• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.250-250
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• 2013

단일벽 탄소나노튜브(Single-walled nanotubes, SWNTs)는 나노스케일의 크기와 우수한 물성으로 인하여, 전자, 에너지, 바이오 분야로의 응용이 기대되고 있다. 특히 SWNTs의 직경을 제어하게 되면 튜브의 전도성 제어가 훨씬 수월하게 되어, 차세대 나노전자소자의 실현을 앞당길 수 있으며 이러한 이유로 많은 연구들이 현재 행해지고 있다. SWNTs의 직경제어 합성을 위해서는 현재 열화학기상증착법(Thermal chemical vapor deposition; TCVD)이 가장 일반적으로 이용되고 있으며, 합성 촉매와 합성되는 튜브의 직경과의 크기 연관성이 알려진 후로는, 촉매의 크기를 제어하여 SWNTs의 직경을 제어하고자 하는 연구들이 활발하게 보고되고 있다. 특히, 촉매 나노입자의 직경이 1~2 nm 이하로 감소될 경우, SWNTs의 직경 분포가 어떻게 변화할 것인지가 최근 가장 중요한 관심사로 남아 있으나, 이러한 크기의 금속입자는 나노입자의 융점저하 현상이 발현되는 영역이므로, SWNTs의 합성온도 영역에서 촉매 금속입자는 반액체(Semi-liquid) 상태로 존재할 것으로 추측하고 있다. 본 연구에서는 고온의 SWNTs 합성환경에서 금속나노촉매의 유동성을 제한하기 위하여 나노사이즈의 기공이 규칙적으로 정렬된 다공성 물질인 제올라이트를 촉매담지체로 이용하였고, 이 때 다양한 합성변수가 SWNTs의 직경에 미치는 영향을 살펴보고자 하였다. SWNTs의 합성을 위해 실리콘 산화막 기판 위에 제올라이트를 도포한 후, 합성 촉매로서 전자빔증발법을 통하여 수 ${\AA}$에서 수 nm 두께의 철 박막을 증착하였다. 합성은 메탄을 원료가스로 하여 TCVD법으로 실시하였다. 주요변수로는 제올라이트 종류, 증착하는 철 박막의 두께, 합성온도를 설정하였으며, 이에 따라 합성된 SWNTs의 합성수율 및 직경분포의 변화를 체계적으로 살펴보았다. SWNTs의 전체적인 합성수율의 변화는 SEM 관찰결과를 이용하였으며, SWNTs의 직경은 AFM 관찰 및 Raman 스펙트럼의 분석에서 도출하였다. 실험결과, 제올라이트 종류에 따라서는 명확한 튜브직경 분포의 변화 없이 비교적 좁은 직경분포를 갖는 SWNTs가 합성되었으며, 합성온도가 $850^{\circ}C$ 이하로 감소되면 합성수율이 현저히 감소되는 것을 알 수 있었다. 촉매박막의 두께가 1 nm 이상인 경우에서는 직경 5 nm 전후의 나노입자가 형성되었으며, 이때 SWNTs의 합성수율은 높았으나 다양한 직경의 튜브가 합성이 된 것을 확인할 수 있었다. 반면, 촉매입자의 크기가 2 nm 이하에서는 합성수율은 다소 저하되었으나, SWNTs의 직경분포의 폭이 상대적으로 훨씬 좁아지는 것을 알 수 있었다. 추후, 극미세 촉매와 저온합성 환경에서의 합성수율 향상을 위한 합성공정의 개량이 지속적으로 요구된다.

• Journal of Mushroom
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• v.19 no.3
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• pp.140-149
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• 2021

Mushroom-derived polysaccharides, which are the primary bioactive constituents, are beneficial for human health. Polysaccharides have immuno-modulation, antitumor, and antioxidant properties. Additionally, they have antiviral properties and protect against chronic radiation stress. In this study, high yield water-soluble polysaccharides were obtained from Pleurotus djamor var. roseus basidiocarps. The crude polysaccharide (CP) was extracted sequentially by hot water and ethanol precipitation. The yield of the brown CPs was 5.6% dw. Diethylaminoethyl cellulose and Sepharose-6B column chromatography of CPs generated several fractions. Total glucan content was determined in all the fractions. The F1 fraction displayed the highest sugar content and was considered as a purified polysaccharide (PP). The total glucan and β-glucan content in the four fractions ranged between 76.85-2.95% and 75.08-1.46%, respectively. The yield of the PPs was 300 mg, and it was obtained as a white powder. The PPs were characterized by Fourier-transform infrared spectroscopy (FTIR) and thin-layer chromatography. The FTIR spectral details confirmed the presence of a xylopentose polysaccharide. The antioxidant activity of the PPs was evaluated using in vitro 1,1-diphenyl-2-picryl-hydrazyl (DPPH) free radical scavenging assay and superoxide radical scavenging assay. The PPs showed strong DPPH free radical and superoxide anion radical scavenging activities in a dose-dependent manner. Purified PPs free of phenolics, protein, and carbohydrates were mainly responsible for the radical scavenging activity. The data suggest the potential of PPs as natural antioxidants.

