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1

Unsteady distributed wall shear stress measurements in fluid flows  

NASA Astrophysics Data System (ADS)

Wall-bounded flows are amongst the most common flows encountered in fluid mechanics. Wall shear stress on the walls of these flow fields is an important engineering quantity as it is responsible for skin friction drag, which is a significant portion of the drag on bodies ranging from airplanes to flow in biological systems. Measuring, understanding and eventually controlling the wall shear stress has implicit financial significance. In general there is limited literature reporting unsteady, distributed wall shear stress measurements, especially in air, due to the lack of sensors to carry out such measurements. This work is a small step in the direction of filling this gap in the literature. A wall shear stress sensor, referred to as the micro-pillar wall shear stress sensor is presented from concept to actual measurements in a wall jet flow field. The micro-pillar shear stress sensor is based on the principle that a micro-pillar on the wall of a wall-bounded flow deflects an amount proportional to the drag force experienced by it. This drag force in turn is proportional to the wall shear stress. Hence, tracking the tip deflection of an array of micro-pillars provides a means to measure the unsteady, distributed wall shear stress. The sensor from design to manufacture along with static and dynamic characterization is presented. It's ability to measure unsteady, distributed wall shear stress is studied using demonstrative experiments. Finally, wall shear stress measurements are carried out on the wall of a three-dimensional turbulent wall jet. The wall jet is subsequently excited and the effect of excitation on the wall shear stress in the near jet exit flow field is studied.

Gnanamanickam, Ebenezer P.

2

An in-plane cantilever for wall shear stress measurement  

NASA Astrophysics Data System (ADS)

A sensor capable of measuring small shear stresses in wind tunnel applications is presented. The sensor utilizes an in-plane cantilever concept for shear stress measurement, designed to minimize intrusiveness into the airflow and allow easy incorporation into wind tunnel test models. The sensor operates independently of input voltage, and can measure <1 Pa shear stresses with a sensitivity of 8.6 (mV V-1) Pa. Altering the geometry of the sensor has a direct effect on the sensitivity and so can be used to adapt the sensor for different applications.

Allen, N. J.; Sims-Williams, D. B.; Wood, D.

2012-07-01

3

Experimental measurements of the normal stresses in sheared Stokesian suspensions  

NASA Astrophysics Data System (ADS)

We present experimental measurements of the normal stresses in sheared Stokesian suspensions. Though the suspending fluid is Newtonian, dispersing rigid non-Brownian particles in it yields a suspension that is non-Newtonian, as it exhibits normal stress differences and an excess isotropic pressure in viscometric flows. At small to moderate concentrations, the normal stresses are very small in magnitude, and hence difficult to measure. This difficulty is compounded by the presence of noise due to unavoidable experimental artifacts. Owing to these limitations, most measurements reported earlier were carried out at relatively high particle concentrations, and some at shear rates large enough that the effects of particle and fluid inertia may have been significant. In our study, we have used a novel technique to measure the small stress levels. This was achieved by applying a sinusoidally varying shear rate with a fixed (low) frequency superimposed on a constant shear rate, and using a lock-in amplifier to measure the Fourier component of the same frequency in the stress signal. We have measured normal stresses in cylindrical-Couette and parallel-plate geometries, and combined these measurements to determine the two normal stress differences for particle volume fractions in the range 0.3 0.45. While the normal stresses are very small at low concentrations, they rise rapidly with increasing concentration. The normal stresses vary linearly with the magnitude of the shear rate, and are independent of its sign. In contrast to polymeric solutions, both normal stress differences are negative, and the first normal stress difference is significantly smaller in magnitude. We compare our data with the results of earlier studies, and observe good agreement.

Singh, Anugrah; Nott, Prabhu R.

2003-09-01

4

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

NASA Astrophysics Data System (ADS)

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

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

2012-10-01

5

Unsteady distributed wall shear stress measurements in fluid flows  

Microsoft Academic Search

Wall-bounded flows are amongst the most common flows encountered in fluid mechanics. Wall shear stress on the walls of these flow fields is an important engineering quantity as it is responsible for skin friction drag, which is a significant portion of the drag on bodies ranging from airplanes to flow in biological systems. Measuring, understanding and eventually controlling the wall

Ebenezer P Gnanamanickam

2010-01-01

6

The Use of Mechanical Twinning in Minerals as a Measure of Shear Stress Magnitudes  

Microsoft Academic Search

Mechanical twinning of minerals is a deformation process that occurs to a first order under a critical resolved shear stress that is independent of temperature and strain rate. Thus unlike critical shear stresses for intracrystalline slip, extrapolations from laboratory measurements to the field situation are not necessary. The critical shear stress for twinning does not appear to be affected by

Terry E. Tullis

1980-01-01

7

The use of mechanical twinning in minerals as a measure of shear stress magnitudes  

Microsoft Academic Search

Mechanical twinning of minerals is a deformation process that occurs to a first order under a critical resolved shear stress that is independent of temperature and strain rate. Thus unlike critical shear stresses for intracrystalline slip, extrapolations from laboratory measurements to the field situation are not necessary. The critical shear stress for twinning does not appear to be affected by

Terry E. Tullis

1980-01-01

8

Effect of the Interfacial Stress Distribution on the Material Interfacial Shear Strength Measurement  

Microsoft Academic Search

An integrated experimental and numerical analysis is carried out to study the interfacial shear strength of bonded materials.\\u000a Two types of shear tests, namely the Iosipescu shear test, and the short-beam shear test are employed to understand the effect\\u000a of interfacial stress on the interfacial shear strength measurements. The measured average shear strengths are very close,\\u000a even though the interfacial

A. Krishnan; L. R. Xu

2010-01-01

9

Direct Measurement of Wave-Induced Bottom Shear Stress Under Irregular Waves  

Microsoft Academic Search

\\u000a Wave-induced bottom shear stress is one of most important parameters in modelling of wave hydrodynamics and coastal sediment\\u000a transport, but has not been accurately estimated so far. A new type of shear plate is developed to measure instantaneous wave\\u000a bottom shear stress under both regular and irregular waves. The shear plate directly measures instantaneous horizontal force\\u000a by applying the Wheatstone

Zaijin You; Baoshu Yin; Guang Huo

10

A method for measurement of turbulent wall shear stress  

Microsoft Academic Search

A cylinder is placed near the wall in the viscous sublayer of a turbulent boundary layer. It is suspended torsionally about its axis. The axis is parallel to the wall and transverse to the mean flow direction. The torque on the cylinder is proportional to the shear stress of the fluid on the wall below. In principle the torque is

Peter M. Wagner; Patrick Leehey

1987-01-01

11

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

PubMed Central

Aortic valve (AV) calcification is a highly prevalent disease with serious impact on mortality and morbidity. Although exact causes and mechanisms of AV calcification are unclear, previous studies suggest that mechanical forces play a role. Since calcium deposits occur almost exclusively on the aortic surfaces of AV leaflets, it has been hypothesized that adverse patterns of fluid shear stress on the aortic surface of AV leaflets promote calcification. The current study characterizes AV leaflet aortic surface fluid shear stresses using Laser Doppler velocimetry and an in vitro pulsatile flow loop. The valve model used was a native porcine valve mounted on a suturing ring and preserved using 0.15% glutaraldehyde solution. This valve model was inserted in a mounting chamber with sinus geometries, which is made of clear acrylic to provide optical access for measurements. To understand the effects of hemodynamics on fluid shear stress, shear stress was measured across a range of conditions: varying stroke volumes at the same heart rate and varying heart rates at the same stroke volume. Systolic shear stress magnitude was found to be much higher than diastolic shear stress magnitude due to the stronger flow in the sinuses during systole, reaching up to 20 dyn/cm2 at mid-systole. Upon increasing stroke volume, fluid shear stresses increased due to stronger sinus fluid motion. Upon increasing heart rate, fluid shear stresses decreased due to reduced systolic duration that restricted the formation of strong sinus flow. Significant changes in the shear stress waveform were observed at 90 beats/ min, most likely due to altered leaflet dynamics at this higher heart rate. Overall, this study represents the most well-resolved shear stress measurements to date across a range of conditions on the aortic side of the AV. The data presented can be used for further investigation to understand AV biological response to shear stresses.

Yap, Choon Hwai; Saikrishnan, Neelakantan; Tamilselvan, Gowthami

2011-01-01

12

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

PubMed

Aortic valve (AV) calcification is a highly prevalent disease with serious impact on mortality and morbidity. Although exact causes and mechanisms of AV calcification are unclear, previous studies suggest that mechanical forces play a role. Since calcium deposits occur almost exclusively on the aortic surfaces of AV leaflets, it has been hypothesized that adverse patterns of fluid shear stress on the aortic surface of AV leaflets promote calcification. The current study characterizes AV leaflet aortic surface fluid shear stresses using Laser Doppler velocimetry and an in vitro pulsatile flow loop. The valve model used was a native porcine valve mounted on a suturing ring and preserved using 0.15% glutaraldehyde solution. This valve model was inserted in a mounting chamber with sinus geometries, which is made of clear acrylic to provide optical access for measurements. To understand the effects of hemodynamics on fluid shear stress, shear stress was measured across a range of conditions: varying stroke volumes at the same heart rate and varying heart rates at the same stroke volume. Systolic shear stress magnitude was found to be much higher than diastolic shear stress magnitude due to the stronger flow in the sinuses during systole, reaching up to 20 dyn/cm(2) at mid-systole. Upon increasing stroke volume, fluid shear stresses increased due to stronger sinus fluid motion. Upon increasing heart rate, fluid shear stresses decreased due to reduced systolic duration that restricted the formation of strong sinus flow. Significant changes in the shear stress waveform were observed at 90 beats/min, most likely due to altered leaflet dynamics at this higher heart rate. Overall, this study represents the most well-resolved shear stress measurements to date across a range of conditions on the aortic side of the AV. The data presented can be used for further investigation to understand AV biological response to shear stresses. PMID:21416247

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

2011-03-18

13

Oscillatory motion based measurement method and sensor for measuring wall shear stress due to fluid flow  

DOEpatents

A shear stress sensor for measuring fluid wall shear stress on a test surface is provided. The wall shear stress sensor is comprised of an active sensing surface and a sensor body. An elastic mechanism mounted between the active sensing surface and the sensor body allows movement between the active sensing surface and the sensor body. A driving mechanism forces the shear stress sensor to oscillate. A measuring mechanism measures displacement of the active sensing surface relative to the sensor body. The sensor may be operated under periodic excitation where changes in the nature of the fluid properties or the fluid flow over the sensor measurably changes the amplitude or phase of the motion of the active sensing surface, or changes the force and power required from a control system in order to maintain constant motion. The device may be operated under non-periodic excitation where changes in the nature of the fluid properties or the fluid flow over the sensor change the transient motion of the active sensor surface or change the force and power required from a control system to maintain a specified transient motion of the active sensor surface.

Armstrong, William D. (Laramie, WY); Naughton, Jonathan (Laramie, WY); Lindberg, William R. (Laramie, WY)

2008-09-02

14

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

PubMed

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

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

2011-04-05

15

The use of mechanical twinning in minerals as a measure of shear stress magnitudes  

NASA Astrophysics Data System (ADS)

Mechanical twinning of minerals is a deformation process that occurs to a first order under a critical resolved shear stress that is independent of temperature and strain rate. Thus unlike critical shear stresses for intracrystalline slip, extrapolations from laboratory measurements to the field situation are not necessary. The critical shear stress for twinning does not appear to be affected by hydrostatic pressure or by fluid pore pressure. Thus unlike the situation when coefficients of friction are used to infer stresses on faults, there need be no uncertainty in the shear stresses that caused twinning in nature, even if the depth of burial or the fluid pressure is unknown. Calcite, dolomite, and clinopyroxene are the rock-forming minerals with the greatest promise for the use of this technique to determine the magnitudes of paleostresses. The critical shear stresses for calcite, dolomite, and clinopyroxene are about 100, 1000, and 1400 bars, respectively. These stresses are in an interesting range for helping to resolve controversies concerning the magnitudes of stresses accompanying faulting. The method has not yet been used extensively, but in separate previous studies, differential stresses as high as 1250 and 2800 bars appear to have accompanied thrust faulting.

Tullis, Terry E.

1980-11-01

16

Shear stress distribution measurement around adherent red cell in microchannel correlated with Poly-L-lysine concentration  

Microsoft Academic Search

Measurement of shear stress distributions surrounding an adherent human red blood cell in microchannel flow was found using an experimental micron resolution particle image velocimetry technique. One micron accurate velocity field measurements can be analyzed using a post processing differencing algorithm to supply shear stress distribution measurements surrounding the cell. The cell to channel height aspect ratio was small enough

Matthew S. Pommer; Carl D. Meinhart

2004-01-01

17

Shear modulus and yield stress measurements of attractive alumina particle networks in aqueous slurries  

Microsoft Academic Search

The shear modulus and yield stress measurements of attractive alumina particle networks in aqueous slurries was determined as a function of volume fraction (0.1 to 0.5), pH (2, 4, 5, 6, and 9), and salt (NHâCl) concentration (0.25M to 2.5M) using both vane and couette rheological tools. Consistent with previous observations concerning the relative strength of attractive particle networks, the

Joseph A. Yanez; Toshi Shikata; Fred F. Lange; Dale S. Pearson

1996-01-01

18

A simple measure of flow disorder and wall shear stress in phase contrast MRI.  

PubMed

A method for estimating the standard deviation of velocity within a voxel is proposed. This estimate is based on data collected using a phase-contrast MRI technique. Simulations are presented to characterize the estimate and in vivo data are shown. Several different uses of the estimate are proposed, including obtaining a measure of wall shear stress, aiding in data combination from different phase-contrast MRI datasets, and mitigation of flow void artifacts. PMID:12594758

Pipe, James G

2003-03-01

19

Estimates of Shear Stress and Measurements of Water Levels in the Lower Fox River near Green Bay, Wisconsin  

USGS Publications Warehouse

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.

Westenbroek, Stephen M.

2006-01-01

20

Use of the thick adherend shear test for shear stress-strain measurements of stiff and flexible adhesives  

Microsoft Academic Search

Five commercial structural adhesives were tested using the thick adherend shear test (TAST). These adhesives have mechanical properties ranging from those of high-strength, heat-cured epoxies to ductile, acrylic-based materials. Consideration was given to the adherend selection and dimensions to approach a uniform shear stress-strain in the bonded area, so that the test could be used with both stiff and flexible

F. Kadioglu; L. F. Vaughn; F. J. Guild; R. D. Adams

2002-01-01

21

Fluid wall shear stress measurements in a model of the human abdominal aorta: oscillatory behavior and relationship to atherosclerosis.  

PubMed

Clinically significant atherosclerosis in the human aorta is most common in the infrarenal segment. This study was initiated to test the hypothesis that flowfield properties are closely related to the localization of plaques in this segment of the arterial system. Wall shear stress was calculated from magnetic resonance velocity measurements of pulsatile flow in an anatomically accurate model of the human abdominal aorta. The wall shear stress values were compared with intimal thickening from 15 post-mortem aortas measured by quantitative morphometry of histological cross sections obtained at standard locations. Wall shear stress oscillated in direction throughout most of the infrarenal aorta, most prominently in the distal region. The time-averaged mean wall shear stress (-1.7 to 1.4 dyn/cm2) was lowest near the posterior wall in this region. These hemodynamic parameters coincided with the locations of maximal intimal thickening. Statistical correlation between oscillatory shear and intimal thickness yielded r = 0.79, P < 0.00001. Low mean shear stresses correlated nearly as well (r = -0.75, P < 0.00005). Comparison of our data with surface maps of Sudan Red staining and early lesions as reported by others revealed similar conclusions. In contrast, pulse and maximum shear stresses did not correlate with plaque localization as has been shown for other sites of selective involvement by atherosclerosis (r < 0.345). Simulated exercise conditions markedly changed the magnitude and pattern of wall shear stress in the distal abdominal aorta. These results demonstrate that in the infrarenal aorta, regions of low mean and oscillating wall shear stresses are predisposed to the development of plaque while regions of relatively high wall shear stress tend to be spared. PMID:7848371

Moore, J E; Xu, C; Glagov, S; Zarins, C K; Ku, D N

1994-10-01

22

Aeolian shear stress ratio measurements within mesquite-dominated landscapes of the Chihuahuan Desert, New Mexico, USA  

NASA Astrophysics Data System (ADS)

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.

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

2006-12-01

23

Watershed Scale Shear Stress From Tethersonde Wind Profile Measurements Under Near Neutral and Unstable Atmospheric Stability  

NASA Astrophysics Data System (ADS)

Mean wind speed profiles were measured in the atmospheric surface layer, using a tethersonde system, above the Ojai Valley Watershed in southern California. The valley is mainly planted with mature avocado and orange trees. The surface shear stress and latent and sensible heat fluxes were measured above the trees which are up to 9 m in height. Near-neutral wind speed profile measurements allowed the determination of the watershed surface roughness (z0 = 1.4 m) and the momentum displacement height (d0 = 7.0 m). The wind speed measurements obtained under unstable atmospheric stability were analyzed using Monin-Obukhov similarity theory. New stability correction functions proposed based on theory and experiments of Kader-Yaglom as well as the now classic Businger-Dyer type functions were tested. The watershed shear stress values calculated using the surface layer wind speed profiles with the new Monin-Obukhov stability functions were found to be improved in comparison with the values obtained with the Businger-Dyer functions under strongly unstable stability conditions. The Monin-Obukhov model with the Businger-Dyer stability correction function underpredicted the momentum flux by 25% under strongly unstable stability conditions, while the new Kader-Yaglom formulation compared well on average (R2 = 0.77) with the surface eddy correlation measurements for all atmospheric stability conditions. The unstable 100-m drag coefficient was found to be u*2/V1002 = 0.0182.

Parlange, M. B.; Katul, G. G.

1995-04-01

24

Experimental technique of measuring dynamic fluid shear stress on the aortic surface of the aortic valve leaflet.  

PubMed

Aortic valve (AV) calcification is a highly prevalent disease with serious impact on mortality and morbidity. The exact cause and mechanism of the progression of AV calcification is unknown, although mechanical forces have been known to play a role. It is thus important to characterize the mechanical environment of the AV. In the current study, we establish a methodology of measuring shear stresses experienced by the aortic surface of the AV leaflets using an in vitro valve model and adapting the laser Doppler velocimetry (LDV) technique. The valve model was constructed from a fresh porcine aortic valve, which was trimmed and sutured onto a plastic stented ring, and inserted into an idealized three-lobed sinus acrylic chamber. Valve leaflet location was measured by obtaining the location of highest back-scattered LDV laser light intensity. The technique of performing LDV measurements near to biological surfaces as well as the leaflet locating technique was first validated in two phantom flow systems: (1) steady flow within a straight tube with AV leaflet adhered to the wall, and (2) steady flow within the actual valve model. Dynamic shear stresses were then obtained by applying the techniques on the valve model in a physiologic pulsatile flow loop. Results show that aortic surface shear stresses are low during early systole (<5 dyn/cm²) but elevated to its peak during mid to late systole at about 18-20 dyn/cm². Low magnitude shear stress (<5 dyn/cm²) was observed during early diastole and dissipated to zero over the diastolic duration. Systolic shear stress was observed to elevate only with the formation of sinus vortex flow. The presented technique can also be used on other in vitro valve models such as congenitally geometrically malformed valves, or to investigate effects of hemodynamics on valve shear stress. Shear stress data can be used for further experiments investigating effects of fluid shear stress on valve biology, for conditioning tissue engineered AV, and to validate numerical simulations. PMID:21744927

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

2011-06-01

25

Shear Stress Measurements During High-Speed Impacts with Sand and Glass Beads  

NASA Astrophysics Data System (ADS)

Right-circular (15 mm OD x 26 mm) and spherical (10mm) projectiles were fired vertically-downward (300-1,000 m/s) into acrylic containers (100-190 mm ID) containing quartz Eglin sand and solid, amorphous glass beads. A variety of shearing conditions were observed; allowing estimation of stresses along the various shearing surfaces. Under certain conditions a false nose was formed of partially-crushed particles on the front of the projectile and the particulate media sheared along the false nose surface. The included angle of the false nose varies with impact velocity (up to a velocity of 375 m/s) and appears to be a residual artifact of initial impact conditions. An analytical model is presented to explain the false nose formation and stability during the projectile deceleration. Other impact conditions resulted in shearing along the surface or surface abrasion. Experimental and theoretical results will be presented.

Cooper, William; Watanabe, Keiko; Yamamoto, Hiroaki; Tanaka, Koichi; Takayama, Kazuyoshi

2011-06-01

26

Shear stress measurements during high-speed impacts with sand and glass beads  

NASA Astrophysics Data System (ADS)

Right-circular (? 15 mm x 26 mm) and spherical (? 10mm) projectiles were fired verticallydownward (300-1,000 m/s) into acrylic containers (? 100-190 mm) containing either quartz Eglin sand or solid, amorphous glass beads. A variety of shearing conditions were observed; allowing estimation of stresses along the various shearing surfaces. Under certain conditions a false nose was formed of partially-crushed particles on the front of the projectile and the particulate media sheared along the false nose surface. The included angle of the false nose varies with impact velocity (up to a velocity of 375 m/s) and appears to be a residual artifact of initial impact conditions. An analytical model is presented to explain the false nose formation and stability during the projectile deceleration. Other impact conditions (especially on the front face of the spherical projectiles) resulted in shearing along the surface or surface abrasion.

Cooper, William

2012-03-01

27

Wall Shear Stress Measurements with a PWM-CTA Driven "Ho-Sensor"  

NASA Astrophysics Data System (ADS)

The MSU developed Pulse Width Modulated-Constant Temperature Anemometer (PWM-CTA) (Foss, J.F., Bohl, D.G. and Hicks, T.J. (1996) "The Pulse Width Modulated-Constant Temperature Anemometer," Meas. Sci. and Tech., vol. 7, pp. 1388-1395.) has been used to operate the shear stress sensor (developed by C-M Ho) (Ho, C.M. and Tai, Y.C., "MEMS and its Applications for Flow Control," J. of Fluids Engr., Vol. 118, pp. 437-447, 1996.) in the IIT shear stress channel. (turbulent shear stress levels of 0.5-8 Pa). The PWM-CTA was modified to a configuration in which the sensor was operated at R=1.2*1.33 kOhms. The resulting transfer function was relatively "flat" with tau/T=A+B(sigma)**n; A=0.424, B=0.0105, n=0.537 (std. dev.=.0613). A sample rate of 32 KHz and a master clock frequency of 525 MHz were used. These values yield a LSB resolution of 0.7 percent at the mid-range shear stress value of 4 Pa. Spectral values (up to the resolved frequency of 16 KHz) and the four moments of the distribution have been compared to the similar values acquired with a Disa 55M system anemometer.

Foss, John; Hicks, Theron; Hites, Michael; Ornt, William

1997-11-01

28

Measurement of the First Normal-Stress Difference at High Shear Rates for a Polyisobutylene/Decalin Solution 'D2',  

National Technical Information Service (NTIS)

Reasonable agreement is found between values of the first normal-stress difference N sub 1 for samples of D2, a polyisobutylene/decalin solution, measured in steady shear flow using three different instruments: a Weissenberg Rheogoniometer (a cone-plate r...

A. S. Lodge T. S. Al-Hadithi K. Walters

1987-01-01

29

Assessment of the wall shear stress measurement with arrayed micro hot-film sensors in a turbulent channel flow  

Microsoft Academic Search

Arrayed micro hot-film sensors for the measure- ment of the streamwise and spanwise wall shear stresses were developed and evaluated in a turbulent channel flow. The bandwidth of the sensor is found to be much narrower than previous estimates in the lit- erature. A numerical analysis of the unsteady thermal field around the sensor chip is made in order to

Takashi Yoshino; Yuji Suzuki; Nobuhide Kasagi; Shoji Kamiunten

2001-01-01

30

Friction ridges in cockroach climbing pads: anisotropy of shear stress measured on transparent, microstructured substrates  

Microsoft Academic Search

The contact of adhesive structures to rough surfaces has been difficult to investigate as rough surfaces are usually irregular\\u000a and opaque. Here we use transparent, microstructured surfaces to investigate the performance of tarsal euplantulae in cockroaches\\u000a (Nauphoeta cinerea). These pads are mainly used for generating pushing forces away from the body. Despite this biological function, shear stress\\u000a (force per unit

Christofer J. Clemente; Jan-Henning Dirks; David R. Barbero; Ullrich Steiner; Walter Federle

2009-01-01

31

Mean-Average Wall Shear Stress Measurements in the Common Carotid Artery  

Microsoft Academic Search

In this study we determined mean-average wall shear stress values in the common carotid artery and assessed if there is a difference in mean-average WSS between: 1) patients with bilateral carotid bifurcation disease and 2) similar-aged volunteers with no evidence of disease. Sixteen patients with bilateral disease of the carotid bifurcation, and 8 volunteers were included in the study. Magnetic

John N. Oshinski; Jay L. Curtin; Francis Loth

2006-01-01

32

The surface hot wire as a means of measuring mean and fluctuating wall shear stress  

Microsoft Academic Search

The paper describes some applications of a wall shear stress sensor technique which is based on hot-wire anemometry. The\\u000a “surface hot wire” is a flush-mounted thermal resistive wire with a tiny slot underneath. The arrangement of this sensor guarantees\\u000a an improved signal-to-noise ratio compared to a common surface hot film. The setup and the application of single sensors and\\u000a of

D. Sturzebecher; S. Anders; W. Nitsche

2001-01-01

33

Shear stress distribution measurement around adherent red cell in microchannel correlated with Poly-L-lysine concentration  

NASA Astrophysics Data System (ADS)

Measurement of shear stress distributions surrounding an adherent human red blood cell in microchannel flow was found using an experimental micron resolution particle image velocimetry technique. One micron accurate velocity field measurements can be analyzed using a post processing differencing algorithm to supply shear stress distribution measurements surrounding the cell. The cell to channel height aspect ratio was small enough to assume negelible pressure changes in the region of the red cell. This channel size enables accurate measurement of the Stokes flow while a poly-L-lysine coating is present in the channel to enable the red cell to adhere to the microchannel wall. A correlation between red cell lysis and poly-L-lysine concentration has also been found to conceptualize changes in membrane tension with varied concentration.

Pommer, Matthew S.; Meinhart, Carl D.

2004-11-01

34

Automatic Earthquake Shear Stress Measurement Method Developed for Accurate Time- Prediction Analysis of Forthcoming Major Earthquakes Along Shallow Active Faults  

NASA Astrophysics Data System (ADS)

The Serata Stressmeter has been developed to measure and monitor earthquake shear stress build-up along shallow active faults. The development work made in the past 25 years has established the Stressmeter as an automatic stress measurement system to study timing of forthcoming major earthquakes in support of the current earthquake prediction studies based on statistical analysis of seismological observations. In early 1982, a series of major Man-made earthquakes (magnitude 4.5-5.0) suddenly occurred in an area over deep underground potash mine in Saskatchewan, Canada. By measuring underground stress condition of the mine, the direct cause of the earthquake was disclosed. The cause was successfully eliminated by controlling the stress condition of the mine. The Japanese government was interested in this development and the Stressmeter was introduced to the Japanese government research program for earthquake stress studies. In Japan the Stressmeter was first utilized for direct measurement of the intrinsic lateral tectonic stress gradient G. The measurement, conducted at the Mt. Fuji Underground Research Center of the Japanese government, disclosed the constant natural gradients of maximum and minimum lateral stresses in an excellent agreement with the theoretical value, i.e., G = 0.25. All the conventional methods of overcoring, hydrofracturing and deformation, which were introduced to compete with the Serata method, failed demonstrating the fundamental difficulties of the conventional methods. The intrinsic lateral stress gradient determined by the Stressmeter for the Japanese government was found to be the same with all the other measurements made by the Stressmeter in Japan. The stress measurement results obtained by the major international stress measurement work in the Hot Dry Rock Projects conducted in USA, England and Germany are found to be in good agreement with the Stressmeter results obtained in Japan. Based on this broad agreement, a solid geomechanical basis to disclose an acting earthquake shear stress S at top of the tectonic plate is established at the depth of 600-800m (Window). This concept is supported by outcome of the Japanese government stress measurement made at the epicenter of the Kobe earthquake of 1995, where S is found to be less than 5 MPa. At the same time S at the earthquake active Ashio mining district was found to be 36 MPa (90 percent of maximum S) at Window. These findings led to formulation of a quantitative method proposed to monitor earthquake triggering potential in and around any growing earthquake stress nucleus along shallow active faults. For future earthquake time prediction, the Stressmeter can be applied first to survey general distribution of earthquake shear stress S along major active faults. A site with its shear stress greater than 30 MPa may be identified as a site of growing stress nucleus. A Stressmeter must be permanently buried at the site to monitor future stress growth toward a possible triggering by mathematical analysis of the stress excursion dynamics. This is made possible by the automatic stress measurement capability of the Stressmeter at a frequency up to 100 times per day. The significance of this approach is a possibility to save lives by time-prediction of a forthcoming major earthquake with accuracy in hours and minutes.

Serata, S.

2006-12-01

35

Measurement of the first normal-stress difference at high shear rates for a polyisobutylene\\/decalin solution “D2”  

Microsoft Academic Search

Reasonable agreement is found between values of the first normal-stress differenceN1 for samples of “D2”, a polyisobutylene\\/decalin solution, measured in steady shear flow using three different instruments: a Weissenberg Rheogoniometer (a cone-plate rotational rheometer), a Torsional Balance (plate-plate rotational) Rheometer, and a Stressmeter (a transverse-slot slit-die rheometer). Viscosity values are also in reasonable agreement. Ranges of variables common to at

A. S. Lodge; T. S. R. Al-Hadithi; K. Walters

1987-01-01

36

Direct, Real-Time Measurement of Shear Stress-Induced Nitric Oxide Produced from Endothelial Cells In Vitro  

PubMed Central

Nitric oxide (NO) produced by the endothelium is involved in the regulation of vascular tone. Decreased NO production or availability has been linked to endothelial dysfunction in hypercholesterolemia and hypertension. Shear stress-induced NO release is a well-established phenomenon, yet the cellular mechanisms of this response are not completely understood. Experimental limitations have hindered direct, real-time measurements of NO under flow conditions. We have overcome these challenges with a new design for a parallel-plate flow chamber. The chamber consists of two compartments, separated by a Transwell® membrane, which isolates a NO recording electrode located in the upper compartment from flow effects. Endothelial cells are grown on the bottom of the membrane, which is inserted into the chamber flush with the upper plate. We demonstrate for the first time direct real-time NO measurements from endothelial cells with controlled variations in shear stress. Step changes in shear stress from 0.1 dyn/cm2 to 6, 10 or 20 dyn/cm2 elicited a transient decrease in NO followed by an increase to a new steady state. An analysis of NO transport suggests that the initial decrease is due to the increased removal rate by convection as flow increases. Furthermore, the rate at which the NO concentration approaches the new steady state is related to the time-dependent cellular response rather than transport limitations of the measurement configuration. Our design offers a method for studying the kinetics of the signaling mechanisms linking NO production with shear stress as well as pathological conditions involving changes in NO production or availability.

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

2010-01-01

37

Soft-Matter Resistive Sensor for Measuring Shear and Pressure Stresses  

NASA Astrophysics Data System (ADS)

Building on emerging paradigms in soft-matter electronics, we introduce liquid-phase electronic sensors that simultaneously measures elastic pressure and shear deformation. The sensors are com- posed of a sheet of elastomer that is embedded with fluidic channels containing eutectic Gallium- Indium (EGaIn), a metal alloy that is liquid at room temperature. Applying pressure or shear traction to the surface of the surrounding elastomer causes the elastomer to elastically deform and changes the geometry and electrical properties of the embedded liquid-phase circuit elements. We introduce analytic models that predict the electrical response of the sensor to prescribed surface tractions. These models are validated with both Finite Element Analysis (FEA) and experimental measurements.

Tepayotl-Ramirez, Daniel; Roberts, Peter; Majidi, Carmel

2013-03-01

38

Stress and strain-controlled measurements of interfacial shear viscosity and viscoelasticity at liquid\\/liquid and gas\\/liquid interfaces  

Microsoft Academic Search

An interfacial rheometer for both stress- and strain-controlled measurements of shear rheological properties at liquid\\/liquid and gas\\/liquid interfaces is presented. The device is based on a rotating or oscillating biconical bob design in combination with a low friction electronically commutated motor system. The interfacial shear stress, viscosity, and dynamic moduli are obtained by solving the Stokes equations (low Reynolds number)

Philipp Erni; Peter Fischer; Erich J. Windhab; Victor Kusnezov; Heiko Stettin; Jörg Läuger

2003-01-01

39

Use of a sliding plate rheometer to measure the first normal stress difference at high shear rates  

Microsoft Academic Search

The use of a sliding plate rheometer (SPR) to determine the first normal stress difference of molten polymers and elastomers\\u000a at high shear rates is demonstrated. The simple shear flow in this instrument is not subject to the flow instabilities that\\u000a limit the use of rotational rheometers to shear rates often below 1 s?1. However, issues of secondary flow and wall

Junke Xu; Stéphane Costeux; John M. Dealy; Mark N. De Decker

2007-01-01

40

Direct Strain Oscillation: a new oscillatory method enabling measurements at very small shear stresses and strains  

Microsoft Academic Search

As shown previously, a rotational rheometer equipped with an electronically commutated motor (EC-motor) allows one to conduct stress and strain experiments with the same rheometer in rotational mode. A new method has now been developed to improve further strain controlled oscillatory measurements by adjusting the strain directly within a single oscillation cycle. Generally, a strain controlled oscillatory test in a

Jörg Läuger; Klaus Wollny; Siegfried Huck

2002-01-01

41

Stress-Strain Curves of Adsorbed Protein Layers at the Air\\/Water Interface Measured with Surface Shear Rheology  

Microsoft Academic Search

Interfacial shear properties of adsorbed protein layers at the air\\/water interface were determined using a Couette-type surface shear rheometer. Such experiments are often used to determine a steady-state ratio between stress and rate of strain, which is then denoted as \\

A. H. Martin; M. A. Bos; M. A. Cohen Stuart; T. van Vliet

2002-01-01

42

Shear stress and plaque development.  

PubMed

Although traditional cardiovascular risk factors 'prime the soil' for atherogenesis systemically, atherosclerosis primarily occurs in a site-specific manner with a predilection towards the inner wall of curvatures and outer wall of bifurcations with sparing of flow-dividers. Wall shear stress is a frictional force exerted parallel to the vessel wall that leads to alteration of the endothelial phenotype, endothelial cell signaling, gene and protein expression leading to a proinflammatory phenotype, reduced nitric oxide availability and disruption of the extracellular matrix, which in turn leads to plaque development. Clinical and experimental data are emerging that suggest the pathobiology associated with abnormal wall shear stress results in atherosclerotic plaque development and progression. PMID:20397828

Dhawan, Saurabh S; Avati Nanjundappa, Ravi P; Branch, Jonathan R; Taylor, W Robert; Quyyumi, Arshed A; Jo, Hanjoong; McDaniel, Michael C; Suo, Jin; Giddens, Don; Samady, Habib

2010-04-01

43

Shear rejuvenation, aging and shear banding in yield stress fluids  

Microsoft Academic Search

The purpose of this work is to simulate shear rejuvenation and aging effects in shear thinning yield stress fluids in a typical rotational rheometer and to provide a common framework to describe the behavior of yield stress materials in general. This is particularly important in the determination of material constants under both steady and unsteady conditions. The breakdown and buildup

Andreas N. Alexandrou; Nicholas Constantinou; Georgios Georgiou

2009-01-01

44

Role of hemodynamic shear stress in cardiovascular disease.  

PubMed

Atherosclerosis is the main cause of morbidity and mortality in the Western world. Inflammation and blood flow alterations are new markers emerging as possible determinants for the development of atherosclerotic lesions. In particular, blood flow exerts a shear stress on vessel walls that alters cell physiology. Shear stress arises from the friction between two virtual layers of a fluid and is induced by the difference in motion and viscosity between these layers. Regions of the arterial tree with uniform geometry are exposed to a unidirectional and constant flow, which determines a physiologic shear stress, while arches and bifurcations are exposed to an oscillatory and disturbed flow, which determines a low shear stress. Atherosclerotic lesions develop mainly in areas of low shear stress, while those exposed to a physiologic shear stress are protected. The presence of areas of the arterial tree with different wall shear stress may explain, in part, the different localization of atherosclerotic lesions in both coronary and extracoronary arteries. The measurement of this parameter may help in identifying atherosclerotic plaques at higher risk as well as in evaluating the efficacy of different pharmacological interventions. Moreover, an altered shear stress is associated with the occurrence of both aortic and intracranial aneurysms, possibly leading to their growth and rupture. Finally, the evaluation of shear stress may be useful for predicting the risk of developing restenosis after coronary and peripheral angioplasty and for devising a coronary stent with a strut design less thrombogenic and more conducive to endothelization. PMID:20970139

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

2010-09-18

45

Experimental validation of a dynamic resonant wall shear stress sensor  

NASA Astrophysics Data System (ADS)

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.

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

2012-10-01

46

Stimulated bioluminescence by fluid shear stress associated with pipe flow  

NASA Astrophysics Data System (ADS)

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

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

2011-01-01

47

Direct measurement of turbulent shear  

NASA Astrophysics Data System (ADS)

A photon correlation method is introduced for measuring components of the shear rate tensor in a turbulent soap film. This new scheme, which is also applicable to three-dimensional flows, is shown to give the same results as laser Doppler velocimetry, but with less statistical noise. The technique yields the mean shear rate s¯, its standard deviation ?, and a simple mathematical transform of the probability density function P(s) of the shear rate itself. We propose a new method that can directly measure shear in 2 dimensional turbulence. This proposed method has better signal to noise ratio than the conventional method. It also yields information about the probability distribution of shear. The proposed method is inexpensive and applicable to 3 dimensional turbulence.

Stefanus, S.; Steers, S.; Goldburg, W. I.

2011-11-01

48

Stress pulse attenuation in shear thickening fluid  

NASA Astrophysics Data System (ADS)

The stress pulse attenuation of the 62 vol/vol. % dense silica particle-ethylene glycol suspension was investigated by using a modified spilt Hopkinson pressure bar. In comparison to the neat ethylene glycol solution, the transmission pulse of the shear thickening is much weaker under the same impact condition. No energy loss is progressed for the neat ethylene glycol solution, thus it can be concluded that the energy dissipation behavior was happened in the silica particle based shear thickening fluid. In this work, the energy dissipation of the shear thickening fluid was reversible.

Jiang, Weifeng; Gong, Xinglong; Xuan, Shouhu; Jiang, Wanquan; Ye, Fang; Li, Xiaofeng; Liu, Taixiang

2013-03-01

49

Vane shear and rheological measurement of estuarine muds.  

National Technical Information Service (NTIS)

The principle aim of the present study is to determine the correlation of the yield stress of cohesive intertidal sediments measured with a field vane shear instrument with laboratory rheological measurements. The secondary aim is the correlation of soils...

A. E. James S. J. Stone

1990-01-01

50

Adjustable shear stress erosion and transport flume  

DOEpatents

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.

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

2002-01-01

51

Shear-induced particle migration in Couette and parallel-plate viscometers: NMR imaging and stress measurements  

Microsoft Academic Search

Couette and parallel plate viscometers are two commonly used flow geometries to characterize shear viscosity of concentrated suspensions. In Couette flow, it is well documented that prolonged shearing causes a decrease in the apparent viscosity of concentrated suspensions due to shear-induced particle migration from the annulus region to the stagnant region under the bob. In this study, the technique of

Andrea W. Chow; Steven W. Sinton; Joseph H. Iwamiya; Thomas S. Stephens

1994-01-01

52

Direct Measurement of Turbulent Shear  

NASA Astrophysics Data System (ADS)

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.

Stefanus, Stefanus; Steers, Stanley; Goldburg, Walter

2010-11-01

53

The Concept of Shear Stress in a Solid Material  

ERIC Educational Resources Information Center

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)

Culpin, M. F.

1974-01-01

54

Shear Stress-Strain Characteristics of Adhesive Layers  

Microsoft Academic Search

Shear behavior data of adhesives are evaluated by a specially constructed torsion device which enables recording of shear moment displacement relationship for thin adhesive layers. Shear strains and stresses were computed from the recorded torsional moment displacement curve by assuming linear shear strain distribution throughout the adhesive thickness and uniform shear strain distribution at the cross-sectional area. The general trend

Dan Peretz

1978-01-01

55

Determination of surface shear stress with the naphthalene sublimation technique  

NASA Astrophysics Data System (ADS)

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

Lee, J. A.; Greeley, Ronald

1987-05-01

56

Passive wireless wall shear stress sensors  

NASA Astrophysics Data System (ADS)

The design and realization of the first ever passive wireless wall shear stress sensors are presented. The sensors are capable of directly measuring shear forces, 4 mPa to 4 Pa, created at the solid-fluid boundary of a flow. To capture the spatially small structures of a turbulent flow, a micromachined, variable-capacitor floating element sensor is designed. Passive wireless capability is achieved with the addition of an inductive coil and interrogating antenna. These sensors will enable characterization of complex flow phenomena. The primary benefit of the system is that the sensors operate without the need of a direct electrical connection. This simplifies installation of the sensors and enables their placement in locations where the rest of the system either will not fit or cannot survive. By using a passive wireless technique, a power source is not required, extending the life of the sensor and simplifying fabrication. The system makes use of frequency separation, allowing one interrogating antenna to query multiple sensors configured as an array simultaneously. Two generations of the wireless sensor are presented. The design, fabrication, packaging, and characterization of two first-generation sensors have dynamic ranges of 37 and 52 dB. Following this work, specific design improvements were identified and integrated into a second-generation sensor design, resulting in an improvement to 62 dB dynamic range and an order of magnitude reduction in parasitic capacitance and humidity sensitivity. Ideas for a third generation are presented, but realization of this design is left for future work.

