Note: This page contains sample records for the topic shear stress measurement from Science.gov.
While these samples are representative of the content of Science.gov,
they are not comprehensive nor are they the most current set.
We encourage you to perform a real-time search of Science.gov
to obtain the most current and comprehensive results.
Last update: August 15, 2014.
1

High resolution, 2-dimensional shear stress measurements from imaging polarimetry  

Microsoft Academic Search

Here we present a novel method for obtaining high-resolution, 2-dimensional shear stress measurements over aerodynamic surfaces, based upon the dynamic birefringence of a shear sensitive, liquid crystal coating. Air flowing over the surface of a liquid crystal coating causes a measurable change in the birefringence of the coating that is dependent upon the magnitude of the shear stress of the

Fletcher Kimura; Werner Kaminsky; Gamal Khalil; James Riley; James Callis

2004-01-01

2

High resolution, 2-dimensional shear stress measurements from imaging polarimetry  

NASA Astrophysics Data System (ADS)

Here we present a novel method for obtaining high-resolution, 2-dimensional shear stress measurements over aerodynamic surfaces, based upon the dynamic birefringence of a shear sensitive, liquid crystal coating. Air flowing over the surface of a liquid crystal coating causes a measurable change in the birefringence of the coating that is dependent upon the magnitude of the shear stress of the airflow. The liquid crystal molecules also orient themselves in the direction of the applied shear stress. Using circularly polarized, monochromatic light and linear polarizers, the birefringence (|sin(?)|) and molecular orientation (extinction angle, ?) can be quantified from relatively straightforward intensity measurements. Through the use of a new imaging device developed in our lab known as Millipol, quantitative birefringence and extinction angle measurements can be made at the rate of 29 Hz. The birefringence and extinction angle data is then calibrated, resulting in real time, 2-dimensional shear stress vector maps with resolutions limited only by the CCD imager.

Kimura, Fletcher; Kaminsky, Werner; Khalil, Gamal; Riley, James; Callis, James

2004-11-01

3

Bed shear stress measurement using flexible micro-rods  

NASA Astrophysics Data System (ADS)

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

Farhadi, Alireza; Sindelar, Christine; Habersack, Helmut

2014-05-01

4

Windtunnel studies of surface shear stress vector distribution measurement using shear sensitive liquid crystal coatings  

Microsoft Academic Search

Shear sensitive liquid crystal coating (SSLCC) can measure surface shear stress vector distribution efficiently with a high\\u000a spatial resolution. The purpose of the present paper is to modify and extend the surface shear stress measurement technique\\u000a determined by Reda et al. to wind tunnel studies. All the facilities employed in the technique are very common and simple.\\u000a The measurement technique

JiSong Zhao; Peter Scholz; LiangXian Gu

5

Dynamic wall shear stress measurements in a turbulent channel flow  

NASA Astrophysics Data System (ADS)

To quantify and understand the dynamics of near wall momentum transfer, high spatial resolution, time-resolved measurements of wall shear stress distribution are essential. In this study, a film-based shear stress sensor has been used to measure the time-resolved local wall shear stress distribution in a turbulent channel flow. Measurements have been undertaken in a turbulent channel flow at Reynolds numbers up to 130,000 based on the bulk velocity and channel height. The measured fluctuating wall shear stress distribution provides spatio-temporal information of the characteristics of near wall structures by detecting their footprints. The span-wise extent of the positive two-point correlation of the stream-wise shear stress fluctuations provides the average width in the order of 100 wall units for the near-wall coherent structures. An investigation of the topological features of the velocity gradient and rate of strain tensors enables us to show an intrinsic characteristic of the near wall flow, which follows a two-dimensional flow pattern.

Amili, Omid; Soria, Julio

2010-11-01

6

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

NASA Astrophysics Data System (ADS)

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

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

2012-10-01

7

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

8

A carbon nanotube sensor for wall shear stress measurement  

Microsoft Academic Search

A novel carbon nanotube (CNT) sensor is being developed to measure the mean and fluctuating wall shear stress (WSS) in a turbulent\\u000a boundary layer. The CNT WSS sensor is based on the thermal principle and featured by high spatial and temporal resolutions\\u000a (in the order of nm and kHz, respectively), low power consumption (in the order of ?W), and a

H. L. Bai; W. J. Li; W. Chow; Y. Zhou

2010-01-01

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

Measurement of shear-stress distribution by liquid-crystal coating  

Microsoft Academic Search

In the present paper, a method for measuring the shear-stress distribution over a solid surface in a fluid flow is studied with a use of shear-sensitive liquid crystal coating. The color response of the liquid crystal coating is calibrated against the various shear stress magnitudes and directions using an experimental test section of laminar channel flow. The measurement of shear

N. Fujisawa; S. Funatani; S. Kosaka

2003-01-01

11

Measurement of shear-stress distribution by liquid-crystal coating  

NASA Astrophysics Data System (ADS)

In the present paper, a method for measuring the shear-stress distribution over a solid surface in a fluid flow is studied with a use of shear-sensitive liquid crystal coating. The color response of the liquid crystal coating is calibrated against the various shear stress magnitudes and directions using an experimental test section of laminar channel flow. The measurement of shear stress distribution is carried out with a use of two color CCD cameras situated side by side. The color to shear stress transformation is conducted by the analysis with use of relative hue as a calibration variable, which is a function of shear stress magnitudes and directions. The usefulness of this technique was confirmed by the measurement of shear stress distribution around a circular cylinder with small span.

Fujisawa, N.; Funatani, S.; Kosaka, S.

2003-04-01

12

Surface temperature and shear stress measurement using liquid crystals  

NASA Astrophysics Data System (ADS)

In this paper a video digital-imaging technique is described that is currently being developed to permit the assessment of surface temperature and shear stress distributions using liquid crystals. The background to liquid crystal research in aerodynamics is given first and this is followed by a description of the experimental apparatus, along with the method of digital analysis of the color components of the liquid crystal traces. Some typical calibrations of the crystals are then presented as well as details of the main aspects that need to be considered when using liquid crystals as a quantitative measurement technique. The use of the technique is then illustrated by taking the simple case of a heated circular jet impinging normally onto a flat plate.

Toy, Norman; Savory, Eric; Disimile, Peter

1991-10-01

13

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

Microsoft Academic Search

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

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

1994-01-01

14

Measurement of shear-stress distribution over a surface by liquid-crystal coating  

Microsoft Academic Search

In this paper, a method for measuring the instantaneous shear-stress distribution over a solid surface in a fluid flow is studied by using a surface-flow visualization technique with a shear-sensitive liquid-crystal coating. The colour response of the liquid-crystal coating is calibrated against the various shear-stress magnitudes and directions with an experimental test section of laminar channel flow. The measurement of

N Fujisawa; A Aoyama; S Kosaka

2003-01-01

15

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) [Castro Valley, CA

1987-01-01

16

Stress optical measurement of the third normal stress difference in polymer melts under oscillatory shear  

Microsoft Academic Search

Results are reported for the dynamic moduli,G' andG?, measured mechanically, and the dynamic third normal stress difference, measured optically, of a series bidisperse linear polymer melts under oscillatory shear. Nearly monodisperse hydrogenated polyisoprenes of molecular weights 53000 and 370000 were used to prepare blends with a volume fraction of long polymer,FL, of 0.10, 0.20, 0.30, 0.50, and 0.75. The results

J. A. Kornfield; G. G. Fuller; D. S. Pearson

1990-01-01

17

Side-implanted piezoresistive shear stress sensor for turbulent boundary layer measurement  

Microsoft Academic Search

In this dissertation, I discuss the device modeling, design optimization, fabrication, packaging and characterization of a micromachined floating element piezoresistive shear stress sensor for the time-resolved, direct measurement of fluctuating wall shear stress in a turbulent flow. This device impacts a broad range of applications from fundamental scientific research to industrial flow control and biomedical applications. The sensor structure integrates

Yawei Li

2008-01-01

18

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

2008-09-02

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

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

21

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

22

Combined measurements of flow-induced shear stress and gene expression of individual endothelial cells  

NASA Astrophysics Data System (ADS)

It is known that endothelial cells respond to the biomechanical forces induced by the blood flow by remodeling their shape. It is also postulated that different shear stress patterns modulate the gene expression of the cells. The mechanism by which they sense shear stress and the mechanotransduction pathway governing the blood-vessel wall interaction is still unknown and object of investigation. We used an optical, non-tactile measurement technique based on ?PIV to investigate the relationship between shear stress distribution, shape and gene expression on a single-cell level. The cells are cultured in parallel flow chambers and subjected to different flow conditions. The fluid flow velocity in several planes over the cell is measured. From the three-dimensional flow field velocity profiles are extracted and used to reconstruct the cell topography and the shear stress distribution over it. This technique allows to achieve a spatial resolution of up to 1 ?m attaining an average of 500 data points for each single cell. The gene expression measurements are performed with a shear responsive pKLF2-EGFP promoter construct transfected in the cells. Results will be shown on endothelial cells subjected to a steady flow inducing a nominal wall shear stress level of 1.5 Pa.

Rossi, Massimiliano; Lindken, Ralph; Hierck, Beerend P.; Westerweel, Jerry

2007-11-01

23

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

Microsoft Academic Search

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, lambda, 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

Devendra Parmar; Danny Sprinkle; Jag Singh

2005-01-01

24

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

Microsoft Academic Search

This study was designed to measure the pixel-by-pixel flow velocity and shear stress from phase-contrast MR images. An optimized\\u000a method was suggested and the use of the method was confirmed. A self-developed, straight steady flow model system was scanned\\u000a by MRI with a velocity-encoded phase-contrast sequence. In-house developed software was used for the pixel-by-pixel flow velocity\\u000a and shear stress measurements

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

2010-01-01

25

Infrared thermography for shear stress field measurements in flows  

Microsoft Academic Search

In thermo-fluid-dynamics, it is known the important role played by boundary layer. Therefore, the present paper wants to dwell on the possibility to enlarge the application of infrared measurement technique, in particular for subsonic flows analysis. Subsonic flows point out important problems of measurement for the low energy content. In order to overcome this drawback, a high thermal resolution camera

M. Malerba; J. Pirisinu; G. L. Rossi

26

A study on reynolds shear stress measurement by LDV  

Microsoft Academic Search

The measurement results by Laser Doppler Velocimetry (LDV) are compared with the direct numerical simulation result by Eggels\\u000a et al.[1] for a cylindrical pipe flow. In the case of a pipe flow, the bias error for mean velocity is very small, because the local\\u000a turbulent intensity is very small all over the pipe cross section. However the difference of the

Mizue Munekata; Hideki Ohba; Kazuyoshi Matsuzaki

2001-01-01

27

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.

Pickard, John E.; Ley, Klaus

2009-01-01

28

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

29

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

30

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

31

Wall shear stress measurement in a turbulent pipe flow using ultrasound Doppler velocimetry  

NASA Astrophysics Data System (ADS)

A turbulent boundary layer of a water flow is investigated by means of pulsed ultrasound Doppler velocimetry. The advantage of this method is the acquisition of complete velocity profiles along the sound propagation line within very short time intervals. The shear stress velocity, used for normalizing the velocity profiles, was determined by fitting the profiles to the universal profiles in a turbulent boundary layer obtained from Prandtl's mixing length theory. A coordinate transformation in the near-wall region is proposed to allocate the velocity data to "true" wall distances. From the experimental values of the wall shear stress velocity, the friction factors for a turbulent pipe flow are calculated and compared to the Blasius law. The overall error in measurement was estimated to +/-8.4%.

Nowak, M.

2002-05-01

32

Shear Stress and Atherosclerosis  

PubMed Central

Hemodynamic shear stress, the frictional force acting on vascular endothelial cells, is crucial for endothelial homeostasis under normal physiological conditions. When discussing blood flow effects on various forms of endothelial (dys)function, one considers two flow patterns: steady laminar flow and disturbed flow because endothelial cells respond differently to these flow types both in vivo and in vitro. Laminar flow which exerts steady laminar shear stress is atheroprotective while disturbed flow creates an atheroprone environment. Emerging evidence has provided new insights into the cellular mechanisms of flow-dependent regulation of vascular function that leads to cardiovascular events such as atherosclerosis, atherothrombosis, and myocardial infarction. In order to study effects of shear stress and different types of flow, various models have been used. In this review, we will summarize our current views on how disturbed flow-mediated signaling pathways are involved in the development of atherosclerosis.

Heo, Kyung-Sun; Fujiwara, Keigi; Abe, Jun-ichi

2014-01-01

33

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

34

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

35

Side-implanted piezoresistive shear stress sensor for turbulent boundary layer measurement  

NASA Astrophysics Data System (ADS)

In this dissertation, I discuss the device modeling, design optimization, fabrication, packaging and characterization of a micromachined floating element piezoresistive shear stress sensor for the time-resolved, direct measurement of fluctuating wall shear stress in a turbulent flow. This device impacts a broad range of applications from fundamental scientific research to industrial flow control and biomedical applications. The sensor structure integrates side-implanted, diffused resistors into the silicon tethers for piezoresistive detection. Temperature compensation is enabled by integrating a fixed, dummy Wheatstone bridge adjacent to the active shear-stress sensor. A theoretical nonlinear mechanical model is combined with a piezoresistive sensing model to determine the electromechanical sensitivity. Lumped element modeling (LEM) is used to estimate the resonant frequency. Finite element modeling is employed to verify the quasi-static and dynamic models. Two dominant electrical noise sources in the piezoresistive shear stress sensor, 1/f noise and thermal noise, and amplifier noise were considered to determine the noise floor. These models were then leveraged to obtain optimal sensor designs for several sets of specifications. The cost function, minimum detectable shear stress (MDS) formulated in terms of sensitivity and noise floor, is minimized subject to nonlinear constraints of geometry, linearity, bandwidth, power, resistance, and manufacturing limitations. The optimization results indicate a predicted optimal device performance with a MDS of O(0.1 mPa) and a dynamic range greater than 75 dB. A sensitivity analysis indicates that the device performance is most responsive to variations in tether width. The sensors are fabricated using an 8-mask, bulk micromachining process on a silicon wafer. An n-well layer is formed to control the space-charge layer thickness of reverse-biased p/n junction-isolated piezoresistors. The sensor geometry is realized using reactive ion etch (RIE) and deep reactive ion etch (DRIE). Hydrogen annealing is employed to smooth the sidewall scalloping caused by DRIE. The piezoresistors are achieved by side-wall boron implantation. The structure is finally released from the backside using the combination of DRIE and RIE. Electrical characterization indicates linear junction-isolated resistors, and a negligible leakage current (<0.12 muA) for the junction-isolated diffused piezoresistors up to a reverse bias voltage of -10 V. Using a known acoustically-excited wall shear stress for calibration, the sensor exhibited a sensitivity of 4.24 muV/Pa, a noise floor of 11.4 mPa/ Hz at 1 kHz, a linear response up to the maximum testing range of 2 Pa, and a flat dynamic response up to the testing limit of 6.7 kHz. These results, coupled with a wind-tunnel suitable package, result in a suitable transducer for turbulence measurements in low-speed flows, a first for piezoresistive MEMS-based direct shear stress sensors.

Li, Yawei

36

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

37

Shear-stress measurement in aerodynamic testing using cholesteric liquid crystals  

Microsoft Academic Search

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

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

1989-01-01

38

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

PubMed Central

Based upon theory, wall shear stress (WSS), an important determinant of endothelial function and gene expression, has been assumed to be constant along the arterial tree and the same in a particular artery across species. In vivo measurements of WSS, however, have shown that these assumptions are far from valid. In this survey we will discuss the assessment of WSS in the arterial system in vivo and present the results obtained in large arteries and arterioles. In vivo WSS can be estimated from wall shear rate, as derived from non-invasively recorded velocity profiles, and whole blood viscosity in large arteries and plasma viscosity in arterioles, avoiding theoretical assumptions. In large arteries velocity profiles can be recorded by means of a specially designed ultrasound system and in arterioles via optical techniques using fluorescent flow velocity tracers. It is shown that in humans mean WSS is substantially higher in the carotid artery (1.1–1.3 Pa) than in the brachial (0.4–0.5 Pa) and femoral (0.3–0.5 Pa) arteries. Also in animals mean WSS varies substantially along the arterial tree. Mean WSS in arterioles varies between about 1.0 and 5.0 Pa in the various studies and is dependent on the site of measurement in these vessels. Across species mean WSS in a particular artery decreases linearly with body mass, e.g., in the infra-renal aorta from 8.8 Pa in mice to 0.5 Pa in humans. The observation that mean WSS is far from constant along the arterial tree implies that Murray’s cube law on flow-diameter relations cannot be applied to the whole arterial system. Because blood flow velocity is not constant along the arterial tree either, a square law also does not hold. The exponent in the power law likely varies along the arterial system, probably from 2 in large arteries near the heart to 3 in arterioles. The in vivo findings also imply that in in vitro studies no average shear stress value can be taken to study effects on endothelial cells derived from different vascular areas or from the same artery in different species. The cells have to be studied under the shear stress conditions they are exposed to in real life.

Hoeks, Arnold P. G.

2008-01-01

39

Suppression of Microstructural Influences on the Acoustoelastic Measurement of Stress by Interchanging Shear Wave Propagation and Polarization Directions  

Microsoft Academic Search

Continuum mechanics predicts that microstructural influences can be removed from acoustoelastic measurements of stress by comparing the velocities of two shear waves whose directions of polarization and propagation have been interchanged. This paper reports an experimental confirmation of the theory based on the angular dependence of horizontally polarized shear waves in aluminum plates. Measurements on 6061-T6 A1 and 1100-H14 Al,

R. B. Thompson; S. S. Lee; J. F. Smith

1983-01-01

40

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

NASA Astrophysics Data System (ADS)

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 combination with the image deformation technique. These experimental methods are applied to the measurement of wall-shear-stress distributions of air flow at a free-stream velocity of 15 m s-1 on a flat plate and an NACA0018 airfoil. The experiments are carried out at zero angle of attack for the flat plate and at 0° and ±6° angles of attack for the airfoil, and then the variations of shear-stress distribution along these surfaces are studied. These measurements in wall shear stresses agree with each other within their experimental uncertainties, suggesting the validity of experimental methods for non-intrusive shear-stress measurements. It is found that the wall-shear-stress distribution shows a small negative value upstream of the reattachment point on the NACA0018 airfoil, which is followed by an increase in shear stresses downstream due to laminar-turbulent transition of boundary layers. Such behavior of wall-shear-stress distribution is well correlated with the mean flow and turbulence characteristics along the airfoil surfaces, which are measured by PIV.

Fujisawa, N.; Oguma, Y.; Nakano, T.

2009-06-01

41

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

42

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

43

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

44

Wall shear stress measurement in a turbulent pipe flow using ultrasound Doppler velocimetry  

Microsoft Academic Search

A turbulent boundary layer of a water flow is investigated by means of pulsed ultrasound Doppler velocimetry. The advantage of this method is the acquisition of complete velocity profiles along the sound propagation line within very short time intervals. The shear stress velocity, used for normalizing the velocity profiles, was determined by fitting the profiles to the universal profiles in

M. Nowak

2002-01-01

45

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

46

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

47

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

48

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

49

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

NASA Astrophysics Data System (ADS)

An interfacial rheometer for both stress- and strain-controlled measurements of shear rheological properties at liquid/liquid and gas/liquid interfaces is presented. The device is based on a rotating or oscillating biconical bob design in combination with a low friction electronically commutated motor system. The interfacial shear stress, viscosity, and dynamic moduli are obtained by solving the Stokes equations (low Reynolds number) along with the Boussinesq-Scriven interfacial stress tensor, which is used for the boundary conditions at the interface. An improved and simple numerical method for the calculation of the velocity distribution in the measuring cell is presented. The scope and limitations of the rheometer are discussed. Results from steady shear and oscillatory experiments as well as creep recovery and stress relaxation tests at both oil/water and air/water interfaces with adsorbed films of a globular protein (ovalbumin) and spread films of a surfactant (sorbitan tristearate) are presented.

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

2003-11-01

50

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

51

Flexible Polymer Sensors for In Vivo Intravascular Shear Stress Analysis  

Microsoft Academic Search

Hemodynamic forces, specifically fluid shear stress, play an important role in the focal nature of arterial plaque formation known as atherosclerosis. We hereby developed biocompatible and flexible intravascular microelectromechanical systems sensor to measure real-time shear stress in the aortas of New Zealand white (NZW) rabbits. Titanium (Ti) and platinum (Pt) were deposited on silicon wafers and patterned to form the

Hongyu Yu; Lisong Ai; Mahsa Rouhanizadeh; Darhsin Patel; Eun Sok Kim; Tzung K. Hsiai

2008-01-01

52

Wall Shear Stress Distribution for Flow around a Circular Cylinder 60  

National Technical Information Service (NTIS)

Although the problem of calculating the shear stress distribution around a cylinder has received considerable attention, no direct measurements have been reported. One of the reasons for this is that instruments for measuring the shear stress are limited ...

H. G. Dimopulos T. J. Hanratty

1967-01-01

53

Variation of compressional velocities in simulated fault gouge under normal and direct shear stress  

Microsoft Academic Search

An experimental method designed to measure ultrasonic velocities in simulated fault gouge subjected to normal and direct shearing stress yields these results. For a well-compacted, unsorted, fine-grained, dry granite gouge under constant normal stress, reversible changes in Vp with shear stress are observed prior to stable sliding. Vp decreases by as much as 9% with increasing shear stress for the

L. Peselnick; J. H. Dieterich; V. I. Mjachkin; G. A. Sobolev

1976-01-01

54

Stress distribution over endothelial cells in shear flow  

NASA Astrophysics Data System (ADS)

High resolution micro-PIV measurements were made over cultured endothelial cells (ECs) immersed in a shear flow. The objective of this study was to determine the relative importance of the spatially varying pressure field over the cells relative to local wall shear stress. Measurements were made over ECs flush mounted in a small rectangular channel flow chamber; flow was laminar with mean wall shear of 10 dynes/cm^2. Using multiple measurement planes, local surface height variations, wall shear and surface pressure could be extracted from the measurements. Data clearly indicate that surface pressure associated with the flow is on the same order as the wall shear. Consequently, the total stress tensor acting on ECs needs to be considered in examing bio-chemical activity in vascular disease.

Leong, C. M.; Voorhees, A.; Wei, T.; Nackman, G. B.

2004-11-01

55

Fluid shear stress threshold regulates angiogenic sprouting.  

PubMed

The density and architecture of capillary beds that form within a tissue depend on many factors, including local metabolic demand and blood flow. Here, using microfluidic control of local fluid mechanics, we show the existence of a previously unappreciated flow-induced shear stress threshold that triggers angiogenic sprouting. Both intraluminal shear stress over the endothelium and transmural flow through the endothelium above 10 dyn/cm(2) triggered endothelial cells to sprout and invade into the underlying matrix, and this threshold is not impacted by the maturation of cell-cell junctions or pressure gradient across the monolayer. Antagonizing VE-cadherin widened cell-cell junctions and reduced the applied shear stress for a given transmural flow rate, but did not affect the shear threshold for sprouting. Furthermore, both transmural and luminal flow induced expression of matrix metalloproteinase 1, and this up-regulation was required for the flow-induced sprouting. Once sprouting was initiated, continuous flow was needed to both sustain sprouting and prevent retraction. To explore the potential ramifications of a shear threshold on the spatial patterning of new sprouts, we used finite-element modeling to predict fluid shear in a variety of geometric settings and then experimentally demonstrated that transmural flow guided preferential sprouting toward paths of draining interstitial fluid flow as might occur to connect capillary beds to venules or lymphatics. In addition, we show that luminal shear increases in local narrowings of vessels to trigger sprouting, perhaps ultimately to normalize shear stress across the vasculature. Together, these studies highlight the role of shear stress in controlling angiogenic sprouting and offer a potential homeostatic mechanism for regulating vascular density. PMID:24843171

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

2014-06-01

56

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) [Carlsbad, NM; Jepsen, Richard A. (Carlsbad, NM) [Carlsbad, NM

2002-01-01

57

Regulation of endothelial connexin40 expression by shear stress.  

PubMed

Endothelial connexin (Cx)40 plays an important role in signal propagation along blood vessel walls, modulating vessel diameter and thereby blood flow. Blood flow, in turn, has been shown to alter endothelial Cx40 expression. However, the timing and shear stress dependence of this relationship have remained unclear, as have the signal transduction pathways involved and the functional implications. Therefore, the aim of this study was to quantify the effects of shear stress on endothelial Cx40 expression, to analyze the role of phosphoinositide 3-kinase (PI3K)/Akt signaling involved, and to assess the possible functional consequences for the adaptation of microvascular networks. First-passage human umbilical vein endothelial cells were exposed to defined shear stress conditions and analyzed for Cx40 using real-time RT-PCR and immunoblot analysis. Shear stress caused long-term induction of Cx40 protein expression, with two short-term mRNA peaks at 4 and 16 h, indicating the dynamic nature of the adaptation process. Maximum shear stress-dependent induction was observed at shear levels between 6 and 10 dyn/cm(2). Simulation of this pattern of shear-dependent Cx expression in a vascular adaptation model of a microvascular network led to an improved fit for the simulated results to experimental measurements. Cx40 expression was greatly reduced by inhibiting PI3K or Akt, with PI3K activity being required for basal Cx40 expression and Akt activity taking part in its shear stress-dependent induction. PMID:22021330

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

2012-01-01

58

Shear strength measurements of lubricants at high pressure  

NASA Technical Reports Server (NTRS)

Measurements of lubricant shear rheological behavior in the amorphous solid region and near the liquid-solid transition are reported on three lubricants under pressure. Elastic, plastic and viscous behavior was observed. The maximum yield shear stress (limiting shear stress) is a function of temperature and pressure and is believed to be the property which determines the maximum traction in elastohydrodynamic contacts such as traction drives.

