Vakarchuk M. B., and VakarchukS. B. “On the Exponential Decay of Vibrations of Damped Elastic Media”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 63, no. 12, Dec. 2011, pp. 1579-01, https://umj.imath.kiev.ua/index.php/umj/article/view/2828.