Sells, Jeremy

57

Optimization of intravascular shear stress assessment in vivo.  

PubMed

The advent of microelectromechanical systems (MEMS) sensors has enabled real-time wall shear stress (WSS) measurements with high spatial and temporal resolution in a 3-D bifurcation model. To optimize intravascular shear stress assessment, we evaluated the feasibility of catheter/coaxial wire-based MEMS sensors in the abdominal aorta of the New Zealand white (NZW) rabbits. Theoretical and computational fluid dynamics (CFD) analyses were performed. Fluoroscope and angiogram provided the geometry of aorta, and the Doppler ultrasound system provided the pulsatile flow velocity for the boundary conditions. The physical parameters governing the shear stress assessment in NZW rabbits included (1) the position and distance from which the MEMS sensors were mounted to the terminal end of coaxial wire or the entrance length, (L(e)), (2) diameter ratios of aorta to the coaxial wire (D(aorta) /D(coaxial wire)=1.5-9.5), and (3) the range of Reynolds numbers (116-1550). At an aortic diameter of 2.4mm and a maximum Reynolds number of 212 (a mean Reynolds number of 64.2), the time-averaged shear stress (tau(ave)) was computed to be 10.06 dyn cm(-2) with a systolic peak at 33.18 dyn cm(-2). In the presence of a coaxial wire (D(aorta)/D(coaxial wire)=6 and L(e)=1.18 cm), the tau(ave) value increased to 15.54 dyn cm(-2) with a systolic peak at 51.25 dyn cm(-2). Real-time intravascular shear stress assessment by the MEMS sensor revealed an tau(ave) value of 11.92 dyn cm(-2) with a systolic peak at 47.04 dyn cm(-2). The difference between CFD and experimental tau(ave) was 18.5%. These findings provided important insights into packaging the MEMS sensors to optimize in vivo shear stress assessment. PMID:19457490

Ai, Lisong; Yu, Hongyu; Takabe, Wakako; Paraboschi, Anna; Yu, Fei; Kim, E S; Li, Rongsong; Hsiai, Tzung K

2009-05-19

58

Shear stress relaxation of dental ceramics determined from creep behavior  

Microsoft Academic Search

Objective. To test the hypothesis that shear stress relaxation functions of dental ceramics can be determined from creep functions measured in a beam-bending viscometer.Methods. Stress relaxation behavior was determined from creep data for the following materials: (1) a veneering ceramic-IPS Empress2® body ceramic (E2V); (2) an experimental veneering ceramic (EXV); (3) a low expansion body porcelain-Vita VMK 68 feldspathic body

Paul H. DeHoff; Kenneth J. Anusavice

2004-01-01

59

Acoustic shear wave displacement measurement using ultrasound  

Microsoft Academic Search

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

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

1996-01-01

60

Shear stress related blood damage in laminar couette flow.  

PubMed

Artificial organs within the blood stream are generally associated with flow-induced blood damage, particularly hemolysis of red blood cells. These damaging effects are known to be dependent on shear forces and exposure times. The determination of a correlation between these flow-dependent properties and actual hemolysis is the subject of this study. For this purpose, a Couette device has been developed. A fluid seal based on fluorocarbon is used to separate blood from secondary external damage effects. The shear rate within the gap is controlled by the rotational speed of the inner cylinder, and the exposure time by the amount of blood that is axially pumped through the device per given time. Blood damage is quantified by the index of hemolysis (IH), which is calculated from photometric plasma hemoglobin measurements. Experiments are conducted at exposure times from texp=25 - 1250 ms and shear rates ranging from tau=30 up to 450 Pa ensuring Taylor-vortex free flow characteristics. Blood damage is remarkably low over a broad range of shear rates and exposure times. However, a significant increase in blood damage can be observed for shear stresses of tau>or= 425 Pa and exposure times of texp>or= 620 ms. Maximum hemolysis within the investigated range is IH=3.5%. The results indicate generally lower blood damage than reported in earlier studies with comparable devices, and the measurements clearly indicate a rather abrupt (i.e., critical levels of shear stresses and exposure times) than gradual increase in hemolysis, at least for the investigated range of shear rates and exposure times. PMID:12780506

Paul, Reinhard; Apel, Jörn; Klaus, Sebastian; Schügner, Frank; Schwindke, Peter; Reul, Helmut

2003-06-01

61

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

PubMed

The drag reducing effect of polymers in a channel flow is well known and it is assumed that the polymer filaments interfere with the turbulent structures in the very near-wall flow. To analyse their precise effect, a micro-pillar shear stress sensor (MPS³) measurement system is developed which allows the detection of wall shear stress at high spatial and temporal resolutions. Different manufacturing techniques for the required micro-pillars are discussed and their influence on the flow is investigated evidencing the non-intrusive character of the pillars. Subsequently, a complete calibration is presented to relate the recorded deflection to wall shear stress values and to assure the correct detection over the whole expected frequency spectrum. A feasibility study about the ability to visualize the two-dimensional wall shear stress distribution completes the discussion about the validity of MPS³. In the last step, the drag reduction of a polymer filament grafted on a micro-pillar compared to a plain pillar and the application of MPS³ in an ocean-type polymer solution are investigated. The results confirm the expected behaviour found in the literature. PMID:21508484

Nottebrock, Bernardo; Grosse, Sebastian; Schröder, Wolfgang

2011-04-20

62

Response of shear stress to ac electric fields under steady shear flow in a droplet-dispersed phase  

NASA Astrophysics Data System (ADS)

We have measured the response of shear stress to ac electric fields under steady shear flow in the droplet-dispersed phase of an immiscible polymer blend. A characteristic mode was found under steady shear flow, the relaxation frequency of which increased with increasing the shear rate. In the frequency dispersion, a scaling relation derived from dimensional analysis was confirmed to hold. The origin of the mode was investigated on the basis of the Maffettone-Minale (MM) model, in which the droplet shape is described by a second-rank tensor. The frequency dispersion of the response was also calculated using a modified MM model.

Na, Yang Ho; Aida, Kohei; Sakai, Ryosuke; Kakuchi, Toyoji; Orihara, Hiroshi

2009-12-01

63

Response of shear stress to ac electric fields under steady shear flow in a droplet-dispersed phase.  

PubMed

We have measured the response of shear stress to ac electric fields under steady shear flow in the droplet-dispersed phase of an immiscible polymer blend. A characteristic mode was found under steady shear flow, the relaxation frequency of which increased with increasing the shear rate. In the frequency dispersion, a scaling relation derived from dimensional analysis was confirmed to hold. The origin of the mode was investigated on the basis of the Maffettone-Minale (MM) model, in which the droplet shape is described by a second-rank tensor. The frequency dispersion of the response was also calculated using a modified MM model. PMID:20365183

Na, Yang Ho; Aida, Kohei; Sakai, Ryosuke; Kakuchi, Toyoji; Orihara, Hiroshi

2009-12-30

64

Torsion apparatus for measuring shear properties of adhesive bonded joints  

Microsoft Academic Search

A napkin-ring torsion apparatus for the study of the shear properties of adhesive bonded joints is described. A high sensitivity capacitance-type extensometer is used for measuring the load-deformation characteristics of the adhesives. Angle of twist sensitivities as high as 6 × 10?8 radians can reliably be achieved. Shear stress is determined by using an extensometer to measure the strain developed

F C Bossler; M C Franzblau; J L Rutherford

1968-01-01

65

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

PubMed Central

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

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

2012-01-01

66

Atherosclerotic plaques: is endothelial shear stress the only factor?  

PubMed

Initiation and development of atherosclerosis has largely been attributed to irregular shear stress patterns and values, in the current literature. Abnormalities such as low shear stress, reversing and oscillatory shear force patterns, as well as temporal variations of shear stress are the most cited factors. However, clinical findings have further indicated that plaques have still been formed and developed in arterial sites that possess relatively more steady and higher shear stresses than those observed in studies correlating low or oscillatory shear stresses with atherosclerosis. These data imply that deviations in shear stress from its normal physiological pattern alone may not be the only factor inducing atherosclerosis, and additional haemodynamics parameter other then shear stress may also contribute to the initiation and development of plaques. In this paper, we hypothesise that the combined effect of wall shear stress and circumferential stress waves, in the form of angular phase difference between the two waves at each cardiac cycle, may be a more accurate determinant of plaque formation and growth. Furthermore, arterial sites that possess more positive values of this angular phase difference may be more prone to plaque formation or development. If proved correct, this theory can transform our understanding of endothelial cell mechanotransduction and mechanobiology, and may lead to design and utilisation of new diagnostic procedures and equipment as predictive and preventive clinical tools for patients with abnormal arterial blood pressure. PMID:23688740

Anssari-Benam, Afshin; Korakianitis, Theodosios

2013-05-17

67

Temporal oscillations of the shear stress and scattered light in a shear-banding--shear-thickening micellar solution.  

PubMed

The results of optical and rheological experiments performed on a viscoelastic solution (cetyltrimethylammonium bromide + sodium salicylate in water) are reported. The flow curve has a horizontal plateau extending between two critical shear rates characteristic of heterogeneous flows formed by two layers of fluid with different viscosities. These two bands which also have different optical anisotropy are clearly seen by direct observation in polarized light. At the end of the plateau, apparent shear thickening is observed in a narrow range of shear rates; in phase oscillations of the shear stress and of the first normal stress difference are recorded in a shearing device operating under controlled strain. The direct observation of the annular gap of a Couette cell in a direction perpendicular to a plane containing the vorticity shows that the turbidity of the whole sample also undergoes time dependent variations with the same period as the shear stress. However no banding is observed during the oscillations and the flow remains homogeneous. PMID:16132153

Azzouzi, H; Decruppe, J P; Lerouge, S; Greffier, O

2005-08-30

68

Measurement of temperature using speckle shearing interferometry.  

PubMed

A laser speckle shearing interferometric technique is used for measuring the temperature profile inside a gaseous flame. The experimental results are compared with the values obtained by a thermocouple and also by speckle photography. Good agreement is seen among the temperatures measured by speckle shearing interferometry, speckle photography, and the thermocouple. Speckle shearing interferometry is easier to implement than speckle photography. This is because in speckle shearing interferometry the accurate positions of the fringes can be known without point-by-point analysis and correction for the halo effect. PMID:20885553

Shakher, C; Nirala, A K

1994-04-10

69

Measurement of Shear Modulus and Shear Strength of Adhesives.  

National Technical Information Service (NTIS)

This study was conducted to develop an easy - to - use test method suitable for wood adherends, with an accuracy approaching that of the torsion tube method commonly used for metal - bonding adhesives. The simple method would be used to measure the shear ...

B. H. River R. H. Gillespie

1978-01-01

70

The role of shear stress in the pathogenesis of atherosclerosis  

Microsoft Academic Search

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,

Kristopher S Cunningham; Avrum I Gotlieb

2005-01-01

71

Transverse shear and normal stresses in nonlinear shell theory  

Microsoft Academic Search

Failure in composite shells often occurs at the interface between material layers due to inter-laminar shear or transverse normal stresses. To understand these failures, it is important to accurately predict the transverse direction stresses that develop due to arbitrary loading on curved shells undergoing large deformations. This work solves the nonlinear, three-dimensional equilibrium equations for through thickness shear and normal

David D. Fox

2000-01-01

72

Interfacial shear stress concentration in FRP-strengthened beams  

Microsoft Academic Search

This paper reports the results of an experimental programme designed to study the interfacial shear stress concentration at the plate curtailment of reinforced concrete (RC) beams strengthened in flexure with externally bonded carbon fibre-reinforced polymer (CFRP). Specifically, the study looks at the relationship between the CFRP plate thickness and the interfacial shear stress concentration at the plate curtailment, the failure

M. Maalej; Y. Bian

2001-01-01

73

Influence of shear stress fluctuation on bed particle mobility  

Microsoft Academic Search

Whether or not a sediment particle is entrained from a channel bed is associated with both average bed shear stress and shear stress fluctuation, the latter being flow-dependent and also related to bed irregularities. In the first part of this study, a preliminary analysis of possible fluctuations induced by bed roughness is presented for the case of an immobile plane

Nian-Sheng Cheng

2006-01-01

74

Basal shear stress of debris flow in the runout phase  

NASA Astrophysics Data System (ADS)

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

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

2013-11-01

75

Dynamic material strength measurement utilizing magnetically applied pressure-shear  

NASA Astrophysics Data System (ADS)

Magnetically applied pressure-shear (MAPS) is a recently developed technique used to measure dynamic material strength developed at Sandia National Laboratories utilizing magneto-hydrodynamic (MHD) drive pulsed power systems. MHD drive platforms generate high pressures by passing a large current through a pair of parallel plate conductors which, in essence, form a single turn magnet coil. Lorentz forces resulting from the interaction of the self-generated magnetic field and the drive current repel the plates and result in a high pressure ramp wave propagating in the conductors. This is the principle by which the Sandia Z Machine operates for dynamic material testing. MAPS relies on the addition of a second, external magnetic field applied orthogonally to both the drive current and the self-generated magnetic field. The interaction of the drive current and this external field results in a shear wave being induced directly in the conductors. Thus both longitudinal and shear stresses are generated. These stresses are coupled to a sample material of interest where shear strength is probed by determining the maximum transmissible shear stress in the state defined by the longitudinal compression. Both longitudinal and transverse velocities are measured via a specialized velocity interferometer system for any reflector (VISAR). Pressure and shear strength of the sample are calculated directly from the VISAR data. Results of tests on several materials at modest pressures (˜10GPa) will be presented and discussed.

Alexander, C. S.

2012-08-01

76

The Effect of Spatial Resolution on Wall Shear Stress Measurements Acquired Using Radial Phase contrast Magnetic Resonance Angiography in the Middle Cerebral Arteries of Healthy Volunteers  

PubMed Central

Introduction Low wall shear stress (WSS) values are frequently observed in arterial regions that are prone to atherosclerotic plaque formation and have also been implicated in the pathogenesis of saccular cerebral aneurysms. Acquisition of WSS values in-vivo has been challenging, especially using non-invasive techniques and within clinically-useful imaging times. We have recently implemented radial phase-contrast techniques that allow high resolution angiograms with velocity information to be acquired within clinically-useful imaging times. Methods 10 healthy volunteers were scanned using PC-VIPR and PC-SOS, two high resolution phase-contrast techniques at spatial resolutions of 0.67×0.67×0.67mm3 and 0.4×0.4×1mm3 respectively. Velocity data from the two acquisitions was imported into a custom Matlab runtime environment that automatically calculated WSS values using Green’s Theorem and B-spline interpolation. Results Time average axial WSS was 1.069 N/m2 (95% confidence interval: 0.8628 < x < 1.276) in the left and right middle cerebral arteries of the 10 healthy volunteers (n=20) when scanned by PC-VIPR, and 1.670 N/m2 when scanned by PC-SOS (95% confidence interval: 1.395 < x < 1.946). This difference in means was statistically significant (p < 0.002). Discussion Previous investigators have found that higher spatial resolution results in higher WSS measurements because smaller voxel size results in fewer partial volume effects. This was true in our study as well. In this study, we found that PC-SOS has significantly higher spatial resolution than PC-VIPR and this followed in the WSS measurements. Conclusion Higher in-plane spatial resolution allows WSS calculations to be performed more accurately because of increased precision near the vessel boundary.

Chang, Warren; Frydrychowicz, Alex; Kecskemeti, Steve; Landgraf, Ben; Johnson, Kevin; Wu, Yijing; Wieben, Oliver; Mistretta, Charles; Turski, Patrick

2011-01-01

77

Measurement of shear impedances of viscoelastic fluids  

SciTech Connect

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.

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

1996-12-31

78

Wall shear stress hot film sensor for use in gases  

NASA Astrophysics Data System (ADS)

The purpose of this work is to present the construction and characterization of a wall shear stress hot film sensor for use in gases made with MEMS technology. For this purpose, several associated devices were used, including a constant temperature feedback bridge and a shear stress calibration device that allows the sensor performance evaluation. The sensor design adopted here is simple, economical and is manufactured on a flexible substrate allowing its application to curved surfaces. Stationary and transient wall shear stress tests were carried on by means of the calibration device, determining its performance for different conditions.

Osorio, O. D.; Silin, N.

2011-05-01

79

ESTIMATION OF SHEAR STRESS WORKING ON SUBMERGED HOLLOW FIBRE MEMBRANE BY CFD METHOD IN MBRs  

NASA Astrophysics Data System (ADS)

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.

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

80

Universality of scaling laws in correlation between velocity and shear stress in turbulent boundary layers  

NASA Astrophysics Data System (ADS)

In this study, we analyse simultaneous measurements (at 50 Hz) of velocity at several heights and shear stress at the surface made during the Utah field campaign for the presence of ranges of scales, where distinct scale-to-scale interactions between velocity and shear stress can be identified. We find that our results are similar to those obtained in a previous study [Venugopal et al., 2003] (contrary to the claim in V2003, that the scaling relations might be dependent on Reynolds number) where wind tunnel measurements of velocity and shear stress were analysed. We use a wavelet-based scale-to-scale cross-correlation to detect three ranges of scales of interaction between velocity and shear stress, namely, (a) inertial subrange, where the correlation is negligible; (b) energy production range, where the correlation follows a logarithmic law; and (c) for scales larger than the boundary layer height, the correlation reaches a plateau.

v., V.; Porte-Agel, F.; Heuer, W.; Marusic, I.

2007-05-01

81

Drag reducing polymers may decrease atherosclerosis by increasing shear in areas normally exposed to low shear stress  

Microsoft Academic Search

Purpose: Drag reducing polymers (DRPs) have been shown to decrease plaque formation. Their mechanism of action is unknown. Atherosclerosis tends to develop in areas of low shear stress. This study investigates whether DRPs increase shear stress in areas normally exposed to low shear stress. Methods: Six dogs underwent surgical plication of the left half of the aorta. A specially modified

Alan P. Sawchuk; Joseph L. Unthank; Michael C. Dalsing

1999-01-01

82

Rotary Flow Channel for Shear Stress Sensor Calibration.  

National Technical Information Service (NTIS)

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(omeg...

A. J. Zuckerwar M. A. Scott

2004-01-01

83

A contact-type piezoresistive micro-shear stress sensor for above-knee prosthesis application  

Microsoft Academic Search

A prototype contact-type micro piezoresistive shear-stress sensor that can be utilized to measure the shear stress between skin of stump and socket of above-knee (AK) prosthesis was designed, fabricated and tested. Micro-electro-mechanical system (MEMS) technology has been chosen for the design because of the low cost, small size and adaptability to this application. In this paper, the finite element method

Ming Chun Hsieh; Yean Kuen Fang; Ming-Shaung Ju; Gin-Shin Chen; Jyh-Jier Ho; C. H. Yang; Pei Ming Wu; G. S. Wu; Terry Yuan-Fang Chen

2001-01-01

84

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

85

Shear Stress Induced Stimulation of Mammalian Cell Metabolism.  

National Technical Information Service (NTIS)

A flow apparatus was developed for the study of the metabolic response of anchorage dependent cells to a wide range of steady and pulsatile shear stresses under well controlled conditions. Human umbilical vein endothelial cell monolayers were subjected to...

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

1988-01-01

86

Methodology for predicting maximum velocity and shear stress in a ...  

Treesearch

Title: Methodology for predicting maximum velocity and shear stress in a sinuous ... patterns, or quite unpredictable, such as major flooding events or tectonic activity. ... and often times can produce catastrophic changes to natural ecosystems.

87

Quantification of shear stress in a meandering native topographic ...  

Treesearch

... system can threaten riverside infrastructure and riparian zones, which may affect the ... Keywords: shear stress, meandering channel patterns, hydraulic model ... We recommend that you also print this page and attach it to the printout of the ...

88

Rheological properties of rubbery polymers at low shear stresses  

Microsoft Academic Search

The rheological behavior of the rubbery amorphous polymers SKB-35 (sodium-butadiene rubber), SKN-26M(butadiene-nitrile rubber), and PIB-85 (polyisobutylene) has been investigated in relation to the creep process. The tests were conducted at low shear stresses, in the constant shear stress regime, on the temperature interval from 0 to 100°C using a parallel-plate viscometer. We have shown, for the first time, by a

G. M. Bartenev; L. G. Glukhatkina

1969-01-01

89

Shear stress-induced calcium transients in endothelial cells from human umbilical cord veins.  

PubMed

1. Changes of the free cytosolic Ca2+ concentration induced by shear stress were measured in Fura-2 acetoxymethyl ester-loaded endothelial cells from human umbilical cord veins. 2. We were able to induce Ca2+ transients in almost every cell by blowing a stream of physiological solution onto a single endothelial cell thereby inducing shear stress between 0 and 50 dyn cm-2. The Ca2+ response could be graded by varying the shear stress, and reached a half-maximal value at a shear stress of 30 dyn cm-2. 3. The shear stress responses critically depended on the extracellular Ca2+ concentration and were absent in a Ca(2+)-free solution. Repetitive application of short pulses of shear stress induced cumulative effects because of the slow decay of the shear stress Ca2+ responses (time constants 82.3 +/- 17.8 s from twenty-five cells). Application of a depolarizing high potassium solution to reduce the driving force for Ca2+ entry decreased the Ca2+ transients in some of the cells. 4. Application of shear stress in the presence of other divalent cations, such as nickel, cobalt or barium, always produced substantial changes in the ratio of the 390/360 nm fluorescence signal, indicating influx of these cations and subsequent quenching of the Fura-2 fluorescence. 5. Shear stress responses in the presence of 10 mM Ca2+ were completely blocked by application of 1 mM La3+. 6. Incubation of the cells with the phorbol ester 12-O-tetradecanoyl phorbol-13-acetate (TPA) did not alter the shear stress response, but completely blocked histamine-induced Ca2+ transients. 7. Small submaximal shear stress potentiated the Ca2+ transients induced by histamine. 8. We conclude that shear stress-dependent Ca2+ signals are induced by an influx of calcium that is not modulated via protein kinase C and not activated by membrane depolarization. The influx pathway is also permeable to divalent cations such as Ni2+, Co2+ and Ba2+, but is blocked by La3+. PMID:1338792

Schwarz, G; Callewaert, G; Droogmans, G; Nilius, B

1992-12-01

90

The Micro-Pillar Shear-Stress Sensor MPS(3) for Turbulent Flow.  

PubMed

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 MPS(3), 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

Große, Sebastian; Schröder, Wolfgang

2009-03-30

91

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

PubMed Central

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.

Grosse, Sebastian; Schroder, Wolfgang

2009-01-01

92

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

PubMed Central

Establishing a relationship between perfusion rate and fluid shear stress in a 3-dimensional cell culture environment is an ongoing and challenging task faced by tissue engineers. In this study, we explore Doppler optical coherence tomography (DOCT) as a potential imaging tool for in situ monitoring of local fluid flow profiles inside porous chitosan scaffolds. From the measured fluid flow profiles, the fluid shear stresses are evaluated. We examine the localized fluid flow and shear stress within low and high porosity chitosan scaffolds, which are subjected to a constant input flow rate of 0.5 ml·min-1. The DOCT results show that the behaviour of the fluid flow and shear stress in micropores is strongly dependent on the micropore interconnectivity, porosity, and size of pores within the scaffold. For low porosity and high porosity chitosan scaffolds examined, the measured local fluid flow and shear stress varied from micropore to micropore with a mean shear stress of 0.49±0.3 dyn·cm-2 and 0.38±0.2 dyn·cm-2, respectively. In addition, we show that the scaffold’s porosity and interconnectivity can be quantified by combining analyses of the 3-dimensional structural and flow images obtained from DOCT.

Jia, Yali; Bagnaninchi, Pierre O.; Yang, Ying; Haj, Alicia El; Hinds, Monica T.; Kirkpatrick, Sean J.; Wang, Ruikang K.

2009-01-01

93

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

NASA Astrophysics Data System (ADS)

Establishing a relationship between perfusion rate and fluid shear stress in a 3D cell culture environment is an ongoing and challenging task faced by tissue engineers. We explore Doppler optical coherence tomography (DOCT) as a potential imaging tool for in situ monitoring of local fluid flow profiles inside porous chitosan scaffolds. From the measured fluid flow profiles, the fluid shear stresses are evaluated. We examine the localized fluid flow and shear stress within low- and high-porosity chitosan scaffolds, which are subjected to a constant input flow rate of 0.5 ml.min-1. The DOCT results show that the behavior of the fluid flow and shear stress in micropores is strongly dependent on the micropore interconnectivity, porosity, and size of pores within the scaffold. For low-porosity and high-porosity chitosan scaffolds examined, the measured local fluid flow and shear stress varied from micropore to micropore, with a mean shear stress of 0.49+/-0.3 dyn.cm-2 and 0.38+/-0.2 dyn.cm-2, respectively. In addition, we show that the scaffold's porosity and interconnectivity can be quantified by combining analyses of the 3D structural and flow images obtained from DOCT.

Jia, Yali; Bagnaninchi, Pierre O.; Yang, Ying; Haj, Alicia El; Hinds, Monica T.; Kirkpatrick, Sean J.; Wang, Ruikang K.

2009-05-01

94

Shear transfer constitutive model for pre-cracked RC plate subjected to combined axial and shear stress  

Microsoft Academic Search

This paper proposes the constitutive model for the shear transfer through the cracks of pre-cracked reinforced concrete (RC) plate subjected to combined axial and shear stress. The plate is a scale model of a shear wall of a nuclear power plant (NPP) building. Twelve plate specimens were initially cracked and then loaded to the failure point by increasing cyclic shear

Katsuhiko Umeki; Yoshio Kitada; Takao Nishikawa; Koichi Maekawa; Mamoru Yamada

2003-01-01

95

Three-dimensional phase contrast velocity mapping acquisition improves wall shear stress estimation in vivo.  

PubMed

The purpose of this study was to evaluate and apply high-resolution three-dimensional phase contrast mapping for estimation of wall shear stress in vivo. A silicon pipe of 8 mm diameter with a 8.3 ml/s steady flow and the entrance of the carotid bifurcation in 10 young healthy volunteers aged 23.6 +/- 3.1 years was studied. Very high resolution three-dimensional and two-dimensional phase contrast mapping sequences with spatial resolutions of 0.31 x 0.31 x 1.5 mm(3) and 0.31 x 0.31 x 3 mm(3), respectively, were compared in vivo and in vitro. Wall shear stress was calculated using multi-sectored, three-dimensional paraboloid fitting. In comparison to the two-dimensional measurements, the three-dimensional method with only half the slice thickness gave higher signal-to-noise ratio and velocity-to-noise ratios both in vivo and in vitro. Wall shear stress derived from the three-dimensional velocity measurements did not differ from the two-dimensional velocity measurements either in vitro or in vivo. Mean wall shear stress was lowest and oscillatory shear index was highest at the outer wall, towards the carotid bifurcation. Three-dimensional velocity mapping increases resolution and image quality and allows estimation of wall shear stress patterns circumferentially and longitudinally in human arteries. PMID:15062929

Wu, Sheng Ping; Ringgaard, Steffen; Pedersen, Erik Morre

2004-04-01

96

Role of cytoplasmic and releasable ADP in platelet aggregation induced by laminar shear stress  

SciTech Connect

We examined the extent of lytic and sublytic platelet injury after exposure of platelets to shear stress and the role in shear-induced PAG of ADP liberated from platelets as a result of shear-induced platelet dense body release and/or platelet damage. Platelets in C-PRP or TAS were subjected to well-defined, laminar shear stress in a rotational viscometer, and PAG (loss of single, nonaggregated platelets), /sup 14/C-serotonin release, and loss from platelets of LDH and /sup 51/Cr were determined. Increased PAG with increasing shear stresses was associated with progressive loss of LDH and /sup 51/Cr. Loss of /sup 51/Cr was consistently in excess of that of LDH, indicating sublytic platelet injury, which was confirmed by electron microscopy. At the lowest shear stress used (50 dynes/cm2), PAG in C-PRP was observed in the absence of detectable loss of /sup 51/Cr or LDH. When platelets in TAS were sheared in the presence of CP/CPK, an enzyme system capable of removing extracellular ADP, PAG was only partially (approximately 40%) inhibited. However, when platelets were preincubated with CP/CPK and ATP (to saturate platelet ADP receptors), shear-induced PAG was almost completely suppressed. Similar results were obtained with PAG induced by collagen in the aggregometer. The findings indicate that (1) shear-induced PAG in this system may occur without measurable lytic or sublytic platelet damage and (2) ADP liberated from platelets as a result of shear-induced release or damage may represent the major if not sole mediator of shear-induced PAG.

Moritz, M.W.; Reimers, R.C.; Baker, R.K.; Sutera, S.P.; Joist, J.H.

1983-04-01

97

SHEAR STRESS PROFILE IN A ROTATING CAGE  

Microsoft Academic Search

The rotating cage apparatus is used in the oil and gas industry as a test to recreate corrosion situations under high shear conditions. Recent work has been done by one of the authors to study the unsteady fluid dynamics of this apparatus as an idealized two- dimensional problem and perform high resolution simulations of the rotating cage using a vortex

Prabhu Ramachandran; Sunder Ramachandran; Michael Greaves; Vladimir Jovancicevic

98

Transient shear stresses on a suspension cell in turbulence.  

PubMed

A model flow field representative of Kolmogorov eddies in turbulence is proposed, and its two parameters are expressed in terms of the known bioreactor variables epsilon, the rate of turbulent power dissipation, and nu, the fluid kinematic viscosity. The trajectory through this flow field of a small sphere representing a cell is determined, and from that the time-varying local shear rate can be found. This allows calculation of the shear stress at any point on the sphere's surface as it rotates in and moves through the model eddy. The maximum shear stress imposed on the cell by the surrounding turbulence has a range of 0.5-5 dyn/cm(2), and can be estimated by 5.33rho(epsilonnu)(1/2). The shear stress has two major frequency components with ranges of 1-4 and 20-80 s(-1); the higher frequency component is estimated by 0.678(epsilon/nu)(1/2). The rotation of the direction of the shear stress vector at each point on the cell's surface is also discussed. Two ways in which external stresses might affect cell growth are proposed. PMID:18595114

Cherry, R S; Kwon, K Y

1990-09-01

99

Interfacial shear stress between single-walled carbon nanotubes and gold surfaces with and without an alkanethiol monolayer.  

PubMed

A novel and effective technique is developed to make the first determination of shear stress between dielectrophoretically assembled single-walled carbon nanotubes (SWNTs) and surfaces. The results demonstrate that we can vary the shear stress by a factor of 20 by functionalizing a gold surface with different alkanethiols. The interfacial shear stress between a small bundle of SWNTs and a gold surface with and without self-assembled monolayers of alkanethiol (2-phenylethanethiol or 2-aminoethanethiol) is determined. The measurements are based on simple NEMS cantilever beams, a nanomanipulator, and a scanning electron microscope (SEM). It is emphasized that the measured quantity is the slack in the nanotube (not the shear stress) induced by the nanomanipulation. The shear stress is determined from the slack through a mechanics model. An average shear stress of 87MPa between SWNTs and gold surfaces is obtained. For the tests on the self-assembled 2-aminoethanethiol surface, an average shear stress of 142MPa is obtained. For the self-assembled 2-phenylethanethiol surface, the shear stress is determined to be around 7.2MPa with an estimated work of adhesion of 0.5J/m(2). PMID:23906860

Pan, Huiyan; Wu, Yu-Chiao; Adams, George G; Miller, Glen P; McGruer, Nicol E

2013-07-11

100

Shear modulus of porcine coronary artery in reference to a new strain measure.  

PubMed

To simplify the stress-strain relationship of blood vessels, we define a logarithmic-exponential (log-exp) strain measure to absorb the nonlinearity. As a result, the constitutive relation between the second Piola-Kirchhoff stress and the log-exp strain can be written as a generalized Hooke's law. In this work, the shear modulus of porcine coronary arteries is determined from the experimental data in inflation-stretch-torsion tests. It is found that the shear modulus with respect to the log-exp strain can be viewed as a material constant in the full range of elasticity, and the incremental shear modulus for Cauchy shear stress and small shear strain at various loading levels can be predicted by the proposed Hooke's law. This result further validates the linear constitutive relation for blood vessels when shear deformation is involved. PMID:17669488

Zhang, Wei; Lu, Xiao; Kassab, Ghassan S

2007-07-31

101

The Shear Stress–Strain Behaviour of Low-modulus Structural Adhesives  

Microsoft Academic Search

The shear stress–strain behaviour of two low-modulus structural adhesives has been measured using the butt-torsion test. The Nadai correction for non-linear shear behaviour is explained as it is necessary to understand how this correction can be applied to butt joints. The results for one adhesive were accurately used to predict the strength of a lap joint, and it was shown

F. Kadioglu; R. D. Adams; F. J. Guild

2000-01-01

102

Shear stress-induced cytoskeletal rearrangement involves caveolae-mediated mechanotransduction  

Microsoft Academic Search

Shear stress alters vascular endothelial cell morphology through remodeling of the actin cytoskeleton. The rapid cytoskeletal responses of bovine aortic cell (BAEC) monolayers to shear (10-12 dynes\\/cm2) were measured in terms of accumulation of di-phosphorylated myosin light chain (MLC). This effect was attenuated by pretreatment with filipin, a cholesterol-sequestering agent known to disrupt the structure of lipid rafts and unique

M. E. Carlile; V. Rizzo

2002-01-01

103

Exploring the Role of Shear Stress and Severe Turbulence in Downstream Fish Passage  

SciTech Connect

Fish may be exposed to damaging levels of fluid shear stress and turbulence while passing through hydroelectric power plants. The generally assumed locations for such potential damage are the turbine and draft tube passages, although it is possible that fish are also injured during passage over the spillway or through sluiceways and fish bypass outfalls. Unless mitigated, fluid-induced injuries and mortality could frustrate efforts to develop advanced, fish-friendly turbines or to provide safe alternate downstream passages. The effects of shear stress and turbulence on fish are poorly understood, in part because of the difficulties in conceptualizing these phenomena, determining their magnitudes and distribution within hydroelectric systems, and then recreating them in a controlled laboratory environment. We define the fluid phenomena that are relevant to the assessment of effects on fish. The magnitudes of fluid stresses associated with man-altered aquatic environments are often considerably higher than those found in natural environments (e.g., normal river flows). However, levels of shear stresses that occur during flash floods appear to be comparable to those expected within a turbine. Past studies of the effects of shear stress on fish are of limited value, mainly because of their narrow scope and lack of instrumentation to measure velocities on appropriately small scales. A laboratory experiment to study the effects of shear stress and turbulence on fish is described.

Cada, G.; Carlson, T.; Ferguson, J.; Richmond, M.; Sale, M.

1999-07-06

104

The mechanism for shear thickening in suspensions  

Microsoft Academic Search

Densely packed suspensions can shear thicken, in which the viscosity increases with shear rate. Video microscopy along with rheology measurements show the shear thickening regime is a transition from negligible particle motion at low stresses to fully developed shear flow at higher stresses. The onset of shear thickening occurs when the shear stress is sufficient to pull particles apart; for

Eric Brown; Heinrich Jaeger

2009-01-01

105

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

SciTech Connect

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.

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

1988-09-01

106

Monitoring biofilm detachment under dynamic changes in shear stress using laser-based particle size analysis and mass fractionation.  

PubMed

Biofilm detachment under a dynamic change in shear stress was monitored using Focused Beam Reflectance Measurements (FBRM, LASENTEC) and mass fractionation. An annular reactor was used to grow biofilm with glucose as substrate. Changing the rotational speed on the inner cylinder of the annular reactor from 150 RPM to 420 RPM induced a step increase in shear stress. It was observed that the rate of detachment increased rapidly after increasing shear stress and then returned to the previous level. Erosion was the dominant process of detachment under steady state operation, whereas sloughing was dominant following the sudden increase in shear stress. After reaching steady state detachment under high shear conditions, the rotational speed was decreased for a 12-hour period. During this brief period of lower shear, the biofilm adjusted to this new condition. When the shear stress was increased again, another sharp increase in effluent solids concentration was observed. A decrease in density indicates that the biofilm became more vulnerable to shear stress after being subjected to this short period of low shear. PMID:12701909

Choi, Y C; Morgenroth, E

2003-01-01

107

Transient Shear Banding in a Simple Yield Stress Fluid  

NASA Astrophysics Data System (ADS)

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 ??. 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 ???0.1s-1, heterogeneous flows could be observed for as long as 105s. These local dynamics account for the ultraslow stress relaxation observed at low shear rates.

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

2010-05-01

108

A nonlinear composite shell element with continuous interlaminar shear stresses  

Microsoft Academic Search

A numerical model for layered composite structures based on a geometrical nonlinear shell theory is presented. The kinematic is based on a multi-director theory, thus the in-plane displacements of each layer are described by independent director vectors. Using the isoparametric apporach a finite element formulation for quadrilaterals is developed. Continuity of the interlaminar shear stresses is obtained within the nonlinear

F. Gruttmann; W. Wagner; L. Meyer; P. Wriggers

1993-01-01

109

Cone-and-Plate Shear Stress Adhesive Test  

Microsoft Academic Search

A test geometry is described which will produce a state of essentially pure constant shear stress in an adhesive bond. The adherends are fabricated from two cylindrical elements, one with a convex conical end section and the other with a flat plate end section. The axes of these two cylinders are aligned and the two end sections are bonded together

J. W. Grant; J. N. Cooper

1987-01-01

110

Variability of Reference Shear Stress in Gravel-Bed Streams  

Microsoft Academic Search

The prediction of sediment transport in gravel bed streams is complicated by heterogeneous bed material and armoring of the bed surface, thus affecting both the availability and mobility of grains on the bed. The application of standard bed-load transport formulae in high gradient, coarse-bedded streams may produce inaccurate results, related to difficulty in defining the critical shear stress for sediment

E. Mueller; J. Pitlick; J. M. Nelson

2003-01-01

111

Critical Shear Stresses in Body-Centered Cubic Lattices  

Microsoft Academic Search

A consideration of the shape and of the atomic configuration of dislocations in a body-centered cubic lattice allows an estimate of the ratio of critical shear stresses on various slip planes as a function of temperature. A comparison with experimental data is satisfactory.

R. Smoluchowski

1952-01-01

112

Shear-Stress Field of a Simple Dislocation Cell  

Microsoft Academic Search

The shear-stress distribution due to a particular example of the simplest, two-dimensional dislocation array, representing a cell of material misoriented with respect to its surroundings, was calculated numerically. The results are found to be virtually independent of the size of the cell, provided its shape and the magnitude of its angular misorientation are kept constant. For cells of same size

T. R. Duncan; Doris Kuhlmann-Wilsdorf

1968-01-01

113

Mass Transport and Shear Stress in the Carotid Artery Bifurcation  

Microsoft Academic Search

The carotid artery bifurcation (CAB) is one of the leading sites for atherosclerosis, a major cause of death and disability in the developed world. The specific processes by which the complex flow found at the bifurcation and carotid sinus promotes plaque formation and growth are not fully understood. Shear stress, mass transport, and flow residence times are considered key factors.

Riley Gorder; Alberto Aliseda

2010-01-01

114

A ROTARY FLOW CHANNEL FOR SHEAR STRESS SENSOR CALIBRATION  

Microsoft Academic Search

. s (neon at room temperature), r = 0.5 m, ? = 754 s-1 (7200 rpm), and h = 50.8 µm, a shear stress of ?w = 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

Allan J. Zuckerwar; Michael A. Scott

115

Introducing Shear Stress in the Study of Bacterial Adhesion  

PubMed Central

During bacterial infections a sequence of interactions occur between the pathogen and its host. Bacterial adhesion to the host cell surface is often the initial and determining step of the pathogenesis. Although experimentally adhesion is mostly studied in static conditions adhesion actually takes place in the presence of flowing liquid. First encounters between bacteria and their host often occur at the mucosal level, mouth, lung, gut, eye, etc. where mucus flows along the surface of epithelial cells. Later in infection, pathogens occasionally access the blood circulation causing life-threatening illnesses such as septicemia, sepsis and meningitis. A defining feature of these infections is the ability of these pathogens to interact with endothelial cells in presence of circulating blood. The presence of flowing liquid, mucus or blood for instance, determines adhesion because it generates a mechanical force on the pathogen. To characterize the effect of flowing liquid one usually refers to the notion of shear stress, which is the tangential force exerted per unit area by a fluid moving near a stationary wall, expressed in dynes/cm2. Intensities of shear stress vary widely according to the different vessels type, size, organ, location etc. (0-100 dynes/cm2). Circulation in capillaries can reach very low shear stress values and even temporarily stop during periods ranging between a few seconds to several minutes 1. On the other end of the spectrum shear stress in arterioles can reach 100 dynes/cm22. The impact of shear stress on different biological processes has been clearly demonstrated as for instance during the interaction of leukocytes with the endothelium 3. To take into account this mechanical parameter in the process of bacterial adhesion we took advantage of an experimental procedure based on the use of a disposable flow chamber 4. Host cells are grown in the flow chamber and fluorescent bacteria are introduced in the flow controlled by a syringe pump. We initially focused our investigations on the bacterial pathogen Neisseria meningitidis, a Gram-negative bacterium responsible for septicemia and meningitis. The procedure described here allowed us to study the impact of shear stress on the ability of the bacteria to: adhere to cells 1, to proliferate on the cell surface 5and to detach to colonize new sites 6 (Figure 1). Complementary technical information can be found in reference 7. Shear stress values presented here were chosen based on our previous experience1 and to represent values found in the literature. The protocol should be applicable to a wide range of pathogens with specific adjustments depending on the objectives of the study.

