volume = {3}, journal = {International Journal for Uncertainty Quantification}, number = {2}, doi = {10.1615/Int.J.UncertaintyQuantification.2012003958}, pages = {101 -- 117}, year = {2013}, language = {en} } @phdthesis{Poethkow, author = {P{\"o}thkow, Kai}, title = {Modeling, Quantification and Visualization of Probabilistic Features in Fields with Uncertainties}, abstract = {Eine grundlegende Eigenschaft von naturwissenschaftlichen Daten ist, dass der wahre Wert einer Gr{\"o}ße nicht beliebig genau bestimmbar ist. Es ist lediglich m{\"o}glich, ihn durch Intervalle einzugrenzen oder die Unsicherheit durch eine Wahrscheinlichkeitsverteilung zu charakterisieren. Dies gilt f{\"u}r alle reellwertigen Daten, sowohl f{\"u}r Mess-, als auch f{\"u}r Simulationsergebnisse. Beispiele sind Messungen von grundlegenden physikalischen Gr{\"o}ßen wie Geschwindigkeit oder auch langfristige Temperaturvorhersagen, die durch Klimamodelle berechnet werden. Die Unsicherheit von Ergebnissen ist eine wichtige Information, die in Natur- und Ingenieurwissenschaften h{\"a}ufig durch Konfidenzintervalle in 1D-Plots und Tabellen angezeigt wird. Im Gegensatz dazu ist es bisher bei der Visualisierung von 2D- und 3D-Daten mithilfe von Standardmethoden meist unm{\"o}glich, die Datenunsicherheit zu repr{\"a}sentieren. Diese Arbeit stellt wahrscheinlichkeitstheoretisch fundierte Methoden vor, die die Analyse und Visualisierung von Skalar-, Vektor- und Tensorfeldern mit Unsicherheiten erm{\"o}glichen. Der Fokus liegt dabei auf der Extraktion von raumzeitlichen geometrischen und topologischen Merkmalen aus den Feldern (z.B. Isokonturen und kritische Punkte). Wir nutzen parametrische und nichtparametrische Zufallsfelder, um Variabilit{\"a}t und r{\"a}umliche Korrelation mathematisch zu modellieren. Die Wahrscheinlichkeitsverteilungen werden aus Ensemble-Datens{\"a}tzen gesch{\"a}tzt, die mehrere Simulationsergebnisse (z.B. basierend auf variierenden Simulationsparametern) zusammenfassen. Wir untersuchen die Konditionszahlen von Merkmalsextraktionsmethoden, um die Sensitivit{\"a}t, d.h. die Verst{\"a}rkung oder Abschw{\"a}chung der Unsicherheit der Ergebnisse relativ zu Unsicherheiten in den Eingangsdaten abzusch{\"a}tzen. Wir stellen einen allgemeiner Ansatz f{\"u}r die probabilistische Merkmalsextraktion vor, der die Basis f{\"u}r die Berechnung r{\"a}umlicher Wahrscheinlichkeitsverteilungen von verschiedenen Merkmalen in Skalar-, Vektor- und Tensorfeldern bildet. In diesem Framework werden Wahrscheinlichkeiten f{\"u}r die Existenz von Merkmalen aus lokalen Randverteilungen und formalen Merkmalsdefinitionen berechnet. Numerisch k{\"o}nnen die Wahrscheinlichkeiten durch Monte-Carlo­-Integration bestimmt werden. Um den hohen Rechenaufwand dieses Ansatzes zu vermeiden, schlagen wir schnelle Berechnungsmethoden vor, wobei Merkmalswahrscheinlichkeiten n{\"a}herungsweise mit Hilfe von Surrogatfunktionen bzw. Lookup-Tabellen gesch{\"a}tzt werden. Die vorgeschlagenen Methoden werden anhand von Daten aus Klima- und Biofluidmechaniksimulationen sowie aus der medizinischen Bildgebung qualitativ und quantitativ evaluiert.}, language = {en} } @inproceedings{AgudoJacomeHegePaetschetal., author = {Agudo J{\´a}come, Leonardo and Hege, Hans-Christian and Paetsch, Olaf and P{\"o}thkow, Kai}, title = {3D Reconstruction, Visualization and Quantification of Dislocations from Transmission Electron Microscopy Stereo-Pairs}, series = {Microscopy and Microanalysis 2016, July 24-28 Columbus, Ohio}, booktitle = {Microscopy and Microanalysis 2016, July 24-28 Columbus, Ohio}, language = {en} } @article{GoubergritsOsmanMevertetal., author = {Goubergrits, Leonid and Osman, Jan and Mevert, Ricardo and Kertzscher, Ulrich and P{\"o}thkow, Kai and Hege, Hans-Christian}, title = {Turbulence in blood damage modeling}, series = {The International Journal of Artificial Organs}, volume = {39}, journal = {The International