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Sample records for flow-induced shear stresses

  1. Flow-induced wall shear stress in abdominal aortic aneurysms: Part II--pulsatile flow hemodynamics.

    PubMed

    Finol, Ender A; Amon, Cristina H

    2002-08-01

    In continuing the investigation of AAA hemodynamics, unsteady flow-induced stresses are presented for pulsatile blood flow through the double-aneurysm model described in Part I. Physiologically realistic aortic blood flow is simulated under pulsatile conditions for the range of time-average Reynolds numbers 50< or =Re(m) < or =300. Hemodynamic disturbance is evaluated for a modified set of indicator functions which include wall pressure (p(w)), wall shear stress (tau(w)), Wall Shear Stress Gradient (WSSG), time-average wall shear stress (tau(w)*), and time-average Wall Shear Stress Gradient WSSG*. At peak flow, the highest shear stress and WSSG levels are obtained at the distal end of both aneurysms, in a pattern similar to that of steady flow. The maximum values of wall shear stresses and wall shear stress gradients are evaluated as a function of the time-average Reynolds number resulting in a fourth order polynomial correlation. A comparison between numerical predictions for steady and pulsatile flow is presented, illustrating the importance of considering time-dependent flow for the evaluation of hemodynamic indicators.

  2. Modeling of flow-induced shear stress applied on 3D cellular scaffolds: Implications for vascular tissue engineering.

    PubMed

    Lesman, Ayelet; Blinder, Yaron; Levenberg, Shulamit

    2010-02-15

    Novel tissue-culture bioreactors employ flow-induced shear stress as a means of mechanical stimulation of cells. We developed a computational fluid dynamics model of the complex three-dimensional (3D) microstructure of a porous scaffold incubated in a direct perfusion bioreactor. Our model was designed to predict high shear-stress values within the physiological range of those naturally sensed by vascular cells (1-10 dyne/cm(2)), and will thereby provide suitable conditions for vascular tissue-engineering experiments. The model also accounts for cellular growth, which was designed as an added cell layer grown on all scaffold walls. Five model variants were designed, with geometric differences corresponding to cell-layer thicknesses of 0, 50, 75, 100, and 125 microm. Four inlet velocities (0.5, 1, 1.5, and 2 cm/s) were applied to each model. Wall shear-stress distribution and overall pressure drop calculations were then used to characterize the relation between flow rate, shear stress, cell-layer thickness, and pressure drop. The simulations showed that cellular growth within 3D scaffolds exposes cells to elevated shear stress, with considerably increasing average values in correlation to cell growth and inflow velocity. Our results provide in-depth analysis of the microdynamic environment of cells cultured within 3D environments, and thus provide advanced control over tissue development in vitro.

  3. Design optimization of scaffold microstructures using wall shear stress criterion towards regulated flow-induced erosion.

    PubMed

    Chen, Yuhang; Schellekens, Michiel; Zhou, Shiwei; Cadman, Joseph; Li, Wei; Appleyard, Richard; Li, Qing

    2011-08-01

    Tissue scaffolds aim to provide a cell-friendly biomechanical environment for facilitating cell growth. Existing studies have shown significant demands for generating a certain level of wall shear stress (WSS) on scaffold microstructural surfaces for promoting cellular response and attachment efficacy. Recently, its role in shear-induced erosion of polymer scaffold has also drawn increasing attention. This paper proposes a bi-directional evolutionary structural optimization (BESO) approach for design of scaffold microstructure in terms of the WSS uniformity criterion, by downgrading highly-stressed solid elements into fluidic elements and/or upgrading lowly-stressed fluidic elements into solid elements. In addition to this, a computational model is presented to simulate shear-induced erosion process. The effective stiffness and permeability of initial and optimized scaffold microstructures are characterized by the finite element based homogenization technique to quantify the variations of mechanical properties of scaffold during erosion. The illustrative examples show that a uniform WSS is achieved within the optimized scaffold microstructures, and their architectural and biomechanical features are maintained for a longer lifetime during shear-induced erosion process. This study provides a mathematical means to the design optimization of cellular biomaterials in terms of the WSS criterion towards controllable shear-induced erosion.

  4. Combined effects of flow-induced shear stress and electromagnetic field on neural differentiation of mesenchymal stem cells.

    PubMed

    Mascotte-Cruz, Juan Uriel; Ríos, Amelia; Escalante, Bruno

    2016-01-01

    Differentiation of bone marrow-derived mesenchymal stem cells (MSCs) into neural phenotype has been induced by either flow-induced shear stress (FSS) or electromagnetic fields (EMF). However, procedures are still expensive and time consuming. In the present work, induction for 1 h with the combination of both forces showed the presence of the neural precursor nestin as early as 9 h in culture after treatment and this result lasted for the following 6 d. In conclusion, the use of a combination of FSS and EMF for a short-time renders in neurite-like cells, although further investigation is required to analyze cell functionality.

  5. Endothelial cell alignment as a result of anisotropic strain and flow induced shear stress combinations

    PubMed Central

    Sinha, Ravi; Le Gac, Séverine; Verdonschot, Nico; van den Berg, Albert; Koopman, Bart; Rouwkema, Jeroen

    2016-01-01

    Endothelial cells (ECs) are continuously exposed in vivo to cyclic strain and shear stress from pulsatile blood flow. When these stimuli are applied in vitro, ECs adopt an appearance resembling their in vivo state, most apparent in their alignment (perpendicular to uniaxial strain and along the flow). Uniaxial strain and flow perpendicular to the strain, used in most in vitro studies, only represent the in vivo conditions in straight parts of vessels. The conditions present over large fractions of the vasculature can be better represented by anisotropic biaxial strains at various orientations to flow. To emulate these biological complexities in vitro, we have developed a medium-throughput device to screen for the effects on cells of variously oriented anisotropic biaxial strains and flow combinations. Upon the application of only strains for 24 h, ECs (HUVECs) aligned perpendicular to the maximum principal strain and the alignment was stronger for a higher maximum:minimum principal strain ratio. A 0.55 Pa shear stress, when applied alone or with strain for 24 h, caused cells to align along the flow. Studying EC response to such combined physiological mechanical stimuli was not possible with existing platforms and to our best knowledge, has not been reported before. PMID:27404382

  6. Endothelial cell alignment as a result of anisotropic strain and flow induced shear stress combinations.

    PubMed

    Sinha, Ravi; Le Gac, Séverine; Verdonschot, Nico; van den Berg, Albert; Koopman, Bart; Rouwkema, Jeroen

    2016-07-12

    Endothelial cells (ECs) are continuously exposed in vivo to cyclic strain and shear stress from pulsatile blood flow. When these stimuli are applied in vitro, ECs adopt an appearance resembling their in vivo state, most apparent in their alignment (perpendicular to uniaxial strain and along the flow). Uniaxial strain and flow perpendicular to the strain, used in most in vitro studies, only represent the in vivo conditions in straight parts of vessels. The conditions present over large fractions of the vasculature can be better represented by anisotropic biaxial strains at various orientations to flow. To emulate these biological complexities in vitro, we have developed a medium-throughput device to screen for the effects on cells of variously oriented anisotropic biaxial strains and flow combinations. Upon the application of only strains for 24 h, ECs (HUVECs) aligned perpendicular to the maximum principal strain and the alignment was stronger for a higher maximum:minimum principal strain ratio. A 0.55 Pa shear stress, when applied alone or with strain for 24 h, caused cells to align along the flow. Studying EC response to such combined physiological mechanical stimuli was not possible with existing platforms and to our best knowledge, has not been reported before.

  7. Computational modeling of flow-induced shear stresses within 3D salt-leached porous scaffolds imaged via micro-CT.

    PubMed

    Voronov, Roman; Vangordon, Samuel; Sikavitsas, Vassilios I; Papavassiliou, Dimitrios V

    2010-05-07

    Flow-induced shear stresses have been found to be a stimulatory factor in pre-osteoblastic cells seeded in 3D porous scaffolds and cultured under continuous flow perfusion. However, due to the complex internal structure of porous scaffolds, analytical estimation of the local shear forces is impractical. The primary goal of this work is to investigate the shear stress distributions within Poly(l-lactic acid) scaffolds via computation. Scaffolds used in this study are prepared via salt leeching with various geometric characteristics (80-95% porosity and 215-402.5microm average pore size). High resolution micro-computed tomography is used to obtain their 3D structure. Flow of osteogenic media through the scaffolds is modeled via lattice Boltzmann method. It is found that the surface stress distributions within the scaffolds are characterized by long tails to the right (a positive skewness). Their shape is not strongly dependent on the scaffold manufacturing parameters, but the magnitudes of the stresses are. Correlations are prepared for the estimation of the average surface shear stress experienced by the cells within the scaffolds and of the probability density function of the surface stresses. Though the manufacturing technique does not appear to affect the shape of the shear stress distributions, presence of manufacturing defects is found to be significant: defects create areas of high flow and high stress along their periphery. The results of this study are applicable to other polymer systems provided that they are manufactured by a similar salt leeching technique, while the imaging/modeling approach is applicable to all scaffolds relevant to tissue engineering. Copyright 2010 Elsevier Ltd. All rights reserved.

  8. Towards the prediction of flow-induced shear stress distributions experienced by breast cancer cells in the lymphatics.

    PubMed

    Morley, S T; Newport, D T; Walsh, M T

    2017-07-24

    Tumour metastasis in the lymphatics is a crucial step in the progression of breast cancer. The dynamics by which breast cancer cells (BCCs) travel in the lymphatics remains poorly understood. The goal of this work is to develop a model capable of predicting the shear stresses metastasising BCCs experience using numerical and experimental techniques. This paper models the fluidic transport of large particles ([Formula: see text] where [Formula: see text] is the particle diameter and W is the channel width) subjected to lymphatic flow conditions ([Formula: see text]), in a [Formula: see text] microchannel. The feasibility of using the dynamic fluid body interaction (DFBI) method to predict particle motion was assessed, and particle tracking experiments were performed. The experiments found that particle translational velocity decreased from the undisturbed fluid velocity with increasing particle size (5-14% velocity lag for [Formula: see text]). DFBI simulations were found to better predict particle behaviour than theoretical predictions; however, mesh restrictions in the near-wall region ([Formula: see text]) result in computationally expensive models. The simulations were in good agreement with the experiments ([Formula: see text] difference) across the channel ([Formula: see text]), with differences up to 25% in the near-wall region. Particles experience a range of shear stresses (0.002-0.12 Pa) and spatial shear gradients ([Formula: see text]) depending on their size and radial position. The predicted shear gradients are far in excess of values associated with BCC apoptosis ([Formula: see text]). Increasing our understanding of the shear stress magnitudes and gradients experienced by BCCs could be leveraged to elucidate whether a particular BCC size or location exists that encourages metastasis within the lymphatics.

  9. High shear flow induces migration of adherent human platelets.

    PubMed

    Kraemer, Bjoern F; Schmidt, Christine; Urban, Benjamin; Bigalke, Boris; Schwanitz, Laura; Koch, Miriam; Seizer, Peter; Schaller, Martin; Gawaz, Meinrad; Lindemann, Stephan

    2011-01-01

    Shear forces are generated in all parts of the vascular system and contribute directly and indirectly to vascular disease progression. Endothelial cells are able to adapt to flow conditions, and are known to polarize and migrate in response to shear forces. Platelets exposed to shear stress are activated and release bioactive molecules from their alpha granules. So far, platelets have been considered to be static cells that do not leave the site of tight adhesion. However, we have recently been able to demonstrate the capacity of platelets to migrate in response to stromal derived factor-1 (SDF-1). In this project, we have demonstrated that platelets accumulate in areas with a high concentration of SDF-1 under flow conditions and respond to high shear stress by cellular polarization, cytoskeletal reorganisation, and flow-directed migration. In this context, we have shown increased Wiskott-Aldrich Syndrome protein (WASP) phosphorylation and intracellular redistribution of focal adhesion kinase (FAK) under high-shear stress conditions. The effect of flow-induced platelet migration has not previously been recognized and offers a new role for platelets as mobile cells. Their migratory potential may enable platelets to cover intimal lesions and contribute to vascular repair.

  10. Shear flow induced unfolding of collapsed polymers.

    NASA Astrophysics Data System (ADS)

    Alexander-Katz, Alfredo; Netz, Roland

    2006-03-01

    In the process of clotting in small vessels, platelets form a plug in an injured zone only in the presence of a protein known as the von Willebrand Factor (vWF). The absence or malfunction of the vWF leads to a bleeding disorder, the so-called von Willebrand disease. It is believed that the protein is collapsed (or globular) when released into the blood flow, and that it undergoes a transition at high shear rates that allows it to bind platelets. Using hydrodynamic simulations of a simple model of the vWF in shear flow, we show that a globular polymer undergoes a globule-stretch transition at a critical shear rate. Below this threshold shear rate the polymer remains collapsed and slightly deformed, while above it the chain displays strong elongations in the direction of the flow. Finally, we discuss the relevance of our results in the case of blood flow, and compare them to the physiological values present in the body.

  11. Flows induced by exponential stretching and shearing plate motions

    NASA Astrophysics Data System (ADS)

    Weidman, Patrick

    2016-11-01

    Boundary-layer solutions for the flow induced by an exponentially stretching surface also sheared in its own plane are given. Prior to this study no similarity solutions have been reported for flows generated by exponentially sheared surfaces concomitant with surface stretching in any form. The method of solution is self-similarity. The results found here are intimately related to those of Magyari and Keller ["Heat and mass transfer in the boundary layers on an exponentially stretching continuous surface," J. Phys. D: Appl. Phys. 32, 577-585 (1999)] who studied the motion and heat transfer induced by an exponentially stretching plate. In addition to two particular cases reported here, a third situation is found where an exponentially stretching surface admits a concomitant arbitrary streamwise shearing motion.

  12. Shear flow induced nanostructure-micostructure transition in a polymeric bicontinuous microemulsion

    NASA Astrophysics Data System (ADS)

    Krishnan, Kasiraman; Bates, Frank S.; Lodge, Timothy P.; Burghardt, Wesley R.

    2001-03-01

    The effects of shear flow on a polymeric bicontinuous microemulsion have been studied using scattering, microscopy and rheology. The microemulsion consists of a ternary blend of poly(ethyl ethylene) (PEE), poly(dimethyl siloxane) (PDMS) and the diblock copolymer PEE-PDMS. Steady shear experiments reveal four regimes as a function of shear rate. At low shear rates (regime I), the bicontinuous nanostructure is unperturbed and the sample behaves as a Newtonian fluid. Shear thinning is observed at intermediate shear rates (regime II) concurrent with the development of anisotropy in the structure. Further increase of shear rate results in flow-induced phase separation; the stress is independent of shear rate in this regime III. Light scattering shows a streak-like pattern perpendicular to the flow direction while microscopy reveals a string-like, micron-sized morphology. Higher shear rates (regime IV) lead to binary blend-like behavior with the block copolymer playing no significant role; the stress increases strongly with the shear rate.

  13. Shear flow-induced detachment kinetics of Dictyostelium discoideum cells from solid substrate.

    PubMed Central

    Décavé, Emmanuel; Garrivier, Daniel; Bréchet, Yves; Fourcade, Bertrand; Bruckert, Franz

    2002-01-01

    Using Dictyostelium discoideum as a model organism of specific and nonspecific adhesion, we studied the kinetics of shear flow-induced cell detachment. For a given cell, detachment occurs for values of the applied hydrodynamic stress above a threshold. Cells are removed from the substrate with an apparent first-order rate constant that strongly depends on the applied stress. The threshold stress depends on cell size and physicochemical properties of the substrate, but is not affected by depolymerization of the actin and tubulin cytoskeleton. In contrast, the kinetics of cell detachment is almost independent of cell size, but is strongly affected by a modification of the substrate and the presence of an intact actin cytoskeleton. These results are interpreted in the framework of a peeling model. The threshold stress and the cell-detachment rate measure the local equilibrium energy and the dissociation rate constant of the adhesion bridges, respectively. PMID:11964228

  14. Flow induced protein nucleation: Insulin oligomerization under shear.

    NASA Astrophysics Data System (ADS)

    Dexter, Andrew; Azadani, Ali; Sorci, Mirco; Belfort, Georges; Hirsa, Amir

    2007-11-01

    A large number of diseases are associated with protein aggregation and misfolding, such as Alzheimer's, Parkinson's and human prion diseases such as Creutzveld-Jakob disease. Characteristic of these diseases is the presence of amyloid fibrils and their precursors, oligomers and protofibrils. Considerable evidence exists that a shearing flow strongly influences amyloid formation both in vitro and in vivo. Furthermore, the stability of protein-based pharmaceuticals is essential for conventional therapeutic preparations and drug delivery systems. By studying the nucleation and growth of insulin fibrils in a well-defined flow system, we expect to identify the flow conditions that impact protein aggregation kinetics and which lead to protein destabilization. The present flow system consists of an annular region bounded by stationary inner and outer cylinders and is driven by rotation of the floor. Preliminary results indicate that a continuous shearing flow can accelerate the aggregation process. The interfacial shear viscosity was found to drastically increase during aggregation and appears to be a useful parameter to probe protein oligomerization and the effects of flow.

  15. Shear flow induced wave couplings in the solar wind

    SciTech Connect

    Poedts, S.; Rogava, A.D. |; Mahajan, S.M. |

    1998-01-01

    A sheared background flow in a plasma induces coupling between different MHD wave modes, resulting in their mutual transformations with corresponding energy redistributing between the modes. In this way, the energy can be transfered from one wave mode to the other, but energy can also be added to or extracted from the background flow. In the present paper it is investigated whether the wave coupling and energy transfer mechanisms can operate under solar wind conditions. It is shown that this is indeed the case. Hence, the long-period waves observed in the solar wind at r > 0.3 AU might be generated by much faster periodic oscillations in the photosphere of the Sun. Other possible consequences for observable beat phenomena in the wind and the acceleration of the solar wind particles are also discussed.

  16. Fluid shear stress threshold regulates angiogenic sprouting.

    PubMed

    Galie, Peter A; Nguyen, Duc-Huy T; Choi, Colin K; Cohen, Daniel M; Janmey, Paul A; Chen, Christopher S

    2014-06-03

    The density and architecture of capillary beds that form within a tissue depend on many factors, including local metabolic demand and blood flow. Here, using microfluidic control of local fluid mechanics, we show the existence of a previously unappreciated flow-induced shear stress threshold that triggers angiogenic sprouting. Both intraluminal shear stress over the endothelium and transmural flow through the endothelium above 10 dyn/cm(2) triggered endothelial cells to sprout and invade into the underlying matrix, and this threshold is not impacted by the maturation of cell-cell junctions or pressure gradient across the monolayer. Antagonizing VE-cadherin widened cell-cell junctions and reduced the applied shear stress for a given transmural flow rate, but did not affect the shear threshold for sprouting. Furthermore, both transmural and luminal flow induced expression of matrix metalloproteinase 1, and this up-regulation was required for the flow-induced sprouting. Once sprouting was initiated, continuous flow was needed to both sustain sprouting and prevent retraction. To explore the potential ramifications of a shear threshold on the spatial patterning of new sprouts, we used finite-element modeling to predict fluid shear in a variety of geometric settings and then experimentally demonstrated that transmural flow guided preferential sprouting toward paths of draining interstitial fluid flow as might occur to connect capillary beds to venules or lymphatics. In addition, we show that luminal shear increases in local narrowings of vessels to trigger sprouting, perhaps ultimately to normalize shear stress across the vasculature. Together, these studies highlight the role of shear stress in controlling angiogenic sprouting and offer a potential homeostatic mechanism for regulating vascular density.

  17. Flow-Induced Stress Distribution in Porous Scaffolds

    NASA Astrophysics Data System (ADS)

    Papavassiliou, Dimitrios; Voronov, Roman; Vangordon, Samuel; Sikavitsas, Vassilios

    2010-11-01

    Flow-induced stresses help the differentiation and proliferation of mesenchymal cells cultured in porous scaffolds within perfusion bioreactors. The distribution of stresses in a scaffold is thus important for understanding the tissue growth process in such reactors. Computational results for flow through Poly-L-Lactic Acid porous scaffolds that have been produced with salt-leaching techniques, and for scaffolds that have been constructed with nonwoven fibers, indicate that the probability density function (pdf) of the wall stress, when normalized with the mean and the standard deviation of the pdf, appears to follow a single type of pdf. The scaffolds were imaged with micro-CT and the simulations were run with lattice Boltzmann methods. The parameters of the distribution can be obtained using Darcy's law and the Blake-Kozeny-Carman equation. Experimental results available in the literature appear to corroborate the computational findings, leading to the conclusion that stresses in high-porosity porous materials follow a single distribution.

  18. Flows induced by power-law stretching surface motion modulated by transverse or orthogonal surface shear

    NASA Astrophysics Data System (ADS)

    Weidman, Patrick

    2017-02-01

    Boundary-layer solutions to Banks' problem for the flow induced by power-law stretching of a plate are obtained for two generalizations that include arbitrary transverse plate shearing motion. In one extension an arbitrary transverse shearing motion is the product of the power-law stretching. In the other extension the streamwise stretching coordinate is added to an arbitrary transverse shearing and together raised to the power of stretching. In addition we find that Banks' power law stretching may be accompanied by orthogonal power-law shear. In all cases, the original boundary-value problem of Banks [1] is recovered. Results are illustrated with velocity profiles both at the plate and at fixed height in the fluid above the plate.

  19. Shear flow-induced formation of tubular cell protrusions in multiple myeloma cells

    PubMed Central

    Porat, Ziv; Yaron, Itamar; Katz, Ben-Zion; Kam, Zvi; Geiger, Benjamin

    2011-01-01

    Exposure of live cells to shear flow induces major changes in cell shape, adhesion to the extracellular matrix, and migration. In the present study, we show that exposure of cultured multiple myeloma (MM) cells to shear flow of 4–36 dynes/cm2 triggers the extension of long tubular protrusions (denoted FLow-Induced Protrusions, or FLIPs) in the direction of the flow. These FLIPs were found to be rich in actin, contain few or no microtubules and, apart from endoplasmic reticulum (ER)-like membranal structures, are devoid of organelles. Studying the dynamics of this process revealed that FLIPs elongate at their tips in a shear force-dependent manner, and retract at their bases. Examination of this force dependence revealed considerable heterogeneity in the mechanosensitivity of individual cells, most likely reflecting the diversity of the malignant B-cell population. The mechanisms underlying FLIP formation following mechanical perturbation, and their relevance to the cellular trafficking of MM cells, are discussed. PMID:21344380

  20. Liquid Crystals Indicate Directions Of Surface Shear Stresses

    NASA Technical Reports Server (NTRS)

    Reda, Daniel C.

    1996-01-01

    Report consisting of main text of U.S. Patent 5,394,752 presents detailed information on one aspect of method of using changes in colors of liquid-crystal coatings to indicate instantaneous directions of flow-induced shear stresses (skin friction) on aerodynamic surfaces.

  1. A conceptual framework for shear flow-induced erosion of soft cohesive sediment beds

    NASA Astrophysics Data System (ADS)

    Winterwerp, J. C.; van Kesteren, W. G. M.; van Prooijen, B.; Jacobs, W.

    2012-10-01

    This paper proposes a conceptual framework for erosion of cohesive sediment beds. We focus on cohesive beds, distinguishing between floc erosion, surface erosion, and mass erosion. By (our) definition, surface erosion is a drained soil mechanical process, whereas mass erosion occurs under undrained conditions. The eroding shear stress is modeled through a probability density function. This yields a continuous description of floc erosion and surface erosion as a function of mean bed shear stress. Furthermore, we assume a distribution for the bed strength. The mean values of the bed strength are derived from soil mechanical theory, assuming that the surface erosion rate is limited by the swelling rate from the undrained shear strength in the bed to its drained value at its surface. The rate of erosion then relates to the undrained shear strength of the soil, and its consolidation (swelling) coefficient. The critical shear stress for erosion is slightly larger than the true cohesion of the bed, i.e., the drained strength, and follows a power law relation with the plasticity index. The conceptual framework proposed herein has been validated against a limited number of experimental data, and has a series of advantages above other methods of direct measuring erodibility, as it is inexpensive and can be used to attain space-covering information on the sediment bed. Moreover, the use of bulk soil mechanical parameters accounts implicitly for the effects of organic material, though the role of, e.g., macrophytobenthos mats and/or bioturbation is difficult to capture a priori.

  2. A Piezoelectric Shear Stress Sensor

    NASA Technical Reports Server (NTRS)

    Kim, Taeyang; Saini, Aditya; Kim, Jinwook; Gopalarathnam, Ashok; Zhu, Yong; Palmieri, Frank L.; Wohl, Christopher J.; Jiang, Xiaoning

    2016-01-01

    In this paper, a piezoelectric sensor with a floating element was developed for shear stress measurement. The piezoelectric sensor was designed to detect the pure shear stress suppressing effects of normal stress generated from the vortex lift-up by applying opposite poling vectors to the: piezoelectric elements. The sensor was first calibrated in the lab by applying shear forces and it showed high sensitivity to shear stress (=91.3 +/- 2.1 pC/Pa) due to the high piezoelectric coefficients of PMN-33%PT (d31=-1330 pC/N). The sensor also showed almost no sensitivity to normal stress (less than 1.2 pC/Pa) because of the electromechanical symmetry of the device. The usable frequency range of the sensor is 0-800 Hz. Keywords: Piezoelectric sensor, shear stress, floating element, electromechanical symmetry

  3. Mechanical stretch and shear flow induced reorganization and recruitment of fibronectin in fibroblasts

    PubMed Central

    Steward, Robert L.; Cheng, Chao-Min; Ye, Jonathan D.; Bellin, Robert M.; LeDuc, Philip R.

    2011-01-01

    It was our objective to study the role of mechanical stimulation on fibronectin (FN) reorganization and recruitment by exposing fibroblasts to shear fluid flow and equibiaxial stretch. Mechanical stimulation was also combined with a Rho inhibitor to probe their coupled effects on FN. Mechanically stimulated cells revealed a localization of FN around the cell periphery as well as an increase in FN fibril formation. Mechanical stimulation coupled with chemical stimulation also revealed an increase in FN fibrils around the cell periphery. Complimentary to this, fibroblasts exposed to fluid shear stress structurally rearranged pre-coated surface FN, but unstimulated and stretched cells did not. These results show that mechanical stimulation directly affected FN reorganization and recruitment, despite perturbation by chemical stimulation. Our findings will help elucidate the mechanisms of FN biosynthesis and organization by furthering the link of the role of mechanics with FN. PMID:22355663

  4. Yield shear stress and disaggregating shear stress of human blood

    NASA Astrophysics Data System (ADS)

    Jung, Jinmu; Lee, Byoung-Kwon; Shin, Sehyun

    2014-05-01

    This review presents two distinct rheological parameters of blood that have the potential to indicate blood circulation adequacy: yield shear stress (YSS) and disaggregating shear stress (DSS). YSS and DSS reflect the strength of red blood cell (RBC) aggregation in suspension under static and dynamic conditions, respectively. YSS, defined as the critical stress to disperse RBC aggregates under static conditions, was found to be dependent upon hematocrit, fibrinogen, and red cell deformability, but not temperature. DSS, defined as the minimum shear stress to disperse RBC aggregates under dynamic conditions, is dependent upon fibrinogen, red cell deformability, and temperature but not hematocrit. Owing to recent advances in measurement technology, these two parameters can be easily measured, and thus, their clinical significance in blood circulation can be verified.

  5. Hemodynamic shear stress and the endothelium in cardiovascular pathophysiology

    PubMed Central

    Davies, Peter F

    2010-01-01

    SUMMARY Endothelium lining the cardiovascular system is highly sensitive to hemodynamic shear stresses that act at the vessel luminal surface in the direction of blood flow. Physiological variations of shear stress regulate acute changes in vascular diameter and when sustained induce slow, adaptive, structural-wall remodeling. Both processes are endothelium-dependent and are systemically and regionally compromised by hyperlipidemia, hypertension, diabetes and inflammatory disorders. Shear stress spans a range of spatiotemporal scales and contributes to regional and focal heterogeneity of endothelial gene expression, which is important in vascular pathology. Regions of flow disturbances near arterial branches, bifurcations and curvatures result in complex spatiotemporal shear stresses and their characteristics can predict atherosclerosis susceptibility. Changes in local artery geometry during atherogenesis further modify shear stress characteristics at the endothelium. Intravascular devices can also influence flow-mediated endothelial responses. Endothelial flow-induced responses include a cell-signaling repertoire, collectively known as mechanotransduction, that ranges from instantaneous ion fluxes and biochemical pathways to gene and protein expression. A spatially decentralized mechanism of endothelial mechanotransduction is dominant, in which deformation at the cell surface induced by shear stress is transmitted as cytoskeletal tension changes to sites that are mechanically coupled to the cytoskeleton. A single shear stress mechanotransducer is unlikely to exist; rather, mechanotransduction occurs at multiple subcellular locations. PMID:19029993

  6. Yield and flow-induced phase transition in colloidal gels under startup shear

    NASA Astrophysics Data System (ADS)

    Johnson, Lilian; Landrum, Benjamin; Zia, Roseanna

    2016-11-01

    We study the micro-mechanical origins of the transition from solid-like to liquid-like behavior during flow startup of colloidal gels via large-scale dynamic simulation, with a view toward understanding connections to energy storage and phase transition. Such materials often exhibit an overshoot in stress, and prior studies of strong, dilute colloidal gels with a stringy microstructure connect this "yield" event to loss of network connectivity. Owing to the importance of Brownian transport in phase separation processes in colloids, here we study a reversible colloidal gel of hard spheres that interact via a short-range attraction of several kT, for which Brownian motion can lead to rapid quiescent coarsening. In the present study, we interrogate the shear stress for a range of imposed flow strengths, monitoring particle-level structure and dynamics, to determine the microscopic picture of gel yield. Our detailed studies of the microstructural evolution and macroscopic response during startup provide insight into the phase behavior during yield. We present a new model of stress development, phase transition, and structural evolution during transient yield in colloidal gels for which ongoing phase separation informs gel phenomenology.

  7. Graphene Nanosheets and Shear Flow Induced Crystallization in Isotactic Polypropylene Nanocomposites

    SciTech Connect

    Z Xu; C Chen; Y Wang; H Tang; Z Li; B Hsiao

    2011-12-31

    Combined effects of graphene nanosheets (GNSs) and shear flow on the crystallization behavior of isotactic polypropylene (iPP) were investigated by in-situ synchrotron wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS) techniques. For crystallization under quiescent condition (at 145 C), the half-crystallization time (t{sub 1/2}) of nanocomposites containing 0.05 and 0.1 wt % GNSs was reduced to at least 50% compared to that of neat iPP, indicating the high nucleation ability of GNSs. The crystallization rate of iPP was directly proportional to the GNS content. Under a relatively weak shear flow (at a rate of 20 s{sup -1} for 5 s duration) and a low degree of supercooling, the neat iPP exhibited an isotropic structure due to the relaxation of row nuclei. However, visible antisotropic crystals appeared in sheared iPP/GNSs nanocomposites, indicating that GNSs induced a network structure hindering the mobility of iPP chains and allowing the survival of oriented row nuclei for a long period of time. The presence of GNSs clearly enhanced the effects of shear-induced nucleation as well as orientation of iPP crystals. Two kinds of nucleating origins coexisted in the sheared nanocomposite melt: heterogeneous nucleating sites initiated by GNSs and homogeneous nucleating sites (row nuclei) induced by shear. The difference of t{sub 1/2} of nanocomposites with and without shear was significantly larger than that of neat iPP. The presence of GNSs and shear flow exhibited a synergistic interaction on promoting crystallization kinetics of iPP, although the effect of GNS concentration was not apparent. From WAXD results of isothermal and nonisothermal crystallization of sheared iPP, it was found that the appearance of {beta}-crystals depended on the preservation of row nuclei, where the {alpha}-crystals were predominant in the iPP/GNSs nanocomposites, indicating that GNSs could directly induce {alpha}-crystals of iPP.

  8. Formation of Microbial Streamers by Flow-Induced Shear and Their Hydrodynamic Effects

    NASA Astrophysics Data System (ADS)

    Gong, J.; Olsen, K. A.; Nguyen, T.; Tice, M. M.; 2012; 2013, G. C.

    2014-12-01

    Microbial streamers are productive elements of surface-attached microbial communities that paradoxically seem to roughen mats under rapid, high shear flows, potentially exposing the mat to greater risk of erosion. They are common features found in modern hot-spring outflow channels, yet their formation mechanisms and effects on mat erosion are poorly understood. We test a hypothesis that streamers are produced by shear-induced viscoelastic deformation, and that streamers grow to heal detached turbulent boundary layers. Laboratory flume experiments were conducted using Particle Image/Tracking Velocimetry (PIV/PTV) to gain quantitative insights into the behavior of flows around small projections constructed from 3D-printed plastics or hydrated EPS gels, as well as artificial streamers. The combined use of fabricated hard and viscoelastic shapes, tracer particles, sheet lasers and high speed cameras allowed visualization of flows and quantitative measurements. Results show that primary and secondary flows (backflow behind projections) combine to produce deformations that drive the elongation of the top and ultimately initiate streamer formation. With insufficient secondary flows, streamers are not able to rise up from the basal mat. This implies that a combination of sufficient topographic relief and flow strength is required for streamers to form. In addition, flow measurements indicate that the presence of artificial streamers made the surface hydraulically smoother, and in effect reducing bed shear at the base. These results suggest a novel set of feedbacks that could reduce net mat erosion in energetic flows, and could help guide the evaluation of biosignatures in sedimentary rocks deposited in the presence of microbial mats.

  9. Shear and Extensional Flow-Induced Particle Orientation in Polypropylene/Clay Nanocomposites

    NASA Astrophysics Data System (ADS)

    Burghardt, Wesley; McCready, Erica

    2013-03-01

    Synchrotron-based in situ x-ray scattering is used to monitor the orientation of dispersed particles in molten polypropylene/clay nanocomposite melts during flow. Nanocomposite samples were prepared via twin screw extrusion processing, and the degree of clay exfoliation assessed in terms of the magnitude of the low frequency enhancement in viscoelasticity. In shear flow, an annular cone and plate flow cell is used which allows measurement of the degree and direction of particle orientation in the flow-gradient (1-2) plane. Samples were also studied in extensional flow, using an SER extensional flow fixture installed in a custom-built convection oven that provides x-ray access. In both shear and extensional flow, only a moderate degree of particle orientation is observed. Extensional flow studies are complicated by (i) the tendency of samples to fail at moderate Hency strain, and (ii) a heterogeneous initial distribution of particle orientation in the SER specimens, prepared by compression molding of extruded pellets of the nanocomposite.

  10. Roles for GP IIb/IIIa and αvβ3 integrins in MDA-MB-231 cell invasion and shear flow-induced cancer cell mechanotransduction.

    PubMed

    Zhao, Fenglong; Li, Li; Guan, Liuyuan; Yang, Hong; Wu, Chunhui; Liu, Yiyao

    2014-03-01

    Adhesion of cancer cell to endothelial cells and the subsequent trans-endothelial migration are key steps in hematogenous metastasis. However, the molecular mechanisms of cancer cell/endothelial cell interaction under hemodynamic shear flow and how shear flow-induced cancer cell mechanotransduction are yet to be fully defined. In this study, we identified that the integrins of both platelet glycoprotein IIb/IIIa (GP IIb/IIIa) and αvβ3 were crucial for hematogenous metastasis of human breast carcinoma MDA-MB-231 cells. The cell migration and invasion were studied by using Millicell cell culture insert system. The numbers of invaded MDA-MB-231 cells significantly increased by thrombin-activated platelets and reduced by eptifibatide, a platelet inhibitor. Meanwhile, RGDWE peptides, a specific inhibitor of αvβ3 integrin, also inhibited MDA-MB-231 cell invasion. We further used a parallel-plate flow chamber to investigate MDA-MB-231 cell adhesion under flow conditions. Alike in static condition, the adhesion capability of MDA-MB-231 cells to endothelial monolayer was also significantly affected by GP IIb/IIIa and αvβ3 integrins. The expression of matrix metalloproteinase-2 (MMP-2), MMP-9 and αvβ3 integrin in MDA-MB-231 cells were up-regulated after low shear stress exposure (1.84 dynes/cm(2), 2 h). Moreover, we also demonstrated that low shear stress induced a sustained activation of p85 (a regulatory subunit of PI3K) and Akt. Pre-treating MDA-MB-231 cells with the specific PI3K inhibitor of LY294002 abolished the shear stress induced-Akt activation, and the expression of MMP-2, MMP-9, vascular endothelial growth factor (VEGF) and αvβ3 integrin were also down-regulated. Immunofluorescence assay showed that low shear stress also induced αvβ3 integrin clustering and nuclear factor-κB (NF-κB) activation. Interestingly, shear stress-induced activation of Akt and NF-κB was attenuated by LM609, a specific antibody of αvβ3 integrin. It suggests that αvβ3

  11. Shape Recovery of Elastic Red Blood Cells from Shear Flow Induced Deformation in Three Dimensions

    NASA Astrophysics Data System (ADS)

    Peng, Yan; Gounley, John

    2015-11-01

    Red blood cells undergo substantial shape changes in vivo. Modeled as an elastic capsule, the shape recovery of a three dimensional biconcave capsule from shear flow is studied for different preferred elastic and bending configuration. The fluid-structure interaction is modeled using the multiple-relaxation time lattice Boltzmann (LBM) and immersed boundary (IBM) methods. Based on the studies of the limited shape memory observed in three dimensions, the shape recovery is caused by the preferred elastic configuration, at least when paired with a constant spontaneous curvature. For these capsules, the incompleteness of the shape recovery observed precludes any conjecture about whether a single or multiple phase(s) are necessary to describe the recovery process. Longer simulations and a more stable methodology will be necessary. Y. Peng acknowledges support from Old Dominion University Research Foundation Grant #503921 and National Science Foundation Grant DMS-1319078.

  12. Shear stress-induced NO production is dependent on ATP autocrine signaling and capacitative calcium entry

    PubMed Central

    Andrews, Allison M.; Jaron, Dov; Buerk, Donald G.; Barbee, Kenneth A.

    2014-01-01

    Flow-induced production of nitric oxide (NO) by endothelial cells plays a fundamental role in vascular homeostasis. However, the mechanisms by which shear stress activates NO production remain unclear due in part to limitations in measuring NO, especially under flow conditions. Shear stress elicits the release of ATP, but the relative contribution of autocrine stimulation by ATP to flow-induced NO production has not been established. Furthermore, the importance of calcium in shear stress-induced NO production remains controversial, and in particular the role of capacitive calcium entry (CCE) has yet to be determined. We have utilized our unique NO measurement device to investigate the role of ATP autocrine signaling and CCE in shear stress-induced NO production. We found that endogenously released ATP and downstream activation of purinergic receptors and CCE plays a significant role in shear stress-induced NO production. ATP-induced eNOS phophorylation under static conditions is also dependent on CCE. Inhibition of protein kinase C significantly inhibited eNOS phosphorylation and the calcium response. To our knowledge, we are the first to report on the role of CCE in the mechanism of acute shear stress-induced NO response. In addition, our work highlights the importance of ATP autocrine signaling in shear stress-induced NO production. PMID:25386222

  13. Stress analysis of shear/compression test

    SciTech Connect

    Nishijima, S.; Okada, T.; Ueno, S.

    1997-06-01

    Stress analysis has been made on the glass fiber reinforced plastics (GFRP) subjected to the combined shear and compression stresses by means of finite element method. The two types of experimental set up were analyzed, that is parallel and series method where the specimen were compressed by tilted jigs which enable to apply the combined stresses, to the specimen. Modified Tsai-Hill criterion was employed to judge the failure under the combined stresses that is the shear strength under the compressive stress. The different failure envelopes were obtained between the two set ups. In the parallel system the shear strength once increased with compressive stress then decreased. On the contrary in the series system the shear strength decreased monotonicly with compressive stress. The difference is caused by the different stress distribution due to the different constraint conditions. The basic parameters which control the failure under the combined stresses will be discussed.

  14. 4D shear stress maps of the developing heart using Doppler optical coherence tomography.

    PubMed

    Peterson, Lindsy M; Jenkins, Michael W; Gu, Shi; Barwick, Lee; Watanabe, Michiko; Rollins, Andrew M

    2012-11-01

    Accurate imaging and measurement of hemodynamic forces is vital for investigating how physical forces acting on the embryonic heart are transduced and influence developmental pathways. Of particular importance is blood flow-induced shear stress, which influences gene expression by endothelial cells and potentially leads to congenital heart defects through abnormal heart looping, septation, and valvulogenesis. However no imaging tool has been available to measure shear stress on the endocardium volumetrically and dynamically. Using 4D structural and Doppler OCT imaging, we are able to accurately measure the blood flow in the heart tube in vivo and to map endocardial shear stress throughout the heart cycle under physiological conditions for the first time. These measurements of the shear stress patterns will enable precise titration of experimental perturbations and accurate correlation of shear with the expression of molecules critical to heart development.

  15. Shear stress facilitates tissue-engineered odontogenesis.

    PubMed

    Honda, M J; Shinohara, Y; Sumita, Y; Tonomura, A; Kagami, H; Ueda, M

    2006-07-01

    Numerous studies have demonstrated the effect of shear stress on osteoblasts, but its effect on odontogenic cells has never been reported. In this study, we focused on the effect of shear stress on facilitating tissue-engineered odontogenesis by dissociated single cells. Cells were harvested from the porcine third molar tooth at the early stage of crown formation, and the isolated heterogeneous cells were seeded on a biodegradable polyglycolic acid fiber mesh. Then, cell-polymer constructs with and without exposure to shear stress were evaluated by in vitro and in vivo studies. In in vitro studies, the expression of both epithelial and mesenchymal odontogenic-related mRNAs was significantly enhanced by shear stress for 2 h. At 12 h after exposure to shear stress, the expression of amelogenin, bone sialoprotein and vimentin protein was significantly enhanced compared with that of control. Moreover, after 7 days, alkaline phosphatase activity exhibited a significant increase without any significant effect on cell proliferation in vitro. In vivo, enamel and dentin tissues formed after 15 weeks of in vivo implantation in constructs exposure to in vitro shear stress for 12 h. Such was not the case in controls. We concluded that shear stress facilitates odontogenic cell differentiation in vitro as well as the process of tooth tissue engineering in vivo.

  16. Determining Shear Stress Distribution in a Laminate

    NASA Technical Reports Server (NTRS)

    Bednarcyk, Brett A.; Aboudi, Jacob; Yarrington, Phillip W.

    2010-01-01

    A "simplified shear solution" method approximates the through-thickness shear stress distribution within a composite laminate based on an extension of laminated beam theory. The method does not consider the solution of a particular boundary value problem; rather, it requires only knowledge of the global shear loading, geometry, and material properties of the laminate or panel. It is thus analogous to lamination theory in that ply-level stresses can be efficiently determined from global load resultants at a given location in a structure and used to evaluate the margin of safety on a ply-by-ply basis. The simplified shear solution stress distribution is zero at free surfaces, continuous at ply boundaries, and integrates to the applied shear load. The method has been incorporated within the HyperSizer commercial structural sizing software to improve its predictive capability for designing composite structures. The HyperSizer structural sizing software is used extensively by NASA to design composite structures. In the case of through-thickness shear loading on panels, HyperSizer previously included a basic, industry-standard, method for approximating the resulting shear stress distribution in sandwich panels. However, no such method was employed for solid laminate panels. The purpose of the innovation is to provide an approximation of the through-thickness shear stresses in a solid laminate given the through-thickness shear loads (Qx and Qy) on the panel. The method was needed for implementation within the HyperSizer structural sizing software so that the approximated ply-level shear stresses could be utilized in a failure theory to assess the adequacy of a panel design. The simplified shear solution method was developed based on extending and generalizing bi-material beam theory to plate-like structures. It is assumed that the through-thickness shear stresses arise due to local bending of the laminate induced by the through-thickness shear load, and by imposing

  17. Fluid shear, intercellular stress, and endothelial cell alignment.

    PubMed

    Steward, Robert; Tambe, Dhananjay; Hardin, C Corey; Krishnan, Ramaswamy; Fredberg, Jeffrey J

    2015-04-15

    Endothelial cell alignment along the direction of laminar fluid flow is widely understood to be a defining morphological feature of vascular homeostasis. While the role of associated signaling and structural events have been well studied, associated intercellular stresses under laminar fluid shear have remained ill-defined and the role of these stresses in the alignment process has remained obscure. To fill this gap, we report here the tractions as well as the complete in-plane intercellular stress fields measured within the human umbilical vein endothelial cell (HUVEC) monolayer subjected to a steady laminar fluid shear of 1 Pa. Tractions, intercellular stresses, as well as their time course, heterogeneity, and anisotropy, were measured using monolayer traction microscopy and monolayer stress microscopy. Prior to application of laminar fluid flow, intercellular stresses were largely tensile but fluctuated dramatically in space and in time (317 ± 122 Pa). Within 12 h of the onset of laminar fluid flow, the intercellular stresses decreased substantially but continued to fluctuate dramatically (142 ± 84 Pa). Moreover, tractions and intercellular stresses aligned strongly and promptly (within 1 h) along the direction of fluid flow, whereas the endothelial cell body aligned less strongly and substantially more slowly (12 h). Taken together, these results reveal that steady laminar fluid flow induces prompt reduction in magnitude and alignment of tractions and intercellular stress tensor components followed by the retarded elongation and alignment of the endothelial cell body. Appreciably smaller intercellular stresses supported by cell-cell junctions logically favor smaller incidence of gap formation and thus improved barrier integrity.

  18. Fluid shear, intercellular stress, and endothelial cell alignment

    PubMed Central

    Steward, Robert; Tambe, Dhananjay; Hardin, C. Corey; Krishnan, Ramaswamy

    2015-01-01

    Endothelial cell alignment along the direction of laminar fluid flow is widely understood to be a defining morphological feature of vascular homeostasis. While the role of associated signaling and structural events have been well studied, associated intercellular stresses under laminar fluid shear have remained ill-defined and the role of these stresses in the alignment process has remained obscure. To fill this gap, we report here the tractions as well as the complete in-plane intercellular stress fields measured within the human umbilical vein endothelial cell (HUVEC) monolayer subjected to a steady laminar fluid shear of 1 Pa. Tractions, intercellular stresses, as well as their time course, heterogeneity, and anisotropy, were measured using monolayer traction microscopy and monolayer stress microscopy. Prior to application of laminar fluid flow, intercellular stresses were largely tensile but fluctuated dramatically in space and in time (317 ± 122 Pa). Within 12 h of the onset of laminar fluid flow, the intercellular stresses decreased substantially but continued to fluctuate dramatically (142 ± 84 Pa). Moreover, tractions and intercellular stresses aligned strongly and promptly (within 1 h) along the direction of fluid flow, whereas the endothelial cell body aligned less strongly and substantially more slowly (12 h). Taken together, these results reveal that steady laminar fluid flow induces prompt reduction in magnitude and alignment of tractions and intercellular stress tensor components followed by the retarded elongation and alignment of the endothelial cell body. Appreciably smaller intercellular stresses supported by cell-cell junctions logically favor smaller incidence of gap formation and thus improved barrier integrity. PMID:25652451

  19. Turbulent shear stresses in compressible boundary layers

    NASA Technical Reports Server (NTRS)

    Laderman, A. J.; Demetriades, A.

    1979-01-01

    Hot-wire anemometer measurements of turbulent shear stresses in a Mach 3 compressible boundary layer were performed in order to investigate the effects of heat transfer on turbulence. Measurements were obtained by an x-probe in a flat plate, zero pressure gradient, two dimensional boundary layer in a wind tunnel with wall to freestream temperature ratios of 0.94 and 0.71. The measured shear stress distributions are found to be in good agreement with previous results, supporting the contention that the shear stress distribution is essentially independent of Mach number and heat transfer for Mach numbers from incompressible to hypersonic and wall to freestream temperature ratios of 0.4 to 1.0. It is also found that corrections for frequency response limitations of the electronic equipment are necessary to determine the correct shear stress distribution, particularly at the walls.

  20. Diffractive Optic Fluid Shear Stress Sensor

    NASA Technical Reports Server (NTRS)

    Wilson, D.; Scalf, J.; Forouhar, S.; Muller, R.; Taugwalder, F.; Gharib, M.; Fourguette, D.; Madarress, D.

    2000-01-01

    Light scattering off particles flowing through a two-slit inteference pattern can be used to measure the shear stress of the fluid. We have designed and fabricated a miniature diffractive optic sensor based on this principle.

  1. Diffractive Optic Fluid Shear Stress Sensor

    NASA Technical Reports Server (NTRS)

    Wilson, D.; Scalf, J.; Forouhar, S.; Muller, R.; Taugwalder, F.; Gharib, M.; Fourguette, D.; Modarress, D.

    2000-01-01

    Light scattering off particles flowing through a two-slit interference pattern can be used to measure the shear stress of the fluid. We have designed and fabricated a miniature diffractive optic sensor based on this principle.

  2. Wall shear stress in collapsed tubes

    NASA Astrophysics Data System (ADS)

    Naili, S.; Ribreau, C.

    1999-01-01

    A small flexural wall rigidity brings unique features to cross-sectional shapes and blood flow within veins, which are characterised by a non-uniform hemodynamical environment acting upon endothelial cells. Velocity fields and related wall shear stress were numerically determined for a large number of conditions, assuming a fully developed, steady, incompressible laminar flow through an uniform smooth pipe with a constant cross-section. It was shown that the flatness greatly influences the resulting distribution of the wall shear stresses along the lumen perimeter. For instance, under a steady longitudinal pressure gradient at about 500 Pascal per meter inside a constant oval-shaped tube, with a lumen perimeter of the order of 5 × 10^{-2} meter, the maximum wall shear stress is found at about 2 Pascal where the local curvature is minimal. On the other hand, the minimal wall shear stress of the order of 1 Pascal is found where the local curvature is maximal. Clear indications have been reported showing that the hemodynamical wall shear stress does alter endothelial cell morphology and orientation. These results are being used for developing an experimental set-up in order to locally map out the characteristic shear stresses looking for endothelial shape modifications whenever a viscous fluid flow is applied.

  3. Measuring Interlayer Shear Stress in Bilayer Graphene

    NASA Astrophysics Data System (ADS)

    Wang, Guorui; Dai, Zhaohe; Wang, Yanlei; Tan, PingHeng; Liu, Luqi; Xu, Zhiping; Wei, Yueguang; Huang, Rui; Zhang, Zhong

    2017-07-01

    Monolayer two-dimensional (2D) crystals exhibit a host of intriguing properties, but the most exciting applications may come from stacking them into multilayer structures. Interlayer and interfacial shear interactions could play a crucial role in the performance and reliability of these applications, but little is known about the key parameters controlling shear deformation across the layers and interfaces between 2D materials. Herein, we report the first measurement of the interlayer shear stress of bilayer graphene based on pressurized microscale bubble loading devices. We demonstrate continuous growth of an interlayer shear zone outside the bubble edge and extract an interlayer shear stress of 40 kPa based on a membrane analysis for bilayer graphene bubbles. Meanwhile, a much higher interfacial shear stress of 1.64 MPa was determined for monolayer graphene on a silicon oxide substrate. Our results not only provide insights into the interfacial shear responses of the thinnest structures possible, but also establish an experimental method for characterizing the fundamental interlayer shear properties of the emerging 2D materials for potential applications in multilayer systems.

  4. Boundary Shear Stress Along Vegetated Streambanks

    NASA Astrophysics Data System (ADS)

    Clark, L. A.; Wynn, T.

    2007-12-01

    Sediment, a leading cause of water quality impairment, damages aquatic ecosystems and interferes with recreational uses and water treatment processes. Streambank retreat can contribute as much as 85% of watershed sediment yield. Vegetation is an important component of stream restoration designs used to control streambank retreat, but vegetation effects on streambank boundary shear stress (SBSS) need to be quantified. The overall goal of this experiment is to predict boundary shear stress along vegetated streambanks. This goal will be met by determining a method for measuring boundary shear stress in the field along hydraulically rough streambanks, evaluating the effects of streambank vegetation on boundary shear stress in the field, and developing predictive methods based on measurable vegetative properties. First, three streambank vegetation types (herbaceous, shrubbery, and woody) will be modeled in a flume study to examine both boundary shear stress measurement theory and instruments for field use. An appropriate method (law of the wall, Reynold's stresses, TKE, or average wall shear stress) and field instrument (ADV, propeller, or Pitot tube) will be selected, resulting in a field technique to measure SBSS. Predictive methods for estimating SBSS, based on common vegetation measurements, will be developed in the flume study and validated with field data. This research is intended to improve our understanding of the role of riparian vegetation in stream morphology by evaluating the effects of vegetation on boundary shear stress, providing insight to the type and density of vegetation required for streambank stability. The results will also aide in quantifying sediment inputs from streambanks, providing quantitative information for stream restoration projects and watershed management planning.

  5. Bottom shear stress in unsteady sewer flow.

    PubMed

    Bares, V; Jirák, J; Pollert, J

    2006-01-01

    The properties of unsteady open-channel turbulent flow were theoretically and experimentally investigated in a circular cross section channel with fixed sediment deposits. Velocity and turbulence distribution data were obtained using an ultrasonic velocity profiler (UVP). Different uniform flow conditions and triangular-shaped hydrographs were analysed. The hydrograph analysis revealed a dynamic wave behaviour, where the time lags of mean cross section velocity, friction velocity, discharge and flow depth were all evident. The bottom shear stress dynamic behaviour was estimated using four different approaches. Measurements of the velocity distribution in the inner region of the turbulent layer and of the Reynolds stress distribution in the turbulent flow provided the analysed data sets of the bottom shear stress. Furthermore, based on the Saint Venant equation, the bottom shear stress time behaviour was studied using both the kinematic and the dynamic flow principles. The dynamic values of the bottom shear stress were compared with those for the steady flow conditions. It is evident that bottom shear stress varies along the generated flood hydrograph and its variation is the function of the flow unsteadiness. Moreover, the kinematic flow principle is not an adequate type of approximation for presented flow conditions.

  6. Flow-induced wall mechanics of patient-specific aneurysmal cerebral arteries: Nonlinear isotropic versus anisotropic wall stress.

    PubMed

    Cornejo, Sergio; Guzmán, Amador; Valencia, Alvaro; Rodríguez, Jose; Finol, Ender

    2014-01-01

    Fluid-structure interaction simulations of three patient-specific models of cerebral aneurysms were carried out with the objective of quantifying the effects of non-Newtonian blood flow and the vessel mechanical behavior on the time-dependent fluid shear and normal stresses, and structural stress and stretch. The average wall shear stress at peak systole was found to be approximately one order of magnitude smaller than the shear stresses in the proximal communicating arteries, regardless of the shape or size of the aneurysms. Spatial distributions of oscillatory shear index were consistent with the reciprocal of wall shear stress distributions at peak systole for all aneurysm geometries, demonstrating that oscillatory shear index correlates inversely with wall shear at this time point in the cardiac cycle. An aneurysm wall modeled with an isotropic material resulted in an underestimation of both the maximum principal stress and stretch, compared to the anisotropic material model. For the three aneurysm geometries, anisotropic peak wall stresses were approximately 50% higher than for an isotropic material. Regardless of the constitutive material, the maximum stresses were consistently located at the aneurysm neck; stresses in the dome were 30% of those in the neck.

  7. Shear-flow induced detachment of Saccharomyces cerevisiae from stainless steel: influence of yeast and solid surface properties.

    PubMed

    Guillemot, Gaëlle; Vaca-Medina, Guadalupe; Martin-Yken, Helene; Vernhet, Aude; Schmitz, Philippe; Mercier-Bonin, Muriel

    2006-05-01

    The present study focused on the shear-induced detachment of Saccharomyces cerevisiae in adhesive contact with a 316L stainless steel surface using a shear stress flow chamber, with a view to determining the respective influence of the yeast surface properties and the support characteristics. The effect of cultivation of S. cerevisiae yeast cells on their subsequent detachment from the solid surface was particularly investigated. In order to elucidate the role of stainless steel, non-metallic supports were used as control, covering a broad range of surface properties such as surface free energy and roughness: polypropylene (hydrophobic), polystyrene (mildly hydrophobic, similar to stainless steel) and glass (hydrophilic). All materials were very smooth with respect to the size of yeast. First, experiments were carried out on two types of yeast cells, just rehydrated in saline solution, a biological model widely used in the literature. The influence of the ionic strength (1.5 and 150 mM NaCl) on glass and stainless steel was evaluated. Unlike on glass, no clear evidence was found for electrostatic repulsion with stainless steel since high adhesion was observed whatever the ionic strength. A lack of correlation in adhesion results was also obtained when considering the surface physico-chemical characteristics of type I (hydrophilic) and type II (hydrophobic) rehydrated cells and those of both polymers. It was postulated that unavoidable "sticky" compounds were present on the cell wall, which could not be completely removed during the successive washings of the rehydrated cell suspension before use. This could dramatically alter the yeast surface properties and modify the adhesion strength, thus clearly demonstrating the necessity to work with yeast coming from fresh cultures. Biologically active yeast cells were then used. Once cultured, type I- and type II-yeast cells were shown to exhibit the same hydrophilic properties. Regardless of the material used, for the

  8. Monocyte recruitment to endothelial cells in response to oscillatory shear stress

    PubMed Central

    Hsiai, Tzung K.; Cho, Sung K.; Wong, Pak K.; Ing, Mike; Salazar, Adler; Sevanian, Alex; Navab, Mohamad; Demer, Linda L.; Ho, Chih-Ming

    2014-01-01

    Leukocyte recruitment to endothelial cells is a critical event in inflammatory responses. The spatial, temporal gradients of shear stress, topology, and outcome of cellular interactions that underlie these responses have so far been inferred from static imaging of tissue sections or studies of statically cultured cells. In this report, we developed micro-electromechanical systems (MEMS) sensors, comparable to a single endothelial cell (EC) in size, to link real-time shear stress with monocyte/EC binding kinetics in a complex flow environment, simulating the moving and unsteady separation point at the arterial bifurcation with high spatial and temporal resolution. In response to oscillatory shear stress (τ) at ± 2.6 dyn/cm2 at a time-averaged shear stress (τave) = 0 and 0.5 Hz, individual monocytes displayed unique to-and-fro trajectories undergoing rolling, binding, and dissociation with other monocyte, followed by solid adhesion on EC. Our study quantified individual monocyte/EC binding kinetics in terms of displacement and velocity profiles. Oscillatory flow induces up-regulation of adhesion molecules and cytokines to mediate monocyte/EC interactions over a dynamic range of shear stress ± 2.6 dyn/cm2 (P= 0.50, n= 10).—Hsiai, T. K., Cho, S. K., Wong, P. K., Ing, M., Salazar, A., Sevanian, A., Navab, M., Demer, L. L., Ho, C.-M. Monocyte recruitment to endothelial cells in response to oscillatory shear stress. FASEB J. 17, 1648–1657 (2003) PMID:12958171

  9. Integrated Shear Stress/Temperature Micromachined Sensors

    NASA Technical Reports Server (NTRS)

    Sheplak, Mark; Cattafesta, Louis N., III; Nishida, Toshikazu

    2002-01-01

    During this project we were able to design and initiate the fabrication of an integrated Micro ElectroMechanical Systems (MEMS)-based shear stress/temperature sensor for flow control applications. A brief summary of the completed activities during this project is presented.

  10. MEMS shear stress sensors for cardiovascular diagnostics.

    PubMed

    Soundararajan, Gopikrishnan; Hsiai, Tzung K; DeMaio, Lucas; Chang, Michael; Chang, Stanley

    2004-01-01

    Coronary artery disease is the leading cause of morbidity and mortality in the industrialized nations. Both biochemical and biomechanical stimuli modulate the pathogenesis of coronary artery diseases. Shear stress acting on the lumen of blood vessels intimately modulates the biological activities of vascular endothelial cells (ECs). We hereby develop microelectro mechanical system (MEMS)-based sensors at the dimension comparable to a single EC to monitor realtime shear stress in fluidic channel. Our goal is to fabricate sensors for ex vivo or in vivo shear stress measurement at Reynolds number commonly encountered in human circulation. The MEMS sensors were designed based on the previously described heat transfer principles. The polysilicon was doped with phosphorous to render the sensing element a high resistivity at 2.5 KOmega. The development of backside wire bonding enabled the application for the vascular geometry. The small dimension (80x2 mum) and the gain amplitude at 71 KHz offered an entry point to measure shear stress with high spatial and temporal resolution.

  11. Shear stress regulates HUVEC hydraulic conductivity by occludin phosphorylation.

    PubMed

    Pang, Zhengyu; Antonetti, David A; Tarbell, John M

    2005-11-01

    Human umbilical vein endothelial cells (HUVECs) display hydraulic conductivity (L(P)) responses to shear stress that differ markedly from the responses of bovine aortic endothelial cells (BAECs). In HUVECs, 5, 10, and 20 dyn cm(-2) steady shear stress transiently increased L(P) with a return to preshear baseline after a 2-h exposure to shear stress. Pure oscillatory shear stress of 0 +/- 20 dyn cm(-2) (mean+/-amplitude) had no effect on L(P), whereas superposition of oscillatory shear stress on steady shear stress suppressed the effect induced by steady shear stress alone. Shear reversal (amplitude greater than mean) was not necessary for the inhibitory influence of oscillatory shear stress. The transient increase of L(P) by steady shear stress was not affected by incubation with BAPTA-AM (10 microM), suggesting calcium independence of the shear response. Decreasing nitric oxide (NO) concentration with L-NMMA (100 microM), a nitric oxide synthase (NOS) inhibitor, did not inhibit the HUVEC L(P) response to shear stress. At the protein level, 10 dyn cm(-2) shear stress did not affect the total content of occludin, but it did elevate the phosphorylation level transiently. The positive correlation between occludin phosphorylation and hydraulic conductivity parallels observations in BAECs and suggests that occludin phosphorylation may be a general mediator of shear-L(P) responses in diverse endothelial cell types.

  12. Evolution of allowable stresses in shear for lumber

    Treesearch

    Robert L. Ethington; William L. Galligan; Henry M. Montrey; Alan D. Freas

    1979-01-01

    This paper surveys research leading to allowable shear stress parallel to grain for lumber. In early flexure tests of lumber, some pieces failed in shear. The estimated shear stress at time of failure was generally lower than shear strength measured on small, clear, straight-grained specimens. This and other engineering observations gave rise to adjustments that...

  13. Flexible Micropost Arrays for Shear Stress Measurement

    NASA Technical Reports Server (NTRS)

    Wohl, Christopher J.; Palmieri, Frank L.; Hopkins, John W.; Jackson, Allen M.; Connell, John W.; Lin, Yi; Cisotto, Alexxandra A.

    2015-01-01

    Increased fuel costs, heightened environmental protection requirements, and noise abatement continue to place drag reduction at the forefront of aerospace research priorities. Unfortunately, shortfalls still exist in the fundamental understanding of boundary-layer airflow over aerodynamic surfaces, especially regarding drag arising from skin friction. For example, there is insufficient availability of instrumentation to adequately characterize complex flows with strong pressure gradients, heat transfer, wall mass flux, three-dimensionality, separation, shock waves, and transient phenomena. One example is the acoustic liner efficacy on aircraft engine nacelle walls. Active measurement of shear stress in boundary layer airflow would enable a better understanding of how aircraft structure and flight dynamics affect skin friction. Current shear stress measurement techniques suffer from reliability, complexity, and airflow disruption, thereby compromising resultant shear stress data. The state-of-the-art for shear stress sensing uses indirect or direct measurement techniques. Indirect measurements (e.g., hot-wire, heat flux gages, oil interferometry, laser Doppler anemometry, small scale pressure drag surfaces, i.e., fences) require intricate knowledge of the studied flow, restrictive instrument arrangements, large surface areas, flow disruption, or seeding material; with smaller, higher bandwidth probes under development. Direct measurements involve strain displacement of a sensor element and require no prior knowledge of the flow. Unfortunately, conventional "floating" recessed components for direct measurements are mm to cm in size. Whispering gallery mode devices and Fiber Bragg Gratings are examples of recent additions to this type of sensor with much smaller (?m) sensor components. Direct detection techniques are often single point measurements and difficult to calibrate and implement in wind tunnel experiments. In addition, the wiring, packaging, and installation

  14. Monocyte recruitment to endothelial cells in response to oscillatory shear stress.

    PubMed

    Hsiai, Tzung K; Cho, Sung K; Wong, Pak K; Ing, Mike; Salazar, Adler; Sevanian, Alex; Navab, Mohamad; Demer, Linda L; Ho, Chih-Ming

    2003-09-01

    Leukocyte recruitment to endothelial cells is a critical event in inflammatory responses. The spatial, temporal gradients of shear stress, topology, and outcome of cellular interactions that underlie these responses have so far been inferred from static imaging of tissue sections or studies of statically cultured cells. In this report, we developed micro-electromechanical systems (MEMS) sensors, comparable to a single endothelial cell (EC) in size, to link real-time shear stress with monocyte/EC binding kinetics in a complex flow environment, simulating the moving and unsteady separation point at the arterial bifurcation with high spatial and temporal resolution. In response to oscillatory shear stress (tau) at +/- 2.6 dyn/cm2 at a time-averaged shear stress (tau(ave))=0 and 0.5 Hz, individual monocytes displayed unique to-and-fro trajectories undergoing rolling, binding, and dissociation with other monocyte, followed by solid adhesion on EC. Our study quantified individual monocyte/EC binding kinetics in terms of displacement and velocity profiles. Oscillatory flow induces up-regulation of adhesion molecules and cytokines to mediate monocyte/EC interactions over a dynamic range of shear stress +/- 2.6 dyn/cm2 (P=0.50, n=10).

  15. APPLYING SHEAR STRESS TO PLURIPOTENT STEM CELLS

    PubMed Central

    Wolfe, Russell P.; Guidry, Julia B.; Messina, Stephanie L.; Ahsan, Tabassum

    2016-01-01

    Summary Thorough understanding of the effects of shear stress on stem cells is critical for the rationale design of large-scale production of cell-based therapies. This is of growing importance as emerging tissue engineering and regenerative medicine applications drive the need for clinically-relevant numbers of both pluripotent stem cells (PSCs) and cells derived from PSCs. Here we describe the use of a custom parallel plate bioreactor system to impose fluid shear stress on a layer of PSCs adhered to protein-coated glass slides. This system can be useful both for basic science studies in mechanotransduction and as a surrogate model for bioreactors used in large-scale production. PMID:25762292

  16. Stent implantation influence wall shear stress evolution

    NASA Astrophysics Data System (ADS)

    Bernad, S. I.; Totorean, A. F.; Bosioc, A. I.; Petre, I.; Bernad, E. S.

    2016-06-01

    Local hemodynamic factors are known affect the natural history of the restenosis critically after coronary stenting of atherosclerosis. Stent-induced flows disturbance magnitude dependent directly on the strut design. The impact of flow alterations around struts vary as the strut geometrical parameters change. Our results provide data regarding the hemodynamic parameters for the blood flow in both stenosed and stented coronary artery under physiological conditions, namely wall shear stress and pressure drop.

  17. Shear Stress Sensing using Elastomer Micropillar Arrays

    NASA Technical Reports Server (NTRS)

    Wohl, Christopher J.; Palmieri, Frank L.; Lin, Yi; Jackson, Allen M.; Cissoto, Alexxandra; Sheplak, Mark; Connell, John W.

    2013-01-01

    The measurement of shear stress developed as a fluid moves around a solid body is difficult to measure. Stresses at the fluid-solid interface are very small and the nature of the fluid flow is easily disturbed by introducing sensor components to the interface. To address these challenges, an array of direct and indirect techniques have been investigated with various advantages and challenges. Hot wire sensors and other indirect sensors all protrude significantly into the fluid flow. Microelectromechanical systems (MEMS) devices, although facilitating very accurate measurements, are not durable, are prone to contamination, and are difficult to implement into existing model geometries. One promising approach is the use of engineered surfaces that interact with fluid flow in a detectable manner. To this end, standard lithographic techniques have been utilized to generate elastomeric micropillar arrays of various lengths and diameters. Micropillars of controlled length and width were generated in polydimethylsiloxane (PDMS) elastomer using a soft-lithography technique. The 3D mold for micropillar replication was fabricated using laser ablative micromachining and contact lithography. Micropillar dimensions and mechanical properties were characterized and compared to shear sensing requirements. The results of this characterization as well as shear stress detection techniques will be discussed.

  18. Bellows flow-induced vibrations

    NASA Technical Reports Server (NTRS)

    Tygielski, P. J.; Smyly, H. M.; Gerlach, C. R.

    1983-01-01

    The bellows flow excitation mechanism and results of comprehensive test program are summarized. The analytical model for predicting bellows flow induced stress is refined. The model includes the effects of an upstream elbow, arbitrary geometry, and multiple piles. A refined computer code for predicting flow induced stress is described which allows life prediction if a material S-N diagram is available.

  19. Shear stress-induced mitochondrial biogenesis decreases the release of microparticles from endothelial cells

    PubMed Central

    Kim, Ji-Seok; Kim, Boa; Lee, Hojun; Thakkar, Sunny; Babbitt, Dianne M.; Eguchi, Satoru; Brown, Michael D.

