Talk by Chun-Jen Chen at Institute of Physics, Academia Sinica (Taiwan), 25 February 2021

The topic of this talk covered the laser experiments enabling active particle steering (upper left), collective motion of such particles (middle) and connection to social animal behaviours, eg. fish school (lower). (Image by C-J Chen.)
On the 25th of February 2021, Chun-Jen gave a talk at the Institute of Physics, Academia Sinica (Taipei, Taiwan) about his research project at University of Konstanz. He explained how active Janus micro-spheres can be propelled and steered at the indivitual level in his experiment system and how such experiments are linked to studies of collective behaviours in living systems. The talk induced vivid discussions with audience of different backgrounds. Chun-Jen also shared experiences regarding PhD life in Germany with prospective young researchers in Taiwan.

Active noise-driven particles under space-dependent friction in one dimension on arXiv

Sketch of the confining potential U(x) = κ|x|, a linear friction gradient γ(x) = γ0+γ1|x| in arbitrary units. The particle, shown by a blue dot on the x-axis, is activated by noise (indicated in red), under the influence of the potential and the friction gradient. Image by D. Breoni.
Active noise-driven particles under space-dependent friction in one dimension

Davide Breoni, Ralf Blossey, Hartmut Löwen
arxiv: 2102.09944

Abstract: We study a Langevin equation describing the stochastic motion of a particle in one dimension with coordinate x, which is simultaneously exposed to a space-dependent friction coefficient γ (x), a confining potential U(x) and non-equilibrium (i.e., active) noise. Specically, we consider frictions γ (x) = γ0 + γ1|x|p and potentials U(x) ∝ |x|p with exponents p = 1; 2 and n = 0; 1; 2. We provide analytical and numerical results for the particle dynamics for short times and the stationary
probability density functions (PDFs) for long times. The short-time behaviour displays diffusive and ballistic regimes while the stationary PDFs display unique characteristic features depending on the exponent values (p; n). The PDFs interpolate between Laplacian, Gaussian and bimodal distributions, whereby a change between these different behaviours can be achieved by a tuning of the friction strengths ratio
γ0 / γ1. Our model is relevant for molecular motors moving on a
one-dimensional track and can also be realized for confined self-propelled colloidal particles.