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1

BED SHEAR STRESS MEASUREMENTS IN DAM BREAK AND SWASH FLOWS  

Microsoft Academic Search

A novel shear plate was used to make direct bed shear stress measurements in laboratory dam break and swash flows on smooth, fixed, impermeable beds. The pressure gradient due to the slope of the fluid free-surface across the plate was measured using pressure transducers. Surface elevation was measured at five locations using acoustic displacement sensors. Flow velocity was measured using

Matthew P. Barnes; Tom E. Baldock

2006-01-01

2

Buried wire gage for wall shear stress measurements  

NASA Technical Reports Server (NTRS)

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

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

1978-01-01

3

Wall Shear stress measurements in the atmosperhic surface layer  

E-print Network

an unprecedented range of Reynolds numbers. The shear stress measurements were made at the unique SLTEST (Sur- face was to further understand similarities that may exist between the SLTEST sur- face layer and the wind tunnel Marusic, Jason Monty, Nicholas Hutchins, and Min Chong Fig. 1. Photograph of the SLTEST measurement site

Marusic, Ivan

4

Fluctuating wall shear stress measurements in the atmospheric surface layer  

Microsoft Academic Search

A new sensor is described for measuring the fluctuating component of the wall shear stress in the atmospheric surface layer over relatively smooth uniform terrain. The sensor was tested at the SLTEST site on the western salt-flats of Utah, giving the first ever direct measurements of this quantity in an atmospheric scale flow. The device consists of a lightweight floating

Weston Daniel Clarence Heuer

2005-01-01

5

Turbulence and shear stress measurements in hypersonic flow  

NASA Technical Reports Server (NTRS)

An assessment has been made of the potential for hot wire and laser anemometer measurements of turbulent fluctuations in hypersonic flow fields. The results of laser velocimeter experiments conducted in two hypersonic wind tunnels are reported and comparisons made with previous hot wire turbulence measurements. A new concept for the measurement of the compressible shear stress terms which combines the attributes of both hot wire and laser anemometry is presented.

Owen, F. K.

1990-01-01

6

Modern developments in shear-stress measurement  

Microsoft Academic Search

This paper reviews three relatively modern categories of skin-friction measurement techniques that are broadly classified as microelectromechanical systems (MEMS)-based sensors, oil-film interferometry, and liquid crystal coatings. The theory, development, limitations, uncertainties, and misconceptions of each of these techniques are presented. Current and future uses of the techniques are also discussed. From this review, it is evident that MEMS-based techniques possess

Jonathan W. Naughton; Mark Sheplak

2002-01-01

7

Fluctuating wall shear stress measurements in the atmospheric surface layer  

NASA Astrophysics Data System (ADS)

A new sensor is described for measuring the fluctuating component of the wall shear stress in the atmospheric surface layer over relatively smooth uniform terrain. The sensor was tested at the SLTEST site on the western salt-flats of Utah, giving the first ever direct measurements of this quantity in an atmospheric scale flow. The device consists of a lightweight floating element whose position is detected using a spherical mirror that deflects a laser beam onto a duo-lateral position sensing photodiode. The sensor has a frequency response of 25 Hz, and a circular sensing area, of 50 mm diameter, making it suitable for atmospheric scale measurements. Measurements were made under near-neutral buoyant conditions at SLTEST using the new sensor and a rake of five sonic anemometers, positioned at wall-normal positions from z = 0.62 m to 2.5 m. Cross-correlations of the wall-shear stress and velocity measurements indicate a structure-inclination angle of 14°, which is consistent with analogous laboratory-scale turbulent boundary layer measurements at three orders of magnitude lower Reynolds number. Other quantities were also found to agree well with canonical laboratory scale results. This includes the RMS of the fluctuating wall-shear stress and the power spectra. The structure of the near-wall turbulence is further studied by looking at the cross-correlations of the two components of fluctuating wall-shear stress with the three components of velocity at the various wall-normal positions, and using VITA analysis.

Heuer, Weston Daniel Clarence

8

Wall shear stress measurements using a new transducer  

NASA Technical Reports Server (NTRS)

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

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

1986-01-01

9

Colors Of Liquid Crystals Used To Measure Surface Shear Stresses  

NASA Technical Reports Server (NTRS)

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

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

1996-01-01

10

SILICON MICROMACHINED SENSORS AND SENSOR ARRAYS FOR SHEAR-STRESS MEASUREMENTS IN AERODYNAMIC FLOWS  

E-print Network

1 SILICON MICROMACHINED SENSORS AND SENSOR ARRAYS FOR SHEAR- STRESS MEASUREMENTS IN AERODYNAMIC Abstract In this thesis we report on a new micromachined floating-element shear-stress sensor for turbulent boundary layer research. Applications in low shear-stress environments such as turbulent boundary layers

Peraire, Jaime

11

Measuring the in situ Erosion Shear Stress of Intertidal Sediments with the Cohesive Strength Meter (CSM)  

Microsoft Academic Search

The shear resistance of muddy sediments directly governs the susceptibility of the sediment to erosion by tidal and wave induced currents. Measurements of the natural erosion shear stress are important in modelling estuarine systems and in determining the possible impact of human disturbance. A second-generation erosion instrument the Cohesive Strength Meter (CSM) designed to measure the critical erosion shear stress

T. J. Tolhurst; K. S. Black; S. A. Shayler; S. Mather; I. Black; K. Baker; D. M. Paterson

1999-01-01

12

Reynolds shear stress measurements in a separated boundary layer flow  

NASA Technical Reports Server (NTRS)

Turbulence measurements were obtained for two cases of boundary layer flow with an adverse pressure gradient, one attached and the other separated. A three-component laser Doppler velocimeter system was used to measure three mean velocity components, all six Reynolds stress components, and all ten velocity triple product correlations. Independent measurements of skin-friction obtained with a laser oil-flow interferometer were used to examine the law of the wall in adverse pressure gradient flows where p(+) is less than 0.05. Strong similiarities were seen between the two adverse pressure gradient flows and free shear layer type flows. Eddy viscosities, dissipation rates, and pressure-strain rates were deduced from the data and compared to various turbulence modeling assumptions.

Driver, David M.

1991-01-01

13

Shear stress transducer concepts  

NASA Astrophysics Data System (ADS)

The measurement of shear stress in a solid propellant rocket motor can be accomplished by discreet transducers embedded in the propellant-insulation interface. However, shear stress transducers and application techniques have not been generally available. CSD has had experience in the past with this type of transducer, and is currently involved in a program that is evaluating new shear transducer concepts. This paper presents the different types of shear stress transducers available, and shows laboratory data on stability and sensitivity. The potential usefulness and drawbacks of each type are presented.

Francis, E. C.; Thompson, R. E.; Heerema, S. W.

1990-07-01

14

Shear wave transducer for stress measurements in boreholes  

DOEpatents

A technique and apparatus for estimating in situ stresses by measuring stress-induced velocity anisotropy around a borehole. Two sets each of radially and tangentially polarized transducers are placed inside the hole with displacement directions either parallel or perpendicular to the principal stress directions. With this configuration, relative travel times are measured by both a pulsed phase-locked loop technique and a cross correlation of digitized waveforms. The biaxial velocity data is used to back-calculate the applied stress.

Mao, Nai-Hsien (Castro Valley, CA)

1987-01-01

15

A shear and vertical stress sensor for physiological measurements using fibre Bragg gratings  

Microsoft Academic Search

In-shoe shear stress sensors are a required tool for the investigation of plantar ulcer development after the onset of diabetes. Recently, several transducers have been developed for measuring in-shoe shear stress. Common drawbacks are the relatively large size of the sensors and the difficulty in interrogating many sensors simultaneously in order to achieve distributed sensing. Fibre Bragg gratings (FBGs) are

Andreas V. Koulaxouzidis; Melanie J. Holmes; Colin V. Roberts; Vincent A. Handerek

2000-01-01

16

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. PMID:21416247

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

2011-01-01

17

Distribution of Early Atherosclerotic Lesions in the Human Abdominal Aorta Correlates with Wall Shear Stresses Measured In Vivo  

Microsoft Academic Search

Objectives: to study the relationship between wall shear stresses measured in vivo and early atherosclerotic lesions in the abdominal aorta. Materials: eight young volunteers for in vivo wall shear-stress measurements. Abdominal aortas from 10 young adults without signs or history of atherosclerotic disease were obtained by autopsy for histomorphometric measurements. Methods: wall shear stresses were measured in the abdominal aorta

E. M Pedersen; S Oyre; M Agerbæk; I. B Kristensen; S Ringgaard; P Boesiger; W. P Paaske

1999-01-01

18

Probe for measuring turbulent real-time shear-stress waves  

NASA Technical Reports Server (NTRS)

To measure spectrum, magnitude, and time-average value of turbulent shear stress in flow of gas use small, hollow sphere suspended in flow to measure drag fluctuations in two 90 deg-directions as function of time.

Cheng, D. Y.

1974-01-01

19

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

USGS Publications Warehouse

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

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

1979-01-01

20

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

21

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

NASA Astrophysics Data System (ADS)

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

Parmar, Devendra; Sprinkle, Danny; Singh, Jag

2005-04-01

22

Wall shear stress measurement in blade end-wall corner region  

NASA Technical Reports Server (NTRS)

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

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

1987-01-01

23

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

NASA Technical Reports Server (NTRS)

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

Reda, Daniel C.; Wilder, Michael C.

1998-01-01

24

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

PubMed Central

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

Yap, Choon Hwai; Saikrishnan, Neelakantan

2015-01-01

25

A new technique for the measurement of surface shear stress vectors using liquid crystal coatings  

NASA Technical Reports Server (NTRS)

Research has recently shown that liquid crystal coating (LCC) color-change response to shear depends on both shear stress magnitude and direction. Additional research was thus conducted to extend the LCC method from a flow-visualization tool to a surface shear stress vector measurement technique. A shear-sensitive LCC was applied to a planar test surface and illuminated by white light from the normal direction. A fiber optic probe was used to capture light scattered by the LCC from a point on the centerline of a turbulent, tangential-jet flow. Both the relative shear stress magnitude and the relative in-plane view angle between the sensor and the centerline shear vector were systematically varied. A spectrophotometer was used to obtain scattered-light spectra which were used to quantify the LCC color (dominant wavelength) as a function of shear stress magnitude and direction. At any fixed shear stress magnitude, the minimum dominant wavelength was measured when the shear vector was aligned with and directed away from the observer; changes in the relative in-plane view angle to either side of this vector/observer aligned position resulted in symmetric Gaussian increases in measured dominant wavelength. Based on these results, a vector measurement methodology, involving multiple oblique-view observations of the test surface, was formulated. Under present test conditions, the measurement resolution of this technique was found to be +/- 1 deg for vector orientations and +/- 5% for vector magnitudes. An approach t o extend the present methodology to full-surface applications is proposed.

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

1994-01-01

26

The Measurement of Wall Shear Stress in the Low-Viscosity Liquids  

NASA Astrophysics Data System (ADS)

The paper is focused on quantitative evaluation of the value of the wall shear stress in liquids with low viscosity by means of the method of the hot film anemometry in a laminar and turbulent flow. Two systems for calibration of probes are described in the paper. The first of these uses an innovative method of probe calibration using a known flow in a cylindrical gap between two concentric cylinders where the inner cylinder is rotated and a known velocity profile and shear rate, or shear stress profile, is calculated from the Navier-Stokes equations. This method is usable for lower values of the wall shear stress, particularly in the areas of laminar flow. The second method is based on direct calibration of the probes using a floating element. This element, with a size of 120x80 mm, is part of a rectangular channel. This method of calibration enables the probe calibration at higher shear rates and is applicable also to turbulent flow. Values obtained from both calibration methods are also compared with results of measurements of the wall shear stress in a straight smooth channel for a certain range of Reynolds numbers and compared with analytical calculations. The accuracy of the method and the influence of various parasitic phenomena on the accuracy of the measured results were discussed. The paper describes in particular the influence of geometric purity of the probe location, the impact of various transfer phenomena, requirements for the measured liquid and layout of the experiment.

Schmirler, M.; Mat?cha, J.; Net?ebská, H.; Ježek, J.; Adamec, J.

2013-04-01

27

Measurement of turbulent wall shear-stress using micro-pillars  

NASA Astrophysics Data System (ADS)

In experimental fluid mechanics, measuring spatially and temporally resolved wall shear-stress (WSS) has proved a challenging problem. The micro-pillar shear-stress sensor (MPS3) has been developed with the goal of filling this gap in measurement techniques. The MPS3 comprises an array of flexible micro-pillars flush mounted on the wall of a wall-bounded flow field. The deflection of these micro-pillars in the presence of a shear field is a direct measure of the WSS. This paper presents the MPS3 development work carried out by RWTH Aachen University and Purdue University. The sensor concept, static and dynamic characterization and data reduction issues are discussed. Also presented are demonstrative experiments where the MPS3 was used to measure the WSS in both water and air. The salient features of the measurement technique, sensor development issues, current capabilities and areas for improvement are highlighted.

Gnanamanickam, E. P.; Nottebrock, B.; Große, S.; Sullivan, J. P.; Schröder, W.

2013-12-01

28

Measurement of shear stress-mediated intracellular calcium dynamics in human dermal lymphatic endothelial cells.  

PubMed

The shear stress applied to lymphatic endothelial cells (LEC) by lymph flow changes dramatically under normal conditions as well as in response to disease conditions and immune reactions. In general, LEC are known to regulate the contraction frequency and strength of lymphatic pumping in response to shear stress. Intracellular calcium concentration ([Ca(2+)]i) is an important factor that regulates lymphatic contraction characteristics. In this study, we measured changes in the [Ca(2+)]i under different shear stress levels and determined the source of this calcium signal. Briefly, human dermal LEC were cultured in custom-made microchannels for 3 days before loading with 2 µM fura-2 AM, a ratiometric calcium dye to measure [Ca(2+)]i. Step changes in shear stress resulted in a rapid increase in [Ca(2+)]i followed by a gradual return to the basal level and sometimes below the initial baseline (45.2 ± 2.2 nM). The [Ca(2+)]i reached a peak at 126.2 ± 5.6 nM for 10 dyn/cm(2) stimulus, whereas the peak was only 71.8 ± 5.4 nM for 1 dyn/cm(2) stimulus, indicating that the calcium signal depends on the magnitude of shear stress. Removal of the extracellular calcium from the buffer or pharmocological blockade of calcium release-activated calcium (CRAC) channels significantly reduced the peak [Ca(2+)]i, demonstrating a role of extracellular calcium entry. Inhibition of endoplasmic reticulum (ER) calcium pumps showed the importance of intracellular calcium stores in the initiation of this signal. In conclusion, we demonstrated that the shear-mediated calcium signal is dependent on the magnitude of the shear and involves ER store calcium release and extracellular calcium entry. PMID:25617358

Jafarnejad, M; Cromer, W E; Kaunas, R R; Zhang, S L; Zawieja, D C; Moore, J E

2015-04-01

29

Accuracy and grid convergence of wall shear stress measured by lattice Boltzmann method  

NASA Astrophysics Data System (ADS)

Based on a two-dimensional Poiseuille and Wormersley flow, accuracy and grid convergence of velocity, shear stress and wall shear stress (WSS) measurements were investigated using the single-relaxation-time (SRT) and multiple-relaxation-time (MRT) lattice Boltzmann models under various open and wall boundary conditions. The results showed that grid convergence of shear stress and WSS are not consistent with that of velocity when flow channels are not aligned to the grids, and strongly rely on the used wall boundary conditions. And the MRT model is slightly superior to the SRT when simulating the complicated border flow. Moreover the WSS should be approximately calculated on the fluid nodes closest to walls under the curved boundary (CB) condition but not for the bounce-back (BB) boundary scheme. As applications, distributions of WSS in a wavy-walled channel and distensible carotid artery were simulated which would much more depend on local roughness of vessel intima than channel diameters.

Kang, Xiuying; Dun, Zhiya

2014-04-01

30

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

E-print Network

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

Padmanabhan, Aravind

31

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

E-print Network

Dynamic pressure and shear stress measurements on the stator wall of whirling annular seals are presented. Two flow conditions (Re=12,000 & 24,000), two seal speeds (Ta=3,300 & 6,600) and three eccentricity ratios (0, 10, & 50% of the clearance...

Winslow, Robert Bradley

1994-01-01

32

Measurements of mean and fluctuating wall shear stress beneath spanwise-invariant separation bubbles  

NASA Astrophysics Data System (ADS)

Pulsed-wire measurements of wall shear stress have been made beneath two separation bubbles. In one a cross flow was generated by means of a (25°) swept separation line. Fluctuating stresses in orthogonal ``streamwise'' and cross-flow directions are very nearly equal and independent of at least moderate cross flow velocity. These fluctuations are largely determined by large-scale motions in the outer flow, whereas the mean shear stresses are not. The pdf of the ``streamwise'' fluctuations is unchanged by the cross flow. When a cross flow is present the pdf of the cross-flow stresses is similar to the ``streamwise'' pdf. Dependence on Reynolds number is the same in both flows.

Hancock, P. E.

33

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

PubMed

A new generation of the "flexure-based microgap rheometer" (the N-FMR) has been developed which is also capable of measuring, in addition to the shear stress, the first normal stress difference of micrometer thin fluid films. This microgap rheometer with a translation system based on compound spring flexures measures the rheological properties of microliter samples of complex fluids confined in a plane couette configuration with gap distances of h = 1-400 ?m up to shear rates of ? = 3000 s(-1). Feed back loop controlled precise positioning of the shearing surfaces with response times <1 ms enables to control the parallelism within 1.5 ?rad and to maintain the gap distance within 20 nm. This precise gap control minimizes squeeze flow effects and allows therefore to measure the first normal stress difference N(1) of the thin film down to a micrometer gap distance, with a lower limit of N(1)/? = 9.375×10(-11) ?/h(2) that depends on the shear viscosity ? and the squared inverse gap. Structural development of complex fluids in the confinement can be visualized by using a beam splitter on the shearing surface and a long working distance microscope. In summary, this new instrument allows to investigate the confinement dependent rheological and morphological evolution of micrometer thin films. PMID:21456802

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

2011-03-01

34

The measurement of shear stress and total heat flux in a nonadiabatic turbulent hypersonic boundary layer  

NASA Technical Reports Server (NTRS)

Turbulent shear stress and direct turbulent total heat-flux measurements have been made across a nonadiabatic, zero pressure gradient, hypersonic boundary layer by using specially designed hot-wire probes free of strain-gauging and wire oscillation. Heat-flux measurements were in reasonably good agreement with values obtained by integrating the energy equation using measured profiles of velocity and temperature. The shear-stress values deduced from the measurements, by assuming zero correlation of velocity and pressure fluctuations, were lower than the values obtained by integrating the momentum equation. Statistical properties of the cross-correlations are similar to corresponding incompressible measurements at approximately the same momentum-thickness Reynolds number.

Mikulla, V.; Horstman, C. C.

1975-01-01

35

Measuring the in situ Erosion Shear Stress of Intertidal Sediments with the Cohesive Strength Meter (CSM)  

NASA Astrophysics Data System (ADS)

The shear resistance of muddy sediments directly governs the susceptibility of the sediment to erosion by tidal and wave induced currents. Measurements of the natural erosion shear stress are important in modelling estuarine systems and in determining the possible impact of human disturbance. A second-generation erosion instrument the Cohesive Strength Meter (CSM) designed to measure the critical erosion shear stress (? oCr) of intertidal sediments in situ is described. The CSM allows measurements of small-scale spatial and temporal variation of sediment stability to be made on a scale and rapidity previously unachievable. New features of specialized hardware are described and the instrument is empirically calibrated in terms of an equivalent horizontal bed shear stress using quartz sand. Some example results from recent field trials on the Königshafen (Sylt-Rømø Bight) are presented. The erosion characteristics of this intertidal flat varied on a cm scale due to the presence of patchy diatom biofilms. Areas with a diatom biofilm were more stable than those without, giving a biostabilization index of 6·2.

Tolhurst, T. J.; Black, K. S.; Shayler, S. A.; Mather, S.; Black, I.; Baker, K.; Paterson, D. M.

1999-08-01

36

Flexible tactile sensor for shear stress measurement using transferred sub-µm-thick Si piezoresistive cantilevers  

NASA Astrophysics Data System (ADS)

We propose a flexible tactile sensor using sub-µm-thick Si piezoresistive cantilevers for shear stress detection. The thin Si piezoresistive cantilevers were fabricated on the device layer of a silicon on insulator (SOI) wafer. By using an adhesion-based transfer method, only these thin and fragile cantilevers were transferred from the rigid handling layer of the SOI wafer to the polydimethylsiloxane layer without damage. Because the thin Si cantilevers have high durability of bending, the proposed sensor can be attached to a thin rod-type structure serving as the finger of a robotic hand. The cantilevers were arrayed in orthogonal directions to measure the X and Y directional components of applied shear stresses independently. We evaluated the bending durability of our flexible tactile sensor and confirmed that the sensor can be attached to a rod with a radius of 10 mm. The sensitivity of the flexible tactile sensor attached to a curved surface was 1.7 × 10-6 Pa-1 on average for a range of shear stresses from -1.8 × 103 to 1.8 × 103 Pa applied along its surface. It independently detected the X and Y directional components of the applied shear stresses.

Noda, Kentaro; Onoe, Hiroaki; Iwase, Eiji; Matsumoto, Kiyoshi; Shimoyama, Isao

2012-11-01

37

Micro-PTV Measurement of the Fluid Shear Stress Acting on Adherent Leukocytes In Vivo  

PubMed Central

Leukocyte adhesion is determined by the balance between molecular adhesive forces and convective dispersive forces. A key parameter influencing leukocyte adhesion is the shear stress acting on the leukocyte. This measure is indispensable for determining the molecular bond forces and estimating cell deformation. To experimentally determine this shear stress, we used microparticle tracking velocimetry analyzing more than 24,000 images of 0.5 ?m fluorescent microbeads flowing within mildly inflamed postcapillary venules of the cremaster muscle in vivo. Green fluorescent protein, expressed under the lysozyme-M promoter, made leukocytes visible. After applying stringent quality criteria, 3 of 69 recordings were fully analyzed. We show that endothelial cells, but not leukocytes, are covered by a significant surface layer. The wall shear rate is nearly zero near the adherent arc of each leukocyte and reaches a maximum at the apex. This peak shear rate is 2–6-fold higher than the wall shear rate in the absence of a leukocyte. Microbead trajectories show a systematic deviation toward and away from the microvessel axis upstream and downstream from the leukocyte, respectively. The flow field around adherent leukocytes in vivo allows more accurate estimates of bond forces in rolling and adherent leukocytes and improved modeling studies. PMID:19450495

Pickard, John E.; Ley, Klaus

2009-01-01

38

Sensor for Direct Measurement of the Boundary Shear Stress in Fluid Flow  

NASA Technical Reports Server (NTRS)

The formation of scour patterns at bridge piers is driven by the forces at the boundary of the water flow. In most experimental scour studies, indirect processes have been applied to estimate the shear and normal stress using measured velocity profiles. The estimations are based on theoretical models and associated assumptions. However, the turbulence flow fields and boundary layer in the pier-scour region are very complex. In addition, available turbulence models cannot account accurately for the bed roughness effect. Direct measurement of the boundary shear and normal stress and their fluctuations are attractive alternatives. However, this approach is a challenging one especially for high spatial resolution and high fidelity measurements. The authors designed and fabricated a prototype miniature shear stress sensor including an EDM machined floating plate and a high-resolution laser optical encoder. Tests were performed both in air as well as operation in water with controlled flow. The sensor sensitivity, stability and signal-to-noise level were measured and evaluated. The detailed test results and a discussion of future work will be presented in this paper.

Bao, Xiaoqi; Badescu, Mircea; Bar-Cohen, Yoseph; Lih, Shyh-Shiuh; Sherrit, Stewart; Chang, Zensheu; Chen, Beck; Widholm, Scott; Ostlund, Patrick

2011-01-01

39

Sensor for direct measurement of the boundary shear stress in fluid flow  

NASA Astrophysics Data System (ADS)

The formation of scour patterns at bridge piers is driven by the forces at the boundary of the water flow. In most experimental scour studies, indirect processes have been applied to estimate the shear and normal stress using measured velocity profiles. The estimations are based on theoretical models and associated assumptions. However, the turbulence flow fields and boundary layer in the pier-scour region are very complex. In addition, available turbulence models cannot account accurately for the bed roughness effect. Direct measurement of the boundary shear and normal stress and their fluctuations are attractive alternatives. However, this approach is a challenging one especially for high spatial resolution and high fidelity measurements. The authors designed and fabricated a prototype miniature shear stress sensor including an EDM machined floating plate and a high-resolution optical encoder. Tests were performed both in air as well as operation in water with controlled flow. The sensor sensitivity, stability and signal-to-noise level were measured and evaluated. The detailed test results and a discussion of future work will be presented in this paper.

Bao, Xiaoqi; Badescu, Mircea; Bar-Cohen, Yoseph; Lih, Shyh-Shiuh; Sherrit, Stewart; Chang, Zensheu; Chen, Beck; Widholm, Scott; Ostlund, Patrick

2011-04-01

40

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

41

Yield shear stress and disaggregating shear stress of human blood  

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

42

Measurements of gap pressure and wall shear stress of a blood pump model.  

PubMed

The centrifugal blood pump with a magnetically suspended impeller has shown its superiority as compared to other artificial hearts. However, there is still insufficient understanding of fluid mechanics related issues in the clearance gap. The design nature of the pump requires sufficient washout in the clearance between the impeller and stationary surfaces. As the gap is only 0.2 mm in width, it is very difficult to conduct measurements with present instrumentation. An enlarged model with 5:1 ratio of the pump has been designed and constructed according to specifications. Dimensionless gap pressure measurements of the model are very close to the prototype. The measurements of wall shear stress of the fluid flow in the clearance gap between the impeller face and inlet casing of a blood pump model were accomplished through hot-wire anemometry and rotating disk apparatus. Regions of relatively high and low shear stresses are identified. These correspond to spots where the likelihood of hemolysis and thrombus formation is high. With the use of dimensional analysis, it is found that the highest wall shear stress is equivalent to 146 Pa which is much lower than the threshold value of 400 Pa for hemolysis reported in the literature. PMID:10964038

Chua, L P; Akamatsu, T

2000-04-01

43

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

44

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

NASA Technical Reports Server (NTRS)

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

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

1995-01-01

45

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

NASA Technical Reports Server (NTRS)

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.; Gilliles, J. A.

2006-01-01

46

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

47

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

NASA Technical Reports Server (NTRS)

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

Reda, Daniel C. (inventor.)

1995-01-01

48

Shear Stress Evaluation of Plastic Packages  

Microsoft Academic Search

A study has been performed to determine the impact of package assembly on shear stress phenomena in plastic encapsulated integrated circuits (IC's). Test structures were used which allowed quantitative measurements of compressive stresses along with qualitative observation of shear Stress effects. Results from experiments with various mold compounds, lead frame materials, and mount compounds Will be presented. The experiments led

D. Edwards; K. GAIL HEINEN; STEVEN K. GROOTHUIS; JESUS E. MARTINEZ

1987-01-01

49

Direct measurements of wall shear stress by buried wire gages in a shock-wave boundary-layer interaction region  

NASA Technical Reports Server (NTRS)

Detailed measurements of wall shear stress (skin friction) were made with specially developed buried wire gages in the interaction regions of a Mach 2.9 turbulent boundary layer with externally generated shocks. Separation and reattachment points inferred by these measurements support the findings of earlier experiments which used a surface oil flow technique and pitot profile measurements. The measurements further indicate that the boundary layer tends to attain significantly higher skin-friction values downstream of the interaction region as compared to upstream. Comparisons between measured wall shear stress and published results of some theoretical calculation schemes show that the general, but not detailed, behavior is predicted well by such schemes.

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

1977-01-01

50

Evaluation of critical shear stresses for consolidated cohesive sediment depositions by using PIV compared with field measurements  

NASA Astrophysics Data System (ADS)

Reservoir sedimentation is a common problem today. Due to the reduced flow velocities, turbulences and bed shear stresses the transported sediment load start to settle. These depositions reduce the worldwide average storage capacity in the range of about 1% per year. However, depending on the climate conditions and the geology in the catchment area this value may vary strongly. Therefore sediment management tasks, especially the removal of already accumulated sediments, have to be developed for each reservoir separately. The critical bed shear stress is a key parameter used to evaluate the different management tasks and depend strongly on the grain size distribution of the inflowing sediments. However, depositions which contain fine particles like clay and silt increase the critical bed shear stress due to occurring cohesive forces and the use of the Shield curve for evaluating the critical shear stress is no longer valid. Additional data is required for estimating the valid critical shear stress at the reservoir bed. In this study the critical shear stress was evaluated for cohesive sediment samples, taken from two different reservoirs, in a flume in the laboratory. The sediment samples were placed in an installed double bottom in the research flume and the discharge was increased stepwise until mass erosion took place (determined by visual inspection). A 2D PIV device was used to measure the flow conditions (velocities and turbulences) over the sediment sample. The obtained values were used to calculate the bed shear stress for the specific discharge rate by the gravity method and the Reynolds stress method. The results of both methods showed good agreement in the comparison of the values, what indicates that nearly uniform flow conditions occurred in the flume. The results from this study showed that the behaviour of natural cohesive sediments depend strongly on the natural conditions as a result of physical, chemical and biological processes. In this case especially the effect of the layer structure in the sediment samples was controlling the erosion mechanism. The results of the experiments showed also that the obtained average shear stress was above most of the values found in previous conducted studies, which may be explained by consolidation effects in the reservoirs. Additional conducted vane strength measurements have been carried out in situ. The in the field obtained vane strength values were set in relation to the critical shear stresses derived by the experimental tests from the laboratory and to data from a previous conducted study to develop a new relation function. This function may be used in future studies for a rough estimation of the critical shear stress, based on in situ measured vane strength values.