    2015-01-01

    The concept of enhancing structural integrity of mitochondria has emerged as a novel therapeutic option for cardiovascular disease. Flow-induced increase in laminar shear stress is a potent physiological stimulant associated with exercise, which exerts atheroprotective effects in the vasculature. However, the effect of laminar shear stress on mitochondrial remodeling within the vascular endothelium and its related functional consequences remain largely unknown. Using in vitro and in vivo complementary studies, here, we report that aerobic exercise alleviates the release of endothelial microparticles in prehypertensive individuals and that these salutary effects are, in part, mediated by shear stress-induced mitochondrial biogenesis. Circulating levels of total (CD31+/CD42a−) and activated (CD62E+) microparticles released by endothelial cells were significantly decreased (∼40% for both) after a 6-mo supervised aerobic exercise training program in individuals with prehypertension. In cultured human endothelial cells, laminar shear stress reduced the release of endothelial microparticles, which was accompanied by an increase in mitochondrial biogenesis through a sirtuin 1 (SIRT1)-dependent mechanism. Resveratrol, a SIRT1 activator, treatment showed similar effects. SIRT1 knockdown using small-interfering RNA completely abolished the protective effect of shear stress. Disruption of mitochondrial integrity by either antimycin A or peroxisome proliferator-activated receptor-γ coactivator-1α small-interfering RNA significantly increased the number of total, and activated, released endothelial microparticles, and shear stress restored these back to basal levels. Collectively, these data demonstrate a critical role of endothelial mitochondrial integrity in preserving endothelial homeostasis. Moreover, prolonged laminar shear stress, which is systemically elevated during aerobic exercise in the vessel wall, mitigates endothelial dysfunction by promoting mitochondrial

  20. Shear stress-induced mitochondrial biogenesis decreases the release of microparticles from endothelial cells.

    PubMed

    Kim, Ji-Seok; Kim, Boa; Lee, Hojun; Thakkar, Sunny; Babbitt, Dianne M; Eguchi, Satoru; Brown, Michael D; Park, Joon-Young

    2015-08-01

    The concept of enhancing structural integrity of mitochondria has emerged as a novel therapeutic option for cardiovascular disease. Flow-induced increase in laminar shear stress is a potent physiological stimulant associated with exercise, which exerts atheroprotective effects in the vasculature. However, the effect of laminar shear stress on mitochondrial remodeling within the vascular endothelium and its related functional consequences remain largely unknown. Using in vitro and in vivo complementary studies, here, we report that aerobic exercise alleviates the release of endothelial microparticles in prehypertensive individuals and that these salutary effects are, in part, mediated by shear stress-induced mitochondrial biogenesis. Circulating levels of total (CD31(+)/CD42a(-)) and activated (CD62E(+)) microparticles released by endothelial cells were significantly decreased (∼40% for both) after a 6-mo supervised aerobic exercise training program in individuals with prehypertension. In cultured human endothelial cells, laminar shear stress reduced the release of endothelial microparticles, which was accompanied by an increase in mitochondrial biogenesis through a sirtuin 1 (SIRT1)-dependent mechanism. Resveratrol, a SIRT1 activator, treatment showed similar effects. SIRT1 knockdown using small-interfering RNA completely abolished the protective effect of shear stress. Disruption of mitochondrial integrity by either antimycin A or peroxisome proliferator-activated receptor-γ coactivator-1α small-interfering RNA significantly increased the number of total, and activated, released endothelial microparticles, and shear stress restored these back to basal levels. Collectively, these data demonstrate a critical role of endothelial mitochondrial integrity in preserving endothelial homeostasis. Moreover, prolonged laminar shear stress, which is systemically elevated during aerobic exercise in the vessel wall, mitigates endothelial dysfunction by promoting

  1. Experimental study on the bed shear stress under breaking waves

    NASA Astrophysics Data System (ADS)

    Hao, Si-yu; Xia, Yun-feng; Xu, Hua

    2017-06-01

    The object of present study is to investigate the bed shear stress on a slope under regular breaking waves by a novel instrument named Micro-Electro-Mechanical System (MEMS) flexible hot-film shear stress sensor. The sensors were calibrated before application, and then a wave flume experiment was conducted to study the bed shear stress for the case of regular waves spilling and plunging on a 1:15 smooth PVC slope. The experiment shows that the sensor is feasible for the measurement of the bed shear stress under breaking waves. For regular incident waves, the bed shear stress is mainly periodic in both outside and inside the breaking point. The fluctuations of the bed shear stress increase significantly after waves breaking due to the turbulence and vortexes generated by breaking waves. For plunging breaker, the extreme value of the mean maximum bed shear stress appears after the plunging point, and the more violent the wave breaks, the more dramatic increase of the maximum bed shear stress will occur. For spilling breaker, the increase of the maximum bed shear stress along the slope is gradual compared with the plunging breaker. At last, an empirical equation about the relationship between the maximum bed shear stress and the surf similarity parameter is given, which can be used to estimate the maximum bed shear stress under breaking waves in practice.

  2. Wrinkling of reinforced plates subjected to shear stresses

    NASA Technical Reports Server (NTRS)

    Seydel, Edgar

    1931-01-01

    An analysis is made here of the problem of long plates with transverse stiffeners subject to shear. A typical example would be a long Wagner beam. The shear stress is calculated at which the web wrinkles and shear stress becomes a maximum. The equation is solved for both a condition of free support and rigidity of support on the edges.

  3. Flow-activated chloride channels in vascular endothelium. Shear stress sensitivity, desensitization dynamics, and physiological implications.

    PubMed

    Gautam, Mamta; Shen, Yue; Thirkill, Twanda L; Douglas, Gordon C; Barakat, Abdul I

    2006-12-01

    Although activation of outward rectifying Cl(-) channels is one of the fastest responses of endothelial cells (ECs) to shear stress, little is known about these channels. In this study, we used whole-cell patch clamp recordings to characterize the flow-activated Cl(-) current in bovine aortic ECs (BAECs). Application of shear stress induced rapid development of a Cl(-) current that was effectively blocked by the Cl(-) channel antagonist 5-nitro-2-(3-phenopropylamino)benzoic acid (100 microM). The current initiated at a shear stress as low as 0.3 dyne/cm(2), attained its peak within minutes of flow onset, and saturated above 3.5 dynes/cm(2) approximately 2.5-3.5-fold increase over pre-flow levels). The Cl(-) current desensitized slowly in response to sustained flow, and step increases in shear stress elicited increased current only if the shear stress levels were below the 3.5 dynes/cm(2) saturation level. Oscillatory flow with a physiological oscillation frequency of 1 Hz, as occurs in disturbed flow zones prone to atherosclerosis, failed to elicit the Cl(-) current, whereas lower oscillation frequencies led to partial recovery of the current. Nonreversing pulsatile flow, generally considered protective of atherosclerosis, was as effective in eliciting the current as steady flow. Measurements using fluids of different viscosities indicated that the Cl(-) current is responsive to shear stress rather than shear rate. Blocking the flow-activated Cl(-) current abolished flow-induced Akt phosphorylation in BAECs, whereas blocking flow-sensitive K(+) currents had no effect, suggesting that flow-activated Cl(-) channels play an important role in regulating EC flow signaling.

  4. Lubricant limiting shear stress effect on EHD film thickness

    NASA Technical Reports Server (NTRS)

    Gecim, B.; Winer, W. O.

    1979-01-01

    A Grubin-like EHD inlet analysis utilizing a non-linear viscous fluid model with a limiting shear stress is reported. The shear rheological equation requirs only a low shear stress viscosity and the limiting shear stress both functions of pressure. Values employed for these properties are taken from measurements on typical lubricants. Reductions of EHD film thickness are found to be up to 40 percent compared with the standard Grubin prediction for typical operating conditions. Slide-roll ratio, limiting shear stress dependence on pressure, and atmospheric pressure value of limiting shear stress are new variables required to determine film thickness with the first two being more important than the last. The EHD film thickness is reduced by increasing slide-roll ratio and/or decreasing the pressure dependence of the limiting shear stress.

  5. Shear stress cleaning for surface departiculation

    NASA Technical Reports Server (NTRS)

    Musselman, R. P.; Yarbrough, T. W.

    1986-01-01

    A cleaning technique widely used by the nuclear utility industry for removal of radioactive surface contamination has proven effective at removing non-hazardous contaminant particles as small as 0.1 micrometer. The process employs a controlled high velocity liquid spray inside a vapor containment enclosure to remove particles from a surface. The viscous drag force generated by the cleaning fluid applies a shear stress greater than the adhesion force that holds small particles to a substrate. Fluid mechanics and field tests indicate general cleaning parameters.

  6. Shear-stress relaxation and ensemble transformation of shear-stress autocorrelation functions

    NASA Astrophysics Data System (ADS)

    Wittmer, J. P.; Xu, H.; Baschnagel, J.

    2015-02-01

    We revisit the relation between the shear-stress relaxation modulus G (t ) , computed at finite shear strain 0 <γ ≪1 , and the shear-stress autocorrelation functions C(t ) | γ and C(t ) | τ computed, respectively, at imposed strain γ and mean stress τ . Focusing on permanent isotropic spring networks it is shown theoretically and computationally that in general G(t ) =C (t ) | τ=C(t ) | γ+Geq for t >0 with Geq being the static equilibrium shear modulus. G (t ) and C(t ) | γ thus must become different for solids and it is impossible to obtain Geq alone from C(t ) | γ as often assumed. We comment briefly on self-assembled transient networks where Geq(f ) must vanish for a finite scission-recombination frequency f . We argue that G(t ) =C (t ) | τ=C(t ) | γ should reveal an intermediate plateau set by the shear modulus Geq(f =0 ) of the quenched network.

  7. Tumor cell cycle arrest induced by shear stress: Roles of integrins and Smad

    PubMed Central

    Chang, Shun-Fu; Chang, Cheng Allen; Lee, Ding-Yu; Lee, Pei-Ling; Yeh, Yu-Ming; Yeh, Chiuan-Ren; Cheng, Cheng-Kung; Chien, Shu; Chiu, Jeng-Jiann

    2008-01-01

    Interstitial flow in and around tumor tissue affects the mechanical microenvironment to modulate tumor cell growth and metastasis. We investigated the roles of flow-induced shear stress in modulating cell cycle distribution in four tumor cell lines and the underlying mechanisms. In all four cell lines, incubation under static conditions for 24 or 48 h led to G0/G1 arrest; in contrast, shear stress (12 dynes/cm2) induced G2/M arrest. The molecular basis of the shear effect was analyzed, and the presentation on molecular mechanism is focused on human MG63 osteosarcoma cells. Shear stress induced increased expressions of cyclin B1 and p21CIP1 and decreased expressions of cyclins A, D1, and E, cyclin-dependent protein kinases (Cdk)-1, -2, -4, and -6, and p27KIP1 as well as a decrease in Cdk1 activity. Using specific antibodies and small interfering RNA, we found that the shear-induced G2/M arrest and corresponding changes in G2/M regulatory protein expression and activity were mediated by αvβ3 and β1 integrins through bone morphogenetic protein receptor type IA-specific Smad1 and Smad5. Shear stress also down-regulated runt-related transcription factor 2 (Runx2) binding activity and osteocalcin and alkaline phosphatase expressions in MG63 cells; these responses were mediated by αvβ3 and β1 integrins through Smad5. Our findings provide insights into the mechanism by which shear stress induces G2/M arrest in tumor cells and inhibits cell differentiation and demonstrate the importance of mechanical microenvironment in modulating molecular signaling, gene expression, cell cycle, and functions in tumor cells. PMID:18310319

  8. Shear stress induced stimulation of mammalian cell metabolism

    NASA Technical Reports Server (NTRS)

    Mcintire, L. V.; Frangos, J. A.; Eskin, S. G.

    1988-01-01

    A flow apparatus was developed for the study of the metabolic response of anchorage dependent cells to a wide range of steady and pulsatile shear stresses under well controlled conditions. Human umbilical vein endothelial cell monolayers were subjected to steady shear stresses of up to 24 dynes/sq cm, and the production of prostacyclin was determined. The onset of flow led to a burst in prostacyclin production which decayed to a long term steady state rate (SSR). The SSR of cells exposed to flow was greater than the basal release level, and increased linearly with increasing shear stress. It is demonstrated that shear stresses in certain ranges may not be detrimental to mammalian cell metabolism. In fact, throughout the range of shear stresses studied, metabolite production is maximized by maximizing shear stress.

  9. Mechanistic theory of margination and flow-induced segregation in confined multicomponent suspensions: Simple shear and Poiseuille flows*

    NASA Astrophysics Data System (ADS)

    Henríquez Rivera, Rafael G.; Zhang, Xiao; Graham, Michael D.

    2016-10-01

    A mechanistic model, derived from kinetic theory, is developed to describe segregation in confined multicomponent suspensions such as blood. It incorporates the two key phenomena arising in these systems at low Reynolds number: hydrodynamic pair collisions and hydrodynamic migration. Two flow profiles are considered: simple shear flow (plane Couette flow) and plane Poiseuille flow. The theory begins by writing the evolution of the number density of each component in the suspension as a master equation with contributions from migration and collisions. By making judicious approximations for the collisions, this system of integrodifferential equations is reduced to a set of drift-diffusion equations. We focus attention on the case of a binary suspension with a deformable primary component that completely dominates the collision dynamics in the system and a trace component that has no effect on the primary. The model captures the phenomena of depletion layer formation and margination observed in confined multicomponent suspensions of deformable particles. The depletion layer thickness of the primary component is predicted to follow a master curve relating it in a specific way to confinement ratio and volume fraction. Results from various sources (experiments, detailed simulations, master equation solutions) with different parameters (flexibility of different components in the suspension, viscosity ratio, confinement, among others) collapse onto the same curve. For sufficiently dilute suspensions the analytical form predicted by the drift-diffusion theory for this curve is in excellent agreement with results from these other sources with only one adjustable parameter. In a binary suspension, several regimes of segregation arise, depending on the value of a "margination parameter" M . Most importantly, in both Couette and Poiseuille flows there is a critical value of M below which a sharp "drainage transition" occurs: one component is completely depleted from the bulk

  10. Wall shear stress estimates in coronary artery constrictions

    NASA Technical Reports Server (NTRS)

    Back, L. H.; Crawford, D. W.

    1992-01-01

    Wall shear stress estimates from laminar boundary layer theory were found to agree fairly well with the magnitude of shear stress levels along coronary artery constrictions obtained from solutions of the Navier Stokes equations for both steady and pulsatile flow. The relatively simple method can be used for in vivo estimates of wall shear stress in constrictions by using a vessel shape function determined from a coronary angiogram, along with a knowledge of the flow rate.

  11. Wall shear stress estimates in coronary artery constrictions

    NASA Technical Reports Server (NTRS)

    Back, L. H.; Crawford, D. W.

    1992-01-01

    Wall shear stress estimates from laminar boundary layer theory were found to agree fairly well with the magnitude of shear stress levels along coronary artery constrictions obtained from solutions of the Navier Stokes equations for both steady and pulsatile flow. The relatively simple method can be used for in vivo estimates of wall shear stress in constrictions by using a vessel shape function determined from a coronary angiogram, along with a knowledge of the flow rate.

  12. Colors Of Liquid Crystals Used To Measure Surface Shear Stresses

    NASA Technical Reports Server (NTRS)

    Reda, D. C.; Muratore, J. J., Jr.

    1996-01-01

    Developmental method of mapping shear stresses on aerodynamic surfaces involves observation, at multiple viewing angles, of colors of liquid-crystal surface coats illuminated by white light. Report describing method referenced in "Liquid Crystals Indicate Directions Of Surface Shear Stresses" (ARC-13379). Resulting maps of surface shear stresses contain valuable data on magnitudes and directions of skin friction forces associated with surface flows; data used to refine mathematical models of aerodynamics for research and design purposes.

  13. Shear versus micro-shear bond strength test: a finite element stress analysis.

    PubMed

    Placido, Eliane; Meira, Josete B C; Lima, Raul González; Muench, Antonio; de Souza, Roberto Martins; Ballester, Rafael Yagüe

    2007-09-01

    This study aimed at comparing the stress distribution in shear and micro-shear test set-ups using finite element analysis, and suggesting some parameter standardization that might have important influence on the results. Two-dimensional plane strain finite element analysis was performed using MSCPatran and MSCMarc softwares. Model configurations were based on published experimental shear and micro-shear test set-ups and material properties were assumed to be isotropic, homogeneous and linear-elastic. Typical values of elastic modulus and Poisson's ratios were assigned to composite, dentin and adhesive. Loading conditions considered a single-node concentrated load at different distances from the dentin-adhesive interface, and proportional geometry (1:5 scale, but fixed adhesive layer thickness in 50microm) with similar calculated nominal strength. The maximum tensile and shear stresses, and stress distribution along dentin-adhesive interfacial nodes were analyzed. Stress distribution was always non-uniform and greatly differed between shear and micro-shear models. A pronounced stress concentration was observed at the interfacial edges due to the geometric change: stress values farther exceeded the nominal strength and tensile stresses were much higher than shear stresses. For micro-shear test, the relatively thicker adhesive layer and use of low modulus composites may lead to relevant stress intensification. An appropriate loading distance was established for each test (1mm for shear and 0.1mm for micro-shear) in which stress concentration would be minimal, and should be standardized for experimental assays. The elastic modulus of bonded composites, relative adhesive layer thickness and load application distance are important parameters to be standardized, once they influence stress concentration.

  14. Role of hemodynamic shear stress in cardiovascular disease.

    PubMed

    Cecchi, Emanuele; Giglioli, Cristina; Valente, Serafina; Lazzeri, Chiara; Gensini, Gian Franco; Abbate, Rosanna; Mannini, Lucia

    2011-02-01

    Atherosclerosis is the main cause of morbidity and mortality in the Western world. Inflammation and blood flow alterations are new markers emerging as possible determinants for the development of atherosclerotic lesions. In particular, blood flow exerts a shear stress on vessel walls that alters cell physiology. Shear stress arises from the friction between two virtual layers of a fluid and is induced by the difference in motion and viscosity between these layers. Regions of the arterial tree with uniform geometry are exposed to a unidirectional and constant flow, which determines a physiologic shear stress, while arches and bifurcations are exposed to an oscillatory and disturbed flow, which determines a low shear stress. Atherosclerotic lesions develop mainly in areas of low shear stress, while those exposed to a physiologic shear stress are protected. The presence of areas of the arterial tree with different wall shear stress may explain, in part, the different localization of atherosclerotic lesions in both coronary and extracoronary arteries. The measurement of this parameter may help in identifying atherosclerotic plaques at higher risk as well as in evaluating the efficacy of different pharmacological interventions. Moreover, an altered shear stress is associated with the occurrence of both aortic and intracranial aneurysms, possibly leading to their growth and rupture. Finally, the evaluation of shear stress may be useful for predicting the risk of developing restenosis after coronary and peripheral angioplasty and for devising a coronary stent with a strut design less thrombogenic and more conducive to endothelization.

  15. On stress collapse in adiabatic shear bands

    NASA Astrophysics Data System (ADS)

    Wright, T. W.; Walter, J. W.

    T HE DYNAMICS of adiabatic shear band formation is considered making use of a simplified thermo/visco/plastic flow law. A new numerical solution is used to follow the growth of a perturbation from initiation, through early growth and severe localization, to a slowly varying terminal configuration. Asymptotic analyses predict the early and late stage patterns, but the timing and structure of the abrupt transition to severe localization can only be studied numerically, to date. A characteristic feature of the process is that temperature and plastic strain rate begin to localize immediately, but only slowly, whereas the stress first evolves almost as if there were no perturbation, but then collapses rapidly when severe localization occurs.

  16. Adjustable shear stress erosion and transport flume

    DOEpatents

    Roberts, Jesse D.; Jepsen, Richard A.

    2002-01-01

    A method and apparatus for measuring the total erosion rate and downstream transport of suspended and bedload sediments using an adjustable shear stress erosion and transport (ASSET) flume with a variable-depth sediment core sample. Water is forced past a variable-depth sediment core sample in a closed channel, eroding sediments, and introducing suspended and bedload sediments into the flow stream. The core sample is continuously pushed into the flow stream, while keeping the surface level with the bottom of the channel. Eroded bedload sediments are transported downstream and then gravitationally separated from the flow stream into one or more quiescent traps. The captured bedload sediments (particles and aggregates) are weighed and compared to the total mass of sediment eroded, and also to the concentration of sediments suspended in the flow stream.

  17. Two-axis direct fluid shear stress sensor

    NASA Technical Reports Server (NTRS)

    Bajikar, Sateesh (Inventor); Scott, Michael A. (Inventor); Adcock, Edward E. (Inventor)

    2011-01-01

    A micro sized multi-axis semiconductor skin friction/wall shear stress induced by fluid flow. The sensor design includes a shear/strain transduction gimble connected to a force collecting plate located at the flow boundary surface. The shear force collecting plate is interconnected by an arm to offset the tortional hinges from the fluid flow. The arm is connected to the shear force collecting plate through dual axis torsional hinges with piezoresistive torsional strain gauges. These gauges are disposed on the tortional hinges and provide a voltage output indicative of applied shear stress acting on the force collection plate proximate the flow boundary surface. Offsetting the torsional hinges creates a force concentration and resolution structure that enables the generation of a large stress on the strain gauge from small shear stress, or small displacement of the collecting plate. The design also isolates the torsional sensors from exposure to the fluid flow.

  18. Endothelial dysfunction following prolonged sitting is mediated by a reduction in shear stress

    PubMed Central

    Restaino, Robert M.; Walsh, Lauren K.; Morishima, Takuma; Vranish, Jennifer R.; Martinez-Lemus, Luis A.; Fadel, Paul J.

    2016-01-01

    We and others have recently reported that prolonged sitting impairs endothelial function in the leg vasculature; however, the mechanism(s) remain unknown. Herein, we tested the hypothesis that a sustained reduction in flow-induced shear stress is the underlying mechanism by which sitting induces leg endothelial dysfunction. Specifically, we examined whether preventing the reduction in shear stress during sitting would abolish the detrimental effects of sitting on popliteal artery endothelial function. In 10 young healthy men, bilateral measurements of popliteal artery flow-mediated dilation were performed before and after a 3-h sitting period during which one foot was submerged in 42°C water (i.e., heated) to increase blood flow and thus shear stress, whereas the contralateral leg remained dry and served as internal control (i.e., nonheated). During sitting, popliteal artery mean shear rate was reduced in the nonheated leg (pre-sit, 42.9 ± 4.5 s−1; and 3-h sit, 23.6 ± 3.3 s−1; P < 0.05) but not in the heated leg (pre-sit, 38.9 ± 3.4 s−1; and 3-h sit, 63.9 ± 16.9 s−1; P > 0.05). Popliteal artery flow-mediated dilation was impaired after 3 h of sitting in the nonheated leg (pre-sit, 7.1 ± 1.4% vs. post-sit, 2.8 ± 0.9%; P < 0.05) but not in the heated leg (pre-sit: 7.3 ± 1.5% vs. post-sit, 10.9 ± 1.8%; P > 0.05). Collectively, these data suggest that preventing the reduction of flow-induced shear stress during prolonged sitting with local heating abolishes the impairment in popliteal artery endothelial function. Thus these findings are consistent with the hypothesis that sitting-induced leg endothelial dysfunction is mediated by a reduction in shear stress. PMID:26747508

  19. Endothelial dysfunction following prolonged sitting is mediated by a reduction in shear stress.

    PubMed

    Restaino, Robert M; Walsh, Lauren K; Morishima, Takuma; Vranish, Jennifer R; Martinez-Lemus, Luis A; Fadel, Paul J; Padilla, Jaume

    2016-03-01

    We and others have recently reported that prolonged sitting impairs endothelial function in the leg vasculature; however, the mechanism(s) remain unknown. Herein, we tested the hypothesis that a sustained reduction in flow-induced shear stress is the underlying mechanism by which sitting induces leg endothelial dysfunction. Specifically, we examined whether preventing the reduction in shear stress during sitting would abolish the detrimental effects of sitting on popliteal artery endothelial function. In 10 young healthy men, bilateral measurements of popliteal artery flow-mediated dilation were performed before and after a 3-h sitting period during which one foot was submerged in 42°C water (i.e., heated) to increase blood flow and thus shear stress, whereas the contralateral leg remained dry and served as internal control (i.e., nonheated). During sitting, popliteal artery mean shear rate was reduced in the nonheated leg (pre-sit, 42.9 ± 4.5 s(-1); and 3-h sit, 23.6 ± 3.3 s(-1); P < 0.05) but not in the heated leg (pre-sit, 38.9 ± 3.4 s(-1); and 3-h sit, 63.9 ± 16.9 s(-1); P > 0.05). Popliteal artery flow-mediated dilation was impaired after 3 h of sitting in the nonheated leg (pre-sit, 7.1 ± 1.4% vs. post-sit, 2.8 ± 0.9%; P < 0.05) but not in the heated leg (pre-sit: 7.3 ± 1.5% vs. post-sit, 10.9 ± 1.8%; P > 0.05). Collectively, these data suggest that preventing the reduction of flow-induced shear stress during prolonged sitting with local heating abolishes the impairment in popliteal artery endothelial function. Thus these findings are consistent with the hypothesis that sitting-induced leg endothelial dysfunction is mediated by a reduction in shear stress.

  20. Shear-Panel Test Fixture Eliminates Corner Stresses

    NASA Technical Reports Server (NTRS)

    Kiss, J. J.; Farley, G. L.; Baker, D. J.

    1984-01-01

    New design eliminates corner stresses while maintaining uniform stress across panel. Shear panel test fixture includes eight frames and eight corner pins. Fixture assembled in two halves with shear panel sandwiched in between. Results generated from this fixture will result in good data base for design of efficient aircraft structures and other applications.

  1. Shear-Panel Test Fixture Eliminates Corner Stresses

    NASA Technical Reports Server (NTRS)

    Kiss, J. J.; Farley, G. L.; Baker, D. J.

    1984-01-01

    New design eliminates corner stresses while maintaining uniform stress across panel. Shear panel test fixture includes eight frames and eight corner pins. Fixture assembled in two halves with shear panel sandwiched in between. Results generated from this fixture will result in good data base for design of efficient aircraft structures and other applications.

  2. Methodology for calculating shear stress in a meandering channel

    Treesearch

    Kyung-Seop Sin

    2010-01-01

    Shear stress in meandering channels is the key parameter to predict bank erosion and bend migration. A representative study reach of the Rio Grande River in central New Mexico has been modeled in the Hydraulics Laboratory at CSU. To determine the shear stress distribution in a meandering channel, the large scale (1:12) physical modeling study was conducted in the...

  3. The shear-stress intensity factor for a centrally cracked stiff-flanged shear web

    NASA Technical Reports Server (NTRS)

    Fichter, W. B.

    1976-01-01

    By use of the principle of superposition the stiff-flanged shear web is modeled mathematically by an infinite elastic strip with fixed longitudinal edges. The shear-stress intensity factor for a central longitudinal crack is calculated for various values of the ratio of strip width to crack length, h/a, in the range 0.1-10. The interaction of the crack with the boundaries is illustrated by boundary shear-stress distributions for three values of h/a. Some implications of the results for the design of damage-tolerant shear webs are discussed briefly.

  4. A model of Barchan dunes including lateral shear stress.

    PubMed

    Schwämmle, V; Herrmann, H J

    2005-01-01

    Barchan dunes are found where sand availability is low and wind direction quite constant. The two dimensional shear stress of the wind field and the sand movement by saltation and avalanches over a barchan dune are simulated. The model with one dimensional shear stress is extended including surface diffusion and lateral shear stress. The resulting final shape is compared to the results of the model with a one dimensional shear stress and confirmed by comparison to measurements. We found agreement and improvements with respect to the model with one dimensional shear stress. Additionally, a characteristic edge at the center of the windward side is discovered which is also observed for big barchans. Diffusion effects reduce this effect for small dunes.

  5. Intracellular pH changes in human aortic smooth muscle cells in response to fluid shear stress

    NASA Technical Reports Server (NTRS)

    Stamatas, G. N.; Patrick, C. W. Jr; McIntire, L. V.

    1997-01-01

    The smooth muscle cell (SMC) layers of human arteries may be exposed to blood flow after endothelium denudation, for example, following balloon angioplasty treatment. These SMCs are also constantly subjected to pressure driven transmural fluid flow. Flow-induced shear stress can alter SMC growth and metabolism. Signal transduction mechanisms involved in these flow effects on SMCs are still poorly understood. In this work, the hypothesis that shear stress alters the intracellular pH (pHi) of SMC is examined. When exposed to venous and arterial levels of shear stress, human aortic smooth muscle cells (hASMC) undergo alkalinization. The alkalinization plateau persisted even after 20 min of cell exposure to flow. Addition of amiloride (10 micromoles) or its 5-(N-ethyl-N-isopropyl) analog (EIPA, 10 micromoles), both Na+/H+ exchanger inhibitors, attenuated intracellular alkalinization, suggesting the involvement of the Na+/H+ exchanger in this response. The same concentrations of these inhibitors did not show an effect on pHi of hASMCs in static culture. 4-Acetamido-4'-isothio-cyanatostilbene-2,2'-disulfonic acid (SITS, 1 mM), a Cl-/HCO3- exchange inhibitor, affected the pHi of hASMCs both in static and flow conditions. Our results suggest that flow may perturb the Na+/H+ exchanger leading to an alkalinization of hASMCs, a different response from the flow-induced acidification seen with endothelial cells at the same levels of shear stress. Understanding the flow-induced signal transduction pathways in the vascular cells is of great importance in the tissue engineering of vascular grafts. In the case of SMCs, the involvement of pHi changes in nitric oxide production and proliferation regulation highlights further the significance of such studies.

  6. Intracellular pH changes in human aortic smooth muscle cells in response to fluid shear stress

    NASA Technical Reports Server (NTRS)

    Stamatas, G. N.; Patrick, C. W. Jr; McIntire, L. V.

    1997-01-01

    The smooth muscle cell (SMC) layers of human arteries may be exposed to blood flow after endothelium denudation, for example, following balloon angioplasty treatment. These SMCs are also constantly subjected to pressure driven transmural fluid flow. Flow-induced shear stress can alter SMC growth and metabolism. Signal transduction mechanisms involved in these flow effects on SMCs are still poorly understood. In this work, the hypothesis that shear stress alters the intracellular pH (pHi) of SMC is examined. When exposed to venous and arterial levels of shear stress, human aortic smooth muscle cells (hASMC) undergo alkalinization. The alkalinization plateau persisted even after 20 min of cell exposure to flow. Addition of amiloride (10 micromoles) or its 5-(N-ethyl-N-isopropyl) analog (EIPA, 10 micromoles), both Na+/H+ exchanger inhibitors, attenuated intracellular alkalinization, suggesting the involvement of the Na+/H+ exchanger in this response. The same concentrations of these inhibitors did not show an effect on pHi of hASMCs in static culture. 4-Acetamido-4'-isothio-cyanatostilbene-2,2'-disulfonic acid (SITS, 1 mM), a Cl-/HCO3- exchange inhibitor, affected the pHi of hASMCs both in static and flow conditions. Our results suggest that flow may perturb the Na+/H+ exchanger leading to an alkalinization of hASMCs, a different response from the flow-induced acidification seen with endothelial cells at the same levels of shear stress. Understanding the flow-induced signal transduction pathways in the vascular cells is of great importance in the tissue engineering of vascular grafts. In the case of SMCs, the involvement of pHi changes in nitric oxide production and proliferation regulation highlights further the significance of such studies.

  7. Numerical determination of shear stress relaxation modulus of polymer glasses.

    PubMed

    Kriuchevskyi, I; Wittmer, J P; Benzerara, O; Meyer, H; Baschnagel, J

    2017-04-01

    Focusing on simulated polymer glasses well below the glass transition, we confirm the validity and the efficiency of the recently proposed simple-average expression [Formula: see text] for the computational determination of the shear stress relaxation modulus G(t). Here, [Formula: see text] characterizes the affine shear transformation of the system at t = 0 and h(t) the mean-square displacement of the instantaneous shear stress as a function of time t. This relation is seen to be particulary useful for systems with quenched or sluggish transient shear stresses which necessarily arise below the glass transition. The commonly accepted relation [Formula: see text] using the shear stress auto-correlation function c(t) becomes incorrect in this limit.

  8. Steady and transient fluid shear stress stimulate NO release in osteoblasts through distinct biochemical pathways

    NASA Technical Reports Server (NTRS)

    McAllister, T. N.; Frangos, J. A.

    1999-01-01

    Fluid flow has been shown to be a potent stimulus in osteoblasts and osteocytes and may therefore play an important role in load-induced bone remodeling. The objective of this study was to investigate the characteristics of flow-activated pathways. Previously we reported that fluid flow stimulates rapid and continuous release of nitric oxide (NO) in primary rat calvarial osteoblasts. Here we demonstrate that flow-induced NO release is mediated by shear stress and that this response is distinctly biphasic. Transients in shear stress associated with the onset of flow stimulated a burst in NO production (8.2 nmol/mg of protein/h), while steady flow stimulated sustained NO production (2.2 nmol/mg of protein/h). Both G-protein inhibition and calcium chelation abolished the burst phase but had no effect on sustained production. Activation of G-proteins stimulated dose-dependent NO release in static cultures of both calvarial osteoblasts and UMR-106 osteoblast-like cells. Pertussis toxin had no effect on NO release. Calcium ionophore stimulated low levels of NO production within 15 minutes but had no effect on sustained production. Taken together, these data suggest that fluid shear stress stimulates NO release by two distinct pathways: a G-protein and calcium-dependent phase sensitive to flow transients, and a G-protein and calcium-independent pathway stimulated by sustained flow.

  9. Steady and transient fluid shear stress stimulate NO release in osteoblasts through distinct biochemical pathways

    NASA Technical Reports Server (NTRS)

    McAllister, T. N.; Frangos, J. A.

    1999-01-01

    Fluid flow has been shown to be a potent stimulus in osteoblasts and osteocytes and may therefore play an important role in load-induced bone remodeling. The objective of this study was to investigate the characteristics of flow-activated pathways. Previously we reported that fluid flow stimulates rapid and continuous release of nitric oxide (NO) in primary rat calvarial osteoblasts. Here we demonstrate that flow-induced NO release is mediated by shear stress and that this response is distinctly biphasic. Transients in shear stress associated with the onset of flow stimulated a burst in NO production (8.2 nmol/mg of protein/h), while steady flow stimulated sustained NO production (2.2 nmol/mg of protein/h). Both G-protein inhibition and calcium chelation abolished the burst phase but had no effect on sustained production. Activation of G-proteins stimulated dose-dependent NO release in static cultures of both calvarial osteoblasts and UMR-106 osteoblast-like cells. Pertussis toxin had no effect on NO release. Calcium ionophore stimulated low levels of NO production within 15 minutes but had no effect on sustained production. Taken together, these data suggest that fluid shear stress stimulates NO release by two distinct pathways: a G-protein and calcium-dependent phase sensitive to flow transients, and a G-protein and calcium-independent pathway stimulated by sustained flow.

  10. Vascular mechanobiology: endothelial cell responses to fluid shear stress.

    PubMed

    Ando, Joji; Yamamoto, Kimiko

    2009-11-01

    Endothelial cells (ECs) lining blood vessel walls respond to shear stress, a fluid mechanical force generated by flowing blood, and the EC responses play an important role in the homeostasis of the circulatory system. Abnormal EC responses to shear stress impair various vascular functions and lead to vascular diseases, including hypertension, thrombosis, and atherosclerosis. Bioengineering approaches in which cultured ECs are subjected to shear stress in fluid-dynamically designed flow-loading devices have been widely used to analyze EC responses at the cellular and molecular levels. Remarkable progress has been made, and the results have shown that ECs alter their morphology, function, and gene expression in response to shear stress. Shear stress affects immature cells, as well as mature ECs, and promotes differentiation of bone-marrow-derived endothelial progenitor cells and embryonic stem cells into ECs. Much research has been done on shear stress sensing and signal transduction, and their molecular mechanisms are gradually coming to be understood. However, much remains uncertain, and many candidates have been proposed for shear stress sensors. More extensive studies of vascular mechanobiology should increase our understanding of the molecular basis of the blood-flow-mediated control of vascular functions.

  11. Stimulated bioluminescence by fluid shear stress associated with pipe flow

    NASA Astrophysics Data System (ADS)

    Jing, Cao; Jiang-an, Wang; Ronghua, Wu

    2011-01-01

    Dinoflagellate can be stimulated bioluminescence by hydrodynamic agitation. Two typical dinoflagellate (Lingulodinium polyedrum and Pyrocystis noctiluca) was choosed to research stimulated bioluminescence. The bioluminescence intensity and shear stress intensity were measured using fully developed pipe flow. There is shear stress threshold to agitate organism bioluminescence. From these experiment, the response thresholds of the stimulated bioluminscence always occurred in laminar flows at a shear stress level of 0.6-3 dyn/cm2. At the same time, the spectral characteristc of dinoflagellate was recorded, the wavelength of them is about 470nm, and the full width at half maximum is approximate 30nm.

  12. Models of flow-induced loading on blood cells in laminar and turbulent flow, with application to cardiovascular device flow.

    PubMed

    Quinlan, Nathan J; Dooley, Patrick N

    2007-08-01

    Viscous shear stress and Reynolds stress are often used to predict hemolysis and thrombosis due to flow-induced stress on blood elements in cardiovascular devices. These macroscopic stresses are distinct from the true stress on an individual cell, which is determined by the local microscale flow field. In this paper the flow-induced stress on blood cells is calculated for laminar and turbulent flow, using simplified models for cells and for turbulent eddies. The model is applied to estimate shear stress on red blood cells in flow through a prosthetic heart valve, using the energy spectral density measured by Liu et al. [J. Biomech. Eng. 122:118-124, 2000]. Results show that in laminar flow, the maximum stress on a cell is approximately equal to the macroscopic viscous shear stress. In turbulent flow through a prosthetic heart valve, the estimated root mean square of flow-induced stress on a cell is at least an order of magnitude less than the Reynolds stress. The results support the hypothesis that smaller turbulent eddies cause higher stress on cells. However, the stress due to an eddy depends on the velocity scale of the eddy as well as its length scale. For the heart valve flow investigated, turbulence contributes to flow-induced stress on cells almost equally across a broad range of the frequency spectrum. The model suggests that Reynolds stress alone is not an adequate predictor of cell damage in turbulent flow, and highlights the importance of the energy spectral density.

  13. Measurement of surface shear stress vector distribution using shear-sensitive liquid crystal coatings

    NASA Astrophysics Data System (ADS)

    Zhao, Ji-Song; Scholz, Peter; Gu, Liang-Xian

    2012-10-01

    The global wall shear stress measurement technique using shear-sensitive liquid crystal (SSLC) is extended to wind tunnel measurements. Simple and common everyday equipment is used in the measurement; in particular a tungsten-halogen light bulb provides illumination and a saturation of SSLC coating color change with time is found. Spatial wall shear stress distributions of several typical flows are obtained using this technique, including wall-jet flow, vortex flow generated by a delta wing and junction flow behind a thin cylinder, although the magnitudes are not fully calibrated. The results demonstrate that SSLC technique can be extended to wind tunnel measurements with no complicated facilities used.

  14. Shear stress regulates endothelial microparticle release.

    PubMed

    Vion, Anne-Clémence; Ramkhelawon, Bhama; Loyer, Xavier; Chironi, Gilles; Devue, Cecile; Loirand, Gervaise; Tedgui, Alain; Lehoux, Stéphanie; Boulanger, Chantal M

    2013-05-10

    Endothelial activation and apoptosis release membrane-shed microparticles (EMP) that emerge as important biological effectors. Because laminar shear stress (SS) is a major physiological regulator of endothelial survival, we tested the hypothesis that SS regulates EMP release. EMP levels were quantified by flow cytometry in medium of endothelial cells subjected to low or high SS (2 and 20 dyne/cm(2)). EMP levels augmented with time in low SS conditions compared with high SS conditions. This effect was sensitive to extracellular signal-regulated protein kinases 1 and 2 (ERK1/2) and Rho kinases inhibitors but unaffected by caspase inhibitors. Low SS-stimulated EMP release was associated with increased endothelial Rho kinases and ERK1/2 activities and cytoskeletal reorganization. Overexpression of constitutively active RhoA stimulated EMP release under high SS. We also examined the effect of nitric oxide (NO) in mediating SS effects. L-NG-nitroarginine methyl ester (L-NAME), but not D-NG-nitroarginine methyl ester, increased high SS-induced EMP levels by 3-fold, whereas the NO donor S-nitroso-N-acetyl-D,L-penicillamine (SNAP) decreased it. L-NAME and SNAP did not affect Rho kinases and ERK1/2 activities. Then, we investigated NO effect on membrane remodeling because microparticle release is abolished in ABCA1-deficient cells. ABCA1 expression, which was greater under low SS than under high SS, was augmented by L-NAME under high SS and decreased by SNAP under low SS conditions. Altogether, these results demonstrate that sustained atheroprone low SS stimulates EMP release through activation of Rho kinases and ERK1/2 pathways, whereas atheroprotective high SS limits EMP release in a NO-dependent regulation of ABCA1 expression and of cytoskeletal reorganization. These findings, therefore, identify endothelial SS as a physiological regulator of microparticle release.

  15. Determination of the Shear Stress Distribution in a Laminate from the Applied Shear Resultant--A Simplified Shear Solution

    NASA Technical Reports Server (NTRS)

    Bednarcyk, Brett A.; Aboudi, Jacob; Yarrington, Phillip W.

    2007-01-01

    The simplified shear solution method is presented for approximating the through-thickness shear stress distribution within a composite laminate based on laminated beam theory. The method does not consider the solution of a particular boundary value problem, rather it requires only knowledge of the global shear loading, geometry, and material properties of the laminate or panel. It is thus analogous to lamination theory in that ply level stresses can be efficiently determined from global load resultants (as determined, for instance, by finite element analysis) at a given location in a structure and used to evaluate the margin of safety on a ply by ply basis. The simplified shear solution stress distribution is zero at free surfaces, continuous at ply boundaries, and integrates to the applied shear load. Comparisons to existing theories are made for a variety of laminates, and design examples are provided illustrating the use of the method for determining through-thickness shear stress margins in several types of composite panels and in the context of a finite element structural analysis.

  16. Simplified Shear Solution for Determination of the Shear Stress Distribution in a Composite Panel from the Applied Shear Resultant

    NASA Technical Reports Server (NTRS)

    Bednarcyk, Brett A.; Aboudi, Jacob; Yarrington, Phillip W.; Collier, Craig S.

    2008-01-01

    The simplified shear solution method is presented for approximating the through-thickness shear stress distribution within a composite laminate or panel based on laminated beam theory. The method does not consider the solution of a particular boundary value problem; rather it requires only knowledge of the global shear loading, geometry, and material properties of the laminate or panel. It is thus analogous to lamination theory in that ply level stresses can be efficiently determined from global load resultants (as determined, for instance, by finite element analysis) at a given location in a structure and used to evaluate the margin of safety on a ply by ply basis. The simplified shear solution stress distribution is zero at free surfaces, continuous at ply boundaries, and integrates to the applied shear load. Comparisons to existing theories are made for a variety of laminates, and design examples are provided illustrating the use of the method for determining through-thickness shear stress margins in several types of composite panels and in the context of a finite element structural analysis.

  17. Human endothelial cell responses to cardiovascular inspired pulsatile shear stress

    NASA Astrophysics Data System (ADS)

    Watson, Matthew; Baugh, Lauren; Black, Lauren, III; Kemmerling, Erica

    2016-11-01

    It is well established that hemodynamic shear stress regulates blood vessel structure and the development of vascular pathology. This process can be studied via in vitro models of endothelial cell responses to pulsatile shear stress. In this study, a macro-scale cone and plate viscometer was designed to mimic various shear stress waveforms found in the body and apply these stresses to human endothelial cells. The device was actuated by a PID-controlled DC gear-motor. Cells were exposed to 24 hours of pulsatile shear and then imaged and stained to track their morphology and secretions. These measurements were compared with control groups of cells exposed to constant shear and no shear. The results showed that flow pulsatility influenced levels of secreted proteins such as VE-cadherin and neuroregulin IHC. Cell morphology was also influenced by flow pulsatility; in general cells exposed to pulsatile shear stress developed a higher aspect ratio than cells exposed to no flow but a lower aspect ratio than cells exposed to steady flow.

  18. Production of functional proteins: balance of shear stress and gravity

    NASA Technical Reports Server (NTRS)

    Goodwin, Thomas John (Inventor); Hammond, Timothy Grant (Inventor); Kaysen, James Howard (Inventor)

    2007-01-01

    The present invention provides a method for production of functional proteins including hormones by renal cells in a three dimensional co-culture process responsive to shear stress using a rotating wall vessel. Natural mixture of renal cells expresses the enzyme 1-a-hydroxylase which can be used to generate the active form of vitamin D: 1,25-diOH vitamin D3. The fibroblast cultures and co-culture of renal cortical cells express the gene for erythropoietin and secrete erythropoietin into the culture supernatant. Other shear stress response genes are also modulated by shear stress, such as toxin receptors megalin and cubulin (gp280). Also provided is a method of treating in-need individual with the functional proteins produced in a three dimensional co-culture process responsive to shear stress using a rotating wall vessel.

  19. Production of functional proteins: balance of shear stress and gravity

    NASA Technical Reports Server (NTRS)

    Goodwin, Thomas John (Inventor); Hammond, Timothy Grant (Inventor); Kaysen, James Howard (Inventor)

    2004-01-01

    The present invention provides a method for production of functional proteins including hormones by renal cells in a three dimensional co-culture process responsive to shear stress using a rotating wall vessel. Natural mixture of renal cells expresses the enzyme 1-a-hydroxylase which can be used to generate the active form of vitamin D: 1,25-diOH vitamin D3. The fibroblast cultures and co-culture of renal cortical cells express the gene for erythropoietin and secrete erythropoietin into the culture supernatant. Other shear stress response genes are also modulated by shear stress, such as toxin receptors megalin and cubulin (gp280). Also provided is a method of treating in-need individual with the functional proteins produced in a three dimensional co-culture process responsive to shear stress using a rotating wall vessel.

  20. Production of functional proteins: balance of shear stress and gravity

    NASA Technical Reports Server (NTRS)

    Goodwin, Thomas John (Inventor); Hammond, Timothy Grant (Inventor); Kaysen, James Howard (Inventor)

    2011-01-01

    A method for the production of functional proteins including hormones by renal cells in a three dimensional culturing process responsive to shear stress uses a rotating wall vessel. Natural mixture of renal cells expresses the enzyme 1-.alpha.-hydroxylase which can be used to generate the active form of vitamin D: 1,25-diOH vitamin D.sub.3. The fibroblast cultures and co-culture of renal cortical cells express the gene for erythropoietin and secrete erythropoietin into the culture supernatant. Other shear stress response genes are also modulated by shear stress, such as toxin receptors megalin and cubulin (gp280). Also provided is a method of treating an in-need individual with the functional proteins produced in a three dimensional co-culture process responsive to shear stress using a rotating wall vessel.

  1. Shear-stress sensitive lenticular vesicles for targeted drug delivery.

    PubMed

    Holme, Margaret N; Fedotenko, Illya A; Abegg, Daniel; Althaus, Jasmin; Babel, Lucille; Favarger, France; Reiter, Renate; Tanasescu, Radu; Zaffalon, Pierre-Léonard; Ziegler, André; Müller, Bert; Saxer, Till; Zumbuehl, Andreas

    2012-08-01

    Atherosclerosis results in the narrowing of arterial blood vessels and this causes significant changes in the endogenous shear stress between healthy and constricted arteries. Nanocontainers that can release drugs locally with such rheological changes can be very useful. Here, we show that vesicles made from an artificial 1,3-diaminophospholipid are stable under static conditions but release their contents at elevated shear stress. These vesicles have a lenticular morphology, which potentially leads to instabilities along their equator. Using a model cardiovascular system based on polymer tubes and an external pump to represent shear stress in healthy and constricted vessels of the heart, we show that drugs preferentially release from the vesicles in constricted vessels that have high shear stress.

  2. Shear-stress sensitive lenticular vesicles for targeted drug delivery

    NASA Astrophysics Data System (ADS)

    Holme, Margaret N.; Fedotenko, Illya A.; Abegg, Daniel; Althaus, Jasmin; Babel, Lucille; Favarger, France; Reiter, Renate; Tanasescu, Radu; Zaffalon, Pierre-Léonard; Ziegler, André; Müller, Bert; Saxer, Till; Zumbuehl, Andreas

    2012-08-01

    Atherosclerosis results in the narrowing of arterial blood vessels and this causes significant changes in the endogenous shear stress between healthy and constricted arteries. Nanocontainers that can release drugs locally with such rheological changes can be very useful. Here, we show that vesicles made from an artificial 1,3-diaminophospholipid are stable under static conditions but release their contents at elevated shear stress. These vesicles have a lenticular morphology, which potentially leads to instabilities along their equator. Using a model cardiovascular system based on polymer tubes and an external pump to represent shear stress in healthy and constricted vessels of the heart, we show that drugs preferentially release from the vesicles in constricted vessels that have high shear stress.

  3. Effect of dynamic shear stress on thermosyphon flooding limit

    SciTech Connect

    El-Genk, M.S.; Saber, H.H.

    1996-12-31

    A one-dimensional, analytical model is developed to predict the flooding limited in closed, two-phase flow thermosyphons. This steady-state model incorporates the shear stress at the liquid-vapor interface as the sum of two terms: (a) the adiabatic shear stress, and (b) the dynamic shear stress, to account for the effect of evaporation at the interface. The calculated values of the liquid films Reynolds number at the onset of flooding are in good agreement with experimental data of other investigators for water and methanol, to within {+-}10%. The results demonstrate that at intermediate and high liquid film Reynolds number, neglecting the dynamic shear stress underestimates the film Reynolds numbers at the onset of flooding by 20% or more.

  4. Vorticity alignment and negative normal stresses in sheared attractive emulsions.

    PubMed

    Montesi, Alberto; Peña, Alejandro A; Pasquali, Matteo

    2004-02-06

    Attractive emulsions near the colloidal glass transition are investigated by rheometry and optical microscopy under shear. We find that (i) the apparent viscosity eta drops with increasing shear rate, then remains approximately constant in a range of shear rates, then continues to decay; (ii) the first normal stress difference N1 transitions sharply from nearly zero to negative in the region of constant shear viscosity; and (iii) correspondingly, cylindrical flocs form, align along the vorticity, and undergo a log-rolling movement. An analysis of the interplay between steric constraints, attractive forces, and composition explains this behavior, which seems universal to several other complex systems.

  5. Surface micromachined differential piezoelectric shear-stress sensors

    NASA Astrophysics Data System (ADS)

    Williams, Randall P.; Kim, Donghwan; Gawalt, David P.; Hall, Neal A.

    2017-01-01

    The ability to measure viscous wall shear stress in high-speed flows is important for verifying simulated results typically obtained from direct numerical simulation in the aerodynamics research community, and robust sensors are required to measure wall shear reliably under such high-speed conditions. This letter summarizes the design, fabrication, and testing of a surface micromachined piezoelectric shear-stress sensor which uses a thin piezoelectric film to generate a voltage proportional to an applied shear stress without additional moving parts. A differential-cell architecture is used to enhance selectivity to shear stress while canceling normal-stress sensitivity. The conceptual design, fabrication details, and experimental measurements of device sensitivity are presented. A finite element model is used to validate the device performance against measurements, and to provide insight into the potential and electric fields underlying the device concept. The potential for understanding device behavior and optimization through modeling is illustrated using finite element analysis results. The minimum detectable shear stress for the sensor is estimated to be 52.9 mPa  √Hz-1 at 1.5 kHz.

  6. Cell adhesion on zein films under shear stress field.

    PubMed

    Han, Yi-Long; Xu, Qin; Lu, Zhiqian; Wang, Jin-Ye

    2013-11-01

    Vascular implants after implantation need to improve the ability of cells to withstand flow-shear stress. As such, we want to test whether zein films could improve the flow-shear stress resistance of cells by control of their surface morphology. We chose Collagen, poly L-lactic acid (PLLA) and three types of zein as the coating films and evaluated the flow-shear stress resistance of NIH3T3, and EA.hy926 on these respective films. The results showed that the retention of two cell lines on Collagen film was better than PLLA and zein films. The cell retention of EA.hy926 on Zein 3 film with higher roughness was better than Zein 1 film with a flat surface in the first 2h. The cell retention of NIH3T3 on a rougher surface was always better than the smoother one under flow-shear stress condition for 6h. Observation of cell morphologies showed that the aspect ratio changed significantly for NIH3T3 cells upon flow-shear stress condition, as shown by reduced numbers of pseudopodia, increased cell rounding and shrinkage. Zein 3 film with higher roughness improved the flow-shear stress resistance of cells and might be used in vascular implant coatings.

  7. Investigation of platelet margination phenomena at elevated shear stress.

    PubMed

    Zhao, Rui; Kameneva, Marina V; Antaki, James F

    2007-01-01

    Thrombosis is a common complication following the surgical implantation of blood contacting artificial organs. Platelet transport, which is an important process of thrombosis and strongly modulated by flow dynamics, has not been investigated under the shear stress level associated with these devices, which may range from tens to several hundred Pascal.The current research investigated platelet transport within blood under supra-physiological shear stress conditions through a micro flow visualization approach. Images of platelet-sized fluorescent particles in the blood flow were recorded within microchannels (2 cm x 100 microm x 100 microm). The results successfully demonstrated the occurrence of platelet-sized particle margination under shear stresses up to 193 Pa, revealing a platelet near-wall excess up to 8.7 near the wall (within 15 microm) at the highest shear stress. The concentration of red blood cells was found to influence the stream-wise development of platelet margination which was clearly observed in the 20% Ht sample but not the 40% Ht sample. Shear stress had a less dramatic effect on the margination phenomenon than did hematocrit. The results imply that cell-cell collision is an important factor for platelet transport under supra-physiologic shear stress conditions. It is anticipated that these results will contribute to the future design and optimization of artificial organs.

  8. Effects of Fluid Shear Stress on Cancer Stem Cell Viability

    NASA Astrophysics Data System (ADS)

    Sunday, Brittney; Triantafillu, Ursula; Domier, Ria; Kim, Yonghyun

    2014-11-01

    Cancer stem cells (CSCs), which are believed to be the source of tumor formation, are exposed to fluid shear stress as a result of blood flow within the blood vessels. It was theorized that CSCs would be less susceptible to cell death than non-CSCs after both types of cell were exposed to a fluid shear stress, and that higher levels of fluid shear stress would result in lower levels of cell viability for both cell types. To test this hypothesis, U87 glioblastoma cells were cultured adherently (containing smaller populations of CSCs) and spherically (containing larger populations of CSCs). They were exposed to fluid shear stress in a simulated blood flow through a 125-micrometer diameter polyetheretherketone (PEEK) tubing using a syringe pump. After exposure, cell viability data was collected using a BioRad TC20 Automated Cell Counter. Each cell type was tested at three physiological shear stress values: 5, 20, and 60 dynes per centimeter squared. In general, it was found that the CSC-enriched U87 sphere cells had higher cell viability than the CSC-depleted U87 adherent cancer cells. Interestingly, it was also observed that the cell viability was not negatively affected by the higher fluid shear stress values in the tested range. In future follow-up studies, higher shear stresses will be tested. Furthermore, CSCs from different tumor origins (e.g. breast tumor, prostate tumor) will be tested to determine cell-specific shear sensitivity. National Science Foundation Grant #1358991 supported the first author as an REU student.

  9. Simple average expression for shear-stress relaxation modulus

    NASA Astrophysics Data System (ADS)

    Wittmer, J. P.; Xu, H.; Baschnagel, J.

    2016-01-01

    Focusing on isotropic elastic networks we propose a simple-average expression G (t ) =μA-h (t ) for the computational determination of the shear-stress relaxation modulus G (t ) of a classical elastic solid or fluid. Here, μA=G (0 ) characterizes the shear transformation of the system at t =0 and h (t ) the (rescaled) mean-square displacement of the instantaneous shear stress τ ̂(t ) as a function of time t . We discuss sampling time and ensemble effects and emphasize possible pitfalls of alternative expressions using the shear-stress autocorrelation function. We argue finally that our key relation may be readily adapted for more general linear response functions.

  10. Simple average expression for shear-stress relaxation modulus.

    PubMed

    Wittmer, J P; Xu, H; Baschnagel, J

    2016-01-01

    Focusing on isotropic elastic networks we propose a simple-average expression G(t)=μ_{A}-h(t) for the computational determination of the shear-stress relaxation modulus G(t) of a classical elastic solid or fluid. Here, μ_{A}=G(0) characterizes the shear transformation of the system at t=0 and h(t) the (rescaled) mean-square displacement of the instantaneous shear stress τ[over ̂](t) as a function of time t. We discuss sampling time and ensemble effects and emphasize possible pitfalls of alternative expressions using the shear-stress autocorrelation function. We argue finally that our key relation may be readily adapted for more general linear response functions.

  11. Trabecular bone remodelling simulation considering osteocytic response to fluid-induced shear stress.

    PubMed

    Adachi, Taiji; Kameo, Yoshitaka; Hojo, Masaki

    2010-06-13

    In bone functional adaptation by remodelling, osteocytes in the lacuno-canalicular system are believed to play important roles in the mechanosensory system. Under dynamic loading, bone matrix deformation generates an interstitial fluid flow in the lacuno-canalicular system; this flow induces shear stress on the osteocytic process membrane that is known to stimulate the osteocytes. In this sense, the osteocytes behave as mechanosensors and deliver mechanical information to neighbouring cells through the intercellular communication network. In this study, bone remodelling is assumed to be regulated by the mechanical signals collected by the osteocytes. From the viewpoint of multi-scale biomechanics, we propose a mathematical model of trabecular bone remodelling that takes into account the osteocytic mechanosensory network system. Based on this model, a computational simulation of trabecular bone remodelling was conducted for a single trabecula under cyclic uniaxial loading, demonstrating functional adaptation to the applied mechanical loading as a load-bearing construct.

  12. Development of In-Fiber Reflective Bragg Gratings as Shear Stress Monitors in Aerodynamic Facilities

    NASA Technical Reports Server (NTRS)

    Parmar, Devendra S.; Sprinkle, Danny R.; Singh, Jag J.

    1998-01-01

    Bragg gratings centered at nominal wavelengths of 1290 nm and 1300 run were inscribed in a 9/125 microns germano-silicate optical fiber, using continuous wave frequency doubled Ar+ laser radiation at 244 nm. Such gratings have been used extensively as temperature and strain monitors in smart structures. They have, however, never been used for measuring aerodynamic shear stresses. As a test of their sensitivity as shear stress monitors, a Bragg fiber attached to a metal plate was subjected to laminar flows in a glass pipe. An easily measurable large flow-induced wavelength shift (Delta Lambda(sub B)) was observed in the Bragg reflected wavelength. Thereafter, the grating was calibrated by making one time, simultaneous measurements of Delta Lambda(sub B) and the coefficient of skin friction (C(sub f)) with a skin friction balance, as a function of flow rates in a subsonic wind tunnel. Onset of fan-induced transition in the tunnel flow provided a unique flow rate for correlating Delta Lambda(sub B) and (C(sub f) values needed for computing effective modulus of rigidity (N(sub eff)) of the fiber attached to the metal plate. This value Of N(sub eff) is expected to remain constant throughout the elastic stress range expected during the Bragg grating aerodynamic tests. It has been used for calculating the value of Cf at various tunnel speeds, on the basis of measured values of Bragg wavelength shifts at those speeds.

  13. Regulation of endothelial connexin40 expression by shear stress.

    PubMed

    Vorderwülbecke, Bernd J; Maroski, Julian; Fiedorowicz, Katarzyna; Da Silva-Azevedo, Luis; Marki, Alex; Pries, Axel R; Zakrzewicz, Andreas

    2012-01-01

    Endothelial connexin (Cx)40 plays an important role in signal propagation along blood vessel walls, modulating vessel diameter and thereby blood flow. Blood flow, in turn, has been shown to alter endothelial Cx40 expression. However, the timing and shear stress dependence of this relationship have remained unclear, as have the signal transduction pathways involved and the functional implications. Therefore, the aim of this study was to quantify the effects of shear stress on endothelial Cx40 expression, to analyze the role of phosphoinositide 3-kinase (PI3K)/Akt signaling involved, and to assess the possible functional consequences for the adaptation of microvascular networks. First-passage human umbilical vein endothelial cells were exposed to defined shear stress conditions and analyzed for Cx40 using real-time RT-PCR and immunoblot analysis. Shear stress caused long-term induction of Cx40 protein expression, with two short-term mRNA peaks at 4 and 16 h, indicating the dynamic nature of the adaptation process. Maximum shear stress-dependent induction was observed at shear levels between 6 and 10 dyn/cm(2). Simulation of this pattern of shear-dependent Cx expression in a vascular adaptation model of a microvascular network led to an improved fit for the simulated results to experimental measurements. Cx40 expression was greatly reduced by inhibiting PI3K or Akt, with PI3K activity being required for basal Cx40 expression and Akt activity taking part in its shear stress-dependent induction.

  14. A model for studying the effect of shear stress on interactions between vascular endothelial cells and smooth muscle cells.

    PubMed

    Chiu, Jeng-Jiann; Chen, Li-Jing; Chen, Cheng-Nan; Lee, Pei-Ling; Lee, Chih-I

    2004-04-01

    Vascular endothelial cells (ECs) are constantly subjected to blood flow-induced shear stress and the influences of neighboring smooth muscle cells (SMCs). In the present study, a coculture flow system was developed to study the effect of shear stress on EC-SMC interactions. ECs and SMCs were separated by a porous membrane with only the EC side subjected to the flow condition. When ECs were exposed to a shear stress of 12 dynes/cm2 for 24 h, the cocultured SMCs tended to orient perpendicularly to the flow direction. This perpendicular orientation of the cocultured SMCs to flow direction was not observed when ECs were exposed to a shear stress of 2 dynes/cm2. Under the static condition, long and parallel actin bundles were observed in the central regions of the cocultured SMCs, whereas the actin filaments localized mainly at the periphery of the cocultured ECs. After 24 h of flow application, the cocultured ECs displayed very long, well-organized, parallel actin stress fibers aligned with the flow direction in the central regions of the cells. Immunostaining of platelet endothelial cell adhesion molecule-1 confirmed the elongation and alignment of the cocultured ECs with the flow direction. Coculture with SMCs under static condition induced EC gene expressions of growth-related oncogene-alpha and monocyte chemotactic protein-1, and shear stress was found to abolish these SMC-induced gene expressions. Our results suggest that shear stress may serve as a down-regulator for the pathophysiologically relevant gene expression in ECs cocultured with SMCs.

  15. Prediction of plantar shear stress distribution by artificial intelligence methods.

    PubMed

    Yavuz, Metin; Ocak, Hasan; Hetherington, Vincent J; Davis, Brian L

    2009-09-01

    Shear forces under the human foot are thought to be responsible for various foot pathologies such as diabetic plantar ulcers and athletic blisters. Frictional shear forces might also play a role in the metatarsalgia observed among hallux valgus (HaV) and rheumatoid arthritis (RA) patients. Due to the absence of commercial devices capable of measuring shear stress distribution, a number of linear models were developed. All of these have met with limited success. This study used nonlinear methods, specifically neural network and fuzzy logic schemes, to predict the distribution of plantar shear forces based on vertical loading parameters. In total, 73 subjects were recruited; 17 had diabetic neuropathy, 14 had HaV, 9 had RA, 11 had frequent foot blisters, and 22 were healthy. A feed-forward neural network (NN) and adaptive neurofuzzy inference system (NFIS) were built. These systems were then applied to a custom-built platform, which collected plantar pressure and shear stress data as subjects walked over the device. The inputs to both models were peak pressure, peak pressure-time integral, and time to peak pressure, and the output was peak resultant shear. Root-mean-square error (RMSE) values were calculated to test the models' accuracy. RMSE/actual shear ratio varied between 0.27 and 0.40 for NN predictions. Similarly, NFIS estimations resulted in a 0.28-0.37 ratio for local peak values in all subject groups. On the other hand, error percentages for global peak shear values were found to be in the range 11.4-44.1. These results indicate that there is no direct relationship between pressure and shear magnitudes. Future research should aim to decrease error levels by introducing shear stress dependent variables into the models.

  16. Elevated Shear Stress in Arteriovenous Fistulae: Is There Mechanical Homeostasis?

    NASA Astrophysics Data System (ADS)

    McGah, Patrick; Leotta, Daniel; Beach, Kirk; Aliseda, Alberto

    2011-11-01

    Arteriovenous fistulae are created surgically to provide access for dialysis in patients with renal failure. The current hypothesis is that the rapid remodeling occurring after the fistula creation is in part a process to restore the mechanical stresses to some preferred level (i.e. mechanical homeostasis). Given that nearly 50% of fistulae require an intervention after one year, understanding the altered hemodynamic stress is important in improving clinical outcomes. We perform numerical simulations of four patient-specific models of functioning fistulae reconstructed from 3D Doppler ultrasound scans. Our results show that the vessels are subjected to `normal' shear stresses away from the anastomosis; about 1 Pa in the veins and about 2.5 Pa in the arteries. However, simulations show that part of the anastomoses are consistently subjected to very high shear stress (>10Pa) over the cardiac cycle. These elevated values shear stresses are caused by the transitional flows at the anastomoses including flow separation and quasiperiodic vortex shedding. This suggests that the remodeling process lowers shear stress in the fistula but that it is limited as evidenced by the elevated shear at the anastomoses. This constant insult on the arterialized venous wall may explain the process of late fistula failure in which the dialysis access become occluded after years of use. Supported by an R21 Grant from NIDDK (DK081823).

  17. Short exposure time sensitivity of white cells to shear stress.

    PubMed

    Carter, Janell; Hristova, Katia; Harasaki, Hiroaki; Smith, W A

    2003-01-01

    White cells are a critical functional element circulating in blood. This study sheared fresh whole bovine blood in stainless steel and polymeric capillary tubes of various lengths and diameters. Flow rate was constant, resulting in a range of exposure times and shear stresses. White cell count, cell integrity (trypan blue exclusion), and phagocytic index (latex bead ingestion) were assayed. It was found that cell function declined at lower stresses than cell count. White cell count was maintained at higher stress levels at the short exposure times used here compared with the published results at longer times. This study suggests that function, not count, is the critical parameter when studying shear effects on white cells, and that, like red cells, there may be an exposure time effect and that white cell function is impacted at stresses lower than are required for hemolysis.

  18. Molecular origins of higher harmonics in large-amplitude oscillatory shear flow: Shear stress response

    NASA Astrophysics Data System (ADS)

    Gilbert, P. H.; Giacomin, A. J.

    2016-10-01

    Recent work has focused on deepening our understanding of the molecular origins of the higher harmonics that arise in the shear stress response of polymeric liquids in large-amplitude oscillatory shear flow. For instance, these higher harmonics have been explained by just considering the orientation distribution of rigid dumbbells suspended in a Newtonian solvent. These dumbbells, when in dilute suspension, form the simplest relevant molecular model of polymer viscoelasticity, and this model specifically neglects interactions between the polymer molecules [R. B. Bird et al., "Dilute rigid dumbbell suspensions in large-amplitude oscillatory shear flow: Shear stress response," J. Chem. Phys. 140, 074904 (2014)]. In this paper, we explore these interactions by examining the Curtiss-Bird model, a kinetic molecular theory designed specifically to account for the restricted motions that arise when polymer chains are concentrated, thus interacting and specifically, entangled. We begin our comparison using a heretofore ignored explicit analytical solution [X.-J. Fan and R. B. Bird, "A kinetic theory for polymer melts. VI. Calculation of additional material functions," J. Non-Newtonian Fluid Mech. 15, 341 (1984)]. For concentrated systems, the chain motion transverse to the chain axis is more restricted than along the axis. This anisotropy is described by the link tension coefficient, ɛ, for which several special cases arise: ɛ = 0 corresponds to reptation, ɛ > 1/8 to rod-climbing, 1/5 ≤ ɛ ≤ 3/4 to reasonable predictions for shear-thinning in steady simple shear flow, and ɛ = 1 to the dilute solution without hydrodynamic interaction. In this paper, we examine the shapes of the shear stress versus shear rate loops for the special cases ɛ = (" separators=" 0 , 1 / 8 , 3 / 8 , 1 ) , and we compare these with those of rigid dumbbell and reptation model predictions.

  19. On the gating of mechanosensitive channels by fluid shear stress

    NASA Astrophysics Data System (ADS)

    Peng, Zhangli; Pak, On Shun; Feng, Zhe; Liu, Allen P.; Young, Yuan-Nan

    2016-12-01

    Mechanosensation is an important process in biological fluid-structure interaction. To understand the biophysics underlying mechanosensation, it is essential to quantify the correlation between membrane deformation, membrane tension, external fluid shear stress, and conformation of mechanosensitive (MS) channels. Smoothed dissipative particle dynamics (SDPD) simulations of vesicle/cell in three types of flow configurations are conducted to calculate the tension in lipid membrane due to fluid shear stress from the surrounding viscous flow. In combination with a simple continuum model for an MS channel, SDPD simulation results suggest that shearing adhered vesicles/cells is more effective to induce membrane tension sufficient to stretch MS channels open than a free shear flow or a constrictive channel flow. In addition, we incorporate the bilayer-cytoskeletal interaction in a two-component model to probe the effects of a cytoskeletal network on the gating of MS channels.

  20. Gyrokinetic Simulation of Residual Stress from Diamagnetic Velocity Shears

    NASA Astrophysics Data System (ADS)

    Waltz, R. E.; Staebler, G. M.; Solomon, W. M.

    2010-11-01

    Residual stress refers to the remaining toroidal angular momentum (TAM) flux (divided by major radius) when the shear in the parallel velocity (and parallel velocity itself) vanishes. Previously [1] we demonstrated with gyrokinetic (GYRO) simulations that TAM pinching from the diamagnetic level shear in the ExB velocity could provide the residual stress needed for spontaneous toroidal rotation. Here we show that the shear in the diamagnetic velocities themselves provide comparable residual stress (and level of stabilization). The sign of the residual stress, quantified by the ratio of TAM flow to ion power flow (M/P), depends on the signs of the various velocity shears as well as ion (ITG) versus electron (TEM) mode directed turbulence. The residual stress from these temperature and density gradient diamagnetic velocity shears is demonstrated in global gyrokinetic simulation of ``null'' rotation DIIID discharges by matching M/P profiles within experimental error. 8pt [1] R.E. Waltz, G.M. Staebler, J. Candy, and F.L. Hinton, Phys. Plasmas 14, 122507 (2007); errata 16, 079902 (2009).

