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Results for “Nonlinear Dynamics”

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At least 1,189 records · Page 66Linked to original sources

PubMed2006

Optimization analysis of decentralised sanitation and re-use system.

With the application of system dynamics, a dynamic nonlinear model reflecting the relationship between decentralised water use and reclaimed water supply and demand has been established. Through a system analysis, the model has been applied to a small residential district to predict and analyse the situation of future use of fresh water, demand and supply of re-used water, and treatment scale of reclaimed water. It is illustrated in this paper that wastewater decentralised treatment and re-use can decrease the consumption of fresh water without lowering the standard of living water for the district residents. On this basis, a rational scale and construction time of the decentralised sanitation and re-use system have been determined. Also, the paper predicts the influencing factors of the increasing water cost and changes in consumers' acceptability to re-use water in the decentralised sanitation and re-use system.

China↗

PubMed1987

Computation, rhythm, and cerebral slow waves.

The trajectories of data and modelling from formerly divergent research efforts now seem to be converging to an unexpected region of the phase space of neuroscience. Computational network theory and simulation assume that temporal rhythm may be a significant parameter for the successful organization of nonlinear analog computation effected by hierarchical sets of biological neurons and of nonbiological circuitry alike. For neurobiology, the apparently chaotic rhythms of cerebral compound field potentials--the electroencephalogram (EEG) and slow waves of event related brain potentials (ERBP)--have long been a phenomenological embarrassment, of only marginal clinical utility. But recent data from molecular biophysics, nonlinear dynamics, artificial intelligence, and scalp-conducted human electrocorticography suggest a possible functional role in the serial gating of neural network computations for the familiar theta-alpha-beta rhythms of the EEG clinic.

Auditory Perception↗

PubMedDate not supplied

Excitability and susceptibility of the brain's electrical activity during sleep: an analysis of late components of AEPs and VEPs.

We investigated ten healthy male subjects and measured late components of AEPs and VEPs during sleep. According to Rechtschaffen and Kales (1968) we performed an off-line scoring procedure of sleep-EEG and averaged the AEPs and VEPs of five different periods, corresponding to sleep stages I, II, III, IV and REM. From the averaged evoked potentials we computed the amplitude-frequency-characteristic (AFC) of the brain (Basar, 1980) during different sleep stages. These AFCs characterize transfer properties of an oscillating system. A comparison of different AFCs has shown that the excitability of the brain depicts a clear alpha resonance during stage I, a pronounced delta resonance during stages II, III and IV, and a theta resonance during REM sleep. A comparison of these results from linear system theory with the nonlinear dynamical behavior of the CNS was performed.

Adult↗

PubMed1998

International migration destination forecast concerning the region "Lazio.".

Artificial Neural Networks (ANN) have been applied to different kinds of problems, when it was necessary to simulate and forecast how nonlinear dynamic complex systems worked since the mid 1980's. Currently, ANNs are proposed either as a substitute technique for database analysis or alternating with more traditional classical statistical analysis. This article presents the results of a statistical and a Neural Network analysis, applied to a sociological database in order to systematically explore how these models work, their applications, and both their strong and weak points.

Artificial Intelligence↗

PubMed2006

Evaluation of unsupervised semantic mapping of natural language with Leximancer concept mapping.

The Leximancer system is a relatively new method for transforming lexical co-occurrence information from natural language into semantic patterns in a nunsupervised manner. It employs two stages of co-occurrence information extraction-semantic and relational-using a different algorithm for each stage. The algorithms used are statistical, but they employ nonlinear dynamics and machine learning. This article is an attempt to validate the output of Leximancer, using a set of evaluation criteria taken from content analysis that are appropriate for knowledge discovery tasks.

Equipment Design↗

PubMed2000

Multiple oscillators provide metastability in rhythm generation.

Biological rhythms such as cardiac and circadian rhythms arise from activity of multiple oscillators with dispersed intrinsic frequencies. It has been proposed that a stable population rhythm, fundamental to normal physiological processes, can be achieved in these systems by synchronization, through mutual entrainment, of individual oscillators. Mutual entrainment, however, is unlikely to be the mechanism underlying the generation of a stable rhythm in a population of multiple weakly coupled or uncoupled oscillators. We have recently identified such a population that is involved in the sympathetic regulation of vascular tone in a thermoregulatory circulation. In this paper, we investigate the stability of the output rhythm of these sympathetic oscillators by subjecting the system to a periodic driving force (the lung inflation cycle-related activity). We show that a population rhythm coupled to the drive can remain stable over a much wider driving frequency range compared with that of any one of its constituent oscillators. This population rhythmicity still exists despite the fact that the dominant frequencies of individual oscillators are not necessarily 1:1 frequency-locked to the drive. We provide evidence to show that this population metastability is achieved through linear and nonlinear dynamic interactions between the driving force and single sympathetic oscillators. Our study suggests that the generation of a stable population rhythm can exist even in the absence of mutual entrainment of its constituents, and this allows the population to generate a stable and flexible patterned response.

