• 열처리공학회지
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• 제25권3호
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• pp.138-145
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• 2012

An ${\alpha}$-Ferrite (Fe) powder dispersed with 4 vol.% of $Al_2O_3$ was successfully produced by a simple miling at 210 K with a mixture of $Fe_2O_3$, Fe and Al ingredient powders, followed by 2 step high temperature consolidation: Hot Pressing (HP) at 1323 K and then Hot Isostatic Pressing at 1423 K. The microstructure of the consolidated material was characterized by standard metallographic techniques such as XRD (X-ray Diffraction), TEM and STEM-EDS. The results of STEM-EDS analysis showed that the HIPed materials comprised a mixture of pure Fe matrix with a grain size of ~20 nm and $Al_2O_3$ with a bimodal size distribution of extremely fine (~5 nm) and medium size dispersoids (~20 nm). The mechanical properties of the consolidated materials were characterized by compressive test and micro Vickers hardness test at room temperature. The results showed that the yield strength of the ODS (Oxide Dispersion Strengthened) Fe alloy are as much as $674{\pm}39$ MPa and the improvement of the yield strength is attributed to the presence of the fine $Al_2O_3$ dispersoid.

• 열처리공학회지
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• 제5권2호
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• pp.85-94
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• 1992

Microstructural evolution of wrought Inconel 718 superalloy with different heat treatment conditions was studied. Heat treatment was performed via conventional(CHT), modified(MHT), Merrick(MeHT) and modified Merrick (MMeHT) methods. The size of ${\gamma}^{\prime}$ and ${\gamma}^{\prime\prime}$ precipitates which are principal strengthening phases in Inconel 718 superalloy increase in order of CHT, MHT, MeHT. For the case of MMeHT, a coexistence of fine ${\gamma}^{\prime\prime}$ precipitate and very coarse particles due to exess growth of ${\gamma}^{\prime\prime}$, which is called bimodal distribution, was observed. CHT gave the finest grain size. (Ti, Nb)C carbide and needle-like ${\delta}$ phase were formed together at grain boundaries for CHT, and were formed both inside and at boundaries of grains for MHT, MeHT and MMeHT. Morphology of partially serrated grain boundaries was developed in all heat treatment conditions except CHT.

• 천문학회보
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• 제36권2호
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• pp.70.2-70.2
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• 2011

We present a study of the metallicities, ages, and alpha-elements of globular clusters (GCs) in nearby giant elliptical galaxies (gEs) (M87, M49, M60, NGC 5128, NGC 1399, NGC 1407, and NGC 4636) using data in the literature. We used only the data for the GCs derived from the comparison of absorption line indices with the single stellar population model. The metallicity distributions of GCs in these gEs are bimodal, showing the existence of metal-poor and metal-rich populations. All these gEs harbor young GCs with ages less than 5 Gyr as well as old GCs. The mean age of the metal-rich GCs ([Fe/H]>-0.9) is about 3 Gyr younger than that of the metal-poor GCs. The mean values for the alpha-elements of the GCs are smaller than or similar to that of the Milky Way GCs. All the GCs in these gEs show an age-metallicity relation; the larger the metallicities of the GCs are, the younger the GCs are. Old GCs with ages > 10 Gyr have two distinct sub-populations (metal poor and metal rich), while young GCs show a broad metallicity distribution with a single peak. We discuss these results in relation with the formation of GCs in gEs.

• 한국분말재료학회지
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• 제2권1호
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• pp.29-35
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• 1995

In this study the calcined condition and characteristic of Cu-Ni-Zn ferrite powder were investigated. The Cu-Ni-Zn ferrite powder has been synthesized by the thermal decomposition of the organic acid salt. This process did not require a strict pH control and provided the uniform composition and fine powder with about 0.3 $\mu\textrm{m}$. The XRD diffraction pattern of this powder showed about 50% spinel phase. The optimum calcination was found to be done at $700^{\circ}C$ for one hour. After the calcination, the amount of spinel increased to 90%. The distribution of the particle size showed bimodal peaks, one was about 0.5 $\mu\textrm{m}$ and the other was about 20 $\mu\textrm{m}$. The large particles of 20 $\mu\textrm{m}$ were the agglomeration of fine Particles. The mean Particle size of the powder was about 0.4 $\mu\textrm{m}$. The powder was compacted under 100 MPa pressure and sintered at 1100~ $1250^{\circ}C$ for one hour in air. The density of ferrites specimen was a function of the sintering temperature. The higher the temperature, the denser the ferrite. The maximum relative density of the sintered ferrite was about 93% at $1250^{\circ}C$. The grain size of sintered specimen at $1200^{\circ}C$ was 5 $\mu\textrm{m}$ and homogeneous.

