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Publicações

1997

SIGIF: A digital signal interchange format with application in neurophysiology

Autores
Cunha, MB; Cunha, JPS; Silva, TOE;

Publicação
IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING

Abstract
In this paper, the authors describe a biomedical digital-signal interchange format. The format supports both raw and processed data, multiple segments, several signal structures and representations, and an open architecture. Its versatility and adaptability allows the software to take advantage of any particular features of the acquisition hardware. The format has been used and improved in routine work during a five-year period involving the cooperation between two hospitals and one engineering research center. In order to support the format, an object oriented C language library has been developed and is also shortly described.

1997

A computer-based fuzzy temperature controller for environmental chambers

Autores
Salgado, P; Cunha, JB; Couto, C;

Publicação
ISIE '97 - PROCEEDINGS OF THE IEEE INTERNATIONAL SYMPOSIUM ON INDUSTRIAL ELECTRONICS, VOLS 1-3

Abstract
This paper describes a computer-based temperature control system for an environmental chamber. The identification of the thermal process was made from the analysis of the collected output data in response to random generated input signals. Using this model it was established the optimal linear and non linear control strategies in order to achieve the desired set-point and to minimize the number of actuations. The actuation over the heating and cooling systems were performed with conventional PID and fuzzy controllers and their responses were compared. This work enhances fuzzy controllers application with self-learning capability to achieve the prescribed control objectives in a near-optimal manner. By applying back-propagation through time it was possible to force the plant block to generate the desired trajectory.

1997

Time addressing of fibre Bragg sensors interrogated via source spectral characteristics

Autores
Ferreira, LA; Dias, PC; Santos, JL;

Publicação
SENSORS AND THEIR APPLICATIONS VIII

Abstract
A passive all-fibre technique for fibre Bragg grating wavelength shift detection previously presented is used here for the demodulation of two Bragg sensors placed in a tree topology and addressed in time. The scheme involves a light source with particular spectral profile that allows the direct tracking of the Bragg wavelength shifts, providing satisfactory resolution over a large dynamic range and direct application in demultiplexing fibre sensing systems. Experimental results are presented relative to the measurement of static and dynamic strain, as well as temperature.

1997

Setting the length of the planning horizon in the vehicle replacement problem

Autores
deSousa, JF; Guimaraes, RC;

Publicação
EUROPEAN JOURNAL OF OPERATIONAL RESEARCH

Abstract
In some formulations of the vehicle replacement problem, in particular those leading to repair limit type models, the alternative policies are evaluated and compared over a fixed planning horizon. Although it has been widely recognised that the optimal policies derived under these formulations depend critically on the length of the horizon, no method has been presented so far to set appropriately this parameter. In this paper. the authors describe a method which overcomes this shortcoming. Once the best policy has been derived from a given finite horizon with length H, such a policy is repeated indefinitely over time and an equivalent annual rent is computed. The parametrisation of H leads to the definition of an annual rent function with a sequence of nearly equidistant local minima. It is suggested that in practice the second local minimum of this function leads to an adequate choice of the parameter H. The method can be applied both to stochastic and deterministic cost modelling situations. The method was tested using both real data from large samples of different types of passenger vehicles and artificially generated data. (C) 1997 Elsevier Science B.V.

1997

Probabilistic choice vs. risk analysis: conflicts and synthesis in power system planning

Autores
Miranda, V; Proenca, LM;

Publicação
IEEE Power Engineering Review

Abstract
This paper shows the conceptual differences between adopting a probabilistic weighting of the futures and a risk averse strategy, in power system planning under uncertain scenarios. It is illustrated with a distribution planning problem, where optimal solutions in both cases are determined by a genetic algorithm. It shows that the probabilistic approach is less safe and cannot detect some interesting solutions.

1997

Real-time parameter estimation of dynamic temperature and humidity models for greenhouse adaptive climate control

Autores
Cunha, JB; Couto, C; Ruano, AEB;

Publicação
MATHEMATICAL AND CONTROL APPLICATIONS IN AGRICULTURE AND HORTICULTURE

Abstract
A real-time parameter estimator for the climate discrete-time dynamic models of a greenhouse located at the North of Portugal are presented. The experiments showed that the second-order models identified for the air temperature and humidity achieve a close agreement between simulated and experimental data. The real-time data acquisition and the recursive identification techniques implemented are used in the simulation and design of an adaptive climate controller to achieve set-point accuracy and minimisation of the energy inputs.

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