bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of locking and stress oscillations in a general curved beam element
Authors: Prathap G. , Naganarayana B. P.
Published: October 2005

In this paper, we have attempted to provide new insights into the phenomenon of shear and membrane locking in a general quadratic curved beam element. Locking is seen to be accompanied by significant quadratic oscillations in the axial force and cubic oscillations in the shear force. The functional reconstitution technique is applied to derive accurate error estimates for the manner in which locking is relieved and for the magnitude of the stress oscillations. The orthogonally correct field‐consistent interpolations are determined for the optimal form of the element using an elegant concept of expanding strain interpolations in terms of Legendre polynomials. The popular two‐point Gaussian integrated version of the element is shown to be non‐orthogonal, resulting in a cubic oscillation in the shear force that curiously vanishes at the Barlow points.
Finite element modelling of crack tip behaviour in viscoelastic materials. Part I: Linear behaviour
Authors: Krishnaswamy P. , Tuttle M. E. , Emery A. F. , Ahmad J.
Published: October 2005

A finite element algorithm which can be used to model either linear or non‐linear viscoelastic material behaviour is described. The algorithm is verified for the linear case by comparing numerical and analytical solutions for (a) a uniaxial tensile specimen, and (b) an infinite plate with a hole subjected to a remote uniaxial stress. The algorithm is then used to determine the stress and strain fields near the tip of a moving crack in a linear viscoelastic medium. Numerical solutions for both growing and healing cracks are compared with results expected based upon the extended correspondence principle. Excellent agreement between theoretical and numerical solutions is obtained in all cases. Sources of numerical error in the FE solution procedure are identified and documented. The algorithm has not been verified for the non‐linear case, since (except for very simple geometries and loading configurations) no closed‐form solutions involving non‐linear viscoelastic material behaviour are available. A comparison between the measured and predicted response of a non‐linear viscoelastic material behaviour will be presented in a following paper.
A unified numerical integration formula for the perfectly plastic von Mises model
Authors: Wu W.
Published: October 2005

The accuracy of numerical integration of the perfectly plastic constitutive equation of von Mises is examined. Based on the analysis of the three existing numerical integration schemes a unified numerical integration formula (UNIF) is derived, which encompasses the three existing schemes as special cases and allows one to integrate the constitutive equation more accurately. According to the UNIF there are, in fact, many integration schemes depending on the direction of the trial stress. The validity of the UNIF is verified by presenting ten contours of constant angular error calculated with the UNIF. We then come to the conclusion that the three widely used schemes are by no means the most accurate ones. Some other schemes with better accuracy are thereby suggested. The determination of the number of substeps is also discussed in conjunction with the UNIF, when a multi‐step method is used.
Boundary element method analysis of stationary thermoelasticity problems in non‐homogeneous media
Authors: Sládek J. , Sládek V. , Markechová I.
Published: October 2005

This paper presents an advanced BEM formulation for the solution of stationary problems of thermoelasticity taking into consideration the thermally induced non‐homogeneity. An iterative scheme is used to determine the displacement fields because the formulation contains a domain‐type integral with displacements. As compared with the existing BEM formulation, this one does not contain a domain integral of the temperature field and, furthermore, the integral representation of stresses is written in the regularized from. Consequently, all the integrals can be computed numerically by using the regular Gaussian quadrature.
Finite elements with displacement interpolated embedded localization lines insensitive to mesh size and distortions
Authors: Dvorkin Eduardo N. , Cuitiño Alberto M. , Gioia Gustavo
Published: October 2005

A new finite element formulation aimed at the solution of problems involving strain localization is presented. The proposed formulation incorporates displacement interpolated embedded localization lines. Results are shown to converge to an ‘exact solution’ when the mesh is refined and also to be quite insensitive to mesh distortions.
A stable alternating direction method for simulating multi‐dimensional solidification problems
Authors: Mampaey F.
Published: October 2005

Application of the Alternating Direction Implicit (ADI) method to study solidification problems reveals some drawbacks. At the interface between different‐materials, temperature oscillations may be recorded at the simulation start which eventually may cause instability. The problems originate from the explicit temperature calculation. Shortcomings may be eliminated by substituting the explicit temperature calculation by an implicit one which is carried out on a limited number of adjacent elements. Results of real solidification problems show that the modified method behaves better than the original ADI method. The new procedure, which is formulated in terms of the finite volume method, eliminates the occurrence of physically incorrect temperature calculations and oscillations initially present in the vicinity of the interface between different materials. When applied to the three‐dimensional solidification problem of the sand coated die, simulation results are in good agreement with experimental data.
Specifications of boundary conditions for Reissner/Mindlin plate bending finite elements
Authors: Häggblad Bo , Bathe Klaus‐Järgen
Published: October 2005

