bluuebunny/crossref_metadata_2025 huggingface dataset:
Out‐of‐plane seismic response of vertically spanning URM walls connected to flexible diaphragms
Authors: Derakhshan Hossein , Griffith Michael C. , Ingham Jason M.
Published: October 2015

A simplified numerical model was used to investigate the out‐of‐plane seismic response of vertically spanning unreinforced masonry (URM) wall strips. The URM wall strips were assumed to span between two flexible diaphragms and to develop a horizontal crack above the wall mid‐height. Three degrees of freedom were used to accommodate the wall displacement at the crack height and at the diaphragm connections, and the wall dynamic stability was studied. The equations of dynamic motion were obtained using principles of rocking mechanics of rigid bodies, and the formulae were modified to include semi‐rigid wall behaviour. Parametric studies were conducted that included calculation of the wall response for different values of diaphragm stiffness, wall properties, applied overburden, wall geometry and earthquake ground motions. The results of the study suggest that stiffening the horizontal diaphragms of typical low‐rise URM buildings will amplify the out‐of‐plane acceleration demand imposed on the wall and especially on the wall–diaphragm connections. It was found that upper‐storey walls connected to two flexible diaphragms had reduced stability for applied earthquake accelerograms having dominant frequency content that was comparable with the frequency of the diaphragms. It was also found that the applied overburden reduced wall stability by reducing the allowable wall rotations. The results of this study suggest that the existing American Society of Civil Engineers recommendations for assessment of vertically spanning walls overestimate the stability of top‐storey walls in multi‐storey buildings in high‐seismic regions or for walls connected to larger period (less stiff) diaphragms. Copyright © 2015 John Wiley & Sons, Ltd.
Paleochannels and Patches: A Geoarchaeological Assessment of Silcrete Sources in the Cumberland Plain, Eastern Australia
Authors: Doelman T. , Webb J. , Williams A. , May J. , Barry F.
Published: October 2015

Although Aboriginal occupation dates to the Pleistocene, silcrete artifacts only begin to dominate archaeological sites found in the Cumberland Plain of western Sydney, eastern Australia, during the mid‐late Holocene. These assemblages routinely include large numbers of backed artifacts. A geoarchaeological survey of five potential silcrete source areas found that silcrete is irregularly distributed along ridgelines within gravel patches that represent paleochannel remnants. Thus, particular parts of the landscape, dictated by the geological history, were more likely to be targeted for stone procurement. The quality of silcrete differs between and within the sources due to variations in grain‐size, degree of silicification, and presence of inclusions/fractures, as well as the destructive influence of bush fires on exposed cobbles, resulting in an overall low abundance of high‐quality silcrete across the Cumberland Plain. Furthermore, a rind or chalky weathering cortex on many cobbles means that testing was required to assess the internal raw material quality. The difficulty in locating suitable raw material for artifact manufacture meant that when good silcrete sources were found, they were heavily targeted. This contextual information provides an essential backdrop in which to understand the archaeology of the Cumberland Plain and broader patterns of landscape use.
Multivariate classification of smokers and nonsmokers using SVM‐RFE on structural MRI images
Authors: Ding Xiaoyu , Yang Yihong , Stein Elliot A. , Ross Thomas J.
Published: October 2015

Voxel‐based morphometry (VBM) studies have revealed gray matter alterations in smokers, but this type of analysis has poor predictive value for individual cases, which limits its applicability in clinical diagnoses and treatment. A predictive model would essentially embody a complex biomarker that could be used to evaluate treatment efficacy. In this study, we applied VBM along with a multivariate classification method consisting of a support vector machine with recursive feature elimination to discriminate smokers from nonsmokers using their structural MRI data. Mean gray matter volumes in 1,024 cerebral cortical regions of interest created using a subparcellated version of the Automated Anatomical Labeling template were calculated from 60 smokers and 60 nonsmokers, and served as input features to the classification procedure. The classifier achieved the highest accuracy of 69.6% when taking the 139 highest ranked features via 10‐fold cross‐validation. Critically, these features were later validated on an independent testing set that consisted of 28 smokers and 28 nonsmokers, yielding a 64.04% accuracy level (binomial P = 0.01). Following classification, exploratory post hoc regression analyses were performed, which revealed that gray matter volumes in the putamen, hippocampus, prefrontal cortex, cingulate cortex, caudate, thalamus, pre‐/postcentral gyrus, precuneus, and the parahippocampal gyrus, were inversely related to smoking behavioral characteristics. These results not only indicate that smoking related gray matter alterations can provide predictive power for group membership, but also suggest that machine learning techniques can reveal underlying smoking‐related neurobiology. Hum Brain Mapp 36:4869–4879, 2015. Published 2015. This article is a U.S. Government work and is in the public domain in the USA.
Acute and sub‐lethal exposure to copper oxide nanoparticles causes oxidative stress and teratogenicity in zebrafish embryos
Authors: Ganesan Santhanamari , Anaimalai Thirumurthi Naveenkumar , Raghunath Azhwar , Vijayakumar Savitha , Perumal Ekambaram
Published: October 2015