Harb, Gabriele; Haun, Stefan

2013-04-01

51

Stress measurements at depth in the vicinity of the San Andreas Fault: Implications for the magnitude of shear stress at depth  

Microsoft Academic Search

Using the hydraulic fracturing technique, we have made a systematic series of in situ measurements in wells drilled near the San Andreas fault. In an attempt to provide constraints for the magnitude of shear stress on the San Andreas fault at depth we have measured both the variation of stress with distance from the fault in relatively shallow (~230 m)

Mark D. Zoback; Hiroaki Tsukahara; Stephen Hickman

1980-01-01

52

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

NASA Technical Reports Server (NTRS)

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

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

1986-01-01

53

Development of a fiber Bragg grating sensor for in-shoe shear stress measurement: design and preliminary results  

NASA Astrophysics Data System (ADS)

In-shoe shear stress sensors are a required tool for the investigation of plantar ulcer development after the onset of diabetes. Recently, several transducers have been developed for measuring in-shoe shear stress using magneto- resistive technology, light intensity modulation, and copolymer piezoelectric materials. Common drawbacks in the previous methods are the relatively large size of the sensors and the difficulty in interrogating many sensors simultaneously in order to achieve distributed sensing. In this paper we demonstrate for the first time a shear stress sensor using Fiber Bragg gratings (FBGs). The small size and the multiplexing capability of FBGs enables quasi- distributed sensing of shear stress on the plantar surface by interrogating a large number of identical sensors. The sensor design is based on the theory of elastic bending of columns. The sensor consists of two FBGs fitted inside a metallic structure which is able to deform elastically under shear stress. This elastic deformation produces strain on the FBGs, which can be detected by measuring the Bragg wavelength shift of the reflected light of each FBG using a CCD spectrometer. Preliminary results on an enlarged version of the sensor have shown the applicability of FBGs for the implementation of the in-shoe sensor.

Koulaxouzidis, Andreas V.; Roberts, V. C.; Holmes, Melanie J.; Handerek, Vincent A.

2000-08-01

54

Measurement of correlation between wall-shear stress and near-wall velocity in the atmospheric surface layer  

Microsoft Academic Search

A new skin friction sensor is described for measurements in the atmospheric surface layer. The device measures instantaneous wall shear stress in two directions with a frequency response up to 25 Hz. The sensor uses a low weight 50 mm diameter floating element whose position is monitored using a laser beam and a two-axis lateral effect photodiode. Experiments were conducted

Weston Heuer; Ivan Marusic

2004-01-01

55

Measurements of wall-shear-stress distribution on an NACA0018 airfoil by liquid-crystal coating and near-wall particle image velocimetry (PIV)  

Microsoft Academic Search

Measurements of wall-shear-stress distributions along curved surfaces are carried out using non-intrusive experimental methods, such as liquid-crystal coating and near-wall particle image velocimetry (PIV). The former method relies on the color change of the liquid-crystal coating sensitive to the wall shear stress, while the latter is based on the direct evaluation of shear stresses through the near-wall PIV measurement in

N. Fujisawa; Y. Oguma; T. Nakano

2009-01-01

56

Stress measurements at depth in the vicinity of the San Andreas fault. Implications for the magnitude of shear stress at depth.  

USGS Publications Warehouse

Using the hydraulic fracturing technique, we have made a systematic series of in situ stress measurements in wells drilled near the San Andreas fault. In an attempt to provide constraints for the magnitude of shear stress on the San Andreas fault at depth we have measured both the variation of stress with distance from the falt in relatively shallow (ca.230 m) wells and the variation of stress with depth in a ca. 1-km-deep well located 4 km from the fault. The shallow wells are located along profiles roughly perpendicular to the fault in the western Mojave desert near Plamdale and in central California where the fault is creeping. In both areas the direction of maximum compression was found to be approximately 45o from the local trend of the San Andreas. The two stress profiles show very similar results: 1) shear stress (on planes parallel to the San Andreas) increases with distance from the fault, more markedely in the western Mojave, 2) the far-field shear stress at ca. 200 m depth is ca. 50 bars ,and 3) the horizontal principal stresses as well as shear stress increase with depth more rapidly in the wells farthest from the fault. -Authors

Zobach, M.D.; Tsukahara, H.; Hickman, S.

1980-01-01

57

Boundary shear stress measurements in undular flows: Application to standing wave bed forms  

Microsoft Academic Search

Waters flowing in natural streams and rivers have the ability to scour and to deposit materials, hence to change the bed topography. It is recognized that undular flows have great potential for sediment transport. In the present study, a fixed-bed model was used to investigate the spatial variations of boundary shear stress under standing waves (i.e., undular flow). The results

H. Chanson

2000-01-01

58

[Shear stress and platelet-derived microparticles].  

PubMed

One of the responses of activated platelets to certain stimuli is the shedding of microparticles. Many studies have attempted to characterize the role of microparticles under various clinical situations or experimental conditions. Pathological levels of fluid shear stress may occur in diseased small arteries and arterioles partially obstructed by atherosclerosis or vasospasm and such shear stress may induce the activation and aggregation of circulating platelets. We investigated whether high shear stress could cause both platelet aggregation and shedding of microparticles from the platelet plasma membrane. A cone-plate viscometer was used to apply shear stress and microparticle formation was measured by flow cytometry. It was found that microparticle formation increased as the duration of shear stress increased. Both microparticles and remnant platelets showed procoagulant activity on their surfaces. Investigation of the mechanisms involved in shear-dependent microparticle generation showed that binding of von Willebrand factor to platelet glycoprotein Ib, influx of extracellular calcium, and activation of platelet calpain were required to generate microparticles under high shear stress conditions. Activation of protein kinase C promoted shear-dependent microparticle formation. These findings suggest that local generation of microparticles in atherosclerotic arteries, the site at which pathological levels of shear stress could occur, contributes to arterial thrombosis by providing and expanding a catalytic surface for the coagulation cascade. PMID:9369069

Nomura, S; Komiyama, Y

1997-10-01

59

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

Microsoft Academic Search

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 arteial system. Wall shear stress was calculated from magnetic resonance velocity measurements of pulsatile flow in an anatomically accurate model of the

James E. Moore Jr; Christopher K. Zarins; David N. Ku

1994-01-01

60

Diffractive Optic Fluid Shear Stress Sensor  

NASA Technical Reports Server (NTRS)

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

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

2000-01-01

61

Diffractive Optic Fluid Shear Stress Sensor  

NASA Technical Reports Server (NTRS)

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

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

2000-01-01

62

Measurement of correlation between wall-shear stress and near-wall velocity in the atmospheric surface layer.  

NASA Astrophysics Data System (ADS)

A new skin friction sensor is described for measurements in the atmospheric surface layer. The device measures instantaneous wall shear stress in two directions with a frequency response up to 25 Hz. The sensor uses a low weight 50 mm diameter floating element whose position is monitored using a laser beam and a two-axis lateral effect photodiode. Experiments were conducted on the Utah salt-flats at the SLTEST facility with the sensor and a rake of 5 sonic anemometers in a vertical array. Under near-neutral conditions the average "inclination angle", obtained from the peak correlation between the wall-shear stress and velocity, is approximately 14^o. This agrees reasonably well with similar measurements in low-Reynolds number boundary layer laboratory experiments.

Heuer, Weston; Marusic, Ivan

2004-11-01

63

Simulation and measurement of surface shear stress over isolated and closely spaced transverse dunes in a wind tunnel  

Microsoft Academic Search

Topographic interactions generate multidirectional and unsteady airflow that limits the application of velocity profile approaches for estimating sediment transport over dunes. Results are presented from a series of wind tunnel simulations using Irwin-type surface-mounted pressure sensors to measure shear stress variability directly at the surface over both isolated and closely spaced sharp-crested model dunes. Findings complement existing theories on secondary

Ian J. Walker; William G. Nickling

2003-01-01

64

A miniaturized optical package for wall shear stress measurements in harsh environments  

NASA Astrophysics Data System (ADS)

We report the development of a time-resolved direct wall shear stress senor using an optical moiré transduction technique for harsh environments. The floating-element sensor is a lateral-position sensor that is micromachined to enable sufficient bandwidth and to minimize spatial aliasing. The optical transduction approach offers several advantages over electrical-based floating element techniques including immunity from electromagnetic interference and the ability to operate in a conductive fluid medium. Packaging for optical sensors presents significant challenges. The bulky nature and size of conventional free-space optics often limit their use to an optical test bench, making them unsuitable for harsh environments. The optical package developed in this research utilizes an array of optical fibers mapped over the moiré fringe. The fiber bundle approach results in a robust package that reduces the overall size of the optics, mitigates vibration between the sensor and optoelectronics and enables in situ measurement. The optical package for sampling the amplified moiré fringe is evaluated using bench top test setups. An optical test bench is constructed to simulate the movement of the moiré fringe on the floating element. High-resolution images of the optical fringe and optical fibers are combined in simulation to model the lateral displacement of the fringe. The performance of several fringe estimation algorithms are studied and evaluated. Based on the optical study, the optical package and post-processing algorithms are implemented on an actual device. Initial device characterization using this approach results in a device sensitivity of 12.4 nm/Pa.

Chen, Tai-An; Mills, David; Chandrasekharan, Vijay; Sheplak, Mark

2014-06-01

65

A comparison and measurement standardisation of four in situ devices for determining the erosion shear stress of intertidal sediments  

NASA Astrophysics Data System (ADS)

Predictive modelling of estuarine sediment erosion and transport requires a description of the erosional properties of the bed. The two main variables of interest are the critical erosion shear stress ( ?cr) and the erosion rate ( ?). A number of different erosion devices exist to measure the erosion shear stress of intertidal sediments in situ. These devices apply different strategies to induce and measure erosion, and the area over which erosion is integrated varies greatly. In addition, the definition of erosion threshold differs between workers. This makes comparison of data collected from different devices very difficult. Four different types of erosion device, Microcosm system, In Situ Erosion Flume (ISEF), SedErode and cohesive strength meter (CSM) were used during the July 1997 EC INTRMUD Humber estuary (UK) field campaign. These devices were deployed simultaneously on the Skeffling intertidal mudflat to allow comparison of the data generated. This involved the comparison of suspended particulate matter (SPM) time series, the nature of the applied shear stress ( ?o) and the area over which erosion was integrated. The initial goal was to develop a standard analysis procedure for comparison of stability measurements. The erosion threshold calculated from area normalised suspended particulate matter (SPM n) time series was relatively comparable between devices especially between the Microcosm and ISEF. However, device size and natural sediment spatial heterogeneity affected the results. The erosion rate varied by orders of magnitude between the different devices. This variation seemed to be due to the considerable differences in device deployment time. In conclusion, SPM data from different devices are broadly comparable, whilst erosion rates are only comparable if the shear stress steps are of the same duration.

Tolhurst, T. J.; Black, K. S.; Paterson, D. M.; Mitchener, H. J.; Termaat, G. R.; Shayler, S. A.

2000-07-01

66

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. PMID:20719252

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

2010-01-01

67

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

NASA Astrophysics Data System (ADS)

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

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

2004-11-01

68

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

69

Shear stress in magnetorheological finishing for glasses.  

PubMed

We report in situ, simultaneous measurements of both drag and normal forces in magnetorheological finishing (MRF) for what is believed to be the first time, using a spot taking machine (STM) as a test bed to take MRF spots on stationary parts. The measurements are carried out over the entire area where material is being removed, i.e., the projected area of the MRF removal function/spot on the part surface, using a dual force sensor. This approach experimentally addresses the mechanisms governing material removal in MRF for optical glasses in terms of the hydrodynamic pressure and shear stress, applied by the hydrodynamic flow of magnetorheological fluid at the gap between the part surface and the STM wheel. This work demonstrates that the volumetric removal rate shows a positive linear dependence on shear stress. Shear stress exhibits a positive linear dependence on a material figure of merit that depends upon Young's modulus, fracture toughness, and hardness. A modified Preston's equation is proposed that better estimates MRF material removal rate for optical glasses by incorporating mechanical properties, shear stress, and velocity. PMID:19412219

Miao, Chunlin; Shafrir, Shai N; Lambropoulos, John C; Mici, Joni; Jacobs, Stephen D

2009-05-01

70

Development of Hybrid Sensor Arrays for Sensor Arrays for Simultaneous Measurement of Pressure and Shear Stress Distribution  

NASA Technical Reports Server (NTRS)

This document reports on the progress in developing hybrid sensors for the simultaneous measurement of pressure and shear stress. The key feature for the success of the proposed hybrid sensor array is the ability to deposit Cu-Ni alloy with proper composition (55 - 45) on a silicon wafer to form a strain gage. This alloy strain gage replaces the normally used Si strain gages in MEMS, which are highly nonlinear and temperature dependent. The copper nickel, with proper composition (55 - 45), was successfully deposited on a silicon wafer with a few trials during this period of the project. Pictures of the Cu-Ni alloy strain gage and the x-ray spectra indicating the composition are shown. The planned tests are also reviewed.

2000-01-01

71

Simultaneous measurement of wall shear stress and arterial distension in FMD studies  

Microsoft Academic Search

In Flow-mediated dilation (FMD) studies, blood flow in the brachial artery is restricted for about 5 minutes by a cuff. When the restriction is removed, the subsequent increase in wall shear rate (WSR) stimulates the release of nitric oxide, a vasodilator, from the endothelial cells into the smooth muscle. Impaired FMD responses, which are considered independent predictors of possible cardiovascular

L. Francalanci; A. Dallai; P. Tortoli; C. Palombo; L. Ghiadoni

2010-01-01

72

Bayesian lensing shear measurement  

NASA Astrophysics Data System (ADS)

We derive an estimator of weak gravitational lensing shear from background galaxy images that avoids noise-induced biases through a rigorous Bayesian treatment of the measurement. The derived shear estimator disposes with the assignment of ellipticities to individual galaxies that is typical of previous approaches to galaxy lensing. Shear estimates from the mean of the Bayesian posterior are unbiased in the limit of large number of background galaxies, regardless of the noise level on individual galaxies. The Bayesian formalism requires a prior, describing the (noiseless) distribution of the target galaxy population over some parameter space; this prior can be constructed from low-noise images of a subsample of the target population, attainable from long integrations of a fraction of the survey field. We find two ways to combine this exact treatment of noise with rigorous treatment of the effects of the instrumental point spread function (PSF) and sampling. The Bayesian model-fitting (BMF) method assigns a likelihood of the pixel data to galaxy models (e.g. Sérsic ellipses), and requires the unlensed distribution of galaxies over the model parameters as a prior. The Bayesian Fourier domain (BFD) method compresses the pixel data to a small set of weighted moments calculated after PSF correction in Fourier space. It requires the unlensed distribution of galaxy moments as a prior, plus derivatives of this prior under applied shear. A numerical test using a simplified model of a biased galaxy measurement process demonstrates that the Bayesian formalism recovers applied shears to <1 part in 103 accuracy as well as providing accurate uncertainty estimates. BFD is the first shear measurement algorithm that is model free and requires no approximations or ad hoc assumptions in correcting for the effects of PSF, noise, or sampling on the galaxy images. These algorithms are good candidates for attaining the part-per-thousand shear inference required for hemisphere-scale weak gravitational lensing surveys. BMF has the drawback that shear biases will occur since galaxies do not fit any finite-parameter model, but has the advantage of being robust to missing data or non-stationary noise. Both BMF and BFD methods are readily extended to use data from multiple exposures and to inference of lensing magnification.

Bernstein, Gary M.; Armstrong, Robert

2014-02-01

73

Quantification of Critical Shear Stress  

NSDL National Science Digital Library

à Photo of angle of repose experiment Provenance: Lonnie Leithold, North Carolina State University at Raleigh Reuse: This item is offered under a Creative Commons Attribution-NonCommercial-ShareAlike license http://creativecommons.org/licenses/by-nc-sa/3.0/ You may reuse this item for non-commercial purposes as long as you provide attribution and offer any derivative works under a similar license. This is a lab activity designed to give students experience with the concept and quantification of critical shear stress.

Lonnie Leithold

74

Measuring the reduced shear  

SciTech Connect

Neglecting the second order corrections in weak lensing measurements can lead to a few percent uncertainties on cosmic shears, and becomes more important for cluster lensing mass reconstructions. Existing methods which claim to measure the reduced shears are not necessarily accurate to the second order when a point spread function (PSF) is present. We show that the method of Zhang (2008) exactly measures the reduced shears at the second order level in the presence of PSF. A simple theorem is provided for further confirming our calculation, and for judging the accuracy of any shear measurement method at the second order based on its properties at the first order. The method of Zhang (2008) is well defined mathematically. It does not require assumptions on the morphologies of galaxies and the PSF. To reach a sub-percent level accuracy, the CCD pixel size is required to be not larger than 1/3 of the Full Width at Half Maximum (FWHM) of the PSF, regardless of whether the PSF has a power-law or exponential profile at large distances. Using a large ensemble (?>10{sup 7}) of mock galaxies of unrestricted morphologies, we study the shear recovery accuracy under different noise conditions. We find that contaminations to the shear signals from the noise of background photons can be removed in a well defined way because they are not correlated with the source shapes. The residual shear measurement errors due to background noise are consistent with zero at the sub-percent level even when the amplitude of such noise reaches about 1/10 of the source flux within the half-light radius of the source. This limit can in principle be extended further with a larger galaxy ensemble in our simulations. On the other hand, the source Poisson noise remains to be a cause of systematic errors. For a sub-percent level accuracy, our method requires the amplitude of the source Poisson noise to be less than 1/80 ? 1/100 of the source flux within the half-light radius of the source, corresponding to collecting roughly 10{sup 4} source photons.

Zhang, Jun, E-mail: jzhang@astro.as.utexas.edu [Texas Cosmology Center, The University of Texas at Austin, Austin, TX 78712 (United States)

2011-11-01

75

Shear stress in atherosclerotic plaque determination.  

PubMed

Atherosclerosis initiates at predictable focal sites near arterial branches and curves, where blood flow is disturbed and shear stress is complex. Endothelial shear stress is the tangential stress derived from the friction of the flowing blood on the endothelial surface of the arterial wall. It is a key factor in modulating endothelial cell gene expression and vascular development and remodeling. Increasing evidences suggest that shear stress patterns have a strong relationship with atherosclerotic features. Moreover, variations in the local artery geometry during atherogenesis further modify flow shear stress characteristics, which contribute to the rupture site at the plaque upstream. In this study, we summarize the mechanistic evidences that associate shear stress patterns with determined atherosclerotic plaque features. An enhanced understanding of the relationship and pathophysiological function of shear stress patterns in atherosclerotic plaque features is essential, which may provide early prediction of clinical risk and guide individualized treatment strategies. In the current review, we analyzed the function of shear stress on the determination of atherosclerotic lesion and provided an update on the mechanotransduction of shear stress, gene expression regulation, and atherosclerotic plaque development and rupture. PMID:25165867

Li, Xiaohong; Yang, Qin; Wang, Zuo; Wei, Dangheng

2014-12-01

76

Relative Contributions of Interface Pressure, Shear Stress, and Temperature on Ischemic-induced, Skin-reactive Hyperemia in Healthy Volunteers: A Repeated Measures Laboratory Study.  

PubMed

Although the primary risk factors for pressure ulcer development - pressure, shear, skin temperature, moisture, and friction - have been identified for decades, the relative contribution of each to this risk remains unclear. To confirm the results of and expand upon earlier research into the relative contributions of interface pressures, shear stress, and skin temperature among 4 healthy volunteers, a study involving 6 additional healthy 40- to 75-year-old volunteers was conducted and results of the 2 studies were pooled. All 3 variables (interface pressures, shear stress, and skin temperature) were systematically and randomly varied. In the prone position, volunteers each underwent 18 test conditions representing different combinations of temperature (28? C, 32? C, 36? C), pressure (8.0 and 13.3 kPa), and shear (0, 6.7, and 14.0 kPa) using a computer-controlled indenter applied to the sacrum for 20 minutes exerting weights of 100 g and 200 g to induce 0.98 N and 1.96 N of shear force, respectively. Each condition was tested twice, resulting in a total of 360 trials. Magnitude of postload reactive hyperemia as an index of ischemia was measured by laser Doppler flowmetry. Fixed effects regression models were used to predict 3 different indices of reactive hyperemic magnitude. Friedman tests were performed to compare the reactive hyperemia among 3 different skin temperatures or shear stresses under the same amount of localized pressure. In all regression models, pressure and temperature were highly significant predictors of the extent of reactive hyperemia (P <0.0001 and P <0.0001, respectively); the contributions of shear stress were not statistically significant (P = 0.149). With higher temperature, reactive hyperemia increased significantly, especially at greater localized pressure and shear stress, and the difference was more profound between 32? C and 36? C than between 28? C and 32? C. These results confirm that, in laboratory settings, temperature is an important factor in tissue ischemia. Additional studies examining the relative importance of pressure, shear, and temperature and potential effects of lowering temperature on tissue ischemia in healthy volunteers and patients at risk for pressure ulcer development are warranted. Because deformation at weight-bearing areas often results in blood flow occlusion, actively lowering the temperature may reduce the severity of ischemia and lower pressure ulcer risk. In this study, shear did not appear to contribute to ischemia in the dermal tissues when assessed using laser Doppler; further work is needed to examine its effect on deeper layers, particularly with regard to nonischemic mechanisms. PMID:25654778

Lachenbruch, Charlie; Tzen, Yi-Ting; Brienza, David; Karg, Patricia E; Lachenbruch, Peter A

2015-02-01

77

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

E-print Network

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

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

2014-01-01

78

Effect of velocity gradients on measurements of turbulent shear stress. [using hot wire sensors  

NASA Technical Reports Server (NTRS)

Experiments were carried out to evaluate the effects of normal velocity gradients on hot wire measurements in a subsonic boundary layer of the same size as the flow investigated by Johnson and Rose (1975). Both hot wire and film anemometers were used to measure the turbulent properties of the boundary layer. A special X-wire probe with one wire vertical and the other at an angle of about 40 deg to the flow was used to demonstrate the gradient effects. The results indicate that major errors are encountered when mean and turbulent velocity gradients exist along the length of hot wire sensors, the problem being more pronounced at high speeds. Although the split film sensor results show a significant improvement over the X-wire sensor, further reduction in the space resolution of sensors by roughly an order of magnitude would appear to be necessary to reduce the error to acceptable values near the wall.

Sandborn, V. A.

1976-01-01

79

Development and calibration of buried wire gages for wall shear stress measurements in fluid flow  

NASA Technical Reports Server (NTRS)

Special methods were developed to arrange 'Buried Wire Gage' inserts flush to the contoured flow surfaces of instrument plugs of a boundary-layer flow apparatus. The fabrication process was aimed at producing proper bonding of the sensor wire to the substrate surface, without causing excessive surface waviness. A large number of gages were built and first calibrated for the resistance-temperature characteristics. The gages were then installed in a flow calibration apparatus and operated from a constant temperature anemometer system for a series of flow settings to derive the calibration constants of each of the gages. The flow settings included a range of subsonic freestream Mach numbers in order to help establish the gage calibration characteristics for compressible flow fields. This paper provides a description of the buried wire gage technique, an explanation of the method evolved for making proper gages, the procedure for calibrating the gages and the results of measurements performed for determining the calibration constants.

Murthy, Sreedhara V.; Steinle, Frank W.

1988-01-01

80

Evaluation of the time dependent surface shear stress in turbulent flows  

NASA Technical Reports Server (NTRS)

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

Sandborn, V. A.

1979-01-01

81

Shear rate specific blood viscosity and shear stress of carotid artery duplex ultrasonography in patients with lacunar infarction  

PubMed Central

Background This study describes a new method for determining site-specific vascular shear stress using dynamic measures of shear rate and blood viscosity (BV) in the carotid arteries, and examines characteristics of carotid arterial shear stress among patients with lacunar infarction. Methods Vascular shear stress measurements were conducted in 37 patients (17 lacunar infarction patients and 20 control subjects) using duplex ultrasonography. Vessel wall diameters and velocities were measured in each arterial segment at peak-systolic (PS) and end-diastolic (ED) phases, for calculation of PS/ED shear rates. PS/ED shear stresses [dyne/cm2] were determined with PS/ED shear rates and shear-rate dependent BV values. For comparison, both values of hematocrit-derived BV and BV measurements at 300 s-1 were used for calculation of shear stress. Results All cardiovascular disease (CVD) risk factors including BV values were similar between the two groups. In both common carotid arteries, PS and ED shear stresses were significantly lower in the patients with lacunar infarction than in controls in multivariate models that included age, sex, and other major CVD risk factors. PS and ED shear stresses using the shear rate specific BV were 4.5% lower and 7.3% higher than those using the two other BVs, respectively. Conclusion Lacunar infarction was associated with reduced carotid arterial shear stress. The use of estimated BV for calculating carotid arterial shear stress provides more accurate assessment of the hemodynamic contribution of shear stress than previous models that have arbitrarily assigned a constant value to this dynamic flow property. PMID:23597083

2013-01-01

82

Determining Shear Stress Distribution in a Laminate  

NASA Technical Reports Server (NTRS)

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

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

2010-01-01

83

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

E-print Network

Determining £ow type, shear rate and shear stress in magmas from bubble shapes and orientations A the shapes and orientations of bubbles (vesicles) in obsidian to estimate shear rates and shear stresses shearing that deforms, and surface tension that rerounds. The ratio of these stresses is the capillary

Manga, Michael

84

Estimating the Viscous Shear Stress at the Water Surface from Active Thermography  

E-print Network

16 Estimating the Viscous Shear Stress at the Water Surface from Active Thermography Christoph S to measure the viscous shear stress µ from active thermography. With a CO2 laser, patterns are written, this vertical velocity profile can be resolved. By resolving the velocity profile, the viscous shear stress can

Garbe, Christoph S.

85

The effect of roughness elements on wind erosion: The importance of surface shear stress distribution  

E-print Network

The effect of roughness elements on wind erosion: The importance of surface shear stress entrainment threshold by the ratio of shear stress on roughness elements to that on the vegetated land surface, and the implications for model accuracy. We use wind tunnel measurements of surface shear stress distributions

86

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

E-print Network

, accounting for hundreds of thousands of deaths each year. A common factor in the majority of these deaths is the develop- ment of atherosclerosis in the arterial and/or coronary vasculature [1]. The interplay of atherosclerosis in the development... Wall Shear Stress in the Arterial System Wall Shear Stress and Atherogenesis the Hypotheses Shear Stress and Velocity Measurements Probe Calibration Previous Wall Shear Stress Studies Statement of the Problem MATERIALS AND METHODS Hot Film...

Dunn, Carl Anthony

1982-01-01

87

Critical shear stresses in cohesive soils  

E-print Network

CRITICAL SHEAR STRESSES IN COHESIVE SOILS A Thesis By ROBERT JAMES REKTORIK Approved as to style and content by: (Committee hairm g- c& ( ead of epartm ( mber) (Member) January 1964 ACKNOWLEDGMENTS I wish to acknowledge the guidance... particle size, and per cent clay. Dunn (7) used a submerged jet to determine the tractive resistance of cohesive soils. A summary of Dunn's conclusions follows: The best method for estimating the critical hydraulic shear stresses for soils...

Rektorik, Robert James

1964-01-01

88

Fluid shear stress threshold regulates angiogenic sprouting  

PubMed Central

The density and architecture of capillary beds that form within a tissue depend on many factors, including local metabolic demand and blood flow. Here, using microfluidic control of local fluid mechanics, we show the existence of a previously unappreciated flow-induced shear stress threshold that triggers angiogenic sprouting. Both intraluminal shear stress over the endothelium and transmural flow through the endothelium above 10 dyn/cm2 triggered endothelial cells to sprout and invade into the underlying matrix, and this threshold is not impacted by the maturation of cell–cell junctions or pressure gradient across the monolayer. Antagonizing VE-cadherin widened cell–cell junctions and reduced the applied shear stress for a given transmural flow rate, but did not affect the shear threshold for sprouting. Furthermore, both transmural and luminal flow induced expression of matrix metalloproteinase 1, and this up-regulation was required for the flow-induced sprouting. Once sprouting was initiated, continuous flow was needed to both sustain sprouting and prevent retraction. To explore the potential ramifications of a shear threshold on the spatial patterning of new sprouts, we used finite-element modeling to predict fluid shear in a variety of geometric settings and then experimentally demonstrated that transmural flow guided preferential sprouting toward paths of draining interstitial fluid flow as might occur to connect capillary beds to venules or lymphatics. In addition, we show that luminal shear increases in local narrowings of vessels to trigger sprouting, perhaps ultimately to normalize shear stress across the vasculature. Together, these studies highlight the role of shear stress in controlling angiogenic sprouting and offer a potential homeostatic mechanism for regulating vascular density. PMID:24843171

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

2014-01-01

89

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

90

Characterization of fractures subjected to normal and shear stress  

NASA Astrophysics Data System (ADS)

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

Choi, Min-Kwang

91

Surface shear stress fluctuations in the atmospheric surface layer  

Microsoft Academic Search

A lightweight, high frequency response (25Hz), floating element sensor was used to measure wall shear stress fluctuations in the atmospheric surface layer formed over a salt flat at the SLTEST site, Utah, USA. The sensor uses a laser position measurement system to track the motion of the floating element which consisted of a 50mm diameter foam disc, as described by

Jason Monty; Nick Hutchins; Min Chong

2005-01-01

92

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

93

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

NASA Astrophysics Data System (ADS)

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

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

2015-02-01

94

Determination of surface shear stress with the naphthalene sublimation technique  

NASA Technical Reports Server (NTRS)

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

1987-01-01

95

BOUNDARY SHEAR STRESS ALONG VEGETATED STREAMBANKS  

EPA Science Inventory

This research is intended to improve our understanding of the role of riparian vegetation in stream morphology by evaluating the effects of vegetation on boundary shear stress, providing insight to the type and density of vegetation required for streambank stability. The resu...

