• Journal of Life Science
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• v.20 no.11
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• pp.1738-1741
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• 2010

Caliper measurements of tumor volume have been widely used in the assessment of tumors in animal models. However, experiments based on caliper data have resulted in unreliable estimates of tumor growth, due to necrotic areas of tumor mass. To overcome this systematic bias, we engineered a new luciferase-expressing rat prostate cancer cell line (MLL-Luc) that produces bioluminescence from viable cancer cells. MLL-Luc cells showed a strong correlation between bioluminescence intensity and cell number ($R^2$=0.99) and also accurately quantified tumor growth, with reduced bioluminescence signals caused by necrotic cells in a subcutaneous MLL-Luc xenograft model. The accurate quantification of tumor growth with bioluminescence imaging (BLI) was confirmed by a better antitumor effect of combination chemotherapy, compared to that based on caliper measurements with a correlation between the bioluminescence signal and tumor volume ($R^2$=0.84). These data suggest that bioluminescent MLL xenografts are a powerful and quantitative tool for monitoring tumor growth and are useful in evaluating the efficacy of anticancer drugs, with less systematic bias.

• Journal of the korean academy of Pediatric Dentistry
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• v.37 no.3
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• pp.345-351
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• 2010

The purpose of this study is to compare microleakage and penetration depths of sealants applied in carious and sound fissures. Extracted premolars(n=80) were divided into 4 groups according to caries status. 1; sound, 2; stained, 3; initial caries, 4; enamel caries. Sealants were applied to the occlusal groove as per manufacturers' instructions, and specimens were thermocycled, stained, sectioned, and examined for microleakage and penetration ability. The results of the present study are as follow: 1. It showed significantly higher microleakage scores in group I than group Two, Three, Four(p<0.05), but no significant difference was found between group Two, Three, and IV(p>0.05). 2. It showed significantly higher penetration scores in group Four (p<0.05), followed by group One, Two, Three, but no significant difference was found between group One, Two, and Three(p>0.05). Based on the results of present study, when the borders of the fissure sealant are on carious enamel, a significantly higher microleakage must be expected. It is considered that depth of enamel caries in the fissure should be taken into account when applying a fissure sealant.

• Korean Journal of Materials Research
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• v.9 no.10
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• pp.1006-1011
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• 1999

B-doped hydrogenated amorphous silicon carbide (a-SiC:H) thin films were prepared by plasma-enhanced chemical-vapor deposition in a gas mixture of $SiH_4$, $CH_4$ and $B_2H_6$. Microstructures and chemical properties of a-SiC:H films grown with varing the volume ratio of $CH_4$ to $SiH_4$ were characterized with various analysis methods including scanning electron microscopy(SEM), X-ray diffractometry(XRD), Raman spectroscopy, Fourier-transform infrared (FTIR) spectroscopy. X-ray photoelectron spectroscopy(XPS), UV absorption spectroscopy and photoconductivity measurements. While Si:H films grown without $CH_4$ showed amorphous state, the addition of $CH_4$ during deposition enhanced the development of a microcrystalline phase. By introducing C atoms into the film, Si-Si and Si--$\textrm{H}_{n}$ bonds of a -Si:H films were gradually replaced by Si-C, C-C, and Si--$\textrm{C}_{n}\textrm{H}_{m}$ bonds. Consequently, the electrical resistivity and optical bandgap of a-SiC:H films were increased with the C concentration in the film.

• Restorative Dentistry and Endodontics
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• v.30 no.2
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• pp.121-127
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• 2005

