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Lee, Hai Gun,Park, Hai Woong,Lee, Do Kyol 대한금속재료학회(대한금속학회) 2000 METALS AND MATERIALS International Vol.6 No.5
A highly homogeneous composite precursor containing nano-scale particles was synthesized from the high-energy attrition milling of a mixture of metallic Y, metallic Cu and barium nitrate (Ba(NO₃)₂) containing 5 wt.% silver. The particle size of the 20 hour attrition-milled precursor was in the range of 30∼80 ㎚ as estimated by the XRD technique and direct TEM observation. With the heat treatment of the attrition-milled precursor, an intermediate precursor with the overall composition Y:Ba:Cu:O=1:2:3:y, y$gt;7 was synthesized. The analyzed Y:Ba:Cu:Ag:O molar ratio of the intermediate precursor by AES/AAS and iodirnetric titration was 1:1.972:3.022:0.323:7.41, which was very close to the estimated composition: 0.5Y₂O₃+2BaCu0_(2.5)+CuO+0.325Ag. Y123-Ag superconductors in powder or bulk forms were prepared using heat treatment or thermomechanical processing of the intermediate precursor containing BaCuO_(2.5). The high oxygen orthorhombic Y123-Ag phase (y$gt;7) was obtained in quenched samples which were held for 30 min or less at 950℃ in ambient air. As the holding time extended to 40 min, the sample was still orthorhombic Y123-Ag (6.7$lt;y$lt;7). The transport critical current density (J_c) at 77 K and zero magnetic field for the quenched sample which was held for 40 min at 950℃ was1.3×10³ A/㎠.
Lee, Hai Gun,Park, Hai Woong 대한금속재료학회(대한금속학회) 2001 METALS AND MATERIALS International Vol.7 No.3
YBa₂Cu₃O_y (Y123) phase was synthesized from the oxide precursor containing BaCuO_(2.5) in two distinct processes. In the first stage, a suitable amount of metallic Y, metallic Cu and barium nitrate (Ba(NO₃)₂) were mixed via attrition milling for 20 h. After 20 h of milling, the particle size of the powder was in the range of 0.05-0.2 ㎛. On subsequent heat treatment of the milled powder at 600℃ for 5 h with continuous argon flow, the intermediate precursor (IP) was synthesized. The IP contained BaCuO_(2.5), Y₂O₃ and CuO and the overall composition of the IP was Y:Ba:Cu:O=1:2:3:7.4. The oxygen content of the IP was higher than that of the corresponding orthorhombic Y123 superconductor. In the second stage, the synthesized IP was converted to the superconducting Y123 phase with heat treatment at 900-1020℃ in air without any additional low temperature oxygenation process. A DTA experiment at 20℃/min in air and a series of rapid heat, soak, and quench experiments showed that the BaCuO_(2.5) constituent of the precursor decomposed at 838℃, which is higher than that of pure BaCuO_(2.5) (760℃). The results of the TGA experiments suggested that the heating rate had a strong influence on the decomposition temperature of the BaCuO_(2.5) of the IP At a heating rate of $gt;50℃/min, the BaCuO_(2.5) did not decompose completely during heating to 1020℃ and form orthorhombic YBa₂Cu₃O_(7-x).
Lee, Kang Jea,Kim, Seung Hwan,Park, Ah Hyun,Lee, Seul Be,Lee, Gun Hee,Yang, Gye-Mo,Pham, Hai Dinh,Thu, Hoang Thi,Cuong, Tran Viet,Suh, Eun-Kyung Optical Society of America 2014 Optics express Vol.22 No.suppl4
<P>Light extraction efficiency of GaN-based light emitting diodes were significantly enhanced using silver nanostructures incorporated in periodic micro-hole patterned multi quantum wells (MQWs). Our results show an enhancement of 60% in the wall-plug efficiency at an injection current of 100 mA when Ag nano-particles were deposited on side facet of MQWs passivated with SiO2. This improvement can be attributed to an increase in the spontaneous emission rate through resonance coupling between localized surface plasmons in Ag nano-particles and the excitons in MQWs.</P>
(Hai Woong Park),(Hai Gun Lee) 대한금속재료학회 ( 구 대한금속학회 ) 2001 METALS AND MATERIALS International Vol.7 No.3
YBa2Cu3Oy(Y123) phase was synthesized from the oxide precursor containing BaCuO2.5 in two distinct processes. In the first stage, a suitable amount of metallic Y, metallic Cu and barium nitrate (Ba(NO3)2) were mixed via attrition milling for 20h. After 20h of milling, the particle size of the powder was in the range of 0.05-0.2um. On subsequent heat treatment of the milled powder at 600℃ for 5h with continuous argon flow, the intermediate precursor (IP) was synthesized. The IP contained BaCuO2.5, Y2O3 and CuO and the overall composition of the IP was Y:Ba:Cu:O=1:2:3:7.4. The oxygen content of the IP was higher than that of the corresponding orthorhombic Y123 superconductor. In the second stage, the synthesized IP was converted to the superconducting Y123 phase with heat treatment at 900-1020℃ in air without any additional low temperature oxygenation process. A DTA experiment at 20℃/min in air and a series of rapid heat, soak, and quench experiments showed that the BaCuO2.5 constituent of the precursor decomposed at 838℃, which is higher than that of pure BaCuO2.5 (760℃). The results of the TGA experiments suggested that the heating rate had a strong influence on the decomposition temperature of the BaCuO2.5 of the IP. At a heating rate of>50℃/min, the BaCuO2.5 did not decompose completely during heating to 1020℃ and form orthorhombic YBa2Cu3O7-x.
