Schematic of How a Ratchet Works at Macro-/Meso-Scale and Nanoscale (image) Science China Press Share Print E-Mail Caption At macro-/meso-scale, an additional perturbation with long-range time correlation is required for unidirectional transport in asymmetric systems. However, at nanoscale, because thermal noise has a significantly long autocorrelation time, unidirectional transport is feasible in asymmetric systems, even in the situation that thermal noise is the only perturbation. In such a situation, extra energy is required to sustain the asymmetry of the system against thermal noise. Credit © Science China Press Usage Restrictions None Share Print E-Mail Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.