Plate bending finite elements based on the Reissner/Mindlin theory offer improved possibilities to pursue reliable finite element analyses. The physical behaviour near the boundary can be modelled in a realistic manner and inherent limitations in the Kirchhoff plate bending elements when modelling curved boundaries can easily be avoided. However, the boundary conditions used are crucial for the quality of the solution. We identify the part of the Reissner/Mindlin solution that controls the boundary layer and examine the behaviour near smooth edges and corners. The presence of boundary layers of different strengths for different sets of boundary conditions is noted. For a corner with soft simply supported edges the boundary layer removes the singular behaviour of Kirchhoff type from the stress resultants. We demonstrate the theoretical results by some numerical studies on simple plate structures which are discretized by an accurate, higher‐order plate element. The results provide guidance in choosing efficient meshes and appropriate boundary conditions in finite element analyses.
Rates of change of closed‐loop eigenvalues and eigenvectors of actively controlled structures
Authors: Pan T. S. , Rao S. S. , Venkayya V. B.
Published: October 2005

The sensitivity of the closed‐loop eigenvalues and eigenvectors of actively controlled flexible structures with distinct eigenvalues is considered. The sensitivity information is essential in the optimization of large space structures with stability/performance robustness, closed‐loop eigenvalues or damping ratios treated as objective or constraint functions. The efficiency of the analytical expressions derived for the rates of change of the closed‐loop eigenvalues with respect to structural design variables is demonstrated through two numerical examples. The utility of the sensitivity of the closed‐loop eigenvalues and eigenvectors in evaluating the derivatives of the stability and performance robustness indices is also indicated and illustrated through numerical examples.
An elliptical growth model of forest fire fronts and its numerical solution
Authors: Richards Gwynfor D.
Published: October 2005

A system of differential equations that describe the growth of a forest fire front in time for variable fuel, weather and topographical conditions is derived. The system is first order, non‐linear and contains parameters that can be obtained from forestry data. A finite difference solution is presented, together with its inherent problems and their solution. Results are presented for a variety of situations that include variable fuel, wind and fire breaks. It is found that the equations and their solution efficiently produce simulations for complex problems.
Compatible description of tool surfaces and FEM meshes for analysing sheet forming operations
Authors: Keum Y. T. , Nakamachi E. , Wagoner R. H. , Lee J. K.
Published: October 2005

Implementation of the 3‐D finite element method (FEM) of sheet forming operations has proceeded slowly. In particular, describing the arbitrary tool surfaces in an accurate and smooth manner, with well behaved first and second derivatives, has been a major obstacle. A new geometric method, suitable for representing any rigid tool surface, has been developed and shown to be superior to the usual schemes. The new method relies on the described tool surface for position data only. The spatial derivatives are obtained by considering only the sheet mesh nodal positions. This new scheme has been implemented with a rigid‐viscoplastic FEM program using general surface descriptions based on B‐splines and linear inter‐polation. Analytic representations of a hemispherical and rounded square punch were also compared. the comparisons show that the proposed method offers several advantages over other general formulations.

1. The new representation is the proper one for formulating the equilibrium condition. Alternate forms can produce spurious results.

2. The proposed method introduces inherently smooth surface derivatives that improve numerical stability, even with crude surface resolution. Suitable test problems show covergence with the new method far past the divergence points of the simulations using the standard general surface description.

3. The method is reasonably efficient, with a time penalty of approximately 30–50 per cent (unoptimized) with respect to analytic surface descriptions.
An automatic remeshing technique for finite element simulation of forming processes
Authors: Habraken A. M. , Cescotto S.
Published: October 2005

An automatic remeshing scheme has been developed to enable finite element simulation of complicated forming processes. In order to avoid the tedious procedures of interrupting the analysis, performing rediscretization, mapping of current state variables and preparing the new set of boundary conditions, a fully automatic remeshing method is described. The different steps of this method are presented with the help of one industrial example.
An adaptive remeshing technique for non‐Newtonian fluid flow
Authors: Dannelongue H. H. , Tanguy P. A.
Published: October 2005

An unstructured mesh generator is integrated in a finite element solver for the adaptive solution of non‐Newtonian fluid flows. An a posteriori error estimate for the equations of motion is presented and is shown to behave according to theoretical convergence rates. The estimate is used to drive the refinement process, and the resulting iterative remeshing algorithm leads to reduction of the error level in the case of an axisymmetric contraction. Original data structures used to speed‐up remeshing and interpolation between unstructured grids are also presented.
Numerical analysis of polymer injection moulding process using finite element method with marker particles
Authors: Matsuhiro Itaru , Shiojima Takeo , Shimazaki Yoji , Daiguji Hisaaki
Published: October 2005

A numerical method for analysing an axisymmetric injection moulding process is presented. A consistent approximation to pressure is applied for a penalty function formulation of Galerkin's finite element method. To analyse the moving free surface and visualize the transient flow pattern, marker particles are introduced. An axisymmetric abrupt cavity, which is filled with a generalized Newtonian fluid, is solved to verify the scheme. As a practical example problem, the transient flow through moulds of a memory disc is analysed.
Computer aided simulation of metal flows in non‐axisymmetric extrusions through bridge dies
Authors: Kiuchi Manabu , Hoshino Michihiko
Published: October 2005

