bluuebunny/crossref_metadata_2025 huggingface dataset:
Correlating the Structural and Photo­physical Features of Pincer Luminophores and Monodentate Ancillary Ligands in PtII Phosphors
Authors: Galstyan Anzhela , Naziruddin Abbas Raja , Cebrián Cristina , Iordache Adriana , Daniliuc Constantin G. , De Cola Luisa , Strassert Cristian A.
Published: October 2015

Phosphorescent PtII complexes featuring pincer luminophores of 2,6‐bis(1,2,4‐triazolyl)pyridine (H2L1) and 2,6‐bis(pyrazolyl)pyridine (H2L3) with a bulky adamantyl or tolyl substituent (H2L4) are systematically compared, and their structural features are correlated with their photophysical properties. The combination with 4‐amylpyridine (Py), triphenylphosphine (P) or benzimidazol‐2‐ylidene (N‐heterocyclic carbene, NHC) donors as monodentate ancillary ligands gave a series of highly luminescent triplet emitters with variable aggregation properties. The molecular structures of four of these complexes, namely, Pt‐L1‐P, Pt‐L1‐NHC, Pt‐L3‐P, and Pt‐L4‐P were garnered from single‐crystal X‐ray diffraction analysis. The coordination complexes displayed green phosphorescence in solution and in the solid state. In doped poly(methyl methacrylate) (PMMA) matrices, most of the complexes exhibited high phosphorescence quantum yields, which reached 59 % for Pt‐L3‐P. A comparative analysis between the spectroscopic data and the computed parameters derived from time‐dependent density functional theory (TD‐DFT) calculations suggests that the emission originates from metal‐perturbed ligand‐centered excited triplet states (3MP‐LC). The radiationless deactivation rate constants of the emissive states can be correlated with the aggregation properties derived from the substitution pattern at the tridentate luminophores and the ancillary ligands, whereas the radiative rate constants are determined by the electronic structures of the complexes. We found that PtII complexes containing pyrazolate donors showed an enhanced charge‐transfer character in the excited state, whereas bulky adamantyl moieties and triphenylphosphine ancillary ligands suppress bimolecular aggregation and quenching phenomena.
Highly Stereoselective Domino Oxa‐Michael/Aza‐Michael/Cyclization: Synthesis of Bicyclic Lactams and Spiroox­indole Skeleton
Authors: Le Goff Ronan , Sanselme Morgane , Lawson Ata Martin , Daïch Adam , Comesse Sébastien
Published: October 2015

An efficient diastereoselective access to all carbon‐substituted oxazolo‐pyrrolidinones, including a quaternary carbon stereocenter, is described. This was achieved by using a domino process between hydroxy halogenoamides and various Michael acceptors. This strategy provided good to high yield and selectivity. Application to the diastereoselective synthesis of an enantioenriched spirooxindole skeleton in high yield and selectivity is also presented.
Electrografting and Controlled Surface Functionalization of Carbon Based Surfaces for Electroanalysis
Authors: Randriamahazaka Hyacinthe , Ghilane Jalal
Published: October 2015

The basic concepts of electrografting on carbon surfaces are reviewed with the emphasis on the prospects of achieving robust, well‐defined compositions and structures of electrode interfaces. The surface functionalization allows tuning the interfacial properties which play an important role in various electrochemical applications, such as sensors and biosensors. Covalent attachment of organic compounds can be achieved by means of the electrochemical reduction of diazonium salts, and oxidation of amine or carboxylate. This review also demonstrates that the electrografting followed by a post‐functionalization is an interesting approach in the designs of well‐defined interface for electrochemical (bio)sensing.
Controls on valley spacing in landscapes subject to rapid base‐level fall
Authors: McGuire Luke A. , Pelletier Jon D.
Published: October 2015

What controls the architecture of drainage networks is a fundamental question in geomorphology. Recent work has elucidated the mechanisms of drainage network development in steadily uplifting landscapes, but the controls on drainage‐network morphology in transient landscapes are relatively unknown. In this paper we exploit natural experiments in drainage network development in incised Plio‐Quaternary alluvial fan surfaces in order to understand and quantify drainage network development in highly transient landscapes, i.e. initially unincised low‐relief surfaces that experience a pulse of rapid base‐level drop followed by relative base‐level stasis. Parallel drainage networks formed on incised alluvial‐fan surfaces tend to have a drainage spacing that is approximately proportional to the magnitude of the base‐level drop. Numerical experiments suggest that this observed relationship between the magnitude of base‐level drop and mean drainage spacing is the result of feedbacks among the depth of valley incision, mass wasting and nonlinear increases in the rate of colluvial sediment transport with slope gradient on steep valley side slopes that lead to increasingly wide valleys in cases of larger base‐level drop. We identify a threshold magnitude of base‐level drop above which side slopes lengthen sufficiently to promote increases in contributing area and fluvial incision rates that lead to branching and encourage drainage networks to transition from systems of first‐order valleys to systems of higher‐order, branching valleys. The headward growth of these branching tributaries prevents the development of adjacent, ephemeral drainages and promotes a higher mean valley spacing relative to cases in which tributaries do not form. Model results offer additional insights into the response of initially unincised landscapes to rapid base‐level drop and provide a preliminary basis for understanding how varying amounts of base‐level change influence valley network morphology. Copyright © 2015 John Wiley & Sons, Ltd.
Polybrominated diphenyl ethers and new polybrominated flame retardants in tree bark from western areas of China
Authors: Li Qiuxu , Jin Jun , Lu Yao , Li Guangyao , He Chang , Wang Ying , Li Peng , Hu Jicheng
Published: October 2015

