• Proceedings of the Korean Magnestics Society Conference
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• 2016.11a
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• pp.156-156
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• 2016

• Proceedings of the Korean Vacuum Society Conference
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• 1998.06a
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• pp.122-122
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• 1998

• Journal of the Korean Ceramic Society
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• v.49 no.4
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• pp.318-324
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• 2012

Reaction-bonded silicon nitrides containing rare-earth oxide sintering additives were densified by gas pressure sintering. The sintering behavior, microstructure and mechanical properties of the resultant specimens were analyzed. For that purpose, $Lu_2O_3-SiO_2$ (US), $La_2O_3$-MgO (AM) and $Y_2O_3-Al_2O_3$ (YA) additive systems were selected. Among the tested compositions, densification of silicon nitride occurred at the lowest temperature when using the $La_2O_3$-MgO system. Since the $Lu_2O_3-SiO_2$ system has the highest melting temperature, full densification could not be achieved after sintering at $1950^{\circ}C$. However, the system had a reasonably high bending strength of 527 MPa at $1200^{\circ}C$ in air and a high fracture toughness of 9.2 $MPa{\cdot}m^{1/2}$. The $Y_2O_3-Al_2O_3$ system had the highest room temperature bending strength of 1.2 GPa.

• Journal of the Korean Magnetics Society
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• v.26 no.2
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• pp.67-69
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• 2016

Recently, cost of rare-earth magnets has been raised, because rare-earth magnets are monopolized and the export is also regulated in China. For this reason, the induction motor is operated without the rare-earth magnets. The efficient development of induction motor is more important for economical scheme. A torque of the induction motor is computed and the correlation between dimension and resistance of the squirrel cage rotor is investigated. Also, the correlation between leakage reactance and torque was analyzed with respect to the same dimension of rotor with different shapes. Therefore, this paper proposes the method of improvement for squirrel cage rotor.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.1 no.1
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• pp.5-16
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• 1991

It was grown Cubic $ZrO_2(10 mol% Y_2O_3)$ single crystals doped with 1 wt% rare earth metal oxides (RE=Ce, Pr, Nd, Eu, Er) by Skull method. It was investigated electrical properties on (111) plane of grown single crystals by Impedance Spectroscopy. It was potted relation between temperature and electrical conductivities and observed the transition at $약300-400^{\circ}$ It was obtained activation energy on the migration of oxygen vacancy between low temperature (before the transition) and high temperature (after the transition till ${\11}500^{\circ}$) and its difference can be seen the activation energy of the formation of oxygen vacancies by break up defect complexes. It was obtained the activation energy according as add yttria and rare earth metal oxides and discussed ionic conduction mechanism. Grown single crystals showed Ce: orange - red, Pr: golden - yellow, Nd: lilac, Eu: light pink, Er: pink due to dopant effect from the light absorption data in the visible range.

• Analytical Science and Technology
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• v.14 no.2
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• pp.103-108
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• 2001

Rare earth elements(REE) were separated by solvent extraction with tri-n-butyl phosphate(TBP) and $NaNO_3$, followed by back extraction with water. The method was applied to the determination of REE to circumvent the spectral interferences of ICP-AES analysis. The effects of the $NaNO_3$ concentration and the addition of hydrophobic solvents on the extraction efficiencies were investigated. Increases of the $NaNO_3$ concentration enhanced the extraction efficiencies of REE, and more than 95% recoveries were obtained at 5M of $NaNO_3$ concentration. On the other hand, addition of hydrophobic solvents lowered the extraction efficiencies. The method was applied to determine the REE in the monazite sample. But the precisions of the analytical results were more than 20%.

• Journal of Environmental Science International
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• v.18 no.6
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• pp.621-632
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• 2009

Rare earth contents(REE) were analysed for the plants, M. sinensis. A. vulgaris and R. crataegitolius, from two different soils serpentine area consisting of serpentinite(SP) and non-serpentine area, containing amphibole schist(AS) of Gapyeong area, and were compared with soils and host rocks. The AS were high with the differences of several times in the top soils, and with the differences of several to ten times in the host rocks relative to the SP. In the same area, the SP were high in the soil, but the rocks for the AS. In the plants, the A. vulgaris were high, but low in the R. crataegitolius. Root parts were higher than the upper parts. Differences between the upper and root parts were big in the SP rather than the AS, and were big in the R. crataegitolius, but small in the M. sinensis. Among the parts of the plants, high elements were shown in the R. crataegitolius of the SP, and the A. vulgaris and M. sinensis of the AS. In the correlation coefficients, most of the REE showed positive relationships among the element pairs, especially high positive correlation coefficients in the upper parts of the SP.Differences of the soils and plants(average) were smalle in the M. sinensis and big in the R. crataegitolius. In the upper parts. contents of the A. vulgaris were close to the soils while the R. crataegitolius showed large discrepancies with the soils. In the root parts, contents of the A. vulgaris showed discrepancies with the soils regardless of soil types, but close in the R. crataegitolius of the SP and M. sinensis of the AS.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.438-439
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• 2013

