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Results for “nonlinear analyses”

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PubMed1985

Application of 7-amino-actinomycin D for the fluorescence microscopical analysis of DNA in cells and polytene chromosomes.

The cytochemical properties of a guanine-specific synthetic fluorescent analogue of actinomycin D, 7-amino-actinomycin D, have been studied in fixed and living preparations of L cells and polytene chromosomes of salivary glands of Chironomus thummi thummi and Drosophila lummei (Hackman). 7-Amino-actinomycin D has been shown to bind to DNA-containing structures, thereby inducing in them a bright red fluorescence. No specific fluorescence has been found in RNA-containing structures treated with this fluorescent probe. The fluorescence pattern of some regions of polytene chromosomes with a known nucleotide composition was analysed. It has been established that 7-amino-actinomycin D induces a very weak fluorescence in GC-poor chromosome regions of the Drosophila lummei toromere structure. Data indicating a nonlinear dependence between the fluorescence intensity of a stained chromosome region and the GC content in its DNA have been obtained. The influence of DNA nucleotide composition in a chromosome region on the fluorescence of 7-amino-actinomycin D is discussed. In combination with quinacrine staining and the Feulgen fluorescence reaction, treatment with 7-amino-actinomycin D provides useful information about the distribution of GC base pairs in the chromosome region under study.

Animals↗

PubMed2004

A biomechanical study of lumbar spondylolysis based on a three-dimensional finite element method.

Biomechanical analyses under compression only, and for a combination of flexion, extension, rotation, and lateral bending were performed to evaluate the stress of the interarticular portion of the lumbar vertebra using a nonlinear three-dimensional finite element method. A detailed three-dimensional L4-L5 motion segment model was developed that took into consideration the material nonlinearities of ligaments and annular fibers and the contact nonlinearities of facet joints. For a more accurate examination, the separation of cortical bone and cancellous bone for both posterior and anterior elements were also considered. The stress in the pars interarticularis was weakest under compression alone, but stronger under compression with lateral bending loading, with flexion, with rotation, and with extension. Under each loading condition, the region of the stress concentration was consistent with the separated region of the spondylolysis observed in clinical situations. Since the stress in the pars interarticularis was high under extension and rotation in particular, those loadings were suggested to be relatively high risk factors leading to spondylolysis.

Compressive Strength↗

PubMed2002

Effortful control: factor structure and relation to externalizing and internalizing behaviors.

Effortful control, a temperamentally based ability to inhibit a dominant response and activate a subdominant response, was assessed on 3 occasions using a comprehensive, age-appropriate behavioral battery in this 4-year longitudinal study of children (N = 103) from toddlerhood to early school age. The focus was twofold: to explore the structure of effortful control in a normally developing sample and to examine the relations between effortful control and adaptive functioning. Exploratory factor analyses supported the contention that effortful control is a complex, multidimensional construct with longitudinally stable factors. Effortful control was also significantly associated with mother-reported total behavior problems in a nonlinear fashion, with lower and higher levels of effortful control contributing to higher total problem scores. These findings have implications for the assessment of temperament in children and, most importantly, for the study of nonlinear contributions of temperament to early childhood behaviors.

Adaptation, Psychological↗

PubMed2005

Human cognition and a pile of sand: a discussion on serial correlations and self-organized criticality.

Recently, G. C. Van Orden, J. G. Holden, and M. T. Turvey (2003) proposed to abandon the conventional framework of cognitive psychology in favor of the framework of nonlinear dynamical systems theory. Van Orden et al. presented evidence that "purposive behavior originates in self-organized criticality" (p. 333). Here, the authors show that Van Orden et al.'s analyses do not test their hypotheses. Further, the authors argue that a confirmation of Van Orden et al.'s hypotheses would not have constituted firm evidence in support of their framework. Finally, the absence of a specific model for how self-organized criticality produces the observed behavior makes it very difficult to derive testable predictions. The authors conclude that the proposed paradigm shift is presently unwarranted.