  1. Shear Load Transfer in High and Low Stress Tendons

    PubMed Central

    Kondratko-Mittnacht, Jaclyn; Duenwald-Kuehl, Sarah; Lakes, Roderic; Vanderby, Ray

    2016-01-01

    Background Tendon is an integral part of joint movement and stability, as it functions to transmit load from muscle to bone. It has an anisotropic, fibrous hierarchical structure that is generally loaded in the direction of its fibers/fascicles. Internal load distributions are altered when joint motion rotates an insertion site or when local damage disrupts fibers/fascicles, potentially causing inter-fiber (or inter-fascicular) shear. Tendons with different microstructure (helical versus linear) may redistribute loads differently. Method of Approach This study explored how shear redistributes axial loads in rat tail tendon (low stress tendons with linear microstructure) and porcine flexor tendon (high stress with helical microstructure) by creating lacerations on opposite sides of the tendon, ranging from about 20-60% of the tendon width, to create various magnitudes of shear. Differences in fascicular orientation were quantified using polarized light microscopy. Results and Conclusions Unexpectedly, both tendon types maintained about 20% of pre-laceration stress values after overlapping cuts of 60% of tendon width (no intact fibers end to end) suggesting that shear stress transfer can contribute more to overall tendon strength and stiffness than previously reported. All structural parameters for both tendon types decreased linearly with increasing laceration depth. The tail tendon had a more rapid decline in post-laceration elastic stress and modulus parameters as well as a more linear and less tightly packed fascicular structure, suggesting that positional tendons may be less well suited to redistribute loads via a shear mechanism. PMID:25700261

  2. Shear load transfer in high and low stress tendons.

    PubMed

    Kondratko-Mittnacht, Jaclyn; Duenwald-Kuehl, Sarah; Lakes, Roderic; Vanderby, Ray

    2015-05-01

    Tendon is an integral part of joint movement and stability, as it functions to transmit load from muscle to bone. It has an anisotropic, fibrous hierarchical structure that is generally loaded in the direction of its fibers/fascicles. Internal load distributions are altered when joint motion rotates an insertion site or when local damage disrupts fibers/fascicles, potentially causing inter-fiber (or inter-fascicular) shear. Tendons with different microstructures (helical versus linear) may redistribute loads differently. This study explored how shear redistributes axial loads in rat tail tendon (low stress tendons with linear microstructure) and porcine flexor tendon (high stress with helical microstructure) by creating lacerations on opposite sides of the tendon, ranging from about 20% to 60% of the tendon width, to create various magnitudes of shear. Differences in fascicular orientation were quantified using polarized light microscopy. Unexpectedly, both tendon types maintained about 20% of pre-laceration stress values after overlapping cuts of 60% of tendon width (no intact fibers end to end) suggesting that shear stress transfer can contribute more to overall tendon strength and stiffness than previously reported. All structural parameters for both tendon types decreased linearly with increasing laceration depth. The tail tendon had a more rapid decline in post-laceration elastic stress and modulus parameters as well as a more linear and less tightly packed fascicular structure, suggesting that positional tendons may be less well suited to redistribute loads via a shear mechanism. Copyright © 2015 Elsevier Ltd. All rights reserved.

  3. Determination of surface shear stress with the naphthalene sublimation technique

    NASA Technical Reports Server (NTRS)

    Lee, J. A.; Greeley, Ronald

    1987-01-01

    Aeolian entrainment and transport are functions of surface shear stress and particle characteristics. Measuring surface shear stress is difficult, however, where logarithmic wind profiles are not found, such as regions around large roughness elements. An outline of a method whereby shear stress can be mapped on the surface around an object is presented. The technique involves the sublimation of naphthalene (C10H8) which is a function of surface shear stress and surface temperature. This technique is based on the assumption that the transfer of momentum, heat and mass are analogous (Reynolds analogy). If the Reynolds analogy can be shown to be correct for a given situation, then knowledge of the diffusion of one property allows the determination of the others. The analytical framework and data acquisition for the method are described. The technique was tested in the Planetary Geology Wind Tunnel. Results show that the naphthalene sublimation technique is a reasonably accurate method for determining shear stress, particularly around objects where numerous point values are needed.

  4. Shear Stress Sensing with Elastic Microfence Structures

    NASA Technical Reports Server (NTRS)

    Cisotto, Alexxandra; Palmieri, Frank L.; Saini, Aditya; Lin, Yi; Thurman, Christopher S; Kim, Jinwook; Kim, Taeyang; Connell, John W.; Zhu, Yong; Gopalarathnam, Ashok; hide

    2015-01-01

    In this work, elastic microfences were generated for the purpose of measuring shear forces acting on a wind tunnel model. The microfences were fabricated in a two part process involving laser ablation patterning to generate a template in a polymer film followed by soft lithography with a two-part silicone. Incorporation of a fluorescent dye was demonstrated as a method to enhance contrast between the sensing elements and the substrate. Sensing elements consisted of multiple microfences prepared at different orientations to enable determination of both shear force and directionality. Microfence arrays were integrated into an optical microscope with sub-micrometer resolution. Initial experiments were conducted on a flat plate wind tunnel model. Both image stabilization algorithms and digital image correlation were utilized to determine the amount of fence deflection as a result of airflow. Initial free jet experiments indicated that the microfences could be readily displaced and this displacement was recorded through the microscope.

  5. Development of a Piezoelectric Shear Stress Gage for Dynamic Loading

    DTIC Science & Technology

    1978-12-01

    properties of both soils and structures in underground tests. The need for shear measurements is well recognized by most workers involved in dynamic... conditon ’- ik Pc 2 = 0 (6) Equation (6) has three possible eigenvalues, each of which corresponds to an eigenvector U’. Each of the eigenvalues and...gage. Our examination of field work shows that measurements of shear stresses at soil -structure interfaces appear to be most appropriate with the

  6. Shear-stress-controlled dynamics of nematic complex fluids.

    PubMed

    Klapp, Sabine H L; Hess, Siegfried

    2010-05-01

    Based on a mesoscopic theory we investigate the nonequilibrium dynamics of a sheared nematic liquid, with the control parameter being the shear stress σ xy (rather than the usual shear rate, γ). To this end we supplement the equations of motion for the orientational order parameters by an equation for γ, which then becomes time dependent. Shearing the system from an isotropic state, the stress-controlled flow properties turn out to be essentially identical to those at fixed γ. Pronounced differences occur when the equilibrium state is nematic. Here, shearing at controlled γ yields several nonequilibrium transitions between different dynamic states, including chaotic regimes. The corresponding stress-controlled system has only one transition from a regular periodic into a stationary (shear-aligned) state. The position of this transition in the σ xy-γ plane turns out to be tunable by the delay time entering our control scheme for σ xy. Moreover, a sudden change in the control method can stabilize the chaotic states appearing at fixed γ.

  7. Effects of dynamic shear and transmural pressure on wall shear stress sensitivity in collecting lymphatic vessels.

    PubMed

    Kornuta, Jeffrey A; Nepiyushchikh, Zhanna; Gasheva, Olga Y; Mukherjee, Anish; Zawieja, David C; Dixon, J Brandon

    2015-11-01

    Given the known mechanosensitivity of the lymphatic vasculature, we sought to investigate the effects of dynamic wall shear stress (WSS) on collecting lymphatic vessels while controlling for transmural pressure. Using a previously developed ex vivo lymphatic perfusion system (ELPS) capable of independently controlling both transaxial pressure gradient and average transmural pressure on an isolated lymphatic vessel, we imposed a multitude of flow conditions on rat thoracic ducts, while controlling for transmural pressure and measuring diameter changes. By gradually increasing the imposed flow through a vessel, we determined the WSS at which the vessel first shows sign of contraction inhibition, defining this point as the shear stress sensitivity of the vessel. The shear stress threshold that triggered a contractile response was significantly greater at a transmural pressure of 5 cmH2O (0.97 dyne/cm(2)) than at 3 cmH2O (0.64 dyne/cm(2)). While contraction frequency was reduced when a steady WSS was applied, this inhibition was reversed when the applied WSS oscillated, even though the mean wall shear stresses between the conditions were not significantly different. When the applied oscillatory WSS was large enough, flow itself synchronized the lymphatic contractions to the exact frequency of the applied waveform. Both transmural pressure and the rate of change of WSS have significant impacts on the contractile response of lymphatic vessels to flow. Specifically, time-varying shear stress can alter the inhibition of phasic contraction frequency and even coordinate contractions, providing evidence that dynamic shear could play an important role in the contractile function of collecting lymphatic vessels. Copyright © 2015 the American Physiological Society.

  8. Effects of dynamic shear and transmural pressure on wall shear stress sensitivity in collecting lymphatic vessels

    PubMed Central

    Kornuta, Jeffrey A.; Nepiyushchikh, Zhanna; Gasheva, Olga Y.; Mukherjee, Anish; Zawieja, David C.

    2015-01-01

    Given the known mechanosensitivity of the lymphatic vasculature, we sought to investigate the effects of dynamic wall shear stress (WSS) on collecting lymphatic vessels while controlling for transmural pressure. Using a previously developed ex vivo lymphatic perfusion system (ELPS) capable of independently controlling both transaxial pressure gradient and average transmural pressure on an isolated lymphatic vessel, we imposed a multitude of flow conditions on rat thoracic ducts, while controlling for transmural pressure and measuring diameter changes. By gradually increasing the imposed flow through a vessel, we determined the WSS at which the vessel first shows sign of contraction inhibition, defining this point as the shear stress sensitivity of the vessel. The shear stress threshold that triggered a contractile response was significantly greater at a transmural pressure of 5 cmH2O (0.97 dyne/cm2) than at 3 cmH2O (0.64 dyne/cm2). While contraction frequency was reduced when a steady WSS was applied, this inhibition was reversed when the applied WSS oscillated, even though the mean wall shear stresses between the conditions were not significantly different. When the applied oscillatory WSS was large enough, flow itself synchronized the lymphatic contractions to the exact frequency of the applied waveform. Both transmural pressure and the rate of change of WSS have significant impacts on the contractile response of lymphatic vessels to flow. Specifically, time-varying shear stress can alter the inhibition of phasic contraction frequency and even coordinate contractions, providing evidence that dynamic shear could play an important role in the contractile function of collecting lymphatic vessels. PMID:26333787

  9. High shear stress induces atherosclerotic vulnerable plaque formation through angiogenesis

    PubMed Central

    Wang, Yi; Qiu, Juhui; Luo, Shisui; Xie, Xiang; Zheng, Yiming; Zhang, Kang; Ye, Zhiyi; Liu, Wanqian; Gregersen, Hans; Wang, Guixue

    2016-01-01

    Rupture of atherosclerotic plaques causing thrombosis is the main cause of acute coronary syndrome and ischemic strokes. Inhibition of thrombosis is one of the important tasks developing biomedical materials such as intravascular stents and vascular grafts. Shear stress (SS) influences the formation and development of atherosclerosis. The current review focuses on the vulnerable plaques observed in the high shear stress (HSS) regions, which localizes at the proximal region of the plaque intruding into the lumen. The vascular outward remodelling occurs in the HSS region for vascular compensation and that angiogenesis is a critical factor for HSS which induces atherosclerotic vulnerable plaque formation. These results greatly challenge the established belief that low shear stress is important for expansive remodelling, which provides a new perspective for preventing the transition of stable plaques to high-risk atherosclerotic lesions. PMID:27482467

  10. A Rotary Flow Channel for Shear Stress Sensor Calibration

    NASA Technical Reports Server (NTRS)

    Zuckerwar, Allan J.; Scott, Michael A.

    2004-01-01

    A proposed shear sensor calibrator consists of a rotating wheel with the sensor mounted tangential to the rim and positioned in close proximity to the rim. The shear stress generated by the flow at the sensor position is simply tau(sub omega) = (mu)r(omega)/h, where mu is the viscosity of the ambient gas, r the wheel radius, omega the angular velocity of the wheel, and h the width of the gap between the wheel rim and the sensor. With numerical values of mu = 31 (mu)Pa s (neon at room temperature), r = 0.5 m, omega = 754 /s (7200 rpm), and h = 50.8 m, a shear stress of tau(sub omega) = 231 Pa can be generated. An analysis based on one-dimensional flow, with the flow velocity having only an angular component as a function of the axial and radial coordinates, yields corrections to the above simple formula for the curvature of the wheel, flatness of the sensor, and finite width of the wheel. It is assumed that the sensor mount contains a trough (sidewalls) to render a velocity release boundary condition at the edges of the rim. The Taylor number under maximum flow conditions is found to be 62.3, sufficiently low to obviate flow instability. The fact that the parameters entering into the evaluation of the shear stress can be measured to high accuracy with well-defined uncertainties makes the proposed calibrator suitable for a physical standard for shear stress calibration.

  11. Nonlinear Reynolds stress model for turbulent shear flows

    NASA Technical Reports Server (NTRS)

    Barton, J. Michael; Rubinstein, R.; Kirtley, K. R.

    1991-01-01

    A nonlinear algebraic Reynolds stress model, derived using the renormalization group, is applied to equilibrium homogeneous shear flow and fully developed flow in a square duct. The model, which is quadratically nonlinear in the velocity gradients, successfully captures the large-scale inhomogeneity and anisotropy of the flows studied. The ratios of normal stresses, as well as the actual magnitudes of the stresses are correctly predicted for equilibrium homogeneous shear flow. Reynolds normal stress anisotropy and attendant turbulence driven secondary flow are predicted for a square duct. Profiles of mean velocity and normal stresses are in good agreement with measurements. Very close to walls, agreement with measurements diminishes. The model has the benefit of containing no arbitrary constants; all values are determined directly from the theory. It seems that near wall behavior is influenced by more than the large scale anisotropy accommodated in the current model. More accurate near wall calculations may well require a model for anisotropic dissipation.

  12. Buried wire gage for wall shear stress measurements

    NASA Technical Reports Server (NTRS)

    Murthy, V. S.; Rose, W. C.

    1978-01-01

    A buried wire gage for measuring wall shear stress in fluid flow was studied and further developed. Several methods of making this relatively new type of gage were examined to arrive at a successful technique that is well-suited for wind-tunnel testing. A series of measurements was made to demonstrate the adequacy of a two-point calibration procedure for these gages. The buried wire gage is also demonstrated to be ideally suited for quantitative measurement of wall shear stress in wind-tunnel testing.

  13. Wall shear stress evolution in carotid artery bifurcation

    NASA Astrophysics Data System (ADS)

    Bernad, S. I.; Bosioc, A. I.; Totorean, A. F.; Petre, I.; Bernad, E. S.

    2017-07-01

    The steady flow in an anatomically realistic human carotid bifurcation was simulated numerically. Main parameters such as wall shear stress (WSS), velocity profiles and pressure distributions are investigated in the carotid artery, namely in bifurcation and sinusoidal enlargement regions. Flow in the carotid sinus is dominated by a single secondary vortex motion accompanied by a strong helical flow. This type of flow is induced primarily by the curvature and asymmetry of the in vivo geometry. Low wall shear stress concentration occurs at both the anterior and posterior aspects of the proximal internal bulb.

  14. Shear stress relaxation of dental ceramics determined from creep behavior.

    PubMed

    DeHoff, Paul H; Anusavice, Kenneth J

    2004-10-01

    To test the hypothesis that shear stress relaxation functions of dental ceramics can be determined from creep functions measured in a beam-bending viscometer. Stress relaxation behavior was determined from creep data for the following materials: (1) a veneering ceramic-IPS Empress2 body ceramic (E2V); (2) an experimental veneering ceramic (EXV); (3) a low expansion body porcelain-Vita VMK 68 feldspathic body porcelain (VB); (4) a high expansion body porcelain-Will Ceram feldspathic body porcelain (WCB); (5) a medium expansion opaque porcelain-Vita feldspathic opaque porcelain (VO); and (6) a high expansion opaque porcelain-Will Ceram feldspathic opaque porcelain (WCO). Laplace transform techniques were used to relate shear stress relaxation functions to creep functions for an eight-parameter, discrete viscoelastic model. Nonlinear regression analysis was performed to fit a four-term exponential relaxation function for each material at each temperature. The relaxation functions were utilized in the ANSYS finite element program to simulate creep behavior in three-point bending for each material at each temperature. Shear stress relaxation times at 575 degrees C ranged from 0.03 s for EXV to 195 s for WCO. Knowledge of the shear relaxation functions for dental ceramics at high temperatures is required input for the viscoelastic element in the ANSYS finite element program, which can used to determine transient and residual stresses in dental prostheses during fabrication.

  15. Strain stiffening and stress heterogeneities in sheared collagen networks

    NASA Astrophysics Data System (ADS)

    Urbach, Jeffrey

    2014-03-01

    Disordered networks of stiff or semi-flexible filaments display unusual mechanical properties, including dramatic stiffening when sheared, but little is known about the spatial distribution of stresses. This talk will introduce the technique of Boundary Stress Microscopy, which adapts the approach of traction force microscopy to rheological measurements in order to quantify the non-uniform surface stresses in sheared soft materials. Our results on networks of the biopolymer collagen, a major component of the extracellular matrix, show stress variations over length scales much larger than the network mesh size. We find that the heterogeneity increases with strain stiffening, with stresses at high strains exceeding average stresses by an order of magnitude. The strain stiffening behavior over a wide range of mesh sizes can be parameterized by a single characteristic strain and associated stress, which describes both the strain stiffening regime and network yielding. The characteristic stress is approximately proportional to network density, but the peak stress at both the characteristic strain and at yielding are remarkably insensitive to concentration. These results show the power of Boundary Stress Microscopy to reveal the nature of stress propagation in disordered soft materials, which is critical for understanding many important mechanical properties, including the ultimate strength of a material and the nature of appropriate microscopic constitutive equations. Supported by the AFOSR (FA9550-10-1-0473) and the NSF (DMR-0804782).

  16. Aspirin Has Limited Ability to Modulate Shear-Mediated Platelet Activation Associated with Elevated Shear Stress of Ventricular Assist Devices

    PubMed Central

    Valerio, Lorenzo; Tran, Phat L.; Sheriff, Jawaad; Brengle, William; Ghosh, Ram; Chiu, Wei-Che; Redaelli, Alberto; Fiore, Gianfranco B.; Pappalardo, Federico; Bluestein, Danny; Slepian, Marvin J.

    2016-01-01

    Continuous flow ventricular assist devices (cfVADs) while effective in advanced heart failure, remain plagued by thrombosis related to abnormal flows and elevated shear stress. To limit cfVAD thrombosis, patients utilize complex anti-thrombotic regimens built upon a foundation of aspirin (ASA). While much data exists on ASA as a modulator of biochemically-mediated platelet activation, limited data exists as to the efficacy of ASA as a means of limiting shear-mediated platelet activation, particularly under elevated shear stress common within cfVADs. We investigated the ability of ASA (20, 25 and 125 μM) to limit shear-mediated platelet activation under conditions of: 1) constant shear stress (30 dyne/cm2 and 70 dyne/cm2); 2) dynamic shear stress, and 3) initial high shear exposure (70 dyne/cm2) followed by low shear exposure – i.e. a platelet sensitization protocol, utilizing a hemodynamic shearing device providing uniform shear stress in vitro. The efficacy of ASA to limit platelet activation mediated via passage through a clinical cfVAD system (DeBakey Micromed) in vitro was also studied. ASA reduced platelet activation only under conditions of low shear stress (38% reduction compared to control, n = 10, p < 0.004), with minimal protection at higher shear stress and under dynamic conditions (n = 10, p > 0.5) with no limitation of platelet sensitization. ASA had limited ability (25.6% reduction in platelet activation rate) to modulate shear-mediated platelet activation induced via cfVAD passage. These findings, while performed under “deconstructed” non-clinical conditions by utilizing purified platelets alone in vitro, provide a potential contributory mechanistic explanation for the persistent thrombosis rates experienced clinically in cfVAD patients despite ASA therapy. An opportunity exists to develop enhanced pharmacologic strategies to limit shear-mediated platelet activation at elevated shear levels associated with mechanical circulatory support

  17. Transient Shear Banding in a Simple Yield Stress Fluid

    NASA Astrophysics Data System (ADS)

    Divoux, Thibaut; Tamarii, David; Barentin, Catherine; Manneville, Sébastien

    2010-05-01

    We report a large set of experimental data which demonstrates that a simple yield stress fluid, i.e., which does not present aging or thixotropy, exhibits transient shear banding before reaching a steady state characterized by a homogeneous, linear velocity profile. The duration of the transient regime decreases as a power law with the applied shear rate γ˙. This power-law behavior, observed here in carbopol dispersions, does not depend on the gap width and on the boundary conditions for a given sample preparation. For γ˙≲0.1s-1, heterogeneous flows could be observed for as long as 105s. These local dynamics account for the ultraslow stress relaxation observed at low shear rates.

  18. A Two-Axis Direct Fluid Shear Stress Sensor

    NASA Technical Reports Server (NTRS)

    Adcock, Edward E.; Scott, Michael A.; Bajikar, Sateesh S.

    2010-01-01

    This innovation is a miniature or micro sized semiconductor sensor design that provides two axis direct non-intrusive measurement of skin friction or wall shear stress in fluid flow. The sensor is fabricated by micro-electro-mechanical system (MEMS) technology, enabling small size and low cost reproductions. The sensors have been fabricated by utilizing MEMS fabrication processes to bond a sensing element wafer to a fluid coupling wafer. This layering technique provides for an out of plane dimension that is on the same order of length as the inplane dimensions. The sensor design has the following characteristics: a shear force collecting plate with dimensions that can be tailored to various application specific requirements such as spatial resolution, temporal resolution and shear force range and resolution. This plate is located coplanar to both the sensor body and flow boundary, and is connected to a dual axis gimbal structure by a connecting column or lever arm. The dual axis gimbal structure has torsional hinges with embedded piezoresistive torsional strain gauges which provide a voltage output that is correlated to the applied shear stress (and excitation current) on force collection plate that is located on the flow boundary surface (hence the transduction method). This combination of design elements create a force concentration and resolution structure that enables the generation of a large stress on the strain gauge from the small shear stress on the flow boundary wall. This design as well as the use of back side electrical contacts establishes a non-intrusive method to quantitatively measure the shear force vector on aerodynamic bodies.

  19. A fluidized bed technique for estimating soil critical shear stress

    USDA-ARS?s Scientific Manuscript database

    Soil erosion models, depending on how they are formulated, always have erodibilitiy parameters in the erosion equations. For a process-based model like the Water Erosion Prediction Project (WEPP) model, the erodibility parameters include rill and interrill erodibility and critical shear stress. Thes...

  20. Streamwise shear stress driven compliant wall for drag reduction

    NASA Astrophysics Data System (ADS)

    Józsa, Tamás István; Viola, Ignazio Maria; Balaras, Elias

    2015-11-01

    The interaction between a viscous fluid and a solid wall in relative motion to each other leads to wall shear stress, which results in often-undesirable friction drag. In fully turbulent flow, it has been shown that a compliant wall whose streamwise velocity is equal to the streamwise flow velocity fluctuation in the buffer layer can lead to drag reduction (Choi et al., JFM, 1994; 262:75-110). Practical exploitation of this mechanism would require knowledge of the instantaneous velocity fluctuations in the near-wall region and active control of the wall velocity. However, the near-wall fluid velocity can be approximated by the wall shear stresses through a first-order Taylor expansion; therefore we propose a passively controlled compliant wall whose streamwise wall velocity is driven by the streamwise wall shear stress fluctuations. We show that this wall behaviour can be modelled with a damped harmonic oscillator, where the damping coefficient is related to the target distance of the flow fluctuation from the wall. Our results suggest that a passively-controlled shear-stress-driven compliant wall can be developed for drag reduction. On-going works include the use of direct numerical simulation where the proposed slip condition is applied to quantify the potential drag reduction.

  1. Calculation of Near-Bank Velocity and Boundary Shear Stress

    USDA-ARS?s Scientific Manuscript database

    Detailed knowledge of the flow and boundary shear stress fields near the banks of natural channels is essential for making accurate calculations of rates of near-bank sediment transport and geomorphic adjustment. This paper presents a test of a relatively simple, fully predictive, numerical method f...

  2. Production of Functional Proteins: Balance of Shear Stress and Gravity

    NASA Technical Reports Server (NTRS)

    Goodwin, Thomas John (Inventor); Hammond, Timothy Grant (Inventor); Haysen, James Howard (Inventor)

    2005-01-01

    The present invention provides for a method of culturing cells and inducing the expression of at least one gene in the cell culture. The method provides for contacting the cell with a transcription factor decoy oligonucleotide sequence directed against a nucleotide sequence encoding a shear stress response element.

  3. Incomplete restoration of homeostatic shear stress within arteriovenous fistulae.

    PubMed

    McGah, Patrick M; Leotta, Daniel F; Beach, Kirk W; Eugene Zierler, R; Aliseda, Alberto

    2013-01-01

    Arteriovenous fistulae are surgically created to provide adequate access for dialysis patients suffering from end-stage renal disease. It has long been hypothesized that the rapid blood vessel remodeling occurring after fistula creation is, in part, a process to restore the mechanical stresses to some preferred level, i.e., mechanical homeostasis. We present computational hemodynamic simulations in four patient-specific models of mature arteriovenous fistulae reconstructed from 3D ultrasound scans. Our results suggest that these mature fistulae have remodeled to return to ''normal'' shear stresses away from the anastomoses: about 1.0 Pa in the outflow veins and about 2.5 Pa in the inflow arteries. Large parts of the anastomoses were found to be under very high shear stresses >15 Pa, over most of the cardiac cycle. These results suggest that the remodeling process works toward restoring mechanical homeostasis in the fistulae, but that the process is limited or incomplete, even in mature fistulae, as evidenced by the elevated shear at or near the anastomoses. Based on the long term clinical viability of these dialysis accesses, we hypothesize that the elevated nonhomeostatic shear stresses in some portions of the vessels were not detrimental to fistula patency.

  4. Vascular smooth muscle cell glycocalyx mediates shear stress-induced contractile responses via a Rho kinase (ROCK)-myosin light chain phosphatase (MLCP) pathway

    PubMed Central

    Kang, Hongyan; Liu, Jiajia; Sun, Anqiang; Liu, Xiao; Fan, Yubo; Deng, Xiaoyan

    2017-01-01

    The vascular smooth muscle cells (VSMCs) are exposed to interstitial flow induced shear stress that may be sensed by the surface glycocalyx, a surface layer composed primarily of proteoglycans and glycoproteins, to mediate cell contraction during the myogenic response. We, therefore, attempted to elucidate the signal pathway of the glycocalyx mechanotransduction in shear stress regulated SMC contraction. Human umbilical vein SMCs (HUVSMCs) deprived of serum for 3–4 days were exposed to a step increase (0 to 20 dyn/cm2) in shear stress in a parallel plate flow chamber, and reduction in the cell area was quantified as contraction. The expressions of Rho kinase (ROCK) and its downstream signal molecules, the myosin-binding subunit of myosin phosphatase (MYPT) and the myosin light chain 2 (MLC2), were evaluated. Results showed that the exposure of HUVSMCs to shear stress for 30 min induced cell contraction significantly, which was accompanied by ROCK1 up-regulation, re-distribution, as well as MYPT1 and MLC activation. However, these shear induced phenomenon could be completely abolished by heparinase III or Y-27632 pre-treatment. These results indicate shear stress induced VSMC contraction was mediated by cell surface glycocalyx via a ROCK-MLC phosphatase (MLCP) pathway, providing evidence of the glycocalyx mechanotransduction in myogenic response. PMID:28191820

  5. Vascular smooth muscle cell glycocalyx mediates shear stress-induced contractile responses via a Rho kinase (ROCK)-myosin light chain phosphatase (MLCP) pathway.

    PubMed

    Kang, Hongyan; Liu, Jiajia; Sun, Anqiang; Liu, Xiao; Fan, Yubo; Deng, Xiaoyan

    2017-02-13

    The vascular smooth muscle cells (VSMCs) are exposed to interstitial flow induced shear stress that may be sensed by the surface glycocalyx, a surface layer composed primarily of proteoglycans and glycoproteins, to mediate cell contraction during the myogenic response. We, therefore, attempted to elucidate the signal pathway of the glycocalyx mechanotransduction in shear stress regulated SMC contraction. Human umbilical vein SMCs (HUVSMCs) deprived of serum for 3-4 days were exposed to a step increase (0 to 20 dyn/cm(2)) in shear stress in a parallel plate flow chamber, and reduction in the cell area was quantified as contraction. The expressions of Rho kinase (ROCK) and its downstream signal molecules, the myosin-binding subunit of myosin phosphatase (MYPT) and the myosin light chain 2 (MLC2), were evaluated. Results showed that the exposure of HUVSMCs to shear stress for 30 min induced cell contraction significantly, which was accompanied by ROCK1 up-regulation, re-distribution, as well as MYPT1 and MLC activation. However, these shear induced phenomenon could be completely abolished by heparinase III or Y-27632 pre-treatment. These results indicate shear stress induced VSMC contraction was mediated by cell surface glycocalyx via a ROCK-MLC phosphatase (MLCP) pathway, providing evidence of the glycocalyx mechanotransduction in myogenic response.

  6. Tidal asymmetry and variability of bed shear stress and sediment bed flux at a site in San Francisco Bay, USA

    USGS Publications Warehouse

    Brennan, Matthew L.; Schoellhamer, David H.; Burau, Jon R.; Monismith, Stephen G.; Winterwerp, J.C.; Kranenburg, C.

    2002-01-01

    The relationship between sediment bed flux and bed shear stress during a pair of field experiments in a partially stratified estuary is examined in this paper. Time series of flow velocity, vertical density profiles, and suspended sediment concentration were measured continuously throughout the water column and intensely within 1 meter of the bed. These time series were analyzed to determine bed shear stress, vertical turbulent sediment flux, and mass of sediment suspended in the water column. Resuspension, as inferred from near-bed measurements of vertical turbulent sediment flux, was flood dominant, in accordance with the flood-dominant bed shear stress. Bathymetry-induced residual flow, gravitational circulation, and ebb tide salinity stratification contributed to the flood dominance. In addition to this flow-induced asymmetry, the erodibility of the sediment appears to increase during the first 2 hours of flood tide. Tidal asymmetry in bed shear stress and erodibility help explain an estuarine turbidity maximum that is present during flood tide but absent during ebb tide. Because horizontal advection was insignificant during most of the observation periods, the change in bed mass can be estimated from changes in the total suspended sediment mass. The square wave shape of the bed mass time series indicates that suspended sediment rapidly deposited in an unconsolidated or concentrated benthic suspension layer at slack tides and instantly resuspended when the shear stress became sufficiently large during a subsequent tide. The variability of bed mass associated with the spring/neap cycle (about 60 mg/cm2) is similar to that associated with the semidiurnal tidal cycle.

  7. Shear stress paradigm for perinatal fractal arterial network remodeling in lambs with pulmonary hypertension and increased pulmonary blood flow.

    PubMed

    Ghorishi, Zahra; Milstein, Jay M; Poulain, Francis R; Moon-Grady, Anita; Tacy, Theresa; Bennett, Stephen H; Fineman, Jeffery R; Eldridge, Marlowe W

    2007-06-01

    Congenital heart disease with increased blood flow commonly leads to the development of increased pulmonary vascular reactivity and pulmonary arterial hypertension by mechanisms that remain unclear. We hypothesized a shear stress paradigm of hemodynamic reactivity and network remodeling via the persistence and/or exacerbation of a fetal diameter bifurcation phenotype [parent diameter d(0) and daughters d(1) >or= d(2) with alpha < 2 in (d(1)/d(0))(alpha) + (d(2)/d(0))(alpha) and area ratio beta < 1 in beta = (d(1)(2)+ d(2)(2))/ d(0)(2)] that mechanically acts as a high resistance magnifier/shear stress amplifier to blood flow. Evidence of a hemodynamic influence on network remodeling was assessed with a lamb model of high-flow-induced secondary pulmonary hypertension in which an aortopulmonary graft was surgically placed in one twin in utero (Shunt twin) but not in the other (Control twin). Eight weeks after birth arterial casts were made of the left pulmonary arterial circulation. Bifurcation diameter measurements down to 0.010 mm in the Shunt and Control twins were then compared with those of an unoperated fetal cast. Network organization, cumulative resistance, and pressure/shear stress distributions were evaluated via a fractal model whose dimension D(0) approximately alpha delineates hemodynamic reactivity. Fetus and Control twin D(0) differed: fetus D(0)=1.72, a high-resistance/shear stress amplifying condition; control twin D(0) = 2.02, an area-preserving transport configuration. The Shunt twin (D(0)=1.72) maintained a fetal design but paradoxically remodeled diameter geometry to decrease cumulative resistance relative to the Control twin. Our results indicate that fetal/neonatal pulmonary hemodynamic reactivity remodels in response to shear stress, but the response to elevated blood flow and pulmonary hypertension involves the persistence and exacerbation of a fetal diameter bifurcation phenotype that facilitates endothelial dysfunction/injury.

  8. The Need for a Shear Stress Calibration Standard

    NASA Technical Reports Server (NTRS)

    Scott, Michael A.

    2004-01-01

    By surveying current research of various micro-electro mechanical systems (MEMS) shear stress sensor development efforts we illustrate the wide variety of methods used to test and characterize these sensors. The different methods of testing these sensors make comparison of results difficult in some cases, and also this comparison is further complicated by the different formats used in reporting the results of these tests. The fact that making these comparisons can be so difficult at times clearly illustrates a need for standardized testing and reporting methodologies. This need indicates that the development of a national or international standard for the calibration of MEMS shear stress sensors should be undertaken. As a first step towards the development of this standard, two types of devices are compared and contrasted. The first type device is a laminar flow channel with two different versions considered: the first built with standard manufacturing techniques and the second with advanced precision manufacturing techniques. The second type of device is a new concept for creating a known shear stress consisting of a rotating wheel with the sensor mounted tangentially to the rim and positioned in close proximity to the rim. The shear stress generated by the flow at the sensor position is simply tau = (mu)r(omega)/h, where mu is the viscosity of the ambient gas, r the wheel radius, omega the angular velocity of the wheel, and h the width of the gap between the wheel rim and the sensor. Additionally, issues related to the development of a standard for shear stress calibration are identified and discussed.

  9. Development of a shear stress sensor to analyse the influence of polymers on the turbulent wall shear stress

    NASA Astrophysics Data System (ADS)

    Nottebrock, Bernardo; Große, Sebastian; Schröder, Wolfgang

    2011-05-01

    The drag reducing effect of polymers in a channel flow is well known and it is assumed that the polymer filaments interfere with the turbulent structures in the very near-wall flow. To analyse their precise effect, a micro-pillar shear stress sensor (MPS3) measurement system is developed which allows the detection of wall shear stress at high spatial and temporal resolutions. Different manufacturing techniques for the required micro-pillars are discussed and their influence on the flow is investigated evidencing the non-intrusive character of the pillars. Subsequently, a complete calibration is presented to relate the recorded deflection to wall shear stress values and to assure the correct detection over the whole expected frequency spectrum. A feasibility study about the ability to visualize the two-dimensional wall shear stress distribution completes the discussion about the validity of MPS3. In the last step, the drag reduction of a polymer filament grafted on a micro-pillar compared to a plain pillar and the application of MPS3 in an ocean-type polymer solution are investigated. The results confirm the expected behaviour found in the literature.

  10. The Role of Shear Failure on Stress Characterization

    NASA Astrophysics Data System (ADS)

    Chan, A. W.; Hauser, M.; Couzens-Schultz, B. A.; Gray, G.

    2014-09-01

    Leak-off pressure and lost circulation data are generally thought to be reflective of minimum stress. We propose an alternative interpretation should be considered where the data may reflect a shear failure along zones of pre-existing weakness rather than opening of tensile fractures against the minimum stress. This mechanism has been discussed in a small number of borehole stability and hydraulic fracture papers, but has not been widely applied to leak-off test or lost circulation interpretation. In this paper, we will revisit and expand the concept introduced recently by Couzens-Schultz and Chan (J Struct Geol, doi: 10.1016/j.jsg.2010.06.013, 2010) based on abnormally low leak-off tests in an active thrust belt to the analysis of lost circulation observations in modern-day deltaic environments. In the Gulf of Mexico, lost circulations historically are interpreted as a representation of the minimum horizontal stress due to initiating or reopening of a fracture in tensile mode. However, shear failure or fault reactivation can occur at pressures well below the minimum far-field stress that is typically considered a safe upper bound for mud pressure if pre-existing planes of weakness such as faults or fracture networks exist. We demonstrated a mud loss event is shown to be inconsistent with the tensile failure mode in a normal stress environment, but in good agreement with expectations for shear failure along pre-existing faults.

  11. Arrest stress of uniformly sheared wet granular matter

    NASA Astrophysics Data System (ADS)

    Ebrahimnazhad Rahbari, S. H.; Brinkmann, M.; Vollmer, J.

    2015-06-01

    We conduct extensive independent numerical experiments considering frictionless disks without internal degrees of freedom (rotation, etc.) in two dimensions. We report here that for a large range of the packing fractions below random-close packing, all components of the stress tensor of wet granular materials remain finite in the limit of zero shear rate. This is direct evidence for a fluid-to-solid arrest transition. The offset value of the shear stress characterizes plastic deformation of the arrested state which corresponds to dynamic yield stress of the system. Based on an analytical line of argument, we propose that the mean number of capillary bridges per particle, ν , follows a nontrivial dependence on the packing fraction, ϕ , and the capillary energy, ɛ . Most noticeably, we show that ν is a generic and universal quantity which does not depend on the driving protocol. Using this universal quantity, we calculate the arrest stress, σa, analytically based on a balance of the energy injection rate due to the external force driving the flow and the dissipation rate accounting for the rupture of capillary bridges. The resulting prediction of σa is a nonlinear function of the packing fraction, ϕ , and the capillary energy, ɛ . This formula provides an excellent, parameter-free prediction of the numerical data. Corrections to the theory for small and large packing fractions are connected to the emergence of shear bands and of contributions to the stress from repulsive particle interactions, respectively.

  12. Normal stress differences in a sheared gas-solid suspension

    NASA Astrophysics Data System (ADS)

    Saha, Saikat; Alam, Meheboob

    2016-11-01

    The stress tensor and normal stress differences are analyzed for a homogeneously sheared gas-solid suspension using Enskog-Boltzmann equation. Inelastic particles are suspended in a viscous fluid of viscosity μf and experience a Stokes drag force. Viscous heating due to shear is compensated by (i) the inelastic collisions between particles and (ii) the drag force experienced by the particles due to the interstitial fluid. Rheology of the particle phase is analyzed with anisotropic-Gaussian as the single particle distribution function. The first (N1) and second (N2) normal stress differences are computed as functions of the density (ν), Stokes number (St) and restitution coefficient (e). A comparison with the existing simulation data shows an excellent agreement for both N1 and N2 over the predictions from other Grad-level theories. Finally, in the limit of St -> ∞ (μf -> 0), the related results from the conventional theory of dry granular flows are recovered.

  13. Sensor for Boundary Shear Stress in Fluid Flow

    NASA Technical Reports Server (NTRS)

    Bao, Xiaoqi; Badescu, Mircea; Sherrit, Stewart; Bar-Cohen, Yoseph; Lih, Shyh-Shiuh; Chang, Zensheu; Trease, Brian P.; Kerenyi, Kornel; Widholm, Scott E.; Ostlund, Patrick N.

    2012-01-01

    The formation of scour patterns at bridge piers is driven by the forces at the boundary of the water flow. In most experimental scour studies, indirect processes have been applied to estimate the shear stress using measured velocity profiles. The estimations are based on theoretical models and associated assumptions. However, the turbulence flow fields and boundary layer in the pier-scour region are very complex and lead to low-fidelity results. In addition, available turbulence models cannot account accurately for the bed roughness effect. Direct measurement of the boundary shear stress, normal stress, and their fluctuations are attractive alternatives. However, most direct-measurement shear sensors are bulky in size or not compatible to fluid flow. A sensor has been developed that consists of a floating plate with folded beam support and an optical grid on the back, combined with a high-resolution optical position probe. The folded beam support makes the floating plate more flexible in the sensing direction within a small footprint, while maintaining high stiffness in the other directions. The floating plate converts the shear force to displacement, and the optical probe detects the plate s position with nanometer resolution by sensing the pattern of the diffraction field of the grid through a glass window. This configuration makes the sensor compatible with liquid flow applications.

  14. MicroRNA-30 mediates anti-inflammatory effects of shear stress and KLF2 via repression of angiopoietin 2.

    PubMed

    Demolli, Shemsi; Doebele, Carmen; Doddaballapur, Anuradha; Lang, Victoria; Fisslthaler, Beate; Chavakis, Emmanouil; Vinciguerra, Manlio; Sciacca, Sergio; Henschler, Reinhard; Hecker, Markus; Savant, Soniya; Augustin, Hellmut G; Kaluza, David; Dimmeler, Stefanie; Boon, Reinier A

    2015-11-01

    MicroRNAs are endogenously expressed small noncoding RNAs that regulate gene expression. Laminar blood flow induces atheroprotective gene expression in endothelial cells (ECs) in part by upregulating the transcription factor KLF2. Here, we identified KLF2- and flow-responsive miRs that affect gene expression in ECs. Bioinformatic assessment of mRNA expression patterns identified the miR-30-5p seed sequence to be highly enriched in mRNAs that are downregulated by KLF2. Indeed, KLF2 overexpression and shear stress stimulation in vitro and in vivo increased the expression of miR-30-5p family members. Furthermore, we identified angiopoietin 2 (Ang2) as a target of miR-30. MiR-30 overexpression reduces Ang2 levels, whereas miR-30 inhibition by LNA-antimiRs induces Ang2 expression. Consistently, miR-30 reduced basal and TNF-α-induced expression of the inflammatory cell–cell adhesion molecules E-selectin, ICAM1 and VCAM1, which was rescued by stimulation with exogenous Ang2. In summary, KLF2 and shear stress increase the expression of the miR-30-5p family which acts in an anti-inflammatory manner in ECs by impairing the expression of Ang2 and inflammatory cell–cell adhesion molecules. The upregulation of miR-30-5p family members may contribute to the atheroprotective effects of shear stress.

  15. Thermal Sensors for Wall-Shear Stress: Reality and Myth

    NASA Astrophysics Data System (ADS)

    Löfdahl, L.; Johansson, P.; Bakchinov, A.; Sen, M.; Gad-El-Hak, M.

    1999-11-01

    Instantaneous wall-shear stress is a quantity of fundamental importance in wall-bounded turbulent flows. While there are many methods capable of measuring the time-averaged value of the wall-shear stress, no reliable technique exists for measuring the time-resolved stress. One of the oldest strategies for wall-shear-stress measurements is based on the so-called thermal principle. Through the years, it has been argued and shown in many investigations that the thermal sensors suffer from large heat losses to the substrate, yielding a larger active sensor area and thus adversely affecting the temporal and spatial response of the probe. The MEMS technology offers possibilities to circumvent these drawbacks. But none of the MEMS-based sensors has gone through the mandatory validation to understand exactly what is being sensed. In this talk, we will present detailed measurements of a MEMS-based thermal sensor designed for an improved response. This is achieved by having a very small (60 μm × 300 μm) heated part separated from the surrounding wall by an insulating polyimide. Results and discussions about important features such as temperature of the surrounding material, response time and dependence on packaging will be presented. It seems that even microsensors are cursed by unacceptable levels of heat conduction to the surrounding solid.

  16. Time-dependent polymer rheology under constant stress and under constant shear conditions.

    NASA Technical Reports Server (NTRS)

    Lee, K. H.; Brodkey, R. S.

    1971-01-01

    A kinetic rate theory previously presented for describing non-Newtonian phenomena has been further modified to predict the flow behavior of viscoelastic materials under constant stress conditions. The thixotropic shear stress or shear rate is predicted by the kinetic theory, and the experimental stress or shear rate is obtained by modifying the thixotropic value by a stress or shear rate retardation term. The retardation term stems from a Maxwellian approach for stress retardation. In order to test the validity of this approach, transient and steady-state data were obtained for two solutions of polymethylmethacrylate in diethylphthalate. Both constant stress measurements and constant shear rate data were taken over a broad range.

  17. Quantification of shear stress in a meandering native topographic channel using a physical hydraulic model

    Treesearch

    Michael E. Ursic

    2011-01-01

    Current guidelines for predicting increases in shear stress in open-channel bends were developed from investigations that were primarily prismatic in cross section. This study provides possible increases in shear stress relative to approach flow conditions resulting from planimetric and topographic geometric features. Boundary shear stress estimates were determined by...

  18. Measurement of the temperature-dependent threshold shear-stress of red blood cell aggregation

    NASA Astrophysics Data System (ADS)

    Lim, Hyun-Jung; Nam, Jeong-Hun; Lee, Yong-Jin; Shin, Sehyun

    2009-09-01

    Red blood cell (RBC) aggregation is becoming an important hemorheological parameter, which typically exhibits temperature dependence. Quite recently, a critical shear-stress was proposed as a new dimensional index to represent the aggregative and disaggregative behaviors of RBCs. The present study investigated the effect of the temperature on the critical shear-stress that is required to keep RBC aggregates dispersed. The critical shear-stress was measured at various temperatures (4, 10, 20, 30, and 37 °C) through the use of a transient microfluidic aggregometry. The critical shear-stress significantly increased as the blood temperature lowered, which accorded with the increase in the low-shear blood viscosity with the lowering of the temperature. Furthermore, the critical shear-stress also showed good agreement with the threshold shear-stress, as measured in a rotational Couette flow. These findings assist in rheologically validating the critical shear-stress, as defined in the microfluidic aggregometry.

  19. Evaluation of the time dependent surface shear stress in turbulent flows

    NASA Technical Reports Server (NTRS)

    Sandborn, V. A.

    1979-01-01

    The time dependent surface shear stress has been evaluated using surface heat transfer measurements. For fully developed turbulent pipe and open channel water flows, and incompressible and compressible turbulent boundary layer air flows the measurements indicate the absolute magnitude of the surface shear stress fluctuations will be greater than two times the mean values. The root-mean-square shear stress fluctuations were of the order of 0.2 to 0.4 times the mean surface shear values. Due to these large surface shear stress fluctuations and the nonlinear relation between heat transfer and shear stress, a special technique has been developed to evaluate the measurements. It was found that the non-linear averaging errors for a hot film-surface shear stress gauge in a fully developed pipe flow was of the order of 10 percent at low velocities. A hot wire-surface shear stress gauge was employed for measurements of turbulent boundary layers in air.

  20. Inverse method for estimating shear stress in machining

    NASA Astrophysics Data System (ADS)

    Burns, T. J.; Mates, S. P.; Rhorer, R. L.; Whitenton, E. P.; Basak, D.

    2016-01-01

    An inverse method is presented for estimating shear stress in the work material in the region of chip-tool contact along the rake face of the tool during orthogonal machining. The method is motivated by a model of heat generation in the chip, which is based on a two-zone contact model for friction along the rake face, and an estimate of the steady-state flow of heat into the cutting tool. Given an experimentally determined discrete set of steady-state temperature measurements along the rake face of the tool, it is shown how to estimate the corresponding shear stress distribution on the rake face, even when no friction model is specified.

  1. Wall shear stress measurements using a new transducer

    NASA Technical Reports Server (NTRS)

    Vakili, A. D.; Wu, J. M.; Lawing, P. L.

    1986-01-01

    A new instrument has been developed for direct measurement of wall shear stress. This instrument is simple and symmetric in design with small moving mass and no internal friction. Features employed in the design of this instrument eliminate most of the difficulties associated with the traditional floating element balances. Vibration problems associated with the floating element skin friction balances have been found to be minimized by the design features and optional damping provided. The unique design of this instrument eliminates or reduces the errors associated with conventional floating-element devices: such as errors due to gaps, pressure gradient, acceleration, heat transfer and temperature change. The instrument is equipped with various sensing systems and the output signal is a linear function of the wall shear stress. Measurement made in three different tunnels show good agreement with theory and data obtained by the floating element devices.

  2. A study on reynolds shear stress measurement by LDV

    NASA Astrophysics Data System (ADS)

    Munekata, Mizue; Ohba, Hideki; Matsuzaki, Kazuyoshi

    2001-03-01

    The measurement results by Laser Doppler Velocimetry (LDV) are compared with the direct numerical simulation result by Eggels et al.[1] for a cylindrical pipe flow. In the case of a pipe flow, the bias error for mean velocity is very small, because the local turbulent intensity is very small all over the pipe cross section. However the difference of the combination of u' and v' have considerable effects on Reynolds shear stress. From our investigation, it is found that the selection of coincidence time that is a necessary parameter for combination of u' and v' is more important in obtaining the accurate Reynolds shear stress. The suitable coincidence time is selected for a jet flow and the effectiveness of coincident time method or equal time interval method with coincidence data is shown.

  3. [Exercise-induced shear stress: Physiological basis and clinical impact].

    PubMed

    Rodríguez-Núñez, Iván; Romero, Fernando; Saavedra, María Javiera

    2016-01-01

    The physiological regulation of vascular function is essential for cardiovascular health and depends on adequate control of molecular mechanisms triggered by endothelial cells in response to mechanical and chemical stimuli induced by blood flow. Endothelial dysfunction is one of the major risk factors for cardiovascular disease, where an imbalance between synthesis of vasodilator and vasoconstrictor molecules is one of its main mechanisms. In this context, the shear stress is one of the most important mechanical stimuli to improve vascular function, due to endothelial mechanotransduction, triggered by stimulation of various endothelial mechanosensors, induce signaling pathways culminating in increased bioavailability of vasodilators molecules such as nitric oxide, that finally trigger the angiogenic mechanisms. These mechanisms allow providing the physiological basis for the effects of exercise on vascular health. In this review it is discussed the molecular mechanisms involved in the vascular response induced by shear stress and its impact in reversing vascular injury associated with the most prevalent cardiovascular disease in our population.

  4. Liquid crystals for unsteady surface shear stress visualization

    SciTech Connect

    Reda, D.C.

    1988-01-01

    Oscillating airfoil experiments were conducted to test the frequency response of thermochromic liquid crystal coatings to unsteady surface shear stresses under isothermal-flow conditions. The model was an NACA-0015 airfoil, exposed to an incompressible flow at a freestream Reynolds number (based on chord) of 1.14 x 10/sup 6/. Angle-of-attack forcing functions were sine waves of amplitude +- 10/degree/ about each of three mean angles of attack: 0/degree/, 10/degree/, and 20/degree/. Frequencies of oscillation were 0.2, 0.6 and 1.2 hertz, corresponding to reduced frequencies of 0.0055, 0.0164 and 0.0328. Data acquisition was accomplished by video recording. Observations showed the liquid crystal technique capable of visualizing high surface shear stress zones over the stated dynamic range in a continuous and reversible manner. 11 refs.

  5. Pressure and wall shear stress in blood hammer - Analytical theory.

    PubMed

    Mei, Chiang C; Jing, Haixiao

    2016-10-01

    We describe an analytical theory of blood hammer in a long and stiffened artery due to sudden blockage. Based on the model of a viscous fluid in laminar flow, we derive explicit expressions of oscillatory pressure and wall shear stress. To examine the effects on local plaque formation we also allow the blood vessel radius to be slightly nonuniform. Without resorting to discrete computation, the asymptotic method of multiple scales is utilized to deal with the sharp contrast of time scales. The effects of plaque and blocking time on blood pressure and wall shear stress are studied. The theory is validated by comparison with existing water hammer experiments. Copyright © 2016. Published by Elsevier Inc.

  6. Mathematical Modeling of Intravascular Blood Coagulation under Wall Shear Stress

    PubMed Central

    Rukhlenko, Oleksii S.; Dudchenko, Olga A.; Zlobina, Ksenia E.; Guria, Georgy Th.

    2015-01-01

    Increased shear stress such as observed at local stenosis may cause drastic changes in the permeability of the vessel wall to procoagulants and thus initiate intravascular blood coagulation. In this paper we suggest a mathematical model to investigate how shear stress-induced permeability influences the thrombogenic potential of atherosclerotic plaques. Numerical analysis of the model reveals the existence of two hydrodynamic thresholds for activation of blood coagulation in the system and unveils typical scenarios of thrombus formation. The dependence of blood coagulation development on the intensity of blood flow, as well as on geometrical parameters of atherosclerotic plaque is described. Relevant parametric diagrams are drawn. The results suggest a previously unrecognized role of relatively small plaques (resulting in less than 50% of the lumen area reduction) in atherothrombosis and have important implications for the existing stenting guidelines. PMID:26222505

  7. Non-volcanic tremor driven by large transient shear stresses

    USGS Publications Warehouse

    Rubinstein, J.L.; Vidale, J.E.; Gomberg, J.; Bodin, P.; Creager, K.C.; Malone, S.D.

    2007-01-01

    Non-impulsive seismic radiation or 'tremor' has long been observed at volcanoes and more recently around subduction zones. Although the number of observations of non-volcanic tremor is steadily increasing, the causative mechanism remains unclear. Some have attributed non-volcanic tremor to the movement of fluids, while its coincidence with geodetically observed slow-slip events at regular intervals has led others to consider slip on the plate interface as its cause. Low-frequency earthquakes in Japan, which are believed to make up at least part of non-volcanic tremor, have focal mechanisms and locations that are consistent with tremor being generated by shear slip on the subduction interface. In Cascadia, however, tremor locations appear to be more distributed in depth than in Japan, making them harder to reconcile with a plate interface shear-slip model. Here we identify bursts of tremor that radiated from the Cascadia subduction zone near Vancouver Island, Canada, during the strongest shaking from the moment magnitude Mw = 7.8, 2002 Denali, Alaska, earthquake. Tremor occurs when the Love wave displacements are to the southwest (the direction of plate convergence of the overriding plate), implying that the Love waves trigger the tremor. We show that these displacements correspond to shear stresses of approximately 40 kPa on the plate interface, which suggests that the effective stress on the plate interface is very low. These observations indicate that tremor and possibly slow slip can be instantaneously induced by shear stress increases on the subduction interface - effectively a frictional failure response to the driving stress. ??2007 Nature Publishing Group.

  8. ENaC regulation by proteases and shear stress

    PubMed Central

    Shi, Shujie; Carattino, Marcelo D.; Hughey, Rebecca P.; Kleyman, Thomas R.

    2013-01-01

    Epithelial Na+ channels (ENaCs) are comprised of subunits that have large extracellular regions linked to membrane spanning domains where the channel pore and gate reside. A variety of external factors modify channel activity by interacting at sites within extracellular regions that lead to conformational changes that are transmitted to the channel gate and alter channel open probability. Our review addresses two external factors that have important roles in regulating channel activity, proteases and laminar shear stress. PMID:23547932

  9. Limiting shear stress and monotonic properties of liquid water

    NASA Astrophysics Data System (ADS)

    Gorshkov, A. I.

    2016-12-01

    Publications in scientific journals in which the authors attempt to experimentally prove that water, the most widespread substance on the Earth, is not a completely classical liquid, have become more frequent recently. This means, first, that water behaves as a solid at very low shear stress, i.e., does not flow, and, second, that the temperature dependences of its different properties are non-monotonic, i.e., possess singularities. We are aware of several such publications [1-5].

  10. Non-volcanic tremor driven by large transient shear stresses.

    PubMed

    Rubinstein, Justin L; Vidale, John E; Gomberg, Joan; Bodin, Paul; Creager, Kenneth C; Malone, Stephen D

    2007-08-02

    Non-impulsive seismic radiation or 'tremor' has long been observed at volcanoes and more recently around subduction zones. Although the number of observations of non-volcanic tremor is steadily increasing, the causative mechanism remains unclear. Some have attributed non-volcanic tremor to the movement of fluids, while its coincidence with geodetically observed slow-slip events at regular intervals has led others to consider slip on the plate interface as its cause. Low-frequency earthquakes in Japan, which are believed to make up at least part of non-volcanic tremor, have focal mechanisms and locations that are consistent with tremor being generated by shear slip on the subduction interface. In Cascadia, however, tremor locations appear to be more distributed in depth than in Japan, making them harder to reconcile with a plate interface shear-slip model. Here we identify bursts of tremor that radiated from the Cascadia subduction zone near Vancouver Island, Canada, during the strongest shaking from the moment magnitude M(w) = 7.8, 2002 Denali, Alaska, earthquake. Tremor occurs when the Love wave displacements are to the southwest (the direction of plate convergence of the overriding plate), implying that the Love waves trigger the tremor. We show that these displacements correspond to shear stresses of approximately 40 kPa on the plate interface, which suggests that the effective stress on the plate interface is very low. These observations indicate that tremor and possibly slow slip can be instantaneously induced by shear stress increases on the subduction interface-effectively a frictional failure response to the driving stress.

  11. Basal shear stress of debris flow in the runout phase

    NASA Astrophysics Data System (ADS)

    D'Agostino, V.; Bettella, F.; Cesca, M.

    2013-11-01

    A laboratory device is proposed to assess the basal shear stresses generated by debris-flow mixtures during their runout phase. The device consists of an inclinable box with a gate facing a deposition plane. The box is filled with a selected debris-flow mixture, and after sudden opening of the gate, the features of the dam-break deposit can be measured. Based on some simplified assumptions of the energy balance, a methodology is proposed to assess basal shear stresses. The device has been tested using sediment samples from debris-flow deposits generated by two catchments of the Dolomites (Cortina d'Ampezzo, Belluno, Italy) by carrying out runout tests for different sediment concentrations by volume. The results show how the static Coulomb friction law is valid in the runout phase, with friction angles on the order of the angle of repose of the same material in dry conditions. The data elaboration also yields an innovative constitutive equation for shear stresses. This relation merges the Coulomb mixture approach with the concept of a one-phase flow with a certain rheology. This integration offers a useful insight into the weaknesses of the rheological approach if it is not properly scaled up to the ambient pressure of interest.

  12. FOXC2 and fluid shear stress stabilize postnatal lymphatic vasculature

    PubMed Central

    Sabine, Amélie; Bovay, Esther; Demir, Cansaran Saygili; Kimura, Wataru; Jaquet, Muriel; Agalarov, Yan; Zangger, Nadine; Scallan, Joshua P.; Graber, Werner; Gulpinar, Elgin; Kwak, Brenda R.; Mäkinen, Taija; Martinez-Corral, Inés; Ortega, Sagrario; Delorenzi, Mauro; Kiefer, Friedemann; Davis, Michael J.; Djonov, Valentin; Miura, Naoyuki; Petrova, Tatiana V.

    2015-01-01

    Biomechanical forces, such as fluid shear stress, govern multiple aspects of endothelial cell biology. In blood vessels, disturbed flow is associated with vascular diseases, such as atherosclerosis, and promotes endothelial cell proliferation and apoptosis. Here, we identified an important role for disturbed flow in lymphatic vessels, in which it cooperates with the transcription factor FOXC2 to ensure lifelong stability of the lymphatic vasculature. In cultured lymphatic endothelial cells, FOXC2 inactivation conferred abnormal shear stress sensing, promoting junction disassembly and entry into the cell cycle. Loss of FOXC2-dependent quiescence was mediated by the Hippo pathway transcriptional coactivator TAZ and, ultimately, led to cell death. In murine models, inducible deletion of Foxc2 within the lymphatic vasculature led to cell-cell junction defects, regression of valves, and focal vascular lumen collapse, which triggered generalized lymphatic vascular dysfunction and lethality. Together, our work describes a fundamental mechanism by which FOXC2 and oscillatory shear stress maintain lymphatic endothelial cell quiescence through intercellular junction and cytoskeleton stabilization and provides an essential link between biomechanical forces and endothelial cell identity that is necessary for postnatal vessel homeostasis. As FOXC2 is mutated in lymphedema-distichiasis syndrome, our data also underscore the role of impaired mechanotransduction in the pathology of this hereditary human disease. PMID:26389677

  13. Experimental study on shear stress distributions in a centrifugal blood pump.

    PubMed

    Mizunuma, Hiroshi; Nakajima, Ryou

    2007-07-01

    Wall shear stress on the pump casing cover was measured using a surface-mounted hot-film sensor. In addition, the shear stress distribution in the pump was qualitatively investigated by means of oil-film visualization. The characteristics of shear stress in the pump are discussed, including the results on the oil-film visualization. The centrifugal blood pump used was a Nikkiso HPM-15 (Nikkiso Co., Ltd, Tokyo, Japan). The hot-film measurement indicated that the shear stress was approximately proportional to the rotating speed, and exceeded 300 Pa when r/R > 0.5 at 3000 rpm. The circumferential average shear stress on the casing cover was of the same order as the characteristic stress sigma obtained from the pump axial torque. These results suggest that the shear stress on the casing cover can be used to evaluate the characteristic shear stress in the pump.

  14. Rheological investigations of ferrofluids with a shear stress controlled rheometer.

    PubMed

    Shahnazian, Hamid; Odenbach, Stefan

    2008-05-21

    The appearance of field- and shear-dependent changes of viscosity-the magnetoviscous effect-is correlated to the formation of chains and structures of magnetic nanoparticles. Moreover, the formation of these structures leads to the appearance of viscoelastic effects or other non-Newtonian features in ferrofluids in the presence of a magnetic field. In order to describe these phenomena, different theoretical approaches have been developed which explain the mechanism of these effects with different assumptions. One point in which these models differ, and which has to be clarified, is the appearance of yield stress and its dependence on magnetic field strength. With this aim, a stress controlled rheometer has been designed to prove the existence of this very small field-dependent yield stress for ferrofluids. The results presented here show a dependence of the yield stress on the magnetic field strength as well as on the interparticle interaction and particle size distribution. Finally, yield stress experiments have been performed for different geometries of the shear cell in order to get more information about the microstructure formed by the magnetic particles.

  15. Viscosity, Shear Waves and Atomic Level Stress Correlations

    NASA Astrophysics Data System (ADS)

    Levashov, Valentin; Morris, James; Egami, Takeshi

    2011-03-01

    The Green-Kubo equation relates the macroscopic stress-stress correlation function to a liquid's viscosity. The concept of the atomic level stresses allows the macroscopic stress-stress correlation function in the equation to be expressed in terms of the space/time correlations between the atomic level stress-stress correlation functions. Molecular dynamics studies show surprisingly long spatial extension of stress-stress correlations and also longitudinal and transverse waves propagating in liquids over ranges exceeding the system size. The results reveal that the range of propagation of shear waves corresponds to the range of distances relevant for viscosity. Thus our results show that viscosity is a fundamentally non-local quantity. We also show that periodic boundary conditions play very non-trivial, previously undiscussed, role in molecular dynamics simulations effectively masking the long range nature of viscosity. This work was supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences.

  16. Measurements of flow-induced birefringence in microfluidics

    PubMed Central

    Sun, Chen-li; Huang, Hung-Yen

    2016-01-01

    In this study, we demonstrate the use of a microscopic circular polariscope to measure the flow-induced birefringence in a microfluidic device that represents the kinematics of fluid motion optically. Unlike the commercial birefringence microscope employed in the previous studies, our approach is able to provide direct measurement of retardance, which quantifies the difference in refractive index of the fluid experienced by the ordinary and extraordinary rays, from one single image frame. This capability facilitates unsteady full-field quantitation of flow-induced birefringence in microfluidics that has never been achieved before. At low flow rates, we find that the value of the retardance is independent of the microfluidic design and proportional to the nominal strain rates. This linearity bridges the measurement of birefringence and the deformation rate in the microflow environment, which yields the stress information of the fluid flow. In addition, the μPIV results confirm that both extensional and shear strain rates contribute to the flow-induced birefringence so that the retardance distribution can be used to represent the field of the principal strain rate in a microfluidic device. The outcome of this study proves that our approach provides a non-invasive method that enables an intuitive full-field representation of stress in the instantaneous flow field in a microfluidic device. PMID:26858809

  17. DPIV prediction of flow induced platelet activation-comparison to numerical predictions.

    PubMed

    Raz, Sagi; Einav, Shmuel; Alemu, Yared; Bluestein, Danny

    2007-04-01

    Flow induced platelet activation (PA) can lead to platelet aggregation, deposition onto the blood vessel wall, and thrombus formation. PA was thoroughly studied under unidirectional flow conditions. However, in regions of complex flow, where the platelet is exposed to varying levels of shear stress for varying durations, the relationship between flow and PA is not well understood. Numerical models were developed for studying flow induced PA resulting from stress histories along Lagrangian trajectories in the flow field. However, experimental validation techniques such as Digital Particle Image Velocimetry (DPIV) were not extended to include such models. In this study, a general experimental tool for PA analysis by means of continuous DPIV was utilized and compared to numerical simulation in a model of coronary stenosis. A scaled up (5:1) 84% eccentric and axisymetric coronary stenosis model was used for analysis of shear stress and exposure time along particle trajectories. Flow induced PA was measured using the PA State (PAS) assay. An algorithm for computing the PA level in pertinent trajectories was developed as a tool for extracting information from DPIV measurements for predicting the flow induced thrombogenic potential. CFD, DPIV and PAS assay results agreed well in predicting the level of PA. In addition, the same trend predicted by the DPIV was measured in vitro using the Platelet Activity State (PAS) assay, namely, that the symmetric stenosis activated the platelets more as compared to the eccentric stenosis.

  18. Molecular Origins of Higher Harmonics in Large-Amplitude Oscillatory Shear Flow: Shear Stress Response

    NASA Astrophysics Data System (ADS)

    Gilbert, Peter; Giacomin, A. Jeffrey; Schmalzer, Andrew; Bird, R. B.

    Recent work has focused on understanding the molecular origins of higher harmonics that arise in the shear stress response of polymeric liquids in large-amplitude oscillatory shear flow. These higher harmonics have been explained using only the orientation distribution of a dilute suspension of rigid dumbbells in a Newtonian fluid, which neglects molecular interactions and is the simplest relevant molecular model of polymer viscoelasticity [R.B. Bird et al., J Chem Phys, 140, 074904 (2014)]. We explore these molecular interactions by examining the Curtiss-Bird model, a kinetic molecular theory that accounts for restricted polymer motions arising when chains are concentrated [Fan and Bird, JNNFM, 15, 341 (1984)]. For concentrated systems, the chain motion transverse to the chain axis is more restricted than along the axis. This anisotropy is described by the link tension coefficient, ɛ, for which several special cases arise: ɛ =0 corresponds to reptation, ɛ > 1 1 8 8 to rod-climbing, 1 1 2 2 >= ɛ >= 3 3 4 4 to reasonable shear-thinning predictions in steady simple shear flow, and ɛ =1 to a dilute solution of chains. We examine the shapes of the shear stress versus shear rate loops for the special cases, ɛ = 0 , 1 0 , 1 8 , 3 3 8 8 8 , 3 3 8 8 , 1 , of the Curtiss-Bird model, and we compare these with those

  19. ESTIMATION OF EFFECTIVE SHEAR STRESS WORKING ON FLAT SHEET MEMBRANE USING FLUIDIZED MEDIA IN MBRs

    NASA Astrophysics Data System (ADS)

    Zaw, Hlwan Moe; Li, Tairi; Nagaoka, Hiroshi; Mishima, Iori

    This study was aimed at estimating effective shear stress working on flat sheet membrane by the addition of fluidized media in MBRs. In both of laboratory-scale aeration tanks with and without fluidized media, shear stress variations on membrane surface and water phase velocity variations were measured and MBR operation was conducted. For the evaluation of the effective shear stress working on membrane surface to mitigate membrane surface, simulation of trans-membrane pressure increase was conducted. It was shown that the time-averaged absolute value of shear stress was smaller in the reactor with fluidized media than without fluidized media. However, due to strong turbulence in the reactor with fluidized media caused by interaction between water-phase and media and also due to the direct interaction between membrane surface and fluidized media, standard deviation of shear stress on membrane surface was larger in the reactor with fluidized media than without media. Histograms of shear stress variation data were fitted well to normal distribution curves and mean plus three times of standard deviation was defined to be a maximum shear stress value. By applying the defined maximum shear stress to a membrane fouling model, trans-membrane pressure curve in the MBR experiment was simulated well by the fouling model indicting that the maximum shear stress, not time-averaged shear stress, can be regarded as an effective shear stress to prevent membrane fouling in submerged flat-sheet MBRs.

  20. Shear stress blunts tubuloglomerular feedback partially mediated by primary cilia and nitric oxide at the macula densa.

    PubMed

    Wang, Lei; Shen, Chunyu; Liu, Haifeng; Wang, Shaohui; Chen, Xinshan; Roman, Richard J; Juncos, Luis A; Lu, Yan; Wei, Jin; Zhang, Jie; Yip, Kay-Pong; Liu, Ruisheng

    2015-10-01

    The present study tested whether primary cilia on macula densa serve as a flow sensor to enhance nitric oxide synthase 1 (NOS1) activity and inhibit tubuloglomerular feedback (TGF). Isolated perfused macula densa was loaded with calcein red and 4,5-diaminofluorescein diacetate to monitor cell volume and nitric oxide (NO) generation. An increase in tubular flow rate from 0 to 40 nl/min enhanced NO production by 40.0 ± 1.2%. The flow-induced NO generation was blocked by an inhibitor of NOS1 but not by inhibition of the Na/K/2Cl cotransporter or the removal of electrolytes from the perfusate. NO generation increased from 174.8 ± 21 to 276.1 ± 24 units/min in cultured MMDD1 cells when shear stress was increased from 0.5 to 5.0 dynes/cm(2). The shear stress-induced NO generation was abolished in MMDD1 cells in which the cilia were disrupted using a siRNA to ift88. Increasing the NaCl concentration of the tubular perfusate from 10 to 80 mM NaCl in the isolated perfused juxtaglomerular preparation reduced the diameter of the afferent arteriole by 3.8 ± 0.1 μm. This response was significantly blunted to 2.5 ± 0.2 μm when dextran was added to the perfusate to increase the viscosity and shear stress. Inhibition of NOS1 blocked the effect of dextran on TGF response. In vitro, the effects of raising perfusate viscosity with dextran on tubular hydraulic pressure were minimized by reducing the outflow resistance to avoid stretching of tubular cells. These results suggest that shear stress stimulates primary cilia on the macula densa to enhance NO generation and inhibit TGF responsiveness.

  1. Fluid Shear Stress Regulates the Invasive Potential of Glioma Cells via Modulation of Migratory Activity and Matrix Metalloproteinase Expression

    PubMed Central

    Qazi, Henry; Shi, Zhong-Dong; Tarbell, John M.

