Resumo
Within the spirit of van Kampen's \Langevin approach", we discuss the limits of validity of rephrasing the non-equilibrium problem of a particle subject to an external (work)
reservoir | a system where the uctuation-dissipation is not veried | into the simpler case with an internal (heat) reservoir for which the uctuations and the dissipation arise
from the same source. Using a convenient mapping of the thermomechanical parameters we show that, counter-intuitively, such approach is not only valid for steady state time independent quantities, but also for time dependent thermostatistical quantities, namely
the injected and dissipated uxes. We connect this result with the problem of large devi- ations and conclude that, in this context, we can only distinguish reservoirs by analysingthe \
uctuations of accumulated uctuations". As a by-product, we learn that the best reference approximation to the large deviation functions of a non-Markovian external reservoir system is not the respective internal reservoir limit | as often assumed and sug-
gested by the Langevin approach | but its internal reservoir analogue system obtained from the mapping of the original thermomechanical parameters.