Soares, Orlando; Gonçalves, Henrique; Martins, António A.; Carvalho, Adriano
With the increasing size of wind power
generation it is required to perform power system stability
analysis that uses dynamic wind generator models.
In this paper are presented all the wind power system
components, including the turbine, the generator, the power
electronic converter and controllers. The aim is to study the
Doubly Fed Induction Generator (DFIG) operation and its
connection to the power system, either during normal operation
or during transient grid fault events.
Two different control system design technologies are present,
the first is performed by standard PI controllers and the second
is based on artificial neural networks.
Teixeira, João Paulo; Ferreira, Débora; Carneiro, Susana Moreira
Algumas técnicas de processamento digital de sinais têm sido usadas para
analisar desordens vocais provocadas por patologias na laringe. Os exames
laringoscópicos usados na detecção dessas patologias são técnicas invasivas que
causam desconforto ao paciente. A Análise acústica vocal das características temporais
e espectrais dos sinais de fala pode ser utilizada como técnica auxiliar à laringoscopia,
tanto para pré-diagnósticos de patologias, bem como no acompanhamento de
tratamentos farmacológicos e pós-cirúrgicos. Neste artigo, descrevem-se algumas
patologias do aparelho fonador que provocam alterações na qualidade da fala
produzida. Depois descrevem-se os algoritmos implementados para determinação da
frequência fundamental (F0) pelo método Cepstral e pelo método da auto-correlação.
Descreve-se também o algoritmo aqui...
Gonçalves, José; Lima, José; Costa, Paulo; Moreira, António
In this paper it is discussed the educational, research and development outcomes that are expected to achieve from a new robot competition, proposed and conceived by the authors, that was recently included in Robotica (the main Robotics Portuguese Competition). The robot competition takes place in an emulated factory plant, where Automatic Guided Vehicles (AGVs) must cooperate to perform tasks. To accomplish their goals the AGVs must deal with localization, navigation, scheduling and cooperation problems, that must be solved autonomously. The presented robot competition can play an important role in education due to the inherent multi-disciplinary concepts that are involved, motivating...
Ferreira, Ângela P.; Costa, A.F.
This paper presents a comprehensive study towards the determination of efficient pole-arc coefficients for axial flux permanent magnet (PM) machines, through investigation of the contribution of volume elements of PMs to the no load flux linkage. The proposed methodology involves the evaluation of flux linkage using a mathematical expression which integrates a function over the volume of PMs instead of the classical integration of the magnetic flux density over the coil surface. The process is implemented using 2D finite element (FE) analysis, and the results shows the pole-arc coefficients that maximize the ratio of the flux linkage over the PM...
Ferreira, Ângela P.; Costa, A.F.
Small-scale wind power applications require a cost effective and mechanically simple generator in order to be a reliable energy source. The use of direct driven generators, instead of geared machines, reduces the number of drive components, which offers the opportunity to reduce costs and increases system reliability and efficiency. For such applications, characterized by low speed of rotation, the axial flux permanent magnet generator is particularly suited, since it can be designed with a large pole number and high torque density.
This paper presents an axial flux permanent magnet synchronous generator, double sided with internal rotor and slotted stators. Such...
Monteiro, Fernando C.; Cadavez, Vasco
This paper presents a method for the detection of OD in the retina which takes advantage of the powerful preprocessing techniques such as the contrast enhancement, Gabor wavelet transform for vessel segmentation, mathematical morphology and Earth Mover’s distance (EMD) as the matching process. The OD detection algorithm is based on matching the expected directional pattern of the retinal blood vessels. Vessel segmentation method produces segmentations by classifying each image pixel as vessel or nonvessel, based on the pixel’s feature vector. Feature vectors are composed of the pixel’s intensity and 2D Gabor wavelet transform responses taken at multiple scales. A simple...
Costa, Paulo; Moreira, António; Gonçalves, José; Lima, José
In this paper it is presented a new robot competition that is going to be included in Robotica 2011, the main Robotics Portuguese Competition. The robot competition takes place in an emulated factory plant, where Automatic Guided Vehicles (AGVs) must cooperate to perform tasks. To accomplish their goals the AGVs must deal with localization, navigation, scheduling and cooperation problems, that must be solved autonomously. One option of prototyping the AGVs is the use of the Lego Mindstorms NXT technology. The presented example can play an important role in education due to the inherent multi-disciplinary concepts that are involved, motivating students...
