Sample records for shear stress measurement

  1. Bed shear stress measurement using flexible micro-rods

    NASA Astrophysics Data System (ADS)

    Farhadi, Alireza; Sindelar, Christine; Habersack, Helmut

    2014-05-01

    River morphodynamics is related to turbulent processes; and among influential factors shear stress is one of utter importance. Precise shear stress determination using direct and indirect methods has being investigated in recent years. Also, instantaneous fluctuation in wall shear stress distribution which can potentially affect erosion processes is being discussed currently. Here, a new method of indirect shear stress measurement using PDMS (Polydimethylsiloxan) flexible micro-rods is evaluated. Their flexural behavior in the flow within the boundary inner layer allows for the calculation of instantaneous shear stress values. The method is already used in medical fluid mechanics and now it is adopted for open channel investigations. A series of measurements were performed in order to investigate these micro-rods and their applicability to fluvial studies. This method may improve our understanding of boundary proximity region and enhance our insight into near bed momentum transfer mechanisms.

  2. Interfacial shear stress measurement using high spatial resolution multiphase PIV

    NASA Astrophysics Data System (ADS)

    André, Matthieu A.; Bardet, Philippe M.

    2015-06-01

    In multiphase flows, form drag and viscous shear stress transfer momentum between phases. For numerous environmental and man-made flows, it is of primary importance to predict this transfer at a liquid-gas interface. In its general expression, interfacial shear stress involves local velocity gradients as well as surface velocity, curvature, and surface tension gradients. It is therefore a challenging quantity to measure experimentally or compute numerically. In fact, no experimental work to date has been able to directly resolve all the terms contributing to the shear stress in the case of curved and moving surfaces. In an attempt to fully resolve the interface shear stress when surface tension gradients are negligible, high-resolution particle image velocimetry (PIV) data are acquired simultaneously on both sides of a water-air interface. The flow consists of a well-conditioned uniform and homogeneous water jet discharging in quiescent air, which exhibits two-dimensional surface waves as a result of a shear layer instability below the surface. PIV provides velocity fields in both phases, while planar laser-induced fluorescence is used to track the interface and obtain its curvature. To compute the interfacial shear stress from the data, several processing schemes are proposed and compared, using liquid and/or gas phase data. Vorticity at the surface, which relates to the shear stress through the dynamic boundary condition at the surface, is also computed and provides additional strategies for estimating the shear. The various schemes are in agreement within the experimental uncertainties, validating the methodology for experimentally resolving this demanding quantity.

  3. 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.

  4. Measurement of the Wall Shear Stress Field Created by a Supersonic Impinging Microjet

    NASA Astrophysics Data System (ADS)

    Schabron, Bridget; Naughton, Jonathan; Alvi, Farrukh

    2009-11-01

    The study of wall shear stress beneath a supersonic impinging microjet was carried out using oil film interferometry. The measurement of wall shear stress in a microjet is an interesting flow both for its practical applications as well as the challenges the surface flow poses. The wall shear stress measurement challenges for this flow included the radially symmetric wall shear stress field, the very high gradients of wall shear stress, optical access issues, and the significant temperature variations on the surface that affect the oil's viscosity. Measurements were made for various jet height above the plate h to jet diameter D ratios and for various pressure ratios. Analysis of the resulting interferograms and the challenges posed by this particular geometry are discussed. The results demonstrate the capability of oil film interferometry, particularly its dynamic range, for measuring wall shear stress in complex flow.

  5. Lateral Stress Measurements and Shear Strength of an Alumina-Filled Epoxy

    Microsoft Academic Search

    K. Kos; J. C. F. Millett; N. K. Bourne; D. Deas

    2006-01-01

    The variation of shear strength with impact stress in an alumina-filled epoxy has been measured with lateral stress gauges. At lower stresses, a degree of hardening behind the shock front has been observed, which diminishes as shock stress increases. It is believed that this is due to a transition from a viscous response dominated by the epoxy matrix, to a

  6. Helix Pre-Tilted Monomer - Polymer Liquid Crystal System for Measurement of Shear Stress Vector

    NASA Astrophysics Data System (ADS)

    Parmar, Devendra; Sprinkle, Danny; Singh, Jag

    2005-04-01

    The direction and magnitude of air flow-induced shear stress vector have been measured selective reflection optical response of a pre-tilted shear sensitive cholesteric helix in a monomer-polymer liquid crystal (LC). Optical wavelength, ?, of the selectively reflected light measured normal to the test surface for a white light incident at ˜ 20 to the normal varies linearly (slope ˜ 0.38 nm/Torr for the investigated system of a monomer LC and a polymer LC Vectra A130) with the shear stress measured in terms the of air flow differential pressure, ?p. This method offers an unique experimental for shear stress vector measurement. Effects of the change in direction of incidence have been discussed from first principles based on a shear stress induced helix tilt and its deformation. It implies from the suggested model that in case of shear stress associated helix deformation, the optical response is likely to reverse on interchanging the directions of the incidence and the reflection for a given shear stress vector. ** Distinguished Research Scientist (Ret.)

  7. An Integrated Silicon Based Wall Pressure-Shear Stress Sensor for Measurements in Turbulent Flows

    NASA Astrophysics Data System (ADS)

    Löfdahl, L.; Kälvesten, E.; Hadzianagnostakis, T.; Stemme, G.

    1996-11-01

    An integrated silicon pressure-shear stress sensor has been designed, fabricated and tested in turbulent wall-boundary layers. The piezoresistive pressure sensor is based on polysilicon diaphragm technology and the thermal shear stress sensor on the gas cooling of a polyimide insulated heated chip. The pressure sensor diaphragm area is 100×100 ?m, the top-area of the shear stress sensor hot chip is 300×60 ?m and the edge-to-edge distance between the two areas is 100 ?m. The measured steady-state power dissipation of the shear stress sensor in a turbulent wall-boundary layer at an over-temperature of 100^oC was P=42 + 1.1 ?_0^0.50 mW where ?0 is the time-average wall shear stress. The new integrated sensor has been applied for the simultaneous measurement of fluctuating pressure and shear stress in a flat plate boundary layer at 4.9×10^3 < Re_? < 1.0×10^4. This has produced pressure-shear stress correlation coefficients between 0.40 and 0.50 for the parallel, and between 0.20 and 0.25 for the perpendicular configuration to the mean flow.

  8. Instrument for measuring the wall shearing stress of turbulent boundary layers

    NASA Technical Reports Server (NTRS)

    Ludwieg, H

    1950-01-01

    It is shown that at a smooth wall in a turbulent boundary layer the velocity profile next to the wall is dependent, aside from the material constants of the flowing medium, only on the shearing stress transmitted to the wall, even with pressure rise or with pressure drop. Consequently, the heat transfer of a small element that is built into the wall and has a higher temperature than that of the flowing medium is a measure of the wall shearing stress. Theoretical considerations indicate that the wall shearing stress of the boundary layer can be defined by means of a heat-transfer measurement with an instrument mounted in the wall. Such an instrument is described. The calibration curve and its directional sensitivity curve are indicated. It permits the determination of the wall shearing stress in magnitude and direction.

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

    PubMed

    Yap, Choon Hwai; Saikrishnan, Neelakantan; Yoganathan, Ajit P

    2012-01-01

    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/cm(2), and reversed in direction at the end of systole for 15-25 ms, and reached a significant negative magnitude of 40-51 dyn/cm(2). Shear stresses from the theoretical model applied to in vivo data showed that shear stresses peaked at 77-92 dyn/cm(2) and reversed in direction for substantial period of time (108-110 ms) during late systole with peak negative shear stress of 35-38 dyn/cm(2). PMID:21465260

  10. Measurements of Snow Avalanche Basal Shear to Normal Stress Ratios (S\\/N)

    Microsoft Academic Search

    P. A. Bartelt; K. Platzer

    2006-01-01

    A long-standing problem in snow science is the value of the basal friction coefficient for dense, flowing avalanches. This parameter is defined by the ratio of shear (S) to normal (N) stress and determines the runout distance of snow avalanches. It is therefore the crucial parameter in hazard mitigation studies. In this paper we present measurements of (S\\/N). The measurements

  11. Silicon micromachined sensors and sensor arrays for shear-stress measurements in aerodynamic flows

    E-print Network

    Padmanabhan, Aravind

    In this thesis we report on a new micromachined floating-element shear-stress sensor for turbulent boundary layer research. Applications in low shear-stress environments such as turbulent boundary layers require extremely ...

  12. American Institute of Aeronautics and Astronautics An Optical Method for Measuring Low Wall Shear Stresses

    E-print Network

    Gregory, James W.

    = Viscosity (kg/sm) = Density of air (kg/m3 ) = Wall shear stress (N/m2 ) = Kinematic viscosity (m2 /s. Gregory US Air Force Academy, USAF Academy, CO 80840 A thermal tuft method for the measurement of low wall

  13. 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.

  14. A sliding plate microgap rheometer for the simultaneous measurement of shear stress and first normal stress difference

    NASA Astrophysics Data System (ADS)

    Baik, Seung Jae; Moldenaers, Paula; Clasen, Christian

    2011-03-01

    A new generation of the "flexure-based microgap rheometer" (the N-FMR) has been developed which is also capable of measuring, in addition to the shear stress, the first normal stress difference of micrometer thin fluid films. This microgap rheometer with a translation system based on compound spring flexures measures the rheological properties of microliter samples of complex fluids confined in a plane couette configuration with gap distances of h = 1-400 ?m up to shear rates of dot ? = 3000 s-1. Feed back loop controlled precise positioning of the shearing surfaces with response times <1 ms enables to control the parallelism within 1.5 ?rad and to maintain the gap distance within 20 nm. This precise gap control minimizes squeeze flow effects and allows therefore to measure the first normal stress difference N1 of the thin film down to a micrometer gap distance, with a lower limit of {{N_1 }/{dot ? }} = 9.375 × 10^{ - 11} {?/{h^2 }} that depends on the shear viscosity ? and the squared inverse gap. Structural development of complex fluids in the confinement can be visualized by using a beam splitter on the shearing surface and a long working distance microscope. In summary, this new instrument allows to investigate the confinement dependent rheological and morphological evolution of micrometer thin films.

  15. Measurements of Snow Avalanche Basal Shear to Normal Stress Ratios (S/N)

    NASA Astrophysics Data System (ADS)

    Bartelt, P. A.; Platzer, K.

    2006-12-01

    A long-standing problem in snow science is the value of the basal friction coefficient for dense, flowing avalanches. This parameter is defined by the ratio of shear (S) to normal (N) stress and determines the runout distance of snow avalanches. It is therefore the crucial parameter in hazard mitigation studies. In this paper we present measurements of (S/N). The measurements are made on a large snow chute instrumente with shear/normal force plates, velocity and flow height sensors. We find that a Mohr-Coulomb relation of the form S=c+bN accurately describes the measurements. The Coulomb friction coefficient b ranges between 0.22 and 0.55. Wet snow flows exhibit significant cohesion c ? 500 Pa. These quantitative values allow us to probe the relation between the basal work rate, internal dissipation and gravitational potential. We show that basal shearing is the primary frictional mechanism retarding snow flows. This mechanism shows no velocity dependence, contrary to many postulated constitutive relations for basal shearing in snow avalanches. Furthermore, we investigate how the basal work rate controls the injection of fluctuation energy at the basal surface. Thus, our experimental results and theoretical considerations help clarify the relationship between basal shearing and internal dissipation in snow avalanches.

  16. Wall shear stress as measured in vivo: consequences for the design of the arterial system

    Microsoft Academic Search

    Robert S. Reneman; Arnold P. G. Hoeks

    2008-01-01

    Based upon theory, wall shear stress (WSS), an important determinant of endothelial function and gene expression, has been\\u000a assumed to be constant along the arterial tree and the same in a particular artery across species. In vivo measurements of\\u000a WSS, however, have shown that these assumptions are far from valid. In this survey we will discuss the assessment of WSS

  17. 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.

  18. Dynamic pressure and shear stress measurements on the stator wall of whirling annular seals 

    E-print Network

    Winslow, Robert Bradley

    1994-01-01

    , m, radial direction Reynolds number, 2pU c/tt Root mean square Shear stress, Pa Tc/(itW~) Time averaged non-dimensional shear stress Taylor number, (pW, ?c/tt)(2c/D)' Mean axial velocity, m/s U/U uu uu* V Average mean axial velocity, m... on the stator wall (at Z/L=0. 5), and the X, Y, and Z axes are defined. Figure 7: Non-dimensional, mean shear stress profiles for the 0/o eccentricity 33 seal. 101 Figure 8: Non-dimensional, mean shear stress profiles for the 10/o eccentricity seal. 102...

  19. ANALYSIS OF SHEAR STRESS IN ASPHALT PAVEMENTS UNDER ACTUAL MEASURED TIRE-PAVEMENT CONTACT PRESSURE

    Microsoft Academic Search

    Kai SU; Lijun SUN; Yoshitaka HACHIYA; Ryota MAEKAWA

    Rutting is one of the most important load-induced distresses found in asphalt pavements. The primary mechanism of rutting is associated with shear deformation rather than densification. Recently, top-down cracking probably attributed to shear failure has also been a frequent occurrence in asphalt pavements. Clearly, shear stress is one of the critical factors affecting pavements performance, and there is a great

  20. Recent Developments in the Use of Liquid Crystal Coatings for Full-Surface Shear Stress Vector Measurements

    NASA Technical Reports Server (NTRS)

    Reda, D. C.; Wilder, M. C.; Zilliac, G.; Hu, K. C.; Whitney, D. J.; Deardorff, D. G.; Moffat, R. J.; Farina, D. J.; Danek, C.; Martinez, R.; Davis, Sanford S. (Technical Monitor)

    1995-01-01

    Under normal white-light illumination and oblique observation, liquid crystal coating (LCC) color-change response to shear depends on both shear stress magnitude as well as the direction of the applied shear relative to the observer's line of sight. These color-change responses were quantified by subjecting a LCC to a wall-jet shear flow and measuring scattered-light spectra using a fiber optic probe and spectrophotometer. At any fixed shear stress magnitude, the maximum color change 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 reductions in measured color change. For this vector/observer aligned orientation, color change was found to scale linearly with increasing shear stress magnitude over an eight-fold range. Based on these results, a surface shear stress vector measurement methodology, involving multiple oblique-view observations of the test surface, was formulated. In the present paper, the experimental approach and data analysis procedure required to extend this vector measurement methodology to full-surface applications will be outlined and progress towards demonstrating this areal capability will be reviewed.

  1. Aeolian Shear Stress Ratio Measurements within Mesquite-Dominated Landscapes of the Chihuahuan Desert, New Mexico, USA

    NASA Technical Reports Server (NTRS)

    King, James; Nickling, W. G.; Gilliles, J. A.

    2006-01-01

    A field study was conducted to ascertain the amount of protection that mesquite-dominated communities provide to the surface from wind erosion. The dynamics of the locally accelerated evolution of a mesquite/coppice dune landscape and the undetermined spatial dependence of potential erosion by wind from a shear stress partition model were investigated. Sediment transport and dust emission processes are governed by the amount of protection that can be provided by roughness elements. Although shear stress partition models exist that can describe this, their accuracy has only been tested against a limited dataset because instrumentation has previously been unable to provide the necessary measurements. This study combines the use of meteorological towers and surface shear stress measurements with Irwin sensors to measure the partition of shear stress in situ. The surface shear stress within preferentially aligned vegetation (within coppice dune development) exhibited highly skewed distributions, while a more homogenous surface stress was recorded at a site with less developed coppice dunes. Above the vegetation, the logarithmic velocity profile deduced roughness length (based on 10-min averages) exhibited a distinct correlation with compass direction for the site with vegetation preferentially aligned, while the site with more homogenously distributed vegetation showed very little variation in the roughness length. This distribution in roughness length within an area, defines a distribution of a resolved shear stress partitioning model based on these measurements, ultimately providing potential closure to a previously uncorrelated model parameter.

  2. Platelet Activation Due to Hemodynamic Shear Stresses: Damage Accumulation Model and Comparison to In Vitro Measurements

    PubMed Central

    Nobili, Matteo; Sheriff, Jawaad; Morbiducci, Umberto; Redaelli, Alberto; Bluestein, Danny

    2009-01-01

    The need to optimize the thrombogenic performance of blood recirculating cardiovascular devices, e.g., prosthetic heart valves (PHV) and ventricular assist devices (VAD), is accentuated by the fact that most of them require lifelong anticoagulation therapy that does not eliminate the risk of thromboembolic complications. The formation of thromboemboli in the flow field of these devices is potentiated by contact with foreign surfaces and regional flow phenomena that stimulate blood clotting, especially platelets. With the lack of appropriate methodology, device manufacturers do not specifically optimize for thrombogenic performance. Such optimization can be facilitated by formulating a robust numerical methodology with predictive capabilities of flow-induced platelet activation. In this study, a phenomenological model for platelet cumulative damage, identified by means of genetic algorithms (GAs), was correlated with in vitro experiments conducted in a Hemodynamic Shearing Device (HSD). Platelets were uniformly exposed to flow shear representing the lower end of the stress levels encountered in devices, and platelet activity state (PAS) was measured in response to six dynamic shear stress waveforms representing repeated passages through a device, and correlated to the predictions of the damage accumulation model. Experimental results demonstrated an increase in PAS with a decrease in “relaxation” time between pulses. The model predictions were in very good agreement with the experimental results. PMID:18204318

  3. 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.

  4. Shear stress and the endothelium

    Microsoft Academic Search

    Barbara J. Ballermann; Alan Dardik; Eudora Eng; Ailian Liu

    1998-01-01

    Shear stress and the endothelium. Vascular endothelial cells (ECs) in vivo are influenced by two distinct hemodynamic forces: cyclical strain due to vessel wall distention by transmural pressure, and shear stress, the frictional force generated by blood flow. Shear stress acts at the apical cell surface to deform cells in the direction of blood flow; wall distention tends to deform

  5. Contactless measurement of bolt axial stress using a shear-wave electromagnetic acoustic transducer

    Microsoft Academic Search

    M. Hirao; H. Ogi; H. Yasui

    2001-01-01

    An ultrasonic method is presented to monitor bolt axial stress using a noncontacting shear-wave electromagnetic acoustic transducer (EMAT). The EMAT generates and detects the shear wave propagating in the axial direction of the bolts. We evaluated the axial stress from the phase shift of the top-to-bottom echo and from the resonance frequency shift; both are induced by the acoustoelastic velocity

  6. Shear-stress measurement in aerodynamic testing using cholesteric liquid crystals

    Microsoft Academic Search

    P. Bonnett; T. V. Jones; D. G. McDonnell

    1989-01-01

    The change in the selective reflection spectra of cholesteric liquid crystals with shear is described, and the results indicate that, although it appears to be a promising technique for flow visualization in aerodynamic testing, the method is only suitable for approximate measurement of shear. An improved method for visualising flow is proposed that utilizes a shear-induced texture change from the

  7. Measurement of wall shear stress in chick embryonic heart using optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Ma, Zhenhe; Dou, Shidan; Zhao, Yuqian; Wang, Yi; Suo, Yanyan; Wang, Fengwen

    2015-03-01

    The cardiac development is a complicated process affected by genetic and environmental factors. Wall shear stress (WSS) is one of the components which have been proved to influence the morphogenesis during early stages of cardiac development. To study the mechanism, WSS measurement is a step with significant importance. WSS is caused by blood flow imposed on the inner surface of the heart wall and it can be determined by calculating velocity gradients of blood flow in a direction perpendicular to the wall. However, the WSS of the early stage embryonic heart is difficult to measure since the embryonic heart is tiny and beating fast. Optical coherence tomography (OCT) is a non-invasive imaging modality with high spatial and temporal resolution, which is uniquely suitable for the study of early stage embryonic heart development. In this paper, we introduce a method to measure the WSS of early stage chick embryonic heart based on high speed spectral domain optical coherence tomography (SDOCT). 4D (x,y,z,t) scan was performed on the outflow tract (OFT) of HH18 (~3 days of incubation) chick embryonic heart. After phase synchronization, OFT boundary segmentation, and OFT center line calculation, Doppler angle of the blood flow in the OFT can be achieved (This method has been described in previous publications). Combining with the Doppler OCT results, we calculate absolute blood flow velocity distribution in the OFT. The boundary of the OFT was segmented at each cross-sectional structural image, then geometrical center of the OFT can be calculated. Thus, the gradients of blood flow in radial direction can be calculated. This velocity gradient near the wall is termed wall shear rate and the WSS value is proportional to the wall shear rate. Based on this method, the WSS at different heart beating phase are compare. The result demonstrates that OCT is capable of early stage chicken embryonic heart WSS study.

  8. Development of buried wire gages for measurement of wall shear stress in Blastane experiments

    NASA Technical Reports Server (NTRS)

    Murthy, S. V.; Steinle, F. W.

    1986-01-01

    Buried Wire Gages operated from a Constant Temperature Anemometer System are among the special types of instrumentation to be used in the Boundary Layer Apparatus for Subsonic and Transonic flow Affected by Noise Environment (BLASTANE). These Gages are of a new type and need to be adapted for specific applications. Methods were developed to fabricate Gage inserts and mount those in the BLASTANE Instrumentation Plugs. A large number of Gages were prepared and operated from a Constant Temperature Anemometer System to derive some of the calibration constants for application to fluid-flow wall shear-stress measurements. The final stage of the calibration was defined, but could not be accomplished because of non-availability of a suitable flow simulating apparatus. This report provides a description of the Buried Wire Gage technique, an explanation of the method evolved for making proper Gages and the calibration constants, namely Temperature Coefficient of Resistance and Conduction Loss Factor.

  9. Accurate and Independent Measurements of Wall-Shear Stress in Turbulent Flows

    NASA Astrophysics Data System (ADS)

    R"Uedi, J.-D.; Duncan, R.; Imayama, S.; Chauhan, K.

    2009-11-01

    Oil Film Interferometry (OFI) is used to directly measure the wall-shear stress in the high Reynolds number turbulent boundary layers from three facilities used for ICET. Various optical arrangements were utilized to collect the digital images generated on transparent plugs integrated into the boundary layer surface. Test-section free stream velocities ranging from 10 to 60 m/s and development lengths from 5.5m to 21 m, resulted in friction velocities varying from 0.35 to 1.65 m/s, corresponding to boundary layer thicknesses varying by factors of nearly four. Silicon oils with viscosities from 20 to 1000 cSt were employed in the measurements, with multiple oils used for several of the test conditions. A reference temperature measurement was used in all three facilities and for the calibration of the oils as a function of temperature in four different laboratories using two types of viscometers. The processing of the images was carried out using several approaches and compared for consistency of the results. Results of the skin friction coefficient from the three wind tunnels are examined and compared as a function of the displacement thickness Reynolds number, as determined from hot-wire and Pitot probe profiles at comparable conditions, and are found to be accurately represented by the logarithmic Rotta relation. The various uncertainties and the final accuracy of this type of measurement are discussed.

  10. Measurements of turbulent shear stress and heat flux in an axisymmetric separated and reattached flow over a longitudinal blunt circular cylinder

    Microsoft Academic Search

    T. Ota; N. Kon; S. Hatakeyama; S. Sato

    1980-01-01

    Turbulent shear stress and heat flux were measured using a hot-wire anemometer in the separated, reattached, and redeveloped regions of an axisymmetric incompressible air flow over a longitudinal circular cylinder having a blunt leading edge. The characteristic features of a turbulent heat flux are detected to be quite different from those of a turbulent shear stress, and in the turbulent

  11. The Effect of Test Machine Compliance on the Measured Shear Punch Yield Stress as Predicted Using Finite Element Analysis

    SciTech Connect

    Toloczko, Mychailo; Abe, Katsunori; Hamilton, Margaret L.; Garner, Francis A.; Kurtz, Richard J.

    2001-10-01

    In previous research involving the use of the shear punch test, it was assumed that the displacement of the punch tip was only slightly different than the crosshead displacement. The present work explores this assumption and its ramifications by simulating the shear punch test with finite element analysis (FEA). The simulations suggest that punch tip displacement is much less than previously assumed, and that for the test frames which have been used, crosshead displacement is over an order of magnitude greater than punch tip displacement. This difference in displacements is thought to be due to test machine and punch compliance, and a simple elasticity calculation of the compliance of the punch, the test machine, and a specimen gives a result which is in agreement with the FEA simulations. The effect of using punch tip displacement on the observed effective shear yield stress was evaluated using FEA simulated shear punch tests on several different metals. Yield was measured at several different offset shear strains with a 1.0% offset shear yield strength measurement providing the best correlation with 0.2% offset uniaxial yield strength. When using the 1.0% offset shear yield values, the previously observed material-to-material variability in the tensile-shear correlation all but disappeared. Based on this work, it appears that the material-to-material variations in prior correlations between uniaxial yield strength and shear yield strength is due to a combination of large test machine compliance and material-to-material differences in the work hardening exponent.

  12. Development of a wall-shear-stress sensor and measurements in mini-channels with partial blockages

    NASA Astrophysics Data System (ADS)

    Afara, Samer; Medvescek, James; Mydlarski, Laurent; Baliga, Bantwal R.; MacDonald, Mark

    2014-05-01

    The design, construction, operation and validation of a wall-shear-stress sensor, and measurements obtained using this sensor in air flows downstream of partial blockages in a mini-channel are presented. The sensor consisted of a hot wire mounted over a small rectangular slot and operated using a constant-temperature anemometer. It was used to investigate flows similar to those within the mini-channels inside notebook computers. The overall goal of the present work was to develop a sensor suitable for measurements of the wall-shear stress in such flows, which can be used to validate corresponding numerical simulations, as the latter are known to be often surprisingly inaccurate. To this end, measurements of the wall-shear stress, and the corresponding statistical moments and power spectral densities, were obtained at different distances downstream of the partial blockage, with blockage ratios of 39.7, 59.2, and 76.3 %. The Reynolds number (based on average velocity and hydraulic diameter) ranged from 100 to 900. The results confirmed the presence of unsteadiness, separation, reattachment, and laminar-turbulent transition in the ostensibly laminar flow of air in mini-channels with partial blockages. The present results demonstrate why accurate numerical predictions of cooling air flows in laptop and notebook computers remain a challenging task.

  13. Clinical measurement of normal and shear stresses on a trans-tibial stump: characteristics of wave-form shapes during walking

    Microsoft Academic Search

    J. E. SANDERS; C. H. DALY; E. M. BURGESS

    1993-01-01

    Stresses on the surface of a stump within a prosthetic socket during walking can potentially traumatise stump tissues. To gain insight into stresses and design parameters that affect them, normal and shear interface stresses were measured on three unilateral trans-tibial amputee subjects during walking trials. During stance phase repeated characteristics in wave-form shapes from different subjects were apparent. They included

  14. Measurements of turbulent shear stress and heat flux in an axisymmetric separated and reattached flow over a longitudinal blunt circular cylinder

    NASA Astrophysics Data System (ADS)

    Ota, T.; Kon, N.; Hatakeyama, S.; Sato, S.

    1980-10-01

    Turbulent shear stress and heat flux were measured using a hot-wire anemometer in the separated, reattached, and redeveloped regions of an axisymmetric incompressible air flow over a longitudinal circular cylinder having a blunt leading edge. The characteristic features of a turbulent heat flux are detected to be quite different from those of a turbulent shear stress, and in the turbulent boundary layer downstream from the reattachment point, the development of the turbulent heat flux is much quicker than that of the turbulent shear stress.

  15. Development of in vivo PIV methods for measurement of wall shear stress in embryonic animal models

    NASA Astrophysics Data System (ADS)

    Kiger, K.; Vennemann, P.; Lindken, R.; Westerweel, J.; Hierck, B. P.; Groenendijk, B.; Poelmann, R. E.; Ursem, N. T. C.; Stekelenburg-de Vos, S.; Ten Hagen, T. M. L.

    2004-11-01

    Measuring the spatially and temporally resolved plasma velocity of whole blood in vivo is desirable in many areas of biomedical research. A nonintrusive velocity measurement technique is needed that can measure instantaneous flow fields at sub-millimeter scales. In the current work, we report on our efforts to adapt Micro Particle Image Velocimetry (?PIV) to measure the plasma velocity in the beating heart of a chicken embryo. In the majority of previous work applying ?PIV to hemodynamic flows, erythrocytes are used to trace the fluid motion. Resolving near-wall phenomena using this technique is limited by the relatively large size of the erythrocytes and near-wall shear migration effects. In the current work, fluorescent liposomes (D ? 400 nm) are added to the flow as a tracer. Because of their small dimension, the liposomes are expected to closely follow the movement of the blood-plasma, as well as maintain their near-wall concentrations under high-shear conditions. The ?PIV system is phase-locked to the heart beat using a pulsed Doppler ultrasound probe to allow for ensemble averaging of the flow field properties. The measurements quantitatively resolve the velocity distribution in the developing ventricle and atrium of the embryo at nine different phases within the cardiac cycle.

  16. In situ measurements of erosion shear stress and geotechnical shear strength of the intertidal sediments of the experimental managed realignment scheme at Tollesbury, Essex, UK

    NASA Astrophysics Data System (ADS)

    Watts, C. W.; Tolhurst, T. J.; Black, K. S.; Whitmore, A. P.

    2003-11-01

    Managed realignment is one of several 'soft' engineering options which may reduce the costs of coastal defence, provide a more 'natural' response to the problem of rising sea levels and at the same time deliver environmental, specifically nature conservation, benefits. The success of this technique depends on the ability of the soils and sediments within the site to resist the erosive action of waves and tidal currents and allow sediment accretion to occur, at least at a rate equal to mean sea-level rise. Once a critical shear stress, ?0 crt exerted by the moving fluids over the bed, is exceeded erosion will occur. A cohesive strength meter (CSM) and the fall-cone method were used to gather data, in situ on the strength and stability of sediments from an experimental managed realignment site and an adjacent, established saltmarsh in south-east England. Following six years of regular tidal cover, the underlying agricultural soil appeared both very strong (mean surface shear strength, ? f=228 kPa) and highly resistant to erosion ( ? 0 crt=6.23 N m -2). During this period much of the site had been covered by sediment, and saltmarsh plants ( Salicornia europaea) had become established above the mean high water neap tide (MHWN) level. Above MHWN level (tidal cover time <15%) sediments had greater bulk densities and lower water contents which resulted in a moderate shear strength (? f=11.6 kPa) and resistance to erosion (? 0 crt=2.45 N m -2) . Below MHWN, where sediment accretion rates were greatest, poor consolidation resulted in very high water contents and low bulk densities. These areas were at the highest potential risk of erosion (? 0 crt=1.5 N m -2) and had very low shear strengths (? f=0.33 kPa) . Where sediment exceeded 25 cm depth, gullies formed allowing their banks and adjacent margins to drain faster than the surrounding sediment. This led to a significant increase in bed strength (? f=10.8 kPa) and stability (? 0 crt=4.3 N m -2) . These gullies were probably the early stages of the complex creek patterns characteristic of the adjacent, established saltmarsh. The established saltmarsh was rich in plants and had a well-developed (aggregated) soil structure. These soils had a moderate to high resistance to erosion (? 0 crt=2.45 N m -2) and shear strength (? f=25.6 kPa) . Undrained sediment shear strength, ?f, obtained with the fall-cone apparatus can also provide a useful indication of critical erosion shear stress, ?0 crt . Values of ?0 crt , measured across this site were all relatively large compared with computed bed stresses arising from locally generated waves. Thus this experimental managed realignment site was found to be primarily depositional and was thus successfully achieving the twin aims of protecting the coast from erosion and extending a rich ecosystem.

  17. Shear stress, vascular remodeling and neointimal formation

    Microsoft Academic Search

    Jolanda J. Wentzel; Frank J. H. Gijsen; Nikos Stergiopulos; Patrick W. Serruys; Cornelis J. Slager; Rob Krams

    2003-01-01

    The role of shear stress in atherosclerosis has been well documented. However, its role in restenosis was underexposed. In this paper a novel in vivo measuring technique and several of its applications related to restenosis will be described. The technique consists of a combination of 3D reconstruction of blood vessels and computational fluid dynamics (CFD). The 3D imaging techniques use

  18. Wrinkling of Stretched Films: Shear Stress

    NASA Technical Reports Server (NTRS)

    Zak, M. A.

    1982-01-01

    Report presents theoretical investigation on nonlinear shearing characteristics of wrinkling films under applied shear stress. Report helps explain force/deflection characteristic of in-planeboom and solar-array blanket structural combinations.

  19. Shear stress and the endothelial transport barrier

    PubMed Central

    Tarbell, John M.

    2010-01-01

    The shear stress of flowing blood on the surfaces of endothelial cells that provide the barrier to transport of solutes and water between blood and the underlying tissue modulates the permeability to solutes and the hydraulic conductivity. This review begins with a discussion of transport pathways across the endothelium and then considers the experimental evidence from both in vivo and in vitro studies that shows an influence of shear stress on endothelial transport properties after both acute (minutes to hours) and chronic (hours to days) changes in shear stress. Next, the effects of shear stress on individual transport pathways (tight junctions, adherens junctions, vesicles and leaky junctions) are described, and this information is integrated with the transport experiments to suggest mechanisms controlling both acute and chronic responses of transport properties to shear stress. The review ends with a summary of future research challenges. PMID:20543206

  20. Time-resolved particle image velocimetry measurements with wall shear stress and uncertainty quantification for the FDA benchmark nozzle model

    E-print Network

    Raben, Jaime S; Robinson, Ronald; Malinauskas, Richard; Vlachos, Pavlos P

    2014-01-01

    We present validation of benchmark experimental data for computational fluid dynamics (CFD) analyses of medical devices using advanced Particle Image Velocimetry (PIV) processing and post-processing techniques. This work is an extension of a previous FDA-sponsored multi-laboratory study, which used a medical device mimicking geometry referred to as the FDA benchmark nozzle model. Time-resolved PIV analysis was performed in five overlapping regions of the model for Reynolds numbers in the nozzle throat of 500, 2,000, 5,000, and 8,000. Images included a two-fold increase in spatial resolution in comparison to the previous study. Data was processed using ensemble correlation, dynamic range enhancement, and phase correlations to increase signal-to-noise ratios and measurement accuracy, and to resolve flow regions with large velocity ranges and gradients, which is typical of many blood-contacting medical devices. Parameters relevant to device safety, including shear stress at the wall and in bulk flow, were comput...

  1. Experimental validation of a dynamic resonant wall shear stress sensor

    NASA Astrophysics Data System (ADS)

    Zhang, Xu; Armstrong, William D.; Lindberg, William R.; Naughton, Jonathan W.

    2012-10-01

    Experimental measurements are used to validate a numerical model of a dynamic resonant wall shear stress sensor. The numerical model consists of an unsteady two-dimensional boundary-layer model for the flow and a simple mechanical model for the sensor itself. The sensor's sensitivity to wall shear stress is experimentally determined in a flat-plate boundary layer, and the results agree closely with those from the numerical simulations. Using the validated model, it is determined that the energy lost in each sensor oscillation due to the interaction between the sensor and fluid increases with increasing mean wall shear stress.

  2. MEMS floating element sensor array for wall shear stress measurement under a turbulent boundary layer

    NASA Astrophysics Data System (ADS)

    Zong, Zhaowang

    A novel electrochromic thin film transistor (EC-TFT) was fabricated and characterized in this work. This concept relies on ion transport to control gating. The channel material is tungsten oxide (WOx), produced by reactive magnetron sputtering. In its oxidized state WO3 is a transparent, wide band gap insulator (> 3 eV). However upon intercalation of light ions (H+, Li+) the material becomes both electrically conducting and opaque to visible light. This allows the EC-TFT to generate a complementary optical response. We optimized the fabrication of individual layers of the EC-TFT, and found that controlling the stoichiometry of WOx is a key step. Using RF magnetron sputtering, it was found that there is a narrow window to obtain material capable of reversible switching. Fully oxidized films proved it is difficult to intercalate ions efficiently. In contrast, insufficient oxygen produced films that were always in a metallic like state. Best results were obtained with the sputter power set at 200 W using O2 fractions of 42%-46% in argon. In the preliminary studies, the device was tested in a two-step fashion. First, devices were placed in solution and cyclic voltammetry was used to set the level of ion intercalation. Samples were then removed from the electrolyte, dried, and the source/drain current was measured on a probe station. This demonstrated the concept of the EC-TFT, showing that the transistor could be turned on and off reversely with a current ratio of Ion/Ioff ~ 1000, and showed significant color change during the intercalation. However, the conductivity in off state was too high to be a promising transistor, the two step approach made the data rather noisy, it was difficult to make good contacts and this was not an in situ measurement. In order to get the in situ measurement, macrodevices with large electrodes were fabricated and characterized, which made it easier to make electrical contacts. However, after the initial cycle the macrodevices were always in on state and could not be turned off because of the dielectric. In addition, it showed no significant color change. The top source/drain structure showed similar behavior as the bottom configuration. It was found that in these configurations the supply of electrons was insufficient to allow intercalation, and permanent defects in the Al2O3 dielectric developed to compensate. To address these issues, 3-terminal devices were fabricated and characterized simultaneously. These devices showed similar behaviors with the preliminary 2-step device. The IDS increased with decreasing gate biasing with a low threshold voltage -0.8 V. In addition, we observed the color changing. However, the conduction through the electrolyte resulted very low on/off ratio (<5). In conclusion, it is the conduction through the electrolyte contributes to the low on/off ratio.

  3. Intimal Thickness Is not Associated With Wall Shear Stress Patterns in the Human Right Coronary Artery

    Microsoft Academic Search

    Anil K. Joshi; Richard L. Leask; Jerry G. Myers; Matadial Ojha; Jagdish Butany; C. Ross Ethier

    2010-01-01

    Objective—Low wall shear stress has been implicated in atherogenesis throughout the arterial tree, including the right coronary artery (RCA). The objective of this study was to determine the level of covariation of intimal thickness and wall shear stress in the human RCA. Methods and Results—Postmortem histological measurements of intimal thickness were compared with wall shear stresses calculated from computational flow

  4. 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 equilibrium both vertically and horizontally, the through-thickness shear stress distribution can be calculated. The resulting shear stresses integrate to the applied shear load, are continuous at the ply interfaces, and are zero at the laminate-free surfaces. If both Qx and Qy shear loads are present, it is assumed that they act independently and that their effects can be superposed. The calculated shear stresses can be rotated within each ply to the principal material coordinates for use in a ply-level failure criterion. The novelty of the simplified shear solution method is its simplicity and the fact that it does not require solution of a particular boundary value problem. The advantages of the innovation are that an approximation of the though-thickness shear stress distribution can be quickly determined for any solid laminate or solid laminate region within a stiffened panel.

  5. Fluid shear stress threshold regulates angiogenic sprouting

    PubMed Central

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

    2014-01-01

    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/cm2 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. PMID:24843171

  6. Adjustable shear stress erosion and transport flume

    DOEpatents

    Roberts, Jesse D. (Carlsbad, NM); Jepsen, Richard A. (Carlsbad, NM)

    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.

  7. Characterization of fractures subjected to normal and shear stress

    NASA Astrophysics Data System (ADS)

    Choi, Min-Kwang

    Results from a series of laboratory experiments to determine fracture specific stiffness, for a fracture subjected to shear and normal stress, are presented and analyzed. The experimental work focuses on the determination of relations between normal and shear fracture specific stiffness and between spatial distribution of fracture specific stiffness and fluid flow through the fracture The ratio of shear to normal fracture specific stiffness is experimentally investigated on a fracture subjected to shear as well as normal stress. Synthetic fractures made of gypsum and lucite were prepared with different fracture surface conditions: either well-mated or non-mated. For well-mated fracture surfaces, asperities were created by casting gypsum against sandpaper. A block of gypsum was cast against the sandpaper and then a second block was cast against the first block such that the two contact surfaces were well-mated. The surface roughness was controlled by using the sandpapers with different average grit size. Non-mated fracture surfaces were fabricated with two lucite blocks that were polished (lucite PL) or sand-blasted (lucite SB) along their contact surface. In the experiments, each specimen was subjected to normal and shear loading while the fracture was probed with transmitted and reflected compressional and shear waves. Shear and normal fracture specific stiffnesses were calculated using the displacement discontinuity theory. For non-mated fractures, the stiffness ratio was not sensitive to the application of shear stress and, as normal stress increased, approached a theoretical ratio which was determined assuming that the transmission of compressional and shear waves was equal. The stiffness ratio obtained from well-mated fractures ranged from 0.5 to 1.4, which deviated from the conventional assumption that shear and normal fracture specific stiffness are equal. The stiffness ratio increased with increasing surface roughness and with increasing shear stress. For well-mated surfaces under normal compression and no shear, the theoretical ratio gave a good approximation to experiment measurements. During shear, at constant load, and for well-mated fractures with large surface roughness, the stiffness ratio strongly depended on the shear fracture specific stiffness and increased with shear up to a maximum prior to failure. The spatial variability of fracture specific stiffness along a fracture was investigated seismically on granite specimens with a single fracture. Seismic measurements on intact and fractured granite specimens were obtained as a function of stress. The granite matrix exhibited stress-sensitivity due to the existence of micro-cracks and was weakly anisotropic, with a ratio of about 0.9 for shear wave velocities in two orthogonal directions. For fractured granite specimens, transmission of P- and S- waves across a fracture significantly increased as the fracture compressed. The increase of transmission was interpreted as the increase of fracture specific stiffness. Spectral analysis on the transmitted waves showed that the transmission of high frequency components of the signals increased and the dinant frequency approached the value of the intact specimen. The heterogeneity of the granite material resulted in a +/-8˜12% variation in stiffness, which depended on the selection of an intact standard. Fracture specific stiffness was estimated at the dominant frequency of 0.3 MHz for normal specific stiffness and 0.5 MHz for shear. Fracture specific stiffness was non-uniformly distributed along the fracture plane and changed locally as a function of stress. The spatial variability of stiffness exceeded the variation of stiffness caused by the heterogeneity of granite matrix. It was found that local fracture geometry, e.g. local surface roughness distribution or local micro slope angles, influenced the magnitude of local shear fracture specific stiffness. The more uniform the asperity heights, the stiffer the fracture. Also, high micro-slope angles increased the shear fracture specific stiffness. The seismic res

  8. The Concept of Shear Stress in a Solid Material

    ERIC Educational Resources Information Center

    Culpin, M. F.

    1974-01-01

    Discusses problems encountered in explaining shear stress of a solid in terms of forces on a "pack of cards". Suggest the use of "pure" shear stress rather than "simple" shear stress in presentation to secure a better understanding. Included is an example illustration E occurrence of pure stress. (CC)

  9. 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.

  10. 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 shear-stress autocorrelation functions C(t ) | ? and C(t ) | ? computed, respectively, at imposed strain ? and mean stress ? . Focusing on permanent isotropic spring networks it is shown theoretically and computationally that in general G(t ) =C (t ) | ?=C(t ) | ?+Geq for t >0 with Geq being the static equilibrium shear modulus. G (t ) and C(t ) | ? thus must become different for solids and it is impossible to obtain Geq alone from C(t ) | ? 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 ) | ?=C(t ) | ? should reveal an intermediate plateau set by the shear modulus Geq(f =0 ) of the quenched network.

  11. Phase-Contrast MRI measurements in intra-cranial aneurysms in-vivo of flow patterns, velocity fields and wall shear stress: A comparison with CFD

    PubMed Central

    Boussel, Loic; Rayz, Vitaliy; Martin, Alastair; Acevedo-Bolton, Gabriel; Lawton, Michael T.; Higashida, Randall; Smith, Wade S.; Young, William L.; Saloner, David

    2010-01-01

    Evolution of intracranial aneurysms is known to be related to hemodynamic forces such as Wall Shear Stress (WSS) and Maximum Shear Stress (MSS). Estimation of these parameters can be performed using numerical simulations (computational fluid dynamics - CFD) but can also be directly measured with MRI using a time-dependent 3D phase-contrast sequence with encoding of each of the three components of the velocity vectors (7D-MRV). In order to study the accuracy of 7D-MRV in estimating these parameters in–vivo, in comparison with CFD, 7D-MRV and patient-specific CFD modeling was performed for three patients who had intracranial aneurysms. A visual and a quantitative analysis of the flow pattern and the distribution of velocities, MSS, and WSS were performed between the two techniques. Spearman's coefficients of correlation between the two techniques were 0.56 for the velocity field, 0.48 for MSS and 0.59 for WSS. Visual analysis and Bland-Altman plots showed a good agreement for flow pattern and velocities but large discrepancies for MSS and WSS. In conclusion, these results indicate that in-vivo 7D-MRV can be used to measure velocity flow fields and to estimate MSS and WSS but is not currently able to provide accurate quantification of these two last parameters. PMID:19161132

  12. BOUNDARY SHEAR STRESS ALONG VEGETATED STREAMBANKS

    EPA Science Inventory

    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 resu...

  13. Determining flow type, shear rate and shear stress in magmas from bubble shapes and orientations

    Microsoft Academic Search

    A. C. Rust; Michael Manga; K. V. Cashman

    2003-01-01

    We interpret the shear environments that produced bubble textures in obsidian samples using the results of theoretical, numerical and experimental studies on the deformation of bubbles in shear flows. In particular, we use the shapes and orientations of bubbles (vesicles) in obsidian to estimate shear rates and shear stresses, and assess flow type (simple vs. pure shear). This technique can

  14. Anticonstrictor effect of endothelium sensitivity to shear stress

    Microsoft Academic Search

    Arthur M. Melkumyants; Sergey A. Balashov; Sergey P. Kartamyshev

    1994-01-01

    The lumen of arterial vessels is controlled by shear stress at the endothelium; increased shear stress relaxes the smooth\\u000a muscle thus evoking arterial dilatation. Since shear stress relates directly to flow rate and inversely to the third power\\u000a of the internal diameter, a decrease in diameter at a constant arterial blood flow augments the shear stress which should\\u000a result in

  15. Yield stress and shear-banding in granular suspensions

    E-print Network

    Abdoulaye Fall; Francois Bertrand; Guillaume Ovarlez; Daniel Bonn

    2009-07-13

    We study the emergence of a yield stress in dense suspensions of non-Brownian particles, by combining local velocity and concentration measurements using Magnetic Resonance Imaging with macroscopic rheometric experiments. We show that the competition between gravity and viscous stresses is at the origin of the development of a yield stress in these systems at relatively low volume fractions. Moreover, it is accompanied by a shear banding phenomenon that is the signature of this competition. However, if the system is carefully density matched, no yield stress is encountered until a volume fraction of 62.7 0.3%.

  16. 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.

  17. A tapered channel microfluidic device for comprehensive cell adhesion analysis, using measurements of detachment kinetics and shear stress-dependent motion

    PubMed Central

    Rupprecht, Peter; Golé, Laurent; Rieu, Jean-Paul; Vézy, Cyrille; Ferrigno, Rosaria; Mertani, Hichem C.; Rivière, Charlotte

    2012-01-01

    We have developed a method for studying cellular adhesion by using a custom-designed microfluidic device with parallel non-connected tapered channels. The design enables investigation of cellular responses to a large range of shear stress (ratio of 25) with a single input flow-rate. For each shear stress, a large number of cells are analyzed (500–1500 cells), providing statistically relevant data within a single experiment. Besides adhesion strength measurements, the microsystem presented in this paper enables in-depth analysis of cell detachment kinetics by real-time videomicroscopy. It offers the possibility to analyze adhesion-associated processes, such as migration or cell shape change, within the same experiment. To show the versatility of our device, we examined quantitatively cell adhesion by analyzing kinetics, adhesive strength and migration behaviour or cell shape modifications of the unicellular model cell organism Dictyostelium discoideum at 21?°C and of the human breast cancer cell line MDA-MB-231 at 37?°C. For both cell types, we found that the threshold stresses, which are necessary to detach the cells, follow lognormal distributions, and that the detachment process follows first order kinetics. In addition, for particular conditions’ cells are found to exhibit similar adhesion threshold stresses, but very different detachment kinetics, revealing the importance of dynamics analysis to fully describe cell adhesion. With its rapid implementation and potential for parallel sample processing, such microsystem offers a highly controllable platform for exploring cell adhesion characteristics in a large set of environmental conditions and cell types, and could have wide applications across cell biology, tissue engineering, and cell screening. PMID:22355300

  18. Boundary layer shear stress in subsonic and supersonic flow

    NASA Technical Reports Server (NTRS)

    Sandborn, V. A.; Horstman, C. C.

    1977-01-01

    A wide range of shear stress distributions for turbulent boundary layers is examined. A solution for the shear stress in terms of the mean flow is obtained for the limiting case of large Reynolds numbers. Attention is given to turbulent boundary layer shear stress, zero pressure gradient flow, increasing pressure gradient flow, and decreasing pressure gradient flow.

  19. The role of dilation and confining stresses in shear thickening of dense suspensions

    E-print Network

    Eric Brown; Heinrich M. Jaeger

    2012-01-05

    Many densely packed suspensions and colloids exhibit a behavior known as Discontinuous Shear Thickening in which the shear stress jumps dramatically and reversibly as the shear rate is increased. We performed rheometry and video microscopy measurements on a variety of suspensions to determine the mechanism for this behavior. Shear profiles and normal stress measurements indicate that, in the shear thickening regime, stresses are transmitted through frictional rather than viscous interactions, and come to the surprising conclusion that the local constitutive relation between stress and shear rate is not necessarily shear thickening. If the suspended particles are heavy enough to settle we find the onset stress of shear thickening tau_min corresponds to a hydrostatic pressure from the weight of the particle packing where neighboring particles begin to shear relative to each other. Above tau_min, dilation is seen to cause particles to penetrate the liquid-air interface of the sheared sample. The upper stress boundary tau_max of the shear thickening regime is shown to roughly match the ratio of surface tension divided by a radius of curvature on the order of the particle size. These results suggest a new model in which the increased dissipation in the shear thickening regime comes from frictional stresses that emerge as dilation is frustrated by a confining stress from surface tension at the liquid-air interface. When instead the suspensions are confined by solid walls and have no liquid-air interface, we find tau_max is set by the stiffness of the most compliant boundary which frustrates dilation. This rheology can be described by a non-local constitutive relation in which the local relation between stress and shear rate is shear thinning, but where the stress increase comes from a normal stress term which depends on the global dilation.

  20. 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

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

    PubMed

    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

  2. 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.

  3. Shear stress and advanced atherosclerosis in human coronary arteries.

    PubMed

    Gijsen, Frank; van der Giessen, Alina; van der Steen, Anton; Wentzel, Jolanda

    2013-01-18

    The role of low and oscillating shear stress as a key factor for localizing early atherosclerotic plaques is generally accepted. Once more advanced plaques protrude into the lumen, the shear stress they are exposed to changes. The influence of shear stress on plaque composition in advanced atherosclerosis is not fully understood. In this review, we discuss our recent studies on the relationship between shear stress and plaque composition and the location of plaque rupture in human coronary arteries. We have shown that elevated shear stress levels can be found over plaques inducing only mild luminal narrowing and are not subjected to treatment. Regional exposure of certain plaque regions to high shear stress is therefore a condition that will pertain for a prolonged period of time. We have also shown that in more advanced atherosclerosis the necrotic core experiences higher shear stress. Low shear stress plaque regions can be found downstream of the plaque and are stiffer. High shear stress plaque regions can be found either at the upstream, shoulder or cap region of the plaque and are softer. The plaque regions with the highest strain levels are the regions that are exposed to the highest shear stress. The high shear stress plaque regions are the only plaque regions that get softer over time. Finally, high shear stress is also associated with the location of plaque rupture in non-culprit lesion in human coronary arteries. Combining our findings with data from literature, we can conclude that advanced coronary plaques grow in the distal regions. The distal plaque regions are exposed to low shear stress, are stiffer and have a stable plaque phenotype. The regions exposed to high shear stress are softer, and are associated with vulnerable plaque features. PMID:23261245

  4. Direct Measurement of Turbulent Shear

    NASA Astrophysics Data System (ADS)

    Stefanus, Stefanus; Steers, Stanley; Goldburg, Walter

    2010-11-01

    Photon Correlation Spectroscopy (PCS) is used to directly measure the mean shear rate s in a turbulent soap film. A 5 mW 633 nm He-Ne laser is focused on the film at a point r, the spot size being w =100 ?m. The scattered light intensity I(t) is analyzed by a correlator that measures the average, over time t, of the correlation function G(?) = /shear s averaged over w and the standard deviation of s. Of special interest is the shear at points r near a solid boundary. The PCS measurements of s (in Hz) are compared with those obtained by laser Doppler velocimetry (LDV). The two techniques yield values of s that agree within a standard deviation. The PCS method has the advantage of compactness and rapid data collection, making it of potential use in biology and medicine. By changing the orientation of the incident and scattered beams, one can measure various components of the shear tensor. The implementation of the PCS method does not require the presence of a mean flow. It can also be applied to three-dimensional turbulence.

  5. 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.

  6. 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.

  7. Influence of particle shape on shear stress in granular media

    E-print Network

    Paris-Sud XI, Université de

    fabric and force anisotropies in shear are responsible for mechanical strength at the scaleInfluence of particle shape on shear stress in granular media Emilien Az´ema1 , Farhang Radja¨i1 of the packing [11, 12, 13, 10]. The shear stress is fully trans- mitted via a "strong" contact network

  8. 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.

  9. 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.

  10. Acoustic shear wave displacement measurement using ultrasound

    Microsoft Academic Search

    Vinayak Dutt; Randall R. Kinnick; James F. Greenleaf

    1996-01-01

    Echo ultrasound can be used to detect and measure acoustic shear waves. Earlier it has been shown that a phase contrast based magnetic resonance imaging technique can be used for cyclic shear wave displacement measurement. Echo ultrasound presents an alternate method for imaging of such shear waves. The ultrasound based method uses the phase of quadrature echo signals to estimate

  11. 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., [Department of Geology and Geophysics, University of Adelaide (Australia); Younker, L.W. [Lawrence Livermore National Lab., CA (United States)

    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.

  12. Determining ow type, shear rate and shear stress in magmas from bubble shapes and orientations

    E-print Network

    Manga, Michael

    the shear environments that produced bubble textures in obsidian samples using the results of theoretical the shapes and orientations of bubbles (vesicles) in obsidian to estimate shear rates and shear stresses conduits, the origin of pyroclastic obsidian, and the emplacement history and dynamics of obsidian flows

  13. 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.

  14. The role of shear stress in the pathogenesis of atherosclerosis

    Microsoft Academic Search

    Kristopher S Cunningham; Avrum I Gotlieb

    2005-01-01

    Although the pathobiology of atherosclerosis is a complex multifactorial process, blood flow-induced shear stress has emerged as an essential feature of atherogenesis. This fluid drag force acting on the vessel wall is mechanotransduced into a biochemical signal that results in changes in vascular behavior. Maintenance of a physiologic, laminar shear stress is known to be crucial for normal vascular functioning,

  15. 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.

  16. Shear Response of Molecularly Thin Liquid Films to an Applied Air Stress

    Microsoft Academic Search

    C. Mathew Mate; Bruno Marchon

    2000-01-01

    The shear response of molecularly thin liquid films on solid substrates when subjected to an applied air stress has been measured. The response corresponds to viscous friction while the same films sheared between two solid surfaces display static friction. These results show that molecularly thin liquid films partially confined by a single solid surface do not solidify as when confined

  17. 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.

  18. 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 indicate that shear stress is an important physical control on benthic macroinvertebrate drift, even at shear stress values lower than those required for bed sediment mobilization. This empirical relationship between shear stress and drift can aid in the prediction of drift concentrations at different discharges and may inform habitat-specific prey density estimates used in bioenergetics models for drift-feeding trout.

  19. [Influence of fluid shear stress on cultured vascular endothelial cells].

    PubMed

    Takakuwa, O

    1990-03-01

    Vascular endothelial cells modulate their functions in response to hemodynamic forces such as fluid shear stress. In the present study, we applied shear to cultured bovine aortic endothelial cells (EC) by using a saecially designed apparatus and examined the effects of their homogenate and conditioned medium on such EC and smooth muscle cell (SMC) functions as adhesion, growth, migration or collagen synthesis. Cultured bovine aortic SMC were stimulated to adhere to wells and grow in the presence of EC conditioned medium. This conditioned medium had no effect on EC adhesion and growth. The activities of stimulating SMC adhesion and growth were almost the same in both EC conditioned medium obtained from static cultures and shear-loaded cultures. Studies with filters in a modified Boyden chamber showed that shear-loaded EC homogenate yielded stimulated SMC migration. Also shear-loaded EC cell layer contained increased amount of collagen compared with static EC cell layer. These observations indicate that:(a) EC secrets the substances which stimulate SMC adhesion and growth, but these functions are not affected by shear stress application, (b) EC produces SMC migration stimulators in response to shear stress, and (c) shear stress can enhance EC collagen synthesis. These results are relevant to EC response to hemodynamic forces and its role in the localization of atherosclerotic lesions in vivo. PMID:2365276

  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)

    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.

