Recursos de colección

Estudo Geral - Universidade de Coimbra (19.630 recursos)

ESTUDO GERAL é a designação do repositório digital da produção científica da Universidade de Coimbra, com o objectivo de divulgar conteúdos digitais de natureza científica de autores ligados à Universidade de Coimbra. A sua criação insere-se no movimento de Acesso Livre à Literatura científica (Open Access), ao qual o Conselho de Reitores das Universidades Portuguesas aderiu em 2006 e que a Universidade de Coimbra subscreveu. À semelhança de outras grandes universidades nacionais e internacionais, a UC tem o maior interesse em aumentar a sua presença na rede informática mundial, sendo cada vez mais - e também por essa via - um emissor de conhecimento e cultura.

FCTUC Eng.Informática - Artigos em Revistas Internacionais

Mostrando recursos 1 - 20 de 44

  1. Robust assertions and fail-bounded behavior

    Prata, Paula; Rela, Mario; Madeira, Henrique; Silva, João Gabriel
    In this paper the behavior of assertion-based error detection mechanisms is characterized under faults injected according to a quite general fault model. Assertions based on the knowledge of the application can be very effective at detecting corruption of critical data caused by hardware faults. The main drawbacks of that approach are identified as being the lack of protection of data outside the section covered by assertions, namely during input and output, and the possible incorrect execution of the assertions. To handle those weak-points the Robust Assertions technique is proposed, whose effectiveness is shown by extensive fault injection experiments. With this technique a system follows a new failure model, that is called Fail- Bounded, where...

  2. Why do some (weird) people inject faults?

    Carreira, João; Silva, João Gabriel

  3. Dynamic structure multiparadigm modeling and simulation

    Barros, Fernando J.
    This article presents the Heterogeneous Flow System Specification (HFSS), a formalism aimed to represent hierarchical and modular hybrid flow systems with dynamic structure. The concept of hybrid flow systems provides a generalization of the conventional concept of hybrid system and it can represent a whole plethora of systems, namely: discrete event systems, multicomponent and multirate numerical methods, multirate and multicomponent sampling systems, event locators and time-varying systems. The ability to join all these types of models makes HFSS an excellent framework for merging components built in different paradigms. We present several examples of model definition in the HFSS formalism and...

  4. Modeling formalisms for dynamic structure systems

    Barros, Fernando J.
    We present a new concept for a system network to represent systems that are able to undergo structural change. Change in structure is defined in general terms, and includes the addition and deletion of systems and the modification of the relations among components. The structure of a system network is stored in the network executive. Any change in structure-related information is mapped into modifications in the network structure.Based on these concepts, we derive three new system specifications that provide a shorthand notation to specify classes of dynamic structure systems. These new formalisms are: dynamic structure discrete time system, dynamic structure...

  5. On the Use of Different Potential Energy Functions in Rare-Gas Cluster Optimization by Genetic Algorithms: Application to Argon Clusters

    Marques, J. M. C.; Pereira, F. B.; Leitão, T.
    We study the effect of the potential energy function on the global minimum structures of argon clusters arising in the optimization performed by genetic algorithms (GAs). We propose a robust and efficient GA which allows for the calculation of all of the putative global minima of ArN (N = 3−78) clusters modeled with four different potentials. Both energetic and structural properties of such minima are compared among each other and with those previously obtained for the Lennard-Jones function. In addition, the possibility of obtaining global minima of one potential through local optimization over the corresponding cluster geometry given by other...

  6. EuQoS: End-to-End Quality of Service over Heterogeneous Networks

    Mingozzi, E.; Stea, G.; Callejo-Rodríguez, M. A.; Enríquez-Gabeiras, J.; García-de-Blas, G.; Ramón-Salquero, F. J.; Burakowski, W.; Beben, A.; Sliwinski, J.; Tarasiuk, H.; Dugeon, O.; Diaz, M.; Baresse, L.; Monteiro, E.

