  We consider the dynamics of a system coupled to a thermal bath, going beyond
the standard two-level system through the addition of an energy excitation
degree of freedom. Further extensions are to systems containing many fermions,
with the master equations modified to take Fermi-Dirac statistics into account,
and to potentials with a time-dependent bias that induce resonant avoided
crossing transitions. The limit $Q \to \infty$, where the interaction rate with
the bath is much greater than all free oscillation rates for the system, is
interrogated. Two behaviors are possible: freezing (quantum Zeno effect) or
synchronization (motional narrowing). We clarify the conditions that give rise
to each possibility, making an explicit connection with quantum measurement
theory. We compare the evolution of quantal coherence for the two cases as a
function of $Q$, noting that full coherence is restored as $Q \to \infty$.
Using an extended master equation, the effect of system-bath interactions on
entanglement in bipartite system states is computed. In particular, we show
that the sychronization case sees bipartite system entanglement fully preserved
in the large $Q$ limit.
