Optimal protocol for a collective flashing ratchet
  We study a system of independent Brownian particles in a flashing ratchet potential that can be turned on or off depending on the position of the particles, with the aim of maximising the speed of the center of mass in the long run. First, an explanation on how to find the optimal protocol using Bellman's principle of optimality for any number of particles is given. Then the problem is numerically solved for a system of 2 particles. Simulations show that the optimal protocol performs better than the maximisation of instantaneous center-of-mass speed, a protocol known to give better results for 2 particles than any open-loop protocol. 
F. Roca, J. P. G. Villaluenga, L. Dinis
cond-mat.stat-mech