bluuebunny/crossref_metadata_2025 huggingface dataset:
Epidural analgesia provides better pain management after live liver donation
Authors: Clarke Hance , Chandy Tony , Srinivas Coimbatore , Ladak Salima , Okubo Nobuhiko , Mitsakakis Nicholas , Holtzman Susan , Grant David , McCluskey Stuart A. , Katz Joel
Published: November 2010

Despite the increase in surgical volumes of live liver donation, there has been very little documentation of the postoperative pain experience. The primary aim of this study was to examine the difference in acute postoperative pain intensity and adverse effects between patients who received intravenous patient-controlled analgesia (IV PCA) or patient-controlled epidural analgesia (PCEA) for pain control after live liver donation surgery. A retrospective chart review was performed of 226 consecutive patients who underwent right living donor hepatic surgery at the Toronto General Hospital, Toronto, Canada. Patients who received as their primary postoperative analgesic modality IV PCA (n = 158) were compared to patients who received PCEA (n = 68). Demographic profiles for the 2 groups were similar with respect to age, sex, and body mass index at the time of surgery. For the first 3 postoperative days, pain intensity was significantly lower in patients who received epidural analgesia (P < 0.01). Clinically significant moderate pain (defined as a Numeric Rating Scale pain score >4) was reported more frequently in the IV PCA group (P < 0.05) along with increased sedation (P < 0.05). Pruritus was reported more frequently in the PCEA group of patients compared to the IV PCA group (P < 0.05). Significant between-group differences were not found for the incidence of postoperative vomiting, the time at which patients began fluid intake, the time to initial ambulation, or the length of hospital stay. In conclusion, epidural analgesia provides better postoperative pain relief, less sedation, but more pruritus than IV PCA after live liver donation. Liver Transpl, 2011. © 2011 AASLD.
Flow‐Induced Polymer Degradation During Ink‐Jet Printing
Authors: A‐Alamry Khalid , Nixon Keith , Hindley Rachel , Odel Jeffrey A. , Yeates Stephen G.
Published: November 2010

We report for the first time evidence of flow‐induced polymer degradation during inkjet printing for both poly(methyl methacrylate) (PMMA) and polystyrene (PS) in good solvent. This has significance for the deposition of functional and biological materials. Polymers having $\overline {M} _{{\rm w}} $ either less than 100 kDa or greater than approximately 1 000 kDa show no evidence of molecular weight degradation. The lower boundary condition is a consequence of low Deborah Number De imposed by the printhead geometry and the upper boundary condition due to visco‐elastic damping. For intermediate molecular weights the effect is greatest at high elongational strain rate and low solution concentration with higher polydispersity polymers being most sensitive to molecular weight degradation. For low polydispersity samples, PDi ≤ 1.3, chain breakage is essentially centro‐symmetric induced either by turbulance or overstretching when the strain rate increases well beyond a critical value, that is the stretching rate is high enough to exceed the rate of relaxation. For higher polydispersity samples chain breakage is consistent with almost random scission along the chain, inferring that the forces required to break the chain are additionally transmitted either by valence bonds, i.e. network chains and junctions or discrete entanglements rather than solely by hydrodynamic interaction.

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The effect of drug treatment on neurogenesis in Parkinson's disease
Authors: O'Sullivan Sean S. , Johnson Mary , Williams David R. , Revesz Tamas , Holton Janice L. , Lees Andrew J. , Perry Elaine K.
Published: November 2010

There has been recent interest in the possibility that impaired neurogenesis may contribute to the decline in neurodegenerative diseases such as Alzheimer's disease and Parkinson's disease (PD). We have investigated the effects of commonly used treatments for PD on neural stem cell (NSC) activity in nondemented patients. Postmortem of brain tissue containing the subventricular zone (SVZ) and ependymal layer cells was obtained from 32 nondemented patients with PD. NSC activity was assessed by immunohistochemical staining for RNA‐binding protein Musashi1. Regression analyses were then used to identify which clinical factors independently influenced NSC activity. Disease duration was negatively associated with SVZ Musashi1 staining, whereas lifetime levodopa was positively associated in this region. Our findings suggest a positive impact of chronic L‐dopa use on the number of NSC in the SVZ of PD patients, which may have relevance for future studies on neuroprotection in neurodegenerative diseases. © 2010 Movement Disorder Society.
Clinical subtypes of Parkinson's disease
Authors: van Rooden Stephanie M. , Colas Fabrice , Martínez‐Martín Pablo , Visser Martine , Verbaan Dagmar , Marinus Johan , Chaudhuri Ray K. , Kok Joost N. , van Hilten Jacobus J.
Published: November 2010

