Goncharenko, M. V., and E. Y. Khruslov. “On the Exponential Decay of Vibrations of Damped Elastic Media”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 63, no. 11, Nov. 2011, pp. 1443-59, https://umj.imath.kiev.ua/index.php/umj/article/view/2817.