  1. 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

  2. SHEAR-WAVE SPLITTING, THE NEW GEOPHYSICS, AND EARTHQUAKE STRESS-FORECASTING SHEAR-WAVE SPLITTING, NEW GEOPHYSICS, AND

    E-print Network

    SHEAR-WAVE SPLITTING, THE NEW GEOPHYSICS, AND EARTHQUAKE STRESS-FORECASTING 1 ___________________________________________ SHEAR-WAVE SPLITTING, NEW GEOPHYSICS, AND EARTHQUAKE STRESS-FORECASTING understanding of fluid-rock deformation: a New Geophysics, where earthquakes can be stress-forecast. Shear

  3. Analysis of the Normal Stress Differences of Viscoelastic Fluids under Large Amplitude Oscillatory Shear Flow

    NASA Astrophysics Data System (ADS)

    Nam, Jung Gun; Hyun, Kyu; Ahn, Kyung Hyun; Lee, Seung Jong

    2008-07-01

    The dynamic response of viscoelastic fluids under large amplitude oscillatory shear (LAOS) has been a subject of long history. In the LAOS flow, the analysis has been mostly focused on shear stress, possibly due to the lack of accurate measurement of normal stresses. However, as the instrumentation advances, it becomes possible to get more reliable data. The development of normal stresses under LAOS flow is a significant nonlinear effect that has been hardly obtainable in previous studies. Analyzing the normal stresses will be helpful in understanding and characterizing nonlinear viscoelastic behavior. In this work, we investigated the behavior of normal stress difference under LAOS flow using viscoelastic fluids including Boger fluid and polyethylene oxide aqueous solution. The first normal stress difference was measured and it was sinusoidal at a frequency twice that of the excitation frequency because of its dependence only on the magnitude of the strain, not on the direction of its operation. It showed a displacement that was equal to the elastic modulus multiplied by the square of the strain amplitude. It was also found that the shape of the first normal stress difference strongly depended on shear strain and frequency. At higher frequency, they showed asymmetric patterns in contrast to the shear stress, and the first normal stress difference became larger in magnitude than the shear stress. And higher harmonics of the first normal stress difference which are the sum of even functions were compared with that of shear stress in terms of Fourier spectra, which was also performed with the help of constitutive equations.

  4. 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.

  5. 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).

  6. Shear Stress-Triggered Nitric Oxide Release From Schlemm's Canal Cells

    PubMed Central

    Ashpole, Nicole E.; Overby, Darryl R.; Ethier, C. Ross; Stamer, W. Daniel

    2014-01-01

    Purpose. Endothelial nitric oxide (NO) synthase is regulated by shear stress. At elevated intraocular pressures when the Schlemm's canal (SC) begins to collapse, shear stress is comparable with that in large arteries. We investigated the relationship between NO production and shear stress in cultured human SC cells. Methods. Schlemm's canal endothelial cells isolated from three normal and two glaucomatous human donors were seeded into Ibidi flow chambers at confluence, cultured for 7 days, and subjected to steady shear stress (0.1 or 10 dynes/cm2) for 6, 24, or 168 hours. Cell alignment with flow direction was monitored, and NO production was measured using 4-amino-5-methylamino-2?,7?-difluorofluorescein (DAF-FM) and Griess reagents. Human trabecular meshwork (TM) and umbilical vein endothelial cells (HUVECs) were used as controls. Results. Normal SC strains aligned with the direction of flow by 7 days. Comparing 0.1 vs. 10 dynes/cm2, NO levels increased by 82% at 24 hours and 8-fold after 7 days by DAF-FM, and similar results were obtained with Griess reagent. Shear responses by SC cells at 24 hours were comparable with HUVECs, and greater than TM cells, which appeared shear-insensitive. Nitric oxide production by SC cells was detectable as early as 6 hours and was inhibited by 100 ?M nitro-L-arginine methyl ester. Two glaucomatous SC cell strains were either unresponsive or lifted from the plate in the face of shear. Conclusions. Shear stress triggers NO production in human SC cells, similar to other vascular endothelia. Increased shear stress and NO production during SC collapse at elevated intraocular pressures may in part mediate IOP homeostasis. PMID:25395486

  7. 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.

  8. 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.

  9. A PZT-based smart aggregate for seismic shear stress monitoring

    NASA Astrophysics Data System (ADS)

    Hou, S.; Zhang, H. B.; Ou, J. P.

    2013-06-01

    A lead zirconate titanate (PZT)-based smart aggregate (SA) is proposed for seismic shear stress monitoring in concrete structures. This SA uses a d15-mode PZT as the sensing element. A calibration test is designed in which a cyclic shear stress with a dominant frequency of the earthquake response spectrum is applied on the two opposite sides of the proposed SA using a specially designed loading mold. The test is repeated on six copies of the proposed SA. The maximum applied shear stress is larger than the shear strength of ordinary concrete to allow measurements during failure. The output voltage of the SA is experimentally verified as varying linearly with the applied stress in the loading range. The sensitivity of the proposed SA to the applied stress under the given boundary conditions is examined. The calibrated sensitivity value is then compared with the calculated value, which is obtained by computing the stress distribution in the SA using finite element analysis (FEA). The calculated values and the calibrated values are approximately the same, indicating that the established finite element (FE) model is reliable. Monotonic loading is also applied on the proposed SA to induce cracks between the SA and the loading mold, and the SA’s response to cracking processes is examined. It is found that the proposed SA underestimates the cracking process. This study demonstrates that the proposed SA can be used in monitoring the overall shear stress development process in concrete during a seismic event.

  10. Precursor Suppression by Shear Stress Relaxation in U-Nb(6-wt%)

    NASA Astrophysics Data System (ADS)

    Hayes, D. B.; Gray, G. T.; Hixson, R. S.; Zurek, A. K.; Vorthman, J. E.; Anderson, W. W.

    2004-07-01

    U-Nb(6-wt%) exhibits plastic yield strength of a few-tenths of a GPa that can vary depending upon the starting microstructure and heat-treatment. However, when a several-mm thick specimen of U-Nb(6-wt%) is shock loaded in the range between 1.5 and 10 GPa, no elastic precursor is observed in interferometer measurements at the rear free surface. The absence of the elastic precursor and other features of the compression and release measurements are explained by assuming shear stress-relaxation rate is dependent upon the shear stress. The resulting stress waves are unsteady and broaden so that shear stress relaxation can occur in the front preventing the plastic yield point from being reached. U-Nb(6-wt%) is known to twin in quasi-static compression and shear-induced, rate-dependent twinning is likely the underlying cause for shear stress relaxation in our experiments. Recent experiments in which U-Nb(6-wt%) was heavily cold-rolled ( work-hardening to ˜25% strain) display no evidence of a precursor, admitting the possibility of a pressure or temperature induced stress-relaxation process.

  11. Measurement of shear impedances of viscoelastic fluids

    SciTech Connect

    Sheen, Shuh-Haw; Chien, Hual-Te; Raptis, A.C.

    1996-12-31

    Shear-wave reflection coefficients from a solid/fluid interface are derived for non-Newtonian fluids that can be described by Maxwell, Voigt, and power-law fluid models. Based on model calculations, we have identified the measurable effects on the reflection coefficients due to fluid non-Newtonian behavior. The models are used to interpret the viscosity data obtained by a technique based on shear impedance measurement.

  12. Shear Strength Measurements in a Shock Loaded Alumina-Filled Epoxy Resin

    Microsoft Academic Search

    K. Kos; J. C. F. Millett; N. K. Bourne; D. Deas

    2005-01-01

    The variation of shear strength with impact stress in an alumina-filled epoxy has been measured with lateral stress gauges. At lower stresses, a degree of hardening behind the shock front has been observed, which decreases as impact stress increases. It is believed that this is due to a transition from a viscous response dominated by the epoxy matrix, to a

  13. Development of a MEMS shear stress sensor for use in wind tunnel applications

    NASA Astrophysics Data System (ADS)

    Barnard, Casey; Meloy, Jessica; Sheplak, Mark; Interdisciplinary Microsystems Group Team

    2013-11-01

    The measurement of mean and fluctuating wall shear-stress in laminar, transitional, and turbulent boundary layers and channel flows has applications both in industry and the scientific community. Currently there is no method for time resolved, direct measurement of wall shear stress at the spatial and temporal scales of turbulent flow structures inside model testing facilities. To address this need, a silicon micromachined differential capacitance shear stress sensor system has been developed. Mean measurements are enabled by custom synchronous modulation/demodulation circuitry, which allows for measurement of both magnitude and phase of incident wall shear stress. Sizes of the largest device features are on the order of relevant viscous length scales, to minimize flow disturbance and provide a hydraulically smooth sensing surface. Static calibration is performed in a flow cell setup, and an acoustic plane wave tube is used for dynamic response data. Normalized sensitivity of 1.34 mV/V/Pa has been observed over a bandwidth of 4.8 kHz, with a minimum detectable signal of 6.5 mPa. Initial results show qualitative agreement with contemporary measurement techniques. The design, fabrication, support electronics, characterization, and preliminary experimental performance of this sensor will be presented. The measurement of mean and fluctuating wall shear-stress in laminar, transitional, and turbulent boundary layers and channel flows has applications both in industry and the scientific community. Currently there is no method for time resolved, direct measurement of wall shear stress at the spatial and temporal scales of turbulent flow structures inside model testing facilities. To address this need, a silicon micromachined differential capacitance shear stress sensor system has been developed. Mean measurements are enabled by custom synchronous modulation/demodulation circuitry, which allows for measurement of both magnitude and phase of incident wall shear stress. Sizes of the largest device features are on the order of relevant viscous length scales, to minimize flow disturbance and provide a hydraulically smooth sensing surface. Static calibration is performed in a flow cell setup, and an acoustic plane wave tube is used for dynamic response data. Normalized sensitivity of 1.34 mV/V/Pa has been observed over a bandwidth of 4.8 kHz, with a minimum detectable signal of 6.5 mPa. Initial results show qualitative agreement with contemporary measurement techniques. The design, fabrication, support electronics, characterization, and preliminary experimental performance of this sensor will be presented. The support of NASA SFW-NRA NNX11AI30A, AFOSR grant #FA 9550-12-1-0469, and Sandia Campus Executive Fellowship are gratefully acknowledged.

  14. Accurate shear measurement with faint sources

    NASA Astrophysics Data System (ADS)

    Zhang, Jun; Luo, Wentao; Foucaud, Sebastien

    2015-01-01

    For cosmic shear to become an accurate cosmological probe, systematic errors in the shear measurement method must be unambiguously identified and corrected for. Previous work of this series has demonstrated that cosmic shears can be measured accurately in Fourier space in the presence of background noise and finite pixel size, without assumptions on the morphologies of galaxy and PSF. The remaining major source of error is source Poisson noise, due to the finiteness of source photon number. This problem is particularly important for faint galaxies in space-based weak lensing measurements, and for ground-based images of short exposure times. In this work, we propose a simple and rigorous way of removing the shear bias from the source Poisson noise. Our noise treatment can be generalized for images made of multiple exposures through MultiDrizzle. This is demonstrated with the SDSS and COSMOS/ACS data. With a large ensemble of mock galaxy images of unrestricted morphologies, we show that our shear measurement method can achieve sub-percent level accuracy even for images of signal-to-noise ratio less than 5 in general, making it the most promising technique for cosmic shear measurement in the ongoing and upcoming large scale galaxy surveys.

  15. An intriguing empirical rule for computing the first normal stress difference from steady shear viscosity data for concentrated polymer solutions and melts

    E-print Network

    Sharma, Vivek

    The Cox–Merz rule and Laun’s rule are two empirical relations that allow the estimation of steady shear viscosity and first normal stress difference, respectively, using small amplitude oscillatory shear measurements. The ...

  16. Reynolds stress and effects of external and self-generated shear flows S. B. Korsholm. P. K. Michelsen, V. Naulin, and J. Juul Rasmussen

    E-print Network

    Reynolds stress and effects of external and self-generated shear flows S. B. Korsholm. P. K interest. As presented analytically in [1] the so-called Reynolds stress gives a measure of the self. A measurement of the Reynolds stress can thus help to predict flows, e.g. shear flows in plasmas as demonstrated

  17. Effect of thermal expansion mismatch and fiber coating on the fiber/matrix interfacial shear stress in ceramic matrix composites

    SciTech Connect

    Brun, M.K.; Singh, R.N. (General Electric Corporate Research and Development, Schenectady, NY (USA))

    1988-09-01

    A modified indentation technique has been used to measure the interfacial shear stress in a number of ceramic matrices containing silicon carbide fibers. It was shown that the frictional component of interfacial stress was essentially zero when matrix thermal expansion was lower than that of the fiber and increased linearly with thermal expansion mismatch when matrix thermal expansion was higher. The interfacial shear stress was lowered when the fibers were coated with BN. Lower matrix shear stresses resulted in a more extensive fiber pullout during the composite fracture.

  18. Rheometry of granular materials in cylindrical Couette cells: Anomalous stress caused by gravity and shear

    NASA Astrophysics Data System (ADS)

    Gutam, Kamala Jyotsna; Mehandia, Vishwajeet; Nott, Prabhu R.

    2013-07-01

    The cylindrical Couette device is commonly employed to study the rheology of fluids, but seldom used for dense granular materials. Plasticity theories used for granular flows predict a stress field that is independent of the shear rate, but otherwise similar to that in fluids. In this paper we report detailed measurements of the stress as a function of depth, and show that the stress profile differs fundamentally from that of fluids, from the predictions of plasticity theories, and from intuitive expectation. In the static state, a part of the weight of the material is transferred to the walls by a downward vertical shear stress, bringing about the well-known Janssen saturation of the stress in vertical columns. When the material is sheared, the vertical shear stress changes sign, and the magnitudes of all components of the stress rise rapidly with depth. These qualitative features are preserved over a range of the Couette gap and shear rate, for smooth and rough walls and two model granular materials. To explain the anomalous rheological response, we consider some hypotheses that seem plausible a priori, but show that none survive after careful analysis of the experimental observations. We argue that the anomalous stress is due to an anisotropic fabric caused by the combined actions of gravity, shear, and frictional walls, for which we present indirect evidence from our experiments. A general theoretical framework for anisotropic plasticity is then presented. The detailed mechanics of how an anisotropic fabric is brought about by the above-mentioned factors is not clear, and promises to be a challenging problem for future investigations.

  19. Albumin Permeability across Endothelial Monolayers under Long-Term Shear Stress

    NASA Astrophysics Data System (ADS)

    Kudo, Susumu; Tsuzaka, Masanori; Ikeda, Mariko; Tanishita, Kazuo

    Endothelial cells lining the inner surface of blood vessels regulate the exchange of molecules between the blood and the vessel wall. This study investigates the effect of long-term shear stress on macromolecule permeability across endothelial monolayers. In vitro system to measure transendothelial permeability to tetramethylrhodamine conjugated albumin under shear stress was developed. The temporal variation in albumin permeability under 1Pa and 4Pa over 48h was quantified using a fluorescence spectrophotometer. At 4Pa, albumin permeability did not show a statistical significant change over 48h. Under shear stress of 1Pa, the average albumin permeability between 12 and 30h was 2.5-fold higher than the average between 0 and 6h. Under shear stress of 1Pa, the average albumin permeability between 36 and 48h was 1.8-fold higher than the average between 12 and 30h. These results show that both the magnitude of, and the length of exposure to, shear stress regulate transendothelial permeability.

  20. The Strength of the Earth's Crust under Horizontal Shear Stress

    Microsoft Academic Search

    M. A. Chinnery

    1964-01-01

    Recent theoretical expressions for the change in stress distribution caused by strike-slip faulting are applied to five real faults, and estimates are made of the maximum shear stress relieved in each case. The calculated values lie between 107 and 10 s dynes\\/cm , and reasonable refinements of the assumptions involved in the cMculation (particularly in the value of the coefficient

  1. On the temperature dependence of the critical resolved shear stress of the ? ?-strengthened superalloy NIMONIC PE16

    Microsoft Academic Search

    Angelika Vennemann; Eckhard Langmaack; Eckhard Nembach

    2002-01-01

    The temperature dependence of ??-strengthening of the commercial nickel-base superalloy NIMONIC PE16 has been investigated by measuring the critical resolved shear stress in the temperature range 373–1173 K and observing the resulting slip line patterns.

  2. An evaluation of the Iosipescu specimen for composite materials shear property measurement

    NASA Technical Reports Server (NTRS)

    Morton, J.; Ho, H.; Tsai, M. Y.; Farley, G. L.

    1992-01-01

    A detailed evaluation of the suitability of the Iosipescu specimen tested in the modified Wyoming fixture is presented. A linear finite element model of the specimen is used to assess the uniformity of the shear stress field in the vicinity of the notch, and demonstrate the effect of the nonuniform stress field upon strain gage measurements used for the determination of composite shear moduli. Based upon test results from graphite-epoxy laminates, the proximity of the load introduction point to the test section and the material orthotropy greatly influence the individual gage readings, however, shear modulus determination is not significantly affected by the lack of pure shear. Correction factors are needed to allow for the nonuniformity of the strain field and the use of the average shear stress in the shear modulus evaluation. The correction factors are determined for the region occupied by the strain gage rosette. A comparison of the strain gage readings from one surface of a specimen with corresponding data from moire interferometry on the opposite face documented an extreme sensitivity of some fiber orientations to eccentric loading which induced twisting and spurious shear stress-strain curves. The discovery of specimen twisting explains the apparently inconsistent shear property data found in the literature. Recommendations for improving the reliability and accuracy of the shear modulus values are made, and the implications for shear strength measurement discussed.

  3. Transient Shear Banding in a Simple Yield Stress Fluid

    E-print Network

    Thibaut Divoux; David Tamarii; Catherine Barentin; Sébastien Manneville

    2010-02-28

    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 $\\dot\\gamma$. 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 $\\dot\\gamma\\lesssim 0.1$ s$^{-1}$, heterogeneous flows could be observed for as long as 10$^5$ s. These local dynamics account for the ultraslow stress relaxation observed at low shear rates.

  4. Measuring shear modulus of individual fibers

    NASA Astrophysics Data System (ADS)

    Behlow, Herbert; Saini, Deepika; Oliviera, Luciana; Skove, Malcolm; Rao, Apparao

    2014-03-01

    Fiber technology has advanced to new heights enabling tailored mechanical properties. For reliable fiber applications their mechanical properties must be well characterized at the individual fiber level. Unlike the tensile modulus, which can be well studied in a single fiber, the present indirect and dynamic methods of measuring the shear properties of fibers suffer from various disadvantages such as the interaction between fibers and the influence of damping. In this talk, we introduce a quasi-static method to directly measure the shear modulus of a single micron-sized fiber. Our simple and inexpensive setup yields a shear modulus of 16 and 2 GPa for a single IM7 carbon fiber and a Kevlar fiber, respectively. Furthermore, our setup is also capable of measuring the creep, hysteresis and the torsion coefficient, and examples of these will be presented.

  5. A shearing technique measuring resistance properties of plant stems

    Microsoft Academic Search

    A. D. Iwaasa; K. A. Beauchemin; J. G. Buchanan-Smith; S. N. Acharya

    1996-01-01

    A shearing technique was developed to measure fracturing properties of plant stems. Shearing force measurements assess the amount of energy required to fragment plant tissue as an indication of resistance to particle breakdown during mastication. The objective of this study was to develop a rapid and inexpensive method of accurately measuring the shearing properties of forage stems. Shearing properties of

  6. Characterization of the brachial artery shear stress following walking exercise

    Microsoft Academic Search

    Jaume Padilla; Ryan A Harris; Lawrence D Rink; Janet P Wallace

    Habitual exercise provides repeated episodes of elevated vascular shear stress (SS), which may be a mechanism for repair of endothelial dysfunction in dis- ease. Our aim was to determine the brachial artery SS during the 3-hour period fol- lowing single bouts of low, moderate, and high-intensity walking exercise. In a ran- domized crossover design, 14 men walked for 45 minutes

  7. 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. PMID:23363216

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

    Technology Transfer Automated Retrieval System (TEKTRAN)

    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...

  9. EHL Film Thickness Limitation Theory Under a Limiting Shear Stress

    Microsoft Academic Search

    Yongbin Zhang; Shizhu Wen

    2002-01-01

    It is numerically shown that the elastohydrodynamic lubrication (EHL) film thickness has a limit under an assumed limiting shear stress of the contact-lubricant interface in isothermal pure rolling line contacts. The prediction of the central film thickness limit is made, and well matches experiments. The present theory shows that, in elastohydrodynamic line contacts, the central film thickness is of molecular

  10. Micromachined Nickel Floating Element Shear Stress Sensor Array , J. Gallmanb

    E-print Network

    White, Robert D.

    Micromachined Nickel Floating Element Shear Stress Sensor Array Z. Zhaoa , J. Gallmanb , R. Whitea (Technic Copper FB) and patterned lithographically. A Nickel structural layer with varied thickness is deposited from a nickel sulfamate plating solution (Technic Nickel Sulfamate SemiBright) and patterned

  11. Shapelets "multiple multipole" shear measurement methods

    E-print Network

    Richard Massey; Alexandre Refregier; David Bacon

    2004-08-31

    The measurement of weak gravitational lensing is currently limited to a precision of ~10% by instabilities in galaxy shape measurement techniques and uncertainties in their calibration. The potential of large, on-going and future cosmic shear surveys will only be realised with the development of more accurate image analysis methods. We present a description of several possible shear measurement methods using the linear "shapelets" decomposition. Shapelets provides a complete reconstruction of any galaxy image, including higher-order shape moments that can be used to generalise the KSB method to arbitrary order. Many independent shear estimators can then be formed for each object, using linear combinations of shapelet coefficients. These estimators can be treated separately, to improve their overall calibration; or combined in more sophisticated ways, to eliminate various instabilities and a calibration bias. We apply several methods to simulated astronomical images containing a known input shear, and demonstrate the dramatic improvement in shear recovery using shapelets. A complete IDL software package to perform image analysis and manipulation in shapelet space can be downloaded from the shapelets web site at http://www.astro.caltech.edu/~rjm/shapelets/ .

  12. Effects of fluid shear stress on polyelectrolyte multilayers by neutron scattering studies.

    PubMed

    Singh, Saurabh; Junghans, Ann; Watkins, Erik; Kapoor, Yash; Toomey, Ryan; Majewski, Jaroslaw

    2015-03-10

    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. A theoretical explanation is given to explain this difference in the effect of shear on hydration of polymeric thin films. PMID:25689755

  13. Estimation of the bed shear stress in vegetated and bare channels with smooth beds

    NASA Astrophysics Data System (ADS)

    Yang, Judy Q.; Kerger, Francois; Nepf, Heidi M.

    2015-05-01

    The shear stress at the bed of a channel influences important benthic processes such as sediment transport. Several methods exist to estimate the bed shear stress in bare channels without vegetation, but most of these are not appropriate for vegetated channels due to the impact of vegetation on the velocity profile and turbulence production. This study proposes a new model to estimate the bed shear stress in both vegetated and bare channels with smooth beds. The model, which is supported by measurements, indicates that for both bare and vegetated channels with smooth beds, within a viscous sublayer at the bed, the viscous stress decreases linearly with increasing distance from the bed, resulting in a parabolic velocity profile at the bed. For bare channels, the model describes the velocity profile in the overlap region of the Law of the Wall. For emergent canopies of sufficient density (frontal area per unit canopy volume a?4.3 m-1), the thickness of the linear-stress layer is set by the stem diameter, leading to a simple estimate for bed shear stress.

  14. 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, ? , follows a nontrivial dependence on the packing fraction, ? , and the capillary energy, ? . Most noticeably, we show that ? is a generic and universal quantity which does not depend on the driving protocol. Using this universal quantity, we calculate the arrest stress, ?a, 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 ?a is a nonlinear function of the packing fraction, ? , and the capillary energy, ? . 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.

  15. 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 effective temperature. PMID:22526981

  16. Experimental detection of flow separation over a plain flap by wall shear stress analysis with and without steady blowing

    NASA Astrophysics Data System (ADS)

    Chabert, Timothée; Dandois, Julien; Garnier, Éric; Jacquin, Laurent

    2014-06-01

    The present article deals with the flow separation detection over a plain flap at a Reynolds number of 2?106 by the analysis of the wall shear stress fluctuations. Natural flow separation is first considered with the study of the evolution of wall shear stress fluctuations measured along the flap chord when the flap deflection angle is progressively increased. Then, steady blowing is applied and its effect on wall shear stress fluctuations is analysed. For both controlled and uncontrolled cases, flow separation criteria are defined, studied and compared. xml:lang="fr"

  17. In vivo wall shear stress and flow reversal in canine thoracic aortae 

    E-print Network

    Dunn, Carl Anthony

    1982-01-01

    velocities and wall shear stresses [17-21]. Which of these parameters is measured is determined by the geo- metry and positioning of the hot film probe, Blood velo- city may be measured by use of a conical probe facing into 10 the flow stream. The wall... would extend downstream and have no effect on the measured shear rate. In reverse flow, however, the thermal boundary layer would reverse direction and overlap the probe tip, resulting in a rise in the point blood temperature, altering the value...

  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. Measurement of normal thrust and evaluation of upper-convected Maxwell models for molten plastics in large amplitude oscillatory shear 

    E-print Network

    Oakley, Jason Glen

    1992-01-01

    modulus curve for a polymer melt. The relaxation modulus is determined experimentally by imposing a step strain on a completely relaxed melt and then measuring the shear stress response. A linear relaxation modulus is s, stress response that depends... in this research are the relaxation modulus and the storage and loss mod- uli The storage and loss moduli are defined in small amplitude oscillatory shear and are independent of strain amplitude, but in the case of large amplitude osmlla, tory shear the stress...

  20. Shear Stress in Smooth Rectangular Open-Channel Flows and Pierre Y. Julien2

    E-print Network

    Julien, Pierre Y.

    Shear Stress in Smooth Rectangular Open-Channel Flows Junke Guo1 and Pierre Y. Julien2 Abstract: The average bed and sidewall shear stresses in smooth rectangular open-channel flows are determined after solving the continuity and momentum equations. The analysis shows that the shear stresses are function

  1. The role of shear stress in the destabilization of vulnerable plaques and related therapeutic implications

    Microsoft Academic Search

    JJ Wentzel; FJH Gijsen; A Thury; AC van der Wal; JA Schaar; PW Serruys; CJ Slager

    2005-01-01

    American Heart Association type IV plaques consist of a lipid core covered by a fibrous cap, and develop at locations of eccentric low shear stress. Vascular remodeling initially preserves the lumen diameter while maintaining the low shear stress conditions that encourage plaque growth. When these plaques eventually start to intrude into the lumen, the shear stress in the area surrounding

  2. Effect of low shear stress on permeability and occludin expression in porcine artery endothelial cells

    Technology Transfer Automated Retrieval System (TEKTRAN)

    INTRODUCTION: Although both fluid shear stress and mass transport of atherogenic substances into the vascular wall are known to be important factors in atherogenesis, there has been little research on the effect of shear stress on vascular permeability. Therefore, the effects of shear stress on the ...

  3. 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.

  4. Mode selective generation of guided waves by systematic optimization of the interfacial shear stress profile

    NASA Astrophysics Data System (ADS)

    Yazdanpanah Moghadam, Peyman; Quaegebeur, Nicolas; Masson, Patrice

    2015-01-01

    Piezoelectric transducers are commonly used in structural health monitoring systems to generate and measure ultrasonic guided waves (GWs) by applying interfacial shear and normal stresses to the host structure. In most cases, in order to perform damage detection, advanced signal processing techniques are required, since a minimum of two dispersive modes are propagating in the host structure. In this paper, a systematic approach for mode selection is proposed by optimizing the interfacial shear stress profile applied to the host structure, representing the first step of a global optimization of selective mode actuator design. This approach has the potential of reducing the complexity of signal processing tools as the number of propagating modes could be reduced. Using the superposition principle, an analytical method is first developed for GWs excitation by a finite number of uniform segments, each contributing with a given elementary shear stress profile. Based on this, cost functions are defined in order to minimize the undesired modes and amplify the selected mode and the optimization problem is solved with a parallel genetic algorithm optimization framework. Advantages of this method over more conventional transducers tuning approaches are that (1) the shear stress can be explicitly optimized to both excite one mode and suppress other undesired modes, (2) the size of the excitation area is not constrained and mode-selective excitation is still possible even if excitation width is smaller than all excited wavelengths, and (3) the selectivity is increased and the bandwidth extended. The complexity of the optimal shear stress profile obtained is shown considering two cost functions with various optimal excitation widths and number of segments. Results illustrate that the desired mode (A0 or S0) can be excited dominantly over other modes up to a wave power ratio of 1010 using an optimal shear stress profile.

  5. Fiber\\/epoxy interfacial shear strength measured by the microdroplet test

    Microsoft Academic Search

    Soo-Keun Kang; Deok-Bo Lee; Nak-Sam Choi

    2009-01-01

    In this study, we analyzed the interfacial shear strength between epoxy and carbon fibers, measured from microdroplet specimens adhered onto a single carbon fiber. Microdroplet specimens exhibited different results of the interfacial strength according to the range of embedded fiber lengths and the calculation methods. The shear stress distributions along the interface were calculated by using the finite element analysis

  6. Initial design and analysis of a capacitive sensor for shear and normal force measurement

    Microsoft Academic Search

    J. L. Novak

    1989-01-01

    Initial experiments characterizing a shunt-mode sensor that simultaneously measures both normal and shear strains due to an applied force vector have been completed. The sensor, termed SCCINS (sensed capacitance changes due to incident normal and shear stress), is based on variations in the physical dimensions of an elastic dielectric due to applied forces. Two sinusoids of the same frequency but

  7. Nanoscale Stress Measurements and Standards

    E-print Network

    Magee, Joseph W.

    Nanoscale Stress Measurements and Standards SEMICONDUCTORS Our objective is to develop accurate measurement methods for the nanoscale stress distributions and surface defects that control device performance % CAGR and 41 % US share. · Measurement of stress distributions around transistors in semiconductor

  8. Adjusting Flow-Mediated Dilation for Shear Stress Stimulus Allows Demonstration of Endothelial Dysfunction in a Population with Moderate Cardiovascular Risk

    Microsoft Academic Search

    Jaume Padilla; Blair D. Johnson; Sean C. Newcomer; Daniel P. Wilhite; Timothy D. Mickleborough; Alyce D. Fly; Kieren J. Mather; Janet P. Wallace

    2009-01-01

    Background\\/Aims: Although normalization of brachial artery flow-mediated dilation (FMD) to individual shear stress (FMD:shear stress ratio) has been proposed to improve this measure of endothelial function, the clinical utility of FMD normalization has not yet been demonstrated. We tested (1) whether following conventional 5-min forearm occlusion, the FMD:shear stress ratio would discriminate a population with moderate cardiovascular risk (MR) from

  9. Impact of shear and curvature on surface gravity wave stress

    NASA Astrophysics Data System (ADS)

    Miranda, P. M. A.; Martins, J. P. A.; Teixeira, M. A. C.

    2009-09-01

    It has been shown that surface gravity wave stress is sensitive to the low level wind profile shape. The simplest way of incorporating those effects in a theoretical model has been recently proposed, using a second order WKB approach, which leads to closed analytical formulae for the surface stress as a function of stability, low level wind and its two first derivatives (shear and curvature). In the present study, we assess the impact of those calculations on global scale gravity wave stress and the corresponding torque, using 6-hourly data from ERA-40 reanalysis, at full resolution. While the theory shows that linear wind shear leads to a reduced stress and curvature may lead to stress enhancement, the present results indicate that the latter effect is dominant. However, when one looks for regionally integrated stress fields for the large mountain ranges, where cancellation effects take place thorough time and space integration, the overall effect is one of drag enhancement in regions of dominant easterly flow, namely Antarctica and East Africa, leading to a slight reduction of the global westerly torque due to mountain waves. Drag enhancement due to wind profile curvature seems to be an important effect in Antarctic flow, where it accounts for a 50% increase in the mean regional torque, with implied consequences for the dynamics of the polar vortex.

  10. Stress-structure relation in dense colloidal melt under forward and instantaneous reversal of shear

    E-print Network

    Amit Kumar Bhattacharjee

    2014-10-29

    Dense supercooled colloidal melt in forward shear from a quiescent state shows overshoot in shear stress at 10% strain with an unchanged fluid structure at equal stress before and after overshoot. In addition, we find overshoot in normal stress with a monotonic increase in osmotic pressure at an identical strain. The first and second normal stress become comparable in magnitude and opposite in sign. Functional dependence of the steady state stress and osmotic pressure with Peclet number demonstrate signature of crossover between Newtonian and nearly- Newtonian regime. Moreover, instantaneous shear reversal from steady state exhibit Bauschinger effect, where strong history dependence is observed depending on the time of flow reversal. The distribution of particulate stress and osmotic pressure at the point of flow reversal is shown to be a signature of the subsequent response. We link the history dependence of the stress-strain curves to changes in the fluid structure measured through the angular components of the radial distribution function. A uniform compression in transition from forward to reversed flowing state is found.

  11. Stress-structure relation in dense colloidal melt under forward and instantaneous reversal of shear

    E-print Network

    Amit Kumar Bhattacharjee

    2015-06-16

    Dense supercooled colloidal melt in forward shear from a quiescent state shows overshoot in shear stress at 10% strain with an unchanged fluid structure at equal stress before and after overshoot. In addition, we find overshoot in normal stress with a monotonic increase in osmotic pressure at an identical strain. The first and second normal stress become comparable in magnitude and opposite in sign. Functional dependence of the steady state stress and osmotic pressure with Peclet number demonstrate signature of crossover between Newtonian and nearly- Newtonian regime. Moreover, instantaneous shear reversal from steady state exhibit Bauschinger effect, where strong history dependence is observed depending on the time of flow reversal. The distribution of particulate stress and osmotic pressure at the point of flow reversal is shown to be a signature of the subsequent response. We link the history dependence of the stress-strain curves to changes in the fluid structure measured through the angular components of the radial distribution function. A uniform compression in transition from forward to reversed flowing state is found.

  12. Stress-structure relation in dense colloidal melts under forward and instantaneous reversal of the shear.

    PubMed

    Bhattacharjee, Amit Kumar

    2015-07-01

    A dense supercooled colloidal melt in forward shear from a quiescent state shows overshoot in the shear stress at 10% strain with an unchanged fluid structure at equal stress before and after overshoot. In addition, we find an overshoot in the normal stress with a monotonic increase in the osmotic pressure at an identical strain. The first and second normal stresses become comparable in magnitude and opposite in sign. A functional dependence of the steady state stress and osmotic pressure with the Péclet number demonstrates the signature of crossover between Newtonian and nearly-Newtonian regimes. Moreover, instantaneous shear reversal from a steady state exhibiting the Bauschinger effect, where a strong history dependence is observed depending on the time of the flow reversal. The distribution of the particulate stress and osmotic pressure at the point of the flow reversal is shown to be a signature of the subsequent response. We link the history dependence of the stress-strain curves to changes in the fluid structure measured through the angular components of the radial distribution function. A uniform compression in the transition from forward to reversed flowing states is found. PMID:26082951

  13. 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.

  14. Direct measurement of shear properties of microfibers.

    PubMed

    Behlow, H; Saini, D; Oliveira, L; Durham, L; Simpson, J; Serkiz, S M; Skove, M J; Rao, A M

    2014-09-01

    As novel fibers with enhanced mechanical properties continue to be synthesized and developed, the ability to easily and accurately characterize these materials becomes increasingly important. Here we present a design for an inexpensive tabletop instrument to measure shear modulus (G) and other longitudinal shear properties of a micrometer-sized monofilament fiber sample, such as nonlinearities and hysteresis. This automated system applies twist to the sample and measures the resulting torque using a sensitive optical detector that tracks a torsion reference. The accuracy of the instrument was verified by measuring G for high purity copper and tungsten fibers, for which G is well known. Two industrially important fibers, IM7 carbon fiber and Kevlar(®) 119, were also characterized with this system and were found to have G = 16.5 ± 2.1 and 2.42 ± 0.32 GPa, respectively. PMID:25273783

  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. Polymer MEMS-based Fabry-Perot shear stress sensor

    Microsoft Academic Search

    Fan-Gang Tseng; Chun-Jun Lin

    2003-01-01

    This paper reports a novel optical fiber-based micro-shear stress sensor utilizing a flexible membrane and double SU-8 resist structures as a moving micro-mirror, together with an optical fiber as a micro-Fabry-Perot interferometer. This sensor can be employed in air or liquid environments with high sensitivity because of its waterproof design. Through UV lithography processes on thick SU-8 resist, the roughness

  17. Mechanical properties of jammed packings of frictionless spheres under applied shear stress

    E-print Network

    Hao Liu; Hua Tong; Ning Xu

    2015-02-03

    By minimizing a thermodynamic-like potential, we unbiasedly sample the potential energy landscape of soft and frictionless spheres under constant shear stress. We obtain zero-temperature jammed states under desired shear stresses and investigate their mechanical properties as a function of the shear stress. As a comparison, we also obtain jammed states from the quasistatic-shear sampling in which the shear stress is not well-controlled. Although the yield stresses determined by both samplings show the same power-law scaling with the compression from point $J$, i.e.~the jamming transition point at zero temperature and shear stress, for finite size systems, the quasistatic-shear sampling leads to a lower yield stress and a higher critical volume fraction of point $J$. The shear modulus of jammed solids decreases when increasing the shear stress. However, the shear modulus does not decay to zero at yielding. This discontinuous change of the shear modulus implies the discontinuous nature of the unjamming transition under nonzero shear stress, which is further verified by the observation of a discontinuous jump of the pressure from jammed solids to shear flows. The pressure jump decreases upon decompression and approaches zero at the critical-like point $J$, in analogy with well-known phase transitions under external field. The analysis of force networks in jammed solids reveals that the force distribution is more sensitive to the increase of the shear stress near point $J$. The force network anisotropy increases with the shear stress. Weak particle contacts near the average force and under large shear stresses exhibit asymmetric angle distribution.

  18. Inhomogeneity problem with a sliding interface under remote shearing stress

    NASA Astrophysics Data System (ADS)

    Zhao, YingTao; Gao, Yang; Wang, MinZhong

    2012-11-01

    The problem of an ellipsoidal inhomogeneity embedded in an infinitely extended elastic medium with sliding interfaces is investigated. An exact solution is presented for such an inhomogeneous system that is subject to remote uniform shearing stress. Both the elastic inclusion and matrix are considered isotropic with a separate elastic modulus. Based on Lur'e's approach to solving ellipsoidal cavity problems through Lamé functions, several harmonic functions are introduced for Papkovich-Neuber displacement potentials. The displacement fields inside and outside the ellipsoidal inclusion are obtained explicitly, and the stress field in the whole domain is consequently determined.

  19. CCM proteins control endothelial ?1 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 ?1 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 ?1 integrin activation, blocks endothelial actin rearrangement and cell reorientation in response to shear stress similarly to ?1 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 ?1 integrin activation and subsequent adaptation of vascular endothelial cells to mechanostimulation by fluid shear stress. PMID:25432514

  20. Contribution to critical shear stress of nanocomposites produced by interaction of screw dislocation with nanoscale inclusion

    Microsoft Academic Search

    Q. H. Fang; Y. Liu; B. Y. Huang; Y. W. Liu; P. H. Wen

    2008-01-01

    The contribution to the critical shear stress of nanocomposites caused by the interaction between screw dislocations and nanoscale circular cylindrical inclusions with interface stresses is derived by means of the Mott and Nabarro's model. The effect of the radius of the nanoscale inclusion and the volume fraction of inclusions as well as the interface stress on the critical shear stress

  1. Microstructured optical fiber Bragg grating-based shear stress sensing in adhesive bonds

    NASA Astrophysics Data System (ADS)

    Sulejmani, Sanne; Sonnenfeld, Camille; Geernaert, Thomas; Luyckx, Geert; Van Hemelrijck, Danny; Mergo, Pawel; Skorupski, Krzysztof; Urbanczyk, Waclaw; Chah, Karima; Thienpont, Hugo; Berghmans, Francis

    2014-05-01

    We present shear stress sensing with a Bragg grating sensor fabricated in a highly birefringent microstructured optical fiber. This sensor has a shear strain sensing resolution of 0.04 pm/?? when embedded in a shear loaded adhesive bond. We achieve discrete shear stress mapping in an adhesive bond by embedding a multitude of these sensors at different locations in the bond line. Experiments and numerical modeling show the limited influence of angular misalignment of the sensor on its shear stress response. Finally, we discuss the cross-sensitivity of this sensor to shear strain and temperature.

  2. 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. PMID:25892988

  3. Field observations of bed shear stress and sediment resuspension on continental shelves, Alaska and California

    USGS Publications Warehouse

    Drake, D.E.; Cacchione, D.A.

    1986-01-01

    Bed shear stress was estimated using wave and current measurements obtained with the GEOPROBE bottom-tripod system during resuspension events in Norton Sound, Alaska, and on the northern California shelf. The boundary-layer model of Grant and Madsen (1979, Journal of Geophysical Research, 84, 1797-1808) was used to compute the bed shear stress under combined wave-generated and quasi-steady currents. Resuspension events were identified by sudden, large increases in light scattering at 1.9 m above the sea floor. The shear-stress values were used to compute the Shields parameter (??). The results for Norton Sound are in excellent agreement with the Shields threshold criterion; the data for the California shelf plot somewhat above the Shields threshold curve, though generally within the scatter envelope. Although the surface sediments in each area contain substantial fine-grained fractions (mean diameters were 0.007 cm in Norton Sound and 0.002 cm on the California shelf), the results do not indicate significant cohesion, because the sediment was entrained at bed shear-stress values close to those predicted by the modified Shields curve for cohesionless fine-grained particles. We suspect that frequent wave stirring and observed plowing of the surface sediment by benthonic animals maintain a high water content and contribute to the ease with which these materials are resuspended. ?? 1986.

  4. Air flow and shear stress modifications resulting from annual wind barriers 

    E-print Network

    Schwartz, Robert Craig

    1992-01-01

    barrier structures upon windward and leeward reductions in surface shearing stress. Vertical prot iles of wind velocity were measured in a wind tunnel at fixed distances windward and leeward of barriers composed of model sorghum and pigeon pea plants... thickness Disturbed boundary layers. Atmospheric stability CHARACTERIZATION OF BARRIER EFFECT . Sheltered distance Summation of velocity measurements Leeward relative velocity minimum Resistance coefficients 28 28 28 32 33 33 34 35 37 37 38...

  5. Resonance shear measurement of nanoconfined ionic liquids.

    PubMed

    Ueno, Kazuhide; Kasuya, Motohiro; Watanabe, Masayoshi; Mizukami, Masashi; Kurihara, Kazue

    2010-04-28

    Two types of imidazolium-based ionic liquid (IL), 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide ([C(4)mim][NTF(2)]) and 1-butyl-3-methylimidazolium tetrafluoroborate ([C(4)mim][BF(4)]), confined between silica surfaces were investigated by surface force apparatus (SFA)-based resonance shear measurements together with surface force measurements. The surface force profiles in the ILs showed oscillatory solvation forces below the characteristic surface separations: 10.0 nm for [C(4)mim][NTf(2)] and 6.9 nm for [C(4)mim][BF(4)]. The more pronounced solvation force found in [C(4)mim][NTf(2)] suggests that the crystal-forming ability of the IL contributes to the stronger layering of the ILs adjacent to the surface. The resonance shear measurement and the physical model analysis revealed that the viscosities of the confined ILs were 1-3 orders of magnitude higher than that of the bulk IL. This paper also focused on the correlation between the resonance shear behaviour and the lubrication property of the ILs, and the suspension rheology in the ILs. An understanding of the solid-IL interface and of ILs confined in nanospace will facilitate the further development of novel applications employing ILs. PMID:20379497

  6. An Evaluation of the Iosipescu Specimen for Composite Materials Shear Property Measurement. Ph.D. Thesis

    NASA Technical Reports Server (NTRS)

    Ho, Henjen

    1991-01-01

    A detailed evaluation of the suitability of the Iosipescu specimen tested in the modified Wyoming fixture is presented. An experimental investigation using conventional strain gage instrumentation and moire interferometry is performed. A finite element analysis of the Iosipescu shear test for unidirectional and cross-ply composites is used to assess the uniformity of the shear stress field in the vicinity of the notch, and demonstrate the effect of the nonuniform stress field upon the strain gage measurements used for the determination of composite shear moduli. From the test results for graphite-epoxy laminates, it is shown that the proximity of the load introduction point to the test section greatly influences the individual gage readings for certain fiber orientations but the effect upon shear modulus measurement is relatively unimportant. A numerical study of the load contact effect shows the sensitivity of some fiber configurations to the specimen/fixture contact mechanism and may account for the variations in the measured shear moduli. A comparison of the strain gage readings from one surface of a specimen with corresponding data from moire interferometry on the opposite face documented an extreme sensitivity of some fiber orientations to eccentric loading which induced twisting and yielded spurious shear stress-strain curves. In the numerical analysis, it is shown that the Iosipescu specimens for different fiber orientations have to be modeled differently in order to closely approximate the true loading conditions. Correction factors are needed to allow for the nonuniformity of the strain field and the use of the average shear stress in the shear modulus evaluation. The correction factors, which are determined for the region occupied by the strain gage rosette, are found to be dependent upon the material orthotropic ratio and the finite element models. Based upon the experimental and numerical results, recommendations for improving the reliability and accuracy of the shear modulus values are made, and the implications for shear strength measurement discussed. Further application of the Iosipescu shear test to woven fabric composites is presented. The limitations of the traditional strain gage instrumentation on the satin weave and high tow plain weave fabrics is discussed. Test results of a epoxy based aluminum particulate composite is also presented. A modification of the Iosipescu specimen is proposed and investigated experimentally and numerically. It is shown that the proposed new specimen design provides a more uniform shear stress field in the test section and greatly reduces the normal and shear stress concentrations in the vicinity of the notches. While the fabrication and the material cost of the proposed specimen is tremendously reduced, it is shown the accuracy of the shear modulus measurement is not sacrificed.

  7. Microvascular permeability to water is independent of shear stress, but dependent on flow direction.

    PubMed

    Adamson, R H; Sarai, R K; Altangerel, A; Clark, J F; Weinbaum, S; Curry, F E

    2013-04-15

    Endothelial cells in a cultured monolayer change from a "cobblestone" configuration when grown under static conditions to a more elongated shape, aligned with the direction of flow, after exposure to sustained uniform shear stress. Sustained blood flow acts to protect regions of large arteries from injury. We tested the hypothesis that the stable permeability state of individually perfused microvessels is also characteristic of flow conditioning. In individually perfused rat mesenteric venular microvessels, microvascular permeability, measured as hydraulic conductivity (Lp), was stable [mean 1.0 × 10(-7) cm/(s × cmH2O)] and independent of shear stress (3-14 dyn/cm(2)) for up to 3 h. Vessels perfused opposite to the direction of normal blood flow exhibited a delayed Lp increase [?Lp was 7.6 × 10(-7) cm/(s × cmH2O)], but the increase was independent of wall shear stress. Addition of chondroitin sulfate and hyaluronic acid to perfusates increased the shear stress range, but did not modify the asymmetry in response to flow direction. Increased Lp in reverse-perfused vessels was associated with numerous discontinuities of VE-cadherin and occludin, while both proteins were continuous around the periphery of forward-perfused vessels. The results are not consistent with a general mechanism for graded shear-dependent permeability increase, but they are consistent with the idea that a stable Lp under normal flow contributes to prevention of edema formation and also enables physiological regulation of shear-dependent small solute permeabilities (e.g., glucose). The responses during reverse flow are consistent with reports that disturbed flows result in a less stable endothelial barrier in venular microvessels. PMID:23417864

  8. Effect of thermal expansion mismatch and fiber coating on the fiber\\/matrix interfacial shear stress in ceramic matrix composites

    Microsoft Academic Search

    M. K. Brun; R. N. Singh

    1988-01-01

    A modified indentation technique has been used to measure the interfacial shear stress in a number of ceramic matrices containing silicon carbide fibers. It was shown that the frictional component of interfacial stress was essentially zero when matrix thermal expansion was lower than that of the fiber and increased linearly with thermal expansion mismatch when matrix thermal expansion was higher.

  9. Validity of Measurement of Shear Modulus by Ultrasound Shear Wave Elastography in Human Pennate Muscle

    PubMed Central

    Miyamoto, Naokazu; Hirata, Kosuke; Kanehisa, Hiroaki; Yoshitake, Yasuhide

    2015-01-01

    Ultrasound shear wave elastography is becoming a valuable tool for measuring mechanical properties of individual muscles. Since ultrasound shear wave elastography measures shear modulus along the principal axis of the probe (i.e., along the transverse axis of the imaging plane), the measured shear modulus most accurately represents the mechanical property of the muscle along the fascicle direction when the probe’s principal axis is parallel to the fascicle direction in the plane of the ultrasound image. However, it is unclear how the measured shear modulus is affected by the probe angle relative to the fascicle direction in the same plane. The purpose of the present study was therefore to examine whether the angle between the principal axis of the probe and the fascicle direction in the same plane affects the measured shear modulus. Shear modulus in seven specially-designed tissue-mimicking phantoms, and in eleven human in-vivo biceps brachii and medial gastrocnemius were determined by using ultrasound shear wave elastography. The probe was positioned parallel or 20° obliquely to the fascicle across the B-mode images. The reproducibility of shear modulus measurements was high for both parallel and oblique conditions. Although there was a significant effect of the probe angle relative to the fascicle on the shear modulus in human experiment, the magnitude was negligibly small. These findings indicate that the ultrasound shear wave elastography is a valid tool for evaluating the mechanical property of pennate muscles along the fascicle direction. PMID:25853777

  10. 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. PMID:21469880

  11. 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.

  12. Direct force wall shear measurements in pressure-driven three-dimensional turbulent boundary layers

    NASA Technical Reports Server (NTRS)

    Mcallister, J. E.; Tennant, M. H.; Pierce, F. J.

    1982-01-01

    Unique, simultaneous direct measurements of the magnitude and direction of the local wall shear stress in a pressure-driven three-dimensional turbulent boundary layer are presented. The flow is also described with an oil streak wall flow pattern, a map of the wall shear stress-wall pressure gradient orientations, a comparison of the wall shear stress directions relative to the directions of the nearest wall velocity as measured with a typical, small boundary layer directionally sensitive claw probe, as well as limiting wall streamline directions from the oil streak patterns, and a comparison of the freestream streamlines and the wall flow streamlines. A review of corrections for direct force sensing shear meters for two-dimensional flows is presented with a brief discussion of their applicability to three-dimensional devices.

  13. Miniature Laser Doppler Velocimeter for Measuring Wall Shear

    NASA Technical Reports Server (NTRS)

    Gharib, Morteza; Modarress, Darius; Forouhar, Siamak; Fourguette, Dominique; Taugwalder, Federic; Wilson, Daniel

    2005-01-01

    A miniature optoelectronic instrument has been invented as a nonintrusive means of measuring a velocity gradient proportional to a shear stress in a flow near a wall. The instrument, which can be mounted flush with the wall, is a variant of a basic laser Doppler velocimeter. The laser Doppler probe volume can be located close enough to the wall (as little as 100 micron from the surface) to lie within the viscosity-dominated sublayer of a turbulent boundary layer. The instrument includes a diode laser, the output of which is shaped by a diffractive optical element (DOE) into two beams that have elliptical cross sections with very high aspect ratios.

  14. An Evaluation of the Iosipescu Specimen for Composite Materials Shear Property Measurement

    Microsoft Academic Search

    J. Morton; H. Ho; M. Y. Tsai; G. L. Farley

    1992-01-01

    A detailed evaluation of the suitability of the Iosipescu specimen tested in the modified Wyoming fixture is presented. A linear finite element model of the specimen is used to assess the uniformity of the shear stress field in the vicinity of the notch, and demonstrate the effect of the nonuniform stress field upon strain gage measurements used for the determination

  15. Effect of normal stress during hydration and shear on the shear strength of GCL/textured geomembrane interfaces

    SciTech Connect

    Hewitt, R.D.; Soydemir, C. [Haley and Aldrich, Inc., Cambridge, MA (United States); Stulgis, R.P. [Haley and Aldrich, Inc., Manchester, NH (United States); Coombs, M.T. [Tufts Univ., Medford, MA (United States)

    1997-11-01

    A laboratory testing program was performed to evaluate the interface shear strength of a geosynthetic clay liner (GCL)/textured geomembrane interface utilizing two pre-shear inundation methods designed to simulate field conditions. Two commercially-available products were tested, a needlepunched and a stitch-bonded GCL. Oedometer swell tests provided swell data for the two products which were used to design the interface shear testing program. Interface shear tests were performed for (1) GCL samples inundated under a low normal stress for a short time and sheared under a higher normal stress, and (2) GCL samples inundated for a longer period under the design normal stress. The results for the two different GCL materials and the two preshear inundation conditions are compared.

  16. Rheology as a tool for measurement of sludge shear.

    PubMed

    Ormeci, Banu

    2008-01-01

    Shear intensity, shear time, and polymer dose are the main parameters that determine the dewaterability of wastewater sludge. Polymer dose required to condition the sludge increases with the increase of shear intensity (G) and shear time (t). Therefore, in order to minimize the polymer demand during conditioning and dewatering, shear should be optimized. Optimization of shear can be achieved if the total shear that the sludge network is exposed to during conditioning and dewatering can be measured and quantified. This is quite a challenge since total shear includes unintended shear introduced during piping and pumping, and currently there is no direct or indirect technique that can measure this unintended shear. Unintended shear increases the polymer demand and shifts the optimum polymer dose to a higher dose, which in turn decreases the cake solids concentration and the efficiency of the dewatering process. Thus, quantification of the unintended shear and adjustment of the polymer dose accordingly are essential for the optimization of dewatering processes. The main objective of this study was to develop a method for sludge shear measurement based on the rheological characteristics of sludge and illustrate its possible applications at treatment plants. The results of this study indicate that the rheological characteristics of sludge can be used to estimate an unknown amount of shear that sludge network is exposed to, and to match the jar-test mixing conditions to that of the full-scale mixers employed at treatment plants. PMID:18957750

  17. 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-? 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

  18. Shear stress and flow dynamics of the femoral vein among obese patients who qualify for bariatric surgery.

    PubMed

    Wiewiora, Maciej; Piecuch, Jerzy; Gl?ck, Marek; Slowinska-Lozynska, Ludmila; Sosada, Krystyn

    2013-01-01

    The aim of this study was to evaluate the effects of obesity on wall shear stress and its relationship to erythrocyte aggregation. We studied 35 morbidly obese patients who were qualified for bariatric surgery. The control group consisted of 20 non-obese people. Blood rheological measurements were performed using the Laser-assisted Optical Rotational Cell Analyzer (Mechatronics, the Netherlands) and a cone-plate viscometer (Brookfield DV-II). The venous flow dynamics were assessed using a duplex ultrasound. The shear rate was estimated from the measured blood flow velocity and the diameter of the femoral vein. Venous wall shear stress was calculated from the whole blood viscosity and the shear rate. The shear rate (P < 0.005) and the venous wall shear stress (P < 0.05) were significantly lower in obese patients compared with the controls. The aggregation index (P < 0.001), syllectogram amplitude - AMP (P < 0.05) and Tslow (P < 0.001) were significantly higher in the obese patients; the aggregation half-time (P < 0.001) and Tfast (P < 0.001) were decreased compared with the control group. Multivariate regression analyses found waist circumference (? -0.31, P < 0.05), thigh circumference (? 0.33, P < 0.05) and Tslow (? -0.47, P < 0.005) to be variables that independently influenced the shear rate. Nevertheless, the AMP (? 0.34, P < 0.05) and Tslow (? -0.47, P < 0.01) were independent predictors that influenced the wall shear stress. This study indicates that there is a relationship between wall shear stress in the femoral vein and the rheological impairment of the RBC among obese patients, but further studies are necessary to confirm this suggestion. PMID:23686091

  19. Stress Heterogeneities in Sheared Type-I Collagen Networks Revealed by Boundary Stress Microscopy

    PubMed Central

    Arevalo, Richard C.; Kumar, Pramukta; Urbach, Jeffrey S.; Blair, Daniel L.

