bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of Land Deals on Peak Discharge and Sediment Transport in the Catchments Around the Grand Ethiopian Renaissance Dam
Authors: Teklemariam Dereje , Lanckriet Sil , Azadi Hossein , Asfaha Tesfaalem Ghebreyohannes , Haile Mitiku , Witlox Frank , Nyssen Jan
Published: October 2016

Land degradation poses a threat to reservoirs because of siltation; hence, sustainable hydropower development necessitates the conservation of upstream catchments. Ethiopia is currently constructing Africa's largest hydropower dam, the Grand Ethiopian Renaissance Dam (GERD), on the Blue Nile. Given the commercialization of large tracts of land in the closer catchments, there is a need to explore the effects on peak discharge and suspended sediment concentration. A field survey was conducted on 20 ephemeral streams to compare annual maximum peak discharges between catchments (0·4 – 15·5 km2), eight of which drain commercial farms and twelve others, land under traditional management. We measured channel characteristics, observed flood marks and applied the empirical Manning equation to calculate peak discharges. SSC samples were taken during each runoff event from a stream in each of the two dominant land management categories. Results indicated that commercial farms contributed for the 51% increase in peak runoff compared to traditionally managed lands. Catchments dominated by commercial farms also have a significantly higher SSC (mean = 6·44 ± 2·23 g l−1) compared to catchments without commercial farms (mean = 2·77 ± 2·31 g l−1). Forests and woodlands have a strong buffering effect upon flood generation while higher peak discharges and sediment transport have generated from crop lands. However, leasing forests and woodland to agricultural companies has resulted in deforestation. Consequently, the increased runoff response may lead to downstream bank erosion and affect downstream communities; the increased sediment transport poses a threat to the multibillion dollar hydropower reservoir of the GERD. Copyright © 2016 John Wiley & Sons, Ltd.
Understanding Polymer‐Cell Attachment
Authors: Venturato Andrea , MacFarlane Gillian , Geng Jin , Bradley Mark
Published: October 2016

The development of polymeric materials with cell adhesion abilities requires an understanding of cell–surface interactions which vary with cell type. To investigate the correlation between cell attachment and the nature of the polymer, a series of random and block copolymers composed of 2‐(dimethylamino)ethyl acrylate and ethyl acrylate are synthesized through single electron transfer living radical polymerization. The polymers are synthesized with highly defined and controlled monomer compositions and exhibited narrow polydispersity indices. These polymers are examined for their performance in the attachment and growth of HeLa and HEK cells, with attachment successfully modeled on monomer composition and polymer chain length, with both cell lines found to preferentially attach to moderately hydrophobic functional materials. The understanding of the biological‐material interactions assessed in this study will underpin further investigations of engineered polymer scaffolds with predictable cell binding performance.

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Colloidal Stability in Water of Modified Carbon Nanotube: Comparison of Different Modification Techniques
Authors: Seneewong‐Na‐Ayutthaya Montira , Pongprayoon Thirawudh , O'Rear Edgar A.
Published: October 2016

The colloidal stability of carbon nanotube (CNT) in water is an important property for several applications. Three different functionalization approaches defined as nondestructive techniques have been carried out to modify the CNT surface and the product CNT compared. First, admicellar polymerization is used to form a water‐soluble polymer on CNT with two different polymers, polyacrylic acid and polyvinyl acetate (PVAc). Second, coatings of soluble biopolymers are applied using dextran and chitosan. Third, mild acid oxidation conditions from the literature are employed with hydrogen peroxide (H2O2) and with potassium permanganate (KMnO4) as oxidizing agents. The colloidal stability of modified CNT is examined by sedimentation and by turbidity measurements along with laser particle size analysis. Thermogravimetric Analysis, energy dispersive X‐ray analysis, scanning electron microscope, and transmission electron microscopy are used to confirm that modification of the CNT is successfully implemented with each technique. Lastly, FT‐Raman is used to assess damage to the CNT structure after modification. A focus of the turbidity measurements is quantitative analysis using numerical integration of variability to evaluate colloidal stability. All modified CNT samples clearly yield improved aqueous dispersions. For each of the three approaches, the better option is KMnO4 for mild acid oxidation, PVAc for admicellar polymerization, and chitosan for biopolymer deposition.

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Facile Preparation of CO2‐Responsive Polymer Nano‐Objects via Aqueous Photoinitiated Polymerization‐Induced Self‐Assembly (Photo‐PISA)
Authors: Tan Jianbo , Zhang Xuechao , Liu Dongdong , Bai Yuhao , Huang Chundong , Li Xueliang , Zhang Li
Published: October 2016

Carbon dioxide (CO2)‐responsive polymer nano‐objects are prepared by photoinitiated reversible addition‐fragmentation chain transfer dispersion polymerization of 2‐hydroxypropyl methacrylate and 2‐(dimethylamino)ethyl methacrylate (DMAEMA) in water at room temperature using a poly(poly(ethylene glycol) methyl ether methacrylate) macromolecular chain transfer agent. Kinetic studies confirm that full monomer conversions are achieved in all cases within 10 min of visible‐light irradiation (405 nm, 0.5 mW cm−2). The effect of DMAEMA on the polymerization is studied in detail, and pure higher order morphologies (worms and vesicles) are prepared by this particular formulation. Finally, CO2‐responsive property of the obtained vesicles is investigated by dynamic light scattering, visual appearance, and transmission electron microscope.

