• The Bulletin of The Korean Astronomical Society
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• v.44 no.2
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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.

• The Bulletin of The Korean Astronomical Society
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• v.45 no.1
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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.

• The Bulletin of The Korean Astronomical Society
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• v.46 no.1
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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.

• Korean Journal of Applied Biomechanics
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• v.19 no.2
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• pp.337-345
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• 2009

The purpose of this study were to find out the differences in kinematic variables of racket movement by performing the tennis serve. Three top male tennis players participated in this study. Three synchronized high-speed cameras were used to record the service action of top players for Three dimensional video analysis. The results of this study showed that (1) the velocity of the tennis racket at impact is important to the generation of racket velocity to Y-axis. This result indicates that forward motion and upward movement of the racket; (2) with respect to racket angular velocity at impact, the fast angular momentum of X-axis is important to generate the velocity of the tennis ball. This result indicate upward movement of the racket with a strong flexor of wrist joint; (3) the velocity of the tennis ball was influenced by the change of angular linking the Z-axis to -X-axis. This result indicates that the high velocity of the tennis ball is obtained from having the racket unitedly moving to the direction of the bill's flight at the acceleration interval and acquiring the distance of acceleration with the racket head vertically to the ground at the back scratching.

• Journal of Internet Computing and Services
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• v.15 no.1
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• pp.171-178
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• 2014

This paper presents dynamic modelling of a virtual object in augmented reality environments when external forces are applied to the object in real-time fashion. In order to simulate a natural behavior of the object we employ the theory of Newtonian physics to construct motion equation of the object according to the varying external forces applied to the AR object. In dynamic modelling process, the physical interaction is taken placed between the augmented object and the physical object such as a haptic input device and the external forces are transferred to the object. The intrinsic properties of the augmented object are either rigid or elastically deformable (non-rigid) model. In case of the rigid object, the dynamic motion of the object is simulated when the augmented object is collided with by the haptic stick by considering linear momentum or angular momentum. In the case of the non-rigid object, the physics-based simulation approach is adopted since the elastically deformable models respond in a natural way to the external or internal forces and constraints. Depending on the characteristics of force caused by a user through a haptic interface and model's intrinsic properties, the virtual elastic object in AR is deformed naturally. In the simulation, we exploit standard mass-spring damper differential equation so called Newton's second law of motion to model deformable objects. From the experiments, we can successfully visualize the behavior of a virtual objects in AR based on the theorem of physics when the haptic device interact with the rigid or non-rigid virtual object.

• Proceedings of the Korea Association of Crystal Growth Conference
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• 1997.06a
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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.

• Korean Journal of Applied Biomechanics
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• v.17 no.2
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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.

• Bulletin of the Society of Naval Architects of Korea
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• v.27 no.2
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• pp.1-12
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• 1990

Interactions between a propeller and vortex system contained in a ship stern flow is treated theoretically. A new formulation to determine the effective velocity distributions is developed, which may be immediately applicable to the design and analysis of compound propulsors under the influence of severe vortical cross-flows around ship stern. An axisymmetric shear flow is represented by a system of ring vortices and the axial variation of the stream lines due to the action of propeller is represented by a cubic function. The strengths of ring vortices, which are varying along the stream lines, are determined by the conservation of angular momentum. Two simplified effective velocity models are proposed to confirm the theory. Sample calculations using the simplified models are made to compare with the results by other investigators.

• Journal of Biomedical Engineering Research
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• v.28 no.2
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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.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.14 no.3
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• pp.49-58
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• 2000

This paper deals with a systematic approach to neural network controller design for static VAR compensator (SVC) using a learning algorithm of error back propagation that accepts error and change of error as inputs, the momentum learning technique is used for reduction of learning time, to improve system stability. A SVC, one of the Flexible AC Transmission System(FACTS), constructed by a fixed capacitor(FC) and a thyristor controlled reactor(TCR), is designed and implemented to improve the damping of a synchronous generator, as well as controlling the system voltage.TO verify the robustness of the proposed method, we considered the dynamic response of generator rotor angle deviation, angular velocity deviation and generator terminal voltage by applying a power fluctuation and rotor angle fluctuation in initial point when heavy load and normal load. Thus, we prove the usefulness of proposed method to improve the stability of single machine-infinite bus with SVC system.