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Plattner A.,ETH Zurich | Maurer H.R.,ETH Zurich | Vorloeper J.,Ruhr West University of Applied Sciences | Blome M.,Konrad Zuse Zentrum fur Informationstechnik
Geophysical Journal International | Year: 2012

We present a novel adaptive model parametrization strategy for the 3-D electrical resistivity tomography problem and demonstrate its capabilities with a series of numerical examples. In contrast to traditional parametrization schemes, which are based on fixed disjoint blocks, we discretize the subsurface in terms of Haar wavelets and adaptively adjust the parametrization as the iterative inversion proceeds. This results in a favourable balance of cell sizes and parameter reliability, that is, in regions where the data constrain the subsurface properties well, our parametrization strategy leads to a fine grid, whereas poorly resolved areas are represented only by a few large blocks. This is documented with eigenvalue analyses and by computing model resolution matrices. During the initial iteration steps, only a few model parameters are involved, which reduces the risk that the regularization dominates the inversion. The algorithm also automatically accounts for non-linear effects caused by pronounced conductivity contrasts. Inside conductive features a finer grid is generated than inside more resistive structures. The automated parameter adaptation is computationally efficient, because the coarsening and refinement subroutines have a nearly linear numerical complexity with respect to the number of model parameters. Because our approach is not tightly coupled to electrical resistivity tomography, it should be straightforward to adapt it to other data types. © 2012 The Author Geophysical Journal International © 2012 RAS. Source


Fugenschuh A.,Konrad Zuse Zentrum fur Informationstechnik | Gausemeier P.,TU Berlin | Seliger G.,TU Berlin | Severengiz S.,TU Berlin
Lecture Notes in Business Information Processing | Year: 2010

Scenario technique is a tool to reveal the knowledge of an expert group about possible and consistent scenarios of the future. The current use of this technique suffers from an inflexibility of the available software. To overcome this shortage, the core part of this solver, i.e. the scenario generation phase, has to be re-implemented. It is demonstrated that this problem can be formulated as an integer linear programming problem. To find all feasible solutions the solver SCIP was adapted. The solutions are then clustered and these clusters are verbally described. The approach is demonstrated by using data from the research project remanufacturing oriented production equipment development, in which scenarios for sustainable value creation were identified and described. © 2010 Springer-Verlag. Source


Ehrig H.,TU Berlin | Golas U.,Konrad Zuse Zentrum fur Informationstechnik | Habel A.,University of Oldenburg | Lambers L.,University of Potsdam | Orejas F.,Polytechnic University of Catalonia
Fundamenta Informaticae | Year: 2012

Graph transformation systems have been studied extensively and applied to several areas of computer science like formal language theory, the modeling of databases, concurrent or distributed systems, and visual, logical, and functional programming. In most kinds of applications it is necessary to have the possibility of restricting the applicability of rules. This is usually done by means of application conditions. In this paper, we continue the work of extending the fundamental theory of graph transformation to the case where rules may use arbitrary (nested) application conditions. More precisely, we generalize the Embedding theorem, and we study how local confluence can be checked in this context. In particular, we define a new notion of critical pair which allows us to formulate and prove a Local Confluence Theorem for the general case of rules with nested application conditions. All our results are presented, not for a specific class of graphs, but for any arbitrary ℳ-adhesive category, which means that our results apply to most kinds of graphical structures. We demonstrate our theory on the modeling of an elevator control by a typed graph transformation system with positive and negative application conditions. © 2012 IOS Press. Source


Yan H.-D.,TU Braunschweig | Lemmens P.,TU Braunschweig | Ahrens J.,TU Braunschweig | Broring M.,TU Braunschweig | And 6 more authors.
Wuli Xuebao/Acta Physica Sinica | Year: 2012

Au nanowire arrays with high aspect ratios are prepared in anode aluminum oxide templates by electrochemical deposition. The obtained structures are investigated by scanning Auger microscopy. Surface plasmon resonances of Au nanowire arrays induce a transverse mode (T mode) and a longitudinal mode (L mode) in the optical absorption, which indicates the strong anisotropy of the Au nanowires. The L mode intensity is related to the angle and polarization of the incident light. The L mode position shows a shift with the increase of aspect ratio of the nanowires. The plasmon coupling between Au nanowires is compared with the H-aggregation of organic chromophores. The blue shift of the L mode in the arrays compared with a single nanowire is induced by multi-coupling of the electromagnetic field between neighbouring nanowires. A finite element method is used to simulate the electric field distributions of a single Au nanowire and an array of plasmonically coupled wires. © 2012 Chinese Physical Society. Source


Kramer T.,Konrad Zuse Zentrum fur Informationstechnik | Kramer T.,Harvard University | Noack M.,Konrad Zuse Zentrum fur Informationstechnik
Astrophysical Journal Letters | Year: 2016

The Rosetta probe around comet 67P/Churyumov-Gerasimenko (67P) reveals an anisotropic dust distribution of the inner coma with jet-like structures. The physical processes leading to jet formation are under debate, with most models for cometary activity focusing on localized emission sources, such as cliffs or terraced regions. Here we suggest, by correlating high-resolution simulations of the dust environment around 67P with observations, that the anisotropy and the background dust density of 67P originate from dust released across the entire sunlit surface of the nucleus rather than from few isolated sources. We trace back trajectories from coma regions with high local dust density in space to the non-spherical nucleus and identify two mechanisms of jet formation: areas with local concavity in either two dimensions or only one. Pits and craters are examples of the first case; the neck region of the bi-lobed nucleus of 67P is an example of the latter case. The conjunction of multiple sources, in addition to dust released from all other sunlit areas, results in a high correlation coefficient (∼0.8) of the predictions with observations during a complete diurnal rotation period of 67P. © 2016. The American Astronomical Society. All rights reserved. Source

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