ESTCB - Artigos em revistas com arbitragem científica
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- Comportamiento de esquistos en los terraplenes y explanadas de los firmes de carreteras en PortugalPublication . Luzia, Rosa; Santos, Luís PicadoEl denominado "Complejo esquisto-grauváquico", que emerge en la zona Centro -Ibérica de la península, puede encontrarse en Portugal desde el Vai/e del Duero hasta la Beira Baixa, en la zona de Castelo Branco, en una banda que continua en Espana, y que al sur coincide aproximadamente con la falla Porto- Coimbra- Badajoz- Córdoba. Este complejo está constituido por material de origen metamórfico, esquistos y grauvacas, normalmente de bajo grado de metamorfismo, y representa una parte importante de la litología portuguesa. Debido al desarrollo de la Red Viaria acaecido en los últimos anos en Portugal, y dado que algunos de los trazados interceptan estas formaciones esquisto- grauvacóides, con frecuencia fue necesario el empleo de los materiales provenientes de las excavaciones. A pesar de todo, estas materiales apenas han sido utilizados como coronación de la explanada de los firmes, lo que en parte es debido al escaso conocimiento que se tiene de sus características. El estudio que se presenta en este artículo tiene como objetivo evaluar las características soporte de los firmes construídos con este tipo de materiales, y analizar su posible empleo como terraplenes, capa de coronación de explanada, o bien como capa granular de una estructura vial, siguiendo algunas especificaciones y recomendaciones de Portugal, Francia y los Estados Unidos de Norteamérica. Para ello, se comienza por hacer una breve caracterización geológica del material proveniente del Complejo esquisto-grauváquico, presentando a continuación una descripción geotécnica y la caracterización del comportamiento mecánico de un material de este tipo, resultado de un estudio experimental realizado en el tramo Raiva - Catraia dos Poços de la IC7. Finalmente se presenta, en forma resumida, el análisis de los resultados de ensayos basados en las especificaciones y recomendaciones aludidas anteriormente.
- Ferramenta de simulação para análise espectral de redes de BraggPublication . Dionísio, Rogério Pais; Lima, Mário J.; Rocha, J.R. Ferreira da; Pinto, J.L.; Teixeira, AntónioAs redes de Bragg (FBG) tornaram-se componentes importantes na redes de comunicações ópticas, pois permitem a realização de várias operações sem a necessidade de conversão opto-electrónica. Este artigo descreve uma ferramenta de software para simulação e caracterização de redes de Bragg por nós inteiramente concebida. A interface gráfica foi programada utilizando o ambiente GUIDE do Matlab. É assim possível analisar um leque variado de FBGs, tendo em consideração os efeitos secundários provocados pela variação do índice de refracção médio, durante o processo de fabrico.
- Architecture of a fieldbus message scheduler coprocessor based on the planning paradigmPublication . Martins, Ernesto V.; Neves, Paulo Alexandre; Fonseca, José A.The use of a centralised planning scheduler in fieldbus-based systems requiring real-time operation has proved to be a good compromise between operational ̄exibility and timeliness guarantees. It is particularly well adapted to embedded systems based on low-processing power microcontrollers due to the low overhead it imposes. In this paper a preliminary implementation of a hardware scheduling coprocessor based on the planning paradigm is presented. The coprocessor is installed in a special node of the fieldbus, the bus arbiter, and generates scheduling tables to be dispatched by the node CPU. With this solution it is possible to decrease the response time to changes in the system con®guration or message parameters of the software- based planning scheduler. This opens the possibility of allowing automatic on-line changes requested by system nodes in addition to the ones requested by human operators, thus improving system reactivity. The paper includes a short review of the planning technique and a discussion on the motivation to develop the coprocessor as well as on recent similar and related work. The coprocessor architecture and several implementation details such as its interface with the arbiter CPU are presented. The initial calculations showing the feasibility of the unit are also derived, together with the first real implementation of the coprocessor itself.
- A comparative study on JPEG-Like and EZW based image codersPublication . Bruno, Roque; Salvado, JoséThis paper presents a comparative study on image coders using the discrete cosine transform and the discrete wavelet transform, addressing in particular the JPEG-like and the EZW based image coders. We compare and evaluate the JPEG Baseline Image coder (using the DCT), a JPEG-like image coder based on the DWT, and an EZW coder, which is also based on the DWT. Taking into account the differences on the architecture of the coders, we compare them by using the same test images, for approximately the same conditions and characteristics, namely the approximately equal compression ratio.
- Evaluation of transform based image coders, using different transforms and techniques in the transform domainPublication . Salvado, José; Roque, BrunoThis paper addresses the most relevant aspects of lossy image coding techniques, and presents an evaluation study on this subject, using several transforms and different methods in the transform domain. We developed different transform based image coders/decoders (codecs) using different transforms, such as the discrete cosine transform, the discrete wavelet transform and the S transform. Besides JPEG Baseline, we also use other techniques and methods in the transform domain such as a DWT based JPEG-like (JPEG DWT), a JPEG DWT with visual threshold (JPEG-VT), a JPEG–like coder based on the ST, and an EZW coder. The codecs were programmed in MATLAB™, using custom and built-in functions. The structures of the codecs are presented, also as some experimental results which allow us evaluate them, and support this study.
