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최익준(I. J. Choi),최호준(H. J. Choi),박훈재(H. J. Park),최석우(S. Choi),정택우(T. W. Jung),박동규(D. K. Park),최성규(S. K. Choi),임성주(S. J. Lim) 한국소성가공학회 2009 한국소성가공학회 학술대회 논문집 Vol.2009 No.5
In this work, closing behavior of the voids generated in a casting process was investigated for various parameters such as reductions in height, void size and billet rotation during hot open die forging process. The reduction in height and path schedule including the number of paths and billet rotation were chosen as key process variables to express the change of geometrical void shape and void closing behavior. On the other hand, values of die overlapping and die width ratio were set to be constant. Extend of void closure was observed and evaluated using tensile test and microscope. Based on the experimental result, it is ensured that void closure do not occur at 15% and 30% reduction in height as well as one or two rotations of a billet. The useful datum obtained from this study could be utilized to establish an optimum path schedule in the open die forging process.
천공유압드릴 장비에서 작업 동작에 따른 연비 측정 및 평가 기술 연구
최진구(J. G. Choi),강주영(J. Y. Kang),김종민(J. M. Kim),배종원(J. W. Bae),이충근(C. G. Lee),이정호(J. H. Lee),김주호(J. H. Kim),이대엽(D. Y. Lee),송윤우(Y. W. Song),김명보(M. B. Kim),조재상(J. S. Cho) 유공압건설기계학회 2017 유공압건설기계학회 학술대회논문집 Vol.2017 No.11
In order to improve the fuel economy of a hydraulic drilling machine, which consumes relatively large amount of fuel compared to other typical construction machinery, a comparison is made between gravimetric fuel consumption using mass flowmeter and CAN signal. And, since the data of CAN signal is close enough to the measured data of a flowmeter, fuel consumption at real work mode is measured and analyzed using CAN signals. A result show that drilling mode occupies about 67.4% of total fuel consumption. It is concluded that this work may contribute to enhance fuel economy of hydraulic drilling machines.
유병우(B.W. Ryu),한정만(J.M. Han),이동욱(D.W. Lee),이종달(J.D. Lee),이병희(B.H. Lee),최성욱(S.W. Choi),문건우(G.W. Moon) 전력전자학회 2009 전력전자학술대회 논문집 Vol.2009 No.1
최근 LCD 모니터, Note PC, 가정용 게임기, Mobile Phone, MP3 등의 소형 전자 제품의 사용이 증가함에 따라 이들 전자제품의 전원 공급에 필요한 다양한 AC/DC 어댑터가 요구된다. AC/DC 어댑터는 밀폐형의 구조를 가지므로, 열적인 문제 때문에 용량과 사이즈가 제한되어 왔다. 하지만 최근에는 소형전자제품의 용량이 점차 증가하고, 더불어 소비자의 휴대성 및 심미적 요구에 부응하기 위하여 소형 및 경량의 고밀도 AC/DC Adapter를 개발하여야 한다. 이를 위해서 높은 수준의 회로 설계 및 방열 기술이 필요하다. 본 논문에서는 Laptop PC에 적용되는 85W급 AC/DC Adapter용 고밀도전원을 개발하고 실험으로 검증하였다.
