Autonomous Engines Driven by Active Matter: Energetics and Design Principles

Abstract

Because of its nonequilibrium character, active matter in a steady state can drive engines that autonomously deliver work against a constant mechanical force or torque. As a generic model for such an engine, we consider systems that contain one or several active components and a single passive one that is asymmetric in its geometrical shape or its interactions. Generally, one expects that such an asymmetry leads to a persistent, directed current in the passive component, which can be used for the extraction of work. We validate this expectation for a minimal model consisting of an active and a passive particle on a one-dimensional lattice. It leads us to identify thermodynamically consistent measures for the efficiency of the conversion of isotropic activity to directed work. For systems with continuous degrees of freedom, work cannot be extracted using a one-dimensional geometry under quite general conditions. In contrast, we put forward two-dimensional shapes of a movable passive obstacle that are best suited for the extraction of work, which we compare with analytical results for an idealised work-extraction mechanism. For a setting with many noninteracting active particles, we use a mean-field approach to calculate the power and the efficiency, which we validate by simulations. Surprisingly, this approach reveals that the interaction with the passive obstacle can mediate cooperativity between otherwise noninteracting active particles, which enhances the extracted power per active particle significantly. arXiv:1905.00373v2 [cond-mat.stat-mech]

Understanding contagion dynamics through microscopic processes in active Brownian particles

“…Since the work of self-driven particles of Viscek et al 15 , the modeling of active agents has been possible following a series of rules for particle interactions, such as alignment, polarization, repulsion, and quorum-sensing 13 , 16 . These interactions often give rise to the understanding of unexpected phenomena such as collective motion, turbulence, giant fluctuations, rectification, and self-organization 16 – 20 , and at the same time, they reproduce what we observe in nature. At the micro-scale, agents can be modeled as active Brownian particles (ABP), where ABP can take up energy from the environment to store it in an internal depot and convert it internal energy into kinetic energy and motion 21 .…”

Dissipation controls transport and phase transitions in active fluids: mobility, diffusion and biased ensembles

“…Recent works have shown that, in nonequilibrium dynamics, the current fluctuations are bounded by the coarse-grained entropy production rate [37][38][39][40][41]. In active fluids, there is no average current of particles provided that no asymmetric external potential is applied [68][69][70]. Yet, the bound on current fluctuations can still be formulated within the mapping of section 3.…”

Entropy Production in Exactly Solvable Systems

“…Stochastic thermodynamics has progressively evolved into an essential tool in the study of non-equilibrium systems as it connects the quantities of interest in traditional thermodynamics, such as work, heat and entropy, to the properties of microscopically resolved fluctuating trajectories [ 1 , 2 , 3 ]. The possibility of equipping stochastic processes with a consistent thermodynamic and information-theoretic interpretation has resulted in a number of fascinating works, with the interface between mathematical physics and the biological sciences proving to be a particularly fertile ground for new insights (e.g., [ 4 , 5 , 6 , 7 , 8 ]). The fact that most of the applications live on the small scale is not surprising, since it is precisely at the microscopic scale that fluctuations start to play a non-negligible role.…”