• Proceedings of the Korea Information Processing Society Conference
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• 2006.05a
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• pp.669-672
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• 2006

고온가스냉각 원자로에서는 고온 안정성 및 핵분열생성물 차단 성능이 우수한 TRISO(tri-tsotropic) 핵연료를 사용하고 있다. TRISO 핵연료 입자는 직경이 약 1 mm인 구 형태로 입자의 중심에는 직경 $0.5{\mu}m$의 핵연료 커널(kernel)이 포함되며 커널 외곽을 코팅 층이 에워싸고 있다. 이 코팅 층은 완충(buffer) PyC(pyrolytic carbon) 층, 내부 PyC 층, SiC 층, 그리고 외부 PyC 층으로 구성되어 있다. 각 코팅 층의 두께는 수십${\sim}$백 ${\mu}m$ 범위이며, 본 연구에서는 각 코팅 층의 두께를 비파괴적으로 측정하기 위하여 마이크로포커스 X-선 발생장치와 고해상도 X-선 평판(flat panel) 검출기로 구성된 정밀한 X-선 래디오그래피 장치를 구성하고, $UO_2$ 핵물질 대신에 $ZrO_2$를 커널로 사용한 모의 TRISO 핵연료 입자에 대한 래디오그래피 영상을 획득한 후 디지털 영상처리기술을 이용하여 코팅 층 사이의 경계선이 구분 가능하도록 영상을 개선하고 디지털 영상처리 알고리즘을 개발하여 코팅 층의 두께를 측정하였다.

• Journal of the Korean Ceramic Society
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• v.46 no.5
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• pp.484-487
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• 2009

$SiC_f$/SiC composites with whiskers and pyrolytic carbon (PyC) coated whiskers in the matrix were fabricated for enhancement of the fracture behaviors by the whisker growing assisted chemical vapor infiltration (WA-CVI) process, respectively. $SiC_f$/SiC composites were also prepared by the conventional CVI process as reference material. The mechanical properties and fracture behaviors were analyzed by comparison of the two types of composites prepared by WA-CVI and conventional CVI. The densities of $SiC_f$/SiC composites were in the range of $2.6{\sim}2.65g/cm^3$. The flexural strengths of composite with whiskers and with those coated by PyC were 650 MPa and 600 MPa, respectively. The tensile strength of composites with whiskers was ${\sim}285$ MPa.

• Journal of Environmental Science International
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• v.12 no.11
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• pp.1145-1157
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• 2003

The surface sediments inside Hallim Harbor, one of the major harbors of Jeju Island, were sampled three times (June, September and December, 2001) and analyzed for 16 polycyclic aromatic hydrocarbons (PAHs), recommended by US-EPA as priority pollutants, to assess their distribution levels and to suggest their possible origins. The concentrations of PAHs ranged from 19 to 496 ng/g on a dry weight basis with a mean value of 245 ng/g, and the levels were low to moderate in comparison with other areas in the world. Based on comparisons of individual and total PAH concentrations with effects-based and equilibrium partitioning-based on sediment quality guidelines, the potential for the biological effects were expected to be low. The sedimentary PAHs may be correlated with organic carbon and mud contents to some extent. From the examinations of the four PAH origin indices, such as LMW/HMW (low molecular weight 2-3 ring PAHs over high molecular weight 4-6 ring PAHs), phenanthrene/anthracene ratio, fluoranthene/pyrene ratio, chrysene/benzo〔a〕anthracene ratio, it can be concluded that the sediment PAH contaminations were ascribed to both pyrolytic and petrogenic origins.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.10a
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• pp.16.2-16.2
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• 2011

