Partial Data for the Calderon Problem in Two Dimensions
  We show in two dimensions that measuring Dirichlet data for the conductivity equation on an open subset of the boundary and, roughly speaking, Neumann data in slightly larger set than the complement uniquely determines the conductivity on a simply connected domain. The proof is reduced to show a similar result for the Schr\"odinger equation. Using Carleman estimates with degenerate weights we construct appropriate complex geometrical optics solutions to prove the results. 
Oleg Yu. Imanuvilov, Gunther Uhlmann and masahiro Yamamoto