Transition Disks – Grain Growth, Planets, or Photoevaporation? T. Birnstiel, P. Pinilla, S. M. Andrews, M. Benisty and B. Ercolano EPJ Web of Conferences, 46 (2013) 02001 Published online: 11 April 2013 DOI: 10.1051/epjconf/20134602001