Showing papers on "Shear stress published in 2020"

Endothelial responses to shear stress in atherosclerosis: a novel role for developmental genes

Abstract: Flowing blood generates a frictional force called shear stress that has major effects on vascular function. Branches and bends of arteries are exposed to complex blood flow patterns that exert low or low oscillatory shear stress, a mechanical environment that promotes vascular dysfunction and atherosclerosis. Conversely, physiologically high shear stress is protective. Endothelial cells are critical sensors of shear stress but the mechanisms by which they decode complex shear stress environments to regulate physiological and pathophysiological responses remain incompletely understood. Several laboratories have advanced this field by integrating specialized shear-stress models with systems biology approaches, including transcriptome, methylome and proteome profiling and functional screening platforms, for unbiased identification of novel mechanosensitive signalling pathways in arteries. In this Review, we describe these studies, which reveal that shear stress regulates diverse processes and demonstrate that multiple pathways classically known to be involved in embryonic development, such as BMP–TGFβ, WNT, Notch, HIF1α, TWIST1 and HOX family genes, are regulated by shear stress in arteries in adults. We propose that mechanical activation of these pathways evolved to orchestrate vascular development but also drives atherosclerosis in low shear stress regions of adult arteries. The shear stress generated by flowing blood has major effects on vascular function, with low shear stress promoting vascular dysfunction and atherosclerosis. This Review describes the latest findings on how endothelial cells decode complex shear stress environments to regulate physiological and pathophysiological responses, highlighting the role of pathways involved in embryonic development.

Hall and ion slip effects on unsteady MHD free convective rotating flow through a saturated porous medium over an exponential accelerated plate

Abstract: In this paper, we have investigated the Hall and ion slip effects on the unsteady magnetohydrodynamic (MHD) free convective rotating flow over an exponentially accelerated inclined plate entrenched in a saturated porous medium with the effect of angle of inclination, variable temperature and concentration. The flow induced by the presence of heat source/sink and destructive reaction. The Laplace transform technique has been used to solve the governing equations. The effects of the non-dimensional parameters on the governing flow velocity, temperature and concentration are examined with graphical profiles. Also for engineering interest the shear stress, Nusselt number and Sherwood number are obtained analytically and discussed computationally with reference to foremost flow parameters. It is reported that the presence of magnetic field prevents the flow reversal. Angle of inclination sustains a retarding effect on velocity distribution. The present study has an immediate application in understanding the drag experienced at the heated and inclined surfaces in a seepage flow.

A novel four-unknown integral model for buckling response of FG sandwich plates resting on elastic foundations under various boundary conditions using Galerkin\'s approach

Abstract: In this work, the buckling analysis of material sandwich plates based on a two-parameter elastic foundation under various boundary conditions is investigated on the basis of a new theory of refined trigonometric shear deformation. This theory includes indeterminate integral variables and contains only four unknowns in which any shear correction factor not used, with even less than the conventional theory of first shear strain (FSDT). Applying the principle of virtual displacements, the governing equations and boundary conditions are obtained. To solve the buckling problem for different boundary conditions, Galerkin\'s approach is utilized for symmetric EGM sandwich plates with six different boundary conditions. A detailed numerical study is carried out to examine the influence of plate aspect ratio, elastic foundation coefficients, ratio, side-to-thickness ratio and boundary conditions on the buckling response of FGM sandwich plates. A good agreement between the results obtained and the available solutions of existing shear deformation theories that have a greater number of unknowns proves to demonstrate the precision of the proposed theory.

Fluid Shear Stress Sensing by the Endothelial Layer.

