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Linear Part (linear + part)
Selected AbstractsEstimation of endogenous adenosine activity at adenosine receptors in guinea-pig ileum using a new pharmacological methodACTA PHYSIOLOGICA, Issue 2 2010K. F. Nilsson Abstract Aim:, Adenosine modulates neurotransmission and in the intestine adenosine is continuously released both from nerves and from smooth muscle. The main effect is modulation of contractile activity by inhibition of neurotransmitter release and by direct smooth muscle relaxation. Estimation of adenosine concentration at the receptors is difficult due to metabolic inactivation. We hypothesized that endogenous adenosine concentrations can be calculated by using adenosine receptor antagonist and agonist and dose ratio (DR) equations. Methods:, Plexus-containing guinea-pig ileum longitudinal smooth muscle preparations were made to contract intermittently by electrical field stimulation in organ baths. Schild plot regressions were constructed with 2-chloroadenosine (agonist) and 8-(p -sulfophenyl)theophylline (8-PST; antagonist). In separate experiments the reversing or enhancing effect of 8-PST and the inhibiting effect of 2-chloroadenosine (CADO) were analysed in the absence or presence of an adenosine uptake inhibitor (dilazep), and nucleoside overflow was measured by HPLC. Results:, Using the obtained DR, baseline adenosine concentration was calculated to 28 nm expressed as CADO activity, which increased dose dependently after addition of 10,6 m dilazep to 150 nm (P < 0.05). HPLC measurements yielded a lower fractional increment (80%) in adenosine during dilazep, than found in the pharmacological determination (440%). Conclusion:, Endogenous adenosine is an important modulator of intestinal neuro-effector activity, operating in the linear part of the dose,response curve. Other adenosine-like agonists might contribute to neuromodulation and the derived formulas can be used to calculate endogenous agonist activity, which is markedly affected by nucleoside uptake inhibition. The method described should be suitable for other endogenous signalling molecules in many biological systems. [source] Non-parametric,parametric model for random uncertainties in non-linear structural dynamics: application to earthquake engineeringEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 3 2004Christophe Desceliers Abstract This paper deals with the transient response of a non-linear dynamical system with random uncertainties. The non-parametric probabilistic model of random uncertainties recently published and extended to non-linear dynamical system analysis is used in order to model random uncertainties related to the linear part of the finite element model. The non-linearities are due to restoring forces whose parameters are uncertain and are modeled by the parametric approach. Jayne's maximum entropy principle with the constraints defined by the available information allows the probabilistic model of such random variables to be constructed. Therefore, a non-parametric,parametric formulation is developed in order to model all the sources of uncertainties in such a non-linear dynamical system. Finally, a numerical application for earthquake engineering analysis is proposed concerning a reactor cooling system under seismic loads. Copyright © 2003 John Wiley & Sons, Ltd. [source] One-body energy decomposition schemes revisited: Assessment of Mulliken-, Grid-, and conventional energy density analyses,INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 11 2009Yasuaki Kikuchi Abstract We propose a new energy density analysis (EDA) that evaluates atomic contributions of all energy terms, i.e., the kinetic, nuclear-attraction, Coulomb, and Hartree,Fock (HF) exchange and density functional theory (DFT) exchange-correlation energies using the Mulliken-type partitioning. Although widely used DFT exchange-correlation functionals are nonlinear expressions in terms of density, they are decomposed into atomic contributions by focusing the linear part of the density. Numerical assessment on Mulliken-EDA, Grid-EDA, and conventional EDA has been carried out for the G2-1 set. Correlations between HF and DFT exchanges demonstrate that a consistent partitioning of all energy terms is essential for EDA. These numerical results confirm that the present Mulliken-EDA offers a more reasonable picture for the atomization process. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [source] Discrete-time low-gain control of linear systems with input/output nonlinearitiesINTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 12 2001T. Fliegner Abstract Discrete-time low-gain control strategies are presented for tracking of constant reference signals for finite-dimensional, discrete-time, power-stable, single-input, single-output, linear systems subject to a globally Lipschitz, non-decreasing input nonlinearity and a locally Lipschitz, non-decreasing, affinely sector-bounded output nonlinearity (the conditions on the output nonlinearities may be relaxed if the input nonlinearity is bounded). Both non-adaptive and adaptive gain sequences are considered. In particular, it is shown that applying error feedback using a discrete-time ,integral' controller ensures asymptotic tracking of constant reference signals, provided that (a) the steady-state gain of the linear part of the plant is positive, (b) the positive gain sequence is ultimately sufficiently small and (c) the reference value is feasible in a very natural sense. The classes of input and output nonlinearities under consideration contain standard nonlinearities important in control engineering such as saturation and deadzone. The discrete-time results are applied in the development of sampled-data low-gain control strategies for finite-dimensional, continuous- time, exponentially stable, linear systems with input and output nonlinearities. Copyright © 2001 John Wiley & Sons, Ltd. [source] Growth and Mechanism of Network-Like Branched Si3N4 NanostructuresJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2010Zhijian Peng The high-yield synthesis of network-like branched silicon nitride (Si3N4) nanostructures by a simple template catalyst-assisted pyrolysis of a polymer precursor, perhydropolysilazane, was reported. The templates were silicon wafers deposited with Fe films of 5,20 nm in thickness. The processes simply involved thermal cross-linking of the preceramic polymer, crushing of the solidified polymer chunks into fine powder, and thermal pyrolysis of the powder under flowing high-purity