Digital technology-assisted teaching and learning is a trend in schools at all levels around the world, and beliefs about technology use are one of the predictors to see if, and to what extent, teachers would adopt technology in their classes. In the field of educational research, drawing tasks are one of the potential research tools that have been shown to reflect participants’ educational beliefs. We propose that the instructions for a drawing task would frame participants’ thinking, as it is difficult for participants to depict images outside the direction of instruction. In the current study, 44 science- majors entering preservice teachers were recruited, and a two-round drawing task along with a random-assigned experimental design were introduced to evaluate this hypothesis. The instruction of the first-round drawing was used to disrupt the framing effect of the instruction of the second-round drawing by activating the participants’ target knowledge. The results indicated that the participants depicted more images of technology use in the second-round drawing after their technology knowledge had been activated, but the pedagogical theme was not significant. Methodological, theoretical, and practical implications of the results are discussed.

Cell transmission model (CTM) is useful for evaluating the performance of urban traffic networks due to its mathematical formalism. This paper explores the application of CTM to develop control strategies for dispersion accident-induced traffic jams and evaluates the efficiency of these strategies. On the other hand, Timed Petri nets (TPNs) perform in discrete event systems because they provide a balance between modeling power and analyzability. This paper focuses on using the developed TPNs to model variable traffic light control systems. One advantage of the proposed methods is that the traffic light behavior is clearly represented in terms of conditions and events, which result in changes in the pre-emption phase. Moreover, this paper also proposes a new control strategy to eliminate the traffic jam propagation by preventing the traffic flow heading in the direction of an accident. The analysis is performed to demonstrate how the models enforce the phase of traffic transitions by a reachability graph with time information. The liveness and reversibility of the proposed model are verified. To the best of our knowledge, this is the first paper to use TPNs to model a variable phase traffic light control system and identify its accident scenarios for the purpose of their complete avoidance. This helps the latest advanced technology in traffic safety related to the intersection of roadways.

Solving states separation problems is an important technique to obtain liveness-enforcing and optimal or near-optimal supervisors for flexible manufacturing systems based on Petri nets. It first generates the model's reachability graph and partitions it into a live zone (LZ) and a deadlock zone (DZ). Then, first-met bad markings (FBMs), which exist in DZ and are the very first entries from LZ to DZ, are forbidden by some designed place invariants (PIs) to prevent the system from entering DZ. This paper studies the reduction of the number of places to be considered in such PI designs. First, the concepts of critical transitions and critical activity places are defined, and a fast algorithm is provided to compute them. Then, the proofs of that only critical activity places need to be considered in such PI designs to forbid all FBMs and/or permit all legal markings in LZ are established.

Cognitive radio (CR) is a promising method suitable for solving inefficiency spectrum policy by opportunistically identifying the vacant portions of the spectrum that are used by primary users (PUs). In cognitive radio ad hoc networks (CRAHNs), secondary users (SUs) can opportunistically utilize the spectrum that is available from PUs. In this paper, we propose a neighbor-aware distance estimated medium access control (NMAC) protocol for CRAHNs to mitigate the hidden and exposed terminal problems of multichannel CRAHNs. In this study, transmitter power control is based on the neighbor-aware estimated distance between SU communication pairs; this increases throughput, and reduces PU outage probability. We also compare our proposed scheme with existing MAC protocols for CRAHNs. We show that the NMAC will improve the channel spatial reuse, the normalized throughput, and reduce PU outage probability.

The theory of regions is an important method to derive an optimal and liveness-enforcing supervisor for a flexible manufacturing systems based on Petri nets. It first partitions the reachability graph into a live zone (LZ) and a deadlock zone (DZ). Then, activity places are used to construct place invariants (PIs) to prevent the system from entering DZ and permit all markings in LZ. This work studies the reduction of the number of places to be considered in the optimal PI designs. First, the concepts of critical transitions and critical activity places are defined, and an algorithm is provided to compute the sets of critical and uncritical activity places. Then, the proof of that only critical activity places need to be considered in such optimal PI designs is established.

