Isabelle Gallagher, Thierry Gallay, Pierre-Louis Lions
On the uniqueness of the solution of the two-dimensional 
Navier-Stokes equation with a Dirac mass as initial vorticity
(190K, Postscript)

ABSTRACT.  We propose two different proofs of the fact that Oseen's vortex is 
the unique solution of the two-dimensional Navier-Stokes equation 
with a Dirac mass as initial vorticity. The first argument, due to 
C.E. Wayne and the second author, is based on an entropy estimate 
for the vorticity equation in self-similar variables. The second 
proof is new and relies on symmetrization techniques for 
parabolic equations.