Browsing by Issue Date, starting with "2011-11"
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- Visualization of Relations Between Financial Indices Using Multidimensional ScallingPublication . Tenreiro Machado, J. A.; Duarte, Gonçalo M.; Duarte, Fernando B.This paper applies Multidimensional scaling techniques for visualizing possible time-varying correlations between twenty five stock market values. The method is useful for observing stable or emerging clusters of stock markets with similar behavior. The graphs may also guide the construction of multivariate econometric models.
- Valorização de Cápsulas de Café e Produção de BiocombustíveisPublication . Silva, Vânia Filipa Monteiro da; Caetano, NídiaAo longo de décadas, as questões afectas à saúde e ambiente não fizeram parte da nossa consciência. E, com um estilo de vida cada vez mais consumista, tem-se observado um aumento significativo da produção de diversos bens e, consequentemente do seus resíduos. O café é um deles. E os resíduos de café são gerados em grandes quantidades,quer no seu estado puro, quer em invólucros metálicos, de papel ou combinações plástico/metal, quando resultantes de doses individuais. Deste modo, no âmbito da promoção de valores ecológicos e do cumprimento da legislação ambiental, cada vez mais exigente, medidas de intervenção para a gestão de resíduos de café têm sido estudadas, enquadrando-as com a realidade e com a viabilidade da sua aplicação. com base no estudo da viabilidade de produção de biocombustíveis a partir da matéria orgânica residual proveniente de diferentes cápsulas de café, que este trabalho visa contribuir para a resolução deste problema. Assim, após recuperação dos constituintes das cápsulas de café (invólucros metálicos e a borra de café), foi efectuada a extracção do óleo extraído e da borra de café (antes e após extracção). Numa fase seguinte, avaliou-se a potencialidade da utilização do óleo na produção do biodiesel, e da borra de café, na produção de bioetanol. Por fim, foi avaliada a composição metálica dos invólucros, tendo em vista a sua valorização. Para efectuar a caracterização da borra de café, foram avaliados diversos parâmetros de entre os quais se pode destacar, a razão carbono: azoto (C/N = 5) e o seu poder calorífico (PCS, entre 4619,2 e 4941 kcal/kg), o teor de celulose (13,5 - 14,8%) e o teor de lenhina total (33,6 e 32,5%). Relativamente ao óleo da borra de café, a sua extracção foi testada usando diversos solventes (hexano, etanol, isopropanol, octano, heptano, mistura de hexano e isopropanol nas proporções 5:5; 6:4; 7:3; 8:2 (v/v), respectivamente). Dos 31 ensaios efectuados, a mistura de hexano e isopropanol, nas proporções de 5:5; foi aquela que permitiu obter os melhores resultados (21,54%) de óleo em 3h de tempo de contacto).
- On the use of VISIR under different course implementationsPublication . Viegas, Maria C.; Marques, Maria A.; Costa-Lobo, Maria; Alves, Gustavo R.; Alberto, António; Dias, Custódio; Azevedo, Manuel; Alves, Mario; Guimarães, Pedro; Gustavsson, IngvarThis paper addresses different course integrations of VISIR. The didactic approaches are summarized and the analysis done provides explanations to some of the problems encountered, plus some guidelines for future implementations. A number of strengths and weaknesses are highlighted, leading to suggestions on how to enhance some strategic approaches to motivate teachers and students to the potential of using VISIR in teaching and learning processes. Proper references to previously published work also help to understand the research background and the lessons derived from a more intensive usage of VISIR.
- Spreading Algorithm for Single-Objective ProblemsPublication . Pires, E. J. Solteiro; Mendes, Luís; Lopes, António M.; Oliveira, P. B. de Moura; Tenreiro Machado, J. A.This paper addresses the problem of finding several different solutions with the same optimum performance in single objective real-world engineering problems. In this paper a parallel robot design was proposed. Thereby, this paper presents a genetic algorithm to optimize uni-objective problems with an infinite number of optimal solutions. The algorithm uses the maximin concept and -dominance to promote diversity over the admissible space. The performance of the proposed algorithm is analyzed with three well-known test functions and one function obtained from practical realworld engineering optimization problems. A spreading analysis is performed showing that the solutions drawn by the algorithm are well dispersed.
