• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제54권10호
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• pp.453-456
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• 2005

We have fabricated superconducting ceramics by chemical process. A high Tc superconducting with a nominal composition of YBaCuO was prepared by the pyrolysis method. The electromagnetic properties in YBaCuO superconductor was studied. In the measurement of current-voltage characteristics, a voltage across the superconducting sample was observed on applying an external magnetic field. The voltage increases with increase in applied magnetic flux, but it becomes constant at about 10$^{-2}$T. The voltage continues to appear the removal of the magnetic field. The appearance of the voltage is ascribed to the trapping of magnetic flux. Depending on the direction of applied magnetic flux less than 2.5$\times$10$^{-5}$ T, the voltage in the magnetized sample increases or decreases.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제55권10호
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• pp.481-484
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• 2006

The electric properties in YBCO superconductor was studied. In the measurement of current-voltage characteristics, a voltage across the superconducting sample was observed on applying an external magnetic field. The voltage increases with increase in applied magnetic flux, but it becomes constant at about $10^{-2}T$. The voltage continues to appear the removal of the magnetic field. The appearance of the voltage is ascribed to the trapping of magnetic flux. Depending on the direction of applied magnetic flux less than $2.5{\times}10^{-5}T$, the voltage in the magnetized sample increases or decreases.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1999년도 하계학술대회 논문집 A
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• pp.376-378
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• 1999

In order to design the current carrying conductor for GIS, it is important to predict temperature-rise when rated current flows. This paper deals with the coupling of Flux2D and analytic method to calculate the heat transfer coefficient. Heat transfer by conduction and convection is considered between the current carrying conductor and $SF_6$ gas. The result shows reasonable temperature distribution.

• 천문학회지
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• 제33권2호
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• pp.123-126
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• 2000

We have developed a near real-time flare alerting system which (1) downloads the latest GOES-l0 1-8 ${\AA}$ X-ray flux 1-min data by an automated ftp program and shell scripts, (2) produces a beep sound in a simple IDL widget program when the flux is larger than a critical value, and (3) makes it possible to do a wireless alerting by a set of portable transceivers. Thanks to the system, we have made successful Ha flare observations by the Solar Flare Telescope in Bohyunsan Optical Astronomy Observatory. This system is expected to be helpful for ground-based flare observers.

• KIEE International Transactions on Electrophysics and Applications
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• 제5C권6호
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• pp.251-256
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• 2005

Directionally melt-textured high $T_c\;(Y_{0.5}Nd_{0.25}Sm_{0.25})Ba_{2}Cu_{3}O_y$ [(YNS)-123] superconductor was systematically investigated by the zone melt growth process in air. A sample prepared by this method showed well-textured microstructure, and $(Y_{0.5}Nd_{0.25}Sm_{0.25})_{2}BaCuO_5$[(YNS)211] inclusions were uniformly dispersed in large $(Y_{0.5}Nd_{0.25}Sm_{0.25})Ba_{2}Cu_{3}O_y$ [(YNS)123] matrix. High irreversibility field and magnetization hysteresis loop of the zone melt-textured (YNS)-123 sample exhibited the enhanced flux pinning, compared with $YBa_{2}Cu_{3}O_y$ (Y-123) sample without RE(rare earth). Critical current density of (YNS)-123 sample was $2.5{\times}10^4\;A/cm^2$ at 2 T and 77 K.

• Journal of Welding and Joining
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• 제34권6호
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• pp.1-10
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• 2016

Flux Cored Wire is the most widely used welding material for Flux Cored Arc Welding these days. This paper introduces the technical aspects of manufacturing FCW and the development trend of FCW for each type of steel and metal. The studies are ongoing to lower the production cost of seamless-type FCW since it has not been generally used in welding shops so far because of it high cost even though the seamless-type FCW has various advantages than folded-type FCW in terms of manufacturing technology. Meanwhile, a technical research has been carried out to develop a rutile type of FCW products which satisfies high toughness after post heat treatment. In addition, for high-speed fillet welding, there has been a development of welding materials which can be welded in Single Auto-Carriage 100 cpm or more and up to Twin Tandem 200 cpm without occurring any welding defect in order to improve the welding productivity. As Zn coated steel is being used recently to improve the corrosion resistance of the automotive parts, a research and development for Metal Cored Wire has been conducted to reduce the Si island produced in welding operation than those produced when using the former solid wires. A development of welding material that guarantees CTOD performance beyond $-40^{\circ}C$ CTOD to $-60^{\circ}C$ is underway by different steel grades, and FCW for super austenitic stainless steel is being developed as the corrosion resistant steel has been upgraded.

