Rectifying the thermal Brownian motion of three-dimensional asymmetric   objects
  We extend the analysis of a thermal Brownian motor reported in Phys. Rev. Lett. 93, 090601 (2004) by C. Van den Broeck, R. Kawai, and P. Meurs to a three-dimensional configuration. We calculate the friction coefficient, diffusion coefficient, and drift velocity as a function of shape and present estimates based on physically realistic parameter values. 
M. van den Broek and C. Van den Broeck