bluuebunny/crossref_metadata_2025_split huggingface dataset:
Role of the spinal canal compliance in regulating posture‐related cerebrospinal fluid hydrodynamics in humans
Authors: Alperin Noam , Burman Ritambhar , Lee Sang H. 
Published: January 2021

Mechanical compliance of a compartment is defined by the change in its volume with respect to a change in the inside pressure. The compliance of the spinal canal regulates the intracranial pressure (ICP) under postural changes. Understanding how gravity affects ICP is beneficial for poorly understood cerebrospinal fluid (CSF)‐related disorders. The aim of this study was to evaluate postural effects on cranial hemo‐ and hydrodynamics. This was a prospective study, which included 10 healthy volunteers (three males, seven females, mean ± standard deviation age: 29 ± 7 years). Cine gradient‐echo phase‐contrast sequence acquired at 0.5 T, “GE double‐doughnut” scanner was used. Spinal contribution to overall craniospinal compliance (CSC), craniospinal CSF stroke volume (SV), magnetic resonance (MR)‐derived ICP (MR‐ICP), and total cerebral blood flow (TCBF) were measured in supine and upright postures using automated blood and CSF flows quantification. Statistical tests performed were two‐sided Student's t‐test, Cohen's d, and Pearson correlation coefficient. MR‐ICP and the craniospinal CSF SV were significantly correlated with the spinal contribution to the overall CSC (r = 0.83, p < 0.05) and (r = 0.62, p < 0.05), respectively. Cranial contribution to CSC increased from 44.5% ± 16% in supine to 74.9% ± 8.4% in upright posture. The average MR‐ICP dropped from 9.9 ± 3.4 mmHg in supine to −3.5 ± 1.5 mmHg. The CSF SV was over 2.5 times higher in the supine position (0.55 ± 0.14 ml) than in the upright position (0.21 ± 0.13 ml). In contrast, TCBF was slightly higher in the supine posture (822 ± 152 ml/min) than in the upright posture (761 ± 139 ml/min), although not statistically significant (p = 0.16). The spinal‐canal compliance contribution to CSC is larger than the cranial contribution in the supine posture and smaller in the upright posture. Thereby, the spinal canal plays a role in modulating ICP upon postural changes. The lower pressure craniospinal CSF system was more affected by postural changes than the higher‐pressure cerebral vascular system. Craniospinal hydrodynamics is affected by gravity and is likely to be altered by its absence in space.Level of Evidence4Technical Efficacy Stage2
In vivo liver thermoacoustic imaging and demonstration based on localization wire
Authors: Xiang Hongjin , Zheng Zhu , Huang Lin , Qiu Tingting , Luo Yan , Jiang Huabei 
Published: January 2021

PurposeLiver disease causes significant morbidity and mortality worldwide. Liver imaging plays an essential role in the noninvasive liver disease evaluation because of the limitation of liver biopsy. This paper aims to image in vivo liver with thermoacoustic imaging (TAI) and demonstrate this liver imaging technique with a cross‐validation method.MethodsThe imaging system composed of a large aperture antenna and a flexible transducer array was used, and we performed the position calibration using the delay and sum algorithm. The localization wire was utilized in the cross‐validation of in vivo liver TAI.ResultsWe successfully validated in vivo liver TAI. In vivo images of different liver lobes without labels were observed. The imaging depth reached about 4 cm.ConclusionsTAI has the potential to image the liver and provide useful dielectric properties of the liver tissue. This study realized the first in vivo liver TAI, suggesting its prospect in detecting liver disease noninvasively.
Phthalate and Bisphenol Urinary Concentrations, Body Fat Measures, and Cardiovascular Risk Factors in Dutch School‐Age Children
Authors: Silva Carolina C. V. , Jaddoe Vincent W. V. , Sol Chalana M. , El Marroun Hanan , Martinez‐Moral Maria‐Pilar , Kannan Kurunthachalam , Trasande Leonardo , Santos Susana 
Published: January 2021

