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Computing with Membranes
 JOURNAL OF COMPUTER AND SYSTEM SCIENCES
, 1998
"... We introduce a new computability model, of a distributed parallel type, based on the notion of a membrane structure. Such a structure consists of several celllike membranes, recurrently placed inside a unique "skin" membrane. A plane representation is a Venn diagram without intersected sets and wit ..."
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Cited by 342 (4 self)
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We introduce a new computability model, of a distributed parallel type, based on the notion of a membrane structure. Such a structure consists of several celllike membranes, recurrently placed inside a unique "skin" membrane. A plane representation is a Venn diagram without intersected sets and with a unique superset. In the regions delimited by the membranes there are placed objects; the obtained construct is called a supercell. These objects are assumed to evolve: each object can be transformed in other objects, can pas through a membrane, or can disolve the membrane in which it is placed. A priority relation between evolution rules can be considered. The evolution is done in parallel for all objects able to evolve. In this way, we obtain a computing device (we call it a supercell system): start with a certain number of objects in a certain membrane and let the system evolve; if it will halt (no object can further evolve), then the computation is finished, with the result given as...
P Systems with Active Membranes: Attacking NP Complete Problems
 JOURNAL OF AUTOMATA, LANGUAGES AND COMBINATORICS
, 1999
"... P systems are parallel Molecular Computing models based on processing multisets of objects in celllike membrane structures. Various variants were already shown to be computationally universal, equal in power to Turing machines. In this paper one proposes a class of P systems whose membranes are the ..."
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Cited by 49 (1 self)
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P systems are parallel Molecular Computing models based on processing multisets of objects in celllike membrane structures. Various variants were already shown to be computationally universal, equal in power to Turing machines. In this paper one proposes a class of P systems whose membranes are the main active components, in the sense that they directly mediate the evolution and the communication of objects. Moreover, the membranes can multiply themselves by division. We prove that this variant is not only computationally universal, but also able to solve NP complete problems in polynomial (actually, linear) time. We exemplify this assertion with the wellknown SAT problem.
On Synchronization in P Systems
"... The P systems were recently introduced as distributed parallel computing models of a biochemical type. Multisets of objects are placed in a hierarchical structure of membranes and they evolve according to given rules, which are applied in a synchronous manner: at each step, all objects which can ..."
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Cited by 27 (3 self)
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The P systems were recently introduced as distributed parallel computing models of a biochemical type. Multisets of objects are placed in a hierarchical structure of membranes and they evolve according to given rules, which are applied in a synchronous manner: at each step, all objects which can evolve, from all membranes, must evolve. We consider here the case when this restriction is removed. As expected, unsynchronized systems (even using catalysts) are weaker than the synchronized ones, providing that no priority relation among rules is considered. The power of P systems is not diminished when a priority is used and, moreover, the catalysts can change their states, among two possible states for each catalyst.
On Unconditional Transfer
 MFCS'96, volume 1113 of LNCS
, 1996
"... . In this paper, we investigate the concept of unconditional transfer within various forms of regulated grammars like programmed grammars, matrix grammars, grammars with regular control, grammars controlled by bicoloured digraphs, and periodically timevariant grammars, especially regarding their de ..."
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Cited by 12 (9 self)
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. In this paper, we investigate the concept of unconditional transfer within various forms of regulated grammars like programmed grammars, matrix grammars, grammars with regular control, grammars controlled by bicoloured digraphs, and periodically timevariant grammars, especially regarding their descriptive capacity. Moreover, we sketch the relations to restricted parallel mechanisms like k, uniformly k, partition, and functionlimited ET0L systems, as well as (unordered) scattered context grammars. In this way, we solve a number of open problems from the literature. 1 Introduction Regulated rewriting is one of the main and classic topics of formal language theory [7, 28], since there, basically contextfree rewriting mechanisms are enriched by different kinds of regulations (we restrict ourselves to contextfree core rules in this paper), hence generally enhancing the generative power of such devices compared to the contextfree languages. In this way, it is possible to describe...
DNA Computing, Sticker Systems, and Universality
 ACTA INFORMATICA
, 1998
"... We introduce the sticker systems, a computability model, which is an abstraction of the computations using the WatsonCrick complementarity as in Adleman's DNA computing experiment, [1]. Several types of sticker systems are shown to characterize (modulo a weak coding) the regular languages, hence th ..."
