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Lee, Jin-A,Lee, Sue-Hyun,Lee, Changhoon,Chang, Deok-Jin,Lee, Yong,Kim, Hyoung,Cheang, Ye-Hwang,Ko, Hyoung-Gon,Lee, Yong-Seok,Jun, Heejung,Bartsch, Dusan,Kandel, Eric R.,Kaang, Bong-Kiun The Rockefeller University Press 2006 The Journal of cell biology Vol.174 No.6
<P>Long-term memory requires transcriptional regulation by a combination of positive and negative transcription factors. <I>Aplysia</I> activating factor (ApAF) is known to be a positive transcription factor that forms heterodimers with ApC/EBP and ApCREB2. How these heterodimers are regulated and how they participate in the consolidation of long-term facilitation (LTF) has not, however, been characterized. We found that the functional activation of ApAF required phosphorylation of ApAF by PKA on Ser-266. In addition, ApAF lowered the threshold of LTF by forming a heterodimer with ApCREB2. Moreover, once activated by PKA, the ApAF–ApC/EBP heterodimer transactivates enhancer response element–containing genes and can induce LTF in the absence of CRE- and CREB-mediated gene expression. Collectively, these results suggest that PKA-activated ApAF–ApC/EBP heterodimer is a core downstream effector of ApCREB in the consolidation of LTF.</P>
Lee, Geumbee,Kim, Jung Wook,Park, Heun,Lee, Jae Yoon,Lee, Hanchan,Song, Changhoon,Jin, Sang Woo,Keum, Kayeon,Lee, Chul-Ho,Ha, Jeong Sook American Chemical Society 2019 ACS NANO Vol.13 No.1
<P>For practical applications of high-performance supercapacitors as wearable energy storage devices attached to skin or clothes, the supercapacitors are recommended to have stable mechanical and electrochemical performances during dynamic deformations, including stretching, due to real-time movements of the human body. In this work, we demonstrate a skin-like, dynamically stretchable, planar supercapacitor (SPS). The SPS consists of buckled manganese/molybdenum (Mn/Mo) mixed oxide@multiwalled carbon nanotube (MWCNT) electrodes; organic gel polymer electrolyte of adiponitrile, succinonitrile, lithium bis(trifluoromethanesulfonyl)imide, and poly(methyl methacrylate); and a porous, elastomeric substrate. The addition of an Mn/Mo mixed oxide to the MWCNT film produces an 8-fold increase in the areal capacitance. The use of an organic solvent-based electrolyte enhances the operation cell voltage to 2 V and air stability to one month under ambient air conditions. The fabricated planar supercapacitors are biaxially stretchable up to 50% strain and maintain ∼90% of their initial capacitance after 1000 repetitive stretching/releasing cycles. Furthermore, the SPS exhibits stable electrochemical performance under dynamic stretching in real time regardless of the strain rate and performs reliably during repetitive bending/spreading motions of an index finger while attached to skin.</P> [FIG OMISSION]</BR>
Sharkskin-mimetic desalination membranes with ultralow biofouling
Choi, Wansuk,Lee, Changhoon,Lee, Dahye,Won, Young June,Lee, Gi Wook,Shin, Min Gyu,Chun, Byoungjin,Kim, Taek-Seung,Park, Hee-Deung,Jung, Hyun Wook,Lee, Jong Suk,Lee, Jung-Hyun The Royal Society of Chemistry 2018 Journal of Materials Chemistry A Vol.6 No.45
<P>Biofouling is a pervasive problem for any materials that are exposed to aquatic environments. Especially, it is a dire problem for the desalination membranes used to sustainably supply clean water, necessitating development of the methods to mitigate membrane biofouling. We present a topological modification approach to achieve ultralow fouling of water desalination membranes by realizing the sharkskin-mimetic (Sharklet) surface patterns and identify their unique antifouling mechanism based on computational fluid dynamics simulation. Our approach relies on a newly developed layered interfacial polymerization that can produce a conformal selective layer on patterned porous supports prepared by phase separation micromolding. The Sharklet-patterned membrane exhibited remarkably low biofouling compared to the conventional membranes with irregular roughness and topologically modulated membranes with simple patterns. Its superior biofouling resistance is attributed to the unique Sharklet geometry that can significantly inhibit biofilm growth. Furthermore, under dynamic flow conditions, the intricate Sharklet geometry induces a complex surface flow by symmetrically generating a secondary flow perpendicular to the primary flow, forming a periodic inflow and outflow along the pattern. The reinforced primary and secondary flows of the Sharklet pattern may further contribute to its excellent biofouling resistance.</P>
EDISON_CFD : 유체공학 교육·연구용 e-Science 기반 시뮬레이션 소프트웨어 및 콘텐츠 개발
이근배(Kuen-Bae Lee),이성욱(Seonguk Lee),이창훈(Changhoon Lee),최정일(Jung-il Choi),이도형(Dohyung Lee),김종암(Chongam Kim) 대한기계학회 2011 대한기계학회 춘추학술대회 Vol.2011 No.10
EDISON_CFD, an abbreviation of EDucation-research Integration through Simulation On the Net for Computational Fluid Dynamics, is a virtual organization designed to support the education research in fluid engineering on the e-Science environment. As the first step, our research group focuses on developing simulation software and contents based on numerical analyses. Through national research projects, many R&D results have been developed and accumulated in universities and research institutes. However, educational contents used for delivering advanced researches to inspire students still lack. Thus, development of software and contents for effective and advanced education & research is necessary. The present work aims to establish the platform of simulation softwares and contents for online education research in fluid engineering using the results of the state-of-art techniques. This will fortify not only the capability of students in fluid engineering but also the national strength in research.
