bluuebunny/crossref_metadata_2025_split huggingface dataset:
Bioinspired Nanotubes from Self‐Assembly of a Linear l,d‐Oligopeptide‐Poly(ethylene glycol) Conjugate
Authors: Punzi Pasqualina , Santis Serena De , Giordano Cesare , Diociaiuti Marco , Novelli Federica , Masci Giancarlo , Scipioni Anita 
Published: December 2014

The preparation and structural organization of a new bioinspired nanomaterial are investigated. A hybrid conjugate is obtained by end‐linking a linear octapeptide with regular alternating enantiomeric sequence to poly(ethylene glycol). This conjugate is able to self‐assemble, forming well‐defined nanorods having core/shell morphology with an internal peptide single channel that has, for the first time, been clearly visualized by transmission electron microscopy (TEM) images. It is remarkable that well‐defined cylindrical nanoparticles can be formed starting from a linear oligopeptide, the synthesis of which is significantly easier than that of the homologous cycles. In addition, the synthetic strategy and the structure of the conjugate ensure a controlled and regular pegylation of the aggregates and high density PEG blocks in the corona, making the nanoparticles more resistant to phagocytosis and able to prevent biofouling. Such features, along with biocompatibility and stability, make these nanoparticles promising candidates for drug delivery.
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Concentric rings K‐space trajectory for hyperpolarized 13C MR spectroscopic imaging
Authors: Jiang Wenwen , Lustig Michael , Larson Peder E. Z. 
Published: December 2014

PurposeTo develop a robust and rapid imaging technique for hyperpolarized 13 C MR Spectroscopic Imaging and investigate its performance.MethodsA concentric rings readout trajectory with constant angular velocity is proposed for hyperpolarized 13C spectroscopic imaging and its properties are analyzed. Quantitative analyses of design tradeoffs are presented for several imaging scenarios. The first application of concentric rings on 13C phantoms and in vivo animal hyperpolarized 13C MR Spectroscopic Imaging studies were performed to demonstrate the feasibility of the proposed method. Finally, a parallel imaging accelerated concentric rings study is presented.ResultsThe concentric rings MR Spectroscopic Imaging trajectory has the advantages of acquisition timesaving compared to echo‐planar spectroscopic imaging. It provides sufficient spectral bandwidth with relatively high efficiency compared to echo‐planar spectroscopic imaging and spiral techniques. Phantom and in vivo animal studies showed good image quality with half the scan time and reduced pulsatile flow artifacts compared to echo‐planar spectroscopic imaging. Parallel imaging accelerated concentric rings showed advantages over Cartesian sampling in g‐factor simulations and demonstrated aliasing‐free image quality in a hyperpolarized 13C in vivo study.ConclusionThe concentric rings trajectory is a robust and rapid imaging technique that fits very well with the speed, bandwidth, and resolution requirements of hyperpolarized 13C MR Spectroscopic Imaging. Magn Reson Med 75:19–31, 2016. © 2015 Wiley Periodicals, Inc.
Funnel control for electrical circuits
Authors: Berger Thomas , Reis Timo 
Published: December 2014

AbstractWe study the zero dynamics and funnel control for linear passive electrical circuits. We show that asymptotic stability of the zero dynamics can be characterized by criteria on the circuit topology. Thereafter we consider the output regulation problem for electrical circuits by funnel control. We show that for circuits with asymptotically stable zero dynamics, the funnel controller achieves tracking of a class of reference signals within a pre‐specified funnel. This result can be relaxed to the case of non‐autonomous zero dynamics by requiring the reference trajectory to evolve within a certain subspace. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Efficient Reduction Method based on Trial Vector Derivatives for Nonlinear Transient Analysis of Multilayer Sheet Structures
Authors: Pichler Florian , Witteveen Wolfgang 
Published: December 2014

