  We assess the prospects for attaining steady nuclear flow equilibrium in
expanding r-process environments where beta decay and/or neutrino capture
determine the nuclear charge-changing rates. For very rapid expansions, we find
that weak steady flow equilibrium normally cannot be attained. However, even
when neutron capture processes freeze out in such nonequilibrium conditions,
abundance ratios of nuclear species in the r-process peaks might still mimic
those attained in weak steady flow. This result suggests that the r-process
yield in a regime of rapid expansion can be calculated reliably only when all
neutron capture, photodisintegration, and weak interaction processes are fully
coupled in a dynamical calculation. We discuss the implications of these
results for models of the r-process sited in rapidly expanding neutrino-heated
ejecta.
