bluuebunny/crossref_metadata_2025 huggingface dataset:
Strong Convergence in Stabilised Degenerate Convex Problems
Authors: Boiger Wolfgang , Carstensen Carsten
Published: February 2009

Solutions to non–convex variational problems typically exhibit enforced finer and finer oscillations called microstructures such that the infimal energy is not attained. Those oscillations are physically meaningful, but finite element approximations typically experience dramatic difficulty in their reproduction. The relaxation of the non–convex minimisation problem by (semi–)convexification leads to a macroscopic model for the effective energy. The resulting discrete macroscopic problem is degenerate in the sense that it is convex but not strictly convex. This paper discusses a modified discretisation by adding a stabilisation term to the discrete energy. It will be announced that, for a wide class of problems, this stabilisation technique leads to strong H1–convergence of the macroscipic variables even on unstructured triangulations. This is in contrast to the work [2] for quasi–uniform triangulations and enables the use of adaptive algorithms for the stabilised formulations. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A hybrid approach to 3‐level FETI
Authors: Klawonn Axel , Rheinbach Oliver
Published: February 2009

Finite Element Tearing and Interconnecting (FETI) methods are nonoverlapping domain decomposition methods which have been proven to be very robust and parallel scalable for a class of elliptic partial differential equations. These methods are also called dual domain decomposition methods since the continuity accross the subdomain boundaries is enforced by Lagrange multipliers and, after elimination of the primal variables, the remaining Schur complement system is solved iteratively in the Lagrange multiplier space using a Krylov space method. Domain decomposition methods iterating on the primal variables are called primal substructuring methods. FETI and FETI–DP methods are different members of the family of dual domain decomposition methods. Their standard versions have in common that the local subproblems and a small global problem are solved exactly by a direct method, essentially representing two different levels within the algorithm. Several extensions of dual and primal iterative substructuring beyond two levels have been proposed in the past, see, e.g., [7] for FETI–DP, and, e.g., Tu [13,12,11] or [9] and [1] for BDDC. In the present article, a hybrid FETI/FETI–DP method is considered and some numerical results are presented. It is noted that independently, there is ongoing research on hybrid FETI methods by Jungho Lee of the Courant Institute. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Meshless Finite Difference Operators from Moving Least Squares Interpolation: Applications to PDEs and Convergence Results
Authors: Nowak Oliver
Published: February 2009

We give a brief introduction to moving least squares interpolation, which is followed by some reflections on the construction of meshless finite difference operators for derivative approximation and present finally a Korovkin–type convergence result for the pure interpolation approach. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical solution of transonic and subsonic flow of compressible inviscid and viscous fluid
Authors: Punčochářová Petra , Kozel Karel , Horáček Jaromír , Fürst Jiří
Published: February 2009

The work presents two numerical solutions of compressible flows problems with high and very low Mach numbers. Both problems are numerically solved by finite volume method and the explicit MacCormack scheme using a grid of quadrilateral cells. Moved grid of quadrilateral cells is considered in the form of conservation laws using Arbitrary Lagrangian–Eulerian method. In the first case, inviscid transonic flow through cascade DCA 8% is presented and the numerical results are compared to experimental data. The second case, numerical solution of unsteady viscous flow in the channel for upstream Mach number M∞=0.012 and frequency of the wall motions 100 Hz is presented. The unsteady case can represent a simplified model of airflow coming from the trachea, through the glottal region with periodically vibrating vocal folds to the human vocal tract. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the Steffensen method under the generalized Lipschitz conditions for the divided difference operator
Authors: Shakhno S. M.
Published: February 2009

Convergence of the Steffensen method for solving nonlinear operator equations in the Banach spaces under the generalized Lipschitz condition for the first–order divided differences is investigated. The conditions and quadratic speed of convergence of this method are found. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Discrete concepts for elliptic optimal control problems with constraints on the gradient of the state
Authors: Deckelnick Klaus , Günther Andreas , Hinze Michael
Published: February 2009

We consider elliptic optimal control problems with constraints on the gradient of the state and propose two distinguish concepts for their discretization. The first concept uses piecewise linear, continuous finite element Ansatz functions for the state, while the second concept uses the lowest order Raviart–Thomas mixed finite element. In both cases variational discretization from [5] is used for the controls. We present optimal finite element error estimates for the numerical solutions and confirm our theoretical findings by a numerical experiment. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On convergence of Lavrentiev regularization for semilinear parabolic optimal control problems with pointwise control and state constraints
Authors: Neitzel Ira , Tröltzsch Fredi
Published: February 2009

We consider Lavrentiev regularization for a class of semilinear parabolic optimal control problems with control constraints and pointwise state constraints and review convergence results for local solutions under Slater type assumptions as well as quadratic growth conditions. Moreover, we state a local uniqueness result for local optima under the assumptions of strict separability of the active sets as well as a second order sufficient condition for the regularized solution. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Reduction of vibration due to change in mass configuration
Authors: Brząkała Aneta , Wójcicki Zbigniew , Majcher Krzysztof
Published: February 2009

