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Perturbation Parameter (perturbation + parameter)
Selected AbstractsOn generalized stochastic perturbation-based finite element methodINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 1 2006Marcin Kami Abstract Generalized nth order stochastic perturbation technique, that can be applied to solve some boundary value or boundary initial problems in computational physics and/or engineering with random parameters is proposed here. This technique is demonstrated in conjunction with the finite element method (FEM) to model 1D linear elastostatics problem with a single random variable. The symbolic computer program is employed to perform computational studies on convergence of the first two probabilistic moments for simple unidirectional tension of a bar. These numerical studies verify the influence of coefficient of variation of the random input and, at the same time, of the perturbation parameter on the first two probabilistic moments of the final solution vector. Copyright © 2005 John Wiley & Sons, Ltd. [source] Numerical study of particulate suspension flow through wavy-walled channelsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 3 2006R. Usha Abstract The particulate suspension flow in a channel whose walls describe a travelling wave motion is examined numerically. A perturbation method is employed and the primitive variables are expanded in a series with the wall amplitude as the perturbation parameter. The boundary conditions are applied at the mean surface of the channel and the first-order perturbation quantities are numerically determined by solving the governing system of ordinary differential equations by shooting technique. The present approach does not impose any restriction on the Reynolds number of the flow and the wave number and frequency of the wavy-walled channel, although it is limited by the linear analysis. The wall shear stress and the positions of flow separation and reattachment points are computed and the influence of the volume fraction density of the particles is examined. The variations of velocity and pressure of the particulate suspension flow with frequency of excitation are also presented. Copyright © 2005 John Wiley & Sons, Ltd. [source] Implementing molecular connectivity theory, a basic tool in modeling drugsJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 8 2007Lionello Pogliani Abstract The concepts of chain graph, general graph, and complete graph have been used to implement the graph framework of molecular connectivity (MC) theory. Some concepts of this theory have been addressed using "external" theoretical concepts belonging mostly to quantum or structural chemistry, with no direct counterpart in graph theory. Thus, while the concept of chain graph can be used to tackle the cis-trans isomerism problem, the concept of pseudograph, or general graph can be used to tackle the description of the sigma -, pi -, and nonbonding n -electrons. The concept of complete graph can instead be used to tackle the electron core problem of the atoms of a molecule. Graph concepts can also be used to tackle the problem of the hydrogen contribution in hydrogen depleted graphs, which are encoded by the aid of a perturbation parameter, which differentiates between compounds with similar hydrogen-suppressed chemical graphs, like the graphs of CH3F and BH2F. These concepts have allowed redesign of a central parameter of MC theory, the valence delta, giving MC indices with improved model quality as exemplified here with different properties for each treated topic. © 2007 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 96:1856,1871, 2007 [source] Convergence and superconvergence analysis of an anisotropic nonconforming finite element methods for semisingularly perturbed reaction,diffusion problemsMATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 12 2008Guoqing Zhu Abstract The numerical approximation by a lower-order anisotropic nonconforming finite element on appropriately graded meshes are considered for solving semisingular perturbation problems. The quasi-optimal-order error estimates are proved in the ,-weighted H1 -norm valid uniformly, up to a logarithmic factor, in the singular perturbation parameter. By using the interpolation postprocessing technique, the global superconvergent error estimates in ,-weighted H1 -norm are obtained. Numerical experiments are given to demonstrate validity of our theoretical analysis. Copyright © 2007 John Wiley & Sons, Ltd. [source] A posteriori error estimation for convection dominated problems on anisotropic meshesMATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 7 2003Gerd Kunert Abstract A singularly perturbed convection,diffusion problem in two and three space dimensions is discretized using the streamline upwind Petrov Galerkin (SUPG) variant of the finite element method. The dominant convection frequently gives rise to solutions with layers; hence anisotropic finite elements can be applied advantageously. The main focus is on a posteriori energy norm error estimation that is robust in the perturbation parameter and with respect to the mesh anisotropy. A residual error estimator and a local problem error estimator are proposed and