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Shear stress

M Vahabi, Bart E Vos, Henri C G de Cagny, Daniel Bonn, Gijsje H Koenderink, F C MacKintosh
Biopolymer gels such as fibrin and collagen networks are known to develop tensile axial stress when subject to torsion. This negative normal stress is opposite to the classical Poynting effect observed for most elastic solids including synthetic polymer gels, where torsion provokes a positive normal stress. As shown recently, this anomalous behavior in fibrin gels depends on the open, porous network structure of biopolymer gels, which facilitates interstitial fluid flow during shear and can be described by a phenomenological two-fluid model with viscous coupling between network and solvent...
March 2018: Physical Review. E
Armand Barbot, Matthias Lerbinger, Anier Hernandez-Garcia, Reinaldo García-García, Michael L Falk, Damien Vandembroucq, Sylvain Patinet
We develop and extend a method presented by Patinet, Vandembroucq, and Falk [Phys. Rev. Lett. 117, 045501 (2016)PRLTAO0031-900710.1103/PhysRevLett.117.045501] to compute the local yield stresses at the atomic scale in model two-dimensional Lennard-Jones glasses produced via differing quench protocols. This technique allows us to sample the plastic rearrangements in a nonperturbative manner for different loading directions on a well-controlled length scale. Plastic activity upon shearing correlates strongly with the locations of low yield stresses in the quenched states...
March 2018: Physical Review. E
Rhiannon Pinney, Tanniemola B Liverpool, C Patrick Royall
We consider the yielding under simple shear of a binary Lennard-Jones glass former whose super-Arrhenius dynamics are correlated with the formation of icosahedral structures. We recast this glass former as an effective system of icosahedra [Pinney et al., J. Chem. Phys. 143, 244507 (2015)JCPSA60021-960610.1063/1.4938424]. Looking at the small-strain region of sheared simulations, we observe that shear rates affect the shear localization behavior particularly at temperatures below the glass transition as defined with a fit to the Vogel-Fulcher-Tamman equation...
March 2018: Physical Review. E
Nga Ling Ko, Liam John, Aaron Gelinne, Maurizio Mandala, George Osol
Although expansive remodeling of the maternal uterine circulation during pregnancy is essential for maintaining uteroplacental perfusion and normal fetal growth, the underlying physiological mechanisms are not well understood. Using a rat model, surgical approaches were used to alter uterine hemodynamics and wall shear stress (WSS) in order to evaluate the effects of WSS and venoarterial communication (e.g. transfer of placentally derived growth signals from post-placental veins to pre-placental arteries) on gestational uterine vascular remodeling...
May 18, 2018: American Journal of Physiology. Heart and Circulatory Physiology
Chenyu Wang, Wenwen Liu, Qingquan Wei, Lufeng Ren, Manqing Tan, Yude Yu
Conventional cell-sized well arrays have advantages of high occupancy, simple operation, and low cost for capturing single-cells. However, they have insufficient space for including reagents required for cell treatment or analysis, which restricts the wide application of cell-sized well arrays as a single-cell research tool alone. Here, we present a novel dual-well array chip, which integrates capture-wells (20  μ m in diameter) with reaction-wells (100  μ m in diameter) and describe a flow method for convenient single-cell analysis requiring neither complicated infra-structure nor high expenditure, while enabling highly efficient single cell trapping (75...
May 2018: Biomicrofluidics
B Eidel, A Gote, A Ohrndorf, H-J Christ
The present work proposes a simple, novel fixation concept for short stem hip endoprostheses, which preserves the pre-surgery force flow through femoral bone to an unprecedented extent. It is demonstrated by finite element analyses that a standard implant model endowed with minor geometrical changes can overcome bone loading reduction and can achieve almost physiological conditions. The numerical results underpin that the key aspect of the novel, so-called "collar cortex compression concept CO4 " is the direct, almost full load transmission from the implant collar to the resected femur cortex, which implies that the implant stem must be smooth and therefore interacts mainly by normal contact with the surrounding bone...
May 14, 2018: Medical Engineering & Physics
Jisong Zhao
Wall shear stress is an important quantity in fluid mechanics, but its measurement is a challenging task. An approach to measure wall shear stress vector distribution using shear-sensitive liquid crystal coating (SSLCC) is described. The wall shear stress distribution on the test surface beneath high speed jet flow is measured while using the proposed technique. The flow structures inside the jet flow are captured and the results agree well with the streakline pattern that was visualized using the oil-flow technique...