A computer aided simulation technique based on the upper bound theorem is developed in order to analyse three‐dimensional metal flows of workpieces in various extrusion processes. The developed method is applied to simulations of forward extrusions of tubes through bridge dies. The effects of die geometry on extrusion pressure, geometries of dead zone and plastic zone and three‐dimensional flow of workpiece are calculated. The results are compared with experimental measurments and fairly good agreement between them is found.
A flow formulation for rate equilibrium equations
Authors: Thompson Erik G. , Yu Szu‐Wei
Published: October 2005

A succinct derivation of a rate equilibrium equation is presented. An Eulerian finite element flow formulation is then developed for the direct solution of the steady state velocity field and Cauchy stress field within an elasto‐plastic material. The formulation is used for the analysis of strip drawing.
Elastic‐viscoplastic implicit formulation for finite element simulation of complex sheet forming processes
Authors: Saran Michal J. , Samuelsson Alf
Published: October 2005

A formulation for numerical simulation of complex forming processes with generally shaped tools is developed. Special attention is drawn to the accuracy, efficiency and robustness. An incremental displacement approach based on Lagrangian formulation as well as an elastic‐viscoplastic material model with Hill's cross‐anisotropy, power law hardening and strain rate sensitivity are assumed. An implicit integration of the constitutive equations is derived. Frictional contact conditions yield additional constraint relations which, together with equilibrium equations, form the basis for derivation of the consistent tangent matrix. To further increase efficiency and accuracy, application of the adaptive remeshing procedures for sheet forming is investigated. The performance of the proposed algorithm is shown by comparison of the numerical results with the analytical solution for an in‐plane stretching test and with the experimental measurements from 3‐D sheet forming pressings where materials, radius and wall dimensions used are similar to those from industrial applications.
On numerical modelling of hot rolling of metals
Authors: Too J. J. M.
Published: October 2005

A transient, thermomechanical model, METFORM, based on viscoplasticity and heat and mass transport theories has been developed specifically for the prediction of the flow behaviour of metals during hot rolling. The coupling of metal flow, heat transport and microstructural changes is discussed and a framework to account for the coupling behaviour is formulated. The model is partially verified by experiments and is applied to the hot strip mill roughing process, with the focus of interest on skid mark effects and related difficulties frequently observed in hot rolling. Methods for overcoming these difficulties are proposed based on the results obtained from the model. The coupling between microstructure development and the variations of local strain, strain gradient and temperature is confirmed by the predicted strain/strain gradients and micrographs obtained from a hot rolling experiment.
Numerical simulation of the superplastic forming of thin sheet components using the finite element method
Authors: Bonet J. , Wood R. D. , Wargadipura A. H. S.
Published: October 2005

Superplastic forming is a manufacturing process whereby titanium or aluminium sheet is blow formed into a die to produce very light and strong aerospace components. Of crucial importance is the prediction of the final thickness distribution and the pressure cycle necessary to maintain superplasticity. This paper discusses a finite element based solution to these problems and presents examples for typical components including diffusion bonding effects.
Applications of a self‐adaptive algorithm to non‐linear finite element analysis
Authors: Lee Sang H. , Hsieh Steve S.
Published: October 2005

A self‐adaptive algorithm has been developed and implemented for the implicit time integration of non‐linear finite element analysis. In this algorithm, a proper time increment for the next time step is estimated based on the deformation pattern at the preceding step. The iteration process for the equalibrium employs expeditious methods such as quasi‐Newton updates and line searches as well as an adaptive stiffness matrix update strategy for efficiency. Convergence difficulties induced from inadequate prediction of step size or the change in non‐linearities are tackled by the bisection method. These procedures were also successfully applied to static problems by ignoring the damping and the inertia forces. The objective of this paper is to demonstrate the applicability and the effectiveness of the adaptive algorithm in a wide spectrum of non‐linear problems. Six example problems are illustrated, some of which are rather novel. As demonstrated in this paper, the self‐adaptive algorithm implemented in MSC/NASTRAN is proving to be versatile, accurate and efficient.
Derivatives of tangential stiffness matrices for equilibrium path descriptions
Authors: Eriksson Anders
Published: October 2005

The paper describes how several procedures, based on expressions from analytical elastic stability theory, are introduced as numerical tools in a general Finite Element program for geometrically non‐linear structural analysis. Especially is discussed how derivatives of the tangential stiffness matrix can be utilized in several contexts in the solution algorithm. These include improved predictions for the step‐wise solution of equilibrium states, identification of critical points and accurate descriptions of initial post‐bifurcation behaviour.

For two plane beam and bar elements, formulations have been developed giving analytical expressions for these derivatives. The corresponding numerical approximations, needed in other element types, are also discussed. The paper discusses the relative efficiency of higher order predictions in relation to these different element types and different solution strategies. Some numerical examples, showing different types of behaviour, are analysed and discussed.
Physical shape functions in finite element analysis of moderately thick plates
Authors: Gilewski Wojciech , Gomuliński Andrzej
Published: October 2005

A new rectangular finite element for moderately thick plates is presented. The element is based on the concept of physical shape functions, i.e. functions which contain in themselves physical and geometrical properties of the element. The analytic formulae of stiffness, geometric stiffness and mass matrices are presented for isotropic material. The element is free from locking and zero energy modes not corresponding to rigid body motions.

