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이창환,정정열,LEE, CHANG-WHAN,JUNG, JUNG-YUL 한국수소및신에너지학회 2018 한국수소 및 신에너지학회논문집 Vol.29 No.3
From the experiments of various temperature and gas compositions, total resistance which is composed of ohmic resistance, anode resistance, cathode resistance and Nernst loss was calculated wit simple assumption. In this work, the anode and the cathode resistance was modelled with new equation which can account for the correlation between the operating temperature and the gas composition. The proposed model can predict the resistance with maximum error of 2.57% and employed in the simulation of molten carbonate fuel cells.
단일-공진기로 구성된 주파수-잠금 회로를 이용한 5-GHz 발진기
이창대(Chang-Dae Lee),이동현(Dong-Hyun Lee),이창환(Chang-Hwan Lee),염경환(Kyung-Whan Yeom) 한국전자파학회 2018 한국전자파학회논문지 Vol.29 No.11
본 논문에서는 VCO와 주파수검출기(frequency detector)에 각각 별도의 공진기를 사용하여 구성된 기존의 주파수-잠금회로(frequency locked loop: FLL) 구조 발진기를 개선하여, 단일-공진기로 구성된 주파수-잠금 회로를 이용한 구조가 단순화된 5-GHz 발진기의 설계제작을 보였다. 이때 공진기는 VCO 및 주파수검출기 구성에 공용으로 사용된다. 제작된 5-GHz 발진기는 고주파 성능이 우수한 Rogers사의 RO4350B와 상용 FR4 3층 기판을 이종-접합하여 구성하였으며, 주파수 잠금은 약 5 GHz에서 일어나며, 3.8 dBm의 출력을 갖는다. 위상잡음은 offset-주파수 1 kHz를 경계로 1 kHz 이상에서는 VCO의 위상잡음을, 1 kHz보다 낮을 때는 FLL 바탕잡음을 갖도록 하였다. 이와 같이 설정된 루프-필터에 대해 위상잡음의 개선은 offset-주파수 100 Hz에서 약 12 dB의 개선을 보였다. In this paper, the design and fabrication of a frequency-locked-loop(FLL) 5-GHz oscillator with a single resonator is presented. The proposed oscillator is the simplified version of the previous FLL oscillator with two separate resonators in the VCO and frequency detector. The resonator is commonly used in the VCO and frequency detector of the proposed oscillator configuration. The 5-GHz oscillator is implemented on the hetero-multilayer substrate composed of a Rogers" RO4350B laminate, which has excellent high-frequency performance, and the commercial FR4 three-layer substrate. The frequency locking occurs at approximately 5 GHz and has an output power of 3.8 dBm. The phase noise has a free-run VCO phase noise at frequencies above 1 kHz, and an FLL background noise at frequencies below 1 kHz. For this loop-filter, the phase noise showed an improvement of approximately 12 dB at the offset-frequency of 100 Hz.
CFD를 통한 용융탄산염 연료전지 단위전지용 셀 프레임 구조 설계
이성주,임치영,이창환,LEE, SUNG-JOO,LIM, CHI-YOUNG,LEE, CHANG-WHAN 한국수소및신에너지학회 2018 한국수소 및 신에너지학회논문집 Vol.29 No.1
In this study, a $100cm^2$ cell frame for a molten carbonate fuel cell was designed using CFD analysis. Electrochemical reactions, gas flow, and the heat transfer in $100cm^2$ cell frame were modeled using COMSOL Multiphysics. Two design variables such as the height of the cell frame and the length of the gas input area were determined to obtain minimized temperature distribution and uniform gas distribution. With two design parameter such as height of the cell frame and the length of the gas flow channel, the temperature difference in the cell fame was decreased to $5^{\circ}C$ and the gas uniformity in the flow channel were achieved.
실험 계획법을 사용한 B-Pillar 성형공정에서 블랭크 형상 최적화
윤형원,최용석,이창환,Youn, Hyung-Won,Choi, Yong-seok,Lee, Chang-Whan 한국금형공학회 2021 한국금형공학회지 Vol.15 No.2
The shape of the blank greatly affects the formability and quality of the product after the stamping process. In this study, the geometry of the B-Pillar blank in the stamping process was optimized using design of experiments. The geometry of the blank for the B-pillar was simplified with the two length values and two radius values. The effects of design variables were studied through the Design of experiments. The stamping process of the B-pillar was predicted with the Finite Element Analysis (FEA). The optimized blank geometry was obtained. It results in the reduced maximum equivalent plastic strain. The local necking and the wrinkling did not occurred with the optimized blank geometry.
