  We present a 1D effective model for the evolution of a cigar-shaped
Bose-Einstein condensate in time dependent potentials whose radial component is
harmonic. We apply this model to investigate the dynamics and expansion of
condensates in 1D optical lattices, by comparing our predictions with recent
experimental data and theoretical results. We also discuss negative-mass
effects which could be probed during the expansion of a condensate moving in an
optical lattice.