Tree bark samples were collected from 15 sites across western China in 2013, and the polybrominated diphenyl ether (PBDE) and new polybrominated flame retardant (NBFR) concentrations in the samples were determined. The mean total PBDE concentration was 51.8 ng/g lipid weight, which was 85.2% to 99.4% lower than in Chinese eastern coastal areas and the E-waste recycling areas. The dominant PBDE congener was BDE209, and its mean concentration was 49 ng/g lipid weight. The mean 2,3,5,6-tetrabromo-p-xylene, pentabromobenzene, pentabromotoluene, and hexabromobenzene concentrations were 0.61 ng/g, 0.97 ng/g, 0.68 ng/g, and 0.68 ng/g lw, respectively. The PBDE and NBFR concentrations in the air at the sampling sites were estimated from the concentrations in the tree bark samples. The estimated mean total PBDE and total NBFR concentrations in air were 58.5 pg/m3 and 2.76 pg/m3, respectively. The sources of NBFR emissions were found to be different from the sources of PBDE emissions, as no relationship was found between the NBFR and PBDE concentrations, and it appeared that sources of measured hexabromobenzene, pentabromobenzene, and pentabromotoluene in tree bark in western China include industrial activity related to the aluminum industry. Environ Toxicol Chem 2016;35:1364–1370. © 2015 SETAC
Price Discovery in Thinly Traded Futures Markets: How Thin is Too Thin?
Authors: Adämmer Philipp , Bohl Martin T. , Gross Christian
Published: October 2015

It is still an unanswered question how much trading activity is needed for efficient price discovery in commodity futures markets. For this purpose, we investigate the price discovery process of two thinly traded agricultural futures contracts traded at the European Exchange in Frankfurt. Our empirical results show that the trading volume threshold which is necessary to facilitate efficient price discovery is very low. As our findings are based on constant and time‐varying vector error correction models, we also show that neglecting time‐variation in the parameters can lead to misleading results. © 2015 Wiley Periodicals, Inc. Jrl Fut Mark 36:851–869, 2016
The Ecological Impact of Conquest and Colonization on a Medieval Frontier Landscape: Combined Palynological and Geochemical Analysis of Lake Sediments from Radzyń Chełminski, Northern Poland
Authors: Brown Alex , Banerjea Rowena , Wynne Amanda Dawn , Stivrins Normunds , Jarzebowski Marc , Shillito Lisa‐Marie , Pluskowski Aleks
Published: October 2015

Slavic and German colonization of the southern Baltic between the 8th and 15th centuries A.D. is well‐documented archaeologically and historically. Despite the large number of pollen profiles from Poland, few palaeoecological studies have examined the ecological impact of a process that was central to the expansion of European, Christian, societies. This study aims to redress this balance through multiproxy analysis of lake sediments from Radzyń Chełminski, Northern Poland, using pollen, element geochemistry (Inductively Coupled‐Optical Emission Spectroscopy [ICP‐OES]), organic content, and magnetic susceptibility. The close association between lake and medieval settlements presents the ideal opportunity to reconstruct past vegetation and land‐use dynamics within a well‐documented archaeological, historical, and cultural context. Three broad phases of increasing landscape impact are visible in the pollen and geochemical data dating from the 8th/9th, 10th/11th, and 13th centuries, reflecting successive phases of Slavic and German colonization. This involved the progressive clearance of oak‐hornbeam dominated woodland and the development of an increasingly open agricultural landscape. Although the castles and towns of the Teutonic Order remain the most visible signs of medieval colonization, the palynological and geochemical data demonstrate that the major phase of woodland impact occurred during the preceding phase of Slavic expansion; Germans colonists were entering a landscape already significantly altered.
Geology of the Murcia Valley and Flood Plain Modifications in the Construction of the Circus Maximus, Rome, Italy
Authors: Carpentieri Elena , de Rita Donatella , Monica Giuseppe Della
Published: October 2015

