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Browsing by Issue Date, starting with "2005-10"

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  • Describing function of systems with nonlinear friction
    Publication . Duarte, Fernando B. M.; Tenreiro Machado, J. A.
    This paper studies the describing function (DF) of systems composed of a mass subjected to nonlinear friction. The friction force is decomposed in three components namely, the viscous, the Coulomb and the static forces. The system dynamics is analyzed in the DF perspective and the reliability of the DF method is evaluated through the signal harmonic content.
    2005-10Conference object Open access Show more
  • An easy procedure for calibrating data systems using interleaving
    Publication . Clemêncio, Filomena; Loureiro, Custódio F. M.; Correia, Carlos M. B. A.
    Interleaving data acquisition channels is a well-known and interesting technique to achieve higher acquisition rates. However, to obtain the expected benefits, a careful look at the interleaving technique and to mismatches that can lead to unwanted harmonic distortion and noise is essential. In this paper we discuss the methods used to interleave existing high-speed, 250 MSPS 8-bit acquisition channels, and the results obtained. The methods presented allowed a good channel calibration in amplitude (amplitude mismatch under 0.1 lsb) and in time (time mismatch between acquisition channels in the ps range, under the specified maximum jitter for the ADC used). A dynamic, by software, amplitude level signal-dependent adjustment procedure is also suggested for signals with reach frequency content that can substantially improve the quality of the acquired signal when using interleaved channels. The techniques presented provide good results even in the presence of noise.
    2005-10Conference object Restricted access Show more
  • The influence of occlusal class in the production of voiceless fricatives
    Publication . Araújo, André; Vilarinho, Helena; Jesus, Luís M. T.
    The aim of this study was to relate the production of voiceless fricatives with the type of dental occlusion. The articulatory gestures during the production of consonant sounds such as the voiceless fricatives /f/, /s/ and /ʃ/, seem to be disturbed for type II class (Angle’s classification) individuals, which frequently require the training of compensatory articulation to get a “normal” acoustic output. This work is central to the first two authors’ clinical practice in Speech and Language Therapy in which it is frequent the need to treat articulatory disorders.
    2005-10Conference object Open access Show more