• Journal of The Korean Astronomical Society
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• v.29 no.1
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• pp.53-62
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• 1996

31 white dwarfs in 10 open clusters are examined, and their maximum mass and the upper mass limit of their progenitors are obtained as $1.22\pm0.02M_{\bigodot}\;and\;7.2\pm0.4M_{\bigodot}$ respectively, suggesting that the upper mass limit of white dwarfs is less than 8M_{\bigodot}$ The final mass of white dwarfs shows no clear correlation with the initial mass of their progenitors, and it is found that a deficient gap of initial mass exists between $\~4\;and\;~5.2M_{\bigodot}$. This gap seems to correspond to the mass range for carbon detonation or deflagration. The total expected numbers of white dwarfs are $11\~22$ in Hyades with 7 known white dwarfs and 17 in Praesepe with 8 known white dwarfs. These known white dwrfs are all younger than the others in both clusters. But one known white dwarf in Pleiades is older one among $2\~3$ expected white dwarfs.

• Proceedings of the KIEE Conference
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• 2008.10c
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• pp.9-11
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• 2008

When a squirrel cage induction motor is loaded, the electromagnetic noise can increase depending on the load current. It is due to the air gap harmonic fluxes from the rotor current induced during loading. This unfavorable noise can be anticipated by calculating the radial force waves in the air gap, vibration mode shapes of them, and stator core natural frequencies of each mode. With the experimental tests with the different rotor slot numbers, the variation of electromagnetic noise is studied between on-loaded and loaded running.

• Proceedings of the KIPE Conference
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• 1998.07a
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• pp.95-98
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• 1998

Applying the magnetically levitated transportation system, which is noncontact bearing system, to solve the problems such as transformation of original form or flaw of iron plate caused by transportation of thin iron plate which required high quality as body of motor vehicle, materials of electronic devices etc.. Magnetic saturation phenomena caused by thickness of iron plate and gap size between magnets. In case of iron plate, the vibration mode will be considered since vibration occurs during transportation. In order to solve the problems caused by vibration, choose the levitation system method using numbers of magnet, magnetic saturation for thickness and length of iron plate with parameters in location and gap of magnet. In this paper, we will suggest the whole design technique of magnetically levitated transportation system, namely method of magnetic attraction and transportation system

• Journal of computational fluids engineering
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• v.10 no.1
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• pp.73-79
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• 2005

Micro sensor is very useful for flow measurements in a number of engineering applications. Especially, it is necessary for the development of MEMS. This paper presents the 3D numerical simulation of flows around a micro flow sensor, which is mounted on a flat plate. The effects of the sensor configuration (i.e. bottom gap) and the Reynolds number on the flow field are numerically investigated. The numerical results indicate that the bottom gap clearly affects the flow fields over the top surface of the sensor. The Reynolds numbers also show a significant influence on the flow nature, especially on the recirculation zone at downstream of the sensor. The present results illustrate a certain improvement on the flow field for the sensor installed at O.5mm above the wall with four pillars, comparing with that directly mounted on the wall.

• Journal of the Korean Society of Safety
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• v.17 no.2
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• pp.8-15
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• 2002

In order to investigate the vibration characteristics of fluid-structure interaction problem, we modeled two identical rectangular plates coupled with fluid. A commercial computer code, ANSYS was used to perform finite element analysis and FEM solutions were compared with the experimental results to verify the finite element model. As a result, comparison of FEM and experiment showed good agreement, and the transverse vibration modes, in-phase and out-of-Phase, were observed alternately in the fluid-coupled system. The effect of fluid gap size on the fluid-coupled natural frequency were investigated. It was shown that the mode numbers increased, the normalized natural frequencies monotonically increased. And it was also found that an increase of the fluid gap reduced the coupled natural frequencies for the in-phase modes but increased the coupled natural frequencies for the out-of phase modes, and eventually converged to the results of an infinite fluid gap.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.3
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• pp.435-442
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• 2000

The present study is conducted to investigate the local heat/mass transfer characteristics for flow through perforated plates. A naphthalene sublimation method is employed to determine the local heat/mass transfer coefficients on the effusion plate. Two parallel perforated plates are arranged for the two different ways: staggered and shifted in one direction. The experiments are conducted for hole pitch-to-diameter ratios of 6.0, for gap distance between the perforated plates of 0.33 to 10 hole diameters, and for Reynolds numbers of 5,000 to 12,000. The result shows that the high transfer region is formed at stagnation region and at the mid-line of the adjacent impinging jets due to secondary vortices and flow acceleration to the effusion hole. For flows through the perforated plates, the mass transfer rates on the surface of the effusion plate are about six to ten times higher than for effusion cooling alone (single perforated plate). More uniform and higher heat/mass transfer characteristic is obtained in overall region with small gap between two perforated plates.

• International Journal of Aeronautical and Space Sciences
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• v.17 no.2
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• pp.139-148
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• 2016

The passive control methods such as horizontal and vertical fences on the lower surface of the bluff body were applied to suppress the vortex shedding and enhance the aerodynamic stability of flow. For investigating the effects of the passive control methods, wind tunnel experiments on the unsteady flow field around a bluff body near a moving ground were performed. The boundary layer and velocity profiles were measured by the Hot Wire Anemometer (HWA) system and the vortex shedding patterns and flow structures in a wake region were visualized via the Particle Image Velocimetry (PIV) system. Also, it is a measuring on moving ground condition that the experimental values of the critical gap distances, Strouhal numbers and aerodynamic force FFT analyses. Through the experiments, we found that the momentum supply due to moving ground caused the vortex shedding at the lower critical gap distance rather than that of fixed ground. The horizontal and vertical fences increase the critical gap distance and it can suppress the vortex shedding. Consequently, the stability characteristics of the bluff body near a moving ground could be effectively enhanced by the simple passive control such as the vertical fences.

• Kyungpook Mathematical Journal
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• v.60 no.2
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• pp.387-399
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• 2020

In this paper, we study a problem of a non-constant entire function f that shares a set S = {a, b, c} with its k-th derivative f^(k), where a, b and c are any three distinct complex numbers. We have found a gap in the statement of the main result of Chang-Fang-Zalcman [10], and with the help of their method, we have generalize their result in a more compact form. As an application, we generalize the famous Brück conjecture [9] with the idea of set sharing.

• International Journal of Contents
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• v.3 no.2
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• pp.40-43
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• 2007

This paper proposed a new modular inverse algorithm based on the right-shifting binary Euclidean algorithm. For an n-bit numbers, the number of operations for the proposed algorithm is reduced about 61.3% less than the classical binary extended Euclidean algorithm. The proposed algorithm implementation shows substantial reduction in computation time over Galois field GF(p).

• Journal of Korean Society for Quality Management
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• v.27 no.1
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• pp.135-150
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• 1999

The second edition of the International Standard ISO/DIS 2859-1(1997) is the revised version of ISO 2859-1(1989). Significant changes in this edition include the following; ⅰ) a new procedure for switching from normal to reduced inspection is used, ⅱ) optional fractional acceptance number sampling plans are added, and ⅲ) reduced plans are changed to eliminate the gap between the acceptance and rejection numbers. In this paper, major changes and additions incorporated into the revised version are discussed.