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부분방전을 이용한 초고압 지중 송전 절연 케이블 내부 결함의 패턴분석
박재화(Jae-Hwa Park),이광열(Kwang-Yeol Lee),채석(Seog Choe),오영석(Young-Seong Oh),김학성(Hack-Sung Kim) 전력전자학회 1998 전력전자학술대회 논문집 Vol.- No.-
The insulation of cables which used for Ultra-High Voltage (UHV) underground power transmission requires excellent insulation capability for high voltage. The typical insulation materials are used XLPE. EPR, etc, but insulation efficiency of these is affected by void or alien substances, existed at the inside of insulators. In this paper, the partial discharge patterns of the defects within insulation cable are observed and analyzed. In this test, void, fiber and metal inclusions which possibly exist in cables, are simulated and investigated the patterns of partial discharges for each models Also the relations between calculated field strength and the insulation breakdown voltage. The experiment shows distinct partial discharge patterns in accordance with the kinds of defects within Insulation cable.<br/> <br/>
도로 교통량 조사를 위한 차종 분류 모델의 성능 향상 연구
박재화(Jae Hwa Park),김병근(Pyong-Kun Kim),강미선(Mi-Seon Kang) 한국통신학회 2021 한국통신학회 학술대회논문집 Vol.2021 No.6
본 논문은 도로 교통량 자동화 조사에 사용되는 차종 분류 모델의 신뢰도 향상을 위해 기존의 데이터를 분석, 가공하여 차종 분류 모델의 성능에 영향을 미치는 요소를 분석하고 성능을 향상시킬 방안을 제안하였다. 제안한 방법은 추가적인 검증이나 수집에 비용을 들이지 않고 최소한의 비용으로 모델의 성능을 높일 수 있을 것으로 기대된다.
HVPE 법에서의 공정변수 조절에 의한 bulk GaN 단결정의 두께 최적화
박재화,이희애,이주형,박철우,이정훈,강효상,강석현,방신영,이성국,심광보,Park, Jae Hwa,Lee, Hee Ae,Lee, Joo Hyung,Park, Cheol Woo,Lee, Jung Hun,Kang, Hyo Sang,Kang, Suk Hyun,Bang, Sin Young,Lee, Seong Kuk,Shim, Kwang Bo 한국결정성장학회 2017 韓國結晶成長學會誌 Vol.27 No.2
다양한 성장온도, V/III 비율, 성장속도과 같은 공정변수의 조절을 통하여 GaN 단결정을 성장시키고, 그에 따른 표면 및 재료 내부의 결함분석을 통하여 고휘도 고출력의 소자적용을 위한 bulk GaN 단결정의 두께를 최적화하였다. 2인치 직경의 sapphire 기판 위에 HVPE(hydride vapor phase epitaxy) 공정변수들을 조절하여, 0.3~7.0 mm 두께의 GaN 결정을 성장시켰다. 성장된 GaN 단결정의 구조분석을 위하여 XRD 분석을 사용하였고, 공정변수의 변화에 따른 표면 특성은 광학 현미경을 이용하여 관찰하였다. 성장된 두께에 따른 결함밀도 분석을 위하여 화학습식 에칭하였고, 에칭된 표면을 SEM으로 관찰하였다. GaN single crystals were grown by controlling of various processing parameters such as growing temperature, V/III ratio and growing rate. We optimized thickness of bulk GaN single crystal by analyzing defect of surface and inside of the GaN single crystal for application to high brightness and power device. 2-inch bulk GaN single crystals were grown by HVPE (hydride vapor phase epitaxy) on sapphire and their thickness was 0.3~7.0 mm. Crystal structure of the grown bulk GaN was analyzed by XRD (X-ray diffraction). The surface characteristics of the grown bulk GaN were observed by OM (optical microscope) and SEM (scanning electron microscopy) with measuring EPD (etch pits density) of the GaN crystals.
