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Sökning: WFRF:(Persson Anders) > Mittuniversitetet

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1.
  • Flodén, Liselott, 1967-, et al. (författare)
  • A myriad shades of green
  • 2009
  • Ingår i: Proceedings of Bridges 2009, Banff, Alberta, Canada.
  • Konferensbidrag (refereegranskat)abstract
    • We discuss the possible application of techniques inspired by the theories of G-convergence and homogenization to understand mixtures of colors and how they appear as observed by the human eye.  The ideas are illustrated by pictures describing the equivalent of a convergence process     for different kinds of mixtures of colors.
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2.
  • Flodén, Liselott, 1967-, et al. (författare)
  • Detection of scales of heterogeneity and parabolic homogenization applying very weak multiscale convergence
  • 2011
  • Ingår i: Annals of Functional Analysis. - Mashdad, Iran : TSMG. - 2008-8752. ; 2:1
  • Tidskriftsartikel (refereegranskat)abstract
    • We apply a new version of multiscale convergence named very weak multiscale convergence to find possible frequencies of oscillation in an unknown coefficient of a diffeential equation from its solution. We also use thís notion to study homogenization of a certain linear parabolic problem with multiple spatial and temporal scales
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3.
  • Flodén, Liselott, 1967-, et al. (författare)
  • Homogenization of parabolic equations with an arbitrary number of scales in both space and time
  • 2014
  • Ingår i: Journal of Applied Mathematics. - Boston : Hindawi Publishing Corporation. - 1110-757X.
  • Tidskriftsartikel (refereegranskat)abstract
    • The main contribution of this paper is the homogenization of the linearparabolic equationtu (x, t) − ·axq1, ...,xqn,tr1, ...,trmu (x, t)= f(x, t)exhibiting an arbitrary finite number of both spatial and temporal scales.We briefly recall some fundamentals of multiscale convergence and providea characterization of multiscale limits for gradients in an evolution settingadapted to a quite general class of well-separated scales, which we nameby jointly well-separated scales (see Appendix for the proof). We proceedwith a weaker version of this concept called very weak multiscale convergence.We prove a compactness result with respect to this latter typefor jointly well-separated scales. This is a key result for performing thehomogenization of parabolic problems combining rapid spatial and temporaloscillations such as the problem above. Applying this compactnessresult together with a characterization of multiscale limits of sequences ofgradients we carry out the homogenization procedure, where we togetherwith the homogenized problem obtain n local problems, i.e. one for eachspatial microscale. To illustrate the use of the obtained result we apply itto a case with three spatial and three temporal scales with q1 = 1, q2 = 2and 0 < r1 < r2.MSC: 35B27; 35K10
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4.
  • Flodén, Liselott, 1967-, et al. (författare)
  • On the determination of effective properties of certain structures with non-periodic temporal oscillations
  • 2009
  • Ingår i: MATHMOD 2009 - 6th Vienna International Conference on Mathematical Modelling. - Wien : Vienna University Press (WUV). - 978-3-901608-35-3 ; s. 2627-2630
  • Konferensbidrag (refereegranskat)abstract
    • We investigate the homogenization of an evolution problem modelled by a parabolic equation, where the coefficient describing the structure is periodic in space but may vary in time in a non-periodic way. This is performed applying a generalization of two-scale convergence called λ-scale convergence. We give a result on the characterization of the λ-scale limit of gradients under certain boundedness assumptions. This is then applied to perform the homogenization procedure. It turns out that, under a certain condition on the rate of change of the temporal variations, the effective property of the given structure can be determined the same way as in periodic cases.
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5.
  • Floden, Liselott, 1967-, et al. (författare)
  • Two-scale convergence: Some remarks and extensions
  • 2013
  • Ingår i: Pure and Applied Mathematics Quarterly. - International press of BOston. - 1558-8599. ; 9:3, s. 461-486
  • Tidskriftsartikel (refereegranskat)abstract
    • We first study the fundamental ideas behind two-scale conver-gence to enhance an intuitive understanding of this notion. The classicaldefinitions and ideas are motivated with geometrical arguments illustratedby illuminating figures. Then a version of this concept, very weak two-scaleconvergence, is discussed both independently and brie°y in the context ofhomogenization. The main features of this variant are that it works alsofor certain sequences of functions which are not bounded inL2  and atthe same time is suited to detect rapid oscillations in some sequences whichare strongly convergent inL2 . In particular, we show how very weaktwo-scale convergence explains in a more transparent way how the oscilla-tions of the governing coe±cient of the PDE to be homogenized causes thedeviation of theG-limit from the weak L2 NxN-limit for the sequence ofcoe±cients. Finally, we investigate very weak multiscale convergence andprove a compactness result for separated scales which extends a previousresult which required well-separated scales.
