Unusual behavior of sound velocity of a Bose gas in an optical superlattice at quasi-one-dimensionLei Chen, Zhu Chen, Wu Li, Zhidong Zhang and Zhaoxin LiangEur. Phys. J. D, 68 12 (2014) 375DOI: https://doi.org/10.1140/epjd/e2014-50489-3