• Journal of the Korean Crystal Growth and Crystal Technology
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• 제30권4호
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• pp.131-135
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• 2020

Single crystal phased CaZrO₃ : Eu³⁺ phosphor have been synthesized by skull melting method. The crystal structure, morphology and optical properties of synthesized phosphor were investigated XRD (X-ray diffraction), SEM (scanning electron microscopy), UV (ultraviolet) fluorescence reaction and PL (photo luminescence). The starting materials having chemical composition of CaO: ZrO₂ : Eu₂O₃= 0.962 : 1.013 : 0.025 mol% were charged into a cold crucible. The cold crucible was 120 mm in inner diameter and 150 mm in inner height, and 3 kg of mixed powder (CaO, ZrO₂ and Eu₂O₃) was completely melted within 1 hour at an oscillation frequency of 3.4 MHz, maintained in the molten state for 2 hours, and finally air-cooled. The XRD results show that synthesized phosphor is stabilized in orthorhombic perovskite structure without any impurity phases. The synthesized phosphor could be excited by UV light (254 or 365 nm) and the emission spectra results indicated that bright red luminescence of CaZrO₃ : Eu³⁺ due to magnetic dipole transition ⁵D₀→⁷F₂ at 615 nm was dominant.

• The Journal of Korean Academy of Prosthodontics
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• 제55권2호
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• pp.135-143
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• 2017

Purpose: This research was conducted to compare the marginal and internal fit of zirconia prostheses fabricated with the model scan method and the intraoral scan method. Materials and methods: In this study, 20 extracted human mandibular first molar was used in the preparation of abutment tooth for the fabrication of zirconia prostheses. In the first group, the model scan method was applied on 10 prepared teeth. In the other group, the intraoral scan method was used on other 10 prepared teeth. Datum of both groups were transmitted to the software system. Afterwards, 20 zirconia prostheses were fabricated using the Ceramill system. Weight technique was used to evaluate the internal gap of the zirconia prostheses. In the Replica technique, marginal gap of the zirconia prostheses were analyzed by optical microscopy. Statistical analysis was based on one-way ANOVA. Results: Model scan group showed lower average weight than intraoral scan group when weight technique was applied, which has significance (P < .05). Also, model scan group showed significantly lower figures in all 5 measurements of replica technique than intraoral scan group (P < .05). Conclusion: Zirconia prostheses of both groups demonstrated clinically acceptable margin and internal fit. However, model scanned zirconia prostheses showed higher marginal and internal fit than intraoral scanned crowns.

• Analytical Science and Technology
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• 제9권3호
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• pp.302-309
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• 1996

Fe-5.7%AI-1.1%Cr-0.5%Si damping alloys containing 0%C and 0.12%C were heat-treated at $800^{\circ}C$ for an hour and then cooled by using some different methods. The damping behaviors of these alloys were observed by optical microscopy, X-ray diffraction and a specific damping capacity(SDC) test. Effect of cooling method on microstructures and the internal stresses of these alloys were negligible while the damping capacity of these alloys was considerably deteriorated by water quenching. The (200) texture was mainly developed by water quenching while the (110) texture by furnace cooling. These results were interpreted by the magnetization behaviors of the ferromagnetic $\alpha$ ferrite. The easy axis of magnetization in <100> direction means that <100> axis has more $180^{\circ}$ magnetic domain walls than $90^{\circ}$ ones. Thus. $180^{\circ}$ magnetic domain walls were more formed by water quenching, which deteriorated the damping capacity of these alloys. Consequently, the amount of magnetic domain walls giving good damping capacity became less so that the damping capacity was poor in water quenching.

• Journal of the Korean Wood Science and Technology
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• 제40권4호
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• pp.244-256
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• 2012

The anatomical characteristics of the ten Indonesian wood species (Gmelina, Jeunjing, Mangium, Durian, Gandaria, Jengkol, Kupa, Mangga, Nanaka and Rambutan) were investigated by optical microscopy. All the species were diffuse-porous with solitary and radial pore multiple. In Mangium, however, tangential pore multiple was observed as well. Tangential diameter of pore was larger than that of radial one except for Jeunjing and Nangka. Nangka showed the largest tangential diameter of pore among the species. Vessel number per $mm^2$ of Mangium, Gandaria and Kupa was higher than that of the other species. Especially Kupa showed highest vessel number. The tangential width of axial parenchyma cell in Gmelina, Mangium, Kupa and Mangga was larger than that of wood fiber, while the other species showed the opposite trend. Mangium was the largest in tangential width of axial parenchyma cell. Rays were homocellular composed only of procumbent cell in Gmelina, Jeunjing and Rambutan. Heterocellular rays composed of procumbent cells in the body and one row of upright and/or square in the margin are observed in Gandaria. Mangium, Durian, Jengkol, Kupa, Mangga and Nangkabody showed heterocellular rays composed of procumbent cells in the body and mostly 1~2 rows of upright and/or square cells in the margin. Crystals occurred in Durian, Gandaria, Jengkol, Jeunjing, Mangga and Rambutan and silica in Jeunjing and Mangga.

