bluuebunny/crossref_metadata_2025 huggingface dataset:
Overexpression of Evi‐1 oncoprotein represses TGF‐β signaling in colorectal cancer
Authors: Deng Xiyun , Cao Yanna , Liu Yan , Li Fazhi , Sambandam Kamalanathan , Rajaraman Srinivasan , Perkins Archibald S. , Fields Alan P. , Hellmich Mark R. , Townsend Courtney M. , Thompson E. Aubrey , Ko Tien C.
Published: December 2011

Human colorectal cancer (CRC) cells are resistant to the anti‐proliferative effect of transforming growth factor‐β (TGF‐β), suggesting that disruption of TGF‐β signaling plays an important role in colorectal carcinogenesis. Ecotropic virus integration site‐1 (Evi‐1) oncoprotein represses TGF‐β signaling by interacting with Smads, but its role in CRC has not been established. The purpose of this study is to determine whether Evi‐1 plays role(s) in CRCs and to characterize Evi‐1 transcript(s) in CRCs. Evi‐1 was overexpressed in 53% of human CRC samples, 100% of colon adenoma samples, and 100% of human colon cancer cell lines tested. Using 5′ RACE, we cloned a novel Evi‐1 transcript (Evi‐1e) from a human CRC tissue and found that this novel transcript was expressed at a higher level in CRC tissues than in normal tissues and was the major Evi‐1 transcript in CRCs. Transient Evi‐1 transfection inhibited TGF‐β‐induced transcriptional activity and reversed the growth inhibitory effect of TGF‐β in MC‐26 mouse colon cancer cells. In conclusion, we have identified overexpression of Evi‐1 oncoprotein as a novel mechanism by which a subset of human CRCs may escape TGF‐β regulation. We have also identified a novel Evi‐1 transcript, Evi‐1e, as the major Evi‐1 transcript expressed in human CRCs. © 2011 Wiley Periodicals, Inc.
A Korean Parkinson's disease family with the LRRK2 p.Tyr1699Cys mutation showing clinical heterogeneity
Authors: Kim Ji Sun , Cho Jin Whan , Shin Hyeeun , Lee Won Yong , Ki Chang‐Seok , Cho Ah Ra , Kim Hee‐Tae
Published: December 2011

Background:

Although leucine‐rich repeat kinase 2 (LRRK2) is the gene most commonly linked to autosomal dominant inherited Parkinson's disease (PD), there have been few reports in Asia, probably because of population‐specific differences in allele frequencies.

Methods:

We identified a large Korean PD family with the p.Tyr1699Cys mutation in LRRK2 and analyzed genealogical, clinical, and genetic data from the family.

Results:

Although the clinical findings of these patients were indistinguishable from those of patients with sporadic PD, the patients with the p.Tyr1699Cys mutation demonstrated clinical heterogeneity including differences in age at onset, rate of disease progression, clinical phenotype, and prognosis.

Conclusions:

This is the first report describing an Asian PD family with the p.Tyr1699Cys mutation in LRRK2. The affected members of this family showed clinical heterogeneity. © 2011 Movement Disorder Society
Importance of β,β‐carotene 15,15′‐monooxygenase 1 (BCMO1) and β,β‐carotene 9′,10′‐dioxygenase 2 (BCDO2) in nutrition and health
Authors: Lietz Georg , Oxley Anthony , Boesch‐Saadatmandi Christine , Kobayashi Daisuke
Published: December 2011

In humans, varying amounts of absorbed β‐carotene are oxidatively cleaved by the enzyme β,β‐carotene 15,15′‐monooxygenase 1 (BCMO1) into two molecules of all‐trans‐retinal. The other carotenoid cleavage enzyme β,β‐carotene 9′,10′‐dioxygenase (BCDO2) cleaves β‐carotene at the 9′,10′ double bond forming β‐apo‐10′‐carotenal and β‐ionone. Although the contribution of BCDO2 to vitamin A formation has long been debated, BCMO1 is currently considered the key enzyme for retinoid metabolism. Furthermore, BCMO1 has limited enzyme activity towards carotenoids other than provitamin A carotenoids, whereas BCDO2 exhibits a broader specificity. Both enzymes are located at different sites within the cell, with BCMO1 being a cytosolic protein and BCDO2 being located in the mitochondria. Expression of BCMO1 in tissues other than the intestine has recently revealed its function for tissue‐specific retinoid metabolism with importance in embryogenesis and lipid metabolism. On the other hand, biological activity of BCDO2 metabolites has been shown to be important in protecting against carotenoid‐induced mitochondrial dysfunction. Single‐nucleotide polymorphisms (SNPs) such as R267S and A379V in BCMO1 can partly explain inter‐individual variations observed in carotenoid metabolism. Advancing knowledge about the physiological role of these two enzymes will contribute to understanding the importance of carotenoids in health and disease.
Multi‐parametric approach to identify coffee components that regulate mechanisms of gastric acid secretion
Authors: Rubach Malte , Lang Roman , Seebach Elisabeth , Somoza Mark M. , Hofmann Thomas , Somoza Veronika
Published: December 2011

Scope

Chlorogenic acid (CA), caffeine (CAFF), pyrogallol (PYR), catechol (CAT), βN‐alkanoyl‐hydroxytryptamides (C5HT) and N‐methylpyridinium (N‐MP) were evaluated for their influence on mechanisms of gastric acid secretion as single compounds and in biomimetic mixtures.