Nano‐copper oxides are a versatile inorganic material. As a result of their versatility, the immense applications and usage end up in the environment causing a concern for the lifespan of various beings. The ambiguities surround globally on the toxic effects of copper oxide nanoparticles (CuO‐NPs). Hence, the present study endeavored to study the sub‐lethal acute exposure effects on the developing zebrafish embryos. The 48 hpf LC50 value was about 64 ppm. Therefore, we have chosen the sub‐lethal dose of 40 and 60 ppm for the study. Accumulation of CuO‐NPs was evidenced from the SEM‐EDS and AAS analyzes. The alterations in the AChE and Na+/K+‐ATPase activities disrupted the development process. An increment in the levels of oxidants with a concomitant decrease in the antioxidant enzymes confirmed the induction of oxidative stress. Oxidative stress triggered apoptosis in the exposed embryos. Developmental anomalies were observed with CuO‐NPs exposure in addition to oxidative stress in the developing embryos. Decreased heart rate and hatching delay hindered the normal developmental processes. Our work has offered valuable data on the connection between oxidative stress and teratogenicity leading to lethality caused by CuO‐NPs. A further molecular mechanism unraveling the uncharted connection between oxidative stress and teratogenicity will aid in the safe use of CuO‐NPs. Copyright © 2015 John Wiley & Sons, Ltd.
On‐wafer characterization setup for model extraction and validation of high‐power GaN HEMT switches
Authors: Pirola M. , Camarchia V. , Quaglia R. , Ramella C.
Published: October 2015

An ad hoc setup for complete on‐chip large‐signal characterization of both series and parallel high‐power GaN high‐electron‐mobility transistor switches has been developed. Thanks to its characteristics, arbitrary loads at both switch terminals (i.e., drain and source) for power levels up to tens of watts can be applied. The setup is suitable for extraction and validation of equivalent circuit and behavioral models. The potentiality of the presented solution is demonstrated by model validation and measurements of series and shunt C‐band high‐power GaN high‐electron‐mobility transistor switches from two commercial foundries. Copyright © 2015 John Wiley & Sons, Ltd.
First olfactory fiber as an anatomical landmark for frontal sinus surgery
Authors: Upadhyay Smita , Buohliqah Lamia , Vieira Junior Gerival , Otto Bradley A. , Prevedello Daniel M. , Carrau Ricardo L.
Published: October 2015

Objectives/Hypothesis

Access to the frontal sinuses is technically challenging owing to their anterosuperior location, diverse anatomy, close proximity to critical structures and the need to work in a relatively narrow space with angled‐lens endoscopes and instruments. This study attempts to study the relationship of the first olfactory fiber with the frontal sinus posterior wall, assessing its fidelity as a surgical landmark during frontal sinus surgery.

Study Design

Anatomic study.

Methods

Fifteen cadaveric specimens were studied. Measurements were obtained bilaterally using the data from individual CT scans. Median A‐P was defined as the anteroposterior (A‐P) diameter measured just lateral to the intersinus septum, paramedian A‐P was measured 5 mm lateral to the septum, and maximum A‐P was defined as the maximum anteroposterior diameter on axial images. A surgical navigation device was used to calculate the distance between the first olfactory fiber and the posterior table of the frontal sinus.

Results

The mean distance between the first olfactory fiber and the posterior wall of the frontal sinus was (4.03 ± 2.7) mm on the right side and (4.2 ± 2.9) mm on the left. This distance strongly correlated with the maximum A‐P diameter of the sinus.

Conclusions

In a cadaveric model, the first olfactory fiber was found to be an average of 4.0 mm posterior to the frontal sinus. The significant variability of this distance should be considered when using the first olfactory fiber to establish the posterior boundary of a frontal sinusotomy. Drilling no further posterior than 7 mm rostral to the first olfactory fiber would be safe in 91% of patients.

Level of Evidence

NA Laryngoscope, 126:1039–1045, 2016
Retrosigmoid versus translabyrinthine approach to acoustic neuroma resection: A comparative cost‐effectiveness analysis
Authors: Semaan Maroun T. , Wick Cameron C. , Kinder Kimberly J. , Stuyt John G. , Chota Rebecca L. , Megerian Cliff A.
Published: October 2015

Objectives/Hypothesis

Approach‐specific economic data of acoustic neuroma (AN) resection is lacking. The purpose of this study was to analyze and compare adjusted total hospital costs, hospital and intensive care unit (ICU) length of stay (LOS), and associated factors in AN patients undergoing resection by translabyrinthine (TL) approach versus retrosigmoid (RS) approach.

Study Design

Retrospective chart review.

Methods

A total of 113 patients with AN undergoing TL (N = 43) or RS (N = 70) surgical resection between 1999 and 2012 were analyzed. Data including age, health status, preoperative hearing, tumor size, postoperative complications, hospital, ICU LOS, and disposition after discharge were collected from medical records and compared between both groups. Cost data was obtained from the hospital finance department and adjusted based on the Consumer Price Index for 2013.