Cognition↗

PubMed2002

Quantitative evaluation of altered hepatic spaces and membrane transport in fibrotic rat liver.

Four animal models were used to quantitatively evaluate hepatic alterations in this study: (1) a carbon tetrachloride control group (phenobarbital treatment only), (2) a CCl(4)-treated group (phenobarbital with CCl(4) treatment), (3) an alcohol-treated group (liquid diet with alcohol treatment), and (4) a pair-fed alcohol control group (liquid diet only). At the end of induction, single-pass perfused livers were used to conduct multiple indicator dilution (MID) studies. Hepatic spaces (vascular space, extravascular albumin space, extravascular sucrose space, and cellular distribution volume) and water hepatocyte permeability/surface area product were estimated from nonlinear regression of outflow concentration versus time profile data. The hepatic extraction ratio of (3)H-taurocholate was determined by the nonparametric moments method. Livers were then dissected for histopathologic analyses (e.g., fibrosis index, number of fenestrae). In these 4 models, CCl(4)-treated rats were found to have the smallest vascular space, extravascular albumin space, (3)H-taurocholate extraction, and water hepatocyte permeability/surface area product but the largest extravascular sucrose space and cellular distribution volume. In addition, a linear relationship was found to exist between histopathologic analyses (fibrosis index or number of fenestrae) and hepatic spaces. The hepatic extraction ratio of (3)H-taurocholate and water hepatocyte permeability/surface area product also correlated to the severity of fibrosis as defined by the fibrosis index. In conclusion, the multiple indicator dilution data obtained from the in situ perfused rat liver can be directly related to histopathologic analyses.

Albumins↗

PubMedDate not supplied

Wall stress as a possible mechanism for the development of transverse intimal tears in aortic dissections.

In aortic dissection intimal tear develops in a transverse direction. Since dissection is associated with the aneurysm of the aorta, its mechanism was investigated by analysing the pressure induced wall stress as a function of 'growth' of the aneurysm. The stresses were determined using a finite element analysis where the aorta was modelled as an isotropic, nonlinear, hyperelastic material. Growth of the aneurysm was simulated by dilating an aortic segment in increments of 10% of the initial diameter. At each dilation luminal pressure of 120 mm Hg was applied and stress determined. In the aneurysm bulb, longitudinal stress increased significantly as the bulb became larger, while circumferential stress changed only a little. In the undilated segment both the longitudinal and circumferential stresses remained relatively unchanged. The increase in the longitudinal stress in the bulb occurred primarily due to change in shape of the aorta from cylindrical to ellipsoidal to spherical. Hence, as the aneurysm 'grows', the longitudinal stress in the bulb increases rapidly and could be responsible for the transverse tear in the aortic dissection.

Aortic Dissection↗

PubMed2000

Spontaneous pattern formation in driven nonlinear lattices

We demonstrate the spontaneous formation of spatial patterns in a damped, ac-driven cubic Klein-Gordon lattice. These patterns are composed of arrays of intrinsic localized modes characteristic for nonlinear lattices. We analyze the modulation instability leading to this spontaneous pattern formation. Our calculation of the modulational instability is applicable in one- and two-dimensional lattices; however, in the analyses of the emerging patterns we concentrate particularly on the two-dimensional case.

Journal Article↗

PubMed2002

Population pharmacokinetic-pharmacodynamic modelling of angiotensin receptor blockade in healthy volunteers.