The clinical heterogeneity of Parkinson's disease (PD) may point at the existence of subtypes. Because subtypes likely reflect distinct underlying etiologies, their identification may facilitate future genetic and pharmacotherapeutic studies. Aim of this study was to identify subtypes by a data‐driven approach applied to a broad spectrum of motor and nonmotor features of PD. Data of motor and nonmotor PD symptoms were collected in 802 patients in two different European prevalent cohorts. A model‐based cluster analysis was conducted on baseline data of 344 patients of a Dutch cohort (PROPARK). Reproducibility of these results was tested in data of the second annual assessment of the same cohort and validated in an independent Spanish cohort (ELEP) of 357 patients. The subtypes were subsequently characterized on clinical and demographic variables. Four similar PD subtypes were identified in two different populations and are largely characterized by differences in the severity of nondopaminergic features and motor complications: Subtype 1 was mildly affected in all domains, Subtype 2 was predominantly characterized by severe motor complications, Subtype 3 was affected mainly on nondopaminergic domains without prominent motor complications, while Subtype 4 was severely affected on all domains. The subtypes had largely similar mean disease durations (nonsignificant differences between three clusters) but showed considerable differences with respect to their association with demographic and clinical variables. In prevalent disease, PD subtypes are largely characterized by the severity of nondopaminergic features and motor complications and likely reflect complex interactions between disease mechanisms, treatment, aging, and gender. © 2010 Movement Disorder Society.
Petri Nets – A Mathematical Formalism to Analyze Chemical Reaction Networks
Authors: Koch Ina
Published: November 2010

In this review we introduce and discuss Petri nets – a mathematical formalism to describe and analyze chemical reaction networks. Petri nets were developed to describe concurrency in general systems. We find most applications to technical and financial systems, but since about twenty years also in systems biology to model biochemical systems. This review aims to give a short informal introduction to the basic formalism illustrated by a chemical example, and to discuss possible applications to the analysis of chemical reaction networks, including cheminformatics. We give a short overview about qualitative as well as quantitative modeling Petri net techniques useful in systems biology, summarizing the state‐of‐the‐art in that field and providing the main literature references. Finally, we discuss advantages and limitations of Petri nets and give an outlook to further development.
Specific absorption rate reduction in parallel transmission by k‐space adaptive radiofrequency pulse design
Authors: Homann Hanno , Graesslin Ingmar , Nehrke Kay , Findeklee Christian , Dössel Olaf , Börnert Peter
Published: November 2010

The specific absorption rate (SAR) is an important safety criterion, limiting many MR protocols with respect to the achievable contrast and scan duration. Parallel transmission enables control of the radiofrequency field in space and time and hence allows for SAR management. However, a trade‐off exists between radiofrequency pulse performance and SAR reduction. To overcome this problem, in this work, parallel transmit radiofrequency pulses are adapted to the position in sampling k‐space. In the central k‐space, highly homogeneous but SAR‐intensive radiofrequency shim settings are used to achieve optimal performance and contrast. In the outer k‐space, the homogeneity requirement is relaxed to reduce the average SAR of the scan. The approach was experimentally verified on phantoms and volunteers using field echo and spin echo sequences. A reduction of the SAR by 25–50% was achieved without compromising image quality. Magn Reson Med, 2011. © 2010 Wiley‐Liss, Inc.
Two‐point dixon method with flexible echo times
Authors: Berglund Johan , Ahlström Håkan , Johansson Lars , Kullberg Joel
Published: November 2010

The two‐point Dixon method is a proton chemical shift imaging technique that produces separated water‐only and fat‐only images from a dual‐echo acquisition. It is shown how this can be achieved without the usual constraints on the echo times. A signal model considering spectral broadening of the fat peak is proposed for improved water/fat separation. Phase errors, mostly due to static field inhomogeneity, must be removed prior to least‐squares estimation of water and fat. To resolve ambiguity of the phase errors, a corresponding global optimization problem is formulated and solved using a message‐passing algorithm. It is shown that the noise in the water and fat estimates matches the Cramér‐Rao bounds, and feasibility is demonstrated for in vivo abdominal breath‐hold imaging. The water‐only images were found to offer superior fat suppression compared with conventional spectrally fat suppressed images. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.
Anisotropic anomalous diffusion assessed in the human brain by scalar invariant indices
Authors: De Santis S. , Gabrielli A. , Bozzali M. , Maraviglia B. , Macaluso E. , Capuani S.
Published: November 2010

A new method to investigate anomalous diffusion in human brain, inspired by the stretched‐exponential model proposed by Hall and Barrick, is proposed here, together with a discussion about its potential application to cerebral white matter characterization. Aim of the work was to show the ability of anomalous diffusion indices to characterize white matter structures, whose complexity is only partially accounted by diffusion tensor imaging indices. MR signal was expressed as a stretched‐exponential only along the principal axes of diffusion; whereas, in a generic direction, it was modeled as a combination of three stretched‐exponentials. Indices to quantify the tissue anomalous diffusion and its anisotropy, independently of the experiment reference frame, were derived. Experimental results, obtained on 10 healthy subjects at 3T, show that the new parameters are highly correlated to intrinsic local geometry when compared with Hall and Barrick indices. Moreover, they offer a different contrast in white matter regions when compared with diffusion tensor imaging. Specifically, the new indices show a higher capability to discriminate among areas of the corpus callosum associated to different distribution in axonal densities, thus offering a new potential tool to detect more specific patterns of brain abnormalities than diffusion tensor imaging in the presence of neurological and psychiatric disorders. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.
Detecting response of rat C6 glioma tumors to radiotherapy using hyperpolarized [1‐13C]pyruvate and 13C magnetic resonance spectroscopic imaging
Authors: Day Sam E. , Kettunen Mikko I. , Cherukuri Murali Krishna , Mitchell James B. , Lizak Martin J. , Morris H. Douglas , Matsumoto Shingo , Koretsky Alan P. , Brindle Kevin M.
Published: November 2010

