Next seminar : Séminaire du LPTMS : Ricard Alert Zenon

Tuesday, July 07 2020 at 15:00:00

Topological Defects, Turbulence, and Phase Separation

Ricard Alert Zenon (Princeton)

ZOOM Meeting ID: 929 5958 3836 Password: 813501 Active fluids display striking collective phenomena not possible in passive fluids. Examples include spontaneous flows powered by microscopic constituents, and phase separation in the absence of attractive interactions. In this talk, I will discuss three aspects of the physics of active fluids, connected with experiments in both biological and artificial soft matter systems. First, I will show that dense colonies of the rod-shaped motile bacterium Myxococcus xanthus form active liquid crystals. I will show that topological defects of the cell alignment field induce flows that lead to the formation of new cell layers, which triggers the development of multicellular structures called fruiting bodies. Second, I will discuss chaotic flows in active liquid crystals. I will show that, as in classic turbulence, the statistical properties of these active flows at low Reynolds number are described by universal scaling laws. Unlike classic turbulence, however, this type of active turbulence requires no energy transfer across scales. Finally, I will present a new mechanism of liquid-gas phase separation in active fluids. I will show that, in addition to repulsive forces that oppose phase separation, artificial self-propelled Janus colloids experience torques that reorient particle motion toward high-density regions, providing a novel route to phase separation.

Last Highlight : Comment une barrière peut être plus haute et plus facile à franchir

Que ce soit en physique, en chimie ou en biologie, les vitesses de réaction sont très souvent limitées par des barrières énergétiques à franchir grâce à l'activation thermique. Des travaux menés par le LPTMS et le LPS d'Orsay en collaboration avec l'Université de Cambridge,  démontrent que l'on peut jouer sur le profil d'une barrière pour en accélérer le franchissement par un objet Brownien : l'optimisation des profils conduit aux barrières les plus élevées.

https://inp.cnrs.fr/fr/cnrsinfo/comment-une-barriere-peut-etre-plus-haute-et-plus-facile-franchir


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