Nonlinear Analysis (nonlinear + analysis)

Distribution by Scientific Domains


Selected Abstracts


Sometimes Higher Heart Rate Variability Is Not Better Heart Rate Variability: Results of Graphical and Nonlinear Analyses

JOURNAL OF CARDIOVASCULAR ELECTROPHYSIOLOGY, Issue 9 2005
PHYLLIS K. STEIN Ph.D.
Objective: To determine the prevalence and effect on traditional heart rate variability (HRV) indices of abnormal HRV patterns in the elderly. Methods: Hourly Poincaré plots and plots of spectral HRV from normal-to-normal interbeat intervals and hourly nonlinear HRV values were examined in a subset of 290 consecutive participants in the Cardiovascular Health Study. Only subjects in normal sinus rhythm with ,18 hours of usable data were included. Eligible subjects were 71 ± 5 years. During 7 years of follow-up, 21.7% had died. Hours were scored as normal (0), borderline (0.5), or abnormal (1) from a combination of plot appearance and HRV. Summed scores were normalized to 100% to create an abnormality score (ABN). Short-term HRV versus each 5th percentile of ABN was plotted and a cutpoint for markedly increased HRV identified. The t -tests compared HRV for subjects above and below this cutpoint. Cox regression evaluated the association of ABN and mortality. Results: Of 5,815 eligible hourly plots, 64.4% were normal, 14.5% borderline, and 21.1% abnormal. HR, SDNN, SDNNIDX, ln VLF and LF power, and power law slope did not differ by the cutpoint for increased short-term HRV, while SDANN and ln ULF power were significantly lower for those above the cutpoint. However, many HRV indices including LF/HF ratio and normalized LF and HF power were significantly different between groups (P < 0.001). Increased ABN was significantly associated with mortality (P = 0.019). Despite similar values for many HRV indices, being in the group above the cutpoint was significantly associated with mortality (P = 0.04). Conclusions: Abnormal HR patterns that elevate many HRV indices are prevalent among the elderly and associated with higher risk of mortality. Consideration of abnormal HRV may improve HRV-based risk stratification. [source]


Usefulness of Nonlinear Analysis of ECG Signals for Prediction of Inducibility of Sustained Ventricular Tachycardia by Programmed Ventricular Stimulation in Patients with Complex Spontaneous Ventricular Arrhythmias

ANNALS OF NONINVASIVE ELECTROCARDIOLOGY, Issue 3 2008
Ornella Durin M.D.
Introduction: The aim of our study was to assess the effectiveness of the nonlinear analysis (NLA) of ECG in predicting the results of invasive electrophysiologic study (EPS) in patients with ventricular arrhythmias. Methods: We evaluated 25 patients with history of cardiac arrest, syncope, sustained, or nonsustained ventricular tachycardia (VT). All patients underwent electrophysiologic study (EPS) and nonlinear analysis (NLA) of ECG. The study group was compared with a control group of 25 healthy subjects, in order to define the normal range of NLA. ECG was processed in order to obtain numerical values, which were analyzed by nonlinear mathematical functions. Patients were classified through the application of a clustering procedure to the whole set of functions, and the correlation between the results of nonlinear analysis of ECG and EPS was tested. Results: NLA assigned all patients with negative EPS to the same class of healthy subjects, whereas the patients in whom VT was inducible had been correctly and clearly isolated into a separate cluster. In our study, the result of NLA with application of the clustering technique was significantly correlated to that of EPS (P < 0.001), and was able to predict the result of EPS, with a negative predictive value of 100% and a positive predictive value of 100%. Conclusions: NLA can predict the results of EPS with good negative and positive predictive value. However, further studies are needed in order to verify the usefulness of this noninvasive tool for sudden death risk stratification in patients with ventricular arrhythmias. [source]


Nonlinear Analysis of Heart Rate Variability: Fractal and Complexity Measures of Heart Rate Behavior

