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Sample records for critical shear stress

  1. CFD simulation of estimating critical shear stress for cleaning flat ...

    Indian Academy of Sciences (India)

    Sumit Kawale

    2017-11-22

    Nov 22, 2017 ... Jet impingement; wall shear stress; cleaning of flat plate; turbulence model; critical shear stress; ... On comparing the theoretical predictions with wall shear ... distance and Reynolds number on peak value of local shear stress ...

  2. Critical wall shear stress for the EHEDG test method

    DEFF Research Database (Denmark)

    Jensen, Bo Boye Busk; Friis, Alan

    2004-01-01

    In order to simulate the results of practical cleaning tests on closed processing equipment, based on wall shear stress predicted by computational fluid dynamics, a critical wall shear stress is required for that particular cleaning method. This work presents investigations that provide a critical...... wall shear stress of 3 Pa for the standardised EHEDG cleaning test method. The cleaning tests were performed on a test disc placed in a radial flowcell assay. Turbulent flow conditions were generated and the corresponding wall shear stresses were predicted from CFD simulations. Combining wall shear...... stress predictions from a simulation using the low Re k-epsilon and one using the two-layer model of Norris and Reynolds were found to produce reliable predictions compared to empirical solutions for the ideal flow case. The comparison of wall shear stress curves predicted for the real RFC...

  3. Critical shear stress produced by interaction of edge dislocation with ...

    Indian Academy of Sciences (India)

    According to the Mott and Nabarro's model, the contribution to the critical shear stress of the material caused by the interaction between edge dislocations and nanoscale cylindrical inhomogeneities with interface stresses is obtained. The influence of the radius and the volume fraction of the inhomogeneity as well as the ...

  4. Temperature dependence of critical resolved shear stress for cubic metals

    International Nuclear Information System (INIS)

    Rashid, H.; Fazal-e-Aleem; Ali, M.

    1996-01-01

    The experimental measurements for critical resolved shear stress of various BCC and FCC metals have been explained by using Radiation Model. The temperature dependence of CRSS for different cubic metals is found to the first approximation, to upon the type of the crystal. A good agreement between experimental observations and predictions of the Radiation Model is found. (author)

  5. Critical bed shear stress and threshold of motion of maerl biogenic gravel

    Science.gov (United States)

    Joshi, Siddhi; Duffy, Garret Patrick; Brown, Colin

    2017-07-01

    A determination of the critical bed shear stress of maerl is a prerequisite for quantifying its mobility, rate of erosion and deposition in conservation management. The critical bed shear stress for incipient motion has been determined for the first time for samples from biogenic free-living maerl beds in three contrasting environments (open marine, intertidal and beach) in Galway Bay, west of Ireland. The bed shear stress was determined using two methods, Law of the Wall and Turbulent Kinetic Energy, in a rotating annular flume and in a linear flume. The velocity profile of flowing water above a bed of natural maerl grains was measured in four runs of progressively increasing flow velocity until the flow exceeded the critical shear stress of grains on the bed. The critical Shields parameter and the mobility number are estimated and compared with the equivalent curves for natural quartz sand. The critical Shields parameters for the maerl particles from all three environments fall below the Shields curve. Along with a previously reported correlation between maerl grain shape and settling velocity, these results suggest that the highly irregular shapes also allow maerl grains to be mobilised more easily than quartz grains with the same sieve diameter. The intertidal beds with the roughest particles exhibit the greatest critical shear stress because the particle thalli interlock and resist entrainment. In samples with a high percentage of maerl and low percentage of siliciclastic sand, the lower density, lower settling velocity and lower critical bed shear stress of maerl results in its preferential transport over the siliciclastic sediment. At velocities ∼10 cm s-1 higher than the threshold velocity of grain motion, rarely-documented subaqueous maerl dunes formed in the annular flume.

  6. Flow rate dependency of critical wall shear stress in a radial-flow cell

    DEFF Research Database (Denmark)

    Detry, J.G.; Jensen, Bo Boye Busk; Sindic, M.

    2009-01-01

    In the present work, a radial-flow cell was used to study the removal of starch particle aggregates from several solid substrates (glass, stainless steel, polystyrene and PTFE) in order to determine the critical wall shear stress value for each case. The particle aggregates were formed by aspersion...... of a water or ethanol suspension of starch granules on the surfaces. Depending on the substrate and on the suspending liquid, the aggregates differed in size and shape. Aggregate removal was studied at two flow rates. At the lower flow rate (Re-inlet = 955), the values of critical wall shear stress...... for the different surfaces suggested that capillary forces were, for all of them, playing an important role in aggregate adhesion since aqueous based aggregates were always more difficult to remove. At the higher flow rate (Re-inlet = 2016) the critical wall shear stress increased as a result of the change...

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

    Science.gov (United States)

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

    2005-01-01

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

  8. Arterial response to shear stress critically depends on endothelial TRPV4 expression.

    Directory of Open Access Journals (Sweden)

    Veronika Hartmannsgruber

    . CONCLUSIONS/SIGNIFICANCE: Genetically encoded loss-of-function of trpv4 results in a loss of shear stress-induced vasodilation, a response pattern critically dependent on endothelial TRPV4 expression. Thus, Ca(2+-influx through endothelial TRPV4 channels is a molecular mechanism contributing significantly to endothelial mechanotransduction.

  9. Arterial Response to Shear Stress Critically Depends on Endothelial TRPV4 Expression

    Science.gov (United States)

    Kacik, Michael; Kaistha, Anuradha; Grgic, Ivica; Harteneck, Christian; Liedtke, Wolfgang; Hoyer, Joachim; Köhler, Ralf

    2007-01-01

    /Significance Genetically encoded loss-of-function of trpv4 results in a loss of shear stress-induced vasodilation, a response pattern critically dependent on endothelial TRPV4 expression. Thus, Ca2+-influx through endothelial TRPV4 channels is a molecular mechanism contributing significantly to endothelial mechanotransduction. PMID:17786199

  10. Critical shear stress for onset of plasticity in a nanocrystalline Cu determined by using nanoindentation

    International Nuclear Information System (INIS)

    Chen, J.; Wang, W.; Qian, L.H.; Lu, K.

    2003-01-01

    The plastic deformation behavior was investigated by using nanoindentation in a magneto-sputtered nanocrystalline (nc) Cu film with an average grain size of 14 nm. The determined critical shear stress to initiate plasticity in the nc-Cu sample (about 8.3 GPa) is identical to that for nucleation of lattice dislocations in an annealed coarse-grained Cu (8.5 GPa), and both values are close to the theoretical shear strength in the dislocation-free single crystal. This observation, in agreement with the atomistic simulation results, supports the argument that the onset of plasticity of the nc-Cu is associated with initiation of dislocation activities at grain boundaries

  11. Measuring the critical resolved shear stresses in Mg alloys by instrumented nanoindentation

    International Nuclear Information System (INIS)

    Sánchez-Martín, R.; Pérez-Prado, M.T.; Segurado, J.; Bohlen, J.; Gutiérrez-Urrutia, I.; Llorca, J.; Molina-Aldareguia, J.M.

    2014-01-01

    One of the main limiting factors in the development of new magnesium (Mg) alloys with enhanced mechanical behavior is the need to use vast experimental campaigns for microstructure and property screening. For example, the influence of new alloying additions on the critical resolved shear stresses (CRSSs) is currently evaluated by a combination of macroscopic single-crystal experiments and crystal plasticity finite-element simulations (CPFEM). This time-consuming process could be considerably simplified by the introduction of high-throughput techniques for efficient property testing. The aim of this paper is to propose a new and fast, methodology for the estimation of the CRSSs of hexagonal close-packed metals which, moreover, requires small amounts of material. The proposed method, which combines instrumented nanoindentation and CPFEM modeling, determines CRSS values by comparison of the variation of hardness (H) for different grain orientations with the outcome of CPFEM. This novel approach has been validated in a rolled and annealed pure Mg sheet, whose H variation with grain orientation has been successfully predicted using a set of CRSSs taken from recent crystal plasticity simulations of single-crystal experiments. Moreover, the proposed methodology has been utilized to infer the effect of the alloying elements of an MN11 (Mg–1% Mn–1% Nd) alloy. The results support the hypothesis that selected rare earth intermetallic precipitates help to bring the CRSS values of basal and non-basal slip systems closer together, thus contributing to the reduced plastic anisotropy observed in these alloys

  12. The effects of green infrastructure on exceedance of critical shear stress in Blunn Creek watershed

    Science.gov (United States)

    Shannak, Sa'd.

    2017-10-01

    Green infrastructure (GI) has attracted city planners and watershed management professional as a new approach to control urban stormwater runoff. Several regulatory enforcements of GI implementation created an urgent need for quantitative information on GI practice effectiveness, namely for sediment and stream erosion. This study aims at investigating the capability and performance of GI in reducing stream bank erosion in the Blackland Prairie ecosystem. To achieve the goal of this study, we developed a methodology to represent two types of GI (bioretention and permeable pavement) into the Soil Water Assessment Tool, we also evaluated the shear stress and excess shear stress for stream flows in conjunction with different levels of adoption of GI, and estimated potential stream bank erosion for different median soil particle sizes using real and design storms. The results provided various configurations of GI schemes in reducing the negative impact of urban stormwater runoff on stream banks. Results showed that combining permeable pavement and bioretention resulted in the greatest reduction in runoff volumes, peak flows, and excess shear stress under both real and design storms. Bioretention as a stand-alone resulted in the second greatest reduction, while the installation of detention pond only had the least reduction percentages. Lastly, results showed that the soil particle with median diameter equals to 64 mm (small cobbles) had the least excess shear stress across all design storms, while 0.5 mm (medium sand) soil particle size had the largest magnitude of excess shear stress. The current study provides several insights into a watershed scale for GI planning and watershed management to effectively reduce the negative impact of urban stormwater runoff and control streambank erosion.

  13. Critical shear stress on the surface of a cuttings bed; Tensao critica de cisalhamento na superficie de um leito de cascalhos

    Energy Technology Data Exchange (ETDEWEB)

    Lacerda, Luciana Mancor [Universidade Estadual Norte Fluminense (UENF), Macae, RJ (Brazil). Lab. de Engenharia de Petroleo]. E-mail: luciana@lenep.uenf.br; Campos, Wellington [PETROBRAS, S.A., Rio de Janeiro, RJ (Brazil). Centro de Pesquisas]. E-mail: campos@cenpes.petrobras.com.br; Braga, Luiz Carvalho [Centro Federal de Educacao Tecnologica (CEFET), Macae, RJ (Brazil). Unidade de Ensino Descentralizada]. E-mail: luiz@lenep.uenf.br

    2000-07-01

    The cuttings transport during the drilling of highly inclined and horizontal wells is hindered by the creation of a cuttings bed in the annulus. In this work, it is shown that the equilibrium height of this bed can be determined from the shear stress on its surface. This fact enables the formulation of a methodology for evaluating the equilibrium height of the cuttings bed through the introduction of a new concept, that of critical shear stress. This is the shear stress that acts on the bed surface at the imminence of movement of the particles on the bed surface. The use of the methodology requires the determination of the acting shear stress and of the required critical shear stress. The acting shear stress is calculated by means of a computer program that solve the motion differential equations in the annular space; covering the cases of the laminar and turbulent flow regimes. The actuating shear stress is a function of flow rate and of the annular geometry in the presence of a cuttings bed; it is also a function of the physical properties of the fluid. On the other hand, the required critical shear stress is a function of the particles diameters and physical properties of the fluid and particles. A mechanistic model for the critical shear stress is also presented. (author)

  14. Comparative study of soil erodibility and critical shear stress between loess and purple soils

    Science.gov (United States)

    Xing, Hang; Huang, Yu-han; Chen, Xiao-yan; Luo, Bang-lin; Mi, Hong-xing

    2018-03-01

    Loess and purple soils are two very important cultivated soils, with the former in the loess region and the latter in southern sub-tropical region of China, featured with high-risks of erosion, considerable differences of soil structures due to differences in mineral and nutrient compositions. Study on soil erodibility (Kr) and critical shear stress (τc) of these two soils is beneficial to predict soil erosion with such models as WEPP. In this study, rill erosion experimental data sets of the two soils are used for estimating their Kr and τc before they are compared to understand their differences of rill erosion behaviors. The maximum detachment rates of the loess and purple soils are calculated under different hydrodynamic conditions (flow rates: 2, 4, 8 L/min; slope gradients: 5°, 10°, 15°, 20°, 25°) through analytical and numerical methods respectively. Analytical method used the derivative of the function between sediment concentration and rill length to estimate potential detachment rates, at the rill beginning. Numerical method estimated potential detachment rates with the experimental data, at the rill beginning and 0.5 m location. The Kr and τc of these two soils are determined by the linear equation based on experimental data. Results show that the methods could well estimate the Kr and τc of these two soils as they remain basically unchanged under different hydrodynamic conditions. The Kr value of loess soil is about twice of the purple soil, whereas the τc is about half of that. The numerical results have good correlations with the analytical values. These results can be useful in modeling rill erosion processes of loess and purple soils.

  15. Effect of nitrogen concentration and temperature on the critical resolved shear stress and strain rate sensitivity of vanadium

    International Nuclear Information System (INIS)

    Rehbein, D.K.

    1980-08-01

    The critical resolved shear stress and strain rate sensitivity were measured over the temperature range from 77 to 400 0 K for vanadium-nitrogen alloys containing from 0.0004 to 0.184 atom percent nitrogen. These properties were found to be strongly dependent on both the nitrogen concentration and temperature. The following observations were seen in this investigation: the overall behavior of the alloys for the temperature and concentration range studied follows a form similar to that predicted; the concentration dependence of the critical resolved shear stress after subtracting the hardening due to the pure vanadium lattice obeys Labusch's c/sup 2/3/ relationship above 200 0 K and Fleischer's c/sup 1/2/ relationship below 200 0 K; the theoretical predictions of Fleischer's model for the temperature dependence of the critical resolved shear stress are in marked disagreement with the behavior found; and the strain rate sensitivity, par. delta tau/par. deltaln γ, exhibits a peak at approximately 100 0 K that decreases in height as the nitrogen concentration increases. A similar peak has been observed in niobium by other investigators but the effect of concentration on the peak height is quite different

  16. A Piezoelectric Shear Stress Sensor

    Science.gov (United States)

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

    2016-01-01

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

  17. SEDflume - High Shear Stress Flume

    Data.gov (United States)

    Federal Laboratory Consortium — The U.S. Army Corps of Engineers High Shear Stress flume (SEDflume) is designed for estimating erosion rates of fine-grained and mixed fine/coarse grained sediments...

  18. Meniscal shear stress for punching.

    Science.gov (United States)

    Tuijthof, Gabrielle J M; Meulman, Hubert N; Herder, Just L; van Dijk, C Niek

    2009-01-01

    Experimental determination of the shear stress for punching meniscal tissue. Meniscectomy (surgical treatment of a lesion of one of the menisci) is the most frequently performed arthroscopic procedure. The performance of a meniscectomy is not optimal with the currently available instruments. To design new instruments, the punching force of meniscal tissue is an important parameter. Quantitative data are unavailable. The meniscal punching process was simulated by pushing a rod through meniscal tissue at constant speed. Three punching rods were tested: a solid rod of Oslash; 3.00 mm, and two hollow tubes (Oslash; 3.00-2.60 mm) with sharpened cutting edges of 0.15 mm and 0.125 mm thick, respectively. Nineteen menisci acquired from 10 human cadaveric knee joints were punched (30 tests). The force and displacement were recorded from which the maximum shear stress was determined (average added with three times the standard deviation). The maximum shear stress for the solid rod was determined at 10.2 N/mm2. This rod required a significantly lower punch force in comparison with the hollow tube having a 0.15 mm cutting edge (plt;0.01). The maximum shear stress for punching can be applied to design instruments, and virtual reality training environments. This type of experiment is suitable to form a database with material properties of human tissue similar to databases for the manufacturing industry.

  19. Stent implantation influence wall shear stress evolution

    Science.gov (United States)

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

    2016-06-01

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

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

    Science.gov (United States)

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

    2009-09-01

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

  1. Shear stresses around circular cylindrical openings

    NARCIS (Netherlands)

    Hoogenboom, P.C.J.; Van Weelden, C.; Blom, C.M.B.

    2010-01-01

    In this paper stress concentrations are studied around circular cylindrical openings or voids in a linear elastic continuum. The loading is such that a uniform shear stress occurs in the continuum, which is disturbed by the opening. The shear stress is in the direction of the centre axis of the

  2. Stress analysis of shear/compression test

    International Nuclear Information System (INIS)

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

    1997-01-01

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

  3. Effects of salinity and particle concentration on sediment hydrodynamics and critical bed-shear-stress for erosion of fine grained sediments used in wetland restoration projects

    Science.gov (United States)

    Ghose-Hajra, M.; McCorquodale, A.; Mattson, G.; Jerolleman, D.; Filostrat, J.

    2015-03-01

    Sea-level rise, the increasing number and intensity of storms, oil and groundwater extraction, and coastal land subsidence are putting people and property at risk along Louisiana's coast, with major implications for human safety and economic health of coastal areas. A major goal towards re-establishing a healthy and sustainable coastal ecosystem has been to rebuild Louisiana's disappearing wetlands with fine grained sediments that are dredged or diverted from nearby rivers, channels and lakes to build land in open water areas. A thorough geo-hydrodynamic characterization of the deposited sediments is important in the correct design and a more realistic outcome assessment of the long-term performance measures for ongoing coastal restoration projects. This paper evaluates the effects of salinity and solid particle concentration on the re-suspension characteristics of fine-grained dredged sediments obtained from multiple geographic locations along the Gulf coast. The critical bed-shear-stress for erosion has been evaluated as a function of sedimentation time. The sediment hydrodynamic properties obtained from the laboratory testing were used in a numerical coastal sediment distribution model to aid in evaluating sediment diversions from the Mississippi River into Breton Sound and Barataria Bay.

  4. Effects of salinity and particle concentration on sediment hydrodynamics and critical bed-shear-stress for erosion of fine grained sediments used in wetland restoration projects

    Directory of Open Access Journals (Sweden)

    M. Ghose-Hajra

    2015-03-01

    Full Text Available Sea-level rise, the increasing number and intensity of storms, oil and groundwater extraction, and coastal land subsidence are putting people and property at risk along Louisiana’s coast, with major implications for human safety and economic health of coastal areas. A major goal towards re-establishing a healthy and sustainable coastal ecosystem has been to rebuild Louisiana’s disappearing wetlands with fine grained sediments that are dredged or diverted from nearby rivers, channels and lakes to build land in open water areas. A thorough geo-hydrodynamic characterization of the deposited sediments is important in the correct design and a more realistic outcome assessment of the long-term performance measures for ongoing coastal restoration projects. This paper evaluates the effects of salinity and solid particle concentration on the re-suspension characteristics of fine-grained dredged sediments obtained from multiple geographic locations along the Gulf coast. The critical bed-shear-stress for erosion has been evaluated as a function of sedimentation time. The sediment hydrodynamic properties obtained from the laboratory testing were used in a numerical coastal sediment distribution model to aid in evaluating sediment diversions from the Mississippi River into Breton Sound and Barataria Bay.

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

    Directory of Open Access Journals (Sweden)

    Zuzana Macek Jilkova

    2014-11-01

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

  6. Evaluating interfacial shear stresses in composite hollo

    Directory of Open Access Journals (Sweden)

    Aiham Adawi

    2016-09-01

    Full Text Available Analytical evaluation of the interfacial shear stresses for composite hollowcore slabs with concrete topping is rare in the literature. Adawi et al. (2014 estimated the interfacial shear stiffness coefficient (ks that governs the behavior of the interface between hollowcore slabs and the concrete topping using push-off tests. This parameter is utilized in this paper to provide closed form solutions for the differential equations governing the behavior of simply supported composite hollowcore slabs. An analytical solution based on the deformation compatibility of the composite section and elastic beam theory, is developed to evaluate the shear stresses along the interface. Linear finite element modeling of the full-scale tests presented in Adawi et al. (2015 is also conducted to validate the developed analytical solution. The proposed analytical solution was found to be adequate in estimating the magnitude of horizontal shear stress in the studied composite hollowcore slabs.

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

    International Nuclear Information System (INIS)

    Liu Hao; Tong Hua; Xu Ning

    2014-01-01

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

  8. Erodibilidade e tensão crítica de cisalhamento em solos de estradas não pavimentadas Erodibility and critical shear stress on unpaved road soils

    Directory of Open Access Journals (Sweden)

    João F. de Oliveira

    2009-12-01

    Full Text Available A falta de um sistema adequado para drenagem de águas pluviais em estradas não pavimentadas é um dos principais fatores que causam a sua degradação e, para que referidos sistemas possam ser adequadamente planejados e dimensionados é necessário o conhecimento de parâmetros de resistência dos solos. Com este trabalho se teve, por objetivo, determinar a erodibilidade e a tensão crítica de cisalhamento para diferentes solos de estradas não pavimentadas. Utilizou-se um simulador de escoamento superficial instalado diretamente nos canais das estradas, sob condição natural e se determinou a perda de solo para diferentes lâminas de escoamento. A erodibilidade e a tensão crítica de cisalhamento foram determinadas por meio do ajuste de curvas relacionando-se a perda de solo em função da tensão cisalhante provocada pelo escoamento. Os resultados alcançados mostraram variações nos valores de erodibilidade e de tensão crítica de cisalhamento das estradas avaliadas. Os valores de erodibilidade encontrados mostraram, quando comparados com valores observados na literatura, elevada suscetibilidade à erosão para as condições de estradas, sendo mais elevados nos solos de textura mais arenosa e siltosa. Os valores de tensão crítica se mostraram bastante próximos aos observados em outros trabalhos.The absence of an adequate drainage system in unpaved roads is one of the main factors for their degradation. For adequate planning knowledge of the resistance parameters of soil is necessary. This study had as its objective the determinatiom of the erodibility and critical shear stress of unpaved road soils. For this work, a runoff simulator was directly installed on road channels, under natural conditions. Different flow depths were applied and the soil loss was measured for each depth. The erodibility and the critical shear stress were determined through adjusted curves relating soil disaggregation and flow shear stress. The results

  9. Motional Effect on Wall Shear Stresses

    DEFF Research Database (Denmark)

    Kock, Samuel Alberg; Torben Fründ, Ernst; Yong Kim, Won

    Atherosclerosis is the leading cause of death and severe disability. Wall Shear Stress (WSS), the stress exerted on vessel walls by the flowing blood is a key factor in the development of atherosclerosis. Computational Fluid Dynamics (CFD) is widely used for WSS estimations. Most CFD simulations...... are based on static models to ease computational burden leading to inaccurate estimations. The aim of this work was to estimate the effect of vessel wall deformations (expansion and bending) on WSS levels....

  10. Evolution of allowable stresses in shear for lumber

    Science.gov (United States)

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

    1979-01-01

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

  11. Shear stress and interleukin-8 (IL-8) on the proliferation ...

    African Journals Online (AJOL)

    Endothelial progenitor cells (EPCs) derived from bone marrow, are also found ... into tissues and neovascularization, the cells are exposed to fluid shear stress. ... Both shear stress and IL-8 can influence the process of EPCs repair in wound.

  12. Stress relaxation of shear in metals during shock loading

    International Nuclear Information System (INIS)

    Glazyrin, V.P.; Platova, T.M.

    1988-01-01

    Constructed determining equation, taking into account stress relaxation of shear, was used to calculate the evolution of plane shock waves of primary and secondary compression in metals. Values of shear stress and viscosity coefficient were

  13. Flexible Micropost Arrays for Shear Stress Measurement

    Science.gov (United States)

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

    2015-01-01

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

  14. Reynolds stress and shear flow generation

    DEFF Research Database (Denmark)

    Korsholm, Søren Bang; Michelsen, Poul; Naulin, V.

    2001-01-01

    The so-called Reynolds stress may give a measure of the self-consistent flow generation in turbulent fluids and plasmas by the small-scale turbulent fluctuations. A measurement of the Reynolds stress can thus help to predict flows, e.g. shear flows in plasmas. This may assist the understanding...... of improved confinement scenarios such as H-mode confinement regimes. However, the determination of the Reynolds stress requires measurements of the plasma potential, a task that is difficult in general and nearly impossible in hot plasmas in large devices. In this work we investigate an alternative method......, based on density measurements, to estimate the Reynolds stress, and demonstrate the validity range of this quantity, which we term the pseudo-Reynolds stress. The advantage of such a quantity is that accurate measurements of density fluctuations are much easier to obtain experimentally. Prior...

  15. prediction of shear resistance factor in flat slabs design using critical

    African Journals Online (AJOL)

    user

    The provisions of the American, Canadian, European and. Model codes, regarding the ... is the applied shear stress. W1 .... perimeter implies a smaller stress while a smaller critical .... should be compared with values provided in this work to validate ... [1] American Concrete Institute : Building code requirement for structural ...

  16. Experimental Research on Boundary Shear Stress in Typical Meandering Channel

    Science.gov (United States)

    Chen, Kai-hua; Xia, Yun-feng; Zhang, Shi-zhao; Wen, Yun-cheng; Xu, Hua

    2018-06-01

    A novel instrument named Micro-Electro-Mechanical System (MEMS) flexible hot-film shear stress sensor was used to study the boundary shear stress distribution in the generalized natural meandering open channel, and the mean sidewall shear stress distribution along the meandering channel, and the lateral boundary shear stress distribution in the typical cross-section of the meandering channel was analysed. Based on the measurement of the boundary shear stress, a semi-empirical semi-theoretical computing approach of the boundary shear stress was derived including the effects of the secondary flow, sidewall roughness factor, eddy viscosity and the additional Reynolds stress, and more importantly, for the first time, it combined the effects of the cross-section central angle and the Reynolds number into the expressions. Afterwards, a comparison between the previous research and this study was developed. Following the result, we found that the semi-empirical semi-theoretical boundary shear stress distribution algorithm can predict the boundary shear stress distribution precisely. Finally, a single factor analysis was conducted on the relationship between the average sidewall shear stress on the convex and concave bank and the flow rate, water depth, slope ratio, or the cross-section central angle of the open channel bend. The functional relationship with each of the above factors was established, and then the distance from the location of the extreme sidewall shear stress to the bottom of the open channel was deduced based on the statistical theory.

  17. Determination of wall shear stress from mean velocity and Reynolds shear stress profiles

    Science.gov (United States)

    Volino, Ralph J.; Schultz, Michael P.

    2018-03-01

    An analytical method is presented for determining the Reynolds shear stress profile in steady, two-dimensional wall-bounded flows using the mean streamwise velocity. The method is then utilized with experimental data to determine the local wall shear stress. The procedure is applicable to flows on smooth and rough surfaces with arbitrary pressure gradients. It is based on the streamwise component of the boundary layer momentum equation, which is transformed into inner coordinates. The method requires velocity profiles from at least two streamwise locations, but the formulation of the momentum equation reduces the dependence on streamwise gradients. The method is verified through application to laminar flow solutions and turbulent DNS results from both zero and nonzero pressure gradient boundary layers. With strong favorable pressure gradients, the method is shown to be accurate for finding the wall shear stress in cases where the Clauser fit technique loses accuracy. The method is then applied to experimental data from the literature from zero pressure gradient studies on smooth and rough walls, and favorable and adverse pressure gradient cases on smooth walls. Data from very near the wall are not required for determination of the wall shear stress. Wall friction velocities obtained using the present method agree with those determined in the original studies, typically to within 2%.

  18. Role of Wall Shear Stress in Cryptosporidium parvum Oocyst Attachment to Environmental Biofilms.

    Science.gov (United States)

    Luo, Xia; Jedlicka, Sabrina S; Jellison, Kristen L

    2017-12-15

    This study investigated Cryptosporidium parvum oocyst deposition onto biofilms as a function of shear stress under laminar or turbulent flow. Annular rotating bioreactors were used to grow stabilized stream biofilms at shear stresses ranging from 0.038 to 0.46 Pa. These steady-state biofilms were then used to assess the impact of hydrodynamic conditions on C. parvum oocyst attachment. C. parvum deposition onto biofilms followed a pseudo-second-order model under both laminar (after a lag phase) and turbulent flows. The total number of oocysts attached to the biofilm at steady state decreased as the hydrodynamic wall shear stress increased. The oocyst deposition rate constant increased with shear stress but decreased at high shear, suggesting that increasing wall shear stress results in faster attachment of Cryptosporidium due to higher mass transport until the shear forces exceed a critical limit that prevents oocyst attachment. These data show that oocyst attachment in the short and long term are impacted differently by shear: higher shear (to a certain limit) may be associated with faster initial oocyst attachment, but lower shear is associated with greater numbers of oocysts attached at equilibrium. IMPORTANCE This research provides experimental evidence to demonstrate that shear stress plays a critical role in protozoan-pathogen transport and deposition in environmental waters. The data presented in this work expand scientific understanding of Cryptosporidium attachment and fate, which will further influence the development of timely and accurate sampling strategies, as well as advanced water treatment technologies, to target protozoan pathogens in surface waters that serve as municipal drinking water sources. Copyright © 2017 American Society for Microbiology.

  19. Interfacial stresses in strengthened beam with shear cohesive zone ...

    Indian Academy of Sciences (India)

    The results of parametric study are compared with those of Smith and Teng. They confirm the accuracy of the proposed approach in predicting both interfacial shear and normal stresses. Keywords. Strengthened beam; interfacial stresses; cohesive zone; shear deformation. 1. Introduction. The FRP plates can be either ...

  20. Triglyceride glucose index and common carotid wall shear stress.

    Science.gov (United States)

    Tripolino, Cesare; Irace, Concetta; Scavelli, Faustina B; de Franceschi, Maria S; Esposito, Teresa; Carallo, Claudio; Gnasso, Agostino

    2014-02-01

    Alterations in wall shear stress contribute to both clinical and subclinical atherosclerosis. Several conditions such as hypertension, diabetes, and obesity can impair shear stress, but the role of insulin resistance has never been investigated. The present study was designed to investigate whether insulin resistance assessed by TyG Index associates with wall shear stress in the common carotid artery. One hundred six individuals were enrolled. Blood pressure, lipids, glucose, and cigarette smoking were evaluated. TyG Index was calculated as log[fasting triglycerides × fasting glucose / 2]. Subjects underwent blood viscosity measurement and echo-Doppler evaluation of carotid arteries to calculate wall shear stress. The association between TyG Index and carotid wall shear stress was assessed by simple and multiple regression analyses. TyG Index was significantly and inversely associated with carotid wall shear stress both in simple (r = -0.44, P glucose greater than 100 mg/dL, and triglycerides greater than 150 mg/dL. The present findings suggest that increasing insulin resistance, as assessed by TyG Index, associates with atherosclerosis-prone shear stress reduction in the common carotid artery.

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

    Energy Technology Data Exchange (ETDEWEB)

    Cao Jing; Wang Jiangan; Wu Ronghua, E-mail: caojing981@126.com [Col. of Electronic Eng., Naval University of Engineering, Wuhan 430033 (China)

    2011-01-01

    Dinoflagellate can be stimulated bioluminescence by hydrodynamic agitation. Two typical dinoflagellate (Lingulodinium polyedrum and Pyrocystis noctiluca) was choosed to research stimulated bioluminescence. The bioluminescence intensity and shear stress intensity were measured using fully developed pipe flow. There is shear stress threshold to agitate organism bioluminescence. From these experiment, the response thresholds of the stimulated bioluminscence always occurred in laminar flows at a shear stress level of 0.6-3 dyn/cm{sup 2}. At the same time, the spectral characteristc of dinoflagellate was recorded, the wavelength of them is about 470nm, and the full width at half maximum is approximate 30nm.

  2. Wall shear stress hot film sensor for use in gases

    International Nuclear Information System (INIS)

    Osorio, O D; Silin, N

    2011-01-01

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

  3. Sedimentation under variable shear stress at lower reach of the Rupnarayan River, West Bengal, India

    Directory of Open Access Journals (Sweden)

    Swapan Kumar Maity

    2017-04-01

    Full Text Available The lower reach of the Rupnarayan River has been deteriorated and incapacitated due to continuous sedimentation (26.57 million m3 shoaling in last 25 years. Attempts have been made to explain the causes and mechanisms of sedimentation in connection to the seasonal fluctuation of shear stress. River depth and water velocity was measured by echo-sounder and current meter respectively. Textural analysis of grains was done by sieving technique. Available and critical shear stress (N/m2 have been calculated following Du Boys (1879, Shield (1936 and Van Ledden (2003 formula. The lack of available energy to transport a particular grain size during low tide (in dry season is the main reason behind the rapid sedimentation in this area. Most of the places (>75% having negative deviation of shear stress (available shear stress lesser than critical shear stress, during low tide are characterized by deposition of sediments. The presence of mud (silt and clay above the critical limit (15% in some of the sediment samples generates the cohesive property, restricts sediments entrainment and invites sedimentation.

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

    Science.gov (United States)

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

    2011-01-01

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

  5. Shear Stress-Relative Slip Relationship at Concrete Interfaces

    Directory of Open Access Journals (Sweden)

    Keun-Hyeok Yang

    2016-01-01

    Full Text Available This study develops a simple and rational shear stress-relative slip model of concrete interfaces with monolithic castings or smooth construction joints. In developing the model, the initial shear cracking stress and relative slip amount at peak stress were formulated from a nonlinear regression analysis using test data for push-off specimens. The shear friction strength was determined from the generalized equations on the basis of the upper-bound theorem of concrete plasticity. Then, a parametric fitting analysis was performed to derive equations for the key parameters determining the shapes of the ascending and descending branches of the shear stress-relative slip curve. The comparisons of predictions and measurements obtained from push-off tests confirmed that the proposed model provides superior accuracy in predicting the shear stress-relative slip relationship of interfacial shear planes. This was evidenced by the lower normalized root mean square error than those in Xu et al.’s model and the CEB-FIB model, which have many limitations in terms of the roughness of the substrate surface along an interface and the magnitude of equivalent normal stress.

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

    Science.gov (United States)

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

    2011-11-01

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

  7. Shear flow generation by Reynolds stress and suppression of resistive g modes

    International Nuclear Information System (INIS)

    Sugama, H.; Horton, W.

    1993-01-01

    The authors have investigated suppression of the resistive g mode turbulence by background shear flow produced by the external source and by the fluctuation-induced Reynolds stress. For that purpose, the authors used the model consisting of the equations describing the electrostatic potential φ≡(φ 0 +φ) and the pressure fluctuation p of the resistive g mode, and the equation for the background poloidal flow. They have done the single-helicity nonlinear simulations using the model equations in the sheared slab configuration. They find that, in the nonlinear turbulent regime, significant suppression of the turbulent transport is realized only when the shear flow v' E exceeds that which makes the fastest-growing linear modes marginally stable. With the shear flow which decreases the fastest linear growth rates by about a half, the turbulent transport in the saturated state is about the same as in the case of no shear flow. As seen from the equation for the background flow v E , the relative efficiency of the external flow and the Reynolds stress for producing shear flow depends on the parameter ν. For large ν, the external flow is a dominant contribution to the total background poloidal shear flow although its strength predicted by the neoclassical theory is not enough to suppress the turbulence significantly. On the other hand, for small ν, they observe that, as the fluctuations grow, the Reynolds stress becomes large and suddenly at some critical point in time shear flow much larger than the external one is generated and leads to the significant reduction of the turbulent transport just like that of the L-H transition in tokamak experiments. It is remarkable that the Reynolds stress due to the resistive g mode fluctuations works not as a conventional viscosity term weakening the shear flow but as a negative viscosity term enhancing it

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

    Science.gov (United States)

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

    2015-08-01

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

  9. Shear flow generation by Reynolds stress and suppression of resistive g-modes

    International Nuclear Information System (INIS)

    Sugama, H.; Horton, W.

    1993-08-01

    Suppression of resistive g-mode turbulence by background shear flow generated from a small external flow source and amplified by the fluctuation-induced Reynolds stress is demonstrated and analyzed. The model leads to a paradigm for the low-to-high (L-H) confinement mode transition. To demonstrate the L-H transition model, single-helicity nonlinear fluid simulations using the vorticity equation for the electrostatic potential, the pressure fluctuation equation and the background poloidal flow equation are used in the sheared slab configuration. The relative efficiency of the external flow and the Reynolds stress for producing shear flow depends on the poloidal flow damping parameter ν which is given by neoclassical theory. For large ν, the external flow is a dominant contribution to the total background poloidal shear flow and its strength predicted by the neoclassical theory is not enough to suppress the turbulence significantly. In contrast, for small ν, we show that the fluctuations drive a Reynolds stress that becomes large and suddenly, at some critical point in time, shear flow much larger than the external flow is generated and leads to an abrupt, order unity reduction of the turbulent transport just like that of the L-H transition in tokamak experiments. It is also found that, even in the case of no external flow, the shear flow generation due to the Reynolds stress occurs through the nonlinear interaction of the resistive g-modes and reduces the transport. To supplement the numerical solutions we derive the Landau equation for the mode amplitude of the resistive g-mode taking into account the fluctuation-induced shear flow and analyze the opposite action of the Reynolds stress in the resistive g turbulence compared with the classical shear flow Kelvin-Helmholtz (K-H) driven turbulence

  10. NUMERICAL SIMULATION OF AN AGRICULTURAL SOIL SHEAR STRESS TEST

    Directory of Open Access Journals (Sweden)

    Andrea Formato

    2007-03-01

    Full Text Available In this work a numerical simulation of agricultural soil shear stress tests was performed through soil shear strength data detected by a soil shearometer. We used a soil shearometer available on the market to measure soil shear stress and constructed special equipment that enabled automated detection of soil shear stress. It was connected to an acquisition data system that displayed and recorded soil shear stress during the full field tests. A soil shearometer unit was used to the in situ measurements of soil shear stress in full field conditions for different types of soils located on the right side of the Sele river, at a distance of about 1 km from each other, along the perpendicular to the Sele river in the direction of the sea. Full field tests using the shearometer unit were performed alongside considered soil characteristic parameter data collection. These parameter values derived from hydrostatic compression and triaxial tests performed on considered soil samples and repeated 4 times and we noticed that the difference between the maximum and minimum values detected for every set of performed tests never exceeded 4%. Full field shear tests were simulated by the Abaqus program code considering three different material models of soils normally used in the literature, the Mohr-Coulomb, Drucker-Prager and Cam-Clay models. We then compared all data outcomes obtained by numerical simulations with those from the experimental tests. We also discussed any further simulation data results obtained with different material models and selected the best material model for each considered soil to be used in tyre/soil contact simulation or in soil compaction studies.

  11. Mean wall-shear stress measurements using the micro-pillar shear-stress sensor MPS3

    International Nuclear Information System (INIS)

    Große, S; Schröder, W

    2008-01-01

    A new sensor to measure the mean turbulent wall-shear stress in turbulent flows is described. The wall-shear stress sensor MPS 3 has been tested in a well-defined fully developed turbulent pipe flow at Reynolds numbers Re b based on the bulk velocity U b and the pipe diameter D in the range of Re b = 10 000–20 000. The results demonstrate a convincing agreement of the mean wall-shear stress obtained with the new sensor technique with analytical and experimental results from the literature. The sensor device consists of a flexible micro-pillar that extends from the wall into the viscous sublayer. Bending due to the exerting fluid forces, the pillar-tip deflection serves as a measure for the local wall-shear stress. The sensor concept, calibration techniques, the achievable accuracy and error estimates, the fields of application and the sensor limits will be discussed. Furthermore, a first estimate of the pillar dynamic response will be derived showing the potential of the sensor to also measure the turbulent fluctuating wall-shear stress

  12. Shear-stress fluctuations and relaxation in polymer glasses

    Science.gov (United States)

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

    2018-01-01

    We investigate by means of molecular dynamics simulation a coarse-grained polymer glass model focusing on (quasistatic and dynamical) shear-stress fluctuations as a function of temperature T and sampling time Δ t . The linear response is characterized using (ensemble-averaged) expectation values of the contributions (time averaged for each shear plane) to the stress-fluctuation relation μsf for the shear modulus and the shear-stress relaxation modulus G (t ) . Using 100 independent configurations, we pay attention to the respective standard deviations. While the ensemble-averaged modulus μsf(T ) decreases continuously with increasing T for all Δ t sampled, its standard deviation δ μsf(T ) is nonmonotonic with a striking peak at the glass transition. The question of whether the shear modulus is continuous or has a jump singularity at the glass transition is thus ill posed. Confirming the effective time-translational invariance of our systems, the Δ t dependence of μsf and related quantities can be understood using a weighted integral over G (t ) .

  13. Stabilization of the Friedmann big bang by the shear stresses

    Science.gov (United States)

    Belinski, V. A.

    2013-11-01

    The window is found in the space of the free parameters of the theory of viscoelastic matter for which the Friedmann singularity is stable. By stability we mean that in the presence of the shear stresses, a generic solution of the equations of relativistic gravity possessing an isotropic singularity exists.

  14. A simple model to understand the role of membrane shear elasticity and stress-free shape on the motion of red blood cells in shear flow

    Science.gov (United States)

    Viallat, Annie; Abkarian, Manouk; Dupire, Jules

    2015-11-01

    The analytical model presented by Keller and Skalak on the dynamics of red blood cells in shear flow described the cell as a fluid ellipsoid of fixed shape. It was extended to introduce shear elasticity of the cell membrane. We further extend the model when the cell discoid physiological shape is not a stress-free shape. We show that spheroid stress-free shapes enables fitting experimental data with values of shear elasticity typical to that found with micropipettes and optical tweezers. For moderate shear rates (when RBCs keep their discoid shape) this model enables to quantitatively determine an effective cell viscosity, that combines membrane and hemoglobin viscosities and an effective shear modulus of the membrane that combines shear modulus and stress-free shape. This model allows determining RBC mechanical parameters both in the tanktreading regime for cells suspended in a high viscosity medium, and in the tumbling regime for cells suspended in a low viscosity medium. In this regime,a transition is predicted between a rigid-like tumbling motion and a fluid-like tumbling motion above a critical shear rate, which is directly related to the mechanical parameters of the cell. A*MIDEX (n ANR-11-IDEX-0001-02) funded by the ''Investissements d'Avenir'', Region Languedoc-Roussillon, Labex NUMEV (ANR-10-LABX-20), BPI France project DataDiag.

  15. A review of shear wave splitting in the crack-critical crust

    Science.gov (United States)

    Crampin, Stuart; Chastin, Sebastien

    2003-10-01

    Over the last 15 years, it has become established that crack-induced stress-aligned shear wave splitting, with azimuthal anisotropy, is an inherent characteristic of almost all rocks in the crust. This means that most in situ rocks are pervaded by fluid-saturated microcracks and consequently are highly compliant. The evolution of such stress-aligned fluid-saturated grain-boundary cracks and pore throats in response to changing conditions can be calculated, in some cases with great accuracy, using anisotropic poro-elasticity (APE). APE is tightly constrained with no free parameters, yet dynamic modelling with APE currently matches a wide range of phenomena concerning anisotropy, stress, shear waves and cracks. In particular, APE has allowed the anisotropic response of a reservoir to injection to be calculated (predicted with hindsight), and the time and magnitude of an earthquake to be correctly stress-forecast. The reason for this calculability and predictability is that the microcracks in the crust are so closely spaced that they form critical systems. This crack-critical crust leads to a new style of geophysics that has profound implications for almost all aspects of pre-fracturing deformation of the crust and for solid-earth geophysics and geology. We review past, present and speculate about the future of shear wave splitting in the crack-critical crust. Shear wave splitting is seen to be a dynamic measure of the deformation of the rock mass. There is some good news and some bad news for conventional geophysics. Many accepted phenomena are no longer valid at high spatial and temporal resolution. A major effect is that the detailed crack geometry changes with time and varies from place to place in response to very small previously negligible changes. However, at least in some circumstances, the behaviour of the rock in the highly complex inhomogeneous Earth may be calculated and the response predicted, opening the way to possible control by feedback. The need is

  16. Sensor for Boundary Shear Stress in Fluid Flow

    Science.gov (United States)

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

    2012-01-01

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

  17. Rivulet flow round a horizontal cylinder subject to a uniform surface shear stress

    KAUST Repository

    Paterson, C.; Wilson, S. K.; Duffy, B. R.

    2014-01-01

    large stationary horizontal cylinder subject to a prescribed uniform azimuthal surface shear stress is investigated. In particular, we focus on the case where the volume flux is downwards but the shear stress is upwards, for which there is always a

  18. The Sheer Stress of Shear Stress: Responses of the Vascular Wall to a Haemodynamic Force

    NARCIS (Netherlands)

    C. Cheng (Caroline (Ka Lai))

    2006-01-01

    textabstractStudies in the hemodynamic field point to a strong relation between shear stress and the onset to vascular diseases such as atherosclerosis. Data from in vitro studies using sheared endothelial cells have provided insight into the possible mechanisms involved. However, the lack of an

  19. Relations Between Shear and Normal Stresses in a Step-Shear Experiment

    DEFF Research Database (Denmark)

    Hassager, Ole; Pedersen, Sven

    1978-01-01

    The Lodge-Meissner step-shear relation for simple fluids is examined. It is demonstrated that the relation depends critically on two assumptions for the integral expansion of the simple fluid: First, the use of the Cauchy strain tensor as strain measure, and second, that the memory functions...... are bounded. It is pointed out that many simple differential and integral models do not satisfy these criteria and hence predict deviations from the Lodge-Meissner relation....

  20. Analysis of Shear Stress and Energy Consumption in a Tubular Airlift Membrane System

    DEFF Research Database (Denmark)

    Ratkovich, Nicolas Rios; Chan, C.C.V.; Berube, P.R.

    2011-01-01

    of fouling by imposing high shear stress near the surface of the membrane. Previously, shear stress histograms (SSH) have been introduced to summarize results from an experimental setup developed to investigate the shear stress imposed on the surface of a membrane under different two-phase flow conditions...

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

    Science.gov (United States)

    Mei, Chiang C; Jing, Haixiao

    2016-10-01

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

  2. The effects of shear and normal stress paths on rock friction

    International Nuclear Information System (INIS)

    Olsson, W.A.

    1990-01-01

    The effect of variable normal stress on the coefficient of friction of smooth artificial surfaces in welded tuff was studied. The shear stress response to changes in normal stress during constant-velocity sliding suggests that friction depends on the history of the normal stress; or, more generally, the path in shear/normal stress space. 6 refs., 5 figs

  3. Evidence for shear stress-mediated dilation of the internal carotid artery in humans

    DEFF Research Database (Denmark)

    Carter, Howard Henry; Atkinson, Ceri L; Heinonen, Ilkka H A

    2016-01-01

    -mediated dilation of larger conduit arteries in humans. There was a strong association between change in shear and diameter of the internal carotid (r=0.68; Ptime in humans, that shear stress is an important stimulus for hypercapnic vasodilation of the internal carotid...... increases carotid shear stress, a known stimulus to vasodilation in other conduit arteries. To explore the hypothesis that shear stress contributes to hypercapnic internal carotid dilation in humans, temporal changes in internal and common carotid shear rate and diameter, along with changes in middle.......01) carotids. Diameter also increased (Ptime course is associated with shear...

  4. Utilization of shear stress for determination of activation energy of the defects created by neutron irradiation

    International Nuclear Information System (INIS)

    Gonzalez, Hector C.; Miralles, Monica

    1996-01-01

    This paper describes an experimental technique used for the determination thermodynamical parameters such as activation energy using the thermal annealing of increments of Critical resolved Shear Stress of the defects created by neutron irradiation at 77 K. The doses chosen for this work was 3.1 x 10 16 n/cm 2 since the defects are stable to plastic deformation and the cascades of atomic displacements do not overlap. Specimens without any prior deformation were used allowing then the single addition of the initial stress to that due to the created defects. (author)

  5. Bed shear stress distribution in straight channels with arbitrary cross section

    DEFF Research Database (Denmark)

    Christensen, Henrik Bo; Fredsøe, Jørgen

    1998-01-01

    The bed shear stress distribution in straight open channels is affected by mechanisms as bed curvature of the cross section profile, shear diffusion, and secondary currents. This paper compares some analytical and numerical methods to estimate the bed shear stress distribution. The methods...

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

    Science.gov (United States)

    Joseph Antony, S.

    2015-03-01

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

  7. Adaptation of endothelial cells to physiologically-modeled, variable shear stress.

    Directory of Open Access Journals (Sweden)

    Joseph S Uzarski

    Full Text Available Endothelial cell (EC function is mediated by variable hemodynamic shear stress patterns at the vascular wall, where complex shear stress profiles directly correlate with blood flow conditions that vary temporally based on metabolic demand. The interactions of these more complex and variable shear fields with EC have not been represented in hemodynamic flow models. We hypothesized that EC exposed to pulsatile shear stress that changes in magnitude and duration, modeled directly from real-time physiological variations in heart rate, would elicit phenotypic changes as relevant to their critical roles in thrombosis, hemostasis, and inflammation. Here we designed a physiological flow (PF model based on short-term temporal changes in blood flow observed in vivo and compared it to static culture and steady flow (SF at a fixed pulse frequency of 1.3 Hz. Results show significant changes in gene regulation as a function of temporally variable flow, indicating a reduced wound phenotype more representative of quiescence. EC cultured under PF exhibited significantly higher endothelial nitric oxide synthase (eNOS activity (PF: 176.0±11.9 nmol/10(5 EC; SF: 115.0±12.5 nmol/10(5 EC, p = 0.002 and lower TNF-a-induced HL-60 leukocyte adhesion (PF: 37±6 HL-60 cells/mm(2; SF: 111±18 HL-60/mm(2, p = 0.003 than cells cultured under SF which is consistent with a more quiescent anti-inflammatory and anti-thrombotic phenotype. In vitro models have become increasingly adept at mimicking natural physiology and in doing so have clarified the importance of both chemical and physical cues that drive cell function. These data illustrate that the variability in metabolic demand and subsequent changes in perfusion resulting in constantly variable shear stress plays a key role in EC function that has not previously been described.

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

    International Nuclear Information System (INIS)

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

    1995-01-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

    Lorencez, C.; Kawaji, M. [Univ. of Toronto (Canada); Murao, Y. [Tokushima Univ. (Japan)] [and others

    1995-09-01

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

  10. Heterogeneous Cytoskeletal Force Distribution Delineates the Onset Ca2+ Influx Under Fluid Shear Stress in Astrocytes

    Directory of Open Access Journals (Sweden)

    Mohammad M. Maneshi

    2018-03-01

    Full Text Available Mechanical perturbations increase intracellular Ca2+ in cells, but the coupling of mechanical forces to the Ca2+ influx is not well understood. We used a microfluidic chamber driven with a high-speed pressure servo to generate defined fluid shear stress to cultured astrocytes, and simultaneously measured cytoskeletal forces using a force sensitive actinin optical sensor and intracellular Ca2+. Fluid shear generated non-uniform forces in actinin that critically depended on the stimulus rise time emphasizing the presence of viscoelasticity in the activating sequence. A short (ms shear pulse with fast rise time (2 ms produced an immediate increase in actinin tension at the upstream end of the cell with minimal changes at the downstream end. The onset of Ca2+ rise began at highly strained areas. In contrast to stimulus steps, slow ramp stimuli produced uniform forces throughout the cells and only a small Ca2+ response. The heterogeneity of force distribution is exaggerated in cells having fewer stress fibers and lower pre-tension in actinin. Disruption of cytoskeleton with cytochalasin-D (Cyt-D eliminated force gradients, and in those cells Ca2+ elevation started from the soma. Thus, Ca2+ influx with a mechanical stimulus depends on local stress within the cell and that is time dependent due to viscoelastic mechanics.

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

    Science.gov (United States)

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

    2013-01-01

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

  12. Shear-Rate-Dependent Behavior of Clayey Bimaterial Interfaces at Landslide Stress Levels

    Science.gov (United States)

    Scaringi, Gianvito; Hu, Wei; Xu, Qiang; Huang, Runqiu

    2018-01-01

    The behavior of reactivated and first-failure landslides after large displacements is controlled by the available shear resistance in a shear zone and/or along slip surfaces, such as a soil-bedrock interface. Among the factors influencing the resistance parameter, the dependence on the shear rate can trigger catastrophic evolution (rate-weakening) or exert a slow-down feedback (rate-strengthening) upon stress perturbation. We present ring-shear test results, performed under various normal stresses and shear rates, on clayey soils from a landslide shear zone, on its parent lithology and other lithologies, and on clay-rock interface samples. We find that depending on the materials in contact, the normal stress, and the stress history, the shear-rate-dependent behaviors differ. We discuss possible models and underlying mechanisms for the time-dependent behavior of landslides in clay soils.

  13. The theoretical shear strength of fcc crystals under superimposed triaxial stress

    Energy Technology Data Exchange (ETDEWEB)

    Cerny, M., E-mail: cerny.m@fme.vutbr.cz [Institute of Engineering Physics, Faculty of Mechanical Engineering, Brno University of Technology, Technicka 2, CZ-616 69 Brno (Czech Republic); Pokluda, J. [Institute of Engineering Physics, Faculty of Mechanical Engineering, Brno University of Technology, Technicka 2, CZ-616 69 Brno (Czech Republic)

    2010-05-15

    The influence of a triaxial stress applied normally to shear planes and shear direction during affine shear deformation of face-centered cubic crystals on the theoretical shear strength is studied for the <112-bar >{l_brace}111{r_brace} shear system using first-principles methods. The applied relaxation procedure guarantees that the modeled system is subjected to a superposition of shear, normal and in-plane stresses with individually adjustable in-plane and normal stress values. The theoretical shear strengths of individual elements prove to be qualitatively different functions of the superimposed stresses. In the special case of hydrostatic loading, however, these functions are qualitatively uniform. This behavior is discussed in terms of the electronic structure.

  14. Risk of shear failure and extensional failure around over-stressed excavations in brittle rock

    Directory of Open Access Journals (Sweden)

    Nick Barton

    2017-04-01

    Full Text Available The authors investigate the failure modes surrounding over-stressed tunnels in rock. Three lines of investigation are employed: failure in over-stressed three-dimensional (3D models of tunnels bored under 3D stress, failure modes in two-dimensional (2D numerical simulations of 1000 m and 2000 m deep tunnels using FRACOD, both in intact rock and in rock masses with one or two joint sets, and finally, observations in TBM (tunnel boring machine tunnels in hard and medium hard massive rocks. The reason for ‘stress-induced’ failure to initiate, when the assumed maximum tangential stress is approximately (0.4–0.5σc (UCS, uniaxial compressive strength in massive rock, is now known to be due to exceedance of a critical extensional strain which is generated by a Poisson's ratio effect. However, because similar ‘stress/strength’ failure limits are found in mining, nuclear waste research excavations, and deep road tunnels in Norway, one is easily misled into thinking of compressive stress induced failure. Because of this, the empirical SRF (stress reduction factor in the Q-system is set to accelerate as the estimated ratio σθmax/σc >> 0.4. In mining, similar ‘stress/strength’ ratios are used to suggest depth of break-out. The reality behind the fracture initiation stress/strength ratio of ‘0.4’ is actually because of combinations of familiar tensile and compressive strength ratios (such as 10 with Poisson's ratio (say 0.25. We exceed the extensional strain limits and start to see acoustic emission (AE when tangential stress σθ ≈ 0.4σc, due to simple arithmetic. The combination of 2D theoretical FRACOD models and actual tunnelling suggests frequent initiation of failure by ‘stable’ extensional strain fracturing, but propagation in ‘unstable’ and therefore dynamic shearing. In the case of very deep tunnels (and 3D physical simulations, compressive stresses may be too high for extensional strain fracturing, and

  15. Development of in-situ rock shear test under low compressive to tensile normal stress

    International Nuclear Information System (INIS)

    Nozaki, Takashi; Shin, Koichi

    2003-01-01

    The purpose of this study is to develop an in-situ rock shear testing method to evaluate the shear strength under low normal stress condition including tensile stress, which is usually ignored in the assessment of safety factor of the foundations for nuclear power plants against sliding. The results are as follows. (1) A new in-situ rock shear testing method is devised, in which tensile normal stress can be applied on the shear plane of a specimen by directly pulling up a steel box bonded to the specimen. By applying the counter shear load to cancel the moment induced by the main shear load, it can obtain shear strength under low normal stress. (2) Some model tests on Oya tuff and diatomaceous mudstone have been performed using the developed test method. The shear strength changed smoothly from low values at tensile normal stresses to higher values at compressive normal stresses. The failure criterion has been found to be bi-linear on the shear stress vs normal stress plane. (author)

  16. Sand transport, shear stress, and the building of a delta

    Science.gov (United States)

    Wagner, W.; Miller, K. L.; Hiatt, M. R.; Mohrig, D. C.

    2017-12-01

    River deltas distribute sediment to the coastal sea through a complex branching network of channels; however, the routing and storage of this sediment in and through the delta is poorly understood. We present results from field studies of the sediment and water transport through the branching Wax Lake Delta on the coast of Louisiana. Two channels studied, Main Pass and East Pass, maintain a near-equal total partitioning of flow and sediment. However, East Pass is narrower and has higher river velocities, lower tidal velocity fluctuations, less alluvial bed cover, and more sediment flux per unit width than Main Pass. We connect these differences to small differences in the geometry of the two channels and feedbacks between these differences. We link trends in measured sediment deposits to both measured and modeled shear velocities in Wax Lake Delta's channels and open water `islands' to understand how hydrologic processes shaped the sedimentary architecture of the delta. These connections define the sediment transport and deposition regimes in the WLD. We extend the results herein to suggest that the relationships between the available sediment and shear stress determines the basic planform of the Wax Lake Delta and cross-sectional geometries of its channels.

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

    Science.gov (United States)

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

    2016-01-01

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

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

    Directory of Open Access Journals (Sweden)

    Ayumi Amemiya

    2016-01-01

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

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

    International Nuclear Information System (INIS)

    Walton, O.R.; Braun, R.L.

    1986-01-01

    Employing nonequilibrium molecular-dynamics methods the effects of two energy loss mechanisms on viscosity, stress, and granular-temperature in assemblies of nearly rigid, inelastic frictional disks undergoing steady-state shearing are calculated. Energy introduced into the system through forced shearing is dissipated by inelastic normal forces or through frictional sliding during collisions resulting in a natural steady-state kinetic energy density (granular-temperature) that depends on the density and shear rate of the assembly and on the friction and inelasticity properties of the disks. The calculations show that both the mean deviatoric particle velocity and the effective viscosity of a system of particles with fixed friction and restitution coefficients increase almost linearly with strain rate. Particles with a velocity-dependent coefficient of restitution show a less rapid increase in both deviatoric velocity and viscosity as strain rate increases. Particles with highly dissipative interactions result in anisotropic pressure and velocity distributions in the assembly, particularly at low densities. At very high densities the pressure also becomes anisotropic due to high contact forces perpendicular to the shearing direction. The mean rotational velocity of the frictional disks is nearly equal to one-half the shear rate. The calculated ratio of shear stress to normal stress varies significantly with density while the ratio of shear stress to total pressure shows much less variation. The inclusion of surface friction (and thus particle rotation) decreases shear stress at low density but increases shear stress under steady shearing at higher densities

  20. Anisotropic frequency response of critical density fluctuation of NIPA gel under oscillation shear

    Energy Technology Data Exchange (ETDEWEB)

    Sugiyama, Masaaki [Research Reactor Institute, Kyoto University, Osaka 590-0494 (Japan)]. E-mail: sugiyama@rri.kyoto-u.ac.jp; Vigild, Martin E. [Danish Polymer Centre, Technical University of Denmark, 2800 Lyngby (Denmark); Fukunaga, Toshiharu [Research Reactor Institute, Kyoto University, Osaka 590-0494 (Japan); Itoh, Keiji [Research Reactor Institute, Kyoto University, Osaka 590-0494 (Japan); Mori, Kazuhiro [Research Reactor Institute, Kyoto University, Osaka 590-0494 (Japan); Sato, Takashi [Department of Engineering Physics and Mechanics, Kyoto University, Kyoto 606-8501 (Japan); Annaka, Masahiko [Department of Chemistry, Kyushu University, Fukuoka 812-8581 (Japan)

    2006-11-15

    A relation between rheology and structure of high density NIPA gel around a critical point on volume phase transition was studied by a simultaneous rheology and small-angle neutron scattering measurement. Just below the critical temperature, the NIPA gel showed softening: G{sup '} and G{sup '}' get closer (G{sup '}>G{sup '}'). At this temperature, the density fluctuation enhanced along the shear direction corresponding to the shear frequency but not to the shear strength. It means that this anisotropy is different from that observed in a statically stretched gel.

  1. Wall shear stress fixed points in blood flow

    Science.gov (United States)

    Arzani, Amirhossein; Shadden, Shawn

    2017-11-01

    Patient-specific computational fluid dynamics produces large datasets, and wall shear stress (WSS) is one of the most important parameters due to its close connection with the biological processes at the wall. While some studies have investigated WSS vectorial features, the WSS fixed points have not received much attention. In this talk, we will discuss the importance of WSS fixed points from three viewpoints. First, we will review how WSS fixed points relate to the flow physics away from the wall. Second, we will discuss how certain types of WSS fixed points lead to high biochemical surface concentration in cardiovascular mass transport problems. Finally, we will introduce a new measure to track the exposure of endothelial cells to WSS fixed points.

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

    Science.gov (United States)

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

    2017-01-04

    The patchy distribution of atherosclerosis within arteries is widely attributed to local variation in haemodynamic wall shear stress (WSS). A recently-introduced metric, the transverse wall shear stress (transWSS), which is the average over the cardiac cycle of WSS components perpendicular to the temporal mean WSS vector, correlates particularly well with the pattern of lesions around aortic branch ostia. Here we use numerical methods to investigate the nature of the arterial flows captured by transWSS and the sensitivity of transWSS to inflow waveform and aortic geometry. TransWSS developed chiefly in the acceleration, peak systolic and deceleration phases of the cardiac cycle; the reverse flow phase was too short, and WSS in diastole was too low, for these periods to have a significant influence. Most of the spatial variation in transWSS arose from variation in the angle by which instantaneous WSS vectors deviated from the mean WSS vector rather than from variation in the magnitude of the vectors. The pattern of transWSS was insensitive to inflow waveform; only unphysiologically high Womersley numbers produced substantial changes. However, transWSS was sensitive to changes in geometry. The curvature of the arch and proximal descending aorta were responsible for the principal features, the non-planar nature of the aorta produced asymmetries in the location and position of streaks of high transWSS, and taper determined the persistence of the streaks down the aorta. These results reflect the importance of the fluctuating strength of Dean vortices in generating transWSS. Copyright © 2016 Elsevier Ltd. All rights reserved.

  3. Energy Consumption Related to Shear Stress for Membrane Bioreactors Used for Wastewater Treatment

    DEFF Research Database (Denmark)

    Ratkovich, Nicolas Rios; Bentzen, Thomas Ruby; Bérube, P.R.

