  The measurements of the 1st and the 3rd harmonics of the AC magnetic
susceptibility, performed on melt grown YBCO samples as a function of the
temperature and the external parameters (frequency and amplitude of AC magnetic
field, intensity of a DC field) were studied by using the Cole-Cole plot
analysis. By considering the AC field dependence of the 3rd harmonics Cole-Cole
plots, we have extracted information about the peculiar behaviour of the I-V
characteristics and, therefore, about the dissipative phenomena in the sample.
The experimental results have been analysed with the help of both analytical
and numerical curves. In particular, the use of a phenomenological expression
for the resistivity allowed us to reproduce the main experimental features,
including the observed invariance of the area inside the Cole-Cole plots and
their behaviour as a function of the AC field.
