Effect of harmonic noise on a Brownian particle in a ratchet periodic potential Z.R. Zhou, L. Bai, C.Z. Shu and L.R. Nie Eur. Phys. J. B, 85 8 (2012) 287 Published online: 20 August 2012 DOI: 10.1140/epjb/e2012-30298-4