    2011-01-01

    . A linear empirical correlation between the average shear stress and the blower power per unit of permeate was made. 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...... stress measurements and CFD simulation were made. It was found that the average shear stress over the membrane surface from the CFD model is similar compared to experimental data (error less than 8 %). However, some differences in the distribution of shear stress throughout the submerged MBR system were...... observed. It was found that the CFD and experimental data was similar in terms of shear stress. On the other hand, for the HS MBR experimental measurements were not made. Nevertheless, as a proper validation was attained with the HF MBR, it was inferred that the CFD results for the HS MBR were accurate...

  4. Evaluation of the interfacial shear strength and residual stress of TiAlN coating on ZIRLO™ fuel cladding using a modified shear-lag model approach

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Y., E-mail: troy.liu@manchester.ac.uk [Materials Performance Centre, School of Materials, The University of Manchester, M13 9PL (United Kingdom); Bhamji, I., E-mail: imran.bhamji@manchester.ac.uk [Materials Performance Centre, School of Materials, The University of Manchester, M13 9PL (United Kingdom); Withers, P.J., E-mail: p.j.withers@manchester.ac.uk [Materials Performance Centre, School of Materials, The University of Manchester, M13 9PL (United Kingdom); Wolfe, D.E., E-mail: dew125@arl.psu.edu [The Pennsylvania State University, University Park, State College, PA 16801 (United States); Motta, A.T., E-mail: atmnuc@engr.psu.edu [The Pennsylvania State University, University Park, State College, PA 16801 (United States); Preuss, M., E-mail: michael.preuss@manchester.ac.uk [Materials Performance Centre, School of Materials, The University of Manchester, M13 9PL (United Kingdom)

    2015-11-15

    This paper investigates the residual stresses and interfacial shear strength of a TiAlN coating on Zr–Nb–Sn–Fe alloy (ZIRLO™) substrate designed to improve corrosion resistance of fuel cladding used in water-cooled nuclear reactors, both during normal and exceptional conditions, e.g. a loss of coolant event (LOCA). The distribution and maximum value of the interfacial shear strength has been estimated using a modified shear-lag model. The parameters critical to this analysis were determined experimentally. From these input parameters the interfacial shear strength between the TiAlN coating and ZIRLO™ substrate was inferred to be around 120 MPa. It is worth noting that the apparent strength of the coating is high (∼3.4 GPa). However, this is predominantly due to the large compressive residuals stress (3 GPa in compression), which must be overcome for the coating to fail in tension, which happens at a load just 150 MPa in excess of this.

  5. Shear-stress and wall-stress regulation of vascular remodeling after balloon angioplasty: effect of matrix metalloproteinase inhibition

    NARCIS (Netherlands)

    C.J. Slager (Cornelis); J. Kloet (Jeroen); J.A.F. Oomen; J.C.H. Schuurbiers (Johan); B.J. de Smet; M.J. Post (Mark); D.P.V. de Kleijn (Dominique); G. Pasterkamp (Gerard); R. Krams (Rob); C. Borst (Cornelius); J.J. Wentzel (Jolanda); I. Andhyiswara (Ivan)

    2001-01-01

    textabstractBACKGROUND: Constrictive vascular remodeling (VR) is the most significant component of restenosis after balloon angioplasty (PTA). Whereas in physiological conditions VR is associated with normalization of shear stress (SS) and wall stress (WS), after PTA

  6. Isotropic-nematic transition in shear flow: State selection, coexistence, phase transitions, and critical behavior

    Science.gov (United States)

    Olmsted, Peter D.; Goldbart, Paul M.

    1992-10-01

    Macroscopic fluid motion can have dramatic consequences near the isotropic-nematic transition in fluids of nematogens. We explore some of these consequences using both deterministic and stochastic descriptions involving coupled hydrodynamic equations of motion for the nematic order parameter and fluid velocity fields. By analyzing the deterministic equations of motion we identify the locally stable states of homogeneous nematic order and strain rate, thus determining the homogeneous nonequilibrium steady states which the fluid may adopt. By examining inhomogeneous steady states we construct the analog of a first-order phase boundary, i.e., a line in the nonequilibrium phase diagram spanned by temperature and applied stress, at which nonequilibrium states may coexist, and which terminates in a nonequilibrium analog of a critical point. From an analysis of the nematic order-parameter discontinuity across the coexistence line, along with properties of the interface between homogeneous states, we extract the analog of classical equilibrium critical behavior near the nonequilibrium critical point. We develop a theory of fluctuations about biaxial nonequilibrium steady states by augmenting the deterministic description with noise terms, to simulate the effect of thermal fluctuations. We use this description to discuss the scattering of polarized light by order-parameter fluctuations near the nonequilibrium critical point and also in weak shear flow near the equilibrium phase transition. We find that fluids of nematogens near an appropriate temperature and strain rate exhibit the analog of critical opalescence, the intensity of which is sensitive to the polarizations of the incident and scattered light, and to the precise form of the critical mode.

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

    Science.gov (United States)

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

    1996-01-01

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

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

    NARCIS (Netherlands)

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

    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

  9. Effect of shear stress on the migration of hepatic stellate cells.

    Science.gov (United States)

    Sera, Toshihiro; Sumii, Tateki; Fujita, Ryosuke; Kudo, Susumu

    2018-01-01

    When the liver is damaged, hepatic stellate cells (HSCs) can change into an activated, highly migratory state. The migration of HSCs may be affected by shear stress due not only to sinusoidal flow but also by the flow in the space of Disse because this space is filled with blood plasma. In this study, we evaluated the effects of shear stress on HSC migration in a scratch-wound assay with a parallel flow chamber. At regions upstream of the wound area, the migration was inhibited by 0.6 Pa and promoted by 2.0 Pa shear stress, compared to the static condition. The platelet-derived growth factor (PDGF)-BB receptor, PDGFR-β, was expressed in all conditions and the differences were not significant. PDGF increased HSC migration, except at 0.6 Pa shear stress, which was still inhibited. These results indicate that another molecular factor, such as PDGFR-α, may act to inhibit the migration under low shear stress. At regions downstream of the wound area, the migration was smaller under shear stress than under the static condition, although the expression of PDGFR-β was significantly higher. In particular, the migration direction was opposite to the wound area under high shear stress; therefore, migration might be influenced by the intercellular environment. Our results indicate that HSC migration was influenced by shear stress intensity and the intercellular environment.

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

    OpenAIRE

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

    2015-01-01

    This study assesses effects of aerobic exercise training on the release of microparticles from endothelial cells and corroborates these findings using an in vitro experimental exercise stimulant, laminar shear stress. Furthermore, this study demonstrated that shear stress-induced mitochondrial biogenesis mediates these effects against endothelial cell activation and injury.

  11. On the use of horizontal acoustic doppler profilers for continuous bed shear stress monitoring

    NARCIS (Netherlands)

    Vermeulen, B.; Hoitink, A.J.F.; Sassi, M.G.

    2013-01-01

    Continuous monitoring of bed shear stress in large river systems may serve to better estimate alluvial sediment transport to the coastal ocean. Here we explore the possibility of using a horizontally deployed acoustic Doppler current profiler (ADCP) to monitor bed shear stress, applying a prescribed

  12. Optimization of multiplane ?PIV for wall shear stress and wall topography characterization

    NARCIS (Netherlands)

    Rossi, M.; Lindken, R.; Westerweel, J.

    2009-01-01

    Multiplane ?PIV can be utilized to determine the wall shear stress and wall topology from the measured flow over a structured surface. A theoretical model was developed to predict the measurement error for the surface topography and shear stress, based on a theoretical analysis of the precision in

  13. Magnitude of shear stress on the san andreas fault: implications of a stress measurement profile at shallow depth.

    Science.gov (United States)

    Zoback, M D; Roller, J C

    1979-10-26

    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 shortterm prediction of large earthquakes.

  14. Experimental determination of the stress/strain situation in a sheared tunnel model with canister

    International Nuclear Information System (INIS)

    Pusch, R.

    1978-03-01

    A previous report concerned a technical matter which could be of great importance as regards the mechanical strength of canisters embedded in a bentonite/quartz buffer mass, i.e. the effect of a differential movement triggered by a critical deviatoric stress condition. Even if this is extremely unlikeley to occur it was considered to be of importance to verify the theoretical expressions for the maximum bending moment and maximum shear force. A special reason was to test the hypothesis that the contact pressure would soon reach a high value and then stay fairly constant when the displacement increased. The theoretical approach requires that the stress/strain properties of the fill are thoroghly investigated and described in therms of a mathematical model. Experience shows that this may be a tedions and difficult task. (L.E.)

  15. Rac1 and Cdc42 GTPases regulate shear stress-driven β-catenin signaling in osteoblasts

    International Nuclear Information System (INIS)

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

    2013-01-01

    that both Rac1 and Cdc42 GTPases are critical regulators in shear stress-driven β-catenin signaling in osteoblasts

  16. Rac1 and Cdc42 GTPases regulate shear stress-driven β-catenin signaling in osteoblasts

    Energy Technology Data Exchange (ETDEWEB)

    Wan, Qiaoqiao; Cho, Eunhye [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 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)

    2013-04-19

    that both Rac1 and Cdc42 GTPases are critical regulators in shear stress-driven β-catenin signaling in osteoblasts.

  17. Contact stresses by rounded punch subject to axial and transverse shear

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Hyung Kyu [Korea Atomic Energy Research Institute, Taejon (Korea, Republic of)

    1999-05-01

    Contact shear stresses by rounded punch were evaluated numerically. Numerical program was successfully implemented by using an influence function method. To simulate the physical fretting problem, a closed load path of shear was considered. The influence functions on surface displacements fo both axial and transverse direction were calculated using a triangular shear traction element. Behaviour of the contact surface, such as stick and slip region during the load path was investigated together with compliance change. Irreversibility of the shear stress was shown. The importance and the utilization of the present research were discussed for analyzing the material failure induced by contact such as fretting wear and fatigue.

  18. Contact stresses by rounded punch subject to axial and transverse shear

    International Nuclear Information System (INIS)

    Kim, Hyung Kyu

    1999-01-01

    Contact shear stresses by rounded punch were evaluated numerically. Numerical program was successfully implemented by using an influence function method. To simulate the physical fretting problem, a closed load path of shear was considered. The influence functions on surface displacements fo both axial and transverse direction were calculated using a triangular shear traction element. Behaviour of the contact surface, such as stick and slip region during the load path was investigated together with compliance change. Irreversibility of the shear stress was shown. The importance and the utilization of the present research were discussed for analyzing the material failure induced by contact such as fretting wear and fatigue

  19. Generation of sheared poloidal flows via Reynolds stress and transport barrier physics

    International Nuclear Information System (INIS)

    Hidalgo, C.; Pedrosa, M.A.; Sanchez, E.; Balbin, R.; Lopez-Fraguas, A.; Milligen, B. van; Silva, C.; Fernandes, H.; Varandas, C.A.F.; Riccardi, C.; Carrozza, R.; Fontanesi, M.; Carreras, B.A.; Garcia, L.

    2000-01-01

    A view of the latest experimental results and progress in the understanding of the role of poloidal flows driven by fluctuations via Reynolds stress is given. Reynolds stress shows a radial gradient close to the velocity shear layer location in tokamaks and stellarators, indicating that this mechanism may drive significant poloidal flows in the plasma boundary. Observation of the generation of ExB sheared flows via Reynolds stress at the ion Bernstein resonance layer has been noticed in toroidal magnetized plasmas. The experimental evidence of sheared ExB flows linked to the location of rational surfaces in stellarator plasmas might be interpreted in terms of Reynolds stress sheared driven flows. These results show that ExB sheared flows driven by fluctuations can play an important role in the generation of transport barriers. (author)

  20. Repetitive Supra-Physiological Shear Stress Impairs Red Blood Cell Deformability and Induces Hemolysis.

    Science.gov (United States)

    Horobin, Jarod T; Sabapathy, Surendran; Simmonds, Michael J

    2017-11-01

    The supra-physiological shear stress that blood is exposed to while traversing mechanical circulatory assist devices affects the physical properties of red blood cells (RBCs), impairs RBC deformability, and may induce hemolysis. Previous studies exploring RBC damage following exposure to supra-physiological shear stress have employed durations exceeding clinical instrumentation, thus we explored changes in RBC deformability following exposure to shear stress below the reported "hemolytic threshold" using shear exposure durations per minute (i.e., duty-cycles) reflective of that employed by circulatory assist devices. Blood collected from 20 male donors, aged 18-38 years, was suspended in a viscous medium and exposed to an intermittent shear stress protocol of 1 s at 100 Pa, every 60 s for 60 duty-cycles. During the remaining 59 s/min, the cells were left at stasis until the subsequent duty-cycle commenced. At discrete time points (15/30/45/60 duty-cycles), an ektacytometer measured RBC deformability immediately after shear exposure at 100 Pa. Plasma-free hemoglobin, a measurement of hemolysis, was quantified via spectrophotometry. Supra-physiological shear stress impaired RBC properties, as indicated by: (1) decreased maximal elongation of RBCs at infinite shear stress following 15 duty-cycles (P supra-physiological shear stress protocol (100 Pa) following exposure to 1 duty-cycle (F (1.891, 32.15) = 12.21, P = 0.0001); and (3) increased plasma-free hemoglobin following 60 duty-cycles (P supra-physiological shear stress, impairs RBC deformability, with the extent of impairment exacerbated with each duty-cycle, and ultimately precipitates hemolysis. © 2017 International Center for Artificial Organs and Transplantation and Wiley Periodicals, Inc.

  1. Wall shear stress fixed points in cardiovascular fluid mechanics.

    Science.gov (United States)

    Arzani, Amirhossein; Shadden, Shawn C

    2018-05-17

    Complex blood flow in large arteries creates rich wall shear stress (WSS) vectorial features. WSS acts as a link between blood flow dynamics and the biology of various cardiovascular diseases. WSS has been of great interest in a wide range of studies and has been the most popular measure to correlate blood flow to cardiovascular disease. Recent studies have emphasized different vectorial features of WSS. However, fixed points in the WSS vector field have not received much attention. A WSS fixed point is a point on the vessel wall where the WSS vector vanishes. In this article, WSS fixed points are classified and the aspects by which they could influence cardiovascular disease are reviewed. First, the connection between WSS fixed points and the flow topology away from the vessel wall is discussed. Second, the potential role of time-averaged WSS fixed points in biochemical mass transport is demonstrated using the recent concept of Lagrangian WSS structures. Finally, simple measures are proposed to quantify the exposure of the endothelial cells to WSS fixed points. Examples from various arterial flow applications are demonstrated. Copyright © 2018 Elsevier Ltd. All rights reserved.

  2. Effects of flow unsteadiness on the wall shear stress

    International Nuclear Information System (INIS)

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

    2012-01-01

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

  3. Defective fluid shear stress mechanotransduction mediates hereditary hemorrhagic telangiectasia

    Science.gov (United States)

    Baeyens, Nicolas; Larrivée, Bruno; Ola, Roxana; Hayward-Piatkowskyi, Brielle; Dubrac, Alexandre; Huang, Billy; Ross, Tyler D.; Coon, Brian G.; Min, Elizabeth; Tsarfati, Maya; Tong, Haibin; Eichmann, Anne

    2016-01-01

    Morphogenesis of the vascular system is strongly modulated by mechanical forces from blood flow. Hereditary hemorrhagic telangiectasia (HHT) is an inherited autosomal-dominant disease in which arteriovenous malformations and telangiectasias accumulate with age. Most cases are linked to heterozygous mutations in Alk1 or Endoglin, receptors for bone morphogenetic proteins (BMPs) 9 and 10. Evidence suggests that a second hit results in clonal expansion of endothelial cells to form lesions with poor mural cell coverage that spontaneously rupture and bleed. We now report that fluid shear stress potentiates BMPs to activate Alk1 signaling, which correlates with enhanced association of Alk1 and endoglin. Alk1 is required for BMP9 and flow responses, whereas endoglin is only required for enhancement by flow. This pathway mediates both inhibition of endothelial proliferation and recruitment of mural cells; thus, its loss blocks flow-induced vascular stabilization. Identification of Alk1 signaling as a convergence point for flow and soluble ligands provides a molecular mechanism for development of HHT lesions. PMID:27646277

  4. 78 FR 38878 - Critical Incident Stress Plans

    Science.gov (United States)

    2013-06-28

    ... Institute (API); American Public Transportation Association (APTA); American Short Line and Regional...-0131, Notice No. 1] RIN 2130-AC00 Critical Incident Stress Plans AGENCY: Federal Railroad... incident stress plans that provide for appropriate support services to be offered to their employees who...

  5. The distribution of wall shear stress downstream of a change in roughness

    International Nuclear Information System (INIS)

    Loureiro, J.B.R.; Sousa, F.B.C.C.; Zotin, J.L.Z.; Silva Freire, A.P.

    2010-01-01

    In the present work, six different experimental techniques are used to characterize the non-equilibrium flow downstream of a rough-to-smooth step change in surface roughness. Over the rough surface, wall shear stress results obtained through the form drag and the Reynolds stress methods are shown to be mutually consistent. Over the smooth surface, reference wall shear stress data is obtained through two optical methods: linear velocity profiles obtained through laser-Doppler anemometry and a sensor surface, the diverging fringe Doppler sensor. The work shows that the two most commonly used methods to determine the wall shear stress, the log-law gradient method and the Reynolds shear stress method, are completely inappropriate in the developing flow region. Preston tubes, on the other hand, are shown to perform well in the region of a non-equilibrium flow.

  6. Fracture permeability under effect of normal and shear stress: A preliminary experimental investigation

    International Nuclear Information System (INIS)

    Mohanty, S.; Manteufel, R.D.; Chowdhury, A.H.

    1995-01-01

    The change in fracture permeability under mechanical loads have been investigated. An apparatus has been developed to measure change in fracture permeability, when a single fracture is subjected to normal and shear stress. Both radial and linear flow experiments have been conducted by modifying a direct shear test apparatus. Preliminary results suggest a 35-percent change in fracture permeability under normal stress to 8 MPa and nearly 350 percent under shear displacement of 9.9254 m (1 in.) at 5 MPa normal stress. Effort is underway to separate the permeability change due to gouge material production from that of due to dilation

  7. Evaluation of shear bond strength and shear stress on zirconia reinforced lithium silicate and high translucency zirconia.

    Directory of Open Access Journals (Sweden)

    Amanda Maria de Oliveira Dal Piva

    2018-01-01

    Full Text Available This study evaluated the shear stress distribution on the adhesive interface and the bond strength between resin cement and two ceramics. For finite element analysis (FEA, a tridimensional model was made using computer-aided design software. This model consisted of a ceramic slice (10x10x2mm partially embedded on acrylic resin with a resin cement cylinder (Ø=3.4 mm and h=3mm cemented on the external surface. Results of maximum principal stress and maximum principal shear were obtained to evaluate the stress generated on the ceramic and the cylinder surfaces. In order to reproduce the in vitro test, similar samples to the computational model were manufactured according to ceramic material (Zirconia reinforced lithium silicate - ZLS and high translucency Zirconia - YZHT, (N=48, n=12. Half of the specimens were submitted to shear bond test after 24h using a universal testing machine (0.5 mm/min, 50kgf until fracture. The other half was stored (a (180 days, water, 37ºC prior to the test. Bond strength was calculated in MPa and submitted to analysis of variance. The results showed that ceramic material influenced bond strength mean values (p=0.002, while aging did not: YZHT (19.80±6.44a, YZHTa (17.95±7.21a, ZLS (11.88±5.40b, ZLSa (11.76±3.32b. FEA results showed tensile and shear stress on ceramic and cylinder surfaces with more intensity on their periphery. Although the stress distribution was similar for both conditions, YZHT showed higher bond strength values; however, both materials seemed to promote durable bond strength.

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

    Science.gov (United States)

    Canto Maya, Christian M.

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

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

    Science.gov (United States)

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

    2017-08-01

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

  10. Laser reflection method for determination of shear stress in low density transitional flows

    Science.gov (United States)

    Sathian, Sarith P.; Kurian, Job

    2006-03-01

    The details of laser reflection method (LRM) for the determination of shear stress in low density transitional flows are presented. The method is employed to determine the shear stress due to impingement of a low density supersonic free jet issuing out from a convergent divergent nozzle on a flat plate. The plate is smeared with a thin oil film and kept parallel to the nozzle axis. For a 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 generated by the shear force is done using a position sensing detector (PSD). The thinning rate of the oil film is directly measured which is the major advantage of the LRM. From the oil film slope history, calculation of the shear stress is done using a three-point formula. The range of Knudsen numbers investigated is from 0.028 to 0.516. Pressure ratio across the nozzle varied from 3,500 to 8,500 giving highly under expanded free jets. The measured values of shear, in the overlapping region of experimental parameters, show fair agreement with those obtained by force balance method and laser interferometric method.

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

    Science.gov (United States)

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

    2018-02-01

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

  12. A thin rivulet or ridge subject to a uniform transverse shear stress at its free surface due to an external airflow

    KAUST Repository

    Sullivan, J. M.

    2012-01-01

    We use the lubrication approximation to analyze three closely related problems involving a thin rivulet or ridge (i.e., a two-dimensional droplet) of fluid subject to a prescribed uniform transverse shear stress at its free surface due to an external airflow, namely a rivulet draining under gravity down a vertical substrate, a rivulet driven by a longitudinal shear stress at its free surface, and a ridge on a horizontal substrate, and find qualitatively similar behaviour for all three problems. We show that, in agreement with previous numerical studies, the free surface profile of an equilibrium rivulet/ridge with pinned contact lines is skewed as the shear stress is increased from zero, and that there is a maximum value of the shear stress beyond which no solution with prescribed semi-width is possible. In practice, one or both of the contact lines will de-pin before this maximum value of the shear stress is reached, and so we consider situations in which the rivulet/ridge de-pins at one or both contact lines. In the case of de-pinning only at the advancing contact line, the rivulet/ridge is flattened and widened as the shear stress is increased from its critical value, and there is a second maximum value of the shear stress beyond which no solution with a prescribed advancing contact angle is possible. In contrast, in the case of de-pinning only at the receding contact line, the rivulet/ridge is thickened and narrowed as the shear stress is increased from its critical value, and there is a solution with a prescribed receding contact angle for all values of the shear stress. In general, in the case of de-pinning at both contact lines there is a critical "yield" value of the shear stress beyond which no equilibrium solution is possible and the rivulet/ridge will evolve unsteadily. In the Appendix, we show that an equilibrium rivulet/ridge with prescribed flux/area is quasi-statically stable to two-dimensional perturbations. © 2012 American Institute of Physics.

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

    DEFF Research Database (Denmark)

    Tuenter, A.; Selwaness, M.; Arias Lorza, A.

    2016-01-01

    estimating equations analysis, adjusting for age, sex and carotid wall thickness. RESULTS: The study group consisted of 93 atherosclerotic carotid arteries of 74 participants. In plaques with higher maximum shear stresses, IPH was more often present (OR per unit increase in maximum shear stress (log......BACKGROUND AND AIMS: Carotid artery plaques with vulnerable plaque components are related to a higher risk of cerebrovascular accidents. It is unknown which factors drive vulnerable plaque development. Shear stress, the frictional force of blood at the vessel wall, is known to influence plaque...... formation. We evaluated the association between shear stress and plaque components (intraplaque haemorrhage (IPH), lipid rich necrotic core (LRNC) and/or calcifications) in relatively small carotid artery plaques in asymptomatic persons. METHODS: Participants (n = 74) from the population-based Rotterdam...

  14. Measuring Shear Stress with a Microfluidic Sensor to improve Aerodynamic Efficiency, Phase I

    Data.gov (United States)

    National Aeronautics and Space Administration — Skin friction drag is directly proportional to the local shear stress of a surface and can be the largest factor in an aerodynamic body's total parasitic drag. The...

  15. Laminar shear stress inhibits endothelial cell metabolism via KLF2-mediated repression of PFKFB3

    NARCIS (Netherlands)

    Doddaballapur, Anuradha; Michalik, Katharina M.; Manavski, Yosif; Lucas, Tina; Houtkooper, Riekelt H.; You, Xintian; Chen, Wei; Zeiher, Andreas M.; Potente, Michael; Dimmeler, Stefanie; Boon, Reinier A.

    2015-01-01

    Cellular metabolism was recently shown to regulate endothelial cell phenotype profoundly. Whether the atheroprotective biomechanical stimulus elicited by laminar shear stress modulates endothelial cell metabolism is not known. Here, we show that laminar flow exposure reduced glucose uptake and

  16. Effect of tip clearance on wall shear stress of an axial LVAD

    Science.gov (United States)

    Sarath, S.; Vikas, R.

    2017-09-01

    Wall shear stress is a crucial parameter used for blood damage analysis, and typically a value of 400 Pa is set as a limit. Tip clearance is a major factor contributing to hemolysis and pump efficiency. In this study, different tip gap configurations are used to analyse the wall shear stress developed on the blade surface of a constant thickness blade design, and a varying thickness blade design using CFD analysis. It was found that, for a particular geometry, as the clearance gap reduces, flow rate over the high wall shear stress area decreases even though the high wall shear stress span is found to extend. For each design, the optimum clearance gap is iteratively attained, keeping the maximum WSS as a limiting factor. Thus a better pump designs is obtained, whose leakage flow patterns are lower than that of the initial design, hence also leading to higher pump efficiency.

  17. Endothelial shear stress estimation in the human carotid artery based on Womersley versus Poiseuille flow

    NARCIS (Netherlands)

    Schwarz, Janina C. V.; Duivenvoorden, Raphaël; Nederveen, Aart J.; Stroes, Erik S. G.; VanBavel, Ed

    2015-01-01

    Endothelial shear stress (ESS) dynamics are a major determinant of atherosclerosis development. The frequently used Poiseuille method to estimate ESS dynamics has important limitations. Therefore, we investigated whether Womersley flow may provide a better alternative for estimation of ESS while

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

    Science.gov (United States)

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

    2015-07-01

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

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

    Science.gov (United States)

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

    2009-08-15

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

  20. Self-organized criticality in a sheared granular stick-slip system

    International Nuclear Information System (INIS)

    Dalton, Fergal; Corcoran, David

    2001-01-01

    We present an analysis of results obtained from a mechanical apparatus consisting of an annular plate shearing over a granular bed. The size, energy dissipation, and duration of slips in the system exhibit power-law distributions and a 1/f 2 power spectrum, in accordance with self-organized criticality. We draw similarities with earthquakes

  1. Structure of high and low shear-stress events in a turbulent boundary layer

    Science.gov (United States)

    Gomit, G.; de Kat, R.; Ganapathisubramani, B.

    2018-01-01

    Simultaneous particle image velocimetry (PIV) and wall-shear-stress sensor measurements were performed to study structures associated with shear-stress events in a flat plate turbulent boundary layer at a Reynolds number Reτ≈4000 . The PIV field of view covers 8 δ (where δ is the boundary layer thickness) along the streamwise direction and captures the entire boundary layer in the wall-normal direction. Simultaneously, wall-shear-stress measurements that capture the large-scale fluctuations were taken using a spanwise array of hot-film skin-friction sensors (spanning 2 δ ). Based on this combination of measurements, the organization of the conditional wall-normal and streamwise velocity fluctuations (u and v ) and of the Reynolds shear stress (-u v ) can be extracted. Conditional averages of the velocity field are computed by dividing the histogram of the large-scale wall-shear-stress fluctuations into four quartiles, each containing 25% of the occurrences. The conditional events corresponding to the extreme quartiles of the histogram (positive and negative) predominantly contribute to a change of velocity profile associated with the large structures and in the modulation of the small scales. A detailed examination of the Reynolds shear-stress contribution related to each of the four quartiles shows that the flow above a low wall-shear-stress event carries a larger amount of Reynolds shear stress than the other quartiles. The contribution of the small and large scales to this observation is discussed based on a scale decomposition of the velocity field.

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

    International Nuclear Information System (INIS)

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

    2006-01-01

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

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

    Science.gov (United States)

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

    2009-05-01

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

  4. Bone morphogenic protein 4 produced in endothelial cells by oscillatory shear stress stimulates an inflammatory response

    Science.gov (United States)

    Sorescu, George P.; Sykes, Michelle; Weiss, Daiana; Platt, Manu O.; Saha, Aniket; Hwang, Jinah; Boyd, Nolan; Boo, Yong C.; Vega, J. David; Taylor, W. Robert; hide

    2003-01-01

    Atherosclerosis is now viewed as an inflammatory disease occurring preferentially in arterial regions exposed to disturbed flow conditions, including oscillatory shear stress (OS), in branched arteries. In contrast, the arterial regions exposed to laminar shear (LS) are relatively lesion-free. The mechanisms underlying the opposite effects of OS and LS on the inflammatory and atherogenic processes are not clearly understood. Here, through DNA microarrays, protein expression, and functional studies, we identify bone morphogenic protein 4 (BMP4) as a mechanosensitive and pro-inflammatory gene product. Exposing endothelial cells to OS increased BMP4 protein expression, whereas LS decreased it. In addition, we found BMP4 expression only in the selective patches of endothelial cells overlying foam cell lesions in human coronary arteries. The same endothelial patches also expressed higher levels of intercellular cell adhesion molecule-1 (ICAM-1) protein compared with those of non-diseased areas. Functionally, we show that OS and BMP4 induced ICAM-1 expression and monocyte adhesion by a NFkappaB-dependent mechanism. We suggest that BMP4 is a mechanosensitive, inflammatory factor playing a critical role in early steps of atherogenesis in the lesion-prone areas.

  5. Orbital fluid shear stress promotes osteoblast metabolism, proliferation and alkaline phosphates activity in vitro

    Energy Technology Data Exchange (ETDEWEB)

    Aisha, M.D. [Institute of Medical Molecular Biotechnology and Faculty of Medicine, Universiti Teknologi MARA, Sungai Buloh 47000, Selangor (Malaysia); Nor-Ashikin, M.N.K. [Institute of Medical Molecular Biotechnology and Faculty of Medicine, Universiti Teknologi MARA, Sungai Buloh 47000, Selangor (Malaysia); DDH, Universiti Teknologi MARA, ShahAlam 40450, Selangor (Malaysia); Sharaniza, A.B.R. [DDH, Universiti Teknologi MARA, ShahAlam 40450, Selangor (Malaysia); Nawawi, H. [Center for Pathology Diagnostic and Research Laboratories, Clinical Training Center, Universiti Teknologi MARA, Sungai Buloh 47000, Selangor (Malaysia); I-PPerForM, Universiti Teknologi MARA, Selayang 47000 Selangor (Malaysia); Froemming, G.R.A., E-mail: gabriele@salam.uitm.edu.my [Institute of Medical Molecular Biotechnology and Faculty of Medicine, Universiti Teknologi MARA, Sungai Buloh 47000, Selangor (Malaysia); I-PPerForM, Universiti Teknologi MARA, Selayang 47000 Selangor (Malaysia)

    2015-09-10

    Prolonged disuse of the musculoskeletal system is associated with reduced mechanical loading and lack of anabolic stimulus. As a form of mechanical signal, the multidirectional orbital fluid shear stress transmits anabolic signal to bone forming cells in promoting cell differentiation, metabolism and proliferation. Signals are channeled through the cytoskeleton framework, directly modifying gene and protein expression. For that reason, we aimed to study the organization of Normal Human Osteoblast (NHOst) cytoskeleton with regards to orbital fluid shear (OFS) stress. Of special interest were the consequences of cytoskeletal reorganization on NHOst metabolism, proliferation, and osteogenic functional markers. Cells stimulated at 250 RPM in a shaking incubator resulted in the rearrangement of actin and tubulin fibers after 72 h. Orbital shear stress increased NHOst mitochondrial metabolism and proliferation, simultaneously preventing apoptosis. The ratio of RANKL/OPG was reduced, suggesting that orbital shear stress has the potential to inhibit osteoclastogenesis and osteoclast activity. Increase in ALP activity and OCN protein production suggests that stimulation retained osteoblast function. Shear stress possibly generated through actin seemed to hold an anabolic response as osteoblast metabolism and functional markers were enhanced. We hypothesize that by applying orbital shear stress with suitable magnitude and duration as a non-drug anabolic treatment can help improve bone regeneration in prolonged disuse cases. - Highlights: • OFS stress transmits anabolic signals to osteoblasts. • Actin and tubulin fibers are rearranged under OFS stress. • OFS stress increases mitochondrial metabolism and proliferation. • Reduced RANKL/OPG ratio in response to OFS inhibits osteoclastogenesis. • OFS stress prevents apoptosis and stimulates ALP and OCN.

  6. On equivalent roughness of mobile bed at high shear stress

    Czech Academy of Sciences Publication Activity Database

    Matoušek, Václav; Krupička, Jan

    2009-01-01

    Roč. 57, č. 3 (2009), s. 191-199 ISSN 0042-790X R&D Projects: GA ČR GA103/06/0428 Institutional research plan: CEZ:AV0Z20600510 Keywords : bed shear * experiment * hydraulic transport * sediment transport Subject RIV: BK - Fluid Dynamics Impact factor: 1.000, year: 2009

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

    International Nuclear Information System (INIS)

    Ulfhammer, Erik; Carlstroem, Maria; Bergh, Niklas; Larsson, Pia; Karlsson, Lena; Jern, Sverker

    2009-01-01

    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 2 ) or high (25 dyn/cm 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.

  8. Pressure-induced forces and shear stresses on rubble mound breakwater armour layers in regular waves

    DEFF Research Database (Denmark)

    Jensen, Bjarne; Christensen, Erik Damgaard; Sumer, B. Mutlu

    2014-01-01

    This paper presents the results from an experimental investigation of the pressure-induced forces in the core material below the main armour layer and shear stresses on the armour layer for a porous breakwater structure. Two parallel experiments were performed which both involved pore pressure...... structure i.e. no additional filter layers were applied. For both experiments, high-speed video recordings were synchronised with the pressure measurements for a detailed investigation of the coupling between the run-up and run-down flow processes and the measured pressure variations. Outward directed...... and turbulence measurements showed that the large outward directed pressure gradients in general coincide, both in time and space, with the maximum bed-shear stresses on the armour layer based on the Reynolds-stresses. The bed-shear stresses were found to result in a Shields parameter in the same order...

  9. Effect of stress-state and spacing on voids in a shear-field

    DEFF Research Database (Denmark)

    Tvergaard, Viggo

    2012-01-01

    in the overall average stress state can be prescribed. This also allows for studies of the effect of different initial void spacing in the two in-plane coordinate directions. The stress states considered are essentially simple shear, with various levels of tensile stresses or compressive stresses superposed, i.......e. low positive stress triaxiality or even negative stress triaxiality. For high aspect ratio unit cells a clear localization band is found inside the cell, which actually represents several parallel bands, due to periodicity. In the materials represented by a low aspect ratio unit cell localization...

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

    Science.gov (United States)

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

    2013-09-20

    Technical scale (≥5l) cultivations of shear stress sensitive microorganisms are often difficult to perform, as common bioreactors are usually designed to maximize the oxygen input into the culture medium. This is achieved by mechanical stirrers, causing high shear stress. Examples for shear stress sensitive microorganisms, for which no specific cultivation systems exist, are many anaerobic bacteria and fungi, such as basidiomycetes. In this work a disposable bag bioreactor developed for cultivation of mammalian cells was investigated to evaluate its potential to cultivate shear stress sensitive anaerobic Eubacterium ramulus and shear stress sensitive basidiomycetes Flammulina velutipes and Pleurotus sapidus. All cultivations were compared with conventional stainless steel stirred tank reactors (STR) cultivations. Good growth of all investigated microorganisms cultivated in the bag reactor was found. E. ramulus showed growth rates of μ=0.56 h⁻¹ (bag) and μ=0.53 h⁻¹ (STR). Differences concerning morphology, enzymatic activities and growth in fungal cultivations were observed. In the bag reactor growth in form of small, independent pellets was observed while STR cultivations showed intense aggregation. F. velutipes reached higher biomass concentrations (21.2 g l⁻¹ DCW vs. 16.8 g l⁻¹ DCW) and up to 2-fold higher peptidolytic activities in comparison to cell cultivation in stirred tank reactors. Copyright © 2013 Elsevier B.V. All rights reserved.

  11. Development of generalized correlation equation for the local wall shear stress

    International Nuclear Information System (INIS)

    Jeon, Yu Mi; Bae, Jun Ho; Park, Joo Hwan

    2010-01-01

    The pressure drop characteristics for a fuel channel are essential for the design and reliable operation of a nuclear reactor. Over several decades, analytical methods have been developed to predict the friction factor in the fuel bundle flows. In order to enhance the accuracy of prediction for the pressure drop in a rod bundle, the influences of a channel wall and the local shear stress distribution should be considered. Hence, the correlation equation for a local shear stress distribution should be developed in order to secure an analytical solution for the friction factor of a rod bundle. For a side subchannel, which has the influence of the channel wall, the local shear stress distribution is dependent on the ratio of wall to diameter (W/D) as well as the ratio of pitch to diameter (P/D). In the case that W/D has the same value with P/D, the local shear stress distribution can be simply correlated with the function of angular position for each value of P/D. While, in the case that W/D has the different value with P/D, the correlation equation should be developed for each case of P/D and W/D. Hence, in the present study, the generalized correlation equation of a local shear stress distribution is developed for a side subchannel in the case that W/D has the different value with P/D

  12. Correlation between vortices and wall shear stress in a curved artery model under pulsatile flow conditions

    Science.gov (United States)

    Cox, Christopher; Plesniak, Michael W.

    2017-11-01

    One of the most physiologically relevant factors within the cardiovascular system is the wall shear stress. The wall shear stress affects endothelial cells via mechanotransduction and atherosclerotic regions are strongly correlated with curvature and branching in the human vasculature, where the shear stress is both oscillatory and multidirectional. Also, the combined effect of curvature and pulsatility in cardiovascular flows produces unsteady vortices. In this work, our goal is to assess the correlation between multiple vortex pairs and wall shear stress. To accomplish this, we use an in-house high-order flux reconstruction Navier-Stokes solver to simulate pulsatile flow of a Newtonian blood-analog fluid through a rigid 180° curved artery model. We use a physiologically relevant flow rate and generate results using both fully developed and uniform entrance conditions, the latter motivated by the fact that flow upstream to a curved artery may not be fully developed. Under these two inflow conditions, we characterize the evolution of various vortex pairs and their subsequent effect on several wall shear stress metrics. Supported by GW Center for Biomimetics and Bioinspired Engineering.

  13. Velocity and shear stress distribution downstream of mechanical heart valves in pulsatile flow.

    Science.gov (United States)

    Giersiepen, M; Krause, U; Knott, E; Reul, H; Rau, G

    1989-04-01

    Ten mechanical valves (TAD 27 mm): Starr-Edwards Silastic Ball, Björk-Shiley Standard, Björk-Shiley Concave-Convex, Björk-Shiley Monostrut, Hall-Kaster (Medtronic-Hall), OmniCarbon, Bicer Val, Sorin, Saint-Jude Medical and Hemex (Duromedics) are investigated in a comparative in vitro study. The velocity and turbulent shear stress profiles of the valves were determined by Laser Doppler anemometry in two different downstream axes within a model aortic root. Depending on the individual valve design, velocity peaks up to 1.5 m/s and turbulent shear stress peaks up to 150 N/m2 were measured during the systolic phase. These shear stress peaks mainly occurred in areas of flow separation and intense momentum exchange. Directly downstream of the valves (measuring axis 0.55.dAorta) turbulent shear stress peaks occurred at peak systole and during the deceleration phase, while in the second measuring axis (1.5.dAorta) turbulence levels were lower. Shear stress levels were high at the borders of the fluid jets. The results are discussed from a fluid-dynamic point of view.

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

    International Nuclear Information System (INIS)

    Abe, Yutaka; Akimoto, Hajime; Murao, Yoshio

    1991-01-01

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

  15. Large scale structures in a turbulent boundary layer and their imprint on wall shear stress

    Science.gov (United States)

    Pabon, Rommel; Barnard, Casey; Ukeiley, Lawrence; Sheplak, Mark

    2015-11-01

    Experiments were performed on a turbulent boundary layer developing on a flat plate model under zero pressure gradient flow. A MEMS differential capacitive shear stress sensor with a 1 mm × 1 mm floating element was used to capture the fluctuating wall shear stress simultaneously with streamwise velocity measurements from a hot-wire anemometer traversed in the wall normal direction. Near the wall, the peak in the cross correlation corresponds to an organized motion inclined 45° from the wall. In the outer region, the peak diminishes in value, but is still significant at a distance greater than half the boundary layer thickness, and corresponds to a structure inclined 14° from the wall. High coherence between the two signals was found for the low-frequency content, reinforcing the belief that large scale structures have a vital impact on wall shear stress. Thus, estimation of the wall shear stress from the low-frequency velocity signal will be performed, and is expected to be statistically significant in the outer boundary layer. Additionally, conditionally averaged mean velocity profiles will be presented to assess the effects of high and low shear stress. This material is based upon work supported by the National Science Foundation Graduate Research Fellowship under Grant No. DGE-1315138.

  16. Hydrodynamic Study of a Hollow Fiber Membrane System Using Experimental and Numerical Derived Surface Shear Stresses

    DEFF Research Database (Denmark)

    Ratkovich, Nicolas Rios; Hunze, M.; Nopens, I.

    2012-01-01

    .39 – 0.69 Pa) were in good agreement, with an error less that 15 %. Based on comparison of the cumulative frequency distribution of shear stresses from experiments and simulation: (i) moderate shear stresses (i.e. 50th percentile) were found to be accurately predicted (model: 0.24 – 0.45 Pa; experimental......Computational Fluids Dynamics (CFD) models can be used to gain insight into the shear stresses induced by air sparging on submerged hollow fiber Membrane BioReactor (MBR) systems. It was found that the average range of shear stresses obtained by the CFD model (0.30 – 0.60 Pa) and experimentally (0......: 0.25 – 0.49 Pa) with an error of less than 5 %; (ii) high shear stresses (i.e. 90th percentile) predictions were much less accurate (model: 0.60 – 1.23 Pa; experimental: 1.04 – 1.90 Pa) with an error up to 38 %. This was attributed to the fact that the CFD model only considers the two-phase flow (50...

  17. Direct measurement of wall shear stress in a reattaching flow with a photonic sensor

    International Nuclear Information System (INIS)

    Ayaz, U K; Ioppolo, T; Ötügen, M V

    2013-01-01

    Wall shear stress measurements are carried out in a planar backward-facing step flow using a micro-optical sensor. The sensor is essentially a floating element system and measures the shear stress directly. The transduction method to measure the floating element deflection is based on the whispering gallery optical mode (WGM) shifts of a dielectric microsphere. This method is capable of measuring floating element displacements of the order of a nanometer. The floating element surface is circular with a diameter of ∼960 µm, which is part of a beam that is in contact with the dielectric microsphere. The sensor is calibrated for shear stress as well as pressure sensitivity yielding 7.3 pm Pa −1 and 0.0236 pm Pa −1 for shear stress and pressure sensitivity, respectively. Hence, the contribution by the wall pressure is less than two orders of magnitude smaller than that of shear stress. Measurements are made for a Reynolds number range of 2000–5000 extending to 18 step heights from the step face. The results are in good agreement with those of earlier reports. An analysis is also carried out to evaluate the performance of the WGM sensor including measurement sensitivity and bandwidth. (paper)

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

    Science.gov (United States)

    Kumar, Amit; Higdon, Jonathan J L

    2010-11-01

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

  19. Factors Associated With Callus in Patients with Diabetes, Focused on Plantar Shear Stress During Gait.

    Science.gov (United States)

    Hamatani, Masako; Mori, Taketoshi; Oe, Makoto; Noguchi, Hiroshi; Takehara, Kimie; Amemiya, Ayumi; Ohashi, Yumiko; Ueki, Kohjiro; Kadowaki, Takashi; Sanada, Hiromi

    2016-11-01

    The aim of this study is to identify whether plantar shear stress in neuropathic patients with diabetes with callus is increased compared with those without callus. The differences in foot deformity, limited joint mobility, repetitive stress of walking, and ill-fitting shoes between patients with callus and those without callus were also determined. Subjects were recruited from the Diabetic Foot Outpatient Clinic. A newly developed in-shoe measurement system, which has flexible and thin insoles, enabled measurement of both plantar pressure and shear stress simultaneously when subjects walked as usual on a 10 m walkway. It was found that plantar shear stress adjusted for weight during the push-off phase was increased by 1.32 times in patients with callus compared with those without callus (mean ± SD: 0.0500 ± 0.0160 vs 0.0380 ± 0.0144, P = .031). Moreover, hallux valgus deformity, reduction in dorsiflexion of the ankle joint and increase in plantar flexion were showed in feet with callus. Increased plantar shear stress may be caused by gait change that patients having callus push off with the metatarsal head instead of the toe as a result of foot deformity and limited joint mobility. It was found that plantar shear stress adjusted for weight during the push-off phase was increased in patients with callus compared with those without callus by using the newly developed measurement system. These results suggest that reduction of plantar shear stress during the push-off phase can prevent callus formation in neuropathic patients with diabetes. © 2016 Diabetes Technology Society.

  20. Exercise-mediated wall shear stress increases mitochondrial biogenesis in vascular endothelium.

    Directory of Open Access Journals (Sweden)

    Boa Kim

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

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

    Science.gov (United States)

    Chen, Andrew; Schumacher, Thomas

    2014-02-01

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

  2. Theory and Practice of Shear/Stress Strain Gage Hygrometry

    Science.gov (United States)

    Shams, Qamar A.; Fenner, Ralph L.

    2006-01-01

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

  3. A film-based wall shear stress sensor for wall-bounded turbulent flows

    Science.gov (United States)

    Amili, Omid; Soria, Julio

    2011-07-01

    In wall-bounded turbulent flows, determination of wall shear stress is an important task. The main objective of the present work is to develop a sensor which is capable of measuring surface shear stress over an extended region applicable to wall-bounded turbulent flows. This sensor, as a direct method for measuring wall shear stress, consists of mounting a thin flexible film on the solid surface. The sensor is made of a homogeneous, isotropic, and incompressible material. The geometry and mechanical properties of the film are measured, and particles with the nominal size of 11 μm in diameter are embedded on the film's surface to act as markers. An optical technique is used to measure the film deformation caused by the flow. The film has typically deflection of less than 2% of the material thickness under maximum loading. The sensor sensitivity can be adjusted by changing the thickness of the layer or the shear modulus of the film's material. The paper reports the sensor fabrication, static and dynamic calibration procedure, and its application to a fully developed turbulent channel flow at Reynolds numbers in the range of 90,000-130,000 based on the bulk velocity and channel full height. The results are compared to alternative wall shear stress measurement methods.

  4. A Multi-Phase Based Fluid-Structure-Microfluidic interaction sensor for Aerodynamic Shear Stress

    Science.gov (United States)

    Hughes, Christopher; Dutta, Diganta; Bashirzadeh, Yashar; Ahmed, Kareem; Qian, Shizhi

    2014-11-01

    A novel innovative microfluidic shear stress sensor is developed for measuring shear stress through multi-phase fluid-structure-microfluidic interaction. The device is composed of a microfluidic cavity filled with an electrolyte liquid. Inside the cavity, two electrodes make electrochemical velocimetry measurements of the induced convection. The cavity is sealed with a flexible superhydrophobic membrane. The membrane will dynamically stretch and flex as a result of direct shear cross-flow interaction with the seal structure, forming instability wave modes and inducing fluid motion within the microfluidic cavity. The shear stress on the membrane is measured by sensing the induced convection generated by membrane deflections. The advantages of the sensor over current MEMS based shear stress sensor technology are: a simplified design with no moving parts, optimum relationship between size and sensitivity, no gaps such as those created by micromachining sensors in MEMS processes. We present the findings of a feasibility study of the proposed sensor including wind-tunnel tests, microPIV measurements, electrochemical velocimetry, and simulation data results. The study investigates the sensor in the supersonic and subsonic flow regimes. Supported by a NASA SBIR phase 1 contract.

  5. Molecular characteristics of stress overshoot for polymer melts under start-up shear flow.

    Science.gov (United States)

    Jeong, Sohdam; Kim, Jun Mo; Baig, Chunggi

    2017-12-21

    Stress overshoot is one of the most important nonlinear rheological phenomena exhibited by polymeric liquids undergoing start-up shear at sufficient flow strengths. Despite considerable previous research, the fundamental molecular characteristics underlying stress overshoot remain unknown. Here, we analyze the intrinsic molecular mechanisms behind the overshoot phenomenon using atomistic nonequilibrium molecular dynamics simulations of entangled linear polyethylene melts under shear flow. Through a detailed analysis of the transient rotational chain dynamics, we identify an intermolecular collision angular regime in the vicinity of the chain orientation angle θ ≈ 20° with respect to the flow direction. The shear stress overshoot occurs via strong intermolecular collisions between chains in the collision regime at θ = 15°-25°, corresponding to a peak strain of 2-4, which is an experimentally well-known value. The normal stress overshoot appears at approximately θ = 10°, at a corresponding peak strain roughly equivalent to twice that for the shear stress. We provide plausible answers to several basic questions regarding the stress overshoot, which may further help understand other nonlinear phenomena of polymeric systems.

  6. Development of Generalized Correlation Equation for the Local Wall Shear Stress

    International Nuclear Information System (INIS)

    Jeon, Yu Mi; Park, Ju Hwan

    2010-06-01

    The pressure drop characteristics for a fuel channel are essential for the design and reliable operation of a nuclear reactor. Over several decades, analytical methods have been developed to predict the friction factor in the fuel bundle flows. In order to enhance the accuracy of prediction for the pressure drop in a rod bundle, the influences of a channel wall and the local shear stress distribution should be considered. Therefore, the correlation equation for a local wall shear stress distribution should be developed in order to secure an analytical solution for the friction factor of a rod bundle. For a side subchannel, which has the influence of the channel wall, the local wall shear stress distribution is dependent on the ratio of wall to diameter (W/D) as well as the ratio of pitch to diameter (P/D). In the case that W/D has the same value with P/D, the local shear stress distribution can be simply correlated with the function of angular position for each value of P/D. While in the case where W/D has a different value than P/D, the correlation equation should be developed for each case of P/D and W/D. Therefore, in the present study, the generalized correlation equation of the local wall shear stress distribution was developed for a side subchannel in the case where W/D has a different value than P/D. Consequently, the generalized correlation equation of a local wall shear stress distribution can be represented by the equivalent pitch to diameter ratio, P'/D for the case that P/D and W/D had a different value

  7. Statistical properties of wall shear stress fluctuations in turbulent channel flows

    International Nuclear Information System (INIS)

    Keirsbulck, L.; Labraga, L.; Gad-el-Hak, M.

    2012-01-01

    Highlights: ► Accurate measurements of instantaneous wall shear stress are conducted. ► LDA is used to measure near-wall streamwise velocity. ► Electrochemical probe is used to measure wall shear stress. ► Frequency response and non-uniform correction methods were used to provide an accurate, well-resolved wall-statistics database. ► Reynolds number dependency of the statistical wall quantities is investigated. - Abstract: Instantaneous velocity and wall shear stress measurements are conducted in a turbulent channel flow in the Kármán number range of Re τ = 74–400. A one-dimensional LDA system is used to measure the streamwise velocity fluctuations, and an electrochemical technique is utilized to measure the instantaneous wall shear stress. For the latter, frequency response and nonuniform correction methods are used to provide an accurate, well-resolved wall statistics database. The Reynolds number dependency of the statistical wall quantities is carefully investigated. The corrected relative wall shear stress fluctuations fit well with the best DNS data available and meet the need for clarification of the small discrepancy observed in the literature between the experimental and numerical results of such quantities. Higher-order statistics of the wall shear stress, spectra, and the turbulence kinetic energy budget at the wall are also investigated. The present paper shows that the electrochemical technique is a powerful experimental method for hydrodynamic studies involving highly unsteady flows. The study brings with it important consequences, especially in the context of the current debate regarding the appropriate scaling as well as the validation of new predictive models of near-wall turbulence.

  8. Computational and experimental assessment of influences of hemodynamic shear stress on carotid plaque.

    Science.gov (United States)

    Zhou, Hui; Meng, Long; Zhou, Wei; Xin, Lin; Xia, Xiangxiang; Li, Shuai; Zheng, Hairong; Niu, Lili

    2017-07-29

    Studies have identified hemodynamic shear stress as an important determinant of endothelial function and atherosclerosis. In this study, we assess the influences of hemodynamic shear stress on carotid plaques. Carotid stenosis phantoms with three severity (30, 50, 70%) were made from 10% polyvinyl alcohol (PVA) cryogel. The phantoms were placed in a pulsatile flow loop with the same systolic/diastolic phase (35/65) and inlet flow rate (16 L/h). Ultrasonic particle imaging velocimetry (Echo PIV) and computational fluid dynamics (CFD) were used to calculate the velocity profile and shear stress distribution in the carotid stenosis phantoms. Inlet/outlet boundary conditions used in CFD were extracted from Echo PIV experiments to make sure that the results were comparable. Echo PIV and CFD results showed that velocity was largest in 70% than those in 30 and 50% at peak systole. Echo PIV results indicated that shear stress was larger in the upper wall and the surface of plaque than in the center of vessel. CFD results demonstrated that wall shear stress in the upstream was larger than in downstream of plaque. There was no significant difference in average velocity obtained by CFD and Echo PIV in 30% (p = 0.25). Velocities measured by CFD in 50% (93.01 cm/s) and in 70% (115.07 cm/s) were larger than those by Echo PIV in 50% (60.26 ± 5.36 cm/s) and in 70% (89.11 ± 7.21 cm/s). The results suggested that Echo PIV and CFD could obtain hemodynamic shear stress on carotid plaques. Higher WSS occurred in narrower arteries, and the shoulder of plaque bore higher WSS than in bottom part.

  9. Measurement and analysis of flow wall shear stress in an interior subchannel of triangular array rods

    International Nuclear Information System (INIS)

    Fakori-Monazah, M.R.; Todreas, N.E.

    1977-08-01

    A simulated model of triangular array rods with pitch to diameter ratio of 1.10 (as a test section) and air as the fluid flow was used to study the LMFBR hydraulic parameters. The wall shear stress distribution around the rod periphery, friction factors, static pressure distributions and turbulence intensity corresponding to various Reynolds numbers ranging from 4140 to 36170 in the central subchannel were measured. Various approaches for measurement of wall shear stress were compared. The measurement was performed using the Preston tube technique with the probe outside diameter equal to 0.014 in

  10. Yield shear stress model of magnetorheological fluids based on exponential distribution

    International Nuclear Information System (INIS)

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

    2014-01-01

    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 Fe 3 O 4 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. - Highlights: • A yield shear stress model of magnetorheological fluids was proposed. • Use exponential distribution to describe the distribution of magnetic chain angles. • Experimental and predicted results were in good agreement for 2 types of MR

  11. NK cell recruitment and exercise: Potential immunotherapeutic role of shear stress and endothelial health.

    Science.gov (United States)

    Evans, William

    2017-11-01

    Positive cancer patient outcomes, including increased time to recurrent events, have been associated with increased counts and function of natural killer (NK) cells. NK cell counts and function are elevated following acute exercise, and the generally accepted mechanism of increased recruitment suggests that binding of epinephrine releases NK cells from endothelial tissue via decreases in adhesion molecules following. I propose that blood flow-induced shear stress may also play a role in NK cell recruitment from the endothelium. Additionally, shear stress may play a role in improving NK cell function by decreasing oxidative stress. The relationship between shear stress and NK cell count and function can be tested by utilizing exercise and local heating with cuff inflation. If shear stress does play an important role, NK cell count and function will be improved in the non-cuffed exercise group, but not the cuffed limb. This paper will explore the mechanisms potentially explaining exercise-induced improvements in NK cell count and function, and propose a model for investigating these mechanisms. This mechanistic insight could aid in providing a novel, safe, relatively inexpensive, and non-invasive target for immunotherapy in cancer patients. Copyright © 2017. Published by Elsevier Ltd.

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

    Science.gov (United States)

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

    2015-04-20

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

  13. Non-Newtonian stress tensor and thermal conductivity tensor in granular plane shear flow

    Science.gov (United States)

    Alam, Meheboob; Saha, Saikat

    2014-11-01

    The non-Newtonian stress tensor and the heat flux in the plane shear flow of smooth inelastic disks are analysed from the Grad-level moment equations using the anisotropic Gaussian as a reference. Closed-form expressions for shear viscosity, pressure, first normal stress difference (N1) and the dissipation rate are given as functions of (i) the density or the area fraction (ν), (ii) the restitution coefficient (e), (iii) the dimensionless shear rate (R), (iv) the temperature anisotropy [ η, the difference between the principal eigenvalues of the second moment tensor] and (v) the angle (ϕ) between the principal directions of the shear tensor and the second moment tensor. Particle simulation data for a sheared hard-disk system is compared with theoretical results, with good agreement for p, μ and N1 over a large range of density. In contrast, the predictions from a Navier-Stokes order constitutive model are found to deviate significantly from both the simulation and the moment theory even at moderate values of e. We show that the gradient of the deviatoric part of the kinetic stress drives a heat current and the thermal conductivity is characterized by an anisotropic 2nd rank tensor for which explicit expressions are derived.

  14. Critical undrained shear strength of sand-silt mixtures under monotonic loading

    Directory of Open Access Journals (Sweden)

    Mohamed Bensoula

    2014-07-01

    Full Text Available This study uses experimental triaxial tests with monotonic loading to develop empirical relationships to estimate undrained critical shear strength. The effect of the fines content on undrained shear strength is analyzed for different density states. The parametric analysis indicates that, based on the soil void ratio and fine content properties, the undrained critical shear strength first increases and then decreases as the proportion of fines increases, which demonstrates the influence of fine content on a soil’s vulnerability to liquefaction. A series of monotonic undrained triaxial tests were performed on reconstituted saturated sand-silt mixtures. Beyond 30% fines content, a fraction of the silt participates in the soil’s skeleton chain force. In this context, the concept of the equivalent intergranular void ratio may be an appropriate parameter to express the critical shear strength of the studied soil. This parameter is able to control the undrained shear strength of non-plastic silt and sand mixtures with different densities.   Resumen Este estudio utiliza evaluaciones experimentales triaxiales con cargas repetitivas para desarrollar relaciones empíricas y estimar la tensión crítica de corte bajo condiciones no drenadas. El efecto de contenido de finos en la tensión de corte sin drenar se analizó en diferentes estados de densidad. El análisis paramétrico indica que, basado en la porosidad del suelo y las propiedades del material de finos, la tensión de corte sin drenar primero se incrementa y luego decrece mientras la proporción de finos aumenta, lo que demuestra la influencia de contenido de finos en la vulnerabilidad del suelo a la licuación. Una serie de las evaluaciones se realizó en  mezclas rehidratadas y saturadas de arena y cieno. Más allá del 30 % de los contenidos finos, una fracción del cieno hace parte principal de la cadena de fuerza del suelo. En este contexto, el concepto de porosidad equivalente

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

    Science.gov (United States)

    Westenbroek, Stephen M.

    2006-01-01

    Turbulent shear stress in the boundary layer of a natural river system largely controls the deposition and resuspension of sediment, as well as the longevity and effectiveness of granular-material caps used to cover and isolate contaminated sediments. This report documents measurements and calculations made in order to estimate shear stress and shear velocity on the Lower Fox River, Wisconsin. Velocity profiles were generated using an acoustic Doppler current profiler (ADCP) mounted on a moored vessel. This method of data collection yielded 158 velocity profiles on the Lower Fox River between June 2003 and November 2004. Of these profiles, 109 were classified as valid and were used to estimate the bottom shear stress and velocity using log-profile and turbulent kinetic energy methods. Estimated shear stress ranged from 0.09 to 10.8 dynes per centimeter squared. Estimated coefficients of friction ranged from 0.001 to 0.025. This report describes both the field and data-analysis methods used to estimate shear-stress parameters for the Lower Fox River. Summaries of the estimated values for bottom shear stress, shear velocity, and coefficient of friction are presented. Confidence intervals about the shear-stress estimates are provided.

  16. Effects of biaxial oscillatory shear stress on endothelial cell proliferation and morphology.

    Science.gov (United States)

    Chakraborty, Amlan; Chakraborty, Sutirtha; Jala, Venkatakrishna R; Haribabu, Bodduluri; Sharp, M Keith; Berson, R Eric

    2012-03-01

    Wall shear stress (WSS) on anchored cells affects their responses, including cell proliferation and morphology. In this study, the effects of the directionality of pulsatile WSS on endothelial cell proliferation and morphology were investigated for cells grown in a Petri dish orbiting on a shaker platform. Time and location dependent WSS was determined by computational fluid dynamics (CFD). At low orbital speed (50 rpm), WSS was shown to be uniform (0-1 dyne/cm(2)) across the bottom of the dish, while at higher orbital speed (100 and 150 rpm), WSS remained fairly uniform near the center and fluctuated significantly (0-9 dyne/cm(2)) near the side walls of the dish. Since WSS on the bottom of the dish is two-dimensional, a new directional oscillatory shear index (DOSI) was developed to quantify the directionality of oscillating shear. DOSI approached zero for biaxial oscillatory shear of equal magnitudes near the center and approached one for uniaxial pulsatile shear near the wall, where large tangential WSS dominated a much smaller radial component. Near the center (low DOSI), more, smaller and less elongated cells grew, whereas larger cells with greater elongation were observed in the more uniaxial oscillatory shear (high DOSI) near the periphery of the dish. Further, cells aligned with the direction of the largest component of shear but were randomly oriented in low magnitude biaxial shear. Statistical analyses of the individual and interacting effects of multiple factors (DOSI, shear magnitudes and orbital speeds) showed that DOSI significantly affected all the responses, indicating that directionality is an important determinant of cellular responses. Copyright © 2011 Wiley Periodicals, Inc.

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

    International Nuclear Information System (INIS)

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

    2002-01-01

    The wall shear rate from a rotating cylinder in a uniform flow was measured with flush-mounted electrochemical mass transfer probes. The experiments were performed using two rectangular electrodes in a sandwich arrangement. Initially, the frequency response of that probe was numerically studied using an inverse mass transfer method in order to restore the whole wall shear stress in the time domain starting from the measured transfer coefficients given by the split probe. The experiments were performed in the range of velocity ratios 0 4, points of zero shear stress on the rotating cylinder vanish, which is in fact consistent with the previous arguments that the cylinder is surrounded by a set of closed streamlines. This experimental study shows that, when their dynamic behaviour is known, the electrochemical probes are able to sense complex fine structures not observed up to now by previous analytical, numerical or experimental methods, even when non-linear effects are not negligible. (orig.)

