\bibitem{Lancon01}     P.~Lan{\c c}on, G.~Batrouni, L.~Lobry, N.~Ostrowsky, \hskip 2mm
                       {\it Drift without Flux: Brownian Walker with a Space-Dependent Diffusion Coefficient},
                       Europhys. Lett. {\bf 54} (1), 28-34, 2001.