회절을 고려한 직립 이안제에 작용하는 파력의 공간적 변화
정재상(Jae-Sang Jung),이창훈(Changhoon Lee) 한국해안해양공학회 2021 한국해안해양공학회 논문집 Vol.33 No.6
본 연구에서는 기존에 선형파 이론으로 제시된 반무한방파제 주변의 회절에 대한 해를 중첩하여 직립 이안제 주변에 발생하는 회절에 관한 해석해를 제시하였다. 그리고, 이를 이용하여 이안제 전면과 후면, 그리고 전·후면에 작용하는 합성파력에 대한 해를 유도하였다. 이안제 전면과 후면에서는 회절파와 중복파, 이안제 양쪽에서 회절한 회절파와 회절파 사이의 간섭에 의해 상대진폭이 공간상에서 주기적으로 변하는 양상을 보였다. 규칙파, 일방향 불규칙파 및 다방향 불규칙파를 대상으로 직립 이안제에 작용하는 파력을 검토하였다. 규칙파 내습시 이안제 전·후 면의 파력을 모두 고려한 최대 합성파력의 경우 회절을 고려하지 않았을 경우에 비해 최대 1.6배까지 파력이 증가하는 것으로 나타났다. 이는 Jung et al.(2021)이 반무한 방파제에 대해 회절효과를 고려하여 검토한 결과인 1.34배보다 큰 수치이다. 이안제에 작용하는 최대파력은 규칙파, 일방향 불규칙파, 다방향 불규칙파 순으로 크게 계산되었다. 파랑이 비스듬히 입사하는 경우 이안제에 수직으로 입사하는 경우보다 최대파력이 크게 나타나는 경우도 발견되었다. 따라서, 이안제를 설계할 때, 회절효과, 이안제 전·후면에 작용하는 파력, 파랑의 입사각의 고려가 중요함을 알 수 있다. In this study, the analytical solution for diffraction near a vertical detached breakwater was suggested by superposing the solutions of diffraction near a semi-infinite breakwater suggested previously using linear wave theory. The solutions of wave forces acting on front, lee and composed wave forces on both side were also derived. Relative wave amplitude changed periodically in space owing to the interactions between diffracting waves and standing waves on front side and the interactions between diffracting waves from both tips of a detached breakwater on lee side. The wave forces on a vertical detached breakwater were investigated with monochromatic, uni-directional random and multi-directional random waves. The maximum composed wave force considering the forces on front and lee side reached maximum 1.6 times of wave forces which doesn’t consider diffraction. This value is larger than the maximum composed wave force of semi-infinite breakwater considering diffraction, 1.34 times, which was suggested by Jung et al. (2021). The maximum composed wave forces were calculated in the order of monochromatic, uni-directional random and multi-directional random waves in terms of intensity. It was also found that the maximum wave force of obliquely incident waves was sometimes larger than that of normally incident waves. It can be known that the considerations of diffraction, the composed wave force on both front and lee side and incident wave angle are important from this study.
0.18 μm CMOS 기반 인덕터를 사용하지 않는 6~18 GHz 7-Bit 28 dB 가변 신호 감쇠기
나윤식(Yun-Sik Na),이상훈(Sanghoon Lee),김재덕(Jaeduk Kim),이왕용(Wangyoung Lee),이창훈(Changhoon Lee),이성호(Sungho Lee),서문교(Munkyo Seo),이성철(Sung Chul Lee) 한국전자파학회 2016 한국전자파학회논문지 Vol.27 No.1
본 논문에서는 6~18 GHz 대역 7-bit 28 dB 가변 신호 감쇠기의 설계 및 측정결과에 대하여 기술하였다. 기존의 switched-T 감쇠기에 칩 사이즈를 최소화하기 위해 인덕터를 사용하지 않았고, 보상용 병렬 커패시터를 추가하여 참조 상태(reference state)와 감쇠 상태간의 위상 변화를 최소화하였다. 설계된 감쇠기는 0.18 μm CMOS 공정을 이용하여 제작하였다. 측정된 감쇠기의 해상도와 전체 감쇠 범위는 각각 0.22 dB 및 28 dB이다. 6~18 GHz의 동작 주파수에서 RMS 감쇠오차는 0.26 dB 이하, 위상 오차는 3.2° 이하로 측정되었으며, 참조상태 손실은 12.4 dB 이하이다. 전체 주파수 범위와 감쇠상태에서 입출력 반사손실은 9.4 dB 이상이다. 패드를 포함하지 않은 칩 면적은 0.11 mm²이다. This paper presents a 6~18 GHz 7-bit digital-controlled attenuator. The proposed attenuator is based on switched-T architecture, but no inductor is used for minimum chip size. The designed attenuator was fabricated using 0.18 μm CMOS process, and characterized using on-wafer testing setup. The resolution(minimum attenuation step) and the maximum attenuation range of the attenuator were measured to be 0.22 dB and 28 dB, respectively. The measured RMS attenuation error and the RMS phase error for 6~18 GHz were less than 0.26 dB and 3.2°, respectively. The reference state insertion loss was less than 12.4 dB at 6~18 GHz. The measured input and output return losses were better than 9.4 dB over all frequencies and attenuation states. The chip size is 0.11 mm² excluding pads.
A Lagrangian Stochastic Model for Turbulent Dispersion
Lee, Changhoon,Kim, Byunggu,Kim, Namhyun The Korean Society of Mechanical Engineers 2001 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.15 No.12
A Lagrangian stochastic model is adopted for the calculations of turbulent dispersion in turbulent channel flows. Dispersion of a fluid particle and relative dispersion between two particles released at the sane location are investigated and compared with the classical seating relations for homogeneous turbulence. The viscous effect is realized by adding a Browinian random walk to the calculation of the position of a particle. The near-wall accumulation of particles is examined.