  18. Convection of wall shear stress events in a turbulent boundary layer

    Science.gov (United States)

    Pabon, Rommel; Mills, David; Ukeiley, Lawrence; Sheplak, Mark

    2017-11-01

    The fluctuating wall shear stress is measured in a zero pressure gradient turbulent boundary layer of Reτ 1700 simultaneously with velocity measurements using either hot-wire anemometry or particle image velocimetry. These experiments elucidate the patterns of large scale structures in a single point measurement of the wall shear stress, as well as their convection velocity at the wall. The wall shear stress sensor is a CS-A05 one-dimensional capacitice floating element from Interdisciplinary Consulting Corp. It has a nominal bandwidth from DC to 5 kHz and a floating element size of 1 mm in the principal sensing direction (streamwise) and 0.2 mm in the cross direction (spanwise), allowing the large scales to be well resolved in the current experimental conditions. In addition, a two sensor array of CS-A05 aligned in the spanwise direction with streamwise separations O (δ) is utilized to capture the convection velocity of specific scales of the shear stress through a bandpass filter and peaks in the correlation. Thus, an average wall normal position for the corresponding convecting event can be inferred at least as high as the equivalent local streamwise velocity. This material is based upon work supported by the National Science Foundation Graduate Research Fellowship under Grant No. DGE-1315138.

  19. Cloning the Gravity and Shear Stress Related Genes from MG-63 Cells by Subtracting Hybridization

    Science.gov (United States)

    Zhang, Shu; Dai, Zhong-quan; Wang, Bing; Cao, Xin-sheng; Li, Ying-hui; Sun, Xi-qing

    2008-06-01

    Background The purpose of the present study was to clone the gravity and shear stress related genes from osteoblast-like human osteosarcoma MG-63 cells by subtractive hybridization. Method MG-63 cells were divided into two groups (1G group and simulated microgravity group). After cultured for 60 h in two different gravitational environments, two groups of MG-63 cells were treated with 1.5Pa fluid shear stress (FSS) for 60 min, respectively. The total RNA in cells was isolated. The gravity and shear stress related genes were cloned by subtractive hybridization. Result 200 clones were gained. 30 positive clones were selected using PCR method based on the primers of vector and sequenced. The obtained sequences were analyzed by blast. changes of 17 sequences were confirmed by RT-PCR and these genes are related to cell proliferation, cell differentiation, protein synthesis, signal transduction and apoptosis. 5 unknown genes related to gravity and shear stress were found. Conclusion In this part of our study, our result indicates that simulated microgravity may change the activities of MG-63 cells by inducing the functional alterations of specific genes.

  20. Volumetric Arterial Wall Shear Stress Calculation Based on Cine Phase Contrast MRI

    NARCIS (Netherlands)

    Potters, Wouter V.; van Ooij, Pim; Marquering, Henk; VanBavel, Ed; Nederveen, Aart J.

    2015-01-01

    PurposeTo assess the accuracy and precision of a volumetric wall shear stress (WSS) calculation method applied to cine phase contrast magnetic resonance imaging (PC-MRI) data. Materials and MethodsVolumetric WSS vectors were calculated in software phantoms. WSS algorithm parameters were optimized

  1. Influence of Sewer Sediments on Flow Friction and Shear Stress Distribution

    DEFF Research Database (Denmark)

    Perrusquia, G.; Petersen, O.; Larsen, Torben

    1995-01-01

    Most sewers contain more or less deposited sediments. The paper discusses the distribution of the boundary shear stresses and the hydraulic resistance in part-full sewer pipes with such deposited sediments. The discussion is based on a series of numerical experiments using a validated numerical...

  2. Simultaneous wall-shear-stress and wide-field PIV measurements in a turbulent boundary layer

    Science.gov (United States)

    Gomit, Guillaume; Fourrie, Gregoire; de Kat, Roeland; Ganapathisubramani, Bharathram

    2015-11-01

    Simultaneous particle image velocimetry (PIV) and hot-film shear stress sensor measurements were performed to study the large-scale structures associated with shear stress events in a flat plate turbulent boundary layer at a high Reynolds number (Reτ ~ 4000). The PIV measurement was performed in a streamwise-wall normal plane using an array of six high resolution cameras (4 ×16MP and 2 ×29MP). The resulting field of view covers 8 δ (where δ is the boundary layer thickness) in the streamwise direction and captures the entire boundary layer in the wall-normal direction. The spatial resolution of the measurement is approximately is approximately 70 wall units (1.8 mm) and sampled each 35 wall units (0.9 mm). In association with the PIV setup, a spanwise array of 10 skin-friction sensors (spanning one δ) was used to capture the footprint of the large-scale structures. This combination of measurements allowed the analysis of the three-dimensional conditional structures in the boundary layer. Particularly, from conditional averages, the 3D organisation of the wall normal and streamwise velocity components (u and v) and the Reynolds shear stress (-u'v') related to a low and high shear stress events can be extracted. European Research Council Grant No-277472-WBT.

  3. Augmentation of wall shear stress inhibits neointimal hyperplasia after stent implantation - Inhibition through reduction of inflammation?

    NARCIS (Netherlands)

    Carlier, SG; van Damme, LCA; Blommerde, CP; Wentzel, JJ; van Langehove, G; Verheye, S; Kockx, MM; Knaapen, MWM; Cheng, C; Gijsen, F; Duncker, DJ; Stergiopulos, N; Slager, CJ; Serruys, PW; Krams, R

    2003-01-01

    Background - Low wall shear stress (WSS) increases neointimal hyperplasia (NH) in vein grafts and stents. We studied the causal relationship between WSS and NH formation in stents by locally increasing WSS with a flow divider (Anti-Restenotic Diffuser, Endoart SA) placed in the center of the stent.

  4. Assessment of shear stress related parameters in the carotid bifurcation using mouse-specific FSI simulations.

    Science.gov (United States)

    De Wilde, David; Trachet, Bram; Debusschere, Nic; Iannaccone, Francesco; Swillens, Abigail; Degroote, Joris; Vierendeels, Jan; De Meyer, Guido R Y; Segers, Patrick

    2016-07-26

    The ApoE(-)(/)(-) mouse is a common small animal model to study atherosclerosis, an inflammatory disease of the large and medium sized arteries such as the carotid artery. It is generally accepted that the wall shear stress, induced by the blood flow, plays a key role in the onset of this disease. Wall shear stress, however, is difficult to derive from direct in vivo measurements, particularly in mice. In this study, we integrated in vivo imaging (micro-Computed Tomography-µCT and ultrasound) and fluid-structure interaction (FSI) modeling for the mouse-specific assessment of carotid hemodynamics and wall shear stress. Results were provided for 8 carotid bifurcations of 4 ApoE(-)(/)(-) mice. We demonstrated that accounting for the carotid elasticity leads to more realistic flow waveforms over the complete domain of the model due to volume buffering capacity in systole. The 8 simulated cases showed fairly consistent spatial distribution maps of time-averaged wall shear stress (TAWSS) and relative residence time (RRT). Zones with reduced TAWSS and elevated RRT, potential indicators of atherosclerosis-prone regions, were located mainly at the outer sinus of the external carotid artery. In contrast to human carotid hemodynamics, no flow recirculation could be observed in the carotid bifurcation region. Copyright © 2015 Elsevier Ltd. All rights reserved.

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

    NARCIS (Netherlands)

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

    2011-01-01

    Episodic increases in shear stress have been proposed as a mechanism that induces training-induced adaptation in arterial wall remodeling in humans. To address this hypothesis in humans, we examined bilateral brachial artery wall thickness using high-resolution ultrasound in healthy men across an

  6. Laminar shear stress modulates endothelial luminal surface stiffness in a tissue-specific manner.

    Science.gov (United States)

    Merna, Nick; Wong, Andrew K; Barahona, Victor; Llanos, Pierre; Kunar, Balvir; Palikuqi, Brisa; Ginsberg, Michael; Rafii, Shahin; Rabbany, Sina Y

    2018-04-17

    Endothelial cells form vascular beds in all organs and are exposed to a range of mechanical forces that regulate cellular phenotype. We sought to determine the role of endothelial luminal surface stiffness in tissue-specific mechanotransduction of laminar shear stress in microvascular mouse cells and the role of arachidonic acid in mediating this response. Microvascular mouse endothelial cells were subjected to laminar shear stress at 4 dynes/cm 2 for 12 hours in parallel plate flow chambers that enabled real-time optical microscopy and atomic force microscopy measurements of cell stiffness. Lung endothelial cells aligned parallel to flow, while cardiac endothelial cells did not. This rapid alignment was accompanied by increased cell stiffness. The addition of arachidonic acid to cardiac endothelial cells increased alignment and stiffness in response to shear stress. Inhibition of arachidonic acid in lung endothelial cells and embryonic stem cell-derived endothelial cells prevented cellular alignment and decreased cell stiffness. Our findings suggest that increased endothelial luminal surface stiffness in microvascular cells may facilitate mechanotransduction and alignment in response to laminar shear stress. Furthermore, the arachidonic acid pathway may mediate this tissue-specific process. An improved understanding of this response will aid in the treatment of organ-specific vascular disease. © 2018 John Wiley & Sons Ltd.

  7. Experimental study of interfacial shear stress for an analogy model of evaporative heat transfer

    International Nuclear Information System (INIS)

    Kwon, Hyuk; Park, GoonCherl; Min, ByungJoo

    2008-01-01

    In this study, we conducted measurements of an evaporative interfacial shear stress in a passive containment cooling system (PCCS). An interfacial shear stress for a counter-current flow was measured from a momentum balance equation and the interfacial friction factor for evaporation was evaluated by using experimental data. A model for the evaporative heat transfer coefficient of a vertical evaporative flat surface was developed based on an analogy between heat and momentum transfer. It was found that the interfacial shear stress increases with the Jacob number, which incorporates the evaporation rate, and the air and water Reynolds numbers. The relationship between the evaporative heat transfer and the interfacial shear stress was evaluated by using the experimental results. This relationship was used to develop a model for an evaporative heat transfer coefficient by using an analogy between heat and mass transfer. The prediction of this model were found to be in good agreement with the experimental data obtained for evaporative heat transfer by Kang and Park. (author)

  8. Extremely high wall-shear stress events in a turbulent boundary layer

    Science.gov (United States)

    Pan, Chong; Kwon, Yongseok

    2018-04-01

    The present work studies the fluctuating characteristics of the streamwise wall-shear stress in a DNS of a turbulent boundary layer at Re τ =1500 from a structural view. The two-dimensional field of the fluctuating friction velocity u‧ τ (x,z) is decomposed into the large- and small-scale components via a recently proposed scale separation algorithm, Quasi-bivariate Variational Mode Decomposition (QB-VMD). Both components are found to be dominated by streak-like structures, which can be regarded as the wall signature of the inner-layer streaks and the outer-layer LSMs, respectively. Extreme positive/negative wall-shear stress fluctuation events are detected in the large-scale component. The former’s occurrence frequency is nearly one order of magnitude higher than the latter; therefore, they contribute a significant portion of the long tail of the wall-shear stress distribution. Both two-point correlations and conditional averages show that these extreme positive wall-shear stress events are embedded in the large-scale positive u‧ τ streaks. They seem to be formed by near-wall ‘splatting’ process, which are related to strong finger-like sweeping (Q4) events originated from the outer-layer positive LSMs.

  9. Cylindrical shell under impact load including transverse shear and normal stress

    International Nuclear Information System (INIS)

    Shakeri, M.; Eslami, M.R.; Ghassaa, M.; Ohadi, A.R.

    1993-01-01

    The general governing equations of shell of revolution under shock loads are reduced to equations describing the elastic behavior of cylindrical shell under axisymmetric impact load. The effect of lateral normal stress, transverse shear, and rotary inertia are included, and the equations are solved by Galerkin finite element method. The results are compared with the previous works of authors. (author)

  10. Interfacial stresses in strengthened beam with shear cohesive zone ...

    Indian Academy of Sciences (India)

    Department of Civil Engineering, University of Constantine 1, Constantine, Algeria e-mail: zergua.abdesselam@umc.edu.dz. MS received 24 April 2014; revised 14 July 2014; accepted 12 September 2014. Abstract. The failure of strengthened beams with fibre-reinforced polymer (FRP) materials is due to high stress ...

  11. Mechanical loading by fluid shear stress of myotube glycocalyx stimulates growth factor expression and nitric oxide production

    NARCIS (Netherlands)

    Juffer, P.; Bakker, A.D.; Klein-Nulend, J.; Jaspers, R.T.

    2014-01-01

    Skeletal muscle fibers have the ability to increase their size in response to a mechanical overload. Finite element modeling data suggest that mechanically loaded muscles in vivo may experience not only tensile strain but also shear stress. However, whether shear stress affects biological pathways

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

    Science.gov (United States)

    Demiray, H

    1997-09-01

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

  13. Role of shear stress in nitric oxide-dependent modulation of renal angiotensin II vasoconstriction.

    Science.gov (United States)

    Endlich, K; Muller, C; Barthelmebs, M; Helwig, J J

    1999-08-01

    1. Renal vasoconstriction in response to angiotensin II (ANGII) is known to be modulated by nitric oxide (NO). Since shear stress stimulates the release of a variety of vasoactive compounds from endothelial cells, we studied the impact of shear stress on the haemodynamic effect of ANGII in isolated perfused kidneys of rats under control conditions and during NO synthase inhibition with L-NAME (100 microM). 2. Kidneys were perfused in the presence of cyclo-oxygenase inhibitor (10 microM indomethacin) with Tyrode's solution of relative viscosity zeta=1 (low viscosity perfusate, LVP) or, in order to augment shear stress, with Tyrode's solution containing 7% Ficoll 70 of relative viscosity zeta=2 (high viscosity perfusate, HVP). 3. Vascular conductance was 3.5+/-0.4 fold larger in HVP as compared with LVP kidneys, associated with an augmentation of overall wall shear stress by 37+/-5%. During NO inhibition, vascular conductance was only 2.5+/-0.2 fold elevated in HVP vs LVP kidneys, demonstrating shear stress-induced vasodilatation by NO and non-NO/non-prostanoid compound(s). 4. ANGII (10 - 100 pM) constricted the vasculature in LVP kidneys, but was without effect in HVP kidneys. During NO inhibition, in contrast, ANGII vasoconstriction was potentiated in HVP as compared with LVP kidneys. 5. The potentiation of ANGII vasoconstriction during NO inhibition has been shown to be mediated by endothelium-derived P450 metabolites and to be sensitive to AT2 receptor blockade in our earlier studies. Accordingly, in HVP kidneys, increasing concentrations of the AT2 receptor antagonist PD123319 (5 and 500 nM) gradually abolished the potentiation of ANGII vasoconstriction during NO inhibition, but did not affect vasoconstriction in response to ANGII in LVP kidneys. 6. Our results demonstrate, that augmentation of shear stress by increasing perfusate viscosity induces vasodilatation in the rat kidney, which is partially mediated by NO. Elevated levels of shear stress attenuate

  14. Statistics on Near Wall Structures and Shear Stress Distribution from 3D Holographic Measurement.

    Science.gov (United States)

    Sheng, J.; Malkiel, E.; Katz, J.

    2007-11-01

    Digital Holographic Microscopy performs 3D velocity measurement in the near-wall region of a turbulent boundary layer in a square channel over a smooth wall at Reτ=1,400. Resolution of ˜1μm over a sample volume of 1.5x2x1.5mm (x^+=50, y^+=60, z^+=50) is sufficient for resolving buffer layer and lower log layer structures, and for measuring instantaneous wall shear stress distributions from velocity gradients in the viscous sublayer. Results, based on 700 instantaneous realizations, provide detailed statistics on the spatial distribution of both wall stress components along with characteristic flow structures. Conditional sampling based on maxima and minima of wall shear stresses, as well as examination of instantaneous flow structures, lead to development of a conceptual model for a characteristic flow phenomenon that seems to generating extreme stress events. This structure develops as an initially spanwise vortex element rises away from the surface, due to local disturbance, causing a local stress minimum. Due to increasing velocity with elevation, this element bends downstream, forming a pair of inclined streamwise vortices, aligned at 45^0 to freestream, with ejection-like flow between them. Entrainment of high streamwise momentum on the outer sides of this vortex pair generates streamwise shear stress maxima, 70 δν downstream, which are displaced laterally by 35 δν from the local minimum.

  15. One-dimensional models of thermal activation under shear stress

    CSIR Research Space (South Africa)

    Nabarro, FRN

    2003-01-01

    Full Text Available - dimensional models presented here may illuminate the study of more realistic models. For the model in which as many dislocations are poised for backward jumps as for forward jumps, the experimental activation volume Vye(C27a) under applied stresses close to C...27a is different from the true activation volume V(C27) evaluated at C27 ?C27a. The relations between the two are developed. A model is then discussed in which fewer dislocations are available for backward than for forward jumps. Finally...

  16. Fracture transmissivity as a function of normal and shear stress: first results in Opalinus Clay

    International Nuclear Information System (INIS)

    Cuss, R.J.; Milodowski, A.; Noy, D.J.; Harrington, J.F.

    2010-01-01

    Document available in extended abstract form only. Rock-mass failure around openings is usually observed in the form of a highly complex fracture network (EDZ), which is heterogeneous in distribution around a circular tunnel opening because of the heterogeneous stress distribution. The orientation of stress with respect to the fracture network is known to be important. The complex heterogeneous stress trajectory and heterogeneous fracture network results in a broad range of stresses and stress directions acting on the open fracture network. During the open stage of a repository, stress will slowly alter as shear movements occur along the fractures, as well as other time-dependent phenomena. As the repository is back filled, the stress field is further altered as the backfill settles and changes volume because of re-saturation. Therefore, a complex and wide ranging stress regime and stress history will result. In a purely mechanical sense, fracture transmissivity is a function of normal stress, shear stress, and fracture aperture. The Selfrac test from Mont Terri showed the change in transmissivity with effective normal stress. This work showed that fracture transmissivity decreased with increasing normal load and that an effective normal stress of 2.5 MPa is sufficient to yield a transmissivity similar to that seen in intact Opalinus clay (OPA). Therefore fracture closure because of normal stresses has been proven to be a quite efficient mechanism in OPA. A new shear rig was designed to investigate the detail of fracture transmissivity in OPA. The experimental configuration uses two prepared blocks that are 60 x 60 mm in size and approximately 20 mm thick. The first test sample had machine ground surfaces in contact with each other, with pore fluid being delivered through the centre of the top block directly to the fracture surface. The experimental programme included two distinct stages. In the first normal load was altered to investigate fracture transmissivity

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

    Science.gov (United States)

    Cordasco, Daniel; Yazdani, Alireza; Bagchi, Prosenjit

    2014-04-01

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

  18. Effect of shear stress on electromagnetic behaviors in superconductor-ferromagnetic bilayer structure

    Science.gov (United States)

    Yong, Huadong; Zhao, Meng; Jing, Ze; Zhou, Youhe

    2014-09-01

    In this paper, the electromagnetic response and shielding behaviour of superconductor-ferromagnetic bilayer structure are studied. The magnetomechanical coupling in ferromagnetic materials is also considered. Based on the linear piezomagnetic coupling model and anti-plane shear deformation, the current density and magnetic field in superconducting strip are obtained firstly. The effect of shear stress on the magnetization of strip is discussed. Then, we consider the magnetic cloak for superconductor-ferromagnetic bilayer structure. The magnetic permeability of ferromagnetic material is obtained for perfect cloaking in uniform magnetic field with magnetomechanical coupling in ferromagnet. The simulation results show that the electromagnetic response in superconductors will change by applying the stress only to the ferromagnetic material. In addition, the performance of invisibility of structure for non-uniform field will be affected by mechanical stress. It may provide a method to achieve tunability of superconducting properties with mechanical loadings.

  19. The role of shear stress and arteriogenesis in maintaining vascular homeostasis and preventing cerebral atherosclerosis

    Directory of Open Access Journals (Sweden)

    David Della-Morte

    2015-01-01

    Full Text Available Shear stress (SS is a biomechanical force that is determined by blood flow, vessel geometry, and fluid viscosity. Although a wide range of known vascular risk factors promote development of atherosclerosis, atherosclerotic changes occur predominately at specific sites within the arterial tree, suggesting a critical role for local factors within the vasculature. Atherosclerotic lesions develop predominantly at branches, bends, and bifurcations in the arterial tree because these sites are exposed to low or disturbed blood flow and low SS. Low SS predisposes arteries to atherosclerosis by causing endothelial dysfunction. A natural system of preexisting cerebral collateral arteries protects against ischemia by bypassing sites of arterial occlusion through a mechanism of arteriogenesis. The main trigger for arteriogenesis is impaired vascular homeostasis (VH in response to local changes in SS induced by ischemia. VH is a critical process for maintaining the physiological function of cerebral circulation. It is regulated through a complex biological system of blood flow hemodynamic and physiological responses to flow changes. Restoration of VH by increasing arteriogenesis and SS may provide a novel therapeutic target for stroke, especially in the elderly, who are more prone to VH impairment. In this review article, we discuss the mechanisms and structures necessary to maintain VH in brain circulation, the role of SS, and risk factors leading to atherosclerosis, including the effects of aging. We also discuss arteriogenesis as an adaptive and protective process in response to ischemic injury, the imaging techniques currently available to evaluate arterogenesis such as magnetic resonance imaging/positron emission tomography (MRI/PET, and the potential therapeutic approaches against ischemic injury that target arteriogenesis.

  20. Resolved shear stress intensity coefficient and fatigue crack growth in large crystals

    Science.gov (United States)

    Chen, QI; Liu, Hao-Wen

    1988-01-01

    Fatigue crack growth in large grain Al alloy was studied. Fatigue crack growth is caused primarily by shear decohesion due to dislocation motion in the crack tip region. The crack paths in the large crystals are very irregular and zigzag. The crack planes are often inclined to the loading axis both in the inplane direction and the thickness direction. The stress intensity factors of such inclined cracks are approximated from the two dimensional finite element calculations. The plastic deformation in a large crystal is highly anisotropic, and dislocation motion in such crystals are driven by the resolved shear stress. The resolved shear stress intensity coefficient in a crack solid, RSSIC, is defined, and the coefficients for the slip systems at a crack tip are evaluated from the calculated stress intensity factors. The orientations of the crack planes are closely related to the slip planes with the high RSSIC values. If a single slip system has a much higher RSSIC than all the others, the crack will follow the slip plane, and the slip plane becomes the crack plane. If two or more slip systems have a high RSSIC, the crack plane is the result of the decohesion processes on these active slip planes.

  1. Critical Velocity for Shear Localization in A Mature Mylonitic Rock Analogue

    Science.gov (United States)

    Takahashi, M.; van den Ende, M.; Niemeijer, A. R.; Spiers, C. J.

    2016-12-01

    Highly localized slip zones, seen within ductile shear zones developed in nature, such as pseudotachylite bands occurring within mylonites, are widely recognized as evidence for earthquake nucleation and/or propagation within and overprinting the ductile regime. To understand brittle/frictional localization processes in ductile shear zones and to connect these to earthquake nucleation and propagation processes, we performed large velocity step-change tests on a brine-saturated, 80:20 (wt. %) halite and muscovite gouge mixture, after forming a mature mylonitic structure through pressure solution creep at low-velocity. The sharp increase in sliding strength that occurs in response to an instantaneous upward velocity-step (direct effect) is an important parameter in determining the potential for and nature of seismic rupture nucleation. We obtained reproducible results regarding low velocity mechanical behavior compared with previous work of Niemeijer and Spiers, [2006], but also obtained new insights into the effects of sudden increases in slip velocity on localization and strength evolution, at velocities above a specific critical velocity Vc ( 20 μm/sec). We found that once a ductile, mylonitic structure has developed in a shear zone, subsequent cataclastic deformation at high velocity (> Vc) is consistently localized in a narrow zone characterized by fine grains of halite aligned in arrays between foliated muscovite Due to this intense localization, structures presumably developed under low velocity conditions were still preserved in large parts of the gouge body. This switch to localized deformation is controlled by the imposed velocity, and becomes most apparent at velocities over Vc. In addition, the direct effect a decreases rapidly when the velocity exceeds Vc. This implies that slip can localize and accelerate towards seismic velocities more or less instantly once Vc is exceeded. Obtaining a measure for Vc in natural faults is therefore of key importance

  2. Effect of shear span, concrete strength and strrup spacing on behavior of pre-stressed concrete beams

    International Nuclear Information System (INIS)

    Ahmad, S.; Bukhari, I.A.

    2007-01-01

    The shear strength of pre-stressed concrete beams is one of the most important factors to be considered in their design. The available data on shear behavior of pre-tensioned prestressed concrete beams is very limited. In this experimental study, pre-tensioned prestressed concrete I-beams are fabricated with normal and high- strength concretes, varying stirrup spacing and shear span-to-depth ratios. 1Wenty one I-beam specimens that are 300 mm deep and 3745-4960mm long are tested up to failure while deflections, cracking pattern, cracking and failure loads were recorded. The research results are compared with ACI 318-02 and Structure Analysis Program, Response 2000. It was observed that with the decrease in concrete strength, failure mode of prestressed concrete beams changes from flexure shear to web shear cracking for values of shear span-to-depth ratio less than 4.75. Increase in stirrup spacing decreased the effectiveness of stirrups in transmitting shear across crack as a result of which failure mode is changed to web shear cracking especially for beams with lower values of shear span-to-depth ratios. ACI code underestimates the shear carrying capacity of prestressed concrete beams with lower values of shear span- to-depth ratios. Response 2000 can be used more effectively in predicting shear behavior of normal strength prestressed concrete beams. (author)

  3. Small-scale multi-axial hybrid simulation of a shear-critical reinforced concrete frame

    Science.gov (United States)

    Sadeghian, Vahid; Kwon, Oh-Sung; Vecchio, Frank

    2017-10-01

    This study presents a numerical multi-scale simulation framework which is extended to accommodate hybrid simulation (numerical-experimental integration). The framework is enhanced with a standardized data exchange format and connected to a generalized controller interface program which facilitates communication with various types of laboratory equipment and testing configurations. A small-scale experimental program was conducted using a six degree-of-freedom hydraulic testing equipment to verify the proposed framework and provide additional data for small-scale testing of shearcritical reinforced concrete structures. The specimens were tested in a multi-axial hybrid simulation manner under a reversed cyclic loading condition simulating earthquake forces. The physical models were 1/3.23-scale representations of a beam and two columns. A mixed-type modelling technique was employed to analyze the remainder of the structures. The hybrid simulation results were compared against those obtained from a large-scale test and finite element analyses. The study found that if precautions are taken in preparing model materials and if the shear-related mechanisms are accurately considered in the numerical model, small-scale hybrid simulations can adequately simulate the behaviour of shear-critical structures. Although the findings of the study are promising, to draw general conclusions additional test data are required.

  4. Orbitally shaken shallow fluid layers. II. An improved wall shear stress model

    Science.gov (United States)

    Alpresa, Paola; Sherwin, Spencer; Weinberg, Peter; van Reeuwijk, Maarten

    2018-03-01

    A new model for the analytical prediction of wall shear stress distributions at the base of orbitally shaken shallow fluid layers is developed. This model is a generalisation of the classical extended Stokes solution and will be referred to as the potential theory-Stokes model. The model is validated using a large set of numerical simulations covering a wide range of flow regimes representative of those used in laboratory experiments. It is demonstrated that the model is in much better agreement with the simulation data than the classical Stokes solution, improving the prediction in 63% of the studied cases. The central assumption of the model—which is to link the wall shear stress with the surface velocity—is shown to hold remarkably well over all regimes covered.

  5. Experimental and CFD Simulation Studies of Wall Shear Stress for Different Impeller Configurations and MBR Activated Sludge

    DEFF Research Database (Denmark)

    Ratkovich, Nicolas Rios; Chan, C.C.V.; Bentzen, Thomas Ruby

    2012-01-01

    in an MBR. Nevertheless, proper experimental validation is required to validate CFD simulation. In this work experimental measurements of shear stress induced by impellers at a membrane surface were made with an electrochemical approach and the results were used to validate CFD simulations. As good results...... appealing for full-scale applications. It has been widely demonstrated that the filtration performances in MBRs can be improved by understanding the shear stress over the membrane surface. Modern tools such as Computational Fluid Dynamics (CFD) can be used to diagnose and understand the shear stress...

  6. Influence of turbulent horseshoe vortex and associated bed shear stress on sediment transport in front of a cylinder

    DEFF Research Database (Denmark)

    Li, Jinzhao; Qi, Meilan; Fuhrman, David R.

    2018-01-01

    -normal distribution for uniform channel-open flows. The comparisons of sediment transport rates where turbulent fluctuations in the bed shear stress are, or are not, taken into account show that the sediment transport rates calculated by the mean bed shear stress are under-predicted. Furthermore, a new sediment......This study concerns the flow and associated sediment transport in front of a cylinder in steady currents. The study comprises (i) flow characteristics induced by the turbulent horseshoe vortex (THV), (ii) bed shear stress within the THV region, and (iii) predicted sediment transport rates...

  7. A wall shear stress sensor using a pair of sidewall doped cantilevers

    Science.gov (United States)

    Nguyen, Thanh-Vinh; Kazama, Ryohei; Takahashi, Hidetoshi; Takahata, Tomoyuki; Matsumoto, Kiyoshi; Shimoyama, Isao

    2017-07-01

    In this paper, we report on a micro-electro mechanical system (MEMS)-based piezoresistive sensor for measuring shear stress induced by an airflow. The advantages of the proposed sensor include a simple sensing method and a high resonance frequency due to the small size of the sensing elements. Our sensor consists of a pair of 3 µm thick cantilevers with piezoresistors formed on the sidewall of their hinges to detect lateral deformation in the cantilevers induced by an airflow. Each cantilever has a 200 µm  ×  400 µm plate supported by two 150 µm long, 4 µm wide beams. The piezoresistors on the two cantilevers are designed to deform in opposite manners when a shear stress is applied and in the same manner when a pressure is applied. Therefore, the applied shear stress can be detected from the difference in the responses of the two cantilevers without becoming conflated with pressure. In this paper, the design, fabrication and evaluation of the proposed sensor are reported and compared to numerical simulation results. From the experimental results, the resolution of the sensor and its first resonance frequency are 1.3 Pa and 3.9 kHz, respectively. Moreover, we show that the effect of temperature on the readout of the sensor can be eliminated using a temperature-compensating piezoresistor fabricated on the same sensor chip. Finally, using the fabricated sensor, the measurement of the shear stress induced by an airflow with velocity between  -10 and 10 m s-1 is demonstrated.

  8. A wall shear stress sensor using a pair of sidewall doped cantilevers

    International Nuclear Information System (INIS)

    Nguyen, Thanh-Vinh; Shimoyama, Isao; Kazama, Ryohei; Takahashi, Hidetoshi; Takahata, Tomoyuki; Matsumoto, Kiyoshi

    2017-01-01

    In this paper, we report on a micro-electro mechanical system (MEMS)-based piezoresistive sensor for measuring shear stress induced by an airflow. The advantages of the proposed sensor include a simple sensing method and a high resonance frequency due to the small size of the sensing elements. Our sensor consists of a pair of 3 µ m thick cantilevers with piezoresistors formed on the sidewall of their hinges to detect lateral deformation in the cantilevers induced by an airflow. Each cantilever has a 200 µ m  ×  400 µ m plate supported by two 150 µ m long, 4 µ m wide beams. The piezoresistors on the two cantilevers are designed to deform in opposite manners when a shear stress is applied and in the same manner when a pressure is applied. Therefore, the applied shear stress can be detected from the difference in the responses of the two cantilevers without becoming conflated with pressure. In this paper, the design, fabrication and evaluation of the proposed sensor are reported and compared to numerical simulation results. From the experimental results, the resolution of the sensor and its first resonance frequency are 1.3 Pa and 3.9 kHz, respectively. Moreover, we show that the effect of temperature on the readout of the sensor can be eliminated using a temperature-compensating piezoresistor fabricated on the same sensor chip. Finally, using the fabricated sensor, the measurement of the shear stress induced by an airflow with velocity between  −10 and 10 m s −1 is demonstrated. (paper)

  9. Relation between psi-splitting and microscopic residual shear stresses in x-ray stress measurement on uni-directionally deformed layers

    International Nuclear Information System (INIS)

    Hanabusa, Takao; Fujiwara, Haruo

    1982-01-01

    The psi-splitting behaviors were investigated for the ground and the milled surface layers of both iron and high speed steel in order to find out the relation among microscopic residual shear stresses. For the high speed steel, the X-ray elastic constants and the residual strains were measured on the carbide phase as well as on the matrix phase. It was clarified that the psi-splitting was caused by a combination of the selective nature of X-ray diffractions and the microscopic residual shear stresses within the interior of cells and the carbide particles. The volume fraction occupied by the cell walls and the residual shear stresses sustained by them were estimated from the equilibrium condition of the microscopic residual shear stresses. The distributions of residual stresses over the deformed layers indicate that the thermal effect is dominant in grinding and the mechanical effect is dominant in milling for forming residual stresses. (author)

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

    Science.gov (United States)

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

    2006-06-01

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

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

    Science.gov (United States)

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

    2011-04-01

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

  12. Shear Stress Enhances Chemokine Secretion from Chlamydia pneumoniae-infected Monocytes.

    Science.gov (United States)

    Evani, Shankar J; Dallo, Shatha F; Murthy, Ashlesh K; Ramasubramanian, Anand K

    2013-09-01

    Chlamydia pneumoniae is a common respiratory pathogen that is considered a highly likely risk factor for atherosclerosis. C. pneumoniae is disseminated from the lung into systemic circulation via infected monocytes and lodges at the atherosclerotic sites. During transit, C. pneumoniae -infected monocytes in circulation are subjected to shear stress due to blood flow. The effect of mechanical stimuli on infected monocytes is largely understudied in the context of C. pneumoniae infection and inflammation. We hypothesized that fluid shear stress alters the inflammatory response of C. pneumoniae -infected monocytes and contributes to immune cell recruitment to the site of tissue damage. Using an in vitro model of blood flow, we determined that a physiological shear stress of 7.5 dyn/cm 2 for 1 h on C. pneumoniae -infected monocytes enhances the production of several chemokines, which in turn is correlated with the recruitment of significantly large number of monocytes. Taken together, these results suggest synergistic interaction between mechanical and chemical factors in C. pneumoniae infection and associated inflammation.

  13. Velocity profile and wall shear stress of saccular aneurysms at the anterior communicating artery.

    Science.gov (United States)

    Yamaguchi, Ryuhei; Ujiie, Hiroshi; Haida, Sayaka; Nakazawa, Nobuhiko; Hori, Tomokatsu

    2008-01-01

    It has recently been shown that the aspect ratio (dome/neck) of an aneurysm correlates well with intraaneurysmal blood flow. Aneurysms with an aspect ratio larger than 1.6 carry a higher risk of rupture. We examined the effect of aspect ratio (AR) on intra-aneurysmal flow using experimental models. Flow visualization with particle imaging velocimetry and measurement of wall shear stress using laser Doppler anemometry were performed on three different aneurysm models: AR 0.5, 1.0, and 2.0. Intraaneurysmal flow consists of inflow, circulation, and outflow. Rapid inflow impinged on the distal neck creating a stagnant point. Rapid flow and maximum wall shear stress were observed in the vicinity of the stagnant point. By changing the Reynold's number, the stagnant point moved. By increasing the AR of the aneurysm, vortices inside the aneurysm sac closed and very slow flow was observed, resulting in very low shear stress markedly at a Reynold's number of 250, compatible with the diastolic phase. In the aneurysm model AR 2.0, both rapid flow at the neck and vortices inside the aneurysm are sufficient to activate platelets, making a thrombus that may anchor on the dome where very slow flow takes place. Hemodynamics in aneurysms larger than AR 2.0 definitely contribute to thrombus formation.

  14. Analysis of Zero Reynolds Shear Stress Appearing in Dilute Surfactant Drag-Reducing Flow

    Directory of Open Access Journals (Sweden)

    Weiguo Gu

    2011-01-01

    Full Text Available Dilute surfactant solution of 25 ppm in the two-dimensional channel is investigated experimentally compared with water flow. Particle image velocimetry (PIV system is used to take 2D velocity frames in the streamwise and wall-normal plane. Based on the frames of instantaneous vectors and statistical results, the phenomenon of zero Reynolds shear stress appearing in the drag-reducing flow is discussed. It is found that 25 ppm CTAC solution exhibits the highest drag reduction at Re = 25000 and loses drag reduction completely at Re = 40000. When drag reduction lies in the highest, Reynolds shear stress disappears and reaches zero although the RMS of the velocity fluctuations is not zero. By the categorization in four quadrants, the fluctuations of 25 ppm CTAC solution are distributed in all four quadrants equally at Re = 25000, which indicates that turnaround transportation happens in drag-reducing flow besides Reynolds shear stress transportation. Moreover, the contour distribution of streamwise velocity and the fluctuations suggests that turbulence transportation is depressed in drag-reducing flow. The viscoelasticity is possible to decrease the turbulence transportation and cause the turnaround transportation.

  15. Padé approximant for normal stress differences in large-amplitude oscillatory shear flow

    Science.gov (United States)

    Poungthong, P.; Saengow, C.; Giacomin, A. J.; Kolitawong, C.; Merger, D.; Wilhelm, M.

    2018-04-01

    Analytical solutions for the normal stress differences in large-amplitude oscillatory shear flow (LAOS), for continuum or molecular models, normally take the inexact form of the first few terms of a series expansion in the shear rate amplitude. Here, we improve the accuracy of these truncated expansions by replacing them with rational functions called Padé approximants. The recent advent of exact solutions in LAOS presents an opportunity to identify accurate and useful Padé approximants. For this identification, we replace the truncated expansion for the corotational Jeffreys fluid with its Padé approximants for the normal stress differences. We uncover the most accurate and useful approximant, the [3,4] approximant, and then test its accuracy against the exact solution [C. Saengow and A. J. Giacomin, "Normal stress differences from Oldroyd 8-constant framework: Exact analytical solution for large-amplitude oscillatory shear flow," Phys. Fluids 29, 121601 (2017)]. We use Ewoldt grids to show the stunning accuracy of our [3,4] approximant in LAOS. We quantify this accuracy with an objective function and then map it onto the Pipkin space. Our two applications illustrate how to use our new approximant reliably. For this, we use the Spriggs relations to generalize our best approximant to multimode, and then, we compare with measurements on molten high-density polyethylene and on dissolved polyisobutylene in isobutylene oligomer.

  16. Exercise-induced heat stress disrupts the shear-dilatory relationship.

    Science.gov (United States)

    Ives, Stephen J; Lefferts, Wesley K; Wharton, Margret; Fehling, Patricia C; Smith, Denise L

    2016-12-01

    What is the central question of this study? Although heat stress is known to increase cardiovascular strain, no study, to date, had explored the potential impact of exercise-induced heat stress on vascular function. What is the main finding and its importance? We found that acute exercise tended to reduce flow-mediated dilatation (FMD), owing in part to reduced reactive hyperaemia/shear stimulus; thus, when FMD is normalized to shear no postexercise deficit exists. Exercise-induced heat stress increased reactive hyperaemia, shear rate, coupled with a sustained FMD postexercise, suggests that exercise-induced heat stress increases the amount of shear stimulus to elicit a similar response, indicating reduced vascular responsiveness, or reserve, which might increase cardiovascular susceptibility. Heat stress increases cardiovascular strain and is of particular concern in occupations, such as firefighting, in which individuals are required to perform strenuous work while wearing personal protective equipment. Sudden cardiac events are associated with strenuous activity and are the leading cause of duty-related death among firefighters, accounting for ∼50% of duty-related fatalities per year. Understanding the acute effects of exercise-induced heat stress (EIHS) on vascular endothelial function may provide insight into the mechanisms precipitating acute coronary events in firefighters. The purpose of this study, therefore, was to determine the effects of EIHS on vascular endothelial function. Using a balanced crossover design, 12 healthy men performed 100 min of moderate-intensity, intermittent exercise with and without EIHS (personal protective equipment or cooling vest, respectively). Measurements of flow-mediated dilatation (FMD), reactive hyperaemia and shear rate area under the curve (SR AUC ) were performed pre- and postexercise. During EIHS, core temperature was significantly higher (38 ± 0.1 versus 37 ± 0.1°C). Postexercise FMD tended to be suppressed

  17. Effective stresses and shear failure pressure from in situ Biot's coefficient, Hejre Field, North Sea

    DEFF Research Database (Denmark)

    Regel, Jeppe Bendix; Orozova-Bekkevold, Ivanka; Andreassen, Katrine Alling

    2017-01-01

    , is significantly different from 1. The log-derived Biot's coefficient is above 0.8 in the Shetland Chalk Group and in the Tyne Group, and 0.6-0.8 in the Heno Sandstone Formation. We show that the effective vertical and horizontal stresses obtained using the log-derived Biot's coefficient result in a drilling......We propose a combination of Biot's equations for effective stress and the expression for shear failure in a rock to obtain an expression for minimum pore pressure in a stable vertical well bore. We show that a Biot's coefficient calculated from logging data in the Hejre Field, North Sea...

  18. Stress growth and relaxation of dendritically branched macromolecules in shear and uniaxial extension

    DEFF Research Database (Denmark)

    Huang, Qian; Costanzo, S.; Das, C.

    2017-01-01

    stress relaxation, suggesting a strong ‘elastic memory’ of the material. These results are 2 described by BoB semi-quantitatively, both in linear and nonlinear shear and extensional regimes. Given the fact that the segments between branch points are less than 3 entanglements long, this is a very...... of stretches of different parts of the polymer appears to be the origin of the slower subsequent relaxation of extensional stress. Concerning the latter effect, for which predictions are not available, it is hoped that the present experimental findings and proposed framework of analysis will motivate further...

  19. Stress relaxation at a gelatin hydrogel-glass interface in direct shear sliding

    Science.gov (United States)

    Gupta, Vinit; Singh, Arun K.

    2018-01-01

    In this paper, we study experimentally the stress relaxation behavior of soft solids such as gelatin hydrogels on a smooth glass surface in direct shear sliding. It is observed experimentally that irrespective of pulling velocity, the sliding block relaxes to the same level of nonzero residual stress. However, residual stress increases with increasing gelatin concentration in the hydrogels. We have also validated a friction model for strong bond formation during steady relaxation in light of the experimental observations. Our theoretical analysis establishes that population of dangling chains at the sliding interface significantly affects the relaxation process. As a result, residual stress increases with increasing gelatin concentration or decreasing mesh size of the three-dimensional structures in the hydrogels. It is also found that the transition time, at which a weak bond converts to strong bond, increases with increasing mesh size of the hydrogels. Moreover, relaxation time constant of a strong bond decreases with increasing mesh size. However, activation length of a strong bond increases with mesh size. Finally, this study signifies the role of residual strength in frictional shear sliding and it is believed that these results should be useful to understand the role of residual stress in stick-slip instability.

  20. Thermal residual stress evaluation based on phase-shift lateral shearing interferometry

    Science.gov (United States)

    Dai, Xiangjun; Yun, Hai; Shao, Xinxing; Wang, Yanxia; Zhang, Donghuan; Yang, Fujun; He, Xiaoyuan

    2018-06-01

    An interesting phase-shift lateral shearing interferometry system was proposed to evaluate the thermal residual stress distribution in transparent specimen. The phase-shift interferograms was generated by moving a parallel plane plate. Based on analyzing the fringes deflected by deformation and refractive index change, the stress distribution can be obtained. To verify the validity of the proposed method, a typical experiment was elaborately designed to determine thermal residual stresses of a transparent PMMA plate subjected to the flame of a lighter. The sum of in-plane stress distribution was demonstrated. The experimental data were compared with values measured by digital gradient sensing method. Comparison of the results reveals the effectiveness and feasibility of the proposed method.

  1. Influence of Coherent Structures on the Wall Shear Stress in Axial Flow Between a Cylinder and a Plane Wall

    International Nuclear Information System (INIS)

    Khabbouchi, Imed; Guellouz, Mohamed Sadok; Tavoularis, Stavros

    2009-01-01

    Synchronised hot-film and hot-wire measurements were made in the narrower region of a rectangular channel containing a cylindrical rod. The hot-film probe was mounted flush with the channel bottom wall to measure the wall shear stress, while the hot-wire probe was placed at a fixed position, selected in order to easily detect the passage of coherent structures. Mean and rms profiles of the wall shear stress show the influence of the gap to diameter ratio on their respective distributions. The latter presented peculiarities that could only be explained by the presence of coherent structures in the flow between the rod and the wall. Evidence of this presence is seen in the velocity power spectra. The strong influence of the coherent structures on the wall shear stress spatial and temporal distributions is established through velocity-wall shear stress cross-correlations functions and through conditionally sampled measurements

  2. Energy Consumption in Terms of Shear Stress for Two Types of Membrane Bioreactors used for Municipal Wastewater Treatment Processes

    DEFF Research Database (Denmark)

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

    2012-01-01

    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...... 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...

  3. Monodimensional estimation of maximum Reynolds shear stress in the downstream flow field of bileaflet valves.

    Science.gov (United States)

    Grigioni, Mauro; Daniele, Carla; D'Avenio, Giuseppe; Barbaro, Vincenzo

    2002-05-01

    Turbulent flow generated by prosthetic devices at the bloodstream level may cause mechanical stress on blood particles. Measurement of the Reynolds stress tensor and/or some of its components is a mandatory step to evaluate the mechanical load on blood components exerted by fluid stresses, as well as possible consequent blood damage (hemolysis or platelet activation). Because of the three-dimensional nature of turbulence, in general, a three-component anemometer should be used to measure all components of the Reynolds stress tensor, but this is difficult, especially in vivo. The present study aimed to derive the maximum Reynolds shear stress (RSS) in three commercially available prosthetic heart valves (PHVs) of wide diffusion, starting with monodimensional data provided in vivo by echo Doppler. Accurate measurement of PHV flow field was made using laser Doppler anemometry; this provided the principal turbulence quantities (mean velocity, root-mean-square value of velocity fluctuations, average value of cross-product of velocity fluctuations in orthogonal directions) needed to quantify the maximum turbulence-related shear stress. The recorded data enabled determination of the relationship, the Reynolds stresses ratio (RSR) between maximum RSS and Reynolds normal stress in the main flow direction. The RSR was found to be dependent upon the local structure of the flow field. The reported RSR profiles, which permit a simple calculation of maximum RSS, may prove valuable during the post-implantation phase, when an assessment of valve function is made echocardiographically. Hence, the risk of damage to blood constituents associated with bileaflet valve implantation may be accurately quantified in vivo.

  4. Shear Stress Induces Phenotypic Modulation of Vascular Smooth Muscle Cells via AMPK/mTOR/ULK1-Mediated Autophagy.

    Science.gov (United States)

    Sun, Liqian; Zhao, Manman; Liu, Aihua; Lv, Ming; Zhang, Jingbo; Li, Youxiang; Yang, Xinjian; Wu, Zhongxue

    2018-03-01

    Phenotypic modulation of vascular smooth muscle cells (VSMCs) is involved in the pathophysiological processes of the intracranial aneurysms (IAs). Although shear stress has been implicated in the proliferation, migration, and phenotypic conversion of VSMCs, the molecular mechanisms underlying these events are currently unknown. In this study, we investigated whether shear stress(SS)-induced VSMC phenotypic modulation was mediated by autophagy involved in adenosine monophosphate-activated protein kinase (AMPK)/mammalian target of rapamycin (mTOR)/Unc-51-like kinase 1 (ULK1) pathway. The results show that shear stress could inhibit the expression of key VSMC contractile genes and induce pro-inflammatory/matrix-remodeling genes levels, contributing to VSMCs phenotypic switching from a contractile to a synthetic phenotype. More importantly, Shear stress also markedly increased the levels of the autophagy marker microtubule-associated protein light chain 3-II (LC3II), Beclin-1, and p62 degradation. The autophagy inhibitor 3-methyladenine (3-MA) significantly blocked shear-induced phenotypic modulation of VSMCs. To further explore the molecular mechanism involved in shear-induced autophagy, we found that shear stress could activate AMPK/mTOR/ULK1 signaling pathway in VSMCs. Compound C, a pharmacological inhibitor of AMPK, significantly reduced the levels of p-AMPK and p-ULK, enhanced p-mTOR level, and finally decreased LC3II and Beclin-1 level, which suggested that activated AMPK/mTOR/ULK1 signaling was related to shear-mediated autophagy. These results indicate that shear stress promotes VSMC phenotypic modulation through the induction of autophagy involved in activating the AMPK/mTOR/ULK1 pathway.

  5. Estimation of gas wall shear stress in horizontal stratified gas-liquid pipe flow

    International Nuclear Information System (INIS)

    Newton, C.H.; Behnia, M.

    1996-01-01

    Two-phase pipe flows occur in many industrial applications, such as condensers and evaporators, chemical processing equipment, nuclear reactors, and oil pipelines. A variety of basic mechanistic flow models for predicting the pressure gradient and liquid loading characteristics of these types of flows to assist in design calculations has emerged over the past two decades, especially for the stratified and slug flow regimes. These models generally rely on a number of basic assumptions and empirical closure equations. Possibly the most notable of these relates to the evaluation of interfacial shear stresses. However, one of the most important yet least discussed assumptions used in most of these models is that the phase wall shear stresses can be accurately estimated from correlations developed for single-phase pipe flows. The object of this article is to present measurements of gas wall shear up to locations in close proximity to the gas-liquid interface for a variety of interface conditions in developed flow, and to determine the effects of the interface on average gas wall friction factors. In this context the interface may be smooth, rippled or wavy

  6. Pulsatility Index as a Diagnostic Parameter of Reciprocating Wall Shear Stress Parameters in Physiological Pulsating Waveforms.

    Directory of Open Access Journals (Sweden)

    Idit Avrahami

    Full Text Available Arterial wall shear stress (WSS parameters are widely used for prediction of the initiation and development of atherosclerosis and arterial pathologies. Traditional clinical evaluation of arterial condition relies on correlations of WSS parameters with average flow rate (Q and heart rate (HR measurements. We show that for pulsating flow waveforms in a straight tube with flow reversals that lead to significant reciprocating WSS, the measurements of HR and Q are not sufficient for prediction of WSS parameters. Therefore, we suggest adding a third quantity-known as the pulsatility index (PI-which is defined as the peak-to-peak flow rate amplitude normalized by Q. We examine several pulsating flow waveforms with and without flow reversals using a simulation of a Womersley model in a straight rigid tube and validate the simulations through experimental study using particle image velocimetry (PIV. The results indicate that clinically relevant WSS parameters such as the percentage of negative WSS (P[%], oscillating shear index (OSI and the ratio of minimum to maximum shear stress rates (min/max, are better predicted when the PI is used in conjunction with HR and Q. Therefore, we propose to use PI as an additional and essential diagnostic quantity for improved predictability of the reciprocating WSS.

  7. Spatio-temporal characteristics of large scale motions in a turbulent boundary layer from direct wall shear stress measurement

    Science.gov (United States)

    Pabon, Rommel; Barnard, Casey; Ukeiley, Lawrence; Sheplak, Mark

    2016-11-01

    Particle image velocimetry (PIV) and fluctuating wall shear stress experiments were performed on a flat plate turbulent boundary layer (TBL) under zero pressure gradient conditions. The fluctuating wall shear stress was measured using a microelectromechanical 1mm × 1mm floating element capacitive shear stress sensor (CSSS) developed at the University of Florida. The experiments elucidated the imprint of the organized motions in a TBL on the wall shear stress through its direct measurement. Spatial autocorrelation of the streamwise velocity from the PIV snapshots revealed large scale motions that scale on the order of boundary layer thickness. However, the captured inclination angle was lower than that determined using the classic method by means of wall shear stress and hot-wire anemometry (HWA) temporal cross-correlations and a frozen field hypothesis using a convection velocity. The current study suggests the large size of these motions begins to degrade the applicability of the frozen field hypothesis for the time resolved HWA experiments. The simultaneous PIV and CSSS measurements are also used for spatial reconstruction of the velocity field during conditionally sampled intense wall shear stress events. This material is based upon work supported by the National Science Foundation Graduate Research Fellowship under Grant No. DGE-1315138.

  8. MiR-21 is induced in endothelial cells by shear stress and modulates apoptosis and eNOS activity

    International Nuclear Information System (INIS)

    Weber, Martina; Baker, Meredith B.; Moore, Jeffrey P.; Searles, Charles D.

    2010-01-01

    Mechanical forces associated with blood flow play an important role in regulating vascular signaling and gene expression in endothelial cells (ECs). MicroRNAs (miRNAs) are a class of noncoding RNAs that posttranscriptionally regulate the expression of genes involved in diverse cell functions, including differentiation, growth, proliferation, and apoptosis. miRNAs are known to have an important role in modulating EC biology, but their expression and functions in cells subjected to shear stress conditions are unknown. We sought to determine the miRNA expression profile in human ECs subjected to unidirectional shear stress and define the role of miR-21 in shear stress-induced changes in EC function. TLDA array and qRT-PCR analysis performed on HUVECs exposed to prolonged unidirectional shear stress (USS, 24 h, 15 dynes/cm 2 ) identified 13 miRNAs whose expression was significantly upregulated (p · ) production. These data demonstrate that shear stress forces regulate the expression of miRNAs in ECs, and that miR-21 influences endothelial biology by decreasing apoptosis and activating the NO · pathway. These studies advance our understanding of the mechanisms by which shear stress forces modulate vascular homeostasis.

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

    Directory of Open Access Journals (Sweden)

    Mickleborough Timothy D

    2008-09-01

    Full Text Available Abstract Background Normalization of brachial artery flow-mediated dilation (FMD to individual shear stress area under the curve (peak FMD:SSAUC ratio has recently been proposed as an approach to control for the large inter-subject variability in reactive hyperemia-induced shear stress; however, the adoption of this approach among researchers has been slow. The present study was designed to further examine the efficacy of FMD normalization to shear stress in reducing measurement variability. Methods Five different magnitudes of reactive hyperemia-induced shear stress were applied to 20 healthy, physically active young adults (25.3 ± 0. 6 yrs; 10 men, 10 women by manipulating forearm cuff occlusion duration: 1, 2, 3, 4, and 5 min, in a randomized order. A venous blood draw was performed for determination of baseline whole blood viscosity and hematocrit. The magnitude of occlusion-induced forearm ischemia was quantified by dual-wavelength near-infrared spectrometry (NIRS. Brachial artery diameters and velocities were obtained via high-resolution ultrasound. The SSAUC was individually calculated for the duration of time-to-peak dilation. Results One-way repeated measures ANOVA demonstrated distinct magnitudes of occlusion-induced ischemia (volume and peak, hyperemic shear stress, and peak FMD responses (all p AUC (p = 0.785. Conclusion Our data confirm that normalization of FMD to SSAUC eliminates the influences of variable shear stress and solidifies the utility of FMD:SSAUC ratio as an index of endothelial function.

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

    Science.gov (United States)

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

    1998-01-01

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

  11. Fracture predictions for cracks exposed to superimposed normal and shear stresses

    International Nuclear Information System (INIS)

    Richard, H.A.

    1985-01-01

    The author developed a special device and a fracture mechanics specimen and proposed a procedure for determining the fracture toughness when Mixed Mode and Mode II stresses are applied. This device makes it possible to generate pure normal stresses, superimposed normal and shearing stresses as well as pure shearing stresses in the cross section of the crack in the specimen, as desired. The so-called CTS fracture mechanics specimen has an edge crack. The load is transferred statically determind from the device to the specimen by means of six studs altogether. The experiments described, which were carried out with specimens made of the brittle materials PMMA (Plexiglas) and Araldit B, clearly show that it is possible to evaluate the validity of the individual fracture hypotheses by suitable experiments. It is also found that the fracture behaviour of different materials varies considerably both in quality and quantity. In conclusion, a practice-oriented fracture criterion is indicated which enables a practice-conforming evaluation of Mixed-Mode crack problems, as is shown by way of examples. (orig./HP) [de

  12. On Shear Stress Distributions for Flow in Smooth or Partially Rough Annuli

    Energy Technology Data Exchange (ETDEWEB)

    Kjellstroem, B; Hedberg, S

    1966-08-15

    It is commonly assumed that for turbulent flow in annuli the radii of zero shear and maximum velocity are coincident. By inspection of the differential equations for such flow and by an integral analysis it is shown that this is not necessarily true. To check whether important differences could occur, experiments were made in which velocity and shear stress distributions were measured in one smooth and two partially rough annuli. The results show no difference in the radii for the smooth annulus, but for the partially rough annuli there was a small but significant difference. This difference explains the breakdown of Hall's transformation theory reported by other investigators. The error introduced by use of Hall's theory is however small, of the order of 10 % or less.

  13. On Shear Stress Distributions for Flow in Smooth or Partially Rough Annuli

    International Nuclear Information System (INIS)

    Kjellstroem, B.; Hedberg, S.

    1966-08-01

    It is commonly assumed that for turbulent flow in annuli the radii of zero shear and maximum velocity are coincident. By inspection of the differential equations for such flow and by an integral analysis it is shown that this is not necessarily true. To check whether important differences could occur, experiments were made in which velocity and shear stress distributions were measured in one smooth and two partially rough annuli. The results show no difference in the radii for the smooth annulus, but for the partially rough annuli there was a small but significant difference. This difference explains the breakdown of Hall's transformation theory reported by other investigators. The error introduced by use of Hall's theory is however small, of the order of 10 % or less

  14. Stress revisited: A critical evaluation of the stress concept

    NARCIS (Netherlands)

    Koolhaas, J.M.; Bartolomucci, A.; Buwalda, B.; de Boer, S.F.; Flügge, G.; Korte, S.M.; Meerloo, P.; Murison, R.; Olivier, B.; Palanza, P.; Richter-Levin, G.; Sgoifo, A.; Steimer, T.; Stiedl, O.; van Dijk, G.; Wöhr, M.; Fuchs, E.

    2011-01-01

    With the steadily increasing number of publications in the field of stress research it has become evident that the conventional usage of the stress concept bears considerable problems. The use of the term 'stress' to conditions ranging from even the mildest challenging stimulation to severely

  15. Stress revisited : a critical evaluation of the stress concept

    NARCIS (Netherlands)

    Koolhaas, J.M.; Bartolomucci, A; Buwalda, B; Flügge, G; de Boer, Sietse; Korte, S M; Meerlo, P; Murison, R; Olivier, B; Palanza, P; Richter-Levin, G; Sgoifo, A; Steimer, T; Stiedl, O; van Dijk, G; Wöhr, M; Fuchs, E

    2011-01-01

    With the steadily increasing number of publications in the field of stress research it has become evident that the conventional usage of the stress concept bears considerable problems. The use of the term 'stress' to conditions ranging from even the mildest challenging stimulation to severely

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

    Directory of Open Access Journals (Sweden)

    Frank C G van Bussel

    Full Text Available Flow-mediated dilation is aimed at normalization of local wall shear stress under varying blood flow conditions. Blood flow velocity and vessel diameter are continuous and opposing influences that modulate wall shear stress. We derived an index FMDv to quantify wall shear stress normalization performance by flow-mediated dilation in the brachial artery. In 22 fasting presumed healthy men, we first assessed intra- and inter-session reproducibilities of two indices pFMDv and mFMDv, which consider the relative peak and relative mean hyperemic change in flow velocity, respectively. Second, utilizing oral glucose loading, we evaluated the tracking performance of both FMDv indices, in comparison with existing indices [i.e., the relative peak diameter increase (%FMD, the peak to baseline diameter ratio (Dpeak/Dbase, and the relative peak diameter increase normalized to the full area under the curve of blood flow velocity with hyperemia (FMD/shearAUC or with area integrated to peak hyperemia (FMD/shearAUC_peak]. Inter-session and intra-session reproducibilities for pFMDv, mFMDv and %FMD were comparable (intra-class correlation coefficients within 0.521-0.677 range. Both pFMDv and mFMDv showed more clearly a reduction after glucose loading (reduction of ~45%, p≤0.001 than the other indices (% given are relative reductions: %FMD (~11%, p≥0.074; Dpeak/Dbase (~11%, p≥0.074; FMD/shearAUC_peak (~20%, p≥0.016 and FMD/shearAUC (~38%, p≤0.038. Further analysis indicated that wall shear stress normalization under normal (fasting conditions is already far from ideal (FMDv << 1, which (therefore does not materially change with glucose loading. Our approach might be useful in intervention studies to detect intrinsic changes in shear stress normalization performance in conduit arteries.

  17. Fatigue crack growth in 2024-T3 aluminum under tensile and transverse shear stresses

    Science.gov (United States)

    Viz, Mark J.; Zehnder, Alan T.

    1994-01-01

    The influence of transverse shear stresses on the fatigue crack growth rate in thin 2024-T3 aluminum alloy sheets is investigated experimentally. The tests are performed on double-edge cracked sheets in cyclic tensile and torsional loading. This loading generates crack tip stress intensity factors in the same ratio as the values computed for a crack lying along a lap joint in a pressurized aircraft fuselage. The relevant fracture mechanics of cracks in thin plates along with the details of the geometrically nonlinear finite element analyses used for the test specimen calibration are developed and discussed. Preliminary fatigue crack growth data correlated using the fully coupled stress intensity factor calibration are presented and compared with fatigue crack growth data from pure delta K(sub I)fatigue tests.

  18. "Virtual shear box" experiments of stress and slip cycling within a subduction interface mélange

    Science.gov (United States)

    Webber, Sam; Ellis, Susan; Fagereng, Åke

    2018-04-01

    What role does the progressive geometric evolution of subduction-related mélange shear zones play in the development of strain transients? We use a "virtual shear box" experiment, based on outcrop-scale observations from an ancient exhumed subduction interface - the Chrystalls Beach Complex (CBC), New Zealand - to constrain numerical models of slip processes within a meters-thick shear zone. The CBC is dominated by large, competent clasts surrounded by interconnected weak matrix. Under constant slip velocity boundary conditions, models of the CBC produce stress cycling behavior, accompanied by mixed brittle-viscous deformation. This occurs as a consequence of the reorganization of competent clasts, and the progressive development and breakdown of stress bridges as clasts mutually obstruct one another. Under constant shear stress boundary conditions, the models show periods of relative inactivity punctuated by aseismic episodic slip at rapid rates (meters per year). Such a process may contribute to the development of strain transients such as slow slip.

  19. Studies on Impingement Effects of Low Density Jets on Surfaces — Determination of Shear Stress and Normal Pressure

    Science.gov (United States)

    Sathian, Sarith. P.; Kurian, Job

    2005-05-01

    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.

