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Kim, C.J.,Kim, Y.J.,Lim, C.Y.,Jun, B.H.,Park, S.D.,Choo, K.N. The Korea Institute of Applied Superconductivity a 2014 한국초전도저온공학회논문지 Vol.16 No.2
Temperature dependence of magnetic moment (m-T) and the magnetization (M-H) at 5 K and 20 K of the in situ processed $MgB_2$ bulk pellets with/without carbon (C) doping were examined. The superconducting critical temperature ($T_c$), the superconducting transition width (${\delta}T$) and the critical current density ($J_c$) were estimated for ten test samples taken from the $MgB_2$ bulk pellets. The reliable m-T characteristics associated with the uniform $MgB_2$ formation were obtained for both $MgB_2$ pellets. The $T_cs$ and ${\delta}Ts$ of all test samples of the undoped $MgB_2$ were the same each other as 37.5 K and 1.5 K, respectively. The $T_cs$ and ${\delta}Ts$ of the C-doped $MgB_2$ were 36.5 K and 2.5 K, respectively. Unlike the m-T characteristics, there existed the difference among the M-H curves of the test samples, which might be caused by the microstructure variation. In spite of the slight $T_c$ decrease, the C doping was effective in enhancing the $J_c$ at 5 K.
Kim, Y.H.,Kim, C.J.,Jun, B.H.,Sung, T.H.,Han, Y.H.,Han, S.C.,Paik, H.J.,Youn, J.S.,No, K. North-Holland 2009 Physica. C, Superconductivity Vol.469 No.15
Rare-earth (RE) (e.g. Sm, Dy, Ce, etc.) doping has been widely investigated to improve critical current density (J<SUB>c</SUB>) of YBa<SUB>2</SUB>Cu<SUB>3</SUB>O<SUB>7-X</SUB> (YBCO) coated conductors (CC). Oxygen partial pressure is known to be a key parameter in terms of affecting the J<SUB>c</SUB> of YBCO films. In this work, the effect of oxygen partial pressure on the microstructure and J<SUB>c</SUB> of a Ce doped YBCO film was examined. Ce doped YBCO films were deposited on (100) SrTiO<SUB>3</SUB> (STO) single crystal substrates at oxygen partial pressures of 2.5, 5.0, and 10.0Torr using a metal organic chemical vapor deposition (MOCVD) method. Due to the enhanced migration of surface adatoms under reduced oxygen partial pressure, a 1wt% Ce doped YBCO film had a stoichiometric, dense surface. In addition, the zero-field J<SUB>c</SUB> (at 77K) of the 1wt% Ce doped YBCO film deposited at reduced oxygen partial pressure was increased. Irrespective of the amount of Ce, the Ce doped YBCO film showed an increased zero-field J<SUB>c</SUB> (at 77K) under reduced oxygen partial pressure.
Pore formation in in situ processed MgB<sub>2</sub> superconductors
Yi, J.H.,Kim, K.T.,Jun, B.H.,Sohn, J.M.,Kim, B.G.,Joo, J.,Kim, C.J. North-Holland 2009 Physica. C, Superconductivity Vol.469 No.15
MgB<SUB>2</SUB> bulks were prepared by an in situ process which utilizes the reaction between boron and magnesium powder. The reaction time was fixed at 0.5h and the temperature was changed from 600<SUP>o</SUP>C to 1000<SUP>o</SUP>C. The density decrease due to pore formation and mass (mainly magnesium) loss during the formation reaction of MgB<SUB>2</SUB> was observed in all samples. In addition to the pore formation, a pellet expansion which can be explained by the outgrowth of MgB<SUB>2</SUB> grains was also observed. Two different mechanisms were adopted to explain the pore formation; Kirkendall pores formed at a temperature below the melting point (m.p.) of magnesium by a difference in the diffusivity between magnesium and boron, and the pores formed at a temperature above the m.p. by melting of magnesium and a capillary movement. The density, T<SUB>c</SUB> and J<SUB>c</SUB> results suggest that the current carrying capacity can be improved by a careful control of the process parameters regarding a pore evolution.
기체 확산 전극을 이용한 이산화탄소의 전기 화학적 환원
임준혁,이경란,김진아,이제근,박정훈,전해수 한국공업화학회 1998 응용화학 Vol.2 No.2
The electrochemical reduction of carbon dioxide to produce alcohols and hydrocarbons has been examined on Cu/PTFE-bonded gas diffusion electrodes. The highest faradaic efficiencies for carbon monoxide, methante, ethylene, methanol and ethanol were 19.3, 12.4, 8.7, 7.3 and 3.8%, respectively. The faradaic efficiency and selectivity for the reduction products were dependent on operating conditions. Best results were found in -2.0 V vs. SCE and KHCO₃ electrolyte.