    2015-01-01

    Disordered fiber networks provide structural support to a wide range of important materials, and the combination of spatial and dynamic complexity may produce large inhomogeneities in mechanical properties, an effect that is largely unexplored experimentally. In this work, we introduce Boundary Stress Microscopy to quantify the non-uniform surface stresses in sheared collagen gels. We find local stresses exceeding average stresses by an order of magnitude, with variations over length scales much larger than the network mesh size. The strain stiffening behavior observed over a wide range of network 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 boundary stress at both the characteristic strain and at yielding are remarkably insensitive to concentration. PMID:25734484

  20. Flow visualization and wall shear stress of a flapping model hummingbird wing

    Microsoft Academic Search

    Erik W. M. Swanton; Blake A. Vanier; Kamran Mohseni

    2010-01-01

    The unsteady low Reynolds number aerodynamics of flapping flight was investigated experimentally through flow visualization\\u000a by suspended particle imagery and wall shear stress measurement from micro-array hot-film anemometry. In conjunction, a mechanism\\u000a was developed to create a flapping motion with three degrees of freedom and adjustable flapping frequency. The flapping kinematics\\u000a and wing shape were selected for dynamic similarity to

  1. Two-Axis Direct Fluid Shear Stress Sensor for Aerodynamic Applications

    NASA Technical Reports Server (NTRS)

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

    2011-01-01

    This miniature or micro-sized semiconductor sensor design provides direct, nonintrusive measurement of skin friction or wall shear stress in fluid flow situations in a two-axis configuration. The sensor is fabricated by microelectromechanical system (MEMS) technology, enabling small size and multiple, low-cost reproductions. The sensors may be fabricated by bonding a sensing element wafer to a fluid-coupling element wafer. Using this layered machine structure provides a truly three-dimensional device.

  2. Dual shear wave induced laser speckle contrast signal and the improvement in shear wave speed measurement.

    PubMed

    Li, Sinan; Cheng, Yi; Eckersley, Robert J; Elson, Daniel S; Tang, Meng-Xing

    2015-06-01

    Shear wave speed is quantitatively related to tissue viscoelasticity. Previously we reported shear wave tracking at centimetre depths in a turbid optical medium using laser speckle contrast detection. Shear wave progression modulates displacement of optical scatterers and therefore modulates photon phase and changes the laser speckle patterns. Time-resolved charge-coupled device (CCD)-based speckle contrast analysis was used to track shear waves and measure the time-of-flight of shear waves for speed measurement. In this manuscript, we report a new observation of the laser speckle contrast difference signal for dual shear waves. A modulation of CCD speckle contrast difference was observed and simulation reproduces the modulation pattern, suggesting its origin. Both experimental and simulation results show that the dual shear wave approach generates an improved definition of temporal features in the time-of-flight optical signal and an improved signal to noise ratio with a standard deviation less than 50% that of individual shear waves. Results also show that dual shear waves can correct the bias of shear wave speed measurement caused by shear wave reflections from elastic boundaries. PMID:26114021

  3. Dual shear wave induced laser speckle contrast signal and the improvement in shear wave speed measurement

    PubMed Central

    Li, Sinan; Cheng, Yi; Eckersley, Robert J; Elson, Daniel S; Tang, Meng-Xing

    2015-01-01

    Shear wave speed is quantitatively related to tissue viscoelasticity. Previously we reported shear wave tracking at centimetre depths in a turbid optical medium using laser speckle contrast detection. Shear wave progression modulates displacement of optical scatterers and therefore modulates photon phase and changes the laser speckle patterns. Time-resolved charge-coupled device (CCD)-based speckle contrast analysis was used to track shear waves and measure the time-of-flight of shear waves for speed measurement. In this manuscript, we report a new observation of the laser speckle contrast difference signal for dual shear waves. A modulation of CCD speckle contrast difference was observed and simulation reproduces the modulation pattern, suggesting its origin. Both experimental and simulation results show that the dual shear wave approach generates an improved definition of temporal features in the time-of-flight optical signal and an improved signal to noise ratio with a standard deviation less than 50% that of individual shear waves. Results also show that dual shear waves can correct the bias of shear wave speed measurement caused by shear wave reflections from elastic boundaries.

  4. Localized 4 Integrin Phosphorylation Directs Shear Stress-Induced Endothelial Cell Alignment

    Microsoft Academic Search

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

    Abstract—Vascular endothelial cells respond to laminar shear stress by aligning in the direction of flow, a process which may,contribute to atheroprotection. Here we report that localized,4 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 4 integrins became phosphorylated on Ser,A)

  5. The role of shear stress in the generation of rupture-prone vulnerable plaques

    Microsoft Academic Search

    JJ Wentzel; FJH Gijsen; JCH Schuurbiers; AC van der Wal; AFW van der Steen; P. W. Serruys; CJ Slager

    2005-01-01

    Blood-flow-induced shear stress acting on the arterial wall is of paramount importance in vascular biology. Endothelial cells sense shear stress and largely control its value in a feedback-control loop by adapting the arterial dimensions to blood flow. Nevertheless, to allow for variations in arterial geometry, such as bifurcations, shear stress control is modified at certain eccentrically located sites to let

  6. Deformation measurements of composite multi-span beam shear specimens by Moire interferometry

    NASA Technical Reports Server (NTRS)

    Post, D.; Czarnek, R.; Joh, D.; Wood, J.

    1984-01-01

    Experimental analyses were performed for determination of in plane deformations and shear strains in unidirectional and quasi-isotropic graphite-epoxy beams. Forty-eight ply beams were subjected to 5 point and 3 point flexure. Whole field measurements were recorded at load levels from about 20% to more than 90% of failure loads. Contour maps of U and W displacement fields were obtained by moire interferometry, using reference gratings of 2400 lines/mm. Clearly defined fringes with fringe orders exceeding 1000 were obtained. Whole field contour maps of shear strains were obtained by a method developed for these tests. Various anomalous effects were detected in the displacement fields. Their analysis indicated excess shear strains in resin rich zones in regions of shear tractions; free edge shear strains in quasi-isotropic specimens in regions of normal stresses; and shear stresses associated with cyclic shear compliances of quasi-isotropic plies in regions of shear tractions. Their contributions could occur independently or in superposition. Qualitative analyses addressed questions of relaxation; influence of contact stress distribution; specimen failure; effect of specimen overhang; nonlinearity; and qualities of 5 and 3 point flexure tests.

  7. 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.

  8. Modeling flow and shear stress fields over unsteady three dimensional dunes

    NASA Astrophysics Data System (ADS)

    Hardy, Richard; Parsons, Dan; Ashworth, Phil; Reesink, Arjan; Best, Jim

    2014-05-01

    The flow field over dunes has been extensively measured in laboratory conditions and there is general understanding on the nature of the flow over dunes formed under equilibrium flow conditions. This has allowed an understanding of bed shear stress to be derived and the development of morpho-dynamic models. However, fluvial systems typically experience unsteady flow and therefore the sediment-water interface is constantly responding and reorganizing to these unsteady flows and stresses, over a range of both spatial and temporal scales. This is primarily through the adjustment of bed forms (including ripples, dunes and bar forms) which then subsequently alter the flow field. This paper investigates, through the application of a numerical model, the influence of these roughness elements on the overall flow and bed shear stress. A series of physical experiments were undertaken in a flume, 16m long and 2m wide, where a fine sand (D50 of 239µm) was water worked under a range of unsteady hydraulic conditions to generate a series of quasi-equilibrium three dimensional bed forms. During the experiments flow was measured with acoustic Doppler velocimeters, (aDv's). On four occasions the flume was drained and the bed topography measured with terrestrial LiDAR to create digital elevation models. This data provide the necessary boundary conditions and validation data for a numerical three dimensional flow model. The prediction of flow over the four static beds demonstrates the spatial distribution of shear stress and the potential sediment transport paths between the dune crests. These appear to be associated with coherent flow structures formed by localized shear flow. These flow predictions are currently being used to develop a fully three dimensional morphodynamic model to further understand dune dynamics under unsteady flow conditions.

  9. Microvascular Endothelial Cells Migrate Upstream and Align Against the Shear Stress Field Created by Impinging Flow

    PubMed Central

    Ostrowski, Maggie A.; Huang, Ngan F.; Walker, Travis W.; Verwijlen, Tom; Poplawski, Charlotte; Khoo, Amanda S.; Cooke, John P.; Fuller, Gerald G.; Dunn, Alexander R.

    2014-01-01

    At present, little is known about how endothelial cells respond to spatial variations in fluid shear stress such as those that occur locally during embryonic development, at heart valve leaflets, and at sites of aneurysm formation. We built an impinging flow device that exposes endothelial cells to gradients of shear stress. Using this device, we investigated the response of microvascular endothelial cells to shear-stress gradients that ranged from 0 to a peak shear stress of 9–210 dyn/cm2. We observe that at high confluency, these cells migrate against the direction of fluid flow and concentrate in the region of maximum wall shear stress, whereas low-density microvascular endothelial cells that lack cell-cell contacts migrate in the flow direction. In addition, the cells align parallel to the flow at low wall shear stresses but orient perpendicularly to the flow direction above a critical threshold in local wall shear stress. Our observations suggest that endothelial cells are exquisitely sensitive to both magnitude and spatial gradients in wall shear stress. The impinging flow device provides a, to our knowledge, novel means to study endothelial cell migration and polarization in response to gradients in physical forces such as wall shear stress. PMID:24461011

  10. Experimental Quantification of Resolved Shear Stresses for Dislocation Motion in TiN.

    PubMed

    Li, N; Misra, A; Shao, S; Wang, J

    2015-07-01

    Experimental quantification of the critical resolved shear stress (CRSS) at the level of unit dislocation glide is still a challenge. By using in situ nanoindentation in a high-resolution transmission electron microscope and strain analysis of the acquired structural images, the CRSS for the motion of individual dislocations on {110}?011? slip system and glide dislocation re-emission from a tilt grain boundary in TiN are quantified. This work offers an approach to measure the local stresses associated with dislocation motion in high-strength materials. PMID:26065576

  11. The free shear layer edgetone and instability measurements

    Microsoft Academic Search

    K. B. M. Q. Zaman; A. K. M. F. Hussain

    1978-01-01

    The hot-wire probe is known to be capable of triggering and sustaining upstream instability modes like the slit jet-wedge edgetone termed the free shear layer tone. In this paper, the hot-wire probe is used to investigate the shear tone phenomenon in axisymmetric and plane free shear layers. For all the measurements reported, the initial boundary layers producing the free shear

  12. Solitary waves on inclined films: their characteristics and the effects on wall shear stress

    NASA Astrophysics Data System (ADS)

    Tihon, J.; Serifi, K.; Argyriadi, K.; Bontozoglou, V.

    2006-07-01

    The properties of solitary waves, developing from inlet disturbances of controlled frequency along an inclined film flow, are systematically studied experimentally and computationally. Time-variations of film height and wall shear stress are measured, using respectively a capacitance probe and an electrodiffusion sensor. Computational data are provided from simulations performed by a Galerkin finite element scheme. The height and spacing of solitary humps, their phase velocity and the wavelength of the preceding capillary ripples are reported as functions of the Reynolds number (10< Re<100) and the inlet frequency (0.5 Hz< f<2.5 Hz). The wall shear stress modulation imposed by the passage of solitary waves is studied experimentally and computationally as a function of Re. Distinct nonlinear characteristics are noted, including a steep maximum and a negative minimum, with the effects intensifying at intermediate Re. All computer predictions are found to be in good quantitative agreement with the experimental data.

  13. On stress and strain in a continuous-discontinuous shear zone undergoing simple shear and volume loss

    NASA Astrophysics Data System (ADS)

    Fagereng, Å.

    2013-05-01

    I summarise observations within a continuous-discontinuous shear zone to discuss the local stress and strain conditions experienced within a mixed rheology shear zone undergoing volume loss and deformation approximating simple shear. The Chrystalls Beach Complex, New Zealand, comprises phacoids formed from dismembered beds by layer-parallel extension, enclosed within a relatively incompetent matrix. Local extension is generally subparallel to the regional direction of shortening, and overall it appears that layer-parallel extension is a geometrical necessity in low angle shear zones where significant flattening occurs in response to simple shear accompanied by volume loss. Preferential stress loading of phacoids is predicted by fibre-loading theory, and the failure of phacoids by brittle fracture is thereby governed by fibre stresses transferred from the matrix. The principal stress orientations in a phacoid are likely rotated relative to the matrix, and either parallel or perpendicular to the phacoid-matrix interface. As preferential loading of phacoids decreases the stress level in the matrix, an increased volume fraction of phacoids increases the strength of the shear zone as a whole. However, only small matrix volume fractions are required for the composite to act nearly as weak as the matrix.

  14. 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.

  15. Magnetically applied pressure-shear : a new technique for direct strength measurement at high pressure (final report for LDRD project 117856).

    SciTech Connect

    Lamppa, Derek C.; Haill, Thomas A.; Alexander, C. Scott; Asay, James Russell

    2010-09-01

    A new experimental technique to measure material shear strength at high pressures has been developed for use on magneto-hydrodynamic (MHD) drive pulsed power platforms. By applying an external static magnetic field to the sample region, the MHD drive directly induces a shear stress wave in addition to the usual longitudinal stress wave. Strength is probed by passing this shear wave through a sample material where the transmissible shear stress is limited to the sample strength. The magnitude of the transmitted shear wave is measured via a transverse VISAR system from which the sample strength is determined.

  16. High shear microfluidics and its application in rheological measurement

    NASA Astrophysics Data System (ADS)

    Kang, Kai; Lee, L. James; Koelling, Kurt W.

    2005-02-01

    High shear rheology was explored experimentally in microchannels (150×150 ?m). Two aqueous polymer solutions, polyethylene oxide (viscoelastic fluid) and hydroxyethyl cellulose (viscous fluid) were tested. Bagley correction was applied to remove the end effect. Wall slip was investigated with Mooney’s analysis. Shear rates as high as 106 s-1 were obtained in the pressure-driven microchannel flow, allowing a smooth extension of the low shear rheological data obtained from the conventional rheometers. At high shear rates, polymer degradation was observed for PEO solutions at a critical microchannel wall shear stress of 4.1×103 Pa. Stresses at the ends of the microchannel also contributed to PEO degradation significantly.

  17. The Effect of Shear and Deviatoric Stress on Permeability Evolution in Fractured Diorite and Novaculite

    NASA Astrophysics Data System (ADS)

    Faoro, I.; Elsworth, D.; Marone, C.; Niemeijer, A.

    2006-12-01

    The evolution of the permeability in fractured rocks, subject to changing stress conditions is a complex issue. In this contribution, we report on experiments in which rock surfaces were sheared under controlled pore pressure and true-triaxial stress conditions while permeability was monitored via flow parallel to the shear direction. Direct shear tests were performed in a pressure vessel under drained conditions on samples of novaculite and of diorite (Coso Geothermal field, CA). Smoothed-faced, prismatic blocks were roughened by grinding with 60# grit, assembled face-to-face, and jacketed within a sealed membrane. Normal stress was applied by a hydraulic ram, and confining- and pore-pressures were maintained via high precision servo- controlled pressure intensifiers. The sample pairs are sheared to 18 mm of final displacement at 5 ?m/sec, at room temperature, and at effective normal stresses ranging from 5 to 20 MPa. Permeability evolution is measured throughout shearing via flow of distilled water from an upstream reservoir at 0.1 MPa and discharged at atmospheric pressure. The permeability of the smooth fracture in novaculite varied only slightly with applied effective normal stress (0.5×10^{-14} m2 at 5 MPa, 10^{-14} m2 at 10 MPa and 10^{-14} m2 at 20 MPa). The corresponding hydraulic apertures were respectively 20 ?m, 15 ?m and 13 ?m. In all three tests, permeability dropped one order of magnitude upon shearing. Steady state values for permeability and shear strength were typically reached after ~ 10 mm of load point displacement. An associated reduction of ~10 ?m was observed in the hydraulic apertures. Similar behavior was recorded in the diorite sample but only at the highest effective normal stresses. The initial permeability of ~10^{-13 m2 dropped four orders of magnitude before reaching a steady state value. This corresponds to a reduction in hydraulic aperture of ~23 ?m, reaching a steady state magnitude of ~1.5 ?m. At lower effective normal stresses diorite shows different behavior. At 5 MPa the initial permeability of 0.5×10^{-14} m2 increases to 10^{-14} m2 at peak strength and drops to 0.5×10^{-14} m2 during steady state frictional sliding. This corresponds to a hydraulic aperture of 20 ?m. At 10 MPa the initial permeability of 10^{-14} m2 (hydraulic aperture 14 ?m) reduces to 10-16 m2 (hydraulic aperture of 2.8 ?m) at peak shear strength, and then partly recovers by one order of magnitude to reach a final steady permeability of 10^{-15} m2 (final hydraulic aperture of 5 ?m). We observe that permeability decreases with an increase in the applied normal load. Moreover, shearing results in a permeability reduction in all cases, and is more pronounced at higher normal stress levels. This is presumably the result of mechanical removal (wear or fracturing) of asperities along the sliding contacts. The removed material subsequently clogs the fracture, reducing the permeability. Chemical analyses of pore fluids will be reported.

  18. Modeling the relation between suction, effective stress and shear strength in partially saturated granular media

    E-print Network

    Toker, Nabi Kartal, 1979-

    2007-01-01

    Decades of geotechnical research firmly established that the mechanical properties (shear strength and deformation characteristics) of soils are related to soil's "effective stress", i.e. the stress carried by the solid ...

  19. Comparison of actual and allowable stress values for out-of-plane shear on masonry walls

    SciTech Connect

    Henderson, R.C.; Wilson, G.S.; Crouch, L.K.; Sneed, W.A. Jr.

    1999-07-01

    This paper presents research results from the testing of 16 masonry wall specimens in direct out-of-plane shear. The wall specimens were two courses high and 1.2 m (48 in.) long. The walls were nongrouted and were constructed with face-shell bedding only. The testing apparatus was configured such that failure mechanisms other than direct out-of-plane shear (i.e., those resulting from flexural and axial loads) were minimized. Shear stress values from the 16 wall tests are compared with allowable shear stress values obtained in ACI 530 / ASCE 5 / TMS 402. These results show that the code allowable shear stress values appear to be unconservative for this application of out-of-plane shear. It was found that the walls tested failed in out-of-shear at an average shear force of 69.8 kN (15,696 lb). This force produced an average shear stress of 0.349 MPa (50.65 psi) based on parabolic stress distribution and 0.885 Mpa (128.36 psi) for pure shear stress.

  20. Teleseismic shear wave splitting measurements in noisyenvironments

    NASA Astrophysics Data System (ADS)

    Restivo, Andrea; Helffrich, George

    1999-06-01

    High noise levels hamper teleseismic shear wave splitting measurements, which bandpass filtering does not always help. To investigate how robust splitting measurements are to noise, we analysed a set of synthetic records with known splitting parameters and added fixed levels of noise. In the presence of weak anisotropy, single-waveform splitting measurements are unreliable when operating with noisy data sets. A practical rule in terms of S/N ratio and splitting delay time parameters is that splitting is confidently detectable at S/N>8, regardless of the wave's original polarization orientation. However, for the evidence of weak anisotropy to be detectable and measurable at an S/N value of 4, the backazimuth separation of the phases from the fast polarization direction needs to be higher than 20 deg. Stacks of individual measurements consistently yield reliable results down to S/N values of 4. Applying stacking to data from DSB (Dublin, Ireland), the fast polarization direction phi and lag time deltat are 58 deg and 0.95 s. This orientation reflects surface trends of deformation in the area, as found elsewhere in the UK. Our result thus reinforces the proposed model that the detected anisotropy in the British Isles originates from lithospheric coherent deformation preserved from the last main tectonic episode.

  1. Adaptive response of vascular endothelial cells to an acute increase in shear stress magnitude

    PubMed Central

    Zhang, Ji

    2012-01-01

    The adaptation of vascular endothelial cells to shear stress alteration induced by global hemodynamic changes, such as those accompanying exercise or digestion, is an essential component of normal endothelial physiology in vivo. An understanding of the transient regulation of endothelial phenotype during adaptation to changes in mural shear will advance our understanding of endothelial biology and may yield new insights into the mechanism of atherogenesis. In this study, we characterized the adaptive response of arterial endothelial cells to an acute increase in shear stress magnitude in well-defined in vitro settings. Porcine endothelial cells were preconditioned by a basal level shear stress of 15 ± 15 dyn/cm2 at 1 Hz for 24 h, after which an acute increase in shear stress to 30 ± 15 dyn/cm2 was applied. Endothelial permeability nearly doubled after 40-min exposure to the elevated shear stress and then decreased gradually. Transcriptomics studies using microarray techniques identified 86 genes that were sensitive to the elevated shear. The acute increase in shear stress promoted the expression of a group of anti-inflammatory and antioxidative genes. The adaptive response of the global gene expression profile is triphasic, consisting of an induction period, an early adaptive response (ca. 45 min) and a late remodeling response. Our results suggest that endothelial cells exhibit a specific phenotype during the adaptive response to changes in shear stress; this phenotype is different than that of fully adapted endothelial cells. PMID:22140046

  2. Evidence of a possible link between poststenotic dilation and wall shear stress.

    PubMed

    Ojha, M; Johnston, K W; Cobbold, R S

    1990-01-01

    The effects of an axisymmetric 65% area reduction stenosis on a pulsatile flow were investigated by use of an in vitro model that permits simultaneous visualization of the flow velocity profiles at seven sites. By use of seven lenses to focus the ultraviolet light from a nitrogen laser, seven thin blue lines were produced in the photochromic solution flowing through the tube. The displacement profiles of the dye traces were photographed, resulting in the acquisition of the velocity profiles. From these traces, the flow pattern was determined, and the wall shear stresses were measured. Turbulence was generated 3.3 to 6.5 tube diameters downstream from the edge of the stenosis, depending on the time in the pulsatile flow cycle. Maximum wall shear stress fluctuations between positive and negative values appeared to lie within 1.6 to 3.3 tube diameters downstream of the stenosis. In several illustrative clinical cases of thoracic outlet arterial compression, the poststenotic dilation was maximum at 2.0 +/- 0.3 vessel diameters downstream. Based on these observations, it is postulated that wall shear stress fluctuations may be important in the development of poststenotic dilation. PMID:2296094

  3. Critical scaling of stresses and correlations with strain rate in overdamped sheared disordered solids

    NASA Astrophysics Data System (ADS)

    Clemmer, Joel; Salerno, Kenneth; Robbins, Mark

    2015-03-01

    Like many nonequilibrium systems, disordered solids exhibit a power-law distribution of avalanches and other critical behavior when driven slowly. We extend molecular dynamics studies of quasistatic shear of 2D and 3D overdamped binary LJ glasses to finite strain rate. Finite-size scaling is used to determine the critical behavior of the shear stress and several measures of temporal and spatial correlations in non-affine displacements. With increasing strain rate, there is a power-law rise in the shear stress with exponent ? extending to lower rates in larger systems. This behavior is governed by the rise in the dynamic correlation length with decreasing stress with exponent ?. The correlation function of non-affine displacements exhibits novel anisotropic power law scaling with q, the magnitude of the wave vector. Its strain rate dependence is used to determine the scaling of the dynamic correlation length in various angular directions. In the quasistatic limit, particle diffusion in 2D is proportional to strain with a system-size dependent diffusion constant. Increasing strain rate, the dynamic correlation length drops below the system-size and the diffusion constant begins to fall. Support provided by: DMR-1006805; NSF IGERT-0801471; OCI-0963185; CMMI-0923018.

  4. Disbond monitoring in adhesive joints using shear stress optical fiber sensors

    NASA Astrophysics Data System (ADS)

    Sulejmani, Sanne; Sonnenfeld, Camille; Geernaert, Thomas; Luyckx, Geert; Mergo, Pawel; Urbanczyk, Waclaw; Chah, Karima; Thienpont, Hugo; Berghmans, Francis

    2014-07-01

    We present dedicated shear stress optical fiber sensors for in situ disbond monitoring of adhesive bonds. The shear stress sensitivity of these sensors is about 60 pm MPa-1, which corresponds to a shear strain sensing resolution of 50 ??. By integrating a combination of three such sensors in the adhesive bond line of a single lap joint, we can assess the internal shear stress distribution when the joint is tensile loaded. Disbonding of this joint was initiated by cyclic tensile loading, and the sensor responses were monitored during this process. Our results show that this sensing system can detect disbonds as small as 100 ?m.

  5. Experimental assessment of Owen's second hypothesis on surface shear stress induced by a fluid during sediment saltation

    NASA Astrophysics Data System (ADS)

    Walter, B.; Horender, S.; Voegeli, C.; Lehning, M.

    2014-09-01

    A widely used, yet thus far unproven, fluid dynamical hypothesis originally presented by P. R. Owen 50 years ago, states that the surface shear stress induced by a fluid on the ground during equilibrium sediment saltation is constant and independent of the magnitude of the fluid velocity and consequently the particle mass flux. This hypothesis is one of the key elements in almost all current model descriptions of sediment erosion. We measured the surface shear stress in a drifting-sand wind tunnel and found Owen's hypothesis being merely an approximation of the real situation. A significant decrease of the fluid stress with increasing wind velocities was measured for low to intermediate particle mass fluxes. For high particle mass fluxes, Owen's hypothesis essentially holds, although a slight increase of the fluid stress was measured.

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

    Technology Transfer Automated Retrieval System (TEKTRAN)

    In physically-based hillslope erosion models, only overland flow shear stress exerted on soil aggregates (grains) is used to estimate concentrated flow soil detachment rates and sediment transport capacity. However, on vegetated hillslopes, only overland flow total shear stress can be obtained usin...

  7. An Analysis of Elastohydrodynamic Lubrication with Limiting Shear Stress: Part I—Theory and Solutions

    Microsoft Academic Search

    Yongbin Zhang; Shizhu Wen

    2002-01-01

    This paper investigates line contact elastohydrodynamic lubrication assuming a limiting shear stress of the fluid-contact interfaces. The film pressures and film thickness distributions are obtained for the slide-roll ratios between a cylinder and a plane. The results show that the interfacial limiting shear stress effect can directly cause a drastic film thickness reduction.

  8. Shear stress regulation of nitric oxide production in uterine and placental artery endothelial cells

    E-print Network

    Chesler, Naomi C.

    Shear stress regulation of nitric oxide production in uterine and placental artery endothelial physiological regulator of endothe- lial Nitric Oxide Synthase (eNOS), leading to rapid rises in nitric oxide: pregnancy, shear stress, nitric oxide, blood flow, rheology Introduction Substantial increases in uterine

  9. Shear stresses on megathrusts: Implications for mountain building behind subduction zones

    Microsoft Academic Search

    Simon Lamb

    2006-01-01

    Shear stresses ? on a subduction megathrust play an important role in determining the forces available for mountain building adjacent to a subduction zone. In this study, the temperatures and shear stresses on megathrusts in 11 subduction zones around the Pacific rim (Hikurangi, Tonga, Izu-Ogasawara, western Nankai, northeastern Japan, Aleutians, western Alaska, Cascadia, northern Chile, southern Chile) and SE Asia

  10. Shear stresses on megathrusts: Implications for mountain building behind subduction zones

    Microsoft Academic Search

    Simon Lamb

    2006-01-01

    Shear stresses tau on a subduction megathrust play an important role in determining the forces available for mountain building adjacent to a subduction zone. In this study, the temperatures and shear stresses on megathrusts in 11 subduction zones around the Pacific rim (Hikurangi, Tonga, Izu-Ogasawara, western Nankai, northeastern Japan, Aleutians, western Alaska, Cascadia, northern Chile, southern Chile) and SE Asia

  11. Differential Global Gene Expression Response Patterns of Human Endothelium Exposed to Shear Stress and Intraluminal Pressure

    Microsoft Academic Search

    Maria Andersson; Lena Karlsson; Per-Arne Svensson; Erik Ulfhammer; Mikael Ekman; Margareta Jernås; Lena M. S. Carlsson; Sverker Jern

    2005-01-01

    We investigated the global gene expression response of endothelium exposed to shear stress and intraluminal pressure and tested the hypothesis that the two biomechanical forces induce a differential gene expression response pattern. Intact living human conduit vessels (umbilical veins) were exposed to normal or high intraluminal pressure, or to low or high shear stress in combination with a physiological level

  12. On the use of shear-lag methods for analysis of stress transfer in unidirectional composites

    Microsoft Academic Search

    John A. Nairn

    1997-01-01

    The ‘shear-lag’ analysis method is frequently used for analysis of stress transfer between the fiber and the matrix in composites. The accuracy of shear-lag methods has not been critically assessed, in part because the assumptions have not been fully understood. This paper starts from the exact equations of elasticity for axisymmetric stress states in transversely isotropic materials and introduces the

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

    Technology Transfer Automated Retrieval System (TEKTRAN)

    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...

  14. Shear Stress Inhibits Apoptosis of Ischemic Brain Microvascular Endothelial Cells

    PubMed Central

    Tian, Shan; Bai, Yulong; Yang, Lin; Wang, Xinggang; Wu, Yi; Jia, Jie; Zhu, Yulian; Cheng, Yong; Zhang, Pengyue; Wu, Junfa; Wang, Nianhong; Xia, Guang; Liao, Hua; Zhang, Yuling; Shen, Xiafeng; Yu, Huixian; Hu, Yongshan

    2013-01-01

    As a therapeutic strategy for ischemic stroke, to restore or increase cerebral blood flow (CBF) is the most fundamental option. Laminar shear stress (LS), as an important force generated by CBF, mainly acts on brain microvascular endothelial cells (BMECs). In order to study whether LS was a protective factor in stroke, we investigated LS-intervented ischemic apoptosis of rat BMECs (rBMECs) through PE Annexin V/7-AAD, JC-1 and Hoechst 33258 staining to observe the membranous, mitochondrial and nuclear dysfunction. Real-time PCR and western blot were also used to test the gene and protein expressions of Tie-2, Bcl-2 and Akt, which were respectively related to maintain membranous, mitochondrial and nuclear norm. The results showed that LS could be a helpful stimulus for ischemic rBMECs survival. Simultaneously, membranous, mitochondrial and nuclear regulation played an important role in this process. PMID:23344049

  15. 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.

  16. 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.

  17. Interferometric Measurement Of Residual Stress

    NASA Technical Reports Server (NTRS)

    Danyluk, Steven; Andonian, A. T.

    1990-01-01

    Stress averaged through thickness of plate measured nondestructively. Theory of elasticity combined with laser interferometric technique into technique for measurement of residual stresses in solid objects - usually in thin, nominally-flat plates. Measurements particularly useful in inspection of wafers of single-crystal silicon for making solar cells or integrated circuits, because stresses remaining after crystal-growing process cause buckling or fracture. Used to predict deflections of plates caused by known applied loads under specified boundary condition, or to infer applied loads that cause known deflections. Also used to relate known deflections to residual stresses equivalent to stresses produced by fictitious applied loads.

  18. Fluid shear stress increases neutrophil activation via platelet-activating factor.

    PubMed

    Mitchell, Michael J; Lin, Kimberly S; King, Michael R

    2014-05-20

    Leukocyte exposure to hemodynamic shear forces is critical for physiological functions including initial adhesion to the endothelium, the formation of pseudopods, and migration into tissues. G-protein coupled receptors on neutrophils, which bind to chemoattractants and play a role in neutrophil chemotaxis, have been implicated as fluid shear stress sensors that control neutrophil activation. Recently, exposure to physiological fluid shear stresses observed in the microvasculature was shown to reduce neutrophil activation in the presence of the chemoattractant formyl-methionyl-leucyl-phenylalanine. Here, however, human neutrophil preexposure to uniform shear stress (0.1-2.75 dyn/cm(2)) in a cone-and-plate viscometer for 1-120 min was shown to increase, rather than decrease, neutrophil activation in the presence of platelet activating factor (PAF). Fluid shear stress exposure increased PAF-induced neutrophil activation in terms of L-selectin shedding, ?M?2 integrin activation, and morphological changes. Neutrophil activation via PAF was found to correlate with fluid shear stress exposure, as neutrophil activation increased in a shear stress magnitude- and time-dependent manner. These results indicate that fluid shear stress exposure increases neutrophil activation by PAF, and, taken together with previous observations, differentially controls how neutrophils respond to chemoattractants. PMID:24853753

  19. Measurements in a pressure-driven and a shear-driven three-dimensional turbulent boundary layer

    NASA Technical Reports Server (NTRS)

    Pierce, F. J.; Mcallister, J. E.

    1982-01-01

    Results of mean velocity field, wall static pressure field and simultaneous, direct force measurements of the local wall shear stress magnitude and direction are reported for a pressure-driven and a shear-driven three-dimensional turbulent boundary layer. These data, particularly the direct force local wall shear data, were obtained to test the validity of several of the near-wall similarity models proposed in the literature for such flows.

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

    PubMed

    Kimura, Tsutomu

    2014-01-01

    It has been pointed out by some researchers 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

  1. 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

  2. Shear stress regulates inflammatory and thrombogenic gene transcripts in cultured human endothelial progenitor cells.

    PubMed

    Lund, Trine; Hermansen, Stig E; Andreasen, Thomas V; Olsen, Jan Ole; Østerud, Bjarne; Myrmel, Truls; Ytrehus, Kirsti

    2010-09-01

    Shear stress has an established effect on mature endothelial cells, but less is known about how shear stress regulates endothelial progenitor cells (EPCs). In vitro expanded EPCs isolated from adult human blood represent a novel tool in regenerative vessel therapy. However, in vitro culturing may generate cells with unfavourable properties. The aim of the present study was therefore to assess whether shear stress may influence the inflammatory and thrombotic phenotype of in vitro expanded EPCs. In late outgrowth EPCs, 6 hours of shear stress (6.0 dynes/cm2) significantly reduced the mRNA levels of IL-8, COX2, and tissue factor (TF) compared to static controls. This was associated with a reduced TF activity. In contrast, mRNA expression of NOS3 was significantly increased following 6 and 24 hours of shear stress. In accordance with this, NOS3 protein expression was increased following 24 hours of shear stress. Overall stimulation with the proinflammatory mediator, TNFalpha, for the final 2 hours increased the mRNA expression of IL-6, IL-8, MCP-1, ICAM1, and TF. However exposure to 6 hours of shear stress significantly suppressed the inductory potential of TNFalpha to increase the mRNA levels of IL-6, IL-8, COX2, and TF. Additionally, TNFalpha increased TF activity approximately 10 times, an effect that was also significantly reduced by exposure to 6 and 24 hours of shear stress. The effect of shear on the gene levels of TF and NOS3 were not blocked by the NOS inhibitor L-NAME. These observations suggest that EPCs are capable of functionally responding to shear stress. PMID:20664910

  3. Clinical investigation of the pressure and shear stress on the trans-tibial stump with a prosthesis

    Microsoft Academic Search

    M Zhang; A. R Turner-Smith; A Tanner; V. C Roberts

    1998-01-01

    A system for measuring pressures and bi-axial shear stresses at the body support interfaces has been developed. This system has been used, in five unilateral trans-tibial amputees, to investigate the stresses at multiple points on the residual limb and prosthetic socket interface during standing and walking. The subjects investigated regularly used a patellar-tendon-bearing socket. The maximum peak pressure at the

  4. Onset of flow in a confined colloidal glass under an imposed shear stress

    E-print Network

    Pinaki Chaudhuri; Jürgen Horbach

    2014-10-26

    A confined colloidal glass, under the imposition of a uniform shear stress, is investigated using numerical simulations. Both at macro- and microscales, the consequent dynamics during the onset of flow is studied. When the imposed stress is gradually decreased, the time scale for the onset of steady flow diverges, associated with long-lived spatial heterogeneities. Near this yield-stress regime, persistent creep in the form of shear-banded structures is observed.

  5. 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.

  6. Vascular remodeling is governed by a VEGFR3-dependent fluid shear stress set point.

    PubMed

    Baeyens, Nicolas; Nicoli, Stefania; Coon, Brian G; Ross, Tyler D; Van den Dries, Koen; Han, Jinah; Lauridsen, Holly M; Mejean, Cecile O; Eichmann, Anne; Thomas, Jean-Leon; Humphrey, Jay D; Schwartz, Martin A

    2015-01-01

    Vascular remodeling under conditions of growth or exercise, or during recovery from arterial restriction or blockage is essential for health, but mechanisms are poorly understood. It has been proposed that endothelial cells have a preferred level of fluid shear stress, or 'set point', that determines remodeling. We show that human umbilical vein endothelial cells respond optimally within a range of fluid shear stress that approximate physiological shear. Lymphatic endothelial cells, which experience much lower flow in vivo, show similar effects but at lower value of shear stress. VEGFR3 levels, a component of a junctional mechanosensory complex, mediate these differences. Experiments in mice and zebrafish demonstrate that changing levels of VEGFR3/Flt4 modulates aortic lumen diameter consistent with flow-dependent remodeling. These data provide direct evidence for a fluid shear stress set point, identify a mechanism for varying the set point, and demonstrate its relevance to vessel remodeling in vivo. PMID:25643397

  7. Electromechanical Apparatus Measures Residual Stress

    NASA Technical Reports Server (NTRS)

    Chern, Engmin J.; Flom, Yury

    1993-01-01

    Nondestructive test exploits relationship between stress and eddy-current-probe resistance. Yields data on residual stress or strain in metal tension/compression specimen (stress or strain remaining in specimen when no stress applied from without). Apparatus is assembly of commercial equipment: tension-or-compression testing machine, eddy-current probe, impedance gain-and-phase analyzer measuring impedance of probe coil, and desktop computer, which controls other equipment and processes data received from impedance gain-and-phase analyzer.

  8. Interfacial shear stress distribution in model composites. I - A Kevlar 49 fibre in an epoxy matrix

    SciTech Connect

    Jahankhani, H.; Galiotis, C. (Queen Mary and Westfield College, London (England))

    1991-05-01

    The technique of Laser Raman Spectroscopy has been applied in the study of aramid fibers, such as Kevlar 49, and aramid/epoxy interfaces. A linear relationship has been found between Raman frequencies and strain upon loading a single Kevlar 49 filament in air. Model composites of single Kevlar 49 fibers embedded in epoxy resins have been fabricated and subjected to various degrees of mechanical deformation. The transfer lengths for reinforcement have been measured at various levels of applied tensile load and the dependence of transfer length upon applied matrix strain has been established. Finally, by balancing the tensile and the shear forces acting along the interface, the interfacial shear stress (ISS) distribution along the embedded fiber was obtained. 52 refs.

  9. Measuring the shear strength ratio of glued joints within the same specimen

    Microsoft Academic Search

    B. Pizzo; P. Lavisci; C. Misani; P. Triboulot; N. Macchioni

    2003-01-01

    Measuring the shear strength of both the glueline and the solid wood with the same test specimen offers the advantages that the comparison is direct and the influence of wood variability is minimized. A new specimen geometry was developed for this purpose, and the test is run with two successive loading steps. Finite element modelling showed that the stress distribution

  10. Relation of vessel wall shear stress to atherosclerosis progression in human coronary arteries.

    PubMed

    Gibson, C M; Diaz, L; Kandarpa, K; Sacks, F M; Pasternak, R C; Sandor, T; Feldman, C; Stone, P H

    1993-02-01

    The purpose of this study was to determine the relation between vessel wall shear stress and the rate of atherosclerosis progression. Quantitative angiography was used to calculate the change in coronary arterial diameter over 3.0 years in patients enrolled in the Harvard Atherosclerosis Reversibility Project pilot study (n = 20 arterial segments). Vessel wall shear stress was calculated by means of a validated finite-difference model of the Navier-Stokes' equation that assumes a coronary flow rate of 8 ml/sec. The correlation between vessel wall shear stress and the change in arterial diameter at multiple points (mean, 70) along the length of the artery was then calculated for each of the 20 segments with a focal stenosis. In 15 of the 20 arterial segments there was a significant correlation (p < 0.05) between low shear stress and an increased rate of atherosclerosis progression. A Fisher's z transformation was then used to combine the correlation coefficients from all 20 segments. Low shear stress was significantly correlated (z = 0.37 +/- 0.00074, p < 0.0001) with an increased rate of atherosclerosis progression. This serial quantitative evaluation of human coronary arteries is consistent with previous data that have suggested that low shear stress promotes atherosclerosis progression. Variations in local vessel wall shear stress may explain the previously reported near-independent rate of atherosclerosis progression in multiple lesions within the same patient despite exposure to the same circulating lipoprotein values and systemic hemodynamics. PMID:8427866

  11. A Micromachined Geometric Moire Interferometric Floating-Element Shear Stress Sensor

    NASA Technical Reports Server (NTRS)

    Horowitz, S.; Chen, T.; Chandrasekaran, V.; Tedjojuwono, K.; Nishida, T.; Cattafesta, L.; Sheplak, M.

    2004-01-01

    This paper presents the development of a floating-element shear stress sensor that permits the direct measurement of skin friction based on geometric Moir interferometry. The sensor was fabricated using an aligned wafer-bond/thin-back process producing optical gratings on the backside of a floating element and on the top surface of the support wafer. Experimental characterization indicates a static sensitivity of 0.26 microns/Pa, a resonant frequency of 1.7 kHz, and a noise floor of 6.2 mPa/(square root)Hz.

  12. Stress measurements in soft rocks

    Microsoft Academic Search

    Robert Corthésy; Maria Helena Leite; Denis E Gill; Bernard Gaudin

    2003-01-01

    The objective of this paper is to demonstrate that accurate and reliable in situ stress measurements can be performed in soft rocks. A quick overview of the mechanical behaviour of soft rocks is presented. After reviewing stress measurement techniques that have been used in soft rocks, the modified doorstopper technique is presented and the advantages it has over other techniques

  13. 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. 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.

  14. 17?-Estradiol Reverses Shear Stress-Mediated LDL Modifications

    PubMed Central

    Hwang, Juliana; Rouhanizadeh, Mahsa; Hamilton, Ryan T.; Lin, Tiantian C.; Eiserich, Jason P.; Hodis, Howard N.; Hsiai, Tzung. K.

    2012-01-01

    Within arterial bifurcations or branching points, oscillatory shear stress (OSS) induces oxidative stress mainly via the NADPH oxidase system. It is unknown whether 17?-estradiol (E2) can regulate OSS-mediated low density lipoprotein (LDL) modifications. Bovine aortic endothelial cells (BAECs) were pre-treated with E2 at 5 nmol/L, followed by exposure to OSS (0 ± 3.0 dynes/cm2sec and 60 cycles/min) in a flow system. E2 decreased OSS-mediated NADPH oxidase mRNA expression, and E2-mediated ·NO production was mitigated by the ·NO synthase inhibitor L-NAME. The rates of O2?· production in response to OSS increased steadily as determined by superoxide dismutase-inhibited ferricytochrome c reduction; however, pre-treatment with E2 decreased OSS-mediated O2?· production (n=4, P<0.05). In the presence of native LDL (50 ?g/mL), E2 also significantly reversed OSS-mediated LDL oxidation as determined by high performance liquid chromatography. In the presence of O2?· donor, xanthine oxidase (XO), E2 further reversed XO-induced LDL lipid peroxidation (n=3, P<0.001). Mass spectra were acquired in the m/z 400–1800 range, revealing XO-mediated LDL protein nitration involving tyrosine 2535 in the ?-2 domains, whereas pre-treatment with E2 reversed this observation, consistent with the changes in nitrotyrosine intensities by the dot blots. E2 plays an indirect antioxidative role. In addition to up-regulation of eNOS and down-regulation of Nox4 expression, E2 influences LDL modifications via lipid peroxidation and protein nitration. PMID:16863990

  15. 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

  16. 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.

  17. 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 ?, 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.

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

    PubMed

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

    2010-06-01

    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

  19. SHEAR WAVE DISPERSION MEASURES LIVER STEATOSIS

    PubMed Central

    Barry, Christopher T.; Mills, Bradley; Hah, Zaegyoo; Mooney, Robert A.; Ryan, Charlotte K.; Rubens, Deborah J.; Parker, Kevin J.

    2012-01-01

    Crawling waves, which are interfering shear wave patterns, can be generated in liver tissue over a range of frequencies. Some important biomechanical properties of the liver can be determined by imaging the crawling waves using Doppler techniques and analyzing the patterns. We report that the dispersion of shear wave velocity and attenuation, that is, the frequency dependence of these parameters, are strongly correlated with the degree of steatosis in a mouse liver model, ex vivo. The results demonstrate the possibility of assessing liver steatosis using noninvasive imaging methods that are compatible with color Doppler scanners and, furthermore, suggest that liver steatosis can be separated from fibrosis by assessing the dispersion or frequency dependence of shear wave propagations. PMID:22178165

  20. Plantar shear stress distributions in diabetic patients with and without neuropathy

    PubMed Central

    Yavuz, Metin

    2014-01-01

    Background The exact pathology of diabetic foot ulcers remains to be resolved. Evidence suggests that plantar shear forces play a major role in diabetic ulceration. Unfortunately, only a few manuscripts exist on the clinical implications of plantar shear. The purpose of this study was to compare global and regional peak plantar stress values in three groups; diabetic patients with neuropathy, diabetic patients without neuropathy and healthy control subjects. Methods Fourteen diabetic neuropathic patients, 14 non-neuropathic diabetic control and 11 non-diabetic control subjects were recruited. Subjects walked on a custom-built stress plate that quantified plantar pressures and shear. Four stress variables were analyzed; peak pressure, peak shear, peak pressure-time and shear-time integral. Findings Global peak values of peak shear (p=0.039), shear-time integral (p=0.002) and pressure-time integral (p=0.003) were significantly higher in the diabetic neuropathic group. Local peak shear stress and shear-time integral were also significantly higher in diabetic neuropathic patients compared to both control groups, in particular, at the hallux and central forefoot. Local peak pressure and pressure-time integral were significantly different between the three groups at the medial and lateral forefoot. Interpretation Plantar shear and shear-time integral magnitudes were elevated in diabetic patients with peripheral neuropathy, which indicates the potential clinical significance of these factors in ulceration. It is thought that further investigation of plantar shear would lead to a better understanding of ulceration pathomechanics, which in turn will assist researchers in developing more effective preventive devices and strategies. PMID:24332719

  1. Frictional Response of Molecularly Thin Liquid Polymer Films Subject to Constant Shear Stress

    NASA Astrophysics Data System (ADS)

    Tschirhart, Charles; Troian, Sandra

    2014-03-01

    Measurements of the frictional response of nanoscale viscous films are typically obtained using the surface force apparatus in which a fluid layer is confined between smooth solid substrates approaching at constant speed or force. The squeezing pressure causes lateral flow from which the shear viscosity can be deduced. Under these conditions however, molecularly thin films tend to solidify wholly or partially and estimates of the shear viscosity can exceed those in macroscale films by many orders of magnitude. This problem can be avoided altogether by examining the response of an initially flat, supported, free surface film subject to comparable values of surface shear stress by application of an external inert gas stream. This method was first conceived by Derjaguin in 1944; more recent studies by Mate et al. at IBM Almaden on complex polymeric systems have uncovered fluid layering and other interesting behaviors. The only drawback is that this alternative technique requires an accurate model for interface distortion. We report on ellipsometric measurements of ultrathin polymeric films in efforts to determine whether the usual interface equations for free surface films based purely on continuum models can be properly extended to nanoscale films. Supported by a Fred and Jean Felberg Fellowship and G. W. Housner Student Discovery Fund.

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

    PubMed Central

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

    2010-01-01

    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. PMID:20363882

  3. Frequency-dependent response of the vascular endothelium to pulsatile shear stress

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Most cells of the circulatory system are exposed to shear forces that occur at the frequency of the heartbeat. However, as a result of the complicated blood flow patterns that occur at arterial branches, small regions of the arterial wall experience fluctuations in shear stress that are dominated by...

  4. Figure 1: Multiplex logarithmic microfluidic perfusion array for probing shear stress effects on stem cells. (A)

    E-print Network

    Voldman, Joel

    on stem cells. (A) Microfluidic perfusion systems exhibit more defined shear stress profiles and consume) for a typical soluble factor (MW~20 kDa) secreted by mouse embryonic stem cells (mESCs) investigated EMBRYONIC STEM CELLS Y.C. Toh1 and J. Voldman1* 1 Massachusetts Institute of Technology, USA ABSTRACT Shear

  5. On velocity profiles and stresses in sheared and vibrated granular systems under variable gravity

    E-print Network

    Kondic, Lou

    On velocity profiles and stresses in sheared and vibrated granular systems under variable gravity that include realistic modeling of physical system boundaries to determine the influence of gravity on velocity, and sheared by a rotated upper wall. In addition to Earth gravity, we consider other gravitational fields

  6. Stress response and structural transitions in sheared gyroidal and lamellar amphiphilic mesophases: Lattice-Boltzmann simulations

    E-print Network

    Harting, Jens

    Stress response and structural transitions in sheared gyroidal and lamellar amphiphilic mesophases and lamellar amphiphilic mesophases to steady shear simulated using a bottom-up lattice-Boltzmann model for amphiphilic fluids and sliding periodic Lees-Edwards bound- ary conditions. We study the gyroid per se above

  7. Effect of shear stress and substrate on endothelial DAPK expression, caspase activity, and apoptosis

    PubMed Central

    2013-01-01

    Background In the vasculature, misdirected apoptosis in endothelial cells leads to pathological conditions such as inflammation. Along with biochemical and molecular signals, the hemodynamic forces that the cells experience are also important regulators of endothelial functions such as proliferation and apoptosis. Laminar shear stress inhibits apoptosis induced by serum depletion, oxidative stress, and tumor necrosis factor ? (TNF?). Death associated protein kinase (DAPK) is a positive regulator of TNF? induced apoptotic pathway. Here we investigate the effect of shear stress on DAPK in endothelial cells on glass or silicone membrane substrate. We have already shown a link between shear stress and DAPK expression and apoptosis in cells on glass. Here we transition our study to endothelial cells on non-glass substrates, such as flexible silicone membrane used for cyclic strain studies. Results We modified the classic parallel plate flow chamber to accommodate silicone membrane as substrate for cells, and validated the chamber for cell viability in shear stress experiments. We found that adding shear stress significantly suppressed TNF? induced apoptosis in cells; while shearing cells alone also increased apoptosis on either substrate. We also found that shearing cells at 12 dynes/cm2 for 6 hours resulted in increased apoptosis on both substrates. This shear-induced apoptosis correlated with increased caspase 3/7 activities and DAPK expression and activation via dephosphorylation of serine 308. Conclusion These data suggest that shear stress induced apoptosis in endothelial cells via increased DAPK expression and activation as well as caspase-3/7 activity. Most in vitro shear stress studies utilize the conventional parallel plate flow chamber where cells are cultured on glass, which is much stiffer than what cells encounter in vivo. Other mechanotransduction studies have utilized the flexible silicone membrane as substrate, for example, in cyclic stretch studies. Thus, this study bridges the gap between shear stress studies on cells plated on glass to studies on different stiffness of substrates or mechanical stimulation such as cyclic strain. We continue to explore the mechanotransduction role of DAPK in endothelial apoptosis, by using substrates of physiological stiffness for shear stress studies, and by using silicone substrate in cyclic stretch devices. PMID:23305096

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

    SciTech Connect

    Workman, A.; Wallwork, A. [AWE, Aldermaston, Reading, RG7 4PR (United Kingdom); Meziere, Y. J. E.; Millett, J. C. F. [Defence Academy of the UK, Cranfield University, Shrivenham, Swindon, SN6 8LA (United Kingdom); Bourne, N. K. [University of Manchester, Sackville Street, Manchester, M60 1QD (United Kingdom)

    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.

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

    SciTech Connect

    Waltz, R. E.; Staebler, G. M. [General Atomics, P.O. Box 85608, San Diego, California 92186-5608 (United States); Solomon, W. M. [Princeton Plasma Physics Laboratory, P.O. Box 451, Princeton, New Jersey 08543-0451 (United States)

    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 the much smaller profile shear residual stress component.

  10. 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.

  11. Experimental studies of shear stress and flow separation in low Reynolds number flows

    E-print Network

    Weldon, Matthew J. (Matthew Jacob)

    2007-01-01

    Presented here is an experimental investigation of the kinematic theory of separation in unsteady two-dimensional flows, and an evaluation of a novel optical shear stress sensor. Fixed separation in the rotor-oscillator ...

  12. Relationship between Microtubule Network Structure and Intracellular Transport in Cultured Endothelial Cells Affected by Shear Stress

    NASA Astrophysics Data System (ADS)

    Kudo, Susumu; Ikezawa, Kenji; Ikeda, Mariko; Tanishita, Kazuo

    Endothelial cells (ECs) that line the inner surface of blood vessels are barriers to the transport of various substances into or from vessel walls, and are continuously exposed to shear stress induced by blood flow in vivo. Shear stress affects the cytoskeleton (e.g., microtubules, microfilaments, intermediate filaments), and affects the transport of macromolecules. Here, the relationship between the microtubule network structure and this transport process for albumin uptake within cultured aortic endothelial cells affected by shear stress was studied. Based on fluorescent images of albumin uptake obtained by using confocal laser scanning microscopy (CLSM), both the microtubule network and albumin uptake in ECs were disrupted by colchicine and were affected by shear stress loading.

  13. An instrumented fastener for shear force measurements in joints

    NASA Technical Reports Server (NTRS)

    Sawyer, James W.; Rothgeb, Timothy M.

    1992-01-01

    Results are presented of a preliminary investigation of instrumented fasteners for use as sensors to measure the shear loads transmitted by individual fasteners installed in double splice joints. Calibration and load verification tests were conducted for instrumented fasteners installed at three fastener torque levels. Calibration test results show that the shear strains obtained from the instrumented fasteners vary linearly with the applied load and that the instrumented fasteners can be effectively used to measure shear loads transmitted by individual fasteners installed in double splice joints. The load distribution between individual fasteners is found to be dependent on the location of the fastener in the joint and the fastener torque level.

  14. Efforts to Reduce Mortality to Hydroelectric Turbine-Passed Fish: Locating and Quantifying Damaging Shear Stresses

    Microsoft Academic Search

    Glenn ?ada; James Loar; Laura Garrison; Richard Fisher; Duane Neitzel

    2006-01-01

    Severe fluid forces are believed to be a source of injury and mortality to fish that pass through hydroelectric turbines.\\u000a A process is described by which laboratory bioassays, computational fluid dynamics models, and field studies can be integrated\\u000a to evaluate the significance of fluid shear stresses that occur in a turbine. Areas containing potentially lethal shear stresses\\u000a were identified near

  15. Fluid shear stress in trabecular bone marrow due to low-magnitude high-frequency vibration.

    PubMed

    Coughlin, Thomas R; Niebur, Glen L

    2012-08-31

    Low-magnitude high-frequency (LMHF) loading has recently received attention for its anabolic effect on bone. The mechanism of transmission of the anabolic signal is not fully understood, but evidence indicates that it is not dependent on bone matrix strain. One possible source of signaling is mechanostimulation of the cells in the bone marrow. We hypothesized that the magnitude of the fluid shear stress in the marrow during LMHF loading is in the mechanostimulatory range. As such, the goal of this study was to determine the range of shear stress in the marrow during LMHF vibration. The shear stress was estimated from computational models, and its dependence on bone density, architecture, permeability, marrow viscosity, vibration amplitude and vibration frequency were examined. Three-dimensional finite element models of five trabecular bone samples from different anatomic sites were constructed, and a sinusoidal velocity profile was applied to the models. In human bone models during axial vibration at an amplitude of 1 g, more than 75% of the marrow experienced shear stress greater than 0.5Pa. In comparison, in vitro studies indicate that fluid induced shear stress in the range of 0.5 to 2.0Pa is anabolic to a variety of cells in the marrow. Shear stress at the bone-marrow interface was as high as 5.0Pa. Thus, osteoblasts and bone lining cells that are thought to reside on the endosteal surfaces may experience very high shear stress during LMHF loading. However, a more complete understanding of the location of the various cell populations in the marrow is needed to quantify the effects on specific cell types. This study suggests the shear stress within bone marrow in real trabecular architecture during LMHF vibration could provide the mechanical signal to marrow cells that leads to bone anabolism. PMID:22784651

  16. DNA microarray reveals changes in gene expression of shear stressed human umbilical vein endothelial cells

    Microsoft Academic Search

    Susan M. McCormick; Suzanne G. Eskin; Larry V. McIntire; Christina L. Teng; Chiung-Mei Lu; Christopher G. Russell; Krishnan K. Chittur

    2001-01-01

    Using DNA microarray screening (GeneFilter 211, Research Genetics, Huntsville, AL) of mRNA from primary human umbilical vein endothelial cells (HUVEC), we identified 52 genes with significantly altered expression under shear stress [25 dynes\\/cm2 for 6 or 24 h (1 dyne = 10 muN), compared with matched stationary controls]; including several genes not heretofore recognized to be shear stress responsive. We

  17. Coronary stent implantation changes 3-D vessel geometry and 3-D shear stress distribution

    Microsoft Academic Search

    Jolanda J. Wentzel; Deirdre M. Whelan; Willem J. van der Giessen; Heleen M. M. van Beusekom; Ivan Andhyiswara; Patrick W. Serruys; Cornelis J. Slager; Rob Krams

    2000-01-01

    Mechanisms of in-stent restenosis are not fully understood. Shear stress is known to play a role in plaque and thrombus formation and is sensitive to changes in regional vessel geometry. Hence, we evaluated the regional changes in 3-D geometry and shear stress induced by stent placement in coronary arteries of pigs.Methods. 3-D reconstruction was performed, applying a combined angiographic and

  18. Elasticity of associative polymer solutions and slip at high shear stress

    Microsoft Academic Search

    Kayvan Sadeghy; David F. James

    2000-01-01

    The rheological behavior of several associative polymers in aqueous solution was examined by carrying out measurements in steady shear, oscillatory shear, and uniaxial extension. The associative polymers were commercial samples and the solution concentrations were in the 1% range, the range where close packing of the micelle-like clusters leads to bridging and the formation of large networks. In steady shear,

  19. An octahedral shear strain-based measure of SNR for 3D MR elastography

    NASA Astrophysics Data System (ADS)

    McGarry, M. D. J.; Van Houten, E. E. W.; Perriñez, P. R.; Pattison, A. J.; Weaver, J. B.; Paulsen, K. D.

