@article {MR2177090,
AUTHOR = {Chitour, Yacine and Coron, Jean-Michel and Garavello, Mauro},
TITLE = {On conditions that prevent steady-state controllability of
certain linear partial differential equations},
JOURNAL = {Discrete Contin. Dyn. Syst.},
FJOURNAL = {Discrete and Continuous Dynamical Systems. Series A},
VOLUME = {14},
YEAR = {2006},
NUMBER = {4},
PAGES = {643--672},
ISSN = {1078-0947},
MRCLASS = {35Kxx},
MRNUMBER = {MR2177090},
}