    2011-01-01

    Background Glioma cells are exposed to elevated interstitial fluid flow during the onset of angiogenesis, at the tumor periphery while invading normal parenchyma, within white matter tracts, and during vascular normalization therapy. Glioma cell lines that have been exposed to fluid flow forces in vivo have much lower invasive potentials than in vitro cell motility assays without flow would indicate. Methodology/Principal Findings A 3D Modified Boyden chamber (Darcy flow through collagen/cell suspension) model was designed to mimic the fluid dynamic microenvironment to study the effects of fluid shear stress on the migratory activity of glioma cells. Novel methods for gel compaction and isolation of chemotactic migration from flow stimulation were utilized for three glioma cell lines: U87, CNS-1, and U251. All physiologic levels of fluid shear stress suppressed the migratory activity of U87 and CNS-1 cell lines. U251 motility remained unaltered within the 3D interstitial flow model. Matrix Metalloproteinase (MMP) inhibition experiments and assays demonstrated that the glioma cells depended on MMP activity to invade, and suppression in motility correlated with downregulation of MMP-1 and MMP-2 levels. This was confirmed by RT-PCR and with the aid of MMP-1 and MMP-2 shRNA constructs. Conclusions/Significance Fluid shear stress in the tumor microenvironment may explain reduced glioma invasion through modulation of cell motility and MMP levels. The flow-induced migration trends were consistent with reported invasive potentials of implanted gliomas. The models developed for this study imply that flow-modulated motility involves mechanotransduction of fluid shear stress affecting MMP activation and expression. These models should be useful for the continued study of interstitial flow effects on processes that affect tumor progression. PMID:21637818

  2. CCM proteins control endothelial β1 integrin dependent response to shear stress

    PubMed Central

    Macek Jilkova, Zuzana; Lisowska, Justyna; Manet, Sandra; Verdier, Claude; Deplano, Valerie; Geindreau, Christian; Faurobert, Eva; Albigès-Rizo, Corinne; Duperray, Alain

    2014-01-01

    ABSTRACT Hemodynamic shear stress from blood flow on the endothelium critically regulates vascular function in many physiological and pathological situations. Endothelial cells adapt to shear stress by remodeling their cytoskeletal components and subsequently by changing their shape and orientation. We demonstrate that β1 integrin activation is critically controlled during the mechanoresponse of endothelial cells to shear stress. Indeed, we show that overexpression of the CCM complex, an inhibitor of β1 integrin activation, blocks endothelial actin rearrangement and cell reorientation in response to shear stress similarly to β1 integrin silencing. Conversely, depletion of CCM2 protein leads to an elongated “shear-stress-like” phenotype even in the absence of flow. Taken together, our findings reveal the existence of a balance between positive extracellular and negative intracellular signals, i.e. shear stress and CCM complex, for the control of β1 integrin activation and subsequent adaptation of vascular endothelial cells to mechanostimulation by fluid shear stress. PMID:25432514

  3. Imaging shear stress distribution and evaluating the stress concentration factor of the human eye

    NASA Astrophysics Data System (ADS)

    Joseph Antony, S.

    2015-03-01

    Healthy eyes are vital for a better quality of human life. Historically, for man-made materials, scientists and engineers use stress concentration factors to characterise the effects of structural non-homogeneities on their mechanical strength. However, such information is scarce for the human eye. Here we present the shear stress distribution profiles of a healthy human cornea surface in vivo using photo-stress analysis tomography, which is a non-intrusive and non-X-ray based method. The corneal birefringent retardation measured here is comparable to that of previous studies. Using this, we derive eye stress concentration factors and the directional alignment of major principal stress on the surface of the cornea. Similar to thermometers being used for monitoring the general health in humans, this report provides a foundation to characterise the shear stress carrying capacity of the cornea, and a potential bench mark for validating theoretical modelling of stresses in the human eye in future.

  4. Imaging shear stress distribution and evaluating the stress concentration factor of the human eye

    PubMed Central

    Joseph Antony, S.

    2015-01-01

    Healthy eyes are vital for a better quality of human life. Historically, for man-made materials, scientists and engineers use stress concentration factors to characterise the effects of structural non-homogeneities on their mechanical strength. However, such information is scarce for the human eye. Here we present the shear stress distribution profiles of a healthy human cornea surface in vivo using photo-stress analysis tomography, which is a non-intrusive and non-X-ray based method. The corneal birefringent retardation measured here is comparable to that of previous studies. Using this, we derive eye stress concentration factors and the directional alignment of major principal stress on the surface of the cornea. Similar to thermometers being used for monitoring the general health in humans, this report provides a foundation to characterise the shear stress carrying capacity of the cornea, and a potential bench mark for validating theoretical modelling of stresses in the human eye in future. PMID:25754336

  5. Wall shear stress indicators in abnormal aortic geometries

    NASA Astrophysics Data System (ADS)

    Prahl Wittberg, Lisa; van Wyk, Stevin; Fuchs, Laszlo; Gutmark, Ephraim; Gutmark-Little, Iris

    2015-11-01

    Cardiovascular disease, such as atherosclerosis, occurs at specific locations in the arterial tree. Characterizing flow and forces at these locations is crucial to understanding the genesis of disease. Measures such as time average wall shear stress, oscillatory shear index, relative residence time and temporal wall shear stress gradients have been shown to identify plaque prone regions. The present paper examines these indices in three aortic geometries obtained from patients whose aortas are deformed due to a genetic pathology and compared to one normal geometry. This patient group is known to be prone to aortic dissection and our study aims to identify early indicators that will enable timely intervention. Data obtained from cardiac magnetic resonance imaging is used to reconstruct the aortic arch. The local unsteady flow characteristics are calculated, fully resolving the flow field throughout the entire cardiac cycle. The Quemada model is applied to account for the non-Newtonian properties of blood, an empirical model valid for different red blood cell loading. The impact of the deformed aortic geometries is analyzed to identify flow patterns that could lead to arterial disease at certain locations.

  6. A method for measurement of turbulent wall shear stress

    NASA Astrophysics Data System (ADS)

    Wagner, Peter M.; Leehey, Patrick

    A cylinder is placed near the wall in the viscous sublayer of a turbulent boundary layer. It is suspended torsionally about its axis. The axis is parallel to the wall and transverse to the mean flow direction. The torque on the cylinder is proportional to the shear stress of the fluid on the wall below. In principle the torque is insensitive to the blockage effect of the cylinder. The device has been tested in a laminar shear flow created in a cone-and-plate apparatus. It shows a long range of linear response. There is no evidence of hysteresis upon flow reversal. Plans for dynamic testing in a turbulent oil channel flow and the applicability of micro-machining techniques from silicon technololgy to the further miniaturization of this gauge are discussed.

  7. Fluid shear stress stimulates phosphorylation-dependent nuclear export of HDAC5 and mediates expression of KLF2 and eNOS.

    PubMed

    Wang, Weiye; Ha, Chang Hoon; Jhun, Bong Sook; Wong, Chelsea; Jain, Mukesh K; Jin, Zheng-Gen

    2010-04-08

    Fluid shear stress generated by steady laminar blood flow protects vessels from atherosclerosis. Krüppel-like factor 2 (KLF2) and endothelial nitric oxide synthase (eNOS) are fluid shear stress-responsive genes and key mediators in flow anti-inflammatory and antiatherosclerotic actions. However, the molecular mechanisms underlying flow induction of KLF2 and eNOS remain largely unknown. Here, we show a novel role of histone deacetylase 5 (HDAC5) in flow-mediated KLF2 and eNOS expression. We found for the first time that fluid shear stress stimulated HDAC5 phosphorylation and nuclear export in endothelial cells through a calcium/calmodulin-dependent pathway. Consequently, flow induced the dissociation of HDAC5 and myocyte enhancer factor-2 (MEF2) and enhanced MEF2 transcriptional activity, which leads to expression of KLF2 and eNOS. Adenoviral overexpression of a HDAC5 phosphorylation-defective mutant (Ser259/Ser498 were replaced by Ala259/Ala498, HDAC5-S/A), which shows resistance to flow-induced nuclear export, suppressed flow-mediated MEF2 transcriptional activity and expression of KLF2 and eNOS. Importantly, HDAC5-S/A attenuated the flow-inhibitory effect on monocyte adhesion to endothelial cells. Taken together, our results reveal that phosphorylation-dependent derepression of HDAC5 mediates flow-induced KLF2 and eNOS expression as well as flow anti-inflammation, and suggest that HDAC5 could be a potential therapeutic target for the prevention of atherosclerosis.

  8. Liposome clusters with shear stress-induced membrane permeability.

    PubMed

    Yoshimoto, Makoto; Tamura, Ryota; Natsume, Tomotaka

    2013-09-01

    Clusters of negatively charged liposomes were prepared by the addition of Ca(2+) and characterized in their structure and membrane permeability under shear stress. The liposomes mainly used were composed of zwitterionic 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), 20 mol% negatively charged 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoglycerol (POPG) and 30 mol% cholesterol. The liposomes with mean diameter of 193 nm were aggregated into the clusters with a distribution peak at about 1.5 μm in the 50mM Tris buffer solution of pH 8.5 at the lipid and Ca(2+) concentrations of 1.0mM and 40 mM, respectively. More than 90% of liposomes were redispersed at the Ca(2+) concentration of 80 mM. POPG-rich liposomes (POPC/POPG/cholesterol=5:65:30 [lipid]=1.0mM) were irreversibly aggregated at [Ca(2+)]≥ 10 mM, indicating the significant contribution of POPC to the reversible clustering of liposomes. The membranes of liposome clusters were impermeable to 5(6)-carboxyfluorescein (CF) in the static liquid system at 25°C due to the decrease in specific surface area of the liposomal system. In the shear flow, in clear contrast, continuous membrane permeation of CF was observed at the shear rate of 1.5 × 10(3)s(-1), exhibiting comparable membrane permeability to the non-clustered liposomes. The theoretical analysis of modified DLVO potential indicated that liposome membranes were not in contact with each other within the clusters. Therefore, the liposome clusters are structurally flexible under the applied shear stress, providing sufficient lipid membrane-water interfacial area for the permeation of CF. The results obtained would be important to control the formation of liposome clusters and their permeabilization for biochemical and biomedical applications.

  9. The release of shear stress in metals under dynamic loading

    NASA Astrophysics Data System (ADS)

    Vignjevic, Rade; Bourne, Neil

    2013-06-01

    Metals under shock loading relieve shear stress by slip after. This work focuses on the types of loading where a metal initially responds entirely elastically and plasticity with deformation mechanisms developing over time and determined by the material's state and microstructure. Finite kinetics in shock is mirrored in several commonly observed responses including elastic precursor decay and the measurement of shear stress histories during load. FCC and BCC metals have different kinetics, with those of BCC metals slower. A model, under development, is implemented here to depict the behaviour observed by assigning a finite time to the return of the state point from the quasi equilibrium yield surface to the equilibrium yield surface. This delays the softening of the material and reproduces observed response in the weak shock regime. The model is based on the assumption that formation and self-organisation of dislocation structures at various scales maximises dissipation rate (minimize the free energy) in the material. Initial validation of the model is performed on tantalum by comparing stress histories under shock and shock-less loading with experimental data in order to assess its ability to reproduce experimentally observed features.

  10. Shear stress activation of nuclear receptor PXR in endothelial detoxification

    PubMed Central

    Wang, Xiaohong; Fang, Xi; Zhou, Jing; Chen, Zhen; Zhao, Beilei; Xiao, Lei; Liu, Ao; Li, Yi-Shuan J.; Shyy, John Y.-J.; Guan, Youfei; Chien, Shu; Wang, Nanping

    2013-01-01

    Endothelial cells (ECs) are constantly exposed to xenobiotics and endobiotics or their metabolites, which perturb EC function, as well as to shear stress, which plays a crucial role in vascular homeostasis. Pregnane X receptor (PXR) is a nuclear receptor and a key regulator of the detoxification of xeno- and endobiotics. Here we show that laminar shear stress (LSS), the atheroprotective flow, activates PXR in ECs, whereas oscillatory shear stress, the atheroprone flow, suppresses PXR. LSS activation of PXR in cultured ECs led to the increased expression of a PXR target gene, multidrug resistance 1 (MDR1). An in vivo study using rats showed that the expression of MDR1 was significantly higher in the endothelium from the descending thoracic aorta, where flow is mostly laminar, than from the inner curvature of aortic arch, where flow is disturbed. Functionally, LSS-activated PXR protects ECs from apoptosis triggered by doxorubicin via the induction of MDR1 and other detoxification genes. PXR also suppressed the expression of proinflammatory adhesion molecules and monocyte adhesion in response to TNF-α and lipopolysaccharide. Overexpression of a constitutively active PXR in rat carotid arteries potently attenuated proinflammatory responses. In addition, cDNA microarray revealed a large number of the PXR-activated endothelial genes whose products are responsible for major steps of detoxification, including phase I and II metabolizing enzymes and transporters. These detoxification genes in ECs are induced by LSS in ECs in a PXR-dependent manner. In conclusion, our results indicate that PXR represents a flow-activated detoxification system to protect ECs against damage by xeno- and endobiotics. PMID:23878263

  11. High-speed high-stress ring shear tests on granular sods and clayey soils

    Treesearch

    Hiroshi Fukuoka; Kyoji Sassa

    1991-01-01

    The purposes of this study is to obtain exact knowledge of the influences on friction angle during shear by shearing speeds. Ring shear tests on sandy and clayey materials have been carried out with a newly developed High-speed High-Stress Ring Shear Apparatus to examine if there are some changes in the frictional behaviors of these materials at high shearing speeds of...

  12. Pulsatile Versus Oscillatory Shear Stress Regulates NADPH Oxidase Subunit Expression

    PubMed Central

    Hwang, Juliana; Ing, Michael H.; Salazar, Adler; Lassègue, Bernard; Griendling, Kathy; Navab, Mohamad; Sevanian, Alex; Hsiai, Tzung K.

    2015-01-01

    Shear stress regulates endothelial nitric oxide and superoxide (O2−·) production, implicating the role of NADPH oxidase activity. It is unknown whether shear stress regulates the sources of reactive species production, consequent low-density lipoprotein (LDL) modification, and initiation of inflammatory events. Bovine aortic endothelial cells (BAECs) in the presence of 50 μg/mL of native LDL were exposed to (1) pulsatile flow with a mean shear stress (τave) of 25 dyne/cm2 and (2) oscillating flow at τave of 0. After 4 hours, aliquots of culture medium were collected for high-performance liquid chromatography analyses of electronegative LDL species, described as LDL− and LDL2−. In response to oscillatory shear stress, gp91phox mRNA expression was upregulated by 2.9±0.3-fold, and its homologue, Nox4, by 3.9±0.9-fold (P<0.05, n=4), with a corresponding increase in O2−· production rate. The proportion of LDL− and LDL2− relative to static conditions increased by 67±17% and 30±7%, respectively, with the concomitant upregulation of monocyte chemoattractant protein-1 expression and increase in monocyte/BAEC binding (P<0.05, n=5). In contrast, pulsatile flow downregulated both gp91phox and Nox4 mRNA expression (by 1.8±0.2-fold and 3.0±0.12-fold, respectively), with an accompanying reduction in O2−· production, reduction in the extent of LDL modification (51±12% for LDL− and 30±7% for LDL2−), and monocyte/BAEC binding. The flow-dependent LDL oxidation is determined in part by the NADPH oxidase activity. The formation of modified LDL via O2−· production may also affect the regulation of monocyte chemoattractant protein-1 expression and monocyte/BAEC binding. PMID:14593003

  13. Experimental Stress Analysis of Stiffened Cylinders with Cutouts : Shear Load

    NASA Technical Reports Server (NTRS)

    Rosecrans, Richard; Schlechte , Floyd R

    1954-01-01

    A cylindrical semimonocoque shell of circular cross section was mounted as a cantilever and loaded by a direct shear at the tip. The cylinder was tested with no cutout, with a rectangular cutout on the tension side, and with the cutout centered on the neutral axis on one side of the cylinder. The cutout was successively enlarged through six sizes varying from 30 degrees to 130 degrees in circumference and from 1 and 2 bays in length. Strain measurements were made with resistance-type wire strain gages near the cutout on the stringers, the skin, and the rings for each case, and the stresses obtained are presented in tables. (author)

  14. Interfacial shear stress in stratified flow in a horizontal rectangular duct

    SciTech Connect

    Lorencez, C.; Kawaji, M.; Murao, Y.

    1995-09-01

    Interfacial shear stress has been experimentally examined for both cocurrent and countercurrent stratified wavy flows in a horizontal interfacial shear stress from the measurements were examined and the results have been compared with existing correlations. Some differences were found in the estimated interfacial shear stress from the measurements were examined and the results have been compared with existing correlations. Some differences were found in the estimated interfacial shear stress values at high gas flow rates which could be attributed to the assumptions and procedures involved in each method. The interfacial waves and secondary motions were also found to have significant effects on the accuracy of Reynolds stress and turbulence kinetic energy extrapolation methods.

  15. On modeling the Reynolds stresses in turbulent shear flows

    NASA Astrophysics Data System (ADS)

    Knoell, Jens

    2000-11-01

    The issue of modeling various turbulent shear flows by virtue of Reynolds stress and related models is addressed on the basis of three interrelated methodologies. First, the idea of algebraic Reynolds stress models is utilized for wall-bounded flows. Second, a solution to the modeled Reynolds stress transport equation is presented for three-dimensional flows yielding a more complex model also valid for non-equilibrium flows. Third, the rapid pressure-strain correlation model as one of the crucial terms in full Reynolds stress closures is modeled for homogeneous and non-homogeneous flows. A nonlinear stress-strain model derived as an equilibrium solution to the modeled Reynolds stress transport equation is modified to account for the near-wall effects in wall-bounded turbulent shear flows. The results based on the new model are compared with numerical and experimental data for channel flows and boundary layers. To include non-equilibrium effects, a higher order model only neglecting turbulent transport effects is developed for three-dimensional flows utilizing the Cayley-Hamilton theorem. The solution is cast in terms of five tensors involving the strain and vorticity field and is valid for the whole range of turbulent time scales. The five coefficients multiplying the tensors are determined by a set of nonlinear first order differential equations. Numerical solutions for various homogeneous flow fields are compared with existing nonlinear stress-strain models. Furthermore, tensor representation theory is utilized for the quadratic expansion of the two-point velocity correlation tensor in terms of the Reynolds stress tensor and a separation vector. This model allows the analytical integration of the Poisson equation for the fluctuating pressure and leads to a model for the rapid part of the pressure-strain correlation. The new methodology is developed for homogeneous flow situations yielding pressure-strain coefficients solely based on numerical two

  16. A review of Reynolds stress models for turbulent shear flows

    NASA Technical Reports Server (NTRS)

    Speziale, Charles G.

    1995-01-01

    A detailed review of recent developments in Reynolds stress modeling for incompressible turbulent shear flows is provided. The mathematical foundations of both two-equation models and full second-order closures are explored in depth. It is shown how these models can be systematically derived for two-dimensional mean turbulent flows that are close to equilibrium. A variety of examples are provided to demonstrate how well properly calibrated versions of these models perform for such flows. However, substantial problems remain for the description of more complex turbulent flows where there are large departures from equilibrium. Recent efforts to extend Reynolds stress models to nonequilibrium turbulent flows are discussed briefly along with the major modeling issues relevant to practical naval hydrodynamics applications.

  17. Endovascular Treatment of Thoracic Aortic Dissection: Hemodynamic Shear Stress Study

    NASA Astrophysics Data System (ADS)

    Tang, Yik Sau; Lai, Siu Kai; Cheng, Stephen Wing Keung; Chow, Kwok Wing

    2012-11-01

    Thoracic Aortic Dissection (TAD), a life threatening cardiovascular disease, occurs when blood intrudes into the layers of the aortic wall, creating a new artificial channel (the false lumen) beside the original true lumen. The weakened false lumen wall may expand, enhancing the risk of rupture and resulting in high mortality. Endovascular treatment involves the deployment of a stent graft into the aorta, thus blocking blood from entering the false lumen. Due to the irregular geometry of the aorta, the stent graft, however, may fail to conform to the vessel curvature, and would create a ``bird-beak'' configuration, a wedge-shaped domain between the graft and the vessel wall. Computational fluid dynamics analysis is employed to study the hemodynamics of this pathological condition. With the `beaking' configuration, the local hemodynamic shear stress will drop below the threshold of safety reported earlier in the literature. The oscillating behavior of the shear stress might lead to local inflammation, atherosclerosis and other undesirable consequences. Supported by the Innovation and Technology Fund of the Hong Kong Government.

  18. Rennet-induced milk coagulation by continuous steady shear stress.

    PubMed

    Konuklar, Gül; Gunasekaran, Sundaram

    2002-06-01

    The effect of continuous steady shear stress (CSSS) on rennet-induced coagulation of milk was studied by measuring the change in viscosity of the system with time. Continuous shear stress (< or =0.5 Pa) applied during coagulation did not counteract the network formation at standard cheese-making conditions. In fact, CSSS of 0.2 Pa promoted coagulation by possibly increasing diffusion, collision, and hydrolization rates due to near-field, attractive hydrodynamic reactions. This was evidenced by the high viscosity of the resultant coagulum. However, the viscosity profile of the coagulum formed in the presence of CSSS followed the same trend as that formed in the absence of CSSS. Viscosity versus time profiles in both cases displayed an initial lag phase followed by a steady increase until a plateau value. The viscosity plateau reached under CSSS was marked with several sudden peaks, indicating the dynamic structure of the coagulum. These peaks in viscosity profiles began to appear after about 1380 s since rennet addition at standard cheese-making conditions. The time at which viscosity first exceeds 40 kPa s was verified to coincide with manual determination of the time at which the coagulum is cut (i.e., cutting time) during cheese making.

  19. Rapid flow-induced responses in endothelial cells

    NASA Technical Reports Server (NTRS)

    Stamatas, G. N.; McIntire, L. V.

    2001-01-01

    Endothelial cells alter their morphology, growth rate, and metabolism in response to fluid shear stress. To study rapid flow-induced responses in the 3D endothelial cell morphology and calcium distribution, coupled fluorescence microscopy with optical sectioning, digital imaging, and numerical deconvolution techniques have been utilized. Results demonstrate that within the first minutes of flow application nuclear calcium is increasing. In the same time frame whole cell height and nuclear height are reduced by about 1 microm. Whole cell height changes may facilitate reduction of shear stress gradients on the luminal surface, whereas nuclear structural changes may be important for modulating endothelial growth rate and metabolism. To study the role of the cytoskeleton in these responses, endothelial cells have been treated with specific disrupters (acrylamide, cytochalasin D, and colchicine) of each of the cytoskeleton elements (intermediate filaments, microfilaments, and microtubules, respectively). None of these compounds had any effect on the shear-induced calcium response. Cytochalasin D and acrylamide did not affect the shear-induced nuclear morphology changes. Colchicine, however, completely abrogated the response, indicating that microtubules may be implicated in force transmission from the plasma membrane to the nucleus. A pedagogical model based on tensegrity theory principles is presented that is consistent with the results on the 3D endothelial morphology.

  20. Rapid flow-induced responses in endothelial cells

    NASA Technical Reports Server (NTRS)

    Stamatas, G. N.; McIntire, L. V.

    2001-01-01

    Endothelial cells alter their morphology, growth rate, and metabolism in response to fluid shear stress. To study rapid flow-induced responses in the 3D endothelial cell morphology and calcium distribution, coupled fluorescence microscopy with optical sectioning, digital imaging, and numerical deconvolution techniques have been utilized. Results demonstrate that within the first minutes of flow application nuclear calcium is increasing. In the same time frame whole cell height and nuclear height are reduced by about 1 microm. Whole cell height changes may facilitate reduction of shear stress gradients on the luminal surface, whereas nuclear structural changes may be important for modulating endothelial growth rate and metabolism. To study the role of the cytoskeleton in these responses, endothelial cells have been treated with specific disrupters (acrylamide, cytochalasin D, and colchicine) of each of the cytoskeleton elements (intermediate filaments, microfilaments, and microtubules, respectively). None of these compounds had any effect on the shear-induced calcium response. Cytochalasin D and acrylamide did not affect the shear-induced nuclear morphology changes. Colchicine, however, completely abrogated the response, indicating that microtubules may be implicated in force transmission from the plasma membrane to the nucleus. A pedagogical model based on tensegrity theory principles is presented that is consistent with the results on the 3D endothelial morphology.

  1. Complete Release of Horizontal Shear Stresses During Geothermal Reservoir Stimulation

    NASA Astrophysics Data System (ADS)

    Schoenball, M.; Gaucher, E.; Wellmann, F.; Kohl, T.

    2013-12-01

    Seismicity can be induced in previously seismically inactive regions by man-made changes of the stress field. Notable stress perturbations are created by injection or withdrawal of fluids such as wastewater, fresh water or hydrocarbons. Over the last decades our knowledge of the physical processes of induced seismicity has improved largely. However, the driving force of seismicity, i.e. the actual perturbation of the stress field in the reservoir during fluid injection, remains largely unknown up to now. Measurements of fluid pressure at the well are not enough to extrapolate the pressure change in the reservoir. Here we study the evolution of the stress field during a massive hydraulic stimulation of a 5 km deep well at the enhanced geothermal system at Soultz-sous-Forêts, France. Fresh water was pumped with rates of 30 to 50 ls-1 for 6 days. Locations of 7215 events with maximum magnitude of MW=2.5 were obtained, for 715 events with MW > 1 focal mechanism solutions were derived. At first we present observations of several peculiar phenomena of the seismicity migration, of fluid flow and earthquake mechanisms following the shut-in of the well, which indicate to yet not understood hydro-mechanical coupling mechanisms in connection with shut-in. In order to analyze the changes of the stress field during and after the stimulation we identify the fracture planes from the two nodal planes by a probability-based method where we incorporate structural geological information gained from well logs and uncertainties of the determination of focal mechanism solutions and independent estimates of the stress field. In principle, this approach is able to incorporate further uncertainties, if available. We then conduct stress inversions resolved in time and depth to study spatio-temporal changes of the stress tensor. Our results show an increasingly perturbed stress state with time with a strong reduction of the horizontal shear stresses in areas of highest seismic activity

  2. Spatially resolved shear distribution in microfluidic chip for studying force transduction mechanisms in cells.

    PubMed

    Wang, Jianbin; Heo, Jinseok; Hua, Susan Z

    2010-01-21

    Fluid shear stress has profound effects on cell physiology. Here we present a versatile microfluidic method capable of generating variable magnitudes, gradients, and different modes of shear flow, to study sensory and force transduction mechanisms in cells. The chip allows cell culture under spatially resolved shear flow conditions as well as study of cell response to shear flow in real-time. Using this chip, we studied the effects of chronic shear stress on cellular functions of Madin-Darby Canine Kidney (MDCK), renal epithelial cells. We show that shear stress causes reorganization of actin cytoskeleton, which suppresses flow-induced Ca(2+) response.

  3. Viscosity, Shear Waves, and Atomic-Level Stress-Stress Correlations

    NASA Astrophysics Data System (ADS)

    Levashov, V. A.; Morris, J. R.; Egami, T.

    2011-03-01

    The Green-Kubo equation relates the macroscopic stress-stress correlation function to a liquid’s viscosity. The concept of the atomic-level stresses allows the macroscopic stress-stress correlation function in the equation to be expressed in terms of the space-time correlations among the atomic-level stresses. Molecular dynamics studies show surprisingly long spatial extension of stress-stress correlations and also longitudinal and transverse waves propagating in liquids over ranges which could exceed the system size. The results reveal that the range of propagation of shear waves corresponds to the range of distances relevant for viscosity. Thus our results show that viscosity is a fundamentally nonlocal quantity. We also show that the periodic boundary conditions play a nontrivial role in molecular dynamics simulations, effectively masking the long-range nature of viscosity.

  4. Viscosity, shear waves, and atomic-level stress-stress correlations.

    PubMed

    Levashov, V A; Morris, J R; Egami, T

    2011-03-18

    The Green-Kubo equation relates the macroscopic stress-stress correlation function to a liquid's viscosity. The concept of the atomic-level stresses allows the macroscopic stress-stress correlation function in the equation to be expressed in terms of the space-time correlations among the atomic-level stresses. Molecular dynamics studies show surprisingly long spatial extension of stress-stress correlations and also longitudinal and transverse waves propagating in liquids over ranges which could exceed the system size. The results reveal that the range of propagation of shear waves corresponds to the range of distances relevant for viscosity. Thus our results show that viscosity is a fundamentally nonlocal quantity. We also show that the periodic boundary conditions play a nontrivial role in molecular dynamics simulations, effectively masking the long-range nature of viscosity.

  5. A model for inter-laminar shear stress in laminated composites

    NASA Astrophysics Data System (ADS)

    Zaki, W.; Nguyen, V.; Umer, R.

    2017-02-01

    The paper presents an analytical model for the estimation of shear stress at the interface of adhesively bonded layers in laminated composites. For this purpose, a new shear stress function is proposed that accounts for the influence of shear lag in laminates assembled using adhesive layers of different types and thicknesses. In addition to the estimation of interfacial stress, the function can be used to determine the difference in normal strains and axial displacements in adjoining layers.

  6. Minimum shear stress range: a criterion for crack path determination

    NASA Astrophysics Data System (ADS)

    Pereira, K.; Abdel Wahab, M.

    2017-05-01

    For problems under proportional mixed-mode conditions, various criteria are used to predict fatigue crack growth directions, most achieving reasonable accuracy. The crack propagation angle is often obtained by maximizing a quantity (for instance, energy or stresses) as function of the stress intensity factors KI and KII. This maximization is generally performed at the instant of maximum fatigue loading and a stress analysis at this instant is sufficient to predict the crack propagation angle and thus the fatigue crack growth direction. However, under non-proportional loading, the maximum values of KI and KII may occur at different instants of the fatigue cycle and so a simple analysis at the maximum loading instant is not appropriate; it is necessary to consider the entire loading cycle history. One possible criterion to treat problems under these circumstances is the minimum shear stress range criterion (MSSR). This paper presents a brief discussion of the most common criteria used for determination of crack propagation direction, focusing on an implementation of MSSR. Its performance is assessed in different conditions and the results are compared to literature data.

  7. Sitting and endothelial dysfunction: The role of shear stress

    PubMed Central

    Thosar, Saurabh S.; Johnson, Blair D.; Johnston, Jeanne D.; Wallace, Janet P.

    2012-01-01

    Summary Sedentary activity is a modifiable life-style behavior and a key component in the etiology of atherosclerotic cardiovascular disease (ACVD). US adults and children spend more than half their waking time in sedentary pursuits. Sedentary activity has been shown to result in impaired insulin sensitivity, impaired metabolic function and attenuated endothelial function, which are classic markers of ACVD. Sedentary activity is defined as ‘sitting without otherwise being active.’ This behavior promotes reduced muscular activity of the lower extremities which decreases leg blood flow, increases blood pooling in the calf, augments mean arterial pressure, and deforms arterial segments resulting in low mean shear stress (SS). SS activates distinct physiological mechanisms which have been proposed to be protective against ACVD; specifically through a SS-induced endothelium-derived nitric oxide mechanism. Reduced bioavailability of nitric oxide creates a pro-oxidant milieu resulting in increased oxidative stress. There is sufficient evidence which demonstrates that endothelial function is attenuated in the presence of oxidative stress. Sedentary activity results in low SS in the lower extremities which may result in increased oxidative stress and impaired endothelial function. This review furthers the use of sitting as model to study the effects of inactivity, discusses possible physiological mechanisms and suggests future directions. PMID:23197245

  8. Role of glypican-1 in endothelial NOS activation under various steady shear stress magnitudes.

    PubMed

    Zeng, Ye; Liu, Jingxia

    2016-11-01

    Blood flow patterns in proatherogenic and antiatherogenic regions are rather different. We hypothesize that the laminar flow with steady shear stress increased nitric oxide (NO) bioavailability while disturbed flow with low shear stress reduced it, which is mediating by glypican-1. Thus, we detected the expression of glypican-1 under different shear stress magnitudes, and tested whether the magnitude of shear stress determines the level of endothelial NO synthase (eNOS) via glypican-1 by using phosphatidylinositol phospholipase C (PI-PLC). Results revealed that the expression of glypican-1 depends on the magnitude and duration of shear stress loading. Activation of eNOS in HUVECs is downregulated by 4dyn/cm(2) of shear stress, but is upregulated by 15dyn/cm(2). Removal of glypican-1 significantly suppressed the 15dyn/cm(2) shear stress-induced eNOS activity, and further reduced the 4dyn/cm(2)-inhibited eNOS activity. Therefore, eNOS activation depends on shear stress magnitudes and is mediated by glypican-1. The role of glypican-1 in mediating the eNOS activation under shear stress might involve in protecting the endothelial function against disturbed flow and enhancing the sensitive of the endothelial cell to laminar flow, supporting a potential role of glypican-1 against atherosclerosis.

  9. A Single Parameter to Characterize Wall Shear Stress Developed from an Underexpanded Axisymmetric Impinging Jet

    NASA Astrophysics Data System (ADS)

    Fillingham, Patrick; Murali, Harikrishnan

    2016-11-01

    Wall shear stress is characterized for underexpanded axisymmetric impinging jets for the application of aerodynamic particle resuspension from a surface. Analysis of the flow field and the wall shear stress resulted from normally impinging axisymmetric jets is conducted using Computational Fluid Dynamics. A normally impinging jet is modeled with a constant area nozzle, while varying height to diameter ratio (H/D) and inlet pressures. Schlieren photography is used to visualize the density gradient of the flow field for validation of the CFD. The Dimensionless Jet Parameter (DJP) is developed to describe flow regimes and characterize the shear stress. The DJP is defined as being proportional to the jet pressure ratio divided by the H/D ratio squared. Maximum wall shear stress is examined as a function of DJP with three distinct regimes: (i) subsonic impingement (DJP<1), (ii) transitional (12). Due to the jet energy dissipation in shock structures, which become a dominant dissipation mechanism in the supersonic impingement regime, wall shear stress is limited to a finite value. Additionally, formation of shock structures in the wall flow were observed for DJP>2 resulting in difficulties with dimensionless analysis. In the subsonic impingement and transitional regimes equations as a function of the DJP are obtained for the maximum wall shear stress magnitude, maximum shear stress location, and shear stress decay. Using these relationships wall shear stress can be predicted at all locations along the impingement surface.

  10. Cell-free layer and wall shear stress variation in microvessels.

    PubMed

    Yin, Xuewen; Zhang, Junfeng

    2012-01-01

    In this study, we simulated multiple red blood cells flowing through straight microvessels with the immersed-boundary lattice-Boltzmann model to examine the shear stress variation on the microvessel surface and its relation to the properties of cell-free layer. Significant variation in shear stress has been observed due to the irregular configuration of blood cells flowing near the microvessel wall. A low shear stress is typically found at locations where there is a cell flowing close to the wall, and a large shear stress at locations with a relatively wide gap between cell and wall. This relationship between the shear stress magnitude and the distance between cell and wall has been attributed to the reverse pressure difference developed between the front and rear sides of a cell flowing near the vessel wall. We further studied the effects of several hemodynamic factors on the variation of shear stress, including the cell deformability, the flow rate, and the aggregation among red blood cells. These simulations show that the shear stress variation is less profound in situations with wider cell-free layers, since the reverse pressure difference around the edge cells is less evident, and the influence of this pressure difference on wall shear stress becomes weaker. This study also demonstrates the complexity of the flow field in the gap between cell and wall. More precise experimental techniques are required accurately measure such shear stress variation in microcirculation.

  11. High Shear Stresses under Exercise Condition Destroy Circulating Tumor Cells in a Microfluidic System

    PubMed Central

    Regmi, Sagar; Fu, Afu; Luo, Kathy Qian

    2017-01-01

    Circulating tumor cells (CTCs) are the primary targets of cancer treatment as they cause distal metastasis. However, how CTCs response to exercise-induced high shear stress is largely unknown. To study the effects of hemodynamic microenvironment on CTCs, we designed a microfluidic circulatory system that produces exercise relevant shear stresses. We explore the effects of shear stresses on breast cancer cells with different metastatic abilities, cancer cells of ovarian, lung and leukemic origin. Three major findings were obtained. 1) High shear stress of 60 dynes/cm2 achievable during intensive exercise killed more CTCs than low shear stress of 15 dynes/cm2 present in human arteries at the resting state. 2) High shear stress caused necrosis in over 90% of CTCs within the first 4 h of circulation. More importantly, the CTCs that survived the first 4 h-circulation, underwent apoptosis during 16–24 h of post-circulation incubation. 3) Prolonged high shear stress treatment effectively reduced the viability of highly metastatic and drug resistant breast cancer cells. As high shear stress had much less damaging effects on leukemic cells mimicking the white blood cells, we propose that intensive exercise may be a good strategy for generating high shear stress that can destroy CTCs and prevent cancer metastasis. PMID:28054593

  12. Coupling between basal shear stresses and internal stresses plays a crucial role in granular avalanches

    NASA Astrophysics Data System (ADS)

    Denlinger, R. P.; Iverson, R. M.

    2004-12-01

    Models of granular avalanches commonly assume that basal shear stresses obey some type of friction rule (for example, the Coulomb rule), but that internal stresses are the same as those in an ideal, frictionless fluid. These assumptions lead to depth-integrated momentum-conservation equations that are essentially identical to those of standard shallow-water theory. Although the simplicity of these equations is appealing, omission of internal friction is inconsistent with the persistent contact between solid fragments and with measurements of laboratory avalanches that cross rugged, irregular, three-dimensional terrain (e.g., Iverson et al., JGR 109, 2004, doi:10.1029/2003JF000084). These inconsistencies have little consequence if avalanches traverse only planar or nearly planar terrain, because such terrain does not produce strong variations in accelerations and accompanying reaction forces. Moreover, effects of the inconsistencies can be camouflaged if an avalanche model is tuned to fit the observed distribution of an avalanche deposit, rather than tested against detailed experimental data. We demonstrate the importance of internal friction in granular avalanches by comparing experimental data to model predictions that assume Coloumb friction governs basal shear stresses, but with internal deviatoric stresses that are either absent or governed by the Coulomb rule. We also demonstrate how local accelerations produced by deflection of avalanches by rugged topography produces strong variations in both basal shear stresses and internal stresses. Forces produced by basal shear stress are coupled to forces generated by internal friction, and this coupling determines the way the flow interacts with terrain. The clear importance of internal stresses indicates that models that neglect them do not offer a sound basis for interpreting avalanche deposits or for forecasting the behavior of future avalanches in the process of hazards evaluation.

  13. Healing and Shear Stress Reduction on Single Fracture of Rock Salt and Limestone under Slide-Hold-Slide Direct Shear Condition

    NASA Astrophysics Data System (ADS)

    Kishida, K.; Yano, T.; Yasuhara, H.

    2012-12-01

    In order to clarify the influence of the holding state on the shear strength in the shear process of a single rock fracture, slide-hold-slide (SHS) direct shear-flow coupling tests were carried out on single rock fractures at several confining stresses and under saturated/unsaturated conditions (Kishida, et al., 2011). Consequently, the mortar specimen could be confirmed as the significant shear strength recovery on the SHS process. In this research, the SHS direct shear tests are carried out on the halite (rock salt) and the limestone. In the case of rock salt, a single tensile fracture is artificially created by cutting away. On the other hand, the limestone has a natural rock joint. The experiments are carried out under various normal confining stress conditions and are employed various holding period at the residual state. Figure 1 shows the shear stress - shear displacement of the SHS direct shear experiments on the rock salt. From all cases, the shear stress increases at the initial phase of the experiments, and then, the shear stress reaches at the peak shear strength. After that, the shear stress slightly decreases such as strain softening. Finally, the shear stress reaches to the residual stress state. In every SHS processes, the shear stress is reducing in various hold period. And then, the shear stress is increasing in the process of re-sliding. The shear stress in the process of re-sliding takes over the value at the start time of the holding process. The shear stress reaches at the peak, and then, it reaches the residual stress state. In all cases, as the holding period becomes longer, it is confirmed that the decrement of the shear stress in the holding process is increasing and the increment of the shear stress at the re-sliding process is increasing. Therefore, it is confirmed that the time dependence of shear strength recovery can be observed. In addition, Dieterich's A constant value for the regression lines (Dieterich, 1972, 1994) is plotted

  14. Analysis of bonded joints. [shear stress and stress-strain diagrams

    NASA Technical Reports Server (NTRS)

    Srinivas, S.

    1975-01-01

    A refined elastic analysis of bonded joints which accounts for transverse shear deformation and transverse normal stress was developed to obtain the stresses and displacements in the adherends and in the bond. The displacements were expanded in terms of polynomials in the thicknesswise coordinate; the coefficients of these polynomials were functions of the axial coordinate. The stress distribution was obtained in terms of these coefficients by using strain-displacement and stress-strain relations. The governing differential equations were obtained by integrating the equations of equilibrium, and were solved. The boundary conditions (interface or support) were satisfied to complete the analysis. Single-lap, flush, and double-lap joints were analyzed, along with the effects of adhesive properties, plate thicknesses, material properties, and plate taper on maximum peel and shear stresses in the bond. The results obtained by using the thin-beam analysis available in the literature were compared with the results obtained by using the refined analysis. In general, thin-beam analysis yielded reasonably accurate results, but in certain cases the errors were high. Numerical investigations showed that the maximum peel and shear stresses in the bond can be reduced by (1) using a combination of flexible and stiff bonds, (2) using stiffer lap plates, and (3) tapering the plates.

  15. Shear Stress-Normal Stress (Pressure) Ratio Decides Forming Callus in Patients with Diabetic Neuropathy

    PubMed Central

    Noguchi, Hiroshi; Takehara, Kimie; Ohashi, Yumiko; Suzuki, Ryo; Yamauchi, Toshimasa; Kadowaki, Takashi; Sanada, Hiromi

    2016-01-01

    Aim. Callus is a risk factor, leading to severe diabetic foot ulcer; thus, prevention of callus formation is important. However, normal stress (pressure) and shear stress associated with callus have not been clarified. Additionally, as new valuables, a shear stress-normal stress (pressure) ratio (SPR) was examined. The purpose was to clarify the external force associated with callus formation in patients with diabetic neuropathy. Methods. The external force of the 1st, 2nd, and 5th metatarsal head (MTH) as callus predilection regions was measured. The SPR was calculated by dividing shear stress by normal stress (pressure), concretely, peak values (SPR-p) and time integral values (SPR-i). The optimal cut-off point was determined. Results. Callus formation region of the 1st and 2nd MTH had high SPR-i rather than noncallus formation region. The cut-off value of the 1st MTH was 0.60 and the 2nd MTH was 0.50. For the 5th MTH, variables pertaining to the external forces could not be determined to be indicators of callus formation because of low accuracy. Conclusions. The callus formation cut-off values of the 1st and 2nd MTH were clarified. In the future, it will be necessary to confirm the effect of using appropriate footwear and gait training on lowering SPR-i. PMID:28050567

  16. Shear Stress-Normal Stress (Pressure) Ratio Decides Forming Callus in Patients with Diabetic Neuropathy.

    PubMed

    Amemiya, Ayumi; Noguchi, Hiroshi; Oe, Makoto; Takehara, Kimie; Ohashi, Yumiko; Suzuki, Ryo; Yamauchi, Toshimasa; Kadowaki, Takashi; Sanada, Hiromi; Mori, Taketoshi

    2016-01-01

    Aim. Callus is a risk factor, leading to severe diabetic foot ulcer; thus, prevention of callus formation is important. However, normal stress (pressure) and shear stress associated with callus have not been clarified. Additionally, as new valuables, a shear stress-normal stress (pressure) ratio (SPR) was examined. The purpose was to clarify the external force associated with callus formation in patients with diabetic neuropathy. Methods. The external force of the 1st, 2nd, and 5th metatarsal head (MTH) as callus predilection regions was measured. The SPR was calculated by dividing shear stress by normal stress (pressure), concretely, peak values (SPR-p) and time integral values (SPR-i). The optimal cut-off point was determined. Results. Callus formation region of the 1st and 2nd MTH had high SPR-i rather than noncallus formation region. The cut-off value of the 1st MTH was 0.60 and the 2nd MTH was 0.50. For the 5th MTH, variables pertaining to the external forces could not be determined to be indicators of callus formation because of low accuracy. Conclusions. The callus formation cut-off values of the 1st and 2nd MTH were clarified. In the future, it will be necessary to confirm the effect of using appropriate footwear and gait training on lowering SPR-i.

  17. Partial ligation-induced carotid artery occlusion induces leukocyte recruitment and lipid accumulation--a shear stress model of atherosclerosis.

    PubMed

    Merino, Hilda; Parthasarathy, Sampath; Singla, Dinender K

    2013-01-01

    Recent studies suggest that disturbed blood flow-induced shear stress can induce atherosclerosis (ATH) in humans and animals without a high fat diet. Therefore, we hypothesize that partial ligation of the left carotid artery can generate disturbed blood flow and shear stress and would lead to ATH in a predisposed genetic model of Apo E(-/-) mice. The partial left carotid artery model was generated by ligating three out of four branches of the left carotid artery compared with controls which experienced similar surgery conditions but no ligation. Animals were sacrificed 2 weeks post-ligation and examined for plaque formation, infiltration of leukocytes, pro-inflammatory immune response, and blood flow velocity. Our findings suggest a significant (p < 0.05) increase in plaque formation and lipid deposition in the partial ligated animals compared with controls, confirmed with hematoxylin and eosin and oil red O staining. Furthermore, there was a significant (p < 0.05) increase in the number of M1 macrophages and release of pro-inflammatory cytokines, IL-6 and TNFα, as compared with the control. Moreover, partial ligated carotid arteries demonstrated disturbed blood flow as their systolic velocity was significantly reduced. In conclusion, our data suggest that partial ligation of the left carotid artery induces disturbed flow and shear stress in the predisposed genetic model of Apo E(-/-) mice and leads to significantly developed ATH. Similarities to clinical patients who develop ATH independent of a high fat diet show that this could be a potential animal model to examine various parameters in ATH.

  18. Interlaminar shear stress effects on the postbuckling response of graphite-epoxy panels

    NASA Technical Reports Server (NTRS)

    Engelstad, S. P.; Knight, N. F., Jr.; Reddy, J. N.

    1990-01-01

    The influence of shear flexibility on overall postbuckling response was assessed, and transverse shear stress distributions in relation to panel failure were examined. Nonlinear postbuckling results are obtained for finite element models based on classical laminated plate theory and first-order shear deformation theory. Good correlation between test and analysis is obtained. The results presented analytically substantiate the experimentally observed failure mode.

  19. Duration of exposure to high fluid shear stress is critical in shear-induced platelet activation-aggregation.

    PubMed

    Zhang, Jian-ning; Bergeron, Angela L; Yu, Qinghua; Sun, Carol; McBride, Latresha; Bray, Paul F; Dong, Jing-fei

    2003-10-01

    Platelet functions are increasingly measured under flow conditions to account for blood hydrodynamic effects. Typically, these studies involve exposing platelets to high shear stress for periods significantly longer than would occur in vivo. In the current study, we demonstrate that the platelet response to high shear depends on the duration of shear exposure. In response to a 100 dyn/cm2 shear stress for periods less than 10-20 sec, platelets in PRP or washed platelets were aggregated, but minimally activated as demonstrated by P-selectin expression and binding of the activation-dependent alphaIIbbeta3 antibody PAC-1 to sheared platelets. Furthermore, platelet aggregation under such short pulses of high shear was subjected to rapid disaggregation. The disaggregated platelets could be re-aggregated by ADP in a pattern similar to unsheared platelets. In comparison, platelets that are exposed to high shear for longer than 20 sec are activated and aggregated irreversibly. In contrast, platelet activation and aggregation were significantly greater in whole blood with significantly less disaggregation. The enhancement is likely via increased collision frequency of platelet-platelet interaction and duration of platelet-platelet association due to high cell density. It may also be attributed to the ADP release from other cells such as red blood cells because increased platelet aggregation in whole blood was partially inhibited by ADP blockage. These studies demonstrate that platelets have a higher threshold for shear stress than previously believed. In a pathologically relevant timeframe, high shear alone is likely to be insufficient in inducing platelet activation and aggregation, but acts synergistically with other stimuli.

  20. Shear stress reduces protease activated receptor-1 expression in human endothelial cells

    NASA Technical Reports Server (NTRS)

    Nguyen, K. T.; Eskin, S. G.; Patterson, C.; Runge, M. S.; McIntire, L. V.

    2001-01-01

    Shear stress has been shown to regulate several genes involved in the thrombotic and proliferative functions of endothelial cells. Thrombin receptor (protease-activated receptor-1: PAR-1) increases at sites of vascular injury, which suggests an important role for PAR-1 in vascular diseases. However, the effect of shear stress on PAR-1 expression has not been previously studied. This work investigates effects of shear stress on PAR-1 gene expression in both human umbilical vein endothelial cells (HUVECs) and microvascular endothelial cells (HMECs). Cells were exposed to different shear stresses using a parallel plate flow system. Northern blot and flow cytometry analysis showed that shear stress down-regulated PAR-1 messenger RNA (mRNA) and protein levels in both HUVECs and HMECs but with different thresholds. Furthermore, shear-reduced PAR-1 mRNA was due to a decrease of transcription rate, not increased mRNA degradation. Postshear stress release of endothelin-1 in response to thrombin was reduced in HUVECs and HMECs. Moreover, inhibitors of potential signaling pathways applied during shear stress indicated mediation of the shear-decreased PAR-1 expression by protein kinases. In conclusion, shear stress exposure reduces PAR-1 gene expression in HMECs and HUVECs through a mechanism dependent in part on protein kinases, leading to altered endothelial cell functional responses to thrombin.

  1. Shear stress reduces protease activated receptor-1 expression in human endothelial cells

    NASA Technical Reports Server (NTRS)

    Nguyen, K. T.; Eskin, S. G.; Patterson, C.; Runge, M. S.; McIntire, L. V.

    2001-01-01

    Shear stress has been shown to regulate several genes involved in the thrombotic and proliferative functions of endothelial cells. Thrombin receptor (protease-activated receptor-1: PAR-1) increases at sites of vascular injury, which suggests an important role for PAR-1 in vascular diseases. However, the effect of shear stress on PAR-1 expression has not been previously studied. This work investigates effects of shear stress on PAR-1 gene expression in both human umbilical vein endothelial cells (HUVECs) and microvascular endothelial cells (HMECs). Cells were exposed to different shear stresses using a parallel plate flow system. Northern blot and flow cytometry analysis showed that shear stress down-regulated PAR-1 messenger RNA (mRNA) and protein levels in both HUVECs and HMECs but with different thresholds. Furthermore, shear-reduced PAR-1 mRNA was due to a decrease of transcription rate, not increased mRNA degradation. Postshear stress release of endothelin-1 in response to thrombin was reduced in HUVECs and HMECs. Moreover, inhibitors of potential signaling pathways applied during shear stress indicated mediation of the shear-decreased PAR-1 expression by protein kinases. In conclusion, shear stress exposure reduces PAR-1 gene expression in HMECs and HUVECs through a mechanism dependent in part on protein kinases, leading to altered endothelial cell functional responses to thrombin.

  2. Impact of bifurcation dual stenting on endothelial shear stress

    PubMed Central

    Chen, Henry Y.; Koo, Bon-Kwon

    2015-01-01

    Despite advances in percutaneous coronary interventions and the introduction of drug eluding stents, in-stent restenosis and stent thrombosis remain a clinically significant problem for bifurcations. The aim of this study is to determine the effect of dual bifurcation stenting on hemodynamic parameters known to influence restenosis and thrombosis. We hypothesized that double stenting, especially with a longer side branch (SB) stent, likely has a negative effect on wall shear stress (WSS), WSS gradient (WSSG), and oscillatory shear index (OSI). To test this hypothesis, we developed computational models of dual stents at bifurcations and non-Newtonian blood simulations. The models were then interfaced, meshed, and solved in a validated finite-element package. Longer and shorter stents at the SB and provisional stenting were compared. It was found that stents placed in the SB at a bifurcation lowered WSS, but elevated WSSG and OSI. Dual stenting with longer SB stent had the most adverse impact on SB endothelial WSS, WSSG, and OSI, with low WSS region up to 50% more than the case with shorter SB stent. The simulations also demonstrated flow disturbances resulting from SB stent struts protruding into the main flow field near the carina, which may have implications on stent thrombosis. The simulations predict a negative hemodynamic role for SB stenting, which is exaggerated with a longer stent, consistent with clinical trial findings that dual-stenting is comparable or inferior to provisional stenting. PMID:26183473

  3. Flow Instability and Wall Shear Stress Ocillation in Intracranial Aneurysms

    NASA Astrophysics Data System (ADS)

    Baek, Hyoungsu; Jayamaran, Mahesh; Richardson, Peter; Karniadakis, George

    2009-11-01

    We investigate the flow dynamics and oscillatory behavior of wall shear stress (WSS) vectors in intracranial aneurysms using high-order spectral/hp simulations. We analyze four patient- specific internal carotid arteries laden with aneurysms of different characteristics : a wide-necked saccular aneurysm, a hemisphere-shaped aneurysm, a narrower-necked saccular aneurysm, and a case with two adjacent saccular aneurysms. Simulations show that the pulsatile flow in aneurysms may be subject to a hydrodynamic instability during the decelerating systolic phase resulting in a high-frequency oscillation in the range of 30-50 Hz. When the aneurysmal flow becomes unstable, both the magnitude and the directions of WSS vectors fluctuate. In particular, the WSS vectors around the flow impingement region exhibit significant spatial and temporal changes in direction as well as in magnitude.

  4. Wrinkling Phenomena of Thin Flat Plates Subjected to Shear Stresses

    NASA Technical Reports Server (NTRS)

    Bollenrath, F

    1931-01-01

    This report covers a series of tests on thin flat elastic strips restrained at two parallel edges and subjected to shear by conversely directed stresses. Theoretical treatments, particularly those of Lilly, Southwell and Skan, and Timoshenko are briefly outlined. The problem to be solved by these tests was to find out whether, and to what extent the conditions and assumptions upon which the calculations are based are complied with in the tests. Three materials were used: celluloid, duralumin, brass. Owing to the high elastic deformability of celluloid, it was not only possible to observe the beginning but also to ascertain the type of deflection. The test data on celluloid was affirmed by the experiments with duralumin and brass.

  5. Endothelial fluid shear stress sensing in vascular health and disease

    PubMed Central

    Baeyens, Nicolas; Bandyopadhyay, Chirosree; Coon, Brian G.; Yun, Sanguk; Schwartz, Martin A.

    2016-01-01

    Endothelial cells transduce the frictional force from blood flow (fluid shear stress) into biochemical signals that regulate gene expression and cell behavior via specialized mechanisms and pathways. These pathways shape the vascular system during development and during postnatal and adult life to optimize flow to tissues. The same pathways also contribute to atherosclerosis and vascular malformations. This Review covers recent advances in basic mechanisms of flow signaling and the involvement of these mechanisms in vascular physiology, remodeling, and these diseases. We propose that flow sensing pathways that govern normal morphogenesis can contribute to disease under pathological conditions or can be altered to induce disease. Viewing atherosclerosis and vascular malformations as instances of pathological morphogenesis provides a unifying perspective that may aid in developing new therapies. PMID:26928035

  6. Understanding the fluid mechanics behind transverse wall shear stress.

    PubMed

    Mohamied, Yumnah; Sherwin, Spencer J; Weinberg, Peter D

    2017-01-04

    The patchy distribution of atherosclerosis within arteries is widely attributed to local variation in haemodynamic wall shear stress (WSS). A recently-introduced metric, the transverse wall shear stress (transWSS), which is the average over the cardiac cycle of WSS components perpendicular to the temporal mean WSS vector, correlates particularly well with the pattern of lesions around aortic branch ostia. Here we use numerical methods to investigate the nature of the arterial flows captured by transWSS and the sensitivity of transWSS to inflow waveform and aortic geometry. TransWSS developed chiefly in the acceleration, peak systolic and deceleration phases of the cardiac cycle; the reverse flow phase was too short, and WSS in diastole was too low, for these periods to have a significant influence. Most of the spatial variation in transWSS arose from variation in the angle by which instantaneous WSS vectors deviated from the mean WSS vector rather than from variation in the magnitude of the vectors. The pattern of transWSS was insensitive to inflow waveform; only unphysiologically high Womersley numbers produced substantial changes. However, transWSS was sensitive to changes in geometry. The curvature of the arch and proximal descending aorta were responsible for the principal features, the non-planar nature of the aorta produced asymmetries in the location and position of streaks of high transWSS, and taper determined the persistence of the streaks down the aorta. These results reflect the importance of the fluctuating strength of Dean vortices in generating transWSS.

  7. Endothelial cation channel PIEZO1 controls blood pressure by mediating flow-induced ATP release

    PubMed Central

    Wang, ShengPeng; Chennupati, Ramesh; Kaur, Harmandeep; Iring, Andras; Wettschureck, Nina

    2016-01-01

    Arterial blood pressure is controlled by vasodilatory factors such as nitric oxide (NO) that are released from the endothelium under the influence of fluid shear stress exerted by flowing blood. Flow-induced endothelial release of ATP and subsequent activation of Gq/G11–coupled purinergic P2Y2 receptors have been shown to mediate fluid shear stress–induced stimulation of NO formation. However, the mechanism by which fluid shear stress initiates these processes is unclear. Here, we have shown that the endothelial mechanosensitive cation channel PIEZO1 is required for flow-induced ATP release and subsequent P2Y2/Gq/G11–mediated activation of downstream signaling that results in phosphorylation and activation of AKT and endothelial NOS. We also demonstrated that PIEZO1-dependent ATP release is mediated in part by pannexin channels. The PIEZO1 activator Yoda1 mimicked the effect of fluid shear stress on endothelial cells and induced vasorelaxation in a PIEZO1-dependent manner. Furthermore, mice with induced endothelium-specific PIEZO1 deficiency lost the ability to induce NO formation and vasodilation in response to flow and consequently developed hypertension. Together, our data demonstrate that PIEZO1 is required for the regulation of NO formation, vascular tone, and blood pressure. PMID:27797339

  8. Direct Shear Tests of Sandstone Under Constant Normal Tensile Stress Condition Using a Simple Auxiliary Device

    NASA Astrophysics Data System (ADS)

    Cen, Duofeng; Huang, Da

    2017-06-01

    Tension-shear failure is a typical failure mode in the rock masses in unloading zones induced by excavation or river incision, etc., such as in excavation-disturbed zone of deep underground caverns and superficial rocks of high steep slopes. However, almost all the current shear failure criteria for rock are usually derived on the basis of compression-shear failure. This paper proposes a simple device for use with a servo-controlled compression-shear testing machine to conduct the tension-shear tests of cuboid rock specimens, to test the direct shear behavior of sandstone under different constant normal tensile stress conditions ( σ = -1, -1.5, -2, -2.5 and -3 MPa) as well as the uniaxial tension behavior. Generally, the fracture surface roughness decreases and the proportion of comminution areas in fracture surface increases as the change of stress state from tension to tension-shear and to compression-shear. Stepped fracture is a primary fracture pattern in the tension-shear tests. The shear stiffness, shear deformation and normal deformation (except the normal deformation for σ = -1 MPa) decrease during shearing, while the total normal deformation containing the pre-shearing portion increases as the normal tensile stress level (| σ|) goes up. Shear strength is more sensitive to the normal tensile stress than to the normal compressive stress, and the power function failure criterion (or Mohr envelope form of Hoek-Brown criterion) is examined to be the optimal criterion for the tested sandstone in the full region of tested normal stress in this study.

  9. Predicting boundary shear stress and sediment transport over bed forms

    USGS Publications Warehouse

    McLean, S.R.; Wolfe, S.R.; Nelson, J.M.

    1999-01-01

    To estimate bed-load sediment transport rates in flows over bed forms such as ripples and dunes, spatially averaged velocity profiles are frequently used to predict mean boundary shear stress. However, such averaging obscures the complex, nonlinear interaction of wake decay, boundary-layer development, and topographically induced acceleration downstream of flow separation and often leads to inaccurate estimates of boundary stress, particularly skin friction, which is critically important in predicting bed-load transport rates. This paper presents an alternative methodology for predicting skin friction over 2D bed forms. The approach is based on combining the equations describing the mechanics of the internal boundary layer with semiempirical structure functions to predict the velocity at the crest of a bedform, where the flow is most similar to a uniform boundary layer. Significantly, the methodology is directed toward making specific predictions only at the bed-form crest, and as a result it avoids the difficulty and questionable validity of spatial averaging. The model provides an accurate estimate of the skin friction at the crest where transport rates are highest. Simple geometric constraints can be used to derive the mean transport rates as long as bed load is dominant.To estimate bed-load sediment transport rates in flows over bed forms such as ripples and dunes, spatially averaged velocity profiles are frequently used to predict mean boundary shear stress. However, such averaging obscures the complex, nonlinear interaction of wake decay, boundary-layer development, and topographically induced acceleration downstream of flow separation and often leads to inaccurate estimates of boundary stress, particularly skin friction, which is critically important in predicting bed-load transport rates. This paper presents an alternative methodology for predicting skin friction over 2D bed forms. The approach is based on combining the equations describing the mechanics of

  10. Surface temperatures and glassy state investigations in tribology, part 3. [limiting shear stress rheological model

    NASA Technical Reports Server (NTRS)

    Bair, S.; Winer, W. O.

    1980-01-01

    Research related to the development of the limiting shear stress rheological model is reported. Techniques were developed for subjecting lubricants to isothermal compression in order to obtain relevant determinations of the limiting shear stress and elastic shear modulus. The isothermal compression limiting shear stress was found to predict very well the maximum traction for a given lubricant. Small amounts of side slip and twist incorporated in the model were shown to have great influence on the rising portion of the traction curve at low slide-roll ratio. The shear rheological model was also applied to a Grubin-like elastohydrodynamic inlet analysis for predicting film thicknesses when employing the limiting shear stress model material behavior.

  11. Magnitude of shear stress on the San Andreas fault: Implications of a stress measurement profile at shallow depth

    USGS Publications Warehouse

    Zoback, M.D.; Roller, J.C.

    1979-01-01

    A profile of measurements of shear stress perpendicular to the San Andreas fault near Palmdale, California, shows a marked increase in stress with distance from the fault. The pattern suggests that shear stress on the fault increases slowly with depth and reaches a value on the order of the average stress released during earthquakes. This result has important implications for both long- and short-term prediction of large earthquakes. Copyright ?? 1979 AAAS.

  12. Shear stress measurements in copper, iron, and mild steel under shock loading conditions

    SciTech Connect

    Millett, J.C.; Bourne, N.K.; Rosenberg, Z.

    1997-03-01

    A series of experiments have been conducted on metals subjected to planar impact loading in which a biaxial stress state and a uniaxial strain state is induced. Longitudinal and transverse stresses have been measured in copper, iron, and mild steel, using manganin stress gauges. The results have been used to calculate shear stress from the difference between the stress components. Results indicate that copper displays an increase in shear stress with pressure, showing similar trends to other work. An increase in dislocation density has been suggested as a possible mechanism. Iron shows a constant shear stress with increasing pressure, again in accordance with other workers. Finally, mild steel has been observed to have a significant increase in shear stress with increasing pressure. The inclusion of a hard second phase in the microstructure is thought to produce a large amount of dislocation debris, again explaining the observed hardening. {copyright} {ital 1997 American Institute of Physics.}

  13. Low Shear Stress Attenuates COX-2 Expression Induced by Resistin in Human Osteoarthritic Chondrocytes.

    PubMed

    Su, Yu-Ping; Chen, Cheng-Nan; Chang, Hsin-I; Huang, Kuo-Chin; Cheng, Chin-Chang; Chiu, Fang-Yao; Lee, Ko-Chao; Lo, Chun-Min; Chang, Shun-Fu

    2017-06-01

    Low shear stress has been proposed to play a reparative role in modulating cartilage homeostasis. Recently, epidemiological studies have found a positive correlation between the resistin level in serum and synovial fluid and osteoarthritis (OA) severity in patients. However, the effect of moderate shear stress on the catabolic stimulation of resistin in OA chondrocytes remains unclear. Hence, this study was to investigate whether low shear stress could regulate resistin-induced catabolic cyclooxygenase (COX)-2 expression in human OA chondrocytes and the underlying mechanism. Human OA chondrocytes and SW1353 chondrosarcoma cells were used in this study. Two modes of low shear stress (2 dyn/cm(2) ), pre-shear and post-shear, were applied to the chondrocytes. A specific activator and siRNAs were used to investigate the mechanism of low shear stress-regulated COX-2 expression of resistin induction. We found that human OA chondrocytes exposed to different modes of low shear stress elicit an opposite effect on resistin-induced COX-2 expression: pre-shear for a short duration attenuates the resistin effect by inhibiting the transcription factor nuclear factor (NF)-κB-p65 subunit and the cAMP response element binding protein; however, post-shear over a longer duration enhances the resistin effect by activating only the NF-κB-p65 subunit. Moreover, our results demonstrated that the regulation of both shear modes in resistin-stimulated COX-2 expression occurs through increasing AMP-activated protein kinase activation and then sirtuin 1 expression. This study elucidates the detailed mechanism of low shear stress regulating the resistin-induced catabolic COX-2 expression and indicates a possible reparative role of moderate shear force in resistin-stimulated OA development. J. Cell. Physiol. 232: 1448-1457, 2017. © 2016 Wiley Periodicals, Inc. © 2016 Wiley Periodicals, Inc.

  14. Modeling aeolian sediment transport thresholds on physically rough Martian surfaces: A shear stress partitioning approach

    NASA Astrophysics Data System (ADS)

    Gillies, John A.; Nickling, William G.; King, James; Lancaster, Nicholas

    2010-09-01

    This paper explores the effect that large roughness elements (0.30 m × 0.26 m × 0.36 m) may have on entrainment of sediment by Martian winds using a shear stress partitioning approach based on a model developed by Raupach et al. (Raupach, M.R., Gillette, D.A., Leys, J.F., 1993. The effect of roughness elements on wind erosion threshold. Journal of Geophysical Research 98(D2), 3023-3029). This model predicts the shear stress partitioning ratio defined as the percent reduction in shear stress on the intervening surface between the roughness elements as compared to the surface in the absence of those elements. This ratio is based on knowledge of the geometric properties of the roughness elements, the characteristic drag coefficients of the elements and the surface, and the assumed effect these elements have on the spatial distribution of the mean and maximum shear stresses. On Mars, unlike on Earth, the shear stress partitioning caused by roughness can be non-linear in that the drag coefficients for the surface as well as for the roughness itself show Reynolds number dependencies for the reported range of Martian wind speeds. The shear stress partitioning model of Raupach et al. is used to evaluate how conditions of the Martian atmosphere will affect the threshold shear stress ratio for Martian surfaces over a range of values of roughness density. Using, as an example, a 125 µm diameter particle with an estimated threshold shear stress on Mars of ≈ 0.06 N m - 2 (shear velocity, u* ≈ 2 m s - 1 on a smooth surface), we evaluate the effect of roughness density on the threshold shear stress ratio for this diameter particle. In general, on Mars higher regional shear stresses are required to initiate particle entrainment for surfaces that have the same physical roughness as defined by the roughness density term ( λ) compared with terrestrial surfaces mainly because of the low Martian atmospheric density.

  15. Wall Shear Stress, Wall Pressure and Near Wall Velocity Field Relationships in a Whirling Annular Seal

    NASA Technical Reports Server (NTRS)

    Morrison, Gerald L.; Winslow, Robert B.; Thames, H. Davis, III

    1996-01-01

    The mean and phase averaged pressure and wall shear stress distributions were measured on the stator wall of a 50% eccentric annular seal which was whirling in a circular orbit at the same speed as the shaft rotation. The shear stresses were measured using flush mounted hot-film probes. Four different operating conditions were considered consisting of Reynolds numbers of 12,000 and 24,000 and Taylor numbers of 3,300 and 6,600. At each of the operating conditions the axial distribution (from Z/L = -0.2 to 1.2) of the mean pressure, shear stress magnitude, and shear stress direction on the stator wall were measured. Also measured were the phase averaged pressure and shear stress. These data were combined to calculate the force distributions along the seal length. Integration of the force distributions result in the net forces and moments generated by the pressure and shear stresses. The flow field inside the seal operating at a Reynolds number of 24,000 and a Taylor number of 6,600 has been measured using a 3-D laser Doppler anemometer system. Phase averaged wall pressure and wall shear stress are presented along with phase averaged mean velocity and turbulence kinetic energy distributions located 0.16c from the stator wall where c is the seal clearance. The relationships between the velocity, turbulence, wall pressure and wall shear stress are very complex and do not follow simple bulk flow predictions.

  16. Interfacial shear stress for smooth and wavy stratified flow in pipes

    SciTech Connect

    Kowalski, J.E.

    1985-01-01

    This paper describes an experimental study of interfacial shear stress for stratified gas-liquid flow in a 50.8 mm (2'') diameter horizontal pipe. The tests were carried out using air/water and freon gas/water flows at pressures 225 and 420 kPa. A new correlation is developed for the interfacial shear stress.

  17. Wall Shear Stress, Wall Pressure and Near Wall Velocity Field Relationships in a Whirling Annular Seal

    NASA Technical Reports Server (NTRS)

    Morrison, Gerald L.; Winslow, Robert B.; Thames, H. Davis, III

    1996-01-01

    The mean and phase averaged pressure and wall shear stress distributions were measured on the stator wall of a 50% eccentric annular seal which was whirling in a circular orbit at the same speed as the shaft rotation. The shear stresses were measured using flush mounted hot-film probes. Four different operating conditions were considered consisting of Reynolds numbers of 12,000 and 24,000 and Taylor numbers of 3,300 and 6,600. At each of the operating conditions the axial distribution (from Z/L = -0.2 to 1.2) of the mean pressure, shear stress magnitude, and shear stress direction on the stator wall were measured. Also measured were the phase averaged pressure and shear stress. These data were combined to calculate the force distributions along the seal length. Integration of the force distributions result in the net forces and moments generated by the pressure and shear stresses. The flow field inside the seal operating at a Reynolds number of 24,000 and a Taylor number of 6,600 has been measured using a 3-D laser Doppler anemometer system. Phase averaged wall pressure and wall shear stress are presented along with phase averaged mean velocity and turbulence kinetic energy distributions located 0.16c from the stator wall where c is the seal clearance. The relationships between the velocity, turbulence, wall pressure and wall shear stress are very complex and do not follow simple bulk flow predictions.

  18. Shear stress partitioning of overland flow on disturbed and undisturbed rangelands

    USDA-ARS?s Scientific Manuscript database

    Physically-based hillslope erosion models commonly estimate soil detachment and transport capacity based on overland flow shear stress applied to soil aggregates. However, vegetation and rock cover counteract the shear stress of overland flow where they occur. Accordingly, partitioning of total sh...

