• Journal of Advanced Marine Engineering and Technology
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• 제38권2호
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• pp.208-216
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• 2014

In case of any coastal ocean near the mouth of huge rivers, low salinity water can be formed due to its large amount of freshwater discharge. For the acoustic analysis on the low salinity environment, some oceanographic data of the East China Sea and the Atlantic Ocean were collected through KODC (Korea Oceanographic Data Center) and NODC (National Oceanographic Data Center) online service. In this paper, the T-S gradient diagram is introduced to show a relation between the gradients of temperature and salinity in view of acoustic surface channel formation. Existence of haline channel, quantitative contribution of gradients of salinity and temperature, effectiveness of the channel formation can be known by the T-S gradient diagram. After applying the collected data into the diagram, tropical regions of the Atlantic Ocean show strong haline channel due to its nearly invariant temperature and drastic change of salinity with depth. The averaged transmission loss in the channel is about 5.7 ~ 7.5 dB less than that out of the channel by the results of acoustic propagation model (RAM: Range independent Acoustic Model). On the other hand, the East China Sea and temperate region of the Atlantic ocean have weaker haline channel with less difference of the averaged transmission loss between in and out of the channel as 3.2 ~ 6.0 dB. Although data samples used in this study have limitation to represent the general physical structures of the three ocean regions, the T-S gradient diagram is shown to be useful and acoustic field affected by low salinity environment is investigated in this study.

• 한국음향학회지
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• 제25권6호
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• pp.298-304
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• 2006

본 논문에서는 천해 음파전달 모의에 적합한 음선기반 광대역 주파수 신호 모의기법을 제안하였다. 본 기법은 깊이에 따라 음속이 선형적으로 변하는 환경 및 층매질에서의 음선추적을 기반으로 평면파 및 구형파의 반사 및 투과, 굴절 그리고 감쇠 등을 고려해 각 고유음선의 위상 및 크기로부터 신호를 모의한다. 본 기법의 가장 큰 특징은 주파수영역을 거치지 않고 시간영역에서 이산화된 신호를 직접 모의함으로써 주파수 대역에 관계없이 계산시간을 단축할 수 있다는 것이다. 끝으로 제안된 기법을 네 가지의 테스트환경에 적용하여 기존의 검증된 모텔 (ORCA, Ram) 의 결과와 비교하여 그 효용성을 검증하였다

• 한국연소학회:학술대회논문집
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• 한국연소학회 2002년도 제24회 KOSCO SYMPOSIUM 논문집
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• pp.123-132
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• 2002

A numerical study was conducted to investigate the combustion phenomena of normal start and unstart processes based on ISL's RAMAC 30 experiments with different diluent amounts and fill pressures in a ram accelerator. The initial projectile launching speed was 1.8 km/s which corresponded to the superdetonative speed of the stoichiometric $H_2/O_2$ mixture diluted with 5 $CO_2$ or 4 $CO_2$. Experiments with same condition except for projectile surface material demonstrated that ignition was successful with an aluminum projectile, but no combustion was observed in case of a steel projectile. In this study, it was found that neither shock nor viscous heating was sufficient to ignite the mixture at a low speed of 1.8 km/s, as was found in the experiments using a steel projectile. However, we could succeed in igniting the mixtures by imposing a minimal amount of additional heat to the combustor section and simulate the normal start and unstart processes found in the experiments with an aluminum projectile. For the numerical simulation of supersonic combustion, multi-species Navier-Stokes equations coupled with a Baldwin-Lomax turbulence model and detailed chemistry reaction equations of $H_2/O_2/CO_2$ suitable for high-pressure gaseous combustion were considered. The governing equations were discretized by a high order accurate upwind scheme and solved in a fully coupled manner with a fully implicit, time accurate integration method. The numerical results matched almost exactly to the experimental results. As a result, it was found that the normal start and unstart processes depended on the strength of gas mixture, development of shock-induced combustion wave stabilized by the first separation bubble, and its size and location.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.403-404
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• 2013

