• The Bulletin of The Korean Astronomical Society
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• v.35 no.1
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• pp.66.1-66.1
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• 2010

Using two-dimensional numerical hydrodynamic simulations, we investigate the star formation rate (SFR) in turbulent, multiphase, galactic gaseous disks. Our simulation domain is axisymmetric, and local in the radial direction and global in the vertical direction. Our models include galactic rotation, vertical density stratification, self-gravity, radiative heating and cooling, and thermal conduction, but do not include spiral-arm features. Turbulence in our models is driven by momentum feedback from supernova explosion events occurring in localized dense regions formed by thermal and gravitational instabilities. Self-consistent radiative heating, representing enhanced/reduced FUV photons from the star formation, is also taken into account. By controlling three parameters (the gas surface density, the stellar disk density, and the angular rotation rate) that characterize local galactic disks, we explore how the SFR depends on the background environmental state. We also discuss the relation between the SFR and the gas surface density found in our numerical models in comparison with observations.

• Bulletin of the Korean Chemical Society
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• v.10 no.5
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• pp.430-433
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• 1989

Molecular reorientation of oblate symmetric top molecules in the presence of internal rotation is investigated and an analytic expression for the spin-rotational relaxation rate of a nucleus attached to the internal rotor is obtained as a function of the internal angular momentum correlation time. The overall reorientation of the symmetric top is treated by the anisotropic rotational diffusion and the internal rotation is assumed to undergo modified extended rotational diffusion. The result is compared with the previous work for the prolate symmetric top molecule and it is shown that both results reduce to the same expression in the spherical top limit.

• Bulletin of the Korean Chemical Society
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• v.15 no.3
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• pp.228-236
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• 1994

The effect of the vibration mode coupling induced by the vibration-rotation interaction on total energy was investigated for the states with zero total angular momentum(J=0) in a quasilinear symmetric triatomic molecule of $AB_2$ type using a model potential function with a slight potential barrier to linearity. It is found that the coupling energy becomes larger for the levels of bend and asymmetric stretch modes and smaller for symmetric stretch mode as the excitation of the vibrational modes occurs. The results for the real molecule of $CH_2^+$, which is quasilinear, generally agree with the results for the model potential function in that common mode selective dependence of coupling energy is exhibited in both cases. The differences between the results for the model and real potential function in H-C-H system are analyzed and explained in terms of heavy mixing of the symmetric stretch and bend mode in excited vibrational states of the real molecule of $CH_2^+$. It is shown that the vibrational mode coupling in the potential energy function is primarily responsible for the broken nodal structure and chaotic behavior in highly excited levels of $CH_2^+$ for J= 0.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.1
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• pp.74.3-75
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• 2019

Recent Integral Field Spectroscopy (IFS) studies revealed that not only late type galaxies (LTGs) but also early type galaxies (ETGs) have various kinds of kinematic rotation. (e.g. not clearly detectable rotation, disk-like rotation, kinematically distinct core (Cappellari 06)) Among the various studies about galactic kinematics, one of the most notable anomalies is the star-gas misalignment. The gas forms stars and stars release gas through mass-loss. In this process, their angular momentum is conserved. Therefore, kinematic decoupling between stars and gas can occur due to external gas inflow or perturbation of components. There are some possible origins of misalignment: cold gas from filaments, hot gas from outer halo, interaction or merging events with galaxies and environmental effects. Misalignment, the black box from mixture of internal and external gas, can be an important keyword for understanding further about galaxies' kinematics and external processes. Using both SAMI IFS data(Sydney-AAO Multi-object Integral field spectrograph Galaxy Survey, Croom+12) and Horizon-AGN simulation(Dubois+14), we examined misaligned galaxies properties and distribution. Because the simulation has lots of galaxies at various z, we were able to study history of formation, evolution and extinction of misalignment, which was hard to be done with observation only.

