SEARCH · PubMed Health

Results for “Nonlinear Dynamics”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,063 records · Page 59Linked to original sources

PubMed2002

The biofield hypothesis: its biophysical basis and role in medicine.

This paper provides a scientific foundation for the biofield: the complex, extremely weak electromagnetic field of the organism hypothesized to involve electromagnetic bioinformation for regulating homeodynamics. The biofield is a useful construct consistent with bioelectromagnetics and the physics of nonlinear, dynamical, nonequilibrium living systems. It offers a unifying hypothesis to explain the interaction of objects or fields with the organism, and is especially useful toward understanding the scientific basis of energy medicine, including acupuncture, biofield therapies, bioelectromagnetic therapies, and homeopathy. The rapid signal propagation of electromagnetic fields comprising the biofield as well as its holistic properties may account for the rapid, holistic effects of certain alternative and complementary medical interventions.

Acupuncture↗

PubMed2005

AGML Central: web based gel proteomic infrastructure.

SUMMARY: AGML Central is a web-based open-source public infrastructure for dissemination of two-dimensional Gel Electrophoresis (2-DE) proteomics data in AGML format (Annotated Gel Markup Language). It includes a growing collection of converters from proprietary formats such as those produced by PDQUEST (BioRad), PHORETIX 2-D (Nonlinear Dynamics) and Melanie (GenBio SA). The resulting unifying AGML formatted entry, with or without the raw gel images, is optionally stored in a database for future reference. AGML Central was developed to provide a common platform for data dissemination and development of 2-DE data analysis tools. This resource responds to an increasing use of AGML for 2-DE public source data representation which requires automated tools for conversion from proprietary formats. Conversion and short-term storage is made publicly available, permanent storage requires prior registering. A JAVA applet visualizer was developed to visualize the AGML data with cross-reference links. In order to facilitate automated access a SOAP web service is also included in the AGML Central infrastructure. AVAILABILITY: http://bioinformatics.musc.edu/agmlcentral.

Database Management Systems↗

PubMed2005

Mathematical characterization of broiler carcass yield dynamics.

Modeling of broiler chicken supply-chain economics depends on robust biological models of growth and yield of broiler chickens. In this paper, 8 dynamic nonlinear broiler carcass and carcass part yield models were evaluated statistically for their suitability for predicting weights of carcass parts. The analysis employed 4 sigmoidal (S) models (Gompertz, modified Gompertz, Richards, and Lopez) describing carcass part weight as a function of age, as well as 3 diminishing returns (DR) models (Lopez, Mitscherlich, and log linear), and a log-linear proportional yield (PY) model, which describe carcass part yield and weight, respectively, as a proportion of feather- and fat-free empty body mass (FFEBM). Three S models with a flexible point of inflection were better able to predict carcass part weights than a fixed point of inflection Gompertz model and, in general, the DR models. The log-linear models were the only models that converged in 100% of the evaluations. The allometric PY model predicted weights for most carcass parts with the smallest degree of error and with substantially less bias than the DR log-linear model. Estimates of the coefficients for the log-linear PY model are included for 12 key carcass parts. Estimates of carcass chemical composition are presented for the log-linear PY model.

Animals↗

PubMed1992

HIV and the brain: evidence of early involvement and progressive damage.

AIDS is often accompanied by progressive encephalopathy and 'subcortical' dementia, but there is uncertainty regarding how early the brain involvement may begin in the course of HIV infection. This study used a cognitive auditory 'oddball' paradigm to elicit sensory and cognitive event related potential (ERP) components from healthy controls and from patients at different stages of HIV infection. Sensory component latencies did not differ between groups, but cognitive components showed progressive delays corresponding to increasingly severe clinical stages of HIV infection. The earliest changes were found among asymptomatic HIV + patients, suggesting that this test is a sensitive indicator of early subclinical CNS damage. In contrast, neither frequency analysis nor nonlinear dynamical analysis of the EEG showed differences between healthy controls and patients.

AIDS-Related Complex↗

PubMedDate not supplied

Modeling and control of a brushless DC axial flow ventricular assist device.

This article presents an integrated model of the human circulatory system that incorporates circulatory support by a brushless DC axial flow ventricular assist device (VAD), and a feedback VAD controller designed to maintain physiologically sufficient perfusion. The developed integrated model combines a network type model of the circulatory system with a nonlinear dynamic model of the brushless DC pump We show that maintaining a reference differential pressure between the left ventricle and aorta leads to adequate perfusion for different pathologic cases, ranging from normal heart to left heart asystole, and widely varying physical activity scenarios from rest to exercise.

Equipment Design↗

PubMed2002

On the functional aspects of variability in postural control.