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A k‐Nearest Neighbours Approach Using Metabolism‐related Fingerprints to Improve In Silico Metabolite Ranking
Authors: Marchant Carol A. , Rosser Edward M. , Vessey Jonathan D.
Published: October 2016

The application of biotransformation dictionaries derived by expert evaluation of known metabolic pathways represents one approach to the prediction of both phase I and phase II xenobiotic metabolites. The ranking of metabolites generated by such dictionaries has previously been achieved through the use of qualitative reasoning rules and quantitative probability values. Using the biotransformation dictionary available in the Meteor expert system, we show that metabolite over‐prediction by both of these methods can be reduced by the adoption of a k‐nearest neighbours methodology in which the likelihood of a predicted biotransformation is determined based on comparison of a query chemical with structurally‐similar substrates with known experimental metabolic data which activate the same biotransformation. Optimal performance was achieved when similarity was defined in terms of a combination of two fingerprints, one describing the overall profile of biotransformations a structure can potentially undergo and the other describing the local environment around the predicted site of metabolism for the particular biotransformation under consideration.
Voxelwise analysis of simultaneously acquired and spatially correlated 18F‐fluorodeoxyglucose (FDG)‐PET and intravoxel incoherent motion metrics in breast cancer
Authors: Ostenson Jason , Pujara Akshat C. , Mikheev Artem , Moy Linda , Kim Sungheon G. , Melsaether Amy N. , Jhaveri Komal , Adams Sylvia , Faul David , Glielmi Christopher , Geppert Christian , Feiweier Thorsten , Jackson Kimberly , Cho Gene Y. , Boada Fernando E. , Sigmund Eric E.
Published: October 2016

Purpose

Diffusion‐weighted imaging (DWI) and 18F‐fluorodeoxyglucose–positron emission tomography (18F‐FDG–PET) independently correlate with malignancy in breast cancer, but the relationship between their structural and metabolic metrics is not completely understood. This study spatially correlates diffusion, perfusion, and glucose avidity in breast cancer with simultaneous PET/MR imaging and compares correlations with clinical prognostics.

Methods

In this Health Insurance Portability and Accountability Act‐compliant prospective study, with written informed consent and approval of the institutional review board and using simultaneously acquired FDG‐PET and DWI, tissue diffusion (Dt), and perfusion fraction (fp) from intravoxel incoherent motion (IVIM) analysis were registered to FDG‐PET within 14 locally advanced breast cancers. Lesions were analyzed using 2D histograms and correlation coefficients between Dt, fp, and standardized uptake value (SUV). Correlations were compared with prognostics from biopsy, metastatic burden from whole‐body PET, and treatment history.

Results

SUV||Dt correlation coefficient significantly distinguished treated (0.11 ± 0.24) from nontreated (−0.33 ± 0.26) patients (P = 0.005). SUV||fp correlations were on average negative for the whole cohort (−0.17 ± 0.13).

Conclusion

Simultaneously acquired and registered FDG‐PET/DWI allowed quantifiable descriptions of breast cancer microenvironments that may provide a framework for monitoring and predicting response to treatment. Magn Reson Med 78:1147–1156, 2017. © 2016 International Society for Magnetic Resonance in Medicine
Post‐injury bladder management strategy influences lower urinary tract dysfunction in the mouse model of spinal cord injury
Authors: Wada Naoki , Shimizu Takahiro , Takai Shun , Shimizu Nobutaka , Kanai Anthony J. , Tyagi Pradeep , Kakizaki Hidehiro , Yoshimura Naoki
Published: October 2016

Aims

To examine the effects of a different number of daily bladder squeezes on bladder dysfunction in mice with spinal cord injury (SCI).

Methods

Spinal cord was transected at the Th8/9 in female C57BL/6N mice. Their bladders were manually squeezed to eliminate urine inside every day for 4 weeks. The mice were divided into three groups depending on the number of bladder squeezes; A: once daily, B: twice daily, C: three times daily. Four weeks after transection, single‐filling cystometry were performed under an awake condition. NGF in the bladder mucosa and mRNA expression of P2X receptors and TRP channels in L6/S1 dorsal root ganglia (DRG) were measured.

Results

Bladder weight in group C was less than that of group A. Bladder capacity, post‐void residual, and the number of non‐voiding contractions during the storage phase were significantly larger in group A compared to group B or C. The level of NGF in groups C were lower compared to group A or B. The expression of P2X3 and TRPA1 in groups B and C was decreased compared to group A. The expression of P2X2 was decreased in groups B compared to group A.

