• 천문학회보
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• 제44권2호
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• pp.45.2-45.2
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• 2019

The main-belt asteroid (5247) Krylov is known as a Non-Principal Axis (NPA) rotator. However, the shape model and spin state of this asteroid were not revealed. The physical model of an asteroid including spin state and shape is regarded to be important to understand its physical properties and dynamical evolution. Thus, in order to reconstruct the physical model of Kryolv, we applied the light curve inversion method using not only the optical light curves observed with ground-based telescopes in three apparitions during 2006, 2016, and 2017, but also the infrared light curves obtained with the Wide-field Infrared Survey Explorer (WISE) in 2010. We found that it is rotating in Short Axis Mode (SAM) with the rotation and precession periods of 368.71 hr and 67.277 hr, respectively. The orientation of the angular momentum vector is (298°, -58°) in the ecliptic coordinate system. The ratio of moments of inertia of the longest axis to the shortest axis is I_a/I_c = 0.36; the ratio of moments of inertia of the intermediate axis to the shortest axis is I_b/I_c = 0.96. Finally, the excitation level of this asteroid is found to be rather low with a ratio of the rotational kinetic energy to the basic spin state energy as E/E₀ ≃ 1.024. We will briefly discuss the possible evolutionary process of Krylov in this presentation.

• 천문학회보
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• 제45권1호
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• pp.39.1-39.1
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• 2020

We examine how the mass assembly of central galaxies depends on their location in the cosmic web. The HORIZON-AGN simulation is analysed at z~2 using the DISPERSE code to extract multi-scale cosmic filaments. We find that the dependency of galaxy properties on large-scale environment is mostly inherited from the (large-scale) environmental dependency of their host halo mass. When adopting a residual analysis that removes the host halo mass effect, we detect a direct and non-negligible influence of cosmic filaments. Proximity to filaments enhances the build-up of stellar mass, a result in agreement with previous studies. However, our multi-scale analysis also reveals that, at the edge of filaments, star formation is suppressed. In addition, we find clues for compaction of the stellar distribution at close proximity to filaments. We suggest that gas transfer from the outside to the inside of the haloes (where galaxies reside) becomes less efficient closer to filaments, due to high angular momentum supply at the vorticity-rich edge of filaments. This quenching mechanism may partly explain the larger fraction of passive galaxies in filaments, as inferred from observations at lower redshifts.

• 천문학회보
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• 제46권1호
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• pp.28.3-29
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• 2021

Galaxies are not just randomly distributed in space; instead, a variety of galaxy alignments have been found over a wide range of scales. Such alignments are the outcome of the combined effect of interacting neighbors and the surrounding large-scale structure. Here, we focus on the spin-orbit alignment (SOA) of galaxy pairs, the dynamical coherence between the spin of a target galaxy and the orbital angular momentum of its neighbor. Based on a recent cosmological hydrodynamic simulation, the IllustrisTNG project, we identify paired galaxies with mass ratios from 1/10 to 10 at z = 0 and statistically analyze their spin-orbit angle distribution. We find a clear preference for prograde orientations (i.e., SOA), which is more prominent for closer pairs. The SOA is stronger for less massive targets in lower-density regions. The SOA witnessed at z = 0 has been developed progressively since z = 2. There is a clear positive correlation between the alignment strength and the interaction duration with its current neighbor. Our results suggest the scenario in which the SOA is developed mainly by interactions with a neighbor for an extended period of time, rather than by the primordial torque exerted by the large-scale structure.

• 한국운동역학회지
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• 제19권2호
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• pp.337-345
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• 2009

본 연구는 테니스 서브 속도에 따른 라켓의 움직임에 대한 운동학적 변인들의 차이를 비교 분석하는데 있다. 연구문제를 해결하기 위해 국내 실업 테니스선수 3명을 대상으로 3대의 고속카메라를 이용하여 3차원 영상분석을 실시하였으며, 다음과 같은 결론을 얻었다. 첫째, 임팩트 순간 라켓의 속도는 전후축 방향으로의 빠른 속도가 중요하며, 이를 위해 라켓의 전방이동이 필요함을 확인하였다. 또한 임팩트 순간까지 라켓의 상향스윙이 이루어지는 것을 확인하였다. 둘째, 임팩트 순간 라켓의 각속도는 좌우축에서의 빠른 각속도가 중요하며, 이를 위해 손목의 강한 굴곡운동이 필요함을 확인하였다. 또한 수직축에서의 각운동도 필요함을 확인하였다. 셋째, 서브 속도는 라켓 가속구간에서 라켓의 증축과 -X축이 이루는 각의 변화를 작게 하는 것이 중요하며, 이는 가속구간에서 라켓을 볼의 진행 방향과 일치하게 이동시켜야 함과 동시에 라켓 가속구간의 시작인 백스크래칭 순간에 라켓을 지면과 수직이 되도록 하여 가속거리를 최대로 하는 것이 서브 속도를 높이는데 중요함을 알 수 있었다.

