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Coimbra, Portugal

Radil T.,Institute Telecomunicaoes | Ramos P.M.,University of Lisbon
Measurement: Journal of the International Measurement Confederation | Year: 2010

This paper describes a new algorithm for parameter estimation of two channel single-tone signals. The algorithm works in the frequency domain and uses least squares optimization to estimate the amplitudes, phases and common frequency of the signals. The estimation process is based on the weighted least squares best-fitting of the theoretical spectrums of single-tone signals on the measured spectrums. The performance of the algorithm is shown on simulated and measured signals in different operating situations. © 2010 Elsevier Ltd. All rights reserved. Source


Ramos P.M.,University of Lisbon | Radil T.,Institute Telecomunicaoes | Janeiro F.M.,University of Evora
Measurement: Journal of the International Measurement Confederation | Year: 2012

In this paper, an in-depth analysis of the implementation issues of sine-fitting algorithms in systems with 32-bit floating point representation is presented. The results obtained in 32-bit systems are compared with the ones obtained in 64-bit floating point representation systems. The four-parameter sine-fitting is an iterative algorithm and the criterion used to detect convergence is even more crucial in 32-bit systems. A modification of the traditional implementation is used to, in some situations, reduce the number of iterations required to converge without compromising the final accuracy or precision of the estimated parameters. It is shown that, as the number of samples increases, the limitations of the 32-bit systems clearly limit the use of the sine-fitting algorithms. Nevertheless, the number of samples at which this effect is detected is much higher than the number of samples usually used so far in stand-alone instrumentation systems. © 2011 Elsevier Ltd. All rights reserved. Source


Ramalho M.B.,Institute Telecomunicaoes | Correia P.L.,Institute Telecomunicaoes | Correia P.L.,University of Lisbon | Soares L.D.,Institute Telecomunicaoes | Soares L.D.,Iscte Instituto Universitario Of Lisbon
IET Computer Vision | Year: 2012

This study proposes a biometric system for personal identification based on three biometric characteristics from the hand, namely: the palmprint, finger surfaces and hand geometry. A protection scheme is applied to the biometric template data to guarantee its revocability, security and diversity among different biometric systems. An error-correcting code (ECC), a cryptographic hash function (CHF) and a binarisation module are the core of the template protection scheme. Since the ECC and CHF operate on binary data, an additional feature binarisation step is required. This study proposes: (i) a novel identification architecture that uses hand geometry as a soft biometric to accelerate the identification process and ensure the system's scalability; and (ii) a new feature binarisation technique that guarantees that the Hamming distance between transformed binary features is proportional to the difference between their real values. The proposed system achieves promising recognition and speed performances on two publicly available hand image databases. © 2012 The Institution of Engineering and Technology. Source


Oliveira L.M.R.,University of Coimbra | Oliveira L.M.R.,University of Algarve | Oliveira L.M.R.,Institute Telecomunicaoes | Cardoso A.J.M.,University of Coimbra | And 3 more authors.
Electric Power Systems Research | Year: 2011

This paper presents the application of the on-load exciting current Extended Park's Vector Approach to diagnose incipient turn-to-turn winding faults in operating power transformers. Experimental and simulation test results demonstrate the effectiveness of the proposed technique, which is based on the spectral analysis of the AC component of the on-load exciting current Park's Vector modulus. © 2011 Elsevier B.V. All rights reserved. Source


Proena J.,Institute Telecomunicaoes | Proena J.,University of Coimbra | Celorico D.,Institute Telecomunicaoes | Candeias S.,Microsoft | And 4 more authors.
Proceedings of the Annual Conference of the International Speech Communication Association, INTERSPEECH | Year: 2015

The automatic evaluation of children's reading performance by detecting and analyzing errors and disfluencies in speech is an important tool to build automatic reading tutors and to complement the current method of manual evaluations of overall reading ability in schools. A large amount of speech from children reading aloud plentiful in errors and disfluencies is needed to train acoustic, disfluency and pronunciation models for an automatic reading assessment system. This paper describes the acquisition and analysis of a read-aloud speech database of European Portuguese from children aged 6-10 from the first to fourth school grades. Towards the goal of detecting all reading errors and disfluencies, we apply a decoding process to the utterances using flexible word level lattices that allow syllable based false starts and repetitions of two or more word sequences. The proposed method proved promising in detecting corrections and repetitions in sentences, and provides an improved alignment of the data, helpful for future annotation tasks. The analysis of the database also shows agreement to government defined curricular goals for reading. Copyright © 2015 ISCA. Source

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