• Journal of The Korean Astronomical Society
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• v.29 no.spc1
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• pp.49-51
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• 1996

New population synthesis models, with the effects of metallicity spread and the horizontal-branch (HB) morphology, provide a way to break the well-known age-metallicity degeneracy in the analysis of the integrated light of elliptical galaxies. Our models suggest that the far- UV radiation of these systems is dominated by a minority population of metal-poor, hot HB stars and their post-HB progeny, while the optical radiation is dominated by a metal-rich population. The systematic variation of UV upturn depends on the contribution from metal-poor, hot HB stars and their post-HB progeny, which in turn depends on the ages of old stellar populations in galaxies. Our result implies a prolonged epoch of galaxy formation, in the sense that more massive galaxies (in denser environments) formed first. Our models also suggest that the strenghth of H$\beta$ index is strongly affected by HB stars, and hence previous age estimation without detailed modeling of the HB would underestimate the ages of ellipticals by $\~$7 Gyr.

• Publications of The Korean Astronomical Society
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• v.25 no.3
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• pp.59-64
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• 2010

The core and global properties of the early-type ("red sequence") galaxies in the Virgo and Fornax clusters are examined using high-quality HST/ACS imaging for 143 galaxies. Rather than dividing neatly into disparate populations having distinct formation and/or evolution histories, many of the core and global properties of these galaxies show smooth and systematic variations along the galaxy luminosity function. The few examples of the rare class of compact elliptical galaxies in our sample all show properties that are strongly suggestive of tidal stripping by massive galaxies; if so, then these systems should not be viewed as populating the low-luminosity extension of so-called "normal" elliptical sequences. These results demonstrate that complete and/or unbiased samples are a pre-requisite for identifying the physical mechanisms that gave rise to the early-type galaxies we observe locally, and how these mechanisms varied with mass and environment.

• Journal of computational fluids engineering
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• v.17 no.1
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• pp.1-7
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• 2012

This paper deals with a parametric study on inclined elliptical dimples to enhance heat transfer in a channel. Three-dimensional Reynolds-averaged Naiver-Stokes equations are solved to estimate flow and heat transfer in dimpled channel. As turbulence closure, the low-Re shear stress transport model is employed. Two non-dimensional geometric variables, dimple ellipse diameter ratio and angle of main diameter to flow direction are selected for the parametric study. The inclined elliptical dimples show higher heat-transfer performance but with higher pressure drop compared to the circular dimples. And there is an optimum inclination angle that gives the maximum heat transfer.

• Journal of the Korean Society for Precision Engineering
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• v.26 no.1
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• pp.82-88
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• 2009

Ultra-precision turning is highly needed to manufacture molds for precision lens. In this study, micro-turning combined with elliptical vibration cutting (EVC), which is known to enhance micro- machining quality, was investigated by installing a rotary stage into the micro-grooving machine. From machining experiments involving materials of copper, brass, and aluminum and single and poly crystalline diamond tools, it was found that EVC produced thinner and curlier chips and that better surface finish could be achieved, compared with conventional turning, owing to prohibition of formation of burrs and built-up edges. Therefore, we found EVC micro turning could be readily utilized to manufacture precision mold.

• Journal of the Korean Society for Precision Engineering
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• v.19 no.7
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• pp.20-27
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• 2002

An analysis model for an elliptical fluid film bearing is described. The principles of hydrodynamic lubrication are outlined together with an expanded version of the governing pressure field equation as related to elliptical journal bearing. Finite element method approximations are given for the pressure field equation and a temperature model, both related to the fluid film thickness. The thermal effects in the lubricant viscosity, lubricant film thickness, variation of the journal rotating speed and influence of turbulence are investigated in this paper A finite element model and an iterative computational process are described, whereby full simultaneously converged field solutions for fluid film thickness, temperature, viscosity, pressure, stiffness and damping coefficient are obtained.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1997.03a
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• pp.136-139
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• 1997

Applications of commercial software DEFORM-3DTM for 3-D simulation in extrusion process are developed for the analysis of twisting of extruded products. Because the elliptical shape has at least one line symmetry, the twisting is not occured during the extrusion. But, the results of extrusion simulation of the elliptical shape show that the twisted boundary of the die surface makes the material inside die surface rotate with the constant angular velocity. Otherwise, the simulation results of the S shaped product show that the twisting can be occured by the only 180$^{\circ}$rotation symmetry of S shape without no line symmetry and show that the angular velocity increases by the only 180$^{\circ}$rotation symmetry without no twisted die surface between on the die entrance section and on the die exit section. The results of the analysis show that the angular velocity of the extruded product changes with die length and friction condition.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.25 no.6
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• pp.467-473
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• 2012

A functionally graded material (FGM) spacer, which the distribution of dielectric permittivity inside an insulator changes spatially, can considerably reduce the electric field concentration around a high-voltage electrode and along the gas-insulator interface when compared to a conventional spacer with a uniform permittivity distribution. In this research, we propose the FGM spacer with an elliptical permittivity distribution instead of that with a distribution of dielectric permittivity varying along a radial direction only in order to improve efficiently the insulation capability. The optimal design of the elliptical FGM spacer configuration is performed by using the response surface methodology (RSM) combined with the steepest descent method (SDM).

• Proceedings of the Korean Society For Composite Materials Conference
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• 2003.04a
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• pp.95-98
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• 2003

In this work, a closed-form analysis is performed to obtain the stiffness coefficients of thin-walled composites beams with elliptical profiles. The analytical model includes the effects of elastic couplings, shell wall thickness, torsion warping and constrained warping. Reissner's semi-complementary energy functional is used to derive the beam force-displacement relations. The theory is validated against MSC/NASTRAN results for coupled composites beams with single-cell elliptical sections. Very good correlation has been noticed for the test cases considered.

• Journal of Auto-vehicle Safety Association
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• v.7 no.2
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• pp.39-43
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• 2015

NDIR (Non-dispersive infrared Rays) alcohol sensor has been prototyped and its temperature characteristics were measured. In order to design novel optical alcohol sensor, elliptical structures with one common foci were modeled and analyzed their optical properties. After analyzing elliptic optical structures, a prototype alcohol sensor module was tested according to the temperature variations from $-20^{\circ}C$ to $35^{\circ}C$. The offset voltages of alcohol sensor decreased from 1.1056 V at the temperature $-20^{\circ}C$ to 0.7339 V at $35^{\circ}C$. However, the highest sensitivity of alcohol sensor showed about $303{\mu}V/ppm$ at room temperature.

• Journal of Mechanical Science and Technology
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• v.20 no.3
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• pp.319-328
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• 2006

A simple approximation method for the stress intensity factor at the tip of the axial semielliptical cracks on the cylindrical vessel is developed. The approximation methods, incorporated in VINTIN (Vessel INTegrity analysis-INner flaws), utilizes the influence coefficients to calculate the stress intensity factor at the crack tip. This method has been compared with other solution methods including 3-D finite element analysis for internal pressure, cooldown, and pressurized thermal shock loading conditions. For these, 3-D finite-element analyses are performed to obtain the stress intensity factors for various surface cracks with t/R=0.1. The approximation solutions are within $\pm2.5%$ of the those of finite element analysis using symmetric model of one-forth of a vessel under pressure loading, and 1-3% higher under pressurized thermal shock condition. The analysis results confirm that the approximation method provides sufficiently accurate stress intensity factor values for the axial semi-elliptical flaws on the surface of the reactor pressure vessel.