  The density-matrix renormalization-group (DMRG) algorithm is extended to
treat time-dependent problems. The method provides a systematic and robust tool
to explore out-of-equilibrium phenomena in quantum many-body systems. We
illustrate the method by showing that attractive interactions enhance the
tunneling current between two Luttinger liquids, whereas repulsive interactions
suppress it, in qualitative agreement with analytical predictions. Enhancement
of the transport current through a quantum dot in the Kondo regime is also
exhibited.