96

Integrated Shear Stress/Temperature Micromachined Sensors  

NASA Technical Reports Server (NTRS)

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

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

2002-01-01

97

In Vitro Shear Stress Measurements Using Particle Image Velocimetry in a Family of Carotid Artery Models: Effect of Stenosis Severity, Plaque Eccentricity, and Ulceration  

PubMed Central

Atherosclerotic disease, and the subsequent complications of thrombosis and plaque rupture, has been associated with local shear stress. In the diseased carotid artery, local variations in shear stress are induced by various geometrical features of the stenotic plaque. Greater stenosis severity, plaque eccentricity (symmetry) and plaque ulceration have been associated with increased risk of cerebrovascular events based on clinical trial studies. Using particle image velocimetry, the levels and patterns of shear stress (derived from both laminar and turbulent phases) were studied for a family of eight matched-geometry models incorporating independently varied plaque features – i.e. stenosis severity up to 70%, one of two forms of plaque eccentricity, and the presence of plaque ulceration). The level of laminar (ensemble-averaged) shear stress increased with increasing stenosis severity resulting in 2–16 Pa for free shear stress (FSS) and approximately double (4–36 Pa) for wall shear stress (WSS). Independent of stenosis severity, marked differences were found in the distribution and extent of shear stress between the concentric and eccentric plaque formations. The maximum WSS, found at the apex of the stenosis, decayed significantly steeper along the outer wall of an eccentric model compared to the concentric counterpart, with a 70% eccentric stenosis having 249% steeper decay coinciding with the large outer-wall recirculation zone. The presence of ulceration (in a 50% eccentric plaque) resulted in both elevated FSS and WSS levels that were sustained longer (?20 ms) through the systolic phase compared to the non-ulcerated counterpart model, among other notable differences. Reynolds (turbulent) shear stress, elevated around the point of distal jet detachment, became prominent during the systolic deceleration phase and was widely distributed over the large recirculation zone in the eccentric stenoses. PMID:25007248

Kefayati, Sarah; Milner, Jaques S.; Holdsworth, David W.; Poepping, Tamie L.

2014-01-01

98

Obtaining the shear stress shear rate relationship and yield stress of liquid foods from Couette viscometry data  

Microsoft Academic Search

A method based on Tikhonov regularisation is used to convert the Couette viscometry data of a number of liquid foods into shear stress vs shear rate relationships. For liquid foods that have a yield stress and if the viscometry data cover the appropriate range of shear stress, Tikhonov regularisation is used to compute simultaneously the yield stress. The versatility of

Y. K. Leong; Y. L. Yeow

2003-01-01

99

The high pressure high shear stress rheology of liquid lubricants  

Microsoft Academic Search

A limiting shear stress model of liquid lubricant shear rheology is offered which accurately represents all available primary data. The model is of the nonlinear Maxwell type with shear modulus taken into the time derivative and broadening of the viscous-plastic transition with pressure. Property relations for viscosity, limiting stress and shear modulus are refined for a polyphenyl ether in particular.

S. Bair; W. O. Winer

1992-01-01

100

Low shear stress gravel-bed river  

USGS Publications Warehouse

A low stress gravel bed river is a river where the cross-sectional average dimensionless shear stress (??*) rarely exceeds 0.047. That is the case for the Gunnison River below Delta in Western Colorado. The cross-sectional average ??* in the Gunnison River has not exceeded 0.047, except at one cross section during one year, in the 87 years of record. A ??* of 0.047 is the critical ??* in the bed-load equation considered to be most applicable to gravel/cobble bed rivers (the Meyer-Peter, Mueller equation). According to this equation, there has been no bed-material movement in the Gunnison River since 1920; in fact there has been bed-material movement and this movement is biologically important. Bed-material is moved when the ??* is 0.016 or larger. Streamflows that cause a ??* of at least 0.016 maintain the aquatic habitat in a low shear stress river.

Milhous, Robert T.

1997-01-01

101

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

PubMed Central

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

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

2012-01-01

102

Yield stress and shear-banding in granular suspensions  

E-print Network

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

Abdoulaye Fall; Francois Bertrand; Guillaume Ovarlez; Daniel Bonn

2009-07-13

103

A Rotary Flow Channel for Shear Stress Sensor Calibration  

NASA Technical Reports Server (NTRS)

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

Zuckerwar, Allan J.; Scott, Michael A.

2004-01-01

104

TURBULENT SHEAR STRESS IN HETEROGENEOUS SEDIMENT-LADEN FLOWS  

E-print Network

TURBULENT SHEAR STRESS IN HETEROGENEOUS SEDIMENT-LADEN FLOWS By Hyoseop Woo,1 Associate Member channels depends very largely on calculations of turbulent shear stresses; typical examples are the beginning of motion of sediment particles and sediment transport in alluvial channels. If shear stress can

Julien, Pierre Y.

105

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

E-print Network

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

Eric Brown; Heinrich M. Jaeger

2012-01-05

106

Estimation of bed shear stresses in the pearl river estuary  

NASA Astrophysics Data System (ADS)

Mean and fluctuating velocities were measured by use of a pulse coherent acoustic Doppler profiler (PC-ADP) and an acoustic Doppler velocimeter in the tidal bottom boundary layer of the Pearl River Estuary. The bed shear stresses were estimated by four different methods: log profile (LP), eddy correlation (EC), turbulent kinetic energy (TKE), and inertial dissipation (ID). The results show that (a) all four methods for estimating bed stresses have advantages and disadvantages, and they should be applied simultaneously to obtain reliable frictional velocity and to identify potential sources of errors; (b) the LP method was found to be the most suitable to estimate the bed stresses in non-stratified, quasi-steady, and homogeneous flows; and (c) in the estuary where the semi-diurnal tidal current is dominant, bed shear stresses exhibit a strong quarter-diurnal variation.

Liu, Huan; Wu, Jia-xue

2015-03-01

107

Feasability study of wall shear stress imaging using microstructured surfaces with flexible micropillars  

Microsoft Academic Search

A new optical sensor technique based on a sensor film with arrays of hair-like flexible micropillars on the surface is presented to measure the temporal and spatial wall shear stress field in boundary layer flows. The sensor principle uses the pillar tip deflection in the viscous sublayer as a direct measure of the wall shear stress. The pillar images are

Ch. Brücker; J. Spatz; W. Schröder

2005-01-01

108

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

E-print Network

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

109

A Two-Axis Direct Fluid Shear Stress Sensor  

NASA Technical Reports Server (NTRS)

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

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

2010-01-01

110

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

PubMed Central

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

Joseph Antony, S.

2015-01-01

111

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

PubMed

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

Joseph Antony, S

2015-01-01

112

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

NASA Astrophysics Data System (ADS)

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

Joseph Antony, S.

2015-03-01

113

Sensor for Boundary Shear Stress in Fluid Flow  

NASA Technical Reports Server (NTRS)

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

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

2012-01-01

114

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

NASA Technical Reports Server (NTRS)

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

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

1996-01-01

115

Application and improvement of Raupach's shear stress partitioning model  

NASA Astrophysics Data System (ADS)

Aeolian processes such as the entrainment, transport and redeposition of sand, soil or snow are able to significantly reshape the earth's surface. In times of increasing desertification and land degradation, often driven by wind erosion, investigations of aeolian processes become more and more important in environmental sciences. The reliable prediction of the sheltering effect of vegetation canopies against sediment erosion, for instance, is a clear practical application of such investigations to identify suitable and sustainable counteractive measures against wind erosion. This study presents an application and improvement of a theoretical model presented by Raupach (Boundary-Layer Meteorology, 1992, Vol.60, 375-395 and Journal of Geophysical Research, 1993, Vol.98, 3023-3029) which allows for quantifying the sheltering effect of vegetation against sediment erosion. The model predicts the shear stress ratios ?S'/? and ?S''/?. Here, ?S is the part of the total shear stress ? that acts on the ground beneath the plants. The spatial peak ?S'' of the surface shear stress is responsible for the onset of particle entrainment whereas the spatial mean ?S' can be used to quantify particle mass fluxes. The precise and accurate prediction of these quantities is essential when modeling wind erosion. Measurements of the surface shear stress distributions ?S(x,y) on the ground beneath live vegetation canopies (plant species: lolium perenne) were performed in a controlled wind tunnel environment to determine the model parameters and to evaluate the model performance. 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 model constant c, which is needed to determine the total stress ? for a canopy of interest and which remained rather unspecified to date, was found to be c ? 0.27. It was also found that the model parameter m, which relates ?S'' with ?S' and which is needed to determine the peak surface shear stress ?S'', is rather impractically defined in the original model formulation, because m is identified to be a function of the wind velocity, the roughness element shape and the roughness density. We propose an alternative, more universal definition of an a-parameter as a substitute for the m-parameter simply linearly relating ?S'' with ?S'. This strong linear relation is supported by the measurements and can be made plausible with simple fluid dynamical arguments. The advantage of a over m is that a is solely a function of the roughness element shape. Finally, a method is presented to determine the new a-parameter for different kinds of roughness elements with relatively simple experimental methods.

Walter, B. A.; Lehning, M.; Gromke, C.

2012-12-01

116

Surface shear stress fluctuations in the atmospheric surface layer  

NASA Astrophysics Data System (ADS)

A lightweight, high frequency response (25Hz), floating element sensor was used to measure wall shear stress fluctuations in the atmospheric surface layer formed over a salt flat at the SLTEST site, Utah, USA. The sensor uses a laser position measurement system to track the motion of the floating element which consisted of a 50mm diameter foam disc, as described by Heuer & Marusic (Meas. Sci. Tech., Vol. 16, 1644- -1649, 2005). The measurements were taken as part of an internationally coordinated experimental program designed to make extensive spatial and temporal measurements of velocity, temperature and wall shear stress of the surface layer. Velocity measurements were made with both a 30m high vertical array and a 100m wide horizontal array of sonic anemometers; 18 anemometers in total were employed. Cross-correlations of shear stress and streamwise velocity fluctuations were analysed in an attempt to identify structure angles in the flow. The results were also compared with experimental data from controlled, laboratory turbulent boundary layers having three orders of magnitude lower Reynolds number.

Monty, Jason; Hutchins, Nick; Chong, Min

2005-11-01

117

Shear stress cleaning for surface departiculation  

NASA Technical Reports Server (NTRS)

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

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

1986-01-01

118

Shear stress induced stimulation of mammalian cell metabolism  

NASA Technical Reports Server (NTRS)

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

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

1988-01-01

119

Wall shear stress estimates in coronary artery constrictions  

NASA Technical Reports Server (NTRS)

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

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

1992-01-01

120

Tooth design to avoid shearing stresses  

SciTech Connect

Teeth disposed on the bit face of a rotating bit are, angularly oriented on the sloping surface of the bit face such that a vertical loading force which is applied to each tooth vectorially sums with a wedging force exerted by the rock formation on each tooth to create a resultant force applied to the diamond cutting element included within the tooth. The angular orientation of the tooth is chosen such that the resultant force is applied to the diamond cutting element in a direction which minimizes shear stress on the element. For example, in the case where the diamond cutting element is an equilateral triangular prismatic element tangentially set on the bit face with one apical edge defined by two adjacent triangular sides outermost on the tooth, the orientation or inclination of the tooth with respect to the vertical loading force and wedge force is such that the resulting force lies near or on the disector of the dihedral angle formed by the apical edge. Similarly, the diamond cutting element is rearwardly raked in the longitudinal direction, generally parallel to the tangential motion during normal drilling as defined by the rotation of the bit, such that the vectorial sum of the vertical loading force in a reactive cutting force applies a resultant force on the diamond cutting element in a direction which minimizes shear stress, namely, in the example in a direction approximately perpendicular to one of the end faces of the triangular prismatic diamond cutting element.

Mengel, H. E.; Munzel, H.

1985-05-07

121

Interfacial shear stress, peeling stress, and die cracking stress in trilayer electronic assemblies  

Microsoft Academic Search

Interfacial shear stress, peeling stress, and die cracking stress due to thermal and elastic mismatch in layered electronic assemblies are one of the major causes of the mechanical failure of electronic packages. A simple but rather accurate method is developed to estimate these thermal stresses for packages with different layer lengths. For layered electronics with thin adhesives, analytical expressions are

Kang Ping Wang; Yonggang Young Huang; Abhijit Chandra; Kai Xiong Hu

2000-01-01

122

Bottom Shear Stresses in Runnels Flanking a Mudflat Channel  

NASA Astrophysics Data System (ADS)

Mudflats are dissected by flow-parallel runnels separated by ridges. These bedforms are usually equispaced with a depth of tens of centimeters. The most accepted hypothesis for runnels formation is the presence of stream-wise helical flows above the mudflat surface. Here we explore an alternative mechanism for the formation and maintenance of runnels that arises near tidal channels draining a mudflat. To this end we present a novel numerical model that determines the distribution of shear stresses inside a runnel. The model is validated with data of tidal velocity and sediment concentration measured in mudflat runnels in Willapa Bay, Washington State, USA. Results show that very shallow flows draining the mudflat platform during ebb are concentrated in the runnels. The corresponding shear stresses are strong enough to erode bottom sediments and keep the runnel flushed. Similar shallow flows during flood might lead to sediment resuspension and further runnel incision. Mudflat runnels in Willapa Bay, WA, USA

Fagherazzi, S.; Mariotti, G.

2010-12-01

123

High shear stress can initiate both platelet aggregation and shedding of procoagulant containing microparticles.  

PubMed

Previous studies have demonstrated that a high level of shear stress can produce platelet aggregation without the addition of any agonist. We investigated whether high shear stress could cause both platelet aggregation and shedding of microparticles from the platelet plasma membrane. A coneplate viscometer was used to apply shear stress and microparticle formation was measured by flow cytometry. It was found that microparticle formation increased as the duration of shear stress increased. Both microparticles and the remnant platelets showed the exposure of procoagulant activity on their surfaces. Investigation of the mechanisms involved in shear-dependent microparticle generation showed that binding of von Willebrand factor (vWF) to platelet glycoprotein lb, influx of extracellular calcium, and activation of platelet calpain were required to generate microparticles under high shear stress conditions. Activation of protein kinase C (PKC) promoted shear-dependent microparticle formation. Epinephrine did not influence microparticle formation, although it enhanced platelet aggregation by high shear stress. These findings suggest the possibility that local generation of microparticles in atherosclerotic arteries, the site that pathologically high shear stress could occur, may contribute to arterial thrombosis by providing and expanding a catalytic surface for the coagulation cascade. PMID:8896411

Miyazaki, Y; Nomura, S; Miyake, T; Kagawa, H; Kitada, C; Taniguchi, H; Komiyama, Y; Fujimura, Y; Ikeda, Y; Fukuhara, S

1996-11-01

124

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

SciTech Connect

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

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

1997-01-30

125

Two-axis direct fluid shear stress sensor  

NASA Technical Reports Server (NTRS)

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

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

2011-01-01

126

Shear stress inhibits apoptosis of human endothelial cells  

Microsoft Academic Search

Physiological levels of shear stress alter the genetic program of cultured endothelial cells and reduce endothelial cell turnover in vivo. To test the hypothesis that shear stress interferes with programmed cell death, apoptosis was induced in human umbilical venous endothelial cells by growth factor withdrawal or incubation with tumor necrosis factor ?(TNF?) for 18 h. Apoptosis was quantified by ELISA

Stefanie Dimmeler; Judith Haendeler; Volker Rippmann; Michael Nehls; Andreas M. Zeiher

1996-01-01

127

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

128

ON THE FUNDAMENTAL FLUCTUATING WALL-SHEAR-STRESS Olivier Cabrit  

E-print Network

of this fundamental wall-shear-stress in three different configura- tions: boundary layer, pipe, and channel flowsON THE FUNDAMENTAL FLUCTUATING WALL-SHEAR-STRESS Olivier Cabrit Department of Mechanical Engineering University of Melbourne Victoria 3010, Australia o.cabrit@unimelb.edu.au Romain Mathis Laboratoire

Marusic, Ivan

129

Shear stress and sediment transport calculations for swash zone modelling  

Microsoft Academic Search

It is shown that the observed difference in sediment transporting efficiency by the swash uprush, compared with the downrush, could be mainly due to greater bed shear stress for a given velocity in the more abruptly accelerated uprush. The bed shear stress generated by an arbitrary free stream velocity time series is modelled in terms of usual wave boundary layer

Peter Nielsen

2002-01-01

130

Prediction of Shear Stress in Cerebral Julia Mikhal  

E-print Network

Prediction of Shear Stress in Cerebral Aneurysms Julia Mikhal Multiscale Modeling & Simulation ­ University of Twente PhD-TW Colloquium ­ April 08, 2010 #12;Cerebral Aneurysm This presentation: Aneurysm for model vessels and aneurysms J.Mikhal: Prediction of Shear Stress in Cerebral Aneurysms #12;Cerebral

Al Hanbali, Ahmad

131

The fluctuating wall-shear stress and the velocity field in the viscous sublayer  

Microsoft Academic Search

The fluctuating wall-shear stress was measured with various types of hot-wire and hot-film sensors in turbulent boundary-layer and channel flows. The rms level of the streamwise wall-shear stress fluctuations was found to be 40 percent of the mean value, which was substantiated by measurements of the streamwise velocity fluctuations in the viscous sublayer. Heat transfer to the fluid via the

Henrik P. Alfredsson; Arne V. Johansson; Joseph H. Haritonidis; Helmut Eckelmann

1988-01-01

132

Oscillatory and Steady Laminar Shear Stress Differentially Affect Human Endothelial Redox State Role of a Superoxide-Producing NADH Oxidase  

Microsoft Academic Search

Atherosclerotic lesions are found opposite vascular flow dividers at sites of low shear stress and oscillatory flow. Since endothelial proinflammatory genes prominent in lesions are regulated by oxidation-sensitive transcriptional control mechanisms, we examined the redox state of cultured human umbilical vein endothelial cells after either oscillatory or steady laminar fluid shear stress. Endothelial oxidative stress was assessed by measuring activity

Gilles W. De Keulenaer; David C. Chappell; Nobukazu Ishizaka; Robert M. Nerem; R. Wayne Alexander; Kathy K. Griendling

133

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

NASA Technical Reports Server (NTRS)

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

Fichter, W. B.

1976-01-01

134

Hemodynamic shear stress and the endothelium in cardiovascular pathophysiology.  

PubMed

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

Davies, Peter F

2009-01-01

135

Hemodynamic shear stress and the endothelium in cardiovascular pathophysiology  

PubMed Central

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

Davies, Peter F

2010-01-01

136

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

137

Interfacial shear stress between a single-walled carbon nanotube and a gold surface after different physical treatments.  

PubMed

The interfacial shear stress between gold and dielectrophoretically assembled single-walled carbon nanotubes can be increased by annealing in N2, by e-beam irradiation, or by e-beam deposition of carbon. For the first time this increase has been measured, using a technique developed by this group that is based on NEMS cantilever measurements combined with modeling. Annealing increases the shear stress by more than a factor of 3 over its value of 87MPa for untreated gold surfaces, while e-beam irradiation increases the shear stress by more than a factor of 2 and carbon deposition increases the shear stress by a smaller amount. PMID:25700215

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

2015-06-01

138

Wall shear stress in intracranial aneurysms and adjacent arteries?  

PubMed Central

Hemodynamic parameters play an important role in aneurysm formation and growth. However, it is difficult to directly observe a rapidly growing de novo aneurysm in a patient. To investigate possible associations between hemodynamic parameters and the formation and growth of intracranial aneurysms, the present study constructed a computational model of a case with an internal carotid artery aneurysm and an anterior communicating artery aneurysm, based on the CT angiography findings of a patient. To simulate the formation of the anterior communicating artery aneurysm and the growth of the internal carotid artery aneurysm, we then constructed a model that virtually removed the anterior communicating artery aneurysm, and a further two models that also progressively decreased the size of the internal carotid artery aneurysm. Computational simulations of the fluid dynamics of the four models were performed under pulsatile flow conditions, and wall shear stress was compared among the different models. In the three aneurysm growth models, increasing size of the aneurysm was associated with an increased area of low wall shear stress, a significant decrease in wall shear stress at the dome of the aneurysm, and a significant change in the wall shear stress of the parent artery. The wall shear stress of the anterior communicating artery remained low, and was significantly lower than the wall shear stress at the bifurcation of the internal carotid artery or the bifurcation of the middle cerebral artery. After formation of the anterior communicating artery aneurysm, the wall shear stress at the dome of the internal carotid artery aneurysm increased significantly, and the wall shear stress in the upstream arteries also changed significantly. These findings indicate that low wall shear stress may be associated with the initiation and growth of aneurysms, and that aneurysm formation and growth may influence hemodynamic parameters in the local and adjacent arteries. PMID:25206394

Wang, Fuyu; Xu, Bainan; Sun, Zhenghui; Wu, Chen; Zhang, Xiaojun

2013-01-01

139

Shear-Sensitive Liquid Crystal Coating Method: Surface-Inclination Effects on Shear Vector Measurements  

NASA Technical Reports Server (NTRS)

The shear-sensitive liquid crystal coating (SSLCC) method is an image-based technique for both visualizing dynamic surface-flow phenomena, such as transition and separation, and for measuring the continuous shear-stress vector distribution acting on an aerodynamic surface. Under proper lighting and viewing conditions (discussed below), the coating changes color in response to an applied aerodynamic shear. This color-change response is continuous and reversible, with a response time of milliseconds, and is a function of both the shear magnitude and the shear vector orientation relative to the observer. The liquid crystal phase of matter is a weakly-ordered, viscous, non-Newtonian fluid state that exists between the nonuniform liquid phase and the ordered solid phase of certain organic compounds. Cholesteric liquid crystal compounds possess a helical molecular arrangement that selectively scatters white light, incident along the helical axis, as a three-dimensional spectrum. This property is linked to the helical pitch length, which is within the range of wavelengths in the visible spectrum. The pitch length, and hence the wavelength of the scattered light, is influenced by shear stress normal to the helical axis. This unique optical property produces a measurable color change in response to an applied shearing force. The full-surface shear stress vector measurement method, developed at NASA-Ames, is schematically illustrated. As with the visualization method, the coated test surface is illuminated from the normal direction with white light and the camera is positioned at an above-plane view angle of approximately 30 deg. Experiments have been initiated at NASA Ames to begin the process of quantifying surface-inclination (surface-curvature) effects on shear vector measurement accuracy. In preliminary experiments, surface-inclination angles theta(sub x), theta(sub y) of 0, +/-5, +/-10, and +/-15 deg were employed. In this arrangement, white-light illumination was positioned normal to the untilted test surface, and the camera above-plane view angle was set at 30 deg relative to the untilted test surface. As can be seen, vector-aligned lambda(sub d) values showed no dependence on theta(sub x) or theta(sub y) for absolute values of these tilt angles is less than or equal to 15 deg. Acquisition and analyses of full-surface color images are presently underway to definitively document the insensitivity limits of the shear vector measurement methodology to surface-slope variations.

Reda, Daniel C.; Wilder, Michael C.; Nixon, David (Technical Monitor)

1998-01-01

140

Measuring cosmic shear with the ring statistics  

Microsoft Academic Search

Context. Commonly used methods of decomposing E- and B-modes in cosmic shear, namely the aperture mass dispersion and the E\\/B-mode shear correlation function, suffer from incomplete knowledge of the two-point correlation function (2PCF) on very small and\\/or very large scales. The ring statistics, the most recently developed cosmic shear measure, improves on this issue and is able to decompose E-

T. Eifler; P. Schneider; E. Krause

2010-01-01

141

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

142

Production of functional proteins: balance of shear stress and gravity  

NASA Technical Reports Server (NTRS)

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

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

2007-01-01

143

Production of functional proteins: balance of shear stress and gravity  

NASA Technical Reports Server (NTRS)

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

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

2004-01-01

144

Production of functional proteins: balance of shear stress and gravity  

NASA Technical Reports Server (NTRS)

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

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

2011-01-01

145

Design and construction of a linear shear stress flow chamber  

Microsoft Academic Search

A new paralle plate flow chamber that has a linear variation of shear stress, starting from a predetermined maximum value\\u000a at the entrance and falling to zero at the exit, has been designed and tested. This is in contrast to the usual rect-angular\\u000a channel plan which produces a constant shear stress over the entire length. The new design is based

Shunichi Usami; Hsuan-Hsu Chen; Yihua Zhao; Shu Chien; Richard Skalak

1993-01-01

146

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. PMID:22574010

Große, Sebastian; Schröder, Wolfgang

2009-01-01

147

Shear induced normal stress differences in aqueous foams  

E-print Network

A finite simple shear deformation of an elastic solid induces unequal normal stresses. This nonlinear phenomenon, known as the Poynting effect, is governed by a universal relation between shear strain and first normal stresses difference, valid for non-dissipative elastic materials. We provide the first experimental evidence that an analog of the Poynting effect exists in aqueous foams where besides the elastic stress, there are significant viscous or plastic stresses. These results are interpreted in the framework of a constitutive model, derived from a physical description of foam rheology.

Vincent Labiausse; Reinhard Hohler; Sylvie Cohen-Addad

2006-09-27

148

Normal stresses in a shear flow of magnetorheological suspensions: viscoelastic versus Maxwell stresses  

E-print Network

1 Normal stresses in a shear flow of magnetorheological suspensions: viscoelastic versus Maxwell Magnetorheological (MR) fluids are suspensions of magnetizable microparticles in a liquid carrier. They present

Paris-Sud XI, Université de

149

Permeability of fault gouge under confining pressure and shear stress.  

USGS Publications Warehouse

The permeability of both clay-rich and non-clay gouges, as well as several pure clays, was studied as a function of confining pressures from 5 to 200 MPa and shear strain to 10. Permeability ranged over 4 orders of magnitude, from around 10-22 to 10-18 m2 (1 darcy = 0.987 X 10-12 m2). Grain size was an important factor in determining permeability, particularly for the clay-rich samples. The permeabilities of the non-clay samples were not significantly different than those of the clays. Strength of the saturated samples under drained (low pore pressure) conditions did not correlate with high or low permeability. However, the low permeabilities of these gouges could be a factor in the measured low shear stresses along fault regions if excess pore pressures were created as a result of shearing or compaction, and this pressure was unable to dissipate through a thick section of the material.-from Authors

Morrow, C.A.; Shi, L.Q.; Byerlee, J.D.

1984-01-01

150

Vorticity Alignment and Negative Normal Stresses in Sheared Attractive Emulsions  

E-print Network

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

Alberto Montesi; Alejandro A. Pena; Matteo Pasquali

2003-06-17

151

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. PMID:19566307

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

2009-01-01

152

Bed Shear Stress under Complex Flow Conditions - The Case of Megech River, Ethiopia  

NASA Astrophysics Data System (ADS)

Bed shear stress is a fundamental variable in river studies to link flow conditions to sediment transport. It is, however, difficult to estimate this variable accurately, particularly in complex flow conditions. This study compares shear stress estimated from the log profile, the depth-slope product and outputs from a two-dimensional hydraulic model. Vertical velocity profile observations from Megech River (one of the main rivers flowing into Lake Tana, upper Blue Nile Basin, Ethiopia) using SEBA Mini current meter M1attached with signal counter Z6-SEBA HAD under typical field conditions are used to evaluate the precision of different methods for estimating local boundary shear stress from velocity measurements. Results show that the velocity profile approach gives consistently lesser shear stress estimates. A comparison of the shear stress distributions derived using the two-dimensional hydraulic model and those estimated using the 1D reach-averaged equation (i.e. the depth-slope product) shows a close correspondence. Mean shear stresses determined using local depth and mean channel slope are only 14% greater than those values determined for the same data using local predictions of both depth and energy slope. As the overall mean shear stress provides a useful index of flow strength, this comparison suggests a good level of confidence in using the reach averaged one-dimensional equation, for which data can easily be collected from cross sectional surveys. However, the variance of the modelled shear stress distribution shows some differences by a factor of 3 to that calculated using the mean channel slope because of the larger uncertainity associated with point depth measurements. Although such models using 1D reach averaged equations are limited to different channel characteristics adhering to diverse model assumptions, they can still provide a useful tool for river-rehabilitation design and assessment, including sediment transport studies.

Mehari, Michael; Dessie, Mekete; Abate, Mengiste

2014-05-01

153

Shear induced drainage in foamy yield-stress fluids  

E-print Network

Shear induced drainage of a foamy yield stress fluid is investigated using MRI techniques. Whereas the yield stress of the interstitial fluid stabilizes the system at rest, a fast drainage is observed when a horizontal shear is imposed. It is shown that the sheared interstitial material behaves as a viscous fluid in the direction of gravity, the effective viscosity of which is controlled by shear in transient foam films between bubbles. Results provided for several bubble sizes are not captured by the R^2 scaling classically observed for liquid flow in particulate systems, such as foams and thus constitute a remarkable demonstration of the strong coupling of drainage flow and shear induced interstitial flow. Furthermore, foam films are found to be responsible for the unexpected arrest of drainage, thus trapping irreversibly a significant amount of interstitial liquid.