Soyer, Magali; Dumenil, Guillaume

2011-01-01

116

Arteries respond to independent control of circumferential and shear stress in organ culture.  

PubMed

Arteries respond to changes in global mechanical parameters (pressure, flow rate, and longitudinal stretching) by remodeling to restore local parameters (circumferential stress, shear stress, and axial strain) to baseline levels. Because a change in a single global parameter results in changes of multiple local parameters, the effects of individual local parameters on remodeling remain unknown. This study uses a novel approach to study remodeling in organ culture based on independent control of local mechanical parameters. The approach is illustrated by studying the short term effects of circumferential and shear stress on remodeling-related biological markers. Porcine carotid arteries were cultured for 3 days at a circumferential stress of 50 or 150 kPa or, in separate experiments, a shear stress of 0.75 or 2.25 Pa. At high circumferential stress, matrix synthesis, smooth muscle cell proliferation, and cell death are significantly greater, but matrix metalloproteinase-2 (MMP-2) and pro-MMP-2 activity are significantly less. In contrast, biological markers measured were unaffected by shear stress. Applications of the proposed approach for improved understanding of remodeling, optimizing mechanical conditioning of tissue engineered arteries, and selection of experimentally motivated growth laws are discussed. PMID:18228146

Wayman, Brian H; Taylor, W Robert; Rachev, Alexander; Vito, Raymond P

2008-01-29

117

Effects of flow unsteadiness on the wall shear stress  

NASA Astrophysics Data System (ADS)

Measurements were performed on pulsating fully turbulent flows in a pipe test rig with a diameter of 100 mm. Sinusoidal oscillatory flow at different frequencies was superimposed on a mean flow of averaged Reynolds number Re=20000 based on the pipe diameter. The measurements have been performed at different forcing frequencies (0.001 < ?+ < 0.08) covering all the oscillatory regimes; quasi-steady, relaxation, quasi laminar and high frequency. The amplitude of the flow oscillation was small enough to allow a linear response in the measurements, i.e., all flow parameters showed an oscillatory behavior at the frequency of the flow. The amplitude of the oscillatory flow was about 10% of the mean velocity in all cases. The results include mean and phase averaged values of different parameters. The centerline velocity was measured by a 2D LDA system. Hot film and constant temperature anemometry system was used to determine the wall shear stress. Bulk velocity and pressure gradient along the pipe were also acquired. The results showed a good agreement with the previous analytical, experimental and numerical results available in the literature.

Amiri, K.; Cervantes, M. J.; Raisee, M.

2012-11-01

118

Mechanical responses and stress fluctuations of a supercooled liquid in a sheared non-equilibrium state.  

PubMed

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

Mizuno, H; Yamamoto, R

2012-04-24

119

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

Microsoft Academic Search

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.

Angelika Vennemann; Eckhard Langmaack; Eckhard Nembach

2002-01-01

120

Shear stress prediction in shock loaded copper  

SciTech Connect

The stress-strain behavior during the shock rise of a 30 kbar and 54 kbar shock in copper is modeled using a plastic constitutive model that includes rate and temperature dependent hardening and accounts for the transition from thermally activated to viscous drag controlled deformation at high strain rates. A slight modification to the treatment of the mobile dislocation density within the model from that originally proposed leads to better agreement with the shock data than achieved previously. The results indicate that the deformation mechanism during the shock rise is a drag mechanism. 9 refs., 4 figs.

Follansbee, P.S.

1991-01-01

121

Endothelial hyperstimulation with increased wall shear stress in hypertensive diabetic type 2 patients  

Microsoft Academic Search

Shear stress is the major endothelial stimulus. Hemorheological changes, with increased blood viscosity have been described in arterial hypertension as well as in type 2 diabetes mellitus. These abnormalities may contribute to endothelial dysfunction through changes in shear stress. Changes in blood rheology and wall shear stress have not been investigated when patients present with both hypertension and type 2

A. Kearney-Schwartz; J.-M. Virion; Y. Khder; J.-F. Stoltz; P. Drouin; F. Zannad

2000-01-01

122

Optimal Thermal Design of Micro Hot-film Wall Shear Stress Sensor  

Microsoft Academic Search

A series of numerical analyses of the unsteady conjugate heat transfer around a micro hot-film sensor are made in order to improve its response in the wall shear stress measurement. It is found that the frequency response of an ideal sensor is limited even in the absence of the heat conduction loss to the substrate. Heat conduction in the fluid

Takashi YOSHINO; Yuji SUZUKI; Nobuhide KASAGI; Shoji KAMIUNTEN

123

Assembly and Reorientation of Stress Fibers Drives Morphological Changes to Endothelial Cells Exposed to Shear Stress  

PubMed Central

Fluid shear stress greatly influences the biology of vascular endothelial cells and the pathogenesis of atherosclerosis. Endothelial cells undergo profound shape change and reorientation in response to physiological levels of fluid shear stress. These morphological changes influence cell function; however, the processes that produce them are poorly understood. We have examined how actin assembly is related to shear-induced endothelial cell shape change. To do so, we imposed physiological levels of shear stress on cultured endothelium for up to 96 hours and then permeabilized the cells and exposed them briefly to fluorescently labeled monomeric actin at various time points to assess actin assembly. Alternatively, monomeric actin was microinjected into cells to allow continuous monitoring of actin distribution. Actin assembly occurred primarily at the ends of stress fibers, which simultaneously reoriented to the shear axis, frequently fused with neighboring stress fibers, and ultimately drove the poles of the cells in the upstream and/or downstream directions. Actin polymerization occurred where stress fibers inserted into focal adhesion complexes, but usually only at one end of the stress fiber. Neither the upstream nor downstream focal adhesion complex was preferred. Changes in actin organization were accompanied by translocation and remodeling of cell-substrate adhesion complexes and transient formation of punctate cell-cell adherens junctions. These findings indicate that stress fiber assembly and realignment provide a novel mode by which cell morphology is altered by mechanical signals.

Noria, Sabrena; Xu, Feng; McCue, Shannon; Jones, Mara; Gotlieb, Avrum I.; Langille, B. Lowell

2004-01-01

124

Critical shear stress for erosion of cohesive soils subjected to temperatures typical of wildfires  

NASA Astrophysics Data System (ADS)

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 (<175°C 175°C-275°C; >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 <175°C, was a maximum (>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.

Moody, John A.; Smith, J. Dungan; Ragan, B. W.

2005-03-01

125

Some constraints on levels of shear stress in the crust from observations and theroy  

Microsoft Academic Search

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

A. McGarr

1980-01-01

126

Surface Shear Stress Around a Single Flexible Live Plant and a Rigid Cylinder  

NASA Astrophysics Data System (ADS)

The sheltering effect of vegetation against soil erosion and snow transport has direct implications on land degradation and local water storage as snow in many arid and semi arid regions. Plants influence the erosion, transport and redeposition of soil and snow by the wind through momentum absorption, local stress concentration, trapping particles in motion and reducing the area of sediment exposed to the wind. The shear stress distributions on the ground beneath plant canopies determine the onset and magnitude of differential soil and snow erosion on rough or vegetated surfaces, but this has been studied exclusively with artificial and rigid vegetation elements thus far. Real plants have highly irregular structures that can be extremely flexible and porous. They align with the flow at higher wind speeds, resulting in considerable changes to the drag and flow regimes relative to rigid imitations of comparable size. We present measurements in the SLF atmospheric boundary layer wind tunnel of the surface shear stress distribution around a live grass plant (Lolium Perenne) and a solid cylinder of comparable size. Irwin sensors are used to measure pressure differences close to the surface which can be calibrated with surface shear stress velocities. The basal to frontal area index of the plant and the cylinder as well as the Reynolds number of the two experimental setups have been checked for similarity and show good agreement. Distinctive differences between the shear stress pattern around the plant and the cylinder can be attributed to the influence of the plant’s porosity and flexibility. The sheltered zone behind the plant is narrower in cross-stream and longer in streamwise direction than that of the cylinder. For the plant, the lowest shear stresses in the sheltered zone are 50% lower than the mean surface shear stress (? = 0.15 N/m2) in the undisturbed flow. The sheltering was higher behind the cylinder with values reduced by 70% relative to background. “Speed-up” zones on both sides of the roughness elements experienced peak shear stress values 60% above background for the plant and almost 130% higher for the cylinder. While the integral sheltering effect of the plant is smaller in size and magnitude than that of the cylinder, the peak shear stresses in the lateral speed up zones are significantly lower. Since the onset of soil erosion occurs when a critical threshold shear stress is experienced, the lower peak shear stress means that plants provide better protection against soil erosion than rigid elements. This result suggests that parameterizations of flow over vegetated surfaces based on measurements of rigid elements may be incorrect. Further work will investigate sheltering and shear stress concentrations as a function of cylinder / plant density using real canopies instead of single objects.

Walter, B. A.; Gromke, C.; Leonard, K. C.; Clifton, A.; Lehning, M.

2010-12-01

127

Shear stress-induced Ca²? mobilization in MDCK cells is ATP dependent, no matter the primary cilium.  

PubMed

Primary cilium has emerged as mechanosensor to subtle flow variations in epithelial cells, but its role in shear stress detection remains controversial. To probe the function of this non-motile organelle in shear stress detection by cells, we compared calcium signalling responses induced by shear stress in ciliated and unciliated MDCK cells. Cytosolic free Ca²? ([Ca²?]i) was measured using Fura-PE3 video imaging fluorescence microscopy in response to shear stress due to laminar flow (385 ?l s?¹). Our results show that both unciliated and ciliated MDCK cells are shear stress sensitive via ATP release and autocrine feedback through purinergic receptors. However, purinergic calcium signals differed in response intensity and receptor subtypes. In unciliated cells, shear stress-induced elevation in [Ca²?]i was predominantly mediated through P2X receptors (P2XR). In contrast, calcium mobilization in ciliated MDCK cells resulted from P2YRs and store-operated Ca²?-permeable channels besides P2XRs. These findings lend support to the hypothesis that ATP release in response to shear stress is independent of the primary cilium and that transduction of mechanical strain into a specific biochemical responses stems on the mobilization of different sets of purinergic receptors. PMID:23528238

Rodat-Despoix, Lise; Hao, Jizhe; Dandonneau, Mathieu; Delmas, Patrick

2013-03-23

128

Impact of shear and curvature on surface gravity wave stress  

NASA Astrophysics Data System (ADS)

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.

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

2009-09-01

129

The use of shear stress for targeted drug delivery.  

PubMed

Stenosed segments of arteries significantly alter the blood flow known from healthy vessels. In particular, the wall shear stress at critically stenosed arteries is at least an order of magnitude higher than in healthy situations. This alteration represents a change in physical force and might be used as a trigger signal for drug delivery. Mechano-sensitive drug delivery systems that preferentially release their payload under increased shear stress are discussed. Therefore, besides biological or chemical markers, physical triggers are a further principle approach for targeted drug delivery. We hypothesize that such a physical trigger is much more powerful to release drugs for vasodilation, plaque stabilization, or clot lysis at stenosed arteries than any known biological or chemical ones. PMID:23645574

Saxer, Till; Zumbuehl, Andreas; Müller, Bert

2013-05-02

130

Liquid crystals for unsteady surface shear stress visualization  

NASA Astrophysics Data System (ADS)

Oscillating airfoil experiments were conducted to test the frequency response of thermochromic liquid crystal coatings to unsteady surface shear stresses under isothermal-flow conditions. The model was an NACA-0015 airfoil, exposed to an incompressible flow at a freestream Reynolds number (based on chord) of 1.14 x 1000000. Angle-of-attack forcing functions were sine waves of amplitude + or - 10 deg about each of three mean angles of attack: 0 deg 10 deg, and 20 deg. Frequencies of oscillation were 0.2, 0.6 and 1.2 hertz, corresponding to reduced frequencies of 0.0055, 0.0164 and 0.0328. Data acquisition was accomplished by video recording. Observations showed the liquid crystal technique capable of visualizing high surface shear stress zones over the stated dynamic range in a continuous and reversible manner.

Reda, D. C.

1988-04-01

131

Liquid crystals for unsteady surface shear stress visualization  

SciTech Connect

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

Reda, D.C.

1988-01-01

132

Structure-Enhanced Yield Shear Stress in Electrorheological Fluids  

NASA Astrophysics Data System (ADS)

A new technology, compression-assisted aggregation, is developed to enhance the strength of electrorheological (ER) fluids. The yield shear stress of ER fluids depends on the fluid microstructure. The unassisted electric-field induced ER structure mainly consists of single chains, whose weak points are at their ends. This new technology produces a structure consisting of robust thick columns with strong ends. As the weak points of the original ER structure are greatly enforced, the new structure makes ER fluids super-strong: At a moderate electric field and moderate pressure the yield shear stress of ER fluids at 35% volume fraction exceeds 100 kPa, well above any requirement for major industrial applications.

Tao, R.; Lan, Y. C.; Xu, X.

133

PEG-albumin supraplasma expansion is due to increased vessel wall shear stress induced by blood viscosity shear thinning  

PubMed Central

We studied the extreme hemodilution to a hematocrit of 11% induced by three plasma expanders: polyethylene glycol (PEG)-conjugated albumin (PEG-Alb), 6% 70-kDa dextran, and 6% 500-kDa dextran. The experimental component of our study relied on microelectrodes and cardiac output to measure both the rheological properties of plasma-expander blood mixtures and nitric oxide (NO) bioavailability in vessel walls. The modeling component consisted of an analysis of the distribution of wall shear stress (WSS) in the microvessels. Our experiments demonstrated that plasma expansion with PEG-Alb caused a state of supraperfusion with cardiac output 40% above baseline, significantly increased NO vessel wall bioavailability, and lowered peripheral vascular resistance. We attributed this behavior to the shear thinning nature of blood and PEG-Alb mixtures. To substantiate this hypothesis, we developed a mathematical model of non-Newtonian blood flow in a vessel. Our model used the Quemada rheological constitutive relationship to express blood viscosity in terms of both hematocrit and shear rate. The model revealed that the net effect of the hemodilution induced by relatively low-viscosity shear thinning PEG-Alb plasma expanders is to reduce overall blood viscosity and to increase the WSS, thus intensifying endothelial NO production. These changes act synergistically, significantly increasing cardiac output and perfusion due to lowered overall peripheral vascular resistance.

Sriram, Krishna; Tsai, Amy G.; Cabrales, Pedro; Meng, Fantao; Acharya, Seetharama A.; Tartakovsky, Daniel M.

2012-01-01

134

PEG-albumin supraplasma expansion is due to increased vessel wall shear stress induced by blood viscosity shear thinning.  

PubMed

We studied the extreme hemodilution to a hematocrit of 11% induced by three plasma expanders: polyethylene glycol (PEG)-conjugated albumin (PEG-Alb), 6% 70-kDa dextran, and 6% 500-kDa dextran. The experimental component of our study relied on microelectrodes and cardiac output to measure both the rheological properties of plasma-expander blood mixtures and nitric oxide (NO) bioavailability in vessel walls. The modeling component consisted of an analysis of the distribution of wall shear stress (WSS) in the microvessels. Our experiments demonstrated that plasma expansion with PEG-Alb caused a state of supraperfusion with cardiac output 40% above baseline, significantly increased NO vessel wall bioavailability, and lowered peripheral vascular resistance. We attributed this behavior to the shear thinning nature of blood and PEG-Alb mixtures. To substantiate this hypothesis, we developed a mathematical model of non-Newtonian blood flow in a vessel. Our model used the Quemada rheological constitutive relationship to express blood viscosity in terms of both hematocrit and shear rate. The model revealed that the net effect of the hemodilution induced by relatively low-viscosity shear thinning PEG-Alb plasma expanders is to reduce overall blood viscosity and to increase the WSS, thus intensifying endothelial NO production. These changes act synergistically, significantly increasing cardiac output and perfusion due to lowered overall peripheral vascular resistance. PMID:22505638

Sriram, Krishna; Tsai, Amy G; Cabrales, Pedro; Meng, Fantao; Acharya, Seetharama A; Tartakovsky, Daniel M; Intaglietta, Marcos

2012-04-13

135

Shear-Stress Partitioning in Live Plant Canopies and Modifications to Raupach's Model  

NASA Astrophysics Data System (ADS)

The spatial peak surface shear stress {tau _S^'' on the ground beneath vegetation canopies is responsible for the onset of particle entrainment and its precise and accurate prediction is essential when modelling soil, snow or sand erosion. This study investigates shear-stress partitioning, i.e. the fraction of the total fluid stress on the entire canopy that acts directly on the surface, for live vegetation canopies (plant species: Lolium perenne) using measurements in a controlled wind-tunnel environment. Rigid, non-porous wooden blocks instead of the plants were additionally tested for the purpose of comparison since previous wind-tunnel studies used exclusively artificial plant imitations for their experiments on shear-stress partitioning. The drag partitioning model presented by Raupach (Boundary-Layer Meteorol 60:375-395, 1992) and Raupach et al. (J Geophys Res 98:3023-3029, 1993), which allows the prediction of the total shear stress ? on the entire canopy as well as the peak {(tau _S ^''/tau )^{1/2}} and the average {(tau _S^'/tau )^{1/2}} shear-stress ratios, is tested against measurements to determine the model parameters and the model's ability to account for shape differences of various roughness elements. It was found that the constant c, needed to determine the total stress ? and which was unspecified to date, can be assumed a value of about c = 0.27. Values for the model parameter m, which accounts for the difference between the spatial surface average {tau _S^' and the peak {tau _S ^'' shear stress, are difficult to determine because m is a function of the roughness density, the wind velocity and the roughness element shape. A new definition for a parameter a is suggested as a substitute for m. This a parameter is found to be more closely universal and solely a function of the roughness element shape. It is able to predict the peak surface shear stress accurately. Finally, a method is presented to determine the new a parameter for different kinds of roughness elements.

Walter, Benjamin; Gromke, Christof; Lehning, Michael

2012-08-01

136

Pulsatile flow and atherosclerosis in the human carotid bifurcation. Positive correlation between plaque location and low oscillating shear stress.  

PubMed

Fluid velocities were measured by laser Doppler velocimetry under conditions of pulsatile flow in a scale model of the human carotid bifurcation. Flow velocity and wall shear stress at five axial and four circumferential positions were compared with intimal plaque thickness at corresponding locations in carotid bifurcations obtained from cadavers. Velocities and wall shear stresses during diastole were similar to those found previously under steady flow conditions, but these quantities oscillated in both magnitude and direction during the systolic phase. At the inner wall of the internal carotid sinus, in the region of the flow divider, wall shear stress was highest (systole = 41 dynes/cm2, diastole = 10 dynes/cm2, mean = 17 dynes/cm2) and remained unidirectional during systole. Intimal thickening in this location was minimal. At the outer wall of the carotid sinus where intimal plaques were thickest, mean shear stress was low (-0.5 dynes/cm2) but the instantaneous shear stress oscillated between -7 and +4 dynes/cm2. Along the side walls of the sinus, intimal plaque thickness was greater than in the region of the flow divider and circumferential oscillations of shear stress were prominent. With all 20 axial and circumferential measurement locations considered, strong correlations were found between intimal thickness and the reciprocal of maximum shear stress (r = 0.90, p less than 0.0005) or the reciprocal of mean shear stress (r = 0.82, p less than 0.001). An index which takes into account oscillations of wall shear also correlated strongly with intimal thickness (r = 0.82, p less than 0.001). When only the inner wall and outer wall positions were taken into account, correlations of lesion thickness with the inverse of maximum wall shear and mean wall shear were 0.94 (p less than 0.001) and 0.95 (p less than 0.001), respectively, and with the oscillatory shear index, 0.93 (p less than 0.001). These studies confirm earlier findings under steady flow conditions that plaques tend to form in areas of low, rather than high, shear stress, but indicate in addition that marked oscillations in the direction of wall shear may enhance atherogenesis. PMID:3994585

Ku, D N; Giddens, D P; Zarins, C K; Glagov, S

137

Non-volcanic tremor driven by large transient shear stresses.  

PubMed

Non-impulsive seismic radiation or 'tremor' has long been observed at volcanoes and more recently around subduction zones. Although the number of observations of non-volcanic tremor is steadily increasing, the causative mechanism remains unclear. Some have attributed non-volcanic tremor to the movement of fluids, while its coincidence with geodetically observed slow-slip events at regular intervals has led others to consider slip on the plate interface as its cause. Low-frequency earthquakes in Japan, which are believed to make up at least part of non-volcanic tremor, have focal mechanisms and locations that are consistent with tremor being generated by shear slip on the subduction interface. In Cascadia, however, tremor locations appear to be more distributed in depth than in Japan, making them harder to reconcile with a plate interface shear-slip model. Here we identify bursts of tremor that radiated from the Cascadia subduction zone near Vancouver Island, Canada, during the strongest shaking from the moment magnitude M(w) = 7.8, 2002 Denali, Alaska, earthquake. Tremor occurs when the Love wave displacements are to the southwest (the direction of plate convergence of the overriding plate), implying that the Love waves trigger the tremor. We show that these displacements correspond to shear stresses of approximately 40 kPa on the plate interface, which suggests that the effective stress on the plate interface is very low. These observations indicate that tremor and possibly slow slip can be instantaneously induced by shear stress increases on the subduction interface-effectively a frictional failure response to the driving stress. PMID:17671500

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

2007-08-01

138

Liquid crystals for unsteady surface shear stress visualization  

Microsoft Academic Search

Oscillating airfoil experiments were conducted to test the frequency response of thermochromic liquid crystal coatings to unsteady surface shear stresses under isothermal-flow conditions. The model was an NACA-0015 airfoil, exposed to an incompressible flow at a freestream Reynolds number (based on chord) of 1.14 x 10⁶. Angle-of-attack forcing functions were sine waves of amplitude +- 10\\/degree\\/ about each of three

Reda

1988-01-01

139

Fluid Shear Stress Induces ß-Catenin Signaling in Osteoblasts  

Microsoft Academic Search

?-Catenin plays a dual role in cells: one at cell–cell junctions and one regulating gene transcription together with TCF (T-cell Factor) in the nucleus. Recently, a role for ?-catenin in osteoblast differentiation and gene expression has begun to be elucidated. Herein we investigated the effects of fluid shear stress (FSS) on ?-catenin signaling. FSS is a well-characterized anabolic stimulus for

S. M. Norvell; M. Alvarez; J. P. Bidwell; F. M. Pavalko

2004-01-01

140

Literacy Measure B - Stress  

Center for Drug Evaluation (CDER)

... Literacy Measure B - Stress. STRESS. Frequency. Percent. Valid Percent. Cumulative Percent. Valid, Correct, 890, 98.5, 98.5, 98.5. Incorrect, 8, .9, .9 ... More results from www.fda.gov/drugs/developmentapprovalprocess/developmentresources

141

Pulse shear stress for anaerobic membrane bioreactor fouling control.  

PubMed

Increase of shear stress at membrane surfaces is a generally applied strategy to minimize membrane fouling. It has been reported that a two-phase flow, better known as slug flow, is an effective way to increase shear stress. Hence, slug flow was introduced into an anaerobic membrane bioreactor for membrane fouling control. Anaerobic suspended sludge was cultured in an anaerobic membrane bioreactor (AMBR) operated with a side stream inside-out tubular membrane unit applying sustainable flux flow regimes. The averaged particle diameter decreased from 20 to 5 microm during operation of the AMBR. However, the COD removal efficiency did not show any significant deterioration, whereas the specific methanogenic activity (SMA) increased from 0.16 to 0.41 gCOD/g VSS/day. Nevertheless, the imposed gas slug appeared to be insufficient for adequate fouling control, resulting in rapidly increasing trans membrane pressures (TMP) operating at a flux exceeding 16 L/m2/h. Addition of powdered activated carbon (PAC) enhanced the effect of slug flow on membrane fouling. However, the combined effect was still considered as not being significant. The tubular membrane was subsequently equipped with inert inserts for creating a locally increased shear stress for enhanced fouling control. Results show an increase in the membrane flux from 16 L/m2/h to 34 L/m2/h after the inserts were mounted in the membrane tube. PMID:22097007

Yang, Jixiang; Spanjers, Henri; van Lier, Jules B

2011-01-01

142

Shear and compression wave measurements in shocked polycrystalline Al2O3  

NASA Astrophysics Data System (ADS)

Experimental techniques have been developed to study the propagation of large-amplitude, one-dimensional shear and compression waves in shocked solids of geophysical interest. Shear wave velocities and amplitudes can be directly measured along with the usual measurements on longitudinal waves. Although shear wave amplitude measurements do not approach the quality of the compression wave data, shear wave velocities can be measured to a precision of better than two percent. Experimental measurements to 90 kbar compressive shock stresses are reported in Al2O3. Within experimental scatter (±2%), our shear wave velocity data are in good agreement with the extrapolation of the ultrasonic measurements. The longitudinal measurements are in good agreement with earlier work. The experimental developments reported here are expected to be important to high pressure geophysics applications because they provide a direct measure of the shear modulus in the shocked state. The shear modulus is not only a more sensitive indicator of the solid state than the longitudinal modulus but in conjunction with the longitudinal wave data can provide the mean stress-volume relations for comparison with static data.

Gupta, Y. M.

1983-05-01

143

Wind waves on a mudflat: The influence of fetch and depth on bed shear stresses  

NASA Astrophysics Data System (ADS)

Wind waves were measured in the Willapa Bay mudflats, Washington State, USA, for two months. Wave height, period, and bed shear stresses were modulated by water depth (0-3.5m), wind speed (0-20m/s), and fetch (1-5km). Good agreement was found between the measured waves and predictions of the wave spectral model SWAN using either simplified 1D flat bottom or 2D geometries. The relationship between bed shear stress and water depth shows a dependence on fetch: the decay of bed shear stress with increasing water depth is gradual for long fetch and rapid for short fetch. This difference is explained by the coupled effects of water depth, wave height and wave period. Due to the fetch-dependent bed shear stress, different morphological consequences for tidal flats of different size are predicted. In small (˜2km) and sheltered tidal flats, waves cause the largest sediment resuspension when water levels are near mean sea level. In extensive tidal flats (˜20km) or in flats exposed to waves propagating from deep water, waves also are effective in causing substrate erosion during high tides or large storm surges.

Mariotti, Giulio; Fagherazzi, Sergio

2013-06-01

144

Wind waves on a mudflat: The influence of fetch and depth on bed shear stresses  

NASA Astrophysics Data System (ADS)

Wind waves were measured in the Willapa Bay mudflats, Washington State, USA, for two months. Wave height, period, and bed shear stresses were modulated by water depth (0-3.5 m), wind speed (0-20 m/s), and fetch (1-5 km). Good agreement was found between the measured waves and predictions of the wave spectral model SWAN using either simplified 1D flat bottom or 2D geometries. The relationship between bed shear stress and water depth shows a dependence on fetch: the decay of bed shear stress with increasing water depth is gradual for long fetch and rapid for short fetch. This difference is explained by the coupled effects of water depth, wave height and wave period. Due to the fetch-dependent bed shear stress, different morphological consequences for tidal flats of different size are predicted. In small (˜2 km) and sheltered tidal flats, waves cause the largest sediment resuspension when water levels are near mean sea level. In extensive tidal flats (˜20 km) or in flats exposed to waves propagating from deep water, waves also are effective in causing substrate erosion during high tides or large storm surges.

Mariotti, Giulio; Fagherazzi, Sergio

145

Inhomogeneity problem with a sliding interface under remote shearing stress  

NASA Astrophysics Data System (ADS)

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.

Zhao, YingTao; Gao, Yang; Wang, MinZhong

2012-11-01

146

A time-resolved hot-wire shear stress probe for turbulent flow: use of laminar flow calibration  

Microsoft Academic Search

A specially-designed rotating rig for producing near Couette flow was used in the calibration of a marginally elevated hot-wire\\u000a shear stress probe. The probe was then used for measurements in both the turbulent boundary layer and pipe flows. Results\\u000a showed that the mean wall shear stress can be accurately predicted and the near wall statistical quantities of intensity,\\u000a skewness and

Y. T. Chew; B. C. Khoo; G. L. Li

1994-01-01

147

A constant stress, parallel plate viscometer without bearing for very low shear stresses  

Microsoft Academic Search

A simple, constant stress viscometer without bearing is described. The rotating part consists of a ferromagnetic disc which floats on the liquid. It is driven and centred by a fast rotating magnetic field. The shear stress can be varied continuously between 5*10-5 and 0.5 Pa by changing the distance between the disc and the rotating magnet.

T. van Vliet; A. E. A. de Groot-Mostert; A. Prins

1981-01-01

148

Bounds on stress concentration factors in finite anti-plane shear  

Microsoft Academic Search

This paper provides an analytical approach for obtaining bounds on elastic stress concentration factors in the theory of finite anti-plane shear of homogeneous, isotropic, incompressible materials. The problem of an infinite slab with traction-free circular cavity subject to a state of finite simple shear deformation is considered. Explicit estimates are obtained for the maximum shearing stress in terms of the

R. Abeyaratne; C. O. Horgan

1983-01-01

149

Gas-wall shear stress distribution in horizontal stratified two-phase flow  

SciTech Connect

Gas-liquid stratified flow is encountered in several industrial applications including the flow of oil and natural gas in petroleum industries, the flow of refrigerants in air conditioning and refrigeration systems and the flow of steam and water in emergency core cooling (ECC) systems in nuclear /reactors during the postulated loss of coolant accidents (LOCA). Gas-wall shear stresses in the stratified gas-liquid flow in pipes are obtained using Preston`s method for measuring skin friction in the turbulent boundary layer. The non-dimensional relationship between the Preston tube reading and wall shear stress over a wide range of single-phase gas flow rates is reported. The wall shear stresses up to positions close to the gas-liquid interface, for various interface conditions, are obtained for the two-phase flow experiment. The distribution of the gas-wall shear stress and the effect of diameter on those distributions are investigated. The friction factors obtained from the experiments are also compared with those reported in the literature.

Wongwises, S.; Pornsee, A.; Siroratsakul, E. [King Mongkut`s Univ. of Technology Thonburi, Bangkok (Thailand)

1999-08-01

150

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

PubMed

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

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

2013-02-15

151

Power Doppler ultrasound evaluation of the shear rate and shear stress dependences of red blood cell aggregation  

Microsoft Academic Search

The use of power Doppler ultrasound at 10 MHz is evaluated as a method to study the shear rate and the shear stress dependences of red blood cell aggregation. This evaluation was based on 6 in vitro experiments conducted in a 1.27-cm diameter tube under steady flow conditions. Porcine whole blood was circulated in the flow model at flow rates

Guy Cloutier; Zhao Qin; Louis-Gilles Durand; Beng Ghee Teh

1996-01-01

152

Pipetting causes shear stress and elevation of phosphorylated stress-activated protein kinase/jun kinase in preimplantation embryos.  

PubMed

Shear stress at 1.2 dynes/cm(2) induces stress-activated protein kinase/jun kinase phosphorylation that precedes and causes apoptosis in embryos (Xie et al., 2006b, Biol Reprod). Pipetting embryos is necessary for many protocols, from in vitro fertilization to collecting embryos prior to analyzing gene expression by microarrays. We sought to determine if pipetting upregulates phosphorylated MAPK8/9 (formerly known as stress-activated protein kinase/jun kinase/SAPK/JNK1, 2). We found that phosphorylated MAPK8/9, a marker of MAPK8/9 activation, is upregulated in a dose-dependent manner by pipetting. Whereas embryos with the zona pellucida removed were more sensitive to stress-induced lethality mediated by 1.2 dynes/cm(2) shear force, phosphorylated MAPK8/9 was induced at lower numbers of pipet triturations in hatched embryos at E4.5. E4.5 embryos were more sensitive to induction of MAPK8/9 than unhatched embryos at E2.5 or E3.5. E3.5 embryos also showed a pipetting dose-dependent induction of FOS protein (formerly known as c-fos), a marker of shear stress in many cell types. Phosphorylated MAPK8/9 measured in ex vivo embryos from E1.5 to E4.5 were expressed at low levels. Embryos that had been pipetted sufficiently to induce phosphorylated MAPK8/9 and FOS had the same number of cells as untreated embryos 24 hr later. This suggests that rapid phosphorylation of MAPK8/9 due to transient shear stress does not mediate long-term negative biological outcomes. But, it is possible that techniques requiring multiple handling events would induce MAPK8/9 and cause biological outcomes or that other biological outcomes are affected by low amounts of transient shear stress. This study suggests that embryo handling prior to experimental measurement of signal transduction phosphoproteins, proteins and mRNA should be performed with care. Indeed, it is likely that shear stress may cause rapid transient changes in hundreds of proteins and mRNA. PMID:17492777

Xie, Y; Wang, F; Puscheck, E E; Rappolee, D A

2007-10-01

153

Slip transition of a polymer melt under shear stress  

NASA Astrophysics Data System (ADS)

We present the first direct measurements of the local velocity of a sheared polymer melt within the first 100 nm from the solid-liquid interface. For high enough shear rates we observe a sharp transition between weak and strong slip (i.e., a nonzero boundary fluid velocity) in the case of weak polymer-surface interactions [polydimethylsiloxane (PDMS) on silanated silica surfaces]. For strong polymer surface interactions the slip is strongly reduced. These results are compared to a theoretical model recently proposed by Brochard and de Gennes.

Migler, K. B.; Hervet, H.; Leger, L.

1993-01-01

154

Shear Fracture of Bulk Metallic Glasses with Controlled Applied Normal Stresses  

SciTech Connect

Bulk metallic glasses (BMGs) often deform by the formation of localized shear bands which is followed by sudden shear fracture. This fracture behavior has been found to depend on not only the shear stress but also the stress normal to the shear plane, and the Mohr-Coulomb criterion has been applied to characterize shear fracture of BMGs. However, systematic verification of its applicability is non-existent because of the inability of controlling the normal to shear stress ratio on the fracture plane in the existing tests performed on BMGs. Here, we use a unique test fixture that is capable of controlling (i) the location of shear fracture and (ii) the normal to shear stress ratio on the fracture plane to perform tests on BMGs to verify the applicability of the Mohr-Coulomb criterion.

Hsueh, Chun-Hway [ORNL; Bei, Hongbin [ORNL; Liu, Chain T [ORNL; Becher, Paul F [ORNL; George, Easo P [ORNL

2008-01-01

155

Shear wave speed measurement using an unfocused ultrasound beam.  

PubMed

Tissue elasticity is related to pathology and, therefore, has important medical applications. Radiation force from a focused ultrasound beam has been used to produce shear waves in tissues for shear wave speed and tissue elasticity measurements. The feasibility of shear wave speed measurement using radiation force for an unfocused ultrasound beam is demonstrated in this study with a linear and a curved array transducer. Consistent measurement of shear wave speed was achieved over a relatively long axial extent (z = 10-40 mm for the linear array, and z = 15-60 mm for the curved array) in three calibrated phantoms with different shear moduli. In vivo measurements on the biceps of a healthy volunteer show consistent increase of shear wave speed for the biceps under 0, 1, 2 and 3 kg loading. Advantages and limitations of unfocused push are discussed. PMID:22766123

Zhao, Heng; Song, Pengfei; Urban, Matthew W; Greenleaf, James F; Chen, Shigao

2012-07-03

156

Influence of shear stress on behaviors of piezoelectric voltages in bone.  

PubMed

The piezoelectric properties of bone play an important role in the bone remodeling process and can be employed in clinical bone repair. In this study, the piezo-voltage of bone between two surfaces of a bone beam under bending deformation was measured using an ultra-high-input impedance bioamplifier. The influence of shear stress on the signs of piezo-voltages in bone was determined by comparing and contrasting the results from three-point and four-point bending experiments. From the three-point bending experiment, the study found that the signs of piezo-voltages depend only on shear stress and are not sensitive to the normal stress. PMID:22084058

Fu, Donghui; Hou, Zhende; Qin, Qing-Hua; Xu, Lianyun; Zeng, Yanjun

2011-11-14

157

Effects of shear stress applied to surfaces in stationary contact on rock friction  

NASA Astrophysics Data System (ADS)

In this paper we show how the applied shear stress affects the frictional strength of granite sliding surfaces initially held in stationary contact. We develop an experimental scheme to perform a slide and hold friction test whereby the shear stress is servocontrolled during the hold period of the test. A series of experiments conducted at a single normal stress of 5 MPa, show the following effects. First, unloading the shear stress during the hold period increases frictional resistance by up to 10-20% a decrease in shear stress linearly increases the frictional resistance of the interface. Secondly, the static friction coefficient increases with the logarithm of contact time. The friction coefficient increases by 0.01 per decade of contact time at near zero shear stress levels, and by more than 0.02 at shear stress levels that are greater than half the sliding friction.

Nakatani, Masao; Mochizuki, Hiromine

158

Role of xanthine oxidoreductase and NAD(P)H oxidase in endothelial superoxide production in response to oscillatory shear stress.  

PubMed

Oscillatory shear stress occurs at sites of the circulation that are vulnerable to atherosclerosis. Because oxidative stress contributes to atherosclerosis, we sought to determine whether oscillatory shear stress increases endothelial production of reactive oxygen species and to define the enzymes responsible for this phenomenon. Bovine aortic endothelial cells were exposed to static, laminar (15 dyn/cm2), and oscillatory shear stress (+/-15 dyn/cm2). Oscillatory shear increased superoxide (O2.-) production by more than threefold over static and laminar conditions as detected using electron spin resonance (ESR). This increase in O2*- was inhibited by oxypurinol and culture of endothelial cells with tungsten but not by inhibitors of other enzymatic sources. Oxypurinol also prevented H2O2 production in response to oscillatory shear stress as measured by dichlorofluorescin diacetate and Amplex Red fluorescence. Xanthine-dependent O2*- production was increased in homogenates of endothelial cells exposed to oscillatory shear stress. This was associated with decreased xanthine dehydrogenase (XDH) protein levels and enzymatic activity resulting in an elevated ratio of xanthine oxidase (XO) to XDH. We also studied endothelial cells lacking the p47phox subunit of the NAD(P)H oxidase. These cells exhibited dramatically depressed O2*- production and had minimal XO protein and activity. Transfection of these cells with p47phox restored XO protein levels. Finally, in bovine aortic endothelial cells, prolonged inhibition of the NAD(P)H oxidase with apocynin decreased XO protein levels and prevented endothelial cell stimulation of O2*- production in response to oscillatory shear stress. These data suggest that the NAD(P)H oxidase maintains endothelial cell XO levels and that XO is responsible for increased reactive oxygen species production in response to oscillatory shear stress. PMID:12958034

McNally, J Scott; Davis, Michael E; Giddens, Don P; Saha, Aniket; Hwang, Jinah; Dikalov, Sergey; Jo, Hanjoong; Harrison, David G

2003-09-04

159

Cell-Activation by Shear Stresses in Abdominal Aortic Aneurysms (AAA)  

NASA Astrophysics Data System (ADS)

Increasing experimental evidence indicates that low and oscillatory shear stresses promote proliferative, thrombotic, adhesive and inflammatory-mediated degenerative conditions throughout the wall of the aorta. These degenerative conditions have been shown to be involved in the pathogenesis of AAAs, a permanent, localized dilatation of the abdominal aorta. The purpose of this study is to measure both the magnitude and the duration of the shear stresses acting on both the arterial walls and on the blood cells inside AAAs, and to characterize their changes as the AAA enlarges. We conducted a parametric in-vitro study of the pulsatile blood flow in elastic models of AAAs while systematically varying the blood flow parameters, and the geometry of the aneurysm's bulging. The instantaneous flow characteristic inside the AAA was measured using DPIV at a sampling rate of 15 Hertz. A "cell-activation parameter" defined as the integral of the product of the magnitude of the shear stress and the time during which the stress acts was computed along each of the blood cell pathlines. The Lagrangian tracking of the blood cells shows that a large majority of them are subjected first to very high level of shear-induced "cell-activation" while later on they are entrained in regions of stasis where their residence time can increase up to several cardiac cycles. This cell-activation followed by the entrainment in low shear regions creates the optimal cell-adhesive and inflammatory-mediated degenerative conditions that are postulated to play an important role in the etiology and progressive enlargement of AAAs.