Lee, Jangwoo,Choi, Kyungho,Park, Jeongim,Moon, Hyo-Bang,Choi, Gyuyeon,Lee, Jeong Jae,Suh, Eunsook,Kim, Hai-Joong,Eun, So-Hee,Kim, Gun-Ha,Cho, Geum Joon,Kim, Sung Koo,Kim, Sungjoo,Kim, Su Young,Kim, Se Elsevier 2018 Science of the Total Environment Vol.626 No.-
<P><B>Abstract</B></P> <P>Bisphenol A (BPA) exposure during the perinatal and postnatal periods increases the susceptibility to disease over the life cycle. However, information on the BPA delivered to fetuses or infants via the placenta and breastfeeding is limited. We determined the BPA exposure levels in various bodily fluids and tissues of pregnant women and described fetus and infant exposures to BPA based on associations and BPA ratios in mother–neonate paired samples. Maternal serum, urine, placenta, breast milk, cord serum, and neonatal urine samples were collected from 318 mother–neonate pairs at six university hospitals in Korea. BPA levels were detected using liquid chromatography tandem mass spectrometry. The ratios of the BPA levels in the other sample types to the levels in maternal serum were calculated. BPA was detected in 79.5–100% of the maternal and fetal samples. The median BPA concentration in the samples decreased in the order of neonatal urine (4.75ng/mL), maternal urine (2.86ng/mL), cord serum (1.71ng/mL), maternal serum (1.56ng/mL), breast milk (0.74ng/mL), and the placenta (0.53ng/g). We estimated the ratios of BPA levels in the other sample types to those in maternal serum. The median (95th percentile) cord serum-to-maternal serum ratio was 1.12 (15.2) for 160 mother–fetal pairs, in which BPA was detected in both samples. The placenta-, maternal urine-, neonatal urine-, and breast milk-to-maternal serum ratios were 0.28 (5.31), 1.79 (29.9), 1.98 (28.2), and 0.51 (10.5), respectively. In addition, the median (95th percentile) cord serum-to-placenta ratio was 4.03 (45.8), and the neonatal urine-to-cord serum ratio was 1.95 (25.6). The 95th percentile values were 14–20-fold greater than the medians. Urine contained the highest BPA concentrations, followed by serum, breast milk, and the placenta. The variations of BPA ratio show individual differences in the amounts of BPA delivered from mother to fetus.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Not enough data on tissue distribution of BPA in mother‑neonate (or fetus) pair </LI> <LI> The order of BPA concentrations in examined tissue or bio-samples are urine in mother and neonates>cord serum>maternal serum>breast milk>placenta. </LI> <LI> BPA in cord serum, significantly associated with in maternal serum and urine but not in others. </LI> <LI> The variations of BPA ratio show individual differences in the amounts of BPA delivered from mother to fetus. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
3-극점 2-영점 보상 회로가 적용된 승압형 DC-DC 컨버터 회로의 안정적 동작에 관한 연구
최건우(Gun-Woo Choi),정해영(Hai-Young Jung),이석현(Seok-Hyun Lee) 한국전자통신학회 2020 한국전자통신학회 논문지 Vol.15 No.5
현대 사회에서 다양한 전기기기들의 시스템 회로를 동작시키기 위해서는 여러 직류 전원이 필요하다. 회로의 정상적인 동작을 위해 안정된 직류의 공급이 필수적으로 요구되고 이를 위한 컨버터의 중요성은 매우 크다고 할 수 있다. 본 연구는 부하 변동에 상관없이 출력전압의 안정적인 공급을 유지할 수 있도록 승압형 DC-DC 컨버터인 KY 컨버터에 3-극점 2-영점 전압 제어기를 적용한 PWM DC-DC 컨버터 회로를 제안하였다. 제안된 컨버터 회로의 정상 동작 특성을 입증하기 위해 기존의 컨버터 회로와 비교하여 PSIM 시뮬레이션 프로그램과 PCB 기판에서의 회로 동작 실험을 수행하였다. In modern society, various DC power supplies are required to operate the system circuits of various electric devices. A stable DC supply is essential for the normal operation of the circuit and the importance of the converter for this is very high. This study proposed a PWM DC-DC converter circuit that applied a 3-pole 2-zero voltage controller to a KY converter, a step-up DC-DC converter, to maintain a stable supply of output voltage regardless of load fluctuations. In order to prove the normal operation characteristics of the proposed converter circuit, a PSIM simulation and a circuit operation experiment on the PCB board were performed in comparison with the conventional converter circuit.