Methods and results

Compounds were tested in coffee representative concentrations. Human gastric cancer cells (HGT‐1) were used to study the proton secretory activity by Ussing chamber experiments and FACS analysis. For activation of EGFr, Akt1, ERK1/2, ATF‐2 and cAMP levels, we performed pathway screening assays. Time‐dependent expression of related genes were determined by real‐time PCR. Part of the data was used for neural network modeling to identify the most relevant compounds. N‐MP increased the expression of the anti‐secretory somatostatin receptor by 114%, whereas C5HT decreased its expression by 52%. N‐MP down‐regulated the pro‐secretory CHRM3 receptor by 36% and the H+,K+‐ATPase by 36%. CAFF stimulated the secretory activity in the functional assays, whereas N‐MP and CA decreased proton secretion. After applying a pathway analysis, we were able to discriminate between CAFF, CA, CAT, C5HT, PYR and histamine‐activating EGFr signaling and N‐MP‐associated ERK1/2 signaling.

Conclusion

By applying a multi‐parametric approach, N‐MP was shown to effectively down‐regulate mechanisms of gastric acid secretion in human parietal gastric cells.
An hp‐Adaptive FEM Procedure based on Continuous Sobolev Embeddings
Authors: Wihler Thomas
Published: December 2011

Suitable continuous Sobolev embeddings are applied in order to derive smoothness estimators for adaptive hp‐refinements in the context of hp‐finite element methods. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Simulation and feed‐forward control of a flexible parallel manipulator
Authors: Burkhardt Markus , Seifried Robert
Published: December 2011

The importance of lightweight constructions are steady increasing since they promise a low energy consumption together with higher movement speeds. However these demand modern, model‐based feed‐forward control designs. Especially the undesired vibrations due to the reduced overall stiffness of such manipulators have to be taken into account. A convenient way to model the dynamical behavior of systems that perform large, nonlinear motions superposed with small, elastic deformations is the floating frame of reference approach in a flexible multibody system. The application of the Newton‐Euler‐Formalism together with D'Alembert's principle to parallel manipulators results in a set of differential‐algebraic equations. Therefore, the consideration of the trajectory tracking problem with so‐called servo constraints appears to be promising. In case of a non‐flat system, the arising set of differential‐algebraic equations, which consists of the system dynamics, the holonomic loop closing constraint equations and the servo constraints embodies nontrivial dynamics. With an oblique projection, the embedded set of ordinary differential equations describing the internal dynamics can be obtained. The stability properties of these dynamics determines the complexity of the feed‐forward control design, as two‐point boundary value problems might have to be solved. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Computation of bounded feed‐forward control for underactuated multibody systems using nonlinear optimization
Authors: Seifried Robert , Bastos Guaraci , Brüls Olivier
Published: December 2011

Underactuation occurs, when only some generalized coordinates have a control input. For end‐effector trajectory tracking a combined feed‐forward and feedback control is often a suitable approach. Feed‐forward control design based on an inverse model for underactuated multibody systems is presented. The starting point is the transformation of the multibody system into a nonlinear input‐output normal‐form. The inverse model follows from this and consists of chains of differentiators, driven internal dynamics and an algebraic part. Especially when using the end‐effector as system output the internal dynamics is often unbounded. In order to obtain a viable feed‐forward control, a bounded solution must be determined. For this task the internal dynamics is solved as a nonlinear optimization problem. Thereby, the coordinates of the internal dynamics define the objective function which is minimized. The equation of the internal dynamics must be fulfilled at each point of a discrete time grid. In addition continuity of the solution is achieved by adding as equality constraint an integration formula, e.g. trapezoidal rule. The optimization problem is then solved by a SQP‐method. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Computational Simulation of Bone Remodeling using Design Space Topology Optimization
Authors: Boyle Christopher , Kim Il Yong
Published: December 2011

The law of bone remodeling, commonly referred to as Wolff's Law, asserts that the internal trabecular bone adapts to external loadings, reorienting with the principal stress trajectories to optimize mechanical efficiency creating a naturally optimum structure. The current study utilized an advanced structural optimization algorithm, called design space toptimization (DSO), to perform a three‐dimensional computational bone remodeling simulation on the human proximal femur and analyse the results to determine the validity of Wolff's hypothesis. DSO optimizes the layout of material by iteratively distributing it into the areas of highest loading, while simultaneously changing the design domain to increase computational efficiency. The large‐scale simulation utilized a 175 µm mesh resolution with over 23.3 million elements. The resulting anisotropic trabecular architecture was compared to both Wolff's trajectory hypothesis and natural femur samples from literature using radiography. The results qualitatively showed several anisotropic trabecular regions that were comparable to the natural human femur. The realistic simulated trabecular geometry suggests that the DSO method can accurately predict bone adaptation due to mechanical loading and that the proximal femur is an optimum structure as Wolff hypothesized. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The linear mechanical model for hand‐arm system
Authors: Pop Aurora‐Felicia , Truţa Aurica , Bălcău Monica , Arghir Mariana
Published: December 2011