AbstractFor the dynamic response of multilayer sheet structures it is important to take nonlinear contact and friction forces between the layers into account. The nonlinearities inside the joints can significantly influence the dynamic behavior of the entire structure. For the dynamic analysis of such structures conventional computational approaches have an unbalanced ratio between computational time and accuracy. In order to overcome this problem, so‐called “Joint Interface Modes” (JIMs) are used. These JIMs, which are problem‐oriented trial vectors, extend the reduction base of classical trial vector based reduction methods. In this contribution a new calculation approach for JIMs based on trial vector derivatives is introduced. The result quality of the presented method is comparable to the direct finite element method but the computational effort is extremely low due to model order reduction. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Contact Modeling in Multibody Systems with Elastic Bodies in High‐Frequency Applications
Authors: Schulze Sebastian , Sextro Walter , Grüter Frank 
Published: December 2014

AbstractThis paper discusses the refinement of multibody models by integration of flexible bodies and by considering nonlinearities from contacts. It presents common approaches for contact modeling in multibody simulations and strategies to include flexible bodies. A contact model is implemented in the elastic multibody model. Experimental results show that significant effects of system dynamics can be modeled by use of a multibody model including elastic bodies and contacts. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Variational Integrators for Thermomechanical Coupled Dynamic Systems with Heat Conduction
Authors: Kern Dominik , Bär Sebastian , Groß Michael 
Published: December 2014

AbstractVariational integrators are modern time‐integration schemes based on a discretization of the underlying variational principle. They thus skip the direct formulation and time discretization of partial differential equations. In mechanics, Hamilton's Principle is approximated by an action sum whose variation should be equal to zero, resulting in discrete Euler‐Lagrange Equations or equivalently in discrete Position‐Momentum Equations. Variational integrators are, by design, structure preserving (symplecticity) and show excellent long‐time behavior. In order to consider the coupling between mechanical and thermal quantities, Hamilton's principle is extended by using the notion of thermacy as thermal analogue to mechanical displacements. From this variational formulation, a variational integrator using the generalized trapezoidal rule is constructed exemplarily. A thermoelastic double pendulum with heat conduction serves as a model problem. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Multibody dynamics with unilateral constraints and friction
Authors: Charles Alexandre , Ballard Patrick 
Published: December 2014

AbstractIn the view of robotics or granular media mechanics, we ask for the statement of the dynamical evolution problem for multibody systems with contacts and friction. The “event driven” approach does not allow to state an evolution problem in a systematic way: it gives a peculiar status to the instants of impact and to the contact points although they are unknowns of the problem. This matter of fact has given rise to a new approach in the frictionless case [4, 6] we generalize to the case including friction. Following to the point of view of Lagrange on the equation of the dynamics, we emphasize the systematic use of virtual powers and duality. This bias suggests to put emphasis on generalized reaction forces in the statement of the evolution problem and not on local reaction forces of the real world. This point of view allows to escape from pathologies e.g. Painlevé paradox [5] and Kane Paradox [3]. The proposed evolution problem accounts for impacts and friction in case of multiple unilateral constraints. We prove the existence and uniqueness of the solution to the associated rate problem. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Evaluation of the adjoint sensitivity analysis for the identification of multibody system parameters
Authors: Oberpeilsteiner Stefan , Steiner Wolfgang 
Published: December 2014

AbstractIn the context of multibody simulation (MBS) system parameter identification within acceptable time can be challenging. One main difficulty is the huge amount of degrees of freedom in multibody systems and therefore the large number of dependent variables. The present work deals with the evaluation of different approaches that can be applied to typical parameter identification problems in MBS. A very powerful possibility is given by the adjoint sensitivity analysis that allows to reduce the computation effort dramatically. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Possibilities and Challenges in Kinematic Modeling of Highly Redundant, Non‐Holonomic and Omnidirectional Mobile Robots
Authors: Stöger Christoph , Gattringer Hubert , Mayr Johannes 
Published: December 2014