The paper concerns the elimination of vibration due to changing the centre of gravity of a system. It is shown that the damping effect can be generated in an oscillating pendulum by a continuous motion of an auxiliary mass. A simple system in form of a variable length pendulum is considered. It is seen that if the pendulum length function is correctly chosen, the Coriolis force will cause additional damping effect in the system. The Floquet method is used to investigate the linear system stability. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Analysis of the Dynamics of Slender Continua Using Karhunen‐Loève‐Transformation
Authors: Göbel M. , Kreuzer E.
Published: February 2009

The dynamics of continua with very small diameter–to–length ratio, like bridges or drill–strings, has been object of mechanical analysis for a long time. While it is often possible to create a well–suited mechanical model, it is difficult to determine the exact current loads and the exact operational state. For drill–strings, the load of the drill–bit depends on the material of the rock, but also on other unknown disturbances like differential sticking which can occur along the drill–string without being noticed directly. Karhunen–Loève–Transformation (KLT) provides a possibility to describe the dynamics of a continuous system with few Characteristic Functions (CF), as long as the motion of the system is stationary. On the other hand, the resulting CFs of the KLT are sensitive to changes in the dynamic system behavior. These changes can result e. g. from the occurrence of stick–slip of the bit or differential sticking of the string. On the basis of a simple model, we show that this sensitivity can be used to detect and characterize such changes. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A semi‐active isolator for torsional vibrations
Authors: Ineichen L.
Published: February 2009

Modern combustion engines produce strong rotational vibrations which could damage elements of the drive train such as the gearbox. A solution to this problem is to mount an isolating device on the output side of the motor. Its function is to filter the torque oscillations to deliver a clean averaged torque to the rest of the drive train. Passive systems have limitations, so that the design of such systems is always a compromise between the effectiveness of the isolation and maximal transmittable average torque. We propose a semi–active system that includes a degressive spring and a hydraulic actuator which can filter effectively the vibrations even if the average torque is high. This isolator is adaptive and doesn't need any command. The stability of this system of the third order is analysed with an averaging method. This leads to some considerations about the design of the control valve of the hydraulic actuator. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Boundary integral equations for viscous incompressible flows in porous media or past porous bodies
Authors: Kohr Mirela , Kohr Gabriela , Wendland Wolfgang L.
Published: February 2009

The purpose of this paper is to present the existence and uniqueness result for a boundary value problem which describes the flow of a viscous incompressible fluid past an arbitrary porous particle with a Lyapunov boundary, which is embedded in a second porous medium, by using the Brinkman model and the potential theory. We use a boundary integral method that reduces the problem to a system of second kind Fredholm integral equations that has a unique solution in some Hölder spaces. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Nonlinear vibration of a quarter‐car model excited by the road surface profile
Authors: Litak Grzegorz , Borowiec Marek
Published: February 2009

We examine the Melnikov criterion for a transition to chaos in case of a single–degree–of–freedom nonlinear oscillator with the Duffing potential with a nonlinear hard stiffness and a kinematic excitation term caused by the road profile. Using the new effective Hamiltonian we have examined appearance of homoclinic orbits in a quarter car model. Cross–sections of stable and unstable manifolds defined the condition of transition to chaos through a homoclinic bifurcation. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Elimination of tall building vibration resulting from ground motions
Authors: Majcher Krzysztof , Brząkała Aneta , Wójcicki Zbigniew
Published: February 2009

In this paper, the vibration problems of tall buildings are considered. The focus is on vibration caused by earthquakes, semi–seismic phenomena and ground vibrations of other origins. The construction consists of the main system and a vibration eliminator (passive tuned mass damper – pendulum type) which is attuned to the first eigenfrequency of the main structure. The analysis focuses on elimination of structure vibration caused by horizontal components of ground motions, while the functioning of the eliminator is simultaneously influenced by the vertical component (parametric effect – the possibility of improper functioning of the device). The vertical periodic movement of the support point can cause changes of the vibration eliminator's stiffness. In such a case parametric excitation occurs in the system, which signifies that parametric resonance may appear. The numerical analysis of the problem was performed with the Newmark method in conjunction with FEM. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Analysis of Nonlinear Quadratic Control in Infinite Time
Authors: Popescu Mihai
Published: February 2009

This study refers to minimization of quadratic functionals in infinite time. The coefficients of the quadratic form are quadratic matrices, function of the state variable. Dynamic constraints are represented by a bilinear differential systems of the form. The necessary extremum conditions determine the adjoint variables λ and the control variables u as functions of state variable, respectively the adjoint system corresponding to those functions. Thus it will be obtained a matrix differential equation where the solution representing the positive defined symmetric matrix P(x), verifies the Riccati algebraic equation. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Elimination of resonant vibration in cable stayed bridges and footbridges by active steering of tension in cables
Authors: Pakos Wojciech , Grosel Jacek , Wójcicki Zbigniew
Published: February 2009

