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Primary Variable (primary + variable)
Selected AbstractsA Cartesian-grid collocation technique with integrated radial basis functions for mixed boundary value problemsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 4 2010Phong B. H. Le Abstract In this paper, high-order systems are reformulated as first-order systems, which are then numerically solved by a collocation method. The collocation method is based on Cartesian discretization with 1D-integrated radial basis function networks (1D-IRBFN) (Numer. Meth. Partial Differential Equations 2007; 23:1192,1210). The present method is enhanced by a new boundary interpolation technique based on 1D-IRBFN, which is introduced to obtain variable approximation at irregular points in irregular domains. The proposed method is well suited to problems with mixed boundary conditions on both regular and irregular domains. The main results obtained are (a) the boundary conditions for the reformulated problem are of Dirichlet type only; (b) the integrated RBFN approximation avoids the well-known reduction of convergence rate associated with differential formulations; (c) the primary variable (e.g. displacement, temperature) and the dual variable (e.g. stress, temperature gradient) have similar convergence order; (d) the volumetric locking effects associated with incompressible materials in solid mechanics are alleviated. Numerical experiments show that the proposed method achieves very good accuracy and high convergence rates. Copyright © 2009 John Wiley & Sons, Ltd. [source] 2D internal flux compatibility equation of the flux Green element method for transient nonlinear potential problemsNUMERICAL METHODS FOR PARTIAL DIFFERENTIAL EQUATIONS, Issue 6 2010Akpofure E. Taigbenu Abstract This article presents the derivation and implementation of the normal directional flux compatibility equation (relationship) at internal nodes when the Green element formulation that consistently provides accurate estimates of the primary variable, and its normal directional derivative (normal flux) is applied in 2D heterogeneous media to steady and transient potential problems. Such a relationship is required to resolve the closure problem due to having fewer integral equations than the number of unknowns at internal nodes. The derivation of the relationship is based on Stokes' theorem, which transforms the contour integral of the normal directional fluxes into a surface integral that is identically zero. The numerical discretization of the compatibility equation is demonstrated with four numerical examples using the six-node quadratic triangular and the four and eight-node rectangular elements. The incorporation of triangular elements into the current formulation demonstrates that the internal compatibility equation can be successfully implemented on irregular grids. The direct calculation of the fluxes significantly enhances the accuracy of the formulation, so that high accuracy, exceeding that of the finite element method, is achieved with very coarse spatial discretization. © 2009 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 2010 [source] Treating intermittent allergic rhinitis: a prospective, randomized, placebo and antihistamine-controlled study of Butterbur extract Ze 339PHYTOTHERAPY RESEARCH, Issue 6 2005Article first published online: 22 AUG 200 Abstract Background: Intermittent allergic rhinitis (IAR) causes patients distress and impairs their work performance and quality of life. A variety of medicines are used by sufferers whose anguish frequently leads to trying new treatments, increasingly from herbal sources. Methods: Prospective, randomized, double-blind, parallel group comparison study of Butterbur extract (Ze 339; 8 mg total petasine; one tablet thrice-daily), fexofenadine (Telfast 180®, one tablet once-daily) and placebo in 330 patients. Protocol and analysis were according to the latest guidelines on new treatments for allergic rhinitis. The primary efficacy variable was a change in symptoms from baseline to endpoint during daytime. The secondary efficacy variables were: (a) as per primary variable (evening/night); (b) Physician's global assessment; (c) Responder rates. Safety was closely monitored. Findings: Both active treatments were individually significantly superior to placebo (p < 0.001) in improving symptoms of IAR, while there were no differences between the two active treatments (p = 0.37). Superiority to placebo was similarly shown during the evening/night (p < 0.001), by physicians' own assessment and by responder rates. Both treatments were well tolerated. Interpretation: Butterbur Ze 339 and Fexofenadine are comparably efficacious relative to placebo. Despite being a herbal drug, Butterbur Ze 339 has now been subject to a series of well controlled trials and should be considered as an alternative treatment for IAR. Copyright © 2005 John Wiley & Sons, Ltd. [source] Efficacy and safety of high-dose budesonide/formoterol (Symbicort®) compared with budesonide administered either concomitantly with formoterol or alone in patients with persistent symptomatic asthmaRESPIROLOGY, Issue 3 2006Christine JENKINS Objective and background: Budesonide/formoterol 160/4.5 µg, two inhalations bd, is an effective and well-tolerated maintenance therapy for patients not controlled on inhaled corticosteroids alone. The authors assessed the efficacy and safety of a higher dose of budesonide/formoterol in patients with persistent symptomatic asthma. Methods: This was a 24-week, double-blind, double-dummy randomized study. Budesonide/formoterol 320/9 µg, two inhalations bd (1280/36 µg/day), was compared with corresponding doses