  The nonlinear response of an adsorbed layer on a periodic substrate to an
external force is studied via a two dimensional uniaxial Frenkel-Kontorova
model. The nonequlibrium properties of the model are simulated by Brownian
molecular dynamics. Dynamical phase transitions between pinned solid, sliding
commensurate and incommensurate solids and hysteresis effects are found that
are qualitatively similar to the results for a Lennard-Jones model, thus
demonstrating the universal nature of these features.