Conclusion

The post‐injury bladder management after SCI with an increased number of daily bladder emptying improves the storage and voiding bladder dysfunction associated with the reduction of NGF in the bladder as well as P2X and TRP transcripts in lumbosacral DRG.
Is bladder neck and urethral mobility associated with urinary incontinence and mode of delivery 4 years after childbirth?
Authors: Volløyhaug Ingrid , van Gruting Isabelle , van Delft Kim , Sultan Abdul H. , Thakar Ranee
Published: October 2016

Aims

To study changes in bladder neck, urethral mobility and urinary incontinence (UI) from pregnancy to 4 years postpartum and demonstrate any association to mode of delivery or presence of levator ani muscle (LAM) injury. Secondly, we aimed to correlate bladder neck and urethral mobility to UI symptoms.

Methods

Prospective study of 180 women, recruited in their first pregnancy and followed up 1 and/or 4 years postpartum. UI symptoms were assessed with a validated questionnaire. All underwent 4D transperineal ultrasound to assess LAM injury, bladder neck descent (BND), retrovesical angle at Valsalva (RVA), and urethral rotation between rest and Valsalva. A mixed model compared changes over time, different delivery modes, and women with and without LAM injury. Spearman's rank correlation tested the correlation of BND, RVA, and urethral rotation to UI symptoms.

Results

BND, RVA, and urethral rotation all increased following delivery. From 1 to 4 years postpartum, a larger increase in BND was found for women delivered vaginally with LAM injury, compared to women with intact LAM (P = 0.02) and women with cesarean section (P = 0.046). One year postpartum, BND and RVA correlated to UI symptoms, rs = 0.22, P = 0.01. Four years postpartum, RVA correlated to UI symptoms, rs = 0.19, P = 0.02.

Conclusions

Although bladder neck and urethral mobility increased from pregnancy to 4 years postpartum irrespective of delivery mode, women with LAM injury had larger increase in BND, suggesting that this is important in the pathogenesis of bladder neck mobility and could lead to pelvic floor dysfunction in the long term.
Long‐term course of sacral anterior root stimulation in spinal cord injured individuals: The fate of the detrusor
Authors: Krebs Jörg , Wöllner Jens , Grasmücke Dennis , Pannek Jürgen
Published: October 2016

Aims

To investigate the long‐term course of the detrusor pressure during sacral anterior root stimulation in spinal cord injury (SCI) patients.

Methods

Retrospective evaluation of 111 patients who had undergone sacral deafferentation and implantation of an anterior root stimulator at a single SCI rehabilitation center with a minimum follow‐up time of 5 years.

Results

The median follow‐up time was 11.7 years (range 5.0‐24.9 years). The maximum detrusor pressure (Pdet_max) during stimulation was higher in men compared to women (P = 0.0004) and decreased over time (P = 0.0006). However, there were no significant (P ≥ 0.06) differences in the median Pdet_max during stimulation between the first measurement time point and any follow‐up time point. The Pdet_max during stimulation decreased from 62 cmH2O (95%CI 57‐73 cmH2O) to 53 cmH2O (95%CI 47‐69 cmH2O) (P = 0.9). The time had also a significant effect on Pdet_max during the storage phase (P < 0.0001) and bladder compliance (P = 0.0007). The Pdet_max during the storage phase decreased, whereas bladder compliance increased during the follow‐up period. There were no significant (P ≥ 0.1) changes over time in bladder capacity, the number of daily stimulations and the residual urine volume after voiding.

Conclusions

The detrusor pressure during sacral anterior root stimulation decreases over time in SCI individuals. However, the changes do not seem to be clinically relevant during the first decade after surgery.
Syntheses, Structures, and Complexation Studies of Tris(organostannyl)methane Derivatives
Authors: Wendji Anicet Siakam , Lutter Michael , Stratmann Lukas M. , Jurkschat Klaus
Published: October 2016

The syntheses of tris(organostannyl)methanes HC(SnXnPh(3‐n))3(1,n=0;2,n=1, X=I;3,n=1, X =F;4,n=1, X=Cl;5,n=1, X=OAc;6,n=2, X=I;7,n=2, X=Cl) and the organostannate complexes Et4N[HC(SnIPh2)3⋅F] (8), Ph4P[HC(SnClPh2)3⋅Cl] (9), and [Ph4P]2[HC(SnCl2Ph)3⋅2 Cl] (10) are reported. The compounds were characterized by1H,13C,19F, and119Sn NMR spectroscopy, IR spectroscopy, electrospray mass spectrometry, and (with the exception of3) single‐crystal X‐ray diffraction analysis. From the reaction between2and AgClO4resulted the unprecedented hexanuclear organotin oxocluster [HC{Sn(ClO4)2Ph2}2Sn(OH)2Ph]2 (11), the molecular structure of which was elucidated by using X‐ray crystallography.
Resolutions and Betti Numbers of Polynomial Modules via Involutive Bases
Authors: Albert Mario , Fetzer Matthias , Seiler Werner M.
Published: October 2016

