Abstract

For a few years we have been studying a biologically motivated problem: in a variety of organisms, there are actively beating filaments that coordinate amongst each other to exert an optimal fluid transport, or swimming efficiency. This coordination comes from mechanical forces, through the fluid, and in some situations possibly through the cell medium. These stress fields are long ranged, typically decaying only with inverse distance, hence the system is many-body. The filaments can be thought of as driven oscillators, in an overdamped regime. However the complex internal degrees of freedom make the filament activity very non-linear. The lengthscales are such that thermal noise is important. These elements combine together to give rich phenomenology. First, if one ignores thermal noise, then the long range coupling gives rise to synchronisation, and the key elements that set the patters in the dynamics are the geometry of the system, and the details of how oscillators are driven. Then, considering noise, there are interesting transitions with the loss of synchronisation. We have looked at these systems with a combination of experiement (using optical traps), numerical simulation (Brownian dynamics) and theory (typically neglecting noise), but many questions remain open. In this informal talk I aim to present this area, overview what we have done, and highlight what we don’t understand.