  Something as simple as Couette and Poiseuille onedimensional flow of a
newtonian fluid between infinite parallel walls provides an illuminating
example of the contrasting physics of laminar and turbulent flow: the
difference between their mean velocity profiles has in one regime the opposite
sign than in the other. This easily verifiable but yet unnoticed behaviour
implies that the physical mechanisms of laminar and turbulent transport are
even more fundamentally different than ordinarily presumed.
