bluuebunny/crossref_metadata_2025_split huggingface dataset:
Finite Element Methods for Elasticity with Error‐Controlled Discretization and Model Adaptivity
Authors: Stein Erwin , Olavi Rüter Marcus 
Published: December 2017

AbstractThe essential topics of classical and advanced adaptive finite element methods (FEMs) for linear and finite elastic deformations of solids and structures are presented in this chapter from both the mechanical and mathematical point of view.As the mechanical and mathematical basis, nonlinear and linearized theories of elasticity are derived in a rigorous way, followed by the classical variational principles of elasticity, which are the basis for FEM, derived for classical and advanced Ritz–Galerkin methods, such as the extended finite element method (XFEM) and the meshfree reproducing kernel particle method (RKPM). Next to the discrete (one‐field) Dirichlet minimization principle, the (two‐field) Hellinger–Reissner stationary dual‐mixed principle and the (three‐field) Hu–Washizu stationary mixed principle are presented, including the main features of the associated FEMs.The main objective of this chapter is the systematic treatment ofa posteriorierror estimators and their applications to bothverification, that is, efficient mesh and particle adaptivity in order to achieve optimal convergence rates for the discretized solutions with prescribed error tolerances, andvalidation, that is, error‐controlled model adaptivity combined withverification.In the framework ofverification, linearized and finite elasticity problems are treated, using both energy‐norm and goal‐orienteda posteriorierror estimators for mesh‐based and meshfree methods. The four basic classes, that is, residual‐type, hierarchical‐type, gradient averaging‐type, and constitutive equation error estimators are presented and applied, for example, to fracture mechanics problems.A challenging topic in the framework ofvalidationis error‐controlled expansive hierarchical modeling of 2D thin‐walled elastic plates and shells to 3D‐elastic continua by dimensional adaptivity of the underlying mathematical models, especially in subdomains with boundary layers and other disturbances where model expansion is necessary for validation.
Elastoplastic and Viscoplastic Deformations in Solids and Structures
Authors: Armero Francisco 
Published: December 2017

AbstractThis chapter presents a summary of some recent developments in the formulation and the numerical integration of elastoplastic and viscoplastic models of solids and structures. A brief description of the constitutive relations in these models in both the infinitesimal and finite deformation ranges is presented first. A key aspect of the elastoplastic models is the yield condition constraining the stress state to the so‐calledelastic domain, with the viscoplastic models resulting in a regularization of this unilateral constraint. This constrained character of the problem leads naturally to the traditional return‐mapping algorithms used in the numerical integration of the local plastic evolution equations. The resulting discrete equations correspond to the so‐calledclosest‐point projectionequations by which an elastic trial state is projected onto the elastic domain. The mathematical structure of these equations is studied to obtain efficient numerical techniques for their solution. In particular, the rich variational structure of the associated problem is investigated in detail. Primal and dual variational formulations are derived for the elastoplastic and viscoplastic models. Both lead to unilaterally constrained elastoplastic problems reflecting the underlying constrained physical system. Augmented Lagrangian extensions of these formulations resulting in unconstrained forms of the discrete equations, both in their primal and dual versions, are also explored. The different numerical algorithms associated with each of these formulations, referred generically as closest‐point projection (CPPM) algorithms, are presented in detail for a general plastic model, not necessarily associated.
Shakedown and Safety Assessment
Authors: Zouain Nestor 
Published: December 2017

AbstractThe main subjects of this chapter are the variational formulations for the computation of a safety factor in shakedown analysis, the numerical procedures available to implement this analysis, and an overview on the wide field of applications and conceptual extensions.In structural engineering and solid mechanics, the wordshakedown, introduced in the 1940s by Prager, became, since then, synonymous with elastic adaptation in the presence of variable loadings, a safe stabilized phenomenon, often due to some limited plastic deformation (or equivalently, due to the residual stress distribution associated with inelastic strains).Concerning the failure analysis of ductile structures, the termsalternating plasticity(AP) andincremental collapse(IC), besidesplastic collapse, are also widely used to identify failure modes under variable loadings. A structure undergoesAPwhen the fluctuating loading program produces, after any arbitrarily large time, some plastic deformation as well as a subsequent vanishing of the net plastic deformation. This induces failure due to low‐cycle fatigue. Likewise, the structure fails byICwhen plastic deformations accumulate in the form of a compatible strain distribution that leads to excessive inelastic deformation.Shakedown analysis allows working under the realistic assumption that only the range of variable loadings is known, unlike the usual prescription of a particular loading history. That is, we deal in this chapter withdirect methodsthat are based solely on the knowledge of a range of load variations (or a reference loading, in limit analysis). It is worth emphasizing that the differences between incremental and direct methods go beyond the computational advantages frequently obtained with the latter ones. In fact, the fundamental questions about whether or not critical loads or cycles do exist, independently from loading histories, can only be answered by the theories of direct methods.The mathematical foundations of shakedown theory strongly rest on optimization theory and the related areas of convex analysis and mathematical programming. This chapter contains simplified derivations of the static, kinematic, and mixed variational principles of shakedown theory by means of the basic techniques of convex analysis. Moreover, numerical procedures suitable to solve the shakedown analysis problem are discussed here in the framework of mathematical programming techniques combined with common procedures in the field of finite element methods.Applications in fundamental examples are then presented, namely (i) a restrained block under thermomechanical loadings; (ii) the classical Bree problem of a tube under variable pressure and temperature, with a more realistic model and including an exact solution; (iii) a plate with a circular hole subjected to variable tractions; (iv) a plate with simulated imperfections showing critical mechanisms with strongly localized deformations; and (v) a pipe elbow under internal pressure and in plane bending moment.
Damage, Material Instabilities, and Failure
Authors: de Borst René , Verhoosel Clemens V. 
Published: December 2017