This paper presents a morphological and hydrogeological reconstruction of the Murcia Valley at the location of the great Roman stadium Circus Maximus in Rome. We reconstruct a valley segment using ERT (electrical resistivity tomography) and geoarchaeological drilling data that identified three main layers. The basal layer, with high resistivity values and convex shapes, is correlated to alluvial gravel and lithified silt‐clay sediments. The middle layer shows low‐to‐medium resistivity values extending to concavities between the basal convex shapes. The very low resistivity values of this middle layer characterize elliptical to circular morphologies and have been ascribed to the presence of water‐saturated clay‐silt and peaty sediments. The surface layer is characterized by widespread lateral inhomogeneity interpreted as anthropogenic fill. The data indicate a pre‐Roman anastomosed alluvial plain subsequently modified by human intervention. In an effort to reclaim the valley for construction of the Circus, the Romans utilized the natural topography and created a central embankment, later becoming the Spina, by filling depressions with sand taken from adjacent bars. Our study contributes to (1) knowledge of the pre‐Roman landscape, (2) understanding anthropogenic modification of the Murcia Valley flood plain, and (3) archaeological interpretation of the monument.
Methyltransferase‐like 17 physically and functionally interacts with estrogen receptors
Authors: Du Peiyun , Yuan Bin , Cao Jia , Zhao Jing , Ding Lihua , Chen Lihan , Ying Sunyang , Jiang Lina , Lin Jiajia , Xu Xiaojie , Cheng Long , Ye Qinong
Published: October 2015

Estrogen exerts its physiological and pathological functions through two estrogen receptors (ERs), ERα and ERβ, which act as transcription factors. Coregulators, including coactivators and corepressors, have been shown to be crucial for regulation of ER transcriptional activity. Although many coregulators have been identified to regulate activities of ERs, novel coregulators are still needed to be investigated. Here, we show that human methyltransferase‐like 17 (METTL17), whose function is unknown, physically interacts with ERα and ERβ, and functionally acts as a coactivator for ERs. METTL17 interacts with ER in vitro and in yeast and mammalian cells. Activation function‐1 (AF1) and AF2 domains of ERs are responsible for the interaction between METTL17 and ERs. Knockdown of METTL17 reduces transcriptional activities of ERα and ERβ in breast cancer cells, whereas METTL17 overexpression increases ERα and ERβ transcriptional activities. Inhibition of METTL17 expression decreases mRNA and protein levels of ER target genes, including PR, cathepsin D, and pS2. Moreover, METTL17 knockdown reduces breast cancer cell growth. These results indicate that METTL17 is a novel coactivator of ERs and may play a role in breast tumorigenesis. © 2015 IUBMB Life, 67(11):861–868, 2015
Valproic acid sensitizes human glioma cells to gefitinib‐induced autophagy
Authors: Chang Cheng‐Yi , Li Jian‐Ri , Wu Chih‐Cheng , Ou Yen‐Chuan , Chen Wen‐Ying , Kuan Yu‐Hsiang , Wang Wen‐Yi , Chen Chun‐Jung
Published: October 2015

Autophagy and apoptosis represent important cellular processes involved in cancer cell killing mechanisms. Epidermal growth factor receptor inhibitor gefitinib and valproic acid have been implicated in the treatment of malignancies including glioma involving autophagic and apoptotic mechanisms. Therefore, it is interesting to investigate whether a combination of gefitinib and valproic acid shows better cancer cell killing effect on human glioma cells. We found that a nontoxic concentration of valproic acid sensitized U87 and T98G glioma cells to gefitinib cytotoxicity by inhibiting cell growth and long‐term clonogenic survival. The augmented consequences were accompanied by the formation of autophagic vacuoles, conversion of microtubule‐associated protein‐1 light chain 3‐II (LC3‐II), and degradation of p62. Autophagy inhibitor 3‐methyladenosine and chloroquine and genetic silencing of LC3 but not broad‐spectrum caspase inhibitor attenuated gefitinib/valproic acid‐induced growth inhibition. Gefitinib/valproic acid‐induced autophagy was accompanied by the activation of liver kinase‐B1 (LKB1)/AMP‐activated protein kinase (AMPK)/ULK1. Silencing of AMPK and ULK1 suppressed gefitinib/valproic acid‐induced autophagy and growth inhibition. Mechanistic studies showed that gefitinib/valproic acid increased intracellular reactive oxygen species generation and N‐acetyl cysteine attenuated gefitinib/valproic acid‐caused autophagy and growth inhibition. In addition to demonstrating the autophagic mechanisms of gefitinib/valproic acid, the results of this study further suggest that intracellular oxidative stress and the LKB1/AMPK signaling might be a potential target for the development of therapeutic strategy against glioma. © 2015 IUBMB Life, 67(11):869–879, 2015
Quantitative study of optical and mechanical bone status using multispectral photoacoustics
Authors: Steinberg Idan , Turko Nir , Levi Omri , Gannot Israel , Eyal Avishay
Published: October 2015

Osteoporosis is a major public health problem worldwide. Here, we present a quantitative multispectral photoacoustic method for the evaluation of bone pathologies which has significant advantages over pure ultrasonic or pure optical methods as it provides both molecular information and bone mechanical status. This is enabled via a simultaneous measurement of the bone's optical properties as well as the speed of sound and ultrasonic attenuation in the bone. To test the method's quantitative predictions, a combined ultrasonic and photoacoustic system was developed. Excitation was performed optically via a portable triple laser‐diode system and acoustically via a single element transducer. Additional dual transducers were used for detecting the acoustic waves that were generated by the two modalities. Both temporal and spectral parameters were compared between different excitation wavelengths and measurement modalities. Short photoacoustic excitation wavelengths allowed sensing of the cortical layer while longer wavelengths produced results which were compatible with the quantitative ultrasound measurements.

