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Ferrimagnetic FexMn₁-x thin films on GaAs(001)
최성열,최정용,홍순철,조성래,박현민,박용섭,이규원,정명화 한국자기학회 2005 한국자기학회 학술연구발표회 논문개요집 Vol.15 No.1
We have successfully grown epitaxial Fe_xMn_(1-x) thin films on GaAs(001) substrate by using MBE(molecular beam epitaxy), exhibiting ferrimagnetic ordering at 750 K. In Fe_xMn_(1-x)(x=0.5) thin film, the coercivity field was 310 Oe and the magnetic moment from the saturated magnetization was 3.17 μ_B at 10 K. The coercivity fields increased with Mn concentrations decease. The crystal structure of Fe_xMn_(1-x)(x=0.8, 0.7, 0.6, and 0.5.) thin films was α-Mn(A12) with a=8.83~8.89 Å.
Epitaxial (Mn0.66Cr0.33)₂As and (Fe0.66Mn0.33)₂As thin films : magnetic and structural properties
최성열,최정용,홍순철,조성래,박현민,박용섭,이규원 한국자기학회 2005 한국자기학회 학술연구발표회 논문개요집 Vol.15 No.1
We grew (Mn_(0.66)Cr_(0.33))₂As and (Fe_(0.66)Mn_(0.33))₂As thin films directly on n-type Si (100) substrate by molecular beam epitaxy (MBE) at the substrate temperature, Ts=300 ℃. The growth was monitored with RHEED (reflection high-energy electron diffraction). We have observed streaky RHEED patterns, indicating the layer-by-layer growth of (Mn_(0.66)Cr_(0.33))₂As and (Fe_(0.66)Mn_(0.33))₂As thin films. We found that the crystal structure of (Mn_(0.66)Cr_(0.33))₂As and (Fe_(0.66)Mn_(0.33))₂As thin films were the tetragonal Mn₂As type with a=3.745 Å and a= 3.70 Å. (Mn_(0.66)Cr_(0.33))₂As thin film shows spin-glass behavior below 130 K, while (Fe_(0.66)Mn_(0.33))As alloy shows ferrimagnetic ordering at around room temperature.
1차원 이류·확산 방정식에 대한 유한차분법과 유한해석법의 비교연구
최성열,조원철,이원환,Choi, Song Yeol,Cho, Won Cheol,Lee, Won Hwan 대한토목학회 1993 대한토목학회논문집 Vol.13 No.3
본 연구는 Navier-Stokes 식의 모형방정식으로 이류 및 확산거동을 갖는 선형화된 Burgers 방정식과 비선형 형태의 Burgers 방정식을 선택하여, 이에 대한 유한차분법과 유한해석법의 수치해를 해석해와 비교하여 봄으로써, 유한해석법의 응용성에 대해 고찰한 것이다. 본 연구를 통하여 얻어진 성과를 요약하면 다음과 같다. Burgers 방정식 및 선형화된 Burgers 방정식의 정상상태의 해석해를 사용하여 두 수치기법에 따른 수치해를 비교해 본 결과, 해석해와의 근사정도를 동일 기준 하에서 살펴볼 때, 유한해석법이 유한차분법보다 우수한 것으로 나타났다. Burgers 방정식의 비정상상태의 해석해에 대한 정확성 또한 유한해석법이 보다 잘 일치하는 것으로 나타났다. 특히 유한해석법은 유한차분법의 사용시 격자 크기의 선택에 따라 해의 수렴과정에서 발생할 수 있는 위상오차에 기인한 진동현상이 전혀 발생하지 않는다는 것을 확인할 수 있었으며, 따라서 유한해석법은 수치기법상 위상오차로부터 자유로운 안정된 해석기법이라고 판단된다. In this study, the applicability of finite analytic method (FAM) is studied by selecting linearized-Burgers equation and Burgers equation which have convective and diffusive behaviors as the model equation of Navier-Stokes equations and by comparing numerical solution of finite difference method (FDM) and finite analytic method. The results are as follows. It is shown that the convergence of FAM for steady-state analytic solution of linearized-Burgers equation and Burgers equation is better than that of FDM under the same criteria. Also the accuracy of FAM for transient solution of Burgers equation is excellent. Especially, it is shown that oscillation phenomenon due to dispersion errors which occur according to the choice of grid size in FDM does not occur in FAM at all. So, it can be thought that FAM is numerically very stable scheme, which is free from dispersion errors.