AbstractThis chapter begins with an overview of damage mechanics. Isotropic and anisotropic models are described, as well as the coupling to plasticity, including the algorithmic treatment. Next, the implications of strain softening, which starts at a certain level of damage accumulation, are discussed as regards important notions such as material stability and ellipticity. The consequences of loss of ellipticity in terms of grid sensitivity of computations are illustrated for static and dynamic instabilities. Next, the important role of cohesive‐zone models is highlighted, both in its original (discrete) format, a derived smeared format, and as an embedded discontinuum description. To avoid the loss of ellipticity, the introduction of higher order continua is necessary. Various higher order continua incorporating damage or coupled damage–plasticity models are discussed, including aspects of numerical implementation. Also, various discretization methods are discussed, which can accommodate the higher order gradients that arise in higher order gradient models, including meshless methods and isogeometric analysis. Also, the phase‐field approach to brittle fracture and its close relation to gradient damage models are demonstrated. Finally, the numerical implementation of cohesive‐zone models in a discrete format is considered. Attention is given to conventional interface elements, meshless methods, approaches that exploit the partition‐of‐unity property of finite element shape functions, and isogeometric finite element analysis.
Computational Concrete Mechanics
Authors: Lackner Roman , Pichler Christian , Traxl Roland , Mang Herbert A. 
Published: December 2017

AbstractThis chapter contains a report on recent developments in the field of computational concrete mechanics, introducing the multiscale concept for simulation of cement‐based materials and, in case of reinforced concrete Reinforced Concrete (RC), of the steel–concrete interaction. Within the framework of this concept, several scales of observation are considered simultaneously in the numerical analysis. Alternatively, material properties, which serve as input for macroscopic analyses, are related to properties of the material phases and their assemblage at finer scales of observation. The benefits of multiscale approaches in computational concrete mechanics are illustrated by the analysis of real‐life structures subjected to various loading conditions, including mechanical loading and thermal and chemical attacks. Macroscopic material properties for plain and reinforced concrete that are related to finer scales of observation are employed.
Incompressible Viscous Flows
Authors: Rannacher Rolf 
Published: December 2017

AbstractIn this article, we describe some approaches to the efficient numerical computation of viscous incompressible flows governed by the Navier–Stokes equations. We concentrate onlaminarflows, stationary as well as nonstationary, for Reynolds numbers of moderate size, and in general domains. The emphasis is on spatial discretization by the finite element method. We discuss the treatment of the incompressibility constraint, the time‐stepping process, techniques of error control and mesh adaptation and the solution of the resulting indefinite algebraic equations.
Computability and Adaptivity inCFD
Authors: Hoffman Johan , Jansson Johan , Jansson Niclas , De Abreu Rodrigo Vilela , Johnson Claes 
Published: December 2017

AbstractWe give a brief introduction to research on adaptive computational methods for laminar compressible and incompressible flows and then focus on computability and adaptivity for turbulent incompressible flow, where we present a framework for adaptive finite element methods with duality‐baseda posteriorierror control for chosen output quantities of interest. We show in concrete examples that outputs such as mean values in time of drag and lift of a bluff body in a turbulent flow are computable to a tolerance of a few percent, for a simple geometry using some hundred thousand mesh points and for complex geometries using some million mesh points.
An In Vitro Model for the Development of Mature Bone Containing an Osteocyte Network
Authors: Iordachescu Alexandra , Amin Harsh D. , Rankin Sara M. , Williams Richard L. , Yapp Clarence , Bannerman Alistair , Pacureanu Alexandra , Addison Owen , Hulley Philippa A. , Grover Liam M. 
Published: December 2017