Julie Goyon; François Bertrand; Olivier Pitois; Guillaume Ovarlez

2010-03-30

154

Fluid Shear Stress Stimulates Phosphorylation of Akt in Human Endothelial Cells Involvement in Suppression of Apoptosis  

Microsoft Academic Search

Fluid shear stress alters the morphology and function of the endothelium by activating several kinases. Furthermore, shear stress potently inhibits apoptosis of endothelial cells. Since activation of Akt kinase has been shown to prevent cell death, we investigated the effects of shear stress on Akt phosphorylation. To test the hypothesis that shear stress interacts with the Akt kinase pathway, human

Stefanie Dimmeler; Birgit Assmus; Corinna Hermann; Judith Haendeler; Andreas M. Zeiher

155

Effects of Shear Stress in Teletaction and Human Perception by Gabriel Moy  

E-print Network

Effects of Shear Stress in Teletaction and Human Perception by Gabriel Moy Research Project and shear stress distributions on a user's skin. Since generating normal and shear stress is more difficult differences in a tactile display with and without shear stress information transmission. Psychophysical

Moy, Gabe

156

Monocyte recruitment to endothelial cells in response to oscillatory shear stress  

E-print Network

Monocyte recruitment to endothelial cells in response to oscillatory shear stress TZUNG K. HSIAI,,1 is a critical event in inflammatory responses. The spatial, temporal gradients of shear stress, topology. In response to oscillatory shear stress ( ) at 2.6 dyn/cm2 at a time-averaged shear stress ( ave) 0 and 0.5 Hz

Wong, Pak Kin

157

Shear stress is normalized in glomerular capillaries following ? nephrectomy.  

PubMed

Loss of significant functional renal mass results in compensatory structural and hemodynamic adaptations in the nephron. While these changes have been characterized in several injury models, how they affect hemodynamic forces at the glomerular capillary wall has not been adequately characterized, despite their potential physiological significance. Therefore, we used intravital multiphoton microscopy to measure the velocity of red blood cells in individual glomerular capillaries of normal rats and rats subjected to ? nephrectomy. Glomerular capillary blood flow rate and wall shear stress were then estimated using previously established experimental and mathematical models to account for changes in hematocrit and blood rheology in small vessels. We found little change in the hemodynamic parameters in glomerular capillaries immediately following injury. At 2 wk postnephrectomy, significant changes in individual capillary blood flow velocity and volume flow rate were present. Despite these changes, estimated capillary wall shear stress was unchanged. This was a result of an increase in capillary diameter and changes in capillary blood rheology in nephrectomized rats. PMID:25587117

Ferrell, Nicholas; Sandoval, Ruben M; Bian, Aihua; Campos-Bilderback, Silvia B; Molitoris, Bruce A; Fissell, William H

2015-03-15

158

Complete Release of Horizontal Shear Stresses During Geothermal Reservoir Stimulation  

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

159

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

NASA Technical Reports Server (NTRS)

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

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

2007-01-01

160

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

NASA Technical Reports Server (NTRS)

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

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

2008-01-01

161

Transverse shear stresses and their sensitivity coefficients in multilayered composite panels  

NASA Technical Reports Server (NTRS)

A computational procedure is presented for the accurate determination of transverse shear stresses and their sensitivity coefficients in flat multilayered composite panels subjected to mechanical and thermal loads. The sensitivity coefficients measure the sensitivity of the transverse shear stresses to variations in the different lamination and material parameters of the panel. The panel is discretized by using either a three-field mixed finite element model based on a two-dimensional first- order shear deformation plate theory or a two-field degenerate solid element with each of the displacement components having a linear variation throughout the thickness of the laminate. The evaluation of transverse shear stresses can be conveniently divided into two phases. The first phase consists of using a superconvergent recovery technique for evaluating the in-plane stresses in the different layers. In the second phase, the transverse shear stresses are evaluated by using piecewise integration, in the thickness direction, of the three-dimensional equilibrium equations. The same procedure is used for evaluating the sensitivity coefficients of the transverse shear stresses. The effectiveness of the computational procedure is demonstrated by means of numerical examples of multilayered cross-ply panels subjected to transverse loading, uniform temperature change, and uniform temperature gradient through the thickness of the panel. In each case the standard of the comparison is taken to be the exact solution of the three dimensional thermoelasticity equations of the panel.

Noor, Ahmed K.; Kim, Yong H.; Peters, Jeanne M.

1994-01-01

162

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

NASA Astrophysics Data System (ADS)

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

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

2011-11-01

163

Shear Stress Analysis in a Ferrofluidic Magnetic Micropump  

Microsoft Academic Search

The article presents analytical and numerical computational fluid dynamics (CFD) simulations of the flow performance in a newly introduced ferrofluidic magnetic micropump, with the purpose of estimating the stress distribution in its flow field. Analytical expressions were developed for the shear stress generated at the upper and lower walls of the pump's channel in terms of dimensionless parameters by solving

M. I. Kilani; A. T. Al Halhouli; S. Büttgenbach

2011-01-01

164

Radiation shear-stress heating in accretion flows  

NASA Technical Reports Server (NTRS)

The effects of radiation shear stresses acting in accretion disks and boundary layers are considered. It is demonstrated that these stresses are dynamically unimportant for nonrelativistic flows. For accretion onto a black hole or nonmagnetic neutron star, where the system is relativistic, radiation shear stresses can contribute substantially to the total luminosity of the system. The spectral and temporal signatures of this form of heating are discussed, and those features which are unique to radiative dissipation are emphasized. The results are in broad agreement with the spectra of the nonmagnetic X-ray binary systems, including Cyg X-1.

Walker, Mark A.

1990-01-01

165

A photoelastic study of the shear stresses associated with the transfer of stress during fibre reinforcement  

Microsoft Academic Search

Theories predicting the magnitudes of shear stresses at the surface of a fibre embedded in an elastic matrix under load are available in the literature. A two-dimensional photoelastic model confirms the existence of high shear stresses near the fibre ends, which peak to values greater than those predicted by theory.The significance of this to fibre reinforced composites is discussed.

W R Tyson; G J Davies

1965-01-01

166

Accurate shear measurement with faint sources  

NASA Astrophysics Data System (ADS)

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

Zhang, Jun; Luo, Wentao; Foucaud, Sebastien

2015-01-01

167

Shear Stress Partitioning in Large Patches of Roughness in the Atmospheric Inertial Sublayer  

NASA Technical Reports Server (NTRS)

Drag partition measurements were made in the atmospheric inertial sublayer for six roughness configurations made up of solid elements in staggered arrays of different roughness densities. The roughness was in the form of a patch within a large open area and in the shape of an equilateral triangle with 60 m long sides. Measurements were obtained of the total shear stress (tau) acting on the surfaces, the surface shear stress on the ground between the elements (tau(sub S)) and the drag force on the elements for each roughness array. The measurements indicated that tau(sub S) quickly reduced near the leading edge of the roughness compared with tau, and a tau(sub S) minimum occurs at a normalized distance (x/h, where h is element height) of approx. -42 (downwind of the roughness leading edge is negative), then recovers to a relatively stable value. The location of the minimum appears to scale with element height and not roughness density. The force on the elements decreases exponentially with normalized downwind distance and this rate of change scales with the roughness density, with the rate of change increasing as roughness density increases. Average tau(sub S): tau values for the six roughness surfaces scale predictably as a function of roughness density and in accordance with a shear stress partitioning model. The shear stress partitioning model performed very well in predicting the amount of surface shear stress, given knowledge of the stated input parameters for these patches of roughness. As the shear stress partitioning relationship within the roughness appears to come into equilibrium faster for smaller roughness element sizes it would also appear the shear stress partitioning model can be applied with confidence for smaller patches of smaller roughness elements than those used in this experiment.

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

2007-01-01

168

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

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

2010-11-01

169

Magnetic field effects on shear and normal stresses in magnetorheological finishing.  

PubMed

We use a recent experimental technique to measure in situ shear and normal stresses during magnetorheological finishing (MRF) of a borosilicate glass over a range of magnetic fields. At low fields shear stresses increase with magnetic field, but become field-independent at higher magnetic fields. Micromechanical models of formation of magnetic particle chains suggest a complex behavior of magnetorheological (MR) fluids that combines fluid- and solid-like responses. We discuss the hypothesis that, at higher fields, slip occurs between magnetic particle chains and the immersed glass part, while the normal stress is governed by the MRF ribbon elasticity. PMID:20940866

Lambropoulos, John C; Miao, Chunlin; Jacobs, Stephen D

2010-09-13

170

Shear-stress controlled dynamics of nematic complex fluids  

E-print Network

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

Sabine H. L. Klapp; Siegfried Hess

2010-05-11

171

Control of surface shear stress by MEMS based transducers  

NASA Astrophysics Data System (ADS)

A micromachined silicon actuator is placed downstream of a stationary vortex generator to investigate the control of the surface shear stress. Polysilicon coil is deposited on a bulk micromachined flap. The AC current passing through the coil induces a time- varying magnetic field to interact with a stationary permanent magnet such that a well-defined oscillatory motion of the flap can be obtained. On the silicon flap, a permalloy layer is electroplated for determining the mean displacement of the actuator. By driving the flap in a proper motion, large surface shear stress reduction can be achieved. Various driving modes of the actuator are examined. The results will be used for designing the adaptive control logic for turbulent shear stress reduction experiment. This work is supported by a AFOSR-URI grant.

Tung, Steve; Ho, Chih-Ming; Jiang, Fukang; Tai, Yu-Chong

1996-11-01

172

Yield shear stress model of magnetorheological fluids based on exponential distribution  

NASA Astrophysics Data System (ADS)

The magnetic chain model that considers the interaction between particles and the external magnetic field in a magnetorheological fluid has been widely accepted. Based on the chain model, a yield shear stress model of magnetorheological fluids was proposed by introducing the exponential distribution to describe the distribution of angles between the direction of magnetic field and the chain formed by magnetic particles. The main influencing factors were considered in the model, such as magnetic flux density, intensity of magnetic field, particle size, volume fraction of particles, the angle of magnetic chain, and so on. The effect of magnetic flux density on the yield shear stress was discussed. The yield stress of aqueous Fe3O4 magnetreological fluids with volume fraction of 7.6% and 16.2% were measured by a device designed by ourselves. The results indicate that the proposed model can be used for calculation of yield shear stress with acceptable errors.

Guo, Chu-wen; Chen, Fei; Meng, Qing-rui; Dong, Zi-xin

2014-06-01

173

Pulsed laser Doppler measurements of wind shear  

NASA Technical Reports Server (NTRS)

There is a need for a sensor at the airport that can remotely detect, identify, and track wind shears near the airport in order to assure aircraft safety. To determine the viability of a laser wind-shear system, the NASA pulsed coherent Doppler CO2 lidar (Jelalian et al., 1972) was installed in a semitrailer van with a rooftop-mounted hemispherical scanner and was used to monitor thunderstorm gust fronts. Wind shears associated with the gust fronts at the Kennedy Space Center (KSC) between 5 July and 4 August 1978 were measured and tracked. The most significant data collected at KSC are discussed. The wind shears were clearly visible in both real-time velocity vs. azimuth plots and in postprocessing displays of velocities vs. position. The results indicate that a lidar system cannot be used effectively when moderate precipitation exists between the sensor and the region of interest.

Dimarzio, C.; Harris, C.; Bilbro, J. W.; Weaver, E. A.; Burnham, D. C.; Hallock, J. N.

1979-01-01

174

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

E-print Network

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

Sharma, Vivek

175

TECHNICAL NOTE: Micro-electro-mechanical-systems direct fluid shear stress sensor arrays for flow control  

Microsoft Academic Search

The design and analysis of non-intrusive micro-electro-mechanical-systems sensors to measure fluid shear stress on the wing surface of a commercial jetliner is presented. A design specification is derived from analysis of flight loading data using computational fluid dynamics. The specification accounts for different flight conditions, aerodynamic smoothness and sensor bandwidth. Capacitive and PZT-based direct fluid shear sensor designs based upon

S. Hunt; A. Rudge; M. Carey; M. Parfitt; J. Geoffrey Chase; Ian Huntsman

2002-01-01

176

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

E-print Network

Reynolds stress and effects of external and self-generated shear flows S. B. Korsholm. P. K. A measurement of the Reynolds stress can thus help to predict flows, e.g. shear flows in plasmas as demonstrated transport. The generation of H-mode confinement regimes seem to be closely related to poloidal shear flows

177

Turbulence wall-shear stress sensor for the atmospheric surface layer  

Microsoft Academic Search

A new sensor is described for measuring the fluctuating component of the wall-shear stress in the atmospheric surface layer over relatively smooth uniform terrain. The sensor was tested at the Surface Layer Turbulence and Environmental Science Test (SLTEST) site on the western salt flats of Utah, giving the first ever direct measurements of this quantity in an atmospheric-scale flow. The

Weston D. C. Heuer; Ivan Marusic

2005-01-01

178

Wave propagation, stress relaxation, and grain-to-grain shearing in saturated, unconsolidated marine sediments  

E-print Network

Wave propagation, stress relaxation, and grain-to-grain shearing in saturated, unconsolidated the application of a dynamic strain. The stress arising from shearing is represented as a random stick translational shear stress-relaxation exponent n radial compressional stress-relaxation exponent N porosity

Buckingham, Michael

179

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

Microsoft Academic Search

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

M. A. Chinnery

1964-01-01

180

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

NASA Technical Reports Server (NTRS)

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

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

1992-01-01

181

Transient Shear Banding in a Simple Yield Stress Fluid  

E-print Network

We report a large set of experimental data which demonstrates that a simple yield stress fluid, i.e. which does not present aging or thixotropy, exhibits transient shear banding before reaching a steady state characterized by a homogeneous, linear velocity profile. The duration of the transient regime decreases as a power law with the applied shear rate $\\dot\\gamma$. This power law behavior, observed here in carbopol dispersions, does not depend on the gap width and on the boundary conditions for a given sample preparation. For $\\dot\\gamma\\lesssim 0.1$ s$^{-1}$, heterogeneous flows could be observed for as long as 10$^5$ s. These local dynamics account for the ultraslow stress relaxation observed at low shear rates.

Thibaut Divoux; David Tamarii; Catherine Barentin; Sébastien Manneville

2010-02-28

182

Influence of cardiac flow rate on turbulent shear stress from a prosthetic heart valve.  

PubMed

Elevated turbulent shear stresses associated with sufficient exposure times are potentially damaging to blood constituents. Since these conditions can be induced by mechanical heart valves, the objectives of this study were to locate the maximum turbulent shear stress in both space and time and to determine how the maximum turbulent shear stress depends on the cardiac flow rate in a pulsatile flow downstream of a tilting disk valve. Two-component, simultaneous, correlated laser velocimeter measurements were recorded at four different axial locations and three different flow rates in a straight tube model of the aorta. All velocity data were ensemble averaged within a 15 ms time window located at approximately peak systolic flow over more than 300 cycles. Shear stresses as high as 992 dynes/cm2 were found 0.92 tube diameters downstream of the monostrut, disk valve. The maximum turbulent shear stress was found to scale with flow rate to the 0.72 power. A repeatable starting vortex was shed from the disk at the beginning of each cycle. PMID:2967905

Schwarz, A C; Tiederman, W G; Phillips, W M

1988-05-01

183

Production of Functional Proteins: Balance of Shear Stress and Gravity  

NASA Technical Reports Server (NTRS)

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

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

2005-01-01

184

A fluidized bed technique for estimating soil critical shear stress  

Technology Transfer Automated Retrieval System (TEKTRAN)

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

185

Liquid Crystals Indicate Directions Of Surface Shear Stresses  

NASA Technical Reports Server (NTRS)

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

Reda, Daniel C.

1996-01-01

186

Calculation of Near-Bank Velocity and Boundary Shear Stress  

Technology Transfer Automated Retrieval System (TEKTRAN)

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

187

Concept Of Critical Shear Stress In Loose Boundary Open Channels  

Microsoft Academic Search

The problem of defining critical flow condition associated with the initial instability of bed material particle has been studied in relation to existing concepts. The data has been collected and analysed to indicate that a distinct condition for the beginning of movement doe not exist. The bed load transport in the proximity of so called critical shear stress is governed

A. S. Paintal

1971-01-01

188

WAVE ACTION AND BOTTOM SHEAR STRESSES IN LAKE ERIE  

EPA Science Inventory

For Lake Erie, the amplitudes and periods of wind-driven, surface gravity waves were calculated by means of the SMB hindcasting method. Bottom orbital velocities and bottom shear stresses were then calculated using linear wave theory and Kajiura's (1968) turbulent oscillating bou...

189

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

190

The Need for a Shear Stress Calibration Standard  

NASA Technical Reports Server (NTRS)

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

Scott, Michael A.

2004-01-01

191

Influence of inherent structure shear stress of supercooled liquids on their shear moduli  

E-print Network

Configurations of supercooled liquids residing in their local potential minimum (i.e. in their inherent structure, IS) were found to support a non-zero shear stress. This IS stress was attributed to the constraint to the energy minimization imposed by boundary conditions, which keep size and shape of the simulation cell fixed. In this paper we further investigate the influence of these boundary conditions on the IS stress. We investigate its importance for the computation of the low frequency shear modulus of a glass obtaining a consistent picture for the low- and high frequency shear moduli over the full temperature range. Hence, we find that the IS stress corresponds to a non-thermal contribution to the fluctuation term in the Born-Green expression. This leads to an unphysical divergence of the moduli in the low temperature limit if no proper correction for this term is applied. Furthermore, we clarify the IS stress dependence on the system size and put its origin on a more formal basis.

Ingo Fuereder; Patrick Ilg

2015-04-13

192

The Origin of Persistent Shear Stress in Supercooled Liquids  

E-print Network

We show that the long time tail of the shear stress autocorrelation, whose growth at large supercooling is responsible for the apparent divergence of the shear viscosity, is a direct result of a residual shear stress in the structures associated with the local potential minima. We argue that the essential mechanical transition experienced by a liquid on cooling occurs at a temperature well above the glass transition temperature and corresponds to the crossover from the high temperature liquid to the viscous liquid, the latter characterised by stress relaxation dominated by the residual stress. Following on from this observation, as the density is decreased, the local potential minima become unable to sustain any persistent stress (and, hence, support a glass transition), in a manner that can be explicitly connected to the interactions between atoms. The reported crossover implies an associated change in the mechanism of dissipation in liquids and, hence, raises the prospect of a coherent microscopic treatment of nonlinear rheology and the relationship between self diffusion and viscosity in supercooled liquids.

Sneha Abraham; Peter Harrowell

2012-05-27

193

The Role of Shear Failure on Stress Characterization  

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

194

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

PubMed

The structure of layer-by-layer (LbL) deposited nanofilm coatings consists of alternating polyethylenimine (PEI) and polystyrenesulfonate (PSS) films deposited on a single crystal quartz substrate. LbL-deposited nanofilms were investigated by neutron reflectomery (NR) in contact with water in the static and fluid shear stress conditions. The fluid shear stress was applied through a laminar flow of the liquid parallel to the quartz/polymer interface in a custom-built solid-liquid interface cell. The scattering length density profiles obtained from NR results of these polyelectrolyte multilayers (PEM), measured under different shear conditions, showed proportional decrease of volume fraction of water hydrating the polymers. For the highest shear rate applied (ca. 6800 s(-1)) the water volume fraction decreased by approximately 7%. The decrease of the volume fraction of water was homogeneous through the thickness of the film. Since there were not any significant changes in the total polymer thickness, it resulted in negative osmotic pressures in the film. The PEM films were compared with the behavior of thin films of thermoresponsive poly(N-isopropylacrylamide) (pNIPAM) deposited via spin-coating. The PEM and pNIPAM differ in their interactions with water molecules, and they showed opposite behaviors under the fluid shear stress. In both cases the polymer hydration was reversible upon the restoration of static conditions. A theoretical explanation is given to explain this difference in the effect of shear on hydration of polymeric thin films. PMID:25689755

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

2015-03-10

195

Stress Measurement System  

NASA Technical Reports Server (NTRS)

Under the Aircraft Structural Integrity program, Langley Research Center and Stress Photonics developed an infrared-based stress measurement system for use in nondestructive evaluation of materials and structures. Stress Photonics commercialized the technology in the DeltaTherm 1000 system, used to compare designs and detect cracks in structures, especially for aging aircraft and bridges. The system combines digital signal processing technology with a special infrared camera to provide instantaneous thermal images and live differential images.

1996-01-01

196

CRITICAL SHEAR STRESSES FOR EROSION AND DEPOSITION OF FINE SUSPENDED SEDIMENTS IN THE FRASER RIVER  

E-print Network

#12;CRITICAL SHEAR STRESSES FOR EROSION AND DEPOSITION OF FINE SUSPENDED SEDIMENTS IN THE FRASER C T I V E Models of cohesive sediment transport require parameters describing the erosion for deposition and erosion were measured. Some tests were repeated with known concentrations of the pulp mill

197

Measuring the Cosmic Shear in Fourier Space  

E-print Network

We propose to measure the weak cosmic shear using the spatial derivatives of the galaxy surface brightness field. The measurement should be carried out in Fourier space, in which the point spread function (PSF) can be transformed to a desired form with multiplications, and the spatial derivatives can be easily measured. This method is mathematically well defined regardless of the galaxy morphology and the form of the PSF, and involves simple procedures of image processing. Furthermore, with high resolution galaxy images, this approach allows one to probe the shape distortions of galaxy substructures, which can potentially provide much more independent shear measurements than the ellipticities of the whole galaxy. We demonstrate the efficiency of this method using computer-generated mock galaxy images.

Jun Zhang

2008-01-24

198

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

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

199

Pseudopod Projection and Cell Spreading of Passive Leukocytes in Response to Fluid Shear Stress  

E-print Network

Pseudopod Projection and Cell Spreading of Passive Leukocytes in Response to Fluid Shear Stress evidence suggests that circulating leukocytes respond to physiological levels of fluid shear stress. This study was designed to examine the shear stress response of individual leukocytes adhering passively

Braslavsky, Ido

200

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

E-print Network

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

Julien, Pierre Y.

201

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

Technology Transfer Automated Retrieval System (TEKTRAN)

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

202

American Institute of Aeronautics and Astronautics A MEMS Floating Element with Bump Shear Stress Sensor  

E-print Network

American Institute of Aeronautics and Astronautics 1 A MEMS Floating Element with Bump Shear Stress element shear stress sensor with bumps has been designed in a 1cm by 1cm chip. The array consists of 256) a linear range up to 13 Pa shear stress; c) a resolution of 44 mPa/rtHz; d) a first mode resonant frequency

White, Robert D.

203

Temporal evolution of cell focal adhesions: experimental observations and shear stress profiles  

E-print Network

Temporal evolution of cell focal adhesions: experimental observations and shear stress profiles D as the growth rate increases. Using a composite mechanics model by which the evolution of the shear stress by the reaching of a minimum shear stress threshold at the FA back edge, or of a maximum difference between

Zaidel-Bar, Ronen

204

ORAL/POSTER REFERENCE: ICF100374OR SHEAR LAG MODELLING OF THERMAL STRESSES IN  

E-print Network

ORAL/POSTER REFERENCE: ICF100374OR SHEAR LAG MODELLING OF THERMAL STRESSES IN UNIDIRECTIONAL A two-dimensional shear lag model is presented to analyze the steady state distributions of stress's modulus and thermal conductivity of the cracked material. KEYWORDS Composites, thermal stresses, shear lag

205

Velocity profiles, stresses, and Bagnold scaling of sheared granular system in zero gravity  

E-print Network

Velocity profiles, stresses, and Bagnold scaling of sheared granular system in zero gravity Oleh, therefore reducing the shear in the system. Next, we present stress distributions both for controlled volume and for controlled stress configurations. We discuss the dependence of solid volume fraction on shear rate under

Kondic, Lou

206

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

E-print Network

Figure 1: Multiplex logarithmic microfluidic perfusion array for probing shear stress effects on stem cells. (A) Microfluidic perfusion systems exhibit more defined shear stress profiles and consume. (B) A 1x6 multiplex logarithmic microfluidic array for simultaneous application of shear stress

Voldman, Joel

207

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

E-print Network

On velocity profiles and stresses in sheared and vibrated granular systems under variable gravity questions in shear flows either with oscillations or without them is the stress dependence on external that, under a wide range of conditions, the stresses scale with the square of the imposed shearing

Kondic, Lou

208

Evidence That Release of Adenosine Triphosphate From Endothelial Cells During Increased Shear Stress Is Vesicular  

E-print Network

: In response to increased shear stress, vascular endothelial cells release adenosine triphosphate (ATP in response to increased shear stress. Preliminary experiments using inhibitors of the cystic fibrosis, in vivo, are constantly subjected to shear stress because of their location on the inside of the lumen

Burnstock, Geoffrey

209

Modeling airflow-related shear stress during heterogeneous constriction and mechanical ventilation  

E-print Network

Modeling airflow-related shear stress during heterogeneous constriction and mechanical ventilation, and Kenneth Lutchen. Modeling airflow-related shear stress during heterogeneous constriction and mechanical airflow-related shear stress to a dangerously high level that may be sufficient to cause injury

Lutchen, Kenneth

210

Combined effects of pulsatile flow and dynamic curvature on wall shear stress in a coronary artery  

E-print Network

Combined effects of pulsatile flow and dynamic curvature on wall shear stress in a coronary artery correlation between atherosclerosis lesion locations and low and oscillating wall shear stresses [2, 4 temporal wall shear stress variations. However, they only considered steady inflow in their studies

Laidlaw, David

211

Shear stress magnitude and directionality modulate growth factor gene expression in  

E-print Network

Shear stress magnitude and directionality modulate growth factor gene expression in preconditioned levels of 12 endothelial growth factor genes in response to alterations in wall shear stress (WSS) under by ECs in response to luminal wall shear stress (WSS)9-15 may contribute to the pathology of intimal

Passerini, Tony

212

Estimation of the wave-related ripple characteristics and induced bed shear stress  

E-print Network

Estimation of the wave-related ripple characteristics and induced bed shear stress Beno^it Camenen on the roughness height and the calculation of the bed shear stress is also discussed. It appeared that the bed shear stress calculation is more sensitive to the empirical coefficient ar introduced in the estimation

Paris-Sud XI, Université de

213

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

E-print Network

Shear stress regulation of nitric oxide production in uterine and placental artery endothelial cells: experimental studies and hemodynamic models of shear stresses on endothelial cells BENJAMIN. of Pediatrics and 4Dept of Animal Sciences, Madison USA ABSTRACT Hemodynamic shear stress is the most powerful

Chesler, Naomi C.

214

High-speed High-Stress Ring Shear Tests on Granular Soils and Clayey Soils1  

E-print Network

High-speed High-Stress Ring Shear Tests on Granular Soils and Clayey Soils1 Hiroshi Fukuoka carried out with a newly developed High-speed High-Stress Ring Shear Apparatus to examine was independent of shear speed un- der the normal stress up to 3.8kgf/cm2, 2 N 5 degrees of change in friction

Standiford, Richard B.

215

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

216

Use of Axisymmetric Shearing as Technological Test Method to gather Flow Stress Data for Metals  

NASA Astrophysics Data System (ADS)

Cutting by shearing creates heavy shear deformation in a layer extending between the two applied shearing edges. Prediction of FEM-simulation is that effective strain and strain rates in the shear zone would reach very high levels even at mode rate shearing velocity. In this article experiments coupled with FEM-analysis are used to evaluate the potential of using a xisymmetric shearing for collecting flow stress data for metal forming purposes. It is shown that if accurate flow stress data are to be collected this way it is important to know how shearing occurs inside the shear zone.

Kandis, Janis; Valberg, Henry; Wenbin, Wu

2011-01-01

217

Direct measurement of shear properties of microfibers.  

PubMed

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

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

2014-09-01

218

Direct measurement of shear properties of microfibers  

SciTech Connect

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

Behlow, H.; Saini, D.; Durham, L.; Simpson, J.; Skove, M. J.; Rao, A. M. [Department of Physics and Astronomy, and Clemson Nanomaterials Center, Clemson University, Clemson, South Carolina 29634 (United States); Oliveira, L. [School of Materials Science and Engineering, Clemson University, Clemson, South Carolina 29634 (United States); Serkiz, S. M. [Department of Physics and Astronomy, and Clemson Nanomaterials Center, Clemson University, Clemson, South Carolina 29634 (United States); Savannah River National Laboratory, Aiken, South Carolina 29808 (United States)

2014-09-15

219

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

220

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

USGS Publications Warehouse

[1] Increased erosion is a well-known response after wildfire. To predict and to model erosion on a landscape scale requires knowledge of the critical shear stress for the initiation of motion of soil particles. As this soil property is temperature-dependent, a quantitative relation between critical shear stress and the temperatures to which the soils have been subjected during a wildfire is required. In this study the critical shear stress was measured in a recirculating flume using samples of forest soil exposed to different temperatures (40??-550??C) for 1 hour. Results were obtained for four replicates of soils derived from three different types of parent material (granitic bedrock, sandstone, and volcanic tuffs). In general, the relation between critical shear stress and temperature can be separated into three different temperature ranges (275??C), which are similar to those for water repellency and temperature. The critical shear stress was most variable (1.0-2.0 N m-2) for temperatures 2.0 N m-2) between 175?? and 275??C, and was essentially constant (0.5-0.8 N m-2) for temperatures >275??C. The changes in critical shear stress with temperature were found to be essentially independent of soil type and suggest that erosion processes in burned watersheds can be modeled more simply than erosion processes in unburned watersheds. Wildfire reduces the spatial variability of soil erodibility associated with unburned watersheds by eliminating the complex effects of vegetation in protecting soils and by reducing the range of cohesion associated with different types of unburned soils. Our results indicate that modeling the erosional response after a wildfire depends primarily on determining the spatial distribution of the maximum soil temperatures that were reached during the wildfire. Copyright 2005 by the American Geophysical Union.

