• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 128
  • 121
  • 42
  • 26
  • 12
  • 6
  • 4
  • 4
  • 3
  • 2
  • 2
  • 1
  • 1
  • 1
  • 1
  • Tagged with
  • 383
  • 383
  • 120
  • 117
  • 53
  • 52
  • 52
  • 50
  • 45
  • 43
  • 39
  • 38
  • 37
  • 33
  • 32
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
41

Associação de redes de Petri com objetos virtuais e reais para controle de ambientes virtuais imersivos e telepresença / Association of Petri nets with virtual and real objects for controlling immersive virtual environments and telepresence

Claiton de Oliveira 25 June 2008 (has links)
A telepresença, como um refinamento da teleoperação, permite que o indivíduo controle não apenas a simulação mas a própria realidade. Uma vez que, esta proporciona a habilidade de manipular a realidade física remotamente em tempo real, através de sua representação virtual. Através da tecnologia de realidade virtual, pode-se criar uma grande diversidade de ambientes apropriados aos mais variados tipos de aplicações, possibilitando simulações de situações do mundo real em um ambiente ou mundo virtual. A aplicação de ambientes virtuais no processo de manufatura está relacionada tanto com a manutenção e treinamento, como também a criação e simulação de protótipos virtuais antes de sua utilização no chão-de-fábrica. O uso de redes de Petri para modelagem de ambientes virtuais, mostra-se como uma poderosa ferramenta gráfica/matemática que pode capturar naturalmente as principais características dos sistemas de realidade virtual, além de proporcionar resultados empíricos interessantes na verificação automática de concorrência e sistemas de tempo real. Por permitir modelar a computação não determinística e paralela, a modelagem de ambientes virtuais com redes de Petri é adequada não apenas para simulação, verificação e validação desses sistemas, mas para o próprio controle dos ambientes modelados. Ao associar os elementos de uma rede de Petri com os elementos do paradigma orientado à objetos de um conjunto de classes que constituem os objetos que irão compor os ambientes virtuais e os sistemas de telepresença, obtém-se uma valiosa ferramenta para o controle dos métodos dos objetos virtuais e reais a serem invocados. O objetivo deste trabalho é o desenvolvimento do modo de associação de redes de Petri com objetos virtuais e reais para controle de ambientes virtuais imersivos e telepresença, com base na descrição de um sistema de autoria de telepresença com controle em RP. Os resultados obtidos trarão avanços quanto ao desenvolvimento e implantação de aplicações de manufatura virtual em um ambiente de visualização 3D imersivo. / The telepresence, as a refinement of teleoperation, allows the individual not only to control the simulation but also the own reality. Since this provides the ability to manipulate the physical reality remotely in real time, through its virtual representation. Through the technology of virtual reality, one can create a wide variety of environments suitable for all kinds of applications, enabling simulations of the situations in a real world environment or virtual world. The application of virtual environments in the manufacturing process is related to both the maintenance and training, and also the creation and simulation of virtual prototypes before their use in the shop-floor. The use of Petri nets for modeling virtual environments, shows itself as a powerful graphics/mathematics tool that can capture the main features of virtual reality systems, as well as offering interesting empirical results in automatic verification of concurrence and real time systems. By allowing to model non-deterministic and parallel computation, modeling of virtual environments with Petri nets is appropriate not only for simulation, verification and validation of these systems, but also for controlling the environments modeled. By associating the elements of a Petri net with the elements of the object oriented paradigm of a set of classes that are the objects that will compose the virtual environments and telepresence systems, one gets a valuable tool for controlling of the methods of virtual and real objects to be invoked. The objective of this work is the development of the mode of association of Petri nets with virtual and real objects for controlling immersive virtual environments and telepresence, based on the description of a telepresence authoring system controlled by PN. The results will bring progress on the development and deployment of virtual manufacturing applications in an immersive 3D visualization environment.
42

Associação de redes de Petri com objetos virtuais e reais para controle de ambientes virtuais imersivos e telepresença / Association of Petri nets with virtual and real objects for controlling immersive virtual environments and telepresence

