  Two one-parametric bifurcation problems for scalar nonautonomous ordinary
differential equations are analyzed assuming the coercivity of the
time-dependent function determining the equation and the concavity of its
derivative with respect to the state variable. The skewproduct formalism leads
to the analysis of the number and properties of the minimal sets and of the
shape of the global attractor, whose abrupt variations determine the occurrence
of local saddle-node, local transcritical and global pitchfork bifurcation
points of minimal sets and of discontinuity points of the global attractor.