Bair, S.; Winer, W. O.

1979-01-01

59

Attempt to Measure the First Normal-Stress Difference N(1) in Shear Flow for a Polyisobutylene/Decalin Solution 'D2b' at Shear Rates up to 10 to the 6th Power/S.  

National Technical Information Service (NTIS)

It is well known that the state of stress for viscoelastic liquids in steady shear flow is determined by a stress sigma and by N1 and N2, the first and second normal stress differences, together with an isotropic contribution which is not of direct rheolo...

A. S. Lodge

1989-01-01

60

Prediction of plantar shear stress distribution by artificial intelligence methods.  

PubMed

Shear forces under the human foot are thought to be responsible for various foot pathologies such as diabetic plantar ulcers and athletic blisters. Frictional shear forces might also play a role in the metatarsalgia observed among hallux valgus (HaV) and rheumatoid arthritis (RA) patients. Due to the absence of commercial devices capable of measuring shear stress distribution, a number of linear models were developed. All of these have met with limited success. This study used nonlinear methods, specifically neural network and fuzzy logic schemes, to predict the distribution of plantar shear forces based on vertical loading parameters. In total, 73 subjects were recruited; 17 had diabetic neuropathy, 14 had HaV, 9 had RA, 11 had frequent foot blisters, and 22 were healthy. A feed-forward neural network (NN) and adaptive neurofuzzy inference system (NFIS) were built. These systems were then applied to a custom-built platform, which collected plantar pressure and shear stress data as subjects walked over the device. The inputs to both models were peak pressure, peak pressure-time integral, and time to peak pressure, and the output was peak resultant shear. Root-mean-square error (RMSE) values were calculated to test the models' accuracy. RMSE/actual shear ratio varied between 0.27 and 0.40 for NN predictions. Similarly, NFIS estimations resulted in a 0.28-0.37 ratio for local peak values in all subject groups. On the other hand, error percentages for global peak shear values were found to be in the range 11.4-44.1. These results indicate that there is no direct relationship between pressure and shear magnitudes. Future research should aim to decrease error levels by introducing shear stress dependent variables into the models. PMID:19725696

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

2009-09-01

61

Couette membrane filtration with constant shear stress.  

PubMed

Recent developments in the field of blood component separation have revealed the usefulness of membrane filtration using couette type configurations and Taylor vortices as an efficient and effective method. The authors have analyzed in detail the physical and chemical effects on whole blood separated into protein rich plasma, and concentrated red blood cell suspensions, using this technique. The authors also have calculated and demonstrated the technical specifications required to provide laminar flow with Taylor Vortex formation throughout the device, as well as those required to retain constant shear stress on the blood components as viscosity changes. By maintaining constant shear stress below a critical level, it is possible to avoid shear induced hemolysis and to maintain maximal separation efficiency throughout the procedure. The device has further been designed to alter the filtration velocity along the membrane so that the critical filtration velocity is nowhere exceeded, i.e., concentration polarization effects are prevented. PMID:3196536

Fischel, R J; Fischel, H; Shatzel, A; Lange, W P; Cahill, D; Gervais, D; Ascher, N L

1988-01-01

62

Effects of physiologically relevant dynamic shear stress on platelet complement activation.  

PubMed

Disturbed shear stress, commonly found in cardiovascular diseases, plays important roles in platelet activation and functions. It has been reported that when activated by elevated shear stress, platelets were able to support complement activation to completion. In this study, through a dynamic cone and plate shearing device, three physiologically relevant shear stresses were applied to platelets, mimicking the shear conditions when platelets pass through a normal left coronary artery (0.05-1?Pa), a 60% stenosis (elevated shear stress at 6.5?Pa for less than 0.1?s), and when platelets are trapped in a recirculation zone past a stenosis (<0.5?Pa). After shear exposure, platelet-surface complement activation (C1q, C4d, iC3b, and SC5b-9 depositions) was measured using a solid-phase ELISA approach and flow cytometry. Production of complement regulatory proteins - C1-inhibitor (C1-INH) and complement receptor 1 (CR1), was also measured. Results demonstrated that low-pulsatile shear stress (recirculation) was able to initiate platelet complement activation, by increasing C1q deposition significantly. Both pathological shear stresses triggered significant increases in C1 inhibitor generation and noticeable changes in CR1 production, effectively preventing complement activation from completion. These results suggested that for platelets, low-pulsatile shear stress may be more pro-atherogenic, compared to elevated shear stress, especially when the shear stress exposure time is short. PMID:21679034

Shanmugavelayudam, Saravan Kumar; Rubenstein, David A; Yin, Wei

2011-01-01

63

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...

64

Vane shear and rheological measurement of estuarine muds.  

National Technical Information Service (NTIS)

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

A. E. James S. J. Stone

1990-01-01

65

Variation of compressional velocities in simulated fault gorge under normal and direct shear stress  

Microsoft Academic Search

An experimental method designed to measure ultrasonic velocities in simulated fault gouge subjected to normal and direct shearing stress is described. For a well-compacted, unsorted, fine-grained, dry granite gouge under constant normal stress, reversible changes in V\\/sub p\\/ with shear stress are observed prior to stable sliding. V\\/sub p\\/ decreases by as much as 9 percent with increasing shear stress

L. Peselnick; J. H. Dieterich; V. I. Mjachkin; G. A. Sobolev

1976-01-01

66

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.

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

2014-01-01

67

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

NASA Astrophysics Data System (ADS)

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

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

68

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

National Technical Information Service (NTIS)

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 ae...

D. C. Reda M. C. Wilder

1998-01-01

69

The high pressure high shear stress rheology of liquid lubricants  

NASA Astrophysics Data System (ADS)

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. The model, with simplifying assumptions, is compared with disk machine results. This model, with change of yield criterion, may be applicable to some shear thinning liquids at low pressure. Limiting shear stress varies with pressure in the same manner as the ultimate shear strength of solid polymers.

Bair, S.; Winer, W. O.

1992-01-01

70

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

71

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.

Rupprecht, Peter; Gole, Laurent; Rieu, Jean-Paul; Vezy, Cyrille; Ferrigno, Rosaria; Mertani, Hichem C.; Riviere, Charlotte

2012-01-01

72

A semi-empirical approach for estimation of bed shear stress in a tailings pond  

Microsoft Academic Search

Wind-driven waves and currents exert shear stress on the bed of a tailings pond. A semi-empirical approach for estimating\\u000a this bed shear stress is presented in this paper. For the first time in a mine tailings storage facility, the current-induced\\u000a component of the bed shear stress was obtained using 1,200-kHz acoustic Doppler current profiler measurements of in situ currents\\u000a and

Laxmi Kant Kachhwal; Ernest K. Yanful; Colin D. Rennie

73

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

74

Performance of a Photonic Wall Shear Stress Sensor  

NASA Astrophysics Data System (ADS)

The performance of a photonic wall shear stress sensor prototype based on the so-called whispering gallery modes (WGM) of polymeric microspheres is investigated in steady and unsteady flows. In this sensor, the shear force due to the fluid flow is transmitted to a Polydimethylsyloxane sphere of several hundred microns in diameter which serves as the sensor. The corresponding optical resonance (WGM) shifts are monitored to determine the wall shear stress. Sensor performance for dynamic range, resolution and bandwidth are studied analytically, and validated experimentally. The validation experiments for the prototype sensor with measurement area of 1mm^2 are made in a two-dimensional channel flow and in an acoustic plane wave tube. These measurements indicate a shear stress resolution of ˜10-3 Pa and a dynamic range of ˜100dB for the prototype. The PDMS sphere used in the prototype has a base-curing-agent ratio of 40:1. Different sensitivities and measurement ranges can be obtained using different PDMS mixing ratios.

Ayaz, Ulas; Ioppolo, Tindaro; Otugen, Volkan

2009-11-01

75

Calculation of turbulent shear stress in supersonic boundary layer flows  

NASA Technical Reports Server (NTRS)

An analysis of turbulent boundary layer flow characteristics and the computational procedure used are discussed. The integrated mass and momentum flux profiles and differentials of the integral quantities are used in the computations so that local evaluation of the streamwise velocity gradient is not necessary. The computed results are compared with measured shear stress data obtained by using hot wire anemometer and laser velocimeter techniques. The flow measurements were made upstream and downstream of an adiabatic unseparated interaction of an oblique shock wave with the turbulent boundary layer on the flat wall of a two dimensional wind tunnel. A comparison of the numerical analysis and actual measurements is made and the effects of small differences in mean flow profiles on the computed shear stress distributions are discussed.

Sun, C. C.; Childs, M. E.

1974-01-01

76

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

77

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

78

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

79

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

80

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

81

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

PubMed Central

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

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

2012-01-01

82

Wall-Shear Stress Distribution in Turbulent Duct Flow  

NASA Astrophysics Data System (ADS)

The wall-shear stress sensor MPS^3 based on flexible micro-pillars has been used to experimentally assess the two-dimensional wall-shear stress distribution in turbulent duct flow at moderate Reynolds number. A sensor array covering an area of 90x125 viscous length-scales along the streamwise and spanwise direction, respectively and 1-D sensor-lines spanning 125 viscous length-scales have been applied. The results evidence the co-existence of low- and high-shear regions representing ``foot-prints'' of near-wall coherent structures. Applying Taylor's hypothesis allows to crudely assess the streamwise length-scales of the near-wall flow field. Especially the low-shear regions attain streamwise dimensions of approximately 1,000 viscous length-scales. These low-shear regions resemble long meandering bands locally interrupted and deflected by regions of high-shear stress. A qualitative comparison evidences the structures detected in the present study to be similar to wall-shear stress distributions reported in the literature and to structures found in higher regions of the boundary layer. The results allow assessing statistics of the streamwise and spanwise wall-shear stress distribution, such as convection velocities of wall-shear stress fluctuations, two-point-, and auto-correlations. Geometric properties of the streak-like wall-shear stress distributions will also be discussed.

Große, Sebastian; Schröder, Wolfgang

2008-11-01

83

Non-Motile Primary Cilia as Fluid Shear Stress Mechanosensors  

PubMed Central

Primary cilia are sensory organelles that transmit extracellular signals into intracellular biochemical responses. Structural and functional defects in primary cilia are associated with a group of human diseases, known as ciliopathies, with phenotypes ranging from cystic kidney and obesity to blindness and mental retardation. Primary cilia mediate mechano- and chemosensation in many cell types. The mechanosensory function of the primary cilia requires the atypical G-protein-coupled receptor polycystin-1 and the calcium-permeable nonselective cation channel polycystin-2. Mechanical stimulations such as fluid-shear stress of the primary cilia initiate intracellular calcium rise, nitric oxide release, and protein modifications. In this review, we describe a set of protocols for cell culture to promote ciliation, mechanical stimulations of the primary cilia, and measurements of calcium rise and nitric oxide release induced by fluid shear stress.

Nauli, Surya M.; Jin, Xingjian; AbouAlaiwi, Wissam A.; El-Jouni, Wassim; Su, Xuefeng; Zhou, Jing

2014-01-01

84

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

85

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

Microsoft Academic Search

A signal-to-noise ratio (SNR) measure based on the octahedral shear strain (the maximum shear strain in any plane for a 3D state of strain) is presented for magnetic resonance elastography (MRE), where motion-based SNR measures are commonly used. The shear strain, gamma, is directly related to the shear modulus, mu, through the definition of shear stress, tau = mugamma. Therefore,

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

2011-01-01

86

Basal shear stress of debris flow in the runout phase  

NASA Astrophysics Data System (ADS)

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

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

2013-11-01

87

Local Flow and Shear Stress Sensor Based on Molecular Rotors.  

National Technical Information Service (NTIS)

A method for detecting local shear stress values using molecular rotors that allows for an extremely sensitive determination of a shear stress field or a flow field, even at very low flow rates. In one embodiment, molecular rotors may be adhered to a fibe...

M. A. Haidekker

2005-01-01

88

Shear stress fluctuations in the granular liquid and solid phases.  

PubMed

We report on experimentally observed shear stress fluctuations in both granular solid and fluid states, showing that they are non-Gaussian at low shear rates, reflecting the predominance of correlated structures (force chains) in the solidlike phase, which also exhibit finite rigidity to shear. Peaks in the rigidity and the stress distribution's skewness indicate that a change to the force-bearing mechanism occurs at the transition to fluid behavior, which, it is shown, can be predicted from the behavior of the stress at lower shear rates. In the fluid state stress is Gaussian distributed, suggesting that the central limit theorem holds. The fiber bundle model with random load sharing effectively reproduces the stress distribution at the yield point and also exhibits the exponential stress distribution anticipated from extant work on stress propagation in granular materials. PMID:16197182

Dalton, F; Farrelly, F; Petri, A; Pietronero, L; Pitolli, L; Pontuale, G

2005-09-23

89

In-vitro wall shear measurements at aortic valve prostheses.  

PubMed

Wall shear distributions during the cardiac cycle at the valve rings of Starr-Edwards, Björk-Shiley and Lillehei-Kaster aortic valves are measured and compared with thresholds reported for shear-induced trauma of blood components. Further, for the disk valves, the influence of pulse rate on wall shear stresses is evaluated. Hot film anemometry with flush-mounted wall shear probes is used as measurement technique in a pulsatile flow mock circuit. The experimental systolic data support the better hemodynamic characteristics of the disk valves over the ball valve also with respect to the threshold shear stresses of flow induced blood trauma. These results are confirmed by postoperative clinical studies, where lower LDH-values are found with the disk than with the ball valves. During diastole, however, high shear stresses are measured and calculated at the valve ring of the Björk-Shiley prosthesis, which can be referred to the non-overlapping closing mechanism. This result is discussed with respect to the often observed thrombus formation at the disk downstream of the smaller orifice of the Björk-Shiley valve. PMID:6736063

Tillmann, W; Reul, H; Herold, M; Bruss, K H; van Gilse, J

1984-01-01

90

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

91

Measurement of temperature using speckle shearing interferometry.  

PubMed

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

Shakher, C; Nirala, A K

1994-04-10

92

The origin of persistent shear stress in supercooled liquids.  

PubMed

The persistence of shear stress fluctuations in viscous liquids is a direct consequence of the non-zero shear stress of the local potential minima which couples stress relaxation to transitions between inherent structures. In simulations of 2D and 3D glass forming mixtures, we calculate the distribution of this inherent shear stress and demonstrate that the variance is independent of temperature and obeys a power law in density. The inherent stress is shown to involve only long wavelength fluctuations, evidence of the central role of the static boundary conditions in determining the residual stress left after the minimization of the potential energy. A temperature T(?) is defined to characterise the crossover from stress relaxation governed by binary collisions at high temperatures to low temperature relaxation dominated by the relaxation of the inherent stress. T(?) is found to coincide with the breakdown of the Stokes-Einstein scaling of diffusion and viscosity. PMID:22779664

Abraham, Sneha; Harrowell, Peter

2012-07-01

93

Oral shear stress predicts flavour perception in viscous solutions.  

PubMed

The perception of sweetness and flavour were studied in viscous solutions containing 50 g/l sucrose, 100 p.p.m. iso-amyl acetate and varying concentrations of three hydrocolloid thickeners (guar gum, lambda-carrageenan and hydroxypropylmethyl cellulose). Zero-shear viscosity of the samples ranged from 1 to 5000 mPas. Perception of both sweetness and aroma was suppressed at thickener concentrations above c* (coil overlap concentration, the point at which there is an abrupt increase in solution viscosity as thickener concentration is increased). Sensory data for the three hydrocolloids was only loosely correlated with their concentration relative to c* (c/c* ratio), particularly above c*. However, when perceptual data were plotted against the Kokini oral shear stress (tau), calculated from rheological measurements, data for the three hydrocolloids aligned to form a master-curve, enabling the prediction of flavour intensity in such systems. The fact that oral shear stress can be used to model sweetness and aroma perception supports the hypothesis that somatosensory tactile stimuli can interact with taste and aroma signals to modulate their perception. PMID:12502520

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

2003-01-01

94

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.

Davies, Peter F

2010-01-01

95

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

96

Red blood cell damage by shear stress for different blood types  

NASA Astrophysics Data System (ADS)

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

Arwatz, Gilad; Bedkowski, Katherine; Smits, Alexander

2011-11-01

97

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

98

Interfacial shear stresses in SiC and Al/sub 2/O/sub 3/ fiber-reinforced glasses  

SciTech Connect

Single fiber pullout tests were performed on silicon carbide and sapphire filaments embedded in glass matrices to determine the interfacial shear strengths both as a function of residual stress and as a function of fiber coating. The effect of residual stress on the interfacial shear stress was studied by altering the glass matrix composition, and hence, the thermal mismatch between fiber and matrix. The presence of a carbon coating on sapphire is sufficient to reduce the interfacial shear stress to measurable levels, while excess carbon at the SiC/glass interface increases the interfacial shear stress. 15 references.

Goettler, R.W.; Faber, K.T.

1988-08-01

99

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

100

Wall shear stress in Görtler vortex boundary layer flow  

NASA Astrophysics Data System (ADS)

The development of wall shear stress in concave surface boundary layer flows in the presence of Görtler vortices was experimentally studied by means of hot-wire measurements. The wavelengths of the vortices were preset by thin vertical perturbation wires so to produce the most amplified wavelengths. Three different vortex wavelengths of 12, 15, and 20 mm were considered, and near-wall velocity measurements were carried out to obtain the ``linear'' layers of velocity profiles in the boundary layers. The wall shear stress coefficient Cf was estimated from the velocity gradient of the ``linear'' layer. The streamwise developments of boundary layer displacement and momentum thickness at both upwash and downwash initially follow the Blasius (laminar boundary layer) curve up to a certain streamwise location. Further downstream, they depart from the Blasius curve such that they increase at upwash and decrease at downwash before finally converge to the same value due to the increased mixing as a consequence of transition to turbulence. The spanwise-averaged wall shear stress coefficient Cf, which initially follows the Blasius curve, increases well above the local turbulent boundary layer value further downstream due to the nonlinear effect of Görtler instability and the secondary instability modes. Three different regions are identified based on the streamwise development of Cf, namely linear, nonlinear, and transition to turbulence regions. The onset of nonlinear region is defined as the streamwise location where the Cf begins to depart from the Blasius curve. In the nonlinear region, the spanwise distribution of Cf at the downwash becomes narrower, and there is no inflection point found further downstream.

Tandiono; Winoto, S. H.; Shah, D. A.

2009-08-01

101

Elevated Glucose Impairs the Endothelial Cell Response to Shear Stress  

Microsoft Academic Search

Early atherosclerotic lesions develop predominantly where laminar blood flow is interrupted and mean shear stress is low,\\u000a indicating that local hemodynamics influence atherosclerotic development. Diabetics develop diffuse atherosclerosis compared\\u000a to nondiabetics, suggesting that diabetic endothelial cells fail to properly sense or respond to fluid shear forces. Using\\u000a an in vitro model we exposed endothelial cells to shear forces using a

Jeremy B. Brower; Jerome H. Targovnik; Benjamin P. Bowen; Michael R. Caplan; Stephen P. Massia

2009-01-01

102

Shear strengths of wood measured by various short beam shear test methods  

Microsoft Academic Search

We conducted three types of short beam shear tests of western hemlock ( Tsuga heterophylla Sarg.) under various span\\/depth ratios, and examined whether the maximum shear stress was used as the shear strength. The following results were obtained. (1) In the short beam shear tests under the three-point loading method, it was difficult to have the specimen failing by horizontal

Hiroshi Yoshihara; Toshifumi Furushima

2003-01-01

103

Surface flow visualization with shear stress sensitivive liquid crystals  

Microsoft Academic Search

The use of non-capsulated liquid crystals, which react directly to wall shear forces, for surface flow visualization, is presented. The temperature sensitivity is avoided by producing a mixture with an event temperature (first red indication temperature) above the expected investigation temperature range. Below the event temperature the liquid crystals are only sensitive to shear stress, resulting in a wavelength variation

K. Pengel

1988-01-01

104

Influence of shear and deviatoric stress on the evolution of permeability in fractured rock  

NASA Astrophysics Data System (ADS)

The evolution of permeability in fractured rock as a function of effective normal stress, shear displacement, and damage remains a complex issue. In this contribution, we report on experiments in which rock surfaces were subject to direct shear under controlled pore pressure and true triaxial stress conditions while permeability was monitored continuously via flow parallel to the shear direction. Shear tests were performed in a pressure vessel under drained conditions on samples of novaculite (Arkansas) and diorite (Coso geothermal field, California). The sample pairs were sheared to 18 mm of total displacement at 5 ?m/s at room temperature and at effective normal stresses on the shear plane ranging from 5 to 20 MPa. Permeability evolution was measured throughout shearing via flow of distilled water from an upstream reservoir discharging downstream of the sample at atmospheric pressure. For diorite and novaculite, initial (preshear) fracture permeability is 0.5-1 × 10-14 m2 and largely independent of the applied effective normal stresses. These permeabilities correspond to equivalent hydraulic apertures of 15-20 ?m. Because of the progressive formation of gouge during shear, the postshear permeability of the diorite fracture drops to a final steady value of 0.5 × 10-17 m2. The behavior is similar in novaculite but the final permeability of 0.5 × 10-16 m2 is obtained only at an effective normal stress of 20 MPa.

Faoro, Igor; Niemeijer, Andre; Marone, Chris; Elsworth, Derek

2009-01-01

105

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

106

Shear-stress sensitive lenticular vesicles for targeted drug delivery  

NASA Astrophysics Data System (ADS)

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

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

2012-08-01

107

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

108

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

PubMed

We present a torsional bridge setup for the electro-mechanical characterization of devices integrated in the surface of silicon beams under mechanical in-plane shear stress. It is based on the application of a torsional moment to the longitudinal axis of the silicon beams, which results in a homogeneous in-plane shear stress in the beam surface. The safely applicable shear stresses span the range of ±50 MPa. Thanks to a specially designed clamping mechanism, the unintended normal stress typically stays below 2.5% of the applied shear stress. An analytical model is presented to compute the induced shear stress. Numerical computations verify the analytical results and show that the homogeneity of the shear stress is very high on the beam surface in the region of interest. Measurements with piezoresistive microsensors fabricated using a complementary metal-oxide-semiconductor process show an excellent agreement with both the computational results and comparative measurements performed on a four-point bending bridge. The electrical connection to the silicon beam is performed with standard bond wires. This ensures that minimal forces are applied to the beam by the electrical interconnection to the external instrumentation and that devices with arbitrary bond pad layout can be inserted into the setup. PMID:22225242

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

2011-12-01

109

Dilute rigid dumbbell suspensions in large-amplitude oscillatory shear flow: Shear stress response  

NASA Astrophysics Data System (ADS)

We examine the simplest relevant molecular model for large-amplitude shear (LAOS) flow of a polymeric liquid: the suspension of rigid dumbbells in a Newtonian solvent. We find explicit analytical expressions for the shear rate amplitude and frequency dependences of the first and third harmonics of the alternating shear stress response. We include a detailed comparison of these predictions with the corresponding results for the simplest relevant continuum model: the corotational Maxwell model. We find that the responses of both models are qualitatively similar. The rigid dumbbell model relies entirely on the dumbbell orientation to explain the viscoelastic response of the polymeric liquid, including the higher harmonics in large-amplitude oscillatory shear flow. Our analysis employs the general method of Bird and Armstrong ["Time-dependent flows of dilute solutions of rodlike macromolecules," J. Chem. Phys. 56, 3680 (1972)] for analyzing the behavior of the rigid dumbbell model in any unsteady shear flow. We derive the first three terms of the deviation of the orientational distribution function from the equilibrium state. Then, after getting the "paren functions," we use these for evaluating the shear stress for LAOS flow. We find the shapes of the shear stress versus shear rate loops predicted to be reasonable.

Bird, R. B.; Giacomin, A. J.; Schmalzer, A. M.; Aumnate, C.

2014-02-01

110

Dilute rigid dumbbell suspensions in large-amplitude oscillatory shear flow: shear stress response.  

PubMed

We examine the simplest relevant molecular model for large-amplitude shear (LAOS) flow of a polymeric liquid: the suspension of rigid dumbbells in a Newtonian solvent. We find explicit analytical expressions for the shear rate amplitude and frequency dependences of the first and third harmonics of the alternating shear stress response. We include a detailed comparison of these predictions with the corresponding results for the simplest relevant continuum model: the corotational Maxwell model. We find that the responses of both models are qualitatively similar. The rigid dumbbell model relies entirely on the dumbbell orientation to explain the viscoelastic response of the polymeric liquid, including the higher harmonics in large-amplitude oscillatory shear flow. Our analysis employs the general method of Bird and Armstrong ["Time-dependent flows of dilute solutions of rodlike macromolecules," J. Chem. Phys. 56, 3680 (1972)] for analyzing the behavior of the rigid dumbbell model in any unsteady shear flow. We derive the first three terms of the deviation of the orientational distribution function from the equilibrium state. Then, after getting the "paren functions," we use these for evaluating the shear stress for LAOS flow. We find the shapes of the shear stress versus shear rate loops predicted to be reasonable. PMID:24559367

Bird, R B; Giacomin, A J; Schmalzer, A M; Aumnate, C

2014-02-21

111

Simple shearing interferometer suitable for vibration measurements  

NASA Astrophysics Data System (ADS)

Recently there has been an increasing interest in the application of shearography for modal analysis of vibrating objects. New interferometric systems, which are simple and flexible are of interest for engineering and industrial applications. An electronic speckle pattern shearing interferometer (ESPSI) with a very simple shearing device is used for study of vibrations. The shearing device consists of two partially reflective glass plates. The reflection coefficients of the coatings are 0.3 and 0.7 respectively. The distance between the two glass plates controls the size of the shear. The versatility of this simple shearing interferometer is shown. It is demonstrated that the ESPSI system can be used for vibration measurements and phase-shifting implemented for fringe analysis. The results obtained are promising for future applications of the system for modal analysis.

