The Aichelburg-Sexl Boost of Domain-Walls and Cosmic Strings
  We consider the application of the Aichelburg-Sexl boost to plane and line distributions of matter. Our analysis shows that for a domain wall the space-time after the boost is flat except on a null hypersurface which is the history of a null shell. For a cosmic string we study the influence of the boost on the conical singularity and give the new value of the conical deficit. 
C. Barrabes, P. A. Hogan and W. Israel