The paper presents a study regarding the linear mechanical models corresponding to hand‐arm system. These models was simplified unused the joint in wrist, elbow and shoulder. Also, for these mechanical models effectuated the equations system that would integrate, it obtained the solutions (displacements and velocities) finally. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Experimental and numerical investigation of different types of articular cartilage replacement materials
Authors: Zhou B. , Stoffel M. , Gavenis K. , Weichert D.
Published: December 2011

The aim of the presented work is to characterize the mechanical properties of different types of articular cartilage replacement materials. For this propose an elastic‐diffusion model is developed to identify the elastic and diffusion properties of the replacement materials. A set of unconfined compression tests were performed with several kinds of implants. By means of finite element simulation integrated with an user‐defined material model, the material parameters were identified. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Simulation of Crack Propagation under Small‐Scale Yielding by means of a Non‐local GTN‐Model
Authors: Hütter Geralf , Linse Thomas , Mühlich Uwe , Kuna Meinhard
Published: December 2011

Today, the local approach to fracture is widely applied to simulate the failure of specimens. For ductile damage processes the Gurson‐Tvergaard‐Needleman model is the quasi‐standard. In the last time non‐local extensions allowed a mesh‐size independent simulation of crack growth. However, most publications dealing with this subject focus upon the convergence regarding global quantities such as the load‐displacement relation. Minor attention is paid to the fields directly at the crack tip. Correspondingly, the interrelationship between the intrinsic length of the model and relevant microscopic damage processes at the crack tip is only partly established until now. In the present study the crack propagation is simulated for an implicitly gradient enriched GTN‐model within a boundary layer in order to overcome influences of the specimen geometry. The different stages of damage evolution are resolved by a fine mesh. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Extended Finite Element Method for hygro‐mechanical analysis of crack propagation in porous materials
Authors: Leonhart Dirk , Meschke Günther
Published: December 2011

In computational structural analyses, strong discontinuities, such as propagating cracks in concrete structures, joints in rocks or shear bands in soft soils, the highly accelerated moisture transport in the opening discontinuities has to be taken into account. The paper is concerned with an Extended Finite Element model for the numerical representation of crack propagation in partially saturated porous materials. Based on an extended variational formulation for the simulation of moisture transport in cracks, enhanced approximations of the displacement field and the moisture flux across the discontinuity are adopted. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Prediction of fracture toughness of embrittled steels by means of the Small Punch Test
Authors: Rasche Stefan , Kuna Meinhard
Published: December 2011

To characterise the randomly distributed strength and fracture toughness of brittle steels, many specimens have to be destroyed. Since the Small Punch Test (SPT) needs only little material, it is a well suited experiment, when only a small volume of material is available. In this study the cleavage fracture of a ferritic steel at low temperature was investigated using the Beremin model. The failure probability is described with a 2‐parameter Weibull distribution in terms of the so‐called Weibull stress, which is calculated using an elastic‐plastic finite element stress analysis. While the transfer of Weibull parameters works well between similar geometries and loading conditions, it works bad in more general cases. Modifications of the Beremin model are necessary to overcome this problem. Recent publications consider a lower threshold value of the Weibull stress, which leads to a lower Weibull modulus and therefore to a stronger volume size effect of strength. The suitability of this approach to transfer cleavage fracture results from SPT to fracture mechanics specimens was investigated. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Analysis of crack formation in bonded lap joints using finite fracture mechanics on the basis of linear elasticity solutions.
Authors: Weißgraeber Philipp , Becker Wilfried
Published: December 2011

In this work, crack formation and the corresponding failure load of bonded lap joints is analyzed. The analysis is based on linear elasticity solutions for bonded lap joints and makes use of the finite fracture mechanics. A hybrid criterion is applied that states the spontaneous formation of a crack of finite size if a stress and an energy criterion are fulfilled simultaneously. The stress distribution of a linear elasticity solution is used for the stress criterion and for the calculation of the incremental energy release rate which is necessary for definition of the energy criterion. The resulting fracture criterion is compared to literature results and shows a good agreement. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Energy‐consistent time‐integration for dynamic finite deformation thermo‐viscoelasticity
Authors: Krüger Melanie , Groß Michael , Betsch Peter
Published: December 2011