Mihaylova, Emilia M.; Whelan, Maurice P.; Toal, Vincent

2004-06-01

112

Measurement of shear impedances of viscoelastic fluids  

SciTech Connect

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

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

1996-12-31

113

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

PubMed

Wall-shear stress results from the relative motion of a fluid over a body surface as a consequence of the no-slip condition of the fluid in the vicinity of the wall. To determine the two-dimensional wall-shear stress distribution is of utter importance in theoretical and applied turbulence research. In this article, characteristics of the Micro-Pillar Shear-Stress Sensor MPS(3), which has been shown to offer the potential to measure the two-directional dynamic wall-shear stress distribution in turbulent flows, will be summarized. After a brief general description of the sensor concept, material characteristics, possible sensor-structure related error sources, various sensitivity and distinct sensor performance aspects will be addressed. Especially, pressure-sensitivity related aspects will be discussed. This discussion will serve as 'design rules' for possible new fields of applications of the sensor technology. PMID:22574010

Große, Sebastian; Schröder, Wolfgang

2009-01-01

114

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

PubMed Central

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

Grosse, Sebastian; Schroder, Wolfgang

2009-01-01

115

Shear strengths of sandstone fractures under true triaxial stresses  

NASA Astrophysics Data System (ADS)

True triaxial shear tests have been performed to determine the peak shear strengths of tension-induced fractures in three Thai sandstones. A polyaxial load frame is used to apply mutually perpendicular lateral stresses (?p and ?o) to the 76 × 76 × 126 mm rectangular block specimens. The normal to the fracture plane makes an angle of 59.1° with the axial (major principal) stress. Results indicate that the lateral stress that is parallel to the fracture plane (?p) can significantly reduce the peak shear strength of the fractures. Under the same normal stress (?n) the fractures under high ?p dilate more than those under low ?p. According to the Coulomb criterion, the friction angle decreases exponentially with increasing ?p/?o ratio and the cohesion decreases with increasing ?p. The lateral stress ?p has insignificant effect on the basic friction angle of the smooth saw-cut surfaces. The fracture shear strengths under ?p = 0 correlate well with those obtained from the direct shear tests. It is postulated that when the fractures are confined laterally by ?p, their asperities are strained into the aperture, and are sheared off more easily compared to those under unconfined condition.

Kapang, Piyanat; Walsri, Chaowarin; Sriapai, Tanapol; Fuenkajorn, Kittitep

2013-03-01

116

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

117

Shear-Stress Effect on Mitochondrial Membrane Potential and Albumin Uptake in Cultured Endothelial Cells  

Microsoft Academic Search

Endothelial cells (ECs) that line the inner surface of blood vessels are continuously exposed to shear stress induced by blood flow in vivo, and shear stress affects ATP-dependent macromolecular transport in ECs. However, the relationship between the ATP production and shear stress is still unclear. We, therefore, evaluated mitochondrial ATP synthesis activity in cultured endothelial cells exposed to shear stress,

Susumu Kudo; Ryoma Morigaki; Junichi Saito; Mariko Ikeda; Kotaro Oka; Kazuo Tanishita

2000-01-01

118

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

119

A hot-wire for detecting wall-shear stress direction  

Microsoft Academic Search

In research on possible techniques for measuring wall shear stresses, a particular double hot-wire probe was designed. The working principle is to keep constant the average temperature of the two wires while the downstream one is heated by the other. The temperature difference indicates the stress while the average temperature acts as the usual hot-wire signal. The instrument was compared

SERGIO DE PONTE; Marco Parrini

1991-01-01

120

Radiation sensitization of tumor cells induced by shear stress: The roles of integrins and FAK.  

PubMed

Recent studies revealed that the interstitial fluid flow in and around tumor tissue not only played an important role in delivering anticancer agents, but also affected the microenvironment, mostly hypoxia, in modulating tumor radio-sensitivity. The current study investigated the hypoxia-independent mechanisms of flow-induced shear stress in sensitizing tumors to radiation. Colon cancer cells were seeded onto glass slides pre-coated with fibronectin. A parallel-plate flow chamber system was used to impose fluid shear stress. Cell proliferation, apoptosis and colony assays were measured after shear stress and/or radiation. Cell cycle analysis and immunoblots of cell adhesion signal molecules were evaluated. The effect of shear stress was reversed by modulating integrin ?1 or FAK. Shear stress of 12dyne/cm(2) for 24h, but not 3h, enhanced the radiation induced cytotoxicity to colon cancer cells. Protein expression of FAK was significantly down-regulated but not transcriptionally suppressed. By modulating integrin ?1 and FAK expression, we demonstrated that shear stress enhanced tumor radiosensitivity by regulating integrin ?1/FAK/Akt as well as integrin ?1/FAK/cortactin pathways. Shear stress in combination with radiation might regulate integrins signaling by recruiting and activating caspases 3/8 for FAK cleavage followed by ubiquitin-mediated proteasomal degradation. Shear stress enhanced the radiation toxicity to colon cancer cells through suppression of integrin signaling and protein degradation of FAK. The results of our study provide a strong rationale for cancer treatment that combines between radiation and strategy in modulating tumor interstitial fluid flow. PMID:24946134

Luo, Chi-Wen; Wu, Chia-Ching; Ch'ang, Hui-Ju

2014-09-01

121

Stress Collapse in Adiabatic Shear Bands.  

National Technical Information Service (NTIS)

The dynamics of adiabatic shear band formation is considered making use of a simplified thermo/visco/plastic flow law. A new numerical solution is used to follow the growth of a perturbation from initiation, through early growth and severe localization, t...

T. W. Wright J. W. Walter

1987-01-01

122

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

123

TNF-? and Shear Stress Induced Large Artery Adaptations  

PubMed Central

Background TNF-? upregulation has been associated with both low and high shear induced arterial remodeling. To address this apparent paradox and to define the biology of TNF-? signaling in large arteries, we tested the hypotheses that differential temporal expression of TNF-? drive shear regulated arterial remodeling. Materials and Methods Both low and high shear environments in the same rabbit were surgically created for common carotid arteries (CCA). CCAs (n=60 total) were harvested after d0, d1, d3, d7, d14 and analyses included morphology, TNF-? and IL-10 mRNA quantitation. In separate experiments, animals received pegylated soluble TNF-? Type I receptor (PEG sTNF-RI) or vehicle via either short or long-term dosing to define the effect of TNF-? blockade. Results The model yielded a 14-fold shear differential (p<0.001) with medial thickening under low shear (p=0.025), and evidence of outward remodeling with high shear (p=0.007). Low shear immediately upregulated TNF-? expression ~50 fold (p<0.001) at d1. Conversely, high shear induced delayed and sustained TNF-? expression (22 fold at d7, p=0.012; 23 fold at d14, p=0.007). Both low and high shear gradually induced IL-10 expression (p=0.002 and p=0.004, respectively). Neither short-term (5-day) nor long-term (14-day) blockage of TNF-? signaling resulted in treatment induced changes in the remodeling of low or high shear arteries. Conclusions Shear stress differentially and temporally regulates TNF-? expression in remodeling large arteries. However, TNF-? blockage did not substantially impact the final shear induced morphology, suggesting that large arteries can remodel in response to flow perturbations independent of TNF-? signaling.

Keith Ozaki, C.; Jiang, Zhihua; Berceli, Scott A.

2007-01-01

124

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

125

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

SciTech Connect

In situ stress determinations in North America, southern Africa, and Australia indicate that on the average the maximum shear stress increases lineary with depth to at least 5.1 km measured in soft rock, such as shale and sandstone, and to 3.7 km in hard rock, including granite and quartzite. Regression lines fitted to the data yield gradients of 3.8 MPa/km and 6.6 MPa/km for soft and hard rock, respectively. Generally, the maximum shear stress in compressional states of stress for which the least principal stress is oriented near vertically is substantially greater than in extensional stress regimes, with the greatest principal stress in a vertical direction. The equations of equilibrium and compatibility can be used to provide functional constraints on the state of stress. If the stress is assumed to vary only with depth z in a given region, then all nonzero components must have the form A+Bz, where A and B are constants which generally differ for various components. This implies that the deviatoric stress changes linearly with depth, and the general solution also allows the directions of the horizontal principal stresses to change monotonically with depth. Solutions to the equations, assuming stress to vary with both z and x, were fit to the observations of Zoback and Roller, who measured stress along a horizontal profile near Palmdale, California. The results indicate that the average shear stress in the upper 8 km of the fault zone is about 3.5 MPa less than the shear stress in the far field, but this far field term, which is part of the solution and has the form A+Bz, cannot be evaluated using the existing constant depth data.

McGarr, A.

1980-11-10

126

Shear Stress Biology of the Endothelium  

Microsoft Academic Search

The relationships between blood flow, mechanotransduction, and the localization of arterial lesions can now be advanced by\\u000a the incorporation of new technologies and the refinement of existing methods in imaging modalities, computational modeling,\\u000a fluid dynamics, and high throughput genomics and proteomics. When combined with traditional cell and molecular technologies,\\u000a a powerful palette of investigative approaches is available to address shear

Peter F. Davies; Jos. A. Spaan; Robert Krams

2005-01-01

127

Internal stresses induced by plastic shear deformation of Zr–(Cu,Ag)–Al bulk metallic glasses  

Microsoft Academic Search

Effective internal shear stress ?i induced by torsional deformation of Zr46(Cu4\\/5Ag1\\/5)46Al8 and Zr46Cu46Al8 bulk metallic glasses different by the glass-forming ability of the maternal melts has been determined by measurements of stress relaxation upon stepwise unloading. It has been found that the ratio ?i\\/?0 (?0 is the initially applied shear stress) decreases upon increasing the temperature from ?0.8 at T=450K

G. V. Afonin; S. V. Khonik; R. A. Konchakov; N. P. Kobelev; A. A. Kaloyan; V. A. Khonik

128

Effect of shear stress on water and LDL transport through cultured endothelial cell monolayers.  

PubMed

Previous animal experiments have shown that the transport of LDL into arterial walls is shear stress dependent. However, little work has probed shear effects on LDL transport in vitro where conditions are well defined and mechanisms are more easily explored. Therefore, we measured shear induced water and LDL fluxes across cultured bovine aortic endothelial (BAEC) monolayers in vitro and developed a three-pore model to describe the transport dynamics. Cell apoptosis was quantified by TdT-mediated dUTP nick end labeling (TUNEL) assay. We also examined the role of nitric oxide (NO) in shear induced water and LDL fluxes by incubating BAEC monolayers with an NO synthase inhibitor, NG-monomethyl-L-arginine (L-NMMA). Our results show that direct exposure of endothelial monolayers to 12 dyn/cm2 shear stress for 3 h elicited a 2.37-fold increase in water flux (Jv), a 3.00-fold increase in LDL permeability (Pe), a 1.32-fold increase in LDL uptake, and a 1.68-fold increase in apoptotic rate. L-NMMA treatment of BAEC monolayers blocked shear induced Jv response, but had no significant effect on shear responses of Pe and cell apoptosis. A long time shear exposure (12 h) of endothelial monolayers reduced Pe and apoptotic rate close to the baseline. These results suggest that an acute change in shear stress from a static baseline state induces increases in water flux that are mediated by an NO dependent mechanism. On the other hand, the permeability of endothelial monolayers to LDL is enhanced by a short term-shear application and reduced nearly to the baseline level by a longer time shear exposure, positively correlated to the leaky junctions forming around apoptotic cells. PMID:24583416

Kang, Hongyan; Cancel, Limary M; Tarbell, John M

2014-04-01

129

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

PubMed

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

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

2013-10-01

130

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

131

Wind shear measuring on board an airliner  

NASA Technical Reports Server (NTRS)

A measurement technique which continuously determines the wind vector on board an airliner during takeoff and landing is introduced. Its implementation is intended to deliver sufficient statistical background concerning low frequency wind changes in the atmospheric boundary layer and extended knowledge about deterministic wind shear modeling. The wind measurement scheme is described and the adaptation of apparatus onboard an A300 airbus is shown. Preliminary measurements made during level flight demonstrate the validity of the method.

Krauspe, P.

1984-01-01

132

Ultrasonic measurement of stress in railroad wheels  

Microsoft Academic Search

The equipment described here generates ultrasonic shear waves using an electromagnetic-acoustic transducer. Precise measurement of the velocity of two orthogonally polarized signals determines the birefringence and allows the calculation of stress. It is necessary to account for the effect of metallurgical texture which can contribute to the birefringence and appear as moderate stress. This system sends a signal through the

Raymond E. Schramm

1999-01-01

133

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

134

On the Intermittency Feature of Shear Stress Fluctuation in Turbulence  

Microsoft Academic Search

Instantaneous shear stress fluctuation is considered for different kinds of flow fields and Reynolds numbers. These fluctuations consist of intermittent sharp spikes and small scale oscillations around the zero-crossing. We introduce the maximum norm to characterize them. This norm is defined as a largest change within a box of finite size. The experimental results indicate that the maximum norm has

Yoshiyuki Tsuji; Brindesh Dhruva

1998-01-01

135

Shear Stress Induction of the Tissue Factor Gene  

Microsoft Academic Search

Using flow channel, we report that the application of a lam- inar shear stress induced a transient increase of tissue factor (TF) procoagulant activity in human umbilical vein endo- thelial cells (HUVEC), which was accompanied by a rapid and transient induction of the TF mRNA in the HUVEC. Functional analysis of the 2.2 kb TF 5 9 promoter indicated that

Ming-Chao Lin; Fanny Almus-Jacobs; Hsuan-Hsu Chen; Graham C. N. Parry; Nigel Mackman; Shu Chien

136

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...

137

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

138

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

139

Shear stress-induced improvement of red blood cell deformability.  

PubMed

Classically, it is known that red blood cell (RBC) deformability is determined by the geometric and material properties of these cells. Experimental evidence accumulated during the last decade has introduced the concept of active regulation of RBC deformability. This regulation is mainly related to altered associations between membrane skeletal proteins and integral proteins, with the latter serving to anchor the skeleton to the lipid matrix. It has been hypothesized that shear stress induces alterations of RBC deformability: the current study investigated the dynamics of the transient improvement in deformability induced by shear stress at physiologically-relevant levels. RBC were exposed to various levels of shear stress (SS) in a Couette type shearing system that is part of an ektacytometer, thus permitting the changes in RBC deformability during the application of SS to be monitored. Initial studies showed that there is an increase in deformability of the RBC subjected to SS in the range of 5-20 Pa, with kinetics characterized by time constants of a few seconds. Such improvement in deformability, expressed by an elongation index (EI), was faster with higher levels of SS and hence yielded shorter time constants: absolute values of EI increased by 3-8% of the starting level. Upon the removal of the shear stress, this response by RBC was reversible with a slower time course compared to the increase in EI during application of SS. Increased calcium concentration in the RBC suspending medium prevented the improvement of deformability. It is suggested that the improvement of RBC deformability by shear forces may have significant effects on blood flow dynamics, at least in tissues supplied by blood vessels with impaired vasomotor reserve, and may therefore serve as a compensating mechanism for the maintenance of adequate microcirculatory perfusion. PMID:23863281

Meram, Ece; Yilmaz, Bahar D; Bas, Ceren; Atac, Nazl?; Yalcin, O; Meiselman, Herbert J; Baskurt, Oguz K

2013-01-01

140

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

NASA Astrophysics Data System (ADS)

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

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

2013-07-01

141

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

142

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

143

Flow separation and shear stress over angle-of-repose bed forms: A numerical investigation  

NASA Astrophysics Data System (ADS)

asymmetric bed forms commonly develop in rivers. The turbulence associated with flow separation that develops over their steep lee side is responsible for the form shear stress which can represent a substantial part of total shear stress in rivers. This paper uses the Delft3D modeling system to investigate the effects of bed form geometry and forcing conditions on flow separation length and associated turbulence, and bed form shear stress over angle-of-repose (30° lee side angle) bed forms. The model was validated with lab measurements that showed sufficient agreement to be used for a systematic analysis. The influence of flow velocity, bed roughness, relative height (bed form height/water depth), and aspect ratio (bed form height/length) on the variations of the normalized length of the flow separation zone, the extent of the wake region (where the turbulent kinetic energy (TKE) was more than 70% of the maximum TKE), the average TKE within the wake region and the form shear stress were investigated. Form shear stress was found not to scale with the size of the flow separation zone but to be related to the product of the normalized extent of the wake region (extent of the wake region/extent of water body above the bed form) and the average TKE within the wake region. The results add to understanding of the hydrodynamics of bed forms and may be used for the development of better parameterizations of small-scale processes for application in large-scale studies.

Lefebvre, Alice; Paarlberg, Andries J.; Winter, Christian

2014-02-01

144

Relationship between Concentration Difference of Different Density Lipoproteins and Shear Stress in Atherosclerosis  

PubMed Central

Previous research has observed concentration polarization in LDL and HDL in the arterial system. However, there is no report that links this concentration polarization to the development of vascular atherosclerosis (AS). Therefore, the purpose of this study is to establish the relationship between concentration difference of LDL and HDL and shear stress using a carotid bifurcation vascular model. PTFE was employed to create the carotid bifurcation model. Endothelial cells were coated on the inner wall of the graft. In a recirculation system, HDL and LDL concentration were measured under two different ICA flow velocities at 5 different locations within our model. We report the following: (1) LDL and HDL concentration difference was observed in both high flow and low flow environments; (2) the degree of LDL and HDL concentration polarization varied depending of high flow and low flow environment; (3) absolute values of concentration difference between LDL and HDL at the inner wall surface decreased with the increase in shear stress when shear stress was more than 1.5?Pa. This variation trend would be more pronounced if shear stress were less than 0.5?Pa. Our study suggests that under the action of shear stress, concentration differences of LDL or HDL create a disturbance in the balance of atherogenic factors and anti-As factors, resulting in the occurrence of AS.

Meng, Wei; Yu, Fengxu; Chen, Huaiqing; Zhang, Jianmin; Zhang, Eryong; Guo, Yingqiang; Shi, Yingkang

2012-01-01

145

Shear stress prediction in shock loaded copper  

SciTech Connect

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

Follansbee, P.S.

1991-01-01

146

Aggregation properties of erythrocytes of whole blood under shear stress by backscattering nephelometry  

NASA Astrophysics Data System (ADS)

The kinetics of aggregation and disaggregation of red blood cells in whole blood subjected to shear stress is different with normal and pathological blood. To measure the kinetics we have applied a backscattering nephelometric technique, and quantitatively registered the alternation of the scattered intensity due to appearance or disappearance of different types of cell aggregates under controlled shear stresses. The latter were obtained in a Couette flow in a thin gap between two concentrical cylinders, the inner one rotating at controlled velocities. The peculiarities of backscattered light signal formation and obtained results were discussed.

Firsov, Nikolai N.; Priezzhev, Alexander V.; Ryaboshapka, Olga M.; Sirko, Igor V.

1993-07-01

147

Trauma of the Erythrocyte Membrane Associated with Low Shear Stress  

PubMed Central

Studies have been performed on erythrocytes that have been subjected to a low shear stress of less than 100 dyn/cm2 in a cone-and-plate viscometer. Alterations that were observed included decreased red cell survival, increased osmotic fragility, changes in the cation permeability of the red cell membrane, and a reduction in membrane-associated acetylcholinesterase activity. Some of these alterations are similar to those accompanying aging. The observed data suggest that one segment of the erythrocyte population is more susceptible to shear-induced damage than the rest of the cells.

Nanjappa, B. N.; Chang, Hsin-Kang; Glomski, Chester A.

1973-01-01

148

Combined effects of flow-induced shear stress and micropatterned surface morphology on neuronal differentiation of human mesenchymal stem cells.  

PubMed

This study investigated the combined effects of surface morphology and flow-induced shear stress on the neuronal differentiation of human mesenchymal stem cells. First, to examine the effect of surface morphology, three patterns were fabricated using photolithography and compared to the flat substrate. After selecting the most effective surface pattern, flow-induced shear stresses (0.10 and 0.25 Pa) were engaged parallel to the direction of the grooves. The degrees of alignment and neurite outgrowth were measured using digital image processing techniques for up to 10 days. Functional evaluations were also performed by monitoring the intracellular calcium concentration and the expression of synaptophysin, ?-tubulin III, and MAP2. Based on these analyses, the pattern of 5 ?m/5 ?m/3 ?m for groove/ridge/depth, respectively, was selected. Next, shear stresses (0.00, 0.10, 0.25 Pa) were applied to the cells on the selected substrate. The shear stresses affected the expression of those markers. The outgrowth measurements indicated that the shear stresses were effective at day 7. However, the effect of shear stresses tended to decrease at day 10. More cells showed higher calcium concentrations under 0.10 Pa. The alignment was also confirmed. Taken together, these results indicated that a shear stress of 0.10 Pa on the substrate of 5 ?m was most effective. Therefore, such combination of mechanical stimuli and surface pattern is expected to promote neuronal differentiation with regard to functional and morphological changes. PMID:23993713

Jeon, Kang Jin; Park, So Hee; Shin, Ji Won; Kang, Yun Gyeong; Hyun, Jin-Sook; Oh, Min Jae; Kim, Seon Yeon; Shin, Jung-Woog

2014-02-01

149

A Study of Turbulence at a Wall Using an Electrochemical Wall Shear-Stress Meter.  

National Technical Information Service (NTIS)

A technique has been developed to measure the instantaneous shear stress at the boundary over which a liquid is flowing. It is being used to study turbulence in the immediate vicinity of a pipe wall. A reaction is conducted on an electrode mounted flush w...

J. E. Mitchell T. J. Hanratty

1966-01-01

150

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

151

Effect of Shear Stress in Shock Initiation of PBX  

NASA Astrophysics Data System (ADS)

Initiation of hot spots-reaction sites in PBX explosives by a linear shock generator has been studied under wide variation of the input shock pressure, from 3 GPa up to 20 GPa. A multi-channel high-resolution optical method based on application of a 96 optical fiber strips has been used for a comprehensive registration of the reaction spot initiation and following the processes of reaction growth or extinction. We have obtained strong evidence that reaction originates in the shear regions established by the induced shock. This suggests that shear has a major role in shock initiation. The pressure field in the front of reacted flow and the minimum size of reaction sites, which results in reaction growth, are defined as a function of the input shock pressure. Effect of shear stress is discussed concerning the grain sizes and mass concentration of HMX in the PBX's.

Plaksin, I.; Campos, J.; Mendes, R.; Ribeiro, J.; Direito, J.; Braga, D.; Coffey, C. S.

2004-07-01

152

Impact of shear and curvature on surface gravity wave stress  

NASA Astrophysics Data System (ADS)

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

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

2009-09-01

153

Dynamic Calibration of a Shear-Stress Sensor by Acoustic Waves  

NASA Astrophysics Data System (ADS)

Many important fluid mechanics phenomena are dominated by turbulent wall-shear, yet continuous, fluctuating wall-shear data can only be obtained by indirect methods (e.g., thin-film anemometry). Recently, silicon micromachining technology has produced a miniature, floating-element shear-stress gauge which directly measures fluctuating wall shear(Padmanabhan, A., et al.), AIAA Paper 96-0422.. Static calibrations demonstrate the linearity of this device over a broad measurement range and spectra indicate a bandwidth in excess of 10 kHz. However, the actual characteristics of the frequency response function, however, are presently unknown and thus, in order to use this device to obtain quantitative turbulence information, the effects of the inherent mass, compliance, and damping of the floating-element structure on the dynamic response must be characterized. To elucidate these effects, an acoustic plane wave generator capable of providing a sinusoidal shear input to the sensor was developed. In this calibration technique, the sinusoidal shear stress is inferred from the cylindrical Stokes' layer solution for a plane acoustic wave. The theoretical aspects of this technique will be discussed and preliminary results presented.

Sheplak, Mark; Padmanabhan, Aravind; Lee, Sarah S.; Schmidt, Martin A.; Breuer, Kenneth S.

1996-11-01

154

Pulsatile atheroprone shear stress affects the expression of transient receptor potential channels in human endothelial cells.  

PubMed

The goal of the study was to assess whether pulsatile atheroprone shear stress modulates the expression of transient receptor potential (TRP) channels, TRPC3, TRPC6, TRPM7, and TRPV1 mRNA, in human umbilical vascular endothelial cells. Exposure of cultured vascular endothelial cells to defined shear stress, producing a constant laminar flow (generating a shear stress of 6 dyne/cm(2)), laminar pulsatile atheroprotective flow (with a mean shear stress of 20 dyne/cm(2)), or laminar atheroprone bidirectional flow (with a mean shear stress of 0 dyne/cm(2)) differentially induced TRPC6 and TRPV1 mRNA as measured by quantitative real-time RT-PCR and normalized to GAPDH expression. Thereby, TRPC6 and TRPV1 mRNA expressions were significantly increased after 24 hours of exposure to an atheroprone flow profile compared with an atheroprotective flow profile. Furthermore, the expression of transcription factors GATA1 and GATA4 was significantly correlated with the expression of TRPC6 mRNA. In contrast, after 24 hours of constant laminar flow, the expression of TRPC6 and TRPV1 mRNA was unchanged, whereas the expression of TRPC3 and TRPM7 was significantly higher in endothelial cells exposed to shear stress in comparison with endothelial cells grown under static conditions. There was a significant association between the expression of TRPC6 and tumor necrosis factor-? mRNA in human vascular tissue. No-flow and atheroprone flow conditions are equally characterized by an increase in the expression of tumor necrosis factor-?; however, inflammation-associated endothelial cell reactions may be further aggravated at atheroprone flow conditions by the increase of TRPV1 and TRPC6, as observed in our study. PMID:22566504

Thilo, Florian; Vorderwülbecke, Bernd J; Marki, Alex; Krueger, Katharina; Liu, Ying; Baumunk, Daniel; Zakrzewicz, Andreas; Tepel, Martin

2012-06-01

155

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

156

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

157

Liquid crystals for unsteady surface shear stress visualization  

SciTech Connect

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

Reda, D.C.