AbstractIndustry as well as the private domain show an increasing interest to the field of mobile robotics. With a higher number of applications, the complexity of the required tasks rises, and therefore the community tends to use robots with many degrees of freedom (DOF). The present paper takes this topic up and focuses on challenges of the kinematical modeling of redundant, non‐holonomic mobile robots by considering a 12 DOF platform. To reach an omnidirectional behaviour, the actuated wheels are diagonally mounted on the chassis. Well known problems resulting from this set‐up are parametric singularities which unnecessarily restrict the motion of the mathematical model. As it turns out, this problem can be avoided by the use of a non‐minimal parametrized model. An additional challenge results from the inverse kinematic (IK) problem on velocity level. The corresponding equations are highly underdetermined and, due to the non‐holonomic wheels, not directly affected by the steering angle velocities. This problem is solved by performing a local optimization on acceleration level. Finally, simulation results are presented. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Self‐Locking in Systems of Multiple Bodies
Authors: Brumme Stephan , Tergeist Mathias , Ostermeyer G.‐P. 
Published: December 2014

AbstractThe phenomenon of self‐locking can be found in many technical applications and common machine parts, such as screws, chocks, and funnels. Despite this, research into this topic is mostly limited to specific applications (e.g., worm gears, screws, kinematic chains). Current works with a general scope are rare. This paper addresses the analysis of self‐locking in different, two‐dimensional, multibody systems, and shall contribute towards a more general analysis. To elaborate on the characteristics of self‐locking, the effect is first shown and explained using simple systems as examples. From these examples, an approach towards a generalized description of self‐locking is proposed, which is used as a foundation for the development of two identification methods. The analysis of the self‐locking mechanism in multibody systems is realized first through an analytical ansatz, and then using a numerical simulation of the examples shown. The analytical and numerical analyses of the systems deliver a criterion, and respectively an algorithm, which enables the identification of self‐locked assemblies in different systems of multiple bodies. The algorithm is designed to identify self‐locking during integration of the equations of motion, whereas the analytic criterion is formulated for static systems with known, increasing external loads. The results of the two analysis methods correspond very well for the given example systems, leading to the conclusion that both methods are equivalent and usable. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Evolution of the Fiber Density in Biological Tissues
Authors: Topol Heiko , Demirkoparan Hasan 
Published: December 2014

AbstractAn important challenge in the field of biomechanics is to understand and to model the properties of fibrous tissues. We consider a matrix‐fiber composite for which the matrix microstructure and its mechanical properties are taken to be constant. The initial fiber distribution is assumed to be unstructured and the mechanical properties of the fibers evolve during deformation. Further we assume that the fiber creation rate is constant while the fiber degeneration is stretch‐dependent. In particular, this study investigates the change of the fiber orientation density when a sudden simple shear is applied to the material. The fiber orientation density depends on the current deformation, the history of the deformation, and the deformation state of the fibers at the time of their creation. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On growth effects in the human liver
Authors: Werner Daniel , Ricken Tim , Holzhütter Hermann‐Georg , König Matthias , Dahmen Uta , Dirsch Olaf 
Published: December 2014

AbstractFatty liver is a common disease in the western society. Different stimuli, such as obesity or abuse of alcohol, cause the liver to store fat within liver cells, the so called hepatocytes. This growth induced by storage of fat influences the perfusion of the overlying structures, i. e. sinusoids, liver lobules, liver lobes, and consequently the liver itself. The scales of these structures reach from few µm (size of a hepatocyte) to several cm (size of liver). In view of finite element (FE) simulations, the necessity of introducing different scales becomes obvious. For the description of growth effects in the liver the relevant quantities are: perfusion of the liver and amount of substances that are needed for production of fat (glycogen and fatty acids). In this work we present a multiphasic continuum mechanical model for the description of micro‐perfusion in the liver lobule using a homogenized multiphasic approach based on the theory of porous media (TPM). Into this model we inserted a zero‐dimensional (0D) kinetic model calculating rates of all relevant substances. So far, the model focuses on the time dependent and spatial zonation of glycogen, since production of fat heavily depends on the stored glycogen. Additionally, a possible method for incorporating fatty acids and therefor also growth will be presented. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Cellular articular cartilage replacement tissues: Modeling and analysis
Authors: Shehadeh Mohammad , Zhou Bei , Stoffel Marcus , Markert Bernd 
Published: December 2014

