  These are the lecture notes to be published in the Proceedings of XXXI
Rencontres de Moriond conference ``Correlated Fermions and Transport in
Mesoscopic Systems'', (20-27 January 1996, Les Arcs, France). The notes are
based on two recent papers [D L. Maslov and M. Stone, Phys. Rev. B 52, R5539
(1995), and D. L. Maslov, ibid., R14368 (1995)].
