| 1. |
- 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, s. 84-99
-
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
|
|
| 2. |
- Flodén, 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 .- 1558-8602. ; 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.
|
|
| 3. |
- Flodén, Liselott, et al.
(författare)
-
Very weak multiscale convergence
- 2010
-
Ingår i: Applied Mathematics Letters. - : Elsevier BV. - 0893-9659 .- 1873-5452. ; 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.
|
|
| 4. |
- 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 .- 1687-0409. ; , 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.
|
|
| 5. |
- Persson, Jens, 1978-
(författare)
-
Homogenization of Some Selected Elliptic and Parabolic Problems Employing Suitable Generalized Modes of Two-Scale Convergence
- 2010
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The present thesis is devoted to the homogenization of certain elliptic and parabolic partial differential equations by means of appropriate generalizations of the notion of two-scale convergence. Since homogenization is defined in terms of H-convergence, we desire to find the H-limits of sequences of periodic monotone parabolic operators with two spatial scales and an arbitrary number of temporal scales and the H-limits of sequences of two-dimensional possibly non-periodic linear elliptic operators by utilizing the theories for evolution-multiscale convergence and λ-scale convergence, respectively, which are generalizations of the classical two-scale convergence mode and custom-made to treat homogenization problems of the prescribed kinds. Concerning the multiscaled parabolic problems, we find that the result of the homogenization depends on the behavior of the temporal scale functions. The temporal scale functions considered in the thesis may, in the sense explained in the text, be slow or rapid and in resonance or not in resonance with respect to the spatial scale function. The homogenization for the possibly non-periodic elliptic problems gives the same result as for the corresponding periodic problems but with the exception that the local gradient operator is everywhere substituted by a differential operator consisting of a product of the local gradient operator and matrix describing the geometry and which depends, effectively, parametrically on the global variable.
|
|
| 6. |
- Persson, Jens, 1978-
(författare)
-
Selected Topics in Homogenization
- 2012
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The main focus of the present thesis is on the homogenization of some selected elliptic and parabolic problems. More precisely, we homogenize: non-periodic linear elliptic problems in two dimensions exhibiting a homothetic scaling property; two types of evolution-multiscale linear parabolic problems, one having two spatial and two temporal microscopic scales where the latter ones are given in terms of a two-parameter family, and one having two spatial and three temporal microscopic scales that are fixed power functions; and, finally, evolution-multiscale monotone parabolic problems with one spatial and an arbitrary number of temporal microscopic scales that are not restricted to be given in terms of power functions. In order to achieve homogenization results for these problems we study and enrich the theory of two-scale convergence and its kins. In particular the concept of very weak two-scale convergence and generalizations is developed, and we study an application of this convergence mode where it is employed to detect scales of heterogeneity.
|
|
| 7. |
- Rineau, F., et al.
(författare)
-
Carbon availability triggers the decomposition of plant litter and assimilation of nitrogen by an ectomycorrhizal fungus
- 2013
-
Ingår i: The ISME Journal. - : nternational Society for Microbial Ecology. - 1751-7362 .- 1751-7370. ; 7:10, s. 2010-2022
-
Tidskriftsartikel (refereegranskat)abstract
- The majority of nitrogen in forest soils is found in organic matter-protein complexes. Ectomycorrhizal fungi (EMF) are thought to have a key role in decomposing and mobilizing nitrogen from such complexes. However, little is known about the mechanisms governing these processes, how they are regulated by the carbon in the host plant and the availability of more easily available forms of nitrogen sources. Here we used spectroscopic analyses and transcriptome profiling to examine how the presence or absence of glucose and/or ammonium regulates decomposition of litter material and nitrogen mobilization by the ectomycorrhizal fungus Paxillus involutus. We found that the assimilation of nitrogen and the decomposition of the litter material are triggered by the addition of glucose. Glucose addition also resulted in upregulation of the expression of genes encoding enzymes involved in oxidative degradation of polysaccharides and polyphenols, peptidases, nitrogen transporters and enzymes in pathways of the nitrogen and carbon metabolism. In contrast, the addition of ammonium to organic matter had relatively minor effects on the expression of transcripts and the decomposition of litter material, occurring only when glucose was present. On the basis of spectroscopic analyses, three major types of chemical modifications of the litter material were observed, each correlated with the expression of specific sets of genes encoding extracellular enzymes. Our data suggest that the expression of the decomposition and nitrogen assimilation processes of EMF can be tightly regulated by the host carbon supply and that the availability of inorganic nitrogen as such has limited effects on saprotrophic activities.
|
|
| 8. |
|
|
| 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.
|
|