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Mitochondrial Dysfunction and Ca2+ Overload Contributes to Hesperidin Induced Paraptosis in Hepatoblastoma Cells, HepG2
Authors: Yumnam Silvia , Hong Gyeong Eun , Raha Suchismita , Saralamma Venu Venkatarame Gowda , Lee Ho Jeong , Lee Won‐Sup , Kim Eun‐Hee , Kim Gon Sup
Published: October 2015

Paraptosis is a programmed cell death which is morphologically and biochemically different from apoptosis. In this study, we have investigated the role of Ca2+ in hesperidin‐induced paraptotic cell death in HepG2 cells. Increase in mitochondrial Ca2+ level was observed in hesperidin treated HepG2 cells but not in normal liver cancer cells. Inhibition of inositol‐1,4,5‐triphosphate receptor (IP3R) and ryanodine receptor also block the mitochondrial Ca2+ accumulation suggesting that the release of Ca2+ from the endoplasmic reticulum (ER) may probably lead to the increase in mitochondrial Ca2+ level. Pretreatment with ruthenium red (RuRed), a Ca2+ uniporter inhibitor inhibited the hesperidin‐induced mitochondrial Ca2+ overload, swelling of mitochondria, and cell death in HepG2 cells. It has also been demonstrated that mitochondrial Ca2+ influxes act upstream of ROS and mitochondrial superoxide production. The increased ROS production further leads to mitochondrial membrane loss in hesperidin treated HepG2 cells. Taken together our results show that IP3R and ryanodine receptor mediated release of Ca2+ from the ER and its subsequent influx through the uniporter into mitochondria contributes to hesperidin‐induced paraptosis in HepG2 cells. J. Cell. Physiol. 231: 1261–1268, 2016. © 2015 Wiley Periodicals, Inc.
Long‐term operation of a two‐stage polyhydroxyalkanoates production process from hardwood sulphite spent liquor
Authors: Queirós Diogo , Fonseca Alexandre , Lemos Paulo C , Serafim Luísa S
Published: October 2015

BACKGROUND

The development of sustainable industrial processes demands the recovery and transformation of their by‐products. The production of polyhydroxyalkanoates (PHAs) by mixed microbial cultures (MMC) is one of the available routes. This study evaluated the possibility of applying a two‐step PHAs production process using an industrial by‐product, hardwood sulphite spent liquor (HSSL), as feedstock for a MMC. The first step consisted in the selection of PHAs‐storing microorganisms using an aerobic dynamic feeding strategy followed by a second step, accumulation.

RESULTS

The selected MMC, despite not being able to use the main carbon source of HSSL, lignosulphonates, revealed the capacity to consume acetate and xylose to accumulate poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) and glucose biopolymer. The maximum PHAs content was relatively low, 6.6%, with a maximum production yield of 0.49 C‐mmol HA C‐mmol S−1 during the selection stage.

CONCLUSION

A MMC was able to adapt to HSSL by consuming acetate and xylose. The imposed operational conditions resulted in a partial selection of the culture, since only acetate‐consuming organisms experienced a real feast/famine regime, resulting in low PHAs production. © 2015 Society of Chemical Industry
Reliability and mechanical durability tests of flexible OLED with ALD coating
Authors: Jimbo Yasuhiro , Tamatsukuri Yuki , Ito Minato , Yokoyama Kohei , Hirakata Yoshiharu , Yamazaki Shunpei
Published: October 2015

To improve the reliability and mechanical durability of a flexible organic light‐emitting diode display, the entire flexible display is coated with an aluminum oxide film by atomic layer deposition (ALD). Because the step coverage of ALD is excellent, the AlOx film was deposited not only on the front and back surfaces but also on the side surfaces of the display. A high‐temperature and high‐humidity preservation test, repetitive bending tests, and a pencil hardness test were conducted on the flexible display with ALD‐AlOx coating. The display survived 500 h of a 65°C, 95% preservation test, endured a 100,000‐time repetitive bending test with a curvature radius of 4 mm, and was found to have a pencil hardness of 4H.
Output Regulation in Differential Variational Inequalities using Internal Model Principle and Passivity‐Based Approach
Authors: Tanwani Aneel
Published: October 2015

We consider the problem of designing state feedback control laws for output regulation in a class of dynamical systems where state trajectories are constrained to evolve within time‐varying, closed, and convex sets. The first main result states sufficient conditions for existence and uniqueness of solutions in such systems. We then design a static state feedback control law using the internal model principle, which results in a well‐posed closed‐loop system and solves the regulation problem. As an application, we demonstrate how control input resulting from the solution of a variational inequality results in regulating the output of the system while maintaining polyhedral state constraints. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modal Analysis of Vehicle Power Trains
Authors: Haslinger Josef , Offner Günter , Sopouch Martin , Zinkiewicz Bianka
Published: October 2015