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

2005-01-01

221

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

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

222

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

223

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

224

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

Microsoft Academic Search

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

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

2009-01-01

225

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

E-print Network

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

Amit Kumar Bhattacharjee

2014-10-29

226

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

227

Nanoscale Stress Measurements and Standards  

E-print Network

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

Magee, Joseph W.

228

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

229

The Behavior Under Shearing Stress of Duralumin Strip with Round, Flanged Holes  

NASA Technical Reports Server (NTRS)

This report presents the results of an investigation to determine the behavior of dural strip with flanged holes in the center when subjected to shear stresses. They buckle under a certain load just as a flat sheet. There is one optimum hole spacing and a corresponding buckling load in shear for each sheet width, sheet thickness, and flange form. Comparison with non-flanged sheets revealed a marked increase of buckling load in shear due to the flanging and a slightly greater displacement. Strips were clamped between two stationary end rails and one sliding center rail at which the shear is applied. The force was measured with a tension stirrup up to 20 tons and a compression dynamometer up to 10 tons. The displacement was recorded with the Zeiss dial gauge. The following were investigated: 1) effect of strip width; 2) strip thickness; 3) diameter of flanging; 4) depth of flanging; 5) and hole distance.

Schussler, Karl

1934-01-01

230

Non-volcanic tremor driven by large transient shear stresses  

USGS Publications Warehouse

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

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

2007-01-01

231

ENaC regulation by proteases and shear stress  

PubMed Central

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

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

2013-01-01

232

Is aortic wall shear stress affected by aging? An image-based numerical study with two age groups.  

PubMed

The size of the larger arteries increases during the entire life, but not much is known about how the change in size affects the blood flow. This study compares the flow field in a group of young males (N = 10, age = 23.5 ± 1.4), with a group of older males (N = 8, age = 58.0 ± 2.8). Aortic geometries were obtained by magnetic resonance imaging, and the aortic blood flow field was computed using computational fluid dynamics. The aortic wall shear stress was obtained from the computations, and it was concluded that time-averaged wall shear stress decreased with increased age, probably as a consequence of increased aortic diameter and decreased stroke volume, which in turn reduces the shear rates in the aorta. However, the oscillatory shear index, which is a measure of the oscillatory nature of the wall shear stress vector, seemed to be unaffected by aging. PMID:25630809

Lantz, Jonas; Renner, Johan; Länne, Toste; Karlsson, Matts

2015-03-01

233

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

234

Shear-stress function approach of hydration layer based on the Green-Kubo formula  

NASA Astrophysics Data System (ADS)

We present the analytic expression of the stress correlation (SC) function for the ubiquitous hydration water layer (HWL) using the Green-Kubo equation and the shear modulus of HWL. The SC function is then experimentally obtained by measuring the viscoelastic properties of HWL using shear-mode dynamic force spectroscopy. Interestingly, the SC changes sign from positive to negative as the HWL thickness increases, where the shear stresses acting on the HWLs bound to two nearby surfaces are out of phase. We also suggest that the repulsive hydration force originates from the SC of HWL. Our results provide the first demonstration of the microscopic understanding of the HWL viscoelasticity and may allow a deeper insight on the HWL dynamics as well as the complex liquids.

Kim, Bongsu; Kwon, Soyoung; Moon, Geol; Jhe, Wonho

2015-03-01

235

Mechanical properties of jammed packings of frictionless spheres under an applied shear stress  

NASA Astrophysics Data System (ADS)

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

Liu, Hao; Tong, Hua; Xu, Ning

2014-11-01

236

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

E-print Network

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

Hao Liu; Hua Tong; Ning Xu

2015-02-03

237

Shear Stress Increases the Residence Time of Adhesion of Pseudomonas aeruginosa  

PubMed Central

Although ubiquitous, the processes by which bacteria colonize surfaces remain poorly understood. Here we report results for the influence of the wall shear stress on the early-stage adhesion of Pseudomonas aeruginosa PA14 on glass and polydimethylsiloxane surfaces. We use image analysis to measure the residence time of each adhering bacterium under flow. Our main finding is that, on either surface, the characteristic residence time of bacteria increases approximately linearly as the shear stress increases (?0–3.5 Pa). To investigate this phenomenon, we used mutant strains defective in surface organelles (type I pili, type IV pili, or the flagellum) or extracellular matrix production. Our results show that, although these bacterial surface features influence the frequency of adhesion events and the early-stage detachment probability, none of them is responsible for the trend in the shear-enhanced adhesion time. These observations bring what we believe are new insights into the mechanism of bacterial attachment in shear flows, and suggest a role for other intrinsic features of the cell surface, or a dynamic cell response to shear stress. PMID:21244830

Lecuyer, Sigolene; Rusconi, Roberto; Shen, Yi; Forsyth, Alison; Vlamakis, Hera; Kolter, Roberto; Stone, Howard A.

2011-01-01

238

Proteomic profiling of human bone marrow mesenchymal stem cells under shear stress.  

PubMed

Mesenchymal stem cells (MSCs) are promising seed cells for tissue engineering of blood vessels. As seed cells, MSCs must endure blood fluid shear stress after transplantation. It has been shown that fluid shear stress can regulate the proliferation and differentiation of MSCs. However, the effects of fluid shear stress on MSCs including the types of proteins modulated are still not well understood. In this study, we exposed human mesenchymal stem cells (HMSCs) to 3 dyn/cm(2) shear stress for 6 h and compared them to a control group using proteomic analysis. Thirteen specific proteins were affected by shear stress, 10 of which were up-regulated. Shear stress especially induced sustained increases in the expression of Annexin A2 and GAPDH, which have been specifically shown to affect HMSCs function. We present here the first comparative proteome analysis of effect of shear stress on HMSCs. PMID:20407807

Yi, Wei; Sun, Yang; Wei, Xufeng; Gu, Chunhu; Dong, Xiaochao; Kang, Xiaojun; Guo, Shuzhong; Dou, Kefeng

2010-08-01

239

CCM proteins control endothelial ?1 integrin dependent response to shear stress  

PubMed Central

ABSTRACT Hemodynamic shear stress from blood flow on the endothelium critically regulates vascular function in many physiological and pathological situations. Endothelial cells adapt to shear stress by remodeling their cytoskeletal components and subsequently by changing their shape and orientation. We demonstrate that ?1 integrin activation is critically controlled during the mechanoresponse of endothelial cells to shear stress. Indeed, we show that overexpression of the CCM complex, an inhibitor of ?1 integrin activation, blocks endothelial actin rearrangement and cell reorientation in response to shear stress similarly to ?1 integrin silencing. Conversely, depletion of CCM2 protein leads to an elongated “shear-stress-like” phenotype even in the absence of flow. Taken together, our findings reveal the existence of a balance between positive extracellular and negative intracellular signals, i.e. shear stress and CCM complex, for the control of ?1 integrin activation and subsequent adaptation of vascular endothelial cells to mechanostimulation by fluid shear stress. PMID:25432514

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

2014-01-01

240

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. PMID:22505638

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

2012-01-01

241

Mechanisms for three kinds of limiting shear stresses appearing in the traction modes of viscous, viscoelastic, and glassy states of lubricants  

NASA Astrophysics Data System (ADS)

We present that the tractional flow of a lubricant shows three kinds of limiting shear stresses at which the shear stresses take place independently of the shear rates in its viscous, viscoelastic, and glassy states. We propose three models on the mechanisms for the limiting shear stresses, based on the data of Brillouin spectra and viscosity of viscoelastic liquids previously reported by us and based on the data of the deformation of glassy polymers referred from others. The Brillouin spectra of a viscoelastic lubricant measured at up to 5 GPa at 25 and 80 °C show that we could not observe a frequency dispersion in sound waves below 0.8 GPa at 80 °C, while we can observe the frequency dispersion above 0.1 MPa at 25 °C owing to the viscosity of the lubricant. This result predicts the viscous limiting shear stress in the viscous state owing to the disappearance of meso-structures by heating and shearing under pressure. The viscosity of a polymer measured around the glass transition temperature (Tg) shows that Tg determined by the viscosity measurement is 27 K lower than that determined by calorimetry. This result predicts the elastic limiting shear stress in the viscoelastic state near the glass transition pressure (Pg) owing to the shear thinning effect by shearing a lubricant film. In addition, there is the plastic limiting shear stress in the glassy state owing to the yield stress at which the tractional flow of a glassy lubricant behaves as a plastic solid.

Kobayashi, H.; Fujita, Y.

2014-06-01

242

Turbulence wall-shear stress sensor for the atmospheric surface layer  

NASA Astrophysics Data System (ADS)

A new sensor is described for measuring the fluctuating component of the wall-shear stress in the atmospheric surface layer over relatively smooth uniform terrain. The sensor was tested at the Surface Layer Turbulence and Environmental Science Test (SLTEST) site on the western salt flats of Utah, giving the first ever direct measurements of this quantity in an atmospheric-scale flow. The device consists of a lightweight floating element whose position is detected using a spherical mirror which deflects a laser beam onto a duo-lateral position-sensing photodiode. The sensor has a frequency response of 25 Hz and a circular sensing area of 50 mm diameter, making it suitable for atmospheric-scale measurements. Preliminary cross-correlation of wall-shear stress and velocity, from simultaneously sampled sonic anemometers, indicates structure-inclination angles that are consistent with analogous laboratory-scale turbulent boundary-layer measurements.

Heuer, Weston D. C.; Marusic, Ivan

2005-08-01

243

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

USGS Publications Warehouse

In situ stress determinations in North America, southern Africa, and Australia indicate that on the average the maximum shear stress increases linearly with depth to at least 5.1 km measured in soft rock, such as shale and sandstone, and to 3.7 km in hard rock, including granite and quartzite. Regression lines fitted to the data yield gradients of 3.8 MPa/km and 6.6 MPa/km for soft and hard rock, respectively. Generally, the maximum shear stress in compressional states of stress for which the least principal stress is oriented near vertically is substantially greater than in extensional stress regimes, with the greatest principal stress in a vertical direction. The equations of equilibrium and compatibility can be used to provide functional constrains on the state of stress. If the stress is assumed to vary only with depth z in a given region, then all nonzero components must have the form A + Bz, where A and B are constants which generally differ for the various components. - Author

McGarr, A.

1980-01-01

244

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

NASA Technical Reports Server (NTRS)

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

Ho, Henjen

1991-01-01

245

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

PubMed Central

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

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

2015-01-01

246

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

USGS Publications Warehouse

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

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

1986-01-01

247

Effect of Fluid Shear Stress on Portal Vein Remodeling in a Rat Model of Portal Hypertension  

PubMed Central

Aims. To explore the effects and mechanisms of fluid shear stress on portal vein remodeling in a rat model of portal hypertension. Methods. Subcutaneous injections of CCl4 were given to establish a rat model of liver cirrhosis and portal hypertension. Biomechanical technology was adopted to determine the dynamic changes of haemodynamic indices and fluid shear stress. Nitric oxide (NO), synthase (NOS), and endothelin-1 (ET-1) of the portal vein blood were measured. Changes in geometric structure and ultrastructure of the portal vein were observed using optical and electron microscopy. Results. After the CC14 injections, rat haemodynamics were notably altered. From week 4 onwards, PVP, PVF, and PVR gradually and significantly increased (P < 0.05 versus baseline). The fluid shear stress declined from week 4 onwards (P < 0.01 versus control group). NO, NOS, and ET-1 increased after repeated CCI4 injections. Hematoxylin and eosin staining showed thickened portal vein walls, with increased inside and outside diameters. Electron microscopy revealed different degrees of endothelial cell degeneration, destruction of basement membrane integrity, proliferating, and hypertrophic smooth muscle cells. Conclusions. Fluid shear stress not only influenced the biomechanical environment of the portal vein but also participated in vascular remodeling.

Wen, Bin; Liang, Jian; Chen, Ran; Peng, Peichun

2015-01-01

248

The Polymer Stress Tensor in Turbulent Shear Flows  

E-print Network

The interaction of polymers with turbulent shear flows is examined. We focus on the structure of the elastic stress tensor, which is proportional to the polymer conformation tensor. We examine this object in turbulent flows of increasing complexity. First is isotropic turbulence, then anisotropic (but homogenous) shear turbulence and finally wall bounded turbulence. The main result of this paper is that for all these flows the polymer stress tensor attains a universal structure in the limit of large Deborah number $\\De\\gg 1$. We present analytic results for the suppression of the coil-stretch transition at large Deborah numbers. Above the transition the turbulent velocity fluctuations are strongly correlated with the polymer's elongation: there appear high-quality "hydro-elastic" waves in which turbulent kinetic energy turns into polymer potential energy and vice versa. These waves determine the trace of the elastic stress tensor but practically do not modify its universal structure. We demonstrate that the influence of the polymers on the balance of energy and momentum can be accurately described by an effective polymer viscosity that is proportional to to the cross-stream component of the elastic stress tensor. This component is smaller than the stream-wise component by a factor proportional to $\\De ^2 $. Finally we tie our results to wall bounded turbulence and clarify some puzzling facts observed in the problem of drag reduction by polymers.

Victor S. L'vov; Anna Pomyalov; Itamar Procaccia; Vasil Tiberkevich

2004-05-11

249

Wave Motion 43 (2005) 2028 Finite-amplitude shear wave in pre-stressed thin elastomers  

E-print Network

Wave Motion 43 (2005) 20­28 Finite-amplitude shear wave in pre-stressed thin elastomers Sia Nemat. Keywords: Finite-amplitude shear waves; Pre-stressed elastomers 1. Introduction Most polymers; accepted 5 May 2005 Available online 17 June 2005 Abstract We examine the elastic shear waves generated

Nemat-Nasser, Sia

250

Nature of stress accommodation in sheared granular material: Insights from 3D numerical modeling  

E-print Network

Nature of stress accommodation in sheared granular material: Insights from 3D numerical modeling distinct accumulations of granular wear material. During shear, this granular material accommodates stress the nature of contact force distributions during 3D granular shear. Our 3D discrete numerical models consist

Mair, Karen

251

Rheology of mustard paste: a controlled stress measurement  

Microsoft Academic Search

Controlled stress measurements on the rheological behaviour of mustard (whole seed, dehulled kernel and meal) pastes were conducted employing a concentric cylinder viscometer in the shear-stress range of 0–20 Pa. The moisture content of the paste was varied between 60% and 80% (dry basis). The different rheological parameters determined included yield stress, flow behaviour index, consistency index and apparent viscosity.

Suvendu Bhattacharya; N. Vasudha; K. S. Krishna Murthy

1999-01-01

252

Intermittent short-duration exposure to low wall shear stress induces intimal thickening in arteries exposed to chronic high shear stress  

Microsoft Academic Search

We sought to determine whether intermittent short-duration exposure to low wall shear stress could induce intimal thickening in arteries chronically exposed to high shear stress. An arteriovenous fistula (AVF) was created between the left common carotid artery and the corresponding external jugular vein in 20 Japanese white male rabbits. After 4 weeks, blood flow was increased 10-fold to 182 T

Hiroshi Nanjo; Eiketsu Sho; Masayo Komatsu; Mien Sho; Christopher K. Zarins; Hirotake Masuda

253

The effect of roughness elements on wind erosion: The importance of surface shear stress distribution  

NASA Astrophysics Data System (ADS)

Representation of surface roughness effects on aeolian sediment transport is a key source of uncertainty in wind erosion models. Drag partitioning schemes are used to account for roughness by scaling the soil entrainment threshold by the ratio of shear stress on roughness elements to that on the vegetated land surface. This approach does not explicitly account for the effects of roughness configuration, which may be important for sediment flux. Here we investigate the significance of roughness configuration for aeolian sediment transport, the ability of drag partitioning approaches to represent roughness configuration effects, and the implications for model accuracy. We use wind tunnel measurements of surface shear stress distributions to calculate sediment flux for a suite of roughness configurations, roughness densities, and wind velocities. Roughness configuration has a significant effect on sediment flux, influencing estimates by more than 1 order of magnitude. Measured and modeled drag partitioning approaches overestimate the predicted flux by 2 to 3 orders of magnitude. The drag partition is sensitive to roughness configuration, but current models cannot effectively represent this sensitivity. The effectiveness of drag partitioning approaches is also affected by estimates of the aerodynamic roughness height used to calculate wind shear velocity. Unless the roughness height is consistent with the drag partition, resulting fluxes can show physically implausible patterns. These results should make us question current assessments of the magnitude of vegetated dryland dust emissions. Representing roughness effects on surface shear stress distributions will reduce uncertainty in quantifying wind erosion, enabling better assessment of its impacts and management solutions.

Webb, Nicholas P.; Okin, Gregory S.; Brown, Shannon

2014-05-01

254

Rheology as a tool for measurement of sludge shear.  

PubMed

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

Ormeci, Banu

2008-01-01

255

Local Stress Relaxation and Shear-banding in a Dry Foam under Shear  

E-print Network

We have developed a realistic simulation of 2D dry foams under quasi-static shear. After a short transient, a shear-banding instability is observed. These results are compared with measurements obtained on real 2D (confined) foams. The numerical model allows us to exhibit the mechanical response of the material to a single plastication event. From the analysis of this elastic propagator, we propose a scenario for the onset and stability of the flow localization process in foams, which should remain valid for most athermal amorphous systems under creep flow.

Alexandre Kabla; Georges Debregeas

2003-06-30

256

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

SciTech Connect

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

Levashov, Valentin A [ORNL; Morris, James R [ORNL; Egami, Takeshi [ORNL

2011-01-01

257

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

258

Dynamic and shear stress rheological properties of guar galactomannans and its hydrolyzed derivatives.  

PubMed

Guar galactomannan from seed of Cyamopsis tetragonolobus was hydrolyzed using acid (HCl), base [Ba(OH)2] and enzyme (mannanase) method to obtain depolymerized substances with possible functional applications as soluble dietary fiber. Rheological behavior of crude, purified, and depolymerized guar gum solutions was studied at 25 °C, using shear stress and dynamic oscillatory measurements, performed with controlled stress rheometer Bohlin CVO (Malvern Instruments) fitted with cone-and-plate geometry. The various guar gums solutions with different viscosities exhibited shear-thinning behavior at high shear rate and Newtonian behavior at low shear rate. At low shear rate, sigma crude guar gum (SCGG), crude guar gum (CGG), acid hydrolyzed guar gum (AHGG) and enzyme hydrolyzed guar gum (EHGG) exhibited viscosities of 18.59, 1.346, 0.149 and 0.022 Pas, respectively. Oscillatory experiments (G", G') of gums solutions showed typical behavior of weak viscoelastic gel. All investigated guar gums were further used for glucose bio-accessibility using a novel in vitro small intestinal model (SIM). All gums solutions resulted in 20% reduction in simulated glucose absorption, indicating a non-significant functionality difference between various guar gums. So, it can be concluded that hydrolyzed guar gums without disturbing their rheological and physiological behavior would be useful for incorporation in various food products as soluble dietary fiber. PMID:25256551

Hussain, Majid; Bakalis, Serafim; Gouseti, Ourania; Zahoor, Tahir; Anjum, Faqir Muhammad; Shahid, Muhammad

2015-01-01

259

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

NASA Technical Reports Server (NTRS)

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.

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

2003-01-01

260

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

261

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

262

Discovered functions for Shear Stress and Pressure Drop of Linear Low Density Polyethylene Using Genetic programming  

E-print Network

Abstract: The estimation of the functions that describe the shear stress and the pressure drop across the short orifice die as a function of shear rate at different mean pressures for linear-low-density polyethylene copolymer (LLDPE) at 190oC is obtained using Genetic Programming (GP). The GP has been running based on experimental data in two cases; shear stress and pressure drop at different mean pressures to produce shear stress and pressure drop for each target mean pressure. The shear rate and mean pressure of linear-low-density polyethylene copolymer have been used as input variables to find the discovered functions. The experimental, calculated and predicted shear stress and pressure drop are compared. The discovered function shows a good match to the experimental data. We find that the GP technique is a good new mechanism of determination of the shear stress and the pressure drop linear-low-density polyethylene copolymer.

263

Modeling bed shear-stress fluctuations in a shallow tidal channel  

NASA Astrophysics Data System (ADS)

Recently, Mathis et al. (2013) developed a model for predicting the instantaneous fluctuations of the wall shear-stress in turbulent boundary layers. This model is based on an inner-outer scale interaction mechanism, incorporating superposition, and amplitude-modulation effects, and the only input required for the model is a time series measurement of the streamwise velocity signal taken in the logarithmic region of the flow. The present study applies this new approach for the first time to environmental flows, for which the near-bed information is typically inaccessible. The data used here are acoustic Doppler velocimeter time series measurements from a shallow tidal channel (Suisun Slough in North San Francisco Bay). We first extract segments of data sharing properties with canonical turbulent boundary layers. The wall (bed) shear-stress model is then applied to these selected data. Statistical and spectral analysis demonstrates that the field data predictions are consistent with laboratory and DNS results. The model is also applied to the whole available data set to demonstrate, even for situations far from the canonical boundary layer case, its ability to preserve the overall Reynolds number trend. The predicted instantaneous bed stress is highly skewed and amplitude modulated with the variations in the large-scale streamwise velocity. Finally, the model is compared to conventional methods employed to predict the bed shear-stress. A large disparity is observed, but the present model is the only one able to predict both the correct spectral content and the probability density function.

Mathis, R.; Marusic, I.; Cabrit, O.; Jones, N. L.; Ivey, G. N.

2014-05-01

264

Stress induced shear wave splitting in Volcanic Regions: Observations and Modelling of Mt. Asama, Japan  

NASA Astrophysics Data System (ADS)

Active volcanoes are dynamic systems that perturb the regional stress field in which they exist, by manner of both the weight of the volume of the mountain and the movement of large masses of magma under pressure. The resulting change in the crustal stress field is hypothesized to affect its seismic properties; in particular the degree and orientation of shear wave birefringence. Initial work into furthering the understanding of the link between volcanism-induced crustal stress and shear wave splitting is presented here. The focus of research is on the 2004 and 2008 eruptions of Mt. Asama in Japan. Previous work has shown that a roughly E-W trending dike, with 0.8m of opening, accompanied the 2004 eruption. This deformation has been modelled with finite element methods and we will constrain the surface deformation with existing GPS data. Methods to model the effects of the resultant stress field on shear wave splitting are laid out, and splitting measurements from earthquake data collected over the 2008 eruption are also presented, continuing on from previous work by Savage et al. [2010]. Preliminary measurements show changes in splitting fast direction at a few stations that coincide with GPS baselines and eruption times in 2008, but the relations are not as straightforward as they were for the larger 2004 eruptions.

Shelley, A. F.; Savage, M. K.; Williams, C. A.; Aoki, Y.

2011-12-01

265

Shear measurements across the northern margin of Whillans Ice Stream  

E-print Network

?6 km from the interstream ridge into the shear margin were installed in November 1997 and resurveyed in January 2000, using GPS methods. A band of arcuate crevasses form where the surficial shear stress reaches ?130 kPa, and a chaotic zone...

van der Veen, Cornelis J.; Jezek, K.; Stearns, Leigh

2007-01-01

266

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

PubMed Central

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

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

2015-01-01

267

Transient Shear Banding in a Simple Yield Stress Fluid Thibaut Divoux,1  

E-print Network

Transient Shear Banding in a Simple Yield Stress Fluid Thibaut Divoux,1 David Tamarii,1 Catherine observed at low shear rates. PACS numbers: 83.60.La, 83.50.Ax, 83.50.Rp Yield stress fluids (YSF) encompass of experimental data which demonstrates that a simple yield stress fluid, i.e. which does not present aging

Paris-Sud XI, Université de

268

Shear induced drainage in foamy yield-stress fluids J. Goyon1,2,*  

E-print Network

1 Shear induced drainage in foamy yield-stress fluids J. Goyon1,2,* , F. Bertrand1 , O. Pitois2 Paris Est, Laboratoire LPMDI, Marne la Vallée, France Abstract: Shear induced drainage of a foamy yield stress fluid is investigated using MRI techniques. Whereas the yield stress of the interstitial fluid

Paris-Sud XI, Université de

269

Transient Shear Banding in a Simple Yield Stress Fluid Thibaut Divoux,1  

E-print Network

Transient Shear Banding in a Simple Yield Stress Fluid Thibaut Divoux,1 David Tamarii,1 Catherine for the ultraslow stress relaxation observed at low shear rates. DOI: 10.1103/PhysRevLett.104.208301 PACS numbers report a large set of experimental data which demonstrates that a simple yield stress fluid, i.e., which

Weeks, Eric R.

270

First normal stress difference and crystallization in a dense sheared granular fluid  

E-print Network

First normal stress difference and crystallization in a dense sheared granular fluid Meheboob Alam (August 28, 2002) The first normal stress difference (N1) and the microstructure in a dense sheared granular fluid are probed using event-driven simulations. N1 is known to be positive (if the stress

Luding, Stefan

271

Evolution of the wall shear stresses during the progressive enlargement of symmetric Abdominal  

E-print Network

29 Chapter 3 Evolution of the wall shear stresses during the progressive enlargement of symmetric stresses acting on the vessel wall. Any structural or conformational wall change has an influence result in altered pressure and wall shear stresses (WSS) and may lead to wall inflammation, thrombus

272

Induction of human vascular endothelial stress fibres by fluid shear stress  

Microsoft Academic Search

Endothelial cells of the arterial vascular system and the heart contain straight actin filament bundles, of which there are few, if any, in the venous endothelium1-4. Since stress fibre-containing endothelial cells within the vascular system tend to be located at sites exposed to particularly high shear stress of blood flow, we have investigated, in an experimental rheological system (Fig. 1),

R.-P. Franke; M. Gräfe; H. Schnittler; D. Seiffge; C. Mittermayer; D. Drenckhahn

1984-01-01

273

On the stress distribution in a thin rectangular plate subjected to shear  

E-print Network

ON TIIE STRESS DISTRIBUTION IN A TKfS RECTANGULAR PLATE SUBJECTED TO SHEAR A Theseus Darol Diane Travis Approved as to Style and Contents C'natrmm of ~ttee IIead of Depar ent J4xgust~ 1953 i Themis Sulmitted to the Graduate Schoo1... for Photoelas- tistically Determining a Shear Stress Dis- tribution in a Plate Subjected to Shear . . ~ . . 1'p Coker~s Final Setup for Photoelastisti- cally-Determining a Shear Stress Distri- bution in a Plate Subjected to Shear Plot (" Depth of Specimen...

Travis, Darol Duane

1953-01-01

274

Two-Axis Direct Fluid Shear Stress Sensor for Aerodynamic Applications  

NASA Technical Reports Server (NTRS)

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

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

2011-01-01

275

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

276

A wafer-bonded floating-element shear stress microsensor with optical position sensing by photodiodes  

Microsoft Academic Search

This paper discusses a noninvasive sensing technique for the direct measurement of low-magnitude shear stresses in laminar and turbulent air flows. The sensing scheme detects the flow-induced in-plane displacement of a microfabricated floating-element structure (500 ?m×500 ?m×7 ?m), using integrated photodiodes. The wall-mounted floating-element sensors were fabricated using a wafer-bonding technology. The sensors were calibrated in a custom-designed laminar flow

Aravind Padmanabhan; Howard Goldberg; Kenneth D. Breuer; Martin A. Schmidt

1996-01-01

277

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

NASA Technical Reports Server (NTRS)

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

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

1984-01-01

278

Shear stress modulates the thickness and architecture of Candida albicans biofilms in a phase-dependent manner  

PubMed Central

Summary Biofilm formation plays an integral role in catheter-associated bloodstream infections caused by Candida albicans. Biofilms formed on catheters placed intravenously are exposed to shear stress caused by blood flow. In this study, we investigated whether shear stress affects the ability of C. albicans to form biofilms. Candida biofilms were formed on catheter discs and exposed to physiological levels of shear stress using a rotating disc system (RDS). Control biofilms were grown under conditions of no flow. Tetrazolium (XTT) assay and dry weight (DW) measurements were used to quantify metabolic activity and biofilm mass respectively. Confocal scanning laser microscopy (CSLM) was used to evaluate architecture and biofilm thickness. After 90 min, cells attached under no-flow exhibited significantly greater XTT activity and DW than those under shear. However, by 24 h, biofilms formed under both conditions had similar XTT activities and DW. Interestingly, thickness of biofilms formed under no-flow was significantly greater after 24 h than of those formed under shear stress, demonstrating that shear exposure results in thinner, but denser biofilms. These studies suggest that biofilm architecture is modulated by shear in a phase-dependent manner. PMID:19076284

Mukherjee, Pranab K.; Chand, David V.; Chandra, Jyotsna; Anderson, James M.; Ghannoum, Mahmoud A.

2010-01-01

279

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

NASA Technical Reports Server (NTRS)

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

Srinivas, S.

1975-01-01

280

A review of Reynolds stress models for turbulent shear flows  

NASA Technical Reports Server (NTRS)

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

Speziale, Charles G.

1995-01-01

281

[The effect of shear stress and flow pattern on proliferation of vascular endothelial cells].  

