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PubMed2000

Power-law behavior of beat-rate variability in monolayer cultures of neonatal rat ventricular myocytes.

It is known that extracardiac factors (nervous, humoral, and hemodynamic) participate in the power-law behavior of heart-rate variability. To assess whether intrinsic properties of cardiac tissue might also be involved, beat-rate variability was studied in spontaneously beating cell cultures devoid of extracardiac influences. Extracellular electrograms were recorded from monolayer cultures of neonatal rat ventricular myocytes under stable incubating conditions for up to 9 hours. The beat-rate time series of these recordings were examined in terms of their Fourier spectra and their Hurst scaling exponents. A non-0 Hurst exponent was found in 21 of 22 preparations (0.29+/-0.09; range, 0.11 to 0.45), indicating the presence of fractal self-similarity in the beat-rate time series. The same preparations exhibited power-law behavior of the power spectra with a power-law exponent of -1.36+/-0.24 (range, -1.04 to -1.96) in the frequency range of 0.001 to 1 Hz. Furthermore, it was found that the power-law exponent was nonstationary over time. These results indicate that the power-law behavior of heart-rate variability is determined not only by extracardiac influences but also by components intrinsic to cardiac tissue. Furthermore, the presence of power-law behavior in monolayer cultures of cardiomyocytes suggests that beat-rate variability might be determined by the complex nonlinear dynamics of processes occurring at the level of the cellular network, eg, interactions among a large number of cell oscillators or metabolic regulatory systems.

Animals↗
PubMed2003

Multifocal electroretinographic features of central retinal vein occlusion.

PURPOSE: To determine the features of wide-field multifocal electroretinography (WF-mfERG) recorded in patients with central retinal vein occlusion (CRVO) and to compare WF-mfERG responses of the affected and fellow eyes. In addition, WF-mfERG responses were also compared by using standard electroretinography (ERG). METHODS: WF-mfERG and ERG responses were recorded from both eyes of 56 patients with CRVO. The WF-mfERG responses, obtained using a custom-built system were grouped into central and peripheral rings. The P1 amplitudes, and P1 and N1 implicit times were grouped and averaged within both rings. Nonparametric statistical analysis was used to compare the ERG results from the affected and fellow eyes. The results were also compared with normative data (5% to 95% confidence limits). RESULTS: CRVO markedly affected all the parameters of the WF-mfERG. In the affected eyes, 98% of the central and 91% of the peripheral P1 implicit times fell outside the normal range, as opposed to 35% of the 30-Hz flicker implicit times. The WF-mfERG responses obtained from eyes with CRVO were significantly different (P<0.01) from those derived from the fellow eye. The central and peripheral P1 implicit times were also abnormal in 59.2% and 46.9% of the fellow eyes, respectively. CONCLUSIONS: WF-mfERG is more susceptible than the standard ERG to changes in the nonlinear dynamics of the eye due to the multiple frequencies of stimulation used to record WF-mfERG responses. WF-mfERG could be a sensitive indicator of the underlying disease affecting the retina in eyes with CRVO and may have a role in the clinical setting.

Adult↗
PubMed2002

Hemofiltration, adsorption, sieving and the challenge of sepsis therapy design.

Circulating inflammatory mediators spilling into the circulation from sites of active inflammation are considered the source of remote tissue injury and associated organ dysfunction in sepsis. Hemofiltration has been proposed as a therapy for sepsis based on its ability to remove circulating inflammatory mediators by sieving or by adsorption, or both. Designing devices and methods for sepsis therapy will require optimization of these two mechanisms. In the present issue of Critical Care Forum, Kellum and Dishart report the relative effects of sieving and adsorption on plasma IL-6 following cecal ligation and puncture in rats. The authors conclude that hemoadsorption is the main mechanism of removal, and discuss some possible implications for filter design but hemoadsorption is well dependant on hemofiltration (the so-called hemofiltration filter adsorption/synergistic effect). It is important to recognize the limitations of conventional systems; Kellum and Dishart have extended our knowledge of hemofiltration filter adsorption, which is quite different from conventional hemoadsorption. If sepsis is a manifestation of a nonlinear dynamic control system out of control, then filtration at modest doses with a large pore filter may succeed as well as high-volume hemofiltration with a conventional cut-off filter. In the present paper, we will explore the strengths and the weaknesses of the 'Kellum and Dishart' study and discussing their findings in the light of the current available literature.