We show here that hyperpolarized [1‐13C]pyruvate can be used to detect treatment response in a glioma tumor model; a tumor type where detection of response with 18fluoro‐2‐deoxyglucose, using positron emission tomography, is limited by the high background signals from normal brain tissue. 13C chemical shift images acquired following intravenous injection of hyperpolarized [1‐13C]pyruvate into rats with implanted C6 gliomas showed significant labeling of lactate within the tumors but comparatively low levels in surrounding brain.Labeled pyruvate was observed at high levels in blood vessels above the brain and from other major vessels elsewhere but was detected at only low levels in tumor and brain.The ratio of hyperpolarized 13C label in tumor lactate compared to the maximum pyruvate signal in the blood vessels was decreased from 0.38 ± 0.16 to 0.23 ± 0.13, (a reduction of 34%) by 72 h following whole brain irradiation with 15 Gy. Magn Reson Med, 2011. © 2010 Wiley‐Liss, Inc.
Hindlimb skeletal muscle function in myostatin‐deficient mice
Authors: Gentry Bettina A. , Ferreira J. Andries , Phillips Charlotte L. , Brown Marybeth
Published: November 2010

Absence of functional myostatin (MSTN) during fetal development results in adult skeletal muscle hypertrophy and hyperplasia. To more fully characterize MSTN loss in hindlimb muscles, the morphology and contractile function of the soleus, plantaris, gastrocnemius, tibialis anterior, and quadriceps muscles in male and female null (Mstn−/−), heterozygous (Mstn+/−), and wild‐type (Mstn+/+) mice were investigated. Muscle weights of Mstn−/− mice were greater than those of Mstn+/+ and Mstn+/− mice. Fiber cross‐sectional area (CSA) was increased in female Mstn−/− soleus and gastrocnemius muscles and in the quadriceps of male Mstn−/− mice; peak tetanic force in Mstn−/− mice did not parallel the increased muscle weight or CSA. Male Mstn−/− muscle exhibited moderate degeneration. Visible pathology in male mice and decreased contractile strength relative to increased muscle weight suggest MSTN loss results in muscle impairment, which is dose‐, sex‐, and muscle‐dependent. Muscle Nerve, 2011
Hereditary inclusion‐body myopathy associated with cardiomyopathy: Report of two siblings
Authors: Chai Yaohui , Bertorini Tulio E. , McGrew Frank A.
Published: November 2010

Hereditary inclusion‐body myopathy (HIBM) or distal myopathy with rimmed vacuoles (DMRV) is an autosomal recessive disorder characterized by preferential involvement of distal muscles in the lower extremities, especially the anterior compartment of the legs, with relative preservation of the quadriceps.This is referred to as quadriceps‐sparing myopathy. Previous reports have revealed exclusive involvement in skeletal muscles. Herein we describe two siblings with typical HIBM/DMRV. The patients developed exertional dyspnea 20–26 years after disease onset. Echocardiogram revealed a cardiomyopathy in both patients. This is the first report of the association between HIBM/DMRV and cardiomyopathy. Muscle Nerve, 2011
Vascular endothelial growth factor helps differentiate neuropathies in rare plasma cell dyscrasias
Authors: Briani Chiara , Fabrizi Gian Maria , Ruggero Susanna , Torre Chiara Dalla , Ferrarini Moreno , Campagnolo Marta , Cavallaro Tiziana , Ferrari Sergio , Scarlato Marina , Taioli Federica , Adami Fausto
Published: November 2010

POEMS syndrome and amyloidosis are rare plasma cell diseases that share common features, including polyneuropathy. The aim of this study was to investigate serum vascular endothelial growth factor (sVEGF) in patients with amyloidosis and to evaluate changes in response to treatment. Twenty‐five patients [17 primary light‐chain amyloidosis (AL‐A), 7 transthyretin amyloidosis (TTR‐A), 1 senile wild‐type TTR‐A] were studied. sVEGF was analyzed by ELISA. Sera from 8 myeloma and 7 POEMS patients were also evaluated. The median sVEGF level was 420 pg/ml in AL‐A and 179 pg/ml in TTR‐A patients; this was significantly lower than in POEMS syndrome (median 2580 pg/ml, P = 0.0002 and 0.001, respectively). sVEGF of AL‐A patients showed no changes in response to treatment. sVEGF was not increased in amyloid patients regardless of neuropathy, and did not mirror the course of the disease. sVEGF should be tested in patients with overlapping and atypical clinical features. Muscle Nerve, 2011
The MG‐QOL15 for following the health‐related quality of life of patients with myasthenia gravis
Authors: Burns Ted M , Grouse C.K , Wolfe Gil I , Conaway Mark R , Sanders Donald B
Published: November 2010

