Bose-Einstein condensation of ultra-cold atomic gases has become an
attractive research topic which draws on distinct fields such nuclear and
atomic physics and nonlinear science. The talk will give a brief introduction on the band-structure of a Bose-condensed gas loaded into an optical lattice with emphasis on the band structure exhibited by the DNLS (Discrete Nonlinear Schrodinger) equation. In particular it will be shown analytically how the modulational (i.e., dynamical) instability of the lowest energy Bloch coincides with the occurrence of a state having a spatial period equal to twice that of the underlying lattice. Supporting numerical results for the continuous model will also be shown. |

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