Results

There were no significant differences in demographic data, preoperative hearing, preoperative health status, or postoperative complication rate. Total hospital LOS and ICU LOS were significantly longer in the RS compared to the TL group (4.3 ± 3.6 vs. 2.6 ± 1.1 days; P < 0.001, and 1.5 ± 1.1 vs. 1.0 ± 0.5 days; P = 0.015, respectively). Tumors were larger in RS compared to the TL group (2.1 ± 1.0 cm vs. 1.5 ± 0.7 cm, respectively; P = 0.002). When patients were stratified by tumor size < or ≥ 2 cm, the total hospital LOS remained greater in the RS group in both subgroups (< and ≥ 2 cm, P < 0.001, and P = 0.031, respectively). However, there was no difference in the total ICU LOS between both subgroups. The adjusted mean total hospital cost was higher in the RS compared to the TL group ($25,069 ± 14,968 vs. $16,799 ± 5,724; P < 0.001). The adjusted mean total hospital cost was greater in the RS group with tumor < 2 cm (P < 0.001) but not significantly different in patients with tumors ≥ 2 cm. Univariate analysis showed that greater tumor size, poorer preoperative health status, the presence of major postoperative complications, and the RS approach were independently significantly associated with higher total hospital LOS (P = 0.001, P = 0.009, P = 0.001, and P < 0.001, respectively) and a higher adjusted total hospital cost (P < 0.001, P = 0.002, P = 0.014, and P < 0.001, respectively).

Conclusion

Hospital LOS and total adjusted costs are significantly less for patients undergoing translabyrinthine acoustic neuroma resection compared to the retrosigmoid approach. Many factors appear to influence these differences. Economic considerations in addition to tumor characteristics and surgeon preference should be considered in future acoustic neuroma resections.

Level of Evidence

2c. Laryngoscope, 126:S5–S12, 2016
Oral cavity squamous cell carcinoma metastatic to central compartment (level 6) lymph nodes
Authors: Likhterov Ilya , Rowe Meghan E. , Khorsandi Azita S. , Urken Mark L.
Published: October 2015

Alterations to drainage pathways in the head and neck as a result of surgical manipulation are not well understood. We present two unusual cases of oral squamous cell carcinoma metastatic to the level 6 nodal compartment following extensive treatment. Both oral squamous cell carcinoma cases exhibited metastases to the central neck compartment following extensive surgery and radiation. Each patient had prior history of multifocal oral cavity disease and recurrent neck metastases requiring salvage lymphadenectomy. Surgical interventions may alter the usual lymphatic drainage patterns. In cases of extensive treatment, all levels of the neck should be monitored for lymph node recurrence. Laryngoscope, 126:1803–1805, 2016
Correlation Between Physicomechanical and Swelling Properties of Weakly Basic Copolymer Hydrogels Based on (Meth)acrylate Polycations as New Smart Materials
Authors: Celik Tayyibe , Orakdogen Nermin
Published: October 2015

2‐Hydroxyethyl methacrylate (HEMA) is incorporated to N,N‐dimethylaminoethyl methacrylate (DMAEMA) fabricating a series of stimuli‐responsive copolymer hydrogels by free radical copolymerization. The increasing comonomer content via adding more HEMA results in a higher network density and, therefore, a lower equilibrium swelling ratio. The uniaxial compressive testing results showed that increasing HEMA in the feed improved the mechanical strength of P(DMAEMA‐co‐HEMA) hydrogels. As HEMA increased, the elastic modulus as well as the effective crosslinked chain density increased. The work strives to provide method to tune mechanical and physical properties for weakly basic copolymer hydrogels based on (meth)acrylate polycations, which is hopefully to guide the design of hydrogels with desirable properties.

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Liquid Chromatography at Critical Conditions of Poly(propylene)
Authors: Bhati Sampat Singh , Macko Tibor , Brüll Robert , Mekap Dibyaranjan
Published: October 2015

Liquid chromatography at critical conditions (LCCC) of poly(propylene) (PP) holds unique potential to further augment the understanding of molecular heterogeneities present in PP. The critical conditions for isotactic poly(propylene) (iPP) and syndiotactic poly(propylene) (sPP) have been identified using porous graphitic carbon as stationary phase and combinations of adsorption and desorption promoting solvents. It is found that 1,2,4‐trichlorobenzene is a stronger desorption promoting eluent compared to 1,2‐dichlorobenzene, while 2‐octanol shows a weaker adsorption promoting effect compared to 2‐ethyl‐1‐hexanol for all stereo‐isomeric forms of PP. The fraction of desorption promoting solvent needs to reach critical conditions decreased in a linear manner with the temperature. High temperature 2D liquid chromatography with infrared detection provides quantitative information about the fractions of the constituents (iPP and ethylene–propylene copolymer) of a model high impact PP sample at LCCC of iPP.

