Wensheng Zhang, Eric T. Chung and Chaowei Wang. (2014). Stability for Imposing Absorbing Boundary Conditions in the Finite Element Simulation of Acoustic Wave Propagation.
            <i>Journal of Computational Mathematics</i>. <i>32</i> (1).
            1-20.
         doi:10.4208/jcm.1310-m3942