Activity Cycles↗

PubMedDate not supplied

[Problems in estimating the dimensions of strange attractors in the analysis of biophysical data].

Basic algorithms of calculating the dimensions of strange attractors from experimental data are considered. A special emphasis is placed on difficulties arising when the methods of solution of the reverse nonlinear dynamic problem are used in the analysis of the behavior of biological systems. These difficulties are associated with a poor convergence and weak stability of estimated values as well as a low degree of statistical confidence. Factors that hamper the estimation of strange attractor dimensions with reasonable accuracy are discussed by the example of analysis of human electrocardiograms. A method for the statistcal estimation of dimensions of attractors is proposed based on multidimensional imitational modeling.

Algorithms↗

PubMed1997

[A comprehensive system for detecting ventricular fibrillation using various signal descriptors].

A novel comprehensive system based on artificial neural networks (ANN) for detecting ventricular fibrillation (VF) using various signal descriptors is proposed. First, by using time-, frequency-domain, and nonlinear dynamics analyses, different kinds of descriptors with different meanings are extracted from cardiac rhythmic signals, and then incorporated into the detection system and make decision automatically via the comprehensive ability of ANN. The detection performance of the system is tested by actual ECG database. Finally, its feasibility in clinical application is discussed.

Decision Making, Computer-Assisted↗

PubMed2000

[Evaluation of autonomic nervous function with heart rate variability and cardiovascular reflex tests in type II diabetes mellitus patients].

OBJECTIVE: To evaluate autonomic nervous function in simple diabetes mellitus patients, diabetic nephropathy(DN) patients and diabetes mellitus patients with accompanying coronary heart disease(DC) by studying heart rate variability (HRV) and cardiovascular reflex tests. METHODS: 57 type II diabetes mellitus patients were divided into 3 groups: 29 of simple diabetes mellitus, 17 of DC, and 11 of DN. The three groups were matched to 15 healthy controls for age, HRV and three cardiovascular reflex tests were performed in all the patients. RESULTS: The overall frequency of abnormal autonomic nervous function in 57 diabetes mellitus patients was 45.6%. All the diabetes mellitus groups especially the DN group were lower than a normal control group in time domain indexes and nonlinear dynamics indexes. As the patterns of R-R interval Poincare plots were concerned, the control group was mainly of comet-shaped pattern, the simple diabetes mellitus group was mainly of torpedo-shaped pattern, while the DN group and the DC group had more irregular patterns. CONCLUSION: Decrease in HRV is an early clinical marker for evolving diabetic autonomic neuropathy. This method may be helpful for evaluating organ dysfunction in diabetes mellitus patients.

Adult↗

PubMedDate not supplied

Usefulness of the Poincaré maps in detection of T-wave alternans in precordial leads of standard ECG--a comparison with the spectral method.

BACKGROUND: T-wave alternans (TWA) at microvolt level is considered as an important non-invasive risk factor for sudden death. Several methods are used to measure such repolarization variations, but each of them has some limitations. The purpose of our study is to assess the usefulness of Poincaré maps, a method based on nonlinear dynamics theory, in detection of repolarization abnormalities. MATERIAL AND METHODS: In 30 postinfarction patients presence of TWA in precordial ECG leads was assessed by the spectral method (SM) and by the Poincaré maps (PM). Quantitative measures of both methods: alternans voltage (AV) and alternans distance (AD) were compared using linear regression. RESULTS: Significant correlation between both measures (r = 0.92, p < 0.01) was found. The value of AD > or = 10 microV was accepted as significant for the presence of T-wave alternans. CONCLUSIONS: Poincaré mapping seems to be a useful and simple method for detection of TWA. The alternans distance equal or greater than 10 microV can be considered as a level determinative for the presence of TWA.

Adult↗

PubMed2002

[Predicting low NOx combustion property of a coal-fired boiler].