The MG‐QOL15 is helpful in informing the clinician about the patient's perception of the extent of and dissatisfaction with myasthenia gravis (MG)‐related dysfunction. The aims of this study were to determine the usefulness of the MG‐QOL15 for following individuals with MG and to guide clinical researchers who plan to use the MG‐QOL15. We assessed sensitivity and specificity for detecting clinical change and evaluated test–retest reliability. Sensitivities and specificities of various cut‐points of change in scores are presented. Also presented are means and standard deviations of MG‐QOL15 scores for all patients and for subgroups of patients. The test–retest reliability coefficient was 98.6%. The MG‐QOL15 has an acceptable longitudinal construct validity. We consider this instrument to be most useful for informing the clinician about the patient's perception and tolerance of MG‐related dysfunction. More objective measures, such as the MG Composite, should also be used to follow disease severity. Muscle Nerve, 2011
Comparison of beneficial effects of undifferentiated cultured bone marrow stromal cells and omental adipose‐derived nucleated cell fractions on sciatic nerve regeneration
Authors: Mohammadi Rahim , Azizi Saeed , Delirezh Nowruz , Hobbenaghi Rahim , Amini Keyvan
Published: November 2010

Adipose tissue is a good source for isolation of cells with stem‐cell–like properties. The effects of undifferentiated cultured bone marrow stromal cells (BMSCs) and omental adipose‐derived nucleated cells (OADNCs) on peripheral nerve regeneration were compared in a rat nerve regeneration model. A 10‐mm sciatic nerve defect was bridged using a vein graft. In one group, the vein was filled with BMSCs and in the other group with OADNCs. Functional study, morphometric indices, and immunohistochemistry indicated there was no significant difference (P > 0.05) between groups in recovery of regenerated axons at 4, 8, and 12 weeks after surgery. OADNCs enhanced regeneration similar to undifferentiated BMSCs. These observations suggest OADNCs represent an effective and cost‐saving cell population due to the shortened time interval from tissue collection to cell injection as well as procedural simplicity. This approach is clinically translatable toward new methods for enhanced peripheral nerve repair without the limitations of BMSC. Muscle Nerve, 2011
Analysis of Guided Lamb Wave Propagation (GW) in Honeycomb Sandwich Panels
Authors: Hosseini Seyed Mohammad Hossein , Gabbert Ulrich
Published: November 2010

The paper aims to introduce the guided lamb wave propagation (GW) in a honeycomb sandwich panels to be used in the health monitoring applications. Honeycomb sandwich panels are well‐known as lightweight structures with a good stiffness behavior and a wide range of applications in different industries. Due to the complex geometry and complicated boundary conditions in such a structure, the development of analytical solutions for describing the wave propagation and the interaction of waves with damages is hardly possible. Therefore dimensional finite element simulations have been used to model GW for different frequency ranges and different sandwich panels with different geometrical properties. The waves, which are highly dispersive, have been excited by thin piezoelectric patches attached to the surface of the structure. In the first step, the honeycomb panel has been simplified as an orthotropic layered continuum medium. The required material data have been calculated by applying a numerical homogenization method for the honeycomb core layer. The wave propagation has been compared in the homogenized model with the real geometry of a honeycomb sandwich panel. Such calculations of high frequency ultrasonic waves are costly, both in creating a proper finite element model as well as in the required calculation time. In this paper the influence of changes in the geometry of the sandwich panel on the wave propagation is presented. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modelling of Wave‐Based SHM Systems Using the Spectral Element Method
Authors: Schulte R. T. , Fritzen C.‐P.
Published: November 2010

In nondestructive testing, the use of ultrasonic elastic waves has proven as one of the most successful techniques to detect structural damage such as cracks or delaminations. Especially, Structural Health Monitoring (SHM) is characterized by permanently installed actuators and sensors. As the capability of most approaches strongly depends on adequate choice of parameters like excitation signals and actuator/sensor positions, there is a growing interest in efficient and accurate simulation tools to be able to perform virtual SHM‐system design. With respect to high frequency excitation an efficient simulation method is required. This contribution presents the formulation of spectral elements for flat shells based on the first order shear deformation theory (FSDT). A load‐dependent geometrical stiffness matrix is included to take static preloads into account. The spectral element method generates an optimally concentrated mass matrix leading to significant savings of memory and to a reduction of complexity of the time integration algorithm. Dispersion curves of the FSDT are compared to those of 3D elasticity theory to determine the useful application range. Numerical and experimental examples for the propagation of waves including the influence of static prestress and the interaction with delamination are presented. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
High order asymptotic approach to the evaluation of near field, radiated by ultrasonic transducer to the layered elastic plates
Authors: Zakharov Dmitry
Published: November 2010