• Korean Journal of Materials Research
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• 제21권5호
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• pp.243-249
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• 2011

To reduce manufacturing costs of crystalline silicon solar cells, silicon wafers have become thinner. In relation to this, the properties of the aluminium-back surface field (Al-BSF) are considered an important factor in solar cell performance. Generally, screen-printing and a rapid thermal process (RTP) are utilized together to form the Al-BSF. This study evaluates Al-BSF formation on a (111) textured back surface compared with a (100) flat back surface with variation of ramp up rates from 18 to $89^{\circ}C$/s for the RTP annealing conditions. To make different back surface morphologies, one side texturing using a silicon nitride film and double side texturing were carried out. After aluminium screen-printing, Al-BSF formed according to the RTP annealing conditions. A metal etching process in hydrochloric acid solution was carried out to assess the quality of Al-BSF. Saturation currents were calculated by using quasi-steady-state photoconductance. The surface morphologies observed by scanning electron microscopy and a non-contacting optical profiler. Also, sheet resistances and bulk carrier concentration were measured by a 4-point probe and hall measurement system. From the results, a faster ramp up during Al-BSF formation yielded better quality than a slower ramp up process due to temperature uniformity of silicon and the aluminium surface. Also, in the Al-BSF formation process, the (111) textured back surface is significantly affected by the ramp up rates compared with the (100) flat back surface.

• Korean Journal of Materials Research
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• 제17권12호
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• pp.642-647
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• 2007

We investigated dry etching of acrylic (PMMA) in $O_2/N_2$ plasmas using a multi-layers electrode reactive ion etching (RIE) system. The multi-layers electrode RIE system had an electrode (or a chuck) consisted of 4 individual layers in a series. The diameter of the electrodes was 150 mm. The etch process parameters we studied were both applied RIE chuck power on the electrodes and % $O_2$ composition in the $N_2/O_2$ plasma mixtures. In details, the RIE chuck power was changed from 75 to 200 W.% $O_2$ in the plasmas was varied from 0 to 100% at the fixed total gas flow rates of 20 sccm. The etch results of acrylic in the multilayers electrode RIE system were characterized in terms of negatively induced dc bias on the electrode, etch rates and RMS surface roughness. Etch rate of acrylic was increased more than twice from about $0.2{\mu}m/min$ to over $0.4{\mu}m/min$ when RIE chuck power was changed from 75 to 200 W. 1 sigma uniformity of etch rate variation of acrylic on the 4 layers electrode was slightly increased from 2.3 to 3.2% when RIE chuck power was changed from 75 to 200 W at the fixed etch condition of 16 sccm $O_2/4\;sccm\;N_2$ gas flow and 100 mTorr chamber pressure. Surface morphology was also investigated using both a surface profilometry and scanning electron microscopy (SEM). The RMS roughness of etched acrylic surface was strongly affected by % $O_2$ composition in the $O_2/N_2$ plasmas. However, RIE chuck power changes hardly affected the roughness results in the range of 75-200 W. During etching experiment, Optical Emission Spectroscopy (OES) data was taken and we found both $N_2$ peak (354.27 nm) and $O_2$ peak (777.54 nm). The preliminarily overall results showed that the multi-layers electrode concept could be successfully utilized for high volume reactive ion etching of acrylic in the future.

• Herbal Formula Science
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• 제22권1호
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• pp.177-192
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• 2014

Objective : In order to investigate the effect of Curcumae Longae Rhizoma(CLR) extract on the hepatocellular carcinogenesis and acute liver damage induced by diethylnitrosamine(DENA) and $CCl_4$ in rats. Methods : Experimental groups were subdivided into four; normal group (Nor), acute liver damage and hepatocellular cancer inducing control group (Con), and CLR extract 200mg/kg/day (CAA) or 400mg/kg/day (CAB) administered groups to Con. Thereafter the changes of the body weight, the liver weight and the weight of liver/100g body weight, total cholesterol, HDL cholesterol, triglyceride, the activities of AST, ALT, ALP, LDH, AFP, SOD, catalase were measured. And we observed by optical and electron microscopy. Result : 1. The body weight was decreased in Con compared with Nor for 5 weeks, but increased in Con compared with Nor from 6 week to 9 week. During experimental period of total 9 weeks, CAA and CAB were increased compared with Con. 2. The liver weight was increased significantly (p<0.05) in Con compared with Nor. The weight of liver/100g body weight was increased significantly (p<0.05) in Con compared with Nor and decreased significantly (p<0.05) in CAB compared with Con. 3. The level of total cholesterol was increased in Con and CAA compared with Nor, but there was not statistically significant. The level of triglyceride was decreased in Con compared with Nor. But increased in CAA and CAB compared with Con. The level of HDL-cholesterol was significantly increased (p<0.05) in CAA and CAB compared with Con. 4. The activities of AST, ALT were increased in Con compared with Nor, but decreased in CAA compared with Con, significantly decreased (p<0.05) in CAB compared with Con. 5. The activities of ALP, LDH were increased in Con compared with Nor, but decreased in CAA and CAB compared with Con. 6. The activities of AFP was increased significantly (p<0.05) in Con compared with Nor, but decreased significantly (p<0.05) in CAA and CAB compared with Con. 7. The activities of SOD were increased in Con, CAA and CAB compared with Nor, but decreased in CAA and CAB compared with Con. The activities of Catalase was more increased in CAA and CAB compared than Con. 8. The results of light microscopical observation, a number of hepatocytes were damaged in Con compared with Nor and CAB. 9. According to the electron microscopical observation, irregular nuclear membrane, condensed nucleoplasm was observed in Con, the experimental group was observed in the nucleus of the well-preserved and evenly developed nucleoplasm. Conclusions : These results suggest that administration of CLR extract suppress or retard on the hepatocellular carcinogenesis and acute liver damage induced by DENA and $CCl_4$ in rats.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• 제30권1호
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• pp.1-9
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• 2020