Salsac, Anne-Virginie; Sparks, Steven; Chomaz, Jean-Marc; Lasheras, Juan C.

2003-11-01

160

The Effect of Desert Shrubs on Shear Stress from the Wind: AN Exploratory Study  

NASA Astrophysics Data System (ADS)

Wind flow near desert surfaces is modified by shrubs, which slow the wind by friction. Shrubs also modify the spatial pattern of the shear stress of wind exerted on the ground surface. This study examines the effect of shrub spacing on these two processes, examined both in a wind tunnel and at field sites in the Mojave and Sonoran Deserts. The wind tunnel experiments involved measurements of wind profiles and surface shear stress for isolated objects and for arrays of objects with varying spacings. The objects used were cylinders and model shrubs. Wind profiles were measured with pitot tubes and surface shear stress was determined with a technique involving the rate of sublimation of naphthalene at points on a naphthalene surface. Flat field sites were selected with scattered shrubs, sufficient fetch, and no nearby topographical obstacles which might modify the wind flow at the site. Wind profiles were obtained with cup anemometers on a seven meter mast and also on a one meter mast which was placed at different locations around a shrub for determination of the near surface flow characteristics. The wind profiles were reduced to determine the values of the profile parameters, which are the zero plane displacement, d, aerodynamic roughness parameter, z _{rm o}, and friction speed, u*. In the wind tunnel, d was consistently negative while z_{rm o} was very high, which indicates that the surface was aerodynamically very rough. In the field, however, the opposite pattern was found, with d above the tops of the shrubs and z_{rm o} very small, showing that wind was effectively skimming over the shrubs and encountering little friction from the surface and the shrubs. The reason for the different wind tunnel and field values of the profile parameters is not known. In the field, there was no discernable pattern in the variation of d with shrub spacing, though z _{rm o} decreased with shrub spacing in a manner consistent with previous studies. The magnitude of the surface shear stress around the cylinders and shrubs in the wind tunnel decreased with object spacing, as expected. The pattern of the surface shear stress also varies with object spacing in that the basic pattern for an isolated object is maintained until the spacing is approximately four times the object height. At denser arrangements, the surface pattern becomes more complex. In the field, a poorly defined trend suggests that surface shear stress also decreases with shrub spacing. No clearly defined spatial pattern of surface stress was found, indicating that the flow is highly complex and generalizations about the pattern will require improved field methods or sample sizes much larger than used in this study.

Lee, Jeffrey Alan

1990-01-01

161

Methods for Determining Streambank Critical Shear Stress and Erodibility: Implications for Erosion Rate Predictions  

NASA Astrophysics Data System (ADS)

According to the US EPA, excess sediment is a significant cause of water quality impairment for rivers. The goal of this study was to compare different methods of determining two parameters used to estimate streambank erosion, soil critical shear stress (?c) and erodibility (kd), and to determine the impact of those differences on streambank erosion predictions. At twenty-five field sites, bank erosion tests were conducted using a submerged jet test device to measure critical shear stress and erodibility for streambanks composed of fine grained soils. Additionally, soil samples were collected and analyzed for particle size distribution, Atterberg limits, bulk density, and root density. Critical shear stress was estimated using Shield¡¦s diagram (SD), and three empirical equations based on percent clay (Pc), plasticity index (Iw), and median particle size (D50). Additionally, using a single set of ?c values, the kd measured by the jet test was compared to two empirical kd relationships. Using these parameter values, streambank erosion rates were predicted for a local stream. Study results showed the measured ?c estimates were as much as four orders of magnitude greater than the SD, Pc, and D50 estimates, indicating the SD and empirical methods underestimate ?c for fine grained soils. The two empirical kd equations produced similar values. Both empirical parameter estimates were generally two orders of magnitude less than the kd values measured in situ. Erosion predictions followed the same trend as the kd data; the measured parameter values produced higher erosion predictions than the two empirical methods, although all three methods resulted in unrealistic erosion estimates. Field validation of these methods over a wide range of soil types is recommended to further develop methods of estimating kd and ?c for streambank soils. Additionally, the effects of riparian vegetation on near bank shear stresses should be explored further.

Clark, L.; Wynn, T.

2006-05-01

162

Spatial Stress and Strain Distributions of Viscoelastic Layers in Oscillatory Shear  

PubMed Central

One of the standard experimental probes of a viscoelastic material is to measure the response of a layer trapped between parallel surfaces, imposing either periodic stress or strain at one boundary and measuring the other. The relative phase between stress and strain yields solid-like and liquid-like properties, called the storage and loss moduli, respectively, which are then captured over a range of imposed frequencies. Rarely are the full spatial distributions of shear and normal stresses considered, primarily because they cannot be measured except at boundaries and the information was not deemed of particular interest in theoretical studies. Likewise, strain distributions throughout the layer were traditionally ignored except in a classical protocol of Ferry, Adler and Sawyer, based on snapshots of standing shear waves. Recent investigations of thin lung mucus layers exposed to oscillatory stress (breathing) and strain (coordinated cilia), however, suggest that the wide range of healthy conditions and environmental or disease assaults lead to conditions that are quite disparate from the “surface loading” and “gap loading” conditions that characterize classical rheometers. In this article, we extend our previous linear and nonlinear models of boundary stresses in controlled oscillatory strain to the entire layer. To illustrate non-intuitive heterogeneous responses, we characterize experimental conditions and material parameter ranges where the maximum stresses migrate into the channel interior.

Lindley, Brandon S.; Forest, M. Gregory; Smith, Breannan D.; Mitran, Sorin M.; Hill, David B.

2010-01-01

163

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

PubMed

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

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

2013-01-01

164

Effects of shear stress applied to surfaces in stationary contact on rock friction  

Microsoft Academic Search

In this paper we show how the applied shear stress affects the frictional strength of granite sliding surfaces initially held in stationary contact. We develop an experimental scheme to perform a slide and hold friction test whereby the shear stress is servocontrolled during the hold period of the test. A series of experiments conducted at a single normal stress of

Masao Nakatani; Hiromine Mochizuki

1996-01-01

165

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

NASA Astrophysics Data System (ADS)

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.

Fagereng, Å.

2013-05-01

166

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

SciTech Connect

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.

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

2010-09-01

167

On modeling the Reynolds stresses in turbulent shear flows  

NASA Astrophysics Data System (ADS)

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

Knoell, Jens

2000-11-01

168

Polarization in Perovskite Manganites induced by Shear Stress  

NASA Astrophysics Data System (ADS)

We found static polarization in perovskite manganite films when they are under shear stress. The phenomenon is omnipresent in films deformed in (at least) monoclinic fashion due to the substrate-imposed strain, whereas it is absent in bulk crystals even though they are distorted in a similar manner in thermal equilibrium. The substrate stress of low symmetry is clearly the driving force for the appearance of the polarization. Optical second-harmonic generation (SHG) confirms the loss of inversion symmetry in strained films and pyroelectricity was detected in insulating films confirming the presence of the static polarization. DFT calculations show that the stable atomic positions in the experimentally observed structure is polar with the shift of the center of gravity of anions relative to that of cations as much as 10-2 å. The calculated polar structure is consistent with the symmetry obtained from the SHG polarimetry.

Miyano, K.; Ogawa, N.; Ida, Y.; Tamaki, R.; Shimizu, K.; Nomura, Y.; Arita, R.; Ogimoto, Y.

2012-02-01

169

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

Microsoft Academic Search

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

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

2005-01-01

170

Caveola ATP synthase mediates ATP release in vascular endothelial cells exposed to shear stress  

Microsoft Academic Search

Endothelial cells (ECs) release ATP in response to shear stress, a mechanical force generated by blood flow, and the ATP released modulates EC functions through activation of purinoceptors. The molecular mechanism of the shear-stress-induced ATP release, however, has not been fully understood. In this study, we have demonstrated that cell-surface ATP synthase is involved in shear stress-induced ATP release. Immunofluorescence

K. Yamamoto; S. Obi; N. Shimizu; S. Kumagaya; J. Ando

2007-01-01

171

Mathematical Model for Shear Stress-strain Relationship of Unsaturated Soil  

Microsoft Academic Search

Shear stress-strain model of unsaturated soil plays an important role in its constitutive law, and it is very interesting and not well solved. In this paper, deficiency of traditional hyperbolic model for unsaturated soil shear stress-strain relationship is analyzed by employing half-value-strength index (HVSI). A new model with 3 parameters for unsaturated soil shear stress-strain relationship is established based on

Wei Wang; Tinghao Lu

2008-01-01

172

Reynolds shear stress and heat flux balance in a turbulent round jet  

Microsoft Academic Search

Measurements are presented of the budgets of the turbulent energy, Reynolds shear stress, and the heat flux in an axisymmetric heated turbulent jet with a coflowing isothermal external stream. The jet-to-external-velocity ratio is 6.6, and the temperature of the jet is 34 C above that of the ambient temperature external stream. The budgets are obtained for both the conventional and

R. A. Antonia; A. Prabhu

1976-01-01

173

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

Microsoft Academic Search

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

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

2010-01-01

174

Shear stress regulates the endothelial Kir2.1 ion channel  

NASA Astrophysics Data System (ADS)

Endothelial cells (ECs) line the mammalian vascular system and respond to the hemodynamic stimulus of fluid shear stress, the frictional force produced by blood flow. When ECs are exposed to shear stress, one of the fastest responses is an increase of K+ conductance, which suggests that ion channels are involved in the early shear stress response. Here we show that an applied shear stress induces a K+ ion current in cells expressing the endothelial Kir2.1 channel. This ion current shares the properties of the shear-induced current found in ECs. In addition, the shear current induction can be specifically prevented by tyrosine kinase inhibition. Our findings identify the Kir2.1 channel as an early component of the endothelial shear response mechanism.

Hoger, Jeff H.; Ilyin, Victor I.; Forsyth, Scott; Hoger, Anne

2002-05-01

175

Effect of Zinc and Nitric Oxide on Monocyte Adhesion to Endothelial Cells under Shear Stress  

PubMed Central

This study describes the effect of zinc on monocyte adhesion to endothelial cells under different shear stress regimens, which may trigger atherogenesis. Human umbilical vein endothelial cells were exposed to steady shear stress (15 dynes/cm2 or 1 dyne/cm2) or reversing shear stress (time average 1 dyne/cm2) for 24 hours. In all shear stress regimes, zinc deficiency enhanced THP-1 cell adhesion, while heparinase III reduced monocyte adhesion following reversing shear stress exposure. Unlike other shear stress regimes, reversing shear stress alone enhanced monocyte adhesion, which may be associated with increased H2O2 and superoxide together with relatively low levels of nitric oxide (NO) production. L-NG-Nitroarginine methyl ester (L-NAME) treatment increased monocyte adhesion under 15 dynes/cm2 and under reversing shear stress. After reversing shear stress monocyte adhesion dramatically increased with heparinase III treatment followed by a zinc scavenger. Static culture experiments supported the reduction of monocyte adhesion by zinc following endothelial cell cytokine activation. These results suggest that endothelial cell zinc levels are important for the inhibition of monocyte adhesion to endothelial cells, and may be one of the key factors in the early stages of atherogenesis.

Lee, Sungmun; Eskin, Suzanne G.; Shah, Ankit K.; Schildmeyer, Lisa A.; McIntire, Larry V.

2011-01-01

176

Development of shear flow thermal rheometer for direct measurement of crystallization fraction of polymer melts under shear deformation  

Microsoft Academic Search

Recently viscoelastic measurement has received considerable attention as a complementary method to estimate the crystallization dynamics under shear. However, because of the complex relationship between the crystallization fraction and dynamic mechanical results, it has been difficult to obtain accurate crystallization fraction under shear. To conduct the direct determination of crystallization fraction under shear, the shear flow thermal rheometer (SFTR) having

W. Nagatake; T. Takahashi; Y. Masubuchi; J.-I. Takimoto; K. Koyama

2000-01-01

177

The dependence of particle permittivity on the shear stress of electrorheological fluids  

NASA Astrophysics Data System (ADS)

A ferroelectric TGS particle/silicone oil electrorheological (ER) fluid is introduced to investigate the dielectric dependence of the ER effect. The dielectric constant of ferroelectric changes violently with temperature at the Curie temperature (Tc). By measuring temperature dependence of shear stress across Tc, the effect of dielectric constant on shear stress can be directly obtained. All the results are more reliable due to the same conditions, such as size, shape, composition of particles, as well as the same chemical nature of particles and interface property between particles and liquid. The measurement was carried out under a high-frequency (1000 Hz) ac electric field where ER effect is dielectric constant dominated. For the first time, the dependence of the ER effect on dielectric mismatch has been quantitatively obtained experimentally. There is an obvious deviation of available theoretical calculations from our measured data. A more rigorous theoretical study should be developed to quantitatively interpret the relation of the shear stress and the permittivity mismatch factor.

Lan, Yucheng; Men, Shouqiang; Zhao, Xiaopeng; Lu, Kunquan

1998-02-01

178

An optical wall shear stress sensor based on whispering gallery modes of dielectric microspheres  

NASA Astrophysics Data System (ADS)

In recent years, whispering gallery modes (WGM) of dielectric resonators have received significant attention. Based on this phenomenon, many applications have been proposed ranging from spectroscopy [1], micro-cavity laser technology [2] and optical communications (switching [3], filtering [4] and wavelength division and multiplexing [5]). WGM phenomenon have also been exploited in several sensor concepts such as protein adsorption [6,7], trace gas detection [8], impurity detection in liquids [9], structural health monitoring of composite materials [10], detection of electric fields [11], magnetic fields [12, 13] and temperature [14, 15] as well as mechanical sensing, such as pressure [16] and force [17,18]. A remarkable feature of the WGMs of dielectric microspheres is that they can exhibit extremely high quality factors (Q -factors). In literature, Q-factors as high as ˜10 10 have been reported [19]. In sensor applications, Q-factors determine the resolution of the sensor. Since WGMs of dielectric microspheres exhibit such high Q values, proposed WGM based sensors have extremely good sensing resolutions. In this dissertation, a WGM based wall shear stress sensor that is capable of measuring the shear stress directly is presented. The proposed sensor's feasibility is studied both analytically and experimentally. The experimental study included sensor development, fabrication, calibration, frequency response, dynamic range and proof of concept. The sensor showed that it has potential to measure the shear stress in a wide range of Reynolds numbers. Finally, the sensor is tested in a real flow environment to provide the first direct shear stress measurement in a real flow.

Ayaz, Ulas Kemal

179

Shear Stress Regulation of Nitric Oxide Production in Uterine and Placental Artery Endothelial Cells: Experimental studies and Hemodynamic Models of Shear Stress Forces on Endothelial Cells  

PubMed Central

Hemodynamic shear stress is the most powerful physiological regulator of endothelial Nitric Oxide Synthase (eNOS), leading to rapid rises in nitric oxide (NO). The substantial increases in uterine and placental blood flows throughout gestation rely heavily on the action of NO. We and others have investigated endothelial function in response to shear stress with cell culture models of shear stress. In order to apply the results of these studies most effectively, we need a more complete understanding of the origin and coupling of the hemodynamic forces and vascular tissue behavior. For example, equations commonly used to calculate in vivo shear stress incorporate assumptions of steady (non-pulsatile) blood flow and constant viscosity of blood (Newtonian fluid). Using computational models, we can estimate a waveform of shear stress over a cardiac cycle and the change in blood viscosity with shear rate and hematocrit levels, two variables that often change with size of vessel and location within a vascular tree. This review discusses hemodynamics as they apply to blood flow in vessels in hopes that an integration of these fields can lead to improved in vitro shear stress experiments and understanding of NO production in uterine and placental vascular physiology during gestation.

Sprague, Benjamin; Chesler, Naomi C.; Magness, Ronald R.

2009-01-01

180

Sitting and endothelial dysfunction: The role of shear stress  

PubMed Central

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

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

2012-01-01

181

Stress-induced Disentanglement Transition in Simple Shear of Entangled Polymer Solutions  

NASA Astrophysics Data System (ADS)

Our recent experiments show(a)that well-entangled polymer solutions undergo a constitutive flow transition when subjected to a shear stress comparable to or higher than the elastic plateau modulus. During such a transition, the measured shear rate may jump orders of magnitude, accompanied by higher flow birefringence and normal stress. More detailed characteristics will be described to elucidate the nature and origin of the observed flow phenomena, which appears to be highly (b)universal and contradicts the current theoretical understanding (c) based on the refined reptation models. (a) P. Tapadia and S.Q. Wang, Phys. Rev. Lett. 91, 198301 (2003). (b) "Transitional Flow Behavior of Entangled Polyisoprene Solutions", A. Philips and S. Q. Wang, presented in the same session at the 2004 March Meeting of APS. (c) J. Bent et al, Science 301, 1691 (2003); R. Graham, A. Likhtman, T. McLeish and S. Milner, J. Rheol. 47, 1171 (2003).

Tapadia, Prashant; Wang, Shi-Qing

2004-03-01

182

Conductivity measurements in a shear-banding wormlike micellar system.  

PubMed

Shear banding in the cetylpyridinium chloride/sodium salicylate micellar system is investigated using electrical conductivity measurements parallel to the velocity and parallel to the vorticity in a cylindrical Couette cell. The measurements show that the conductivity parallel to the velocity (vorticity) increases (decreases) monotonically with applied shear rate. The shear-induced anisotropy is over one order of magnitude lower than the anisotropy of the N(c) nematic phase. The steady-state conductivity measurements indicate that the anisotropy of the shear induced low-viscosity (high shear rate) phase is not significantly larger than the anisotropy of the high viscosity (low shear rate) phase. We estimate that the micelles in the shear induced low viscosity band are relatively short, with a characteristic length to diameter ratio of 5-15. The relaxation behavior following the onset of shear is markedly different above and below the first critical value ?1, in agreement with results obtained by other methods. The transient measurements show that the overall anisotropy of the sample decreases as the steady state is approached, i.e., the micellar length/the degree of order decrease. PMID:20866620

Photinos, Panos J; López-González, M R; Hoven, Corey V; Callaghan, Paul T

2010-07-09

183

Effect of nonuniform stresses on measured DSS stress-strain behavior  

Microsoft Academic Search

This paper presents results of a laboratory investigation of the influence of the nonuniform stresses imposed by the Geonor direct simple-shear (DSS) apparatus on measured stress-strain behavior. The investigation concentrated on the influence of the apparatus on the measured strain-softening behavior of cohesive soils during constant volume (undrained) shear. Special DSS tests were conducted on an elastic material and cohesive

Don J. DeGroot; John T. Germaine; Charles C. Ladd

1994-01-01

184

Shear-Stress Intensity Factors for Elastic Sheets with Cover Plates.  

National Technical Information Service (NTIS)

Shear stress intensity factors are calculated for three problems concerning inextensible cover plates either bonded to or embedded in an elastic sheet which is under uniaxial tension. The stress intensity factors are small when the ratio of sheet thicknes...

W. B. Fichter

1974-01-01

185

Measuring and predicting Stress Distribution under Tractive Devices in Undisturbed Soils  

Microsoft Academic Search

The objective of this study was to compare predicted stresses with measured stresses within the soil profile underneath a tractor rear tyre as affected by soil type, dynamic load, and contact pressure. The major principal stress, octahedral normal stress, and octahedral shearing stress were compared. A three-dimensional non-linear finite element model was used to predict soil profile stresses while stress

Nidal H Abu-Hamdeh; Randall C Reeder

2003-01-01

186

A Modified Dynamic Model for Shear Stress Induced ATP Release from Vascular Endothelial Cells  

Microsoft Academic Search

A modified dynamic model is proposed for shear stress induced adenosine triphosphate (ATP) release from endothelial cells\\u000a (ECs) in order to incorporate the activation mechanism by time-varying shear stress. The dynamic behavior of ATP concentration\\u000a at the endothelium-fluid interface by viscous shear flow is investigated via simulation studies. The numerical results demonstrate\\u000a that the ATP concentration against time at the

Cheng Xiang; Lingling Cao; Kairong Qin; Zhe Xu; Ben M. Chen

2007-01-01

187

Shear strength measurements in a shock loaded commercial silastomer  

NASA Astrophysics Data System (ADS)

The shock-induced shear strength of a commercial silastomer, trade name Sylgard 184™, has been determined using laterally mounted manganin stress gauges. Shear strength has been observed to increase with increasing shock amplitude, in common with many other materials. Shear strength has also been observed to increase slightly behind the shock front as well. It is believed that a combination of polymer chain entanglement and cross linking between chains is responsible. Finally, a ramp on the leading edge of the lower amplitude stress traces has been observed. It has been suggested that this is due to shock-induced collapse of free space between the polymer chains. Similar explanations have been used to explain the apparent non-linearity of the shock velocity with particle velocity at low shock amplitudes.

Millett, J. C. F.; Whiteman, G.; Stirk, S. M.; Bourne, N. K.

2011-05-01

188

Development of a novel bioreactor to apply shear stress and tensile strain simultaneously to cell monolayers  

Microsoft Academic Search

To date many bioreactor experiments have investigated the cellular response to isolated in vitro forces. However, in vivo, wall shear stress (WSS) and tensile hoop strain (THS) coexist. This article describes the techniques used to build and validate a novel vascular tissue bioreactor, which is capable of applying simultaneous wall shear stress and tensile stretch to multiple cellular substrates. The

Liam T. Breen; Peter E. McHugh; Brendan A. McCormack; Gordon Muir; Nathan J. Quinlan; Kevin B. Heraty; Bruce P. Murphy

2006-01-01

189

Critical shear stress for erosion of cohesive soils subjected to temperatures typical of wildfires  

Microsoft Academic Search

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

John A. Moody; J. Dungan Smith; B. W. Ragan

2005-01-01

190

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

Microsoft Academic Search

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

Simon Lamb

2006-01-01

191

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

Microsoft Academic Search

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

Simon Lamb

2006-01-01

192

Pulsatile Versus Oscillatory Shear Stress Regulates NADPH Oxidase Subunit Expression: Implication for Native LDL Oxidation  

Microsoft Academic Search

Shear stress regulates endothelial nitric oxide and superoxide (O 2 · ) production, implicating the role of NADPH oxidase activity. It is unknown whether shear stress regulates the sources of reactive species production, consequent low-density lipoprotein (LDL) modification, and initiation of inflammatory events. Bovine aortic endothelial cells (BAECs) in the presence of 50 g\\/mL of native LDL were exposed to

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

2003-01-01

193

A shear stress sensor for tactile sensing with the piezoresistive cantilever standing in elastic material  

Microsoft Academic Search

In this paper, we propose a tactile sensor with standing piezoresistive cantilevers embedded in an elastic material. The sensor detects the shear stress applied on its surface. Each standing piezoresistive cantilever in the elastic material detects a certain axial component of applied shear stress. By arranging this standing piezoresistive cantilever in orthogonal directions, the directions and the magnitudes of applied

Kentaro Noda; Kazunori Hoshino; Kiyoshi Matsumoto; Isao Shimoyama

2006-01-01

194

Stress concentration factors in finite anti-plane shear: numerical calculations and analytical estimates  

Microsoft Academic Search

In two recent papers [1, 2], an analytical approach for obtaining bounds on elastic stress concentration factors in the theory of finite anti-plane shear of homogeneous isotropic incompressible materials was presented. For the problem of an infinite slab, with a traction-free circular or elliptical cavity, subject to a state of finite simple shear deformation, explicit estimates for the stress concentration

C. O. Horgan; S. A. Silling

1987-01-01

195

Effect of Shear Stress on Permeability of Vascular Endothelial Monolayer Cocultured with Smooth Muscle Cells  

NASA Astrophysics Data System (ADS)

Effect of fluid shear stress on permeability of endothelial monolayer was investigated using an endothelial cell (EC)-smooth muscle cell (SMC) cocultured model (CM). Permeability of ECs to bovine serum albumin was measured after exposure to shear stress of 1.5Pa for 48 hours. Morphology and VE-cadherin expression of ECs in CM was almost same as of ECs cultured alone (monocultured model, MM). Under static condition, EC permeability was 5.1±3.0 × 10-6cm/sec (mean±SD) in MM and 6.5±3.4 × 10-6cm/sec in CM. After exposure to shear stress, EC permeability in CM (2.2±1.9 × 10-6cm/sec, p < 0.05) significantly decreased compared with the static model. However, EC permeability in MM (3.9±3.2 × 10-6cm/sec) did not significantly change compared with static cultured condition. These results suggested that cellular interactions between ECs and SMCs have important influences on EC permeability.

Sakamoto, Naoya; Ohashi, Toshiro; Sato, Masaaki

196

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

NASA Astrophysics Data System (ADS)

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

Mitchell, Michael J.; King, Michael R.

2013-01-01

197

In Vivo Wall Shear Measurements within the Developing Zebrafish Heart  

PubMed Central

Physical forces can influence the embryonic development of many tissues. Within the cardiovascular system shear forces resulting from blood flow are known to be one of the regulatory signals that shape the developing heart. A key challenge in investigating the role of shear forces in cardiac development is the ability to obtain shear force measurements in vivo. Utilising the zebrafish model system we have developed a methodology that allows the shear force within the developing embryonic heart to be determined. Accurate wall shear measurement requires two essential pieces of information; high-resolution velocity measurements near the heart wall and the location and orientation of the heart wall itself. We have applied high-speed brightfield imaging to capture time-lapse series of blood flow within the beating heart between 3 and 6 days post-fertilization. Cardiac-phase filtering is applied to these time-lapse images to remove the heart wall and other slow moving structures leaving only the red blood cell movement. Using particle image velocimetry to calculate the velocity of red blood cells in different regions within the heart, and using the signal-to-noise ratio of the cardiac-phase filtered images to determine the boundary of blood flow, and therefore the position of the heart wall, we have been able to generate the necessary information to measure wall shear in vivo. We describe the methodology required to measure shear in vivo and the application of this technique to the developing zebrafish heart. We identify a reduction in shear at the ventricular-bulbar valve between 3 and 6 days post-fertilization and demonstrate that the shear environment of the ventricle during systole is constantly developing towards a more uniform level.

Jamison, R. Aidan; Samarage, Chaminda R.; Bryson-Richardson, Robert J.; Fouras, Andreas

2013-01-01

198

In Vivo Wall Shear Measurements within the Developing Zebrafish Heart.  

PubMed

Physical forces can influence the embryonic development of many tissues. Within the cardiovascular system shear forces resulting from blood flow are known to be one of the regulatory signals that shape the developing heart. A key challenge in investigating the role of shear forces in cardiac development is the ability to obtain shear force measurements in vivo. Utilising the zebrafish model system we have developed a methodology that allows the shear force within the developing embryonic heart to be determined. Accurate wall shear measurement requires two essential pieces of information; high-resolution velocity measurements near the heart wall and the location and orientation of the heart wall itself. We have applied high-speed brightfield imaging to capture time-lapse series of blood flow within the beating heart between 3 and 6 days post-fertilization. Cardiac-phase filtering is applied to these time-lapse images to remove the heart wall and other slow moving structures leaving only the red blood cell movement. Using particle image velocimetry to calculate the velocity of red blood cells in different regions within the heart, and using the signal-to-noise ratio of the cardiac-phase filtered images to determine the boundary of blood flow, and therefore the position of the heart wall, we have been able to generate the necessary information to measure wall shear in vivo. We describe the methodology required to measure shear in vivo and the application of this technique to the developing zebrafish heart. We identify a reduction in shear at the ventricular-bulbar valve between 3 and 6 days post-fertilization and demonstrate that the shear environment of the ventricle during systole is constantly developing towards a more uniform level. PMID:24124507

Jamison, R Aidan; Samarage, Chaminda R; Bryson-Richardson, Robert J; Fouras, Andreas

2013-10-04

199

Brachial artery adaptation to lower limb exercise training: role of shear stress.  

PubMed

Lower limb exercise increases upper limb conduit artery blood flow and shear stress, and leg exercise training can enhance upper limb vascular function. We therefore examined the contribution of shear stress to changes in vascular function in the nonexercising upper limbs in response to lower limb cycling exercise training. Initially, five male subjects underwent bilateral brachial artery duplex ultrasound to measure blood flow and shear responses to 30-min cycling exercise at 80% of maximal heart rate. Responses in one forearm were significantly (P < 0.05) attenuated via cuff inflation throughout the exercise bout. An additional 11 subjects participated in an 8-wk cycle training study undertaken at a similar intensity, with unilateral cuff inflation around the forearm during each exercise bout. Bilateral brachial artery flow-mediated dilation responses to a 5-min ischemic stimulus (FMD%), an ischemic handgrip exercise stimulus (iEX), and endothelium-independent NO donor administration [glyceryl trinitrate (GTN)] were measured at 2, 4, and 8 wk. Cycle training increased FMD% in the noncuffed limb at week 2, after which time responses returned toward baseline levels (5.8 ± 4.1, 8.6 ± 3.8, 7.4 ± 3.5, 6.0 ± 2.3 at 0, 2, 4 and 8 wk, respectively; ANOVA: P = 0.04). No changes in FMD% were observed in the cuffed arm. No changes were evident in response to iEX or GTN in either the cuffed or noncuffed arms (P > 0.05) across the 8-wk intervention period. Our data suggest that lower limb cycle training induces a transient increase in upper limb vascular function in healthy young humans, which is, at least partly, mediated via shear stress. PMID:22403347

Birk, Gurpreet K; Dawson, Ellen A; Atkinson, Ceri; Haynes, Andrew; Cable, N Timothy; Thijssen, Dick H J; Green, Daniel J

2012-03-08

200

The Brachial Artery Remodels to Maintain Local Shear Stress Despite the Presence of Cardiovascular Disease Risk Factors  

PubMed Central

Objective Under physiological conditions, arteries remodel in response to changes in blood flow to maintain local shear stress. Risk factors and developing atherosclerosis may be associated with maladaptive remodeling that produces relatively large arteries with low levels of shear stress. Recent studies have shown that the brachial artery and other peripheral arteries are enlarged in patients with risk factors and cardiovascular disease, and we tested the hypothesis that this finding represents maladaptive remodeling. Methods and Results We measured brachial artery diameter and flow by ultrasound and calculated shear stress in a diverse cohort of 1,583 subjects (age 53±17 years, 62% male, and 51% with coronary artery disease and/or peripheral arterial disease). In a stepwise linear regression model, age (P<0.001), gender (P<0.001), body mass index (P<0.001), hypertension (P=0.005), and hypercholesterolemia (P=0.02) were associated with larger brachial diameter. Older age was associated with lower shear stress (P<0.01), consistent with maladaptive remodeling. However, body mass index, hypertension, hypercholesterolemia, and prevalent atherosclerosis were associated with proportionate changes in blood flow and no difference in shear stress compared to reference groups, suggesting adaptive remodeling. Conclusions These findings suggest that enlargement of the brachial artery in the setting of obesity, hypertension, hypercholesterolemia, and atherosclerosis reflects adaptive remodeling. The results provide further support for the concept that arterial remodeling is an important homeostatic response that is maintained despite the presence of risk factors and developing atherosclerosis.

Chung, William B.; Hamburg, Naomi M.; Holbrook, Monika; Shenouda, Sherene M.; Dohadwala, Mustali M.; Terry, Dellara F.; Gokce, Noyan; Vita, Joseph A.

2009-01-01

201

Evaluation of Stress Anisotropy and Shearing Stress Using an Eddy Current Method with a Tangential-Rectangular Coil  

NASA Astrophysics Data System (ADS)

In establishing a system to evaluate residual stress, it is important to design the system so that it can also evaluate the stress anisotropy, since this is introduced into metallic materials by surface processes such as grinding and polishing. The shearing stress is also an important parameter when the shear strength has to be considered, since tensile stress can cause stress corrosion cracking. Thus, a method to nondestructively evaluate the stress anisotropy and shearing stress in a short time is required. In this paper, a nondestructive eddy current method using a tangential-rectangular coil was used to accomplish this. The material under test was stainless steel, Japanese Industrial Standard (JIS) SUS316L, ground or polished by an angle grinder. The stress anisotropy caused by the grinding and polishing processes was evaluated by the eddy current method with the tangential-rectangular coil. To vary the stress state, some specimens were treated with cavitation peening after grinding with the angle grinder. The results demonstrate that the stress anisotropy, shearing stress and peening intensity can be evaluated by the eddy current method using the tangential-rectangular coil. From the results, it was concluded that the maximum shearing stress and the direction of the principal stress could be determined.

Sekine, Yuichi; Soyama, Hitoshi

202

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

PubMed

We demonstrated recently that plasma concentrations of asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide (NO) synthase, are increased by high salt intake concomitantly with a decrease in plasma levels of NO in human hypertension. We investigated the effect of shear stress on ADMA release in 2 types of cells: transformed human umbilical vein endothelial cells (HUVECs; cell line ECV-304) and HUVECs. Exposure of ECV-304 cells and HUVECs to shear stress with the use of a cone-plate viscometer enhanced gene expression of protein arginine methyltransferase (PRMT-1), ADMA synthase. In HUVECs, the ratio of PRMT-1 to glyceraldehyde 3-phosphate dehydrogenase mRNA was increased by 2-fold by a shear stress of > or =15 dyne/cm2. A dominant-negative mutant of IkappaB kinase alpha and troglitazone at 8 micromol/L, an activator of peroxisome proliferator-activated receptor gamma, abolished the shear stress-induced increase in PRMT-1 gene expression in parallel with the blockade of nuclear factor (NF)-kappaB translocation into the nucleus. The activity of dimethylarginine dimethylaminohydrolase, the degradation enzyme of ADMA, was unchanged after shear stress < or =15 dyne/cm2 and was enhanced by 1.48+/-0.06-fold (P<0.05) by shear stress at 25 dyne/cm2. The release of ADMA was increased by 1.64+/-0.10-fold (P<0.05) by shear stress at 15 dyne/cm2 but was not affected by shear stress at 25 dyne/cm2. These results indicate that shear stress enhances gene expression of PRMT-1 and ADMA release via activation of the NF-kappaB pathway. Shear stress at higher magnitudes facilitates the degradation of ADMA, thus returning ADMA release levels to baseline. PMID:14557285

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

2003-10-13

203

Validating Measures of Teacher Stress.  

ERIC Educational Resources Information Center

|A validation study in the development of empirical measures of teacher stress is presented. Role-related, task-based, and environmental stress measures demonstrated internal consistency and provided reliable and valid multivariate assessment of teacher stress. (PN)|

Pettegrew, Loyd S.; Wolf, Glenda E.

1982-01-01

204

Wall shear stress from a rotating cylinder in cross flow using the electrochemical technique  

NASA Astrophysics Data System (ADS)

The wall shear rate from a rotating cylinder in a uniform flow was measured with flush-mounted electrochemical mass transfer probes. The experiments were performed using two rectangular electrodes in a sandwich arrangement. Initially, the frequency response of that probe was numerically studied using an inverse mass transfer method in order to restore the whole wall shear stress in the time domain starting from the measured transfer coefficients given by the split probe. The experiments were performed in the range of velocity ratios 04, points of zero shear stress on the rotating cylinder vanish, which is in fact consistent with the previous arguments that the cylinder is surrounded by a set of closed streamlines. This experimental study shows that, when their dynamic behaviour is known, the electrochemical probes are able to sense complex fine structures not observed up to now by previous analytical, numerical or experimental methods, even when non-linear effects are not negligible.

Labraga, L.; Bourabaa, N.; Berkah, T.

2002-07-01

205

Measuring shear strength of soft-tissue adhesives.  

PubMed

A method for evaluating strength of adhesives for hydrogels and soft tissues is presented. Quantitative measurements of shear strength for applications in tissue engineering and biomedicine are performed in torsion using a rheometer. Small, disk shaped specimens of soft biological tissues and/or hydrogels (8 mm diameter, 1-2 mm thick) are mounted onto rheometer tools and then bonded together using the adhesive to be tested. The torsional loading geometry imposes simple shear without deforming the planar adhesive bond, in contrast to the lap-shear test. It retains the advantages of the napkin ring test while reducing artifacts due to cutting and handling soft specimens. The method is demonstrated by measuring the shear strength of two types of biomedical adhesives (cyanoacrylate and polyethylene glycol-based) between model hydrogels (gelatin) and tissues (corneal stroma and skin). PMID:22323271

Wang, Muzhou; Kornfield, Julia A

2012-02-10

206

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

NASA Astrophysics Data System (ADS)

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.

Chaudhuri, Pinaki; Horbach, Jürgen

2013-10-01

207

Geometric functions of stress intensity factor solutions for spot welds in lap-shear specimens  

Microsoft Academic Search

In this paper, the stress intensity factor solutions for spot welds in lap-shear specimens are investigated by finite element analyses. Three-dimensional finite element models are developed for lap-shear specimens to obtain accurate stress intensity factor solutions. In contrast to the existing investigations of the stress intensity factor solutions based on the finite element analyses, various ratios of the sheet thickness,

D.-A. Wang; P.-C. Lin; J. Pan

2005-01-01

208

Evaluation of interfacial shear strength and residual stress of sol–gel derived fluoridated hydroxyapatite coatings on Ti6Al4V substrates  

Microsoft Academic Search

Interfacial shear strength is one of the critical properties in bioceramic coatings on metal implants because it directly affects the success of implantation and long-term stability. In this study, shear strain lag method was employed to evaluate the interfacial shear strength of sol–gel derived fluoridated hydroxyapatite (FHA) coatings on Ti6Al4V substrates. The residual stresses were measured using the “wafer curvature

S. Zhang; Y. S. Wang; X. T. Zeng; K. Cheng; M. Qian; D. E. Sun; W. J. Weng; W. Y. Chia

2007-01-01

209

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

SciTech Connect

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.

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

1991-05-01

210

Tetrahedral vs. polyhedral mesh size evaluation on flow velocity and wall shear stress for cerebral hemodynamic simulation  

Microsoft Academic Search

Haemodynamic factors, in particular wall shear stresses (WSSs) may have significant impact on growth and rupture of cerebral aneurysms. Without a means to measure WSS reliably in vivo, computational fluid dynamic (CFD) simulations are frequently employed to visualise and quantify blood flow from patient-specific computational models. With increasing interest in integrating these CFD simulations into pretreatment planning, a better understanding

Martin Spiegel; Thomas Redel; Y. Jonathan Zhang; Tobias Struffert; Joachim Hornegger; Robert G. Grossman; Arnd Doerfler; Christof Karmonik

2011-01-01

211

Shear stress at the interface of coaxial composites determined by the resonance of low-amplitude vibrations  

Microsoft Academic Search

The aim of this work is to determine the viscoelastic behaviour of the interface in a coaxial composite material made of a tough shield and a ductile core. The elastic modulus and the amplitude-independent internal friction are measured using a longitudinal oscillating resonant system at 50 kHz. The contribution of the interface is modelled as a shear stress that modifies

Élida B. Hermida; Diego G. Melo

2003-01-01

212

The SDSS Coadd: Cosmic Shear Measurement  

SciTech Connect

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}.

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

213

Vascular endothelial responses to altered shear stress: pathologic implications for atherosclerosis.  

PubMed

Atherosclerosis preferentially develops at branches and curvatures of the arterial tree, where blood flow is disturbed from a laminar pattern, and wall shear stress is non-uniform and has an irregular distribution. Vascular endothelial cells (ECs), which form an interface between the flowing blood and the vessel wall, are exposed to blood flow-induced shear stress. There is increasing evidence suggesting that laminar blood flow and sustained high shear stress modulate the expression of EC genes and proteins that function to protect against atherosclerosis; in contrast, disturbed blood flow and the associated low and reciprocating shear stress upregulate proatherosclerotic genes and proteins that promote development of atherosclerosis. Understanding of the effects of shear stress on ECs will provide mechanistic insights into its role in the pathogenesis of atherosclerosis. The aim of this review article is to summarize current findings on the effects of shear stress on ECs, in terms of their signal transduction, gene expression, structure, and function. These endothelial cellular responses have important relevance to understanding the pathophysiological effects of altered shear stress associated with atherosclerosis and thrombosis and their complications. PMID:18608132

Chiu, Jeng-Jiann; Usami, Shunichi; Chien, Shu

2009-01-01

214

Shear stress responses of adult blood outgrowth endothelial cells seeded on bioartificial tissue.  

PubMed

Human blood outgrowth endothelial cells (HBOECs) are expanded from circulating endothelial progenitor cells in peripheral blood and thus could provide a source of autologous endothelial cells for tissue-engineered vascular grafts. To examine the suitability of adult HBOECs for use in vascular tissue engineering, the shear stress responsiveness of these cells was examined on bioartificial tissue formed from dermal fibroblasts entrapped in tubular fibrin gels. HBOECs adhered to this surface, deposited collagen IV and laminin, and remained adherent when exposed to 15 dyn/cm(2) shear stress for 24 h. The shear stress responses of HBOECs were compared to human umbilical vein endothelial cells (HUVECs). As with HUVECs, HBOECs upregulated vascular cell adhesion molecule-1 and intercellular adhesion molecule-1 when exposed to tumor necrosis factor (TNF)-? and shear stress decreased the expression of these adhesion molecules on TNF-?-activated monolayers. Nitric oxide production was elevated by shear stress, but did not vary between cell types. Both cell types decreased platelet adhesion to the bioartificial tissue, whereas pre-exposing the cells to flow decreased platelet adhesion further. These results illustrate the potential utility for HBOECs in vascular tissue engineering, as not only do the cells adhere to bioartificial tissue and remain adherent under physiological shear stress, they are also responsive to shear stress signaling. PMID:21599543

Ahmann, Katherine A; Johnson, Sandra L; Hebbel, Robert P; Tranquillo, Robert T

2011-07-01

215

CCD evaluation for estimating measurement precision in lateral shearing interferometry  

NASA Astrophysics Data System (ADS)

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.