It is well known that one of the most time consuming problem in non‐destructive evaluation (NDE) is the near‐field modeling. In our approach the near field radiated by an ultrasonic transducer (UT) to the first Fresnel zone is approximated in the frequency domain by a closed form asymptotic solution based on the 3‐D generalized orthogonality conditions of Lamb waves and on the stationary phase method. As shown, these asymptotics permit us to elucidate the physics and to work out a numerical algorithm which is about 104 times faster than any direct way of computation. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
An Experimental/Numerical Investigation on Drag Reduction by Dimples
Authors: Lienhart Hermann , Breuer Michael , Köksoy Cagatay
Published: November 2010

The paper is concerned with experimental and numerical investigations of the turbulent flow over dimpled surfaces. Shallow dimples distributed regularly over the wall of a plane channel with large aspect ratio are used to study their effect on the skin‐friction drag. The resulting pressure drop in the channel was measured for smooth and dimpled walls. In addition to these investigations on internal flows, an external flow study was performed and boundary‐layer profiles were measured using a Pitot‐tube rake. Complementary to the measurements, direct numerical simulations for the internal flow configuration with and without dimples were carried out for two different grid resolutions and analyzed in detail. The objective was to clarify whether or not dimples cause reduction of the skin‐friction drag. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Determination of rotation vectors from multi‐point data and practical applications
Authors: Mladenova Clementina
Published: November 2010

The present work aims to present a different set of parameters for Euclidean motions which have a definite physical interpretation. The orientation here is obtained via vector‐parameters which are elements of a Lie group with a nice and clear composition law. The method is quite convenient for describing of rigid body and manipulators motions such as scene and image processing and recognition. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modular Modelling and Control of Redundant Robots
Authors: Oberhuber Bernhard , Gattringer Hubert , Hofer Andreas , Bremer Hartmut
Published: November 2010

When robots should work in interaction with humans, the robots have to comply. Not only the human is acting in the environment of the robot, the environment itself is vaguely defined. A modular articulated redundant robot with 7 joints is considered. The joints are actuated by brushless DC motors combined with Harmonic Drive gears. The development of the differential equations of the robot is done with the projection equation in subsystem description. The resulting dynamic behavior is used for feedback control design. To obtain the robust numerical inverse kinematics, singular value avoidance and additional conditions have to be added like joint damping and the limits of working space. Three different impedance controllers for human robot interaction are considered. The first active one uses a 6 axes force/torque sensor to regulate the compliance in joint space. The second one performs the same task in Cartesian space with respect to the end‐effector. The passive approach does not require additional sensors at all and also includes the null‐space of the redundant structure in addition to Cartesian end‐effector movements. This scheme is based solely on the feedback of joint positions and their time derivatives. Measurements and simulation results are presented. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A flexible approach to the simulation of hybrid multibody systems
Authors: Sänger Nicolas , Betsch Peter
Published: November 2010

The present works deals with the incorporation of both flexible beam and shell structures into the realm of flexible multibody dynamics. Geometrically exact beam formulations based on classical Simo‐Reissner kinematics are suitable for modelling beam‐type flexible components in the context of finite‐deformation multibody dynamics. So geometrically exact shell formulations are based on Reissner‐Mindlin kinematics.

In [2], a flexible framework for dealing with flexible structural elements in a multibody context is described. A specific isoparametric finite element discretization of a shell formulation leads to semi‐discrete equations of motions assuming the form of differential‐algebraic equations (DAEs). A compatible isoparametric formulation of beams has already been developed in [1].

The uniform DAE framework makes possible the incorporation of alternative finite element formulations. In addition to that, various time‐stepping schemes such as energy‐momentum methods or variational integrators can be applied. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
An implicit approach to predict the dynamics of granular media
Authors: Samiei Kasra , Peters Bernhard , Bolten Matthias , Frommer Andreas
Published: November 2010

The objective of this study is to present an implicit method to predict the dynamics of granular particles. In the proposed methodology, the dynamics equation of colliding particles are solved implicitly which means the positions of particles at the next time step are also used to compute the next state of the particles. This is in contrast with the explicit approach where only known i.e. past information is used to calculate the new positions. The method is tested in a simple setting where a spherical particle is in continuous movement between two boundary walls. The results show that considerably larger time steps are enabled with the implicit method compared to the explicit method. Future work will compare the overall efficiency of the implicit and explicit methods in more detail. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Two DOF model with friction to simulate rope climbing accident
Authors: Tatzko Sebastian
Published: November 2010

A two degree of freedom model is considered consisting of an elastic rope with a point mass on each end. The rope is hanging over a fixed drum and the contact is modeled frictional. The Eytelwein formula for rope friction can not directly be solved for the rope forces, because of the elasticity of the rope. An extended way to calculate the rope forces will be shown and used to solve the equations of motion for the system. Some numerical results show the motion of the two masses. The considered mechanical system was used to simulate a lead climbing accident. In the case of lead climbing one end of the rope is tied rigidly to the climber then goes through a carabiner that is fixed in the wall and runs down to a second person called the belayer. The elasticity of the rope makes sure that the forces acting on the climber stay low and avoid a sudden stop. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Deep Drawing Simulations Based on Microstructural Data
Authors: Phan Van Tung , Jöchen Katja , Melcher Andreas , Böhlke Thomas
Published: November 2010

