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@article{cockrell2011jasa, title = {A Modal Wentzel-Kramers-Brillouin Approach to Calculating the Waveguide Invariant for Non-ideal Waveguides}, author = {Kevin L. Cockrell and Henrik Schmidt}, journal = {The Journal of the Acoustical Society of America}, pages = {72-83}, number = {1}, volume = {130}, month = {Jyly}, year = {2011}}