May 17, 2018: Sensors
Heather Grimm, Jan Kretzschmar, Marc D Cook, Michael D Brown
INTRODUCTION: Optimal vascular function is a hallmark of cardiovascular health. Specifically, the balance of vasoconstricting and vasodilating substances is recognized as a marker of vascular health. One of the greatest challenges to vascular health and vasodilatory balance is tumor necrosis factor alpha (TNFα) mediated inflammation. Uncovering effective strategies that maintain a vascular environment that is more vasodilatory and anti-thrombotic in the face of an inflammatory challenge is favorable...
April 30, 2018: Medicine and Science in Sports and Exercise
Shi Shang, Yanting Zheng, Ming Shen, Xianfeng Yang, Jun Xu
To investigate head-brain injuries caused by windshield impact on riders using electric self-balancing scooters (ESS). Numerical vehicle ESS crash scenarios are constructed by combining the finite element (FE) vehicle model and multibody scooter/rider models. Impact kinematic postures of the head-windshield contact under various impact conditions are captured. Then, the processes during head-windshield contact are reconstructed using validated FE head/laminated windshield models to assess the severity of brain injury caused by the head-windshield contact...
2018: Applied Bionics and Biomechanics
Jian-Li Shao, Pei Wang, Feng-Guo Zhang, An-Min He
Previous researches have revealed the importance of shear and the orientation dependence in the structural transition of iron. In this work, we introduce a series of shear deformations by adjusting the strain ratio between the longitudinal ([001]) and transversal ([010] and [100]) directions, and then investigate this structural transition under different anisotropic compressions with molecular dynamics simulations. It is found that the shear deformation can lower the transition pressure notably, and even change the nucleation structure and morphology...
May 16, 2018: Scientific Reports
G Aquila, M B Morelli, F Vieceli Dalla Sega, F Fortini, P Nigro, C Caliceti, M Ferracin, M Negrini, A Pannuti, M Bonora, P Pinton, R Ferrari, P Rizzo
Ivabradine, a heart rate reducing agent, protects the vascular system by unidentified mechanisms. We sought to determine the effects of the treatment with ivabradine, started before plaque formation, on early transcriptional changes and endothelium lesions in regions of aorta subjected to disturbed blood flow. Six week-old apolipoprotein E-deficient (ApoE-/- ) mice, fed a low-fat diet, were treated with ivabradine to determine the effect on transcriptional changes (2-and 4-week treatment) and on lesions formation (19-week treatment) in the endothelium of the aortic arch...
February 2018: Journal of Physiology and Pharmacology: An Official Journal of the Polish Physiological Society
Koichi Onda, Tokushi Kizuka
Tensile deformation of dislocation-free copper (Cu) nanocontacts (NCs) having widths of less than 6 nm was performed in a transmission electron microscope. The deformation behavior was observed In Situ via lattice imaging and the force acting on the NCs was simultaneously measured. The critical shear stress (CSS) for slip occurred in the NCs was estimated using the observed atomic configuration and the values of the forces. The relation of CSS with the minimum cross-sectional area of the NCs was investigated...
January 1, 2018: Journal of Nanoscience and Nanotechnology
Federica Sacco, Bruno Paun, Oriol Lehmkuhl, Tinen L Iles, Paul A Iaizzo, Guillaume Houzeaux, Mariano Vázquez, Constantine Butakoff, Jazmin Aguado-Sierra
The aim of the present study is to characterize the hemodynamics of left ventricular (LV) geometries to examine the impact of trabeculae and papillary muscles (PMs) on blood flow using high performance computing (HPC). Five pairs of detailed and smoothed LV endocardium models were reconstructed from high-resolution magnetic resonance images (MRI) of ex-vivo human hearts. The detailed model of one LV pair is characterized only by the PMs and few big trabeculae, to represent state of art level of endocardial detail...
2018: Frontiers in Physiology
Sabrina Hsiung, Anki Knutsson, Jenifer Vallejo, Pontus Dunér, Suvi E Heinonen, Ann-Cathrine Jönsson-Rylander, Eva Bengtsson, Jan Nilsson, Anna Hultgårdh-Nilsson
The mechanisms responsible for macrovascular complications in diabetes remain to be fully understood. Recent studies have identified impaired vascular repair as a possible cause of plaque vulnerability in diabetes. This notion is supported by observations of a reduced content of fibrous proteins and smooth muscle cell mitogens in carotid endarterectomy from diabetic patients along with findings of decreased circulating levels of endothelial progenitor cells. In the present study we used a diabetic mouse model to characterize how hyperglycemia affects arterial repair responses...
