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장승엽 동국대학교 WISE(와이즈)캠퍼스 신라문화연구소 2020 新羅文化 Vol.57 No.-
This study analyzes the road vestiges excavated and researched in Gyeongju area, which was the royal place during ancient Silla Kingdom in order to check the structure of the road system during that period. Though there are many road vestiges found in Gyeongju area, most of them were interpreted as the roads made during Silla Kingdom and Unified Silla Kingdom. Most of the researchers have not focused on the sequence of the times on the study of ancient roads but has limited the study on the Bangrije of Silla to the road made in Unified Silla kingdom. This kind of research trend led to the result of interpreting the time based on only the soil layer and Archaeological Relics made in Unified Silla Kingdom even though they are only the visible aspects of the Archaeological Relics. The author judged that it was wrong to judge the timing of the excavated relics based on the excavated relics. The author believes that it is not right to judge the length of use of the road just by its appearance, as the soil layer of the road has been severely disturbed and the upper floors have been damaged recently. In addition, most road markings must be connected to the boundary of the research area before they can be connected to the surrounding site. Once the road is constructed, it can be used consistently through improvements and repairs if necessary. Based on this, we analyzed 64 roads found in Gyeongju. The road Archaeological Relics estimated to have been made in the Unified Silla period and the traces considered to have been used during the Joseon era were compared with other data. In addition, they compared the directions of the roads in the ancient maps and the modern maps produced during the Japanese Empire State and saw if they were related to each other. They then compared with aerial photographs of Gyeongju, which were taken in 1954, to identify changes in terrain and roads leading to modern times. As a result, the road and surrounding Archaeological Relics whose artifacts can span up to Joseon Kingdom were found out and the roads were confirmed which connected to the main area located in Gyeongju area by period. This means that a road was either used for a period only or continuously used at the new space as time goes by. These results confirm that there shall be new research on the road vestiges of many roads which has been researched. However. as shown in the fact that even a confirmed road vestige can be connected to the research and excavation site. So, the total interpretation shall not be made with a part of the Archaeological Relics only. Likewise, the study has limitation as it cannot escape the assumption to some extent. Notwithstanding this, for the study of the period of road and how long it lasted, it is necessary to always make the comprehensive comparison and review of the related data.
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고로슬래그 미분말을 65% 치환한 고성능 콘크리트의 자기 및 건조수축 특성
장승엽,류화성,윤용식,권성준 한국구조물진단유지관리공학회 2017 한국구조물진단유지관리공학회 논문집 Vol.21 No.3
고로슬래그 미분말은 공학적으로 우수한 건설산업 부산물이며, 최근들어 환경부하 저감 및 사용 활성화를 위해 대단위 슬래그 치 환 콘크리트가 많이 연구되고 있다. 본 연구에서는 목표 강도를 50 MPa로 설정하고 고로슬래그미분말 치환률을 65%로 고려한 대단위 치환 슬 래그 콘크리트를 제조하여 건조수축특성과 초지재령 특성을 평가하였다. 이를 위해 3 수준의 콘크리트를 제조하였으며, 슬럼프 플로우, 강도, 건조 및 자기수축에 대한 실험을 수행하였다. 실험결과, 보통 포틀랜트 시멘트를 100% 함유한 콘크리트(OPC 100)에 비하여 재령 7일전의 강 도는 약간 감소하였으나, 슬래그 치환 배합은 수화에 필요한 충분한 자유수를 가졌으므로 28일 재령에서는 우수한 강도 발현을 나타내었다. 또 한 재령 3일까지 큰 자기수축으로 인하여, OPC 100 배합에서는 건조수축이 크게 평가되었지만, 65% 고로슬래그 미분말을 치환한 배합에서는 초기재령의 자기수축 성능이 개선되어 우수한 건조수축거동을 나타내었다. 특히 단순 질량 치환배합(BS 65)보다 물-결합재비(0.27)와 단위수 량(163kg/m3)을 낮춘 OPTBS 65에서 더욱 우수한 건조수축 및 자기수축 거동을 나타내었다. GGBFS (Ground Granulated Blast Furnace Slag) is a byproduct with engineering advantages and HVSC (High Volume Slag Concrete) is widely attempted due to active utilization and reduction of eco-load. In the present work, characteristics of drying shrinkage and early-aged behavior are evaluated for the concrete with 65% replacement ratio of GGBFS and 50MPa of design strength. For the work, 3 different mix conditions are considered and several tests including slump flow, compressive strength, drying and autogeneous shrinkage are performed. From the test, OPC 100 mixture without replacement shows higher strength development before 7 days, however the strength reduction in concrete replaced with GGBFS is not significant due to sufficient free water for cement hydration. OPC 100 mixture also shows significant drying shrinkage due to a great autogeneous shrinkage before 3 days. In the concrete with GGBFS replacement, the drying shrinkage behavior is improved due to relatively small deformation by autogeneous shrinkage. The mixture (OPT BS 65) with lower w/b ratio (0.27) and unit content of water (160kg/m3) shows more improved shrinkage behavior than BS 65 mixture which has simple replacement of GGBFS with 0.30 of w/b and 165kg/m3 of water unit content.
