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Nonlinear Parameters (nonlinear + parameter)

Distribution by Scientific Domains

Medical Sciences	37%
Mathematics and Statistics	25%

Selected Abstracts

Asteroid photometric and polarimetric phase curves: Joint linear-exponential modeling

METEORITICS & PLANETARY SCIENCE, Issue 12 2009
K. Muinonen
Here we model the two phase curves jointly at phase angles ,25° using a linear-exponential model, accounting for the opposition effect in disk-integrated brightness and the negative branch in the degree of linear polarization. We apply the MCMC methods to V-band phase curves of asteroids 419 Aurelia (taxonomic class F), 24 Themis (C), 1 Ceres (G), 20 Massalia (S), 55 Pandora (M), and 64 Angelina (E). We show that the photometric and polarimetric phase curves can be described using a common nonlinear parameter for the angular widths of the opposition effect and negative-polarization branch, thus supporting the hypothesis of common physical mechanisms being responsible for the phenomena. Furthermore, incorporating polarimetric observations removes the indeterminacy of the opposition effect for 1 Ceres. We unveil a trend in the interrelation between the enhancement factor of the opposition effect and the angular width: the enhancement factor decreases with decreasing angular width. The minimum polarization and the polarimetric slope at the inversion angle show systematic trends when plotted against the angular width and the normalized photometric slope parameter. Our new approach allows improved analyses of possible similarities and differences among asteroidal surfaces. [source]

Analysis of OTA-C filters with weakly nonlinear transconductors

INTERNATIONAL JOURNAL OF CIRCUIT THEORY AND APPLICATIONS, Issue 7 2008
Slawomir KozielArticle first published online: 11 OCT 200
Abstract An efficient approach for analysis of nonlinear distortion in OTA-C filters with weakly nonlinear transconductors is presented. The procedure is developed based on an algebraic description of a general OTA-C filter structure and, therefore, the results are valid for any filter architecture within OTA-C class. On the basis of the proposed method, explicit formulas for calculating a gain compression/expansion ratio in an arbitrary OTA-C filter are developed. The formulas are easy to implement and use in computer-aided filter design tools. For illustration purposes, several filter structures are considered. The accuracy of the method is verified by comparing the results with the exact values of gain compression/expansion ratio achieved by integrating the differential system that determines the time response of OTA-C filter. The presented approach can be generalized in order to consider other nonlinear parameters. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Nonlinear wave function expansions: A progress report

INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 15 2007
Ron Shepard
Abstract Some recent progress is reported for a novel nonlinear expansion form for electronic wave functions. This expansion form is based on spin eigenfunctions using the Graphical Unitary Group Approach and the wave function is expanded in a basis of product functions, allowing application to closed and open shell systems and to ground and excited electronic states. Each product basis function is itself a multiconfigurational expansion that depends on a relatively small number of nonlinear parameters called arc factors. Efficient recursive procedures for the computation of reduced one- and two-particle density matrices, overlap matrix elements, and Hamiltonian matrix elements result in a very efficient computational procedure that is applicable to very large configuration state function (CSF) expansions. A new energy-based optimization approach is presented based on product function splitting and variational recombination. Convergence of both valence correlation energy and dynamical correlation energy with respect to the product function basis dimension is examined. A wave function analysis approach suitable for very large CSF expansions is presented based on Shavitt graph node density and arc density. Some new closed-form expressions for various Shavitt Graph and Auxiliary Pair Graph statistics are presented. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 [source]

Heart Rate Variability and Sympathetic Skin Response in Male Patients Suffering From Acute Alcohol Withdrawal Syndrome

ALCOHOLISM, Issue 9 2006
Karl-Jürgen Bär
Background: Many symptoms of alcohol withdrawal (AW) such as tachycardia or elevated blood pressure might be explained by increased peripheral and central adrenergic activity. In contrast to many neurochemical studies of sympathetic activation during AW, only very few studies investigated autonomic balance using neurophysiological methods. Methods: We investigated heart rate variability (HRV) and sympathetic skin response (SSR) in male patients suffering from mild AW syndrome (n=20, no treatment required) and in patients with moderate to severe AW syndrome (n=20, clomethiazole treatment) in the acute stage. Sympathovagal influence was quantified using measures of time and frequency domain of HRV as well as modern nonlinear parameters (compression entropy). Furthermore, we obtained latencies and amplitudes of SSR to quantify isolated sympathetic influence. Measures were obtained during the climax of withdrawal symptomatology before treatment, 1 day after climax, and shortly before discharge from hospital. Alcohol withdrawal scores were obtained and correlated to autonomic measures. Results: Ambulatory blood pressure and AW scores revealed characteristic withdrawal symptoms in both patient groups. Apart from the nonlinear parameter compression entropy, Hc, measures of HRV revealed no sign of autonomic dysfunction in contrast to the significantly increased heart rates at the time of admission. Latencies and amplitudes of SSR did not indicate any increase of sympathetic activity. A negative correlation was found between Hc and mental withdrawal symptoms. Conclusions: We show here that classical measures for autonomic nervous system activity such as HRV and SSR are not suitable for describing the autonomic changes seen in acute AW, although a major role for the sympathetic nervous system has been proposed. This might be due to multiple dysregulation of metabolites in AWS or to subtle alcohol-induced damage to neuronal structures, issues that should be addressed in future studies. [source]