Barbosa, José; Leitão, Paulo
Multi-agents systems and holonic manufacturing systems are suitable approaches to design a new and alternative class of production control systems, based on the decentralization of control functions over distributed autonomous and cooperative entities. However, in spite of their enormous potential they lack some aspects related to interoperability, migration, optimisation in decentralised structures and truly self-adaptation. This paper discusses the advantages of combining these paradigms with complementary paradigms, such as service-oriented architectures, and enhancing them with biologically inspired algorithms and techniques, such as emergent behaviour and self-organization, to reach a truly robust, agile and adaptive control system. An example of applying...
Mendes, João M.; Leitão, Paulo; Colombo, Armando W.
Service-oriented Computing (SOC) is being applied in industrial manufacturing automation to face the current demand for modular, flexible and reconfigurable solutions. Highlighted from the other existing methodologies, SOC may carry an alternative but natural solution to design and engineer manufacturing automation systems and consequently the ability to seamless integrate into the modern IT-enterprise. However, SOC still has a long way to be adopted by industrial solutions, mainly fulfilling the particularities of the manufacturing domain. This paper discusses the applicability of the SOC in industrial manufacturing automation by using a SWOT (Strengths, Weaknesses, Opportunities, and Threats) analysis. The discussed aspects show...
Fernandes, Rui Vitor
Typical error control techniques are not very well suited for video transmission. On the other hand, video transmission over error prone channels has increased greatly, e.g., over IP and wireless networks. These two facts combined together provided the necessary motivation for the development of a new set of techniques (error concealment) capable of dealing with transmission errors in video systems. These techniques can be categorized according with the approach they take to solve the problem. This categorization is presented, describing the assumptions in which they are based and giving a few examples in each category. Finally, the advantages and disadvantages...
Salgado, Paulo; Cunha, Manuela; Pavão, João; Igrejas, Getúlio
This paper presents a possibilistic fuzzy clustering algorithm that is applied to a multidimensional fuzzy set or fuzzy rules. This method can be used to decompose the fuzzy system into an hierarchical structure. The methodology presented leads to a fuzzy partition of the fuzzy rules, one for each cluster, which corresponds to a new set of fuzzy sub-systems. This technique is tested to organize the fuzzy model into a new and more comprehensive structure.
Ferreira, Rayssa; Amaral, J.S.; Igrejas, Getúlio; Rodrigues, Pedro
The antibiogram performed by the disc diffusion method is a test frequently used in clinical microbiology. In this test, the result is given by the diameter of the inhibition zone formed around the antibiotic disc. In general, this measurement is performed manually. The main objective of this work was to develop an automatic image analysis system to assess the susceptibility of microorganisms to different antibiotics. As a first step, several images of antibiograms were obtained. Subsequently the images were subjected to image processing techniques. After the elimination of noise, the Hough transform was used to detect the antibiotic discs. Next,...
Rodrigues, Pedro; Amaral, J.S.; Igrejas, Getúlio
In this project we present an intelligent fall detector system based on a 3-axis accelerometer and a neural network model that allows recognizing several possible motion situations and performing an emergency call only when a fall situation occurs, with low false negatives rate and low false positives rate. The system is based on a two module platform. The first one is a Mobile Station (MS) and should be carried always by the person. An accelerometer is implemented in this module and its information is transferred via a radio-frequency channel (RF) to the Base Station (BS). The BS is fixed and...
Rodrigues, Pedro; Amaral, J.S.; Santos, Alberto; Igrejas, Getúlio
The development of a methodology for cultivar discrimination and selection during on-line quality selection could be a relevant tool for certain industries that use hazelnuts as ingredients in processed food products. The aim of this work was to obtain a computer vision system that enables an automatic recognition of six hazelnuts cultivars from 3 different origins (US, Italy and Spain). To achieve this objective, an algorithm for tuning the segmentation between the hazelnut shell and crown was developed. Important morphological features that allow the correct identification of the cultivar present in an image were obtained from the segmentation process. Finally,...