We describe a novel approach to the computation of free resolutions and of Betti numbers of polynomial modules based on a combination of the theory of involutive bases with algebraic discrete Morse theory. This approach allows for the first time to compute Betti numbers (even single ones) without determining a whole resolution which in many cases drastically reduces the computation time. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Higher order unfitted FEM for Stokes interface problems
Authors: Lederer Philip , Pfeiler Carl‐Martin , Wintersteiger Christoph , Lehrenfeld Christoph
Published: October 2016

We consider the discretization of a stationary Stokes interface problem in a velocity‐pressure formulation. The interface is described implicitly as the zero level of a scalar function as it is common in level set based methods. Hence, the interface is not aligned with the mesh. An unfitted finite element discretization based on a Taylor‐Hood velocity‐pressure pair and an XFEM (or CutFEM) modification is used for the approximation of the solution. This allows for the accurate approximation of solutions which have strong or weak discontinuities across interfaces which are not aligned with the mesh. To arrive at a consistent, stable and accurate formulation we require several additional techniques. First, a Nitsche‐type formulation is used to implement interface conditions in a weak sense. Secondly, we use the ghost penalty stabilization to obtain an inf‐sup stable variational formulation. Finally, for the highly accurate approximation of the implicitly described geometry, we use a combination of a piecewise linear interface reconstruction and a parametric mapping of the underlying mesh. We introduce the method and discuss results of numerical examples. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Fuzzy‐Based Analysis of a Hill‐Type Muscle Model
Authors: Fehr Jörg , Fuhrer Julian , Kleinbach Christian , Hanss Michael , Eberhard Peter
Published: October 2016

Among the most challenging problems in present day mechanics is the realistic simulation of the human kinetic behavior which requires correct modeling of the muscles – the human actuators. We are, therefore, implementing and validating a 1‐D massless Hill‐type muscle model in the program Neweul‐M2. As a part of this effort, various anatomical and physiological parameters need to be chosen prior to the simulation. These parameters are always subject to natural variability or scatter.

Therefore, it is important to consider those parameters as uncertain fuzzy parameters and then determine the sensitivity measures of the parameters involved in various simulation scenarios using the program Famous. The applied sensitivity analysis quantifies the influence of individual parameters or subsets of parameters on the output quantity of interest. Thus, this analysis identifies those parameters with large influence on the simulation response of muscles which, therefore, needs to be chosen very carefully. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Surrogate Modelling for Real‐time Predictions of Mechanised Tunnelling Processes with Interval Data
Authors: Freitag Steffen , Cao Ba‐Trung , Meschke Günther
Published: October 2016

Finite element simulations are commonly used to investigate the soil‐structure interactions of mechanised tunnelling processes, such as to provide predictions on the expected surface settlement field. For real‐time predictions during the tunnel construction, the finite element model is substituted by a hybrid surrogate model combining Artificial Neural Network and Proper Orthogonal Decomposition approaches. The surrogate model is employed to predict time‐variant interval surface settlement fields for selected scenarios of the tunnelling process steering parameters in real‐time considering uncertain geotechnical parameters as intervals. For this purpose, the surrogate model in [1], which is based on a Recurrent Neural Network and Gappy Proper Orthogonal Decomposition technique, is split into surrogate models for midpoint and radius computations of the interval data. The online computation time of the new surrogate modelling approach is only a few seconds, which enables tu apply it for real‐time predictions and to support the Tunnel Boring Machine steering. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Passive Rotation Compensation in Parallel Kinematics Using Quaternions
Authors: Du Shucen , Schlattmann Josef , Schulz Stefan , Seibel Arthur
Published: October 2016

In this paper, an approach to compute the passive rotation in a parallel hexapod structure is introduced which is based on quaternions. The advantage of this approach is that it prevents from unnecessary trigonometric or inverse trigonometric functions, which reduces rounding errors and saves memory. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Variational multirate integration in multi‐body dynamics
Authors: Gail Tobias , Leyendecker Sigrid , Ober‐Blöbaum Sina
Published: October 2016

For systems that contain slow and fast dynamics, variational multirate integration schemes are used. These schemes split the system into parts which are simulated using two time grids consisting of micro and macro nodes. This formulation can be extended for multi‐body systems. The rigid multi‐body system is described by the so called director formulation and constraints describing the joints connecting the bodies. With the Lagrange multiplier method, the constraints are introduced into the equations of motion. A way to implement the null space method into the variational multirate framework is shown and the influence on the number of unknowns is investigated. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optimal feedback control for constrained mechanical systems
Authors: Glaas Daniel , Leyendecker Sigrid
Published: October 2016