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

2013-06-01

216

Energy consumption in terms of shear stress for two types of membrane bioreactors used for municipal wastewater treatment processes  

NASA Astrophysics Data System (ADS)

Two types of submerged membrane bioreactors (MBR): hollow fiber (HF) and hollow sheet (HS), have been studied and compared in terms of energy consumption and average shear stress over the membrane wall. The analysis of energy consumption was made using the correlation to determine the blower power and the blower power demand per unit of permeate volume. Results showed that for the system geometries considered, in terms the of the blower power, the HF MBR requires less power compared to HS MBR. However, in terms of blower power per unit of permeate volume, the HS MBR requires less energy. The analysis of shear stress over the membrane surface was made using computational fluid dynamics (CFD) modelling. Experimental measurements for the HF MBR were compared with the CFD model and an error less that 8% was obtained. For the HS MBR, experimental measurements of velocity profiles were made and an error of 11% was found. This work uses an empirical relationship to determine the shear stress based on the ratio of aeration blower power to tank volume. This relationship is used in bubble column reactors and it is extrapolate to determine shear stress on MBR systems. This relationship proved to be overestimated by 28% compared to experimental measurements and CFD results. Therefore, a corrective factor is included in the relationship in order to account for the membrane placed inside the bioreactor.

Ratkovich, Nicolas; Bentzen, Thomas R.; Rasmussen, Michael R.

2012-10-01

217

Estimates of bottom roughness length and bottom shear stress in South San Francisco Bay, California  

USGS Publications Warehouse

A field investigation of the hydrodynamics and the resuspension and transport of participate matter in a bottom boundary layer was carried out in South San Francisco Bay (South Bay), California, during March-April 1995. Using broadband acoustic Doppler current profilers, detailed measurements of turbulent mean velocity distribution within 1.5 m above bed have been obtained. A global method of data analysis was used for estimating bottom roughness length zo and bottom shear stress (or friction velocities u*). Field data have been examined by dividing the time series of velocity profiles into 24-hour periods and independently analyzing the velocity profile time series by flooding and ebbing periods. The global method of solution gives consistent properties of bottom roughness length zo and bottom shear stress values (or friction velocities u*) in South Bay. Estimated mean values of zo and u* for flooding and ebbing cycles are different. The differences in mean zo and u* are shown to be caused by tidal current flood-ebb inequality, rather than the flooding or ebbing of tidal currents. The bed shear stress correlates well with a reference velocity; the slope of the correlation defines a drag coefficient. Forty-three days of field data in South Bay show two regimes of zo (and drag coefficient) as a function of a reference velocity. When the mean velocity is >25-30 cm s-1, the ln zo (and thus the drag coefficient) is inversely proportional to the reference velocity. The cause for the reduction of roughness length is hypothesized as sediment erosion due to intensifying tidal currents thereby reducing bed roughness. When the mean velocity is <25-30 cm s-1, the correlation between zo and the reference velocity is less clear. A plausible explanation of scattered values of zo under this condition may be sediment deposition. Measured sediment data were inadequate to support this hypothesis, but the proposed hypothesis warrants further field investigation.

Cheng, R. T.; Ling, C. -H.; Gartner, J. W.; Wang, P. F.

1999-01-01

218

Quantifying elasticity and viscosity from measurement of shear wave speed dispersion  

Microsoft Academic Search

The propagation speed of shear waves is related to frequency and the complex stiffness (shear elasticity and viscosity) of the medium. A method is presented to solve for shear elasticity and viscosity of a homogeneous medium by measuring shear wave speed dispersion. Harmonic radiation force, introduced by modulating the energy density of incident ultrasound, is used to generate cylindrical shear

Shigao Chen; Mostafa Fatemi; James F. Greenleaf

2004-01-01

219

WHEEL RIM RESIDUAL STRESS MEASUREMENTS  

Microsoft Academic Search

Beneficial, as-manufactured, residual compressive stresses in wheel rims are introduced during the rim quenching operation. Such compressive stresses are known to help inhibit the formation of rim fatigue cracks and thus are important to wheel safety. This paper describes measurements of stresses in new wheel rims at a wrought wheel manufacturing facility, and also use of rim stress measurement for

Cameron Lonsdale; Francois Demilly; Valerio Del Fabbro

220

Wall Shear Stress Assessment in the Common Carotid Artery of End-Stage Renal Failure Patients  

Microsoft Academic Search

Under physiological circumstances in the common carotid artery (CCA), mean wall shear stress (WSS), defined as mean wall shear rate (WSR) times local whole blood viscosity (WBV), is maintained at approximately 1.5 Pa. In patients with end-stage renal failure (ESRF) whole blood viscosity is low and it is not unlikely that mean WSS is lower in these patients than in

S. K. Samijo; R. Barkhuysen; J. M. Willigers; K. M. L. Leunissen; L. A. F. Ledoux; A. P. G. Hoeks

2002-01-01

221

Comparison of the Shear Stress-strain Behaviour of some Structural Adhesives  

Microsoft Academic Search

The shear stress-strain behaviour of structural adhesives provides important data for the designer. Shear modulus, strength, and elastic and plastic strain to failure have been determined using a torsional butt joint technique which is relatively quick to perform and is believed to be very accurate. A range of structural adhesives have been compared, which has highlighted some important differences in

L. G. Stringer

1985-01-01

222

Turbulence measurements in a nearly homogeneous shear flow  

NASA Astrophysics Data System (ADS)

A technique is described for conducting turbulence measurements in a nominally homogeneous turbulent shear flow with a moderate rate of strain. The shear flow was generated in the 7.2-m-long working section of a open-circuit wind tunnel of conventional design, in which a nominally uniform gradient of mean velocity was produced by a shear generator of the type described by Tavoularis and Corrsin (1981). Turbulence measurements were made using a dual-channel DISA 55M01 CTA system with PSI 6141 signal conditioners. Results were found to lie between, and to be broadly consistent with, the results of similar measurements previously taken on flows with higher or lower rates of strain.

Gibson, M. M.; Kanellopoulos, V. E.

223

Influence of Clamping Stresses in the Shear Strength of Concrete Slabs Under Uniform Loads  

Microsoft Academic Search

Experimental results have shown shear capacities of concrete slabs under uniform loads sometimes considerably higher than those predicted by current concrete codes. Vertical compressive stresses transverse to the beam axis, or clamping stresses, are neglected in these analyses. The present study includes results from analytical and experimental research that was conducted to investigate the influence of clamping stresses on the

Ana B. Acevedo; Evan C. Bentz; Michael P. Collins

2009-01-01

224

A Z-Axis Quartz Cross-Fork Micromachined Gyroscope Based on Shear Stress Detection  

PubMed Central

Here we propose a novel quartz micromachined gyroscope. The sensor has a simple cross-fork structure in the x-y plane of quartz crystal. Shear stress rather than normal stress is utilized to sense Coriolis’ force generated by the input angular rate signal. Compared to traditional quartz gyroscopes, which have two separate sense electrodes on each sidewall, there is only one electrode on each sidewall of the sense beam. As a result, the fabrication of the electrodes is simplified and the structure can be easily miniaturized. In order to increase sensitivity, a pair of proof masses is attached to the ends of the drive beam, and the sense beam has a tapered design. The structure is etched from a z-cut quartz wafer and the electrodes are realized by direct evaporation using the aperture mask method. The drive mode frequency of the prototype is 13.38 kHz, and the quality factor is approximately 1,000 in air. Therefore, the gyroscope can work properly without a vacuum package. The measurement ability of the shear stress detection design scheme is validated by the Coriolis’ force test. The performance of the sensor is characterized on a precision rate table using a specially designed readout circuit. The experimentally obtained scale factor is 1.45 mV/°/s and the nonlinearity is 3.6% in range of ±200 °/s.

Xie, Liqiang; Wu, Xuezhong; Li, Shengyi; Wang, Haoxu; Su, Jianbin; Dong, Peitao

2010-01-01

225

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

PubMed Central

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.

2013-01-01

226

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

NASA Astrophysics Data System (ADS)

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

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

2011-04-01

227

Heterogeneity and the Role of Normal Stresses during the Extensional Thinning of Non-Brownian Shear-Thickening Fluids  

Microsoft Academic Search

We contrast the extensional and shear dynamics of non-Brownian suspensions as a function of particle concentration. We show that the thinning rate selected during the viscoelastic pinch-off of a liquid bridge is related to the shear rate at which normal stresses become positive, which differs from the shear rate at the onset of shear thickening. By tracking particles, we demonstrate

Matthieu Roché; Hamid Kellay; Howard A. Stone

2011-01-01

228

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

PubMed

Flocs were produced by adding three cationic polymers (10% charge density, 3.0x10(5) g/mol molecular weight; 40% charge density, 1.1x10(5) g/mol molecular weight; and 100% charge density, 1.2x10(5) g/mol molecular weight) to 90 nm diameter silica particles. The shear yield stresses of the consolidated sediment beds from settled and centrifuged flocs were determined via the vane technique. The polymer charge density plays an important role in influencing the shear yield stresses of sediment beds. The shear yield stresses of sediment beds from flocs induced by the 10% charged polymer were observed to increase with an increase in polymer dose, initial solid concentration and background electrolyte concentration at all volume fractions. In comparison, polymer dose has a marginal effect on the shear yield stresses of sediment beds from flocs induced by the 40% and 100% charged polymers. The shear yield stresses of sediments from flocs induced by the 40% charged polymer are independent of salt concentration whereas the addition of salt decreases the shear yield stresses of sediments from flocs induced by the 100% charged polymer. When flocculated at the optimum dose for each polymer (12 mg/g silica for the 10% charged polymer at 0.03 M NaCl, 12 mg/g for 40% and 2 mg/g for 100%), shear yield stress increases as polymer charge increases. The effects observed are related to the flocculation mechanism (bridging, patch attraction or charge neutralisation) and the magnitude of the adhesive force. Comparison of shear and compressive yield stresses show that the network is only slightly weaker in shear than in compression. This is different than many other systems (mainly salt and pH coagulation) which have shear yield stress much less than compressive yield stress. The existing models relating the power law exponent of the volume fraction dependence of the shear yield stress to the network fractal structure are not satisfactory to predict all the experimental behaviour. PMID:19414185

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

2009-04-14

229

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

SciTech Connect

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.

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

230

Visualising shear stress distribution inside flow geometries containing pharmaceutical powder excipients using photo stress analysis tomography and DEM simulations  

NASA Astrophysics Data System (ADS)

For the first time, photo stress analysis tomography (PSAT) is applied to probe the distribution of maximum shear stress and direction of major principal stress field within `powder' assemblies inside hopper geometries, and further supported by discrete element model (DEM) simulations. The results show that for decrease in hopper angle, the direction of major principle stress aligns with the direction of gravity which could promote flow rate under dynamic conditions. Conversely, the propensity of developing relatively more non-homogeneous distribution of shear resistance zones inside powder assemblies increases with the hopper angle, which could subsequently decrease their macroscopic flow rate.

Albaraki, Saeed; Antony, S. Joseph.; Arowosola, C. Babatunde

2013-06-01

231

Stress Analysis of Adhesively-bonded Joints Under In-plane Shear Loading  

Microsoft Academic Search

A closed-form stress analysis of an adhesively-bonded lap joint subjected to spatially-varying in-plane shear loading is presented. The solution, while similar to Volkersen's treatment of tension loaded lap joints, is inherently two-dimensional and, in general, predicts a multi-component adhesive shear stress state. A finite difference numerical solution of the derived governing differential equation is used to verify the accuracy of

Hyonny Kim; Keith T. Kedward

2001-01-01

232

Association of SIRT1 expression with shear stress induced endothelial progenitor cell differentiation.  

PubMed

Shear stress imposed by blood flow is crucial for differentiation of endothelial progenitor cells (EPCs). Histone deacetylase SIRT1 has been shown to play a pivotal role in many physiological processes. However, association of SIRT1 expression with shear stress-induced EPC differentiation remains to be elucidated. The present study was designed to determine the effect of SIRT1 on EPC differentiation induced by shear stress, and to seek the underlying mechanisms. Human umbilical cord blood-derived EPCs were exposed to laminar shear stress of 15 dyn/cm(2) by parallel plate flow chamber system. Shear stress enhanced EPC differentiation toward endothelial cells (ECs) while inhibited to smooth muscle cells (SMCs). The expressions of phospho-Akt, SIRT1 and histone H3 acetylation (Ac-H3) in EPCs were detected after exposure to shear stress for 2, 6, 12, and 24 h, respectively. Shear stress significantly activated Akt phosphorylation, augmented SIRT1 expression and downregulated Ac-H3. SIRT1 siRNA in EPCs diminished the expression of EC markers, but increased the expression of SMC markers, and resulted in upregulation of Ac-H3. Whereas, resveratrol, an activator of SIRT1, had the opposite effects on both EPC differentiation and histone H3 acetylation. Wortmannin, an inhibitor of PI3-kinase, suppressed endothelial differentiation of EPCs, decreased SIRT1, and upregulated Ac-H3 expression. In addition, SIRT1 promoted tube formation of EPCs in matrix gels. These results provided a mechanobiological basis of shear stress-induced EPC differentiation into ECs and suggest that PI3k/Akt-SIRT1-Ac-H3 pathway is crucial in such a process. PMID:22740055

Cheng, Bin-Bin; Yan, Zhi-Qiang; Yao, Qing-Ping; Shen, Bao-Rong; Wang, Ji-Yao; Gao, Li-Zhi; Li, Yu-Qing; Yuan, Hai-Tao; Qi, Ying-Xin; Jiang, Zong-Lai

2012-12-01

233

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

Microsoft Academic Search

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

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

234

Increased shear stress–released NO and decreased endothelial calcium in rat isolated perfused juxtamedullary nephrons  

Microsoft Academic Search

Increased shear stress–released NO and decreased endothelial calcium in rat isolated perfused juxtamedullary nephrons.BackgroundNitric oxide is an important vasodilator released from endothelial cells by the calcium-dependent endothelial nitric oxide synthase (NOS). We considered it important to investigate how shear stress\\/perfusion pressure influenced endothelial cell calcium concentration, nitric oxide release, and autoregulation of the afferent arteriole, since this arteriole controls glomerular

JÁNOS PITTNER; MATS WOLGAST; DANIEL CASELLAS; A. Erik G. Persson

2005-01-01

235

Pulsatile Versus Oscillatory Shear Stress Regulates NADPH Oxidase Subunit Expression Implication for Native LDL Oxidation  

Microsoft Academic Search

Shear stress regulates endothelial nitric oxide and superoxide (O 2·) production, implicating the role of NADPH oxidase activity. It is unknown whether shear stress regulates the sources of reactive species production, consequent low-density lipoprotein (LDL) modification, and initiation of inflammatory events. Bovine aortic endothelial cells (BAECs) in the presence of 50 g\\/mL of native LDL were exposed to (1) pulsatile

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

2010-01-01

236

Shear Stress Influences Spatial Variations in Vascular Mn-SOD Expression  

PubMed Central

Fluid shear stress modulates vascular production of endothelial superoxide anion (O2?) and nitric oxide (?NO). Whether the characteristics of shear stress influence the spatial variations in mitochondrial manganese superoxide dismutase (Mn-SOD) expression in vasculatures is not well-defined. We constructed a 3-D Computational Fluid Dynamics model simulating spatial variations in shear stress at the arterial bifurcation. In parallel, explants of arterial bifurcations were sectioned from the human left main coronary bifurcation and right coronary arteries for immunohisto-localization of Mn-SOD expression. We demonstrated that Mn-SOD staining was prominent in the athero-protective regions, but was nearly absent in the lateral wall of arterial bifurcation. Pulsatile shear stress (PSS: mean shear stress ?ave= 23 dyn·cm?2) up-regulated Mn-SOD mRNA expression at a higher level than did oscillatory shear stress (OSS: ?ave= 0.02 dyn·cm?2 ± 3.0 dyn·cm?2·s?1 at 1 Hz) in cultured bovine aortic endothelial cells (PSS by 11.3±0.4-fold versus OSS by 5.0±0.5-fold. p < 0.05, n=4). Furthermore, PSS decreased the extent of Low Density Lipoprotein (LDL) nitration, whereas OSS increased by Liquid chromatography and tandem mass spectrometry (P < 0.05, n=4). Treatment with Mn-SOD siRNA significantly increased intracellular nitrotyrosine level in presence of LDL (n=4, p < 0.5). Our findings indicate that shear stress in the athero-prone versus athero-protective regions regulates spatial variations in mitochondrial Mn-SOD expression. Shear stress modulated LDL protein nitration via Mn-SOD expression.

Ai, Lisong; Rouhanizadeh, Mahsa; Wu, Joseph C.; Takabe, Wakako; Yu, Hongyu; Alavi, Mohammad; Chu, Yi; Miller, Jordan; Heistad, Donald D.; Hsiai, Tzung K.

2010-01-01

237

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

NASA Astrophysics Data System (ADS)

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

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

2003-07-01

238

Optimization of the shear stress induced by ultrasonically-stimulated oscillating MBs: A theoretical investigation  

NASA Astrophysics Data System (ADS)

Shear stress induced by ultrasonically-stimulated MBs has been associated with sonoporation and sonothrombolysis. In this study, the dynamics of oscillating MBs is investigated numerically using the Hoff model for varying parameters (MB radius (Ro), pulse frequency and acoustic pressure) and the average shear stress was calculated using the Rooney model. The MB oscillations were maintained below a normalized radial oscillation of two to avoid inertial cavitation. The simulations demonstrated that the shear stress induced by MBs increased significantly at exposure frequencies of non-integer multiples of the resonance frequency (fr), only above a pressure threshold. The pressure threshold, located at the saddle node bifurcation point where the MB oscillation increases suddenly, depended on MB size, pulse frequency and shell properties. The shear stress induced by a 4 um oscillating MB increased by 10-fold when exposed to 8.85 MHz (2.93fr) compared to the maximum shear stress at the MB resonance frequency (3.02 MHz). This increase is concomitant with the saddle node bifurcation in normalized radial oscillations from 1.12 to 1.69 at 1.53 MPa. In conclusion, ultrasound exposure frequency and acoustic pressure can be tailored to maximize and control the shear stress induced by MBs undergoing stable oscillation for optimizing ultrasound therapeutic bioeffects.

Sojahrood, Amin Jafari; Karshafian, Raffi; Kolios, Michael C.

2012-10-01

239

Temporal oscillations of the shear stress and scattered light in a shear-banding-shear-thickening micellar solution  

Microsoft Academic Search

The results of optical and rheological experiments performed on a viscoelastic solution (cetyltrimethylammonium bromide + sodium salicylate in water) are reported. The flow curve has a horizontal plateau extending between two critical shear rates characteristic of heterogeneous flows formed by two layers of fluid with different viscosities. These two bands which also have different optical anisotropy are clearly seen by

H. Azzouzi; J. P. Decruppe; S. Lerouge; O. Greffier

2005-01-01

240

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

Microsoft Academic Search

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

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

2006-01-01

241

Concentration Polarization of High-Density Lipoprotein and Its Relation with Shear Stress in an In Vitro Model  

PubMed Central

The purpose of this study was to determine the concentration polarization of high-density lipoprotein (HDL) at the surface of the carotid artery under conditions of steady flow and to establish its relationship with shear stress using an in vitro vascular simulation model of carotid bifurcation. Shear stress, HDL concentration at the surface, and the ratio of HDL concentration at the surface to concentration in bulk flow were measured at different locations within the model under high-speed (1.451 m/s) and low-speed (0.559 m/s) flow. HDL showed concentration polarization at the surface of the carotid artery model, particularly in the internal carotid artery sinus. With decreasing flow velocity, the shear stress at the surface also decreased, and HDL concentration polarization increased. The concentration polarization of HDL was negatively and strongly correlated with shear stress at both low- (r = ?0.872, P < .001) and high-speed flow (r = ?0.592, P = .0018).

Meng, Wei; Yu, Fengxu; Chen, Huaiqing; Zhang, Jianmin; Zhang, Eryong; Dian, Ke; Shi, Yingkang

2009-01-01

242

Sensor for Viscosity and Shear Strength Measurement  

SciTech Connect

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.

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

1998-10-20

243

Shear Strength Measurement Benchmarking Tests for K Basin Sludge Simulants  

SciTech Connect

Equipment development and demonstration testing for sludge retrieval is being conducted by the K Basin Sludge Treatment Project (STP) at the MASF (Maintenance and Storage Facility) using sludge simulants. In testing performed at the Pacific Northwest National Laboratory (under contract with the CH2M Hill Plateau Remediation Company), the performance of the Geovane instrument was successfully benchmarked against the M5 Haake rheometer using a series of simulants with shear strengths (?) ranging from about 700 to 22,000 Pa (shaft corrected). Operating steps for obtaining consistent shear strength measurements with the Geovane instrument during the benchmark testing were refined and documented.

Burns, Carolyn A.; Daniel, Richard C.; Enderlin, Carl W.; Luna, Maria; Schmidt, Andrew J.

2009-06-10

244

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

NASA Astrophysics Data System (ADS)

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.

Greenleaf, James F.; Chen, Shigao

2007-03-01

245

Significance of extensional stresses to red blood cell lysis in a shearing flow.  

PubMed

Traditionally, an empirical power-law model relating hemolysis to shear stress and exposure time has been used to estimate hemolysis related to flow--however, this basis alone has been insufficient in attempts to predict hemolysis through computational fluid dynamics. Because of this deficiency, we sought to re-examine flow features related to hemolysis in a shearing flow by computationally modeling a set of classic experiments performed in a capillary tube. Simulating 21 different flows of varying entrance contraction ratio, flowrate and viscosity, we identified hemolysis threshold streamlines and analyzed the stresses present. Constant damage thresholds for radial and axial extensional stresses of approximately 3000 Pa for exposure times on the order of microseconds were observed, while no such threshold was found for the maximum shear stress or gradient of the shear stress. The extensional flow seen at the entrance of the capillary appears to be most consistently related to hemolysis. An account of how extensional stresses can lead to lysis of a red cell undergoing tank-tread motion in a shearing flow is provided. This work shows that extensional components of the stress tensor are integral in causing hemolysis for some flows, and should be considered when attempting to predict hemolysis computationally. PMID:21298343

Down, Linden A; Papavassiliou, Dimitrios V; O'Rear, Edgar A

2011-02-05

246

On the approximate representation of velocity and shear stress distributions in low-speed boundary layers  

NASA Astrophysics Data System (ADS)

A method for the representation of mean shear stress and velocity profiles in low speed, laminar and turbulent boundary layers is described. It has a unique advantage over existing techniques in that the distributions of velocity and stress may be related by any turbulence model. This makes the profiles particularly useful as starting solutions for complex flow calculations. Two methods for obtaining the mean shear stress distribution are proposed. The first uses a near wall solution of the x momentum equation and an 'intermittency' or 'smoothing' function. The alternative approach represents the shear stress distribution using a power series with suitable boundary conditions specified at the wall and at the edge of the boundary layer. In both cases the velocity profiles are obtained by integrating the shear stress profiles using a turbulence model or by setting the turbulent Reynolds stresses to zero in the case of laminar flow. Velocity profiles, shear stress profiles and integral properties obtained from the technique are compared with experimental data and predictions from the Cebeci-Smith full field method. Predictions for laminar flow profiles are compared with the Falkner-Skan solutions.

Carter, Philip; Poll, D. I. A.

247

Working Principle Simulations of a Dynamic Resonant Wall Shear Stress Sensor Concept  

PubMed Central

This paper discusses a novel dynamic resonant wall shear stress sensor concept based on an oscillating sensor operating near resonance. The interaction between the oscillating sensor surface and the fluid above it is modelled using the unsteady laminar boundary layer equations. The numerical experiment shows that the effect of the oscillating shear stress is well correlated by the Hummer number, the ratio of the steady shear force caused by the outside flow to the oscillating viscous force created by the sensor motion. The oscillating shear stress predicted by the fluid model is used in a mechanical model of the sensor to predict the sensor's dynamic motion. Static calibration curves for amplitude and frequency influences are predicted. These results agree with experimental results on some extent, and shows some expectation for further development of the dynamic resonant sensor concept.

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

2008-01-01

248

Role of shear-stress-induced VEGF expression in endothelial cell survival  

PubMed Central

Vascular endothelial growth factor (VEGF) plays a crucial role in developmental and pathological angiogenesis. Expression of VEGF in quiescent adult tissue suggests a potential role in the maintenance of mature blood vessels. We demonstrate, using a Vegf–lacZ reporter mouse model, that VEGF is expressed by arterial but not by venous or capillary endothelial cells (ECs) in vivo. Using an in vitro model, we show that arterial shear stress of human umbilical vein ECs (HUVECs) decreases apoptosis and increases VEGF expression, which is mediated by the induction of Krüppel-like factor 2 (KLF2). Additionally, shear stress stimulates the expression of VEGF receptor 2 (VEGFR2) and is associated with its activation. Knockdown of VEGF in shear stressed HUVECs blocks the protective effect of shear stress, resulting in EC apoptosis equivalent to that in control ECs cultured under static conditions. Similarly, treatment of ECs subjected to arterial shear stress with the VEGF receptor tyrosine kinase inhibitor SU1498, or VEGFR2 neutralizing antiserum, led to increased apoptosis, demonstrating that the mechanoprotection from increased shear is mediated by VEGFR2. Taken together, these studies suggest that arterial flow induces VEGF–VEGFR2 autocrine–juxtacrine signaling, which is a previously unidentified mechanism for vascular EC survival in adult arterial blood vessels.

dela Paz, Nathaniel G.; Walshe, Tony E.; Leach, Lyndsay L.; Saint-Geniez, Magali; D'Amore, Patricia A.

2012-01-01

249

Wall friction measurement in the absence of mean shear  

NASA Astrophysics Data System (ADS)

The dimensionless frictional force f between a pipe wall and a flowing turbulent fluid is f=?s /U^2, where U is mean flow speed in the x-direction, ? is kinematic viscosity, and s=u y , where the y axis is perpendicular to the flow direction. The derivative is evaluated at the wall, y = 0. Described here a scheme for measuring f in a turbulent fluid where s is close to zero. Hence the source of frictional dissipation is from fluctuations in the shear about its mean, namely s^2. This type of shear is encountered in turbulence in a closed container such as a food mixer. The scheme, which involves photon correlation spectroscopy, averages the shear rate over a laser spot size w ˜ 100 ?m or smaller. The scheme yields the probability density function (PDF) of components of the shear rate tensor and the moments of of the PDF. The theory will be described briefly and measurements will be presented where s ˜ 0. In that limit f is redefined to be f =u' sij/?, where sij is the dominant component being measured, and u' is the rms fluctuations of the velocity.

Stefanus, Stefanus; Castiglione, James; Cerbus, Rory; Goldburg, Walter

2012-02-01

250

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

NASA Astrophysics Data System (ADS)

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.

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

2004-12-01

251

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

NASA Astrophysics Data System (ADS)

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.

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

2007-12-01

252

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

NASA Astrophysics Data System (ADS)

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.

Fourrié, Grégoire; Keirsbulck, Laurent; Labraga, Larbi

2013-10-01

253

The congenital bicuspid aortic valve can experience high-frequency unsteady shear stresses on its leaflet surface  

PubMed Central

The bicuspid aortic valve (BAV) is a common congenital malformation of the aortic valve (AV) affecting 1% to 2% of the population. The BAV is predisposed to early degenerative calcification of valve leaflets, and BAV patients constitute 50% of AV stenosis patients. Although evidence shows that genetic defects can play a role in calcification of the BAV leaflets, we hypothesize that drastic changes in the mechanical environment of the BAV elicit pathological responses from the valve and might be concurrently responsible for early calcification. An in vitro model of the BAV was constructed by surgically manipulating a native trileaflet porcine AV. The BAV valve model and a trileaflet AV (TAV) model were tested in an in vitro pulsatile flow loop mimicking physiological hemodynamics. Laser Doppler velocimetry was used to make measurements of fluid shear stresses on the leaflet of the valve models using previously established methodologies. Furthermore, particle image velocimetry was used to visualize the flow fields downstream of the valves and in the sinuses. In the BAV model, flow near the leaflets and fluid shear stresses on the leaflets were much more unsteady than for the TAV model, most likely due to the moderate stenosis in the BAV and the skewed forward flow jet that collided with the aorta wall. This additional unsteadiness occurred during mid- to late-systole and was composed of cycle-to-cycle magnitude variability as well as high-frequency fluctuations about the mean shear stress. It has been demonstrated that the BAV geometry can lead to unsteady shear stresses under physiological flow and pressure conditions. Such altered shear stresses could play a role in accelerated calcification in BAVs.

Yap, Choon Hwai; Saikrishnan, Neelakantan; Tamilselvan, Gowthami; Vasilyev, Nikolai

2012-01-01

254

The congenital bicuspid aortic valve can experience high-frequency unsteady shear stresses on its leaflet surface.  

PubMed

The bicuspid aortic valve (BAV) is a common congenital malformation of the aortic valve (AV) affecting 1% to 2% of the population. The BAV is predisposed to early degenerative calcification of valve leaflets, and BAV patients constitute 50% of AV stenosis patients. Although evidence shows that genetic defects can play a role in calcification of the BAV leaflets, we hypothesize that drastic changes in the mechanical environment of the BAV elicit pathological responses from the valve and might be concurrently responsible for early calcification. An in vitro model of the BAV was constructed by surgically manipulating a native trileaflet porcine AV. The BAV valve model and a trileaflet AV (TAV) model were tested in an in vitro pulsatile flow loop mimicking physiological hemodynamics. Laser Doppler velocimetry was used to make measurements of fluid shear stresses on the leaflet of the valve models using previously established methodologies. Furthermore, particle image velocimetry was used to visualize the flow fields downstream of the valves and in the sinuses. In the BAV model, flow near the leaflets and fluid shear stresses on the leaflets were much more unsteady than for the TAV model, most likely due to the moderate stenosis in the BAV and the skewed forward flow jet that collided with the aorta wall. This additional unsteadiness occurred during mid- to late-systole and was composed of cycle-to-cycle magnitude variability as well as high-frequency fluctuations about the mean shear stress. It has been demonstrated that the BAV geometry can lead to unsteady shear stresses under physiological flow and pressure conditions. Such altered shear stresses could play a role in accelerated calcification in BAVs. PMID:22821994

Yap, Choon Hwai; Saikrishnan, Neelakantan; Tamilselvan, Gowthami; Vasilyev, Nikolai; Yoganathan, Ajit P

2012-07-20

255

An ultrasonic technique for measuring stress in fasteners  

SciTech Connect

High temperature bolting alloys are extensively used in the thermal power generation industry as for example, reheat ESV and Governor valve studs. Remnant life assessment methodologies and plant maintenance procedures require the monitoring of the operational stress levels in these fasteners. Some conventional ultrasonic techniques require longitudinal wave measurements to be undertaken when the nut on the bolt is loosened and then re-tightened. Other techniques use a combination of shear waves and longitudinal waves. In this paper, the problems and pitfalls associated with various ultrasonic techniques for measuring stress in bolts, is discussed. An ultrasonic technique developed for measuring the stress in Durehete 1055 bolts is presented. Material from a textured rolled bar has been used as a test bed in the development work. The technique uses shear wave birefringence and compression waves at several frequencies to measure texture, fastener length and the average stress. The technique was developed by making ultrasonic measurements on bolts tensioned in universal testing machines and a hydraulic nut. The ultrasonic measurements of residual stress have been checked against strain gauge measurements. The Durehete bolts have a hollow cylinder geometry of restricted dimensions, which significantly alters compression and shear wave velocities from bulk values and introduces hoop stresses which can be measured by rotating the polarization of the shear wave probe. Modelling of the experimental results has been undertaken using theories for the elastic wave propagation through waveguides. The dispersion equations allow the velocity and length of the fastener to be measured ultrasonically in some situations where the length of the fastener can not be measured directly with a vernier caliper or micrometer and/or where it is undesirable to loosen nuts to take calibration readings of the shear and compression wave velocities.

Stevens, K. J. [Materials Performance Technologies Ltd, PO Box 31-310, Lower Hutt (New Zealand); Day, P.; Byron, D. [Genesis Power Ltd, Huntly Power Station, Private Bag 501, Huntly (New Zealand)

1999-12-02

256

Fluid shear stress on endothelial cells modulates mechanical tension across VE-cadherin and PECAM-1.  

PubMed

Fluid shear stress (FSS) from blood flow acting on the endothelium critically regulates vascular morphogenesis, blood pressure, and atherosclerosis. FSS applied to endothelial cells (ECs) triggers signaling events including opening of ion channels, activation of signaling pathways, and changes in gene expression. Elucidating how ECs sense flow is important for understanding both normal vascular function and disease. EC responses to FSS are mediated in part by a junctional mechanosensory complex consisting of VE-cadherin, PECAM-1, and VEGFR2. Previous work suggested that flow increases force on PECAM-1, which initiates signaling. Deletion of PECAM-1 blocks responses to flow in vitro and flow-dependent vascular remodeling in vivo. To understand this process, we developed and validated FRET-based tension sensors for VE-cadherin and PECAM-1 using our previously developed FRET tension biosensor. FRET measurements showed that in static culture, VE-cadherin in cell-cell junctions bears significant myosin-dependent tension, whereas there was no detectable tension on VE-cadherin outside of junctions. Onset of shear stress triggered a rapid (<30 s) decrease in tension across VE-cadherin, which paralleled a decrease in total cell-cell junctional tension. Flow triggered a simultaneous increase in tension across junctional PECAM-1, while nonjunctional PECAM-1 was unaffected. Tension on PECAM-1 was mediated by flow-stimulated association with vimentin. These data confirm the prediction that shear increases force on PECAM-1. However, they also argue against the current model of passive transfer of force through the cytoskeleton to the junctions, showing instead that flow triggers cytoskeletal remodeling, which alters forces across the junctional receptors. PMID:23684974

Conway, Daniel E; Breckenridge, Mark T; Hinde, Elizabeth; Gratton, Enrico; Chen, Christopher S; Schwartz, Martin A

2013-05-16

257

Shear stress induces preimplantation embryo death that is delayed by the zona pellucida and associated with stress-activated protein kinase-mediated apoptosis.  

PubMed

In this study, we discovered that embryos sense shear stress and sought to characterize the kinetics and the enzymatic mechanisms underlying induction of embryonic lethality by shear stress. Using a rotating wall vessel programmed to produce 1.2 dynes/cm2 shear stress, it was found that shear stress caused lethality within 12 h for E3.5 blastocysts. Embryos developed an approximate 100% increase in mitogen-activated protein kinase 8/9 (formerly known as stress-activated protein kinase/junC kinase 1/2) phosphorylation by 6 h of shear stress that further increased to approximately 350% by 12 h. Terminal deoxynucleotidyltransferase dUTP nick end labeling/apoptosis was at baseline levels at 6 h and increased to approximately 500% of baseline at 12 h, when irreversible commitment to death occurred. A mitogen-activated protein kinase 8/9 phosphorylation inhibitor, D-JNKI1, was able to inhibit over 50% of the apoptosis, suggesting a causal role for mitogen-activated protein kinase 8/9 phosphorylation in the shear stress-induced lethality. The E2.5 (compacted eight-cell/early morula stage) embryo was more sensitive to shear stress than the E3.5 (early blastocyst stage) embryo. Additionally, zona pellucida removal significantly accelerated shear stress-induced lethality while having no lethal effect on embryos in the static control. In conclusion, preimplantation embryos sense shear stress, chronic shear stress is lethal, and the zona pellucida lessens the lethal and sublethal effects of shear stress. Embryos in vivo would not experience as high a sustained velocity or shear stress as induced experimentally here. Lower shear stresses might induce sufficient mitogen-activated protein kinase 8/9 phosphorylation that would slow growth or cause premature differentiation if the zona pellucida were not intact. PMID:16571875

Xie, Yufen; Wang, Fangfei; Zhong, Wenjing; Puscheck, Elizabeth; Shen, Hayley; Rappolee, D A

2006-03-29

258

Computational assessment of bicuspid aortic valve wall-shear stress: implications for calcific aortic valve disease.  

PubMed

The bicuspid aortic valve (BAV) is associated with a high prevalence of calcific aortic valve disease (CAVD). Although abnormal hemodynamics has been proposed as a potential pathogenic contributor, the native BAV hemodynamic stresses remain largely unknown. Fluid-structure interaction models were designed to quantify the regional BAV leaflet wall-shear stress over the course of CAVD. Systolic flow and leaflet dynamics were computed in two-dimensional tricuspid aortic valve (TAV) and type-1 BAV geometries with different degree of asymmetry (10 and 16% eccentricity) using an arbitrary Lagrangian–Eulerian approach. Valvular performance and regional leaflet wallshear stress were quantified in terms of valve effective orifice area (EOA), oscillatory shear index (OSI) and temporal shear magnitude (TSM). The dependence of those characteristics on the degree of leaflet calcification was also investigated. The models predicted an average reduction of 49% in BAV peak-systolic EOA relative to the TAV. Regardless of the anatomy, the leaflet wall-shear stress was side-specific and characterized by high magnitude and pulsatility on the ventricularis and low magnitude and oscillations on the fibrosa. While the TAV and non-coronary BAV leaflets shared similar shear stress characteristics, the base of the fused BAV leaflet fibrosa exhibited strong abnormalities, which were modulated by the degree of calcification (6-fold, 10-fold and 16-fold TSM increase in the normal, mildly and severely calcified BAV, respectively, relative to the normal TAV). This study reveals the existence of major differences in wall-shear stress pulsatility and magnitude on TAV and BAV leaflets. Given the ability of abnormal fluid shear stress to trigger valvular inflammation, the results support the existence of a mechano-etiology of CAVD in the BAV. PMID:22294208

Chandra, Santanu; Rajamannan, Nalini M; Sucosky, Philippe

2012-09-01

259

THE SDSS CO-ADD: COSMIC SHEAR MEASUREMENT  

SciTech Connect

Stripe 82 in the Sloan Digital Sky Survey was observed multiple times, allowing deeper images to be constructed by co-adding the data. Here, we analyze the ellipticities of background galaxies in this 275 deg{sup 2} region, searching for evidence of distortions due to cosmic shear. We do so using measurements of both the shear-shear correlation function and power spectrum, with the latter determined using both ''quadratic'' and ''pseudo'' estimation techniques. We show how we verified these methods using mock catalogs. We also describe our methods for modeling and correcting for the effects of the point-spread function (PSF) in our shape measurements, and we also describe our prescription for estimating photometric redshifts (photo-z's) for our galaxy sample. In particular, we assess the impact of potential systematic effects due to the PSF and to photo-z's, and show that these are under control in our analysis. We find consistent correlation function and power spectrum results, where the E-mode cosmic shear signal 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}{sup 0.7}{sub m}{sigma}{sub 8} = 0.252{sup +0.032}{sub -{sub 0.052}}.

Lin Huan; Dodelson, Scott; Soares-Santos, Marcelle; Annis, James; Hao Jiangang; Johnston, David; Kubo, Jeffrey M.; Reis, Ribamar R. R. [Center for Particle Astrophysics, Fermi National Accelerator Laboratory, Batavia, IL 60510 (United States); Seo, Hee-Jong [Berkeley Center for Cosmological Physics, LBL and Department of Physics, University of California, Berkeley, CA 94720 (United States); Simet, Melanie [Department of Astronomy and Astrophysics, University of Chicago, Chicago, IL 60637 (United States)

2012-12-10

260

The Effects of Low-Shear Mechanical Stress on Yersinia pestis Virulence  

Microsoft Academic Search

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,

Abidat Lawal; Olufisayo A. Jejelowo; Jason A. Rosenzweig

2010-01-01

261

Hydrostatic and shear consolidation tests with permeability measurements on Waste Isolation Pilot Plant crushed salt  

SciTech Connect

Crushed natural rock salt is a primary candidate for use as backfill and barrier material at the Waste Isolation Pilot Plant (WIPP) and therefore Sandia National Laboratories (SNL) has been pursuing a laboratory program designed to quantify its consolidation properties and permeability. Variables that influence consolidation rate that have been examined include stress state and moisture content. The experimental results presented in this report complement existing studies and work in progress conducted by SNL. The experiments described in this report were designed to (1) measure permeabilities of consolidated specimens of crushed salt, (2) determine the influence of brine saturation on consolidation under hydrostatic loads, and 3) measure the effects of small applied shear stresses on consolidation properties. The laboratory effort consisted of 18 individual tests: three permeability tests conducted on specimens that had been consolidated at Sandia, six hydrostatic consolidation and permeability tests conducted on specimens of brine-saturated crushed WIPP salt, and nine shear consolidation and permeability tests performed on crushed WIPP salt specimens containing 3 percent brine by weight. For hydrostatic consolidation tests, pressures ranged from 1.72 MPa to 6.90 MPa. For the shear consolidation tests, confining pressures were between 3.45 MPa and 6.90 MPa and applied axial stress differences were between 0.69 and 4.14 MPa. All tests were run under drained conditions at 25{degrees}C.