• 인터넷정보학회논문지
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• 제15권1호
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• pp.171-178
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• 2014

본 논문에서는 실시간으로 가상현실의 증강객체에 외부의 힘이 작용할 때 증강된 가상 객체의 동적 모델링 방법을 제시하였다. 가상객체의 자연스러운 움직임을 시뮬레이션 하기 위하여 AR 객체에 적용되는 외부의 힘의 변화에 대하여 Newton의 운동법칙을 적용하여 객체의 움직임을 설명하는 식을 생성하였다. 동적 모델링 과정에서 증강된 객체와 햅틱 장비간의 실질적 상호작용이 발생하며 이때 외부의 힘이 가상객체에 전달된다. 증강된 객체의 고유특성은 강체 혹은 탄성체의 성질을 갖는 모델이다. 강체의 동적 모델링에서는 선형 모멘텀과 각속도 모멘텀을 모두 고려하여 증강된 객체와 햅틱 스틱이 충돌할 때 수행하였다. 비강체의 동적 모델링에 있어서는 탄성체의 변형 모델은 내외의 힘과 제한요소에 자연적으로 반응하기 때문에 물리기반 시뮬레이션 방법을 적용하였다. 증강된 탄성체는 햅틱 인터페이스를 통해 사용자에 의하여 발생하는 힘의 특성과 모델의 고유 특성에 따라 자연스럽게 변형된다. 변형 물체의 모델링을 위하여 Newton의 제 2 운동법칙이라 불리는 질량-스프링 연결 시스템을 적용하였다. 실험을 통하여 증강된 강체와 비강체의 성질을 지닌 가상 객체에 햅틱 장비에 의한 햅틱 상호작용이 발생 할 때 객체의 변환을 자연스럽게 가시화 할 수 있었다.

• 한국결정성장학회:학술대회논문집
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• 한국결정성장학회 1997년도 Proceedings of the 12th KACG Technical Meeting and the 4th Korea-Japan EMGS (Electronic Materials Growth Symposium)
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• pp.197-201
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• 1997

The momentum, heat and mass trasfer phenomena in the silicon melt of the Czochralki crystal growth system are calculated using a three dimensional numerical simulation thechnique. Even though axisymmetrical boundary conditions are imposed to all calculations in a 3cm diameter crucible, several types of non-axisymmetric profiles of velocities, temperature and oxygen concentration appeared in the melt. Because of the non-axisymmetric profiles of velocities, temperature and oxygen concentration appeared in the melt. Because of the non-axisymmetric profiles and rotations of fluid induced by the crucible rotation, temperatures and oxygen concentrations in the silicon melt fluctuate. The rotating velocity of the profile is calculated from the phase shift of the data of temperature or oxygen at two different points which have same radius from center but 90 degree angular difference. From this calculation, it is found that the rotating veolocity of the oxygen and temperature is different from the crucible rotation rates. Therefore the frequencies of the oscillating temperature and oxygen concentrations are not same to the frequencies of the crucible rotations. Futhermore, the components of the frequencies of the temperature and oxygen concentration at the same point are not same. The fluctuation behaviors of the temperature or oxygen themselves are also different when the points are different. The calculation show that the temperature and the oxygen concentration near the interface also fluctuate. The results suggest that the striation pattern found in the grown silicon single crystals may ben generated by the oxygen concentration and the temperature oscillations of the melt occurred near the interface.

• 한국운동역학회지
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• 제17권2호
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• pp.157-166
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• 2007

