• Journal of Powder Materials
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• v.19 no.5
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• pp.348-355
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• 2012

Cold spray deposition using Titanium powder was carried out to investigate the effects of powder morphology and powder preheating on the coating properties such as porosity and hardness. The in-flight particle velocity of Ti powder in cold spray process was directly measured using the PIV (particle image velocimetry) equipment. Two types of powders (spherical and irregular ones) were used to manufacture cold sprayed coating layer. The results showed that the irregular morphology particle appeared higher in-flight particle velocity than that of the spherical one under the same process condition. The coating layer using irregular morphology powder represented lower porosity level and higher hardness. Two different preheating conditions (no preheating and preheating at $500^{\circ}C$) were used in the process of cold spraying. The porosity decreased and the hardness increased by conducting preheating at $500^{\circ}C$. It was found that the coating properties using different preheating conditions were dependent not on the particle velocity but on the deformation temperature of particle. The deposition mechanism of particles in cold spray process was also discussed based on the experimental results of in flight-particle velocity.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.8
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• pp.56-64
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• 2005

It is prerequisite that we have to fomulate the nonlinear mathematical modeling to design the guidance and control system of rotorcraft-based unmanned aerial vehicle using a small-scaled commercial helicopter. The small-scaled helicopters are very different from the full-scale helicopters in dynamic behavior such as high rotation speed and high frequency dynamic characteristics. In this paper, the formulation of the mathematical model of the small-scaled helicopter to minimize the complexity is presented by component and source build-up approach. It is linearized at the trim condition of hovering and forward flight and analyzed the flight modes. The results of this approach have general trends but a little difference. To verify this approach, it is necessary to compare this theoretical model with experimental results by system identification using flight test as a next research topic.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.6
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• pp.134-141
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• 2019

This paper is a study on design improvement of rotorcraft horizontal stabilizer. The rotorcraft horizontal stabilizer stabilizes the behavior of the pitch, yaw, etc. from the aircraft. Because of this role, horizontal stabilizers are a major component (Flight Safety Part) that affects flight safety on rotorcraft. However, when the rotorcraft was operated in domestic, cracks were found in the inner structure of the horizontal stabilizer and design improvement was needed. In this paper, we identified the two causes of the horizontal stabilizer crack defects through fracture analysis and structural analysis. The first is the tightening torque when the bolt is tightened, and the second is the lead-lag behavior of aircraft. In order to improve these two causes, bolt fastening method, flange structure and thickness were changed and composite ring was applied. In order to verify the design improvement, the structural analysis was performed and the structural strength was improved. Also Fatigue analysis of the internal structure (Rib 1) was performed and it was confirmed that the requirements were satisfied.

• Biomedical Science Letters
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• v.6 no.4
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• pp.269-279
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• 2000

This present study was investigated to elucidate degenerative changes according to the change of habitual environment on the myocytes of doves by restricting them from flight that is instinct behavior of this animal and strong exercise. To restrict doves from flight, they were confined in the cage (1 $m^3$) for 2 months. After this period, the myocardium of the experimental group was compared to that of wild doves in the ultrastructural and cytochemical ways. In addition, stereological changes were also examined. The results were as followings: 1. The body weight of the confined experimental groups was higher than that of the wild doves, but the ratios of the pectoral muscle/body weight (p<0.05) and the heart/body weight were lower. 2. At the ultrastructural level, the myocardium of confined doves appeared as wavy fibers in the smaller area than in the myocardium of wild doves. Also, the length of sarcomeres was longer in the confined doves. The number of sarcoplasmic reticulum and capillary was smaller in the myocardium of confined doves. 3. Cytochemical examinations showed that the activities of cytochrome oxidase were lowered in the confined doves. 4. Stereological analysis revealed that the density of myofibrils was greater in the confined doves. In contrast the volume density of sarcoplasmic reticulum (p<0.05) and the surface density of mitochondrial inner membrane (p<0.05) was lower in the confined doves, while the numerical density of mitochondrial inner membrane was higher (p<0.05). These results suggest that even the short period of restricted exercise can induce negative effects on the functions of myocytes of doves that are adapted for the strong exercise such as flight. Therefore, the maintenance of prolonged exercise seems to be one of the important factors that are critical to retain the functions of myocardium.

• Proceedings of the KIEE Conference
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• 1995.07c
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• pp.1385-1387
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• 1995

The Monte Carlo method for studying the steady-state behavior of electrons under the influence of a electric field is described. In this simulation used a Free Flight Time technique based on determination of the increase in kinetic energy between two collisions. The electron behavior in the cathode region of a corona discharge has been analysed using this method; spatial variations of the energy and excitation, ionization, and the multiplication of electrons were discussed.

