Search

Site response analyses are crucial for estimating local effects on ground shaking during earthquakes. However, recent investigations utilizing KiK-net borehole array data have revealed a consistent underprediction of high-frequency ground motion by both equivalent linear and fully nonlinear methods, contrary to expectations. This study reassess the accuracy of 1D site response analysis methods, including equivalent linear, frequency-dependent equivalent linear model, and nonlinear analysis, by integrating depth-dependent stiffness and adjusted shear wave velocity. Nine instrumented vertical arrays, featuring a total of 132 recorded ground motions, are subjected to analysis. For the sites and ground motions considered, the results indicate that the nonlinear method performs without significant bias, whereas the equivalent linear and frequency-dependent equivalent linear methods tend to respectively underestimate and overestimate high-frequency results. To enhance accuracy, it is recommended to incorporate depth-dependent stiffness and adjusted shear wave velocity when predicting high-frequency ground motion in site response analyses. [ABSTRACT FROM AUTHOR]

In this paper, we propose a simple approach to the construction of a general class of L -stable explicit second-order one-step methods for solving stiff problems. These methods are nonlinear and derive from a novel approximation for the right-hand side functions of differential equations inspired by the nonstandard finite difference methodology introduced by Mickens. Through rigorous mathematical analysis, it is proved that the proposed numerical methods are not only explicit and L -stable, but also convergent of order two. Therefore, they are suitable and efficient to solve stiff problems. The proposed numerical methods generalize and improve a nonstandard explicit integration scheme for initial value problems formulated by Ramos (2007). Moreover, the present approach can be extended to construct A -stable and L -stable high-order explicit one-step methods for differential equations. Finally, the theoretical findings and advantages of the developed numerical methods are supported and illustrated by a series of numerical experiments in which stiff problems are considered. [ABSTRACT FROM AUTHOR]

The article discusses a calculation technique for a reinforced concrete building with a braced frame on an earthquake. It allows to produce an adequate assessment of a of seismic stability level. A direct simulation of concrete, reinforcement and their binding with the help of volumetric and core finite elements is fulfilled. The paper presents the concrete work chart and considers mathematical models for the material. The authors propose calculation technique of reinforced concrete buildings with the actual reinforcement taking into account. The results of the numerical calculations of structural elements (crossbar) are compared to the field experiments conducted by US Department of Transportation Federal Highway Administration. The article examines the level of seismic stability of buildings with a braced frame, the actual reinforcement taking into account when calculating on a seismic action. [ABSTRACT FROM AUTHOR]

In our previous work, we have developed a sudden cardiac death index (SCDI) using electrocardiogram (ECG) signals that could effectively predict the occurrence of SCD four minutes before the onset. Thus, the prediction of SCD before its onset by using heart rate variability (HRV) signals is a worthwhile task for further investigation. Therefore, in this paper, a new novel methodology to automatically classify the HRV signals of normal and subjects at risk of SCD by using nonlinear techniques has been presented. In this study, we have predicted SCD by analyzing four-minutes of HRV signals (separately for each one-minute interval) prior to SCD occurrence by using nonlinear features such as Renyi entropy (REnt), fuzzy entropy (FE), Hjorth's parameters (activity, mobility and complexity), Tsallis entropy (TEnt), and energy features of discrete wavelet transform (DWT) coefficients. All the clinically significant features obtained are ranked using their t -value and fed to classifiers such as K-nearest neighbor (KNN), decision tree (DT), and support vector machine (SVM). In this work, we have achieved an accuracy of 97.3%, 89.4%, 89.4%, and 94.7% for prediction of SCD one, two, three, and four minutes prior to the SCD onset respectively using SVM classifier. Furthermore, we have also developed a novel SCD Index (SCDI) by using nonlinear HRV signal features to classify the normal and SCD prone HRV signals. Our proposed technique is able to identify the person at risk of developing SCD four minutes earlier, thereby providing sufficient time for the clinicians to respond with treatment in Intensive Care Units (ICU). Thus, this proposed technique can thus serve as a valuable tool for increasing the survival rate of many cardiac patients. [ABSTRACT FROM AUTHOR]