  20. Purinergic signaling is required for fluid shear stress-induced NF-{kappa}B translocation in osteoblasts

    Energy Technology Data Exchange (ETDEWEB)

    Genetos, Damian C., E-mail: dgenetos@ucdavis.edu [Department of Anatomy, Cell Biology, and Physiology, School of Veterinary Medicine, University of California, Davis, CA (United States); Karin, Norman J. [Cell Biology and Biochemistry, Pacific Northwest National Laboratory, Richland, WA (United States); Geist, Derik J. [Department of Orthopaedic Surgery, Indiana University School of Medicine, Indianapolis, IN (United States); Donahue, Henry J. [Division of Musculoskeletal Sciences, Department of Orthopaedics and Rehabilitation, Pennsylvania State College of Medicine, Hershey, PA (United States); Duncan, Randall L. [Department of Orthopaedic Surgery, Indiana University School of Medicine, Indianapolis, IN (United States)

    2011-04-01

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

  1. Flow through internal elastic lamina affects shear stress on smooth muscle cells (3D simulations).

    Science.gov (United States)

    Tada, Shigeru; Tarbell, John M

    2002-02-01

    We describe a three-dimensional numerical simulation of interstitial flow through the medial layer of an artery accounting for the complex entrance condition associated with fenestral pores in the internal elastic lamina (IEL) to investigate the fluid mechanical environment around the smooth muscle cells (SMCs) right beneath the IEL. The IEL was modeled as an impermeable barrier to water flow except for the fenestral pores, which were assumed to be uniformly distributed over the IEL. The medial layer was modeled as a heterogeneous medium composed of a periodic array of cylindrical SMCs embedded in a continuous porous medium representing the interstitial proteoglycan and collagen matrix. Depending on the distance between the IEL bottom surface and the upstream end of the proximal layer of SMCs, the local shear stress on SMCs right beneath the fenestral pore could be more than 10 times higher than that on the cells far removed from the IEL under the conditions that the fenestral pore diameter and area fraction of pores were kept constant at 1.4 microm and 0.05, respectively. Thus these proximal SMCs may experience shear stress levels that are even higher than endothelial cells exposed to normal blood flow (order of 10 dyn/cm(2)). Furthermore, entrance flow through fenestral pores alters considerably the interstitial flow field in the medial layer over a spatial length scale of the order of the fenestral pore diameter. Thus the spatial gradient of shear stress on the most superficial SMC is noticeably higher than computed for endothelial cell surfaces.

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

    Science.gov (United States)

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

    1999-01-01

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

  3. Enhancing PIV image and fractal descriptor for velocity and shear stresses propagation around a circular pier

    Directory of Open Access Journals (Sweden)

    Alireza Keshavarzi

    2017-07-01

    Full Text Available In this study, the fractal dimensions of velocity fluctuations and the Reynolds shear stresses propagation for flow around a circular bridge pier are presented. In the study reported herein, the fractal dimension of velocity fluctuations (u′, v′, w′ and the Reynolds shear stresses (u′v′ and u′w′ of flow around a bridge pier were computed using a Fractal Interpolation Function (FIF algorithm. The velocity fluctuations of flow along a horizontal plane above the bed were measured using Acoustic Doppler Velocity meter (ADV and Particle Image Velocimetry (PIV. The PIV is a powerful technique which enables us to attain high resolution spatial and temporal information of turbulent flow using instantaneous time snapshots. In this study, PIV was used for detection of high resolution fractal scaling around a bridge pier. The results showed that the fractal dimension of flow fluctuated significantly in the longitudinal and transverse directions in the vicinity of the pier. It was also found that the fractal dimension of velocity fluctuations and shear stresses increased rapidly at vicinity of pier at downstream whereas it remained approximately unchanged far downstream of the pier. The higher value of fractal dimension was found at a distance equal to one times of the pier diameter in the back of the pier. Furthermore, the average fractal dimension for the streamwise and transverse velocity fluctuations decreased from the centreline to the side wall of the flume. Finally, the results from ADV measurement were consistent with the result from PIV, therefore, the ADV enables to detect turbulent characteristics of flow around a circular bridge pier.

  4. The influence of geometric factors on the wall shear stress distribution in realistic human coronary arteries

    OpenAIRE

    Santos, Jorge André Piedade Pinhal dos

    2009-01-01

    Dissertação apresentada na Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa para a obtenção do grau de Mestre em Engenharia Biomédica. A presente dissertação foi desenvolvida no Erasmus Medical Center em Roterdão, Holanda Background: Atherosclerosis is the main cause of death in the Western society. It is a geometrically focal disease, affecting preferentially vessel areas of low wall shear stress (SS), which induces the expression of atherogenic genes. To predict wall ...

  5. Flow and bed shear stresses in scour protections around a pile in a current

    DEFF Research Database (Denmark)

    Nielsen, Anders Wedel; Liu, Xiaofeng; Sumer, B. Mutlu

    2013-01-01

    on it in an unfavourable manner. Using physical models and 3D computational fluid dynamic (CFD) numerical simulations, the velocity and bed shear stresses are investigated in complex scour protections around mono piles in steady current. In the physical model the scour protections consisted of an upper cover layer...... simulations are capable of calculating the flow velocities when the scour protection is represented by regular arranged spheres, while the turbulence in general is underestimated. The velocity can also be calculated using porous media flow approach, but the accuracy is not as good as for spheres...

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

    DEFF Research Database (Denmark)

    Thilo, Florian; Vorderwülbecke, Bernd J; Marki, Alex

    2012-01-01

    in comparison with endothelial cells grown under static conditions. There was a significant association between the expression of TRPC6 and tumor necrosis factor-α mRNA in human vascular tissue. No-flow and atheroprone flow conditions are equally characterized by an increase in the expression of tumor necrosis......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...

  7. Shear stress induces cell apoptosis via a c-Src-phospholipase D-mTOR signaling pathway in cultured podocytes

    Energy Technology Data Exchange (ETDEWEB)

    Huang, Chunfa, E-mail: chunfa.huang@case.edu [Louis Stokes Cleveland Veteran Affairs Medical Center, Case Western Reserve University (United States); Department of Medicine, Case Western Reserve University (United States); Rammelkamp Center for Research and Education, MetroHealth System Campus, Cleveland, OH 44106 (United States); Bruggeman, Leslie A. [Department of Medicine, Case Western Reserve University (United States); Rammelkamp Center for Research and Education, MetroHealth System Campus, Cleveland, OH 44106 (United States); Hydo, Lindsey M. [Louis Stokes Cleveland Veteran Affairs Medical Center, Case Western Reserve University (United States); Miller, R. Tyler [Louis Stokes Cleveland Veteran Affairs Medical Center, Case Western Reserve University (United States); Department of Medicine, Case Western Reserve University (United States); Rammelkamp Center for Research and Education, MetroHealth System Campus, Cleveland, OH 44106 (United States)

    2012-06-10

    The glomerular capillary wall, composed of endothelial cells, the glomerular basement membrane and the podocytes, is continually subjected to hemodynamic force arising from tractional stress due to blood pressure and shear stress due to blood flow. Exposure of glomeruli to abnormal hemodynamic force such as hyperfiltration is associated with glomerular injury and progressive renal disease, and the conversion of mechanical stimuli to chemical signals in the regulation of the process is poorly understood in podocytes. By examining DNA fragmentation, apoptotic nuclear changes and cytochrome c release, we found that shear stress induced cell apoptosis in cultured podocytes. Meanwhile, podocytes exposed to shear stress also stimulated c-Src phosphorylation, phospholipase D (PLD) activation and mammalian target of rapamycin (mTOR) signaling. Using the antibodies against c-Src, PLD{sub 1}, and PLD{sub 2} to perform reciprocal co-immunoprecipitations and in vitro PLD activity assay, our data indicated that c-Src interacted with and activated PLD{sub 1} but not PLD{sub 2}. The inhibition of shear stress-induced c-Src phosphorylation by PP{sub 2} (a specific inhibitor of c-Src kinase) resulted in reduced PLD activity. Phosphatidic acid, produced by shear stress-induced PLD activation, stimulated mTOR signaling, and caused podocyte hypertrophy and apoptosis.

  8. Influence of type-I fimbriae and fluid shear stress on bacterial behavior and multicellular architecture of early Escherichia coli biofilms at single-cell resolution.

    Science.gov (United States)

    Wang, Liyun; Keatch, Robert; Zhao, Qi; Wright, John A; Bryant, Clare E; Redmann, Anna L; Terentjev, Eugene M

    2018-01-12

    Biofilm formation on abiotic surfaces in food and medical industry can cause severe contamination and infection, yet how biological and physical factors determine cellular architecture of early biofilms and bacterial behavior of the constituent cells remains largely unknown. In this study we examine the specific role of type-I fimbriae in nascent stages of biofilm formation and the response of micro-colonies to environmental flow shear at single-cell resolution. The results show that type-I fimbriae are not required for reversible adhesion from plankton, but critical for irreversible adhesion of Escherichia coli ( E.coli ) MG1655 forming biofilms on polyethylene terephthalate (PET) surfaces. Besides establishing a firm cell-surface contact, the irreversible adhesion seems necessary to initiate the proliferation of E.coli on the surface. After application of shear stress, bacterial retention is dominated by the 3D architecture of colonies independent of the population and the multi-layered structure could protect the embedded cells from being insulted by fluid shear, while cell membrane permeability mainly depends on the biofilm population and the duration time of the shear stress. Importance Bacterial biofilms could lead to severe contamination problems in medical devices and food processing equipment. However, biofilms are usually studied at a rough macroscopic level, thus little is known about how individual bacterial behavior within biofilms and multicellular architecture are influenced by bacterial appendages (e.g. pili/fimbriae) and environmental factors during early biofilm formation. We apply Confocal Laser Scanning Microscopy (CLSM) to visualize E.coli micro-colonies at single-cell resolution. Our findings suggest that type-I fimbriae are vital to the initiation of bacterial proliferation on surfaces and that the responses of biofilm architecture and cell membrane permeability of constituent bacteria to fluid shear stress are different, which are

  9. Interaction between a normal shock wave and a turbulent boundary layer at high transonic speeds. Part 2: Wall shear stress

    Science.gov (United States)

    Liou, M. S.; Adamson, T. C., Jr.

    1979-01-01

    An analysis is presented of the flow in the two inner layers, the Reynolds stress sublayer and the wall layer. Included is the calculation of the shear stress at the wall in the interaction region. The limit processes considered are those used for an inviscid flow.

  10. Family Stress in Pediatric Critical Care.

    Science.gov (United States)

    Hagstrom, Sandra

    This mixed methods study explored stress in families whose children were hospitalized in the pediatric intensive care unit (PICU) for more than one week. The study aim was to describe sources of stress for families whose children require extended hospitalization in the PICU. Data collection included semi-structured interviews and completion of the Family Inventory of Life Events and Family System Stressor Strength Inventory. Themes reported in this paper are separation, not knowing, and the child's illness and distress. Additional research is needed to validate these findings in families of other cultures and structures, and in other PICUs. Copyright © 2016 Elsevier Inc. All rights reserved.

  11. Fabrication of simulated plate fuel elements: Defining role of out-of-plane residual shear stress

    Energy Technology Data Exchange (ETDEWEB)

    Rakesh, R., E-mail: rakesh.rad87@gmail.com [DAE Graduate Fellows, IIT Bombay, Powai, Mumbai 400076 (India); Metallic Fuels Division, BARC, Trombay, Mumbai 400085 (India); Kohli, D. [DAE Graduate Fellows, IIT Bombay, Powai, Mumbai 400076 (India); Metallic Fuels Division, BARC, Trombay, Mumbai 400085 (India); Sinha, V.P.; Prasad, G.J. [Metallic Fuels Division, BARC, Trombay, Mumbai 400085 (India); Samajdar, I. [Department of Metallurgical Engineering and Materials Science, IIT Bombay, Powai, Mumbai 400076 (India)

    2014-02-01

    Bond strength and microstructural developments were investigated during fabrication of simulated plate fuel elements. The study involved roll bonding of aluminum–aluminum (case A) and aluminum–aluminum + yttria (Y{sub 2}O{sub 3}) dispersion (case B). Case B approximated aluminum–uranium silicide (U{sub 3}Si{sub 2}) ‘fuel-meat’ in an actual plate fuel. Samples after different stages of fabrication, hot and cold rolling, were investigated through peel and pull tests, micro-hardness, residual stresses, electron and micro-focus X-ray diffraction. Measurements revealed a clear drop in bond strength during cold rolling: an observation unique to case B. This was related to significant increase in ‘out-of-plane’ residual shear stresses near the clad/dispersion interface, and not from visible signatures of microstructural heterogeneities.

  12. Rivulet flow round a horizontal cylinder subject to a uniform surface shear stress

    KAUST Repository

    Paterson, C.

    2014-09-14

    © 2014 © The Author, 2014. Published by Oxford University Press; all rights reserved. For Permissions, please email: journals.permissions@oup.com. The steady flow of a slowly varying rivulet with prescribed flux in the azimuthal direction round a large stationary horizontal cylinder subject to a prescribed uniform azimuthal surface shear stress is investigated. In particular, we focus on the case where the volume flux is downwards but the shear stress is upwards, for which there is always a solution corresponding to a rivulet flowing down at least part of one side of the cylinder. We consider both a rivulet with constant non-zero contact angle but slowly varying width (that is, de-pinned contact lines) and a rivulet with constant width but slowly varying contact angle (that is, pinned contact lines), and show that they have qualitatively different behaviour. When shear is present, a rivulet with constant non-zero contact angle can never run all the way from the top to the bottom of the cylinder, and so we consider the scenario in which an infinitely wide two-dimensional film of uniform thickness covers part of the upper half of the cylinder and \\'breaks\\' into a single rivulet with constant non-zero contact angle. In contrast, a sufficiently narrow rivulet with constant width can run all the way from the top to the bottom of the cylinder, whereas a wide rivulet can do so only if its contact lines de-pin, and so we consider the scenario in which the contact lines of a wide rivulet de-pin on the lower half of the cylinder.

  13. Estimation of basal shear stresses from now ice-free LIA glacier forefields in the Swiss Alps

    Science.gov (United States)

    Fischer, Mauro; Haeberli, Wilfried; Huss, Matthias; Paul, Frank; Linsbauer, Andreas; Hoelzle, Martin

    2013-04-01

    In most cases, assessing the impacts of climatic changes on glaciers requires knowledge about the ice thickness distribution. Miscellaneous methodological approaches with different degrees of sophistication have been applied to model glacier thickness so far. However, all of them include significant uncertainty. By applying a parameterization scheme for ice thickness determination relying on assumptions about basal shear stress by Haeberli and Hoelzle (1995) to now ice-free glacier forefields in the Swiss Alps, basal shear stress values can be calculated based on a fast and robust experimental approach. In a GIS, the combination of recent (1973) and Little Ice Age (LIA) maximum (around 1850) glacier outlines, central flowlines, a recent Digital Elevation Model (DEM) and a DEM of glacier surface topography for the LIA maximum allows extracting local ice thickness over the forefield of individual glaciers. Subsequently, basal shear stress is calculated via the rheological assumption of perfect-plasticity relating ice thickness and surface slope to shear stress. The need of only very few input data commonly stored in glacier inventories permits an application to a large number of glaciers. Basal shear stresses are first calculated for subsamples of glaciers belonging to two test sites where the LIA maximum glacier surface is modeled with DEMs derived from accurate topographic maps for the mid 19th century. Neglecting outliers, the average resulting mean basal shear stress is around 80 kPa for the Bernina region (range 25-100 kPa) and 120 kPa (range 50-150 kPa) for the Aletsch region. For the entire Swiss Alps it is 100 kPa (range 40-175 kPa). Because complete LIA glacier surface elevation information is lacking there, a DEM is first created from reconstructed height of LIA lateral moraines and trimlines by using a simple GIS-based tool. A sensitivity analysis of the input parameters reveals that the performance of the developed approach primarily depends on the

  14. PIV Measurement of Wall Shear Stress and Flow Structures within an Intracranial Aneurysm Model

    Science.gov (United States)

    Chow, Ricky; Sparrow, Eph; Campbell, Gary; Divani, Afshin; Sheng, Jian

    2012-11-01

    The formation and rupture of an intracranial aneurysm (IA) is a debilitating and often lethal event. Geometric features of the aneurysm bulb and upstream artery, such as bulb size, bulb shape, and curvature of the artery, are two groups of factors that define the flow and stresses within an IA. Abnormal flow stresses are related to rupture. This presentation discusses the development of a quasi-3D PIV technique and its application in various glass models at Re = 275 and 550 to experimentally assess at a preliminary level the impact of geometry and flow rate. Some conclusions are to be drawn linking geometry of the flow domain to rupture risk. The extracted results also serve as the baseline case and as a precursor to a companion presentation by the authors discussing the impact of flow diverters, a new class of medical devices. The PIV experiments were performed in a fully index-matched flow facility, allowing for unobstructed observations over complex geometry. A reconstruction and analysis method was devised to obtain 3D mean wall stress distributions and flow fields. The quasi 3D measurements were reconstructed from orthogonal planes encompassing the entire glass model, spaced 0.4mm apart. Wall shear stresses were evaluated from the near-wall flow viscous stresses.

  15. Wall morphology, blood flow and wall shear stress: MR findings in patients with peripheral artery disease

    Energy Technology Data Exchange (ETDEWEB)

    Galizia, Mauricio S.; Barker, Alex; Collins, Jeremy; Carr, James [Northwestern University, Department of Radiology, Feinberg School of Medicine, Chicago, IL (United States); Liao, Yihua [Northwestern University' s Feinberg School of Medicine, Department of Preventive Medicine, Chicago, IL (United States); McDermott, Mary M. [Northwestern University' s Feinberg School of Medicine, Department of Preventive Medicine, Chicago, IL (United States); Northwestern University' s Feinberg School of Medicine, Department of Medicine, Chicago, IL (United States); Markl, Michael [Northwestern University, Department of Radiology, Feinberg School of Medicine, Chicago, IL (United States); Northwestern University, Department Biomedical Engineering, McCormick School of Engineering, Chicago, IL (United States)

    2014-04-15

    To investigate the influence of atherosclerotic plaques on femoral haemodynamics assessed by two-dimensional (2D) phase-contrast (PC) magnetic resonance imaging (MRI) with three-directional velocity encoding. During 1 year, patients with peripheral artery disease and an ankle brachial index <1.00 were enrolled. After institutional review board approval and written informed consent, 44 patients (age, 70 ± 12 years) underwent common femoral artery MRI. Patients with contra-indications for MRI were excluded. Sequences included 2D time-of-flight, proton-density, T1-weighted and T2-weighted MRI. Electrocardiogram (ECG)-gated 2D PC-MRI with 3D velocity encoding was acquired. A radiologist classified images in five categories. Blood flow, velocity and wall shear stress (WSS) along the vessel circumference were quantified from the PC-MRI data. The acquired images were of good quality for interpretation. There were no image quality problems related to poor ECG-gating or slice positioning. Velocities, oscillatory shear stress and total flow were similar between patients with normal arteries and wall thickening/plaque. Patients with plaques demonstrated regionally increased peak systolic WSS and enhanced WSS eccentricity. Combined multi-contrast morphological imaging of the peripheral arterial wall with PC-MRI with three-directional velocity encoding is a feasible technique. Further study is needed to determine whether flow is an appropriate marker for altered endothelial cell function, vascular remodelling and plaque progression. (orig.)

  16. Prediction of wall shear stresses in transitional boundary layers using near-wall mean velocity profiles

    International Nuclear Information System (INIS)

    Jeon, Woo Pyung; Shin, Sung Ho; Kang, Shin Hyoung

    2000-01-01

    The local wall shear stress in transitional boundary layer was estimated from the near-wall mean velocity data using the principle of Computational Preston tube Method(CPM). The previous DNS and experimental databases of transitional boundary layers were used to demonstrate the accuracy of the method and to provide the applicable range of wall unit y + . The skin friction coefficients predicted by the CPM agreed well with those from previous studies. To reexamine the applicability of the CPM, near-wall hot-wire measurements were conducted in developing transitional boundary layers on a flat plate with different freestream turbulence intensities. The intermittency profiles across the transitional boundary layers were reasonably obtained from the conditional sampling technique. An empirical correlation between the representative intermittency near the wall and the free parameter K 1 of the extended wall function of CPM has been newly proposed using the present and other experimental data. The CPM has been verified as a useful tool to measure the wall shear stress in transitional boundary layer with reasonable accuracy

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

    Science.gov (United States)

    Fourrié, Grégoire; Keirsbulck, Laurent; Labraga, Larbi

    2013-10-01

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

  18. Measurements of wall shear stress in a planar turbulent Couette flow with porous walls

    Science.gov (United States)

    Beuther, Paul

    2013-11-01

    Measurements of drag on a moving web in a multi-span festoon show a stronger than expected dependency on the porosity of the web. The experiments suggest a wall shear stress 3-4 times larger than non-porous webs or historical Couette flow data for solid walls. Previous DNS studies by Jimenez et al. (JFM Vol 442) of boundary layers with passive porous surfaces predict a much smaller increase in wall shear stress for a porous wall of only 40%. Other DNS studies by Quadrio et al. (JFM Vol 576) of porous walls with periodic transpiration do show a large increase in drag under certain periodic conditions of modest amplitude. Although those results are aligned in magnitude with this study, the exact reason for the observed high drag for porous webs in this present study is not understood because there was no external disturbance applied to the web. It can be hypothesized that natural flutter of the web results in a similar mechanism shown in the periodic DNS study, but when the natural flutter was reduced by increasing web tension, there was only a small decrease of the drag. A key difference in this study is that because of the multiple parallel spans in a festoon, any transpiration in one layer must act in the opposite manner on the adjacent span.

  19. Influence of shear stress and size on viability of endothelial cells exposed to gold nanoparticles

    Science.gov (United States)

    Fede, C.; Albertin, Giovanna; Petrelli, L.; De Caro, R.; Fortunati, I.; Weber, V.; Ferrante, Camilla

    2017-09-01

    Screening nanoparticle toxicity directly on cell culture can be a fast and cheap technique. Nevertheless, to obtain results in accordance with those observed in live animals, the conditions in which cells are cultivated should resemble the one encountered in live systems. Microfluidic devices offer the possibility to satisfy this requirement, in particular with endothelial cell lines, because they are capable to reproduce the flowing media and shear stress experienced by these cell lines in vivo. In this work, we exploit a microfluidic device to observe how human umbilical vein endothelial cells (HUVEC) viability changes when subject to a continuous flow of culture medium, in which spherical citrate-stabilized gold nanoparticles of different sizes and at varying doses are investigated. For comparison, the same experiments are also run in multiwells where the cells do not experience the shear stress induced by the flowing medium. We discuss the results considering the influence of mode of exposure and nanoparticle size (24 and 13 nm). We observed that gold nanoparticles show a lower toxicity under flow conditions with respect to static and the HUVEC viability decreases as the nanoparticle surface area per unit volume increases, regardless of size.

  20. Magnetoelastic shear wave propagation in pre-stressed anisotropic media under gravity

    Science.gov (United States)

    Kumari, Nirmala; Chattopadhyay, Amares; Singh, Abhishek K.; Sahu, Sanjeev A.

    2017-03-01

    The present study investigates the propagation of shear wave (horizontally polarized) in two initially stressed heterogeneous anisotropic (magnetoelastic transversely isotropic) layers in the crust overlying a transversely isotropic gravitating semi-infinite medium. Heterogeneities in both the anisotropic layers are caused due to exponential variation (case-I) and linear variation (case-II) in the elastic constants with respect to the space variable pointing positively downwards. The dispersion relations have been established in closed form using Whittaker's asymptotic expansion and were found to be in the well-agreement to the classical Love wave equations. The substantial effects of magnetoelastic coupling parameters, heterogeneity parameters, horizontal compressive initial stresses, Biot's gravity parameter, and wave number on the phase velocity of shear waves have been computed and depicted by means of a graph. As a special case, dispersion equations have been deduced when the two layers and half-space are isotropic and homogeneous. The comparative study for both cases of heterogeneity of the layers has been performed and also depicted by means of graphical illustrations.

  1. Medial tibial stress syndrome: a critical review

    NARCIS (Netherlands)

    Moen, Maarten H.; Tol, Johannes L.; Weir, Adam; Steunebrink, Miriam; de Winter, Theodorus C.

    2009-01-01

    Medial tibial stress syndrome (MTSS) is one of the most common leg injuries in athletes and soldiers. The incidence of MTSS is reported as being between 4% and 35% in military personnel and athletes. The name given to this condition refers to pain on the posteromedial tibial border during exercise,

  2. Experimental analysis of minimum shear stress to drag particles in a horizontal bed; Analise experimental da tensao de cisalhamento minima para arraste de particulas em um leito horizontal

    Energy Technology Data Exchange (ETDEWEB)

    Dornelas, Breno Almeida; Soares, Edson Jose [Universidade Federal do Espirito Santo. Departamento de Engenharia Mecanica (Brazil)], e-mails: bad@ucl.br, edson@ct.ufes.br; Quirino Filho, Joao Pedro; Loureiro, Bruno Venturini [Faculdade do Centro Leste (UCL). Laboratorio de Fluidos e Fenomenos de Transporte (Brazil)], e-mails: joaoquirino@ucl.br, brunovl@ucl.br

    2009-12-15

    Efficient hole cleaning is still a challenge in well bore drilling to produce oil and gas. The critical point is the horizontal drilling that inherently tends to form a bed of sediment particles at the well bottom during drilling. The cuttings bed erosion depends mainly on the shear stress promoted by the drilling fluid flow. The shear stress required to cause drag in the cuttings bed is investigated according to the fluid and particles properties, using an experimental assembly, composed of: a system for fluid circulation, a particle box, a pump system and measuring equipment. The observation area is a box below the flow line in an acrylic duct used to calibrate sand particles. The test starts with the pumps in a low frequency which is increased in steps. At each frequency level, images are captured of carried particles and the established flow rate is recorded. The images are analyzed when the dragged particle is no longer random and sporadic, but becomes permanent. The shear stress is identified by the PKN correlation (by Prandtl, von Karman, and Nikuradse) for the minimum flow rate necessary to cause drag. Results were obtained for just water and water-glycerin solution flows. (author)

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

    Science.gov (United States)

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

    2008-09-04

    Normalization of brachial artery flow-mediated dilation (FMD) to individual shear stress area under the curve (peak FMD:SSAUC ratio) has recently been proposed as an approach to control for the large inter-subject variability in reactive hyperemia-induced shear stress; however, the adoption of this approach among researchers has been slow. The present study was designed to further examine the efficacy of FMD normalization to shear stress in reducing measurement variability. Five different magnitudes of reactive hyperemia-induced shear stress were applied to 20 healthy, physically active young adults (25.3 +/- 0. 6 yrs; 10 men, 10 women) by manipulating forearm cuff occlusion duration: 1, 2, 3, 4, and 5 min, in a randomized order. A venous blood draw was performed for determination of baseline whole blood viscosity and hematocrit. The magnitude of occlusion-induced forearm ischemia was quantified by dual-wavelength near-infrared spectrometry (NIRS). Brachial artery diameters and velocities were obtained via high-resolution ultrasound. The SSAUC was individually calculated for the duration of time-to-peak dilation. One-way repeated measures ANOVA demonstrated distinct magnitudes of occlusion-induced ischemia (volume and peak), hyperemic shear stress, and peak FMD responses (all p index of endothelial function.

  4. Shear stress induced by an interstitial level of slow flow increases the osteogenic differentiation of mesenchymal stem cells through TAZ activation.

    Directory of Open Access Journals (Sweden)

    Kyung Min Kim

    Full Text Available Shear stress activates cellular signaling involved in cellular proliferation, differentiation, and migration. However, the mechanisms of mesenchymal stem cell (MSC differentiation under interstitial flow are not fully understood. Here, we show the increased osteogenic differentiation of MSCs under exposure to constant, extremely low shear stress created by osmotic pressure-induced flow in a microfluidic chip. The interstitial level of shear stress in the proposed microfluidic system stimulated nuclear localization of TAZ (transcriptional coactivator with PDZ-binding motif, a transcriptional modulator of MSCs, activated TAZ target genes such as CTGF and Cyr61, and induced osteogenic differentiation. TAZ-depleted cells showed defects in shear stress-induced osteogenic differentiation. In shear stress induced cellular signaling, Rho signaling pathway was important forthe nuclear localization of TAZ. Taken together, these results suggest that TAZ is an important mediator of interstitial flow-driven shear stress signaling in osteoblast differentiation of MSCs.

  5. Critical water stress levels in Pinus patula seedlings and their ...

    African Journals Online (AJOL)

    Critical water stress levels in Pinus patula seedlings and their relation to measures of seedling morphology. ... Southern Forests: a Journal of Forest Science ... A pot trial was implemented to determine the effect of soil water stress following transplanting on shoot water potential and stomatal conductance of Pinus patula ...

  6. Numerical Study of the Critical Impact Velocity in Shear. Appendix Number 1

    National Research Council Canada - National Science Library

    Klosak, M

    1996-01-01

    .... A numerical study of impact shearing of a layer has been performed by the FE code ABAQUS. It was intended to verify available experimental results for VAR 4340 steel 52 HRC, obtained by direct...

  7. Controlling Shear Stress in 3D Bioprinting is a Key Factor to Balance Printing Resolution and Stem Cell Integrity.

    Science.gov (United States)

    Blaeser, Andreas; Duarte Campos, Daniela Filipa; Puster, Uta; Richtering, Walter; Stevens, Molly M; Fischer, Horst

    2016-02-04

    A microvalve-based bioprinting system for the manufacturing of high-resolution, multimaterial 3D-structures is reported. Applying a straightforward fluid-dynamics model, the shear stress at the nozzle site can precisely be controlled. Using this system, a broad study on how cell viability and proliferation potential are affected by different levels of shear stress is conducted. Complex, multimaterial 3D structures are printed with high resolution. This work pioneers the investigation of shear stress-induced cell damage in 3D bioprinting and might help to comprehend and improve the outcome of cell-printing studies in the future. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  8. Wall Shear Stress Estimation of Thoracic Aortic Aneurysm Using Computational Fluid Dynamics

    Directory of Open Access Journals (Sweden)

    J. Febina

    2018-01-01

    Full Text Available An attempt has been made to evaluate the effects of wall shear stress (WSS on thoracic aortic aneurysm (TAA using Computational Fluid Dynamics (CFD. Aneurysm is an excessive localized swelling of the arterial wall due to many physiological factors and it may rupture causing shock or sudden death. The existing imaging modalities such as MRI and CT assist in the visualization of anomalies in internal organs. However, the expected dynamic behaviour of arterial bulge under stressed condition can only be effectively evaluated through mathematical modelling. In this work, a 3D aneurysm model is reconstructed from the CT scan slices and eventually the model is imported to Star CCM+ (Siemens, USA for intensive CFD analysis. The domain is discretized using polyhedral mesh with prism layers to capture the weakening boundary more accurately. When there is flow reversal in TAA as seen in the velocity vector plot, there is a chance of cell damage causing clots. This is because of the shear created in the system due to the flow pattern. It is observed from the proposed mathematical modelling that the deteriorating WSS is an indicator for possible rupture and its value oscillates over a cardiac cycle as well as over different stress conditions. In this model, the vortex formation pattern and flow reversals are also captured. The non-Newtonian model, including a pulsatile flow instead of a steady average flow, does not overpredict the WSS (15.29 Pa compared to 16 Pa for the Newtonian model. Although in a cycle the flow behaviour is laminar-turbulent-laminar (LTL, utilizing the non-Newtonian model along with LTL model also overpredicted the WSS with a value of 20.1 Pa. The numerical study presented here provides good insight of TAA using a systematic approach to numerical modelling and analysis.

  9. Hydrostatic pressure and shear stress affect endothelin-1 and nitric oxide release by endothelial cells in bioreactors.

    Science.gov (United States)

    Vozzi, Federico; Bianchi, Francesca; Ahluwalia, Arti; Domenici, Claudio

    2014-01-01

    Abundant experimental evidence demonstrates that endothelial cells are sensitive to flow; however, the effect of fluid pressure or pressure gradients that are used to drive viscous flow is not well understood. There are two principal physical forces exerted on the blood vessel wall by the passage of intra-luminal blood: pressure and shear. To analyze the effects of pressure and shear independently, these two stresses were applied to cultured cells in two different types of bioreactors: a pressure-controlled bioreactor and a laminar flow bioreactor, in which controlled levels of pressure or shear stress, respectively, can be generated. Using these bioreactor systems, endothelin-1 (ET-1) and nitric oxide (NO) release from human umbilical vein endothelial cells were measured under various shear stress and pressure conditions. Compared to the controls, a decrease of ET-1 production by the cells cultured in both bioreactors was observed, whereas NO synthesis was up-regulated in cells under shear stress, but was not modulated by hydrostatic pressure. These results show that the two hemodynamic forces acting on blood vessels affect endothelial cell function in different ways, and that both should be considered when planning in vitro experiments in the presence of flow. Understanding the individual and synergic effects of the two forces could provide important insights into physiological and pathological processes involved in vascular remodeling and adaptation. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  10. MiR-21 is induced in endothelial cells by shear stress and modulates apoptosis and eNOS activity

    Energy Technology Data Exchange (ETDEWEB)

    Weber, Martina; Baker, Meredith B.; Moore, Jeffrey P. [Division of Cardiology, Emory University, 1639 Pierce Drive, WMB 319, Atlanta, GA 30322 (United States); Searles, Charles D., E-mail: csearle@emory.edu [Division of Cardiology, Emory University, 1639 Pierce Drive, WMB 319, Atlanta, GA 30322 (United States); Atlanta Veterans Administration Medical Center, 1670 Clarimont Road, Decatur, GA 30033 (United States)

    2010-03-19

    Mechanical forces associated with blood flow play an important role in regulating vascular signaling and gene expression in endothelial cells (ECs). MicroRNAs (miRNAs) are a class of noncoding RNAs that posttranscriptionally regulate the expression of genes involved in diverse cell functions, including differentiation, growth, proliferation, and apoptosis. miRNAs are known to have an important role in modulating EC biology, but their expression and functions in cells subjected to shear stress conditions are unknown. We sought to determine the miRNA expression profile in human ECs subjected to unidirectional shear stress and define the role of miR-21 in shear stress-induced changes in EC function. TLDA array and qRT-PCR analysis performed on HUVECs exposed to prolonged unidirectional shear stress (USS, 24 h, 15 dynes/cm{sup 2}) identified 13 miRNAs whose expression was significantly upregulated (p < 0.05). The miRNA with the greatest change was miR-21; it was increased 5.2-fold (p = 0.002) in USS-treated versus control cells. Western analysis demonstrated that PTEN, a known target of miR-21, was downregulated in HUVECs exposed to USS or transfected with pre-miR-21. Importantly, HUVECs overexpressing miR-21 had decreased apoptosis and increased eNOS phosphorylation and nitric oxide (NO{sup {center_dot}}) production. These data demonstrate that shear stress forces regulate the expression of miRNAs in ECs, and that miR-21 influences endothelial biology by decreasing apoptosis and activating the NO{sup {center_dot}} pathway. These studies advance our understanding of the mechanisms by which shear stress forces modulate vascular homeostasis.

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

    Science.gov (United States)

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

    2008-02-01

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

  12. Associations among everyday stress, critical life events, and sexual problems.

    Science.gov (United States)

    Bodenmann, Guy; Ledermann, Thomas; Blattner, Denise; Galluzzo, Claudia

    2006-07-01

    This study addresses the question of how stress is linked to sexual problems among women and men in close relationships. Psychological symptoms, relationship quality, internal daily stress (i.e., originating within the couple such as conflicts, worry for the partner), external daily stress (i.e., stress arising outside the couple such as job stress, stressful relatives, and so forth), and critical life events were examined with regard to their association with different sexual problems. The results support the hypotheses that (1) there is an incremental effect of stress on sexual problems after controlling for psychological symptoms and relationship quality, and that (2) it is primarily internal daily stress and in some cases critical life events rather than external daily stress that are related to sexual problems, particularly hypoactive sexual desire in women and men, sexual aversion in women, vaginismus in women, and premature ejaculation in men. Our findings indicate that the treatment of these sexual problems should address relationship issues and include a focus on helping individuals improve their stress management skills within their couple relationship.

  13. Exercise-induced shear stress is associated with changes in plasma von Willebrand factor in older humans

    OpenAIRE

    Gonzales, Joaquin U.; Thistlethwaite, John R.; Thompson, Benjamin C.; Scheuermann, Barry W.

    2009-01-01

    Shear stress is the frictional force of blood against the endothelium, a stimulus for endothelial activation and the release of von Willebrand factor (vWF). This study tested the hypothesis that the increase in shear stress associated with exercise correlates with plasma vWF. Young (n = 14, 25.7 ± 5.4 y) and older (n = 13, 65.6 ± 10.7 y) individuals participated in 30 min of dynamic handgrip exercise at a moderate intensity. Brachial artery diameter and blood flow were measured using ultrasou...

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

    Science.gov (United States)

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

    1977-01-01

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

  15. Interaction between a normal shock wave and a turbulent boundary layer at high transonic speeds. II - Wall shear stress

    Science.gov (United States)

    Liou, M. S.; Adamson, T. C., Jr.

    1980-01-01

    Asymptotic methods are used to calculate the shear stress at the wall for the interaction between a normal shock wave and a turbulent boundary layer on a flat plate. A mixing length model is used for the eddy viscosity. The shock wave is taken to be strong enough that the sonic line is deep in the boundary layer and the upstream influence is thus very small. It is shown that unlike the result found for laminar flow an asymptotic criterion for separation is not found; however, conditions for incipient separation are computed numerically using the derived solution for the shear stress at the wall. Results are compared with available experimental measurements.

  16. Whole-body heat stress and exercise stimulate the appearance of platelet microvesicles in plasma with limited influence of vascular shear stress.

    Science.gov (United States)

    Wilhelm, Eurico N; González-Alonso, José; Chiesa, Scott T; Trangmar, Steven J; Kalsi, Kameljit K; Rakobowchuk, Mark

    2017-11-01

    Intense, large muscle mass exercise increases circulating microvesicles, but our understanding of microvesicle dynamics and mechanisms inducing their release remains limited. However, increased vascular shear stress is generally thought to be involved. Here, we manipulated exercise-independent and exercise-dependent shear stress using systemic heat stress with localized single-leg cooling (low shear) followed by single-leg knee extensor exercise with the cooled or heated leg (Study 1, n  = 8) and whole-body passive heat stress followed by cycling (Study 2, n  = 8). We quantified femoral artery shear rates (SRs) and arterial and venous platelet microvesicles (PMV-CD41 + ) and endothelial microvesicles (EMV-CD62E + ). In Study 1, mild passive heat stress while one leg remained cooled did not affect [microvesicle] ( P  ≥ 0.05). Single-leg knee extensor exercise increased active leg SRs by ~12-fold and increased arterial and venous [PMVs] by two- to threefold, even in the nonexercising contralateral leg ( P  body passive heat stress increased arterial [PMV] compared with baseline (mean±SE, from 19.9 ± 1.5 to 35.5 ± 5.4 PMV . μ L -1. 10 3 , P  stress increased [PMV] further in the venous circulation (from 27.5 ± 2.2 at baseline to 57.5 ± 7.2 PMV . μ L -1. 10 3 during cycling with heat stress, P  body heat stress may increase arterial [PMV], and intense exercise engaging either large or small muscle mass promote PMV formation locally and systemically, with no influence upon [EMV]. Local shear stress, however, does not appear to be the major stimulus modulating PMV formation in healthy humans. © 2017 The Authors. Physiological Reports published by Wiley Periodicals, Inc. on behalf of The Physiological Society and the American Physiological Society.

  17. Flow under standing waves Part 1. Shear stress distribution, energy flux and steady streaming

    DEFF Research Database (Denmark)

    Gislason, Kjartan; Fredsøe, Jørgen; Deigaard, Rolf

    2009-01-01

    The conditions for energy flux, momentum flux and the resulting streaming velocity are analysed for standing waves formed in front of a fully reflecting wall. The exchange of energy between the outer wave motion and the near bed oscillatory boundary layer is considered, determining the horizontal...... energy flux inside and outside the boundary layer. The momentum balance, the mean shear stress and the resulting time averaged streaming velocities are determined. For a laminar bed boundary layer the analysis of the wave drift gives results similar to the original work of Longuet-Higgins from 1953......-dimensional simulations of standing waves have also been made by application of a general purpose Navier-Stokes solver. The results agree well with those obtained by the boundary layer analysis. Wave reflection from a plane sloping wall is also investigated by using the same numerical model and by physical laboratory...

  18. Yield strength, shear stress and toughness of YBCO samples textured by Bridgman technique

    International Nuclear Information System (INIS)

    Roa, J J; Capdevila, X G; Martinez, M; Segarra, M; Jimenez-Pique, E

    2008-01-01

    Mechanical properties of the orthorhombic phase of YBa 2 Cu 3 O 7-δ (Y-123) at room temperature have been investigated at different applied loads using nanoindentation technique. The study was carried out for several monodomains on the (001) planes for textured Bridgman samples with dispersed Y 2 BaCuO 5 (Y-211) particles as pinning centers. The yield strength (σ ys ), shear stress (τ m ) and toughness (K IC ) of Y123/Y211composite was determined at different applied loads. First and second mechanical properties have been calculated though the Hertz equations and the last one with Lawn et al. equations. Finally, the ultra-low imprints obtained by nanoindentation have been correlated with parameters obtained by Field Emission Scanning Electron Microscope (FE-SEM)

  19. Shear stress from hot-film sensors in unsteady gas flow

    International Nuclear Information System (INIS)

    Cole, K.D.

    1991-01-01

    In this paper a data analysis procedure is proposed for obtaining unsteady wall shear stress from flush-mounted hot-film anemometer measurements. The method is based on a two-dimensional heat transfer model of the unsteady heat transfer in both the hot-film sensor and in the gas flow. The sensor thermal properties are found from preliminary calibration experiments at zero flow. Numerical experiments are used to demonstrate the data analysis method using simulated sensor signals that are corrupted with noise. The numerical experiments show that noise in the data propagates into the results so that data smoothing may be important in analyzing experimental data. Because the data analysis procedure is linear, a linear digital filter is constructed that could be used for processing large amounts of experimental data. However, further refinements will be needed before the method can be applied to experimental data

  20. Surface shear stress dependence of gas transfer velocity parameterizations using DNS

    Science.gov (United States)

    Fredriksson, S. T.; Arneborg, L.; Nilsson, H.; Handler, R. A.

    2016-10-01

    Air-water gas-exchange is studied in direct numerical simulations (DNS) of free-surface flows driven by natural convection and weak winds. The wind is modeled as a constant surface-shear-stress and the gas-transfer is modeled via a passive scalar. The simulations are characterized via a Richardson number Ri=Bν/u*4 where B, ν, and u* are the buoyancy flux, kinematic viscosity, and friction velocity respectively. The simulations comprise 0Ric or kg=AShearu*Sc-n, Ri

  1. Relation between wall shear stress and carotid artery wall thickening MRI versus CFD

    DEFF Research Database (Denmark)

    Cibis, Merih; Potters, Wouter V.; Selwaness, Mariana

    2016-01-01

    Wall shear stress (WSS), a parameter associated with endothelial function, is calculated by computational fluid dynamics (CFD) or phase-contrast (PC) MRI measurements. Although CFD is common in WSS (WSSCFD) calculations, PC-MRI-based WSS (WSSMRI) is more favorable in population studies; since...... it is straightforward and less time consuming. However, it is not clear if WSSMRI and WSSCFD show similar associations with vascular pathology. Our aim was to test the associations between wall thickness (WT) of the carotid arteries and WSSMRI and WSSCFD. The subjects (n=14) with an asymptomatic carotid plaque who...... underwent MRI scans two times within 4 years of time were selected from the Rotterdam Study. We compared WSSCFD and WSSMRI at baseline and follow-up. Baseline WSSMRI and WSSCFD values were divided into 3 categories representing low, medium and high WSS tertiles. WT of each tertile was compared by a one...

  2. A potential model for drug screening by simulating the effect of shear stress in vivo on endothelium.

    Science.gov (United States)

    Xu, Yingqian; Wang, Bochu; Deng, Jia; Liu, Zerong; Zhu, Liancai

    2013-01-01

    The purpose of this paper was to research the potential of a dynamic cell model in drug screening by studying the influence of microvascular wall shear stress on the drug absorption of endothelial cells compared to that in the static state. The cells were grown and seeded on gelatin-coated glass slides and were pretreated with extracts of Salviae miltiorrhizae (200 μg/ml) for 1 h. Then oxidative stress damage was produced by H2O2 (300 μmol/l) for 0.5 h under the 1.5 dyn/cm2 shear stress incorporated in a parallel plate flow chamber. Morphological analysis was conducted with an inverted microscope and image analysis software, and high performance liquid chromatography-mass spectrometry was used for the detection of active compounds. We compared the drug absorption in the dynamic group with that in the static group. In the dynamic model, five compounds and two new metabolite peaks were detected. However, in the static model, four compounds were absorbed by cells, and one metabolite peak was found. This study indicated that there were some effects on the absorption and metabolism of drugs under the microvascular shear stress compared to that under stasis. We infer that shear stress in the microcirculation situation in vivo played a role in causing the differences between drug screening in vitro and in vivo.

  3. A Multi-scale Refined Zigzag Theory for Multilayered Composite and Sandwich Plates with Improved Transverse Shear Stresses

    Science.gov (United States)

    Iurlaro, Luigi; Gherlone, Marco; Di Sciuva, Marco; Tessler, Alexander

    2013-01-01

    The Refined Zigzag Theory (RZT) enables accurate predictions of the in-plane displacements, strains, and stresses. The transverse shear stresses obtained from constitutive equations are layer-wise constant. Although these transverse shear stresses are generally accurate in the average, layer-wise sense, they are nevertheless discontinuous at layer interfaces, and thus they violate the requisite interlaminar continuity of transverse stresses. Recently, Tessler applied Reissner's mixed variational theorem and RZT kinematic assumptions to derive an accurate and efficient shear-deformation theory for homogeneous, laminated composite, and sandwich beams, called RZT(m), where "m" stands for "mixed". Herein, the RZT(m) for beams is extended to plate analysis, where two alternative assumptions for the transverse shear stresses field are examined: the first follows Tessler's formulation, whereas the second is based on Murakami's polynomial approach. Results for elasto-static simply supported and cantilever plates demonstrate that Tessler's formulation results in a powerful and efficient structural theory that is well-suited for the analysis of multilayered composite and sandwich panels.

  4. Reinforced concrete membrane elements subjected to reversed cyclic in-plane shear stress

    International Nuclear Information System (INIS)

    Ohmori, N.; Tsubota, H.; Inoue, N.; Watanabe, S.; Kurihara, K.

    1987-01-01

    The response of reinforced concrete elements subjected to reversed cyclic in-plane shear stresses can be predicted by an analytical model, which considers equilibrium, compatibility and stress-strain relationships including hysteresis loop of unloading and reloading stages all expressed in terms of average stresses and average strains. The analytical results show that the dominant hysteretic behaviours in regard to decrease of stiffness during unloading, successive slip phenomena and restoration of compressive stiffness at the reloading stages are well simulated analytically. The results agree quite well with the observed behaviours. As for the envelope curve of the hysteretic response there remain the discrepancies that the stiffness and ultimate strength are a bit larger than the observed results, especially in the case of a panel with a large reinforcement ratio. Such descrepancies are also found in the predicted results of monotonic loading and more precise studies are necessary to evaluate more accurate envelope curves under not only reversed cyclic loading but also monotonic loading. (orig./HP)

  5. Software for determining the direction of movement, shear and normal stresses of a fault under a determined stress state

    Science.gov (United States)

    Álvarez del Castillo, Alejandra; Alaniz-Álvarez, Susana Alicia; Nieto-Samaniego, Angel Francisco; Xu, Shunshan; Ochoa-González, Gil Humberto; Velasquillo-Martínez, Luis Germán

    2017-07-01

    In the oil, gas and geothermal industry, the extraction or the input of fluids induces changes in the stress field of the reservoir, if the in-situ stress state of a fault plane is sufficiently disturbed, a fault may slip and can trigger fluid leakage or the reservoir might fracture and become damaged. The goal of the SSLIPO 1.0 software is to obtain data that can reduce the risk of affecting the stability of wellbores. The input data are the magnitudes of the three principal stresses and their orientation in geographic coordinates. The output data are the slip direction of a fracture in geographic coordinates, and its normal (σn) and shear (τ) stresses resolved on a single or multiple fracture planes. With this information, it is possible to calculate the slip tendency (τ/σn) and the propensity to open a fracture that is inversely proportional to σn. This software could analyze any compressional stress system, even non-Andersonian. An example is given from an oilfield in southern Mexico, in a region that contains fractures formed in three events of deformation. In the example SSLIPO 1.0 was used to determine in which deformation event the oil migrated. SSLIPO 1.0 is an open code application developed in MATLAB. The URL to obtain the source code and to download SSLIPO 1.0 are: http://www.geociencias.unam.mx/ alaniz/main_code.txt, http://www.geociencias.unam.mx/ alaniz/ SSLIPO_pkg.exe.

  6. Influence of the tilt angle of Percutaneous Aortic Prosthesis on Velocity and Shear Stress Fields

    Directory of Open Access Journals (Sweden)

    Bruno Alvares de Azevedo Gomes

    Full Text Available Abstract Background: Due to the nature of the percutaneous prosthesis deployment process, a variation in its final position is expected. Prosthetic valve placement will define the spatial location of its effective orifice in relation to the aortic annulus. The blood flow pattern in the ascending aorta is related to the aortic remodeling process, and depends on the spatial location of the effective orifice. The hemodynamic effect of small variations in the angle of inclination of the effective orifice has not been studied in detail. Objective: To implement an in vitro simulation to characterize the hydrodynamic blood flow pattern associated with small variations in the effective orifice inclination. Methods: A three-dimensional aortic phantom was constructed, reproducing the anatomy of one patient submitted to percutaneous aortic valve implantation. Flow analysis was performed by use of the Particle Image Velocimetry technique. The flow pattern in the ascending aorta was characterized for six flow rate levels. In addition, six angles of inclination of the effective orifice were assessed. Results: The effective orifice at the -4° and -2° angles directed the main flow towards the anterior wall of the aortic model, inducing asymmetric and high shear stress in that region. However, the effective orifice at the +3° and +5° angles mimics the physiological pattern, centralizing the main flow and promoting a symmetric distribution of shear stress. Conclusion: The measurements performed suggest that small changes in the angle of inclination of the percutaneous prosthesis aid in the generation of a physiological hemodynamic pattern, and can contribute to reduce aortic remodeling.

  7. Human dental pulp cells exhibit bone cell-like responsiveness to fluid shear stress.

    Science.gov (United States)

    Kraft, David Christian Evar; Bindslev, Dorth Arenholt; Melsen, Birte; Klein-Nulend, Jenneke

    2011-02-01

    For engineering bone tissue to restore, for example, maxillofacial defects, mechanosensitive cells are needed that are able to conduct bone cell-specific functions, such as bone remodelling. Mechanical loading affects local bone mass and architecture in vivo by initiating a cellular response via loading-induced flow of interstitial fluid. After surgical removal of ectopically impacted third molars, human dental pulp tissue is an easily accessible and interesting source of cells for mineralized tissue engineering. The aim of this study was to determine whether human dental pulp-derived cells (DPC) are responsive to mechanical loading by pulsating fluid flow (PFF) upon stimulation of mineralization in vitro. Human DPC were incubated with or without mineralization medium containing differentiation factors for 3 weeks. Cells were subjected to 1-h PFF (0.7 ± 0.3 Pa, 5 Hz) and the response was quantified by measuring nitric oxide (NO) and prostaglandin E₂ (PGE₂) production, and gene expression of cyclooxygenase (COX)-1 and COX-2. We found that DPC are intrinsically mechanosensitive and, like osteogenic cells, respond to PFF-induced fluid shear stress. PFF stimulated NO and PGE₂ production, and up-regulated COX-2 but not COX-1 gene expression. In DPC cultured under mineralizing conditions, the PFF-induced NO, but not PGE₂, production was significantly enhanced. These data suggest that human DPC, like osteogenic cells, acquire responsiveness to pulsating fluid shear stress in mineralizing conditions. Thus DPC might be able to perform bone-like functions during mineralized tissue remodeling in vivo, and therefore provide a promising new tool for mineralized tissue engineering to restore, for example, maxillofacial defects.

  8. CRITICAL INCIDENTS AND CRITICAL INCIDENT STRESS MANAGEMENT (CISM – AN EMPLOYEE ASSISTANCE PROGRAMME (EAP PERSPECTIVE

    Directory of Open Access Journals (Sweden)

    Terblanche, Lourie

    2014-04-01

    Full Text Available Employees are increasingly becoming victims of critical incidents. From a systems theory point of view, it is necessary to acknowledge the impact of critical incidents not only on the personal life of the employee, but on the workplace itself. Employees respond differently to critical incidents, which makes it even more complicated when this reaches the point of requiring therapeutic intervention. The most common response to critical incidents may be the risk of developing post-traumatic stress disorder (PTSD and/or depression. This reality requires management – through the Employee Assistance Programme (EAP – to be able to effectively deal with such critical incidents.

  9. Medial tibial stress syndrome: a critical review.

    Science.gov (United States)

    Moen, Maarten H; Tol, Johannes L; Weir, Adam; Steunebrink, Miriam; De Winter, Theodorus C

    2009-01-01

    Medial tibial stress syndrome (MTSS) is one of the most common leg injuries in athletes and soldiers. The incidence of MTSS is reported as being between 4% and 35% in military personnel and athletes. The name given to this condition refers to pain on the posteromedial tibial border during exercise, with pain on palpation of the tibia over a length of at least 5 cm. Histological studies fail to provide evidence that MTSS is caused by periostitis as a result of traction. It is caused by bony resorption that outpaces bone formation of the tibial cortex. Evidence for this overloaded adaptation of the cortex is found in several studies describing MTSS findings on bone scan, magnetic resonance imaging (MRI), high-resolution computed tomography (CT) scan and dual energy x-ray absorptiometry. The diagnosis is made based on physical examination, although only one study has been conducted on this subject. Additional imaging such as bone, CT and MRI scans has been well studied but is of limited value. The prevalence of abnormal findings in asymptomatic subjects means that results should be interpreted with caution. Excessive pronation of the foot while standing and female sex were found to be intrinsic risk factors in multiple prospective studies. Other intrinsic risk factors found in single prospective studies are higher body mass index, greater internal and external ranges of hip motion, and calf girth. Previous history of MTSS was shown to be an extrinsic risk factor. The treatment of MTSS has been examined in three randomized controlled studies. In these studies rest is equal to any intervention. The use of neoprene or semi-rigid orthotics may help prevent MTSS, as evidenced by two large prospective studies.

  10. Stress, coping and presenteeism in nurses assisting critical and potentially critical patients

    Directory of Open Access Journals (Sweden)

    Juliane Umann

    2014-10-01

    Full Text Available Objective to verify the associations between stress, Coping and Presenteeism in nurses operating on direct assistance to critical and potentially critical patients. Method this is a descriptive, cross-sectional and quantitative study, conducted between March and April 2010 with 129 hospital nurses. The Inventory of stress in nurses, Occupational and Coping Questionnaire Range of Limitations at Work were used. For the analysis, the Kolmogorov-Smirnov test, correlation coefficient of Pearson and Spearman, Chi-square and T-test were applied. Results it was observed that 66.7% of the nurses showed low stress, 87.6% use control strategies for coping stress and 4.84% had decrease in productivity. Direct and meaningful relationships between stress and lost productivity were found. Conclusion stress interferes with the daily life of nurses and impacts on productivity. Although the inability to test associations, the control strategy can minimize the stress, which consequently contributes to better productivity of nurses in the care of critical patients and potentially critical.

  11. Stress in closed thin-walled tubes of single box subjected by shear forces and application to airfoils

    Directory of Open Access Journals (Sweden)

    Zebbiche Toufik

    2014-09-01

    Full Text Available The presented work is to develop a numerical computation program to determine the distribution of the shear stress to shear in closed tubes with asymmetric single thin wall section with a constant thickness and applications to airfoils and therefore determining the position and value of the maximum stress. In the literature, there are exact analytical solutions only for some sections of simple geometries such as circular section. Hence our interest is focused on the search of approximate numerical solutions for more complex sections used in aeronautics. In the second stage the position of the shear center is determined so that the section does not undergo torsion. The analytic function of the boundary of the airfoil is obtained by using the cubic spline interpolation since it is given in the form of tabulated points.

  12. Residual stresses and critical diameter in vitreous matrix materials

    International Nuclear Information System (INIS)

    Mastelaro, Valmor R.; Zanotto, Edgar D.

    1995-01-01

    The present study was undertaken to test the validity of existing models for: i) the residual internal stresses which arise due to thermal and elastic mismatch in duplex systems, and ii) the critical particle diameter for spontaneous cracking. Partially crystallized 1,07 Na 2 O-2 Ca O-3 Si O 2 - 6% P 2 O 5 glasses were studied. The experimental residual stress was in excellent agreement with the calculated value, however, the critical particle diameter, estimated by an energy balance approach, was more than ten times smaller than the experimental value. This discrepancy indicates that the energy model is not applicable in this case. (author)

  13. A two-dimensional continuum model of biofilm growth incorporating fluid flow and shear stress based detachment

    KAUST Repository

    Duddu, Ravindra; Chopp, David L.; Moran, Brian

    2009-01-01

    of the biofilm. The model considers fluid flow around the biofilm surface, the advection-diffusion and reaction of substrate, variable biomass volume fraction and erosion due to the interfacial shear stress at the biofilm-fluid interface. The key assumptions

  14. Modelling tidal current-induced bed shear stress and palaeocirculation in an epicontinental seaway: the Bohemian Cretaceous Basin, Central Europe

    Czech Academy of Sciences Publication Activity Database

    Mitchell, A. J.; Uličný, David; Hampson, G. J.; Allison, P. A.; Gorman, G. J.; Piggott, M. D.; Wells, M. R.; Pain, C. C.

    2010-01-01

    Roč. 57, č. 2 (2010), s. 359-388 ISSN 0037-0746 R&D Projects: GA AV ČR(CZ) IAA300120609 Institutional research plan: CEZ:AV0Z30120515 Keywords : bed shear stress * Bohemian Cretaceous Basin * epicontinental sea * tidal circulation * Turonian Subject RIV: DB - Geology ; Mineralogy Impact factor: 2.229, year: 2010

  15. Energy Consumption in Terms of Shear Stress for Two Types of Membrane Bioreactors Used for Municipal Wastewater Treatment Processes

    DEFF Research Database (Denmark)

    Ratkovich, Nicolas Rios; Bentzen, Thomas Ruby; Bérube, P.R.

    2011-01-01

    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...

  16. Contrast-enhanced micro-CT imaging in murine carotid arteries: A new protocol for computing wall shear stress

    NARCIS (Netherlands)

    Xing, R. (Ruoyu); Wilde, D. (David); McCann, G. (Gayle); Y. Ridwan (Yanto); J.T.C. Schrauwen (Jelle); A.F.W. Steen (Antonius F.W.); F.J.H. Gijsen (Frank); Heiden, K. (Kim)

    2016-01-01

    textabstractBackground: Wall shear stress (WSS) is involved in the pathophysiology of atherosclerosis. The correlation between WSS and atherosclerosis can be investigated over time using a WSS-manipulated atherosclerotic mouse model. To determine WSS in vivo, detailed 3D geometry of the vessel

  17. The impact of different aperture distribution models and critical stress criteria on equivalent permeability in fractured rocks

    DEFF Research Database (Denmark)

    Bisdom, Kevin; Bertotti, Giovanni; Nick, Hamid

    2016-01-01

    Predicting equivalent permeability in fractured reservoirs requires an understanding of the fracture network geometry and apertures. There are different methods for defining aperture, based on outcrop observations (power law scaling), fundamental mechanics (sublinear length-aperture scaling...... in the fraction of open fractures. For the applied stress conditions, Coulomb predicts that 50% of the network is critically stressed, compared to 80% for Barton-Bandis peak shear. The impact of the fracture network on equivalent permeability depends on the matrix hydraulic properties, as in a low...

  18. Computational modeling for prediction of the shear stress of three-dimensional isotropic and aligned fiber networks.

    Science.gov (United States)

    Park, Seungman

    2017-09-01

    Interstitial flow (IF) is a creeping flow through the interstitial space of the extracellular matrix (ECM). IF plays a key role in diverse biological functions, such as tissue homeostasis, cell function and behavior. Currently, most studies that have characterized IF have focused on the permeability of ECM or shear stress distribution on the cells, but less is known about the prediction of shear stress on the individual fibers or fiber networks despite its significance in the alignment of matrix fibers and cells observed in fibrotic or wound tissues. In this study, I developed a computational model to predict shear stress for different structured fibrous networks. To generate isotropic models, a random growth algorithm and a second-order orientation tensor were employed. Then, a three-dimensional (3D) solid model was created using computer-aided design (CAD) software for the aligned models (i.e., parallel, perpendicular and cubic models). Subsequently, a tetrahedral unstructured mesh was generated and flow solutions were calculated by solving equations for mass and momentum conservation for all models. Through the flow solutions, I estimated permeability using Darcy's law. Average shear stress (ASS) on the fibers was calculated by averaging the wall shear stress of the fibers. By using nonlinear surface fitting of permeability, viscosity, velocity, porosity and ASS, I devised new computational models. Overall, the developed models showed that higher porosity induced higher permeability, as previous empirical and theoretical models have shown. For comparison of the permeability, the present computational models were matched well with previous models, which justify our computational approach. ASS tended to increase linearly with respect to inlet velocity and dynamic viscosity, whereas permeability was almost the same. Finally, the developed model nicely predicted the ASS values that had been directly estimated from computational fluid dynamics (CFD). The present

  19. Effect of stress management interventions on job stress among nurses working in critical care units.

    Science.gov (United States)

    Light Irin, C; Bincy, R

    2012-01-01

    Stress in nurses affects their health and increases absenteeism, attrition rate, injury claims, infection rates and errors in treating patients. This in turn significantly increases the cost of employment in healthcare units. Proper management of stress ensures greater efficiency at work place and improved wellbeing of the employee. Therefore, a pre-experimental study was conducted among 30 Critical Care Unit nurses working inMedical College Hospital, Thiruvananthapuram, (Kerala) to assess the effect of stress management interventions such as Job Stress Awareness, Assertiveness Training, Time Management, andProgressive Muscle Relaxation on job stress. The results showed that caring for patients, general job requirements and workload were the major sources of stress for the nurses. The level of severe stress was reduced from 60 percent to 20 percent during post-test. The Stress Management Interventions were statistically effective in reducing the stress of nurses at p<0.001 level.

  20. A multi-component parallel-plate flow chamber system for studying the effect of exercise-induced wall shear stress on endothelial cells.

