Iveta R. Pimentel

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We study the Lyapunov exponent for electron and phonon excitations, in pure and random Fibonacci quasicrystal chains, using an exact real space renormalization group method, which allows the calculation of the Lyapunov exponent as a function of the energy. It is shown that the Lyapunov exponent on a pure Fibonacci chain has a self-similar structure,(More)
We study the spin excitations and the transverse susceptibility of a two-dimensional antiferromagnet doped with a small concentration of holes in the t-J model. The motion of holes generates a renormalization of the magnetic properties. The Green ́s functions are calculated in the selfconsistent Born approximation. It is shown that the long-wavelength spin(More)
The understanding of brain activity, and in particular events such as epileptic seizures, lies on the characterisation of the dynamics of the neural networks. The theory of non-linear dynamics provides signal analysis techniques which may give new information on the behaviour of such networks. Methods: We calculated correlation dimension maps for 19-channel(More)
A parasystole from a heart-transplant patient is analysed using a beat-to-beat RR interval time series obtained from an electrocardiogram (ECG). The dysrhythmia, resulting from the co-existence of two pacemakers, the sinus node and an ectopic focus, presents distinctive regular patterns, with transitions from one pattern to another occurring abruptly. It is(More)
INTRODUCTION The variability observed in the heart rate may reflect fundamental aspects of cardiac activity. It has been under discussion whether heart rate variability (HRV) is due to noise or chaos, which is irregular behavior occurring in deterministic nonlinear systems. METHODS AND RESULTS Using chaos analysis techniques, we analyzed HRV of five(More)
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