Fig. 1: Five scenarios of internal dissipation in an active swimmer.
From: Minimum entropy production by microswimmers with internal dissipation
a An active droplet with a fluid-fluid interface, driven by tangential forces at the interface. b A swimmer driven by tangential forces at an outer surface (dotted line). c A swimmer driven by normal forces at an outer surface. d A swimmer driven by unconstrained forces, allowing both tangential and normal components, at an outer surface. e A surface-driven swimmer with internal dissipation in the surface layer (green). The magenta arrows denote the active tractions, defined as the forces exerted by the fluid on the swimmer.
