• Journal of The Korean Astronomical Society
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• v.34 no.1
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• pp.31-33
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• 2001

The collision effects in particles of the accretion disk are examined by the use of small perturbation. The collision force is assumed to be equal to 2 vV. From the equations governing collisions of such particles the local dispersion relation is obtained.

• Publications of The Korean Astronomical Society
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• v.12 no.1
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• pp.149-157
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• 1997

The collision model of the disk, based on collisions between the particles in the disk, is summarized. The dependence of disk stability on the collision of the particles is demonstrated. The energy spectrum produced in the disk is numerically calculated. We concluded that the results are not largely different from those of the standard disk model. It implies that the collision of the particles inside the disk may be considered here.

• Publications of The Korean Astronomical Society
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• v.11 no.1
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• pp.125-137
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• 1996

The collision of two particles in the accretion disk may lead to be a mechanism of heat generation. By using hydrodynamic equations, the mean free path, the collision frequency and the deflection angle due to the collision of the particles are derived as a function of the mass accretion rate. The mean free path seems to be a smaller fraction compared to the dimension parameter of the system. The radiative flux in the disk is obtained under the influence of the collision of the particles.

• Journal of The Korean Astronomical Society
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• v.33 no.3
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• pp.173-175
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• 2000

The time-dependence of an $\alpha$-disk model under the influence of collisions of particles is examined. Collisions with viscosity tend to take away angular momentum. Both effects cause the disk to rotate more rapidly. The disk gradually contracts with increasing time.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.1
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• pp.50.2-50.2
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• 2016

Continuous accretion of metal-poor gas can explain the discrepancy between the number of observed G-dwarfs and the number predicted by the "simple model" of galactic evolution. The maximum accretion rate estimated based upon approaching high velocity clouds (HVCs) can be up to ${\sim}0.4M_{\odot}{\cdot}yr^{-1}$ which is comparable with the accretion rate required by many chemical evolution models that is at least ${\sim}0.45M_{\odot}{\cdot}yr^{-1}$. However, it is not clear to what extent the exchange of gas between the disk and the cloud can occur when an HVC collides with the galactic disk. Therefore, we examined a series of HVC-Disk collision simulations using the FLASH 2.5 hydrodynamics simulation code. The outcomes of our simulations show that an HVC will more likely take away substances from the galactic disk rather than adding new material to the disk. We define this as an HVC having a "negative fuel rate". Further results in our study also indicate that the process and amount of fuel rate change can have various forms depending on the density, radius and velocity of an approaching HVC. The simulations in our study covers HVCs with a neutral hydrogen volume density from $1.0{\times}10^{-2}cm^{-3}$ to $41.0cm^{-3}$, radius of 200 pc to 1000 pc and velocity in the range between $40km{\cdot}s^{-1}$ and $100km{\cdot}s^{-1}$.