Patients with non-specific low back pain (LBP) may use postural control strategies that differ from healthy subjects. To study these possible differences, we measured the amount and structure of postural sway, and the response to muscle vibration in a working cohort of 215 subjects. Subjects were standing on a force plate in bipedal stance. In the first trial the eyes were open, no perturbation applied. In the following 6 trials, vision was occluded and subjects stood under various conditions of vibration/no vibration of the lumbar spine or m. Triceps Surae (TSM) on firm surface and on foam surface. We performed a factor analysis to reduce the large amount of variables that are available to quantify all effects. Subjects with LBP showed the same amount of sway as subjects without LBP, but the structure of their sway pattern was less regular with higher frequency content. Subjects with LBP also showed a smaller response to TSM vibration, and a slower balance recovery after cessation of vibration when standing on a solid surface. There was a weak but significant association between smaller responses to TSM vibration and an irregular, high frequency sway pattern, independent from LBP. A model for control of postural sway is proposed. This model suggests that subjects with LBP use more co-contraction and less cognitive control, to maintain a standing balance when compared to subjects without LBP. In addition, a reduced weighting of proprioceptive signals in subjects with LBP is suggested as an explanation for the findings in this study. [ABSTRACT FROM AUTHOR]

Highlights: [•] We analyzed the amount and structure of center of pressure fluctuations. [•] Elderly subjects stood on different surfaces which approach daily life situations. [•] Motor outputs were task-dependent with different results for anterior–posterior and medial–lateral sway. [•] The adaptation to altered postural demands takes place on different time scales. [•] Standing with one foot on a step seems to be a challenging situation for the elderly. [ABSTRACT FROM AUTHOR]

Abstract: The estimation problem in a high regression model with structured sparsity is investigated. An algorithm using a two-step block thresholding procedure called GR-LOL is provided. Convergence rates are produced: they depend on simple coherence-type indices of the Gram matrix – easily checkable on the data – as well as sparsity assumptions of the model parameters measured by a combination of l 1 within-blocks with , between-blocks norms. The simplicity of the coherence indicator suggests ways to optimize the rates of convergence when the group structure is not naturally given by the problem or is unknown. In such a case, an auto-driven procedure is provided to determine the regressor groups (number and contents). An intensive practical study compares our grouping methods with the standard LOL algorithm. We prove that the grouping rarely deteriorates the results but can improve them very significantly. GR-LOL is also compared with group-Lasso procedures and exhibits a very encouraging behavior. The results are quite impressive, especially when GR-LOL algorithm is combined with a grouping pre-processing. [Copyright &y& Elsevier]

Abstract: We investigate the monetary policy of the Federal Reserve Board during six periods in US economic history 1959–2008. In particular, we examine the Fed''s response to changes in three guiding variables: inflation, π, unemployment, U, and industrial production, y, during periods with low and high economic stability. We identify separate responses for the Fed''s change in interest rate depending upon (i) the current rate, FF, and the guiding variables’ level below or above their average values and (ii) recent movements in inflation and unemployment. The change in rate, ΔFF, can then be calculated. We identify policies that both increased and decreased economic stability. [Copyright &y& Elsevier]

Highlights: • We analyzed fetal heart rate of normal and acidemic fetuses. • We used conventional and nonlinear features for the signal analysis. • Addition of nonlinear features improves accuracy of classification. • The best nonlinear features are: Lempel Ziv complexity and Sample entropy. • Combination of conventional and nonlinear features provides the best accuracy. Abstract: Fetal heart rate (FHR) is used to evaluate fetal well-being and enables clinicians to detect ongoing hypoxia during delivery. Routine clinical evaluation of intrapartum FHR is based on macroscopic morphological features visible to the naked eye. In this paper we evaluated conventional features and compared them to the nonlinear ones in the task of intrapartum FHR classification. The experiments were performed using a database of 217 FHR records with objective annotations, i.e. pH measurement. We have proven that the addition of nonlinear features improves accuracy of classification. The best classification results were achieved using a combination of conventional and nonlinear features with sensitivity of 73.4%, specificity of 76.3%, and F-measure of 71.9%. The best selected nonlinear features were: Lempel Ziv complexity, Sample entropy, and fractal dimension estimated by Higuchi method. Since the results of automatic signal evaluation are easily reproducible, the process of FHR evaluation can become more objective and may enable clinicians to focus on additional non-cardiotocography parameters influencing the fetus during delivery. [Copyright &y& Elsevier]

Abstract: Objective: The aim of this study was to test whether a new heart rate variability (HRV) complexity measure, the Point Correlation Dimension (PD2i), provides diagnostic information regarding early subclinical autonomic dysfunction in diabetes mellitus (DM). We tested the ability of PD2i to detect diabetic autonomic neuropathy (DAN) in asymptomatic young DM patients without overt neuropathy and compared them to age- and gender-matched controls. Methods: HRV in DM type 1 patients (n =17, 10 female, 7 male) aged 12.9–31.5years (duration of DM 12.4±1.2years) was compared to that in a control group of 17 healthy matched probands. The R–R intervals were measured over 1h using a telemetric ECG system. Results: PD2i was able to detect ANS dysfunction with p =0.0006, similar to the best discriminating MSE scale, with p =0.0002. Conclusions: The performance of PD2i to detect DAN in asymptomatic DM patients is similar to the best discriminative power of previously published complexity measures. Significance: The PD2i algorithm may prove to be an easy to perform and clinically useful tool for the early detection of autonomic neuropathy in DM type 1 patients, especially given its minimal data requirements. [Copyright &y& Elsevier]

