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김동환,황차원,김남진,임상혁,구동건,김태희,차재민,류봉기,Kim, Dong-Hwan,Hwang, Cha-Won,Kim, Nam-Jin,Im, Sang-Hyeok,Gwoo, Dong-Gun,Kim, Tae-Hee,Cha, Jae-Min,Ryu, Bong-Ki 한국세라믹학회 2011 한국세라믹학회지 Vol.48 No.1
The investigation is directed to lead free (Pb-free) frits that can be used for organic light emitting diode, plasma display screen devices and other sealing materials. $P_2O_5$-SnO system glasses have been prepared for Pb-free low temperature glass frit. Structure and properties of the glasses with the composition SnO-$xB_2O_3-(60-x)P_2O_5$ (x=0, 5, 10, 15, 20, 25, 30, 35, 40 mol%) were characterized by infrared spectra (IR), X-ray diffraction(XRD), Density, Molar volume, Thermo mechanical analysis(TMA) and weight loss after immersion test. Glass transition temperature($T_g$), dilatometric softening temperature($T_d$) and chemical durability increased, and coefficient of thermal expansion($\alpha$) decrease with the substitution of $B_2O_3$ for $P_2O_5$ in the range of 0~25 mol%.
Effects of Substituting B2O3 for P2O5 on the Structures and Properties of V2O5-P2O5 Glass Systems
Kyungseok Han,황차원,Dong Hwan Kim,Donggun Gwoo,Taehee Kim,Wongyu Choi,Kyungbum Kee,김종환,류봉기 대한금속·재료학회 2012 ELECTRONIC MATERIALS LETTERS Vol.8 No.6
V2O5-B2O3-P2O5 glasses with various compositions were prepared using a normal melt quenching technique,and their characteristics and structural properties were investigated using different techniques. Replacement of P2O5 by B2O3 was found to improve the thermal properties, chemical durability, and room-temperature conductivity. The observed variations in the properties may be correlated with changes in the internal glass network as a result of changes in the chemical composition. Vanadium ions are believed to be present in three possible valence states, namely V3+, V4+, and V5+, and the ratios of these states depend on the glass composition. The observed increases in chemical durability and room-temperature conductivity are assumed to be related to increases in the mean crosslinking density, increases in the number of bridging oxygens,and electron hopping between vanadate ions in different valence states.
유준상,허수정,황원,차원철 대한의료정보학회 2023 Healthcare Informatics Research Vol.29 No.1
Objectives: Although medical artificial intelligence (AI) systems that assist healthcare professionals in critical care settingsare expected to improve healthcare, skepticism exists regarding whether their potential has been fully actualized. Therefore,we aimed to conduct a qualitative study with physicians and nurses to understand their needs, expectations, and concerns regardingmedical AI; explore their expected responses to recommendations by medical AI that contradicted their judgments;and derive strategies to implement medical AI in practice successfully. Methods: Semi-structured interviews were conductedwith 15 healthcare professionals working in the emergency room and intensive care unit in a tertiary teaching hospital inSeoul. The data were interpreted using summative content analysis. In total, 26 medical AI topics were extracted from the interviews. Eight were related to treatment recommendation, seven were related to diagnosis prediction, and seven were relatedto process improvement. Results: While the participants expressed expectations that medical AI could enhance their patients’outcomes, increase work efficiency, and reduce hospital operating costs, they also mentioned concerns regarding distortionsin the workflow, deskilling, alert fatigue, and unsophisticated algorithms. If medical AI decisions contradicted theirjudgment, most participants would consult other medical staff and thereafter reconsider their initial judgment. Conclusions:Healthcare professionals wanted to use medical AI in practice and emphasized that artificial intelligence systems should betrustworthy from the standpoint of healthcare professionals. They also highlighted the importance of alert fatigue managementand the integration of AI systems into the workflow.