This study was to compare the major kinematic factors between the success and failure group on performing the back somersault motion in floor exercise. Three gymnasts(height : $167.3{\pm}2.88cm$, age : $22.0{\pm}1.0years$, body weight : $64.4{\pm}2.3kg$) were participated in this study. The kinematic data was recorded at 60Hz with four digital video camera. Two successful motions and failure motions for each subject were selected for three dimensional analysis. 1. Success Trail It was appear that success trail was larger than failure group in projection velocity, but success trail was smaller than failure trail in projection angle. Also it was appear that success trail was longer than failure group in the time required. Hand segment velocity and maximum velocity in success trail were larger than those in failure trail, and this result was increasing the projection velocity and finally increasing the vertical height of center of mass. At the take-off(event 2), flection amount of hip and knee joint angle was contributed to the optimal condition for the take-off and at the peak point, hip and knee joint angle was maximum flexed for reducing the moment of inertia. Also in this point, upper extremities of success trail extended more than those of failure trail. in this base, success trail in upward phase(p3) 2. Failure Trail It was appear that failure trail was smaller than success trail in projection velocity, but failure trail was larger than success trail in projection angle. Also it was appear that failure trail was more short than success trail in the time required. Hand segment velocity and maximum velocity in failure trail were smaller than those in success trail, and this result was reducing the projection velocity and finally reducing the vertical high of center of mass. At the take-off(event 2), flection amount of hip and knee joint angle wasn't contributed to the optimal condition for the take-off and at the peak point, hip and knee joint angle wasn't maximum flexed for reducing the moment of inertia. Also in this point, upper extremities of failure trail didn't extended more than those of success trail.

• 대한조선학회지
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• 제27권2호
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• pp.1-12
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• 1990

선미후류에 포함된 보오텍스 시스템과 프로펠러와의 상호작용을 이론적으로 해석하여 유효반류를 계산하는 방법을 제안하였다. 선미주위의 복잡한 유동을 Poincare의 방정식을 사용하여 수학적으로 표시하였고 임의의 점에서의 교란속도를 물체 표면에 분포되어 있는 쏘오스 및 보오텍스에 의한 유기속도의 표면적분과 유체중 위치하는 쏘오스 및 보오텍스에 의한 유기속도의 체적적분의 함으로 표시하였다. 이 식으로부터 유효속도(effective velocity)를 유체중 보오텍스에 의한 유기속도의 체적적분으로 정의하였다. 유체중의 보오텍스의 위치와 세기는 불균일한 호칭속도(nominal velocity)분포에 포함되어 있는 보오텍스로부터 프로펠러가 작동할 때의 유선변화를 고려하여 보오텍스 운동역학(vortex dynamics)을 만족하도록 결정된다. 이론을 검증하기 위한 계산예로써 축대칭 전단류(shear flow)중 원판형 추진장치가 작동할 때 프로펠러에 의한 유선변화 모형을 변화시켜 유효속도를 계산하였고 양력판 이론에 의한 값과 비교하였다.

• 대한의용생체공학회:의공학회지
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• 제28권2호
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• pp.187-194
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• 2007

The purpose of this study is to determine the characteristics of ground reaction force(GRF) in golf swing for various slopes of flat lie and uphill lies of 5 and 10 degrees. Five right-handed professional golfers were selected for the experiment and the 7 iron club was used. We used four forceplates to measure GRF and synchronized with the three-dimensional motion analysis system. Results showed that slope did not affect the total time for golf swing, but the time until the impact had a tendency to slightly increase for the uphill lie(p<0.05). The medial-lateral GRF of the right foot increased toward the medial direction during back swing, but less increases were found with the angle of uphill lie(p<0.05). The GRF of the left foot increased rapidly toward the medial direction at the uncocking and the impact during down swing, but decreased with the increase in the angle of uphill lie(p<0.05). The anterior-posterior GRF of both feet showed almost the same for different slopes. With the slopes, the vertical GRF of the right foot increased, but the vertical GRF of left foot decreased(p<0.05). Uphill lies would have negative effect to provide the angular momentum during back swing, restricting pelvic and trunk rotations, and to provide the precise timing and strong power during down swing, limiting movements of body's center of mass. The present study could provide valuable information to quantitatively analyze the dynamics of golf swing. Further study would be required to understand detailed mechanism in golf swing under different conditions.

• 조명전기설비학회논문지
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• 제14권3호
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• pp.49-58
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• 2000

본 논문에서는 FACTS(Flexible AC Transnission System)로 분류되는 여라 기기중 기존의 전압제어 및 무효 전력보상기들이 가지고 있는 바속응성과 불연속성 문제를 해결해줄 수 있는 정지형 무효전력 보상가(Static Var Compensator : SVC)를 포함한 전력계통에 신경회로망 제어기를 적용하여 안정화에 관하여 연구하였다. 제안된 신경회로망 제어기는 오차와 오차변화량을 입력하는 오차역전과 학습 알고리즘을 사용하고, 학습시간올 단축하기 위해 모멘텀 방법을 사용하였다. 제안된 방법의 강인섬을 입증하기 위해 중부하시 및 정상부하시에 초기 전력을 변동시킨 경우와 초기에 회천자각을 변동시킨 경우에 대하여 시스렘의 회전자각, 각속도 편차 특성 및 단 자전압의 동특성을 고찰하여 다른 시스템보다 응답특성이 우수합을 보였다.