The main goal of the present work is to develop two structure‐preserving time integrators, which are based on the works of Öttinger [1] (GENERIC formalism), Romero [2] (Thermodynamically consistent (TC) algorithm) and Groß [3] (enhanced hybrid Galerkin (ehG) method) and compare them with standard integrators considering a thermoviscoelastic double pendulum. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Aspects on the Functional Optimization of an Industrial Robot Structure Implemented in Military Logistical Activities
Authors: Petrişor Silviu Mihai , Bârsan Ghiţă , Badea Dorel
Published: December 2011

The authors of the present paper outline aspects on the optimization of the a TR‐type industrial robot structure movements in order to generate the manipulation space to a flexible manufacturing cell with a parallel organization designed for the pallet and container operation of paint‐filled recipients. The paper contains the direct and inverted geometrical modelling of the robot structure using the 3*3 rotation matrix method and the algebra method. After knowing the characteristic point movement of the prehension device, graphics for the variation of the TR robot's general coordinates and for the trajectory of the prehension device's characteristic point of its work space were performed by using the Mathematica 6.0 soft. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Starting‐point strategy for interior‐point algorithms for lower‐bound shakedown analysis
Authors: Simon Jaan‐Willem , Weichert Dieter , Höwer Daniel
Published: December 2011

Shakedown analysis by using the lower‐bound theorem leads to computationally intensive nonlinear convex optimization problems with a large number of unknowns and constraints. Interior‐point algorithms such as recently developed by the authors have proven to be efficient for the solution of these problems. For convergence and efficiency of the iterative process of these algorithms the choice of the starting‐point is crucial. It should be inside of the feasible region and well‐centered for fast convergence.

No general method exists for the construction of optimum starting‐points and only few investigations have been published on this issue. In this paper the physical meaning of the involved variables in shakedown problems is used to optimize starting‐points. The efficiency of the new method is illustrated by a numerical examples and comparison with an alternative approach. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Testing of screw joint hybrid composite materials
Authors: Żółkiewski Sławomir
Published: December 2011

Laminate composite materials have excellent coefficient of stiffness to weight and because of this laminates are very widely applied often replacing raditional materials. A very interesting group of such a type materials are the hybrid ones. A main disadvantage of hybrid composite materials is the weak impact strength. The paper presents results of testing handmade screw joint hybrid composite materials. Results of testing are compared with numerical analysis based on the Finite Elements Method. Investigations were made on designed for this purpose the statical stresses laboratory stand. The testing specimens were made by a contact method (handmade laminating) and laminar mats or woven fabrics spreading (resin supersaturated). (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Mode interactions and resonances of an elastic fluid‐conveying tube
Authors: Jurisits Richard , Steindl Alois
Published: December 2011

We consider the non‐linear two‐dimensional oscillations of a fluid conveying tube using dynamical bifurcation theory. The tube is clamped at the upper end, and at its free lower end a point mass is fixed. The tube is assumed to be slender and flexurally elastic, and its transversal motion is constrained by two symmetrically arranged springs. The flow rate of the incompressible fluid is used as a distinguished parameter in the problem. By determining the stability regions in parameter space, it is investigated whether Hopf and/or steady‐state bifurcations may occur, as it was found for similar cases in previous works [1,3]. The non‐linear behaviour close to the bifurcation points is analyzed. Of specific interest are low‐order resonances. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical simulation of interface effects in martensitic phase transformation
Authors: Goodarzi Mehdi , Hackl Klaus
Published: December 2011

This work is the succession of our micromechanical modeling of interface effects in martensite laminate microstructure based on energy methods. We augment our model with finite element implementation of a first‐order one‐dimensional laminate. The numerical results are in good agreement with observed morphology and accommodation patterns of microstructure. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modeling of strain‐induced crystallization in natural rubbers
Authors: Poshtan Emad A. , Dargazany Roozbeh , Itskov Mikhail
Published: December 2011

Strain‐Induced Crystallization (SIC) is a phenomenon characterized by a considerable increase in stiffness of natural rubbers. In this contribution, this phenomenon is studied in filled natural rubbers and a constitutive model of SIC is proposed. The influence of SIC on the mechanical behavior is described by means of the entropic strain energy subjected to a change due the crystallization. The distribution of crystallines is formulated on the basis of a statistical approach. Their contribution to the partial immobilization of polymer chains is accounted for by assuming the crystalline phase and the amorphous phase to be two separate networks. Finally, the model is compared with available experimental results of uniaxial tension tests. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
FEM‐BEM coupling with non‐conforming interfaces
Authors: Rammerstorfer Franz , Schanz Martin
Published: December 2011

In order to treat wave propagation phenomena in coupled domains, a combined approach of Finite Element Methods (FEM) and Boundary Element Methods (BEM) is presented. The coupling is done within the framework of Tearing and Interconnecting methods (FETI/BETI), which are special non‐overlapping domain decomposition methods. The coupling conditions are incorporated in a weak sense, which allows non‐conforming interface discretization, i.e., the Mortar Method is used. A numerical example is given to verify the algorithm. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A solid shell finite element formulation to simulate the behaviour of thin dielectric elastomer structures
Authors: Zwecker Sandro , Klinkel Sven
Published: December 2011

