  Current can be pumped through a closed system by changing parameters (or
fields) in time. The Kubo formula allows to distinguish between dissipative and
non-dissipative contributions to the current. We obtain a Green function
expression and an $S$ matrix formula for the associated terms in the
generalized conductance matrix: the "geometric magnetism" term that corresponds
to adiabatic transport; and the "Fermi golden rule" term which is responsible
to the irreversible absorption of energy. We explain the subtle limit of an
infinite system, and demonstrate the consistency with the formulas by Landauer
and Buttiker, Pretre and Thomas. We also discuss the generalization of the
fluctuation-dissipation relation, and the implications of the Onsager
reciprocity.