An approach to minimize the control costs and ensuring a stable deviation control is the Riccati controller and we want to use it to control constrained dynamical systems (differential algebraic equations of Index 3). To describe their discrete dynamics, a constrained variational integrators [1] is used. Using a discrete version of the Lagrange‐d’Alembert principle yields a forced constrained discrete Euler‐Lagrange equation in a position‐momentum form that depends on the current and future time steps [2]. The desired optimal trajectory (qopt, popt) and according control input uopt is determined solving the discrete mechanics and optimal control (DMOC) algorithm [3] based on the variational integrator. Then, during time stepping of the perturbed system, the discrete Riccati equation yields the optimal deviation control input uR. Adding uopt and uR to the discrete Euler‐Lagrange equation causes a structure preserving trajectory as both DMOC and Riccati equations are based on the same variational integrator. Furthermore, coordinate transformations are implemented (minimal, redundant and nullspace) enabling the choice of different coordinates in the feedback loop and in the optimal control problem. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Varying Workpiece Dynamics in Milling Stability Analysis
Authors: Hamann Dominik , Eberhard Peter
Published: October 2016

Dynamic stability of a milling process with varying workpiece dynamics is investigated. The milling tool moves along the workpiece with a prescribed feed rate, whereby the contact point shifts. Furthermore, the workpiece dynamics is affected by material removal. The resultant varying workpiece dynamics is taken into account by parametric model order reduction including modal truncation. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Experimental‐based material parameter identification of oocytes
Authors: Dittmann Johannes , Töpfer Dagmar , Böl Markus
Published: October 2016

In comparison to other eukaryotic cells, mammalian oocytes are characterised by a relative high diameter allowing in turn a straightforward micromechanical testing to study their mechanical properties. The structure of mammalian oocytes is characterised by the so‐called zona pellucida (ZP), a thick glycoprotein layer, surrounding the cells interior, the ooplasm. In contrast to other cells, where the load is mainly carried by inner cell structures, in case of oocytes a huge amount of external loads is carried by the ZP. Aim of this work is the determination of the mechanical properties of oocytes. Therefore, a micromechanical setup has been developed and installed on a microscope. Beside the determination of the force‐strain relation during loading, the deformation of the oocytes has been recorded optically, too. Both, the force‐strain curves and the optical recordings build the basis for a proper parameter identification technique based on the inverse finite element method. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
From functional properties of frost‐resistant plant tissues towards customised construction materials ‐ A continuum‐mechanical approach
Authors: Eurich Lukas , Schott Rena , Wagner Arndt , Roth‐Nebelsick Anita , Ehlers Wolfgang
Published: October 2016

Temperatures below freezing point represent a common threat to standard construction materials, as a phase change of the pore content from liquid water to solid ice frequently leads to damage. However, frost‐resistant plants are able to withstand many cycles of freezing and thawing without any damage. Hence, the objective is to identify and analyse structural factors of frost‐resistant plant tissues and to develop a model, which includes their functional behaviour. Since frost‐resistant plant tissues are formed by ordered arrangements of cells with prescribed shape and size, they can be understood as an (anisotropic) natural porous material. Therefore, a customised modelling strategy based on the Theory of Porous Media (TPM) is proposed, which allows for the description of structural traits and the formation of ice within plant tissues. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Problems in parameter identification of the passive response in human arteries
Authors: Gilbert Rose Rogin , Hartmann Stefan , Kudela László , Rank Ernst , Yosibash Zohar , Yossef Ofry
Published: October 2016

Identification of unique material parameters for the media and adventitia in the case of arteries involves many challenges. Tension‐inflation experiments were performed on the internal mammary artery and the axial force and the radial displacements were used to identify the material parameters. It will be shown that these experimental data are not sufficient to uniquely identify the material parameters of the passive response in human arteries. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Force enhancement and stability of finite element muscle models
Authors: Heidlauf Thomas , Klotz Thomas , Rode Christian , Siebert Tobias , Röhrle Oliver
Published: October 2016

A continuum‐mechanical finite element model of skeletal muscle contractions that includes force enhancement based on actin‐titin interaction is presented. This model can simulate muscles with a descending limb in the total force‐length relation, which has previously led to unstable behaviour. The model predictions are in agreement with results of active stretch experiments. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On data‐guided optimal control simulation of human motion
Authors: Hoffmann Ramona , Taetz Bertram , Miezal Markus , Bleser Gabriele , Leyendecker Sigrid
Published: October 2016

This work investigates the combination of optical motion capturing data with optimal control simulations of human motion, which can be important in a wide range of applications in the professional as well as the private sector, ranging from health and ergonomics over human‐machine‐interaction to sports and games [1–3]. There are methodically very different approaches to include optical measurement data in the simulation of human motion, see e.g. [4–6]. Two different approaches to combine data and simulation are investigated in this work. Either we use a soft constraints approach, where the difference of simulated and measured marker positions is part of the objective function (1), or we formulate an hard constraints approach with nonlinear constraints that set an upper bound on this difference (2), while the objective function is purely physiologically motivated. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On a bi‐scale and tri‐phasic model for the description of growth in biological tissue using the example of the human liver
Authors: Waschinsky Navina , Werner Daniel , Ricken Tim , Dahmen Uta , Dirsch Olaf
Published: October 2016