  7. Design and analysis of stochastic local search for the multiobjective traveling salesman problem

    Paquete, Luís; Stützle, Thomas

  8. Evolution of a multi-agent system in a cyclical environment

    Baptista, Tiago; Costa, Ernesto
    Abstract The synchronisation phenomena in biological systems is a current and recurring subject of scientific study. This topic, namely that of circadian clocks, served as inspiration to develop an agent-based simulation that serves the main purpose of being a proof-of-concept of the model used in the BitBang framework, that implements a modern autonomous agent model. Despite having been extensively studied, circadian clocks still have much to be investigated. Rather than wanting to learn more about the internals of this biological process, we look to study the emergence of this kind of adaptation to a daily cycle. To that end we...

  9. PROQOS—Dynamic SLA Management in DiffServ Space Links

    Pessoa, Manuel; Alves, António; Quadros, Gonçalo; Boavida, Fernando; Henke, Michael; Natcheva, Milva; Halke, Patrick; Maurutschek, Peter; Huskic, Zenon; Wagner, Kurt; Zeppenfeldt, Frank; Donadio, Roberto
    Several base elements for the provision of quality of service guarantees have been developed in the recent past. Of these, the Differentiated Services (DiffServ) architecture stands out as the most promising. In spite of this, various issues remain, especially when multidomain DiffServ services are concerned. In this case, some forms of distributed management of Service Level Agreements that allow the specification, exchange, enforcement and monitoring of quality of service data must be in place. Although, again, some isolated solutions exist for each of these problems, considerable effort is necessary to make them work together. The project presented in this paper...

  10. All the Truth About NEvAr

    Machado, Penousal; Cardoso, Amílcar
    The use of Evolutionary Computation approaches to generate images has reached a great popularity. This led to the emergence of a new art form—Evolutionary Art—and to the proliferation of Evolutionary Art Tools. In this paper, we present an Evolutionary Art Tool, NEvAr, the experimental results achieved, and the work methodology used to generate images. In NEvAr, useful individuals are stored in a database in order to allow their reuse. This database is playing an increasingly important role in the creation of new images, which led us to the development of automatic seeding procedures, also described. The automation of fitness assignment...

  11. QoS Support for Multi-user Sessions in IP-based Next Generation Networks

    Cerqueira, Eduardo; Veloso, Luis; Neto, Augusto; Curado, Marilia; Monteiro, Edmundo; Mendes, Paulo
    Abstract A combined control of multimedia quality level, mobility and allocation of network resources is essential for the success of next generation mobile networks. In this context, this article presents the Multi-user Session Control (MUSC) solution to control the quality level of multimedia sessions shared by multiple-users, providing Quality of Service (QoS) mapping and QoS adaptation for those sessions over heterogeneous and mobile networks. MUSC uses the self-organized principle to coordinate QoS mapping and QoS adaptation mechanisms with mobility and resource allocation controllers, allowing the adaptation of a session to the current network conditions and the dynamic selection of the...

  12. M&M's: Building Binary Software Components for Supporting Mobile-Agent Enabled Applications

    Marques, Paulo; Silva, Luís; Silva, João Gabriel
    Mobile Agents provide a new promising paradigm for developing distributed applications. Nevertheless, although the basic concept has been around for some years and many agent platforms are available both from the industry and research community, there are currently few examples where the technology has been deployed in the real world. One important reason for this is that using the current available agent frameworks it is quite difficult to develop applications without having to center them completely on the agents and on the agent infrastructure. In this paper, we present the M&M project, taking place at the University of Coimbra. In...

  13. AIDA: a methodology independent support tool for educational software authoring

    Mendes, António José; Mendes, Teresa
    Many authoring tools have been proposed in an attempt to find more effective ways to face the challenge of developing educational software. However, most of them are reported to be restrictive, since they are strongly connected to a specific educational software development methodology. The AIDA (Ambiente Integrado para o Desenvolvimento de Aplicações educacionais) authoring environment was developed at the University of Coimbra having as its main objectives the support of most of the activities involved in authoring and making educational software development easier. The AIDA system is based on a design module, i.e. a prototyping tool allowing the creation of...

