• Journal of Mechanical Science and Technology
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• v.15 no.7
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• pp.889-894
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• 2001

In this study, the performances of various turbulence closure models are evaluated in the calculation of a transonic flow over axisymmetric bump. k-$\varepsilon$, explicit algebraic stress, and two Reynolds stress models, i.e., GL model proposed by Gibson & Launder and SSG model proposed by Speziale, Sarkar and Gatski, are chosen as turbulence closure models. SSG Reynolds stress model gives best predictions for pressure coefficients and the location of shock. The results with GL model also show quite accurate prediction of pressure coefficients down-stream of shock wave. However, in the predictions of mean velocities and turbulent stresses, the results are not so satisfactory as in the prediction of pressure coefficients.

• Journal of Korean Ophthalmic Optics Society
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• v.7 no.2
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• pp.209-215
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• 2002

This study investigated the crystal growth, crystalline structure and the basic optical properties of $SnSe/BaF_2$ epilayers. The SnSe epilayer was grown on $BaF_2$(111) insulating substrates using a hot wall epitaxy(HWE) technique. It was found from the analysis of X-ray diffraction patterns that $SnSe/BaF_2$ epilayer was growing to single crystal with orthorhombic structure oriented [111] along the growth direction. Using Rutherford back scattering(RBS), the atomic ratios of the SnSe was found to be stoichiometric, almost 50 : 50. The best values for the full width at half maximum (FWHM) of the DCXRD was 163 arcsec for SnSe epilarer. The epilayer-thickness dependence of the FWHM of the DCXRD shows that the quality of the $SnSe/BaF_2$ is as expected. The dielectric function ${\varepsilon}$(E) of a semiconductor is closely related to its electronic energy band structure and such relation can be drawn from features around the critical points in the optical spectra. The real and imaginary parts(${\varepsilon}_1$ and ${\varepsilon}_2$) of the dielectric function ${\varepsilon}$ of SnSe were measured. These data are analyzed using a theoretical model known as the model dielectric function(MDF). The optical constants related to dielectric function such as the complex refractive index(n*-n+ik), absorption coefficient (${\alpha}$) and normal- incidence reflectivity (R) are also presented for $SnSe/BaF_2$.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.4
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• pp.541-550
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• 1997

Computational and experimental investigations on the three-dimensional flowfield through an automotive cooling fan are carried out in this work. Steady, incompressible, three-dimensional, turbulent flow through a rotating axial-flow fan is analyzed with Reynolds averaged Navier-Stokes equations and standard k-.epsilon. turbulence model. The governing equations are discretized with finite-volume approximations in non-orthogonal curvilinear coordinates. Computational static pressures on the casing wall agree well with the experimental data which are measured in this work. And, they are sensitive to the change of tip clearance. The flowfield is not significantly affected by the thickness of the blade. The k-.omega. model gives the static pressure rise on the casing wall which is similar to that with the k-.epsilon. model.

• The KSFM Journal of Fluid Machinery
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• v.13 no.4
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• pp.25-30
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• 2010

Flow analysis and performa nce evaluation have been performed for a ventilation axial-flow fan with different positions of the motor. Two different positions of motor have been tested; one is in front of the impeller and the other is behind the impeller. Flow analyses are performed by solving three-dimensional Reynolds-averaged Navier-Stokes equations through a finite-volume solver. Preliminary numerical calculations are carried out to test the performances of different turbulence models, i.e., SST model, k-$\omega$ model, and k-$\varepsilon$ model with and without using empirical wall function in the flow analysis. The validation of numerical analyses has been performed in comparison with the experimental data. The numerical results for the performance characteristics of the ventilation axial-flow fan with two different positions of the motor have been presented.

• Journal of computational fluids engineering
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• v.6 no.2
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• pp.22-31
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• 2001

The two-dimensional unsteady incompressible viscous flow behind rectangular bluff bodies between two parallel plates was analyzed numerically. The steady state flow and the vortex flow behind rectangular bluff bodies in the channel were investigated for two regimes i.e., the laminar(Re = 100, 300, 500) and the turbulent flows(Re = 10⁴∼10/sup 6/). The vortex shedding was generated by a physical disturbance(6%) numerically imposed at the rear of the bluff bodies for a short time. It was observed that the perturbed flow became periodic after a transient period. And in the case of unsteady inflow, the sinusoidal pulsatile flow was applied as the inlet condition in the turbulent flow of Reynolds number of 1.0×10/sup 5/. FLUENT code was employed to solve the problems. The power-law scheme was used to get stable linearized equations and the PISO algorithm was applied to finding the solution of them.