ObjectiveThe purpose of this study was to investigate the associations of urinary phthalates and bisphenols at age 6 years old with body fat and cardiovascular risk factors at 6 and 10 years and with the change from 6 to 10 years.MethodsAmong 471 Dutch children, the phthalates and bisphenols urinary concentrations at 6 years and BMI, fat mass index, android fat mass, blood pressure, glucose, insulin, and lipids blood concentrations at 6 and 10 years were measured.ResultsAn interquartile range increase in di‐n‐octyl phthalate (DNOP) metabolites concentrations at 6 years was associated with an increased risk of overweight at 6 and 10 years (odds ratio: 1.44; 95% CI: 1.11‐1.87, and 1.43; 95% CI: 1.09‐1.86, respectively). Also, higher DNOP metabolites concentrations were associated with higher fat mass index at 6 years, higher systolic blood pressure at 10 years, a decrease in high‐density lipoprotein cholesterol, and an increase in triglycerides concentrations from 6 to 10 years (P < 0.05). Higher total bisphenols and bisphenol A concentrations were associated with a decrease in BMI from 6 to 10 years (P < 0.01).ConclusionsDNOP metabolites are associated with overweight and an adverse cardiovascular profile in childhood. Total bisphenols and bisphenol A are associated with a decrease in BMI from 6 to 10 years.
Dynamic Stability of Viscoelastic Bars under Pulsating Axial Loads
Authors: Kern Dominik , Gypstuhl Richard , Groß Michael 
Published: January 2021

AbstractRecent applications require the extension of stability theory to axially loaded viscoelastic bars. For elastic bars it is known that a pulsating load leads to a Mathieu equation. Meaning, there are some instable regions before the static buckling load and some stable regions beyond, depending on the excitation (amplitude, frequency, offset). To fill this gap we follow along the lines of Weidenhammer and adopt the classical Euler‐Bernoulli beam kinematics for coupled longitudinal and bending vibrations. Modeling viscoelasticity by the Standard Linear Solid model introduces an internal variable. Hence, there are auxiliary transversal and longitudinal displacements corresponding to the internal variable in addition to the physical transversal and longitudinal displacements of the bar centerline. The modeling further assumes only longitudinal vibrations in the stable regime, thus there are no bending vibrations and the description simplifies to a system of linear partial differential equations. Further, a one‐sided coupling is assumed for the stability analysis, i.e. the longitudinal vibrations are prescribed and induce bending vibrations. Still, the time‐variant coefficients of the transversal dynamics make it difficult to find an analytical solution. Consequently, an approximation is obtained by Ritz method from Hamilton's principle. Applying the eigenforms of elastic buckling as trial functions finally leads to a system of rheolinear ordinary differential equations. Its stability chart with respect to static and harmonic load components is calculated numerically by Floquet theory.
Predicting laser‐induced cavitation near a solid substrate
Authors: Denner Fabian , Evrard Fabien , Reuter Fabian , Gonzalez-Avila Silvestre Roberto , van Wachem Berend , Ohl Claus-Dieter 
Published: January 2021

AbstractThe asymmetric collapse of cavitation bubbles near a solid substrate generates large wall shear stresses, the precise magnitude of which is still not known with certainty. By comparing numerical simulations and experiments of a laser‐induced cavitation bubble near a solid substrate, we demonstrate that an accurate measurement of the pressure pulse emitted during bubble inception and of the maximum bubble radius allow a unique initialisation of the simulation. This allows an accurate reproduction of the asymmetric collapse, with reliable predictions of the shear stress and pressure generated at the substrate.
Structure‐preserving discretization of a port‐Hamiltonian formulation of the non‐isothermal Euler equations
Authors: Hauschild Sarah-Alexa , Marheineke Nicole 
Published: January 2021

AbstractThe port‐Hamiltonian (pH) formulation of partial‐differential equations (pdes) and their numerical treatment have been elaborately studied lately. In this context we consider the non‐isothermal flow of a compressible fluid. Starting from the pdes we derive a pH formulation for Euler‐type equations in the weak sense on one pipe. One advantage of pH systems is that fundamental physical properties, like energy dissipation and mass conservation, are encoded in the system structure. Therefore, structure‐preservation during approximation is most important. Based on the weak form we introduce a structure‐preserving Galerkin approximation with mixed finite elements. A numerical example supports the theoretical results.
Stability analysis of nonholonomic extremum seeking systems via Lie brackets approximations
Authors: Grushkovskaya Victoria 
Published: January 2021

