  We consider a frustrated spin model with a glassy dynamics characterized by a
slow component and a fast component in the relaxation process. The slow process
involves variables with critical behavior at finite temperature T_p and has a
global character like the (structural) alpha-relaxation of glasses. The fast
process has a more local character and can be associated to the beta-relaxation
of glasses. At temperature T>T_p the fast relaxation follows the non-Arrhenius
behavior of the slow variables. At T ~< T_p the fast variables have an
Arrhenius behavior, resembling the alpha-beta bifurcation of fragile glasses.
The model allows us to analyze the relation between the dynamics and the
thermodynamics.