AbstractLong‐term studies reveal that mechanical stimulation causes growth and remodeling phenomena within biological tissues. The main aim of this research is to fully understand and control these phenomena. For accomplishing that, two steps are considered: first, we determine a suitable numerical model based on different approaches by a comparative study using experimental validations, and second, investigate the mechanical properties of the tissue specimens after a remodeling process.We start with the first step by choosing a convenient model that mimics the biotissue for running the numerical simulations in the second step. There are different models available that determine the mechanical properties of soft replacement tissues seeded with human chondrocytes in modern medical applications. It is our objective to achieve a common methodology of theory and experiments that allows the determination of the mechanical properties of the native material. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the multi‐component modelling of human brain tissue to survey clinical interventions
Authors: Wagner Arndt , Ehlers Wolfgang 
Published: December 2014

AbstractSerious diseases within the brain's tissue often require a medical intervention, such as the treatment of brain tumours. The present contribution aims at predicting the expected impacts of a scheduled clinical procedure via numerical simulations based on a sophisticated constitutive model. The enormous complexity of the tissue's microscopic composition encourages the application of the Theory of Porous Media (TPM), providing a well‐suited way to model the brain's tissue aggregate in a compact manner on the macroscale. In particular, a multi‐component model is used which is strongly related to the drug‐delivery problem within the brain's tissue, cf. [2]. In this model, the solid skeleton is given by the tissue cells (with cell content) and the vascular walls. This solid skeleton is perfused by two mobile but basically separated pore‐liquid constituents, the blood and the overall interstitial fluid constituent. To provide the particular description of administered therapeutic agents within the overall interstitial fluid, this real mixture is treated as a chemical solution of two components. These are the liquid solvent and the dissolved therapeutic agent (drug). Numerical examples demonstrate the applicability of the derived model. In particular, infusions of therapeutics into the extra‐cellular space (ECS) are simulated under various conditions and complemented by an evaluation of the local numerical sensitivity to survey the influence of certain involved parameters. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical crack path prediction considering orthotropic effects and experimental verification
Authors: Judt Paul , Ricoeur Andreas , Linek Günter 
Published: December 2014

AbstractFor a reliable prediction of crack paths, on the one hand the accurate calculation of crack tip loading quantities is inevitable, on the other hand orthotropic features of the fracture toughness need to be taken into account. The interplay of crack tip loading and material response due to fracture is still unclear and seems to have a crucial effect on crack path predictions. Numerical tools for the accurate calculation of crack tip loading quantities using path‐invariant J‐integrals and interaction integrals (I‐integral) are presented. Here, global approaches are beneficial when considering crack tips approaching other crack faces or internal boundaries. Curved crack faces have to be taken into account and special treatment regarding crack face integrals is necessary. Experimental investigations are carried out at standard CT‐specimens of rolled aluminum alloy Al‐7075 exhibiting a directional orthotropy of the fracture toughness. Considering that property, the numerically predicted crack paths based on FE calculations show very good agreement with subcritically grown paths obtained from experiments. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical simulations of spalling tests in order to investigate material properties of UHPC
Authors: Dally T. , Reppel T. , Weinberg K. 
Published: December 2014