Current research in nonlinear dynamics and chaos theory has challenged traditional perspectives that associate high variability with performance decrement and pathology. It is argued that variability can play a functional role in postural control and that reduction of variability is associated with changes in balance with aging and neurological disease.

Aging↗

PubMed2001

Stochastic modeling and prediction of experimental seizures in Sprague-Dawley rats.

Most seizure prediction methods are based on nonlinear dynamic techniques, which are highly computationally expensive, thus limiting their clinical usefulness. The authors propose a different approach for prediction that uses a stochastic Markov chain model. Seizure (Ts) and interictal (Ti) durations were measured from 11 rats treated with 3-mercaptopropionic acid. The duration of a seizure Ts was used to predict the time (Ti2) to the next one. Ts and Ti were distributed bimodally into short (S) and long (L), generating four probable transitions: S --> S, S --> L, L --> S, and L --> L. The joint probability density f (Ts, Ti2) was modeled, and was used to predict Ti2 given Ts. An identical model predicted Ts given the duration Ti1 of the preceding interictal interval. The median prediction error was 3.0 +/- 3.5 seconds for Ts (given Ti1) and 6.5 +/- 2.0 seconds for Ti2 (given Ts). In comparison, ranges for observed values were 2.3 seconds < Ts < 120 seconds and 6.6 seconds < Ti < 782 seconds. These results suggest that stochastic models are potentially useful tools for the prediction of seizures. Further investigation of the probable temporal interdependence between the ictal and interictal states may provide valuable insight into the dynamics of the epileptic brain.

3-Mercaptopropionic Acid↗

PubMed2001

Algorithms to analyze ventricular fibrillation signals.

Prediction of the success of defibrillation to avoid myocardial injury and performance feedback during CPR requires algorithms to analyze ventricular fibrillation signals. This report reviews investigations on different parameters of ventricular fibrillation electrocardiographic signals, including amplitude, frequency, bispectral analysis, amplitude spectrum area, wavelets, nonlinear dynamics, N(alpha) histograms, and combinations of several of these parameters. To date, no satisfactory methods have been found that cope with CPR artifacts and show adequate predictive power of successful defibrillation. The usual limitations of the studies are the small number of subjects, which precludes separation into training and test data. Because many investigations are animal studies of untreated short ventricular fibrillation, the results may be different for prolonged ventricular fibrillation in humans. The universality of threshold values has to be examined, and promising new parameters have to be monitored over longer time periods and analyzed for the effects of chest compressions, ventilation, and concomitant vasopressor therapy.

Algorithms↗

PubMed1997

The biochemical basis of synaptic plasticity and neurocomputation: a new theory.

The recent finding that dendritic spines (on which 90% of all excitatory synapses on pyramidal cells are formed) are not permanent structures but are continually being formed and adsorbed has implications for the present theoretical basis of neurocomputation, which is largely based on the concept of fixed nerve nets. This evidence would tend to support the recent theories of Edelman, Freeman, Globus, Pribram and others that neuronal networks in the brain operate mainly as nonlinear dynamic, chaotic systems. This paper presents a hypothesis of a possible neurochemical mechanism underlying this synaptic plasticity based on reactive oxygen species and toxic 0-semiquinones derived from catecholamines (i) by the enzyme prostaglandin H synthetase induced by glutamatergic NMDA receptor activation and (ii) by reactive nitrogen species derived from nitric oxide in a low ascorbate environment. A key factor in this neuromodulation may be the fact that catecholamines are potent antioxidants and free radical scavengers and are thus able to affect the redox mediated balance at the glutamate receptors between synapse formation and synapse removal that may be a key factor in neurocomputational plasticity. But catecholamines are also easily oxidized to neurotoxic 0-semiquinones and this may be relevant to the pathology of several diseases including schizophrenia. The relationship between dopamine release and positive reinforcement is relevant to this hypothesis.

Animals↗

PubMed1999

Noise stabilization of self-organized memories.

We investigate a nonlinear dynamical system which "remembers" preselected values of a system parameter. The deterministic version of the system can encode many parameter values during a transient period, but in the limit of long times, almost all of them are forgotten. Here we show that a certain type of stochastic noise can stabilize multiple memories, enabling many parameter values to be encoded permanently. We present analytic results that provide insight both into the memory formation and into the noise-induced memory stabilization. The relevance of our results to experiments on the charge-density wave material NbSe3 is discussed.

Journal Article↗

PubMed1999

Onset of oscillatory binary fluid convection in finite containers.