    2011-07-01

    A signal-to-noise ratio (SNR) measure based on the octahedral shear strain (the maximum shear strain in any plane for a 3D state of strain) is presented for magnetic resonance elastography (MRE), where motion-based SNR measures are commonly used. The shear strain, ?, is directly related to the shear modulus, ?, through the definition of shear stress, ? = ??. Therefore, noise in the strain is the important factor in determining the quality of motion data, rather than the noise in the motion. Motion and strain SNR measures were found to be correlated for MRE of gelatin phantoms and the human breast. Analysis of the stiffness distributions of phantoms reconstructed from the measured motion data revealed a threshold for both strain and motion SNR where MRE stiffness estimates match independent mechanical testing. MRE of the feline brain showed significantly less correlation between the two SNR measures. The strain SNR measure had a threshold above which the reconstructed stiffness values were consistent between cases, whereas the motion SNR measure did not provide a useful threshold, primarily due to rigid body motion effects.

  20. [Integrins mediate the migration of HepG2 cells induced by low shear stress].

    PubMed

    Lijuan, Wang; Liu, Xiaoheng; Yu, Hongchi; Zhou, Fating; Chen, Huilin; Liu, Qianqi

    2014-04-01

    Low shear stress is a component of the tumor microenvironment in vivo and plays a key role in regulating cancer cell migration and invasion. The integrin, as a mechano-sensors mediating and integrating mechanical and chemical signals, induce the adhesion between cells and extracellular matrix (ECM). The purpose of this study is to investigate the effect of low shear stress (1.4 dyn/cm2)on the migration of HepG2 cells and the expression of integrin. Scratch wound migration assay was performed to examine the effect of low shear stress on the migration of HepG2 cells at 0 h, 1 h, 2 h and 4 h, respectively. F-actin staining was used to detect the expression of F-actin in HepG2 cells treated with low shear stress at 2 h and 4 h. Western blot analysis was carried out to determine the effect of low shear stress on the expression of integrin at different durations. The results showed that the migrated distance of HepG2 cells and the expression of F-actin increased significantly compared with the controls. The integrin alpha subunits showed a different time-dependent expression, suggesting that various subunits of integrin exhibit different effects in low shear stress regulating cancer cells migration. PMID:25039138

  1. Hemodynamic Shear Stress and Endothelial Dysfunction in Hemodialysis Access

    PubMed Central

    Fitts, Michelle K.; Pike, Daniel B.; Anderson, Kasey; Shiu, Yan-Ting

    2014-01-01

    Surgically-created blood conduits used for chronic hemodialysis, including native arteriovenous fistulas (AVFs) and synthetic AV grafts (AVGs), are the lifeline for kidney failure patients. Unfortunately, each has its own limitations: AVFs often fail to mature to become useful for dialysis and AVGs often fail due to stenosis as a result of neointimal hyperplasia, which preferentially forms at the graft-venous anastomosis. No clinical therapies are currently available to significantly promote AVF maturation or prevent neointimal hyperplasia in AVGs. Central to devising strategies to solve these problems is a complete mechanistic understanding of the pathophysiological processes. The pathology of arteriovenous access problems is likely multi-factorial. This review focuses on the roles of fluid-wall shear stress (WSS) and endothelial cells (ECs). In arteriovenous access, shunting of arterial blood flow directly into the vein drastically alters the hemodynamics in the vein. These hemodynamic changes are likely major contributors to non-maturation of an AVF vein and/or formation of neointimal hyperplasia at the venous anastomosis of an AVG. ECs separate blood from other vascular wall cells and also influence the phenotype of these other cells. In arteriovenous access, the responses of ECs to aberrant WSS may subsequently lead to AVF non-maturation and/or AVG stenosis. This review provides an overview of the methods for characterizing blood flow and calculating WSS in arteriovenous access and discusses EC responses to arteriovenous hemodynamics. This review also discusses the role of WSS in the pathology of arteriovenous access, as well as confounding factors that modulate the impact of WSS. PMID:25309636

  2. Wall Shear Stress – an Important Determinant of Endothelial Cell Function and Structure – in the Arterial System in vivo

    Microsoft Academic Search

    Robert S. Reneman; Theo Arts; Arnold P. G. Hoeks

    2006-01-01

    It has been well established that wall shear stress is an important determinant of endothelial cell function and gene expression as well as of its structure. There is increasing evidence that low wall shear stress, as pres- ent in artery bifurcations opposite to the flow divider where atherosclerotic lesions preferentially originate, expresses an atherogenic endothelial gene profile. Besides, wall shear

  3. Effects of bottom shear stresses on the wave-induced dynamic response in a porous seabed: PORO-WSSI (shear) model

    NASA Astrophysics Data System (ADS)

    Ye, J.; Jeng, D.-S.

    2011-12-01

    When ocean waves propagate over the sea floor, dynamic wave pressures and bottom shear stresses exert on the surface of seabed. The bottom shear stresses provide a horizontal loading in the wave-seabed interaction system, while dynamic wave pressures provide a vertical loading in the system. However, the bottom shear stresses have been ignored in most previous studies in the past. In this study, the effects of the bottom shear stresses on the dynamic response in a seabed of finite thickness under wave loading will be examined, based on Biot's dynamic poro-elastic theory. In the model, an " u- p" approximation will be adopted instead of quasi-static model that have been used in most previous studies. Numerical results indicate that the bottom shear stresses has certain influences on the wave-induced seabed dynamic response. Furthermore, wave and soil characteristics have considerable influences on the relative difference of seabed response between the previous model (without shear stresses) and the present model (with shear stresses). As shown in the parametric study, the relative differences between two models could up to 10% of p 0, depending on the amplitude of bottom shear stresses.

  4. An implementation of Bayesian lensing shear measurement

    NASA Astrophysics Data System (ADS)

    Sheldon, Erin S.

    2014-10-01

    The Bayesian gravitational shear estimation algorithm developed by Bernstein & Armstrong can potentially be used to overcome multiplicative noise bias and recover shear using very low signal-to-noise ratio (S/N) galaxy images. In that work, the authors confirmed that the method is nearly unbiased in a simplified demonstration, but no test was performed on images with realistic pixel noise. Here, I present a full implementation for fitting models to galaxy images, including the effects of a point spread function (PSF) and pixelization. I tested the implementation using simulated galaxy images modelled as Sérsic profiles with n = 1 (exponential) and n = 4 (De Vaucouleurs'), convolved with a PSF and a flat pixel response function. I used a round Gaussian model for the PSF to avoid potential PSF-fitting errors. I simulated galaxies with mean observed, post-PSF full width at half-maximum equal to approximately 1.2 times that of the PSF, with lognormal scatter. I also drew fluxes from a lognormal distribution. I produced independent simulations, each with pixel noise tuned to produce different mean S/N ranging from 10-1000. I applied a constant shear to all images. I fitted the simulated images to a model with the true Sérsic index to avoid modelling biases. I recovered the input shear with fractional error ?g/g < 2 × 10-3 in all cases. In these controlled conditions, and in the absence of other multiplicative errors, this implementation is sufficiently unbiased for current surveys and approaches the requirements for planned surveys.

  5. Acute shear stress direction dictates adherent cell remodeling and verifies shear profile of spinning disk assays.

    PubMed

    Fuhrmann, Alexander; Engler, Adam J

    2015-02-01

    Several methods have been developed to quantify population level changes in cell attachment strength given its large heterogeneity. One such method is the rotating disk chamber or 'spinning disk' 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

  6. Wall shear stress characterization of a 3D bluff-body separated flow

    NASA Astrophysics Data System (ADS)

    Fourrié, Grégoire; Keirsbulck, Laurent; Labraga, Larbi

    2013-10-01

    Efficient flow control strategies aimed at reducing the aerodynamic drag of road vehicles require a detailed knowledge of the reference flow. In this work, the flow around the rear slanted window of a generic car model was experimentally studied through wall shear stress measurements using an electrochemical method. The mean and fluctuating wall shear stress within the wall impact regions of the recirculation bubble and the main longitudinal vortex structures which develop above the rear window are presented. Correlations allow a more detailed characterization of the recirculation phenomenon within the separation bubble. In the model symmetry plane the recirculation structure compares well with simpler 2D configurations; specific lengths, flapping motion and shedding of large-scale vortices are observed, these similarities diminish when leaving the middle plane due to the strong three-dimensionality of the flow. A specific attention is paid to the convection processes occurring within the recirculation: a downstream convection velocity is observed, in accordance with 2D recirculations from the literature, and an upstream convection is highlighted along the entire bubble length which has not been underlined in some previous canonical configurations.

  7. Evaluations of wall shear stress in the standpipe of a circulating fluidized bed

    SciTech Connect

    Monazam, E.R.; Shadle, L.J.

    2008-05-13

    Shear stress was obtained in the standpipe of a Circulating Fluidized Bed (CFB) for a light cork particles under a variety of flow conditions. The shear stress data were estimated using incremental gas phase pressure drop readings, and an estimate of the bed height to predict the hydrostatic pressure drop [(dp/dy) = ?s (1-?) g+4?sw/D]. In addition, we have also obtained data on aeration rate in the standpipe, particle circulation rate and riser gas flow rate. Analysis of the results using a one-dimensional momentum equation reveal that the observed forced per unit area may be attributed to wall friction. The resulting shear stress demonstrates that as the aeration air in the standpipe was increased the shear at the wall was decreased. An attempt was made to model solids friction factor as a function of particle velocity and it was compared to the other literature correlations.

  8. Viscoelastic shear properties of human vocal fold mucosa: measurement methodology and empirical results.

    PubMed

    Chan, R W; Titze, I R

    1999-10-01

    A standard method for the empirical rheological characterization of viscoelastic materials was adopted to measure the viscoelastic shear properties of human vocal-fold mucosal tissues (the superficial layer of lamina propria). A parallel-plate rotational rheometer was employed to measure shear deformation of viscoelastic tissue samples, which were deformed between two rigid circular plates rotating in small-amplitude sinusoidal oscillations. Elastic and viscous shear moduli of the samples were then quantified as a function of oscillation frequency (0.01 to 15 Hz) based on shear stresses and strains recorded by the rheometer. Data were obtained from 15 excised human larynges (10 male and 5 female). Results showed that the elastic shear modulus mu and the damping ratio zeta of human vocal-fold mucosa were relatively constant across the range of frequencies observed, while the dynamic viscosity eta decreased monotonically with frequency (i.e., shear thinning). Intersubject differences in mu and eta as large as an order of magnitude were observed, part of which may reflect age-related and gender-related differences. Some molecular interpretations of the findings are discussed. PMID:10530024

  9. Stress-Driven Melt Segregation and Shear Localization in Partially Molten Aggregates: Experiments in Torsion

    NASA Astrophysics Data System (ADS)

    King, D. S.; Kohlstedt, D. L.; Zimmerman, M. E.

    2007-12-01

    Simple shear experiments of partially molten aggregates have demonstrated that shear induces organized patterns of melt distribution and strain localization [1,2]. New torsion experiments on partially molten aggregates of olivine + chromite + 4 vol.% mid-ocean ridge basalt provide additional insights into the interactions between deformation and melt segregation. Samples were deformed at constant strain rates ranging from 3x10-5 to 3x10-4 /s, corresponding to shear stresses of ~60 and ~100 MPa, respectively. When samples are sheared, melt segregates into distinct melt-rich bands oriented ~15° antithetic to the shear direction. The melt fraction in the bands ranges from 0.1 to 0.2. In samples deformed at higher stress, bands are narrower and more closely spaced. At a shear stress of ~60 MPa bands are ~21 ?m wide and spaced ~104 ?m apart. At a shear stress of ~100 MPa bands are ~15?m wide and spaced ~71 ?m apart. Melt segregation occurs in both the dislocation creep and diffusion creep regimes. Our experiments demonstrate that melt-rich bands form at a strain of ~100% regardless of the stress at which the sample is deformed. Near this strain threshold, the behavior of the sample changes from strain hardening to strain softening. This observation indicates that, in addition to providing high-permeability pathways through which melt can travel, melt bands also become zones of localized deformation. Strain is partitioned and localized into melt-rich bands because of a viscosity reduction in regions of elevated melt fraction. This process of stress driven melt segregation has implications for melt transport in many geological settings, including beneath mid-ocean ridges, and for the formation of shear zones in partially molten rocks. [1] Zimmerman, M. et al., Geophys. Res. Lett., 26, 1999. [2]Holtzman, B. et al., Geochem. Geophys. Geosyst., 4, 2003.

  10. Composite material shear property measurement using the Iosipescu specimen

    NASA Technical Reports Server (NTRS)

    Ho, Henjen; Budiman, Haryanto T.; Tsai, Ming-Yi; Morton, John; Farley, Gary L.

    1992-01-01

    A detailed evaluation of the suitability of the Iosipescu specimen tested in the modified Wyoming fixture is presented. Finite element analysis and moire interferometry are used to assess the uniformity of the shear stress field in the test section of unidirectional and cross-ply graphite-epoxy composites. The nonuniformity of the strain field and the sensitivity of some fiber orientations to the specimen/fixture contact mechanics are discussed. The shear responses obtained for unidirectional and cross-ply graphite-epoxy composites are discussed and problems associated with anomalous behavior are addressed. An experimental determination of the shear response of a range of material systems using strain gage instrumentation and moire interferometry is performed.

  11. Tension Fields in Originally Curved, Thin Sheets During Shearing Stresses

    NASA Technical Reports Server (NTRS)

    Wagner, H; Ballerstedt, W

    1935-01-01

    The analysis of the stresses in the sheet and stiffeners is predicated upon the direction of the wrinkles, particularly the tensile stresses (principal stresses). This analysis and the calculation of stresses after buckling form the subject of the present article. It includes: 1) metal cylinders with closely spaced longitudinal stiffeners; 2) metal cylinders with closely spaced transverse rings.

  12. CCD evaluation for estimating measurement precision in lateral shearing interferometry

    NASA Astrophysics Data System (ADS)

    Liu, Bingcai; Li, Bing; Tian, Ailing; Li, Baopeng

    2013-06-01

    Because of larger measurement ability of wave-front deviation and no need of reference plat, the lateral shearing interferometry based on four step phase shifting has been widely used for wave-front measurement. After installation shearing interferograms are captured by CCD camera, and the actual phase data of wave-front can be calculated by four step phase shift algorithm and phase unwrapping. In this processing, the pixel resolution and gray scale of CCD camera is the vital factor for the measurement precision. In this paper, Based on the structure of lateral shearing surface interferometer with phase shifting, pixel resolution more or less for measurement precision is discussed. Also, the gray scale is 8 bit, 12 bit or 16 bit for measurement precision is illustrated by simulation.

  13. Acoustic radiation stress measurement

    NASA Technical Reports Server (NTRS)

    Cantrell, John H., Jr.; Yost, William T.

    1987-01-01

    Ultrasonic radio frequency tone-bursts are launched into a sample of material tested. The amplitude of the tone-bursts and the slope of the resulting static displacement pulses are measured. These measurements are used to calculate the nonlinearities of the materials.

  14. The FASEB Journal Research Communication Fluid shear stress primes mouse embryonic stem cells

    E-print Network

    Voldman, Joel

    The FASEB Journal · Research Communication Fluid shear stress primes mouse embryonic stem cells stress is a ubiquitous environmen- tal cue experienced by stem cells when they are being differentiated or expanded in perfusion cultures. How- ever, its role in modulating self-renewing stem cell phenotypes

  15. Rac1 mediates laminar shear stress-induced vascular endothelial cell migration

    PubMed Central

    Huang, Xianliang; Shen, Yang; Zhang, Yi; Wei, Lin; Lai, Yi; Wu, Jiang; Liu, Xiaojing; Liu, Xiaoheng

    2013-01-01

    The migration of endothelial cells (ECs) plays an important role in vascular remodeling and regeneration. ECs are constantly subjected to shear stress resulting from blood flow and are able to convert mechanical stimuli into intracellular signals that affect cellular behaviors and functions. The aim of this study is to elucidate the effects of Rac1, which is the member of small G protein family, on EC migration under different laminar shear stress (5.56, 10.02, and 15.27 dyn/cm2). The cell migration distance under laminar shear stress increased significantly than that under the static culture condition. Especially, under relative high shear stress (15.27 dyn/cm2) there was a higher difference at 8 h (P < 0.01) and 2 h (P < 0.05) compared with static controls. RT-PCR results further showed increasing mRNA expression of Rac1 in ECs exposed to laminar shear stress than that exposed to static culture. Using plasmids encoding the wild-type (WT), an activated mutant (Q61L), and a dominant-negative mutant (T17N), plasmids encoding Rac1 were transfected into EA.hy 926 cells. The average net migration distance of Rac1Q61L group increased significantly, while Rac1T17N group decreased significantly in comparison with the static controls. These results indicated that Rac1 mediated shear stress-induced EC migration. Our findings conduce to elucidate the molecular mechanisms of EC migration induced by shear stress, which is expected to understand the pathophysiological basis of wound healing in health and diseases. PMID:24430179

  16. Regional variation of wall shear stress in ascending thoracic aortic aneurysms.

    PubMed

    Rinaudo, Antonino; Pasta, Salvatore

    2014-06-18

    The development of an ascending thoracic aortic aneurysm is likely caused by excessive hemodynamic loads exerted on the aneurysmal wall. Computational fluid-dynamic analyses were performed on patient-specific ascending thoracic aortic aneurysms obtained from patients with either bicuspid aortic valve or tricuspid aortic valve to evaluate hemodynamic and wall shear parameters, imparting aneurysm enlargement. Results showed an accelerated flow along the outer aortic wall with helical flow in the aneurysm center for bicuspid aortic valve ascending thoracic aortic aneurysms. In a different way, tricuspid aortic valve ascending thoracic aortic aneurysms exhibited normal systolic flow without substantial secondary pattern. Analysis of wall shear parameters evinced a high and locally varying wall shear stress on the outer aortic wall and high temporal oscillations in wall shear stress (oscillatory shear index) on either left or right side of aneurysmal aorta. These findings may explain the asymmetric dilatation typically observed in ascending thoracic aortic aneurysms. Simulations of a hypertensive scenario revealed an increase in wall shear stress upon 44% compared to normal systemic pressure models. Computational fluid-dynamics-based analysis may allow identification of wall shear parameters portending aneurysm dilatation and hence guide preventative intervention. PMID:24942163

  17. Critical resolved shear stress anomalies of the L1 2-long-range ordered ??-phase of the superalloy NIMONIC 105

    Microsoft Academic Search

    Astrid Nitz; Eckhard Nembach

    1999-01-01

    The critical resolved shear stress ?0NIM?? of the multicomponent nickel-rich L12-long-range ordered ??-phase ??NIM has been measured in tension (t) and compression (c) tests. Precipitates of ??NIM strengthen the commercial nickel-base superalloy NIMONIC 105. The nominal orientations hkl of the single crystal axes were: [001], [011], 1?11, and 1?23; the deformation temperatures (T) ranged from 283 to 1150 K. The

  18. The SDSS Coadd: Cosmic Shear Measurement

    SciTech Connect

    Lin, Huan; /Fermilab; Dodelson, Scott; /Fermilab /Chicago U., EFI /Chicago U., KICP; Seo, Hee-Jong; /UC, Berkeley; Soares-Santos, Marcelle; /Fermilab; Annis, James; /Fermilab; Hao, Jiangang; /Fermilab; Johnston, David; /Fermilab; Kubo, Jeffrey M.; /Fermilab; Reis, Ribamar R.R.; /Fermilab /Rio de Janeiro Federal U.; Simet, Melanie; /Chicago U., EFI /Chicago U., KICP

    2011-11-01

    Stripe 82 in the Sloan Digital Sky Survey was observed multiple times, allowing deeper images to be constructed by coadding the data. Here we analyze the ellipticities of background galaxies in this 275 square degree region, searching for evidence of distortions due to cosmic shear. The E-mode is detected in both real and Fourier space with > 5-{sigma} significance on degree scales, while the B-mode is consistent with zero as expected. The amplitude of the signal constrains the combination of the matter density {Omega}{sub m} and fluctuation amplitude {sigma}{sub 8} to be {Omega}{sub m}{sup 0.7} {sigma}{sub 8} = 0.276{sub -0.050}{sup +0.036}.

  19. Microscopic origins of shear stress in dense fluid-grain mixtures

    E-print Network

    Donia Marzougui; Bruno Chareyre; Julien Chauchat

    2015-04-14

    A numerical model is used to simulate rheometer experiments at constant normal stress on dense suspensions of spheres. The complete model includes sphere-sphere contacts using a soft contact approach, short range hydrodynamic interactions defined by frame-invariant expressions of forces and torques in the lubrication approximation, and drag forces resulting from the poromechanical coupling computed with the DEM-PFV technique. Series of simulations in which some of the coupling terms are neglected highlight the role of the poromechanical coupling in the transient regimes. They also reveal that the shear component of the lubrication forces, though frequently neglected in the literature, has a dominant effect in the volume changes. On the other hand, the effects of lubrication torques are much less significant. The bulk shear stress is decomposed into contact stress and hydrodynamic stress terms whose dependency on a dimensionless shear rate - the so called viscous number $I_v$ - are examined. Both contributions are increasing functions of $I_v$, contacts contribution dominates at low viscous number ($I_v$ 0.15, consistently with a phenomenological law infered by other authors. Statistics of microstructural variables highlight a complex interplay between solid contacts and hydrodynamic interactions. In contrast with a popular idea, the results suggest that lubrication may not necessarily reduce the contribution of contact forces to the bulk shear stress. The proposed model is general and applies directly to sheared immersed granular media in which pore pressure feedback plays a key role (triggering of avalanches, liquefaction).

  20. 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.

  1. A flexible micromachined optical sensor for simultaneous measurement of pressure and shear force distribution on foot

    NASA Astrophysics Data System (ADS)

    Wang, Wei-Chih; Panergo, Reynold R.; Galvanin, Christopher M.; Ledoux, William; Sangeorzan, Bruce; Reinhall, Per G.

    2003-07-01

    Lower limb complications associated with diabetes include the development of plantar ulcers that can lead to infection and subsequent amputation. While it is known from force plate analyses that there are medial/lateral and anterior/posterior shear components of the ground reaction force, there is little known about the actual distribution of this force during daily activities, nor about the role that shear plays in causing plantar ulceration. Furthermore, one critical reason why these data have not been obtained previously is the lack of a validated, widely used, commercially available shear sensor, in part because of the various technical issues associated with shear measurement. Here we have developed novel means of tranducing plantar shear and pressure stress via a new microfabricated optical system. The pressure/shear sensor consists of an array of optical waveguides lying in perpendicular rows and columns separated by elastomeric pads. A map of pressure and shear stress is constructed based on observed macro bending through the intensity attenuation from the physical deformation of two adjacent perpendicular optical waveguides. The uniqueness of the sensor is in its batch fabrication process, which involves injection molding and embossing techniques with Polydimethylsiloxane (PDMS) as the optical medium. Here we present the preliminary results of the prototype. The sensor has been shown to have low noise and responds linearly to applied loads. The smallest detectable force on each sensor element based on the current setup is ~0.1 N. The smallest area we have resolved in our mesh sensor is currently 950x950?m2

  2. A novel shear reduction insole effect on the thermal response to walking stress, balance, and gait.

    PubMed

    Wrobel, James S; Ammanath, Peethambaran; Le, Tima; Luring, Christopher; Wensman, Jeffrey; Grewal, Gurtej S; Najafi, Bijan; Pop-Busui, Rodica

    2014-11-01

    Shear stresses have been implicated in the formation of diabetes-related foot ulcers. The aim of this study was to evaluate the effect of a novel shear-reducing insole on the thermal response to walking, balance, and gait. Twenty-seven diabetes peripheral neuropathy patients were enrolled and asked to take 200 steps in both intervention and standard insoles. Thermal foot images of the feet were taken at baseline (1) following a 5-minute temperature acclimatization and (2) after walking. Testing order was randomized, and a 5-minute washout period was used between testing each insole condition. Sudomotor function was also assessed. Gait and balance were measured under single and dual task conditions using a validated body worn sensor system. The mean age was 65.1 years, height was 67.3 inches, weight was 218 pounds, and body mass index was 33.9, 48% were female, and 82% had type 2 diabetes. After walking in both insole conditions, foot temperatures increased significantly in standard insoles. The intervention insole significantly reduced forefoot and midfoot temperature increases (64.1%, P = .008; 48%, P = .046) compared to standard insoles. There were significant negative correlations with sudomotor function and baseline temperatures (r = .53-.57). The intervention demonstrated 10.4% less gait initiation double support time compared to standard insoles (P = .05). There were no differences in static balance measures. We found significantly lower forefoot and midfoot temperature increases following walking with shear-reducing insoles compared to standard insoles. We also found improvements in gait. These findings merit future study for the prevention of foot ulcer. PMID:25107709

  3. 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.

  4. 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.

  5. 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

    2015-03-01

    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.

  6. Measurement of mechanical properties of homogeneous tissue with ultrasonically induced shear waves

    NASA Astrophysics Data System (ADS)

    Greenleaf, James F.; Chen, Shigao

    2007-03-01

    Fundamental mechanical properties of tissue are altered by many diseases. Regional and systemic diseases can cause changes in tissue properties. Liver stiffness is caused by cirrhosis and fibrosis. Vascular wall stiffness and tone are altered by smoking, diabetes and other diseases. Measurement of tissue mechanical properties has historically been done with palpation. However palpation is subjective, relative, and not quantitative or reproducible. Elastography in which strain is measured due to stress application gives a qualitative estimate of Young's modulus at low frequency. We have developed a method that takes advantage of the fact that the wave equation is local and shear wave propagation depends only on storage and loss moduli in addition to density, which does not vary much in soft tissues. Our method is called shearwave dispersion ultrasonic velocity measurement (SDUV). The method uses ultrasonic radiation force to produce repeated motion in tissue that induces shear waves to propagate. The shear wave propagation speed is measured with pulse echo ultrasound as a function of frequency of the shear wave. The resulting velocity dispersion curve is fit with a Voight model to determine the elastic and viscous moduli of the tissue. Results indicate accurate and precise measurements are possible using this "noninvasive biopsy" method. Measurements in beef along and across the fibers are consistent with the literature values.

  7. Analyses of Failure Mechanisms and Residual Stresses in Graphite/Polyimide Composites Subjected to Shear Dominated Biaxial Loads

    NASA Technical Reports Server (NTRS)

    Kumosa, M.; Predecki, P. K.; Armentrout, D.; Benedikt, B.; Rupnowski, P.; Gentz, M.; Kumosa, L.; Sutter, J. K.

    2002-01-01

    This research contributes to the understanding of macro- and micro-failure mechanisms in woven fabric polyimide matrix composites based on medium and high modulus graphite fibers tested under biaxial, shear dominated stress conditions over a temperature range of -50 C to 315 C. The goal of this research is also to provide a testing methodology for determining residual stress distributions in unidirectional, cross/ply and fabric graphite/polyimide composites using the concept of embedded metallic inclusions and X-ray diffraction (XRD) measurements.

  8. Viscosity, granular-temperature, and stress calculations for shearing assemblies of inelastic, frictional disks

    Microsoft Academic Search

    Otis R. Walton; ROBERT L. BRAUN

    1986-01-01

    Employing nonequilibrium molecular-dynamics methods the effects of two energy loss mechanisms on viscosity, stress, and granular-temperature in assemblies of nearly rigid, inelastic frictional disks undergoing steady-state shearing are calculated. Energy introduced into the system through forced shearing is dissipated by inelastic normal forces or through frictional sliding during collisions resulting in a natural steady-state kinetic energy density (granular-temperature) that depends

  9. Method and apparatus for measuring stress

    DOEpatents

    Thompson, R.B.

    1983-07-28

    A method and apparatus for determining stress in a material independent of micro-structural variations and anisotropies. The method comprises comparing the velocities of two horizontally polarized and horizontally propagating ultrasonic shear waves with interchanged directions of propagation and polarization. The apparatus for carrying out the method comprises periodic permanent magnet-electromagnetic acoustic transducers for generating and detecting the shear waves and means for determining the wave velocities.

  10. Flexible shear stress sensor skin for aerodynamics applications

    Microsoft Academic Search

    Fukang Jiang; Yong Xu; Tianxiang Weng; Zhigang Han; Yu-Chong Tai; Adam Huang; Chih-Ming Ho; Scott Newbern

    2000-01-01

    Packaging for a large distributed sensing system is a challenging topic. Using flexible skin technology solves many of these problems. Combining with the newly developed backside contact technique, sensor packaging is made even easier by completely avoiding the fragile bonding wires. This paper describes the improved flexible MEMS technology and its application to the fabrication and packaging of practical shear

  11. Granular Shear Zone Formation: Acoustic Emission Measurements and Fiber-bundle Models

    NASA Astrophysics Data System (ADS)

    Michlmayr, Gernot; Or, Dani

    2013-04-01

    We couple the acoustic emissions method with conceptual models of granular material behavior for investigation of granular shear zone formation and to assess eminence of landslide hazard. When granular materials are mechanically loaded or sheared, they tend to produce discrete events of force network restructuring, and frictional interaction at grain contacts. Such abrupt perturbations within the granular lattice release part of the elastic energy stored in the strained material. Elastic waves generated by such events can be measured as acoustic emissions (AE) and may be used as surrogates for intermittent structural transitions associated with shear zone formation. To experimentally investigate the connection between granular shearing and acoustic signals we performed an array of strain-controlled shear-frame tests using glass beads. AE were measured with two different systems operating at two frequency ranges. High temporal resolution measurements of the shear stresses revealed the presence of small fluctuations typically associated with low-frequency (< 20 kHz) acoustic bursts. Shear stress jumps and linked acoustic signals give account of discrete events of grain network rearrangements and obey characteristic exponential frequency-size distributions. We found that statistical features of force jumps and AE events depend on mechanical boundary conditions and evolve during the straining process. Activity characteristics of high-frequency (> 30 kHz) AE events is linked to friction between grains. To interpret failure associated AE signals, we adapted a conceptual fiber-bundle model (FBM) that describes some of the salient statistical features of failure and associated energy production. Using FBMs for the abrupt mechanical response of the granular medium and an associated grain and force chain AE generation model provides us with a full description of the mechanical-acoustical granular shearing process. Highly resolved AE may serve as a diagnostic tool not only for detection of shear zone development and straining in granular matter and but also for investigating internal grain scale mechanical processes. The AE method could be integrated into monitoring networks of landslide-prone slopes and other early warning systems for abrupt mass release (snow avalanches).

  12. 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

  13. Exercise-Mediated Wall Shear Stress Increases Mitochondrial Biogenesis in Vascular Endothelium

    PubMed Central

    Kim, Boa; Lee, Hojun; Kawata, Keisuke; Park, Joon-Young

    2014-01-01

    Objective Enhancing structural and functional integrity of mitochondria is an emerging therapeutic option against endothelial dysfunction. In this study, we sought to investigate the effect of fluid shear stress on mitochondrial biogenesis and mitochondrial respiratory function in endothelial cells (ECs) using in vitro and in vivo complementary studies. Methods and Results Human aortic- or umbilical vein-derived ECs were exposed to laminar shear stress (20 dyne/cm2) for various durations using a cone-and-plate shear apparatus. We observed significant increases in the expression of key genes related to mitochondrial biogenesis and mitochondrial quality control as well as mtDNA content and mitochondrial mass under the shear stress conditions. Mitochondrial respiratory function was enhanced when cells were intermittently exposed to laminar shear stress for 72 hrs. Also, shear-exposed cells showed diminished glycolysis and decreased mitochondrial membrane potential (??m). Likewise, in in vivo experiments, mice that were subjected to a voluntary wheel running exercise for 5 weeks showed significantly higher mitochondrial content determined by en face staining in the conduit (greater and lesser curvature of the aortic arch and thoracic aorta) and muscle feed (femoral artery) arteries compared to the sedentary control mice. Interestingly, however, the mitochondrial biogenesis was not observed in the mesenteric artery. This region-specific adaptation is likely due to the differential blood flow redistribution during exercise in the different vessel beds. Conclusion Taken together, our findings suggest that exercise enhances mitochondrial biogenesis in vascular endothelium through a shear stress-dependent mechanism. Our findings may suggest a novel mitochondrial pathway by which a chronic exercise may be beneficial for vascular function. PMID:25375175

  14. Plastic Coupling and Stress Relaxation During Nonproportional Axial-Shear Strain-Controlled Loading

    NASA Technical Reports Server (NTRS)

    Lissenden, Cliff J.; Arnold, Steven M.; Saleeb, Atef F.

    2001-01-01

    A nonproportional strain-controlled load path consisting of two segments was applied to the cobalt-based alloy Haynes 188 at 650 C. The first segment was purely axial; the aria1 strain was then held constant while the shear strain was increased during the second segment. The alloy exhibited about a 95-percent reduction in axial stress (298 to 15 MPa during shear straining. This reduction was due primarily to plastic coupling, but time-dependent stress relaxation also occurred. A rate-independent plasticity model approximated the stress reduction due to plastic coupling reasonably well, but as expected was unable to account for time-dependent stress relaxation. A viscoplasticity model capable of predicting the interaction between stress relaxation and plastic coupling also predicted the plastic coupling reasonably well. The accuracy of the viscoplastic model is shown to depend greatly upon the set of nonunique material parameters, which must be characterized from a sufficiently large range of load histories.

  15. An instrumented fastener for shear force measurements in joints

    NASA Technical Reports Server (NTRS)

    Sawyer, J. W.; Rothgeb, T. M.

    1994-01-01

    A preliminary investigation has been conducted on instrumented fasteners for use as sensors to measure the shear loads transmitted by individual fasteners installed in double-splice joints. Calibration and load verification tests were conducted for instrumented fasteners installed at three fastener torque levels. Results from calibration tests show that the shear strains obtained from the instrumented fasteners vary linearly with the applied load and that the instrumented fasteners can be effectively used to measure shear loads transmitted by individual fasteners installed in double-splice joints. Tests were also conducted with three instumented fasteners installed in a typical double-splice joint. The test results showed that the load distribution between individual fasteners is dependent on the location of the fastener in the joint and the fastener torque level.

  16. Measuring Local Strain Rates In Ductile Shear Zones: A New Approach From Deformed Syntectonic Dykes

    NASA Astrophysics Data System (ADS)

    Sassier, C.; Leloup, P.; Rubatto, D.; Galland, O.; Yue, Y.; Ding, L.

    2006-12-01

    At the Earth surface, deformation is mostly localized in fault zones in between tectonic plates. In the upper crust, the deformation is brittle and the faults are narrow and produce earthquakes. In contrast, deformation in the lower ductile crust results in larger shear zones. While it is relatively easy to measure in situ deformation rates at the surface using for example GPS data, it is more difficult to determinate in situ values of strain rate in the ductile crust. Such strain rates can only be estimated in paleo-shear zones. Various methods have been used to assess paleo-strain rates in paleo-shear zones. For instance, cooling and/or decompression rates associated with assumptions on geothermic gradients and shear zone geometry can lead to such estimates. Another way to estimate strain rates is the integration of paleo-stress measurements in a power flow law. But these methods are indirect and imply strong assumptions. Dating of helicitic garnets or syntectonic fibres are more direct estimates. However these last techniques have been only applied in zones of low deformation and not in major shear zones. We propose a new direct method to measure local strain rates in major ductile shear zones from syntectonic dykes by coupling quantification of deformation and geochronology. We test our method in a major shear zone in a well constrained tectonic setting: the Ailao-Shan - Red River Shear Zone (ASRRsz) located in SE Asia. For this 10 km wide shear zone, large-scale fault rates, determined in three independent ways, imply strain rates between 1.17×10^{-13 s-1 and 1.52×10^{-13 s-1 between 35 and 16 Ma. Our study focused on one outcrop where different generations of syntectonic dykes are observed. First, we quantified the minimum shear strain ? for each dyke using several methods: (1) by measuring the stretching of dykes with a surface restoration method (2) by measuring the final angle of the dykes with respect to the shear direction and (3) by combining the two previous methods. From the less to the most deformed dykes, minimum ? values vary between 0.2 to ~10, respectively. Second, we determined the ages of emplacement of each dyke by ion microprobe U-Pb dating of monazites. We obtained three groups of ages at 22Ma, 24-26Ma and 30Ma. Our geochronological data are in good agreement with our structural data, the most deformed dykes being the oldest. The strain rates deduced from these measurements are on the order of 10^{-14}s-1, that is slower than values previously deduced from indirect methods. However, this value only corresponds to a minimum local strain rate. That new method developed to estimate local minimum strain rates in a major ductile shear zone seems to be reliable and could be applied to other shear zones. Such an approach applied at several locations along a single shear zone could also provide new opportunities to understand the evolution of a whole shear system.

  17. Bottom shear stress and SSC control on the morphological evolution of estuarine intertidal mudflats

    NASA Astrophysics Data System (ADS)

    Deloffre, Julien; Verney, Romaric; Lafite, Robert

    2014-05-01

    The supply and fate of fine-grained suspended sediment is of primary importance to the functioning and evolution of estuaries. Intertidal mudflats are habitats of high ecological value: feeding ground for birds, fish species and other biota. Estuarine intertidal mudflats can also contain buried contaminants that can be potentially released in the estuarine system. Thus physical processes such as erosion and sedimentation are fundamental from both applied and environmental viewpoint. Sedimentation and erosion rates/fluxes are mainly driven by hydrodynamics, particles/sediment properties, bedforms and sediment supply. Few high-frequency field-investigation studies compared tidal scale processes simultaneously in the water column and on the mudflat surface. The aim of this paper is to determine the thresholds values (bottom shear stress and SSC) that control the morphological evolution of estuarine intertidal mudflats (< 10% of sand) on semi-diurnal tidal scale. This field-based study combines high-resolution and high-frequency measurements of turbulence and SSC in the water column (using ADV) and bed height (using altimeter) on intertidal mudflat surface in three macrotidal estuaries. Such approach on semi-diurnal scale permitted to accurately understand relationships between hydrodynamics in the boundary layer and sedimentary processes above intertidal mudflats. Results emphasize the role of waves, sediment supply and consolidation state of surface sediments on sedimentary processes over intertidal mudflats. Bottom shear stresses on studied intertidal mudflats were recorded always sufficiently low (<1N.m-2) to permit settling of fine particles during flood tide and/or high-water slack. Sedimentation occurrence and rate on studied intertidal mudflat was found to be driven by (i) the SSC near the bed (if > 0.1g.l-1) and (ii) the absence of significant waves. Wind-generated waves can prevent sedimentation or induce erosion if the bottom shear stress exceeds 1N.m-2. Further inspections demonstrate that the occurrence and the amplitude of erosion are also governed by consolidation state of the surface sediment and water level on the mudflat.

  18. 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.

  19. Rac1 and Cdc42 GTPases regulate shear stress-driven ?-catenin signaling in osteoblasts

    SciTech Connect

    Wan, Qiaoqiao; Cho, Eunhye [Department of Biomedical Engineering, Indiana University-Purdue University Indianapolis, Indianapolis, IN 46202 (United States)] [Department of Biomedical Engineering, Indiana University-Purdue University Indianapolis, Indianapolis, IN 46202 (United States); Yokota, Hiroki [Department of Biomedical Engineering, Indiana University-Purdue University Indianapolis, Indianapolis, IN 46202 (United States) [Department of Biomedical Engineering, Indiana University-Purdue University Indianapolis, Indianapolis, IN 46202 (United States); Department of Anatomy and Cell Biology, Indiana University School of Medicine, Indianapolis, IN 46202 (United States); Na, Sungsoo, E-mail: sungna@iupui.edu [Department of Biomedical Engineering, Indiana University-Purdue University Indianapolis, Indianapolis, IN 46202 (United States)] [Department of Biomedical Engineering, Indiana University-Purdue University Indianapolis, Indianapolis, IN 46202 (United States)

    2013-04-19

    Highlights: •Shear stress increased TCF/LEF activity and stimulated ?-catenin nuclear localization. •Rac1, Cdc42, and RhoA displayed distinct dynamic activity patterns under flow. •Rac1 and Cdc42, but not RhoA, regulate shear stress-driven TCF/LEF activation. •Cytoskeleton did not significantly affect shear stress-induced TCF/LEF activation. -- Abstract: Beta-catenin-dependent TCF/LEF (T-cell factor/lymphocyte enhancing factor) is known to be mechanosensitive and an important regulator for promoting bone formation. However, the functional connection between TCF/LEF activity and Rho family GTPases is not well understood in osteoblasts. Herein we investigated the molecular mechanisms underlying oscillatory shear stress-induced TCF/LEF activity in MC3T3-E1 osteoblast cells using live cell imaging. We employed fluorescence resonance energy transfer (FRET)-based and green fluorescent protein (GFP)-based biosensors, which allowed us to monitor signal transduction in living cells in real time. Oscillatory (1 Hz) shear stress (10 dynes/cm{sup 2}) increased TCF/LEF activity and stimulated translocation of ?-catenin to the nucleus with the distinct activity patterns of Rac1 and Cdc42. The shear stress-induced TCF/LEF activity was blocked by the inhibition of Rac1 and Cdc42 with their dominant negative mutants or selective drugs, but not by a dominant negative mutant of RhoA. In contrast, constitutively active Rac1 and Cdc42 mutants caused a significant enhancement of TCF/LEF activity. Moreover, activation of Rac1 and Cdc42 increased the basal level of TCF/LEF activity, while their inhibition decreased the basal level. Interestingly, disruption of cytoskeletal structures or inhibition of myosin activity did not significantly affect shear stress-induced TCF/LEF activity. Although Rac1 is reported to be involved in ?-catenin in cancer cells, the involvement of Cdc42 in ?-catenin signaling in osteoblasts has not been identified. Our findings in this study demonstrate that both Rac1 and Cdc42 GTPases are critical regulators in shear stress-driven ?-catenin signaling in osteoblasts.

  20. Stress calculations for assemblies of inelastic speres in uniform shear

    Microsoft Academic Search

    O. R. Walton; R. L. Braun

    1986-01-01

    Summary Previous work on assemblies of inelastic, frictional disks is extended to three dimensions in a molecular-dynamics study of steady shearing flow of an idealized granular material consisting of equal-sized spherical particles that are smooth but inelastic. Cumulative time and space averages are calculated for several diagnostic quantities including the kinetic and potential energy densities, the R.M.S. (deviatoric) velocity and

  1. Surface figure measurements of radio telescopes with a shearing interferometer

    Microsoft Academic Search

    E. Serabyn; T. G. Phillips; C. R. Masson

    1991-01-01

    A new technique for determining the surface figure of large submillimeter wavelength telescopes is presented, which is based on measuring the telescope's focal plane diffraction pattern with a shearing interferometer. In addition to the instrumental theory, results obtained using such an interferometer on the 10.4-m diam telescope of the Caltech Submillimeter Observatory are discussed. Using wavelengths near 1 mm, a

  2. Measurement of Oblique Impact-generated Shear Waves

    NASA Technical Reports Server (NTRS)

    Dahl, J. M.; Schultz, P. H.

    2001-01-01

    Experimental strain measurements reveal that oblique impacts can generate shear waves with displacements as large as those in the P-wave. Large oblique impacts may thus be more efficient sources of surface disruption than vertical impacts. Additional information is contained in the original extended abstract.

  3. Mechanosensitive microRNAs - Role in Endothelial Responses to Shear Stress and Redox State

    PubMed Central

    Marin, Traci; Gongol, Brendan; Chen, Zhen; Woo, Brian; Subramaniam, Shankar; Chien, Shu; Shyy, John Y-J

    2013-01-01

    Endothelial functions are highly regulated by imposed shear stress in vivo. The characteristics of shear stress determine mechanotransduction events that regulate phenotypic outcomes including redox and inflammatory states. Recent data indicates that microRNAs (miRs) in vascular endothelial cells (ECs) play an essential role in shear stress-regulated endothelial responses. More specifically, athero-protective pulsatile flow (PS) induces miRs that inhibit mediators of oxidative stress and inflammation while promoting those involved in maintaining vascular homeostasis. Conversely, oscillatory flow (OS) elicits the opposing networks. This is exemplified by the PS-responsive transcription factor, krueppel-like factor 2 (KLF2), which regulates miR expression but is also regulated by OS-sensitive miRs to ultimately regulate the oxidative and inflammatory state of the endothelium. In this review, we outline important findings demonstrating the multifaceted roles of shear stress-regulated miRs in endothelial redox and inflammatory balance. Furthermore, we discuss the use of algorithms in deciphering signaling networks differentially regulated by PS and OS. PMID:23727269

  4. The measurement of applied and residual stresses in metals using ultrasonic waves

    Microsoft Academic Search

    D. I. Crecraft

    1967-01-01

    The results of measurements of the stress-induced velocity variations of both longitudinal and shear ultrasonic waves in the megacycle region are quoted for steel, aluminium and copper, and the corresponding third-order elastic constants calculated. The methods of measuring the small velocity changes due to both stress and preferential grain alignment are discussed, and some attempts at separating the two effects

  5. Sensor for Viscosity and Shear Strength Measurement

    SciTech Connect

    Dillon, J.; Moore, J.E. Jr.; Ebadian, M.A.; Jones, W.K.

    1998-10-20

    Measurement of the physical properties (viscosity and density) of waste slurries is critical in evaluating transport parameters to ensure turbulent flow through transport pipes. The environment for measurement and sensor exposure is extremely harsh; therefore, reliability and ruggedness are critical in the sensor design. The work for this project will be performed in three phases. The first phase, carried out in FY96, involved (1) an evaluation of acoustic and other methods for viscosity measurement; (2) measurement of the parameters of slurries over the range of percent solids found in tanks and transport systems; (3) a comparison of physical properties (e.g., viscosity and density) to percent solids found composition; and (4) the design of a prototype sensor. The second phase (FY97) will involve the fabrication of a prototype hybrid sensor to measure the viscosity and mechanical properties of slurries in remote, high-radiation environments. Two different viscometer designs are being investigated in this study: a magnetostrictive pulse wave guide viscometer; an oscillating cylinder viscometer. In FY97, the Hemispheric Center for Environmental Technology (HCET) at Florida International University (FIU), which has printed circuit, thick film, thin film, and co-fired ceramic fabrication capability, will fabricate five probes for demonstration after technology selection and evaluation.

  6. Proteolytic Activity Attenuates the Response of Endothelial Cells to Fluid Shear Stress

    PubMed Central

    Altshuler, Angelina E.; Morgan, Mary J.; Chien, Shu; Schmid-Schönbein, Geert W.

    2012-01-01

    Recent evidence indicates that several experimental pathophysiological conditions are associated with elevated protease activity in plasma, which impacts endothelial function. We hypothesize that extracellular structures bound to the endothelial cell (EC) membrane may be degraded by proteolytic activity and cause the cells to respond abnormally to physiological shear stress (12 dyn/cm2). To test this hypothesis, cultured bovine aortic endothelial cells (BAECs) were exposed to low levels of a serine protease, trypsin. Extracellular mechanosensor densities of the glycocalyx and vascular endothelial growth factor receptor 2 (VEGFR-2) were determined. Metabolic dysfunction was tested by examining insulin receptor and glucose uptake levels. Protease treatment impaired the cells’ ability to align in the direction of fluid flow after 12 hours of shear stress; however, cells realigned after an additional 12 hours of shear stress with protease inhibition. Proteases caused reduction in the densities of glycocalyx, VEGFR-2, and insulin receptor in static and shear conditions, except for static VEGFR-2 cells. Under static conditions, protease-treated endothelial cells had reduced glucose uptake compared to untreated controls. Under shear, however, glucose uptake for protease-treated BAECs was greater than untreated controls. In conclusion, protease activity in plasma alters the exofacial membrane components of ECs and may interfere with mechanotransduction. PMID:22545072

  7. By activating matrix metalloproteinase-7, shear stress promotes chondrosarcoma cell motility, invasion and lung colonization

    PubMed Central

    Guan, Pei-Pei; Yu, Xin; Guo, Jian-Jun; Wang, Yue; Wang, Tao; Li, Jia-Yi; Konstantopoulos, Konstantinos; Wang, Zhan-You; Wang, Pu

    2015-01-01

    Interstitial fluid flow and associated shear stress are relevant mechanical signals in cartilage and bone (patho)physiology. However, their effects on chondrosarcoma cell motility, invasion and metastasis have yet to be delineated. Using human SW1353, HS.819.T and CH2879 chondrosarcoma cell lines as model systems, we found that fluid shear stress induces the accumulation of cyclic AMP (cAMP) and interleukin-1? (IL-1?), which in turn markedly enhance chondrosarcoma cell motility and invasion via the induction of matrix metalloproteinase-7 (MMP-7). Specifically, shear-induced cAMP and IL-1? activate PI3-K, ERK1/2 and p38 signaling pathways, which lead to the synthesis of MMP-7 via transactivating NF-?B and c-Jun in human chondrosarcoma cells. Importantly, MMP-7 upregulation in response to shear stress exposure has the ability to promote lung colonization of chondrosarcomas in vivo. These findings offer a better understanding of the mechanisms underlying MMP-7 activation in shear-stimulated chondrosarcoma cells, and provide insights on designing new therapeutic strategies to interfere with chondrosarcoma invasion and metastasis. PMID:25823818

  8. Three-Dimensional Computational Fluid Dynamics Modeling of Alterations in Coronary Wall Shear Stress Produced by Stent Implantation

    Microsoft Academic Search

    Ismail Guler; Lars E. Olson; Douglas A. Hettrick; Judy R. Kersten; David C. Warltier; Paul S. Pagel

    2003-01-01

    Rates of coronary restenosis after stent implantation vary with stent design. Recent evidence suggests that alterations in wall shear stress associated with different stent types and changes in local vessel geometry after implantation may account for this disparity. We tested the hypothesis that wall shear stress is altered in a three-dimensional computational fluid dynamics (CFD) model after coronary implantation of

  9. Fluid Shear Stress Induces a Biphasic Response of Human Monocyte Chemotactic Protein 1 Gene Expression in Vascular Endothelium

    Microsoft Academic Search

    Yeun-Jund Shyy; Hsyue-Jen Hsieh; Shunichi Usami; Shu Chien

    1994-01-01

    The focal distribution of atherosclerotic lesions in the arterial tree is related to the local shear stress generated by blood flow, but the molecular basis of the atherogenic response of endothelial cells in these lesion-prone areas is still unclear. We report that shear stress mediates a biphasic response of monocyte chemotactic protein 1 (MCP-1) gene expression in vascular endothelial cells

  10. Usefulness of shear stress pattern in predicting neointima distribution in sirolimus-eluting stents in coronary arteries

    Microsoft Academic Search

    Frank J. H. Gijsen; Remko M. Oortman; Jolanda J. Wentzel; Johan C. H. Schuurbiers; Kengo Tanabe; Muzaffer Degertekin; Jurgen M. Ligthart; Attila Thury; Pim J. de Feyter; Patrick W. Serruys; Cornelis J. Slager

    2003-01-01

    The true 3-dimensional neointimal thickness distribution in sirolimus-eluting stents was investigated in relation to the shear stress distribution, which was obtained from computational fluid dynamics calculations. Small pits were observed between the stent struts in all patients, and a significant inverse relation between neointimal thickness and shear stress was found, indicating that deeper pits were present in the outside curve

  11. Development of a shear measurement sensor for measuring forces at human-machine interfaces.

    PubMed

    Cho, Young Kuen; Kim, Seong Guk; Kim, Donghyun; Kim, Hyung Joo; Ryu, Jeicheong; Lim, Dohyung; Ko, Chang-Yong; Kim, Han Sung

    2014-12-01

    Measuring shear force is crucial for investigating the pathology and treatment of pressure ulcers. In this study, we introduced a bi-axial shear transducer based on strain gauges as a new shear sensor. The sensor consisted of aluminum and polyvinyl chloride plates placed between quadrangular aluminum plates. On the middle plate, two strain gauges were placed orthogonal to one another. The shear sensor (54 mm × 54 mm × 4.1 mm), which was validated by using standard weights, displayed high accuracy and precision (measurement range, -50 to 50 N; sensitivity, 0.3N; linear relationship, R(2)=0.9625; crosstalk error, 0.635% ± 0.031%; equipment variation, 4.183). The shear force on the interface between the human body and a stand-up wheelchair was measured during sitting or standing movements, using two mats (44.8 cm × 44.8 cm per mat) that consisted of 24 shear sensors. Shear forces on the sacrum and ischium were almost five times higher (15.5 N at last posture) than those on other sites (3.5 N on average) during experiments periods. In conclusion, the proposed shear sensor may be reliable and useful for measuring the shear force on human-machine interfaces. PMID:25445984

  12. Shear Stress Transmission Model for the Flagellar Rotary Motor

    PubMed Central

    Mitsui, Toshio; Ohshima, Hiroyuki

    2008-01-01

    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 charasteristic torque-velocity relationship of the flagellar rotation. PMID:19325821

  13. 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.

  14. Evaluation of Transverse Thermal Stresses in Composite Plates Based on First-Order Shear Deformation Theory

    NASA Technical Reports Server (NTRS)

    Rolfes, R.; Noor, A. K.; Sparr, H.

    1998-01-01

    A postprocessing procedure is presented for the evaluation of the transverse thermal stresses in laminated plates. The analytical formulation is based on the first-order shear deformation theory and the plate is discretized by using a single-field displacement finite element model. The procedure is based on neglecting the derivatives of the in-plane forces and the twisting moments, as well as the mixed derivatives of the bending moments, with respect to the in-plane coordinates. The calculated transverse shear stiffnesses reflect the actual stacking sequence of the composite plate. The distributions of the transverse stresses through-the-thickness are evaluated by using only the transverse shear forces and the thermal effects resulting from the finite element analysis. The procedure is implemented into a postprocessing routine which can be easily incorporated into existing commercial finite element codes. Numerical results are presented for four- and ten-layer cross-ply laminates subjected to mechanical and thermal loads.

  15. In situ stress measurements near the Ross shaft pillar, Homestake Mine, South Dakota

    SciTech Connect

    Johnson, J.C.; Pariseau, W.G.; Scott, D.F.; Jenkins, F.M.

    1993-01-01

    In situ stresses are important input data for the design of safe, stable slope layouts and extraction sequences. However, it is commonly assumed that normal and shear stress gradients in a stress field are negligible and, consequently, that stresses are uniform throughout the region of analysis. To evaluate these assumptions and to provide input for an analysis of a shaft pillar mining plan, in situ stresses were measured at the Homestake Mine, Lead, SD. The results showed that normal stresses within the shaft pillar were less than, but comparable to, those estimated from finite-element modeling. Shear stresses were an order of magnitude less than normal stresses and varied considerably from site to site. Possible causes of this variability include effects of scale, elastic moduli, anisotropy, and axial strain. Because of the variability, it is not possible to determine the magnitude of horizontal stress gradients.

  16. Fluid Shear Stress Pre-Conditioning Promotes Endothelial Morphogenesis of Embryonic Stem Cells Within Embryoid Bodies

    PubMed Central

    Nsiah, Barbara A.; Ahsan, Tabassum; Griffiths, Sarah; Cooke, Marissa; Nerem, Robert M.

