Concealment by uniform motion
  The perceived lateral position of a transmitted beam, upon propagating through a slab made of homogeneous, isotropic, dielectric material at an oblique angle, can be controlled through varying the velocity of the slab. In particular, by judiciously selecting the slab velocity, the transmitted beam can emerge from the slab with no lateral shift in position. Thereby, a degree of concealment can be achieved. This concealment is explored in numerical calculations based on a 2D Gaussian beam. 
Tom G. Mackay (University of Edinburgh), Akhlesh Lakhtakia   (Pennsylvania State University)