1988-01-01

158

Effect of state of stress on velocity of low-amplitude shear waves propagating along principal stress directions in dry sand  

Microsoft Academic Search

The effect of state of stress on shear wave velocity was examined for shear waves propagated as body waves through a sand mass. Testing was performed in a triaxial testing device, which was designed to hold a cubic soil sample measuring 7 ft (2.1 m) on a side and which was used to apply an isotropic, biaxial or triaxial state

D. P. Knox; K. H. Stokoe II; S. E. Kopperman

1982-01-01

159

Non-volcanic tremor driven by large transient shear stresses.  

PubMed

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

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

2007-08-01

160

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.

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

2013-01-01

161

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

162

The use of a torsion machine to measure the shear strength and modulus of unidirectional carbon fibre reinforced plastic composites  

Microsoft Academic Search

A torsion apparatus, in which a solid rod specimen is subjected to a shear stress field only, has been used to measure the shear modulus and strength of unidirectional carbon fibre reinforced plastics. Because of the absence of tensile and compressive forces, a more accurate value of the shear strength is obtained than from a test such as the short

N. L. Hancox

1972-01-01

163

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

164

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

PubMed Central

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

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

2012-01-01

165

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

166

Endothelial metallothionein expression and intracellular free zinc levels are regulated by shear stress  

PubMed Central

We examined the effects of fluid shear stress on metallothionein (MT) gene and protein expression and intracellular free zinc in mouse aorta and in human umbilical vein endothelial cells (HUVECs). Immunostaining of the endothelial surface of mouse aorta revealed increased expression of MT protein in the lesser curvature of the aorta relative to the descending thoracic aorta. HUVECs were exposed to high steady shear stress (15 dyn/cm2), low steady shear stress (1 dyn/cm2), or reversing shear stress (mean of 1 dyn/cm2, 1 Hz) for 24 h. Gene expression of three MT-1 isoforms, MT-2A, and zinc transporter-1 was upregulated by low steady shear stress and reversing shear stress. HUVECs exposed to 15 dyn/cm2 had increased levels of free zinc compared with cells under other shear stress regimes and static conditions. The increase in free zinc was partially blocked with an inhibitor of nitric oxide synthesis, suggesting a role for shear stress-induced endothelial nitric oxide synthase activity. Cells subjected to reversing shear stress in zinc-supplemented media (50 ?M ZnSO4) had increased intracellular free zinc, reduced surface intercellular adhesion molecule-1 expression, and reduced monocyte adhesion compared with cells exposed to reversing shear stress in normal media. The sensitivity of intracellular free zinc to differences in shear stress suggests that intracellular zinc levels are important in the regulation of the endothelium and in the progression of vascular disease.

Conway, Daniel E.; Lee, Sungmun; Eskin, Suzanne G.; Shah, Ankit K.; Jo, Hanjoong

2010-01-01

167

Shear stress increases the residence time of adhesion of Pseudomonas aeruginosa.  

PubMed

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

2011-01-19

168

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

169

Miniature Laser Doppler Velocimeter for Measuring Wall Shear  

NASA Technical Reports Server (NTRS)

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

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

2005-01-01

170

Studies on Impingement Effects of Low Density Jets on Surfaces - Determination of Shear Stress and Normal Pressure  

NASA Astrophysics Data System (ADS)

This paper presents the results of the Laser Reflection Method (LRM) for the determination of shear stress due to impingement of low-density free jets on flat plate. For thin oil film moving under the action of aerodynamic boundary layer the shear stress at the air-oil interface is equal to the shear stress between the surface and air. A direct and dynamic measurement of the oil film slope is measured using a position sensing detector (PSD). The thinning rate of oil film is directly measured which is the major advantage of the LRM over LISF method. From the oil film slope history, direct calculation of the shear stress is done using a three-point formula. For the full range of experiment conditions Knudsen numbers varied till the continuum limit of the transition regime. The shear stress values for low-density flows in the transition regime are thus obtained using LRM and the measured values of shear show fair agreement with those obtained by other methods. Results of the normal pressure measurements on a flat plate in low-density jets by using thermistors as pressure sensors are also presented in the paper. The normal pressure profiles obtained show the characteristic features of Newtonian impact theory for hypersonic flows.

Sathian, Sarith. P.; Kurian, Job

2005-05-01

171

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

NASA Astrophysics Data System (ADS)

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.

Drake, David E.; Cacchione, David A.

172

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

173

Shear-wave splitting in the crust: Regional compressive stress from polarizations of fast shear-waves  

NASA Astrophysics Data System (ADS)

When propagating through anisotropic rocks in the crust, shear-waves split into faster and slower components with almost orthogonal polarizations. For nearly vertical propagation the polarization of fast shearwave (PFS) is parallel to both the strike of the cracks and the direction of maximum horizontal stress, therefore it is possible to use PFS to study stress in the crust. This study discusses several examples in which PFS is applied to deduce the compressive stress in North China, Longmenshan fault zone of east edge of Tibetan plateau and Yunnan zone of southeast edge of Tibetan plateau, also discusses temporal variations of PFS orientations of 1999 Xiuyan earthquake sequences of northeastern China. The results are consistent to those of other independent traditional stress measurements. There is a bridge between crustal PFS and the crustal principal compressive stress although there are many unclear disturbance sources. This study suggests the PFS results could be used to deduce regional and in situ principal compressive stress in the crust only if there are enough seismic stations and enough data. At least, PFS is a useful choice in the zone where there are a large number of dense seismic stations.

Gao, Yuan; Shi, Yutao; Wu, Jing; Tai, Lingxue

2012-02-01

174

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

NASA Astrophysics Data System (ADS)

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

175

Differential activation and inhibition of RhoA by fluid flow induced shear stress in chondrocytes.  

PubMed

Physical force environment is a major factor that influences cellular homeostasis and remodelling. It is not well understood, however, as a potential role of force intensities in the induction of cellular mechanotransduction. Using a fluorescence resonance energy transfer-based approach, we asked whether activities of GTPase RhoA in chondrocytes are dependent on intensities of flow-induced shear stress. We hypothesized that RhoA activities can be either elevated or reduced by selecting different levels of shear-stress intensities. The result indicates that C28/I2 chondrocytes have increased RhoA activities in response to high shear stress (10 or 20?dyn/cm(2) ), whereas a decrease in activity was seen with an intermediate shear stress of 5?dyn/cm(2) . No changes were seen under low shear stress (2?dyn/cm(2) ). The observed two-level switch of RhoA activities is closely linked to the shear-stress-induced alterations in actin cytoskeleton and traction forces. In the presence of constitutively active RhoA (RhoA-V14), intermediate shear stress suppressed RhoA activities, while high shear stress failed to activate them. In chondrocytes, expression of various metalloproteinases is, in part, regulated by shear and normal stresses through a network of GTPases. Collectively, the data suggest that intensities of shear stress are critical in differential activation and inhibition of RhoA activities in chondrocytes. PMID:23408748

Wan, Qiaoqiao; Kim, Seung Joon; Yokota, Hiroki; Na, Sungsoo

2013-06-01

176

Interlaminar Shear Stress Effects on the Postbuckling Response of Graphite-Epoxy Panels.  

National Technical Information Service (NTIS)

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 classica...

S. P. Engelstad N. F. Knight J. N. Reddy

1990-01-01

177

A New Model to Calculate Friction Coefficients and Shear Stresses in Thermal Drilling  

SciTech Connect

A new analytical model for thermal drilling (also known as friction drilling) has been developed. The model distinguishes itself from recent work of other investigators by improving on two aspects: (1) the new model defines material plastic flow in terms of the yield in shear rather than the yield in compression, and (2) it uses a single, variable friction coefficient instead of assuming two unrelated friction coefficients in fixed values. The time dependence of the shear stress and friction coefficient at the hole walls, which cannot be measured directly in thermal drilling, can be calculated using this model from experimentally-measured values of the instantaneous thrust force and torque. Good matches between the calculated shear strengths and the handbook values for thermally drilling low carbon steel confirm the model's validity.

Qu, Jun [ORNL; Blau, Peter Julian [ORNL

2008-01-01

178

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

179

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

180

Modeling bed shear-stress fluctuations in a shallow tidal channel  

NASA Astrophysics Data System (ADS)

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

181

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

182

Mass Transport and Shear Stress in the Carotid Artery Bifurcation  

NASA Astrophysics Data System (ADS)

The carotid artery bifurcation (CAB) is one of the leading sites for atherosclerosis, a major cause of death and disability in the developed world. The specific processes by which the complex flow found at the bifurcation and carotid sinus promotes plaque formation and growth are not fully understood. Shear stress, mass transport, and flow residence times are considered key factors. Although the governing equations closely link shear stress and mass transfer, the pulsatile, transitional, and detached flow found at the CAB can lead to differences between regions of WSS and mass transfer statistics. In this study, CAB geometries are reconstructed from patient specific 3D ultrasound medical imaging. Using ANSYS FLUENT, the fluid flow and scalar transport was solved using realistic flow conditions and various mass transfer boundary conditions. The spatial and temporal resolution was validated against the analytical solution of the Graetz-Nusselt problem with constant wall flux to ensure the scalar transport is resolved for a Peclet number up to 100,000. High residence time regions are investigated by determining the number of cardiac cycles required to flush out the carotid sinus. The correlations between regions of low WSS, high OSI, and scalar concentration are computed and interpreted in the context of atherosclerotic plaque origin and progression.

Gorder, Riley; Aliseda, Alberto

2010-11-01

183

Instantaneous Wall Shear Stress and Velocity Fluctuations in Turbulent Pipe Flow  

Microsoft Academic Search

Simultaneous measurement of velocity fluctuations (u') and the instantaneous wall shear stress (tau_w) were carried out in a high Reynolds number pipe flow (water) facility designed and constructed in collaboration with D.P. Lathropfootnote now at Emory University, Atlanta, Ga.. Constant temperature anemometry with a flush-mounted film probe for tauw and a cylindrical hot-film boundary layer probe for u' were used

Rustom Bhiladvala; Inigo San Gil; K. R. Sreenivasan

1996-01-01

184

Intracellular calcium oscillation in MG63 cells induced by steady and pulsed shear stresses  

Microsoft Academic Search

An optically transparent micro-cell chip was fabricated with a polydimethylsiloxane (PDMS) channel structure and cover glass and was used to examine the intracellular calcium responses of a single cell to steady and pulsed shear stresses of various durations to investigate the optimal duration of mechanical stimulation in MG-63 cells (human osteoblast-like bone cell line). Intracellular calcium responses were measured using

Jong Heon Jeon; Ok Chan Jeong

185

Individual and Combined Effects of Shear Stress Magnitude and Spatial Gradient on Endothelial Cell Gene Expression  

Microsoft Academic Search

Abstract The apparent tendency of atherosclerotic lesions to form in complex,blood flow environmentshas led to many theories regarding the importance of hemodynamic,forces in endothelium-mediated atherosusceptibility. The effects of shear stress magnitude and spatial shear stress gradient on endothelial cell gene expression in vitrowere,examined,in this study. Converging-width flow channels were designed to impose physiological ranges of shear stress gradient and magnitude

Jeffrey A. LaMack; Morton H. Friedman

2007-01-01

186

The fabrication and integration of a novel shear stress sensor array and its wind tunnel test  

Microsoft Academic Search

A new generation of micro shear stress sensors and flexible PCB for the general purpose of flow separation detection and control\\u000a is presented here. A novel MEMS shear stress sensor array featuring integration of discrete micro sensors and polyimide substrate\\u000a has been developed. Then, CFD (Computational Fluid Dynamics) simulations were performed to estimate the corresponding shear\\u000a stress distribution within the

K. Liu; W. Z. Yuan; B. H. Ma; S. Chen; C. Y. Jiang

2008-01-01

187

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.

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

2010-01-01

188

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

189

Measurement of shear waves in tissue  

Microsoft Academic Search

The wavelength of a propagating pulse of shear wave within tissue is related to the local shear modulus and density through the speed of propagation. If the pulse does not produce standing waves, then the wavelength is a function of the tissue properties and not boundary conditions. Methods for imaging such waves using ultrasound and magnetic resonance imaging have recently

J. F. Greenleaf; V. Dutt; R. Muthupillai; A. Manduca; R. L. Ehman

1996-01-01

190

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

PubMed Central

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

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

2011-01-01

191

Effect of zinc and nitric oxide on monocyte adhesion to endothelial cells under shear stress.  

PubMed

This study describes the effect of zinc on monocyte adhesion to endothelial cells under different shear stress regimens, which may trigger atherogenesis. Human umbilical vein endothelial cells were exposed to steady shear stress (15 dynes/cm(2) or 1 dyne/cm(2)) or reversing shear stress (time average 1 dyne/cm(2)) for 24 h. In all shear stress regimes, zinc deficiency enhanced THP-1 cell adhesion, while heparinase III reduced monocyte adhesion following reversing shear stress exposure. Unlike other shear stress regimes, reversing shear stress alone enhanced monocyte adhesion, which may be associated with increased H(2)O(2) and superoxide together with relatively low levels of nitric oxide (NO) production. L-N(G)-Nitroarginine methyl ester (L-NAME) treatment increased monocyte adhesion under 15 dynes/cm(2) and under reversing shear stress. After reversing shear stress, monocyte adhesion dramatically increased with heparinase III treatment followed by a zinc scavenger. Static culture experiments supported the reduction of monocyte adhesion by zinc following endothelial cell cytokine activation. These results suggest that endothelial cell zinc levels are important for the inhibition of monocyte adhesion to endothelial cells, and may be one of the key factors in the early stages of atherogenesis. PMID:22009315

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

2012-03-01

192

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

NASA Astrophysics Data System (ADS)

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

Ayaz, Ulas Kemal

193

Modeling flow and shear stress fields over unsteady three dimensional dunes  

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

194

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

195

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

PubMed Central

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

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

2009-01-01

196

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.

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

2013-01-01

197

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

198

Vascular imaging by ultrasound: 3D reconstruction of flow velocity fields for endothelial shear stress calculation.  

PubMed

A new method for quantitative reconstruction of a three dimensional (3D) velocity field from ultrasound color doppler mapping (USCDM) images is used here to calculate the shear stress distribution on the endothelial layer of an artery. Measurements of a few spatially unrestricted USCDM transverse cross sectional images of the artery, and of several echo-ultrasound B-mode images of the same area, are required for reconstructing the geometry of the vessel's endothelial surface. The calculation is based on assuming a physical model of flow, and solving the Continuity and the Navier-Stokes equations numerically for a steady flow of an incompressible Newtonian fluid at constant temperature within a non-flexible tube. The correct choice of the penalty parameter in the finite element method (FEM) algorithm provides proper convergence of the reconstruction. The endothelial shear stress is calculated from the gradient of the velocity field at each point of the vessel's inner surface. PMID:9330728

Adam, D R; Burstein, P

1997-01-01

199

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

200

Wall shear stress modulation in a turbulent flow subjected to imposed unsteadiness with adverse pressure gradient  

NASA Astrophysics Data System (ADS)

The modulation characteristics of the turbulent wall shear stress measured in a plane diffuser subjected to imposed velocity oscillations are presented. The measurements reported in this paper pertain to nearly 150 different flows: imposed oscillations with three amplitudes and six frequencies, two different diverging channels and four streamwise positions. Only the most significant data are analyzed and discussed. The imposed unsteadiness affects the time-mean flow under the effect of the adverse pressure gradient (APG), in contrast to the canonical unsteady turbulent wall layers. The laminar viscous solution that adequately describes the amplitude and phase of the wall shear stress in channel flows in the high-imposed frequency regime is no longer valid in unsteady turbulent boundary layers subjected to APG. The latter modifies also the behavior of the phase shifts of the modulations in the turbulent quantities. The time lag of the wall shear stress turbulent intensity decreases as the pressure gradient increases. Some of these structural modifications are explained by the effect of the eddy viscosity that plays a key role in the vorticity diffusion process as the APG increases.

Sedat Tardu, F.; Maestri, Rogeiro

2010-06-01

201

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

202

Attachment, morphology and adherence of human endothelial cells to vascular prosthesis materials under the action of shear stress.  

PubMed

In an effort to improve the long-term patency of vascular prostheses several groups now advocate seeding autologous endothelial cells (ECs) onto the lumen of the vessel prior to implantation, a procedure that involves pre-treating the prosthesis material with fibrin, collagen and/or other matrix molecules to promote cell attachment and retention. In this study, we examined the degree to which human umbilical venous endothelial cells (HUVECs) adhered to three materials commonly used polymeric vascular prosthesis that had been coated with the same commercial extra cellular matrix proteins, and after exposure to fluid shear stresses representative of femoro-distal bypass in a cone-and-plate shearing device. We quantified cell number, area of coverage and degree of cell spreading using image analysis techniques. The response of cells that adhered to the surface of each material, and following exposure to fluid shear stress, depended on surface treatment, topology and cell type. Whereas collagen coating improved primary cellular adhesion and coverage significantly, the degree of spreading depended on the underlying surface structure and on the application of the shear stress. In some cases, fewer than 30% of cells remained on the surface after only 1-h exposure to physiological levels of shear stress. The proportion of the surface that was covered by cells also decreased, despite an increase in the degree to which individual cells spread on exposure to shear stress. Moreover, the behaviour of HUVECs was distinct from that of fibroblasts, in that the human ECs were able to adapt to their environment by spreading to a much greater extent in response to shear. The quality of HUVEC attachment, as measured by extent of cell coverage and resistance to fluid shear stress, was greatest on expanded polytetrafluoroethylene samples that had been impregnated with Type I/III collagen. PMID:15522747

Feugier, P; Black, R A; Hunt, J A; How, T V

2005-05-01

203

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

Microsoft Academic Search

The asymmetrical four-point bend (AFPB) shear test, which is the subject of this paper, was originally developed by Slepetz et al. to evaluate the shear properties of large metallic specimens and polymer composites. Similar to the Iosipescu test, the AFPB test also provides a nearly pure-shear stress state with an unnotched specimen. However, since the AFPB test involves point loading

Ö Ünal; D. J. Barnard; I. E. Anderson

1999-01-01

204

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

205

Regulation of the endothelin system by shear stress in human endothelial cells  

PubMed Central

In this study, the effect of shear stress on the expression of genes of the human endothelin-1 system was examined. Primary cultures of human umbilical vein endothelial cells (HUVEC) were exposed to laminar shear stress of 1, 15 or 30 dyn cm?2 (i.e. 0.1, 1.5 or 3 N m?2) (venous and two different arterial levels of shear stress) in a cone-and-plate viscometer.Laminar shear stress transiently upregulates preproendothelin-1 (ppET-1) mRNA, reaching its maximum after 30 min (approx 1.7-fold increase). In contrast, long-term application of shear stress (24 h) causes downregulation of ppET-1 mRNA in a dose-dependent manner.Arterial levels of shear stress result in downregulation of endothelin-converting enzyme-1 isoform ECE-1a (predominating in HUVEC) to 36.2 ± 8.5%, and isoform ECE-1b mRNA to 72.3 ± 1.9% of static control level.The endothelin-1 (ET-1) release is downregulated by laminar shear stress in a dose-dependent manner.This downregulation of ppET-1 mRNA and ET-1 release is not affected by inhibition of protein kinase C (PKC), or tyrosine kinase. Inhibition of endothelial NO synthase (L-NAME, 500 ?m) prevents downregulation of ppET-1 mRNA by shear stress.In contrast, increasing degrees of long-term shear stress upregulate endothelin receptor type B (ETB) mRNA by a NO- and PKC-, but not tyrosine kinase-dependent mechanism.In conclusion, our data suggest the downregulation of human endothelin synthesis, and an upregulation of the ETB receptor by long-term arterial laminar shear stress. These effects might contribute to the vasoprotective and anti-arteriosclerotic potential of arterial laminar shear stress.

Morawietz, Henning; Talanow, Roland; Szibor, Marten; Rueckschloss, Uwe; Schubert, Andreas; Bartling, Babett; Darmer, Dorothea; Holtz, Juergen

2000-01-01

206

Regulation of the endothelin system by shear stress in human endothelial cells.  

PubMed

In this study, the effect of shear stress on the expression of genes of the human endothelin-1 system was examined. Primary cultures of human umbilical vein endothelial cells (HUVEC) were exposed to laminar shear stress of 1, 15 or 30 dyn cm-2 (i.e. 0.1, 1.5 or 3 N m-2) (venous and two different arterial levels of shear stress) in a cone-and-plate viscometer. Laminar shear stress transiently upregulates preproendothelin-1 (ppET-1) mRNA, reaching its maximum after 30 min (approx 1.7-fold increase). In contrast, long-term application of shear stress (24 h) causes downregulation of ppET-1 mRNA in a dose-dependent manner. Arterial levels of shear stress result in downregulation of endothelin-converting enzyme-1 isoform ECE-1a (predominating in HUVEC) to 36.2 +/- 8.5 %, and isoform ECE-1b mRNA to 72.3 +/- 1.9 % of static control level. The endothelin-1 (ET-1) release is downregulated by laminar shear stress in a dose-dependent manner. This downregulation of ppET-1 mRNA and ET-1 release is not affected by inhibition of protein kinase C (PKC), or tyrosine kinase. Inhibition of endothelial NO synthase (L-NAME, 500 microm) prevents downregulation of ppET-1 mRNA by shear stress. In contrast, increasing degrees of long-term shear stress upregulate endothelin receptor type B (ETB) mRNA by a NO- and PKC-, but not tyrosine kinase-dependent mechanism. In conclusion, our data suggest the downregulation of human endothelin synthesis, and an upregulation of the ETB receptor by long-term arterial laminar shear stress. These effects might contribute to the vasoprotective and anti-arteriosclerotic potential of arterial laminar shear stress. PMID:10856127

Morawietz, H; Talanow, R; Szibor, M; Rueckschloss, U; Schubert, A; Bartling, B; Darmer, D; Holtz, J

2000-06-15

207

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

NASA Astrophysics Data System (ADS)

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

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

2006-12-01

208

In vitro laser Doppler anemometry of pulsatile flow velocity and shear stress measurements downstream from a jellyfish valve in the mitral position of a ventricular assist device  

Microsoft Academic Search

Thrombus formation and hemolysis have both been linked to the dynamic flow characteristics of heart valve prostheses. To enhance our understanding of the flow characteristics past the mitral position of a jellyfish (JF) valve in the left ventricle under physiological pulsatile flow conditions, in vitro laser Doppler anemometry (LDA) measurements were carried out. The hydrodynamic performance of the JF valve

Yos Morsi; Masahisa Kogure; Mitsuo Umezu

1999-01-01

209

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

210

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

NASA Astrophysics Data System (ADS)

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

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

2010-09-01

211

Disbond monitoring in adhesive joints using shear stress optical fiber sensors  

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

212

Control of circumferential wall stress and luminal shear stress within intact vascular segments perfused ex vivo.  

PubMed

Proportional, integral, and derivative (PID) controllers have proven to be robust in controlling many applications, and remain the most widely used control system architecture. The purpose of this work was to use this architecture for designing and tuning two PID controllers. The first was used to control the physiologic arterial circumferential wall stress (CWS) and the second to control the physiologic arterial shear stress (SS) imposed on intact vascular segments that were implanted into an ex vivo vascular perfusion system (EVPS). In order to most accurately control the stresses imposed onto vascular segments perfused ex vivo, analytical models were derived to calculate the CWS and SS. The mid-vein-wall CWS was calculated using the classical Lame solution for thick-walled cylinders in combination with the intraluminal pressure and outer diameter measurements. Similarly, the SS was calculated using the Hagen-Poiseuille equation in combination with the flow rate and outer diameter measurements. Performance of each controller was assessed by calculating the root mean square of the error (RMSE) between the desired and measured process variables. The performance experiments were repeated ten times (N=10) and an average RMSE was reported for each controller. RMSE standard deviations were calculated to demonstrate the reproducibility of the results. Sterile methods were utilized for making blood gas and temperature measurements in order to maintain physiologic levels within the EVPS. Physiologic blood gases (pH, pO(2), and pCO(2)) and temperature within the EVPS were very stable and controlled manually. Blood gas and temperature levels were recorded hourly for several (N=9) 24 h perfusion experiments. RMSE values for CWS control (0.427+/-0.027 KPa) indicated that the system was able to generate a physiologic CWS wave form within 0.5% error of the peak desired CWS over each cardiac cycle. RMSE values for SS control (0.005+/-0.0007 dynescm(2)) indicated that the system was able to generate a physiologic SS wave form within 0.3% error of the peak desired SS over each cardiac cycle. Physiologic pH, pO(2), pCO(2), and temperature levels were precisely maintained within the EVPS. The built-in capabilities and overall performance of the EVPS described in this study provide us with a novel tool for measuring molecular responses of intact vascular segments exposed to precisely simulated arterial biomechanical conditions. PMID:19045510

El-Kurdi, Mohammed S; Vipperman, Jeffrey S; Vorp, David A

2008-10-01

213

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

214

Spatial distribution of wall shear stress in common carotid artery by color Doppler flow imaging.  

