Emilia Petrisor
Destruction of invariant circles of nontwist maps
(3797K, Postscript)
ABSTRACT. The aim of this paper is two--fold: first, to prove that the main cause
of the destruction of invariant circles of the quadratic nontwist
standard map is its folding property, and second, to
illustrate numerically and
give arguments that support a conjecture concerning the regularity of motion in the region where the map changes its sign of twist.
In order to locate regions in the infinite annulus, where a quadratic nontwist map exhibits different types of motion one associates to the map
some non---invariant curves, such that their definition and relative
position in the phase space give information on the dynamics of
the orbits crossing them.