• 대한전기학회:학술대회논문집
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• 대한전기학회 2003년도 학술회의 논문집 정보 및 제어부문 B
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• pp.735-739
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• 2003

This paper presents a direct seek control algorithm for swing-arm type dual stage servo system that consists of a coarse actuator and a fine actuator. The proposed scheme is to design a control system that attenuates the effect of dynamic coupling between the two actuators so that the seek operation can be performed in a single-shot with stability. In an optical drive system with dual stage servo mechanism, the effect of dynamic coupling between the two actuators needs to be handled during the coarse seek operation due to its inherent structure. In an extreme case, the two actuators can collide each other, which leads to critical degradation of the seek performance. To handle this problem, our proposed control scheme is to generate the drive signals such that the two actuators behave as if they are a single fixed body. To this end, a feedforward controller and two feedback controllers are designed that enable the current drive system perform wide range of track seek. Simulation results are provided to show the validity and feasibility of our proposed algorithm.

• 한국초전도ㆍ저온공학회논문지
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• 제24권4호
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• pp.16-24
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• 2022

Applications of REBa₂Cu₃O_7-δ tapes require joints with a simple manufacturing process, low resistance and good mechanical properties. In the present study, we successfully developed a copper diffusion joint between Cu-stabilized REBa₂Cu₃O_7-δ tapes that meets the above requirements without solder simply by applying flux, heat and pressurization. After a 3 min thermocompression process at approximately 150 δ and 336 MPa in air, two tapes were directly connected between Cu stabilizers by copper diffusion, which was proven by microstructure analysis. The specific resistivity of the copper diffusion joint reached 5.8 nΩ·cm² (resistance of 0.4 nΩ for a 306 mm splicing length) at 77 K in the self-field. The axial tensile stress reached 200 N without critical current degradation. The results show promise for the preparation of copper diffusion joints to be used in coils, attached tapes, and wire/cable terminals.

• 한국초전도ㆍ저온공학회논문지
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• 제8권3호
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• pp.5-8
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• 2006

The effect of annealing time in Metal Organic Deposition(MOD) method was investigated at reduced total pressure. As the total annealing pressure was reduced, the growth rate of YBCO films increased from 0.14nm/sec at atmospheric pressure to 4.2nm/sec at 1 Torr. For the total pres sure of 700, 500, 300, 100, and 1 Torr, the optimal annealing times of 60, 40, 20, 10, 2minutes were found in our experimental conditions. When the an nealing time was short, poor crystallinity or un-reacted phase was obtained. Also, the degradation of YBCO films occurred when exposed longer to the humid ambient at the high annealing temperature. The reduced pressure was found effective to in crease the growth rate and to control the pore size of the YBCO films in MOD method. A fast growth of MOD-YBCO films was realized with high critical current density over $1MA/cm^2$ using reduced pressure annealing. Large pores, usually observed at atmospheric pressure in MOD method, disappeared and also, the number of pores was reduced.

• Nuclear Engineering and Technology
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• 제54권12호
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• pp.4422-4430
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• 2022

Studying the effects of gamma radiation on the instrumentation and control (I&C) system of a nuclear power plant is critical to the successful and reliable operation of the plant. In the accidental scenario, the adverse environment of ionizing radiation affects the performance of the I&C system and it leads to inaccurate and incomprehensible results. This paper reports the effects of gamma radiation on the AT89C51RD2, a commercial-off-the-shelf 8-bit high-performance flash microcontroller. The microcontroller, selected for the device under test for this study is used in the remote terminal unit for a nuclear power plant. The custom circuits were made to test the microcontroller under different gamma doses using a ⁶⁰Co gamma source in both ex-situ and in-situ modes. The device was exposed to a maximum dose of 1.5 kGy. Under this hostile environment, the performance of the microcontroller was studied in terms of device current and voltage changes. It was observed that the microcontroller device can operate up to a total absorbed dose of approximately 0.6 kGy without any failure or degradation in its performance.