In this study, modal analysis of vehicle power trains is based on the linearization of the underlying equations of motions at specified time instants. The equations of motion represent a flexible multi‐body system where force‐elements (joints) connect different bodies. Whenever the linearization leads to an ordinary differential equation with constant coefficients, a standard eigenvalue procedure is used, to compute eigenvalues and mode shapes. The concept is applied to a vehicle power train. Comparison of the results with a commercial software product provide good agreement. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Real‐Time Simulation of Elastic Multibody Systems with Application in Vehicle Dynamics
Authors: Schmitt Alexander , Seifried Robert
Published: October 2015

Real‐time simulation models are widely used for vehicle development, usually built up as rigid multibody systems. However, since lightweight structures are commonly used, body deformation is no longer negligible and rigid multibody simulations may be inaccurate. This work presents a real‐time capable full vehicle model with a flexible car body, derived from a finite element model, whose performance has been improved by model order reduction. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Performance assessment of a trajectory‐tracking approach for a manipulator with uncertainties using inverse fuzzy arithmetic
Authors: Walz Nico‐Philipp , Hanss Michael
Published: October 2015

A trajectory‐tracking approach for a parallel kinematic manipulator with flexible links is investigated with respect to its robustness to undesired initial oscillations. For this purpose, an inverse fuzzy arithmetical scheme is presented and applied, in order to estimate allowable bounds on the initial conditions such that a certain tolerance band around the desired trajectory is not violated. The uncertainty bounds on the initial conditions obtained from this identification procedure indicate the influence of the disturbances on the tracking error, and thus also the robustness and the performance of the control scheme. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A numerical method for the servo constraint problem of underactuated mechanical systems
Authors: Yang Yinping , Betsch Peter , Altmann Robert
Published: October 2015

Servo constraints are used in inverse dynamics simulations of discrete mechanical systems, especially for trajectory tracking control problems [1], whose desired outputs are represented by state variables and treated as servo constraints [2]. Servo constraint problems can be classified into fully actuated and underactuated multibody systems, and the equations of motion take the form of differential algebraic equations (DAEs) including holonomic and servo constraints. For fully actuated systems, control inputs can be solved from the equations by model inversion, as the input distribution matrix is nonsingular and invertible. However, underactuated systems have more degrees of freedom than control inputs. The input distribution matrix is not invertible, and in contrast to passive constraints, the realization of servo constraints with the use of control forces can range from orthogonal to tangential [3]. Therefore, it is challenging for the determination of control inputs which force the underactuated system to realize the partly specified motion. For differentially flat underactuated systems, the differentiation index of DAEs may exceed three. Hence we need to apply specific index reduction techniques, such as the projection approach applied in [3], [4], and [6]. The present work applies index reduction by minimal extension [5] to differentially flat underactuated crane systems and shows that the index can be reduced from five to three and even to one. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Mechanics of cell‐division: A new continuum model for growth inhomogeneities
Authors: Bolea Albero Antonio , Böl Markus
Published: October 2015

The self‐reproduction ability of mitotic cells results in an increase of the number of cells with the same characteristics in living bodies. While cells grow in volume and divide themselves, the living body consequently grows in mass and volume. Further, if the factors which regulate the growth process are inhomogeneously distributed, growth takes place at different rates and directions. In this work we aim to provide a new continuum model for growing tissues. More specifically, the model considers the reorientation of the cell‐division plane in mitotic cells depending on the stress field of the growing body. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Computational simulation of piezo‐electrically stimulated bone remodeling surrounding teeth implant
Authors: Shirazi Beheshtiha Alireza , Nackenhorst Udo
Published: October 2015

Since the natural ligament responsible for the fixation of teeth in jawbone is destroyed when artificial replacements are implanted, the mechanical stimulation of the bone is reversed. Idea of this research project is the development of active implants which provide additional electrical stimulation for bone adaption. A new electromechanically driven bone remodeling theory will be developed and the osseointegration of bone implants has been simulated by means of bio‐active interface theory. The thin bone‐implant interface is described by the Drucker‐Prager plasticity model. Besides the consistent combination of electromechanical bone remodeling simulation, 3D‐finite element model of lower mandible has been reconstructed. As the micromotions at the implant‐abutment level are reported to be a major determinant of longterm implant success, the osseointegration process is limited by micromotion threshold. The applicability is indicated on a dental implant in order to optimize new developed techniques for activating implants with piezo‐electric coatings. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Application of a cohesive zone element for the prediction of damage in nano/micro coating
Authors: Rezaei Shahed , Wulfinghoff Stephan , Kebriaei Reza , Reese Stefanie
Published: October 2015

