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Wee, Sung-Hun,Hong, Hee-Song,Kim, Young-Hwan,Yoo, Sang-Im,Kang, Joonhee 대한금속재료학회 2003 METALS AND MATERIALS International Vol.9 No.5
We have systematically investigated the effects of processing parameters, including various oxygen pressures (Po₂) ranging from 200 to 1000 mTorr and substrate temperatures (T_(s)) ranging from 500 to 750 ℃, on the characteristics of Bi-substituted yttrium iron garnet (Bi:YIG) films grown on (111) gadolinium gallium garnet (GGG) substrates. Bi:YIG films were grown using a pulsed laser deposition method with an ArF excimer laser (λ=193 nm). Although the compositions of all the Bi:YIG films grown at the constant T_(s) of 600 ℃ were close to the target composition irrespective of Po₂, the Bi contents were slightly increased with increasing Po₂, which was consistent with the variation in Faraday rotation angles (θ_(F)). In addition, the crystallinity of the Bi:YIG films was deteriorated with increasing Po₂, and their grains became irregular. At T_(s) above 700 ℃, Bi-deficient yttrium iron garnet films were grown. Consequently, high quality epitaxial Bi:YIG films exhibiting Faraday rotation angles of -1.0 ~ -1.5 degree/㎛ were successfully grown at the substrate temperatures in the range of 500~650 ℃ when the Po2 of 200 mTorr was used.
Wee, Sung-Hun,Moon, Seung-Hyun,Yoo, Sang-Im The Korean Society of Superconductivity and Cryoge 2009 한국초전도저온공학회논문지 Vol.11 No.2
We report a successful fabrication of $high-J_c\;NdBa_2Cu_3O_{7-{\delta}}$ (NdBCO) films on $SrTiO_3$(STO) (100) substrates by pulsed laser deposition (PLD) in a relatively wide processing window. Under various oxygen pressures controlled by either 1%$O_2$/Ar mixture gas or pure $O_2$ gas, strongly c-axis oriented NdBCO films were grown at the substrate temperature $(T_s)\;of\;800^{\circ}C$ in 800 mTorr with 1%$O_2$/Ar gas and also in 400 and 800 mTorr with pure $O_2$ gas. These samples exhibited $T_c$ values over 90K and $J_c$ values of $2.8-3.5MA/cm^2$ at 77K in self-field (77K, sf). On the other hand, $J_c$ values over $1A/cm^2$ were obtained at the temperature regions of $700-830^{\circ}C$ in 800 mTorr with 1%$O_2$/Ar gas at those of $750-830^{\circ}C$ in 800 mTorr with pure $O_2$ gas. Unlike previous reports, resent results support that the PLD processing window for high-Jc NdBCO films is not narrow.
Phase and microstructure evolution during the TFA-MOD process of YBCO films
Wee, Sung-Hun,Shin, Geo-Myung,Hong, Gye-Won,Yoo, Sang-Im The Korean Society of Superconductivity and Cryoge 2007 한국초전도저온공학회논문지 Vol.9 No.2
We report the phase and microstructure evolutions of metal trifluoroacetate (TFA) precursor films in the TFA-MOD process of YBCO films on the LAO (100) substrates. It was confirmed that the precursor films were decomposed into $Y_2O_3$, $BaF_2$, and CuO nanoparticles after the initial heat treatment up to 400$^{\circ}C$. After a subsequent heat treatment at higher temperatures ranging from 700 to 850$^{\circ}C$ for 2 h, these nano-sized phases are converted into YBCO films. High Jc(77K, sf)-YBCO thin films (over 2 MA/$cm^2$) were successfully fabricated with firing temperatures ranging from 775 to 850$^{\circ}C$ for 2 h, where films were composed of dense microstructures with large grains.
