Origin of cosmological constant from Bulk manifold

The problem about cosmological constant is a difficult and important problem, people even don't know what it is really originated from. In this letter, the authors show up a kind of origin of the cosmological constant from the viewpoint of some extra dimensional spaces, obtain different values of the cosmological constant under different circumstances, acquire the evolution function with time t. And we achieve a cosmological constant that may be fitted with modern astronomic observation. (authors)