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Loss of signal transducer and activator of transcription 1 is associated with prostate cancer recurrence
Authors: Hatziieremia Sophia , Mohammed Zahra , McCall Pamela , Willder Jennifer M. , Roseweir Antonia K. , Underwood Mark A. , Edwards Joanne
Published: October 2015

STAT1 loss has previously been implicated in cell line studies to modify prostate cancer cell growth and survival, however the clinical significance of this has not previously been established. This study investigated if STAT1 loss was associated with patient outcome measures and the phenotypic consequence of STAT1 silencing. STAT1 expression was assessed in two patient cohorts with localised (n = 78) and advanced prostate cancer at initial diagnosis (n = 39) by immunohistochemistry (IHC). Impact of STAT1 silencing on prostate cancer cells lines was assessed using Cell Death detection ELISA, TLDA gene signature apoptosis arrays, WST‐1 assay, xCELLigence system, clonogenic assay, and wound healing assay. In the localised patient cohort, low expression of STAT1 was associated with shorter time to disease recurrence (3.8 vs 7.3 years, P = 0.02) and disease specific survival (6.6 vs 9.3 years, P = 0.05). In the advanced patient cohort, low expression was associated with shorter time to disease recurrence (2.0 vs 3.9 years, P = 0.001). When STAT1 was silenced in PC3 cells (AR negative) and LNCaP cells (AR positive) silencing did not influence levels of apoptosis in either cell line and had little effect on cell viability in the LNCaP cells. In contrast, STAT1 silencing in the PC3 cells resulted in a pronounced increase in cell viability (WST‐1 assay: mock silenced vs STAT1 silenced, P < 0.001), clonagenicity (clonogenic assay: mock silenced vs STAT1 silenced, P < 0.001), and migration (wound healing: mock silenced vs STAT1 silenced, P < 0.001). In conclusion, loss of STAT1 may promote prostate cancer recurrence in AR negative patients via increasing cell viability. © 2015 Wiley Periodicals, Inc.
Geodiverse routing with path delay and skew requirement under area‐based challenges
Authors: Cheng Yufei , Medhi Deep , Sterbenz James P. G.
Published: October 2015

With the increasing frequency of natural disasters and intentional attacks that challenge communication networks, vulnerability to cascading, and regional‐correlated challenges is escalating. Given the high complexity and large traffic load of communication networks, these correlated challenges cause substantial damage to reliable network communication. In this work, we extend the GeoDivRP routing protocol to consider delay‐skew requirement when using multiple geographically diverse paths for telecommunication networks under area‐based challenges. We present a flow‐diverse minimum‐cost routing multicommodity flow problem. Furthermore, we present a nonlinear delay‐skew optimization problem to balance between delay and traffic skew on paths. We investigate the tradeoff between the delay and skew in choosing multiple geodiverse paths. We implement GeoDivRP in ns‐3 to use the optimized paths given by the two optimization solutions and demonstrate their effectiveness compared to open shortest path first Equal‐Cost Multi‐Path routing in terms of overall link utilization. It guarantees the delay‐skew constraint provided by the upper layer while satisfies the traffic demand imposed by multiple routing commodities in the telecommunication networks. © 2015 Wiley Periodicals, Inc. NETWORKS, Vol. 66(4), 335–346 2015
A laminate‐based modelling approach for rate‐dependent switching in ferroelectric materials
Authors: Dusthakar Dinesh K , Menzel Andreas , Svendsen Bob
Published: October 2015

This contribution focuses on the sequential laminate‐based modelling approach for the numerical simulation of the complex electromechanical material behaviour of ferroelectric single crystals. The construction of engineered domain configurations by using the method of sequential lamination in order to study the domain evolution and polarisation switching in ferroelectric single crystals has recently been carried out in the works of [1–4]. By fulfilling the kinematic and polarisation compatibility conditions between the domain structures in a crystal, the proposed laminate‐based formulation is governed by an energy‐enthalpy function and by a dissipation potential. The mixed energy‐enthalpy, written in terms of the total strains, electric field and a set of internal variables, here the multi‐rank laminate volume fractions, governs the dissipative electromechanical response of the ferroelectric crystal, whereas the rate‐dependent dissipation potential formulated in terms of the flux of the internal variables describes the time‐dependent evolution of the multi‐rank laminate volume fractions, subjected to inequality constraints. The model reproduces experimentally observed hysteresis and butterfly curves, characteristic for single crystal ferroelectric materials, when subjected to homogeneous electromechanical loading conditions. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Relaxing mixed integer optimal control problems using a time transformation
Authors: Ringkamp Maik , Ober‐Blöbaum Sina , Leyendecker Sigrid
Published: October 2015

Mixed integer control systems are used to model dynamical behavior that can change instantly, for example a driving car with different gears. Changing a gear corresponds to an instant change of the differential equation what is achieved in the model by changing the value of the integer control function. The optimal control of a mixed integer control system by a discretize‐then‐optimize approach leads to a mixed integer optimization problem that is not differentiable with respect to the integer variables, such that gradient based optimization methods can not be applied. In this work, differentiability with respect to all optimization variables is achieved by reformulating the mixed integer optimal control problem (MIOCP). A fixed integer control function and a time transformation are introduced. The combination of both allows to change the sequence of active differential equations by partially deactivating the fixed integer control function. In contrast to other works, here different fixed integer control functions are taken into account. Advantages of so called control consistent (CC) fixed integer control functions are discussed and confirmed on a numerical example. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Learning Robot Force/Position Control for Repetitive High Speed Applications with Unknown Non–Linear Contact Stiffness
Authors: Parzer Herbert , Gattringer Hubert , Müller Andreas , Naderer Ronald
Published: October 2015

