ИСТИНА

The emergence of directed motion and energy conversion in small-scale systems from unbiased nonequilibrium fluctuations (induced by a chemical reaction or any other external process) has motivated our investigation in this area. We consider reciprocating motion on the nanoscale and its rectification to directional motion using a simple model of two fluctuating states with transitions between them occuring through two fluctuating reaction channels. Fluctuations of the states and channels are described by a dichotomous process with the state-dependent rate constants which contain the contributions from both equilibrium and nonequilibrium noise. A generalized driving force of the reciprocating and directional motion is caused, first, by the contribution from state and channel energy fluctuations and, second, by the nonequilibrium entropic contribution from the difference between state-dependent rate constants. The model considered is equivalent to the flashing-potential model with a periodic two-well potential which includes potential well minima and potential barrier maxima, each fluctuating between two values. As shown, in the absence of the load force, the reciprocating motion can arise not only as a result of nonequilibrium fluctuations of wells and barriers but also due to the nonequilibrium entropic contribution at the nonfluctuating potential relief. At the same time, initiation of the directional motion requires antisymmetric fluctuations of potential barriers which determine the rectification coefficient for the reciprocating motion. The efficiency of energy conversion from nonequilibrium source to the directional motion is calculated and the conditions are established which allow the efficiency to approach unity.