연구논문 : 초등학생을 위한 과학적 실험 설계 지식 생성 학습 프로그램의 개발 및 적용
박재화 ( Jae Hwa Park ),신동훈 ( Dong Hoon Shin ) 한국초등과학교육학회 2014 초등과학교육 Vol.33 No.3
The purpose of this study is to develop a program for elementary school students` scientific experimental design knowledge generation. This study also investigated the effects of their experimental design ability, as well as the change in the type and elaborateness of their experimental design by applying the program. The subjects of this study was 4 classes in 6th grade of an elementary school located in Seoul, KOREA. The classes were divided into experimental and comparative groups. While the treatment was applied to the experimental group, the comparative group was taught using conventional methods. The pre-test and post-test for students` capability of building scientific experimental design knowledge were conducted to compare the ability of experimental design, the change in the type and elaborateness of experimental design. The findings in this study are as follows: First, the program appeared to be effective in improving experimental design ability. Furthermore, the program appeared to be more effective in generating a higher level of the experimental design type and elaborateness. Therefore, in order to improve experimental design knowledge generation ability, the program can be utilized as effective learning model in elementary school.
HVPE로 성장된 GaN의 용융 KOH/NaOH 습식화학에칭
박재화,홍윤표,박철우,김현미,오동근,최봉근,이성국,심광보,Park, Jae Hwa,Hong, Yoon Pyo,Park, Cheol Woo,Kim, Hyun Mi,Oh, Dong Keun,Choi, Bong Geun,Lee, Seong Kuk,Shim, Kwang Bo 한국결정성장학회 2014 한국결정성장학회지 Vol.24 No.4
수소화기상증착에피탁시로 성장된 GaN 단결정의 표면 특성을 정밀하게 측정하기 위해, 용융 KOH/NaOH 습식화학에칭법을 적용하였다. KOH/NaOH 습식화학에칭법에 에칭속도는 기존의 황산, 인산과 같은 etchant에 비해 느린데, 이는 불용성 코팅층의 형성에 의한 것이다. 따라서 이 방법으로 etch pits density를 더 효율적으로 평가할 수 있었다. 성장된 GaN 단결정을 XRD(X-Ray Diffraction), XRC(X-ray rocking curve)로 결정성을 분석하였으며, 에칭 특성과 표면 형상은 주자전자현미경을 이용하여 관찰하였다. 에칭 실험 결과 격자결함들이 독립적으로 잘 분리되어 있고 그들의 형태가 명확하게 나타나는 최적 에칭 조건은 $410^{\circ}C$, 25분이었다. 이 조건에서 얻은 결함밀도 값은 $2.45{\times}10^6cm^{-2}$이었으며, 이는 상업적으로 이용 가능 한 정도의 재료임을 확인할 수 있었다. The hydride vapor phase epitaxy (HVPE) grown GaN samples to precisely measure the surface characteristics was applied to a molten KOH/NaOH wet chemical etching. The etching rate by molten KOH/NaOH wet chemical etching method was slower than that by conventional etching methods, such as phosphoric and sulfuric acid etching, which may be due to the formation of insoluble coating layer. Therefore, the molten KOH/NaOH wet chemical etching is a better efficient method for the evaluation of etch pits density. The grown GaN single crystals were characterized by using X-ray diffraction (XRD) and X-ray rocking curve (XRC). The etching characteristics and surface morphologies were studied by scanning electron microscopy (SEM). From etching results, the optimum etching condition that the etch pits were well independently separated in space and clearly showed their shape, was $410^{\circ}C$ and 25 min. The etch pits density obtained by molten KOH/NaOH wet chemical etching under optimum etching condition was around $2.45{\times}10^6cm^{-2}$, which is commercially an available materials.