OBJECTIVE: To compare the pharmacokinetic and pharmacodynamic characteristics of angiotensin II receptor antagonists as a therapeutic class. DESIGN: Population pharmacokinetic-pharmacodynamic modelling study. METHODS: The data of 14 phase I studies with 10 different drugs were analysed. A common population pharmacokinetic model (two compartments, mixed zero- and first-order absorption, two metabolite compartments) was applied to the 2685 drug and 900 metabolite concentration measurements. A standard nonlinear mixed effect modelling approach was used to estimate the drug-specific parameters and their variabilities. Similarly, a pharmacodynamic model was applied to the 7360 effect measurements, i.e. the decrease of peak blood pressure response to intravenous angiotensin challenge recorded by finger photoplethysmography. The concentration of drug and metabolite in an effect compartment was assumed to translate into receptor blockade [maximum effect (Emax) model with first-order link]. RESULTS: A general pharmacokinetic-pharmacodynamic (PK-PD) model for angiotensin antagonism in healthy individuals was successfully built up for the 10 drugs studied. Representatives of this class share different pharmacokinetic and pharmacodynamic profiles. Their effects on blood pressure are dose-dependent, but the time course of the effect varies between the drugs. CONCLUSIONS: The characterisation of PK-PD relationships for these drugs gives the opportunity to optimise therapeutic regimens and to suggest dosage adjustments in specific conditions. Such a model can be used to further refine the use of this class of drugs.

Angiotensin Receptor Antagonists↗

PubMed1999

Differences among heart rate variability measures after anesthesia and cardiac surgery.

OBJECTIVE: To determine whether there are differences among measures of heart rate variability (HRV; traditional and nonlinear) after anesthesia and cardiac surgery. DESIGN: Prospective. SETTING: University hospital. PARTICIPANTS: Patients scheduled for cardiac surgery. INTERVENTIONS: None. Medical management was not varied as part of this study. MEASUREMENTS AND MAIN RESULTS: HRV was measured in 13 patients from electrocardiograms (ECGs) recorded before anesthesia, during anesthesia but before cardiac surgery, and on the first postoperative day. Anesthesia was induced with moderate-dose fentanyl. For each ECG, HRV was measured from series of 400 heartbeat intervals using standard deviation (SD), approximate entropy (ApEn), and point correlation dimension (PD2). Multivariate repeated-measures analyses of variance on ranks and Spearman correlations were performed. All HRV measures decreased significantly with anesthesia. Postoperatively, ApEn recovered to original values. PD2 and SD did not recover with consciousness and were significantly less than original values. Correlations among ApEn, PD2, and SD were weak. CONCLUSIONS: Nonlinear measures of HRV differ among themselves after anesthesia and cardiac surgery. The use of multiple nonlinear and traditional measures may improve the effectiveness of using HRV to assess the cardiovascular system.

Anesthesia↗

PubMed1983

Structured exploratory data analysis (SEDA) of finger ridge-count inheritance: II. Association arrays in parent-offspring and sib-sib pairs.

Familial similarity of the dermatoglyphic trait values of finger ridge-count scores and pattern intensity index is examined for 125 nuclear families from the Velanadu Brahmin population of Southern India by the method of association arrays. This methodology assesses parent-offspring and sibship similarity through a collection of measures of dependence that is sensitive to a variety of nonlinear trends and stochastic relationships between trait values. The method is used in conjunction with various weights to determine the relationship between family size and the level and form of dependence. These analyses reveal that siblings are most strongly associated for ridge-counts of the middle digit and less associated for the thumb and fifth digit ridge-counts. Further, sibship similarity for ridge-counts increases with family size for the thumb and fifth digit but remains relatively constant over all family sizes for the middle finger. Family size effects are also observed for total ridge-counts of the left hand, right hand, and both hands combined, and for the pattern intensity index. These effects of family size may be due to the most pronounced changes occurring in the amniotic environment between the first and second pregnancy, which are most strongly manifested in the sibship associations of smaller families.

Dermatoglyphics↗

PubMed1993

A neural network approach to the classification of autism.

A nonlinear pattern recognition system, neural network technology, was explored for its utility in assisting in the classification of autism. It was compared with a more traditional approach, simultaneous and stepwise linear discriminant analyses, in terms of the ability of each methodology to both classify and predict persons as having autism or mental retardation based on information obtained from a new structured parent interview: the Autistic Behavior Interview. The neural network methodology was superior to discriminant function analysis both in its ability to classify groups (92 vs. 85%) and to generalize to new cases that were not part of the training sample (92 vs. 82%). Interrater and test-retest reliabilities and measures of internal consistency were satisfactory for most of the subscales in the Autistic Behavior Interview. The implications of neural network technology for diagnosis, in general, and for understanding of possible core deficits in autism are discussed.