Abstract: Blood flow produces mechanical frictional forces, parallel to the blood flow exerted on the endothelial wall of the vessel, the so-called wall shear stress (WSS). WSS sensing is associated with several vascular pathologies, but it is first a physiological phenomenon. Endothelial cell sensitivity to WSS is involved in several developmental and physiological vascular processes such as angiogenesis and vascular morphogenesis, vascular remodeling, and vascular tone. Local conditions of blood flow determine the characteristics of WSS, i.e., intensity, direction, pulsatility, sensed by the endothelial cells that, through their effect of the vascular network, impact WSS. All these processes generate a local-global retroactive loop that determines the ability of the vascular system to ensure the perfusion of the tissues. In order to account for the physiological role of WSS, the so-called shear stress set point theory has been proposed, according to which WSS sensing acts locally on vessel remodeling so that WSS is maintained close to a set point value, with local and distant effects of vascular blood flow. The aim of this article is (1) to review the existing literature on WSS sensing involvement on the behavior of endothelial cells and its short-term (vasoreactivity) and long-term (vascular morphogenesis and remodeling) effects on vascular functioning in physiological condition; (2) to present the various hypotheses about WSS sensors and analyze the conceptual background of these representations, in particular the concept of tensional prestress or biotensegrity; and (3) to analyze the relevance, explanatory value, and limitations of the WSS set point theory, that should be viewed as dynamical, and not algorithmic, processes, acting in a self-organized way. We conclude that this dynamic set point theory and the biotensegrity concept provide a relevant explanatory framework to analyze the physiological mechanisms of WSS sensing and their possible shift toward pathological situations.

Shear Thickening of Concentrated Suspensions: Recent Developments and Relation to Other Phenomena

Abstract: Shear thickening is the increase of the apparent viscosity as shear rate or shear stress increases. This phenomenon is pronounced in concentrated (dense) suspensions of both colloidal-scale and lar...

A comprehensive review on the natural, forced, and mixed convection of non-Newtonian fluids (nanofluids) inside different cavities

Abstract: Convection heat transfer in cavities has attracted much attention from researchers. Many kinds of nanofluids have exhibited non-Newtonian behavior and been employed as heat transfer fluids in cavities. In a non-Newtonian fluid, shear stress and strain do not have a linear relationship. Such fluids do not follow Newton’s law of shear stress. As a result, researchers have used such models as the power-law or Bingham to formulate the behavior of non-Newtonian fluids and provide a numerical solution. In this study, first the non-Newtonian nanofluids were summarized. And then two well-known models, namely the power-law and Bingham models, are introduced, which was followed by empirical studies in non-Newtonian fluids or nanofluids. Then a summary of studies on nanofluids and non-Newtonian fluids inside different types of cavities was provided. Moreover, some tables are presented summarizing numerical studies into cavities containing nanofluids or non-Newtonian fluids and their significant findings.

Influence of boundary conditions on the bending and free vibration behavior of FGM sandwich plates using a four-unknown refined integral plate theory

Abstract: The influence of boundary conditions on the bending and free vibration behavior of functionally graded sandwich plates resting on a two-parameter elastic foundation is examined using an original novel high order shear theory. The Hamilton\'s principle is used herein to derive the equations of motion. The number of unknowns and governing equations of the present theory is reduced, and hence makes it simple to use. This theory includes indeterminate integral variables and contains only four unknowns in which any shear correction factor not used, with even less than the conventional theory of first shear strain (FSDT). Unlike any other theory, the number of unknown functions involved in displacement field is only four, as against five, six or more in the case of other shear deformation theories. Galerkin\'s approach is utilized for FGM sandwich plates with six different boundary conditions. The accuracy of the proposed solution is checked by comparing it with other closed form solutions available in the literature.

Permeability and fluid flow-induced wall shear stress in bone scaffolds with TPMS and lattice architectures: A CFD analysis

Abstract: Fluid flow dynamics within porous scaffolds for tissue engineering play a critical role in the transport of fundamental materials to the cells and in controlling the biocompatibility of the scaffold. Properties such as permeability and fluid flow-induced wall shear stress characterize the biological behavior of the scaffolds. Bioactivity depends on the diffusion of oxygen and other nutritious elements through the porous medium and fluid flow-induced shear stress is known as the dominant mechanical stimulant of cell differentiation and proliferation within the scaffolds. In this study, eight different bone scaffold models with a constant porosity of 80% were designed computationally using the TPMS and lattice-based structures. We investigated the fluid flow within the scaffolds using CFD analysis. The results of the work showed that scaffold architecture has a significant impact on the permeability and that scaffold permeability can vary up to three times depending on the architecture. The scaffolds with the minimal variation in their channel size exhibited the highest permeability. We investigated the distribution statistics of wall shear stress on the walls of the scaffolds and showed that a correlation between the architecture of the scaffolds and the distribution statistics of wall shear stress did not exist. The outcomings of this work can be promising in designing better scaffolds in tissue engineering from a biological point of view.

