bluuebunny/crossref_metadata_2025 huggingface dataset:
Cytoplasmic PML: From Molecular Regulation to Biological Functions
Authors: Jin Guoxiang , Gao Yuan , Lin Hui‐Kuan
Published: November 2013

The tumor suppressor promyelocytic leukemia protein (PML) is predominantly localized in the nucleus, where it is essential for the formation and stabilization of the PML nuclear bodies (PML‐NBs). PML‐NBs are involved in the regulation of numerous cellular functions, such as tumorigenesis, DNA damage and antiviral responses. Despite its nuclear localization, a small portion of PML has been found in the cytoplasm. A number of studies recently demonstrated that the cytoplasmic PML (cPML) has diverse functions in many cellular processes including tumorigenesis, metabolism, antiviral responses, cell cycle regulation, and laminopothies. In this prospective, we will summarize the current viewpoints on the regulation and biological significance of cPML and discuss the important questions that still need to be further answered. J. Cell. Biochem. 115: 812–818, 2014. © 2013 Wiley Periodicals, Inc.
Environmental changes in Baffin Bay during the Holocene based on the physical and magnetic properties of sediment cores
Authors: ST‐ONGE MARIE‐PIER , ST‐ONGE GUILLAUME
Published: November 2013

The physical and magnetic properties of four long sediment cores (HU2008‐029‐034PC, ‐038PC, ‐042PC and ‐070PC) sampled in Northern (Smith Sound and Jones Sound) and Eastern (Disko Bugt) Baffin Bay were analysed to reconstruct the Holocene environmental changes in Baffin Bay. Radiocarbon dating of each core revealed sedimentation rates of up to 136 cm ka−1. Except for specific intervals, magnetic properties and ratios reveal that the magnetic remanence is mostly carried by magnetite and that changes in magnetic grain size and concentration are indicative of environmental variations associated with ice‐rafted debris, sea‐ice, meltwater pulses or terrigenous inputs. These variations indicate that all four cores, which cover a period from 12 360 cal a BP to the present, have sedimentary facies that correspond to the major climatic changes of the Holocene: deglaciation and the climatic optimum. In addition, two cores (HU2008‐029‐038PC and ‐070PC) present the signal of two climatic events with a local influence during the Neoglacial period.
Evaluation of capecitabine and oxaliplatin administered prior to and then concomitant to radiotherapy in high risk locally advanced rectal cancer
Authors: Gao Yuan‐Hong , An Xin , Sun Wei‐Jiang , Cai Juan , Cai Mu‐Yan , Kong Ling‐Heng , Lin Jun‐Zhong , Liu Guo‐Chen , Tang Jing‐Hua , Wu Xiao‐Jun , Chen Gong , Pan Zhi‐Zhong , Ding Pei‐Rong
Published: November 2013

Background and Objectives

Systemic failure remains a predominant issue in locally advanced rectal cancer (LARC). A new strategy using capecitabine and oxaliplatin (XELOX regimen) administered prior to and then concomitant to radiotherapy for high risk LARC is developed in our practice. The aim of the present study was to evaluate the short‐term efficacy and toxicities of this strategy.

Methods

Patients were treated with one cycle XELOX regimen (oxaliplatin 130 mg/m2 on day 1 with capecitabine 1,000 mg/m2 twice daily for 14 days every 3 weeks), followed by chemoradiation (50 Gy over 5 weeks) with modified XELOX regimen (oxaliplatin dose reduction to 100 mg/m2), and total mesorectal excision. Tumor response, toxicities, and surgical complications were recorded.

Results

Forty‐two patients treated with the strategy were identified. All patients completed planned dose of induction chemotherapy and concurrent chemoradiotherapy. Grade 3 toxicities were thrombocytopenia (4.8%), diarrhea (7.1%), proctitis (4.8%), and radiation dermatitis (7.1%). Five patients (12.5%) developed postoperative complications. Pathologic complete response (pCR) and nearly pCR were achieved in 7 (15.0%) and 13 patients (35.0%).

Conclusions

The preliminary results suggest that induction chemotherapy followed by chemoradiotherapy with capecitabine and oxaliplatin in LARC is well tolerated. The strategy achieves favorable short term outcome in terms of pCR and nearly pCR rate, which warrants further investigation. J. Surg. Oncol. 2014 109:478–482. © 2013 Wiley Periodicals, Inc.
Nationwide survey of the outcomes of living donor liver transplantation for hepatoblastoma in Japan
Authors: Sakamoto Seisuke , Kasahara Mureo , Mizuta Koichi , Kuroda Tatsuo , Yagi Takahito , Taguchi Tomoaki , Inomata Yukihiro , Umeshita Koji , Uemoto Shinji
Published: November 2013