This paper proposes a learning robot force/position control for high speed force trajectory following. Following high speed force trajectories in different repetitve robotic applications is a challenging field in robot force control. If the end–effector should provide a contact force while following a position trajectory in the non–force controlled direction a parallel force / position control is suitable. However, when it comes to high speed tasks this force control method reaches its limit. The problem can be solved by using an iterative learning control method in combination with the parallel force/position control. In this paper the learning force control method is introduced and experimental results are presented. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Impulse‐based control of simple oscillators within the nonsmooth mechanics approach
Authors: Schindler Thorsten , Mayet Johannes , Seiwald Philipp
Published: October 2015

An impulse‐based control scheme for a simple spring‐mass oscillator subject to set‐valued friction forces is presented. In contrast to PD or PID control laws, the proposed control law prevents non‐zero steady state errors and limit cycles. Motivated by Wouw and Leine [1], it is shown that impulse‐based control laws can lead to satisfactory behavior if the oscillator starts sticking. In order to realize a practical implementation, the equations of motion are extended by a mathematical model of the actuator dynamics. The analysis is undertaken in the framework of nonsmooth mechanical systems. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Relaxed incremental variational approach for damage in arteries
Authors: Balzani Daniel , Schmidt Thomas
Published: October 2015

In this contribution, several extensions of the relaxed incremental variational damage model by BALZANI & ORTIZ [1] are provided, in order to appropriately account for the description of arterial tissues. In particular, the one‐dimensional formulation from [1] is combined with a numerical homogenization scheme. Moreover, hysteresis behavior is included and a new optimization strategy is used to determine the bifurcation parameters when checking for a loss of convexity. The performance of the proposed model is demonstrated in a three‐dimensional finite element simulation of a overstretched simplified atherosclerotic artery. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A porous media approach for plantar tissue during gait
Authors: Boso Daniela P. , Sciumè Giuseppe , Pizzocaro Mattia , Schrefler Bernhard A.
Published: October 2015

Recently a new computational model, based on the thermodynamically constrained averaging theory, has been proposed to predict tumor initiation and proliferation and afterwards to study plantar tissue mechanics. The foot tissue is modeled as an elastic porous medium, in large strain regime and completely filled by a fluid phase. By considering the interstitial fluid, it is possible to mimic the viscoelastic behavior of the plantar tissue observed experimentally. Being the global response of the bi‐phase system viscoelastic, it is shown that the duration of stance as well as of each of gait cycle has an influence on tissue stress field. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Comparison of Preconditioners for the Steklov–Poincaré Formulation of the Fluid‐Structure Coupling in Hemodynamics
Authors: Deparis S. , Forti D. , Heinlein A. , Klawonn A. , Quarteroni A. , Rheinbach O.
Published: October 2015

A Fluid–Structure Interaction (FSI) problem can be reinterpreted as a heterogeneous problem with two subdomains. It is possible to describe the coupled problem at the interface between the fluid and the structure, yielding a nonlinear Steklov–Poincaré problem. The linear system can be linearized by Newton iterations on the interface and the resulting linear problem can be solved by the preconditioned GMRES method. In this work we investigate the behavior of preconditioners of Neumann–Neumann and Dirichlet–Neumann type. We find that, in the context of hemodynamics, the Dirichlet– Neumann, i.e., using Dirichlet boundary conditions on the fluid side and Neumann on the structure side, outperforms the Neumann–Neumann method, except when a weighting is used such that it basically reduces to the Dirichlet–Neumann method. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Extremal loading of soft fibrous tissues: multi‐scale mechanics and constitutive modeling
Authors: Linka Kevin , Khiêm Vu Ngoc , Itskov Mikhail
Published: October 2015

In the current contribution, we present a multi‐scale constitutive model capturing macroscopic inelastic effects (like stress softening and permanent set) in soft tissues under cyclic loading. Soft biological tissues can be described as a biological composite material. The extracellular matrix is hereby reinforced by collagen fibers which themself are an assembly of collagen fibrils embedded in a proteoglycan (PG) rich matrix. Micro‐damage induced by cyclic loading is treated by an interaction scenario between the fibrils and the PGs. At the low strain regime PGs promote sliding between fibrils [1] which leads to the yielding of statistical distributed overlapping segments. The breakage of the PG‐bridges is defined by a decreasing PG‐density. Due to the accumulated damage of the PG connections at high tissue strains, the strains at the fibril level increases. This finally drives the over‐stretching of the fibrils, which is associated with a permanent rupture of the hydrogen bonds inside of the tropocollagen molecules [2]. The so obtained model is in line with recent experimental findings [1, 2] and was additionally validated against experimental data available in literature. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Rupture in soft biological tissues modeled by a phase‐field method
Authors: Raina Arun , Miehe Christian
Published: October 2015

