The directed transport of active Brownian particle chains in spatially inhomogeneous thermal environments is governed by the interplay among activity, external driving, spatial asymmetry, and thermal fluctuations. In this work, we numerically investigate the transport of an active Brownian particle chain confined in a two-dimensional periodic channel subjected to a temperature gradient. An system of Langevin equations is constructed by incorporating an asymmetric periodic potential, shear flow, spatially dependent translational and rotational diffusion, elastic coupling between neighboring particles, and particle self-propulsion. The stochastic equations are interpreted in the Itô sense and numerically integrated using the Euler–Maruyama scheme. By systematically varying the shear rate, potential-asymmetry parameter, relative temperature difference, base temperature, and self-propulsion speed, we examine how these nonequilibrium mechanisms cooperate or compete to determine the transport direction and efficiency of the particle chain.
In the absence of a temperature difference, shear flow alone cannot generate directed transport when the periodic potential is spatially symmetric. Once spatial asymmetry is introduced, however, the coupling between the asymmetric periodic potential and shear flow produces pronounced rectification, and the average transport velocity exhibits a nonmonotonic dependence on the shear rate. This behavior results from the competition between shear-induced particle motion and the directional selectivity imposed by the asymmetric potential. When a temperature gradient is introduced, the resulting spatially inhomogeneous thermal fluctuations substantially modify the transport behavior. The temperature-gradient effect competes with the asymmetric potential and shear flow, thereby suppressing or enhancing the original rectification depending on the parameter regime and, more importantly, producing transitions between positive and negative transport. The calculated parameter maps further demonstrate that the transport-reversal boundary can be continuously shifted by tuning the relative temperature difference, shear rate, and potential asymmetry, indicating that the transport direction is not controlled by a single driving mechanism but by their combined competition.
The base temperature provides an additional means of regulating the transport by changing the overall level of thermal fluctuations. Increasing the thermal scale generally weakens the directional selectivity associated with barrier crossing, although its influence depends on the potential asymmetry and other driving parameters. Activity introduces another competing mechanism. Moderate self-propulsion can facilitate barrier crossing and enhance directed transport, whereas sufficiently strong self-propulsion can weaken the original rectification mechanism and even induce transport reversal. Thus, the transport behavior arises from a balance among shear-induced advection, spatially asymmetric barrier crossing, inhomogeneous thermal fluctuations, and persistent active motion. Calculations for different chain lengths and system sizes show that the principal transport characteristics and reversal behavior remain qualitatively robust within the parameter ranges considered.
These results establish a physical picture in which the asymmetric periodic potential provides directional selectivity, shear flow controls the ability of the chain to explore and cross potential barriers, the temperature gradient redistributes thermal fluctuations spatially, and self-propulsion modifies both barrier-crossing dynamics and the competition among the other transport mechanisms. Their interplay enables not only continuous regulation of the transport efficiency but also controllable reversal of the transport direction. The present study therefore provides insight into the nonequilibrium transport of elastically coupled active particles in thermally inhomogeneous environments and may offer a theoretical basis for controlling collective transport in micro- and nanoscale active-matter systems.