• Journal of computational fluids engineering
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• v.4 no.3
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• pp.63-70
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• 1999

A Direct simulation Monte-Carlo (DSMC) code is developed, which employs the Monte-Carlo statistical sampling technique to investigate hypersonic rarefied gas flows accompanying chemical reactions. The DSMC method is a numerical simulation technique for analyzing the Boltzmann equation by modeling a real gas flow using a representative set of molecules. Due to the limitations in computational requirements. the present method is applied to a flow around a simple two-dimensional object in exit velocity of 7.6 km/sec at an altitude of 90 km. For the calculation of chemical reactions an air model with five species (O₂, N₂, O, N, NO) and 19 chemical reactions is employed. The simulated result showed various rarefaction effects in the hypersonic flow with chemical reactions.

• Proceedings of the Materials Research Society of Korea Conference
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• 2003.03a
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• pp.110-110
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• 2003

LED의 품위가 높아지고 고 광방출을 위한 전기적 출력이 높아질수록 LED 자체에서 발생하는 열이 아주 중요한 요소로 제출되고 있다. 본 실험에서는 여러 가지 LED 모델의 열적특성을 분석하여 가장 최적화된 모델을 생성하려고 한다 실험방법은 유한요소법을 사용하는 소프트웨어 ANSYS를 이용하여 여러 가지 LED 모델을 생성하고 입력조건과 경계조건을 집어넣고 해석한 후 결과를 분석하여 각종 모델의 최고 온도를 알 수 있다 그 다음 여러 가지 모델의 최고 온도를 비교하여 가장 최적화된 LED모델을 발견하고 또한 열적으로 영향 주는 요소들을 도출 해낼 수 있다. 이러한 분석은 금후 고휘도 LED램프생산성에 중요한 기반기술로 사료된다.

• 유체기계공업학회:학술대회논문집
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• 2006.08a
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• pp.147-150
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• 2006

A new class of heat transfer fluid with higher thermal conductivity, called nanofluids has been developed by Dr. S. Choi about decade ago. Many exciting experimental and theoretical results have been reported worldwide to predict the thermal conductivity enhancement of nanofluids, however, they sometimes show excessive large discrepancies between each other. This kind of disagreements in thermal conductivity data is partly ascribable to the accuracy of the measuring apparatus, that is, mostly used THM(transient hot-wire method). New thermal conductivity measuring method whose principle is different from that of conventional THM is proposed in this article and measurements and uncertainty analysis were made for the three nanofluid samples with different particle concentration of pure, 2% and 4% of AlN nanofluids.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.13 no.2
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• pp.285-289
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• 1995

This paper describes the determination of geoid using height data measured by GPS and Spirit Levelling. The GPS data of the 88 stations were used to determine the geoid undulation (N) which can be easily obtained by subtracting the orthometric height(H) from the ellipsoidal height(h). From the geoid undulation (N) calculated at each station mentioned above, geoid plots with a contour interval of 0.25 m were drawn using two interpolation methods. The following interpolation methods were applied and compared with each other: Minimum Curvature Method and Least Squares Fitted Plane. Comparison between geometric geoid and gravimetric geoid undulation by FFT technique was carried out.

• Journal of Advanced Marine Engineering and Technology
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• v.31 no.5
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• pp.522-530
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• 2007

In order to extract small hydropower in the very low specific speed range of $n_s<10$, a Positive Displacement Turbine (PDT) has been proposed and steady performances have been determined experimentally. However, the suppression of large pressure fluctuation is inevitable for practical application of PDT. Therefore, present study adopted 4-lobe helical type robe to reduce the pressure fluctuation. The results show that 4-lobe helical type robe can be adopted to suppress the pressure fluctuation drastically. Moreover, efficiency and unit power of the turbine with newly proposed 4-lobe helical type lobe are higher than those of the turbine with 3-lobe straight type robe.