Objectives: The purpose of this case study is to assess workers' exposure to carbon nanotubes(CNTs) and characterize particles aerosolized during the process of producing CNT-enabled polytetrafuoroethylene(PTFE) composites at a worksite in Korea. Methods: Personal breathing zone and area samples were collected for determining respirable concentrations of elemental carbon(EC) using NIOSH(National Institute for Occupational Safety and Health) Method 5040. Personal exposure to nano-sized particles was measured as the number concentration and mean diameter using personal ultrafine particle monitors. The number concentration by particle size was measured using optical particle sizers(OPS) and scanning mobility particle sizers(SMPS). Transmission electron microscopy (TEM) area samples were collected on TEM grids and analyzed to characterize the size, morphology, and chemistry of the particles. Results: Respirable EC concentrations ranged from 0.04 to 0.24 ㎍/㎥, which were below 23% of the exposure limit recommended by NIOSH and lower than background concentrations. Number concentrations by particle size measured using OPS and SMPS were not noticeably elevated during CNT-PTFE composite work. Instant increase of number concentrations of nano-sized particles was observed during manual sanding of CNT-PTFE composites. Both number concentrations and mean diameters did not show a statistically significant difference between workers handing CNT-added and not-added materials. TEM analyses revealed the emission of free-standing CNTs and CNT-PTFE aggregate particles from the powder supply task and composite particles embedded with CNTs from the computer numerical control(CNC) machining task with more than tens of micrometers in diameter. No free-standing CNT particles were observed from the CNC machining task. Conclusions: Significant worker exposure to respirable CNTs was not found, but the aerosolization of CNTs and CNT-embedded composite particles were observed during handing of CNT-PTFE powders and CNC machining of CNT-PTFE composites. Considering the limited knowledge on the toxicity of CNTs and CNT composite particles to date, it seems prudent to take a precautionary approach for the protection of workers' health.

• The Journal of Internal Korean Medicine
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• 제32권3호
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• pp.397-410
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• 2011

Objectives : This study was designed to investigate the effect of Injinsammul-tang (IJS) on hepatocellular carcinogenesis in rats. Methods : Sprague Dawley (SD) rats of control and treatment groups received intraperitoneal injection of 50 mg/kg/day diethylnitrosamine (DENA) weekly for 8 weeks. Experimental rats were classified into 3 groups; normal group (Nor), hepatic cancer induced control group (Con), and IJS extract 250 mg/kg administered group (IST) after being injected with DENA. Thereafter the changes of body weight, liver weight and weight of liver/100g body weight, the activities of aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (ALP), lactate dehydrogenase (LDH), and superoxide dismutase (SOD) were measured. Gross anatomy and optical microscopy were also observed. Results : The body weight decreased in Con and IST compared with the Nor. The weight of liver and the weight of liver/100g body weight increased significantly in Con and IST compared with the Nor. The activities of AST, ALT, ALP, LDH increased in the Con compared with Nor, but decreased in IST compared with Con. The activities of SOD increased in the Con and IST compared with Nor. Upon naked eye and light microscopic examination, IJS improved the morphological and histopathological changes of liver caused by DENA-induced hepatic neoplasm. The number of hepatic p53 positive cells decreased in the IST compared with Con. Conclusions : Most of the results did not show a significant effect, but some of the results showed a significant effect. It can be estimated that IJS has some effects on hepatocellular carcinogenesis induced by DENA in rats, and further studies will be needed.

• Analytical Science and Technology
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• 제5권1호
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• pp.143-152
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• 1992

Corrosion resistances in various acids and high temperature oxidation properties have been investigated for the Ni-base superalloy KM 1557. Corrosion tests were performed in $H_2SO_4$, HCl, $HNO_3$, $H_3PO_4$ and $CH_3COOH$. Oxidation tests were carried out in air for 20 and 110hrs at $900^{\circ}C$, $950^{\circ}C$ and $1050^{\circ}C$. Hot corrosion tests were done in salt bath of 75% $Na_2SO_4-25%$ NaCl at $900^{\circ}C$ for 20hrs. After the tests, the samples were observed by optical microscopy and analysed by EPMA and X-ray mapping in order to investigate the distribution of composition. It was shown that corrosion resistances in various acids and hot salt bath were proven to be excellent. It was suggested that the amounts of oxides were determined mainly by the depth of internal and intergranular $Al_2O_3$ oxide layers.