bluuebunny/crossref_metadata_2025_split huggingface dataset:
Split‐Hopkinson‐Pressure‐Bar simulations using MPM
Authors: Maassen S. F. , Niekamp R. , Schröder J. , Wiederkehr P. , Theisen W. 
Published: January 2021

AbstractThe material point method (MPM) represents a discretization method that combines the beneficial aspects of a Lagrangian representation of material within an Eulerian solution scheme. Deformable bodies are discretized with material points that carry mass, kinematical quantities such as velocity and material history variables. The material points are not connected via a Lagrangian mesh but a computational background mesh. This mesh is arbitrary and hence not subject to critical distortion. Due to this aspect, the MPM shows promising potential to large deformation problems. In the context of the ”Virtual Machining” project, the MPM will be elaborated for metal cutting simulations of a 42CrMo4 heat treatable steel. The first steps towards this application are experimental investigations on the material parameters. To gather data on the rate dependence in the constitutive response of 42CroMo4, Split‐Hopkinson‐Pressure‐Bar (SHPB) experiments were performed. These tests are subject to numerical analysis using the MPM to get a first impression of the method in this kind of problem. This contribution represents a proof of concept for an SHPB analysis on the here chosen MPM scheme.
Multiscale modeling of Retinal Hypoxia due to Age‐related Macular Degeneration
Authors: Timothy Jithender J. , Holla Vijaya , Meschke Günther 
Published: January 2021

AbstractAge‐related macular degeneration (AMD) is the leading cause of vision loss in older adults above the age of 50. AMD is attributed to the degeneration and loss of normal function of the outer retina in the macular region. Presence of extracellular material called drusen between the Bruch's membrane (BrM) and the retinal pigment epithelium (RPE) is the hallmark of AMD. Moreover, thickening and reduced diffusivity of the BrM has been observed in patients with AMD. In this paper, we investigate the influence of the BrM microstructure and the drusen size on oxygen transport in the outer retina using a multiscale computational modeling approach. The proposed framework comprises of a cascade lattice micromechanics model for characterizing the overall diffusivity of the BrM, a finite element model for simulating oxygen transport from the vascular system to the photoreceptors and a cellular potts model for simulating morphological changes to the outer retina due to drusen development. Simulations for various levels of BrM blockage and drusen size on oxygen supply to the photoreceptors are presented and their significance on AMD development discussed.
Computational analysis of the influence of drusen growth on the morphology of RPE due to Age‐related Macular Degeneration
Authors: Holla Vijaya , Timothy Jithender J. , Meschke Günther 
Published: January 2021

AbstractAge‐related macular degeneration (AMD) is a disease that affects the macular region of the outer retina. AMD is characterized by the presence of large extracellular debris called drusen between the Bruch's Membrane (BrM) in the choroid and the retinal pigment epithelium (RPE) in the outer retina. An important feature of AMD is the degenerative changes in the RPE and the photoreceptors that leads to the deterioration and loss of central vision. In this contribution, the effect of drusen size on the morphological changes in the RPE, BrM and photoreceptors are investigated using the cellular potts model (CPM) and machine learning. Numerical simulation of the influence of drusen growth and its effect on the morphology of the outer retinal layers of the macula is presented and the implications for AMD progression discussed.
Reformulating Bilevel Problems by SQP Embedding
Authors: Schäfer Kai , Fliege Jörg , Flaßkamp Kathrin , Büskens Christof 
Published: January 2021

AbstractDue to their inherently complex structure, bilevel optimization problems are often transformed into single‐level problems in order to make them numerically solvable. In this work, we present a novel reformulation strategy, in which we introduce sets of variables and constraints that represent the process of numerically solving the lower‐level problem based on a full step exact Hessian sequential quadratic programming method. The reformulated problem approximates a solution to the original one in the following sense: For a suitable number of imitated lower‐level iteration steps, the lower‐level problem is approximately solved in case a feasible point is found. The approach is illustrated by an example.
A Newmark space‐time approach in structural mechanics
Authors: Bamer Franz , Shirafkan Nima , Cao Xiaodan , Oueslati Abdelbacet , Stoffel Marcus , De Saxcé Géry , Markert Bernd 
Published: January 2021

AbstractIn this contribution, we present a non‐incremental time integration scheme using the implicit Newmark approximations. The result is one space‐time equation that can be solved using the proper general decomposition ansatz.
Active Damping of Thin Film Shape Memory Alloy Devices
Authors: Ahmadi S. , Jacob K. , Wendler F. , Padhy A. , Kohl M. 
Published: January 2021