ANNALS OF NONINVASIVE ELECTROCARDIOLOGY, Issue 2 2000
Juha S. Perkiömäki M.D.
Many new methods of analyzing heart rate (HR) variability have been developed to describe the features in HR behavior that cannot be detected by traditional time- and frequency-domain methods. Some of the new methods, such as analysis of fractal correlation properties and complexity of HR dynamics, have provided clinically useful information in various patient populations. Importantly, some fractal analysis methods are better risk predictors of mortality than traditional HR variability measures, and analysis of complexity of HR dynamics has been shown to predict the spontaneous onset of atrial fibrillation. New analysis methods based on nonlinear dynamics are a promising tool for better understanding of normal and abnormal HR behavior. More work will be needed to establish the clinical applicability of traditional and new analysis methods of HR variability. [source]


Six-week postpartum maternal depressive symptoms and 4-month mother,infant self- and interactive contingency,

INFANT MENTAL HEALTH JOURNAL, Issue 5 2008
Beatrice Beebe
Associations of 6-week maternal depressive symptoms [Center for Epidemiological Studies Depression Scale (CES-D)] with 4-month mother,infant self- and interactive contingency patterns during face-to-face play were investigated in 132 dyads. Self- and interactive contingency (auto- and lagged cross-correlation, respectively) were assessed by multilevel time-series analysis. Infant and mother gaze, facial and vocal affect, touch, and spatial orientation behaviors were coded second-by-second from split-screen videotape, and a multimodal measure of facial,visual "engagement" was constructed, generating nine modality pairings. With higher CES-D, the self-contingency of both partners was lowered in most modalities. With higher CES-D, interactive contingency values were both heightened (in some modalities) and lowered (in others), varying by partner. These results are consistent with an optimal midrange model. With higher CES-D, interactive contingency showed the following patterns: (a) Mothers and their infants had a reciprocal orientational sensitivity; (b) mothers and infants manifested a reciprocal intermodal discordance in attention versus affect coordination, lowering gaze coordination, but heightening affective coordination; (c) infants heightened, but mothers lowered, touch coordination with partner touch,an "infant approach,mother withdraw" touch pattern. Nonlinear analyses indicated that altered self- and interactive contingency were similar at both the low ("denial") as well as the high ("endorsement") poles of depressive symptoms, in half the findings. These complex, multimodal findings define different aspects of communication disturbance, with relevance for therapeutic intervention. [source]


Temporal Patterns of Atrial Arrhythmia Recurrences in Patients with Implantable Defibrillators: Implications for Assessing Antiarrhythmic Therapies

JOURNAL OF CARDIOVASCULAR ELECTROPHYSIOLOGY, Issue 4 2002
LINA A. SHEHADEH M.S.
Temporal Patterns of Atrial Arrhythmias.Introduction: The statistical measures commonly used to assess therapies for recurrent atrial arrhythmias (such as time to first recurrence) often assume a uniformly random pattern of arrhythmic events over time. However, the true temporal pattern of atrial arrhythmia recurrences is unknown. The aim of this study was to use linear and nonlinear analyses to characterize the temporal pattern of atrial arrhythmia recurrences in patients with implantable cardioverter defibrillators. Methods and Results: The time and date of atrial tachyarrhythmias recorded in 65 patients with combined atrial and ventricular defibrillators were used to construct a probability density function (PDF) and a model of a Poisson distribution of arrhythmic events for each patient. Average patient age was 66 ± 10 years and follow-up was 7.8 ± 4.8 months. A total of 10,759 episodes of atrial tachyarrhythmias were analyzed (range 43 to 618 episodes per patient). The PDF fit a power law distribution for all 65 patients, with an average r2= 0.89 ± 0.08. The PDF distribution differed significantly from the model Poisson distribution in 47 of 65 patients (P = 0.0002). Differences from the Poisson distribution were noted for patients both taking (30/43 patients; P < 0.015) and not taking (17/22 patients; P < 0.017) antiarrhythmic drugs. Median time between atrial arrhythmia detections for all 65 patients was 10.8 minutes. Conclusion: In implantable cardioverter defibrillator patients, the temporal pattern of frequent recurrences of atrial tachyarrhythmias usually is characterized by a power law distribution. The unique statistical properties of this type of distribution should be considered in designing outcome measures for treatment of atrial tachyarrhythmias. [source]


