Resistive upper critical fields and irreversibility lines of optimally-doped high-T_c cuprates

We present the resistively-determined upper critical field H^{rho}_{c2}(T) and the irreversibility lines H^{rho}_{irr}(T) of various high-T_c cuprates, deduced from measurements in 61-T pulsed magnetic fields applied parallel to the c-axis. The SHAPE of both H^{rho}_{c2}(T) and H^{rho}_{irr}(T) depends monotonically on the anisotropy of the material and none of the samples show saturation of H^{rho}(T) at low temperatures. The anomalous positive curvature, d^2 H^{rho}/dT^2 > 0, is the strongest in materials with the largest normal-state anisotropy, regardless of whether anisotropy is varied by changing the carrier concentration or by comparing a variety of optimally-doped compounds.