  We give a method of describing thermodynamical transport phenomena, based on
a quantum scattering theoretical approach. We consider a quantum system of
particles connected to thermodynamical reservoirs by leads. The effects of the
reservoirs are imposed as an asymptotic condition at the end of the leads. We
derive an expression for a current of a conserved quantity, which is
independent of the details of the Hamiltonian operator. The Landauer formula
and its generalizations are derived from this method.