We present an application of the phase‐field method of fracture to the simulation of artery rupture at large strains. To achieve this, the crack driving force function associated with the evolution of the crack phase‐field is modified to account for the inherent anisotropy of the soft biological tissues. The phase‐field methods present a promising and innovative approach to the thermodynamically consistent modeling of fracture. A key advantage lies in the prediction of the complex crack topologies where the cohesive zone approaches to fracture are known to suffer. A regularized crack surface functional is introduced that Γ‐converges to a sharp crack topology for vanishing length scale parameter. The evaluation of the phase‐field follows the minimization of this crack surface functional. The phase‐field variable can be treated as a geometric quantity whose evolution is coupled to the anisotropic bulk response in a modular format in terms of a crack driving state function. A stress‐based anisotropic failure criterion is introduced whose maximum value from the deformation history drives the irreversible crack phase‐field. The formulation is verified by the finite element based simulation of a real arterial cross‐section undergoing rupture in a two‐dimensional setting when subjected to inflation pressure. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Towards the continuum‐mechanical modelling of metastatic tumour growth in the brain
Authors: Schröder Patrick , Wagner Arndt , Ehlers Wolfgang
Published: October 2015

The growth of metastases in the brain increases the state of stress, create leaky blood vessels and disrupt regular brain cells. Essential steps during the development of metastases are the infiltration of the tissue, the nutrient‐dependent growth and the stimulation of blood‐vessel sprouting. A promising medical treatment can be obtained by the direct infusion of a therapeutic solution into the tissue. Besides experiments, computational models can improve the understanding of brain metastases. In this regard, the liquid‐saturated brain tissue represents a porous material. Therefore, the framework of the Theory of Porous Media (TPM) provides an excellent tool for its description. The continuum‐mechanical theory of a multi‐constituent model and mechanisms of metastases growth are presented in this contribution. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the Influence of Growth in Perfusion Dependent Biological Systems – at the Example of the Human Liver
Authors: Werner Daniel , Ricken Tim , Dahmen Uta , Dirsch Olaf , Holzhütter Hermann‐Georg , König Matthias
Published: October 2015

Biochemical reactions in the liver are a complex non‐linear and time depending coupled function‐perfusion‐mechanisms. The metabolism of the liver, e.g. nutrient storage, is directly coupled to its blood perfusion. Growth phenomena, such as accumulation of fat, have a strong impact onto micro‐perfusion within the liver. Here, we present the results of a computational model that describes selected coupled functionalities. The metabolic processes take place in the liver cells, the hepatocytes, which are arranged in a delicate system of capillaries, so called sinusoids. Nutrients, oxygen, and other components of the blood are transported through the sinusoids. Due to this highly complex inner structure of the lobules it is impracticable to give a microscopic geometrical description in a continuum mechanical manner. Therefore, a homogenization scheme based on the theory of porous media (TPM) is used; [1]. In case of the presented liver model we consider a porous solid body, that consists of tissue and fat, and a fluid representing blood. In each phase several miscible components are considered. For the microscopic cell level use has been made of an embedded set of ordinary differential equations (ODE) that mimics a simplified metabolism, e.g. glucose utilization and production; [2]. In case of growth of the fat phase we follow a phenomenological approach. Numerical examples for this coupled process are presented and discussed. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical simulation of the fracturing processes in masonry arches
Authors: Carpinteri Alberto , Lacidogna Giuseppe , Accornero Federico , Invernizzi Stefano
Published: October 2015

Masonry arch structures, and, more generally, vaulted structures, are traditionally assessed using a well‐established approach, such as linear elasticity or limit analysis, whereby system behaviour at the intermediate stage – which occurs when the material's tensile strength has been exceeded but the collapse mechanism has not yet formed – is disregarded. A more accurate interpretation requires a thorough analysis that can take into account the intermediate cracking stage and uses a constitutive law providing a closer approximation to the actual behaviour of the material. In this paper, an evolutionary fracturing process analysis for the stability assessment of masonry arches is presented. This method makes it possible to capture the damaging process that takes place when the conditions evaluated by means of linear elastic analysis no longer apply and before the conditions assessed through limit analysis set in. Furthermore, the way the thrust line is affected by the opening of cracks and the redistribution of internal stresses can be checked numerically. The results obtained with the described approach are compared with a numerical simulation performed with the finite element code Diana (TNO, The Netherlands) adopting discrete cracking with cohesive laws. Finally, the case study of the arch of the Mosca Bridge over the Dora River in Turin, Italy, is described. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Global approaches for accurate loading analyses and crack path predictions at single and two‐cracks systems
Authors: Judt Paul , Ricoeur Andreas
Published: October 2015

Based on the work by Eshelby, the path‐independent Jk‐, M‐, L‐ and interaction‐ or Ik‐integrals were introduced and applied to cracks for the accurate calculation of crack tip loading quantities. Applying the FE‐method to solve boundary value problems with cracks, numerically inaccurate values are observed within the crack tip region affecting the accuracy of local approaches. Simulating crack paths, local approaches face further problems as cracks are running towards interfaces, internal boundaries or other crack faces. Within global approaches, path‐independent integrals are calculated along remote contours far from the crack tip, essentially exploiting numerically reliable data requiring special treatment only for the near‐tip crack faces. To provide path‐independence, additional integrals along interfaces, internal boundaries and crack faces are necessary.

