  We present a derivation of the Redfield formalism for treating the
dissipative dynamics of a time-dependent quantum system coupled to a classical
environment. We compare such a formalism with the master equation approach
where the environments are treated quantum mechanically. Focusing on a
time-dependent spin-1/2 system we demonstrate the equivalence between both
approaches by showing that they lead to the same Bloch equations and, as a
consequence, to the same characteristic times $T_{1}$ and $T_{2}$ (associated
with the longitudinal and transverse relaxations, respectively). These
characteristic times are shown to be related to the operator-sum representation
and the equivalent phenomenological-operator approach. Finally, we present a
protocol to circumvent the decoherence processes due to the loss of energy (and
thus, associated with $T_{1}$). To this end, we simply associate the
time-dependence of the quantum system to an easily achieved modulated
frequency. A possible implementation of the protocol is also proposed in the
context of nuclear magnetic resonance.
