  In systems possessing spatial or dynamical symmetry breaking, Brownian motion
combined with symmetric external input signals, deterministic or random, alike,
can assist directed motion of particles at the submicron scales. In such cases,
one speaks of "Brownian motors". In this review the constructive role of
Brownian motion is exemplified for various one-dimensional setups, mostly
inspired by the cell molecular machinery: working principles and
characteristics of stylized devices are discussed to show how fluctuations,
either thermal or extrinsic, can be used to control diffusive particle
transport. Recent experimental demonstrations of this concept are reviewed with
particular attention to transport in artificial nanopores and optical traps,
where single particle currents have been first measured. Much emphasis is given
to two- and three-dimensional devices containing many interacting particles of
one or more species; for this class of artificial motors, noise rectification
results also from the interplay of particle Brownian motion and geometric
constraints. Recently, selective control and optimization of the transport of
interacting colloidal particles and magnetic vortices have been successfully
achieved, thus leading to the new generation of microfluidic and
superconducting devices presented hereby. Another area with promising potential
for realization of artificial Brownian motors are microfluidic or granular
set-ups.....