AbstractBone is a dynamic tissue that remodels continuously in response to local mechanical and chemical stimuli. This process can also result in maladaptive ectopic bone in response to injury, yet pathological differences at the molecular and structural levels are poorly understood. A number of in vivo models exist but can often be too complex to allow isolation of factors which may stimulate disease progression. A self‐structuring model of bone formation is presented using a fibrin gel cast between two calcium phosphate ceramic anchors. Femoral periosteal cells, seeded into these structures, deposit an ordered matrix that closely resembles mature bone in terms of chemistry (collagen:mineral ratio) and structure, which is adapted over a period of one year in culture. Raman spectroscopy and X‐ray diffraction confirm that the mineral is hydroxyapatite associated with collagen. Second‐harmonic imaging demonstrates that collagen is organized similarly to mature mouse femora. Remarkably, cells differentiated to the osteocyte phase are linked by canaliculi (as demonstrated with nano‐computed tomography) and remained viable over the full year of culture. It is demonstrated that novel drugs can prevent ossification in constructs. This model can be employed to study bone formation in an effort to encourage or prevent ossification in a range of pathologies.
A Hybrid Electromagnetic–Triboelectric Energy Harvester Using a Dual Halbach Magnet Array Powered by Human‐Body‐Induced Motion
Authors: Salauddin Md , Cho Hyunok , Park Jae Yeong 
Published: December 2017

AbstractA highly miniaturized hybridization of electromagnetic–triboelectric energy harvesters with different mechanisms in one harvester is proposed using a Halbach magnet array from human‐body‐induced motion, and it is theoretically and experimentally validated. In particular, the proposed dual Halbach array allows the concentrated magnetic flux lines to interact with the same coil in a manner that produces maximum flux linkage. To obtain much higher power generation at low‐amplitude and low‐frequency vibrations, the proposed harvester is comprised of a Halbach magnet array, sandpaper‐based microstructure polydimethylsiloxane (PDMS), a triboelectric, and magnetic springs. A prototype of the hybrid energy harvester is fabricated and tested, both using a vibration exciter test, and by manual handshaking. Under vibration exciter test, the fabricated hybrid harvester prototype delivers a high output current and power of 4.5 mA and 12.51 mW, respectively, corresponding to a volume power density of 411 W m−3 under a loading resistance of 617 Ω at 6.5 Hz resonant frequency and 0.5g acceleration. The hybrid prototype is also capable of delivering output current and power of 3.55 mA and 7.35 mW, respectively, if driven by handshaking vibration. The fabricated hybridized harvester exhibits much higher power density than similar recently reported works.
Broadband Terahertz Circular‐Polarization Beam Splitter
Authors: Lee Wendy S. L. , Nirantar Shruti , Headland Daniel , Bhaskaran Madhu , Sriram Sharath , Fumeaux Christophe , Withayachumnankul Withawat 
Published: December 2017

AbstractSplitting circularly polarized waves is desirable for high‐data‐rate wireless communications and study of molecular chirality at terahertz frequencies. Typically, this functionality is achieved using bulk optical systems with limitations in material availability, bandwidth, and efficiency. As an alternative, metasurfaces with spatially varying broadband birefringence are employed to attain the same functionality. It is demonstrated that a metasurface designed with gradually rotated birefringent resonators can deflect normally incident left‐handed circularly polarized and right‐handed circularly polarized waves into different directions. This beam splitting functionality is maintained over an experimentally demonstrated relative deflection bandwidth of 53%, namely, covering the band of 0.58–1.00 THz.
Application of nanostructure ZnLI2 complex in construction of optical pH sensor
Authors: Shahamirifard Seyed Alireza , Ghaedi Mehrorang , Montazerozohori Morteza 
Published: December 2017

This is for the first time that application of complex nanostructure is reported as pH indicator in PVC matrix. This new optical pH sensor was constructed based on incorporation of ZnLI2 complex nanostructure in PVC matrix. The synthesized nanostructure ZnLI2 complex was characterized by SEM and XRD technique. The membrane solution was speared on the glass plate to provide thin film and the membrane surface morphology was investigated via field emission scanning microscope (FE‐SEM) technique. Central composite design (CCD) combined with desirability function (DF) was applied to find the best experimental composition of membrane providing the highest absorbance. These conditions were found in correspondence with 3 mg of pH indicator, 3 mg of ionic additive and 1.5 mg/mg of DBP/PVC weight ratio. Under optimum conditions, the proposed pH sensor has two linear working ranges of 4 ‐ 8 at 393 nm (R2 = 0.9897) and 5 ‐ 8 (R2 = 0.9982) at 570 nm with response time of 4 min. The pKa of proposed pH optical sensor was calculated through three methods that found to be 5.63. The present optical sensor shows stability after 2 months without any significant divergence in response properties (less than 5% RSD). Furthermore, current pH optode was exhibited good repeatability (RSD = 1.14%) as well as reproducibility (RSD = 4.06%). No significant variation was observed on sensor response with increasing the ionic strength in the range of 0.0–0.5 M of sodium chloride. All above features indicated that the proposed sensor can be successfully used for detection of pH in solutions with different ionic strength.
The underestimated magnitude and decline trend in near‐surface wind over China
Authors: Jiang Ying , Xu Xiyan , Liu Hanwu , Dong Xuguang , Wang Wenben , Jia Gensuo 
Published: December 2017