The paper presented proposes a new approach to the elimination of vibration in cable stayed bridges and footbridges which may be applied to dynamic analysis of modern cable stayed bridges with typical structure systems. The reduction of the vibration is to be achieved by way of active steering of the tension in cables. The problem of eigenproblem sensitivity analysis with respect to change of the cable tension in cable stayed footbridges and bridges is considered. In the future, the information gained from the sensitivity analysis may be used to calculate how to steer the cable tension in a way that will ensure the most efficient resonant vibration elimination. Particular notice has been paid to the vibration of cables. The matrix equation of motion of a three–dimensional computer model of the structure has been created with the help of a non–standard use of standard computer software leaning on Finite Element Method (FEM). The system Mathematica and the authors' own program have also been used to analyze the eigenproblem sensitivity of bridges. An example has been provided. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Accessibility Conditions of Distributed‐Parameter Systems
Authors: Rieger Karl , Schlacher Kurt
Published: February 2009

This contribution is focused on the accessibility of distributed–parameter systems, where in particular the exact accessibility along a trajectory is considered. Based on a covariant description of a dynamic system within a differential geometrical framework a system–theoretical analysis is motivated by a transformation group approach and it is shown how (local) accessibility criteria can be derived successively. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Stability of autonomous vehicle formations using an ISS small‐gain theorem for networks
Authors: Dashkovskiy Sergey N. , Rüffer Björn S. , Wirth Fabian R.
Published: February 2009

We consider a formation of vehicles moving on the two dimensional plane. The movement of each vehicle is described by a system of ordinary differential equations with inputs. The formation is maintained using autonomous controls that are designed to maintain fixed relative distances and orientations between vehicles. Moreover this formation should track a given trajectory on the plane. The vehicles can measure the relative distances and angles to their neighbors. These values are the inputs from one system to another. With the help of a general ISS small–gain theorem for networks we will show that the dynamics of such a formation is stable for the given controls. The notion of local input–to– state stability (local ISS) will be used for this purpose. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Transient resonance problems in the case of the series of short duration loads
Authors: Mironowicz Władysław , Sęk Marcin
Published: February 2009

The indicated in the title of this paper vibration problem concern the ferroconcrete slab – type industrial ceilings. The presence of unilateral constraints which my arise as a result of construction damages is taken into consideration. As an example, it is analysed a construction of a ceiling in shape of a rectangular slab supported on a regular net of columns and a non deformed solid, being a model of a machine, placed on the construction. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The influence of parametric excitation on floating bodies
Authors: Zelei A. , Stepan G.
Published: February 2009

In the present study, we investigate the possibility of stabilizing a floating body that is unstable without parametric excitation. We prescribe a non–stationary geometric constraint, that is, the centre of gravity is moved periodically in vertical direction. This periodic movement causes the parametric excitation described by a non–autonomous differential equation. By using the stability chart of the Mathieu equation, we can find sets of parameters where the stabilization of the floating body is realizable. This can help in the stabilization of a canoeist, but it can also cause stable ships to capsize. Numerical simulations and an experiment were also accomplished to confirm that the stability chart derived for the case of the floating body is realistic. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Regularization Parameter Selection in Total Variation Based Image Denoising
Authors: Dong Yiqiu , Hintermüller Michael , Rincon Monserrat
Published: February 2009

A new approach of selecting the regularization parameter in a multiscale total variation model is proposed. The method is combined with a primal–dual algorithm to get a new iteration method for noise removal. Numerical results illustrate significant improvement over other popular methods. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Approximation by generalized Shannon sampling operators generated by band‐limited kernels
Authors: Tamberg Gert
Published: February 2009

In this paper we consider some generalized Shannon sampling operators, which are defined by band–limited kernels. In particular, we use dilated an averaged versions of some previously known kernels. We give also some examples of using sampling operators in imaging applications. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Influence of magnetic field on the rheological properties of liquid GaInSn alloy
Authors: Borin Dmitry , Odenbach Stefan , Nikrityuk Petr
Published: February 2009

In this work we studied experimentally the effect of an applied magnetic field and shear rate on the viscosity of a liquid GaInSn alloy. The experimental investigations were performed at room temperature in a homebuilt shear stress controlled rheometer. To consider the magnetohydrodynamical effects occurring in the melt numerical simulation of the flow field in the melt have been made. The results show a remarkable increase of the viscosity with increasing magnetic field strength. With increasing shear rate applied to the liquid GaInSn alloy a reduction of the change of viscosity is found. As first assumption this rheological behavior of GaInSn can be accounted to the presence of solid oxide fractions in the melt. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optimal control in fluid mechanics by finite elements with symmetric stabilization
Authors: Braack Malte
Published: February 2009

We formulate four properties for a finite element discretization of the Oseen system which are sufficient to derive a quasi–optimal a priori estimate in the context of optimal control problems. In particular, local projection stabilization and edge–oriented stabilization result to be quasi–optimal for optimal control problems with the Oseen system. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Measurements of transient flow fields driven by a discontinuously applied rotating magnetic field
Authors: Raebiger D. , Eckert S. , Gerbeth G.
Published: February 2009

