@article{SEDP_1998-1999____A17_0, author = {Lebeau, Gilles}, title = {The wave equation with oscillating density~: observability at low frequency}, journal = {S\'eminaire \'Equations aux d\'eriv\'ees partielles (Polytechnique) dit aussi "S\'eminaire Goulaouic-Schwartz"}, note = {talk:17}, pages = {1--11}, publisher = {Centre de math\'ematiques Laurent Schwartz, \'Ecole polytechnique}, year = {1998-1999}, zbl = {1061.35043}, mrnumber = {1721335}, language = {en}, url = {http://archive.numdam.org/item/SEDP_1998-1999____A17_0/} }