• Smart Structures and Systems
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• 제15권2호
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• pp.335-353
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• 2015

Previous long-term measurements of the Uldolmok tidal current power plant showed that the structure's natural frequencies fluctuate with a constant cycle-i.e., twice a day with changes in tidal height and tidal current velocity. This study aims to improve structural health monitoring (SHM) techniques for offshore structures under a harsh tidal environment like the Uldolmok Strait. In this study, lab-scale experiments on a simplified offshore structure as a lab-scale test structure were conducted in a circulating water channel to thoroughly investigate the causes of fluctuation of the natural frequencies and to validate the displacement estimation method using multimetric data fusion. To this end, the numerical study was additionally carried out on the simplified offshore structure with damage scenarios, and the corresponding change in the natural frequency was analyzed to support the experimental results. In conclusion, (1) the damage that occurred at the foundation resulted in a more significant change in natural frequencies compared with the effect of added mass; moreover, the structural system became nonlinear when the damage was severe; (2) the proposed damage index was able to indicate an approximate level of damage and the nonlinearity of the lab-scale test structure; (3) displacement estimation using data fusion was valid compared with the reference displacement using the vision-based method.

• 항공우주기술
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• 제4권1호
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• pp.57-65
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• 2005

정지궤도위성과 같은 차세대 대형위성의 우주궤도환경 모사를 위해 한국항공우주연구원은 유효직경 Φ8m, 유효길이 L10m의 대형 열진공챔버를 구축해오고 있다. 우주환경은 고진공 환경이며 태양 복사열에 의한 고온 환경 및 극저온이 반복되는 가혹한 환경으로 특징지어진다. 가혹한 우주환경에 의해서 위성체의 주요부품에 기능장애가 초래되기도 하고 이는 결국 임무의 실패로 이어지기도 한다. 위와 같은 이유들로 인하여 위성체는 지상에서 우주환경시험을 거쳐 기능 및 작동상태를 점검해야 하며, 이를 위해서는 우주환경을 모사할 수 있는 우주환경 모사장비가 필요하다. 본 논문에서는 대형 열진공 챔버를 효율적이고, 안정적으로 구동을 위한 모든 제어로직이 포함되어 있다.

• 한국응용곤충학회지
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• 제40권1호
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• pp.51-58
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• 2001

동충하초로 불리우는 곤충병원진균(Paecilomycesjaponicus)이 의약적으로 상품화되어 사용되고 있으며,누에(Bombyxmori)가 이 진균의 최적 기주로 선발되어 자실테 생산에 이용되고 있다. 현재 이 균주의 처리는 갓 탈피한 누에 5령 유충에 접종하고 고온(30\"C),다습(약 90%상대 습도)및 24시간 절식 조건에서 스트레스에 의한 면역 저하를 유도하여 균주 접종율을 높히는 방식을 취하고 있다. 본 연구는 면역반응 중개에 중요한 eicosanoid반응을 억제시키는 dexamethas-one(DEX)을 이용하여 물리적 스트레스 환경의 조성 없이도 누에에 면역 저하를 유도시키려는 목적으로 수행되었다. 누에 $\lrcorner$령 유충에 주입된 DEX(1007g)는 병원진균의 혈구치사 능력을 뚜렷 이 증가시켰다. 또 DEX(1007g)는 작은혹형성이나 피막형성에서 나타나는 혈구응집 반응이나, phenoloxidase활성으로 측정된 누에의 세포성 면역 반응을 뚜렷이 저하시켰다 효과적 병원진균 의 충체 처리를 위해 곤충체의 부착 능력을 제고시켜 접종율을 높히는 것으로 본 연구에서 판명된 Triton-X(0.05%)를 모든 충체 처리 용액에 이용되었다. DEX(100$\mu\textrm{g}$)단독처리가 기존의 물리 적 스트레스 환경 처리를 통한 방법과 유사한 수준으로 병원진균의 접종율을 나타냈다. 본 연구는 DEX가 동충하초 접종율을 제고시킬 수 있음을 시사했고, 누에는 이러한 진균 병원체에 대해 서 eicosanoid를 이용하여 세포성 면역을 발현하는 것으로 제시하고 있다.고 있다.