Timed Petri nets (TPNs) are useful for performance evaluation of discrete event systems due to their mathematical formalism. This paper focuses on their use to model the preemption of emergency vehicle systems. The advantage of the proposed approach is the clear presentation of traffic light behaviors in terms of conditions and events that cause the preemption of phases being changed. The resulting models allow one to identify and thus avoid urgent spectacles in such systems by conditions and events of the model that control the phase of traffic light alternations. Moreover, this work proposes a new emergency vehicle preemption policy to ensure that emergency vehicles can pass through intersections with no or less delay. The analysis is performed to demonstrate how the models enforce the phase of traffic transitions by a reachability graph with time information. The liveness and reversibility of the proposed model are verified. To our knowledge, this is the first work that employs TPNs to model an emergency vehicle preemption system and identify its urgent spectacles for the purpose of their complete avoidance. This helps advance the state-of-the-art in traffic safety related to the intersection of roadways.

Timed Petri nets (TPNs) have been utilized as visual formalism for the modeling of complex discrete-event dynamic systems. They illuminate the features in describing the properties of causality and concurrency. Moreover, it is well known that a synchronized TPN (STPN) allows us to present all of the concurrent states in a complex TPN. In this paper, we propose a new methodology to design and analyze an urban traffic network control system by using the STPN. In addition, the applications of the STPN to eight-phase, six-phase, and two-phase traffic-light control systems are modularized. The advantage of the proposed approach is the clear presentation of the behaviors of traffic lights in terms of the conditions and events that cause phase alternations. Moreover, the size of the urban traffic network control system can be easily extended with our proposed modular technique. An analysis of the control models is performed via a reachability graph method to demonstrate how the models enforce the transitions of the traffic lights.

Timed Petri net (TPN) has been utilized as a visual formalism for the modeling of complex discrete event dynamic systems. It illuminates the features on describing properties of causality and concurrency. Moreover, it is well-known that synchronized timed Petri net (STPN) allows us to present all of the concurrent states in complex TPN. In this paper, we propose a new methodology to design, analyze and implement an urban traffic network control system by using STPN. The applications of STPN to eight-phase, six-phase and two-phase traffic lights are illustrated. The advantage of the proposed approach is the clear presentation of traffic lights' behaviors in terms of conditions and events that cause the phases alternations. Moreover, the reach ability and reversibility properties of the control STPN will be obtained.

A transition-controlled deadlock detection and recovery prevention policy is presented for a subclass of Petri nets used to model flexible manufacturing systems. The subclass is called systems of simple sequential processes with resources (S 3 PR). The proposed policy is different from the standard deadlock prevention policies. Instead of adding control places, this policy adds a controlled transition to solve a group of deadlocked markings that have the same graph-based property. Finally, the results of our study indicate that the proposed policy appears to be more permissive than those existing ones that add control places.

Deadlock prevention policies are used to solve the deadlock problems of FMSs. The theory of regions is recognized as the unique method for obtaining maximally permissive (i.e., optimal) controllers in the existing literature. In this paper, the selective siphons and critical markings method [17] is merged in the new deadlock prevention policy. First of all, reachability graph is still needed. Second, CMTSIs are identified. Further, selective siphons and critical markings method is used to check if all dead/quasi-dead markings of CMTSIs are covered by these selective siphons. Furthermore, choose anyone CMTSI that belongs to a same selective siphon to be processed. Finally, controllers are therefore obtained. Experimental results indicate that the computational cost can be reduced again. Besides, it is the most efficient policy to obtain maximal permissive behavior of Petri net models.

Deadlock prevention, deadlock detection, and deadlock avoidance strategies are used to solve the deadlock problems of flexible manufacturing systems. The theory of regions is recognized as the unique method for obtaining maximally permissive (i.e., optimal) controllers in the existing literature. All legal and live maximal behavior of a Petri net model can be preserved by using a marking/transition-separation instance (MTSI). However, obtaining them is an extremely time consuming problem. This work proposes crucial MTSIs that allow designers to employ much fewer MTSIs to deal with deadlocks. The advantage of the proposed policy is that an optimal deadlock controller can be obtained with drastically reduced computation. Experimental results, by varying the markings of given net structures, indicate that it is the most efficient policy to obtain such controllers.

A novel approach for probabilistic timed structure that is based on combining the formalisms of timed automata and probabilistic automata representation of the system is proposed. This paper presents an algorithm that combines probability measure and clock variables constructed model. Hence, their real-valued clocks can measure the passage of time and transitions can be probabilistic such that it can be expressed as a discrete probability distribution on the set of target states. The usage of clock variables and the specification of state space are illustrated with real value time applications. The transitions between states are probabilistic by events which describe either the occurrence of faults or normal working conditions. Additionally, the passage of discrete time and transitions can be probabilistic by mean of the theory of expectation sets to obtain a unified measure reasoning strategy. Finally, an example where a probabilistic time model is used to measure a robot of a system is also presented.

