Geometry-induced rectification for an active object

TL;DR

This paper demonstrates that geometric asymmetry can induce rectified motion in active objects among passive particles, revealing a new mechanism for microscopic motor design based on shape-induced rectification.

Contribution

It introduces the novel concept that active objects can have their motion rectified by shape asymmetry in passive environments, reversing the common passive-active roles.

Findings

Active objects exhibit rectified motion due to geometric asymmetry.

Passive mode shows weak, less diffusive rectification without energy input.

The mechanism suggests a new design principle for microscopic motors.

Abstract

Study on a rectified current induced by active particles has received a great attention due to its possible application to a microscopic motor in biological environments. Insertion of an {\em asymmetric} passive object amid many active particles has been regarded as an essential ingredient for generating such a rectified motion. Here, we report that the reverse situation is also possible, where the motion of an active object can be rectified by its geometric asymmetry amid many passive particles. This may describe an unidirectional motion of polar biological agents with asymmetric shape. We also find a weak but less diffusive rectified motion in a {\em passive} mode without energy pump-in. This "moving by dissipation" mechanism could be used as a design principle for developing more reliable microscopic motors.