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Résumé |
Over the past twenty years, great progress has been made in our understanding
of how granular matter flows, a topic of both basic and practical interest. A
distinctive feature of granular flows is that they display a flow threshold and
a maximal packing fraction, beyond which no permanent flow is possible (jamming
transition). In this seminar, I will illustrate how physical phenomena at the
particle level (fluid drag, colloidal forces, particle agitation) can
profoundly affect the flow behavior of a mixture of grains and fluids close to
the jamming transition. First, I will show that the short-time response of a
dense suspension under impact is entirely controlled by the coupling between
transient effects (Reynolds dilatancy) and the fluid pressure. I will then
discuss how the addition of short-range repulsive forces between grains can
conspire with friction to yield the dramatic shear-thickening behavior
displayed by some suspensions like cornstarch. Finally, I will show how the
sensor of gravity of plants relies on intracellular micro-avalanches flowing in
an active liquid.
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