Several examples are presented for static, initial stability and free vibration problems.
Automatic quadrilateral/triangular free‐form mesh generation for planar regions
Authors: Sezer Levent , Zeid Ibrahim
Published: October 2005

Automation of finite element mesh generation holds great benefits for mechanical product development and analysis. In addition to freeing engineers from mundane tasks, automation of mesh generation reduces product cycle design and eliminates human‐related errors. Most of the existing mesh generation methods are either semi‐automatic or require specific topological information. A fully automatic free‐form mesh generation method is described in this paper to alleviate some of these problems. The method is capable of meshing singly or multiply connected convex/concave planar regions. These regions can be viewed as crosssectional areas of 2 1/2 D objects analysed as plane stress, plane strain or axisymmetric stress problems. In addition to being fully automatic, the method produces quadrilateral or triangular elements with aspect rations near one. Moreover, it does not require any topological constraints on the regions to be meshed; i.e. it provides free‐form mesh generation. The input to the method includes the region's boundary curves, the element size and the mesh grading information. The method begins by decomposing the planar region to be meshed into convex subregions. Each subregion is meshed by first generating nodes on its boundaries using the input element size. The boundary nodes are then offset to mesh the subregion. The resulting meshes are merged together to form the final mesh. The paper describes the method in detail, algorithms developed to implement it and sample numerical examples. Results on parametric studies of the method performance are also discussed.
Multiplier methods for engineering optimization
Authors: Arora J. S. , Chahande A. I. , Paeng J. K.
Published: October 2005

Multiplier methods used to solve the constrained engineering optimization problem are described. These methods solve the problem by minimizing a sequence of unconstrained problems defined using the cost and constraint functions. The methods, proposed in 1969, have been determined to be quite robust, although not as efficient as other algorithms. They can be more effective for some engineering applications, such as optimum design and control of large scale dynamic systems. Since 1969 several modifications and extensions of the methods have been developed. Therefore, it is important to review the theory and computational procedures of these methods so that more efficient and effective ones can be developed for engineering applications. Recent methods that are similar to the multiplier methods are also discussed. These are continuous multiplier update, exact penalty and exponential penalty methods.
Dynamic analysis and computer simulation of variable‐mass multi‐rigid‐body systems
Authors: McPhee J. J. , Dubey R. N.
Published: October 2005

In this paper we present a general procedure for analysing the motion of a multi‐rigid‐body system that is capturing and/or ejecting mass. The motivations for this work are given in the introductory section, followed by a description of the mathematical model we have used to represent a variable‐mass system. Using a control volume approach, the differential equations of motion are derived in vector‐dyadic form. The non‐linear scalar components of these equations have been encoded into a Fortran‐77 program that uses a fourth‐order Runge‐Kutta algorithm to compute a numerical solution for the motion of a given physical system; we describe the development of this simulation program and its use of the conformal rotation vector to represent orientations. An application of the program to the dynamic analysis of a specific variable‐mass problem is presented, and a comparison of the numerical results to an analytical solution is used to assess the accuracy of the software. In the concluding section, the advantages and limitations of the underlying formulation are discussed.
An approach to dynamics and control of orbiting flexible structures
Authors: Modi V. J. , Suleman A. , Ng A. C. , Morita Y.
Published: October 2005

A relatively general formulation for studying the dynamics of an arbitrary spacecraft with interconnected flexible bodies is developed accounting for thermal deflection, transient system inertias, shift in the centre of mass, shear deformations, rotary inertias and geometric non‐linearities. The computer implementation has been carried out through symbolic manipulation of the equations of motion. Versatility of the formulation is indicated through application to problems of contemporary interest.
Systematic construction of equations of motion for rigid‐flexible multibody systems containing open and closed kinematic loops
Authors: Nikravesh Parviz E. , Ambrosio Jorge A. C.
Published: October 2005

A systematic method for formulating the equations of motion for multibody systems containing rigid and flexible bodies is presented. The method of using joint co‐ordinates to derive the minimum number of equations of motion is utilized for rigid bodies and the finite element method is employed for flexible bodies. The equations of motion for flexible bodies are simplified into several steps using (a) a lumped mass assumption, (b) static condensation and (c) modal superposition. The combined rigid and flexible body formulation can be used to simulate dynamic response in a variety of applications such as ride handling, rollover and the crash analysis of vehicles, space structures, and biomechanical problems.
Dynamic analysis of spatial flexible multibody systems using joint co‐ordinates
Authors: Pereira M. S. , Proença P. L.
Published: October 2005

