• Proceedings of the KAIS Fall Conference
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• 2008.11a
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• pp.72-75
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• 2008

기존 배전계통에 있어서의 조류는 변전소에서 선로말단을 향한 단방향이지만, 분산전원이 연계된 배전계통의 경우에는 그 출력 용량의 여부에 따라 양방향의 전력조류가 발생할 가능성이 있어, 계통운용상 여러가지의 문제점이 야기될 수 있다. 특히, 태양광발전이 배전선로에 연계되어 운전되는 경우, 동일 뱅크의 타배전선로에서 사고가 발생하면 태양광발전이 연계된 건전한 배전선로의 보호협조기기(리클로져)가 오동작하는 사고가 발생하는 경우가 실 계통에서 빈번하게 발생하고 있다. 이에 의하여 건전한 선로의 부하가 정전을 경험하는 심각한 문제점이 발생한다. 따라서 본 논문에서는 MATLAB/SIMULINK을 이용하여 모델링과 시뮬레이션을 수행하여, 상기의 보호협조기의 오동작 문제점을 분석하고 해석하였다.

• Wind and Structures
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• v.9 no.5
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• pp.357-367
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• 2006

Unsteady 3D Reynolds Averaged Navier-Stokes (URANS) solver is used to simulate the turbulent flow past an isolated prismatic cylinder at Re=37,400. The aspect ratio of height to base width of the body is 5. The turbulence closure is achieved through a non-linear $k-{\varepsilon}$ model. The applicability of this model to predict unsteady forces associated with this flow is examined. The study shows that the present URANS solver with standard wall functions predicts all the major unsteady phenomena showing closer agreement with experiment. This investigation concludes that URANS simulations with the non-linear $k-{\varepsilon}$ model as a turbulence closure provides a promising alternative to LES with view to study flows having complex features.

• Journal of Microbiology
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• v.33 no.4
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• pp.334-338
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• 1995

The electrophoretic karyotypes of 6 species in different Fusarium sections were examined by using contour-clamped homogeneous electric field (CHEF) gel electrophoresis. Intact chromosomal DNA was prepared from protoplasts and up to 9 distinct bands were separated on 0.7% or 0.8% agarose gel under several different conditions. Putative chromosome numbers varied from 6 to 9 amd polymorphic karyotypes were observed in different Fusarium sections. Using Schizosaccharomyces pombe and Saccharomyces cerevisiae chromosomes as standards, the sizes of the Fusarium spp. chromosomes were estimated. The electrophoretic karyotypes of F. moniliforme and F. subglutinans (section Liseola) were similar. Unidentified filamentour fungi, F. beomiforme was much closer to F. axysporum (section Elecgans) in karyotype and the karyotypes of F. napiforme were more similar to those of section Liseola than any other sections. F. graminearum (section Discolor) had a distinctive electrophoretic karyotype.

• Journal of Mechanical Science and Technology
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• v.17 no.8
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• pp.1226-1233
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• 2003

Experimental heat transfer data for single-phase water flow in the annuli with corrugated inner tubes are presented. In the annuli with parallel flow, ten different annular arrangements are considered. For water flow rate in 1,700${\gamma}$$\^$*/). As P/e becomes closer to 8 in the range below the radius ratio (${\gamma}$$\^$*/) of 0.5, Nusselt numbers increase. However, Nusselt numbers decrease in the range above the radius ratio (${\gamma}$$\^$*/) of 0.5 because flow reattachment position becomes farther in the narrower clearance.

• Nutrition Research and Practice
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• v.6 no.5
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• pp.436-443
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• 2012

Previous Korean total diet studies (KTDSs) have estimated dietary exposure to toxic chemicals based on 110-120 representative foods selected from over 500 foods appeared in the Korea National Health & Nutrition Examination Surveys (KNHANES), which would result in a possible underestimation. In order to find measures for a closer-to-real estimate of dietary exposure to heavy metals, this study examined the feasibility of mapping foods to the representative foods in the KTDS by comparing estimates. In mapping, those foods not analyzed in the 2009 KTDS (443 out of 559 foods appeared in the 2007 KNHANES) were mapped to the 114 representative foods used in the 2009 KTDS based on the closeness in regards to biological systematics and morphological similarity. Dietary exposures to total mercury and lead were re-estimated using the content of total mercury and lead in 114 foods analyzed in the 2009 KTDS, food intake, and individual's own body weight for respondents in the 2007 KNHANES instead of mean body weight of Koreans used in the 2009 KTDS. The re-estimates of exposure with mapping were approximately 50% higher than the original estimates reported in the 2009 KTDS. In addition, mapping enabled the comparison of percentile distribution of the exposure among populations of different age groups. In conclusion, estimates via mapping resulted in a more comprehensive estimation of dietary exposure to heavy metals present in foods that Koreans consume.

• Journal of computational fluids engineering
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• v.17 no.3
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• pp.68-74
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• 2012

Near-wall effect on wakes behind particles is one of the important factors in precise tracking of particles in turbulent flows. However, most aerodynamic force models for particles did not fully consider the wall effect. In the present study, we focused on changes of hydrodynamic forces acting on a particle depending on wall proximity. To this end, we developed an immersed boundary method with multi-direct forcing incorporated to a fully implicit decoupling procedure for incompressible flows. We validate the present immersed boundary method through two-dimensional simulations of flow over a circular cylinder. Comprehensive parametric studies on the effect of the wall proximity on the drag and lift forces acting on an immersed circular cylinder in a channel flow are performed in order to investigate general flow patterns behind the circular cylinder for a wide range of Reynolds number (0.01 ${\leq}$ Re ${\leq}$ 200). As the cylinder is closer to the wall, the drag coefficient decreases while the lift coefficient increases with a local maximum. Maximum drag and lift coefficients for different wall proximities decrease with increment of Reynolds number. Normalized drag and lift coefficients by their maximum values show universal correlations between the coefficients and wall proximity in a low Reynolds number regime (Re ${\leq}$ 1).

