@inproceedings{pavel2004a,
title={A lower bound to the spectral threshold in curved tubes},
author={Pavel Exner, P Freitas, and D Krejik},
url={http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20191020123614091280590},
booktitle={Proceedings of the Royal Society of London. Series A: Mathematical, Physical and Engineering Sciences},
volume={460},
number={2052},
pages={3457-3467},
year={2004},
}
Pavel Exner, P Freitas, and D Krejik. A lower bound to the spectral threshold in curved tubes. 2004. Vol. 460. In Proceedings of the Royal Society of London. Series A: Mathematical, Physical and Engineering Sciences. pp.3457-3467. http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20191020123614091280590.