of budesonide during weeks 1,12 and budesonide plus formoterol via separate inhalers during weeks 1,24. Efficacy was assessed during weeks 1,12; the primary variable was morning PEF. Safety was assessed over weeks 1,24. Results: Patients (n = 456; aged 12,79 years) had a mean reversibility in FEV1 of 28% and mean pre-study inhaled corticosteroid dose of 1038 µg/day. Mean morning PEF increased by 37 L/min and 36 L/min with budesonide/formoterol and budesonide plus formoterol, respectively, versus an increase of 5 L/min with budesonide (P < 0.001 for both vs. budesonide). Budesonide/formoterol increased time to first mild exacerbation (P < 0.005) versus budesonide. Budesonide/formoterol and budesonide plus formoterol had similar efficacy. All treatments were well tolerated and the incidence of class-related adverse events was similarly low in all groups. Changes in serum potassium and plasma cortisol were comparable across treatments. Conclusions: High-dose budesonide/formoterol (320/9 µg, two inhalations bd) is effective and well tolerated in patients with persistent symptomatic asthma. The findings also support the safety of regular high-dose formoterol (36 µg/day). [source] Ratio Estimation with Measurement Error in the Auxiliary VariateBIOMETRICS, Issue 2 2009Timothy G. Gregoire Summary With auxiliary information that is well correlated with the primary variable of interest, ratio estimation of the finite population total may be much more efficient than alternative estimators that do not make use of the auxiliary variate. The well-known properties of ratio estimators are perturbed when the auxiliary variate is measured with error. In this contribution we examine the effect of measurement error in the auxiliary variate on the design-based statistical properties of three common ratio estimators. We examine the case of systematic measurement error as well as measurement error that varies according to a fixed distribution. Aside from presenting expressions for the bias and variance of these estimators when they are contaminated with measurement error we provide numerical results based on a specific population. Under systematic measurement error, the biasing effect is asymmetric around zero, and precision may be improved or degraded depending on the magnitude of the error. Under variable measurement error, bias of the conventional ratio-of-means estimator increased slightly with increasing error dispersion, but far less than the increased bias of the conventional mean-of-ratios estimator. In similar fashion, the variance of the mean-of-ratios estimator incurs a greater loss of precision with increasing error dispersion compared with the other estimators we examine. Overall, the ratio-of-means estimator appears to be remarkably resistant to the effects of measurement error in the auxiliary variate. [source] Evolution of Academic Emergency Medicine over a Decade (1991-2001)ACADEMIC EMERGENCY MEDICINE, Issue 10 2002E. John Gallagher MD Abstract Objective: To test the hypothesis that emergency medicine (EM) has made significant, quantifiable progress within U.S. academic medicine over the past ten years, 1991-2001. Methods: Baseline (7/1/1991) and comparison (7/1/2001) data sets contained all Liaison Committee on Medical Education (LCME)-accredited schools, Association of Academic Chairs of Emergency Medicine (AACEM)-recognized academic departments of EM, Residency Review Committee (RRC)-accredited EM residencies, and Association of American Medical Colleges (AAMC)-designated academic medical centers. The increase over ten years in the two primary variables of academic departmental status, and EM residencies located at academic medical centers, was examined in the aggregate, then stratified by medical schools grouped by academic rank. Differences over time are expressed as simple proportions, bounded by 95% confidence intervals (95% CIs). Results: Between 1991 and 2001, the proportion of academic departments of EM at medical schools increased from 18% to 48% (95% CI for difference of 30%= 19% to 41%). The proportion of EM residencies at academic medical centers increased from 42% to 66% (95% CI for a difference of 24%= 11% to 36%). The largest increment of 37% (95% CI = 22% to 52%) in academic departments of EM, and of 36% (95% CI = 20% to 52%) in EM residencies located at academic medical centers, occurred within medical schools whose academic rank was above the median. Conclusions: A quantitatively and statistically significant increase in academic departments of EM within medical schools and EM residency programs at academic medical centers has occurred over the past decade. Half of all medical schools now have academic departments of EM, and two-thirds of academic medical centers house EM residency programs. This has taken place largely within institutions whose academic ranking places them among the top half of all U.S. medical schools. [source] Flow simulation on moving boundary-fitted grids and application to fluid,structure interaction problemsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 4 2006Martin Engel Abstract We present a method for the parallel numerical simulation of transient three-dimensional fluid,structure interaction problems. Here, we consider the interaction of incompressible flow in the fluid domain and linear elastic deformation in the solid domain. The coupled problem is tackled by an approach based on the classical alternating Schwarz method with non-overlapping subdomains, the subproblems are solved alternatingly and the coupling conditions are realized via the exchange of boundary conditions. The elasticity problem is solved by a standard linear finite element method. A main issue