PubMed

The non-random distribution of atherosclerosis was related to local hemodynamic environment. The stabilization of endothelium was important in this process. We studied the effect of magnitude of shear stress on proliferation of endothelial cells. It was shown the proliferation of endothelial cells was inhibited by shear stress, and was related to the magnitude of shear stress. A parallel plate sudden-expansion flow chamber was constructed, and the effect of flow pattern was also studied. It was shown the inhibition effect produced by shear stress was decreased in this chamber. PMID:14565004

Hu, Jiang; Hu, Jia; Gao, Yuxin; Li, Tao; Tao, Zulai

2003-09-01

282

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

PubMed Central

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

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

2014-01-01

283

Laminar shear stress promotes endothelial cell migration and inhibits cell apoptosis in the presence of hydroxyurea.  

PubMed

Cell migration plays important roles in both physiological and pathological processes. Recent studies have shown that hydroxyurea, which is an anti-proliferative inhibitor, can affect cell morphology and specific gene expression of endothelial cells (ECs). In vivo, the functions of ECs are modulated by shear stress. It is well known that shear stress can have effects on EC migration by affecting cell morphology, cytoskeletal arrangement and cell-cell junction, and activating mechanosensors, inducing the changes of signaling pathways, and then increasing or decreasing the expression of gene and protein. However, the influences of hydroxyurea on EC function under shear stress are still unclear. In present study, we investigated the effects of hydroxyurea on EC proliferation, apoptosis and migration under laminar shear stress. The results showed that hydroxyurea prevented growth of ECs in a dose-dependent manner. Hydroxyurea at 2 mM completely inhibited the proliferation of ECs. The results also demonstrated that hydroxyurea induced EC apoptosis, but it was inhibited by 15.27 dyn/cm2 laminar shear stress. Furthermore, shear stress induced cell migration in the presence of hydroxyurea. Therefore, 2 mM hydroxyurea, which completely inhibited the proliferation of HUVECs, could be used to eliminate any confounding effect of shear stress on proliferation in shear stress-induced cell migration. These results also do confirm that shear stress plays important roles in achieving and maintaining the stabilization of ECs. PMID:21791174

Zeng, Y; Liu, X H; Shen, Y; Lai, Y; Liu, X J

2011-01-01

284

Bed Forms Modulating Temporal Peaks on Near-Bank Shear Stresses, the Wabash River Case  

NASA Astrophysics Data System (ADS)

There is a great body of experimental work showing how bed forms modulate bed roughness, flow field structure, and sediment transport rates in straight flumes. Recently, it was observed that migrating bed forms produce temporal and spatial peaks of shear stresses along the outer bank of an experimental meandering channel. These stresses are about 50% larger than the shear stresses exerted by the mean near-bank flow. As fluvial erosion bank erosion rates are typically linearly related to applied shear stress, the migration rate of the bend may be significantly increased. However, this hypothesis has never been tested in the field, where bed forms could be more complex than those found in experimental cases. Herein, only fluvial erosion is considered, while geotechnical processes occurring at the outer bank are not accounted for. Detailed measurements of hydrodynamics (using acoustic Doppler profiler), bed morphology (using multibeam and RTK GPS) and bank morphology (using laser scanner) were conducted at two bends on the Wabash River along the Illinois and Indiana Stateline. The bed morphology exhibited different scales of bed forms, ranging from dunes to ripples. Using Wavelet analysis to discriminate the bed morphology it was possible to separate the ripples and dunes structures resulting in a bed without bed forms, which shows the typical erosion (outer bank)/deposition (inner bank) arrangement in meandering channels. Using a fully three-dimensional Reynolds-Averaged Navier-Stokes (RANS) numerical model, two cases are simulated: [1] bend with bed forms, and [2] bend without bed forms to test the above hypothesis. The results show that the three-dimensional flow field is compares well to that observed for both scenarios. Further, peaks in shear stresses along the outer bank are indeed observed, which are correlated to the location of the bed forms with respect to the bend. Further conclusion and its importance for long-term morphodynamics of meandering channels are described.

Abad, J. D.; Frias, C. E.; Langendoen, E. J.; Best, J.; Rhoads, B. L.; Konsoer, K. M.; Garcia, M. H.

2013-12-01

285

Analysis of fluid flow and wall shear stress patterns inside partially filled agitated culture well plates.  

PubMed

The appearance of highly resistant bacterial biofilms in both community and hospitals environments is a major challenge in modern clinical medicine. The biofilm structural morphology, believed to be an important factor affecting the behavioral properties of these "super bugs", is strongly influenced by the local hydrodynamics over the microcolonies. Despite the common use of agitated well plates in the biology community, they have been used rather blindly without knowing the flow characteristics and influence of the rotational speed and fluid volume in these containers. The main purpose of this study is to characterize the flow in these high-throughput devices to link local hydrodynamics to observed behavior in cell cultures. In this work, the flow and wall shear stress distribution in six-well culture plates under planar orbital translation is simulated using Computational Fluid Dynamics (CFD). Free surface, flow pattern and wall shear stress for two shaker speeds (100 and 200 rpm) and two volumes of fluid (2 and 4 mL) were investigated. Measurements with a non-intrusive optical shear stress sensor and High Frame-rate Particle Imaging Velocimetry (HFPIV) are used to validate CFD predictions. An analytical model to predict the free surface shape is proposed. Results show a complex three-dimensional flow pattern, varying in both time and space. The distribution of wall shear stress in these culture plates has been related to the topology of flow. This understanding helps explain observed endothelial cell orientation and bacterial biofilm distributions observed in culture dishes. The results suggest that the mean surface stress field is insufficient to capture the underlying dynamics mitigating biological processes. PMID:22042624

Salek, M Mehdi; Sattari, Pooria; Martinuzzi, Robert J

2012-03-01

286

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. PMID:19876820

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

2009-01-01

287

Shear strength and stress distribution in wet granular media  

NASA Astrophysics Data System (ADS)

We investigate the shear strength and stress distribution properties of wet granular media in the pendular state where the liquid is mainly in the form of capillary bonds between particles. This work is based on a 3D discrete-element approach (molecular dynamics) with spherical particles enriched by a capillary force law. We show that the capillary force can be expressed as an explicit function of the gap and volume of the liquid bridge. The length scales involved in this expression are analyzed by comparing with direct integration of the Laplace-Young equation. In the simulations, we consider a maximum number density of liquid bonds in the bulk in agreement with equilibrium of each liquid bridge. This liquid bond number is a decisive parameter for the overall cohesion of wet granular materials. It is shown that the shear strength can be expressed as a function of liquid bond characteristics. The expression proposed initially by Rumpf is thus generalized to account for size polydispersity We show that this expression is in good agreement with our experimental data that will be briefly described. At low confining stress, the tensile action of capillary bonds induces a self-stressed particle network organized in a bi-percolating structure of positive and negative particle pressures. Various statistical descriptors of the microstructure and bond force network are used to characterize this partition. Two basic properties emerge: (i) The highest particle pressure is located in the bulk of each phase (positive and negative particle pressures); (ii) The lowest pressure level occurs at the interface between the two phases, involving also the largest connectivity of the particles via tensile and compressive bonds.

Richefeu, Vincent; Radjaï, Farhang; El Youssoufi, Moulay Saïd

2009-06-01

288

XIAP is essential for shear stress-enhanced Tyr-576 phosphorylation of FAK  

SciTech Connect

Research highlights: {yields} Laminar shear stress phosphorylates Tyr-576 in FAK. {yields} XIAP is essential for shear stress-induced phosphorylation of Tyr-576. {yields} XIAP knockdown induces shear stress-triggered translocation of FAK into nucleus. {yields} XIAP regulates ERK activation by maintaining the Src-accessible location of FAK. -- Abstract: In endothelial cells, X-chromosome linked inhibitor of apoptosis protein (XIAP) regulates cell survival, migration and adhesion. We have recently found that XIAP recruits focal adhesion kinase (FAK) into integrin-associated focal adhesions, controlling cell migration. However, little is understood about the molecular mechanisms by which FAK modulation is controlled by XIAP. In this study, we show that XIAP modulates FAK activity through the control of FAK phosphorylation. In bovine aortic endothelial cells (BAEC), phosphorylation of Tyr-576 in FAK is elevated by laminar shear stress. This elevated phosphorylation appears to be responsible for shear stress-stimulated ERK activation. We found that XIAP knockdown reduces shear stress-enhanced phosphorylation of Tyr-576 and induces shear stress-triggered translocation of FAK into nucleus. Nuclear translocation of FAK reduces contact between FAK and Src, a kinase which phosphorylates Tyr-576. This spatial segregation of FAK from Src decreases Tyr-576 phosphorylation and thus shear-stimulated ERK activation. Taken together, our results demonstrate that XIAP plays a key role in shear stress-stimulated ERK activation by maintaining the Src-accessible location of FAK.

Ahn, Sunyoung [Department of Molecular Biology and Institute of Nanosensor and Biotechnology, BK21 Graduate Program for RNA Biology, Dankook Univiersity, 126, Jukjeon-dong, Suji-gu, Yongin-si, Gyeonggi-do, 448-701 (Korea, Republic of)] [Department of Molecular Biology and Institute of Nanosensor and Biotechnology, BK21 Graduate Program for RNA Biology, Dankook Univiersity, 126, Jukjeon-dong, Suji-gu, Yongin-si, Gyeonggi-do, 448-701 (Korea, Republic of); Park, Heonyong, E-mail: heonyong@dankook.ac.kr [Department of Molecular Biology and Institute of Nanosensor and Biotechnology, BK21 Graduate Program for RNA Biology, Dankook Univiersity, 126, Jukjeon-dong, Suji-gu, Yongin-si, Gyeonggi-do, 448-701 (Korea, Republic of)] [Department of Molecular Biology and Institute of Nanosensor and Biotechnology, BK21 Graduate Program for RNA Biology, Dankook Univiersity, 126, Jukjeon-dong, Suji-gu, Yongin-si, Gyeonggi-do, 448-701 (Korea, Republic of)

2010-08-20

289

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

NASA Technical Reports Server (NTRS)

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

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

2001-01-01

290

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

291

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

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

292

Shear stress effects on plant cell suspension cultures in a rotating wall vessel bioreactor  

Microsoft Academic Search

  A rotating wall vessel, designed for growth of mammalian cells under microgravity, was used to study shear effects on Taxus cuspidata plant suspension cell cultures. Shear stress, as quantified by defined shear fields of Couette viscometers, improved specific\\u000a cell growth rates and was detrimental to volumetric product formation rates.

X Sun; J C Linden

1999-01-01

293

Evaluation of Shear-Induced Platelet Activation Models Under Constant and Dynamic Shear Stress Loading Conditions Relevant to Devices  

PubMed Central

The advent of implantable blood-recirculating devices such as left ventricular assist devices and prosthetic heart valves provides a viable therapy for patients with end-stage heart failure and valvular disease. However, device-generated pathological flow patterns result in thromboembolic complications that require complex and lifelong anticoagulant therapy, which entails hemorrhagic risks and is not appropriate for certain patients. Optimizing the thrombogenic performance of such devices utilizing numerical simulations requires the development of predictive platelet activation models that account for variations in shear-loading rates characterizing blood flow through such devices. Platelets were exposed in vitro to both dynamic and constant shear stress conditions emulating those found in blood-recirculating devices in order to determine their shear-induced activation and sensitization response. Both these behaviors were found to be dependent on the shear loading rates, in addition to shear stress magnitude and exposure time. We then critically examined several current models and evaluated their predictive capabilities using these results. Shear loading rate terms were then included to account for dynamic aspects that are either ignored or partially considered by these models, and model parameters were optimized. Independent optimization for each of the two types of shear stress exposure conditions tested resulted in different sets of best-fit constants, indicating that universal optimization may not be possible. Inherent limitations of the current models require a paradigm shift from these integral-based discretized power law models to better address the dynamic conditions encountered in blood-recirculating devices. PMID:23400312

Sheriff, Jawaad; Soares, João Silva; Xenos, Michalis; Jesty, Jolyon; Bluestein, Danny

2013-01-01

294

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

E-print Network

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

Toker, Nabi Kartal, 1979-

2007-01-01

295

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

SciTech Connect

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

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

1999-07-01

296

Shear stress-induced von Willebrand factor binding to platelet glycoprotein Ib initiates calcium influx associated with aggregation.  

PubMed

Platelets subjected to elevated levels of fluid shear stress in the absence of exogenous agonists will aggregate. Shear stress-induced aggregation requires von Willebrand factor (vWF) multimers, extracellular calcium (Ca2+), adenosine diphosphate (ADP), and platelet membrane glycoprotein (GP)Ib and GPIIb-IIIa. The sequence of interaction of vWF multimers with platelet surface receptors and the effect of these interactions on platelet activation have not been determined. To elucidate the mechanism of shear stress-induced platelet aggregation, suspensions of washed platelets were subjected to different levels of uniform shear stress (15 to 120 dyne/cm2) in an optically modified cone and plate viscometer. Cytoplasmic ionized calcium ([Ca2+]i) and aggregation of platelets were monitored simultaneously during the application of shear stress; [Ca2+]i was measured using indo-1 loaded platelets and aggregation was measured as changes in light transmission. Basal [Ca2+]i was approximately 60 to 100 nmol/L. An increase of [Ca2+]i (up to greater than 1,000 nmol/L) was accompanied by synchronous aggregation, and both responses were dependent on the shear force and the presence of vWF multimers. EGTA chelation of extracellular Ca2+ completely inhibited vWF-mediated [Ca2+]i and aggregation responses to shear stress. Aurin tricarboxylic acid, which blocks the GPIb recognition site on the vWF monomer, and 6D1, a monoclonal antibody to GPIb, also completely inhibited platelet responses to shear stress. The tetrapeptide RGDS and the monoclonal antibody 10E5, which inhibit vWF binding to GPIIb-IIIa, partially inhibited shear stress-induced [Ca2+]i and aggregation responses. The combination of creatine phosphate/creatine phosphokinase, which converts ADP to adenosine triphosphate and blocks the effect of ADP released from stimulated platelets, inhibited shear stress-induced platelet aggregation without affecting the increase of [Ca2+]i. Neither the [Ca2+]i nor aggregation response to shear stress was inhibited by blocking platelet cyclooxygenase metabolism with acetylsalicylic acid. These results indicate that GPIb and extracellular Ca2+ are absolutely required for vWF-mediated [Ca2+]i and aggregation responses to imposed shear stress, and that the interaction of vWF multimers with GPIIb-IIIa potentiates these responses. Shear stress-induced elevation of platelet [Ca2+]i, but not aggregation, is independent of the effects of release ADP, and both responses occur independently of platelet cyclooxygenase metabolism. These results suggest that shear stress induces the binding of vWF multimers to platelet GPIb and this vWF-GPIb interaction causes an increase of [Ca2+]i and platelet aggregation, both of which are potentiated by vWF binding to the platelet GPIIb-IIIa complex. PMID:1611079

Chow, T W; Hellums, J D; Moake, J L; Kroll, M H

1992-07-01

297

Influence of the shear stress applied during the flow stoppage and the rest on the mechanical properties of thixotropic suspensions  

E-print Network

Influence of the shear stress applied during the flow stoppage and the rest on the mechanical suspensions as a function of the shear stress history applied during their flow stoppage and their aging in their solid state. We show that their elastic modulus and yield stress depend strongly on the shear stress

Paris-Sud XI, Université de

298

JOURNAL OF GEOPHYSICAL RESEARCH, VOL. ???, XXXX, DOI:10.1029/, Fast approximation of bed shear stress in oscillatory1  

E-print Network

: FAST APPROXIMATION OF BED SHEAR STRESS Abstract. Studies of bedform evolution require an understanding variation in the stresses exerted by fluid flow, particularly the5 bed shear stress. Evaluating for approximating bed shear stresses via10 a generic linear but non-local model, and show that for oscillatory flow

Perron, Taylor

299

Intermittent short-duration exposure to low wall shear stress induces intimal thickening in arteries exposed to chronic high shear stress  

Microsoft Academic Search

We sought to determine whether intermittent short-duration exposure to low wall shear stress could induce intimal thickening in arteries chronically exposed to high shear stress. An arteriovenous fistula (AVF) was created between the left common carotid artery and the corresponding external jugular vein in 20 Japanese white male rabbits. After 4 weeks, blood flow was increased 10-fold to 182 ± 39 ml\\/min

Hiroshi Nanjo; Eiketsu Sho; Masayo Komatsu; Mien Sho; Christopher K. Zarins; Hirotake Masuda

2006-01-01

300

Observations of wave shear stress on a steep beach  

NASA Astrophysics Data System (ADS)

Observations are presented of the wave shear stress on a steeply sloping beach. Above the wave boundary layer (WBL), positive values of were observed and are attributed to a combination of both wave shoaling due to the large-scale bed slope, and dissipation due to wave breaking, in agreement with the wave theory of Zou et al. (2003). Within the WBL, observed vertical profiles of were also in good agreement with theory, in cases where the wave height was small. As wave heights increased, however, the WBL profile of generally did not agree with theory. Near-simultaneous rotary sonar observations of the bed suggest the disagreement with theory was due to the presence of orbital-scale ripples, which the present theory does not accommodate.

Wilson, G. W.; Hay, A. E.; Bowen, A. J.

2014-11-01

301

Wrinkling Phenomena of Thin Flat Plates Subjected to Shear Stresses  

NASA Technical Reports Server (NTRS)

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

Bollenrath, F

1931-01-01

302

Shear stress in arterial stenoses: a momentum integral model.  

PubMed

A mathematical model is developed to investigate blood flow in arterial stenoses up to Reynolds numbers of 1000. The approach is based on Thwaites' method, normally used to treat laminar boundary layer development over a body in a freestream. The model is applicable to any axisymmetric stenosis geometry in all laminar physiological flow regimes, has a minimum of externally input parameters and is implemented as a short program on a personal computer. Maximum bounds on the expected errors are derived by comparison with known results from Poiseuille flow in a pipe. Agreement with shear stresses reported by other researchers using computational fluid dynamics is within 13% rms. The method has been specifically designed to be a useful predictive tool for biomedical investigators. PMID:9880062

Reese, J M; Thompson, D S

1998-11-01

303

Flow Instability and Wall Shear Stress Ocillation in Intracranial Aneurysms  

NASA Astrophysics Data System (ADS)

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

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

2009-11-01

304

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

NASA Technical Reports Server (NTRS)

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

Bair, S.; Winer, W. O.

1980-01-01

305

Forced free-shear layer measurements  

NASA Technical Reports Server (NTRS)

Detailed three-dimensional three-component phase averaged measurements of the spanwise and streamwise vorticity formation and evolution in acoustically forced plane free-shear flows have been obtained. For the first time, phase-averaged measurements of all three velocity components have been obtained in both a mixing layer and a wake on three-dimensional grids, yielding the spanwise and streamwise vorticity distributions without invoking Taylor's hypothesis. Initially, two-frequency forcing was used to phase-lock the roll-up and first pairing of the spanwise vortical structures in a plane mixing layer. The objective of this study was to measure the near-field vortical structure morphology in a mixing layer with 'natural' laminar initial boundary layers. For the second experiment the second and third subharmonics of the fundamental roll-up frequency were added to the previous two-frequency forcing in order to phase-lock the roll-up and first three pairings of the spanwise rollers in the mixing layer. The objective of this study was to determine the details of spanwise scale changes observed in previous time-averaged measurements and flow visualization of unforced mixing layers. For the final experiment, single-frequency forcing was used to phase-lock the Karman vortex street in a plane wake developing from nominally two-dimensional laminar initial boundary layers. The objective of this study was to compare measurements of the three-dimensional structure in a wake developing from 'natural' initial boundary layers to existing models of wake vortical structure.

Leboeuf, Richard L.

1994-01-01

306

Polyethylene terephthalate membrane grafted with peptidomimetics: endothelial cell compatibility and retention under shear stress.  

PubMed

The present work aimed to treat a polyethylene terephthalate (PET) surface to make the biomaterial more 'attractive' in terms of attachment and shear stress response to endothelial cells with a view to possible applications in vascular grafting. A surface wet-chemistry protocol was applied to graft track-etched PET membranes with RGD peptidomimetics based on the tyrosine template and active at the nano-level vs. isolated human ?v?3 receptor, which was monitored by X-ray photoelectron spectroscopy, contact angle measurement and atomic force microscopy for characterization. A primary culture of human saphenous vein endothelial cells was used before and after sterilization of the membranes (heat treatment or ?-ray irradiation) to test the benefit of grafting. The optimal surface concentrations of grafted molecules were around 50?pmol/cm². Compared to GRGDS, the peptidomimetics promoted cell attachment with similar or slightly better performances. Endothelialized grafted supports were further exposed to 2?h of shear stress mimicking arterial conditions. Cells were lost on non-grafted PET whereas cells on grafted polymers sterilized by ?-ray irradiation withstood forces with no significant difference in focal contacts. At the mRNA level, cells on functionalized PET were able to respond to shear stress with NFkB upregulation. Thus, grafting of peptidomimetics as ligands of the ?v?3 integrin could be a relevant strategy to improve the adhesion of human endothelial cells and to obtain an efficient endothelialized PET for the surgery of small-diameter vascular prostheses. PMID:23565647

Rémy, Murielle; Bareille, Reine; Rerat, Vincent; Bourget, Chantal; Marchand-Brynaert, Jacqueline; Bordenave, Laurence

2013-01-01

307

The effect of turbulent viscous shear stress on red blood cell hemolysis.  

PubMed

Non-physiologic turbulent flow occurs in medical cardiovascular devices resulting in hemodynamic stresses that may damage red blood cells (RBC) and cause hemolysis. Hemolysis was previously thought to result from Reynolds shear stress (RSS) in turbulent flows. A more recent hypothesis suggests that turbulent viscous shear stresses (TVSS) at spatial scales similar in size to RBCs are related to their damage. We applied two-dimensional digital particle image velocimetry to measure the flow field of a free-submerged axisymmetric jet that was utilized to hemolyze porcine RBCs in selected locations. Assuming a dynamic equilibrium for the sub-grid scale (SGS) energy flux between the resolved and the sub-grid scales, the SGS energy flux was calculated from the strain rate tensor computed from the resolved velocity fields. The SGS stress was determined by the Smagorinsky model, from which the turbulence dissipation rate and then TVSS were estimated. Our results showed the hemolytic threshold of the Reynolds stresses was up to 517 Pa, and the TVSSs were at least an order of magnitude less than the RSS. The results provide further insight into the relationship between turbulence and RBC damage. PMID:24619800

Yen, Jen-Hong; Chen, Sheng-Fu; Chern, Ming-Kai; Lu, Po-Chien

2014-06-01

308

Shear stress partitioning of overland flow on disturbed and undisturbed rangelands  

Technology Transfer Automated Retrieval System (TEKTRAN)

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

309

Nonlinear stress and fluctuation dynamics of sheared disordered wet foam Ethan Pratt and Michael Dennin  

E-print Network

Nonlinear stress and fluctuation dynamics of sheared disordered wet foam Ethan Pratt and Michael of California at Irvine, Irvine, Ca 92697 (Dated: January 12, 2003) Sheared wet foam, which stores elastic energy in bubble deformations, relaxes stress through bubble rearrangements. The intermittency of bubble

Dennin, Michael

310

Shear stress partitioning of overland flow on disturbed and undisturbed rangelands  

Technology Transfer Automated Retrieval System (TEKTRAN)

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

311

Basal shear stress of the Ross ice streams from control method Ian Joughin1  

E-print Network

motion of the Ross ice streams (Ice Streams A, B, C, D, E, and F, also called Mercer, Whillans, KambBasal shear stress of the Ross ice streams from control method inversions Ian Joughin1 Jet inversions to determine the basal shear stress beneath the Ross ice streams where new high

Boyce, C. Kevin

312

The role of death-associated protein kinase (DAPK) in endothelial apoptosis under fluid shear stress.  

PubMed

Endothelial cells are the interface between hemodynamic fluid flow and vascular tissue contact. They actively translate physical and chemical stimuli into intracellular signaling cascades which in turn regulate cell function, and endothelial dysfunction leads to inflammation and diseased conditions. For example, atherosclerosis, a chronic vascular disease, favorably develops in regions of disturbed fluid flow and low shear stress. Apoptosis, or programmed cell death, must be properly regulated to maintain homeostasis in the vascular wall. The loss of apoptosis control, as seen in low shear stress regions, is implicated in various diseases such as atherosclerosis and cancer. Death-associated protein kinase (DAPK) is a pro-apoptotic regulator for various cell types that is localized in the cell cytoskeleton and regulates changes in cytoplasm associated with apoptosis. Yet its role in endothelial cells remains unclear. Laminar shear stress inhibits cytokine, oxidative stress, and serum starvation induced endothelial apoptosis, while extended shearing elicit structural changes and cell alignment. We hypothesize that DAPK potentially plays a role in attenuating endothelial apoptosis in response to shear stress. We found that shear stress regulates DAPK expression and apoptotic activity in endothelial cells. In fact, shear stress alone induces DAPK and apoptosis, but has the opposite effect in the presence of apoptotic triggers such as tissue necrosis factor ? (TNF?). This review summarizes mechanisms of endothelial mechanotransduction and apoptosis, and explores the potential of DAPK as a novel signaling pathway involved in mediating protective effects of shear stress on the vasculature. PMID:23806751

Rennier, Keith; Ji, Julie Y

2013-08-14

313

Effects of the loss of symmetry on the wall shear stresses in Abdominal Aortic Aneurysms  

E-print Network

the method described in Chapter 2. C. Results 1. Flow characteristics in abdominal aortic aneurysms Flow75 Chapter 4 Effects of the loss of symmetry on the wall shear stresses in Abdominal Aortic Aneurysms A. Introduction Owing to their effect on the endothelial cells, wall shear stresses appear

314

Wall shear stress and endothelial cells dysfunction in the context of abdominal aortic aneurysms  

E-print Network

Wall shear stress and endothelial cells dysfunction in the context of abdominal aortic aneurysms Z7342,13384 Marseille Keywords: wall shear stress, abdominal aortic aneurysm, endothelial cells, mechanotransduction 1. Introduction The formation of aneurysm of abdominal aorta (AAA), is a multi

Paris-Sud XI, Université de

315

Modelling the shear strength of soils in the general stress space  

Microsoft Academic Search

The shear strength of loose soils and soils which have reached critical state is not significantly affected by the value of the intermediate principal stress and can therefore be approximated sufficiently by the Mohr–Coulomb hexagon in the deviatoric plane. The Mohr–Coulomb hexagon, however, tends to underestimate the peak shear strength of dense soils for any stress state other than triaxial

Konstantinos Georgiadis; D. M Potts; L Zdravkovic

2004-01-01

316

INTERPRETATION OF UNDRAINED SHEAR STRENGTH OF UNSATURATED SOILS IN TERMS OF STRESS STATE VARIABLES  

Microsoft Academic Search

The unsaturated soil, shear strength theory can be used to interpret the meaning of undrained shear strength in terms of two stress state variables, net normal stress, (? - ua) and matric suction, (ua - uw), assuming both linear and nonlinear failure envelopes with respect to matric suction. The interpretation of the theory is applied to the test results from

S. K. Vanapalli; D. G. Fredlund

317

Predicting boundary shear stress and sediment transport over bed forms  

USGS Publications Warehouse

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

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

1999-01-01

318

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

Microsoft Academic Search

The critical resolved shear stress to transmit a screw dislocation through a non-slipping (welded) bimaterial interface is\\u000a studied as a function of the elastic mismatch across the interface and the nonlinear shear stress-relative shear displacement\\u000a relation across the incoming and outgoing slip planes. This study extends the work of Pacheco and Mura (1969), by using a\\u000a numerical approach that incorporates

Peter M. Anderson; Xiaoj. Xin

319

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

NASA Technical Reports Server (NTRS)

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

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

1998-01-01

320

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

321

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

PubMed

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

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

2014-05-20

322

Residual stress measurement and analysis using ultrasonic techniques.  

NASA Technical Reports Server (NTRS)

A technique which utilizes ultrasonic radiation has been developed to measure residual stresses in metals. This technique makes it possible to detect and measure the magnitude of the principle stresses and also to obtain their direction. The velocities of ultrasonic waves in materials are measured as the time to travel a fixed path length, and the change in transit time is related to the applied stress. The linear relationship obtained allows a procedure based on this principle to be used for the measurement of residual stress using surface waves and shear waves. A method for plotting stress profiles through a material using surface waves uses varying frequencies for the ultrasonic wave. A limitation of the shear wave method is considered. The system used for this technique is called the Modified Time of Flight System.

Noronha, P. J.; Chapman, J. R.; Wert, J. J.

1973-01-01

323

Studies on stress distribution in pavements subjected to surface shear forces  

PubMed Central

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

KIMURA, Tsutomu

2014-01-01

324

Interferometric Measurement Of Residual Stress  

NASA Technical Reports Server (NTRS)

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

Danyluk, Steven; Andonian, A. T.

1990-01-01

325

CALCULATIONS OF SLIP OF NISQUALLY GLACIER ON ITS BED : NO SIMPLE RELATION OF SLIDING VELOCITY TO SHEAR STRESS  

Microsoft Academic Search

Measurements on Nisqually Glacier, Mounth Rainier National Park, Washington, at a profile fixed in space, give 22 yearly values of surface velocity (ws), surface slope (a), and changes in ice thickness (\\/;)• During this period (1943-66), us, a and h changed continuously by large amounts. These data were used to calculate values of shear stress (T) on the bed and

Mark F. MEIER

326

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

E-print Network

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.