    Science.gov (United States)

    Wang, Yan-Xia; Xiang, Cheng; Liu, Bo; Zhu, Yong; Luan, Yong; Liu, Shu-Tian; Qin, Kai-Rong

    2016-12-28

    In vivo studies have demonstrated that reasonable exercise training can improve endothelial function. To confirm the key role of wall shear stress induced by exercise on endothelial cells, and to understand how wall shear stress affects the structure and the function of endothelial cells, it is crucial to design and fabricate an in vitro multi-component parallel-plate flow chamber system which can closely replicate exercise-induced wall shear stress waveforms in artery. The in vivo wall shear stress waveforms from the common carotid artery of a healthy volunteer in resting and immediately after 30 min acute aerobic cycling exercise were first calculated by measuring the inner diameter and the center-line blood flow velocity with a color Doppler ultrasound. According to the above in vivo wall shear stress waveforms, we designed and fabricated a parallel-plate flow chamber system with appropriate components based on a lumped parameter hemodynamics model. To validate the feasibility of this system, human umbilical vein endothelial cells (HUVECs) line were cultured within the parallel-plate flow chamber under abovementioned two types of wall shear stress waveforms and the intracellular actin microfilaments and nitric oxide (NO) production level were evaluated using fluorescence microscope. Our results show that the trends of resting and exercise-induced wall shear stress waveforms, especially the maximal, minimal and mean wall shear stress as well as oscillatory shear index, generated by the parallel-plate flow chamber system are similar to those acquired from the common carotid artery. In addition, the cellular experiments demonstrate that the actin microfilaments and the production of NO within cells exposed to the two different wall shear stress waveforms exhibit different dynamic behaviors; there are larger numbers of actin microfilaments and higher level NO in cells exposed in exercise-induced wall shear stress condition than resting wall shear stress condition

  1. Low-level shear stress promotes migration of liver cancer stem cells via the FAK-ERK1/2 signalling pathway.

    Science.gov (United States)

    Sun, Jinghui; Luo, Qing; Liu, Lingling; Song, Guanbin

    2018-07-28

    Cancer stem cells (CSCs) are a small subpopulation of tumour cells that have been proposed to be responsible for cancer initiation, chemotherapy resistance and cancer recurrence. Shear stress activated cellular signalling is involved in cellular migration, proliferation and differentiation. However, little is known about the effects of shear stress on the migration of liver cancer stem cells (LCSCs). Here, we studied the effects of shear stress that are generated from a parallel plated flow chamber system, on LCSC migration and the activation of focal adhesion kinase (FAK) and extracellular signal regulated kinase1/2 (ERK1/2), using transwell assay and western blot, respectively. We found that 2 dyne/cm 2 shear stress loading for 6 h promotes LCSC migration and activation of the FAK and ERK1/2 signalling pathways, whereas treatment with the FAK phosphorylation inhibitor PF573228 or the ERK1/2 phosphorylation inhibitor PD98059 suppressed the shear stress-promoted migration, indicating the involvement of FAK and ERK1/2 activation in shear stress-induced LCSC migration. Additionally, atomic force microscopy (AFM) analysis showed that shear stress lowers LCSC stiffness via the FAK and ERK1/2 pathways, suggesting that the mechanism by which shear stress promotes LCSC migration might partially be responsible for the decrease in cell stiffness. Further experiments focused on the role of the actin cytoskeleton, demonstrating that the F-actin filaments in LCSCs are less well-defined after shear stress treatment, providing an explanation for the reduction in cell stiffness and the promotion of cell migration. Overall, our study demonstrates that shear stress promotes LCSC migration through the activation of the FAK-ERK1/2 signalling pathways, which further results in a reduction of organized actin and softer cell bodies. Copyright © 2018 Elsevier B.V. All rights reserved.

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

    International Nuclear Information System (INIS)

    Fujisawa, N; Oguma, Y; Nakano, T

    2009-01-01

    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

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

    Science.gov (United States)

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

    2010-11-01

    Manned space exploration has created a need to evaluate the effects of spacelike stress on pathogenic and opportunistic microbes astronauts could carry with them to the International Space Station and beyond. Yersinia pestis (YP) causes bubonic, septicemic, and pneumonic plague and is capable of killing infected patients within 3-7 days. In this study, low-shear modeled microgravity (LSMMG), a spacelike stress, was used to physically stress YP; and its effects on proliferation, cold growth, and type III secretion system (T3SS) function were evaluated. YP was grown to saturation in either LSMMG or normal gravity (NG) conditions prior to being used for RAW 246.7 cell infections, HeLa cell infections, and Yop secretion assays. A mutant strain of YP (ΔyopB) that lacks the ability to inject Yersinia outer membrane proteins (Yops) into the host cell was used as a negative control in cell infection experiments. Our experimental results indicate that YP cultivated under LSMMG resulted in reduced YopM production and secretion compared to its NG-grown counterpart. Similarly, NG-grown YP induced more cell rounding in HeLa cells than did the LSMMG-grown YP, which suggests that LSMMG somehow impairs T3SS optimum function. Also, LSMMG-grown YP used to infect cultured RAW 246.7 cells showed a similar pattern of dysfunction in that it proliferated less than did its NG-grown counterpart during an 8-hour infection period. This study suggests that LSMMG can attenuate bacterial virulence contrary to previously published data that have demonstrated LSMMG-induced hypervirulence of other Gram-negative enterics.

  4. An experimental study for the interface shear stress of near vertical air-water separated flow on evaporation

    International Nuclear Information System (INIS)

    Kwon, H.; Park, G. C.

    2000-01-01

    The object of experiment is improved model of evaporative heat transfer coefficient using interfacial friction factor on evaporation. Experiments have been conducted with near-vertical(87 .deg.) flat plate on evaporation for air-water countercurrent stratified flow. Experiment facility is consisted of 1.7m length and 0.2 X 0.005m cross section, the one side direct heating system which have 10kw power capacity. The interfacial shear stress, pressure drop and temperatures in test section were measured. These parameters were measured by DP-103 pressure transducer, K-type thermocouple, RTD and Hot Wire Anemometer(HWA). Experimental results were inclination as increased interfacial shear stress with increased the evaporation rate. Interfacial shear stress was increased as increased water flow rate and air flow rate too. For the evaluation of the measured evaporative heat transfer coefficients and physical understanding of the evaporation phenomena, the evaporative heat transfer coefficients were obtained through the simple calculation process by the use of mass transfer coefficient correlation and the experimental data of wavy film surface effect on shear and on evaporation

  5. Alterations in cancer cell mechanical properties after fluid shear stress exposure: a micropipette aspiration study

    Directory of Open Access Journals (Sweden)

    Chivukula VK

    2015-01-01

    Full Text Available Venkat Keshav Chivukula,1 Benjamin L Krog,1,2 Jones T Nauseef,2 Michael D Henry,2 Sarah C Vigmostad1 1Department of Biomedical Engineering, 2Department of Molecular Physiology and Biophysics, Holden Comprehensive Cancer Center, University of Iowa, Seamans Center for the Engineering Arts and Sciences, Iowa City, IA, USA Abstract: Over 90% of cancer deaths result not from primary tumor development, but from metastatic tumors that arise after cancer cells circulate to distal sites via the circulatory system. While it is known that metastasis is an inefficient process, the effect of hemodynamic parameters such as fluid shear stress (FSS on the viability and efficacy of metastasis is not well understood. Recent work has shown that select cancer cells may be able to survive and possibly even adapt to FSS in vitro. The current research seeks to characterize the effect of FSS on the mechanical properties of suspended cancer cells in vitro. Nontransformed prostate epithelial cells (PrEC LH and transformed prostate cancer cells (PC-3 were used in this study. The Young's modulus was determined using micropipette aspiration. We examined cells in suspension but not exposed to FSS (unsheared and immediately after exposure to high (6,400 dyn/cm2 and low (510 dyn/cm2 FSS. The PrEC LH cells were ~140% stiffer than the PC-3 cells not exposed to FSS. Post-FSS exposure, there was an increase of ~77% in Young's modulus after exposure to high FSS and a ~47% increase in Young's modulus after exposure to low FSS for the PC-3 cells. There was no significant change in the Young's modulus of PrEC LH cells post-FSS exposure. Our findings indicate that cancer cells adapt to FSS, with an increased Young's modulus being one of the adaptive responses, and that this adaptation is specific only to PC-3 cells and is not seen in PrEC LH cells. Moreover, this adaptation appears to be graded in response to the magnitude of FSS experienced by the cancer cells. This is the first study

  6. Examining critical care nurses' critical incident stress after in hospital cardiopulmonary resuscitation (CPR).

    Science.gov (United States)

    Laws, T

    2001-05-01

    The object of this study was to determine if critical care nurses' emotional responses to having performed cardiopulmonary resuscitation were indicative of critical incident stress. A descriptive approach was employed using a survey questionnaire of 31 critical care nurses, with supportive interview data from 18 of those participants. Analysis of the data generated from the questionnaire indicated that the respondents experienced thought intrusion and avoidance behaviour. A majority of those interviewed disclosed that they had experienced a wide range of emotional stressors and physical manifestations in response to having performed the procedure. The findings from both questionnaire and interview data were congruent with signs of critical incident stress, as described in the literature. This has been found to be detrimental to employees' mental health status and, for this reason, employers have a duty of care to minimise the risk of its occurrence and to manage problems as they arise.

  7. Time-Resolved Particle Image Velocimetry Measurements with Wall Shear Stress and Uncertainty Quantification for the FDA Nozzle Model.

    Science.gov (United States)

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

    2016-03-01

    We present advanced particle image velocimetry (PIV) processing, post-processing, and uncertainty estimation techniques to support the validation of computational fluid dynamics analyses of medical devices. This work is an extension of a previous FDA-sponsored multi-laboratory study, which used a medical device mimicking geometry referred to as the FDA benchmark nozzle model. Experimental measurements were performed using time-resolved PIV at five overlapping regions of the model for Reynolds numbers in the nozzle throat of 500, 2000, 5000, and 8000. Images included a twofold increase in spatial resolution in comparison to the previous study. Data was processed using ensemble correlation, dynamic range enhancement, and phase correlations to increase signal-to-noise ratios and measurement accuracy, and to resolve flow regions with large velocity ranges and gradients, which is typical of many blood-contacting medical devices. Parameters relevant to device safety, including shear stress at the wall and in bulk flow, were computed using radial basis functions. In addition, in-field spatially resolved pressure distributions, Reynolds stresses, and energy dissipation rates were computed from PIV measurements. Velocity measurement uncertainty was estimated directly from the PIV correlation plane, and uncertainty analysis for wall shear stress at each measurement location was performed using a Monte Carlo model. Local velocity uncertainty varied greatly and depended largely on local conditions such as particle seeding, velocity gradients, and particle displacements. Uncertainty in low velocity regions in the sudden expansion section of the nozzle was greatly reduced by over an order of magnitude when dynamic range enhancement was applied. Wall shear stress uncertainty was dominated by uncertainty contributions from velocity estimations, which were shown to account for 90-99% of the total uncertainty. This study provides advancements in the PIV processing methodologies over

  8. Bending and Shear Stresses Developed by the Instantaneous Arrest of the Root of a Moving Cantilever Beam

    Science.gov (United States)

    Stowell, Elbridge, Z; Schwartz, Edward B; Houbolt, John C

    1945-01-01

    A theoretical and experimental investigation has been made of the behavior of a cantilever beam in transverse motion when its root is suddenly brought to rest. Equations are given for determining the stresses, the deflections, and the accelerations that arise in the beam as a result of the impact. The theoretical equations, which have been confirmed experimentally, reveal that, at a given percentage of the distance from root to tip, the bending stresses for a particular mode are independent of the length of the beam, whereas the shear stresses vary inversely with the length.

  9. Stress Analysis for the Critical Metal Structure of Bridge Crane

    Science.gov (United States)

    Ling, Zhangwei; Wang, Min; Xia, Junfang; Wang, Songhua; Guo, Xiaolian

    2018-01-01

    Based on the type of connection between the main girder and end beam of electrical single beam crane, the finite element analysis model of a full portal crane was established. The stress distribution of the critical structure under different loading conditions was analyzed. The results shown that the maximum Mises stress and deflection of the main girder were within the allowable range. And the connecting location between end beam web and main girder had higher stress than other region, especially at the lower edge and upper edge of the end beam web and the area near the bolt hole of upper wing panel. Therefore it is important to inspect the connection status, the stress condition and the crack situation nearing connection location during the regular inspection process to ensure the safety of the connection between the main girder and end beam.

  10. Role of Myoendothelial Gap Junctions in the Regulation of Human Coronary Artery Smooth Muscle Cell Differentiation by Laminar Shear Stress

    Directory of Open Access Journals (Sweden)

    Zongqi Zhang

    2016-07-01

    Full Text Available Background/Aims: Smooth muscle cells may dedifferentiate into the synthetic phenotype and promote atherosclerosis. Here, we explored the role of myoendothelial gap junctions in phenotypic switching of human coronary artery smooth muscle cells (HCASMCs co-cultured with human coronary artery endothelial cells (HCAECs exposed to shear stress. Methods: HCASMCs and HCAECs were seeded on opposite sides of Transwell inserts, and HCAECs were exposed to laminar shear stress of 12 dyn/cm2 or 5 dyn/cm2. The myoendothelial gap junctions were evaluated by using a multi-photon microscope. Results: In co-culture with HCAECs, HCASMCs exhibited a contractile phenotype, and maintained the expression of differentiation markers MHC and H1-calponin. HCASMCs and HCAECs formed functional intercellular junctions, as evidenced by colocalization of connexin(Cx40 and Cx43 on cellular projections inside the Transwell membrane and biocytin transfer from HCAECs to HCASMCs. Cx40 siRNA and 18-α-GA attenuated protein expression of MHC and H1-calponin in HCASMCs. Shear stress of 5 dyn/cm2 increased Cx43 and decreased Cx40 expression in HCAECs, and partly inhibited biocytin transfer from HCAECs to HCASMCs, which could be completely blocked by Cx43 siRNA or restored by Cx40 DNA transfected into HCAECs. The exposure of HCAECs to shear stress of 5 dyn/cm2 promoted HCASMC phenotypic switching, manifested by morphological changes, decrease in MHC and H1-calponin expression, and increase in platelet-derived growth factor (PDGF-BB release, which was partly rescued by Cx43 siRNA or Cx40 DNA or PDGF receptor signaling inhibitor. Conclusions: The exposure of HCAECs to shear stress of 5 dyn/cm2 caused the dysfunction of Cx40/Cx43 heterotypic myoendothelial gap junctions, which may be replaced by homotypic Cx43/Cx43 channels, and induced HCASMC transition to the synthetic phenotype associated with the activation of PDGF receptor signaling, which may contribute to shear stress

  11. Posttraumatic stress disorder in critical illness survivors: a metaanalysis.

    Science.gov (United States)

    Parker, Ann M; Sricharoenchai, Thiti; Raparla, Sandeep; Schneck, Kyle W; Bienvenu, O Joseph; Needham, Dale M

    2015-05-01

    To conduct a systematic review and metaanalysis of the prevalence, risk factors, and prevention/treatment strategies for posttraumatic stress disorder symptoms in critical illness survivors. PubMed, Embase, CINAHL, PsycINFO, and Cochrane Library from inception through March 5, 2014. Eligible studies met the following criteria: 1) adult general/nonspecialty ICU, 2) validated posttraumatic stress disorder instrument greater than or equal to 1 month post-ICU, and 3) sample size greater than or equal to 10 patients. Duplicate independent review and data abstraction from all eligible titles/abstracts/full-text articles. The search identified 2,817 titles/abstracts, with 40 eligible articles on 36 unique cohorts (n = 4,260 patients). The Impact of Event Scale was the most common posttraumatic stress disorder instrument. Between 1 and 6 months post-ICU (six studies; n = 456), the pooled mean (95% CI) Impact of Event Scale score was 20 (17-24), and the pooled prevalences of clinically important posttraumatic stress disorder symptoms (95% CI) were 25% (18-34%) and 44% (36-52%) using Impact of Event Scale thresholds greater than or equal to 35 and greater than or equal to 20, respectively. Between 7 and 12 months post-ICU (five studies; n = 698), the pooled mean Impact of Event Scale score was 17 (9-24), and pooled prevalences of posttraumatic stress disorder symptoms were 17% (10-26%) and 34% (22-50%), respectively. ICU risk factors for posttraumatic stress disorder symptoms included benzodiazepine administration and post-ICU memories of frightening ICU experiences. Posttraumatic stress disorder symptoms were associated with worse quality of life. In European-based studies: 1) an ICU diary was associated with a significant reduction in posttraumatic stress disorder symptoms, 2) a self-help rehabilitation manual was associated with significant posttraumatic stress disorder symptom reduction at 2 months, but not 6 months; and 3) a nurse-led ICU follow-up clinic did not reduce

  12. Matrix mechanics and fluid shear stress control stem cells fate in three dimensional microenvironment.

    Science.gov (United States)

    Chen, Guobao; Lv, Yonggang; Guo, Pan; Lin, Chongwen; Zhang, Xiaomei; Yang, Li; Xu, Zhiling

    2013-07-01

    Stem cells have the ability to self-renew and to differentiate into multiple mature cell types during early life and growth. Stem cells adhesion, proliferation, migration and differentiation are affected by biochemical, mechanical and physical surface properties of the surrounding matrix in which stem cells reside and stem cells can sensitively feel and respond to the microenvironment of this matrix. More and more researches have proven that three dimensional (3D) culture can reduce the gap between cell culture and physiological environment where cells always live in vivo. This review summarized recent findings on the studies of matrix mechanics that control stem cells (primarily mesenchymal stem cells (MSCs)) fate in 3D environment, including matrix stiffness and extracellular matrix (ECM) stiffness. Considering the exchange of oxygen and nutrients in 3D culture, the effect of fluid shear stress (FSS) on fate decision of stem cells was also discussed in detail. Further, the difference of MSCs response to matrix stiffness between two dimensional (2D) and 3D conditions was compared. Finally, the mechanism of mechanotransduction of stem cells activated by matrix mechanics and FSS in 3D culture was briefly pointed out.

  13. High wall shear stress and spatial gradients in vascular pathology: a review.

    Science.gov (United States)

    Dolan, Jennifer M; Kolega, John; Meng, Hui

    2013-07-01

    Cardiovascular pathologies such as intracranial aneurysms (IAs) and atherosclerosis preferentially localize to bifurcations and curvatures where hemodynamics are complex. While extensive knowledge about low wall shear stress (WSS) has been generated in the past, due to its strong relevance to atherogenesis, high WSS (typically >3 Pa) has emerged as a key regulator of vascular biology and pathology as well, receiving renewed interests. As reviewed here, chronic high WSS not only stimulates adaptive outward remodeling, but also contributes to saccular IA formation (at bifurcation apices or outer curves) and atherosclerotic plaque destabilization (in stenosed vessels). Recent advances in understanding IA pathogenesis have shed new light on the role of high WSS in pathological vascular remodeling. In complex geometries, high WSS can couple with significant spatial WSS gradient (WSSG). A combination of high WSS and positive WSSG has been shown to trigger aneurysm initiation. Since endothelial cells (ECs) are sensors of WSS, we have begun to elucidate EC responses to high WSS alone and in combination with WSSG. Understanding such responses will provide insight into not only aneurysm formation, but also plaque destabilization and other vascular pathologies and potentially lead to improved strategies for disease management and novel targets for pharmacological intervention.

  14. In vivo 3-dimensional Magnetic Resonance Wall Shear Stress Estimation in Ascending Aortic Dilatation

    Science.gov (United States)

    Bieging, Erik T.; Frydrychowicz, Alex; Wentland, Andrew; Landgraf, Benjamin R.; Johnson, Kevin M.; Wieben, Oliver; François, Christopher J.

    2011-01-01

    Purpose To estimate surface-based wall shear stress (WSS) and evaluate flow patterns in ascending aortic dilatation (AscAD) using a high-resolution, time-resolved, three-dimensional (3D), three-directional velocity encoded, radially undersampled phase contrast magnetic resonance sequence (4D PC-MRI). Materials and Methods 4D PC-MRI was performed in 11 patients with AscAD (46.3±22.0 years) and 10 healthy volunteers (32.9±13.4 years) after written informed consent and IRB-approval. Following manual vessel wall segmentation of the ascending aorta (MATLAB, The Mathworks, Natick, MA), a 3D surface was created using spline interpolation. Spatial WSS variation based on surface division in 12 segments and temporal variation were evaluated in AscAD and normal aortas. Visual analysis of flow patterns was performed based on streamlines and particle traces using EnSight (v9.0, CEI, Apex, NC). Results AscAD was associated with significantly increased diastolic WSS, decreased systolic to diastolic WSS ratio, and delayed onset of peak WSS (all P wall of the ascending aorta. Vortical flow with highest velocities along the anterior wall and increased helical flow during diastole were observed in AscAD compared to controls. Conclusion Changes in WSS in the ascending aorta of AscAD correspond to observed alterations in flow patterns compared to controls. PMID:21563242

  15. Effect of shear stress and free radicals induced by ultrasound on erythrocytes

    International Nuclear Information System (INIS)

    Kondo, T.; Fukushima, Y.; Kon, H.; Riesz, P.

    1989-01-01

    The present study was undertaken to elucidate the mechanism of hemolysis induced by ultrasound. Ar or N2O gas was used to distinguish between cavitation with or without free radical formation (hydroxyl radicals and hydrogen atoms). Free radical formation was examined by the method of spin trapping combined with ESR. After sonication of erythrocyte suspensions, several structural and functional parameters of the erythrocyte membrane--hemolysis, membrane fluidity, membrane permeability, and membrane deformability--were examined. Although free radical formation was observed in the erythrocyte suspensions sonicated in the presence of Ar, no free radical formation was observed in the presence of N2O. However, the hemolysis behavior induced by ultrasound was similar in the presence of Ar or N2O. The membrane fluidity, permeability, and deformability of the remaining unlysed erythrocytes after sonication in the presence of Ar or N2O were unchanged and identical to those of the control cells. On the other hand, after gamma irradiation (700 Gy), the hemolysis behavior was quite different from that after sonication, and the membrane properties were significantly changed. These results suggest that hemolysis induced by sonication was due to mechanical shearing stress arising from cavitation, and that the membrane integrity of the remaining erythrocytes after sonication was the same as that of control cells without sonication. The triatomic gas, N2O, may be useful for ultrasonically disrupting cells without accompanying free radical formation

  16. Effects of plasticization and shear stress on phase structure development and properties of soy protein blends.

    Science.gov (United States)

    Chen, Feng; Zhang, Jinwen

    2010-11-01

    In this study, soy protein concentrate (SPC) was used as a plastic component to blend with poly(butylene adipate-co-terephthalate) (PBAT). Effects of SPC plasticization and blend composition on its deformation during mixing were studied in detail. Influence of using water as the major plasticizer and glycerol as the co-plasticizer on the deformation of the SPC phase during mixing was explored. The effect of shear stress, as affected by SPC loading level, on the phase structure of SPC in the blends was also investigated. Quantitative analysis of the aspect ratio of SPC particles was conducted by using ImageJ software, and an empirical model predicting the formation of percolated structure was applied. The experimental results and the model prediction showed a fairly good agreement. The experimental results and statistic analysis suggest that both SPC loading level and its water content prior to compounding had significant influences on development of the SPC phase structure and were correlated in determining the morphological structures of the resulting blends. Consequently, physical and mechanical properties of the blends greatly depended on the phase morphology and PBAT/SPC ratio of the blends.

  17. Pressure and Stress Prediction in the Nankai Accretionary Prism: A Critical State Soil Mechanics Porosity-Based Approach

    Science.gov (United States)

    Flemings, Peter B.; Saffer, Demian M.

    2018-02-01

    We predict pressure and stress from porosity in the Nankai accretionary prism with a critical state soil model that describes porosity as a function of mean stress and maximum shear stress, and assumes Coulomb failure within the wedge and uniaxial burial beneath it. At Ocean Drilling Program Sites 1174 and 808, we find that pore pressure in the prism supports 70% to 90% of the overburden (λu = 0.7 to 0.9), for a range of assumed friction angles (5-30°). The prism pore pressure is equal to or greater than that in the underthrust sediments even though the porosity is lower within the prism. The high pore pressures lead to a mechanically weak wedge that supports low maximum shear stress, and this in turn requires very low basal traction to remain consistent with the observed narrowly tapered wedge geometry. We estimate the décollement friction coefficient (μb) to be 0.08-0.38 (ϕb' = 4.6°-21°). Our approach defines a pathway to predict pressure in a wide range of environments from readily observed quantities (e.g., porosity and seismic velocity). Pressure and stress control the form of the Earth's collisional continental margins and play a key role in its greatest earthquakes. However, heretofore, there has been no systematic approach to relate material state (e.g., porosity), pore pressure, and stress in these systems.

  18. Effect of temperature on the rheological properties with shear stress limit of iron oxide nanoparticle modified bentonite drilling muds

    Directory of Open Access Journals (Sweden)

    Ahmed S. Mohammed

    2017-09-01

    Full Text Available In this study, the effect of temperature on the rheological properties and weight loss of a water based bentonite drilling mud modified with iron oxide nanoparticle (nanoFe2O3 was investigated. The bentonite contents in the drilling muds were varied up to 6% by the weight of water and temperature was varied from 25 °C to 85 °C. The nanoFe2O3 content was varied between 0 and 1% by the weight of the drilling mud to modify the rheological properties of the drilling mud. The nanoFe2O3 and bentonite clay were characterized using the X-ray diffraction analysis (XRD and thermal gravimetric analysis (TGA. In the TGA study, the total weight loss at 800 °C for the bentonite decreased from 13% to 1.16%, a 91% reduction when the bentonite clay was mixed with 1% of nanoFe2O3. The results also showed that 1% of nanoFe2O3 increased the rheological properties of the drilling mud. The nanoFe2O3 modification increased the yield stress (τo and plastic viscosity (PV by 45–200% and 20–105% respectively based on the bentonite content and temperature of the drilling mud. The shear thinning behavior of the bentonite drilling mud with and without nanoFe2O3 has been quantified using the hyperbolic model and compared with three parameters Herschel–Bulkley model. The results showed that the hyperbolic model predicted the shear thinning relationship between the shear stress and shear strain rate of the nanoFe2O3 modified bentonite drilling mud very well. Also the hyperbolic model has a maximum shear stress limit whereas the Herschel–Bulkley model did not have a limit on the maximum shear stress. Based on the hyperbolic model the maximum shear stress for the 2%, 4% and 6% bentonite drilling muds without nanoFe2O3 at room temperature were 25 Pa, 35 Pa and 51 Pa respectively. The maximum shear stress for the 2%, 4% and 6% bentonite drilling muds modified with 1% nanoFe2O3 at 25 °C were 59 Pa, 84 Pa and 140 Pa respectively, hence an increase of 135–175

  19. Shear stress upregulates regeneration-related immediate early genes in liver progenitors in 3D ECM-like microenvironments.

    Science.gov (United States)

    Nishii, Kenichiro; Brodin, Erik; Renshaw, Taylor; Weesner, Rachael; Moran, Emma; Soker, Shay; Sparks, Jessica L

    2018-05-01

    The role of fluid stresses in activating the hepatic stem/progenitor cell regenerative response is not well understood. This study hypothesized that immediate early genes (IEGs) with known links to liver regeneration will be upregulated in liver progenitor cells (LPCs) exposed to in vitro shear stresses on the order of those produced from elevated interstitial flow after partial hepatectomy. The objectives were: (1) to develop a shear flow chamber for application of fluid stress to LPCs in 3D culture; and (2) to determine the effects of fluid stress on IEG expression in LPCs. Two hours of shear stress exposure at ∼4 dyn/cm 2 was applied to LPCs embedded individually or as 3D spheroids within a hyaluronic acid/collagen I hydrogel. Results were compared against static controls. Quantitative reverse transcriptase polymerase chain reaction was used to evaluate the effect of experimental treatments on gene expression. Twenty-nine genes were analyzed, including IEGs and other genes linked to liver regeneration. Four IEGs (CFOS, IP10, MKP1, ALB) and three other regeneration-related genes (WNT, VEGF, EpCAM) were significantly upregulated in LPCs in response to fluid mechanical stress. LPCs maintained an early to intermediate stage of differentiation in spheroid culture in the absence of the hydrogel, and addition of the gel initiated cholangiocyte differentiation programs which were abrogated by the onset of flow. Collectively the flow-upregulated genes fit the pattern of an LPC-mediated proliferative/regenerative response. These results suggest that fluid stresses are potentially important regulators of the LPC-mediated regeneration response in liver. © 2017 Wiley Periodicals, Inc.

  20. On magma fragmentation by conduit shear stress: Evidence from the Kos Plateau Tuff, Aegean Volcanic Arc

    Science.gov (United States)

    Palladino, Danilo M.; Simei, Silvia; Kyriakopoulos, Konstantinos

    2008-12-01

    Large silicic explosive eruptions are the most catastrophic volcanic events. Yet, the intratelluric mechanisms underlying are not fully understood. Here we report a field and laboratory study of the Kos Plateau Tuff (KPT, 161 ka, Aegean Volcanic Arc), which provides an excellent geological example of conduit processes that control magma vesiculation and fragmentation during intermediate- to large-scale caldera-forming eruptions. A prominent feature of the KPT is the occurrence of quite unusual platy-shaped tube pumice clasts in pyroclastic fall and current deposits from the early eruption phases preceding caldera collapse. On macroscopic and SEM observations, flat clast faces are elongated parallel to tube vesicles, while transverse surfaces often occur at ~ 45° to vesicle elongation. This peculiar pumice texture provides evidence of high shear stresses related to strong velocity gradients normal to conduit walls, which induced vesiculation and fragmentation of the ascending magma. Either an increasing mass discharge rate without adequate enlargement of a narrow central feeder conduit or a developing fissure-like feeder system related to incipient caldera collapse provided suitable conditions for the generation of plate tube pumice within magma volumes under high shear during the pre-climactic KPT eruption phases. This mechanism implies that the closer to the conduit walls (where the stronger are the velocity gradients) the larger was the proportion of plate vs. conventional (lensoid) juvenile fragments in the ascending gas-pyroclast mixture. Consequently, plate pumice clasts were mainly entrained in the outer portions of the jet and convecting regions of a sustained, Plinian-type, eruption column, as well as in occasional lateral blast currents generated at the vent. As a whole, plate pumice clasts in the peripheral portions of the column were transported at lower altitudes and deposited by fallout or partial collapse closer to the vent relative to lensoid ones

  1. Determination of the Critical Stress Associated with Dynamic Phase Transformation in Steels by Means of Free Energy Method

    Directory of Open Access Journals (Sweden)

    Clodualdo Aranas

    2018-05-01

    Full Text Available The double differentiation method overestimates the critical stress associated with the initiation of dynamic transformation (DT because significant amounts of the dynamic phase must be present in order for its effect on the work hardening rate to be detectable. In this work, an alternative method (referred to here as the free energy method is presented based on the thermodynamic condition that the driving force is equal to the total energy obstacle during the exact moment of transformation. The driving force is defined as the difference between the DT critical stress (measured in the single-phase austenite region and the yield stress of the fresh ferrite that takes its place. On the other hand, the energy obstacle consists of the free energy difference between austenite and ferrite, and the work of shear accommodation and dilatation associated with the phase transformation. Here, the DT critical stresses in a C-Mn steel were calculated using the free energy method at temperatures ranging from 870 °C to 1070 °C. The results show that the calculated critical stress using the present approach appears to be more accurate than the values measured by the double differentiation method.

  2. Three-dimensional flow structure and patterns of bed shear stress in an evolving compound meander bend

    Science.gov (United States)

    Engel, Frank; Rhoads, Bruce L.

    2016-01-01

    Compound meander bends with multiple lobes of maximum curvature are common in actively evolving lowland rivers. Interaction among spatial patterns of mean flow, turbulence, bed morphology, bank failures and channel migration in compound bends is poorly understood. In this paper, acoustic Doppler current profiler (ADCP) measurements of the three-dimensional (3D) flow velocities in a compound bend are examined to evaluate the influence of channel curvature and hydrologic variability on the structure of flow within the bend. Flow structure at various flow stages is related to changes in bed morphology over the study timeframe. Increases in local curvature within the upstream lobe of the bend reduce outer bank velocities at morphologically significant flows, creating a region that protects the bank from high momentum flow and high bed shear stresses. The dimensionless radius of curvature in the upstream lobe is one-third less than that of the downstream lobe, with average bank erosion rates less than half of the erosion rates for the downstream lobe. Higher bank erosion rates within the downstream lobe correspond to the shift in a core of high velocity and bed shear stresses toward the outer bank as flow moves through the two lobes. These erosion patterns provide a mechanism for continued migration of the downstream lobe in the near future. Bed material size distributions within the bend correspond to spatial patterns of bed shear stress magnitudes, indicating that bed material sorting within the bend is governed by bed shear stress. Results suggest that patterns of flow, sediment entrainment, and planform evolution in compound meander bends are more complex than in simple meander bends. Moreover, interactions among local influences on the flow, such as woody debris, local topographic steering, and locally high curvature, tend to cause compound bends to evolve toward increasing planform complexity over time rather than stable configurations.

  3. Numerical Simulations of the Effects of a Tidal Turbine Array on Near-Bed Velocity and Local Bed Shear Stress

    Directory of Open Access Journals (Sweden)

    Philip A. Gillibrand

    2016-10-01

    Full Text Available We apply a three-dimensional hydrodynamic model to consider the potential effects of energy extraction by an array of tidal turbines on the ambient near-bed velocity field and local bed shear stress in a coastal channel with strong tidal currents. Local bed shear stress plays a key role in local sediment dynamics. The model solves the Reynold-averaged Navier-Stokes (RANS equations on an unstructured mesh using mixed finite element and finite volume techniques. Tidal turbines are represented through an additional form drag in the momentum balance equation, with the thrust imparted and power generated by the turbines being velocity dependent with appropriate cut-in and cut-out velocities. Arrays of 1, 4 and 57 tidal turbines, each of 1.5 MW capacity, were simulated. Effects due to a single turbine and an array of four turbines were negligible. The main effect of the array of 57 turbines was to cause a shift in position of the jet through the tidal channel, as the flow was diverted around the tidal array. The net effect of this shift was to increase near-bed velocities and bed shear stress along the northern perimeter of the array by up to 0.8 m·s−1 and 5 Pa respectively. Within the array and directly downstream, near-bed velocities and bed shear stress were reduced by similar amounts. Changes of this magnitude have the potential to modify the known sand and shell banks in the region. Continued monitoring of the sediment distributions in the region will provide a valuable dataset on the impacts of tidal energy extraction on local sediment dynamics. Finally, the mean power generated per turbine is shown to decrease as the turbine array increased in size.

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

    Science.gov (United States)

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

    2010-01-01

    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. PMID:20123196

  5. Effects of iodinated contrast media on common carotid and brachial artery blood flow and wall shear stress

    International Nuclear Information System (INIS)

    Irace, C.; Tamburini, S.; Bertucci, B.; Franceschi, M.S. de; Gnasso, A.

    2006-01-01

    The aim of our study was to evaluate the effect of the intravenous contrast media iomeprol on wall shear stress, blood flow and vascular parameters in the common carotid and brachial artery. Thirty outpatients undergoing thoracic or abdominal spiral CT scans were studied. The internal diameter and flow velocity of the common carotid and brachial artery were evaluated by ultrasound, and blood viscosity was measured before and after low osmolality iomeprol (Iomeron 350) injection. The wall shear stress, blood flow and pulsatility index were calculated. To test the differences between groups, the Wilcoxon rank test and Mann Whitney U test were applied. Blood viscosity decreased slightly, but significantly after contrast media (4.6±0.7 vs. 4.5±0.7 mPa.s, P=0.02). Contrarily, blood flow and wall shear stress did not change in the common carotid artery, but significantly decreased in the brachial artery (0.9±0.4 vs. 0.6±0.3 ml/s, P<0.0001, and 41.5±13.9 vs. 35.3±11.0 dynes/cm2, P<0.002, respectively), whereas the pulsatility index significantly increased in the brachial artery (5.0±3.3 vs. 7.5±5.3, P<0.001). Iomeprol injection causes blood flow and wall shear stress reduction of the brachial artery; the rise in the pulsatility index suggests an increase in peripheral vascular resistance. Further investigation is needed to evaluate whether these modifications can be clinically relevant. (orig.)

  6. Numerical modeling of injection, stress and permeability enhancement during shear stimulation at the Desert Peak Enhanced Geothermal System

    Science.gov (United States)

    Dempsey, David; Kelkar, Sharad; Davatzes, Nick; Hickman, Stephen H.; Moos, Daniel

    2015-01-01

    Creation of an Enhanced Geothermal System relies on stimulation of fracture permeability through self-propping shear failure that creates a complex fracture network with high surface area for efficient heat transfer. In 2010, shear stimulation was carried out in well 27-15 at Desert Peak geothermal field, Nevada, by injecting cold water at pressure less than the minimum principal stress. An order-of-magnitude improvement in well injectivity was recorded. Here, we describe a numerical model that accounts for injection-induced stress changes and permeability enhancement during this stimulation. In a two-part study, we use the coupled thermo-hydrological-mechanical simulator FEHM to: (i) construct a wellbore model for non-steady bottom-hole temperature and pressure conditions during the injection, and (ii) apply these pressures and temperatures as a source term in a numerical model of the stimulation. In this model, a Mohr-Coulomb failure criterion and empirical fracture permeability is developed to describe permeability evolution of the fractured rock. The numerical model is calibrated using laboratory measurements of material properties on representative core samples and wellhead records of injection pressure and mass flow during the shear stimulation. The model captures both the absence of stimulation at low wellhead pressure (WHP ≤1.7 and ≤2.4 MPa) as well as the timing and magnitude of injectivity rise at medium WHP (3.1 MPa). Results indicate that thermoelastic effects near the wellbore and the associated non-local stresses further from the well combine to propagate a failure front away from the injection well. Elevated WHP promotes failure, increases the injection rate, and cools the wellbore; however, as the overpressure drops off with distance, thermal and non-local stresses play an ongoing role in promoting shear failure at increasing distance from the well.

  7. Thinner regions of intracranial aneurysm wall correlate with regions of higher wall shear stress: a 7.0 tesla MRI

    Science.gov (United States)

    Blankena, Roos; Kleinloog, Rachel; Verweij, Bon H.; van Ooij, Pim; ten Haken, Bennie; Luijten, Peter R.; Rinkel, Gabriel J.E.; Zwanenburg, Jaco J.M.

    2016-01-01

    Purpose To develop a method for semi-quantitative wall thickness assessment on in vivo 7.0 tesla (7T) MRI images of intracranial aneurysms for studying the relation between apparent aneurysm wall thickness and wall shear stress. Materials and Methods Wall thickness was analyzed in 11 unruptured aneurysms in 9 patients, who underwent 7T MRI with a TSE based vessel wall sequence (0.8 mm isotropic resolution). A custom analysis program determined the in vivo aneurysm wall intensities, which were normalized to signal of nearby brain tissue and were used as measure for apparent wall thickness (AWT). Spatial wall thickness variation was determined as the interquartile range in AWT (the middle 50% of the AWT range). Wall shear stress was determined using phase contrast MRI (0.5 mm isotropic resolution). We performed visual and statistical comparisons (Pearson’s correlation) to study the relation between wall thickness and wall shear stress. Results 3D colored AWT maps of the aneurysms showed spatial AWT variation, which ranged from 0.07 to 0.53, with a mean variation of 0.22 (a variation of 1.0 roughly means a wall thickness variation of one voxel (0.8mm)). In all aneurysms, AWT was inversely related to WSS (mean correlation coefficient −0.35, P<0.05). Conclusions A method was developed to measure the wall thickness semi-quantitatively, using 7T MRI. An inverse correlation between wall shear stress and AWT was determined. In future studies, this non-invasive method can be used to assess spatial wall thickness variation in relation to pathophysiologic processes such as aneurysm growth and –rupture. PMID:26892986

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

    Science.gov (United States)

    Serata, S.

    2006-12-01

    The Serata Stressmeter has been developed to measure and monitor earthquake shear stress build-up along shallow active faults. The development work made in the past 25 years has established the Stressmeter as an automatic stress measurement system to study timing of forthcoming major earthquakes in support of the current earthquake prediction studies based on statistical analysis of seismological observations. In early 1982, a series of major Man-made earthquakes (magnitude 4.5-5.0) suddenly occurred in an area over deep underground potash mine in Saskatchewan, Canada. By measuring underground stress condition of the mine, the direct cause of the earthquake was disclosed. The cause was successfully eliminated by controlling the stress condition of the mine. The Japanese government was interested in this development and the Stressmeter was introduced to the Japanese government research program for earthquake stress studies. In Japan the Stressmeter was first utilized for direct measurement of the intrinsic lateral tectonic stress gradient G. The measurement, conducted at the Mt. Fuji Underground Research Center of the Japanese government, disclosed the constant natural gradients of maximum and minimum lateral stresses in an excellent agreement with the theoretical value, i.e., G = 0.25. All the conventional methods of overcoring, hydrofracturing and deformation, which were introduced to compete with the Serata method, failed demonstrating the fundamental difficulties of the conventional methods. The intrinsic lateral stress gradient determined by the Stressmeter for the Japanese government was found to be the same with all the other measurements made by the Stressmeter in Japan. The stress measurement results obtained by the major international stress measurement work in the Hot Dry Rock Projects conducted in USA, England and Germany are found to be in good agreement with the Stressmeter results obtained in Japan. Based on this broad agreement, a solid geomechanical

  9. Critical-like features of stress response in frictional packings

    International Nuclear Information System (INIS)

    Cakir, Abdullah; Silbert, Leonardo E

    2015-01-01

    The mechanical response of static, unconfined, overcompressed face centred cubic, granular arrays is studied using large-scale, discrete element method simulations. Specifically, the stress response due to the application of a localised force perturbation—the Green function technique—is obtained in granular packings generated over several orders of magnitude in both the particle friction coefficient and the applied forcing. We observe crossover behaviour in the mechanical state of the system characterised by the changing nature of the resulting stress response. The transition between anisotropic and isotropic stress response exhibits critical-like features through the identification of a diverging length scale that distinguishes the spatial extent of anisotropic regions from those that display isotropic behaviour. A multidimensional phase diagram is constructed that parameterises the response of the system due to changing friction and force perturbations. (paper)

  10. The effect of chlorination and hydrodynamic shear stress on the persistence of bacteriophages associated with drinking water biofilms.

    Science.gov (United States)

    Pelleieux, S; Mathieu, L; Block, J-C; Gantzer, C; Bertrand, I

    2016-10-01

    This work aimed to assess at pilot scale the effect of chlorination and water flushing on 2-month-old drinking water biofilms and, above all, on biofilm-associated F-specific RNA bacteriophages MS2, GA and Qβ. Chlorination (4 mg l(-1) ) was applied first with a hydrodynamic shear stress of 1 Pa and second with an increase in hydrodynamic shear stress to 10 Pa. Despite a rapid decrease in the number of biofilm bacteria and associated phages, infectious phages were still detected on surfaces after completion of the 150 min cleaning procedure. The resulting sequence of phage removal was: GA > Qβ ≫ MS2. The effect of chlorine on biofilm bacteria and biofilm-associated phages was limited to the upper layers of the biofilm and was not enhanced by an increase in hydrodynamic shear stress. A smaller decrease was observed for MS2 than for GA or Qβ after completion of the cleaning procedure. The differences observed between the three phages suggest that the location of the viral particles in the biofilm, which is related to their surface properties, affects the efficiency of chlorine disinfection. © 2016 The Society for Applied Microbiology.

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

    Science.gov (United States)

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

    2014-05-01

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

  12. Bicuspid aortic valves are associated with increased wall and turbulence shear stress levels compared to trileaflet aortic valves.

    Science.gov (United States)

    Saikrishnan, Neelakantan; Mirabella, Lucia; Yoganathan, Ajit P

    2015-06-01

    Congenital bicuspid aortic valves (BAVs) are associated with accelerated disease progression, such as leaflet calcification and ascending aorta dilatation. Although common underlying genetic factors have been implicated in accelerated disease in BAV patients, several studies have suggested that altered hemodynamics also play a role in this disease process. The present study compares turbulence and wall shear stress (WSS) measurements between various BAV and trileaflet aortic valve (TAV) models to provide information for mechanobiological models of BAV disease. BAV and TAV models were constructed from excised porcine aortic valves to simulate parametric variations in BAV stenosis, hemodynamics and geometry. Particle image velocimetry experiments were conducted at physiological pressure conditions to characterize velocity fields in the ascending aorta. The velocity fields were post-processed to calculate turbulence, viscous and wall shear stresses in the ascending aorta. Stenosed BAV models showed the presence of eccentric systolic jets, causing increased WSS. Lower cardiac output resulted in a narrower jet, lower turbulence and lower viscous shear stress (VSS). The specific severe stenosis BAV model studied here showed reduced WSS due to reduction in non-fused leaflet mobility. Dilation of the aorta did not affect any turbulence or VSS, but reduced the WSS. In comparison with BAVs, TAVs have similar VSS values, but much smaller WSS and turbulence levels. These increased turbulence  and WSS levels in BAVs may play a key role in amplifying the biological responses of the ascending aorta wall and valvular leaflets, and support the hemodynamic underpinnings of BAV disease processes.

  13. Exercise-induced shear stress is associated with changes in plasma von Willebrand factor in older humans.

    Science.gov (United States)

    Gonzales, Joaquin U; Thistlethwaite, John R; Thompson, Benjamin C; Scheuermann, Barry W

    2009-07-01

    Shear stress is the frictional force of blood against the endothelium, a stimulus for endothelial activation and the release of von Willebrand factor (vWF). This study tested the hypothesis that the increase in shear stress associated with exercise correlates with plasma vWF. Young (n = 14, 25.7 +/- 5.4 years) and older (n = 13, 65.6 +/- 10.7 years) individuals participated in 30 min of dynamic handgrip exercise at a moderate intensity. Brachial artery diameter and blood flow were measured using ultrasound Doppler and blood samples were collected before, immediately after, and following 30 min of recovery from exercise with plasma levels of vWF. Plasma levels of vWF increased (P exercise. The change in plasma vWF was linearly correlated with the increase in shear stress during exercise in older individuals (post-exercise: r = 0.78, 30 min recovery: r = 0.77, P < 0.01), but no association was found in the young individuals. These changes in plasma levels of vWF in humans suggest that aging influences endothelial activation and hemostasis.

  14. Analysis of wall shear stress around a competitive swimmer using 3D Navier-Stokes equations in CFD.

    Science.gov (United States)

    Popa, C V; Zaidi, H; Arfaoui, A; Polidori, G; Taiar, R; Fohanno, S

    2011-01-01

    This paper deals with the flow dynamics around a competitive swimmer during underwater glide phases occurring at the start and at every turn. The influence of the head position, namely lifted up, aligned and lowered, on the wall shear stress and the static pressure distributions is analyzed. The problem is considered as 3D and in steady hydrodynamic state. Three velocities (1.4 m/s, 2.2 m/s and 3.1 m/s) that correspond to inter-regional, national and international swimming levels are studied. The flow around the swimmer is assumed turbulent. The Reynolds-averaged Navier-Stokes (RANS) equations are solved with the standard k-ω turbulent model by using the CFD (computational fluid dynamics) numerical method based on a volume control approach. Numerical simulations are carried out with the ANSYS FLUENT® CFD code. The results show that the wall shear stress increases with the velocity and consequently the drag force opposing the movement of the swimmer increases as well. Also, high wall shear stresses are observed in the areas where the body shape, globally rigid in form, presents complex surface geometries such as the head, shoulders, buttocks, heel and chest.

  15. Effect of shear stress on iPSC-derived human brain microvascular endothelial cells (dhBMECs).

    Science.gov (United States)

    DeStefano, Jackson G; Xu, Zinnia S; Williams, Ashley J; Yimam, Nahom; Searson, Peter C

    2017-08-04

    The endothelial cells that form the lumen of capillaries and microvessels are an important component of the blood-brain barrier. Cell phenotype is regulated by transducing a range of biomechanical and biochemical signals in the local microenvironment. Here we report on the role of shear stress in modulating the morphology, motility, proliferation, apoptosis, and protein and gene expression, of confluent monolayers of human brain microvascular endothelial cells derived from induced pluripotent stem cells. To assess the response of derived human brain microvascular endothelial cells (dhBMECs) to shear stress, confluent monolayers were formed in a microfluidic device. Monolayers were subjected to a shear stress of 4 or 12 dyne cm -2 for 40 h. Static conditions were used as the control. Live cell imaging was used to assess cell morphology, cell speed, persistence, and the rates of proliferation and apoptosis as a function of time. In addition, immunofluorescence imaging and protein and gene expression analysis of key markers of the blood-brain barrier were performed. Human brain microvascular endothelial cells exhibit a unique phenotype in response to shear stress compared to static conditions: (1) they do not elongate and align, (2) the rates of proliferation and apoptosis decrease significantly, (3) the mean displacement of individual cells within the monolayer over time is significantly decreased, (4) there is no cytoskeletal reorganization or formation of stress fibers within the cell, and (5) there is no change in expression levels of key blood-brain barrier markers. The characteristic response of dhBMECs to shear stress is significantly different from human and animal-derived endothelial cells from other tissues, suggesting that this unique phenotype that may be important in maintenance of the blood-brain barrier. The implications of this work are that: (1) in confluent monolayers of dhBMECs, tight junctions are formed under static conditions, (2) the formation

  16. Low shear stress induces vascular eNOS uncoupling via autophagy-mediated eNOS phosphorylation.

    Science.gov (United States)

    Zhang, Jun-Xia; Qu, Xin-Liang; Chu, Peng; Xie, Du-Jiang; Zhu, Lin-Lin; Chao, Yue-Lin; Li, Li; Zhang, Jun-Jie; Chen, Shao-Liang

    2018-05-01

    Uncoupled endothelial nitric oxide synthase (eNOS) produces O 2 - instead of nitric oxide (NO). Earlier, we reported rapamycin, an autophagy inducer and inhibitor of cellular proliferation, attenuated low shear stress (SS) induced O 2 - production. Nevertheless, it is unclear whether autophagy plays a critical role in the regulation of eNOS uncoupling. Therefore, this study aimed to investigate the modulation of autophagy on eNOS uncoupling induced by low SS exposure. We found that low SS induced endothelial O 2 - burst, which was accompanied by reduced NO release. Furthermore, inhibition of eNOS by L-NAME conspicuously attenuated low SS-induced O 2 - releasing, indicating eNOS uncoupling. Autophagy markers such as LC3 II/I ratio, amount of Beclin1, as well as ULK1/Atg1 were increased during low SS exposure, whereas autophagic degradation of p62/SQSTM1 was markedly reduced, implying impaired autophagic flux. Interestingly, low SS-induced NO reduction could be reversed by rapamycin, WYE-354 or ATG5 overexpression vector via restoration of autophagic flux, but not by N-acetylcysteine or apocynin. eNOS uncoupling might be ascribed to autophagic flux blockade because phosphorylation of eNOS Thr495 by low SS or PMA stimulation was also regulated by autophagy. In contrast, eNOS acetylation was not found to be regulated by low SS and autophagy. Notably, although low SS had no influence on eNOS Ser1177 phosphorylation, whereas boosted eNOS Ser1177 phosphorylation by rapamycin were in favor of the eNOS recoupling through restoration of autophagic flux. Taken together, we reported a novel mechanism for regulation of eNOS uncoupling by low SS via autophagy-mediated eNOS phosphorylation, which is implicated in geometrical nature of atherogenesis. Copyright © 2018 Elsevier B.V. All rights reserved.

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

    International Nuclear Information System (INIS)

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

    2013-01-01

    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 E r × 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 E r × B sheared flows in the development of residual stresses and intrinsic rotation. (letter)

  18. Wall shear stress in portal vein of cirrhotic patients with portal hypertension.

    Science.gov (United States)

    Wei, Wei; Pu, Yan-Song; Wang, Xin-Kai; Jiang, An; Zhou, Rui; Li, Yu; Zhang, Qiu-Juan; Wei, Ya-Juan; Chen, Bin; Li, Zong-Fang

    2017-05-14

    To investigate wall shear stress (WSS) magnitude and distribution in cirrhotic patients with portal hypertension using computational fluid dynamics. Idealized portal vein (PV) system models were reconstructed with different angles of the PV-splenic vein (SV) and superior mesenteric vein (SMV)-SV. Patient-specific models were created according to enhanced computed tomography images. WSS was simulated by using a finite-element analyzer, regarding the blood as a Newtonian fluid and the vessel as a rigid wall. Analysis was carried out to compare the WSS in the portal hypertension group with that in healthy controls. For the idealized models, WSS in the portal hypertension group (0-10 dyn/cm 2 ) was significantly lower than that in the healthy controls (10-20 dyn/cm 2 ), and low WSS area (0-1 dyn/cm 2 ) only occurred in the left wall of the PV in the portal hypertension group. Different angles of PV-SV and SMV-SV had different effects on the magnitude and distribution of WSS, and low WSS area often occurred in smaller PV-SV angle and larger SMV-SV angle. In the patient-specific models, WSS in the cirrhotic patients with portal hypertension (10.13 ± 1.34 dyn/cm 2 ) was also significantly lower than that in the healthy controls ( P portal hypertension, the low WSS area extended to wider levels and the magnitude of WSS reached lower levels, thereby being more prone to disturbed flow occurrence. Cirrhotic patients with portal hypertension show dramatic hemodynamic changes with lower WSS and greater potential for disturbed flow, representing a possible causative factor of PV thrombosis.

  19. Augmentative effect of pulsatility on the wall shear stress in tube flow.

    Science.gov (United States)

    Nakata, M; Tatsumi, E; Tsukiya, T; Taenaka, Y; Nishimura, T; Nishinaka, T; Takano, H; Masuzawa, T; Ohba, K

    1999-08-01

    Wall shear stress (WSS) has been considered to play an important role in the physiological and metabolic functions of the vascular endothelial cells. We investigated the effects of the pulse rate and the maximum flow rate on the WSS to clarify the influence of pulsatility. Water was perfused in a 1/2 inch transparent straight cylinder with a nonpulsatile centrifugal pump and a pulsatile pneumatic ventricular assist device (VAD). In nonpulsatile flow (NF), the flow rate was changed 1 to 6 L/min by 1 L/min increments to obtain standard values of WSS at each flow rate. In pulsatile flow (PF), the pulse rate was controlled at 40, 60, and 80 bpm, and the maximum flow rate was varied from 3.3 to 12.0 L/min while the mean flow rate was kept at 3 L/min. The WSS was estimated from the velocity profile at measuring points using the laser illuminated fluorescence method. In NF, the WSS was 12.0 dyne/cm2 at 3 L/min and 33.0 dyne/cm2 at 6 L/min. In PF, the pulse rate change with the same mean, and the maximum flow rate did not affect WSS. On the other hand, the increase in the maximum flow rate at the constant mean flow rate of 3 L/min augmented the mean WSS from 13.1 to 32.9 dyne/cm2. We concluded that the maximum flow rate exerted a substantial augmentative effect on WSS, and the maximum flow rate was a dominant factor of pulsatility in this effect.

  20. [Second victim : Critical incident stress management in clinical medicine].

    Science.gov (United States)

    Schiechtl, B; Hunger, M S; Schwappach, D L; Schmidt, C E; Padosch, S A

    2013-09-01

    Critical incidents in clinical medicine can have far-reaching consequences on patient health. In cases of severe medical errors they can seriously harm the patient or even lead to death. The involvement in such an event can result in a stress reaction, a so-called acute posttraumatic stress disorder in the healthcare provider, the so-called second victim of an adverse event. Psychological distress may not only have a long lasting impact on quality of life of the physician or caregiver involved but it may also affect the ability to provide safe patient care in the aftermath of adverse events. A literature review was performed to obtain information on care giver responses to medical errors and to determine possible supportive strategies to mitigate negative consequences of an adverse event on the second victim. An internet search and a search in Medline/Pubmed for scientific studies were conducted using the key words "second victim, "medical error", "critical incident stress management" (CISM) and "critical incident stress reporting system" (CIRS). Sources from academic medical societies and public institutions which offer crisis management programs where analyzed. The data were sorted by main categories and relevance for hospitals. Analysis was carried out using descriptive measures. In disaster medicine and aviation navigation services the implementation of a CISM program is an efficient intervention to help staff to recover after a traumatic event and to return to normal functioning and behavior. Several other concepts for a clinical crisis management plan were identified. The integration of CISM and CISM-related programs in a clinical setting may provide efficient support in an acute crisis and may help the caregiver to deal effectively with future error events and employee safety.

  1. Shape and compliance of endothelial cells after shear stress in vitro or from different aortic regions: scanning ion conductance microscopy study.

    Directory of Open Access Journals (Sweden)

    Claire M F Potter

    Full Text Available To measure the elongation and compliance of endothelial cells subjected to different patterns of shear stress in vitro, and to compare these parameters with the elongation and compliance of endothelial cells from different regions of the intact aorta.Porcine aortic endothelial cells were cultured for 6 days under static conditions or on an orbital shaker. The shaker generated a wave of medium, inducing pulsatile shear stress with a preferred orientation at the edge of the well or steadier shear stress with changing orientation at its centre. The topography and compliance of these cells and cells from the inner and outer curvature of ex vivo porcine aortic arches were measured by scanning ion conductance microscopy (SICM.Cells cultured under oriented shear stress were more elongated and less compliant than cells grown under static conditions or under shear stress with no preferred orientation. Cells from the outer curvature of the aorta were more elongated and less compliant than cells from the inner curvature.The elongation and compliance of cultured endothelial cells vary according to the pattern of applied shear stress, and are inversely correlated. A similar inverse correlation occurs in the aortic arch, with variation between regions thought to experience different haemodynamic stresses.

  2. The role of shear stress and altered tissue properties on endothelial to mesenchymal transformation and tumor-endothelial cell interaction.

    Science.gov (United States)

    Mina, Sara G; Huang, Peter; Murray, Bruce T; Mahler, Gretchen J

    2017-07-01

    Tumor development is influenced by stromal cells in aspects including invasion, growth, angiogenesis, and metastasis. Activated fibroblasts are one group of stromal cells involved in cancer metastasis, and one source of activated fibroblasts is endothelial to mesenchymal transformation (EndMT). EndMT begins when the endothelial cells delaminate from the cell monolayer, lose cell-cell contacts, lose endothelial markers such as vascular endothelial-cadherin (VE-cadherin), gain mesenchymal markers like alpha-smooth muscle actin (α-SMA), and acquire mesenchymal cell-like properties. A three-dimensional (3D) culture microfluidic device was developed for investigating the role of steady low shear stress (1 dyne/cm 2 ) and altered extracellular matrix (ECM) composition and stiffness on EndMT. Shear stresses resulting from fluid flow within tumor tissue are relevant to both cancer metastasis and treatment effectiveness. Low and oscillatory shear stress rates have been shown to enhance the invasion of metastatic cancer cells through specific changes in actin and tubulin remodeling. The 3D ECM within the device was composed of type I collagen and glycosaminoglycans (GAGs), hyaluronic acid and chondroitin sulfate. An increase in collagen and GAGs has been observed in the solid tumor microenvironment and has been correlated with poor prognosis in many different cancer types. In this study, it was found that ECM composition and low shear stress upregulated EndMT, including upregulation of mesenchymal-like markers (α-SMA and Snail) and downregulated endothelial marker protein and gene expression (VE-cadherin). Furthermore, this novel model was utilized to investigate the role of EndMT in breast cancer cell proliferation and migration. Cancer cell spheroids were embedded within the 3D ECM of the microfluidic device. The results using this device show for the first time that the breast cancer spheroid size is dependent on shear stress and that the cancer cell migration rate

  3. Generation of sheared poloidal flows by electrostatic and magnetic Reynolds stress in the boundary plasma of HT-7 tokamak

    International Nuclear Information System (INIS)

    Xu, G.S.; Wan, B.N.; Li, J.

    2005-01-01

    The radial profiles of electrostatic and magnetic Reynolds stress (Maxwell stress) have been measured in the plasma boundary region of HT-7 tokamak. Experimental results show that the radial gradient of electrostatic Reynolds stress (ERS) changes sign across the last closed flux surface, and the neoclassical flow damping and the damping due to charge exchange processes are balanced by the radial gradient of ERS, which sustains the equilibrium sheared flow structure in a steady state. The contribution of magnetic Reynolds stress was found unimportant in a low β plasma. Detailed analyses indicate that the propagation properties of turbulence in radial and poloidal directions and the profiles of potential fluctuation level are responsible for the radial structure of ERS. (author)

  4. A thin rivulet or ridge subject to a uniform transverse shear stress at its free surface due to an external airflow

    KAUST Repository

    Sullivan, J. M.; Paterson, C.; Wilson, S. K.; Duffy, B. R.

    2012-01-01

    We use the lubrication approximation to analyze three closely related problems involving a thin rivulet or ridge (i.e., a two-dimensional droplet) of fluid subject to a prescribed uniform transverse shear stress at its free surface due

  5. Inverted Basal Shear Stress of Antarctic and Greenland Ice Streams and Glaciers, Version 1

    Data.gov (United States)

    National Aeronautics and Space Administration — This data set includes basal shear distributions inferred from surface observations - surface ice velocities (Joughin et al., 2010, Rignot et al., 2011), bed and...

  6. In vitro shear stress measurements using particle image velocimetry in a family of carotid artery models: effect of stenosis severity, plaque eccentricity, and ulceration.

    Directory of Open Access Journals (Sweden)

    Sarah Kefayati

    Full Text Available 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.

  7. Numerical modeling of shear stimulation in naturally fractured geothermal reservoirs

    OpenAIRE

    Ucar, Eren

    2018-01-01

    Shear-dilation-based hydraulic stimulations are conducted to create enhanced geothermal systems (EGS) from low permeable geothermal reservoirs, which are initially not amenable to energy production. Reservoir stimulations are done by injecting low-pressurized fluid into the naturally fractured formations. The injection aims to activate critically stressed fractures by decreasing frictional strength and ultimately cause a shear failure. The shear failure leads to a permanent ...

  8. A two-dimensional continuum model of biofilm growth incorporating fluid flow and shear stress based detachment

    KAUST Repository

    Duddu, Ravindra

    2009-05-01

    We present a two-dimensional biofilm growth model in a continuum framework using an Eulerian description. A computational technique based on the eXtended Finite Element Method (XFEM) and the level set method is used to simulate the growth of the biofilm. The model considers fluid flow around the biofilm surface, the advection-diffusion and reaction of substrate, variable biomass volume fraction and erosion due to the interfacial shear stress at the biofilm-fluid interface. The key assumptions of the model and the governing equations of transport, biofilm kinetics and biofilm mechanics are presented. Our 2D biofilm growth results are in good agreement with those obtained by Picioreanu et al. (Biotechnol Bioeng 69(5):504-515, 2000). Detachment due to erosion is modeled using two continuous speed functions based on: (a) interfacial shear stress and (b) biofilm height. A relation between the two detachment models in the case of a 1D biofilm is established and simulated biofilm results with detachment in 2D are presented. The stress in the biofilm due to fluid flow is evaluated and higher stresses are observed close to the substratum where the biofilm is attached. © 2008 Wiley Periodicals, Inc.