Brodsky, N.S. [RE/SPEC, Inc., Rapid City, SD (United States)

1994-03-01

262

Forsterite to wadsleyite phase transformation under shear stress and consequences for the Earth's mantle transition zone  

NASA Astrophysics Data System (ADS)

We have studied the phase transformation of forsterite to wadsleyite under shear stress at the Earth's transition zone pressure and temperature conditions. Two-step experiments were performed using a multi-anvil press. First, we hot pressed iron-free forsterite at 6 or 11 GPa and 1100 °C. Then we deformed a slab of this starting material using a direct simple shear assembly at 16 GPa and 1400 °C for 1, 15, 35, 40, or 60 min. Both the starting material and the deformed samples were characterized using optical and scanning electron microscopy including measurements of crystal preferred orientations (CPO) by electron back scattered diffraction (EBSD), transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FTIR). The phase transformation occurs very rapidly, in less than 1 min, and metastable forsterite relics are not observed after deformation. The grain size of wadsleyite is slightly smaller than the forsterite starting material. The water contents obtained from FTIR analyses in forsterite and wadsleyite are 65-124 wt ppm H 2O and 114-736 wt ppm H 2O, respectively, which are well below water solubility at similar conditions in the presence of free water. Wadsleyite aggregates display weak CPO patterns with [1 0 0] axes concentrated at low angle to the shear direction, [0 1 0] axes perpendicular to the shear plane and nearly random [0 0 1] axes. Only a few dislocations were observed in wadsleyite with TEM. This observation is consistent with the assumption that most dislocations formed during the initial high-stress stages of these stress-relaxation experiments, were consumed in the phase transformation, probably enhancing the transformation rate. CPO patterns vary as a function of the water content: with increasing water content the density of [1 0 0] axes parallel to the shear direction decreases, and the density of [0 0 1] axes increases. Viscoplastic self-consistent modeling of CPO evolution using previously reported glide systems for wadsleyite, i.e., [1 0 0]{0 k l} and 1/2 <1 1 1>{1 0 1}, cannot reproduce the measured CPO, unless the [0 0 1](0 1 0) system, for which dislocations have not been observed by TEM, is also activated. In addition, wadsleyite grain growth suggests the participation of diffusion-assisted processes in deformation. Calculated anisotropies for P and S-waves using measured CPO are always below 1%. This very low anisotropy is due to both the low finite strain achieved in the experiments, which leads to weak wadsleyite CPO, and to the diluting effect of added majorite. The present experiments emphasize the importance of stress, grain size evolution and water content in the forsterite to wadsleyite phase transformation and subsequent deformation in the transition zone.

Demouchy, S.; Mainprice, D.; Tommasi, A.; Couvy, H.; Barou, F.; Frost, D. J.; Cordier, P.

2011-01-01

263

Wall shear measurements of turbulent flow over backward facing step  

NASA Astrophysics Data System (ADS)

This paper is aim to generalize our recent developments of an extension of particle image velocimetry (PIV) measurement technique, named as Interfacial PIV (noted as IPIV). It enables us to deal with near-wall flows over curved walls by means of conformal transformation. In addition, if the displacement of tracer in wall-normal direction is less than its diameter, IPIV could instantaneously and precisely measure the wall shear gradient as well as draw out the tangential velocity profile. Our integration of measured velocity gradients upward from wall could provide a continuous profile with single pixel resolution. In this communication, we extend our wall shear measurement technique to stereo-PIV setup. Validation of IPIV wall shear measurement to 2-dimensional and 3-dimensional synthetic images of turbulent flows over a wavy bed is performed. In practice, experiment with backward-facing step (BFS) at a low Reynolds number of 2800 is examined. A system of two two-component PIV (2CPIV) coupled with a stereo-PIV (SPIV) is conducted to inquire the flow structure. Applications of IPIV to our 2CPIV and SPIV experimental images are also described.

Duy, Nguyen Thien; Craig, Wells John; Chuong Vinh, Nguyen

2009-11-01

264

Basal shear and normal stresses of dry and wet snow avalanches after a slope deviation  

Microsoft Academic Search

Basal shear and normal force measurements of dry and wet snow avalanches and slush flows from the Weissfluhjoch snow chute are presented. This chute contains two slope angle transitions in order to measure the effect of slope deviations on the normal and shear force distributions. Slope deviations are typically encountered near snow sheds and the dynamic forces resulting from them

K. Platzer; P. Bartelt; C. Jaedicke

2007-01-01

265

Localized shear deformation and softening of bulk metallic glass: stress or temperature driven?  

PubMed Central

Metallic glasses due to their unique combination of physical and chemical properties have a great potential in various applications: materials for construction, medical, MEMs devices and so on. The deformation mechanism in metallic glasses is very much different from that in conventional crystalline materials and not yet fully understood. Here we are trying to find out what drives shear deformation in metallic glasses. The compression experiments of the bulk metallic glassy (BMG) samples coated with tin, Rose metal and indium were performed. There were no melting sites of the coating observed near individual shear bands. Melting occurred only near fracture surface, near microcracks and in the places of shear band concentrations. The results indicate that shear banding is rather a stress driven process while the temperature rise that was observed takes place due to friction forces in the viscous supercooled liquid thin layer in the shear bands.

Ketov, S. V.; Louzguine-Luzgin, D. V.

2013-01-01

266

Localized shear deformation and softening of bulk metallic glass: stress or temperature driven?  

PubMed

Metallic glasses due to their unique combination of physical and chemical properties have a great potential in various applications: materials for construction, medical, MEMs devices and so on. The deformation mechanism in metallic glasses is very much different from that in conventional crystalline materials and not yet fully understood. Here we are trying to find out what drives shear deformation in metallic glasses. The compression experiments of the bulk metallic glassy (BMG) samples coated with tin, Rose metal and indium were performed. There were no melting sites of the coating observed near individual shear bands. Melting occurred only near fracture surface, near microcracks and in the places of shear band concentrations. The results indicate that shear banding is rather a stress driven process while the temperature rise that was observed takes place due to friction forces in the viscous supercooled liquid thin layer in the shear bands. PMID:24100784

Ketov, S V; Louzguine-Luzgin, D V

2013-10-08

267

Localized shear deformation and softening of bulk metallic glass: stress or temperature driven?  

NASA Astrophysics Data System (ADS)

Metallic glasses due to their unique combination of physical and chemical properties have a great potential in various applications: materials for construction, medical, MEMs devices and so on. The deformation mechanism in metallic glasses is very much different from that in conventional crystalline materials and not yet fully understood. Here we are trying to find out what drives shear deformation in metallic glasses. The compression experiments of the bulk metallic glassy (BMG) samples coated with tin, Rose metal and indium were performed. There were no melting sites of the coating observed near individual shear bands. Melting occurred only near fracture surface, near microcracks and in the places of shear band concentrations. The results indicate that shear banding is rather a stress driven process while the temperature rise that was observed takes place due to friction forces in the viscous supercooled liquid thin layer in the shear bands.

Ketov, S. V.; Louzguine-Luzgin, D. V.

2013-10-01

268

Cultivation of shear stress sensitive microorganisms in disposable bag reactor systems.  

PubMed

Technical scale (?5l) cultivations of shear stress sensitive microorganisms are often difficult to perform, as common bioreactors are usually designed to maximize the oxygen input into the culture medium. This is achieved by mechanical stirrers, causing high shear stress. Examples for shear stress sensitive microorganisms, for which no specific cultivation systems exist, are many anaerobic bacteria and fungi, such as basidiomycetes. In this work a disposable bag bioreactor developed for cultivation of mammalian cells was investigated to evaluate its potential to cultivate shear stress sensitive anaerobic Eubacterium ramulus and shear stress sensitive basidiomycetes Flammulina velutipes and Pleurotus sapidus. All cultivations were compared with conventional stainless steel stirred tank reactors (STR) cultivations. Good growth of all investigated microorganisms cultivated in the bag reactor was found. E. ramulus showed growth rates of ?=0.56h(-1) (bag) and ?=0.53h(-1) (STR). Differences concerning morphology, enzymatic activities and growth in fungal cultivations were observed. In the bag reactor growth in form of small, independent pellets was observed while STR cultivations showed intense aggregation. F. velutipes reached higher biomass concentrations (21.2gl(-1) DCW vs. 16.8gl(-1) DCW) and up to 2-fold higher peptidolytic activities in comparison to cell cultivation in stirred tank reactors. PMID:23892193

Jonczyk, Patrick; Takenberg, Meike; Hartwig, Steffen; Beutel, Sascha; Berger, Ralf G; Scheper, Thomas

2013-07-26

269

Obligatory role of hyperaemia and shear stress in microvascular adaptation to repeated heating in humans  

PubMed Central

The endothelium, a single layer of cells lining the entire circulatory system, plays a key role in maintaining vascular health. Endothelial dysfunction independently predicts cardiovascular events and improvement in endothelial function is associated with decreased vascular risk. Previous studies have suggested that exercise training improves endothelial function in macrovessels, a benefit mediated via repeated episodic increases in shear stress. However, less is known of the effects of shear stress modulation in microvessels. In the present study we examined the hypothesis that repeated skin heating improves cutaneous microvascular vasodilator function via a shear stress-dependent mechanism. We recruited 10 recreationally active males who underwent bilateral forearm immersion in warm water (42°C), 3 times per week for 30 min. During these immersion sessions, shear stress was manipulated in one arm by inflating a pneumatic cuff to 100 mmHg, whilst the other arm remained uncuffed. Vasodilatation to local heating, a NO-dependent response assessed using laser Doppler, improved across the 8 week intervention period in the uncuffed arm (cutaneous vascular conductance week 0 vs. week 4 at 41°C: 1.37 ± 0.45 vs. 2.0 ± 0.91 units, P= 0.04; 42°C: 2.06 ± 0.45 vs. 2.68 ± 0.83 units; P= 0.04), whereas no significant changes were evident in the cuffed arm. We conclude that increased blood flow, and the likely attendant increase in shear stress, is a key physiological stimulus for enhancing microvascular vasodilator function in humans.

Green, Daniel J; Carter, Howard H; Fitzsimons, Matthew G; Cable, N Timothy; Thijssen, Dick HJ; Naylor, Louise H

2010-01-01

270

Upregulation of Superoxide Dismutase and Nitric Oxide Synthase Mediates the Apoptosis-Suppressive Effects of Shear Stress on Endothelial Cells  

Microsoft Academic Search

Physiological levels of laminar shear stress completely abrogate apoptosis of human endothelial cells in response to a variety of stimuli and might therefore importantly contribute to endothelial integrity. We show here that the apoptosis-suppressive effects of shear stress are mediated by upregulation of Cu\\/Zn SOD and NO synthase. Shear stress-mediated inhibition of endothelial cell apoptosis in response to exogenous oxygen

Stefanie Dimmeler; Corinna Hermann; Jan Galle; Andreas M. Zeiher

2010-01-01

271

Shear Stress Induces the Release of an Endothelial Elastase: Role in Integrin ?v?3-Mediated FGF2 Release  

Microsoft Academic Search

Background\\/Aims: Laminar shear stress is an important stimulus in the endothelium-dependent control of vascular tone and of vascular remodeling processes. Based on previous studies demonstrating integrin-mediated release of fibroblast growth factor 2 (FGF-2), we investigated whether shear stress-induced integrin activation requires the involvement of an extracellular protease. Methods: Cultured porcine aortic endothelial cells (PAEC) were exposed to laminar shear stress

Theres Hennig; Christina Mogensen; Julian Kirsch; Ulrich Pohl; Torsten Gloe

2011-01-01

272

Analysis of complete plasticity assumption for solid circular shaft under pure torsion and calculation of shear stress  

Microsoft Academic Search

The distribution of shear stress on the cross-section of plastic metal solid circular shaft under pure torsion yielding, the\\u000a applicability of complete plastic model assumption and the shear stress formula were researched. Based on the shear stress\\u000a formula of circular shaft under pure torsion in elastic stage, the formula of torque in elastic stage and the definition of\\u000a yield, it

Guang-lian Liu; Ming-hui Huang; Qing Tan; Xian-fang Li; Zhen Liu

2011-01-01

273

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

Microsoft Academic Search

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

Otis R. Walton; ROBERT L. BRAUN

1986-01-01

274

Significance of Extensional Stresses to Red Blood Cell Lysis in a Shearing Flow  

Microsoft Academic Search

Traditionally, an empirical power-law model relating hemolysis to shear stress and exposure time has been used to estimate\\u000a hemolysis related to flow—however, this basis alone has been insufficient in attempts to predict hemolysis through computational\\u000a fluid dynamics. Because of this deficiency, we sought to re-examine flow features related to hemolysis in a shearing flow\\u000a by computationally modeling a set of

Linden A. Down; Dimitrios V. Papavassiliou; Edgar A. O’Rear

2011-01-01

275

Computation of the fluid-induced shear stress in bioreactor-cultured 3D cell systems  

Microsoft Academic Search

Fluid-induced shear is known to enhance chondrogenesis on animal cells. We have developed a computational fluid dynamic model of the flow through chondrocyte seeded scaffolds cultured inside a novel bioreactor in which the culture medium flows through the constructs' microstructure. The median shear stress imposed to the cells in the bioreactor culture, as predicted by the CFD model, is 3·10-3

F. Boschetti; M. T. Raimondi; G. B. Fiore; G. Dubini; L. Falcone; A. Remuzzi; E. Marinoni; M. Marazzi; R. Pietrabissa

2002-01-01

276

Exercise-mediated changes in conduit artery wall thickness in humans: role of shear stress  

Microsoft Academic Search

Episodic increases in shear stress have been proposed as a mechanism that induces training-induced adaptation in arterial wall remodeling in humans. To address this hypothesis in humans, we examined bilateral brachial artery wall thickness using high-resolution ultrasound in healthy men across an 8-wk period of bilateral handgrip training. Unilaterally, shear rate was attenuated by cuff inflation around the forearm to

D. H. J. Thijssen; E. A. Dawson; I. C. van den Munckhof; T. M. Tinken; E. den Drijver; N. Hopkins; N. T. Cable; D. J. Green

2011-01-01

277

Dynamic modeling for shear stress induced ATP release from vascular endothelial cells  

Microsoft Academic Search

A dynamic model is proposed for shear stress induced adenosine triphosphate (ATP) release from endothelial cells (ECs). The\\u000a dynamic behavior of the ATP\\/ADP concentration at the endothelial surface by viscous shear flow is investigated through simulation\\u000a studies based on the dynamic ATP release model. The numerical results demonstrate that the ATP\\/ADP concentration against time\\u000a at endothelium-fluid interface predicted by the

Kai Rong Qin; Cheng Xiang; Zhe Xu; Ling Ling Cao; Shuzhi Sam Ge; Zong Lai Jiang

2008-01-01

278

Influence of shear bond strength on compressive strength and stress–strain characteristics of masonry  

Microsoft Academic Search

The paper is focused on shear bond strength–masonry compressive strength relationships and the influence of bond strength\\u000a on stress–strain characteristics of masonry using soil–cement blocks and cement–lime mortar. Methods of enhancing shear bond\\u000a strength of masonry couplets without altering the strength and modulus of masonry unit and the mortar are discussed in detail.\\u000a Application of surface coatings and manipulation of

B. V. Venkatarama Reddy; Ch. V. Uday Vyas

2008-01-01

279

Unified analytical stress — strain curve for quasibrittle geomaterial in uniaxial tension, direct shear and uniaxial compression  

Microsoft Academic Search

Considering strain localization in the form of a narrow band initiated just at peak stress, three analytical expressions for\\u000a stress — strain curves of quasibrittle geomaterial (such as rock and concrete) in uniaxial tension, direct shear and uniaxial\\u000a compression were presented, respectively. The three derived stress — strain curves were generalized as a unified formula.\\u000a Beyond the onset of strain

Xue-bin Wang

2006-01-01

280

Dynamic shear stress regulation of inflammatory and thrombotic pathways in baboon endothelial outgrowth cells.  

PubMed

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

Ankeny, Randall F; Hinds, Monica T; Nerem, Robert M

2013-03-19

281

Dispersion and shear modulus measurements of porcine liver.  

PubMed

A narrow-band ultrasonic shear-wave imaging technique for estimating phase speed was applied to fresh and thermally damaged porcine liver in vitro. Two constitutive models were applied to the measurements to represent rheological behavior of the tissue and estimate the complex shear modulus at frequencies between 50 and 300 Hz. Our results were compared to similar values from the literature to assess how well models represent liver measurements over a range of shear-wave frequencies, experimental conditions and mammalian species. We found remarkable consistency in some parameters but not in others, suggesting that the Kelvin-Voigt model commonly applied in elasticity-imaging situations is representative of tissue dispersion but the description it offers is incomplete. Data are consistent with the theory that viscoelastic contrast is more likely due to changes in protein and other biomolecular-scale structures than from tissue anatomy larger than a cell. Dispersion measurements at frequencies between 0.5-1000 kHz are needed to more completely evaluate models for the viscoelastic behavior liver. PMID:21213570

Orescanin, Marko; Qayyum, Muqeem A; Toohey, Kathleen S; Insana, Michael F

2010-10-01

282

Development of a novel bioreactor to apply shear stress and tensile strain simultaneously to cell monolayers  

NASA Astrophysics Data System (ADS)

To date many bioreactor experiments have investigated the cellular response to isolated in vitro forces. However, in vivo, wall shear stress (WSS) and tensile hoop strain (THS) coexist. This article describes the techniques used to build and validate a novel vascular tissue bioreactor, which is capable of applying simultaneous wall shear stress and tensile stretch to multiple cellular substrates. The bioreactor design presented here combines a cone and plate rheometer with flexible substrates. Using such a combination, the bioreactor is capable of applying a large range of pulsatile wall shear stress (-30 to +30 dyn/cm2) and tensile hoop strain (0%-12%). The WSS and THS applied to the cellular substrates were validated and calibrated. In particular, curves were produced that related the desired WSS to the bioreactor control parameters. The bioreactor was shown to be biocompatible and noncytotoxic and suitable for cellular mechanical loading studies in physiological condition, i.e., under simultaneous WSS and THS conditions.

Breen, Liam T.; McHugh, Peter E.; McCormack, Brendan A.; Muir, Gordon; Quinlan, Nathan J.; Heraty, Kevin B.; Murphy, Bruce P.

2006-10-01

283

Imaging the cellular response to transient shear stress using stroboscopic digital holography  

NASA Astrophysics Data System (ADS)

We use stroboscopic quantitative phase microscopy to study cell deformation and the response to cavitation bubbles and transient shear stress resulting from laser-induced breakdown of an optically trapped nanoparticle. A bi-directional transient displacement of cytoplasm is observed during expansion and collapse of the cavitation bubble. In some cases, cell deformation is only observable at the microsecond time scale without any permanent change in cell shape or optical thickness. On a time scale of seconds, the cellular response to shear stress and cytoplasm deformation typically leads to retraction of the cellular edge most exposed to the flow, rounding of the cell body and, in some cases, loss of cellular dry mass. These results give a new insight into the cellular response to cavitation induced shear stress and related plasma membrane permeabilization. This study also demonstrates that laser-induced breakdown of a nanoparticle offers localized cavitation, which interacts with a single cell but without causing cell lysis.

Antkowiak, Maciej; Arita, Yoshihiko; Dholakia, Kishan; Gunn-Moore, Frank

2011-12-01

284

Liquid crystals for surface shear stress visualization on wind turbine airfoils  

SciTech Connect

Experiments were conducted on the Sandia 17-m vertical axis wind turbine to test the liquid-crystal/surface-shear-stress visualization technique in field environments. A Sandia natural-laminar-flow airfoil served as the test surface. Initial feasibility experiments were conducted under high-tip-speed-ratio, high-Reynolds-number conditions, which resulted in low angle-of-attack, quasi-steady flow fields. Data acquisition was accomplished with a tower-mounted movie camera and 35mm color film. Liquid crystal coatings sensitive only to surface shear stress, and insensitive to temperature changes for temperatures below 50/degree/C, were utilized. Observations of coating color changes showed the liquid crystal technique capable of visualizing surface shear stress distributions, including (by contrast) regions of separated flow, under field-test conditions. 10 refs., 3 figs.

Reda, D.C.; Smith, R.W.; Bryant, T.C.; Schluter, L.L.

1988-01-01

285

Experimental study of a textural transition in liquid crystals under shear stress induced by surface friction  

NASA Astrophysics Data System (ADS)

Results of a study of the optical response of liquid crystals with helical supramolecular structure to surfacefriction-induced shear stress in aerodynamic experiments are reported. The effect of re-orientation of molecules from confocal (light-scattering) to planar (selectively reflecting light) texture is considered. The textural transition is examined by the spectral and colorimetric methods. Dependences of the reflection spectra of the formed planar texture on time and on the mean shear-stress level were obtained. It is shown that the dependence of the texture transition time on the shear-stress level can be approximated, in a logarithmic scale, with a linear dependence; this allows using the effect for flow diagnostics.

Zharkova, G. M.; Kovrizhina, V. N.; Petrov, A. P.

2013-09-01

286

Velocity correlations in dense granular shear flows: Effects on energy dissipation and normal stress  

NASA Astrophysics Data System (ADS)

We study the effect of precollisional velocity correlations on granular shear flow by molecular dynamics simulations of an inelastic hard sphere system. Comparison of the simulations with kinetic theory reveals that the theory overestimates both the energy dissipation rate and the normal stress in the dense flow region. We find that the relative normal velocity of colliding particles is smaller than that expected from random collisions, and the discrepancies in the dissipation and the normal stress can be adjusted by introducing the idea of the collisional temperature, from which we conclude that the velocity correlation neglected in the kinetic theory is responsible for the discrepancies. Our analysis of the distributions of the precollisional velocity suggests that the correlation grows through multiple inelastic collisions during the time scale of the inverse of the shear rate. As for the shear stress, the discrepancy is also found in the dense region, but it depends strongly on the particle inelasticity.

Mitarai, Namiko; Nakanishi, Hiizu

2007-03-01

287

Oral Shear Stress Predicts Flavour Perception in Viscous Solutions  

Microsoft Academic Search

The perception of sweetness and flavour were studied in viscous solutions containing 50 g\\/l sucrose, 100 p.p.m. iso-amyl acetate and varying concentrations of three hydrocolloid thickeners (guar gum, ?-carrageenan and hydroxypropylmethyl cellulose). Zero-shear viscosity of the samples ranged from 1 to 5000 mPas. Perception of both sweetness and aroma was suppressed at thickener concentrations above c* (coil overlap concentration, the

David J. Cook; Tracey A. Hollowood; Robert S. T. Linforth; Andrew J. Taylor

2003-01-01

288

Pressure-shear stress wave analysis in plate impact experiments  

Microsoft Academic Search

Numerical results are presented for the combined longitudinal and shear wave propagation in an elastic-viscoplastic solid as it occurs in high strain-rate plate impact experiments. Special attention is paid to the initial stage of the impact experiment and the effects of the specimen thickness, elastic impedances of flyer-anvil plates, and viscoplastic properties of materials on the time to reach a

Wei Tong

1997-01-01

289

Ultrasonic measurement of stress in railroad wheels  

NASA Astrophysics Data System (ADS)

The equipment described here generates ultrasonic shear waves using an electromagnetic-acoustic transducer. Precise measurement of the velocity of two orthogonally polarized signals determines the birefringence and allows the calculation of stress. It is necessary to account for the effect of metallurgical texture which can contribute to the birefringence and appear as moderate stress. This system sends a signal through the thickness of a railroad wheel rim, digitizes the first echo, locks onto a cycle, and calculates the time when it crosses zero amplitude. Signal averaging yields the arrival time of a signal at about 90 ?s with a standard deviation of 2-4 ns. In screening the residual stress in the rims of cast-steel railroad wheels, this system has a total error of ~+/-60 MPa; most of this is due to variability of the texture measured in several stress-relieved blocks cut from wheels. The initial measurements were on wheels in which the manufacture had induced known levels of thermal damage. Results from destructive radial saw cuts through the rims allowed qualitative evaluation of the nondestructive measurements. Most components in this equipment are commercially available.

Schramm, Raymond E.

1999-02-01

290

Maximal wall shear stress in arterial stenoses: application to the internal carotid arteries.  

PubMed

Maximal wall shear stress (MWSS) in the convergent part of a stenosis is calculated by the interactive boundary-layer theory. A dimensional analysis of the problem shows that MWSS depends only on a few measurable parameters. A simple relationship between MWSS and these parameters is obtained, validated, and used to calculate the magnitude of MWSS in a carotid stenosis, as a function of the patency of the circle of Willis and the stenotic pattern. This demonstrates the huge effect of collateral pathways. Elevated MWSS are observed even in moderate stenoses, provided they are associated with a contralateral occlusion, a large anterior, and narrow posterior communicating arteries, suggesting a potential risk of embolus release in this configuration. PMID:11192389

Lorthois, S; Lagrée, P Y; Marc-Vergnes, J P; Cassot, F

2000-12-01

291

Novel high bandwidth wall shear stress sensor for ultrasonic cleaning applications  

NASA Astrophysics Data System (ADS)

Ultrasonic cleaning is due to the action of cavitation bubbles. The details of the cleaning mechanisms are not revealed or confirmed experimentally, yet several studies suggest that the wall shear stresses generated are very high, i.e. of the order of several thousand Pascal. Ultrasonic cleaning applications span a wide range from semiconductor manufacturing, to low pressure membrane cleaning, and the in the medical field cleaning of surgical instruments. We have developed a novel sensor to monitor and quantify cleaning activity which is (1) very sturdy, (2) has a high bandwidth of several megahertz, (3) is cheap in manufacturing costs, and (4) of very small size. We analyze the sensor signal by comparing its response time correlated to single laser induced cavitation bubbles using high-speed photography. Additionally, we will present first measurements in ultrasonic cleaning bathes using again high-speed photography. A preliminary discussion on the working mechanism of the sensor will be presented.

Gonzalez-Avila, S. Roberto; Prabowo, Firdaus; Ohl, Claus-Dieter

2010-11-01

292

Fluid shear stress stimulates membrane phospholipid metabolism in cultured human endothelial cells.  

PubMed

There is evidence suggesting that fluid shear stress activates phospholipid turnover in endothelial cells, but it is not clear which phospholipids are involved in the transduction of the flow signal. Cultured human umbilical-vein endothelial cells were prelabeled with [14C]-arachidonic acid and subjected to laminar shear stresses of 0.4, 1.4 and 22 dyn/cm2 for times up to 30 min, after which the distribution of the radioactivity in the phospholipids was determined. We observed decreases in labeled phosphatidylinositol, phosphatidylethanolamine and phosphatidic acid at 10-30 s, and increases in labeled diacylglycerol (DG) and free arachidonate, as well as a simultaneous elevation in inositol 1,4,5-triphosphate (IP3) levels. A second peak in IP3 levels was observed 10 min after the onset of shear. This is in contrast with agonist-stimulated endothelial cells, where IP3 levels go back to initial values within a few minutes after stimulation. The flow-induced IP3 response was the same in the presence or absence of ATP and serum in the perfusing medium. These results are consistent with the activation of phospholipase C, phospholipase A2 and DG lipase by shear stress. This suggests that several phospholipids are involved in the production of free arachidonic acid and DG, which are likely to be important mediators of the shear stress signal. In addition, flow may lead to a chronic stimulation of endothelial-cell metabolism. PMID:1489890

Bhagyalakshmi, A; Berthiaume, F; Reich, K M; Frangos, J A

293

Measuring Environmental Stress  

ERIC Educational Resources Information Center

Infrared remote sensors, plus photometric interpretation and digital data analysis are being used to record the stresses on air, water, vegetation and soil. Directly recorded photographic information has been the most effective recording media for remote sensing. (BT)

Walker, John E.; Dahm, Douglas B.

1975-01-01

294

Measuring Environmental Stress  

ERIC Educational Resources Information Center

|Infrared remote sensors, plus photometric interpretation and digital data analysis are being used to record the stresses on air, water, vegetation and soil. Directly recorded photographic information has been the most effective recording media for remote sensing. (BT)|

Walker, John E.; Dahm, Douglas B.

1975-01-01

295

Shear stress-induced volume decrease in C11-MDCK cells by BK-?/?4  

PubMed Central

Large-conductance, calcium-activated potassium channels (BK) are expressed in principal cells (PC) and intercalated cells (IC) in mammalian nephrons as BK-?/?1 and BK-?/?4, respectively. IC, which protrude into the lumens of tubules, express substantially more BK than PC despite lacking sufficient Na-K-ATPase to support K secretion. We previously showed in mice that IC exhibit size reduction when experiencing high distal flows induced by a high-K diet. We therefore tested the hypothesis that BK-?/?4 are regulators of IC volume via a shear stress (?)-induced, calcium-dependent mechanism, resulting in a reduction in intracellular K content. We determined by Western blot and immunocytochemical analysis that C11-Madin-Darby canine kidney cells contained a predominance of BK-?/?4. To determine the role of BK-?/?4 in ?-induced volume reduction, we exposed C11 cells to ? and measured K efflux by flame photometry and cell volume by calcein staining, which changes inversely to cell volume. With 10 dynes/cm2, calcein intensity significantly increased 39% and monovalent cationic content decreased significantly by 37% compared with static conditions. Furthermore, the shear-induced K loss from C11 was abolished by the reduction of extracellular calcium, addition of 5 mM TEA, or BK-?4 small interfering (si) RNA, but not by addition of nontarget siRNA. These results show that BK-?/?4 plays a role in shear-induced K loss from IC, suggesting that BK-?/?4 regulate IC volume during high-flow conditions. Furthermore, these results support the use of C11 cells as in vitro models for studying BK-related functions in IC of the kidney.

Holtzclaw, J. David; Liu, Liping; Grimm, P. Richard

2010-01-01

296

Quantifying turbulent wall shear stress in a subject specific human aorta using large eddy simulation.  

PubMed

In this study, large-eddy simulation (LES) is employed to calculate the disturbed flow field and the wall shear stress (WSS) in a subject specific human aorta. Velocity and geometry measurements using magnetic resonance imaging (MRI) are taken as input to the model to provide accurate boundary conditions and to assure the physiological relevance. In total, 50 consecutive cardiac cycles were simulated from which a phase average was computed to get a statistically reliable result. A decomposition similar to Reynolds decomposition is introduced, where the WSS signal is divided into a pulsating part (due to the mass flow rate) and a fluctuating part (originating from the disturbed flow). Oscillatory shear index (OSI) is plotted against time-averaged WSS in a novel way, and locations on the aortic wall where elevated values existed could easily be found. In general, high and oscillating WSS values were found in the vicinity of the branches in the aortic arch, while low and oscillating WSS were present in the inner curvature of the descending aorta. The decomposition of WSS into a pulsating and a fluctuating part increases the understanding of how WSS affects the aortic wall, which enables both qualitative and quantitative comparisons. PMID:22209366

Lantz, Jonas; Gårdhagen, Roland; Karlsson, Matts

2011-12-29

297

Stress measurements in soft rocks  

Microsoft Academic Search

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

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

2003-01-01

298

The Critical Shear Stress to Transmit A Peierls Screw Dislocation Across A Non-slipping Interface  

NASA Astrophysics Data System (ADS)

The critical resolved shear stress to transmit a screw dislocation through a non-slipping (welded) bimaterial interface is studied as a function of the elastic mismatch across the interface and the nonlinear shear stress-relative shear displacement relation across the incoming and outgoing slip planes. This study extends the work of Pacheco and Mura (1969), by using a numerical approach that incorporates a variety of slip plane relations and by adopting a formulation by Beltz and Rice (1991) that accounts for the finite interplanar spacing across a slip plane. The geometry is specialized to the case when slip planes are perpendicular to the interface and numerical results are obtained for values of mismatch, ??, in elastic modulus equal to 20% of the average value. Numerical results in this regime confirm the Pacheco and Mura observation that the critical resolved shear stress is proportional to the mismatch in elastic shear modulus. A significant new result is that the critical resolved shear stress increases with the unstable stacking fault energy of the slip planes, but is relatively insensitive to the maximum shear strength of the slip planes. A simple model is constructed which adequately captures the dependence on stacking fault energy and elastic modulus mismatch. It is with pleasure and gratitude that this work is presented on the commemoration of the 60th birthday of Prof. James Rice, who as Ph.D. advisor to one of the authors (PMA), instilled a sense of enthusiasm and formalism to study dislocation-defect interactions of the type described herein.

Anderson, Peter M.; Xin, Xiaoj.

299

Algebraic stress modeling in a buoyancy controlled turbulent shear flow  

Microsoft Academic Search

The paper presents an application of the algebraic stress modeling (ASM) technique to the prediction of the flow in a turbulent round buoyant jet. In the ASM approach, algebraic formulas are obtained for the Reynolds stresses and for the components of the turbulent heat flux. In the model used here, transport equations are solved for the turbulence kinetic energy, its

F. Tamanini

1977-01-01

300

Shear stress triggers insertion of voltage-gated potassium channels from intracellular compartments in atrial myocytes.  

PubMed

Atrial myocytes are continuously exposed to mechanical forces including shear stress. However, in atrial myocytes, the effects of shear stress are poorly understood, particularly with respect to its effect on ion channel function. Here, we report that shear stress activated a large outward current from rat atrial myocytes, with a parallel decrease in action potential duration. The main ion channel underlying the increase in current was found to be Kv1.5, the recruitment of which could be directly observed by total internal reflection fluorescence microscopy, in response to shear stress. The effect was primarily attributable to recruitment of intracellular pools of Kv1.5 to the sarcolemma, as the response was prevented by the SNARE protein inhibitor N-ethylmaleimide and the calcium chelator BAPTA. The process required integrin signaling through focal adhesion kinase and relied on an intact microtubule system. Furthermore, in a rat model of chronic hemodynamic overload, myocytes showed an increase in basal current despite a decrease in Kv1.5 protein expression, with a reduced response to shear stress. Additionally, integrin beta1d expression and focal adhesion kinase activation were increased in this model. This data suggests that, under conditions of chronically increased mechanical stress, the integrin signaling pathway is overactivated, leading to increased functional Kv1.5 at the membrane and reducing the capacity of cells to further respond to mechanical challenge. Thus, pools of Kv1.5 may comprise an inducible reservoir that can facilitate the repolarization of the atrium under conditions of excessive mechanical stress. PMID:24065831

Boycott, Hannah E; Barbier, Camille S M; Eichel, Catherine A; Costa, Kevin D; Martins, Raphael P; Louault, Florent; Dilanian, Gilles; Coulombe, Alain; Hatem, Stéphane N; Balse, Elise

2013-09-24

301

Shear and transverse stress in a thin superconducting layer in simplified coated conductor architecture with a pre-existing detachment  

NASA Astrophysics Data System (ADS)

The thermal-electro-mechanical behavior of second generation YBa2Cu3O7-? coated conductors subjected to thermal cooling and electric charging is investigated in this paper. Shear stress at the interface and transverse normal stress in the film are analyzed through the elasticity theory. The plane strain approach is assumed, and a singular integral equation governing the problem is derived in terms of the interfacial shear stress, thermal strain, and the electromagnetic force. After that, we evaluate the shear and transverse stress distribution in the conductor during cool down and electric charging, respectively. The results show that large residual compressive stress (about 150 MPa) and interfacial shear stress (about 400 MPa) remain in the conductor during cool down. In the electric charging process while small compared to the thermal one destructive tensile stress present near the edges of the conductor. Effects of the stiffness of substrate on the stress distribution in the conductor are investigated also.

Jing, Ze; Yong, Huadong; Zhou, Youhe

2013-07-01

302

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

PubMed Central

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.

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

2012-01-01

303

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

PubMed

Tissue scaffolds aim to provide a cell-friendly biomechanical environment for facilitating cell growth. Existing studies have shown significant demands for generating a certain level of wall shear stress (WSS) on scaffold microstructural surfaces for promoting cellular response and attachment efficacy. Recently, its role in shear-induced erosion of polymer scaffold has also drawn increasing attention. This paper proposes a bi-directional evolutionary structural optimization (BESO) approach for design of scaffold microstructure in terms of the WSS uniformity criterion, by downgrading highly-stressed solid elements into fluidic elements and/or upgrading lowly-stressed fluidic elements into solid elements. In addition to this, a computational model is presented to simulate shear-induced erosion process. The effective stiffness and permeability of initial and optimized scaffold microstructures are characterized by the finite element based homogenization technique to quantify the variations of mechanical properties of scaffold during erosion. The illustrative examples show that a uniform WSS is achieved within the optimized scaffold microstructures, and their architectural and biomechanical features are maintained for a longer lifetime during shear-induced erosion process. This study provides a mathematical means to the design optimization of cellular biomaterials in terms of the WSS criterion towards controllable shear-induced erosion. PMID:21950901

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

2011-08-01

304

Assessing Mitochondrial Redox Status by Flow Cytometric Methods: Vascular Response to Fluid Shear Stress  

PubMed Central

Mitochondria are an important source of superoxide production contributing to physiological and pathological responses, including vascular oxidative stress that is relevant to cardiovascular diseases. Vascular oxidative stress is intimately linked with pro-inflammatory states and atherosclerosis. Oxidized low density lipoprotein (OxLDL) modulates intracellular redox status and induces apoptosis in endothelial cells. Hemodynamic, specifically, fluid shear stress imparts both biomechanical and metabolic effects on vasculature. Mitochondria are an important source of superoxide production contributing to vascular oxidative stress with relevance to cardiovascular diseases. We hereby present biophysical and biochemical approaches, including fluorescence-activate cell sorting, to assess the dynamics of vascular redox status

Li, Rongsong; Jen, Nelson; Yu, Fei; Hsiai, Tzung K.

2011-01-01

305

Cylindrical cavity with a circumferential edge crack subjected to a uniform shearing stress  

NASA Astrophysics Data System (ADS)

This paper contains an analysis of the stress distribution in an elastic medium having cylindrical cavity with a circumferential edge crack when it is deformed by the application of uniform shearing stress. By making a suitable representation of the stress function for the problem, the problem is reduced to the solution of a pair of singular integral equations. This pair of singular integral equations is solved numerically, and the stress intensity factor due to the effect of the crack size is calculated. Also the crack opening displacements are displayed in graphical forms.

Lee, Doo-Sung; Sohn, Se-Won

2005-09-01

306

Endothelial Cell Membrane Sensitivity to Shear Stress is Lipid Domain Dependent  

PubMed Central

Blood flow-associated shear stress causes physiological and pathophysiological biochemical processes in endothelial cells that may be initiated by alterations in plasma membrane lipid domains characterized as liquid-ordered (lo), such as rafts or caveolae, or liquid-disordered (ld). To test for domain–dependent shear sensitivity, we used time-correlated single photon counting instrumentation to assess the photophysics and dynamics of the domain-selective lipid analogues DiI-C12 and DiI-C18 in endothelial cells subjected to physiological fluid shear stress. Under static conditions, DiI-C12 fluorescence lifetime was less than DiI-C18 lifetime and the diffusion coefficient of DiI-C12 was greater than the DiI-C18 diffusion coefficient, confirming that DiI-C12 probes ld, a more fluid membrane environment, and DiI-C18 probes the lo phase. Domains probed by DiI-C12 exhibited an early (10 s) and transient decrease of fluorescence lifetime after the onset of shear while domains probed by DiI-C18 exhibited a delayed decrease of fluorescence lifetime that was sustained for the 2 min the cells were subjected to flow. The diffusion coefficient of DiI-C18 increased after shear imposition, while that of DiI-C12 remained constant. Determination of the number of molecules (N) in the control volume suggested that DiI-C12-labeled domains increased in N immediately after step-shear, while N for DiI-C18-stained membrane transiently decreased. These results demonstrate that membrane microdomains are differentially sensitive to fluid shear stress.

Tabouillot, Tristan; Muddana, Hari S.; Butler, Peter J.

