bluuebunny/crossref_metadata_2025_split huggingface dataset:
A new and efficient numerical method based on shifted fractional‐order Jacobi operational matrices for solving some classes of two‐dimensional nonlinear fractional integral equations
Authors: Maleknejad Khosrow , Rashidinia Jalil , Eftekhari Tahereh 
Published: January 2021

AbstractThe aim of this paper is to present a new and efficient numerical method to approximate the solutions of two‐dimensional nonlinear fractional Fredholm and Volterra integral equations. For this aim, the two‐variable shifted fractional‐order Jacobi polynomials are introduced and their operational matrices of fractional integration and product are derived. These operational matrices and shifted fractional‐order Jacobi collocation method are utilized to reduce the understudy equations to systems of nonlinear algebraic equations. Then, the arising systems can be solved by the Newton method. Discussion on the convergence analysis and error bound of the proposed method is presented. The efficiency, accuracy, and validity of the presented method are demonstrated by its application to three test examples and by comparing our results with the results obtained by existing numerical methods in the literature recently.
Adiposity Measures and Morning Serum Cortisol in African Americans: Jackson Heart Study
Authors: Kluwe Bjorn , Zhao Songzhu , Kline David , Ortiz Robin , Brock Guy , Echouffo‐Tcheugui Justin B. , Sims Mario , Kalyani Rita R. , Golden Sherita H. , Joseph Joshua J. 
Published: January 2021

ObjectiveAltered hormonal regulation, including cortisol, is a proposed mechanism linking adiposity to obesity‐related disorders. We examined the association of anthropometric, adipokine, and body fat distribution measures of adiposity with morning serum cortisol in an African American (AA) cohort.MethodsWe investigated the cross‐sectional associations of adiposity measures (BMI, waist circumference, leptin, adiponectin, leptin:adiponectin ratio, subcutaneous and visceral adipose tissue) and liver attenuation with cortisol in the Jackson Heart Study. Linear regression models were used to analyze the association between exposures and cortisol. Models were adjusted for multiple covariates.ResultsAmong 4,211 participants, a 1‐SD higher BMI and waist circumference were associated with a 3.92% and 3.05% lower cortisol, respectively. A 1‐SD higher leptin and leptin:adiponectin ratio were associated with a 6.48% and 4.97% lower morning serum cortisol, respectively. A 1‐SD higher subcutaneous adipose tissue was associated with a 4.97% lower cortisol (all P < 0.001). There were no associations of liver attenuation or visceral adipose tissue with cortisol.ConclusionsSeveral measures of adiposity are associated with lower morning serum cortisol among AAs, with leptin having the greatest magnitude. Future studies examining the role of morning serum cortisol in the pathway from adiposity to cardiometabolic disease in AAs are warranted.
Interpregnancy Weight Change and Gestational Diabetes Mellitus: A Systematic Review and Meta‐Analysis
Authors: Martínez‐Hortelano Jose Alberto , Cavero‐Redondo Iván , Álvarez‐Bueno Celia , Díez‐Fernández Ana , Hernández‐Luengo Montserrat , Martínez‐Vizcaíno Vicente 
Published: January 2021

ObjectiveThis study aimed to synthesize evidence regarding the association between interpregnancy weight change (IPWC) and gestational diabetes mellitus (GDM) in the subsequent pregnancy.MethodsMEDLINE, EMBASE, Cochrane Library, and Web of Science were searched from inception to May 10, 2020. This review included studies that reported the association between IPWC and GDM in the subsequent pregnancy without restriction on study design, IPWC classification, or parity. The “no weight change” interpregnancy category was defined by each study, and data were synthesized to analyze the risk of GDM according to weight change.ResultsThirteen observational studies were included. A higher risk of GDM in the subsequent pregnancy when there was interpregnancy weight gain (odds ratio [OR] = 1.56; 95% CI: 1.30‐1.83; I2 = 82.30%) was found. However, interpregnancy weight loss was associated with lower risk of GDM in the subsequent pregnancy (OR = 0.83; 95% CI: 0.68‐0.98; I2 = 58.10%), but the decrease in the risk of GDM in the subsequent pregnancy was greater among women with pregestational BMI higher than 25 kg/m2 (OR = 0.58; 95% CI: 0.39‐0.77; I2 = 0.00%).ConclusionsThe risk of GDM in the subsequent pregnancy increases with interpregnancy weight gain, whereas it decreases with interpregnancy weight loss.
Alpha‐Melanocyte–Stimulating Hormone is Elevated in Hypothalamic Obesity Associated with Childhood Craniopharyngioma
Authors: Emet Dicle Canoruc , Ozon Alev , Alikasifoglu Ayfer , Kandemir Nurgun , Gonc Nazlı 
Published: January 2021

