DYNAMICS OF UNBOUND VORTICES IN THE 2-DIMENSIONAL XYAND ANISOTROPIC HEISENBERG MODELS F. G. Mertens, A. R. Bishop, M. E. Gouvea and G. M. Wysin J. Phys. Colloques, 49 C8 (1988) C8-1385-C8-1386 DOI: 10.1051/jphyscol:19888635