Ktonas, PY, Golemati S, Xanthopoulos P, Sakkalis V, Ortigueira MD, Tsekou H, Zervakis M, Paparrigopoulos T, Soldatos CR.
2007.
Potential dementia biomarkers based on the time-varying microstructure of sleep EEG spindles. 2007 29th Annual International Conference of the IEEE Engineering in Medicine and Biology Society. :2464–2467.
AbstractThe time-varying microstructure of sleep EEG spindles may have clinical significance in dementia studies. In this work, the sleep spindle is modeled as an AM-FM signal and parameterized in terms of six parameters, three quantifying the instantaneous envelope (IE) and three quantifying the instantaneous frequency (IF) of the spindle model. The IE and IF waveforms of sleep spindles from patients with dementia and normal controls were estimated using the time-frequency technique of complex demodulation (CD). Sinusoidal curve-fitting using a matching pursuit (MP) approach was applied to the IE and IF waveforms for the estimation of the six model parameters. Specific differences were found in sleep spindle instantaneous frequency dynamics between spindles from dementia subjects and spindles from controls.
Ortigueira, MD, Serralheiro AJ.
2007.
Pseudo-fractional ARMA modelling using a double Levinson recursion. IET Control Theory & Applications. 1:173., Number 1: IEEE
AbstractThe modelling of fractional linear systems through ARMA models is addressed. To perform this study, a new recursive algorithm for impulse response ARMA modelling is presented. This is a general algorithm that allows the recursive construction of ARMA models from the impulse response sequence. This algorithm does not need an exact order specification, as it gives some insights into the correct orders. It is applied to modelling fractional linear systems described by fractional powers of the backward difference and the bilinear transformations. The analysis of the results leads to propose suitable models for those systems.
Ortigueira, MD.
2007.
Riesz Potentials as Centred Derivatives. Advances in Fractional Calculus. :93–112.: Springer Netherlands
AbstractGeneralised fractional centred differences and derivatives are studied in this Chapter. These generalise to real orders the existing ones valid for even and odd positive integer orders. For each one, suitable integral formulations are presented. The limit computation inside the integrals leads to generalisations of the Cauchy derivative. Their computations using a special path lead to the well known Riesz potentials. A study for coherence is done by applying the definitions to functions with Fourier transform. The existence of inverse Riesz potentials is also studied.
Ortigueira, MD.
2007.
Riesz potentials as centred derivatives, September. 2nd Symposium on Fractional Derivatives and Their Applications. (
J Sabatier, OP Agrawal, Machado, J.A.T., Eds.).:93–112.: Springer
AbstractGeneralised fractional centred differences and derivatives are studied in this chapter. These generalise to real orders the existing ones valid for even and odd positive integer orders. For each one, suitable integral formulations are presented. The limit computation inside the integrals leads to generalisations of the Cauchy derivative. Their computations using a special path lead to the well known Riesz potentials. A study for coherence is done by applying the definitions to functions with Fourier transform. The existence of inverse Riesz potentials is also studied.
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