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6.
  • Flodén, Liselott, et al. (författare)
  • Very weak multiscale convergence
  • 2010
  • Ingår i: Applied Mathematics Letters. - 0893-9659. ; 23:10, s. 1170-1173
  • Tidskriftsartikel (refereegranskat)abstract
    • We briefly recall the concept of multiscale convergence, which is a generalization of two-scale convergence. Then we investigate a related concept, called very weak multiscale convergence, and prove a compactness result with respect to this type of convergence. Finally we illustrate how this result can be used to study homogenization problems with several scales of oscillations.
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7.
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8.
  • Holmbom, Anders, 1958-, et al. (författare)
  • A note on parabolic homogenization with a mismatch between the spatial scales
  • 2013
  • Ingår i: Abstract and Applied Analysis. - Hindawi Publishing Corporation. - 1085-3375. ; s. Art. no. 329704
  • Tidskriftsartikel (refereegranskat)abstract
    • We consider the homogenization of the linear parabolic problem rho(x/epsilon(2))partial derivative(t)u(epsilon)(x,t) - del . (a(x/epsilon(1), t/epsilon(2)(1))del u(epsilon) (x,t)) = f(x,t) which exhibits a mismatch between the spatial scales in the sense that the coefficient a(x/epsilon(1), t/epsilon(2)(1)) of the elliptic part has one frequency of fast spatial oscillations, whereas the coefficient rho(x/epsilon(2)) of the time derivative contains a faster spatial scale. It is shown that the faster spatialmicroscale does not give rise to any corrector termand that there is only one local problemneeded to characterize the homogenized problem. Hence, the problem is not of a reiterated type even though two rapid scales of spatial oscillation appear.
9.
  • Tourancheau, Sylvain, 1982-, et al. (författare)
  • Evaluation of quality of experience in interactive 3D visualization: methodology and results
  • 2012
  • Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - SPIE - International Society for Optical Engineering. - 9780819489357 ; s. Art. no. 82880O
  • Konferensbidrag (refereegranskat)abstract
    • Human factors are of high importance in 3D visualization, but subjective evaluation of 3D displays is not easy because of a high variability among users. This study aimed to evaluate and compare two different 3D visualization systems (a market stereoscopic display, and a state-of-the-art multi-view display) in terms of task performance and quality of experience (QoE), in the context of interactive visualization. An adapted methodology has been designed in order to focus on 3D differences and to reduce the influence of all other factors. 36 subjects took part in an experiment during which they were asked to solve different tasks in a synthetic 3D scene. After the experiment, they were asked to judge the quality of their experience, according to specific features. Results showed that scene understanding and precision was significantly better on the multi-view display. Concerning the quality of experience, visual comfort was judged significantly better on the multi-view display and visual fatigue was reported by 52% of the subjects on the stereoscopic display. This study has permitted to identify some factors influencing QoE such as prior experience and stereopsis threshold.
10.
  • Tourancheau, Sylvain, 1982-, et al. (författare)
  • Subjective evaluation of user experience in interactive 3D-visualization in a medical context
  • 2012
  • Ingår i: Proceedings of the SPIE, vol 8318: Conference on Image Perception, Observer Performance, and Technology Assessment, San Diego, CA, USA, 4 - 9 February 2012. - SPIE - International Society for Optical Engineering. ; s. Art. no. 831814
  • Konferensbidrag (refereegranskat)abstract
    • New display technologies enable the usage of 3D-visualization in a medical context. Even though user performance seems to be enhanced with respect to 2D thanks to the addition of recreated depth cues, human factors, and more particularly visual comfort and visual fatigue can still be a bridle to the widespread use of these systems. This study aimed at evaluating and comparing two different 3D visualization systems (a market stereoscopic display, and a state-of-the-art multi-view display) in terms of quality of experience (QoE), in the context of interactive medical visualization. An adapted methodology was designed in order to subjectively evaluate the experience of users. 14 medical doctors and 15 medical students took part in the experiment. After solving different tasks using the 3D reconstruction of a phantom object, they were asked to judge their quality of the experience, according to specific features. They were also asked to give their opinion about the influence of 3D-systems on their work conditions. Results suggest that medical doctors are opened to 3D-visualization techniques and are confident concerning their beneficial influence on their work. However, visual comfort and visual fatigue are still an issue of 3D-displays. Results obtained with the multi-view display suggest that the use of continuous horizontal parallax might be the future response to these current limitations.
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