Recently, liver transplantation (LT) has been increasingly performed for unresectable hepatoblastoma (HB) with acceptable results. We conducted a national survey of cases undergoing living donor liver transplantation (LDLT) for HB to evaluate their outcomes. Thirty-nine patients (28 males and 11 females with a median age at LDLT of 3.6 years) who had undergone LDLT for HB by the end of 2009 were enrolled in this study. The clinical data were collected from their medical records via a questionnaire survey in 2011 (median follow-up = 4.6 years). Thirteen patients (33.3%) had extrahepatic lesions before LDLT. Thirty-eight patients (97.4%) received chemotherapy, and 15 (38.5%) underwent hepatectomy before LDLT. Twenty-seven patients (69.2%) were alive without recurrence after LDLT, and 12 patients (30.8%) suffered from recurrence. The most common site of recurrence was the lung (9 cases), which was followed by the graft liver (6 cases). The median interval from LDLT to recurrence was 5.5 months. Four of the 9 cases (44.4%) with lung metastasis underwent surgical resection, and 3 were alive without any tumor recurrence. Eight patients died because of tumor recurrence. The multivariate landmark analysis revealed that the independent recurrence risk factors were a high alpha-fetoprotein (AFP) level at diagnosis [≥500,000 ng/mL; hazard ratio (HR) = 7.86, P = 0.010], the presence of extrahepatic lesions before LDLT (HR = 3.82, P = 0.042), and a high AFP level at LDLT (≥4000 ng/mL; HR = 9.19, P = 0.036). The actuarial 3- and 5-year patient survival rates were 84.3% and 77.3%, respectively. In conclusion, with appropriate timing for scheduled LT, LDLT provides a valuable alternative treatment with excellent results for children with HB. Liver Transpl 20:333-346, 2014. © 2013 AASLD.
Convenient Synthesis of a Polyester‐co‐Polyether Block for Assembling Biocompatible Hyperbranched Macromolecules
Authors: Elkin Igor , Hildgen Patrice
Published: November 2013

Synthesis of a novel multifunctional block based on asymmetrically substituted pentaerythritol, succinic acid, and tetraethylene glycol is reported. The proposed reaction conditions allow selective preparation of the product in high overall yield. The block can be used in the assembly of biocompatible polyester‐co‐polyether (PEPE) hyperbranched macromolecules, which allows the product to be considered as a promising intermediate for the development of new biomedical dendrimers. As an example, the use of the “block by block” strategy is employed to obtain a second‐generation dendron. It is shown that the approach is much more efficient than the pathway of step‐by‐step grafting of separate molecular fragments.

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Micron‐Sized Polymer Particles by Membrane Emulsification
Authors: Simons J.M.M. , Keurentjes J.T.F. , Meuldijk J.
Published: November 2013

Dispersions of micron‐sized styrene droplets in water were produced by straight through microchannel arrays. The monomer droplets have been polymerized by suspension polymerization using an initiator system, which was only oil soluble. A significant amount of submicron particles was formed by secondary nucleation. The side reaction was emulsion polymerization, which was confirmed by the molecular weight distribution of the reaction product. Suppression of secondary nucleation was only partially possible by using the water soluble inhibitor NaNO2. Increasing the monomer to water ratio before polymerization resulted in less emulsion polymerization. Molecular weight was found to be strongly dependent on the initiator concentration as well as on the inhibitor concentration. It was demonstrated that polymer particles with a diameter of about 10 μm can be produced using emulsification of the monomer by microchannel arrays prior to polymerization.
Quantification of Colour Formation in PET Depending on SSP Residence Time, Temperature, and Oxygen Concentration
Authors: Rieckmann Thomas , Besse Katharina , Frei Fabian , Völker Susanne
Published: November 2013

A systematic approach was carried out to quantify the discolouration of different poly(ethylene terephthalate) (PET) samples such as virgin bottle‐grade resins, bottle‐to‐bottle recycled chips, and bottle‐to‐bottle recycled flakes. The PET samples were treated in a fixed bed reactor in the solid‐state. The possible influencing parameters such as residence time, temperature, and oxygen partial pressure were studied by analysing the CIELAB b*‐coordinate (axis = yellow to blue) with a spectrophotometer at the end of the experiment. The PET samples were analysed once as chips respectively flakes retained from the experiments and again as plates obtained from a following standardised melting procedure. The combination of experiments and literature review results in the proposal of different discolouration mechanisms, which are influenced by temperature, residence time, and oxygen concentration. Using the design of experiments (DoE) approach, a mathematical model was compiled that can be used to predict the yellowing of the different PET grades.
A Theoretical and Experimental Kinetic Investigation of the ROP of L,L‐Lactide in the Presence of Polyalcohols
Authors: Karidi Konstantina , Pladis Prokopios , Kiparissides Costas
Published: November 2013

The present work deals with the experimental and theoretical investigation of the ring‐opening polymerization of L,L‐lactide with stannous octoate as a catalyst for the production of high molecular weight polymers with improved physical and mechanical properties. The polymerization of L,L‐lactide was experimentally studied at various temperatures and different monomer to initiator concentration ratio values. Subsequently, co‐initiators with different number of hydroxyl groups (i.e., 1,4‐butanediol, glycerol, di‐trimethylolpropane and polyglycidol) were utilized to obtain branched or star shaped polymers. A comprehensive mathematical model was developed based on a detailed kinetic mechanism to predict the dynamic evolution of monomer conversion and molecular weight averages (i.e., Mn, Mw of PLLA). The predictive capabilities of the mathematical model are demonstrated by a direct comparison of model predictions with literature and new experimental data on monomer conversion as well as number and weight average molecular‐weight of PLLA.
Microencapsulation of Fragrance and Natural Volatile Oils for Application in Cosmetics, and Household Cleaning Products
Authors: Tekin Rumeysa , Bac Nurcan , Erdogmus Huseyin
Published: November 2013