  19. Modeling changes in rill erodibility and critical shear stress on native surface roads

    Treesearch

    Randy B. Foltz; Hakjun Rhee; William J. Elliot

    2008-01-01

    This study investigated the effect of cumulative overland flow on rill erodibility and critical shear stress on native surface roads in central Idaho. Rill erodibility decreased exponentially with increasing cumulative overland flow depth; however, critical shear stress did not change. The study demonstrated that road erodibility on the studied road changes over the...

  20. Capillary tone: cyclooxygenase, shear stress, luminal glycocalyx, and hydraulic conductivity (Lp)

    PubMed Central

    Williams, Donna A; Flood, Mary H

    2015-01-01

    Control of capillary hydraulic conductivity (Lp) is the physiological mechanism that underpins systemic hydration. Capillaries form the largest surface of endothelial cells in any species with a cardiovascular system and all capillaries are exposed to the flow-induced force, shear stress (τ). Vasoactive molecules such as prostacyclin (cyclooxygenase product, COX) are released from endothelial cells in response to τ. Little is known about how COX activity impacts capillary Lp. The purpose here was to assess Lp in situ following an acute Δτ stimulus and during COX1/COX2 inhibition. Mesenteric true capillaries (TC) of Rana pipiens (pithed) were cannulated for Lp assessment using the modified Landis technique. Rana were randomized into Control and Test groups. Two capillaries per animal were used (perfusate, 10 mg·mL−1 BSA/frog Ringer's; superfusate, frog Ringer's or indomethacin (10−5 mol·L−1) mixed in frog Ringer's solution). Three distinct responses of Lp to indomethacin (TC2) were demonstrated (TC1 and TC2 medians: Test Subgroup 1, 3.0 vs. 1.8; Test Subgroup 2, 18.2 vs. 2.2; Test Subgroup 3, 4.2 vs. 10.2 × 10−7 cm·sec−1·cm H2O−1). Multiple regression analysis revealed a relationship between capillary Lp and systemic red blood cell concentration or hematocrit, plasma protein concentration, and Δτ (Test Subgroup 1, R2 = 0.59, P < 0.0001; Test Subgroup 2, R2 = 0.96, P = 0.002), but only during COX inhibition. Maintaining red blood cell and plasma protein levels within a normal range may control barrier function in a healthy state. Recovering barrier function may be an unrecognized benefit of transfusions during blood loss or edema formation. PMID:25896981

  1. Capillary tone: cyclooxygenase, shear stress, luminal glycocalyx, and hydraulic conductivity (Lp).

    PubMed

    Williams, Donna A; Flood, Mary H

    2015-04-01

    Control of capillary hydraulic conductivity (Lp) is the physiological mechanism that underpins systemic hydration. Capillaries form the largest surface of endothelial cells in any species with a cardiovascular system and all capillaries are exposed to the flow-induced force, shear stress (τ). Vasoactive molecules such as prostacyclin (cyclooxygenase product, COX) are released from endothelial cells in response to τ. Little is known about how COX activity impacts capillary Lp. The purpose here was to assess Lp in situ following an acute Δτ stimulus and during COX1/COX2 inhibition. Mesenteric true capillaries (TC) of Rana pipiens (pithed) were cannulated for Lp assessment using the modified Landis technique. Rana were randomized into Control and Test groups. Two capillaries per animal were used (perfusate, 10 mg·mL(-1) BSA/frog Ringer's; superfusate, frog Ringer's or indomethacin (10(-5) mol·L(-1)) mixed in frog Ringer's solution). Three distinct responses of Lp to indomethacin (TC2) were demonstrated (TC1 and TC2 medians: Test Subgroup 1, 3.0 vs. 1.8; Test Subgroup 2, 18.2 vs. 2.2; Test Subgroup 3, 4.2 vs. 10.2 × 10(-7) cm·sec(-1)·cm H2O(-1)). Multiple regression analysis revealed a relationship between capillary Lp and systemic red blood cell concentration or hematocrit, plasma protein concentration, and Δτ (Test Subgroup 1, R(2) = 0.59, P < 0.0001; Test Subgroup 2, R(2) = 0.96, P = 0.002), but only during COX inhibition. Maintaining red blood cell and plasma protein levels within a normal range may control barrier function in a healthy state. Recovering barrier function may be an unrecognized benefit of transfusions during blood loss or edema formation.

  2. Fluid shear stress sensitizes cancer cells to receptor-mediated apoptosis via trimeric death receptors

    NASA Astrophysics Data System (ADS)

    Mitchell, Michael J.; King, Michael R.

    2013-01-01

    Cancer metastasis, the process of cancer cell migration from a primary to distal location, typically leads to a poor patient prognosis. Hematogenous metastasis is initiated by intravasation of circulating tumor cells (CTCs) into the bloodstream, which are then believed to adhere to the luminal surface of the endothelium and extravasate into distal locations. Apoptotic agents such as tumor necrosis factor apoptosis-inducing ligand (TRAIL), whether in soluble ligand form or expressed on the surface of natural killer cells, have shown promise in treating CTCs to reduce the probability of metastasis. The role of hemodynamic shear forces in altering the cancer cell response to apoptotic agents has not been previously investigated. Here, we report that human colon cancer COLO 205 and prostate cancer PC-3 cells exposed to a uniform fluid shear stress in a cone-and-plate viscometer become sensitized to TRAIL-induced apoptosis. Shear-induced sensitization directly correlates with the application of fluid shear stress, and TRAIL-induced apoptosis increases in a fluid shear stress force- and time-dependent manner. In contrast, TRAIL-induced necrosis is not affected by the application fluid shear stress. Interestingly, fluid shear stress does not sensitize cancer cells to apoptosis when treated with doxorubicin, which also induces apoptosis in cancer cells. Caspase inhibition experiments reveal that shear stress-induced sensitization to TRAIL occurs via caspase-dependent apoptosis. These results suggest that physiological fluid shear forces can modulate receptor-mediated apoptosis of cancer cells in the presence of apoptotic agents.

  3. Response of hot element wall shear stress gages in laminar oscillating flows

    NASA Technical Reports Server (NTRS)

    Cook, W. J.; Murphy, J. D.; Giddings, T. A.

    1986-01-01

    An experimental investigation of the time-dependent response of hot element wall shear stress gages in unsteady periodic air flows is reported. The study has focused on wall shear stress in laminar oscillating flows produced on a flat plate by a free stream velocity composed of a mean component and a superposed sinusoidal variation. Two types of hot element gages, platinum film and flush wire, were tested for values of reduced frequency ranging from 0.14 to 2.36. Values of the phase angle of the wall shear stress variation relative to the free stream velocity, as indicated by the hot element gages, are compared with numerical prediction. The comparisons show that the gages indicate a wall shear stress variation that lags the true variation, and that the gages will also not indicate the correct wall shear stress variation in periodic turbulent flows.

  4. Role of shear stress on composition, diversity and dynamics of biofilm bacterial communities.

    PubMed

    Rochex, Alice; Godon, Jean-Jacques; Bernet, Nicolas; Escudié, Renaud

    2008-12-01

    This article evaluates the effect of shear stress on the composition of biofilm bacterial communities. For the first time, a Conical Couette-Taylor Reactor (CCTR) was used to develop biofilms at varying shear stresses (from 0.055 to 0.27 Pa) and provided a useful model for studying the effect of hydrodynamics on biofilms. The composition, diversity and dynamics of biofilm bacterial communities were analysed using the PCR-SSCP fingerprint method. Results clearly demonstrate a link between shear stress and composition of the microbial communities. High shear stresses decrease biofilm diversity and the analysis of biofilm community dynamics suggests that shear stress would slow down biofilm maturation and tend to maintain a young biofilm.

  5. Response of hot element wall shear stress gages in laminar oscillating flows

    NASA Technical Reports Server (NTRS)

    Cook, W. J.; Murphy, J. D.; Giddings, T. A.

    1986-01-01

    An experimental investigation of the time-dependent response of hot element wall shear stress gages in unsteady periodic air flows is reported. The study has focused on wall shear stress in laminar oscillating flows produced on a flat plate by a free stream velocity composed of a mean component and a superposed sinusoidal variation. Two types of hot element gages, platinum film and flush wire, were tested for values of reduced frequency ranging from 0.14 to 2.36. Values of the phase angle of the wall shear stress variation relative to the free stream velocity, as indicated by the hot element gages, are compared with numerical prediction. The comparisons show that the gages indicate a wall shear stress variation that lags the true variation, and that the gages will also not indicate the correct wall shear stress variation in periodic turbulent flows.

  6. Effect of shear stress on the high-pressure behaviour of nitromethane: Raman spectroscopy in a shear diamond anvil cell

    NASA Astrophysics Data System (ADS)

    Hebert, Philippe; Isambert, Aude; Petitet, Jean-Pierre; Zerr, Andreas

    2009-06-01

    A detailed description of the reaction mechanisms occurring in shock-induced decomposition of condensed energetic materials is very important for a comprehensive understanding of detonation. Besides pressure and temperature effects, shear stress has also been proposed to play an important role in the initiation and decomposition mechanisms. In order to study this effect, a Shear Diamond Anvil Cell (SDAC) has been developed. It is actually a classical DAC with the upper diamond anvil rotating about the compression axis relative to the opposite anvil. In this paper, we present a Raman spectroscopy study of the effect of shear stress on the high-pressure behaviour of nitromethane. Two major effects of shear stress are observed in our experiments. The first one is a lowering of the pressures at which the different structural modifications that nitromethane undergoes are observed. The second effect is observed at 28 GPa where sudden decomposition of the sample occurs just after shear application. Observation of the sample after decomposition shows the presence of a black residue which is composed of carbon as indicated by the Raman spectrum. [1] Manaa, M. R., Fried, L. E., and Reed, E. J., Journal of Computer-Aided Materials Design, 10, pp 75-97, 2003.

  7. Quantification of Shear Stresses Within a Transtibial Prosthetic Socket.

    PubMed

    Schiff, Adam; Havey, Robery; Carandang, Gerard; Wickman, Amy; Angelico, John; Patwardhan, Avinash; Pinzur, Michael

    2014-08-01

    There is a paucity of objectively recorded data delineating the pattern of weightbearing distribution within the prosthetic socket of patients with transtibial amputation. Our current knowledge is based primarily on information obtained from finite element analysis computer models. Four high-functioning transtibial amputees were fit with similar custom prosthetic sockets. Three load cells were incorporated into each socket at high stress contact areas predicted by computer modeling. Dynamic recording of prosthetic socket loading was accomplished during rising from a sitting position, stepping from a 2-leg stance to a 1-leg stance, and during the initiation of walking. By comparing the loads measured at each of the 3 critical locations, anterior/posterior shear, superior/inferior shear, and end weightbearing were recorded. The same load pattern in all 4 subjects was found during each of the 3 functional activities. The load transmission at the distal end of the amputation residual limbs was negligible. Consistent forces were observed in both the anterior/posterior and superior/inferior planes. Correlation coefficients were used to compare the loads measured in each of the 4 subjects, which ranged from a low of .82 to a high of .98, where a value approaching 1.0 implies a linear relationship amongst subjects. This experimental model appears to have accurately recorded loading within a transtibial prosthetic socket consistent with previously reported finite element analysis computer models. This clinical model will allow objective measurement of weightbearing within the prosthetic socket of transtibial amputees and allow objective comparison of weightbearing distribution within the prosthetic sockets of patients who have undergone creation of different versions of a transtibial amputation residual limb and prosthetic socket designs. © The Author(s) 2014.

  8. Characteristics of the response of the iliac artery to wall shear stress in the anaesthetized pig.

    PubMed

    Kelly, R F; Snow, H M

    2007-07-15

    The functional significance of shear stress-induced vasodilatation in large conduit arteries is unclear since changes in the diameter have little effect on the resistance to blood flow. However, changes in diameter have a relatively large effect on wall shear stress which suggests that the function of flow-mediated dilatation is to reduce wall shear stress. The mean and pulsatile components of shear stress vary widely throughout the arterial system and areas of low mean and high amplitude of wall shear stress are prone to the development of atheroma. In this study, using an in vivo model with the ability to control flow rate and amplitude of flow independently, we investigated the characteristics of the response of the iliac artery to variations in both the mean and amplitude of wall shear stress. The results of this study confirm that increases in mean wall shear stress are an important stimulus for the release of nitric oxide by the endothelium as indicated by changes in arterial diameter and show for the first time, in vivo, that increases in the amplitude of the pulsatile component of shear stress have a small but significant inhibitory effect on this response. A negative feedback mechanism was identified whereby increases in shear stress brought about by increases in blood flow are reduced by the release of nitric oxide from the endothelium causing dilatation of the artery, thus decreasing the stimulus to cell adhesion and, through a direct action of nitric oxide, inhibiting the process of cell adhesion. The results also provide an explanation for the uneven distribution of atheroma throughout the arterial system, which is related to the ratio of pulsatile to mean shear stress and consequent variability in the production of NO.

  9. Effect of shear stress on asymmetric dimethylarginine release from vascular endothelial cells.

    PubMed

    Osanai, Tomohiro; Saitoh, Masayuki; Sasaki, Satoko; Tomita, Hirofumi; Matsunaga, Toshiro; Okumura, Ken

    2003-11-01

    We demonstrated recently that plasma concentrations of asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide (NO) synthase, are increased by high salt intake concomitantly with a decrease in plasma levels of NO in human hypertension. We investigated the effect of shear stress on ADMA release in 2 types of cells: transformed human umbilical vein endothelial cells (HUVECs; cell line ECV-304) and HUVECs. Exposure of ECV-304 cells and HUVECs to shear stress with the use of a cone-plate viscometer enhanced gene expression of protein arginine methyltransferase (PRMT-1), ADMA synthase. In HUVECs, the ratio of PRMT-1 to glyceraldehyde 3-phosphate dehydrogenase mRNA was increased by 2-fold by a shear stress of > or =15 dyne/cm2. A dominant-negative mutant of IkappaB kinase alpha and troglitazone at 8 micromol/L, an activator of peroxisome proliferator-activated receptor gamma, abolished the shear stress-induced increase in PRMT-1 gene expression in parallel with the blockade of nuclear factor (NF)-kappaB translocation into the nucleus. The activity of dimethylarginine dimethylaminohydrolase, the degradation enzyme of ADMA, was unchanged after shear stress < or =15 dyne/cm2 and was enhanced by 1.48+/-0.06-fold (P<0.05) by shear stress at 25 dyne/cm2. The release of ADMA was increased by 1.64+/-0.10-fold (P<0.05) by shear stress at 15 dyne/cm2 but was not affected by shear stress at 25 dyne/cm2. These results indicate that shear stress enhances gene expression of PRMT-1 and ADMA release via activation of the NF-kappaB pathway. Shear stress at higher magnitudes facilitates the degradation of ADMA, thus returning ADMA release levels to baseline.

  10. Optimization of MR phase-contrast-based flow velocimetry and shear stress measurements.

    PubMed

    Kim, Taeho; Seo, Ji-Hyea; Bang, Seong-Sik; Choi, Hyeon-Woo; Chang, Yongmin; Lee, Jongmin

    2010-02-01

    This study was designed to measure the pixel-by-pixel flow velocity and shear stress from phase-contrast MR images. An optimized method was suggested and the use of the method was confirmed. A self-developed, straight steady flow model system was scanned by MRI with a velocity-encoded phase-contrast sequence. In-house developed software was used for the pixel-by-pixel flow velocity and shear stress measurements and the measurements were compared with physically measured mean velocity and shear stress. A comparison between the use of the in-house velocimetry software and a commercial velocimetry system was also performed. Curved steady flow models were scanned by phase-contrast MRI. Subsequently, velocity and shear stress were measured to confirm the shifted peak flow velocity and shear stress toward the outer side of the lumen. Peak velocity and shear stress were calculated for both the inner and outer half of the lumen and were statistically compared. The mean velocity measured with the use of in-house software had a significant correlation with the physical measurements of mean velocity; in addition, the measurement was more precise compared to the commercial system (R(2) = 0.85 vs. 0.75, respectively). The calculated mean shear stress had a significant correlation with the physical measurements of mean shear stress (R(2) = 0.95). The curved flow model showed a significantly shifted peak velocity and shear stress zones toward the outside of the flow (P < 0.0001). The technique to measure pixel-by-pixel velocity and shear stress of steady flow from velocity-encoded phase-contrast MRI was optimized. This technique had a good correlation with physical measurements and was superior to a commercially available system.

  11. Non-canonical Wnt signalling modulates the endothelial shear stress flow sensor in vascular remodelling

    PubMed Central

    Franco, Claudio A; Jones, Martin L; Bernabeu, Miguel O; Vion, Anne-Clemence; Barbacena, Pedro; Fan, Jieqing; Mathivet, Thomas; Fonseca, Catarina G; Ragab, Anan; Yamaguchi, Terry P; Coveney, Peter V; Lang, Richard A; Gerhardt, Holger

    2016-01-01

    Endothelial cells respond to molecular and physical forces in development and vascular homeostasis. Deregulation of endothelial responses to flow-induced shear is believed to contribute to many aspects of cardiovascular diseases including atherosclerosis. However, how molecular signals and shear-mediated physical forces integrate to regulate vascular patterning is poorly understood. Here we show that endothelial non-canonical Wnt signalling regulates endothelial sensitivity to shear forces. Loss of Wnt5a/Wnt11 renders endothelial cells more sensitive to shear, resulting in axial polarization and migration against flow at lower shear levels. Integration of flow modelling and polarity analysis in entire vascular networks demonstrates that polarization against flow is achieved differentially in artery, vein, capillaries and the primitive sprouting front. Collectively our data suggest that non-canonical Wnt signalling stabilizes forming vascular networks by reducing endothelial shear sensitivity, thus keeping vessels open under low flow conditions that prevail in the primitive plexus. DOI: http://dx.doi.org/10.7554/eLife.07727.001 PMID:26845523

  12. Flow-induced crystallization in isotactic polypropylene

    NASA Astrophysics Data System (ADS)

    Hamad, Fawzi Ghassan

    Brief intervals of strong flow stretch chains in a semicrystalline polymer melt, which results in an increase in the nuclei number density and a transformation of the crystal structure. This flow-induced crystallization (FIC) phenomenon is explored in this study using highly isotactic polypropylene (iPP) samples. Using one synthesized and five commercial linear isotactic polypropylene samples, we investigate the FIC behavior by imposing shear onto these samples in a rotational rheometer. Equipped with a good temperature control and flexible shear protocol, we apply different temperature and flow conditions. The magnitude of the FIC effect varies with basic processing parameters (shear rate, specific work, crystallization temperature, and shearing temperature) and material properties (totalistic, molecular weight distribution, and particle concentration in the polymer). The scope of this study is to systematically investigate the influences of these parameters on FIC. The FIC effects that are investigated in this dissertation are: crystallization kinetics, persistence time of flow-induced nuclei, and crystal morphology. The crystallization time was measured in the rheometer by monitoring the onset of crystallization after quenching samples sheared above Tm. These samples were subsequently used to study their flow-induced nuclei persistence time and crystal morphology. The lifetime of flow-induced nuclei was determined by measuring the time required to return from FIC back to quiescent crystallization using a differential scanning calorimeter. The crystal morphology was imaged using polarized optical microscopy and atomic force microscopy. We investigated the influence of specific work on the three FIC characteristics, and found three regimes that are separated by the critical work ( Wc) and the saturation work (Wsat) thresholds. Below the critical work threshold, the morphology is composed of mostly spherulite crystals, which keep a constant volume, and a small

  13. Critical combinations of shear and direct axial stress for curved rectangular panels

    NASA Technical Reports Server (NTRS)

    Schildcrout, Murry; Stein, Manuel

    1949-01-01

    A solution is presented for the problem of the buckling of curved rectangular panels subjected to combined shear and direct axial stress. Charts giving theoretical critical combinations of shear and direct axial stress are presented for panels having five different length-width ratios. Because the actual critical compressive stress of rectangular panels having substantial curvature is known to be much lower than the theoretical value, a semiempirical method of analysis of curved panels subjected to combined shear and direct axial stress is presented for use in design. (author

  14. Localized α4 Integrin Phosphorylation Directs Shear Stress-Induced Endothelial Cell Alignment

    PubMed Central

    Goldfinger, Lawrence E.; Tzima, Eleni; Stockton, Rebecca; Kiosses, William B.; Kinbara, Kayoko; Tkachenko, Eugene; Gutierrez, Edgar; Groisman, Alex; Nguyen, Phu; Chien, Shu; Ginsberg1, Mark H.

    2009-01-01

    Vascular endothelial cells respond to laminar shear stress by aligning in the direction of flow, a process which may contribute to athero-protection. Here we report that localized α4 integrin phosphorylation is a mechanism for establishing the directionality of shear stress-induced alignment in microvascular endothelial cells. Within 5 minutes of exposure to a physiological level of shear stress, endothelial α4 integrins became phosphorylated on Ser988. In wounded monolayers, phosphorylation was enhanced at the downstream edges of cells relative to the source of flow. The shear-induced α4 integrin phosphorylation was blocked by inhibitors of cAMP-dependent protein kinase A (PKA), an enzyme involved in the alignment of endothelial cells under prolonged shear. Moreover, shear-induced localized activation of the small GTPase Rac1, which specifies the directionality of endothelial alignment, was similarly blocked by PKA inhibitors. Furthermore, endothelial cells bearing a non-phosphorylatable α4(S988A) mutation failed to align in response to shear stress, thus establishing α4 as a relevant PKA substrate. We thereby show that shear-induced PKA-dependent α4 integrin phosphorylation at the downstream edge of endothelial cells promotes localized Rac1 activation, which in turn directs cytoskeletal alignment in response to shear stress. PMID:18583710

  15. Studies on stress distribution in pavements subjected to surface shear forces

    PubMed Central

    KIMURA, Tsutomu

    2014-01-01

    It has been pointed out by some researchers1,2) that road pavements are subjected to vertical stress due to vehicles on them as well as shear stress at the time of braking or acceleration of vehicles. In this paper, the results of elastic analysis to obtain the rigorous solution for an elastic two-layer system subjected to surface shear stress are described and it is shown that the effect of shear stresses applied at the surface gives rise to fairly large stresses in the system. On the basis of these findings, the author attempts to explain why pavement failure takes place frequently at places such as crossings and curved parts where pavements are subjected to high magnitude of surface shear stresses. PMID:24522154

  16. The production of turbulent stress in a shear flow by irrotational fluctuations

    NASA Technical Reports Server (NTRS)

    Gartshore, I. S.; Durbin, P. A.; Hunt, J. C. R.

    1983-01-01

    Attention is given to the way in which external turbulence affects an initially turbulence-free region in which there is a mean velocity gradient. External turbulence induces irrotational fluctuations in the sheared region which interact with the shear to produce rotational velocity fluctuations and mean Reynolds stresses. Since the actual front between the initial external turbulence and the shear flow is a randomly contorted surface, the turbulence near the front is intermittent, and is presently included in the form of a simple statistical model. In wind tunnel tests, turbulent shear stress was found to grow from zero to significant values in the interaction region. Observed stress magnitude and extent agrees with predictions, and it is concluded that turbulent stresses can be produced by irrotational fluctuations in a region of mean shear.

  17. Effect of tree roots on a shear zone: modeling reinforced shear stress.

    Treesearch

    Kazutoki Abe; Robert R. Ziemer

    1991-01-01

    Tree roots provide important soil reinforcement that impoves the stability of hillslopes. After trees are cut and roots begin to decay, the frequency of slope failures can increase. To more fully understand the mechanics of how tree roots reinforce soil, fine sandy soil containing pine roots was placed in a large shear box in horizontal layers and sheared across a...

  18. Mechanotransduction Signaling in Podocytes from Fluid Flow Shear Stress.

    PubMed

    Srivastava, Tarak; Dai, Hongying; Heruth, Daniel P; Alon, Uri S; Garola, Robert E; Zhou, Jianping; Duncan, R Scott; El-Meanawy, Ashraf; McCarthy, Ellen T; Sharma, Ram; Johnson, Mark L; Savin, Virginia J; Sharma, Mukut

    2017-09-06

    Recently we and others have found that hyperfiltration-associated increase in biomechanical forces, namely tensile stress and fluid flow shear stress (FFSS) can directly and distinctly alter podocyte structure and function. The ultrafiltrate flow over the major processes and cell body generates FFSS to podocyte. Our previous work suggests that COX2-PGE2-EP2 axis plays an important role in mechanoperception of FFSS in podocyte (Srivastava et al. Am J Physiol Renal Physiol 307: F1323-F1333, 2014). To address mechanotransduction of the perceived mechanical stimulus through EP2 receptor, cultured podocytes were exposed to FFSS (2 dynes/cm2) for 2hrs. Total RNA from cells at the end of treatment, 2h post-FFSS and 24h post-FFSS was used for whole exon array analysis. The differentially regulated genes (p<0.01) were analyzed using bioinformatics tools Enrichr and Ingenuity Pathway Analysis to predict pathways/ molecules. Candidate pathways were validated using Western blot analysis, and then further confirmed to be resulting from a direct effect of PGE2 on podocytes. Results show that FFSS-induced mechanotransduction as well as exogenous PGE2 activate the Akt-GSK3β-β-catenin (Ser552) and ERK/MAPK but not the cAMP-PKA signal transduction cascades. These pathways are reportedly associated with FFSS-induced and EP2-mediated signaling in other epithelial cells as well. Current regimen for treating hyperfiltration-mediated injury largely depends on targeting the Renin-Angiotensin-Aldosterone System. Present study identifies specific transduction mechanisms and provides novel information on the direct effect of FFSS on podocytes. These results suggest that targeting EP2 receptor-mediated signaling pathways holds therapeutic significance for delaying progression chronic kidney disease secondary to hyperfiltration. Copyright © 2017, American Journal of Physiology-Renal Physiology.

  19. Sediment transport and shear stress partitioning in a vegetated flow

    NASA Astrophysics Data System (ADS)

    Le Bouteiller, Caroline; Venditti, J. G.

    2015-04-01

    Vegetation is a common feature in natural coastal and riverine water ways, interacting with both the water flow and sediment transport. However, the physical processes governing these interactions are still poorly understood, which makes it difficult to predict sediment transport and morphodynamics in a vegetated environment. We performed a simple experiment to study how sediment transport responds to the presence of flexible, single-blade vegetation, and how this response is influenced by the vegetation density. We found that the skin friction and sediment transport are reduced in a plant patch, and that this effect is larger for denser vegetation. We then evaluated several methods to calculate the skin friction in a vegetated flow, which is the key to sediment transport prediction. Among these, the inversion of bed load transport formulas and the Einstein and Banks (1950) methods appeared to produce the most reasonable values of the skin friction. Finally, we suggest using the parameter α, which is the ratio of the skin friction computed by these methods to the total bed shear stress, to make more realistic sediment transport predictions in morphodynamic models.

  20. Flow instability and wall shear stress variation in intracranial aneurysms

    PubMed Central

    Baek, H.; Jayaraman, M. V.; Richardson, P. D.; Karniadakis, G. E.

    2010-01-01

    We investigate the flow dynamics and oscillatory behaviour of wall shear stress (WSS) vectors in intracranial aneurysms using high resolution numerical simulations. We analyse three representative patient-specific internal carotid arteries laden with aneurysms of different characteristics: (i) a wide-necked saccular aneurysm, (ii) a narrower-necked saccular aneurysm, and (iii) a case with two adjacent saccular aneurysms. Our simulations show that the pulsatile flow in aneurysms can be subject to a hydrodynamic instability during the decelerating systolic phase resulting in a high-frequency oscillation in the range of 20–50 Hz, even when the blood flow rate in the parent vessel is as low as 150 and 250 ml min−1 for cases (iii) and (i), respectively. The flow returns to its original laminar pulsatile state near the end of diastole. When the aneurysmal flow becomes unstable, both the magnitude and the directions of WSS vectors fluctuate at the aforementioned high frequencies. In particular, the WSS vectors around the flow impingement region exhibit significant spatio-temporal changes in direction as well as in magnitude. PMID:20022896

  1. Wall shear stress distributions on stented patent ductus arteriosus

    NASA Astrophysics Data System (ADS)

    Kori, Mohamad Ikhwan; Jamalruhanordin, Fara Lyana; Taib, Ishkrizat; Mohammed, Akmal Nizam; Abdullah, Mohammad Kamil; Ariffin, Ahmad Mubarak Tajul; Osman, Kahar

    2017-04-01

    A formation of thrombosis due to hemodynamic conditions after the implantation of stent in patent ductus arteriosus (PDA) will derived the development of re-stenosis. The phenomenon of thrombosis formation is significantly related to the distribution of wall shear stress (WSS) on the arterial wall. Thus, the aims of this study is to investigate the distribution of WSS on the arterial wall after the insertion of stent. Three dimensional model of patent ductus arteriosus inserted with different types of commercial stent are modelled. Computational modelling is used to calculate the distributions of WSS on the arterial stented PDA. The hemodynamic parameters such as high WSS and WSSlow are considered in this study. The result shows that the stented PDA with Type III stent has better hemodynamic performance as compared to others stent. This model has the lowest distributions of WSSlow and also the WSS value more than 20 dyne/cm2. From the observed, the stented PDA with stent Type II showed the highest distributions area of WSS more than 20 dyne/cm2. This situation revealed that the high possibility of atherosclerosis to be developed. However, the highest distribution of WSSlow for stented PDA with stent Type II indicated that high possibility of thrombosis to be formed. In conclusion, the stented PDA model calculated with the lowest distributions of WSSlow and WSS value more than 20dyne/cm2 are considered to be performed well in stent hemodynamic performance as compared to other stents.

  2. Surface chemistry modulates osteoblasts sensitivity to low fluid shear stress.

    PubMed

    Xing, Juan; Li, Yan; Lin, Manping; Wang, Jinfeng; Wu, Jinchuan; Ma, Yufei; Wang, Yuanliang; Yang, Li; Luo, Yanfeng

    2014-11-01

    Low fluid shear stress (FSS) is the mechanical environment encountered by osteoblasts in implanted bones or native bones of bed rest patients. High sensitivity of osteoblasts to low FSS is beneficial to osteogenesis. We hypothesize that this sensitivity might be regulated by chemical microenvironment provided by scaffolds. To confirm this hypothesis, self-assembled monolayers (SAMs) were used to provide various surface chemistries including OH, CH3 , and NH2 while parallel-plate fluid flow system produced low FSS (5 dynes/cm(2) ). Alterations in S-phase cell fraction, alkaline phosphatase activity, fibronectin (Fn), and collagen type I (COL I) secretion compared to those without FSS exposure were detected to characterize the sensitivity. Osteoblasts on OH and CH3 SAMs demonstrated obvious sensitivity while on NH2 SAMs negligible sensitivity was observed. Examination of the cell aspect ratio, orientation, and focal adhesions before and after FSS exposure indicates that the full spreading and robust focal adhesions on NH2 SAMs should be responsible for the negligible sensitivity through increasing the cell tolerance to low FSS. Despite the higher sensitivity, the Fn and COL I depositions on both OH and CH3 SAMs after FSS exposure were still less than on NH2 SAMs without FSS exposure. These results suggest that elaborate design of surface chemical compositions is essential for orchestration of surface chemistry with low FSS to realize both high sensitivity and high matrix secretion, facilitating the formation of functional bone tissues in implanted bone.

  3. Vascular wall shear stress in zebrafish model of early atherosclerosis

    NASA Astrophysics Data System (ADS)

    Choi, Woorak; Seo, Eunseok; Yeom, Eunseop; Lee, Sang Joon

    2016-11-01

    Although atherosclerosis is a multifactorial disease, the role of hemodynamic force has strong influence on the outbreak of the disease. Low and oscillating wall shear stress (WSS) is associated with the incidence of atherosclerosis. Many researchers have investigated relationships between WSS and the occurrence of atherosclerosis using in vitro and in vivo models. However, these models possess technological limitations in mimicking real biophysiological conditions and monitoring the temporal progression of atherosclerosis. In this study, a hypercholesterolaemic zebrafish model was established as a novel model to resolve these technical limitations. WSS in blood vessels of 15 days post-fertilisation zebrafish was measured using a micro PIV technique, and the spatial distribution of lipids inside blood vessels was quantitatively visualized using a confocal microscopy. As a result, lipids are mainly deposited in the regions of low WSS. The oscillating WSS is not induced by blood flows in the zebrafish disease model. The present hypercholesterolaemic zebrafish model would be useful for understanding the effect of WSS on the early stage of atherosclerosis. This work was supported by the National Research Foundation of Korea (NRF) under a Grant funded by the Korean government (MSIP) (No. 2008-0061991).

  4. Characterizations and Correlations of Wall Shear Stress in Aneurysmal Flow

    PubMed Central

    Arzani, Amirhossein; Shadden, Shawn C.

    2016-01-01

    Wall shear stress (WSS) is one of the most studied hemodynamic parameters, used in correlating blood flow to various diseases. The pulsatile nature of blood flow, along with the complex geometries of diseased arteries, produces complicated temporal and spatial WSS patterns. Moreover, WSS is a vector, which further complicates its quantification and interpretation. The goal of this study is to investigate WSS magnitude, angle, and vector changes in space and time in complex blood flow. Abdominal aortic aneurysm (AAA) was chosen as a setting to explore WSS quantification. Patient-specific computational fluid dynamics (CFD) simulations were performed in six AAAs. New WSS parameters are introduced, and the pointwise correlation among these, and more traditional WSS parameters, was explored. WSS magnitude had positive correlation with spatial/temporal gradients of WSS magnitude. This motivated the definition of relative WSS gradients. WSS vectorial gradients were highly correlated with magnitude gradients. A mix WSS spatial gradient and a mix WSS temporal gradient are proposed to equally account for variations in the WSS angle and magnitude in single measures. The important role that WSS plays in regulating near wall transport, and the high correlation among some of the WSS parameters motivates further attention in revisiting the traditional approaches used in WSS characterizations. PMID:26592536

  5. Contact Pressure and Shear Stress Analysis on Conforming Contact Problem

    NASA Astrophysics Data System (ADS)

    Nagatani, Haruo; Imou, Akitoshi

    Two methods to solve a conforming contact problem are proposed. First method is general and can be applicable to the contact case between elastic arbitrary shape bodies. For verification FEA is performed on the convex-concave sphere contact, and the result of this method is well corresponding to the FEA result. However, the accuracy deteriorates when the mesh aspect ratio is extremely large. This phenomenon is caused by the usage of numerical integration for the calculation of influence coefficient. The second method is devised to avoid this problem, while this improved method is applicable only to the case when the contact area can be considered to be on a cylinder surface. By using this method, the contact pressure can be obtained without the deterioration even in the case of edge load occurring between ball bearing race shoulder and ball. The results of the contact pressure and the shear stress that is necessary for bearing life estimation are compared with the FEA result, which showed well correspondence.

  6. CCM proteins control endothelial β1 integrin dependent response to shear stress.

    PubMed

    Macek Jilkova, Zuzana; Lisowska, Justyna; Manet, Sandra; Verdier, Claude; Deplano, Valerie; Geindreau, Christian; Faurobert, Eva; Albigès-Rizo, Corinne; Duperray, Alain

    2014-11-28

    Hemodynamic shear stress from blood flow on the endothelium critically regulates vascular function in many physiological and pathological situations. Endothelial cells adapt to shear stress by remodeling their cytoskeletal components and subsequently by changing their shape and orientation. We demonstrate that β1 integrin activation is critically controlled during the mechanoresponse of endothelial cells to shear stress. Indeed, we show that overexpression of the CCM complex, an inhibitor of β1 integrin activation, blocks endothelial actin rearrangement and cell reorientation in response to shear stress similarly to β1 integrin silencing. Conversely, depletion of CCM2 protein leads to an elongated "shear-stress-like" phenotype even in the absence of flow. Taken together, our findings reveal the existence of a balance between positive extracellular and negative intracellular signals, i.e. shear stress and CCM complex, for the control of β1 integrin activation and subsequent adaptation of vascular endothelial cells to mechanostimulation by fluid shear stress. © 2014. Published by The Company of Biologists Ltd.

  7. Effect of shear stress on migration and integrin expression in macaque trophoblast cells.

    PubMed

    Soghomonians, Arlen; Barakat, Abdul I; Thirkill, Twanda L; Blankenship, Thomas N; Douglas, Gordon C

    2002-05-08

    During fetal development, trophoblast cells enter endometrial capillaries, migrate within the uterine vasculature, and eventually reside within spiral arteries of the uterus. This invasive activity is accompanied by upregulation of trophoblast beta1 integrin expression. Fluid mechanical shear stress regulates migration and expression of adhesion molecules in vascular endothelial cells, but nothing is known about the effects of shear stress on trophoblast cells. We tested the hypothesis that shear stress regulates the motility and beta1 integrin expression of trophoblast cells. Early gestation macaque trophoblast cells were cultured in 1 x 1-mm square cross-section capillary tubes within which the flow field was determined using three-dimensional computational fluid dynamic simulations. Trophoblast cells in the capillary tubes were exposed to a steady shear stress of 7.5, 15, or 30 dyn/cm2 for up to 24 h. In the absence of flow, trophoblast cells were highly dynamic with constant nondirectional positional shifts but with no net cell migration. Exposure of the cells to shear stress within 24-72 h of cell plating significantly increased the level of this activity and led to net cell migration in the direction of flow. Shear stress also increased the expression and altered the topography of beta1 integrin. These results suggest that shear stress regulates trophoblast motility and beta1 integrin expression in vitro.

  8. Cooperative effects of matrix stiffness and fluid shear stress on endothelial cell behavior.

    PubMed

    Kohn, Julie C; Zhou, Dennis W; Bordeleau, François; Zhou, Allen L; Mason, Brooke N; Mitchell, Michael J; King, Michael R; Reinhart-King, Cynthia A

    2015-02-03

    Arterial hemodynamic shear stress and blood vessel stiffening both significantly influence the arterial endothelial cell (EC) phenotype and atherosclerosis progression, and both have been shown to signal through cell-matrix adhesions. However, the cooperative effects of fluid shear stress and matrix stiffness on ECs remain unknown. To investigate these cooperative effects, we cultured bovine aortic ECs on hydrogels matching the elasticity of the intima of compliant, young, or stiff, aging arteries. The cells were then exposed to laminar fluid shear stress of 12 dyn/cm(2). Cells grown on more compliant matrices displayed increased elongation and tighter EC-cell junctions. Notably, cells cultured on more compliant substrates also showed decreased RhoA activation under laminar shear stress. Additionally, endothelial nitric oxide synthase and extracellular signal-regulated kinase phosphorylation in response to fluid shear stress occurred more rapidly in ECs cultured on more compliant substrates, and nitric oxide production was enhanced. Together, our results demonstrate that a signaling cross talk between stiffness and fluid shear stress exists within the vascular microenvironment, and, importantly, matrices mimicking young and healthy blood vessels can promote and augment the atheroprotective signals induced by fluid shear stress. These data suggest that targeting intimal stiffening and/or the EC response to intima stiffening clinically may improve vascular health.

  9. Research on measurement of bed shear stress under wave-current interaction

    NASA Astrophysics Data System (ADS)

    Xu, Hua; Xia, Yun-feng; Ma, Bing-he; Hao, Si-yu; Zhang, Shi-zhao; Du, De-jun

    2015-06-01

    The movement of sediment in estuary and on coast is directly restricted by the bed shear stress. Therefore, the research on the basic problem of sediment movement by the bed shear stress is an important way to research the theory of sediment movement. However, there is not a measuring and computing method to measure the bed shear stress under a complicated dynamic effect like wave and current. This paper describes the measurement and test research on the bed shear stress in a long launder of direct current by the new instrument named thermal shearometer based on micro-nanotechnology. As shown by the research results, the thermal shearometer has a high response frequency and strong stability. The measured results can reflect the basic change of the bed shear stress under wave and wave-current effect, and confirm that the method of measuring bed shear stress under wave-current effect with thermal shearometer is feasible. Meanwhile, a preliminary method to compute the shear stress compounded by wave-current is put forward according to the tested and measured results, and then a reference for further study on the basic theory of sediment movement under a complicated dynamic effect is provided.

  10. Shear stress variation induced by red blood cell motion in microvessel.

    PubMed

    Xiong, Wenjuan; Zhang, Junfeng

    2010-08-01

    We simulated red blood cells flowing in microvessel to examine the induced wall shear stress variation. A typical peak-valley-peak structure is observed, and it is analyzed in terms of its magnitude, spatial influencing range, and temporal elapsed duration. Effects of red cell deformability, microvessel size, and flow velocity have been investigated. The corresponding variation characters have also been related to cell deformation and flow field. Simulation results show that the variation magnitude is mainly determined by the gap size between cell and vessel wall, while the spatial range of the shear stress variation depends on the cell length as well as the microvessel size. For a certain point on the vessel wall, the shear stress variation lasts a short time at a higher flow velocity, and vice versa. As the cell concentration in the microvessel increases, the shear stress variation structure changes accordingly with the two peaks from two close cells merging together, and eventually only one peak is observed at a hematocrit of 30.72%. However, the effect of hematocrit on the variation magnitude of shear stress is less obvious, and the dynamic nature of shear stress is still significant. This represents the first attempt to study the dynamic shear stress variation on microvessel as red blood cells flow by, and the information obtained in this study could be valuable to relevant research, for example, the mechanotransduction in the endothelia glycocalyx layer.

  11. Numerical and experimental demonstration of shear stress measurement at thick steel plates using acoustoelasticity

    NASA Astrophysics Data System (ADS)

    Abbasi, Zeynab; Ozevin, Didem

    2015-04-01

    The purpose of this article is to numerically quantify the stress state of complex loaded thick steel plates using the fundamental theory of acoustoelasticity, which is the relationship with stress and ultrasonic velocity in the nonlinear regime. The normal and shear stresses of a thick plate can be measured using a phased array placement of ultrasonic sensors and Rayleigh ultrasonic waves. Three measurement angles (i.e., 0 45 and 90 degrees) are selected since three measurements are needed to solve the stress tensor in an isotropic plate. The ultrasonic data is influenced significantly by the frequency of the Rayleigh waves as well as the thickness of the plate being examined; consequently the overall experimental process is influenced by the measurement parameters. In this study, a numerical demonstration is implemented to extract the nonlinearity coefficients using a 3D structural geometry and Murnaghan material model capable of examining the effects of various plate thicknesses and ultrasonic frequencies on the shear stress measurement. The purpose is that as the thickness becomes smaller, the shear stress becomes negligible at the angled measurement. For thicker cross section, shear stress becomes influential if the depth of penetration of Rayleigh wave is greater than the half of the thickness. The correlation between the depth of penetration and shear stress is then obtained. The numerical results are compared with 1 MHz ultrasonic frequency and a 3/8 inch thick steel plate loaded uniaxially while the measurement direction is angled to have the presence of shear stress in the measurement direction.

  12. Endothelial dysfunction and monocyte recruitment in cells exposed to non-uniform shear stress.

    PubMed

    Cicha, Iwona; Goppelt-Struebe, Margarete; Yilmaz, Atilla; Daniel, Werner G; Garlichs, Christoph D

    2008-01-01

    Atherosclerosis results from a combination of local blood flow patterns and systemic risk factors. We investigated whether non-uniform shear stress at bifurcations induces pro-atherogenic endothelial dysfunction and monocyte recruitment. Bifurcating flow-through cell culture slides were used to expose HUVECs to laminar or non-uniform shear stress for 18 h at 10 dyne/cm(2). For the adhesion assay, HUVECs were subsequently perfused with medium containing THP-1 monocytes for 1 h. Protein expression was determined by immunofluorescence. In areas exposed to laminar shear stress, alignment of endothelial cells with the flow was observed, accompanied by upregulation of eNOS and downregulation of connective tissue growth factor (CTGF). In contrast, cells exposed to non-uniform shear stress near the outer walls of bifurcations were characterized by irregular, unaligned shape, induction of endothelin-1 and CTGF, as well as reduced eNOS expression. These atherogenic effects of non-uniform shear stress were prevented when cells were treated with statins (1 mumol/l) during flow. Under non-uniform shear stress, a slight induction of VCAM-1, ICAM-1, and E-/P-selectin was observed. In agreement with this, monocyte recruitment, which was nearly undetectable under laminar shear stress, was moderately induced by non-uniform shear stress (P<0.02). In conclusion, inhibition of antioxidative eNOS and upregulation of atherogenic proteins is the first step in non-uniform shear stress-mediated endothelial dysfunction, which in vivo in the presence of atherogenic risk factors may further enhance monocyte recruitment into the artery wall.

  13. Acute Shear Stress Direction Dictates Adherent Cell Remodeling and Verifies Shear Profile of Spinning Disc Assays

    PubMed Central

    Fuhrmann, Alexander; Engler, Adam J.

    2015-01-01

    Several methods have been developed to quantify population level changes in cell attachment strength given its large heterogeneity. One such method is the rotating disc chamber or “spinning disc” in which a range of shear forces are applied to attached cells to quantify detachment force, i.e. attachment strength, which can be heterogeneous within cell populations. However, computing the exact force vectors that act upon cells is complicated by complex flow fields and variable cell morphologies. Recent observations suggest that cells may remodel their morphology and align during acute shear exposure, but contrary to intuition, shear is not orthogonal to the radial direction. Here we theoretically derive the magnitude and direction of applied shear and demonstrate that cells, under certain physiological conditions, align in this direction within minutes. Shear force magnitude is also experimentally verified which validates that for spread cells shear forces and not torque or drag dominate in this assay, and demonstrates that the applied force per cell area is largely independent of initial morphology. These findings suggest that direct quantified comparison of the effects of shear on a wide array of cell types and conditions can be made with confidence using this assay without the need for computational or numerical modeling. PMID:25619322

  14. Impact of wall shear stress on initial bacterial adhesion in rotating annular reactor.

    PubMed

    Saur, Thibaut; Morin, Emilie; Habouzit, Frédéric; Bernet, Nicolas; Escudié, Renaud

    2017-01-01

    The objective of this study was to investigate the bacterial adhesion under different wall shear stresses in turbulent flow and using a diverse bacterial consortium. A better understanding of the mechanisms governing microbial adhesion can be useful in diverse domains such as industrial processes, medical fields or environmental biotechnologies. The impact of wall shear stress-four values ranging from 0.09 to 7.3 Pa on polypropylene (PP) and polyvinyl chloride (PVC)-was carried out in rotating annular reactors to evaluate the adhesion in terms of morphological and microbiological structures. A diverse inoculum consisting of activated sludge was used. Epifluorescence microscopy was used to quantitatively and qualitatively characterize the adhesion. Attached bacterial communities were assessed by molecular fingerprinting profiles (CE-SSCP). It has been demonstrated that wall shear stress had a strong impact on both quantitative and qualitative aspects of the bacterial adhesion. ANOVA tests also demonstrated the significant impact of wall shear stress on all three tested morphological parameters (surface coverage, number of objects and size of objects) (p-values < 2.10-16). High wall shear stresses increased the quantity of attached bacteria but also altered their spatial distribution on the substratum surface. As the shear increased, aggregates or clusters appeared and their size grew when increasing the shears. Concerning the microbiological composition, the adhered bacterial communities changed gradually with the applied shear.

  15. Analysis of the complex stress state during early loading in cylindrical compression-shear specimens

    NASA Astrophysics Data System (ADS)

    Pfeiffer, S.; Frint, P.; F-X Wagner, M.

    2017-03-01

    In most engineering applications, materials are subjected to complex load cases rather than the simple uniaxial ones typically used for material characterization. To experimentally study the material behavior under a combination of compression and shear, an inclined compression specimen can be used. This specimen has been applied in various earlier experimental studies, typically to investigate shear localization under quasi-static or impact loading. In this contribution, we analyze the stress state in a compression-shear specimen in detail using an elastic-ideal plastic finite element simulation. The effects of specimen aspect ratio (height/diameter), inclination angle, and friction conditions between specimen and tool plates are investigated using the material parameters of different conventional steels as input. Shear stress distributions in characteristic shear directions on specific planes in the specimen that control the subsequent plastic deformation behavior are evaluated. Our results show that, even in the absence of friction, shear stresses are distributed heterogeneously in the inclined specimen, which differs from the stress distribution in a conventional compression specimen. Moreover, the highest shear and equivalent stresses always occur at the edges of the short diagonal plane of the specimen, independent of the investigated parameters. This study contributes to a more detailed understanding of the elasto-plastic mechanics in compression-shear specimens, and it specifically provides information for the analysis of the onset of early plastic deformation.

  16. Fiber bundle models for stress release and energy bursts during granular shearing

    NASA Astrophysics Data System (ADS)

    Michlmayr, Gernot; Or, Dani; Cohen, Denis

    2012-12-01

    Fiber bundle models (FBMs) offer a versatile framework for representing transitions from progressive to abrupt failure in disordered material. We report a FBM-based description of mechanical interactions and associated energy bursts during shear deformation of granular materials. For strain-controlled shearing, where elements fail in a sequential order, we present analytical expressions for strain energy release and failure statistics. Results suggest that frequency-magnitude characteristics of fiber failure vary considerably throughout progressive shearing. Predicted failure distributions were in good agreement with experimentally observed shear stress fluctuations and associated bursts of acoustic emissions. Experiments also confirm a delayed release of acoustic emission energy relative to shear stress buildup, as anticipated by the model. Combined with data-rich acoustic emission measurements, the modified FBM offers highly resolved contact-scale insights into granular media dynamics of shearing processes.

  17. Red blood cell damage by shear stress for different blood types

    NASA Astrophysics Data System (ADS)

    Arwatz, Gilad; Bedkowski, Katherine; Smits, Alexander

    2011-11-01

    In surgical practice, blood damage caused by medical devices is often a limiting factor in the duration of an acute procedure or in chronic exposures such as hemodialysis. In order to establish guidelines for designing medical devices, a study was conducted to determine the relationship between shear stress and damage to red blood cells using a concentric Couette device. By measuring the hemolysis level for various shear stresses and exposure times, a non-dimensional relationship between shear stress and blood damage for different blood types was established. Funding provided by Princeton University's Project X.

  18. Impact of peptide micropatterning on endothelial cell actin remodeling for cell alignment under shear stress.

    PubMed

    Chollet, Céline; Bareille, Reine; Rémy, Murielle; Guignandon, Alain; Bordenave, Laurence; Laroche, Gaetan; Durrieu, Marie-Christine

    2012-12-01

    HSVEC behavior under physiological shear stress in vitro is investigated on PET surfaces micropatterned with both RGDS and WQPPRARI peptides. This technique allows (i) creating geometries on surface to guide cell orientation under shear stress and (ii) controlling surface chemical composition in order to modulate cell behavior. Under shear stress, endothelial cells adhere on patterned PET surfaces and present a more rapid orientation in flow direction in comparison to cells cultured on homogeneous surfaces. Micropatterned surfaces presenting a large surface area ratio of RGDS/WQPPRARI peptides induce fibrillar adhesion, while surfaces presenting an equal RGDS/WQPPRARI peptides surface area ratio preferentially induce focal adhesion.

  19. Method for measuring surface shear stress magnitude and direction using liquid crystal coatings

    NASA Technical Reports Server (NTRS)

    Reda, Daniel C. (Inventor)

    1995-01-01

    A method is provided for determining surface shear magnitude and direction at every point on a surface. The surface is covered with a shear stress sensitive liquid crystal coating and illuminated by white light from a normal direction. A video camera is positioned at an oblique angle above the surface to observe the color of the liquid crystal at that angle. The shear magnitude and direction are derived from the color information. A method of calibrating the device is also provided.

  20. Interlaminar shear stress effects on the postbuckling response of graphite-epoxy panels

    NASA Technical Reports Server (NTRS)

    Engelstad, S. P.; Reddy, J. N.; Knight, N. F., Jr.

    1990-01-01

    The objectives of the study are to assess the influence of shear flexibility on overall postbuckling response, and to examine transverse shear stress distributions in relation to panel failure. Nonlinear postbuckling results are obtained for finite element models based on classical laminated plate theory and first-order shear deformation theory. Good correlation between test and analysis is obtained. The results presented in this paper analytically substantiate the experimentally observed failure mode.

  1. An Experimental Investigation of the Risk of Triggering Geological Disasters by Injection under Shear Stress

    NASA Astrophysics Data System (ADS)

    Liu, Yixin; Xu, Jiang; Peng, Shoujian

    2016-12-01

    Fluid injection has been applied in many fields, such as hazardous waste deep well injection, forced circulation in geothermal fields, hydraulic fracturing, and CO2 geological storage. However, current research mainly focuses on geological data statistics and the dominating effects of pore pressure. There are only a few laboratory-conditioned studies on the role of drilling boreholes and the effect of injection pressure on the borehole wall. Through experimental phenomenology, this study examines the risk of triggering geological disasters by fluid injection under shear stress. We developed a new direct shear test apparatus, coupled Hydro-Mechanical (HM), to investigate mechanical property variations when an intact rock experienced step drilling borehole, fluid injection, and fluid pressure acting on the borehole and fracture wall. We tested the peak shear stress of sandstone under different experimental conditions, which showed that drilling borehole, water injection, and increased pore pressure led to the decrease in peak shear stress. Furthermore, as pore pressure increased, peak shear stress dispersion increased due to crack propagation irregularity. Because the peak shear stress changed during the fluid injection steps, we suggest that the risk of triggering geological disaster with injection under shear stress, pore, borehole, and fluid pressure should be considered.

  2. An Experimental Investigation of the Risk of Triggering Geological Disasters by Injection under Shear Stress

    PubMed Central

    Liu, Yixin; Xu, Jiang; Peng, Shoujian

    2016-01-01

    Fluid injection has been applied in many fields, such as hazardous waste deep well injection, forced circulation in geothermal fields, hydraulic fracturing, and CO2 geological storage. However, current research mainly focuses on geological data statistics and the dominating effects of pore pressure. There are only a few laboratory-conditioned studies on the role of drilling boreholes and the effect of injection pressure on the borehole wall. Through experimental phenomenology, this study examines the risk of triggering geological disasters by fluid injection under shear stress. We developed a new direct shear test apparatus, coupled Hydro-Mechanical (HM), to investigate mechanical property variations when an intact rock experienced step drilling borehole, fluid injection, and fluid pressure acting on the borehole and fracture wall. We tested the peak shear stress of sandstone under different experimental conditions, which showed that drilling borehole, water injection, and increased pore pressure led to the decrease in peak shear stress. Furthermore, as pore pressure increased, peak shear stress dispersion increased due to crack propagation irregularity. Because the peak shear stress changed during the fluid injection steps, we suggest that the risk of triggering geological disaster with injection under shear stress, pore, borehole, and fluid pressure should be considered. PMID:27929142

  3. An Experimental Investigation of the Risk of Triggering Geological Disasters by Injection under Shear Stress.

    PubMed

    Liu, Yixin; Xu, Jiang; Peng, Shoujian

    2016-12-08

    Fluid injection has been applied in many fields, such as hazardous waste deep well injection, forced circulation in geothermal fields, hydraulic fracturing, and CO2 geological storage. However, current research mainly focuses on geological data statistics and the dominating effects of pore pressure. There are only a few laboratory-conditioned studies on the role of drilling boreholes and the effect of injection pressure on the borehole wall. Through experimental phenomenology, this study examines the risk of triggering geological disasters by fluid injection under shear stress. We developed a new direct shear test apparatus, coupled Hydro-Mechanical (HM), to investigate mechanical property variations when an intact rock experienced step drilling borehole, fluid injection, and fluid pressure acting on the borehole and fracture wall. We tested the peak shear stress of sandstone under different experimental conditions, which showed that drilling borehole, water injection, and increased pore pressure led to the decrease in peak shear stress. Furthermore, as pore pressure increased, peak shear stress dispersion increased due to crack propagation irregularity. Because the peak shear stress changed during the fluid injection steps, we suggest that the risk of triggering geological disaster with injection under shear stress, pore, borehole, and fluid pressure should be considered.

  4. Experimental measurement of dynamic fluid shear stress on the ventricular surface of the aortic valve leaflet

    PubMed Central

    Yap, Choon Hwai; Saikrishnan, Neelakantan

    2015-01-01

    Aortic valve (AV) calcification is a highly prevalent disease with serious impact on mortality and morbidity. The exact causes and mechanisms of AV calcification are unclear, although previous studies suggest that mechanical forces play a role. It has been clinically demonstrated that calcification preferentially occurs on the aortic surface of the AV. This is hypothesized to be due to differences in the mechanical environments on the two sides of the valve. It is thus necessary to characterize fluid shear forces acting on both sides of the leaflet to test this hypothesis. The current study is one of two studies characterizing dynamic shear stress on both sides of the AV leaflets. In the current study, shear stresses on the ventricular surface of the AV leaflets were measured experimentally on two prosthetic AV models with transparent leaflets in an in vitro pulsatile flow loop using two-component Laser Doppler Velocimetry (LDV). Experimental measurements were utilized to validate a theoretical model of AV ventricular surface shear stress based on the Womersley profile in a straight tube, with corrections for the opening angle of the valve leaflets. This theoretical model was applied to in vivo data based on MRI-derived volumetric flow rates and valve dimension obtained from the literature. Experimental results showed that ventricular surface shear stress was dominated by the streamwise component. The systolic shear stress waveform resembled a half-sinusoid during systole and peaks at 64–71 dyn/cm2, and reversed in direction at the end of systole for 15–25 ms, and reached a significant negative magnitude of 40–51 dyn/cm2. Shear stresses from the theoretical model applied to in vivo data showed that shear stresses peaked at 77–92 dyn/cm2 and reversed in direction for substantial period of time (108–110 ms) during late systole with peak negative shear stress of 35–38 dyn/cm2. PMID:21465260

  5. Shear stress effects on growth and activity of Lactobacillus delbrueckii subsp. bulgaricus.

    PubMed

    Arnaud, J P; Lacroix, C; Foussereau, C; Choplin, L

    1993-05-01

    Cells are frequently submitted to shear stresses during industrial processes. Shear stress can be either beneficial or detrimental to the cells depending on the organism and on the level of intensity. The present work was designed to study the effect of shear stress on cell activity of a widely used lactic acid bacterium, Lactobacillus delbrueckii subsp. bulgaricus (L. bulgaricus). A constant shear stress bioreactor, based on Couette device, was developed and used to control shear stress from 0 to 72 Pa during a 4-h cultivation of a supplemented whey permeate medium with L. bulgaricus at 42 degrees C. In order to reach high shear stresses and to perform experiments within the laminar flow range where hydrodynamic conditions are accurately defined, the medium was thickened with carboxymethylcellulose (CMC). pH, cell counts, optical density, lactose and lactic acid concentrations were monitored during culture, and cell activity was evaluated after culture and after a freezing treatment at -80 degrees C, using a standardized activity test based on optical density measurement. Cell metabolism was significantly improved by intermediate shear stress levels (36 and 54 Pa) during culture. Furthermore, biomass concentration, evaluated by optical density, was clearly higher at 36 Pa. Cell lengthening was observed, which was mainly related to the presence of CMC and partly to shear stress level, especially at 36 Pa. Hydrodynamic conditions during culture could affect the membrane permeability of the cell and its resistance to freezing. Cells cultivated at 72 Pa were certainly weakened by shearing forces, and these cultures exhibited lag times twice as long after freezing as those grown at 36 Pa. Furthermore, after freezing, cultures grown at 36 Pa had shorter lag times than at 0 Pa (1.1 and 1.3 h, respectively) and higher specific growth rates (1.24 and 0.99 h-1, respectively).

  6. Acute and chronic exposure to shear stress have opposite effects on endothelial permeability to macromolecules.

    PubMed

    Warboys, Christina M; Eric Berson, R; Mann, Giovanni E; Pearson, Jeremy D; Weinberg, Peter D

    2010-06-01

    Endothelial properties are affected by mechanical stresses. Several studies have shown that an acute application of shear stress increases the permeability of endothelial monolayers in culture. We investigated whether more prolonged application of shear has the opposite effect. Porcine aortic endothelial cells were cultured on Transwell filters to assess monolayer permeability to albumin. The medium above the cells was swirled using an orbital shaker; resultant shears were computed to lie within the physiological range. Acute application of shear increased permeability, but chronic application reduced it. The effect of chronic but not acute shear was reversed by inhibiting nitric oxide (NO) synthesis. The effect of chronic shear was also reversed by inhibiting phosphatidylinositol 3-OH kinase (PI3K) and soluble guanylyl cyclase. None of these interventions affected permeability under static conditions, and inhibition of cyclooxygenase was without effect. Chronic shear decreased mitosis rates by a fraction comparable to the reduction in permeability, but this effect was not reversed by inhibiting NO synthesis. We conclude that chronic application of shear stress reduces endothelial permeability to macromolecules by a PI3K-NO-cGMP-dependent mechanism. Since atherosclerosis can be triggered by excessive entry of plasma macromolecules into the arterial wall, the phenomenon may help explain the atheroprotective effects of shear and NO.

  7. Visualization and Measurement of Surface Shear Stress Vector Distributions Using Liquid Crystal Coatings

    NASA Technical Reports Server (NTRS)

    Reda, Daniel C.; Wilder, Michael C.

    1998-01-01

    When a shear-sensitive liquid crystal coating is illuminated from the normal direction by white light and observed from an oblique above-plane view angle, its color-change response to shear depends on both shear stress vector magnitude and the direction of the applied shear vector relative to the observer's in-plane line of sight. At any point, the maximum color change is always seen or measured when the local shear vector is aligned with, and directed away from, the observer; the magnitude of the color change at this vector/observer aligned orientation scales directly with shear stress magnitude. Conversely, any point exposed to a shear vector with a component directed toward the observer exhibits a noncolor-change response, always characterized by a rusty red or brown color, independent of both shear magnitude and direction. Based on this knowledge, full-surface shear stress vector visualization and measurement methodologies were formulated and successfully demonstrated. The present paper reviews the observations and measurements that led to the development of these methodologies and applications of both are discussed.

  8. The Effect of Dynamic Stress on Shear Strength and Stability in Laboratory Faults

    NASA Astrophysics Data System (ADS)

    Savage, H. M.; Marone, C.

    2003-12-01

    Recent studies show that earthquake-induced stress changes can trigger fault slip, change seismicity rates, and possibly cause additional damaging earthquakes. Investigations of stress transfer often focus on changes in the static stress state. However, dynamic stressing can lead to destabilization of creep motion and resonant behavior including stick-slip instability, both locally and at greater distances from the earthquake event. Studies of stress transfer commonly find that earthquake triggering occurs from small changes in stress and is delayed relative to the arrival of maximum stress. This phenomena cannot be explained by the Coulomb failure model, which predicts a constant failure threshold independent of stressing rate or time. We test the effects of dynamic shearing, using oscillations of shear loading rate and we compare results to theory. Using a double direct shear configuration, we sheared 3mm thick layers of glass beads (size distribution 105-149 microns) at room temperature. Glass beads are an ideal substance for these tests due to the repeatability of stick-slip events in terms of their magnitude and recurrence interval at constant velocity. The samples were loaded to quasi-periodic failure under a normal stress of 5 MPa (eliminating any changes in stick-slip behavior with displacement) and a background shear loading rate with a sinusoidal oscillation superimposed. Amplitude and frequency of the sine wave were varied, along with background shear loading rate, to determine any systematic shear stress response. We studied amplitudes ranging from 1-30 microns/sec, frequencies ranging from 0.01-10 Hz and load rates of 0.1-20 microns/sec. Although loading rate changes sign, shear stress remains positive throughout the experiment. Shear stress response was determined by studying systematic variations in stick-slip properties, e.g. amplitude of stress drop, frequency, and phase of the stick-slip stress drops compared to the imposed loading rate

  9. Fluid shear stress stimulates prostaglandin and nitric oxide release in bone marrow-derived preosteoclast-like cells

    NASA Technical Reports Server (NTRS)

    McAllister, T. N.; Du, T.; Frangos, J. A.

    2000-01-01

    Bone is a porous tissue that is continuously perfused by interstitial fluid. Fluid flow, driven by both vascular pressure and mechanical loading, may generate significant shear stresses through the canaliculi as well as along the bone lining at the endosteal surface. Both osteoblasts and osteocytes produce signaling factors such as prostaglandins and nitric in response to fluid shear stress (FSS); however, these humoral agents appear to have more profound affects on osteoclast activity at the endosteal surface. We hypothesized that osteoclasts and preosteoclasts may also be mechanosensitive and that osteoclast-mediated autocrine signaling may be important in bone remodeling. In this study, we investigated the effect of FSS on nitric oxide (NO), prostaglandin E(2) (PGE(2)), and prostacyclin (PGI(2)) release by neonatal rat bone marrow-derived preosteoclast-like cells. These cells were tartrate-resistant acid phosphatase (TRAP) positive, weakly nonspecific esterase (NSE) positive, and capable of fusing into calcitonin-responsive, bone-resorbing, multinucleated cells. Bone marrow-derived preosteoclast-like cells exposed for 6 h to a well-defined FSS of 16 dynes/cm(2) produced NO at a rate of 7.5 nmol/mg protein/h, which was 10-fold that of static controls. This response was completely abolished by 100 microM N(G)-amino-L-arginine (L-NAA). Flow also stimulated PGE(2) production (3.9 microg/mg protein/h) and PGI(2) production (220 pg/mg protein/h). L-NAA attenuated flow-induced PGE(2) production by 30%, suggesting that NO may partially modulate PGE(2) production. This is the first report demonstrating that marrow derived cells are sensitive to FSS and that autocrine signaling in these cells may play an important role in load-induced remodeling and signal transduction in bone. Copyright 2000 Academic Press.

  10. Effect of Wall Shear Stress on Corrosion Inhibitor Film Performance

    NASA Astrophysics Data System (ADS)

    Canto Maya, Christian M.

    In oil and gas production, internal corrosion of pipelines causes the highest incidence of recurring failures. Ensuring the integrity of ageing pipeline infrastructure is an increasingly important requirement. One of the most widely applied methods to reduce internal corrosion rates is the continuous injection of chemicals in very small quantities, called corrosion inhibitors. These chemical substances form thin films at the pipeline internal surface that reduce the magnitude of the cathodic and/or anodic reactions. However, the efficacy of such corrosion inhibitor films can be reduced by different factors such as multiphase flow, due to enhanced shear stress and mass transfer effects, loss of inhibitor due to adsorption on other interfaces such as solid particles, bubbles and droplets entrained by the bulk phase, and due to chemical interaction with other incompatible substances present in the stream. The first part of the present project investigated the electrochemical behavior of two organic corrosion inhibitors (a TOFA/DETA imidazolinium, and an alkylbenzyl dimethyl ammonium chloride), with and without an inorganic salt (sodium thiosulfate), and the resulting enhancement. The second part of the work explored the performance of corrosion inhibitor under multiphase (gas/liquid, solid/liquid) flow. The effect of gas/liquid multiphase flow was investigated using small and large scale apparatus. The small scale tests were conducted using a glass cell and a submersed jet impingement attachment with three different hydrodynamic patterns (water jet, CO 2 bubbles impact, and water vapor cavitation). The large scale experiments were conducted applying different flow loops (hilly terrain and standing slug systems). Measurements of weight loss, linear polarization resistance (LPR), and adsorption mass (using an electrochemical quartz crystal microbalance, EQCM) were used to quantify the effect of wall shear stress on the performance and integrity of corrosion inhibitor

  11. Impact of wall shear stress on initial bacterial adhesion in rotating annular reactor

    PubMed Central

    Saur, Thibaut; Morin, Emilie; Habouzit, Frédéric; Bernet, Nicolas

    2017-01-01

    The objective of this study was to investigate the bacterial adhesion under different wall shear stresses in turbulent flow and using a diverse bacterial consortium. A better understanding of the mechanisms governing microbial adhesion can be useful in diverse domains such as industrial processes, medical fields or environmental biotechnologies. The impact of wall shear stress—four values ranging from 0.09 to 7.3 Pa on polypropylene (PP) and polyvinyl chloride (PVC)—was carried out in rotating annular reactors to evaluate the adhesion in terms of morphological and microbiological structures. A diverse inoculum consisting of activated sludge was used. Epifluorescence microscopy was used to quantitatively and qualitatively characterize the adhesion. Attached bacterial communities were assessed by molecular fingerprinting profiles (CE-SSCP). It has been demonstrated that wall shear stress had a strong impact on both quantitative and qualitative aspects of the bacterial adhesion. ANOVA tests also demonstrated the significant impact of wall shear stress on all three tested morphological parameters (surface coverage, number of objects and size of objects) (p-values < 2.10−16). High wall shear stresses increased the quantity of attached bacteria but also altered their spatial distribution on the substratum surface. As the shear increased, aggregates or clusters appeared and their size grew when increasing the shears. Concerning the microbiological composition, the adhered bacterial communities changed gradually with the applied shear. PMID:28207869

  12. Wall shear stress at the initiation site of cerebral aneurysms.

    PubMed

    Geers, A J; Morales, H G; Larrabide, I; Butakoff, C; Bijlenga, P; Frangi, A F

    2017-02-01

    Hemodynamics are believed to play an important role in the initiation of cerebral aneurysms. In particular, studies have focused on wall shear stress (WSS), which is a key regulator of vascular biology and pathology. In line with the observation that aneurysms predominantly occur at regions of high WSS, such as bifurcation apices or outer walls of vascular bends, correlations have been found between the aneurysm initiation site and high WSS. The aim of our study was to analyze the WSS field at an aneurysm initiation site that was neither a bifurcation apex nor the outer wall of a vascular bend. Ten cases with aneurysms on the A1 segment of the anterior cerebral artery were analyzed and compared with ten controls. Aneurysms were virtually removed from the vascular models of the cases to mimic the pre-aneurysm geometry. Computational fluid dynamics (CFD) simulations were created to assess the magnitude, gradient, multidirectionality, and pulsatility of the WSS. To aid the inter-subject comparison of hemodynamic variables, we mapped the branch surfaces onto a two-dimensional parametric space. This approach made it possible to view the whole branch at once for qualitative evaluation. It also allowed us to empirically define a patch for quantitative analysis, which was consistent among subjects and encapsulated the aneurysm initiation sites in our dataset. To test the sensitivity of our results, CFD simulations were repeated with a second independent observer virtually removing the aneurysms and with a 20 % higher flow rate at the inlet. We found that branches harboring aneurysms were characterized by high WSS and high WSS gradients. Among all assessed variables, the aneurysm initiation site most consistently coincided with peaks of temporal variation in the WSS magnitude.

