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Proceedings of the 14th International Conference on Neural Information Processing Systems: Natural and Synthetic

作者： Jesper Tegnér Ádám Kepecs Stockholm Bioinformatics Center Dept. of Numerical Analysis & Computing Science Royal Institute for Technology Stockholm Sweden Volen Center for Complex Systems Brandeis University Waltham MA

Hebbian learning rules are generally formulated as static rules. Under changing condition (e.g. neoromodulation, input statistics) most rules are sensitive to parameters. In particular, recent work has focused on two different formulations of spike-timing-dependent plasticity rules. Additive STDP [1] is remarkably versatile but also very fragile, whereas multiplicative STDP [2, 3] is more robust but lacks attractive features such as synaptic competition and rate stabilization. Here we address the problem of robustness in the additive STDP rule. We derive an adaptive control scheme, where the learning function is under fast dynamic control by postsynaptic activity to stabilize learning under a variety of conditions. Such a control scheme can be implemented using known biophysical mechanisms of synapses. We show that this adaptive rule makes the additive STDP more robust. Finally, wo give an example how meta plasticity of the adaptive rule can be used to guide STDP into different type of learning regimes.

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Real-time tracking meets online grasp planning

Real-time tracking meets online grasp planning

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IEEE International Conference on Robotics and Automation (ICRA)

作者： D. Kragic A.T. Miller P.K. Allen Computer Vision and Active Perception Numerical Analysis and Computer Science Royal Institute of Technology Stockholm Sweden Department of Computer Science Columbia University New York NY USA

ISBN: (纸本)0780365763

Describes a synergistic integration of a grasping simulator and a real-time visual tracking system, that work in concert to (1) find an object's pose, (2) plan grasps and movement trajectories, and (3) visually monitor task execution. Starting with a CAD model of an object to be grasped, the system can find the object's pose through vision which then synchronizes the state of the robot workcell with an online, model-based grasp planning and visualization system we have developed called GraspIt. GraspIt can then plan a stable grasp for the object, and direct the robotic hand system to perform the grasp. It can also generate trajectories for the movement of the grasped object, which are used by the visual control system to monitor the task and compare the actual grasp and trajectory with the planned ones. We present experimental results using typical grasping tasks.

关键词： Meeting planning Monitoring Control systems Robot control Robot vision systems Visual servoing Computer science Computational modeling Analytical models Computer simulation

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Evolutionary design and development of image meta-analysis environments based on object-relational database mediator technology

Evolutionary design and development of image meta-analysis e...

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International Working Conference on Scientific and Statistical Database Management

作者： J. Fredriksson P. Svensson Department of Numerical Analysis and Computer Science Royal Institute of Technology Stockholm Sweden Division of Human Brain Research Department of Neuroscience Karolinska Institute Stockholm Sweden Department of Data and Information Fusion Swedish Defence Research Agency Stockholm Sweden

ISBN: (纸本)0769512186

Discusses how emerging object-relational database mediator technology can be used to integrate academic freeware and commercial-off-the-shelf software components to create a sequence of gradually more complex and powerful, yet always syntactically and semantically homogeneous, database-centred image meta-analysis environments. We show how this may be done by defining and utilising a use-case-based evolutionary design and development process. This process allows subsystems to be produced largely independently by several small specialist subprojects, turning the system integration work into a high-level domain modelling task.

关键词： Image databases Relational databases numerical analysis Humans Image storage Object oriented databases Visual databases Computer science Neuroscience Process design

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A finite element based level-set method for multiphase flow applications

A finite element based level-set method for multiphase flow ...

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作者： Tornberg, Anna-Karin Engquist, Björn Department of Numerical Analysis and Computing Science Royal Institute of Technology S-100 44 Stockholm Sweden

A numerical method for simulating incompressible two-dimensional multiphase flow is presented. The method is based on a level-set formulation discretized by a finiteelement technique. The treatment of the specific features of this problem, such as surface tension forces acting at the interfaces separating two immiscible fluids, as well as the density and viscosity jumps that in general occur across such interfaces, have been integrated into the finite-element framework. Using a method based on the weak formulation of the Navier-Stokes equations has its advantages. In this formulation, the singular surface tension forces are included through line integrals along the interfaces, which are easily approximated quantities. In addition, differentiation of the discontinuous viscosity is avoided. The discontinuous density and viscosity are included in the finite element integrals. A strategy for the evaluation of integrals with discontinuous integrands has been developed based on a rigorous analysis of the errors associated with the evaluation of such integrals. numerical tests have been performed. For the case of a rising buoyant bubble the results are in good agreement with results from a fronttracking method. The run presented here is a run including topology changes, where initially separated areas of one fluid merge in different stages due to buoyancy effects.

关键词： Viscosity

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Consolidation of concentrated suspensions - numerical simulations using a two-phase fluid model

Consolidation of concentrated suspensions - Numerical simula...

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作者： Gustavsson, Katarina Oppelstrup, Jesper Department of Numerical Analysis and Computing Science Royal Institute of Technology S-100 44 Stockholm Sweden

We investigate numerically a mathematical model of a consolidation process of a dense, flocculated suspension. The suspension is treated as a two-constituent mixture of a fluid and solid particles by an Eulerian two-phase fluid model. We characterize the suspension by constitutive relations concerning the stresses, interaction forces and interparticle forces. A numerical solver for a two dimensional test case is developed using finite difference methods both in time and space. In the numerical experiments, the suspension is confined to a closed box and consolidates due to a constant gravity field directed toward the bottom. To study the effect of shear, 2D simulations are performed where the bottom wall of the box is moving with a constant speed.

