  Conductivity measurements reflect vortex solid melting in YBCO films.
Field-independent glass exponents nu_g=1.9 and z_g=4.0 describe the transition
T_g(H) for 0<H<26 T. At low fields, 3D XY exponents nu_{XY}=0.63 and
z_{XY}=1.25 are also observed, with z_{XY} smaller than expected. These compete
with glass scaling according to multicritical theory. A predicted power-law
form of T_g(H) is observed for 0.5T_c<T_g<T_c. For T_g<0.5T_c, 3D XY scaling
fails, but a lowest Landau level analysis becomes possible, obtaining T_{c2}(H)
with positive curvature.