• Current Optics and Photonics
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• 제8권4호
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• pp.382-390
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• 2024

Laser propagation through atmospheric disturbances is vital for applications such as laser optical communication, satellite laser ranging (SLR), laser guide stars (LGS) for adaptive optics (AO), and laser energy transmission systems. Beam degradation, including energy loss and pointing errors caused by atmospheric turbulence, requires thorough numerical analysis. This paper investigates the impact of laser beam parameters on ground-to-space laser propagation up to an altitude of 100 km using vertical atmospheric disturbance profiles from the Geochang SLR Observatory in South Korea. The analysis is confined to 100 km since sodium LGS forms at this altitude, and beyond this point, beam propagation can be considered free space due to the absence of optical disturbances. Focusing on a 100-watt class laser, this study examines parameters such as laser wavelengths, beam size (diameter), beam jitter, and beam quality (M²). Findings reveal that jitter, with an influence exceeding 70%, is the most critical parameter for long-exposure radius and pointing error. Conversely, M², with an influence over 45%, is most significant for short-exposure radius and scintillation.

• 한국재료학회지
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• 제5권5호
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• pp.598-605
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• 1995

Thin films of $YB_{2}Cu_{3}O_{7-d}$ were prepared on various substrated of MgO(100), $SrTiO_{3}$, and $LaAlO_{3}$ by using off-axis magentron sputtering methods and annealing in-situ. The prarameters of film fabrication processes had been optimized through a "follow the lcoal maxima" strategy to yield good quality films in therms of the critical temperature $T_{c}$ and the critical current density $J_{c}$. Optimizedproecsses employing a plane magndtron and an cylindrical magnetron yielded $T_{c}$>90K along with $J_{c}$$10^{6}$A/$\textrm{cm}^2$ at 77K and > 2${\times}$$10^{7}$A/$\textrm{cm}^2$ at 5K. The sampels, however, showed degradationinthe properties, after chemical etching for fabrication of microbridges with the line width of 2-10 mocrons. In particular, the value of $T_{c}$ for the microbridges of 2microns was as small as 80%. The degradation was strongly dependent on the line width through a formula : $T_{c}$(e)=$T_{c}$)b) [1-a exp(-1000 bL)} where $T_{c}$(e) and $T_{c}$ (b) are the values of $T_{c}$ in the absolute scale measured after and before chemical etching, respectively and L is the line width in mm. By utilizing a best fitting technique, the proper constant values of a and to b were found as exp(-1.2) and 0.22, respectively. This formula was very useful in estimatiing the upper limit of the device operationtemperature.

• 한국정보통신학회논문지
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• 제25권2호
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• pp.280-285
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• 2021

VNDN 기술을 커넥티드 차량의 인포테인먼트 응용 서비스를 위한 통신 기술로 활용할 시 데이터가 통신의 주체가 되는 데이터중심네트워킹 기술 실현이 가능하며, 차량 보안 공격 및 해킹, 장거리 데이터 전송 시 성능 저하, 잦은 데이터 끊김 현상 등 현재의 호스트 중심 인터넷에 기반한 커넥티드 차량의 인포테인먼트 응용 서비스 기술이 갖는 한계를 극복 할 수 있다. VNDN 안에 지연에 매우 민감한 critical 정보 데이터를 RSU(Road Side Unit) 등에게 푸쉬 기반으로 전달해 주기 위한 Data 패킷 포워딩 이슈는 VNDN 기반 응용 서비스 실현을 위해 해결해야 할 이슈 중 하나이며, 이를 해결하기 위해 먼저 NDN 환경하에서 푸쉬 기반 데이터 트래픽을 지원해주기 위한 현존하는 포워딩 기법들을 포괄적으로 분석해 보고 각 기법 들을 성능 측면에서 비교 분석해 본다. 이를 통해 VNDN 환경하에서 보다 향상된 푸쉬 기반 중요 데이터 포워딩 기법 연구를 위한 사전 지식으로 활용되어질 수 있기를 기대한다.