  14. Stabilizing Pre-Run-Time Schedules With the Help of Grace Time

    Magalhães, Antonio Pessoa; Silva, João Gabriel
    This paper discusses the stability of a feasible pre-run-time schedule for a transient overload introduced by processes re-execution during an error recovery action. It shows that the stability of a schedule strictly tuned to meet hard deadlines is very small, invalidating thus backward error recovery. However, the stability of the schedule always increases when a real-time process is considered as having a nominal and a hard deadline separated by a non-zero grace time. This is true for sets of processes having arbitrary precedence and exclusion constraints, and executed on a single or multiprocessor based architecture. Grace time is not just...

  15. Approximate Query Answering Using Data Warehouse Striping

    Bernardino, Jorge R.; Furtado, Pedro S.; Madeira, Henrique C.
    This paper presents and evaluates a simple but very effective method to implement large data warehouses on an arbitrary number of computers, achieving very high query execution performance and scalability. The data is distributed and processed in a potentially large number of autonomous computers using our technique called data warehouse striping (DWS). The major problem of DWS technique is that it would require a very expensive cluster of computers with fault tolerant capabilities to prevent a fault in a single computer to stop the whole system. In this paper, we propose a radically different approach to deal with the problem...

  16. On Text-based Mining with Active Learning and Background Knowledge Using SVM

    Silva, Catarina; Ribeiro, Bernardete
    Abstract Text mining, intelligent text analysis, text data mining and knowledge-discovery in text are generally used aliases to the process of extracting relevant and non-trivial information from text. Some crucial issues arise when trying to solve this problem, such as document representation and deficit of labeled data. This paper addresses these problems by introducing information from unlabeled documents in the training set, using the support vector machine (SVM) separating margin as the differentiating factor. Besides studying the influence of several pre-processing methods and concluding on their relative significance, we also evaluate the benefits of introducing background knowledge in a SVM...

  17. Modeling and simulation of parallel adaptive divide-and-conquer algorithms

    Barros, Fernando
    Abstract Conventional modeling and simulation formalisms only give support to the representation of model behavior, providing no constructs for describing changes in model structure. However, some systems are better modeled by self-reconfigurable formalisms. We have developed the Discrete Flow System Specification (DFSS) to exploit dynamic structure, component-based and hierarchical model construction. Due to structural similarity, dynamic self-configuring DFSS models offer a good description of systems, like adaptive algorithms and reconfigurable computer architectures. In this paper, we present the modeling and simulation of a parallel adaptive divide-and-conquer integration algorithm in the CaosTalk modeling and simulation framework, a realization of the DFSS...

  18. EuQoS approach for resource allocation in Ethernet networks

    Carmo, Maxweel Silva; Silva, Jorge Sá; Monteiro, Edmundo
    Although the equipment currently available for Ethernet LANs provides basic quality of service (QoS) capabilities, as the ability of prioritizing traffic flows, it does not support more complex mechanisms like admission control or the ability of participating in a signalling process. This paper presents a survey on the QoS support and on resource allocation for LAN Ethernet networks, and describes a new proposal in the scope of the EuQoS project. The proposed solution is validated as proof of concept both by simulation and real testbeds. EuQoS is an FP6 IST Integrated Project with the aim of proposing, developing and studying...

  19. Industrial visual inspection of lime granules by neural networks

    Carvalho, P.; Costa, N.; Ribeiro, B.; Dourado, A.
    Lime granule quality inspection is an important task in the pulp and paper industry. In this paper a new method, build-up on a neural network and a path search method, is introduced for lime granule automatic visual inspection. Several correction steps to Landau's method are also introduced.

  20. A self-organizing fuzzy controller with a fixed maximum number of rules and an adaptive similarity factor

    Dias, Joana Matos; Dourado, António
    This paper proposes a self-organizing fuzzy controller with a broad generality for minimum phase and stable systems. The controller learns the rules on-line with a minimum knowledge about the process. The rule base is built and permanenetly actualized from input-output real time data and has a fixed maximum number of rules (FMNR). An (on-line) adaptive similarity factor implements a special efficient inference technique. Feedforward and predictive effect is introduced in fuzzification and defuzzification stages. The defuzzification is carried out in such a way that as the learning process progresses the interval of the control becomes more and more accurate. Results...

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