In this note we are going to shed new light on some aspects of the theory of the radical axis. For a rather complete account of this theory, see Chapter VIII of [1]. We are going to make use of but the most basic properties of radical axes (the existence of the radical axis and of the radical center), and prove some possibly new facts along with a few known ones. First we introduce several conv...

New results are presented for the degeneracy condition of elastic waves in anisotropic materials. The condition for the existence of acoustic axes involves a traceless symmetric third order tensor that must vanish identically. It is shown that all previous representations of the degeneracy condition follow from this acoustic axis tensor. The conditions for existence of acoustic axes in elastic ...