• 한국초전도ㆍ저온공학회논문지
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• 제22권3호
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• pp.7-12
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• 2020

Electromechanical properties of REBCO CC tapes are known to be limited by defects (cracks) that form in the brittle REBCO layer. These defects could be inherently acquired during the CC tapes' manufacturing process, such as slitting, and which can be initiated at the CC tapes' edges. If propagated and long enough, they are believed to cause critical current degradation and can substantially decrease the delamination strength of CC tapes. Currently, commercially available CC tapes from various manufacturers utilize different growth techniques for depositing the REBCO layers on the substrates in their CC tapes preparation. Their epitaxial techniques, unfortunately, cannot perfectly avoid the formation of particles, in which sometimes acts as current blocking defects, known as outgrowths. Collective research regarding the composition, size, and formation of these particles for various CC tapes with different deposition techniques are particularly uncommon in a single study. Most importantly, these particles might interact in one way or another to the existing cracks. Therefore, systematic investigation on the interactions between the cracks' development mechanism and particles on the REBCO superconducting layers of practical CC tapes are of great importance, especially in the design of superconducting devices. Here, a proper etching process was employed for the CC tapes to expose and observe the REBCO layers, clearly. The scanning electron microscope, field emission scanning microscope, and energy-dispersive x-ray spectroscopy were utilized to observe the interactions between cracks and particles in various practical CC tapes. Particle compositions were identified whether as non-superconducting or superconducting and in what manner it interacts with the cracks were studied.

• 인터넷정보학회논문지
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• 제11권4호
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• pp.143-158
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• 2010

기업의 전자기밀유출은 생존을 위협하는 피해를 입힌다. 중소기업은 유출사실을 알아도 적절히 대응하지 못하는 현실에서 추적 불가능한 유출을 원천봉쇄하는 전자기밀보호 시스템으로만 전자기밀정보는 보호된다. 현재 DRM 기반 문서보호 시스템은 전자기밀 보호에 여러 보안 취약점을 보인다. 본 논문은 전자기밀정보의 불법유출 경로 및 취약점을 분석하여, 가장 위험한 내부자 유출시도조차 불가능하게 하는 보안조건을 만족시키면서도 성능저하가 없는 그룹통신 기반 시스템의 구조를 연구하였다. 구조의 핵심은 암호화 상태로 유통, 암호키와 기밀정보파일의 분리원칙, 다중 엔티티(entity)의 DSA 기반 다중 인증기법으로 간단한 정보도용으로는 기밀정보를 얻을 수 없는 시스템의 기본 구조의 설계를 논의한다.

• Journal of Electrochemical Science and Technology
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• 제5권1호
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• pp.1-18
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• 2014

Li-air cell is an exotic type of energy storage and conversion device considered to be half battery and half fuel cell. Its successful commercialization highly depends on the timely development of key components. Among these key components, the catalyst (i.e., the core portion of the air electrode) is of critical importance and of the upmost priority. Indeed, it is expected that these catalysts will have a direct and dramatic impact on the Li-air cell's performance by reducing overpotentials, as well as by enhancing the overall capacity and cycle life of Li-air cells. Unfortunately, the technological advancement related to catalysts is sluggish at present. Based on the insights gained from this review, this sluggishness is due to challenges in both the commercialization of the catalyst, and the fundamental studies pertaining to its development. Challenges in the commercialization of the catalyst can be summarized as 1) the identification of superior materials for Li-air cell catalysts, 2) the development of fundamental, material-based assessments for potential catalyst materials, 3) the achievement of a reduction in both cost and time concerning the design of the Li-air cell catalysts. As for the challenges concerning the fundamental studies of Li-air cell catalysts, they are 1) the development of experimental techniques for determining both the nano and micro structure of catalysts, 2) the attainment of both repeatable and verifiable experimental characteristics of catalyst degradation, 3) the development of the predictive capability pertaining to the performance of the catalyst using fundamental material properties. Therefore, under the current circumstances, it is going to be an extremely daunting task to develop appropriate catalysts for the commercialization of Li-air batteries; at least within the foreseeable future. Regardless, nano materials are expected to play a crucial role in this field.