09:15 to 10:00 J Le Rousseau Carleman estimate for stratified media: the case of a diffusive interface INI 1 10:00 to 10:45 E Francini (Università degli Studi di Firenze)Some issues on the inverse conductivity problem with a complex coefficient In this talk I will present some results concerning the possibility of recovering some features of a complex valued coefficient form boundary data of its solutions. INI 1 10:45 to 11:15 Morning Coffee 11:15 to 12:00 P Stefanov (Purdue University)The Identification problem in SPECT: uniqueness, non-uniqueness and stability We study the problem of recovery both the attenuation $a$ and the source $f$ in the attenuated X-ray transform in the plane. We study the linearization as well. It turns out that there is a natural Hamiltonian flow that determines which singularities we can recover. If the perturbation $\delta a$ is supported in a compact set that is non-trapping for that flow, then the problem is well posed. Otherwise, it may not be, and at least in the case of radial $a$, $f$, it is not. We present uniqueness and non-uniqueness results both for the linearized and the non-linear problem; as well as a H\"older stability estimate. INI 1 12:00 to 12:45 A Lechleiter (École Polytechnique)Sampling methods for time domain inverse scattering problems We consider inverse scattering problems for the wave equation in the time domain: find the shape of a Dirichlet scattering object from time domain measurements of scattered waves. For this time domain inverse problem, we introduce sampling methods, a well-known family of techniques for corresponding frequency domain inverse scattering problems. The problem setting and the time domain algorithm incorporate two basic features: The data consists of measurement of causal waves, and the inversion algorithm directly works on the time domain data without using a Fourier transformation. Time-domain sampling methods naturally incorporate a continuum of frequencies in the inversion algorithm. Consequently, they induce the potential to improve the reconstruction quality when compared to methods working at one single frequency. INI 1 12:45 to 13:30 Lunch at Wolfson Court 18:15 to 19:00 Dinner at Murray Edwards College (Residents only)