This paper presents a systematic method for deriving the minimum number of equations of motion for spatial flexible multibody systems. Relative kinematics are developed using relative joint co‐ordinates and relative joint velocities to formulate a minimum number of equations of motion. The present method takes advantage of the simplicity of the absolute co‐ordinate formulation and computational efficiency of the relative joint co‐ordinate formulation. The system equations of motion are first formulated in terms of a coupled set of absolute reference co‐ordinates and elastic modal co‐ordinates. These equations are transformed to the joint co‐ordinate space by use of a velocity transformation matrix including the elastic modal velocities. A computer algorithm is proposed and extended to closed loop mechanisms. One example of a flexible vehicle is presented and the results are discussed to illustrate the computational efficiency of the method.
Effects of softening in elastic‐plastic structural dynamics
Authors: Maier G. , Perego U.
Published: October 2005

Softening, understood as unstable behaviour of material or structural components, is considered herein for its possible consequences on the overall behaviour of discrete dynamic models of elastic–plastic beam structures, in the absence of geometric effects. It is shown that multiplicity of incremental solutions (response bifurcations) and manifestations of overall instability may occur. The bifurcated responses may exhibit different scenarios for the same excitation: e.g. shakedown or local damage up to failure. An insight into and criteria for such occurrences are achieved by formulating the rate and the finite increment problem as linear complementarity problems. Period doubling and deterministic chaos under harmonic excitation are observed when reversible (holonomic) softening behaviour is assumed. The strong sensitivity of the phenomena investigated with respect to the choice of the structural model is pointed out. The findings are elucidated by illustrative examples.
Second order approximations in structural genesis and shape finding
Authors: Mlejnek H. P. , Jehle U. , Schirrmacher R.
Published: October 2005

The introduction of second order sensitivities to behaviour approximation in structural optimization is applied and investigated. Numerical computation of second derivatives is considered and evaluated. Two approaches in shape optimization are involved, namely shape finding by moving boundaries and shape genesis by distributing mass in a specified design domain. A series of examples is engaged to work out the benefits of second order information in both the above fields.
Shape optimization of two dimensional bodies by boundary changing method and thickness changing method
Authors: Hasegawa Akira
Published: October 2005

When we use FEM as a structural analyser, we have two methods for the optimization of two dimensional bodies. The first method is the boundary changing method in which the co‐ordinates of nodes should be changed to the optimum location without changing the thickness of elements. The second method is the thickness changing method in which the thickness of elements should be changed to the optimum values without changing the co‐ordinates of nodes. In this paper, we study the two optimum methods in the condition of uniform stress distribution, and the element area distribution method, which is one of the boundary shape changing methods, has been developed.
Multicriteria optimization of pin‐jointed structures with overall stability constraints
Authors: Kacianauskas Rimantas , Kutas Remigijus , Maciulevicius Daumantas
Published: October 2005

The optimization problem of elastic pin‐jointed structures for overall stability conditions is presented in this paper. Two optimality criteria, the minimum of volume and the maximum of critical load, are taken into account. The optimization problem is presented as a non‐linear multicriteria mathematical programming problem.

Dimensional analysis enables natural division of the problem into two stages: optimization in space of non‐dimensional variables with following specification of final dimensions.

The sensitivity analysis and incremental solution scheme are used for the discription and solution of the optimization problem. Two sets of examples illustrate given models and a compromise solution. In the first sample of problems the optimization of the cross‐sectional areas of the structure is considered while shape optimization is given in the second sample. Mathematical models of both examples are illustrated by numerical results. The shape optimization problem is characterized by a multiplicity of buckling modes and leads to complicated non‐convex mathematical programming problems. Given examples are representative of complexities associated with practical problems.
Sensitivity analysis—the basis for optimization
Authors: Kibsgaard Steen
Published: October 2005

The present paper contains a numerical study on semi‐analytical design sensitivity analysis. The paper describes the dissimilarities of sensitivities due to mesh refinement for a total of five different plane stress elements. Furthermore, we discuss which mesh relocation technique to use in order to perform an efficient sensitivity analysis, i.e. whether a relocation of nodes on the entire domain is necessary, or whether we can fulfil the accuracy requirements by only relocating the boundary nodes.
Design sensitivity coefficients for elasto‐viscoplastic problems by boundary element methods
Authors: Zhang Q. , Mukherjee S. , Chandra A.
Published: October 2005

This paper is concerned with accurate and efficient determination of design sensitivity coefficients (DSCs) for solid mechanics problems with small strains and rotations, but with material non‐linearities present (elasto‐plastic or elasto‐viscoplastic problems). This approach is based on direct differentiation (DDA) of the relevant derivative boundary element method (DBEM) formulation of the problem. Analytical differentiation of the DBEM equations leads to singular integral equations for the DSCs with weakly (logarithmically for 2‐D) singular kernels which are easy to deal with. Also, stress components and their sensitivities are obtained on the boundary of a body with great accuracy. These quantities are typically difficult to obtain accurately from finite element methods (FEM).