PubMed

The purpose of this study is to provide a novel approach for measuring the spatial distribution of wall shear stress (WSS) in common carotid artery in vivo. WSS distributions were determined by digital image processing from color Doppler flow imaging (CDFI) in 50 healthy volunteers. In order to evaluate the feasibility of the spatial distribution, the mean values of WSS distribution were compared to the results of conventional WSS calculating method (Hagen-Poiseuille formula). In our study, the mean value of WSS distribution from 50 healthy volunteers was (6.91?±?1.20) dyne/cm(2), while it was (7.13?±?1.24) dyne/cm(2) by Hagen-Poiseuille approach. The difference was not statistically significant (t?=?-0.864, p?=?0.604). Hence, the feasibility of the spatial distribution of WSS was proved. Moreover, this novel approach could provide three-dimensional distribution of shear stress and fusion image of shear stress with ultrasonic image for each volunteer, which made WSS "visible". In conclusion, the spatial distribution of WSS could be used for WSS calculation in vivo. Moreover, it could provide more detailed values of WSS distribution than those of Hagen-Poiseuille formula. PMID:22832893

Wang, Chao; Chen, Ming; Liu, Sheng-lin; Liu, Yi; Jin, Jia-mei; Zhang, Yu-hui

2013-06-01

215

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

Microsoft Academic Search

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

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

2005-01-01

216

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

Microsoft Academic Search

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

Simon Lamb

2006-01-01

217

Finite-amplitude shear wave in pre-stressed thin elastomers  

Microsoft Academic Search

We examine the elastic shear waves generated in a thin pre-stressed elastomer layer that is sandwiched between two relatively thick steel plates and is subjected to an elastic shear wave traveling in one of the steel plates. The elastomer layer has been deformed in uni-axial strain in advance, producing in the layer very large axial and lateral compressive stresses of

Sia Nemat-Nasser; Alireza V. Amirkhizi

2005-01-01

218

Extracellular finger domain modulates the response of the epithelial sodium channel to shear stress.  

PubMed

The epithelial sodium channel (ENaC) is regulated by multiple extracellular stimuli, including shear stress. Previous studies suggest that the extracellular finger domains of ENaC ? and ? subunits contain allosteric regulatory modules. However, the role of the finger domain in the shear stress response is unknown. We examined whether mutations of specific residues in the finger domain of the ? subunit altered the response of channels to shear stress. We observed that Trp substitutions at multiple sites within the tract ?Lys-250-?Leu-290 altered the magnitude or kinetics of channel activation by shear stress. Consistent with these findings, deletion of two predicted peripheral ? strands (?Ile-251-?Tyr-268) led to slower channel activation by shear stress, suggesting that these structures participate in the shear stress response. The effects of mutations on the shear stress response did not correlate with their effects on allosteric Na(+) inhibition (i.e. Na(+) self-inhibition), indicating a divergence within the finger domain regarding mechanisms by which the channel responds to these two external stimuli. This result contrasts with well correlated effects we previously observed at sites near the extracellular mouth of the pore, suggesting mechanistic convergence in proximity to the pore. Our results suggest that the finger domain has an important role in the modulation of channel activity in response to shear stress. PMID:22408250

Shi, Shujie; Blobner, Brandon M; Kashlan, Ossama B; Kleyman, Thomas R

2012-05-01

219

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

220

INITIAL DEVELOPMENT OF A MEMS WALL SHEAR STRESS SENSOR FOR PROPULSION APPLICATIONS  

Microsoft Academic Search

This paper describes preliminary research on the development of a MEMS based shear stress sensor for applications in the hypersonic aeropropulsion wind tunnels at the GASL Division of Allied Aerospace. Typically, when attempting to determine combustor performance (i.e. efficiency) using computer codes, assumptions are made with regards to the skin friction coefficient, required as an input. Obtaining direct shear stress

Mathew McCarthy; Luc G. Fréchette; Vijay Modi; Nicholas Tiliakos

221

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

Microsoft Academic Search

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

S. R. S PARKS; J.-M. C HOMAZ; J. C. L ASHERAS

222

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

Microsoft Academic Search

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

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

2006-01-01

223

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

NASA Astrophysics Data System (ADS)

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

Sekine, Yuichi; Soyama, Hitoshi

224

Finite Size Analysis of Zero-Temperature Jamming Transition under Applied Shear Stress by Minimizing a Thermodynamic-Like Potential  

NASA Astrophysics Data System (ADS)

By finding local minima of a thermodynamic-like potential, we generate jammed packings of frictionless spheres under constant shear stress ? and obtain the yield stress ?y by sampling the potential energy landscape. For three-dimensional systems with harmonic repulsion, ?y satisfies the finite size scaling with the limiting scaling relation ?y˜? -?c,?, where ?c,? is the critical volume fraction of the jamming transition at ?=0 in the thermodynamic limit. The finite size scaling implies a length ? ˜(?-?c,?)-? with ?=0.81±0.05, which turns out to be a robust and universal length scale exhibited as well in the finite size scaling of multiple quantities measured without shear and independent of particle interaction. Moreover, comparison between our new approach and quasistatic shear reveals that quasistatic shear tends to explore low-energy states.

Liu, Hao; Xie, Xiaoyi; Xu, Ning

2014-04-01

225

Finite size analysis of zero-temperature jamming transition under applied shear stress by minimizing a thermodynamic-like potential.  

PubMed

By finding local minima of a thermodynamic-like potential, we generate jammed packings of frictionless spheres under constant shear stress ? and obtain the yield stress ?y by sampling the potential energy landscape. For three-dimensional systems with harmonic repulsion, ?y satisfies the finite size scaling with the limiting scaling relation ?y??-?c,?, where ?c,? is the critical volume fraction of the jamming transition at ?=0 in the thermodynamic limit. The finite size scaling implies a length ??(?-?c,?)-? with ?=0.81±0.05, which turns out to be a robust and universal length scale exhibited as well in the finite size scaling of multiple quantities measured without shear and independent of particle interaction. Moreover, comparison between our new approach and quasistatic shear reveals that quasistatic shear tends to explore low-energy states. PMID:24765985

Liu, Hao; Xie, Xiaoyi; Xu, Ning

2014-04-11

226

SHEAR WAVE DISPERSION MEASURES LIVER STEATOSIS  

PubMed Central

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

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

2012-01-01

227

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

228

The joint effect of laser and shear stress treatments for the surface strengthening of Zr alloys  

NASA Astrophysics Data System (ADS)

In order to improve the surface strength, the structural evolution and mechanical properties of 47Zr-45Ti-5Al-3V alloys treated by laser and shear stress are investigated by X-ray diffraction (XRD), microhardness tester, and nanoindentation. The results indicate that the combined treatment of laser and shear stress is more advantageous than that of single laser or single shear stress to the surface strengthening of Zr alloys. ? phase and ? phase in the surface layer almost transform into fine ? phase completely during laser treatment, which plays a fine grain strengthening effect. The followed treatment of shear stress can transform ? phase into ? phase, which plays a dispersion strengthening effect, and induces a mass of dislocation which plays a dislocation strengthening effect. Higher plasticity and fine size of ? phase are helpful to restrain the appearance of cracks during the treatment of shear stress.

Zhao, Wei; Li, Jian; Jiang, Xiao; Xi, Mingzhe; Gao, Shiyou

2013-12-01

229

Cosmic shears should not be measured in conventional ways  

NASA Astrophysics Data System (ADS)

A long-standing problem in weak lensing is about how to construct cosmic shear estimators from galaxy images. Conventional methods average over a single quantity per galaxy to estimate each shear component. We show that any such shear estimators must reduce to a highly non-linear form when the galaxy image is described by three parameters (pure ellipse), even in the absence of the point spread function (PSF). In the presence of the PSF, we argue that this class of shear estimators are not likely to exist. Alternatively, we propose a new way of measuring the cosmic shear: instead of averaging over a single value from each galaxy, we average over two numbers, and then take the ratio to estimate the shear component. In particular, the two numbers correspond to the numerator and denominator that generate the quadrupole moments of the galaxy image in Fourier space, as proposed by Zhang. This yields a statistically unbiased estimate of the shear component. Consequently, measurements of the n-point spatial correlations of the shear fields should also be modified: one needs to derive the ratio of the two correlation functions to get the desired unbiased shear correlation.

Zhang, Jun; Komatsu, Eiichiro

2011-06-01

230

Conductivity measurements in a shear-banding wormlike micellar system  

NASA Astrophysics Data System (ADS)

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

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

2010-07-01

231

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

232

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

233

Wall Shear Stress Induced by Taylor Bubbles in Inclined Flow Channels  

NASA Astrophysics Data System (ADS)

The motion of single air bubbles in flat channels is experimentally investigated. The electrodiffusion technique of near-wall flow diagnostics is applied to measure the wall shear stress distribution under large rising bubbles. The measurements are synchronized with the visual observation of bubble movement by a high-speed camera. The analysis of video records provides information on the bubble shape and terminal velocity. The experiments are carried out for three different channel configuration (with heights of 1.5, 4, and 8 mm), cover a wide range of channel inclination angles (from horizontal to vertical position), and dealing with both the bubbles in stagnant and in co-flowing water. The directionally sensitive, two-strip electrodiffusion probe is proved to be an effective tool to investigate the near-wall flow response to translating bubbles. It provides information not only on the wall shear rate distribution, but also detects the location of near-wall flow reversal, gives an estimate of the thickness of liquid film separating the large bubble from the wall, and provides also the characteristics of capillary waves appearing in the bubble tail region. The effect of channel inclination angle on the modification of wall shear stress distribution along the upper and bottom wall is also discussed.

Tihon, J.; P?nkavová, V.; Vejražka, J.

2013-04-01

234

The SDSS Coadd: Cosmic Shear Measurement  

Microsoft Academic Search

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- significance on

Huan Lin; Scott Dodelson; Hee-Jong Seo; Marcelle Soares-Santos; James Annis; Jiangang Hao; David Johnston; Jeffrey M. Kubo; Ribamar R. R. Reis; Melanie Simet

2011-01-01

235

SWAS: A shear-wave analysis system for semi-automatic measurement of shear-wave splitting above small earthquakes  

Microsoft Academic Search

The complexity of shear wave-arrivals above small earthquakes makes the polarisations and time-delays of shear-wave splitting above small earthquakes difficult to measure. We report a semi-automatic shear-wave analysis system, SWAS, that appears to combine the benefits of both visual and automatic techniques. Initially, SWAS automatically estimates shear-wave polarisations and picks shear-wave arrivals by an expert system, which provides sufficiently accurate

Yuan Gao; Ping Hao; Stuart Crampin

2006-01-01

236

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

PubMed

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

Kimura, Tsutomu

2014-01-01

237

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.

KIMURA, Tsutomu

2014-01-01

238

Wind stress and near-surface shear in the equatorial Atlantic Ocean  

NASA Astrophysics Data System (ADS)

upper ocean response to wind stress is examined using 8 months of unique near-surface moored velocity, temperature, and salinity data at 0°N, 23°W in the equatorial Atlantic. The effects of wind stress and shear on the time-varying eddy viscosity are inferred using the surface shear-stress boundary condition. Parameterizations of eddy viscosity as a function of wind stress and shear versus wind stress alone are then examined. In principle, eddy viscosity should be proportional to the inverse shear, but how it is represented implicitly or explicitly can affect estimates of the near-surface flow field. This result may explain some discrepancies that have arisen from using parameterizations based only on wind stress to characterize the effects of turbulent momentum mixing.

Wenegrat, Jacob O.; McPhaden, Michael J.; Lien, Ren-Chieh

2014-02-01

239

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

240

Modeling shear wave splitting due to stress-induced anisotropy, with an application to Mount Asama Volcano, Japan  

NASA Astrophysics Data System (ADS)

We use numerical modeling to investigate the proposed stress-based origin for changing anisotropy at Mount Asama Volcano, Japan. Stress-induced anisotropy occurs when deviatoric stress conditions are applied to rocks which are permeated by microcracks and compliant pore space, leading to an anisotropic distribution of open crack features. Changes to the local stress field around volcanoes can thus affect the anisotropy of the region. The 2004 eruption of Mount Asama Volcano coincided with time-varying shear wave splitting measurements, revealing changes in anisotropy that were attributed to stress changes associated with the eruption. To test this assertion, we create a model that incorporates knowledge of the volcanic stress, ray tracing, and estimation of the anisotropy to produce synthetic shear wave splitting results using a dyke stress model. Anisotropy is calculated in two ways, by considering a basic case of having uniform crack density and a case where the strength of anisotropy is related to dry crack closure from deviatoric stress. Our results show that this approach is sensitive to crack density, crack compliance, and the regional stress field, all of which are poorly constrained parameters. In the case of dry crack closure, results show that modeled stress conditions produce a much smaller degree of anisotropy than indicated by measurements. We propose that the source of anisotropy changes at Asama is tied to more complex processes that may precipitate from stress changes or other volcanic processes, such as the movement of pore fluid.

Shelley, Adrian; Savage, Martha; Williams, Charles; Aoki, Yosuke; Gurevich, Boris

2014-05-01

241

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

242

A semi-empirical model for the wavevector-frequency spectrum of turbulent wall-shear stress  

Microsoft Academic Search

Attention is given to a semiempirical model of the wavevector-frequency spectral density of streamwise turbulent wall-shear stress. On the basis of contour plots of spectra of streamwise velocity in the sublayer of turbulent pipe flow measured by Morrison et al. (1971), properties of a suitable trial model are deduced. With guidance also from the formation of a plausible source model,

D. M. Chase

1993-01-01

243

Image-shearing camera for direct measurement of surface strains.  

PubMed

This paper describes a new image-shearing camera which focuses two laterally sheared images at the film plane. With coherent illumination, this camera becomes a shearing interferometer, which directly measures the derivatives of the surface displacements. This strain measuring tool enjoys several advantages over the conventional, holographic, and speckle interferometry, namely, (1) better fringe quality (than speckle interferometry); (2) does not require special vibration isolation; (3) very simple optical setup; (4) direct determination of strains; and (5) extended controllable range of sensitivity. PMID:20208872

Hung, Y Y; Liang, C Y

1979-04-01

244

Shear Stress Regulates Late EPC Differentiation via Mechanosensitive Molecule-Mediated Cytoskeletal Rearrangement  

PubMed Central

Background Previous studies have demonstrated that endothelial progenitor cells (EPCs), in particular late EPCs, play important roles in endothelial maintenance and repair. Recent evidence has revealed shear stress as a key regulator for EPC differentiation. However, the underlying mechanisms regulating the shear stress–induced EPC differentiation have not been understood completely. The present study was undertaken to further investigate the effects of shear stress on the late EPC differentiation, and to elucidate the signal mechanism involved. Methodology/Principal Finding In vitro and in vivo assays revealed that cytoskeletal remodeling was involved in the shear stress-upregulated expression of endothelial markers vWF and CD31 in late EPCs, with subsequently increased in vivo reendothelialization after arterial injury. Moreover, shear stress activated several mechanosensitive molecules including integrin ?1, Ras, ERK1/2, paxillin and FAK, which were all involved in both cytoskeletal rearrangement and cell differentiation in response to shear stress in late EPCs. Conclusions/Significance Shear stress is a key regulator for late EPC differentiation into endothelial cells, which is important for vascular repair, and the cytoskeletal rearrangement mediated by the activation of the cascade of integrin ?1, Ras, ERK1/2, paxillin and FAK is crucial in this process.

Li, Hong; Cui, Xiaodong; Zhang, Xiaoyun; Li, Xin; Jing, Xu; Wu, Haiyan; Avsar, Emil

2013-01-01

245

Shear stress-dependent expression of apoptosis-regulating genes in endothelial cells.  

PubMed

Laminar shear stress exerts potent anti-apoptotic effects. Therefore, we analyzed the influence of laminar shear stress on the expression of apoptosis-regulating genes in human umbilical vein endothelial cells (HUVEC). Application of high levels of laminar shear stress (15 and 30 dyn/cm(2)) decreased the susceptibility of HUVEC to undergo apoptosis, whereas low shear stress (1 dyn/cm(2)) had no effect. These diminished signs of apoptosis were accompanied by a decreased mRNA expression of apoptosis-inducing Fas receptor. Furthermore, mRNA and protein expression of anti-apoptotic, soluble Fas isoform FasExo6Del and anti-apoptotic Bcl-x(L) were induced. Surprisingly, high shear stress also elevated mRNA and protein expression of pro-apoptotic Bak. The shear stress-induced up-regulation of Bcl-x(L) and Bak mRNA can be abrogated by inhibition of the endothelial NO synthase. We propose that altered expression of Bcl-x(L) and the Fas system is involved in the protective effect of laminar shear stress against apoptosis in human endothelial cells. PMID:11095978

Bartling, B; Tostlebe, H; Darmer, D; Holtz, J; Silber, R E; Morawietz, H

2000-11-30

246

Measuring displacement derivatives by electronic speckle pattern shearing interferometry (ESPSI)  

NASA Astrophysics Data System (ADS)

Electronic speckle pattern shearing interferometry (ESPSI), also known as shearography, is a whole-field optical technique used to measure approximately the fields of displacement derivatives. The accurate measurements of these derivatives have two problems: first, although ESPSI results are approximately equal to the derivatives, they are equal to the derivatives only if the shear distance tends to zero, hence, if experimental data rendered by ESPSI are taken directly as equal to the derivatives, the measurements may carry an important shearing error; second, ESPSI yields values relative to a reference value at a specific location of the field that can be very difficult to determine accurately. In this paper, we propose a general procedure to compensate the shearing error and to introduce the reference by adding two quantities to the values rendered by ESPSI. As an example, we measured a displacement derivative field induced on a metallic sheet specimen by applying tensile load.

Labbe, Fernando; Cordero, Raúl R.; Martínez, Amalia; Rodríguez-Vera, Ramón

2005-08-01

247

Flow instability and wall shear stress variation in intracranial aneurysms  

PubMed Central

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

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

2010-01-01

248

Differential Reynolds stress closure modeling of compressible shear flows  

NASA Astrophysics Data System (ADS)

The most important difference between turbulence in high and low Mach number flows stems from the changing role and action of pressure at different speed regimes. In the rapidly distorted turbulence regime, this effect is well captured by rapid distortion theory (RDT) which shows that gradient Mach number characterizes the role/action of pressure very accurately. Thus motivated, we develop a new rapid pressure-strain correlation model for high-speed compressible shear flows in which the closure coefficients are functions of the local gradient Mach number. The functional dependence of the model coefficients on the Mach number is obtained by comparison against RDT data. This closure naturally leads to a pressure-dilatation closure model. Further analysis reveals that a modification of the dissipation equation is also mandatory to accommodate the pressure-dilatation closure physics. Full differential Reynolds stress closure calculations of plane supersonic mixing layers are performed and comparison with the experimental data of Goebel and Dutton shows that the model exhibits good overall agreement without any further model calibration.

Gomez, Carlos; Girimaji, Sharath

2011-11-01

249

Implantation of a Carotid Cuff for Triggering Shear-stress Induced Atherosclerosis in Mice  

PubMed Central

It is widely accepted that alterations in vascular shear stress trigger the expression of inflammatory genes in endothelial cells and thereby induce atherosclerosis (reviewed in 1 and 2). The role of shear stress has been extensively studied in vitro investigating the influence of flow dynamics on cultured endothelial cells 1,3,4 and in vivo in larger animals and humans 1,5,6,7,8. However, highly reproducible small animal models allowing systematic investigation of the influence of shear stress on plaque development are rare. Recently, Nam et al. 9 introduced a mouse model in which the ligation of branches of the carotid artery creates a region of low and oscillatory flow. Although this model causes endothelial dysfunction and rapid formation of atherosclerotic lesions in hyperlipidemic mice, it cannot be excluded that the observed inflammatory response is, at least in part, a consequence of endothelial and/or vessel damage due to ligation. In order to avoid such limitations, a shear stress modifying cuff has been developed based upon calculated fluid dynamics, whose cone shaped inner lumen was selected to create defined regions of low, high and oscillatory shear stress within the common carotid artery 10. By applying this model in Apolipoprotein E (ApoE) knockout mice fed a high cholesterol western type diet, vascular lesions develop upstream and downstream from the cuff. Their phenotype is correlated with the regional flow dynamics 11 as confirmed by in vivo Magnetic Resonance Imaging (MRI) 12: Low and laminar shear stress upstream of the cuff causes the formation of extensive plaques of a more vulnerable phenotype, whereas oscillatory shear stress downstream of the cuff induces stable atherosclerotic lesions 11. In those regions of high shear stress and high laminar flow within the cuff, typically no atherosclerotic plaques are observed. In conclusion, the shear stress-modifying cuff procedure is a reliable surgical approach to produce phenotypically different atherosclerotic lesions in ApoE-deficient mice.

Kuhlmann, Michael T.; Cuhlmann, Simon; Hoppe, Irmgard; Krams, Rob; Evans, Paul C.; Strijkers, Gustav J.; Nicolay, Klaas; Hermann, Sven; Schafers, Michael

2012-01-01

250

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

251

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

NASA Astrophysics Data System (ADS)

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

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

2012-10-01

252

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

253

The Importance of Resolved Shear Stress and Dilation at the Instant of Cycloid Cusp Formation on Europa  

NASA Astrophysics Data System (ADS)

Chains of arcuate fractures called cycloids or flexi are nearly ubiquitous on the ice surface of Europa and are typically among the youngest lineaments visible. Cycloids, by definition, consist of two or more arcuate segments and at least one cusp, although many cycloids may form long chains containing several segments and cusps. Cycloid segments meet at cusps, which are typically defined by a sharp kink. The current model for cycloid formation suggests that cycloids grow as tensile fractures in the diurnal tidal stress field on Europa, which constantly changes in magnitude and orientation, rotating clockwise in the southern hemisphere and counter-clockwise in the northern hemisphere. In this model, cycloids form perpendicular to the maximum tensile stress direction and grow in a curving path as the principal stresses rotate. Cycloids form cusps since a number of hours pass between the time when a segment is inactive and the time when the next segment initiates. This tensile crack model has seemingly isolated the dominant driving mechanism for cycloid growth (i.e. diurnal stress). Nonetheless, this model fails to account for the likely mechanics of crack development in the extant stress field at cycloid cusps. Our data indicate that cusp angles (the angular change from one segment to the next) are all less than 90° , which geometrically necessitates resolved shear stress on an existing cycloid segment at the time of cusp formation. The only loading condition in which there would be zero resolved shear stress (for cusp angles < 45° ) would be if the two horizontal principal stresses coincidentally resolved equal and opposite shear stresses on the existing segment, causing the resolved shear stresses to balance out. This scenario is impossible for the average cusp angle of 56° (based on 126 measured cusps), as it would geometrically require the minimum tensile stress to be more tensile than the maximum tensile stress. The existence of resolved shear stress must therefore be accounted for in cycloid growth models. When shear stress is resolved onto a crack, tailcracks may form in the extensional quadrants. For pure strike-slip sliding, tensile stress is theoretically maximized at 70.5° from the trend of the slipping feature in the extensional quadrants. We surveyed strike-slip faults on Europa having observable offsets and associated tailcracks and measured a wide variability in tailcrack angles with respect to fault strike, averaging 54° and ranging from 30 to 80° . This variability in tailcrack angle can be mathematically attributed to concurrent opening and shearing along faults on Europa. High-angle tailcracks reflect pure strike-slip motions, whereas progressively lower angle tailcracks indicate increasing ratios of opening to strike-slip motion of the crack surfaces at the instant of tailcrack development. We advocate that rotating diurnal stresses can similarly form cycloids by initiating a cycloid segment in the form of a tailcrack, thus forming a cusp. The sense of shearing that is geometrically required during cusp formation is consistent with the formation of cusps by tailcrack initiation. The formation of cycloid cusps by tailcracking is also consistent with the observation that average cycloid cusp angles are almost identical to average tailcrack take-off angles along ridge-like strike-slip faults on Europa. These results suggest that a component of opening must accompany shearing during the formation of both cycloid cusps and tailcracks along strike-slip faults, but that the mechanical development of these two features is nonetheless identical.

Marshall, S. T.; Kattenhorn, S. A.

2004-12-01

254

Tidally driven stress accumulation and shear failure of Enceladus's tiger stripes  

Microsoft Academic Search

Straddling the south polar region of Saturn's moon Enceladus, the four principal “tiger stripe” fractures are a likely source of tectonic activity and plume generation. Here we investigate tidally driven stress conditions at the tiger stripe fractures through a combined analysis of shear and normal diurnal tidal stresses and accounting for additional stress at depth due to the overburden pressure.

Bridget Smith-Konter; Robert T. Pappalardo

2008-01-01

255

Role of symmetry-breaking induced by Er × B shear flows on developing residual stresses and intrinsic rotation in the TEXTOR tokamak  

NASA Astrophysics Data System (ADS)

Direct measurements of residual stress (force) have been executed at the edge of the TEXTOR tokamak using multitip Langmuir and Mach probes, together with counter-current NBI torque to balance the existing toroidal rotation. Substantial residual stress and force have been observed at the plasma boundary, confirming the existence of a finite residual stress as possible mechanisms to drive the intrinsic toroidal rotation. In low-density discharges, the residual stress displays a quasi-linear dependence on the local pressure gradient, consistent with theoretical predictions. At high-density shots the residual stress and torque are strongly suppressed. The results show close correlation between the residual stress and the Er × B flow shear rate, suggesting a minimum threshold of the E × B flow shear required for the k? symmetry breaking. These findings provide the first experimental evidence of the role of Er × B sheared flows in the development of residual stresses and intrinsic rotation.