To analyse the behaviour of thin structures of dielectric elastomer (DE) material a solid shell finite element is presented. The main characteristics of DEs are a non‐linear hyper elastic behaviour, the quasi‐incompressibility, and the ability to transform electric energy into mechanical work. Applying a voltage to thin DE structures may produce large elongation strains of 120‐380%. These large strains, the efficient electro‐mechanical coupling, and the light weight make DEs very attractive for the usage in actuators. Thus, there is a need for detailed research. With respect to the electro‐mechanical coupling a constitutive model is presented. An electric stress tensor and a total stress tensor are introduced by considering the electrical body force and couple in the balance of linear momentum and angular momentum, respectively. The governing equations are derived and embedded in the solid shell formulation. The element formulation is based on a Hu‐Washizu mixed variational principle using six independent fields: displacements, electric potential, strains, electric field, mechanical stresses, and dielectric displacements. It allows large deformations and accounts for physical nonlinearities to capture two of the main characteristics of DEs. The shell element could be applied for the modelling of arbitrary curved thin structures. The ability of the present element formulation is demonstrated in several examples. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Homogenization with uncertain input data
Authors: Kreuter Daniel , Sepahvand Kheirollah , Beitelschmidt Michael
Published: December 2011

In this paper a fast homogeniztaion technique is used to calculate effective material parameter if the input data are uncertain. The technique uses the Polynomial Chaos Expansion to approximate the distribution of the uncertain input data und the calculated output data. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical modeling of atomistic‐to‐continuum coupling based on bridging domain method
Authors: Marenić Eduard , Sorić Jurica , Tonković Zdenko
Published: December 2011

Nano‐submodeling is an approach that enables insertion of nano‐refined submodel (atomistic) in the global model (continuum). In this work analysis of the spurious effects that may arise in the concurrent atomistic‐to‐continuum coupling is performed. The coupling is based on the overlapping domain decomposition (ODD) method called bridging domain [1, 2] (similar is Arlequin [3] method) where different models are overlapped and the displacements compatibility is enforced via Lagrange multipliers (LM). Some coupling options such as energy weighting, coupling zone geometry and LM field interpolation are tested. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Application of Homogenization Techniques to a Seismic Problem
Authors: Moos Christoph , Hackl Klaus
Published: December 2011

The subduction channel is a concept to explain certain phenomena observed by geoscientists around subduciton zones. Although many theories concering this have been formulated, the proof of the existence of such a channel is still open. We use homogenization techniques for wave propagation properties of the material to account for the microstrucural effects on seismic waves in such a supposed subduction channel. In order to assist the search for it we want to reveal the effects that it would have on elastic waves propagating in the crust, which are observed via surface measurement. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the Homogenization of Material Forces
Authors: Ricker Sarah , Mergheim Julia , Steinmann Paul , Müller Ralf
Published: December 2011

The work at hand treats the extension of the classical computational homogenization scheme towards the multi‐scale computation of material quantities like the Eshelby stresses and material forces. To this end, two approaches are elaborated and their consistency with respect to the virtual work principle, in terms of a Hill‐Mandel type condition, is checked. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Self‐similar turbulent boundary layer in pressure gradient
Authors: Vigdorovich Igor
Published: December 2011

Self‐similar flows in a turbulent boundary layer when the free‐stream velocity is specified as a power function of longitudinal coordinate are investigated. The self‐similar formulation not only simplifies solving of the problem by reducing the equations of motion to ordinary differential equations but also provides a mean for formulating closure conditions. It is shown that for the class of flows under consideration that depend on three governing parameters the dimensionless mixing length is a function of the normalised distance from the wall and the exponent in the law specifying the free‐stream velocity distribution in the outer region and a universal function of local Reynolds number in the wall region, the latter corollary being true even when the skin friction vanishes. In calculations this function is set to be independent of pressure gradient, which gives the results very close to experimental data.

There exist four different self‐similar flow regimes. Each regime is related to its similarity parameter, one of which is the well‐known Clauser equilibrium parameter and the other three are established for the first time. In case of adverse pressure gradient when the exponent lies within certain limits, which depend on Reynolds number, the problem has two solutions with different values of the boundary layer thickness and skin friction, which points out the possibility of hysteresis in near‐separating flow. Separation occurs not at the minimum value of the exponent that corresponds to the strongest adverse pressure gradient but at a higher one whose dependence on Reynolds number is calculated in the paper. The results of the theory are in good agreement with experimental data. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Fully implicit time discretization for a free surface flow problem
Authors: Bänsch Eberhard , Weller Stephan
Published: December 2011

One of the challenges in the numerics of free surface flows is the coupling of the flow field to the geometry of the domain. The most simple approach is an explicit decoupling, i.e. computing the flow field with geometrical information of a prior time step and then updating the geometry. This widely used approach leads to a severe CFL condition of the type $\Delta t \le C\sqrt{{\rm We}}\;h^{3 \over 2}$, which may prescribe infinitesimally small time step sizes in the interesting case of a small Weber number (i.e. high surface tension). A semi‐implicit approach utilizing the fact that $x^{n+1} = x^n + \Delta t\, u^{n+1}_{|\Gamma}$, where xk is a parametrization of the capillary boundary Γ, is also available [1]. This approach can be proven to be unconditionally stable but is of first order only. It also suffers from relatively strong numerical dissipation.