AbstractThe paper presents a novel family of dynamic extremum seeking controls for nonholonomic systems with output described by a convex function. It is assumed that the vector fields of the system satisfy the controllability rank condition with first‐ and second‐order Lie brackets. The proposed algorithm consists of two components. The first one is the stabilizing model‐based component constructed based on control strategies for nonholonomic systems. The second one is the extremum seeking model‐free component relying only on the values of the output of the system. The resulting control strategy optimizes the system behavior in the sense of minimizing its output. Namely, the main result of the paper states practical exponential stability of the optimal point, at which the output takes its minimal value.
Transversal vibrations of a toothed belt in linear drives during operation
Authors: Schnürer Dominik , Holl Helmut J. 
Published: January 2021

AbstractVibrations of the toothed belt of a linear drive can affect the dynamic positioning accuracy and smoothness which is important for practical applications. An analytical, one‐dimensional model of a belt section is derived, taking into account the preload and flexural rigidity, as well as the non‐linear cable effect and the acceleration forces due to the belt mass. In addition to the case of constant belt length, the temporal change of the length as a result of the axial motion is an essential part of the modeling. The solution of the equation of motion is limited to the dominant transverse deflection of the belt. For the longitudinal extension, the assumption of a quasi‐static solution is taken. A FEM program is implemented to calculate the solution for given operation conditions. The evaluations are made for selected motions according to a path planning with trapezoidal velocity profiles. A modification of individual parameters, based on a practical parameter set, enables the analysis of the respective effects.
Turbulent swirl flow analysis by Kolmogorov's similarity hypotheses
Authors: Čantrak Ðorđe S. , Janković Novica Z. , Nedeljković Miloš S. 
Published: January 2021

AbstractTurbulent swirl flow generated by the axial fans in pipe is investigated in this paper by using Kolmogorov's similarity hypotheses. It is shown that energy in the inertial subrange is divided among eddies after the “−5/3” law, i.e. Φww ∝ f−5/3, where Φww is spectral density for circumferential velocity and f is the frequency. This is presented for two various axial fans, of which one is carefully designed to generat Rankine vortex, while the second one has solid body circumferential velocity profile.
A semi‐explicit integration scheme for weakly‐coupled poroelasticity with nonlinear permeability
Authors: Altmann Robert , Maier Roland , Unger Benjamin 
Published: January 2021

AbstractWithin the time integration of linear elliptic‐parabolic problems such as poroelasticity, large systems have to be solved in every time step. With a semi‐explicit approach, these systems decouple, leading to a remarkable speed‐up. This paper indicates that this idea can also be applied to nonlinear problems such as poroelasticity with nonlinear permeability. To see this, we consider a related toy problem.
GR decompositions and their relations to Cholesky‐like factorizations
Authors: Benner Peter , Penke Carolin 
Published: January 2021

AbstractFor a given matrix, we are interested in computing GR decompositions A = GR, where G is an isometry with respect to given scalar products. The orthogonal QR decomposition is the representative for the Euclidian scalar product. For a signature matrix, a respective factorization is given as the hyperbolic QR decomposition. Considering a skew‐symmetric matrix leads to the symplectic QR decomposition. The standard approach for computing GR decompositions is based on the successive elimination of subdiagonal matrix entries. For the hyperbolic and symplectic case, this approach does in general not lead to a satisfying numerical accuracy. An alternative approach computes the QR decomposition via a Cholesky factorization, but also has bad stability. It is improved by repeating the procedure a second time. In the same way, the hyperbolic and the symplectic QR decomposition are related to the LDLT and a skew‐symmetric Cholesky‐like factorization. We show that methods exploiting this connection can provide better numerical stability than elimination‐based approaches.
Rot‐free finite elements for gradient‐enhanced formulations at finite strains
Authors: Riesselmann Johannes , Ketteler Jonas , Schedensack Mira , Balzani Daniel 
Published: January 2021

AbstractThis contribution presents a mixed C0 continuous finite element approach for gradient enriched formulations. The approach is based on a split of the Lagrange multiplier into a gradient and a rotational part, through which a decoupled set of variational equations is obtained. Application to numerical examples in the finite strain gradient elasticity framework unveils the reduced computational effort due to the decoupled character of the global system of equations such as the ability to avoid stress localization.
Towards a mathematical model for single molecule structured illumination microscopy
Authors: Hockmann Mathias , Kunis Stefan , Kurre Rainer 
Published: January 2021