- A Fractional Order Identification of a Mechanical Transmission System with Known FailuresPublication . Gutiérrez, R.; Rosário, J. M.; Tenreiro Machado, J. A.To compete in the global market the manufacturers must introduce new high quality products in short time. This ideal requires a fast evaluation of new products and the guarantee of availability of the critical machines in a production line, typically by reducing the maintenance shut-downs. Roughly, the diagnosis’ process consist in comparing the machine’s actual behavior with the known one under a specific (common) failure, namely monitoring any change of its dynamics. Unfortunately, the manufacturers rarely supply any dynamical model and consequently it is identified using naive transfer function structures of integer order. In this respective, we evaluate an integer second order model and a similar structure of a fractional one to identify a system under different types of failures. The fractional order model outperforms the integer one, suggesting that it represents better the machine condition when using compact equations.
- Cooperative Transportation of an Object based on Fractional Order ControllersPublication . Figueiredo, Carlos M.; Couceiro, Micael S.; Ferreira, N. M. Fonseca; Tenreiro Machado, J. A.Advanced control techniques have been used in simulations to overcome nonlinear phenomena in order to describe the performance of robots with two rotational (RR) degrees-of-freedom (dof). Given the current state-of-the-art, fractional order algorithms lead to better performance when compared to integer order controllers. Also, the development of simulation platforms allows evaluating the best control methodology. In this context, the use of RR robots attached to mobile platforms, denoted in this paper as RR mobile robots, demonstrates a remarkable ability in manipulating and transporting objects. The present work aims to study two cooperative RR mobile robots by analyzing the manipulator’s trajectory and the forces applied to the common load. Are considered two robotic platforms based on an 8-bit microcontroller with inverse kinematics based on the Denavit-Hartenberg formulation and fractional order PID controllers inspired in the Grünwald-Letnikov definition.
- Capacidade de diferentes medidas de adiposidade para discriminar o risco metabólico em adolescentesPublication . Moreira, Carla Marisa Maia; Santos, Rute; Vale, Susana; Santos, Paula; Abreu, Sandra; Marques, Ana; Soares-Miranda, Luisa; Mota, JorgeEste estudo tem como objectivo determinar o poder discriminante das diferentes medidas de adiposidade: índice de massa corporal (IMC), perímetro da cintura (PC) e rácio cintura-altura (RCA) na identificação do risco metabólico em adolescentes açorianos.
- Some Notes About the Fermi-Pasta-Ulam ProblemPublication . Tenreiro Machado, J. A.During 1953, at Los Alamos, Fermi, Pasta and Ulam (FPU) developed computer simulations of a mechanical system composed of masses and springs [1]. We should also refer Mary Tsingou that helped in the programming of the computer Maniac. The idea formulated by Enrico Fermi was to simulate the one-dimensional analogue of atoms in a crystal by mean of a chain of particles linked by springs fixed at the extreme points. The springs were modeled by a term following a linear model (Hooke’s law) and a nonlinear term either quadratic (FPU -α), or cubic (FPU -β). These researchers found a dynamics considerably different from what linear systems would suggest. In fact, they thought that the system would exhibit “thermalization”, that is, a behavior in which the influence of the initial modes of vibration would fade, becoming all modes excited equally. Nevertheless, the simulations revealed a complex quasi-periodic dynamics. They thought that the energy introduced into the first frequency mode (k = 1) should drift to the other modes until the equipartition of energy would be reached. For the first instants of the simulation the higher modes (k = 2, 3,…) were successively excited, reaching almost an equipartition state, but after some time they verified that almost all energy was back to the first mode. Further simulations revealed the repetition of this phenomenon and that a kind of recurrence emerges, being recovered replicas of the initial state [2-4].
- Alteração no consumo de fruta e sopa durante a gravidez e a sua associação com o índice de massa corporal pré-gestacionalPublication . Abreu, Sandra; Santos, Paula Clara; Moreira, Carla; Vale, Susana; Santos, Rute; Soares-Miranda, Luísa; Mota, Jorge; Moreira, PedroEncontra-se descrito que durante a gravidez, em benefício da saúde do feto, a mulher altera alguns dos seus hábitos alimentares. O objectivo deste estudo foi determinar as alterações no consumo de fruta e sopa na gravidez de acordo com o IMC pré-gestacional.
- Fractional Order Darwinian Particle Swarm OptimizationPublication . Couceiro, Micael S.; Ferreira, N. M. Fonseca; Tenreiro Machado, J. A.The Darwinian Particle Swarm Optimization (DPSO) is an evolutionary algorithm that extends the Particle Swarm Optimization (PSO) using natural selection, or survival-of-the-fittest, to enhance the ability to escape from local optima. This paper presents a method for controlling the convergence rate of the DPSO using fractional calculus (FC) concepts. The fractional order (FO) DPSO, denoted as FO-DPSO, is tested using several well-known functions and the relationship between the fractional order velocity and the convergence of the algorithm is observed.