In this study, polyurethane‐urea microcapsules containing fabric softener fragrance (TeddysoftTM, by EPS) as active agents were produced by interfacial polymerization. Size, shape and morphology of the microcapsules were studied by using an optical microscope and scanning electron microscope. The effectiveness of the fragrance containing microcapsules was tested by washing hand towels in a commercial washing machine. Textile impregnation and the durability of the fragrance impregnation effect were evaluated qualitatively by perfumers, and by headspace GC analysis. Optical and scanning electron microscopic results indicated that increasing the stirring rate during the emulsion step results in microcapsules with smaller particle size, but at some point morphologies were adversely affected.
Specialised tools for a better comprehension of olefin polymerisation reactors
Authors: McKenna Timothy F.L. , Boisson Christophe , Monteil Vincent , Ranieri Elena , Tioni Estevan
Published: November 2013

2 laboratory‐scale reactor systems suitable for gas phase, and for solution or slurry polymerisations are discussed. The underlying concept behind the design and use of these reactors is that they can be used to understand the impact of conditions specific to different time scales and/or length scales inherent to large reactors that are difficult to recreate at the laboratory scale. For instance the fixed bed gas phase reactor is used to study the influence of different relative gas/solid velocities on the evolution of the molecular weight distribution of the nascent polymer. It is shown that in certain conditions, changing the heat transfer characteristics does not change the observed yield, but will impact the polymer properties. In the case of the solution reactor, the concept is to design and use a reactor to study the activation of unsupported metallocenes. Here it is shown that different metallocenes have very different activation profiles to a point where a stopped flow reactor might not be the ideal tool for their study.
Properties of Smart‐Scaled PTFE‐Tubular Reactors for Continuous Emulsion Polymerization Reactions
Authors: Lueth Fabian Gabriel , Pauer Werner , Moritz Hans‐Ulrich
Published: November 2013

This article presents a novel design of smart scale PTFE tubular reactor systems for continuous polymerization reactions. To optimize the flow pattern, CFD calculations and RTD experiments were done. These results led to an unique tube geometry combined with a specialized arrangement of static mixers. A comparison of heat transfer properties of two different types of tubular reactors shows the feasibility of using PTFE instead of stainless steel as reactor construction material. The versatility of the operation modes is demonstrated for emulsion copolymerization experiments with the same recipe but at the different modes.
Polyolefin Composite Synthesis: From Small Scale to kg Material
Authors: Scheel Saskia , Rosehr André , Poeppel Artur , Luinstra Gerrit A.
Published: November 2013

Polyolefin composites were prepared by the in situ polymerization technique. Experiments were performed with mixtures of aluminum silicates and multi walled carbon nanotubes as fillers in 1 L reactors. The mixture of fillers was sonicated in toluene solution before polymerization, leading to a more stable dispersion in the solvent. Scale up to 10 L reactions gives access to kg material with well‐dispersed filler in polypropylene. The thermal properties (Tm, Tc) of the composite are basically unchanged to polypropylene without filler, like the crystallinity is.
Semi‐Batch Copolymerization of Propylene Oxide and Carbon Dioxide
Authors: Nörnberg Benjamin , Spottog Carmen , Rahlf Anne , Korashvili Revaz , Berlin Claas , Luinstra Gerrit A.
Published: November 2013

A nanoscopic heterogeneous catalyst system based on zinc glutarate is used to prepare poly(propylene carbonate) (PPC) from CO2 and propylene oxide (PO). The catalyst was exposed to a defined humid atmosphere. The water uptake resulted in a deactivation to a minimum of 25% of the original activity, depending on time of exposure and water concentration. In addition, the progress of the copolymerization at constant pressure was monitored by measuring the CO2 uptake. It is shown that the rate is linear with time after an initial phase and that this rate is in linear correlation with the amount of catalyst. The copolymerization was also performed in several modes of discontinuous addition of PO. The productivity of the catalyst was in the range of 1.6–2.0 kg PPC/g Zn, the highest productivity reported for the zinc carboxylate catalyst system so far. High molecular weights of around 220 kg/mol (Mw) and low polydispersities of 2.2–2.5 were achieved in all experiments.
Curcumin promotes exosomes/microvesicles secretion that attenuates lysosomal cholesterol traffic impairment
Authors: Canfrán‐Duque Alberto , Pastor Óscar , Quintana‐Portillo Rocío , Lerma Milagros , de la Peña Gema , Martín‐Hidalgo Antonia , Fernández‐Hernando Carlos , Lasunción Miguel A. , Busto Rebeca
Published: November 2013

Scope

Exosomes/microvesicles are originated from multivesicular bodies that allow the secretion of endolysosome components out of the cell. In the present work, we investigated the effects of curcumin, a polyphenol, on exosomes/microvesicles secretion in different cells lines, using U18666A as a model of intracellular cholesterol trafficking impairment.

