803 research outputs found
A deformable microswimmer in a swirl: capturing and scattering dynamics
Inspired by the classical Kepler and Rutherford problem, we investigate an
analogous set-up in the context of active microswimmers: the behavior of a
deformable microswimmer in a swirl flow. First we identify new steady bound
states in the swirl flow and analyze their stability. Second we study the
dynamics of a self-propelled swimmer heading towards the vortex center, and we
observe the subsequent capturing and scattering dynamics. We distinguish
between two major types of swimmers, those that tend to elongate
perpendicularly to the propulsion direction and those that pursue a parallel
elongation. While the first ones can get caught by the swirl, the second ones
were always observed to be scattered, which proposes a promising escape
strategy. This offers a route to design artificial microswimmers that show the
desired behavior in complicated flow fields. It should be straightforward to
verify our results in a corresponding quasi-two-dimensional experiment using
self-propelled droplets on water surfaces.Comment: 13 pages, 8 figure
Dynamics of a linear magnetic "microswimmer molecule"
In analogy to nanoscopic molecules that are composed of individual atoms, we
consider an active "microswimmer molecule". It is built up from three
individual magnetic colloidal microswimmers that are connected by harmonic
springs and hydrodynamically interact with each other. In the ground state,
they form a linear straight molecule. We analyze the relaxation dynamics for
perturbations of this straight configuration. As a central result, with
increasing self-propulsion, we observe an oscillatory instability in accord
with a subcritical Hopf bifurcation scenario. It is accompanied by a
corkscrew-like swimming trajectory of increasing radius. Our results can be
tested experimentally, using for instance magnetic self-propelled Janus
particles, supposably linked by DNA molecules.Comment: 6 pages, 8 figure
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