ObjectiveThe purpose of this study was to investigate the peripheral concentrations of leptin and neuropeptides taking part in the melanocortin pathway in hypothalamic obesity (HO) associated with craniopharyngioma (CP) and to find a peripheral marker for diagnosis.MethodsThirty‐one patients (52% girls; median age 16 years) with CP were enrolled in the study group. They were grouped as CP with obesity (CPobesity, n = 17) and CP without obesity (CPnonobesity, n = 14). Two control groups without CP consisted of 27 children with obesity (OC) (55% girls; median age 13.8 years) and 25 children without obesity (normal control [NC]) (72% girls; median age 14.5 years). Obesity was defined as BMI percentile ≥ 95%. Fasting serum concentrations of leptin, brain‐derived neurotrophic factor (BDNF), and alpha‐melanocyte–stimulating hormone (α‐MSH) were measured in the groups.ResultsLeptin and BDNF concentrations were correlated with BMI SD score (SDS) in controls (OC + NC) and CP. However, there was no correlation between α‐MSH and BMI‐SDS in CP or control groups. After adjusting for age, sex, and BMI‐SDS, α‐MSH was found to be significantly higher in CPobesity than in other groups, whereas leptin and BDNF were comparable among the four groups.ConclusionsSerum BDNF, just like leptin, increased with BMI, regardless of hypothalamic damage. On the contrary, α‐MSH concentration was significantly high in HO, designating a potential biomarker for HO in CP.
Maximum principle of optimal control of a Cahn–Hilliard–Navier–Stokes model with state constraints
Authors: Tachim Medjo Theodore , Tone Cristina , Tone Florentina 
Published: January 2021

AbstractWe investigate in this article Pontryagin's maximum principle for a class of control problems associated with a Cahn–Hilliard–Navier–Stokes model in a two dimensional bounded domain. The model consists of the Navier–Stokes equations for the velocity v, coupled with a Cahn–Hilliard model for the order (phase) parameter . We derive Pontryagin's maximum principle for the control problems assuming that a solution exists. Let us note that the coupling between the Navier–Stokes and the Cahn–Hilliard systems makes the analysis of the control problem more involved.
Vorticity‐stream function approaches are inappropriate to solve the surface Navier‐Stokes equation on a torus
Authors: Nitschke Ingo , Reuther Sebastian , Voigt Axel 
Published: January 2021

AbstractThe growing interest in interfacial flows in engineering and biological applications demands to numerically solve the incompressible surface (Navier)‐Stokes equation. A common approach, based on a vorticity‐stream function formulation reformulates the equation into a system of scalar‐valued surface partial differential equations, for which various numerical methods have been developed. However, on surfaces, which are not simply connected, this approach is not appropriate. We here explain the underlying situation and provide details and examples.
The impact of fiber properties on the material coefficients of short fiber‐reinforced composites
Authors: Rauter Natalie , Lammering Rolf 
Published: January 2021

AbstractHomogenization techniques lead to a deterministic description of a microstructure. However, the components of the microstructure for example of short fiber‐reinforced composites (SFRC) show probabilistic characteristics. In this study, a numerical approach is presented to analyze the influence of these probabilistic characteristics of the fiber length, diameter, orientation and fiber volume fraction on the elasticity tensor. The plausibility of the presented numerical approach is proven by the symmetry of the resulting elasticity tensor as well as the overall assumption of transversely‐isotropic material behavior for SFRC indicated by the elasticity tensor structure. The simulations based on PBT GF 30 reveal, that the elasticity coefficients are significantly influenced by the stochastic distribution of the fiber orientation. Besides this, except for C11, the stochastic properties of the fiber length, the fiber diameter and the fiber volume fraction only slightly influence the mean of the elasticity coefficients.
Phase Field Simulations of Wetting Based on Molecular Simulations
Authors: Diewald Felix , Heier Michaela , Lautenschläger Martin , Kuhn Charlotte , Langenbach Kai , Hasse Hans , Müller Ralf 
Published: January 2021

