  A modified form of the vortex-lattice melting line is arrived at by
incorporating the effects of critical behavior at the melting transition.
Beginning with the universal form established by Blatter and Ivlev [Physical
Review Letters 70, 2621 (1993)] which includes both thermal and quantum
fluctuations, we then use the vortex relaxation time of a vortex-glass with a
finite transition temperature that follows from the scaling theory of Fisher,
Fisher, and Huse [Physical Review B, 43, 130 (1991)]. This new form of the
melting line is demonstrated to fit over the entire melting line of
Y(1-x)Pr(x)Ba2Cu3O6.97 (x = 0 - 0.4) samples within the temperature range 0.03
< T/Tc < 1 (H < 45 tesla) implying no crossover in dynamics from 3D to 2D.
Generically it can be seen that a change in dimensionality of the vortex
fluctuations along the melting line must be accompanied by a corresponding
change in the critical exponents nu and z. Such a change is observed for the
highly anisotropic cuprate superconductor Bi2Sr2CaCu2O8.
