Purpose: We analyzed the heart rate variability (RR intervals) by means of nonlinear dynamics methods: Poincaré plot (return map), approximate entropy (ApEn) and detrended fluctuation analysis (DFA). The purpose of this study was the quantitative and qualitative assessment of heart rate variability by means of these nonlinear dynamics methods. Material and methods: The Poincaré plot is a scatte...

Nonlinear time series analysis has been widely used to search for signatures of low-dimensional chaos in light curves emanating from astrophysical bodies. A particularly popular example is the microquasar GRS 1915+105, whose irregular but systematic X-ray variability has been well studied using data acquired by the Rossi X-ray Timing Explorer (RXTE). With a view to building simpler models of X-...

The effect of day-night variations was evaluated in both a female and a male population of healthy subjects. A total of 239 subjects were included in this study, of which 119 male and 120 female. 24 hour Holter recordings were used to analyze heart rate variability. Power spectral indices (total power, low and high frequency power) were calculated together with the nonlinear indices fractal dim...

Alternative explanations for disease and other population cycles typically include extrinsic environmental drivers, such as climate variability, and intrinsic nonlinear dynamics resulting from feedbacks within the system, such as species interactions and density dependence. Because these different factors can interact in nonlinear systems and can give rise to oscillations whose frequencies diff...

We propose a nonlinear ocean forecasting technique based on a combination of genetic algorithms and empirical orthogonal function (EOF) analysis. The method is used to forecast the space-time variability of the sea surface temperature (SST) in the Alboran Sea. The genetic algorithm finds the equations that best describe the behaviour of the different temporal amplitude functions in the EOF deco...

Nonlinear dynamics, a branch of the basic sciences that studies complex physical systems, offers novel approaches to long-standing problems of physiological form and function. The nonlinear concept of fractals, introduced and developed over the last decade, provides insights into the organization of complex structures such as the tracheobronchial tree and heart, as well as into the dynamics of ...

We study how pairs of neurons transfer correlated input currents into correlated spikes. Over rapid time scales, correlation transfer increases with both spike time variability and rate; the dependence on variability disappears at large time scales. This persists for a nonlinear membrane model and for heterogeneous cell pairs, but strong nonmonotonicities follow from refractory effects. We pres...

Movement variability is considered essential to typical motor development. However, multiple theoretical perspectives and measurement tools have limited interpretation of the importance of movement variability in biological systems. The complementary use of linear and nonlinear measures have recently allowed for the evaluation of not only the magnitude of variability but also the temporal struc...

[1] Based on the analysis of a low-order tropical atmosphere-ocean model we propose a nonlinear mechanism explaining several features of the observed El Niño-Southern Oscillation (ENSO) phenomenon: ENSO irregularity, ENSO Amplitude Modulations and decadal tropical climate variability. The mechanism suggested here is based on the idea of homoclinic/heteroclinic orbits, an inherently nonlinear co...