• The Bulletin of The Korean Astronomical Society
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• v.38 no.2
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• pp.79.2-79.2
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• 2013

The distributions of Horizontal Branch (HB) star color, temperature, and mass encode a great deal of information on the stellar evolutionary and (possibly) dynamical processes taking place in Globular Clusters (GCs). An accurate physical modeling of the Red Giant Branch (RGB) mass-loss process is key to solving the so-called second parameter problem. In my poster I will present the most recent advancements of an analytical model for mass-loss along the RGB. The model predicts the HB mass distribution with remarkable accuracy over a sample of 4 GCs. These results were submitted as a paper to ApJ (Pasquato et al. 2013, ApJ submitted), but here I expand on them presenting refinements to the model and a comparison with HB masses obtained from Galex ultraviolet observations.

• Journal of the Mineralogical Society of Korea
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• v.12 no.1
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• pp.11-22
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• 1999

Thermal behavior of dickite was studied by thermal analysis, X-ray diffraction analysis, electron microprobe analysis, and scanning electron microscopy, Dickite has an endothermic peak at about$ 650^{\circ}C$ and an exothermic one at $960^{\circ}C$ in the differential thermal analysis. The endothermic reaction is assigned to the decomposition of dickite to meta-dickite. Hydroxyl radicals are removed from dickite structure by the reaction, resulting in the weight loss about 10.5~14.5% and appearance of a 14$\AA$ phase different from other kaolin minerals. The reaction slowly proceed in the range of $200^{\circ}C$. As the completion of decomposition, aciclular mullite forms at the expense of meta-dickite plates with random crystallographic relationship. Mullites have diverse silica versus alumina ratio. The exothermic reaction without weight loss seems to be due to the formation of spinel and amorphous silica. The spinel phase shows cryptocrystalline globular morphology accompanying a little amount of silica. From spinel phase shows cryptocrystalling globular morphology accompanying a little amount of silica. From this work, it is suggested that mullite is formed from meta-dickite much lower temperature than the reported one in the previous works.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.10a
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• pp.660-663
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• 2004

Recently in the automotive industries, light and high quality material is strongly required because of emissions regulation issues. In the electromagnetic stirring process, it has many merits that are the exact control ability about material processing and a good point of the protection of environment. In this paper, the morphology of the change of primary Al phase in A356 alloy by electro magnetic stirrer was investigated to obtain the globular structure. The parameters are the current, stirring time, pouring temperature and cooling rate of different wall thickness; 5mm, 15mm, 25mm respectively. By proper selection of the processing parameters, globular primary particles can be obtained by electromagnetic stirrer.

• Bulletin of the Korean Space Science Society
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• 2004.04a
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• pp.89-89
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• 2004

It is believed that age controls horizontal-branch (HB) morphology of Globular Clusters besides metallicity (first parameter). However, other second parameter candidates, such as He abundance and alpha elements enhancement, could also affect HB morphology. These effects may influence to the age measurements from the main-sequence turnoff (MSTO) as well. We will measure the variations of age caused by each second parameter candidate at HB and MSTO respectively, using the well known second parameter pair M3 and Ml3. (omitted)

• Steel and Composite Structures
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• v.15 no.2
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• pp.151-162
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• 2013

In this study, an electrolyzing device for the production of metal powders was designed and fabricated. The production of copper powders was performed using a variety of current densities, anode-cathode distances and power removal times. The effect of these parameters on powder particle size and shape was determined. Particle size was measured using a laser diffraction unit while the powder shape was determined by SEM. Experimental results show that an increase in current density leads to a decrease in powder particle size. In addition particle shape changed from globular dendritic to acicular dendritic with increasing the current density. Distance between the cathode and anode also showed a similar influence on powder particle size and shape. An increase in time of powder removal led to an increase in powder particle size, as the shape changed from acicular dendritic to globular dendritic.

• Journal of Astronomy and Space Sciences
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• v.15 no.1
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• pp.39-48
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• 1998

We present the results of a search for photometric variable blue straggler stars(BSSs) in the globular cluster M53. Six of 151 probable BSSs are identified as variable candidates based on the robust variable star detection technique of Welch & Stetson (1993). Most variable BSS candidates appear to occupy the instability strip in the color-magnitude deagram, and they appear to have visual light amplitudes of 0.2 mag-0.3 mag. Further observations are required, however, to resolve the natrue of variabil-ity between pulsating stars and eclipsing binaries for these variable BSS candidates.

• Journal of Astronomy and Space Sciences
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• v.16 no.2
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• pp.115-130
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• 1999

We report the discovery of 17 new RR Lyrae variables in the central region ($\rleq1'$) of the globular cluster M53. There candidates were identified by using the Welch & Stetson (1993) technique and confirmed by checking individual light curves in both B and V bands. The color-magnitude diagram of the horizontal-branch stars in the central region is compared with that for stars observed in the outer region by Rey et al. (1998). Including the new data from this study, we estimate the fraction of c typeRR Lyrae variables, n(c)/n(ab + c), to be 0.43 which agrees well with the valuse of other Oosterhoff group II clusters.

• Journal of Astronomy and Space Sciences
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• v.23 no.2
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• pp.97-104
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• 2006

From the BV images of the metal-poor globular cluster NGC 1904 obtained with the 2K CCD camera equipped on the BOAO 1.8m telescope, we construct (B - V, V) color-magnitude diagram of the cluster. The apparent V magnitudes of the RGB bump and tip have been measured from the luminosity function of the iteratively selected RGB stars in NGC 1904. Theoretical absolute $M_v$ magnitudes of the RGB bump and tip are estimated using the Yonsei-Yale isochrones. The distance modulus of NGC 1904 has been derived by comparing the observed apparent V magnitude with the estimated absolute $M_v$ magnitude of the RGB bump and tip.

• Journal of Welding and Joining
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• v.15 no.2
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• pp.72-80
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• 1997

The spatter generation rate of GMA welding with $CO_2$ gas shielding was measured with the change of welding conditions such as wire feeding rate and welding voltage and then the results were analized with the accompanying changes in metal transfer mode and in bead geometry. The spatter generation rate (SGR) was relatively low not only wit the short circuit transfer but with the truely globular transfer mode. However, the SGR resulted with the mixed mode were consistantly high. The resultant wave pattern of mixed mode was due to the coexistance of short-circuit and globular transfer and characterized by the frequent appearance of instantaneous short circuit. Considering the result of SGR and that of bead geometry, it could be concluded that when the wire feeding rate (or welding current) was either low or high, the optimum bead shape could be obtained along with the low spatter generation. However, in the middle range of wire feeding rate, the optimum bead shape was only obtained in the mixed mode condition resulting in the high spatter generation.

• Transactions of Materials Processing
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• v.7 no.4
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• pp.364-374
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• 1998

It is the objective of this study to analyze the effect of various process variables on the quality of extruded product and extrusion force for semi-solid extrusion of Al2024 with solid phase structure of globular type by the finite element method. Process variables are initial solid fraction, ram speed, semi-angle of die, and reduction in area. The results of experiment are compared with those of simulation in order to verify the usefulness of the developed finite element program. The flow and deformation of semi-solid alloy are analyzed by coupling by coupling the deformation of porous skeleton and the flow of liquid phase. It is also assumed that initial solid fraction is homogeneous.