• Journal of the Korean Vacuum Society
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• v.17 no.1
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• pp.51-57
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• 2008

we have demonstrated structural evolution and optical properties of Si-nanowires (NWs) synthesized on Si (111) substrates with nanoscale Au-Si islands by rapid thermal chemical vapor deposition (RTCVD). The Au-Si nano-islands (10-50nm in diameter) were employed as a liquid-droplet catalysis to grow Si-NWs via vapor-liquid-solid mechanism. The Si-NWs were grown by a mixture gas of SiH4 and H2 at a pressure of 1.0 Torr and temperatures of $500{\sim}600^{\circ}C$. Scanning electron microscopy measurements showed that the Si-NWs are uniformly sized and vertically well-aligned along <111> direction on Si (111) surfaces. The resulting NWs are ${\sim}60nm$ in average diameter and ${\sim}5um$ in average length. High resolution transmission microscopy measurements indicated that the NWs are single crystals covered with amorphous SiOx layers of ${\sim}3nm$ thickness. In addition, the optical properties of the NWs were investigated by micro-Raman spectroscopy. The downshift and asymmetric broadening of the Si main optical phonon peak were observed in Raman spectra of Si-NWs, which indicates a minute stress effects on Raman spectra due to a slight lattice distortion led by lattice expansion of Si-NW structures.

• Proceedings of the KAIS Fall Conference
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• 2003.06a
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• pp.181-184
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• 2003

ZnwO₄는 높은 품질계수에 의해 주파수 선택성이 뛰어나지만 다층형태의 고주파 무선부품으로의 응용을 위해서는 높은 소결온도(1100℃), 큰 음의 공진주파수 온도계수(-70ppm/℃), 낮은 유전율(15.5) 둥에 대한 보정이 필요하다. 본 연구에서는 ZnwO₄에 TiO₂ 및 LiF를 첨가하여 ZnwO₄의 저손실특성을 유지하면서 주파수 온도안정성 및 저온소결성을 부여하고자 하였다. 큰 양의 공진주파수 온도계수(＋400ppm/℃) 및 유전율(100)을 갖는 TiO₂의 첨가는 공진주파수 온도계수를 음의 값에서 양의 값으로 변화시켰으며 유전율의 증가를 가져왔다. TiO₂를 20 mol％ 첨가한 경우 공진주파수 온도 계수가 0에 가깜고 유전율 19.4에 품질계수 50000㎓의 특성을 얻을 수 있었으나 소결온도는 1100℃로 높은 소결온도를 보였다. ZnwO₄에 TiO₂가 첨가된 혼합체에 LiF의 첨가는 액상형성에 의해 소결온도를 1100℃에서 850℃로 크게 저하시킬 수 있었다. LiF는 첨가는 LiF 자체의 큰 공진주파수 온도계수에 의해 온도계수를 음의 값으로 변화시켰다. 따라서 TiO₂ 및 LiF의 적당량의 첨가는 온도 안정성을 갖는 저손실 ZnwO₄-TiO₂-LiF계 LTCC 소재를 제조할 수 있었다.

• Journal of the Korean Geotechnical Society
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• v.19 no.4
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• pp.155-165
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• 2003

A series of one-dimensional cylinder sedimentation test, seepage consolidation test and two-dimensional deposition model test were conducted to examine the characteristics of deposition and volume change of dredged soils containing the high water content, and these experimental results were compared with the sedimentary conditions of actual dredged-reclaimed fields to obtain the relations of a volume change by settling what is required for design. In addition, the change of water content and the distribution of fine grained soils after sedimentation were investigated. Thus, it was concluded that deposition height increased lineary as substantial soil volume increased, and also the elevation of interface increasea proportionately at both the starting time and the finishing time of virtual self-weight consolidation in one-dimensional sedimentation. Furthermore, the two-dimensional model test results were shown to describe the plain distribution of water content and fine grained silt where dredged soil was deposited by two dimensional flowing, and the water content was distributed to wide range from the minimum water content 30% to maximum 180% according to the passed amount of №200 sieve percentage.

• Clinical and Experimental Reproductive Medicine
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• v.35 no.3
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• pp.223-229
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• 2008

Objective: This pilot study was performed to investigate the effect of metformin on insulin resistance, hormone levels, and lipid profiles in non-obese patients with polycystic ovary syndrome. Methods: This study included 16 non-obese patients with polycystic ovary syndrome diagnosed at our hospital from June 2006 to September 2007. Blood samples were collected before and 6 months after metformin treatment for analysis of fasting serum glucose levels, fasting serum insulin levels, a glycemic response to 75 g oral glucose tolerance test (OGTT), and hormonal blood profile including FSH, LH, estradiol, testosterone, free testosterone, serum lipid profiles. Insulin resistance was estimated by calculating fasting glucose/insulin ratio (FGIR), 2 hr glucose/insulin ratio after 75 g glucose load. And we investigated insulin resistance and pancreatic beta cell function by calculating HOMA beta cell function and HOMA IR. Results: After the treatment of metformin, there was significant increase in 2 hr glucose/insulin ratio after 75 g glucose load (p=0.04) and decrease in HOMA IR (p=0.000). But serum lipid profiles did not change significantly. Also the metformin treatment induced a significant reduction in serum free testosterone and LH levels, and LH/FSH ratio (p=0.001, p=0.000, p=0.034). Conclusion: This pilot study showed that metformin might be effective in improving insulin sensitivity, ameliorating hyperandrogenemia in non-obese patients with polycystic ovary syndrome. Further investigations with larger number of patients and long-term observations are necessary to determine the role of metformin.