    2014-01-01

    Pluripotent embryonic stem cells (ESCs) are capable of differentiating into all mesoderm-derived cell lineages, including endothelial, hematopoietic, and cardiac cell types. Common strategies to direct mesoderm differentiation of ESCs rely on exposing the cells to a series of biochemical and biophysical cues at different stages of differentiation to promote maturation toward specific cell phenotypes. Shear forces that mimic cardiovascular physiological forces can evoke a myriad of responses in somatic and stem cell populations, and have, thus, been studied as a means to direct stem cell differentiation. However, elucidating the effects of shear pre-conditioning on the subsequent vascular differentiation and morphogenesis of ESCs has yet to be examined. In this study, ESC monolayers were subjected to physiological shear (5?dyn/cm2) or static conditions for 2 days on collagen IV-coated substrates before initiating embryoid body (EB) differentiation. Immediately after the pre-conditioning period, shear pre-conditioned and statically cultured ESCs exhibited similar morphologies and largely retained a pluripotent phenotype; however, ESCs exposed to fluid shear expressed increased levels of endothelial marker genes Flk-1 (?3-fold), VE-cadherin (?3-fold), and PECAM (?2-fold), compared with statically cultured ESCs. After 7 days of EB culture, ?70% of EBs formed from shear pre-conditioned ESCs expressed significantly higher levels of endothelial marker genes compared with EBs formed from statically cultured ESCs. Interestingly, unlike EBs formed from statically cultured ESCs, EBs formed from fluid shear stress pre-conditioned ESCs exhibited a centrally localized region of VE-cadherin+ cells that persisted for at least 10 days of differentiation. These results demonstrate that fluid shear stress pre-conditioning not only promotes ESC endothelial gene expression but also subsequently impacts the organization of endothelial cells within EBs. Together, these studies highlight a novel approach to promote in vitro morphogenesis of developmental vasculogenic models and potentially promote pre-vascularization of tissue-engineered constructs derived from pluripotent stem cells. PMID:24138406

  17. Detection of stress field shear components by a piezoelectric polymer tactile sensor

    Microsoft Academic Search

    D. De Rossi; A. Nannini; C. Domenici; R. Francesconi

    1988-01-01

    A partial implementation of a multielement tactile sensor based on piezoelectric polymer technology is presented. The sensor's ability to resolve the shear stress component acting on it under axisymmetric, normal loading at its boundary is demonstrated. This feature is thought to be instrumental in revealing slippage detection during object grasping and manipulation

  18. Analysis on the effect of geometrical design parameters on maximum shear stresses in an electromagnetic micropump

    NASA Astrophysics Data System (ADS)

    Al-Halhouli, A. T.

    2010-02-01

    In this work, the concept of recently introduced electromagnetic pump has been presented. This pump has been proposed for pumping biomedical fluids carrying particles sensitive to shear stresses. Its working concept depends on controlling the rotation of two pistons placed in a circular channel in opposing polarity under the influence of a moving electromagnetic field. Analytical and numerical investigations on the effect of pump geometrical parameters on shear stresses at different boundary conditions are performed. The geometrical parameters include: channel aspect ratio (channel width to height) and channel radius ratio (inner to outer radius). Non-dimensional simple analytical shear stress expressions that are valid for a wide range of geometrical design parameters and variety of fluids are derived. CFD simulations have been used to verify the analytical expressions within the range of studied parameters. Obtained results showed that the analytical models predict the wall maximum shear stresses with an error less than 5% for w / h<=1.0 at high radius ratios and with an error less than10% for Ri / Ro >=0.3. These results help the designer in fabricating the micropump to be suitable for biomedical applications, where saving the particles carried in fluids from damage is of high importance.

  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, and molecular diffusivity. Adhesion was not limited by the settling rate and was highly specific to ?(5)?(1) integrin. Total internal reflection fluorescence microscopy showed that CB-EPCs produced multiple contacts of ?(5)?(1) with the surface and the contact area grew during the first 20 min of attachment. These results demonstrate that CB-EPC adhesion from blood can occur under physiological levels of shear stress. PMID:21112278

  20. Review of the shear-stress transport turbulence model experience from an industrial perspective

    Microsoft Academic Search

    Florian R. Menter

    2009-01-01

    The present author was asked to provide an update on the status and the more recent developments around the shear-stress transport (SST) turbulence model for this special issue of the journal. The article is therefore not intended as a comprehensive overview of the status of engineering turbulence modelling in general, nor on the overall turbulence modelling strategy for ANSYS computational

  1. Shear stress magnitude and directionality modulate growth factor gene expression in

    E-print Network

    Passerini, Tony

    Shear stress magnitude and directionality modulate growth factor gene expression in preconditioned ( 15) dynes/cm2 or low magnitude WSS reversal ( 2.5 dynes/cm2 ) for 6 hours. A focused complementary increase in WSS ( 10) or to WSS reversal. Low magnitude retrograde WSS evoked significant (P

  2. Quantitative morphodynamics of endothelial cells within confluent cultures in response to fluid shear stress.

    PubMed Central

    Dieterich, P; Odenthal-Schnittler, M; Mrowietz, C; Krämer, M; Sasse, L; Oberleithner, H; Schnittler, H J

    2000-01-01

    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. PMID:10968992

  3. 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. PMID:23738621

  4. 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.

  5. Wall Shear Stress and Atherosclerosis: Numerical Blood Flow Simulations in the Mouse Aortic Arch

    Microsoft Academic Search

    P. RUENGSAKULRACH; A. K. JOSHIb; S. FREMESc; A. K. Joshi; S. Fremes; S. Foster

    2008-01-01

    The aims of this study were (1) to demonstrate the feasibility of computational fluid dynamic (CFD) modelling of realistic blood flow in the mouse aortic arch, and (2) to determine the relation of wall shear stress and atherosclerosis in the mouse aortic arch. ApoE knockout mice were chosen for this study. The blood flow fraction in the major branches of

  6. Wall Shear Stress and Atherosclerosis: Numerical Blood Flow Simulations in the Mouse Aortic Arch

    Microsoft Academic Search

    P. RUENGSAKULRACH; A. K. JOSHI; S. FREMES; J. BUTANY; Y. LENBURY

    The aims of this study were (1) to demonstrate the feasibility of computational fluid dynamic (CFD) modelling of realistic blood flow in the mouse aortic arch, and (2) to determine the relation of wall shear stress and atherosclerosis in the mouse aortic arch. ApoE knockout mice were chosen for this study. The blood flow fraction in the major branches of

  7. Effect of Aeration Induced Shear Stress on the Settleability and Activity of Activated Sludge

    Microsoft Academic Search

    Feng Qian; Xue Zhao Xia; Chen Li Na; Li Hai Yan

    2009-01-01

    For the optimization on function of activated sludge system, the effects of aeration induced shear stress on the settleability and activity of activated sludge were studied. Laboratory experiments were carried out using six identical bioreactors. All of the aerated stirred bioreactors, of 2 L each in working volume and seeded with activated sludge, were operated as sequencing batch reactors (SBR)

  8. A biomedical engineering approach to investigating flow and wall shear stress in contracting lymphatics

    E-print Network

    Dixon, James Brandon

    2006-08-16

    information regarding lymphocyte velocity (-4 to 10 mm/sec), vessel diameter (25 to 165 um), and particle location. Fluid modeling was performed to obtain reasonable estimates of wall shear stress (-8 to 17 dynes/cm2). One of the difficulties encountered...

  9. A Wafer-Bonded, Floating Element Shear-Stress Sensor Using a Geometric Moire Optical Transduction Technique

    NASA Technical Reports Server (NTRS)

    Horowitz, Stephen; Chen, Tai-An; Chandrasekaran, Venkataraman; Tedjojuwono, Ken; Cattafesta, Louis; Nishida, Toshikazu; Sheplak, Mark

    2004-01-01

    This paper presents a geometric Moir optical-based floating-element shear stress sensor for wind tunnel turbulence measurements. The sensor was fabricated using an aligned wafer-bond/thin-back process producing optical gratings on the backside of a floating element and on the top surface of the support wafer. Measured results indicate a static sensitivity of 0.26 microns/Pa, a resonant frequency of 1.7 kHz, and a noise floor of 6.2 mPa/(square root)Hz.

  10. IQ Domain GTPase-Activating Protein 1 is Involved in Shear Stress-Induced Progenitor-Derived Endothelial Cell Alignment

    PubMed Central

    Rami, Lila; Auguste, Patrick; Thebaud, Noélie B.; Bareille, Reine; Daculsi, Richard; Ripoche, Jean; Bordenave, Laurence

    2013-01-01

    Shear stress is one of mechanical constraints which are exerted by blood flow on endothelial cells (ECs). To adapt to shear stress, ECs align in the direction of flow through adherens junction (AJ) remodeling. However, mechanisms regulating ECs alignment under shear stress are poorly understood. The scaffold protein IQ domain GTPase activating protein 1 (IQGAP1) is a scaffold protein which couples cell signaling to the actin and microtubule cytoskeletons and is involved in cell migration and adhesion. IQGAP1 also plays a role in AJ organization in epithelial cells. In this study, we investigated the potential IQGAP1 involvement in the endothelial cells alignment under shear stress. Progenitor-derived endothelial cells (PDECs), transfected (or not) with IQGAP1 small interfering RNA, were exposed to a laminar shear stress (1.2 N/m2) and AJ proteins (VE-cadherin and ?-catenin) and IQGAP1 were labeled by immunofluorescence. We show that IQGAP1 is essential for ECs alignment under shear stress. We studied the role of IQGAP1 in AJs remodeling of PDECs exposed to shear stress by studying cell localization and IQGAP1 interactions with VE-cadherin and ?-catenin by immunofluorescence and Proximity Ligation Assays. In static conditions, IQGAP1 interacts with VE-cadherin but not with ?-catenin at the cell membrane. Under shear stress, IQGAP1 lost its interaction from VE-cadherin to ?-catenin. This “switch” was concomitant with the loss of ?-catenin/VE-cadherin interaction at the cell membrane. This work shows that IQGAP1 is essential to ECs alignment under shear stress and that AJ remodeling represents one of the mechanisms involved. These results provide a new approach to understand ECs alignment under to shear stress. PMID:24278215

  11. Absolute Measurement Of Laminar Shear Rate Using Photon Correlation Spectroscopy

    E-print Network

    Elliot Jenner; Brian D'Urso

    2015-05-11

    An absolute measurement of the components of the shear rate tensor $\\mathcal{S}$ in a fluid can be found by measuring the photon correlation function of light scattered from particles in the fluid. Previous methods of measuring $\\mathcal{S}$ involve reading the velocity at various points and extrapolating the shear, which can be time consuming and is limited in its ability to examine small spatial scale or short time events. Previous work in Photon Correlation Spectroscopy has involved only approximate solutions, requiring free parameters to be scaled by a known case, or different cases, such as 2-D flows, but here we present a treatment that provides quantitative results directly and without calibration for full 3-D flow. We demonstrate this treatment experimentally with a cone and plate rheometer.

  12. Supersonic shear imaging provides a reliable measurement of resting muscle shear elastic modulus.

    PubMed

    Lacourpaille, Lilian; Hug, François; Bouillard, Killian; Hogrel, Jean-Yves; Nordez, Antoine

    2012-03-01

    The aim of the present study was to assess the reliability of shear elastic modulus measurements performed using supersonic shear imaging (SSI) in nine resting muscles (i.e. gastrocnemius medialis, tibialis anterior, vastus lateralis, rectus femoris, triceps brachii, biceps brachii, brachioradialis, adductor pollicis obliquus and abductor digiti minimi) of different architectures and typologies. Thirty healthy subjects were randomly assigned to the intra-session reliability (n = 20), inter-day reliability (n = 21) and the inter-observer reliability (n = 16) experiments. Muscle shear elastic modulus ranged from 2.99 (gastrocnemius medialis) to 4.50 kPa (adductor digiti minimi and tibialis anterior). On the whole, very good reliability was observed, with a coefficient of variation (CV) ranging from 4.6% to 8%, except for the inter-operator reliability of adductor pollicis obliquus (CV = 11.5%). The intraclass correlation coefficients were good (0.871 ± 0.045 for the intra-session reliability, 0.815 ± 0.065 for the inter-day reliability and 0.709 ± 0.141 for the inter-observer reliability). Both the reliability and the ease of use of SSI make it a potentially interesting technique that would be of benefit to fundamental, applied and clinical research projects that need an accurate assessment of muscle mechanical properties. PMID:22370174

  13. Rac1 and Cdc42 GTPases regulate shear stress-driven ?-catenin signaling in osteoblasts

    PubMed Central

    Wan, Qiaoqiao; Cho, Eunhye; Yokota, Hiroki; Na, Sungsoo

    2013-01-01

    Beta-catenin-dependent TCF/LEF (T-cell factor/lymphocyte enhancing factor) is known to be mechanosensitive and an important regulator for promoting bone formation. However, the functional connection between TCF/LEF activity and Rho family GTPases is not well understood in osteoblasts. Herein we investigated the molecular mechanisms underlying oscillatory shear stress-induced TCF/LEF activity in MC3T3-E1 osteoblast cells using live cell imaging. We employed fluorescence resonance energy transfer (FRET)-based and green fluorescent protein (GFP)-based biosensors, which allowed us to monitor signal transduction in living cells in real time. Oscillatory (1 Hz) shear stress (10 dynes/cm2) increased TCF/LEF activity and stimulated translocation of ?-catenin to the nucleus with the distinct activity patterns of Rac1 and Cdc42. The shear stress-induced TCF/LEF activity was blocked by the inhibition of Rac1 and Cdc42 with their dominant negative mutants or selective drugs, but not by a dominant negative mutant of RhoA. In contrast, constitutively active Rac1 and Cdc42 mutants caused a significant enhancement of TCF/LEF activity. Moreover, activation of Rac1 and Cdc42 increased the basal level of TCF/LEF activity, while their inhibition decreased the basal level. Interestingly, disruption of cytoskeletal structures or inhibition of myosin activity did not significantly affect shear stress-induced TCF/LEF activity. Although Rac1 is reported to be involved in ?-catenin in cancer cells, the involvement of Cdc42 in ?-catenin signaling in osteoblasts has not been identified. Our findings in this study demonstrate that both Rac1 and Cdc42 GTPases are critical regulators in shear stress-driven ?-catenin signaling in osteoblasts. PMID:23524265

  14. Endothelial colony-forming cells show a mature transcriptional response to shear stress.

    PubMed

    Egorova, Anastasia D; DeRuiter, Marco C; de Boer, Hetty C; van de Pas, Simone; Gittenberger-de Groot, Adriana C; van Zonneveld, Anton J; Poelmann, Robert E; Hierck, Beerend P

    2012-01-01

    Endothelial progenitor cells (EPC) play a central role in endothelial maintenance and repair. Endothelial colony-forming cells (ECFC) form a subpopulation of EPC. ECFC are readily attainable, can be easily isolated, possess a high proliferation potential, and are therefore a promising source of endothelial cells (EC) for future cardiovascular therapeutic applications. The extent to which these cells respond to shear stress as adult vascular EC remains to be elucidated. Here, we study the transcriptional response of ECFC induced by shear stress and compare it with the response of mature arterial and venous cells. ECFC, as well as human umbilical vein EC (HUVEC) and human umbilical artery EC (HUAEC), were subjected to low (0.5 Pa) and high (2.5 Pa) shear stress. The endothelial differentiation phenotype and transcriptional responses were analyzed using immunocytochemistry and quantitative polymerase chain reaction (Q-PCR). Performing absolute quantification of copy numbers by Q-PCR allows comparing the responses of cell types relative to each other. Our data show that isolated ECFC resemble mature EC in cobblestone morphology and endothelial marker expression. Absolute Q-PCR quantification revealed that although being truly endothelial, ECFC do not fully resemble HUVEC or HUAEC in the expression of specific differentiation markers. When subjected to shear stress, ECFC show a mature response to fluid flow, comparable to that of HUVEC and HUAEC. The capacity of endothelial progenitors to respond to fluid flow in a similar manner to HUVEC and HUAEC highlights the universal response of EC to fluid shear stress, independently of their endothelial differentiation status. This property supports the use of these cells as an EC source for tissue engineering applications. PMID:22101679

  15. The Role of Pre-stress in Shear Wave Generation from Explosions

    NASA Astrophysics Data System (ADS)

    Preston, L. A.; Aldridge, D. F.

    2011-12-01

    Seismic waves propagating within the Earth are small perturbations in stress and strain superimposed on an existing three-dimensional (3D) stress field. This ambient stress state, commonly referred to as "tectonic stress" or "pre-stress", may be significant in or near zones of active tectonic deformation, such as the Nevada Test Site. The effect of pre-stress on seismic waveforms generated by and propagated from an underground explosion (chemical or nuclear) is poorly understood at present. However, seismologists reasonably speculate that pre-stress may contribute to the anomalously large amount of shear wave energy often observed from such sources. In order to quantitatively investigate the effects of pre-stress, we are developing an explicit, time-domain, finite-difference (FD) algorithm for simulating 3D seismic wave propagation within an isotropic elastic medium subject to an existing static stress state. The usual stress-strain constitutive relations are augmented with additional terms involving both the ambient stress tensor and its gradient. The elastic medium is represented by nine 3D fields (i.e., mass density, two Lamé parameters, and six independent pre-stress tensor components). The numerical algorithm is implemented on a conventional 3D staggered grid using centered FD operators that are second-order accurate in time and fourth-order accurate in space. We are also developing mathematical dispersion relations, for both continuous and discrete space-time, characterizing seismic wave propagation within a 3D isotropic elastic medium under pre-stress. In the continuous case, the phase speed(s) of a plane wave propagating within a homogeneous and isotropic elastic body are obtained by extracting the appropriate roots of a cubic polynomial. Although the phase speed is independent of frequency (as in the usual zero-pre-stress situation), it depends on propagation direction, analogous to an anisotropic elastic medium. In the discrete case, phase speed depends on both frequency and direction. Important questions regarding the level of pre-stress required to produce noticeable effects on seismic waveforms need to be investigated. Of particular interest is quantification of the coupling between pure pressure and shear to understand how an ambient stress field generates shear waves from explosions. Although this effect is expected to be small, given the location of many test sites in tectonically active regions, it may be significant. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

  16. Comparison of erythrocyte dynamics in shear flow under different stress-free configurations

    NASA Astrophysics Data System (ADS)

    Cordasco, Daniel; Yazdani, Alireza; Bagchi, Prosenjit

    2014-04-01

    An open question that has persisted for decades is whether the cytoskeleton of a red blood cell is stress-free or under a stress. This question is important in the context of theoretical modeling of cellular motion under a flowing condition where it is necessary to make an assumption about the stress-free state. Here, we present a 3D numerical study to compare the cell dynamics in a simple shear flow under two different stress-free states, a biconcave discocyte representing the resting shape of the cell, and a nearly spherical oblate shape. We find that whether the stress-free states make a significant difference or not depends on the viscosity of the suspending medium. If the viscosity is close to that of blood plasma, the two stress-free states do not show any significant difference in cell dynamics. However, when the suspending medium viscosity is well above that of the physiological range, as in many in vitro studies, the shear rate separating the tank-treading and tumbling dynamics is observed to be higher for the biconcave stress-free state than the spheroidal state. The former shows a strong shape oscillation with repeated departures from the biconcave shape, while the latter shows a nearly stable biconcave shape. It is found that the cell membrane in the biconcave stress-free state is under a compressive stress and a weaker bending force density, leading to a periodic compression of the cell. The shape oscillation then leads to a higher energy barrier against membrane tank-tread leading to an early transition to tumbling. However, if the cells are released with a large off-shear plane angle, the oscillations can be suppressed due to an azimuthal motion of the membrane along the vorticity direction leading to a redistribution of the membrane points and lowering of the energy barrier, which again results in a nearly similar behavior of the cells under the two different stress-free states. A variety of off-shear plane dynamics is observed, namely, rolling, kayaking, precession, and a new dynamics termed "hovering." For the physiological viscosity range, the shear-plane tumbling appears to be relatively less common, while the rolling is observed to be more stable.

  17. X-ray Scattering Measurements of Particle Orientation in a Sheared Polymer/Clay Dispersion

    SciTech Connect

    Pujari, Saswati; Dougherty, Leah; Mobuchon, Christoph; Carreau, Pierre J.; Heuzey, Marie-Claude; Burghardt, Wesley R. (Ecole); (NWU); (Ecole)

    2012-01-20

    We report steady and transient measurements of particle orientation in a clay dispersion subjected to shear flow. An organically modified clay is dispersed in a Newtonian polymer matrix at a volume fraction of 0.02, using methods previously reported by Mobuchon et al. (Rheol Acta 46: 1045, 2007). In accord with prior studies, mechanical rheometry shows yield stress-like behavior in steady shear, while time dependent growth of modulus is observed following flow cessation. Measurements of flow-induced orientation in the flow-gradient plane of simple shear flow using small-angle and wide-angle X-ray scattering (SAXS and WAXS) are reported. Both SAXS and WAXS reveal increasing particle orientation as shear rate is increased. Partial relaxation of nanoparticle orientation upon flow cessation is well correlated with time-dependent changes in complex modulus. SAXS and WAXS data provide qualitatively similar results; however, some quantitative differences are attributed to differences in the length scales probed by these techniques.

  18. Smith, E. R., and Kraus, N. C. 2007. Longshore and Sand Transport Calculated by Time-Dependent Shear Stress. Proceedings Coastal Sediments '07 Conference, ASCE Press, Reston,

    E-print Network

    US Army Corps of Engineers

    Smith, E. R., and Kraus, N. C. 2007. Longshore and Sand Transport Calculated by Time- Dependent SAND TRANSPORT CALCULATED BY TIME-DEPENDENT SHEAR STRESS Ernest R. Smith1 and Nicholas C. Kraus1 1. U.C.Kraus@erdc.usace.army.mil. Abstract: Based on longshore sand transport experiments performed in a large basin, measured sand transport

  19. SHEAR STRENGTH MEASURING EQUIPMENT EVALUATION AT THE COLD TEST FACILITY

    SciTech Connect

    MEACHAM JE

    2009-09-09

    Retrievals under current criteria require that approximately 2,000,000 gallons of double-shell tank (DST) waste storage space not be used to prevent creating new tanks that might be susceptible to buoyant displacement gas release events (BDGRE). New criteria are being evaluated, based on actual sludge properties, to potentially show that sludge wastes do not exhibit the same BDGRE risk. Implementation of the new criteria requires measurement of in situ waste shear strength. Cone penetrometers were judged the best equipment for measuring in situ shear strength and an A.P. van den berg Hyson 100 kN Light Weight Cone Penetrometer (CPT) was selected for evaluation. The CPT was procured and then evaluated at the Hanford Site Cold Test Facility. Evaluation demonstrated that the equipment with minor modification was suitable for use in Tank Farms.

  20. A shear test method to measure shear strength of metallic materials and solder joints using small specimens

    SciTech Connect

    Uenal, O.; Barnard, D.J.; Anderson, I.E. [Ames Lab., IA (United States). Metallurgy and Ceramics Program] [Ames Lab., IA (United States). Metallurgy and Ceramics Program

    1999-01-08

    The asymmetrical four-point bend (AFPB) shear test, which is the subject of this paper, was originally developed by Slepetz et al. to evaluate the shear properties of large metallic specimens and polymer composites. Similar to the Iosipescu test, the AFPB test also provides a nearly pure-shear stress state with an unnotched specimen. However, since the AFPB test involves point loading as opposed to distributed surface loading in the case of the Iosipescu test, the shear force generated in this method depends on the fixture dimensions. Therefore, its use has been very limited. Recently, it was shown that this method could be used to evaluate high temperature shear properties of small ceramic composite joints. Thus, as an extension to the earlier aforementioned work, the goal of this study was to investigate the application of AFPB test method to small metallic test specimens. In this work, the Iosipescu shear test was also used to check the accuracy of results from the AFPB tests. The stress analysis of this test method by finite element modeling (FEM) will be published elsewhere.

  1. A microfluidic device to apply shear stresses to polarizing ciliated airway epithelium using air flow.

    PubMed

    Trieu, Dennis; Waddell, Thomas K; McGuigan, Alison P

    2014-11-01

    Organization of airway epithelium determines ciliary beat direction and coordination for proper mucociliary clearance. Fluidic shear stresses have the potential to influence ciliary organization. Here, an in vitro fluidic flow system was developed for inducing long-term airflow shear stresses on airway epithelium with a view to influencing epithelial organization. Our system consists of a fluidic device for cell culture, integrated into a humidified airflow circuit. The fluidic device has a modular design and is made from a combination of polystyrene and adhesive components incorporated into a 6-well filter membrane insert. We demonstrate the system operates within physiologically relevant shear and pressure ranges and estimate the shear stress exerted on the epithelial cell layer as a result of air flow using a computational model. For both the bronchial epithelial cell line BEAS2B and primary human tracheal airway epithelial cells, we demonstrate that cells remain viable within the device when exposed to airflow for 24?h and that normal differentiation and cilia formation occurs. Furthermore, we demonstrate the utility of our device for exploring the impact of exposing cells to airflow: our tool enables quantification of cytoskeletal organization, and is compatible with in situ bead assays to assess the orientation of cilia beating. PMID:25553181

  2. Measurement of the shear modulus of single-layer graphene

    Microsoft Academic Search

    Thomas Metcalf; Xiao Liu; Jeremy Robinson; Keith Perkins; Brian Houston

    2011-01-01

    We have measured the shear modulus of large area (2mm x 5mm), single-layer (90--95%) polycrystalline graphene sheets and found values consistent with theoretical predictions of G=200 GPa. The graphene was grown by chemical vapor deposition onto a copper foil and subsequently transferred onto a mechanical resonator known as a double-paddle oscillator (DPO). DPOs are fabricated from single-crystal, 0.3mm thick silicon

  3. Staphylococcus aureus biofilm formation and tolerance to antibiotics in response to oscillatory shear stresses of physiological levels.

    PubMed

    Kostenko, Victoria; Salek, Mohammad Mehdi; Sattari, Pooria; Martinuzzi, Robert John

    2010-08-01

    Bacterial infections in the blood system are usually associated with blood flow oscillation generated by some cardiovascular pathologies and insertion of indwelling devices. The influence of hydrodynamically induced shear stress fluctuations on the Staphylococcus aureus biofilm morphology and tolerance to antibiotics was investigated. Fluctuating shear stresses of physiologically relevant levels were generated in wells of a six-well microdish agitated by an orbital shaker. Numerical simulations were performed to determine the spatial distribution and local fluctuation levels of the shear stress field on the well bottom. It is found that the local biofilm deposition and morphology correlate strongly with shear stress fluctuations and maximum magnitude levels. Tolerance to killing by antibiotics correlates with morphotype and is generally higher in high shear regions. PMID:20528928

  4. Quantification of Wall Shear Stress in Large Blood Vessels Using Lagrangian Interpolation Functions with Cine Phase-Contrast Magnetic Resonance Imaging

    Microsoft Academic Search

    Christopher P. Cheng; David Parker; Charles A. Taylor

    2002-01-01

    Arterial wall shear stress is hypothesized to be an important factor in the localization of atherosclerosis. Current methods to compute wall shear stress from magnetic resonance imaging (MRI) data do not account for flow profiles characteristic of pulsatile flow in noncircular vessel lumens. We describe a method to quantify wall shear stress in large blood vessels by differentiating velocity interpolation

  5. Tests of collision operators using laboratory measurements of shear Alfven wave dispersion and D. J. Thuecks,

    E-print Network

    California at Los Angles, University of

    POP33461 Tests of collision operators using laboratory measurements of shear Alfv´en wave) Measurements of shear Alfv´en waves are used to test the predictions of a variety of different electron colli the dielectric tensor. Laboratory measurements of the parallel phase velocity and damping of shear Alfv´en waves

  6. Computers & Geosciences 34 (2008) 226234 An Expert System for measuring shear-wave splitting above

    E-print Network

    2008-01-01

    Computers & Geosciences 34 (2008) 226­234 An Expert System for measuring shear-wave splitting above Abstract As part of the development of a system for routinely measuring shear-wave splitting, this paper introduces an Expert System (ES) to measure the polarisations and time-delays of seismic shear-wave splitting

  7. The effect of shear stress on solitary waves in arteries.

    PubMed

    Demiray, H

    1997-09-01

    In the present work, we study the propagation of solitary waves in a prestressed thick walled elastic tube filled with an incompressible inviscid fluid. In order to include the geometric dispersion in the analysis the wall inertia and shear deformation effects are taken into account for the inner pressure-cross-sectional area relation. Using the reductive perturbation technique, the propagation of weakly non-linear waves in the long-wave approximation is examined. It is shown that, contrary to thin tube theories, the present approach makes it possible to have solitary waves even for a Mooney-Rivlin (M-R) material. Due to dependence of the coefficients of the governing Korteweg-deVries equation on initial deformation, the solution profile changes with inner pressure and the axial stretch. The variation of wave profiles for a class of elastic materials are depicted in graphic forms. As might be seen from these illustrations, with increasing thickness ratio, the profile of solitary wave is steepened for a M-R material but it is broadened for biological tissue. PMID:9281908

  8. The influence of wall slip on yield stress and viscoelastic measurements of cement paste

    Microsoft Academic Search

    Aaron W. Saak; Hamlin M. Jennings; Surendra P. Shah

    2001-01-01

    The influence of wall slip on the shear yield stress and modulus of cement paste was investigated using a rotational rheometer with smooth-walled concentric cylinders and a vane. The results show that the concentric cylinders suffer from slip during yield stress measurements due to the formation of a water-rich layer at the walls of the cylinders. The use of a

  9. Effect of simulated microgravity on osteocytes responding to fluid shear stress

    NASA Astrophysics Data System (ADS)

    Yang, Xiao; Sun, Lian-Wen; Wu, Xin-Tong; Wang, Xiao-Nan; Fan, Yu-Bo

    2013-03-01

    Osteocytes, as most abundant cells and major mechanical sensor in bone, play an important role in the mechanism of microgravity-induced bone loss. The response of osteocytes to fluid flow stress under simulated microgravity was investigated in this study. MLO-Y4, an osteocyte-like cell line, was cultured under simulated microgravity condition for 5 days. Then cells were sheared at 15 dyn/cm2 in flow chamber. After 15 min shear, nitric oxide (NO) was examined by Griess Reagent and prostaglandin E2 (PGE2) by ELISA. After 6 h shear, alkaline phosphatase (ALP) was examined by PNPP, osteocalcin (OC) and procollagen type I N propeptide (PINP) by ELISA. Cells were divided into four groups: CON (1 G with no shear), CON-S (1 G with shear), SM (simulated microgravity with no shear) and SM-S (simulated microgravity with shear). The results showed that (1) NO, ALP activity, OC and PINP increased significantly while PGE2 showed no change in SM compared with CON. (2) NO, PGE2, ALP activity and PINP increased significantly while OC decreased significantly in CON-S compared with CON. (3) NO in SM-S had no significant difference compared to SM, PGE2 and OC increased while ALP activity and PINP decreased significantly in SM-S compared with SM. (4) The increasing amplitude of PGE2 and OC, the decreasing amplitude of ALP activity in SM-S to SM was lower than that in CON-S to CON. In addition, some changes of F-actin cytoskeleton were observed by confocal microscopy. All results indicated that the response induced by fluid shear in osteocytes could be inhibited by simulated microgravity, namely the mechanosensibility of osteocytes decreased under simulated microgravity. This may partly contribute to the mechanism of microgravity-induced osteoporosis and will be helpful to find out effective description.

  10. Residual stress Part 1 Measurement techniques

    E-print Network

    Cambridge, University of

    Overview Residual stress Part 1 ­ Measurement techniques P. J. Withers and H. K. D. H. Bhadeshia Residual stress is that which remains in a body that is stationary and at equilibrium with its surroundings, beneficial residual stresses can be introduced deliberately. Residual stresses are more difficult to predict

  11. Fluid shear stress induces the clustering of heparan sulfate via mobility of glypican-1 in lipid rafts

    PubMed Central

    Zeng, Ye; Waters, Michele; Andrews, Allison; Honarmandi, Peyman; Ebong, Eno E.; Rizzo, Victor

    2013-01-01

    The endothelial glycocalyx plays important roles in mechanotransduction. We recently investigated the distribution and interaction of glycocalyx components on statically cultured endothelial cells. In the present study, we further explored the unknown organization of the glycocalyx during early exposure (first 30 min) to shear stress and tested the hypothesis that proteoglycans with glycosaminoglycans, which are localized in different lipid microdomains, respond distinctly to shear stress. During the initial 30 min of exposure to shear stress, the very early responses of the glycocalyx and membrane rafts were detected using confocal microscopy. We observed that heparan sulfate (HS) and glypican-1 clustered in the cell junctions. In contrast, chondroitin sulfate (CS), bound albumin, and syndecan-1 did not move. The caveolae marker caveolin-1 did not move, indicating that caveolae are anchored sufficiently to resist shear stress during the 30 min of exposure. Shear stress induced significant changes in the distribution of ganglioside GM1 (a marker for membrane rafts labeled with cholera toxin B subunit). These data suggest that fluid shear stress induced the cell junctional clustering of lipid rafts with their anchored glypican-1 and associated HS. In contrast, the mobility of CS, transmembrane bound syndecan-1, and caveolae were constrained during exposure to shear stress. This study illuminates the role of changes in glycocalyx organization that underlie mechanisms of mechanotransduction. PMID:23851278

  12. Characterizing Wave- and Current-Induced Bottom Shear Stress: U.S. Middle Atlantic Bight

    NASA Astrophysics Data System (ADS)

    Dalyander, S.; Butman, B.

    2011-12-01

    The combined action of waves and currents at the seabed creates bottom shear stress, impacting local geology, habitat, and anthropogenic use. In this study, a methodology is developed to characterize the magnitude of benthic disturbance based on spatially and seasonally-resolved statistics (mean, standard deviation, 95th percentile) of wave-current bottom shear stress. The frequency of stress forcing is used to distinguish regions dominated by storms (return interval longer than 33 hours) from those dominated by the tides (periods shorter than 33 hours). In addition, the relative magnitude of the contribution to stress from waves, tides, and storm-driven currents is investigated by comparing wave stress, tidal current stress, and stress from the residual current (currents with tides removed), as well as through cross-correlation of wave and current stress. The methodology is applied to numerical model time-series data for the Middle Atlantic Bight (MAB) off the U.S. East Coast for April 2010 to April 2011; currents are provided from the Integrated Ocean Observing System (IOOS) operational hydrodynamic forecast Experimental System for Predicting Shelf and Slope Optics (ESPreSSO) and waves are provided from a Simulating WAves Nearshore (SWAN) hindcast developed for this project. Spatial resolution of the model is about 5 km and time-series wave and current data are at 1 and 2-hours respectively. Regions of the MAB delineated by stress characteristics include a tidally-dominated shallow region with relative high stress southeast of Massachusetts over Nantucket Shoals; a coastal band extending offshore to about 30 m water depth dominated by waves; a region dominated by waves and wind-driven currents offshore of the Outer Banks of North Carolina; and a low stress region southeast of Long Island, approximately coincident with an area of fine-grained sediments called the "Mud Patch". Comparison of the stress distribution with surface sediment texture data shows that coarser sediments are typically found in regions of higher stress forcing and finer sediments in regions of weaker stress, consistent with the conceptual model of finer sediments being winnowed away in areas of stronger stress. Estimates of sea floor mobility across the MAB are attained using the observed sediment texture data to establish critical stress thresholds for initiation of sediment movement. Relatively high mobility (critical stress exceeded 30-40% of the year) is observed over Nantucket Shoals and in a band along the coast out to a depth of 30-40 m. These results may have application for placement or design of offshore structures such as wind turbines, and assist in habitat delineation for benthic species.

  13. Measurement of the shear modulus of single-layer graphene

    NASA Astrophysics Data System (ADS)

    Metcalf, Thomas; Liu, Xiao; Robinson, Jeremy; Perkins, Keith; Houston, Brian

    2011-03-01

    We have measured the shear modulus of large area (2mm × 5 mm), single-layer (90--95%) polycrystalline graphene sheets and found values consistent with theoretical predictions of G = 200 GPa. The graphene was grown by chemical vapor deposition onto a copper foil and subsequently transferred onto a mechanical resonator known as a double-paddle oscillator (DPO). DPOs are fabricated from single-crystal, 0.3mm thick silicon wafers, and have a torsional vibratory mode at 5500 Hz which has a very large quality factor, Q = 5 ×107 , at low (<10 K) temperatures, giving the DPO a high sensitivity to a film deposited on its torsional element. Such a film increases the (lumped-element) spring constant of the resonator, and the film's shear modulus can be deduced from the subsequent resonant frequency shift. Work supported by the Office of Naval Research.

  14. Characterizing wave- and current- induced bottom shear stress: U.S. middle Atlantic continental shelf

    USGS Publications Warehouse

    Dalyander, P. Soupy; Butman, Bradford; Sherwood, Christopher R.; Signell, Richard P.; Wilkin, John L.

    2013-01-01

    Waves and currents create bottom shear stress, a force at the seabed that influences sediment texture distribution, micro-topography, habitat, and anthropogenic use. This paper presents a methodology for assessing the magnitude, variability, and driving mechanisms of bottom stress and resultant sediment mobility on regional scales using numerical model output. The analysis was applied to the Middle Atlantic Bight (MAB), off the U.S. East Coast, and identified a tidally-dominated shallow region with relatively high stress southeast of Massachusetts over Nantucket Shoals, where sediment mobility thresholds are exceeded over 50% of the time; a coastal band extending offshore to about 30 m water depth dominated by waves, where mobility occurs more than 20% of the time; and a quiescent low stress region southeast of Long Island, approximately coincident with an area of fine-grained sediments called the “Mud Patch”. The regional high in stress and mobility over Nantucket Shoals supports the hypothesis that fine grain sediment winnowed away in this region maintains the Mud Patch to the southwest. The analysis identified waves as the driving mechanism for stress throughout most of the MAB, excluding Nantucket Shoals and sheltered coastal bays where tides dominate; however, the relative dominance of low-frequency events varied regionally, and increased southward toward Cape Hatteras. The correlation between wave stress and local wind stress was lowest in the central MAB, indicating a relatively high contribution of swell to bottom stress in this area, rather than locally generated waves. Accurate prediction of the wave energy spectrum was critical to produce good estimates of bottom shear stress, which was sensitive to energy in the long period waves.

  15. Measuring Autophagy in Stressed Cells

    PubMed Central

    Sharifi, Marina N.; Mowers, Erin E.; Drake, Lauren E; Macleod, Kay F

    2015-01-01

    Macro-autophagy is a major catabolic process in the cell used to degrade protein aggregates, dysfunctional organelles and intracellular pathogens that would otherwise become toxic. Autophagy also generates energy and metabolites for the cell through recycling of degraded autophagosomal cargo, which can be particularly important for cell viability under stress. The significance of changes in the rates of autophagic flux for cellular function and disease is being increasingly appreciated, and interest in measuring autophagy in different experimental systems is growing accordingly. Here, we describe key methodologies used in the field to measure autophagic flux, including monitoring LC3 processing by western blot, fluorescent cell staining, and flow cytometry, in addition to changes in the levels or posttranslational modifications of other autophagy markers, such as p62/Sqstm1 and the Atg5–Atg12 conjugate. We also describe what cellular stresses may be used to induce autophagy and how to control for changes in the rates of autophagic flux as opposed to inhibition of flux. Finally, we detail available techniques to monitor autophagy in vivo. PMID:25804753

  16. Transport phenomena in zonal centrifuge rotors. I. Velocity and shear-stress distributions of fluid during acceleration.

    PubMed

    Hsu, H W

    1968-09-01

    An analysis is presented for the evaluation of velocity components and shear-stress distributions of fluid in zonal centrifuge rotors during acceleration. Analytical expressions for the distribution of tangential and radial velocity components and the tangential shear-stress and the radial shear-stress distributions of fluid are obtained for the transient case. Characteristics of each distribution for a typical density gradient liquid in a zonal centrifuge rotor are computed from the relations derived, and are presented as figures. An unusual phenomenon-the tangential velocity of the gradient exceeding the velocity of the rotor during a particular period of acceleration-is demonstrated. PMID:5678322

  17. Overcoming shear stress of microalgae cultures in sparged photobioreactors.

    PubMed

    Barbosa, Maria J; Hadiyanto; Wijffels, René H

    2004-01-01

    In the present work we identified and quantified the effect of hydrodynamic stress on two different microalgae strains, Dunaliella tertiolecta and D. salina, cultivated in bench-scale bubble columns. The cell death rate constant increased with increasing gas-entrance velocity at the sparger. Dunaliella salina was slightly more sensitive than D. tertiolecta. The critical gas-entrance velocities were approximately 50 and 30 m s(-1) for D. tertiolecta and D. salina, respectively. The effects of gas-flow rate, culture height, and nozzle diameter on the death rate constant were also studied. From these results it was concluded that bubble rising and bubble bursting are not responsible for cell death. Regarding nozzle diameter, small nozzles were more detrimental to cells. The bubble formation at the sparger was found to be the main event leading to cell death. PMID:14705014

  18. Relationship between Magnetic Domain Structures and Shear Stress in Magnetic Minerals of Geological Materials

    NASA Astrophysics Data System (ADS)

    Yagyu, E.; Kanamaru, T.; Takemura, T.

    2014-12-01

    The magnetic properties of rocks are affected by geomagnetic fields, heat and shearing stresses after formation. The shear stress associated with tectonic stress, for example, from a fault, can cause magnetic domain­-wall displacement. The wall displacement is thought to reflect the magnetic domain structure. Therefore, the hysteresis of strain, which rocks are subjected to in fault movements, can be used to estimate the structural disturbances of the magnetic domain. Previous studies have shown that the stress effect on magnetic domains can be observed by using industrial and synthetic materials, such as Si-Fe alloys (Chikazumi & Suzuki, 1995). However, few studies have used natural geological materials to study the effect of stress on magnetic domains. This study's objective is to verify the shear stress history of rocks by observing the magnetic domain structures via the Bitter method and magnetic force microscopy (MFM). Here, the Bitter method is the powder pattern method, whereby a colloidal suspension of the magnetic powder is prepared from magnetic materials, and the patterns of the domain wall produced by ferromagnetic particles are observed under a microscope. On observing the domain structures of industrial and synthetic materials, the remnant stress on the surface layer is removed after mechanical polishing (Hoffmann et al., 1987) because the remnant stress influences the domain structures. There are several technical problems during the observation of rocks compared with those during observation of industrial and synthetic materials. Electrolytical polishing does not work because the electrical conductivity is very low (e.g., Hoffmann et al., 1987). In previous studies of the observation of magnetic domains of rock minerals, the surface strain layer was removed by polishing with colloidal silica (Ozdemir, 1995,etc). In this study, we will attempt to conduct a verification experiment and observations of the magnetic domain structures in natural minerals of rocks, and would like to discuss the relationship between the shear stress and magnetic domain structures. Here, the polishing method was according to Hoffmann et al. (1987), and the magnetic domain was observed by the Bitter method and MFM. As a result, we can observe the magnetic domain walls, and each domain wall has a spacing of 3-5 ?m.

  19. Exploring German Bight coastal morphodynamics based on modelled bed shear stress

    NASA Astrophysics Data System (ADS)

    Kösters, Frank; Winter, Christian

    2014-02-01

    The prediction of large-scale coastal and estuarine morphodynamics requires a sound understanding of the relevant driving processes and forcing factors. Data- and process-based methods and models suffer from limitations when applied individually to investigate these systems and, therefore, a combined approach is needed. The morphodynamics of coastal environments can be assessed in terms of a mean bed elevation range (BER), which is the difference of the lowest to highest seabed elevation occurring within a defined time interval. In this study of the coastal sector of the German Bight, North Sea, the highly variable distribution of observed BER for the period 1984-2006 is correlated to local bed shear stresses based on hindcast simulations with a well-validated high-resolution (typically 1,000 m in coastal settings) process-based numerical model of the North Sea. A significant correlation of the 95th percentile of bed shear stress and BER was found, explaining between 49 % and 60 % of the observed variance of the BER under realistic forcing conditions. The model then was applied to differentiate the effects of three main hydrodynamic drivers, i.e. tides, wind-induced currents, and waves. Large-scale mapping of these model results quantify previous qualitative suggestions: tides act as main drivers of the East Frisian coast, whereas waves are more relevant for the morphodynamics of the German west coast. Tidal currents are the main driver of the very high morphological activity of the tidal channels of the Ems, Weser and Elbe estuaries, the Jade Bay, and tidal inlets between the islands. This also holds for the backbarrier tidal flats of the North Frisian Wadden Sea. The morphodynamics of the foreshore areas of the barrier island systems are mainly wave-driven; in the deeper areas tides, waves and wind-driven currents have a combined effect. The open tidal flats (outer Ems, Neuwerker Watt, Dithmarschen Bight) are affected by a combination of tides, wind-driven currents and waves. Model performance should be measurably improved by integrating the roles of other key drivers, notably sediment dynamics and salt marsh stabilisation.

  20. Propose a Wall Shear Stress Divergence to Estimate the Risks of Intracranial Aneurysm Rupture

    PubMed Central

    Zhang, Y.; Takao, H.; Murayama, Y.; Qian, Y.

    2013-01-01

    Although wall shear stress (WSS) has long been considered a critical indicator of intracranial aneurysm rupture, there is still no definite conclusion as to whether a high or a low WSS results in aneurysm rupture. The reason may be that the effect of WSS direction has not been fully considered. The objectives of this study are to investigate the magnitude of WSS (|WSS|) and its divergence on the aneurysm surface and to test the significance of both in relation to the aneurysm rupture. Patient-specific computational fluid dynamics (CFD) was used to compute WSS and wall shear stress divergence (WSSD) on the aneurysm surface for nineteen patients. Our results revealed that if high |WSS| is stretching aneurysm luminal surface, and the stretching region is concentrated, the aneurysm is under a high risk of rupture. It seems that, by considering both direction and magnitude of WSS, WSSD may be a better indicator for the risk estimation of aneurysm rupture (154). PMID:24191140

  1. Interfibrillar shear stress is the loading mechanism of collagen fibrils in tendon

    PubMed Central

    Szczesny, Spencer E.; Elliott, Dawn M.

    2014-01-01

    Despite the critical role tendons play in transmitting loads throughout the musculoskeletal system, little is known about the microstructural mechanisms underlying their mechanical function. Of particular interest is whether collagen fibrils in tendon fascicles bear load independently or if load is transferred between fibrils through interfibrillar shear forces. We conducted multiscale experimental testing and developed a microstructural shear lag model to explicitly test whether interfibrillar shear load transfer is indeed the fibrillar loading mechanism in tendon. Experimental correlations between fascicle macroscale mechanics and microscale interfibrillar sliding suggest that fibrils are discontinuous and share load. Moreover, for the first time, we demonstrate that a shear lag model can replicate the fascicle macroscale mechanics as well as predict the microscale fibrillar deformations. Since interfibrillar shear stress is the fundamental loading mechanism assumed in the model, this result provides strong evidence that load is transferred between fibrils in tendon and possibly other aligned collagenous tissues. Conclusively establishing this fibrillar loading mechanism and identifying the involved structural components should help develop repair strategies for tissue degeneration and guide the design of tissue engineered replacements. PMID:24530560

  2. Interfibrillar shear stress is the loading mechanism of collagen fibrils in tendon.

    PubMed

    Szczesny, Spencer E; Elliott, Dawn M

    2014-06-01

    Despite the critical role tendons play in transmitting loads throughout the musculoskeletal system, little is known about the microstructural mechanisms underlying their mechanical function. Of particular interest is whether collagen fibrils in tendon fascicles bear load independently or if load is transferred between fibrils through interfibrillar shear forces. We conducted multiscale experimental testing and developed a microstructural shear lag model to explicitly test whether interfibrillar shear load transfer is indeed the fibrillar loading mechanism in tendon. Experimental correlations between fascicle macroscale mechanics and microscale interfibrillar sliding suggest that fibrils are discontinuous and share load. Moreover, for the first time, we demonstrate that a shear lag model can replicate the fascicle macroscale mechanics as well as predict the microscale fibrillar deformations. Since interfibrillar shear stress is the fundamental loading mechanism assumed in the model, this result provides strong evidence that load is transferred between fibrils in tendon and possibly other aligned collagenous tissues. Conclusively establishing this fibrillar loading mechanism and identifying the involved structural components should help develop repair strategies for tissue degeneration and guide the design of tissue engineered replacements. PMID:24530560

  3. Low-Shear modeled microgravity alters the Salmonella enterica serovar typhimurium stress response in an RpoS-independent manner

    NASA Technical Reports Server (NTRS)

    Wilson, James W.; Ott, C. Mark; Ramamurthy, Rajee; Porwollik, Steffen; McClelland, Michael; Pierson, Duane L.; Nickerson, Cheryl A.

    2002-01-01

    We have previously demonstrated that low-shear modeled microgravity (low-shear MMG) serves to enhance the virulence of a bacterial pathogen, Salmonella enterica serovar Typhimurium. The Salmonella response to low-shear MMG involves a signaling pathway that we have termed the low-shear MMG stimulon, though the identities of the low-shear MMG stimulon genes and regulatory factors are not known. RpoS is the primary sigma factor required for the expression of genes that are induced upon exposure to different environmental-stress signals and is essential for virulence in mice. Since low-shear MMG induces a Salmonella acid stress response and enhances Salmonella virulence, we reasoned that RpoS would be a likely regulator of the Salmonella low-shear MMG response. Our results demonstrate that low-shear MMG provides cross-resistance to several environmental stresses in both wild-type and isogenic rpoS mutant strains. Growth under low-shear MMG decreased the generation time of both strains in minimal medium and increased the ability of both strains to survive in J774 macrophages. Using DNA microarray analysis, we found no evidence of induction of the RpoS regulon by low-shear MMG but did find that other genes were altered in expression under these conditions in both the wild-type and rpoS mutant strains. Our results indicate that, under the conditions of these studies, RpoS is not required for transmission of the signal that induces the low-shear MMG stimulon. Moreover, our studies also indicate that low-shear MMG can be added to a short list of growth conditions that can serve to preadapt an rpoS mutant for resistance to multiple environmental stresses.

  4. Characterization of Abnormal Wall Shear Stress Using 4D Flow MRI in Human Bicuspid Aortopathy.

    PubMed

    van Ooij, Pim; Potters, Wouter V; Collins, Jeremy; Carr, Maria; Carr, James; Malaisrie, S Chris; Fedak, Paul W M; McCarthy, Patrick M; Markl, Michael; Barker, Alex J

    2015-06-01

    There exists considerable controversy surrounding the timing and extent of aortic resection for patients with BAV disease. Since abnormal wall shear stress (WSS) is potentially associated with tissue remodeling in BAV-related aortopathy, we propose a methodology that creates patient-specific 'heat maps' of abnormal WSS, based on 4D flow MRI. The heat maps were created by detecting outlier measurements from a volumetric 3D map of ensemble-averaged WSS in healthy controls. 4D flow MRI was performed in 13 BAV patients, referred for aortic resection and 10 age-matched controls. Systolic WSS was calculated from this data, and an ensemble-average and standard deviation (SD) WSS map of the controls was created. Regions of the individual WSS maps of the BAV patients that showed a higher WSS than the mean + 1.96SD of the ensemble-average control WSS map were highlighted. Elevated WSS was found on the greater ascending aorta (35% ± 15 of the surface area), which correlated significantly with peak systolic velocity (R (2) = 0.5, p = 0.01) and showed good agreement with the resected aortic regions. This novel approach to characterize regional aortic WSS may allow clinicians to gain unique insights regarding the heterogeneous expression of aortopathy and may be leveraged to guide patient-specific resection strategies for aorta repair. PMID:25118671

  5. The role of shear stress in Blood-Brain Barrier endothelial physiology

    Microsoft Academic Search

    Luca Cucullo; Mohammed Hossain; Vikram Puvenna; Nicola Marchi; Damir Janigro

    2011-01-01

    Background  One of the most important and often neglected physiological stimuli contributing to the differentiation of vascular endothelial\\u000a cells (ECs) into a blood-brain barrier (BBB) phenotype is shear stress (SS). With the use of a well established humanized\\u000a dynamic in vitro BBB model and cDNA microarrays, we have profiled the effect of SS in the induction\\/suppression of ECs genes and related

  6. Stress response and structural transitions in sheared gyroidal and lamellar amphiphilic mesophases: Lattice-Boltzmann simulations

    Microsoft Academic Search

    Nélido González-Segredo; Jens Harting; Giovanni Giupponi; Peter V. Coveney

    2006-01-01

    We report on the stress response of gyroidal and lamellar amphiphilic mesophases to steady shear simulated using a bottom-up lattice-Boltzmann model for amphiphilic fluids and sliding periodic (Lees-Edwards) boundary conditions. We study the gyroid per se (above the sponge-gyroid transition, of high crystallinity) and the molten gyroid (within such a transition, of shorter-range order). We find that both mesophases exhibit

  7. Slower Onset of Low Shear Stress Leads to Less Neointimal Thickening in Experimental Vein Grafts

    Microsoft Academic Search

    Zachary K. Baldwin; Amito Chandiwal; Wendy Huang; James E. Vosicky; Viji Balasubramanian; Michael A. Curi; Lewis B. Schwartz

    2006-01-01

    Vein grafts respond to low flow and shear stress (?w) by generating thicker walls and smaller lumens through the processes of neointimal hyperplasia and remodeling. Clinically,\\u000a however, vein grafts with obviously low ?w, such as those distal to high-grade proximal obstructions, are not infrequently found to be widely patent and pliable. One\\u000a possible explanation for this phenomenon may be that

  8. Shear stress is not sufficient to control growth of vascular networks: a model study.

    PubMed

    Hacking, W J; VanBavel, E; Spaan, J A

    1996-01-01

    Local vessel wall shear stress is considered to be important for vessel growth. This study is a theoretical investigation of how this mechanism contributes to the structure of a vascular network. The analyses and simulations were performed on vascular networks of increasing complexity, ranging from single-vessel resistance to large hexagonal networks. These networks were perfused by constant-flow sources, constant-pressure sources, or pressure sources with internal resistances. The mathematical foundation of the local endothelial shear stress and vessel wall adaptation was as follows: delta d/delta t = K*(tau-tau desired)*d, where d is vessel diameter, tau desired is desired shear stress, and K is a growth factor. Single vessels and networks with vessels in series developed stable optimal diameters when perfused at constant flow or with a constant-pressure source with internal resistance. However, when constant-pressure perfusion was applied, these vessels developed ever-increasing diameters or completely regressed. In networks with two vessels in parallel, only one; vessel attained an optimal diameter and the other regressed, irrespective of the nature of the perfusion source. Finally, large hexagonal networks regressed to a single vessel when perfused with a pressure source with internal resistance. The behavior was independent of variation in parameters, although the adaptation rate and the diameter of the final vessel were altered. Similar conclusions hold for models of vascular trees. We conclude that the effect of shear stress on vascular diameter alone does not lead to stable network structures, and additional factor(s) must be present. PMID:8769773

  9. An Analysis of Elastohydrodynamic Lubrication with Limiting Shear Stress: Part II — Load Influence

    Microsoft Academic Search

    Yongbin Zhang; Shizhu Wen

    2002-01-01

    This paper studies the load-carrying capacity of elastohydrodynamic lubrication (EHL) film subjected to isothermal condition incorporating the interfacial limiting shear stress. The slide-roll ratio varied from 0.0 to 2.0 and light, modest and heavy loads were respectively employed. A special attention was concentrated on the total lubricant flow entrained into the contact when different loads were used. It was indicated

  10. Endothelial cell cytoskeletal alignment independent of fluid shear stress on micropatterned surfaces

    Microsoft Academic Search

    Keri B. Vartanian; Sean J. Kirkpatrick; Stephen R. Hanson; Monica T. Hinds

    2008-01-01

    Endothelial cells (ECs) in athero-protective regions are elongated with actin and microtubule fibers aligned parallel to the direction of blood flow. Fluid shear stress (FSS) affects EC shape and functions, but little is known about shape-dependent EC properties that are independent of FSS. To evaluate these properties, ECs were elongated on micropatterned (MP) 25?m wide collagen-coated lanes (MPECs) and characterized

  11. U–6Nb shear stress relaxation in compression waves (IJP 585AV)

    Microsoft Academic Search

    D. B. Hayes; G. T. Gray III; R. S. Hixson; C. A. Hall; M. E. Byers; J. E. Vorthman

    2009-01-01

    When uranium alloyed with 6-wt% niobium (U–6Nb) is rapidly compressed in uniaxial strain experiments, shear stress is observed to relax with a characteristic time of 30±7ns. In shock wave experiments, this relaxation inhibits the development of an elastic precursor commonly seen in other materials. When U–6Nb is cold-rolled to pre-twin and significantly increase the density of dislocations in the material,

  12. Vertical distribution of wave shear stress in variable water depth: Theory and field observations

    Microsoft Academic Search

    Qingping Zou; Anthony J. Bowen; Alex E. Hay

    2006-01-01

    A generalized analytical model is developed to describe the vertical distribution of wave-induced shear stress in the presence of bottom slope, bottom friction and depth-induced wave breaking in the shoaling region and surf zone. The theory is compared to data obtained on an unbarred beach in 3.7-m mean water depth over a 2° bottom slope. Bottom slope and bottom friction

  13. Relationship Between Neointimal Thickness and Shear Stress After Wallstent Implantation in Human Coronary Arteries

    Microsoft Academic Search

    Jolanda J. Wentzel; Rob Krams; Johan C. H. Schuurbiers; Jan A. Oomen; Jeroen Kloet; Willem J. van der Giessen; Patrick W. Serruys; Cornelis J. Slager

    2010-01-01

    Background—In-stent restenosis by excessive intimal hyperplasia reduces the long-term clinical efficacy of coronary stents. Because shear stress (SS) is related to plaque growth in atherosclerosis, we investigated whether variations in SS distribution are related to variations in neointima formation. Methods and Results—In 14 patients, at 6-month follow-up after coronary Wallstent implantation, 3D stent and vessel reconstruction was performed with a

  14. Quantification of Hemodynamic Wall Shear Stress in Patients with Bicuspid Aortic Valve Using Phase-Contrast MRI

    PubMed Central

    Barker, Alex J.; Lanning, Craig; Shandas, Robin

    2010-01-01

    Bicuspid aortic valve (BAV) is often concomitant with aortic dilatation, aneurysm, and dissection. This valve lesion and its complications may affect positional and temporal wall shear stress (WSS), a parameter reported to regulate transcriptional events in vascular remodeling. Thus, this pilot study seeks to determine if the WSS in the ascending aorta (AAo) of BAV patients differs from control patients. Phase-contrast magnetic resonance imaging (PC-MRI) was used to perform flow analysis at the level of the AAo in 15 BAV and 15 control patients. Measurement of the aorta dimensions, flow rates, regurgitant fraction (RF), flow reversal ratio (FRR), temporal and spatial WSS, and shear range indices (SRI) were performed. The BAV and control group showed a significant difference between the circumferentially averaged WSS (p = 0.03) and positional WSS at systole (minimum p<0.001). Regressions found that SRI (r = 0.77, p<0.001), RF (r = 0.68, p<0.001), and WSS at systole (r = 0.66, p<0.001) were correlated to AAo size. The spatial distribution and magnitude of systolic WSS in BAV patients (?6.7 ± 4.3 dynes/cm2) differed significantly from control patients (?11.5 ± 6.6 dynes/cm2, p = 0.03). The SRI metric, a measure of shear symmetry along the lumen circumference, was also significantly different (p = 0.006) and indicated a heterogenic pattern of dilatation in the BAV patients. PMID:19953319

  15. Acute laminar shear stress reversibly increases human glomerular endothelial cell permeability via activation of endothelial nitric oxide synthase

    PubMed Central

    Bevan, Heather S.; Slater, Sadie C.; Clarke, Hayley; Cahill, Paul A.; Mathieson, Peter W.; Welsh, Gavin I.