Adsorption↗
PubMed2004

Bio-inspired nano-sensor-enhanced CNN visual computer.

Nanotechnology opens new ways to utilize recent discoveries in biological image processing by translating the underlying functional concepts into the design of CNN (cellular neural/nonlinear network)-based systems incorporating nanoelectronic devices. There is a natural intersection joining studies of retinal processing, spatio-temporal nonlinear dynamics embodied in CNN, and the possibility of miniaturizing the technology through nanotechnology. This intersection serves as the springboard for our multidisciplinary project. Biological feature and motion detectors map directly into the spatio-temporal dynamics of CNN for target recognition, image stabilization, and tracking. The neural interactions underlying color processing will drive the development of nanoscale multispectral sensor arrays for image fusion. Implementing such nanoscale sensors on a CNN platform will allow the implementation of device feedback control, a hallmark of biological sensory systems. These biologically inspired CNN subroutines are incorporated into the new world of analog-and-logic algorithms and software, containing also many other active-wave computing mechanisms, including nature-inspired (physics and chemistry) as well as PDE-based sophisticated spatio-temporal algorithms. Our goal is to design and develop several miniature prototype devices for target detection, navigation, tracking, and robotics. This paper presents an example illustrating the synergies emerging from the convergence of nanotechnology, biotechnology, and information and cognitive science.

Animals↗
PubMed2003

A very-short-term intermittency of fetal heart rates and developmental milestone.

We noticed that fetal heart rates (FHR) of immature fetuses intermittently showed unstable sudden and brief falls below baseline FHR that occur over a few or several heartbeats. The frightening falls do not occur in mature fetuses. In nonlinear dynamics, the degree of such abrupt falls in time series is quantified as intermittency. We aimed to investigate the nature and maturational changes of intermittency of the FHR in normal fetuses and to present the intermittency values of normal fetuses according to gestational weeks. FHR data of 450 normal fetuses between 23 and 40 wk of gestation were studied. We performed multifractal analysis and highlighted a very-short-term intermittency (C1alpha, 4 </= scale < 16 heartbeats). The C1alpha values exhibited a strong negative linear correlation (r = -0.732, p = 0.0001) with the gestational weeks. At 27-28, 29-30, 33-34, and 37-38 gestational weeks, the C1alpha values were significantly lower than those of the previous 2 or 4 gestational weeks. The maturation of normal fetuses is related to decreasing the severity of the unstable sudden and brief falls in FHR that is measured by C1alpha, the very-short-term intermittency. The C1alpha values according to the gestational weeks that we presented can be used as credible normal milestone values when estimating the degree of maturity of certain FHR. Because the C1alpha captures the degree of the unstable fall in FHR, the C1alpha may also be used in identifying sick fetuses that are associated with hemodynamic instability and sudden bradycardia.

Female↗
PubMed2004

The electric fish Brachyhypopomus pinnicaudatus produces jamming avoidance responses to signals that are harmonically related to its own discharges.