nitrogen. The collected white network-like branched nanostructures are ,-Si3N4 of hexagonal phase, and their microstructures, in which the diameters of each linear part of the network-like nanostructure varied in a very wide range from tens of nanometers to hundreds of nanometers, strongly depend on the applied growth parameters, where the key factors are the heating rate and catalyst thickness for change in the diameters. It was proposed that the Si3N4 nanonetworks were formed through "metal-absorption on the surface of nanostructures" model by vapor,liquid,solid mechanism. The reaction mechanism of Si3N4 nanonetworks was also discussed. [source] Semiparametric inference in generalized mixed effects modelsJOURNAL OF THE ROYAL STATISTICAL SOCIETY: SERIES B (STATISTICAL METHODOLOGY), Issue 5 2008María José Lombardía Summary., The paper presents a study of the generalized partially linear model including random effects in its linear part. We propose an estimator that combines likelihood approaches for mixed effects models, with kernel methods. Following the methodology of Härdle and co-workers, we introduce a test for the hypothesis of a parametric mixed effects model against the alternative of a semiparametric mixed effects model. The critical values are estimated by using a bootstrap procedure. The asymptotic theory for the methods is provided, as are the results of a simulation study. These verify the feasibility and the excellent behaviour of the methods for samples of even moderate size. The usefulness of the methodology is illustrated with an application in which the objective is to estimate forest coverage in Galicia, Spain. [source] Method of lines with boundary elements for 1-D transient diffusion-reaction problemsNUMERICAL METHODS FOR PARTIAL DIFFERENTIAL EQUATIONS, Issue 4 2006P.A. Ramachandran Abstract Time-dependent differential equations can be solved using the concept of method of lines (MOL) together with the boundary element (BE) representation for the spatial linear part of the equation. The BE method alleviates the need for spatial discretization and casts the problem in an integral format. Hence errors associated with the numerical approximation of the spatial derivatives are totally eliminated. An element level local cubic approximation is used for the variable at each time step to facilitate the time marching and the nonlinear terms are represented in a semi-implicit manner by a local linearization at each time step. The accuracy of the method has been illustrated on a number of test problems of engineering significance. © 2005 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 2006 [source] A robust method for the joint estimation of yield coefficients and kinetic parameters in bioprocess modelsBIOTECHNOLOGY PROGRESS, Issue 3 2009V. Vastemans Abstract Bioprocess model structures that require nonlinear parameter estimation, thus initialization values, are often subject to poor identification performances because of the uncertainty on those initialization values. Under some conditions on the model structure, it is possible to partially circumvent this problem by an appropriate decoupling of the linear part of the model from the nonlinear part of it. This article provides a procedure to be followed when these structural conditions are not satisfied. An original method for decoupling two sets of parameters, namely, kinetic parameters from maximum growth, production, decay rates, and yield coefficients, is presented. It exhibits the advantage of requiring only initialization of the first subset of parameters. In comparison with a classical nonlinear estimation procedure, in which all the parameters are freed, results show enhanced robustness of model identification with regard to parameter initialization errors. This is illustrated by means of three simulation case studies: a fed-batch Human Embryo Kidney cell cultivation process using a macroscopic reaction scheme description, a process of cyclodextrin-glucanotransferase production by Bacillus circulans, and a process of simultaneous starch saccharification and glucose fermentation to lactic acid by Lactobacillus delbrückii, both based on a Luedeking-Piret model structure. Additionally, perspectives of the presented procedure in the context of systematic bioprocess modeling are promising. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009 [source] A pseudospectral Fourier method for a 1D incompressible two-fluid modelINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 6 2008H. Holmås Abstract This paper presents an accurate and efficient pseudospectral (PS) Fourier method for a standard 1D incompressible two-fluid model. To the knowledge of the authors, it is the first PS method developed for the purpose of modelling waves in multiphase pipe flow. Contrary to conventional numerical methods, the PS method combines high accuracy and low computational costs with flexibility in terms of handling higher order derivatives and different types of partial differential equations. In an effort to improve the description of the stratified wavy flow regime, it can thus serve as a valuable tool for testing out new two-fluid model formulations. The main part of the algorithm is based on mathematical reformulations of the governing equations combined with extensive use of fast Fourier transforms. All the linear operations, including differentiations, are performed in Fourier space, whereas the nonlinear computations are performed in physical space. Furthermore, by exploiting the concept of an integrating factor, all linear parts of the problem are integrated analytically. The remaining nonlinear parts are advanced in time using a Runge,Kutta solver with an adaptive time step control. As demonstrated in the results section, these steps in sum yield a very accurate, fast and stable numerical method. A grid refinement analysis is used to compare the spatial convergence with the convergence rates of finite difference (FD) methods of up to order six. It is clear that the exponential convergence of the PS method is by far superior to the algebraic convergence of the FD schemes. Combined with the fact that the scheme is unconditionally linearly stable, the resulting increase in accuracy opens for several orders of magnitude savings in computational time. Finally, simulations of small amplitude, long wavelength sinusoidal waves are presented to illustrate the remarkable ability of the PS method to reproduce the linear stability properties of the two-fluid model. Copyright © 2008 John Wiley & Sons, Ltd. [source] | ||||||||||||||||