M. Borromeo

Recycled noise rectification: An automated Maxwell's daemon

The one-dimensional motion of a massless Brownian particle on a symmetric periodic substrate can be rectified by reinjecting its driving noise through a realistic recycling procedure. If the recycled noise is multiplicatively coupled to the substrate, the ensuing feedback system works like a passive Maxwells daemon, capable of inducing a net current that depends on both the delay and the autocorrelation times of the noise signals. Extensive numerical simulations show that the underlying rectification mechanism is a resonant nonlinear effect: The observed currents can be optimized for an appropriate choice of the recycling parameters with immediate application to the design of nanodevices for particle transport.

Deterministic ratchets: Route to diffusive transport

The rectification efficiency of an underdamped ratchet operated in the adiabatic regime increases according to a scaling current-amplitude curve as the damping constant approaches a critical threshold; below threshold the rectified signal becomes extremely irregular and eventually its time average drops to zero. Periodic (locked) and diffusive (fully chaotic) trajectories coexist on fine tuning the amplitude of the input signal. The transition from regular to chaotic transport in noiseless ratchets has been studied numerically.

Transport by bi-harmonic drives: from harmonic to vibrational mixing

Transport in a one-dimensional symmetric device can be activated by the combination of thermal noise and a bi-harmonic drive. The results of extensive simulations allow us to distinguish between two apparently different bi-harmonic regimes: (i) harmonic mixing, where the two drive frequencies are commensurate but not too high; (ii) vibrational mixing, where one harmonic drive component possesses a high frequency but finite amplitude-to-frequency ratio. A comparison with the earlier theoretical predictions shows that at present the analytical understanding of nonlinear frequency mixing is still not satisfactory.

THERMAL DECAY OF A METASTABLE ELASTIC STRING

Abstract Thermal nucleation of kink-antikink pairs in an elastic string subjected to a washboard potential is analyzed in the classical limit at low temperature. The nucleation rate is calculated analytically for values of the tilt up to close the instability threshold. Numerical simulation is shown to support our predictions in the diverse parameter regimes.

Deterministic ratchets: From confined to diffusive chaos

An AC driven, noiseless, underdamped Brownian particle moving on an asymmetric periodic substrate provides an interesting example of deterministic ratchet: In the adiabatic regime periodic and chaotic trajectories coexist on fine tuning the amplitude of the input signal; the transition from regular to chaotic transport happens through an intermediate class of trajectories exhibiting confined chaos.