Jamming avoidance responses (JARs) are exhibited by pairs of pulse type electric fish that discharge with similar frequencies whenever their individual pulses are about to coincide: responses consist of the transient shortenings in inter-discharge intervals in the fish with the higher frequency. This study describes and models novel forms of JARs observed in sexually mature male or female Brachyhypopomus pinnicaudatus. One novel JAR was observed in male-female pairs in their natural habitat. It happened when the baseline frequencies were not similar but, rather, when one was almost twice that of the other; moreover, the transient interval shortenings occurred not in the fish with the higher frequency but in the slower one. Transient interval shortenings similar to those in all natural JARs were observed in individual fish in tanks and submitted to periodic electrical pulse trains. They happened not only when pulse frequencies were slightly lower than the unperturbed frequency emitted by the fish but also when slightly lower than the frequency's sub- or higher harmonics (e.g. one half or twice). The proposed model satisfactorily reproduces all experimental observations. In it, forthcoming inter-pulse intervals reflect the differences between the cophases of pulses that arrive within the 'sensitive windows' belonging to either consecutive (i.e. one and the next) or alternating (e.g. every other, every three) intervals. Paired pulse fish embody interacting oscillators, and, in particular, JARs embody either quasiperiodic phase walk-throughs and intermittencies or periodic and locked forms. Hence, their study would profit by the powerful theories and approaches advanced by nonlinear dynamics.

Animal Communication↗
PubMed1993

Fractal analysis of steady-state-flicker visual evoked potentials: feasibility.

Electrophysiological models of visual evoked potential recording have assumed that response variability is caused predominantly by random noise added to a true steady signal. Since neuronal geometry has a fractal structure, neural activity may demonstrate deterministic nonlinear dynamics, i.e., chaos. We recorded several-minute time-series traces of the visual evoked potential magnitude in response to full-field flicker from three glaucoma patients and one normal subject. When plotted in phase space, the steady-state response derived from a lock-in amplifier shows an apparent so-called strange attractor (extended nonrepeating loops) rather than the pattern expected from a signal-plus-noise model (a fuzzy dot). The fractal dimension of this attractor may be a more sensitive indicator of early optic-nerve damage than are visual evoked potential latency or amplitude measures.

Electrophysiology↗
PubMed2003

Emergence of linear wave segments and predictable traits in saturated nonlinear media.

We find the key behind the existence traits of asymptotic saturated nonlinear optical solitons in the emergence of linear wave segments. These traits, produced by the progressive relegation of nonlinear dynamics to wave tails, allow a direct and versatile analytical prediction of self-trapping existence conditions and simple soliton scaling laws, which we confirm experimentally in saturated-Kerr self-trapping observed in photorefractives. This approach provides the means to correctly evaluate beam tails in the saturated regime, which is instrumental in the prediction of soliton interaction forces.

Journal Article↗
PubMed2003

Deterministic chaos in a diode-pumped Nd:YAG laser passively Q switched by a Cr4+:YAG crystal.

We report the experimental observation and numerical simulation of deterministic chaos in a diode-pumped Nd:YAG solid-state laser that is passively Q switched by a Cr4+:YAG crystal saturable absorber. We show that apart from the stable Q-switched operation the laser can also exhibit complicated nonlinear dynamics, including the period-doubling route to chaos and periodic windows.

Journal Article↗
PubMed2004

Surface plasmon polariton propagation in nanoscale metal gap waveguides.

Based on finite-difference time-domain simulation of the propagation characteristics of surface plasmon polaritons (SPPs) in optical circuits made from metal gap waveguides (MGWs) with nanometric gap widths, we theoretically demonstrate that two structures that consist of splitting and recombining MGWs and of coupling MGWs can be used as nanoscale Mach-Zehnder interferometers. MGW arrays show capabilities for array imaging and for controlling the flow of SPPs. Other potential applications of coupling MGWs, as SPP switches, directional couplers, and even as a nanoscale counterpart for observing linear and nonlinear dynamic behavior of electromagnetic fields, are also predicted and discussed. Our results point to an interesting way to manipulate optical signals and provide efficient sensing in nanophotonic architectures.

Journal Article↗
PubMed2004

Unidirectional lasing from a microcavity with a rounded isosceles triangle shape.