This experimental study considers the transient liquid metal flow which is generated inside a cylindrical container by discontinuously applying a rotating magnetic field (RMF). The focus is on the fluid motion arising from the impulsive spin–up from the resting state. The ultrasonic Doppler velocimetry (UDV) has been used to determine profiles of the fluid velocity in the ternary alloy GaInSn. The azimuthal and vertical velocity components have been measured allowing for an analysis of both the primary, swirling flow and the secondary flow in the radial–meridional plane. The experimental results show an excellent agreement with recently published numerical results. The investigations reveal that the recirculating flow in the radial–meridional plane undergoes characteristic oscillations. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
MHD turbulence in a channel with spanwise field
Authors: Krasnov Dmitry , Zikanov Oleg , Schumacher Joerg , Boeck Thomas
Published: February 2009

We study turbulent channel flow of an electrically conducting liquid with a homogeneous magnetic field imposed in the spanwise direction. The Lorentz force is modelled using the quasistatic approximation. Direct and large–eddy simulations are performed for hydrodynamic Reynolds numbers Re=10000 and Re=20000 and the Hartmann number varying in a wide range. The main effect of the magnetic field is the suppression of turbulent velocity fluctuations and momentum transfer in the wall–normal direction. Comparing the results from direct and large–edddy simulations we show that the dynamic Smagorinsky model accurately reproduces the flow transformation. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Rectification, mixing, self‐induced oscillations, measurement and control in asymmetrically grooved channels
Authors: Beronov K. N. , Osorio Nesme A. , Fridman I. , Delgado A.
Published: February 2009

Two separate constructions used in advanced microfluidics are combined to achieve controlled mixing and mass transport at maximum efficiency over minimal distance. One is the use of grooves to enhance mixing – an intensively investigated technique employed in electronic components cooling. So far, only grooves of ectangular cross–sections were used. The other construction builds on the well known effect of partial rectification in axially asymmetric channels and has been employed for valvless pumping. It is now shown that a cascade of axially asymmetric grooves retains and even improves the rectification efficiency of a single nozzle while offering the potential of simultaneous mixing enhancement by a factor of more than 2. The latter is achieved in a certain range of moderate Reynolds numbers characterized by self–induced oscillations at much higher frequency than that of flow actuation. Tuning the pressure drop provides precise control of the effective flow rate, up to suppression or reversion. The duration and intensity of mixing and shearing can thus be adjusted within a broad range and effected in very short channels without additional actuators. In the regime of self–induced oscillations, a few identical sensors with sufficient temporal resolution for temperature or concentration allow reliable determination of the flow rate as well as of the admixture composition of the transported fluid. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Microcomputed tomography analysis of ferrofluids used as drug carriers for cancer treatment
Authors: Rahn Helene , Odenbach Stefan
Published: February 2009

Two new approaches, Magnetic Drug Targeting (MDT) and Magnetic Hyperthermia, are being investigated in order to reduce side effects generated by common ways of cancer treatment. MDT and MHT are based on the use of magnetic nanoparticles: for MDT the nanoparticles are used as drug carriers and for MHT the nanoparticles are used to induce local heat transfer within the tumour. The success of these therapeutic approaches depends among other things on the correct distribution of the magnetic nanoparticles within the tumour tissue. Computed tomography analysis has been performed on tumour tissue after MDT in order to examine this distribution. The measurements have been performed in two different laboratories, one based on a synchrotron radiation, and another one on a cone X–ray source. First results show that the drug carriers are contained in the vessel system of the tumour as well as concentrated in the surrounding area of the veins. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Theoretical investigation of the flow in a stenosis
Authors: Travnikov Vadim , Böhme Gert
Published: February 2009

The theoretical investigation of the flow in stenosis is presented. We use a new formulation of the incompressible Navier–Stokes equation in terms of an auxiliary field that differs from the velocity by a gauge transformation [1]. The gauge freedom allows us to formulate simple boundary conditions for the auxiliary field and the gauge field as well. The gauge field eliminates the pressure distribution in the Navier–Stokes equation. The numerical investigation of the creeping flow, depending on the geometrical parameters of the system, is performed. The influence of the pressure drop has been taken into account. An excellent agreement with the analytical results in frames of the film theory was observed. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Adaptive multiresolution schemes for reaction‐diffusion systems
Authors: Bendahmane Mostafa , Bürger Raimund , Ruiz Ricardo , Schneider Kai
Published: February 2009

This note outlines a fully adaptive multiresolution scheme with local time stepping for the efficient numerical solution of (possibly degenerate) reaction–diffusion systems. A new numerical example showing Turing–type pattern formation is presented. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Boundary Integral Method for Compressible Stokes Flow
Authors: Köster Daniel
Published: February 2009

A recently developed type of biochip employs ultrasonic surface acoustic waves (SAWs) as a microscale pumping and mixing mechanism for fluids. The driving force for fluid flow is an effect of nonlinear acoustics known as acoustic streaming. We recently studied a two–scale numerical model to describe this effect, which was discretized using classical finite element methods.

