\sim (T - T_{\rm VG})^{(1-z)\nu}, \eqno(2.22)$$ where $T_{\rm VG}(B)$ is the VG transition line (in type II limit), and $z$ ($> 4$) and $\nu$ are, respectively, dynamical exponent and the exponent of correlation length $\xi_{\rm VG}(T)$ in VG critical region (in type II limit). $\sigma_{G, xx}$ is given by a sum of eqs.(2.21) and (2.22). A crossover between the behaviors (2.21) and (2.22) occurs when \[18\] $$\xi_{\rm VG}(T) \sim L_{\rm cr}(B)=\sqrt{{{\phi_0}
\over {B \Delta_{\rm eff}(T)}} \biggl( 1 + {{\Delta^{(p)}} \over {4 h^2
\Delta_\Phi}} \biggr)}. \eqno(2.23)$$ Namely, if $L_{\rm cr}(B)$ is beyond the system size, the behavior (2.21) may be seen like a true critical behavior in type II limit in cleaner systems, and, in a clean sample, the exponent of vanishing resistivity is $B$-dependent and will increase from $\nu(z-3)$ to $\nu(z-1)$ with increasing $B$ in an apparently continuous manner \[18\]. In fact, a $B$-dependent exponent was observed in the vortex slush regime of a YBCO sample, and the expected universal behavior (2.22) seems to have been found in higher fields than $B_{\rm ucp}$ \[40\]. A similar behavior was observed previously in other experiments: the resistivity exponent in a moderately disordered sample was $B$-dependent and smaller than the expected one (2.22) 