최근 scaling down의 한계에 부딪힌 DRAM과 Flash Memory를 대체하기 위한 차세대 메모리(Next Generation Memory)에 대한 연구가 활발히 진행되고 있다. ITRS (international technology roadmap for semiconductors)에 따르면 PRAM (phase change RAM), RRAM (resistive RAM), STT-MRAM (spin transfer torque magnetic RAM) 등이 차세대 메모리로써 부상하고 있다. 그 중 RRAM은 간단한 구조로 인한 고집적화, 빠른 program/erase 속도 (100~10 ns), 낮은 동작 전압 등의 장점을 갖고 있어 다른 차세대 메모리 중에서도 높은 평가를 받고 있다 [1]. 현재 RRAM은 주로 금속-산화물계(Metal-Oxide) 저항 변화 물질을 기반으로 연구가 활발하게 진행되고 있다. 하지만 근본적으로 공정 과정에서 산소에 의한 오염으로 인해 수율이 낮은 문제를 갖고 있으며, Endurance 및 Retention 등의 신뢰성이 떨어지는 단점이 있다. 따라서, 본 연구진은 산소 오염에 의한 신뢰성 문제를 근본적으로 해결할 수 있는 다양한 금속-질화물(Metal-Nitride) 기반의 저항 변화 물질을 제안해 연구를 진행하고 있으며, 우수한 열적 안정성($>450^{\circ}C$, 높은 종횡비, Cu 확산 방지 역할, 높은 공정 호환성 [2] 등의 장점을 가진 WN 박막을 저항 변화 물질로 사용하여 저항 변화 메모리를 구현하기 위한 연구를 진행하였다. WN 박막은 RF magnetron sputtering 방법을 사용하여 Ar/$N_2$ 가스를 20/30 sccm, 동작 압력 20 mTorr 조건에서 120 nm 의 두께로 증착하였고, E-beam Evaporation 방법을 통하여 Ti 상부 전극을 100 nm 증착하였다. I-V 실험결과, WN 기반의 RRAM은 양전압에서 SET 동작이 일어나며, 음전압에서 RESET 동작을 하는 bipolar 스위칭 특성을 보였으며, 읽기 전압 0.1 V에서 ~1 order의 저항비를 확보하였다. 신뢰성 분석 결과, $10^3$번의 Endurance 특성 및 $10^5$초의 긴 Retention time을 확보할 수 있었다. 또한, 고저항 상태에서는 Space-charge-limited Conduction, 저저항 상태에서는 Ohmic Conduction의 전도 특성을 보임에 따라 저항 변화 메카니즘이 filamentary conduction model로 확인되었다 [3]. 본 연구에서 개발한 WN 기반의 RRAM은 우수한 저항 변화 특성과 함께 높은 재료적 안정성, 그리고 기존 반도체 공정 호환성이 매우 높은 강점을 갖고 있어 핵심적인 차세대 메모리가 될 것으로 기대된다.

• 천문학논총
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• 제4권1호
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• pp.1-15
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• 1989

A jet plasmoid model for 3C.449 has been constructed by introducing a plasma.ejecting black hole orbiting around the center of its parent cD galaxy. We examined the characteristics of the jet trajectory by varying the values of (1) orbiting radius and velocity of the black hole, (2) plasma ejection velocity, (3) size, mass and space velocity of the parent galaxy, (4) size of the galactic core and (5) the density of the intergalactic medium. In our model calculation the effect of the gravity by the parent galaxy and the ram pressure by the intergalactic medium have been taken in account. It is found that our dynamical model accounts reasonably well for the observed structure of 3C449. Our proposed model suggests that the buoyancy force near the galactic center plays an important role in the formation of the curved structure of the radio jet.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2000년도 하계종합학술대회 논문집(2)
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• pp.262-265
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• 2000

This paper describes design of a (32, 28) Reed Solomon decoder for optical compact disk provides double error detecting and correcting capability. The most complex circuit in the RS decoder is part for solving the error location numbers from error location polynomial, and the circuit has great influence on overall decoder complexity. We use RAM based architecture with Euclid algorithm, Chien search algorithm and Forney algorithm. We have developed VHDL model and Performed logic synthesis using the SYNOPSYS CAD tool. Then, the RS decoder has been implemented with FPGA. The total umber of gate is about 11,000 gates and it operates at 20MHz.

