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THE UFFO SLEWING MIRROR TELESCOPE FOR EARLY OPTICAL OBSERVATION FROM GAMMA RAY BURSTS
NAM, JIWOO,AHMAD, S.,AHN, K.,BARRILLON, P.,BRANDT, S.,BUDTZ-JØRGENSEN, C.,CASTRO-TIRADO, A. J.,CHANG, S.-H.,CHEN, C.-R.,CHEN, P.,CHOI, Y. J.,CONNELL, P.,DAGORET-CAMPAGNE, S.,EYLES, C.,GROSSAN, B.,HUAN World Scientific 2013 Modern physics letters A Vol.28 No.2
<P> While some space born observatories, such as SWIFT and FERMI, have been operating, early observation of optical after grow of GRBs is still remained as an unexplored region. The Ultra-Fast Flash Observatory (UFFO) project is a space observatory for optical follow-ups of GRBs, aiming to explore the first 60 seconds of GRBs optical emission. Using fast moving mirrors to redirect our optical path rather than slewing the entire spacecraft, UFFO is utilized to catch early optical emissions from GRB within 1 sec. We have developed the UFFO Pathfinder Telescope which is going to be on board of the Lomonosov satellite and launched in middle of 2012. We will discuss about scientific potentials of the UFFO project and present the payload development status, especially for Slewing Mirror Telescope which is the key instrument of the UFFO-pathfinder mission. </P>
Ultra Fast Flash Observatory to observe the prompt photons from Gamma Ray Bursts
Jiwoo Nam,Steven Boggs,G. Ripov,Bruce Grossan,Jin-A Jeon,Joo-Young Jin,Ae-Ra Jung,Ji-Eun Kim,Minsoo Kim,Yong-Kweon Kim,P. Klimov,B. Khrenov,Chang-hwan Lee,Jik Lee,Go-Woon Na,Shin-Woo Nam,Il-Heung Park 한국천문학회 2009 天文學會報 Vol.34 No.1
남지우(Jiwoo Nam),유홍선(Hong Sun Ryou),조성욱(Seong Wook Cho) 한국산학기술학회 2017 한국산학기술학회논문지 Vol.18 No.10
제동 장치는 기계장치의 사용자나 시스템의 안전관점에서 가장 중요한 요소 중 하나이며, 작동 조건 내에서 신뢰성 있는 제동력이 유지 되어야 한다. 일반적으로 브레이크는 운동에너지를 마찰을 통해 열에너지로 변환하여 회전하는 기계장치를 제동한다. 운동에너지가 열에너지로 전환되는 과정에서 고온의 열이 발생하여 기계적 거동에 영향을 준다. 마찰열은 브레이크 시스템의 열팽창 및 마찰계수 변화 등에 영향을 주고 제어되지 않는 고온은 브레이크 성능을 저하시킨다. 따라서 브레이크의 발열을 예측하고 이를 제어하는 것은 중요하다. 마찰열을 예측하기 위한 다양한 수치해석 연구들이 수행되었지만, 계산의 효율 및 재원의 한계로 수치해석의 경계조건을 다양한 형태로 가정하여 마찰열 예측 연구를 수행하였다. 가정된 마찰열 거동은 실제 열전달 온도 분포 경황과 차이가 있고 이를 이용한 냉각 효과나 열응력 수치해석 결과의 신뢰성이 부족하다. 이러한 한계점을 극복하고 마찰열 예측 시뮬레이션 절차를 정립하기 위하여 본 연구에서는 열-구조 결합 요소를 사용하여 브레이크 시스템의 마찰열 발생을 직접적으로 모사하는 시뮬레이션을 수행하였다. 본 논문은 Finite Element Method(FEM)을 이용하여 브레이크 작동에 따른 마찰열 발생을 모사하고 열분포 특성을 분석하기 위해 브레이크 모델을 대상으로 열-구조 연성요소를 적용한 수치해석 연구를 수행하였다. 이 연구는 마찰열 직접 모사의 필요성을 제안하고 시뮬레이션에 필요한 정보를 제공할 수 있다 판단된다. The braking system is one of the most important components in vehicles and machines. It must exert a reliable braking force when they are brought to a halt. Generally, frictional heat is generated by converting kinetic energy into heat energy through friction. As the kinetic energy is converted into heat energy, high temperature heat is generated which affects the mechanical behavior of the braking system. Frictional heat affects the thermal expansion and friction coefficient of the brake system. If the temperature is not controlled, the brake performance will be decreased. Therefore, it is important to predict and control the heat generation of the brake. Various numerical analysis studies have been carried out to predict the frictional heat, but they assumed the existence of boundary conditions in the numerical analysis to simulate the frictional heat, because the simulation of frictional heat is difficult and time consuming. The results were based on the assumption that the frictional heat is different from the actual temperature distribution in a rotating brake system. Therefore, the reliability of the cooling effect or thermal stress using the results of these studies is insufficient. In order to overcome these limitations and establish a simulation procedure to predict the frictional heat, this study directly simulates the frictional heat generation by using a thermal-structure coupling element. In this study, we analyzed the thermo-mechanical behavior of a brake model, in order to investigate the thermal characteristics of brake systems by using the Finite Element method (FEM). This study suggests the necessity to directly simulatethe frictional heating and it is hoped that it can provide the necessary information for simulations.
