Orateur
Massimo VILLARINI
(Modena)
Description
We give an example of a free circle action on the 7-dimensional sphere whose orbits have unbounded lenghts (equivalently: unbounded periods).As an application we construct a smooth vector field X in a neighbourhood U of the origin in the 8-dimensional real space such that : U - (0) is foliated by closed integrale curves, the differential DX(0) generate a 1-parametri group of rotations, but X is not orbitally equivalent to its linearization at the origin, hence proving that Poincare' Centre Theorem, true for planar non-degenerate centers is not generalizable in 8 dimensioni.