Adolescent↗

PubMed1992

Dynamic control of breathing during exercise and hypercapnia.

The dynamic influences of end-tidal CO2 and exercise on ventilation are compared when CO2 and exercise are imposed separately and when they are imposed simultaneously. Five human subjects are studied. The subjects performed three trials: random work rate forcing, random CO2 inhalation and their simultaneous loading. The work rate was varied between 20 and 80 W as a pseudorandom binary sequence. The concentration of inspired CO2 was varied randomly between 0 and 7 per cent, adjusted so that it produced approximately the same amount of ventilatory fluctuations as the random work load. The relative contribution of each variable was analysed using multivariate autoregressive analysis at frequencies ranging from 0.1 to 1 cycle min-1. The results show that the dynamics of the response to CO2 inhalation, exercise and their combination are nonlinear and that the combination of CO2 inhalation and exercise magnifies the nonlinear behaviour. Ventilation is largely unaffected by either work rate or end-tidal CO2 at 1 cycle min-1. During simultaneous CO2 and work rate forcing, ventilation tends to follow the change in the end-tidal CO2.

Adult↗

PubMed1974

A dynamical model for human population.

We analyze a simple, deterministic model of the dynamics of population changes in a bisexual, reproductive system based on marriage. Our model is one of a general class, special cases of which have been previously discussed within the framework of population biology by D. G. Kendall, L. A. Goodman, J. H. Pollard, and others. Here, we extend and complete previous analyses of systems characterized by first-degree homogeneous, unbounded marriage functions, allowing for arbitrary birth and death rates. The dynamics of the model is determined by three coupled first-order, nonlinear differential equations, similar to those used in the description of chemical reactions and of radioactive decay chains. Solutions of the differential equation system are classified according to the associated patterns of birth and death rates of the two sexes, and growth and stability properties are discussed. This preliminary report gives conditions sufficient to insure the existence of a unique, exponential mode of population growth or decay, with a finite ratio of the sexes. We also exhibit other conditions which, in contrast to the standard, linear demographic analysis of Lotka, guarantee that the sex ratio asymptotically becomes infinite. The model manifests a delicate balance between the vital parameters that alerts one to the possibility of selfaggravating distortions of the sex ratio, once a monogamous society's fertility falls below the replacement value.

Birth Rate↗

PubMed1992

The regulation of immunological responses to parasitic infections and the development of tolerance.

It is well established that specific unresponsiveness to immunization can be induced by prolonged exposure to antigenic proteins. More generally, many parasitic infections, such as the helminth worms and the Leishmania parasites, appear to be able to persist in some of their human hosts over long periods of time, via what appears to be an ability to induce defective or inappropriate T-cell responses (= tolerance). Recent research has suggested that cytokines, produced by specific subsets of CD4+ T-cells (characterized by cytokine secretory profiles and growth properties), have an important, and often complex, role in promoting or inhibiting host protective immunity to parasitic infections. By examination of the population dynamics of the stimulation and regulation of cellular responses to infection, via the use of simple mathematical models, we show that nonlinear interactions between CD4+ T-cell subsets and their secreted cytokines can result in either host protection or immunological unresponsiveness, depending on the magnitude and duration of exposure to parasitic infection. Analyses also identify a possible mechanism to explain the stimulation of two separate peaks of enhanced T-cell-mediated responses over a wide range of levels of antigenic exposure.

Animals↗

PubMed2005

Tracking butterfly flight paths across the landscape with harmonic radar.