A computer program for general two‐dimensional (plane strain and plane stress) problems has been developed based on the above formulation. Numerical results are presented for some sample problems and these are compared against direct solutions. The agreement between the DBEM and direct solutions is excellent for these examples.
a posteriori Error estimation for triangular and tetrahedral quadratic elements using interior residuals
Authors: Baehmann Peggy L. , Shephard Mark S. , Flaherty Joseph E.
Published: October 2005

A reliable and accurate a posteriori error estimator for quadratic triangular and tetrahedral elements is presented. Its application in an automated, adaptive finite element modelling system for elasticity problems demonstrates its ability to accurately estimate the error in the energy norm. A local version of this error estimator is also used to determine the multiple level h‐refinement necessary to improve the finite element mesh.
An integrated approach for automated generation of two/three dimensional finite element grids using spatial occupancy enumeration and delaunay triangulation
Authors: Ramakrishnan C. V. , Ramakrishnan S. , Kumar Ashish , Bhattacharya Marina
Published: October 2005

The paper describes the development of an automated triangulation algorithm for arbitrary domains. The method involves octree decomposition and subdomain meshing using Delaunay triangulation. Extension to three dimensional objects involving curved boundary surfaces is briefly described.
Conjugate direction methods for helmholtz problems with complex‐valued wavenumbers
Authors: Paulsen Keith D. , Lynch Daniel R. , Liu Weiping
Published: October 2005

The convergence behaviour of conjugate direction methods for Helmholtz problems with complex‐valued wavenumbers is studied. The model problem is a Galerkin discretization of the scalar Helmholtz equation on square arrays of 2D and 3D, C° linear elements. A series of controlled experiments is performed which use the dimensionless wavenumber and the algebraic size of the system of equations to completely characterize the iterative performance of the solvers. The effects of algebraic size are examined as functions of both mesh refinement and mesh extension within the limits of present‐day workstation computing environments. A comparison is drawn between the conjugate direction methods investigated and the equivalent time‐domain solution obtained through explicit time‐stepping.
Configuration design sensitivity analysis of built‐up structures part I: Theory
Authors: Twu Sung‐Ling , Choi Kyung K.
Published: October 2005

A continuum based configuration design sensitivity analysis method is developed for built‐up structures that include truss, beam, plane elastic solid and plate design components. The configuration design variation of a structural component can be characterized by changes in the domain shape and in the orientation of the component. A variational approach is then used to incorporate both shape and orientation effects in the same energy equation. A continuum shape design sensitivity analysis method that utilizes the material derivative idea of continuum mechanics is employed to account for effects of shape variation. An approach that is similar to the continuum shape design sensitivity analysis method is developed in this paper to account for the effect of orientation variation. Variations of energy bilinear and load linear forms, with respect to both shape and orientation design variables, are derived for each structural component. Using the adjoint variable or direct differentiation method, configuration design sensitivity results for built‐up structures are obtained in terms of the design velocity fields. Configuration design sensitivity analyses of both static and eigenvalue responses are considered.
On the consideration of unilateral contact and friction in cracks. The boundary integral method
Authors: Theocaris P. S. , Panagiotopoulos P. D.
Published: October 2005

The scope of the present paper is the study of cracks having a given geometry by taking into account unilateral contact and friction phenomena between the two sides of the crack. The arising problem is highly non‐classical because of the inequality relations describing the unilateral contact and friction interface conditions. The indirect BIEM is extended appropriately in order to treat this problem. Numerical examples concerning the calculation of stress intensity factors under the unilateral contact and friction interface conditions illustrate the developed method.
Dexamethasone Alleviates Meconium‐Induced Airway Hyperresponsiveness and Lung Inflammation in Rabbits
Authors: Mokry Juraj , Mokra Daniela , Antosova Martina , Bulikova Janka , Calkovska Andrea , Nosalova Gabriela
Published: October 2005

The effects of dexamethasone on in vitro airway reactivity associated with lung inflammation were investigated in rabbits with meconium aspiration. Oxygen‐ventilated adult rabbits received an intratracheal bolus of 4 ml/kg body weight of saline (Sal, n = 4) or human meconium (25 mg/ml). Thirty minutes later, meconium‐instilled animals intravenously received 0.5 mg/kg of dexamethasone (Dexa, n = 6), or were left without treatment (Meco, n = 5). The animals were ventilated for a further 5 hr and then sacrificed. The left lungs were lavaged with saline, and the white blood cell (WBC) count was estimated. Tracheal and right‐lung tissue strips were placed into organ chambers with Krebs‐Henseleit solution. Cumulative doses of histamine (10−8–10−3 mol/l) and acetylcholine (10−8–10−3 mol/l) were added to the chambers, and recordings of contractions were made after a 30‐min loading phase with a tension of 4 grams, and another 30‐min adaptation phase with a tension of 2 g. Tracheal smooth muscle in vitro reactivity to histamine was higher in the Meco than in the Sal group, and dexamethasone decreased the reactivity compared to the Meco group (P < 0.05). Lung tissue in vitro reactivity to histamine was slightly higher in the Meco than in the Sal group (P > 0.05), and dexamethasone decreased the reactivity compared to both the Meco and Sal groups (P < 0.05). No between‐group differences were observed in tracheal or lung in vitro reactivity to acetylcholine (P > 0.05). In the Meco group, blood WBC (P > 0.05) and neutrophil (P < 0.05) counts were lower than in the Sal and Dexa groups. Lung neutrophils and eosinophils were higher in both the Meco and Dexa groups than in the Sal group (P < 0.01). Dexamethasone decreased neutrophils (P < 0.05) compared to the Meco group. Meconium‐induced airway hyperreactivity to histamine and lung inflammation were alleviated by dexamethasone. Pediatr Pulmonol. © 2005 Wiley‐Liss, Inc.
Influence of corona treatment decay on print quality in water‐borne flexographic printing of low‐density polyethylene‐coated paperboard
Authors: Mesic Behudin , Lestelius Magnus , Engström Gunnar
Published: October 2005