Graphene has attracted significant attention due to its unique characteristics and promising nanoelectronic device applications. For practical device applications, it is essential to synthesize high-quality and large-area graphene films. Graphene has been synthesized by eloborated mechanical exfoliation of highly oriented pyrolytic graphite, chemical reduction of exfoliated grahene oxide, thermal decomposition of silicon carbide, and chemical vapor deposition (CVD) on metal substrates such as Ni, Cu, Ru etc. The CVD has advantages over some of other methods in terms of mass production on large-areas substrates and it can be easily separated from the metal substrate and transferred to other desired substrates. Especially, plasma-enhanced CVD (PECVD) can be very efficient to synthesize high-quality graphene. Little information is available on the synthesis of graphene by PECVD even though PECVD has been demonstrated to be successful in synthesizing various carbon nanostructures such as carbon nanotubes and nanosheets. In this study, we synthesized graphene on $Ni/SiO_2/Si$ and Cu plate substrates with CH4 diluted in $Ar/H_2$ (10%) by using an inductively-coupled PECVD (ICPCVD). High-quality graphene was synthesized at as low as $700^{\circ}C$ with 600 W of plasma power while graphene layer was not formed without plasma. The growth rate of graphene was so fast that graphene films fully covered on substrate surface just for few seconds $CH_4$ gas supply. The transferred graphene films on glass substrates has a transmittance at 550 nm is higher 94%, indicating 1~3 monolayers of graphene were formed. FETs based on the grapheme films transferred to $Si/SiO_2$ substrates revealed a p-type. We will further discuss the synthesis of graphene and doped graphene by ICPVCD and their characteristics.

• Journal of the Korean Wood Science and Technology
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• v.35 no.6
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• pp.31-42
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• 2007

To investigate the pyrolytic and anatomical characteristics of Korean softwood, Pinus densi-flora, Pinus rigida and Larix leptolepis, and hardwood, Acer palntatum, Fraxinus rhynchophylla and Quercus variabilis, chemical components analysis, TG-DTA (Thermogravimetric Analysis & Differential Thermal Analysis), MBA (Methylene Blue Adsorption) test and SEM observation were carried out. For TG-DTA, samples were carbonized up to $800^{\circ}C$ at the heating rate of $10^{\circ}C$/min under $N_2$ flows 1 l/min using thermogravimetric analyzer. Chemical component analysis of all samples resulted in typical contents of major wood component. In TG-DTA results, softwood showed higher char yield than hardwood, and lignin displayed the highest char yield among the major wood components. All samples showed typical TGA, DTG and DTA curves for wood pyrolysis except a few differences between softwood and hardwood. Content of lignin influenced its pyrolysis characteristics, while molecular structure of lignin affected not only the weight loss but also the yield of char. In MBA test results, MBA of softwoods was higher than that of hardwoods. Char of Pinus densiflora showed the highest MBA, but its degree was lower than activated carbon or fine charcoal about 23 and 4 times, respectively. SEM observation showed carbonization process preserves wood structure and retain the micro-structure of wood fibers.

• Korean Chemical Engineering Research
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• v.56 no.6
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• pp.901-908
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• 2018

Graphite is used as a sample anode active material. However, since the maximum theoretical capacity is limited to $372mA\;h\;g^{-1}$, a new anode active material is required for the development of a high capacity lithium ion battery. The maximum theoretical capacity of Si is $4200mA\;h\;g^{-1}$, which is higher than that of graphite. However, it is not suitable for direct application to the anode active material because it has a volume expansion of 400%. In order to minimize the decrease of the discharge capacity due to the volume expansion, the Si was pulverized by the dry method to reduce the mechanical stress and the volume change of the reaction phase, and the change of the volume was suppressed by coating the carbon layers to the particle size controlled Si particles. And carbon fiber is grown like a thread on the particle surface to control secondary volume expansion and improve electrical conductivity. The physical and chemical properties of the materials were measured by XRD, SEM and TEM, and their electrochemical properties were evaluated. In this study, we have investigated the synthesis method that can be used as anode active material by improving cycle characteristics of Si.

• Clean Technology
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• v.16 no.3
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• pp.198-205
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• 2010

