We propose a mechanism which produces periodic variations of the degree of
predictability in dynamical systems. It is shown that even in the absence of
noise when the control parameter changes periodically in time, below and above
the threshold for the onset of chaos, stochastic resonance effects appears. As
a result one has an alternation of chaotic and regular, i.e. predictable,
evolutions in an almost periodic way, so that the Lyapunov exponent is positive
but some time correlations do not decay.Comment: 9 Pages + 3 Figures, RevTeX 3.0, sub. J. Phys.