is that the flow solver has to be able to handle time-dependent domains. To this end, we present a technique to solve the incompressible Navier,Stokes equation in three-dimensional domains with moving boundaries. This numerical method is a generalization of a finite volume discretization using curvilinear coordinates to time-dependent coordinate transformations. It corresponds to a discretization of the arbitrary Lagrangian,Eulerian formulation of the Navier,Stokes equations. Here the grid velocity is treated in such a way that the so-called Geometric Conservation Law is implicitly satisfied. Altogether, our approach results in a scheme which is an extension of the well-known MAC-method to a staggered mesh in moving boundary-fitted coordinates which uses grid-dependent velocity components as the primary variables. To validate our method, we present some numerical results which show that second-order convergence in space is obtained on moving grids. Finally, we give the results of a fully coupled fluid,structure interaction problem. It turns out that already a simple explicit coupling with one iteration of the Schwarz method, i.e. one solution of the fluid problem and one solution of the elasticity problem per time step, yields a convergent, simple, yet efficient overall method for fluid,structure interaction problems. Copyright © 2005 John Wiley & Sons, Ltd. [source] Energy consideration for designing supercharged ram jet enginesINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 2 2008Amro M. Al-QutubArticle first published online: 20 JUN 200 Abstract The present work investigates the energy considerations and performance characteristics of a newly proposed supercharged ram jet engine. Thermodynamics and fluid mechanics analyses were developed to predict specific thrust, thrust-specific fuel consumption (TSFC), overall efficiency, and thrust-to-weight ratio of the engine. Compressor pressure ratio and efficiency, combustor temperature, and pressure losses in the burner and nozzle are considered as primary variables in the engine performance analysis. Performance characteristics are calculated to illustrate the effect of each parameter independently at different flight speeds. This is done while maintaining other parameters at given typical operating values. A computer program was developed to perform the iterative calculations. Results indicate that the compressor pressure ratio and the combustion product temperature are the most critical parameters in determining the performance of the engine. At compressor pressure ratio of 1.15,1.2, the typical static thrust-to-weight ratio is at maximum. Increasing combustion product temperature increases the thrust-to-weight ratio as well as TSFC. Finally, newly developed high power-to-weight ratio IC engine makes it possible for the supercharged ram jet engine to achieve high performance, in terms of thrust-to-weight ratio and TSFC. Copyright © 2007 John Wiley & Sons, Ltd. [source] Fountain flow revisited: The effect of various fluid mechanics parametersAICHE JOURNAL, Issue 5 2010Evan Mitsoulis Abstract Numerical simulations have been undertaken for the benchmark problem of fountain flow present in injection-mold filling. The finite element method (FEM) is used to provide numerical results for both cases of planar and axisymmetric domains under laminar, isothermal, steady-state conditions for Newtonian fluids. The effects of inertia, gravity, surface tension, compressibility, slip at the wall, and pressure dependence of the viscosity are all considered individually in parametric studies covering a wide range of the relevant parameters. These results extend previous ones regarding the shape of the front, and in particular the centerline front position, as a function of the dimensionless parameters. The pressures from the simulations have been used to compute the excess pressure losses in the system (front pressure correction or exit correction). Inertia leads to highly extended front positions relative to the inertialess Newtonian values, which are 0.895 for the planar case and 0.835 for the axisymmetric one. Gravity acting in the direction of flow shows the same effect, while gravity opposing the flow gives a reduced bulge of the fountain. Surface tension, slip at the wall, and compressibility, all decrease the shape of the front. Pressure-dependence of the viscosity leads to increased front position as a corresponding dimensionless parameter goes from zero (no effect) to higher values of the pressure-shift factor. The exit correction increases monotonically with inertia, compressibility, and gravity, while it decreases monotonically with slip and pressure-dependence of the viscosity. Contour plots of the primary variables (velocity-pressure) show interesting trends compared with the base case (zero values of the dimensionless parameters and of surface tension). © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Changes in Technology and Preferences: A General Equilibrium Explanation of Rapid Growth in TradeAUSTRALIAN ECONOMIC PAPERS, Issue 1 2000Peter B. Dixon We use a computable general equilibrium model in an explanation of the recent rapid growth in Australia's trade, particularly intra-industry trade. Relative to previous studies of trade growth based on multiple regression analysis, our approach allows us to: (i) work at a detailed industry level; (ii) use primary variables to represent changes in technology and preferences rather than proxies; and (iii) use a framework based on explicit microeconomic foundations. We find that most of the growth in Australia's trade relative to GDP is explained by changes in technology and preferences. [source] | ||||||||||||||||