  9. Job stress and cardiovascular disease: a theoretic critical review.

    Science.gov (United States)

    Kristensen, T S

    1996-07-01

    During the last 15 years, the research on job stress and cardiovascular diseases has been dominated by the job strain model developed by R. Karasek (1979) and colleagues (R. Karasek & T. Theorell, 1990). In this article the results of this research are briefly summarized, and the theoretical and methodological basis is discussed and criticized. A sociological interpretation of the model emphasizing theories of technological change, qualifications of the workers, and the organization of work is proposed. Furthermore, improvements with regard to measuring the job strain dimensions and to sampling the study base are suggested. Substantial improvements of the job strain research could be achieved if the principle of triangulation were used in the measurements of stressors, stress, and sickness and if occupation-based samples were used instead of large representative samples.

  10. Coping with traumatic stress in journalism: a critical ethnographic study.

    Science.gov (United States)

    Buchanan, Marla; Keats, Patrice

    2011-04-01

    Journalists who witness trauma and disaster events are at risk for physical, emotional, and psychological injury. The purpose of this paper is to present the results of a critical ethnographic study among 31 Canadian journalists and photojournalists with regard to coping strategies used to buffer the effects of being exposed to trauma and disaster events and work-related stress. The findings are the result of in-depth individual interviews and six workplace observations with journalists across Canada. The most commonly reported coping strategies were: avoidance strategies at work, use of black humor, controlling one's emotions and memories, exercise and other physical activities, focusing on the technical aspects, and using substances. Recommendations for addressing the effects of work-related stress within this population are provided.

  11. Utilization of shear stress for determination of activation energy of the defects created by neutron irradiation; Utilizacion de la tension de fluencia en la determinacion de la energia de activacion de defectos producidos por irradiacion neutronica

    Energy Technology Data Exchange (ETDEWEB)

    Gonzalez, Hector C.; Miralles, Monica [Comision Nacional de Energia Atomica, Buenos Aires (Argentina)

    1996-07-01

    This paper describes an experimental technique used for the determination thermodynamical parameters such as activation energy using the thermal annealing of increments of Critical resolved Shear Stress of the defects created by neutron irradiation at 77 K. The doses chosen for this work was 3.1 x 10 {sup 16} n/cm{sup 2} since the defects are stable to plastic deformation and the cascades of atomic displacements do not overlap. Specimens without any prior deformation were used allowing then the single addition of the initial stress to that due to the created defects. (author)

  12. Interaction between the Stress Phase Angle (SPA and the Oscillatory Shear Index (OSI Affects Endothelial Cell Gene Expression.

    Directory of Open Access Journals (Sweden)

    Ronny Amaya

    Full Text Available Hemodynamic forces play an important role in the non-uniform distribution of atherosclerotic lesions. Endothelial cells are exposed simultaneously to fluid wall shear stress (WSS and solid circumferential stress (CS. Due to variations in impedance (global factors and geometric complexities (local factors in the arterial circulation a time lag arises between these two forces that can be characterized by the temporal phase angle between CS and WSS (stress phase angle-SPA. Asynchronous flows (SPA close to -180° that are most prominent in coronary arteries have been associated with localization of atherosclerosis. Reversing oscillatory flows characterized by an oscillatory shear index (OSI that is great than zero are also associated with atherosclerosis localization. In this study we examined the relationship between asynchronous flows and reversing flows in altering the expression of 37 genes relevant to atherosclerosis development. In the case of reversing oscillatory flow, we observed that the asynchronous condition upregulated 8 genes compared to synchronous hemodynamics, most of them proatherogenic. Upregulation of the pro-inflammatory transcription factor NFκB p65 was confirmed by western blot, and nuclear translocation of NFκB p65 was confirmed by immunofluorescence staining. A comparative study between non-reversing flow and reversing flow found that in the case of synchronous hemodynamics, reversing flow altered the expression of 11 genes, while in the case of asynchronous hemodynamics, reversing flow altered the expression of 17 genes. Reversing flow significantly upregulated protein expression of NFκB p65 for both synchronous and asynchronous conditions. Nuclear translocation of NFκB p65 was confirmed for synchronous and asynchronous conditions in the presence of flow reversal. These data suggest that asynchronous hemodynamics and reversing flow can elicit proatherogenic responses in endothelial cells compared to synchronous

  13. 3-D flow characterization and shear stress in a stenosed carotid artery bifurcation model using stereoscopic PIV technique.

    Science.gov (United States)

    Kefayati, Sarah; Poepping, Tamie L

    2010-01-01

    The carotid artery bifurcation is a common site of atherosclerosis which is a major leading cause of ischemic stroke. The impact of stenosis in the atherosclerotic carotid artery is to disturb the flow pattern and produce regions with high shear rate, turbulence, and recirculation, which are key hemodynamic factors associated with plaque rupture, clot formation, and embolism. In order to characterize the disturbed flow in the stenosed carotid artery, stereoscopic PIV measurements were performed in a transparent model with 50% stenosis under pulsatile flow conditions. Simulated ECG gating of the flowrate waveform provides external triggering required for volumetric reconstruction of the complex flow patterns. Based on the three-component velocity data in the lumen region, volumetric shear-stress patterns were derived.

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

    Directory of Open Access Journals (Sweden)

    Puvenna Vikram

    2011-05-01

    Full Text Available Abstract Background One of the most important and often neglected physiological stimuli contributing to the differentiation of vascular endothelial cells (ECs into a blood-brain barrier (BBB phenotype is shear stress (SS. With the use of a well established humanized dynamic in vitro BBB model and cDNA microarrays, we have profiled the effect of SS in the induction/suppression of ECs genes and related functions. Results Specifically, we found a significant upregulation of tight and adherens junctions proteins and genes. Trans-endothelial electrical resistance (TEER and permeability measurements to know substances have shown that SS promoted the formation of a tight and highly selective BBB. SS also increased the RNA level of multidrug resistance transporters, ion channels, and several p450 enzymes. The RNA level of a number of specialized carrier-mediated transport systems (e.g., glucose, monocarboxylic acid, etc. was also upregulated. RNA levels of modulatory enzymes of the glycolytic pathway (e.g., lactate dehydrogenase were downregulated by SS while those involved in the Krebs cycle (e.g., lactate and other dehydrogenases were upregulated. Measurements of glucose consumption versus lactate production showed that SS negatively modulated the glycolytic bioenergetic pathways of glucose metabolism in favor of the more efficient aerobic respiration. BBB ECs are responsive to inflammatory stimuli. Our data showed that SS increased the RNA levels of integrins and vascular adhesion molecules. SS also inhibited endothelial cell cycle via regulation of BTG family proteins encoding genes. This was paralleled by significant increase in the cytoskeletal protein content while that of membrane, cytosol, and nuclear sub-cellular fractions decreased. Furthermore, analysis of 2D gel electrophoresis (which allows identifying a large number of proteins per sample of EC proteins extracted from membrane sub-cellular endothelial fractions showed that SS increased

  15. Flow and wall shear stress characterization after endovascular aneurysm repair and endovascular aneurysm sealing in an infrarenal aneurysm model.

    Science.gov (United States)

    Boersen, Johannes T; Groot Jebbink, Erik; Versluis, Michel; Slump, Cornelis H; Ku, David N; de Vries, Jean-Paul P M; Reijnen, Michel M P J

    2017-12-01

    Endovascular aneurysm repair (EVAR) with a modular endograft has become the preferred treatment for abdominal aortic aneurysms. A novel concept is endovascular aneurysm sealing (EVAS), consisting of dual endoframes surrounded by polymer-filled endobags. This dual-lumen configuration is different from a bifurcation with a tapered trajectory of the flow lumen into the two limbs and may induce unfavorable flow conditions. These include low and oscillatory wall shear stress (WSS), linked to atherosclerosis, and high shear rates that may result in thrombosis. An in vitro study was performed to assess the impact of EVAR and EVAS on flow patterns and WSS. Four abdominal aortic aneurysm phantoms were constructed, including three stented models, to study the influence of the flow divider on flow (Endurant [Medtronic, Minneapolis, Minn], AFX [Endologix, Irvine, Calif], and Nellix [Endologix]). Experimental models were tested under physiologic resting conditions, and flow was visualized with laser particle imaging velocimetry, quantified by shear rate, WSS, and oscillatory shear index (OSI) in the suprarenal aorta, renal artery (RA), and common iliac artery. WSS and OSI were comparable for all models in the suprarenal aorta. The RA flow profile in the EVAR models was comparable to the control, but a region of lower WSS was observed on the caudal wall compared with the control. The EVAS model showed a stronger jet flow with a higher shear rate in some regions compared with the other models. Small regions of low WSS and high OSI were found near the distal end of all stents in the common iliac artery compared with the control. Maximum shear rates in each region of interest were well below the pathologic threshold for acute thrombosis. The different stent designs do not influence suprarenal flow. Lower WSS is observed in the caudal wall of the RA after EVAR and a higher shear rate after EVAS. All stented models have a small region of low WSS and high OSI near the distal outflow

  16. Evaluation of critical resolved shear strength and deformation mode in proton-irradiated austenitic stainless steel using micro-compression tests

    Energy Technology Data Exchange (ETDEWEB)

    Jin, Hyung-Ha; Ko, Eunsol; Kwon, Junhyun; Hwang, Seong Sik [Nuclear Materials Safety Research Division, Korea Atomic Energy Research Institute, 989-111 Daedeok-daero, Yuseong-gu, Daejeon, 305-353 (Korea, Republic of); Shin, Chansun, E-mail: c.shin@mju.ac.kr [Department of Materials Science and Engineering, Myongji University, 116 Myongji-ro, Cheoin-gu, Youngin, Gyeonggi-do, 449-728 (Korea, Republic of)

    2016-03-15

    Micro-compression tests were applied to evaluate the changes in the strength and deformation mode of proton-irradiated commercial austenitic stainless steel. Proton irradiation generated small dots at low dose levels and Frank loops at high dose levels. The increase in critical resolved shear stresses (CRSS) was measured from micro-compression of pillars and the Schmid factor calculated from the measured loading direction. The magnitudes of the CRSS increase were in good agreement with the values calculated from the barrier hardening model using the measured size and density of radiation defects. The deformation mode changed upon increasing the irradiation dose level. At a low radiation dose level, work hardening and smooth flow behavior were observed. Increasing the dose level resulted in the flow behavior changing to a distinct heterogeneous flow, yielding a few large strain bursts in the stress–strain curves. The change in the deformation mode was related to the formation and propagation of defect-free slip bands. The effect of the orientation of the pillar or loading direction on the strengths is discussed.

  17. Measuring a critical stress for continuous prevention of marine biofouling accumulation with aeration.

    Science.gov (United States)

    Menesses, Mark; Belden, Jesse; Dickenson, Natasha; Bird, James

    2017-10-01

    When cleaning the hull of a ship, significant shear stresses are needed to remove established biofouling organisms. Given that there exists a link between the amount of time that fouling accumulates and the stress required to remove it, it is not surprising that more frequent grooming requires less shear stress. Yet, it is unclear if there is a minimum stress needed to prevent the growth of macrofouling in the limit of continuous grooming. This manuscript shows that single bubble stream aeration provides continuous grooming and prevents biofouling accumulation in regions where the average wall stress exceeds ~0.01 Pa. This value was found by comparing observations of biofouling growth from field studies with complementary laboratory measurements that probe the associated flow fields. These results suggest that aeration and other continuous grooming systems must exceed a wall stress of 0.01 Pa to prevent macrofouling accumulation.

  18. Normal stress differences from Oldroyd 8-constant framework: Exact analytical solution for large-amplitude oscillatory shear flow

    Science.gov (United States)

    Saengow, C.; Giacomin, A. J.

    2017-12-01

    The Oldroyd 8-constant framework for continuum constitutive theory contains a rich diversity of popular special cases for polymeric liquids. In this paper, we use part of our exact solution for shear stress to arrive at unique exact analytical solutions for the normal stress difference responses to large-amplitude oscillatory shear (LAOS) flow. The nonlinearity of the polymeric liquids, triggered by LAOS, causes these responses at even multiples of the test frequency. We call responses at a frequency higher than twice the test frequency higher harmonics. We find the new exact analytical solutions to be compact and intrinsically beautiful. These solutions reduce to those of our previous work on the special case of the corotational Maxwell fluid. Our solutions also agree with our new truncated Goddard integral expansion for the special case of the corotational Jeffreys fluid. The limiting behaviors of these exact solutions also yield new explicit expressions. Finally, we use our exact solutions to see how η∞ affects the normal stress differences in LAOS.

  19. Numerical prediction of cavitating flow around a hydrofoil using pans and improved shear stress transport k-omega model

    Directory of Open Access Journals (Sweden)

    Zhang De-Sheng

    2015-01-01

    Full Text Available The prediction accuracies of partially-averaged Navier-Stokes model and improved shear stress transport k-ω turbulence model for simulating the unsteady cavitating flow around the hydrofoil were discussed in this paper. Numerical results show that the two turbulence models can effectively reproduce the cavitation evolution process. The numerical prediction for the cycle time of cavitation inception, development, detachment, and collapse agrees well with the experimental data. It is found that the vortex pair induced by the interaction between the re-entrant jet and mainstream is responsible for the instability of the cavitation shedding flow.

  20. Interaction between drug delivery vehicles and cells under the effect of shear stress

    DEFF Research Database (Denmark)

    Godoy-Gallardo, Maria; Ek, Pramod Kumar; Jansman, M. M. T.

    2015-01-01

    models. An important factor within the complex and dynamic human in vivo environment is the shear flow observed within our circulatory system and many other tissues. Within this review, recent advances to leverage microfluidic devices to better mimic these conditions through novel in vitro assays...

  1. Pseudodynamic Source Characterization for Strike-Slip Faulting Including Stress Heterogeneity and Super-Shear Ruptures

    KAUST Repository

    Mena, B.; Dalguer, L. A.; Mai, Paul Martin

    2012-01-01

    . (2004), we propose new relationships for PD models for moderate‐to‐large strike‐slip earthquakes that include local supershear rupture speed due to stress heterogeneities. We conduct dynamic rupture simulations using stochastic initial stress

  2. Influence of Reinforcement Anisotropy on the Stress Distribution in Tension and Shear of a Fusion Magnet Insulation System

    Science.gov (United States)

    Humer, K.; Raff, S.; Prokopec, R.; Weber, H. W.

    2008-03-01

    A glass fiber reinforced plastic laminate, which consists of half-overlapped wrapped Kapton/R-glass-fiber reinforcing tapes vacuum-pressure impregnated in a cyanate ester/epoxy blend, is proposed as the insulation system for the ITER Toroidal Field coils. In order to assess its mechanical performance under the actual operating conditions, cryogenic (77 K) tensile and interlaminar shear tests were done after irradiation to the ITER design fluence of 1×1022 m-2 (E>0.1 MeV). The data were then used for a Finite Element Method (FEM) stress analysis. We find that the mechanical strength and the fracture behavior as well as the stress distribution and the failure criteria are strongly influenced by the winding direction and the wrapping technique of the reinforcing tapes.

  3. Soft-Matter Resistive Sensor for Measuring Shear and Pressure Stresses

    Science.gov (United States)

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

    2013-03-01

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

  4. Microfluidic device to study cell transmigration under physiological shear stress conditions

    DEFF Research Database (Denmark)

    Kwasny, Dorota; Kiilerich-Pedersen, Katrine; Moresco, Jacob Lange

    2011-01-01

    The development of new drug therapies relies on studies of cell transmigration in in vitro systems. Migration has traditionally been studied using two methods, the Boyden chamber and a shear flow chamber assay. Though, commonly applied in cell transmigration studies, they are far from imitating a...... of the developed microfluidic migration assay. The presented device is inexpensive, easy to fabricate and disposable, having a potential to be applied in basic research as well as in the drug development process.......The development of new drug therapies relies on studies of cell transmigration in in vitro systems. Migration has traditionally been studied using two methods, the Boyden chamber and a shear flow chamber assay. Though, commonly applied in cell transmigration studies, they are far from imitating...

  5. Stress and vascular responses: atheroprotective effect of laminar fluid shear stress in endothelial cells: possible role of mitogen-activated protein kinases.

    Science.gov (United States)

    Yoshizumi, Masanori; Abe, Jun-Ichi; Tsuchiya, Koichiro; Berk, Bradford C; Tamaki, Toshiaki

    2003-03-01

    Atherosclerosis preferentially occurs in areas of turbulent blood flow and low fluid shear stress, whereas laminar blood flow and high shear stress are atheroprotective. Inflammatory cytokines, such as tumor necrosis factor-alpha (TNF-alpha), stimulate expression of endothelial cell (EC) genes that may promote atherosclerosis. Recent findings suggest a steady laminar blood flow decreases EC apoptosis and inhibits TNF-mediated EC activation. EC apoptosis or activation is suggested to be involved in plaque erosion, which may lead to platelet aggregation. TNF-alpha regulates gene expression in ECs, in part, by stimulating mitogen-activated protein (MAP) kinases, which phosphorylate transcription factors. We hypothesized that steady laminar flow inhibits cytokine-mediated activation of MAP kinases in ECs. To test this hypothesis, we determined the effects of steady laminar flow (shear stress = 12 dynes/cm(2)) on TNF-alpha-stimulated activity of three MAP kinases in human umbilical vein ECs (HUVEC): extracellular signal-regulated kinase (ERK1/2), c-Jun N-terminal kinase (JNK), and p38. TNF-alpha activated ERK1/2, JNK, and p38 maximally at 15 min in HUVEC. Pre-exposing HUVEC for 10 min to flow inhibited TNF-alpha activation of JNK, but showed no significant effect on ERK1/2 or p38 activation. Incubation of HUVEC with PD98059, a specific ERK1/2 inhibitor, blocked the flow-mediated inhibition of TNF activation of JNK. Transfection studies with dominant-negative constructs of the protein kinase MEK5 suggested an important role for big mitogen-activated protein kinase 1 (BMK1) in flow-mediated regulation of EC activation by TNF-alpha. Understanding the mechanisms by which steady laminar flow regulates JNK activation by cytokines may provide insight into the atheroprotective mechanisms induced by laminar blood flow.

  6. An experimental study on the normal stress of magnetorheological fluids

    International Nuclear Information System (INIS)

    Jiang, Jile; Tian, Yu; Ren, Dongxue; Meng, Yonggang

    2011-01-01

    The dependence of the normal stress on the shear rate and magnetic field strength in the shear flow of magnetorheological (MR) fluids has been studied experimentally. An obvious normal stress could be observed when the applied magnetic field was higher than a critical value. The normal stress increases considerably with increase of the shear rate and magnetic field, and decreases suddenly and significantly upon the onset of shear thickening in MR fluids. The ratio of shear stress to normal stress, an analogue of the friction coefficient, increases with increase of the shear rate, but decreases with increase of the applied magnetic field. Along with the shear stress, the normal stress in MR fluids could provide a more comprehensive understanding of the MR effect, and the evolution of the particle structure in shear flow, and may have important implications for preparing high performance magnetostrictive elastomers with high force output along the magnetic field direction

  7. Loading direction-dependent shear behavior at different temperatures of single-layer chiral graphene sheets

    Science.gov (United States)

    Zhao, Yang; Dong, Shuhong; Yu, Peishi; Zhao, Junhua

    2018-06-01

    The loading direction-dependent shear behavior of single-layer chiral graphene sheets at different temperatures is studied by molecular dynamics (MD) simulations. Our results show that the shear properties (such as shear stress-strain curves, buckling strains, and failure strains) of chiral graphene sheets strongly depend on the loading direction due to the structural asymmetry. The maximum values of both the critical buckling shear strain and the failure strain under positive shear deformation can be around 1.4 times higher than those under negative shear deformation. For a given chiral graphene sheet, both its failure strain and failure stress decrease with increasing temperature. In particular, the amplitude to wavelength ratio of wrinkles for different chiral graphene sheets under shear deformation using present MD simulations agrees well with that from the existing theory. These findings provide physical insights into the origins of the loading direction-dependent shear behavior of chiral graphene sheets and their potential applications in nanodevices.

  8. Enhancement of human mesenchymal stem cell infiltration into the electrospun poly(lactic-co-glycolic acid) scaffold by fluid shear stress.

    Science.gov (United States)

    Kim, Min Sung; Lee, Mi Hee; Kwon, Byeong-Ju; Koo, Min-Ah; Seon, Gyeung Mi; Park, Jong-Chul

    The infiltration of the cells into the scaffolds is important phenomenon to give them good biocompatibility and even biodegradability. Fluid shear stress is one of the candidates for the infiltration of cells into scaffolds. Here we investigated the directional migration of human mesenchymal stem cells and infiltration into PLGA scaffold by fluid shear stress. The human mesenchymal stem cells showed directional migrations following the direction of the flow (8, 16 dyne/cm(2)). In the scaffold models, the fluid shear stress (8 dyne/cm(2)) enhanced the infiltration of cells but did not influence on the infiltration of Poly(lactic-co-glycolic acid) particles. Copyright © 2015 Elsevier Inc. All rights reserved.

  9. Heat-And-Mass Transfer Relationship to Determine Shear Stress in Tubular Membrane Systems

    DEFF Research Database (Denmark)

    Ratkovich, Nicolas Rios; Nopens, Ingmar

    2012-01-01

    The main drawback of Membrane Bioreactors (MBRs) is the fouling of the membrane. One way to reduce this fouling is through controlling the hydrodynamics of the two-phase slug flow near the membrane surface. It has been proven in literature that the slug flow pattern has a higher scouring effect...... to remove particulates due to the high shear rates and high mass transfer between the membrane surface and the bulk region. However, to calculate the mass transfer coefficient in an efficient and accurate way is not straightforward. Indeed, for accurate determination, numerous complex experimental...

  10. Measured resolved shear stresses and Bishop-Hill stress states in individual grains of austenitic stainless steel

    DEFF Research Database (Denmark)

    Juul, Nicolai Ytterdal; Oddershede, Jette; Beaudoin, Armand

    2017-01-01

    somewhat from the theoretical expectation. These deviations are found to originate from a larger tensile stress component than in the theoretical Bishop-Hill stress states and to be associated also with deviations from axisymmetric plastic strain. This conclusion was supported by finite-element crystal...

  11. Shear wave elastography using ultrasound: effects of anisotropy and stretch stress on a tissue phantom and reactive lymph nodes in the neck

    Directory of Open Access Journals (Sweden)

    Ha Young Lee

    2017-01-01

    Full Text Available Purpose The purpose of this study was to evaluate how the anisotropy and the static stretch stress of the cervical musculature influence the measured shear modulus in a tissue-mimicking phantom and in cervical lymph nodes in vivo by using shear wave elastography (SWE. Methods SWE was performed on a phantom using a pig muscle and on the middle jugular cervical lymph nodes in six volunteers. Tissue elasticity was quantified using the shear modulus and a supersonic shear wave imaging technique. For the phantom study, first, the optimal depth for measurement was determined, and then, SWE was performed in parallel and perpendicular to the muscle fiber orientation with and without strain stress. For the in vivo study, SWE was performed on the cervical lymph nodes in parallel and perpendicular to the sternocleidomastoid muscle fiber direction with and without neck stretching. The mean values of the shear modulus (meanSM were then analyzed. Results In the phantom study, the measured depth significantly influenced the meanSM with a sharp decrease at the depth of 1.5 cm (P<0.001. Strain stress increased the meanSM, irrespective of the muscle fiber orientation (P<0.001. In the in vivo study, the meanSM values obtained in parallel to the muscle fiber orientation were greater than those obtained perpendicular to the fiber orientation, irrespective of the stretch stress (P<0.001. However, meanSM was affected significantly by the stretch stress parallel to the muscle fiber orientation (P<0.001. Conclusion The anisotropic nature of the cervical musculature and the applied stretch stress explain the variability of the SWE measurements and should be identified before applying SWE for the interpretation of the measured shear modulus values.

  12. 3D Discrete Dislocation Dynamics: Influence of Segment Mobility on Critical Shear Stress

    Czech Academy of Sciences Publication Activity Database

    Záležák, Tomáš; Dlouhý, Antonín

    2015-01-01

    Roč. 128, č. 4 (2015), s. 654-656 ISSN 0587-4246. [ISPMA 13 - International Symposium on Physics of Materials /13./. Praha, 31.08.2014-04.09.2014] R&D Projects: GA MŠk(CZ) EE2.3.20.0214; GA ČR(CZ) GA14-22834S Institutional support: RVO:68081723 Keywords : metal matrix composites * discrete dislocation dynamics * high temperature creep Subject RIV: JG - Metallurgy Impact factor: 0.525, year: 2015

  13. Starting solutions for the flow of second grade fluids in a rectangular channel due to an oscillating shear stress

    Science.gov (United States)

    Vieru, Dumitru; Fetecau, Corina; Rana, Mehwish

    2012-05-01

    The unsteady motion of a second grade fluid between two parallel side walls perpendicular to a plate is studied by means of the Fourier sine and cosine transforms. Initially, the fluid is at rest and at time t = 0+, the plate applies an oscillating shear to the fluid. The solutions that have been obtained, presented under integral and series form and written as a sum between steady time-periodic and transient solutions can be easily reduced to the similar solutions for Newtonian fluids performing the same motion. They describe the motion of the fluid some time after its initiation. After that time, when the transient solutions disappear, the motion of the fluid is described by the steady time-periodic solutions that are independent of the initial conditions. In the absence of side walls, more exactly when the distance between walls tends to infinity, all solutions reduce to those corresponding to the motion over an infinite plate. As it was to be expected, the steady time-periodic solutions corresponding to sine and cosine oscillations of the shear stress on the boundary differ by a phase shift. Finally, the influence of side walls on the fluid motion, the required time to reach the steady periodic flow, as well as the distance between walls for which the velocity of the fluid in the middle of the channel is unaffected by their presence are established by numerical calculus and graphical illustrations. As expected, the time needed to reach the steady periodic flows is lower in the presence of side walls. It is lower for Newtonian fluids in comparison with second grade fluids and greater for sine oscillations in comparison to the cosine oscillations of the boundary shear.

  14. Determination of PVB interlayer’s shear modulus and its effect on normal stress distribution in laminated glass panels

    Science.gov (United States)

    Hána, T.; Eliášová, M.; Machalická, K.; Vokáč, M.

    2017-10-01

    Noticing the current architecture, there are many examples of glass bearing members such as beams, panes, ribs stairs or even columns. Most of these elements are made of laminated glass from panes bonded by polymer interlayer so the task of transferring shear forces between the glass panes needs to be investigated due to the lack of knowledge. This transfer depends on stiffness of polymer material, which is affected by temperature and load duration. It is essential to catch the safe side with limit cases when designing these members if the exact material behaviour is not specified. There are lots of interlayers for structural laminated glass applications available on a market. Most of them exhibit different properties, which need to be experimentally verified. This paper is focused on tangent shear modulus of PVB (polyvinyl-buthyral) interlayer and its effect on the stress distribution in glass panes when loaded. This distribution may be determined experimentally or numerically, respectively. This enables to design structural laminated glass members more effectively regarding price and safety. Furthermore, this is the way, how to extend the use of laminated glass in architectural design.

  15. Impact of competitive flow on wall shear stress in coronary surgery: computational fluid dynamics of a LIMA-LAD model.

    Science.gov (United States)

    Nordgaard, Håvard; Swillens, Abigail; Nordhaug, Dag; Kirkeby-Garstad, Idar; Van Loo, Denis; Vitale, Nicola; Segers, Patrick; Haaverstad, Rune; Lovstakken, Lasse

    2010-12-01

    Competitive flow from native coronary vessels is considered a major factor in the failure of coronary bypass grafts. However, the pathophysiological effects are not fully understood. Low and oscillatory wall shear stress (WSS) is known to induce endothelial dysfunction and vascular disease, like atherosclerosis and intimal hyperplasia. The aim was to investigate the impact of competitive flow on WSS in mammary artery bypass grafts. Using computational fluid dynamics, WSS was calculated in a left internal mammary artery (LIMA) graft to the left anterior descending artery in a three-dimensional in vivo porcine coronary artery bypass graft model. The following conditions were investigated: high competitive flow (non-significant coronary lesion), partial competitive flow (significant coronary lesion), and no competitive flow (totally occluded coronary vessel). Time-averaged WSS of LIMA at high, partial, and no competitive flow were 0.3-0.6, 0.6-3.0, and 0.9-3.0 Pa, respectively. Further, oscillatory WSS quantified as the oscillatory shear index (OSI) ranged from (maximum OSI = 0.5 equals zero net WSS) 0.15 to 0.35, OSI similar to the no competitive flow condition. Graft flow is highly dependent on the degree of competitive flow. High competitive flow was found to produce unfavourable WSS consistent with endothelial dysfunction and subsequent graft narrowing and failure. Partial competitive flow, however, may be better tolerated as it was found to be similar to the ideal condition of no competitive flow.

  16. Is the Critical Shields Stress for Incipient Sediment Motion Dependent on Bed Slope in Natural Channels? No.

    Science.gov (United States)

    Phillips, C. B.; Jerolmack, D. J.

    2017-12-01

    Understanding when coarse sediment begins to move in a river is essential for linking rivers to the evolution of mountainous landscapes. Unfortunately, the threshold of surface particle motion is notoriously difficult to measure in the field. However, recent studies have shown that the threshold of surface motion is empirically correlated with channel slope, a property that is easy to measure and readily available from the literature. These studies have thoroughly examined the mechanistic underpinnings behind the observed correlation and produced suitably complex models. These models are difficult to implement for natural rivers using widely available data, and thus others have treated the empirical regression between slope and the threshold of motion as a predictive model. We note that none of the authors of the original studies exploring this correlation suggested their empirical regressions be used in a predictive fashion, nevertheless these regressions between slope and the threshold of motion have found their way into numerous recent studies engendering potentially spurious conclusions. We demonstrate that there are two significant problems with using these empirical equations for prediction: (1) the empirical regressions are based on a limited sampling of the phase space of bed-load rivers and (2) the empirical measurements of bankfull and critical shear stresses are paired. The upshot of these problems limits the empirical relations predictive capacity to field sites drawn from the same region of the bed-load river phase space and that the paired nature of the data introduces a spurious correlation when considering the ratio of bankfull to critical shear stress. Using a large compilation of bed-load river hydraulic geometry data, we demonstrate that the variation within independently measured values of the threshold of motion changes systematically with bankfull shields stress and not channel slope. Additionally, we highlight using several recent datasets

  17. IMAGE ANALYSIS FOR MODELLING SHEAR BEHAVIOUR

    Directory of Open Access Journals (Sweden)

    Philippe Lopez

    2011-05-01

    Full Text Available Through laboratory research performed over the past ten years, many of the critical links between fracture characteristics and hydromechanical and mechanical behaviour have been made for individual fractures. One of the remaining challenges at the laboratory scale is to directly link fracture morphology of shear behaviour with changes in stress and shear direction. A series of laboratory experiments were performed on cement mortar replicas of a granite sample with a natural fracture perpendicular to the axis of the core. Results show that there is a strong relationship between the fracture's geometry and its mechanical behaviour under shear stress and the resulting damage. Image analysis, geostatistical, stereological and directional data techniques are applied in combination to experimental data. The results highlight the role of geometric characteristics of the fracture surfaces (surface roughness, size, shape, locations and orientations of asperities to be damaged in shear behaviour. A notable improvement in shear understanding is that shear behaviour is controlled by the apparent dip in the shear direction of elementary facets forming the fracture.

  18. Interfacial shear stress and hold-up in an air-water annular two-phase flow

    International Nuclear Information System (INIS)

    Fukano, T.; Ousaka, A.; Kawakami, Y.; Tominaga, A.

    1991-01-01

    This paper reports on an experimental investigation that was made into hold-up, frictional pressure drop and interfacial shear stress of an air-water two-phase annular flow in horizontal and vertical up- and downward flows to make clear the effects of tube diameter and flow direction on them. The tube diameters examined are 10mm, 16mm and 26mm. Both the hold-up and the pressure drop considerably changed with time. Especially, the amplitude of the variation of the hold-up was quite larger in comparison with its averaged value in the cause of disturbance wave flow. for the time averaged hold-up and interfacial friction factor, we got new correlations, by which we can estimate them within an accuracy of ±20% and ±30%, respectively, independent of the flow direction and the tube diameter

  19. Wall Shear Stress Restoration in Dialysis Patient's Venous Stenosis: Elucidation via 3D CFD and Shape Optimization

    Science.gov (United States)

    Mahmoudzadeh Akherat, S. M. Javid; Cassel, Kevin; Hammes, Mary; Boghosian, Michael; Illinois Institute of Technology Team; University of Chicago Team

    2016-11-01

    Venous stenosis developed after the growth of excessive neointimal hyperplasia (NH) in chronic dialysis treatment is a major cause of mortality in renal failure patients. It has been hypothesized that the low wall shear stress (WSS) triggers an adaptive response in patients' venous system that through the growth of neointimal hyperplastic lesions restores WSS and transmural pressure, which also regulates the blood flow rate back to physiologically acceptable values which is violated by dialysis treatment. A strong coupling of three-dimensional CFD and shape optimization analyses were exploited to elucidate and forecast this adaptive response which correlates very well topographically with patient-specific clinical data. Based on the framework developed, a medical protocol is suggested to predict and prevent dialysis treatment failure in clinical practice. Supported by the National Institute of Diabetes and Digestive and Kidney Diseases of the National Institutes of Health (R01 DK90769).

  20. Statistical analysis of the turbulent Reynolds stress and its link to the shear flow generation in a cylindrical laboratory plasma device

    International Nuclear Information System (INIS)

    Yan, Z.; Yu, J. H.; Holland, C.; Xu, M.; Mueller, S. H.; Tynan, G. R.

    2008-01-01

    The statistical properties of the turbulent Reynolds stress arising from collisional drift turbulence in a magnetized plasma column are studied and a physical picture of turbulent driven shear flow generation is discussed. The Reynolds stress peaks near the maximal density gradient region, and is governed by the turbulence amplitude and cross-phase between the turbulent radial and azimuthal velocity fields. The amplitude probability distribution function (PDF) of the turbulent Reynolds stress is non-Gaussian and positively skewed at the density gradient maximum. The turbulent ion-saturation (Isat) current PDF shows that the region where the bursty Isat events are born coincides with the positively skewed non-Gaussian Reynolds stress PDF, which suggests that the bursts of particle transport appear to be associated with bursts of momentum transport as well. At the shear layer the density fluctuation radial correlation length has a strong minimum (∼4-6 mm∼0.5C s /Ω ci , where C s is the ion acoustic speed and Ω ci is the ion gyrofrequency), while the azimuthal turbulence correlation length is nearly constant across the shear layer. The results link the behavior of the Reynolds stress, its statistical properties, generation of bursty radially going azimuthal momentum transport events, and the formation of the large-scale shear layer.

  1. STURM: Resuspension mesocosms with realistic bottom shear stress and water column turbulence for benthic-pelagic coupling studies: Design and Applications

    Science.gov (United States)

    Sanford, L. P.; Porter, E.; Porter, F. S.; Mason, R. P.

    2016-02-01

    Shear TUrbulence Resuspension Mesocosm (STURM) tanks, with high instantaneous bottom shear stress and realistic water column mixing in a single system, allow more realistic benthic-pelagic coupling studies that include sediment resuspension. The 1 m3 tanks can be programmed to produce tidal or episodic sediment resuspension over extended time periods (e.g. 4 weeks), over muddy sediments with or without infaunal organisms. The STURM tanks use a resuspension paddle that produces uniform bottom shear stress across the sediment surface while gently mixing a 1 m deep overlying water column. The STURM tanks can be programmed to different magnitudes, frequencies, and durations of bottom shear stress (and thus resuspension) with proportional water column turbulence levels over a wide range of mixing settings for benthic-pelagic coupling experiments. Over eight STURM calibration settings, turbulence intensity ranged from 0.55 to 4.52 cm s-1, energy dissipation rate from 0.0032 to 2.65 cm2 s-3, the average bottom shear stress from 0.0068 to 0.19 Pa, and the instantaneous bottom shear stress from 0.07 to 2.0 Pa. Mixing settings can be chosen as desired and/or varied over the experiment, based on the scientific question at hand. We have used the STURM tanks for four 4-week benthic-pelagic coupling ecosystem experiments with tidal resuspension with or without infaunal bivalves, for stepwise erosion experiments with and without infaunal bivalves, for experiments on oyster biodeposit resuspension, to mimic storms overlain on tidal resuspension, and for experiments on the effects of varying frequency and duration of resuspension on the release of sedimentary contaminants. The large size of the tanks allows water quality and particle measurements using standard oceanographic instrumentation. The realistic scale and complexity of the contained ecosystems has revealed indirect feedbacks and responses that are not observable in smaller, less complex experimental systems.

  2. Nonlinear panel flutter in a rarefied atmosphere - Aerodynamic shear stress effects

    Science.gov (United States)

    Resende, Hugo B.

    1991-01-01

    The panel flutter phenomenon is studied assuming free-molecule flow. This kind of analysis is relevant in the case of hypersonic flight vehicles traveling at high altitudes, especially in the leeward portion of the vehicle. In these conditions the aerodynamic shear can be expected to be considerably larger than the pressure at a given point, so that the effects of such a loading are incorporated into the structural model. This is accomplished by introducing distributed longitudinal and bending moment loads. The former can lead to buckling of the panel, with the second mode in the case of a simply-supported panel playing a important role, and becoming the dominant mode in the solution. The presence of equivalent springs in the longitudinal direction at the panel's ends also becomes of relative importance, even for the evaluation of the linear flutter parameter. Finally, the behavior of the system is studied in the presence of applied compressive forces, that is, classical buckling.

  3. Ultrasound Shear Wave Elastography for Liver Disease. A Critical Appraisal of the Many Actors on the Stage.

    Science.gov (United States)

    Piscaglia, F; Salvatore, V; Mulazzani, L; Cantisani, V; Schiavone, C

    2016-02-01

    In the last 12 - 18 months nearly all ultrasound manufacturers have arrived to implement ultrasound shear wave elastography modality in their equipment for the assessment of chronic liver disease; the few remaining players are expected to follow in 2016.When all manufacturers rush to a new technology at the same time, it is evident that the clinical demand for this information is of utmost value. Around 1990, there was similar demand for color Doppler ultrasound; high demand for contrast-enhanced ultrasonography was evident at the beginning of this century, and around 2010 demand increased for strain elastography. However, some issues regarding the new shear wave ultrasound technologies must be noted to avoid misuse of the resulting information for clinical decisions. As new articles are expected to appear in 2016 reporting the findings of the new technologies from various companies, we felt that the beginning of this year was the right time to present an appraisal of these issues. We likewise expect that in the meantime EFSUMB will release a new update of the existing guidelines 1 2.The first ultrasound elastography method became available 13 years ago in the form of transient elastography with Fibroscan(®) 3. It was the first technique providing non-invasive quantitive information about the stiffness of the liver and hence regarding the amount of fibrosis in chronic liver disease 3. The innovation was enormous, since a non-invasive modality was finally available to provide findings otherwise achievable only by liver biopsy. In fact, prior to ultrasound elastography, a combination of conventional and Doppler ultrasound parameters were utilized to inform the physician about the presence of cirrhosis and portal hypertension 4. However, skilled operators were required, reproducibility and diagnostic accuracy were suboptimal, and it was not possible to differentiate the pre-cirrhotic stages of fibrosis. All these limitations were substantially improved by

  4. High fluid shear strain causes injury in silver shark: Preliminary implications for Mekong hydropower turbine design

    Energy Technology Data Exchange (ETDEWEB)

    Baumgartner, L. J. [New South Wales Department of Primary Industries, Narrandera Fisheries Centre, Narrandera NSW Australia; Institute of Land, Water and Society, Charles Sturt University, Albury NSW Australia; Thorncraft, G. [Faculty of Agriculture, Forestry and Fisheries, National University of Laos, Vientiane Lao People’s Democratic Republic; Phonekhampheng, O. [Faculty of Agriculture, Forestry and Fisheries, National University of Laos, Vientiane Lao People’s Democratic Republic; Boys, C. [New South Wales Department of Primary Industries, Port Stephens Fisheries Institute, Nelson Bay NSW Australia; Navarro, A. [Institute of Land, Water and Society, Charles Sturt University, Albury NSW Australia; Robinson, W. [Institute of Land, Water and Society, Charles Sturt University, Albury NSW Australia; Brown, R. [Pacific Northwest National Laboratory, Richland WA USA; Deng, Z. D. [Pacific Northwest National Laboratory, Richland WA USA

    2017-02-09

    Fluid shear arises when two bodies of water, travelling at different velocities, intersect. Fish entrained at the interface of these two water masses will experience shear stress; which can be harmful. The stress magnitude is dependent on waterbody mass and velocity; with the fish impact largely related to body size. Elevated shear stress occurs where rapidly flowing water passes near spillways, across screens, within turbine draft tubes or other passage routes. A flume was used to determine critical tolerances of silver shark (Balantiocheilos melanopterus) to different shear stress rates generated by a high velocity jet. Fish experienced higher levels of injury and mortality as shear stress was increased. Excessive shear forces had damaging impacts on fish. Mortality occurred at shear levels higher that 600/s. It is important that developers should attempt to model potential shear profiles expected during turbine passage in selected designs. These data will be critical to determine potential impacts on fish. If the likelihood of adverse impact is high, then alternative designs which have lower shear stress could be explored.

  5. Effect of shear stress on 86Rb+ efflux and cytosolic Ca2+ of calf pulmonary artery endothelial cells (CPAEs)

    International Nuclear Information System (INIS)

    Alevriadou, B.R.; Mo, M.; Rickman, D.S.; Eskin, S.G.; McIntire, L.V.; Schilling, W.P.

    1991-01-01

    The effect of flow-induced shear stress (SS) on membrane K + permeability and cytosolic free Ca 2+ , [Ca 2+ ] i , was investigated by measuring 86 Rb + efflux and fura-2 fluorescence in CPAEs using a parallel plate flow chamber. Increasing SS from 1 to 2.4, 4.8 or 10 dyn/cm 2 produced a graded, transient increase in 86 Rb + efflux which peaked within 1 min and subsequently declined rapidly towards pre-stimulus levels. Mathematical modeling confirmed that the transient increase in 86 Rb + efflux did not reflect a washout phenomenon. Upon returning SS to 1 dyn/cm 2 , 86 Rb + efflux initially decreased, but returned slowly to basal values. In contrast, application of bradykinin (BK) at a constant SS of either 0.33 or 1 dyn/cm 2 produced a transient increase in 86 Rb + efflux that was followed by a sustained elevated phase during which time efflux gradually returned to pre-stimulus levels. To determine the mechanism by which shear stress increases K + permeability, the effect of tetrabutylammonium ion (TBA), a selective inhibitor of Ca 2+ -dependent K + channels (K Ca ), on both the BK- and SS-induced increases in 86 Rb + efflux, was examined. TBA inhibited the BK-stimulated increase in 86 Rb + efflux >90% under both stationary and flow conditions and significantly reduced SS-dependent 86 Rb + efflux 38.3%. These results suggest that increased 86 Rb + efflux from CPAEs with SS occurs, at least in part, via K Ca and suggests that SS increases cytosolic Ca 2+ . However, when measured using fura-2-loaded CPAEs, SS was without significant effect on [Ca 2+ ] i

  6. Stress and Coping of Critical Care Nurses After Unsuccessful Cardiopulmonary Resuscitation.

    Science.gov (United States)

    McMeekin, Dawn E; Hickman, Ronald L; Douglas, Sara L; Kelley, Carol G

    2017-03-01

    Participation by a critical care nurse in an unsuccessful resuscitation can create a unique heightened level of psychological stress referred to as postcode stress, activation of coping behaviors, and symptoms of posttraumatic stress disorder (PTSD). To explore the relationships among postcode stress, coping behaviors, and PTSD symptom severity in critical care nurses after experiencing unsuccessful cardiopulmonary resuscitations and to see whether institutional support attenuates these repeated psychological traumas. A national sample of 490 critical care nurses was recruited from the American Association of Critical-Care Nurses' eNewsline and social media. Participants completed the Post-Code Stress Scale, the Brief COPE (abbreviated), and the Impact of Event Scale-Revised, which were administered through an online survey. Postcode stress and PTSD symptom severity were weakly associated ( r = 0.20, P = .01). No significant associations between coping behaviors and postcode stress were found. Four coping behaviors (denial, self-distraction, self-blame, and behavioral disengagement) were significant predictors of PTSD symptom severity. Severity of postcode stress and PTSD symptoms varied with the availability of institutional support. Critical care nurses show moderate levels of postcode stress and PTSD symptoms when asked to recall an unsuccessful resuscitation and the coping behaviors used. Identifying the critical care nurses most at risk for PTSD will inform the development of interventional research to promote critical care nurses' psychological well-being and reduce their attrition from the profession. ©2017 American Association of Critical-Care Nurses.

  7. Effects of different aging statuses and strain rate on the adiabatic shear susceptibility of 2195 aluminum-lithium alloy

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Y. [School of Materials Science and Engineering, Central South University, Changsha 410083, Hunan (China); State Key Laboratory of Explosion Science and Technology, Beijing 100081 (China); Tan, G.Y., E-mail: yangyanggroup@163.com [School of Materials Science and Engineering, Central South University, Changsha 410083, Hunan (China); Chen, P.X. [School of Materials Science and Engineering, Central South University, Changsha 410083, Hunan (China); Zhang, Q.M. [State Key Laboratory of Explosion Science and Technology, Beijing 100081 (China)

    2012-06-01

    The adiabatic shear susceptibility of 2195 aluminum-lithium alloy was investigated by means of split Hopkinson pressure bar. The stress collapse in true stress-true strain curves and true stress-time curves was observed. The adiabatic shear susceptibility of different aging statuses and strain rate were discussed by means of metallography observation. The critical strain, stress collapse time and formation energy of adiabatic shear bands were compared. The results show that different aging statuses and strain rate have significant influences on adiabatic shear behaviors of 2195 aluminum-lithium alloy. The peak-aged specimen has the highest adiabatic shearing susceptibility, while the under-aged specimen has the least adiabatic shear susceptibility. The susceptibility of adiabatic shearing increases with the increases of strain rate.

  8. Shear failure of granular materials

    Science.gov (United States)

    Degiuli, Eric; Balmforth, Neil; McElwaine, Jim; Schoof, Christian; Hewitt, Ian

    2012-02-01

    Connecting the macroscopic behavior of granular materials with the microstructure remains a great challenge. Recent work connects these scales with a discrete calculus [1]. In this work we generalize this formalism from monodisperse packings of disks to 2D assemblies of arbitrarily shaped grains. In particular, we derive Airy's expression for a symmetric, divergence-free stress tensor. Using these tools, we derive, from first-principles and in a mean-field approximation, the entropy of frictional force configurations in the Force Network Ensemble. As a macroscopic consequence of the Coulomb friction condition at contacts, we predict shear failure at a critical shear stress, in accordance with the Mohr-Coulomb failure condition well known in engineering. Results are compared with numerical simulations, and the dependence on the microscopic geometric configuration is discussed. [4pt] [1] E. DeGiuli & J. McElwaine, PRE 2011. doi: 10.1103/PhysRevE.84.041310

  9. Stress Effects on the Hippocampus: A Critical Review

    Science.gov (United States)

    Kim, Eun Joo; Pellman, Blake; Kim, Jeansok J.

    2015-01-01

    Uncontrollable stress has been recognized to influence the hippocampus at various levels of analysis. Behaviorally, human and animal studies have found that stress generally impairs various hippocampal-dependent memory tasks. Neurally, animal studies have revealed that stress alters ensuing synaptic plasticity and firing properties of hippocampal…

  10. Effect of Contact Conditions on Void Coalescence at Low Stress Triaxiality Shearing

    DEFF Research Database (Denmark)

    Dahl, Jonas; Nielsen, Kim Lau; Tvergaard, Viggo

    2012-01-01

    , the deformed voids develop into shapes that closely resemble micro-cracks. It is found that the predictions using the frictionless pseudo-contact approach are in rather good agreement with corresponding simulations that fully account for frictionless contact. In particular, good agreement is found at close...... to zero stress triaxiality. Furthermore, it is shown that accounting for friction at the void surface strongly postpones the onset of coalescence, hence, increasing the overall material ductility. The changes in overall material behavior are here presented for a wide range of initial material and loading...... conditions, such as various stress triaxialities, void sizes, and friction coefficients....

  11. Large eddy simulation in a rotary blood pump: Viscous shear stress computation and comparison with unsteady Reynolds-averaged Navier-Stokes simulation.

    Science.gov (United States)

    Torner, Benjamin; Konnigk, Lucas; Hallier, Sebastian; Kumar, Jitendra; Witte, Matthias; Wurm, Frank-Hendrik

    2018-06-01

    Numerical flow analysis (computational fluid dynamics) in combination with the prediction of blood damage is an important procedure to investigate the hemocompatibility of a blood pump, since blood trauma due to shear stresses remains a problem in these devices. Today, the numerical damage prediction is conducted using unsteady Reynolds-averaged Navier-Stokes simulations. Investigations with large eddy simulations are rarely being performed for blood pumps. Hence, the aim of the study is to examine the viscous shear stresses of a large eddy simulation in a blood pump and compare the results with an unsteady Reynolds-averaged Navier-Stokes simulation. The simulations were carried out at two operation points of a blood pump. The flow was simulated on a 100M element mesh for the large eddy simulation and a 20M element mesh for the unsteady Reynolds-averaged Navier-Stokes simulation. As a first step, the large eddy simulation was verified by analyzing internal dissipative losses within the pump. Then, the pump characteristics and mean and turbulent viscous shear stresses were compared between the two simulation methods. The verification showed that the large eddy simulation is able to reproduce the significant portion of dissipative losses, which is a global indication that the equivalent viscous shear stresses are adequately resolved. The comparison with the unsteady Reynolds-averaged Navier-Stokes simulation revealed that the hydraulic parameters were in agreement, but differences for the shear stresses were found. The results show the potential of the large eddy simulation as a high-quality comparative case to check the suitability of a chosen Reynolds-averaged Navier-Stokes setup and turbulence model. Furthermore, the results lead to suggest that large eddy simulations are superior to unsteady Reynolds-averaged Navier-Stokes simulations when instantaneous stresses are applied for the blood damage prediction.

  12. Influences of Shear History and Infilling on the Mechanical Characteristics and Acoustic Emissions of Joints

    Science.gov (United States)

    Meng, Fanzhen; Zhou, Hui; Wang, Zaiquan; Zhang, Liming; Kong, Liang; Li, Shaojun; Zhang, Chuanqing

    2017-08-01

    Filled joints, which are characterized by high deformability and low shear strength, are among the most critical discontinuities in rock mass and may be sheared repeatedly when subject to cyclic loading. Shear tests were carried out on tension splitting joints, with soil and granular cement mortar particles used as infillings, and the effects of the shear history on the mechanical behavior and acoustic emission (AE) of clean and filled joints were studied. The maximum strength in the subsequent shears was approximately 60% of the peak strength of the first shear for a clean joint, and the friction angle degraded from 63° to 45° after the first shear. The maximum shear strength of the filled joints was lower than 35% of the peak strength of the clean joint under the same normal stress. The change in the shear strength of filled joints with the number of shearing cycles was closely related to the transformation of the shear medium. Rolling friction occurred and the shear strength was low for the granular particle-filled joint, but the strength was elevated when the particles were crushed and sliding friction occurred. The AEs were significantly reduced during the second shear for the clean joint, and the peak AEs were mainly obtained at or near the turning point of the shear stress curve for the filled joint. The AEs were the highest for the cement particle-filled joint and lowest for the dry soil-filled joint; when subjected to repeated shears, the AEs were more complex because of the continuous changes to the shear medium. The evolution of the AEs with the shear displacement can accurately reflect the shear failure mechanism during a single shear process.

  13. Effect of fabric structure and polymer matrix on flexural strength, interlaminar shear stress, and energy dissipation of glass fiber-reinforced polymer composites

    Science.gov (United States)

    We report the effect of glass fiber structure and the epoxy polymer system on the flexural strength, interlaminar shear stress (ILSS), and energy absorption properties of glass fiber-reinforced polymer (GFRP) composites. Four different GFRP composites were fabricated from two glass fiber textiles of...

  14. Age-related changes in aortic 3D blood flow velocities and wall shear stress: Implications for the identification of altered hemodynamics in patients with aortic valve disease

    NARCIS (Netherlands)

    van Ooij, Pim; Garcia, Julio; Potters, Wouter V.; Malaisrie, S. Chris; Collins, Jeremy D.; Carr, James C.; Markl, Michael; Barker, Alex J.

    2016-01-01

    To investigate age-related changes in peak systolic aortic 3D velocity and wall shear stress (WSS) in healthy controls and to investigate the importance of age-matching for 3D mapping of abnormal aortic hemodynamics in bicuspid aortic valve disease (BAV). 4D flow MRI (fields strengths = 1.5-3T;

  15. Residual stress distribution of a 6061-T6 aluminum alloy under shear deformation

    International Nuclear Information System (INIS)

    Reyes-Ruiz, C.; Figueroa, I.A.; Braham, C.; Cabrera, J.M.; Zanellato, O.; Baiz, S.; Gonzalez, G.

    2016-01-01

    There is a lack of information with regards to the friction effect in ECAPed aluminum alloys, even though it might substantially modify the deformation at the surface. In this work, the friction effect at the surface and the deformation heterogeneity in the ECAPed aluminum alloy 6061-T6 were characterized. X-Ray diffraction was used to determine residual stresses (RS) on the sample surface. The volumetric sections were characterized by Synchrotron diffraction at ESRF beamline ID15B (Grenoble, France). It was found that the microhardness mapping and residual stress results showed a good agreement with the finite element analysis for the first layer studied. Minor strain variation, Δd/d as a function of (hkl) planes, for the different analyzed sections was found. The study also showed that there was an incomplete symmetry in the residual stress near the surface, even at up to a depth of 400 µm. The regions with higher deformation were found to be at the top and bottom parts of the sample, while the central region showed stress variations of up to 50 MPa.

  16. Analysis of the yielding behavior of electrorheological suspensions by controlled shear stress experiments

    Czech Academy of Sciences Publication Activity Database

    Pavlínek, V.; Sáha, P.; Perez-Gonzales, K.; de Vargas, L.; Stejskal, Jaroslav; Quadrat, Otakar

    2006-01-01

    Roč. 16, 1-2 (2006), s. 14-18 ISSN 1430-6395 R&D Projects: GA ČR GA202/06/0419 Institutional research plan: CEZ:AV0Z40500505 Keywords : electrorheology * yield stress * suspensions * polyaniline Subject RIV: CD - Macromolecular Chemistry

  17. Residual stress distribution of a 6061-T6 aluminum alloy under shear deformation

    Energy Technology Data Exchange (ETDEWEB)

    Reyes-Ruiz, C.; Figueroa, I.A. [Instituto de Investigaciones en Materiales, Universidad Nacional Autónoma de México, Circuito exterior S/N, Cd. Universitaria, A.P. 70-360, Coyoacán C.P. 04510 (Mexico); Braham, C. [Laboratoire Procédés et Ingénierie Mécanique et Matériaux, CNRS UMR 8006, ENSAM-CNAM, 151, Bd de l’Hôpital, 75013 Paris (France); Cabrera, J.M. [Departamento de Ciencia de los Materiales e Ingeniería Metalúrgica, ETSEIB-Universidad Politécnica de Cataluña, Av Diagonal 647, 08028 Barcelona (Spain); Fundació CTM Centre Tecnológic, Pl. de la Ciencia 2, 08243 Manresa (Spain); Zanellato, O.; Baiz, S. [Laboratoire Procédés et Ingénierie Mécanique et Matériaux, CNRS UMR 8006, ENSAM-CNAM, 151, Bd de l’Hôpital, 75013 Paris (France); Gonzalez, G., E-mail: joseggr@unam.mx [Instituto de Investigaciones en Materiales, Universidad Nacional Autónoma de México, Circuito exterior S/N, Cd. Universitaria, A.P. 70-360, Coyoacán C.P. 04510 (Mexico)

    2016-07-18

    There is a lack of information with regards to the friction effect in ECAPed aluminum alloys, even though it might substantially modify the deformation at the surface. In this work, the friction effect at the surface and the deformation heterogeneity in the ECAPed aluminum alloy 6061-T6 were characterized. X-Ray diffraction was used to determine residual stresses (RS) on the sample surface. The volumetric sections were characterized by Synchrotron diffraction at ESRF beamline ID15B (Grenoble, France). It was found that the microhardness mapping and residual stress results showed a good agreement with the finite element analysis for the first layer studied. Minor strain variation, Δd/d as a function of (hkl) planes, for the different analyzed sections was found. The study also showed that there was an incomplete symmetry in the residual stress near the surface, even at up to a depth of 400 µm. The regions with higher deformation were found to be at the top and bottom parts of the sample, while the central region showed stress variations of up to 50 MPa.

  18. High shear microfluidics and its application in rheological measurement

    Energy Technology Data Exchange (ETDEWEB)

    Kang, Kai; Lee, L.James; Koelling, Kurt W. [The Ohio State University, Department of Chemical Engineering, Columbus, OH (United States)

    2005-02-01

    High shear rheology was explored experimentally in microchannels (150 x 150 {mu}m). Two aqueous polymer solutions, polyethylene oxide (viscoelastic fluid) and hydroxyethyl cellulose (viscous fluid) were tested. Bagley correction was applied to remove the end effect. Wall slip was investigated with Mooney's analysis. Shear rates as high as 10{sup 6} s {sup -1} were obtained in the pressure-driven microchannel flow, allowing a smooth extension of the low shear rheological data obtained from the conventional rheometers. At high shear rates, polymer degradation was observed for PEO solutions at a critical microchannel wall shear stress of 4.1 x 10 {sup 3} Pa. Stresses at the ends of the microchannel also contributed to PEO degradation significantly. (orig.)

  19. High shear microfluidics and its application in rheological measurement

    Science.gov (United States)

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

    2005-02-01

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

  20. Stress- and Structure-Induced Anisotropy in Southern California From Two Decades of Shear Wave Splitting Measurements

    Science.gov (United States)

    Li, Zefeng; Peng, Zhigang

    2017-10-01

    We measure shear wave splitting (SWS) parameters (i.e., fast direction and delay time) using 330,000 local earthquakes recorded by more than 400 stations of the Southern California Seismic Network (1995-2014). The resulting 232,000 SWS measurements (90,000 high-quality ones) provide a uniform and comprehensive database of local SWS measurements in Southern California. The fast directions at many stations are consistent with regional maximum compressional stress σHmax. However, several regions show clear deviations from the σHmax directions. These include linear sections along the San Andreas Fault and the Santa Ynez Fault, geological blocks NW to the Los Angeles Basin, regions around the San Jacinto Fault, the Peninsular Ranges near San Diego, and the Coso volcanic field. These complex patterns show that regional stresses and active faults cannot adequately explain the upper crustal anisotropy in Southern California. Other types of local structures, such as local rock types or tectonic features, also play significant roles.

  1. Self-Critical Perfectionism, Acculturative Stress, and Depression among International Students

    Science.gov (United States)

    Rice, Kenneth G.; Choi, Chun-Chung; Zhang, Yanmei; Morero, Yanina Ines; Anderson, Debra

    2012-01-01

    The authors tested a classic diathesis-stress, stress-enhancement model of perfectionism with subgroups of Chinese (N = 129) and Asian Indian (N = 166) international graduate students attending a major U.S. university. More specifically, the authors tested whether self-critical perfectionism, acculturative stress, and their interaction accounted…

  2. Gamification in Stress Management Apps: A Critical App Review

    Science.gov (United States)

    Christmann, Corinna A; Bleser, Gabriele

    2017-01-01

    Background In today’s society, stress is more and more often a cause of disease. This makes stress management an important target of behavior change programs. Gamification has been suggested as one way to support health behavior change. However, it remains unclear to which extend available gamification techniques are integrated in stress management apps, and if their occurrence is linked to the use of elements from behavior change theory. Objective The aim of this study was to investigate the use of gamification techniques in stress management apps and the cooccurrence of these techniques with evidence-based stress management methods and behavior change techniques. Methods A total of 62 stress management apps from the Google Play Store were reviewed on their inclusion of 17 gamification techniques, 15 stress management methods, and 26 behavior change techniques. For this purpose, an extended taxonomy of gamification techniques was constructed and applied by 2 trained, independent raters. Results Interrater-reliability was high, with agreement coefficient (AC)=.97. Results show an average of 0.5 gamification techniques for the tested apps and reveal no correlations between the use of gamification techniques and behavior change techniques (r=.17, P=.20), or stress management methods (r=.14, P=.26). Conclusions This leads to the conclusion that designers of stress management apps do not use gamification techniques to influence the user’s behaviors and reactions. Moreover, app designers do not exploit the potential of combining gamification techniques with behavior change theory. PMID:28592397

  3. Inhibition of Hb Binding to GP1bα Abrogates Hb-Mediated Thrombus Formation on Immobilized VWF and Collagen under Physiological Shear Stress.

    Science.gov (United States)

    Annarapu, Gowtham K; Singhal, Rashi; Peng, Yuandong; Guchhait, Prasenjit

    2016-01-01

    Reports including our own describe that intravascular hemolysis increases the risk of thrombosis in hemolytic disorders. Our recent study shows that plasma Hb concentrations correlate directly with platelet activation in patients with paroxysmal nocturnal hemoglobinuria (PNH). The binding of Hb to glycoprotein1bα (GP1bα) increases platelet activation. A peptide AA1-50, designed from N-terminal amino acid sequence of GP1bα significantly inhibits the Hb binding to GP1bα as well as Hb-induced platelet activation. This study further examined if the Hb-mediated platelet activation plays any significant role in thrombus formation on subendothelium matrix under physiological flow shear stresses and the inhibition of Hb-platelet interaction can abrogate the above effects of Hb. Study performed thrombus formation assay in vitro by perfusing whole blood over immobilized VWF or collagen type I in presence of Hb under shear stresses simulating arterial or venous flow. The Hb concentrations ranging from 5 to 10 μM, commonly observed level in plasma of the hemolytic patients including PNH, dose-dependently increased thrombus formation on immobilized VWF under higher shear stress of 25 dyne/cm2, but not at 5 dyne/cm2. The above Hb concentrations also increased thrombus formation on immobilized collagen under both shear stresses of 5 and 25 dyne/cm2. The peptide AA1-50 abrogated invariably the above effects of Hb on thrombus formation. This study therefore indicates that the Hb-induced platelet activation plays a crucial role in thrombus formation on immobilized VWF or collagen under physiological flow shear stresses. Thus suggesting a probable role of this mechanism in facilitating thrombosis under hemolytic conditions.