Igrejas, Getúlio; Amaral, J.S.; Rodrigues, Pedro; Oliveira, M.B.P.P.
Several samples of four types of vegetable oils (sunflower, soybean, corn and peanut oils) produced and/or refined in Portugal were analyzed for their fatty acid composition. Data obtained was used to build a fuzzy model to predict the amounts of different vegetable oils (VO) in commercial blends. The strategy used was a combination of a fuzzy clustering method (Fuzzy C-means) and a Takagi-Sugeno fuzzy model. Model was tested with the data from the analysis of simulated blended VO prepared in the laboratory. Results proved the ability of the model in predicting the blend composition. The model was then used to...
Cerdeira, T.; Lima, R.; Oliveira, M.; Monteiro, Fernando C.; Ishikawa, Takuji; Imai, Yohsuke; Yamaguchi, Takami
In microcirculation the cell-free layer is believed to reduce the friction between red blood cells (RBCs) and endothelial
cells and consequently reduce blood flow resistance. However, the complex formation of the cell-free layer has not
yet been convincingly described mainly due to multi-physical and hemorheological factors that affect this phenomenon.
In this experimental work, we study the effect of hematocrit (Hct) on the thickness of the cell-free layer in straight circular
polydimethylsiloxane (PDMS) microchannels. The channels studied are 73 ± 2 mm in diameter, flexible and circular
to mimic blood vessels. The images are captured using confocal microscopy and are post-processed using Image J and
Coelho, J.P.; Cunha, José Boaventura; Oliveira, Paulo
In some control systems structures, like predictive control, mathematical models
for the control process must be derived. Those models can be obtained by a broad class
of methods like parametric models applied to experimental data. In this context, and for
systems with multiple operation regimes, the Hidden Markov model, due to its properties,
is a convincing choice. However the parameter estimation of this type of models involves
the optimization of a non-convex cost function. So the Baum-Welch method only can find
sub-optimal parameters. This article shows that the use of the Taguchi method minimizes the
training algorithm sensibility local minima.
Araújo, João; Cunha, José Boaventura; Oliveira, Paulo; Pires, Eduardo S.; Coelho, J.P.
Food Processing Industries produce large amounts of wastewater with high
environmental impact. Due to the high content of suspended matter and inadequate pH
value of the wastewater, national laws prohibit direct discharges of the influent to the
environment. This work describes the design and operation of a wastewater treatment
plant installed in the Sortegel food-processing company located in Sortes, Portugal. This
industry uses the water collected from groundwater wells to process raw materials and to
wash the equipments, being the volume of wastewater produced season dependent (80 to
300m3/day). Results show that the implemented wastewater treatment plant and the
automation solutions generate treated effluents that comply with the...
Braga, Daniela; Teixeira, João Paulo; Coelho, Luís; Freitas, D.
Neste trabalho apresenta-se uma base de dados de fala espontânea com etiquetagem linguística, prosódica e pragmática em Português Europeu (PE). Esta informação pode ser encontrada num ficheiro de texto que é associado ao sinal de fala, sendo por isso possível analisar simultaneamente as várias dimensões em questão. O objectivo deste trabalho consiste em criar um corpus de fala etiquetado em que seja possível correlacionar a dimensão acústica e prosódica do sinal com o seu significado linguístico e pragmático, sobretudo tendo em atenção as dimensões emocionais e estilísticas do discurso.
Constituem motivações subjacentes a este trabalho a necessidade de controlar a...
Barros, Maria João; Braga, Daniela; Freitas, D.; Teixeira, João Paulo; Latsch, Vagner
In this paper we analyse and describe the phonetic behavior of the non-tonic back closed vowel [u] in European Portuguese (EP) in what respects its quality and relative duration. Slow and faster speech was used. The objective of this work is to contribute with experimental results in order to obtain a more accurate comprehension of this vowel’s profile, which can be integrated and extended to other non-tonic vowels’ behaviors in the EP non-tonic vowel system. This may represent an important improvement in synthetic speech quality and naturalness, as it concerns acoustical parameters, rhythm and supra-segmental features, which means prosody. This...