2012-01-01

307

On the relationship between the work of adhesion and the critical shear stress for the onset of flow instabilities  

Microsoft Academic Search

The relationship between the critical shear stress for the onset of flow instabilities and the work of adhesion at the interface has been evaluated experimentally for a series of polyolefins on several steels, brasses, and coated steels. The critical shear stress was considerably affected by the chemical nature of the die. Low-surface-energy materials were found to produce smooth extrudates presumably

H. J. Larrazabal; A. N. Hrymak; J. Vlachopoulos

2006-01-01

308

Calculation of Turbulence Intensities and Shear Stresses on Concave Surfaces by Extending the Low Reynolds Turbulence Model for Curved walls  

Microsoft Academic Search

In this paper we examine the effect of concave curvatures on turbulent flows using numerical solutions of boundary layer equations on concave surfaces. Turbulence intensities and turbulent shear stress were calculated in the mentioned case. It is obvious that the turbulent intensities and turbulent shear stress are increased on concave walls compared with flat plates under the same conditions. It

A. B. Khoshnevis

309

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

Microsoft Academic Search

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

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

2003-01-01

310

Cleaning in place: effect of local wall shear stress variation on bacterial removal from stainless steel equipment  

Microsoft Academic Search

Local wall shears stress analysis as well as cleanability experiments on different pieces of equipment in various circuit arrangements were performed. Pieces of equipment used in this work, stainless steel made, were representative of production lines: straight pipes of different diameters, sudden or gradual contraction or expansion pipes.Local wall shear stress values, obtained by an electrochemical method, were shown to

Caroline Lelièvre; Patrick Legentilhomme; Cécile Gaucher; Jack Legrand; Christine Faille; Thierry Bénézech

2002-01-01

311

High-order oscillatory contributions to shear stress under standing regular wave groups: Theory and experimental evidence  

NASA Astrophysics Data System (ADS)

In this paper, the oscillatory contributions to the steady shear stress of regular wave groups propagating over plane beds in the laminar regime are investigated theoretically and experimentally. Assuming weak nonlinearity, it was found that weak-unsteady motions induced by regular wave groups and second-order harmonics induced by nonlinear bottom boundary layer (BBL) dynamics contribute to the same order. Wave reflection was found to be an additional mechanism to generate high-order contributions to the steady shear stress. High-order oscillatory contributions to the steady shear stress generate small-amplitude perturbations to the steady streaming through the BBL. As a result, steady secondary circulation cells can be distinguished in the wave group-induced BBL. The magnitude and length scale of the measured small-amplitude perturbations are consistent with the theoretical predictions. Moreover, it is shown that the oscillatory contributions are selected according to their characteristic timescale with distance to the bed. The results could have important implications for understanding BBL dynamics and transport and the transition to the perturbed laminar regime in multiple-scale oscillatory flows.

SáNchez-Badorrey, Elena; Mans, Christian; Bramato, Simona; Losada, Miguel A.

2009-03-01

312

Collaborative effects of electric field and fluid shear stress on fibroblast migration.  

PubMed

Cells are inherently exposed to a number of different biophysical stimuli such as electric fields, shear stress, and tensile or compressive stress from the extracellular environment in vivo. Each of these biophysical cues can work simultaneously or independently to regulate cellular functions and tissue integrity in both physiological and pathological conditions. Thus, it is vital to understand the interaction of multiple stimuli on cells by decoupling and coupling the stimuli in simple combinations and by investigating cellular behaviors in response to these cues. Here, we report a novel microfluidic platform to apply the combinatorial stimulation of an electric field and fluid shear stress by controlling two directional cues independently. An integrated microfluidic platform was developed using soft lithography to monitor the cellular migration in real-time in response to an electric field and fluid shear stress in single, simultaneous, and sequential modes. When each of these stimulations is applied separately, normal human dermal fibroblasts migrate toward the anode and in the direction of fluid flow in a dose-dependent manner. Simultaneous stimulation with an electric field and shear stress, which mimics a wound in vivo, enhances the directional migration of fibroblasts by increasing both directedness and trajectory speed, suggesting the plausible scenario of cooperation between two physical cues to promote wound healing. When an electric field and shear stress are applied sequentially, migration behavior is affected by the applied stimulation as well as pre-existing stimulating conditions. This microfluidic platform can be utilized to understand other microenvironments such as embryogenesis, angiogenesis and tumor metastasis. PMID:23450300

Song, Sukhyun; Han, Hana; Ko, Ung Hyun; Kim, Jaemin; Shin, Jennifer H

2013-04-21

313

Arteries Respond to Independent Control of Circumferential and Shear Stress in Organ Culture  

Microsoft Academic Search

Arteries respond to changes in global mechanical parameters (pressure, flow rate, and longitudinal stretching) by remodeling to restore local parameters (circumferential stress, shear stress, and axial strain) to baseline levels. Because a change in a single global\\u000a parameter results in changes of multiple local parameters, the effects of individual local parameters on remodeling remain\\u000a unknown. This study uses a novel

Brian H. Wayman; W. Robert Taylor; Alexander Rachev; Raymond P. Vito

2008-01-01

314

Shear Stress and Cyclic Strain Modulation of Gene Expression in Vascular Endothelial Cells  

Microsoft Academic Search

Vascular endothelial cells are exposed to a complex humoral and hemodynamic environment. Investigations over the last two decades have demonstrated that hemodynamic forces cause alterations in endothelial cell function. More specifically, blood flow-induced wall shear stress and cyclic strain modulate gene expression of various bioactive molecules synthesized and secreted by endothelial cells. Although there currently is not a known unifying

L. V. McIntire

1995-01-01

315

Electrical Impedance Study of Cultured Endothelial Cells Under Fluid Shear Stress  

Microsoft Academic Search

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

Chunzhi Dong; Natacha Depaola; Charles R. Keese; Ivar Giaever

2004-01-01

316

On the problem of the critical resolved shear stress saturation at low temperatures  

Microsoft Academic Search

At low temperatures the critical resolved shear stress in alkali halides and metals is temperature independent. This paper offers an explanation for this behavior which utilizes the inertial properties of dislocations. This model appears to be consistent with the deformation mechanisms for these materials. The crux of this explanation concerns the temperature dependence of the viscosity that moving dislocations experience.

A. A. Krokhin; L. N. Gumen

1995-01-01

317

Development of a general method for designing microvascular networks using distribution of wall shear stress.  

PubMed

In the present study, theoretical formulations for calculation of optimal bifurcation angle and relationship between the diameters of mother and daughter vessels using the power law model for non-Newtonian fluids are developed. The method is based on the distribution of wall shear stress in the mother and daughter vessels. Also, the effect of distribution of wall shear stress on the minimization of energy loss and flow resistance is considered. It is shown that constant wall shear stress in the mother and daughter vessels provides the minimum flow resistance and energy loss of biological flows. Moreover, the effects of different wall shear stresses in the mother and daughter branches, different lengths of daughter branches in the asymmetric bifurcations and non-Newtonian effect of biological fluid flows on the bifurcation angle and the relationship between the diameters of mother and daughter branches are considered. Using numerical simulations for non-Newtonian models such as power law and Carreau models, the effects of optimal bifurcation angle on the pressure drop and flow resistance of blood flow in the symmetric bifurcation are investigated. Numerical simulations show that optimal bifurcation angle decreases the pressure drop and flow resistance especially for bifurcations at large Reynolds number. PMID:23891174

Sayed Razavi, Mohammad; Shirani, Ebrahim

2013-07-25

318

POLYACRYLAMIDE EFFECTS ON CRITICAL SHEAR STRESS AND RILL ERODIBILITY FOR A RANGE OF SOILS  

Technology Transfer Automated Retrieval System (TEKTRAN)

The effect of PAM application rate on critical shear stress and erosion was determined for 7 different soils, with a wide range of textural and chemical properties. At least four PAM application rates were tested on each of the soils, ranging from 0.1 to 80 kg ha-1. Flow rates ranging from 4 to 56 L...

319

Characterization of a Silicon-Micromachined Thermal Shear-Stress Sensor.  

National Technical Information Service (NTIS)

A detailed characterization is presented of a silicon-micromachined thermal shear-stress sensor employing a thin-film platinum-sensing element on top of a silicon-nitride membrane that is stretched over a vacuum cavity. The sensor was operated in a consta...

M. Sheplak V. Chandrasekaran A. Cain T. Nishida L. N. Cattafesta

2002-01-01

320

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

NASA Astrophysics Data System (ADS)

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.

Al-Halhouli, A. T.

2010-02-01

321

Enhanced Mass Transfer and Wall Shear Stress in Multiphase Slug Flow  

Microsoft Academic Search

This paper presents a study of mass transfer and wall shear stress in slug flow in a large diameter horizontal pipeline using the electrochemical limiting current technique. Since the mass transfer in slug flow is very different from that in full pipe flow, the extrapolation of the mass transfer correlation developed in single-phase flow to multiphase flow will cause a

Hongwei Wang; Ji Cai; Christoph Bosch; William Jepson; Tao Hong

2002-01-01

322

Similarity solutions of free shear flows with mean Reynolds stress turbulence models  

Microsoft Academic Search

A numerical method for modeling free shear flows is presented, and involves use of the governing equations for the mean Reynolds stress (MRS) in a similarity form. The calculations are applied to a steady, incompressible, two dimensional jet as an example, with a constraint placed on the streamwise momentum flux. Account is taken of the streamwise and cross stream velocities.

P. E. Wood; L. G. Leal

1983-01-01

323

A Molecular Viscoelasticity Interpretation of the Wall Shear Stress Threshold in the Toms Effect.  

National Technical Information Service (NTIS)

The turbulent-flow friction reduction produced by very low concentrations of linear macromolecules in good solvents was shown by Virk and by Elata and Tirosh to occur only when the pipe wall shear stress exceeds a particular threshold value for each polym...

A. G. Fabula J. L. Lumley W. D. Taylor

1965-01-01

324

A shear stress regulated assembly route to silica nanotubes and their closely packed hollow mesostructures.  

PubMed

Ready to load: A shear stress regulated assembly route has been used to fabricate silica nanotubes and hollow mesostructures thereof. The packed silica nanotubes were employed as support for loading gold nanoparticles for efficiently catalyzing the epoxidation of styrene with high conversion and selectivity towards styrene oxide. PMID:24038757

Wang, Chun; Wei, Jing; Yue, Qin; Luo, Wei; Li, Yuhui; Wang, Minghong; Deng, Yonghui; Zhao, Dongyuan

2013-09-05

325

Evaluation of the effect of stent strut profile on shear stress distribution using statistical moments  

Microsoft Academic Search

BACKGROUND: In-stent restenosis rates have been closely linked to the wall shear stress distribution within a stented arterial segment, which in turn is a function of stent design. Unfortunately, evaluation of hemodynamic performance can only be evaluated with long term clinical trials. In this work we introduce a set of metrics, based on statistical moments, that can be used to

Juan Mejia; Bilal Ruzzeh; Rosaire Mongrain; Richard Leask; Olivier F Bertrand

2009-01-01

326

Upregulation of TRAF-3 by shear stress blocks CD40-mediated endothelial activation  

PubMed Central

Atherosclerosis is an inflammatory disease of large arteries that is initiated through the activation of endothelium by proinflammatory mediators. CD40 receptor stimulation has been implicated in the pathogenesis of atherosclerosis. One of the most important atheroprotective stimuli is the viscous drag (shear stress) generated by the streaming blood acting on the endothelial monolayer. Here, we demonstrate that shear stress prevents CD40 ligand–induced endothelial cell activation, and we identify upregulation of TNF receptor–associated factor-3 (TRAF-3) as a potent CD40-inhibitory mechanism. Shear stress specifically upregulates TRAF-3 in cultured endothelial cells. Moreover, in the endothelial cells overlying human atherosclerotic plaques, TRAF-3 expression is upregulated in areas with high shear stress. Overexpression of TRAF-3 inhibits endothelial expression of proinflammatory cytokines and tissue factor and blocks DNA-binding activity of the transcription factor AP-1; it thereby prevents CD40-induced endothelial activation. Thus, upregulation of TRAF-3 represents a novel mechanism for preserving the functional integrity of the endothelial monolayer.

Urbich, Carmen; Mallat, Ziad; Tedgui, Alain; Clauss, Matthias; Zeiher, Andreas M.; Dimmeler, Stefanie

2001-01-01

327

Dynamic Adhesion of Umbilical Cord Blood Endothelial Progenitor Cells under Laminar Shear Stress  

PubMed Central

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.

Angelos, Mathew G.; Brown, Melissa A.; Satterwhite, Lisa L.; Levering, Vrad W.; Shaked, Natan T.; Truskey, George A.

2010-01-01

328

Effect of Shear Stress on Asymmetric Dimethylarginine Release From Vascular Endothelial Cells  

Microsoft Academic Search

We demonstrated recently that plasma concentrations of asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide (NO) synthase, are increased by high salt intake concomitantly with a decrease in plasma levels of NO in human hypertension. We investigated the effect of shear stress on ADMA release in 2 types of cells: transformed human umbilical vein endothelial cells (HUVECs; cell line

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

2010-01-01

329

In Vitro Shear Stress-Induced Platelet Activation: Sensitivity of Human and Bovine Blood.  

PubMed

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

Lu, Qijin; Hofferbert, Bryan V; Koo, Grace; Malinauskas, Richard A

2013-06-01

330

Feedback Control of Near-Wall Reynolds Shear Stress in Wall-Turbulence  

Microsoft Academic Search

A new idealized control scheme is proposed for drag reduction in wall-turbulence and its effects are studied by means of DNS of turbulent pipe flow. The control input is given as a function of sensed streamwise velocity fluctuation above the wall in order to suppress the near-wall Reynolds shear stress, which is directly related to the turbulent skin friction drag

Koji FUKAGATA; Nobuhide KASAGI

2004-01-01

331

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

Microsoft Academic Search

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

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

2011-01-01

332

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

Microsoft Academic Search

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 &etal;, 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

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

2011-01-01

333

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

Microsoft Academic Search

We employ discrete element three-dimensional simulations that include realistic modeling of physical system boundaries to determine the influence of gravity on velocity profiles and stresses for frictional inelastic particles that are confined in an angular Couette cell, and sheared by a rotated upper wall. In addition to Earth gravity, we consider other gravitational fields, in particular those of the Moon

Oleh Baran; Lou Kondic

2006-01-01

334

The calculation of stress intensity factors for combined tensile and shear loading  

Microsoft Academic Search

Stress intensity calculations are presented for cases of combined tensile and shear loading for a linear elastic material. Using functions of a complex variable, a theory is developed to determine the direction of maximum energy release rate. A finite element method using virtual crack extensions is also used to determine the energy release rate for crack extensions in various directions

T. K. Hellen; W. S. Blackburn

1975-01-01

335

Identification of two novel shear stress responsive elements in rat angiotensin I converting enzyme promoter.  

PubMed

Mechanical forces contribute to maintenance of cardiovascular homeostasis via the control of release and production of vasoactive substances. We demonstrated previously that shear stress decreases rat ACE activity and expression. Using a reporter gene approach and mutagenesis, we show now that the classic shear stress responsive element or SSRE (GAGACC) contained within 1,274 bp of this promoter is not functional in response to shear stress (15 dyn/cm2, 18 h) [for the wild-type ACE promoter (WLuc), static control (C) = 107 +/- 6.5%, shear stress (SS) = 65.9 +/- 9.4%, n = 8; for the promoter with the classic SSRE mutated (WSS-mut), C = 100 +/- 8.2%, SS = 60.2 +/- 5.2%, n = 10, respectively]. Analysis of progressive deletion mutants unraveled a 57-bp fragment, position -251 to -195, from the transcription start site, containing functional SSRE (for WLuc, C = 107 +/- 6.5%, SS = 65.9 +/- 9.4%, n = 8; for 378, C = 100 +/- 6.4%, SS = 60.4 +/- 4.3%, n = 11; for 251, C = 99.7 +/- 2.6%, SS = 63.2 +/- 5.5%, n = 7; for 194, C = 104.6 +/- 8.1%, SS = 92.4 +/- 6.9%, n = 9). This fragment responded to shear stress even in the context of a heterologous promoter. Finally, functional analysis of mutated candidate regulatory elements identified by gel shift, DNase I footprint, and conservation of aligned sequences revealed that only the double mutant (Barbie/GAGA-mut) but not isolated disruption of the Barbie (WBarbie-mut) or the GAGA (WGAGA-mut) prevented the shear-stress-induced response (for Barbie/GAGA-mut, C = 97.9 +/- 5%, SS = 99.4 +/- 7.2%, n = 6; for WBarbie-mut, C = 106.1 +/- 8.6%, SS = 65.9 +/- 9.4%, n = 6; for WGAGA-mut, C = 100.1 +/- 2.9%, SS = 66.7 +/- 1.6, n = 6;). Taken together, these data provide direct evidence for the new role of Barbie and GAGA boxes in mediating the shear-stress-induced downregulation of rat ACE expression and demonstrate that the classic SSRE (GAGACC) is not functional under the experimental conditions tested. PMID:14872008

Miyakawa, Ayumi Aurea; de Lourdes Junqueira, Maria; Krieger, José Eduardo

2004-04-13

336

Shear stress modulates RAGE-mediated inflammation in a model of diabetes-induced metabolic stress  

PubMed Central

Atherosclerosis occurs preferentially at sites of disturbed blood flow despite the influence of risk factors contributing to systemic inflammation. The receptor for advanced glycation endproducts (RAGE) is a prominent mediator of inflammation in diabetes that is upregulated in atherosclerotic plaques. Our goal was to elucidate a role for arterial hemodynamics in the regulation of RAGE expression and activity. Endothelial RAGE expression was elevated at sites of flow disturbance in the aortas of healthy swine. To demonstrate a direct role for physiological shear stress (SS) in modulating RAGE expression, human aortic endothelial cells (HAEC) were exposed to high SS (HSS; 15 dyn/cm2), which downregulated RAGE by fourfold, or oscillatory SS (OSS; 0 ± 5 dyn/cm2), which upregulated RAGE by threefold, compared with static culture at 4 h. In a model of diabetes-induced metabolic stress, HAEC were chronically conditioned under high glucose (25 mM) and then simultaneously stimulated with TNF-? (0.5 ng/ml) and the RAGE ligand high mobility group box 1 (HMGB1). A 50% increase in VCAM-1 expression over TNF-? was associated with increased cytoplasmic and mitochondrial reactive oxygen species and NF-?B activity. This increase was RAGE-specific and NADPH oxidase dependent. In activated HAEC, OSS amplified HMGB1-induced VCAM-1 (3-fold) and RAGE (1.6-fold) expression and proportionally enhanced monocyte adhesion to HAEC in a RAGE-dependent manner, while HSS mitigated these increases to the level of TNF-? alone. We demonstrate that SS plays a fundamental role in regulating RAGE expression and inflammatory responses in the endothelium. These findings may provide mechanistic insight into how diabetes accelerates the nonrandom distribution of atherosclerosis in arteries.

DeVerse, J. Sherrod; Bailey, Keith A.; Jackson, Kaleena N.

2012-01-01

337

Shear stress behavior in mesoscale simulations of granular materials  

NASA Astrophysics Data System (ADS)

3D mesoscale simulations of shock propagation in porous solids and powders have been performed with the Eulerian hydrocode GEODYN. The results indicate that voids can have a profound effect on the stress state in the material behind the shock front. The simulations can explain experimentally observed wave profiles that are difficult to interpret in the context of the classical elastic-plastic theory. In particular, a quasielastic precursor is observed in reshock simulations. This effect persists even at extremely low porosity values, down to 0.1% by volume. Stress relaxation is pronounced in simulations involving wave propagation, but is not observed in uniform ramp loading. In this sense, the relaxation phenomenon is non-local in nature and classic continuum models are inadequate for its description. Simulations show that the response of highly porous powders is dominated by deviatoric stress relaxation in the shock regime. We propose an enhancement which can be easily integrated into most existing porous material continuum models for modeling the shockinduced relaxation phenomena observed in the mesoscale simulation. The model calculates the microkinetic energy generated by dynamic loading and stores it as an internal state variable. The rate of production and dissipation of microkinetic energy and other model parameters are calibrated based on the mesoscale results. The augmented continuum model represents the deviatoric stress behavior observed under different regimes of dynamic loading.

Fujino, Don; Lomov, Ilya; Antoun, Tarabay; Vitali, Efrem

2012-03-01

338

Resveratrol attenuates apoptosis of pulmonary microvascular endothelial cells induced by high shear stress and proinflammatory factors.  

PubMed

Endothelial injury usually underlies the initial pathologic step of cardiovascular diseases. Primary endothelial cell (EC) apoptosis and secondary hyperproliferation both contribute to the development of atherosclerosis and luminal occlusion. In order to investigate the effects of resveratrol (RSV) on EC apoptosis, we applied high shear stress (HSS) with proinflammatory factors [tumor necrosis factor alpha (TNF-?) plus cycloheximide] to human pulmonary microvascular ECs (PMVECs) through an artificial capillary system. Intracellular reactive oxygen species (ROS) was measured by spectrofluorometry using dihydrorhodamine 123 fluorescent probe. Apoptosis and proliferation was determined by flow cytometric analysis. Protein expression was examined by Western blot. HSS plus inflammation significantly raised the ROS and the apoptosis level of PMVECs, which could be diminished by RSV pretreatment. In a 7-days incubation assay, RSV effectively inhibited the initial increase in apoptosis and thereby prevented subsequent PMVEC hyperproliferation induced by HSS plus inflammation. Mercaptosuccinate, a glutathione peroxidase (GPx-1) inhibitor or nicotinamide, a silent information regulator 2/sirtuin 1 (SIRT1) inhibitor could attenuate the antiapoptotic action of RSV on PMVECs; and RSV treatment upregulated GPx-1 and SIRT1 expression in PMVECs. In conclusion, RSV, probably by activating SIRT1 signaling pathway, inhibits the oxidative-stress-dependent phenotypical shift of ECs induced by HSS and proinflammatory factors in vitro. PMID:21892612

Xia, Liang; Ding, Fang; Zhu, Jun-Hui; Fu, Guo-Sheng

2011-09-03

339

Separating Fluid Shear Stress from Acceleration during Vibrations in Vitro: Identification of Mechanical Signals Modulating the Cellular Response  

PubMed Central

The identification of the physical mechanism(s) by which cells can sense vibrations requires the determination of the cellular mechanical environment. Here, we quantified vibration-induced fluid shear stresses in vitro and tested whether this system allows for the separation of two mechanical parameters previously proposed to drive the cellular response to vibration – fluid shear and peak accelerations. When peak accelerations of the oscillatory horizontal motions were set at 1g and 60Hz, peak fluid shear stresses acting on the cell layer reached 0.5Pa. A 3.5-fold increase in fluid viscosity increased peak fluid shear stresses 2.6-fold while doubling fluid volume in the well caused a 2-fold decrease in fluid shear. Fluid shear was positively related to peak acceleration magnitude and inversely related to vibration frequency. These data demonstrated that peak shear stress can be effectively separated from peak acceleration by controlling specific levels of vibration frequency, acceleration, and/or fluid viscosity. As an example for exploiting these relations, we tested the relevance of shear stress in promoting COX-2 expression in osteoblast like cells. Across different vibration frequencies and fluid viscosities, neither the level of generated fluid shear nor the frequency of the signal were able to consistently account for differences in the relative increase in COX-2 expression between groups, emphasizing that the eventual identification of the physical mechanism(s) requires a detailed quantification of the cellular mechanical environment.

Uzer, Gunes; Manske, Sarah L; Chan, M Ete; Chiang, Fu-Pen; Rubin, Clinton T; Frame, Mary D; Judex, Stefan

2012-01-01

340

Hydrophoretic high-throughput selection of platelets in physiological shear-stress range.  

PubMed

A gentle, but fast means for low-stress, high-throughput platelet purification is of significant clinical and biotechnological utility. Current implementations to sort platelets, however, require an external physical field, specialized buffer, or the harsh separation condition of high shear stress that tends to cause platelet stimulation. Here we report the use of hydrophoretic size separation in a wider channel and its parallelization to augment its throughput capability, maintaining physiological shear-stress range. We demonstrate a parallelized device comprising 10 stacks of the wide-channel hydrophoresis device, yielding a throughput of 2.9 million cells s(-1) and a platelet purity of 76.8%. The use of the wide channel for hydrophoresis also facilitates clogging-free separation by sorting blood clots and plaques. The wide-channel hydrophoresis offers the potential for gentle, fast, clogging-free sorting of rare blood cells with extreme throughput capabilities. PMID:21072435

Choi, Sungyoung; Ku, Taeyun; Song, Seungjeong; Choi, Chulhee; Park, Je-Kyun

2010-11-12

341

Effect of simulated microgravity on osteocytes responding to fluid shear stress  

NASA Astrophysics Data System (ADS)

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.

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

2013-03-01

342

Migration of human mesenchymal stem cells under low shear stress mediated by mitogen-activated protein kinase signaling.  

PubMed

Human mesenchymal stem cells (hMSCs) are attractive candidates for cell-based tissue repair approaches and have been used as vectors for delivering therapeutic genes to sites of injury. It is believed that hMSCs are able to detect and respond to shear stress due to blood and interstitial fluid flow through mechanotransduction pathways after transplantation. However, information regarding hMSC migration under shear stress and its mechanism is still limited. In this study, we examined the effect of shear stress on hMSC migration and the role of mitogen-activated protein kinases (MAPKs) in their migration. Shear stress between 0.2 and 10 Pa, which was produced by the flow medium, was exerted on fluorescently labeled hMSCs. Cell migration was evaluated using the scratch wound assay, and images were captured using a microscope equipped with a digital 3CCD camera. The results showed that hMSCs subjected to a shear stress of 0.2 Pa caused notably faster wound closure than statically cultured hMSCs, while migration in the 0.5- and 1-Pa shear stress group did not differ significantly from that in the control group. Shear stress >2 Pa markedly inhibited hMSC migration. hMSCs subjected to a shear stress of 0.2 Pa displayed an increase in extracellular signal-regulated kinases 1/2 (ERK1/2), c-Jun N-terminal kinases (JNK), and p38 MAPK activation for up to 60 min, while a shear stress of 2 Pa abrogated the activation. JNK and p38 MAPK inhibitors completely abolished the effect of shear stress on hMSC migration, while significant differences were observed between the ERK1/2 inhibitor-treated static control and shear stress groups. Taken together, these results demonstrate that low shear stress effectively induces hMSC migration and that JNK and p38 MAPK play more prominent roles in shear stress-induced migration than ERK1/2. PMID:22375921

Yuan, Lin; Sakamoto, Naoya; Song, Guanbin; Sato, Masaaki

2012-04-20

343

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

NASA Astrophysics Data System (ADS)

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.

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

2011-12-01

344

Method and apparatus for measuring stress  

DOEpatents

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.

Thompson, R. Bruce (Ames, IA)

1985-06-11

345

Pulsed Discharge Through Wetland Vegetation as a Control on Bed Shear Stress and Sediment Transport Affecting Everglades Restoration  

NASA Astrophysics Data System (ADS)

The ridge and slough landscape is a patterned peatland within the Florida Everglades in which elevated ridges of emergent vegetation are regularly interspersed among open-water sloughs with floating and submerged vegetation. Landscape features are aligned parallel to the historic flow direction. Degradation of patterning over the past 100 years coincides with diminished flow resulting from drainage and construction of levees and canals. A goal of restoration is to increase flow velocities and redistribution of particles and solutes in attempt to preserve remnant patterning and restore degraded portions of the ridge and slough landscape. To explore different management strategies that could induce sediment redistribution in the ridge and slough landscape, we simulated velocity profiles and bed shear stresses for different combinations of surface water stage, water surface slope, and vegetation community structure, based on field measurements and laboratory experiments. A mixing length approach, in which the minimum of stem spacing and distance from a solid boundary determined eddy scale, was used to simulate velocity profiles and bed shear stress in vegetated arrays. Simplified velocity profiles based only on vegetation frontal area above the bed and the Karman-Prandtl logarithmic law near the bed closely were used to approximate solutions of the one-dimensional Navier-Stokes equations for large-scale simulation. Estimates of bed shear stress were most sensitive to bed roughness, vegetation community structure, and energy slope. Importantly, our simulations illustrate that velocity and bed shear stress cannot be increased substantially in the Everglades simply by increasing surface-water stage. This result comes directly from the dependence of velocity and shear stress on vegetation frontal area and the fact that emergent vegetation stems protrude through the water column even during times of relatively deep water in the Everglades. Since merely increasing water depth is not likely to increase water velocity and entrainment, it is necessary instead that restoration focus on increasing energy slope as a means to entrain sediment within sloughs and redistribute it to ridges. Surface-water gravity waves caused by hurricanes or pulsed releases of water from impounded areas may be the most effective mechanism for achieving sediment redistribution in the Everglades and other wetland and riparian environments with abundant emergent vegetation.

Larsen, L. E.; Harvey, J. W.; Crimaldi, J. P.

2007-12-01

346

Adaptation of Endothelial Cells to Physiologically-Modeled, Variable Shear Stress  

PubMed Central

Endothelial cell (EC) function is mediated by variable hemodynamic shear stress patterns at the vascular wall, where complex shear stress profiles directly correlate with blood flow conditions that vary temporally based on metabolic demand. The interactions of these more complex and variable shear fields with EC have not been represented in hemodynamic flow models. We hypothesized that EC exposed to pulsatile shear stress that changes in magnitude and duration, modeled directly from real-time physiological variations in heart rate, would elicit phenotypic changes as relevant to their critical roles in thrombosis, hemostasis, and inflammation. Here we designed a physiological flow (PF) model based on short-term temporal changes in blood flow observed in vivo and compared it to static culture and steady flow (SF) at a fixed pulse frequency of 1.3 Hz. Results show significant changes in gene regulation as a function of temporally variable flow, indicating a reduced wound phenotype more representative of quiescence. EC cultured under PF exhibited significantly higher endothelial nitric oxide synthase (eNOS) activity (PF: 176.0±11.9 nmol/105 EC; SF: 115.0±12.5 nmol/105 EC, p?=?0.002) and lower TNF-a-induced HL-60 leukocyte adhesion (PF: 37±6 HL-60 cells/mm2; SF: 111±18 HL-60/mm2, p?=?0.003) than cells cultured under SF which is consistent with a more quiescent anti-inflammatory and anti-thrombotic phenotype. In vitro models have become increasingly adept at mimicking natural physiology and in doing so have clarified the importance of both chemical and physical cues that drive cell function. These data illustrate that the variability in metabolic demand and subsequent changes in perfusion resulting in constantly variable shear stress plays a key role in EC function that has not previously been described.

Uzarski, Joseph S.; Scott, Edward W.; McFetridge, Peter S.

2013-01-01

347

A simplified model to predict the tensile and shear stress–strain behaviour of fibreglass\\/aluminium laminates  

Microsoft Academic Search

Mechanical tests were carried out on a fibreglass\\/aluminium hybrid laminate, made of 0\\/90 S2-glass\\/epoxy laminae and Al 2024 T3 sheets, in order to find its tensile stress–tensile strain curve, residual tensile strain in correspondence of predetermined normal stress levels, and shear stress–shear strain curve. The basic layers were also suitably characterized, and a moderate anisotropy, reflecting the fabrication process, was

P. Iaccarino; A. Langella; G. Caprino

2007-01-01

348

Comparison of network theory predictions with stress\\/time data in shear and elongation for a low-density polyethylene melt  

Microsoft Academic Search

Summary Experimental data are presented which show the variation with time of the shear stress and primary normal stress difference during shear flow with a stepfunction shear rate; the material (“Melt I” at 150 °C) is a low-density polyethylene melt for which stress-growth and elastic recovery data in elongational flow experiments have been previously reported. A method of comparing the

A. S. Lodge; J. Meissner

1973-01-01

349

Effects of Fluid Shear Stress on eNOS mRNA Expression and NO Production in Human Endothelial Progenitor Cells  

Microsoft Academic Search

The increases in physiological levels of fluid shear stress have beneficial effects on vascular homeostasis. Endothelial progenitor cells (EPCs) play an important role in the maintenance of endothelial integrity. We hypothesized that shear stress-mediated vascular protection is related to the upregulation of endothelial nitric oxide synthase expression in EPCs. The human EPCs exposed to in vitro shear stress levels of

Jun Tao; Zhen Yang; Jie-Mei Wang; Chang Tu; Shi-Rong Pan

2006-01-01

350

Comparison of shear and microtensile failure stresses in the repair of dental composite restorations  

Microsoft Academic Search

Failure of dental composite restorations frequently occurs. To preserve tooth structure, repair of existing restorations can be done by relayering (composite-to-composite-bonding). This study compares shear and microtensile failure in composite-to-composite-bonding. Disk-shaped and rectangular-blocks of a nanohybrid and nanofilled composite were prepared for shear and microtensile measurements, respectively. Half of all specimens were aged using thermocycling. Non-aged and thermocycled specimens were

Margareta Rinastiti; Widowati Siswomihardjo; Mutlu Ozcan

2011-01-01

351

Effects of Enzymes and Oxidizing Agents on Shear Stress Relaxation of Wheat Flour Dough: Additions of Protease, Glucose Oxidase, Ascorbic Acid, and Potassium Bromate  

Microsoft Academic Search

Cereal Chem. 75(3):331-337 Measuring shear stress relaxation with an established research rheo- meter after slowly applying large strain proved useful for characterizing the effects of different chemical and enzymatic additives. Baking tests done with and without added ascorbic acid indicated that the method can be used for predicting effects of such additives on breadbaking quality. The relaxation process for dough

Katarina Wikström; Ann-Charlotte Eliasson

1998-01-01

352

Laboratory measurements of compressional and shear wave speeds through methane hydrate  

SciTech Connect

Simultaneous measurements of compressional and shear wave speeds through polycrystalline methane hydrate have been made. Methane hydrate, grown directly in a wave speed measurement chamber, was uniaxially compacted to a final porosity below 2%. At 277 K, the compacted material's compressional wave speed was 3650 {+-} 50 m/s. The shear wave speed, measured simultaneously, was 1890 {+-} 30 m/s. From these wave speed measurements, we derive Vp/Vs, Poisson's Ratio, bulk, shear and Young's moduli.

Durham, W B; Waite, WF; Pinkston, J C; Stern, L A; Kirby, S H; Helgerud, M B; Nur, A

1999-10-25

353

Laboratory measurements of compressional and shear wave speeds through methane hydrate  

USGS Publications Warehouse

Simultaneous measurements of compressional and shear wave speeds through polycrystalline methane hydrate have been made. Methane hydrate, grown directly in a wave speed measurement chamber, was uniaxially compacted to a final porosity below 2%. At 277 K, the compacted material had a compressional wave speed of 3650 ?? 50 m/s. The shear wave speed, measured simultaneously, was 1890 ?? 30 m/s. From these wave speed measurements, we derive V(p)/V(s), Poisson's ratio, bulk, shear, and Young's moduli.

Waite, W. F.; Helgerud, M. B.; Nur, A.; Pinkston, J. C.; Stern, L. A.; Kirby, S. H.; Durham, W. B.

2000-01-01

354

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

PubMed

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

Zeng, Ye; Waters, Michele; Andrews, Allison; Honarmandi, Peyman; Ebong, Eno E; Rizzo, Victor; Tarbell, John M

2013-07-12

355

Apparatus for measuring the shear strength of adhesive joints at high temperatures and methods for constructing the adhesive joints  

Microsoft Academic Search

A machine for measuring the shear strengths of metal-metal adhesive joints in the temperature range 20-350°C is described, in which a steadily increasing torsional load is applied to the joint (a butt-joint between two cylinders) and the load is measured using a torsion bar. Precautions have been taken to ensure that no peeling or bending stresses are involved and that

R T Humpidge; B J Taylor

1967-01-01

356

Bone morphogenetic protein 4: Potential regulator of shear stress-induced graft neointimal atrophy  

PubMed Central

Objective Placement in baboons of a distal femoral arteriovenous fistula increases shear stress through aortoiliac polytetrafluoroethylene (PTFE) grafts and induces regression of a preformed neointima. Atrophy of the neointima might be controlled by shear stress-induced genes, including the bone morphogenetic proteins (BMPs). We have investigated the expression and function of BMPs 2, 4, and 5 in the graft neointima and in cultured baboon smooth muscle cells (SMCs). Methods Baboons received bilateral aortoiliac PTFE grafts and 8 weeks later, a unilateral femoral arteriovenous fistula. Results Quantitative polymerase chain reaction showed that high shear stress increased BMP2, 4, and 5 messenger RNA (mRNA) in graft intima between 1 and 7 days, while noggin (a BMP inhibitor) mRNA was decreased. BMP4 most potently (60% inhibition) inhibited platelet-derived growth factor-stimulated SMC proliferation compared with BMP2 and BMP5 (31% and 26%, respectively). BMP4 also increased SMC death by 190% ±10%. Noggin reversed the antiproliferative and proapoptotic effects of BMP4. Finally, Western blotting confirmed BMP4 protein upregulation by high shear stress at 4 days. BMP4 expression demonstrated by in situ hybridization was confined to endothelial cells. Conclusions Increased BMPs (particularly BMP4) coupled with decreased noggin may promote high shear stress-mediated graft neointimal atrophy by inhibiting SMC proliferation and increasing SMC death. Clinical Relevance Pharmacologic therapy to prevent luminal stenosis or restenosis after vascular reconstruction is directed at inhibiting intimal hyperplasia and smooth muscle cell growth. An alternative approach might be to induce intimal atrophy after luminal narrowing has developed. This approach would be particularly useful for treating stenosis in stented vessels or synthetic bypass grafts because intimal hyperplasia is the only mechanism for luminal narrowing. Furthermore, it would permit the physician to treat the population of patients (about 30%) who actually develop a problem with stenosis or restenosis. We have previously provided proof of principle that an established neointima can be induced to atrophy in baboon polytetrafluoroethylene grafts, but not in normal artery, by simply switching from normal to high blood flow and shear stress. In this study, we provide evidence that members of the bone morphogenetic protein family may play a role in this neointimal atrophy.

Hsieh, Patrick C. H.; Kenagy, Richard D.; Mulvihill, Eileen R.; Jeanette, Joseph P.; Wang, Xi; Chang, Cindy M. C.; Yao, Zizhen; Ruzzo, Walter L.; Justice, Suzanne; Hudkins, Kelly L.; Alpers, Charles E.; Berceli, Scott; Clowes, Alexander W.

2006-01-01

357

Estimate Interface Shear Stress of Woven Ceramic Matrix Composites from Hysteresis Loops  

NASA Astrophysics Data System (ADS)

An approach to estimate the fiber/matrix interface shear stress of woven ceramic matrix composites during fatigue loading has been developed in this paper. Based on the analysis of the microstructure, the woven ceramic matrix composites were divided into four elements of 0o warp yarns, 90o weft yarns, matrix outside of the yarns and the open porosity. When matrix cracking and fiber/matrix interface debonding occur upon first loading to the peak stress, it is assumed that fiber slipping relative to matrix in the interface debonded region of the 0o warp yarns is the mainly reason for the occurrence of the hysteresis loops of woven ceramic matrix composiets during unloading and subsequent reloading. The unloading interface reverse slip length and reloading interface new slip length are determined by the interface slip mechanisms. The hysteresis loops of three different cases have been derived. The hysteresis loss energy for the strain energy lost per volume during corresponding cycle is formulated in terms of the fiber/matrix interface shear stress. By comparing the experimental hysteresis loss energy with the computational values, the fiber/matrix interface shear stress of woven ceramic matrix composites corresponding to different cycles can then be derived. The theoretical results have been compared with experimental data of two different woven ceramic composites.

Li, Longbiao; Song, Yingdong

2013-03-01

358

A Multichannel Dampened Flow System for Studies on Shear Stress-Mediated Mechanotransduction  

PubMed Central

Shear stresses are powerful regulators of cellular function and potent mediators of the development of vascular disease. We have designed and optimized a system allowing the application of flow to cultured cells in a multichannel format. By using a multichannel peristaltic pump, flow can be driven continuously in the system for long-term studies in multiple isolated flow loops. A key component of the system is a dual-chamber pulse dampener that removes the pulsatility of the flow without the need for having an open system or elevated reservoir. We optimized the design parameters of the pulse dampening chambers for the maximum reduction in flow pulsation while minimizing the fluid needed for each isolated flow channel. Human umbilical vein endothelial cells (HUVECs) were exposed to steady and pulsatile shear stress using the system. We found that cells under steady flow had a marked increased production of eNOS and formation of actin stress fibers in comparison to those under pulsatile flow conditions. Overall, the results confirm the utility of the device as a practical means to apply shear stress to cultured cells in the multichannel format and provide steady, long term flow to microfluidic devices.

Voyvodic, Peter L.; Min, Daniel; Baker, Aaron B.

2012-01-01

359

Manufacture of high aspect ratio micro-pillar wall shear stress sensor arrays  

NASA Astrophysics Data System (ADS)

In the field of experimental fluid mechanics the measurement of unsteady, distributed wall shear stress has proved historically challenging. Recently, sensors based on an array of flexible micro-pillars have shown promise in carrying out such measurements. Similar sensors find use in other applications such as cellular mechanics. This work presents a manufacturing technique that can manufacture micro-pillar arrays of high aspect ratio. An electric discharge machine (EDM) is used to manufacture a micro-drilling tool. This micro-drilling tool is used to form holes in a wax sheet which acts as the mold for the micro-pillar array. Silicone rubber is cast in these molds to yield a micro-pillar array. Using this technique, micro-pillar arrays with a maximum aspect ratio of about 10 have been manufactured. Manufacturing issues encountered, steps to alleviate them and the potential of the process to manufacture similar micro-pillar arrays in a time-efficient manner are also discussed.

Gnanamanickam, Ebenezer P.; Sullivan, John P.