In this paper, new global approaches of path‐independent integrals are presented and applied to the calculation of crack paths at two‐cracks systems. A second focus is directed to the accurate loading analysis and crack path prediction considering anisotropic properties and material interfaces. The numerical model provides crack paths which are in good agreement with those obtained from crack growth experiments. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Follower forces as an inverse contact algorithm
Authors: Konyukhov A. , Schweizerhof K. , Izi R.
Published: October 2015

Follower forces on a surface are defined as the forces which are keeping their constant directions with regard to the surface. A typical example is pressure, which is acting always in the direction of the normal. The linearization is necessary in order to solve a problem using an implicit scheme in the case of large deformations. Consider, for example, pressure p acting on a surface s, defined by the vector r(ξ1, ξ2). In this case, a weak form is written as:

Formally, as shown in [1], [2] the following linearization can be formulated as

which is recovering an apparent unsymmetrical structure with regard to Δu and δu and, therefore, corresponding unsymmetrical tangent matrix. Though, the system is initially conservative an initially looking unsymmetrical structure is derived due to the linearization of the normal in the Cartesian coordinate system. A special complicated transformation for integrals with closed boundaries was necessary to show the symmetry in this case, see in [3], [4]. Nevertheless, as mentioned by Simo in [5], linearization in a covariant form is always leading to the symmetric structure for conservative systems.

Application of the covariant derivation has become a standard tool within the geometrically exact theory of contact interaction, see in [6], [7]. The corresponding symmetry of tangent matrices for all conservative cases is then automatically fulfilled, moreover, they are obtained for all contact pairs such as surface‐to‐surface, curve‐to‐curve, curve‐to‐surface in a close covariant form. Using these transformations, one can treat contact tractions not as unknown variables to be computed, but as given external forces which are keeping their direction in the local coordinate system. This case we can call an inverse contact algorithm. The main results of the geometrically exact theory for contact interactions for surface‐to‐surface contact pairs are outlined first in order to obtain all relationships for the inverse contact algorithm. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Investigations on clamping effects with Die‐Less‐Hydroforming‐Structures
Authors: Metzger Andreas , Ruff Daniel C. , Ummenhofer Thomas
Published: October 2015

When using a special forming technology called “Die‐Less Hydroforming” to create objects, due to the lack of a conventional forming tool (like a die or a punch) and depending on a particular cutting of the blank geometry, it is possible to generate some special clamping effects when inflating the seal‐welded blanks. In our contribution, we present results of a study of these clamping effects in extracts, which have been investigated by means of practical inflating tests as well as numerical forming simulations using LS‐DYNA with “Die‐Less‐Hydroforming”‐samples having a special geometry that looks like a “Pac‐Man”. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Stress concentration control in the problem of plane elasticity theory
Authors: Odishelidze Nana , Criado Aldeanueva Francisco , Criado Francisco
Published: October 2015

In engineering practice, one of the important problems is the problem of finding full‐strength contours which permits to control stress concentration at the hole boundary. The article addresses the mixed problem of plane elasticity theory for doubly‐connected domain with partially unknown boundary conditions. In the presented work the stress state of the given body and full‐strength contours were defined. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On one contact problem of plane elasticity theory with partially unknown boundary
Authors: Tsintsadze Magda , Odishelidze Nana
Published: October 2015

Applications of elastic plates weakened with full‐strength holes are of great interest in several mechanical constructions (building practice, in mechanical engineering, shipbuilding, aircraft construction, etc). It's proven that in case of infinite domains the minimum of tangential normal stresses (tangential normal moments) maximal values will be obtained on such contours, where these values maintain constant(the full strength holes). The solvability of these problems allow to control stress optimal distribution at the hole boundary via appropriate hole shape selection. The paper addresses a problem of plane elasticity theory for a doubly connected domain S on the plane z = x + iy, which external boundary is an isosceles trapezoid boundary; the internal boundary is required full‐strength hole including the origin of coordinates. In the provided work the unknown full‐strength contour and stressed state of the body were determined. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Kink banding in laminated composite structures
Authors: Völlmecke Christina , Zidek Robert A. E.
Published: October 2015

An analytical model for kink band deformations occurring in laminated composites is proposed based on geometric and potential energy principles. Whilst nonlinear material behaviour and imperfections are included the model considers a symmetric, multi‐directional laminate lay‐up where the kink band is assumed to occur in the central 0° laminae. First results compared to data in the literature are presented offering encouragement. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Rotordynamics of Two‐Pole Turbo Generators with Refined Modelling of the Unbalanced Magnetic Pull
Authors: Boy Felix , Hetzler Hartmut
Published: October 2015

Within this contribution the rotordynamic behaviour of two‐pole turbo generators is discussed. In the investigation a basic model originally proposed by Kellenberger [1], introducing a refined description of the unbalanced magnetic pull (UMP), is reviewed and extended. The analysis comprises the investigation of lateral stability behaviour and stationary torque characteristic for a magnetic eccentricity. There are two main results of the contribution: firstly it is shown, that the non‐radial component of the UMP has the same structure as the restoring forces due to a non‐circular shaft, but opposite sign. Secondly it can be seen from the extended model, that an eccentric point of application of the UMP may change the systems stationary torque characteristic significantly. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the chaotic behavior of the non‐ideal vibrating systems
Authors: Chiroiu Veturia , Dumitriu Dan
Published: October 2015

