Vice ratchets

Botanical ratchets.

Ratcheting surfaces are a common motif in nature and appear in plant awns and grasses. They are known to proffer selective advantages for seed dispersion and burial. In two simple model experiments, we show that these anisotropically toothed surfaces naturally serve as motion rectifiers and generically move in a unidirectional manner, when subjected to temporally and spatially symmetric excitat...

Quantum Ratchets

We investigate quantum Brownian motion in adiabatically rocked ratchet systems. Above a crossover temperature Tc tunneling events are rare, yet they already substantially enhance the classical particle current. Below Tc, quantum tunneling prevails and the classical predictions grossly underestimate the transport. Upon approaching T ­ 0 the quantum current exhibits a tunneling induced reversal, ...

Quantum Ratchets

The concept of thermal ratchets is extended to the system governed by quantum mechanics. We study a tight-binding model with an asymmetric periodic potential contacting with a heat bath under an external oscillating field as a specific example of quantum ratchet. Dynamics of a density operator of this system is studied numerically by using the quantum Liouville equation. Finite net current is f...

Thermal Ratchets

Intrinsic Ratchets

We present a generic formalism to describe Brownian motion of particles with intrinsic asymmetry and give predictions for the drift behavior in unbiased time-dependent force fields. Our findings are supported by molecular dynamics simulations. Introduction. – In view of their potential applications in bioand nanotechnology, Brownian motors have in recent years been the object of intensive resea...