• The Bulletin of The Korean Astronomical Society
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• v.38 no.2
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• pp.37.1-37.1
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• 2013

We present our study of analyzing the photometric properties of the globular cluster (GC) system which resides in the extended halo of the central bright Coma cluster galaxy NGC 4874. The core of the Coma cluster of galaxies (Abell 1656) was observed with both the HST Advanced Camera for Surveys (ACS) in the F475W (g475) and F814W (I814) and Wide Field Camera 3 IR Channel (WFC3/IR) in the F160W (H160) filters. The data analysis procedure and GC candidate selection criteria are briefly described. We investigate the interesting "tilt" features in color-magnitude diagrams for this GC system and their link to the nonlinear color-metallicity relation for GCs. The NGC 4874's GC system exhibits a bimodal distribution in the optical g475-I814 color and much more than half the GCs fall in the red side at g475-I814 ~ 1.1. This bimodality is weakened in the optical-IR I814-H160 color; the quantitative analysis on the features of both color distributions using the Gaussian Mixture Modeling code proves the bimodalities are different. Both colors, thus, cannot linearly reflect the bimodality of an underlying metallicity, supporting the suggestion that observed bimodalities in extragalactic GC colors are the metallicity-to-color projection effect.

• 한국해양학회지
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• v.26 no.1
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• pp.38-46
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• 1991

size data of 1,044 surface sediments from Korean shelf area were compiled and reexamined. Size distribution curves of the sediments are unimodal (31% of the total number), bimodal (54%), or multimodal 915%), Size curves of the sediments and modal subpopulations of the mixed sediments show resemblance to normal curve in shape. The modal mean value shows systematic change along a direction inside the Recent mud belts of the southeastern Yellow Sea and west of Korea Strait. It was found that the areas covered by unimodal sand are minimal value areas of heavy metal and suspended sediment-concentration in the southeastern Yellow Sea and northern East China transport processes during Recent time. It was also found that the mode analysis is useful method to extract information from sediment size data.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2000.11a
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• pp.116-119
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• 2000

The advantage of plasma-sprayed coating is their good resistance against thermal shock due to the porous state of the coated layer with a consequently low Youngs modulus. However, the existence of many pores with a bimodal distribution and a laminar structure in the coating reduces coating strength and oxidation protection of the base metals. In order to counteract these problems, there have been many efforts to obtain dense coatings by spraying under low pressure or vacuum and by controlling particle size and morphology of the spraying materials. The aim of the present study is to survey the effects of the HIP treatment between 1100 and 130$0^{\circ}C$ on plasma-sprayed oxide coating of A1$_2$O$_3$, A1$_2$O$_3$-SiO$_2$on the metal substrate (type C18N10T stainless steel). These effects were characterized by phase identification, Vickers hardness measurement, and tensile test before and after HIPing. These results show that high-pressure treatment has an advantage for improving adhesive strength and Vickers hardness of plasma-sprayed coatings.

• Environmental Mutagens and Carcinogens
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• v.19 no.1
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• pp.7-13
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• 1999

The mouse lymphoma thymidine kinase (tk+/-) gene assay (MOLY) using L5178Y tk+/- mouse lymphoma cell line is one of the mammalian forward mutation assays. It is well known that MOLY has many advantages and more sensitive than the other mammalian forward mutation assays such as x-linked hyposanthine phosphoribosyltransferase (hprt) gene assay. The target gene of MOLY is a heterozygous tk+/- gene located in 11 chromosome of L5178Y tk+/- cell, so it is able to detect the wide range of genetic changes like point mutation, deletion, rearrangement, and mitotic recombination within tk gene or deletion of entire chromosome 11. MOLY has relatively short expression time (2-3 days) compared to 1 week of hprt gene assay. MOLY can also induce relatively high mutant frequency so a large number of events can be recorded. The bimodal distribution of colony size which may indicate gene mutation and chromosome breakage potential of chemicals according to mutation scale such as large normal-growing mutants and small slow-growing mutants can be observed in this assay. The statistical analysis of data can be performed using the MUTANT program developed by York Electronic Research in association with Hazelton as recommended by the UKEMS (United Kingdom Environmental Mutagen Society) guidelines. This report reviewed MOLY using the microtiter cloning technique (microwell assay).

• The Bulletin of The Korean Astronomical Society
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• v.37 no.1
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• pp.61.1-61.1
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• 2012

We examine both optical and optical/near-infrared (NIR) color distributions of the globular cluster (GC) system in the core of the Coma cluster of galaxies (Abell 1656), centered on the giant elliptical galaxy NGC 4874, to study how non-linearities in the color-metallicity relations of GC systems in large elliptical galaxies are linked to bimodal optical color distributions. Since optical-NIR color distributions of extragalactic GC systems reflect the underlying features of the metallicity distributions, we also present the color-color relation for this GC system. In order to do this, we combine F160W ($H_{160}$) NIR imaging data acquired with the Wide Field Camera 3 IR Channel (WFC3/IR), newly installed on Hubble Space Telescope (HST), with F475W ($g_{475}$) and FF814W ($I_{814}$) optical imaging data from the HST Advanced Camera for Surveys (ACS). To quantitatively explain the feature of color distributions, we use the Gaussian Mixture Modeling (GMM) code. Finally, we show the radial distribution of the GCs in the field of NGC 4874.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.6
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• pp.1661-1668
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• 1990