Many tools in production technology are nowadays coated to obtain a satisfactory lifetime and degradation resistance. Therefore, the main goal of this study is to investigate antiadhesive and wear resistant coatings made of ceramics, plastics and metals produced by High Power Pulsed Magnetron Sputtering (HPPMS) technique [1]. A cohesive zone element technique (CZ) is applied to model the interactions of the coatings and the substrate surfaces (see [2]). This goes along with the investigations of the delamination and failure behavior of the involved surfaces. To illustrate the applicability of the model, several structural simulations are performed. The developed CZ element model is capable of modeling the separation, the contact and also the irreversible reloading conditions in both normal and tangential directions [3]. The model is further developed to be applicable for different structures including different bonding behaviors, with a higher stability. The talk concludes with a detailed discussion of the numerical results of different material and interface properties. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Fitting stress intensity factors from crack opening displacements in 2D and 3D XFEM
Authors: Schätzer Markus , Fries Thomas‐Peter
Published: October 2015

The computation of stress intensity factors (SIFs) by crack opening displacements (CODs) is discussed in linear elastic fracture mechanics (LEFM) with stressfree crack surfaces, in the context of the extended finite element method (XFEM) and a hybrid explicit‐implicit crack description. Herein, the approximated CODs are compared with the expected openings for a pure mode I, II and III. The analytical modes are evaluated in a reference coordinate system, which is aligned with the (curved) crack surface and extracted from the implicit level‐set functions. This approach allows without any significant modifications, an intuitive and efficient computation of SIFs in 2D and 3D even of curved cracks. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A novel treatment of crack boundary conditions in phase field models of fracture
Authors: Strobl Michael , Seelig Thomas
Published: October 2015

In the phase field approach for fracture an additional scalar field is introduced in order to describe the state of the material between intact and fully broken. So far, for the loading dependent degradation of stiffness (damage) either the volumetric‐deviatoric split of strain [1, 2] or the spectral decomposition [3, 4] is used. In contrast to such an isotropic degradation of stiffness, the fully broken state represents a crack with a particular orientation. Both aforementioned approaches do not take the crack orientation into account. This may lead to the violation of the crack boundary conditions. In order to satisfy these conditions the phase field approach is modified here by taking the orientation of the crack into account. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optimization of two‐layered steel/aluminum hollow cylinders under combined load
Authors: Apatay Tunç , Mack Werner
Published: October 2015

Subject of the investigation is a two‐layered tube under generalized plane strain subject to a combination of internal pressure and an elevated temperature at the inner surface. Criterion for the permissible stress is the yield criterion by von Mises, and the elastic limits are given as well as a way for a straightforward optimization procedure in respect of the weight of the device is shown. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Shrink fit with FGM‐hub subject to heating and rotation
Authors: Arslan Eray , Mack Werner
Published: October 2015

Subject of the investigation is an elastically designed shrink fit with solid inclusion and functionally graded hub. It is shown that in case of radially decreasing density not only a saving of weight but also a considerably better performance at rotation may be achieved which predominates over a marginally worse evolution of the interface pressure with increasing temperature. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Frequency veering and mode degeneration of a rectangular disc
Authors: Brouet Francois , Twiefel Jens , Wallaschek Jörg
Published: October 2015

In typical applications as ultrasonic welding horns, the oscillators are designed to be driven in the longitudinal mode. Modal interactions occur at critical aspect ratios, resulting in a poor uniformity of the output surface and assessing the geometry as critical. In this contribution, a method is presented for a simple rectangular disc how to eliminate the modal interaction and decouple the longitudinal mode from other modes. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
T‐splines discretizations for large deformation contact problems
Authors: Dimitri Rossana , Zavarise Giorgio
Published: October 2015

A T‐spline‐based isogeometric analysis is applied to frictional contact problems between deformable bodies in the context of large deformations. The continuum is discretized with cubic T‐splines and cubic NURBS (Non‐Uniform Rational B‐Splines) for comparison purposes. A Gauss‐point‐to‐surface (GPTS) formulation is combined with the penalty method to treat the normal and friction contact constraints in the discretized setting. It is demonstrated that the proposed formulation combined with analysis‐suitable T‐spline interpolations, is a computationally accurate and efficient technology for local and global solutions of contact problems. T‐spline analysis models are generated using commercially available T‐spline modeling software without intermediate mesh generation or geometry clean‐up steps. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Flexure Hinge Mechanisms Modeled by Nonlinear Euler‐Bernoulli‐Beams
Authors: Friedrich Robert , Lammering Rolf
Published: October 2015

A flexure hinge is an innovative engineering solution for providing relative motion between two adjacent stiff members by the elastic deformation of an arbitrary shaped flexible connector. In the literature, modeling of compliant mechanisms incorporating flexure hinges is mainly focused on linear methods. However, geometrically nonlinear effects cannot be ignored generally. This study presents a nonlinear modeling technique for flexure hinges based on the Euler‐Bernoulli beam theory, in contrast to the predominant linear modeling approaches. Higher order beam elements of variable cross‐section are employed to model the flexure hinge region. A Newton‐Raphson scheme is applied to solve the resulting nonlinear system equations. The proposed approach reduces the overall degrees of freedom and is computationally efficient compared to commonly applied 3D finite element methods. A compliant displacement amplification mechanism is studied by means of the proposed method, where an excellent agreement with results of a reference solution is achieved. The modeling approach is suitable for the structural optimization of compliant mechanisms towards a less intuitive design process. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Fluid pressure penetration for advanced FEA of metal‐to‐metal seals
Authors: Gorash Yevgen , Dempster William , Nicholls William D. , Hamilton Robert
Published: October 2015