• 한국세라믹학회지
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• 제53권5호
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• pp.506-510
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• 2016

The eutectic melt of BaO-CuO flux is known to be a potential sintering aid for $Ba(Zr,Y)O_3$ (BZY) electrolyte for proton-conducting ceramic fuel cells (PCFCs). A density of BZY higher than 97% of theoretical density can be achieved via sintering at $1300^{\circ}C$ for 2 h using a flux composed of 28 mol% BaO and 72 mol% CuO. In the present study, chemical and structural evolution of BaO-CuO flux throughout the sintering process was investigated. An intermediate holding step at $1100^{\circ}C$ leads to formation of various impurity compounds such as $BaCuO_{1.977}$, $Ba_{0.92}Cu_{1.06}O_{2.28}$ and $Cu_{16}O_{14.15}$, which exhibit significantly larger unit cell volumes than the matrix. The presence of such secondary compounds with large lattice mismatch can potentially lead to mechanical failure. On the other hand, direct heating to the final sintering temperature produced CuO and $Cu_2O$ as secondary phases, whose unit cell volumes are close to that of the matrix. Therefore, the final composition of the flux is strongly affected by the thermal history, and a proper sintering schedule should be used to obtain the desired properties of the final product.

• Journal of Welding and Joining
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• 제21권7호
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• pp.59-64
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• 2003

Microstructure and shear strength of Sn-Zn lead-free solders and Au/Ni/Cu UBM joint under thermal aging conditions was investigated. The samples were aged isothermally at 10$0^{\circ}C$ and 15$0^{\circ}C$ for 300, 600, and 900 hours. The IMCs(Intermetallic Compound) at the interface between solder and UBM were examined by FESEM and TEM. The results showed that the shear strength was decreased with aging time and temperature. The solder ball with high activated RA flux had about 8.2% higher shear strength than that of RMA flux. Poor wetting and many voids were observed in the fractured solder joint with of RMA flux. The decreased shear strengths were caused by IMC growth and Zn grain coarsening. Zn reacted with Au and then was transformed to the $\beta$ -AuZn compound. Although AuZn grew first, $r-Ni_5Zn_{21}$ compounds were formed with aging time. The layers indicated by $Ni_5Zn_{21}(1)$, (2), and (3) were formed with the thickness of ∼0.7 ${\mu}{\textrm}{m}$, ∼4 ${\mu}{\textrm}{m}$, and ∼2 ${\mu}{\textrm}{m}$, respectively.

• 한국조명전기설비학회지:조명전기설비
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• 제10권3호
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• pp.55-63
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• 1996

본 논문에서는 CRPWM 인버터로 구동되는 유동전동기의 벡터젝어를 구현하였다. 회전자자속은 회전자 좌표계 자속모델을 이용하여 추정하였으며 전류제어기는 고정좌표계 삼각파 비교 제어기를 사용하였다. 회전자자속의 추정, 속도제어기, 자속제어기, 벡터회전, 상 변화 등의 연산은 80C196 마이크로 콘트롤러를 사용하여 실시간 제어를 하였으며 전류 제어기는 마이크로 콘트롤러의 처리부담을 덜어주기 위해 아날로그회로로 구현하였다. 제안한 시스템에 대하여 시뮬레이션을 통하여 타당성을 검토하였으며 실험을 통하여 전류제어 특성과 시스템의 과도 응답 특성이 우수함을 보였다.

• Transactions on Electrical and Electronic Materials
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• 제6권5호
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• pp.193-197
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• 2005

We investigated fault current limiting characteristics of the flux-lock type superconducting fault current limiter (SFCL), which consisted of a primary winding and several secondary windings connected in series between $high-T_C$ superconducting (HTSC) thin films. Each YBCO thin film has a 2 mm wide and 42 cm long meander line with 14 stripes of different length. The power imbalance due to the slight difference of Ie between YBCO current limiting elements causes the significant power burden on YBCO element with lower $I_C$. We confirmed from our experiments that the mutual coupling between the primary winding and secondary windings of the flux-lock type SFCL reduced the power imbalance between YBCO current limiting elements compared with the resistive type SFCL connected in series.