• 한국안전학회지
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• 제10권3호
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• pp.42-46
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• 1995

To purpose of this study is to model design and motion analysis of tangential cam mechanism using personal computer system. The CAD(Computer Aided Design) system used in this study was constructed with CPU(Central Processing Unit) 80486, RAM(Random Access Memory) 8M, CGA graphic card. By using developed program for tangential cam mechanism, we designed tangential cam models and analysed displacement, velocity, acceleration of follower.

• 한국멀티미디어학회논문지
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• 제23권10호
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• pp.1318-1330
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• 2020

The purpose of this study is to identify the effect of the innovation characteristics that AI Elderly Care Robots have on elderly consumers and to verify the acceptance or mediated resistance by the elderly of the innovation characteristics. Research was conducted throughout this study of the characteristics of the elderly so that the study results could contribute to the improvement of the quality and manufacture of AI Elderly Care Robots by lowering the psychological resistance of the elderly. Survey questions were answered by senior citizens aged 65 and older. The SPSS25 and AMOS22 programs were used for analysis. The analysis confirmed that innovation resistance has a significant mediated effect on the characteristics of elderly consumers and their willingness to accept the innovation characteristics of the AI Elderly Care Robots. Through this study, Ram's innovation resistance model has been verified empirically and it is estimated that by considering the specificities of elderly consumers and using the information to contribute to the development and modification of AI Elderly Care Robots will increase the willingness of the elderly to accept the innovation characteristics of the AI Elderly Care Robots.

• 인터넷정보학회논문지
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• 제6권1호
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• pp.65-72
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• 2005

플래시 메모리는 이동형 컴퓨팅 환경에서 휴대용 정보기기를 지원하는 우수한 미디어이다. 플래시 메모리는 비휘발성, 낮은 전력소모, 빠른 데이터 접근 속도 등의 특징으로 휴대용 정보기기용 데이터베이스의 핵심 저장 모듈이 되었다. 하지만, 일반 RAM 메모리에 비하여 상대적으로 느린 연산 특성을 고려하여 기존의 트랜잭션 처리 기법을 개선할 필요가 있다. 이를 위하여, 본 논문은 플래시인지 트랜잭션 관리(Flash-Aware Transaction Management: FATM) 기법을 제안한다. FATM은 SRAM과 W-cache를 활용하여 트랜잭션 처리 성능을 높인다. 또한, 성능 검증을 위하여 시뮬레이션 모델을 제안하였으며, 실험 결과 분석을 통하여 FATM이 기존의 트랜잭션 처리 기법보다 우수함을 확인하였다.

• 전기학회논문지P
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• 제64권4호
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• pp.220-230
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• 2015

Rolling stock RAMS is a field of engineering which integrates reliability, availability, maintainability and safety (RAMS) characteristics into an inherent product design property through rolling stock system engineering process. It is implemented to achieve operational objectives successfully, and recently the RAMS has become a rapidly growing engineering discipline because it has a great potential to ensure safety and improve cost effectiveness. However, the Korean rolling stock industry has not yet implemented RAMS management in the rolling stock engineering process, despite the issue having been addressed since the introduction of the KTX. Thus, this paper discusses the processes, methods and techniques for RAMS assessment in three parts. Firstly, it outlines a process of the overall RAMS performance assessment for achieving technical RAMS design criteria. Secondly, it discusses a process for assessing the operational RAM and allocating the RAM. This paper also proposes a model for assessing safety-based risk management, which includes five analytic techniques for identifying the causes and consequences of a system failure. Finally, a case example is provided for the risk assessment of the pneumatic braking device.