AbstractThe thermomechanical coupling in shape memory alloys (SMAs) provides an effective mechanism of vibration damping by a cyclic structural phase transition. Here, we present simulations for an active SMA damper device based on a polycrystalline film materials, in which active damping via the one‐way shape memory effect is exploited. We apply an extension of a previously reported superelastic model, that combines transition state kinetics with a phase field approach for the case of shock loading. By this approach, we are able to describe the time‐resolved active damping performance of the device in agreement with experimental results.
A deep learning‐based ensemble filter for nonlinear data assimilation
Authors: Hoang Truong-Vinh , Matthies Hermann G. 
Published: January 2021

AbstractThis article presents a novel deep learning‐based ensemble conditional mean filter (DL‐EnCMF) for nonlinear data assimilation. The filter's key component is the approximation of the conditional expectation (CE) using deep neural networks (DNNs). We implement the DL‐EnCMF for tracking the states of the Lorenz‐63 system. Numerical results show that the DL‐EnCMF outperforms the ensemble Kalman filter (EnKF)—a common technique for data assimilation.
Thermomechanical phase‐field fracture modeling of fluid‐saturated porous media
Authors: Nguyen Cam-Lai , Sweidan Abdel Hassan , Heider Yousef , Markert Bernd 
Published: January 2021

AbstractIn this work, the problem of brittle fracture in a fluid‐saturated porous material is extended by considering the non‐isothermal states of the sample. The temperature field will affect the problem in two aspects: 1) Temperature‐dependent material parameters, such as elasticity modulus (E) and critical energy release rate (Gc). 2) Thermal expansion due to thermo‐mechanical volume coupling. In hydraulic fracturing, we further study the effect of the temperature difference between the injected fluid and the surrounding porous media ambient on the crack behavior. The modeling of the porous media domain is based on the macroscopic theory of porous media (TPM), whereas the phase‐field method (PFM) is applied to approximate the sharp crack edges by diffusive ones. In the numerical implementation, the coupled system of partial differential equations will be solved using the FEM in order to simulate the heat transition in the crack and non‐crack regions.
Crack path comparisons of a mixed phase‐field fracture model and experiments in punctured EPDM strips
Authors: Fehse Andreas , Kröger Nils Hendrik , Mang Katrin , Wick Thomas 
Published: January 2021

AbstractWorking on quasi‐static phase‐field fracture modeling in nearly incompressible solids for crack propagation is a challenging task. To avoid arising locking effects therein, a mixed form for the solid displacement equation is developed, resulting in two unknowns: a displacement field and a hydro‐static pressure variable. In order to fulfil an inf‐sup condition, stable Taylor‐Hood elements are employed for the displacement‐pressure system. The irreversibility condition of the crack evolution is handled by help of a primal‐dual active set method. To get both a sharper crack and reasonable computational costs, adaptive meshes are used based on a predictor‐corrector scheme. The crack paths from the numerical simulations are compared on the experimentally observed crack paths in carbon black filled ethylene propylene diene monomer (EPDM) rubber strips. The punctured EPDM strips with a hole and a given notch at different heights are stretched till total failure.
The Loewner framework for nonlinear identification and reduction of Hammerstein cascaded dynamical systems
Authors: Karachalios Dimitrios S. , Gosea Ion Victor , Antoulas Athanasios C. 
Published: January 2021

AbstractWe present an algorithm for data‐driven identification and reduction of nonlinear cascaded systems with Hammerstein structure. The proposed algorithm relies on the Loewner framework (LF) which constitutes a non‐intrusive algorithm for identification and reduction of dynamical systems based on interpolation. We address the following problem: the actuator (control input) enters a static nonlinear block. Then, this processed signal is used as an input for a linear time‐invariant system (LTI). Additionally, it is considered that the orders of the linear transfer function and of the static nonlinearity are not a priori known.
Limit cycle computation of self‐excited dynamic systems using nonlinear modes
Authors: Tatzko Sebastian , Stender Merten , Jahn Martin , Hoffmann Norbert 
Published: January 2021