2012-12-01

360

FBG sensor networks for the estimation of boundary shear stress around the novel piers  

NASA Astrophysics Data System (ADS)

The paper reports results obtained from a field test site in structural monitoring-a "test-to-failure," measuring strain using Fiber Bragg gratings (FBGs) sensor networks on a novel drilled concrete test pier in Huaihe river zone,Anhui province,China. To undertake the study, FBG-based sensors were chosen ,metallic recoated ,steel-tube packaged , and incorporated with steel rebars in this concrete structure. The sensors were interrogated using a compact system based on wavelength-division multiplexing (WDM) and F-P scanning approach. Throughout the test, the FBG sensors were continuously monitored, the incremental increases in the strain caused by boundary shear stress could be seen. The sensors were able to follow the resulting induced changes in load of over a range in excess of 2.5M Newton just prior to failure of the pier and representing extreme levels of strain for such a novel mechanical structure. The measurements made with the FBG-based system were found to be in agreement with the changes expected in the structure, produced by the self-balanced loading applied. The study has demonstrated the successful use of FBG sensor networks used in a test of this root type pier foundation, consequently made assessment about the health and security of the highway bridge.

Lü, Chengang; Zhang, Ruifeng; Li, Kejia; Wu, Xing; Ge, Chunfeng

2010-05-01

361

Nonaffine measures of particle displacements in sheared colloidal glasses.  

PubMed

The nonaffine motion of particles is central to the relaxation and flow of glasses. It is usually assumed in plasticity theories that nonaffine rearrangements are localized and uncorrelated. Here we present evidence that this assumption may not hold. We investigate and compare systematically different measures of nonaffinity in a sheared colloidal glass by tracking the motion of the individual particles directly with confocal microscopy. We show that besides differences in the appearance and degree of localization of nonaffine displacements, the nature of their fluctuations is very similar. At intermediate times, all spatial correlation functions display robust power-law behavior, clearly demonstrating long-range correlations and critical behavior of the driven glass, in contrast to the assumptions of plasticity theories. We show that on long-time scales, correlations become finite and plasticity theories may apply. PMID:22587096

Chikkadi, V; Schall, P

2012-03-29

362

Slope measurement of bent plates using double grating shearing interferometry  

SciTech Connect

A grating-based shearing interferometeric setup for slope measurement of bent plates has been proposed. The specimen under test is illuminated by a collimated beam from the laser. Light reflected from the specimen passes through two identical holographic gratings placed in tandem. The grating frequency has been so chosen that the diffracted orders from each grating are separated out distinctly. Two first-order beams diffracted from each of the gratings superpose in space. In the resulting interferogram, the fringes due to slope information of the object are visualized. Mathematical formulation for experimental determination of slope values has been undertaken. Validation of the experimental results with theoretical predictions in case of cantilever beam provides good correlation. The main advantage of the technique has been the realization of very compact geometry without the need for spatial filtering arrangement commonly associated with the grating-based techniques used to date.

Dhanotia, Jitendra; Prakash, Shashi; Rana, Santosh; Sasaki, Osami

2011-06-20

363

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

NASA Astrophysics Data System (ADS)

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.

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

2013-01-01

364

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

USGS Publications Warehouse

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.

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

2013-01-01

365

Thickness-shear vibration of an elastic plate carrying an array of rigid microbeams with consideration of couple stresses  

Microsoft Academic Search

We study thickness-shear vibration of an elastic plate carrying an array of rigid microbeams with their bottoms attached to the top surface of the plate. The beams undergo rigid-body translation and rotation when the plate is in thickness-shear motion. The plate is modeled by the couple-stress theory of elasticity to properly take into account both the shear forces and the

Runyu Zhang; Jiemin Xie; Yuantai Hu; Jiashi Yang; Xuedong Chen

366

Identification of complex shear modulus from measured shear strains on a circular disc subjected to a transient torque  

NASA Astrophysics Data System (ADS)

A method for identification of complex shear modulus from measured shear strains on a circular disc subjected to a transient torque at its centre has been established. It is based on the evolution of an outgoing shear wave between two radial positions at which the associated shear strains are measured. The two-dimensional shear wave solutions used are exact in the sense of three-dimensional theory. Therefore, in principle, there is no frequency beyond which they are not valid. The method requires a minimum disc size, which is related to the duration of the load. The non-parametric results become inaccurate at frequencies near zero and at certain problematic frequencies where the excitation of the disc is weak or non-existent. These frequencies may be moved outside the frequency range of interest by sufficiently decreasing the duration of the load. If there are problematic frequencies within this range, the results of parametric identification become more accurate than those of non-parametric identification. Parametric results from experimental tests with loads having different amplitudes and durations agree well with each other in accord with the assumed linearity of the tested polypropylene material.

Mousavi, S.; Hillström, L.; Lundberg, B.

2008-06-01

367

On the relations between notch stress and crack stress intensity in plane shear and mixed mode loading  

NASA Astrophysics Data System (ADS)

The relations between notch stress and crack stress intensity in the case of plane shear loading (mode II) are established based on Muskhelishvili's solution for the elliptical hole and conforming with Creager's solution for the blunt crack. Convergence investigations for the limit value formulae are included. Formulae for fictitious crack tip rounding according to Neuber's microstructural support hypothesis are given for mode II loading and extended to mixed mode loading. Short cracks are included. The findings are applied to the slit tips of cruciform welded joints.

Radaj, D.; Zhang, S.

1993-03-01

368

Shear thinning behavior of monolayer liquid lubricant films measured by fiber wobbling method  

NASA Astrophysics Data System (ADS)

It is essential to clarify mechanical properties of monolayer lubricant films coated on magnetic disks under shearing motion for designing future hard disk drives with ultra-low flying height. Many of previous researchers reported that strong shear rate dependence of viscoelasticity was one of the typical phenomena observed with molecularly thin liquid films. However, it has not been clarified whether or not perfluoropolyether (PFPE) lubricant films, which are used for the head-disk interface (HDI) lubrication, show shear thinning behavior under actual HDI conditions. In this study, we used the fiber wobbling method that can achieve both highly-sensitive shear force measurement and precise gap control and measured shear rate dependence of viscoelastic properties of monolayer PFPE films coated on the magnetic disk. Our experimental results showed that shear thinning does occur at high shear rate ranged from 102 to 106 s-1.

Hamamoto, Y.; Itoh, S.; Fukuzawa, K.; Zhang, H.

2010-11-01

369

Measurement of stresses in MEMS structures by stress release  

Microsoft Academic Search

The paper presents a recently developed method of measuring frozen elastic stresses in micro components and devices. The approach bases on stress release at the component surface by focused ion beam (FIB) milling. Stresses are deduced from the experimentally determined deformation field around the FIB milling pattern, applying reasonable stress hypotheses and appropriate modeling of the stress release field. Because

Dietmar Vogel; Neus Sabate; Astrid Gollhardt; Bernd Michel

2007-01-01

370

Trabecular Shear Stress Amplification and Variability in Human Vertebral Cancellous Bone: Relationship with Age, Gender, Spine Level and Trabecular Architecture  

PubMed Central

Trabecular shear stress magnitude and variability have been implicated in damage formation and reduced bone strength associated with bone loss for human vertebral bone. This study addresses the issue of whether these parameters change with age, gender or anatomical location, and if so whether this is independent of bone mass. Additionally, 3D-stereology-based architectural parameters were examined in order to establish the relationship between stress distribution parameters and trabecular architecture. Eighty cancellous bone specimens were cored from the anterior region of thoracic 12 and donor-matched lumbar 1 vertebrae from a randomly selected population of 40 cadavers. The specimens were scanned at 21-?m voxelsize using microcomputed tomography (?CT) and reconstructed at 50 ?m. Bone volume fraction (BV/TV), trabecular number (Tb.N), trabecular thickness (Tb.Th), trabecular separation (Tb.Sp), bone surface-to-volume ratio (BS/BV), degree of anisotropy (MIL1/MIL3), and connectivity density (-#Euler/Vol) were calculated directly from micro-CT images. Large-scale finite-element models were constructed and superoinferior compressive loading was simulated. Apparent cancellous modulus (EFEM) was calculated. The average trabecular von Mises stress generated per uniaxial apparent stress (??VM/?app)and coefficient of variation of trabecular von Mises stresses (COV) were calculated as measures of the magnitude and variability of shear stresses in the trabeculae. Mixed-models and regression were used for analysis. ??VM/?app and COV were not different between genders and vertebrae. Both ??VM/?app and COV increased with age accompanied by a decrease in BV/TV. Strong relationship of ??VM/?app with BV/TV was found whereas COV was strongly related to EFEM/(BV/TV). The results from T12 and L1 were not different and highly correlated with each other. The relationship of ??VM/?app with COV was observed to be different between males and females. This difference could not be explained by architectural parameters considered in this study. Our results support the relevance of trabecular shear stress amplification and variability in age-related vertebral bone fragility. The relationships found are expected to help understand the micro-mechanisms by which cancellous bone mass and mechanical properties are modulated through a collection of local stress parameters.

Yeni, Yener N.; Zelman, Eric A.; Divine, George W.; Kim, Do-Gyoon; Fyhrie, David P.

2008-01-01

371

Flow Shear Stress and Atherosclerosis: A Matter of Site Specificity  

PubMed Central

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.

Nigro, Patrizia; Abe, Jun-ichi

2011-01-01

372

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

Microsoft Academic Search

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

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

2011-01-01

373

A micromachined flow shear-stress sensor based on thermal transfer principles  

Microsoft Academic Search

Microhot-film shear-stress sensors have been developed by using surface micromachining techniques. The sensor consists of a suspended silicon-nitride diaphragm located on top of a vacuum-sealed cavity. A heating and heat-sensing element, made of polycrystalline silicon material, resides on top of the diaphragm. The underlying vacuum cavity greatly reduces conductive heat loss to the substrate and therefore increases the sensitivity of

Chang Liu; Jin-Biao Huang; Zhenjun Zhu; Fukang Jiang; S. Tung; Yu-Chong Tai; Chih-Ming Ho

1999-01-01

374

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

Microsoft Academic Search

Interstitial flow in and around tumor tissue affects the mechanical microenvironment to modulate tumor cell growth and metastasis. We investigated the roles of flow-induced shear stress in modulating cell cycle distribution in four tumor cell lines and the underlying mechanisms. In all four cell lines, incubation under static conditions for 24 or 48 h led to G0\\/G1 arrest; in contrast,

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

2008-01-01

375

Turbulent shear stress profiles in a bubbly channel flow assessed by particle tracking velocimetry  

Microsoft Academic Search

Particle tracking velocimetry (PTV) is applied to a bubbly two-phase turbulent flow in a horizontal channel at Re = 2 × 104 to investigate the turbulent shear stress profile which had been altered by the presence of bubbles. Streamwise and vertical velocity components of liquid phase are obtained using a shallow focus imaging method under backlight photography. The size of bubbles injected through a

Y. Murai; Y. Oishi; Y. Takeda; F. Yamamoto

2006-01-01

376

Role of the cytoskeleton in flow (shear stress)-induced dilation and remodeling in resistance arteries  

Microsoft Academic Search

Cytoskeletal proteins determine cell shape and integrity and membrane-bound structures connected to extracellular components\\u000a allow tissue integrity. These structural elements have an active role in the interaction of blood vessels with their environment.\\u000a Shear stress due to blood flow is the most important force stimulating the endothelium. The role of cytoskeletal proteins\\u000a in endothelial responses to flow has been studied

Laurent Loufrani; Daniel Henrion

2008-01-01

377

Skimmilk crossflow microfiltration performance versus permeation flux to wall shear stress ratio  

Microsoft Academic Search

Crossflow microfiltration (MF) of skimmilk with a ceramic membrane (0.1 ?m mean pore diameter) for the separation of casein micelles from whey proteins was performed at various constant flux, J (30–109 1 h?1 m?2) and efficient wall shear stress, ?weff (23–97 Pa).The ratio (J?weff) constitutes a basic parameter which characterizes competition between of convection and erosion at the membrane\\/solution interface.

O. Le Berre; G. Daufin

1996-01-01

378

Shear Stress Magnitude and Duration Modulates Matrix Composition and Tensile Mechanical Properties in Engineered Cartilaginous Tissue  

PubMed Central

Cartilage tissue-engineering strategies aim to produce a functional extracellular matrix similar to that of the native tissue. However, none of the myriad approaches taken have successfully generated a construct possessing the structure, composition, and mechanical properties of healthy articular cartilage. One possible approach to modulating the matrix composition and mechanical properties of engineered tissues is through the use of bioreactor-driven mechanical stimulation. In this study, we hypothesized that exposing scaffold-free cartilaginous tissue constructs to seven days of continuous shear stress at 0.001-Pa or 0.1-Pa would increase collagen deposition and tensile mechanical properties compared to that of static controls. Histologically, type II collagen staining was evident in all construct groups, while a surface layer of type I collagen increased in thickness with increasing shear stress magnitude. The areal fraction of type I collagen was higher in the 0.1-Pa group (25.2±2.2%) than either the 0.001-Pa (13.6±3.8%) or the static (7.9%±1.5%) groups. Type II collagen content, as assessed by ELISA, was also higher in the 0.1-Pa group (7.5±2.1%) compared to the 0.001-Pa (3.0±2.25%) or static groups (3.7±3.2%). Temporal gene expression analysis showed a flow-induced increase in type I and II collagen expression within 24 hours of exposure. Interestingly, while the 0.1-Pa group showed higher collagen content, this group retained less sulfated glycosaminoglycans in the matrix over time in bioreactor culture. Increases in both tensile Young's modulus and ultimate strength were observed with increasing shear stress, yielding constructs possessing a modulus of nearly 5-MPa and strength of 1.3-MPa. This study demonstrates that shear stress is a potent modulator of both the amount and type of synthesized extracellular matrix constituents in engineered cartilaginous tissue with corresponding effects on mechanical function.

Gemmiti, Christopher V.; Guldberg, Robert E.

2009-01-01

379

Axl receptor activation mediates laminar shear stress anti-apoptotic effects in human endothelial cells  

Microsoft Academic Search

Objective: Laminar Shear Stress (SS) induces cytosolic acidification and protects endothelial cells (ECs) from apoptosis. Our prior studies showed that acidification protects ECs from serum deprivation-induced apoptosis by a mechanism directly involving Axl-receptor activation. Aim of the present study was to determine whether the anti-apoptotic action of SS involves acidification-dependent Axl activation. Methods and results: Axl mRNA and protein levels

Daniela D'Arcangelo; Valeria Ambrosino; Maria Giannuzzo; Carlo Gaetano; Maurizio C. Capogrossi

2006-01-01

380

Shear Stress Induces Differentiation of Arterial Endothelial Cells From Murine Embryonic Stem Cells  

Microsoft Academic Search

\\u000a The development of vasculature in the embryo has been assumed to depend on the influence of fluid mechanical forces, but the\\u000a cellular and molecular mechanisms of its development are still poorly understood. The aim of the present study was to investigate\\u000a whether shear stress affects embryonic stem (ES) cell differentiation. When VEGF receptor 2 (VEGF2)-positive murine ES cells\\u000a were exposed

Kimiko Yamamoto; Tomomi Masumura; Nobutaka Shimizu; Syotaro Obi; Joji Ando

381

Caveolin-1 is transiently dephosphorylated by shear stress-activated protein tyrosine phosphatase mu  

Microsoft Academic Search

Endothelial cells are subjected to hemodynamic shear stress, which regulates multiple vascular functions partially by the caveolin-1-dependent mechanisms. Caveolin-1 is a principal protein in the plasma membrane microdomains called caveolae and interacts with various signaling molecules. Recently, caveolin-1 was elucidated to be phosphorylated on tyrosine 14. However, it is not known how phosphorylation of caveolin-1 is controlled in endothelium. In

Jaeyoung Shin; Hanjoong Jo

2006-01-01

382

Mode I stress intensity factor solutions for spot welds in lap-shear specimens  

Microsoft Academic Search

The analytical solutions of the mode I stress intensity factor for spot welds in lap-shear specimens are investigated based on the classical Kirchhoff plate theory for linear elastic materials. First, closed-form solutions for an infinite plate containing a rigid inclusion under counter bending conditions are derived. The development of the closed-form solutions is then used as a guide to develop

P.-C. Lin; D.-A. Wang; J. Pan

2007-01-01

383

Shear stress influences the pluripotency of murine embryonic stem cells in stirred suspension bioreactors.  

PubMed

Pluripotent embryonic stem cells (ESCs) have been used increasingly in research as primary material for various tissue-engineering applications. Pluripotency, or the ability to give rise to all cells of the body, is an important characteristic of ESCs. Traditional methods use leukaemia inhibitory factor (LIF) to maintain murine embryonic stem cell (mESC) pluripotency in static and bioreactor cultures. When LIF is removed from mESCs in static cultures, pluripotency genes are downregulated and the cultures will spontaneously differentiate. Recently we have shown the maintenance of pluripotency gene expression of mESCs in stirred suspension bioreactors during differentiation experiments in the absence of LIF. This is undesired in a differentiation experiment, where the goal is downregulation of pluripotency gene expression and upregulation of gene expression characteristic to the differentiation. Thus, the objective of this study was to examine how effectively different levels of shear stress [100 rpm (6 dyne/cm(2) ), 60 rpm (3 dyne/cm(2) )] maintained and influenced pluripotency in suspension bioreactors. The pluripotency markers Oct-4, Nanog, Sox-2 and Rex-1 were assessed using gene expression profiles and flow-cytometry analysis and showed that shear stress does maintain and influence the gene expression of certain pluripotency markers. Some significant differences between the two levels of shear stress were seen and the combination of shear stress and LIF was observed to synergistically increase the expression of certain pluripotency markers. Overall, this study provides a better understanding of the environmental conditions within suspension bioreactors and how these conditions affect the pluripotency of mESCs. Copyright © 2012 John Wiley & Sons, Ltd. PMID:22653738

Gareau, Tia; Lara, Giovanna G; Shepherd, Robert D; Krawetz, Roman; Rancourt, Derrick E; Rinker, Kristina D; Kallos, Michael S

2012-06-01

384

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

Microsoft Academic Search

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

D. I. Crecraft

1967-01-01

385

Fluid Shear Stress Stimulates Prostaglandin and Nitric Oxide Release in Bone Marrow-Derived Preosteoclast-like Cells1  

Microsoft Academic Search

Bone is a porous tissue that is continuously perfused by interstitial fluid. Fluid flow, driven by both vascu- lar pressure and mechanical loading, may generate significant shear stresses through the canaliculi as well as along the bone lining at the endosteal surface. Both osteoblasts and osteocytes produce signaling fac- tors such as prostaglandins and nitric in response to fluid shear

T. N. McAllister; J. A. Frangos

2000-01-01

386

Transtensional Crustal State of Stress in the Eastern California Shear Zone Derived From 3D Finite Element Analysis  

Microsoft Academic Search

Kinematic studies of deformation within the Eastern California Shear Zone conclude that the observed surface displacements are partitioned between a large dextral shear component of the plate boundary deformation and a smaller extensional component of the Basin & Range tectonics. Consequently, transtension is widely expressed in the ECSZ. The state of stress in the ECSZ can be generally characterised by

P. Connolly; A. Eckert

2007-01-01

387

Fluid-Flow Induced Wall Shear Stress and Epithelial Ovarian Cancer Peritoneal Spreading  

PubMed Central

Epithelial ovarian cancer (EOC) is usually discovered after extensive metastasis have developed in the peritoneal cavity. The ovarian surface is exposed to peritoneal fluid pressures and shear forces due to the continuous peristaltic motions of the gastro-intestinal system, creating a mechanical micro-environment for the cells. An in vitro experimental model was developed to expose EOC cells to steady fluid flow induced wall shear stresses (WSS). The EOC cells were cultured from OVCAR-3 cell line on denuded amniotic membranes in special wells. Wall shear stresses of 0.5, 1.0 and 1.5 dyne/cm2 were applied on the surface of the cells under conditions that mimic the physiological environment, followed by fluorescent stains of actin and ?-tubulin fibers. The cytoskeleton response to WSS included cell elongation, stress fibers formation and generation of microtubules. More cytoskeletal components were produced by the cells and arranged in a denser and more organized structure within the cytoplasm. This suggests that WSS may have a significant role in the mechanical regulation of EOC peritoneal spreading.

Avraham-Chakim, Liron; Elad, David; Zaretsky, Uri; Kloog, Yoel; Jaffa, Ariel; Grisaru, Dan

2013-01-01

388

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

PubMed

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

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

2006-06-01

389

Dynamic yielding, shear thinning, and stress rheology of polymer-particle suspensions and gels.  

PubMed

The nonlinear rheological version of our barrier hopping theory for particle-polymer suspensions and gels has been employed to study the effect of steady shear and constant stress on the alpha relaxation time, yielding process, viscosity, and non-Newtonian flow curves. The role of particle volume fraction, polymer-particle size asymmetry ratio, and polymer concentration have been systematically explored. The dynamic yield stress decreases in a polymer-concentration- and volume-fraction-dependent manner that can be described as apparent power laws with effective exponents that monotonically increase with observation time. Stress- or shear-induced thinning of the viscosity becomes more abrupt with increasing magnitude of the quiescent viscosity. Flow curves show an intermediate shear rate dependence of an effective power-law form, becoming more solidlike with increasing depletion attraction. The influence of polymer concentration, particle volume fraction, and polymer-particle size asymmetry ratio on all properties is controlled to a first approximation by how far the system is from the gelation boundary of ideal mode-coupling theory (MCT). This emphasizes the importance of the MCT nonergodicity transition despite its ultimate destruction by activated barrier hopping processes. Comparison of the theoretical results with limited experimental studies is encouraging. PMID:16268724

Kobelev, Vladimir; Schweizer, Kenneth S

2005-10-22

390

RGD-dependent mechanotransduction of suspension cultured Taxus cell in response to shear stress.  

PubMed

Plant cells cultured in bioreactors are strongly influenced by mechanical forces. However, the molecular mechanism of plant cell mechanoreception has maintained unclear. In animal cells, the Arg-Gly-Asp (RGD) motif can be found in proteins of the extracellular matrix. Integrins link the intracellular cytoskeleton of cells with the extracellular matrix by recognizing this RGD motif. Integrin has been demonstrated to function as an apparatus not only for adhesion but also for mechanotransduction. In plant cells, the molecules that mediate the structural continuity between wall and membrane are unknown. Here, we found that synthetic RGD peptide could dramatically reduce the level of phosphorylation of MAPK-like cascades that are activated by shear stress and reduce the alkalinization response, production of reactive oxygen species (ROS) and accumulation of phenolics by Taxus cuspidata cells during shear stress. These results implicate that a RGD recognition system may exist in Taxus cells and play an important role in signal transduction of shear stress. Although the Arabidopsis genome database shows that the plant seems to lack a homologue of animal integrin, plant cells may use other RGD-binding proteins to recognize the RGD motif. The correlative mechanism is discussed. PMID:17429942

Gao, Hong; Gong, Yan-Wen; Yuan, Ying-Jin

2007-04-13

391

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

NASA Astrophysics Data System (ADS)

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.

Gorder, Riley; Aliseda, Alberto

2009-11-01

392

Visualization of Simulated Endothelial Shear Stress and Blood Flow in Coronary Arteries  

NASA Astrophysics Data System (ADS)

Low endothelial shear stress (ESS) identifies areas of atherosclerotic disease lesion formation in the coronary arteries. However, it is impossible to directly measure ESS in vivo for an entire arterial tree. As part of the Multiscale Hemodynamics Project, computed tomography angiography (CTA) data is being used to obtain patient specific heart and coronary system geometries and then MUPHY, a multi-physics and multi-scale simulation code combining microscopic Molecular Dynamics (MD) with a hydro-kinetic Lattice Boltzmann (LB) method, is applied in order to simulate blood flow through the coronary arteries. Having effective visualizations of the simulation's multidimensional output, including ESS, is vital for the quick and thorough non-invasive evaluation of the patient. To this end, we have developed new visualization tools and techniques to make the simulation's output useful in a clinical diagnostic setting, examined the effectiveness of 2D versus 3D representations, and explored blood flow representations. The visualization methods developed are also applicable to other areas of fluid dynamics.

Borkin, Michelle; Feldman, Charles L.; Pfister, Hanspeter; Melchionna, Simone; Kaxiras, Efthimios

2010-11-01

393

Quantitative measurements of shear wave polarizations at the Anza seismic network, southern California: Implications for shear wave splitting and earthquake prediction  

Microsoft Academic Search

The authors analyze shear wave polarizations using an automated method which provides unbiased and quantitative measurements of the polarization and the duration of linear motion following the shear wave arrival (the linearity interval). Initial shear wave particle motions are strongly aligned at four stations, a feature that is not predicted by focal mechanisms. The particle motion alignment is most likely

Richard C. Aster; Peter M. Shearer; Jon Berger

1990-01-01

394

Nucleation and Propagation of Dynamic Earthquake Rupture Under Constrained Stochastic Shear Stress  

NASA Astrophysics Data System (ADS)

Nucleation, propagation and arrest of dynamic rupture are strongly influenced by the distribution of shear stress on the fault plane. Whether or not a seismic instability grows into a moderate to large earthquake, but also the temporal properties (propagation velocity, slip velocity) of sustained rupture depend on the statistical properties of the initial stress fields. Though the incipient stresses are not known for future earthquakes, their physically consistent stochastic characterization will help to include effects of rupture dynamics into earthquake scenario calculations for improved near-source seismic hazard assessment. We therefore study the characterization of heterogeneous stress distributions to explore and quantify their effects on nucleation and propagation of dynamic rupture. Our numerical model consists of a planar fault plane in an elastic medium. Friction on the fault follows a linear slip-weakening law, while the frictional coefficients, the critical slip-weakening distance and normal stress are constant across the fault plane. Shear stress is generated using a spatial random field model, constrained to a fractal wave-number spectrum with a flat part below a given corner wavenumber k_c. Tectonic loading is assumed to occur by homogeneously increasing the initial stress. The critical stress state, at which instability occurs, is found approximately by a trial and error procedure. We find that the resulting nucleation zone in general has a complex shape, but whose dimensions can be related to nucleation lengths that have been analytically derived for simple cases. The critical stress load that has to be added to reach the critical state depends on the ratio A(k_{nuc)/A_0. Here A_0 is the spectral amplitude of the initial shear stress in the flat part below k_c and A(knuc) is the amplitude at wave number knuc associated with the nucleation length. The average stress level at the critical state of nucleation, which controls the temporal evolution of dynamic rupture, also depends on this spectral amplitude ratio. To relate our dynamic modeling to directly observable quantities, we also analyze the macroscopic rupture parameters (seismic moment, moment rate and seismic energy).

Ripperger, J.; Mai, P. M.; Ampuero, J.

2005-12-01

395

Shear stress gradient over endothelial cells in a curved microchannel system  

Microsoft Academic Search

Our purpose was to test a scale model of the microcirculation by measuring the shear forces to which endothelial cells were exposed, and comparing this to computer simulations. In vitro experiments were performed to measure the 2-dimensional projected velocity profile along endothelial cell lined microchannels (D-shaped, 10–30 ?m radius, n = 15), or in microchannels without endothelial cells (n =

Mary D. S. Frame; Gary B. Chapman; Yoshia Makino; Ingrid H. Sarelius

1998-01-01

396

Turbulence significantly increases pressure and fluid shear stress in an aortic aneurysm model under resting and exercise flow conditions.  

PubMed

The numerical models of abdominal aortic aneurysm (AAA) in use do not take into account the non-Newtonian behavior of blood and the development of local turbulence. This study examines the influence of pulsatile, turbulent, non-Newtonian flow on fluid shear stresses and pressure changes under rest and exercise conditions. We numerically analyzed pulsatile turbulent flow, using simulated physiological rest and exercise waveforms, in axisymmetric-rigid aortic aneurysm models (AAMs). Discretization of governing equations was achieved using a finite element scheme. Maximum turbulence-induced shear stress was found at the distal end of an AAM. In large AAMs (dilated to undilated diameter ratio = 3.33) at peak systolic flow velocity, fluid shear stress during exercise is 70.4% higher than at rest. Our study provides a numerical, noninvasive method for obtaining detailed data on the forces generated by pulsatile turbulent flow in AAAs that are difficult to study in humans and in physical models. Our data suggest that increased flow turbulence results in increased shear stress in aneurysms. While pressure readings are fairly uniform along the length of an aneurysm, the kinetic energy generated by turbulence impacting on the wall of the distal half of the aneurysm increases fluid and wall shear stress at this site. If the increased fluid shear stress results in further dilation and hence further turbulence, wall stress may be a mechanism for aneurysmal growth and eventual rupture. PMID:17349339

Khanafer, Khalil M; Bull, Joseph L; Upchurch, Gilbert R; Berguer, Ramon

2007-01-01

397

Stress Jumps of Charged Colloidal Suspensions, Measurement of the Elastic-like and Viscous-like Stress Components  

Microsoft Academic Search

The shear properties of highly deionized 111.6 ± 2.8 nm diameter polystyrene spheres in water with volume fractions ranging from 0.246 to 0.419 were measured. All suspensions were iridescent at rest, indicating that they had a crystal-like mesostructure. The suspensions studied exhibited viscous-like and elastic-like stress components; the viscous-like component is explicit in shear rate and thus will instantaneously dissipate

Michael E. Mackay; Babak Kaffashi

1995-01-01

398

Lidar wind shear measurements in the planetary boundary layer  

NASA Astrophysics Data System (ADS)

Lidar measurements of wind velocity profiles by slant sounding in the PBL accompanied by ground-based measurements and a comparison with radio- and kytoon data have been carried out in the country during a period of 32 hours. We also carried out similar investigations studying the influence of various micro- and mesoscale phenomena on the wind velocity stratification. In the present work, parts of the preliminary results from two lidar campaigns (1988, 1990) in the region of Sofia are described. Some results of lidar measurements of wind velocity profiles in case of a stable PBL formation after the sunset are presented. The results are obtained during the BLEX'90 (Boundary Layer Experiment). This campaign aimed to perform an investigation of various phenomena and processes in the PBL over an urban area. Some observations of a wind shear appearance during a cold front invasion over the region of Sofia are also presented. These results are derived in the course of the International Boundary Layer Experiment ZOND '88 (teams from the Institute of Atmospheric Optics/Siberian Branch of the USSR Academy of Sciences and from the Institute of Electronics of the Bulgarian Academy of Sciences).

Kolev, Ivan N.; Parvanov, Orlin; Kaprielov, Boiko

1992-08-01

399

Racial differences in the responses to shear stress in human umbilical vein endothelial cells  

PubMed Central

Background: African American ethnicity is an independent risk factor for exaggerated oxidative stress, which is related to inflammation, hypertension, and cardiovascular disease. Recently, we reported that in vitro oxidative stress and inflammation levels differ between African American and Caucasian human umbilical vein endothelial cells (HUVECs), African American HUVECs having higher levels of both. However, it remains to be shown whether the cells would respond differently to external stimuli. Methods: We used a cone and plate viscometer to apply laminar shear stress (LSS) as an aerobic exercise mimetic to compare the responses by race. HUVECs were exposed to static conditions (no LSS), low LSS (5 dyne/cm2), and moderate LSS (20 dyne/cm2). Results: It was found that African American HUVECs had higher levels of oxidative stress under static conditions, and when LSS was applied protein expression levels (NADPH oxidase NOX2, NOX4 and p47phox subunits, eNOS, SOD2, and catalase) and biomarkers (NO, SOD, and total antioxidant capacity) were modulated to similar levels between race. Conclusion: African American HUVECs may be more responsive to LSS stimulus indicating that aerobic exercise prescriptions may be valuable for this population since the potential exists for large in vivo improvements in oxidative stress levels along the endothelial layer in response to increased shear flow.

Feairheller, Deborah L; Park, Joon-Young; Rizzo, Victor; Kim, Boa; Brown, Michael D

2011-01-01

400

Effect of the glycocalyx layer on transmission of interstitial flow shear stress to embedded cells.  

PubMed

In this paper, a simple theoretical model is developed to describe the transmission of force from interstitial fluid flow to the surface of a cell covered by a proteoglycan / glycoprotein layer (glycocalyx) and embedded in an extracellular matrix. Brinkman equations are used to describe flow through the extracellular matrix and glycocalyx layers and the solid mechanical stress developed in the glycocalyx by the fluid flow loading is determined. Using reasonable values for the Darcy permeability of extracellular matrix and glycocalyx layers and interstitial flow velocity, we are able to estimate the fluid and solid shear stresses imposed on the surface of embedded vascular, cartilage and tumor cells in vivo and in vitro. The principal finding is that the surface solid stress is typically one to two orders of magnitude larger than the surface fluid stress. This indicates that interstitial flow shear stress can be sensed by the cell surface glycocalyx, supporting numerous recent observations that interstitial flow can induce mechanotransduction in embedded cells. This study may contribute to understanding of interstitial flow-related mechanobiology in embryogenesis, tumorigenesis, tissue physiology and diseases and has implications in tissue engineering. PMID:22411016

Tarbell, John M; Shi, Zhong-Dong

2012-03-13

401

Effect of surface shear stress on the attachment of Pseudomonas fluorescens to stainless steel under defined flow conditions.  

PubMed

The application of the radial-flow growth chamber to the study of the initial stages of bacterial adhesion to surfaces under flowing conditions is reported. The adhesive properties of the bacterium Pseudomonas fluorescens (NCIB 9046) to stainless steel (type AISI 316) were found to be highly dependent on surface shear stress and the time and concentration of cells used in the incubation procedure. Maximum levels of adhesion occurred in zones of lowest surface shear stress, particularly less than 6-8 Nm(-2). Adhesion was still noticeable at shear stresses even up to 130 Nm(-2). Significant detachment of cells from a monolayer attached under static conditions was found to occur at surface shear stresses in excess of 10-12 Nm(-2). PMID:18546107

Duddridge, J E; Kent, C A; Laws, J F

1982-01-01

402

Effect of surface shear stress on the attachment of Pseudomonas fluorescens to stainless steel under defined flow conditions  

SciTech Connect

The ease with which microorganisms grow on submerged surfaces is the cause of certain industrial problems (i.e. fouling and corrosion of pipelines, heat exchangers, cooling towers, etc.). Application of the radical-flow growth chamber to the study of the initial stages of bacterial adhesion to surfaces under flowing conditions is reported. The adhesive properties of the bacterium Pseudomonas fluorescens (NCIB9046) to stainless steel (type AISI 316 were found to highly dependent on surface shear stress and the time and concentration of cells used in the incubation procedure. Maximum levels of adhesion occurred in zones of lowest surface shear stress, particularly less than 6-8 Nm/sup -2/, Adhesion was still noticeable to shear stresses even up to 130 Nm/sup -2/. Significant detachment of cells from a monolayer attached under static conditions was found to occur at surface shear stresses in excess of 10-12 Nm/sup -2/. (JMT)

Duddridge, J.E.; Kent, C.A.; Laws, J.F.

1982-01-01

403

Flux-pinning-induced interfacial shearing and transverse normal stress in a superconducting coated conductor long strip  

NASA Astrophysics Data System (ADS)

In this paper, a theoretical model is proposed to analyze the transverse normal stress and interfacial shearing stress induced by the electromagnetic force in the superconducting coated conductor. The plane strain approach is used and a singular integral equation is derived. By assuming that the critical current density is magnetic field independent and the superconducting film is infinitely thin, the interfacial shearing stress and normal stress in the film are evaluated for the coated conductor during the increasing and decreasing in the transport current, respectively. The calculation results are discussed and compared for the conductor with different substrate and geometry. The results indicate that the coated conductor with stiffer substrate and larger width experiences larger interfacial shearing stress and less normal stress in the film.

Jing, Ze; Yong, Huadong; Zhou, Youhe

2012-08-01

404

Additional shear resistance from fault roughness and stress levels on geometrically complex faults  

NASA Astrophysics Data System (ADS)

The majority of crustal faults host earthquakes when the ratio of average background shear stress ?b to effective normal stress ?eff is ?b/?eff?0.6. In contrast, mature plate-boundary faults like the San Andreas Fault (SAF) operate at ?b/?eff?0.2. Dynamic weakening, the dramatic reduction in frictional resistance at coseismic slip velocities that is commonly observed in laboratory experiments, provides a leading explanation for low stress levels on mature faults. Strongly velocity-weakening friction laws permit rupture propagation on flat faults above a critical stress level ?pulse/?eff?0.25. Provided that dynamic weakening is not restricted to mature faults, the higher stress levels on most faults are puzzling. In this work, we present a self-consistent explanation for the relatively high stress levels on immature faults that is compatible with low coseismic frictional resistance, from dynamic weakening, for all faults. We appeal to differences in structural complexity with the premise that geometric irregularities introduce resistance to slip in addition to frictional resistance. This general idea is quantified for the special case of self-similar fractal roughness of the fault surface. Natural faults have roughness characterized by amplitude-to-wavelength ratios ? between 10-3 and 10-2. Through a second-order boundary perturbation analysis of quasi-static frictionless sliding across a band-limited self-similar interface in an ideally elastic solid, we demonstrate that roughness induces an additional shear resistance to slip, or roughness drag, given by ?drag=8?3?2G??/?min, for G?=G/(1-?) with shear modulus Gand Poisson's ratio ?, slip ?, and minimum roughness wavelength ?min. The influence of roughness drag on fault mechanics is verified through an extensive set of dynamic rupture simulations of earthquakes on strongly rate-weakening fractal faults with elastic-plastic off-fault response. The simulations suggest that fault rupture, in the form of self-healing slip pulses, becomes probable above a background stress level ?b??pulse+?drag. For the smoothest faults (?˜10-3), ?drag is negligible compared to frictional resistance, so that ?b??pulse?0.25?eff. However, on rougher faults (?˜10-2), roughness drag can exceed frictional resistance. We expect that ?drag ultimately departs from the predicted scaling when roughness-induced stress perturbations activate pervasive off-fault inelastic deformation, such that background stress saturates at a limit (?b?0.6?eff) determined by the finite strength of the off-fault material. We speculate that this strength, and not the much smaller dynamically weakened frictional strength, determines the stress levels at which the majority of faults operate.

Fang, Zijun; Dunham, Eric M.

2013-07-01

405

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

Microsoft Academic Search

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

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

406

Fluid Shear Stress Differentially Regulates gpr3, gpr6, and gpr12 Expression in Human Umbilical Vein Endothelial Cells  

Microsoft Academic Search

Fluid shear stress is a major factor involved in the control of gene expression in vascular endothelial cells. Sphingosine 1-phosphate has emerged as a multifaceted regulator of endothelial cell function and its high affinity S1P1 receptor is one among the many shear stress regulated genes. We recently identified the orphan G protein coupled receptors gpr3, gpr6 and gpr12 as additional

Kirsten Uhlenbrock; Jochen Huber; Ali Ardati; Andreas Busch; Evi Kostenis

2003-01-01

407

Modelling the nonlinear shear stress–strain response of glass fibre-reinforced composites. Part I: Experimental results  

Microsoft Academic Search

The ASTM D3518\\/D3518M-94(2001) Standard Test Method for “In-plane shear response of polymer matrix composite materials by tensile test of a ±45° laminate” is based on the uni-axial tensile stress–strain response of a ±45° composite laminate which is symmetrically laminated about the midplane. For long glass fibre-reinforced epoxy composites, the test shows a highly nonlinear shear stress–strain curve. This work is

W. Van Paepegem; I. De Baere; J. Degrieck

2006-01-01

408

Lowering Caveolin-1 Expression in Human Vascular Endothelial Cells Inhibits Signal Transduction in Response to Shear Stress  

Microsoft Academic Search

Vascular endothelial cells have an extensive response to physiological levels of shear stress. There is evidence that the protein caveolin-1 is involved in the early phase of this response. In this study, caveolin-1 was downregulated in human endothelial cells by RNAi. When these cells were subjected to a shear stress of 15?dyn\\/cm2 for 10 minutes, activation of Akt and ERK1\\/2

M. M. J. Kamphuis; A. A. Poot; J. Feijen; I. Vermes

2009-01-01

409

A computational study of local stress intensity factor solutions for kinked cracks near spot welds in lap-shear specimens  

Microsoft Academic Search

In this paper, the local stress intensity factor solutions for kinked cracks near spot welds in lap-shear specimens are investigated by finite element analyses. Based on the experimental observations of kinked crack growth mechanisms in lap-shear specimens under cyclic loading conditions, three-dimensional and two-dimensional plane-strain finite element models are established to investigate the local stress intensity factor solutions for kinked

D.-A. Wang; J. Pan

2005-01-01

410

Non-Newtonian models for molecular viscosity and wall shear stress in a 3D reconstructed human left coronary artery  

Microsoft Academic Search

The capabilities and limitations of various molecular viscosity models, in the left coronary arterial tree, were analyzed via: molecular viscosity, local and global non-Newtonian importance factors, wall shear stress (WSS) and wall shear stress gradient (WSSG). The vessel geometry was acquired using geometrically correct 3D intravascular ultrasound (3D IVUS). Seven non-Newtonian molecular viscosity models, plus the Newtonian one, were compared.

Johannes V. Soulis; George D. Giannoglou; Yiannis S. Chatzizisis; Kypriani V. Seralidou; George E. Parcharidis; George E. Louridas

2008-01-01