The micro–scale part of the model describes the propagation of damped acoustic waves. Since the used equations are linear and homogeneous, it is natural to look toward a boundary integral method and attempt a coupling with the FEM scheme still employed in the macro–scale model part. One main ingredient for this approach, namely explicit formulas for free–space Green's functions describing damped acoustics, appear to be novel. We will describe some details of the new scheme, which shows a promising gain of efficiency compared to using FEM for damped acoustics. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Nonequispaced fast Fourier transforms without oversampling
Authors: Kunis Stefan
Published: February 2009

Recently, the fast Fourier transform (FFT) has been generalised for arbitrary sampling nodes by the use of approximation schemes. We show that such nonequispaced FFTs can be implemented without oversampling, i.e., no extra memory besides the input and output array is needed. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Supply chains in life‐science applications
Authors: Langemann Dirk
Published: February 2009

The systemic investigation of the energy metabolism in the frame of the selfish–brain theory focusses on supply chains from the energy exploration in the remote environment to the energy consumption by neurons in the brain. Modelling this, the main difficulty consists in the selection of significant core models among the enormous number of known substances and regulatory mechanisms, which are afflicted with considerable incertainties in general. We investigate general supply chains and deduce indispensable elements in the regulatory mechanisms from available observations. A critical selection of system properties and underlying mechanisms enables us to simulate observations, which cannot be explained by the classical glucastatic and lipostatic theory. These observations are e.g. the nearly constant energy level in the brain, the different response of the periphery and the brain to atrophic periods and finally, the development of diabetes. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Parameters Identification as Identification of External Loads
Authors: Menshikov Yu.
Published: February 2009

Substitution of traditional problem of parameters identification to a problem of identification of some additional external load to researched system is offered in conditions, when the initial information on researched parameter and about statistical properties of measurements is absent or is insignificant. Such substitution is always possible as the contribution of any parameter can be considered as the contribution of additional external load in the response of researched system. At the given approach the mistake in a choice of structure of mathematical model with identified parameters does not lead to principle errors of the solution. This additional load compensates all errors. Besides it is possible to carry out check of a hypothesis about a constancy of parameter size.The problem was reduced to solution of the integral equation of the first kind with an inexact kernel and inexact right part. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Robust Error Estimates for Adaptive Phase Field Simulations
Authors: Bartels Sören , Müller Rüdiger
Published: February 2009

Phase field equations are commonly used as a regularized model, where bulk phases are separated by interface regions that have a thickness of the order γ. Their numerical analysis is well established for a fixed parameter size γ, but conventional error estimates depend exponentially on γ−1 and thus become useless in the relevant case if γ→0. Technical applications include e.g. the simulation of Sn–Cu alloys for the production of lead free solder or Ni–Al alloys used for rotor blade surfaces. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Preconditioned Uzawa Algorithm for Elastic Contact Problems
Authors: Pop Nicolae
Published: February 2009

After finite element discretization of the elastic contact problems with friction, we obtain a big sparse non–symmetric and nonlinear systems of equations, and in many cases ill–conditioned. Solving these systems by direct methods or classical iterative methods are non efficient and with bad convergence properties. One way to overcome these difficulties is to use the preconditioned Uzawa–type algorithms. On this paper we focus on the transformation of the generalized Signorini elastic contact problems into a saddle point problem of some augmented Lagrangian functional and give a preconditioning technique for Uzawa algorithm. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Regulation von Immunsystem und Allergien. Retinoide, Vitamin A und Pro‐Vitamin‐A‐Carotinoide
Authors: Rühl Ralph
Published: February 2009

Vitamin A und Pro‐Vitamin‐A‐Carotinoide sind in hohen Konzentrationen in der westlichen Ernährung enthalten. Eine humane Vitamin‐A‐Defizienz kommt in westlichen Ländern daher extrem selten vor. Eine Überversorgung mit Vitamin A tritt jedoch häufig auf und kann möglicherweise ein wesentlicher Faktor bei der gesteigerten Prävalenz von atopischen Erkrankungen in westlichen Ländern sein. Dabei spielt der Einfluss von Vitamin A auf das Immunsystem eine mögliche entscheidende Rolle.

Retinsäuren, die haupt‐aktiven Derivate des Vitamin A, sind spezifische und selektive Aktivatoren von nukleären Hormon‐Rezeptoren und sind somit wichtige nahrungsrelevante Metaboliten für das Immunsystem. Die Regulation spezifischer Immunantworten auf Allergien ist in einem großen Maße abhängig von Retinoiden. Konzentrationen von Vitamin A und Pro‐Vitamin‐A‐Carotinoiden in unserer Nahrung, und somit später im Körper, können spezifische Immunfunktionen sowohl positiv als auch negativ beeinflussen.
Zur Sicherheit von Vitaminen. Nebenwirkungen, Kontraindikationen und Intoxikationen
Authors: Golly Ines C.
Published: February 2009