Pinaki Chaudhuri; Jürgen Horbach

2014-10-26

327

Shear-induced Reynolds stress at the edge of L-mode tokamak plasmas  

Microsoft Academic Search

The turbulent flux of momentum—or Reynolds stress—is a mechanism responsible for the generation of sheared flow by turbulence. The structure of the flux-surface-averaged stress is investigated in the edge region of an L-mode tokamak plasma. The stress induced by the perpendicular tilting of ballooning modes is considered. In addition to the tilting by the E × B flow shear, which

N. Fedorczak; P. H. Diamond; G. Tynan; P. Manz

2012-01-01

328

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

329

Evolution of the wall shear stresses during the progressive enlargement of symmetric abdominal aortic aneurysms  

NASA Astrophysics Data System (ADS)

The changes in the evolution of the spatial and temporal distribution of the wall shear stresses (WSS) and gradients of wall shear stresses (GWSS) at different stages of the enlargement of an abdominal aortic aneurysm (AAA) are important in understanding the aetiology and progression of this vascular disease since they affect the wall structural integrity, primarily via the changes induced on the shape, functions and metabolism of the endothelial cells. Particle image velocimetry (PIV) measurements were performed in in vitro aneurysm models, while changing their geometric parameters systematically. It has been shown that, even at the very early stages of the disease, i.e. increase in the diameter ? 50%, the flow separates from the wall and a large vortex ring, usually followed by internal shear layers, is created. These lead to the generation of WSS that drastically differ in mean and fluctuating components from the healthy vessel. Inside the AAA, the mean WSS becomes negative along most of the aneurysmal wall and the magnitude of the WSS can be as low as 26% of the value in a healthy abdominal aorta.

Salsac, A.-V.; Sparks, S. R.; Chomaz, J.-M.; Lasheras, J. C.

2006-08-01

330

A Detailed Analysis of Guard-Heated Wall Shear Stress Sensors for Turbulent Flows Seyed Ali Ale Etrati Khosroshahi  

E-print Network

A Detailed Analysis of Guard-Heated Wall Shear Stress Sensors for Turbulent Flows by Seyed Ali Ale A Detailed Analysis of Guard-Heated Wall Shear Stress Sensors for Turbulent Flows by Seyed Ali Ale Etrati-dimensional analysis of the performance of multi-element guard-heated hot-film wall shear stress microsensors

Victoria, University of

331

Reference: Bid. Bull. 188: 46-56. (February/March, 1995) The Effects of Hydrodynamic Shear Stress on  

E-print Network

Reference: Bid. Bull. 188: 46-56. (February/March, 1995) The Effects of Hydrodynamic Shear Stress organisms, but turbulence-induced shear stresses may limit fertilization and interfere with normal effects of environmentally relevant shear stresses on fer- tilization in the purple sea urchin

Denny, Mark

332

Geophys. J. Int. (1997) 129,439-449 Shear-wave anisotropy and the stress field from borehole recordings  

E-print Network

Geophys. J. Int. (1997) 129,439-449 Shear-wave anisotropy and the stress field from borehole theory (APE) for modelling the response of shear-wave splitting to differential stress. They suggest that the stress field is complicated, where the leading shear-wave polarizations often exhibit fault

Edinburgh, University of

333

Mechanics of Materials 26 (1997) 6380 On the Use of Shear-Lag Methods for Analysis of Stress Transfer in  

E-print Network

The "shear-lag" analysis method is frequently used for analysis of stress transfer between the fiber the accuracy of shear-lag analysis on any problem. Some sample calculations were done for stress transfer from axial stress in the fiber and total strain energy in the specimen provided the shear-lag parameter most

Nairn, John A.

334

Importance of wind conditions, fetch, and water levels on wave-generated shear stresses in shallow intertidal basins  

E-print Network

Importance of wind conditions, fetch, and water levels on wave-generated shear stresses in shallow July 2009; published 30 September 2009. [1] Wave-generated shear stresses are the main mechanism, and wind direction on water depth, fetch, and the resulting wave-generated shear stresses. We identify four

Fagherazzi, Sergio

335

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

NASA Astrophysics Data System (ADS)

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

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

2009-06-01

336

Stress Measurement by Geometrical Optics  

NASA Technical Reports Server (NTRS)

Fast, simple technique measures stresses in thin films. Sample disk bowed by stress into approximately spherical shape. Reflected image of disk magnified by amount related to curvature and, therefore, stress. Method requires sample substrate, such as cheap microscope cover slide, two mirrors, laser light beam, and screen.

Robinson, R. S.; Rossnagel, S. M.

1986-01-01

337

Galanin protects against nerve injury after shear stress in primary cultured rat cortical neurons.  

PubMed

The neuropeptide galanin and its receptors (GalR) are found to be up-regulated in brains suffering from nerve injury, but the specific role played by galanin remains unclear. This study aimed to explore the neuroprotective role of galanin after shear stress induced nerve injury in the primary cultured cortical neurons of rats. Our results demonstrated that no significant changes in cell death and viability were found after galanin treatment when subjected to a shear stress of 5 dyn/cm(2) for 12 h, after increasing magnitude of shear stress to 10 dyn/cm(2) for 12 h, cell death was significantly increased, while galanin can inhibit the nerve injury induced by shear stress with 10 dyn/cm(2) for 12 h. Moreover, Gal2-11 (an agonist of GalR2/3) could also effectively inhibit shear stress-induced nerve injury of primary cultured cortical neurons in rats. Although GalR2 is involved in the galanin protection mechanism, there was no GalR3 expression in this system. Moreover, galanin increased the excitatory postsynaptic currents (EPSCs), which can effectively inhibit the physiological effects of shear stress. Galanin was also found to inhibit the activation of p53 and Bax, and further reversed the down regulation of Bcl-2 induced by shear stress. Our results strongly demonstrated that galanin plays a neuroprotective role in injured cortical neurons of rats. PMID:23691051

Liu, Meili; Song, Wei; Li, Ping; Huang, Yan; Gong, Xianghui; Zhou, Gang; Jia, Xiaoling; Zheng, Lisha; Fan, Yubo

2013-01-01

338

A Micromachined Geometric Moire Interferometric Floating-Element Shear Stress Sensor  

NASA Technical Reports Server (NTRS)

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

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

2004-01-01

339

Turbulent stresses as a function of shear rate in a local disk model  

E-print Network

We present local numerical models of accretion disk turbulence driven by the magnetorotational instability with varying shear rate. The resulting turbulent stresses are compared with predictions of a closure model in which triple correlations are modelled in terms of quadratic correlations. This local model uses five nondimensional parameters to describe the properties of the flow. We attempt to determine these closure parameters for our simulations and find that the model does produce qualitatively correct behaviour. In addition, we present results concerning the shear rate dependency of the magnetic to kinetic energy ratio. We find both the turbulent stress ratio and the total stress to be strongly dependent on the shear rate.

A. J. Liljeström; M. J. Korpi; P. J. Käpylä; A. Brandenburg; W. Lyra

2008-11-14

340

Shear stress induced by a gas bubble pulsating in an ultrasonic field near a wall.  

PubMed

Some of the effects that therapeutic ultrasound has in medicine and biology may be associated with steady oscillations of gas bubbles in liquid, very close to tissue surface. The bubble oscillations induce on the surface steady shear stress attributed to microstreaming. A mathematical simulation of the problem for both free and capsulated bubbles, known as contrast agents, is presented here. The simulation is based on a solution of Laplace's equation for potential flow and existing models for microstreaming. The solution for potential flow was obtained numerically using a boundary integral method. The solution provides the evolution of the bubble shape, the distribution of the velocity potential on the surface, and the shear stress along the surface. The simulation shows that significant shear stresses develop on the surface when the bubble bounces near the tissue surface. In this case, pressure amplitude of 20 kPa generates maximal steady shear stress of several kilo Pascal. Substantial shear stress on the tissue surface takes place inside a circular zone with a radius about half of the bubble radius. The predicted shear stress is greater than stress that causes hemolysis in blood and several orders of magnitude greater than the physiological stress induced on the vessel wall by the flowing blood. PMID:15344403

Krasovitski, Boris; Kimmel, Eitan

2004-08-01

341

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

342

A z-axis quartz cross-fork micromachined gyroscope based on shear stress detection.  

PubMed

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. PMID:22294887

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

2010-01-01

343

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

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

344

Development of a Reflective Polymer-Dispersed Liquid Crystal Shear Measurement System  

NASA Astrophysics Data System (ADS)

Polymer-dispersed liquid crystals as a shear force measurement system offer many advantages over conventional single-point measurement systems. They are non-intrusive while offering ideal 2-dimensional mapping of shear stresses across a surface. Furthermore, the inclusion of the liquid crystals within a polymer matrix allows for a reversible sensor that is self-adherent to testing surfaces. Previous testing has examined small-scale surface mapping and clear samples through which light may pass. This paper examines the expansion of polymer-dispersed liquid crystals to larger area mapping as well as reflective measurements, with measurements taken in multiple shear force configurations, confirming the validity of the reflective data.

DeBenedictis, Gina

345

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

346

An implementation of Bayesian lensing shear measurement  

NASA Astrophysics Data System (ADS)

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

Sheldon, Erin S.

2014-10-01

347

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

E-print Network

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

Harting, Jens

348

P-104: Shearing Effects of Stressed Liquid Crystals with Various Liquid Crystal Domain Sizes  

Microsoft Academic Search

Stressed liquid crystals (SLCs) are fast light modulating materials based on polymer\\/liquid crystal composites. We used polarizing microscopy and fluorescence confocal microscopy to investigate liquid crystal domain sizes and shearing mechanism for SLCs with different domain sizes. We observed the stretch of polymer matrices and the reshaping of liquid crystal domains in SLCs during shearing. In addition, we demonstrated the

Guoqiang Zhang; John L. West; Anatoliy Glushchenko; Ivan Smalyukh; Oleg Lavrentovich

2005-01-01

349

A mechanosensory complex that mediates the endothelial cell response to fluid shear stress  

Microsoft Academic Search

Shear stress is a fundamental determinant of vascular homeostasis, regulating vascular remodelling, cardiac development and atherogenesis, but the mechanisms of transduction are poorly understood. Previous work showed that the conversion of integrins to a high-affinity state mediates a subset of shear responses, including cell alignment and gene expression. Here we investigate the pathway upstream of integrin activation. PECAM-1 (which directly

Eleni Tzima; Mohamed Irani-Tehrani; William B. Kiosses; Elizabetta Dejana; David A. Schultz; Britta Engelhardt; Gaoyuan Cao; Horace Delisser; Martin Alexander Schwartz

2005-01-01

350

FLOCCULATION OF FINE-GRAINED LAKE SEDIMENTS DUE TO A UNIFORM SHEAR STRESS  

EPA Science Inventory

Experiments were performed to investigate the effects of fluid shear on the flocculation of fine-grained lake sediments in fresh water. In these experiments, a Couette viscometer was used to apply a uniform shear stress to a sediment suspension. he sediments were from the Detroit...

351

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

Technology Transfer Automated Retrieval System (TEKTRAN)

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

352

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

SciTech Connect

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

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

2011-04-15

353

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

354

Theory to Predict Shear Stress on Cells in Turbulent Blood Flow  

PubMed Central

Shear stress on blood cells and platelets transported in a turbulent flow dictates the fate and biological activity of these cells. We present a theoretical link between energy dissipation in turbulent flows to the shear stress that cells experience and show that for the case of physiological turbulent blood flow: (a) the Newtonian assumption is valid, (b) turbulent eddies are universal for the most complex of blood flow problems, and (c) shear stress distribution on turbulent blood flows is possibly universal. Further we resolve a long standing inconsistency in hemolysis between laminar and turbulent flow using the theoretical framework. This work demonstrates that energy dissipation as opposed to bulk shear stress in laminar or turbulent blood flow dictates local mechanical environment of blood cells and platelets universally. PMID:25171175

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

2014-01-01

355

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

E-print Network

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

Weldon, Matthew J. (Matthew Jacob)

2007-01-01

356

NOTES: A modification to a variable shear stress air turbine viscometer  

Microsoft Academic Search

A concentric cylinder air turbine viscometer previously described has been modified to extend the lower limit of shear stress to the region of 0·2 dyn cm?2. The effect of bearing pressure on calibration has been investigated.

S. S. Davis

1969-01-01

357

Hemodynamic Shear Stress and Endothelial Dysfunction in Hemodialysis Access  

PubMed Central

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

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

2014-01-01

358

Haemodynamic shear stress activates a K+ current in vascular endothelial cells  

Microsoft Academic Search

The endothelial lining of blood vessels is subjected to a wide range of haemodynamically-generated shear-stress forces throughout the vascular system1. In vivo and in vitro, endothelial cells change their morphology2,3 and biochemistry4 in response to shear stress in a force- and time-dependent way, or when a critical threshold is exceeded5'6. The initial stimulus-response coupling mechanisms have not been identified, however.

Søren-Peter Olesen; David Claphamt; Peter Davies

1988-01-01

359

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

Microsoft Academic Search

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

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

2001-01-01

360

Flexible shear-stress sensor skin and its application to unmanned aerial vehicles  

Microsoft Academic Search

Shear-stress information is of great interest for many fluidic dynamic monitoring\\/diagnostics application. To obtain such information on non-planar surfaces has long been a significant challenge. This paper describes the development of flexible shear-stress sensor skin and its application on the detection of leading edge flow separation for delta planform unmanned aerial vehicles (UAVs). The sensor skin contains a 1-D array

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

2003-01-01

361

Why Do Granular Materials Stiffen with Shear Rate? A Test of Novel Stress-Based Statistics  

E-print Network

Recent experiments exhibit a rate-dependence for granular shear such that the stress grows linearly in the logarithm of the shear rate, \\dot{\\gamma}. Assuming a generalized activated process mechanism, we show that these observations are consistent with a recent proposal for a stress-based statistical ensemble. By contrast, predictions for rate-dependence using conventional energy-based statistical mechanics to describe activated processes, predicts a rate dependence that of (\\ln (\\dot{\\gamma}))^{1/2}.

Robert P. Behringer; Dapeng Bi; Bulbul Chakraborty; Silke Henkes; Robert R. Hartley

2008-10-27

362

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

Microsoft Academic Search

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

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

2006-01-01

363

Characteristics of arterial wall shear stress which cause endothelium-dependent vasodilatation in the anaesthetized dog  

PubMed Central

The effects of changes in the mean and amplitude of arterial wall shear stress on endothelium-dependent arterial dilatation of the iliac artery of the anaesthetized dog were examined. Changes in the mean and amplitude of blood flow and wall shear stress were brought about by varying local peripheral resistance and stroke volume using a distal infusion of acetylcholine and the stimulation of the left ansa subclavia. Changes in the diameter of a segment of the iliac artery with the endothelium intact, relative to a segment with no endothelium, were used as an index of the release of nitric oxide. The increase in mean blood flow was from 84 ± 12 to 527 ± 53 ml min?1 and in amplitude was from 365 ± 18 to 695 ± 38 ml min?1 (means ±s.e.m.). The increase in mean wall shear stress was from 1.78 ± 0.30 to 7.66 ± 1.01 N m?2 and in amplitude was from 7.37 ± 0.46 to 13.9 ± 2.00 N m?2 (means ±s.e.m.). Increases in mean shear stress caused an increase in the diameter only of the section of artery with endothelium; the slope of the relationship was 0.064 ± 0.006 mm N?1 m2 (mean ±s.e.m., P < 0.001); changes in the amplitude of shear stress did not cause an increase in diameter. Changes in both the mean and amplitude of shear stress had no significant effect on the diameter of the section of artery with no endothelium. These findings coupled with the known anti-atheroma effects of nitric oxide and the effect of shear stress on cell adhesion and platelet aggregation offer a possible explanation for the disposition of atheroma in those parts of the arterial system which have low mean and high amplitude of wall shear stress. PMID:11251063

Snow, H M; Markos, F; O'Regan, D; Pollock, K

2001-01-01

364

IL-8 gene induction by low shear stress: pharmacological evaluation of the role of signaling molecules.  

PubMed

Shear stress can modulate endothelial cell function by regulating gene expression. We have previously demonstrated that low shear stress (4.2 dyn/cm(2)) induces the expression of interleukin-8 (IL-8) gene in endothelial cells. The present study was undertaken to further investigate both the effects of shear stress on IL-8 expression and the mechanisms controlling IL-8 mRNA up-regulation in human umbilical vein endothelial cells (HUVEC). We show that shear stress (from 2.23 to 19.29 dyn/cm(2)) induces the IL-8 expression at both the mRNA and protein levels by stimulating transcription. In order to determine the possible contribution of G protein, HUVEC were pretreated with an inhibitor of G-protein activation, GDPbetaS, which abrogated the low shear stress-induced IL-8 gene expression. Such gene expression was also partially inhibited by the tyrosine kinase inhibitor (tyrphostin-25) and in addition by EGTA, BATPA/AM (the intracellular Ca(2+) chelator), Verapamil (a Ca(2+) channel blocker), cAMP-dependent protein kinase inhibitor (KT5720) and phospholipase C inhibitor (neomycin). However, the cGMP-dependent protein kinase inhibitor, KT5823, had no effect on such expression. These findings therefore demonstrate the involvement of several signaling molecules, including tyrosine kinase, G protein, calcium, phospholipase C, and cAMP-dependent protein kinase, in the low shear stress-induced IL-8 gene expression. PMID:18556829

Cheng, Min; Liu, Xiaoheng; Li, Yi; Tang, Rong; Zhang, Wensheng; Wu, Jiang; Li, Liang; Liu, Xiaojing; Gang, Yang; Chen, Huaiqing

2007-01-01

365

Macro-scale Topology Optimization for Controlling Internal Shear Stress in a Porous Scaffold Bioreactor  

E-print Network

Shear stress is an important physical factor that regulates proliferation, migration and morphogenesis. In particular, the homeostasis of blood vessels is dependent on shear stress. To mimic this process ex vivo, efforts have been made to seed scaffolds with vascular and other cell types in the presence of growth factors and under pulsatile flow conditions. However, the resulting bioreactors lack information on shear stress and flow distributions within the scaffold. Consequently, it is difficult to interpret the effects of shear stress on cell function. Such knowledge would enable researchers to improve upon cell culture protocols. Recent work has focused on optimizing the microstructural parameters of the scaffold to fine tune the shear stress. In this study, we have adopted a different approach whereby flows are redirected throughout the bioreactor along channels patterned in the porous scaffold to yield shear stress distributions that are optimized for uniformity centered on a target value. A topology optimization algorithm coupled to computational fluid dynamics simulations was devised to this end. The channel topology in the porous scaffold was varied using a combination of genetic algorithm and fuzzy logic. The method is validated by experiments using magnetic resonance imaging (MRI) readouts of the flow field.

K. Youssef; J. J. Mack; M. L. Iruela-Arispe; L. -S. Bouchard

2012-01-09

366

Arterial Shear Stress Reduces Eph-B4 Expression in Adult Human Veins  

PubMed Central

Vein graft adaptation to the arterial environment is characterized by loss of venous identity, with reduced Ephrin type-B receptor 4 (Eph-B4) expression but without increased Ephrin-B2 expression. We examined changes of vessel identity of human saphenous veins in a flow circuit in which shear stress could be precisely controlled. Medium circulated at arterial or venous magnitudes of laminar shear stress for 24 hours; histologic, protein, and RNA analyses of vein segments were performed. Vein endothelium remained viable and functional, with platelet endothelial cell adhesion molecule (PECAM)-expressing cells on the luminal surface. Venous Eph-B4 expression diminished (p = .002), Ephrin-B2 expression was not induced (p = .268), and expression of osteopontin (p = .002) was increased with exposure to arterial magnitudes of shear stress. Similar changes were not found in veins placed under venous flow or static conditions. These data show that human saphenous veins remain viable during ex vivo application of shear stress in a bioreactor, without loss of the venous endothelium. Arterial magnitudes of shear stress cause loss of venous identity without gain of arterial identity in human veins perfused ex vivo. Shear stress alone, without immunologic or hormonal influence, is capable of inducing changes in vessel identity and, specifically, loss of venous identity. PMID:25191151

Model, Lynn S.; Hall, Michael R.; Wong, Daniel J.; Muto, Akihito; Kondo, Yuka; Ziegler, Kenneth R.; Feigel, Amanda; Quint, Clay; Niklason, Laura; Dardik, Alan

2014-01-01

367

Microfluidic perfusion culture chip providing different strengths of shear stress for analysis of vascular endothelial function.  

PubMed

We developed a microfluidic perfusion cell culture chip that provides three different shear stress strengths and a large cell culture area for the analysis of vascular endothelial functions. The microfluidic network was composed of shallow flow-control channels of three different depths and deep cell culture channels. The flow-control channels with high fluidic resistances created shear stress strengths ranging from 1.0 to 10.0 dyn/cm(2) in the cell culture channels. The large surface area of the culture channels enabled cultivation of a large number (approximately 6.0 × 10(5)) of cells. We cultured human umbilical vein endothelial cells (HUVECs) and evaluated the changes in cellular morphology and gene expression in response to applied shear stress. The HUVECs were aligned in the direction of flow when exposed to a shear stress of 10.0 dyn/cm(2). Compared with conditions of no shear stress, endothelial nitric oxide synthase mRNA expression increased by 50% and thrombomodulin mRNA expression increased by 8-fold under a shear stress of 9.5 dyn/cm(2). PMID:24630614

Hattori, Koji; Munehira, Yoichi; Kobayashi, Hideki; Satoh, Taku; Sugiura, Shinji; Kanamori, Toshiyuki

2014-09-01

368

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

NASA Astrophysics Data System (ADS)

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

Fuhrmann, Alexander; Engler, Adam J.

2015-02-01

369

Measurement of residual stress in bent pipelines  

NASA Astrophysics Data System (ADS)

Buried gas and oil pipelines can be subjected to unexpected bending loads caused by such earth movements as earthquakes, wash-outs, road building, or mining subsidence as well as by denting from unintentional digging. In order to make a fitness-for-service assessment, it is necessary to measure any residual stresses that are left in the pipe wall as well as the degree of plastic flow within regions of severe damage. A portable instrument that uses EMATs to rapidly measure ultrasonic shear wave birefringence in the wall of a pipe has been developed and applied to a 5 m (15 ft) long section of 0.56 m (22 in) diameter linepipe loaded in three point bending by a 22 MN (five million pound) load frame. The results showed that: (1) a large correction for shear wave anisotropy caused by texture in the steel had to be introduced and (2) the degree of plastic flow could be deduced from changes in the texture contribution alone. An attempt to separate the stress and texture effects by using SH wave modes in the pipe wall proved unreliable because of magnetostrictive effects in the periodic permanent magnet EMATs used for these experiments.

Alers, G. A.; McColskey, J. D.

2002-05-01

370

The fundamental difference between shear alpha viscosity and turbulent magnetorotational stresses  

E-print Network

Numerical simulations of turbulent, magnetized, differentially rotating flows driven by the magnetorotational instability are often used to calculate the effective values of alpha viscosity that is invoked in analytical models of accretion discs. In this paper we use various dynamical models of turbulent magnetohydrodynamic stresses, as well as numerical simulations of shearing boxes, to show that angular momentum transport in MRI-driven accretion discs cannot be described by the standard model for shear viscosity. In particular, we demonstrate that turbulent magnetorotational stresses are not linearly proportional to the local shear and vanish identically for angular velocity profiles that increase outwards.

Martin E. Pessah; Chi-kwan Chan; Dimitrios Psaltis

2008-02-18

371

Natural Convection Flow near a Vertical Plate that Applies a Shear Stress to a Viscous Fluid  

PubMed Central

The unsteady natural convection flow of an incompressible viscous fluid near a vertical plate that applies an arbitrary shear stress to the fluid is studied using the Laplace transform technique. The fluid flow is due to both the shear and the heating of the plate. Closed-form expressions for velocity and temperature are established under the usual Boussinesq approximation. For illustration purposes, two special cases are considered and the influence of pertinent parameters on the fluid motion is graphically underlined. The required time to reach the steady state in the case of oscillating shear stresses on the boundary is also determined. PMID:24278110

Rubbab, Qammar; Vieru, Dumitru; Fetecau, Corina; Fetecau, Constantin

2013-01-01

372

Shear stress sensing with Bragg grating-based sensors in microstructured optical fibers.  

PubMed

We demonstrate shear stress sensing with a Bragg grating-based microstructured optical fiber sensor embedded in a single lap adhesive joint. We achieved an unprecedented shear stress sensitivity of 59.8 pm/MPa when the joint is loaded in tension. This corresponds to a shear strain sensitivity of 0.01 pm/µ?. We verified these results with 2D and 3D finite element modeling. A comparative FEM study with conventional highly birefringent side-hole and bow-tie fibers shows that our dedicated fiber design yields a fourfold sensitivity improvement. PMID:24105585

Sulejmani, Sanne; Sonnenfeld, Camille; Geernaert, Thomas; Luyckx, Geert; Van Hemelrijck, Danny; Mergo, Pawel; Urbanczyk, Waclaw; Chah, Karima; Caucheteur, Christophe; Mégret, Patrice; Thienpont, Hugo; Berghmans, Francis

2013-08-26

373

Stress response and structural transitions in sheared gyroidal and lamellar amphiphilic mesophases: lattice-Boltzmann simulations  

E-print Network

We report on the stress response of gyroidal and lamellar amphiphilic mesophases to steady shear simulated using a bottom-up lattice-Boltzmann model for amphiphilic fluids and sliding periodic (Lees-Edwards) boundary conditions. We study the gyroid per se (above the sponge-gyroid transition, of high crystallinity) and the molten gyroid (within such a transition, of shorter-range order). We find that both mesophases exhibit shear-thinning, more pronounced and at lower strain rates for the molten gyroid. At late times after the onset of shear, the skeleton of the crystalline gyroid becomes a structure of interconnected irregular tubes and toroidal rings, mostly oriented along the velocity ramp imposed by the shear, in contradistinction with free-energy Langevin-diffusion studies which yield a much simpler structure of disentangled tubes. We also compare the shear stress and deformation of lamellar mesophases with and without amphiphile when subjected to the same shear flow applied normal to the lamellae. We find that the presence of amphiphile allows (a) the shear stress at late times to be higher than in the case without amphiphile, and (b) the formation of rich patterns on the sheared interface, characterised by alternating regions of high and low curvature.

Nelido Gonzalez-Segredo; Jens Harting; Giovanni Giupponi; Peter V. Coveney

2006-01-20

374

Measurement of modal damping by electronic speckle shearing interferometry  

Microsoft Academic Search

A time-average electronic speckle shearing interferometer (ESSI) has been used for modal damping measurement. This is effected by a new fringe enhancement technique. The damping factor of a cantilever measured by using this technique agrees well with the value measured by using the accelerometer method. The study shows that time-average speckle interferometry can be used as a convenient tool for

W. O. Wong; K. T. Chan

1998-01-01

375

Glycocalyx acting as a mechanotransducer of fluid shear stress  

E-print Network

It is widely recognized that fluid shearing forces acting on endothelial cells (ECs) have a profound effect on EC morphology, structure and function. Recent investigations in vivo have indicated the presence of a thick ...

Yao, Yu, Ph. D. Massachusetts Institute of Technology

2005-01-01

376

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

377

Ultrasonic measurement of axial stress  

NASA Technical Reports Server (NTRS)

The theory of acoustic propagation in strained media is examined, with particular emphasis on rod (bolt) geometries. The continuous wave (CW) approach is the basis of the study, and the theory is developed from a frequency domain analysis standpoint in order to obtain an applied stress/normalized frequency shift relationship. CW measurements may be influenced by such factors as propagation effects, mode conversion, frequency, material properties, and geometry. After the first loading cycle, axial stress measurements for a preloading with an initial frequency of 4.995 36 MHz dropped to 4.989 19 MHz, indicating a 6.17 kHz change. CW and pseudo-CW ultrasonic techniques are found to be reliable for axial stress measurements, and acoustic attenuation measurements correlated to residual stress fields may possibly involve transducer phase cancellation. It is thus concluded that signal drop is an artifact of the transducer directivity, rather than an actual acoustic power decrease.

Heyman, J. S.; Chern, E. J.

1982-01-01

378

The influence of grading on the shear strength of loose sands in stress-controlled ring shear tests  

Microsoft Academic Search

Three silica sand samples—well graded, intermediately graded, and narrowly graded—having different uniformity coefficients,\\u000a were constituted to allow the investigation of the influence of particle size distribution on their mechanical behavior. Using\\u000a a ring shear apparatus, samples were tested under a wide range of laboratory conditions. Results of the tests clearly indicate\\u000a that, for specimens confined under identical stress conditions, well-graded

Ogbonnaya Igwe; Kyoji Sassa; Fawu Wang

2007-01-01

379

Measurement of interfacial shear strength in SiC-fiber/Si3N4 composites  

NASA Technical Reports Server (NTRS)

An indentation method for measuring shear strength in brittle matrix composites was applied to SiC-fiber/Si3N4-matrix samples. Three methods were used to manufacture the composites: reaction bonding of a Si/SiC preform, hot-pressing, and nitrogen-overpressure sintering. An indentation technique developed by Marshall for thin specimens was used to measure the shear strength of the interface and the interfacial friction stresses. This was done by inverting the sample after the initial push through and retesting the pushed fibers. SEM observations showed that the shear strength was determined by the degree of reaction between the fiber and the matrix unless the fiber was pushed out of its (well-bonded) sheath.

Laughner, James W.; Bhatt, Rham T.