• Proceedings of the Korean Geotechical Society Conference
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• 2009.09a
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• pp.194-205
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• 2009

In geotechnical engineering, the mechanical characteristics of soil, the main material of geotechnical engineering, is highly related to the confining stress. Reduced-scale physical modeling is often conducted to evaluate the performance or to verify the behavior of the geotechnical systems. However, reduced-scale physical modeling cannot replicate the behavior of the full-scale prototype because the reduced-scale causes difference of self weight stress level. Geotechnical centrifuges are commonly used for physical model tests to compensate the model for the stress level. Physical modeling techniques using centrifuge are widely adopted in most of geotechnical engineering fields these days due to its various advantages. In this paper, fundamentals of geotechnical centrifuge modeling and its application area are explained. State-of-the-art geotechnical centrifuge equipment is also described as an example of KOCED geotechnical centrifuge facility at KAIST.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.30 no.4
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• pp.76-91
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• 2022

면세점 판매 채널이 다양화되고 스마트 여객 증대 등 쇼핑 성향의 변화로 인해 인천공항 면세점 객단가는 하락하고 있다. 면세점 매출액 감소에 따라 사업 다각화 및 고도화 등 대응 노력이 필요하다. 따라서 인천공항 면세점 이용객의 쇼핑 행태 및 면세점 트렌드 변화에 적기 대응을 위한 기초자료 및 마케팅 강화 방안을 제시하는 데 궁극적인 목적이 있다. 본 연구는 인천공항 면세점 내·외국인 구매자/비구매자, 환승객을 대상으로 쇼핑실태를 심층 조사하여 행동 특성을 분석하였으며, 그 결과 내국인과 외국인, 환승객별로 인구통계학 특성, 여행 특성, 쇼핑 특성에서 차이가 나타났다. 인천공항 면세점 이용객별 중요하게 인지하는 요소와 만족하는 요소를 파악하고 개선할 부분을 파악하였다. 이로써 인천공항 면세점 운영정책 수립 및 기본방향 설정을 위한 기초자료로 활용할 수 있고, 인천공항 면세점 마케팅 강화 및 활성화를 위한 전략 방안을 제시하는 데 의의가 있다.

• Proceedings of the Korean Society of Disaster Information Conference
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• 2023.11a
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• pp.143-144
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• 2023

항공사가 매년 정기적으로 수행하고 있는 정기 안전 교육 프로그램(Safety Training Programs)을 통한 객실승무원의 안전인식(Safe Recognition) 변화와 직접적인 사고 발생 시 즉시 행동으로 연계되는 안전행동(Safety Behavior)을 연구하여 항공안전의 목표를 달성하고, 사고를 방지하여 항공사의 신뢰도를 향상시키고 다른산업에서 직원안전교육을 수행할 경우 안전교육의 내용,절차, 횟수등을 제시하는 지표로 활용하고자 한다. 본 연구에서는 항공사 객실승무원의 안전 교육 프로그램이 객실승무원 안전인식과 행동에 미치는 영향을 분석하고, 안전인식이 정기안전교육 프로그램과 안전행동의 관계에 있어서 매개효과(mediating effect)가 있는지 파악해보고자 한다.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.22 no.1
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• pp.114-123
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• 2014

Due to the recent aircraft accidents both in Ethiopian airline and Malaysian airline, almost all the media are focusing the importance of the airline safety. Especially, media's eyes and ears are interested in the reasons why Malaysia airline's missing presumed as by either terrorist attack or pilot's mistake. Safety Behaviors of pilot are viewed as the most important human factor issues among researchers. This is because, if it were the case of a commercial airline, pilot's safety behavior would be directly related to the lives of couple of hundreds passengers. This paper considers the antecedents of this safety behaviors as pilot's leadership, pilot's leadership and self-efficacy. This paper has tried to find out which human factors of a pilot would have significant impact on their safety behaviors. According to the empirical research result from SEM (Structural Equation Model), it was found out both the leadership and self-efficacy of a pilot had direct impact on their safety behaviors through safety motivation. Thus it could be concluded that flight crew must follow the instruction of a pilot who had the authority of the flight operation. The managerial implication are discussed in the conclusion part of this paper. As an implication, this paper concluded that it would be necessary to do further research on pilot's leadership and self-efficacy.

• Journal of Mechanical Science and Technology
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• v.14 no.3
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• pp.320-330
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• 2000

It is desirable to perform nondestructive evaluation (NDE) to assess material properties and part homogeneity because the manufacturing of carbon/carbon brake disks requires complicated and costly processes. In this work several ultrasonic techniques were applied to carbon/carbon brake disks (322mm ad, 135mm id) for the evaluation of spatial variations in material properties that are attributable to the manufacturing process. In a large carbon/carbon disk manufactured by chemical vapor infiltration (CYI) method, the spatial variation of ultrasonic velocity was measured and found to be consistent with the densification behavior in CYI process. Low frequency (e.g., 1-5MHz) through-transmission scans based on both amplitude and time-of-flight of the ultrasonic pulse were used for mapping out the material property inhomogeneity. Images based on both the amplitude and the time-of-flight of the transmitted ultrasonic pulse showed significant variation in the radial direction. The radial variations in ultrasonic velocity and attenuation were attributed to a density variation caused by the more efficient densification of pitch impregnation near the id and od and by the less efficient densification away from the exposed edged of the disk. Ultrasonic velocities in the edges of the disk. Ultrasonic velocities in the thickness direction were also measured as a function of location using dry-coupling transducers ; the results were consistent with the densification behavior. However, velocities in the in-plane directions (circumferential and radial) seemed to be affected more by the relative contents of fabric and chopped fiber, and less by the void content.