| 1. |
- Bouzid, Mehdi, et al.
(author)
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Non-local rheology of dense granular flows
- 2017
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In: EPJ Web of Conferences. - : EDP Sciences. - 2101-6275 .- 2100-014X. ; 140
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Journal article (peer-reviewed)abstract
- The rheology of dense granular flows is studied numerically in a shear cell controlled at constant pressure and shear stress, confined between two granular shear flows. We show that a liquid state can be achieved even far below the yield stress, whose flow can be described with the same rheology as above the yield stress. A non-local constitutive relation is derived from dimensional analysis through a gradient expansion and calibrated using the spatial relaxation of velocity profiles observed under homogeneous stresses. Both for frictional and frictionless grains, the relaxation length is found to diverge as the inverse square root of the distance to the yield point, on both sides of that point. We also make use of a micro-rheometer to determine the influence of a distant shear band on the local rheological behaviour. Finally, we compare various approaches based on different non-local constitutive relations and choices for the fluidity parameter. We emphasise that, to discriminate between the different approaches proposed in the literature, one has to go beyond the predictions derived from linearisation around a uniform stress profile, such as that obtained in a simple shear cell. We argue that future tests can be based on the nature of the chosen fluidity parameter, and the related boundary conditions, as well as the hypothesis made to derive the models and the dynamical mechanisms underlying their dynamics.
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| 2. |
- Salvatore, Delphine B., et al.
(author)
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Investigation at Residue Level of the Early Steps during the Assembly of Two Proteins into Supramolecular Objects
- 2011
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In: Biomacromolecules. - : American Chemical Society (ACS). - 1526-4602 .- 1525-7797. ; 12:6, s. 2200-2210
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Journal article (peer-reviewed)abstract
- Understanding the driving forces governing protein assembly requires the characterization of interactions at molecular level. We focus on two homologous oppositely charged proteins, lysozyme and alpha-lactalbumin, which can assemble into microspheres. The assembly early steps were characterized through the identification of interacting surfaces monitored at residue level by NMR chemical shift perturbations by titrating one N-15-labeled protein with its unlabeled partner. While a-lactalbumin has a narrow interacting site, lysozyme has interacting sites scattered on a broad surface. The further assembly of these rather unspecific heterodimers into tetrarners leads to the establishment of well-defined interaction sites. Within the tetramers, most of the electrostatic charge patches on the protein surfaces are shielded. Then, hydrophobic interactions, which are possible because alpha-lactalbumin is in a partially folded state, become preponderant, leading to the formation of larger oligomers. This approach will be particularly useful for rationalizing the design of protein assemblies as nanoscale devices.
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