- Artificial neural networks and neuro-fuzzy systems for modelling and controlling real systems: a comparative studyPublication . Vieira, José Barros; Dias, Fernando; Mota, AlexandreThis article presents a comparison of artificial neural networks andneuro-fuzzy systems appliedfor modelling andcontrolling a real system. The main objective is to model and control the temperature inside of a kiln for the ceramic industry. The details of all system components are described. The steps taken to arrive at the direct and inverse models using the two architectures: adaptive neuro fuzzy inference system and feedforward neural networks are described and compared. Finally, real-time control results using internal model control strategy are resented. Using available Matlab software for both algorithms, the objective is to show the implementation steps for modelling and controlling a real system. Finally, the performances of the two solutions were comparedthrough different parameters for a specific real didactic case
- Generic POLCA : a production and materials flow control mechanism for quick response manufacturingPublication . Fernandes, Nuno O.; Silva, Sílvio do CarmoA production and materials flow control mechanism for quick response manufacturing (QRM) is proposed. This is called generic paired-cell overlapping loops of cards with authorization (GPOLCA). It is an adaptation of the POLCA mechanism developed as part of the QRM strategy. GPOLCA implements an input–output control order release strategy based on an inventory of production authorization cards instead of materials. It is best suited for companies that manufacture large variety of products with variable demand. A description of GPOLCA is made together with a comparative study of its performance in relation with other mechanisms namely MRP and POLCA. The results show that GPOLCA attains better performance.
- On the use of infrared thermography in studies with air curtain devicesPublication . Neto, Luís; Silva, Manuel Gameiro da; Costa, José J.Among the different existing methods to characterise the aerodynamic sealing effect provided by an air curtain device placed over the opening between two contiguous compartments, infrared thermography has revealed to be a very useful tool. Besides allowing the capture, in an expedite way, of instantaneous images of the temperature field in the neighbourhood of the door, the technique hereon described has other advantages, in terms of quick and easy setup, low intrusive character and liability of obtained results. To apply this method, a large sheet of paper was stretched in the direction perpendicular to the opening where the air curtain device has placed to allow the registration of pictures or video sequences with an infrared camera setup in its maximum sensitivity. Good concordance between the thermographs obtained with this technique and the temperature fields measured for the same plane with a rack of 16 low velocity omni-directional thermal anemometer probes allowed its validation. Various elucidative examples of the use of this technique as a complementary tool for analysis and visualization of the complex physical phenomena occurring for the studied flow are presented in this article.
- A reduced-CP approach to SC/FDE block transmission for broadband wireless communicationsPublication . Gusmão, António; Torres, Paulo; Dinis, Rui; Esteves, NelsonFor conventional cyclic prefix (CP)-assisted single-carrier/frequency-domain equalization (SC/FDE) implementations, as well as for orthogonal frequency-division multiplexing (OFDM) implementations, the CP length is known to be selected on the basis of the expected maximum delay spread. Next, the data block size can be chosen to be large enough to minimize the CP overhead, yet small enough to make the channel variation over the block negligible. This paper considers the possibility of reducing the overall CP assistance, when transmitting sequences of SC blocks, while avoiding an excessively long fast Fourier transform window for FDE purposes and keeping good FDE performances through low-complexity, noniterative receiver techniques. These techniques, which take advantage of specially designed frame structures, rely on a basic algorithm for decision-directed correction (DDC) of the FDE inputs when the CP is not long enough to cope with the time-dispersive channel effects. More specifically, we present and evaluate a novel class of reduced-CP SC/FDE schemes, which takes advantage of a special frame structure for replacing "useless" CP redundancy by fully useful channel coding redundancy, with the help of the DDC algorithm. When using the DDC-FDE technique with these especially designed frame structures, the impact of previous decisions, which are not error-free, is shown to be rather small, thereby allowing a power-efficiency advantage (in addition to the obvious bandwidth-efficiency advantage) over conventional block transmission implementations under full-length CP. Additionally, the DDC algorithm is also shown to be useful to improve the power efficiency of these conventional implementations.
- A turbo FDE technique for reduced-CP SC-based block transmission systemsPublication . Gusmão, António; Torres, Paulo; Dinis, Rui; Esteves, NelsonFor conventional cyclic-prefix (CP)-assisted block transmission systems, the CP length is selected on the basis of the expected maximum delay spread. With regard to single-carrier (SC)-based block transmission implementations, a full-length CP is recommendable, since it allows good performances through the use of simple frequency-domain equalization (FDE) techniques. In this letter, a soft-decision-directed correction (SDDC)-aided turbo FDE technique is presented for reduced-CP SC-based block transmission systems using conventional frame structures. The relations with some already known iterative FDE techniques are established, and a set of performance results is reported and discussed. The advantages of the proposed approach are emphasized, namely, the possibility of approximately achieving (besides the obvious bandwidth efficiency gain) the maximum power efficiency gain that a strong CP reduction allows.