The blob is back: diffusion of an active elastic membrane*

This work deals with the free motion of an active elastic membrane defined as a two-dimensional network of active stochastic particles interacting by nonlinear hard springs. Notice that in this model, the rotational dynamics of each particle is stochastic and independent from the others, and yet it moves. By proposing a discrete model, it is numerically found that irrespective of the active membrane's size, its long-time mean-square displacement --with respect to its center of mass-- behaves linearly in time. However, at short times, it is seen that 'the blob' has a superdiffusive dynamics (with a power in time alpha around four and five) which depends on the blob's size. For example, for a small blob (N=25 particles) it is observed that alpha is around five, whereas for N=961, alpha is around four. The effects of rotational noise, propulsion speed and nonlinearity on the motion of this 'blob' are also studied.