Atomic scale engines: Taking a turn

We investigate a new approach which has been recently introduced to constru ct microscopic engines whose main characteristic is the possibility to dete rmine dynamically the direction of motion. The approach is based on the tra nsformation of the supplied energy into directed motion through a dynamical competition between the intrinsic lengths of the moving object and the sub strate. The engines are able to move translationally or rotationally and ca n perform useful functions such as pulling of a cargo. We discuss possible realizations and introduce some ingredients, such as turns and switches, im portant for creating a microscopic 'railway system.'