Outer automorphisms of Burnside groups

The free Burnside group of exponent n, B(r,n), is the quotient of the free group of rank r by the subgroup generated by all n-th powers. This group was introduced in 1902 by W. Burnside who asked wether it has to be finite or not. Since the work of P.S. Novikov and S.I. Adian in the late sixties, it is knows that for exponent n large enough the answer is no. In this talk, we are interested in the outer automorphisms of B(r,n). Using a geometrical formulation of the small cancellation theory, we explore the following questions : Which elements of Out(B(r,n)) have infinite order? Does Out(B(r,n)) contain abelian or non-abelian free subgroups?