Time-Driven Computations in P Systems

It is a well-known fact that the time of execution of a (biochemical) reaction depends on many factors, and, in particular, on the current situation of the whole system. With this motivation in mind, we propose a model of computation based on membrane systems where the various rewriting rules have different times of execution and, moreover, the time of execution of each rule can vary during the computation, depending on the configuration of the whole system (in this sense, the computation is "time-driven"). We show that such systems are universal in a very simple framework: a regular time-mapping suffices to obtain universality for systems with minimal cooperation (one catalyst).