  13. Variable and Conflicting Shear Stress Estimates Inside an Aeolian Boundary Layer with Active Sand Transport

    NASA Astrophysics Data System (ADS)

    Baas, A. C. W.; Lee, Z. S.

    2015-12-01

    This contribution presents a comparison between two methods for measuring shear stress in an atmospheric internal boundary layer over a beach surface under optimum conditions, using wind velocities measured synchronously at 13 heights over a 1.7 m vertical array using ultrasonic anemometry. The Reynolds decomposition technique determines at-a-point shear stresses at each measurement height, while the Law-of-the-Wall yields a single boundary layer estimate based on fitting a logarithmic velocity profile through the array data. Analysis reveals significant inconsistencies between estimates derived from the two methods, on both a whole-event basis and as time-series. Despite a near-perfect fit of the Law-of-the-Wall, the point estimates of Reynolds shear stress vary greatly between heights, calling into question the assumed presence of a constant stress layer. A comparison with simultaneously measured sediment transport finds no relationship between transport activity and the discrepancies in shear stress estimates. Results do show, however, that Reynolds shear stress measured nearer the bed exhibits slightly better correlation with sand transport rate. The findings serve as a major cautionary message to the interpretation and application of single-height measurements of Reynolds shear stress and their equivalence to Law-of-the-Wall derived estimates, and these concerns apply widely to boundary layer flows in general.

  14. Shear-coupled grain-boundary migration dependence on normal strain/stress

    NASA Astrophysics Data System (ADS)

    Combe, N.; Mompiou, F.; Legros, M.

    2017-08-01

    In specific conditions, grain-boundary (GB) migration occurs in polycrystalline materials as an alternative vector of plasticity compared to the usual dislocation activity. The shear-coupled GB migration, the expected most efficient GB based mechanism, couples the GB motion to an applied shear stress. Stresses on GB in polycrystalline materials seldom have, however, a unique pure shear component. This work investigates the influence of a normal strain on the shear coupled migration of a Σ 13 (320 )[001 ] GB in a copper bicrystal using atomistic simulations. We show that the yield shear stress inducing the GB migration strongly depends on the applied normal stress. Beyond, the application of a normal stress on this GB qualitatively modifies the GB migration: while the Σ 13 (320 )[001 ] GB shear couples following the 〈110 〉 migration mode without normal stress, we report the observation of the 〈010 〉 mode under a sufficiently high tensile normal stress. Using the nudge elastic band method, we uncover the atomistic mechanism of this 〈010 〉 migration mode and energetically characterize it.

  15. Interaction of wall shear stress magnitude and gradient in the prediction of arterial macromolecular permeability.

    PubMed

    LaMack, Jeffrey A; Himburg, Heather A; Li, Xue-Mei; Friedman, Morton H

    2005-04-01

    Large spatial shear stress gradients have anecdotally been associated with early atherosclerotic lesion susceptibility in vivo and have been proposed as promoters of endothelial cell dysfunction in vitro. Here, experiments are presented in which several measures of the fluid dynamic shear stress, including its gradient, at the walls of in vivo porcine iliac arteries, are correlated against the transendothelial macromolecular permeability of the vessels. The fluid dynamic measurements are based on postmortem vascular casts, and permeability is measured from Evans blue dye (EBD) uptake. Time-averaged wall shear stress (WSS), as well as a new parameter termed maximum gradient stress (MGS) that describes the spatial shear stress gradient due to flow acceleration at a given point, are mapped for each artery and compared on a point-by-point basis to the corresponding EBD patterns. While there was no apparent relation between MGS and EBD uptake, a composite parameter, WSS(-0.11) MGS(0.044), was highly correlated with permeability. Notwithstanding the small exponents, the parameter varied widely within the region of interest. The results suggest that sites exposed to low wall shear stresses are more likely to exhibit elevated permeability, and that this increase is exacerbated in the presence of large spatial shear stress gradients.

  16. Torsional bridge setup for the characterization of integrated circuits and microsensors under mechanical shear stress.

    PubMed

    Herrmann, M; Gieschke, P; Ruther, P; Paul, O

    2011-12-01

    We present a torsional bridge setup for the electro-mechanical characterization of devices integrated in the surface of silicon beams under mechanical in-plane shear stress. It is based on the application of a torsional moment to the longitudinal axis of the silicon beams, which results in a homogeneous in-plane shear stress in the beam surface. The safely applicable shear stresses span the range of ±50 MPa. Thanks to a specially designed clamping mechanism, the unintended normal stress typically stays below 2.5% of the applied shear stress. An analytical model is presented to compute the induced shear stress. Numerical computations verify the analytical results and show that the homogeneity of the shear stress is very high on the beam surface in the region of interest. Measurements with piezoresistive microsensors fabricated using a complementary metal-oxide-semiconductor process show an excellent agreement with both the computational results and comparative measurements performed on a four-point bending bridge. The electrical connection to the silicon beam is performed with standard bond wires. This ensures that minimal forces are applied to the beam by the electrical interconnection to the external instrumentation and that devices with arbitrary bond pad layout can be inserted into the setup.

  17. Torsional bridge setup for the characterization of integrated circuits and microsensors under mechanical shear stress

    NASA Astrophysics Data System (ADS)

    Herrmann, M.; Gieschke, P.; Ruther, P.; Paul, O.

    2011-12-01

    We present a torsional bridge setup for the electro-mechanical characterization of devices integrated in the surface of silicon beams under mechanical in-plane shear stress. It is based on the application of a torsional moment to the longitudinal axis of the silicon beams, which results in a homogeneous in-plane shear stress in the beam surface. The safely applicable shear stresses span the range of ±50 MPa. Thanks to a specially designed clamping mechanism, the unintended normal stress typically stays below 2.5% of the applied shear stress. An analytical model is presented to compute the induced shear stress. Numerical computations verify the analytical results and show that the homogeneity of the shear stress is very high on the beam surface in the region of interest. Measurements with piezoresistive microsensors fabricated using a complementary metal-oxide-semiconductor process show an excellent agreement with both the computational results and comparative measurements performed on a four-point bending bridge. The electrical connection to the silicon beam is performed with standard bond wires. This ensures that minimal forces are applied to the beam by the electrical interconnection to the external instrumentation and that devices with arbitrary bond pad layout can be inserted into the setup.

  18. Gyrokinetic simulation of momentum transport with residual stress from diamagnetic level velocity shears

    SciTech Connect

    Waltz, R. E.; Staebler, G. M.; Solomon, W. M.

    2011-04-15

    Residual stress refers to the remaining toroidal angular momentum (TAM) flux (divided by major radius) when the shear in the equilibrium fluid toroidal velocity (and the velocity itself) vanishes. Previously [Waltz et al., Phys. Plasmas 14, 122507 (2007); errata 16, 079902 (2009)], we demonstrated with GYRO [Candy and Waltz, J. Comp. Phys. 186, 545 (2003)] gyrokinetic simulations that TAM pinching from (ion pressure gradient supported or diamagnetic level) equilibrium ExB velocity shear could provide some of the residual stress needed to support spontaneous toroidal rotation against normal diffusive loss. Here we show that diamagnetic level shear in the intrinsic drift wave velocities (or ''profile shear'' in the ion and electron density and temperature gradients) provides a comparable residual stress. The individual signed contributions of these small (rho-star level) ExB and profile velocity shear rates to the turbulence level and (rho-star squared) ion energy transport stabilization are additive if the rates are of the same sign. However because of the additive stabilization effect, the contributions to the small (rho-star cubed) residual stress is not always simply additive. If the rates differ in sign, the residual stress from one can buck out that from the other (and in some cases reduce the stabilization.) The residual stress from these diamagnetic velocity shear rates is quantified by the ratio of TAM flow to ion energy (power) flow (M/P) in a global GYRO core simulation of a ''null'' toroidal rotation DIII-D [Mahdavi and Luxon, Fusion Sci. Technol. 48, 2 (2005)] discharge by matching M/P profiles within experimental uncertainty. Comparison of global GYRO (ion and electron energy as well as particle) transport flow balance simulations of TAM transport flow in a high-rotation DIII-D L-mode quantifies and isolates the ExB shear and parallel velocity (Coriolis force) pinching components from the larger ''diffusive'' parallel velocity shear driven component and

  19. Deformation and Stress Response of Carbon Nanotubes/UHMWPE Composites under Extensional-Shear Coupling Flow

    NASA Astrophysics Data System (ADS)

    Wang, Junxia; Cao, Changlin; Yu, Dingshan; Chen, Xudong

    2017-05-01

    In this paper, the effect of varying extensional-shear couple loading on deformation and stress response of Carbon Nanotubes/ ultra-high molecular weight polyethylene (CNTs/UHMWPE) composites was investigated using finite element numerical simulation, with expect to improve the manufacturing process of UHMWPE-based composites with reduced stress and lower distortion. When applying pure extensional loading and pure X-Y shear loading, it was found that the risk of a structural breakage greatly rises. For identifying the coupling between extensional and shear loading, distinct generations of force loading were defined by adjusting the magnitude of extensional loading and X-Y shear loading. It was shown that with the decrement of X-Y shear loading the deformation decreases obviously where the maximal Mises stress in Z-direction at 0.45 m distance is in the range from 24 to 10 MPa and the maximal shear stress at 0.61 m distance is within the range from 0.9 to 0.3 MPa. In addition, all the stresses determined were clearly below the yield strength of CNTs/UHMWPE composites under extensional-shear couple loading.

  20. Quantification of Interfibrillar Shear Stress in Aligned Soft Collagenous Tissues via Notch Tension Testing

    PubMed Central

    Szczesny, Spencer E.; Caplan, Jeffrey L.; Pedersen, Pal; Elliott, Dawn M.

    2015-01-01

    The mechanical function of soft collagenous tissues is largely determined by their hierarchical organization of collagen molecules. While collagen fibrils are believed to be discontinuous and transfer load through shearing of the interfibrillar matrix, interfibrillar shear stresses have never been quantified. Scaling traditional shear testing procedures down to the fibrillar length scale is impractical and would introduce substantial artifacts. Here, through the use of a novel microscopic variation of notch tension testing, we explicitly demonstrate the existence of interfibrillar shear stresses within tendon fascicles and provide the first measurement of their magnitude. Axial stress gradients along the sample length generated by notch tension testing were measured and used to calculate a value of 32 kPa for the interfibrillar shear stress. This estimate is comparable to the interfibrillar shear stress predicted by previous multiscale modeling of tendon fascicles, which supports the hypothesis that fibrils are discontinuous and transmit load through interfibrillar shear. This information regarding the structure-function relationships of tendon and other soft collagenous tissues is necessary to identify potential causes for tissue impairment with degeneration and provide the foundation for developing regenerative repair strategies or engineering biomaterials for tissue replacement. PMID:26469396

  1. Quantification of Interfibrillar Shear Stress in Aligned Soft Collagenous Tissues via Notch Tension Testing

    NASA Astrophysics Data System (ADS)

    Szczesny, Spencer E.; Caplan, Jeffrey L.; Pedersen, Pal; Elliott, Dawn M.

    2015-10-01

    The mechanical function of soft collagenous tissues is largely determined by their hierarchical organization of collagen molecules. While collagen fibrils are believed to be discontinuous and transfer load through shearing of the interfibrillar matrix, interfibrillar shear stresses have never been quantified. Scaling traditional shear testing procedures down to the fibrillar length scale is impractical and would introduce substantial artifacts. Here, through the use of a novel microscopic variation of notch tension testing, we explicitly demonstrate the existence of interfibrillar shear stresses within tendon fascicles and provide the first measurement of their magnitude. Axial stress gradients along the sample length generated by notch tension testing were measured and used to calculate a value of 32 kPa for the interfibrillar shear stress. This estimate is comparable to the interfibrillar shear stress predicted by previous multiscale modeling of tendon fascicles, which supports the hypothesis that fibrils are discontinuous and transmit load through interfibrillar shear. This information regarding the structure-function relationships of tendon and other soft collagenous tissues is necessary to identify potential causes for tissue impairment with degeneration and provide the foundation for developing regenerative repair strategies or engineering biomaterials for tissue replacement.

  2. Fluorescent molecular rotor for the study of membrane fluidity in endothelial cells under fluid shear stress

    NASA Astrophysics Data System (ADS)

    Haidekker, Mark A.; Frangos, John A.

    2000-04-01

    Molecular rotors are fluorescent probes that change quantum yield with the viscosity of their environment. When integrated into the cell membrane, they can be used to probe viscosity changes of the membrane. Fluid shear stress is hypothesized to increase membrane fluidity in the membrane of endothelial cells, a change that leads to the activation of heterotrimetric G proteins, thus activating a signal transduction cascade. This hypothesis was examined using a molecular rotor, 9-dicyanovinyl-julolidine (DCVJ) as membrane probe. The principal response, a decease of fluorescence intensity caused by increased membrane fluidity, was obtained by adding a fluidity-increasing agent to the cells. In a parallel-plate flow chamber, a confluent layer of DCVJ-labeled human umbilical cord venous endothelial cells were exposed to different levels of fluid shear stress. With increased shear, a reduced fluorescence intensity was observed, indicating an increase of membrane fluidity. Step changes of fluid shear stress caused an approximately linear drop of fluorescence within 5 seconds, showing fast and almost full recovery after shear stopped. A linear relationship between shear stress and membrane fluidity changes was also observed. This study not only shows the suitability of the molecular rotor DCVJ as a membrane fluidity probe, but also provides evidence for the direct link between fluid shear stress and membrane fluidity, and suggests that the membrane is the primary flow mechanosensor of the cell.

  3. Wall shear stress measurement in blade end-wall corner region

    NASA Technical Reports Server (NTRS)

    Bhargava, R.; Raj, R.; Boldman, D. R.

    1987-01-01

    The magnitude and the direction of wall shear stress and surface pressure in the blade end-wall corner region were investigated. The measurements were obtained on a specially designed Preston tube, the tip of which could be concentrically rotated about its axis of rotation at the measurement location. The magnitude of wall shear stress in the vicinity of the corner was observed to increase significantly (170 percent) compared to its far-upstream value; the increase was consistently higher on the blade surface compared to the value on the plate surface of the blade end-wall corner. On both surfaces in the blade end-wall corner, the variation of the wall shear stress direction was found to be more predominant in the vicinity of the blade leading-edge location. The trend of the measured wall shear stress direction showed good agreement with the limiting streamline directions obtained from the flow visualization studies.

  4. The Micro-Pillar Shear-Stress Sensor MPS3 for Turbulent Flow

    PubMed Central

    Große, Sebastian; Schröder, Wolfgang

    2009-01-01

    Wall-shear stress results from the relative motion of a fluid over a body surface as a consequence of the no-slip condition of the fluid in the vicinity of the wall. To determine the two-dimensional wall-shear stress distribution is of utter importance in theoretical and applied turbulence research. In this article, characteristics of the Micro-Pillar Shear-Stress Sensor MPS3, which has been shown to offer the potential to measure the two-directional dynamic wall-shear stress distribution in turbulent flows, will be summarized. After a brief general description of the sensor concept, material characteristics, possible sensor-structure related error sources, various sensitivity and distinct sensor performance aspects will be addressed. Especially, pressure-sensitivity related aspects will be discussed. This discussion will serve as ‘design rules’ for possible new fields of applications of the sensor technology. PMID:22574010

  5. Theory to predict shear stress on cells in turbulent blood flow.

    PubMed

    Morshed, Khandakar Niaz; Bark, David; Forleo, Marcio; Dasi, Lakshmi Prasad

    2014-01-01

    Shear stress on blood cells and platelets transported in a turbulent flow dictates the fate and biological activity of these cells. We present a theoretical link between energy dissipation in turbulent flows to the shear stress that cells experience and show that for the case of physiological turbulent blood flow: (a) the Newtonian assumption is valid, (b) turbulent eddies are universal for the most complex of blood flow problems, and (c) shear stress distribution on turbulent blood flows is possibly universal. Further we resolve a long standing inconsistency in hemolysis between laminar and turbulent flow using the theoretical framework. This work demonstrates that energy dissipation as opposed to bulk shear stress in laminar or turbulent blood flow dictates local mechanical environment of blood cells and platelets universally.

  6. Estimation of turbulent shear stress in free jets: application to valvular regurgitation.

    PubMed

    Winoto, S H; Shah, D A; Liu, H

    1996-01-01

    In an attempt to better assess the severity of valvular regurgitation, an in-vitro experiment has been conducted to estimate turbulent shear stress levels within free jets issuing from different orifice shapes and sizes by means of hot-wire anemometry. On the basis of the measured mean velocities and the jet profiles, the distributions of the normalized kinematic turbulent shear stress (uv/Um2) were estimated for different jets by using an equation available for self-preserving circular jet. The results indicate that the equation can estimate the distributions of uv/Um2 independent of the orifice shape and Reynolds number of the jet. For the range of Reynolds numbers considered, the estimation of maximum turbulent shear stress inferred from these distributions suggests that the critical shear stress level of approximately 200 N/m2, corresponding to destruction of blood cells, is exceeded for typical blood flow velocity of 5 m/s at the valvular lesion.

  7. An equilibrium method for prediction of transverse shear stresses in a thick laminated plate

    NASA Technical Reports Server (NTRS)

    Chaudhuri, R. Z.

    1986-01-01

    First two equations of equilibrium are utilized to compute the transverse shear stress variation through thickness of a thick laminated plate after in-plane stresses have been computed using an assumed quadratic displacement triangular element based on transverse inextensibility and layerwise constant shear angle theory (LCST). Centroid of the triangle is the point of exceptional accuracy for transverse shear stresses. Numerical results indicate close agreement with elasticity theory. An interesting comparison between the present theory and that based on assumed stress hybrid finite element approach suggests that the latter does not satisfy the condition of free normal traction at the edge. Comparison with numerical results obtained by using constant shear angle theory suggests that LCST is close to the elasticity solution while the CST is closer to classical (CLT) solution. It is also demonstrated that the reduced integration gives faster convergence when the present theory is applied to a thin plate.

  8. Animal models of surgically manipulated flow velocities to study shear stress-induced atherosclerosis.

    PubMed

    Winkel, Leah C; Hoogendoorn, Ayla; Xing, Ruoyu; Wentzel, Jolanda J; Van der Heiden, Kim

    2015-07-01

    Atherosclerosis is a chronic inflammatory disease of the arterial tree that develops at predisposed sites, coinciding with locations that are exposed to low or oscillating shear stress. Manipulating flow velocity, and concomitantly shear stress, has proven adequate to promote endothelial activation and subsequent plaque formation in animals. In this article, we will give an overview of the animal models that have been designed to study the causal relationship between shear stress and atherosclerosis by surgically manipulating blood flow velocity profiles. These surgically manipulated models include arteriovenous fistulas, vascular grafts, arterial ligation, and perivascular devices. We review these models of manipulated blood flow velocity from an engineering and biological perspective, focusing on the shear stress profiles they induce and the vascular pathology that is observed. Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.

  9. Panoramic diagnostics of shear stresses on the channel wall with a step using the liquid crystals

    NASA Astrophysics Data System (ADS)

    Zharkova, G. M.; Kovrizhina, V. N.; Petrov, A. P.; Pod'yachev, S. P.

    2016-11-01

    Measurements results on the shear stresses of surface friction by means of thin-film coatings based on cholesteric liquid crystals and specialized software for digital processing of experimental video are presented in the paper. The calibration dependencies of shear stress relative to the hue and azimuth angle as well as shear stress spatial distribution at subsonic turbulent flow ( V ∝ = 84 m/s) around a step, trapezoidal in plane (Reynolds number calculated for step height h, Re h = 2.57•104), with a base angle of 46° were derived for two geometries of experiment. The experiments demonstrated high sensitivity of liquid crystals to rearrangement of the near-wall flow structure and possibility to obtain quantitative data about mean shear stress levels.

  10. GEF-H1 is necessary for neutrophil shear stress-induced migration during inflammation.

    PubMed

    Fine, Noah; Dimitriou, Ioannis D; Rullo, Jacob; Sandí, María José; Petri, Björn; Haitsma, Jack; Ibrahim, Hisham; La Rose, Jose; Glogauer, Michael; Kubes, Paul; Cybulsky, Myron; Rottapel, Robert

    2016-10-10

    Leukocyte crawling and transendothelial migration (TEM) are potentiated by shear stress caused by blood flow. The mechanism that couples shear stress to migration has not been fully elucidated. We found that mice lacking GEF-H1 (GEF-H1(-/-)), a RhoA-specific guanine nucleotide exchange factor (GEF), displayed limited migration and recruitment of neutrophils into inflamed tissues. GEF-H1(-/-) leukocytes were deficient in in vivo crawling and TEM in the postcapillary venules. We demonstrated that although GEF-H1 deficiency had little impact on the migratory properties of neutrophils under static conditions, shear stress triggered GEF-H1-dependent spreading and crawling of neutrophils and relocalization of GEF-H1 to flotillin-2-rich uropods. Our results identify GEF-H1 as a component of the shear stress response machinery in neutrophils required for a fully competent immune response to bacterial infection. © 2016 Fine et al.

  11. Influence of polymer charge on the shear yield stress of silica aggregated with adsorbed cationic polymers.

    PubMed

    Zhou, Ying; Yu, Hai; Wanless, Erica J; Jameson, Graeme J; Franks, George V

    2009-08-15

    Flocs were produced by adding three cationic polymers (10% charge density, 3.0x10(5) g/mol molecular weight; 40% charge density, 1.1x10(5) g/mol molecular weight; and 100% charge density, 1.2x10(5) g/mol molecular weight) to 90 nm diameter silica particles. The shear yield stresses of the consolidated sediment beds from settled and centrifuged flocs were determined via the vane technique. The polymer charge density plays an important role in influencing the shear yield stresses of sediment beds. The shear yield stresses of sediment beds from flocs induced by the 10% charged polymer were observed to increase with an increase in polymer dose, initial solid concentration and background electrolyte concentration at all volume fractions. In comparison, polymer dose has a marginal effect on the shear yield stresses of sediment beds from flocs induced by the 40% and 100% charged polymers. The shear yield stresses of sediments from flocs induced by the 40% charged polymer are independent of salt concentration whereas the addition of salt decreases the shear yield stresses of sediments from flocs induced by the 100% charged polymer. When flocculated at the optimum dose for each polymer (12 mg/g silica for the 10% charged polymer at 0.03 M NaCl, 12 mg/g for 40% and 2 mg/g for 100%), shear yield stress increases as polymer charge increases. The effects observed are related to the flocculation mechanism (bridging, patch attraction or charge neutralisation) and the magnitude of the adhesive force. Comparison of shear and compressive yield stresses show that the network is only slightly weaker in shear than in compression. This is different than many other systems (mainly salt and pH coagulation) which have shear yield stress much less than compressive yield stress. The existing models relating the power law exponent of the volume fraction dependence of the shear yield stress to the network fractal structure are not satisfactory to predict all the experimental behaviour.

  12. Shear Stress Drives Local Variation in Invertebrate Drift in a Large River

    NASA Astrophysics Data System (ADS)

    Muehlbauer, J. D.; Kennedy, T.; Yackulic, C. B.

    2013-12-01

    Recent advances in physical stream flow measurements using acoustic Doppler current profilers (ADCPs) have yielded important insights in hydrology and geomorphology related to discharge and processes such as bed sediment incipient motion. These measurements also have underappreciated potential for use in ecological studies. For example, invertebrate drift, or the downstream transport of benthic-derived invertebrates, is a fundamental process in streams and rivers: it is both critical to the maintenance of benthic invertebrate populations and provides a key mechanism of resource delivery to drift-feeding fishes. However, there is substantial uncertainty regarding the factors that drive spatial variation in invertebrate drift, particularly in large rivers. While laboratory studies in flumes have demonstrated the importance of shear stress in initiating invertebrate drift (similar to studies of bed sediment critical shear stress in fluvial geomorphology), field-based evaluations of the relationship between shear stress and drift would be beneficial. Such field studies, however, are rare. Here, we evaluate the relationship between localized shear stress (N/m2) and invertebrate drift concentrations (#/m3) for the Colorado River downstream of Glen Canyon Dam (steady discharge of 228 m3/s during study). Invertebrate drift was quantified at 25 stations throughout the 25 km long Glen Canyon tailwater segment. We link these drift measurements to empirical measurements of water column shear stress derived from ADCP data, taken at the location of each drift sample and 250 m upstream of each drift sampling location (50 total profiles). Invertebrate drift concentrations varied strongly throughout the 25 km reach, and much of this variation can be explained by localized differences in shear stress. Species composition in the drift also varied with shear stress, suggesting that shear stress exerts a differential control on drift initiation for individual taxa. These results

  13. Effects of different types of fluid shear stress on endothelial cell proliferation and survival.

    PubMed

    Kadohama, Takayuki; Nishimura, Kengo; Hoshino, Yuji; Sasajima, Tadahiro; Sumpio, Bauer E

    2007-07-01

    We attempted to clarify the effect of different types of shear stress on endothelial cell (EC) proliferation and survival. Bovine aortic ECs were subjected to either steady laminar, 1 Hz pulsatile, or 1 Hz to and fro shear at 14 dyne/cm(2). % of BrdU positive EC was 14.3 +/- 1.6% in steady, 21.5 +/- 3.2% in pulsatile, and 11.4 +/- 2.4% in to and fro after 4 h, respectively (P < 0.05). Pulsatile shear compared with static control. Rapamycin reduced BrdU incorporation in all shear regimens (P < 0.001). However, it was still higher in EC exposed to pulsatile shear than the other regimens (P < 0.005). PD98059 completely abolished the increased BrdU incorporation in all shear regimens, including pulsatile shear. Pulsatile shear had significantly elevated ERK1/2 phosphorylation at 5 min compared with steady (P < 0.05) and to and fro shear (P < 0.01) while there was no significant difference in pp70(S6k) phosphorylation between any shear regimen. The ratio of apoptotic cells in serum deprived EC in the presence of steady laminar, pulsatile and to and fro shear for 4 h were 2.7 +/- 0.78%, 2.7 +/- 0.42%, and 2.9 +/- 0.62%, respectively while after the addition of serum for 4 h, it was 4.3 +/- 0.73%. All shear regimens phosphorylated AKT in a time-dependent manner with no significant difference between regimens. Our results demonstrate that different types of shear stress regimens have different effects on EC and may account for the variable response of EC to hemodynamics in the circulation.

  14. A High shear stress segment along the San Andreas Fault: Inferences based on near-field stress direction and stress magnitude observations in the Carrizo Plain Area

    SciTech Connect

    Castillo, D. A.,; Younker, L.W.

    1997-01-30

    Nearly 200 new in-situ determinations of stress directions and stress magnitudes near the Carrizo plain segment of the San Andreas fault indicate a marked change in stress state occurring within 20 km of this principal transform plate boundary. A natural consequence of this stress transition is that if the observed near-field ``fault-oblique`` stress directions are representative of the fault stress state, the Mohr-Coulomb shear stresses resolved on San Andreas sub-parallel planes are substantially greater than previously inferred based on fault-normal compression. Although the directional stress data and near-hydrostatic pore pressures, which exist within 15 km of the fault, support a high shear stress environment near the fault, appealing to elevated pore pressures in the fault zone (Byerlee-Rice Model) merely enhances the likelihood of shear failure. These near-field stress observations raise important questions regarding what previous stress observations have actually been measuring. The ``fault-normal`` stress direction measured out to 70 km from the fault can be interpreted as representing a comparable depth average shear strength of the principal plate boundary. Stress measurements closer to the fault reflect a shallower depth-average representation of the fault zone shear strength. If this is true, only stress observations at fault distances comparable to the seismogenic depth will be representative of the fault zone shear strength. This is consistent with results from dislocation monitoring where there is pronounced shear stress accumulation out to 20 km of the fault as a result of aseismic slip within the lower crust loading the upper locked section. Beyond about 20 km, the shear stress resolved on San Andreas fault-parallel planes becomes negligible. 65 refs., 15 figs.

  15. Shear Stress in Nickel and Ni-60Co under One-Dimensional Shock Loading

    SciTech Connect

    Workman, A.; Wallwork, A.; Meziere, Y. J. E.; Millett, J. C. F.; Bourne, N. K.

    2006-07-28

    The dynamic response of pure nickel (Ni), and its alloy, Ni-60Co (by weight %), has been investigated during one-dimensional shock loading. Few materials' properties are different and the only significantly altered feature is the reduced stacking fault energy (SFE) for the Ni-60Co. This paper considers the effect of this reduced SFE on the shear strength. Data (in terms of shock stress, particle velocity and shock velocity) are also presented. The influence on the shear stress, {tau} of cobalt additions in nickel are then investigated and presented. Results indicate that the lateral stress is increasing in both materials with the increasing impact stress. The shear stress was found to be higher in the nickel than in the Ni-60Co. The progressive decrease of the lateral stress noted during loading indicates a complex mechanism of deformation behind the shock front.

  16. Shear stress-induced apoptosis of adherent neutrophils: A mechanism for persistence of cardiovascular device infections

    PubMed Central

    Shive, Matthew S.; Salloum, Mariah L.; Anderson, James M.

    2000-01-01

    The mechanisms underlying problematic cardiovascular device-associated infections are not understood. Because the outcome of the acute response to infection is largely dependent on the function of neutrophils, the persistence of these infections suggests that neutrophil function may be compromised because of cellular responses to shear stress. A rotating disk system was used to generate physiologically relevant shear stress levels (0–18 dynes/cm2; 1 dyne = 10 μN) at the surface of a polyetherurethane urea film. We demonstrate that shear stress diminishes phagocytic ability in neutrophils adherent to a cardiovascular device material, and causes morphological and biochemical alterations that are consistent with those described for apoptosis. Complete neutrophil apoptosis occurred at shear stress levels above 6 dynes/cm2 after only 1 h. Morphologically, these cells displayed irreversible cytoplasmic and nuclear condensation while maintaining intact membranes. Analysis of neutrophil area and filamentous actin content demonstrated concomitant decreases in both cell area and actin content with increasing levels of shear stress. Neutrophil phagocytosis of adherent bacteria decreased with increasing shear stress. Biochemical alterations included membrane phosphatidylserine exposure and DNA fragmentation, as evaluated by in situ annexin V and terminal deoxynucleotidyltransferase-mediated dUTP end labeling (TUNEL) assays, respectively. The potency of the shear-stress effect was emphasized by comparative inductive studies with adherent neutrophils under static conditions. The combination of tumor necrosis factor-α and cycloheximide was ineffective in inducing >21% apoptosis after 3 h. These findings suggest a mechanism through which shear stress plays an important role in the development of bacterial infections at the sites of cardiovascular device implantation. PMID:10823909

  17. Bonded joint and method. [for reducing peak shear stress in adhesive bonds

    NASA Technical Reports Server (NTRS)

    Sainsbury-Carter, J. B. (Inventor)

    1974-01-01

    An improved joint is described for reducing the peak shear stress in adhesive bonds when adhesives are used to bond two materials which are in a lapped relationship and which differ in value of modulus of elasticity. An insert placed between the adhesive and one of the two materials acts to cushion the discontinuity of material stiffness thereby reducing the peak shear stress in the adhesive bond.

  18. High shear stress relates to intraplaque haemorrhage in asymptomatic carotid plaques.

    PubMed

    Tuenter, A; Selwaness, M; Arias Lorza, A; Schuurbiers, J C H; Speelman, L; Cibis, M; van der Lugt, A; de Bruijne, M; van der Steen, A F W; Franco, O H; Vernooij, M W; Wentzel, J J

    2016-08-01

    Carotid artery plaques with vulnerable plaque components are related to a higher risk of cerebrovascular accidents. It is unknown which factors drive vulnerable plaque development. Shear stress, the frictional force of blood at the vessel wall, is known to influence plaque formation. We evaluated the association between shear stress and plaque components (intraplaque haemorrhage (IPH), lipid rich necrotic core (LRNC) and/or calcifications) in relatively small carotid artery plaques in asymptomatic persons. Participants (n = 74) from the population-based Rotterdam Study, all with carotid atherosclerosis assessed on ultrasound, underwent carotid MRI. Multiple MRI sequences were used to evaluate the presence of IPH, LRNC and/or calcifications in plaques in the carotid arteries. Images were automatically segmented for lumen and outer wall to obtain a 3D reconstruction of the carotid bifurcation. These reconstructions were used to calculate minimum, mean and maximum shear stresses by applying computational fluid dynamics with subject-specific inflow conditions. Associations between shear stress measures and plaque composition were studied using generalized estimating equations analysis, adjusting for age, sex and carotid wall thickness. The study group consisted of 93 atherosclerotic carotid arteries of 74 participants. In plaques with higher maximum shear stresses, IPH was more often present (OR per unit increase in maximum shear stress (log transformed) = 12.14; p = 0.001). Higher maximum shear stress was also significantly associated with the presence of calcifications (OR = 4.28; p = 0.015). Higher maximum shear stress is associated with intraplaque haemorrhage and calcifications. Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.

  19. Shear stress causes nuclear localization of endothelial glucocorticoid receptor and expression from the GRE promoter.

    PubMed

    Ji, Julie Y; Jing, Huiyan; Diamond, Scott L

    2003-02-21

    We tested the hypothesis that steady laminar shear stress activates the glucocorticoid receptor (GR) and its transcriptional signaling pathway in an effort to investigate the potential involvement of GR in shear stress-induced antiatherosclerosis actions in the vasculature. In both bovine aortic endothelial cells (BAECs) and NIH3T3 cells expressing GFP-GR chimeric protein, wall shear stress of 10 or 25 dynes/cm2 caused a marked nuclear localization of GFP-GR within 1 hour to an extent comparable to induction with 25 micromol/L dexamethasone. The shear mediated nuclear localization of GFP-GR was significantly reduced by 25 micromol/L of the MEK1 inhibitor (PD098059) or the PI 3-kinase inhibitor (LY294002). Also, Western blots demonstrated translocation of endogenous GR into nucleus of sheared BAECs. Promoter construct studies using glucocorticoid response element (GRE)-driven expression of secreted alkaline phosphatase (SEAP) indicated that BAECs exposed to shear stress of 10 and 25 dynes/cm2 for 8 hours produced >9-fold more SEAP (n=6; P<0.005) than control cells, a level comparable to that observed with dexamethasone. Shear stress enhanced SEAP expression at 6 hours was reduced 50% (n=5; P<0.005) by MEK1/2 or PI 3-kinase inhibitors, but not by the NO inhibitor, L-NAME. Finally, in human internal mammary artery, endothelial GR is found to be highly nuclear localized. We report a new shear responsive transcriptional element, GRE. The finding that hemodynamic forces can be as potent as high dose glucocorticoid steroid in activating GR and GRE-regulated expression correlates with the atheroprotective responses of endothelial cells to unidirectional arterial shear stress.

  20. Activation and shedding of platelet glycoprotein IIb/IIIa under non-physiological shear stress.

    PubMed

    Chen, Zengsheng; Mondal, Nandan K; Ding, Jun; Koenig, Steven C; Slaughter, Mark S; Griffith, Bartley P; Wu, Zhongjun J

    2015-11-01

    The purpose of this study was to investigate the influence of non-physiological high shear stress on activation and shedding of platelet GP IIb/IIIa receptors. The healthy donor blood was exposed to three levels of high shear stresses (25, 75, 125 Pa) from the physiological to non-physiological status with three short exposure time (0.05, 0.5, 1.5 s), created by a specific blood shearing system. The activation and shedding of the platelet GPIIb/IIIa were analyzed using flow cytometry and enzyme-linked immunosorbent assay. In addition, platelet P-selectin expression of sheared blood, which is a marker for activated platelets, was also analyzed. The results from the present study showed that the number of activated platelets, as indicated by the surface GPIIb/IIIa activation and P-selectin expression, increased with increasing the shear stress level and exposure time. However, the mean fluorescence of GPIIb/IIIa on the platelet surface, decreased with increasing the shear stress level and exposure time. The reduction of GPIIb/IIIa on the platelet surface was further proved by the reduction of further activated platelet GPIIb/IIIa surface expression induced by ADP and the increase in GPIIb/IIIa concentration in microparticle-free plasma with increasing the applied shear stress and exposure time. It is clear that non-physiological shear stress induce a paradoxical phenomenon, in which both activation and shedding of the GPIIb/IIIa on the platelet surface occur simultaneously. This study may offer a new perspective to explain the reason of both increased thrombosis and bleeding events in patients implanted with high shear blood-contacting medical devices.

  1. Effect of Varying Fluid Shear Stress on Cancer Stem Cell Viability & Protein Expression

    NASA Astrophysics Data System (ADS)

    Domier, Ria; Kim, Yonghyun; Dozier, David; Triantafillu, Ursula

    2013-11-01

    Cancer stem cells cultured in vitro in stirred bioreactors are exposed to shear stress. By observing the effect of shear stress on cancer stem cell viability, laboratory cell growth could be optimized. In addition, metastasized cancer stem cells in vivo are naturally exposed to shear stress, a factor influencing stem cell differentiation, while circulating in the bloodstream. Changes in protein expression after exposure to shear stress could allow for identification and targeting of circulating cancer cells. In this study, blood flow through capillaries was simulated by using a syringe pump to inject suspensions of Kasumi-1 leukemia stem cells into model blood vessels composed of PEEK tubing 125 microns in diameter. The Hagen-Poisseuille equation was used to solve for operating flow rates based on specified amounts of shear stress. After exposure, cell counts and viabilities were observed using an optical microscope and proteins were analyzed using Western blotting. It was observed that at a one minute exposure to stress, cell viability increased as the amount of shear was increased from 10 to 60 dynes per square centimeter. Results from this research are applicable to optimization of large-scale stem cell growth in bioreactors as well as to the design of targeted cancer therapies. Funding from NSF REU grant #1062611 is gratefully acknowledged.

  2. Human brain microvascular endothelial cells resist elongation due to shear stress.

    PubMed

    Reinitz, Adam; DeStefano, Jackson; Ye, Mao; Wong, Andrew D; Searson, Peter C

    2015-05-01

    Endothelial cells in straight sections of vessels are known to elongate and align in the direction of flow. This phenotype has been replicated in confluent monolayers of bovine aortic endothelial cells and human umbilical vein endothelial cells (HUVECs) in cell culture under physiological shear stress. Here we report on the morphological response of human brain microvascular endothelial cells (HBMECs) in confluent monolayers in response to shear stress. Using a microfluidic platform we image confluent monolayers of HBMECs and HUVECs under shear stresses up to 16 dyne cm(-2). From live-cell imaging we quantitatively analyze the cell morphology and cell speed as a function of time. We show that HBMECs do not undergo a classical transition from cobblestone to spindle-like morphology in response to shear stress. We further show that under shear stress, actin fibers are randomly oriented in the cells indicating that there is no cytoskeletal remodeling. These results suggest that HBMECs are programmed to resist elongation and alignment under shear stress, a phenotype that may be associated with the unique properties of the blood-brain barrier.

  3. Vascular endothelial cell membranes differentiate between stretch and shear stress through transitions in their lipid phases.

    PubMed

    Yamamoto, Kimiko; Ando, Joji

    2015-10-01

    Vascular endothelial cells (ECs) respond to the hemodynamic forces stretch and shear stress by altering their morphology, functions, and gene expression. However, how they sense and differentiate between these two forces has remained unknown. Here we report that the plasma membrane itself differentiates between stretch and shear stress by undergoing transitions in its lipid phases. Uniaxial stretching and hypotonic swelling increased the lipid order of human pulmonary artery EC plasma membranes, thereby causing a transition from the liquid-disordered phase to the liquid-ordered phase in some areas, along with a decrease in membrane fluidity. In contrast, shear stress decreased the membrane lipid order and increased membrane fluidity. A similar increase in lipid order occurred when the artificial lipid bilayer membranes of giant unilamellar vesicles were stretched by hypotonic swelling, indicating that this is a physical phenomenon. The cholesterol content of EC plasma membranes significantly increased in response to stretch but clearly decreased in response to shear stress. Blocking these changes in the membrane lipid order by depleting membrane cholesterol with methyl-β-cyclodextrin or by adding cholesterol resulted in a marked inhibition of the EC response specific to stretch and shear stress, i.e., phosphorylation of PDGF receptors and phosphorylation of VEGF receptors, respectively. These findings indicate that EC plasma membranes differently respond to stretch and shear stress by changing their lipid order, fluidity, and cholesterol content in opposite directions and that these changes in membrane physical properties are involved in the mechanotransduction that activates membrane receptors specific to each force.

  4. Doppler optical coherence tomography imaging of local fluid flow and shear stress within microporous scaffolds

    NASA Astrophysics Data System (ADS)

    Jia, Yali; Bagnaninchi, Pierre O.; Yang, Ying; Haj, Alicia El; Hinds, Monica T.; Kirkpatrick, Sean J.; Wang, Ruikang K.

    2009-05-01

    Establishing a relationship between perfusion rate and fluid shear stress in a 3D cell culture environment is an ongoing and challenging task faced by tissue engineers. We explore Doppler optical coherence tomography (DOCT) as a potential imaging tool for in situ monitoring of local fluid flow profiles inside porous chitosan scaffolds. From the measured fluid flow profiles, the fluid shear stresses are evaluated. We examine the localized fluid flow and shear stress within low- and high-porosity chitosan scaffolds, which are subjected to a constant input flow rate of 0.5 ml.min-1. The DOCT results show that the behavior of the fluid flow and shear stress in micropores is strongly dependent on the micropore interconnectivity, porosity, and size of pores within the scaffold. For low-porosity and high-porosity chitosan scaffolds examined, the measured local fluid flow and shear stress varied from micropore to micropore, with a mean shear stress of 0.49+/-0.3 dyn.cm-2 and 0.38+/-0.2 dyn.cm-2, respectively. In addition, we show that the scaffold's porosity and interconnectivity can be quantified by combining analyses of the 3D structural and flow images obtained from DOCT.

  5. ESTIMATION OF SHEAR STRESS WORKING ON SUBMERGED HOLLOW FIBRE MEMBRANE BY CFD METHOD IN MBRs

    NASA Astrophysics Data System (ADS)

    Zaw, Hlwan Moe; Li, Tairi; Nagaoka, Hiroshi

    This study was conducted to evaluate shear stress working on submerged hollow fibre membrane by CFD (Computation Fluid Dynamics) method in MBRs. Shear stress on hollow fibre membrane caused by aeration was measured directly using a two-direction load sensor. The measurement of water-phase flow velocity was done also by using laser doppler velocimeter. It was confirmed that the shear stress was possible to be evaluated from the water-phase flow velocityby the result of comparison of time average shear stress actually measured with one hollow fibre membrane and the one calculated by the water-phase flow velocity. In the estimation of the water-phase flow velocity using the CFD method, time average water-phase flow velocity estimated by consideration of the fluid resistance of the membrane module nearly coincided with the measured values, and it was shown that it was possible to be estimated also within the membrane module. Moreover, the measured shear stress and drag force well coincided with the values calculated from the estimated water-phase flow velocity outside of membrane module and in the center of membrane module, and it was suggested that the shear stress on the hollow fibre membrane could be estimated by the CFD method in MBRs.

  6. Doppler optical coherence tomography imaging of local fluid flow and shear stress within microporous scaffolds

    PubMed Central

    Jia, Yali; Bagnaninchi, Pierre O.; Yang, Ying; Haj, Alicia El; Hinds, Monica T.; Kirkpatrick, Sean J.; Wang, Ruikang K.

    2009-01-01

    Establishing a relationship between perfusion rate and fluid shear stress in a 3-dimensional cell culture environment is an ongoing and challenging task faced by tissue engineers. In this study, we explore Doppler optical coherence tomography (DOCT) as a potential imaging tool for in situ monitoring of local fluid flow profiles inside porous chitosan scaffolds. From the measured fluid flow profiles, the fluid shear stresses are evaluated. We examine the localized fluid flow and shear stress within low and high porosity chitosan scaffolds, which are subjected to a constant input flow rate of 0.5 ml·min-1. The DOCT results show that the behaviour of the fluid flow and shear stress in micropores is strongly dependent on the micropore interconnectivity, porosity, and size of pores within the scaffold. For low porosity and high porosity chitosan scaffolds examined, the measured local fluid flow and shear stress varied from micropore to micropore with a mean shear stress of 0.49±0.3 dyn·cm-2 and 0.38±0.2 dyn·cm-2, respectively. In addition, we show that the scaffold’s porosity and interconnectivity can be quantified by combining analyses of the 3-dimensional structural and flow images obtained from DOCT. PMID:19566307

  7. Orbital fluid shear stress promotes osteoblast metabolism, proliferation and alkaline phosphates activity in vitro.

    PubMed

    Aisha, M D; Nor-Ashikin, M N K; Sharaniza, A B R; Nawawi, H; Froemming, G R A

    2015-09-10

    Prolonged disuse of the musculoskeletal system is associated with reduced mechanical loading and lack of anabolic stimulus. As a form of mechanical signal, the multidirectional orbital fluid shear stress transmits anabolic signal to bone forming cells in promoting cell differentiation, metabolism and proliferation. Signals are channeled through the cytoskeleton framework, directly modifying gene and protein expression. For that reason, we aimed to study the organization of Normal Human Osteoblast (NHOst) cytoskeleton with regards to orbital fluid shear (OFS) stress. Of special interest were the consequences of cytoskeletal reorganization on NHOst metabolism, proliferation, and osteogenic functional markers. Cells stimulated at 250 RPM in a shaking incubator resulted in the rearrangement of actin and tubulin fibers after 72 h. Orbital shear stress increased NHOst mitochondrial metabolism and proliferation, simultaneously preventing apoptosis. The ratio of RANKL/OPG was reduced, suggesting that orbital shear stress has the potential to inhibit osteoclastogenesis and osteoclast activity. Increase in ALP activity and OCN protein production suggests that stimulation retained osteoblast function. Shear stress possibly generated through actin seemed to hold an anabolic response as osteoblast metabolism and functional markers were enhanced. We hypothesize that by applying orbital shear stress with suitable magnitude and duration as a non-drug anabolic treatment can help improve bone regeneration in prolonged disuse cases.

  8. Application of Entropy Concept for Shear Stress Distribution in Laminar Pipe Flow

    NASA Astrophysics Data System (ADS)

    Choo, Yeon Moon; Choo, Tai Ho; Jung, Donghwi; Seon, Yun Gwan; Kim, Joong Hoon

    2016-04-01

    In the river fluid mechanics, shear stress is calculated from frictional force caused by viscosity and fluctuating velocity. Traditional shear stress distribution equations have been widely used because of their simplicity. However, they have a critical limitation of requiring energy gradient which is generally difficult to estimate in practice. Especially, measuring velocity/velocity gradient on the boundary layer is difficult in practice. It requires point velocity throughout the entire cross section to calculate velocity gradient. This study proposes shear stress distribution equations for laminar flow based on entropy theory using mean velocity and entropy coefficient. The proposed equations are demonstrated and compared with measured shear stress distribution using Nikuradse's data. Results showed that the coefficient of determination is around 0.99 indicating that the proposed method well describes the true shear stress distribution. Therefore, it was proved that shear stress distribution can be easily and accurately estimated by using the proposed equations. (This research was supported by a gran(13AWMP-B066744-01) from Advanced Water Management Research Program funded by Ministry of Land, Infrastructure and Transport of Korean Government)

  9. Transverse shear stresses and their sensitivity coefficients in multilayered composite panels

    NASA Technical Reports Server (NTRS)

    Noor, Ahmed K.; Kim, Yong H.; Peters, Jeanne M.

    1994-01-01

    A computational procedure is presented for the accurate determination of transverse shear stresses and their sensitivity coefficients in flat multilayered composite panels subjected to mechanical and thermal loads. The sensitivity coefficients measure the sensitivity of the transverse shear stresses to variations in the different lamination and material parameters of the panel. The panel is discretized by using either a three-field mixed finite element model based on a two-dimensional first- order shear deformation plate theory or a two-field degenerate solid element with each of the displacement components having a linear variation throughout the thickness of the laminate. The evaluation of transverse shear stresses can be conveniently divided into two phases. The first phase consists of using a superconvergent recovery technique for evaluating the in-plane stresses in the different layers. In the second phase, the transverse shear stresses are evaluated by using piecewise integration, in the thickness direction, of the three-dimensional equilibrium equations. The same procedure is used for evaluating the sensitivity coefficients of the transverse shear stresses. The effectiveness of the computational procedure is demonstrated by means of numerical examples of multilayered cross-ply panels subjected to transverse loading, uniform temperature change, and uniform temperature gradient through the thickness of the panel. In each case the standard of the comparison is taken to be the exact solution of the three dimensional thermoelasticity equations of the panel.

  10. Transverse shear stresses and their sensitivity coefficients in multilayered composite panels

    NASA Technical Reports Server (NTRS)

    Noor, Ahmed K.; Kim, Yong H.; Peters, Jeanne M.

    1994-01-01

    A computational procedure is presented for the accurate determination of transverse shear stresses and their sensitivity coefficients in flat multilayered composite panels subjected to mechanical and thermal loads. The sensitivity coefficients measure the sensitivity of the transverse shear stresses to variations in the different lamination and material parameters of the panel. The panel is discretized by using either a three-field mixed finite element model based on a two-dimensional first- order shear deformation plate theory or a two-field degenerate solid element with each of the displacement components having a linear variation throughout the thickness of the laminate. The evaluation of transverse shear stresses can be conveniently divided into two phases. The first phase consists of using a superconvergent recovery technique for evaluating the in-plane stresses in the different layers. In the second phase, the transverse shear stresses are evaluated by using piecewise integration, in the thickness direction, of the three-dimensional equilibrium equations. The same procedure is used for evaluating the sensitivity coefficients of the transverse shear stresses. The effectiveness of the computational procedure is demonstrated by means of numerical examples of multilayered cross-ply panels subjected to transverse loading, uniform temperature change, and uniform temperature gradient through the thickness of the panel. In each case the standard of the comparison is taken to be the exact solution of the three dimensional thermoelasticity equations of the panel.

  11. Using two soft computing methods to predict wall and bed shear stress in smooth rectangular channels

    NASA Astrophysics Data System (ADS)

    Khozani, Zohreh Sheikh; Bonakdari, Hossein; Zaji, Amir Hossein

    2017-03-01

    Two soft computing methods were extended in order to predict the mean wall and bed shear stress in open channels. The genetic programming (GP) and Genetic Algorithm Artificial Neural Network (GAA) were investigated to determine the accuracy of these models in estimating wall and bed shear stress. The GP and GAA model results were compared in terms of testing dataset in order to find the best model. In modeling both bed and wall shear stress, the GP model performed better with RMSE of 0.0264 and 0.0185, respectively. Then both proposed models were compared with equations for rectangular open channels, trapezoidal channels and ducts. According to the results, the proposed models performed the best in predicting wall and bed shear stress in smooth rectangular channels. The obtained equation for rectangular channels could estimate values closer to experimental data, but the equations for ducts had poor, inaccurate results in predicting wall and bed shear stress. The equation presented for trapezoidal channels did not have acceptable accuracy in predicting wall and bed shear stress either.

  12. Arterial Shear Stress Reduces Eph-B4 Expression in Adult Human Veins

    PubMed Central

    Model, Lynn S.; Hall, Michael R.; Wong, Daniel J.; Muto, Akihito; Kondo, Yuka; Ziegler, Kenneth R.; Feigel, Amanda; Quint, Clay; Niklason, Laura; Dardik, Alan

    2014-01-01

    Vein graft adaptation to the arterial environment is characterized by loss of venous identity, with reduced Ephrin type-B receptor 4 (Eph-B4) expression but without increased Ephrin-B2 expression. We examined changes of vessel identity of human saphenous veins in a flow circuit in which shear stress could be precisely controlled. Medium circulated at arterial or venous magnitudes of laminar shear stress for 24 hours; histologic, protein, and RNA analyses of vein segments were performed. Vein endothelium remained viable and functional, with platelet endothelial cell adhesion molecule (PECAM)-expressing cells on the luminal surface. Venous Eph-B4 expression diminished (p = .002), Ephrin-B2 expression was not induced (p = .268), and expression of osteopontin (p = .002) was increased with exposure to arterial magnitudes of shear stress. Similar changes were not found in veins placed under venous flow or static conditions. These data show that human saphenous veins remain viable during ex vivo application of shear stress in a bioreactor, without loss of the venous endothelium. Arterial magnitudes of shear stress cause loss of venous identity without gain of arterial identity in human veins perfused ex vivo. Shear stress alone, without immunologic or hormonal influence, is capable of inducing changes in vessel identity and, specifically, loss of venous identity. PMID:25191151

  13. Integration of basal topographic cues and apical shear stress in vascular endothelial cells.

    PubMed

    Morgan, Joshua T; Wood, Joshua A; Shah, Nihar M; Hughbanks, Marissa L; Russell, Paul; Barakat, Abdul I; Murphy, Christopher J

    2012-06-01

    In vivo, vascular endothelial cells (VECs) are anchored to the underlying stroma through a specialization of the extracellular matrix, the basement membrane (BM) which provides a variety of substratum associated biophysical cues that have been shown to regulate fundamental VEC behaviors. VEC function and homeostasis are also influenced by hemodynamic cues applied to their apical surface. How the combination of these biophysical cues impacts fundamental VEC behavior remains poorly studied. In the present study, we investigated the impact of providing biophysical cues simultaneously to the basal and apical surfaces of human aortic endothelial cells (HAECs). Anisotropically ordered patterned surfaces of alternating ridges and grooves and isotropic holed surfaces of varying pitch (pitch = ridge or hole width + intervening groove or planar regions) were fabricated and seeded with HAECs. The cells were then subjected to a steady shear stress of 20 dyne/cm(2) applied either parallel or perpendicular to the direction of the ridge/groove topography. HAECs subjected to flow parallel to the ridge/groove topography exhibited protagonistic effects of the two stimuli on cellular orientation and elongation. In contrast, flow perpendicular to the substrate topography resulted in largely antagonistic effects. Interestingly, the behavior depended on the shape and size of the topographic features. HAECs exhibited a response that was less influenced by the substratum and primarily driven by flow on isotropically ordered holed surfaces of identical pitch to the anistropically ordered surfaces of alternating ridges and grooves. Simultaneous presentation of biophysical cues to the basal and apical aspects of cells also influenced nuclear orientation and elongation; however, the extent of nuclear realignment was more modest in comparison to cellular realignment regardless of the surface order of topographic features. Flow-induced HAEC migration was also influenced by the ridge

  14. Effect of shear stress on water and LDL transport through cultured endothelial cell monolayers.

    PubMed

    Kang, Hongyan; Cancel, Limary M; Tarbell, John M

    2014-04-01

    Previous animal experiments have shown that the transport of LDL into arterial walls is shear stress dependent. However, little work has probed shear effects on LDL transport in vitro where conditions are well defined and mechanisms are more easily explored. Therefore, we measured shear induced water and LDL fluxes across cultured bovine aortic endothelial (BAEC) monolayers in vitro and developed a three-pore model to describe the transport dynamics. Cell apoptosis was quantified by TdT-mediated dUTP nick end labeling (TUNEL) assay. We also examined the role of nitric oxide (NO) in shear induced water and LDL fluxes by incubating BAEC monolayers with an NO synthase inhibitor, NG-monomethyl-L-arginine (L-NMMA). Our results show that direct exposure of endothelial monolayers to 12 dyn/cm2 shear stress for 3 h elicited a 2.37-fold increase in water flux (Jv), a 3.00-fold increase in LDL permeability (Pe), a 1.32-fold increase in LDL uptake, and a 1.68-fold increase in apoptotic rate. L-NMMA treatment of BAEC monolayers blocked shear induced Jv response, but had no significant effect on shear responses of Pe and cell apoptosis. A long time shear exposure (12 h) of endothelial monolayers reduced Pe and apoptotic rate close to the baseline. These results suggest that an acute change in shear stress from a static baseline state induces increases in water flux that are mediated by an NO dependent mechanism. On the other hand, the permeability of endothelial monolayers to LDL is enhanced by a short term-shear application and reduced nearly to the baseline level by a longer time shear exposure, positively correlated to the leaky junctions forming around apoptotic cells.

  15. Influence of high deformation rate, brain region, transverse compression, and specimen size on rat brain shear stress morphology and magnitude.

    PubMed

    Haslach, Henry W; Gipple, Jenna M; Leahy, Lauren N

    2017-01-26

    An external mechanical insult to the brain, such as a blast, may create internal stress and deformation waves, which have shear and longitudinal components that can induce combined shear and compression of the brain tissue. To isolate the consequences of such interactions for the shear stress and to investigate the role of the extracellular fluid in the mechanical response, translational shear stretch at 10/s, 60/s, and 100/s translational shear rates under either 0% or 33% fixed transverse compression is applied without preconditioning to rat brain specimens. The specimens from the cerebrum, the cerebellum grey matter, and the brainstem white matter are nearly the full length of their respective regions. The translational shear stress response to translational shear deformation is characterized by the effect that each of four factors, high deformation rate, brain region, transverse compression, and specimen size, have on the shear stress magnitude averaged over ten specimens for each combination of factors. Increasing the deformation rate increases the magnitude of the shear stress at a given translational shear stretch, and as tested by ANOVAs so does applying transverse fixed compression of 33% of the thickness. The stress magnitude differs by the region that is the specimen source: cerebrum, cerebellum or brainstem. The magnitude of the shear stress response at a given deformation rate and stretch depends on the specimen length, called a specimen size effect. Surprisingly, under no compression a shorter length specimen requires more shear stress, but under 33% compression a shorter length specimen requires less shear stress, to meet a required shear deformation rate. The shear specimen size effect calls into question the applicability of the classical shear stress definition to hydrated soft biological tissue.

  16. Dynamic deformation and recovery response of red blood cells to a cyclically reversing shear flow: Effects of frequency of cyclically reversing shear flow and shear stress level.

    PubMed

    Watanabe, Nobuo; Kataoka, Hiroyuki; Yasuda, Toshitaka; Takatani, Setsuo

    2006-09-01

    Dynamic deformation and recovery responses of red blood cells (RBCs) to a cyclically reversing shear flow generated in a 30-microm clearance, with the peak shear stress of 53, 108, 161, and 274 Pa at the frequency of 1, 2, 3, and 5 Hz, respectively, were studied. The RBCs' time-varying velocity varied after the glass plate velocity without any time lag, whereas the L/W change, where L and W were the major and minor axes of RBCs' ellipsoidal shape, exhibited a rapid increase and gradual decay during the deformation and recovery phase. The time of minimum L/W occurrence lagged behind the zero-velocity time of the glass plate (zero stress), and the delay time normalized to the one-cycle duration remained constant at 8.0%. The elongation of RBCs at zero stress time became larger with the reversing frequency. A simple mechanical model consisting of an elastic linear element during a rapid elongation period and a parallel combination of elements such as a spring and dashpot during the nonlinear recovery phase was suggested. The dynamic response behavior of RBCs under a cyclically reversing shear flow was different from the conventional shape change where a steplike force was applied to and completely released from the RBCs.

  17. A new technique for the measurement of surface shear stress vectors using liquid crystal coatings

    NASA Technical Reports Server (NTRS)

    Reda, Daniel C.; Muratore, J. J., Jr.

    1994-01-01

    Research has recently shown that liquid crystal coating (LCC) color-change response to shear depends on both shear stress magnitude and direction. Additional research was thus conducted to extend the LCC method from a flow-visualization tool to a surface shear stress vector measurement technique. A shear-sensitive LCC was applied to a planar test surface and illuminated by white light from the normal direction. A fiber optic probe was used to capture light scattered by the LCC from a point on the centerline of a turbulent, tangential-jet flow. Both the relative shear stress magnitude and the relative in-plane view angle between the sensor and the centerline shear vector were systematically varied. A spectrophotometer was used to obtain scattered-light spectra which were used to quantify the LCC color (dominant wavelength) as a function of shear stress magnitude and direction. At any fixed shear stress magnitude, the minimum dominant wavelength was measured when the shear vector was aligned with and directed away from the observer; changes in the relative in-plane view angle to either side of this vector/observer aligned position resulted in symmetric Gaussian increases in measured dominant wavelength. Based on these results, a vector measurement methodology, involving multiple oblique-view observations of the test surface, was formulated. Under present test conditions, the measurement resolution of this technique was found to be +/- 1 deg for vector orientations and +/- 5% for vector magnitudes. An approach t o extend the present methodology to full-surface applications is proposed.

  18. Experimental research of mechanical behavior of porcine brain tissue under rotational shear stress.

    PubMed

    Li, Gang; Zhang, Jianhua; Wang, Kan; Wang, Mingyu; Gao, Changqing; Ma, Chao

    2016-04-01

    The objective of this paper is to investigate mechanical behavior of porcine brain tissue with a series of rotational shear stress control experiments. To this end, several experiments including stress sweep tests, frequency sweep tests and quasi-static creep tests were designed and conducted with a standard rheometer (HAAKE RheoStress6000). The effects of the loading stress rates to mechanical properties of brain tissue were also studied in stress sweep tests. The results of stress sweep tests performed on the same brain showed that brain tissue had an obvious regional inhomogeneity and the mechanical damage occurred at the rotational shear stress of 10-15Pa. The experimental data from three different loading stress rates demonstrated that the mechanical behavior of porcine brain tissue was loading stress rate dependent. With the decrease of loading stress rate, a stiffer mechanical characteristic of brain tissue was observed and the occurrence of mechanical damage can be delayed to a higher stress. From the results of frequency sweep tests we found that brain tissue had almost completely elastic properties at high frequency area. The nonlinear creep response under the rotational shear stress of 1, 3, 5, 7 and 9Pa was shown in results of creep tests. A new nonlinear viscoelastic solid model was proposed for creep tests and matched well with the test data. Considering the regional differences, loading stress rates and test conditions effects, loss tangent tan δ in porcine brain tissue showed a high uniformity of 0.25-0.45.

  19. Analysis of shearing stress in the limited durability of bovine pericardium used as a biomaterial.

    PubMed

    Carrera San Martin, A; García Paez, J M; García Sestafe, J V; Herrero, E J; Navidad, R; Cordón, A; Castillo-Olivares, J L

    1998-02-01

    The objective of the study was to determine the shearing stress exerted by the suture thread under conditions of normal working stress. Thirty-six samples of calf pericardium, similar to that employed in the manufacture of bioprosthetic cardiac valve leaflets, were subjected to tensile testing. Prior to the trial, a continuous suture was sewn in the central zone of each sample, at a 45 degrees angle to the longest axis of the sample, using commercially-available threads (silk, Gore-Tex, Surgilene and nylon). Application of the Mohr circle for combined wear revealed that the shearing stress ranged between 2.68-fold greater (for samples sewn with silk) and 5.48-fold greater (for samples sewn with nylon) than the working tensile stress in the region of the suture. It is concluded that the shearing stress is responsible for the limited durability of sutured samples of calf pericardium prepared to simulate bioprosthetic cardiac valve leaflets.

  20. The production of turbulent stress in a shear flow by irrotational fluctuations

    NASA Technical Reports Server (NTRS)

    Gartshore, I. S.; Durbin, P. A.; Hunt, J. C. R.

    1983-01-01

    This paper examines, both theoretically and experimentally, the effect produced by irrotational fluctuations, associated with a nearby turbulent field, in a region where the turbulence is initially very low but where there is a mean shear. Calculations are based on rapid distortion theory and experiments use linearized hot wire anemometers in an open circuit wind tunnel. Turbulent shear stress is observed to grow from zero to significant values in the interaction region. The magnitude and extent of this observed shear stress agree reasonably well with predictions of the analysis, when intermittency effects are included. It is concluded that turbulent stresses can be produced by irrotational fluctuations in a region of mean shear and that this effect can be estimated using rapid distortion theory if the overall strain ratio is not large.

  1. Working Principle Simulations of a Dynamic ResonantWall Shear Stress Sensor Concept.

    PubMed

    Zhang, Xu; Naughton, Jonathan W; Lindberg, William R

    2008-04-17

    This paper discusses a novel dynamic resonant wall shear stress sensor concept based on an oscillating sensor operating near resonance. The interaction between the oscillating sensor surface and the fluid above it is modelled using the unsteady laminar boundary layer equations. The numerical experiment shows that the effect of the oscillating shear stress is well correlated by the Hummer number, the ratio of the steady shear force caused by the outside flow to the oscillating viscous force created by the sensor motion. The oscillating shear stress predicted by the fluid model is used in a mechanical model of the sensor to predict the sensor's dynamic motion. Static calibration curves for amplitude and frequency influences are predicted. These results agree with experimental results on some extent, and shows some expectation for further development of the dynamic resonant sensor concept.

  2. Effect of cell size and shear stress on bacterium growth rate

    NASA Astrophysics Data System (ADS)

    Fadlallah, Hadi; Jarrahi, Mojtaba; Herbert, Éric; Peerhossaini, Hassan; PEF Team

    2015-11-01

    Effect of shear stress on the growth rate of Synechocystis and Chlamydomonas cells is studied. An experimental setup was prepared to monitor the growth rate of the microorganisms versus the shear rate inside a clean room, under atmospheric pressure and 20 °C temperature. Digital magnetic agitators are placed inside a closed chamber provided with airflow, under a continuous uniform light intensity over 4 weeks. In order to study the effect of shear stress on the growth rate, different frequencies of agitation are tested, 2 vessels filled with 150 ml of each specie were placed on different agitating system at the desired frequency. The growth rate is monitored daily by measuring the optical density and then correlate it to the cellular concentration. The PH was adjusted to 7 in order to maintain the photosynthetic activity. Furthermore, to measure the shear stress distribution, the flow velocity field was measured using PIV. Zones of high and low shear stress were identified. Results show that the growth rate is independent of the shear stress magnitude, mostly for Synechocystis, and with lower independency for Chlamydomonas depending on the cell size for each species.

  3. Numerical study of shear stress distribution at sand ripple surface in wind tunnel flow

    NASA Astrophysics Data System (ADS)

    Bar, Nitsan; Elperin, Tov; Katra, Itzhak; Yizhaq, Hezi

    2016-06-01

    The mechanism responsible for the formation and sustainability of sand ripples sheared by a uniform air flow is not well understood, despite the significant attention that has been given to it ever since the pioneering studies of Bagnold (1941). In this study we explore ANSYS Fluent simulations of fine-scale turbulent flow structure in the vicinity of 2D sand ripples with particular emphasis on shear stress distribution at the sand bed. The flow parameters in the simulations were pertinent to the wind tunnel experiments for studying sand ripples formation. The simulations show that the shear stress at the crest is about 2.5 times larger than the shear stress at the trough and that in most of the simulations a separation bubble has been developed at the lee slope. In contrast to wind tunnel experiments the simulations show that ripples will be flattened at wind speed of 9 m/s as shear stress at the ripples surface exceeds the fluid threshold. This discrepancy between the calculations and real wind tunnel measurements are due to the important role of the saltation layer on the decrease of the shear stress at the surface. Without this effect ripples cannot grow higher and will be diminished at quite moderate winds.

  4. 4-Dimensional light-sheet microscopy to elucidate shear stress modulation of cardiac trabeculation.

    PubMed

    Lee, Juhyun; Fei, Peng; Packard, René R Sevag; Kang, Hanul; Xu, Hao; Baek, Kyung In; Jen, Nelson; Chen, Junjie; Yen, Hilary; Kuo, C-C Jay; Chi, Neil C; Ho, Chih-Ming; Li, Rongsong; Hsiai, Tzung K

    2016-05-02

    Hemodynamic shear forces are intimately linked with cardiac development, during which trabeculae form a network of branching outgrowths from the myocardium. Mutations that alter Notch signaling also result in trabeculation defects. Here, we assessed whether shear stress modulates trabeculation to influence contractile function. Specifically, we acquired 4D (3D + time) images with light sheets by selective plane illumination microscopy (SPIM) for rapid scanning and deep axial penetration during zebrafish morphogenesis. Reduction of blood viscosity via gata1a morpholino oligonucleotides (MO) reduced shear stress, resulting in downregulation of Notch signaling and attenuation of trabeculation. Arrest of cardiomyocyte contraction either by troponin T type 2a (tnnt2a) MO or in weak atriumm58 (wea) mutants resulted in reduced shear stress and downregulation of Notch signaling and trabeculation. Integrating 4D SPIM imaging with synchronization algorithm demonstrated that coinjection of neuregulin1 mRNA with gata1 MO rescued trabeculation to restore contractile function in association with upregulation of Notch-related genes. Crossbreeding of Tg(flk:mCherry) fish, which allows visualization of the vascular system with the Tg(tp1:gfp) Notch reporter line, revealed that shear stress-mediated Notch activation localizes to the endocardium. Deleting endocardium via the clochesk4 mutants downregulated Notch signaling, resulting in nontrabeculated ventricle. Subjecting endothelial cells to pulsatile flow in the presence of the ADAM10 inhibitor corroborated shear stress-activated Notch signaling to modulate trabeculation.

  5. PEG-albumin supraplasma expansion is due to increased vessel wall shear stress induced by blood viscosity shear thinning.

    PubMed

    Sriram, Krishna; Tsai, Amy G; Cabrales, Pedro; Meng, Fantao; Acharya, Seetharama A; Tartakovsky, Daniel M; Intaglietta, Marcos

    2012-06-15

    We studied the extreme hemodilution to a hematocrit of 11% induced by three plasma expanders: polyethylene glycol (PEG)-conjugated albumin (PEG-Alb), 6% 70-kDa dextran, and 6% 500-kDa dextran. The experimental component of our study relied on microelectrodes and cardiac output to measure both the rheological properties of plasma-expander blood mixtures and nitric oxide (NO) bioavailability in vessel walls. The modeling component consisted of an analysis of the distribution of wall shear stress (WSS) in the microvessels. Our experiments demonstrated that plasma expansion with PEG-Alb caused a state of supraperfusion with cardiac output 40% above baseline, significantly increased NO vessel wall bioavailability, and lowered peripheral vascular resistance. We attributed this behavior to the shear thinning nature of blood and PEG-Alb mixtures. To substantiate this hypothesis, we developed a mathematical model of non-Newtonian blood flow in a vessel. Our model used the Quemada rheological constitutive relationship to express blood viscosity in terms of both hematocrit and shear rate. The model revealed that the net effect of the hemodilution induced by relatively low-viscosity shear thinning PEG-Alb plasma expanders is to reduce overall blood viscosity and to increase the WSS, thus intensifying endothelial NO production. These changes act synergistically, significantly increasing cardiac output and perfusion due to lowered overall peripheral vascular resistance.

