When did BBC apply for the TARDIS trademark ?
Artron energy is said to be the " residue of TARDIS engines " , and is also found in Time Lord brains and bodies of other time travellers ( " The Deadly Assassin " , 1976 ; " Four to Doomsday " , 1982 ; " The Wedding of Sarah Jane Smith " , 2009 ; " Death of the Doctor " , 2010 ; " The Doctor 's Wife " , 2011 ; " The Power of Three " , 2012 ) .