Oliveira, Claiton de 25 June 2008 (has links)
A telepresença, como um refinamento da teleoperação, permite que o indivíduo controle não apenas a simulação mas a própria realidade. Uma vez que, esta proporciona a habilidade de manipular a realidade física remotamente em tempo real, através de sua representação virtual. Através da tecnologia de realidade virtual, pode-se criar uma grande diversidade de ambientes apropriados aos mais variados tipos de aplicações, possibilitando simulações de situações do mundo real em um ambiente ou mundo virtual. A aplicação de ambientes virtuais no processo de manufatura está relacionada tanto com a manutenção e treinamento, como também a criação e simulação de protótipos virtuais antes de sua utilização no chão-de-fábrica. O uso de redes de Petri para modelagem de ambientes virtuais, mostra-se como uma poderosa ferramenta gráfica/matemática que pode capturar naturalmente as principais características dos sistemas de realidade virtual, além de proporcionar resultados empíricos interessantes na verificação automática de concorrência e sistemas de tempo real. Por permitir modelar a computação não determinística e paralela, a modelagem de ambientes virtuais com redes de Petri é adequada não apenas para simulação, verificação e validação desses sistemas, mas para o próprio controle dos ambientes modelados. Ao associar os elementos de uma rede de Petri com os elementos do paradigma orientado à objetos de um conjunto de classes que constituem os objetos que irão compor os ambientes virtuais e os sistemas de telepresença, obtém-se uma valiosa ferramenta para o controle dos métodos dos objetos virtuais e reais a serem invocados. O objetivo deste trabalho é o desenvolvimento do modo de associação de redes de Petri com objetos virtuais e reais para controle de ambientes virtuais imersivos e telepresença, com base na descrição de um sistema de autoria de telepresença com controle em RP. Os resultados obtidos trarão avanços quanto ao desenvolvimento e implantação de aplicações de manufatura virtual em um ambiente de visualização 3D imersivo. / The telepresence, as a refinement of teleoperation, allows the individual not only to control the simulation but also the own reality. Since this provides the ability to manipulate the physical reality remotely in real time, through its virtual representation. Through the technology of virtual reality, one can create a wide variety of environments suitable for all kinds of applications, enabling simulations of the situations in a real world environment or virtual world. The application of virtual environments in the manufacturing process is related to both the maintenance and training, and also the creation and simulation of virtual prototypes before their use in the shop-floor. The use of Petri nets for modeling virtual environments, shows itself as a powerful graphics/mathematics tool that can capture the main features of virtual reality systems, as well as offering interesting empirical results in automatic verification of concurrence and real time systems. By allowing to model non-deterministic and parallel computation, modeling of virtual environments with Petri nets is appropriate not only for simulation, verification and validation of these systems, but also for controlling the environments modeled. By associating the elements of a Petri net with the elements of the object oriented paradigm of a set of classes that are the objects that will compose the virtual environments and telepresence systems, one gets a valuable tool for controlling of the methods of virtual and real objects to be invoked. The objective of this work is the development of the mode of association of Petri nets with virtual and real objects for controlling immersive virtual environments and telepresence, based on the description of a telepresence authoring system controlled by PN. The results will bring progress on the development and deployment of virtual manufacturing applications in an immersive 3D visualization environment.
43

Compilation de réseaux de Petri : modèles haut niveau et symétries de processus / Compilation of Petri nets : high-level models and process symmetries

Fronc, Lukasz 28 November 2013 (has links)
Cette thèse s'intéresse à la vérification de systèmes automatisables par model-checking. La question sous-jacente autour de laquelle se construit la contribution est la recherche d'un compromis entre différents objectifs potentiellement contradictoires : la décidabilité des systèmes à vérifier, l'expressivité des formalismes de modélisation, l'efficacité de la vérification, et la certification des outils utilisés. Dans ce but, on choisit de baser la modélisation sur des réseaux de Petri annotés par des langages de programmation réels. Cela implique la semi-décidabilité de la plupart des questions puisque la responsabilité de la terminaison est remise entre les mains du modélisateur (tout comme la terminaison des programmes est de la responsabilité du programmeur). Afin d'exploiter efficacement ces annotations, on choisit ensuite une approche de compilation de modèle qui permet de générer des programmes efficaces dans le langage des annotations, qui sont alors exécutées de la manière la plus efficace. De plus, la compilation est optimisée en tirant partie des spécificités de chaque modèle et nous utilisons l'approche de model-checking explicite qui autorise cette richesse d'annotations tout en facilitant le diagnostique et en restant compatible avec la simulation (les modèles compilés peuvent servir à de la simulation efficace). Enfin, pour combattre l'explosion combinatoire, nous utilisons des techniques de réductions de symétries qui permettent de réduire les temps d'exploration et l'espace mémoire nécessaire. / This work focuses on verification of automated systems using model-checking techniques. We focus on a compromise between potentially contradictory goals: decidability of systems to be verified, expressivity of modeling formalisms, efficiency of verification, and certification of used tools. To do so, we use high level Petri nets annotated by real programming languages. This implies the semi-decidability of most of problems because termination is left to the modeler (like termination of programs is left to the programmer). To handle these models, we choose a compilation approach which produces programs in the model annotation language, this allows to execute them efficiently. Moreover, this compilation is optimizing using model peculiarities. However, this rich expressivity leads to the use of explicit model-checking which allows to have rich model annotations but also allows to easily recover errors from verification, and remains compatible with simulation (these compiled models can be used for efficient simulation). Finally, to tackle the state space explosion problem, we use reduction by symmetries techniques which allow to reduce exploration times and state spaces.
44

