R. Freund:
"Energy-controlled P systems";
in: "Membrane Computing. International Workshop, WMC-CdeA 2002, Curtea de Arges, Romania", Gh. Paun et al. (ed.); issued by: Workshop on Membrane Computing; Springer, LNCS 2597, 2003, ISBN: 3-540-00611-7, 247 - 260.