Net Diagram Research Articles

Stability analysis of an adaptive fuzzy control system using Petri Nets and learning automata

A hybrid intelligent control system that combines the theories of fuzzy logic and variable structure systems (VSS) is presented. This control architecture is viewed as a discrete event system (DES) and its properties are studied using the corresponding Petri Net diagram. The equivalence between this controller and a learning finite state automaton is revealed. The validity of the method is supported by simulation results concerning an arc-welding process and a mobile robot moving in a partially unknown environment.

A computer network based control architecture for autonomous distributed multirobot systems

This paper presents the specification and implementation procedure using a microcomputer network based autonomous distributed control architecture for industrial multirobot systems. The procedure is based on the concept of data flow network controlled by communicating sequential processes to perform coordinated tasks. Robots and other computerized industrial devices such as conveyors and manufacturing machines are defined as object-oriented Petri nets. A modular and hierarchical approach is adopted to define a set of Petri net type diagrams which represent concurrent activities of control processes for such devices. Asynchronous and synchronous interactions are modelled by places and transitions, respectively, in global process interaction nets. The control software is implemented on a computer network using Inmos transputers with true parallel processing and message passing primitives efficiently handled in hardware. Petri net based models are directly and efficiently transformed to corresponding codes in occam, the high level parallel programming language defined for the transputer.

Polymorphism of Extended Fullerene Networks: Geometrical Parameters and Electronic Structures

Abstract The morphology of fullerene networks can be widely extended by introducing heptagonal or octagonal rings, which produce a Gaussian negative curvature. Their presence makes it possible to form donut-, coil- and sponge-shaped networks of carbon atoms. We discuss the geometry of the polymorphous forms based on the net diagram method relative to a honeycomb lattice, and further study the electronic structures constructed by the network of electrons system. Special emphasis is put on how the geometrical paramateres, which specify the relative arrangement of polygonal ring, control the electronic structures in the various extended-fullerene networks. In addition, we mention that the presence of a certain type of edge in fullerene network derives critical localized edge stages at the Fermi level.

Formalized Drawing of Fullerene Nets. 1. Algorithm and Exhaustive Generation of Isomeric Structures

Abstract A simple formalism for unfolding the fullerene structure onto a planar lattice is proposed. We recommend using deltahedra containing twelve penta-coordinated vertices as the geometrical precursors of fullerenes, and unfolding them onto a planar lattice according to Dürer’s style. This old style has several unique features that allow a priori drawing of diagrams that fold to fullerenes. Combined with the known algorithm for generating approximate atomic coordinates from the connectivity, which can be readily read off from the net diagram, the present method provides an alternative way of exhaustive generation of isomeric fullerene structures.

Declarative operations on nets

To increase the expressiveness of knowledge representations, the graph-theoretical basis of semantic networks is reconsidered. Directed labeled graphs are generalized to directed recursive labelnode hypergraphs, which permit a most natural representation of multi-level structures and n-ary relationships. This net formalism is embedded into the relational/functional programming language RELFUN. Operations on (generalized) graphs are specified in a declarative fashion to enhance readability and maintainability. For this, nets are represented as nested RELFUN terms kept in a normal form by rules associated directly with their constructors. These rules rely on equational axioms postulated in the formal definition of the generalized graphs as a constructor algebra. Certain kinds of sharing in net diagrams are mirrored by binding common subterms to logical variables. A package of declarative transformations on net terms is developed. It includes generalized set operations, structure-reducing operations and extended path searching. The generation of parts lists is given as an application in mechanical engineering. Finally, imperative net storage and retrieval operations are discussed.

Production based language simulation of Petri nets

Petri net models are often of limited usefulness because the sys tems they represent are too complex to be represented in a clear manner. By using a Production Based Language simulation, the number of elements that must be explicitly drawn in the net diagram can be greatly reduced. A simulation such as this sim plifies the net without compromising the integrity of the model itself. This is demonstrated here by the OPS5 Production Based Language simulation of a communications protocol Petri net. Using this simulation and an error generator, an automated method of testing the protocol is shown.

Petri net representation of decision models

Models of decision-making organizations supported by command, control, and communication systems are represented using the Petri net formalism. A small set of primitives, defining the correspondence between decision models, signals, and functions and their Petri net counterparts, is proposed. A new decision signal-routing demultiplexer is added to the Petri net formalism to represent internal decision-making in the model. Using the above primitives, any decision-making structure can be modeled by a Petri net diagram. An array is introduced that describes the interactions between decision-makers, and an algorithm is presented for the calculation of delay when synchronous protocols are used.

Steady‐State Lateral Movement of Water Through the Unsaturated Zone of an Unconfined Aquifera

ABSTRACTIn a steady‐state condition the lateral flow rate through the unsaturated zone of an unconfined aquifer increases with a decreasing rate as the depth of the unsaturated zone increases while hydraulic gradient is kept constant. This flow rate reaches a maximum as the depth of the zone is increased. This maximum flow rate is computed by various methods such as an aquifer model, graphical integration of the characteristic hydraulic conductivity curve and a flow net diagram. Based on these calculations a simple method is outlined for estimation of steady‐state flow rate through the unsaturated zone of an unconfined aquifer. It is also concluded that in shallow unconfined aquifers the contribution of the flow through the unsaturated zone to the total lateral flow can be significant.

Turing Machines, Finite Automata and Neural Nets

This paper 1 compares the notions of Turing machine, finite automaton and neural net. A new notation is introduced to replace net diagrams. “Equivalence” theorems are proved for nets with receptors, and finite automata; and for nets with receptors and effectors, and Turing machines. These theorems are discussed in relation to papers of Copi, Elgot and Wright; Rabin and Scott; and McCulloch and Pitts. It is shown that sets of positive integers “accepted” by finite automata are recursive; and a strengthened form of a theorem of Kleene is proved.