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Dynamics and propulsion modes of anchored and freely moving, frictional filament of active, polar, Brownian particles

Arvind Gopinath (Max Planck Institute ), Raghunath Chelakkot (Harvard University), Tobias Schneider (MPIDS)

Hydrodynamics of Swimming Microorganisms

Tue 4:20 - 5:40

Barus-Holley 191

We study the dynamics and oscillatory motions of active, self-propelled, Brownian particles that are connected together to form a connected filament subject to local frictional forces that arise from the ambient medium. When the frictional chain is prevented from translating freely by anchoring one end, we find that tuning the boundary condition enables is to obtain stable deformation modes. Specifically, a clamped end reproduces the graceful beating motions of flagella. On the other hand when the filament is anchored via a frictionless pivot, we obtain a transition from flagella-like beating to steadily rotating tight coils. For very long filaments, excluded volume interactions result in loopy, meandering conformations. Strong noise in the system disrupts the regularity of the oscillations. Relaxing the constraint at the anchored end and allowing for the chain to translate yields an autonomous self propulsive chain. The interplay between friction (dissipation), polarity (active forcing) and elasticity (bending) yields a spectrum of motile shapes with tunable efficiencies. We use a combination of detailed numerical simulations, mean-field scaling analysis, non-linear bifurcation theory and classical passage time theory to demarcate the phase diagram as a function of the filament length, passive elasticity, propulsion force and noise. In contrast to most studies of locomotion at low Reynolds number which prescribe the shape of the organism (typically as a slender filament with prescribed kinematics), the nature of our chain allows is to prescribe the active forces locally, and calculate the resulting shapes. Additionally these results provide a framework to interpret the dynamics of animated flexible filaments in the active cytoskeleton.