FRACTAL DIMENSIONS AND F(ALPHA SPECTRUM OF CHAOTIC SETS NEAR CRISES

We study numerically the behaviour of the generalized dimensions D(q) and the f(alpha) spectrum in dependence on a control parameter in the parametrically driven, damped pendulum. We find a continuous transitio n of the D(q) of a chaotic attractor near a boundary crisis to those c haracterizing a chaotic saddle into which the attractor is converted w hen the crisis occurs. At an interior crisis a chaotic saddle collides with a small chaotic attractor and both chaotic sets merge to a large chaotic attractor. In the vicinity of the crisis-value of the control parameter the D(q) of the large attractor are close to the D(q) of th e small attractor for positive q and near to those of the chaotic sadd le for non-positive q. Correspondingly. the f(alpha) spectrum of the l arge chaotic attractor near the crisis-value is very broad and has a t ypical phase-transition-like shape.