Wee, Sung-Hun,Moon, Seung-Hyun,Park, Chan,Yoo, Sang-Im The Korean Society of Superconductivity and Cryoge 2004 한국초전도저온공학회논문지 Vol.6 No.4
We report a successful fabrication of high-$J_C$ $NdBa_2Cu_3O_{7-{\delta}}$ (NdBCO) films on (100) $SrTiO_3$ substrates by pulsed laser deposition (PLD) in high oxygen pressures ranging from 400 to 800 mTorr. Fabricated NdBCO films exhibited only c-axis orientation, good out-of-plane and in-plane textures, and also excellent superconducting properties, including critical temperature ($T_C$) and critical current density ($J_C$) of above 90 K and the highest of $3.1MA/cm^2$ at 77 K in self-field, implying that NdBCO is a perspective alternative to YBCO for coated conductor. In low oxygen pressures ranging from 100 to 200 mTorr, however, the films showed a-, c-mixed orientation and degraded $T_{C,zero}$ values due to the formation of $Nd_{1+x}Ba_{2-x}Cu_3O_{7-{\delta}}$-type solid solutions with an excessive substitution of $Nd^{3+}$ ions for the $Ba^{2+}$ sites.
건설폐토석 재활용 유해성 관리를 위한 미규제 중금속 함량특성에 관한 연구
위성도 ( Sung Do Wee ),김남석 ( Nam Seok Kim ),황용우 ( Yong Woo Hwang ),최영훈 ( Young Hun Choi ) 한국전과정평가학회 2022 한국전과정평가학회지 Vol.23 No.1
본 연구는 신축 건설현장에서 발생하는 건설폐토석의 미규제 중금속 전함량 농도특성 확인을 통해 재활용 유해성 관리에 대한 고찰을 하는데 그 목적이 있다. 25개 지점의 건설폐토석 시료에서 Mn, Ba, Sb, Se, Be, V 전함량 특성을 현행 토양공정시험기준에 준하여 분석하였다. 분석 결과, 건설폐토석의 Mn 농도는 (174.24~1109.4) mg/kg, Ba 농도는 (29.08~609.05) mg/kg으로, 국내 자연배경토양 일부 및 본 연구의 배경토양 농도보다 상대적으로 높게 검출되었다. 또한 일부 지점에서 Ba의 검출농도는 국외 폐기물 함량규제 기준치(500 mg/kg)에 근접하거나 초과하는 수치로 확인되었다. 이러한 화학적 특성평가와 함께 물리적 특성을 추가로 평가하여, 이를 기반으로 재활용 과정에서 발생할 수 있는 환경영향에 대한 분석평가를 진행한다면 건설폐토석의 품질과 활용도를 높이는데 기여할 것으로 판단된다. The purpose of this study is to consider the recycling management of hazardous substances through the confirmation of the concentration characteristics of the unregulated heavy metals total content in construction waste stones generated at new construction sites. The total content of Mn, Ba, Sb, Se, Be and V was analyzed in accordance with the current soil contamination test standards in 25 construction earth waste sample. As a result of the analysis, the Mn concentration of the construction waste earth was (174.24~1109.4) mg/kg and Ba concentration was (29.08~609.05) mg/kg, and these detection values were higher than concentration of domestic natural background soil and reference soil. In addition, the Ba concentration was confirmed as closed or exceeded to concentration of the content regulatory standard of overseas waste(500 mg/kg). It is judged that if the analysis evaluation of the environmental impact that may occurred during recycling process is conducted based on chemical and physical characteristics evaluation, it will contribute to improving the quality and utilization of waste earth.
Flexible and Scalable Formation for Unicycle Robots
Dong Hun Kim(김동헌),Young Kwun Lee(이용권),Sung-Ill Kim(김성일),Wee-Jae Shin(신위재),Hyun-Woo Lee(이현우) 한국지능시스템학회 2005 한국지능시스템학회 학술발표 논문집 Vol.15 No.2
This paper presents a self-organizing scheme for multi-agent swarm systems based on coupled nonlinear oscillators (CNOs). In this scheme, unicycle robots self-organize to flock and arrange group formation through attractive and repulsive forces among themselves. It is also shown how localized distributed controls are utilized throughout group behaviors such as formation and migration. In the paper, the proposed formation ensures safe separation and good cohesion performance among the robots. Several examples show that the proposed method for group formation performs the group behaviors such as reference path following, obstacle avoidance and flocking, and the formation characteristics such as flexibility and scalability, effectively.