(:notitlegroup:) 

   @article{schmidt_93,
    title     = {Numerically Stable Global Matrix Approach to Radiation and Scattering from
                Spherically Stratified Shells},
    author    = {Henrik Schmidt},
    journal   = {Journal Acoustical Society of America},
    pages     = {2420--2430},
    volume    = {94(4)},
    year      = {1993}}