AbstractWhile structured illumination microscopy (SIM) is a widely used super‐resolution microscopy technique for densely labelled samples, we apply a modified version of the matrix pencil method to single molecule imaging. We prove that under reasonable conditions we can recover up to two times more molecule positions compared to conventional microscopy exactly from noiseless data and include numerical examples illustrating benefits as well as limitations of the algorithm.
Extension of the eigenerosion approach to ductile crack propagation at large strains and its application on hard metal microstructures
Authors: Wingender Dennis , Balzani Daniel 
Published: January 2021

AbstractThe efficient operation of mechanized tunnel drilling machines is strongly determined by the wear resistance of the applied mining tools. Especially in chisels, but also partly in cutting disks, hard metals are used. Their wear mechanism is dominated by surface spalling, i.e. subcritical crack propagation through the material's microstructure mainly consisting of a ductile metal matrix and carbide inclusions. Since this process is mainly governed by the morphology of the microstructure and the mechanical behavior of the individual phases, simulations at the microscale enable the design of improved materials. In this contribution a method for the modeling of this process is presented. The approach is based on the eigenerosion framework introduced in [1] and an algorithmic scheme for large strains is given, which extends the small strain implementation in [2]. For the phases at the microscale the finite strain plasticity formulation [3] is applied. Furthermore, simulations are carried out on the microscale by applying the Finite Cell Method [4] on hard metal microstructures. Here, a specific cell arrangement is constructed which minimizes the required number of cells for a given microstructure morphology. By evaluating the results of these simulations, failure of the material can be investigated on a microscopic level and improvements of the material morphology regarding wear can be realized.
Possibilities and drawbacks using arbitrary precision numbers for structural analysis
Authors: Klarmann Simon , Wackerfuß Jens 
Published: January 2021

AbstractIn various areas of computational mechanics, rounding errors can have a considerable influence on the quality of the simulation results; in some cases, these lead to the termination of the numerical calculation. Rounding errors are caused by limited accuracy in the representation of floating point numbers. Current codes usually use double precision numbers (p = 16 significant digits). Until now, modern multi‐precision libraries with which floating‐point numbers can be processed with arbitrary accuracy are largely unused.The aim of this article is to show the possibilities and limitations of such libraries in the context of computational mechanics. The accuracy of computations from p = 8 up to p = 128 will be investigated. Examples will be selected which are particularly sensitive to rounding errors. On the basis of a first academic example it is examined which calculation accuracy is necessary to carry out a static analysis on a cantilever beam with a slenderness of up to 1049 with a standard beam FE formulation. In a second example, a load‐bearing structure is analyzed in which the stiffness of its supporting members differs by several powers. Finally, the disadvantages associated with the higher calculation accuracy (CPU time, memory requirements) are discussed.
Determination of the sound insulation property of 2D periodic wall structures by a fluid‐structure interaction model
Authors: Perras Elias , Zhang Chuanzeng 
Published: January 2021

AbstractThe propagation of acoustic and elastic waves in periodical structures, often referred to as phononic crystals (PCs), can be drastically restricted. In the so‐called band‐gaps, which are certain frequency ranges, the wave propagation is prohibited in the PCs. The location and the width of the band‐gaps are determined by the geometrical and the material properties of the PCs. The purpose of this work is to analyze the sound insulation capabilities of wall structures consisting of two‐dimensional (2D) PCs, which are referred to as the PC walls. Since no analytical methods exist to determine the sound insulation capabilities of such geometrically complex periodic structures, a fully coupled fluid‐structure interaction (FSI) model is developed based on the finite element method (FEM). The PC walls are optimized to realize desirable band‐gaps within the audible frequency range. Numerical examples are presented and discussed to demonstrate that the sound insulation capabilities of periodically structured walls are far superior to that of the traditional wall structures in the frequency band‐gaps of the PC walls.
Image‐based stress analysis of porous freeze casts
Authors: Birk Carolin , Lupascu Doru C. , Vadalaà Miriana , Saputra Albert 
Published: January 2021