For the first time, the flight paths of five butterfly species were successfully tracked using harmonic radar within an agricultural landscape. Until now, butterfly mobility has been predominantly studied using visual observations and mark-recapture experiments. Attachment of a light-weight radar transponder to the butterfly's thorax did not significantly affect behaviour or mobility. Tracks were analysed for straightness, duration, displacement, ground speed, foraging and the influence of linear landscape features on flight direction. Two main styles of track were identified: (A) fast linear flight and (B) slower nonlinear flights involving a period of foraging and/or looped sections of flight. These loops potentially perform an orientation function, and were often associated with areas of forage. In the absence of forage, linear features did not provide a guiding effect on flight direction, and only dense treelines were perceived as barriers. The results provide tentative support for non-random dispersal and a perceptual range of 100-200 m for these species. This study has demonstrated a methodology of significant value for future investigation of butterfly mobility and dispersal.

Animals↗

PubMed2006

Pharmacokinetic modelling of the interaction between St John's wort and ciclosporin A.

AIMS: St John's wort (SJW) decreases the blood concentration of ciclosporin A (CsA), which may result in allograft rejection. In addition, the time course of this interaction is not parallel with the administration of SJW. We aimed to develop a pharmacokinetic model to predict the time profile of blood CsA concentrations during and after the intake of SJW. METHODS: We developed a pharmacokinetic model incorporating turnover of detoxicating proteins, with the assumption that the amount of detoxicating proteins is in inverse proportion to the ratio of trough blood concentration to daily dose (C/D ratio) of CsA. First, we collected time profiles of blood CsA during and after the intake of SJW from the literature. Next, we analysed the relationship between D/C ratio and the daily dose of SJW at steady state. Subsequently, the developed model was simultaneously fitted to the time profiles of C/D ratios by using a nonlinear least-squares method to obtain model parameters. RESULTS: The model analysis revealed that the induction of the detoxicating proteins by SJW was saturable with an elimination rate constant of the detoxicating proteins (ke) of 4.72 month(-1). Elimination half-life of the detoxicating proteins calculated from the ke value was 4.4 days, suggesting that the dose of CsA should be carefully monitored for up to 2 weeks after the cessation of SJW intake. CONCLUSIONS: The present model may provide additional information for use in identifying optimal dosage regimens of CsA during and after the intake of SJW to prevent an adverse drug interaction between CsA and SJW.

Cyclosporine↗

PubMed2004

Photoinduction of surface-relief gratings during all-optical poling of polymer films.

Using the all-optical poling method, we observed the formation of a surface-relief grating (SRG) in an amorphous polymer film containing azo dye molecules in side chain positions. The experiment consists of a seeding-type process. We used a recently described experimental setup that permits a periodic nonlinear pattern to be produced by the index dispersion of glass. The particular configuration permits photoinduced translation diffusion of the azo chromophores to be observed as the origin of the SRG formation. Analyses of the gratings recorded by use of s (TE) and p (TM) polarization of the writing beams are conducted by atomic-force microscopy. The effect is attributed to mass transport from regions of high isomerization activity to regions of lower activity.

Journal Article↗

PubMed1986

Toxicokinetics of caffeine elimination in an infant.

The kinetics of caffeine elimination were followed in a ten month old female acutely intoxicated on a street form of the drug. Urine drug screening by gas chromatography-mass spectrometry also showed the presence of ephedrine, phenylpropanolamine, caffeine, theophylline and theobromine. Blood analyses using high pressure liquid chromatography gave evidence for the presence of theobromine, theophylline, caffeine and 1,7-dimethylxanthine. Sequentially taken blood samples determined that the initial stage of caffeine elimination was nonlinear. The Vmax = 27.6 micrograms/ml/hr and Km = 284.6 micrograms/ml. At a plasma level of approximately 30 micrograms/ml the elimination became first order with ke = 0.097 hr-1 and t 1/2 = 7.1 hr. The metabolic generation of theophylline and its elimination were also studied. Theophylline ke = 0.069 hr-1 and t 1/2 = 10.0 hr. Elimination of both drugs was anomalously long for a child of this age.

Caffeine↗