INTRINSIC GEOMETRICAL BOUNDARIES FOR THE CRITICAL CURRENTS INSIDE YBa2Cu3O7-x SINGLE CRYSTALS A. Sulpice, P. Lejay, R. Tournier et J. Chaussy J. Phys. Colloques, 49 C8 (1988) C8-2109-C8-2110 DOI: 10.1051/jphyscol:19888948