More attention was paid to the low NOx combustion property of the high capacity tangential firing boiler, but the NOx emission and unburned carbon content in fly ash of coal burned boiler were complicated, they were affected by many factors, such as coal character, boiler's load, air distribution, boiler style, burner style, furnace temperature, excess air ratio, pulverized coal fineness and the uniformity of the air and coal distribution, etc. In this paper, the NOx emission property and unburned carbon content in fly ash of a 600 MW utility tangentially firing coal burned boiler was experimentally investigated, and taking advantage of the nonlinear dynamics characteristics and self-learning characteristics of artificial neural network, an artificial neural network model on low NOx combustion property of the high capacity boiler was developed and verified. The results illustrated that such a model can predicate the NOx emission concentration and unburned carbon content under various operating conditions, if combined with the optimization algorithm, the operator can find the best operation condition of the low NOx combustion.

Carbon↗

PubMed2002

[Future scale and market capacity of urban water environmental infrastructure in China: a system dynamic model].

With the application of system dynamics, a dynamic, nonlinear model (SDMUWEIC) was developed in this paper in order to reflect the relationships of population, economic, resources and environment. Through a systematic procedure of model validation and uncertainty analysis, the model was applied for predicting and analyzing the future market capacity and constituents of urban water infrastructure. It illustrated the volumes and trends of potential capital market in construction, general mechanical equipments and water treatment instruments as well as their relevant influencing factors including water pricing and urbanization rate. Several different scenarios were further under test to reveal the sensitivity of different uncertain components.

Environment↗

PubMed2003

Parabolic bursting induced by veratridine in rat injured sciatic nerves.

A specific bursting, parabolic bursting induced by veratridine, has been observed in rat injured sciatic nerve. With the help of Plant model, the biophysical mechanism for such a phenomenon is revealed from the viewpoint of nonlinear dynamical theory. The slow sodium influx educed by veratridine and the calcium-dependent potassium outflux are regarded as the two slow variables, which are responsible for the parabolic bursting. Furthermore, the roles that veratridine plays in the emergence of the parabolic bursting, namely inhibiting the inactivation of sodium channels and eliciting the slow sodium influx, are clarified.

Animals↗

PubMed1992

Loss of 'complexity' and aging. Potential applications of fractals and chaos theory to senescence.

The concept of "complexity," derived from the field of nonlinear dynamics, can be adapted to measure the output of physiologic processes that generate highly variable fluctuations resembling "chaos." We review data suggesting that physiologic aging is associated with a generalized loss of such complexity in the dynamics of healthy organ system function and hypothesize that such loss of complexity leads to an impaired ability to adapt to physiologic stress. This hypothesis is supported by observations showing an age-related loss of complex variability in multiple physiologic processes including cardiovascular control, pulsatile hormone release, and electroencephalographic potentials. If further research supports this hypothesis, measures of complexity based on chaos theory and the related geometric concept of fractals may provide new ways to monitor senescence and test the efficacy of specific interventions to modify the age-related decline in adaptive capacity.

Aging↗

PubMed2004

Singular spectrum analysis applied to backscattered ultrasound signals from in vitro human cancellous bone specimens.

Mean scatterer spacing (MSS) holds particular promise for the detection of changes in quasiperiodic tissue microstructures such as may occur during development of disease in the liver, spleen, or bones. Many techniques that may be applied for MSS estimation (temporal and spectral autocorrelation, power spectrum and cepstrum, higher order statistics, and quadratic transformation) characterize signals that contain a mixture of periodic and nonperiodic contributions. In contrast, singular spectrum analysis (SSA), a method usually applied in nonlinear dynamics, first identifies components of signals corresponding to periodic structures and, second, identifies dominant periodicity. Thus, SSA may better separate periodic structures from nonperiodic structures and noise. Using an ultrasound echo simulation model, we previously demonstrated SSA's potential to identify MSS of structures in quasiperiodic scattering media. The current work aims to observe the behavior of MSS estimation by SSA using ultrasound measurements in phantom materials (two parallel, nylon-line phantoms and four foam phantoms of different densities). The SSA was able to estimate not only the nylon-line distances but also nylon-line thickness. The method also was sensitive to the average pore-size differences of the four sponges. The algorithms then were applied to characterize human cancellous bone microarchitectures. Using 1-MHz center-frequency, radio-frequency ultrasound signals, MSS was measured in 24 in vitro bone samples and ranged from 1.0 to 1.7 mm. The SSA MSS estimates correlate significantly to MSS measured independently from synchrotron microtomography, r2 = 0.68. Thus, application of SSA to backscattered ultrasound signals seems to be useful for providing information linked to tissue microarchitecture that is not evident from clinical images.

Aged↗

PubMed2004

How brain influences neuro-cardiovascular dysfunction.