AbstractA self‐excited dynamic system is able to oscillate periodically by itself. Corresponding solutions of the autonomous differential equation are called limit cycles or periodic attractors. To find these solutions, a simple approach would be brute‐force search for the corresponding basins of attraction. However, grid searching might become unfeasible with increasing number of degrees of freedom. Instead, solution path continuation techniques are often used to keep computational costs low. As the continuation of solution branches and their bifurcations provides only solutions which are connected to each other, isolas and detached branches are missed out. We present a method for fast limit cycle detection of self‐excited systems with isolas based on nonlinear modes. A nonlinear mode, often referred to as nonlinear normal mode, is defined as a periodic motion of the undamped and unforced mechanical system. For nonconservative systems however, e.g. with friction nonlinearity, damping cannot be neglected as it is characteristic for the oscillators nonlinear dynamics. Therefore, the Extended Periodic Motion Concept (E‐PMC) was proposed recently to find periodic solutions of nonconservative nonlinear systems. In this work, the E‐PMC is applied to self‐excited dynamic systems in order to find periodic attractors along its nonlinear modes. Zero crossings of the nonlinear damping curve indicate autonomous solutions which can be used as starting points for single parameter continuation. Thus, solutions corresponding to the main branch and detached curves in the solution space are connected by nonlinear modes. The proposed method is applied to a frictional oscillator with cubic stiffness and proves to be robust in the search for isolated periodic solutions that are already known from literature.
Prevalence of short stature among children in China: A systematic review
Authors: Li Fulun , Liu Ke , Zhao Qianlong , Chen Junyi , Liu Lingfei , Xie Qingmu , Yang Jing 
Published: January 2021

ABSTRACTImportanceThe prevalence and characteristics of short stature (SS) among children in China should be assessed to provide guidance for planning and implementation of nationwide public health policies. Thus far, there have been no accurate estimates of the prevalence of SS in China.ObjectiveTo analyze the prevalence of SS among children in China and to explore the influences of sex, area, age, study year, and study site on prevalence rates.MethodsRelevant literature was identified by searching the following databases: PubMed, Embase, The Cochrane Library, Chinese Biomedical Literature, China Knowledge Resource Integrated, WeiPu, and WanFang databases. Meta‐analysis was carried out using STATA 11.2.ResultsThis meta‐analysis included 39 studies with 348 326 Chinese participants; the studies covered 20 provinces, municipalities, and autonomous regions. The pooled prevalence of SS was 3.2% (95% confidence interval [CI], 2.6%–3.7%; I2 = 99.8%). The prevalence of SS in boys and girls were 3.1% (95% CI, 2.5%–3.7%) and 3.2% (95% CI, 2.6%–3.9%), respectively. The sex difference was not statistically significant (P > 0.05). The prevalence of SS was higher in rural areas than in urban areas (4.7% [95% CI, 3.6%–5.8%] vs. 2.8% [95% CI, 2.2%–3.4%]; P < 0.001). The prevalence of SS was higher in West China (5.2%; 95% CI, 4.4%–6.0%) than in Northeast China (0.6%; 95% CI, 0.3%–0.8%), East China (2.3%; 95% CI, 1.9%–2.8%), or Central China (2.9%; 95% CI, 1.9%–3.9%).InterpretationThe prevalence of SS among children was higher in western and rural areas of China. Close attention to children’s growth and development is needed to prevent the occurrence of SS.
Portal venous gas resulting from umbilical vein catheterization in a very‐low‐birth‐weight infant with no interruption in early feeding
Authors: Wang Jun , Yue Guang , Yang Hua , Li Jing , Ju Rong 
Published: January 2021

ABSTRACTIntroductionPortal venous gas (PVG) is common in necrotizing enterocolitis and occasionally occurs in neonates after umbilical vein catheterization (UVC). Therefore, determining the cause of PVG requires further clinical evaluation in these cases.Case presentationWe report the case of a very‐low‐birth‐weight infant who underwent UVC after birth. PVG was an unexpected finding on ultrasound following catheterization. The UVC was immediately removed and replaced with a peripherally inserted central catheter. The infant’s physical examination was unremarkable. Bedside X‐ray revealed neither PVG nor pneumatosis intestinalis, which would indicate the onset of necrotizing enterocolitis. After full evaluation, breastfeeding was started on the same day. The infant did not develop feeding intolerance, necrotizing enterocolitis, or other disorders.ConclusionPVG occasionally occurs in neonates who undergo UVC and is considered to be caused by exogenous gases. PVG is more easily detected with ultrasound than with X‐ray and does not affect early feeding in premature infants.
Self‐talk in middle childhood: A mechanism for motivational resilience during learning
Authors: Flanagan Róisín M. , Symonds Jennifer E. 
Published: January 2021

