R. Freund, Gh. Paun, M. Pérez-Jiménez:
"Tissue-like P Systems with Channel-States";
in: "Second Brainstorming Week on Membrane Computing", Gh. Paun, A. Riscos-Núñez, A. Romero-Jiménez, F. Sancho-Caparrini (ed.); Universidad de Sevilla, Sevilla, 2004, 206 - 223.
http://aleph.ub.tuwien.ac.at/F?base=tuw01&func=find-c&ccl_term=AC04968495