Anat Ratnovsky^∗,†, Matthew Mellema^*, Steven S. An^∗,‡, Jeffrey J. Fredberg^*, Stephanie A. Shore^*

Molecular & Cellular Biomechanics, Vol.4, No.3, pp. 143-158, 2007, DOI:10.3970/mcb.2007.004.143

Abstract Obesity is a risk factor for asthma. The purpose of this study was to determine whether metformin, an agent used in the treatment of an obesity-related condition (type II diabetes), might have therapeutic potential for modifying the effects of obesity on airway smooth muscle (ASM) function. Metformin acts via activation of AMP-activated protein kinase (AMPK), a cellular sensor of energy status. In cultured murine ASM cells, metformin (0.2--2 mM) caused a dose-dependent inhibition of cell proliferation induced by PDGF (10^-8 M) and serotonin (10^-4 M). Another AMPK activator, 5-aminoimidazole-4-carboxamide-1-ß-D-riboruranoside (AICAR), also inhibited PDGF-induced proliferation. Furthermore, cells More >

G.V. Norton^*, J.C. Novarini^†

Molecular & Cellular Biomechanics, Vol.4, No.2, pp. 75-86, 2007, DOI:10.3970/mcb.2007.004.075

Abstract Ultrasonic imaging in medical applications involves propagation and scattering of acoustic waves within and by biological tissues that are intrinsically dispersive. Analytical approaches for modeling propagation and scattering in inhomogeneous media are difficult and often require extremely simplifying approximations in order to achieve a solution. To avoid such approximations, the direct numerical solution of the wave equation via the method of finite differences offers the most direct tool, which takes into account diffraction and refraction. It also allows for detailed modeling of the real anatomic structure and combination/layering of tissues. In all cases the correct… More >

D. Moens¹, M. De Munck, D. Vandepitte

CMES-Computer Modeling in Engineering & Sciences, Vol.22, No.2, pp. 129-150, 2007, DOI:10.3970/cmes.2007.022.129

Abstract Recently, an interval finite element methodology has been developed to calculate envelope frequency response functions of uncertain structures with interval parameters. The methodology is based on a hybrid interval implementation of the modal superposition principle. This hybrid procedure consists of a preliminary optimization step, followed by an interval arithmetic procedure. The final envelope frequency response functions have been proved to give a very good approximation of the actual response range of the interval problem. Initially, this method was developed for undamped structures. Based on the theoretical principles of this approach, this paper introduces a new… More >

C. Jiang¹, X. Han^1,2

CMES-Computer Modeling in Engineering & Sciences, Vol.22, No.2, pp. 97-118, 2007, DOI:10.3970/cmes.2007.022.097

Abstract A new uncertain optimization method is developed based on intervals and an approximation management model. A general uncertain optimization problem is considered in which the objective function and constraints are both nonlinear and uncertain, and intervals are used to model the uncertainty existing in the system. Based on a possibility degree of interval,anonlinear interval number programming (NINP) method is proposed. A deterministic objective function is constructed to maximize the possibility degree of the uncertain objective function, and the uncertain constraints are changed into deterministic ones by introducing some possibility degree levels. If the optimal possibility degree More >

L. Parussini¹, V. Pediroda²

CMES-Computer Modeling in Engineering & Sciences, Vol.22, No.1, pp. 41-64, 2007, DOI:10.3970/cmes.2007.022.041

Abstract In this paper the Non-Intrusive Polynomial Chaos Method coupled to a Fictitious Domain approach has been applied to one- and two-dimensional elliptic problems with geometric uncertainties, in order to demonstrate the accuracy and convergence of the methodology. The main advantage of non-intrusive formulation is that existing deterministic solvers can be used. A new Least-Squares Spectral Element method has been employed for the analysis of deterministic differential problems obtained by Non-Intrusive Polynomial Chaos. This algorithm employs a Fictitious Domain approach and for this reason its main advantage lies in the fact that only a Cartesian mesh More >

I.S. Raju¹, E.H. Glaessgen¹, B.H. Mason¹, T. Krishnamurthy¹, C.G. Davila¹

CMES-Computer Modeling in Engineering & Sciences, Vol.22, No.1, pp. 1-30, 2007, DOI:10.3970/cmes.2007.022.001

Abstract A detailed finite element analysis of the right rear lug of the American Airlines Flight 587 - Airbus A300-600R was performed as part of the National Transportation Safety Board's failure investigation of the accident that occurred on November 12, 2001. The loads experienced by the right rear lug were evaluated using global models of the vertical tail, local models near the right rear lug, and a global-local analysis procedure. The right rear lug was analyzed using two modeling approaches. In the first approach, solid-shell type modeling was used, and in the second approach, layered-shell type… More >

Xianwu Ling¹, S.N. Atluri¹

CMES-Computer Modeling in Engineering & Sciences, Vol.21, No.1, pp. 81-92, 2007, DOI:10.3970/cmes.2007.021.081

Abstract In this work, single wall carbon nanotubes (SWNTs) are shown to obey a hyperelastic constitutive model at moderate strains and temperatures. We consider the finite temperature effect via the local harmonic approach. The equilibrium configurations were obtained by minimizing the Helmholtz free energy of a representative atom in an atom-based cell model. We show that the strain energy can be fitted by two cubic polynomials, which consequently produces for the linear elasticity a linearly increasing tangent modulus below a critical strain and an almost linearly decreasing tangent modulus beyond the critical strain. To avoid the More >

Chein-Shan Liu¹

CMES-Computer Modeling in Engineering & Sciences, Vol.21, No.1, pp. 53-66, 2007, DOI:10.3970/cmes.2007.021.053

Abstract A newly modified Trefftz method is developed to solve the exterior and interior Dirichlet problems for two-dimensional Laplace equation, which takes the characteristic length of problem domain into account. After introducing a circular artificial boundary which is uniquely determined by the physical problem domain, we can derive a Dirichlet to Dirichlet mapping equation, which is an exact boundary condition. By truncating the Fourier series expansion one can match the physical boundary condition as accurate as one desired. Then, we use the collocation method and the Galerkin method to derive linear equations system to determine the More >

S. Sabchevski¹, I. Zhelyazkov², M. Thumm³, S. Illy⁴, B. Piosczyk⁵, T.-M. Tran^6,7, J. Gr. Pagonakis⁸

CMES-Computer Modeling in Engineering & Sciences, Vol.20, No.3, pp. 203-220, 2007, DOI:10.3970/cmes.2007.020.203

Abstract Computer aided design of powerful gyrotrons for electron cyclotron resonance heating and current drive of fusion plasmas requires adequate physical models and efficient software packages for analysis, comparison and optimization of their electron-optical systems through numerical experiments. In this paper, we present and discuss the current status of the simulation tools available to the researchers involved in the development of multi-megawatt gyrotrons for the ITER project, review some of their recent upgrades and formulate directions for further modifications and improvements. Illustrative examples used represent results from recent numerical investigations of real constructions. Some physical problems More >

Chein-Shan Liu ¹

CMES-Computer Modeling in Engineering & Sciences, Vol.20, No.2, pp. 111-122, 2007, DOI:10.3970/cmes.2007.020.111

Abstract A highly accurate new solver is developed to deal with interior and exterior mixed-boundary value problems for two-dimensional Laplace equation, including the singular ones. To promote the present study, we introduce a circular artificial boundary which is uniquely determined by the physical problem domain, and derive a Dirichlet to Robin mapping on that artificial circle, which is an exact boundary condition described by the first kind Fredholm integral equation. As a consequence, we obtain a modified Trefftz method equipped with a characteristic length factor, ensuring that the new solver is stable because the condition number More >