• The Journal of the Korea Contents Association
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• v.22 no.9
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• pp.583-591
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• 2022

The purpose of this study was to determine the incidence of dental erosion according to the type of lactic acid bacteria fermented oil and to identify a method for preventing dental erosion. For the lactic acid bacteria fermented milk, liquid fermented milk, condense-stirred type fermented milk, and condense-drink type fermented milk were used, and bovine tooth specimens used in the experiment were used. As a method to prevent dental erosion, the method of adding calcium to the lactic acid bacteria fermented milk, the method of applying high and low concentrations of fluoride to the teeth before exposure to the lactic acid bacteria fermented milk, and the method of applying these two methods together were measured to measure the preventive effect of dental erosion. As a result of immersing the specimen in the experimental beverage, the surface hardness of liquid fermented milk decreased the most. When comparing the difference in surface hardness before and after prophylaxis care, the Ca 2% group and the NaF 0.05%+Ca 0.5% group showed no significant difference from the negative control group, confirming that it is an effective method for preventing dental erosion. However, considering the change in taste and the stability of ingredients, a method of adding calcium at a low concentration rather than adding a high concentration of calcium is proposed. Therefore, it is recommended to use low-concentration calcium and low-concentration fluoride together to recognize the possibility of dental erosion when ingesting lactic acid bacteria and to prevent dental erosion caused by it.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.8 no.1
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• pp.187-192
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• 1998

Generally the solidified microstructures of materials consist of the columnar and equiaxed dendritic regions, and many theoretical studies about columnar-to-equiaxed transition have been done because that is closely related to the mechanical and physical properties of products. In this study, the modified equation based on the Hunt's analytical columnar-to-equiaxed transition condition which was derived from heterogeneous nucleation and grain growth in front of the columnar dendrite tip under directional solidification, was obtained applying the growth-velocity-dependent distribution coefficient and liquidus slope to Hunt's. The effects of the number of nucleation sites, nucleation temperature, alloy composition, growth velocity and liquid temperature gradient on the transition for Al-Cu alloys have been investigated.

• KSBB Journal
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• v.11 no.6
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• pp.649-653
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• 1996

Imnmobilization characteristics of Thiobacillus sp. IW which oxidizes sulfur compound was studied to use the bacterium in odor controlling equipment for the future. The optimum growth conditions for Thiobacillus sp. IW were pH7, $30^{\circ}C$ and the generation time was 38min, which was extremely fast compared with other sulfur oxidizing bacteria. Optimum growth conditions in activated carbon as a carrier was pH5, $35^{\circ}C$ and those in bioceramics was pH 7∼8, $35^{\circ}C$. Cell growth immobilized in bioceramics was more stable in pH, temperature change than that immobilized in activated carbon and total number of cells in bioceramics were also higher. Based on these results, the bioceramics is thought to be better carrier in immobilization of Thiobacillus sp. IW.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.07a
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• pp.519-522
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• 2004

첨가제로 $Bi2O_3$를 첨가하고, 소결 온도를 변화시켜 고주파 내역에서 전자기적 특성이 안정적으로 유지될 수 있는 Ni-Zn 페라이트를 제조하고자 하였다. $Bi2O_3$의 첨가는 액상을 형성하여 소결을 촉진시키며, 0.3 wt% 첨가된 시편에서는 비정상 입자를 성장시켜 높은 전력 손실 특성을 나타내었다. 그러나 $Bi2O_3$의 적정한 첨가는 소결을 촉진시켜 밀도를 증가시키며, 균일한 입자를 형성하여 전력 손실이 감소하였다. Ni-Zn 페라이트에 $Bi2O_3$의 첨가는 공명 주파수 범위의 제어가 가능하며, 소결 촉진 및 밀도의 증가를 가져와 안정적인 재료를 제조할 수 있었다. 투자율의 일정성이 특정 주파수 10MHz 부근에서 급증하면서 급감하는 것은 공명이 생기고, 이러한 현장은 자벽 공명 또는 자벽의 이동에 의해 나타나는 것으로 보여진다.

• Polymer(Korea)
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• v.30 no.6
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• pp.471-477
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• 2006

Ion exchange metal composite(IPMC) has toughness equivalent to the range of human's muscle, transformation-actuation force by relatively low voltage and the fast response time. Thus, as a new method for preparing thicker IPMC, the solution casting method to make the films of various thicknesses out of liquid nation was attempted in this study. To reduce the surface resistance of electrode, the first plated electrode prepared by Oguro method was replated with Au and Ir using ion beam assisted deposition(IBAD). The microstructures of electrode surfaces before and after IBAD plating were investigated using SEM. The change of water and ion-conductivity in IPMC were measured under applied voltage. The displacement and driving force of IPMCs with various thicknesses were measured to evaluate the driving properties.

• Korean Journal of Materials Research
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• v.11 no.7
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• pp.585-589
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• 2001

Many experimental results have revealed that the development of cavitaition during tensile deformation is limited by the Presence of liquid phases. However, the presence of liquid phases does not always lead to high-strain-rate superplasticity, because too much liquid causes intergranular decohesion at grain boundaries/interfaces in metal-matrix composites. Thus, it is important to examine the nature of interfaces of superplastic composites in order to understand the origin of superplastic flow related to liquid grain boundaries during high-strain-rate superplastic deformation. This study shows that a large elongation is obtained at the temperature, that is close to the onset temperature for partial melting in the superplastic composites, but the elongation significantly decreases at slightly higher temperatures, which are close to the end temperature fur partial melting. This indicates that there is an optimum amount of the liquid phase for obtaining high-strain-rate superplasticity in these materials.