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Fast Interlock System for Machine Protection in PLS-II
Mujin Lee,Taekyun Ha,이재유,Suk-Ho Ahn,황일문 한국물리학회 2020 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.76 No.4
We overview the system design of the Pohang Light Source-II (PLS-II), and demonstrate that synchrotron radiation is the cause of a recent incident that damaged the vacuum components. To preclude further incidents, we designed a system that shuts off the beam if such damage is imminent. We used an ANSYS simulation to estimate the appropriate time allowed for this shut-off then. A Fast Interlock System is implemented to accomplish beam shut-off within this time. In bench test, this system shut down the beam within the acceptable time. The installation and the operation of the Fast Interlock System in PLS-II is planned.
Hopping Nature of Magnetic Skyrmion Motion
Mujin You,Moojune Song,Seungmo Yang,Tae-Seong Ju,Min Gyu Albert Park,Kyoung-Whan Kim,Kab-Jin Kim 한국자기학회 2021 한국자기학회 학술연구발표회 논문개요집 Vol.31 No.2
It is essential to study the dynamics of magnetic solitons such as domain walls (DWs), vertical Bloch lines (VBLs), and vortices for understanding physical features of emergent excitation. Skyrmion, a topologically protected magnetic soliton, drew a lot of attention because of its nanoscale size, low current controllability, and topological stability, which makes it an attractive candidate for technological applications, such as magnetic memory and logic devices. However, due to the complicated energy landscape and stochastic thermal motion, analyzing the current-induced dynamics of a skyrmion in the actual world is difficult, necessitating statistical treatment. Using magneto-optical Kerr effect (MOKE) microscopy and a blob-tracking method, we discover the current-induced hopping motion of skyrmions in the W/CoFeB/Ta/MgO ferromagnetic thin film. Skyrmions follow a different scaling behavior compared with magnetic DWs, which follow the conventional creep scaling law in the 2D regime. We show that skyrmions display a stochastic particle-like hopping motion, as evidenced by the stop-start characteristics of skyrmion motion at low current density (7.0 × 10<SUP>7</SUP> ~ 1.6 × 10<SUP>9</SUP> A/m²), thermal diffusion, and forward-and-backward movement. Collective segment theory with the bottleneck process shows that skyrmions exhibit hopping-like scaling behavior because of geometric constraints coming from the closed boundaries. Our study on the rigid-particle model further verifies the hopping nature of skyrmions. Our findings provide fundamental and physical insights into the stochastic motion of particles in the weakly-driven regime, which will be useful to many pioneers in the field.
오무진(Mujin Oh),최수길(Sugil Choi),이세형(Seihyung Lee),백광열(Gwangyeol Baek),원종성(Jongsung Won),배태수(Taesoo Bae),탁태오(Taeoh Tak) 한국자동차공학회 2009 한국자동차공학회 학술대회 및 전시회 Vol.2009 No.11
This research deals with biomechanic analysis of steering motion of drivers and application to the configuration design of steering wheels. Upper body motion of a driver is obtained by motion capture of steering motion in a mockup driving seat with a steering system capable of applying external torque due to various driving environment. Combined dynamic model that includes driver's upper body muskuloskeletal system and the steering system is setup. Through inverse dynamic analysis by providing motion data obtained from motion capture and external steering torque, muscle forces in the arms are calculated. EMG and muscle forces are compared to validate the computed results, which showed good correlation. Parameter study of muscle force due to different configurations of steering wheel and driver's posture is performed in order to establish theoretical basis for biomechanic based steering wheel design.