• Progress in Medical Physics
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• v.32 no.3
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• pp.70-81
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• 2021

Purpose: This study was designed to investigate the dosimetric difference between intensity-modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) in head and neck cancer (HNC). The study primarily focuses on low-dose spillage evaluation between these two techniques. Methods: This retrospective study involved 45 patients with HNC. The treatment plans were generated using the IMRT and VMAT techniques for all patients. Dosimetric comparisons were performed in terms of target coverage, organ-at-risk (OAR) sparing, and various parameters, including conformity index, uniformity index, homogeneity index, conformation number, low-dose volumes, and normal tissue integral dose (NTID). Results: No significant (P>0.05) difference in planning target volume coverage (D_95%) was observed between IMRT and VMAT plans for supraglottic larynx, hard palate, and tongue cancers. A decrease in dose volumes ranging from 1 Gy to 30 Gy was observed for VMAT plans compared with those for IMRT plans, except for V_1Gy and V_30Gy for supraglottic larynx cancer and V_1Gy for tongue cancer. Moreover, decreases (P<0.05) in NTID were observed for VMAT plans compared with that for IMRT plans in supraglottic larynx (4.50%), hard palate (12.80%), and tongue (7.76%) cancers. In contrast, a slight increase in monitor units for VMAT compared with those for IMRT in supraglottic larynx (0.46%), hard palate (2.54%), and tongue (7.56%) cancers. Conclusions: For advanced-stage HNC, both IMRT and VMAT offer satisfactory clinical plans. VMAT offers a conformal and homogeneous dose distribution with comparable OAR sparing and higher dose falloff outside the target volume than IMRT, which provides an edge to reduce the risk of secondary malignancies for HNC over IMRT.

• Korean Journal of Optics and Photonics
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• v.32 no.4
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• pp.147-152
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• 2021

We report high-power continuous-wave operation of a Yb-doped fiber laser at 1070 nm, pumped by high-power laser diodes at 976 nm. Based on theoretical calculation of the stimulated Raman scattering and temperature distribution in the fiber, we construct a bidirectionally pumped Yb-fiberlaser system incorporating a pair of fiber Bragg gratings and a cladding light stripper. The fiber laser yields 3.0 kW of continuous-wave output at 1070 nm in a diffraction-limited beam with M² ≈ 1.26 for 4.1 kW of incident pump power, corresponding to a slope efficiency of 81.5%. The prospects for further power scaling are discussed.

• Journal of Mushroom
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• v.16 no.4
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• pp.299-303
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• 2018

Flammulina velutipes, which is a white rot fungus, is a commercially important edible mushroom and is produced in large quantities with the help of an automated and mechanized cultivation system in Korea. F. velutipes has the lowest distribution rate among domestic cultivars, estimated at about 20 percent. As most white cultivars of F. velutipes produced and exported to Korea were introduced from Japan, farmers pay large amounts of royalties. Therefore, we have developed a new, purely domestic cultivar, "Baeke," to substitute for Japanese cultivars, which has improved storage characteristics for export. Baeke was bred by mating two monokaryotic strains isolated from ASI 4216-18 (Hansol) and ASI 4217-26 (Baekjung). Baeke showed faster mycelial growth and higher mycelial density upon incubation for seven days at $25^{\circ}C$ on PDA media than the control variety. The mycelial growth of Baeke was even maintained at $30^{\circ}C$ unlike the control. The lengths of pilei and stipes in Baeke harvested in the optimal stage were $11.2{\pm}0.5mm$ and $125{\pm}5.4mm$, respectively, and they were $11{\pm}0.5mm$ and $141.9{\pm}5.7mm$, respectively, in the control harvested in the optimal stage. The yields of Baeke ($257.4{\pm}13.5g$) and control ($270.7{\pm}17.8g$) per 1,100ml in bottle cultivation showed no significant difference. Overall, our results showed that Baeke was at par with foreign varieties of Flammulina velutipes in terms of quality and yield and had a uniformly shaped fruitbody, which added to its commercial value.

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.2
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• pp.130-134
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• 2019

In this paper, a laser-based non-contact load cell is newly developed for measuring forces in prestressed concrete tendons. First, alumina particles have been sprayed onto an empty load cell which has no strain gauges on it, and the layer has been used as a passive stress sensor. Then, the spectral shifts in fluorescence spectroscopy have been measured using a laser-based spectroscopic system under various force levels, and it has been found that the relation of applied force and spectral shift is linear in a lab-scale test. To validate the field applicability of the customized load cell, a full-scale prestressed concrete specimen has been constructed in a yard. During the field test, it was, however, found that the coating surface has irregular stress distribution. Therefore, the location of a probe has to be fixed onto the customized load cell for using the coating layer as a passive stress sensor. So, a prototype customized load cell has been manufactured, which consists of a probe mount on its casing. Then, by performing lab-scale uniaxial compression tests with the prototype load cell, a linear relation between compression stress and spectrum shift at a specific point where laser light had been illuminated has been detected. Thus, it has a high possibility to use the prototype load cell as a force sensor of prestressed concrete tendons.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.29 no.3
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• pp.83-90
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• 2019