The human liver is important for hepatic metabolism regulations which depend on complex and time depending biochemical reactions coupled to the hemodynamic blood perfusion. Growth effects can impair the perfusion and therefore affect the metabolism. Such influences can be observed during the accumulation of fat in the liver tissue. The fat accumulation results from the lipid metabolism which comprises synthesis and degradation of lipids in liver cells. Individual addictions to alcohol and high fat diets are possible causes which result in an excessive synthesis of lipids. The liver sensitively reacts to such changes which could affect the viability of the organ. To observe these coupled influences of perfusion‐metabolism‐growth effects we use a computational model with a multi‐component/tri‐phasic/bi‐scale approach to simulate the functionality of the human liver with respect to fat deposition. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Simulation of the gelation process of hydrogel droplets in 3D bioprinting
Authors: Zhou Bei , Heider Yousef , Blaeser Andreas , Raith Stefan , Fischer Horst , Markert Bernd
Published: October 2016

The aim of this work is to numerically simulate the gelation of a crosslinking polymer, which is a very complex process involving chemical reactions and phase transitions from a viscous fluid to a viscoelastic solid. A phenomenological model is proposed to simulate the gelation process of agarose droplets, considering the thermal boundary conditions. The numerical model is implemented using the finite element package FlexPDE. The temperature‐ and time‐dependent degree of gelation and the deformation of the droplets during the gelation process are investigated. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Closed‐form solutions for stress singularities at bi‐material wedges in Reissner‐Mindlin plates
Authors: Felger Julian , Becker Wilfried
Published: October 2016

In this work, stress singularities in isotropic bi‐material junctions are investigated using Reissner‐Mindlin plate theory by means of a complex potential formalism. The governing system of partial differential equations is solved employing methods of asymptotic analysis. The resulting asymptotic near‐fields including the singularity exponent λ are obtained in a closed‐form analytical manner as solutions of a corresponding eigenvalue problem. The singular solution character is discussed for different geometrical configurations. In particular, the present study investigates the influence of the material constants on the singularity exponent. It is shown, that the Reissner‐Mindlin theory allows for distinguishing between singularities of the bending moments and the transverse shear forces. Further, stronger singularities than the classical crack‐tip singularity are observed. The results allow for further application such as a combination with numerical methods. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Phase‐field approach to fracture for finite‐deformation contact problems
Authors: Franke Marlon , Hesch Christian , Dittmann Maik
Published: October 2016

The present contribution deals with a variationally consistent Mortar contact algorithm applied to a phase‐field fracture approach for finite deformations, see [4]. A phase‐field approach to fracture allows for the numerical simulation of complex fracture patterns for three dimensional problems, extended recently to finite deformations (see [2] for more details). In a nutshell, the phase‐field approach relies on a regularization of the sharp (fracture‐) interface. In order to improve the accuracy, a fourth‐order Cahn‐Hilliard phase‐field equation is considered, requiring global C1 continuity (see [1]), which will be dealt with using an isogeometrical analysis (IGA) framework. Additionally, a newly developed hierarchical refinement scheme is applied to resolve for local physical phenomena e.g. the contact zone (see [3] for more details). The Mortar method is a modern and very accurate numerical method to implement contact boundaries. This approach can be extended in a straightforward manner to transient phase‐field fracture problems. The performance of the proposed methods will be examined in a representative numerical example. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Influence of material data input on accuracy of fatigue assessments for beam weldments
Authors: Gorash Yevgen , Comlekci Tugrul , MacKenzie Donald
Published: October 2016

This numerical study investigates the effects of fatigue material data and finite element types on accuracy of residual life assessments under HCF conditions. The bending of cross‐beam connections is simulated in ANSYS Workbench for three different combinations of beam profiles. The weldments are made of the high‐strength steel grades C350LO and C450LO according to AS3678. The stress analysis of weldments is implemented with solid and shell elements using linear material and geometry consideration. The stress distributions are transferred to the embedded fatigue code nCode DesignLife. For both variants of FE‐mesh, the nominal stress in the weld toes is extracted by splitting the total stress into membrane and bending components and filtering out non‐linear component. Considering the effects of bending, size and mean stress, failure locations and fatigue life are predicted using the Volvo method and rules from ASME BPV Code. Three different pairs of experimental S‐N curves (stiff and flexible) are used as material data input for fatigue analysis. The obtained numerical predictions are compared to the experimental results for shell FE‐models. The predictions using the S‐N curves for an equivalent steel demonstrate the best accuracy proving the fact that specific material data input is more effective than a generic data. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Excitation strategies for vibration based damage detection using piezoelectric transducers and machine learning
Authors: Hesser Daniel Frank , Markert Bernd
Published: October 2016

Damage detection methods of structural components have been extensively evaluated in theoretical and experimental research studies in the last few years. In this context, machine learning algorithms are used to evaluate the health state of structures. This work assesses the dependency of various excitation frequencies in guided‐wave based structural health monitoring (SHM) systems and the performance of damage detection, which are barely investigated, in particular in SHM technologies using machine learning approaches. Machine learning can be directly used in SHM applications including environmental effects (noise, imperfection, statistical tests, etc.) to train a new system and to solve the inverse problem. Thereby, the piezoelectric effect is used to apply guided‐waves through the structure or to measure the vibration response of flexible structures. The important outcome of this study is to improve the efficiency and performance of SHM systems by optimising the excitation frequency using machine learning approaches. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A regularization technique for the XFEM: extension to finite deformations, inelastic material behaviour and multifield problems
Authors: Loehnert Stefan , Beese Steffen
Published: October 2016