What are Technical Hurdles of Verification for North Korea’s Nuclear Program?
최성열,전은주 한국방사성폐기물학회 2022 방사성폐기물학회지 Vol.20 No.1
The denuclearization of North Korea was unpredictable and resulted in radical changes. Despite the skepticism and disappointment surrounding denuclearization, it is important for certain verification technologies to establish what is technically possible or practically impossible, and how reliable these technical means are. This article presents the technical hurdles in nuclear verification by systematically categorizing them into issues of correctness and completeness. Moreover, it addresses the safety and security risks during the denuclearization process, including the radiological impact on humans, environmental effects, and the illegal transfer of material, information, and technologies.
FDTD 병렬화 알고리즘을 이용한 무선랜용 마이크로스트립 대역통과 필터 설계
최성열,박경수,고영호 대한전기학회 2004 전기학회논문지C Vol.53 No.7(C)
In this paper, the four-pole elliptic function microstrip filter at 2.4GHz band with fractional bandwidth of 4% is realized using compact miniaturized hairpin resonators. The parallel algorithm FDTD method is used to analyze S-parameter of hairpin resonator filter more accurately, and to calculate the electric coupling and magnetic coupling among the hairpin resonators. Absorbing boundary conditions for mesh termination used Sulivan's simplified PML and the FDTD code was paralleled by MPI for IBM SP2 which had enhanced calculation speed. The experimental measurements are performed by HP8720D vector network analyzer. Measured results on fabricated hairpin type cross coupled bandpass filters show good agreements with theoretic results.
최성열,조원철,이원환,Choi, Song Yeol,Cho, Won Cheol,Lee, Won Hwan 대한토목학회 1992 대한토목학회논문집 Vol.12 No.3
광양만의 지형변화에 따른 유황변화를 수심방향으로 적분된 2 차원 조석방정식을 사용하여 검토하였다. 연구결과 부두건설에 따른 해수면적의 감소로 인해 광양만으로 유입하는 조석량이 작아졌으며, 이로 인해 묘도를 중심으로한 만 외측에서는 조위차가 약간 커졌으며, 만내측에서는 전반적으로 수위가 하강한 것으로 나타났고, 특히 간조시의 수위 하강현상이 뚜렷하게 나타났다. 유속의 변화양상은 광양만 전체에 걸쳐 건설전 보다 작아졌으나, 광양동천에서 만으로 유입되는 수로에서는 수로 단변의 축소로 유속이 증가한 것으로 나타났다. 또한 대조기 시에 광양만으로 유입하는 수어천, 광양동천, 그리고 만의 외부경계인 섬진강으로 부터의 홍수량을 100 년 빈도로 한 결과, 섬진강하구에서는 약 1.2 m 그리고 광양만 내측에서는 약 0.3 m 의 수면상승을 초래하는 것으로 나타났다. The variation of flow pattern caused by the topographical change of Kwangyang bay, is analyzed using the numerical tidal model for the depth-integrated two- dimensional long wave equation. The results of study are as follows. Due to pier construction, the area of water surface is deceased and the water inflow into the Kwangyang bay is reduced. For this result, at the outer bay of Myo island, the tidal range is slightly increased. And at the inner bay, water level is dropped generally, and especially at the time of low water tide, the phenomena of water level drop obviously appears. According to the variation pattern, flow velocities is lower than those of non-construction condition over the Kwangyang bay. But at the channel(from Kwangyang east stream) flowing into the east Kwangyang bay, for the contraction of channel profile, flow velocity is increased. The study based on the 100 year frequency design flood discharge from Sueocheon(river) and Dongcheon(river) which are flowing into the bay and Seomjin River flowing along the boundary of the bay is also performed. During the spring tide condition, the results showed the rise of water level about 1.2 m at Seomjin River Estuary and 0.3 m at inner bay is occurred.