ULTRASONIC INVESTIGATION OF MODIFIED CRITICAL BEHAVIOUR IN THE STRONG RANDOM-FIELD SYSTEM Dy ( As0.17V0.83) O4 J. H. Page et J. T. Graham J. Phys. Colloques, 49 C8 (1988) C8-1227-C8-1228 DOI: 10.1051/jphyscol:19888556