• Journal of Ecology and Environment
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• 제31권2호
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• pp.97-105
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• 2008

Subsocial behavior of the genus Cryptocercus cockroaches has been believed as primitive traits of termite eusociality. Thus, it has been believed that understanding Cryptocercus subsociality is a pre-requisite stage to infer evolutionary route of the eusociality in termites. Woodroaches of Cryptocercus are also well known because of its peculiar characteristics including adults living monogamously in pairs, semelparous reproduction, xylophagy, obligatory association between adults and their offspring, slow development, and anal trophallaxis by adults. Based on the previously accumulated data, we try to understand two major components of Cryptocercus life history, development and reproduction. We hypothesize that harsh winter and length of winter might be one of the main causes driving the appearance of the delayed development and semelparous reproduction in Cryptocercus life history.

• 대한임베디드공학회논문지
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• 제2권3호
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• pp.138-144
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• 2007

Wireless Sensor Network(WSN) consists of a lot of light-weight sensor nodes with the capability of wireless communication. Studies have been done to improve stability and fault-tolerancy of WSN because the sensor nodes are basically vulnerable to the harsh environment. Specially, the time synchronization among sensor nodes becomes a challenging issue in WSN. All the local times should always keep the same with each other in the sensor field to perform data aggregation and energy-aware communication in WSN. In this paper, a new time synchronization technique is proposed to operate efficiently irrespective of the number of sensor nodes and the number of hops needed to cover all sensor nodes for synchronization. Simulation results show that the proposed technique has the lowest amount of packet traffic among the several time synchronization techniques.

• 대한기계학회논문집A
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• 제27권7호
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• pp.1193-1199
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• 2003

Maintaining track tension in tracked vehicles minimizes the excessive load on the tracks and prevents the peal-off of tracks from the road-wheel, and adequately guarantees the stable and improved driving of the tracked vehicles. However, the track tension cannot be easily measured due to the limitation in the sensor technology, harsh environment, etc. In this study, the track tension is estimated in realtime from the measurable signals of tracked vehicles and controlled based on a fuzzy logic controller. The proposed control system is implemented on tracked vehicles and its performance is evaluated under various driving conditions.

• 전기저널
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• 통권451호
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• pp.46-58
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• 2014

2013년 말, 전세계에 운행중인 원자력발전소 원자로는 434기로 총 용량은 371.6GW(e)이며, 이 중 약 80%는 20년 이상 사용되었다. 많은 회원국들은 최우선 순위로 자신들의 원자력발전소 운행 기간을 원래의 예상 기간인 30~40년 보다 길게 허용했다. 그렇다면 원자력발전소의 어려운 환경에서 기존의 케이블을 어떻게 적격 판정할 것인가. 본 원고는 원자력발전소의 저전압 케이블의 적격, 상태 모니터링 및 관리에 대한 연구 사항을 기술하였다.

• Advances in robotics research
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• 제2권2호
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• pp.141-149
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• 2018

In image processing and robotic applications, two-dimensional (2D) black and white patterned planar markers are widely used. However, these markers are not detectable in low visibility environment and they are not changeable. This research proposes an active and adaptive marker node, which displays 2D marker patterns using light emitting diode (LED) arrays for easier recognition in the foggy or turbid underwater environments. Because each node is made to blink at a different frequency, active LED marker nodes were distinguishable from each other from a long distance without increasing the size of the marker. We expect that the proposed system can be used in various harsh conditions where the conventional marker systems are not applicable because of low visibility issues. The proposed system is still compatible with the conventional marker as the displayed patterns are identical.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집E
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• pp.607-612
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• 2001

Based on the flow characteristics around a piercing cylinder, a free surface-flow velocitmetry which can be used in extremely harsh environment such as molten steel flow was developed. The velocimetry is consisted of finite length cylinder, load detecting elastic plate, electric signal transducer and data acquisition H/W and S/W. Using such a velocimetry, two velocity measurement schemes were established which one is flow resistance detecting scheme and the other is Karman Vortex frequency detecting scheme. For calibration of each scheme, realistic flow water model was used and in followings, detailed calibration processes were explained.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1996년도 하계학술대회 논문집 A
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• pp.3-5
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• 1996

A sensorless drive of induction motor has several advantage: low cost and availability in a harsh environment. Most of sensorless control schemes are based on the direct estimation of rotor speed from state observer. This study proposes a new sensorless control scheme. The proposed scheme is based on a reference model control which the error between the model and plant outputs decays to zero as time proceeds. The actuating signal is calculated from the fuzzy controller which increases the system stability and robustness. The simulation results indicate a good dynamic performance.