장막 침윤이 없는 위암 환자에서 수술 후 보조적 화학 요법에 대한 전향적 연구 -중간 보고-
김용호,김병식,이창환,김완수,육정환,오성태,박건춘,Kim Yong-Ho,Kim Byung-Sik,Lee Chang-Hwan,Kim Wan Su,Yook Jung-Whan,Oh Sung-Tae,Park Kun-Choon 대한위암학회 2001 대한위암학회지 Vol.1 No.4
Purpose: We have carried out prospective randomized clinical trial to compare survival benefit and side effect among three postoperative adjuvant chemotherapeutic regimens in serosa-negative gastric cancer patients. Materials and Methods: Total 317 cases were recognized as serosa negative and randomized into three groups at operating room. Out of them, 172 cases were excluded because of various reasons and 135 cases were analyzed finally; Group A 36 cases, Group B 49 cases, Group C 50 cases. Group A were treated with intravenous FP combination therapy, group B with MF combination therapy and group C with oral $UFT^{(R)}$ (mixture of Tegafur and Uracil) for one year. The median follow-up period was 30 months. Results: $88.9\%$ of Group A, $83.7\%$ of Group B and $90.4\%$ of Group C received adequate chemotherapy. The complication rates of Group A ($44.4\%$) was significantly higher than group B ($20.4\%$) and group C ($24.0\%$)(P<0.05). Most frequent complications were nausea and vomiting. The 3-year survival rates and disease-free survival rates were $92.2\%$ and $89.9\%$ respectively (Group A: $96.6\%,\;87.8\%$, B: $90.3\%,\;87.7\%$, C: $95.7\%,\;93.8\%$). There were no significant differences in survival rate and disease-free survival rate among the three groups (P>0.05). Conclusion: This study might suggest that the survival benefit of postoperative adjuvant chemotherapy for gastric Pseudomonas aeruginosa, and therefore it may be a useful adjunct tool for detection of Pseudomonas aeruginosa infection in combination with other conventional techniques.
마그네슘 합금 판재의 평면 DIC 측정을 위한 지그 개발과 이를 활용한 단축 변형 특성 분석
강정은,유지윤,최인규,유제형,이창환,Kang, Jeong-Eun,Yoo, Ji-Yoon,Choi, In-Kyu,YU, Jae Hyeong,Lee, Chang-Whan 한국금형공학회 2021 한국금형공학회지 Vol.15 No.2
The specific strength of magnesium alloy is four times that of iron and 1.5 times that of aluminum. For this reason, its use is increasing in the transportation industry which is promoting weight reduction. At room temperature, magnesium alloy has low formability due to Hexagonal closed packed (HCP) structure with relatively little slip plane. However, as the molding temperature increases, the formability of the magnesium alloy is greatly improved due to the activation of other additional slip systems, and the flow stress and elongation vary greatly depending on the temperature. In addition, magnesium alloys exhibit asymmetrical behavior, which is different from tensile and compression behavior. In this study, a jig was developed that can measure the plane deformation behavior on the surface of a material in tensile and compression tests of magnesium alloys in warm temperature. A jig was designed to prevent buckling occurring in the compression test by applying a certain pressure to apply it to the tensile and compression tests. And the tensile and compressive behavior of magnesium at each temperature was investigated with the developed jig and DIC equipment. In each experiment, the strain rate condition was set to a quasi-static strain rate of 0.01/s. The transformation temperature is room temperature, 100℃. 150℃, 200℃, 250℃. As a result of the experiment, the flow stress tended to decrease as the temperature increased. The maximum stress decreased by 60% at 250 degrees compared to room temperature. Particularly, work softening occurred above 150 degrees, which is the recrystallization temperature of the magnesium alloy. The elongation also tended to increase as the deformation temperature increased and increased by 60% at 250 degrees compared to room temperature. In the compression experiment, it was confirmed that the maximum stress decreased as the temperature increased.