    2011-01-01

    Laminar shear stress is a key determinant of systemic vascular behavior, including through activation of endothelial nitric oxide synthase (eNOS), but little is known of its role in the glomerulus. We confirmed eNOS expression by glomerular endothelial cells (GEnC) in tissue sections and examined effects of acute exposure (up to 24 h) to physiologically relevant levels of laminar shear stress (10–20 dyn/cm2) in conditionally immortalized human GEnC. Laminar shear stress caused an orientation of GEnC and stress fibers parallel to the direction of flow and induced Akt and eNOS phosphorylation along with NO production. Inhibition of the phophatidylinositol (PI)3-kinase/Akt pathway attenuated laminar shear stress-induced eNOS phosphorylation and NO production. Laminar shear stress of 10 dyn/cm2 had a dramatic effect on GEnC permeability, reversibly decreasing the electrical resistance across GEnC monolayers. Finally, the laminar shear stress-induced reduction in electrical resistance was attenuated by the NOS inhibitors l-NG-monomethyl arginine (l-NMMA) and l-NG-nitroarginine methyl ester (l-NAME) and also by inhibition of the PI3-kinase/Akt pathway. Hence we have shown for GEnC in vitro that acute permeability responses to laminar shear stress are dependent on NO, produced via activation of the PI3-kinase/Akt pathway and increased eNOS phosphorylation. These results suggest the importance of laminar shear stress and NO in regulating the contribution of GEnC to the permeability properties of the glomerular capillary wall. PMID:21775480

  16. Flow Shear Stress and Atherosclerosis: A Matter of Site Specificity

    PubMed Central

    Nigro, Patrizia; Abe, Jun-ichi

    2011-01-01

    Abstract It is well accepted that atherosclerosis occurs in a site-specific manner especially at branch points where disturbed blood flow (d-flow) predisposes to the development of plaques. Investigations both in vivo and in vitro have shown that d-flow is pro-atherogenic by promoting oxidative and inflammatory states in the artery wall. In contrast, steady laminar blood flow (s-flow) is atheroprotective by inhibition of oxidative stress and inflammation in the vessel wall. The mechanism for inflammation in endothelial cells (ECs) exposed to d-flow has been well studied and includes redox-dependent activation of apoptosis signal-regulating kinase 1 (ASK1) and Jun NH2-terminal kinase (JNK) that ultimately lead to the expression of adhesive molecules. In contrast, s-flow leads to the activation of the mitogen extracellular-signal-regulated kinase kinase 5/extracellular signal-regulated kinase-5 (MEK5/ERK5) pathway that prevents pro-inflammatory signaling. Important transcriptional events that reflect the pro-oxidant and pro-inflammatory condition of ECs in d-flow include the activation of activator protein 1 (AP-1) and nuclear factor kappaB (NF?B), whereas in s-flow, activation of Krüppel-like factor 2 (KLF2) and nuclear factor erythroid 2-like 2 (Nrf2) are dominant. Recent studies have shown that protein kinase c zeta (PKC?) is highly activated under d-flow conditions and may represent a molecular switch for EC signaling and gene expression. The targeted modulation of proteins activated in a site-specific manner holds the promise for a new approach to limit atherosclerosis. Antioxid. Redox Signal. 15, 1405–1414. PMID:21050140

  17. Stress intensity factors in bonded half planes containing inclined cracks and subjected to antiplane shear loading

    NASA Technical Reports Server (NTRS)

    Bassani, J. L.; Erdogan, F.

    1979-01-01

    The antiplane shear problem for two bonded dissimilar half planes containing a semi-infinite crack or two arbitrarily located collinear cracks is considered. For the semi-infinite crack the problem is solved for a concentrated wedge load and the stress intensity factor and the angular distribution of stresses are calculated. For finite cracks the problem is reduced to a pair of integral equations. Numerical results are obtained for cracks fully imbedded in a homogeneous medium, one crack tip touching the interface, and a crack crossing the interface for various crack angles.

  18. Stress intensity factors in bonded half planes containing inclined cracks and subjected to antiplane shear loading

    NASA Technical Reports Server (NTRS)

    Bassani, J. L.; Erdogan, F.

    1978-01-01

    The antiplane shear problem for two bonded dissimilar half planes containing a semi-infinite crack or two arbitrarily located collinear cracks was considered. For the semi-infinite crack the problem was solved for a concentrated wedge load and the stress intensity factor and the angular distribution of stresses were calculated. For finite cracks the problem was reduced to a pair of integral equations. Numerical results were obtained for cracks fully imbedded in a homogeneous medium, one crack tip touching the interface, and a crack crossing the interface for various crack angles.

  19. Efforts to reduce mortality to hydroelectric turbine-passed fish: locating and quantifying damaging shear stresses.

    PubMed

    Cada, Glenn; Loar, James; Garrison, Laura; Fisher, Richard; Neitzel, Duane

    2006-06-01

    Severe fluid forces are believed to be a source of injury and mortality to fish that pass through hydroelectric turbines. A process is described by which laboratory bioassays, computational fluid dynamics models, and field studies can be integrated to evaluate the significance of fluid shear stresses that occur in a turbine. Areas containing potentially lethal shear stresses were identified near the stay vanes and wicket gates, runner, and in the draft tube of a large Kaplan turbine. However, under typical operating conditions, computational models estimated that these dangerous areas comprise less than 2% of the flow path through the modeled turbine. The predicted volumes of the damaging shear stress zones did not correlate well with observed fish mortality at a field installation of this turbine, which ranged from less than 1% to nearly 12%. Possible reasons for the poor correlation are discussed. Computational modeling is necessary to develop an understanding of the role of particular fish injury mechanisms, to compare their effects with those of other sources of injury, and to minimize the trial and error previously needed to mitigate those effects. The process we describe is being used to modify the design of hydroelectric turbines to improve fish passage survival. PMID:16485161

  20. Mass Transport and Shear Stress as Mediators of Flow Effects on Atherosclerotic Plaque Origin and Growth

    NASA Astrophysics Data System (ADS)

    Gorder, Riley; Aliseda, Alberto

    2009-11-01

    The carotid artery bifurcation (CAB) is one of the leading site for atherosclerosis, a major cause of mortality and morbidity in the developed world. The specific mechanisms by which perturbed flow at the bifurcation and in the carotid bulge promotes plaque formation and growth are not fully understood. Shear stress, mass transport, and flow residence times are considered dominant factors. Shear stress causes restructuring of endothelial cells at the arterial wall which changes the wall's permeability. Long residence times are associated with enhanced mass transport through increased diffusion of lipids and white blood cells into the arterial wall. Although momentum and mass transfer are traditionally coupled by correlations similar to Reynolds Analogy, the complex flow patterns present in this region due to the pulsatile, transitional, detached flow associated with the complex geometry makes the validity of commonly accepted assumptions uncertain. We create solid models of the CAB from MRI or ultrasound medical images, build flow phantoms on clear polyester resin and use an IOR matching, blood mimicking, working fluid. Using PIV and dye injection techniques the shear stress and scalar transport are experimentally investigated. Our goal is to establish a quantitative relationship between momentum and mass transfer under a wide range of physiologically normal and pathological conditions.

  1. 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.

  2. LIF measurements of scalar mixing in turbulent shear layers

    NASA Technical Reports Server (NTRS)

    Karasso, Paris S.; Mungal, M. G.

    1993-01-01

    The structure of shear layer flows at high Reynolds numbers remains a very interesting problem. Straight mixing layers have been studied and yielded information on the probability density function (pdf) of a passive scalar across the layer. Konrad and Koochesfahani & Dimotakis measured the pdf of the mixture fraction for mixing layers of moderate Reynolds numbers, each about 25,000 (Re based on velocity difference and visual thickness). Their measurements showed a 'non-marching' pdf (central hump which is invariant from edge to edge across the layer), a result which is linked to the visualizations of the spanwise Kelvin-Helmholtz (K-H) instability mode, which is the primary instability for plane shear layer flows. A secondary instability mode, the Taylor-Gortler (T-G) instability, which is associated with streamwise vortical structures, has also been observed in shear layers. Image reconstruction by Jimenez et al. and volume renderings by Karasso & Mungal at low Re numbers have demonstrated that the K-H and the T-G instability modes occur simultaneously in a non-mutually destructive way, evidence that supports the quasi two-dimensional aspect of these flows and the non-marching character of the pdf at low Reynolds numbers. At higher Re numbers though, the interaction of these two instability modes is still unclear and may affect the mixing process. In this study, we perform measurements of the concentration pdf of plane mixing layers for different operating conditions. At a speed ratio of r = U(sub 1)/U(sub 2) = 4:1, we examine three Reynolds number cases: Re = 14,000, Re = 31,000, and Re = 62,000. Some other Re number cases' results, not presented in detail, are invoked to explain the behavior of the pdf of the concentration field. A case of r = 2.6:1 at Re = 20,000 is also considered. The planar laser-induced fluorescence technique is used to yield quantitative measurements. The different Re are obtained by changing the velocity magnitudes of the two streams. The question of resolution of these measurements is addressed. In order to investigate the effects of the initial conditions on the development and the structure of the mixing layer, the boundary layer on the high-speed side of the splitter plate is tripped. The average concentration and the average mixed fluid concentration are also calculated to further understand the changes in the shear layer for the different cases examined.

  3. Shear-wave velocity variation in jointed rock: an attempt to measure tide-induced variations

    SciTech Connect

    Beem, L.I.

    1987-08-01

    The use of the perturbation of seismic wave velocities by solid earth tides as a possible method of exploration for fractured media is discussed. Velocity of compressional seismic waves in fractured homogeneous rock has been observed to vary through solid earth tide cycles by a significant 0.5-0.9%. This variation of seismic velocities may be attributed to the opening and closing of joints by tidal stresses. In an attempt to see if shear-wave velocities show a similar velocity variation, a pneumatic shear-wave generator was used for the source. The 5 receivers, 3-component, 2.0 Hz, moving-coil geophones, were connected to a GEOS digital recorder. The two receivers located 120 m and 110 m from the source showed large shear-to-compression amplitude ratio and a high signal-to-noise ratio. A glaciated valley was chosen for the experiment site, since topography is flat and the granodiorite is jointed by a set of nearly orthogonal vertical joints, with superimposed horizontal sheeting joints. A slight velocity variation was noted in the first 200 consecutive firings; after which, the amplitude of the shear-wave begun to increase. This increase has been attributed to the compacting of the soil beneath the shear-wave generator (SWG). In the future, the soil will be compacted prior to placing the SWG or the SWG will be coupled directly to the rock to alleviate the amplitude fluctuation problem. This research may have application in exploration for fracture permeability in the rock mass between existing wells, by measuring seismic velocities from well to well through the tidal cycle.

  4. On the Effect of Apex Geometry on Wall Shear Stress and Pressure in a 2-D Arterial Bifurcation

    NASA Astrophysics Data System (ADS)

    Robertson, Anne; Haljasmaa, Igor; Galdi, Giovanni

    2000-11-01

    There is strong evidence to support the hypothesis that vascular geometry plays an important role in the initiation and development of cerebral aneurysms as well as other vascular diseases through its influence on hemodynamics. Cerebral aneurysms are nearly always found at arterial bifurcations in and near the Circle of Willis. It is commonly believed that the cause of initiation and development of cerebral aneurysms is at least indirectly related to the effect of hemodynamic wall pressure and shear stress on the arterial tissue at arterial bifurcations. In this work, we use analytical and numerical approaches to investigate the hypothesis that local geometric factors can have a significant impact on the magnitude and spatial gradients of wall pressure and shear stress at the apex of arterial bifurcations. We find that sharp corners such as those at arterial bifurcations and the juncture between grafted vessels can be a source of localized high wall pressure and shear stress. In fact, it can be shown analytically that perfectly sharp corners (zero radius of curvature) will lead to unbounded magnitudes of shear stress and pressure . As the radius of curvature is increased (the corner is rounded), the maximum in magnitude in wall shear stress shifts away from the apex to the lateral sides of the bifurcation. Significantly, the unbounded pressure and shear stress at perfectly sharp corners are unrelated to the fluid inertia. As shown here, the large values of pressure and shear stress which have previously been reported in studies in sharp corner models (zero radius of curvature) are grid dependent approximations for unbounded pressure and shear stress.

  5. Normalization of flow-mediated dilation to shear stress area under the curve eliminates the impact of variable hyperemic stimulus

    Microsoft Academic Search

    Jaume Padilla; Blair D Johnson; Sean C Newcomer; Daniel P Wilhite; Timothy D Mickleborough; Alyce D Fly; Kieren J Mather; Janet P Wallace

    2008-01-01

    BACKGROUND: Normalization of brachial artery flow-mediated dilation (FMD) to individual shear stress area under the curve (peak FMD:SSAUC ratio) has recently been proposed as an approach to control for the large inter-subject variability in reactive hyperemia-induced shear stress; however, the adoption of this approach among researchers has been slow. The present study was designed to further examine the efficacy of

  6. Differential regulation of protease activated receptor-1 and tissue plasminogen activator expression by shear stress in vascular smooth muscle cells

    NASA Technical Reports Server (NTRS)

    Papadaki, M.; Ruef, J.; Nguyen, K. T.; Li, F.; Patterson, C.; Eskin, S. G.; McIntire, L. V.; Runge, M. S.

    1998-01-01

    Recent studies have demonstrated that vascular smooth muscle cells are responsive to changes in their local hemodynamic environment. The effects of shear stress on the expression of human protease activated receptor-1 (PAR-1) and tissue plasminogen activator (tPA) mRNA and protein were investigated in human aortic smooth muscle cells (HASMCs). Under conditions of low shear stress (5 dyn/cm2), PAR-1 mRNA expression was increased transiently at 2 hours compared with stationary control values, whereas at high shear stress (25 dyn/cm2), mRNA expression was decreased (to 29% of stationary control; P<0.05) at all examined time points (2 to 24 hours). mRNA half-life studies showed that this response was not due to increased mRNA instability. tPA mRNA expression was decreased (to 10% of stationary control; P<0.05) by low shear stress after 12 hours of exposure and was increased (to 250% of stationary control; P<0.05) after 24 hours at high shear stress. The same trends in PAR-1 mRNA levels were observed in rat smooth muscle cells, indicating that the effects of shear stress on human PAR-1 were not species-specific. Flow cytometry and ELISA techniques using rat smooth muscle cells and HASMCs, respectively, provided evidence that shear stress exerted similar effects on cell surface-associated PAR-1 and tPA protein released into the conditioned media. The decrease in PAR-1 mRNA and protein had functional consequences for HASMCs, such as inhibition of [Ca2+] mobilization in response to thrombin stimulation. These data indicate that human PAR-1 and tPA gene expression are regulated differentially by shear stress, in a pattern consistent with their putative roles in several arterial vascular pathologies.

  7. Mis-sizing of stent promotes intimal hyperplasia: impact of endothelial shear and intramural stress

    PubMed Central

    Chen, Henry Y.; Sinha, Anjan K.; Choy, Jenny S.; Zheng, Hai; Sturek, Michael; Bigelow, Brian; Bhatt, Deepak L.

    2011-01-01

    Stent can cause flow disturbances on the endothelium and compliance mismatch and increased stress on the vessel wall. These effects can cause low wall shear stress (WSS), high wall shear stress gradient (WSSG), oscillatory shear index (OSI), and circumferential wall stress (CWS), which may promote neointimal hyperplasia (IH). The hypothesis is that stent-induced abnormal fluid and solid mechanics contribute to IH. To vary the range of WSS, WSSG, OSI, and CWS, we intentionally mismatched the size of stents to that of the vessel lumen. Stents were implanted in coronary arteries of 10 swine. Intravascular ultrasound (IVUS) was used to size the coronary arteries and stents. After 4 wk of stent implantation, IVUS was performed again to determine the extent of IH. In conjunction, computational models of actual stents, the artery, and non-Newtonian blood were created in a computer simulation to yield the distribution of WSS, WSSG, OSI, and CWS in the stented vessel wall. An inverse relation (R2 = 0.59, P < 0.005) between WSS and IH was found based on a linear regression analysis. Linear relations between WSSG, OSI, and IH were observed (R2 = 0.48 and 0.50, respectively, P < 0.005). A linear relation (R2 = 0.58, P < 0.005) between CWS and IH was also found. More statistically significant linear relations between the ratio of CWS to WSS (CWS/WSS), the products CWS × WSSG and CWS × OSI, and IH were observed (R2 = 0.67, 0.54, and 0.56, respectively, P < 0.005), suggesting that both fluid and solid mechanics influence the extent of IH. Stents create endothelial flow disturbances and intramural wall stress concentrations, which correlate with the extent of IH formation, and these effects were exaggerated with mismatch of stent/vessel size. These findings reveal the importance of reliable vessel and stent sizing to improve the mechanics on the vessel wall and minimize IH. PMID:21926337

  8. An in vitro comparative study of intracanal fluid motion and wall shear stress induced by ultrasonic and polymer rotary finishing files in a simulated root canal model.

    PubMed

    Koch, Jon; Borg, John; Mattson, Abby; Olsen, Kris; Bahcall, James

    2012-01-01

    Objective. This in vitro study compared the flow pattern and shear stress of an irrigant induced by ultrasonic and polymer rotary finishing file activation in an acrylic root canal model. Flow visualization analysis was performed using an acrylic canal filled with a mixture of distilled water and rheoscopic fluid. The ultrasonic and polymer rotary finishing file were separately tested in the canal and activated in a static position and in a cyclical axial motion (up and down). Particle movement in the fluid was captured using a high-speed digital camera and DaVis 7.1 software. The fluid shear stress analysis was performed using hot film anemometry. A hot-wire was placed in an acrylic root canal and the canal was filled with distilled water. The ultrasonic and polymer rotary finishing files were separately tested in a static position and in a cyclical axial motion. Positive needle irrigation was also tested separately for fluid shear stress. The induced wall shear stress was measured using LabVIEW 8.0 software. PMID:22461994

  9. Shear stress enhances microcin B17 production in a rotating wall bioreactor, but ethanol stress does not

    NASA Technical Reports Server (NTRS)

    Gao, Q.; Fang, A.; Pierson, D. L.; Mishra, S. K.; Demain, A. L.

    2001-01-01

    Stress, including that caused by ethanol, has been shown to induce or promote secondary metabolism in a number of microbial systems. Rotating-wall bioreactors provide a low stress and simulated microgravity environment which, however, supports only poor production of microcin B17 by Escherichia coli ZK650, as compared to production in agitated flasks. We wondered whether the poor production is due to the low level of stress and whether increasing stress in the bioreactors would raise the amount of microcin B17 formed. We found that applying shear stress by addition of a single Teflon bead to a rotating wall bioreactor improved microcin B17 production. By contrast, addition of various concentrations of ethanol to such bioreactors (or to shaken flasks) failed to increase microcin B17 production. Ethanol stress merely decreased production and, at higher concentrations, inhibited growth. Interestingly, cells growing in the bioreactor were much more resistant to the growth-inhibitory and production-inhibitory effects of ethanol than cells growing in shaken flasks.

  10. An evaluation of the Iosipescu specimen for composite materials shear property measurement

    Microsoft Academic Search

    Henjen Ho

    1991-01-01

    A detailed evaluation of the suitability of the Iosipescu specimen tested in the modified Wyoming fixture is presented. An experimental investigation using conventional strain gage instrumentation and moire interferometry is performed. A finite element analysis of the Iosipescu shear test for unidirectional and cross-ply composites is used to assess the uniformity of the shear stress field in the vicinity of

  11. In situ monitoring of localized shear stress and fluid flow within developing tissue constructs by Doppler optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Jia, Yali; Bagnaninchi, Pierre O.; Wang, Ruikang K.

    2008-02-01

    Mechanical stimuli can be introduced to three dimensional (3D) cell cultures by use of perfusion bioreactor. Especially in musculoskeletal tissues, shear stress caused by fluid flow generally increase extra-cellular matrix (ECM) production and cell proliferation. The relationship between the shear stress and the tissue development in situ is complicated because of the non-uniform pore distribution within the cell-seeded scaffold. In this study, we firstly demonstrated that Doppler optical coherence tomography (DOCT) is capable of monitoring localized fluid flow and shear stress in the complex porous scaffold by examining their variation trends at perfusion rate of 5, 8, 10 and 12 ml/hr. Then, we developed the 3D porous cellular constructs, cell-seeded chitosan scaffolds monitored during several days by DOCT. The fiber based fourier domain DOCT employed a 1300 nm superluminescent diode with a bandwidth of 52 nm and a xyz resolution of 20×20×15 ?m in free space. This setup allowed us not only to assess the cell growth and ECM deposition by observing their different scattering behaviors but also to further investigate how the cell attachment and ECM production has the effect on the flow shear stress and the relationship between flow rate and shear stress in the developing tissue construct. The possibility to monitor continuously the constructs under perfusion will easily indicate the effect of flow rate or shear stress on the cell viability and cell proliferation, and then discriminate the perfusion parameters affecting the pre-tissue formation rate growth.

  12. A new experimental system for simultaneous application of cyclic tensile strain and fluid shear stress to tenocytes in vitro.

    PubMed

    Maeda, Eijiro; Hagiwara, Yasufumi; Wang, James H-C; Ohashi, Toshiro

    2013-12-01

    Tenocyte mechanotransduction has been of great interest to researchers in tendon mechanobiology and biomechanics. In vivo, tenocytes are subjected to tensile strain and fluid shear stress, but most studies of tenocyte mechanobiology have been to understand how tenocytes regulate their functions in response to tensile strain. Thus, there is still much to know about tenocyte responses to fluid shear stress, partly due to the difficulty of devising a suitable experimental set-up and understanding the exact magnitude of imposed fluid shear stress. Therefore, this study was performed to test a new experimental system, which is suitable for the application of tensile strain and fluid shear stress to tenocytes in vitro. It was experimentally and numerically confirmed that tenocytes could maintain their in situ morphology within microfabricated microgrooves; also, physiological tensile strain and a wide range of fluid shear stress magnitudes can be applied to these cells. Indeed, it was demonstrated that the combined stimulation of cyclic tensile strain and oscillatory fluid shear stress induced a greater synergetic effect on tenocyte calcium response and significantly increased the percentage of tenocyte exhibiting increases in intracellular Ca(2+) concentration compared to the solo applications of these two modes of mechanical stimulation. The experimental system presented here is suitable for research of tenocyte mechanobiology, particularly mechanotransduction events, which were difficult to study using previous experimental models like explants and cell monolayers. PMID:23881419

  13. The Measurement of Stress among College Students.

    ERIC Educational Resources Information Center

    Hensley, Wayne E.

    This paper reports on a study to develop a scale of stress measurement and its use with undergraduate students (N=269) at a large land grant mid-Atlantic university. Students, within the classroom setting, were given a questionnaire containing 52 potentially stressful hypothetical situations and were asked to indicate the degree of stress they…

  14. Effects of shear stress pattern and magnitude on mesenchymal transformation and invasion of aortic valve endothelial cells.

    PubMed

    Mahler, Gretchen J; Frendl, Christopher M; Cao, Qingfeng; Butcher, Jonathan T

    2014-11-01

    Understanding the role of mechanical forces on cell behavior is critical for tissue engineering, regenerative medicine, and disease initiation studies. Current hemodynamic bioreactors are largely limited to 2D substrates or the application of general flow conditions at a tissue level, which eliminates the investigation of some essential physiological and pathological responses. One example is the mesenchymal transformation of endothelial cells in response to shear stress. Endothelial to mesenchymal transformation (EndMT) is a valve morphogenic mechanism associated with aortic valve disease initiation. The aortic valve experiences oscillatory shear on the disease-susceptible fibrosa, and the role of hemodynamics on adult EndMT is unknown. The goal of this work was to develop and characterize a microfluidic bioreactor that applies physiologically relevant laminar or oscillatory shear stresses to endothelial cells and permits the quantitative analysis of 3D cell-extracellular matrix (ECM) interactions. In this study, porcine aortic valve endothelial cells were seeded onto 3D collagen I gels and exposed to different magnitudes of steady or oscillatory shear stress for 48?h. Cells elongated and aligned perpendicular to laminar, but not oscillatory shear. Low steady shear stress (2?dyne/cm(2) ) and oscillatory shear stress upregulated EndMT (ACTA2, Snail, TGFB1) and inflammation (ICAM1, NFKB1) related gene expression, EndMT-related (?SMA) protein expression, and matrix invasion when compared with static controls or cells exposed to high steady shear (10 and 20?dyne/cm(2) ). Our system enables direct testing of the role of shear stress on endothelial cell mesenchymal transformation in a dynamic, 3D environment and shows that hemodynamics regulate EndMT in adult valve endothelial cells. PMID:24898772

  15. Cantilever measurements of surface stress, surface reconstruction, film stress and magnetoelastic stress of monolayers

    Microsoft Academic Search

    Dirk Sander; Zhen Tian; Jürgen Kirschner

    2008-01-01

    We re view the application of cantilever-based stress measurements in surface sci- ence and magnetism. The application of thin (thickness appr. 0.1 mm) single crystalline substrates as cantilevers has been used successfully to measure adsorbate-induced surface stress changes, lattice misfit induced film stress, and magneto-elastic stress of ferromagnetic monolayers. Surface stress changes as small as 0.01 N\\/m can be readily

  16. Measurement of interfacial shear strength in SiC-fiber/Si sub 3 N sub 4 composites

    SciTech Connect

    Laughner, J.W. (New York State College of Ceramics at Alfred Univ., Alfred, NY (US)); Bhatt, R.T. (NASA-Lewis Research Center, Cleveland, OH (US))

    1989-10-01

    This paper reports an indentation method for measuring shear strength in brittle matrix composites applied to SiC-fiber/Si{sub 3}N{sub 4}-matrix samples. Three methods were used to manufacture the composites: reaction bonding of a Si/SiC preform, hot-pressing, and nitrogen- overpressure sintering. An indentation technique developed by Marshall for thin specimens was used to measure the shear strength of the interface and the interfacial friction stresses. This was done by inverting the sample after the initial push through and retesting the pushed fibers. SEM observations showed that the shear strength was determined by the degree of reaction between the fiber and the matrix unless the fiber was pushed out of its (well-bonded) sheath.

  17. The effect of a homogenizing optic on residual stresses and shear strength of laser brazed ceramic/steel-joints

    NASA Astrophysics Data System (ADS)

    Südmeyer, I.; Rohde, M.; Besser, H.; Grein, M.; Liesching, B.; Schneider, J.

    2011-03-01

    Oxide and non oxide ceramics (Al2O3, SiC) were brazed to commercial steel with active filler alloys using a CO2-laser (l = 10.64 ?m). Two different laser intensity profiles were used for heating up the compound: A laser output beam presenting a Gaussian profile and a homogenized, nearly top head profile were applied for joining the compounds in an Argon stream. The temperature distribution with and without the homogenizing optic was measured during the process and compared to the results of a finite element model simulating the brazing process with the different laser intensity profiles. Polished microsections were prepared for characterization of the different joints by scanning electron micrographs and EDXanalysis. In order to evaluate the effects of the different laser intensity profiles on the compound, the shear strengths of the braze-joints were determined. Additionally residual stresses which were caused by the gradient of thermal expansion between ceramic and metal were determined by finite element modeling. The microsections did not exhibit differences between the joints, which were brazed with different laser profiles. However the shear tests proved, that an explicit increase of compound strength up to 34 MPa of the ceramic/metal joints can be achieved with the top head profile, whereas the joints brazed with the Gaussian profile achieved only shear strength values of 24 MPa. Finally tribological pin-on-disc tests proved the capability of the laser brazed joints with regard to the application conditions.

  18. Residual stress measurement in YBCO thin films.

    SciTech Connect

    Cheon, J. H.; Singh, J. P.

    2002-05-13

    Residual stress in YBCO films on Ag and Hastelloy C substrates was determined by using 3-D optical interferometry and laser scanning to measure the change in curvature radius before and after film deposition. The residual stress was obtained by appropriate analysis of curvature measurements. Consistent with residual thermal stress calculations based on the thermal expansion coefficient mismatch between the substrates and YBCO film, the measured residual stress in the YBCO film on Hastelloy C substrate was tensile, while it was compressive on the Ag substrate. The stress values measured by the two techniques were generally in good agreement, suggesting that optical interferometry and laser scanning have promise for measuring residual stresses in thin films.

  19. Beef Longissimus Slice Shear Force Measurement Among Steak Locations and Institutions

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The objectives of this study were 1) to evaluate slice shear force on every longissimus thoracis et lumborum steak to determine which steaks were appropriate for slice shear force measurement and 2) to train six other institutions to conduct slice shear force and then determine the among and within ...

  20. Correlation of predicted and measured thermal stresses on an advanced aircraft structure with similar materials

    NASA Technical Reports Server (NTRS)

    Jenkins, J. M.

    1979-01-01

    A laboratory heating test simulating hypersonic heating was conducted on a heat-sink type structure to provide basic thermal stress measurements. Six NASTRAN models utilizing various combinations of bar, shear panel, membrane, and plate elements were used to develop calculated thermal stresses. Thermal stresses were also calculated using a beam model. For a given temperature distribution there was very little variation in NASTRAN calculated thermal stresses when element types were interchanged for a given grid system. Thermal stresses calculated for the beam model compared similarly to the values obtained for the NASTRAN models. Calculated thermal stresses compared generally well to laboratory measured thermal stresses. A discrepancy of signifiance occurred between the measured and predicted thermal stresses in the skin areas. A minor anomaly in the laboratory skin heating uniformity resulted in inadequate temperature input data for the structural models.

  1. Predicting equilibrium states with Reynolds stress closures in channel flow and homogeneous shear flow

    NASA Technical Reports Server (NTRS)

    Abid, R.; Speziale, C. G.

    1992-01-01

    Turbulent channel flow and homogeneous shear flow have served as basic building block flows for the testing and calibration of Reynolds stress models. A direct theoretical connection is made between homogeneous shear flow in equilibrium and the log-layer of fully-developed turbulent channel flow. It is shown that if a second-order closure model is calibrated to yield good equilibrium values for homogeneous shear flow it will also yield good results for the log-layer of channel flow provided that the Rotta coefficient is not too far removed from one. Most of the commonly used second-order closure models introduce an ad hoc wall reflection term in order to mask deficient predictions for the log-layer of channel flow that arise either from an inaccurate calibration of homogeneous shear flow or from the use of a Rotta coefficient that is too large. Illustrative model calculations are presented to demonstrate this point which has important implications for turbulence modeling.

  2. Impact of blood rheology on wall shear stress in a model of the middle cerebral artery

    PubMed Central

    Bernabeu, Miguel O.; Nash, Rupert W.; Groen, Derek; Carver, Hywel B.; Hetherington, James; Krüger, Timm; Coveney, Peter V.

    2013-01-01

    Perturbations to the homeostatic distribution of mechanical forces exerted by blood on the endothelial layer have been correlated with vascular pathologies, including intracranial aneurysms and atherosclerosis. Recent computational work suggests that, in order to correctly characterize such forces, the shear-thinning properties of blood must be taken into account. To the best of our knowledge, these findings have never been compared against experimentally observed pathological thresholds. In this work, we apply the three-band diagram (TBD) analysis due to Gizzi et al. (Gizzi et al. 2011 Three-band decomposition analysis of wall shear stress in pulsatile flows. Phys. Rev. E 83, 031902. (doi:10.1103/PhysRevE.83.031902)) to assess the impact of the choice of blood rheology model on a computational model of the right middle cerebral artery. Our results show that, in the model under study, the differences between the wall shear stress predicted by a Newtonian model and the well-known Carreau–Yasuda generalized Newtonian model are only significant if the vascular pathology under study is associated with a pathological threshold in the range 0.94–1.56 Pa, where the results of the TBD analysis of the rheology models considered differs. Otherwise, we observe no significant differences. PMID:24427534

  3. Impact of blood rheology on wall shear stress in a model of the middle cerebral artery.

    PubMed

    Bernabeu, Miguel O; Nash, Rupert W; Groen, Derek; Carver, Hywel B; Hetherington, James; Krüger, Timm; Coveney, Peter V

    2013-04-01

    Perturbations to the homeostatic distribution of mechanical forces exerted by blood on the endothelial layer have been correlated with vascular pathologies, including intracranial aneurysms and atherosclerosis. Recent computational work suggests that, in order to correctly characterize such forces, the shear-thinning properties of blood must be taken into account. To the best of our knowledge, these findings have never been compared against experimentally observed pathological thresholds. In this work, we apply the three-band diagram (TBD) analysis due to Gizzi et al. (Gizzi et al. 2011 Three-band decomposition analysis of wall shear stress in pulsatile flows. Phys. Rev. E 83, 031902. (doi:10.1103/PhysRevE.83.031902)) to assess the impact of the choice of blood rheology model on a computational model of the right middle cerebral artery. Our results show that, in the model under study, the differences between the wall shear stress predicted by a Newtonian model and the well-known Carreau-Yasuda generalized Newtonian model are only significant if the vascular pathology under study is associated with a pathological threshold in the range 0.94-1.56 Pa, where the results of the TBD analysis of the rheology models considered differs. Otherwise, we observe no significant differences. PMID:24427534

  4. Automation of Shear-Wave Splitting Measurements using Cluster Analysis

    Microsoft Academic Search

    N. A. Teanby; J.-M. Kendall; M. van der Baan

    2004-01-01

    The propagation of two orthogonally polarized shear waves, or shear- wave splitting, is arguably the most robust indication of seismic anisotropy in the Earth. This splitting can be parameterized in terms of the polarization of the fast shear-wave ! and the lag time between fast and slow components dt. These two parameters provide constraints on the mechanism causing the anisotropy.

  5. Use of shear-stress-sensitive, temperature-insensitive liquid crystals for hypersonic boundary-layer transition detection

    SciTech Connect

    Aeschliman, D.P.; Croll, R.H.; Kuntz, D.W.

    1997-04-01

    The use of shear-stress-sensitive, temperature-insensitive (SSS/TI) liquid crystals (LCs) has been evaluated as a boundary-layer transition detection technique for hypersonic flows. Experiments were conducted at Mach 8 in the Sandia National Laboratories Hypersonic Wind Tunnel using a flat plate model at near zero-degree angle of attack over the freestream unit Reynolds number range 1.2-5.8x10{sup 6}/ft. Standard 35mm color photography and Super VHS color video were used to record LC color changes due to varying surface shear stress during the transition process for a range of commercial SSS liquid crystals. Visual transition data were compared to an established method using calorimetric surface heat-transfer measurements to evaluate the LC technique. It is concluded that the use of SSS/TI LCs can be an inexpensive, safe, and easy to use boundary-layer transition detection method for hypersonic flows. However, a valid interpretation of the visual records requires careful attention to illumination intensity levels and uniformity, lighting and viewing angles, some prior understanding of the general character of the flow, and the selection of the appropriate liquid crystal for the particular flow conditions.

  6. Local shear stress and its correlation with local volume fraction in concentrated non-Brownian suspensions: Lattice Boltzmann simulation

    NASA Astrophysics Data System (ADS)

    Lee, Young Ki; Ahn, Kyung Hyun; Lee, Seung Jong

    2014-12-01

    The local shear stress of non-Brownian suspensions was investigated using the lattice Boltzmann method coupled with the smoothed profile method. Previous studies have only focused on the bulk rheology of complex fluids because the local rheology of complex fluids was not accessible due to technical limitations. In this study, the local shear stress of two-dimensional solid particle suspensions in Couette flow was investigated with the method of planes to correlate non-Newtonian fluid behavior with the structural evolution of concentrated particle suspensions. Shear thickening was successfully captured for highly concentrated suspensions at high particle Reynolds number, and both the local rheology and local structure of the suspensions were analyzed. It was also found that the linear correlation between the local particle stress and local particle volume fraction was dramatically reduced during shear thickening. These results clearly show how the change in local structure of suspensions influences the local and bulk rheology of the suspensions.

  7. Local shear stress and its correlation with local volume fraction in concentrated non-Brownian suspensions: lattice Boltzmann simulation.

    PubMed

    Lee, Young Ki; Ahn, Kyung Hyun; Lee, Seung Jong

    2014-12-01

    The local shear stress of non-Brownian suspensions was investigated using the lattice Boltzmann method coupled with the smoothed profile method. Previous studies have only focused on the bulk rheology of complex fluids because the local rheology of complex fluids was not accessible due to technical limitations. In this study, the local shear stress of two-dimensional solid particle suspensions in Couette flow was investigated with the method of planes to correlate non-Newtonian fluid behavior with the structural evolution of concentrated particle suspensions. Shear thickening was successfully captured for highly concentrated suspensions at high particle Reynolds number, and both the local rheology and local structure of the suspensions were analyzed. It was also found that the linear correlation between the local particle stress and local particle volume fraction was dramatically reduced during shear thickening. These results clearly show how the change in local structure of suspensions influences the local and bulk rheology of the suspensions. PMID:25615103

  8. A control systems approach to quantify wall shear stress normalization by flow-mediated dilation in the brachial artery.

    PubMed

    van Bussel, Frank C G; van Bussel, Bas C T; Hoeks, Arnold P G; Op 't Roodt, Jos; Henry, Ronald M A; Ferreira, Isabel; Vanmolkot, Floris H M; Schalkwijk, Casper G; Stehouwer, Coen D A; Reesink, Koen D

    2015-01-01

    Flow-mediated dilation is aimed at normalization of local wall shear stress under varying blood flow conditions. Blood flow velocity and vessel diameter are continuous and opposing influences that modulate wall shear stress. We derived an index FMDv to quantify wall shear stress normalization performance by flow-mediated dilation in the brachial artery. In 22 fasting presumed healthy men, we first assessed intra- and inter-session reproducibilities of two indices pFMDv and mFMDv, which consider the relative peak and relative mean hyperemic change in flow velocity, respectively. Second, utilizing oral glucose loading, we evaluated the tracking performance of both FMDv indices, in comparison with existing indices [i.e., the relative peak diameter increase (%FMD), the peak to baseline diameter ratio (Dpeak/Dbase), and the relative peak diameter increase normalized to the full area under the curve of blood flow velocity with hyperemia (FMD/shearAUC) or with area integrated to peak hyperemia (FMD/shearAUC_peak)]. Inter-session and intra-session reproducibilities for pFMDv, mFMDv and %FMD were comparable (intra-class correlation coefficients within 0.521-0.677 range). Both pFMDv and mFMDv showed more clearly a reduction after glucose loading (reduction of ~45%, p?0.001) than the other indices (% given are relative reductions): %FMD (~11%, p?0.074); Dpeak/Dbase (~11%, p?0.074); FMD/shearAUC_peak (~20%, p?0.016) and FMD/shearAUC (~38%, p?0.038). Further analysis indicated that wall shear stress normalization under normal (fasting) conditions is already far from ideal (FMDv < 1), which (therefore) does not materially change with glucose loading. Our approach might be useful in intervention studies to detect intrinsic changes in shear stress normalization performance in conduit arteries. PMID:25693114

  9. Purinergic signaling is required for fluid shear stress-induced NF-{kappa}B translocation in osteoblasts

    SciTech Connect

    Genetos, Damian C., E-mail: dgenetos@ucdavis.edu [Department of Anatomy, Cell Biology, and Physiology, School of Veterinary Medicine, University of California, Davis, CA (United States); Karin, Norman J. [Cell Biology and Biochemistry, Pacific Northwest National Laboratory, Richland, WA (United States)] [Cell Biology and Biochemistry, Pacific Northwest National Laboratory, Richland, WA (United States); Geist, Derik J. [Department of Orthopaedic Surgery, Indiana University School of Medicine, Indianapolis, IN (United States)] [Department of Orthopaedic Surgery, Indiana University School of Medicine, Indianapolis, IN (United States); Donahue, Henry J. [Division of Musculoskeletal Sciences, Department of Orthopaedics and Rehabilitation, Pennsylvania State College of Medicine, Hershey, PA (United States)] [Division of Musculoskeletal Sciences, Department of Orthopaedics and Rehabilitation, Pennsylvania State College of Medicine, Hershey, PA (United States); Duncan, Randall L. [Department of Orthopaedic Surgery, Indiana University School of Medicine, Indianapolis, IN (United States)] [Department of Orthopaedic Surgery, Indiana University School of Medicine, Indianapolis, IN (United States)

    2011-04-01

    Fluid shear stress regulates gene expression in osteoblasts, in part by activation of the transcription factor NF-{kappa}B. We examined whether this process was under the control of purinoceptor activation. MC3T3-E1 osteoblasts under static conditions expressed the NF-{kappa}B inhibitory protein I{kappa}B{alpha} and exhibited cytosolic localization of NF-{kappa}B. Under fluid shear stress, I{kappa}B{alpha} levels decreased, and concomitant nuclear localization of NF-{kappa}B was observed. Cells exposed to fluid shear stress in ATP-depleted medium exhibited no significant reduction in I{kappa}B{alpha}, and NF-{kappa}B remained within the cytosol. Similar results were found using oxidized ATP or Brilliant Blue G, P2X{sub 7} receptor antagonists, indicating that the P2X{sub 7} receptor is responsible for fluid shear-stress-induced I{kappa}B{alpha} degradation and nuclear accumulation of NF-{kappa}B. Pharmacologic blockage of the P2Y6 receptor also prevented shear-induced I{kappa}B{alpha} degradation. These phenomena involved neither ERK1/2 signaling nor autocrine activation by P2X{sub 7}-generated lysophosphatidic acid. Our results suggest that fluid shear stress regulates NF-{kappa}B activity through the P2Y{sub 6} and P2X{sub 7} receptor.

  10. A Numerical Experiment on the Role of Surface Shear Stress in the Generation of Sound

    NASA Technical Reports Server (NTRS)

    Shariff, Karim; Wang, Meng; Merriam, Marshal (Technical Monitor)

    1996-01-01

    The sound generated due to a localized flow over an infinite flat surface is considered. It is known that the unsteady surface pressure, while appearing in a formal solution to the Lighthill equation, does not constitute a source of sound but rather represents the effect of image quadrupoles. The question of whether a similar surface shear stress term constitutes a true source of dipole sound is less settled. Some have boldly assumed it is a true source while others have argued that, like the surface pressure, it depends on the sound field (via an acoustic boundary layer) and is therefore not a true source. A numerical experiment based on the viscous, compressible Navier-Stokes equations was undertaken to investigate the issue. A small region of a wall was oscillated tangentially. The directly computed sound field was found to to agree with an acoustic analogy based calculation which regards the surface shear as an acoustically compact dipole source of sound.

  11. Correlation of compressive and shear stress with spalling of plasma-sprayed ceramic materials

    NASA Technical Reports Server (NTRS)

    Mullen, R. L.; Mcdonald, G.; Hendricks, R. C.; Hofle, M. M.

    1983-01-01

    Ceramics on metal substrates for potential use as high temperature seals or other applications are exposed to forces originating from differences in thermal expansion between the ceramic and the metal substrate. This report develops a relationship between the difference in expansion of the ceramic and the substrate, defines conditions under which shear between the ceramic and the substrate occurs, and those under which bending forces are produced in the ceramic. The off-axis effect of compression forces resulting from high temperature plastic flow of the ceramic producing buckling of the ceramic is developed. Shear is associated with the edge or boundary stresses on the component while bending is associated with the distortion of an interior region. Both modes are significant in predicting life of the ceramic. Previously announced in STAR as N83-27016

  12. Networklike propagation of cell-level stress in sheared random foams.

    PubMed

    Evans, Myfanwy E; Kraynik, Andrew M; Reinelt, Douglas A; Mecke, Klaus; Schröder-Turk, Gerd E

    2013-09-27

    Quasistatic simple shearing flow of random monodisperse soap froth is investigated by analyzing surface evolver simulations of spatially periodic foams. Elastic-plastic behavior is caused by irreversible topological rearrangements (T1s) that occur when Plateau's laws are violated; the first T1 determines the elastic limit and frequent T1 avalanches sustain the yield-stress plateau at large strains. The stress and shape anisotropy of individual cells is quantified by Q, a scalar derived from an interface tensor that gauges the cell's contribution to the global stress. During each T1 avalanche, the connected set of cells with decreasing Q, called the stress release domain, is networklike and nonlocal. Geometrically, the networklike nature of the stress release domains is corroborated through morphological analysis using the Euler characteristic. The stress release domain is distinctly different from the set of cells that change topology during a T1 avalanche. Our results highlight the connection between the unique rheological behavior of foams and the complex large-scale cooperative rearrangements of foam cells that accompany distinctly local topological transitions. PMID:24116819

  13. Homework Stress: Construct Validation of a Measure

    ERIC Educational Resources Information Center

    Katz, Idit; Buzukashvili, Tamara; Feingold, Liat

    2012-01-01

    This article presents 2 studies aimed at validating a measure of stress experienced by children and parents around the issue of homework, applying Benson's program of validation (Benson, 1998). Study 1 provides external validity of the measure by supporting hypothesized relations between stress around homework and students' and parents' positive…

  14. An In Situ Ultrasonic Technique for Simultaneous Measurement of Longitudinal and Shear Wave Speeds in Solids

    Microsoft Academic Search

    T. H. Kidd; S. Zhuang; G. Ravichandran

    2007-01-01

    Ultrasonic wave speed measurements are widely used to infer the elastic properties of solids. In the standard method, longitudinal\\u000a and shear transducers are used separately to measure the corresponding wave speeds in a material. A new experimental method\\u000a is introduced for simultaneously measuring the longitudinal and the shear wave speeds using a single set of longitudinal or\\u000a shear transducers. The

  15. Shear stress induces cell apoptosis via a c-Src-phospholipase D-mTOR signaling pathway in cultured podocytes

    SciTech Connect

    Huang, Chunfa, E-mail: chunfa.huang@case.edu [Louis Stokes Cleveland Veteran Affairs Medical Center, Case Western Reserve University (United States) [Louis Stokes Cleveland Veteran Affairs Medical Center, Case Western Reserve University (United States); Department of Medicine, Case Western Reserve University (United States); Rammelkamp Center for Research and Education, MetroHealth System Campus, Cleveland, OH 44106 (United States); Bruggeman, Leslie A. [Department of Medicine, Case Western Reserve University (United States) [Department of Medicine, Case Western Reserve University (United States); Rammelkamp Center for Research and Education, MetroHealth System Campus, Cleveland, OH 44106 (United States); Hydo, Lindsey M. [Louis Stokes Cleveland Veteran Affairs Medical Center, Case Western Reserve University (United States)] [Louis Stokes Cleveland Veteran Affairs Medical Center, Case Western Reserve University (United States); Miller, R. Tyler [Louis Stokes Cleveland Veteran Affairs Medical Center, Case Western Reserve University (United States) [Louis Stokes Cleveland Veteran Affairs Medical Center, Case Western Reserve University (United States); Department of Medicine, Case Western Reserve University (United States); Rammelkamp Center for Research and Education, MetroHealth System Campus, Cleveland, OH 44106 (United States)

    2012-06-10

    The glomerular capillary wall, composed of endothelial cells, the glomerular basement membrane and the podocytes, is continually subjected to hemodynamic force arising from tractional stress due to blood pressure and shear stress due to blood flow. Exposure of glomeruli to abnormal hemodynamic force such as hyperfiltration is associated with glomerular injury and progressive renal disease, and the conversion of mechanical stimuli to chemical signals in the regulation of the process is poorly understood in podocytes. By examining DNA fragmentation, apoptotic nuclear changes and cytochrome c release, we found that shear stress induced cell apoptosis in cultured podocytes. Meanwhile, podocytes exposed to shear stress also stimulated c-Src phosphorylation, phospholipase D (PLD) activation and mammalian target of rapamycin (mTOR) signaling. Using the antibodies against c-Src, PLD{sub 1}, and PLD{sub 2} to perform reciprocal co-immunoprecipitations and in vitro PLD activity assay, our data indicated that c-Src interacted with and activated PLD{sub 1} but not PLD{sub 2}. The inhibition of shear stress-induced c-Src phosphorylation by PP{sub 2} (a specific inhibitor of c-Src kinase) resulted in reduced PLD activity. Phosphatidic acid, produced by shear stress-induced PLD activation, stimulated mTOR signaling, and caused podocyte hypertrophy and apoptosis.

  16. Physics of the Earth and Planetary Interiors 159 (2006) 114 A review of techniques for measuring shear-wave

    E-print Network

    2006-01-01

    for measuring shear-wave splitting above small earthquakes Stuart Crampina,b,c,, Yuan Gaoa,c a Shear-Wave 2006; accepted 15 June 2006 Abstract Seismic shear-wave splitting is difficult to measure accurately for measuring time-delays and polarisations of shear-wave splitting above small earthquakes. These range from

  17. Age-related decline in reendothelialization capacity of human endothelial progenitor cells is restored by shear stress.

    PubMed

    Xia, Wen Hao; Yang, Zhen; Xu, Shi Yue; Chen, Long; Zhang, Xiao Yu; Li, Jing; Liu, Xing; Qiu, Yan Xia; Shuai, Xin Tao; Tao, Jun

    2012-06-01

    Aging is associated with dysfunction of endothelial progenitor cells (EPCs), and shear stress has a beneficial impact on EPC function; however, the effects of aging and shear stress on the endothelial repair capacity of EPCs after arterial injury have not been reported. Here we investigated the influence of aging and shear stress on the reendothelialization capacity of human EPCs and the related molecular mechanism. Compared with EPCs isolated from young subjects, EPCs from the elderly displayed an impaired migration and adhesion in vitro and demonstrated a significantly reduced reendothelialization capacity in vivo after transplantation into nude mice with carotid artery denudation injury. Shear stress pretreatment enhances the migration, adhesion, and reendothelialization capacity in both young and elderly EPCs; however, it was to a greater extent in EPCs from the elderly. Although basal CXC chemokine receptor 4 (CXCR4) expression was similar in EPCs from the 2 age groups, the stromal cell derived factor 1-induced CXCR4 and Janus kinase 2 phosphorylations were much lower in the elderly than in young EPCs. Shear stress treatment upregulated CXCR4 expression and phosphorylation and, importantly, restored the stromal cell-derived factor 1/CXCR4-dependent Janus kinase 2 phosphorylation in the elderly EPCs. Furthermore, short hairpin RNA-mediated knockdown of CXCR4 expression or pretreatment with Janus kinase 2 inhibitor diminished the enhancement in the migration, adhesion, and reendothelialization capacity of the elderly EPCs from shear stress treatments. Thus, our study demonstrates that upregulation of the CXCR4/Janus kinase 2 pathway by shear stress contributes to the enhanced reendothelialization capacity of EPCs from elderly men. PMID:22547440

  18. Effect of simulated microgravity on nitric oxide synthase activity of osteocyte-like cell line MLO-Y4 in response to fluid shear stress

    NASA Astrophysics Data System (ADS)

    Sun, Lian-Wen; Yang, Xiao; Fan, Yu-Bo

    It is well known that microgravity could induce bone loss. However, the mechanism remains poorly understood. Osteocytes are extremely sensitive to fluid shear stress, even more than osteobleasts. The effect of simulated microgravity on osteocytes in response to fluid shear was investigated in this study in order to see if the mechanosensibility of osteocytes changed under simulated microgravity. The osteocyte-like cell line, MLO-Y4, was cultured and divided into four groups, including control (CON), control and shear (CONS), rotary (RT), rotary and shear (RTS). In RT and RTS, the cells were cultured in the rotary cell culture system to simulate microgravity condition. After 5 days, the cells in RTS and CONS were subjected to flow shear for 15 min. Then nitric oxide synthase (NOS) activity in the cells was measured using assay kit. The results showed that NOS activity in respond to fluid shear decreased significantly in RTS compared with CONS. In addition, there was significant difference in NOS activity between CONS and CON while no significant difference between RTS and RT. These indicates that the mechanosensibility of osteocytes decreased under simulated microgravity and this maybe the partly causes of the poor effect of exercise to counter microgravity-induced-bone loss. However, further research need to be done to support this finding.

  19. Induction and functional significance of the heme oxygenase system in pathological shear stress in vivo.

    PubMed

    Kang, Lu; Hillestad, Matthew L; Grande, Joseph P; Croatt, Anthony J; Barry, Michael A; Farrugia, Gianrico; Katusic, Zvonimir S; Nath, Karl A

    2015-06-01

    The present study examined the heme oxygenase (HO) system in an in vivo murine model of pathological shear stress induced by partial carotid artery ligation. In this model, along with upregulation of vasculopathic genes, HO-1 is induced in the endothelium and adventitia, whereas HO-2 is mainly upregulated in the endothelium. Within minutes of ligation, NF-?B, a transcription factor that upregulates vasculopathic genes and HO-1, is activated. Failure to express either HO-1 or HO-2 exaggerates the reduction in carotid blood flow and exacerbates vascular injury. After artery ligation, comparable induction of HO-2 occurred in HO-1(+/+) and HO-1(-/-) mice, whereas HO-1 induction was exaggerated in HO-2(-/-) mice compared with HO-2(+/+) mice. Upregulation of HO-1 by an adeno-associated viral vector increased vascular HO-1 expression and HO activity and augmented blood flow in both ligated and contralateral carotid arteries. Acute inhibition of HO activity decreased flow in the ligated carotid artery, whereas a product of HO, carbon monoxide (CO), delivered by CO-releasing molecule-3, increased carotid blood flow. In conclusion, in the partial carotid artery ligation model of pathological shear stress, this study provides the first demonstration of 1) upregulation and vasoprotective effects of HO-1 and HO-2 and the vasorelaxant effects of CO as well as 2) vascular upregulation of HO-1 in vivo by an adeno-associated viral vector that is attended by a salutary vascular response. Induction of HO-1 may reside in NF-?B activation, and, along with induced HO-2, such upregulation of HO-1 provides a countervailing vasoprotective response in pathological shear stress in vivo. PMID:25820397

  20. Flow through internal elastic lamina affects shear stress on smooth muscle cells (3D simulations).

    PubMed

    Tada, Shigeru; Tarbell, John M

    2002-02-01

    We describe a three-dimensional numerical simulation of interstitial flow through the medial layer of an artery accounting for the complex entrance condition associated with fenestral pores in the internal elastic lamina (IEL) to investigate the fluid mechanical environment around the smooth muscle cells (SMCs) right beneath the IEL. The IEL was modeled as an impermeable barrier to water flow except for the fenestral pores, which were assumed to be uniformly distributed over the IEL. The medial layer was modeled as a heterogeneous medium composed of a periodic array of cylindrical SMCs embedded in a continuous porous medium representing the interstitial proteoglycan and collagen matrix. Depending on the distance between the IEL bottom surface and the upstream end of the proximal layer of SMCs, the local shear stress on SMCs right beneath the fenestral pore could be more than 10 times higher than that on the cells far removed from the IEL under the conditions that the fenestral pore diameter and area fraction of pores were kept constant at 1.4 microm and 0.05, respectively. Thus these proximal SMCs may experience shear stress levels that are even higher than endothelial cells exposed to normal blood flow (order of 10 dyn/cm(2)). Furthermore, entrance flow through fenestral pores alters considerably the interstitial flow field in the medial layer over a spatial length scale of the order of the fenestral pore diameter. Thus the spatial gradient of shear stress on the most superficial SMC is noticeably higher than computed for endothelial cell surfaces. PMID:11788405

  1. Cantilever measurements of surface stress, surface reconstruction, film stress and magnetoelastic stress of monolayers

    PubMed Central

    Sander, Dirk; Tian, Zhen; Kirschner, Jürgen

    2008-01-01

    We review the application of cantilever-based stress measurements in surface science and magnetism. The application of thin (thickness appr. 0.1 mm) single crystalline substrates as cantilevers has been used successfully to measure adsorbate-induced surface stress changes, lattice misfit induced film stress, and magneto-elastic stress of ferromagnetic monolayers. Surface stress changes as small as 0.01 N/m can be readily measured, and this translates into a sensitivity for adsorbate-coverage well below 0.01 of one layer. Stress as large as several GPa, beyond the elasticity limits of high strength materials, is measured, and it is ascribed to the lattice misfit between film and substrate. Our results point at the intimate relation between surface stress and surface reconstruction, stress-induced structural changes in epitaxially strained films, and strain-induced modifications of the magneto-elastic coupling in ferromagnetic monolayers.