A variety files made of stainless steel (S-S) or nickel-titanium (Ni-Ti) are used during endodontic treatment. The purpose of tt)is study was to evaluate the corrosion susceptibility of S-S and Ni-Ti endodontic files. Three brands of files were used for this study: $K-flex^{(R)}$ S-S files (Maillefer, USA), $Profile^{(R)}$ Ni-Ti files (Maillefer, USA), $K-3^{(R)}$ Ni-Ti files (SybronEndo. USA). 120 files of each brands (21mm, ISO size $\#20$) were divided into 12 groups according to 1) sterilization methods using Autoclave or Ethylene Oxide (E-O) gas, 2) Irrigation solutions using $5.25\%$ NaOCl or Saline, 3) the number of sterilization (1, 5, 10 times), After above procedures, each of the files was inspected by three examiners with a light microscope and camera at X25. Each file was judged and ranked according to the following criteria: 0;, no corrosion, 1; mild corrosion, 2; moderate corrosion, and 3; severe corrosion. The files of high score were examined under the Scanning Electron Microscope. Data were statistically analyzed with the Kruskal-Wallis test (p < 0.05). Most of the ten time-autoclaved files had showed mild to moderate corrosion. But, one or five time-autoclaved files did not show corrosive surface. NaOCl treatment and E-O gas sterilization did not influence on corrosion. There was a significant difference in corrosion susceptibility between sterilization methods and the number of autoclaving. However, there was no significant difference between brands and file materials.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.10 no.1
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• pp.66-72
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• 2000

The behavior of nucleation and crystallization in the $Li_2O_3-SiO_2$ glass heat-treated at different condition under the conventional and microwave processing was studied by differential thermal analysis (DTA), X-ray diffractometry (XRD), optical microscopy (OM), and electrical conductivity measurement. Nucleation temperature and temperature of maximum nucleation rate in both conventionally and microwave heat-treated samples were 460~$500^{\circ}C$ and $580^{\circ}C$, respectively. It was expected that the probability for bulk crystallization increased in microwave heat-treated sample, compared to conventionally heat-treated one. Degree of crystallization increased with increasing crystallization temperature in both conventionally and microwave heat-treated samples. However, pattern of crystallization growth under microwave processing appeared to be quite different from that under the conventional one due to its internal or volumetric heating. Electrical conductivity of conventionally and microwave heat-treated samples were 1.337~2.299, 0.281~~$0.911{\times}10^{-7}\Omega {\textrm}{cm}^{-1}$, respectively.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.15 no.3
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• pp.93-98
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• 2005

The crystal growth of calcite at a low temperature range was carried out by the hydrothermal method using amorphous calcium carbonate which has excellent solubility in water. Amorphous calcium carbonate was prepared by the wet chemical reaction of a stoichiometric mixture of $CaCl_2\;and\;Na_2CO_3$. An important factor was the reaction temperature and time taken in preparation of the amorphous calcium carbonate. From the solubility results calculated by the weight loss method, $NH_4NO_3$ solutions were found to be the most promising solvents to grow calcite single crystals. The hydrothermal conditions for high growth rates of calcite single crystals were as follows: starting material: amorphous calcium carbonate, solvent: 0.01 m $NH_4NO_3$, temperature: $180^{\circ}C$, duration: 30 days. And properties of calcite single crystals were follows: dislocation density: $10^6{\sim}10cm^{-2}$, UV-visible transmittance: about 80% from 190 to 400 nm and birefringence: $0.17{\sim}0.18$. Also, it can be known from the FT-IR results that the absorption peak by injection of $HCO_3^-\;and\;OH^-$ ions was not shown.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.20-20
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• 2008

최근 LEDs가 동일 효율의 전구에 비해 에너지 절감 효과 크며 신뢰성이 뛰어나다기 때문에 기존 광원을 빠르게 대체해 나가고 있다. 특히 자외선 파장을 가지는 LEDs는 발열이 낮아 냉각장치가 필요 없으며, 수명이 길어 기존 UV lamp에 비해 많은 장점을 가지고 있기 때문에 많은 관심을 밭고 있다. 그럼에도 불구하고 자외선 LEDs는 제조 단가가 높고 power가 낮아 소요량이 많은 등 아직 해결해야 할 부분이 많기 때문에 이를 해결하기 위해 여러가지 재료와 다양한 구조가 고려되고 있다. 그 중 ZnO는 II-VI족 화합물 반도체로써 UV영역의 넓은 밴드갭(3.37eV)을 가지는 투명한 재료이다. 특히 ZnO는 60meV의 큰 엑시톤 결합에너지를 가지며, 가시광 영역에서 높은 투과율을 가지고, 상온에서 물리적, 화학적으로 안정하기 때문에 UV sensor, UV laser, UV converter, UV LEDs 등 광소자 분야에서 연구가 활발히 진행되고 있다. ZnO가 광소자의 발광재료로써 높은 효율을 얻기 위해서는 결정성을 높여 내부 결함을 감소시키며, 발광 면적을 높일 수 있는 구조가 요구된다. 특히 MOCVD 법으로 성장한 나노막대는 에피성장되어 높은 결정성을 기대할 수 있으며, 성장 조건을 조절함으로써 나노막대의 aspect ratio와 밀도 제어할 수 있기 때문에 표면적을 효과적으로 넓혀 높은 발광효율을 얻을 수 있다. 본 실험에서는 MOCVD 법으로 실리콘과 사파이어 기판 위에 다양한 성장 온도를 가진 나노구조를 성장 시키고 온도에 따른 형상 변화와 특성을 평가하였다. ZnO 의 성장온도가 약 $360^{\circ}C$ 일 때, 밀도가 조밀하고 기판에 수직 배열한 균일한 나노막대가 성장되었으며 우수한 결정성, 광학적 특성이 나타남을 SEM, TEM, PL, XRD를 사용하여 확인하였다.

