%0 Journal Article %T Decay of correlations in suspension semi-flows of angle-multiplying maps %A Masato Tsujii %J Mathematics %D 2005 %I arXiv %X We consider suspension semi-flows of angle-multiplying maps on the circle. Under a $C^r$generic condition on the ceiling function, we show that there exists an anisotropic Sobolev space contained in the $L^2$ space such that the Perron-Frobenius operator for the time-$t$-map acts on it and that the essential spectral radius of that action is bounded by the square root of the inverse of the minimum expansion rate. This leads to a precise description on decay of correlations and extends the result of M. Pollicott. %U http://arxiv.org/abs/math/0511338v3