Sintering and Crystallization Behavior in B₂O₃ Contained Li₂O-Al₂O₃-SiO₂ Glass
임상혁,김동환,나영훈,김남진,황차원,차재민,류봉기 대한금속·재료학회 2010 ELECTRONIC MATERIALS LETTERS Vol.6 No.2
This study looks at crystallization and sintering behavior in B₂O₃ containing Li₂O-Al₂O₃-SiO₂ glass powder. The sintered sample was produced with glass powders measuring 44 μm. The relative density and transmittance of the sintered samples showed the highest value at the temperature of 650°C. At temperatures higher than 650°C, crystal growth occurred to decrease the densification of B₂O3-Li₂O-Al₂O₃-SiO₂ (BLAS) glass powder. The main crystalline phase in the glass powder was â-spodumene. From non-isothermal differential thermal analysis, the crystallization of particles (Φ = 44 μm) was observed at 640°C to 684°C with respect to the heating rate. The activation energy of crystallization (EC) and the Avrami constant (n) calculated by Kissinger and Ozawa equations indicated that the surface and the bulk crystallization occurred simultaneously in the glass. The optimum sintering temperature of this glass powder was 650°C without crystal growth of β-spodumene,although nucleation or nano-crystal growth occurred.
$B_2$$O_3$첨가에 따른 Zinc Phosphate Glasses의 화학적 안정화
류봉기,이병철,이성욱,황차원,이종성 한국세라믹학회 2001 한국세라믹학회지 Vol.38 No.6
Zinc-phosphate glasses에 B$_2$O$_3$를 도입하여 borate, phosphate, boro-phosphate networks가 혼재되어 있는 highly cross-linked structures를 형성시켜 Phosphate glasses의 화학적 안정화를 검토하였다. Raman 측정 결과 B$_2$O$_3$와 P$_2$O$_{5}$는 잘 혼화된 polynary networks를 이루고 있으며, 이렇게 하여 증진된 구조적 cross-linking에 의하여 xB$_2$O$_3$.(1-x)Zn$_2$P$_2$O$_{7}$ glasses의 T$_{g}$, T$_{d}$는 증가하였고 동시에 CTE는 감소하는 결과를 가져왔다.
소형위성용 전기추진시스템을 위한 연료공급부의 발사환경 시험평가
김연호(Younho Kim),강석현(Seokhyun Kang),정연황(Yunhwang Jung),강성민(Seongmin Kang),선종호(Jongho Seon),이상현(Sang-Hyun Lee),차원호(Won-Ho Cha),은희광(Hee-Kwang Eun) 한국항공우주학회 2014 韓國航空宇宙學會誌 Vol.42 No.12
소형인공위성에 적용을 목적으로 전기추진시스템의 연료공급부가 개발되었다. 연료공급부는 연료로 사용되는 제논을 높은 압력과 밀도의 가스상태로 저장하게 된다. 제논은 상온에서 임계점을 갖는데 발사환경에서 과도상태로 시스템에 영향을 미칠 수 있다. 따라서 발사환경에 대한 본 시스템의 기능적ㆍ구조적 안정성은 지상시험을 통한 검증이 필요하다. 본문에서는 연료공급부의 설계점과 검증시험내용을 논하고 시험결과를 정리하였다. 검증시험을 통해 본 시스템이 발사환경에 대하여 안정성을 확보하고 있는 것을 확인하였다. A Fuel Feeding Unit of electric propulsion system has been developed for the small-satellite applications. The fuel feeding unit stores the xenon gas with high pressure and density as a fuel. Xenon can affect to system stability since xenon has the transient condition under the critical point which is in ambient temperature on the launch environment. The functional and structural stability on the launch environment needs verification through the ground tests. The design points and verification tests of the system were discussed and test results were described on this text. The system stability on the launch environment was verified through these verification tests.