Petri nets have been recognized as one of the most powerful tools for modeling FMSs. The reason is that PNs are suited well to represent FMS characteristics such as present relations, concurrence, conflict and synchronization. On the other hand, it is well known that the marking/transition-separation instances (MTSIs) method with the theory of regions has been recognized as the best (i.e. maximally permissive) policy in deadlock problems. However, its major shortcoming is the state explosion and redundant inequalities problem since the reachability graph of a plant model has to be generated when one wants to find all MTSIs. For improving these drawbacks, this paper uses the reduction method and proposes a novel concept of the crucial marking/transition-separation instances (CMTSI) which is the key of MTSIs based on Petri nets and the theory of regions. According to our experimental results, our deadlock prevention policy is more efficient in existing literatures based on the theory of regions.

Statechart has been utilized as a visual formalism for the modeling of complex systems. It illuminates the features on describing properties of causality and concurrency. This paper focuses on the use of statecharts to model the preemption of emergency vehicles system. The advantage of the proposed approach is the clear presentation of traffic lights' behaviors in terms of conditions and events that cause the preemption phase. Moreover, the paper also proposes a new emergency vehicle preemption policy that provides the emergency vehicles can pass through the intersections with minimal delay. The analysis of the control models is performed to demonstrate how the models enforce the lights' transitions by reachability tree method. And then the reachability and reversibility properties of the control statecharts will be obtained.

Statechart has been utilized as a visual formalism for the modeling of complex systems. It illuminates the features on describing properties of causality, concurrency and synchronization. In this paper, we try to describe a behavioral logical operations language by using Statecharts. The logical operation is a date structure that is used to represent by a Boolean function. This paper used them to analyze the models which are modeled by using Statecharts. Their formalism provides a clear means for presenting control logic. Finally, an example of traffic light controller system is examined successfully.

The theory of regions has been recognized as the best control policy for obtaining a maximally permissive controller in existing literature. All legal and live maximal behavior of the Petri nets model can be held by using the marking/transition-separation instance (MTSI) method. It has been established that the requirement of all sets of MTSIs is a problem in conventional studies stems from time consuming. However, the new crucial marking/transition-separation instance (CMTSIs) allows designers to employ few MTSIs to deal with system deadlocks. The advantage of the proposed policy is that the computational cost can be reduced due to few MTSIs involved in. The paper unveils a maximally permissive controller with the efficient computation can be obtained by our control policy. Experimental results, by varying the markings of given net structures, indicate that the CMTSI method is the most efficient policy among the close related approaches in existing literature.

Deterministic and stochastic Petri nets (DSPNs) are well utilized as a visual and mathematical formalism to model discrete event systems. This paper proposes to use them to model parallel railroad level crossing (LC) control systems. Their applications to both single- and double-track railroad lines are illustrated. The resulting models allow one to identify and thus avoid critical scenarios in such systems by conditions and events of the model that control the phase of traffic light alternations. Their analysis is performed to demonstrate how the models enforce the phase of traffic transitions by a reachability graph method. Their important properties are verified. To our knowledge, this is the first work that employs DSPNs to model a parallel railroad LC system and identify its critical scenarios for the purpose of their complete avoidance. This helps advance the state of the art in traffic safety related to the intersection of railroads and roadways.

This paper presents an efficient method to obtain a maximally permissive deadlock prevention policy for a flexible manufacturing system based on theory of regions. The theory of regions policy can provides an optimal deadlock prevention controller which is based on the reachability graph. However, its disadvantage is the state explosion problem since all marking/transition-separation instances (MTSIs) have to be identified. For improving the shortcoming, this paper proposes a new concept of the crucial marking/transition-separation instances (CMTSIs). Experimental results indicate that the proposed control policy in this paper is more efficient than the closely related approaches in the literature.

The direct torque control has been utilized as a general formalism methodology for AC rotary motors. However, the technical skill in the implementation of permanent magnet linear synchronous motors does not seem to be performed yet. Based on the reason, this paper focuses on the use of a modified flux estimator to implement direct thrust control method for the motor systems. This paper presents a fuzzy controller and a direct thrust control policy for the motor control systems. The advantage of the proposed approach is that the clear presentation of the system behavior and readiness for implementation. Finally, some results of the simulation are met as expected.