In this paper, Mg-doped AlN epilayers for power semiconductor devices are grown by mixed-source hydride vapor phase epitaxy. Magnesium is used as p-type dopant material in the grown AlN epilayer. The AlN epilayers on the GaN-templated sapphire substrate and GaN-templated-patterned sapphire substrate (PSS), respectively, as the base substrates for device application, were selectively grown. The surface and the crystal structures of the AlN epilayers were investigated by field emission scanning electron microscopy (FE-SEM) and high-resolution-X-ray diffraction (HR-XRD). From the X-ray photoelectron spectroscopy (XPS) and Raman spectra results, the p-type AlN epilayers grown by using the mixed-source HVPE method could be applied to power devices.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.31 no.3
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• pp.103-111
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• 2021

Hexagonal shape Si crystals were grown by the mixed-source hydride vapor phase epitaxy (HVPE) method of mixing solid materials such as Si, Al and Ga. In the newly designed atmospheric pressure mixed-source HVPE method, nuclei are formed by the interaction between GaCl_n, AlCl_n and SiCl_n gases at a high temperature of 1200℃. In addition, it is designed to generate a precursor gas with a high partial pressure due to the rapid reaction of Si and HCl gas. The properties of hexagonal Si crystals were investigated through scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDS), high-resolution X-ray diffraction (HR-XRD), and Raman spectrum. From these results, it is expected to be applied as a new material in the Si industry.

• Nuclear Engineering and Technology
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• v.54 no.1
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• pp.318-325
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• 2022

In this study, composites containing undoped and barium-doped Bi₂WO₆:Ba²⁺were investigated for their shielding against diagnostic X-ray. At first, Bi₂WO₆ and barium-doped Bi₂WO₆ were synthesized with different weight percentages of barium oxide through a hydrothermal process. The as-synthesized nanostructures were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and Raman spectroscopy (RS). After that, some shields were generated with undoped and barium-doped Bi₂WO₆:Ba²⁺ nanostructure particles incorporated into polyvinyl chloride (PVC) polymer with different thicknesses and 15% weight of the nanostructure. Finally, the prepared samples were exposed to an X-ray tube at 40, 80, and 120 kV voltages, 10 mAs and, 44.5 cm SID (i.e. the distance from the X-ray beam source to the specimen). Linear and mass attenuation coefficients were also calculated for different samples. The results indicated that, among the samples, the one with 7.5 mmol barium-doped Bi₂WO₆ had the most attenuation at the voltage of 40kV, and the attenuation coefficients would increase with an increase in the amount of barium. The samples with 15 and 17.5 mmol barium-doped Bi₂WO₆ had higher attenuation than the others at 80 and 120 kV. Moreover, the half-value layer (HVL), tenth-value layer (TVL) and 0.25 mm lead equivalent thickness were calculated for all the samples. The lowest HVL value was for the sample with 7.5 mmol barium-doped Bi₂WO₆. As the result clearly show, an increment in the barium-doping content leads to a decrease in both HVL and TVL. In every three voltages, 0.25 mm lead equivalent thickness of the barium-doped composites (7.5 mmol and 15 mmol) had less than the other composites. The lowest value of 0.25 mm lead equivalent thickness was 7.5 barium-doped in 40 kV voltage and 15 mmol barium-doped in 80 kV and 120 kV voltages. These results were obtained only for 15% weight of the nanostructure.

• Journal of Conservation Science
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• v.37 no.2
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• pp.77-89
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• 2021

In this study, materials and color formation techniques were assessed for black potteries excavated from the Janghyeon-dong, Jungsan-dong and Gyodong-ri sites during the Proto-Three Kingdoms period in Ulsan, Korea. Although the black potteries were black superficially, the inner cores were either black or reddish yellow. Microscopy analysis identified that body clay was used for reddish iron oxide rich soils with quartz, alkali feldspar and mica, along with grains of myrmechite texture. Additionally, as marginal differences exist in the contents of SiO₂, Fe₂O₃ and CaO, the composition of the host rock and clay distributed around the sites was affected. Thus, we can deduce that pottery was made by soiling at a short distance. Raman spectroscopy results revealed that the black layer of the black pottery was used as amorphous combustion carbon. In addition, as a transparent layer of brown lacquer was observed on the substrate that was in contact with the surface layer, the black layer of the pottery induced black color development by a combination of combustion carbon and lacquer. Based on the mineral composition and microtexture of the body clay, the firing temperature of the potteries seemed to range from 750 to 850℃, whereas the lacquer layer was pyrolyzed at 468℃ by thermal analysis. Therefore, a combined layer of combustion carbon and lacquer, which formed the black color, was painted after the body clay was fired.