Methods and results

In both HepG2 hepatocarcinoma cells and THP‐1 differentiated macrophages, treatment with curcumin affected the size and the localization of endosome/lysosomes accumulated by U18666A, and reduced the cholesterol cell content. To ascertain the mechanism, we analyzed the incubation medium. Curcumin stimulated the release of cholesterol and the lysosomal β‐hexosaminidase enzyme, as well as the exosome markers, flotillin‐2 and CD63. Electron microscopy studies demonstrated the presence of small vesicles similar to exosomes/microvesicles in the secretion fluid. These vesicles harbored CD63 on their surface, indicative of their endolysosomal origin. These effects of curcumin were particularly intense in cells treated with U18666A.

Conclusion

These findings indicate that curcumin ameliorates the U18666A‐induced endolysosomal cholesterol accumulation by shuttling cholesterol and presumably other lipids out of the cell via exosomes/microvesicles secretion. This action may contribute to the potential of curcumin in the treatment of lysosomal storage diseases.
Mathematical Modeling of NMRP of Styrene–Divinylbenzene over the Pre‐ and Post‐Gelation Periods Including Cyclization
Authors: Aguiar Leandro G. , Gonçalves Miguel A. D. , Pinto Virgínia D. , Dias Rolando C. S. , Costa Mário Rui P. F. N. , Giudici Reinaldo
Published: November 2013

Nitroxide‐mediated polymerization of styrene‐divinylbenzene has been modeled using generating functions of length distributions, pseudo‐kinetic propagations, and numerical fractionation with the crosslinking rate depending on generation. Cyclization reactions are tackled by balances of sequences, yielding fair predictions of the measured pendant double bond concentration. With reduction in crosslinking, agreement for the experiments at 90 °C between predicted and measured weight‐average, molecular weight, and weight fraction of gel is observed. A much higher relative crosslinking reactivity is observed at 130 °C as compared to 90 °C, likely an effect of the chain mobility.
Fractional order hybrid system dynamics
Authors: (Stevanović) Hedrih Katica R.
Published: November 2013

Dynamics of multi deformable bodies coupled by standard light fractional order discrete continuum layers is described by coupled partial fractional order differential equations. A mathematical analogy and phenomenological mapping between generalized coordinates of fractional order discrete chain systems and eigen time functions correspond to one of infinite numbers of eigen amplitude functions of dynamics of multi deformable bodies (beams, plates or membranes) coupled by standard light fractional order discrete continuum layers are identified. Eigen fractional order vibration modes are approximately determined analytically and graphically presented. A number of theorems is defined and proofed. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modeling of the dynamic phenomena “stick‐slip” and “whirl” of a drill string demonstrator
Authors: Ostermeyer Georg‐Peter , Kueck Armin
Published: November 2013

Vibrations of drill strings in oil and gas well bores can reduce drilling performance or lead to damage of drill string components. These vibrations are neither optically observable nor measurable because of the geological formation. Hence usually simulations are used to understand the dynamic behavior. The test stand “OSTrator” adds more insight to this problem. The demonstrator represents a scaled drill rig granting direct access to the complex dynamic behavior of the real drill string. Two phenomena are of special interest: the stick‐slip effect, a torsional oscillation, and the whirl effect, a periodic torsional‐lateral movement with permanent wall contact. Since the OSTrator was built for showcase purposes, it has to be piloted in and out Stick‐Slip and Whirl domains by a control algorithm. Therefore efficient multi‐body‐systems able to represent these two effects in faster than real time are demanded. In this presentation, the modeling of the stick‐slip and the whirl effect are discussed. The models should be able to predict these effects and supply data to avoid or confront them. Key questions are the modeling of the wall contact and the resistance at the drill bit. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Discrete Element Approach for Wave Propagation in Thin Rods
Authors: Stühler Sven , Fleissner Florian , Seifried Robert , Eberhard Peter
Published: November 2013

Wave propagation and evoked side effects, such as material failure, are important parts of analysis of dynamically exposed structures like buildings or machinery. One of the numerical analysis tools for wave propagation is the well‐known Finite Element Method (FEM) with its impressive performance but also with the drawback of not being able to model easily material failure, discontinuities and contacts. In contrast, the Discrete Element Method (DEM) is capable to describe these effects on a meso‐scale more easily. The here selected concept is based on a DEM particle which is considered as deformable, and can establish and remove lasting bonds with other particles. The simulation example used is a thin rod that has been an extensive numerical and experimental research subject since the last century. A longitudinal wave is excited within the thin rod by simulating an impact on one end of the rod in a free‐free configuration. It is found, that the simulation data, the velocity profile and the resulting displacement at the end of the rod, are in good agreement with experimental obtained data. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Development of a miniature robot based on experience that is inspired by nature
Authors: Stevanović Ilija , Rašuo Boško
Published: November 2013