Within the XFEM often near linear dependencies between the standard degrees of freedom and enriched degrees of freedom and also among enriched degrees of freedom occur. During the last years, several remedies to that problem have been presented. Here, an extension of the regularization technique described in [1] to finite deformation problems and inelastic material behaviour as well as to multifield problems is proposed. © 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Influence of deformation history parameters on softening behaviour of concrete
Authors: Monnamitheen Abdul Gafoor A. H. , Dinkler Dieter
Published: October 2016

The aim of this study is to investigate elasticity based damage models in which the isotropic damage is driven by different history parameters under uniaxial setting. This leads to a suitable history parameter for the description of material strain‐softening realistically. Existing damage evolution laws from literatures are used to compare the results using strain and energy equivalence principles. A suitable damage evolution law which is similar to Weibull's failure distribution is proposed in the framework of energy equivalence. Numerical results exhibit good agreement with experimental results. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Crack propagation for the material force approach using adaptive meshing
Authors: Qinami Aurel , Kaliske Michael
Published: October 2016

In this publication, a contribution of the material force approach in Linear Elastic Fracture Mechanics (LEFM) is studied. The fracture criterion and crack propagation direction are depicted using material force which follow the Griffith theory. The implementation of this criterion is based on a purely thermodynamic description. Discrete modelling of crack propagation, apart of its mechanics, requires special techniques for manipulation of the finite element mesh for a given structure. The well known node splitting algorithm can be implemented and combined with r‐ or h‐adaptive approaches. The former one consists in moving specific nodes in the direction of a crack path. This method is easier to handle but it suffers from the degradation of finite elements. The latter one is more effective when an external remeshing process for a certain area around crack tip is used. This increases the computation cost, but on the other hand, it improves accuracy of results. For both models, an effective data structure needs to be created which has to be generated after each adaptation of the mesh configuration. This significantly increases the computation time. These methods allow realistic modelling of the crack path according to the crack driving force direction. In this work, both methods are considered separately and combined for two‐ and three‐dimensional simple geometry specimens where linear elastic material behavior is taken into account. These methods are tested for tension specimens in mode I and mixed mode. A three‐dimensional torsion simulation is investigated as well. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
PC expansion for material parameters using artificial data and statistical methods
Authors: Caylak Ismail , Nörenberg Nicole , Mahnken Rolf
Published: October 2016

This paper investigates the uncertainty of a hyper‐elastic model by random material parameters as stochastic variables. For its stochastic discretization a polynomial chaos (PC) is used to expand the coefficients into deterministic and stochastic parts. Then, from experimental data in combination with artificial data for elastomers the distribution of the force‐displacement curves are known. In the numerical example the PC‐based stochastic and the deterministic parameter identification are used for generation of the distribution of Ogden's material parameters. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Patch coupling with the isogeometric dual mortar approach
Authors: Dornisch Wolfgang , Müller Ralf
Published: October 2016

The use of a common set of basis functions for design and analysis is the main paradigm of isogeometric analysis. The characteristics of the commonly used non‐uniform rational B‐splines (NURBS) surfaces require methods to handle non‐conforming meshes to attain an efficient computational framework. The isogeometric mortar method uses constrained approximation spaces to enforce a coupling of deformations at the interface between patches in a weak manner. This method neither requires additional degrees of freedom nor the choice of empirical parameters. The main drawback of the standard isogeometric mortar approach is the non‐local support of the mortar basis functions along the interface. This yields a large number of nodes per element for elements adjacent to the interface. Thus, the computational costs increase significantly for mesh refinement. This issue is remedied by the use of dual basis functions for the mortar method, which is referred to as dual mortar method. In this contribution several choices for the dual basis functions for B‐splines are proposed and compared. A special focus is set on the support of the dual basis functions and on the support of the resulting mortar basis functions. Numerical examples show the influence of the choice for the dual basis functions on the accuracy of the global stress distribution, on the fulfillment of the interface conditions and on numerical efficiency. The use of approximate dual basis functions is shown to be competitive to computations of conforming meshes in terms of accuracy and efficiency. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Specimen design for high precision tension‐compression tests
Authors: Kanzenbach Lars , Naumann Christoph , Ihlemann Jörn
Published: October 2016

In this contribution a new specimen, which enables high precision tension‐compression testing, is presented. Due to a special mounting geometry, tests from a compression strain of −45 % up to a tension strain of 400 % can be performed with a nearly homogeneous deformation field within the measuring zone. Consequently, the mechanical behavior of rubber, which exhibits phenomena like Mullins effect, Payne effect, recovery and relaxation behavior, can be characterized within experimental investigations. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Structure analysis of higher‐order variational integrators and implementation of SUNDMAN adaptivity in time
Authors: Masser Robin , Bartelt Matthias , Groß Michael
Published: October 2016

