• Molecules and Cells
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• v.41 no.11
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• pp.964-970
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• 2018

Atherosclerosis preferentially involves in prone area of low and disturbed blood flow while steady and high levels of laminar blood flow are relatively protected from atherosclerosis. Disturbed flow induces endoplasmic reticulum (ER) stress and the unfolded protein response (UPR). ER stress is caused under stress that disturbs the processing and folding of proteins resulting in the accumulation of misfolded proteins in the ER and activation of the UPR. Prolonged or severe UPR leads to activate apoptotic signaling. Recent studies have indicated that disturbed flow significantly up-regulated $p-ATF6{\alpha}$, $p-IRE1{\alpha}$, and its target spliced XBP-1. However, the role of laminar flow in ER stress-mediated endothelial apoptosis has not been reported yet. The present study thus investigated the role of laminar flow in ER stress-dependent endothelial cell death. The results demonstrated that laminar flow protects ER stress-induced cleavage forms of PARP-1 and caspase-3. Also, laminar flow inhibits ER stress-induced $p-eIF2{\alpha}$, ATF4, CHOP, spliced XBP-1, ATF6 and JNK pathway; these effects are abrogated by pharmacological inhibition of PI3K with wortmannin. Finally, nitric oxide affects thapsigargin-induced cell death in response to laminar flow but not UPR. Taken together, these findings indicate that laminar flow inhibits UPR and ER stress-induced endothelial cell death via PI3K/Akt pathway.

• Journal of computational fluids engineering
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• v.19 no.3
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• pp.37-43
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• 2014

In this paper, hydraulic & thermal developing and fully developed laminar forced convection flow of a water-$Al_2O_3$ nanofluid in a circular horizontal tube with uniform heat flux at the wall, are investigated numerically. A single phase model employed with temperature independent properties. The thermal entrance length is presented in this paper. The variations of the convective heat transfer coefficient and shear stress are shown in the entrance region and fully developed region along different nanoparticles concentration and Reynolds numbers. Convective heat transfer coefficient for nanofluids is larger than that of the base fluid. It is shown that heat transfer is enhanced and shear stress is increased as the particle volume concentration increases. The heat transfer improves, as Reynolds number increases.

• Transactions of the Korean Society of Mechanical Engineers
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• v.11 no.1
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• pp.88-96
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• 1987

A method is presented to calculate the fiction factor and velocity distribution of asymmetric flow in rough channels and annuli. This method is derived from an assumption of linearly-varying shear stress which is different from Maubach's constant shear stress assumption. This method gives continuous velocity gradient at the position of maximum velocity and the predicted velocity profiles are in better agreements with experimental data than those obtained by Maubach's method. In this paper, a new correlation of roughness function is proposed and the predictions of friction factors by this correlation agree well with experimental data.

• Bulletin of the Korean Chemical Society
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• v.7 no.4
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• pp.257-262
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• 1986

Thixotropy is a time-dependent shear-thinning phenomenon. We derived a new thixotropic formula which is based on the generalized viscosity formula of Ree and Eyring, $f={\Sigma}\frac{X_i}{{\alpha}_i}sinh^{-1}$ () (Refer to the text concerning the notation.) The following is postulated: (1) thixotropy occurs when small flow units attached to a large flow unit separate from the latter under stress (2) elastic energy(${\omega}$) is stored on the large flow unit during the flow process, and (3) the stored energy contributes to decrease the activation energy for flow. A new thixotropic formula was derived by using these postulations, $f={\frac}{X_0{\beta}_0}{\alpha_0}{\dot{s}}+{\frac}{X_1{\beta}_1}{{\alpha}_1}{\dot{s}}+{\frac}{X_2}{{\alpha_x}}sinh^{-1}$[$({\beta}_0)_2$ exp $(-C_2{\dot{s}}^2/RT){\cdot}{\dot{s}}$] f is the shear stress, and s is the rate of shear. In case of concentrated solutions where the Newtonian flow units have little contribution to the viscosity of the system, the above equation becomes, $f=\frac{X_2}{\alpha_2}sinh^{-1}$[$({\beta}_0)_2$ exp $(-C_2{\dot{s}}^2/RT){\cdot}{\dot{s}}$]. In order to confirm these formulas, we applied to TiO2(anatase and rutile)-water, printing ink and mayonnaise systems. Good agreements between the experiment and theory were observed.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.2 no.2
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• pp.107-113
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• 2001

This work presents field-dependent Bingham and response characteristics of MR fluids under shear and flow modes. Two different types of magneto-viscometers are designed and manufactured for the shear and flow modes. respectively. For the MR fluid to be tested, MRF-132LD of Lord co. is employed. The field-dependent yield stress is experimentally distilled at various temperatures using the magneto-viscometers. Time responses of the MR fluids to step electric fields are also evaluated under two operating modes.

