@article{Bec-Jol-Tso-2000,
    author={Éliane Bécache and Patrick Joly and Chrysoula Tsogka },
    title={An analysis of new mixed finite elements for the approximation 
           of wave propagation problems. },
    doi={10.1137/S0036142998345499 },
    journal={SIAM J. Numer. Anal. },
    year={2000 },
    volume={37, no. 4 },
    pages={1053--1084},
}