AbstractManufacturing techniques that can produce surfaces with a defined microstructure are in the focus of current research efforts. The ability to manufacture such surfaces gives rise to the need for numerical models that can predict the wetting properties of a given microstructure and can help to optimize these surfaces with respect to certain wetting properties. The present phase field (PF) model for wetting is linked to molecular dynamics (MD) simulations by the usage of the MD based perturbed Lennard‐Jones truncated and shifted (PeTS) equation of state as well as a MD based viscosity correlation. The lower computational effort of the PF simulations compared to MD simulations enables the model to simulate wetting scenarios on the microscale.
Computation of the Sharpest Bounds on Probabilities under the Influence of Polymorphic Uncertainties
Authors: Miska Niklas , Balzani Daniel 
Published: January 2021

AbstractThis contribution focuses on the combination of the Optimal Uncertainty Quantification framework with fuzzy numbers for a polymorphic uncertainty quantification. The combination allows an integrated approach for the investigation and comparison of different combinations of intervals, which are used as input quantity for the OUQ framework.
An anisotropic phase‐field model at finite strains for composite fracture
Authors: Yin Bo , Kaliske Michael 
Published: January 2021

AbstractPhase‐field modeling has been intensively studied and demonstrated to appropriately capture complex fracture evolutions. Experimental evidence indicates that the fracture evolution is largely relying on the constitutive relations of the engineering materials, e.g. anisotropic properties. In general, anisotropic failure characteristics are governed by the mechanical response and the fracture evolution simultaneously. The work at hand introduces an anisotropic phase‐field modeling for composite material's fracture, which uses only one phase‐field variable to evaluate the fracture status of the matrix and the fiber materials simultaneously. As a result, an equivalent crack surface energy density function is established. Furthermore, the constitutive laws are consistently derived by a straightforward variational principle. Consequently, an interesting numerical example is shown to demonstrate the capabilities of this approach.
Lattice Boltzmann Simulation of Plane Strain Problems
Authors: Schlüter Alexander , Yan Sikang , Reinirkens Thomas , Kuhn Charlotte , Müller Ralf 
Published: January 2021

AbstractThe Lattice Boltzmann Method (LBM), e.g. in [3] and [4], can be interpreted as an alternative method for the numerical solution of partial differential equations. The LBM is usually applied to solve fluid flows. However, the interpretation of the LBM as a general numerical tool, allows to extend the LBM to solid mechanics as well. In this spirit, the LBM has been studied in recent years. First publications [5], [6] present a LBM scheme for the numerical solution of the dynamic behavior of a linear elastic solid under simplified deformation assumptions. For so‐called anti‐plane shear deformation, the only non‐zero displacement component is governed by the two‐dimensional wave equation. In this work, the existing LBM for the two‐dimensional wave equation is extended to more general plane strain problems. The algorithm reduces the plane strain problem to the solution of two separate wave equations for the volume dilatation and the non‐zero component of the rotation vector, respectively.
Efficient multivariate inversion of the NFFT
Authors: Kircheis Melanie , Potts Daniel 
Published: January 2021

AbstractVarious applications such as MRI, solution of PDEs, etc. need to perform an inverse nonequispaced fast Fourier transform (iNFFT), i. e., compute Fourier coefficients from given nonequispaced data. In contrast to iterative solvers we introduce a direct method for this inversion in the overdetermined setting. For this purpose, we use the matrix representation of the NFFT. Modifying one of the matrix factors leads to an optimization problem, which can be solved in a precomputational step using normal equations. Therefore, we are able to compute an inverse NFFT up to a certain accuracy by means of a modified adjoint NFFT and therefore preserve its arithmetic complexity.
Correction of Wave Signals for PMMA Split Hopkinson Pressure Bar Setups
Authors: Bieler Sören , Weinberg Kerstin 
Published: January 2021