Background: Recently backward walking is used by physical therapists to strengthen the hamstring muscles and thus improve the function of the knee joint of anterior cruciate ligament deficient patients. The aim of this study was to examine the stride-to-stride variability of anterior cruciate ligament deficient patients during backward walking. The variation of how a motor behavior emerges in time is best captured by tools derived from nonlinear dynamics, for which the temporal sequence in a series of values is the facet of interest. Methods: Fifteen patients with unilateral anterior cruciate ligament deficiency and eleven healthy controls walked backwards at their self-selected speed on a treadmill while three-dimensional knee kinematics were collected (100Hz). A nonlinear measure, the largest Lyapunov Exponent was calculated from the resulted knee joint flexion–extension data of both groups to assess the stride-to-stride variability. Findings: Both knees of the deficient patients exhibited significantly lower Lyapunov Exponent values as compared to the healthy control group revealing more rigid movement pattern. The intact knee of the deficient patients showed significantly lower Lyapunov Exponent values as compared to the deficient knee. Interpretation: Anterior cruciate ligament (ACL) deficiency leads to loss of optimal variability regardless of the walking direction (forwards in previous studies or backwards here) as compared to healthy individuals. This could imply diminished functional responsiveness to the environmental demands for both knees of ACL deficient patients which could result in the knees being more susceptible to injury. [Copyright &y& Elsevier]

Abstract: This review discusses nonlinear chromatographic methods of importance for proper characterization of the adsorption processes in analytical chromatographic systems, with focus on reversed-phase liquid chromatography. Linear methods such as the linear solvation energy relationship (LSER) method and the Snyder–Dolan hydrophobic-subtraction model will also be reviewed briefly. The nonlinear methods for adsorption isotherm determination and the tools for further treatment of the nonlinear adsorption data will be extensively treated in a way suitable for the general chromatographer. Applications of the various methods will be given and the outcome and conclusions will be discussed. Special emphasis will be placed on discussing the possibilities of combining linear and nonlinear methods in order to obtain a deeper and more complete investigation of the interactions in the actual phase system. [Copyright &y& Elsevier]

Abstract: Cerebral autoregulation describes the process by which cerebral blood flow is maintained despite fluctuations in cerebral perfusion pressure. The assessment of cerebral autoregulation is a key to the optimisation of cerebral perfusion pressure in patients with brain injury. This review evaluates the current evidence for transcranial Doppler in the assessment of cerebral autoregulation. The study of cerebral autoregulation classically assesses changes in cerebral perfusion pressure secondary to changes in systemic blood pressure. It is defined static autoregulation if blood pressure changes are progressive, thereby allowing a steady-state autoregulatory response to be completed. For sudden changes in blood pressure, the autoregulatory response is defined as dynamic. The static and dynamic components of cerebral autoregulation have been approached using linear mathematical models (models based in direct correlations). Over the past decade, demonstration of the nonstationary (the property of changing over time or space) behaviour of cerebral autoregulation has emphasised the benefit obtained in using nonlinear statistical models (models based on changeable functions), suggesting that these methods may improve the mathematical representation of cerebral autoregulation. Despite the multiple determinants involved in cerebral autoregulation, it appears feasible to reliably assess cerebral autoregulation through the combination of linear and nonlinear methods. Nonlinear methods appear attractive in the research setting, but the challenge is how to adopt these methods to the clinical setting. (E-mail: 30489jbr@comb.es) [Copyright &y& Elsevier]

Abstract: Objective: The aim of this study was to test whether new heart rate variability (HRV) complexity measures provide diagnostic information regarding early subclinical autonomic dysfunction in diabetes mellitus (DM). Methods: HRV in DM type 1 patients (n =17, 10f, 7m) aged 12.9–31.5 years (duration of DM 12.4±1.2 years) was compared to a control group of 17 healthy matched probands. The length of R–R intervals was measured over 1h using a telemetric ECG system. In addition to linear measures, we assessed HRV complexity measures, including multiscale entropy (MSE), compression entropy and various symbolic dynamic measures (Shannon and Renyi entropies, normalized complexity index (NCI), and pattern classification). Results: HRV magnitude was significantly reduced in patients with DM. Several HRV complexity parameters (MSE at scales 2–4, Renyi entropy, NCI) were also significantly reduced in diabetics. MSE indices and compression entropy did not correlate with linear measures. Conclusions: The magnitude and complexity of HRV are reduced in young patients with DM, indicating vagal dysfunction. Significance: The quantification of HRV complexity in combination with its magnitude may provide an improved diagnostic tool for cardiovascular autonomic neuropathy in DM. [Copyright &y& Elsevier]