In this paper, using nature as inspiration, micro robot is designed. Utilizing the basic principles of the biological systems motion and modern software tools Matlab Simulink and SolidWorks a mathematical analysis and simulation of its mechanism for movement are developed. It will be shown that the Bionics along with use of modern software can be a powerful engineering tool. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the mechanics of fluid‐like growth in solid materials
Authors: Bolea Albero Antonio , Böl Markus
Published: November 2013

Living materials can change in mass and volume depending on the availability of nutrients and on its mechanical environment. During growth phenomena, even with mechanical properties as solids, some living materials present fluid‐like characteristics. Bodies with such behaviour can be deformed as elastic bodies under the application of loads and constrains. However, their growth can be described as the flow of the new material contribution as these loads and constrains do not let the body grow in an isotropic way. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Towards modelling the dynamics of a 3D continuum‐mechanical two‐muscle musculoskeletal system
Authors: Sprenger Michael , Schmitt Syn , Röhrle Oliver
Published: November 2013

Computational expenses restrict the usage of continuum mechanics in modelling (parts of) the musculoskeletal system, although, continuum mechanics would provide the possibility to represent the complex mechanical behaviour of a muscle‐tendon complex (MTC). This work provides an overview on a modelling framework, which aims to achieve forward‐dynamics simulations of musculoskeletal systems by coupling three‐dimensional continuum‐mechanical‐based finite element simulations to rigid‐body simulations based on a simplified two‐muscle upper arm model. Here, the focus is on implementing a sophisticated representation of the skeletal MTC and tissue‐bone interaction. The three‐dimensional continuum‐mechanical description of the skeletal muscle is described within the framework of finite elasticity. To model the MTC, two additional parameters are introduced providing the possibility to describe muscle tissue, tendon tissue, and soft tissue within one set of constitutive equations. Further, a realistic fibre orientation for the skeletal muscles and contact mechanics between the muscles and the bones is considered. For different elbow flexion angle positions, the muscles' mechanical state is compared with and without considering contact mechanics. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Porous‐media simulation of bone‐cement spreading during vertebroplasty
Authors: Wagner Arndt , Bleiler Christian , Stadelmann Vincent , Windolf Markus , Gueorguiev‐Rüegg Boyko , Köstler Harald , Boger Andreas , Röhrle Oliver , Ehlers Wolfgang
Published: November 2013

The reinforcement of porous vertebral cancellous bone by the injection of bone cement is a practical procedure for the stabilisation of osteoporotic compression fractures and other weakening lesions. This contribution concerns the reproduction and prediction of the resulting bone‐cement distribution during the injection procedure by means of numerical simulation. A detailed micromechanical (locally single‐phasic) model exhibits the drawback that all geometrical and physical transition conditions of the individual parts of the complex aggregate have to be known. Therefore, we rather proceed from a macroscopic (and multi‐constituent) continuum‐mechanical model based on the Theory of Porous Media. In this regard, the homogenisation of the underlying micro‐structure results in a model of three constituents: these are the solid bone skeleton, which is saturated by the liquid bone marrow that may be displaced by the injected liquid bone cement. The influence of the micro‐architecture of the pore space on the spreading of the bone cement is considered by a spatial diversification of the anisotropic permeability tensors, obtained through image processing techniques applied to medical imaging data (µCT). The numerical investigation of the strongly coupled problem enables the study of vertebroplasty and allows for the comparison between the simulation results and the experimentally determined bone‐cement distribution that were imaged during injections. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A parametric study on creep‐fatigue endurance of welded joints
Authors: Gorash Yevgen , Chen Haofeng
Published: November 2013

This work is devoted to parametric study on creep‐fatigue endurance of the steel AISI type 316N(L) weldments defined as type 3 according to R5 Vol. 2/3 procedure at 550°C. The study is implemented using a novel direct method known as the Linear Matching Method (LMM) and based upon the creep‐fatigue evaluation procedure considering time fraction rule for creep‐damage assessment. Seven geometrical configurations of the weldment, which are characterised by individual values of a geometrical parameter ρ, are proposed. Parameter ρ, which represents different grades of TIG dressing, is a ratio between the radius of the fillet of the remelted metal on a weld toe and the thickness of welded plates. For each configuration, the total number of cycles to failure N* in creep‐fatigue conditions is assessed numerically for different loading cases including normalised bending moment $\tilde{M}$ and dwell period Δt. The obtained set of N* is extrapolated by the analytic function dependent on $\tilde{M}$, Δt and ρ. Proposed function for N* shows good agreement with numerical results obtained by the LMM. It is used for the identification of Fatigue Strength Reduction Factors (FSRFs) effected by creep and dependent on Δt and ρ. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
3D finite elements to model electromechanical coupled solids at failure
Authors: Linder Christian
Published: November 2013

This work presents an extension of newly developed 3D finite elements to model failure in purely mechanical based materials [1, 2] to electromechanical coupled materials. Following the approach suggested in [6] for the plane setting, new finite elements are developed, which in addition to resolving strong discontinuities in the mechanical displacement field are capable of modeling strong discontinuities in 3D also in the electric potential. An application to a 3D off‐centered three point bending test under combined mechanical and electrical loading outlines the performance of the newly developed finite elements. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The XFEM with an Implicit‐Explicit Crack Description for a Plane‐Strain Hydraulic Fracture Problem
Authors: Weber Nikolai , Fries Thomas‐Peter
Published: November 2013