AbstractThe Split‐Hopkinson Pressure Bar (SHPB) is a common experimental setup to investigate the dynamic properties of materials. For soft materials the SHPB setup has to be customize using plastic bars. Because such bars show wave attenuation and dispersion, the measured wave signals have to be corrected. In this study a method of signal correction by means of a spectral analysis is presented.
A fully coupled two‐phase bone material model
Authors: Blaszczyk Mischa , Hackl Klaus 
Published: January 2021

AbstractSimulation of wave propagation in bone has important applications, including improvements in sonography‐based early detection of medical conditions like osteoporosis as a fast, cheap and risk‐free diagnosis tool [1]. In modeling, the problem is often reduced to only mechanical effects. Recent research includes electrical and magnetic effects as well [2].Here we present a fully coupled two‐phase approach for modeling bone considering mechanical, electrical and magnetic effects. The first phase describes cortical bone as a piezoelectric [3] and insulating solid. The second phase models bone marrow as a viscoelastic and conducting solid. Electrical and magnetic effects are coupled via the Maxwell equations. Based on energy methods in mechanics, a thermodynamically consistent material model is established and the weak and strong form of the boundary value problem are derived. A finite element approach is implemented and example calculations are shown.
Shape optimization of the X0‐specimen for biaxial experiments
Authors: Liedmann Jan , Gerke Steffen , Barthold Franz-Joseph , Brünig Michael 
Published: January 2021

AbstractThe mechanical damage and fracture behavior of ductile sheet metals strongly depend on the stress state and intensity. Thus, for adequate characterization of the material behavior, it is crucial to have specimens that cover different and preferably distinct stress states, especially in the inelastic domain. In this paper, the geometry of the X0‐specimen is optimized to achieve a distinct stress triaxiality distribution in the region of damage and fracture occurrence, depending on two different load cases in a biaxial testing environment. The shape optimization is gradient based and the gradients of the objective and constraint functions are computed analytically by means of variational principles. The resulting geometries show improvements in terms of the intensity of the stress state numerically as well as experimentally.
A macroscopic model for magneto‐active elastomers based on microscopic simulations
Authors: Kalina Karl A. , Metsch Philipp , Brummund Jörg , Kästner Markus 
Published: January 2021

AbstractHerein, the development and calibration of a macroscopic model for magneto‐active elastomers based on data generated from computational homogenizations is presented. The advantage of this strategy is the possibility to adjust the model independent of any macroscopic sample geometry. Using the calibrated model, the magnetostrictive and magnetorheological effect of macroscopic samples are simulated within a wide range of magnetic fields.
Extension of an analytical solution of a unified formulation to the frequency response of composite plates with viscoelastic layers
Authors: Jackstadt Alexander , Kärger Luise 
Published: January 2021

AbstractResulting from their high stiffness and low weight, lightweight structures made from fiber reinforced polymers are usually prone to vibrations. The inclusion of viscoelastic interlayers can provide a viable mean to passively damp these structures due to constrained layer damping. For the modeling of such structures, a layerwise approach based on the Generalized Unified Formulation has previously been proven suitable for static load cases.This contribution presents an analytical procedure to determine the frequency response and vibration characteristics of such heterogeneous laminates incorporating viscoelastic layers. Specifically, simply supported plates modeled by the Generalized Unified Formulation are considered and solved using Navier type solutions. The approach is validated by comparison with 3D finite element models. Particular focus is put on the order of expansion in thickness direction needed to accurately predict the frequency response of the laminate.
Optimal Sensor Placement for Thermo‐Elastic Coupled Machine Models
Authors: Naumann Andreas , Herzog Roland 
Published: January 2021

AbstractAccuracy requirements for machine tools demand an accurate positioning of the tool center point. Due to the heat sources, for example the friction and heat loss of motors, a machine can undergo complicated deformations during operation. While the location of mounted sources are known in advance, there are also process dependent sources, like hot chips after chip off. Furthermore many material parameters and most coupling parameters are not known exactly, or have an unknown temperature dependency.We consider a coupled thermo‐elastic finite element model of a simplified machine tool. We include uncertain heat sources and exchange parameters and present an optimal sensor placement approach to capture the sources.
Microstructure simulation using self‐consistent clustering analysis
Authors: Waimann Johanna , Gierden Christian , Schmidt Annika , Svendsen Bob , Reese Stefanie 
Published: January 2021

