Efficiency of Brownian Motors
  The efficiency of different types of Brownian motors is calculated analytically and numerically. We find that motors based on flashing ratchets present a low efficiency and an unavoidable entropy production. On the other hand, a certain class of motors based on adiabatically changing potentials, named reversible ratchets, exhibit a higher efficiency and the entropy production can be arbitrarily reduced. 
J.M.R. Parrondo, J.M. Blanco, F.J. Cao, and R. Brito (Universidad   Complutense de Madrid, Spain)