Im Rahmen der Prävention und Therapie mit Vitaminpräparaten sind die Heilberufe besonders gefordert, ihre Expertise in die Beratung sowohl von Verbrauchern als auch Patienten einzubringen. Entgegen der weltweit verbreiteten Ansicht vieler Verbraucher, die den Vitaminen nur Positives abgewinnen und diesen Substanzen grundsätzlich unkritisch gegenüberstehen, macht insbesondere die langfristige Einnahme hoher Dosen eine Nutzen‐Risiko‐Abwägung für den einzelnen Verbraucher/Patienten erforderlich.
Vitamine in der Schwangerschaft. Welche Vitaminpräparate empfehle ich der Schwangeren?
Authors: Mayer Sonja
Published: February 2009

Wissenschaftlich nachgewiesene Wirksamkeit von Folsäure zur Risikoreduktion von Neuralrohrdefekten, ein eklatanter Mehrbedarf von z.B. 58 % Pyridoxin und 50 % Folsäure sowie ein Mangel an diesen B‐Vitaminen, Vitamin A und Vitamin D sprechen eindeutig für die Supplementierung in der Schwangerschaft. Aufgrund teratogener Effekte ist bei Vitamin A und Vitamin D auf Höchstdosen zu achten.
Vitamine zwischen Mangelvermeidung und Prävention. Wunsch und Wirklichkeit
Authors: Hahn Andreas
Published: February 2009

Aus ernährungswissenschaftlicher Sicht besitzt eine adäquate Vitaminversorgung nicht nur die Aufgabe, Mangelerscheinungen zu vermeiden, sondern trägt auch dazu bei, chronisch‐degenerativen Erkrankungen vorzubeugen. Auf Bevölkerungsebene ergibt sich in Deutschland im Mittel rechnerisch mit Ausnahme von Folsäure und Vitamin D eine insgesamt ausreichende Zufuhrsituation. Allerdings ist erkennbar, dass auch bei anderen Vitaminen in einem teilweise erheblichen Teil der Bevölkerung nicht die wünschenswerte Aufnahme erreicht wird. Zwar sind schwerwiegende Vitaminmangelerscheinungen dabei sehr selten zu finden, bisweilen treten aber latente Defizite auf, die sich in unspezifischen Symptomen äußern können. Nach der derzeitigen Studienlage kann eine optimierte Vitaminversorgung zur Prävention verschiedener Erkrankungen beitragen. Interventionsstudien konnten deshalb vor allem dann eine entsprechende Wirkung von Vitaminsupplementen zeigen, wenn die Studienteilnehmer zuvor schlecht versorgt waren. Ob und in welchem Umfang zusätzliche Vitamingaben bei bereits guter Vitaminversorgung von Nutzen sind, bleibt nach wie vor offen.
Neue Antibiotika in Sicht?
Authors: Holzgrabe Ulrike
Published: February 2009

In den letzten 40 Jahren wurden nur zwei neue Antibiotikagruppen aufgefunden, und zwar die Oxazolidinone (Linezolid) und die Lipopeptide (Daptomycin), die neue Zielstrukturen bedienen, um ihre bakerizide Wirkung zu entfalten. Übrigens wurden beide Gruppen – wie auch die wenigen anderen Substanzen in der Pipeline wie Glycolipodepsipeptide (Ramoplanin), Pleuromutiline (Retapamulin) oder Glycosyltransferase‐Inhibitoren (Moenomycin) – schon vor sehr langer Zeit aufgefunden, aber damals aus verschiedenerlei Gründen wie z.B. Toxizität nicht weiterentwickelt.
Red red wine
Authors: Bajer M. , Bezbradica S. , Buzek F. , Renz H. , Schröder K. , Song M. , Zündorf I. , Dingermann T.
Published: February 2009

Vielleicht kann – wie Neil Diamond einst meinte – Rotwein über eine verlorene Liebe hinweg helfen; pharmazeutisch interessanter ist, ob wirklich Rotwein und hier vor allem das Resveratrol für das “French Paradoxon” verantwortlich ist. Demnach schützen sich die Franzosen trotz vielen Tabakonsums und cholesterinreicher Ernährung mit Rotwein vor Herzinfarkten.
PCR/LDR/capillary electrophoresis for detection of single‐nucleotide differences between fetal and maternal DNA in maternal plasma
Authors: Yi Ping , Chen Zhuqin , Zhao Yan , Guo Jianxin , Fu Huabin , Zhou Yuanguo , Yu Lili , Li Li
Published: February 2009

Background

The discovery of fetal DNA in maternal plasma has opened up an approach for noninvasive diagnosis. We have now assessed the possibility of detecting single‐nucleotide differences between fetal and maternal DNA in maternal plasma by polymerase chain reaction (PCR)/ligase detection reaction((LDR)/capillary electrophoresis.

Methods

PCR/LDR/capillary electrophoresis was applied to detect the genotype of c.454–397T>gene (ESR1) from experimental DNA models of maternal plasma at different sensitivity levels and 13 maternal plasma samples.αC in estrogen receptor.

Results

(1) Our results demonstrated that the technique could discriminate low abundance single‐nucleotide mutation with a mutant/normal allele ratio up to 1:10 000. (2) Examination of ESR1 c.454–397T>C genotypes by using the method of restriction fragment length analysis was performed in 25 pregnant women, of whom 13 pregnant women had homozygous genotypes. The c.454–397T>C genotypes of paternally inherited fetal DNA in maternal plasma of these 13 women were detected by PCR/LDR/capillary electrophoresis, which were accordant with the results of umbilical cord blood.