investigated. The analysis reveals that the upper error bound depends on the alignment of the anisotropies of the mesh and of the solution. Hence reliable error estimation is possible for suitable anisotropic meshes. The lower error bound depends on the problem data via a local mesh Peclet number. Thus efficient error estimation is achieved for small mesh Peclet numbers. Altogether, error estimation approaches for isotropic meshes are successfully extended to anisotropic elements. Several numerical experiments support the analysis. Copyright © 2003 John Wiley & Sons, Ltd. [source] On the Hamiltonicity Gap and doubly stochastic matricesRANDOM STRUCTURES AND ALGORITHMS, Issue 4 2009Vivek S. Borkar Abstract We consider the Hamiltonian cycle problem embedded in singularly perturbed (controlled) Markov chains. We also consider a functional on the space of stationary policies of the process that consists of the (1,1)-entry of the fundamental matrices of the Markov chains induced by these policies. We focus on the subset of these policies that induce doubly stochastic probability transition matrices which we refer to as the "doubly stochastic policies." We show that when the perturbation parameter, ,, is sufficiently small, the minimum of this functional over the space of the doubly stochastic policies is attained at a Hamiltonian cycle, provided that the graph is Hamiltonian. We also show that when the graph is non-Hamiltonian, the above minimum is strictly greater than that in a Hamiltonian case. We call the size of this difference the "Hamiltonicity Gap" and derive a conservative lower bound for this gap. Our results imply that the Hamiltonian cycle problem is equivalent to the problem of minimizing the variance of the first hitting time of the home node, over doubly stochastic policies. © 2008 Wiley Periodicals, Inc. Random Struct. Alg., 2009 [source] A linear model of gravity wave drag for hydrostatic sheared flow over elliptical mountainsTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 620 2006M. A. C. Teixeira Abstract An analytical model of orographic gravity wave drag due to sheared flow past elliptical mountains is developed. The model extends the domain of applicability of the well-known Phillips model to wind profiles that vary relatively slowly in the vertical, so that they may be treated using a WKB approximation. The model illustrates how linear processes associated with wind profile shear and curvature affect the drag force exerted by the airflow on mountains, and how it is crucial to extend the WKB approximation to second order in the small perturbation parameter for these effects to be taken into account. For the simplest wind profiles, the normalized drag depends only on the Richardson number, Ri, of the flow at the surface and on the aspect ratio, ,, of the mountain. For a linear wind profile, the drag decreases as Ri decreases, and this variation is faster when the wind is across the mountain than when it is along the mountain. For a wind that rotates with height maintaining its magnitude, the drag generally increases as Ri decreases, by an amount depending on , and on the incidence angle. The results from WKB theory are compared with exact linear results and also with results from a non-hydrostatic nonlinear numerical model, showing in general encouraging agreement, down to values of Ri of order one. Copyright © 2006 Royal Meteorological Society [source] Association Between Birth Control Pills and Voice QualityTHE LARYNGOSCOPE, Issue 6 2004Ofer Amir PhD Abstract Objectives/Hypothesis: The objective was to extend our knowledge of the effect of birth control pills on voice quality in women based on various acoustic measures. Study Design: A longitudinal comparative study of 14 healthy young women over a 36- to 45-day period. Methods: Voices of seven women who used birth control pills and seven women who did not were recorded repeatedly approximately 20 times. Voice samples were analyzed acoustically, using an extended set of frequency perturbation parameters (jitter, relative average perturbation, pitch period perturbation quotient), amplitude perturbation parameters (shimmer, amplitude average perturbation quotient), and noise indices (noise-to-harmonics ratio, voice turbulence index). Results: Voice quality and stability were found to be better among the women who used birth control pills. Lower values were found for all acoustic measures with the exception of voice turbulence index. Results also provided preliminary indication for vocal changes associated with the days preceding ovulation. Conclusion: In contrast to the traditional view of oral contraceptives as a risk factor for voice quality, and in keeping with the authors' previous work, the data in the present study showed that not only did oral contraceptives have no adverse effect on voice quality but, in effect, most acoustic measures showed improved voice quality among women who used the birth control pill. The differences in the noise indices between groups may also shed light on the nature of the effect of sex hormones on vocal fold activity. It was suggested that hormonal fluctuations may have more of an effect on vocal fold regulation of vibration than on glottal adduction. [source] | |||||||||||||