In this paper, we investigate the use of different higher‐order polynomial bases for the temporal approximation as well as various higher‐order quadrature rules. The resulting time integration schemes partially differ in their numerical properties, especially in order convergence and energy error. Further, an adaptivity of the time increment to optimize the computational effort is implemented using a time transformation according to SUNDMAN. Using an example with viscoelastic material behavior that models a bungee jumper, we show its advantages to minimize the energy error. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Interface finite elements within a three dimensional frictional contact formulation
Authors: Michaloudis Georgios , Konyukhov Alexander , Gebbeken Norbert
Published: October 2016

This contribution presents a finite element appropriate for the modeling of general interfaces, incorporating normal contact conditions as well as description of the tangential interaction on the interface. The finite element is formulated as a solid element and its kinematics take into account the kinematics of both Master and Slave. A covariant approach is adopted for the exact representation of the geometry of the interface and all parameters are expressed in terms of local coordinate systems. An elastoplastic associative constitutive law assuming plastic deformations, which is numerically implemented as a frictional law describes the tangential interaction of the contact surfaces. In this way a three‐dimensional Segment‐to‐Segment frictional contact formulation, applying an associative plasticity law instead of the Coulomb friction law is presented. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Solving the linear inhomogeneous differential equation in the simulation model of passenger car tire
Authors: Sarkisov Pavel , Prokop Günther , Wensch Jörg
Published: October 2016

The paper represents an analysis of different approaches to solve a specific practical task – to find a solution of the inhomogeneous differential equation, which describes tire lateral deformation by means of the beam theory. The equation has fourth order and is linear, the inhomogeneneous part is discrete nonmonotone function. The options to substitute this function with polynomial, linear segments or Fourier series are compared concerning solution error and computation time. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A‐priori error estimates for consistent, refined theories for thin structures
Authors: Schneider Patrick , Kienzler Reinhold
Published: October 2016

We propose an extension of the uniform approximation approach towards the simultaneous truncation of the associated dual energy. In the talk, we derive a hierarchy of approximating theories and corresponding a‐priori error estimates for their solutions, for the special case of an isotropic, linear elastic, one‐dimensional structural member with rectangular cross‐section. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical analysis of reinforced concrete structures with particular focus on bond behaviour
Authors: Stein Timo , Kowalsky Ursula , Dinkler Dieter
Published: October 2016

A non‐linear bond model is presented, capturing bond behaviour between concrete and reinforcing ribbed steel bars. An existing model, where coupled thermal‐hygric‐mechanical‐chemical (THMC‐) processes are already modelled for pure concrete, will be extended by the presented bond model. Against this background and due to the resulting requirements the approach of a geometrically consistent consideration of the reinforcement is chosen, neglecting the bar ribs in the geometric model. All bond mechanisms are considered by the additional bond model in between concrete and reinforcement. With this procedure the principle of a formal treatment and general description, used in the existing model describing the different processes, is not only continued, but also transferred regarding the three components concrete, steel and bond. The bond model is discretized by interface elements, which describe curved surfaces in 3D space. The presented non‐linear bond model incorporates the mechanical interaction of the bar rips with adjacent concrete as well as the damage of the bond zone. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Notes on a novel finite element for anisotropy at large strains
Authors: Viebahn Nils , Schröder Jörg , Wriggers Peter , Balzani Daniel
Published: October 2016

A locking phenomenon can be observed in the case of anisotropic elasticity, due to high stiffness in preferred directions. In this contribution we propose a formulation with the goal to overcome this locking problem. We apply a Simplified Kinematic for the Anisotropic part of the free‐energy by means of a constant approximation of the right Cauchy‐Green tensor. For the tested boundary value problem the SKA‐element performs excellent and behaves extremely robust. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the piezotronics and tactile sensing virtual simulation
Authors: Chiroiu Veturia
Published: October 2016

A flexible finger with muscles made of Nitinol wires and the skin made of auxetic material is analyzed from the tactile sensing point of view. The recognizing of the shape and texture of 3D objects is performed by simulation the action of an array of nanopiezotronic transistors integrated into the skin. The array of nanopiezotronic transistors makes possible the detection of the pressure‐induced changes in the auxetic skin. The shape and texture of the objects is best estimated by determining the surface and texture as an n‐ellipsoid defined by 12 parameters. An inverse problem is solved in order to find these parameters from the condition that the n‐ellipsoid best fits the set of data points probed by touch with the finger. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Asymptotic behavior of solutions of nonlinear systems with multiple imaginary eigenvalues
Authors: Grushkovskaya Victoria
Published: October 2016

The paper is devoted to the analysis of the decay rate of solutions of a nonlinear system with two pairs of purely imaginary eigenvalues. The main result is the power estimate for the norm of solutions. It is proven that the order of such estimate varies for cases of a diagonalizable matrix of linear approximation, and for a matrix containing a Jordan block. Another result of this work provides sufficient asymptotic stability conditions regardless of forms higher than the third order. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)