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Ferroelectric Properties of Multiferroic Hexagonal ErMnO3 Thin Films
장승엽,Daesu Lee,Jung-Hyuk Lee,Pattukkannu Murugavel,정진석 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.55 No.2
The authors investigated the ferroelectric properties of epitaxial thin films of hexagonal ErMnO3 fabricated on Pt(111)/Al2O3(0001) substrates. The ferroelectric characteristics were observed with a reasonable remnant polarization value (3.0 μC/cm2 at 160 K). However, the films exhibited an unusual antiferroelectric-like behavior with a temperature- and an electric-field-dependence. The coercive field showed an abrupt increase below the antiferromagneitc ordering temperature, indicating the possibility of interference between ferroelectric domains and antiferromagnetic domains. The authors investigated the ferroelectric properties of epitaxial thin films of hexagonal ErMnO3 fabricated on Pt(111)/Al2O3(0001) substrates. The ferroelectric characteristics were observed with a reasonable remnant polarization value (3.0 μC/cm2 at 160 K). However, the films exhibited an unusual antiferroelectric-like behavior with a temperature- and an electric-field-dependence. The coercive field showed an abrupt increase below the antiferromagneitc ordering temperature, indicating the possibility of interference between ferroelectric domains and antiferromagnetic domains.
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차세대 고효율 전력반도체 연구: GaN HFET 전력스위칭 소자
장승엽,문성운,박진홍 한국물리학회 2015 새물리 Vol.65 No.1
Based on current research results, we introduce a GaN heterojunction field-effect transistor (HFET) for a next-generation power semiconductor device. The wide bandgap (E$_{G}$ = 3.4 eV) and the high-temperature stability of GaN make it attractive for high-power device applications. The low on-resistance and the fast switching speed of the GaN HFET will allow low-loss and high-power operation to be realized and consequently, allow the system size to be reduced. Here, first, we introduce the basics of the power semiconductor; then, we focus on the properties of the GaN HFET and the key technologies to make the GaN HFET a next-generation power switching device. 차세대 전력반도체 소자로 각광받고 있는 GaN 이종접합 전계효과 트랜지스터 (heterojunction field-effect transistor, HFET) 전력스위칭 소자에 대한 연구를 소개하고자 한다. GaN HFET는 와이드 밴드갭 (wide bandgap, E$_{G}$ = 3.4 eV) 특징과 고온 안정성 등의 재료적인 장점 및 이종접합 (heterojunction) 에 의한 2차원 전자가스 (2DEG) 를 활용하는 구조로 전력스위칭 소자로 큰 장점을 가진다. GaN HFET 전력스위칭 소자의 낮은 온저항, 높은 스위칭 속도는 고효율, 고주파 동작을 가능하게 하여, 전력 분배/변환 효율의 개선 및 전력 시스템 소형화를 가능하게 한다. 본 논문에서는 전력반도체에 대한 간단한 소개부터 시작하여, GaN 물질 특성 및 기본적인 HFET 소자 특성에 대해 기술하고, 현재 GaN HFET 전력스위칭 소자 구현의 핵심 기술에 대해 논의하고자 한다.
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PLD Growth of Epitaxially-stabilized 5d Perovskite SrIrO3 Thin Films
장승엽,문순재,전병철,정진석 한국물리학회 2010 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.56 No.6
We have investigated the details of the growth behavior of epitaxially-stabilized 5d perovskite SrIrO3 thin films deposited by using a pulsed laser deposition method. During the deposition,a marked decrease in plume size was observed, which was accompanied by the formation of Irrich conical structures on the surface of the polycrystalline SrIrO3 target. High-resolution X-ray diffraction studies revealed that films thicker than certain thickness exhibited a mixed character of a high-quality phase and a relatively poor-quality phase while thinner films showed a high crystalline quality. These observations offer valuable information on the correlation between the plume status and the crystalline quality of iridate thin films.
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