• Journal of the Korean Society of Visualization
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• v.16 no.1
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• pp.30-36
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• 2018

In the present study, we investigate the flow characteristics of a quadrotor UAV in a hovering mode by measuring multiple two-dimensional velocity fields in the wake. The experiment is conducted at Re = 24,000 in a chamber large enough to neglect the ground effect, where Re is the Reynolds number based on the rotor chord length and the rotor tip speed. The rotational speed of the rotor is determined by an optical tachometer so that the lift force can be balanced with the weight of the UAV. The velocity field measured on the center plane of the rotor shows that the vortices are shedding from the tip of the rotor, inducing large fluctuations in the streamwise velocity along the wake shear layer. The strength of the rotor-tip vortex shedding is asymmetric with respect to the rotor axis due to the interaction between the rotor and the wake centerline of each rotor is inclined to the center of the UAV due to the pressure difference caused by the induced velocity. The wake from each rotor moves closer to each other while traveling in the streamwise direction, and then is merged together inducing large fluctuations in the transverse velocity. Due to the wake merging, on the center plane of the UAV, the velocity increases in the streamwise direction showing two-peak structure in the streamwise velocity contours.

• Korean journal of food and cookery science
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• v.28 no.5
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• pp.623-628
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• 2012

The study was about to produce red ginsengs easily, using a household microwave oven to promote the consumption of fresh ginsengs in the home. Producing red ginsengs with a household microwave oven 'defrost function' takes 13 minutes (A), 'cook function' 6 minutes (B), and finally, 'defrost function' 44 minutes (C). For characteristics of microwave-produced red ginsengs, total saponin loss, color of powder, polyphenol content and saponin composition were compared with common red ginsengs. The color test for red ginseng powder showed that the color of household microwave-produced 6-minute cooked red ginseng (B) or 44-minute defrosted red ginseng (C) was closer to that of the common red ginsengs (E). The total saponin content in water eluted during red ginseng production showed that the saponin loss in microwave red ginseng was negligible compared to the common red ginsengs. Microwave red ginsengs showed no difference in phenol content that of the and higher total ginsenoside content than common red ginsengs. The ginsenoside $Rg_1$, Re, Rf, $Rg_2+Rh_1$, $Rb_1$, Rc, $Rb_2$, $Rb_3$, Rd and $Rg_3$ contents of microwave red ginsengs (A, B) were higher compared to that of the common red ginsengs; the ginsenoside Re, Rc, $Rb_2$, $Rb_3$, Rd and $Rg_3$ contents of 44-minute defrosted red ginseng (C) were higher compared to the common red ginsengs. It is considered that red ginseng production, using microwave oven at home, can be a fast and convenient way to produce highly functional red ginsengs with high ginsenoside content.

• Restorative Dentistry and Endodontics
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• v.35 no.2
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• pp.106-115
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• 2010

The purpose of this study was to evaluate the microtensile bond strength (${\mu}TBS$), failure modes and bonding interfaces of self-etching and three self-adhesive resin cements to dentin and indirect composite resin. Cylindrical composite blocks (Tescera, Bisco Inc.) were luted with resin cements (PA: Panavia F 2.0, Kuraray Medical Inc., RE: RelyX Unicem Clicker, 3M ESPE., MA: Maxem, Kerr Co., BI: BisCem, Bisco Inc.) on the prepared occlusal dentin surfaces of 20 extracted molars. After storage in distilled water for 24 h, $1.0\;mm\;{\times}\;1.0\;mm$ composite-dentin beams were prepared. ${\mu}TBS$ was tested at a cross-head speed of 0.5 mm/min. Data were analyzed with one-way ANOVA and Tukey's HSD test. Dentin sides of all fractured specimens and interfaces of resin cements-dentin or resin cements-composite were examined at FESEM (Field Emission-Scanning Electron Microscope). In conclusion, PA and RE showed higher bond strength and closer adaptation than MA and BI when indirect composite blocks were luted to dentin using a self-etching and three self-adhesive resin cements.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.33 no.4
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• pp.264-271
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• 2009

Characteristics of a counter flowing diffusion flame, which is formulated by an oppositely-injected methane-jet flow in a narrow channel of a uniform air flow. The location of the flame fronts and the flame lengths were compared by changing the flow rates of fuel. To distinguish the effects of the narrow channel on the diffusion flame, a numerical simulation for an ideal two-dimensional flame was conducted. Overall trends of the flame behavior were similar in both numerical and experimental results. With the increase of the ratio of jet velocity to air velocity flame front moved farther upstream. It is thought that the flow re-direction in the channel suppresses fuel momentum more significantly due to the higher temperature and increased viscosity of burned gas. Actual flames in a narrow channel suffer heat loss to the ambient and it has finite length of diffusion flame in contrast to the numerical results of infinite flame length. Thus a convective heat loss was additionally employed in numerical simulation and closer results were obtained. These results can be used as basic data in development of a small combustor of a nonpremixed flame.