• Journal of Power System Engineering
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• v.5 no.1
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• pp.21-26
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• 2001

This paper represents the turbulent intensity, the turbulent kinetic energy and Reynolds shear stress in the X-Y plane of cone type swirl gas burner measured by using X-probe from the hot-wire anemometer system. The experiment is carried out at flowrate 350 and $450{\ell}/min$ respectively in the test section of subsonic wind tunnel. The turbulent intensity and the turbulent kinetic energy show that the maximum value is formed in the narrow slits distributed radially on the edge of a cone type swirl burner, hence, the combustion reaction is anticipated to occur actively near this region. And the turbulent intensities ${\upsilon}\;and\;{\omega}$ are disappeared faster than the turbulent intensity u due to the inclined flow velocity ejecting from the swirl vanes of a cone type baffle plate of burner. Moreover, the Reynolds shear stress $u{\upsilon}$ is distributed about three times as large as the Reynolds shear stress $u{\omega}$ in the outer region of the cone type gas burner.

• Journal of computational fluids engineering
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• v.16 no.4
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• pp.28-38
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• 2011

Large eddy simulation(LES) of fully developed turbulent pipe flow has been performed to investigate the effect of Reynolds number on the flow field at $Re_{\tau}$=180, 395, 590 based on friction velocity and pipe radius. A dynamic subgrid-scale model for the turbulent subgrid-scale stresses was employed to close the governing equations. The mean flow properties, mean velocity profiles and turbulent intensities obtained from the present LES are in good agreement with the previous numerical and experimental results currently available. The Reynolds number effects were observed in the mean velocity profile, root-mean-square of velocity fluctuations, Reynolds shear stress and turbulent viscosity.

• Journal of Biosystems Engineering
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• v.14 no.1
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• pp.33-40
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• 1989

The flow properties of water added com-cob-mix(CCM) were studied in order to provide basic information for designing its pumping system. For the study, a model system similar to actual situation was constructed. From the experiment, it can be concluded that the flow properties of the water added CCM has close relationship with its moisture content as follows; 1. The pressure drop caused by friction was very low when the moisture content of water added CCM was more than 70%. However, when the moisture content of the material is about 60%, the pressure drop increases up to 10 kPa/m at low pumping speed, and 20 kPa/m at high pumping speed, respectively. 2. The water added CCM having about 65% moisture content showed pseudo-plastic flow characteristics. 3. As the moisture content of the material decreases, the shear stress increases more rapidly than the shear rate does. Finally, below approximately 60% moisture, the shear stress becomes a linear relationship with the shear rate. 4. It was possible to pump the material having the moisture content down to 58% through a pipe having 80 mm diameter by a pump operating at 234 rpm. However, by either increasing the diameter of the pipe or decreasing the pumping speed, it can be possible to pump the material having lower moisture content than 55%.

• Korean Journal of Exercise Nutrition
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• v.23 no.1
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• pp.7-12
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• 2019

[Purpose] The purpose of the study was to determine the combined effects of resveratrol supplementation with high-flow LSS on mitochondrial biogenesis in human vascular endothelial cells. [Methods] Cultured human umbilical vein endothelial cells were treated with 20 μM of RSV. For the shear experiments, cells grown to a >90% confluence were exposed to physiological levels of LSS (5 to 20 dyne/cm2) for 12 to 36 hours using a cone and plate shear apparatus. Gene expressions were analyzed by western blotting. [Results] Depletion of mitochondrial integrity was directly associated with increase in endothelial activation/dysfunction. The expressions of mitochondrial biogenesis regulator genes, such as SIRT1, PGC-1α, and TFAM, and the mitochondrial contents were significantly increased after treatment with both resveratrol and high-flow LSS for 12 hours. However, supplementation of resveratrol to high-flow LSS for a prolonged duration had no synergistic effect on the levels of mitochondrial biogenesis regulator gene expressions and mitochondrial content compared to the LSS treatment alone. [Conclusion] The present study demonstrated that the supplementation of resveratrol to high-flow LSS has no synergistic effects on enhancing mitochondrial integrity in human vascular endothelial cells.

• Journal of the Korean Geotechnical Society
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• v.30 no.7
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• pp.5-15
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• 2014

Abandoned mine deposits are exposed to various physico-chemical geo-environmental hazards and disasters, such as acid mine drainage, water contamination, erosion, and landslides. This paper presents the ring shear characteristics of waste materials. The ring shear box with a rotatable O-ring was used in this study. Three tests were performed: (i) Shear stress-time relationship for given normal stress and shear speed, (ii) shear stress as a function of shear speed, and (iii) shear stress as a function of normal stress. For a given normal stress (50 kPa) and speed (0.1 mm/sec), the materials tested exhibit a strain softening behavior, regardless of drainage condition. The peak and residual shear stresses were determined for each normal stress and shear speed. The shear stress was measured when shear speed is equal to 0.01, 0.1, 1, 10, 50, 100 mm/sec or when normal stress is equal to 20, 40, 60, 80, 100, 150 kPa. From the test results, we found that the shear stress increases with increasing shear speed. The shear stress also increases with increasing normal stress. However, different types of shearing mode were observed in drained and undrained conditions. Under drained condition, particle crushing was observed from the shearing zone to the bottom of lower ring. Under undrained condition, particle crushing was observed only at the shearing zone, which has approximately 1 cm thick. It means that a significant high shear speed under undrained condition can result in increased landslide hazard.