@article{articlecaa928e8,
title   = {On the energy estimates of the wave equation with time dependent propagation speed asymptotically monotone functions},
author = {Ebert, Marcelo Rempel and Fitriana, Laila and Hirosawa, Fumihiko},
year = {2015},
doi = {10.1016/j.jmaa.2015.06.051},
journal   = {Journal of Mathematical Analysis and Applications}
}