Average Mean Escape Time for an Overdamped Spatially-Periodic System and Application to Josephson Junction ＊

We investigate the average mean escape time of particles over a potential barrier for an overdamped spatially periodic system driven by thermal fluctuations and subject to a dc constant bias force and an ac time-oscillatory drive. Some new anomalous behaviors of the average mean escape time are found, including： multiple reso- nant activation, multiple anti-Resonant activation, and thermally weakened stability. Some of the experimental verifications of these results are theoretically applied to the Josephson junction.