We present a fully implicit approach using a backward differentiation formula to achieve a time discretization method that is of second order and only minimally dissipative. A numerical example of an oscillating drop showing very low numerical dissipation and second order convergence as well as numerical evidence for the stability of the method is presented. Since the method requires the solution of a highly nonlinear coupled system, possible preconditioners for this system are discussed, including a lower order decoupling. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Thin Film Exfoliation in the Zone of Trapped Elastic Wave Localization
Authors: Abramyan Andrey , Indeitsev Dmitriy , Mochalova Yulia , Semenov Boris
Published: December 2011

In modern constructions, thin‐layer coats are often used as protecting or strengthening elements. Deformations of such constructions may cause significant stresses on the interface between the base and the coat because of the difference in their physical mechanical properties, which leads to the destruction or detachment of the cover. The impact of static or shock loads on the emergence and development of delamination in multilayer constructions has been studied fairly well, but much less is known about destructions of this type under nonstationary (vibrational) loads. The interest in the latter is caused by the fact that even small variable actions may cause the localization of oscillations in a neighborhood of inhomogeneities (such as inclusions, defects, construction elements, etc.) [1] (and lead to the emergence and growth of defects, which strongly affects the reliability and functionality of the whole construction. The possibility of the localization of oscillations near initial delamination and the impact of localization on the growth of the delamination are studied and a model for analyzing conditions under which a detachment zone grows or ceases to grow is suggested. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Wave propagation in finite structures due to transient loading with application to pyroshock simulation
Authors: Jüngel Nikolas , Lacher Alexander , von Wagner Utz
Published: December 2011

Pyroshocks are transient motions of a structure caused by e.g. explosion of ordnance devices. Prior to their launching space modules have to be tested for fulfillment of strict requirements concerning the expected acceleration during a space mission. Since, in practical applications, this is still based on empirical knowledge and time consuming testing procedures, an analytical way to face this problem is the modelling of a pyroshock test device for the simulation of mechanical impacts on plates carrying the module to be tested. From the mechanical point of view, the problem is described by the wave propagation in a disk or a plate carrying a point mass and being exposed to a punctual load caused by the impact of a sphere. The displacement field is calculated semi‐analytically by the use of a modal approach, HERTZian contact theory as well as the GALERKIN procedure. In order to systematically determine the optimum setup leading to a desired acceleration signal an evolution strategy is used as well as comparisons with experimental and FEM results have been made. The present procedure allows for a better and faster simulation and predictability of pyroshock tests. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modelling of Lamb wave propagation in composite plate excited by surface bonded piezoelectrical actuators
Authors: Karmazin Alexander , Kirillova Evgenia , Seemann Wolfgang , Syromyatnikov Pavel
Published: December 2011

Transient propagation of Lamb waves in a multilayered infinite composite plate with the arbitrary elastic anisotropy of each layer is considered in this paper. Integral representations of wave fields, an algorithm of computing the Green's matrix of the multilayered medium in Fourier domain and some methods of the Fourier transform inversion are used as basic analytical research instruments. The piezoelectrical transducers frequently used for Lamb wave excitation are modelled in this paper as surface sources with stresses concentrated on the boundaries of actuators. The contribution of each wave mode to a whole amplitude, focusing of Lamb waves and influence of the geometry of the surface source are discussed in this paper by numerical examples. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Dusty shock wave interaction – formation of fully dispersed waves and particle focusing effect
Authors: Osiptsov Alexander , Golubkina Irina
Published: December 2011

The problem of regular (symmetric and asymmetric) interaction of plane shock waves in a steady‐state dusty gas flow is considered. For near‐sonic flows with a fairly high particle mass loading, the possibility of the formation of wave structures is revealed, in which either all or only some of the incident or reflected waves degenerate into so‐called fully dispersed waves, i.e. zones in which no discontinuities appear in the parameters of each phase. For stronger shock waves and low particle mass concentration, the effect of aerodynamic particle focusing and the formation of a narrow high‐concentration beam of particles behind the point of the interaction of the waves are detected on the basis of parametric numerical calculations. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Theoretical and Experimental Investigations of Piezoelectrically Excited Travelling Waves in Cylindrical Tubes
Authors: Wallaschek Jörg , Renner Andreas
Published: December 2011

Flügge's equations of motion for cylindrical shells are used to analyze the generation of travelling waves in a tube of an ultrasonic travelling wave transport system. The vibration‐shape of a semi‐infinite acrylic tube with structural damping excited by a piezoelectric ring at the end is calculated and the influence of the driving frequency is shown.