The direct thrust control has been utilized as a general formalism methodology for permanent magnet linear synchronous motors. And also fuzzy Petri nets can support an effective rule to deduce the inexact information. Based on the reasons, this paper focuses on the use of fuzzy Petri nets to model the switching table for obtaining optimal voltage vector patterns. The main idea is proposed a methodology to perform switching-table-based direct thrust control by fuzzy Petri net model. The advantage of the proposed approach is that the optimum voltage vectors can be obtained by the fuzzy Petri net model directly. Finally, the correct flux vector control behaviors and position tracking performances can be performed.

An urban network of signalized intersections can be suitably modeled as discrete event system, in which the traffic light alternations are described by means of timed coloured Petri nets (TCPN). In this paper, a model of such a network via TCPN is used to state and solve the problem of coordinating several traffic lights with six and two phases. Moreover, the analysis of the control TCPN models is performed by occurrence graphs (OG) method. And then the relation of the liveliness and reversibility of the control TCPN will be obtained. Finally, an urban traffic lights' control structure with nine intersections will be realized. To our knowledge, this is the first work that employs TCPN to obtain the models of the urban traffic lights.

Statechart has been utilized as a visual formalism for the modeling of complex systems. It illuminates the features on describing properties of causality, concurrency and synchronization. This paper focuses on the use of statecharts to model an urban traffic lights control system. The applications of statecharts to eight-phase, six-phase and two-phase traffic lights are illustrated. The advantage of the proposed approach is the clear presentation of traffic lights' behaviors in terms of conditions and events that cause the phase alternations. Moreover, the paper also proposes a new modeling methodology, called concurrent state graphs, that allows us to present all the concurrent states in complex statecharts. The analysis of the control models is performed to demonstrate how the models enforce the lights' transitions by reachability tree method. And then the reachability and reversibility properties of the control statecharts will be obtained. Finally, an urban traffic lights' control system with nine intersections will be realized. To our knowledge, this is the first work that employs statecharts to obtain the models of the urban traffic light control system.

A siphon-based algorithm for deadlock prevention of a type of Petri nets called$hboxS^3hboxPMR$, which is a subclass of$hboxS^3hboxPGR^2$, is presented in this correspondence. The proposed method is an iterative approach by adding two kinds of control places called ordinary control (OC) places and weighted control (WC) places to the original model to prevent siphons from being unmarked. An OC place with ordinary arcs, which optimally prevent a siphon from becoming unmarked, is employed whenever it is possible, and otherwise, the WC places that adopt a conservative policy of controlling the release of parts into the system are used. Furthermore, this algorithm is not only for the subclass Petri nets but also for$hboxS^3hboxPR$,$hboxES^3hboxPR$,$hboxS^2hboxLSPR$, and$hboxS^3hboxPGR^2$nets. The authors prove the liveness and reversibility of the controlled net, and hence establish the correctness of the deadlock prevention policy. Finally, numerical experiments indicate that the proposed policy appears to be more permissive than closely related approaches in the literature.

In this paper we present timed colour Petri nets (TCPN) to model a sophisticated traffic signal control system. The traffic signals that has not only red, amber, and green lights but also has the green lights that includes straightforward, turn left and turn right signals. Especially, at the same time, other direction can allow the vehicles turn right on the red light. To our knowledge, this is the first time work that proposed a methodology to model the extended four-phase traffic signal control system using TCPN. Comparison with Petri nets, our method can easily observe the duration time of each traffic signal. Furthermore, our system's structure is compactness and its interpretation is explicit. The liveness and reversibility of the traffic signal control system model is approved.

This paper present a siphon-based algorithm of deadlock prevention for a type of Petri nets called S/sup 3/PMR, a subclass of S/sup 3/PGR/sup 2/. The proposed method is an iterative approach by adding two kinds of control places called ordinary control places and weighted control places to the original model to prevent siphons from being unmarked. An ordinary control place with ordinary arcs that optimally prevents the related siphon from becoming unmarked is employed whenever it is possible and otherwise weighted control places that adopt a conservative policy of controlling the release of parts into the system are used. Furthermore, this algorithm is not only for the subclass Petri nets but also for S/sup 3/PR, ES/sup 3/PR, S/sup 2/LSPR and S/sup 3/PGR/sup 2/ nets.