For the optimization of process chains in sheet metal forming it is required to accurately describe each partial process of the chain, e.g. rolling, press hardening and deep drawing. The prediction of the thickness distribution and the residual stresses in the blank has to be of high reliability, since the subsequent behavior of the semi‐finished product in the following subprocesses strongly depends on the process history. Therefore, high‐quality simulations have to be carried out which incorporate real microstructural data [1,2,3]. In this contribution, the ferritic steel DC04 is analyzed. A finite strain crystal plasticity model is used, for the application of which micro pillar compression tests were carried out experimentally and numerically to identify the material parameters of DC04. For the validation of the model, a two‐dimensional EBSD data set has been discretized by finite elements and subjected to homogeneous displacement boundary conditions describing a large strain uniaxial tensile test. The results have been compared to experimental measurements of the specimen after the tensile test. Furthermore, a deep drawing process is simulated, which is based on a two‐scale Taylor‐type model at the integration points of the finite elements. At each integration point, the initial texture data given by the aforementioned EBSD measurements is assigned to the model. By applying this method, we predict the earing profiles of differently textured sheet metals. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Calibration of a polychromatic CT equipment for biological tissue samples enriched with magnetic nanoparticles.
Authors: Rahn Helene , Odenbach Stefan
Published: November 2010

Micro‐computed tomography (µCT) is a widely used imaging technique. Tomography has been used to study the distribution of magnetic nanoparticles within cancerous tissue after minimal‐invasive cancer treatments such as magnetic drug targeting and magnetic hyperthermia. But not only the distribution is a relevant factor for the sucess of these therapeutic aproaches. The concentration of the magnetic nanoparticles within the respective tissue is also of great impact. In this paper we present a calibration procedure of a µCT‐equipment for biological tissue samples enriched with magnetic nanoparticles developed to enable a semi‐quantitative evaluation of 3‐dimensional data sets. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A new modelling approach for the description of tissues at cell level
Authors: Seydewitz Robert , Böl Markus
Published: November 2010

The understanding of tissues from a biomechanical perspective requires a deeper knowledge about cell mechanics. A lot of experimental and theoretical investigation has already been done to consider cells' behaviour under various conditions. Several types of cells exist, each with specific properties. In this work, the cell microstructure is characterized and explained via tensegrity systems. In doing so, we consider in a first step a simple cubic shaped cell built up by trusses and ropes that are discretized by finite 1D elements. This simplified microstructure represents the micro/cell level on the integration point of the finite element discretization at macro level. By using an appropriate homogenization technique for the micro level, it is assumed to gain a more detailed view on deformations occur on cell level. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Continuum‐Mechanical Analysis of Human Brain Tissue
Authors: Wagner Arndt , Ehlers Wolfgang
Published: November 2010

The effective treatment of brain diseases, such as malignant brain tumours, is generally constricted by the controlled contribution of therapeutic agents. Novel brain tumour therapy proceeds from a direct infusion of the drug into the extra‐vascular space of the nervous brain tissue (convection‐enhanced delivery). This is carried out using catheter to bypass the blood‐brain barrier, which effectively separates brain tissue from the intra‐vascular space and hence hamper drug delivery through the bloodstream. The dilation of the target tissue, as response to the local pressure increase, initiates interstitial fluid flow and, thus, the distribution of the chemical agents. An adequate constitutive model of the complex tissue aggregate in the framework of the Theory of Porous Media is essential in order to assist modern clinical application via numerical simulations. The presented model consists of an elastically deformable solid skeleton, provided by the tissue cells, permeated by two viscous, materially incompressible pore‐liquid phases, interstitial fluid and blood plasma. Both liquids are mobile within the solid skeleton and separated from each other. With regard to simulate a drug infusion process in the extra‐vascular space, the interstitial fluid is treated as a solution of a liquid solvent and a dissolved therapeutic solute. The constitutive assumptions for the involved constituents are adjusted in order to describe the physical behaviour of human brain tissue. The presented numerical examples illustrate the fundamental effects during an infusion process. Therefore, the resulting set of coupled partial differential equations is spatially discretised using hexahedral mixed finite elements with an implicit (backward) Euler time integration scheme to solve the considered problem in a monolithic manner for the primary variables. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical Simulation of Spot‐Weld Joints under Crash Loading
Authors: Basaran Merdan , Wölkerling Sven David , Feucht Markus , Weichert Dieter
Published: November 2010