• 한국분말재료학회지
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• 제11권2호
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• pp.165-170
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• 2004

Growth behavior of two different types of grains, faceted and rounded, in a liquid matrix has been studied in the (75WC-25TiCN)-30Co system. Powder samples were sintered above the eutectic temperature for various times under a carbon saturated condition. (Ti,W)(C,N) grains with a rounded shape and WC grains with a faceted shape coexisted in the same Co based liquid. With increasing sintering time, the average size of (Ti.W)(C,N) grains increased continuously and very large WC grains appeared. The growth of rounded (Ti,W)(C,N) grains followed a cubic law, r^3-r^3_0$=kt, where r is the average size of the grains, $r_0$ the initial average size, k the proportionality constant and t the sintering time. indicating a diffusion-controlled growth. On the other hand, the growth of the faceted WC grains resulted in a bimodal grain size distribution, showing an abnormal grain growth. These observations show that the growth behavior of different types of grains is governed by their shape, faceted or rounded, even in the same liquid matrix.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2000년도 추계학술대회 논문집
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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 modules. 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.

• 한국재료학회지
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• 제15권11호
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• pp.690-696
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• 2005

The ultrastructure ore of a nanostructured apatite film nucleated from solution was studied to gain insights into that of bone minerals which is the most important constituent to sustain the strength of bones. Needle-shaped apatite crystal plates with a bimodal size distribution $(\~100\;to\;\~1000 nm)$ were randomly distributed and they were found to grow parallel to the c-axis ([002]), driven by the reduction of surface energy. Between these randomly distributed needle-shaped apatite crystals which are parallel to the film, apatite crystals (20-40nm) with the normal of the grains quasi-perpendicular to the c-axis were observed. These observations suggest that the apatite film is the interwoven structure of apatite crystals with the c-axis parallel and quasi-perpendicular to the fan. In some regions, amorphous calcium phosphate, which is a precursor of apatite, was also observed. In the amorphous phase, small crystalline particle with the size of 2-3 nm were observed. These particles were quite similar, in size and shape, to those observed in the femoral trabecular bone, suggesting the nucleation of apatites by a biomimetic process in vitro is similar to that in vivo.

• Journal of Preventive Medicine and Public Health
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• 제19권2호
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• pp.177-183
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• 1986

Subjective symptoms, counts of blood cells and liver function test were conducted on 198 male workers who were exposed to toluene in Kyungin area from September to November, 1986. According to the level of urinary hippuric acid concentration, the total sample was classified into the high exposure group ($concentration{\geqq}3g/1$) and the low exposure group(concentration<3g/1). The following findings were obtained by comparing the two group: 1) Contrary to the previous findings. the urinary hippuric acid concentration of toluene exposed workers showed bimodal distribution. It meant that the toluene exposed workers were mixed with the non-exposed or minimal exposed workers. 2) The high exposure group showed a lower level of leucocytes counts ($6,630{\pm}1,860{\mu}l$) than the low exposure group ($6,340{\pm}1,960/{\mu}l$). 3) The high exposure group showed a higher level of SGOT, SGPT and r-GTP than the low exposure group (p<0.05). 4) The high exposure group complained much more subjective symptoms (e. g. skin rash, loss of appetite, palpitation) than the low exposure group.

• 말소리와 음성과학
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• 제10권4호
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• pp.31-37
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• 2018

Pitch trajectories reflect a continuous variation of vocal fold movements over time. This study examined the pitch trajectories of English vowels produced by 139 American English speakers, statistically analyzing their trajectories using the Generalized Additive Mixed Models (GAMMs). First, Praat was used to read the sound data of Hillenbrand et al. (1995). A pitch analysis script was then prepared, and six pitch values at the corresponding time points within each vowel segment were collected and checked. The results showed that the group of men produced the lowest pitch trajectories, followed by the groups of women, boys, then girls. The density line showed a bimodal distribution. The pitch values at the six corresponding time points formed a single dip, which changed gradually across the vowel segment from 204 to 193 to 196 Hz. The normality tests performed on the pitch data rejected the null hypothesis. Nonparametric tests were therefore conducted to discover the significant differences in the values among the four groups. The GAMMs, which analyzed all the pitch data, produced significant results among the pitch values at the six corresponding time points but not between the two groups of boys and girls. The GAMMs also revealed that the two groups were significantly different only at the first and second time points. Accordingly, the methodology of this study and its findings may be applicable to future studies comparing curvilinear data sets elicited by experimental conditions.

• 천문학회보
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• 제46권1호
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• pp.34.2-34.2
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• 2021

SPT-CL J2106-5844 is the most massive galaxy cluster at z>1 discovered to date. It has been known to be an isolated system with a singular, well-defined halo. However, recent studies provide lines of evidence for its merging state. We strengthen the case with the multi-wavelength observations from ALMA, ACA, ASKAP, ATCA, and Chandra. With the sensitive, high resolution ALMA+ACA observations, we reconstruct the ICM pressure map from the thermal SZ effect. It reveals two main gas components that are associated with the mass clumps inferred from the weak-lensing analysis. Furthermore, the X-ray hardness map supports the bimodal gas distribution. With these multi-wavelength data, we probe the merger phase in SPT-CL J2106-5844.