This numerical study investigates the behaviour of the contact faces in the metal‐to‐metal seal of a typical pressure relief valve in the commercial FE‐package ANSYS. The valve geometry is simplified to an axisymmetric problem, which comprises a simple representative geometry consisting of only three components. A cylindrical nozzle, which has a valve seat on top, contacts with a disk, which is preloaded by a compressed linear spring. Analysis considerations include the effects of the Fluid Pressure Penetration (FPP) across the valve seat which exists at two different scales. In‐service observations show that there is certain limited fluid leakage through the valve seat at operational pressures about 90% of the set pressure, which is caused by the fluid penetrating into surface asperities at the microscale. At the macroscale, non‐linear FE‐analysis using the FPP technique available in ANSYS revealed that there is also a limited amount of fluid penetrating into gap, which is caused primarily by the global plastic deformation of the valve seat. Accurate prediction of the fluid pressure profile over the valve seat is addressed in this study by considering the FPP interaction on both scales. The shape of this pressure profile introduces an additional component of the spring force, which needs to be considered to provide a reliable sealing. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Evaluation of a Finite Element Approach for Damping Determination
Authors: Hentschel Olaf Peter , Bonhage Marius , Panning‐von Scheidt Lars , Wallaschek Jörg
Published: October 2015

In this paper, a well‐known law for material damping description (see [1]) is verified. Thereby, material damping is characterized as a function of local stress amplitudes. To identify the resulting structural damping, a calculation of local stresses is necessary. In a first step, an analytical approach is used to calculate the damping on the basis of the stress distribution. In a second step, the local stress distribution of the described structure is calculated using a finite element approach. In this context, damping is calculated using the identified discrete stress values through the structure. By varying the mesh density, the resulting damping is compared to the calculated damping using the analytical results. Finally, it can be seen that the quality of the calculated damping value depends on the quality of the calculated stress value and therefore on the mesh density. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Experimental investigations on PP‐PE foil specimens
Authors: Sguazzo Carmen , Hartmann Stefan
Published: October 2015

In the present work, we present an experimental characterization of a thermoplastic copolymer made out of Polypropylene and Polyethylene (PP‐PE); a polymer that is, for example, used as a core material for layered sandwich composites. The rate‐dependence and the temperature‐dependence were investigated by means of tensile tests within the large deformation range and by shear tests. The experiments were monitored using a Digital Image Correlation (DIC) system. The main goal of the experimental campaign is related to the development of a constitutive model. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Predicting delamination in multilayered CFRP laminates accounting for different failure modes
Authors: Simon Jaan‐Willem , Höwer Daniel , Reese Stefanie
Published: October 2015

Carbon fiber reinforced plastics (CFRP) are mostly used in multilayered laminates, which consist of several very thin layers stacked over each other. For such laminated structures, delamination represents one of the most critical states of failure. In order to predict both the onset as well as the propagation of delamination, a cohesive zone‐like continuum damage model is proposed in this paper. This damage model is directly incorporated into a solid‐shell finite element with finite thickness. Further, the formulation is capable of considering the interaction of different failure modes. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the influence of vibrations on macroscopic frictional contacts
Authors: Hammerschmidt Antonia , von Wagner Utz
Published: October 2015

Ultrasonic vibrations in the micrometer amplitude range have been proven to be capable to influence frictional contacts with respect to decreasing friction coefficients in experiments on small test set‐ups solely loaded by their small weight [1]. In this paper experimental results on applying this effect to large objects are presented. To get large vibration amplitudes and velocities detailed pre‐investigation on the excitation of the structures in contact have been performed. These structures are investigated in a roller rig designed for these purposes. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the Effect of Contact Compliance on Vibrational Smoothing of Dry Friction
Authors: Kapelke Simon , Seemann Wolfgang
Published: October 2015

High‐frequency vibrations may be utilized in order to smooth the characteristics of dry friction at low sliding velocities and, consequently, quench undesired friction induced phenomena. Many studies have been published so far, most of them using classical Coulomb friction models and yielding compact results. Unfortunately, the agreement with related experimental results is insufficient. As the Coulomb model overestimates the smoothing effect, improved modelling seems to be necessary. Based on Dahl's friction model, the effect of longitudinal and transverse high‐frequency vibrations on a 1‐DoF‐friction oscillator is investigated here. Accounting for contact compliance, a reduction of the smoothing effect is observed. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Synchronization effects in rotors partly filled with fluid
Authors: Keisenberg Tobias , Ostermeyer Georg‐Peter
Published: October 2015

In fluid‐filled rotors self‐excited vibrations occur induced by a surface wave of the fluid. A characteristic property is the instability over the full range of angular velocity above the Eigenfrequency of the system. A possible explanation is the occurrence of synchronization effects between fluid and rotor.

The behaviour of rotors partly filled with fluid was mostly studied under the aspect of stability in steady‐state conditions. For non‐steady‐state investigations, discrete models with reduced number of degrees of freedom and reasonable ability to model the system behaviour are desirable due to the complexity of fluid modelling.