AbstractIn order to evaluate the material composition of Ultra High Performance Concrete (UHPC), material properties such as dynamic tensile strength or fracture strength and also the fracture energy under impact loading are of significant importance. The use of a modified Hopkinson Bar enables the determination of the required data. On the basis of experimental investigations our contribution deals with the numerical finite element simulation of the Hopkinson Bar test. The propagation of stress waves is reproduced by means of a special time‐integration scheme. We simulate the propagation of cracks by using adaptive cohesive elements including a corresponding separation law. The critical energy release rate (Griffith‐energy) is calculated and compared to the values determined by experimental results. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Fracture toughness investigations on UHPC by spalling tests
Authors: Khosravani M.R. , Wagner P. , Frohlich D. , Trettin R. , Weinberg K. 
Published: December 2014

AbstractUltra High Performance Concrete (UHPC) is defined as a new generation of concrete which shows improved performance and higher strength than traditional concrete. This allows to realize slender and much more durable structures and in this way significantly reduces the required resources. Despite its huge potential in construction, technical information about this new type of material is still limited. This contribution presents investigations on the dynamic mechanical behavior and properties of UHPC specimens by spalling experiments. Two different recipes were used to compare the properties. Due to the special specimen geometry (slender cylindrical) a flowable consistency was required to enable a sufficient degassing of the mixtures.For the test, a Split Hopkinson Pressure Bar (SHPB) has been modified and used. A high speed photograph system was focused on the fragmentation process during the test. On the basis of these experiments the dynamic E‐moduli as well as the dynamic tensile strength of the UHPC specimens were determined. By observation of the specific crack patterns on each tested specimen and corresponding times, the dynamic fracture energy is calculated.Numerical simulations also were performed and compared to the experimental result. It is concluded that the dynamic tensile strength of the UHPC increases at higher strain rates. The results of the current study provide technical information about fracture and dynamic behavior of UHPC and the obtained values could be used for future computational models. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Lifetime prediction of a rocket combustion chamber wall by a viscoplastic damage model
Authors: Fassin Marek , Tini Vivian , Vladimirov Ivaylo , Reese Stefanie 
Published: December 2014

AbstractRegeneratively cooled nozzle structures of Reusable Launch Vehicles (RLV) belong to the most critical components of a space shuttle main engine. The so‐called doghouse effect is a failure mode in the rocket combustion chamber wall, which has been observed experimentally. Within the Collaborative Research Centre SFB‐TR 40 of the German Research Foundation (DFG), new technologies for the future space‐transport‐systems are being developed. By using a new continuum mechanical approach, motivated by a rheological model, we are able to reproduce the doghouse effect. Moreover we intend to give reliable lifetime predictions for rocket combustion chamber structures so that in future components can be tested virtually instead of conducting real experiments. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A FEM model for lifetime prediction of Ancorsteel1000C in rolling contact fatigue
Authors: Özden U.A. , Giang N.A. , Chen G. , Bezold A. , Broeckmann C. 
Published: December 2014

AbstractAncorsteel1000C is commonly used for important components including bearing rollers, gears, connecting rods, wheels and rails; most failures of these components are caused by rolling contact fatigue (RCF). In this study the fatigue damage indicator based on Fatemi‐Socie critical plane were determined in a local hot spot area in finite element (FE) model in case of Hertzian stress with zero slip condition. The simulation results compared with respect to experimental data, which is in good agreement. Therefore, this approach can be implemented as a useful tool for lifetime calculations in RCF in the process of structure fatigue design. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Damage modelling and lifetime prediction of adhesively bonded joints under sustained loading with constant and variable amplitudes
Authors: Kroll Ulrich , Matzenmiller Anton 
Published: December 2014

AbstractThe lifetime of adhesively bonded joints under service loading is predicted by a linear viscoelastic traction–separation model, which is enhanced by an isotropic damage approach. Therefore, a scalar damage variable is defined according to the concept of effective stresses based on the hypothesis of strain equivalence in the framework of continuum damage mechanics. The damage evolution is driven by a specific equivalent stress, adapted for ductile adhesives. Experimental data acknowledge the validity of the proposed model for the lifetime prediction of adhesive joints. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)