Conclusions

PCR/LDR/capillary electrophoresis has very high sensitivity to distinguish low abundance single nucleotide differences and can discriminate point mutations and single‐nucleotide polymorphisms(SNPs) of paternally inherited fetal DNA in maternal plasma. Copyright © 2009 John Wiley & Sons, Ltd.
Should the first‐trimester aneuploidy screen be maternal age adjusted? Screening by absolute risk versus risk adjusted to maternal age
Authors: Gebb Juliana , Dar Pe'er
Published: February 2009

Objective

To compare the absolute risk (AR) screening approach to the current approach of risk adjusted to maternal age in patients undergoing first‐trimester screening (FTS).

Material and Methods

Three‐stage retrospective analysis of 3073 pregnancies that had FTS during 2006–2007. (1) Distribution analysis of AR as defined by (final FTS risk)/(risk by age). (2) Analysis of the screen‐positive group by the AR method. (3) Analysis of the screen‐positive advanced maternal age (AMA) patients.

Results

(1) AR > 1 was found in 151 (4.9%) patients, and AR > 1.2, 2 and 3 was found in 4, 3.1 and 2%, respectively. (2) 145 (4.7%) of the 3073 patients screened positive. Twelve were diagnosed with chromosomal abnormalities and 3 with major anomalies. All had AR > 1.2. Of the 145 (55.8%) screen positives, 81 had AR > 1.2. AR was significantly higher in the chromosomally abnormal as compared to normal gestations (t‐test, p < 0.01). (3)Of the 145 screen positives, 103 were AMA. Only 39 (28%) had an AR > 1.2.

Conclusions

The AR screening approach, using AR > 1.2 as a cut‐off, captured all abnormal pregnancies diagnosed by the current screening method. This method offers lower false positive (FP) rates to AMA women and has the potential for higher detection rates in younger women. Copyright © 2009 John Wiley & Sons, Ltd.
Fetal dilated cardiomyopathy: an unsuspected presentation of methylmalonic aciduria and hyperhomocystinuria, cblC type
Authors: De Bie Isabelle , Nizard Sonia Dal Pozzo , Mitchell Grant A.
Published: February 2009

Objective

To report the prenatal presentation with dilated cardiomyopathy of methylmalonic aciduria and homocystinuria, cblC type [cobalamin C (cblC) deficiency] (MIM 277400).

Method

We describe a boy with cblC deficiency who presented prenatally with fetal ultrasound findings of dilated cardiomyopathy and growth restriction.

Results

Dilated cardiomyopathy and growth retardation were detected in the third trimester of an initially uncomplicated pregnancy. Investigations were negative for chromosomal and other known causes. Growth restriction persisted but fetal heart function improved. Postnatal biochemical evaluation revealed combined methylmalonic acidemia and homocystinemia. Molecular investigations confirmed cblC deficiency. Initiation of treatment was followed by rapid clinical improvement.

Conclusion

Prenatal dilated cardiomyopathy can be the presenting sign of cblC deficiency. Inborn errors of metabolism should be considered in the investigation of prenatally diagnosed dilated cardiomyopathy in view of the possible impact on treatment and future reproductive options, in some of these conditions. Copyright © 2009 John Wiley & Sons, Ltd.
Isolated fetal umbilical vein varix—prenatal sonographic diagnosis and suggested management
Authors: Weissmann‐Brenner Alina , Simchen Michal J. , Moran Orit , Kassif Eran , Achiron Reuven , Zalel Yaron
Published: February 2009

Objective

To present our experience with fetuses with umbilical vein varix (UVV), to investigate possible risk factors and to suggest a management scheme of evaluation.

Study Design

A study of 14 pregnancies complicated with isolated UVV was performed. Data collected included sonographic characteristics of the UVV, pregnancy outcome including induction of labour, mode of delivery, birthweight, and neonatal complications.

Results

UVV was diagnosed at a median gestational age of 27.5 weeks' gestation (range: 22–34 weeks). The average diameter of the UVV at diagnosis was 10.6 mm (range: 8–15 mm), and the maximal diameter during follow‐up was 12.8 mm (range: 10–18 mm). The median gestational age at delivery was 36.1 weeks (range: 34–40 weeks), with an average birthweight of 2834 g (range: 1725–3715 g). Five women underwent emergent cesarean section. In fetuses with turbulent flow in the UVV there was a tendency to larger maximal sizes of the UVV, earlier gestational age at delivery and smaller birthweight. There were no cases of fetal or neonatal demise.

Conclusions

We suggest that fetuses with UVV should be followed weekly from diagnosis to 28 weeks, and twice a week afterwards. Induction of labour should be considered at 36–37 weeks' gestation or at signs of fetal distress. Copyright © 2009 John Wiley & Sons, Ltd.
Physical activity preferences of ovarian cancer survivors
Authors: Stevinson Clare , Capstick Valerie , Schepansky Alexandra , Tonkin Katia , Vallance Jeffrey K. , Ladha Aliya B. , Steed Helen , Faught Wylam , Courneya Kerry S.
Published: February 2009

Objective: Regular physical activity is positively associated with quality of life in ovarian cancer survivors, but no data exist on how best to promote activity in this population. This study investigated the interests and preferences of ovarian cancer survivors with regard to physical activity participation.