Youn, J.S.,No, K.,Kim, Y.H.,Mahmood, A.,Jun, B.H.,Han, Y.H.,Sung, T.H.,Kim, C.J. North-Holland 2009 Physica. C, Superconductivity Vol.469 No.15
To understand the effect of BaCeO<SUB>3</SUB> on a Y<SUB>2</SUB>BaCuO<SUB>5</SUB> (Y211) distribution, Y<SUB>1.5</SUB>Ba<SUB>2</SUB>Cu<SUB>3</SUB>O<SUB>x</SUB> (Y1.5) superconductors with/without 1wt.% BaCeO<SUB>3</SUB> additions were prepared by a top-seeded melt-textured growth (TSMG) process. Two different BaCeO<SUB>3</SUB> powders (as-synthesized (coarse powder) and an attrition-milled (fine powder)) were used and the size effect was compared with that obtained from a Y1.5 sample with no addition. A refinement of the Y211 particles was achieved for both the as-synthesized and attrition-milled BaCeO<SUB>3</SUB> additions. The distribution of the Y211 particles was most uniform in the Y1.5 sample prepared with the attrition-milled BaCeO<SUB>3</SUB> powder due to the reduced size of the Y211-free regions by the fine size BaCeO<SUB>3</SUB> addition. The highest J<SUB>c</SUB> was achieved in the Y1.5 sample prepared with the attrition-milled BaCeO<SUB>3</SUB> powder. The J<SUB>c</SUB> result agreed well with the microstructure variations by the addition of BaCeO<SUB>3</SUB> powders.
권광진,전재억,정진서,황영모,박후명,하만경 한국공작기계학회 2004 한국공작기계학회 춘계학술대회논문집 Vol.2004 No.-
Ratio that robot occupies is low level worldwide fairly in susdension wire, electricity electron and neutralization learning industry and domestic industry of this is staying in average leve. Can speak that grafting of robotic machine and neutralization learning industry is high in terms of side of creation of the added value or progress of technology rightly hereupon. This research raises or designed multi-function handling robot that can make welding, assembly conveniently catching large size work water
Bae, J.W.,Kang, S.H.,Lee, Y.J.,Jun, K.W. Korean Society of Industrial and Engineering Chemi 2009 Journal of industrial and engineering chemistry Vol.15 No.4
The synthesis of dimethyl ether (DME) from biomass-derived model synthesis gas has been investigated on Cu-ZnO-Al<SUB>2</SUB>O<SUB>3</SUB>/Zr-ferrierite bifunctional catalysts. The catalysts are prepared by co-precipitation-impregnation method using Na<SUB>2</SUB>CO<SUB>3</SUB>, K<SUB>2</SUB>CO<SUB>3</SUB> and (NH<SUB>4</SUB>)<SUB>2</SUB>CO<SUB>3</SUB> as the precipitants. The catalytic activity tests reveal that the best yield of DME can be obtained on the catalyst precipitated by using (NH<SUB>4</SUB>)<SUB>2</SUB>CO<SUB>3</SUB>. Detailed characterization studies conducted on the catalysts to measure their properties such as surface area, acidity by temperature-programmed desorption of ammonia (NH<SUB>3</SUB>-TPD), reducibility of Cu oxide by temperature-programmed reduction (TPR), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS) and copper surface area and particle size measurements by N<SUB>2</SUB>O titration method. Increasing the number of moderate acidic sites and facilitation of easily reducible copper species with small particle size are found to be the prime reasons for the superior functionality of the (NH<SUB>4</SUB>)<SUB>2</SUB>CO<SUB>3</SUB> precipitated catalyst. The usage of (NH<SUB>4</SUB>)<SUB>2</SUB>CO<SUB>3</SUB> also leaves no residual ions, whereas the presence of residual K<SUP>+</SUP> and Na<SUP>+</SUP> ions in the case of K<SUB>2</SUB>CO<SUB>3</SUB> and Na<SUB>2</SUB>CO<SUB>3</SUB> precipitated catalysts leads to lower activity and selectivity.
산란대기하에서 광위성 통신 업링크의 양각에 따른 송신 안테나의 설계
김영권,이종규,전석빈,한종석,김준환 延世大學校 電波通信共同硏究所 1996 電波通信論文誌 Vol.2 No.1
Today's wireless communication needs the super-high speed for picture transmission and high-speed data transmission as well as voice. The optical(laser) communication is suitable for this demands because of the very wide optical bandwidth. But to fulfill the optical communication, the atmospheric attenuation of cloudy weather must be overcome. Under the weather condition of haze, fog, rain, and snow, the atmospheric attenuation, which affects on the optical satellite up-link communication between geo-satellite and earth station, was studied in this paper. In this case, the scattering attenuation and absorption is the most serious effect. The poiting error weaken the optical receiving power, too. These three attenuation factors directly influence the diameter of optical transmitting antenna. In this paper, the anttena diameter of the earth station was calculated according to the elevation angle, weather condition and transmission rate. The specification of this paper's simualtion was the 10[W] ?? laser as an optical source, and the binary FSK as a modulation method and the optical heterodyne receiver. The diameter of the optical cassegrain receiving antenna was assummed 1[m], the coding gain was set to 10[dB], and the BER(Bit Error Rate) was set to ???. As a result, the diameter of the transmitting antenna is distributed from centimeters to about 100 meters according to the weather condition, elevation angle and transmission rate. In case of the 10[Mbps] transmission rate, the receiving anttena diameter under the condition of haze is designed below 2[cm]. Fog makes the anttena diameter over 5[m]. Rain makes the anttena diameter below 3[m]. And snow makes over 10[m] anttena. Above values was calculated in the region of 30° ~ 90° elevation angle.