The Extended Finite Element Method (XFEM) with an implicit‐explicit crack description is used to solve a plane‐strain hydraulic fracture problem. In its typical form, a hydraulic fracture problem combines the physical processes of fluid flow, solid deformation, and fracture propagation. The crack is described implicitly using three level‐sets to evaluate enrichment functions and to locate the enriched region. Additionally, an explicit crack description is used to update the crack during propagation. This approach is applied to a partially fluid‐filled crack in an semi‐infinite elastic solid without leak off and compared to the reference solution given in the literature. The results for the crack opening, pressure and crack length for various values of the fluid fraction are in good agreement with the analytical solutions. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Dual‐mixed variational formulation and hp finite element method for axisymmetric shell problems in elastodynamics
Authors: Tóth Balázs
Published: November 2013

A new dimensionally reduced axisymmetric shell model is presented briefly for modeling time‐dependent problems. This is based on the extended version of the three‐field dual‐mixed variational formulation of elastostatics [1, 2] to linear elastodynamics, the independent fields of which are the non‐symmetric stress tensor, the displacement‐ and the rotation vector. An important property of the related shell model is that the classical kinematical hypotheses regarding the deformation of the normal to the shell middle surface are not used, i.e., unmodified three‐dimensional constitutive equations are applied. The computational performance of the new h‐ and p‐version axisymmetric shell finite elements is tested through a representative cylindrical shell problems. The development presented in this paper has been motivated by the fact that efficient dual‐mixed hp plate and shell finite elements were managed previously to be developed for elastostatics by [1‐5]. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
An improved modeling approach for circular flexure hinges with application to geometry optimization
Authors: Friedrich Robert , Lammering Rolf
Published: November 2013

Within this paper, a modeling approach for flexure hinges based on the Euler‐Bernoulli beam theory for beams of variable cross section is investigated in a static analysis. The proposed approach is implemented in a finite beam element routine, for which two different discretizations are discussed. The results are compared to a full scale three dimensional model. It is shown that a circular flexure hinge cannot be modeled accurately with one element. An improved model with three elements across the flexure hinge length is presented which shows excellent accordance with the reference model. A geometry optimization is realized based on the improved, low‐DOF model. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Isogeometric Collocation: Cost Comparison with Galerkin Methods and Extension to Adaptive Hierarchical NURBS Discretizations
Authors: Schillinger Dominik , Evans John A. , Reali Alessandro , Scott Michael A. , Hughes Thomas J.R.
Published: November 2013

Collocation is based on the discretization of the strong form of the underlying partial differential equations, which requires basis functions of sufficient order and smoothness. Consequently, the use of isogeometric analysis (IGA) for collocation suggests itself, since splines can be readily adjusted to any order in polynomial degree and continuity required by the differential operators. In addition, they can be generated for domains of arbitrary geometric and topological complexity, directly linked to and fully supported by CAD technology. The major advantage of isogeometric collocation over Galerkin type IGA is the minimization of the computational effort for numerical quadrature. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the Wellbore Contact of Drill Strings in a Finite Element Model
Authors: Shi Minzhe , Srisupattarawanit Tarin , Schiefer Frank , Ostermeyer Georg‐Peter
Published: November 2013

In drill string dynamics the Finite Element Method is usually applied to models of very long drill strings in a wellbore with arbitrary curvature. Taking account of geometrical constraint between the drill string and the wellbore, a high density of nodes is necessary. This density is much higher than the one needed to describe the natural vibrations properly, so this firstly leads to an extension of the computing time. A penalty function is frequently utilized to describe the contact problem between the drill string and the wellbore where the contact normal force acts only on the nodal points of the drill string. It was recognized that only node‐to‐surface contact models cannot fulfill this geometrical constraint, because the segment between two nodal points deeply penetrates the wellbore wall in some cases. A process with Gaussian points along the segment in time domain will be introduced, so that the drill string will be described according to this geometrical constraint with good accuracy but with a smaller density of nodes and less computing time. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modeling of the Wear Particle Flow in Tribological Contacts
Authors: Tergeist Mathias , Müller Michael , Ostermeyer Georg‐Peter
Published: November 2013

The dynamics of tribological systems with pronounced memory effects are characterized by the complex coupling of mechanical, thermal, and chemical processes. At the Institute of Dynamics and Vibrations in Braunschweig, Cellular Automata have been developed that facilitate the evaluation of dynamics in technically relevant systems within a reasonable time. The flow of wear material is decisive for the formation, localization, and reconstitution of load‐bearing structures or films. In this paper, two opposed frictional contacts are chosen exemplarily for the investigation of the wear particle flow: a vehicle brake system and the sanding of wood. For this purpose, a modeling technique is proposed that is based on established force laws for micro particles and differentiates mechanisms of transport for different phases of the particle movement. The resulting transport of a single particle interacting with the topology of the frictional gap is analyzed for varying particle properties and process parameters. In a second step the insights are transferred to a set of rules for a Cellular Automaton which allows for quick evaluation and the incorporation of coupled effects. The validity and quality of the model transfer are discussed. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Algorithmic Consistency in Computational Inelasticity – a Conceptual Completion
Authors: Eidel Bernhard , Stumpf Felipe , Schröder J.
Published: November 2013