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Cited by 12 (3 self)
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We introduce the sticker systems, a computability model, which is an abstraction of the computations using the WatsonCrick complementarity as in Adleman's DNA computing experiment, [1]. Several types of sticker systems are shown to characterize (modulo a weak coding) the regular languages, hence the power of finite automata. One variant is proven to be equivalent to Turing machines. Another one is found to have a strictly intermediate power.
Membrane Computing with External Output
, 1998
"... A supercell system consists of computing cells which are organized hierarchically by the inclusion relation: cells may include cells, which again may include cells, etc. Each cell is enclosed by its membrane. Each cell is an independent computing agent with its own computing program, which produces ..."
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Cited by 12 (2 self)
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A supercell system consists of computing cells which are organized hierarchically by the inclusion relation: cells may include cells, which again may include cells, etc. Each cell is enclosed by its membrane. Each cell is an independent computing agent with its own computing program, which produces objects. The interaction between cells consists of the exchange of objects through membranes. The output of a computation is a partially ordered set of objects which leave the supercell through its external membrane. The fundamental properties of computations in such supercell systems with external output are investigated. These include the computing power, normal forms, and basic decision problems.
A Predicate for Separating Language Classes
, 1995
"... : We show how a predicate can be used to separate language classes in a remarkably concise way, e.g., L(P,CF\Gamma) and L(P,CF\Gamma,ut). It has been a longstanding open problem whether appearance checking enhances the power of programmed grammars or not. By now, two independent complicated proofs ..."
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Cited by 10 (9 self)
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: We show how a predicate can be used to separate language classes in a remarkably concise way, e.g., L(P,CF\Gamma) and L(P,CF\Gamma,ut). It has been a longstanding open problem whether appearance checking enhances the power of programmed grammars or not. By now, two independent complicated proofs appeared for the separation result in question [4, 3]. In this note, we present another decidability argument which readily implies the abovementioned result and is also applicable to other situations. Let h : \Sigma ! \Delta be an arbitrary homomorphism, R ` \Sigma be a regular language, and L ` \Sigma be a language from some language class L. Consider the predicate P h;R;L on \Delta defined by P h;R;L (w) () w 2 h(R " L): If L is a subfamily of a language class comprising only of recursive languages which is closed under arbitrary homomorphisms and intersection with regular sets, then the above predicate is decidable for L, i.e., for every h, R, and L 2 L, there is an alg...
Remarks on Regulated Limited ET0L Systems and Regulated ContextFree Grammars
, 1996
"... We continue the studies of the second author on regulated uniformly klimited and regulated klimited ET0L systems. We focus on the permitting and forbidding random context regulation. Especially, we establish some results on (regulated) propagating (uniformly) klimited ET0L systems which were not ..."
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Cited by 9 (7 self)
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We continue the studies of the second author on regulated uniformly klimited and regulated klimited ET0L systems. We focus on the permitting and forbidding random context regulation. Especially, we establish some results on (regulated) propagating (uniformly) klimited ET0L systems which were not solved in [2, 18, 21, 22]. Moreover, relations to recurrent programmed languages introduced by von Solms are exhibited.
Accepting Array Grammars With Control Mechanisms
 New Trends in Formal Languages, volume 1218 of LNCS
, 1996
"... . We consider (ndimensional) array grammars in the accepting mode with various control mechanisms and compare these families of array grammars with the corresponding families obtained by array grammars in the generating mode. 1 Introduction Accepting grammars together with various control mechanis ..."
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Cited by 8 (8 self)
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. We consider (ndimensional) array grammars in the accepting mode with various control mechanisms and compare these families of array grammars with the corresponding families obtained by array grammars in the generating mode. 1 Introduction Accepting grammars together with various control mechanisms were introduced in [1] for the string case. Recent ideas concerning these grammars were exposed in [2]. The main results of the paper concern the relations between the families of array languages obtained by accepting array grammars in this way and array languages described by the corresponding types of generating array grammars. Compared with the string case, we find many similarities, e.g., accepting programmed array grammars without appearance checking are just as powerful as their generating counterparts, and accepting ordered grammars can describe every recursively enumerable array language. On the other hand, the family of accepting regular programmed twodimensional array languages...