Mechanisms that may explain the association between brain-heart connection leading to abnormal heart rate variability (HRV) and blood pressure variability (BVP) resulting into increased morbidity and mortality due to cardiovascular diseases (CVD), are reviewed. Medline search till December, 2001 and articles published in various national and international journals were reviewed. Experts working in the field were also consulted. There is compelling evidence that saturated and total fat and sedentary behaviour can enhance sympathetic activity and increase the secretion of catecholamine, cortisol and serotonin, whereas omega-3 fatty acid supplementation may enhance parasympathetic activity and increase the secretion of acetylcholine in the hippocampus. While increased sympathetic activity has adverse effects on HRV and BPV, increased parasympathetic activity has beneficial effects and can directly inhibit sympathetic tone. A large body of evidence is available demonstrating that abnormal HRV measured over a 24-hour period, or for 7 days, provides information on the risk of subsequent death in subjects with and without heart disease. Meditation, beta blockers, ACE inhibitors, n-3 fatty acids, trimetazidine and oestrogen may have a beneficial influence on HRV. However, no definite and specific therapy is currently available to improve the prognosis for patients with abnormal HRV and blood pressure variability (BPV). Low HRV has been most commonly associated with a risk of arrhythmias and arrhythmic death, unstable angina, myocardial infarction, progression of heart failure and atherosclerosis. There is a need to develop a consensus on the measure of HRV for clinical purposes and whether 7-day record is necessary and practical. New analysis methods based on nonlinear dynamics may be more useful in risk stratification. More precise insight into the patho-physiological link between HRV and nutrition may be applied to clinical practice and used to direct therapy for prevention of disease risk.

Autonomic Nervous System↗

PubMedDate not supplied

[National Re-survey of Arterial Hypertension (RENAHTA). Mexican consolidation of the cardiovascular risk factors. national follow-up cohort].

OBJECTIVE: Based on a National Re-survey on Hypertension (HTA) and other cardiovascular risk factors performed in Mexico during 2003 and 2004 in the adult population with HTA, as identified in the 2000 National Survey of Health, this study was planed to determine: 1) morbidity and mortality rates; 2) the incidence and interrelation with other risk factors, such as overweight, obesity, dyslipidemia, nephropathy and diabetes; 3) the main risk factors associated to HTA involved in its complications, need for hospitalization and number of days; and, 4) the degree of therapeutical adhesion and the type of antihypertensive drugs used. METHODS: The survey was of type III using the step by step method described by WHO. Sampling was weighed a priori taking into account a national prevalence average of HTA of 30.05% and its corresponding rate for each federal state. Permissible maximum error in the estimation = 0.28. Effect of design = 4.5; and, Rate of awaited answer (0.70). RESULTS: From the initial 14,567 interviewed patients, 1,165 (8%) subjects were considered non-hypertensive or false positives at the 2000 survey. From the 13,402 remaining patients, 335 died during the first 2 years of pursuit, which implies an annual mortality of approximately 1.15% in the hypertensive population. Thus, 13,067 survivors were subjected to the final analysis. The mean age at the re-survey was 45.6 +/- 12.6; 40.5% were men (n = 5,295). There was a statistically significant difference in height, but not in weight between both genders. The control HTA was raised 14.6% in the year 2000 and 19.2% in 2004. The prevalence of diabetes was duplicated from 16% to 30% (< .001). Fifty four percent of the whole population required hospitalization at least once during the period of study. The rates of overweight, obesity, and dyslipidemia rose significantly (p < 0.05) independently from age, federal state, and gender. CONCLUSION: RENAHTA shows the impact of hypertension on the morbidity and mortality during the 3.1 +/- 1.5 years of follow-up in Mexico. It alerts us on the need to reinforce the strategies of attention and prevention of this crucial risk factor and of screening the dynamic nonlinear interaction between the main cardiovascular risk factors in Mexico. New hypotheses are proposed for the metabolic syndrome.

Adult↗

PubMed2005

The psychophysics of tactile amplitude summation: a test of the nGamma nonlinear model.

This research applied Gregson's n Gamma nonlinear model (Gregson 1988, 1992, 1995, 1998) to the process of tactile amplitude summation. Participants were presented with simultaneous pairs of vibrations and rated the total perceived intensity of the resultant percept as both the amplitude of the stimuli and their spatial separations were manipulated. The multidimensional response surface for each participant was then compared with that predicted by the 2 Gamma Case 2 model. While the fit between data and theory was strong in all cases (mean r triangle up 2 = .86), analysis of residuals revealed evidence of a second nonlinear process. In contrast, a multivariate version of the psychophysical function was found to account for a substantially smaller proportion of the variability in the data (mean r triangle up 2 = .67). The results confirmed that summative effects similar to those observed in other modalities occur in the tactile modality, and provide an initial demonstration that the mathematics of nonlinear dynamics may help to explain the processing of tactile patterns.

Forecasting↗