Small area estimation of poverty indicators

THE CANADIAN JOURNAL OF STATISTICS, Issue 3 2010
Isabel Molina
Abstract The authors propose to estimate nonlinear small area population parameters by using the empirical Bayes (best) method, based on a nested error model. They focus on poverty indicators as particular nonlinear parameters of interest, but the proposed methodology is applicable to general nonlinear parameters. They use a parametric bootstrap method to estimate the mean squared error of the empirical best estimators. They also study small sample properties of these estimators by model-based and design-based simulation studies. Results show large reductions in mean squared error relative to direct area-specific estimators and other estimators obtained by "simulated" censuses. The authors also apply the proposed method to estimate poverty incidences and poverty gaps in Spanish provinces by gender with mean squared errors estimated by the mentioned parametric bootstrap method. For the Spanish data, results show a significant reduction in coefficient of variation of the proposed empirical best estimators over direct estimators for practically all domains. The Canadian Journal of Statistics 38: 369,385; 2010 © 2010 Statistical Society of Canada Les auteurs proposent d'estimer les paramètres non linéaires d'une population de petits domaines en utilisant une méthode bayésienne empirique. L'emphase est mise sur les indicateurs de pauvreté comme paramètres non linéaires d'intérêt particuliers, mais ils proposent une méthodologie qui s'applique à des paramètres non linéaires plus généraux. Ils utilisent une méthode de rééchantillonnage paramétrique pour estimer l'erreur quadratique moyenne du meilleur estimateur empirique. À l'aide de simulations basées sur le modèle et sur le plan de sondage, ils étudient les propriétés de ces estimateurs pour les petits échantillons. Les résultats obtenus montrent une grande réduction de l'erreur quadratique moyenne par rapport aux estimateurs propres aux régions et les autres estimateurs obtenus par recensements « simulés». Les auteurs ont aussi appliqué la méthodologie proposée à l'estimation des incidences de pauvreté et des disparités, en fonction du sexe, du niveau de la pauvreté des provinces espagnoles. Les erreurs quadratiques moyennes sont estimées en utilisant la méthode de rééchantillonnage paramétrique citée auparavant. Pour les données espagnoles, les résultats montrent une réduction substantielle du coefficient de variation des meilleurs estimateurs empiriques proposés par rapport aux estimateurs spécifiques pour pratiquement tous les domaines. La revue canadienne de statistique 38: 369,385; 2010 © 2010 Société statistique du Canada [source]

Influence of Age on Linear and Nonlinear Measures of Autonomic Cardiovascular Modulation

ANNALS OF NONINVASIVE ELECTROCARDIOLOGY, Issue 2 2010
Michael K. Boettger M.D.
Background: Age has been identified as an independent risk factor for cardiovascular diseases. In addition, autonomic imbalance toward sympathetic preponderance has been shown to facilitate the occurrence of heart disease. Here, we aimed to assess autonomic modulation of cardiovascular parameters during normal ageing applying well-established linear and novel nonlinear parameters. Methods: Linear and nonlinear measures of heart rate variability and complexity as well as measures of QT interval variability and baroreflex sensitivity were obtained from a total of 131 healthy, medication-free participants from a continuous age range between 20 and 90 years, who were allocated to three different age groups. Results: Heart rate variability and complexity significantly decreased with age, while regularity of heart rate time series increased. In addition, QT interval variability linearly increased with age, while baroreflex sensitivity showed a pronounced decrease. Overall, concerning effects of ageing, linear and nonlinear parameters showed equal differentiation between groups. Conclusion: These data indicate a shift of autonomic balance toward sympathetic predominance in higher age groups, limiting the reactiveness of the cardiovascular system to adjust to different demands and increasing the risk for developing tachyarrhythmias. Ann Noninvasive Electrocardiol 2010;15(2):165,174 [source]

Dynamic Conditionally Linear Mixed Models for Longitudinal Data

BIOMETRICS, Issue 1 2002
M. Pourahmadi
Summary. We develop a new class of models, dynamic conditionally linear mixed models, for longitudinal data by decomposing the within-subject covariance matrix using a special Cholesky decomposition. Here ,dynamic' means using past responses as covariates and ,conditional linearity' means that parameters entering the model linearly may be random, but nonlinear parameters are nonrandom. This setup offers several advantages and is surprisingly similar to models obtained from the first-order linearization method applied to nonlinear mixed models. First, it allows for flexible and computationally tractable models that include a wide array of covariance structures; these structures may depend on covariates and hence may differ across subjects. This class of models includes, e.g., all standard linear mixed models, antedependence models, and Vonesh-Carter models. Second, it guarantees the fitted marginal covariance matrix of the data is positive definite. We develop methods for Bayesian inference and motivate the usefulness of these models using a series of longitudinal depression studies for which the features of these new models are well suited. [source]