계단형 텅스텐 결정면의 질소 흡착에 관한 연구 : Ⅱ. W(210) 및 W(310)면
최대선(D. S. Choi),한종훈(J. H. Han),백선목(S. M. Paik),박노길(N. G. Park),김욕욱(Y. W. Kim),황정남(C. N. Whang) 한국진공학회(ASCT) 1996 Applied Science and Convergence Technology Vol.5 No.4
장전자 방출법으로 텡스텐 (210)면 및 (310)면(100)면의 질소 흡착에 의한 일함수의 변화에 heat of desorption을 측정하였으며 Thermal Desortion Spectra(TDS) 결과로부터 adsorption site를 예측하였다. 텅스텐 (210)면 및 (310)면에 에 질소가 흡착될 때 흡착율에 따라 일함수는 증가하다가 각 면에 대하여 흡착율 5 Langmuir일때 최대 변화량 0.29 eV및 0.20 eV에서 포화되었다. TDS 결과는 이 면들은 낮은 dose의 영역에서 각각 3개의 흡착 site가 있음을 보였으며 이 흡착 site들 중 α₁state의 spectrum의 강도는 (210)면에서 보다 (310)면에서 상대적으로 강해짐을 보였다. 또한 (210)와 (310)면의 α₁ 과 β₂ state의 흡착 site에 흡착된 질소의 dipole moment의 방향은 이 흡착 site들에 대응되는 (100)면의 α₁ 과 β₂state의 흡착 site에 흡착된 질소의 dipole moment의 방향과 반대 방향으로 측정되었으며 이 현상으로부터 질소의 상대적인 흡착 위치를 예측하였다. The heat of desorption and the work function change induced by nitrogen adsorption on the stepped tungstein surface planes, W(210) and W(310), are measured using the Field Electron Emission Microscope(FEM). The adsoption sites are predicted from the Thermal Desortion Spectra(TDS). The work function change of both W(210) and W(310) planes increase as increasing the nitrogen dose and saturates at the nitrogen dose about 5 Langmuir to 0.29 eV and 0.20 ev respectively. We find three adsorption site on each plane for the low dose range. The TDS result shows that the intensity of α₁, state on W(310) is much stronger than that of α₁ state on W(210), and the direction of nitrogen dipole moment adsorbed on the sites correspond to α₁, and β₂ states on W(210) and W(310) planes are in the opposite direction to that of the equivalent states on W(100) plane. From this observation we can predict the relative atomic position in the zdirection (perpendicular direction to the surface) of nitrogen molecules/atoms adsorbed on these sites.
BRIEF REPORTS ON KAISTSAT-4 MISSION ANALYSIS
J. Seon,K. I. Seon,S. H. Kim,K. W. Min,B. J. Kim,R. C. K. Yong,L. F. Leong,H. J. Chun,H. S. Chang,H. S. Kim,J. S. Bae,Y. W. Choi,S. R. LEE,Y. H. Shin,K. S. Ryu,J. J. Lee,D. H. Lee,D. J. Park 한국우주과학회 2000 Journal of Astronomy and Space Sciences Vol.17 No.2
Choi, S.B.,Lee, J.W.,Kim, N.S.,Na, S.H.,Keown, J.F.,Van Vleck, L.D. Asian Australasian Association of Animal Productio 2000 Animal Bioscience Vol.13 No.2
The objectives of this study of Hanwoo (Korean Cattle) were 1) to estimate genetic parameters for direct and maternal genetic effects for birth weight, weaning weight, and six months weight which can be used for genetic evaluations and 2) to compare models with and without grandmatemal effects. Data were obtained from the National Livestock Research Institute in Rural Development Administration (RDA) of Korea and were used to estimate genetic parameters for birth weight (BW, n=10,889), weaning weight at 120-d (WW, n=8,637), and six month weight (W6, n=8,478) in Hanwoo. Total number of animals in pedigrees was 14,949. A single-trait animal model was initially used to obtain starting values for multiple-trait animal models. Estimates of genetic parameters were obtained with MTDFREML using animal models and derivative-free REML (Boldman et al., 1995). Estimates of direct heritability for BW, WW, and W6 analyzed as single-traits were 0.09, 0.03, and 0.02 from Model 3 which included direct and maternal genetic, maternal permanental environmental effects, and effects due to sire ${\times}$ region ${\times}$ year-season interaction, respectively. Ignoring sire ${\times}$ region ${\times}$ year-season interaction effect in the model (Model 2) resulted in larger estimates for direct heritability than for Model 3. Estimates of maternal heritability for BW, WW and W6 were 0.04, 0.05, and 0.07 from Model 3, respectively. The estimates of direct-maternal genetic correlation were positive for BW, WW, and W6 with Model 3 but were negative with Model 2 for WW and W6. Estimates of direct genetic correlations between BW and WW, BW and W6, and WW and W6 were large: 0.52, 0.45, and 0.90, respectively. Genetic correlations were also large and positive for maternal effects for BW with maternal effects for WW and W6 (0.69 and 0.74), and even larger for WW with W6 (0.97). The log likelihood values were the same for models including grandmatemal effects as for models including maternal effects for all traits. These results indicate that grandmatemal effects are not important for these traits for Hanwoo or that the data structure was not adequate for estimating parameters for a grandmatemal model.