Finite element analysis of plain weave composites for flexural failure

POLYMER COMPOSITES, Issue 4 2010
Ömer Soykasap
This article presents finite element analysis for flexural behavior of woven composites considering the fiber and the matrix and their interactions. Finite element model using Abaqus program is developed to predict the homogenized properties of plain-weave T300/LTM45 composite. Initially, curved beam elements are used to model each resin-infiltrated fiber bundle. Geometrically, nonlinear analyses of the model with periodic boundary conditions are carried out to obtain effective in-plane and bending properties of the composite. Statistical analysis is presented to study the stiffness variability. The flexural failure of a single-ply composite is estimated based on the homogenized material properties, and is compared with previously published data. The model is able to correct the significant errors in the stiffnesses of the composite and captures the failure behavior accurately. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers [source]


Influence of Semi-Rigid Connections and Local Joint Damage on Progressive Collapse of Steel Frameworks

COMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 3 2010
Yuxin Liu
This article extends the threat-independent method for progressive-failure analysis of rigid frames to analysis accounting for semi-rigid connections. The influence of joint damage caused by disengagement of member(s) is also considered in the analysis, and the degree of damage is modeled by a health index. A compound element model is employed to include the contributions of nonlinear behavior of beam-to-column connections, connection and member-end damage, member inelasticity, member shear deformation, and geometrical nonlinearity to structural response. Four beam collapse modes are illustrated for the progressive collapse analysis associated with debris loading generated when disengaged structural components fall onto lower parts of the structure. The impact effect is taken into account for the quasi-static nonlinear analysis by utilizing an impact amplification factor according to GSA and DoD guidelines. Any progressive collapse occurring thereafter involves a series of collapse events associated with topological changes of the frame. The analysis procedure is illustrated for the progressive collapse behavior of two planar steel frames. The results demonstrate that the proposed method is potentially an effective tool for the progressive collapse analysis of semi-rigid steel frames under abnormal loading events. [source]


Case studies of damage to 19-storey irregular steel moment-frame buildings under near-source ground motion

EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 7 2007
Swaminathan Krishnan
Abstract This paper describes the three-dimensional nonlinear analysis of six 19-storey steel moment-frame buildings, designed per the 1997 Uniform Building Code, under strong ground motion records from near-source earthquakes with magnitudes in the range of 6.7,7.3. Three of these buildings possess a reentrant corner irregularity, while the remaining three possess a torsional plan irregularity. The records create drift demands of the order of 0.05 and plastic rotation demands of the order of 4,5% of a radian in the buildings with reentrant corners. These values point to performance at or near ,Collapse Prevention'. Twisting in the torsionally sensitive buildings causes the plastic rotations on the moment frame on one face of the building (4,5% of a radian) to be as high as twice of that on the opposite face (2,3% of a radian). The asymmetric yield pattern implies a lower redundancy in the lateral force-resisting system as the failure of the heavily loaded frame could result in a total loss of resistance to torsion. Copyright © 2006 John Wiley & Sons, Ltd. [source]


Generation of spatially nonuniform ground motion for nonlinear analysis of a concrete arch dam

EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 11 2006
S. W. Alves
Abstract An accelerometer array at Pacoima Dam with three locations along the base and abutments recorded ground motion from a magnitude 4.3 earthquake on 13 January 2001. These records present an opportunity to study spatial nonuniformity for the motion in a canyon. Topographic amplification is characterized by ratios of response spectral displacement between locations, and seismic wave travel times are studied using cross-correlation functions to obtain delays. Results of the analysis of the 2001 earthquake records are used to generate ground motion for the 1994 Northridge earthquake to replace records that were not able to be fully digitized. The ground motion generated for the Northridge earthquake is used as input to a finite element model of Pacoima Dam. The response of the model is consistent with observations of Pacoima Dam after the Northridge earthquake. Comparison of the response due to nonuniform input with the response due to uniform input demonstrates the importance of accounting for spatial nonuniformity because of the significance that the pseudostatic component has for the response to nonuniform input. Copyright © 2006 John Wiley & Sons, Ltd. [source]


Multi-dimensional combustion waves for Lewis number close to one

MATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 3 2007
A. Ducrot
Abstract This paper is devoted to the study of multi-dimensional travelling wave solution for a thermo-diffusive model, describing the propagation of curved flames in an infinite cylinder. The linear dependence of the components of the reaction rate together with the existence of an ignition temperature ensure that the corresponding linearized operator does not satisfy the Fredholm property. A direct consequence is that solvability conditions for the linearized operator are not known and classical methods of nonlinear analysis cannot be directly applied. We prove in this paper existence results of such travelling waves, by first introducing a suitable re-formulation of the equations and then by choosing suitable weighted spaces that allows us to move the essential spectrum away from zero. Copyright © 2006 John Wiley & Sons, Ltd. [source]