关键词： Suspensions (fluids)

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NLC₂-decomposition in polynomial time

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International Journal of Foundations of Computer science 2000年第3期11卷 373-395页

作者： Johansson, Öjvind Department of Numerical Analysis and Computer Science Royal Institute of Technology SE-100 44 Stockholm Sweden

NLCk is a family of algebras on vertex-labeled graphs introduced by Wanke. An NLC-decomposition of a graph is a derivation of this graph from single vertices using the operations in question. The width of the decompos... 详细信息

NLC_k is a family of algebras on vertex-labeled graphs introduced by Wanke. An NLC-decomposition of a graph is a derivation of this graph from single vertices using the operations in question. The width of the decomposition is the number of labels used, and the NLC-width of the graph is the smallest width among its NLC-decompositions. Many difficult graph problems can be solved efficiently with dynamic programming if an NLC-decomposition of low width is given for the input graph. It is unknown, though, whether arbitrary graphs of NLC-width at most k can be decomposed with k labels in polynomial time. So far this has been possible only for k = 1, which corresponds to cographs. In this paper, an algorithm is presented that works for k = 2. It runs in O(n ⁴log n) time and uses O(n²) space. Related concepts: clique-decomposition, clique-width. © 2000 World Scientific Publishing Company.

关键词： clique-width cograph Graph algebra graph decomposition NLC-width

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Tracking techniques for visual servoing tasks

Tracking techniques for visual servoing tasks

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IEEE International Conference on Robotics and Automation (ICRA)

作者： D. Kragic H.I. Christensen Computer Vision and Active Perception Lab Department of Numerical Analysis and Computing Science Royal Institute of Technology Stockholm Sweden Centre for Autonomous Sys Department of Numerical Analysis and Computing Science Royal Institute of Technology Stockholm Sweden

Many of today's visual servoing systems rely on the use of markers on the object to provide features for control. There is thus a need for a visual system that provides control features regardless of the appearance of the object. Region based tracking is a natural approach since it does not require any special type of features. In this paper we present two different approaches to region based tracking: 1) a multi-resolution gradient based approach (using optical flow); and 2) a discrete feature based search approach. We present experiments conducted with both techniques for different types of image motions. Finally, the performance, drawbacks and limitations of used techniques are discussed.

关键词： Visual servoing Robots Tracking Computer vision numerical analysis Control systems Grippers Image motion analysis Motion estimation Visual system

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A real-time system for epipolar geometry and ego-motion estimation

A real-time system for epipolar geometry and ego-motion esti...

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Conference on Computer Vision and Pattern Recognition (CVPR)

作者： M. Bjorkman J.-O. Eklundh Computational Vision and Active Perception Laboratory CVAP Department of Numerical Analysis and Computing Science Royal Institute of Technology Stockholm Sweden

A visually guided mobile platform acting in a dynamic environment needs information, delivered from cues such as stereo and motion. In this paper a binocular stereo system, capable of dynamic vergence and ego-motion estimation, will be presented. The ability to dynamically verge the cameras is essential for visual tasks such as tracking, recognition and manipulation, since the computation of 3D geometry will be considerably simplified at fixation. We will show that the epipolar geometry of the presented system can be estimated in real-time. The number of degrees of freedom has been minimized, without affecting the flexibility of the system. Reconstructed 3D data is used in order to determine the ego-motion of the platform, at a very low computational cost. Finally, it will be shown how disparity maps and estimated ego-motion can facilitate the localization of independently moving objects.

关键词： Real time systems Cameras Computer vision Stereo vision Robot vision systems Motion estimation Computational geometry Calibration Counting circuits numerical analysis

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Vibrational properties of the one-component σ phase

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Physical Review B 2000年第5期62卷 3223-3223页

作者： S. I. Simdyankin S. N. Taraskin M. Dzugutov S. R. Elliott Department of Numerical Analysis and Computing Science Royal Institute of Technology SE–100 44 Stockholm Sweden Department of Chemistry University of Cambridge Lensfield Road Cambridge CB2 1EW United Kingdom

A structural model of a one-component σ-phase crystal has been constructed by means of molecular dynamics simulation. The phonon dispersion curves and the vibrational density of states were computed for this model. The dependence of the vibrational properties on the thermodynamical parameters was investigated. The vibrational density of states of the σ-phase structure is found to be similar to that of a one-component glass with icosahedral local order. On the basis of this comparison it is concluded that the σ phase can be considered to be a good crystalline reference structure for this glass.

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Real-time maintenance of figure-ground segmentation 1st

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1st International Conference on Computer Vision Systems, ICVS 1999

作者： Nordlund, Peter Eklundh, Jan-Olof Department of Numerical Analysis and Computing Science Royal Institute of Technology StockholmS-100 44 Sweden

ISBN: (纸本)3540654593

An approach to figure-ground segmentation based on a 2-dimensional histogram in feature space is presented. The histogram is then analyzed with a peak-finding algorithm designed with real-time performance in mind. The most significant peaks in the histogram are back-projected to the image to produce an object mask. The method is applied to segmentation based on a 2-D color space and also on a combination of motion and stereo disparities. Experiments with a system grabbing images direct from a CCD-camera with real-time performance having typical frame-rates of about 10 Hz is presented. © Springer-Verlag Berlin Heidelberg 1999.

关键词： CCD cameras

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