AbstractAll individuals possess an inner voice that helps them to navigate life and its challenges. However, little is known about how children use self‐talk to maintain their momentary engagement during academic tasks. Using qualitative methods, this study investigated how 19 children (aged 8–12 years) from one primary school prospectively used self‐talk to maintain their motivation. Vignettes were used to prompt children's reports on what they would say to themselves to stay motivated during challenges they might typically encounter in the classroom. These included becoming frustrated or tired, and having to choose between work and play. The data were deductively coded into 11 coping families typically measured in academic settings within the framework of motivational resilience. The data were then inductively coded within the best represented coping families to uncover subthemes of coping. The results extend the motivational resilience literature and illustrate the multidimensional nature of coping with challenges in classrooms.
Developmental plasticity of Brachypodium distachyon in response to P deficiency: Modulation by inoculation with phosphate‐solubilizing bacteria
Authors: Baudson Caroline , Delory Benjamin M. , Spaepen Stijn , du Jardin Patrick , Delaplace Pierre 
Published: January 2021

AbstractBackgroundMineral phosphorus (P) fertilizers must be used wisely in order to preserve rock phosphate, a limited and non‐renewable resource. The use of bio‐inoculants to improve soil nutrient availability and trigger an efficient plant response to nutrient deficiency is one potential strategy in the attempt to decrease P inputs in agriculture.MethodAn in vitro co‐cultivation system was used to study the response of Brachypodium distachyon to contrasted P supplies (soluble and poorly soluble forms of P) and inoculation with P solubilizing bacteria. Brachypodium's responses to P conditions and inoculation with bacteria were studied in terms of developmental plasticity and P use efficiency.ResultsBrachypodium showed plasticity in its biomass allocation pattern in response to variable P conditions, specifically by prioritizing root development over shoot productivity under poorly soluble P conditions. Despite the ability of the bacteria to solubilize P, shoot productivity was depressed in plants inoculated with bacteria, although the root system development was maintained. The negative impact of bacteria on biomass production in Brachypodium might be attributed to inadequate C supply to bacteria, an increased competition for P between both organisms under P‐limiting conditions, or an accumulation of toxic bacterial metabolites in our cultivation system. Both P and inoculation treatments impacted root system morphology. The modulation of Brachypodium's developmental response to P supplies by P solubilizing bacteria did not lead to improved P use efficiency.ConclusionOur results support the hypothesis that plastic responses of Brachypodium cultivated under P‐limited conditions are modulated by P solubilizing bacteria. The considered experimental context impacts plant–bacteria interactions. Choosing experimental conditions as close as possible to real ones is important in the selection of P solubilizing bacteria. Both persistent homology and allometric analyses proved to be useful tools that should be considered when studying the impact of bio‐inoculants on plant development in response to varying nutritional context.
The Differential Effect of First‐Time Single‐Point Cane Use between Healthy Young and Older Adults
Authors: Omana Humberto , Madou Edward , Divine Alison , Wittich Walter , Hill Keith D. , Johnson Andrew M. , Holmes Jeffrey D. , Hunter Susan W. 
Published: January 2021