Xu, Y.; Hidalgo, C.; Shesterikov, I.; Berte, M.; Dumortier, P.; Van Schoor, M.; Vergote, M.; Krämer-Flecken, A.; Koslowski, R.; the TEXTOR Team

2013-07-01

256

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

PubMed Central

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

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

2010-01-01

257

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

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

258

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

NASA Astrophysics Data System (ADS)

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

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

2011-07-01

259

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

260

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

PubMed Central

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

2013-01-01

261

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

262

Composite material shear property measurement using the Iosipescu specimen  

NASA Technical Reports Server (NTRS)

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

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

1992-01-01

263

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

NASA Astrophysics Data System (ADS)

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

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

264

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

NASA Technical Reports Server (NTRS)

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

Chaudhuri, R. Z.

1986-01-01

265

A Rheological Study of Ceramic Suspensions at Very Low Shearing Stresses.  

National Technical Information Service (NTIS)

The rheological behavior of aqueous suspensions of ceramic materials was investigated at very low shearing stresses. A sensitive coaxial cylinder viscometer of original design was used. A sanitaryware slip was studied in this investigation. Flow behavior ...

J. C. Sikra G. W. Phelps H. T. Smyth

1974-01-01

266

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

267

Pressure and Shear - Definitions, Relationships and Measurements  

Microsoft Academic Search

Preamble: The terms are often used to describe the force that causes deformation and the deformation itself. The definitions given here are from an engineering perspective but specifically address the wheelchair seat cushion or bed support surface environment. Often terms for stress (force) and strain (distortion) are confused, especially when the forces come from different directions. The resulting tissue strain

Geoff Taylor

268

Instrument effects on stress jump measurements  

Microsoft Academic Search

Stress jumps occur in fluids that possess a viscous contribution to their total stress. On cessation of shear, such a fluid will show an instantaneous loss of stress, while some of the stress will remain and subsequently decay in some manner, either exponential or otherwise. The results in this paper show that filtering, present in most rheometers, will eliminate the

M. E. Mackay; C.-H. Liang; P. J. Halley

1992-01-01

269

Liquid crystal coatings for surface shear stress visualization in hypersonic flows  

Microsoft Academic Search

Experiments were conducted to test the surface-shear-stress visualization capabilities of shear-stress-sensitive\\/temperature- insensitive liquid crystal compounds in hypersonic flow. Liquid crystal coatings were applied to the surface of a conical model, which was then exposed to a high-unit-Reynolds-number (2.3 à 10⁷\\/m) Mach 5 flow. The coating was illuminated by white light, and its response to the various flow situations was monitored

D. C. Reda; D. P. Aeschliman

1990-01-01

270

The role of shear stress in the pathogenesis of discrete subaortic stenosis: implications for surgical treatment.  

PubMed

Discrete subaortic stenosis (DSS) is characterized by the presence of an obstructing membrane in the left ventricular outflow tract (LVOT). Evidence suggests that the formation of DSS represents a fibroproliferative reaction of the endocardium occurring in response to alterations in shear stress caused by geometric abnormalities within the LVOT. The aim of this review is to discuss the role of altered LVOT shear stress in the pathogenesis of DSS, and its implications in surgical decision making. PMID:21560809

Silbiger, Jeffrey J

2011-03-01

271

Effects of Shear Stress on Wound-Healing Angiogenesis in the Rabbit Ear Chamber  

Microsoft Academic Search

Recent studies indicate that wall shear stress plays a significant role in the physiological adaptation of the vascular system. This study focused on the effect of sustained wall shear stress on wound-healing angiogenesis by exploring the morphologic and hemodynamic changes in developing microvesselsin vivothrough the tissue repair process. Rabbits were treated with the ?1blocker prazosin (50 mg\\/L in water) orally

Shigeru Ichioka; Masahiro Shibata; Keisuke Kosaki; Yuko Sato; Kiyonori Harii; Akira Kamiya

1997-01-01

272

Association between Ischemic Stroke and Vascular Shear Stress in the Carotid Artery  

PubMed Central

Background and Purpose Vascular shear stress is essential for maintaining the morphology and function of endothelial cells. We hypothesized that shear stress in the internal carotid artery (ICA) may differ between patients with ischemic stroke and healthy control subjects. Methods ICA shear stress was calculated in 143 controls and 122 patients with ischemic stroke who had a normal ICA or an ICA with <50% stenosis. The stroke group included patients who presented with a first-ever or recurrent ischemic stroke but excluded cardioembolic stroke and uncertain etiologies. Of the 122 patients, 107 (87.7%) and 15 (12.3%) patients were categorized as first-ever and recurrent stroke, respectively. Results Carotid diameters were significantly larger, and both peak-systolic and end-diastolic velocities were significantly lower in patients with ischemic stroke than in controls (all p values <0.05). Mean values of peak-systolic and end-diastolic shear stress in both ICAs were significantly lower in patients with ischemic stroke in models that adjusted for age, sex, and vascular risk factors (p for trend <0.05). The ICA shear stress was lowest in patients with recurrent stroke or the subtype of small-vessel occlusion. Higher peak-systolic and end-diastolic shear stresses in both ICAs were independently and negatively associated with ischemic stroke after adjusting for potential confounders (all p values <0.05). Conclusions ICA shear stresses were significantly lower in patients with ischemic stroke than in control subjects. Future studies should attempt to define the causal relationship between carotid arterial shear stress and ischemic stroke.

Lee, Jun-Young; Rosenson, Robert S.

2014-01-01

273

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

274

Shear stress is associated with markers of plaque vulnerability and MMP-9 activity.  

PubMed

Background: Vulnerable plaque has been associated with local macrophage accumulation and local high matrix metalloproteinase-2 (MMP-2) and MMP-9 activity. Since shear stress is a known local modulator of plaque location, we have determined whether local shear stress was associated with local plaque composition and with local MMP activity.Methods and results: In 17 NZW rabbits plaque was generated by denudation of the infrarenal aorta over a region of 5 cm and feeding them a high cholesterol diet for 2 months. After 2 months, a motorised IVUS pullback of the infrarenal aorta was performed with a 40 MHz IVUS catheter (CVIS, Boston Scientific, USA). IVUS derived vessel wall-lumen contours were reconstructed in 3D with in-house developed software. These reconstructions served as an input for a computational fluid dynamics technique, from which the 3-D shear stress field was calculated. Plaque regions were divided in 5 regions (n=8) to identify the location of highest macrophage accumulation or selected on basis of shear stress to identify whether high shear stress selects macrophage accumulation (n=8). In a second series, shear stress values were used to select regions -containing both latent and active MMP-2 and MMP-9. Segments were sectioned with a microtome and stained for smooth muscle cells (SMC), macrophages (MPhi) and collagen (COL). MPhi, displayed the highest density upstream of the plaque (6.9+/-2.4%, p<0.05), while SMC accumulated downstream (74.8+/-1.9%) of the plaque. High shear stress was associated with MPhi accumulation and MMP-9 activity (p<0.05). Conclusion: Upstream location of macrophages in plaques is associated with high shear stress and MMP-9 accumulation. These findings are discussed in relation to rheological theories reported previously in atherosclerosis. PMID:19755269

Krams, R; Cheng, C; Helderman, F; Verheye, S; van Damme, L C A; Mousavi Gourabi, B; Tempel, D; Segers, D; de Feyter, P; Pasterkamp, G; De Klein, D; de Crom, R; van der Steen, A F W; Serruys, P W

2006-08-01

275

Purinergic signaling is required for fluid shear stress-induced NF-?B translocation in osteoblasts  

Microsoft Academic Search

Fluid shear stress regulates gene expression in osteoblasts, in part by activation of the transcription factor NF-?B. We examined whether this process was under the control of purinoceptor activation. MC3T3-E1 osteoblasts under static conditions expressed the NF-?B inhibitory protein I?B? and exhibited cytosolic localization of NF-?B. Under fluid shear stress, I?B? levels decreased, and concomitant nuclear localization of NF-?B was

Damian C. Genetos; Norman J. Karin; Derik J. Geist; Henry J. Donahue; Randall L. Duncan

2011-01-01

276

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

NASA Astrophysics Data System (ADS)

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 \\langle \\tilde{v}_r \\tilde{v}_{\\bot} \\rangle 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 is a negative viscosity effect, a magnetic-shear-induced Reynolds stress—called \\hat{s} -residual stress—arises as a consequence of a residual spatial tilting of ballooning modes by the magnetic shear in a poloidally up-down asymmetric magnetic geometry. A model is derived in the weak flow shear regime under the approximation of circular flux surfaces. The amplitude of this residual stress is of the order of the square of the radial velocity fluctuations in the scrape-off layer (SOL), and in the immediate radial vicinity of the separatrix if an X-point exists. Its amplitude drops rapidly to zero towards the plasma core, thus appearing as a source of transverse rotation at the interface. Its non-linear dependence on the electric shear is discussed in the context of the weak electric shear effect on the poloidal shape of the ballooning envelope. The local \\hat{s} -residual stress is non-uniform poloidally and changes sign according to the up/down position of SOL end-plates with respect to the ?B × B direction. The electric- and magnetic-shear-induced stresses are then included in a flux-surface-averaged 1D model of mean flow conservation at the plasma edge, including the SOL volume. In L-mode weak shear regimes, it is shown that changing the plasma geometry from ?B × B away from the divertor to ?B × B towards the divertor approximately doubles the electric shear strength inside the separatrix, as reported in experiments. This shear-induced stress also enters the toroidal momentum balance, where it appears as a significant source of momentum in the immediate vicinity of the separatrix. Balanced by the toroidal viscosity only, it can sustain toroidal flow gradients of the order of a km s-1 cm-1 at the separatrix, with a sign also dependent on the plasma geometry. These momentum sources arising from symmetry breaking at the boundary of the confined region may explain why low to high mode power thresholds are lower in favourable than unfavourable configurations, and may be important for the issue of optimal plasma shapes with respect to edge intrinsic shear.

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

2012-10-01

277

Wall shear stress distributions in a model of normal and constricted small airways.  

PubMed

Previous studies have highlighted flow shear stress as a possible damage mechanism for small airways, in particular those liable to constriction through disease or injury due to mechanical ventilation. Flow experiments in vitro have implicated shear stress as a relevant factor for mechanotransduction pathways with respect to airway epithelial cell function. Using computational fluid dynamics analysis, this study reports velocity profiles and calculations for wall shear stress distributions in a three-generation, asymmetric section of the small airways subjected to a steady, inspiratory flow. The results show distal variation of wall shear stress distributions due to velocity gradients on the carina side of each daughter airway branch. The maximum wall shear stresses in both normal and constricted small airways are shown to exceed those calculated using data from previous simpler one-dimensional experimental analyses. These findings have implications for lung cell flow experiments involving shear stress in the consideration of both normal airway function and pathology due to mechanotransduction mechanisms. PMID:24618983

Evans, David J; Green, Anthony S; Thomas, Nicholas K

2014-04-01

278

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

NASA Astrophysics Data System (ADS)

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

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

2012-10-01

279

Monocyte recruitment to endothelial cells in response to oscillatory shear stress  

PubMed Central

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

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

2014-01-01

280

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

281

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.

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

2013-01-01

282

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

283

Surface Flow Visualization with Shear Stress Sensitivive Liquid Crystals.  

National Technical Information Service (NTIS)

The use of non-capsulated liquid crystals, which react directly to wall shear forces, for surface flow visualization, is presented. The temperature sensitivity is avoided by producing a mixture with an event temperature (first red indication temperature) ...

K. Pengel

1988-01-01

284

A semi-empirical model for the wavevector-frequency spectrum of turbulent wall-shear stress  

NASA Astrophysics Data System (ADS)

Attention is given to a semiempirical model of the wavevector-frequency spectral density of streamwise turbulent wall-shear stress. On the basis of contour plots of spectra of streamwise velocity in the sublayer of turbulent pipe flow measured by Morrison et al. (1971), properties of a suitable trial model are deduced. With guidance also from the formation of a plausible source model, an explicit model form for the shear-stress spectrum is proposed. In this, the viscous-penetration scale (nu/omega) exp 1/2 plays a prominent role, along with an outer scale. The trial model is fitted to the Morrison et al. contours to derive suggested values for the model parameters. The resulting computed spectral density at low wavenumbers is comparable to the indicated experimental level of low-wavenumber turbulent wall pressure. Since the contribution to the latter spectrum associated with a viscous wall condition at low wavenumbers has been shown to be equal to that of wavevector-oriented wall-shear stress, this viscous contribution is suggested to dominate the wall-pressure spectrum as well. The frequency spectrum of streamwise wall-shear stress at a point is also computed and compared with experimental results.

Chase, D. M.

1993-08-01

285

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

PubMed Central

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

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

2009-01-01

286

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

Microsoft Academic Search

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

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

2006-01-01

287

Analysis of shearing stress in the limited durability of bovine pericardium used as a biomaterial.  

PubMed

The objective of the study was to determine the shearing stress exerted by the suture thread under conditions of normal working stress. Thirty-six samples of calf pericardium, similar to that employed in the manufacture of bioprosthetic cardiac valve leaflets, were subjected to tensile testing. Prior to the trial, a continuous suture was sewn in the central zone of each sample, at a 45 degrees angle to the longest axis of the sample, using commercially-available threads (silk, Gore-Tex, Surgilene and nylon). Application of the Mohr circle for combined wear revealed that the shearing stress ranged between 2.68-fold greater (for samples sewn with silk) and 5.48-fold greater (for samples sewn with nylon) than the working tensile stress in the region of the suture. It is concluded that the shearing stress is responsible for the limited durability of sutured samples of calf pericardium prepared to simulate bioprosthetic cardiac valve leaflets. PMID:15348911

Carrera San Martin, A; García Paez, J M; García Sestafe, J V; Herrero, E J; Navidad, R; Cordón, A; Castillo-Olivares, J L

1998-02-01

288

Modified electronic speckle pattern shearing interferometry for simultaneous derivative map measurements  

NASA Astrophysics Data System (ADS)

Electronic speckle pattern shearing interferometry (ESPSI) allows for the measurement of displacement derivative maps. To monitor the stress/strain state of an object surface and its material properties, it is necessary to measure more than one displacement derivative map. The conventional configuration of ESPSI has been modified by parallel adaptation of Michelson shearing interferometers and an optoelectronic/image processing head with the capability of simultaneous capturing of 2 images. The automatic analysis of speckle fields is performed by temporal phase stepping method with the separation of the information by orthogonal polarization states. In the paper the opto-mechanical and electronic configuration of the system is presented. The experimental results obtained in the modified ESPIS system, when applied to determination of shear strain in a tensile loaded aluminium specimen are also presented.

Dymny, Grzegorz; Kujawinska, Malgorzata; Waldner, Stephan

1997-09-01

289

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

290

Impairment of autophagy in endothelial cells prevents shear-stress-induced increases in nitric oxide bioavailability.  

PubMed

Autophagy is a lysosomal catabolic process by which cells degrade or recycle their contents to maintain cellular homeostasis, adapt to stress, and respond to disease. Impairment of autophagy in endothelial cells studied under static conditions results in oxidant stress and impaired nitric oxide (NO) bioavailability. We tested the hypothesis that vascular autophagy is also important for induction of NO production caused by exposure of endothelial cells to shear stress (i.e., 3 h × ?20 dyn/cm(2)). Atg3 is a requisite autophagy pathway mediator. Control cells treated with non-targeting control siRNA showed increased autophagy, reactive oxygen species (ROS) production, endothelial NO synthase (eNOS) phosphorylation, and NO production upon exposure to shear stress (p < 0.05 for all). In contrast, cells with >85% knockdown of Atg3 protein expression (via Atg3 siRNA) exhibited a profound impairment of eNOS phosphorylation, and were incapable of increasing NO in response to shear stress. Moreover, ROS accumulation and inflammatory cytokine production (MCP-1 and IL-8) were exaggerated (all p < 0.05) in response to shear stress. These findings reveal that autophagy not only plays a critical role in maintaining NO bioavailability, but may also be a key regulator of oxidant-antioxidant balance and inflammatory-anti-inflammatory balance that ultimately regulate endothelial cell responses to shear stress. PMID:24941409

Bharath, Leena P; Mueller, Robert; Li, Youyou; Ruan, Ting; Kunz, David; Goodrich, Rebekah; Mills, Tyler; Deeter, Lance; Sargsyan, Ashot; Anandh Babu, Pon Velayutham; Graham, Timothy E; Symons, J David

2014-07-01

291

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

PubMed

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

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

2011-06-01

292

Problems with ultrasonic measurements of shear modules of structured media.  

PubMed

The elastic constants of linearly elastic, isotropic or anisotropic bone material are required for many numerical simulations. These constants are often measured ultrasonically, but this can lead to mistakes, especially if shear modules of spongiosa are considered. The reason is that spongiosa is a structure composed of trabeculae, each of which acts as a kind of beam which allows longitudinal, shear and also bending waves to propagate; the bending waves are as fast as the longitudinal waves and are indistinguishable from the shear waves. Furthermore, mistakes in measuring Young's modulus cannot be avoided in every case. Several numerical simulations of wave propagations in homogeneous media, and especially in periodically and irregularly structured media, were carried out via the application of explicit finite element codes. Results showing the above-mentioned effects are presented and discussed. These can help to explain in detail why mistakes may occur during ultrasonic measurements. PMID:17289452

Besdo, D; Besdo, S; Behrens, B-A; Bouguecha, A

2007-09-01

293

Turbulence measurements in a nearly homogeneous shear flow  

NASA Astrophysics Data System (ADS)

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

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

294

An ultrasonic technique for measuring stress in fasteners  

SciTech Connect

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

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

1999-12-02

295

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

SciTech Connect

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

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

2008-05-13

296

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

297

A review of techniques for measuring shear-wave splitting above small earthquakes  

NASA Astrophysics Data System (ADS)

Seismic shear-wave splitting is difficult to measure accurately because of the complexity of the shear-wave signal. A variety of techniques have been developed for measuring time-delays and polarisations of shear-wave splitting above small earthquakes. These range from 'display' techniques, where measurements depend on visual examination of rotated seismograms and polarisation diagrams, through a range of increasingly automatic techniques, to what are almost fully automatic processes. All techniques have disadvantages. Visual techniques are subjective and, although arguably the most accurate, are tedious and time-consuming. More automated techniques work well on noise-free impulsive near-classic examples of shear-wave splitting, but on typical records either require visual checking or need to pass stringent selection criteria which may severely limit the data and bias the results. The accompanying paper presents a combination of visual and automatic techniques to provide a user-friendly semi-automatic measurement technique. Such techniques are important because the new understanding of fluid-rock deformation suggests that shear-wave splitting monitors the low-level deformation of fluid-saturated microcracks in hydrocarbon production processes, as well as the accumulation of stress before earthquakes, and other applications.

Crampin, Stuart; Gao, Yuan

2006-11-01

298

Purinergic signaling is required for fluid shear stress-induced NF-?B translocation in osteoblasts.  

PubMed

Fluid shear stress regulates gene expression in osteoblasts, in part by activation of the transcription factor NF-?B. We examined whether this process was under the control of purinoceptor activation. MC3T3-E1 osteoblasts under static conditions expressed the NF-?B inhibitory protein I?B? and exhibited cytosolic localization of NF-?B. Under fluid shear stress, I?B? levels decreased, and concomitant nuclear localization of NF-?B was observed. Cells exposed to fluid shear stress in ATP-depleted medium exhibited no significant reduction in I?B?, and NF-?B remained within the cytosol. Similar results were found using oxidized ATP or Brilliant Blue G, P2X(7) receptor antagonists, indicating that the P2X(7) receptor is responsible for fluid shear-stress-induced I?B? degradation and nuclear accumulation of NF-?B. Pharmacologic blockage of the P2Y6 receptor also prevented shear-induced I?B? degradation. These phenomena involved neither ERK1/2 signaling nor autocrine activation by P2X(7)-generated lysophosphatidic acid. Our results suggest that fluid shear stress regulates NF-?B activity through the P2Y(6) and P2X(7) receptor. PMID:21237152

Genetos, Damian C; Karin, Norman J; Geist, Derik J; Donahue, Henry J; Duncan, Randall L

2011-04-01

299

A Phenomenological Model for Wind Speed and Shear Stress Profiles in Vegetation Cover Layers.  

NASA Astrophysics Data System (ADS)

A phenomenological model for the mean wind speed and Reynolds shear stress profiles with height in a vegetation cover layer is derived from forms suggested by truncation of the equations of turbulent fluid motion at second order in fluctuating velocity products. The initial formulation is unique in that the force per unit volume resisting fluid motion is treated as a body force having a height-dependent character. The body force is assumed to be proportional to the instantaneous speed squared and in the opposite direction from the instantaneous velocity. Viscous forces are ignored as are all pressure forces except for a steady vertical pressure gradient. Closure of the, equations is effected by a phenomenological assumption linking the static pressure and the square of the mean wind speed. The mean wind speed profile predicted by the model is an exponential in the cumulative drag area per unit planform area as a function of height, which is a simple exponential in height for cover with uniform plant area density. Comparisons of predicted profiles of wind speed and Reynolds shear stress with measurements show the model to be relatively robust.

Albini, F. A.

1981-11-01

300

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

NASA Astrophysics Data System (ADS)

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

Fourrié, Grégoire; Keirsbulck, Laurent; Labraga, Larbi

2013-10-01

301

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

NASA Astrophysics Data System (ADS)

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

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

2007-12-01

302

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

NASA Astrophysics Data System (ADS)

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

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

2004-12-01

303

Electromechanical Apparatus Measures Residual Stress  

NASA Technical Reports Server (NTRS)

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

Chern, Engmin J.; Flom, Yury

1993-01-01

304

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

PubMed

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

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

2013-06-01

305

A quantitative comparison of mechanical blood damage parameters in rotary ventricular assist devices: shear stress, exposure time and hemolysis index.  

PubMed

Ventricular assist devices (VADs) have already helped many patients with heart failure but have the potential to assist more patients if current problems with blood damage (hemolysis, platelet activation, thrombosis and emboli, and destruction of the von Willebrand factor (vWf)) can be eliminated. A step towards this goal is better understanding of the relationships between shear stress, exposure time, and blood damage and, from there, the development of numerical models for the different types of blood damage to enable the design of improved VADs. In this study, computational fluid dynamics (CFD) was used to calculate the hemodynamics in three clinical VADs and two investigational VADs and the shear stress, residence time, and hemolysis were investigated. A new scalar transport model for hemolysis was developed. The results were compared with in vitro measurements of the pressure head in each VAD and the hemolysis index in two VADs. A comparative analysis of the blood damage related fluid dynamic parameters and hemolysis index was performed among the VADs. Compared to the centrifugal VADs, the axial VADs had: higher mean scalar shear stress (sss); a wider range of sss, with larger maxima and larger percentage volumes at both low and high sss; and longer residence times at very high sss. The hemolysis predictions were in agreement with the experiments and showed that the axial VADs had a higher hemolysis index. The increased hemolysis in axial VADs compared to centrifugal VADs is a direct result of their higher shear stresses and longer residence times. Since platelet activation and destruction of the vWf also require high shear stresses, the flow conditions inside axial VADs are likely to result in more of these types of blood damage compared with centrifugal VADs. PMID:22938355

Fraser, Katharine H; Zhang, Tao; Taskin, M Ertan; Griffith, Bartley P; Wu, Zhongjun J

2012-08-01

306

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

307

Novel double path shearing interferometer in corneal topography measurements  

NASA Astrophysics Data System (ADS)

The paper presents an approach for measurements of corneal topography by use of a patent pending double path shearing interferometer (DPSI). Laser light reflected from the surface of the cornea is divided and directed to the inputs of two interferometers. The interferometers use lateral shearing of wavefronts in two orthogonal directions. A tilt of one of the mirrors in each interferometric setup perpendicularly to the lateral shear introduces parallel carrier frequency fringes at the output of each interferometer. There is orthogonal linear polarization of the laser light used in two DPSI. Two images of fringe patters are recorded by a high resolution digital camera. The obtained fringe patterns are used for phase difference reconstruction. The phase of the wavefront was reconstructed by use of algorithms for a large grid based on discrete integration. The in vivo method can also be used for tear film stability measurement, artificial tears and contact lens tests.

Licznerski, Tomasz J.; Jaronski, Jaroslaw; Kosz, Dariusz

2005-09-01

308

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

PubMed

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/cm(2)). 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/cm(2)) 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

309

In vivo measurement of the complex shear modulus of rat mammary tumors using shear wave imaging techniques  

Microsoft Academic Search

This paper summarizes dynamic measurements of shear modulus constants acquired for spontaneously growing rat mammary tumors. Measurements are compared with histology to determine tumor types. We also report on 3D shear-wave velocity fields acquired from an inhomogeneous hydrogel phantom with known mechanical properties. Phantom measurements enable us to interpret the effects of tissue structure and geometry on viscoelastic parameter estimates,

Yue Wang; Marko Orescanin; Michael F. Insana

2010-01-01

310

Yield stress, volume change, and shear strength behaviour of unsaturated soils: validation of the SFG model  

Microsoft Academic Search

The model recently presented by Sheng, Fredlund, and Gens, known as the SFG model, provides a consistent explanation of yield stress, shear strength, and volume change behaviour of unsaturated soils as functions of suction. All these functions are based on one single equation that defines the volume change with suction and stress changes. This pa- per provides a systematic validation

Annan Zhou; Daichao Sheng

2009-01-01

311

Analysis of shearing stress in the limited durability of bovine pericardium used as a biomaterial  

Microsoft Academic Search

The objective of the study was to determine the shearing stress exerted by the suture thread under conditions of normal working stress. Thirty-six samples of calf pericardium, similar to that employed in the manufacture of bioprosthetic cardiac valve leaflets, were subjected to tensile testing. Prior to the trial, a continuous suture was sewn in the central zone of each sample,

A. CARRERA SAN MARTIN; J. M. GARCIA PAEZ; J. V. GARCIA SESTAFE; E. JORGE HERRERO; R NAVIDAD; A CORDON; J. L CASTILLO-OLIVARES

1998-01-01

312

Muscle shear modulus measured with ultrasound shear-wave elastography across a wide range of contraction intensity.  

