@article{COCV_2020__26_1_A14_0,
     author = {Cui, Yan and Laurent, Camille and Wang, Zhiqiang},
     title = {On the observability inequality of coupled wave equations: the case without boundary},
     journal = {ESAIM: Control, Optimisation and Calculus of Variations},
     publisher = {EDP-Sciences},
     volume = {26},
     year = {2020},
     doi = {10.1051/cocv/2020004},
     mrnumber = {4064475},
     zbl = {1441.35156},
     language = {en},
     url = {http://www.numdam.org/articles/10.1051/cocv/2020004/}
}