이지우 ( Jiwoo Lee ),남소혜 ( So Hye Nam ),이장호 ( Jang Ho Lee ),유동열 ( Dong Ryeol Yoo ),김진희 ( Jin Hee Kim ),김미정 ( Mee Jeong Kim ),김명환 ( Myung-hwan Kim ) 대한내과학회 2019 대한내과학회지 Vol.94 No.5
원발성 췌장 림프종은 췌장 종양 중에서 매우 드문 질환이다. 원발성 췌장 림프종의 치료는 대부분 외과적 수술보다는 항암 치료 또는 방사선 치료를 먼저 시행하므로 췌장에 발생하는 다른 종양과의 감별진단이 중요하다. 또한 본 증례와 같이 림프종 중에서도 조직 아형에 따라 치료 원칙이 차이가 있을 수 있으므로 정확한 조직 진단이 치료 방침을 결정하는 데 중요하다. 저자들은 췌장 두부 종양에서 초음파 내시경 유도하에 중심부 바늘 조직 검사를 시행해서 국내에서 처음으로 원발성 췌장 MALT 림프종을 진단하였기에 이를 보고한다. Primary lymphoma of pancreatic mucosa-associated lymphoid tissue (MALT) is extremely rare. Initial suspicion of primary pancreatic lymphoma is hampered by its low incidence. However, it should always be included in a differential diagnosis of pancreatic mass with unusual features, because an accurate diagnosis can avoid unnecessary surgical intervention. A 70-year-old woman presented with melena associated with a mass on the pancreatic head. Endoscopic ultrasonography-guided core-needle biopsy of the pancreatic mass revealed MALT lymphoma. The patient is currently undergoing radiation therapy. We present a case of primary lymphoma of the pancreatic MALT with a review of the literature. (Korean J Med 2019;94:443-448)
Yu, Jiwoo,Nam, Dae-Hyun,Lee, Young-Joo,Joo, Young-Chang The Korean Microelectronics and Packaging Society 2016 마이크로전자 및 패키징학회지 Vol.23 No.2
We developed a flexible and micro-thick electromagnetic interference (EMI) shielding nanofabric layer that also functions as a water resisting and heat sinking material. Electrospinning followed by a simple heat treatment process was carried on to produce the EMI-shielding Ni/C hybrid nanofibers. The ambient oxygen partial pressure ($pO_2$ = 0.1, 0.7, 1.3 Torr) applied during the heat treatment was varied in order to optimize the effectiveness of EMI-shielding by modifying the size and crystallinity of the magnetic Ni nanoparticles distributed throughout the C nanofibers. Permittivity and permeability of the nanofibers under the electromagnetic (EM) wave frequency range of 300 MHz~1 GHz were measured, which implied the EMI-shielding effectiveness (SE) optimization at $pO_2$ = 0.7 Torr during the heat treatment. The materials' heat diffusivity for both in-plane direction and vertical direction was measured to confirm the anisotropic thermal diffusivity that can effectively deliver and sink the local heat produced during device operations. Also, the nanofibers were aged at room temperature in oxygen ambient for water resisting function.
Rate control to reduce bitrate fluctuation on HEVC
Yoo, Jonghun,Nam, Junghak,Ryu, Jiwoo,Sim, Donggyu The Institute of Electronics and Information Engin 2012 IEIE Transactions on Smart Processing & Computing Vol.1 No.3
This paper proposes a frame-level rate control algorithm for low delay video applications to reduce the fluctuations in the bitrate. The proposed algorithm minimizes the bitrate fluctuations in two ways with minimal coding loss. First, the proposed rate control applies R-Q model to all frames including the first frame of every group of pictures (GOP) except for the first one of a sequence. Conventional rate control algorithms do not use any R-Q models for the first frame of each GOP and do not estimate the generated-bit. An unexpected output rate result from the first frame affects the remainder of the pictures in the rate control. Second, a rate-distortion (R-D) cost is calculated regardless of the hierarchical coding structure for low bitrate fluctuations because the hierarchical coding structure controls the output bitrate in rate distortion optimization (RDO) process. The experimental results show that the average variance of per-frame bits with the proposed algorithm can reduce by approximately 33.8% with a delta peak signal-to-noise ratio (PSNR) degradation of 1.4dB for a "low-delay B" coding structure and by approximately 35.7% with a delta-PSNR degradation of 1.3dB for a "low-delay P" coding structure, compared to HM 8.0 rate control.