AbstractThis study reports the magnitude, spatial pattern and temporal trend of near‐surface wind speed (NWS) by comparing 20th century simulations in Coupled Model Intercomparison Project phase 5 (CMIP5) and 3 (CMIP3) and the climate reanalyses with measurements at 563 weather stations in China over 1961–2005. Both CMIP5 and CMIP3 agree quite well with observations in reproducing the spatial pattern of annual mean NWS. CMIP5 models are superior to CMIP3 models in hindcasting the magnitude and spatial pattern of seasonal mean NWS, the temporal trend in annual and seasonal mean NWS. Although both CMIP3 and CMIP5 reproduced the decline trend in the annual and seasonal mean NWS, the hindcasted decline rate is smaller than observed decline trend by the magnitude of one order. The ensemble of optimal models that are better correlated to observations in both NWS and temporal trend possesses advantages over individual model hindcast and reanalyses. The reanalyzed data are not able to represent the observed either the spatial pattern or the decline trend of NWS. The analyses presented here reveal the uncertainties in the current wind field products including reanalyses and model outputs and highlight the benefits of parameterization development and increased horizontal resolution in the new‐generation CMIP models.
Visual Motion Prediction and Verbal False Memory Performance in Autistic Children
Authors: Tewolde Furtuna G. , Bishop Dorothy V. M. , Manning Catherine 
Published: December 2017

Recent theoretical accounts propose that atypical predictive processing can explain the diverse cognitive and behavioral features associated with autism, and that difficulties in making predictions may be related to reduced contextual processing. In this pre‐registered study, 30 autistic children aged 6–14 years and 30 typically developing children matched in age and non‐verbal IQ completed visual extrapolation and false memory tasks to assess predictive abilities and contextual processing, respectively. In the visual extrapolation tasks, children were asked to predict when an occluded car would reach the end of a road and when an occluded set of lights would fill up a grid. Autistic children made predictions that were just as precise as those made by typically developing children, across a range of occlusion durations. In the false memory task, autistic and typically developing children did not differ significantly in their discrimination between items presented in a list and semantically related, non‐presented items, although the data were insensitive, suggesting the need for larger samples. Our findings help to refine theoretical accounts by challenging the notion that autism is caused by pervasively disordered prediction abilities. Further studies will be required to assess the relationship between predictive processing and context use in autism, and to establish the conditions under which predictive processing may be impaired. Autism Res 2018, 11: 509–518. © 2017 The Authors Autism Research published by International Society for Autism Research and Wiley Periodicals, Inc.Lay SummaryIt has been suggested that autistic individuals have difficulties making predictions and perceiving the overall gist of things. Yet, here we found that autistic children made similar predictions about hidden objects as non‐autistic children. In a memory task, autistic children were slightly less confused about whether they had heard a word before, when words were closely related in meaning. We conclude that autistic children do not show difficulties with this type of prediction.
Alcohol consumption during adolescence: A link between mitochondrial damage and ethanol brain intoxication
Authors: Tapia‐Rojas Cheril , Mira Rodrigo G. , Torres Angie K. , Jara Claudia , Pérez María José , Vergara Erick H. , Cerpa Waldo , Quintanilla Rodrigo A. 
Published: December 2017

AbstractAdolescence is a period of multiple changes where social behaviors influence interpersonal‐relations. Adolescents live new experiences, including alcohol consumption which has become an increasing health problem. The age of onset for consumption has declined in the last decades, and additionally, the adolescents now uptake greater amounts of alcohol per occasion. Alcohol consumption is a risk factor for accidents, mental illnesses or other pathologies, as well as for the appearance of addictions, including alcoholism. An interesting topic to study is the damage that alcohol induces on the central nervous system (CNS) in the young population. The brain undergoes substantial modifications during adolescence, making brain cells more vulnerable to the ethanol toxicity. Over the last years, the brain mitochondria have emerged as a cell organelle which is particularly susceptible to alcohol. Mitochondria suffer severe alterations which can be exacerbated if the amount of alcohol or the exposure time is increased. In this review, we focus on the changes that the adolescent brain undergoes after drinking, placing particular emphasis on mitochondrial damage and their consequences against brain function. Finally, we propose the mitochondria as an important mediator in alcohol toxicity and a potential therapeutic target to reduce or treat brain conditions associated with excessive alcohol consumption.