This paper communicates a new algorithmic concept, how higher‐order Runge‐Kutta (RK) methods for time integration of viscoelastic constitutive laws can be introduced into nonlinear finite element methods in order (i) to obtain the full nominal order p in time integration, (ii) to ensure that global equilibrium is only required at the end of time intervals Δt but not in the interior at RK‐stages, and (iii) to obtain –based on (i) and (ii)– a considerable speed‐up compared with Backward‐Euler. The condition to realize (i)–(iii) is, that the approximation of total strain in time must be of the same order as the time‐integration method, which is a completion of the concept of algorithmic consistency in computational inelasticity. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Phase‐field simulation of the electro‐mechanical response of ferroelectrics during Piezoresponse Force Microscopy
Authors: Thai Huy , Keip Marc‐André , Schröder Jörg
Published: November 2013

The contribution adresses the simulation of ferroelectric matrials in the framework of the Piezoresponse Force Microscopy (PFM). Based on the PFM, ferroelectric domain structures can be analyzed in great detail by measuring the electrically induced mechanical deformations of the surface of a ferroelectric. We employ a flexible continuum‐mechanical model based on the phase‐field method in order to analyze the behavior of ferroelectric microstructures numerically. Since ferroelectric materials are often highly anisotropic, the phase‐field formulation will account for transversely isotropic symmetry. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On Molecular Statics Simulation of Ferroelectric Barium Titanate
Authors: Endres Florian , Steinmann Paul
Published: November 2013

The present contribution deals with the atomistic modelling of ferroelectric barium titanate. In this context a core‐shell model is implemented in a Molecular Static algorithm. Furthermore, Coulomb forces are simulated by the Wolf summation method in order to allow for a small cut off radius. We discuss the core‐shell model, molecular statics as a finite elements approach and present some numerical results. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Computational modeling of shape memory fibers in conforming and non‐conforming compound structures
Authors: Kohlhaas Benedikt , Klinkel Sven
Published: November 2013

In this work a material model for shape memory alloy (SMA) fibers is presented. A constitutive model is provided which aims for computational use. The presented model incorporates all relevant material nonlinear phenomena. It takes pseudoplasticity into account as well as pseudoelasticity and further the shape memory effect (SME). The constrained SME (CSME) and the two‐way SME are covered by the presented material model. The constitutive model is implemented in a one‐dimensional truss formulation and in a 3D‐rebar element. Both formulations are used to model fiber composite structures. Those are described by the use of a non‐conforming and a conforming mesh on the mesoscale. The numerical examples show the capability of the formulation. Different meshing strategies for the fiber–matrix compound are discussed. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the absence of a preferred configuration in constitutive relations of finite strain elasto‐plasticity
Authors: Shutov A. V. , Ihlemann J.
Published: November 2013

There exists a large variety of different techniques used to generalize the Prandtl‐Reuss relations of small strain elasto‐plasticity to finite strains. Obviously, any systematic study of such generalization techniques should be based on some sound principles. In this work, one aspect is taken into account, concerning arbitrary isochoric change of the local reference configuration. We analyze some models of finite strain elasto‐plasticity in order to find out if the specific choice of the reference configuration can affect the predicted stress response. For material models which remain invariant under the reference change, no preferred reference configuration exists. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Liquefaction in fluid‐saturated soils
Authors: Schenke Maik , Markert Bernd , Ehlers Wolfgang
Published: November 2013

Liquefaction phenomena can be observed if fluid‐saturated soils are subjected to transient loading conditions, as they arise, for instance, during earthquakes. The term “liquefaction” comprises more specific liquefaction phenomena, such as flow liquefaction, which is an instability phenomenon in loose soils, and cyclic mobility, which is associated with medium‐dense to dense soils, where, in contrast to flow liquefaction, the overall stability of the granular assembly is maintained. However, soil liquefaction is always associated with a pore‐pressure build‐up, which consequently reduces the intergranular frictional forces, and thus, the load bearing capacity of the fluid‐saturated soil. In order to model these particular liquefaction phenomena, we proceed from a continuum‐mechanical framework based on the Theory of Porous Media (TPM), where the solid skeleton is described as an elasto‐(visco)plastic material with isotropic hardening and a stress‐dependent failure surface. The numerical solution of the resulting coupled system of partial differential equations is carried out by the finite‐element method (FEM). (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Multi‐Mechanism Model for Cutting Simulations Combining Visco‐plastic Asymmetry and Phase Transformation
Authors: Cheng Chun , Mahnken Rolf , Uhlmann Eckart , Ivanov Ivan Mitkov
Published: November 2013