This paper analyses a simple minimal model and shows synchronization effects between fluid and rotor model. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Ductile failure with gradient plasticity coupled to the phase‐field fracture at finite strains
Authors: Aldakheel Fadi , Raina Arun , Miehe Christian
Published: October 2015

Most metals fail in a ductile fashion, i.e, fracture is preceded by significant plastic deformation. The modeling of failure in ductile metals must account for complex phenomena at micro‐scale, such as nucleation, growth and coalescence of micro‐voids. In this work, we start with von‐Mises plasticity model without considering void generation. The modeling of macroscopic cracks can be achieved in a convenient way by the continuum phase field approaches to fracture, which are based on the regularization of sharp crack discontinuities [1]. This avoids the use of complex discretization methods for crack discontinuities and can account for complex crack patterns. The key aspect of this work is the extension of the energetic and the stress‐based phase field driving force function in brittle fracture to account for a coupled elasto‐plastic response in line with our recent work [3]. We develop a new theoretical and computational framework for the phase field modeling of ductile fracture in elastic‐plastic solids. To account for large strains, the constitutive model is constructed in the logarithmic strain space, which simplify the model equations and results in a formulation similar to small strains. We demonstrate the modeling capabilities and algorithmic performance of the proposed formulation by representative simulations of ductile failure mechanisms in metals. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the variational formulation and implementation of Allen‐Cahn and Cahn‐Hilliard‐type phase field theories
Authors: Bartels Alexander , Mosler Jörn
Published: October 2015

Phase field theory is a promising framework for analyzing evolving microstructures in materials. Phenomena like those related to microstructures in Ni‐based superalloys, twin structures in martensites or precipitation in Al‐alloys can be predicted by phase field theory. While phase transformations such as those characterizing twinning are captured by an Allen‐Cahn‐type approach, a Cahn‐Hilliard‐type formulation is used, if the respective interface motion is driven by the concentration of the species. Although the Allen‐Cahn and the Cahn‐Hilliard formulation are indeed different, they do share some similarities. To be more precise, a Cahn‐Hilliard model is obtained by enforcing balance of mass in the Allen‐Cahn approach. Within an energy‐based formulation this can be implemented by adding additional energy terms to the underlying Allen‐Cahn energy. Such a universal energy‐based framework is elaborated in this presentation. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Micro‐macro modelling of fiber reinforced composites exhibiting elastoplastic deformation
Authors: Bedzra Rex , Simon Jaan‐W. , Stier Bertram , Reese Stefanie
Published: October 2015

Fiber reinforced plastics such as carbon fiber‐reinforced composites are typically characterized by their high siffness to weight ratio making them particularly attractive in lightweight construction. In addition, the architecture of these materials means that the correct modelling of their orthotropy is very important. In this work, volume averaged stress‐strain responses are generated from a micro representative volume element (RVE). A nonlinear macro constitutive material model accounting for anisotropic plasticity is proposed. The model is fitted and compared to the micro stress‐strain response. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Towards a finite element simulation of coating by means of thermal spraying
Authors: Berthelsen Rolf , Tomath Dennis , Denzer Ralf , Menzel Andreas
Published: October 2015

Metal sheet forming processes like deep drawing are applied in order to produce carriage parts in mass production. Therefore, forming tools are required that are well protected against wear. For such forming tools, wear resistant surfaces are, e.g., produced by thermal spraying of hard material coatings. The thermal spraying process itself is a highly transient thermo‐mechanical process. In order to gain a better understanding of the heat input and transfer during thermal spraying, a simulation framework for thermal spraying processes is presented. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Primary and secondary instabilities in soft bilayered systems
Authors: Budday Silvia , Andres Sebastian , Steinmann Paul , Kuhl Ellen
Published: October 2015

Wrinkling phenomena emerging from mechanical instabilities in inhomogeneously compressed soft bilayered systems can evoke a wide variety of surface morphologies. Applications range from undesired instabilities in engineering structures such as sandwich panels, via fabricating surfaces with controlled buckling patterns of unique properties, to wrinkling phenomena in living matter such as lungs, mucosas, and brain convolutions. While moderate compression evokes periodic sinusoidal wrinkles, higher compression induces secondary instabilities ‐ the surface bifurcates into increasingly complex morphologies. Periodic wrinkling has already been extensively studied, but the rich pattern formation in the highly nonlinear post‐buckling regime remains poorly understood. Here, we establish a computational model of differential growth to explore the evolving buckling pattern of a growing layer bonded to a non‐growing substrate. Our model provides a mechanistic understanding of growth‐induced primary and secondary instabilities. We show that amongst all possible secondary bifurcations, the mode of period‐doubling is energetically favorable. We experimentally validate our numerical results by examining buckling of a compressed polymer film on a soft foundation. Our computational studies have broad applications in the microfabrication of distinct surface patterns as well as in the morphogenesis of living systems, where growth is progressive and the formation of structural instabilities is critical to biological function. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)