This paper compares FE simulations of spot‐weld joints for dual‐phase steel under different load cases by using damage models of Gurson‐Tvergaard‐Needleman (GTN) and its two extensions, GTN‐Johnson‐Cook and GTN‐Hutchinson. Spot‐weld specimens have three zones depending with different material properties: Base material, heat‐affected zone and fusion zone. The characterization of the base material is straightforward. The other two zones are characterized with specifically heat‐treated specimens. For each zone, flat smooth tensile, flat notched tensile and Iosipescu‐shear specimen are used in order to obtain the damage behavior for different triaxiality values. GTN damage model parameters are calibrated with the help of smooth and notched flat tensile specimens. The parameters of the above mentioned extensions of GTN damage model are identified with the help of Iosipescu‐shear specimen. Finally, the calibrated material models are used in the FE simulation of the spot‐weld specimens under quasi static‐load case (10 mm/min) for loading directions of 0°, 30°, 60°, 90°. The numerical force‐displacement results are in good agreement with experimental results. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Study of Experimental Methods for Interface Problems Based on Virtual Testing
Authors: Brylka Barthel , Fritzen Felix , Böhlke Thomas , Weidenmann Kay
Published: November 2010

The effective properties of fiber reinforced materials depend strongly on the properties of the interface between the phases. In the particular case of glass fiber reinforced thermoplastics, this bonding is inherently weak and needs to be improved, e.g., by addition of compatibilyzers. Reliable experimental setups are needed in order to investigate the effects of such additives on the interface properties. In this contribution, the sensitivity of push out experiments with respect to the microstructure and test setup are examined in order to find such an experimental configuration. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modeling and numerical simulations of rate and temperature‐dependent damage and fracture in aluminum alloys
Authors: Gerke Steffen , Brünig Michael
Published: November 2010

The paper deals with a continuum damage model and corresponding numerical simulations of the inelastic deformation and failure behavior of aluminum alloys. The focus is on generalized plasticity, damage and fracture approaches taking into account different tiaxialities as well as rate and temperature‐dependence. Furthermore, the special intent of the present work are dynamic applications. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Exponential Finite Elements for a Phase Field Fracture Model
Authors: Kuhn Charlotte , Müller Ralf
Published: November 2010

Sharp interface material models can be related to phase field models by introducing an order parameter, whose value is assigned to the different phases of a material. The elastic material law is coupled to the evolution equation of the order parameter and cracking is addressed as a phase transition problem instead of a moving boundary value problem. A regularization parameter ϵ controls the width of the diffuse cracks represented by the order parameter and the underlying sharp interface model can be recovered from the phase field model by the limit ϵ → 0. However, in numerical simulations using standard finite elements with linear shape functions, the minimum value of ϵ is restricted by the grid size and therefore the discretization of the crack field requires extensive mesh refinement for small values of ϵ. In this work, we construct special 2d shape functions which take into account the exponential character of the crack field and its dependence on the parameter ϵ. Especially in simulations with small values of ϵ and a rather coarse mesh, the elements with exponential shape functions perform significantly better than standard linear elements. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Contact Problems for Interface Cracks under Harmonic Loading
Authors: Menshykov Oleksandr V. , Menshykova Maryna V. , Guz Igor A. , Mikucka Vita A.
Published: November 2010

The linear crack located at the bimaterial interface between dissimilar homogeneous linearly elastic materials under normally incident harmonic tension‐compression wave is considered in the study. The problem is solved by the method of boundary integral equations using an iterative algorithm. The dynamic stress intensity factors are computed as functions of the loading frequency taking the contact interaction of the opposite crack's faces into account. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Deformation and Damaging of Composites with Transversally‐isotropic Components under Compressive Loading
Authors: Nazarenko Lidija , Khoroshun Leonid , Müller Wolfgang H. , Wille Ralf
Published: November 2010

In the present paper, the problem of deformation and damage of composites with a porous isotropic matrix and transversally‐isotropic unidirectional fibers under compressive loading is considered when microdamages are accumulated in the fiber. Fractured micro‐volumes are modelled by a system of randomly distributed quasi spherical pores. The Shleicher‐Nadai fracture criterion is used as a condition for the origin of micro‐pores (micro‐damage) based on the assumption of a rigid material. The limit value of the strength of the material is assumed as a stochastic function of coordinates. By using a numerical procedure, the solution of the above problem is found. The nonlinear stress‐strain diagrams for a transversally‐isotropic composite are obtained for the case of uniaxial compression‐tension along the fibers. The nonlinearity of the deformations of the composite is caused by accumulation of micro‐damages in the matrix. The influence of the physical‐mechanical properties of materials, of the volume concentration, of the porosity of components, of the geometrical parameters of the structure, and of the character of the scatter of the strength in the material on the micro‐damage of the material and, as a consequence, the influence on the macro‐stress‐macro‐strain diagram is analyzed. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Tire Model for Individual Car Indoor Noise Simulation
Authors: Chiarello Raffaela , Nackenhorst Udo
Published: November 2010

Aim of this project is to provide a physical motivated tire model in state space description for the car indoor noise simulation. The basis is a very detailed and validated finite element model of a reference tire, originally developed for outdoor noise radiation simulation, [1]. This contribution focuses on the structure born noise pathway in the frequency domain up to 200 Hz. The modeling approach is based on the assumption that a broad class of passenger car tires can be fitted with one finite element model, because the structural modes appear in principle identical in this frequency range. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Topology optimization based on the finite cell method
Authors: Düster Alexander , Parvizian Jamshid , Rank Ernst
Published: November 2010