해양에서의 선박사고 예방에 관한 연구 : 울산해역을 중심으로
박재화(Park, Jae-Hwa),문국경(Moon, Kuk-Kyoung) 한국공안행정학회 2021 한국공안행정학회보 Vol.30 No.2
2014년 세월호 참사를 계기로 해양선박사고에 대한 국민들의 관심이 증폭 되었고, 유사 사고가 재발되지 않도록 정부차원의 다각적인 노력이 이루어 졌다. 이러한 노력에도 불구하고 울산해역에서는 2019년 염포부두 화물선 폭발사고, 2012년 석정호 전복사고 등 연간 100여건 이상의 해상선박사고가 발생한 바 있다. 우리나라 액체화물 물동량의 30%를 차지하고 있고, 울산항, 현대중공업 등 8개 국가임해시설이 위치하고 있는 울산해역의 중요성을 감안, 본 연구는 해양경찰청 해상조난사고 통계를 활용하여 최근 10년간 울산해역에서 발생한 해양선박사고를 우리나라 전체사고와 비교, 분석하여 시사점을 찾고자 진행하였다. 특히, 울산 해역에서 발생한 선박사고를 사고형태, 사고원인, 사고에 영향을 미치는 환경요인(시간, 공간, 선박특징)으로 구분하여 분석하였다. 분석결과, 울산해역의 해양선박사고는 전국 평균과 비슷한 형태를 보이고 있는 반면, 울산해역에 통항하는 선박특징(선령, 톤수) 등 일부 요인에 따라 전국평균과 다른 특징을 보이고 있음을 파악하였다. 즉, 울산해역에서는 전국 평균에 비해 중형급 선박의 사고가 많았고, 사고선박의 선령이 높아 선박의 노후도가 높다는 특징이 있었다. 본 연구는 울산해역의 해양선박사고를 줄이기 위한 근본대책으로서 정부차원에서 사고 예방활동을 위한 조직 보강, 기관간 협업체계 보완, 지자체의 노력 강화, 민간차원의 지원 증대 필요성, 해외사례 적용·검토 등 정책적 개선방안을 제시하였다. Ulsan sea area accounts for 30% of Korea’s liquid cargo volume. In that area, eight important coastal facilities are located, including Hyundai Heavy industries and Kori Nuclear Power Plant. This study was conducted to find implications by analyzing maritime accidents in the Ulsan sea area. This study compared and analyzed marine accidents in the Ulsan sea area and the entire Korea sea area by using statistics on maritime distress accidents from the Korea Coast Guard for 10 years from 2010 to 2019. In particular, this study analyzed ship accidents by dividing them into accident types, accidents causes, and environmental factors. As a result of the analysis, it was found that the marine accidents in the Ulsan sea area showed a similar shape to the average of the national ship accidents, while the characteristics of the marine ship accidents in the Ulsan sea area were different from the national average according to some factors such as the characteristics of ship passing through the Ulsan sea area. This study suggested policy improvement measures such as preventive activities at the government level in order to reduce marine accidents.
1980-2019년 기간 동안 소아청소년 알레르기질환에서 항원 감작의 변화
정재화 ( Jae Hwa Jung ),김가은 ( Ga Eun Kim ),박미르 ( Mireu Park ),김수연 ( Soo Yeon Kim ),김민정 ( Min Jung Kim ),이용주 ( Yong Ju Lee ),김윤희 ( Yoon Hee Kim ),김경원 ( Kyung Won Kim ),손명현 ( Myung Hyun Sohn ) 대한천식알레르기학회 2021 Allergy Asthma & Respiratory Disease Vol.9 No.4
Purpose: Allergen sensitization is constantly changing, and understanding these changes can help manage and prevent allergic diseases. This research analyzed and compared the changes in allergen sensitization in children diagnosed with allergic diseases us-ing the skin test and the multiple allergen simultaneous test. Methods: We retrospectively analyzed the data on children who were diagnosed with allergic diseases and received immunother-apy at Yonsei Medical Center from 1980 to 1998 and they were screened for allergen sensitization at Severance Hospital from 2005 to 2019. Results: Between 1980 and 1998, and between 2005 and 2019, data on 3,205 (male, 70.3%; mean age, 7.2±2.9 years) and 15,318 children (male, 62.8%; mean age, 8.8±4.5 years) were analyzed. The sensitized allergens that appeared in the 1980-1998 included Dermatophagoides farinae (91.0%), Dermatophagoides pteronyssinus (76.3%), cockroach (13.5%), and Alternaria (11.5%), in order of frequency; further, the sensitized allergens that appeared in the 2005-2019 included D. farinae (45.0%), D. pteronyssinus (39.6%), cat dander (12.2%), and dog dander (9.1%), in order of frequency. D. farinae and D. pteronyssinus demonstrated the highest sensitization rates, although the rates decreased gradually. The sensitization to cat dander and dog dander showed a growing trend, and sensiti-zation to Humulus japonicus, Candida, and cockroach decreased after 2005. Conclusion: Over the past 40 years, the allergen sensitization in Korean children with allergic diseases has increased. These changes reflect lifestyle and environmental changes and influence allergic disease management approaches. Thus, changes in allergic sensi-tization should be monitored continuously. (Allergy Asthma Respir Dis 2021;9:208-215)