S. Nicaise, BOUNDARY EXACT CONTROLLABILITY OF TRANSMI SSION PROBLEMS BY ADDITION OF INTERNAL CONTROLS, Comptes rendus de l'Academie des sciences. Serie 1, Mathematique, 321(8), 1995, pp. 969-974
We prove the exact controllability of hyperbolic transmission problems
with mixed boundary conditions when singularities occur. The two prop
osed methods consist in acting by a classical boundary control whose s
upport does not contain a neighbourhood of the singular points, and by
adding internal controls located near these singular points (see [6],
[5], [7] where such a method was introduced).