This work present a new class of Petri nets extended from systems of simple sequential processes with resources (S/sup 3/PR)[J, Ezpeleta et al., 1995] for modeling manufacturing systems where only parts can interact with resources, and resources alone cannot interact with one another. The new class of net that is called ES/sup 3/PR where deadlocks are related to unmarked siphons. ES/sup 3/PR properly includes S/sup 3/PR, augmented marked graphs and sub-classes of RCN merged nets where firing a transition may only generate parallel process for parts. As a result, ES/sup 3/PR can model far more complex manufacturing process flows and resource sharing than these nets. We also present an algorithm of deadlock prevention for the class of Petri nets. The proposed method is an iterative approach by adding two kinds of control places called ordinary control place and weighted control place to the original model to prevent siphons from being unmarked. One is added a control place to an original net with its related arcs such that the controlled net is still an ordinary Petri net; the other is added a control place to the net with its related arcs such the controlled net become to a generalized Petri net. In addition, the weighted control place assures that there are no new unmarked siphons generated. We have obtained the relation of the proposed algorithm and the liveness and reversibility of the controlled net. Finally, a flexible manufacturing example is presented for illustrating the method.

Statecharts have been proposed as a visual formalism for the behavioral of complex systems. The dynamical behavior of an elevation is a example to illustrate the operation of statechart systems because it shares with many other discrete event systems (DESs) the features of: simple actions, aggregating complexity of state descriptions, and great variety of possible control strategies and resulting trajectories. This paper applies the statechart terminologies to cope with the difficult situation of elevator system problems. In this paper, we present the modeling, control and implementation of an elevator system. A statechart-based for an elevator controller design and implementation is proposed. The intended advantage of the proposed controller is that using statechart terminologies, we can describe the system's behavior over time, including the dynamics of activities, and the conditions and events that cause states to change and other occurrences to take place. Moreover, A statechart-based approach is adopted to model the operation flows in the elevator system, and from the hierarchical tree of the elevator system, we can construct its statecharts model.

Huang et al. (2001) proposed a deadlock prevention policy based on Petri net siphons for flexible manufacturing systems (FMS). The current paper presents an analysis to show that in terms of control, the proposed policy appears to be more permissive than previous siphon-based approaches. Specifically, two siphon-based methods are compared with this approach. One is Ezpeleta et al.'s (1995) work for S/sup 3/PR nets and the other is Huang et al.'s (2001) work called a two-stage policy due to its two stages of preventing deadlocks. All these three rely on the addition of control places to the original net model to prevent siphons from being unmarked. The differences lie in the exact locations and sequences of adding the control places. Our analysis starts with the development of several theoretical results followed an experimental study. Through reachability analysis, all of the experiments indicate that the proposed policy appears to be more permissive than the other two. In addition, the two-stage policy appears to be more permissive than Ezpeleta et al.'s approach.

We present a new deadlock prevention algorithm for a class Petri nets. A new class of net that is extended from S/sup 3/PR, called ES/sup 3/PR, where deadlocks are related to unmarked siphons. This method is an iterative approach by adding two kinds of control places, called the ordinary control place and weighted control place, to the original model to prevent siphons from being unmarked. We obtained the relation of the algorithm, liveness and reversibility of the controlled net. Finally, a flexible manufacturing example is presented for illustrating the method.

Presents a class of Petri nets called process nets with resources (PNRs) for modeling manufacturing systems where only parts can interact with resources, and resources alone cannot interact with one another. PNRs properly includes S/sup 3/PR, augmented marked graphs, and, sub-classes of RCN merged nets and ERCN merged nets where firing a transition may only generate parallel processes for parts but not for resources. As a result, PNRs can model far more complex manufacturing process flows and resource sharing than these nets. To construct a PNR, we first build a process net to specify the process flow for each part type. A process net is a consistent, conservative, strongly-connected, and live Petri net and satisfies three conditions. Then resource places denoting the availability of resource types are added to the process nets such that for each resource place, the input and output transitions of the resource place generate a transition sub-net. For qualitative analysis, we show that reversibility of a PNR is assured if and only if there exists no unmarked siphon. Liveness of a PNR can be verified by checking the potential firability of each isolated process net, which is a process net with all resources allocated to it. For certain sub-classes of process nets, conditions for potential liveness are obtained.