Summary: Objectives: Nocturnal pulse oximetry is a widely used alternative to polysomnography (PSG) in screening for obstructive sleep apnea (OSA) syndrome. Several oximetric indexes have been derived from nocturnal blood oxygen saturation (SaO2). However, they suffer from several limitations. The present study is focused on the usefulness of nonlinear methods in deriving new measures from oximetry signals to improve the diagnostic accuracy of classical oximetric indexes. Specifically, we assessed the validity of central tendency measure (CTM) as a screening test for OSA in patients clinically suspected of suffering from this disease. Materials and methods: We studied 187 subjects suspected of suffering from OSA referred to the sleep unit. A nocturnal pulse oximetry study was applied simultaneously to a conventional PSG. Three different index groups were compared. The first one was composed by classical indexes provided by our oximeter: oxygen desaturation indexes (ODIs) and cumulative time spent below a saturation of 90% (CT90). The second one was formed by indexes derived from a nonlinear method previously studied by our group: approximate entropy (ApEn). The last one was composed by indexes derived from a CTM analysis. Results: For a radius in the scatter plot equal to 1, CTM values corresponding to OSA positive patients (0.30±0.20, mean±S.D.) were significantly lower (p ≪0.001) than those values from OSA negative subjects (0.71±0.18, mean±S.D.). CTM was significantly correlated with classical indexes and indexes from ApEn analysis. CTM provided the highest correlation with the apnea–hipopnea index AHI (r =−0.74, p <0.0001). Moreover, it reached the best results from the receiver operating characteristics (ROC) curve analysis, with 90.1% sensitivity, 82.9% specificity, 88.5% positive predictive value, 85.1% negative predictive value, 87.2% accuracy and an area under the ROC curve of 0.924. Finally, the AHI derived from the quadratic regression curve for the CTM showed better agreement with the AHI from PSG than classical and ApEn derived indexes. Conclusion: The results suggest that CTM could improve the diagnostic ability of SaO2 signals recorded from portable monitoring. CTM could be a useful tool for physicians in the diagnosis of OSA syndrome. [Copyright &y& Elsevier]

We employ a damped Newton multigrid algorithm to solve a nonlinear system arising from a finite-difference discretization of an elliptic flame sheet problem. By selecting the generalized minimum residual method as the linear smoother for the multigrid algorithm, we conduct a series of numerical experiments to investigate the behavior and efficiency of the multigrid solver in solving the linearized systems, by choosing several preconditioners for the Krylov subspace method. It is shown that the overall efficiency of the damped Newton multigrid algorithm is highly related to the quality of the preconditioner chosen and the number of smoothing steps done on each level. ILU preconditioners based on the Jacobian pattern are found to be robust and provide efficient smoothing but at an expensive cost of storage. It is also demonstrated that the technique of mesh sequencing and multilevel correction scheme provides significant CPU saving for fine grid calculations by limiting the growth of the Krylov iterations. [Copyright &y& Elsevier]

Shakedown analysis for elastic–perfect plastic structures is discussed and a fast incremental-iterative solution method is proposed, suitable for the FEM analyses of large structures.The theoretical motivations of the proposed method are discussed in detail and an example of its implementation is described with reference to plane frame analysis.Some numerical results are presented showing the numerical performances of the method. [Copyright &y& Elsevier]

• An industrial reduction gearbox was bench-tested. • Gear tooth damage detection results are reported. • Real signals were investigated using linear and nonlinear analysis. • The nonlinear recurrence method effectively differentiates the degree of tooth damage. Linear and nonlinear analyses served to detect the degree of tooth damage in a cylindrical gear. The gear in question is widely used in industrial applications and is often subject to gear tooth damage. Multiple-sourced vibrations affecting the test stand may distort or conceal the vibration components responsible for tooth failure. Given its construction, the test stand offers low stiffness, and additional control and measurement equipment further contribute to overall vibrations. Therefore, the vibration signal is likely to contain various disturbances, which further hinder correct diagnosis. Basic vibroacoustic signal analysis methods, which were employed at a preliminary stage, failed to produce unambiguous and satisfactory results. Hence, nonlinear recurrence analysis of gear operation dynamics was applied. It is assumed that the occurrence of damage to the gear will impede the regularity of drive transmission. The adopted research method addresses the limitations of a two-state diagnosis of gear condition (no damage/damage) by allowing the extent of gear tooth damage to be specified. [ABSTRACT FROM AUTHOR]