We present an extension of the Finite Cell Method (FCM) to topology optimization utilizing the Fully Stressed Design (FSD) approach. The proposed method is briefly explained in 2D and its potential is demonstrated by means of a linear elastic 3D problem. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Correlation of constraint conditions in Koiter's initial postbuckling analysis and in the consistently linearized eigenvalue problem
Authors: Höfinger Gerhard , Jia Xin , Mang Herbert A.
Published: November 2010

Koiter's postbuckling analysis and the consistently linearized eigenvalue problem are used in sensitivity analysis of the postbuckling behavior of elastic structures. A classification of structures can be made on basis of the eigenvector of the eigenvalue problem. This classification distinguishes between structures with different quality of conversion from imperfections sensitivity into imperfection insensitivity, which is expressed in terms of the coefficients of Koiter's initial postbuckling analysis. Mathematically, this connection is expressed in the correlation of constraint equations. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the consistent discretization in time of nonlinear thermo‐elastodynamics
Authors: Krüger Melanie , Groß Michael , Betsch Peter
Published: November 2010

The main goal of the present work is to describe two structure‐preserving time integrators, which have been proposed by Romero [1] (Thermodynamically Consistent (TC) algorithm) and Groß [2] (enhanced hybrid Galerkin (ehG) method) and to compare them with standard integrators. The numerical results of the two schemes are compared in the context of a thermoelastic two‐dimensional double pendulum. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On a concept to avoid electromechanical locking in a piezoelectric finite beam element
Authors: Legner Dieter , Wackerfuß Jens , Klinkel Sven , Wagner Werner
Published: November 2010

Within the development process of piezoelectric sensor and actuator applications, numerical tools are essential. These tools solve approximately the electromechanical boundary value problems received from physical descriptions. Since many piezoelectric components are generally thin rod like structures, a piezoelectric finite beam element is presented in this contribution which can be used effectively to analyze a wide range of piezoelectric devices. The mechanical strains and the electric field are coupled by the constitutive relations. This results in incompatibilities within the numerical approximations in case of bending dominated problems, which can be compared to those causing the well‐known shear locking in purely mechanical problems. This effect occurs in standard finite element formulations, where the mechanical and electrical degrees of freedom are derived from standard kinematic assumptions. The present element formulation is based on the classical Timoshenko beam theory, extended by a piezoelectric part. Each finite element node contains eight degrees of freedom: three displacements, three rotations and the electrical potential on the top and the bottom of the beam. The related fields are interpolated with linear approximation functions. In order to overcome the described problem of incompatible approximation spaces, a mixed multi‐field variational approach is introduced, wherein six independent fields are considered. These are the displacements, strains, stresses, electric potential, electric field and the dielectric displacements. It allows for 3D constitutive equations and approximations of the strains and the electric field independent of the linear interpolation functions. Throughout the beam's cross section, a set of special polynomial approaches for strains and electric field components is proposed. This leads to well‐balanced approximation functions regarding coupling of electrical and mechanical fields. Thus, electromechanical locking does not occur as is demonstrated by means of several numerical examples. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Linear and nonlinear response of pipeline suspension bridge due to moving fluid
Authors: Prokopowicz Dawid , Bryja Danuta
Published: November 2010

Basing on the nonlinear dynamic model of flexible pipeline suspended by spatial system of cables, described in Ref. [1], the linear and nonlinear vibrations are investigated in order to estimate the nonlinear effects. The model is based on substructure technique and formulated including features specific to analyzed structure, for example large displacements and time dependent parameters appearing in equations of motion due to fluid flowing inside the pipeline. Due to the fact that modelling problem for the analyzed structure is one's own complicated, a simple case when the conveying fluid is idealized simply as a ballast moving inside the pipe is considered. This paper presents a short numerical analysis of linear and nonlinear, static and dynamic response of exemplary structure for three different cases: during filling the pipe with fluid, when the pipeline is completely filled and during emptying the pipe. Moreover, for the linear problem, the influence of a speed of the fluid on the stability of the pipeline suspension bridge is investigated. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Verification of an anisotropic Coulomb adhesion‐friction law for contact surfaces with periodic structure
Authors: Schmied Christoph , Konyukhov Alexander , Schweizerhof Karl
Published: November 2010

Sliding friction forces and so‐called adhesion forces are the main mechanical characteristics to describe contact interaction. Both together are representing 2D surface constitutive laws in analogy to e.g. elasto‐plasticity for 3D continua. The classical model to generalize the Coulomb friction law into anisotropic domains is to introduce an anisotropic friction tensor. Michalowski and Mroz in [1] proposed the structure of the friction tensor considering the sliding of a rigid block on an inclined surface. Zmitrowicz in [2] developed the theoretical basis for the structure of the friction tensor on symmetry groups for the tensor. The current contribution is aimed at verification of this modeling process based on a homogenization procedure for a very fine discretization representing the exact structure of the surface. The validation issue with realistic experiments given in [4] is discussed as well. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)