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Sökning: LAR1:mah > Heyden Anders

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  • Alpkvist, Erik, et al. (författare)
  • A new mathematical model for chemotactic bacterial colony growth
  • 2004
  • Ingår i: Water Science & Technology. - IWA Publishing. - 0273-1223. ; 49:11-12, s. 187-192
  • Tidskriftsartikel (refereegranskat)abstract
    • A new continuum model for the growth of a single species biofilm is proposed. The geometry of the biofilm is described by the interface between the biomass and the surrounding liquid. Nutrient transport is given by the solution of a semi-linear Poisson equation. In this model we study the morphology of a chemotactic bacterial colony, which grows in the direction of increasing nutrient concentration. Numerical simulations using the level set method and finite difference schemes are presented. The results show rich heterogeneous morphology.
  • Bernstoen, Christian, et al. (författare)
  • Image analysis for monitoring of crack growth in hydropower concrete structures
  • 2009
  • Ingår i: Measurement. - Elsevier. - 0263-2241. ; 42:6, s. 878-893
  • Tidskriftsartikel (refereegranskat)abstract
    • A digital image analysis technique for crack monitoring using a standard web-camera has been further developed to acquire continuous data sets on crack development in concrete dams. The method is based on an existing robust and straightforward non-contact method for experimental deformation analysis. It allows for the measurement of suspected serious cracks, identified from inspections, through a sequence of images captured at intervals. The crack opening displacements at the surface of investigated objects are obtained by an algorithm that makes it possible to automatically track the motions of discrete markers painted on the object surface markers and compute their centre of mass in a sequence of images. The data acquisition process is straightforward and is well suited for this type of environment. Results from laboratory experiments and a field-test on a commuter bridge in Sweden are presented. The study implies that the technique can be useful for hydropower concrete structure applications. (C) 2009 Elsevier Ltd. All rights reserved.
  • Dahl, Ola, et al. (författare)
  • Dynamic Structure and Motion Estimation based on Non-linear Adaptive Observers
  • 2008
  • Ingår i: Proceedings International Conference on Pattern Recognition. - International Association of Pattern Recognition.
  • Tidskriftsartikel (refereegranskat)abstract
    • Structure and motion estimation from long image sequences is a an important and difficult problem in computer vision. We propose a novel approach based on nonlinear and adaptive observers based on a dynamic model of the motion. The estimation of the threedimensional position and velocity of the camera as well as the three-dimensional structure of the scene is done by observing states and parameters of a nonlinear dynamic system, containing a perspective transformation in the output equation, often referred to as a perspective dynamic system. An advantage of the proposed method is that it is filter-based, i.e. it provides an estimate of structure and motion at each time instance, which is then updated based on a novel image in the sequence. The observer demonstrates a trade-off compared to a more computer vision oriented approach, where no specific assumptions regarding the motion dynamics are required, but instead additional feature points are needed. Finally, the performance of the proposed method is shown in simulated experiments.
  • Dahl, Ola, et al. (författare)
  • Exact Observer Error Linearization for Perspective Dynamic Systems
  • 2008
  • Ingår i: Procedings SSBA 2008. - Swedish Society for Automated Image Analysis. ; s. 43-46
  • Konferensbidrag (övrigt vetenskapligt)abstract
    • Estimation of 3D position information from 2D images in computer vision systems can be formulated as a state estimation problem for a nonlinear perspective dynamic system. The state estimation can be performed using different kinds of nonlinear observers. In this paper we investigate observer error linearization, where the goal is to find a coordinate transformation that results in a system for which a linear observer can be constructed. It is shown that using a state transformation combined with an output transformation, the system admits an observer form which leads to an observer with linear error dynamics.
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