  Transport measurements carried out on twinned ybco films are compared to the
predictions of a previously proposed model suggesting that the vortices move
along the films twin boundaries that behave as rows of Josephson weak links
[P.Bernstein and J.F.Hamet, J.Appl.Phys.95 (2004) 2569]. The obtained results
suggest that, except if the films are very thin, the twin boundaries consist of
superimposed rows of weak links with mean height,ds, whose mean length along
the TBs is an universal function of T/Tc, the reduced temperature. This
conclusion yields a general expression for the critical surface current density
of the films as a function of T/Tc and of the number of superimposed weak links
rows, while the critical current density depends on ds. A comparison of the
measurements reported by various authors shows that the nature of the substrate
and the growth technique have both a strong effect on ds . The existence of
superimposed weak links rows is attributed to extended defects generated by
y2o3 inclusions.
