  A model of Brownian particles with the ability to take up energy from the
environment, to store it in an internal depot, and to convert internal energy
into kinetic energy of motion, is discussed. The general dynamics outlined in
Sect. 2 is investigated for the deterministic and stochastic particle's motion
in a non-fluctuating ratchet potential. First, we discuss the attractor
structure of the ratchet system by means of computer simulations. Dependent on
the energy supply, we find either periodic bound attractors corresponding to
localized oscillations, or one/two unbound attractors corresponding to directed
movement in the ratchet potential. Considering an ensemble of particles, we
show that in the deterministic case two currents into different directions can
occur, which however depend on a supercritical supply of energy. Considering
stochastic influences, we find the current only in one direction. We further
investigate how the current reversal depends on the strength of the stochastic
force and the asymmetry of the potential. We find both a critical value of the
noise intensity for the onset of the current and an optimal value where the net
current reaches a maximum. Eventually, the dynamics of our model is compared
with other ratchet models previously suggested.
