The absorption of energy by driven system can be calculated by linear response (Kubo) only if the driven transitions are much slower compared with the relaxation rate. In the mesoscopic regime we assume that the relaxation effect is weak, and consequently a theory that goes beyond Kubo is required.  Our semi linear response theory use a resistor network analogy (see illustration below) in order to calculate the rate of energy absorption. Connected sequences of transitions are essential in order to have non-vanishing result, as in the theory of percolation. The original motivation for introducing this theory [1] was the study of mesosopic conductance.  The same idea was later used [2] to develop a theory for the rate of energy absorption by metallic grains.