The decrease in the corona treatment effect with time and its influence on the flexographic printability of low‐density polyethylene‐coated paperboard were studied. After corona treatment, sheets were stored in different ways. Some sheets were stored in a laboratory atmosphere, while others were protected from exposure to light, air, moisture and dust in polyethylene bags. The tendency for ink to spread on the surfaces was studied using contact angle measurements. Printability was evaluated as print density, dot gain, uncovered (white) and mottling. The results obtained show that the surface energy of the protected sheets decreased with time, but not as much and not as quickly as that of the unprotected sheets. In the case of the protected sheets, the percentage uncovered areas and mottling remained constant, but for the unprotected sheets they increased with increasing time after the corona treatment. No significant differences were seen in the other print quality measures. Copyright © 2005 John Wiley & Sons, Ltd.
EDXRF determination of impurities in potassium dihydrogenphosphate single crystals and raw materials
Authors: Belikov K. N. , Mikhailova L. I. , Spolnik Z. M. , Van Grieken R.
Published: October 2005

A fast and simple preconcentration procedure for recovering various cation impurities from potassium dihydrogenphosphate (KDP) single crystals and raw materials, followed by energy‐dispersive X‐ray fluorescence analysis (EDXRF), is described. The technique is based on the adsorption of metal 8‐hydroxyquinoline complexes from aqueous solutions of KDP on activated carbon, separation of the concentrate on a Nuclepore filter and subsequent determination by EDXRF. To fix activated carbon powder on a filter surface, an amount of 1‐hexadecanol is added to the KDP solution during the preconcentration procedure. The optimum conditions for the best recovery of the impurities were established. It was shown that a preconcentration factor of 100 can be achieved and the detection limit for a number of elements was down to 0.01 µg g−1. The relative standard deviations were 6–17% for element concentrations of 0.2 µg g−1. The method was successfully applied to the determination of Fe, Co, Cu, Ni, Zn, Mn, Ti and Bi in KDP single crystals and raw materials. Copyright © 2005 John Wiley & Sons, Ltd.
Asymmetric behavior of archaeal prolyl‐tRNA synthetase
Authors: Ambrogelly Alexandre , Kamtekar Satwik , Stathopoulos Constantinos , Kennedy Dexter , Söll Dieter
Published: October 2005

Archaeal prolyl‐tRNA synthetases differ from their bacterial counterparts: they contain an additional domain (about 70 amino acids) appended to the carboxy‐terminus and lack an editing domain inserted into the class II catalytic core. Biochemical and structural approaches have generated a wealth of information on amino acid and tRNA specificities for both types of ProRSs, but have left a number of aspects unexplored. We report here that the carboxy‐terminal domain of Methanocaldococcus jannaschii ProRS is not involved in tRNA binding since its deletion only mildly affects the kinetic parameters for the enzyme. We also demonstrate that M. jannaschii ProRS is a homodimeric enzyme that is functionally asymmetric; only one of the two active sites at a time is able to form prolyl‐adenylate, and only one tRNA molecule binds per dimer. Together with previous reports our results show that asymmetry might be a general feature of the aminoacylation reaction catalyzed by dimeric aminoacyl‐tRNA synthetases from both classes.
Differentiation of circulating endothelial progenitor cells to a cardiomyogenic phenotype depends on E‐cadherin
Authors: Koyanagi Masamichi , Urbich Carmen , Chavakis Emmanouil , Hoffmann Jörg , Rupp Stefan , Badorff Cornel , Zeiher Andreas M. , Starzinski-Powitz Anna , Haendeler Judith , Dimmeler Stefanie
Published: October 2005

Progenitor cells may contribute to cardiac regeneration. Here, we investigated the role of cadherins and integrins for differentiation of human adult circulating endothelial progenitor cells (EPCs) into cardiomyocytes (CM) in a co‐culture system. N‐ and E‐cadherin were expressed in EPCs and were localized at the interface between EPCs and CM. Incubation of a blocking antibody against E‐cadherin reduced the expression of CM marker protein in EPCs. Blocking antibodies against N‐ or P‐cadherin or the β1‐ and β2‐integrins were not effective. These data suggested that cell‐to‐cell communication mediated by E‐cadherin contributes to the acquirement of a cardiomyogenic phenotype of human endothelial progenitor cells.
Identification and characterization of a triacylglycerol lipase in Arabidopsis homologous to mammalian acid lipases
Authors: El-Kouhen Karim , Blangy Stéphanie , Ortiz Emilia , Gardies Anne-Marie , Ferté Natalie , Arondel Vincent
Published: October 2005