In a turbulent premixed flame stabilized by the streamline step, and dominated by a coherent eddy, a flame micro-structure was investigated with analyzing the signals of temperature, the ion current, and schieren phtographs simultaneously. Generally the contours of large scale coherent eddies of schlieren photographs was considered as the flame front, however, the main reaction can be occurred within the eddy as a structure of fine flamelets scale. The surrounding burned gas of flamelets could not propagate to a unburned mixture, obstructing flamelets from propagating to a unburned mixture. Consequently, it could restrain flashback. The main reaction region was found to be located at higher temperature of the burned gas rather than at maximum rms of fluctuating temperature. The peak probability of higher temperature was 6 times greater than that of lower temperature. As it was difficult to infer a flame structure from PDF distribution of the fluctuating temperature in form of bimodal shape, it should be taken into consideration with other informations related to the sensitive flame front, for instance, ion current.

• Journal of Korean Society for Atmospheric Environment
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• v.11 no.3
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• pp.263-272
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• 1995

Characteristics of anbient at Korean, Cheju Island have been studied during the intensive field study period on March 11 .sim. 17, 1994 in collaboration with other research organizations from Korea and abroad. The particle size distribution was measured using an Electrical Aerosol Analyzer(EAA) and an Optical particle Counter(OPC). Fine particles(PM1 and PM3) have been collected by filter pack samplers and their ionic compositions have been analyzed. sampling errors inherent to the filter pack sampling method are discussed and the method to analyze those errors are presented. The rine mass concentrations of this study show very similar mass concentrations when Seoul is clear. This is somewhat surprising result, because the most of researchers believe that Kosan is one of the cleanest area in Korea. Bimodal volume size distributions with peak values around 0.1 .sim. 0.2.mu.m and 3.mu.m in particle dimeter were observed for most of the measurement period, particle mass loadings and ionic composition data show a large fraction of particles are from non-sea salt origins. Estimation of water content and acidity of particles based on measurement by a gas/particle equilibrium model, SCAPE, reveals that the pH values of particles are comparable to or lower than those estimated based on measurements in Los Angeles, U.S.A. during the SCAQS study. These findings with the meteorological conditions during the study period suggest that the particles collected during the period have originated from outside Cheju Island.

• Water for future
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• v.27 no.2
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• pp.129-137
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• 1994

The surface hydrology of large land areas is susceptible to several preferred stable states with transitions between stable states induced y stochastic fluctuation. This comes about due to the close coupling of land surface and atmospheric interaction. An interesting and important issue is the duration of residence in each mode. Mean transtion times between the stable modes are analyzed for different model parameters or climatic types. In an example situation of this differential equation exhibits a bimodal probability distribution of soil moisture states. Uncertainty analysis regarding the model parameters is performed using a Monte-Carlo simulation method. The method developed in this research may reveal some important characteristics of soil moisture or precipitation over a large area, in particular, those relating to abrupt changes in soil moisture or precipitation having extremely variable duration.

• Journal of the Korean Society for Heat Treatment
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• v.26 no.6
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• pp.279-287
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• 2013

Oxide Dispersion Strengthened (ODS) Fe with $Al_2O_3$ dispersoid was successfully produced by reactive milling with a mixture of Fe, $Fe_3O_4$ (Magnetite), $Fe_2O_3$ (Hematite) and Al reactants at cryogenic temperature. The milled powders were consolidated by Vacuum Hot Press (HP) at 1323 K, and the consolidated materials were characterized by Transmission Electron Microscopy (TEM), Scanning Transmission Electron Microscopy (STEM), and Energy Dispersive Spectroscopy (EDS); the yield strength and the hardness of the consolidated materials were determined by compressive test and Vickers hardness test at room temperature. The grain size of the materials was estimated by X-ray Diffraction technique using the scherrer's formula. The TEM observations showed that the microstructure was comprised with a mixture of nanocrystalline Fe matrix and $Al_2O_3$ nano-dispersoids with a bimodal size distribution; the 0.2% off-set yield strength of the materials was as high as $758{\pm}29$ MPa and the Vickers hardness was $358{\pm}2$. The effect of the cryogenic milling and addition of extra Fe powder was discussed on the suppression of MSR (Mechanically induced Self-sustaining Reaction) for the desired microstructural evolution of ODS alloys.

• Journal of Powder Materials
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• v.17 no.2
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• pp.136-141
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• 2010

Bismuth-telluride based $(Bi_{0.2}Sb_{0.8})_2Te_3$ thermoelectric powders were fabricated by two-step planetary milling process which produces bimodal size distribution ranging $400\;nm\;{\sim}\;2\;{\mu}m$. The powders were reduced in hydrogen atmosphere to minimize oxygen contents which cause degradation of thermoelectric performance by decreasing electrical conductivity. Oxygen contents were decreased from 0.48% to 0.25% by the reduction process. In this study, both the as-synthesized and the reduced powders were consolidated by the spark plasma sintering process at $350^{\circ}C$ for 10 min at the heating rate of $100^{\circ}C/min$ and then their thermoelectric properties were investigated. The sintered samples using the reduced p-type thermoelectric powders show 15% lower specific electrical resistivity ($0.8\;m{\Omega}{\cdot}cm$) than those of the as-synthesized powders while Seebeck coefficient and thermal conductivity do not change a lot. The results confirmed that ZT value of thermoelectric performance at room temperature was improved by 15% due to high electric conductivity caused by the controlled oxygen contents present at bismuth telluride materials.