Nanoliquid film flow due to a moving substrate and heat transfer

Abstract: The present work analyzed the flow and heat transfer of the nanoliquid film flow over a moving inclined substrate. The motion of nanoparticles is induced by the action of both the gravitational force as well as the substrate movement. The hydrodynamic and thermal layers developing along the channel with a constant film thickness are resolved analytically. The corresponding pressure distribution, velocity field, temperature field and the physical quantities of wall shear stress as well as wall heat transfer rate are formulated in closed-form expressions. Seven different types of nanofluids are accounted for. Thermophysical properties of these particles enable us to visualize the flow and thermal development of the nanoliquid films in terms of the clean base fluid by the help of the defined shape factors. The considered mathematical model is validated against the available data in cases of special flow configurations. The carbon nanotubes are shown to have the highest heat transfer rates as compared to the other nanoparticles. On the other hand, the film thickness is much reduced and the wall shear is much amplified in the presence of silver nanoparticles.

Ferroelastic-switching-driven colossal shear strain and piezoelectricity in a hybrid ferroelectric

Abstract: Materials that can produce large controllable strains are widely used in shape memory devices, actuators and sensors Great efforts have been made to improve the strain outputs of various material systems Among them, ferroelastic transitions underpin giant reversible strains in electrically-driven ferro/piezoelectrics and thermally- or magneticallydriven shape memory alloys However, large-strain ferroelastic switching in conventional ferroelectrics is very challenging while magnetic and thermal controls are not desirable for applications Here, we demonstrate an unprecedentedly large shear strain up to 215 % in a hybrid ferroelectric, C6H5N(CH3)3CdCl3 The strain response is about two orders of magnitude higher than those of top-performing conventional ferroelectric polymers and oxides It is achieved via inorganic bond switching and facilitated by the structural confinement of the large organic moieties, which prevents the undesired 180-degree polarization switching Furthermore, Br substitution can effectively soften the bonds and result in giant shear piezoelectric coefficient (d35 ~ 4800 pm/V) in Br-rich end of the solid solution, C6H5N(CH3)3CdBr3xCl3(1-x) The superior electromechanical properties of the compounds promise their potential in lightweight and high energy density devices, and the strategy described here should inspire the development of next-generation piezoelectrics and electroactive materials based on hybrid ferroelectrics

A novel computational approach to functionally graded porous plates with graphene platelets reinforcement

Abstract: In this study, we numerically investigate static and free vibration responses of functionally graded (FG) porous plates with graphene platelets (GPLs) reinforcement using an efficient polygonal finite element method (PFEM). While the bending strain field is approximated through quadratic serendipity shape functions, the shear strain field is calculated by employing Wachspress basis functions. In order to eliminate the shear locking phenomenon, Timoshenko's beam theory is utilized to determine assumed strain fields on each side of polygonal domain. The present formulation possesses various outstanding features: (a) is valid for triangular, quadrilateral and polygonal elements; (b) can conveniently implement various different plate theories via choosing appropriate transverse shear function; (c) eliminates the shear locking phenomenon; (d) does not increase degrees of freedom (DOFs) per polygonal element despite employing the quadratic serendipity shape functions and (e) obtains more accurate and stable results than those of other PFEMs. Various dispersions of internal pores as well as GPLs into metal matrix through the thickness of plate are examined. The effective material properties varying across the plate's thickness can be estimated by Halpin-Tsai model for Young's modulus and the rule of a mixture for Poisson's ratio and mass density. The effect of several important parameters such as porosity coefficient, weight fraction and dimensions of GPLs, distribution of porosity and GPLs into metal matrix are thoroughly investigated via various numerical examples.

Shear Stress Regulation of Endothelial Glycocalyx Structure Is Determined by Glucobiosynthesis.

Abstract: Objective: Endothelial cells exposed to laminar shear stress express a thick glycocalyx on their surface that plays an important role in reducing vascular permeability and endothelial anti-inflamma...

