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- Lenhof, Bernd, 1975-, et al.
(författare)
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A comparison of variational formats for porous media subjected to dynamic loading
- 2011
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Ingår i: International Journal for Numerical and Analytical Methods in Geomechanics. - 0363-9061. ; 35:7, s. 807-823
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a comparison of two variational formats for fully saturated porous media subjected to dynamic loading, whereby the general situation of relative fluid acceleration is considered: (1) the classical three-field (u, p, w)-format and (2) a novel two-field (u, p)-format, where the seepage velocity w is a spatially 'local' field whose treatment resembles that of internal variables in material models. The limited numerical comparison shows that the (u, p)-format competes well with the (u, p, w)-format. Indeed, it is consistent with the general acceleration modeling in the full range of permeabilities. Moreover, in the low permeability regime (where the magnitude of w is insignificant), the new format reflects the situation pertinent to 'added-mass' and is more efficient than the classical (u, p, w)-format. Finally, the (u, p)-format can conveniently be implemented in existing FE-codes based on the 'added mass' formulation.
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| 4. |
- Li, Lizhen, 1977-, et al.
(författare)
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Protective role of reactive astrocytes in brain ischemia.
- 2008
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Ingår i: Journal of cerebral blood flow and metabolism : official journal of the International Society of Cerebral Blood Flow and Metabolism. - 0271-678X. ; 28:3, s. 468-81
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Tidskriftsartikel (refereegranskat)abstract
- Reactive astrocytes are thought to protect the penumbra during brain ischemia, but direct evidence has been lacking due to the absence of suitable experimental models. Previously, we generated mice deficient in two intermediate filament (IF) proteins, glial fibrillary acidic protein (GFAP) and vimentin, whose upregulation is the hallmark of reactive astrocytes. GFAP(-/-)Vim(-/-) mice exhibit attenuated posttraumatic reactive gliosis, improved integration of neural grafts, and posttraumatic regeneration. Seven days after middle cerebral artery (MCA) transection, infarct volume was 210 to 350% higher in GFAP(-/-)Vim(-/-) than in wild-type (WT) mice; GFAP(-/-), Vim(-/-) and WT mice had the same infarct volume. Endothelin B receptor (ET(B)R) immunoreactivity was strong on cultured astrocytes and reactive astrocytes around infarct in WT mice but undetectable in GFAP(-/-)Vim(-/-) astrocytes. In WT astrocytes, ET(B)R colocalized extensively with bundles of IFs. GFAP(-/-)Vim(-/-) astrocytes showed attenuated endothelin-3-induced blockage of gap junctions. Total and glutamate transporter-1 (GLT-1)-mediated glutamate transport was lower in GFAP(-/-)Vim(-/-) than in WT mice. DNA array analysis and quantitative real-time PCR showed downregulation of plasminogen activator inhibitor-1 (PAI-1), an inhibitor of tissue plasminogen activator. Thus, reactive astrocytes have a protective role in brain ischemia, and the absence of astrocyte IFs is linked to changes in glutamate transport, ET(B)R-mediated control of gap junctions, and PAI-1 expression.
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| 9. |
- Draganis, Andreas, 1984-, et al.
(författare)
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An Arbitrary Lagrangian Eulerian Formulation For Simulation Of Wheel-Rail Contact
- 2010
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Ingår i: Proceedings of NSCM-23: the 23rd Nordic Seminar on Computational Mechanics, Anders Eriksson, Gunnar Tibert, 21-22 Oktober, 2010, KTH, Stockholm. - 0348-467X. ; 2010, s. 173-176
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Konferensbidrag (refereegranskat)abstract
- A novel ALE-formulation of a rolling wheel is presented in the context of finite element simulations. Numerical examples illustrate the proposed strategy for a two-dimensional problem.
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| 10. |
- Draganis, Andreas, 1984-, et al.
(författare)
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Modelling the thermomechanical wheel–rail interface during rolling contact
- 2012
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Ingår i: Proceedings of the 9th International Conference on Contact Mechanics and Wear of Rail/Wheel Systems (CM2012).
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Konferensbidrag (refereegranskat)abstract
- A theoretical and computational framework for the analysis of thermomechanically coupled transient rolling contact based on an arbitrary Lagrangian–Eulerian (ALE) kinematical description is developed. A finite element formulation featuring 2D cylinder–plate rolling contact is implemented. The implementation features penalty- type contact formulations for normal/tangential mechanical and thermal contact. It is noted that the ALE formulation allows for a simplified time description, a compact computational domain and localized mesh refinement. Numerical simulations considering stationary rolling conditions featuring full slip are presented.
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