  6. Orbital fluid shear stress promotes osteoblast metabolism, proliferation and alkaline phosphates activity in vitro

    SciTech Connect

    Aisha, M.D.; Nor-Ashikin, M.N.K.; Sharaniza, A.B.R.; Nawawi, H.; Froemming, G.R.A.

    2015-09-10

    Prolonged disuse of the musculoskeletal system is associated with reduced mechanical loading and lack of anabolic stimulus. As a form of mechanical signal, the multidirectional orbital fluid shear stress transmits anabolic signal to bone forming cells in promoting cell differentiation, metabolism and proliferation. Signals are channeled through the cytoskeleton framework, directly modifying gene and protein expression. For that reason, we aimed to study the organization of Normal Human Osteoblast (NHOst) cytoskeleton with regards to orbital fluid shear (OFS) stress. Of special interest were the consequences of cytoskeletal reorganization on NHOst metabolism, proliferation, and osteogenic functional markers. Cells stimulated at 250 RPM in a shaking incubator resulted in the rearrangement of actin and tubulin fibers after 72 h. Orbital shear stress increased NHOst mitochondrial metabolism and proliferation, simultaneously preventing apoptosis. The ratio of RANKL/OPG was reduced, suggesting that orbital shear stress has the potential to inhibit osteoclastogenesis and osteoclast activity. Increase in ALP activity and OCN protein production suggests that stimulation retained osteoblast function. Shear stress possibly generated through actin seemed to hold an anabolic response as osteoblast metabolism and functional markers were enhanced. We hypothesize that by applying orbital shear stress with suitable magnitude and duration as a non-drug anabolic treatment can help improve bone regeneration in prolonged disuse cases. - Highlights: • OFS stress transmits anabolic signals to osteoblasts. • Actin and tubulin fibers are rearranged under OFS stress. • OFS stress increases mitochondrial metabolism and proliferation. • Reduced RANKL/OPG ratio in response to OFS inhibits osteoclastogenesis. • OFS stress prevents apoptosis and stimulates ALP and OCN.

  7. Role of shear stress in the blister formation of cerebral aneurysms.

    PubMed

    Shojima, Masaaki; Nemoto, Shigeru; Morita, Akio; Oshima, Marie; Watanabe, Eiju; Saito, Nobuhito

    2010-11-01

    The development of cerebral aneurysms is related to hemodynamic stress. To elucidate the role of shear stress in the blister formation of cerebral aneurysms. Among 82 aneurysms detected during catheter-based 3D rotational angiography (3DRA), 4 aneurysms enlarged with blister formation during a mean follow-up period of 10.1 month. Three of these 4 aneurysms were analyzed in this study. The regions of blister formation were characterized by comparing 3DRA before and after blister formation, and computational fluid dynamic simulations were performed based on the aneurysm geometry before blister formation. The spatially averaged shear magnitude was lower in the aneurysm region (0.97 ± 0.39 Pa) than in the parent artery (2.75 ± 0.92 Pa). The spatially averaged shear magnitude of the blister-forming area was extremely low (0.48 ± 0.12 Pa), and the shear magnitude dropped precipitately to subphysiological levels, resulting in a high shear gradient near the border of the blister-forming area. These data suggest that low shear magnitude may trigger the progression of cerebral aneurysms and that blister formation is associated with high shear gradient in the large region of low shear magnitude on the aneurysm wall.

  8. Some constraints on levels of shear stress in the crust from observations and theroc

    SciTech Connect

    McGarr, A.

    1980-11-10

    In situ stress determinations in North America, southern Africa, and Australia indicate that on the average the maximum shear stress increases lineary with depth to at least 5.1 km measured in soft rock, such as shale and sandstone, and to 3.7 km in hard rock, including granite and quartzite. Regression lines fitted to the data yield gradients of 3.8 MPa/km and 6.6 MPa/km for soft and hard rock, respectively. Generally, the maximum shear stress in compressional states of stress for which the least principal stress is oriented near vertically is substantially greater than in extensional stress regimes, with the greatest principal stress in a vertical direction. The equations of equilibrium and compatibility can be used to provide functional constraints on the state of stress. If the stress is assumed to vary only with depth z in a given region, then all nonzero components must have the form A+Bz, where A and B are constants which generally differ for various components. This implies that the deviatoric stress changes linearly with depth, and the general solution also allows the directions of the horizontal principal stresses to change monotonically with depth. Solutions to the equations, assuming stress to vary with both z and x, were fit to the observations of Zoback and Roller, who measured stress along a horizontal profile near Palmdale, California. The results indicate that the average shear stress in the upper 8 km of the fault zone is about 3.5 MPa less than the shear stress in the far field, but this far field term, which is part of the solution and has the form A+Bz, cannot be evaluated using the existing constant depth data.

  9. Forward modeling of ice topography on Mars to infer basal shear stress conditions

    NASA Astrophysics Data System (ADS)

    Banks, M. E.; Pelletier, J. D.

    2008-01-01

    Understanding the history of ice caps on Mars could reveal important information about Martian geologic and climatic history. To do this, an ice reconstruction model is needed that operates over complex topography and can be constrained with a limited number of free parameters. In this study we developed a threshold-sliding model for ice cap morphology based on the classic model of Nye later incorporated into the models of Reeh and colleagues. We have updated the Nye-Reeh model with a new numerical algorithm. Although the model was originally developed to model perfectly plastic deformation, it is applicable to any ice body that deforms when a threshold basal shear stress is exceeded. The model requires three inputs: a digital elevation model of bed topography, a ``mask'' grid that defines the position of the ice terminus, and a function defining the threshold basal shear stress. To test the robustness of the model, the morphology of the Greenland ice sheet is reconstructed using an empirical equation between threshold basal shear stress and ice surface slope. The model is then used to reconstruct the morphology of ice draping impact craters on the margins of the south polar layered deposits using an inferred constant basal shear stress of ~0.6 bar for the majority of the examples. This inferred basal shear stress value is almost 1/3 of the average basal shear stress calculated for the Greenland ice sheet. What causes this lower basal shear stress value on Mars is unclear but could involve the strain-weakening behavior of ice.

  10. Shear Stress Partitioning in Large Patches of Roughness in the Atmospheric Inertial Sublayer

    NASA Technical Reports Server (NTRS)

    Gillies, John A.; Nickling, William G.; King, James

    2007-01-01

    Drag partition measurements were made in the atmospheric inertial sublayer for six roughness configurations made up of solid elements in staggered arrays of different roughness densities. The roughness was in the form of a patch within a large open area and in the shape of an equilateral triangle with 60 m long sides. Measurements were obtained of the total shear stress (tau) acting on the surfaces, the surface shear stress on the ground between the elements (tau(sub S)) and the drag force on the elements for each roughness array. The measurements indicated that tau(sub S) quickly reduced near the leading edge of the roughness compared with tau, and a tau(sub S) minimum occurs at a normalized distance (x/h, where h is element height) of approx. -42 (downwind of the roughness leading edge is negative), then recovers to a relatively stable value. The location of the minimum appears to scale with element height and not roughness density. The force on the elements decreases exponentially with normalized downwind distance and this rate of change scales with the roughness density, with the rate of change increasing as roughness density increases. Average tau(sub S): tau values for the six roughness surfaces scale predictably as a function of roughness density and in accordance with a shear stress partitioning model. The shear stress partitioning model performed very well in predicting the amount of surface shear stress, given knowledge of the stated input parameters for these patches of roughness. As the shear stress partitioning relationship within the roughness appears to come into equilibrium faster for smaller roughness element sizes it would also appear the shear stress partitioning model can be applied with confidence for smaller patches of smaller roughness elements than those used in this experiment.

  11. The Role of Shear Stress in Arteriovenous Fistula Maturation and Failure: A Systematic Review.

    PubMed

    Browne, Leonard D; Bashar, Khalid; Griffin, Philip; Kavanagh, Eamon G; Walsh, Stewart R; Walsh, Michael T

    2015-01-01

    Non-maturation and post-maturation venous stenosis are the primary causes of failure within arteriovenous fistulae (AVFs). Although the exact mechanisms triggering failure remain unclear, abnormal hemodynamic profiles are thought to mediate vascular remodelling and can adversely impact on fistula patency. The review aims to clarify the role of shear stress on outward remodelling during maturation and evaluate the evidence supporting theories related to the localisation and development of intimal hyperplasia within AVFs. A systematic review of studies comparing remodelling data with hemodynamic data obtained from computational fluid dynamics of AVFs during and after maturation was conducted. Outward remodelling occurred to reduce or normalise the level of shear stress over time in fistulae with a large radius of curvature (curved) whereas shear stress was found to augment over time in fistulae with a small radius of curvature (straight) coinciding with minimal to no increases in lumen area. Although this review highlighted that there is a growing body of evidence suggesting low and oscillating shear stress may stimulate the initiation and development of intimal medial thickening within AVFs. Further lines of evidence are needed to support the disturbed flow theory and outward remodelling findings before surgical configurations and treatment strategies are optimised to conform to them. This review highlighted that variation between the time of analysis, classification of IH, resolution of simulations, data processing techniques and omission of various shear stress metrics prevented forming pooling of data amongst studies. Standardised measurements and data processing techniques are needed to comprehensively evaluate the relationship between shear stress and intimal medial thickening. Advances in image acquisition and flow quantifications coupled with the increasing prevalence of longitudinal studies commencing from fistula creation offer viable techniques and

  12. Accurate prediction of wall shear stress in a stented artery: newtonian versus non-newtonian models.

    PubMed

    Mejia, Juan; Mongrain, Rosaire; Bertrand, Olivier F

    2011-07-01

    A significant amount of evidence linking wall shear stress to neointimal hyperplasia has been reported in the literature. As a result, numerical and experimental models have been created to study the influence of stent design on wall shear stress. Traditionally, blood has been assumed to behave as a Newtonian fluid, but recently that assumption has been challenged. The use of a linear model; however, can reduce computational cost, and allow the use of Newtonian fluids (e.g., glycerine and water) instead of a blood analog fluid in an experimental setup. Therefore, it is of interest whether a linear model can be used to accurately predict the wall shear stress caused by a non-Newtonian fluid such as blood within a stented arterial segment. The present work compares the resulting wall shear stress obtained using two linear and one nonlinear model under the same flow waveform. All numerical models are fully three-dimensional, transient, and incorporate a realistic stent geometry. It is shown that traditional linear models (based on blood's lowest viscosity limit, 3.5 Pa s) underestimate the wall shear stress within a stented arterial segment, which can lead to an overestimation of the risk of restenosis. The second linear model, which uses a characteristic viscosity (based on an average strain rate, 4.7 Pa s), results in higher wall shear stress levels, but which are still substantially below those of the nonlinear model. It is therefore shown that nonlinear models result in more accurate predictions of wall shear stress within a stented arterial segment.

  13. Real-time quantification of endothelial response to shear stress and vascular modulators.

    PubMed

    DeStefano, Jackson G; Williams, Ashley; Wnorowski, Alexa; Yimam, Nahom; Searson, Peter C; Wong, Andrew D

    2017-03-27

    Quiescence is commonly used to describe the inactive state of endothelial cells (ECs) in monolayers that have reached homeostasis. Experimentally quiescence is usually described in terms of the relative change in cell activity (e.g. turnover, speed, etc.) in response to a perturbation (e.g. solute, shear stress, etc.). The objective of this study is to provide new insight into EC quiescence by quantitatively defining the morphology and activity of confluent cell monolayers in response to shear stress and vascular modulators. Confluent monolayers of human umbilical vein ECs (HUVECs) were subjected to a range of shear stresses (4-16 dyne cm(-2)) under steady flow. Using phase contrast, time-lapse microscopy and image analysis, we quantified EC morphology, speed, proliferation, and apoptosis rates over time and detected differences in monolayer responses under various media conditions: basal media supplemented with growth factors, interleukin-8, or cyclic AMP. In all conditions, we observed a transition from cobblestone to spindle-like morphology in a dose-dependent manner due to shear stress. Cyclic AMP enhanced the elongation and alignment of HUVECs due to shear stress and reduced steady state cell speed. We observed the lowest proliferation rates below 8 dyne cm(-2) and found that growth factors and cyclic AMP reduced proliferation and apoptosis; interleukin-8 similarly decreased proliferation, but increased apoptosis. We have quantified the response of ECs in confluent monolayers to shear stress and vascular modulators in terms of morphology, speed, proliferation and apoptosis and have established quantifiable metrics of cell activity to define vascular quiescence under shear stress.

  14. Shear Stress Partitioning in Large Patches of Roughness in the Atmospheric Inertial Sublayer

    NASA Technical Reports Server (NTRS)

    Gillies, John A.; Nickling, William G.; King, James

    2007-01-01

    Drag partition measurements were made in the atmospheric inertial sublayer for six roughness configurations made up of solid elements in staggered arrays of different roughness densities. The roughness was in the form of a patch within a large open area and in the shape of an equilateral triangle with 60 m long sides. Measurements were obtained of the total shear stress (tau) acting on the surfaces, the surface shear stress on the ground between the elements (tau(sub S)) and the drag force on the elements for each roughness array. The measurements indicated that tau(sub S) quickly reduced near the leading edge of the roughness compared with tau, and a tau(sub S) minimum occurs at a normalized distance (x/h, where h is element height) of approx. -42 (downwind of the roughness leading edge is negative), then recovers to a relatively stable value. The location of the minimum appears to scale with element height and not roughness density. The force on the elements decreases exponentially with normalized downwind distance and this rate of change scales with the roughness density, with the rate of change increasing as roughness density increases. Average tau(sub S): tau values for the six roughness surfaces scale predictably as a function of roughness density and in accordance with a shear stress partitioning model. The shear stress partitioning model performed very well in predicting the amount of surface shear stress, given knowledge of the stated input parameters for these patches of roughness. As the shear stress partitioning relationship within the roughness appears to come into equilibrium faster for smaller roughness element sizes it would also appear the shear stress partitioning model can be applied with confidence for smaller patches of smaller roughness elements than those used in this experiment.

  15. The Role of Shear Stress in Arteriovenous Fistula Maturation and Failure: A Systematic Review

    PubMed Central

    Browne, Leonard D.; Bashar, Khalid; Griffin, Philip; Kavanagh, Eamon G.; Walsh, Stewart R.; Walsh, Michael T.

    2015-01-01

    Introduction Non-maturation and post-maturation venous stenosis are the primary causes of failure within arteriovenous fistulae (AVFs). Although the exact mechanisms triggering failure remain unclear, abnormal hemodynamic profiles are thought to mediate vascular remodelling and can adversely impact on fistula patency. Aim The review aims to clarify the role of shear stress on outward remodelling during maturation and evaluate the evidence supporting theories related to the localisation and development of intimal hyperplasia within AVFs. Methods A systematic review of studies comparing remodelling data with hemodynamic data obtained from computational fluid dynamics of AVFs during and after maturation was conducted. Results Outward remodelling occurred to reduce or normalise the level of shear stress over time in fistulae with a large radius of curvature (curved) whereas shear stress was found to augment over time in fistulae with a small radius of curvature (straight) coinciding with minimal to no increases in lumen area. Although this review highlighted that there is a growing body of evidence suggesting low and oscillating shear stress may stimulate the initiation and development of intimal medial thickening within AVFs. Further lines of evidence are needed to support the disturbed flow theory and outward remodelling findings before surgical configurations and treatment strategies are optimised to conform to them. This review highlighted that variation between the time of analysis, classification of IH, resolution of simulations, data processing techniques and omission of various shear stress metrics prevented forming pooling of data amongst studies. Conclusion Standardised measurements and data processing techniques are needed to comprehensively evaluate the relationship between shear stress and intimal medial thickening. Advances in image acquisition and flow quantifications coupled with the increasing prevalence of longitudinal studies commencing from fistula

  16. Exploring the Role of Shear Stress and Severe Turbulence in Downstream Fish Passage

    SciTech Connect

    Cada, G.; Carlson, T.; Ferguson, J.; Richmond, M.; Sale, M.

    1999-07-06

    Fish may be exposed to damaging levels of fluid shear stress and turbulence while passing through hydroelectric power plants. The generally assumed locations for such potential damage are the turbine and draft tube passages, although it is possible that fish are also injured during passage over the spillway or through sluiceways and fish bypass outfalls. Unless mitigated, fluid-induced injuries and mortality could frustrate efforts to develop advanced, fish-friendly turbines or to provide safe alternate downstream passages. The effects of shear stress and turbulence on fish are poorly understood, in part because of the difficulties in conceptualizing these phenomena, determining their magnitudes and distribution within hydroelectric systems, and then recreating them in a controlled laboratory environment. We define the fluid phenomena that are relevant to the assessment of effects on fish. The magnitudes of fluid stresses associated with man-altered aquatic environments are often considerably higher than those found in natural environments (e.g., normal river flows). However, levels of shear stresses that occur during flash floods appear to be comparable to those expected within a turbine. Past studies of the effects of shear stress on fish are of limited value, mainly because of their narrow scope and lack of instrumentation to measure velocities on appropriately small scales. A laboratory experiment to study the effects of shear stress and turbulence on fish is described.

  17. Suppression of endothelial t-PA expression by prolonged high laminar shear stress

    SciTech Connect

    Ulfhammer, Erik; Carlstroem, Maria; Bergh, Niklas; Larsson, Pia; Karlsson, Lena; Jern, Sverker

    2009-02-06

    Primary hypertension is associated with an impaired capacity for acute release of endothelial tissue-type plasminogen activator (t-PA), which is an important local protective response to prevent thrombus extension. As hypertensive vascular remodeling potentially results in increased vascular wall shear stress, we investigated the impact of shear on regulation of t-PA. Cultured human endothelial cells were exposed to low ({<=}1.5 dyn/cm{sup 2}) or high (25 dyn/cm{sup 2}) laminar shear stress for up to 48 h in two different experimental models. Using real-time RT-PCR and ELISA, shear stress was observed to time and magnitude-dependently suppress t-PA transcript and protein secretion to approximately 30% of basal levels. Mechanistic experiments revealed reduced nuclear protein binding to the t-PA specific CRE element (EMSA) and an almost completely abrogated shear response with pharmacologic JNK inhibition. We conclude that prolonged high laminar shear stress suppresses endothelial t-PA expression and may therefore contribute to the enhanced risk of arterial thrombosis in hypertensive disease.

  18. Inhibition of bacterial and leukocyte adhesion under shear stress conditions by material surface chemistry.

    PubMed

    Patel, Jasmine D; Ebert, Michael; Stokes, Ken; Ward, Robert; Anderson, James M

    2003-01-01

    Biomaterial-centered infections, initiated by bacterial adhesion, persist due to a compromised host immune response. Altering implant materials with surface modifying endgroups (SMEs) may enhance their biocompatibility by reducing bacterial and inflammatory cell adhesion. A rotating disc model, which generates shear stress within physiological ranges, was used to characterize adhesion of leukocytes and Staphylococcus epidermidis on polycarbonate-urethanes and polyetherurethanes modified with SMEs (polyethylene oxide, fluorocarbon and dimethylsiloxane) under dynamic flow conditions. Bacterial adhesion in the absence of serum was found to be mediated by shear stress and surface chemistry, with reduced adhesion exhibited on materials modified with polydimethylsiloxane and polyethylene oxide SMEs. In contrast, bacterial adhesion was enhanced on materials modified with fluorocarbon SMEs. In the presence of serum, bacterial adhesion was primarily neither material nor shear dependent. However, bacterial adhesion in serum was significantly reduced to < or = 10% compared to adhesion in serum-free media. Leukocyte adhesion in serum exhibited a shear dependency with increased adhesion occurring in regions exposed to lower shear-stress levels of < or = 7 dyne/cm2. Additionally, polydimethylsiloxane and polyethylene oxide SMEs reduced leukocyte adhesion on polyether-urethanes. In conclusion, these results suggest that surface chemistry and shear stress can mediate bacterial and cellular adhesion. Furthermore, materials modified with polyethylene oxide SMEs are capable of inhibiting bacterial adhesion, consequently minimizing the probability of biomaterial-centered infections.

  19. Effect of shear stress in ferroelectric solid solutions with coexisting phases

    NASA Astrophysics Data System (ADS)

    Lu, Xiaoyan; Zhang, Hangbo; Zheng, Limei; Cao, Wenwu

    2017-08-01

    One common feature of ferroelectric solid solutions with large piezoelectricity is the coexistence of two or more phases. Due to the strain mismatch among coexisting phases, adaptive structures near the interfaces or domain walls develop to maintain the atomic coherency. Shear stresses commonly exist, especially when the domain size is small. The effect of shear stresses on phase morphology in Pb(Zr1-xTix)O3 solid solutions with compositions within the morphotropic phase boundary region was studied within the framework of Landau phenomenological theory. Our results show that the coexisting rhombohedral (R) and tetragonal (T) phases can be modified to form stable or metastable R-like and/or T-like monoclinic phases under shear stresses. Large stresses may also induce first order or second order phase transitions.

  20. Shear wave transducer for stress measurements in boreholes

    DOEpatents

    Mao, Nai-Hsien

    1987-01-01

    A technique and apparatus for estimating in situ stresses by measuring stress-induced velocity anisotropy around a borehole. Two sets each of radially and tangentially polarized transducers are placed inside the hole with displacement directions either parallel or perpendicular to the principal stress directions. With this configuration, relative travel times are measured by both a pulsed phase-locked loop technique and a cross correlation of digitized waveforms. The biaxial velocity data is used to back-calculate the applied stress.

  1. Bi-crystallographic lattice structure directs grain boundary motion under shear stress

    NASA Astrophysics Data System (ADS)

    Wan, Liang; Han, Weizhong; Chen, Kai

    2015-08-01

    Shear stress driven grain boundary (GB) migration was found to be a ubiquitous phenomenon in small grained polycrystalline materials. Here we show that the GB displacement shift complete (DSC) dislocation mechanism for GB shear coupled migration is still functioning even if the geometry orientation of the GBs deviates a few degrees from the appropriate coincidence site lattice (CSL) GBs. It means that any large angle GB can have a considerable chance to be such a “CSL-related GB” for which the shear coupled GB migration motion can happen by the GB DSC dislocation mechanism. We conclude that the CSL-DSC bi-crystallographic lattice structure in GB is the main reason that GB can migrate under shear stress.

  2. Activation of integrins in endothelial cells by fluid shear stress mediates Rho-dependent cytoskeletal alignment

    PubMed Central

    Tzima, Eleni; del Pozo, Miguel Angel; Shattil, Sanford J.; Chien, Shu; Schwartz, Martin Alexander

    2001-01-01

    Fluid shear stress is a critical determinant of vascular remodeling and atherogenesis. Both integrins and the small GTPase Rho are implicated in endothelial cell responses to shear but the mechanisms are poorly understood. We now show that shear stress rapidly stimulates conformational activation of integrin αvβ3 in bovine aortic endothelial cells, followed by an increase in its binding to extracellular cell matrix (ECM) proteins. The shear-induced new integrin binding to ECM induces a transient inactivation of Rho similar to that seen when suspended cells are plated on ECM proteins. This transient inhibition is necessary for cytoskeletal alignment in the direction of flow. The results therefore define the role of integrins and Rho in a pathway leading to endothelial cell adaptation to flow. PMID:11532928

  3. Shear stress-induced redistribution of the glycocalyx on endothelial cells in vitro.

    PubMed

    Bai, Ke; Wang, Wen

    2014-04-01

    The glycocalyx is the inner most layer of the endothelium that is in direct contact with the circulating blood. Shear stress affects its synthesis and reorganization. This study focuses on changes in the spatial distribution of the glycocalyx caused by shear stimulation and its recovery following the removal of the shear stress. Sialic acid components of the glycocalyx on human umbilical vain endothelial cells are observed using confocal microscopy. The percentage area of the cell membrane covered by the glycocalyx, as well as the average fluorescence intensity ratio between the apical and edge areas of the cell is used to assess the spatial distribution of the glycocalyx on the cell membrane. Our results show that following 24 h shear stimulation, the glycocalyx relocates near the edge of endothelial cells (i.e., cell-cell junction regions). Following the removal of the shear stress, the glycocalyx redistributes and gradually appears in the apical region of the cell membrane. This redistribution is faster in the early hours (<4 h) after shear stimulation than that in the later stage (e.g., between 8 and 24 h). We further investigate the recovery of the glycocalyx after its enzyme degradation under either static or shear flow conditions. Our results show that following 24 h recovery under shear flow, the glycocalyx reappears predominantly near the edge of endothelial cells. Static and shear flow conditions result in notable changes in the spatial recovery of the glycocalyx, but the difference is not statistically significant. We hypothesize that newly synthesized glycocalyx is not structurally well developed. Its weak interaction with flow results in less than significant redistribution, contrary to what has been observed for a well-developed glycocalyx layer.

  4. Evidence for Shear Stress-Mediated Dilation of the Internal Carotid Artery in Humans.

    PubMed

    Carter, Howard H; Atkinson, Ceri L; Heinonen, Ilkka H A; Haynes, Andrew; Robey, Elisa; Smith, Kurt J; Ainslie, Philip N; Hoiland, Ryan L; Green, Daniel J

    2016-11-01

    Increases in arterial carbon dioxide tension (hypercapnia) elicit potent vasodilation of cerebral arterioles. Recent studies have also reported vasodilation of the internal carotid artery during hypercapnia, but the mechanism(s) mediating this extracranial vasoreactivity are unknown. Hypercapnia increases carotid shear stress, a known stimulus to vasodilation in other conduit arteries. To explore the hypothesis that shear stress contributes to hypercapnic internal carotid dilation in humans, temporal changes in internal and common carotid shear rate and diameter, along with changes in middle cerebral artery velocity, were simultaneously assessed in 18 subjects at rest and during hypercapnia (6% carbon dioxide). Middle cerebral artery velocity increased significantly (69±10-103±17 cm/s; P<0.01) along with shear in both the internal (316±52-518±105 1/s; P<0.01) and common (188±40-275±61 1/s; P<0.01) carotids. Diameter also increased (P<0.01) in both carotid arteries (internal: +6.3±2.9%; common: +5.8±3.0%). Following hypercapnia onset, there was a significant delay between the onset of internal carotid shear (22±12 seconds) and diameter change (85±51 seconds). This time course is associated with shear-mediated dilation of larger conduit arteries in humans. There was a strong association between change in shear and diameter of the internal carotid (r=0.68; P<0.01). These data indicate, for the first time in humans, that shear stress is an important stimulus for hypercapnic vasodilation of the internal carotid artery. The combination of a hypercapnic stimulus and continuous noninvasive, high-resolution assessment of internal carotid shear and dilation may provide novel insights into the function and health of the clinically important extracranial arteries in humans. © 2016 American Heart Association, Inc.

  5. Shear stress-induced mechanotransduction protein deregulation and vasculopathy in a mouse model of progeria

    PubMed Central

    2014-01-01

    Introduction A mouse model of progeria derived by insertion of the human mutant LMNA gene (mLMNA), producing mutant lamin A, shows loss of smooth muscle cells in the media of the ascending aorta. We hypothesized that high shear stress, in the presence of mutant lamin A, induces this vasculopathy and tried to define the molecular and cellular basis for aortic vasculopathy. Methods Ascending and descending aortas from wild type (WT) and mLMNA+ mice were compared using proteomics, Western blots, PCR and immunostaining. To determine whether high fluidic shear stress, known to occur in the ascending aorta, contributed to the vasculopathy, we exposed descending aortas of mLMNA+ mice, with no apparent vasculopathy, to 75 dynes/cm2 shear stress for 30 minutes using a microfluidic system. Results When the mice were one year of age, expression of several mechanotransduction proteins in the ascending aorta, including vimentin, decreased in mLMNA+ mice but no decrease occurred in the descending aorta. High fluidic shear stress produced a significant reduction in vimentin of mLMNA+ mice but not in similarly treated WT mice. Conclusions The occurrence of mutant lamin A and high shear stress correlate with a reduction in the level of mechanotransduction proteins in smooth muscle cells of the media. Reduction of these proteins may contribute over time to development of vasculopathy in the ascending aorta in progeria syndrome. PMID:24661531

  6. Estimation of shear stress by using a myocardial bridge-mural coronary artery simulating device.

    PubMed

    Ding, Hao; Yang, Qian; Shang, Kun; Lan, Hailian; Lv, Jie; Liu, Zhilin; Liu, Yang; Sheng, Lixing; Zeng, Yanjun

    2016-10-07

    This study was aimed at developing a myocardial bridge-mural coronary artery simulative device and analyzing the relationship between shear stress on the mural coronary artery and atherosclerosis. A myocardial bridge-mural coronary artery simulative device was used to simulate experiments in vitro. In the condition of maintaining any related parameters such as system temperature, average flow rate, and heart rate, we calculated and observed changes in proximal and distal mean values, and oscillatory value of shear stress on the mural coronary artery by regulating the compression level of the myocardial bridge to the mural coronary artery. Under 0% compression, no significant differences were observed in distal and proximal mean values and oscillatory value of the shear stress on the mural coronary artery. With the increase in the degree of compression, the mean shear stress at the distal end was greater than that at the proximal end, but the oscillatory value of the shear stress at the proximal end was greater than that at the distal end. The experimental results of this study indicate that myocardial bridge compression leads to abnormal hemodynamics at the proximal end of the mural coronary artery. This abnormal phenomenon is of great significance in the study of atherosclerosis hemodynamic pathogenesis, which has potential clinical value for pathological effects and treatments of myocardial bridge.

  7. Nature's rheologists: Lymphatic endothelial cells control migration in response to shear stress

    NASA Astrophysics Data System (ADS)

    Fuller, Gerald; Dunn, Alex; Surya, Vinay

    2015-03-01

    Endothelial cells (ECs) line the inner surface of blood and lymphatic vessels and are sensitive to fluid flow as part of their physiological function. EC organization, migration and vessel development are profoundly influenced by shear stresses, with important implications in cardiovascular disease and tumor metastasis. How ECs sense fluid flow is a central and unanswered question in cardiovascular biology. We developed a high-throughput live-cell flow chamber that models the gradients in wall shear stress experienced by ECs in vivo. Live-cell imaging allows us to probe cellular responses to flow, most notably EC migration, which has a key role in vessel remodeling. We find that most EC subtypes, including ECs from the venous, arterial, and microvascular systems, migrate in the flow direction. In contrast, human lymphatic microvascular ECs (hLMVECs) migrate against flow and up spatial gradients in wall shear stress. Further experiments reveal that hLMVECs are sensitive to the magnitude, direction, and the local spatial gradients in wall shear stress. Lastly, recent efforts have aimed to link this directional migration to spatial gradients in cell-mediated small molecule emission that may be linked to the gradient in wall shear stress.

  8. Relationship between Concentration Difference of Different Density Lipoproteins and Shear Stress in Atherosclerosis

    PubMed Central

    Meng, Wei; Yu, Fengxu; Chen, Huaiqing; Zhang, Jianmin; Zhang, Eryong; Guo, Yingqiang; Shi, Yingkang

    2012-01-01

    Previous research has observed concentration polarization in LDL and HDL in the arterial system. However, there is no report that links this concentration polarization to the development of vascular atherosclerosis (AS). Therefore, the purpose of this study is to establish the relationship between concentration difference of LDL and HDL and shear stress using a carotid bifurcation vascular model. PTFE was employed to create the carotid bifurcation model. Endothelial cells were coated on the inner wall of the graft. In a recirculation system, HDL and LDL concentration were measured under two different ICA flow velocities at 5 different locations within our model. We report the following: (1) LDL and HDL concentration difference was observed in both high flow and low flow environments; (2) the degree of LDL and HDL concentration polarization varied depending of high flow and low flow environment; (3) absolute values of concentration difference between LDL and HDL at the inner wall surface decreased with the increase in shear stress when shear stress was more than 1.5 Pa. This variation trend would be more pronounced if shear stress were less than 0.5 Pa. Our study suggests that under the action of shear stress, concentration differences of LDL or HDL create a disturbance in the balance of atherogenic factors and anti-As factors, resulting in the occurrence of AS. PMID:22481972

  9. Development of a new contact-type piezoresistive micro-shear-stress sensor

    NASA Astrophysics Data System (ADS)

    Hsieh, M. C.; Fang, Yean-Kuen; Ju, M. S.; Ho, Jyh-Jier; Ting, S. F.

    2002-04-01

    A prototype contact type micro piezoresistive shear-stress sensor that can be utilized to measure the shear stress between skin of stump and socket of Above-Knee (AK) prosthesis was designed, fabricated and tested. Micro-electro-mechanical system (MEMS) technology has been chosen for the design because of the low cost, small size and adaptability to this application. In this paper, the Finite Element Method (FEM) package ANSYS has been employed for the stress analysis of the micro shear-stress sensors. The sensors contain two X-ducers that will transform the stresses into an output voltage. In the developed sensor, a 3000X3000X3000 micrometers (superscript 3/ square membrane is formed by bulk micromachining of an n-type <100> monolithic silicon. The piezoresistive strain gauges were implanted with boron ions with a dose of 10(superscript 15/ atoms/cm(superscript 2/. Static characteristics of the shear sensor were determined through a series of calibration tests. The fabricated sensor exhibits a sensitivity of 0.13mV/mA-Mpa for a 1.4N full scales shear force range and the overall mean hysteresis error is than 3.5%. In addition, the results simulated by FEM are validated by comparison with experimental investigations.

  10. Cultivation of shear stress sensitive microorganisms in disposable bag reactor systems.

    PubMed

    Jonczyk, Patrick; Takenberg, Meike; Hartwig, Steffen; Beutel, Sascha; Berger, Ralf G; Scheper, Thomas

    2013-09-20

    Technical scale (≥5l) cultivations of shear stress sensitive microorganisms are often difficult to perform, as common bioreactors are usually designed to maximize the oxygen input into the culture medium. This is achieved by mechanical stirrers, causing high shear stress. Examples for shear stress sensitive microorganisms, for which no specific cultivation systems exist, are many anaerobic bacteria and fungi, such as basidiomycetes. In this work a disposable bag bioreactor developed for cultivation of mammalian cells was investigated to evaluate its potential to cultivate shear stress sensitive anaerobic Eubacterium ramulus and shear stress sensitive basidiomycetes Flammulina velutipes and Pleurotus sapidus. All cultivations were compared with conventional stainless steel stirred tank reactors (STR) cultivations. Good growth of all investigated microorganisms cultivated in the bag reactor was found. E. ramulus showed growth rates of μ=0.56 h⁻¹ (bag) and μ=0.53 h⁻¹ (STR). Differences concerning morphology, enzymatic activities and growth in fungal cultivations were observed. In the bag reactor growth in form of small, independent pellets was observed while STR cultivations showed intense aggregation. F. velutipes reached higher biomass concentrations (21.2 g l⁻¹ DCW vs. 16.8 g l⁻¹ DCW) and up to 2-fold higher peptidolytic activities in comparison to cell cultivation in stirred tank reactors. Copyright © 2013 Elsevier B.V. All rights reserved.

  11. Large scale structures in a turbulent boundary layer and their imprint on wall shear stress

    NASA Astrophysics Data System (ADS)

    Pabon, Rommel; Barnard, Casey; Ukeiley, Lawrence; Sheplak, Mark

    2015-11-01

    Experiments were performed on a turbulent boundary layer developing on a flat plate model under zero pressure gradient flow. A MEMS differential capacitive shear stress sensor with a 1 mm × 1 mm floating element was used to capture the fluctuating wall shear stress simultaneously with streamwise velocity measurements from a hot-wire anemometer traversed in the wall normal direction. Near the wall, the peak in the cross correlation corresponds to an organized motion inclined 45° from the wall. In the outer region, the peak diminishes in value, but is still significant at a distance greater than half the boundary layer thickness, and corresponds to a structure inclined 14° from the wall. High coherence between the two signals was found for the low-frequency content, reinforcing the belief that large scale structures have a vital impact on wall shear stress. Thus, estimation of the wall shear stress from the low-frequency velocity signal will be performed, and is expected to be statistically significant in the outer boundary layer. Additionally, conditionally averaged mean velocity profiles will be presented to assess the effects of high and low shear stress. This material is based upon work supported by the National Science Foundation Graduate Research Fellowship under Grant No. DGE-1315138.

  12. Mechanical responses and stress fluctuations of a supercooled liquid in a sheared non-equilibrium state.

    PubMed

    Mizuno, H; Yamamoto, R

    2012-04-01

    A steady shear flow can drive supercooled liquids into a non-equilibrium state. Using molecular dynamics simulations under steady shear flow superimposed with oscillatory shear strain for a probe, non-equilibrium mechanical responses are studied for a model supercooled liquid composed of binary soft spheres. We found that even in the strongly sheared situation, the supercooled liquid exhibits surprisingly isotropic responses to oscillating shear strains applied in three different components of the strain tensor. Based on this isotropic feature, we successfully constructed a simple two-mode Maxwell model that can capture the key features of the storage and loss moduli, even for highly non-equilibrium state. Furthermore, we examined the correlation functions of the shear stress fluctuations, which also exhibit isotropic relaxation behaviors in the sheared non-equilibrium situation. In contrast to the isotropic features, the supercooled liquid additionally demonstrates anisotropies in both its responses and its correlations to the shear stress fluctuations. Using the constitutive equation (a two-mode Maxwell model), we demonstrated that the anisotropic responses are caused by the coupling between the oscillating strain and the driving shear flow. Due to these anisotropic responses and fluctuations, the violation of the fluctuation-dissipation theorem (FDT) is distinct for different components. We measured the magnitude of this violation in terms of the effective temperature. It was demonstrated that the effective temperature is notably different between different components, which indicates that a simple scalar mapping, such as the concept of an effective temperature, oversimplifies the true nature of supercooled liquids under shear flow. An understanding of the mechanism of isotropies and anisotropies in the responses and fluctuations will lead to a better appreciation of these violations of the FDT, as well as certain consequent modifications to the concept of an

  13. Arteries respond to independent control of circumferential and shear stress in organ culture.

    PubMed

    Wayman, Brian H; Taylor, W Robert; Rachev, Alexander; Vito, Raymond P

    2008-05-01

    Arteries respond to changes in global mechanical parameters (pressure, flow rate, and longitudinal stretching) by remodeling to restore local parameters (circumferential stress, shear stress, and axial strain) to baseline levels. Because a change in a single global parameter results in changes of multiple local parameters, the effects of individual local parameters on remodeling remain unknown. This study uses a novel approach to study remodeling in organ culture based on independent control of local mechanical parameters. The approach is illustrated by studying the short term effects of circumferential and shear stress on remodeling-related biological markers. Porcine carotid arteries were cultured for 3 days at a circumferential stress of 50 or 150 kPa or, in separate experiments, a shear stress of 0.75 or 2.25 Pa. At high circumferential stress, matrix synthesis, smooth muscle cell proliferation, and cell death are significantly greater, but matrix metalloproteinase-2 (MMP-2) and pro-MMP-2 activity are significantly less. In contrast, biological markers measured were unaffected by shear stress. Applications of the proposed approach for improved understanding of remodeling, optimizing mechanical conditioning of tissue engineered arteries, and selection of experimentally motivated growth laws are discussed.

  14. Impact of a mechanical shear stress on intracellular trafficking.

    PubMed

    Aubertin, Kelly; Tailleur, Julien; Wilhelm, Claire; Gallet, François

    2017-08-09

    Intracellular trafficking mainly takes place along the microtubules, and its efficiency depends on the local architecture and organization of the cytoskeletal network. In this work, the cytoplasm of stem cells is subjected to mechanical vortexing at a frequency of up to 1 Hz, by using magnetic chains of endosomes embedded in the cell body, in order to locally perturb the network structure. The consequences are evaluated on the directionality and processivity of the spontaneous motion of endosomes. When the same chains are used both to shear the cell medium and to probe the intracellular traffic, a substantial decrease in transport efficiency is detected after applying the mechanical shear. Interestingly, when using different objects to apply the shear and to probe the spontaneous motion, no alteration of the transport efficiency can be detected. We conclude that shaking the vesicles mainly causes their unbinding from the cytoskeletal tracks, but has little influence on the integrity of the network itself. This is corroborated by active microrheology measurements, performed with chains actuated by a magnetic field, and showing that the mechanical compliance of the cytoplasm is similar before and after slow vortexing.

  15. Rheological regional properties of brain tissue studied under cyclic creep/ recovery shear stresses

    NASA Astrophysics Data System (ADS)

    Boudjema, F.; Lounis, M.; Khelidj, B.; Bessai, N.

    2015-04-01

    The rheological properties of brain tissue were studied by repeated creep-recovery shear tests under static conditions for different regions. Corpus callosum CC, Thalamus Th and Corona radiata CR. Non-linear viscoelastic model was also proposed to characterize the transient/steady states of shear creep results. From the creep-recovery data it was obvious that the brain tissues show high regional anisotropy. However. the both samples exhibit fluid viscoelastic properties in the first shear stress cycle of 100 Pa, while this behaviour evolutes to solid viscoelastic with cyclic effect.

  16. Influence of thickness and permeability of endothelial surface layer on transmission of shear stress in capillaries

    NASA Astrophysics Data System (ADS)

    Zhang, SongPeng; Zhang, XiangJun; Tian, Yu; Meng, YongGang; Lipowsky, Herbert

    2015-07-01

    The molecular coating on the surface of microvascular endothelium has been identified as a barrier to transvascular exchange of solutes. With a thickness of hundreds of nanometers, this endothelial surface layer (ESL) has been treated as a porous domain within which fluid shear stresses are dissipated and transmitted to the solid matrix to initiate mechanotransduction events. The present study aims to examine the effects of the ESL thickness and permeability on the transmission of shear stress throughout the ESL. Our results indicate that fluid shear stresses rapidly decrease to insignificant levels within a thin transition layer near the outer boundary of the ESL with a thickness on the order of ten nanometers. The thickness of the transition zone between free fluid and the porous layer was found to be proportional to the square root of the Darcy permeability. As the permeability is reduced ten-fold, the interfacial fluid and solid matrix shear stress gradients increase exponentially two-fold. While the interfacial fluid shear stress is positively related to the ESL thickness, the transmitted matrix stress is reduced by about 50% as the ESL thickness is decreased from 500 to 100 nm, which may occur under pathological conditions. Thus, thickness and permeability of the ESL are two main factors that determine flow features and the apportionment of shear stresses between the fluid and solid phases of the ESL. These results may shed light on the mechanisms of force transmission through the ESL and the pathological events caused by alterations in thickness and permeability of the ESL.

  17. Bed shear stress estimation on an open intertidal flat using in situ measurements

    NASA Astrophysics Data System (ADS)

    Zhu, Q.; van Prooijen, B. C.; Wang, Z. B.; Ma, Y. X.; Yang, S. L.

    2016-12-01

    Accurate estimations for the bed shear stress are essential to predict the erosion and deposition processes in estuaries and coasts. This study used high-frequency in situ measurements of water depths and near-bed velocities to estimate bed shear stress on an open intertidal flat in the Yangtze Delta, China. To determine the current-induced bed shear stress (τc) the in situ near-bed velocities were first decomposed from the turbulent velocity into separate wave orbital velocities using two approaches: a moving average (MA) and energy spectrum analysis (ESA). τc was then calculated and evaluated using the log-profile (LP), turbulent kinetic energy (TKE), modified TKE (TKEw), Reynolds stress (RS), and inertial dissipation (ID) methods. Wave-induced bed shear stress (τw) was estimated using classic linear wave theory. The total bed shear stress (τcw) was determined based on the Grant-Madsen wave-current interaction model (WCI). The results demonstrate that when the ratio of significant wave height to water depth (Hs/h) is greater than 0.25, τcw is significantly overestimated because the vertical velocity fluctuations are contaminated by the surface waves generated by high winds. In addition, wind enhances the total bed shear stress as a result of the increases in both τw and τc generated by the greater wave height and reinforcing of vertical turbulence, respectively. From a comparison of these various methods, the TKEw method associated with ESA decomposition was found to be the best approach because: (1) this method generates the highest mean index of agreement; (2) it uses vertical velocities that are less affected by Doppler noise; and (3) it is less sensitive to the near-bed stratification structure and uncertainty in bed location and roughness.

  18. 4-Dimensional light-sheet microscopy to elucidate shear stress modulation of cardiac trabeculation

    PubMed Central

    Lee, Juhyun; Fei, Peng; Packard, René R. Sevag; Kang, Hanul; Xu, Hao; Baek, Kyung In; Jen, Nelson; Chen, Junjie; Yen, Hilary; Chi, Neil C.; Ho, Chih-Ming; Hsiai, Tzung K.

    2016-01-01

    Hemodynamic shear forces are intimately linked with cardiac development, during which trabeculae form a network of branching outgrowths from the myocardium. Mutations that alter Notch signaling also result in trabeculation defects. Here, we assessed whether shear stress modulates trabeculation to influence contractile function. Specifically, we acquired 4D (3D + time) images with light sheets by selective plane illumination microscopy (SPIM) for rapid scanning and deep axial penetration during zebrafish morphogenesis. Reduction of blood viscosity via gata1a morpholino oligonucleotides (MO) reduced shear stress, resulting in downregulation of Notch signaling and attenuation of trabeculation. Arrest of cardiomyocyte contraction either by troponin T type 2a (tnnt2a) MO or in weak atriumm58 (wea) mutants resulted in reduced shear stress and downregulation of Notch signaling and trabeculation. Integrating 4D SPIM imaging with synchronization algorithm demonstrated that coinjection of neuregulin1 mRNA with gata1 MO rescued trabeculation to restore contractile function in association with upregulation of Notch-related genes. Crossbreeding of Tg(flk:mCherry) fish, which allows visualization of the vascular system with the Tg(tp1:gfp) Notch reporter line, revealed that shear stress–mediated Notch activation localizes to the endocardium. Deleting endocardium via the clochesk4 mutants downregulated Notch signaling, resulting in nontrabeculated ventricle. Subjecting endothelial cells to pulsatile flow in the presence of the ADAM10 inhibitor corroborated shear stress–activated Notch signaling to modulate trabeculation. PMID:27018592

  19. Effects of fluid shear stress on polyelectrolyte multilayers by neutron scattering studies

    SciTech Connect

    Singh, Saurabh; Junghans, Ann; Watkins, Erik; Kapoor, Yash; Toomey, Ryan; Majewski, Jaroslaw

    2015-02-17

    The structure of layer-by-layer (LbL) deposited nanofilm coatings consists of alternating polyethylenimine (PEI) and polystyrenesulfonate (PSS) films deposited on a single crystal quartz substrate. LbL-deposited nanofilms were investigated by neutron reflectomery (NR) in contact with water in the static and fluid shear stress conditions. The fluid shear stress was applied through a laminar flow of the liquid parallel to the quartz/polymer interface in a custom-built solid–liquid interface cell. The scattering length density profiles obtained from NR results of these polyelectrolyte multilayers (PEM), measured under different shear conditions, showed proportional decrease of volume fraction of water hydrating the polymers. For the highest shear rate applied (ca. 6800 s–1) the water volume fraction decreased by approximately 7%. The decrease of the volume fraction of water was homogeneous through the thickness of the film. Since there were not any significant changes in the total polymer thickness, it resulted in negative osmotic pressures in the film. The PEM films were compared with the behavior of thin films of thermoresponsive poly(N-isopropylacrylamide) (pNIPAM) deposited via spin-coating. The PEM and pNIPAM differ in their interactions with water molecules, and they showed opposite behaviors under the fluid shear stress. In both cases the polymer hydration was reversible upon the restoration of static conditions. Furthermore, a theoretical explanation is given to explain this difference in the effect of shear on hydration of polymeric thin films.

  20. Lamin A/C deficiency reduces circulating tumor cell resistance to fluid shear stress

    PubMed Central

    Denais, Celine; Chan, Maxine F.; Wang, Zhexiao; Lammerding, Jan

    2015-01-01

    Metastasis contributes to over 90% of cancer-related deaths and is initiated when cancer cells detach from the primary tumor, invade the basement membrane, and enter the circulation as circulating tumor cells (CTCs). While metastasis is viewed as an inefficient process with most CTCs dying within the bloodstream, it is evident that some CTCs are capable of resisting hemodynamic shear forces to form secondary tumors in distant tissues. We hypothesized that nuclear lamins A and C (A/C) act as key structural components within CTCs necessary to resist destruction from elevated shear forces of the bloodstream. Herein, we show that, compared with nonmalignant epithelial cells, tumor cells are resistant to elevated fluid shear forces in vitro that mimic those within the bloodstream, as evidenced by significant decreases in cellular apoptosis and necrosis. Knockdown of lamin A/C significantly reduced tumor cell resistance to fluid shear stress, with significantly increased cell death compared with parental tumor cell and nontargeting controls. Interestingly, lamin A/C knockdown increased shear stress-induced tumor cell apoptosis, but did not significantly affect cellular necrosis. These data demonstrate that lamin A/C is an important structural component that enables tumor cell resistance to fluid shear stress-mediated death in the bloodstream, and may thus facilitate survival and hematogenous metastasis of CTCs. PMID:26447202

  1. Application of a Reynolds Stress Turbulence Model to the Compressible Shear Layer

    DTIC Science & Technology

    1990-02-01

    source vector containing the terms causing production, destruc- tion and redistribution of the Reynolds stresses . To numerically obtain the solution...OTIC FiLE Copy W. . NASA Contractor Report 182002 ICASE Report No. 90-18 0 ZICASE APPLICATION OF A REYNOLDS STRESS TURBULENCE MODEL TO THE...Virginia 23665-5225 k L APPLICATION OF A REYNOLDS STRESS TURBULENCE . MODEL TO THE COMPRESSIBLE SHEAR LAYER S. Sarkar1 .1’eSo For Institute for

  2. Determining erodibility, critical shear stress, and allowable discharge estimates for cohesive channels: case study in the Powder River Basin of Wyoming

    SciTech Connect

    Thoman, R.W.; Niezgoda, S.L.

    2008-12-15

    The continuous discharge of coalbed natural gas-produced (CBNG-produced) water within ephemeral, cohesive channels in the Powder River Basin (PRB) of Wyoming can result in significant erosion. A study was completed to investigate channel stability in an attempt to correlate cohesive soil properties to critical shear stress. An in situ jet device was used to determine critical shear stress (tau{sub c}) and erodibility (k{sub d}); cohesive soil properties were determined following ASTM procedures for 25 reaches. The study sites were comprised of erodible to moderately resistant clays with tau{sub c} ranging from 0.11 to 15.35 Pa and k{sub d} ranging from 0.27 to 2.38 cm{sup 3}/N s. A relationship between five cohesive soil characteristics and tau{sub c} was developed and presented for use in deriving tau{sub c} for similar sites. Allowable discharges for CBNG-produced water were also derived using tau{sub c} and the tractive force method. An increase in the allowable discharge was found for channels in which vegetation was maintained. The information from this case study is critical to the development of a conservative methodology to establish allowable discharges while minimizing flow-induced instability.

  3. Dynamic Shear Stress Regulation of Inflammatory and Thrombotic Pathways in Baboon Endothelial Outgrowth Cells

    PubMed Central

    Hinds, Monica T.; Nerem, Robert M.

    2013-01-01

    Endothelial outgrowth cells (EOCs) have garnered much attention as a potential autologous endothelial source for vascular implants or in tissue engineering applications due to their ease of isolation and proliferative ability; however, how these cells respond to different hemodynamic cues is ill-defined. This study investigates the inflammatory and thrombotic response of baboon EOCs (BaEOCs) to four hemodynamic conditions using the cone and plate shear apparatus: steady, laminar shear stress (SS); pulsatile, nonreversing laminar shear stress (PS); oscillatory, laminar shear stress (OS); and net positive, pulsatile, reversing laminar shear stress (RS). In summary, endothelial nitric oxide synthase (eNOS) mRNA was significantly upregulated by SS compared to OS. No differences were found in the mRNA levels of the inflammatory markers intercellular adhesion molecule-1 (ICAM-1), E-selectin, and vascular cell adhesion molecule-1 (VCAM-1) between the shear conditions; however, OS significantly increased the number of monocytes bound when compared to SS. Next, SS increased the anti-thrombogenic mRNA levels of CD39, thrombomodulin, and endothelial protein-C receptor (EPCR) compared to OS. SS also significantly increased CD39 and EPCR mRNA levels compared to RS. Finally, no significant differences were detected when comparing pro-thrombotic tissue factor mRNA or its activity levels. These results indicate that shear stress can have beneficial (SS) or adverse (OS, RS) effects on the inflammatory or thrombotic potential of EOCs. Further, these results suggest SS hemodynamic preconditioning may be optimal in increasing the efficacy of a vascular implant or in tissue-engineered applications that have incorporated EOCs. PMID:23406430

  4. Estimation of in-situ stresses in concrete members using polarized ultrasonic shear waves

    NASA Astrophysics Data System (ADS)

    Chen, Andrew; Schumacher, Thomas

    2014-02-01

    Ultrasonic testing is commonly used to detect flaws, estimate geometries, and characterize properties of materials and structures. Acoustoelasticity refers to the dependency of stress wave velocity with applied stresses and is a phenomenon that has been known by geophysicists since the 1960s. A way to capitalize on this effect for concrete applications is by using ultrasonic shear waves which are particularly sensitive to applied stresses when polarized in the direction of the applied stress. The authors conducted an experiment on a 150 mm (6 in.) diameter concrete cylinder specimen with a length of 305 mm (12 in.) that was loaded in discrete load steps to failure. At each load step two ultrasonic shear waves were transmitted through the specimen, one with the polarization perpendicular and the other transverse to the applied stress. The velocity difference between the two sets of polarized shear waves was found to correlate with the applied stress in the specimen. Two potential applications for this methodology include estimation of stresses in pre-stressed concrete bridge girders and investigation of load redistribution in structural support elements after extreme events. This paper introduces the background of the methodology, presents an analysis of the collected data, and discusses the relationship between the recorded signals and the applied stress.

  5. Crack initiation observation and local stress analysis in shear fracture tests of ultra-high strength steels

    NASA Astrophysics Data System (ADS)

    Ma, Ninshu; Takada, Kenji; Sugimoto, Nao

    2016-08-01

    To investigate the local strain and stress at the crack initiation position in shear fracture test pieces of ultra-high strength steels, a butterfly shear fracture specimen was employed. The crack initiation position and propagation direction were observed during shear fracture tests by high speed cameras and investigated through analysing the fracture surface by scanning electron microscope. Further, the finite element method was employed and the stress-triaxiality at the crack initiation position was investigated. It can be obtained that the crack initiated at the position where the stress state is close to uniaxial tensile state or plane strain state more than pure shear stress state.

  6. Modeling the curvature and interface shear stress of GaN-sapphire system

    NASA Astrophysics Data System (ADS)

    Li, Jia; Shi, Junjie; Wu, Jiejun; Liu, Huizhao

    2016-03-01

    The curvature and interface shear stress of GaN-sapphire system are studied by establishing the mechanical equations based on two main assumptions: (a) the thickness of GaN film can be compared to the thickness of sapphire substrate, and (b) the thickness of GaN film is non-uniform. Our results show that the curvature of GaN-sapphire system is a variable within the whole circular system. The interface shear stress changes direction around at the middle of radius for the circular system, and the curvature have an important effect on the interface shear stress due to the consideration of non-uniform thickness for GaN film.

  7. The Effects of Hemodynamic Shear Stress on Stemness of Acute Myelogenous Leukemia (AML)

    NASA Astrophysics Data System (ADS)

    Raddatz, Andrew; Triantafillu, Ursula; Kim, Yonghyun (John)

    2015-11-01

    Cancer stem cells (CSCs) have recently been identified as the root cause of tumors generated from cancer cell populations. This is because these CSCs are drug-resistant and have the ability to self-renew and differentiate. Current methods of culturing CSCs require much time and money, so cancer cell culture protocols, which maximize yield of CSCs are needed. It was hypothesized that the quantity of Acute myelogenous leukemia stem cells (LSCs) would increase after applying shear stress to the leukemia cells based on previous studies with breast cancer in bioreactors. The shear stress was applied by pumping the cells through narrow tubing to mimic the in vivo bloodstream environment. In support of the hypothesis, shear stress was found to increase the amount of LSCs in a given leukemia population. This work was supported by NSF REU Site Award 1358991.

  8. Online quantitative phase imaging of vascular endothelial cells under fluid shear stress utilizing digital holographic microscopy

    NASA Astrophysics Data System (ADS)

    Odenthal-Schnittler, Maria; Schnittler, Hans Joachim; Kemper, Björn

    2016-03-01

    We have explored the utilization of quantitative phase imaging with digital holographic microscopy (DHM) as a novel tool for quantifying the dynamics of morphologic parameters (morphodynamics) of confluent endothelial cell layers under fluid shear stress conditions. Human umbilical vein endothelial cells (HUVECs) were exposed to fluid shear stress in a transparent cone/plate flow device (BioTech-Flow-System) and imaged with a modular setup for quantitative DHM phase imaging for up to 48 h. The resulting series of quantitative phase image sequences were analyzed for the average surface roughness of the cell layers and cell alignment. Our results demonstrate that quantitative phase imaging is a powerful and reliable tool to quantify the dynamics of morphological adaptation of endothelial cells to fluid shear stress.

  9. Alteration of mean wall shear stress near an oscillating stagnation point.

    PubMed

    Hazel, A L; Pedley, T J

    1998-04-01

    The site opposite an end-to-side anastomosis, resulting from femoral bypass surgery, and the carotid sinus are two regions well known to be prone to fibrous intimal hyperplasia or atherogenesis, respectively. The blood flow at these two sites features a stagnation point, which oscillates in strength and position. Mathematical models are used to determine some of the features of such a flow; in particular, the mean wall shear stress is calculated. The positional oscillations cause a significant change in the distribution and magnitude of the mean wall shear stress from that of the well-studied case of a stagnation point that oscillates only in strength. It is therefore proposed that the recorded effect of time dependence in the flow upon atherogenesis could still be a result of the distribution of the mean and not the time-varying components of the wall shear stress.

  10. An integrated temperature-compensated flexible shear-stress sensor microarray with concentrated leading-wire.

    PubMed

    Tang, Jian; Liu, Wu; Zhang, Weiping; Sun, Yongming; Chen, Honghai

    2016-02-01

    Flexible shear stress sensor is quite important for characterizing curved surface flows. In this work, a novel integrated shear stress sensor microarray is designed with twenty parallel channels, which share the concentrated leading-wire to transmit the ground signal. Electrical pads in rows are easily connected to the circuits with two separate Wheatstone bridges and constant-temperature-difference mode operation is provided for the hot-wires. Temperature crosstalk between adjacent hot-wires is prevented well and the effectiveness of the temperature compensated circuits is verified. Relatively large output response is obtained as the shear stress varies and the sensitivity of the sensors is measured about 0.086 V(2)/Pa(1/3) with nonlinearity lower than 1%, revealing high performance characteristic of the sensors.

  11. Imaging the cellular response to transient shear stress using stroboscopic digital holography.

    PubMed

    Antkowiak, Maciej; Arita, Yoshihiko; Dholakia, Kishan; Gunn-Moore, Frank

    2011-12-01

    We use stroboscopic quantitative phase microscopy to study cell deformation and the response to cavitation bubbles and transient shear stress resulting from laser-induced breakdown of an optically trapped nanoparticle. A bi-directional transient displacement of cytoplasm is observed during expansion and collapse of the cavitation bubble. In some cases, cell deformation is only observable at the microsecond time scale without any permanent change in cell shape or optical thickness. On a time scale of seconds, the cellular response to shear stress and cytoplasm deformation typically leads to retraction of the cellular edge most exposed to the flow, rounding of the cell body and, in some cases, loss of cellular dry mass. These results give a new insight into the cellular response to cavitation induced shear stress and related plasma membrane permeabilization. This study also demonstrates that laser-induced breakdown of a nanoparticle offers localized cavitation, which interacts with a single cell but without causing cell lysis.

  12. Investigation of shear stress on a shock front in solid high explosives (HE)

    SciTech Connect

    Bat'kov, Y.V.; Fishman, N.D.; Novikov, S.A.

    1983-11-01

    This article gives results of an experimental investigation of the dependence of the critical shear stress at the shock front in cast TNT and in a cast TH 50/50 composite on the magnitude of the shock compression pressure in a range to 4.0 GPa (e.g. to the beginning of excitation of the explosive transformation). The principal stresses were measured by manganin sensors located in the high explosive under investigation in two mutually perpendicular directions in the tests. Stationary shocks were produced in the explosive specimens under investigation by using an explosive apparatus of the ''laminate'' type. It is determined that the magnitude of the shear stress grows linearly for the cast explosives investigated as the pressure grows, and exceeds considerably the static values of the shear strength.

  13. Imaging the cellular response to transient shear stress using stroboscopic digital holography

    NASA Astrophysics Data System (ADS)

    Antkowiak, Maciej; Arita, Yoshihiko; Dholakia, Kishan; Gunn-Moore, Frank

    2011-12-01

    We use stroboscopic quantitative phase microscopy to study cell deformation and the response to cavitation bubbles and transient shear stress resulting from laser-induced breakdown of an optically trapped nanoparticle. A bi-directional transient displacement of cytoplasm is observed during expansion and collapse of the cavitation bubble. In some cases, cell deformation is only observable at the microsecond time scale without any permanent change in cell shape or optical thickness. On a time scale of seconds, the cellular response to shear stress and cytoplasm deformation typically leads to retraction of the cellular edge most exposed to the flow, rounding of the cell body and, in some cases, loss of cellular dry mass. These results give a new insight into the cellular response to cavitation induced shear stress and related plasma membrane permeabilization. This study also demonstrates that laser-induced breakdown of a nanoparticle offers localized cavitation, which interacts with a single cell but without causing cell lysis.

  14. PI16 is a shear stress and inflammation-regulated inhibitor of MMP2

    PubMed Central

    Hazell, Georgina G. J.; Peachey, Alasdair M. G.; Teasdale, Jack E.; Sala-Newby, Graciela B.; Angelini, Gianni D.; Newby, Andrew C.; White, Stephen J.

    2016-01-01

    Raised endothelial shear stress is protective against atherosclerosis but such protection may be lost at sites of inflammation. We found that four splice variants of the peptidase inhibitor 16 (PI16) mRNA are among the most highly shear stress regulated transcripts in human coronary artery endothelial cells (HCAECs), in vitro but that expression is reduced by inflammatory mediators TNFα and IL-1β. Immunohistochemistry demonstrated that PI16 is expressed in human coronary endothelium and in a subset of neointimal cells and medial smooth muscle cells. Adenovirus-mediated PI16 overexpression inhibits HCAEC migration and secreted matrix metalloproteinase (MMP) activity. Moreover, PI16 inhibits MMP2 in part by binding an exposed peptide loop above the active site. Our results imply that, at high endothelial shear stress, PI16 contributes to inhibition of protease activity; protection that can be reversed during inflammation. PMID:27996045

  15. Gyrokinetic simulation of momentum transport with residual stress from diamagnetic level velocity shears

    NASA Astrophysics Data System (ADS)

    Waltz, R. E.; Staebler, G. M.; Solomon, W. M.

    2011-04-01

    Residual stress refers to the remaining toroidal angular momentum (TAM) flux (divided by major radius) when the shear in the equilibrium fluid toroidal velocity (and the velocity itself) vanishes. Previously [Waltz et al., Phys. Plasmas 14, 122507 (2007); errata 16, 079902 (2009)], we demonstrated with GYRO [Candy and Waltz, J. Comp. Phys. 186, 545 (2003)] gyrokinetic simulations that TAM pinching from (ion pressure gradient supported or diamagnetic level) equilibrium E ×B velocity shear could provide some of the residual stress needed to support spontaneous toroidal rotation against normal diffusive loss. Here we show that diamagnetic level shear in the intrinsic drift wave velocities (or "profile shear" in the ion and electron density and temperature gradients) provides a comparable residual stress. The individual signed contributions of these small (rho-star level) E ×B and profile velocity shear rates to the turbulence level and (rho-star squared) ion energy transport stabilization are additive if the rates are of the same sign. However because of the additive stabilization effect, the contributions to the small (rho-star cubed) residual stress is not always simply additive. If the rates differ in sign, the residual stress from one can buck out that from the other (and in some cases reduce the stabilization.) The residual stress from these diamagnetic velocity shear rates is quantified by the ratio of TAM flow to ion energy (power) flow (M/P) in a global GYRO core simulation of a "null" toroidal rotation DIII-D [Mahdavi and Luxon, Fusion Sci. Technol. 48, 2 (2005)] discharge by matching M/P profiles within experimental uncertainty. Comparison of global GYRO (ion and electron energy as well as particle) transport flow balance simulations of TAM transport flow in a high-rotation DIII-D L-mode quantifies and isolates the E ×B shear and parallel velocity (Coriolis force) pinching components from the larger "diffusive" parallel velocity shear driven component and

  16. Interface shear stresses during ambulation with a below-knee prosthetic limb

    PubMed Central

    Sanders, Joan E.; Daly, Colin H.; Burgess, Ernest M.

    2015-01-01

    Shear stresses on a residual limb in a prosthetic socket are considered clinically to contribute to tissue breakdown in below-knee amputees. When applied simultaneously with normal stresses, they can cause injury within the skin or can generate an abrasion on the surface. To gain insight into shear stresses and parameters that affect them, interface stresses were recorded on below-knee amputee subjects during walking trials. On the tibial flares, resultant shear ranged from 5.6 kPa to 39.0 kPa, while on the posterior surface it ranged from 5.0 kPa to 40.7 kPa. During stance phase, anterior resultant shears on a socket were directed toward the apex while posterior resultant shears were directed downward approximately perpendicular to the ground. Waveform shapes were usually double-peaked, with the first peak at 25% to 40% into stance phase and the second peak at 65% to 85% into stance. Application of these results to residual limb tissue mechanics and prosthetic design is discussed. PMID:1432723

  17. Shear-stress fluctuations in self-assembled transient elastic networks

    NASA Astrophysics Data System (ADS)

    Wittmer, J. P.; Kriuchevskyi, I.; Cavallo, A.; Xu, H.; Baschnagel, J.

    2016-06-01

    Focusing on shear-stress fluctuations, we investigate numerically a simple generic model for self-assembled transient networks formed by repulsive beads reversibly bridged by ideal springs. With Δ t being the sampling time and t(f ) ˜1 /f the Maxwell relaxation time (set by the spring recombination frequency f ), the dimensionless parameter Δ x =Δ t /t(f ) is systematically scanned from the liquid limit (Δ x ≫1 ) to the solid limit (Δ x ≪1 ) where the network topology is quenched and an ensemble average over m -independent configurations is required. Generalizing previous work on permanent networks, it is shown that the shear-stress relaxation modulus G (t ) may be efficiently determined for all Δ x using the simple-average expression G (t ) =μA-h (t ) with μA=G (0 ) characterizing the canonical-affine shear transformation of the system at t =0 and h (t ) the (rescaled) mean-square displacement of the instantaneous shear stress as a function of time t . This relation is compared to the standard expression G (t ) =c ˜(t ) using the (rescaled) shear-stress autocorrelation function c ˜(t ) . Lower bounds for the m configurations required by both relations are given.

  18. A novel in vitro loading system to produce supraphysiologic oscillatory fluid shear stress

    PubMed Central

    Oest, Megan E.; Miller, Mark A.; Howard, Karen I.; Mann, Kenneth A.

    2014-01-01

    A multi-well fluid loading (MFL) system was developed to deliver oscillatory subphysiologic to supraphysiologic fluid shear stresses to cell monolayers in vitro using standard multi-well culture plates. Computational fluid dynamics modeling with fluid-structure interactions was used to quantify the squeeze film fluid flow between an axially displaced piston and the well plate surface. Adjusting the cone angle of the piston base modulated the fluid pressure, velocity, and shear stress magnitudes. Modeling results showed that there was near uniform fluid shear stress across the well with a linear drop in pressure across the radius of the well. Using the MFL system, RAW 264.7 osteoclastic cells were exposed to oscillatory fluid shear stresses of 0, 0.5, 1.5, 4, 6, and 17 Pa. Cells were loaded 1 h per day at 1 Hz for two days. Compared to sub-physiologic and physiologic levels, supraphysiologic oscillatory fluid shear induced upregulation of osteoclastic activity as measured by tartrate-resistant acid phosphatase activity and formation of mineral resorption pits. Cell number remained constant across all treatment groups. PMID:24275439

  19. Shear-stress fluctuations in self-assembled transient elastic networks.

    PubMed

    Wittmer, J P; Kriuchevskyi, I; Cavallo, A; Xu, H; Baschnagel, J

    2016-06-01

    Focusing on shear-stress fluctuations, we investigate numerically a simple generic model for self-assembled transient networks formed by repulsive beads reversibly bridged by ideal springs. With Δt being the sampling time and t_{☆}(f)∼1/f the Maxwell relaxation time (set by the spring recombination frequency f), the dimensionless parameter Δx=Δt/t_{☆}(f) is systematically scanned from the liquid limit (Δx≫1) to the solid limit (Δx≪1) where the network topology is quenched and an ensemble average over m-independent configurations is required. Generalizing previous work on permanent networks, it is shown that the shear-stress relaxation modulus G(t) may be efficiently determined for all Δx using the simple-average expression G(t)=μ_{A}-h(t) with μ_{A}=G(0) characterizing the canonical-affine shear transformation of the system at t=0 and h(t) the (rescaled) mean-square displacement of the instantaneous shear stress as a function of time t. This relation is compared to the standard expression G(t)=c[over ̃](t) using the (rescaled) shear-stress autocorrelation function c[over ̃](t). Lower bounds for the m configurations required by both relations are given.

  20. A Multi-Phase Based Fluid-Structure-Microfluidic interaction sensor for Aerodynamic Shear Stress

    NASA Astrophysics Data System (ADS)

    Hughes, Christopher; Dutta, Diganta; Bashirzadeh, Yashar; Ahmed, Kareem; Qian, Shizhi

    2014-11-01

    A novel innovative microfluidic shear stress sensor is developed for measuring shear stress through multi-phase fluid-structure-microfluidic interaction. The device is composed of a microfluidic cavity filled with an electrolyte liquid. Inside the cavity, two electrodes make electrochemical velocimetry measurements of the induced convection. The cavity is sealed with a flexible superhydrophobic membrane. The membrane will dynamically stretch and flex as a result of direct shear cross-flow interaction with the seal structure, forming instability wave modes and inducing fluid motion within the microfluidic cavity. The shear stress on the membrane is measured by sensing the induced convection generated by membrane deflections. The advantages of the sensor over current MEMS based shear stress sensor technology are: a simplified design with no moving parts, optimum relationship between size and sensitivity, no gaps such as those created by micromachining sensors in MEMS processes. We present the findings of a feasibility study of the proposed sensor including wind-tunnel tests, microPIV measurements, electrochemical velocimetry, and simulation data results. The study investigates the sensor in the supersonic and subsonic flow regimes. Supported by a NASA SBIR phase 1 contract.