  4. Investigation of Shear Stud Performance in Flat Plate Using Finite Element Analysis

    Directory of Open Access Journals (Sweden)

    T.S. Viswanathan

    2014-09-01

    Full Text Available Three types of shear stud arrangement, respectively featuring an orthogonal, a radial and a critical perimeter pattern, were evaluated numerically. A numerical investigation was conducted using the finite element software ABAQUS to evaluate their ability to resist punching shear in a flat plate. The finite element analysis here is an application of the nonlinear analysis of reinforced concrete structures using three-dimensional solid finite elements. The nonlinear characteristics of concrete were achieved by employing the concrete damaged plasticity model in the finite element program. Transverse shear stress was evaluated using finite element analysis in terms of shear stress distribution for flat plate with and without shear stud reinforcement. The model predicted that shear studs placed along the critical perimeter are more effective compared to orthogonal and radial patterns.

  5. Study of the inhomogeneity of critical current under in-situ tensile stress for YBCO tape

    Science.gov (United States)

    Zhu, Y. P.; Chen, W.; Zhang, H. Y.; Liu, L. Y.; Pan, X. F.; Yang, X. S.; Zhao, Y.

    2018-07-01

    A Hall sensor system was used to measure the local critical current of YBCO tape with high spatial resolution under in-situ tensile stress. The hot spot generation and minimum quench energy of YBCO tape, which depended on the local critical current, was calculated through the thermoelectric coupling model. With the increase in tensile stress, the cracks which have different dimensions and critical current degradation arose more frequently and lowered the thermal stability of the YBCO tape.

  6. Critical brain circuits at the intersection between stress and learning.

    Science.gov (United States)

    Bangasser, Debra A; Shors, Tracey J

    2010-07-01

    The effects of stressful life experience on learning are pervasive and vary greatly both within and between individuals. It is therefore unlikely that any one mechanism will underlie these complicated processes. Nonetheless, without identifying the necessary and sufficient circuitry, no complete mechanism or set of mechanisms can be identified. In this review, we provide two anatomical frameworks through which stressful life experience can influence processes related to learning and memory. In the first, stressful experience releases stress hormones, primarily from the adrenals, which directly impact brain areas engaged in learning. In the second, stressful experience indirectly alters the circuits used in learning via intermediary brain regions. Importantly, these intermediary brain regions are not integral to the stress response or learning itself, but rather link the consequences of a stressful experience with circuits used to learn associations. As reviewed, the existing literature provides support for both frameworks, with somewhat more support for the first but sufficient evidence for the latter which involves intermediary structures. Once we determine the circumstances that engage each framework and identify which one is most predominant, we can begin to focus our efforts on describing the neuronal and hormonal mechanisms that operate within these circuits to influence cognitive processes after stressful life experience.

  7. 19 mm sized bileaflet valve prostheses' flow field investigated by bidimensional laser Doppler anemometry (part II: maximum turbulent shear stresses)

    Science.gov (United States)

    Barbaro, V; Grigioni, M; Daniele, C; D'Avenio, G; Boccanera, G

    1997-11-01

    The investigation of the flow field generated by cardiac valve prostheses is a necessary task to gain knowledge on the possible relationship between turbulence-derived stresses and the hemolytic and thrombogenic complications in patients after valve replacement. The study of turbulence flows downstream of cardiac prostheses, in literature, especially concerns large-sized prostheses with a variable flow regime from very low up to 6 L/min. The Food and Drug Administration draft guidance requires the study of the minimum prosthetic size at a high cardiac output to reach the maximum Reynolds number conditions. Within the framework of a national research project regarding the characterization of cardiovascular endoprostheses, an in-depth study of turbulence generated downstream of bileaflet cardiac valves is currently under way at the Laboratory of Biomedical Engineering of the Istituto Superiore di Sanita. Four models of 19 mm bileaflet valve prostheses were used: St Jude Medical HP, Edwards Tekna, Sorin Bicarbon, and CarboMedics. The prostheses were selected for the nominal Tissue Annulus Diameter as reported by manufacturers without any assessment of valve sizing method, and were mounted in aortic position. The aortic geometry was scaled for 19 mm prostheses using angiographic data. The turbulence-derived shear stresses were investigated very close to the valve (0.35 D0), using a bidimensional Laser Doppler anemometry system and applying the Principal Stress Analysis. Results concern typical turbulence quantities during a 50 ms window at peak flow in the systolic phase. Conclusions are drawn regarding the turbulence associated to valve design features, as well as the possible damage to blood constituents.

  8. Emergency and crisis management: critical incident stress management for first responders and business organisations.

    Science.gov (United States)

    Guenthner, Daniel H

    2012-01-01

    A literature review was performed on critical incident stress after September 11th, 2001 (9/11), and Hurricanes Katrina and Rita, which focused on the need to implement a holistic critical incident stress management programme for first responders and business organisations. Critical incident stress management is required to handle acute stress and other distress in the face of natural or man-made disasters, including terrorist attacks. A holistic approach to community resilience through a well-planned and implemented critical incident stress management programme has been shown in the literature to promote self-help and self-efficacy of individuals and organisations. The interventions and programme elements defined clearly show how a number of different intervention and prevention strategies will promote business and community resilience and also self-efficacy in a culturally-diverse community and organisation. Implementing a critical incident stress management programme within a responding business organisation is critical because of the fact that first responders are the most susceptible every day to exposure to critical incidents that will affect their mental health; and business employees will suffer some of the same maladies as first responders in the event of a disaster or crisis. Utilising the framework provided, a holistic critical incident stress management programme can be implemented to help reduce the effects of burnout, absenteeism, acute stress, post-traumatic stress, substance use and traumatic stress, and to work to promote community resilience and toughen individuals against the effects of stress. Taking care of the needs of the employees of a business organisation, and of those of first responders, is clearly required.

  9. Pseudodynamic Source Characterization for Strike-Slip Faulting Including Stress Heterogeneity and Super-Shear Ruptures

    KAUST Repository

    Mena, B.

    2012-08-08

    Reliable ground‐motion prediction for future earthquakes depends on the ability to simulate realistic earthquake source models. Though dynamic rupture calculations have recently become more popular, they are still computationally demanding. An alternative is to invoke the framework of pseudodynamic (PD) source characterizations that use simple relationships between kinematic and dynamic source parameters to build physically self‐consistent kinematic models. Based on the PD approach of Guatteri et al. (2004), we propose new relationships for PD models for moderate‐to‐large strike‐slip earthquakes that include local supershear rupture speed due to stress heterogeneities. We conduct dynamic rupture simulations using stochastic initial stress distributions to generate a suite of source models in the magnitude Mw 6–8. This set of models shows that local supershear rupture speed prevails for all earthquake sizes, and that the local rise‐time distribution is not controlled by the overall fault geometry, but rather by local stress changes on the faults. Based on these findings, we derive a new set of relations for the proposed PD source characterization that accounts for earthquake size, buried and surface ruptures, and includes local rise‐time variations and supershear rupture speed. By applying the proposed PD source characterization to several well‐recorded past earthquakes, we verify that significant improvements in fitting synthetic ground motion to observed ones is achieved when comparing our new approach with the model of Guatteri et al. (2004). The proposed PD methodology can be implemented into ground‐motion simulation tools for more physically reliable prediction of shaking in future earthquakes.

  10. Stress effect on the critical current of Ti-Nb-Zr-Ta multifilamentary superconductors

    International Nuclear Information System (INIS)

    Monju, Yoshiyuki; Tatara, Isamu

    1978-01-01

    The tensile behaviour at R.T., 77K, 4.2K and the degradation of the critical current with stress have been measured on multifilamentary Ti-Nb-Zr-Ta alloy superconductors. The assembly of the stress effect apparatus is as follows; At the center of the 60KOe superconducting solenoid coil, sample wire is hold around an FRP spool and the wire ends are gripped to the load train. Current is supplied through helium vapourcooled flexible leads up to 2000 A. It was clear that a definite degradation of the critical current with stress was not observed up to the stress equal to one third of the fracture stress at 4.2K. This stress value should be defined the maximum allowable stress of alloy superconductors examined from stress effects. (author)

  11. Influence of Normal and Shear Stress on the Hydraulic Transmissivity of Thin Cracks in a Tight Quartz Sandstone, a Granite, and a Shale

    Science.gov (United States)

    Rutter, Ernest H.; Mecklenburgh, Julian

    2018-02-01

    Transmissivity of fluids along fractures in rocks is reduced by increasing normal stress acting across them, demonstrated here through gas flow experiments on Bowland shale, and oil flow experiments on Pennant sandstone and Westerly granite. Additionally, the effect of imposing shear stress at constant normal stress was determined, until frictional sliding started. In all cases, increasing shear stress causes an accelerating reduction of transmissivity by 1 to 3 orders of magnitude as slip initiated, as a result of the formation of wear products that block fluid pathways. Only in the case of granite, and to a lesser extent in the sandstone, was there a minor amount of initial increase of transmissivity prior to the onset of slip. These results cast into doubt the commonly applied presumption that cracks with high resolved shear stresses are the most conductive. In the shale, crack transmissivity is commensurate with matrix permeability, such that shales are expected always to be good seals. For the sandstone and granite, unsheared crack transmissivity was respectively 2 and 2.5 orders of magnitude greater than matrix permeability. For these rocks crack transmissivity can dominate fluid flow in the upper crust, potentially enough to permit maintenance of a hydrostatic fluid pressure gradient in a normal (extensional) faulting regime.

  12. Circulatory shear flow alters the viability and proliferation of circulating colon cancer cells

    Science.gov (United States)

    Fan, Rong; Emery, Travis; Zhang, Yongguo; Xia, Yuxuan; Sun, Jun; Wan, Jiandi

    2016-06-01

    During cancer metastasis, circulating tumor cells constantly experience hemodynamic shear stress in the circulation. Cellular responses to shear stress including cell viability and proliferation thus play critical roles in cancer metastasis. Here, we developed a microfluidic approach to establish a circulatory microenvironment and studied circulating human colon cancer HCT116 cells in response to a variety of magnitude of shear stress and circulating time. Our results showed that cell viability decreased with the increase of circulating time, but increased with the magnitude of wall shear stress. Proliferation of cells survived from circulation could be maintained when physiologically relevant wall shear stresses were applied. High wall shear stress (60.5 dyne/cm2), however, led to decreased cell proliferation at long circulating time (1 h). We further showed that the expression levels of β-catenin and c-myc, proliferation regulators, were significantly enhanced by increasing wall shear stress. The presented study provides a new insight to the roles of circulatory shear stress in cellular responses of circulating tumor cells in a physiologically relevant model, and thus will be of interest for the study of cancer cell mechanosensing and cancer metastasis.

  13. Gamification in Stress Management Apps: A Critical App Review.

    Science.gov (United States)

    Hoffmann, Alexandra; Christmann, Corinna A; Bleser, Gabriele

    2017-06-07

    In today's society, stress is more and more often a cause of disease. This makes stress management an important target of behavior change programs. Gamification has been suggested as one way to support health behavior change. However, it remains unclear to which extend available gamification techniques are integrated in stress management apps, and if their occurrence is linked to the use of elements from behavior change theory. The aim of this study was to investigate the use of gamification techniques in stress management apps and the cooccurrence of these techniques with evidence-based stress management methods and behavior change techniques. A total of 62 stress management apps from the Google Play Store were reviewed on their inclusion of 17 gamification techniques, 15 stress management methods, and 26 behavior change techniques. For this purpose, an extended taxonomy of gamification techniques was constructed and applied by 2 trained, independent raters. Interrater-reliability was high, with agreement coefficient (AC)=.97. Results show an average of 0.5 gamification techniques for the tested apps and reveal no correlations between the use of gamification techniques and behavior change techniques (r=.17, P=.20), or stress management methods (r=.14, P=.26). This leads to the conclusion that designers of stress management apps do not use gamification techniques to influence the user's behaviors and reactions. Moreover, app designers do not exploit the potential of combining gamification techniques with behavior change theory. ©Alexandra Hoffmann, Corinna A Christmann, Gabriele Bleser. Originally published in JMIR Serious Games (http://games.jmir.org), 07.06.2017.

  14. Critical incidents and critical incident stress management (CISM) - an employee assistance programme (EAP) perspective

    OpenAIRE

    Terblanche, Lourie; van Wyk, André

    2014-01-01

    Employees are increasingly becoming victims of critical incidents. From a systems theory point of view, it is necessary to acknowledge the impact of critical incidents not only on the personal life of the employee, but on the workplace itself. Employees respond differently to critical incidents, which makes it even more complicated when this reaches the point of requiring therapeutic intervention. The most common response to critical incidents may be the risk of developing post-traumatic s...

  15. The Critical Role of Potassium in Plant Stress Response

    Directory of Open Access Journals (Sweden)

    Min Wang

    2013-04-01

    Full Text Available Agricultural production continues to be constrained by a number of biotic and abiotic factors that can reduce crop yield quantity and quality. Potassium (K is an essential nutrient that affects most of the biochemical and physiological processes that influence plant growth and metabolism. It also contributes to the survival of plants exposed to various biotic and abiotic stresses. The following review focuses on the emerging role of K in defending against a number of biotic and abiotic stresses, including diseases, pests, drought, salinity, cold and frost and waterlogging. The availability of K and its effects on plant growth, anatomy, morphology and plant metabolism are discussed. The physiological and molecular mechanisms of K function in plant stress resistance are reviewed. This article also evaluates the potential for improving plant stress resistance by modifying K fertilizer inputs and highlights the future needs for research about the role of K in agriculture.

  16. Air bubbles induce a critical continuous stress to prevent marine biofouling accumulation

    Science.gov (United States)

    Belden, Jesse; Menesses, Mark; Dickenson, Natasha; Bird, James

    2017-11-01

    Significant shear stresses are needed to remove established hard fouling organisms from a ship hull. Given that there is a link between the amount of time that fouling accumulates and the stress required to remove it, it is not surprising that more frequent grooming requires less shear stress. One approach to mitigate marine biofouling is to continuously introduce a curtain of air bubbles under a submerged surface; it is believed that this aeration exploits the small stresses induced by rising bubbles to continuously prevent accumulation. Although curtains of rising bubbles have successfully prevented biofouling accumulation, it is unclear if a single stream of bubbles could maintain a clean surface. In this talk, we show that single bubble stream aeration can prevent biofouling accumulation in regions for which the average wall stress exceeds approximately 0.01 Pa. This value is arrived at by comparing observations of biofouling growth and prevention from field studies with laboratory measurements that probe the associated flow fields. We also relate the spatial and temporal characteristics of the flow to the size and frequency of the rising bubbles, which informs the basic operating conditions required for aeration to continuously prevent biofouling accumulation.

  17. Shear machines

    International Nuclear Information System (INIS)

    Astill, M.; Sunderland, A.; Waine, M.G.

    1980-01-01

    A shear machine for irradiated nuclear fuel elements has a replaceable shear assembly comprising a fuel element support block, a shear blade support and a clamp assembly which hold the fuel element to be sheared in contact with the support block. A first clamp member contacts the fuel element remote from the shear blade and a second clamp member contacts the fuel element adjacent the shear blade and is advanced towards the support block during shearing to compensate for any compression of the fuel element caused by the shear blade (U.K.)

  18. Fabrication of artificial arteriovenous fistula and analysis of flow field and shear stress by using μ-PIV technology

    Energy Technology Data Exchange (ETDEWEB)

    Park, Sun Cheol; Kim, Hyun Kyu [Div. of Vascular Surgery, Dept. of Surgery, College of Medicine, The Catholic University of Korea, Seoul (Korea, Republic of); Song, Ryun Geun; Kim, Sun Ho; Lee, Jin Kee [School of Mechanical Engineering, Sungkyunkwan University, Suwon (Korea, Republic of); Kim, Seung Hyun [School of Engineering, Brown University, Providence (United States)

    2016-12-15

    Radio-cephalic arteriovenous fistula (RC-AVF) is an operation performed to achieve vascular access for hemodialysis. Although RC-AVF is a reliable and well-known method, this technique presents high rates of early failure depending on the vessel condition. These failures are due to blood shear stress around the anastomosis site and the vascular access failure caused by thrombosis secondary to stenosis formation, as well as vascular access reocclusion after percutaneous interventions. In this work, we fabricate in vitro 3D RC-AVF by using polydimethylsiloxane and 3D printing technology to understand the underlying mechanism and predict AVF failure. Micro- Particle image velocimetry (μ-PIV) focusing on the cardiac pulse cycle is used to measure the velocity field within the artificial blood vessel. Results are confirmed by numerical simulation. Accordingly, the in vitro AVF model agrees well with the simulations. Overall, this research would provide the future possibility of using the proposed method to reduce in vivo AVF failure for various conditions.

  19. Modeling of time dependent localized flow shear stress and its impact on cellular growth within additive manufactured titanium implants.

    Science.gov (United States)

    Zhang, Ziyu; Yuan, Lang; Lee, Peter D; Jones, Eric; Jones, Julian R

    2014-11-01

    Bone augmentation implants are porous to allow cellular growth, bone formation and fixation. However, the design of the pores is currently based on simple empirical rules, such as minimum pore and interconnects sizes. We present a three-dimensional (3D) transient model of cellular growth based on the Navier-Stokes equations that simulates the body fluid flow and stimulation of bone precursor cellular growth, attachment, and proliferation as a function of local flow shear stress. The model's effectiveness is demonstrated for two additive manufactured (AM) titanium scaffold architectures. The results demonstrate that there is a complex interaction of flow rate and strut architecture, resulting in partially randomized structures having a preferential impact on stimulating cell migration in 3D porous structures for higher flow rates. This novel result demonstrates the potential new insights that can be gained via the modeling tool developed, and how the model can be used to perform what-if simulations to design AM structures to specific functional requirements. © 2014 Wiley Periodicals, Inc.

  20. NOX4-dependent Hydrogen peroxide promotes shear stress-induced SHP2 sulfenylation and eNOS activation.

    Science.gov (United States)

    Sánchez-Gómez, Francisco J; Calvo, Enrique; Bretón-Romero, Rosa; Fierro-Fernández, Marta; Anilkumar, Narayana; Shah, Ajay M; Schröder, Katrin; Brandes, Ralf P; Vázquez, Jesús; Lamas, Santiago

    2015-12-01

    Laminar shear stress (LSS) triggers signals that ultimately result in atheroprotection and vasodilatation. Early responses are related to the activation of specific signaling cascades. We investigated the participation of redox-mediated modifications and in particular the role of hydrogen peroxide (H2O2) in the sulfenylation of redox-sensitive phosphatases. Exposure of vascular endothelial cells to short periods of LSS (12 dyn/cm(2)) resulted in the generation of superoxide radical anion as detected by the formation of 2-hydroxyethidium by HPLC and its subsequent conversion to H2O2, which was corroborated by the increase in the fluorescence of the specific peroxide sensor HyPer. By using biotinylated dimedone we detected increased total protein sulfenylation in the bovine proteome, which was dependent on NADPH oxidase 4 (NOX4)-mediated generation of peroxide. Mass spectrometry analysis allowed us to identify the phosphatase SHP2 as a protein susceptible to sulfenylation under LSS. Given the dependence of FAK activity on SHP2 function, we explored the role of FAK under LSS conditions. FAK activation and subsequent endothelial NO synthase (eNOS) phosphorylation were promoted by LSS and both processes were dependent on NOX4, as demonstrated in lung endothelial cells isolated from NOX4-null mice. These results support the idea that LSS elicits redox-sensitive signal transduction responses involving NOX4-dependent generation of hydrogen peroxide, SHP2 sulfenylation, and ulterior FAK-mediated eNOS activation. Copyright © 2015 Elsevier Inc. All rights reserved.

  1. Use of controlled dynamic impacts on hierarchically structured seismically hazardous faults for seismically safe relaxation of shear stresses

    Science.gov (United States)

    Ruzhich, Valery V.; Psakhie, Sergey G.; Levina, Elena A.; Shilko, Evgeny V.; Grigoriev, Alexandr S.

    2017-12-01

    In the paper we briefly outline the experience in forecasting catastrophic earthquakes and the general problems in ensuring seismic safety. The purpose of our long-term research is the development and improvement of the methods of man-caused impacts on large-scale fault segments to safely reduce the negative effect of seismodynamic failure. Various laboratory and large-scale field experiments were carried out in the segments of tectonic faults in Baikal rift zone and in main cracks in block-structured ice cove of Lake Baikal using the developed measuring systems and special software for identification and treatment of deformation response of faulty segments to man-caused impacts. The results of the study let us to ground the necessity of development of servo-controlled technologies, which are able to provide changing the shear resistance and deformation regime of fault zone segments by applying vibrational and pulse triggering impacts. We suppose that the use of triggering impacts in highly stressed segments of active faults will promote transferring the geodynamic state of these segments from a metastable to a more stable and safe state.

  2. Notch1 and 4 Signaling Responds to an Increasing Vascular Wall Shear Stress in a Rat Model of Arteriovenous Malformations

    Directory of Open Access Journals (Sweden)

    Jian Tu

    2014-01-01

    Full Text Available Notch signaling is suggested to promote the development and maintenance of cerebral arteriovenous malformations (AVMs, and an increasing wall shear stress (WSS contributes to AVM rupture. Little is known about whether WSS impacts Notch signaling, which is important for understanding the angiogenesis of AVMs. WSS was measured in arteriovenous fistulas (AVF surgically created in 96 rats at different time points over a period of 84 days. The expression of Notch receptors 1 and 4 and their ligands, Delta1 and 4, Jagged1, and Notch downstream gene target Hes1 was quantified in “nidus” vessels. The interaction events between Notch receptors and their ligands were quantified using proximity ligation assay. There was a positive correlation between WSS and time (r=0.97; P<0.001. The expression of Notch receptors and their ligands was upregulated following AVF formation. There was a positive correlation between time and the number of interactions between Notch receptors and their ligands aftre AVF formation (r=0.62, P<0.05 and a positive correlation between WSS and the number of interactions between Notch receptors and their ligands (r=0.87, P<0.005. In conclusion, an increasing WSS may contribute to the angiogenesis of AVMs by activation of Notch signaling.

  3. PEG-albumin plasma expansion increases expression of MCP-1 evidencing increased circulatory wall shear stress: an experimental study.

    Directory of Open Access Journals (Sweden)

    C Makena Hightower

    Full Text Available Treatment of blood loss with plasma expanders lowers blood viscosity, increasing cardiac output. However, increased flow velocity by conventional plasma expanders does not compensate for decreased viscosity in maintaining vessel wall shear stress (WSS, decreasing endothelial nitric oxide (NO production. A new type of plasma expander using polyethylene glycol conjugate albumin (PEG-Alb causes supra-perfusion when used in extreme hemodilution and is effective in treating hemorrhagic shock, although it is minimally viscogenic. An acute 40% hemodilution/exchange-transfusion protocol was used to compare 4% PEG-Alb to Ringer's lactate, Dextran 70 kDa and 6% Hetastarch (670 kDa in unanesthetized CD-1 mice. Serum cytokine analysis showed that PEG-Alb elevates monocyte chemotactic protein-1 (MCP-1, a member of a small inducible gene family, as well as expression of MIP-1α, and MIP-2. MCP-1 is specific to increased WSS. Given the direct link between increased WSS and production of NO, the beneficial resuscitation effects due to PEG-Alb plasma expansion appear to be due to increased WSS through increased perfusion and blood flow rather than blood viscosity.

  4. Flow shear stress differentially regulates endothelial uptake of nanocarriers targeted to distinct epitopes of PECAM-1.

    Science.gov (United States)

    Han, Jingyan; Shuvaev, Vladimir V; Davies, Peter F; Eckmann, David M; Muro, Silvia; Muzykantov, Vladimir R

    2015-07-28

    Targeting nanocarriers (NC) to endothelial cell adhesion molecules including Platelet-Endothelial Cell Adhesion Molecule-1 (PECAM-1 or CD31) improves drug delivery and pharmacotherapy of inflammation, oxidative stress, thrombosis and ischemia in animal models. Recent studies unveiled that hydrodynamic conditions modulate endothelial endocytosis of NC targeted to PECAM-1, but the specificity and mechanism of effects of flow remain unknown. Here we studied the effect of flow on endocytosis by human endothelial cells of NC targeted by monoclonal antibodies Ab62 and Ab37 to distinct epitopes on the distal extracellular domain of PECAM. Flow in the range of 1-8dyn/cm(2), typical for venous vasculature, stimulated the uptake of spherical Ab/NC (~180nm diameter) carrying ~50 vs 200 Ab62 and Ab37 per NC, respectively. Effect of flow was inhibited by disruption of cholesterol-rich plasmalemma domains and deletion of PECAM-1 cytosolic tail. Flow stimulated endocytosis of Ab62/NC and Ab37/NC via eliciting distinct signaling pathways mediated by RhoA/ROCK and Src Family Kinases, respectively. Therefore, flow stimulates endothelial endocytosis of Ab/NC in a PECAM-1 epitope specific manner. Using ligands of binding to distinct epitopes on the same target molecule may enable fine-tuning of intracellular delivery based on the hemodynamic conditions in the vascular area of interest. Copyright © 2015 Elsevier B.V. All rights reserved.

  5. Evaluation of Aortic Blood Flow and Wall Shear Stress in Aortic Stenosis and Its Association With Left Ventricular Remodeling

    Science.gov (United States)

    von Knobelsdorff-Brenkenhoff, Florian; Karunaharamoorthy, Achudhan; Trauzeddel, Ralf Felix; Barker, Alex J; Blaszczyk, Edyta; Markl, Michael; Schulz-Menger, Jeanette

    2016-01-01

    Background Aortic stenosis (AS) leads to variable stress for the left ventricle (LV) and consequently a broad range of LV remodeling. Study aim was to describe blood flow patterns in the ascending aorta of AS patients and determine their association with remodeling. Methods and Results Thirty-seven patients with AS (14 mild, 8 moderate, 15 severe; age 63±13 years) and 37 healthy controls (age 60±10 years) underwent 4D-flow MRI. Helical and vortical flow formations and flow eccentricity were assessed in the ascending aorta. Normalized flow displacement from the vessel center and peak systolic wall shear stress (WSSpeak) in the ascending aorta were quantified. LV remodeling was assessed based on LV mass index (LVMI-I) and the ratio of LV mass to enddiastolic volume (relative wall mass; RWM). Marked helical and vortical flow formation and eccentricity were more prevalent in patients with AS than in healthy subjects, and AS patients exhibited an asymmetric and elevated distribution of WSSpeak. In AS, aortic orifice area was strongly negatively associated with vortical flow formation (p=0.0274), eccentricity (p=0.0070) and flow displacement (p=0.0021). Bicuspid aortic valve was associated with more intense helical (p=0.0098) and vortical flow formation (p=0.0536), higher flow displacement (p=0.11) and higher WSSpeak (p=0.0926). LVM-I and RWM were significantly associated with aortic orifice area (p=0.0611, p=0.0058) and flow displacement (p=0.0058, p=0.0283). Conclusions In this pilot study, AS leads to abnormal blood flow pattern and WSSpeak in the ascending aorta. In addition to aortic orifice area, normalized flow displacement was significantly associated with LV remodeling. PMID:26917824

  6. Origin of shear thickening in semidilute wormlike micellar solutions and evidence of elastic turbulence

    International Nuclear Information System (INIS)

    Marín-Santibáñez, Benjamín M.; Pérez-González, José; Rodríguez-González, Francisco

    2014-01-01

    The origin of shear thickening in an equimolar semidilute wormlike micellar solution of cetylpyridinium chloride and sodium salicylate was investigated in this work by using Couette rheometry, flow visualization, and capillary Rheo-particle image velocimetry. The use of the combined methods allowed the discovery of gradient shear banding flow occurring from a critical shear stress and consisting of two main bands, one isotropic (transparent) of high viscosity and one structured (turbid) of low viscosity. Mechanical rheometry indicated macroscopic shear thinning behavior in the shear banding regime. However, local velocimetry showed that the turbid band increased its viscosity along with the shear stress, even though barely reached the value of the viscosity of the isotropic phase. This shear band is the precursor of shear induced structures that subsequently give rise to the average increase in viscosity or apparent shear thickening of the solution. Further increase in the shear stress promoted the growing of the turbid band across the flow region and led to destabilization of the shear banding flow independently of the type of rheometer used, as well as to vorticity banding in Couette flow. At last, vorticity banding disappeared and the flow developed elastic turbulence with chaotic dynamics

  7. Using digital holographic microscopy for simultaneous measurements of 3D near wall velocity and wall shear stress in a turbulent boundary layer

    Science.gov (United States)

    Sheng, J.; Malkiel, E.; Katz, J.

    2008-12-01

    A digital holographic microscope is used to simultaneously measure the instantaneous 3D flow structure in the inner part of a turbulent boundary layer over a smooth wall, and the spatial distribution of wall shear stresses. The measurements are performed in a fully developed turbulent channel flow within square duct, at a moderately high Reynolds number. The sample volume size is 90 × 145 × 90 wall units, and the spatial resolution of the measurements is 3 8 wall units in streamwise and spanwise directions and one wall unit in the wall-normal direction. The paper describes the data acquisition and analysis procedures, including the particle tracking method and associated method for matching of particle pairs. The uncertainty in velocity is estimated to be better than 1 mm/s, less than 0.05% of the free stream velocity, by comparing the statistics of the normalized velocity divergence to divergence obtained by randomly adding an error of 1 mm/s to the data. Spatial distributions of wall shear stresses are approximated with the least square fit of velocity measurements in the viscous sublayer. Mean flow profiles and statistics of velocity fluctuations agree very well with expectations. Joint probability density distributions of instantaneous spanwise and streamwise wall shear stresses demonstrate the significance of near-wall coherent structures. The near wall 3D flow structures are classified into three groups, the first containing a pair of counter-rotating, quasi streamwise vortices and high streak-like shear stresses; the second group is characterized by multiple streamwise vortices and little variations in wall stress; and the third group has no buffer layer structures.

  8. Influence of Additive Manufactured Scaffold Architecture on the Distribution of Surface Strains and Fluid Flow Shear Stresses and Expected Osteochondral Cell Differentiation.

    Science.gov (United States)

    Hendrikson, Wim J; Deegan, Anthony J; Yang, Ying; van Blitterswijk, Clemens A; Verdonschot, Nico; Moroni, Lorenzo; Rouwkema, Jeroen

    2017-01-01

    Scaffolds for regenerative medicine applications should instruct cells with the appropriate signals, including biophysical stimuli such as stress and strain, to form the desired tissue. Apart from that, scaffolds, especially for load-bearing applications, should be capable of providing mechanical stability. Since both scaffold strength and stress-strain distributions throughout the scaffold depend on the scaffold's internal architecture, it is important to understand how changes in architecture influence these parameters. In this study, four scaffold designs with different architectures were produced using additive manufacturing. The designs varied in fiber orientation, while fiber diameter, spacing, and layer height remained constant. Based on micro-CT (μCT) scans, finite element models (FEMs) were derived for finite element analysis (FEA) and computational fluid dynamics (CFD). FEA of scaffold compression was validated using μCT scan data of compressed scaffolds. Results of the FEA and CFD showed a significant impact of scaffold architecture on fluid shear stress and mechanical strain distribution. The average fluid shear stress ranged from 3.6 mPa for a 0/90 architecture to 6.8 mPa for a 0/90 offset architecture, and the surface shear strain from 0.0096 for a 0/90 offset architecture to 0.0214 for a 0/90 architecture. This subsequently resulted in variations of the predicted cell differentiation stimulus values on the scaffold surface. Fluid shear stress was mainly influenced by pore shape and size, while mechanical strain distribution depended mainly on the presence or absence of supportive columns in the scaffold architecture. Together, these results corroborate that scaffold architecture can be exploited to design scaffolds with regions that guide specific tissue development under compression and perfusion. In conjunction with optimization of stimulation regimes during bioreactor cultures, scaffold architecture optimization can be used to improve

  9. Fatigue life assessment of thin-walled welded joints under non-proportional load-time histories by the shear stress rate integral approach

    Directory of Open Access Journals (Sweden)

    A. Bolchoun

    2016-10-01

    Full Text Available Fatigue life tests under constant and variable amplitude loadings were performed on the tube-tube thin-walled welded specimens made of magnesium (AZ31 and AZ61 alloys. The tests included pure axial, pure torsional and combined in-phase and out-of-phase loadings with the load ratio  RR " ", " " 1  . For the tests with variable amplitude loads a Gaußdistributed loading spectrum with S L 4 5 10  cycles was used. Since magnesium welds show a fatigue life reduction under out-of-phase loads, a stress-based method, which takes this behavior into account, is proposed. The out-of-phase loading results in rotating shear stress vectors in the section planes, which are not orthogonal to the surface. This fact is used in order to provide an out-of-phase measure of the load. This measure is computed as an area covered by the shear stress vectors in all planes over a certain time interval, its computation involves the shear stress and the shear stress rate vectors in the individual planes. Fatigue life evaluation for the variable amplitudes loadings is performed using the Palmgren-Miner linear damage accumulation, whereas the total damage of every cycle is split up into two components: the amplitude component and the out-of-phase component. In order to compute the two components a modification of the rainflow counting method, which keeps track of the time intervals, where the cycles occur, must be used. The proposed method also takes into account different slopes of the pure axial and the pure torsional Wöhler-line by means of a Wöhler-line interpolation for combined loadings

  10. Self-critical perfectionism, daily stress, and disclosure of daily emotional events.

    Science.gov (United States)

    Richardson, Clarissa M E; Rice, Kenneth G

    2015-10-01

    Although disclosure of stressful events can alleviate distress, self-critical perfectionism may pose an especially strong impediment to disclosure during stress, likely contributing to poorer psychological well-being. In the current study, after completing a measure of self-critical perfectionism (the Discrepancy subscale of the Almost Perfect Scale--Revised; Slaney, Rice, Mobley, Trippi, & Ashby, 2001), 396 undergraduates completed measures of stress and disclosure at the end of each day for 1 week. Consistent with hypotheses and previous research, multilevel modeling results indicated significant intraindividual coupling of daily stress and daily disclosure where disclosure was more likely when experiencing high stress than low stress. As hypothesized, Discrepancy moderated the relationship between daily stress and daily disclosure. Individuals higher in self-critical perfectionism (Discrepancy) were less likely to engage in disclosure under high stress, when disclosure is often most beneficial, than those with lower Discrepancy scores. These results have implications for understanding the role of stress and coping in the daily lives of self-critical perfectionists. (c) 2015 APA, all rights reserved).

  11. Dealing Collectively with Critical Incident Stress Reactions in High Risk Work Environments

    DEFF Research Database (Denmark)

    Müller-Leonhardt, Alice; Strøbæk, Pernille Solveig; Vogt, joachim

    2015-01-01

    organisations. Indeed, we found that the CISM programme once integrated within the socio-cultural patterns of this specific working environment enhanced not only individual feelings of being supported but also organisational safety culture. Keywords: coping; safety culture; critical incident stress management......aim of this paper is to shift the representation of coping patterns within high risk occupations to an existential part of cultural pattern and social structure, which characterises high reliability organisations. Drawing upon the specific peer model of critical incident stress management (CISM......), in which qualified operational peers support colleagues who experienced critical incident stress, the paper discusses critical incident stress management in air traffic control. Our study revealed coping patterns that co-vary with the culture that the CISM programme fostered within this specific high...

  12. An In Vitro Comparative Study of Intracanal Fluid Motion and Wall Shear Stress Induced by Ultrasonic and Polymer Rotary Finishing Files in a Simulated Root Canal Model

    OpenAIRE

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

    2012-01-01

    Objective. This in vitro study compared the flow pattern and shear stress of an irrigant induced by ultrasonic and polymer rotary finishing file activation in an acrylic root canal model. Flow visualization analysis was performed using an acrylic canal filled with a mixture of distilled water and rheoscopic fluid. The ultrasonic and polymer rotary finishing file were separately tested in the canal and activated in a static position and in a cyclical axial motion (up and down). Particle moveme...

  13. Critical applied stresses for a crack initiation from a sharp V-notch

    Directory of Open Access Journals (Sweden)

    L. Náhlík

    2014-10-01

    Full Text Available The aim of the paper is to estimate a value of the critical applied stress for a crack initiation from a sharp V-notch tip. The classical approach of the linear elastic fracture mechanics (LELM was generalized, because the stress singularity exponent differs from 0.5 in the studied case. The value of the stress singularity exponent depends on the V-notch opening angle. The finite element method was used for a determination of stress distribution in the vicinity of the sharp V-notch tip and for the estimation of the generalized stress intensity factor depending on the V-notch opening angle. Critical value of the generalized stress intensity factor was obtained using stability criteria based on the opening stress component averaged over a critical distance d from the V-notch tip and generalized strain energy density factor. Calculated values of the critical applied stresses were compared with experimental data from the literature and applicability of the LEFM concept is discussed.

  14. Rôle of contrast media viscosity in altering vessel wall shear stress and relation to the risk of contrast extravasations.

    Science.gov (United States)

    Sakellariou, Sophia; Li, Wenguang; Paul, Manosh C; Roditi, Giles

    2016-12-01

    Iodinated contrast media (CM) are the most commonly used injectables in radiology today. A range of different media are commercially available, combining various physical and chemical characteristics (ionic state, osmolality, viscosity) and thus exhibiting distinct in vivo behaviour and safety profiles. In this paper, numerical simulations of blood flow with contrast media were conducted to investigate the effects of contrast viscosity on generated vessel wall shear stress and vessel wall pressure to elucidate any possible relation to extravasations. Five different types of contrast for Iodine fluxes ranging at 1.5-2.2gI/s were modelled through 18G and 20G cannulae placed in an ideal vein at two different orientation angles. Results demonstrate that the least viscous contrast media generate the least maximum wall shear stress as well as the lowest total pressure for the same flow rate. This supports the empirical clinical observations and hypothesis that more viscous contrast media are responsible for a higher percentage of contrast extravasations. In addition, results support the clinical hypothesis that a catheter tip directed obliquely to the vein wall always produces the highest maximum wall shear stress and total pressure due to impingement of the contrast jet on the vessel wall. Copyright © 2016 IPEM. Published by Elsevier Ltd. All rights reserved.

  15. Predicting bed shear stress and its role in sediment dynamics and restoration potential of the Everglades and other vegetated flow systems

    Science.gov (United States)

    Larsen, Laurel G.; Harvey, Judson; Crimaldi, John P.

    2009-01-01

    Entrainment of sediment by flowing water affects topography, habitat suitability, and nutrient cycling in vegetated floodplains and wetlands, impacting ecosystem evolution and the success of restoration projects. Nonetheless, restoration managers lack simple decision-support tools for predicting shear stresses and sediment redistribution potential in different vegetation communities. Using a field-validated numerical model, we developed state-space diagrams that provide these predictions over a range of water-surface slopes, depths, and associated velocities in Everglades ridge and slough vegetation communities. Diminished bed shear stresses and a consequent decrease in bed sediment redistribution are hypothesized causes of a recent reduction in the topographic and vegetation heterogeneity of this ecosystem. Results confirmed the inability of present-day flows to entrain bed sediment. Further, our diagrams showed bed shear stresses to be highly sensitive to emergent vegetation density and water-surface slope but less sensitive to water depth and periphyton or floating vegetation abundance. These findings suggested that instituting a pulsing flow regime could be the most effective means to restore sediment redistribution to the Everglades. However, pulsing flows will not be sufficient to erode sediment from sloughs with abundant spikerush, unless spikerush density first decreases by natural or managed processes. Our methods provide a novel tool for identifying restoration parameters and performance measures in many types of vegetated aquatic environments where sediment erosion and deposition are involved.

  16. Characterisation of human induced pluripotent stem cell-derived endothelial cells under shear stress using an easy-to-use microfluidic cell culture system.

    Science.gov (United States)

    Ohtani-Kaneko, Rsituko; Sato, Kenjiro; Tsutiya, Atsuhiro; Nakagawa, Yuka; Hashizume, Kazutoshi; Tazawa, Hidekatsu

    2017-10-09

    Induced pluripotent stem cell-derived endothelial cells (iPSC-ECs) can contribute to elucidating the pathogenesis of heart and vascular diseases and developing their treatments. Their precise characteristics in fluid flow however remain unclear. Therefore, the aim of the present study is to characterise these features. We cultured three types of ECs in a microfluidic culture system: commercially available human iPS-ECs, human umbilical vein endothelial cells (HUVECs) and human umbilical artery endothelial cells (HUAECs). We then examined the mRNA expression levels of endothelial marker gene cluster of differentiation 31 (CD31), fit-related receptor tyrosine kinase (Flk-1), and the smooth muscle marker gene smooth muscle alpha-actin, and investigated changes in plasminogen activator inhibitor-1 (PAI-1) secretion and intracellular F-actin arrangement following heat stress. We also compared expressions of the arterial and venous marker genes ephrinB2 and EphB4, and the endothelial gap junction genes connexin (Cx) 37, 40, and 43 under fluidic shear stress to determine their arterial or venous characteristics. We found that iPS-ECs had similar endothelial marker gene expressions and exhibited similar increases in PAI-1 secretion under heat stress as HUVECs and HUAECs. In addition, F-actin arrangement in iPSC-ECs also responded to heat stress, as previously reported. However, they had different expression patterns of arterial and venous marker genes and Cx genes under different fluidic shear stress levels, showing that iPSC-ECs exhibit different characteristics from arterial and venous ECs. This microfluidic culture system equipped with variable shear stress control will provide an easy-to-use assay tool to examine characteristics of iPS-ECs generated by different protocols in various laboratories and contribute to basic and applied biomedical researches on iPS-ECs.

  17. Intensive care diaries reduce new onset post traumatic stress disorder following critical illness

    DEFF Research Database (Denmark)

    Jones, Christina; Bäckman, Carl; Capuzzo, Maurizia

    2010-01-01

    Patients recovering from critical illness have been shown to be at risk of developing Post Traumatic Stress disorder (PTSD). This study was to evaluate whether a prospectively collected diary of a patient's intensive care unit (ICU) stay when used during convalescence following critical illness...

  18. Development of shear bands in amorphous-crystalline metallic alloys

    International Nuclear Information System (INIS)

    Pozdnyakov, V.A.

    2004-01-01

    A theoretical study is made into conditions of shear band evolution in amorphous-crystalline alloys with various morphological types of structural constituents. The condition of shear band evolution in thin amorphous alloys in the interior of the crystalline matrix is obtained. It is shown that a scale effect exists which manifests itself in suppression of the process of localized plastic flow with amorphous alloy thickness decreasing down to the limit. The analysis of the condition for shear band evolution in an amorphous alloy with nanocrystalline inclusions is accomplished. The relationship of a critical stress of shear band evolution to a volume fraction of disperse crystal inclusions is obtained. A consideration is also given to the evolution of shear bands in the material containing amorphous and crystalline areas of micro meter size. For the alloy with the structure of this type conditions for propagation of localized flows by a relay race type mechanism are determined [ru

  19. Stress induced degradation of critical currents in filamentary Nb3Sn

    International Nuclear Information System (INIS)

    McDougall, I.L.

    1976-01-01

    An investigation of the critical stress and strain values of bronze, Nb 3 Sn composites at 4.2 K has been made with simultaneous determination of critical currents in a field of 2.5 Tesla. Evidence of grain boundary microcrack formation has been found associated with reversible degradation of critical current. At a critical strain characteristic of the composite geometry these cracks propagate to give a GB fracture network. A compound with a small grain size formed at low temperatures has the best mechanical properties with a critical strain to the onset of reversible degradation of about 0.5%. (author)

  20. Treatment with platelet lysate induces endothelial differentation of bone marrow mesenchymal stem cells under fluid shear stress.

    Science.gov (United States)

    Homayouni Moghadam, Farshad; Tayebi, Tahereh; Moradi, Alireza; Nadri, Hamid; Barzegar, Kazem; Eslami, Gilda

    2014-01-01

    By considering stem cell-based therapies as a new hope for the treatment of some tragic diseases, marrow stromal cells or marrow mesenchymal stem cells (MSCs) were considered as a suitable and safe multipotential cell source for this new therapeutic approach. For this purpose, many investigations have been performed on differentiation of MSCs toward specific cell lines to overcome the demand for providing the organ specific cells for cell therapy or preparation of engineered tissues. In the present study, differentiation of MSCs to endothelial cells (ECs) by mechanical and chemical stimulation was evaluated. Fluid shear stress (FSS) was used as mechanical inducer, while platelet lysate (PL) and estradiol (E) were used as chemical induction factors. MSCs were placed under FSS with different forces (2, 5 and 10dyn/cm(2)) for different periods (6, 12 and 24 hours). In some groups, PL and E were added to the culture media to evaluate their effect on expression of EC specific markers. This investigation revealed that FSS with low tension (2.5-5 dyn/cm(2)) for a long time (24 hours) or high tension (10 dyn/cm(2)) in short time (6 hours) in the presence of PL could differentiate MSCs toward ECs. The presence of PL was necessary for initiation of endothelial differentiation, and in the absence of PL, there was not any expression of CD34 and Cadherin5 (Cdh5) among cells. Adding E to the culture medium did not change the rate of endothelial differentiation under FSS. Generated endothelial progenitors could produce von Willebrand factor (vWF) after two weeks culture and also they formed tubular structures after culture on matrigel.

  1. Development of a system for measuring wall shear stress in blood vessels using magnetic resonance imaging and computational fluid dynamics

    International Nuclear Information System (INIS)

    Yoshida, Keita; Nagao, Taisuke; Okada, Kouji; Miyazaki, Shohei; Yang, Xiaomei; Yamazaki, Youichi; Murase, Kenya

    2008-01-01

    We developed a system for measuring the wall shear stress (WSS) in blood vessels using magnetic resonance imaging (MRI) and computational fluid dynamics (CFD). The time-dependent velocity at the center of the blood vessel was measured by phase-contrast MRI and was approximated by finite Fourier series, which was used for generating the velocity profile at the inlet for the boundary condition to the CFD method. To validate the CFD method, we compared the WSS obtained by the CFD method with the theoretical value in a straight cylinder with various radii for both steady and pulsatile flows. We also investigated the dependence of the WSS on the inlet velocity profile incorporated into the CFD method. For steady flow, there was a good agreement between the WSS obtained by the CFD method and the theoretical value. For pulsatile flow, there was a relatively good agreement between them when the radius of the cylinder was 2.5 mm and the inlet velocity profile was given by the Womersley solution for fully developed pulsatile flow in a straight circular cylinder. When the radius of the cylinder was 5 mm and/or the inlet velocity profile was assumed to be parabolic, large differences were observed between them, suggesting that the assumption of fully developed flow does not hold true in these cases. In human studies, the vortex due to the secondary blood flow in the carotid arterial sinus was clearly observed. The WSS in the bifurcation was the highest, while that in the carotid arterial sinus was the smallest. In conclusion, the system presented here appears to be useful for measuring the WSS in blood vessels and for analyzing the cause and/or extent of atherosclerosis, and our results suggest that the inlet velocity profile should be carefully considered. (author)

  2. Journalists' Occupational Stress: A Comparative Study between Reporting Critical Events and Domestic News.

    Science.gov (United States)

    Monteiro, Susana; Marques-Pinto, Alexandra

    2017-07-27

    Nowadays, journalism is considered a stressful occupation, not only due to the stress perceived in journalists' daily work but also due to the critical, potentially traumatic events they report. However, research on journalists' occupational stress in both these professional settings is still scarce. This study aims to characterize and compare occupational stress variables perceived by journalists in their daily work and in critical scenarios. Taking the Holistic Model of Occupational Stress by Nelson and Simmons (2003) as a framework, 25 Portuguese journalists, all with experience in reporting critical events, were interviewed on their perceptions of some core variables of the model: occupational stressors, distress and eustress emotional reactions, and the consequences of these experiences on their well-being. Differences among these core variables, according to the number of deployments to a critical event, were statistically analysed in order to ascertain whether repeated exposure to trauma influenced journalists' occupational stress perceptions. The data content analysis showed that occupational stressors and emotional reactions differed across settings, while the consequences associated with journalists' experiences were perceived as being mainly negative in both occupational contexts. Significant differences were identified in some of these variables according to the number of deployments to a critical event (p studies.

  3. Increased Dicarbonyl Stress as a Novel Mechanism of Multi-Organ Failure in Critical Illness

    Directory of Open Access Journals (Sweden)

    Bas C. T. van Bussel

    2017-02-01

    Full Text Available Molecular pathological pathways leading to multi-organ failure in critical illness are progressively being unravelled. However, attempts to modulate these pathways have not yet improved the clinical outcome. Therefore, new targetable mechanisms should be investigated. We hypothesize that increased dicarbonyl stress is such a mechanism. Dicarbonyl stress is the accumulation of dicarbonyl metabolites (i.e., methylglyoxal, glyoxal, and 3-deoxyglucosone that damages intracellular proteins, modifies extracellular matrix proteins, and alters plasma proteins. Increased dicarbonyl stress has been shown to impair the renal, cardiovascular, and central nervous system function, and possibly also the hepatic and respiratory function. In addition to hyperglycaemia, hypoxia and inflammation can cause increased dicarbonyl stress, and these conditions are prevalent in critical illness. Hypoxia and inflammation have been shown to drive the rapid intracellular accumulation of reactive dicarbonyls, i.e., through reduced glyoxalase-1 activity, which is the key enzyme in the dicarbonyl detoxification enzyme system. In critical illness, hypoxia and inflammation, with or without hyperglycaemia, could thus increase dicarbonyl stress in a way that might contribute to multi-organ failure. Thus, we hypothesize that increased dicarbonyl stress in critical illness, such as sepsis and major trauma, contributes to the development of multi-organ failure. This mechanism has the potential for new therapeutic intervention in critical care.

  4. Shear-Wave Splitting in a Critical Crust: the Next Step Biréfringence des ondes transversales dans les croûtes critiques : la prochaine étape

    Directory of Open Access Journals (Sweden)

    Crampin S.

    2006-12-01

    Full Text Available Arguably, shear-wave splitting displaying azimuthal anisotropy has not lived up to its initial promise of opening a new window for understanding cracks and stress in the crust. This paper reviews two recent related developments which appear to renew these initial hopes and provide new opportunities for monitoring, modelling, and even predicting, the (pre-fracturing deformation of fluid-saturated microcracked rock. A recently developed model of anisotropic poro-elasticity (APE for the stress-induced evolution of fluid-saturated microcracked rock matches a wide range of otherwise inexplicable or dissociated phenomena and appears to be a good first-order approximation to the evolution of fluid-saturated microcracked rock. Since the parameters that control small-scale (pre-fracturing deformation also control shear-wave splitting, it appears that the evolution of fluid-saturated microcracked rock can be directly monitored by shear-wave splitting, and the response to future changes predicted by APE. The success of APE-modelling and observations of shear-wave splitting imply that almost all rock is close to a state of fracture criticality associated with the percolation threshold, when shear-strength is lost and through-going fractures can propagate. This confirms other evidence for the self-organized criticality of in situ rock. The significance of this identification is that the small-scale physics that controls the whole phenomena can now be identified as the stress-induced manipulation of fluids around intergranular microcracks. This has the possibly unique advantage amongst critical systems that details of the pre-fracturing deformation and the approach to the criticality threshold (in this case the proximity to fracturing can be monitored at each locality by appropriate observations of shear-wave splitting. This paper reviews the these developments and discusses their implications and applications, particularly the implications of self

  5. Effects of different aging statuses and strain rate on the adiabatic shear susceptibility of 2195 aluminum–lithium alloy

    International Nuclear Information System (INIS)

    Yang, Y.; Tan, G.Y.; Chen, P.X.; Zhang, Q.M.

    2012-01-01

    The adiabatic shear susceptibility of 2195 aluminum–lithium alloy was investigated by means of split Hopkinson pressure bar. The stress collapse in true stress–true strain curves and true stress–time curves was observed. The adiabatic shear susceptibility of different aging statuses and strain rate were discussed by means of metallography observation. The critical strain, stress collapse time and formation energy of adiabatic shear bands were compared. The results show that different aging statuses and strain rate have significant influences on adiabatic shear behaviors of 2195 aluminum–lithium alloy. The peak-aged specimen has the highest adiabatic shearing susceptibility, while the under-aged specimen has the least adiabatic shear susceptibility. The susceptibility of adiabatic shearing increases with the increases of strain rate.

  6. MicroRNA-101 mediates the suppressive effect of laminar shear stress on mTOR expression in vascular endothelial cells

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Kui; Fan, Wendong; Wang, Xing; Ke, Xiao [Division of Cardiology, First Affiliated Hospital of Sun Yat-sen University, Guangzhou 510080 (China); Wu, Guifu, E-mail: eecpchina@yahoo.com.cn [Key Laboratory on Assisted Circulation, Ministry of Health, Guangzhou 510080 (China); Hu, Chengheng, E-mail: huchenghengpci@yahoo.com.cn [Division of Cardiology, First Affiliated Hospital of Sun Yat-sen University, Guangzhou 510080 (China)

    2012-10-12

    Highlights: Black-Right-Pointing-Pointer Laminar shear stress upregulates miR-101 expression in vascular endothelial cells. Black-Right-Pointing-Pointer miR-101 represses mTOR expression through a specific 3 Prime UTR binding site. Black-Right-Pointing-Pointer Overexpression of miR-101 inhibits G1/S transition and endothelial cell proliferation. Black-Right-Pointing-Pointer Blockade of miR-101 attenuates the suppressive effect of laminar flow on mTOR expression. -- Abstract: Shear stress associated with blood flow plays an important role in regulating gene expression and cell function in endothelial cells (ECs). MicroRNAs (miRNAs) are highly conserved, small non-coding RNAs that negatively regulate the expression of target genes by binding to the mRNA 3 Prime -untranslated region (3 Prime UTR) at the posttranscriptional level involved in diverse cellular processes. This study demonstrates that microRNA-101 in response to laminar shear stress (LSS) is involved in the flow regulation of gene expression in ECs. qRT-PCR analysis showed that miR-101 expression was significantly upregulated in human umbilical vein endothelial cells (HUVECs) exposed to 12 dyn/cm{sup 2} laminar shear stress for 12 h. We found that transfection of miR-101 significantly decreased the luciferase activity of plasmid reporter containing the 3 Prime UTR of mammalian target of rapamycin (mTOR) gene. Western analysis revealed that the protein level of mTOR was significantly reduced in ECs transfected with miR-101. Furthermore, miR-101 overexpression induced cell cycle arrest at the G1/S transition and suppressed endothelial cell proliferation. Finally, transfection of miR-101 inhibitors attenuated the suppressive effects of LSS on mTOR expression, which identified the efficacy of loss-of-function of miR-101 in laminar flow-treated ECs. In conclusion, we have demonstrated that upregulation of miR-101 in response to LSS contributes to the suppressive effects of LSS on mTOR expression and EC

  7. Evaluation of mechanical properties of construction joint between new and old concrete under combined tensile and shear stresses; Shinkyu concrete no uchitsugime no incho sendan oryokuka no kyodo tokusei no hyoka

    Energy Technology Data Exchange (ETDEWEB)

    Ujiike, I. [Ehime University, Ehime (Japan). Faculty of Engineering; Yoshida, N. [Shikoku Railway Company, Kagawa (Japan); Morishita, S. [Oriental Construction Co. Ltd., Tokyo (Japan)

    1998-01-15

    The objective of this study is to examine the mechanical properties of construction joints between existing and newly placed concrete under combined tensile and shear stresses. Loading tests are conducted by using push off type specimens. The joint surface of existing concrete is roughened by shot blast and a half of the specimen is reconstructed by new concrete using ultra rapid hardening cement. The insufficient treatment of joint surface of the old concrete causes the lowering of tensile rigidity, while shearing rigidity is almost the same as that of the other specimen. The shearing and tensile rigidities of non jointed concrete and concrete shot blasted properly are not dependent on the combination of shearing and tensile forces. For the jointed concrete shot blasted insufficiently, the shearing rigidity decreases with the increase of tensile force and the tensile digidity also becomes lower by the action of shearing force. Both the tensile strength and shearing strength of jointed concrete become small compared to those of non jointed concrete. The ratio of reduction in tensile strength is larger than that in shearing strength. The strength of jointed concrete under combined tensile and shear stresses can be evaluated by Mohr`s failure envelope expressed by parabola tangent to both tensile strength circle and compressive strength circle. 7 refs., 12 figs., 2 tabs.

  8. Interaction between a normal shock wave and a turbulent boundary layer at high transonic speeds. Part 1: Pressure distribution. Part 2: Wall shear stress. Part 3: Simplified formulas for the prediction of surface pressures and skin friction

    Science.gov (United States)

    Adamson, T. C., Jr.; Liou, M. S.; Messiter, A. F.

    1980-01-01

    An asymptotic description is derived for the interaction between a shock wave and a turbulent boundary layer in transonic flow, for a particular limiting case. The dimensionless difference between the external flow velocity and critical sound speed is taken to be much smaller than one, but large in comparison with the dimensionless friction velocity. The basic results are derived for a flat plate, and corrections for longitudinal wall curvature and for flow in a circular pipe are also shown. Solutions are given for the wall pressure distribution and the shape of the shock wave. Solutions for the wall shear stress are obtained, and a criterion for incipient separation is derived. Simplified solutions for both the wall pressure and skin friction distributions in the interaction region are given. These results are presented in a form suitable for use in computer programs.

  9. Stress evaluation of metallic material under steady state based on nonlinear critically refracted longitudinal wave

    Science.gov (United States)

    Mao, Hanling; Zhang, Yuhua; Mao, Hanying; Li, Xinxin; Huang, Zhenfeng

    2018-06-01

    This paper presents the study of applying the nonlinear ultrasonic wave to evaluate the stress state of metallic materials under steady state. The pre-stress loading method is applied to guarantee components with steady stress. Three kinds of nonlinear ultrasonic experiments based on critically refracted longitudinal wave are conducted on components which the critically refracted longitudinal wave propagates along x, x1 and x2 direction. Experimental results indicate the second and third order relative nonlinear coefficients monotonically increase with stress, and the normalized relationship is consistent with simplified dislocation models, which indicates the experimental result is logical. The combined ultrasonic nonlinear parameter is proposed, and three stress evaluation models at x direction are established based on three ultrasonic nonlinear parameters, which the estimation error is below 5%. Then two stress detection models at x1 and x2 direction are built based on combined ultrasonic nonlinear parameter, the stress synthesis method is applied to calculate the magnitude and direction of principal stress. The results show the prediction error is within 5% and the angle deviation is within 1.5°. Therefore the nonlinear ultrasonic technique based on LCR wave could be applied to nondestructively evaluate the stress of metallic materials under steady state which the magnitude and direction are included.

  10. Stress and coping of Hong Kong Chinese family members during a critical illness.

    Science.gov (United States)

    Chui, Winter Y-Y; Chan, Sally W-C

    2007-02-01

    The present study aimed to investigate the stress and coping strategies of Hong Kong Chinese families during a critical illness and to examine the relationships between stress and coping. Admissions to intensive care unit are usually an unanticipated event, which imposes stress on the family. Family's wellness is one of the significant factors affecting patient's well-beings. Much work has been conducted in Western societies. Stress and coping in Chinese families of critically ill patients have rarely been discussed. Structured face-to-face interviews were conducted, using the Impact of Events Scale and the Family Crisis Oriented Personal Evaluation Scales. A convenience sample of 133 participants was recruited from a regional hospital in Hong Kong. Many were patients' children with age between 30 and 49. A total of 39.1% (n = 52) of the participants were males and 60.9% (n = 81) were females. The participants experienced high level of stress (mean = 25.1, SD = 8.3). Higher level of stress were experienced by female (t = -4.6; d.f. = 1, 131; P = 0.00), those with lower educational attainment (F = 3.0; d.f. = 2, 130; P = 0.05) and those whose relatives were admitted to the intensive care unit unexpectedly (t = -2.2; d.f. = 1; P = 0.03). Patients' length of stay in the unit was significantly correlated with levels of stress (r = 0.5, P stress had significant correlation with coping strategies utilization (r = 0.5, P stress-coping pattern 'fatalistic voluntarism'. This study contributes to the understanding of Hong Kong Chinese families' stress and coping during a critical illness. Comprehensive assessments of family members' psychosocial needs are important to plan appropriate interventions to alleviate their stress and strengthen their coping skills. The findings will serve as guidance for nurses in delivering culturally sensitive and competent interventions.

  11. Experimental study on critical breaking stress of float glass under elevated temperature

    International Nuclear Information System (INIS)

    Wang, Yu; Wang, Qingsong; Shao, Guangzheng; Chen, Haodong; Sun, Jinhua; He, Linghui; Liew, K.M.

    2014-01-01

    Highlights: • Critical breaking stresses of clear, ground and coated glass were measured. • Breaking stress and strain of smooth glass were measured from 25 °C to 400 °C. • At approximately 100 °C, critical stress reached the minimum value. • Surface treatment and ambient temperature have notable effects on glass breaking. - Abstract: Cracking and subsequent fallout of glass may significantly affect fire dynamics in compartments. Moreover, the breaking tensile stress of glass, a crucial parameter for breakage occurrence, is the least well known among mechanical properties. In this work, a series of experiments were conducted, through mechanical tensile tests, to directly measure the breaking stress of float glass using Material Testing System 810 apparatus. Clear, ground and coated glass samples with a thickness of 6 mm were measured under ambient conditions, with a room temperature of 25 °C. The breaking stress of smooth glass samples was also measured at 75 °C, 100 °C, 125 °C, 150 °C, 200 °C, 300 °C and 400 °C, respectively. The results show that surface treatment may decrease the critical tensile stress of glass panes. The average breaking stress also fluctuates considerably, from 26.60 to 35.72 MPa with the temperature variations investigated here. At approximately 100 °C, critical stress reached the minimum value at which glass breakage occurs more easily. In addition, the thermal expansion coefficient was established using a thermal dilatometer, to obtain the maximum temperature difference float glass can withstand. It is intended that these results will provide some practical guidelines for fire safety engineers

  12. Steady shear rate rheology of suspensions, as described by the gaint floc model

    NARCIS (Netherlands)

    Stein, H.N.; Laven, J.

