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Author

  • Hadwiger, Markus (8)
  • Aboulhassan, Amal (4)
  • Baum, Daniel (4)
  • Wodo, Olga (4)
  • Amassian, Aram (2)
  • Engelke, Wito (2)
  • Ganapathysubramanian, Baskar (2)
  • Hotz, Ingrid (2)
  • Kratz, Andrea (2)
  • Kuhn, Alexander (2)
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  • Lagrangian Coherent Structures (LCS) (1)
  • finite-time Lyapunov exponents (FTLE) (1)
  • flow field visualization (1)
  • time lines (1)
  • time-dependent vector fields (1)

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  • Visual Data Analysis (8)
  • Image Analysis in Biology and Materials Science (1)
  • Vergleichende Visualisierung (1)

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Adaptive Screen-Space Sampling for Volume Ray-Casting (2011)
Kratz, Andrea ; Reininghaus, Jan ; Hadwiger, Markus ; Hotz, Ingrid
This work is concerned with adaptive screen-space sampling for volume ray-casting. The goal is to reduce the number of rays being cast into the scene and, thus, the overall number of sampling points. We guarantee reliable images through explicit error control using an error estimator that is founded in the field of finite element methods (FEM). FEM theory further provides a well-founded theory to prove the efficiency of the presented algorithm via convergence analysis. We, therefore, compare the convergence behavior of our method against uniform subdivisions and a refinement scheme that was presented in the context of CPU volume ray-casting. Minimizing the number of sampling points is of interest for rendering large datasets where each evaluation might need an expensive decompression. Furthermore, with increasing screen resolutions high-resolution images are created more efficiently with our method.
Improved Visual Exploration and Hybrid Rendering of Stress Tensor Fields via Shape-Space Clustering. (2011)
Kratz, Andrea ; Hadwiger, Markus ; Hotz, Ingrid
A Novel Framework for Visual Detection and Exploration of Performance Bottlenecks in Organic Photovoltaic Solar Cell Materials (2015)
Aboulhassan, Amal ; Baum, Daniel ; Wodo, Olga ; Ganapathysubramanian, Baskar ; Amassian, Aram ; Hadwiger, Markus
The current characterization methods of the Bulk Heterojunction (BHJ) - the main material of the new Organic Photovoltaic solar cells - are limited to the analysis of global fabrication parameters. This reduces the efficiency of the BHJ design process, since it misses critical information about the local performance bottlenecks in the morphology of the material. In this paper, we propose a novel framework that fills this gap through visual charac- terization and exploration of local structure-performance correlations. We propose a new formula that correlates the structural features to the performance bottlenecks. Since research into BHJ materials is highly multidisci- plinary, we enable a visual feedback strategy that allows the scientists to build intuition about the best choices of fabrication parameters. We evaluate the usefulness of our proposed system by obtaining new BHJ characteri- zations. We furthermore show that our approach could reduce the previous work-flow time from days to minutes.
A Novel Framework for Visual Detection and Exploration of Performance Bottlenecks in Organic Photovoltaic Solar Cell Materials (2015)
Aboulhassan, Amal ; Baum, Daniel ; Wodo, Olga ; Ganapathysubramanian, Baskar ; Amassian, Aram ; Hadwiger, Markus
Current characterization methods of the so-called Bulk Heterojunction (BHJ), which is the main material of Organic Photovoltaic (OPV) solar cells, are limited to the analysis of global fabrication parameters. This reduces the efficiency of the BHJ design process, since it misses critical information about the local performance bottlenecks in the morphology of the material. In this paper, we propose a novel framework that fills this gap through visual characterization and exploration of local structure-performance correlations. We also propose a formula that correlates the structural features with the performance bottlenecks. Since research into BHJ materials is highly multidisciplinary, our framework enables a visual feedback strategy that allows scientists to build intuition about the best choices of fabrication parameters. We evaluate the usefulness of our proposed system by obtaining new BHJ characterizations. Furthermore, we show that our approach could substantially reduce the turnaround time.
Comparative Visual Analysis of Structure-Performance Relations in Complex Bulk-Heterojunction Morphologies (2017)
Aboulhassan, Amal ; Sicat, Ronell ; Baum, Daniel ; Wodo, Olga ; Hadwiger, Markus
The structure of Bulk-Heterojunction (BHJ) materials, the main component of organic photovoltaic solar cells, is very complex, and the relationship between structure and performance is still largely an open question. Overall, there is a wide spectrum of fabrication configurations resulting in different BHJ morphologies and correspondingly different performances. Current state- of-the-art methods for assessing the performance of BHJ morphologies are either based on global quantification of morphological features or simply on visual inspection of the morphology based on experimental imaging. This makes finding optimal BHJ structures very challenging. Moreover, finding the optimal fabrication parameters to get an optimal structure is still an open question. In this paper, we propose a visual analysis framework to help answer these questions through comparative visualization and parameter space exploration for local morphology features. With our approach, we enable scientists to explore multivariate correlations between local features and performance indicators of BHJ morphologies. Our framework is built on shape-based clustering of local cubical regions of the morphology that we call patches. This enables correlating the features of clusters with intuition-based performance indicators computed from geometrical and topological features of charge paths.
Time Line Cell Tracking for the Approximation of Lagrangian Coherent Structures with Subgrid Accuracy (2013)
Kuhn, Alexander ; Engelke, Wito ; Rössl, Christian ; Hadwiger, Markus ; Theisel, Holger
Lagrangian Coherent Structures (LCS) have become a widespread and powerful method to describe dynamic motion patterns in time-dependent flow fields. The standard way to extract LCS is to compute height ridges in the Finite Time Lyapunov Exponent (FTLE) field. In this work, we present an alternative method to approximate Lagrangian features for 2D unsteady flow fields that achieves subgrid accuracy without additional particle sampling. We obtain this by a geometric reconstruction of the flow map using additional material constraints for the available samples. In comparison to the standard method, this allows for a more accurate global approximation of LCS on sparse grids and for long integration intervals. The proposed algorithm works directly on a set of given particle trajectories and without additional flow map derivatives. We demonstrate its application for a set of computational fluid dynamic examples, as well as trajectories acquired by Lagrangian methods, and discuss its benefits and limitations.
Comparative Visual Analysis of Structure-Performance Relations in Complex Bulk-Heterojunction Morphologies (2017)
Aboulhassan, Amal ; Sicat, Ronell ; Baum, Daniel ; Wodo, Olga ; Hadwiger, Markus
The structure of Bulk-Heterojunction (BHJ) materials, the main component of organic photovoltaic solar cells, is very complex, and the relationship between structure and performance is still largely an open question. Overall, there is a wide spectrum of fabrication configurations resulting in different BHJ morphologies and correspondingly different performances. Current state- of-the-art methods for assessing the performance of BHJ morphologies are either based on global quantification of morphological features or simply on visual inspection of the morphology based on experimental imaging. This makes finding optimal BHJ structures very challenging. Moreover, finding the optimal fabrication parameters to get an optimal structure is still an open question. In this paper, we propose a visual analysis framework to help answer these questions through comparative visualization and parameter space exploration for local morphology features. With our approach, we enable scientists to explore multivariate correlations between local features and performance indicators of BHJ morphologies. Our framework is built on shape-based clustering of local cubical regions of the morphology that we call patches. This enables correlating the features of clusters with intuition-based performance indicators computed from geometrical and topological features of charge paths.
Time Line Cell Tracking for the Approximation of Lagrangian Coherent Structures with Subgrid Accuracy (2014)
Kuhn, Alexander ; Engelke, Wito ; Rössl, Christian ; Hadwiger, Markus ; Theisel, Holger
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