Conférencier: François Nicoleau, Nantes

Résumé: Let  $\Omega \subset \R^n$, $n \geq 3$, be a fixed smooth bounded domain, and let $\gamma$ be a smooth conductivity in $\overline{\Omega}$. Consider a non-zero frequency$\lambda_0$ which does not belong to the Dirichlet spectrum of $L_\gamma = -{\rm div} (\gamma \nabla \cdot)$. Then, there exists an infinite number of pairs of smooth non-isometric conductivities $(\gamma_1, \gamma_2)$ on $\overline{\Omega}$, which are close to $\gamma$  and such that the associated DN maps at frequency $\lambda_0$  are identical.