We report that unidirectional lasing emission can be generated from a rounded isosceles triangular microcavity within a low nkD range, where n is the refractive index, k is the vacuum wave number, and D is the characteristic size of the microcavity. It is shown that unidirectional resonance modes have relatively high-Q values and in a nonlinear dynamic model appear as stationary lasing solutions with a low threshold. The formation of a whispering-gallery-type pattern along the rounded part on the symmetry axis is responsible for the unidirectionality of the resonances.

Journal Article↗
PubMed2006

Long-range multifilamentation of femtosecond laser pulses versus air pressure.

We examine the nonlinear dynamics of femtosecond filaments in air at different pressures. Emphasis is placed on the changes in multiple filamentation patterns produced by terawatt laser pulses. Principal modifications induced by pressure variations apply to the onset distance, size, and number of the filaments inside the laser bundle.

Journal Article↗
PubMed2006

Chaotic stimulated Brillouin scattering near the threshold in a fiber.

We investigate the nonlinear dynamic behavior of stimulated Brillouin scattering (SBS) near threshold in the absence of feedback. When a cw Nd:YAG laser is injected into a single-mode optical fiber, the SBS signal exhibits intermittently appearing irregular self-pulsations near the threshold. By examining the time series of the SBS signals, we verify that the irregular SBS signal is one of the chaotic phenomena appearing near the bifurcation point.

Journal Article↗
PubMed2006

Lidar detection using a dual-frequency source.

A new technique of dual-frequency Doppler-lidar measurement is investigated. This technique is based on the use of a coherently locked, tunable, dual-frequency laser source and is shown to accurately measure velocities as small as 26 mum/s. It is generated by exploiting the nonlinear dynamics of a semiconductor laser through a proper combination of optical injection and operating conditions.

Journal Article↗
PubMed2003

Approximate entropy of human respiratory movement during eye-closed waking and different sleep stages.

STUDY OBJECTIVE: The breath-to-breath variability of respiratory parameters changes with sleep stage. This study investigates any alteration in the approximate entropy (ApEn) of respiratory movement as a gauge of complexity in respiration, by stage of consciousness, in the light of putative brain interactions. PARTICIPANTS: Eight healthy men, who were between the ages of 23 and 29 years, were investigated. MEASUREMENTS AND RESULTS: The signals of chest wall movement and EEG were recorded from 10:30 PM to 6:00 AM. After analog-to-digital conversion, the ApEn of respiratory movement (3 min) and EEG (20 s) were computed. Surrogate data were tested for nonlinearity in the original time series. The most impressive reduction in the ApEn of respiratory movement was associated with stage IV sleep, when the ApEn of the EEG was also statistically significantly decreased. A statistically significant linear relation is found between the ApEn of both variables. Surrogate data indicated that respiratory movement had nonlinear properties during all stages of consciousness that were investigated. CONCLUSION: Respiratory movement and EEG signals are more regular during stage IV sleep than during other stages of consciousness. The change in complexity described by the ApEn of respiration depends in part on the ApEn of the EEG, suggesting the involvement of nonlinear dynamic processes in the coordination between brain and lungs.

Adult↗
PubMedDate not supplied

Parametrically excited oscillation of stay cable and its control in cable-stayed bridges.

This paper presents a nonlinear dynamic model for simulation and analysis of a kind of parametrically excited vibration of stay cable caused by support motion in cable-stayed bridges. The sag, inclination angle of the stay cable are considered in the model, based on which, the oscillation mechanism and dynamic response characteristics of this kind of vibration are analyzed through numerical calculation. It is noted that parametrically excited oscillation of a stay cable with certain sag, inclination angle and initial static tension force may occur in cable-stayed bridges due to deck vibration under the condition that the natural frequency of a cable approaches to about half of the first model frequency of the bridge deck system. A new vibration control system installed on the cable anchorage is proposed as a possible damping system to suppress the cable parametric oscillation. The numerical calculation results showed that with the use of this damping system, the cable oscillation due to the vibration of the deck and/or towers will be considerably reduced.

Journal Article↗