Starting with an exponential ansatz the frequency dependent wavenumbers can be determined. Three frequency bands with different combinations of imaginary, real and complex wavenumbers can be found. Supposing a semi‐infinite tube with given boundary conditions at the end of excitation the vibrations of the tube can be calculated depending on the frequency. Simulation agrees well with experimental results. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical analyis of turbulent flow in a Coanda ejector
Authors: Alexandru Dumitrache , Florin Frunzulica , Horia Dumitrescu , Octavian Preotu
Published: December 2011

The task of this study is to investigate the influence of various geometric parameters and pressure ratios on the Coanda ejector performance. For numerically investigations we use an implicit formulation of the compressible Reynolds‐average Navier‐Stokes equations (RANS) for axisymmetric flow with a shear stress transport k − ω (SST model) turbulence model. The numerically results was obtained for a total pressure range 1‐5 Bars, imposed at the reservoir inlet. The effect of various factors, such as, the pressure ratio, primary nozzle and ejector configurations on the system performance has been evaluated based on defined performance parameters. The numerical results have been compared with theoretical and experimental results for a given Coanda ejector configuration. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Motion of a Ferrofluid in a Periodic Magnetic Field due to Surface Deformation
Authors: Popp Jana , Zeidis Igor , Zimmermann Klaus , Böhm Valter , Gärtner Ralf
Published: December 2011

The article considers a plane flow of an incompressible, viscous magnetizable fluid. Cause of the flow is an alternating magnetic field, which consequently affects the free surface to periodical deformation. The proof of a peristaltic material transport is desired. The STOKES approximation for creeping flows and the two‐dimensional continuity equation serve for governing equations. The methods used include power series expansion with regard to the small ratio of ε perturbed and unperturbed fraction of the magnetic field. The analytical result is discussed with regard to functional parameters. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Analysis of supersonic flow in Oswatitsch inlet configuration
Authors: Vuković Danijel , Matijašević Dubravko , Vrdoljak Milan
Published: December 2011

The aim of this work is a study of the flow parameters relevant for the Oswatitsch intake configuration. Geometry of the cone and inlet are equivalent to those on MiG‐21bis fighter aircraft. Supersonic flow parameters for a channeled cone were studied at two different operational Mach numbers. Center body cone is movable along longitudinal axis and analysis is focused on specific positions for supersonic flight regimes. To study the problem, numerical model of axisymmetric two‐dimensional Euler flow is applied. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Stability of solutions to Cauchy problem on linear approximation and branching equation in the root subspace
Authors: Trenogin Vladilen , Kim‐Tyan Luiza , Loginov Boris
Published: December 2011

Stability of solutions to Cauchy problem on linear approximation for differential equation in Banach space E with degenerate linearization is studied from viewpoint of branching equation in the root subspace. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Parameter estimation for DAE models in a multiple experiment context
Authors: Kircheis Robert , Körkel Stefan
Published: December 2011

Parameter estimation for PDE models is a recent topic of our research. After discretization in space we get a system of DAEs. We here present the techniques we use (e.g., Multiple Shooting, generalized Gauss‐Newton) to fit the parameters. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Locally Optimal Block Preconditioned Conjugate Gradient Method for Hierarchical Matrices
Authors: Benner Peter , Mach Thomas
Published: December 2011

We present a method of almost linear complexity to approximate some (inner) eigenvalues of symmetric self‐adjoint integral or differential operators. Using ℋ‐arithmetic the discretisation of the operator leads to a large hierarchical (ℋ‐) matrix M. We assume that M is symmetric, positive definite. Then we compute the smallest eigenvalues by the locally optimal block preconditioned conjugate gradient method (LOBPCG), which has been extensively investigated by Knyazev and Neymeyr.

Hierarchical matrices were introduced by W. Hackbusch in 1998. They are data‐sparse and require only O(nlog2 n) storage. There is an approximative inverse, besides other matrix operations, within the set of ℋ‐matrices, which can be computed in linear‐polylogarithmic complexity. We will use the approximative inverse as preconditioner in the LOBPCG method.

Further we combine the LOBPCG method with the folded spectrum method to compute inner eigenvalues of M. This is equivalent to the application of LOBPCG to the matrix Mμ = (M − μI)2. The matrix Mμ is symmetric, positive definite, too.