Executable system architecting using systems modeling language in conjunction with Colored Petri Nets - a demonstration using the GEOSS network centric system

Wang, Renzhong, January 2007 (has links) (PDF)
Thesis (M.S.)--University of Missouri--Rolla, 2007. / Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed November 30, 2007) Includes bibliographical references (p. 199-209).
45

Audio browsing of automaton-based hypertext

Ustun, Selen 30 September 2004 (has links)
With the wide-spread adoption of hypermedia systems and the World Wide Web (WWW) in particular, these systems have evolved from simple systems with only textual content to those that incorporate a large content base, which consists of a wide variety of document types. Also, with the increase in the number of users, there has grown a need for these systems to be accessible to a wider range of users. Consequently, the growth of the systems along with the number and variety of users require new presentation and navigation mechanisms for a wider audience. One of the new presentation methods is the audio-only presentation of hypertext content and this research proposes a novel solution to this problem for complex and dynamic systems. The hypothesis is that the proposed Audio Browser is an efficient tool for presenting hypertext in audio format, which will prove to be useful for several applications including browsers for visually-impaired and remote users. The Audio Browser provides audio-only browsing of contents in a Petri-based hypertext system called Context-Aware Trellis (caT). It uses a combination of synthesized speech and pre-recorded speech to allow its user to listen to contents of documents, follow links, and get information about the navigation process. It also has mechanisms for navigating within documents in order to allow users to view contents more quickly.
46

Model aware execution of composite web services

Zurowska, Karolina 15 August 2008
In the Service Oriented Architecture (SOA) services are computational elements that are published, discovered, consumed and aggregated across platform and organizational borders. The most commonly used technology to achieve SOA are Web Services (WSs). This is due to standardization process (WSDL, SOAP, UDDI standards) and a wide range of available infrastructure and tools. A very interesting aspect of WSs is their composeability. WSs can be easily aggregated into complex workflows, called Composite Web Services (CWSs). These compositions of services enable further reuse and in this way new, even more complex, systems are built.<p>Although there are many languages to specify or implement workflows, in the service-oriented systems BPEL (Business Process Execution Language) is widely accepted. With this language WSs are orchestrated and then executed with specialized engines (like ActiveBPEL). While being very popular, BPEL has certain limitations in monitoring and optimizing executions of CWSs. It is very hard with this language to adapt CWSs to changes in the performance of used WSs, and also to select the optimal way to execute a CWS. <p>To overcome the limitations of BPEL, I present a model-aware approach to execute CWSs. To achieve the model awareness the Coloured Petri Nets (CPN) formalism is considered as the basis of the execution of CWSs. This is different than other works in using formal methods in CWSs, which are restricted to purposes like verification or checking of correctness. Here the formal and unambiguous notation of the CPN is used to model, analyze, execute and monitor CWSs. Furthermore this approach to execute CWSs, which is based on the CPN formalism, is implemented in the model-aware middleware. It is also demonstrated how the middleware improves the performance and reliability of CWSs.
47

Model aware execution of composite web services

Zurowska, Karolina 15 August 2008 (has links)
In the Service Oriented Architecture (SOA) services are computational elements that are published, discovered, consumed and aggregated across platform and organizational borders. The most commonly used technology to achieve SOA are Web Services (WSs). This is due to standardization process (WSDL, SOAP, UDDI standards) and a wide range of available infrastructure and tools. A very interesting aspect of WSs is their composeability. WSs can be easily aggregated into complex workflows, called Composite Web Services (CWSs). These compositions of services enable further reuse and in this way new, even more complex, systems are built.<p>Although there are many languages to specify or implement workflows, in the service-oriented systems BPEL (Business Process Execution Language) is widely accepted. With this language WSs are orchestrated and then executed with specialized engines (like ActiveBPEL). While being very popular, BPEL has certain limitations in monitoring and optimizing executions of CWSs. It is very hard with this language to adapt CWSs to changes in the performance of used WSs, and also to select the optimal way to execute a CWS. <p>To overcome the limitations of BPEL, I present a model-aware approach to execute CWSs. To achieve the model awareness the Coloured Petri Nets (CPN) formalism is considered as the basis of the execution of CWSs. This is different than other works in using formal methods in CWSs, which are restricted to purposes like verification or checking of correctness. Here the formal and unambiguous notation of the CPN is used to model, analyze, execute and monitor CWSs. Furthermore this approach to execute CWSs, which is based on the CPN formalism, is implemented in the model-aware middleware. It is also demonstrated how the middleware improves the performance and reliability of CWSs.
48

A Study on Switching Operation Decision Making by Using Petri Nets for Power Distribution Systems