May 14, 2018: Scientific Reports
Erfan Mohagheghian, Junyu Luo, Junjian Chen, Gaurav Chaudhary, Junwei Chen, Jian Sun, Randy H Ewoldt, Ning Wang
Increasing evidence shows that mechanical stresses are critical in regulating cell functions, fate, and diseases. However, no methods exist that can quantify isotropic compressive stresses. Here we describe fluorescent nanoparticle-labeled, monodisperse elastic microspheres made of Arg-Gly-Asp-conjugated alginate hydrogels (elastic round microgels, ERMGs). We generate 3D displacements and calculate strains and tractions exerted on an ERMG. Average compressive tractions on an ERMG are 570 Pa within cell layers and 360 Pa in tumor-repopulating cell (TRC) colonies grown in 400-Pa matrices...
May 14, 2018: Nature Communications
Mirko Bonfanti, Stavroula Balabani, Mona Alimohammadi, Obiekezie Agu, Shervanthi Homer-Vanniasinkam, Vanessa Díaz-Zuccarini
Aortic dissection (AD) is a complex and highly patient-specific vascular condition difficult to treat. Computational fluid dynamics (CFD) can aid the medical management of this pathology, yet its modelling and simulation are challenging. One aspect usually disregarded when modelling AD is the motion of the vessel wall, which has been shown to significantly impact simulation results. Fluid-structure interaction (FSI) methods are difficult to implement and are subject to assumptions regarding the mechanical properties of the vessel wall, which cannot be retrieved non-invasively...
May 11, 2018: Medical Engineering & Physics
Purnendu K M Prithipaul, Michael Kokkolaras, Damiano Pasini
This work considers vascular stents with tubular geometry assumed to follow a periodic arrangement of repeating unit cells. Structural and hemodynamic metrics are presented to assess alternative stent geometries, each defined by the topology of the unit cell. Structural metrics include foreshortening, elastic recoil and radial stiffness, whereas hemodynamic performance is described by a wall shear stress index quantifying the impact of in-stent restenosis. A representative volume element (RVE) modelling approach is used, and results are compared to those obtained from full simulations of entire stents...
May 11, 2018: Medical Engineering & Physics
Peng Wang, Lianhua Zhu, Wei Su, Lei Wu, Yonghao Zhang
The nonlinear oscillation of rarefied gas flow inside a two-dimensional rectangular cavity is investigated on the basis of the Shakhov kinetic equation. The gas dynamics, heat transfer, and damping force are studied numerically via the discrete unified gas-kinetic scheme for a wide range of parameters, including gas rarefaction, cavity aspect ratio, and oscillation frequency. Contrary to the linear oscillation where the velocity, temperature, and heat flux are symmetrical and oscillate with the same frequency as the oscillating lid, flow properties in nonlinear oscillatory cases turn out to be asymmetrical, and second-harmonic oscillation of the temperature field is observed...
April 2018: Physical Review. E
K C Le, T M Tran
The thermodynamic dislocation theory developed for nonuniform plastic deformations is used here to simulate the stress-strain curves for crystals subjected to antiplane shear-controlled load reversal. We show that the presence of the positive back stress during the load reversal reduces the magnitude of shear stress required to pull excess dislocations back to the center of the specimen. There, the excess dislocations of opposite signs meet and annihilate each other leading to the Bauschinger effect.
April 2018: Physical Review. E
Joshua A Dijksman, Lenka Kovalcinova, Jie Ren, Robert P Behringer, Miroslav Kramar, Konstantin Mischaikow, Lou Kondic
We carry out a direct comparison of experimental and numerical realizations of the exact same granular system as it undergoes shear jamming. We adjust the numerical methods used to optimally represent the experimental settings and outcomes up to microscopic contact force dynamics. Measures presented here range from microscopic through mesoscopic to systemwide characteristics of the system. Topological properties of the mesoscopic force networks provide a key link between microscales and macroscales. We report two main findings: (1) The number of particles in the packing that have at least two contacts is a good predictor for the mechanical state of the system, regardless of strain history and packing density...
April 2018: Physical Review. E
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