1989-01-01

380

On the expected relationships among apparent stress, static stress drop, effective shear fracture energy, and efficiency  

USGS Publications Warehouse

We consider expected relationships between apparent stress ??a and static stress drop ????s using a standard energy balance and find ??a = ????s (0.5 - ??), where ?? is stress overshoot. A simple implementation of this balance is to assume overshoot is constant; then apparent stress should vary linearly with stress drop, consistent with spectral theories (Brune, 1970) and dynamic crack models (Madariaga, 1976). Normalizing this expression by the static stress drop defines an efficiency ??sw = ??sa/????s as follows from Savage and Wood (1971). We use this measure of efficiency to analyze data from one of a number of observational studies that find apparent stress to increase with seismic moment, namely earthquakes recorded in the Cajon Pass borehole by Abercrombie (1995). Increases in apparent stress with event size could reflect an increase in seismic efficiency; however, ??sw for the Cajon earthquakes shows no such increase and is approximately constant over the entire moment range. Thus, apparent stress and stress drop co-vary, as expected from the energy balance at constant overshoot. The median value of ??sw for the Cajon earthquakes is four times lower than ??sw for laboratory events. Thus, these Cajon-recorded earthquakes have relatively low and approximately constant efficiency. As the energy balance requires ??sw = 0.5 - ??, overshoot can be estimated directly from the Savage-Wood efficiency; overshoot is positive for Cajon Pass earthquakes. Variations in apparent stress with seismic moment for these earthquakes result primarily from systematic variations in static stress drop with seismic moment and do not require a relative decrease in sliding resistance with increasing event size (dynamic weakening). Based on the comparison of field and lab determinations of the Savage-Wood efficiency, we suggest the criterion ??sw > 0.3 as a test for dynamic weakening in excess of that seen in the lab.

Beeler, N.M.; Wong, T.-F.; Hickman, S.H.

2003-01-01

381

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

PubMed Central

Summary Fluid shear stress (FSS) from blood flow acting on the endothelium critically regulates vascular morphogenesis, blood pressure and atherosclerosis [1]. FSS applied to endothelial cells (EC) triggers signaling events including opening of ion channels, activation of signaling pathways and changes in gene expression. Elucidating how ECs sense flow 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 [2]. Previous work suggested that flow increases force on PECAM-1, which initiates signaling [2–4]. Deletion of PECAM-1 blocks responses to flow in vitro and flow-dependent vascular remodeling in vivo [2, 5]. 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 [6]. 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 sec) 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 non-junctional 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 [7], 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; A Schwartz, Martin

2013-01-01

382

Effect of shear stress and growth conditions on detachment and physical properties of biofilms.  

PubMed

Detachment is one of the major processes determining the physical structure and microbial functionalities of biofilms. To predict detachment, it is necessary to take the mechanical properties of the biofilm and the effect of both hydrodynamic and growth conditions into account. In this work, experiments were conducted with biofilms developed under various shear stresses and with various substrate natures. In addition, two cases were considered in order to differentiate between the effect of hydrodynamic factors and growth factors: the biofilms were directly grown under the targeted shear stress (?) condition or they were precultivated under very low shear stress (0.01 Pa) and then exposed to high shear stress in the range of 0.1-13 Pa. An exponential and asymptotic decrease of the biofilm thickness and mass with increasing ? was observed in both cases. On contrary density, expressed as the biofilm dry mass on a known substratum divided by the average thickness increased with ?. Denitrifying biofilms always showed greater thickness and density than oxic biofilms. These results showed the presence of a compact basal layer that resisted shear stresses as high as 13 Pa whatever the culture conditions. Above this basal layer, the cohesion was lower and depended on the shear stress applied during biofilm development. The application of shear stress to the biofilms resulted in both detachment and compression, but detachment prevailed for the upper part of the biofilms and compression prevailed for the basal layers. A model of biofilm structure underlying the stratified character of this aggregate is given in terms of density and cohesion. PMID:22898671

Paul, Etienne; Ochoa, Juan Carlos; Pechaud, Yoan; Liu, Yu; Liné, Alain

2012-11-01

383

Rac1 mediates laminar shear stress-induced vascular endothelial cell migration  

PubMed Central

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

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

2013-01-01

384

Dependence of dynamic shear modulus of uniform sands on stress level and density  

Microsoft Academic Search

The first part of this study is a description and analysis of experimental investigations conducted to determine the nonlinear stress–strain behaviors of uniform sands when subjected to cyclic loadings at small strain levels. A series of torsional shear tests are performed under undrained conditions to analyze the variations in the stress–strain properties of saturated uniform sands consolidated to specified confining

S. Altun; A. B. Goktepe

2006-01-01

385

Acoustic radiation stress measurement  

NASA Technical Reports Server (NTRS)

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

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

1987-01-01

386

Suppression of endothelial t-PA expression by prolonged high laminar shear stress  

SciTech Connect

Primary hypertension is associated with an impaired capacity for acute release of endothelial tissue-type plasminogen activator (t-PA), which is an important local protective response to prevent thrombus extension. As hypertensive vascular remodeling potentially results in increased vascular wall shear stress, we investigated the impact of shear on regulation of t-PA. Cultured human endothelial cells were exposed to low ({<=}1.5 dyn/cm{sup 2}) or high (25 dyn/cm{sup 2}) laminar shear stress for up to 48 h in two different experimental models. Using real-time RT-PCR and ELISA, shear stress was observed to time and magnitude-dependently suppress t-PA transcript and protein secretion to approximately 30% of basal levels. Mechanistic experiments revealed reduced nuclear protein binding to the t-PA specific CRE element (EMSA) and an almost completely abrogated shear response with pharmacologic JNK inhibition. We conclude that prolonged high laminar shear stress suppresses endothelial t-PA expression and may therefore contribute to the enhanced risk of arterial thrombosis in hypertensive disease.

Ulfhammer, Erik; Carlstroem, Maria; Bergh, Niklas; Larsson, Pia; Karlsson, Lena [Clinical Experimental Research Laboratory, Sahlgrenska University Hospital/Ostra, SE 416 85 Gothenburg (Sweden); Institute of Medicine, University of Gothenburg, Gothenburg (Sweden); Jern, Sverker [Clinical Experimental Research Laboratory, Sahlgrenska University Hospital/Ostra, SE 416 85 Gothenburg (Sweden); Institute of Medicine, University of Gothenburg, Gothenburg (Sweden)], E-mail: sverker.jern@gu.se

2009-02-06

387

Instability due to second normal stress jump in two-layer shear flow of the Giesekus fluid  

E-print Network

Instability due to second normal stress jump in two-layer shear flow of the Giesekus fluid Yuriko Y the effect of a jump in the second normal stress difference, the analysis is focused on flows where the shear rate and first normal stress difference are continuous across the interface. In this case, the flow

Renardy, Yuriko

388

Effects of shear stress on nitric oxide and matrix protein gene expression in human osteoarthritic chondrocytes in vitro  

Microsoft Academic Search

Mechanical loading alters articular cartilage metabolism. However, mechanisms underlying intracellular signaling and communication between cells in response to mechanical stresses remain enigmatic. This study tested the hypothesis that shear stress-induced nitric oxide (NO) production participates in the regulation of matrix protein gene expression. The data presented here demonstrate that exposure of human osteoarthritic chondrocytes to a continuously applied shear stress

Mel S. Lee; Michael C. D. Trindade; Takashi Ikenoue; David J. Schurman; Stuart B. Goodman

2002-01-01

389

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

390

In-situ shear stress indicator using heated strain gages at the flow boundary  

NASA Astrophysics Data System (ADS)

This work borrows the concept of hot-wire anemometry and sketch a technique that uses local heat transfer to infer the flow field and the corresponding stress. Conventional strain gages were mounted at the flow solid boundary as the heat source and acrylic boundary was chosen for its low thermal conductivity ensuring heat accumulation when a gage is energized. The gage would now work in slightly overheated state and its self-heating leads to an additional thermal strain. When exposed to a flow field, heat is brought away by local forced convection, resulting in deviations in gage signal from that developed in quiescent liquid. We have developed a facility to achieve synchronous gage measurements at different locations on a solid boundary. Three steady flow motions were considered: circular Couette flow, rectilinear uniform flow, and rectilinear oscillating flow. Preliminary tests show the gage reading does respond to the imposed flow through thermal effects and greater deviation was measured in flows of higher shear strain rates. The correlation between the gage signals and the imposed flow field is further examined by theoretical analysis. We also introduced a second solid boundary to the vicinity of the gage in the two rectilinear flows. The gage readings demonstrate rises in its magnitudes indicating wall amplification effect on the local shear strain, agreeing to the drag augmentation by a second solid boundary reported in many multiphase flow literatures.

Yeh, Chi-An; Yang, Fuling

2011-11-01

391

Turbulence stress measurements in a nonadiabatic hypersonic boundary layer  

NASA Technical Reports Server (NTRS)

Turbulent shear stress and direct turbulent total heat-flux measurements have been made across a nonadiabatic, zero pressure gradient, hypersonic boundary layer by using specially designed hot-wire probes free of strain-gauging and wire oscillation. Heat-flux measurements were in reasonably good agreement with values obtained by integrating the energy equation using measured profiles of velocity and temperature. The shear-stress values deduced from the measurements, by assuming zero correlation of velocity and pressure fluctuations, were lower than the values obtained by integrating the momentum equation. Statistical properties of the cross-correlations are similar to corresponding incompressible measurements at approximately the same momentum-thickness Reynolds number.

Mikulla, V.; Horstman, C. C.

1975-01-01

392

Fluid Shear Stress Alters the Hemostatic Properties of Endothelial Outgrowth Cells  

PubMed Central

Surface endothelialization is an attractive means to improve the performance of small diameter vascular grafts. While endothelial outgrowth cells (EOCs) are considered a promising source of autologous endothelium, the ability of EOCs to modulate coagulation-related blood activities is not well understood. The goal of this study was to assess the role of arterial flow conditions on the thrombogenic phenotype of EOCs. EOCs derived from baboon peripheral blood, as well as mature arterial endothelial cells from baboons, were seeded onto adsorbed collagen, then exposed to physiologic levels of fluid shear stress. For important hemostatic pathways, cellular responses to shear stress were characterized at the gene and protein level and confirmed with a functional assay for activated protein C (APC) activity. For EOCs, fluid shear stress upregulated gene and protein expression of anticoagulant and platelet inhibitory factors, including thrombomodulin, tissue factor pathway inhibitor, and nitric oxide synthase 3 (eNOS). Fluid shear stress significantly altered the functional activity of EOCs by increasing APC levels. This study demonstrates that fluid shear stress is an important determinant of EOC hemostatic properties. Accordingly, manipulation of EOC phenotype by mechanical forces may be important for the development of thrombo-resistant surfaces on engineered vascular implants. PMID:21787250

Ensley, Ann E.; Nerem, Robert M.; Anderson, Deirdre E.J.; Hanson, Stephen R.

2012-01-01

393

Fluid shear stress alters the hemostatic properties of endothelial outgrowth cells.  

PubMed

Surface endothelialization is an attractive means to improve the performance of small diameter vascular grafts. While endothelial outgrowth cells (EOCs) are considered a promising source of autologous endothelium, the ability of EOCs to modulate coagulation-related blood activities is not well understood. The goal of this study was to assess the role of arterial flow conditions on the thrombogenic phenotype of EOCs. EOCs derived from baboon peripheral blood, as well as mature arterial endothelial cells from baboons, were seeded onto adsorbed collagen, then exposed to physiologic levels of fluid shear stress. For important hemostatic pathways, cellular responses to shear stress were characterized at the gene and protein level and confirmed with a functional assay for activated protein C (APC) activity. For EOCs, fluid shear stress upregulated gene and protein expression of anticoagulant and platelet inhibitory factors, including thrombomodulin, tissue factor pathway inhibitor, and nitric oxide synthase 3 (eNOS). Fluid shear stress significantly altered the functional activity of EOCs by increasing APC levels. This study demonstrates that fluid shear stress is an important determinant of EOC hemostatic properties. Accordingly, manipulation of EOC phenotype by mechanical forces may be important for the development of thrombo-resistant surfaces on engineered vascular implants. PMID:21787250

Ensley, Ann E; Nerem, Robert M; Anderson, Deirdre E J; Hanson, Stephen R; Hinds, Monica T

2012-01-01

394

Nitric oxide secretion by endothelial cells in response to fluid shear stress, aspirin, and temperature.  

PubMed

Current vascular grafts have a high incidence of failure, especially in the grafts less than 6 mm in diameter, due to thrombus formation. Nitric oxide (NO) is released by endothelium and has some beneficial influences such as an antithrombotic effect. We hypothesized that applying different shear stress regiments and low temperature or aspirin would result in an increase in the amount of NO release from human umbilical vein endothelial cells (HUVECs) and decrease in platelet aggregation in the same manner as expected in vivo. HUVECs were cultured into the intraluminal surface of silicone tubes. HUVECs were subjected for 60 min to different parameters of shear stress, temperature, aspirin, and platelets or a combination in a perfusion bioreactor by monitoring NO secretion. We found that shear stress leads to an elevation of NO production in HUVECS, independent of the shear stress magnitude (0.9 or 1.8 dyne/cm(2) ). The magnitude of this response increased with a decrease in temperature. Our results also show that by addition of platelets in combination with aspirin to media circulation, no thrombus formation occurred during the test time. Presence of aspirin resulted in marked increase in NO levels. In conclusion, shear stresses, temperature lowering, and aspirin increase the amount of NO release from HUVECs. Also no thrombus formation was detected in our experimental setting. © 2014 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 103A: 1231-1237, 2015. PMID:24838707

Kabirian, Fatemeh; Amoabediny, Ghassem; Haghighipour, Nooshin; Salehi-Nik, Nasim; Zandieh-Doulabi, Behrouz

2015-03-01

395

Microscopic origins of shear stress in dense fluid-grain mixtures  

E-print Network

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

Donia Marzougui; Bruno Chareyre; Julien Chauchat

2015-04-14

396

Estimation of shear stress in counter-current gas-liquid annular two-phase flow  

NASA Astrophysics Data System (ADS)

The accuracy of the correlations of the friction factor is important for the counter-current flow (CCF) analysis with two-fluid model. However, existing two fluid model codes use the correlations of friction factors for co-current flow or correlation developed based on the assumption of no wall shear stress. The assessment calculation for two fluid model code with those existing correlations of friction factors shows the falling water flow rate is overestimated. Analytical model is developed to calculate the shear stress distribution in water film at CCF in order to get the information on the shear stress at the interface and the wall. The analytical results with the analysis model and Bharathan's CCF data shows that the wall shear stress acting on the falling water film is almost the same order as the interfacial shear stress and the correlations for co-current flow cannot be applied to the counter-current flow. Tentative correlations of the interfacial and the wall friction factors are developed based on the results of the present study.

Abe, Yutaka; Akimoto, Hajime; Murao, Yoshio

1991-01-01

397

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 ?=0.56 h?¹ (bag) and ?=0.53 h?¹ (STR). Differences concerning morphology, enzymatic activities and growth in fungal cultivations were observed. In the bag reactor growth in form of small, independent pellets was observed while STR cultivations showed intense aggregation. F. velutipes reached higher biomass concentrations (21.2 g l?¹ DCW vs. 16.8 g l?¹ DCW) and up to 2-fold higher peptidolytic activities in comparison to cell cultivation in stirred tank reactors. PMID:23892193

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

2013-09-20

398

Dispersive aortic cannulas reduce aortic wall shear stress affecting atherosclerotic plaque embolization.  

PubMed

Neurologic complications during on-pump cardiovascular surgery are often induced by mobilization of atherosclerotic plaques, which is directly related to enhanced wall shear stress. In the present study, we numerically evaluated the impact of dispersive aortic cannulas on aortic blood flow characteristics, with special regard to the resulting wall shear stress profiles. An idealized numerical model of the human aorta and its branches was created and used to model straight as well as bent dispersive aortic cannulas with meshlike tips inserted in the distal ascending aorta. Standard cannulas with straight beveled or bent tips served as controls. Using a recently optimized computing method, simulations of pulsatile and nonpulsatile extracorporeal circulation were performed. Dispersive aortic cannulas reduced the maximum and average aortic wall shear stress values to approximately 50% of those with control cannulas, while the difference in local values was even larger. Moreover, under pulsatile circulation, dispersive cannulas shortened the time period during which wall shear stress values were increased. The turbulent kinetic energy was also diminished by utilizing dispersive cannulas, reducing the risk of hemolysis. In summary, dispersive aortic cannulas decrease aortic wall shear stress and turbulence during extracorporeal circulation and may therefore reduce the risk of endothelial and blood cell damage as well as that of neurologic complications caused by atherosclerotic plaque mobilization. PMID:25205180

Assmann, Alexander; Gül, Fethi; Benim, Ali Cemal; Joos, Franz; Akhyari, Payam; Lichtenberg, Artur

2015-03-01

399

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

400

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

401

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

E-print Network

a part of my life. TABLE OF CONTENTS CHAPTER I INTRODUCTION . . Page I. l Role of Rheology in Plastics Processing. . . . . . . I. 2 Properties I. 3 Large Amplitude Oscillatory Shear I. 4 Measurement of First Normal Stress Difference . . I. 5... Constitutive Equations . . 2 3 8 10 11 THEORY 15 II. 1 Kinetic Network Theory II. 2 Runge-Kutta Ordinary Differentral Equation Solver. . . . II. 3 Spectral Analysss II. 4 Obtaining A Relaxation Spectrum from Oscillatory Shear Data . 15 19 20 22...

Oakley, Jason Glen

1992-01-01

402

A noninvasive method to estimate wall shear rate using ultrasound  

Microsoft Academic Search

Wall shear stress (blood viscosity × wall shear rate), imposed by the flowing blood, and blood pressure are the main mechanical forces acting on a blood vessel wall. Accurate measurement of wall shear stress is important when investigating the development of vascular disease, since both high and low wall shear stresses have been cited as factors leading to vessel wall

Peter J. Brands; Arnold P. G. Hoeks; Leo Hofstra; Robert S. Reneman

1995-01-01

403

Structures Formed in Experimentally Sheared Artificial Fault Gouge: Precise Statistical Measurements  

NASA Astrophysics Data System (ADS)

The physical parameters governing earthquakes change with the ongoing formation and evolution of structures, formed in the course of a single or multiple earthquakes, within a particular fault zone or in a broad volume containing interacting tectonic faults. Our precise knowledge of these complex phenomena is still elusive. Especially, works considering geometrical evolution of shear structures under controlled conditions are rare. In order to gain some insights we accomplished a set of 12 laboratory experiments using a servo-controlled direct-shear apparatus, under room temperature and without controlling the air humidity. Two fault gouge layers (industrially produced quartz powder, average particle size of 5 ? m, and pre-shear thickness of 1.5, 2.0 and 3.0 mm,) were sandwiched between three granite blocks. The middle block was slid in order to create frictional structures within the simulated gouge. The total imposed shear strain varies between 0.14 and 11.80. The post-shear gouge layer thickness ranges from 0.99-2.11 mm. Each experiment was run under a constant normal stress (varying from 10-44 MPa through the experiments) and at a constant shear velocity (0.07, 0.7 and 7 ? m/s, through the experiments). Later, in cross-sections of solidified by epoxy glue gouge (parallel to the shear direction, normal to the gouge walls,) we quantified the numerous R-shears, according to their density distribution, fracture thickness (measured perpendicularly to the fracture walls), fracture angle and morphology, and fracture length. In gouge views parallel to the sliding blocks, we measured fracture length and along-strike R-shear morphology. Although the latter data are with lower quality, both observational sets provide precise statistical fracture data as well snapshots of evolving 3D structures. We observe shear localization with decreasing gouge layer thickness and with increasing normal stress. The average density of major fractures increases from 2.83 to 3.67 [fracture/cm] for decrease of the post-shear gouge layer thickness. This is at the expense of a considerable decrease of visible more diffusive minor fractures. On the other hand, the fractures formed at lower normal stress are more irregular and show average fracture density of 4.48 [fracture/cm]. The latter decreases down to 3.64 at higher normal stress, as the fracture morphology becomes more regular. The fracture density increases abruptly from zero, after a small total shear strain (0.15-0.50), and later the change is slower or none with the increase of the total shear strain; the fractures are already localized and they accommodate most of the brittle deformation. Also we observe weak polarity in fracture development in accordance to the sliding sense, especially in the subset of fractures starting from the gouge wall and dying out within the gouge layer. More such fractures are developed along the leading part of the sliding blocks. Our results throw new light over the formation and development of fault-related structures and their dependency on the earthquake-governing physical parameters.

Dilov, T.; Yoshida, S.; Kato, A.; Nakatani, M.; Mochizuki, H.; Otsuki, K.

2004-12-01

404

Estimation of in-situ stresses in concrete members using polarized ultrasonic shear waves  

NASA Astrophysics Data System (ADS)

Ultrasonic testing is commonly used to detect flaws, estimate geometries, and characterize properties of materials and structures. Acoustoelasticity refers to the dependency of stress wave velocity with applied stresses and is a phenomenon that has been known by geophysicists since the 1960s. A way to capitalize on this effect for concrete applications is by using ultrasonic shear waves which are particularly sensitive to applied stresses when polarized in the direction of the applied stress. The authors conducted an experiment on a 150 mm (6 in.) diameter concrete cylinder specimen with a length of 305 mm (12 in.) that was loaded in discrete load steps to failure. At each load step two ultrasonic shear waves were transmitted through the specimen, one with the polarization perpendicular and the other transverse to the applied stress. The velocity difference between the two sets of polarized shear waves was found to correlate with the applied stress in the specimen. Two potential applications for this methodology include estimation of stresses in pre-stressed concrete bridge girders and investigation of load redistribution in structural support elements after extreme events. This paper introduces the background of the methodology, presents an analysis of the collected data, and discusses the relationship between the recorded signals and the applied stress.

Chen, Andrew; Schumacher, Thomas

2014-02-01

405

Influence of thickness and permeability of endothelial surface layer on transmission of shear stress in capillaries  

NASA Astrophysics Data System (ADS)

The molecular coating on the surface of microvascular endothelium has been identified as a barrier to transvascular exchange of solutes. With a thickness of hundreds of nanometers, this endothelial surface layer (ESL) has been treated as a porous domain within which fluid shear stresses are dissipated and transmitted to the solid matrix to initiate mechanotransduction events. The present study aims to examine the effects of the ESL thickness and permeability on the transmission of shear stress throughout the ESL. Our results indicate that fluid shear stresses rapidly decrease to insignificant levels within a thin transition layer near the outer boundary of the ESL with a thickness on the order of ten nanometers. The thickness of the transition zone between free fluid and the porous layer was found to be proportional to the square root of the Darcy permeability. As the permeability is reduced ten-fold, the interfacial fluid and solid matrix shear stress gradients increase exponentially two-fold. While the interfacial fluid shear stress is positively related to the ESL thickness, the transmitted matrix stress is reduced by about 50% as the ESL thickness is decreased from 500 to 100 nm, which may occur under pathological conditions. Thus, thickness and permeability of the ESL are two main factors that determine flow features and the apportionment of shear stresses between the fluid and solid phases of the ESL. These results may shed light on the mechanisms of force transmission through the ESL and the pathological events caused by alterations in thickness and permeability of the ESL.

Zhang, SongPeng; Zhang, XiangJun; Tian, Yu; Meng, YongGang; Lipowsky, Herbert

2015-03-01

406

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. PMID:24100784

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

2013-01-01

407

Composite Interlaminar Shear Fracture Toughness, G(sub 2c): Shear Measurement of Sheer Myth?  

NASA Technical Reports Server (NTRS)

The concept of G2c as a measure of the interlaminar shear fracture toughness of a composite material is critically examined. In particular, it is argued that the apparent G2c as typically measured is inconsistent with the original definition of shear fracture. It is shown that interlaminar shear failure actually consists of tension failures in the resin rich layers between plies followed by the coalescence of ligaments created by these failures and not the sliding of two planes relative to one another that is assumed in fracture mechanics theory. Several strain energy release rate solutions are reviewed for delamination in composite laminates and structural components where failures have been experimentally documented. Failures typically occur at a location where the mode 1 component accounts for at least one half of the total G at failure. Hence, it is the mode I and mixed-mode interlaminar fracture toughness data that will be most useful in predicting delamination failure in composite components in service. Although apparent G2c measurements may prove useful for completeness of generating mixed-mode criteria, the accuracy of these measurements may have very little influence on the prediction of mixed-mode failures in most structural components.

OBrien, T. Kevin

1997-01-01

408

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

409

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

410

Migration arising from gradients in shear stress: Particle distributions in Poiseuille flow  

NASA Technical Reports Server (NTRS)

Experimental evidence for the existence of shear induced migration processes is reviewed and the mechanism by Leighton and Acrivos (1987b) is described in detail. The proposed mechanism is shown to lead to the existence of an additional shear induced migration in the presence of gradients in shear stress such as would be found in Poiseuille flow, and which may be used to predict the amplitude of the observed short-term viscosity increase. The concentration and velocity profiles which result from such a migration are discussed in detail and are compared to the experimental observations of Karnis, Goldsmith and Mason (1966).

Leighton, D. T., Jr.

1988-01-01

411

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

PubMed Central

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

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

2014-01-01

412

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

NASA Technical Reports Server (NTRS)

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

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

2002-01-01

413

Origins of the anomalous stress behavior in charged colloidal suspensions under shear  

NASA Astrophysics Data System (ADS)

Numerical simulations are conducted to determine microstructure and rheology of sheared suspensions of charged colloidal particles at a volume fraction of ?=0.33 . Over broad ranges of repulsive force strength F0 and Péclet number Pe, dynamic simulations show coexistence of ordered and disordered stable states with the state dependent on the initial condition. In contrast to the common view, at low shear rates, the disordered phase exhibits a lower viscosity (?r) than the ordered phase, while this behavior is reversed at higher shear rates. Analysis shows the stress reversal is associated with different shear induced microstructural distortions in the ordered and disordered systems. Viscosity vs shear rate data over a wide range of F0 and Pe collapses well upon rescaling with the long-time self-diffusivity. Shear thinning viscosity in the ordered phase scaled as ?r˜Pe-0.81 at low shear rates. The microstructural dynamics revealed in these studies explains the anomalous behavior and hysteresis loops in stress data reported in the literature.

Kumar, Amit; Higdon, Jonathan J. L.

2010-11-01

414

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

415

Reynolds number effects on surface shear stress patterns around isolated hemispheres  

NASA Technical Reports Server (NTRS)

Obstacles projecting into the wind stream alter the shear stress on the surface around them, thus altering the erosion, transportation, and deposition of aeolian sediment. The effect of Reynolds number on the pattern of shear stress on the surface around an isolated hemisphere was investigated. An understanding of Reynolds number effects is necessary if wind tunnel results are to be scaled up to natural situations for meaningful applications. The experiment shows that the surface shear stress pattern is strongly affected by Reynolds number, at least within the range of Re used (1360 to 2977). This is presumably due to a decrease in flow around the sides of the hemisphere and an increase in flow over the object as the Reynolds number increases.

Lee, J. A.; Greeley, Ronald

1987-01-01

416

Runge-Kutta method for wall shear stress of blood flow in stenosed artery  

NASA Astrophysics Data System (ADS)

A mathematical model of blood flow through stenotic artery is considered. A stenosis is defined as the partial occlusion of the blood vessels due to the accumulation of cholesterols, fats and the abnormal growth of tissue on the artery walls. The development of stenosis in the artery is one of the factors that cause problem in blood circulation system. This study was conducted to determine the wall shear stress of blood flow in stenosed artery. Modified mathematical model is used to analyze the relationship of the wall shear stress versus the length and height of stenosis. The existing models that have been created by previous researchers are solved using fourth order Runge-Kutta method. Numerical results show that the wall shear stress is proportionate to the length and height of stenosis.

Awaludin, Izyan Syazana; Ahmad, Rokiah@Rozita

2014-06-01

417

Effects of cold exposure and shear stress on endothelial nitric oxide synthase activation.  

PubMed

Endothelial nitric oxide synthase (eNOS) is the primary enzyme that produces nitric oxide (NO), which plays an important role in blood vessel relaxation. eNOS activation is stimulated by various mechanical forces, such as shear stress. Several studies have shown that local cooling of the human finger causes strong vasoconstriction, followed after several minutes by cold-induced vasodilation (CIVD). However, the role played by endothelial cells (ECs) in blood vessel regulation in respond to cold temperatures is not fully understood. In this study, we found that low temperature alone does not significantly increase or decrease eNOS activation in ECs. We further found that the combination of shear stress with temperature change leads to a significant increase in eNOS activation at 37°C and 28°C, and a decrease at 4°C. These results show that ECs play an important role in blood vessel regulation under shear stress and low temperature. PMID:21820412

Binti Md Isa, Kamariah; Kawasaki, Naoto; Ueyama, Keiichi; Sumii, Tateki; Kudo, Susumu

2011-08-26

418

Magnetoacoustic stress measurements in steel  

NASA Technical Reports Server (NTRS)

Uniaxial stress effects on the low-field magnetoacoustic interaction have been studied using bulk compressional waves and Rayleigh surface waves in numerous steel samples having various impurity concentrations (Namkung et al., 1984). The results invariably showed that the initial slope of acoustic natural velocity variations, with respect to net induced magnetization parallel to the stress axis, is positive under tension and negative under compression. The results of current measurements in railroad rail steel having about 0.68 wt percent carbon content are typical for medium range carbon steels. The low-field natural velocity slope in this particular type of steel, which is almost zero when unstressed, becomes steeper with increased magnitude of stress in both directions. Hence, the nondestructive determination of the sign of residual stress in railroad wheels and rails is possible using this technique. This paper discusses the basic physical mechanism underlying the experimental observations and presents the results obtained in railroad rail steel.

Namkung, M.; Utrata, D.; Allison, S. G.; Heyman, J. S.

1985-01-01

419

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

NASA Technical Reports Server (NTRS)

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

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

2001-01-01

420

Surface figure measurements of radio telescopes with a shearing interferometer  

Microsoft Academic Search

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

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

1991-01-01