Relationship between Structure and Optical Properties in the CdO-B2O3-SiO2 Glass System
Taehee Kim,Donggun Gwoo,김종환,Wongyu Choi,Kyungseok Han,Kyungbum Kee,황차원,류봉기 대한금속·재료학회 2012 ELECTRONIC MATERIALS LETTERS Vol.8 No.6
To study the compositional dependence of the optical properties and atomic structure of glasses, the CdOB2O3-SiO2 ternary glasses, which are known as highly photoconductive glasses, have been investigated. The photoconductivity of glasses containing CdO was investigated in a previous study, because of their potential applications in photoelectronic devices. The thermo-mechanical analysis and the Fourier transform infrared (FT-IR) spectra of the glass samples were measured to determine the structural variation of these glasses. Using transmittance measurements, we calculated the optical energy band gap. This paper presents results for control of the optical energy band gap 3.8 ~ 3.2 eV in cadmium-borosilicate glass system while the structural properties undergo monotonic changes.
과학기술위성 3호용 홀 추력기 시스템 비행모델 연구개발
서미희(Mihui Seo),이종섭(Jongsub Lee),신구환(Goo-Hwan Shin),박홍영(Hong-Yong Park),서정기(Jung-Ki Seo),장태성(Tae-Seong Jang),차원호(Won-Ho Cha),이성호(Seong-Ho Lee),조희근(Hee-Keun Cho),전은용(Eunyong Chun),정연황(Yunhwang Jeong),선종 한국추진공학회 2012 한국추진공학회 학술대회논문집 Vol.2012 No.11
최근 들어 위성군, 편대비행 등과 같은 고등임무의 가능성에 의해 소형위성에 대한 관심이 갈수록 커지고 있으며 관련 연구개발이 활발히 진행되고 있다. 이와 같이 위성의 활용범위를 넓히기 위해서는 정밀한 위성의 자세제어와 상황에 따른 궤도수정 혹은 천이 기술을 가능케 하는 고효율 저전력 전기추력기가 반드시 필요하다. 국내기술에 의한 전기추력기의 기술 확보를 목표로 저전력 홀(Hall)방식 전기추력기의 연구개발이 국내 여러 기관들의 협력 하에 지난 수년 간 진행되어, 2012년 12월 발사예정인 과학기술위성 3호를 위한 추력부, 전력부, 연료부 및 제어부로 구성된 홀 추력기 통합시스템의 비행모델의 개발이 완료되었다. 개발된 비행모델은 양극전력 200 W, 제논 연료유량 8 sccm으로 11 mN 추력과 35.5 % 추진효율, 1270~1300 s의 비추력을 발생시켜 연구개발 목표치를 상회하는 결과를 얻었으며, 진동시험, 열진공시험 및 통합 성능시험을 수행하여 우주와 유사한 환경 하에서 정상동작하는 것을 확인하였다. 개발된 홀 추력기는 과학기술위성 3호 뿐만 아니라 국내에서 개발 제작되는 소형 인공위성의 다양한 임무수행에 있어 활용가능성을 높여줄 것이며, kW급 이상의 홀추력기 개발에 초석이 될 것으로 기대한다. As the small satellites are expected to replace the large satellite for some of the advanced missions through constellation and formation flying, the low power and high performance propulsion system, i.e. electrical thruster, is considered to be a key element that enable detailed attitude control and orbit transfer of the satellite. In order to achieve the domestic electric propulsion technology, a flight model of the compact 10 mN class Hall thruster propulsion system (HPS) for STSAT-3 has been developed as collaborative research with several domestic institutions. The HPS consists of thruster head unit, power processing module, xenon feeding system, and propulsion control module. Performance test of the flight model Hall thruster demonstrates 11 mN thrust, 35.5% thrust efficiency, 1270~1300 s specific impulse at 200 W anode power and 8 sccm Xe flow rate. The integration test, vibration test, and vacuum·thermal test were performed to verify the normal operation of the HPS under the space and launch environment.