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Matière active et écoulements : jets de bactéries et nageurs interfaciaux

Abstract : This work address different situations where active matter, made out of self-propelled particles, is submitted to external constraints.In a first part, we consider the response of magnetotactic bacteria –capable of swim alignment along magnetic field lines- directed through an hourglass shape geometry. We characterize the dynamic properties of the system, both at the individual bacteria scale and at the scale of the jammed region or of the induced outgoing jet. We show that in high density regions, couplings between the bacteria interactions, swim velocity and magnetic forcing take a much more complex form than had been considered so far in theoretical models.In a second chapter, we are addressing a new active system made out of camphor disks lying at the air-water interface. First of all, we study in details the individual swim properties of such particles, which spontaneously break the system symmetry to start moving. In particular, we show that all experimental data can be rationalized within the framework of a very simple model of this complex problem where hydrodynamic flows and surfactant transports are coupled through Marangoni stress.In a last chapter, we addressed the collective dynamics of an assembly of such interfacial swimmers that interact through the flow and chemical fields they generate. At intermediate swimmers concentrations, an intermittent swim regime appears characterized by pseudo-periodic activity bursts. Using tools and concepts from the turbulence domain, we show that, remarkably, this simple system exhibits dynamical properties matching the ones of canonical turbulence as predicted by Kolmogorov in the 40s. This demonstration opens up rich perspectives in the historical domain of turbulence together with in the emerging one of active matter
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Submitted on : Friday, July 13, 2018 - 5:50:06 PM
Last modification on : Monday, October 19, 2020 - 10:54:27 AM
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  • HAL Id : tel-01839096, version 1



Ronan Kervil. Matière active et écoulements : jets de bactéries et nageurs interfaciaux. Mécanique des fluides [physics.class-ph]. Université de Lyon, 2018. Français. ⟨NNT : 2018LYSE1039⟩. ⟨tel-01839096⟩



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