Ke, Yu-Lung 23 June 2001 (has links)
In this dissertation, the artificial intelligent Petri nets is applied to find the optimal switching operation for service restoration and feeder loading balance for 18-feeders distribution systems that containing the whole 24-hours load profiles of service zones. After the fault location has been identified and isolated for a system fault contingency, the Petri nets model with inference mechanism is derived and applied to solve the optimal load transfer among distribution feeders. For system normal operation condition, the load balancing among distribution feeders is obtained by the Petri nets model to enhance the operation efficiency of distribution systems. The switching operation, which will result in the loading balance among distribution feeders, is derived by the Petri nets model according to the loading cost of distribution systems. To determine the effectiveness of the proposed methodology, a Taipower (Taiwan Power Company) distribution system which serves a mixed types of customers is selected to perform the computer simulation. It is found that the Petri nets approach can enhance the solution process of fault restoration with proper load transfer and improve feeder load balance for distribution systems by considering the load characteristics of the service customers.
49

Power system fault analysis based on intelligent techniques and intelligent electronic device data

Luo, Xu 17 September 2007 (has links)
This dissertation has focused on automated power system fault analysis. New contributions to fault section estimation, protection system performance evaluation and power system/protection system interactive simulation have been achieved. Intelligent techniques including expert systems, fuzzy logic and Petri-nets, as well as data from remote terminal units (RTUs) of supervisory control and data acquisition (SCADA) systems, and digital protective relays have been explored and utilized to fufill the objectives. The task of fault section estimation is difficult when multiple faults, failures of protection devices, and false data are involved. A Fuzzy Reasoning Petri-nets approach has been proposed to tackle the complexities. In this approach, the fuzzy reasoning starting from protection system status data and ending with estimation of faulted power system section is formulated by Petri-nets. The reasoning process is implemented by matrix operations. Data from RTUs of SCADA systems and digital protective relays are used as inputs. Experiential tests have shown that the proposed approach is able to perform accurate fault section estimation under complex scenarios. The evaluation of protection system performance involves issues of data acquisition, prediction of expected operations, identification of unexpected operations and diagnosis of the reasons for unexpected operations. An automated protection system performance evaluation application has been developed to accomplish all the tasks. The application automatically retrieves relay files, processes relay file data, and performs rule-based analysis. Forward chaining reasoning is used for prediction of expected protection operation while backward chaining reasoning is used for diagnosis of unexpected protection operations. Lab tests have shown that the developed application has successfully performed relay performance analysis. The challenge of power system/protection system interactive simulation lies in modeling of sophisticated protection systems and interfacing the protection system model and power system network model seamlessly. An approach which utilizes the "compiled foreign model" mechanism of ATP MODELS language is proposed to model multifunctional digital protective relays in C++ language and seamlessly interface them to the power system network model. The developed simulation environment has been successfully used for the studies of fault section estimation and protection system performance evaluation.
50

Robust manufacturing system design using petri nets and bayesian methods

Sharda, Bikram 10 October 2008 (has links)
Manufacturing system design decisions are costly and involve significant investment in terms of allocation of resources. These decisions are complex, due to uncertainties related to uncontrollable factors such as processing times and part demands. Designers often need to find a robust manufacturing system design that meets certain objectives under these uncertainties. Failure to find a robust design can lead to expensive consequences in terms of lost sales and high production costs. In order to find a robust design configuration, designers need accurate methods to model various uncertainties and efficient ways to search for feasible configurations. The dissertation work uses a multi-objective Genetic Algorithm (GA) and Petri net based modeling framework for a robust manufacturing system design. The Petri nets are coupled with Bayesian Model Averaging (BMA) to capture uncertainties associated with uncontrollable factors. BMA provides a unified framework to capture model, parameter and stochastic uncertainties associated with representation of various manufacturing activities. The BMA based approach overcomes limitations associated with uncertainty representation using classical methods presented in literature. Petri net based modeling is used to capture interactions among various subsystems, operation precedence and to identify bottleneck or conflicting situations. When coupled with Bayesian methods, Petri nets provide accurate assessment of manufacturing system dynamics and performance in presence of uncertainties. A multi-objective Genetic Algorithm (GA) is used to search manufacturing system designs, allowing designers to consider multiple objectives. The dissertation work provides algorithms for integrating Bayesian methods with Petri nets. Two manufacturing system design examples are presented to demonstrate the proposed approach. The results obtained using Bayesian methods are compared with classical methods and the effect of choosing different types of priors is evaluated. In summary, the dissertation provides a new, integrated Petri net based modeling framework coupled with BMA based approach for modeling and performance analysis of manufacturing system designs. The dissertation work allows designers to obtain accurate performance estimates of design configurations by considering model, parameter and stochastic uncertainties associated with representation of uncontrollable factors. Multi-objective GA coupled with Petri nets provide a flexible and time saving approach for searching and evaluating alternative manufacturing system designs.

Page generated in 0.0791 seconds