AbstractTo capture all the individual microstructural effects of complex and heterogeneous materials in structural finite element simulations, a two‐scale simulation approach is necessary. Since the computational effort of such two‐scale simulations is extremely high, different methods exist to overcome this problem. In terms of a FFT‐based microscale simulation, one possibility is to use a reduced set of frequencies leading to a reduced numerical solution of the Lippmann‐Schwinger equation [?]. In a post‐processing step, highly resolved microstructural fields may then be reconstructed by using the compressed sensing technique [?]. Since the stress evaluation of this method is in real space and therefore not reduced, it is most beneficial in terms of linear elastic material behavior. Another very recent method to reduce the computational effort of a microscale simulation is the self‐consistent clustering analysis [?,?]. Such a self‐consistent clustering analysis is split into an offline and an online stage. Within the offline stage, the material points of the high‐fidelity representation of the unit cell are grouped into clusters with similar material behavior. Thereafter, in the online stage, a self‐consistent clustering analysis is used to solve the boundary value problem by a clustered Lippmann‐Schwinger equation. Since the generation of clusters may be based on linear elastic simulations, we propose to use a reduced set of frequencies for these simulations to improve the efficiency of the total algorithm. Elastic and elasto‐plastic composites are investigated in a small strain setting as representative simulation examples.
A dynamical model for the calcineurin‐NFATc signaling pathway and muscle fiber shifting
Authors: Villota-Narvaez Yesid , Ramírez-Martínez Angélica , Garzón-Alvarado Diego , Röhrle Oliver 
Published: January 2021

AbstractTraining exercise produces skeletal muscle adaptation: at the organ scale, as anatomical changes; and at the myofiber scale, as mitochondrial and protein type content. The protein content of a myofiber is controlled by the calcineurin‐NFATc signaling pathway: exercise triggers the pathway, and its final product is the translocation of dephosphorylated NFATc to the nucleus. Once in the nucleus, NFATc controls the state of the gene program to encode the slow or the fast fiber type characteristics. In the long term, the adaptation of the fiber type characteristics produces a shift in muscle fiber type: an increase in the number of myofibers of the fast type (which means that myofibers of the slow type shift to fast type) is related to force production; and an increase in the number of myofibers of the slow type (myofibers of the fast type shift to slow type) is related to fatigue resistance. These macroscopic features, i.e. force production and fatigue resistance, are the main target of most training protocols; however, little attention is focused on the limitations imposed by the fiber distribution of muscles at the organ scale. Based on the calcineurin‐NFATc signaling pathway, we represented an exercise stimulus by a cytosolic calcium signal, and simulated the dynamics of NFATc in the nucleus. In this contribution, we present a dynamical model for the calcineurin‐NFATc signaling pathway to describe the time course of dephosphorilated NFATc in the nucleus. We used an experimental report of a continuous stimulation pattern for calibration, and an experimental report of a pulsed stimulation pattern for comparison; we obtained a good agreement between the simulations and the experimental measurements.
A Multiscale and Multiphase Model of Function‐Perfusion Growth Processes in the Human Liver
Authors: Lambers Lena , Suditsch Marlon , Wagner Arndt , Ricken Tim 
Published: January 2021

AbstractDue to an ageing society and unhealthy living conditions, liver diseases like non‐alcoholic fatty liver disease (NAFLD) or liver cancer will account for an increasing proportion of deaths in the coming years. Using a mathematical model, the underlying function‐perfusion processes of both diseases are investigated. We developed a multiscale and multiphase model for the simulation of hepatic processes on the lobular and cell scale. The lobular scale is described with partial differential equations (PDEs) based on the Theory of Porous Media (TPM), whereas on the cellular scale the metabolic processes are calculated using ordinary differential equations (ODEs). Since NAFLD and the development of a liver tumor lead to tissue growth as well as changes in the blood perfusion, growth and remodelling processes in the human liver are evaluated.