Usefulness of Nonlinear Analysis of ECG Signals for Prediction of Inducibility of Sustained Ventricular Tachycardia by Programmed Ventricular Stimulation in Patients with Complex Spontaneous Ventricular Arrhythmias

ANNALS OF NONINVASIVE ELECTROCARDIOLOGY, Issue 3 2008
Ornella Durin M.D.
Introduction: The aim of our study was to assess the effectiveness of the nonlinear analysis (NLA) of ECG in predicting the results of invasive electrophysiologic study (EPS) in patients with ventricular arrhythmias. Methods: We evaluated 25 patients with history of cardiac arrest, syncope, sustained, or nonsustained ventricular tachycardia (VT). All patients underwent electrophysiologic study (EPS) and nonlinear analysis (NLA) of ECG. The study group was compared with a control group of 25 healthy subjects, in order to define the normal range of NLA. ECG was processed in order to obtain numerical values, which were analyzed by nonlinear mathematical functions. Patients were classified through the application of a clustering procedure to the whole set of functions, and the correlation between the results of nonlinear analysis of ECG and EPS was tested. Results: NLA assigned all patients with negative EPS to the same class of healthy subjects, whereas the patients in whom VT was inducible had been correctly and clearly isolated into a separate cluster. In our study, the result of NLA with application of the clustering technique was significantly correlated to that of EPS (P < 0.001), and was able to predict the result of EPS, with a negative predictive value of 100% and a positive predictive value of 100%. Conclusions: NLA can predict the results of EPS with good negative and positive predictive value. However, further studies are needed in order to verify the usefulness of this noninvasive tool for sudden death risk stratification in patients with ventricular arrhythmias. [source]


Kombiniertes Verfahren zur wirklichkeitsnahen Berechnung schlanker Stahlbetonstabtragwerke

BETON- UND STAHLBETONBAU, Issue 10 2006
Uwe Starossek Univ.-Prof.
Der wirklichkeitsnahen und damit nichtlinearen Berechnung von allgemeinen Stahlbetontragwerken kommt eine wachsende Bedeutung zu. Eine Kombination des allgemeinen Weggrößenverfahrens, des Übertragungsverfahrens und eines Querschnittsmoduls führt zu einem effektiven Berechnungsverfahren für allgemeine Stabtragwerke aus Stahl- und Spannbeton. Neben der stofflichen Nichtlinearität berücksichtigt das Verfahren auch geometrische Nichtlinearität mit großen Verformungen. Die übergeordnete Berechnung des Systems erfolgt inkrementell und iterativ mit dem allgemeinen Weggrößenverfahren. Auf Stabebene wird ein erweitertes Übertragungsverfahren zur Bestimmung der Stabendschnittgrößen und der Steifigkeitsmatrix eingesetzt. Die Formulierung des Übertragungsverfahrens erfolgt in einem rekursiven Schema für einen verformten Stab, der in Abhängigkeit vom Steifigkeitsgradienten in einzelne Abschnitte diskretisiert wird. Das nichtlineare Materialverhalten einschließlich Rißbildung, Entfestigung und Fließen der Bewehrung wird im Querschnittsmodul über eine Querschnittsintegration erfaßt. Combined method for a realistic analysis of slender reinforced concrete frames A more realistic and, hence, nonlinear analysis of reinforced concrete structures is becoming increasingly important. A combination of the displacement method, the transfer matrix method, and a cross section module is suggested which leads to an effective analysis method for general reinforced and prestressed concrete frames. The combined method considers both material and geometrical nonlinearities including large deformations. The first level computation of the system is incrementally and iteratively carried out by the displacement method. At element level, an extended transfer matrix method is used for determining both the internal forces at the element end nodes and the stiffness matrix. The transfer matrix method is recursively applied to the deformed element, which is discretized into individual segments whose number and lengths depend on the stiffness gradient. The cross section module is based on cross-sectional integration. It takes into account nonlinear material behavior including cracking, softening, and yielding of reinforcement. [source]