The paper discusses the chaotic behavior of a vibrating structure coupled to an energy source. The structural response of this system may act like energy sink under certain conditions so that a part of the energy supplied by the source is spend to vibrate the structure rather than increasing the drive speed, according to the Sommerfeld effect [1]. The energy source is influenced by the response of the system and consequently, the system exhibits jumps at critical values of the energy source. The system mimics a disappearance of the energy in the resonance regions which can affect the stability of the system, sending it to chaos [2‐4]. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
1 : 3‐Resonance in a Hopf–Hopf bifurcation
Authors: Steindl Alois
Published: October 2015

We investigate the bifurcating solutions at a Hopf–Hopf interaction point with an internal 1 : 3 resonance. It turns out, that the transitions from single to mixed modes can be described by Duffing or Mathieu szenarios. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On vibrations in non‐linear, forced, friction‐excited systems
Authors: Tiedemann Merten , Stender Merten , Hoffmann Norbert
Published: October 2015

To accelerate the development of non‐linear, friction‐excited systems, i.e. automotive friction brakes, novel test procedures are being developed. These include the study of the system's forced vibrations. However, there is a lack of knowledge concerning feasible test procedures, the assessment of the gathered data, and the possible vibration phenomena. In this context, the contribution at hand discusses vibrations in non‐linear, forced, friction‐excited systems. In the pre‐flutter regime proposed criteria for identification of parameter regions in which limit cycle oscillations can occur are challenged. In the post‐flutter regime frequency spectra for different excitation conditions are studied. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modeling the moisture and temperature dependent material behavior of adhesive bonds
Authors: Goldschmidt Florian , Diebels Stefan
Published: October 2015

Although bonding has been known for a long time, the mechanical behavior of adhesive bonded joints comes more and more into the focus of scientific attention. During usage, adhesives are exposed to environmental influences like temperature, moisture and radiation. Due to the fact that adhesives usually consist of polymers, these influences change their mechanical behavior.

In the presented work, a viscoelastic cross‐linked polyurethane that behaves incompressible is investigated. A three‐dimensional mechanical model is presented, which takes into consideration influences of changes in temperature as well as in the moisture concentration inside the adhesive layer and its thickness on the mechanical behavior. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Transition from hyperelastic micromorphic to micropolar and microstrain continua
Authors: Leismann Thorben , Mahnken Rolf
Published: October 2015

Micromorphic continua are equipped with additional degrees of freedom in comparison to the classical continuum, representing micro deformations of the material points of a body. They are also provided with a higher order gradient. Therefore, they are able to account for material size‐effects and to regularize the boundary value problem, when localization phenomena arise. Arbitrary micro deformations are allowed for in the micromorphic continuum, while the special cases micropolar continuum and microstrain continuum merely allow for micro rotation and micro strain, respectively. This paper is concerned with the transition from a micromorphic to a micropolar and a microstrain continuum. Three simple constitutive models are shown, which represent the three different continua. Additionally, the role of the micropolar and microstrain part in a micromorphic continuum is illustrated by a numerical example. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Shape control of piezolaminated thin‐walled structures using nonlinear piezoelectric actuators
Authors: Mekala Narasimha Rao , Sachdeva Tarun , Schröder Kai‐Uwe
Published: October 2015

In the present paper a 2D‐shell finite element model is proposed to carry out static analysis of piezolaminated composite shells by incorporating nonlinear constitutive relations in order to describe the electromechanical coupling under strong electric fields. The present shell element has 5 mechanical DOFs and 3 electrical DOFs per node. The developed composite piezolaminated shell element is employed to study the static behavior and shaping of spherical antenna reflector laminated with piezo‐patches under both weak and strong electric fields. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modeling Dynamic Recrystallization in Polycrystalline Materials via Probability Distribution Functions
Authors: Nguyen Hai Van , Ebrahimzade Vahid , Hackl Klaus , Renner Jörg , Trinh Bach Tuyet
Published: October 2015

A model of dynamic recrystallization in polycrystalline materials is investigated in this work. Within this model a probability distribution function representing a polycrystalline aggregate is introduced. This function characterizes the state of individual grains by grain size and dislocation density. By specifying free energy and dissipation within the polycrystalline aggregate an evolution equation for the probability density function is derived via a thermodynamic extremum principle. For distribution functions describing a state of dynamic equilibrium we obtain a partial differential equation in parameter space. To facilitate numerical treatment of this equation, the equation is further modified by introducing an appropriately rescaled variable. In this the source term is considered to account for nucleation of grains. Then the differential equation is solved by an implicit time‐integration scheme based on a marching algorithm [2]. From the obtained distribution function macroscopic quantities like average strain and stress can be calculated. Numerical results of the theory are subsequently presented. The model is compared to an existing implementation in Abaqus as well. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)