  2. Deformation in the Rutford ice stream, West Antarctica: measuring shear-wave anisotropy from icequakes

    NASA Astrophysics Data System (ADS)

    Kendall, Michael; Harland, Sophie; Stuart, Graham; Baird, Alan; Lloyd, Geoff; Smith, Andy; Pritchard, Hamish; Brisbourne, Alex

    2013-04-01

    Ice streams provide major drainage pathways for the Antarctic ice sheet. The stress distribution and style of flow in such ice streams produces elastic and rheological anisotropy, which informs ice flow modelling as to how ice masses respond to external changes such as global warming. Here we analyse elastic anisotropy in the Rutford ice stream, West Antarctica, using observations of shear wave splitting from three-component icequake seismograms to characterise ice deformation via crystal preferred orientation. Over 110 high quality measurements are made on 41 events recorded at five stations temporarily deployed near the ice stream grounding line. To the best of our knowledge this is the first well-documented observation of shear wave splitting from Antarctic icequakes. The magnitude of the splitting ranges from 2ms to 80ms and suggest a maximum of 6% shear wave splitting. The fast shear wave polarisation direction is roughly perpendicular to ice flow direction. We consider three mechanisms for ice anisotropy: a cluster model (VTI model); a girdle model (and HTI model); and crack-induced anisotropy (an HTI model). Based on the data we can rule out a VTI mechanism as the sole cause of anisotropy - an HTI component is needed, which may be due to ice crystal a-axis alignment in the direction of flow or the alignment of cracks or ice-films in the plane perpendicular to the flow direction. The results may suggest a combination of mechanisms are at play, which represent vertical variations in the symmetry of ice-crystal anisotropy in an ice stream, as predicted by ice fabric models.

  3. Real-Time Intravascular Shear Stress in the Rabbit Abdominal Aorta

    PubMed Central

    Ai, Lisong; Yu, Hongyu; Dai, Wangde; Hale, Sharon L.; Kloner, Robert A.

    2012-01-01

    Fluid shear stress is intimately linked with the biological activities of vascular cells. A flexible microelectromechanical system (MEMS) sensor was developed to assess spatial- and temporal-varying components of intravascular shear stress (ISS) in the abdominal aorta of adult New Zealand white (NZW) rabbits. Real-time ISS (ISSreal-time) was analyzed in comparison with computational fluid dynamics (CFD) simulations for wall shear stress (WSS). Three-dimensional abdominal arterial geometry and mesh were created using the GAMBIT software. Simulation of arterial flow profiles was established by FLUENT. The Navier–Stokes equations were solved for non-Newtonian blood flow. The coaxial-wire-based MEMS sensor was deployed into the abdominal arteries of rabbits via a femoral artery cutdown. Based on the CFD analysis, the entrance length of the sensor on the coaxial wire (0.4 mm in diameter) was less than 10 mm. Three-dimensional fluoroscope and contrast dye allowed for visualization of the positions of the sensor and ratios of vessel to coaxial wire diameters. Doppler ultrasound provided the velocity profiles for the CFD boundary conditions. If the coaxial wire were positioned at the center of vessel, the CFD analysis revealed a mean ISS value of 31.1 with a systolic peak at 102.8 dyn · cm?2. The mean WSS was computed to be 10.1 dyn · cm?2 with a systolic peak at 33.2 dyn · cm?2, and the introduction of coaxial wire increased the mean WSS by 5.4 dyn · cm?2 and systolic peak by 18.0 dyn · cm?2. Experimentally, the mean ISS was 11.9 dyn · cm?2 with a systolic peak at 47.0 dyn · cm?2. The waveform of experimental ISS was similar to that of CFD solution with a 30.2% difference in mean and 8.9% in peak systolic shear stress. Despite the difference between CD and experimental results, the flexible coaxial-wire-based MEMS sensors provided a possibility to assess real-time ISS in the abdominal aorta of NZW rabbits. PMID:19527952

  4. Effect of temperature and shear direction on yield stress by

    Microsoft Academic Search

    Hideki Tonda; Shinji Ando

    2002-01-01

    The yield shear stress ?\\u000a \\u000a y\\u000a due to \\u000a $$\\\\left\\\\{ {11\\\\bar 22} \\\\right\\\\}\\\\left\\\\langle {\\\\overline {11} 23} \\\\right\\\\rangle $$\\u000a second-order pyramidal slip system in cadmium, zinc, and magnesium hcp crystals increased with increasing temperature. This\\u000a results is interpreted by two thermally activated processes as follows: (1) the dissociation of a (c+a) edge dislocation with a Burgers vector of \\u000a $$1\\/3\\\\left\\\\langle {\\\\overline {11} 23}

  5. Effect of temperature and shear direction on yield stress by {11

    Microsoft Academic Search

    Hideki Tonda; Shinji Ando

    2002-01-01

    The yield shear stress ?\\u000a \\u000a y\\u000a due to {11\\u000a $$\\\\bar 2$$\\u000a 2}?\\u000a $$\\\\overline {11} $$\\u000a 23? second-order pyramidal slip system in cadmium, zinc, and magnesium hcp crystals increased with increasing temperature.\\u000a This result is interpreted by two thermally activated processes as follows: (1) the dissociation of a (c+a) edge dislocation with a Burgers vector of 1\\/3?\\u000a $$\\\\overline {11} $$\\u000a 23?

  6. An investigation of shearing stresses in a cantilevered rectangular prismatic bar subjected to bending 

    E-print Network

    Meadow, Charles Joe

    1963-01-01

    OF SCALE FACTORS The models or screens used for collecting experimental data bear little physical resemblance to the rectangular bar for which the exact shearing stresses are to be determined. Models of this type are known as dissimilar models. However... 54 14. Experimental Values for the Center-Line Deflections of Screen D under Loads Shown in Table 10 55 15. Comparison of Theoretical and Experimental Correction Factors . 56 LIST OF SYMBOLS Cross-sect tonal area a, b One-half the cross...

  7. Method of determining shear stress employing a monomer-polymer laminate structure

    NASA Technical Reports Server (NTRS)

    Singh, Jag J. (inventor); Eftekhari, Abe (inventor); Parmar, Devendra S. (inventor)

    1993-01-01

    A laminate structure attached to the test surface of an article is presented. The laminate structure is comprised of a liquid crystal polymer substrate. A light absorbing coating is applied to the substrate and is thin enough to permit bonding steric interaction between the liquid crystal polymer substrate and an overlying liquid crystal monomer thin film. Light is directed through and reflected by the liquid crystal monomer thin film and unreflected light is absorbed by the underlying coating. The wavelength of the reflected light is indicative of the shear stress experienced by the test surface.

  8. Computational Fluid Dynamics Analysis to Determine Shear Stresses and Rates in a Centrifugal Left Ventricular Assist Device

    PubMed Central

    Selgrade, Brian Paul; Truskey, George A.

    2014-01-01

    Axial flow left ventricular assist devices (LVADs) are a significant improvement in mechanical circulatory support. However, patients with these devices experience degradation of large von Willebrand factor (vWF) multimers, which is associated with bleeding and may be caused by high shear stresses within the LVAD. In this study, we used computational fluid mechanics to determine the wall shear stresses, shear rates, and residence times in a centrifugal LVAD and assess the impact on these variables caused by changing impeller speed and changing from a shrouded to a semi-open impeller. In both LVAD types, shear rates were well over 10 000/s in several regions. This is high enough to degrade vWF, but it is unclear if residence times, which were below 5 ms in high-shear regions, are long enough to allow vWF cleavage. Additionally, wall shear stresses were below the threshold stress of 10 Pa only in the outlet tube so it is feasible to endothelialize this region to enhance its biocompatibility. PMID:22360826

  9. Geophysical Prospecting 35, 187-196, 1987 IN SITU MEASUREMENTS OF SHEAR-WAVE

    E-print Network

    Snieder, Roel

    Geophysical Prospecting 35, 187-196, 1987 IN SITU MEASUREMENTS OF SHEAR-WAVE VELOCITY I N SEDIMENTS,R. and NOLET,G. 1987, In Situ Measurement of Shear-Wave Velocity in Sediments with Higher-Mode Rayleigh Waves properties of these Rayleigh waves were measured in the 2-D amplitude spectrum-orf,k-spectrum-and resulted

  10. Fine-tuning of DDES and IDDES formulations to the k-? shear stress transport model

    NASA Astrophysics Data System (ADS)

    Gritskevich, M. S.; Garbaruk, A. V.; Menter, F. R.

    2013-06-01

    Modifications are proposed of two recently developed hybrid CFD (computational fluid dynamics) strategies, Delayed Detached Eddy Simulation (DDES), and DDES with Improved wall-modeling capability (IDDES). The modifications are aimed at fine-tuning of these approaches to the k-? SST (shear stress transport) background RANS (Reynolds-averaged Navier-Stokes) model. The first one includes recalibrated empirical constants in the shielding function of the Spalart-Allmaras (SA) based DDES which are shown to be suboptimal (not providing a needed level of elimination of the Model Stress Depletion (MSD)) for the SST-based DDES model. For the SST-IDDES variant, in addition to that, a simplification of the original SA-based formulation is proposed, which does not cause any visible degradation of the model performance. Both modifications are extensively tested on a range of attached and separated flows (developed channel, backward-facing step, periodic hills, wall-mounted hump, and hydrofoil with trailing edge separation).

  11. Rock Joint Surfaces Measurement and Analysis of Aperture Distribution under Different Normal and Shear Loading using GIS

    NASA Astrophysics Data System (ADS)

    Sharifzadeh, M.; Mitani, Y.; Esaki, T.

    2008-04-01

    The geometry of the rock joint is a governing factor for joint mechanical and hydraulic behaviour. A new method for evaluating the aperture distribution, based on measurement of joint surfaces and three dimensional characteristics of each surface, is developed. This method allows one to determine and visualize the aperture distribution under different normal stresses and shear displacements, which is difficult to observe experimentally. A new laser scanner system is designed and developed for joint surface measurements. Special attention is paid to both surfaces’ data gained by measurements and processing, such as x-y coordinate table modification, data referencing, and matching between upper and lower surfaces. The surfaces of an artificial joint in granite are measured, processed, analyzed and three dimensional approaches are carried out for surface characterization. Parameters such as “asperity’s heights”, “slope angles”, and “aspects” distribution at micro scale, local concentration of elements and their spatial localization at local scale are determined by Geographic Information System (GIS). These parameters are used for joint surfaces matching and its real behavior quantitative analysis. The upper surface is brought down to make contact with the lower surface and the distance between the two surfaces is evaluated from the joint mean experimental aperture, which is obtained from normal and shear tests. Changes of aperture distribution at different normal stresses and various shear displacements are visualized and interpreted. Increasing normal load causes negative changes in aperture frequency distribution which indicates high joint matching. However, increasing shear displacement causes a rapid increase in the aperture and positive changes in the aperture frequency distribution, which could be due to un-matching, surface anisotropy and spatial localization of contact points with proceeding shear.

  12. The Interaction between Fluid Wall Shear Stress and Solid Circumferential Strain Affects Endothelial Gene Expression

    PubMed Central

    Amaya, Ronny; Pierides, Alexis; Tarbell, John M.

    2015-01-01

    Endothelial cells lining the walls of blood vessels are exposed simultaneously to wall shear stress (WSS) and circumferential stress (CS) that can be characterized by the temporal phase angle between WSS and CS (stress phase angle – SPA). Regions of the circulation with highly asynchronous hemodynamics (SPA close to -180°) such as coronary arteries are associated with the development of pathological conditions such as atherosclerosis and intimal hyperplasia whereas more synchronous regions (SPA closer to 0°) are spared of disease. The present study evaluates endothelial cell gene expression of 42 atherosclerosis-related genes under asynchronous hemodynamics (SPA=-180 °) and synchronous hemodynamics (SPA=0 °). This study used a novel bioreactor to investigate the cellular response of bovine aortic endothelial cells (BAECS) exposed to a combination of pulsatile WSS and CS at SPA=0 or SPA=-180. Using a PCR array of 42 genes, we determined that BAECS exposed to non-reversing sinusoidal WSS (10±10 dyne/cm2) and CS (4 ± 4 %) over a 7 hour testing period displayed 17 genes that were up regulated by SPA = -180 °, most of them pro-atherogenic, including NF?B and other NF?B target genes. The up regulation of NF?B p50/p105 and p65 by SPA =-180° was confirmed by Western blots and immunofluorescence staining demonstrating the nuclear translocation of NF?B p50/p105 and p65. These data suggest that asynchronous hemodynamics (SPA=-180 °) can elicit proatherogenic responses in endothelial cells compared to synchronous hemodynamics without shear stress reversal, indicating that SPA may be an important parameter characterizing arterial susceptibility to disease. PMID:26147292

  13. Quantitative surface stress measurements using a microcantilever

    NASA Astrophysics Data System (ADS)

    Godin, Michel; Tabard-Cossa, Vincent; Grütter, Peter; Williams, Peter

    2001-07-01

    A method for calculating the surface stress associated with the deflection of a micromechanical cantilever is presented. This method overcomes some of the limitations associated with Stoney's formula by circumventing the need to know the cantilever's Young's modulus, which can have a high level of uncertainty, especially for silicon nitride cantilevers. The surface stress is calculated using readily measurable cantilever properties, such as its geometry, spring constant, and deflection. The method is applicable to both rectangular and triangular cantilevers. A calibration of the deflection measurement is also presented. The surface stress measurement is accurate to within 4%-7%.

  14. Impact of Wall Shear Stress and Pressure Variation on the Stability of Atherosclerotic Plaque

    NASA Astrophysics Data System (ADS)

    Taviani, V.; Li, Z. Y.; Sutcliffe, M.; Gillard, J.

    Rupture of vulnerable atheromatous plaque in the carotid and coronary arteries often leads to stroke and heart attack respectively. The mechanism of blood flow and plaque rupture in stenotic arteries is still not fully understood. A three dimensional rigid wall model was solved under steady and unsteady conditions assuming a time-varying inlet velocity profile to investigate the relative importance of axial forces and pressure drops in arteries with asymmetric stenosis. Flow-structure interactions were investigated for the same geometry and the results were compared with those retrieved with the corresponding one dimensional models. The Navier-Stokes equations were used as the governing equations for the fluid. The tube wall was assumed linearly elastic, homogeneous isotropic. The analysis showed that wall shear stress is small (less than 3.5%) with respect to pressure drop throughout the cycle even for severe stenosis. On the contrary, the three dimensional behavior of velocity, pressure and wall shear stress is in general very different from that predicted by one dimensional models. This suggests that the primary source of mistakes in one dimensional studies comes from neglecting the three dimensional geometry of the plaque. Neglecting axial forces only involves minor errors.

  15. Interstitial flow through the internal elastic lamina affects shear stress on arterial smooth muscle cells.

    PubMed

    Tada, S; Tarbell, J M

    2000-05-01

    Interstitial flow through the tunica media of an artery wall in the presence of the internal elastic lamina (IEL), which separates it from the subendothelial intima, has been studied numerically. A two-dimensional analysis applying the Brinkman model as the governing equation for the porous media flow field was performed. In the numerical simulation, the IEL was modeled as an impermeable barrier to water flux, except for the fenestral pores, which were uniformly distributed over the IEL. The tunica media was modeled as a heterogeneous medium composed of a periodic array of cylindrical smooth muscle cells (SMCs) embedded in a fiber matrix simulating the interstitial proteoglycan and collagen fibers. A series of calculations was conducted by varying the physical parameters describing the problem: the area fraction of the fenestral pore (0. 001-0.036), the diameter of the fenestral pore (0.4-4.0 microm), and the distance between the IEL and the nearest SMC (0.2-0.8 microm). The results indicate that the value of the average shear stress around the circumference of the SMC in the immediate vicinity of the fenestral pore could be as much as 100 times greater than that around an SMC in the fully developed interstitial flow region away from the IEL. These high shear stresses can affect SMC physiological function. PMID:10775138

  16. Molecular responses of phospholipids of Taxus cuspidata (Japanese yew) to hydrodynamic shear stress in bubble columns.

    PubMed

    Zhong, Cheng; Yang, Song; Yuan, Ying-Jin

    2009-08-01

    Molecular responses of phospholipids of Taxus cuspidata (Japanese yew) cells to hydrodynamic shear stress were investigated by using two bubble columns with different nozzle sizes. T. cuspidata cells cultured in bubble columns responded with an increase in cell membrane permeability when compared with shake-flask culture, corresponding to the alteration of phospholipid constitutions. Phospholipid differences between bubble columns and shake-flask cultures were analysed by using LC/ESI (liquid chromatography/electrospray ionization)-MS coupled with PCA (principal component analysis). It was found that PA (phosphatidic acid) is the main molecular species of potential biomarkers. The amount of PA was found to increase, whereas PC (phosphatidylcholine) and PI (phosphatidylinositol) decreased after 96 h of cultivation in bubble columns, corresponding to the obvious increase in membrane permeability after 96 h of culture in such columns. A decrease in the nozzle size of the bubble column led to a more significant difference in phospholipids. These results suggest that PA accumulation plays an important role in the membrane degradation induced by hydrodynamic shear stress. PMID:19200058

  17. Electrical Impedance Study of Cultured Endothelial Cells Under Fluid Shear Stress

    NASA Astrophysics Data System (ADS)

    Dong, Chunzhi; Depaola, Natacha; Keese, Charles R.; Giaever, Ivar

    2004-03-01

    The lumen of blood vessels is lined with a monolayer of endothelial cells (EC). In this work, electric cell-substrate impedance sensing (ECIS) was used to monitor the effect of fluid shear stress (FSS) on the morphology and function of cultured EC layers. Confluent layers of bovine aortic endothelial cells (BAEC) were grown on small gold electrodes and exposed to different flow conditions, while the impedance of the system was monitored. When the cells are subjected to FSS, the impedance rapidly increases 5-10%, and if the FSS is removed after a few minutes duration, the impedance returns back to the initial level in about 10 minutes. If the FSS remains for a long duration, the impedance will decrease 20-30% over a 10-15 hour period but ultimately returns to the original value, as the cells apparently accommodate to the FSS condition. These results suggest that ECIS may provide a sensitive means to study the response of EC to shear stress in vitro.

  18. Quantitative surface stress measurements using a microcantilever

    Microsoft Academic Search

    Michel Godin; Vincent Tabard-Cossa; Peter Grütter; Peter Williams

    2001-01-01

    A method for calculating the surface stress associated with the deflection of a micromechanical cantilever is presented. This method overcomes some of the limitations associated with Stoney's formula by circumventing the need to know the cantilever's Young's modulus, which can have a high level of uncertainty, especially for silicon nitride cantilevers. The surface stress is calculated using readily measurable cantilever

  19. DATA ANALYSIS FOR STRESS MEASUREMENTS BY OVERCORING

    E-print Network

    Paris-Sud XI, Université de

    DATA ANALYSIS FOR STRESS MEASUREMENTS BY OVERCORING: NEW OPTIMIZATION TECHNIQUES LIZEUR A., Pr. Eng. INERIS. BAUCHERON V., Gr. Student, University Nancy I ABSTRACT The data processing for in situ measunements by overcoring (or stress-relief in gênerai) is classically performed by the least squares method

  20. Surface morphology of platelet adhesion influenced by activators, inhibitors and shear stress

    NASA Astrophysics Data System (ADS)

    Watson, Melanie Groan

    Platelet activation involves multiple events, one of which is the generation and release of nitric oxide (NO), a platelet aggregation inhibitor. Platelets simultaneously send and receive various agents that promote a positive and negative feedback control system during hemostasis. Although the purpose of platelet-derived NO is not fully understood, NO is known to inhibit platelet recruitment. NO's relatively large diffusion coefficient allows it to diffuse more rapidly than platelet agonists. It may thus be able to inhibit recruitment of platelets near the periphery of a growing thrombus before agonists have substantially accumulated in those regions. Results from two studies in our laboratory differed in the extent to which platelet-derived NO decreased platelet adhesion. Frilot studied the effect of L-arginine (L-A) and NG-Methyl-L-arginine acetate salt (L-NMMA) on platelet adhesion to collagen under static conditions in a Petri dish. Eshaq examined the percent coverage on collagen-coated and fibrinogen-coated microchannels under shear conditions with different levels of L-A and Adenosine Diphosphate (ADP). Frilot's results showed no effect of either L-A or L-NMMA on surface coverage, thrombus size or serotonin release, while Eshaq's results showed a decrease in surface coverage with increased levels of L-A. A possible explanation for these contrasting results is that platelet-derived NO may be more important under flow conditions than under static conditions. For this project, the effects of L-A. ADP and L-NMMA on platelet adhesion were studied at varying shear stresses on protein-coated glass slides. The surface exposed to platelet-rich-plasma in combination with each chemical solution was observed under AFM, FE-SEM and fluorescence microscopy. Quantitative and qualitative comparisons of images obtained with these techniques confirmed the presence of platelets on the protein coatings. AFM images of fibrinogen and collagen-coated slides presented characteristic differences. Adhered platelets were identified, particularly with the AFM. The effects of chemical additives were examined under the same microscopy techniques. The resulting fluorescent microscopy data suggests statistical differences between the percent surface coverage of different shear regions on the glass slides. No statistically significant change in surface coverage was found with the addition of ADP on fibrinogen-coated slides, but showed differences on collagen with all chemicals. However, in high shear regions. L-A produced a significant decrease in platelet adhesion and L-NMMA produced a statistically significant increase in platelet adhesion on fibrinogen and collagen-coated slides. The AFM images of the chemical additives provided no differences between one another except with ADP. The no shear and low shear conditions provided no variations between AFM images via visual confirmation and statistical significance. The only AFM image shear region differences were obtained from low to high shear regions and static to high shear regions comparisons. The objective of this project was to determine whether the static conditions used by Frilot and the dynamic conditions used by Eshaq could explain the different effects of L-A observed in those studies. In addition, the ability of the fluorescent imaging technique to quantify platelet adhesion was examined by comparison of fluorescent imaging to AFM and FE-SEM. The results of this study were consistent with both the lack of an effect of chemical additives under static conditions reported by Frilot and the reduction of platelet adhesion in response to L-A reported by Eshaq.

  1. Stress buildup under start-up shear flows in self-assembled transient networks of telechelic associating polymers.

    PubMed

    Koga, Tsuyoshi; Tanaka, Fumihiko; Kaneda, Isamu; Winnik, Françoise M

    2009-08-01

    The nonaffine transient network theory is used to study the time development of the shear and normal stresses under start-up shear flows in networks formed by self-assembled telechelic, hydrophobically modified water-soluble polymers. The initial slope, strain hardening, and overshoot of the shear stress are studied in detail in relation to the nonlinear tension-elongation curve of the elastically active chains in the network. The condition for the occurrence of strain hardening (upward deviation of the stress from the reference curve defined by the linear moduli) is found to be gamma > gammac(A), where gamma is the shear rate, gamma(c) is its critical value for strain hardening, and A is the amplitude of the nonlinear term in the tension of a chain. The critical shear rate gamma(c) is calculated as a function of A. It is approximately 6.3 (in the time unit of the reciprocal thermal dissociation rate) for a nonlinear chain with A = 10. The overshoot time t(max) when the stress reaches a maximum and the total deformation gamma(max) = gamma(t max) accumulated before the peak time are obtained in terms of the molecular parameters of the polymer chain. The maximum deformation gamma(max) turns out to depend weakly upon the shear rate gamma. The first and second normal stress differences are also studied on the basis of the exact numerical integration of the theoretical model by paying special attention to their overshoot, undershoot, and sign change as a function of the shear rate. These theoretical results are compared with recent rheological experiments of the solutions of telechelic hydrophobically modified poly(ethylene oxide)s carrying short branched alkyl chains (2-decyl-tetradecyl) at both ends. PMID:19438184

  2. Longitudinal and Lateral Stress Measurements in Stainless Steel 304L Under 1d Shock Loading

    NASA Astrophysics Data System (ADS)

    Whiteman, G.; Millett, J. C. F.; Bourne, N. K.

    2007-12-01

    Interest in the behaviour of the common stainless steel grade 304 at high rates of strain is always high due to the materials regular use in industry. Longitudinal and lateral stresses during the shock loading of SS-304L have been measured using manganin stress gauges. The shear strength has been shown to increase with impact stress. Comparison with a pure fcc metal (nickel) shows a significant increase in strength. Strengths are similar to those of mild steel, but the rate of increase with impact stress is much greater in SS-304L. These results are discussed in terms of structure and degree of alloying.

  3. Longitudinal and Lateral Stress Measurements in Stainless Steel 304 Under 1D Shock Loading

    NASA Astrophysics Data System (ADS)

    Whiteman, G.; Millett, J. C. F.; Winter, R. E.; Bourne, N. K.

    2007-06-01

    Interest in the behaviour of the common stainless steel grade 304 at high rates of strain is always high due to the materials regular use in industry. Longitudinal and lateral stresses during the shock loading of stainless steel 304 have been measured using manganin stress gauges. The shear strength has been shown to increase with impact stress. Comparison with a pure fcc metal (nickel) shows a significant increase in strength. Strengths are similar to those of mild steel, but the rate of increase with impact stress is much greater in SS304. These results are discussed in terms of structure and degree of alloying.

  4. On the stress distribution in a thin rectangular plate subjected to shear 

    E-print Network

    Travis, Darol Duane

    1953-01-01

    Mng stresses, that it is found necessary to ms' experiments on other materials such as india-rubber or plasticine These afford strains sufficiently large for accurate measurement, while their elastic properties are such that they may be considered...

  5. MiR-21 is induced in endothelial cells by shear stress and modulates apoptosis and eNOS activity

    SciTech Connect

    Weber, Martina; Baker, Meredith B.; Moore, Jeffrey P. [Division of Cardiology, Emory University, 1639 Pierce Drive, WMB 319, Atlanta, GA 30322 (United States)] [Division of Cardiology, Emory University, 1639 Pierce Drive, WMB 319, Atlanta, GA 30322 (United States); Searles, Charles D., E-mail: csearle@emory.edu [Division of Cardiology, Emory University, 1639 Pierce Drive, WMB 319, Atlanta, GA 30322 (United States); Atlanta Veterans Administration Medical Center, 1670 Clarimont Road, Decatur, GA 30033 (United States)

    2010-03-19

    Mechanical forces associated with blood flow play an important role in regulating vascular signaling and gene expression in endothelial cells (ECs). MicroRNAs (miRNAs) are a class of noncoding RNAs that posttranscriptionally regulate the expression of genes involved in diverse cell functions, including differentiation, growth, proliferation, and apoptosis. miRNAs are known to have an important role in modulating EC biology, but their expression and functions in cells subjected to shear stress conditions are unknown. We sought to determine the miRNA expression profile in human ECs subjected to unidirectional shear stress and define the role of miR-21 in shear stress-induced changes in EC function. TLDA array and qRT-PCR analysis performed on HUVECs exposed to prolonged unidirectional shear stress (USS, 24 h, 15 dynes/cm{sup 2}) identified 13 miRNAs whose expression was significantly upregulated (p < 0.05). The miRNA with the greatest change was miR-21; it was increased 5.2-fold (p = 0.002) in USS-treated versus control cells. Western analysis demonstrated that PTEN, a known target of miR-21, was downregulated in HUVECs exposed to USS or transfected with pre-miR-21. Importantly, HUVECs overexpressing miR-21 had decreased apoptosis and increased eNOS phosphorylation and nitric oxide (NO{sup {center_dot}}) production. These data demonstrate that shear stress forces regulate the expression of miRNAs in ECs, and that miR-21 influences endothelial biology by decreasing apoptosis and activating the NO{sup {center_dot}} pathway. These studies advance our understanding of the mechanisms by which shear stress forces modulate vascular homeostasis.

  6. Shearing Photoelasticity

    NASA Astrophysics Data System (ADS)

    Rupeng, Wang; Bin, Du; Zhu, Xu

    1988-12-01

    The physical conception of shearing photoelasticity is established on the base of the image photocarrier Tablot effect and shearing moire method. The mathmatical formula is derived. The theory and technique of the shearing photoelasticity is presented . The information of ?n/?Si can be dirived to separate principal stresses in 3-D photoelasticity.

  7. Scaling of viscous shear zones with depth-dependent viscosity and power-law stress-strain-rate dependence

    NASA Astrophysics Data System (ADS)

    Moore, James D. P.; Parsons, Barry

    2015-07-01

    One of the unresolved questions concerning fault deformation is the degree and cause of localization of shear at depth beneath a fault. Geologic observations of exhumed shear zones indicate that while the motion is no longer planar, it can still be localized near the down-dip extension of the fault; however, the degree of localization is uncertain. We employ simple analytic and numerical models to investigate the structural form of distributed shear beneath a strike-slip fault, and the relative importance of the physical mechanisms that have the potential to localize a shear zone. For a purely depth dependent viscosity, ? = ?0 exp (-z/z0), we find that a shear zone develops with a half-width ? _w˜ ?{z_0} for small z0 at the base of the layer, where lengths are non-dimensionalized by the layer thickness (d km). Including a non-linear stress-strain-rate relation (dot{? }? ? ^n) scales ?w by 1/?{n}, comparable to deformation length scales in thin viscous sheet calculations. We find that the primary control on the shear-zone width is the depth dependence of viscosity that arises from the temperature dependence of viscosity and the increase in temperature with depth. As this relationship is exponential, scaling relations give a dimensional half-width that scales approximately as tilde{?}_w? T_{1/2}?{Rd/nQ? } km, where T_{1/2} (K) is the temperature at the midpoint of the layer, R (J mol-1 K-1) the gas constant, Q (J mol-1) the activation energy and ? (K km-1) the geothermal gradient. This relation predicts the numerical results for the parameter range consistent with continental rheologies to within 2-5 per cent and shear-zone half-widths from 2 to 6 km. The inclusion of shear-stress heating reduces ?w by only an additional 5-25 per cent, depending on the initial width of the shear zone. While the width of the shear zone may not decrease significantly, local temperature increases from shear-stress heating range from 50 to 300 °C resulting in a reduction in viscosities beneath the fault of several orders of magnitude and a concomitant reduction in the stresses needed to drive the motion.

  8. A new method for estimating shear-wave velocity in marine sediments from radiation impedance measurements

    NASA Astrophysics Data System (ADS)

    Kimura, Masao

    2005-11-01

    Shear-wave velocity is one of the important parameters that characterize the physical properties of marine sediments. In this study, a new method is proposed for measuring shear-wave velocity in marine sediments by using radiation impedance. Shear-wave velocities for three kinds of urethane rubber with different Japanese Industrial Standards hardness values were obtained by radiation impedance and time-of-flight measurement techniques. It was shown that the values of the shear-wave velocity measured by the radiation impedance method were consistent with those of time-of-flight measurements. It was then shown that the shear-wave velocities for air- and water-saturated beach sands are different. It was also found that the indicated shear-wave velocity is dependent on the vibrating plate radius because the instrument measures an average shear-wave velocity within a depth window beneath the plate; the larger the plate radius, the deeper the averaging window. Finally, measurements were made on two-layered media in which air-saturated beach sand or urethane rubber was covered with air-saturated clay, and the relationship between the thickness of the clay layer and the indicated shear-wave velocity was investigated.

  9. Estimating the influence of stress on elastic wave velocities from measurements made at different scales on sandstone facies

    NASA Astrophysics Data System (ADS)

    Wandler, Aaron Vallejo

    Knowing how stress influences velocity is crucial for seismic reservoir monitoring because seismic reflection signatures are sensitive to the dynamic processes related to production or injection. In this thesis, I address this issue by conducting research to quantify the influence of stress on elastic wave velocities at different measurement scales. I compare the influence of stress on elastic wave velocities measured from borehole sonic data, time-lapse multicomponent surface seismic data, and laboratory core experiments. To make this comparison, I develop a methodology by combining a series of existing techniques to estimate the influence of stress on shear-wave velocity acquired from crossed-dipole borehole sonic data. By combining the crossed-dipole radial profile of shear wave velocity with the redistribution of stress caused by the presence of a borehole, I establish a relationship between velocity and stress from borehole measurements made within the reservoir. Previously, information about the influence of stress on elastic wave velocity has been primarily obtained through laboratory measurements. To estimate the magnitude of far-field principal stresses at the reservoir level in the subsurface I first integrate the formation bulk density well log to approximate the stress exerted by the overburden. Then, I use radial profiles of shear-wave slowness obtained from borehole sonic data to estimate the far-field principal horizontal stresses. Estimates of the far-field principal stresses are needed to model the stress redistribution caused by the drillout of a borehole. To study the influence that borehole stress redistribution has on shear-wave velocity, I combine the borehole stresses that influence a vertically propagating fast shear wave and the radial profile of the fast shear wave velocity. I use an excess compliance rock physics model to extrapolate the borehole shear wave velocity/stress relationship to predict the influence stress has on compressional wave velocity. Time-lapse multicomponent surface seismic data were recorded to monitor a water alternating gas (CO2) injection scheme for enhanced oil recovery. Interpretations of the time-lapse seismic data, in conjunction with a reservoir simulation model, indicate regions of increased reservoir pore pressure. To simulate the reservoir conditions during a water alternating gas injection scheme, I conducted laboratory core experiments in which I measured compressional and shear-wave velocities as a function of confining pressure, pore pressure, fluid type (which included CO2 in the gas and supercritical phase), and lithology. The shear wave velocity from the borehole sonic data and the time-lapse multicomponent surface seismic data show a very similar response to changes in stress. The laboratory experiments indicate the core velocity measurements are less sensitive to a change in stress than both the borehole and seismic data. Borehole sonic data provide an alternative and, in this case, a more accurate method than laboratory core measurements for estimating stress-induced changes in shear-wave velocity within a reservoir. An accurate rock-physics relationship between shear-wave velocity and effective stress is required for a quantitative interpretation of pore pressure changes from multicomponent time-lapse seismic data.

  10. Measuring advection and diffusion of colloids in shear flow.

    PubMed

    Duits, M H G; Ghosh, S; Mugele, F

    2015-06-01

    An analysis of the dynamics of colloids in shear flow can be challenging because of the superposition of diffusion and advection. We present a method that separates the two motions, starting from the time-dependent particle coordinates. The restriction of the tracking to flow lanes and the subtraction of estimated advective displacements are combined in an iterative scheme that eventually makes the spatial segmentation redundant. Tracking errors due to the neglect of lateral diffusion are avoided, while drifts parallel and perpendicular to the flow are eliminated. After explaining the principles of our method, we validate it against both computer simulations and experiments. A critical overall test is provided by the mean square displacement function at high Peclet numbers (up to 50). We demonstrate via simulations how the measurement accuracy depends on diffusion coefficients and flow rates, expressed in units of camera pixels and frames. Also, sample-specific issues are addressed: inaccuracies in the velocity profile for dilute suspensions (volume fraction ?0.03) and tracking errors for concentrated ones (VF ? 0.3). An analysis of experiments with colloidal spheres flowing through microchannels corroborates these findings and indicates perspectives for studies on transport, mixing, or rheology in microfluidic environments. PMID:25965857

  11. Stress state in the upper crust around the source region of the 1891 Nobi earthquake through shear wave polarization anisotropy

    NASA Astrophysics Data System (ADS)

    Hiramatsu, Yoshihiro; Iidaka, Takashi

    2015-12-01

    We investigate shear wave polarization anisotropy in the upper crust around the source region of the 1891 Nobi earthquake, central Japan. At most stations, the orientation of the faster polarized shear wave is parallel to the axes of the maximum horizontal compressional strain rate and stress, indicating that stress-induced anisotropy is dominant in the analyzed region. Furthermore, near the source faults, the orientation of the faster polarized shear wave is oblique to the strike of the source faults. This suggests that microcracks parallel to the strike of the source fault, which would be produced by the fault movement of the Nobi earthquake, have healed with the healing of the faults. For stress-induced anisotropy, time delays normalized by path length in the anisotropic upper crust as a function of the differential strain rate are coincident with those in the inland high strain rate zone, Japan. These data, together with those of a previous study, show that the variation in the stressing rate, estimated from shear wave splitting, is close to that estimated from geodetic observation. This implies that the variation in the stressing rate in the brittle upper crust is linked to that in the strain rate on the ground surface.

  12. Mechanical Measurement of Gels: Pre-stress and Failure

    NASA Astrophysics Data System (ADS)

    Fakhouri, Sami; Hutchens, Shelby; Crosby, Alfred

    2013-03-01

    A recently developed technique, Cavitation Rheology (CR), provides a means of measuring the mechanical properties of soft materials on length scales from ~ 0 . 1 ?m to mm at a specific location. CR involves inflation of a small bubble at the tip of a syringe needle which has been inserted into a material. After insertion, the pressure in the syringe is raised until a critical point where the material fails, resulting in rapid inflation of a cavity at the syringe tip. The critical pressure for failure can provide information about the materials properties of the system such as the elastic modulus, E, the critical strain energy release rate, Gc, and the surface energy, ?. Modulus measurements by CR have been made in many synthetic gels and biological tissues with similar accuracy to shear rheology. However, as CR requires insertion of a needle into the subject material, measurements are inherently made in a pre-stressed state. In this work, we have examined the pre-stress associated with needle insertion and the influence of this stress on failure in a synthetic gel of PMMA-PnBA-PMMA triblock copolymer in 2-ethylhexanol.

  13. Measurement of Applied Stresses and Residual Stresses on a Residual Stress Model by Applying Two Different Loads

    Microsoft Academic Search

    T. Kihara

    Applied stresses on a residual stress model have previously been obtained by measuring the residual stresses and the resultant\\u000a stresses generated by applying a load. The present paper reports that the applied stresses and the residual stresses on the\\u000a residual stress model can be obtained by measuring two resultant stresses generated by applying loads of two different magnitudes.\\u000a In the

  14. A dynamic jamming point for shear thickening suspensions

    NASA Astrophysics Data System (ADS)

    Brown, Eric; Jaeger, Heinrich

    2008-11-01

    Densely packed suspensions can shear thicken, in which the viscosity increases with shear rate. We performed rheometry measurements on two model systems: corn starch in water and glass spheres in oils. In both systems we observed shear thickening up to a critical packing fraction ?c (=0.55 for spherical grains) above which the flow abruptly transitions to shear thinning. The viscosity and yield stress diverge as power laws at ?c. Extrapolating the dynamic ranges of shear rate and stress in the shear thickening regime up to ?c suggests a finite change in shear stress with zero change in shear rate. This is a dynamic analog to the jamming point with a yield stress at zero shear rate.

  15. Simulation of two- and three-dimensional dense-fluid shear flows via nonequilibrium molecular dynamics: Comparison of time-and-space-averaged stresses from homogeneous Doll's and Sllod shear algorithms with those from boundary-driven shear

    NASA Astrophysics Data System (ADS)

    Hoover, Wm. G.; Hoover, Carol G.; Petravic, Janka

    2008-10-01

    Homogeneous shear flows (with constant strainrate dvx/dy ) are generated with the Doll’s and Sllod algorithms and compared to corresponding inhomogeneous boundary-driven flows. We use one-, two-, and three-dimensional smooth-particle weight functions for computing instantaneous spatial averages. The nonlinear normal-stress differences are small, but significant, in both two and three space dimensions. In homogeneous systems the sign and magnitude of the shearplane stress difference, Pxx-Pyy , depend on both the thermostat type and the chosen shearflow algorithm. The Doll’s and Sllod algorithms predict opposite signs for this normal-stress difference, with the Sllod approach definitely wrong, but somewhat closer to the (boundary-driven) truth. Neither of the homogeneous shear algorithms predicts the correct ordering of the kinetic temperatures: Txx>Tzz>Tyy .

  16. The auto-correlation function of the extragalactic background light. I. Measuring gravitational shear.

    NASA Astrophysics Data System (ADS)

    van Waerbeke, L.; Mellier, Y.; Schneider, P.; Fort, B.; Mathez, G.

    1997-01-01

    A new method for measuring the shear induced by gravitational light deflection is proposed. It is based on analyzing the anisotropy induced in the auto-correlation function of the extragalactic background light which is produced by very faint distant galaxies. The auto-correlation function can be measured `locally', and its anisotropy is caused by the tidal gravitational field of the deflecting mass distribution in the foreground of these faint background galaxies. Since the method does not require individual galaxy detection, it can be used to measure the shear of extremely faint galaxies which are not detectable individually, but are present in the noise. The shear estimated from the auto-correlation function of the image provides an independent measurement which can be compared to the shear obtained from the distortion of individual galaxy images. Combining these two independent estimates clearly increases the sensitivity of shear measurements. In addition, our new method may allow to determine the local magnification caused by the deflector if the auto-correlation function is caused by a large number density of faint galaxies; in this case, the intrinsic auto-correlation function may provide a `standard source' with respect to which shear and magnification can be obtained. Applications to real and synthetic data are shown and the feasibility of our new method is demonstrated. In particular, we present the shear maps obtained with our new method for the double QSO 2345+007 and the cluster Cl0024+16 and compare them to published shear maps.

  17. Design of a squeeze film magnetorheological brake considering compression enhanced shear yield stress of magnetorheological fluid

    NASA Astrophysics Data System (ADS)

    Sarkar, C.; Hirani, H.

    2013-02-01

    A magnetorheological brake, consisting of rotating disks immersed in a MR fluid and enclosed in an electromagnet, is proposed to replace the conventional heavy weight low response hydraulic disk brake. The frictional characteristics of the proposed brake can be controlled by regulating the yield stress of the MR fluid as function of magnetic field and normal compressive force. The controllable yield stress retards the surfaces of rotating disks, thus MR fluid can be used as a brake lining material. The present research work attempts designing a squeeze film MR brake by accounting compression enhanced shear yield stress of magnetorheological fluid. Theoretical calculations indicate that the estimated braking torque of the six plate squeeze film MR brake, under compression, is in the order of 600Nm. To validate the theoretical design and its findings, a prototype of single-plate squeeze film MR disk brake has been developed. Experimental test setup helps to illustrate braking torque under different control currents (0.0 to 1.25 A).

  18. Response of chondrocytes to shear stress: antagonistic effects of the binding partners Toll-like receptor 4 and caveolin-1.

    PubMed

    Wang, Pu; Zhu, Fei; Tong, Ziqiu; Konstantopoulos, Konstantinos

    2011-10-01

    Osteoarthritis (OA) is often a consequence of excessive mechanical loading of cartilage, which produces hydrostatic stress, tensile strain, and fluid flow. Application of high fluid shear to chondrocytes recapitulates the earmarks of OA, as evidenced by the induction of cyclooxygenase-2, prostaglandins (PGs), and interleukin-6 (IL-6). Here, we delineated the signaling pathway by which high fluid shear mediates the temporal regulation of IL-6 synthesis in human chondrocytes. We determined that Toll-like receptor 4 (TLR4) and caveolin-1 are binding partners in chondrocytes. Their expression is temporally regulated by fluid shear via the sequential up-regulation of microsomal PGE synthase-1 (mPGES-1) and L-PGDS. High shear stress rapidly induces an 8-fold up-regulation of TLR4 expression via an mPGES-1-dependent pathway, whereas prolonged shear exposure concurrently down-regulates TLR4 by >4-fold and up-regulates caveolin-1 expression by > 2.5-fold in an L-PGDS-dependent manner. TLR4 and caveolin-1 exert opposing effects on the activation of ERK1/2, PI3-K and PKA signaling pathways, which, in turn, regulate the NF-?B-dependent IL-6 synthesis in a time-dependent fashion. Reconstructing the signaling network regulating shear-induced IL-6 expression in chondrocytes may provide insights for developing therapeutic strategies to combat osteoarthritis. PMID:21715681

  19. The free shear layer edgetone and instability measurements. [of jet flow

    NASA Technical Reports Server (NTRS)

    Zaman, K. B. M. Q.; Hussain, A. K. M. F.

    1978-01-01

    The hot-wire probe is known to be capable of triggering and sustaining upstream instability modes like the slit jet-wedge edgetone termed the free shear layer tone. In this paper, the hot-wire probe is used to investigate the shear tone phenomenon in axisymmetric and plane free shear layers. For all the measurements reported, the initial boundary layers producing the free shear layers are documented (at 0.2 cm upstream from the lip) and classified as laminar. It is shown that the free shear layer, inherently different from the fully vortical slit jet, produces a different tone behavior. The data on the free shear layer tone eigenfunctions and eigenvalues suggest that the feedback is hydrodynamic rather than acoustic.

  20. The equivalence of enthalpy and shear stress relaxation in rhyolitic obsidians and quantification of the liquid-glass transition in volcanic processes

    Microsoft Academic Search

    R. J. Stevenson; D. B. Dingwell; S. L. Webb; N. S. Bagdassarov

    1995-01-01

    The relaxation of enthalpy and shear stress has been investigated for six silicic volcanic obsidians (calc-alkaline rhyolitic obsidians from Ben Lomond dome, New Zealand, Erevan Dry Fountain, Armenia and Little Glass Butte, USA; peralkaline obsidians from Mayor Island, New Zealand and Eburru, Kenya and a macusanite obsidian from SE Peru). The temperature-dependences of enthalpy and shear stress relaxation are obtained

  1. Flow (shear stress)-mediated remodeling of resistance arteries in diabetes Emilie Vessires, Lamine M. Freidja, Laurent Loufrani, Cline Fassot, Daniel Henrion.

    E-print Network

    Boyer, Edmond

    Flow (shear stress)-mediated remodeling of resistance arteries in diabetes Emilie Vessières, Lamine hypertrophy and improvement of arterial contractility and endothelium-mediated dilation. Shear stress occlusion of a large artery. In diabetes, an excessive ROS production is associated with the formation

  2. Dean vortices: comparison of numerical simulation of shear stress and improvement of mass transfer in membrane processes at low permeation fluxes

    Microsoft Academic Search

    Ph Moulin; D Veyret; F Charbit

    2001-01-01

    In order to rationalize the effect of Dean vortices on mass transfer improvement during membrane filtration, we present preliminary calculations of the wall shear stress in curved tube with non-porous walls. Previous experimental work has already shown strong positive effect of Dean vortices on mass transfer. In this paper, a numerical simulation of shear stress is proposed in order to

  3. Bone morphogenic protein 4 produced in endothelial cells by oscillatory shear stress stimulates an inflammatory response

    NASA Technical Reports Server (NTRS)

    Sorescu, George P.; Sykes, Michelle; Weiss, Daiana; Platt, Manu O.; Saha, Aniket; Hwang, Jinah; Boyd, Nolan; Boo, Yong C.; Vega, J. David; Taylor, W. Robert; Jo, Hanjoong

    2003-01-01

    Atherosclerosis is now viewed as an inflammatory disease occurring preferentially in arterial regions exposed to disturbed flow conditions, including oscillatory shear stress (OS), in branched arteries. In contrast, the arterial regions exposed to laminar shear (LS) are relatively lesion-free. The mechanisms underlying the opposite effects of OS and LS on the inflammatory and atherogenic processes are not clearly understood. Here, through DNA microarrays, protein expression, and functional studies, we identify bone morphogenic protein 4 (BMP4) as a mechanosensitive and pro-inflammatory gene product. Exposing endothelial cells to OS increased BMP4 protein expression, whereas LS decreased it. In addition, we found BMP4 expression only in the selective patches of endothelial cells overlying foam cell lesions in human coronary arteries. The same endothelial patches also expressed higher levels of intercellular cell adhesion molecule-1 (ICAM-1) protein compared with those of non-diseased areas. Functionally, we show that OS and BMP4 induced ICAM-1 expression and monocyte adhesion by a NFkappaB-dependent mechanism. We suggest that BMP4 is a mechanosensitive, inflammatory factor playing a critical role in early steps of atherogenesis in the lesion-prone areas.

  4. Stress analysis of the cracked lap shear specimens: An ASTM round robin

    NASA Technical Reports Server (NTRS)

    Johnson, W. S.

    1986-01-01

    This ASTM Round Robin was conducted to evaluate the state of the art in stress analysis of adhesively bonded joint specimens. Specifically, the participants were asked to calculate the strain-energy-release rate for two different geometry cracked lap shear (CLS) specimens at four different debond lengths. The various analytical techniques consisted of 2- and 3-dimensional finite element analysis, beam theory, plate theory, and a combination of beam theory and finite element analysis. The results were examined in terms of the total strain-energy-release rate and the mode I to mode II ratio as a function of debond length for each specimen geometry. These results basically clustered into two groups: geometric linear or geometric nonlinear analysis. The geometric nonlinear analysis is required to properly analyze the CLS specimens. The 3-D finite element analysis gave indications of edge closure plus some mode III loading. Each participant described his analytical technique and results. Nine laboratories participated.

  5. Stress analysis of the cracked-lap-shear specimen - An ASTM round-robin

    NASA Technical Reports Server (NTRS)

    Johnson, W. S.

    1987-01-01

    This ASTM Round Robin was conducted to evaluate the state of the art in stress analysis of adhesively bonded joint specimens. Specifically, the participants were asked to calculate the strain-energy-release rate for two different geometry cracked lap shear (CLS) specimens at four different debond lengths. The various analytical techniques consisted of 2- and 3-dimensional finite element analysis, beam theory, plate theory, and a combination of beam theory and finite element analysis. The results were examined in terms of the total strain-energy-release rate and the mode I to mode II ratio as a function of debond length for each specimen geometry. These results basically clustered into two groups: geometric linear or geometric nonlinear analysis. The geometric nonlinear analysis is required to properly analyze the CLS specimens. The 3-D finite element analysis gave indications of edge closure plus some mode III loading. Each participant described his analytical technique and results. Nine laboratories participated.

  6. The effects of stenting on shear stress: relevance to endothelial injury and repair.

    PubMed

    Van der Heiden, Kim; Gijsen, Frank J H; Narracott, Andrew; Hsiao, Sarah; Halliday, Ian; Gunn, Julian; Wentzel, Jolanda J; Evans, Paul C

    2013-07-15

    Stent deployment following balloon angioplasty is used routinely to treat coronary artery disease. These interventions cause damage and loss of endothelial cells (EC), and thus promote in-stent thrombosis and restenosis. Injured arteries are repaired (intrinsically) by locally derived EC and by circulating endothelial progenitor cells which migrate and proliferate to re-populate denuded regions. However, re-endothelialization is not always complete and often dysfunctional. Moreover, the molecular and biomechanical mechanisms that control EC repair and function in stented segments are poorly understood. Here, we propose that stents modify endothelial repair processes, in part, by altering fluid shear stress, a mechanical force that influences EC migration and proliferation. A more detailed understanding of the biomechanical processes that control endothelial healing would provide a platform for the development of novel therapeutic approaches to minimize damage and promote vascular repair in stented arteries. PMID:23592806

  7. Feasibility of optical coherence elastography measurements of shear wave propagation in homogeneous tissue equivalent phantoms

    PubMed Central

    Razani, Marjan; Mariampillai, Adrian; Sun, Cuiru; Luk, Timothy W. H.; Yang, Victor X. D.; Kolios, Michael C.

    2012-01-01

    In this work, we explored the potential of measuring shear wave propagation using optical coherence elastography (OCE) based on a swept-source optical coherence tomography (OCT) system. Shear waves were generated using a 20 MHz piezoelectric transducer (circular element 8.5 mm diameter) transmitting sine-wave bursts of 400 ?s, synchronized with the OCT swept source wavelength sweep. The acoustic radiation force (ARF) was applied to two gelatin phantoms (differing in gelatin concentration by weight, 8% vs. 14%). Differential OCT phase maps, measured with and without the ARF, demonstrate microscopic displacement generated by shear wave propagation in these phantoms of different stiffness. We present preliminary results of OCT derived shear wave propagation velocity and modulus, and compare these results to rheometer measurements. The results demonstrate the feasibility of shear wave OCE (SW-OCE) for high-resolution microscopic homogeneous tissue mechanical property characterization. PMID:22567590

  8. Feasibility of optical coherence elastography measurements of shear wave propagation in homogeneous tissue equivalent phantoms.

    PubMed

    Razani, Marjan; Mariampillai, Adrian; Sun, Cuiru; Luk, Timothy W H; Yang, Victor X D; Kolios, Michael C

    2012-05-01

    In this work, we explored the potential of measuring shear wave propagation using optical coherence elastography (OCE) based on a swept-source optical coherence tomography (OCT) system. Shear waves were generated using a 20 MHz piezoelectric transducer (circular element 8.5 mm diameter) transmitting sine-wave bursts of 400 ?s, synchronized with the OCT swept source wavelength sweep. The acoustic radiation force (ARF) was applied to two gelatin phantoms (differing in gelatin concentration by weight, 8% vs. 14%). Differential OCT phase maps, measured with and without the ARF, demonstrate microscopic displacement generated by shear wave propagation in these phantoms of different stiffness. We present preliminary results of OCT derived shear wave propagation velocity and modulus, and compare these results to rheometer measurements. The results demonstrate the feasibility of shear wave OCE (SW-OCE) for high-resolution microscopic homogeneous tissue mechanical property characterization. PMID:22567590

  9. The determination of the Reynolds shear stress distribution in the transition region resulting from a sudden increase in wall roughness in a two-dimensional channel 

    E-print Network

    Heilhecker, Joe Keith

    1962-01-01

    for X-array Probe and Single Wire Probe Velocity Distributions for Selected Smooth and Rough Wall Stations 15 Distribution of Reynolds Shear Stresses in Transition Region froxn Smooth Wall to Rough Wall IB Velocity Profiles in the Transition... Region 19 TABLE OF SYMBOLS channel width static pressure difference between total pressure and static pressure r, 8 subscripts denoting rough wall section and smooth wall section, respectively Tr T s rough wall shear stress and smooth wall shear...

  10. Design and Validation of a Novel Bioreactor to Subject Aortic Valve Leaflets to Side-Specific Shear Stress

    Microsoft Academic Search

    Ling Sun; Nalini M. Rajamannan; Philippe Sucosky

    2011-01-01

    Hemodynamic stresses are presumed to play an important role in the development of calcific aortic valve disease (CAVD). The\\u000a elucidation of the shear stress mechanisms involved in the pathogenesis of CAVD has been hampered by the complexity of the\\u000a native unsteady and side-specific valvular flow environment. To address this gap, this article describes the design and validation\\u000a of a novel

  11. Measurement of Internal Stress in Glass Articles

    SciTech Connect

    Shepard, Chester L.; Cannon, Bret D.; Khaleel, Mohammad A.

    2003-08-01

    We have developed a method for measurement of internal stress in glass articles. The method utilizes Rayleigh-scattered light from a properly polarized laser beam propagating through glass at an oblique angle. This light is imaged with an electronic focal plane array camera. The method is similar to earlier published methods except for the inclusion of an externally controlled phase retarder. The phase retarder allows for the success of the method. The method is suitable for use on flat or curved glass and is applicable over a broad range of residual stresses. Experimental results are provided showing the in-plane stress throughout the thickness of a television glass sample.

  12. Average shear stress estimation of Nojima fault from fission-track analytical data

    NASA Astrophysics Data System (ADS)

    Murakami, M.; Tanaka, H.