Methods: A provincial, population‐based postal survey of ovarian cancer survivors in Alberta, Canada, was performed including measures of self‐reported physical activity, medical and demographic variables, and physical activity preferences.

Results: A total of 359 women participated (51.4% response rate). Over half expressed interest in participating in a physical activity program (53.8%), with a further 32.9% maybe interested. The most common preferences were for programs to be home‐based (48.9%), start post‐treatment (69.5%), and involve walking (62.7%). There were differences in preferences based on demographic, but not medical, factors.

Conclusion: The majority of ovarian cancer survivors expressed interest in participating in physical activity programs; however, some preferences varied by demographic factors. Designing physical activity interventions according to these preferences may optimize adherence and outcomes in ovarian cancer survivors. Copyright © 2009 John Wiley & Sons, Ltd.
The use of the Pareto shape parameter as a leading indicator of process safety performance
Authors: Henselwood Fred
Published: February 2009

Metrics addressing process safety incident performance typically focus on frequency and severity statistics. Often, these lagging metrics are not overly sensitive to actual performance, making trending and forecasting difficult. This article presents the results from a statistical study of a large incident dataset where changes in the Pareto shape parameter were observed as a function of time. This approach has been found to give far better insight into process safety performance than traditional incident metrics and readily relates back to concepts such as the “incident triangle” and “layers of protection.” Through the application of this approach, trends within process safety incident performance have been observed earlier, and more accurate forecasting has allowed for the identification of anomalies. In turn, these critical observations have allowed for the better structuring and targeting of process safety programs. Although incident data are generally considered as a lagging indicator, this approach has clearly reduced the lag time associated with this type of data and has given valuable insight into the current status of process safety performance. © 2009 American Institute of Chemical Engineers Process Saf Prog 2009
Safe management of unforeseen delays in mechanical integrity inspection schedules
Authors: Willis James H. , Thomas Harold W. , Dunbobbin Brian R.
Published: February 2009

The days of “frequent” annual maintenance outages where mechanical integrity (MI) testing and inspections are performed are gone. The new reality of modern industrial gas and chemical plant operation includes increasing durations between scheduled maintenance down time that have sometimes reached 5 years and beyond. In addition, in the interest of keeping initial capital cost under control, there is constant pressure to restrict redundant architectures and systems intended to allow maintenance while running the plant.

Safety systems that have the potential for unrevealed failures lead to required plant down times to properly test and inspect those systems. Because our customers expect high reliability with long runs between maintenance outages it is prudent to design our facilities and MI plans to meet the agreed commercial strategy. However, unforeseen events can cause delays in maintenance outages and thus our window to complete mandatory MI activities. Air Products' process for reviewing the consequence and likelihood of these delays allows appropriate action to be taken to ensure continued safe operation while complying with customer needs to reschedule downtime windows to the greatest extent possible.

This article outlines the policy used to review and manage the effects of inspection and test delays on facility risk. The hazard review process is administered and documented through the company's existing management of change process. The review itself is handled using a team with diverse technical expertise that can uncover and address key factors affecting safety. Levels of approval are based on the expected length of the planned delay. Duration of the extension (planned delays) dictates the level of technical reviews and provides guidance as to whether qualitative or quantitative techniques are appropriate. In either case, mitigation techniques may be used to temporarily manage the increased level of risk associated with the inspection or test delay.

The implementation of this recommended process is challenging as the plant culture migrates from one of local decision and control to one of understanding the multidisciplinary safety impact these delays create. The preferred solution is always to find a way to perform the task as planned or by using alternate “on stream” inspection methods without requiring an extension review. © 2009 American Institute of Chemical Engineers Process Saf Prog, 2009
Using measured performance as a process safety leading indicator
Authors: Harrington Kenneth H. , Thomas Harold W. , Kadri Shakeel
Published: February 2009

Periodic demands on layers of protection (i.e., prealarms, safety instrumented functions, relief devices, emergency response systems, etc.) are precursors to more serious incidents. The failure of one or more layers of protection is always part of an accident sequence. When they occur documenting these demands and the associated consequences in a way to facilitate analysis, provides a means to measure process safety management performance. Although process safety metrics are still in their adolescence, this article reviews experiences of development and implementation of a “Challenges to Safety Systems” process safety performance indicator. This article includes a discussion of automating significant portions of the data collection process based on the technical work documented by the CCPS PERD (Process Equipment Reliability Database) initiative. The article also recommends various metrics that can be calculated and describes how the initial foundation developed to support improved process safety can be leveraged to achieve other benefits, such as design improvements and improvements in the reliability, operation, and maintenance of the facility. © 2009 American Institute of Chemical Engineers Process Saf Prog, 2009