Numerical experiments illustrate the behavior of the suggested approach. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optimal control of hydroforming processes
Authors: Koller Daniela , Ulbrich Stefan
Published: December 2011

We consider an optimal control problem for sheet metal hydroforming. As a first step derivative free optimization algorithms are used to control the time dependent blank holder force and the fluid pressure, which are typical control variables. Our goal is to obtain a desired final configuration. We present numerical examples for 2D and 3D ABAQUS simulations for the hydroforming process of complexly curved sheet metals with bifurcated cross‐sections. Since a single ABAQUS simulation takes a long time, optimization algorithms based on reduced models are under investigation. The reduced order model is based on a Galerkin solver for the elastoplasticity problem. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Gyroscopic Stabilization of 2nd‐Order‐Systems with Indefinite Damping
Authors: Damm Tobias , Homeyer Jan
Published: December 2011

We consider the gyroscopic stabilization of the unstable system ẍ + D ẋ + Kx = 0 with positive definite stiffness matrix K. The indefinite damping matrix D is responsible for the instability of the system. The modelling of sliding bearings can lead to negative damping, see [6]. A gyroscopic stabilization of an unstable mechanical system with indefinite damping matrix was investigated in [4] in the case of matrix order n = 2 using the Routh‐Hurwitz criterion. The question was raised whether an unstable system can be stabilized by adding a gyroscopic term Gẋ with a suitable skew‐symmetric matrix G = −GT. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Stream Function Approach to Optical Flow with Applications to Fluid Transport Dynamics
Authors: Luttman Aaron , Bollt Erik , Basnayake Ranil , Kramer Sean
Published: December 2011

Optical flow is one of the classical problems in computer vision, but it has recently also been adapted to applications from other fields, such as fluid mechanics and dynamical systems. If the goal is to analyze the dynamics of system whose evolution is governed by a flow field that is the gradient of a potential function – which describes many flows in fluid dynamics – it is natural to approach the optical flow problem by reconstructing the potential function, also called the stream function, rather than reconstructing the components of the flow directly. This alternate approach allows one to impose scientific priors, via regularization, directly on the flow itself rather than on its components independently. We demonstrate the stream function formulation of optical flow and its application to reconstructing an oceanic fluid flow driven by satellite measurements. It is also shown how these flow fields can be used to analyze mixing and mass transport in the fluid system being imaged. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Separation of Edges in X‐Ray Images by Microlocal Analysis
Authors: Storath Martin
Published: December 2011

In many x‐ray images, we find crossing structures, for example the rib bones of a thorax image. Hence, many edges in such images intersect with other edges. We propose a new algorithm, which simultaneously detects and separates such crossing edges. We prove the functionality of the algorithm under the geometric assumption that the edges possess different orientations at the points of intersection. To this end, we model edges as singularities of distributions with a submanifold structure and define the edge orientation to be the orientation of the corresponding singularity in the sense of microlocal analysis. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The application of the Ehrlich‐Aberth method to structured polynomial eigenvalue problems
Authors: Noferini Vanni
Published: December 2011

An algorithm for the application of the Ehrlich‐Aberth method to polynomial eigenvalue problems (PEPs) is proposed. The computational complexity of the algorithm is only quadratic with respect to the degree of the polynomial, where customary matrix methods have cubic complexity. For the case of some structured PEPs a strategy is given in order to exploit the structure and obtain the induced coupling in the spectrum. Numerical experiments are provided for the particular case of even/odd PEPs. This communication is based on joint work with Dario A. Bini and Luca Gemignani. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Thiourethane thermoset coatings from bio‐based thiols
Authors: Yan Jingling , Ariyasivam Sharonie , Weerasinghe Dimuthu , He Jie , Chisholm Bret , Chen Zhigang , Webster Dean
Published: December 2011

Three bio‐based thiols were synthesized via the thermal thiol‐ene reactions between sucrose soya ester (SSE) and multifunctional thiols; then, thiourethane coatings were produced from these thiols and their coating properties were studied. A series of high bio‐renewable content thiol oligomers were synthesized according to the previously reported thermal thiol‐ene reaction. Fourier transform infrared spectra (FTIR) confirmed the complete consumption of the double bonds in SSE, and gel permeation chromatography confirmed the formation of high‐molecular‐weight oligomers. The viscosity of these oligomers remained low due to their compact and branched structures. Thermoset thiourethane coatings were prepared from these thiol oligomers and polyisocyanate trimer resins with dibutyltin diacetate as the catalyst. FTIR spectra confirmed the formation of the thiourethane group. However, coatings based on isophorone diisocyanate (IPDI) polyisocyanate resin showed a lower degree of cure because of the decreased resin mobility due to the rigid cyclohexane ring. Generally, all the coatings showed good adhesion to aluminum panels, and had high gloss. However, they exhibited low tensile strength, modulus and chemical resistance due to the flexibility of the fatty acid chain. Coatings based on more rigid IPDI‐based polyisocyanate showed higher Tg, hardness and direct impact resistance compared with the hexamethylene‐diisocyanate (HDI) based polyisocyanate counterparts. Thermogravimetric analysis results showed that coatings based on mercaptanized soybean oil have better thermal stability than those from di‐pentene dimercaptan or glycol di‐3‐mercaptopropionate. Two Tg values were found by both differential scanning calorimetry and dynamic mechanical thermal analysis of thiourethanes from HDI‐based polyisocyanate and di‐pentene dimercaptan or glycol di‐3‐mercaptopropionate based oligomers due to phase separation resulting from the poor compatibility between HDI‐based polyisocyanate and the respective oligomers. Copyright © 2011 Society of Chemical Industry