PubMed

Introduction: In this study we examine the repeatability of measuring muscle shear modulus using ultrasound shear-wave elastography between trials and between days, and the association between shear modulus and contraction intensity over a wide range of intensities. Methods: Shear modulus of the biceps brachii was determined using ultrasound shear-wave elastography during static elbow flexion (up to 60% of maximal contraction) in healthy young adults. Results: The correspondence of shear modulus was confirmed in phantoms between the manufacturer-calibrated values and the shear-wave elastography values. The intraclass correlation coefficient of muscle shear modulus was high: 0.978 between trials and 0.948 between days. Shear modulus increased linearly with elbow flexion torque across contraction intensity, and its slope was associated negatively with muscle strength. Conclusions: Muscle shear modulus measured with ultrasound shear-wave elastography may be useful for inferring muscle stiffness across a wide range of contraction intensity. In addition, it has high repeatability between trials and between days. Muscle Nerve 50: 103-113, 2014. PMID:24155045

Yoshitake, Yasuhide; Takai, Yohei; Kanehisa, Hiroaki; Shinohara, Minoru

2014-07-01

313

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

314

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

315

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

316

Macrorheology and adaptive microrheology of endothelial cells subjected to fluid shear stress  

PubMed Central

Vascular endothelial cells (ECs) respond to temporal and spatial characteristics of hemodynamic forces by alterations in their adhesiveness to leukocytes, secretion of vasodilators, and permeability to blood-borne constituents. These physiological and pathophysiological changes are tied to adaptation of cell mechanics and mechanotransduction, the process by which cells convert forces to intracellular biochemical signals. The exact time scales of these mechanical adaptations, however, remain unknown. We used particle-tracking microrheology to study adaptive changes in intracellular mechanics in response to a step change in fluid shear stress, which simulates both rapid temporal and steady features of hemodynamic forces. Results indicate that ECs become significantly more compliant as early as 30 s after a step change in shear stress from 0 to 10 dyn/cm2 followed by recovery of viscoelastic parameters within 4 min of shearing, even though shear stress was maintained. After ECs were sheared for 5 min, return of shear stress to 0 dyn/cm2 in a stepwise manner did not result in any further rheological adaptation. Average vesicle displacements were used to determine time-dependent cell deformation and macrorheological parameters by fitting creep function to a linear viscoelastic liquid model. Characteristic time and magnitude for shear-induced deformation were 3 s and 50 nm, respectively. We conclude that ECs rapidly adapt their mechanical properties in response to shear stress, and we provide the first macrorheological parameters for time-dependent deformations of ECs to a physiological forcing function. Such studies provide insight into pathologies such as atherosclerosis, which may find their origins in EC mechanics.

Dangaria, Jhanvi H.; Butler, Peter J.

2011-01-01

317

Analytical modeling of the interfacial shearing stress in dual-coated optical fiber specimens subjected to tension.  

PubMed

A simple analytical model is developed for the evaluation of interfacial shearing stress at the glass fiber surface in dual-coated optical fiber specimens subjected to tension. The analysis has been performed for pull-out testing and in situ evaluation of Young's (shear) modulus of the primary coating material and is aimed at assessment of the effect of the materials properties and the specimen's geometry on the magnitude and distribution of interfacial shearing stress. It is shown that the longitudinal distribution of this stress is nonuniform and that, for the given specimen's length, its maximum value increases with a decrease in the thickness of the primary coating. It is concluded that, while currently used 1-cm-long specimens with approximately 30-µm-thick primary coatings are acceptable, shorter specimens (say, 5 mm long) are expected to result in more stable experimental data. The results obtained can be useful for comparing the adhesive strength of the primary coating material in fibers of different lengths and with different coating designs, as well as for the evaluation of Young's (shear) modulus of this material from the measured axial displacement of the glass fiber. PMID:20829909

Suhir, E

1993-06-01

318

Wave Induced Seabed Effective Stress Distribution Including Rotational Shear Effect.  

National Technical Information Service (NTIS)

The stability of a seabed under wave action has been the subject of a number of recent studies. Among them are theoretical analyses using elastic or visco-elastic soil models, laboratory investigations of soil under rotational shear loading and wave tank ...

C. K. Shen Z. L. Wang L. R. Herrmann

1986-01-01

319

Ultrasonic measurement of stress in railroad wheels  

NASA Astrophysics Data System (ADS)

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

Schramm, Raymond E.

1999-02-01

320

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

NASA Astrophysics Data System (ADS)

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

Michlmayr, Gernot; Or, Dani

2013-04-01

321

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

322

Sea Ice Thickness Measurements Using Shear Wave Reflections.  

National Technical Information Service (NTIS)

Because of the lack of success in measuring sea ice thickness with normal acoustic means, a method utilizing shear waves or 'S' waves was tried during the summer of 1971 off Point Barrow, Alaska. A 551A*Textronic oscilloscope and polaroid camera were used...

G. P. Vance D. D. Benefield D. M. Egan

1971-01-01

323

The effect of growth orientation on the resolved shear stresses for horizontal Bridgman grown GaAs crystals  

Microsoft Academic Search

An effective method based on double tensor transformation is proposed for the resolved shear stress calculation in the crystals with arbitrary growth axis orientation. Employing this method the influence of the crystal orientation on the resolved shear stresses is investigated for the horizontal Bridgman grown GaAs crystals. The stress patterns give a theoretical basis for the evaluation of the role

Edmund Dobrocka

1990-01-01

324

Pro-Atherogenic Shear Stress and HIV Proteins Synergistically Upregulate Cathepsin K in Endothelial Cells.  

PubMed

Major advances in highly active antiretroviral therapies (HAART) have extended the lives of people living with HIV, but there still remains an increased risk of death by cardiovascular diseases (CVD). HIV proteins have been shown to contribute to cardiovascular dysfunction with effects on the different cell types that comprise the arterial wall. In particular, HIV-1 transactivating factor (Tat) has been shown to bind to endothelial cells inducing a range of responses that contribute to vascular dysfunction. It is well established that hemodynamics also play an important role in endothelial cell mediated atherosclerotic development. When exposed to low or oscillatory shear stress, such as that found at branches and bifurcations, endothelial cells contribute to proteolytic vascular remodeling by upregulating cathepsins, potent elastases and collagenases that contribute to altered biomechanics and plaque formation. Mechanisms to understand the influence of Tat on shear stress mediated vascular remodeling have not been fully elucidated. Using an in vivo HIV-Tg mouse model and an in vitro cone and plate shear stress bioreactor to actuate physiologically relevant pro-atherogenic or atheroprotective shear stress on human aortic endothelial cells, we have shown synergism between HIV proteins and pro-atherogenic shear stress to increase endothelial cell expression of the powerful protease cathepsin K, and may implicate this protease in accelerated CVD in people living with HIV. PMID:24719048

Parker, Ivana Kennedy; Roberts, Ladeidra Monet; Hansen, Laura; Gleason, Rudolph L; Sutliff, Roy L; Platt, Manu O

2014-06-01

325

Shear stress-induced mechanotransduction protein deregulation and vasculopathy in a mouse model of progeria  

PubMed Central

Introduction A mouse model of progeria derived by insertion of the human mutant LMNA gene (mLMNA), producing mutant lamin A, shows loss of smooth muscle cells in the media of the ascending aorta. We hypothesized that high shear stress, in the presence of mutant lamin A, induces this vasculopathy and tried to define the molecular and cellular basis for aortic vasculopathy. Methods Ascending and descending aortas from wild type (WT) and mLMNA+ mice were compared using proteomics, Western blots, PCR and immunostaining. To determine whether high fluidic shear stress, known to occur in the ascending aorta, contributed to the vasculopathy, we exposed descending aortas of mLMNA+ mice, with no apparent vasculopathy, to 75 dynes/cm2 shear stress for 30 minutes using a microfluidic system. Results When the mice were one year of age, expression of several mechanotransduction proteins in the ascending aorta, including vimentin, decreased in mLMNA+ mice but no decrease occurred in the descending aorta. High fluidic shear stress produced a significant reduction in vimentin of mLMNA+ mice but not in similarly treated WT mice. Conclusions The occurrence of mutant lamin A and high shear stress correlate with a reduction in the level of mechanotransduction proteins in smooth muscle cells of the media. Reduction of these proteins may contribute over time to development of vasculopathy in the ascending aorta in progeria syndrome.

2014-01-01

326

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

NASA Astrophysics Data System (ADS)

Shear stresses ? on a subduction megathrust play an important role in determining the forces available for mountain building adjacent to a subduction zone. In this study, the temperatures and shear stresses on megathrusts in 11 subduction zones around the Pacific rim (Hikurangi, Tonga, Izu-Ogasawara, western Nankai, northeastern Japan, Aleutians, western Alaska, Cascadia, northern Chile, southern Chile) and SE Asia (northern Sumatra) have been determined. The main constraint is that vertical normal stresses beneath the highlands behind the subduction zone are nearly equal to horizontal normal stresses, in the plane of a trench- or arc-normal section. For a typical brittle and ductile megathrust rheology, frictional shear stress ? = ??gz, for depth z, and ductile shear stress ? = A exp (B/RT) at temperature T, where ?, A, B are rheological parameters treated as constants. Rheological constants common to all the megathrusts (?crust, ?mantle, B) are determined by simultaneously solving for the force balance in the overlying wedge and megathrust thermal structure, using a simplex minimization algorithm, taking account of the induced mantle corner flow at depth (65 ± 15 km (2?)) and constant radiogenic heating (0.65 ± 0.3 ?W m-3 (2?)) throughout the crust. The A constants are solved individually for each subduction zone, assuming that the maximum depth of interplate slip earthquakes marks the brittle-ductile transition. The best fit solution shows two groupings of megathrusts, with most subduction zones having a low mean shear stress in the range 7-15 MPa (?crust = 0.032 ± 0.006, ?mantle = 0.019 ± 0.004) and unable to support elevations >2.5 km. For a typical frictional sliding coefficient ˜0.5, the low effective coefficients of friction suggest high pore fluid pressures at ˜95% lithostatic pressure. Tonga and northern Chile require higher shear stresses with ?crust = 0.095 ± 0.024, ?mantle = 0.026 ± 0.007, suggesting slightly lower pore fluid pressures, at ˜81% lithostatic. Ductile shear in the crust is poorly resolved but in the mantle appears to show a strong power law dependency, with B = 36 ± 18 kJ mol-1. Amantle values are sensitive to the precise value of B but are in the range 1-20 kPa. The power law exponent n for mantle flow is poorly constrained but is likely to be large (n > 4). The brittle-ductile transition in the crust occurs at temperatures in the range 370°C-512°C, usually close to the base of the crust and in the mantle at much lower temperatures (180°C-300°C), possibly reflecting a marked change in pore fluid pressure or quasi ductile and subfrictional properties. In subduction zones where the subducted slab is older than 50 Ma, a significant proportion of the integrated shear force on the megathrust is taken up where it cuts the mantle and temperatures are ?300°C. In much younger subduction zones, the stress transmission is confined mainly to the crust. The shear stresses, particularly in the crust, may be kept low by some sort of lubricant such as abundant water-rich trench fill, which lowers the frictional sliding coefficient or effective viscosity and/or raises pore fluid pressure. The unusual high stress subduction zone in northern Chile lacks significant trench fill and may be poorly lubricated, with a mean shear stress ˜37 MPa required to support elevations >4 km in the high Andes. However, where the crust is thin in sediment-starved and poorly lubricated subduction zones, such as Tonga, the mean shear stress will still be low. Sediment may lubricate megathrusts accommodating underthrusting of continental crust, such as in the Himalayas or eastern central Andes, which have a low mean shear stress ˜15 MPa.

Lamb, Simon

2006-07-01

327

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

PubMed

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

Ketov, S V; Louzguine-Luzgin, D V

2013-01-01

328

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

PubMed Central

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

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

2013-01-01

329

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

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

330

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

Microsoft Academic Search

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

K. Platzer; P. Bartelt; C. Jaedicke

2007-01-01

331

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

332

Finite element model investigation of fault shear stress accumulation due to elastic loading and viscous relaxation.  

NASA Astrophysics Data System (ADS)

Shear stresses on faults drive earthquake ruptures. Therefore their initial spatial distributions along faults become one of the first order controls on how large an earthquake grows, and their interseismic accumulation between earthquakes strongly influences the seismogenic potential of a fault. Here we investigate in a generic fault zone model using a finite element code, how the accumulation of shear stress along faults are influenced by the type of asperity (geometrical vs. stress), interseismic loading rate, and the viscoelastic properties of the fault zone and adjacent materials. Shear stress accumulation along faults during the interseismic period is usually considered to be the result of slow elastic tectonic loading on frictionally locked fault interfaces. However, many rocks exhibit viscoelastic behavior over geological time scales. Thus if fault rocks and the surrounding host rock exhibit such time-dependent deformational behavior, interseismic loading of stresses along faults may not be simply described by time-independent linear elastic solutions. Time-dependent viscoelastic deformation relaxes stress over time and can alter the spatial pattern of stress heterogeneity along faults. Preliminary results of the modeling suggest that spatial diffusion of stress heterogeneities can occur due to viscoelastic effects especially when geometrical complexity is introduced at the fault surface. The interplay between relaxation time constants and tectonic loading rate will be further investigated to identify whether a particular rheology or tectonic setting is prone to stress relaxation effects due to viscous deformation.

Sone, Hiroki

2014-05-01

333

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

334

Averaging interval selection for the calculation of Reynolds shear stress for studies of boundary layer turbulence.  

NASA Astrophysics Data System (ADS)

It is widely recognised that boundary layer turbulence plays an important role in sediment transport dynamics in aeolian environments. Improvements in the design and affordability of ultrasonic anemometers have provided significant contributions to studies of aeolian turbulence, by facilitating high frequency monitoring of three dimensional wind velocities. Consequently, research has moved beyond studies of mean airflow properties, to investigations into quasi-instantaneous turbulent fluctuations at high spatio-temporal scales. To fully understand, how temporal fluctuations in shear stress drive wind erosivity and sediment transport, research into the best practice for calculating shear stress is necessary. This paper builds upon work published by Lee and Baas (2012) on the influence of streamline correction techniques on Reynolds shear stress, by investigating the time-averaging interval used in the calculation. Concerns relating to the selection of appropriate averaging intervals for turbulence research, where the data are typically non-stationary at all timescales, are well documented in the literature (e.g. Treviño and Andreas, 2000). For example, Finnigan et al. (2003) found that underestimating the required averaging interval can lead to a reduction in the calculated momentum flux, as contributions from turbulent eddies longer than the averaging interval are lost. To avoid the risk of underestimating fluxes, researchers have typically used the total measurement duration as a single averaging period. For non-stationary data, however, using the whole measurement run as a single block average is inadequate for defining turbulent fluctuations. The data presented in this paper were collected in a field study of boundary layer turbulence conducted at Tramore beach near Rosapenna, County Donegal, Ireland. High-frequency (50 Hz) 3D wind velocity measurements were collected using ultrasonic anemometry at thirteen different heights between 0.11 and 1.62 metres above the bed. A technique for determining time-averaging intervals for a series of anemometers stacked in a close vertical array is presented. A minimum timescale is identified using spectral analysis to determine the inertial sub-range, where energy is neither produced nor dissipated but passed down to increasingly smaller scales. An autocorrelation function is then used to derive a scaling pattern between anemometer heights, which defines a series of averaging intervals of increasing length with height above the surface. Results demonstrate the effect of different averaging intervals on the calculation of Reynolds shear stress and highlight the inadequacy of using the total measurement duration as a single block average. Lee, Z. S. & Baas, A. C. W. (2012). Streamline correction for the analysis of boundary layer turbulence. Geomorphology, 171-172, 69-82. Treviño, G. and Andreas, E.L., 2000. Averaging Intervals For Spectral Analysis Of Nonstationary Turbulence. Boundary-Layer Meteorology, 95(2): 231-247. Finnigan, J.J., Clement, R., Malhi, Y., Leuning, R. and Cleugh, H.A., 2003. Re-evaluation of long-term flux measurement techniques. Part I: Averaging and coordinate rotation. Boundary-Layer Meteorology, 107(1): 1-48.

Lee, Zoe; Baas, Andreas

2013-04-01

335

The role of von Willebrand factor and fibrinogen in platelet aggregation under varying shear stress.  

PubMed Central

Exposure of platelets to shear stress leads to aggregation in the absence of exogenous agonists. We have now found that different adhesive proteins and platelet membrane glycoproteins are involved in aggregation depending on the shear stress conditions and the concentration of divalent cations in the medium. When blood is collected with trisodium citrate as anticoagulant, which causes a decrease in the levels of external ionized calcium ([Ca2+]o), platelet aggregation can be induced under low shear force (12 dyn/cm2) and is mediated by fibrinogen binding to the glycoprotein IIb-IIIa complex. Aggregates formed under these conditions are not stable, and when shear force is increased to 68 dyn/cm2, disaggregation results. By contrast, platelets from blood collected with hirudin as anticoagulant, wherein [Ca2+]o is within normal plasma levels, do not undergo low shear-induced aggregation; however, after exposure to a shear force above 80 dyn/cm2, aggregation is observed but only when von Willebrand factor is present and can interact with both its platelet binding sites, glycoprotein Ib-IX and glycoprotein IIb-IIIa. Fibrinogen is not involved in high shear-induced aggregation which, in fact, occurs normally in patients with severe afibrinogenemia. Thus, von Willebrand factor in the absence of exogenous agonists can mediate platelet aggregation in experimental conditions that may mimic the hemorheological situation of partially occluded arteries. This pathway of platelet aggregation involving only one adhesive ligand and two membrane adhesion receptors may play a relevant role in thrombogenesis.

Ikeda, Y; Handa, M; Kawano, K; Kamata, T; Murata, M; Araki, Y; Anbo, H; Kawai, Y; Watanabe, K; Itagaki, I

1991-01-01

336

Quantitative calculation of local shear deformation in adiabatic shear band for Ti6Al4V  

Microsoft Academic Search

JOHNSON-COOK(J-C) model was used to calculate flow shear stress—shear strain curve for Ti-6Al-4V in dynamic torsion test. The predicted curve was compared with experimental result. Gradient-dependent plasticity(GDP) was introduced into J-C model and GDP was involved in the measured flow shear stress—shear strain curve, respectively, to calculate the distribution of local total shear deformation(LTSD) in adiabatic shear band(ASB). The predicted

Xue-bin WANG

2007-01-01

337

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

SciTech Connect

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

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

1994-03-01

338

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

339

Liquid crystals for surface shear stress visualization on wind turbine airfoils  

SciTech Connect

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

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

1988-01-01

340

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

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

341

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

NASA Astrophysics Data System (ADS)

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

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

2006-10-01

342

Liquid crystals for surface shear stress visualization on wind turbine airfoils  

NASA Astrophysics Data System (ADS)

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

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

343

Wideband measurement of shear induced birefringence by quadrupole method  

NASA Astrophysics Data System (ADS)

We developed a new method for the measurement of the dynamic birefringence induced by the alternating shear deformation in fluid samples. A quadrupole piezoactuator generates the pure shear deformation in the frequency range from 1 Hz to 5 kHz and causes the molecular orientation, or the anisotropic conformation of polymers and molecular associations, which is observed by the optical ellipsometry technique. The spectrum of the shear-induced birefringence observed for the isotropic phase of the liquid crystal p-n-hexyl p'-cyanobiphenyl (6CB) shows linear dependence on the frequency up to 5 kHz, corroborating the effective band of the experimental system. The sensitivity of the system was demonstrated by the quantitative measurement of the birefringence for the isotropic phase of p-n-pentyl p'-cyanobiphenyl (5CB). The system was also applied to the aqueous solution of the worm such as micelles and the result shows the relaxation of shear induced birefringence at around 10 Hz, which agrees well with the previous reports.

Hosoda, M.; Horii, K.; Nomura, H.; Sakai, K.

2006-05-01

344

THE SDSS CO-ADD: COSMIC SHEAR MEASUREMENT  

SciTech Connect

Stripe 82 in the Sloan Digital Sky Survey was observed multiple times, allowing deeper images to be constructed by co-adding the data. Here, we analyze the ellipticities of background galaxies in this 275 deg{sup 2} region, searching for evidence of distortions due to cosmic shear. We do so using measurements of both the shear-shear correlation function and power spectrum, with the latter determined using both ''quadratic'' and ''pseudo'' estimation techniques. We show how we verified these methods using mock catalogs. We also describe our methods for modeling and correcting for the effects of the point-spread function (PSF) in our shape measurements, and we also describe our prescription for estimating photometric redshifts (photo-z's) for our galaxy sample. In particular, we assess the impact of potential systematic effects due to the PSF and to photo-z's, and show that these are under control in our analysis. We find consistent correlation function and power spectrum results, where the E-mode cosmic shear signal is detected in both real and Fourier space with >5{sigma} significance on degree scales, while the B-mode is consistent with zero as expected. The amplitude of the signal constrains the combination of the matter density {Omega}{sub m} and fluctuation amplitude {sigma}{sub 8} to be {Omega}{sup 0.7}{sub m}{sigma}{sub 8} = 0.252{sup +0.032}{sub -{sub 0.052}}.

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

2012-12-10

345

SHEAR STRESS DURING EARLY EMBRYONIC STEM CELL DIFFERENTIATION PROMOTES HEMATOPOIETIC AND ENDOTHELIAL PHENOTYPES  

PubMed Central

Pluripotent embryonic stem cells (ESCs) are a potential source for cell-based tissue engineering and regenerative medicine applications, but their translation into clinical use will require efficient and robust methods for promoting differentiation. Fluid shear stress, which can be readily incorporated into scalable bioreactors, may be one solution for promoting endothelial and hematopoietic phenotypes from ESCs. Here we applied laminar shear stress to differentiating ESCs using a 2D adherent parallel plate configuration to systematically investigate the effects of several mechanical parameters. Treatment similarly promoted endothelial and hematopoietic differentiation for shear stress magnitudes ranging from 1.5 to 15 dyne/cm2 and for cells seeded on collagen-, fibronectin-, or laminin-coated surfaces. Extension of the treatment duration consistently induced an endothelial response, but application at later stages of differentiation was less effective at promoting hematopoietic phenotypes. Furthermore, inhibition of the FLK1 protein (a VEGF receptor) neutralized the effects of shear stress, implicating the membrane protein as a critical mediator of both endothelial and hematopoietic differentiation by applied shear. Using a systematic approach, studies such as these help elucidate the mechanisms involved in force-mediated stem cell differentiation and inform scalable bioprocesses for cellular therapies.

Wolfe, Russell P.; Ahsan, Tabassum

2014-01-01

346

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

347

K+-channel blockade inhibits shear stress-induced pulmonary vasodilation in the ovine fetus.  

PubMed

To determine whether K+-channel activation mediates shear stress-induced pulmonary vasodilation in the fetus, we studied the hemodynamic effects of K+-channel blockers on basal pulmonary vascular resistance and on the pulmonary vascular response to partial compression of the ductus arteriosus (DA) in chronically prepared late-gestation fetal lambs (128-132 days gestation). Study drugs included tetraethylammonium (TEA; Ca2+-dependent K+-channel blocker), glibenclamide (Glib; ATP-dependent K+-channel blocker), charybdotoxin (CTX; preferential high-conductance Ca2+-dependent K+-channel blocker), apamin (Apa; low-conductance Ca2+-dependent K+-channel blocker), and 4-aminopyridine (4-AP; voltage-dependent K+-channel blocker). Catheters were inserted in the left pulmonary artery (LPA) for selective drug infusion and in the main pulmonary artery, aorta, and left atrium to measure pressure. An inflatable vascular occluder was placed around the DA. LPA flow was measured with an ultrasonic flow transducer. Animals were treated with saline, high- or low-dose TEA, Glib, Apa, CTX, CTX plus Apa, or 4-AP injected into the LPA. DA compression caused a time-related decrease in pulmonary vascular resistance in the control, Glib, Apa, CTX, CTX plus Apa, and low-dose TEA groups but not in the high-dose TEA and 4-AP groups. These data suggest that pharmacological blockade of Ca2+- and voltage-dependent K+-channel activity but not of low-conductance Ca2+- and ATP-dependent K+-channel activity attenuates shear stress-induced fetal pulmonary vasodilation. PMID:9950883

Storme, L; Rairigh, R L; Parker, T A; Cornfield, D N; Kinsella, J P; Abman, S H

1999-02-01

348

Dynamic deformation capability of a red blood cell under a cyclically reciprocating shear stress.  