Monitoring and correction of the stress in an anchor bolt based on Pulse Pre‐Pumped Brillouin Optical Time Domain Analysis

Abstract: This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. © 2020 The Authors. Energy Science & Engineering published by the Society of Chemical Industry and John Wiley & Sons Ltd. 1State Key Laboratory of Mining Disaster Prevention and Control Co-founded by Shandong Provence and the Ministry of Science and Technology, Shandong University of Science and Technology, Qingdao, China 2School of Energy and Mining Engineering, Xi'an University of Science and Technology, Xi'an, China 3The State Key Laboratory of Coal Mine Disaster Dynamics and Control in Chongqing University, Chongqing, China 4China Coal Technology and Engineering Group Shenyang Research Institute, Fushun, China 5State Key Laboratory of Coal Safety Technology, Fushun, China

Characterisation of stress and moisture-dependent resilient behaviour for compacted clays in South China

Abstract: In order to predict the resilient modulus of compacted clays, the material indicator tests, repeated load triaxial test, and pressure plate test for compacted clays from South China were carried out. The soil–water characteristic curve (SWCC) was described using the Fredlund and Xing’s model. And a logarithmic function between the soil suction and resilient modulus was built. Then, a new variable named the minimum bulk stress was defined to separate the shear effect of soil samples from the bulk stress, which avoids the bulk stress reflects two contrary effects, namely hardening effect and softening effect. Subsequently, the influences of the degree of compaction, soil suction, minimum bulk stress, and octahedral shear stress on the resilient modulus were analysed. In the following, a new resilient modulus prediction model of compacted clays, which took the soil suction, minimum bulk stress, and octahedral shear stress as the model variables, was developed and verified using the data of different cohesive...

The propagation mechanism of an oblique straight crack in a rock sample and the effect of osmotic pressure under in-plane biaxial compression

Abstract: In this paper, the propagation mechanism of an oblique straight crack has been studied theoretically, which reveals its mechanical characteristics under in-plane biaxial compression. Firstly, the stress components away from the boundary are derived based on the superposition principle. The normal stress components are strengthened and shear stress component is restrained compared to the uniaxial condition. Then the relationship between stresses and stress intensity factors is analyzed, and the effect of stresses on the strength of cracked rocks is discussed. The analysis of wing crack growth shows that the reliable experimental results are very demanding for sample preparation. Based on Mohr-Coulomb criterion and Mohr’s stress circles, the failure mechanism of cracked rocks is analyzed, and the physical meaning of some formulas is vividly displayed. Moreover, we study the relationship between friction angle θ0 and angle β, which determines the minimum compressive strength of cracked rocks. There are evidences that the increase of crack opening width leads to β0 (a value of β) away from the theoretical value determined by sliding crack model, so that the role of stress σx can no longer be ignored. Theoretically speaking, for an initially closed crack, we find that, for the first time, both wing crack growth and shear compression failure are more likely to occur when the angle β between 22.5 and 45 degrees combining the statistical results of Barton and Choubey (Rock Mech Rock Eng 10:1–54, 1977). As for an initially open crack, the characteristics of stress intensity factors and circumferential stresses are also discussed, especially when σ1 equals σ3. Finally, we study the effect of osmotic pressure on stresses and stress intensity factors, the weakening of the properties of crack surfaces by water is also considered, and the mechanical behavior of a rock sample with an oblique straight crack changes dramatically.

Multi-corneal barrier-on-a-chip to recapitulate eye blinking shear stress forces.

Abstract: Human corneal epithelium coexists with tear fluids and shows its barrier functionality under the dynamic conditions of eye blinking. However, the current in vitro cell culture settings for corneal epithelial cells lack the dynamic flow conditions to recapitulate the shear stress of eye blinking, hindering corneal function evaluation. We developed a microfluidic platform enabling the dynamic culture of the human corneal barrier with recapitulation of eye blinking. The device consisted of upper and lower channels separated by a porous membrane. Human corneal epithelial cells (HCE-T) were seeded on the porous membrane (upper channel) and cultured for ten days. The cells formed a barrier with high expression of zonula occludens 1 (ZO-1) tight junction protein on day seven, and the translocation of fluorescein sodium across the barrier in the microfluidic device was comparable to that in the transwell system, used as a control. Then, bidirectional and unidirectional flows were applied in the upper and lower channels, respectively, and the cells in the upper channels were stimulated with 0.6 dyn s cm-2 shear stress. After 24 h, while the fluid stimuli did not affect cell adhesion, they facilitated the expression of cytokeratin 19 (CK-19) intermediate filaments in cells, indicating the strengthening of the barrier function. Furthermore, morphological single-cell analysis revealed an increase in the cell body area rather than nuclei. We envision that this multi-corneal barrier-on-a-chip device will unlock new possibilities in ophthalmic drug development and will be useful for studying the effects of eye blinking shear stress on the ocular surface.