• Korean Journal of Materials Research
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• v.18 no.10
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• pp.535-541
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• 2008

Growth behavior of InGaN/GaN self-assembled quantum dots (QDs) was investigated with respect to different growth parameters in low pressure metalorganic chemical vapor deposition. Locally formed examples of three dimensional InGaN islands were confirmed from the surface observation image with increasing indium source ratio and growth time. The InGaN/GaN QDs were formed in Stranski-Krastanow (SK) growth mode by the continuous supply of metalorganic (MO) sources, whereas they were formed in the Volmer-Weber (V-W) growth mode by the periodic interruption of the MO sources. High density InGaN QDs with $1{\sim}2nm$ height and $40{\sim}50nm$ diameter were formed by the S-K growth mode. Dome shape InGaN dots with $200{\sim}400nm$ diameter were formed by the V-W growth mode. InN content in InGaN QDs was estimated to be reduced with the increase of growth temperature. A strong peak between 420-460 nm (2.96-2.70 eV) was observed for the InGaN QDs grown by S-K growth mode in photoluminescence spectrum together with the GaN buffer layer peak at 362.2 nm (3.41 eV).

• Journal of the Korean Ceramic Society
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• v.30 no.4
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• pp.265-272
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• 1993

Effect of mixing homogeneity in powder mixtures of Si3N4 and sintering additive (10mol% YAG) prepared by coprecipitation on the mechanical properties of pressureless-sintered body was investigated. Sintering was performed in a graphtie furnace at 1850℃ for 0.5h under 0.15MPa N2 atmosphere using Si3N4 powder bed. Results from the measurement of Young's modulus, Vickers hardness, 4-point-bending strength, and KIC for the coprecipitation-treated (CP) and the mechanically-mixed specimens(MM) showed that a remarkable improvement in flexural strength and Weibull parameter can be achieved for the CPspecimens: (677±68MPa, 12.0) for CP samples and (539±108MPa, 5.5) for MM. Other properties were almost same irrespective of preparation methods.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2006.05a
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• pp.308-313
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• 2006

The effect of coating time on surface properties of the TiN-coated high speed steel(SKH51) by arc ion plating is and presented in this paper. Surface roughness, micro-hardness, coated thickness, atomic distribution of TiN and adhesion strength are measured for various coating times. It has been shown that the coating time has a deep influence more than 60 minites on the micro-hardness, coated thickness, atomic distribution of Ti and adhesion strength of the SKH51 steels, but that the coating time has little influence on the surface roughness.

• The Korean Journal of Applied Statistics
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• v.3 no.2
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• pp.39-53
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• 1990

For the present study two sets of artificially unbalanced data of being $n_{ij}>0$ and ${n_{1j}}{/geq}0$ were used. The Hypotheses that are commonly used in ANOVA were examined by computing the sums of squares associated with the hypotheses under various postulated models, using Searle's R($\mid$)-notation.

• Korean Journal of Soil Science and Fertilizer
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• v.33 no.6
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• pp.405-415
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• 2000

To determine application rate of elemental sulfur to adjust pH of alkaline soil, buffer curve method was investigated. The elemental sulfur required to control pH 8.3 to pH 6.3 by buffer curve calculation was treated in two soils of silty loam and sandy loam, and the sulfur-mixed soils were moistened with 50% of water holding capacity during incubation of 6 weeks at $30^{\circ}C$. Soil pH was lowered with incubation and reached to target point after 4 weeks of incubation, and elemental sulfur was oxidised entirely to sulfate. This means that buffer curve has the accuracy to determine sulfur application rate in alkaline soil. However it is estimated that application rate of sulfur should be carefully determined in the field scale. Excess application of elemental sulfur resulted in extremely low soil pH and caused the hinderance of lettuce growth by nutritional imbalance and ion toxicity. To simplify the determination procedure of sulfur requirement, buffer curve method by addition of 0.1N-HCl solution as unit of mL was developed, it was compared with theroutine methods which diluted $H_2SO_4$ solution and $Ca(OH)_2$ are added as cmolc per kg soil to adjust each pH step. Buffer capacities, cmolc kg $soil^{-1}$ $pH^{-1}$, calculated from two buffer curves were not significantly different. The result indicates that buffer curve method by 0.1N-HCl can be used to adjust high pH of alkaline soil.