PubMed

Red blood cells (RBCs) in the cardiovascular devices are exposed to varying degree of the shear stress from all the directions. However the RBCs' deformability or the deformation capability under such a shear stress is not well understood. In this study, we designed and built a system that can induce a cyclically reciprocating shear stress to a RBC suspension. The arm of the cyclically reciprocating shear stress device was attached to the upper piece of the parallel glass plates between which a suspension of human RBCs (1% hematocrit whole blood diluted in a 32 weight% dextran phosphate buffer solution) was contained. The cyclic reciprocating motion of the upper glass plate of 3.0 mm stroke length was produced using a slider-crank shaft mechanism that was linked to an eccentric cam-motor system. Each rotation of the motor produced a 3.0 mm stroke each in the forward and backward direction of the slider block. The clearance between the two glass plates was adjusted to 30 micrometer. The cyclic reciprocating glass plate apparatus was attached to a light microscope stage (IX71 Olympus with x40 objective lens) for illumination with a 350 watt metal halide light source. A high speed camera (MEMREMCAM fx-K3 Nac, 5000 frames per second with shutter kept open) was attached to the microscope to capture the deformation process of the RBCs under cyclic shear stress. The preliminary result indicated that the correlation between the amplitude of the maximum shear stress and the RBCs' deformability. This indicates a potential application of the cyclic reciprocating device to evaluate the temporal response of the RBCs deformability prior to its destruction. The future study will focus on the study of the relative velocity of the erythrocytes with respect to the velocity of the reciprocating plate. PMID:17271457

Watanabe, N; Yasuda, T; Kataoka, H; Takatani, S

2004-01-01

349

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

PubMed

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

Lantz, Jonas; Gårdhagen, Roland; Karlsson, Matts

2012-10-01

350

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

NASA Astrophysics Data System (ADS)

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

Deloffre, Julien; Verney, Romaric; Lafite, Robert

2014-05-01

351

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

PubMed Central

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

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

2010-01-01

352

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

SciTech Connect

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

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

2013-04-19

353

Spatial relationships between shearing stresses and pressure on the plantar skin surface during gait  

PubMed Central

Based on the hypothesis that diabetic foot lesions have a mechanical etiology, extensive efforts have sought to establish a relationship between ulcer occurrence and plantar pressure distribution. However, these factors are still not fully understood. The purpose of this study was to simultaneously record shear and pressure distributions in the heel and forefoot and to answer whether: (i) peak pressure and peak shear for anterior-posterior (AP) and medio-lateral (ML) occur at different locations, and if (ii) peak pressure is always centrally located between sites of maximum AP and ML shear stresses. A custom built system was used to collect shear and pressure data simultaneously on 11 subjects using the 2-step method. The peak pressure was found to be 362 kPa ±106 in the heel and 527 kPa ± 123 in the forefoot. In addition, the average peak shear values were higher in the forefoot than in the heel. The greatest shear on the plantar surface of the forefoot occurred in the anterior direction (mean and std dev: 37.7 ±7.6 kPa), whereas for the heel, peak shear on the foot was in the posterior direction (21.2 ±5 kPa). The results of this study suggest that the interactions of the shear forces caused greater “spreading” in the forefoot and greater tissue “dragging” in the heel. The results also showed that peak shear stresses do not occur at the same site or time as peak pressure. This may be an important factor in locating where skin breakdown occurs in patients at high-risk for ulceration.

Stucke, Samantha; McFarland, Daniel; Goss, Larry; Fonov, Sergey; McMillan, Grant R.; Tucker, Amy; Berme, Necip; Guler, Hasan Cenk; Bigelow, Chris; Davis, Brian L.

2011-01-01

354

Theory and Practice of Shear/Stress Strain Gage Hygrometry  

NASA Technical Reports Server (NTRS)

Mechanical hygrometry has progressed during the last several decades from crude hygroscopes to state-of-the art strain-gage sensors. The strain-gage devices vary from different metallic beams to strain-gage sensors using cellulose crystallite elements, held in full shear restraint. This old technique is still in use but several companies are now actively pursuing development of MEMS miniaturized humidity sensors. These new sensors use polyimide thin film for water vapor adsorption and desorption. This paper will provide overview about modern humidity sensors.

Shams, Qamar A.; Fenner, Ralph L.

2006-01-01

355

Stress Analysis of Beams with Shear Deformation of the Flanges  

NASA Technical Reports Server (NTRS)

This report discusses the fundamental action of shear deformation of the flanges on the basis of simplifying assumptions. The theory is developed to the point of giving analytical solutions for simple cases of beams and of skin-stringer panels under axial load. Strain-gage tests on a tension panel and on a beam corresponding to these simple cases are described and the results are compared with analytical results. For wing beams, an approximate method of applying the theory is given. As an alternative, the construction of a mechanical analyzer is advocated.

Kuhn, Paul

1937-01-01

356

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

PubMed Central

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

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

2013-01-01

357

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

PubMed

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

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

2013-10-01

358

Shear stress modulates macrophage-induced urokinase plasminogen activator expression in human chondrocytes  

PubMed Central

Introduction Synovial macrophages, which can release proinflammatory factors, are responsible for the upregulation of cartilage-breakdown proteases and play critical roles in cartilage degradation during the progression of osteoarthritis (OA). In addition, shear stress exerts multifunctional effects on chondrocytes by inducing the synthesis of catabolic or anabolic genes. However, the interplay of macrophages, chondrocytes, and shear stress during the regulation of cartilage function remains poorly understood. We investigated the mechanisms underlying the modulation of human chondrocyte urokinase plasminogen activator (uPA) expression by macrophages and shear stress. Methods Human chondrocytes were stimulated by peripheral blood-macrophage- conditioned medium (PB-MCM), or exposure of chondrocytes cultured in PB-MCM to different levels of shear stress (2 to 20 dyn/cm2). Real-time polymerase chain reaction was used to analyze uPA gene expression. Inhibitors and small interfering RNA were used to investigate the mechanism for the effects of PB-MCM and shear stress in chondrocytes. Results Stimulation of human chondrocytes with PB-MCM was found to induce uPA expression. We demonstrated that activation of the JNK and Akt pathways and NF-?B are critical for PB-MCM-induced uPA expression. Blocking assays by using IL-1ra further demonstrated that IL-1? in PB-MCM is the major mediator of uPA expression in chondrocytes. PB-MCM-treated chondrocytes subjected to a lower level of shear stress showed inhibition of MCM-induced JNK and Akt phosphorylation, NF-?B activation, and uPA expression. The PB-MCM-induced uPA expression was suppressed by AMP-activated protein kinase (AMPK) agonist. The inhibitor or siRNA for AMPK abolished the shear-mediated inhibition of uPA expression. Conclusions These data support the hypothesis that uPA upregulation stimulated by macrophages may play an active role in the onset of OA and in the shear-stress protection against this induction.

2013-01-01

359

Measurement of in vivo local shear modulus using MR elastography multiple-phase patchwork offsets  

Microsoft Academic Search

Magnetic resonance elastography (MRE) is a method that can visualize the propagating and standing shear waves in an object being measured. The quantitative value of a shear modulus can be calculated by estimating the local shear wavelength. Low-frequency mechanical motion must be used for soft, tissue-like objects because a propagating shear wave rapidly attenuates at a higher frequency. Moreover, a

M. Suga; T. Matsuda; K. Minato; O. Oshiro; K. Chihara; Jun Okamoto; O. Takizawa; M. Komori; T. Takahashi

2003-01-01

360

SHEAR STRENGTH MEASURING EQUIPMENT EVALUATION AT THE COLD TEST FACILITY  

SciTech Connect

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

MEACHAM JE

2009-09-09

361

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

NASA Astrophysics Data System (ADS)

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

Jing, Ze; Yong, Huadong; Zhou, Youhe

2013-07-01

362

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

PubMed Central

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

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

2011-01-01

363

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

PubMed

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

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

2011-08-01

364

Proteomic analysis of Staphylococcus aureus biofilm cells grown under physiologically relevant fluid shear stress conditions  

PubMed Central

Background The biofilm forming bacterium Staphylococcus aureus is responsible for maladies ranging from severe skin infection to major diseases such as bacteremia, endocarditis and osteomyelitis. A flow displacement system was used to grow S. aureus biofilms in four physiologically relevant fluid shear rates (50, 100, 500 and 1000 s-1) to identify proteins that are associated with biofilm. Results Global protein expressions from the membrane and cytosolic fractions of S. aureus biofilm cells grown under the above shear rate conditions are reported. Sixteen proteins in the membrane-enriched fraction and eight proteins in the cytosolic fraction showed significantly altered expression (p?shear. These 24 proteins were identified using nano-LC-ESI-MS/MS. They were found to be associated with various metabolic functions such as glycolysis / TCA pathways, protein synthesis and stress tolerance. Increased fluid shear stress did not influence the expression of two important surface binding proteins: fibronectin-binding and collagen-binding proteins. Conclusions The reported data suggest that while the general metabolic function of the sessile bacteria is minimal under high fluid shear stress conditions, they seem to retain the binding capacity to initiate new infections.

2014-01-01

365

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

PubMed Central

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

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

2012-01-01

366

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

PubMed

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

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

2012-03-01

367

Temperature Measurements and Shear Modes with Penning Trap Ion Crystals.  

NASA Astrophysics Data System (ADS)

We describe current experimental attempts to study shear modes and measure heating rates in ion crystals confined in a Penning trap. Up to 10^6 ^9Be^+ ions are laser-cooled to temperatures less than 10 mK where they form a crystalline state. Since the Penning trap uses static fields for confinement, the trap can be much larger ( ˜4 cm diameter) than rf traps ( ˜0.05 cm diameter) and still maintain large ion motional frequencies (> 1 MHz). Larger trap electrodes should decrease the heating and decoherence rates observed in rf traps due to fluctuating patch fields on the trap electrodes. Therefore the Penning trap may provide a good environment for quantum information processing. Current efforts to measure the heating of the ions using a stimulated-Raman temperature measurement will be described as well as attempts to excite shear modes through phase modulation of a rotating electric field. These shear modes exist only in a crystalline (as opposed to a liquid) plasma and provide a sensitive probe of the ion correlations. As the lowest frequency modes of the system they could be an important factor in determining the usefulness of the Penning trap for quantum information experiments.

Jensen, M.; Bollinger, J. J.; Kriesel, J. M.

2002-05-01

368

The effect of growth orientation on the resolved shear stresses for horizontal Bridgman grown GaAs crystals  

NASA Astrophysics Data System (ADS)

An effective method based on double tensor transformation is proposed for the resolved shear stress calculation in the crystals with arbitrary growth axis orientation. Employing this method the influence of the crystal orientation on the resolved shear stresses is investigated for the horizontal Bridgman grown GaAs crystals. The stress patterns give a theoretical basis for the evaluation of the role of the thermal stresses in the process of dislocation generation in these crystals.

Dobrocka, Edmund

1990-07-01

369

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

PubMed Central

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

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

2012-01-01

370

Endothelial Cell Membrane Sensitivity to Shear Stress is Lipid Domain Dependent  

PubMed Central

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

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

2012-01-01

371

A hybrid stress approach for laminated composite plates within the First-order Shear Deformation Theory  

Microsoft Academic Search

This paper presents a hybrid stress approach for the analysis of laminated composite plates. The plate mechanical model is based on the so called First-order Shear Deformation Theory, rationally deduced from the parent three-dimensional theory. Within this framework, a new quadrilateral four-node finite element is developed from a hybrid stress formulation involving, as primary variables, compatible displacements and elementwise equilibrated

F. Daghia; S. de Miranda; F. Ubertini; E. Viola

2008-01-01

372

Cohesive-Shear-Lag Model for Cycling Stress-Strain Behavior of Unidirectional Ceramic Matrix Composites  

Microsoft Academic Search

During fatigue tests of fiber-reinforced ceramic matrix composites (CMCs), the stress-strain hysteresis loops undergo typically through various changes in shape and size before they stabilize after many cycles. These hysteresis loops are a good representation of intrinsic deformation and damage modes occurring in the materials. The present study proposes a cohesive-shear-lag model to analyze the cyclic stress-strain behavior of unidirectional

B. Yang; S. Mall

2003-01-01

373

Shear-lag versus finite element models for stress transfer in fiber-reinforced composites  

Microsoft Academic Search

The stress transfer from broken to unbroken fibers in fiber-reinforced polymer-matrix (PMC) and aluminum-matrix (AMC) composites is studied using a detailed 3D finite element model (FEM) and using the standard shear-lag model (SLM). The stress transfer predicted by the SLM is in good agreement with the FEM results for the PMC at high fiber volume fractions but not at low

Z. Xia; T. Okabe; W. A. Curtin

2002-01-01

374

Development of tactile sensors for simultaneous, detection of normal and shear stresses  

Microsoft Academic Search

A novel tactile sensor is analyzed and verified by intensive experiments. By using micro-cantilever beams, on which the strain gauge layers (Pt\\/Ti) are deposited, the corresponding induced strains can be detected and converted into electric resistance change, with respect to either applied normal stress or shear stress. The four micro-cantilever beams are allocated in the fashion such that any adjacent

Yu-Ming Huang; Nan-Chyuan Tsai; Jing-Yao Lai

2010-01-01

375

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

NASA Technical Reports Server (NTRS)

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

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

1998-01-01

376

Evolution of shear stress, protein expression, and vessel area in an animal model of arterial dilatation in hemodialysis grafts  

PubMed Central

Purpose To evaluate the wall shear stress, protein expression of matrix metalloproteinases-2 (MMP-2), -9 (MMP-9), and the inhibitors (tissue inhibitor of matrix metalloproteinases-1 (TIMP-1), and -2 (TIMP-2)), and vessel area over time in a porcine model for hemodialysis polytetrafluoroethylene (PTFE) grafts. Materials and methods In 21 pigs, subtotal renal infarction was performed and 28 days later, a PTFE graft was placed to connect the carotid artery to the ipsilateral jugular vein. Phase contrast MR was used to measure blood flow and vessel area at 1, 3, 7, and 14 days after graft placement. Wall shear stress was estimated from Poiseuille’s law. Animals were sacrificed at day 3 (N=7), day 7 (N=7), and day 14 (N=7) and expression of MMP-2, MMP-9, TIMP-1, and TIMP-2 were determined at the grafted and control arteries. Results The mean wall shear stress of the grafted artery was higher than the control artery at all time points (P<0.05). It peaked by day 3 and decreased by days 7–14 as the vessel area nearly doubled. By days 7–14, there was a significant increase in active MMP-2 followed by a significant increase in pro and active MMP-9 by day 14 (P<0.05, grafted artery versus control). TIMP-1 expression peaked by day 7 and then decreased while TIMP-2 expression was decreased at days 7–14. Conclusions The wall shear stress of the grafted artery peaks by day 3 with increased MMP-2 activity by days 7–14 followed by pro and active MMP-9 by day 14 and the vessel area nearly doubled.

Misra, Sanjay; Fu, Alex A.; Misra, Khamal D.; Glockner, James F.; Mukhopadyay, Debabrata

2010-01-01

377

Olprinone attenuates excessive shear stress through up-regulation of endothelial nitric oxide synthase in a rat excessive hepatectomy model.  

PubMed

After extended hepatectomy, excessive shear stress in the remnant liver causes postoperative liver failure. Olprinone (OLP), a selective phosphodiesterase inhibitor, has been reported to improve microcirculation and attenuate inflammation. The aim of this study was to investigate the effects of OLP on shear stress in rats with an excessive hepatectomy (EHx) model. In this study, EHx comprised 90% hepatectomy with ligation of the left and right Glisson's sheaths in Lewis rats. OLP or saline was intraperitoneally administered with an osmotic pump 48 hours before EHx. To evaluate the shear stress, we measured the portal vein (PV) pressure. We also assessed sinusoidal endothelial cell injury by immunohistochemistry and electron microscopy. Furthermore, we assessed apoptosis in the liver with the terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling method. Treatment with OLP up-regulated hepatic endothelial nitric oxide synthase (eNOS) expression. The increase in the PV pressure due to Glisson's sheath ligation was attenuated in OLP-treated rats during a 30-minute period after ligation. Treatment with OLP preserved sinusoidal endothelial cells and reduced apoptosis in the remnant liver. The probability of survival in the OLP-treated rats was significantly better than that in the controls (33.3% versus 13.3%). Furthermore, the postoperative eNOS activity in the OLP-treated rats was higher than that in the controls. The administration of N?-nitro-l-arginine methyl ester to OLP-treated rats eliminated the effects of OLP on PV pressure and survival after EHx. Therefore, we concluded that OLP attenuates excessive shear stress through the up-regulation of eNOS and improves the survival rate after EHx. PMID:21254346

Yamanaka, Kenya; Hatano, Etsuro; Narita, Masato; Kitamura, Koji; Yanagida, Atsuko; Asechi, Hiroyuki; Nagata, Hiromitsu; Taura, Kojiro; Nitta, Takashi; Uemoto, Shinji

2011-01-01

378

Patterns of Living ?-Actin Movement in Wounded Human Coronary Artery Endothelial Cells Exposed to Shear Stress  

Microsoft Academic Search

We previously demonstrated that physiologic levels of shear stress enhance endothelial repair. Cell spreading and migration, but not proliferation, were the major mechanisms accounting for the increases in wound closure rate (Albuquerque et al., 2000, Am. J. Physiol. Heart Circ. Physiol. 279, H293–H302). However, the patterns and movements of ?-actin filaments responsible for cell motility and translocation in human coronary

Maria Luiza C. Albuquerque; Annette S. Flozak

2001-01-01

379

A non-Newtonian model based on limiting shear stress and slip planes—parametric studies  

Microsoft Academic Search

Parametric studies and corresponding results are presented using a rheological model based on the limiting shear stress and possible occurrence of slip planes. The model is applied to elastohydrodynamically lubricated line contacts with smooth surfaces and isothermal conditions. A few investigations are carried out where different parameters are varied. The first study investigates the influence on the film thickness distribution

Jonas Ståhl; Bo O. Jacobson

2003-01-01

380

Intermittency feature of shear stress fluctuation in high-Reynolds-number turbulence  

Microsoft Academic Search

Instantaneous shear stress fluctuations are considered for high-Reynolds-number (up to Rlambda~104) turbulent flow field using the concept of maximum norm. The maximum norm is defined as the largest change within a box of a given size. We have applied this technique to a variety of flow fields and a wide range of Reynolds numbers. Results indicated that the maximum norm

Yoshiyuki Tsuji; Brindesh Dhruva

1999-01-01

381

Interaction between Wall Shear Stress and Circumferential Strain Affects Endothelial Cell Biochemical Production  

Microsoft Academic Search

The wall shear stress (WSS) of flowing blood and the circumferential strain (CS) driven by the pressure pulse interact to impose a dynamic force pattern on endothelial cells (ECs) which can be characterized by the temporal phase angle between WSS and CS, a quantity which varies significantly throughout the circulation. To study the interaction of WSS and CS on endothelial

Yuchen Qiu; John M. Tarbell

2000-01-01

382

Shear stress selectively upregulates intercellular adhesion molecule-1 expression in cultured human vascular endothelial cells.  

PubMed Central

Hemodynamic forces induce various functional changes in vascular endothelium, many of which reflect alterations in gene expression. We have recently identified a cis-acting transcriptional regulatory element, the shear stress response element (SSRE), present in the promoters of several genes, that may represent a common pathway by which biomechanical forces influence gene expression. In this study, we have examined the effect of shear stress on endothelial expression of three adhesion molecules: intercellular adhesion molecule-1 (ICAM-1), which contains the SSRE in its promoter, and E-selectin (ELAM-1) and vascular cell adhesion molecule-1 (VCAM-1), both of which lack the SSRE. Cultured human umbilical vein endothelial cells, subjected to a physiologically relevant range of laminar shear stresses (2.5-46 dyn/cm2) in a cone and plate apparatus for up to 48 h, showed time-dependent but force-independent increases in surface immunoreactive ICAM-1. Upregulated ICAM-1 expression was correlated with increased adhesion of the JY lymphocytic cell line. Northern blot analysis revealed increased ICAM-1 transcript as early as 2 h after the onset of shear stress. In contrast, E-selectin and vascular cell adhesion molecule-1 transcript and cell-surface protein were not upregulated at any time point examined. This selective regulation of adhesion molecule expression in vascular endothelium suggests that biomechanical forces, in addition to humoral stimuli, may contribute to differential endothelial gene expression and thus represent pathophysiologically relevant stimuli in inflammation and atherosclerosis. Images

Nagel, T; Resnick, N; Atkinson, W J; Dewey, C F; Gimbrone, M A

1994-01-01

383

Flow patterns and shear stress investigation and in vitro studies of blood pump  

Microsoft Academic Search

The long-term clinical use of blood pumps is dependent on the bio-compatibility. Blood trauma especially hemolysis is closely related to the flow fields in the pumps according to the homodynamic. Computational fluid dynamics technique has been used to visualize the flow patterns and distribution of shear stress in two pumps with different impeller designs and to evaluate the hemolysis level.

Fangqun Wang; Qinlin Wu; Teng Jing; Linlin Liu; Kunxi Qian

2010-01-01

384

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

PubMed Central

Late outgrowth endothelial progenitor cells (EPCs) represent a promising cell source for rapid reendothelialization of damaged vasculature after expansion ex vivo and injection into the bloodstream. We characterized the dynamic adhesion of umbilical-cord-blood-derived EPCs (CB-EPCs) to surfaces coated with fibronectin. CB-EPC solution density affected the number of adherent cells and larger cells preferentially adhered at lower cell densities. The number of adherent cells varied with shear stress, with the maximum number of adherent cells and the shear stress at maximum adhesion depending upon fluid viscosity. CB-EPCs underwent limited rolling, transiently tethering for short distances before firm arrest. Immediately before arrest, the instantaneous velocity decreased independent of shear stress. A dimensional analysis indicated that adhesion was a function of the net force on the cells, the ratio of cell diffusion to sliding speed, and molecular diffusivity. Adhesion was not limited by the settling rate and was highly specific to ?5?1 integrin. Total internal reflection fluorescence microscopy showed that CB-EPCs produced multiple contacts of ?5?1 with the surface and the contact area grew during the first 20 min of attachment. These results demonstrate that CB-EPC adhesion from blood can occur under physiological levels of shear stress.

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

2010-01-01

385

Flow patterns and shear stress waveforms in intracranial aneurysms: The effect of pulsatility  

Microsoft Academic Search

The wall shear stress on the dome of intracranial aneurysms has been hypothesized to be an important factor in aneurysm pathology and depends strongly on the hemodynamics inside the dome. The importance of patient-specific geometry on the hemodynamics of aneurysms has long been established but the significance of patient-specific inflow waveform is largely unexplored. In this work we seek to

Fotis Sotiropoulos; Trung Le; Iman Borazjani

2009-01-01

386

A new ring-shear device for testing rocks under high normal stress and dynamic conditions  

Microsoft Academic Search

A new ring-shear device was developed to investigate the sliding mechanism of earthquake-triggered large rock avalanches. The loading capacity of the new device is adequate to apply dynamic normal force and torque to a rock specimen to simulate the dynamic stress path of the sliding surface in an earthquake. A rock sample taken from Cholan Formation at the Tsaoling landslide

Cheng-Jie Liao; Der-Her Lee; Jian-Hong Wu; Chia-Ze Lai

2011-01-01

387

Effects of fluid shear stress on the expression of Omi/HtrA2 in human umbilical vein endothelial cells.  

PubMed

To investigate the molecular mechanisms of laminar shear stress on the inhibition of apoptosis in endothelial cells, human umbilical vein endothelial cells (HUVECs) were starved in medium containing 2% fetal bovine serum (FBS) and treated with 15 dyne/cm2 shear stress. We confirmed that 15 dyne/cm2 shear stress inhibited the expression of Omi/HtrA2 at the mRNA and protein levels in cultured HUVECs. Furthermore, the release of Omi/HtrA2 from the mitochondria was induced by removal of basic fibroblast growth factor and decrease of FBS in the medium, while shear stress inhibited its release under the same conditions. These results suggest that downregulation of Omi/HtrA2 may contribute to the potent anti-atherosclerotic effect of shear stress by preventing endothelial cells from entering apoptosis. PMID:23123883

Sun, Liang-Liang; Zhang, Le; Meng, Xiang-Lan; Zhang, Feng; Zhao, Yun; Jin, Xin

2013-01-01

388

Endothelial cell responses to atheroprone flow are driven by two separate flow components: low time-average shear stress and fluid flow reversal  

PubMed Central

To simulate the effects of shear stress in regions of the vasculature prone to developing atherosclerosis, we subjected human umbilical vein endothelial cells to reversing shear stress to mimic the hemodynamic conditions at the wall of the carotid sinus, a site of complex, reversing blood flow and commonly observed atherosclerosis. We compared the effects of reversing shear stress (time-average: 1 dyn/cm2, maximum: +11 dyn/cm2, minimum: ?11 dyn/cm2, 1 Hz), arterial steady shear stress (15 dyn/cm2), and low steady shear stress (1 dyn/cm2) on gene expression, cell proliferation, and monocyte adhesiveness. Microarray analysis revealed that most differentially expressed genes were similarly regulated by all three shear stress regimens compared with static culture. Comparisons of the three shear stress regimens to each other identified 138 genes regulated by low average shear stress and 22 genes regulated by fluid reversal. Low average shear stress induced increased cell proliferation compared with high shear stress. Only reversing shear stress exposure induced monocyte adhesion. The adhesion of monocytes was partially inhibited by the incubation of endothelial cells with ICAM-1 blocking antibody. Increased heparan sulfate proteoglycan expression was observed on the surface of cells exposed to reversing shear stress. Heparinase III treatment significantly reduced monocyte adhesion. Our results suggest that low steady shear stress is the major impetus for differential gene expression and cell proliferation, whereas reversing flow regulates monocyte adhesion.

Conway, Daniel E.; Williams, Marcie R.; Eskin, Suzanne G.

2010-01-01

389

Acoustoelastic birefringence effect in wood I: effect of applied stresses on the velocities of ultrasonic shear waves propagating transversely to the stress direction  

Microsoft Academic Search

The velocity changes of ultrasonic shear waves propagating transversely to the applied stress direction in wood were investigated. The wave oscillation directions were parallel and normal to the uniaxially applied stress direction. The velocities of the shear waves for both oscillations decreased as the compressive load increased, and increased as the tensile load increased. The velocity of the normally oscillated

Masumi Hasegawa; Yasutoshi Sasaki

2004-01-01

390

Sox18 preserves the pulmonary endothelial barrier under conditions of increased shear stress.  

PubMed

Shear stress secondary to increased pulmonary blood flow (PBF) is elevated in some children born with