The onset of oscillatory convection in binary fluid mixtures in a two-dimensional domain with realistic boundary conditions on all boundaries is determined as a function of the fluid parameters and the aspect ratio Gamma of the container. The first unstable mode has either odd or even parity under left-right reflection. Depending on Gamma and the separation ratio S, this mode has the form of a standing wave, or a "chevron," consisting of a pair of waves propagating outwards from the cell center (or, in some cases, inwards towards it). Codimension--two points at which odd and even parity modes are simultaneously marginally stable are determined, as are various Takens-Bogdanov points. For fixed S infinity, and to the gap (in Rayleigh number and oscillation frequency) between successively unstable modes. The results quantify the parameter regime in which the weakly nonlinear dynamics of the system can be described in terms of the interaction of the first odd and even parity oscillatory modes.

Journal Article↗

PubMed1999

Amplification of weak signals and stochastic resonance via on-off intermittency with symmetry breaking.

Nonlinear dynamical systems possessing reflection symmetry have an invariant subspace in the phase space. The dynamics within the invariant subspace can be random or chaotic. As a system parameter changes, the motion transverse to the invariant subspace can lose stability, leading to on-off intermittency. Under certain conditions, the bursting behavior is symmetry breaking. We demonstrate the possibility of observing multiplicative noise(chaos)-induced amplification of weak signal and stochastic resonance via on-off intermittency with symmetry breaking in a general class of symmetrical systems. Differences of this mechanism of stochastic resonance to that in noisy bistable or threshold systems are discussed.

Journal Article↗

PubMed2000

Order parameter description of walk-off effect on pattern selection in degenerate optical parametric oscillators

Degenerate optical parametric oscillators can exhibit both uniformly translating fronts and nonuniformly translating envelope fronts under the walk-off effect. The nonlinear dynamics near threshold is shown to be described by a real convective Swift-Hohenberg equation, which provides the main characteristics of the walk-off effect on pattern selection. The predictions of the selected wave vector and the absolute instability threshold are in very good quantitative agreement with numerical solutions found from the equations describing the optical parametric oscillator.

Journal Article↗

PubMed2000

Anticipating chaotic synchronization

Dissipative chaotic systems with a time-delayed feedback can drive near-identical systems in such a way that the driven systems anticipate the drivers by synchronizing with their (arbitrarily distant) future states. This counterintuitive behavior is globally stable, robust, and a pure result of the interplay between delayed feedback and dissipation. Thus it constitutes a rather universal phenomenon of nonlinear dynamics. For small anticipation times, anticipating synchronization also occurs in chaotic systems without a memory term in the driver.

Journal Article↗

PubMed2000

Damped stochastic system driven by colored noise: analytical solution by a path integral approach

We consider the nonlinear non-Markovian stochastic process associated with the damped nonlinear dynamical system driven by Ornstein-Uhlenbeck noise. An approximate Fokker-Planck-type equation governing the above stochastic process is derived using the path-integral approach. The stationary probability density function (SPDF) of the above process is then computed using the matrix continued fraction method. The SPDF compares favorably with the corresponding digital simulation results obtained by us.

Journal Article↗

PubMed2000

Symmetry-breaking on-off intermittency under modulation: robustness of supersensitivity, resonance, and information gain

Nonlinear dynamical systems possessing an invariant subspace in the phase space and chaotic or stochastic motion within the subspace often display on-off intermittency close to the threshold of stability of the subspace. In a class of symmetric systems, the intermittency is symmetry breaking [Ying-Cheng Lai, Phys. Rev. E 53, R4267 (1996)]. We report interesting and practically important universal behavior of robustness of supersensitivity, resonance, and information gain in this class of systems when subjected to a weak modulation. While intermittent loss of synchronization may be harmful to the application of high-quality synchronization of coupled chaotic systems, the features reported here may lead to interesting application of on-off intermittency.

Journal Article↗

PubMed2000

Intrawell stochastic resonance versus interwell stochastic resonance in underdamped bistable systems

We show that, for periodically driven noisy underdamped bistable systems, an intrawell stochastic resonance can exist, together with the conventional interwell stochastic resonance, resulting in a double maximum in the power spectral amplitude at the forcing frequency as a function of the noise intensity. The locations of the maxima correspond to matchings of deterministic and stochastic time scales in the system. In this paper we present experimental evidence of these phenomena and a phemonological nonadiabatic description in terms of a noise-controlled nonlinear dynamic resonance.

Journal Article↗

PubMed2000

Suppressing complexity via the slaving principle

The complexity of a nonlinear dynamic system can be suppressed by adding an external period force with appropriate choice of frequency and amplitude directly on the slowly changing variable of the system. Numerical results indicate that the method not only can suppress chaos but also is robust to the additive external noise.

Journal Article↗