This study uses computer simulations to examine how an asymmetric gear can be driven by Brownian particles that interact in a non-reciprocal manner. Unlike many active matter systems, the particles are not self-propelled. Instead, the non-reciprocal interactions break action-reaction symmetry and produce a net force that drives the system out of equilibrium. The gear has an asymmetric shape, which helps select a preferred direction of rotation.
We find that the rotation direction of the gear is influenced by both its asymmetry and parameters of system. When system parameters are identical, gears with two structures of opposite chirality exhibit equal magnitudes of average angular velocity, differing only in their rotational directions. For a specific gear, the rotation speed increases with the strength of the non-reciprocal interaction and shows a non-monotonic dependence on temperature and particle density. Interestingly, under high density conditions, the rotation direction can reverse. At low temperatures, particle clusters form and lead to reversed motion, while higher temperatures restore rotation in the original direction.
This work illustrates how non-reciprocal interactions can be used to generate directed motion in passive structures such as gears. It offers one possible approach to controlling motion in small-scale systems without external energy input, and may contribute to the design of simple nanoscale machines.
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