Triacylglycerol (TAG) lipases have been thoroughly characterized in mammals and microorganisms. By contrast, very little is known on plant TAG lipases. An Arabidopsis cDNA called AtLip1 (At2g15230), which exhibits strong homology to lysosomal acid lipase, was found to drive the synthesis of an active TAG lipase when expressed in the baculovirus system. The lipase had a maximal activity at pH 6 and the specific activity was estimated to be about 45 μmol min−1
mg−1 protein using triolein as a substrate. Knock‐out mutant analysis showed no phenotype during germination indicating that this enzyme is fully dispensable for TAG storage breakdown during germination. Northern blot analyses indicated that the transcript is present in all tissues tested.
Viral and cellular oncogenes induce rapid mitochondrial translocation of p53 in primary epithelial and endothelial cells early in apoptosis
Authors: Nemajerova Alice , Wolff Sonja , Petrenko Oleksi , Moll Ute M.
Published: October 2005

In p53‐dependent apoptosis in response to genotoxic and hypoxic stress, a fraction of induced wild‐type p53 rapidly translocates to mitochondria, triggering a rapid first wave of mitochondrial membrane permeabilization and apoptosis that is later fortified by the transcriptional program of p53. However, whether this direct mitochondrial program also occurs upon oncogenic stress is unknown. In normal cells, oncogenic signals can induce a p53‐dependent fail‐safe mechanism to counter uncontrolled proliferation by engaging p53‐dependent apoptosis. To address whether mitochondrial p53 contributes to oncogene‐induced fail‐safe apoptosis, p53 translocation was determined in primary human epithelial and endothelial cells overexpressing c‐Myc, E1A or E2F1. Serum starvation of these cells, but not of control cells, triggered rapid p53 accumulation at mitochondria, accompanied by cytochrome c and SMAC release and followed by apoptosis. Our data establishes the contribution of the transcription‐independent mitochondrial p53 pathway to apoptosis of primary cells in response to deregulated oncogenes.
The cyanobacterium Anabaena sp. PCC 7120 has two distinct β‐carotene ketolases: CrtO for echinenone and CrtW for ketomyxol synthesis
Authors: Mochimaru Mari , Masukawa Hajime , Takaichi Shinichi
Published: October 2005

Two β‐carotene ketolases, CrtW and CrtO, are widely distributed in bacteria, although they show no significant sequence homology with each other. The cyanobacterium Anabaena sp. PCC 7120 was found to have two homologous genes. In the crtW deleted mutant, myxol 2′‐fucoside was present, but ketomyxol 2′‐fucoside was absent. In the crtO deleted mutant, β‐carotene was accumulated, and the amount of echinenone was decreased. Therefore, CrtW catalyzed myxol 2′‐fucoside to ketomyxol 2′‐fucoside, and CrtO catalyzed β‐carotene to echinenone. This cyanobacterium was the first species found to have both enzymes, which functioned in two distinct biosynthetic pathways.
Inhibition of RhoA‐mediated SRF activation by p116Rip
Authors: Mulder Jacqueline , Ariaens Aafke , van Horck Francis P.G. , Moolenaar Wouter H.
Published: October 2005

p116Rip, originally identified as a binding partner of activated RhoA, is an actin‐binding protein that interacts with the regulatory myosin‐binding subunit (MBS) of myosin‐II phosphatase and is essential for Rho‐regulated cytoskeletal contractility. Here, we have examined the role of p116Rip in RhoA‐mediated activation of the transcription factor SRF. We show that p116Rip oligomerizes via its C‐terminal coiled‐coil domain and, when overexpressed, inhibits RhoA‐induced SRF activation without affecting RhoA‐GTP levels. Mutant forms of p116Rip that fail to oligomerize or bind to MBS are still capable of inhibiting SRF activity. Our results suggest that p116Rip interferes with RhoA‐mediated transcription through its ability to disassemble the actomyosin cytoskeleton downstream of RhoA.
Claudins upregulation in human colorectal cancer
Authors: de Oliveira Silvia Souza , de Oliveira Ivanir Martins , De Souza Wanderley , Morgado-Díaz José Andrés
Published: October 2005

In colorectal cancer tight junction molecular and morphological alterations are poorly understood. In this study, adenocarcinoma tissues and their paired normal mucosa (n
= 12) were analyzed for tight junction alterations molecular. The expression of claudin‐1, ‐3 and ‐4 was upregulated 5.7‐, 1.5‐ and 2.4‐fold, respectively, in colorectal tumor tissues in comparison to the normal ones. Although tight junction remains in the cancerous epithelium, its barrier function was altered. Despite claudins overexpression, paracellular permeability to ruthenium red was increased and a significant disorganization of tight junction strands was observed in freeze fracture replicas. Whereas the functional significance of claudin overexpression in colorectal cancer is unclear, these proteins can become potential markers and targets in colorectal cancer.