We develop a multi‐mechanism model for strainrate‐ and temperature‐dependent asymmetric plastic material behavior accompanied by phase transformations, which are important phenomena in steel production processes. To this end the well‐known Johnson‐Cook model is extended by the concept of weighting functions, and it is combined with a model of tranformation‐induced plasticity (TRIP) based on Leblond's approach. The bulk model is formulated within a thermodynamic framework at large strains, and it will be specialized and applied to cutting processes in steel production. In the examples parameters are identified for the material DIN 100Cr6, and we illustrate the characteristic effects of our multimechanism model, such as strain softening due to temperature, rate dependence and temperature dependence as well as the SD‐effect. A finite‐element simulation illustrates the different mechanisms for a cutting process. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Implicit stress integration method of Shape Memory material model
Authors: Dunić Vladimir , Slavković Radovan , Busarac Nenad , Slavković Vukašin , Živković Miroslav
Published: November 2013

The phenomenological SMA material model proposed by Lagoudas [1] is modified and implemented in finite element software PAK [2]. Critical thermodynamic force is derived to match implicit integration method. All variables are derived to depend on effective values of stress, strain and martensitic volume fraction. One scalar equation need to be solved in the integration point using trial stress direction for each time step. The integration in the trial deviatoric stress direction provides possibility to solve large strain problems using the algorithms developed for small strains. Two one‐dimensional and one non‐proportional large strain example verified accuracy of proposed modifications. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the wear of brake pads
Authors: Ren Haichuan , Ostermeyer Georg‐Peter
Published: November 2013

Within measurements of brake pads on the IDS high load Tribometer, the wear of pads was investigated by a new non‐contact wear measurement under low normal pressures and low temperatures. The first results show that the wear of the pad in the sliding friction is nearly proportional to the friction work, and inversely proportional to the shear strength. The results are also interpreted by the adhesion theory of friction and Archard's equation. On the basis of further interpretations of shear strength and extension of adhesion theory of friction, the wear is derived as a piecewise linear function, which can evaluate explicitly the effect factors of wear and relative correlations at different pressures and different temperatures. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Mixed Variational Principles and Robust Finite Element Design of Gradient Plasticity at Finite Strains
Authors: Aldakheel Fadi , Mauthe Steffen , Miehe Christian
Published: November 2013

The modeling of size effects in elastic‐plastic solids, such as the width of shear bands or the grain size dependence in polycrystals, must be based on non‐standard theories which incorporate length‐scales. This is achieved by models of strain gradient plasticity, incorporating spatial gradients of selected micro‐structural fields which describe the evolving dissipative mechanisms. The key aspect of this work is to provide a rigorous incremental variational formulation and mixed finite element design of additive finite gradient plasticity in the logarithmic strain space. We start from a mixed saddle point principle for metric‐type plasticity, which is specified for the important model problem of isochoric plasticity with gradient‐extended hardening/softening response. To this end, we propose a novel finite element design of the coupled problem incorporating a local‐global solution strategy of short‐ and long‐range fields. This includes several new aspects, such as extended Q1P0‐type and MINI‐type finite elements for gradient plasticity [4]. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On a Deformation‐Driven Continuum‐Related Parrinello‐Rahman Molecular Dynamics
Authors: Ulz Manfred H.
Published: November 2013

Investigations into the atomistic‐to‐continuum coupling are recently pursued in literature. A hierarchical modelling in terms of a macroscale treated by continuum mechanics and the microscale governed by statistical mechanics may be a very fruitful combination. If the microscale is simulated with the help of molecular dynamics, the isostress‐isoenthalpic ensemble as proposed by Parrinello and Rahman presents a beneficial choice. This statistical ensemble is remarkable as the equations of motion are derived from a Lagrangian. Recently, this Lagrangian was situated into a continuum mechanics setting. This paper investigates the behavior of this continuum‐related Lagrangian in a kinetics‐driven setting (by imposing an external stress) and a kinematics‐driven setting (by imposing the shape of the molecular dynamics cell) in terms of a numerical example. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Inverse analysis of a non‐linear viscous fluid based on dissipated energy measured with a simple‐shear rheometer
Authors: Abali B. Emek , Müller Wolfgang H. , Georgievskii D. V.
Published: November 2013

Oscillatory rheometer measurements are used to determine the material parameters of a NEWTONian fluid model, which can be expressed by a linear constitutive relation. However, rheological materials, such as polymer melts, mixture of oils, or food paste, can only be modeled as non‐NEWTONian fluids by using non‐linear constitutive relations. Since the rheometer measures the energy loss in the induction motor due to shear loading of the viscous material, this can be used as the objective function for a regression analysis. The dissipated energy will be obtained as outlined in [1]. The goal of this work is to explain how to determine the parameters of a non‐linear material model by using the energy loss that is measured in a rheometer. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Some Remarks on the Numerical Solution of a Strain Gradient Plasticity Theory
Authors: Bayerschen Eric , Wulfinghoff Stephan , Böhlke Thomas
Published: November 2013

A one‐dimensional strain gradient plasticity model is reviewed in the context of Finite Element Method (FEM) solvability. It is found that under certain conditions specified the resulting system of two coupled partial differential equations in space and time leads to a symmetric global stiffness matrix. This is achieved upon standard weak form approach and yields a favorable system for an efficient numerical solution. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)