AbstractBackgroundWalking aids are often introduced to older adults to enable independent mobility. Single‐point canes are the most common device used. Benefits are tempered by research suggesting that walking aids increase fall risk. A better understanding of the effect of walking aid use on gait performance is required.ObjectiveTo evaluate differences in the effect of initial single‐point cane use on gait between younger (YAs) and older adults (OAs).DesignCross‐sectional.SettingCommunity‐dwelling.ParticipantsTwenty‐six YAs (mean age ± standard deviation [SD]: 23.7 ± 2.8 years) and 25 OAs (mean age ± SD: 70.8 ± 14.1 years) participated. Inclusion criteria were 18 to 35 years of age for YAs or ≥50 years for OAs, be able to ambulate unassisted, and without any condition affecting mobility.InterventionsNot applicable.Main Outcome Measure(s)Gait velocity and stride time variability under different walking path configurations (straight path, Groningen Meander Walking Test, Figure‐of‐8 Walk Test) and conditions (unassisted walking, walking with a single‐point cane, and walking with a single‐point cane while completing a cognitive task) were recorded in a laboratory. The arithmetic task of subtracting 1s from 100 was used as the secondary cognitive task. Data analysis included separate three‐way mixed analyses of variance (ANOVAs; path/condition/group).ResultsThere was a statistically significant two‐way interaction between walking path and condition for velocity (P < .001, ω2 = 0.03) and stride time variability (P = .032, ω2 = 0.02). In addition, a significant main effect of group was also observed (velocity: P = .004, ω2 = 0.07; stride time variability: P = .001, ω2 = 0.09).ConclusionsUsing a single‐point cane decreased velocity and increased stride time variability in both YAs and OAs. However, the cognitive load and effect on gait of initial cane use was not different between age groups. Standardized guidelines aimed at facilitating a clientʼs transition toward the safe use of a walking aid are needed. Future research should evaluate if training can mitigate some of the adverse changes to gait stability observed with initial walking aid use.
Betanidin isomerisation and decarboxylation, thermodynamic and charge transfer dye properties towards dye sensitised solar cells application
Authors: Costa Rene , Pogrebnoi Alexander , Pogrebnaya Tatiana 
Published: January 2021

AbstractAlong with attractiveness of natural dyes for solar technologies, the instability is a well‐known drawback of the dyes, which impedes their usage for dye sensitised solar cells (DSSCs) application. The planar isomer appeared to be predominant in equilibrium vapour despite its less energetic stability. Both betanidins belong to red–purple pigments betacyanins, which experimentally demonstrated good adsorption in a visible range. In this study, the structural, thermodynamic, and optoelectronic properties of betanidins have been determined from density functional theory (DFT) and time‐dependent DFT (TD–DFT) computations. On the basis of the thermodynamic approach, isomerisation reaction between two structural conformers of betanidin, bent and planar, and also decarboxylation reactions have been analysed. The planar isomer appeared to be predominant in equilibrium vapour despite its less energetic stability; both betanidin molecules exhibit an inclination to decay into decarboxylated betanidin and CO2. As for worthy optoelectronic properties and applicability in DSSCs, the dyes considered satisfy most requirements to sensitise the semiconductor TiO2 and be regenerated by electrolytes. Adsorption of the dyes at the TiO2 surface has been simulated; for the dye@TiO2 complexes, the binding energies, electronic spectra, and relevant molecular orbital (MO) isosurfaces have been computed and discussed.
Methanol synthesis from CO2 using Ni and Cu supported Fe catalytic system: Understanding the role of nonthermal plasma surface discharge
Authors: Joshi Nitesh , Loganathan Sivachandiran 
Published: January 2021

AbstractThe present study combines nonthermal plasma (NTP) and thermal catalysis to exploit the synergism for direct conversion of CO2 to CH3OH using H2. Series of catalyst, that is, CuO/QW, NiO/QW, Fe2O3/QW, NiO/Fe2O3/QW, CuO/Fe2O3/QW have been tested for CO2 conversion and CH3OH selectivity. And it was observed that 5 wt% CuO/Fe2O3/QW exhibited better CO2 conversion and CH3OH selectivity as compared to other catalysts. With 5 wt% CuO/Fe2O3/QW, at 200°C and 2‐W NTP input power (100 ml/min feed flow and 1:3 ratio of CO2 and H2) about 16.7% CO2 conversion and 32.7% CH3OH selectivity have been reached. Indeed, the highest of 9.32 mmol h−1 gcat−1 of CH3OH space‐time yield is obtained over CuO/Fe2O3/QW, which is about two times higher than the reported value in the literature (4.41 mmol h−1 gcat−1 of CH3OH using Cu/ZnO/Al2O3, 30°C, feed flow 40 ml/min, and 30‐W input power).
Discrete‐time systems with slope restricted nonlinearities: Zames–Falb multiplier analysis using external positivity
Authors: Turner Matthew C. , Drummond Ross 
Published: January 2021

AbstractThis article exploits positive systems theory in the search for Zames–Falb multipliers for the analysis of discrete‐time Lurie systems, where the nonlinearity is assumed to be slope‐restricted. Although a similar problem has been tackled in a continuous time context, the results in discrete‐time take a different form and require a somewhat different approach to overcome certain technical problems. The work has two compelling features: (i) the arising algorithms are completely convex; and (ii) numerical results compare well with the state‐of‐the‐art in some cases, providing the least conservative result in one instance.