Microelectronic devices의 접촉저항의 향상을 위해 Metal silicides의 형성 mechanism과 전기적 특성에 대한 연구가 많이 이루어지고 있다. 지난 수십년에 걸쳐, Ti silicide, Co silicide, Ni silicide 등에 대한 개발이 이루어져 왔으나, 계속적인 저저항 접촉 소재에 대한 요구에 의해 최근에는 Rare earth silicide에 관한 연구가 시작되고 있다. Rare-earth silicide는 저온에서 silicides를 형성하고, n-type Si과 낮은 schottky barrier contact (~0.3 eV)를 이룬다. 또한, 비교적 낮은 resistivity와 hexagonal AlB2 crystal structure에 의해 Si과 좋은 lattice match를 가져 Si wafer에서 high quality silicide thin film을 성장시킬 수 있다. Rare earth silicides 중에서 ytterbium silicide는 가장 낮은 electric work function을 갖고 있어 낮은 schottky barrier 응용에서 쓰이고 있다. 이로 인해, n-channel schottky barrier MOSFETs의 source/drain으로써 주목받고 있다. 특히 ytterbium과 molybdenum co-deposition을 하여 증착할 경우 thin film 형성에 있어 안정적인 morphology를 나타낸다. 또한, ytterbium silicide와 마찬가지로 낮은 면저항과 electric work function을 갖는다. 그러나 ytterbium silicide에 molybdenum을 화합물로써 높은 농도로 포함할 경우 높은 schottky barrier를 형성하고 epitaxial growth를 방해하여 silicide film의 quality 저하를 야기할 수 있다. 본 연구에서는 ytterbium과 molybdenum의 co-deposition에 따른 silicide 형성과 전기적 특성 변화에 대한 자세한 분석을 TEM, 4-probe point 등의 다양한 분석 도구를 이용하여 진행하였다. Ytterbium과 molybdenum을 co-deposition하기 위하여 기판으로 $1{\sim}0{\Omega}{\cdot}cm$의 비저항을 갖는 low doped n-type Si (100) bulk wafer를 사용하였다. Native oxide layer를 제거하기 위해 1%의 hydrofluoric (HF) acid solution에 wafer를 세정하였다. 그리고 고진공에서 RF sputtering 법을 이용하여 Ytterbium과 molybdenum을 동시에 증착하였다. RE metal의 경우 oxygen과 높은 반응성을 가지므로 oxidation을 막기 위해 그 위에 capping layer로 100 nm 두께의 TiN을 증착하였다. 증착 후, 진공 분위기에서 rapid thermal anneal(RTA)을 이용하여 $300{\sim}700^{\circ}C$에서 각각 1분간 열처리하여 ytterbium silicides를 형성하였다. 전기적 특성 평가를 위한 sheet resistance 측정은 4-point probe를 사용하였고, Mo doped ytterbium silicide와 Si interface의 atomic scale의 미세 구조를 통한 Mo doped ytterbium silicide의 형성 mechanism 분석을 위하여 trasmission electron microscopy (JEM-2100F)를 이용하였다.

• Asian-Australasian Journal of Animal Sciences
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• v.25 no.7
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• pp.1029-1037
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• 2012

The present study was designed to investigate the effect of ${\alpha}$-melanocyte-stimulating hormone (${\alpha}$-MSH), nitric oxide (NO) and L-cysteine on melanin production and expression of related genes MC1R, Tyr, Tyrp-1 and Tyrp-2 in muzzle melanocytes of differently colored three native Hanwoo cattle. Muzzle samples were taken from black, brindle and brown Hanwoo and purified melanocytes were cultured with ${\alpha}$-MSH, nitric oxide and L-cysteine at 100 nM, $50{\mu}M$ and 0.07 mg/ml of media respectively. The amounts of total melanin, eumelanin and mRNA expression at Tyr, Tyrp-1, Tyrp-2 and MC1R levels were quantified. ${\alpha}$-MSH and nitric oxide significantly increased (p<0.05) the amount of total melanin in black and brindle whereas eumelanin production in brown Hanwoo muzzle melanocytes. On the contrary, L-cysteine greatly (p<0.05) depressed the eumelanin production in black color but increased in brown. Simultaneously, up regulation of Tyr by nitric oxide and ${\alpha}$-MSH and down regulation of Tyr, Tyrp-2 and MC1R genes by L-cysteine were observed in muzzle melanocytes of all three phenotypes. The results of this study revealed nitric oxide and ${\alpha}$-MSH contribute hyper-pigmentation by enhancing eumelanogenesis whereas L-cysteine contributes to pheomelanin production in different colored Hanwoo muzzle melanocytes.

• Asian-Australasian Journal of Animal Sciences
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• v.33 no.3
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• pp.373-381
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• 2020

There is a need for newer feed additives due to legal prohibition on inclusion of growth promoting antibiotics in livestock diets in several countries due to antimicrobial resistance. In this context, rare earth elements (REE) have gained attention among animal nutritionists as potential growth promoters. Currently, several studies have reported better weight gain, milk production, egg laying capacity and feed conversion efficiency among different breeds of farm animals following supplementation with REE, with however largely inconsistent results. Furthermore, REE supplementation has also shown to improve ruminal fibrolytic and proteolytic activities as well as flavor of meat with negligible residues in edible tissue, however the mechanism behind this action is still unclear. According to existing research, due to their poor absorption and similarity with calcium REE might exert their action locally on gut microbial populations within the gastrointestinal tract (GIT). Moreover, REE have also shown anti-inflammatory, anti-oxidative as well as immune stimulating effects. The present review aims to broaden the knowledge about use of REE as feed additives for livestock and sum up efficacy of REE supplementation on performance and health of animals by comparing the findings. Till date, researches with REE have shown properties that make them a promising, new and safe alternative feed additive but further exploration is recommended to optimize effects and clarify discrepancy of various results before practical proposals can be drafted.