Journal of Artificial Organs}, number = {4}, doi = {10.5301/ijao.5000476}, pages = {147 -- 210}, abstract = {Purpose: To account for the impact of turbulence in blood damage modeling, a novel approach based on the generation of instantaneous flow fields from RANS simulations is proposed. Methods: Turbulent flow in a bileaflet mechanical heart valve was simulated using RANS-based (SST k-ω) flow solver using FLUENT 14.5. The calculated Reynolds shear stress (RSS) field is transformed into a set of divergence-free random vector fields representing turbulent velocity fluctuations using procedural noise functions. To consider the random path of the blood cells, instantaneous flow fields were computed for each time step by summation of RSS-based divergence-free random and mean velocity fields. Using those instantaneous flow fields, instantaneous pathlines and corresponding point-wise instantaneous shear stresses were calculated. For a comparison, averaged pathlines based on mean velocity field and respective viscous shear stresses together with RSS values were calculated. Finally, the blood damage index (hemolysis) was integrated along the averaged and instantaneous pathlines using a power law approach and then compared. Results: Using RSS in blood damage modeling without a correction factor overestimates damaging stress and thus the blood damage (hemolysis). Blood damage histograms based on both presented approaches differ. Conclusions: A novel approach to calculate blood damage without using RSS as a damaging parameter is established. The results of our numerical experiment support the hypothesis that the use of RSS as a damaging parameter should be avoided.}, language = {en} } @inproceedings{JacomeEggelerPoethkowetal., author = {J{\´a}come, Leonardo Agudo and Eggeler, Gunter and P{\"o}thkow, Kai and Paetsch, Olaf and Hege, Hans-Christian}, title = {Three-Dimensional Characterization of Superdislocation Interactions in the High Temperature and Low Stress Creep Regime of Ni-Base Superalloy Single Crystals}, series = {Proceedings of CREEP 2015 - 13th International Conference on Creep and Fracture of Engineering Materials and Structures, May 31 - June 4, 2015, Toulouse, France}, booktitle = {Proceedings of CREEP 2015 - 13th International Conference on Creep and Fracture of Engineering Materials and Structures, May 31 - June 4, 2015, Toulouse, France}, pages = {16 -- 17}, abstract = {Monocrystaline Ni-base superalloys are the material of choice for first row blades in jet engine gas turbines. Using a novel visualization tool for 3D reconstruction and visualization of dislocation line segments from stereo-pairs of scanning transmission electron microscopies, the superdislocation substructures in Ni-base superalloy LEK 94 (crept to ε = 26\%) are characterized. Probable scenarios are discussed, how these dislocation substructures form.}, language = {en} } @article{PoethkowHege2011, author = {P{\"o}thkow, Kai and Hege, Hans-Christian}, title = {Positional Uncertainty of Isocontours: Condition Analysis and Probabilistic Measures}, series = {IEEE Transactions on Visualization and Computer Graphics}, volume = {17}, journal = {IEEE Transactions on Visualization and Computer Graphics}, number = {10}, doi = {10.1109/TVCG.2010.247}, pages = {1393 -- 1406}, year = {2011}, language = {en} } @article{PetzPoethkowHege2012, author = {Petz, Christoph and P{\"o}thkow, Kai and Hege, Hans-Christian}, title = {Probabilistic Local Features in Uncertain Vector Fields with Spatial Correlation}, series = {Computer Graphics Forum}, volume = {31}, journal = {Computer Graphics Forum}, number = {3}, pages = {1045 -- 1054}, year = {2012}, language = {en} } @article{GoubergritsSchallerKertzscheretal.2012, author = {Goubergrits, Leonid and Schaller, Jens and Kertzscher, Ulrich and van den Bruck, Nils and P{\"o}thkow, Kai and Petz, Christoph and Hege, Hans-Christian and Spuler, Andreas}, title = {Statistical wall shear stress maps of ruptured and unruptured middle cerebral artery aneurysms}, series = {J. R. Soc. Interface}, volume = {9}, journal = {J. R. Soc. Interface}, number = {69}, doi = {10.1098/rsif.2011.0490}, pages = {677 -- 688}, year = {2012}, language = {en} } @article{AgudoJacomeHegePaetschetal., author = {Agudo J{\´a}come, Leonardo and Hege, Hans-Christian and Paetsch, Olaf and P{\"o}thkow, Kai}, title = {Three-dimensional reconstruction and quantification of dislocation substructures from transmission electron microscopy stereo pairs}, series = {Ultramicroscopy}, volume = {195}, journal = {Ultramicroscopy}, doi = {10.1016/j.ultramic.2018.08.015}, pages = {157 -- 170}, abstract = {A great amount of material properties is strongly influenced by dislocations, the carriers of plastic deformation. It is therefore paramount to have appropriate tools to quantify dislocation substructures with regard to their features, e.g., dislocation density, Burgers vectors or line direction. While the transmission electron microscope (TEM) has been the most widely-used equipment implemented to investigate dislocations, it usually is limited to the two-dimensional (2D) observation of three-dimensional (3D) structures. We reconstruct, visualize and quantify 3D dislocation substructure models from only two TEM images (stereo pairs) and assess the results. The reconstruction is based on the manual interactive tracing of filiform objects on both images of the stereo pair. The reconstruction and quantification method are demonstrated on dark field (DF) scanning (S)TEM micrographs of dislocation substructures imaged under diffraction contrast conditions. For this purpose, thick regions (>300 nm) of TEM foils are analyzed, which are extracted from a Ni-base superalloy single crystal after high temperature creep deformation. It is shown how the method allows 3D quantification from stereo pairs in a wide range of tilt conditions, achieving line length and orientation uncertainties of 3\% and 7°, respectively. Parameters that affect the quality of such reconstructions are discussed.}, language = {en} } @misc{AgudoJacomeHegePaetschetal., author = {Agudo J{\´a}come, Leonardo and Hege, Hans-Christian and Paetsch, Olaf and P{\"o}thkow, Kai}, title = {Three-Dimensional Reconstruction and Quantification of Dislocation Substructures from Transmission Electron Microscopy Stereo-Pairs}, issn = {1438-0064}, url = {http://nbn-resolving.de/urn:nbn:de:0297-zib-70339}, abstract = {A great amount of material properties is strongly influenced by dislocations, the carriers of plastic deformation. It is therefore paramount to have appropriate tools to quantify dislocation substructures with regard to their features, e.g., dislocation density, Burgers vectors or line direction. While the transmission electron microscope (TEM) has been the most widely-used equipment implemented to investigate dislocations, it usually is limited to the two-dimensional (2D) observation of three-dimensional (3D) structures. We reconstruct, visualize and quantify 3D dislocation substructure models from only two TEM images (stereo-pairs) and assess the results. The reconstruction is based on the manual interactive tracing of filiform objects on both images of the stereo-pair. The reconstruction and quantification method are demonstrated on dark field (DF) scanning (S)TEM micrographs of dislocation substructures imaged under diffraction contrast conditions. For this purpose, thick regions (> 300 nm) of TEM foils are analyzed, which are extracted from a Ni-base superalloy single crystal after high temperature creep deformation. It is shown how the method allows 3D quantification from stereo-pairs in a wide range of tilt conditions, achieving line length and orientation uncertainties of 3 \% and 7°, respectively. Parameters that affect the quality of such reconstructions are discussed.}, language = {en} }