• Korean Chemical Engineering Research
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• v.51 no.5
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• pp.622-627
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• 2013

Colloidal silica is used in various industrial products such as chemical mechanical polishing slurry for planarization of silicon and sapphire wafer, organic-inorganic hybrid coatings, binder of investment casting, etc. An accurate determination of particle size and dispersion stability of silica sol is demanded because it has a strong influence on surface of wafer, film of coatings or bulks having mechanical, chemical and optical properties. The study herein is discussed on the effect of measurement results of average particle size, sol viscosity and electrophoretic mobility of particle according to the volume fraction of eight types of silica sol with different size and surface properties of silica particles which are presented by the manufacturer. The measured particle size and the mobility of these sol were changed by volume fraction or particle size due to highly active surface of silica particle and change of concentration of counter ion by dilution of silica sol. While in case the measured sizes of small particles less than 60 nm are increased with increasing volume fraction, the measured sizes of larger particles than 60 nm are slightly decreased. The mobility of small particle such as 12 nm are decreased with increase of viscosity. However, the mobility of 100 nm particles under 0.048 volume fraction are increased with increasing volume fraction and then decreased over higher volume fraction.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.22 no.6
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• pp.274-278
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• 2012

$TiO_2$ can be used optically and is applied on many areas such as gas sensor, solar cell and photocatalysis. Electrospun nanofibers have received great interest for development and utilization in some novel applications, such as chemical sensors, dye-sensitized solar cell and photo catalysis. In this study, pure $TiO_2$ and Ga-doped $TiO_2$ nanofibers synthesized by a modified electrospinning method. The Ga doped $TiO_2$ solution is prepared by mixing poly vinyl pyrrolidone, ethyl alcohol, and titanium (IV) isopropoxide. By electrospinning these sols, nanofibers were fabricated. These fibers are heat-treated at $800^{\circ}C$ in air. The prepared pure $TiO_2$ and Ga-doped $TiO_2$ nanofibers samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy.

• Polymer(Korea)
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• v.36 no.2
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• pp.245-250
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• 2012

Branched polypropylenes (PP) with long chain branch were prepared by solid state reaction with three different branching agent of 0.3 wt% content. The chemical structures, non-isothermal crystallization behavior and complex viscosity of the branched PP were investigated by FTIR, DSC, optical microscope, and dynamic rheological measurement. The chemical structure of the branched PP was confirmed by the existence of =C-H stretching peak of the branching agent at 3100 $cm^{-1}$. There was no distinct change in melting temperature in case of PP-D-0-3 and PP-F-0-3, but PP-H-0-3 indicated a decrease in melting temperature. The decrease in melting temperature was interpreted by the fact that the degradation reaction of PP was more dominant than branched reaction, and confirmed by a decrease in complex viscosity. The non-isothermal crystallization behavior of the branched PP was analyzed using by Avrami equation. The Avrami exponent of PP was 3, and the values of the branched PP with DVB and FS were below 3. The activation energy of PP calculated by Kissinger method was 25 kJ/mol, and there were no big difference in activation energies of the branched PPs compared to PP.