    2001-01-01

    The break-down of a particle network by shear is described as the development of shear planes: a region able to withstand low shear stresses may break down under a larger stress; thus with increasing shear stress and shear rate, the mutual distance (A) between successive shear planes decreases

  13. 3D finite element analysis of stress distributions and strain energy release rates for adhesive bonded flat composite lap shear joints having pre-existing delaminations

    Energy Technology Data Exchange (ETDEWEB)

    Parida, S. K.; Pradhan, A. K. [Indian Institute of Technology, Bhubaneswar (India)

    2014-02-15

    The rate of propagation of embedded delamination in the strap adherend of lap shear joint (LSJ) made of carbon/epoxy composites has been evaluated employing three-dimensional non-linear finite elements. The delamination has been presumed to pre-exist in the thin resin layer between the first and second plies of the strap adherend. The inter-laminar peel and shear stress distributions have been studied in details and are seen to be predominantly three-dimensional in nature. The components of strain energy release rate (SERR) corresponding to the opening, sliding and cross sliding modes of delamination are significantly different at the two fronts of the embedded delamination. The sequential release of multi-point constraint (MPC) finite elements in the vicinity of the delamination fronts enables to simulate the growth of the delamination at either ends. This simulation procedure can be utilized effectively for evaluation of the status of the structural integrity of the bonded joints.

  14. Stress-strain relation of bentonite at undrained shear. Laboratory tests to investigate the influence of material composition and test technique

    Energy Technology Data Exchange (ETDEWEB)

    Dueck, Ann; Boergesson, Lennart; Johannesson, Lars-Erik (Clay Technology AB, Lund (Sweden))

    2010-12-15

    This report describes a laboratory study conducted to update the material model of the buffer material used in the analyses of the effect of a rock shear through a deposition hole. The study considers some new conditions and is especially focused on the reference case with MX-80Ca developed for SR-Site (MX-80 ion exchanged to Ca). The material model is based on relations between density, swelling pressure, shear strength and rate of strain. The reference model is described by Boergesson et al. (2010). The laboratory study is focused on undrained stress-strain-strength properties, which have been studied mainly by conducting triaxial tests and unconfined compression tests. The test results are compared to the earlier measurements and models which show that the new results fit very well into the general picture and models. For the new conditions suitable values of constants included in the model are proposed

  15. Stress-strain relation of bentonite at undrained shear. Laboratory tests to investigate the influence of material composition and test technique

    International Nuclear Information System (INIS)

    Dueck, Ann; Boergesson, Lennart; Johannesson, Lars-Erik

    2010-12-01

    This report describes a laboratory study conducted to update the material model of the buffer material used in the analyses of the effect of a rock shear through a deposition hole. The study considers some new conditions and is especially focused on the reference case with MX-80Ca developed for SR-Site (MX-80 ion exchanged to Ca). The material model is based on relations between density, swelling pressure, shear strength and rate of strain. The reference model is described by Boergesson et al. (2010). The laboratory study is focused on undrained stress-strain-strength properties, which have been studied mainly by conducting triaxial tests and unconfined compression tests. The test results are compared to the earlier measurements and models which show that the new results fit very well into the general picture and models. For the new conditions suitable values of constants included in the model are proposed

  16. Role of urodynamics in stress urinary incontinence: A critical appraisal

    Science.gov (United States)

    Yande, Shirish Dattatraya; Joglekar, Omkar Vinay; Joshi, Maya

    2016-01-01

    Introduction: Role of urodynamics prior to surgery of stress urinary incontinence (SUI) is under constant debate. Demonstration of the presence of detrusor overactivity is the only aspect that has been emphasized in the literature so far. We believe that there are number of other factors which may influence the evaluation and in turn the choice of surgical management and prediction of outcome of treatment. They are as follows: (1) Presence of voiding inefficiency, (2) asymptomatic detrusor overactivity, (3) and severity of SUI. These features may complicate the precise evaluation of patients of SUI. The main objective of this study is to analyze the dynamics of leakage and voiding using urodynamics. This study also aims at correlating these findings with clinical information. Materials and Methods: One hundred consecutive cases referred to our center for preoperative evaluation of SUI were recruited in the study prospectively. All patients were interrogated using International Consultation on Incontinence Questionnaire. All patients underwent complete urodynamic evaluation including uroflowmetry, filling cystometry, leak point pressure measurement, and pressure flow studies, according to Good Urodynamic Practice guidelines. Patients’ symptoms were correlated with urodynamic findings, with special emphasis on the presence of detrusor overactivity, severity of SUI, voiding efficiency, and presence of bladder outlet obstruction. Clinical information and urodynamic findings were correlated using Chi-square test. Results: There is a statistically significant correlation between the presence of symptoms of urge urinary incontinence and urodynamic findings of detrusor overactivity at P incontinence (in addition to SUI) and urodynamic findings of intrinsic sphincter deficiency at P incontinence and incidental finding of detrusor overactivity at P urinary incontinence can predictably diagnose detrusor overactivity in these cases. However, the incidence of asymptomatic

  17. Critical stresses in pintle, weldment and top head of nuclear waste container

    International Nuclear Information System (INIS)

    Ladkany, S.G.; Kniss, B.R.

    1992-01-01

    Critical stresses in the pintle, the weldment, and the top heads (flat and curved), of a high level nuclear waste container are evaluated under an annular loading. This loading is three times larger than the expected normal operating load. Results show that the shape and the thickness of the pintle and the top head, along with the thickness of the weldment, substantially affect the magnitude of the critical stresses and distortions in the various components (i.e. pintle, shell, and heads) when they are supporting a load. Stiffer top heads and pintles and larger weldment sizes reduce the critical stresses in all welded joints. Various shapes of curved top heads were investigated. In this paper an ASME flanged and dished top head, which has the same thickness as the canister, is analyzed

  18. Model-based analysis of high shear wet granulation from batch to continuous processes in pharmaceutical production - A critical review

    DEFF Research Database (Denmark)

    Kumar, Ashish; Gernaey, Krist; De Beer, Thomas

    2013-01-01

    of the developments, the review focuses on the twin-screw granulator as a device for continuous HSWG and attempts to critically evaluate the current process. As a result, a set of open research questions are identified. These questions need to be answered in the future in order to fill the knowledge gap...... that currently exists both at micro- and macro-scale, and which is currently limiting the further development of the process to its full potential in pharmaceutical applications....

  19. Literature review of post-traumatic stress disorder in the critical care population.

    Science.gov (United States)

    Morrissey, Matthew; Collier, Elizabeth

    2016-06-01

    To determine which factors relate to the development of post-traumatic stress disorder, in adult patients who are admitted to critical care units. Patient survival rates from critical care areas are improving each year and this has led to interest in the long-term outcomes for patients who have been discharged from such environments. Patients typically require invasive and extensive treatment, which places a stress on physical and mental health. Prevalence estimates of post-traumatic stress disorder in the critical care discharge population vary from 5-63%, yet it remains unclear what the predisposing factors are. A systematised review. Subject heading and keyword searches were conducted in MEDLINE, CINAHL, PsycINFO and ScienceDirect, with 23 articles identified that examined the relationship between critical care and the development of post-traumatic stress disorder. Three main themes were identified; Critical Care Factors, Patient Factors and Experience Factors. Eight key and three potential causative factors were found: younger age, female, previous psychiatric history, length of ICU stay, benzodiazepine sedation, use of stress hormones, delusional memory and traumatic memory, delirium, GCS score of ≤9 on admission & use of mechanical restraint. Post-traumatic stress reactions can be strongly related to the development and presence of traumatic and delusional memories. Younger patients may exclude themselves from research to avoid their traumatic thoughts. The role of prior psychiatric illness is unknown. Distinction between 'factual' and 'false' or delusional memory as occurs in the literature maybe unhelpful in understanding trauma reactions. There are around 38,000 occupied critical care beds each year in England. The scale of the issue is therefore substantial. Risk factors can be isolated from available evidence and provide a rudimentary risk assessment tool to inform practice development in this area. © 2016 John Wiley & Sons Ltd.

  20. Critical disease windows shaped by stress exposure alter allocation trade-offs between development and immunity.

    Science.gov (United States)

    Kirschman, Lucas J; Crespi, Erica J; Warne, Robin W

    2018-01-01

    Ubiquitous environmental stressors are often thought to alter animal susceptibility to pathogens and contribute to disease emergence. However, duration of exposure to a stressor is likely critical, because while chronic stress is often immunosuppressive, acute stress can temporarily enhance immune function. Furthermore, host susceptibility to stress and disease often varies with ontogeny; increasing during critical developmental windows. How the duration and timing of exposure to stressors interact to shape critical windows and influence disease processes is not well tested. We used ranavirus and larval amphibians as a model system to investigate how physiological stress and pathogenic infection shape development and disease dynamics in vertebrates. Based on a resource allocation model, we designed experiments to test how exposure to stressors may induce resource trade-offs that shape critical windows and disease processes because the neuroendocrine stress axis coordinates developmental remodelling, immune function and energy allocation in larval amphibians. We used wood frog larvae (Lithobates sylvaticus) to investigate how chronic and acute exposure to corticosterone, the dominant amphibian glucocorticoid hormone, mediates development and immune function via splenocyte immunohistochemistry analysis in association with ranavirus infection. Corticosterone treatments affected immune function, as both chronic and acute exposure suppressed splenocyte proliferation, although viral replication rate increased only in the chronic corticosterone treatment. Time to metamorphosis and survival depended on both corticosterone treatment and infection status. In the control and chronic corticosterone treatments, ranavirus infection decreased survival and delayed metamorphosis, although chronic corticosterone exposure accelerated rate of metamorphosis in uninfected larvae. Acute corticosterone exposure accelerated metamorphosis increased survival in infected larvae. Interactions

  1. Stress and burnout among critical care fellows: preliminary evaluation of an educational intervention

    Directory of Open Access Journals (Sweden)

    Kianoush Kashani

    2015-07-01

    Full Text Available Background: Despite a demanding work environment, information on stress and burnout of critical care fellows is limited. Objectives: To assess 1 levels of burnout, perceived stress, and quality of life in critical care fellows, and 2 the impact of a brief stress management training on these outcomes. Methods: In a tertiary care academic medical center, 58 critical care fellows of varying subspecialties and training levels were surveyed to assess baseline levels of stress and burnout. Twenty-one of the 58 critical care fellows who were in the first year of training at the time of this initial survey participated in a pre-test and 1-year post-test to determine the effects of a brief, 90-min stress management intervention. Results: Based on responses (n=58 to the abbreviated Maslach Burnout Inventory, reported burnout was significantly lower in Asian fellows (p=0.04 and substantially higher among graduating fellows (versus new and transitioning fellows (p=0.02. Among the intervention cohort, burnout did not significantly improve – though two-thirds of fellows reported using the interventional techniques to deal with stressful situations. Fellows who participated in the intervention rated the effectiveness of the course as 4 (IQR=3.75–5 using the 5-point Likert scale. Conclusions: In comparison with the new and transitioning trainees, burnout was highest among graduating critical care fellows. Although no significant improvements were found in first-year fellows’ burnout scores following the single, 90-min training intervention, participants felt the training did provide them with tools to apply during stressful situations.

  2. Stress and burnout among critical care fellows: preliminary evaluation of an educational intervention.

    Science.gov (United States)

    Kashani, Kianoush; Carrera, Perliveh; De Moraes, Alice Gallo; Sood, Amit; Onigkeit, James A; Ramar, Kannan

    2015-01-01

    Despite a demanding work environment, information on stress and burnout of critical care fellows is limited. To assess 1) levels of burnout, perceived stress, and quality of life in critical care fellows, and 2) the impact of a brief stress management training on these outcomes. In a tertiary care academic medical center, 58 critical care fellows of varying subspecialties and training levels were surveyed to assess baseline levels of stress and burnout. Twenty-one of the 58 critical care fellows who were in the first year of training at the time of this initial survey participated in a pre-test and 1-year post-test to determine the effects of a brief, 90-min stress management intervention. Based on responses (n=58) to the abbreviated Maslach Burnout Inventory, reported burnout was significantly lower in Asian fellows (p=0.04) and substantially higher among graduating fellows (versus new and transitioning fellows) (p=0.02). Among the intervention cohort, burnout did not significantly improve--though two-thirds of fellows reported using the interventional techniques to deal with stressful situations. Fellows who participated in the intervention rated the effectiveness of the course as 4 (IQR=3.75-5) using the 5-point Likert scale. In comparison with the new and transitioning trainees, burnout was highest among graduating critical care fellows. Although no significant improvements were found in first-year fellows' burnout scores following the single, 90-min training intervention, participants felt the training did provide them with tools to apply during stressful situations.

  3. Stress- and Chemistry-Mediated Permeability Enhancement/Degradation in Stimulated Critically-Stressed Fractures

    Energy Technology Data Exchange (ETDEWEB)

    Derek Elsworth; Abraham S. Grader; Chris Marone; Phillip Halleck; Peter Rose; Igor Faoro; Joshua Taron; André Niemeijer; Hideaki Yasuhara

    2009-03-30

    This work has investigated the interactions between stress and chemistry in controlling the evolution of permeability in stimulated fractured reservoirs through an integrated program of experimentation and modeling. Flow-through experiments on natural and artificial fractures in Coso diorite have examined the evolution of permeability under paths of mean and deviatoric stresses, including the role of dissolution and precipitation. Models accommodating these behaviors have examined the importance of incorporating the complex couplings between stress and chemistry in examining the evolution of permeability in EGS reservoirs. This document reports the findings of experiment [1,2] and analysis [3,4], in four sequential chapters.

  4. Stress levels of critical care doctors in India: A national survey.

    Science.gov (United States)

    Amte, Rahul; Munta, Kartik; Gopal, Palepu B

    2015-05-01

    Doctors working in critical care units are prone to higher stress due to various factors such as higher mortality and morbidity, demanding service conditions and need for higher knowledge and technical skill. The aim was to evaluate the stress level and the causative stressors in doctors working in critical care units in India. A two modality questionnaire-based cross-sectional survey was conducted. In manual mode, randomly selected delegates attending the annual congress of Indian Society of Critical Care Medicine filled the questionnaire. In the electronic mode, the questionnaires were E-mailed to critical care doctors. These questionnaires were based on General Health Questionnaire-12 (GHQ-12). Completely filled 242 responses were utilized for comparative and correlation analysis. Prevalence of moderate to severe stress level was 40% with a mean score of 2 on GHQ-12 scale. Too much responsibility at times and managing VIP patients ranked as the top two stressors studied, while the difficult relationship with colleagues and sexual harassment were the least. Intensivists were spending longest hours in the Intensive Care Unit (ICU) followed by pulmonologists and anesthetists. The mean number of ICU bed critical care doctors entrusted with was 13.2 ± 6.3. Substance abuse to relieve stress was reported as alcohol (21%), anxiolytic or antidepressants (18%) and smoking (14%). Despite the higher workload, stress levels measured in our survey in Indian critical care doctors were lower compared to International data. Substantiation of this data through a wider study and broad-based measures to improve the quality of critical care units and quality of the lives of these doctors is the need of the hour.

  5. Effect of stress on the critical current of NbTi multifilamentary composite wire

    International Nuclear Information System (INIS)

    Ekin, J.W.; Fickett, F.R.; Clark, A.F.

    1977-01-01

    Superconducting composites within large-scale magnets can be subjected to high stresses. These stresses arise from several sources, chief among them being the winding tension and prestressing during construction of the magnet, the thermomechanical forces incurred during thermal cycling to cryogenic temperatures, and especially in large-scale systems, the magnetomechanical forces generated when the magnet is energized. Typically, data on the critical-current characteristics of superconducting composites are obtained on wires that are in an unstressed state. Very little is known, however, about how the critical current behaves in wires experiencing stresses of the type described above. To measure these effects, short sample critical current tests were made under conditions simultaneously simulating the mechanical and magnetic environments of high-field superconducting magnets. The program was initiated both to form a basis for the fundamental understanding of stress effects on superconductor stability and to provide engineering data for optimizing design and construction of high-field magnets. The preliminary results indicate that NbTi multifilamentary superconducting composite wires are not characterized by a single critical current vs. field curve, but rather by a family of curves, each corresponding to a different operating stress level

  6. The Viability of Single Cancer Cells after Exposure to Hydrodynamic Shear Stresses in a Spiral Microchannel: A Canine Cutaneous Mast Cell Tumor Model

    Directory of Open Access Journals (Sweden)

    Dettachai Ketpun

    2017-12-01

    Full Text Available Our laboratory has the fundamental responsibility to study cancer stem cells (CSC in various models of human and animal neoplasms. However, the major impediments that spike our accomplishment are the lack of universal biomarkers and cellular heterogeneity. To cope with these restrictions, we have tried to apply the concept of single cell analysis, which has hitherto been recommended throughout the world as an imperative solution pack for resolving such dilemmas. Accordingly, our first step was to utilize a predesigned spiral microchannel fabricated by our laboratory to perform size-based single cell separation using mast cell tumor (MCT cells as a model. However, the impact of hydrodynamic shear stresses (HSS on mechanical cell injury and viability in a spiral microchannel has not been fully investigated so far. Intuitively, our computational fluid dynamics (CFD simulation has strongly revealed the formations of fluid shear stress (FSS and extensional fluid stress (EFS in the sorting system. The panel of biomedical assays has also disclosed cell degeneration and necrosis in the model. Therefore, we have herein reported the combinatorically detrimental effect of FSS and EFS on the viability of MCT cells after sorting in our spiral microchannel, with discussion on the possibly pathogenic mechanisms of HSS-induced cell injury in the study model.

  7. Experimental Study of Pressure Drop and Wall Shear Stress Characteristics of γ /Al2O3-Water Nanofluid in a Circular pipe under Turbulent flow induced vibration.

    Directory of Open Access Journals (Sweden)

    Adil Abbas AL-Moosawy

    2016-09-01

    Full Text Available Experimental study of γ /Al2O3 with mean diameter of less than 50 nm was dispersed in the distilled water that flows through a pipe consist of five sections as work station ,four sections made of carbon steel metal and one sections made of Pyrex glass pipe, with five nanoparticles volume concentrations of 0%,0.1%,0.2%,0.3%,and 0.4% with seven different volume flow rates 100, 200 , 300, 400, 500, 600 ,and 700ℓ/min were investigated to calculated pressure distribution for the cases without rubber ,with 3mm rubber and with 6mm rubber used to support the pipe. Reynolds number was between 20000 and 130000. Frequency value through pipe was measured for all stations of pipe for all cases. The results show that the pressure drop and wall shear stress of the nanofluid increase by increasing the nanoparticles volume concentrations or Reynolds number, the values of frequency through the pipe increase continuously when wall shear stress increases and the ratio of increment increases as nanofluid concentrations increase. Increasing of vibration frequency lead to increasing the friction factor between the pipe and the wall and thus increasing in pressure drop. Several equations between the wall shear stress and frequency for all volume concentration and for three cases without rubber, with rubber has 3mm thickness ,and with rubber has 6mm thickness. Finally, the results led to that γ /Al2O3 could function as a good and alternative conventional working fluid in heat transfer applications. A good agreement is seen between the experimental and those available in the literature

  8. Effect of the critical size of initial voids on stress-induced migration

    International Nuclear Information System (INIS)

    Aoyagi, Minoru

    2004-01-01

    The stress-induced migration phenomenon is one of the problems related to the reliability of metal interconnections in semiconductor devices. This phenomenon causes voids and fractures in interconnections. The basic feature of this phenomenon is vacancy migration to minute initial voids. Expanding initial voids grow into larger voids and fractures. The purpose of this work is to theoretically clarify the effects of residual thermal stress and void surface stress on the behavior of the initial voids which exist immediately after a passivation process. Using a spherical metal sample with a spherical void under external stress, vacancy absorption or emission was investigated between the void surface and the sample surface. The behavior of vacancies and atoms was also investigated in interconnections under residual thermal stress. We show that the void or sample surface becomes a vacancy sink or source, depending on the mutual relationship between the surface stress due to the surface-free energy and the residual thermal stress. We also reveal that the initial voids, which exist immediately after a passivation process, grow into larger voids and fractures when the size of the initial voids exceeds the critical size. If the size of the initial void can be controlled to below the critical size, voids and fractures do not occur

  9. Feasibility of Residual Stress Nondestructive Estimation Using the Nonlinear Property of Critical Refraction Longitudinal Wave

    Directory of Open Access Journals (Sweden)

    Yu-Hua Zhang

    2017-01-01

    Full Text Available Residual stress has significant influence on the performance of mechanical components, and the nondestructive estimation of residual stress is always a difficult problem. This study applies the relative nonlinear coefficient of critical refraction longitudinal (LCR wave to nondestructively characterize the stress state of materials; the feasibility of residual stress estimation using the nonlinear property of LCR wave is verified. The nonlinear ultrasonic measurements based on LCR wave are conducted on components with known stress state to calculate the relative nonlinear coefficient. Experimental results indicate that the relative nonlinear coefficient monotonically increases with prestress and the increment of relative nonlinear coefficient is about 80%, while the wave velocity only decreases about 0.2%. The sensitivity of the relative nonlinear coefficient for stress is much higher than wave velocity. Furthermore, the dependence between the relative nonlinear coefficient and deformation state of components is found. The stress detection resolution based on the nonlinear property of LCR wave is 10 MPa, which has higher resolution than wave velocity. These results demonstrate that the nonlinear property of LCR wave is more suitable for stress characterization than wave velocity, and this quantitative information could be used for residual stress estimation.

  10. Coefficient of Friction Patterns Can Identify Damage in Native and Engineered Cartilage Subjected to Frictional-Shear Stress

    Science.gov (United States)

    Whitney, G. A.; Mansour, J. M.; Dennis, J. E.

    2015-01-01

    The mechanical loading environment encountered by articular cartilage in situ makes frictional-shear testing an invaluable technique for assessing engineered cartilage. Despite the important information that is gained from this testing, it remains under-utilized, especially for determining damage behavior. Currently, extensive visual inspection is required to assess damage; this is cumbersome and subjective. Tools to simplify, automate, and remove subjectivity from the analysis may increase the accessibility and usefulness of frictional-shear testing as an evaluation method. The objective of this study was to determine if the friction signal could be used to detect damage that occurred during the testing. This study proceeded in two phases: first, a simplified model of biphasic lubrication that does not require knowledge of interstitial fluid pressure was developed. In the second phase, frictional-shear tests were performed on 74 cartilage samples, and the simplified model was used to extract characteristic features from the friction signals. Using support vector machine classifiers, the extracted features were able to detect damage with a median accuracy of approximately 90%. The accuracy remained high even in samples with minimal damage. In conclusion, the friction signal acquired during frictional-shear testing can be used to detect resultant damage to a high level of accuracy. PMID:25691395

  11. Coefficient of Friction Patterns Can Identify Damage in Native and Engineered Cartilage Subjected to Frictional-Shear Stress.

    Science.gov (United States)

    Whitney, G A; Mansour, J M; Dennis, J E

    2015-09-01

    The mechanical loading environment encountered by articular cartilage in situ makes frictional-shear testing an invaluable technique for assessing engineered cartilage. Despite the important information that is gained from this testing, it remains under-utilized, especially for determining damage behavior. Currently, extensive visual inspection is required to assess damage; this is cumbersome and subjective. Tools to simplify, automate, and remove subjectivity from the analysis may increase the accessibility and usefulness of frictional-shear testing as an evaluation method. The objective of this study was to determine if the friction signal could be used to detect damage that occurred during the testing. This study proceeded in two phases: first, a simplified model of biphasic lubrication that does not require knowledge of interstitial fluid pressure was developed. In the second phase, frictional-shear tests were performed on 74 cartilage samples, and the simplified model was used to extract characteristic features from the friction signals. Using support vector machine classifiers, the extracted features were able to detect damage with a median accuracy of approximately 90%. The accuracy remained high even in samples with minimal damage. In conclusion, the friction signal acquired during frictional-shear testing can be used to detect resultant damage to a high level of accuracy.

  12. Evaluation of stress distribution due to shearing in non-oriented electrical steel by using synchrotron radiation

    Directory of Open Access Journals (Sweden)

    Yoshiaki Zaizen

    2016-05-01

    Full Text Available The influence of the shearing process on the iron loss of non-oriented electrical steels with grain sizes of 10 μm-150 μm was investigated. The deterioration ratio of iron loss was clearly smaller in sample with small grain sizes. The droop height, reflecting the amount of plastic deformation, displayed a good relationship with the deterioration of iron loss under the effect of the material grain size. To clarify the strain distribution around the sheared edge, the elastic strain in a sheet sample with the thickness of 0.30 mm and grain size of 10 μm was evaluated by using synchrotron radiation. The width of the region of elastic strain due to shearing was two or three times of the material thickness. The results of the plastic strain distribution obtained by the measurements were then used to estimate the iron loss deterioration rate in 5 mm width sheared samples. The estimated loss deteriotation coincided with the actual measured iron loss.

  13. Evaluation of stress distribution due to shearing in non-oriented electrical steel by using synchrotron radiation

    Energy Technology Data Exchange (ETDEWEB)

    Zaizen, Yoshiaki, E-mail: y-zaizen@jfe-steel.co.jp; Omura, Takeshi; Senda, Kunihiro [Steel Research Laboratory, JFE Steel Corporation, Kawasakidori 1,Mizushima, Kurashiki,712-8511 (Japan); Fukumura, Masaru [Steel Research Laboratory, JFE Steel Corporation, Kawasaki, Kanagawa 210-0855 (Japan); Toda, Hiroaki [Steel Business Planning Dept, JFE Steel Corporation, Tokyo 100-0011 (Japan)

    2016-05-15

    The influence of the shearing process on the iron loss of non-oriented electrical steels with grain sizes of 10 μm-150 μm was investigated. The deterioration ratio of iron loss was clearly smaller in sample with small grain sizes. The droop height, reflecting the amount of plastic deformation, displayed a good relationship with the deterioration of iron loss under the effect of the material grain size. To clarify the strain distribution around the sheared edge, the elastic strain in a sheet sample with the thickness of 0.30 mm and grain size of 10 μm was evaluated by using synchrotron radiation. The width of the region of elastic strain due to shearing was two or three times of the material thickness. The results of the plastic strain distribution obtained by the measurements were then used to estimate the iron loss deterioration rate in 5 mm width sheared samples. The estimated loss deteriotation coincided with the actual measured iron loss.

  14. Oscillatory fluid flow induces the osteogenic lineage commitment of mesenchymal stem cells: The effect of shear stress magnitude, frequency, and duration.

    Science.gov (United States)

    Stavenschi, Elena; Labour, Marie-Noelle; Hoey, David A

    2017-04-11

    A potent regulator of bone anabolism is physical loading. However, it is currently unclear whether physical stimuli such as fluid shear within the marrow cavity is sufficient to directly drive the osteogenic lineage commitment of resident mesenchymal stem cells (MSC). Therefore, the objective of the study is to employ a systematic analysis of oscillatory fluid flow (OFF) parameters predicted to occur in vivo on early MSC osteogenic responses and late stage lineage commitment. MSCs were exposed to OFF of 1Pa, 2Pa and 5Pa magnitudes at frequencies of 0.5Hz, 1Hz and 2Hz for 1h, 2h and 4h of stimulation. Our findings demonstrate that OFF elicits a positive osteogenic response in MSCs in a shear stress magnitude, frequency, and duration dependent manner that is gene specific. Based on the mRNA expression of osteogenic markers Cox2, Runx2 and Opn after short-term fluid flow stimulation, we identified that a regime of 2Pa shear magnitude and 2Hz frequency induces the most robust and reliable upregulation in osteogenic gene expression. Furthermore, long-term mechanical stimulation utilising this regime, elicits a significant increase in collagen and mineral deposition when compared to static control demonstrating that mechanical stimuli predicted within the marrow is sufficient to directly drive osteogenesis. Copyright © 2017. Published by Elsevier Ltd.

  15. Aerobic exercise acutely prevents the endothelial dysfunction induced by mental stress among subjects with metabolic syndrome: the role of shear rate.

    Science.gov (United States)

    Sales, Allan R K; Fernandes, Igor A; Rocha, Natália G; Costa, Lucas S; Rocha, Helena N M; Mattos, João D M; Vianna, Lauro C; Silva, Bruno M; Nóbrega, Antonio C L

    2014-04-01

    Mental stress induces transient endothelial dysfunction, which is an important finding for subjects at cardiometabolic risk. Thus, we tested whether aerobic exercise prevents this dysfunction among subjects with metabolic syndrome (MetS) and whether an increase in shear rate during exercise plays a role in this phenomenon. Subjects with MetS participated in two protocols. In protocol 1 (n = 16), endothelial function was assessed using brachial artery flow-mediated dilation (FMD). Subjects then underwent a mental stress test followed by either 40 min of leg cycling or rest across two randomized sessions. FMD was assessed again at 30 and 60 min after exercise or rest, with a second mental stress test in between. Mental stress reduced FMD at 30 and 60 min after the rest session (baseline: 7.7 ± 0.4%, 30 min: 5.4 ± 0.5%, and 60 min: 3.9 ± 0.5%, P exercise prevented this reduction (baseline: 7.5 ± 0.4%, 30 min: 7.2 ± 0.7%, and 60 min: 8.7 ± 0.8%, P > 0.05 vs. baseline). Protocol 2 (n = 5) was similar to protocol 1 except that the first period of mental stress was followed by either exercise in which the brachial artery shear rate was attenuated via forearm cuff inflation or exercise without a cuff. Noncuffed exercise prevented the reduction in FMD (baseline: 7.5 ± 0.7%, 30 min: 7.0 ± 0.7%, and 60 min: 8.7 ± 0.8%, P > 0.05 vs. baseline), whereas cuffed exercise failed to prevent this reduction (baseline: 7.5 ± 0.6%, 30 min: 5.4 ± 0.8%, and 60 min: 4.1 ± 0.9%, P exercise prevented mental stress-induced endothelial dysfunction among subjects with MetS, and an increase in shear rate during exercise mediated this effect.

  16. Stress Induced Hyperglycemia and the Subsequent Risk of Type 2 Diabetes in Survivors of Critical Illness

    Science.gov (United States)

    Plummer, Mark P.; Finnis, Mark E.; Phillips, Liza K.; Kar, Palash; Bihari, Shailesh; Biradar, Vishwanath; Moodie, Stewart; Horowitz, Michael; Shaw, Jonathan E.; Deane, Adam M.

    2016-01-01

    Objective Stress induced hyperglycemia occurs in critically ill patients who have normal glucose tolerance following resolution of their acute illness. The objective was to evaluate the association between stress induced hyperglycemia and incident diabetes in survivors of critical illness. Design Retrospective cohort study. Setting All adult patients surviving admission to a public hospital intensive care unit (ICU) in South Australia between 2004 and 2011. Patients Stress induced hyperglycemia was defined as a blood glucose ≥ 11.1 mmol/L (200 mg/dL) within 24 hours of ICU admission. Prevalent diabetes was identified through ICD-10 coding or prior registration with the Australian National Diabetes Service Scheme (NDSS). Incident diabetes was identified as NDSS registration beyond 30 days after hospital discharge until July 2015. The predicted risk of developing diabetes was described as sub-hazard ratios using competing risk regression. Survival was assessed using Cox proportional hazards regression. Main Results Stress induced hyperglycemia was identified in 2,883 (17%) of 17,074 patients without diabetes. The incidence of type 2 diabetes following critical illness was 4.8% (821 of 17,074). The risk of diabetes in patients with stress induced hyperglycemia was approximately double that of those without (HR 1.91 (95% CI 1.62, 2.26), phyperglycemia identifies patients at subsequent risk of incident diabetes. PMID:27824898

  17. Formation mechanisms of the powder porosity generated in the neighborhood of the shear plane

    International Nuclear Information System (INIS)

    Makino, K.; Kuramitsu, K.; Hoshikawa, H.; Mori, H.

    1988-01-01

    In recent years, the sophisticated technology on the process of powder feeding, packing, mixing, and compacting, by which homogeneous powder products can be manufactured in fine ceramics and electronics industries, is being established. And, in order to develop the technology, it is necessary to make clear the formation mechanism of powder porosity in the neighborhood of shear plane generated in the powder bed. However, this has not yet been sufficiently elucidated. In this paper, a single-plane shear tester which can simultaneously measure three quantities of stress, strain, and the powder porosity in the neighborhood of shear plane, was devised by using an X-ray radiograph system, and these three quantities were systematically measured under various shearing conditions. Next, a formation model of the powder porosity in the neighborhood of shear plane, composed of powder yield locus, critical state line, and Mohr stress semi, was experimentally checked by the three measured quantities mentioned above

  18. Predictors of post-traumatic stress disorder following critical illness: A mixed methods study.

    Science.gov (United States)

    Battle, Ceri E; James, Karen; Bromfield, Tom; Temblett, Paul

    2017-11-01

    Post-traumatic stress disorder has been reported in survivors of critical illness. The aim of this study was to investigate the predictors of post-traumatic stress disorder in survivors of critical illness. Patients attending the intensive care unit (ICU) follow-up clinic completed the UK-Post-Traumatic Stress Syndrome 14-Questions Inventory and data was collected from their medical records. Predictors investigated included age, gender, Apache II score, ICU length of stay, pre-illness psychopathology; delirium and benzodiazepine administration during ICU stay and delusional memories of the ICU stay following discharge. A total of 198 patients participated, with 54 (27%) patients suffering with post-traumatic stress disorder. On multivariable logistic regression, the significant predictors of post-traumatic stress disorder were younger age, lower Apache II score, pre-illness psychopathology and delirium during the ICU stay. The predictors of post-traumatic stress disorder in this study concur with previous research however a lower Apache II score has not been previously reported.

  19. [Prediabetes as a riskmarker for stress-induced hyperglycemia in critically ill adults].

    Science.gov (United States)

    García-Gallegos, Diego Jesús; Luis-López, Eliseo

    2017-01-01

    It is not known if patients with prediabetes, a subgroup of non-diabetic patients that usually present hyperinsulinemia, have higher risk to present stress-induced hyperglycemia. The objective was to determine if prediabetes is a risk marker to present stress-induced hyperglycemia. Analytic, observational, prospective cohort study of non-diabetic critically ill patients of a third level hospital. We determined plasmatic glucose and glycated hemoglobin (HbA1c) at admission to diagnose stress-induced hyperglycemia (glucose ≥ 140 mg/dL) and prediabetes (HbA1c between 5.7 and 6.4%), respectively. We examined the proportion of non-prediabetic and prediabetic patients that developed stress hyperglycemia with contingence tables and Fisher's exact test for nominal scales. Of 73 patients studied, we found a proportion of stress-induced hyperglycemia in 6.6% in those without prediabetes and 61.1% in those with prediabetes. The Fisher's exact test value was 22.46 (p Prediabetes is a risk marker for stress-induced hyperglycemia in critically ill adults.

  20. Absolute hypoxic exercise training enhances in vitro thrombin generation by increasing procoagulant platelet-derived microparticles under high shear stress in sedentary men.

    Science.gov (United States)

    Chen, Yu-Wen; Chen, Yi-Ching; Wang, Jong-Shyan

    2013-05-01

    HS (high shear) stress associated with artery stenosis facilitates TG (thrombin generation) by increasing the release of procoagulant PDMPs (platelet-derived microparticles). Physical exercise and hypoxia may paradoxically modulate vascular thrombotic risks. The aim of the present study was to investigate how exercise training with/without hypoxia affected TG mediated by PDMPs under physio-pathological shear flows. A total of 75 sedentary males were randomly divided into five groups (n=15 in each group): 21% O2 [NC (normoxic control)] or 15% O2 [HC (hypoxic control)] at rest or were trained at 50% of peak work rate under 21% O2 [NT (normoxic training)] or 15% O2 [HAT (hypoxic-absolute training)], or 50% of HR (heart rate) reserve under 15% O2 [HRT (hypoxic-relative training)] for 30 min/day, 5 days/week for 4 weeks. The PDMP characteristics and dynamic TG were measured by flow cytometry and thrombinography respectively. Before the intervention, strenuous exercise markedly increased the PDMP count (14.8%) and TG rate (19.5%) in PDMP-rich plasma at 100 dynes/cm2 of shear stress (Pexercise. Conversely, HAT notably promoted the PDMP count (37.3%) and TG rate (38.9%) induced by HS (Pexercise. We conclude that both HRT and NT depress similarly HS-mediated TG during exercise, but HAT accelerates the prothrombotic response to vigorous exercise. These findings provide new insights into how exercise training under a hypoxic condition influences the risk of thrombosis associated with stenotic arteries.

  1. Low intensity shear stress increases endothelial ELR+ CXC chemokine production via a focal adhesion kinase-p38{beta} MAPK-NF-{kappa}B pathway.

    Science.gov (United States)

    Shaik, Sadiq S; Soltau, Thomas D; Chaturvedi, Gaurav; Totapally, Balagangadhar; Hagood, James S; Andrews, William W; Athar, Mohammad; Voitenok, Nikolai N; Killingsworth, Cheryl R; Patel, Rakesh P; Fallon, Michael B; Maheshwari, Akhil

    2009-02-27

    CXC chemokines with a glutamate-leucine-arginine (ELR) tripeptide motif (ELR(+) CXC chemokines) play an important role in leukocyte trafficking into the tissues. For reasons that are not well elucidated, circulating leukocytes are recruited into the tissues mainly in small vessels such as capillaries and venules. Because ELR(+) CXC chemokines are important mediators of endothelial-leukocyte interaction, we compared chemokine expression by microvascular and aortic endothelium to investigate whether differences in chemokine expression by various endothelial types could, at least partially, explain the microvascular localization of endothelial-leukocyte interaction. Both in vitro and in vivo models indicate that ELR(+) CXC chemokine expression is higher in microvascular endothelium than in aortic endothelial cells. These differences can be explained on the basis of the preferential activation of endothelial chemokine production by low intensity shear stress. Low shear activated endothelial ELR(+) CXC chemokine production via cell surface heparan sulfates, beta(3)-integrins, focal adhesion kinase, the mitogen-activated protein kinase p38beta, mitogen- and stress-associated protein kinase-1, and the transcription factor.

  2. Determination of threshold shear stress to drag particles in cuttings bed; Determinacao da tensao de cisalhamento minima para arraste de particulas em um leito fluidizado

    Energy Technology Data Exchange (ETDEWEB)

    Loureiro, Bruno Venturini; Siqueira, Renato do Nascimento [Faculdade do Centro Leste (UCL), Serra, ES (Brazil). Lab. de Fenomenos de Transporte], e-mail: brunovl@ucl.br, e-mail: renatons@ucl.br

    2006-07-01

    Drilling of horizontal wells for oil and gas production needs an efficient cleaning process due to settling of particles removed during the drilling process, which settles on the inferior part of the annular space between the drilling column and the walls of the well. The erosion of the bed is an important physical phenomenon to petroleum and gas industry since it can improve the opening of the wells. This work aims to estimate the threshold shear stress necessary to start the erosion process in a sediment bed. An experimental apparatus was built from simplifications of the problem in order to measure the flow rate and identify the beginning of the process. The experiment consists of a rectangular duct with aspect ratio ({lambda} = h/b) of 1/3 and non dimensional length (L{sup *} = L/h) of 75. The sediment bed to be eroded was placed at 60< x{sup *}<66. Using the flow rate and the boundary conditions, a discretization of the problem was carried out to permit a computational solution using the finite volume method and hence, determine the shear stress. This work used particles with up to 3.0 mm and modeled the flow considering a bed with equivalent roughness. (author)

  3. The influence of fluid shear stress on the expression of Cbfa1 in MG-63 cells cultured under different gravitational conditions

    Science.gov (United States)

    Zhang, S.; Wang, B.; Cao, X. S.; Yang, Z.; Sun, X. Q.

    2008-12-01

    AuthorPurposeThis study was aimed to explore the effect of flow shear stress on the expression of Cbfa1 in human osteosarcoma cells and to survey its functional alteration in simulated microgravity. After culture for 48 h in two different gravitational environments, i.e. 1 G terrestrial gravitational condition and simulated microgravity condition, human osteosarcoma cells (MG-63) were treated with 0.5 or 1.5 Pa fluid shear stress (FSS) in a flow chamber for 15, 30, and 60 min, respectively. The total RNA in cells was isolated. RT-PCR analysis was made to examine the gene expression of Cbfa1. The total protein of cells was extracted and the expression of Cbfa1 protein was detected by means of Western blotting. ResultsMG-63 cells cultured in 1 G condition reacted to FSS treatment with an enhanced expression of Cbfa1. Compared with no-FSS control group, Cbfa1 mRNA expression increased significantly at 30 and 60 min with the treatment of FSS ( P cells cultured in simulated microgravity by using clinostat, the expression of Cbfa1 was significantly different between 1 G and simulated microgravity conditions at each test time ( P cultured in simulated microgravity, Cbfa1 mRNA expression increased significantly at 30 and 60 min with the treatment of FSS ( P osteosarcoma cells. And this inducible function of FSS was adversely affected by simulated microgravity.

  4. Heat transfer, velocity-temperature correlation, and turbulent shear stress from Navier-Stokes computations of shock wave/turbulent boundary layer interaction flows

    Science.gov (United States)

    Wang, C. R.; Hingst, W. R.; Porro, A. R.

    1991-01-01

    The properties of 2-D shock wave/turbulent boundary layer interaction flows were calculated by using a compressible turbulent Navier-Stokes numerical computational code. Interaction flows caused by oblique shock wave impingement on the turbulent boundary layer flow were considered. The oblique shock waves were induced with shock generators at angles of attack less than 10 degs in supersonic flows. The surface temperatures were kept at near-adiabatic (ratio of wall static temperature to free stream total temperature) and cold wall (ratio of wall static temperature to free stream total temperature) conditions. The computational results were studied for the surface heat transfer, velocity temperature correlation, and turbulent shear stress in the interaction flow fields. Comparisons of the computational results with existing measurements indicated that (1) the surface heat transfer rates and surface pressures could be correlated with Holden's relationship, (2) the mean flow streamwise velocity components and static temperatures could be correlated with Crocco's relationship if flow separation did not occur, and (3) the Baldwin-Lomax turbulence model should be modified for turbulent shear stress computations in the interaction flows.

  5. A Critical SUMO1 Modification of LKB1 Regulates AMPK Activity during Energy Stress

    KAUST Repository

    Ritho, Joan

    2015-07-23

    SUMOylation has been implicated in cellular stress adaptation, but its role in regulating liver kinase B1 (LKB1), a major upstream kinase of the energy sensor AMP-activated protein kinase (AMPK), is unknown. Here, we show that energy stress triggers an increase in SUMO1 modification of LKB1, despite a global reduction in both SUMO1 and SUMO2/3 conjugates. During metabolic stress, SUMO1 modification of LKB1 lysine 178 is essential in promoting its interaction with AMPK via a SUMO-interacting motif (SIM) essential for AMPK activation. The LKB1 K178R SUMO mutant had defective AMPK signaling and mitochondrial function, inducing death in energy-deprived cells. These results provide additional insight into how LKB1-AMPK signaling is regulated during energy stress, and they highlight the critical role of SUMOylation in maintaining the cell’s energy equilibrium.

  6. A Critical SUMO1 Modification of LKB1 Regulates AMPK Activity during Energy Stress

    KAUST Repository

    Ritho, Joan; Arold, Stefan T.; Yeh, Edward  T.H.

    2015-01-01

    SUMOylation has been implicated in cellular stress adaptation, but its role in regulating liver kinase B1 (LKB1), a major upstream kinase of the energy sensor AMP-activated protein kinase (AMPK), is unknown. Here, we show that energy stress triggers an increase in SUMO1 modification of LKB1, despite a global reduction in both SUMO1 and SUMO2/3 conjugates. During metabolic stress, SUMO1 modification of LKB1 lysine 178 is essential in promoting its interaction with AMPK via a SUMO-interacting motif (SIM) essential for AMPK activation. The LKB1 K178R SUMO mutant had defective AMPK signaling and mitochondrial function, inducing death in energy-deprived cells. These results provide additional insight into how LKB1-AMPK signaling is regulated during energy stress, and they highlight the critical role of SUMOylation in maintaining the cell’s energy equilibrium.

  7. Fast assessment of the critical principal stress direction for multiple separated multiaxial loadings

    Directory of Open Access Journals (Sweden)

    M. Cova

    2015-07-01

    Full Text Available The critical plane calculation for multiaxial damage assessment is often a demanding task, particularly for large FEM models of real components. Anyway, in actual engineering requests, sometime, it is possible to take advantage of the specific properties of the investigated case. This paper deals with the problem of a mechanical component loaded by multiple, but “time-separated”, multiaxial external loads. The specific material damage is dependent from the max principal stress variation with a significant mean stress sensitivity too. A specifically fitted procedure was developed for a fast computation, at each node of a large FEM model, of the direction undergoing the maximum fatigue damage; the procedure is defined according to an effective stress definition based on the max principal stress amplitude and mean value. The procedure is presented in a general form, applicable to the similar cases.

  8. Discontinuous Shear Thickening and Dilatancy: Frictional Effects in Viscous Suspensions

    Science.gov (United States)

    Morris, Jeffrey

    2015-03-01

    Shear thickening in concentrated suspensions has been well-known for quite a long time, yet a firm consensus on the basis for very abrupt or ``discontinuous'' shear thickening (DST) seen in suspensions of large solid fraction, ϕ, has not been reached. This work addresses the DST phenomenon, and proposes a simulation method based in the Stokesian Dynamics algorithm to explore the role of various forces between the particles, including hydrodynamic, conservative potential, and frictional interactions. This work shows that allowance for friction between spherical particles suspended in a viscous liquid causes a significant reduction in the jamming solid fraction of the mixture, ϕmax, taken as the maximum fraction at which the suspension will flow. A consequence of this is a shifting of the singularity in the effective viscosity, η, to smaller ϕmax, and the frictional suspension has a larger viscosity than does the frictionless suspension of the same solid fraction, as is clear from the standard empirical modeling of η (ϕ) =(1 - ϕ /ϕmax) - α , α ~ 2 . When a counterbalancing repulsive force between the particles, representative for example of charge-induced repulsion, is incorporated in the dynamics, the mixture undergoes a transition from frictionless to frictional interactions, and from low to high effective viscosity, at a critical shear rate. Comparison with experimental data shows remarkable agreement in the features of DST captured by the method. The basic algorithm and results of both rate-controlled and stress-controlled simulations will be presented. Like the shear stress, the magnitude of the normal stress exerted by the suspended particles also increases abruptly at the critical shear rate, consistent with the long-standing notion that dilatancy and shear-thickening are synonymous. We will show that considering all shear thickening materials as dilatant is a misconception, but demonstrate the validity of the connection of dilatancy with DST in

  9. Experimental and numerical determination of critical stress intensity factor of aluminum curved thin sheets under tensile stress

    Energy Technology Data Exchange (ETDEWEB)

    Heidarvand, Majid; Soltani, Naser; Hajializadeh, Farshid [University of Tehran, Tehran (Iran, Islamic Republic of)

    2017-05-15

    We determined the fracture toughness of aluminum curved thin sheets using tensile stress tests and finite element method. We applied Linear elastic fracture mechanics (LEFM) and Feddersen procedure to evaluate stress intensity factor of the samples with central wire-cut cracks and fatigue cracks with different lengths to investigate the notch radius effect. Special fixture design was utilized to establish uniform stress distribution at the crack zone. Less than 9 % difference was found between the wire-cut and the fatigue cracked samples. Since generating central fatigue crack with different lengths required so much effort, wire-cut cracked samples were used to determine critical stress intensity factor. Finite element analysis was also performed on one-quarter of the specimen using both the singular Borsum elements and the regular isoparametric elements to further investigate fracture toughness of the samples. It was observed that the singular elements presented better results than the isoparametric ones. A slight difference was also found between the results obtained from finite element method using singular elements and the experimental results.

  10. Critical Incident Stress Management (CISM) in complex systems: cultural adaptation and safety impacts in healthcare.

    Science.gov (United States)

    Müller-Leonhardt, Alice; Mitchell, Shannon G; Vogt, Joachim; Schürmann, Tim

    2014-07-01

    In complex systems, such as hospitals or air traffic control operations, critical incidents (CIs) are unavoidable. These incidents can not only become critical for victims but also for professionals working at the "sharp end" who may have to deal with critical incident stress (CIS) reactions that may be severe and impede emotional, physical, cognitive and social functioning. These CIS reactions may occur not only under exceptional conditions but also during every-day work and become an important safety issue. In contrast to air traffic management (ATM) operations in Europe, which have readily adopted critical incident stress management (CISM), most hospitals have not yet implemented comprehensive peer support programs. This survey was conducted in 2010 at the only European general hospital setting which implemented CISM program since 2004. The aim of the article is to describe possible contribution of CISM in hospital settings framed from the perspective of organizational safety and individual health for healthcare professionals. Findings affirm that daily work related incidents also can become critical for healthcare professionals. Program efficiency appears to be influenced by the professional culture, as well as organizational structure and policies. Overall, findings demonstrate that the adaptation of the CISM program in general hospitals takes time but, once established, it may serve as a mechanism for changing professional culture, thereby permitting the framing of even small incidents or near misses as an opportunity to provide valuable feedback to the system. Copyright © 2014 Elsevier Ltd. All rights reserved.

  11. Experimental study and FEM simulation of the simple shear test of cylindrical rods

    Science.gov (United States)

    Wirti, Pedro H. B.; Costa, André L. M.; Misiolek, Wojciech Z.; Valberg, Henry S.

    2018-05-01

    In the presented work an experimental simple shear device for cutting cylindrical rods was used to obtain force-displacement data for a low-carbon steel. In addition, and FEM 3D-simulation was applied to obtain internal shear stress and strain maps for this material. The experimental longitudinal grid patterns and force-displacement curve were compared with numerical simulation results. Many aspects of the elastic and plastic deformations were described. It was found that bending reduces the shear yield stress of the rod material. Shearing starts on top and bottom die-workpiece contact lines evolving in an arc-shaped area. Due to this geometry, stress concentrates on the surface of the rod until the level of damage reaches the critical value and the fracture starts here. The volume of material in the plastic zone subjected to shearing stress has a very complex shape and is function of a dimensionless geometrical parameter. Expressions to calculate the true shear stress τ and strain γ from the experimental force-displacement data were proposed. The equations' constants are determined by fitting the experimental curve with the stress τ and strain γ simulation point tracked data.

  12. Effects of Stress on Critical Care Nurses: A National Cross-Sectional Study.

    Science.gov (United States)

    Vahedian-Azimi, Amir; Hajiesmaeili, Mohammadreza; Kangasniemi, Mari; Fornés-Vives, Joana; Hunsucker, Rita L; Rahimibashar, Farshid; Pourhoseingholi, Mohammad A; Farrokhvar, Leily; Miller, Andrew C

    2017-01-01

    Health care is a demanding field, with a high level of responsibility and exposure to emotional and physical danger. High levels of stress may result in depression, anxiety, burnout syndrome, and in extreme cases, post-traumatic stress disorder. The aim of this study was to determine which personal, professional, and organizational variables are associated with greater perceived stress among critical care nurses for purposes of developing integrative solutions to decrease stress in the future. We conducted a correlation research survey using a cross-sectional design and an in-person survey method. The questionnaire consisted of 2 parts: (1) socioeconomic, professional, and institutional variables and (2) work stressors. Surveys were conducted between January 1, 2011, and December 1, 2015. Multistage cluster random sampling was utilized for data collection. Inclusion criteria were (1) age ≥18 years, (2) registered nurse, (3) works in the intensive care unit (ICU), and (4) willing and able to complete the survey. We surveyed 21 767 ICU nurses in Iran and found that male sex, lower levels of peer collaboration, working with a supervisor in the unit, nurse-patient ratios, and working in a surgical ICU were positively associated with greater stress levels. Increasing age and married status were negatively associated with stress. Intensive care unit type (semi-closed vs open), ICU bed number, shift time, working on holidays, education level, and demographic factors including body mass index, and number of children were not significantly associated with stress levels. As the largest study of its kind, these findings support those found in various European, North, and South American studies. Efforts to decrease workplace stress of ICU nurses by focusing on facilitating peer collaboration, improving resource availability, and staffing ratios are likely to show the greatest impact on stress levels.

  13. About a mechanism of the influence of shear stress for viscosity of the blood in vessels of small diameter

    Directory of Open Access Journals (Sweden)

    Лев Николаевич Катюхин

    2014-12-01

    Full Text Available It is proposed a physiological and experimentally confirmed explanation of Fåhraeus-Lindqvist-effect in capillaries using the profile analyses of osmotic deformability of red blood cells. It was shown the dose-dependent change of the erythrocytes deformability in the stage of isotropic spheres after forming artificial water pores (nystatin and occlusion (PbCl2 of available pores. The Sigma-effect reducing of hematocrit and viscosity in a shear flow of blood through the vessels of a small diameter was conditioned by the interchange of liquid phase between the erythrocyte and the plasma.

  14. Study on shear properties of coral sand under cyclic simple shear condition

    Science.gov (United States)

    Ji, Wendong; Zhang, Yuting; Jin, Yafei

    2018-05-01

    In recent years, the ocean development in our country urgently needs to be accelerated. The construction of artificial coral reefs has become an important development direction. In this paper, experimental studies of simple shear and cyclic simple shear of coral sand are carried out, and the shear properties and particle breakage of coral sand are analyzed. The results show that the coral sand samples show an overall shear failure in the simple shear test, which is more accurate and effective for studying the particle breakage. The shear displacement corresponding to the peak shear stress of the simple shear test is significantly larger than that corresponding to the peak shear stress of the direct shear test. The degree of particle breakage caused by the simple shear test is significantly related to the normal stress level. The particle breakage of coral sand after the cyclic simple shear test obviously increases compared with that of the simple shear test, and universal particle breakage occurs within the whole particle size range. The increasing of the cycle-index under cyclic simple shear test results in continuous compacting of the sample, so that the envelope curve of peak shearing force increases with the accumulated shear displacement.

  15. Shear strength behavior of geotextile/geomembrane interfaces

    Directory of Open Access Journals (Sweden)

    Belén M. Bacas

    2015-12-01

    Full Text Available This paper aims to study the shear interaction mechanism of one of the critical geosynthetic interfaces, the geotextile/geomembrane, typically used for lined containment facilities such as landfills. A large direct shear machine is used to carry out 90 geosynthetic interface tests. The test results show a strain softening behavior with a very small dilatancy (<0.5 mm and nonlinear failure envelopes at a normal stress range of 25–450 kPa. The influences of the micro-level structure of these geosynthetics on the macro-level interface shear behavior are discussed in detail. This study has generated several practical recommendations to help professionals to choose what materials are more adequate. From the three geotextiles tested, the thermally bonded monofilament exhibits the best interface shear strength under high normal stress. For low normal stress, however, needle-punched monofilaments are recommended. For the regular textured geomembranes tested, the space between the asperities is an important factor. The closer these asperities are, the better the result achieves. For the irregular textured geomembranes tested, the nonwoven geotextiles made of monofilaments produce the largest interface shear strength.

  16. Effects of increasing the allowable compressive stress at release on the shear strength of prestressed concrete girders.

    Science.gov (United States)

    2008-09-01

    In recent years, several research projects have been conducted to study the feasibility of increasing the allowable : compressive stress in concrete at prestress transfer, currently defined as 0.60f'ci in the AASHTO LRFD Bridge : Design Specification...

  17. Evaluation of ring shear testing as a characterization method for powder flow in small-scale powder processing equipment

    DEFF Research Database (Denmark)

    Søgaard, Søren Vinter; Pedersen, Troels; Allesø, Morten

    2014-01-01

    Powder flow in small-scale equipment is challenging to predict. To meet this need, the impact of consolidation during powder flow characterization, the level of consolidation existing during discharge of powders from a tablet press hopper and the uncertainty of shear and wall friction measurements...... normal stress were approximately 200Pa and 114Pa, respectively, in the critical transition from the converging to the lower vertical section of the hopper. The lower limit of consolidation for the shear and wall friction test was approximately 500Pa and 200Pa, respectively. At this consolidation level......, the wall and shear stress resolution influences the precision of the measured powder flow properties. This study highlights the need for an improved experimental setup which would be capable of measuring the flow properties of powders under very small consolidation stresses with a high shear stress...

  18. Viscosity of dilute suspensions of rigid bead arrays at low shear: accounting for the variation in hydrodynamic stress over the bead surfaces.

    Science.gov (United States)

    Allison, Stuart A; Pei, Hongxia

    2009-06-11

    In this work, we examine the viscosity of a dilute suspension of irregularly shaped particles at low shear. A particle is modeled as a rigid array of nonoverlapping beads of variable size and geometry. Starting from a boundary element formalism, approximate account is taken of the variation in hydrodynamic stress over the surface of the individual beads. For a touching dimer of two identical beads, the predicted viscosity is lower than the exact value by 5.2%. The methodology is then applied to several other model systems including tetramers of variable conformation and linear strings of touching beads. An analysis is also carried out of the viscosity and translational diffusion of several dilute amino acids and diglycine in water. It is concluded that continuum hydrodynamic modeling with stick boundary conditions is unable to account for the experimental viscosity and diffusion data simultaneously. A model intermediate between "stick" and "slip" could possibly reconcile theory and experiment.

  19. Effect of simulated weightlessness on the expression of Cbfα1 induced by fluid shear stress in MG-63 osteosarcoma cells.

    Science.gov (United States)

    Yang, Z.; Zhang, S.; Wang, B.; Sun, X. Q.

    Objective The role of mechanical load in the functional regulation of osteoblasts becomes an emphasis in osseous biomechanical researches recently This study was aim to explore the effect of flow shear stress on the expression of Cbf alpha 1 in human osteosarcoma cells and to survey its functional alteration in simulated weightlessness Method After cultured for 72 h in two different gravitational environments i e 1G terrestrial gravitational condition and simulated weightlessness condition human osteosarcoma cells MG-63 were treated with 0 5 Pa or 1 5 Pa fluid shear stress FSS in a flow chamber for 15 30 60 min respectively The total RNA in cells was isolated Transcription PCR analysis was made to examine the gene expression of Cbf alpha 1 And the total protein of cells was extracted and the expression of Cbf alpha 1 protein was detected by means of Western Blotting Results MG-63 cultured in 1G condition reacted to FSS treatment with an enhanced expression of Cbf alpha 1 Compared with no FSS control group Cbf alpha 1 mRNA and protein expression increased significantly at 30 and 60 min with the treatment of FSS P 0 01 And there was remarkable difference on the Cbf alpha 1 mRNA and protein expression between the treatments of 0 5 Pa and 1 5 Pa FSS at 30 min or 60 min P 0 01 As to the osteoblasts cultured in simulated weightlessness by using clinostat the expression of Cbf alpha 1 was significantly different between 1G and simulated weightlessness conditions at each test time P 0 05 Compared with no FSS

  20. Computational analysis of integrated biosensing and shear flow in a microfluidic vascular model

    Science.gov (United States)

    Wong, Jeremy F.; Young, Edmond W. K.; Simmons, Craig A.

    2017-11-01

    Fluid flow and flow-induced shear stress are critical components of the vascular microenvironment commonly studied using microfluidic cell culture models. Microfluidic vascular models mimicking the physiological microenvironment also offer great potential for incorporating on-chip biomolecular detection. In spite of this potential, however, there are few examples of such functionality. Detection of biomolecules released by cells under flow-induced shear stress is a significant challenge due to severe sample dilution caused by the fluid flow used to generate the shear stress, frequently to the extent where the analyte is no longer detectable. In this work, we developed a computational model of a vascular microfluidic cell culture model that integrates physiological shear flow and on-chip monitoring of cell-secreted factors. Applicable to multilayer device configurations, the computational model was applied to a bilayer configuration, which has been used in numerous cell culture applications including vascular models. Guidelines were established that allow cells to be subjected to a wide range of physiological shear stress while ensuring optimal rapid transport of analyte to the biosensor surface and minimized biosensor response times. These guidelines therefore enable the development of microfluidic vascular models that integrate cell-secreted factor detection while addressing flow constraints imposed by physiological shear stress. Ultimately, this work will result in the addition of valuable functionality to microfluidic cell culture models that further fulfill their potential as labs-on-chips.

  1. Critical Review of EU Nuclear Stress Tests in Bulgaria, Hungary, Romania and Ukraine

    International Nuclear Information System (INIS)

    Becker, O.; Lorenz, P.; Wallner, A.

    2012-01-01

    In March 2011, the core melt accidents at the Fukushima Daiichi 1 nuclear power plant (NPP) showed the world that the nuclear industry cannot prevent severe accidents from happening. The accidents in Japan proved that highly unlikely accidents cannot be excluded. The Fukushima accident confirmed the mistrust towards nuclear power among the Japanese but also European citizens. In reaction to the devastating nuclear disaster in Japan the European Council concluded in March 2011, that the safety of all EU nuclear plants should be reviewed on the basis of a comprehensive and transparent risk and safety assessment ('stress tests'). The EU Nuclear Safety Regulators Group – ENSREG took over the task to provide a “targeted reassessment of the safety margins of nuclear power plants”, thus examining whether the safety margins which were used in the licensing of NPPs are sufficient to cover unexpected events. It is important to understand that the stress tests could not take into account all key safety issues such as the capability to prevent accidents - the scope of the stress tests defined by ENSREG didn´t promise to deliver a comprehensive risk and safety assessment. According to some observers the stress tests were mainly set up to improve the confidence in the safety of European NPPs. Nevertheless, the stress tests provided some interesting findings concerning safety: This study assesses the safety of the nuclear power plants in Bulgaria, Hungary, Romania and the Ukraine. The introduction contains an overview of the content and procedure of the stress tests. This “Critical Review of the Stress Tests” is based on the national stress tests reports written by the national nuclear safety authorities and on the Peer review country reports attached to the Peer review report - Stress tests performed on European nuclear power plants written by the Peer review Teams, the Peer Review Board respectively, and endorsed by ENSREG [ENSREG 2012a, ENSREG 2012c]. It

  2. Critical Review of EU Nuclear Stress Tests in Bulgaria, Hungary, Romania and Ukraine

    Energy Technology Data Exchange (ETDEWEB)

    Becker, O.; Lorenz, P.; Wallner, A.

    2012-07-01

    In March 2011, the core melt accidents at the Fukushima Daiichi 1 nuclear power plant (NPP) showed the world that the nuclear industry cannot prevent severe accidents from happening. The accidents in Japan proved that highly unlikely accidents cannot be excluded. The Fukushima accident confirmed the mistrust towards nuclear power among the Japanese but also European citizens. In reaction to the devastating nuclear disaster in Japan the European Council concluded in March 2011, that the safety of all EU nuclear plants should be reviewed on the basis of a comprehensive and transparent risk and safety assessment ('stress tests'). The EU Nuclear Safety Regulators Group – ENSREG took over the task to provide a “targeted reassessment of the safety margins of nuclear power plants”, thus examining whether the safety margins which were used in the licensing of NPPs are sufficient to cover unexpected events. It is important to understand that the stress tests could not take into account all key safety issues such as the capability to prevent accidents - the scope of the stress tests defined by ENSREG didn´t promise to deliver a comprehensive risk and safety assessment. According to some observers the stress tests were mainly set up to improve the confidence in the safety of European NPPs. Nevertheless, the stress tests provided some interesting findings concerning safety: This s