  1. A novel in vitro loading system to produce supraphysiologic oscillatory fluid shear stress.

    PubMed

    Oest, Megan E; Miller, Mark A; Howard, Karen I; Mann, Kenneth A

    2014-01-22

    A multi-well fluid loading (MFL) system was developed to deliver oscillatory subphysiologic to supraphysiologic fluid shear stresses to cell monolayers in vitro using standard multi-well culture plates. Computational fluid dynamics modeling with fluid-structure interactions was used to quantify the squeeze film fluid flow between an axially displaced piston and the well plate surface. Adjusting the cone angle of the piston base modulated the fluid pressure, velocity, and shear stress magnitudes. Modeling results showed that there was near uniform fluid shear stress across the well with a linear drop in pressure across the radius of the well. Using the MFL system, RAW 264.7 osteoclastic cells were exposed to oscillatory fluid shear stresses of 0, 0.5, 1.5, 4, 6, and 17 Pa. Cells were loaded 1 h per day at 1 Hz for two days. Compared to sub-physiologic and physiologic levels, supraphysiologic oscillatory fluid shear induced upregulation of osteoclastic activity as measured by tartrate-resistant acid phosphatase activity and formation of mineral resorption pits. Cell number remained constant across all treatment groups. © 2013 Published by Elsevier Ltd.

  2. [The anticonstrictor effect of endothelial sensitivity to shear stress].

    PubMed

    Mel'kumiants, A M; Balashov, S A; Kartamyshev, S P

    1996-04-01

    Responses of the femoral artery to drops in transmural pressure and to norepinephrine revealed the anticonstrictor effect of the endothelium sensitivity upon a stress action. The effect was less obvious at high flow rate. The data obtained suggests that the endothelium sensitivity to stress inhibits the arterial constrictor responses irrespective of the nature of the constrictor stimuli.

  3. Flow-induced corrosion behavior of absorbable magnesium-based stents.

    PubMed

    Wang, Juan; Giridharan, Venkataraman; Shanov, Vesselin; Xu, Zhigang; Collins, Boyce; White, Leon; Jang, Yongseok; Sankar, Jagannathan; Huang, Nan; Yun, Yeoheung

    2014-12-01

    The aim of this work was to study corrosion behavior of magnesium (Mg) alloys (MgZnCa plates and AZ31 stents) under varied fluid flow conditions representative of the vascular environment. Experiments revealed that fluid hydrodynamics, fluid flow velocity and shear stress play essential roles in the corrosion behavior of absorbable magnesium-based stent devices. Flow-induced shear stress (FISS) accelerates the overall corrosion (including localized, uniform, pitting and erosion corrosions) due to the increased mass transfer and mechanical force. FISS increased the average uniform corrosion rate, the localized corrosion coverage ratios and depths and the removal rate of corrosion products inside the corrosion pits. For MgZnCa plates, an increase of FISS results in an increased pitting factor but saturates at an FISS of ∼0.15Pa. For AZ31 stents, the volume loss ratio (31%) at 0.056Pa was nearly twice that (17%) at 0Pa before and after corrosion. Flow direction has a significant impact on corrosion behavior as more severe pitting and erosion corrosion was observed on the back ends of the MgZnCa plates, and the corrosion product layer facing the flow direction peeled off from the AZ31 stent struts. This study demonstrates that flow-induced corrosion needs be understood so that Mg-based stents in vascular environments can be effectively designed.

  4. Theory and Practice of Shear/Stress Strain Gage Hygrometry

    NASA Technical Reports Server (NTRS)

    Shams, Qamar A.; Fenner, Ralph L.

    2006-01-01

    Mechanical hygrometry has progressed during the last several decades from crude hygroscopes to state-of-the art strain-gage sensors. The strain-gage devices vary from different metallic beams to strain-gage sensors using cellulose crystallite elements, held in full shear restraint. This old technique is still in use but several companies are now actively pursuing development of MEMS miniaturized humidity sensors. These new sensors use polyimide thin film for water vapor adsorption and desorption. This paper will provide overview about modern humidity sensors.

  5. Shear stress transmission model for the flagellar rotary motor.

    PubMed

    Mitsui, Toshio; Ohshima, Hiroyuki

    2008-09-01

    Most bacteria that swim are propelled by flagellar filaments, which are driven by a rotary motor powered by proton flux. The mechanism of the flagellar motor is discussed by reforming the model proposed by the present authors in 2005. It is shown that the mean strength of Coulomb field produced by a proton passing the channel is very strong in the Mot assembly so that the Mot assembly can be a shear force generator and induce the flagellar rotation. The model gives clear calculation results in agreement with experimental observations, e g., for the characteristic torque-velocity relationship of the flagellar rotation.

  6. Stress Analysis of Beams with Shear Deformation of the Flanges

    NASA Technical Reports Server (NTRS)

    Kuhn, Paul

    1937-01-01

    This report discusses the fundamental action of shear deformation of the flanges on the basis of simplifying assumptions. The theory is developed to the point of giving analytical solutions for simple cases of beams and of skin-stringer panels under axial load. Strain-gage tests on a tension panel and on a beam corresponding to these simple cases are described and the results are compared with analytical results. For wing beams, an approximate method of applying the theory is given. As an alternative, the construction of a mechanical analyzer is advocated.

  7. Critical bed shear stress and threshold of motion of maerl biogenic gravel

    NASA Astrophysics Data System (ADS)

    Joshi, Siddhi; Duffy, Garret Patrick; Brown, Colin

    2017-07-01

    A determination of the critical bed shear stress of maerl is a prerequisite for quantifying its mobility, rate of erosion and deposition in conservation management. The critical bed shear stress for incipient motion has been determined for the first time for samples from biogenic free-living maerl beds in three contrasting environments (open marine, intertidal and beach) in Galway Bay, west of Ireland. The bed shear stress was determined using two methods, Law of the Wall and Turbulent Kinetic Energy, in a rotating annular flume and in a linear flume. The velocity profile of flowing water above a bed of natural maerl grains was measured in four runs of progressively increasing flow velocity until the flow exceeded the critical shear stress of grains on the bed. The critical Shields parameter and the mobility number are estimated and compared with the equivalent curves for natural quartz sand. The critical Shields parameters for the maerl particles from all three environments fall below the Shields curve. Along with a previously reported correlation between maerl grain shape and settling velocity, these results suggest that the highly irregular shapes also allow maerl grains to be mobilised more easily than quartz grains with the same sieve diameter. The intertidal beds with the roughest particles exhibit the greatest critical shear stress because the particle thalli interlock and resist entrainment. In samples with a high percentage of maerl and low percentage of siliciclastic sand, the lower density, lower settling velocity and lower critical bed shear stress of maerl results in its preferential transport over the siliciclastic sediment. At velocities ∼10 cm s-1 higher than the threshold velocity of grain motion, rarely-documented subaqueous maerl dunes formed in the annular flume.

  8. Pulsatile atheroprone shear stress affects the expression of transient receptor potential channels in human endothelial cells.

    PubMed

    Thilo, Florian; Vorderwülbecke, Bernd J; Marki, Alex; Krueger, Katharina; Liu, Ying; Baumunk, Daniel; Zakrzewicz, Andreas; Tepel, Martin

    2012-06-01

    The goal of the study was to assess whether pulsatile atheroprone shear stress modulates the expression of transient receptor potential (TRP) channels, TRPC3, TRPC6, TRPM7, and TRPV1 mRNA, in human umbilical vascular endothelial cells. Exposure of cultured vascular endothelial cells to defined shear stress, producing a constant laminar flow (generating a shear stress of 6 dyne/cm(2)), laminar pulsatile atheroprotective flow (with a mean shear stress of 20 dyne/cm(2)), or laminar atheroprone bidirectional flow (with a mean shear stress of 0 dyne/cm(2)) differentially induced TRPC6 and TRPV1 mRNA as measured by quantitative real-time RT-PCR and normalized to GAPDH expression. Thereby, TRPC6 and TRPV1 mRNA expressions were significantly increased after 24 hours of exposure to an atheroprone flow profile compared with an atheroprotective flow profile. Furthermore, the expression of transcription factors GATA1 and GATA4 was significantly correlated with the expression of TRPC6 mRNA. In contrast, after 24 hours of constant laminar flow, the expression of TRPC6 and TRPV1 mRNA was unchanged, whereas the expression of TRPC3 and TRPM7 was significantly higher in endothelial cells exposed to shear stress in comparison with endothelial cells grown under static conditions. There was a significant association between the expression of TRPC6 and tumor necrosis factor-α mRNA in human vascular tissue. No-flow and atheroprone flow conditions are equally characterized by an increase in the expression of tumor necrosis factor-α; however, inflammation-associated endothelial cell reactions may be further aggravated at atheroprone flow conditions by the increase of TRPV1 and TRPC6, as observed in our study.

  9. Estimation of wall shear stress in bypass grafts with computational fluid dynamics method.

    PubMed

    Goubergrits, L; Affeld, K; Wellnhofer, E; ZurbrüggR; Holmer, T

    2001-03-01

    Coronary artery bypass graft (CABG) operation for coronary artery disease with different types of grafts has a large clinical application world wide. Immediately after this operation patients are usually relieved of their chest pain and have improved cardiac function. However, after a while, these bypass grafts may fail due to for example, neointimal hyperplasia or thrombosis. One of the causes for this bypass graft failure is assumed to be the blood flow with low wall shear stress. The aim of this research is to estimate the wall shear stress in a graft and thus to locate areas were wall shear stress is low. This was done with the help of a blood flow computer model. Post-operative biplane angiograms of the graft were recorded, and from these the three-dimensional geometry of the graft was reconstructed and imported into the computational fluid dynamics (CFD) program FLUENT. The stationary diastolic flow through the grafts was calculated, and the wall shear stress distribution was estimated. This procedure was carried out for one native vessel and two different types of bypass grafts. One bypass graft was a saphenous vein and the other one was a varicose saphenous vein encased in a fine, flexible metal mesh. The mesh was attached to give the graft a defined diameter. The computational results show that each graft has distinct areas of low wall shear stress. The graft with the metal mesh has an area of low wall shear stress (< 1 Pa, stationary flow), which is four times smaller than the respective areas in the other graft and in the native vessel. This is thought to be caused by the smaller and more uniform diameter of the metal mesh-reinforced graft.

  10. Critical shear stress for erosion of cohesive soils subjected to temperatures typical of wildfires

    USGS Publications Warehouse

    Moody, J.A.; Dungan, Smith J.; Ragan, B.W.

    2005-01-01

    [1] Increased erosion is a well-known response after wildfire. To predict and to model erosion on a landscape scale requires knowledge of the critical shear stress for the initiation of motion of soil particles. As this soil property is temperature-dependent, a quantitative relation between critical shear stress and the temperatures to which the soils have been subjected during a wildfire is required. In this study the critical shear stress was measured in a recirculating flume using samples of forest soil exposed to different temperatures (40??-550??C) for 1 hour. Results were obtained for four replicates of soils derived from three different types of parent material (granitic bedrock, sandstone, and volcanic tuffs). In general, the relation between critical shear stress and temperature can be separated into three different temperature ranges (275??C), which are similar to those for water repellency and temperature. The critical shear stress was most variable (1.0-2.0 N m-2) for temperatures 2.0 N m-2) between 175?? and 275??C, and was essentially constant (0.5-0.8 N m-2) for temperatures >275??C. The changes in critical shear stress with temperature were found to be essentially independent of soil type and suggest that erosion processes in burned watersheds can be modeled more simply than erosion processes in unburned watersheds. Wildfire reduces the spatial variability of soil erodibility associated with unburned watersheds by eliminating the complex effects of vegetation in protecting soils and by reducing the range of cohesion associated with different types of unburned soils. Our results indicate that modeling the erosional response after a wildfire depends primarily on determining the spatial distribution of the maximum soil temperatures that were reached during the wildfire. Copyright 2005 by the American Geophysical Union.

  11. The Effects of Static Coulomb, Normal and Shear Stress Changes on Earthquake Occurrence in Southern California

    NASA Astrophysics Data System (ADS)

    Strader, A. E.; Jackson, D. D.

    2011-12-01

    Deng & Sykes (1997) found a strong correlation between receiver earthquake location and positive increase in Coulomb stress (ΔCFF). Assuming a coefficient of friction of 0.6, and resolving stresses onto assumed fault planes with uniform orientation parallel to average Pacific-North American plate motion, they found that only 15% of receiver earthquakes occur in "stress shadows" where the Coulomb stress change should impede faulting. We extended their study by adding two source earthquakes (Hector Mine, 1999 and El Mayor-Cucupah, 2010), and calculating the stress changes at the locations of 134 receiver earthquakes with magnitude 4.4 and greater after 1999. We examined shear stress, normal stress, and Coulomb stress, resolving stresses onto four different hypothetical fault planes: smoothed seismicity-based planes, a weighted average of nearby fault-plane orientations, and the two nodal planes of weighed average moment tensors of nearby earthquakes. We also computed shear, normal, and Coulomb stress histories oriented according to the four choices of fault orientation, and tested the effect of total stress change on receiver earthquake magnitude. Our chi square test results indicate that, with 95% confidence, receiver earthquakes do not tend to avoid stress shadows, and that the choice of plane onto which stress is resolved does not affect the result. On average, 39% of earthquakes occur at the time of maximum stress at the event location, with no significant variation depending on the choice of rupture plane or type of stress change. We found no correlation between earthquake magnitude and total stress change at the events' locations. These results suggest that instantaneous cumulative Coulomb stress, as we and Deng & Sykes modeled it, does not strongly control the locations of future earthquakes. The lack of correlation between Coulomb stress change and magnitude suggests that modeled Coulomb stress change does not control the size of earthquakes once they

  12. On-Chip Evaluation of Shear Stress Effect on Cytotoxicity of Mesoporous Silica Nanoparticles

    PubMed Central

    Kim, Donghyuk; Lin, Yu-Shen; Haynes, Christy L.

    2011-01-01

    In this work, nanotoxicity in the bloodstream was modeled and the cytotoxicity of sub-50 nm mesoporous silica nanoparticles to human endothelial cells was investigated under microfluidic flow conditions. Compared to traditional in vitro cytotoxicity assays performed under static conditions, unmodified mesoporous silica nanoparticles show higher and shear stress-dependent toxicity to endothelial cells under flow conditions. Interestingly, even under flow conditions, highly organo-modified mesoporous silica nanoparticles show no significant toxicity to endothelial cells. This paper clearly demonstrates that shear stress is an important factor to be considered in in vitro nanotoxicology assessments and provides a simple device for pursuing this consideration. PMID:22032307

  13. Distribution of shear stress over smooth muscle cells in deformable arterial wall.

    PubMed

    Dabagh, Mahsa; Jalali, Payman; Konttinen, Yrjö T; Sarkomaa, Pertti

    2008-07-01

    A biphasic, anisotropic model of the deformable aortic wall in combination with computational fluid dynamics is used to investigate the variation of shear stress over smooth muscle cells (SMCs) with transmural pressure. The media layer is modeled as a porous medium consisting of SMCs and a homogeneous porous medium of interstitial fluid and elastin, collagen and proteoglycans fibers. Interstitial fluid enters the media through fenestral pores, which are distributed over the internal elastic lamina (IEL). The IEL is considered as an impermeable barrier to fluid flow except at fenestral pores. The thickness and the radius of aortic wall vary with transmural pressure ranging from 10 to 180 mm Hg. It is assumed that SMCs are cylinders with a circular cross section at 0 mm Hg. As the transmural pressure increases, SMCs elongate with simultaneous change of cross sectional shape into ellipse according to the strain field in the media. Results demonstrate that the variation of shear stress within the media layer is significantly dependent on the configuration and cross sectional shape of SMCs. In the staggered array of SMCs, the shear stress over the first SMC nearest to the IEL is about 2.2 times lower than that of the square array. The shear stress even over the second nearest SMC to the IEL is considerably higher (about 15%) in the staggered array. In addition to configuration and cross sectional shape of SMCs, the variation of structural properties of the media layer with pressure and the sensitivity of the local shear stress to the minimum distance between SMCs and the IEL (reducing with transmural pressure) between SMCs and the IEL are studied. At 180 mm Hg, the ratio of the local shear stress of the nearest SMC to that of the second nearest SMC is 4.8 in the square array, whereas it reduces to about 1.8 in the staggered array. The importance of the fluid shear stress is associated with its role in the biomolecular state of smooth muscle cells bearing the shear

  14. The significance of electrically induced shear stress in drainage of thin aqueous films

    NASA Astrophysics Data System (ADS)

    Ajaev, Vladimir; Ketelaar, Christiaan

    2014-11-01

    We develop a model of drainage of a microscale thin aqueous film separating a gas bubble and a solid wall. In contrast to previous studies, the electrostatic effects are accounted for not only in the normal but also in the shear stress balance at the liquid-gas interface. We show that the action of the tangential component of the electric field leads to potentially strong spatially variable shear stress at the deforming charged interface. This previously overlooked effect turns out to be essential for correctly estimating the long-time drainage rates. Time-dependent fluid interface shapes predicted by our model are in very good agreement with the experimental data.

  15. Significance of electrically induced shear stress in drainage of thin aqueous films

    NASA Astrophysics Data System (ADS)

    Ketelaar, Christiaan; Ajaev, Vladimir S.

    2015-05-01

    We develop a novel model of drainage of microscale thin aqueous film separating a gas bubble and a solid wall. In contrast to previous studies, the electrostatic effects are accounted for not only in the normal but also in the shear stress balance at the liquid-gas interface. We show that the action of the tangential component of the electric field leads to potentially strong spatially variable shear stress at the deforming charged interface. This previously overlooked effect turns out to be essential for correctly estimating the long-time drainage rates. Comparison of time-dependent fluid interface shapes predicted by our model with the experimental data is discussed.

  16. Shear stress-induced Ets-1 modulates protease inhibitor expression in microvascular endothelial cells.

    PubMed

    Milkiewicz, Malgorzata; Uchida, Cassandra; Gee, Eric; Fudalewski, Tomasz; Haas, Tara L

    2008-11-01

    Elevated shear stress within the skeletal muscle microvasculature is implicated in the induction of a longitudinal splitting form of angiogenesis, which is characterized by the lack of basement membrane breakage. We investigated whether the transcriptional regulator, Ets-1, is responsive to changes in hemodynamic forces and if so, whether Ets-1 controls microvascular endothelial cell integrity by inducing the expression of inhibitors of matrix degrading proteases. Rats were treated with prazosin for 2, 4, and 7 days to increase in microvascular shear stress in hindlimb skeletal muscles. In complimentary in vitro experiments, rat microvascular skeletal muscle endothelial cells were exposed to laminar shear stress (15 dyne/cm(2)) for 0.5, 2, and 24 h. TaqMan PCR analysis of laser microdissected capillaries isolated from EDL muscles demonstrated transient (after 2 days) induction of Ets-1 gene expression. In cultured cells, a transient up-regulation of Ets-1 mRNA was observed after 2 h shear stimulation, accompanied by increased phosphorylation of Ets-1 and enhanced Ets-1 DNA binding activity. This response was modulated by ERK1/2 and p38 MAP kinases, but was not dependent on NOS or COX-2 activity. PAI-1, TIMP-1 and TIMP-3 mRNA were elevated significantly in prazosin treated EDL, and in response to shear stimulation in vitro. In cultured endothelial cells, Ets-1 RNA interference abolished the shear-induced increases in Ets-1, PAI-1, TIMP-1, and TIMP-3 mRNA expression. These results suggest that enhanced laminar shear stress may act to preserve the integrity of microvascular walls in part through Ets-1-dependent induction of protease inhibitors.

  17. Surface Shear Stress Around a Single Flexible Live Plant and a Rigid Cylinder

    NASA Astrophysics Data System (ADS)

    Walter, B. A.; Gromke, C.; Leonard, K. C.; Clifton, A.; Lehning, M.

    2010-12-01

    The sheltering effect of vegetation against soil erosion and snow transport has direct implications on land degradation and local water storage as snow in many arid and semi arid regions. Plants influence the erosion, transport and redeposition of soil and snow by the wind through momentum absorption, local stress concentration, trapping particles in motion and reducing the area of sediment exposed to the wind. The shear stress distributions on the ground beneath plant canopies determine the onset and magnitude of differential soil and snow erosion on rough or vegetated surfaces, but this has been studied exclusively with artificial and rigid vegetation elements thus far. Real plants have highly irregular structures that can be extremely flexible and porous. They align with the flow at higher wind speeds, resulting in considerable changes to the drag and flow regimes relative to rigid imitations of comparable size. We present measurements in the SLF atmospheric boundary layer wind tunnel of the surface shear stress distribution around a live grass plant (Lolium Perenne) and a solid cylinder of comparable size. Irwin sensors are used to measure pressure differences close to the surface which can be calibrated with surface shear stress velocities. The basal to frontal area index of the plant and the cylinder as well as the Reynolds number of the two experimental setups have been checked for similarity and show good agreement. Distinctive differences between the shear stress pattern around the plant and the cylinder can be attributed to the influence of the plant’s porosity and flexibility. The sheltered zone behind the plant is narrower in cross-stream and longer in streamwise direction than that of the cylinder. For the plant, the lowest shear stresses in the sheltered zone are 50% lower than the mean surface shear stress (τ = 0.15 N/m2) in the undisturbed flow. The sheltering was higher behind the cylinder with values reduced by 70% relative to background.

  18. Mechanism and kinetics of biofilm growth process influenced by shear stress in sewers.

    PubMed

    Ai, Hainan; Xu, Jingwei; Huang, Wei; He, Qiang; Ni, Bingjie; Wang, Yinliang

    2016-01-01

    Sewer biofilms play an important role in the biotransformation of substances for methane and sulfide emission in sewer networks. The dynamic flows and the particular shear stress in sewers are the key factors determining the growth of the sewer biofilm. In this work, the development of sewer biofilm with varying shear stress is specifically investigated to gain a comprehensive understanding of the sewer biofilm dynamics. Sewer biofilms were cultivated in laboratory-scale gravity sewers under different hydraulic conditions with the corresponding shell stresses are 1.12 Pa, 1.29 Pa and 1.45 Pa, respectively. The evolution of the biofilm thickness were monitored using microelectrodes, and the variation in total solids (TS) and extracellular polymer substance (EPS) levels in the biofilm were also measured. The results showed that the steady-state biofilm thickness were highly related to the corresponding shear stresses with the biofilm thickness of 2.4 ± 0.1 mm, 2.7 ± 0.1 mm and 2.2 ± 0.1 mm at shear stresses of 1.12 Pa, 1.29 Pa and 1.45 Pa, respectively, which the chemical oxygen demand concentration is 400 mg/L approximately. Based on these observations, a kinetic model for describing the development of sewer biofilms was developed and demonstrated to be capable of reproducing all the experimental data.

  19. Flow induced migration in polymer melts – Theory and simulation

    SciTech Connect

    Dorgan, John Robert Rorrer, Nicholas Andrew

    2015-04-28

    Flow induced migration, whereby polymer melts are fractionated by molecular weight across a flow field, represents a significant complication in the processing of polymer melts. Despite its long history, such phenomena remain relatively poorly understood. Here a simple analytical theory is presented which predicts the phenomena based on well-established principles of non-equilibrium thermodynamics. It is unambiguously shown that for purely viscous materials, a gradient in shear rate is needed to drive migration; for purely viscometric flows no migration is expected. Molecular scale simulations of flow migration effects in dense polymer melts are also presented. In shear flow the melts exhibit similar behavior as the quiescent case; a constant shear rate across the gap does not induce chain length based migration. In comparison, parabolic flow causes profound migration for both unentangled and entangled melts. These findings are consistent with the analytical theory. The picture that emerges is consistent with flow induced migration mechanisms predominating over competing chain degradation mechanisms.

  20. Seasonal Variation in Basal Shear Stress Beneath the Greenland Ice Sheet

    NASA Astrophysics Data System (ADS)

    Joughin, I.; Alley, R. B.; Behn, M. D.; Das, S. B.; Flowers, G. E.

    2015-12-01

    Over the last decade, it has been well established that in the ablation zone of the Greenland Ice Sheet, surface melt water makes its way to the bed and seasonally modulates ice-flow speed. With a conventional sliding law, the basal shear stress is proportional to the nonlinear product of the sliding speed and the effective pressure (difference between ice overburden and water pressure). Thus, when seasonal surface melting raises subglacial water pressure, it lowers the effective pressure, requiring additional sliding to restore the basal shear stress to maintain an overall force balance. This variation need not be uniform, however, and the basal hydrological system may produce variability at different spatial scales. To examine variability at scales of a few ice thicknesses, we use control-method inverse techniques to determine the basal shear stress using a shallow-shelf, ice-flow model constrained by speckle-tracked velocities measured over 11 and 22-day intervals. We begin by determining a reference basal shear stress estimated for a typical winter velocity field (typically over a 30-by-50 km region). We then determine the corresponding estimates for the region during periods of enhanced summer flow. In general, we find that relative to the winter data, summer basal shear stress tends to increase in areas of steep surface slope (high driving stress) and decrease, despite elevated speeds, in low slope regions, which often correspond to the basins where supraglacial lakes form. Computing the ratio of summer to winter effective pressure indicates little seasonal change in effective pressure for areas of high basal shear stress and a summer decrease in low-slope regions. This pattern is consistent with surface and bed slopes that drive water away from areas of high slopes and stress concentration (e.g., where ice flows over bedrock bumps) toward weak, low-slope regions of the bed. The net result is that, during the summer delivery of water to the bed, basal shear

  1. The microchannel flow model under shear stress and higher frequencies.

    PubMed

    Parker, Kevin J

    2017-02-24

    The microchannel flow model provides a framework for considering the effect of the vascular bed on the time domain and frequency domain response of soft tissues. The derivation originates with a single small fluid filled vessel in an elastic medium under uniaxial compression. A fractal branching vasculature is also assumed to be present in the tissue under consideration. This short technical note considers two closely related issues. First, the response of the element under compression or shear as a function of the orientation of the fluid-filled vessel is considered. Second, the transition from quasistatic (Poiseuille's Law) to dynamic (Womersley equations) fluid flow is examined to better predict the evolution of behavior at higher frequencies. These considerations expand the conceptual framework of the microchannel flow model, particularly the range and limits of validity.

  2. The microchannel flow model under shear stress and higher frequencies

    NASA Astrophysics Data System (ADS)

    Parker, K. J.

    2017-04-01

    The microchannel flow model provides a framework for considering the effect of the vascular bed on the time domain and frequency domain response of soft tissues. The derivation originates with a single small fluid-filled vessel in an elastic medium under uniaxial compression. A fractal branching vasculature is also assumed to be present in the tissue under consideration. This note considers two closely related issues. First, the response of the element under compression or shear as a function of the orientation of the fluid-filled vessel is considered. Second, the transition from quasistatic (Poiseuille’s Law) to dynamic (Womersley equations) fluid flow is examined to better predict the evolution of behavior at higher frequencies. These considerations expand the conceptual framework of the microchannel flow model, particularly the range and limits of validity.

  3. The effect of bilayer composition on calcium ion transport facilitated by fluid shear stress.

    PubMed

    Giorgio, T D; Yek, S H

    1995-10-04

    Passive calcium ion permeability across liposome bilayers is increased during exposure to fluid shear forces attainable in the mammalian vasculature. In this study, liposomes prepared from three different lipid mixtures (phosphatidylcholine alone; phosphatidylcholine and cholesterol; a mixture of anionic and cationic phospholipids plus cholesterol) are exposed to uniform shear stress in a rotational viscometer. Liposome permeability to calcium ion is estimated from continuous measurement of free intraliposome calcium ion concentration using a fluorescence technique. Calcium ion permeability in the absence of fluid force and susceptibility to shear-induced permeability modulation are positively correlated with estimated bilayer compressibility. Fluid shear forces are presumed to influence bilayer packing and modulate defect formation in proportion to bilayer compressibility. Bilayer defects produced by fluid forces may increase liposome permeability.

  4. The Behavior Under Shearing Stress of Duralumin Strip with Round, Flanged Holes

    NASA Technical Reports Server (NTRS)

    Schussler, Karl

    1934-01-01

    This report presents the results of an investigation to determine the behavior of dural strip with flanged holes in the center when subjected to shear stresses. They buckle under a certain load just as a flat sheet. There is one optimum hole spacing and a corresponding buckling load in shear for each sheet width, sheet thickness, and flange form. Comparison with non-flanged sheets revealed a marked increase of buckling load in shear due to the flanging and a slightly greater displacement. Strips were clamped between two stationary end rails and one sliding center rail at which the shear is applied. The force was measured with a tension stirrup up to 20 tons and a compression dynamometer up to 10 tons. The displacement was recorded with the Zeiss dial gauge. The following were investigated: 1) effect of strip width; 2) strip thickness; 3) diameter of flanging; 4) depth of flanging; 5) and hole distance.

  5. Shear Stress Increases the Residence Time of Adhesion of Pseudomonas aeruginosa

    PubMed Central

    Lecuyer, Sigolene; Rusconi, Roberto; Shen, Yi; Forsyth, Alison; Vlamakis, Hera; Kolter, Roberto; Stone, Howard A.

    2011-01-01

    Although ubiquitous, the processes by which bacteria colonize surfaces remain poorly understood. Here we report results for the influence of the wall shear stress on the early-stage adhesion of Pseudomonas aeruginosa PA14 on glass and polydimethylsiloxane surfaces. We use image analysis to measure the residence time of each adhering bacterium under flow. Our main finding is that, on either surface, the characteristic residence time of bacteria increases approximately linearly as the shear stress increases (∼0–3.5 Pa). To investigate this phenomenon, we used mutant strains defective in surface organelles (type I pili, type IV pili, or the flagellum) or extracellular matrix production. Our results show that, although these bacterial surface features influence the frequency of adhesion events and the early-stage detachment probability, none of them is responsible for the trend in the shear-enhanced adhesion time. These observations bring what we believe are new insights into the mechanism of bacterial attachment in shear flows, and suggest a role for other intrinsic features of the cell surface, or a dynamic cell response to shear stress. PMID:21244830

  6. Wind-invariant saltation heights imply linear scaling of aeolian saltation flux with shear stress.

    PubMed

    Martin, Raleigh L; Kok, Jasper F

    2017-06-01

    Wind-driven sand transport generates atmospheric dust, forms dunes, and sculpts landscapes. However, it remains unclear how the flux of particles in aeolian saltation-the wind-driven transport of sand in hopping trajectories-scales with wind speed, largely because models do not agree on how particle speeds and trajectories change with wind shear velocity. We present comprehensive measurements, from three new field sites and three published studies, showing that characteristic saltation layer heights remain approximately constant with shear velocity, in agreement with recent wind tunnel studies. These results support the assumption of constant particle speeds in recent models predicting linear scaling of saltation flux with shear stress. In contrast, our results refute widely used older models that assume that particle speed increases with shear velocity, thereby predicting nonlinear 3/2 stress-flux scaling. This conclusion is further supported by direct field measurements of saltation flux versus shear stress. Our results thus argue for adoption of linear saltation flux laws and constant saltation trajectories for modeling saltation-driven aeolian processes on Earth, Mars, and other planetary surfaces.

  7. Wind-invariant saltation heights imply linear scaling of aeolian saltation flux with shear stress

    PubMed Central

    Martin, Raleigh L.; Kok, Jasper F.

    2017-01-01

    Wind-driven sand transport generates atmospheric dust, forms dunes, and sculpts landscapes. However, it remains unclear how the flux of particles in aeolian saltation—the wind-driven transport of sand in hopping trajectories—scales with wind speed, largely because models do not agree on how particle speeds and trajectories change with wind shear velocity. We present comprehensive measurements, from three new field sites and three published studies, showing that characteristic saltation layer heights remain approximately constant with shear velocity, in agreement with recent wind tunnel studies. These results support the assumption of constant particle speeds in recent models predicting linear scaling of saltation flux with shear stress. In contrast, our results refute widely used older models that assume that particle speed increases with shear velocity, thereby predicting nonlinear 3/2 stress-flux scaling. This conclusion is further supported by direct field measurements of saltation flux versus shear stress. Our results thus argue for adoption of linear saltation flux laws and constant saltation trajectories for modeling saltation-driven aeolian processes on Earth, Mars, and other planetary surfaces. PMID:28630907

  8. Non-Newtonian stress tensor and thermal conductivity tensor in granular plane shear flow

    NASA Astrophysics Data System (ADS)

    Alam, Meheboob; Saha, Saikat

    2014-11-01

    The non-Newtonian stress tensor and the heat flux in the plane shear flow of smooth inelastic disks are analysed from the Grad-level moment equations using the anisotropic Gaussian as a reference. Closed-form expressions for shear viscosity, pressure, first normal stress difference (N1) and the dissipation rate are given as functions of (i) the density or the area fraction (ν), (ii) the restitution coefficient (e), (iii) the dimensionless shear rate (R), (iv) the temperature anisotropy [ η, the difference between the principal eigenvalues of the second moment tensor] and (v) the angle (ϕ) between the principal directions of the shear tensor and the second moment tensor. Particle simulation data for a sheared hard-disk system is compared with theoretical results, with good agreement for p, μ and N1 over a large range of density. In contrast, the predictions from a Navier-Stokes order constitutive model are found to deviate significantly from both the simulation and the moment theory even at moderate values of e. We show that the gradient of the deviatoric part of the kinetic stress drives a heat current and the thermal conductivity is characterized by an anisotropic 2nd rank tensor for which explicit expressions are derived.

  9. Hemodynamic wall shear stress profiles influence the magnitude and pattern of stenosis in a pig AV fistula.

    PubMed

    Krishnamoorthy, Mahesh K; Banerjee, Rupak K; Wang, Yang; Zhang, Jianhua; Roy, Abhijit Sinha; Khoury, Saeb F; Arend, Lois J; Rudich, Steve; Roy-Chaudhury, Prabir

    2008-12-01

    Venous stenosis is a significant problem in arteriovenous fistulae, likely due to anatomical configuration and wall shear stress profiles. To identify linkages between wall shear stress and the magnitude and pattern of vascular stenosis, we produced curved and straight fistulae in a pig model. A complete wall stress profile was calculated for the curved configuration and correlated with luminal stenosis. Computer modeling techniques were then used to derive a wall shear stress profile for the straight arteriovenous fistula. Differences in the wall shear stress profile of the curved and straight fistula were then related to histological findings. There was a marked inverse correlation between the magnitude of wall shear stress within different regions of the curved arteriovenous fistula and luminal stenosis in these same regions. There were also significantly greater differences in wall shear stress between the outer and inner walls of the straight as compared to curved arteriovenous fistula, which translated into a more eccentric histological pattern of intima-media thickening. Our results suggest a clear linkage between anatomical configuration, wall shear stress profiles, and the pattern of luminal stenosis and intima-media thickening in a pig model of arteriovenous fistula stenosis. These results suggest that fistula failure could be reduced by using computer modeling prior to surgical placement to alter the anatomical and, consequently, the wall shear stress profiles in an arteriovenous fistula.

  10. Transforming Growth Factor-β Signaling Cascade Induced by Mechanical Stimulation of Fluid Shear Stress in Cultured Corneal Epithelial Cells.

    PubMed

    Utsunomiya, Tsugiaki; Ishibazawa, Akihiro; Nagaoka, Taiji; Hanada, Kazuomi; Yokota, Harumasa; Ishii, Nobuhito; Yoshida, Akitoshi

    2016-11-01

    Because blinking is regarded as mechanical stimulation of fluid shear stress on the corneal epithelial cells, we investigated the effects of fluid shear stress on cultured human corneal epithelial cells (HCECs). The HCECs were exposed to shear stress (0, 1.2, 12 dyne/cm2) with the parallel-plate type of flow chamber. Wound healing, cellular proliferation, growth factor expression, TGF-β1 concentration in the culture supernatant, and phosphorylation of SMAD2 were investigated. Monolayers of HCECs exposed to shear stress had delayed wound healing and decreased proliferation compared with those of the static control (0 dyne/cm2). With increasing shear stress, TGF-β1 expression and phosphorylation of SMAD2 increased significantly, but the levels of total TGF-β1 in the culture supernatant decreased significantly. Delayed wound healing, decreased proliferation, and phosphorylation of the SMAD2 by shear stress were canceled out with a TGF-β receptor inhibitor. Fluid shear stress on the HCECs affected TGF-β signaling, which was associated with delayed wound healing. Mechanical stress by blinking might involve TGF-β signaling, and activation of TGF-β might be a key factor in wound healing of the corneal epithelium. Further studies should investigate the molecular mechanism of shear stress-induced activation of TGF-β.

  11. Estimates of Shear Stress and Measurements of Water Levels in the Lower Fox River near Green Bay, Wisconsin

    USGS Publications Warehouse

    Westenbroek, Stephen M.

    2006-01-01

    Turbulent shear stress in the boundary layer of a natural river system largely controls the deposition and resuspension of sediment, as well as the longevity and effectiveness of granular-material caps used to cover and isolate contaminated sediments. This report documents measurements and calculations made in order to estimate shear stress and shear velocity on the Lower Fox River, Wisconsin. Velocity profiles were generated using an acoustic Doppler current profiler (ADCP) mounted on a moored vessel. This method of data collection yielded 158 velocity profiles on the Lower Fox River between June 2003 and November 2004. Of these profiles, 109 were classified as valid and were used to estimate the bottom shear stress and velocity using log-profile and turbulent kinetic energy methods. Estimated shear stress ranged from 0.09 to 10.8 dynes per centimeter squared. Estimated coefficients of friction ranged from 0.001 to 0.025. This report describes both the field and data-analysis methods used to estimate shear-stress parameters for the Lower Fox River. Summaries of the estimated values for bottom shear stress, shear velocity, and coefficient of friction are presented. Confidence intervals about the shear-stress estimates are provided.

  12. Measured Resolved Shear Stresses and Bishop Hill Stress States in Individual Grains of Austenitic Stainless Steel (Postprint)

    DTIC Science & Technology

    2017-09-13

    and c44 ¼ 119 MPa [33]. Error bars and covariance matrices on these parameters are estimated by the FitAllB program,ase (PA): distribution unlimited...stress tensor for each grain. Error bars on all resolved shear stress components have been derived based on the covariance matrices from FitAllB and...based on assuming equal and diagonal covariance matrices for all observations (reflections) assigned to a specific grain, which has proven to work well

  13. Shear-stress function approach of hydration layer based on the Green-Kubo formula

    NASA Astrophysics Data System (ADS)

    Kim, Bongsu; Kwon, Soyoung; Moon, Geol; Jhe, Wonho

    2015-03-01

    We present the analytic expression of the stress correlation (SC) function for the ubiquitous hydration water layer (HWL) using the Green-Kubo equation and the shear modulus of HWL. The SC function is then experimentally obtained by measuring the viscoelastic properties of HWL using shear-mode dynamic force spectroscopy. Interestingly, the SC changes sign from positive to negative as the HWL thickness increases, where the shear stresses acting on the HWLs bound to two nearby surfaces are out of phase. We also suggest that the repulsive hydration force originates from the SC of HWL. Our results provide the first demonstration of the microscopic understanding of the HWL viscoelasticity and may allow a deeper insight on the HWL dynamics as well as the complex liquids.

  14. [Determining wall shear stress in artificial blood pumps of heart assist devices].

    PubMed

    Debaene, P; Aguilera, D; Kertzscher, U; Affeld, K

    2002-01-01

    The walls in blood pumps are made of artificial material and thus are thrombogenic to a lesser or larger degree. Also the flow plays a role: a blood flow with no flow separations and stagnation zones is required to avoid the generation of thrombi. A precondition for solving this problem is the assessment of the wall shear rate. However this parameter is difficult to assess because of the deformability of the walls and the pulsation of the flow. Two methods are proposed to estimate the wall shear stress in bloodpumps. The paint erosion method allows a characterisation of the flow near the wall. The second method is a special development of standard Particle Image Velocimetry (PIV). A vector field of the flow close to the wall results. Both methods should permit the assessment of the wall shear stress in bloodpumps.

  15. Measurement of turbulent wall shear-stress using micro-pillars

    NASA Astrophysics Data System (ADS)

    Gnanamanickam, E. P.; Nottebrock, B.; Große, S.; Sullivan, J. P.; Schröder, W.

    2013-12-01

    In experimental fluid mechanics, measuring spatially and temporally resolved wall shear-stress (WSS) has proved a challenging problem. The micro-pillar shear-stress sensor (MPS3) has been developed with the goal of filling this gap in measurement techniques. The MPS3 comprises an array of flexible micro-pillars flush mounted on the wall of a wall-bounded flow field. The deflection of these micro-pillars in the presence of a shear field is a direct measure of the WSS. This paper presents the MPS3 development work carried out by RWTH Aachen University and Purdue University. The sensor concept, static and dynamic characterization and data reduction issues are discussed. Also presented are demonstrative experiments where the MPS3 was used to measure the WSS in both water and air. The salient features of the measurement technique, sensor development issues, current capabilities and areas for improvement are highlighted.

  16. A stress-controlled shear cell for small-angle light scattering and microscopy

    NASA Astrophysics Data System (ADS)

    Aime, S.; Ramos, L.; Fromental, J. M.; Prévot, G.; Jelinek, R.; Cipelletti, L.

    2016-12-01

    We develop and test a stress-controlled, parallel plates shear cell that can be coupled to an optical microscope or a small angle light scattering setup, for simultaneous investigation of the rheological response and the microscopic structure of soft materials under an imposed shear stress. In order to minimize friction, the cell is based on an air bearing linear stage, the stress is applied through a contactless magnetic actuator, and the strain is measured through optical sensors. We discuss the contributions of inertia and of the small residual friction to the measured signal and demonstrate the performance of our device in both oscillating and step stress experiments on a variety of viscoelastic materials.

  17. Collaborative effects of electric field and fluid shear stress on fibroblast migration.

    PubMed

    Song, Sukhyun; Han, Hana; Ko, Ung Hyun; Kim, Jaemin; Shin, Jennifer H

    2013-04-21

    Cells are inherently exposed to a number of different biophysical stimuli such as electric fields, shear stress, and tensile or compressive stress from the extracellular environment in vivo. Each of these biophysical cues can work simultaneously or independently to regulate cellular functions and tissue integrity in both physiological and pathological conditions. Thus, it is vital to understand the interaction of multiple stimuli on cells by decoupling and coupling the stimuli in simple combinations and by investigating cellular behaviors in response to these cues. Here, we report a novel microfluidic platform to apply the combinatorial stimulation of an electric field and fluid shear stress by controlling two directional cues independently. An integrated microfluidic platform was developed using soft lithography to monitor the cellular migration in real-time in response to an electric field and fluid shear stress in single, simultaneous, and sequential modes. When each of these stimulations is applied separately, normal human dermal fibroblasts migrate toward the anode and in the direction of fluid flow in a dose-dependent manner. Simultaneous stimulation with an electric field and shear stress, which mimics a wound in vivo, enhances the directional migration of fibroblasts by increasing both directedness and trajectory speed, suggesting the plausible scenario of cooperation between two physical cues to promote wound healing. When an electric field and shear stress are applied sequentially, migration behavior is affected by the applied stimulation as well as pre-existing stimulating conditions. This microfluidic platform can be utilized to understand other microenvironments such as embryogenesis, angiogenesis and tumor metastasis.

  18. Effects of biaxial oscillatory shear stress on endothelial cell proliferation and morphology.

    PubMed

    Chakraborty, Amlan; Chakraborty, Sutirtha; Jala, Venkatakrishna R; Haribabu, Bodduluri; Sharp, M Keith; Berson, R Eric

    2012-03-01

    Wall shear stress (WSS) on anchored cells affects their responses, including cell proliferation and morphology. In this study, the effects of the directionality of pulsatile WSS on endothelial cell proliferation and morphology were investigated for cells grown in a Petri dish orbiting on a shaker platform. Time and location dependent WSS was determined by computational fluid dynamics (CFD). At low orbital speed (50 rpm), WSS was shown to be uniform (0-1 dyne/cm(2)) across the bottom of the dish, while at higher orbital speed (100 and 150 rpm), WSS remained fairly uniform near the center and fluctuated significantly (0-9 dyne/cm(2)) near the side walls of the dish. Since WSS on the bottom of the dish is two-dimensional, a new directional oscillatory shear index (DOSI) was developed to quantify the directionality of oscillating shear. DOSI approached zero for biaxial oscillatory shear of equal magnitudes near the center and approached one for uniaxial pulsatile shear near the wall, where large tangential WSS dominated a much smaller radial component. Near the center (low DOSI), more, smaller and less elongated cells grew, whereas larger cells with greater elongation were observed in the more uniaxial oscillatory shear (high DOSI) near the periphery of the dish. Further, cells aligned with the direction of the largest component of shear but were randomly oriented in low magnitude biaxial shear. Statistical analyses of the individual and interacting effects of multiple factors (DOSI, shear magnitudes and orbital speeds) showed that DOSI significantly affected all the responses, indicating that directionality is an important determinant of cellular responses.

  19. Cultivation of shear stress sensitive and tolerant microalgal species in a tubular photobioreactor equipped with a centrifugal pump.

    PubMed

    Michels, Michiel H A; van der Goot, Atze Jan; Vermuë, Marian H; Wijffels, René H

    2016-01-01

    The tolerance to shear stress of Tetraselmis suecica, Isochrysis galbana, Skeletonema costatum, and Chaetoceros muelleri was determined in shear cylinders. The shear tolerance of the microalgae species strongly depends on the strain. I. galbana, S. costatum, and C. muelleri exposed to shear stress between 1.2 and 5.4 Pa resulted in severe cell damage. T. suecica is not sensitive to stresses up to 80 Pa. The possibility to grow these algae in a tubular photobioreactor (PBR) using a centrifugal pump for recirculation of the algae suspension was studied. The shear stresses imposed on the algae in the circulation tubes and at the pressure side of the pump were 0.57 and 1.82 Pa, respectively. The shear stress tolerant T. suecica was successfully cultivated in the PBR. Growth of I. galbana, S. costatum, and C. muelleri in the tubular PBR was not observed, not even at the lowest pumping speed. For the latter shear sensitive strains, the encountered shear stress levels were in the order of magnitude of the determined maximum shear tolerance of the algae. An equation was used to simulate the effect of possible damage of microalgae caused by passages through local high shear zones in centrifugal pumps on the total algae culture in the PBR. This simulation shows that a culture of shear stress sensitive species is bound to collapse after only limited number of passages, confirming the importance of considering shear stress as a process parameter in future design of closed PBRs for microalgal cultivation.

  20. Measuring Surface-Shear Stress in a Wind Tunnel

    NASA Technical Reports Server (NTRS)

    Lemos, F.; Higuchi, H.

    1983-01-01

    Two-wire skin friction gage gives both magnitude and direction of mean and fluctuating stresses. Heated wires lie at surface of gage, measure airflow by cooling effect. Wires perpendicular to each other to measure flow direction as well as magnitude. Used successfully in various turbulent flow fields, including separating three-dimensional boundary layer over cone at high angle of incidence.

  1. Ageing under Shear: Effect of Stress and Temperature Field

    NASA Astrophysics Data System (ADS)

    Shukla, Asheesh; Joshi, Yogesh M.

    2008-07-01

    In this work we studied the effect of oscillatory stress and temperature on the ageing dynamics of aqueous suspension of laponite. At the higher magnitude of stress, elastic and viscous moduli of the system underwent a sharp rise with the ageing time. The age at the onset of rise and the sharpness of the same increased with the magnitude of stress. We propose that at the beginning of ageing, the strain associated with the oscillatory stress field affects the lower modes in the relaxation time distribution. The higher modes, which are not significantly affected by the deformation field, continue to grow increasing the viscosity of the system thereby lowering the magnitude of the deformation field. Progressive decrease in the later reduces the range of relaxation modes affected by it. This dynamics eventually leads to an auto-catalytic increase in the elastic and viscous moduli. An increase in temperature accelerates the ageing process by shifting the ageing dynamics to a lower ageing time. This is due the microscopic relaxation dynamics, which causes ageing, becomes faster with increase in the temperature.

  2. Microflow-induced shear stress on biomaterial wall by ultrasound-induced encapsulated microbubble oscillation

    NASA Astrophysics Data System (ADS)

    Hu, Ji-Wen; Qian, Sheng-You; Sun, Jia-Na; Lü, Yun-Bin; Hu, Ping

    2015-09-01

    A model of an ultrasound-driven encapsulated microbubble (EMB) oscillation near biomaterial wall is presented and used for describing the microflow-induced shear stress on the wall by means of a numerical method. The characteristic of the model lies in the explicit treatment of different types of wall for the EMB responses. The simulation results show that the radius-time change trends obtained by our model are consistent with the existing models and experimental results. In addition, the effect of the elastic wall on the acoustic EMB response is stronger than that of the rigid wall, and the shear stress on the elastic wall is larger than that of the rigid wall. The closer the EMB to the wall, the greater the shear stress on the wall. The substantial shear stress on the wall surface occurs inside a circular zone with a radius about two-thirds of the bubble radius. This paper may be of interest in the study of potential damage mechanisms to the microvessel for drug and gene delivery due to sonoporation. Projects supported by the National Natural Science Foundation of China (Grant Nos. 11174077 and 11474090), the Natural Science Foundation of Hunan Province, China (Grant No. 13JJ3076), the Science Research Program of Education Department of Hunan Province, China (Grant No. 14A127), and the Doctoral Fund of University of South China (Grant No. 2011XQD46).

  3. Development of a MEMS dual-axis differential capacitance floating element shear stress sensor

    SciTech Connect

    Barnard, Casey; Griffin, Benjamin

    2015-09-01

    A single-axis MEMS wall shear stress sensor with differential capacitive transduction method is produced. Using a synchronous modulation and demodulation interface circuit, the system is capable of making real time measurements of both mean and fluctuating wall shear stress. A sensitivity of 3.44 mV/Pa is achieved, with linearity in response demonstrated up to testing limit of 2 Pa. Minimum detectable signals of 340 μPa at 100 Hz and 120 μPa at 1 kHz are indicated, with a resonance of 3.5 kHz. Multiple full scale wind tunnel tests are performed, producing spectral measurements of turbulent boundary layers in wind speeds ranging up to 0.5 Ma (18 Pa of mean wall shear stress). The compact packaging allows for minimally invasive installation, and has proven relatively robust over multiple testing events. Temperature sensitivity, likely due to poor CTE matching of packaged materials, is an ongoing concern being addressed. These successes are being directly leveraged into a development plan for a dual-axis wall shear stress sensor, capable of producing true vector estimates at the wall.

  4. Quantitative morphodynamics of endothelial cells within confluent cultures in response to fluid shear stress.

    PubMed

    Dieterich, P; Odenthal-Schnittler, M; Mrowietz, C; Krämer, M; Sasse, L; Oberleithner, H; Schnittler, H J

    2000-09-01

    To evaluate shear stress-induced effects on cultured cells we have extended the mechanical setup of a multichannel in vitro rheological system and developed software allowing entire processing control and image data analysis. The values of cell motility, degree of orientation (alignment), and cell elongation were correlated as a function of time (morphodynamics). Collective and individual endothelial cells within confluent cultures displayed a shear stress-dependent characteristic phase behavior of the following time course: resting conditions (phase I), change of motility (phase II), onset of alignment (phase III), and finally cell elongation (phase IV). Especially cell motility was characterized by a randomized zigzag movement around mean trajectories (fluctuations) together with mean cell locomotion. Onset of shear stress caused a down-regulation of fluctuations of 30% within <10 min and simultaneously increased locomotion velocities preferring the flow direction (phase II). After a lag period of 10 to 20 min cells orientated in the direction of flow (phase III) without significant cell elongation, which finally occurs within hours (phase IV). These data provide first evidence that cells within confluent endothelial monolayers respond to shear stress with a characteristic phase behavior.

  5. Effect of fluid shear stress on portal vein remodeling in a rat model of portal hypertension.

    PubMed

    Wen, Bin; Liang, Jian; Deng, Xin; Chen, Ran; Peng, Peichun

    2015-01-01

    Aims. To explore the effects and mechanisms of fluid shear stress on portal vein remodeling in a rat model of portal hypertension. Methods. Subcutaneous injections of CCl4 were given to establish a rat model of liver cirrhosis and portal hypertension. Biomechanical technology was adopted to determine the dynamic changes of haemodynamic indices and fluid shear stress. Nitric oxide (NO), synthase (NOS), and endothelin-1 (ET-1) of the portal vein blood were measured. Changes in geometric structure and ultrastructure of the portal vein were observed using optical and electron microscopy. Results. After the CC14 injections, rat haemodynamics were notably altered. From week 4 onwards, PVP, PVF, and PVR gradually and significantly increased (P < 0.05 versus baseline). The fluid shear stress declined from week 4 onwards (P < 0.01 versus control group). NO, NOS, and ET-1 increased after repeated CCI4 injections. Hematoxylin and eosin staining showed thickened portal vein walls, with increased inside and outside diameters. Electron microscopy revealed different degrees of endothelial cell degeneration, destruction of basement membrane integrity, proliferating, and hypertrophic smooth muscle cells. Conclusions. Fluid shear stress not only influenced the biomechanical environment of the portal vein but also participated in vascular remodeling.

  6. Molecular Dynamics Study for Channel Size Dependence of Shear Stress Between Droplet and Wall.

    PubMed

    Fukushima, Akinori; Mima, Toshiki; Kinefuchi, Ikuya; Tokumasu, Takashi

    2015-04-01

    In this study, the channel size dependence of the shear stress between water droplets and solid walls in nm-order channel was analyzed. We considered a several different-sized and highly hydrophobic channel whose macroscopic contact angle was about 150 degrees. We have evaluated the shear stress and the normal pressure by molecular dynamics simulation. Analyzing shear stress and normal pressure based on the macroscopic model, we have discussed the difference between the macroscopic model based on hydrodynamics and the microscopic model. As a result, in the high hydrophobic case, it became clear that the shear stress depends on the channel size due to the large Laplace pressure. Furthermore, in the case that the channel size was less than 50 A, the normal pressure by the molecular simulation didn't agree with the expected value from the Young-Laplace equation. From this study it was clear that molecular simulation is needed when the channel size is less than 40 A.

  7. Shear stress tolerance of Streptococcus mutans aggregates determined by microfluidic funnel device (μFFD).

    PubMed

    Shumi, Wahhida; Kim, So Hyun; Lim, Jeesun; Cho, Kyung-Suk; Han, Hwataik; Park, Sungsu

    2013-05-01

    Dental caries are initiated by the attachment of Streptococcus mutans aggregates to the surface of teeth. Bacterial adhesion to the interproximal space, the space between adjacent teeth, has not been investigated due to the lack of devices that mimic the space. Herein, we describe a method for determining the effect of shear stress and sucrose on the attachment of S. mutans aggregates to the interproximal space using microfluidic funnel device (μFFD). Using μFFD, the shear stress tolerance of sucrose-independent and sucrose-dependent S. mutans aggregates (larger than 50 μm in diameter) trapped in the funnel was tested against various flow rates of saliva solution (5 to 50 μl/min). Sucrose-independent aggregates were completely removed from the funnel walls at a low flow rate (10 μl/min) within 7 min., while sucrose-dependent aggregates were removed from the walls only at higher flow rates (25 and 50 μl/min) within several minutes. These results suggest that sucrose-dependent aggregates are more tolerant of shear stress than sucrose-independent aggregates, and are more likely to remain in the region with the smallest shear stress in the teeth.

  8. Oscillatory motion based measurement method and sensor for measuring wall shear stress due to fluid flow

    DOEpatents

    Armstrong, William D [Laramie, WY; Naughton, Jonathan [Laramie, WY; Lindberg, William R [Laramie, WY

    2008-09-02

    A shear stress sensor for measuring fluid wall shear stress on a test surface is provided. The wall shear stress sensor is comprised of an active sensing surface and a sensor body. An elastic mechanism mounted between the active sensing surface and the sensor body allows movement between the active sensing surface and the sensor body. A driving mechanism forces the shear stress sensor to oscillate. A measuring mechanism measures displacement of the active sensing surface relative to the sensor body. The sensor may be operated under periodic excitation where changes in the nature of the fluid properties or the fluid flow over the sensor measurably changes the amplitude or phase of the motion of the active sensing surface, or changes the force and power required from a control system in order to maintain constant motion. The device may be operated under non-periodic excitation where changes in the nature of the fluid properties or the fluid flow over the sensor change the transient motion of the active sensor surface or change the force and power required from a control system to maintain a specified transient motion of the active sensor surface.

  9. Basal shear stress and choice of sliding relation in Antarctic Ice Sheet simulations

    NASA Astrophysics Data System (ADS)

    Gladstone, Rupert M.; Zwinger, Thomas; Moore, John C.

    2017-04-01

    The choice of basal sliding relation can have a large impact on simulated dynamic behaviour of the Antarctic Ice Sheet. Given that effective pressure at the bed (which depends on sub-glacial hydrology) is a key factor governing sliding behaviour, and that many of the current generation of ice sheet models do not feature hydrology models, we ask whether sliding relations featuring a parameterised representation of effective pressure at the bed are likely to offer advantages over simpler non-pressure-dependent sliding relations. Using a Stokes flow ice dynamic model we have carried out an inversion from observed surface velocities using the adjoint method to infer basal shear stress under the Antarctic Ice Sheet. We find a gradual reduction of basal shear stress as the grounding line is approached for many major Antarctic ice streams, suggesting that a simple sliding relation in which basal shear stress is a power law function of sliding velocity may not be appropriate. We plot the spatial distribution of a sliding coefficient tuned to match our inverted Antarctic basal shear stress for several different published sliding relations, and discuss the implications of these spatial distributions to the choice of a suitable sliding relation.

  10. The effect of roughness elements on wind erosion: The importance of surface shear stress distribution

    USDA-ARS?s Scientific Manuscript database

    Representation of surface roughness effects on aeolian sediment transport is a key source of uncertainty in wind erosion models. Drag partitioning schemes are used to account for roughness by scaling the soil entrainment threshold by the ratio of shear stress on roughness elements to that on the veg...

  11. Assessment of shear stress related parameters in the carotid bifurcation using mouse-specific FSI simulations.

    PubMed

    De Wilde, David; Trachet, Bram; Debusschere, Nic; Iannaccone, Francesco; Swillens, Abigail; Degroote, Joris; Vierendeels, Jan; De Meyer, Guido R Y; Segers, Patrick

    2016-07-26

    The ApoE(-)(/)(-) mouse is a common small animal model to study atherosclerosis, an inflammatory disease of the large and medium sized arteries such as the carotid artery. It is generally accepted that the wall shear stress, induced by the blood flow, plays a key role in the onset of this disease. Wall shear stress, however, is difficult to derive from direct in vivo measurements, particularly in mice. In this study, we integrated in vivo imaging (micro-Computed Tomography-µCT and ultrasound) and fluid-structure interaction (FSI) modeling for the mouse-specific assessment of carotid hemodynamics and wall shear stress. Results were provided for 8 carotid bifurcations of 4 ApoE(-)(/)(-) mice. We demonstrated that accounting for the carotid elasticity leads to more realistic flow waveforms over the complete domain of the model due to volume buffering capacity in systole. The 8 simulated cases showed fairly consistent spatial distribution maps of time-averaged wall shear stress (TAWSS) and relative residence time (RRT). Zones with reduced TAWSS and elevated RRT, potential indicators of atherosclerosis-prone regions, were located mainly at the outer sinus of the external carotid artery. In contrast to human carotid hemodynamics, no flow recirculation could be observed in the carotid bifurcation region.

  12. In Vitro Bone Cell Models: Impact of Fluid Shear Stress on Bone Formation

    PubMed Central

    Wittkowske, Claudia; Reilly, Gwendolen C.; Lacroix, Damien; Perrault, Cecile M.

    2016-01-01

    This review describes the role of bone cells and their surrounding matrix in maintaining bone strength through the process of bone remodeling. Subsequently, this work focusses on how bone formation is guided by mechanical forces and fluid shear stress in particular. It has been demonstrated that mechanical stimulation is an important regulator of bone metabolism. Shear stress generated by interstitial fluid flow in the lacunar-canalicular network influences maintenance and healing of bone tissue. Fluid flow is primarily caused by compressive loading of bone as a result of physical activity. Changes in loading, e.g., due to extended periods of bed rest or microgravity in space are associated with altered bone remodeling and formation in vivo. In vitro, it has been reported that bone cells respond to fluid shear stress by releasing osteogenic signaling factors, such as nitric oxide, and prostaglandins. This work focusses on the application of in vitro models to study the effects of fluid flow on bone cell signaling, collagen deposition, and matrix mineralization. Particular attention is given to in vitro set-ups, which allow long-term cell culture and the application of low fluid shear stress. In addition, this review explores what mechanisms influence the orientation of collagen fibers, which determine the anisotropic properties of bone. A better understanding of these mechanisms could facilitate the design of improved tissue-engineered bone implants or more effective bone disease models. PMID:27896266

  13. Cloning the Gravity and Shear Stress Related Genes from MG-63 Cells by Subtracting Hybridization

    NASA Astrophysics Data System (ADS)

    Zhang, Shu; Dai, Zhong-quan; Wang, Bing; Cao, Xin-sheng; Li, Ying-hui; Sun, Xi-qing

    2008-06-01

    Background The purpose of the present study was to clone the gravity and shear stress related genes from osteoblast-like human osteosarcoma MG-63 cells by subtractive hybridization. Method MG-63 cells were divided into two groups (1G group and simulated microgravity group). After cultured for 60 h in two different gravitational environments, two groups of MG-63 cells were treated with 1.5Pa fluid shear stress (FSS) for 60 min, respectively. The total RNA in cells was isolated. The gravity and shear stress related genes were cloned by subtractive hybridization. Result 200 clones were gained. 30 positive clones were selected using PCR method based on the primers of vector and sequenced. The obtained sequences were analyzed by blast. changes of 17 sequences were confirmed by RT-PCR and these genes are related to cell proliferation, cell differentiation, protein synthesis, signal transduction and apoptosis. 5 unknown genes related to gravity and shear stress were found. Conclusion In this part of our study, our result indicates that simulated microgravity may change the activities of MG-63 cells by inducing the functional alterations of specific genes.

  14. In vitro shear stress-induced platelet activation: sensitivity of human and bovine blood.

    PubMed

    Lu, Qijin; Hofferbert, Bryan V; Koo, Grace; Malinauskas, Richard A

    2013-10-01

    As platelet activation plays a critical role in physiological hemostasis and pathological thrombosis, it is important in the overall hemocompatibility evaluation of new medical devices and biomaterials to assess their effects on platelet function. However, there are currently no widely accepted in vitro test methods to perform this assessment. In an effort to develop effective platelet tests for potential use in medical device evaluation, this study compared the sensitivity of platelet responses to shear stress stimulation of human and bovine blood using multiple platelet activation markers. Fresh whole blood samples anticoagulated with heparin or anticoagulant citrate dextrose, solution A (ACDA) were exposed to shear stresses up to 40 Pa for 2 min using a cone-and-plate rheometer model. Platelet activation was characterized by platelet counts, platelet surface P-selectin expression, and serotonin release into blood plasma. The results indicated that exposure to shear stresses above 20 Pa caused significant changes in all three of the platelet markers for human blood and that the changes were usually greater with ACDA anticoagulation than with heparin. In contrast, for bovine blood, the markers did not change with shear stress stimulation except for plasma serotonin in heparin anticoagulated blood. The differences observed between human and bovine platelet responses suggest that the value of using bovine blood for in vitro platelet testing to evaluate devices may be limited.

  15. Diagnostics of boundary layer transition by shear stress sensitive liquid crystals

    NASA Astrophysics Data System (ADS)

    Shapoval, E. S.

    2016-10-01

    Previous research indicates that the problem of boundary layer transition visualization on metal models in wind tunnels (WT) which is a fundamental question in experimental aerodynamics is not solved yet. In TsAGI together with Khristianovich Institute of Theoretical and Applied Mechanics (ITAM) a method of shear stress sensitive liquid crystals (LC) which allows flow visualization was proposed. This method allows testing several flow conditions in one wind tunnel run and does not need covering the investigated model with any special heat-insulating coating which spoils the model geometry. This coating is easily applied on the model surface by spray or even by brush. Its' thickness is about 40 micrometers and it does not spoil the surface quality. At first the coating obtains some definite color. Under shear stress the LC coating changes color and this change is proportional to shear stress. The whole process can be visually observed and during the tests it is recorded by camera. The findings of the research showed that it is possible to visualize boundary layer transition, flow separation, shock waves and the flow image on the whole. It is possible to predict that the proposed method of shear stress sensitive liquid crystals is a promise for future research.

  16. Cell-matrix adhesion characterization using multiple shear stress zones in single stepwise microchannel

    NASA Astrophysics Data System (ADS)

    Kim, Min-Ji; Doh, Il; Bae, Gab-Yong; Cha, Hyuk-Jin; Cho, Young-Ho

    2014-08-01

    This paper presents a cell chip capable to characterize cell-matrix adhesion by monitoring cell detachment rate. The proposed cell chip can supply multiple levels of shear stress in single stepwise microchannel. As epithelial-mesenchymal transition (EMT), one of hallmarks of cancer metastasis is closely associated to the interaction with extracelluar matrix (ECM), we took advantage of two lung cancer cell models with different adhesion properties to ECM depending their epithelial or mesenchymal properties, including the pair of lung cancer cells with (A549sh) or without E-cadherin expression (A549sh-Ecad), which would be optimal model to examine the alteration of adhesion properties after EMT induction. The cell-matrix adhesion resisting to shear stress appeared to be remarkably differed between lung cancer cells. The detachment rate of epithelial-like H358 and mesenchymal-like H460 cells was 53%-80% and 25%-66% in the shear stress range of 34-60 dyn/cm2, respectively. A549sh-Ecad cells exhibits lower detachment rate (5%-9%) compared to A549sh cells (14%-40%). By direct comparison of adhesion between A549sh and A549sh-Ecad, we demonstrated that A549shE-cad to mimic EMT were more favorable to the ECM attachment under the various levels of shear stress. The present method can be applied to quantitative analysis of tumor cell-ECM adhesion.

  17. Direct Measurement Sensor of the Boundary Shear Stress in Fluid Flow

    NASA Technical Reports Server (NTRS)

    Badescu, Mircea; Bao, Xiaoqi; Bar-Cohen, Yoseph; Chang, Zensheu; Kerenyi, Kornel; Lih, Shyh-Shiuh; Sherrit, Stewart; Trease, Brian P.; Widholm, Scott

    2010-01-01

    The flow fields and boundary erosion that are associated with scour at bridge piers are very complex. Direct measurement of the boundary shear stress and boundary pressure fluctuations in experimental scour research has always been a challenge and high spatial resolution and fidelity have been almost impossible. Most researchers have applied an indirect process to determine shear stress using precise measured velocity profiles. Laser Doppler Anemometry and Particle Image Velocimetry are common techniques used to accurately measure velocity profiles. These methods are based on theoretical assumptions to estimate boundary shear stress. In addition, available turbulence models cannot very well account for the effect of bed roughness which is fundamentally important for any CFD simulation. The authors have taken on the challenge to advance the magnitude level to which direct measurements of the shear stress in water flow can be performed. This paper covered the challenges and the efforts to develop a higher accuracy and small spatial resolution sensor. Also, preliminary sensor designs and test results are presented.

  18. Influence of shear stress magnitude and direction on atherosclerotic plaque composition

    PubMed Central

    Mehta, Vikram V.; Bovens, Sandra M.; Mohri, Zahra; Poulsen, Christian Bo; Gsell, Willy; Tremoleda, Jordi L.; Towhidi, Leila; de Silva, Ranil; Petretto, Enrico; Krams, Rob

    2016-01-01

    The precise flow characteristics that promote different atherosclerotic plaque types remain unclear. We previously developed a blood flow-modifying cuff for ApoE−/− mice that induces the development of advanced plaques with vulnerable and stable features upstream and downstream of the cuff, respectively. Herein, we sought to test the hypothesis that changes in flow magnitude promote formation of the upstream (vulnerable) plaque, whereas altered flow direction is important for development of the downstream (stable) plaque. We instrumented ApoE−/− mice (n = 7) with a cuff around the left carotid artery and imaged them with micro-CT (39.6 µm resolution) eight to nine weeks after cuff placement. Computational fluid dynamics was then performed to compute six metrics that describe different aspects of atherogenic flow in terms of wall shear stress magnitude and/or direction. In a subset of four imaged animals, we performed histology to confirm the presence of advanced plaques and measure plaque length in each segment. Relative to the control artery, the region upstream of the cuff exhibited changes in shear stress magnitude only (p < 0.05), whereas the region downstream of the cuff exhibited changes in shear stress magnitude and direction (p < 0.05). These data suggest that shear stress magnitude contributes to the formation of advanced plaques with a vulnerable phenotype, whereas variations in both magnitude and direction promote the formation of plaques with stable features. PMID:27853578

  19. Dynamic adhesion of umbilical cord blood endothelial progenitor cells under laminar shear stress.

    PubMed

    Angelos, Mathew G; Brown, Melissa A; Satterwhite, Lisa L; Levering, Vrad W; Shaked, Natan T; Truskey, George A

    2010-12-01

    Late outgrowth endothelial progenitor cells (EPCs) represent a promising cell source for rapid reendothelialization of damaged vasculature after expansion ex vivo and injection into the bloodstream. We characterized the dynamic adhesion of umbilical-cord-blood-derived EPCs (CB-EPCs) to surfaces coated with fibronectin. CB-EPC solution density affected the number of adherent cells and larger cells preferentially adhered at lower cell densities. The number of adherent cells varied with shear stress, with the maximum number of adherent cells and the shear stress at maximum adhesion depending upon fluid viscosity. CB-EPCs underwent limited rolling, transiently tethering for short distances before firm arrest. Immediately before arrest, the instantaneous velocity decreased independent of shear stress. A dimensional analysis indicated that adhesion was a function of the net force on the cells, the ratio of cell diffusion to sliding speed,