12 - Active Processes

Summary

Active nonequilibrium processes are characterized by the coupling of an ionic current or a mechanical motion to a chemical reaction. This coupling induces energy transduction, satisfying Onsager reciprocal relations in the linear regime close to equilibrium and the bivariate fluctuation relation in regimes farther away from equilibrium. These considerations concern, in particular, molecular motors as well as active colloidal particles that are self-propelled by chemical reactions catalyzed at their surface and diffusiophoresis. These active processes can be described by stochastic processes obeying bivariate fluctuation relations for the coupled currents. The mechanochemical coupling can be characterized in terms of the linear and nonlinear response coefficients, as well as the efficiencies defined in the different regimes of energy transduction, i.e., propulsion by the chemical reaction on the one hand, and the synthesis of fuel from products on the other hand.