• Journal of computational fluids engineering
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• v.20 no.3
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• pp.35-40
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• 2015

Centrifugal pumps consume considerable amounts of energy in various industrial applications. Therefore, improving the efficiency of pumps machine is a crucial challenge in industrial world. This paper presents numerical investigation of flow characteristics in volutes of centrifugal pumps in order to compare the energy consumption. A wide range of volumetric flow rate has been investigated for each case. The standard k-${\varepsilon}$ is adopted as the turbulence model. The impeller rotation is simulated employing the Multi Reference Frames(MRF) method. First, two different conventional design methods, i.e., the constant angular momentum(CAM) and the constant mean velocity (CMV) are studied and compared to a baseline volute model. The CAM volute profile is a logarithmic spiral. The CMV volute profile shape is an Archimedes spiral curve. The modified volute models show lower head value than baseline volute model, but in case of efficiency graph, CAM curve has higher values than others. Finally for this part, CAM curve is selected to be used in the simulation of different cross-section shape. Two different types of cross-section are generated. One is a simple rectangular shape, and the other one is fan shape. In terms of different cross-section shape, simple rectangular geometry generated higher head and efficiency. Overall, simulation results showed that the volute designed using constant angular momentum(CAM) method has higher characteristic performances than one by CMV volute.

• Coupled systems mechanics
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• v.7 no.5
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• pp.611-626
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• 2018

We theoretically consider a possible influence of periodic oceanic tides on non-periodic changes in the dynamics of the Earth and Moon over a long time scale. A particular emphasis will be placed on the contribution from rotating tidal waves, which rotate along the inner edge of an oceanic basin surrounded by topographic boundary. We formulate the angular momentum and the mechanical energy of the rotating tidal wave in terms of celestial parameters with regard to the Earth and Moon. The obtained formula are used to discuss how the energy dissipation in the rotating tidal wave should be relevant to the secular variation in the Earth's spin rotation and the Earth-Moon distance. We also discuss the applicability of the formula to general oceanic binary planets subject to tidal coupling.

• Korean Journal of Applied Biomechanics
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• v.18 no.4
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• pp.179-189
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• 2008

The purpose of this study was to investigate interjoint and intersegmental coordination of lower segments in skill process. For the investigation, we examined the difference of resultant linear velocity of segments and angle vs angle graph. Novice subjects were 9 male middle school students who have never been experienced a taekwondo. We analyzed kinematic variables of Side Kick motion through videographical analysis. The conclusions were as follows. 1. Examining the graph of novice subjects' maximal resultant linear velocity of the thigh, shank, and foot segment, as it gets closer to the end of the training, the maximal resultant linear velocity in each segment increases which can be assumed to be a result of the effective momentum transfer between adjacent segments. 2 This research showed a sequential transfer from trunk, to thigh, and then to shank as it gets closer to the end of learning at intersegment angular velocity, and it also showed pattern of throwlike motion and pushlike motion. 3. In three dimension of flexion-extension, adduction-abduction and internal-external rotation of the thigh and shank segment, the angle-angle diagram of knee joint and of hip joint showed that dynamic change was indicated at the beginning of learning but stable coordination pattern was indicated like skilled subject as novice subjects became skilled.

• 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.

• Korean Journal of Applied Biomechanics
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• v.20 no.1
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• pp.41-47
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• 2010

The purpose of this study was to evaluate the kinematic effect of upper extremity usage for the scoccer instep kick motion. Ten male university students were recruited as the subjects. Temporal parameters, ball velocity, velocity of CG, angle of segment, angular velocity, and trunk orientation angle were determined for each trial. The results showed that temporal parameters in WU and WORU were significantly less than those found in WOU during pre impact phase. These indicated that no usage of upper extremity may increase excessive setup time in order to improve the accuracy of instep kick. Angle of right knee in WOU at LC was significantly greater than corresponding value for WU since angular momentum contributions of the lower limb were not effectively balanced by contributions of the upper limb. We found that the lower extremity movement was controlled by lateral movement in the trunk as a result of no usage of the upper extremity, resulting in the relatively greater trunk rotation in WOU.

• 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.