    2006-12-01

    Zircon fission-track (FT) thermochronometry is suitable to provide the age of the seismogenic pseudotachylytes and to constrain the seismic histories of the faults in tectonically active regions because recent high-temperature and short-term annealing experiments indicate that spontaneous FTs in zircon are totally annealed at the temperature-time conditions of ordinary pseudotachylyte formation [Murakami et al., 2006]. Murakami and Tagami, [2004] determined zircon FT age of ~2 mm thick pseudotachylyte collected from the trench of Nojima fault, and found that the zircon FT system of the pseudotachylyte was totally reset at ~56 Ma. We apply the FT thermochronological data to estimate average shear stress of the fault quantitatively. Zircon and apatite FT ages from outcrops of granodiorite near the drilling site were reported to be 74 and 44 Ma, respectively [Murakami et al. 2002; Ito, 2004]. The cooling rates of 5.3 °C / Ma from 74 to 44 Ma and 1.8 °C / Ma from 44 Ma to the present were yielded roughly by the calculation, and were equivalent to approximate 0.2 mm/yr and 0.08 mm/yr, respectively, based on the geothermal gradient of 23 °C/km [Kitajima et al., 2001]. On the cooling rate, the depth of the pseudotachylyte formation at 56 Ma was estimated at around 6 km. In addition, because FTs in zircon were totally annealed at the temperature-time conditions of approximate 910 °C for 4 sec [Murakami et al., 2006], more than 750 °C of temperature was raised when the ~2 mm thick pseusotachylyte formed at 56 Ma. Heating value supplied to the pseudotachylyte zone per unit area is therefore estimated to be 4 × 106 J / m2 from the raised temperature, assuming that the density and specific heat capacity of the pseudotachylyte is 2600 kg / m3 and 800 J / kgK, respectively. Then, average shear stress is estimated to be very low, approximate 4 MPa, depending on an assumption.

  13. Triboluminescent Fiber-Optic Sensors Measure Stresses

    NASA Technical Reports Server (NTRS)

    Rogowski, Robert S.

    1994-01-01

    Triboluminescence exploited in fiber-optic sensor system for measuring changes in pressures, strains, vibrations, and acoustic emissions, in structural members. Sensors embedded in members for in situ monitoring of condition of structure. System passive in sense no source of radiation required to interrogate optical fiber. Technique has potential for wide range of applications in which detection and measurement of structural stress required.

  14. Variations in shear strength properties of clay-rich sediments over the effective stress range of 0.1 to 100 MPa

    NASA Astrophysics Data System (ADS)

    Casey, B.; Germaine, J. T.; Flemings, P. B.; Fahy, B. P.

    2014-12-01

    We conducted experiments on clay-rich sediments over the effective stress range of 0.1 MPa to 100 MPa and found that critical state friction angle and undrained strength vary systematically as a function of both stress level and sediment composition. We tested sediments from a diverse range of geologic backgrounds using a suite of triaxial systems specially designed for low, medium and high stresses. We used the resedimentation technique to prepare fully saturated samples of identical composition for testing. During the consolidation phase of triaxial tests specimens were subjected to one-dimensional compression, which produces a more realistic stress-strain response during shearing when compared to the more common approach of using isotropic compression. We measured friction angles as low as 12 degrees for a confining pressure of 63 MPa, and observed a decrease of undrained strength ratio by almost two-thirds when viewed over three orders of magnitude in stress. Clay-rich materials, particularly those with a large smectite fraction, display a more rapid decrease in both friction angle and undrained strength ratio with increasing effective stress when compared to more silty materials. We also observed similar trends for the horizontal-to-vertical effective stress ratio (Ko); Ko generally increases with effective stress level during normal compression, and this increase is most pronounced for smectite-rich sediments. We measured values of Ko as high as 0.90 at effective stresses approaching 100 MPa. This finding implies that high horizontal stresses can develop at depth solely due to normal mechanical compression, and that tectonic stresses, creep, or geologic unloading are not necessary to justify them. Furthermore, we establish, for the first time, a general relationship between Ko and the undrained strength of sediments. Higher values of Ko are associated with both lower friction angles and lower undrained strengths. Our experimental results reveal aspects of sediment behavior at high effective stress that have not previously been observed, and provide useful information on how both shear resistance and horizontal stress evolve within basins.

  15. Response of chondrocytes to shear stress: antagonistic effects of the binding partners Toll-like receptor 4 and caveolin-1

    PubMed Central

    Wang, Pu; Zhu, Fei; Tong, ZiQiu; Konstantopoulos, Konstantinos

    2011-01-01

    Osteoarthritis (OA) is often a consequence of excessive mechanical loading of cartilage, which produces hydrostatic stress, tensile strain, and fluid flow. Application of high fluid shear to chondrocytes recapitulates the earmarks of OA, as evidenced by the induction of cyclooxygenase-2, prostaglandins (PGs), and interleukin-6 (IL-6). Here, we delineated the signaling pathway by which high fluid shear mediates the temporal regulation of IL-6 synthesis in human chondrocytes. We determined that Toll-like receptor 4 (TLR4) and caveolin-1 are binding partners in chondrocytes. Their expression is temporally regulated by fluid shear via the sequential up-regulation of microsomal PGE synthase-1 (mPGES-1) and L-PGDS. High shear stress rapidly induces an 8-fold up-regulation of TLR4 expression via an mPGES-1-dependent pathway, whereas prolonged shear exposure concurrently down-regulates TLR4 by >4-fold and up-regulates caveolin-1 expression by > 2.5-fold in an L-PGDS-dependent manner. TLR4 and caveolin-1 exert opposing effects on the activation of ERK1/2, PI3-K and PKA signaling pathways, which, in turn, regulate the NF-?B-dependent IL-6 synthesis in a time-dependent fashion. Reconstructing the signaling network regulating shear-induced IL-6 expression in chondrocytes may provide insights for developing therapeutic strategies to combat osteoarthritis.—Wang, P., Zhu, F., Tong, Z., Konstantopoulos, K. Response of chondrocytes to shear stress: antagonistic effects of the binding partners Toll-like receptor 4 and caveolin-1. PMID:21715681

  16. Membrane cholesterol modulates the fluid shear stress response of polymorphonuclear leukocytes via its effects on membrane fluidity.

    PubMed

    Zhang, Xiaoyan; Hurng, Jonathan; Rateri, Debra L; Daugherty, Alan; Schmid-Schönbein, Geert W; Shin, Hainsworth Y

    2011-08-01

    Continuous exposure of polymorphonuclear leukocytes (PMNLs) to circulatory hemodynamics points to fluid flow as a biophysical regulator of their activity. Specifically, fluid flow-derived shear stresses deactivate leukocytes via actions on the conformational activities of proteins on the cell surface. Because membrane properties affect activities of membrane-bound proteins, we hypothesized that changes in the physical properties of cell membranes influence PMNL sensitivity to fluid shear stress. For this purpose, we modified PMNL membranes and showed that the cellular mechanosensitivity to shear was impaired whether we increased, reduced, or disrupted the organization of cholesterol within the lipid bilayer. Notably, PMNLs with enriched membrane cholesterol exhibited attenuated pseudopod retraction responses to shear that were recovered by select concentrations of benzyl alcohol (a membrane fluidizer). In fact, PMNL responses to shear positively correlated (R(2) = 0.96; P < 0.0001) with cholesterol-related membrane fluidity. Moreover, in low-density lipoprotein receptor-deficient (LDLr(-/-)) mice fed a high-fat diet (a hypercholesterolemia model), PMNL shear-responses correlated (R(2) = 0.5; P < 0.01) with blood concentrations of unesterified (i.e., free) cholesterol. In this regard, the shear-responses of PMNLs gradually diminished and eventually reversed as free cholesterol levels in blood increased during 8 wk of the high-fat diet. Collectively, our results provided evidence that cholesterol is an important component of the PMNL mechanotransducing capacity and elevated membrane cholesterol impairs PMNL shear-responses at least partially through its impact on membrane fluidity. This cholesterol-linked perturbation may contribute to dysregulated PMNL activity (e.g., chronic inflammation) related to hypercholesterolemia and causal for cardiovascular pathologies (e.g., atherosclerosis). PMID:21525434

  17. Membrane cholesterol modulates the fluid shear stress response of polymorphonuclear leukocytes via its effects on membrane fluidity

    PubMed Central

    Zhang, Xiaoyan; Hurng, Jonathan; Rateri, Debra L.; Daugherty, Alan; Schmid-Schönbein, Geert W.

    2011-01-01

    Continuous exposure of polymorphonuclear leukocytes (PMNLs) to circulatory hemodynamics points to fluid flow as a biophysical regulator of their activity. Specifically, fluid flow-derived shear stresses deactivate leukocytes via actions on the conformational activities of proteins on the cell surface. Because membrane properties affect activities of membrane-bound proteins, we hypothesized that changes in the physical properties of cell membranes influence PMNL sensitivity to fluid shear stress. For this purpose, we modified PMNL membranes and showed that the cellular mechanosensitivity to shear was impaired whether we increased, reduced, or disrupted the organization of cholesterol within the lipid bilayer. Notably, PMNLs with enriched membrane cholesterol exhibited attenuated pseudopod retraction responses to shear that were recovered by select concentrations of benzyl alcohol (a membrane fluidizer). In fact, PMNL responses to shear positively correlated (R2 = 0.96; P < 0.0001) with cholesterol-related membrane fluidity. Moreover, in low-density lipoprotein receptor-deficient (LDLr?/?) mice fed a high-fat diet (a hypercholesterolemia model), PMNL shear-responses correlated (R2 = 0.5; P < 0.01) with blood concentrations of unesterified (i.e., free) cholesterol. In this regard, the shear-responses of PMNLs gradually diminished and eventually reversed as free cholesterol levels in blood increased during 8 wk of the high-fat diet. Collectively, our results provided evidence that cholesterol is an important component of the PMNL mechanotransducing capacity and elevated membrane cholesterol impairs PMNL shear-responses at least partially through its impact on membrane fluidity. This cholesterol-linked perturbation may contribute to dysregulated PMNL activity (e.g., chronic inflammation) related to hypercholesterolemia and causal for cardiovascular pathologies (e.g., atherosclerosis). PMID:21525434

  18. An Analysis of the Internal Structure of Gouge Layers Under Shear Stresses and a Trial for Prediction of Slips

    NASA Astrophysics Data System (ADS)

    Yoshioka, N.

    2009-12-01

    Shear loading tests on gouge layers and experiments using photo-elastic materials have revealed the detailed processes how the gouge layers finally reach the failure (large stick-slip) under shear loading. In the shear loading tests, an upper block is horizontally loaded on a gouge layer. The upper block shows, without exception, a fairly large horizontal and at the same time vertical movements prior to a final stick-slip. The upper block is lifted up, keeping the sliding surface horizontal, the locus of which is a circular arc (see Figure). This makes the gouge layer look like dilating. The radius of the arc is determined by the thickness and the diameter distribution of the gouge layer. The strength of the layer, which is defined as the shear stress at the time when the final stick-slip just begins, depends on the arc radius: the shorter the radius is, the stronger the layer is. The experiments using photo-elastic materials show that the internal structure of the gouge layers is not homogeneous and only a portion of gouges contribute to sustain the external forces by forming columnar structure (stress chains). Under the vertical force only, a number of vertical columns are created. After the application of shear forces, new columnar structures with very low angle are produced. They gradually replace the initial vertical structure. From the observations of both the shear loading tests and the photo-elastic experiments, it is suggested that the shear forces self-organizedly produce a columnar structure and make the columns rotate and produce a large amount of horizontal and vertical displacements prior to the final large slip. At the final stage of shear loading, the forces added to the layer seems to be uniformly distributed. These observations will be useful for predicting slips on the faults.

  19. Reference: Bid. Bull. 188: 46-56. (February/March, 1995) The Effects of Hydrodynamic Shear Stress on

    E-print Network

    Denny, Mark

    on Fertilization and Early Development of the Purple Sea Urchin Strongylocentrotus purpuratus KRISTINA S. MEAD to reproduction in free-spawning animals. Not only can breaking waves quickly dilute the gametes shed by spawning organisms, but turbulence-induced shear stresses may limit fertilization and interfere with normal

  20. Physiological mechanisms of vascular response induced by shear stress and effect of exercise in systemic and placental circulation

    PubMed Central

    Rodríguez, Iván; González, Marcelo

    2014-01-01

    Physiological vascular function regulation 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 main risk factors of cardiovascular pathology, where the imbalance between the synthesis of vasodilator and vasoconstrictor molecules is common in the development of vascular disorders in systemic and placental circulation. In the placenta, an organ without autonomic innervations, the local control of vascular tone is critical for maintenance of fetal growth and mechanisms that underlie shear stress response induced by blood flow are essential during pregnancy. In this field, shear stress induced by moderate exercise is one of the most important mechanisms to improve vascular function through nitric oxide synthesis and stimulation of mechanical response of endothelial cells triggered by ion channels, caveolae, endothelial NO synthase, and vascular endothelial growth factor, among others. The demand for oxygen and nutrients by tissues and organs, especially in placentation and pregnancy, determines blood flow parameters, and physiological adaptations of vascular beds for covering metabolic requirements. In this regard, moderate exercise versus sedentarism shows potential benefits for improving vascular function associated with the enhancement of molecular mechanisms induced by shear stress. In this review, we collect evidence about molecular bases of physiological response to shear stress in order to highlight the relevance of moderate exercise-training for vascular health in adult and fetal life. PMID:25278895

  1. Risk assessment of erosion from concentrated flow on rangelands using overland flow distribution and shear stress partitioning

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Erosion rates of overland flow on rangelands tend to be relatively low, but under certain conditions where flow is concentrated, soil loss can be significant. Therefore, a rangeland site can be highly vulnerable to soil erosion where overland flow is likely to concentrate and exert high shear stress...

  2. Blood flow dynamics in patient-specific cerebral aneurysm models: The relationship between wall shear stress and aneurysm area index

    Microsoft Academic Search

    Alvaro Valencia; Hernan Morales; Rodrigo Rivera; Eduardo Bravo; Marcelo Galvez

    2008-01-01

    Hemodynamics plays an important role in the progression and rupture of cerebral aneurysms. The temporal and spatial variations in wall shear stress (WSS) within the aneurysmal sac are hypothesized to be correlated with the growth and rupture of the aneurysm. The current work describes the blood flow dynamics in 34 patient-specific models of saccular aneurysms located in the region of

  3. Chronic in vitro shear stress stimulates endothelial cell retention on prosthetic vascular grafts and reduces subsequent in vivo neointimal thickness

    Microsoft Academic Search

    Alan Dardik; Ailian Liu; Barbara J. Ballermann

    1999-01-01

    Objective: The absence of endothelial cells at the luminal surface of a prosthetic vascular graft potentiates thrombosis and neointimal hyperplasia, which are common causes of graft failure in humans. This study tested the hypothesis that pretreatment with chronic in vitro shear stress enhances subsequent endothelial cell retention on vascular grafts implanted in vivo. Methods: Cultured endothelial cells derived from Fischer

  4. The Turbulent Structures Around Clusters Formed Under A Range of Armoring Shear Stresses and Grain Size Distributions

    E-print Network

    Curran, Joanna C.

    The Turbulent Structures Around Clusters Formed Under A Range of Armoring Shear Stresses and Grain surface and an armored surface layer forms. As the surface armor forms, a surface structure develops clusters naturally developed during bed armoring. The series of experiments created armored beds using four

  5. Measurement of local stress for microelectronics applications

    NASA Astrophysics Data System (ADS)

    Zheng, Dawei

    For quality control and reliability analysis in semiconductor manufacturing, it is crucial to access the localized stress in devices due to process integration in thin film deposition, etching, passivation and thermal treatment. Presented in this dissertation is the exploration of a new methodology to access localized stress in patterned microstructures. It is called the "micro-bending-beam method". In order to evaluate the residual stress distribution in a thin film pattern residing on a silicon wafer, the Si underlying the pattern was thinned down uniformly so that its deflection, caused by the residual stress, could be measured. If the etched-back surface remains optically flat and reflective, then the bending of the diaphragm would be equivalent to its surface profile, which could be readily measured by a Twyman-Green laser interferometer. A procedure called "numerical etching" was implemented to simulate the Si etching process, which linked the stress state of the microstructure on a bulk wafer to that on a Si diaphragm. An initial stress field in the pattern was assumed, its effect on the bending of the Si diaphragm beneath was calculated and compared to the measured value. The discrepancy between them was used to modify the initially assumed stress field and repeated until satisfactory matches were achieved at each diaphragm thickness. The applicability of the micro-bending-beam method was demonstrated by resolving the residual stress in an electroless Ni bump. It was found that for a relatively thick diaphragm, the "plate" effect dominated; for a relatively thin diaphragm, the "membrane" effect dominated; at intermediate thickness, both effects existed. A general algorithm to solve non-linear equations where both bending stiffness and residual stress in a diaphragm must be considered was invented, and named "non-linear sequential analysis". It was found that for a pre-stressed pattern sitting on a stress-free Si diaphragm starting at to and thinned down to tn, there existed an "optimum" thickness of the diaphragm where the deformation was maximum. For the same structure, if a residual tensile stress existed in the Si diaphragm, then this optimum thickness would shift to a smaller value and the magnitude of this deformation would decrease as well. Furthermore, the shape of the diaphragm deformation was also a strong function of the diaphragm thickness.

  6. Measuring Residual Stress Using Nonlinear Ultrasound

    NASA Astrophysics Data System (ADS)

    Liu, M.; Kim, J.-Y.; Qu, J.; Jacobs, L. J.

    2010-02-01

    Near-surface compressive residual stresses, which are generated by shot peening, are known to retard crack initiation and thus extend the fatigue life of a metal component. The ability to effectively measure these near-surface residual stresses would greatly help predict the fatigue life of shot-peened components. This research uses the nonlinear surface acoustic wave technique to measure the residual stresses in a shot-peened component. Experiments are conducted on three different aluminum alloy (AA 7075) samples: as-received with no peeing, and shot-peened at the Almen intensities of 8A and 16A. Surface roughness measurements are also carried out for these three samples. The nonlinear ultrasonic results show that the measured acoustic nonlinearity parameter increases by 81% and 115% for the 8A and 16A samples. These large increases in measured acoustic nonlinearity clearly indicate the potential of the nonlinear ultrasonic technique as an NDE tool to measure the near-surface residual stresses. The effects of surface roughness on the ultrasonic measurement are briefly examined. Finally, a preliminary model prediction is presented to interpret the experimental results.

  7. True Shear Parallel Plate Viscometer

    NASA Technical Reports Server (NTRS)

    Ethridge, Edwin; Kaukler, William

    2010-01-01

    This viscometer (which can also be used as a rheometer) is designed for use with liquids over a large temperature range. The device consists of horizontally disposed, similarly sized, parallel plates with a precisely known gap. The lower plate is driven laterally with a motor to apply shear to the liquid in the gap. The upper plate is freely suspended from a double-arm pendulum with a sufficiently long radius to reduce height variations during the swing to negligible levels. A sensitive load cell measures the shear force applied by the liquid to the upper plate. Viscosity is measured by taking the ratio of shear stress to shear rate.

  8. Wall Shear stress measurements in the atmosperhic surface layer

    E-print Network

    Marusic, Ivan

    was to further understand similarities that may exist between the SLTEST sur- face layer and the wind tunnel]. The geophysically driven air flow is therefore thought to share im- portant characteristics with common wind-tunnel boundary layers, albeit at three orders of magnitude higher Reynolds number. Thus, another goal

  9. Mucus Secretion and Cytoskeletal Modifications in Cultured Nasal Epithelial Cells Exposed to Wall Shear Stresses

    PubMed Central

    Even-Tzur, Nurit; Kloog, Yoel; Wolf, Michael; Elad, David

    2008-01-01

    The nasal epithelium is continuously subjected to wall shear stresses (WSS) induced by respiratory airflows. An in vitro experimental model was developed to expose nasal epithelial cells cultured under air-liquid interface conditions to steady airflow-induced WSS. Mucus secretion from epithelial goblet cells was quantified using an enzyme-linked lectinosorbent assay, and modifications of the cytoskeletal structure were qualitatively evaluated from fluorescent stains of actin and ?-tubulin fibers. The results show increased mucus secretion from cells subjected to WSS of 0.1 and 1.0 dyne/cm2 for more than 15 min in comparison with unstressed cells. The integrity levels of ?-tubulin fibers were significantly lower in cells subjected to WSS than in unstressed cells. The increased mucus secretion in response to WSS was approximately the same in Taxol-free and Taxol-treated cultures, which indicates that there is no direct connection between ?-tubulin fragmentation and mucus secretion. The stressed cells regained their normal cytoskeletal appearance 24 h after the exposure to WSS. The results of this study suggest that WSS have an important role in the mechanical regulation of the nasal surface epithelium function. PMID:18487304

  10. Experimental investigations of the time and flow-direction responses of shear-stress-sensitive liquid crystal coatings

    NASA Technical Reports Server (NTRS)

    Reda, Daniel C.; Muratore, Joseph J., Jr.; Heineck, James T.

    1993-01-01

    Time and flow-direction responses of shearstress-sensitive liquid crystal coatings were explored experimentally. For the time-response experiments, coatings were exposed to transient, compressible flows created during the startup and off-design operation of an injector-driven supersonic wind tunnel. Flow transients were visualized with a focusing Schlieren system and recorded with a 1000 frame/sec color video camera. Liquid crystal responses to these changing-shear environments were then recorded with the same video system, documenting color-play response times equal to, or faster than, the time interval between sequential frames (i.e., 1 millisecond). For the flow-direction experiments, a planar test surface was exposed to equal-magnitude and known-direction surface shear stresses generated by both normal and tangential subsonic jet-impingement flows. Under shear, the sense of the angular displacement of the liquid crystal dispersed (reflected) spectrum was found to be a function of the instantaneous direction of the applied shear. This technique thus renders dynamic flow reversals or flow divergences visible over entire test surfaces at image recording rates up to 1 KHz. Extensions of the technique to visualize relatively small changes in surface shear stress direction appear feasible.

  11. Shear stress stimulates phosphorylation of eNOS at Ser(635) by a protein kinase A-dependent mechanism

    NASA Technical Reports Server (NTRS)

    Boo, Yong Chool; Hwang, Jinah; Sykes, Michelle; Michell, Belinda J.; Kemp, Bruce E.; Lum, Hazel; Jo, Hanjoong

    2002-01-01

    Shear stress stimulates nitric oxide (NO) production by phosphorylating endothelial NO synthase (eNOS) at Ser(1179) in a phosphoinositide-3-kinase (PI3K)- and protein kinase A (PKA)-dependent manner. The eNOS has additional potential phosphorylation sites, including Ser(116), Thr(497), and Ser(635). Here, we studied these potential phosphorylation sites in response to shear, vascular endothelial growth factor (VEGF), and 8-bromocAMP (8-BRcAMP) in bovine aortic endothelial cells (BAEC). All three stimuli induced phosphorylation of eNOS at Ser(635), which was consistently slower than that at Ser(1179). Thr(497) was rapidly dephosphorylated by 8-BRcAMP but not by shear and VEGF. None of the stimuli phosphorylated Ser(116). Whereas shear-stimulated Ser(635) phosphorylation was not affected by phosphoinositide-3-kinase inhibitors wortmannin and LY-294002, it was blocked by either treating the cells with a PKA inhibitor H89 or infecting them with a recombinant adenovirus-expressing PKA inhibitor. These results suggest that shear stress stimulates eNOS by two different mechanisms: 1) PKA- and PI3K-dependent and 2) PKA-dependent but PI3K-independent pathways. Phosphorylation of Ser(635) may play an important role in chronic regulation of eNOS in response to mechanical and humoral stimuli.

  12. Bending and Shear Stresses Developed by the Instantaneous Arrest of the Root of a Moving Cantilever Beam

    NASA Technical Reports Server (NTRS)

    Stowell, Elbridge, Z; Schwartz, Edward B; Houbolt, John C

    1945-01-01

    A theoretical and experimental investigation has been made of the behavior of a cantilever beam in transverse motion when its root is suddenly brought to rest. Equations are given for determining the stresses, the deflections, and the accelerations that arise in the beam as a result of the impact. The theoretical equations, which have been confirmed experimentally, reveal that, at a given percentage of the distance from root to tip, the bending stresses for a particular mode are independent of the length of the beam, whereas the shear stresses vary inversely with the length.

  13. Thickness Measurement of Fracture Fluid Gel Filter Cake after Static Build Up and Shear Erosion 

    E-print Network

    Xu, Ben

    2011-08-08

    tested as an effective tool to measure the filter cake thickness. A correlation for crosslinked guar fracture fluid filter cake thickness was produced. An experiment setup used to shear erode the filter cake was built and tested. The results showed...

  14. Damage detection of shear connectors under moving loads with relative displacement measurements

    NASA Astrophysics Data System (ADS)

    Li, Jun; Hao, Hong

    2015-08-01

    This paper investigates the use of relative displacement measurements from the newly developed relative displacement sensors to identify the damage of shear connectors in composite bridges. Continuous Wavelet Transform and Hilbert-Huang Transform are applied to analyze the measured dynamic responses and to identify the damage of shear connectors in the composite bridge model under moving loads. Comparative studies by using the relative displacement, acceleration and displacement measurements respectively for the damage detection are conducted. A comparative study of using relative displacements and acceleration responses of the bridge under ambient excitations to monitor the shear connector conditions is also conducted. Numerical and experimental studies demonstrate that both relative displacement and acceleration measurements can identify the location and the instant of damage occurrence in shear connectors when the bridge is under moving loads. The results demonstrate that relative displacement is a better response quantity for structural health monitoring of composite bridges.

  15. Modeling and Phantom Studies of Ultrasonic Wall Shear Rate Measurements Using Coded Pulse Excitation

    PubMed Central

    Tsou, Jean K.; Liu, Jie; Insana, Michael F.

    2009-01-01

    Wall shear rate (WSR) is the derivative of blood velocity with respect to vessel radius at the endothelial cell (EC) surface. The product of WSR and blood viscosity is the wall shear stress (WSS) that has been identified as an important factor for atherosclerosis development. High echo signal-to-noise ratio (eSNR) and high spatial resolution are crucial for minimizing the errors in WSR estimates. By transmitting coded pulses with time-bandwidth product greater than one, high eSNR from weak blood scatter can be achieved without increasing instantaneous power or sacrificing spatial resolution. This paper summarizes a series of measurements in a straight tube (5-mm diameter), constant velocity flow phantom using a 10 MHz transducer (60% bandwidth, f/1.5) imaged with a 72° Doppler angle, 125 MHz sampling frequency and 1 kHz pulse repetition frequency. Measurements were made using a frequency-modulated (FM) code, phase-modulated (PM) codes, and uncoded broadband and narrow band pulse transmissions. Both simulation and experimental results show that coded-pulse excitation increases accuracy and precision in WSR estimation for laminar flow over a broad range of peak velocity values when compared to standard pulsing techniques in noise-limited conditions (eSNR < 30 dB). The code sequence and its length are selected to balance range lobe suppression with eSNR and echo coherence enhancements to minimize WSR errors. In our study, the combination of an eight bit Optimal coded pulse with a Wiener compression filter yielded the highest WSR estimation performance. PMID:16615576

  16. The Effects of Low-Shear Mechanical Stress on Yersinia pestis Virulence

    NASA Astrophysics Data System (ADS)

    Lawal, Abidat; Jejelowo, Olufisayo A.; Rosenzweig, Jason A.

    2010-11-01

    Manned space exploration has created a need to evaluate the effects of spacelike stress on pathogenic and opportunistic microbes astronauts could carry with them to the International Space Station and beyond. Yersinia pestis (YP) causes bubonic, septicemic, and pneumonic plague and is capable of killing infected patients within 3-7 days. In this study, low-shear modeled microgravity (LSMMG), a spacelike stress, was used to physically stress YP; and its effects on proliferation, cold growth, and type III secretion system (T3SS) function were evaluated. YP was grown to saturation in either LSMMG or normal gravity (NG) conditions prior to being used for RAW 246.7 cell infections, HeLa cell infections, and Yop secretion assays. A mutant strain of YP (?yopB) that lacks the ability to inject Yersinia outer membrane proteins (Yops) into the host cell was used as a negative control in cell infection experiments. Our experimental results indicate that YP cultivated under LSMMG resulted in reduced YopM production and secretion compared to its NG-grown counterpart. Similarly, NG-grown YP induced more cell rounding in HeLa cells than did the LSMMG-grown YP, which suggests that LSMMG somehow impairs T3SS optimum function. Also, LSMMG-grown YP used to infect cultured RAW 246.7 cells showed a similar pattern of dysfunction in that it proliferated less than did its NG-grown counterpart during an 8-hour infection period. This study suggests that LSMMG can attenuate bacterial virulence contrary to previously published data that have demonstrated LSMMG-induced hypervirulence of other Gram-negative enterics.

  17. System and method for measuring residual stress

    DOEpatents

    Prime, Michael B. (Los Alamos, NM)

    2002-01-01

    The present invention is a method and system for determining the residual stress within an elastic object. In the method, an elastic object is cut along a path having a known configuration. The cut creates a portion of the object having a new free surface. The free surface then deforms to a contour which is different from the path. Next, the contour is measured to determine how much deformation has occurred across the new free surface. Points defining the contour are collected in an empirical data set. The portion of the object is then modeled in a computer simulator. The points in the empirical data set are entered into the computer simulator. The computer simulator then calculates the residual stress along the path which caused the points within the object to move to the positions measured in the empirical data set. The calculated residual stress is then presented in a useful format to an analyst.

  18. Effects of a Pomegranate Fruit Extract rich in punicalagin on oxidation-sensitive genes and eNOS activity at sites of perturbed shear stress and atherogenesis

    Microsoft Academic Search

    Filomena de Nigris; Sharon Williams-Ignarro; Vincenzo Sica; Lilach O. Lerman; Francesco P. D'Armiento; Russell E. Byrns; Amelia Casamassimi; Daniela Carpentiero; Concetta Schiano; Daigo Sumi; Carmela Fiorito; Louis J. Ignarro; Claudio Napoli

    2007-01-01

    Background: Atherosclerosis is enhanced in arterial segments exposed to disturbed flow. Perturbed shear stress increases the expression of oxidation-sensitive responsive genes (such as ELK-1 and p-CREB). Polyphenolic antioxidants contained in the juice derived from the pomegranate contribute to the reduction of oxidative stress and atherogenesis during disturbed shear stress. Aim of the study: To evaluate the effects of intervention with

  19. Torsional stress measurement by axial displacement

    Microsoft Academic Search

    J. J. Deer

    1971-01-01

    An apparatus is described for the measurement of torque by converting angular displacement to axial displacement. A stress-responsive pulley is loosely mounted on a drive shaft by a plain bearing and a short screw-threaded section. The pulley is attached to the shaft by means of a torsion spring. In use a retarding effect upon the pulley causes angular displacement within

  20. Residual and applied stress measurements at IPNS

    SciTech Connect

    Richardson, J.W. Jr.

    1991-01-01

    The Intense Pulsed Neutron Source (IPNS) at Argonne National Laboratory has operated as a user facility since 1981. From the early days on, highly precise measurement of structural parameters including lattice constants has been a major objective of developments on the powder diffractometers at IPNS. The General Purpose Powder Diffractometer (GPPD) combines excellent instrumental resolution -- roughly independent of d-spacing -- with good neutron flux to provide an exceptional tool for the measurement of residual and applied stresses.

  1. Residual and applied stress measurements at IPNS

    SciTech Connect

    Richardson, J.W. Jr.

    1991-12-31

    The Intense Pulsed Neutron Source (IPNS) at Argonne National Laboratory has operated as a user facility since 1981. From the early days on, highly precise measurement of structural parameters including lattice constants has been a major objective of developments on the powder diffractometers at IPNS. The General Purpose Powder Diffractometer (GPPD) combines excellent instrumental resolution -- roughly independent of d-spacing -- with good neutron flux to provide an exceptional tool for the measurement of residual and applied stresses.

  2. Cenozoic block rotation according to a conjugate shear system in central Europe — indications from palaeomagnetic measurements

    NASA Astrophysics Data System (ADS)

    Schreiber, U.; Rotsch, S.

    1998-12-01

    Results of palaeomagnetic measurements in the middle Tertiary volcanic provinces of Siebengebirge and Westerwald (northeastern Rhenish Massif, Germany) indicate that block rotation of the northeastern Rhenish Massif of the order of 10° to 16° has occurred since the Late Oligocene. Contemporaneous subsidence in the Upper Rhine graben, Neuwied basin, and Lower Rhine basin and intensive faulting in the Hessian depression document a new period of intraplate tectonism in central Europe. In the Tertiary, presumably from the Eocene to the Miocene, the axis of maximum horizontal stress rotated from the NNE-SSW to the NNW-SSE and the NW-SE direction, respectively. The new stress conditions may be responsible for the development of a conjugate shear system in central Europe north of the Alps. A model of a conjugate shear system is presented: a sinistral divergent strike-slip fault extends SSW-NNE from the Upper Rhine graben to the north. The fault splits up into two branches in the area of the Hessian depression. A conjugate dextral wrench fault system develops from the Bavarian Pfahl zone (southeastern Germany) to the Rhenish Massif. About 200 km to the northeast, a parallel dextral strike-slip fault is known from the southern Lower Saxony basin to the north of the Osning zone and Harz mountains. The northeastern block of the Rhenish Massif was created between dextral strike-slip faults. The block began clockwise rotation presumably in the Late Oligocene due to small changes in direction of the maximum horizontal compressive stress from NNW to NW and contemporaneous extension of the western European crust to the southwest. It is assumed that the block rotation is responsible for the V-shaped opening of the Lower Rhenish basin, and anticlockwise micro-block rotation within the Hessian depression. Opening between the rotating and nonrotating crust along the recent Rhine river in the central part of the Rhenish Massif formed triangular transrotational basins (basin of Neuwied) due to movements of crustal blocks in the western Rhenish Massif bounded by WNW-ESE dextral faults. Fault-plane solutions from recent earthquakes in the Rhine system support the model of block rotation and related crustal movements. Due to rotation of the northeastern Rhenish Massif the continuation of the Upper Rhine graben development to the north is prevented.

  3. RC beams shear-strengthened with FRP: Stress distributions in the FRP reinforcement

    Microsoft Academic Search

    X. Z. Lu; J. F. Chen; L. P. Ye; J. G. Teng; J. M. Rotter

    2009-01-01

    Reinforced concrete (RC) beams may be strengthened for shear with externally bonded fibre reinforced polymer (FRP) composites through complete wrapping, U-jacketing or bonding on their sides only. The two main shear failure modes of such strengthened beams are FRP rupture and debonding. In both modes of failure, the contribution of the bonded FRP reinforcement to the shear capacity of the

  4. Advanced Human Carotid Plaque Progression Correlates Positively with Flow Shear Stress Using Follow-Up Scan Data: An In Vivo MRI Multi-Patient 3D FSI Study

    PubMed Central

    Yang, Chun; Canton, Gador; Yuan, Chun; Ferguson, Marina; Hatsukami, Thomas S.; Tang, Dalin

    2010-01-01

    Although it has been well-accepted that atherosclerosis initiation and early progression correlate negatively with flow wall shear stresses (FSS), increasing evidence suggests mechanisms governing advanced plaque progression are not well understood. Fourteen patients were scanned 2–4 times at 18 month intervals using a histologically validated multi-contrast magnetic resonance imaging (MRI) protocol to acquire carotid plaque progression data. Thirty-two scan pairs (baseline and follow-up scans) were formed with slices matched for model construction and analysis. 3D fluid-structure interaction (FSI) models were constructed and plaque wall stress (PWS) and flow shear stress (FSS) were obtained from all matching lumen data points (400–1000 per plaque; 100 points per matched slice) to quantify correlations with plaque progression measured by vessel wall thickness increase (WTI). Using FSS and PWS data from follow-up scan, 21 out of 32 scan pairs showed a significant positive correlation between WTI and FSS (positive/negative/no significance ratio = 21/8/3), and 26 out of 32 scan pairs showed a significant negative correlation between WTI and PWS (positive/negative/no significance ratio = 2/26/4). The mean FSS value of lipid core nodes (n=5294) from all 47 plaque models was 63.5 dyn/cm2, which was 45% higher than that from all normal vessel nodes (n=27553, p<0.00001)). The results from this intensive FSI study indicate that flow shear stress from follow-up scan correlates positively with advanced plaque progression which is different from what has been observed in plaque initiation and early-stage progression. It should be noted that the correlation results do not automatically lead to any causality conclusions. PMID:20570268

  5. Viscosity measurement based on shear-wave laser speckle contrast analysis

    NASA Astrophysics Data System (ADS)

    Cheng, Yi; Li, Sinan; Eckersley, Robert J.; Elson, Daniel S.; Tang, Meng-Xing

    2013-12-01

    Tissue viscosity is correlated with tissue pathological changes and provides information for tissue characterization. In this study, we report an optical method to track continuous shear-wave propagation at centimeter depths in an optically turbid medium. Shear-wave attenuation coefficients were measured at multiple frequencies using shear-wave laser speckle contrast analysis (SW-LASCA) to quantitatively estimate tissue viscosity using the Voigt model. Shear waves were generated within tissue-mimicking phantoms by an amplitude-modulated ultrasound (modulation frequency: 100 to 600 Hz) and tracked by time-resolved laser speckle contrast difference received on a charged-coupled device camera. Averaged contrast difference over a selected time window was related to shear-wave amplitude and used to calculate the shear-wave attenuation coefficient. Phantoms of varying viscosities (0.1 and 0.3 Pa s) were studied. Attenuation coefficients for different shear-wave frequencies (100 to 600 Hz) were calculated. Derived viscosity values had a maximum standard deviation of 9%, and these values were consistent with the independent measurements reported in a previous study using nonoptical methods.

  6. Direct measurement of strain rates in ductile shear zones: A new method based on syntectonic dikes

    NASA Astrophysics Data System (ADS)

    Sassier, C.; Leloup, P. H.; Rubatto, D.; Galland, O.; Yue, Y.; Lin, Ding

    2009-01-01

    We describe a new method to estimate directly ductile strain rates at an outcrop scale from the deformation of dikes emplaced within a shear zone. The method is tested in a well-constrained shear zone: the Ailao Shan-Red River shear zone, for which global strain rates can be calculated from published fault rates. The strain rate was determined by measuring independently the shear strain (?) recorded by the dikes and the age (t) of dikes emplacement. The shear strain was quantified by three different methods that take into account either the stretching of the dikes or their angle variations during deformation or both of them. The values of minimum shear strains range between 0.2 and 9.7 for the less to the most deformed dikes, respectively. The ages of dike emplacement were obtained by Th-Pb sensitive high-resolution ion microprobe (SHRIMP) dating of monazites. We obtained three groups of ages: the younger age is 22.55 ± 0.25 Ma, the intermediate age is 26.81 ± 0.66 Ma, and the oldest ages are 29.89 ± 0.46 Ma and 29.93 ± 0.38 Ma. The geochronological data are in agreement with the structural data, the most deformed dikes being the oldest. The minimum strain rates deduced from these measurements are 3 to 4 × 10-14 s-1, which is consistent with previous estimates of geological strain rates in ductile shear zones.

  7. Enhancement of human mesenchymal stem cell infiltration into the electrospun poly(lactic-co-glycolic acid) scaffold by fluid shear stress.

    PubMed

    Kim, Min Sung; Lee, Mi Hee; Kwon, Byeong-Ju; Koo, Min-Ah; Seon, Gyeung Mi; Park, Jong-Chul

    2015-07-17

    The infiltration of the cells into the scaffolds is important phenomenon to give them good biocompatibility and even biodegradability. Fluid shear stress is one of the candidates for the infiltration of cells into scaffolds. Here we investigated the directional migration of human mesenchymal stem cells and infiltration into PLGA scaffold by fluid shear stress. The human mesenchymal stem cells showed directional migrations following the direction of the flow (8, 16 dyne/cm(2)). In the scaffold models, the fluid shear stress (8 dyne/cm(2)) enhanced the infiltration of cells but did not influence on the infiltration of Poly(lactic-co-glycolic acid) particles. PMID:26002463

  8. Extracellular Bacterial Pathogen Induces Host Cell Surface Reorganization to Resist Shear Stress

    PubMed Central

    Mikaty, Guillain; Soyer, Magali; Mairey, Emilie; Henry, Nelly; Dyer, Dave; Forest, Katrina T.; Morand, Philippe; Guadagnini, Stéphanie; Prévost, Marie Christine; Nassif, Xavier; Duménil, Guillaume

    2009-01-01

    Bacterial infections targeting the bloodstream lead to a wide array of devastating diseases such as septic shock and meningitis. To study this crucial type of infection, its specific environment needs to be taken into account, in particular the mechanical forces generated by the blood flow. In a previous study using Neisseria meningitidis as a model, we observed that bacterial microcolonies forming on the endothelial cell surface in the vessel lumen are remarkably resistant to mechanical stress. The present study aims to identify the molecular basis of this resistance. N. meningitidis forms aggregates independently of host cells, yet we demonstrate here that cohesive forces involved in these bacterial aggregates are not sufficient to explain the stability of colonies on cell surfaces. Results imply that host cell attributes enhance microcolony cohesion. Microcolonies on the cell surface induce a cellular response consisting of numerous cellular protrusions similar to filopodia that come in close contact with all the bacteria in the microcolony. Consistent with a role of this cellular response, host cell lipid microdomain disruption simultaneously inhibited this response and rendered microcolonies sensitive to blood flow–generated drag forces. We then identified, by a genetic approach, the type IV pili component PilV as a triggering factor of plasma membrane reorganization, and consistently found that microcolonies formed by a pilV mutant are highly sensitive to shear stress. Our study shows that bacteria manipulate host cell functions to reorganize the host cell surface to form filopodia-like structures that enhance the cohesion of the microcolonies and therefore blood vessel colonization under the harsh conditions of the bloodstream. PMID:19247442

  9. The atherosusceptible endothelium: endothelial phenotypes in complex haemodynamic shear stress regions in vivo

    PubMed Central

    Davies, Peter F.; Civelek, Mete; Fang, Yun; Fleming, Ingrid

    2013-01-01

    Atherosclerosis initiates at predictable focal sites and develops to a spatially regional disease with limited distribution. There is compelling evidence that links haemodynamics to the localized origin of atherosclerotic lesions. Arterial flow in vivo is unsteady, dynamically complex, and regionally variable. Sites susceptible to atherosclerosis near arterial branches and curves are associated with regions of disturbed blood flow that contain repetitive phases of flow reversal resulting in steep multidirectional temporal and spatial gradients of wall shear stresses. Endothelium in atherosusceptible regions relative to protected sites shows activation of endoplasmic reticulum (ER) stress and the unfolded protein response (UPR), the altered expression of pro-inflammatory Nuclear Factor kappa B (NF?B) and oxidant/antioxidant pathways, and low expression of major protective factors, notably endothelial nitric oxide synthase and Kruppel-like Factors KLF2 and KLF4. At some atherosusceptible locations, reactive oxygen species levels are significantly elevated. Here we describe flow-related phenotypes identified in steady-state in vivo and outline some of the molecular mechanisms that may contribute to pre-lesional atherosusceptibility as deduced from complementary cell experiments in vitro. We conclude that disturbed flow is a significant local risk factor for atherosclerosis that induces a chronic low-level inflammatory state, an adaptive response to ensure continued function at the expense of increased susceptibility to atherogenesis. Surprisingly, when challenged by short-term hypercholesterolaemia in vivo, atherosusceptible endothelial phenotype was resistant to greater pro-inflammatory expression, suggesting that sustained hyperlipidaemia is required to overcome these protective characteristics. PMID:23619421

  10. Wall shear stress-based model for adhesive dynamics of red blood cells in malaria.

    PubMed

    Fedosov, Dmitry A; Caswell, Bruce; Karniadakis, George Em

    2011-05-01

    Red blood cells (RBCs) infected by the Plasmodium falciparum (Pf-RBCs) parasite lose their membrane deformability and they also exhibit enhanced cytoadherence to vascular endothelium and other healthy and infected RBCs. The combined effect may lead to severe disruptions of normal blood circulation due to capillary occlusions. Here we extend the adhesion model to investigate the adhesive dynamics of Pf-RBCs as a function of wall shear stress (WSS) and other parameters using a three-dimensional, multiscale RBC model. Several types of adhesive behavior are identified, including firm adhesion, flipping dynamics, and slow slipping along the wall. In particular, the flipping dynamics of Pf-RBCs observed in experiments appears to be due to the increased stiffness of infected cells and the presence of the solid parasite inside the RBC, which may cause an irregular adhesion behavior. Specifically, a transition from crawling dynamics to flipping behavior occurs at a Young's modulus approximately three times larger than that of healthy RBCs. The simulated dynamics of Pf-RBCs is in excellent quantitative agreement with available microfluidic experiments if the force exerted on the receptors and ligands by an existing bond is modeled as a nonlinear function of WSS. PMID:21539775

  11. Wall Shear Stress-Based Model for Adhesive Dynamics of Red Blood Cells in Malaria

    PubMed Central

    Fedosov, Dmitry A.; Caswell, Bruce; Karniadakis, George Em

    2011-01-01

    Red blood cells (RBCs) infected by the Plasmodium falciparum (Pf-RBCs) parasite lose their membrane deformability and they also exhibit enhanced cytoadherence to vascular endothelium and other healthy and infected RBCs. The combined effect may lead to severe disruptions of normal blood circulation due to capillary occlusions. Here we extend the adhesion model to investigate the adhesive dynamics of Pf-RBCs as a function of wall shear stress (WSS) and other parameters using a three-dimensional, multiscale RBC model. Several types of adhesive behavior are identified, including firm adhesion, flipping dynamics, and slow slipping along the wall. In particular, the flipping dynamics of Pf-RBCs observed in experiments appears to be due to the increased stiffness of infected cells and the presence of the solid parasite inside the RBC, which may cause an irregular adhesion behavior. Specifically, a transition from crawling dynamics to flipping behavior occurs at a Young's modulus approximately three times larger than that of healthy RBCs. The simulated dynamics of Pf-RBCs is in excellent quantitative agreement with available microfluidic experiments if the force exerted on the receptors and ligands by an existing bond is modeled as a nonlinear function of WSS. PMID:21539775

  12. Recapitulating physiological and pathological shear stress and oxygen to model vasculature in health and disease

    PubMed Central

    Abaci, Hasan Erbil; Shen, Yu-I; Tan, Scott; Gerecht, Sharon

    2014-01-01

    Studying human vascular disease in conventional cell cultures and in animal models does not effectively mimic the complex vascular microenvironment and may not accurately predict vascular responses in humans. We utilized a microfluidic device to recapitulate both shear stress and O2 levels in health and disease, establishing a microfluidic vascular model (?VM). Maintaining human endothelial cells (ECs) in healthy-mimicking conditions resulted in conversion to a physiological phenotype namely cell elongation, reduced proliferation, lowered angiogenic gene expression and formation of actin cortical rim and continuous barrier. We next examined the responses of the healthy ?VM to a vasotoxic cancer drug, 5-Fluorouracil (5-FU), in comparison with an in vivo mouse model. We found that 5-FU does not induce apoptosis rather vascular hyperpermeability, which can be alleviated by Resveratrol treatment. This effect was confirmed by in vivo findings identifying a vasoprotecting strategy by the adjunct therapy of 5-FU with Resveratrol. The ?VM of ischemic disease demonstrated the transition of ECs from a quiescent to an activated state, with higher proliferation rate, upregulation of angiogenic genes, and impaired barrier integrity. The ?VM offers opportunities to study and predict human ECs with physiologically relevant phenotypes in healthy, pathological and drug-treated environments. PMID:24818558

  13. Focal association between wall shear stress and clinical coronary artery disease progression.

    PubMed

    Timmins, Lucas H; Molony, David S; Eshtehardi, Parham; McDaniel, Michael C; Oshinski, John N; Samady, Habib; Giddens, Don P

    2015-01-01

    Wall shear stress (WSS) has been investigated as a potential prospective marker to identify rapidly progressing coronary artery disease (CAD) and potential for lesions to acquire vulnerable characteristics. Previous investigations, however, are limited by a lack of understanding of the focal association between WSS and CAD progression (i.e., data are notably spatially averaged). Thus, the aim of this investigation was to examine the focal association between WSS and coronary atherosclerosis progression, and compare these results to those determined by spatial averaging. Five patients with CAD underwent baseline and 6-month follow-up angiographic and virtual histology-intravascular ultrasound imaging to quantify CAD progression. Patient-specific computational fluid dynamics models were constructed to compute baseline WSS values, which were either averaged around the entire artery circumference or examined in focal regions (sectors). Analysis of data within each sector (n = 3871) indicated that circumferentially averaged and sector WSS values were statistically different (p < 0.05) and exhibited poor agreement (concordance correlation coefficient = 0.69). Furthermore, differences were observed between the analysis techniques when examining the association of WSS and CAD progression. This investigation highlights the importance of examining spatially heterogeneous variables at a focal level to reduce the affect of data reduction and warrants implementation in a larger clinical study to determine the predictive power in prospectively identifying rapidly progressing and/or vulnerable coronary plaques. PMID:25316593

  14. Influence of Oscillating Flow on LDL Transport and Wall Shear Stress in the Normal Aortic Arch

    PubMed Central

    Soulis, J; Giannoglou, G; Dimitrakopoulou, M; Papaioannou, V; Logothetides, S; Mikhailidis, D

    2009-01-01

    Lipid accumulation in the aortic wall is an important factor in the development of atherosclerosis. The Low Density Lipoprotein (LDL) at the surface of the endothelium in relation to Wall Shear Stress (WSS) in the normal human aortic arch under unsteady, normal flow and mass conditions was computationally analysed. Concave sides of the aortic arch exhibit, relatively to the convex ones, elevated LDL levels at the surface of the endothelium for all time steps. At the peak systolic velocity, the LDL level reaches a value 23.0% higher than that at entrance in the ascending-descending aorta region. The corresponding LDL levels at the surface of the endothelium for the near minimum entrance velocity instant reaches 26.0%. During the cardiac cycle, the highest area averaged normalized LDL taken up as compared to the lowest one is 0.69%. WSS plays an important role in the lipid accumulation. Low WSS regions are exposed to high LDL levels at the surface of the endothelium. Regions of elevated LDL levels do not necessarily co-locate to the sites of lowest WSS. The near wall paths of the velocities might be the most important factor for the elevated LDL levels at the surface of the endothelium. PMID:19834577

  15. Effect of shear stress alteration on atherosclerotic plaque vulnerability in cholesterol-fed rabbits.

    PubMed

    den Dekker, Wijnand K; Tempel, Dennie; Speelman, Lambert; Huizingh, Jeroen; Ramos, Allan; Gijsen, Frank J; Wentzel, Jolanda J; Cheng, Caroline; Duckers, Henricus J

    2014-05-14

    Previously, we created an experimental murine model for the induction of vulnerable plaque (VP). Although this murine model offers the opportunity to study the different molecular biological pathways that regulate plaque destabilization, the size of the animals severely limits the use of the model for in vivo diagnostics and percutaneous interventions. This study aimed to create a VP model in the rabbit, based on the murine model, to aid the assessment and development of novel diagnostic and interventional tools. New Zealand white rabbits were fed on a 2% cholesterol diet. After 1 week, a shear stress-altering device was implanted around the right carotid artery. Twelve weeks after cast placement, the carotid artery was isolated and processed for (immuno-)histological analysis to evaluate the presence of a VP phenotype. Atherosclerotic plaques with high lipid and macrophage content, low vascular smooth muscle cell content and intimal neovascularization were located upstream and downstream of the cast. The plaques lacked a significant necrotic core. In conclusion, we were able to create atherosclerotic plaques with a phenotype beyond that of a fatty streak, with a high percentage of lipids and macrophages, a thick cap with some vascular smooth muscle cells and neovascularization. However, as there was only a small necrotic core, the overall phenotype seems less vulnerable as compared to the thin fibrous cap atheroma in patients. PMID:24829311

  16. Statistical wall shear stress maps of ruptured and unruptured middle cerebral artery aneurysms

    PubMed Central

    Goubergrits, L.; Schaller, J.; Kertzscher, U.; van den Bruck, N.; Poethkow, K.; Petz, Ch.; Hege, H.-Ch.; Spuler, A.

    2012-01-01

    Haemodynamics and morphology play an important role in the genesis, growth and rupture of cerebral aneurysms. The goal of this study was to generate and analyse statistical wall shear stress (WSS) distributions and shapes in middle cerebral artery (MCA) saccular aneurysms. Unsteady flow was simulated in seven ruptured and 15 unruptured MCA aneurysms. In order to compare these results, all geometries must be brought in a uniform coordinate system. For this, aneurysms with corresponding WSS data were transformed into a uniform spherical shape; then, all geometries were uniformly aligned in three-dimensional space. Subsequently, we compared statistical WSS maps and surfaces of ruptured and unruptured aneurysms. No significant (p > 0.05) differences exist between ruptured and unruptured aneurysms regarding radius and mean WSS. In unruptured aneurysms, statistical WSS map relates regions with high (greater than 3 Pa) WSS to the neck region. In ruptured aneurysms, additional areas with high WSS contiguous to regions of low (less than 1 Pa) WSS are found in the dome region. In ruptured aneurysms, we found significantly lower WSS. The averaged aneurysm surface of unruptured aneurysms is round shaped, whereas the averaged surface of ruptured cases is multi-lobular. Our results confirm the hypothesis of low WSS and irregular shape as the essential rupture risk parameters. PMID:21957117

  17. Effect of shear stress and free radicals induced by ultrasound on erythrocytes

    SciTech Connect

    Kondo, T.; Fukushima, Y.; Kon, H.; Riesz, P.

    1989-03-01

    The present study was undertaken to elucidate the mechanism of hemolysis induced by ultrasound. Ar or N2O gas was used to distinguish between cavitation with or without free radical formation (hydroxyl radicals and hydrogen atoms). Free radical formation was examined by the method of spin trapping combined with ESR. After sonication of erythrocyte suspensions, several structural and functional parameters of the erythrocyte membrane--hemolysis, membrane fluidity, membrane permeability, and membrane deformability--were examined. Although free radical formation was observed in the erythrocyte suspensions sonicated in the presence of Ar, no free radical formation was observed in the presence of N2O. However, the hemolysis behavior induced by ultrasound was similar in the presence of Ar or N2O. The membrane fluidity, permeability, and deformability of the remaining unlysed erythrocytes after sonication in the presence of Ar or N2O were unchanged and identical to those of the control cells. On the other hand, after gamma irradiation (700 Gy), the hemolysis behavior was quite different from that after sonication, and the membrane properties were significantly changed. These results suggest that hemolysis induced by sonication was due to mechanical shearing stress arising from cavitation, and that the membrane integrity of the remaining erythrocytes after sonication was the same as that of control cells without sonication. The triatomic gas, N2O, may be useful for ultrasonically disrupting cells without accompanying free radical formation.

  18. Pre-registration diploma student nurse stress and coping measures

    Microsoft Academic Search

    William Evans; Billy Kelly

    2004-01-01

    The aim of this study is to examine the stress experiences and coping abilities of student nurses. A survey design was employed to examine the stress experiences of Diploma student nurses in a large Dublin Teaching Hospital. A questionnaire was utilized that measured and explored five specific constructs pertinent to student nurse stress. These included clinical stress, academic stress, coping,

  19. A mechanical model of the San Andreas fault and SAFOD Pilot Hole stress measurements

    USGS Publications Warehouse

    Chery, J.; Zoback, M.D.; Hickman, S.

    2004-01-01

    Stress measurements made in the SAFOD pilot hole provide an opportunity to study the relation between crustal stress outside the fault zone and the stress state within it using an integrated mechanical model of a transform fault loaded in transpression. The results of this modeling indicate that only a fault model in which the effective friction is very low (<0.1) through the seismogenic thickness of the crust is capable of matching stress measurements made in both the far field and in the SAFOD pilot hole. The stress rotation measured with depth in the SAFOD pilot hole (???28??) appears to be a typical feature of a weak fault embedded in a strong crust and a weak upper mantle with laterally variable heat flow, although our best model predicts less rotation (15??) than observed. Stress magnitudes predicted by our model within the fault zone indicate low shear stress on planes parallel to the fault but a very anomalous mean stress, approximately twice the lithostatic stress. Copyright 2004 by the American Geophysical Union.

  20. In situ speckle observation of Tyrano\\/BMAS composites in shear strength measurements

    Microsoft Academic Search

    Yasuhiro Tanabe; Yohsuke Ishiguro; Eiichi Yasuda

    2003-01-01

    Strain profiles of specimens during interlaminar shear strength tests, short beam and double-notched compression, were measured by a speckle interference method using TyranoTR-related fiber-reinforced BaO–MgO–Al2O3–SiO2 glass matrix composites with different surface finished fibers. The speckle interference method could detect changes in shear strain during the tests before the initiation of crack(s). Crack initiation could be detected earlier\\/easier by the speckle