AbstractAn automatic image‐based mesh generation and modeling approach is applied to static stress analysis of porous materials produced by freeze casting. The scaled boundary finite element method is employed due to its seemles integration with octree meshes. Several aspects related to image processing and numerical efficiency are discussed in order to evaluate the suitability of the SBFEM in the context of modeling foam‐like samples with highly irregular microstructural details.
Bimodal parametric excitation of a micro‐ring gyroscope
Authors: Barakat Ahmed A. , Lima Roberta , Sampaio Rubens , Hagedorn Peter 
Published: January 2021

AbstractParametric excitation in vibratory systems is known well over hundred years. Recently it is also being exploited in Micro‐electromechanical Systems (MEMS). One example of these are micro‐ring gyroscopes, which are used in the automotive, the navigation and in the space industries. The sensitivity of such gyroscopes can be impaired by signal noise induced through parasitic capacitance between drive and sense electrodes. Applying parametric excitation and exploiting parametric amplification recently was shown to open new promising paths. On the theoretical side of parametric vibrations, recently it was found that the simultaneous parametric excitations in two coordinates or more with phase difference can lead to very interesting phenomena. The micro‐ring gyroscope is a good example of making use of parametric excitation and amplification to solve some of the problems in the modern MEMS. This work aims at modelling a micro‐ring gyroscope with two simultaneous phase lagged parametric excitations. The equations of motion can be derived using Hamilton's principle, both for an inextensible as well as for the extensible ring, and in the fully symmetric cases the eigenvalue problem can be solved analytically. The completely symmetric problem, leads to two eigenfunctions for any given eigenfrequency, except for the fundamental ones. The axial symmetry is in general destroyed by the way in which the vibrating ring is elastically supported by discrete elastic supports. Instead of truly double eigenfrequencies, the problem then has pairs of two closely spaced eigenfrequencies. In the simplest case, the ring can then be described by two generalized coordinates. Making use of direct excitation of each of the modes, as well as parametric excitation, makes it possible to exploit parametric resonance and parametric amplification. This has been applied before for the micro‐ring gyroscope, however not for the case of parametric excitation in two coordinates and with phase lag between the two parametric excitations. Taking into account this phase lag as an additional parameter, opens several new ways of sensing the angular velocity of the moving base of the micro‐ring gyroscope.
Closed‐form stress solution of open holes in a finite domain
Authors: Nguyen-Hoang Minh , Becker Wilfried 
Published: January 2021

AbstractOpen holes are essential design features in many technical structures. For a lightweight optimal design precise stress analysis tools are vital. Focus of this contribution is the stress field determination of an open hole in a rectangular plate of finite width by analytical means, particularly the Airy stress function. This is beneficial in terms of computational effort. To obtain results of high precision, the stress boundary conditions at the straight edges as well as along the hole boundary must be fulfilled. This is reached by supplementing the field modelling the corresponding infinite dimensions problem – the Kirsch solution – with auxiliary functions.
Perspectives in the modeling of biopolymer aerogel networks subject to wetting
Authors: Rege Ameya , Gurikov Pavel , Kalmár József , Milow Barbara 
Published: January 2021

AbstractAlginate‐based aerogels were shown to be non‐cytotoxic and to feature good cell adhesion, thus drawing their attention towards tissue engineering and regenerative medicine [1]. To this end, their mechanical properties under dry as well as wet conditions were subsequently investigated [2]. Upon wetting, these aerogels showed strong stiffening in their mechanical behavior. In this work, a micromechanically motivated model approach to describe this phenomenon is proposed. The nanofibers in the aerogel network are considered to undergo structural rearrangement upon being subjected to water. Furthermore, the collapse of the micropores (pore diameter below 5 nm) results in the formation of local hydrogel‐like network phase. The constitutive model is based upon the assumption that the total network can be decomposed into a hydrogel‐like network and a restructured aerogel network. The aerogel network is described based on the micromechanical model proposed by Rege et al. [3], while the hydrogel‐like network is modeled based on the phenomenological approach of Gent [4]. This first approach towards modeling shows reliable results against the experimental stress‐strain curves of alginate‐starch aerogels [5].