• Economic and Environmental Geology
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• v.28 no.2
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• pp.139-145
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• 1995

Tungsten skarn mineralization of the Sangdong mine is localized in the interbedded limestone layers of the Myobong Slate Formation and in the limestone of the Pungchon Limestone Formation of Cambrian age. Fluid inclusion, gas composition and Nd-Sr isotope for granites and skarns have been investigated. Gas compositions show $CO_2$ rich in the Sangdong granite and CH, rich in the Nonggeori and Eopyeong granites. The initial $^{87}Sr/^{86}Sr$ and $^{143}Nd/^{144}Nd$ ratios of the Sangdong granites have 0.714~0.716(${\varepsilon}_{Sr}$=138~162) and 0.51173~0.51178(${\varepsilon}_{Nd}$=-14.4~15.5), respectively. And their two stage model ages range from 1687 to 1764 Ma. The granite characterized by high strontium initial ratios and negative eNd value could have originated from the old continental crust source. Low homogenization temperature of the Sangdong granite having $203{\sim}296^{\circ}C$ with 1.9~9.2 NaCl equiv. wt% indicates the post-magmatic hydrothermal alteration temperature. Skarn ore fluid responsible for tungsten mineralization has been evolved from CH, rich fluid of early pyroxene garnet skarn to $CO_2$ rich later quartz-mica skarn.

• Korean Journal of Pharmacognosy
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• v.44 no.2
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• pp.118-124
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• 2013

Mast cells is the key effector cells for IgE-mediated allergic responses. In this study, we investigated whether Rhus trichocarpa extract (RT) inhibited IgE-mediated allergic responses in mast cells and an allergic animal model. We further tried to find its mechanism of action in mast cells. We found that RT suppressed antigen-stimulated degranulation and production of TNF-${\alpha}$ and IL-4 in rat basophilic leukemia (RBL)-2H3 mast cells and bone marrow-derived mast cells (BMMC), as well as IgE-mediated passive cutaneous anaphylaxis (PCA) in mice. As the mechanism of action of RT, it inhibited the activation of spleen tyrosine kinase (Syk), a pivotal signaling molecule for activation of mast cells and that of LAT, a downstream adaptor molecule of Syk in $Fc{\varepsilon}RI$-mediated signal pathways. RT also suppressed the activation of mitogen-activated protein (MAP) kinases and Akt. The current results demonstrated for the first time that RT has the anti-allergic effect through inhibiting degranulation and secretion of cytokines by suppression of Syk in antigen-stimulated mast cells. Therefore, RT might be useful for allergic diseases.

• Journal of Korea Water Resources Association
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• v.37 no.12
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• pp.1065-1074
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• 2004

This study aims at the introduction of new catchment shape descriptor, developed by Moussa(2003), based on equivalent ellipse and the assessment of its hydrologic applicability. Two descriptors a+b and a+b+${\varepsilon}OM$were correlated to the lag time and those were applied to the estimation of representative values of Nash model parameters. They are applied in order to examine the practicality to 3 catchments in Korea, catchments in Korea, respectively, i.e. Pyeongchanggang catchment in Han river, Bocheongcheon catchment in Geum river and Wicheon catchment in Nakdong river. As a result both of two descriptors show higher correlations to the lag lime than classical geomorphologic factors and hereby Moussa's suggestion(2003) is confirmed. For the sake of simplicity the former is recommended. Also representative IUHs derived from this study show consistent basin response characteristics. It is desirable to conduct further more case studies on many other basins.

• Analytical Science and Technology
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• v.20 no.4
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• pp.339-346
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• 2007

To search the ninhydrin derivatives that have high chromogenic and fluorogenic properties, molecular holographic quantitative structure property relationship (HQSPR) models on the reactivity between glycine and ninhydrin analogues as latent fingerprint detector were derived and investigated quantitatively. The ${\varepsilon}LUMO$ (e.v.) energy of ninhydrin molecule was an important factor to reactivity of ninhydrin. And, it is suggested that the nucleophilic reaction by orbital-controlled reaction from the frontier molecular orbital (FMO) interaction between glycine and ninhydrin derivatives was more superior than that of electrophilic reaction by charged controlled reaction. The analytical results in atomic contribution maps also shows that the reactivity of ninhydrin was increased by meta-substituents as strong electron withdrawing groups on the benzo ring. Therefore, it is sugested by HQSPR and QSPR model that the 5,6-dinitroninhydrin molecule would increase the reactivity as much as three times as compared to none substituted ninhydrin molecule.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.6
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• pp.813-821
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• 1997

Three-dimensional turbulent incompressible flow through the tip clearance of a linear turbine rotor cascade with high turning angle has been analyzed numerically. As a preliminary study to predict the tip clearance loss realistically, a generalized k-.epsilon. model derived by RNG (renormalized group) method is used for the modeling of Reynolds stresses to account for the strain rate of turbulent flow. The effects of the tip clearance flow on the passage vortex, the total pressure loss are considered qualitatively. The existences of vena contract and tip clearance vortex have been confirmed and it has been shown that as the size of the tip clearance increases, the accumulated flow through the tip clearance and the total pressure loss downstream of the cascade increase.