Two sets of thermal reaction experiment for chlorinated hydrocarbons were performed using an isothermal tubular-flow reactor in order to investigate thermal decomposition, including product distribution of chlorinated hydrocarbons. The effects of $H_2$ or Ar as the reaction atmosphere on the thermal decomposition and product distribution for dichloromethane($CH_2Cl_2$) was examined. The experimental results showed that higher conversion of $CH_2Cl_2$ was obtained under $H_2$ atmosphere than under Ar atmosphere. This phenomenon indicates that reactive-gas $H_2$ reaction atmosphere was found to accelerate $CH_2Cl_2$ decomposition. The $H_2$ plays a key role in acceleration of $CH_2Cl_2$ decomposition and formation of dechlorinated light hydrocarbons, while reducing PAH and soot formation through hydrodechlorination process. It was also observed that $CH_3Cl,\;CH_4,\;C_2H_6,\;C_2H_4$ and HCl in $CH_2Cl_2/H_2$ reaction system were the major products with some minor products including chloroethylenes. The $CH_2Cl_2$/Ar reaction system gives poor carbon material balance above reaction temperature of $750^{\circ}C$. Chloroethylenes and soot were found to be the major products and small amounts of $CH_3Cl$ and $C_2H_2$ were formed above $750^{\circ}C$ in $CH_2Cl_2$/Ar. The thermal decomposition reactions of chloroform($CHCl_3$) with argon reaction atmosphere in the absence or the presence of $CH_4$ were carried out using the same tubular flow reactor. The slower $CH_3Cl$ decay occurred when $CH_4$ was added to $CH_3Cl$/Ar reaction system. This is because :$CCl_2$ diradicals that had been produced from $CHCl_3$ unimolecular dissociation reacted with $CH_4$. It appears that the added $CH_4$ worked as the :$CCl_2$ scavenger in the $CHCl_3$ decomposition process. The product distributions for $CHCl_3$ pyrolysis under argon bath gas were distinctly different for the two cases: one with $CH_4$ and the other without $CH_4$. The important pyrolytic reaction pathways to describe the important features of reagent decay and intermediate product distributions, based upon thermochemistry and kinetic principles, were proposed in this study.

• Journal of Chest Surgery
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• v.24 no.2
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• pp.161-170
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• 1991

Clinical results with the Mechanical cardiac valves were reviewed for 261 patients who underwent cardiac valve replacement from September, 1985 to July, 1990. of the Mechanical valves used, 156 were Carbomedics, 109 Duromedics, 52 St. Jude and 11 Bjork-Shiley. Overall hospital mortality was 14 out of 261[5,36%]: 9 out of 159[5.66%] for MVR, 1 out of 35[2.86%] for AVR and 4 out of 67[5.96%] for DVR[AVR+MVR]. Two hundred and forty seven operative survivors were followed up for a total 466.8 patient-years, ranged from 1 month to 4.9 years [a mean 1.8 years] and the follow up was 96.0%. There were 12 valve-related complications: three from thromboembolism, three from valve thrombosis, three from prosthetic valve endocarditis, two from paravalvular leak and the other one from hemorrhage. Actuarial rate free from all valve-related complication at 4.9 years was 96$\pm$1.3%. There were 11 late deaths: two from thromboembolism, one from valve thrombosis, one from prosthetic valve endocarditis, one from hemorrhage and the others 6 from non-valve-related complications. Actuarial survival rate at 4.9 years was 94$\pm$2.0%. 96$\pm$3.0% for MVR, 94$\pm$4.2% for AVR and 91$\pm$3.7% for DVR[AVR+MVR]. And there are 7 reoperations: three from paraprosthetic leak, two from prosthetic valve endocarditis and two from valve thrombosis. Actuarial rate free from reoperation at 9 years was 96$\pm$2.9%. On the basis of this 4.9 years of experience, the pyrolytic carbon mechanical valves appears to be an excellent mechanical prosthesis for cardiac valve replacement, in terms of hemodynamic performance, low mortality and low thrombogenecity.

• Journal of Environmental Science International
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• v.14 no.2
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• pp.105-119
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• 2005

The surface sediments inside Songsanpo and Seogwipo Harbors, major harbors of Jeju Island, were collected three times (June, September and December, 2001) and analyzed for 16 polycyclic aromatic hydrocarbons (PAHs) recommended by US-EPA as priority pollutants to assess their distribution levels and their biological effects on the marine organisms, and to suggest their possible origins. The concentrations of total PAHs inside Songsanpo and Seogwipo Harbors ranged from 41 to 288 ng/g on a dry weight basis with a mean value of 121 ng/g and from 14 to 268 ng/g with a mean value of 119 ng/g, respectively, and the levels were low as compared with those in other areas of the world. The sedimentary PAHs may be correlated with organic carbon and mud content to some extent. Based on comparisons of individual and total concentrations with effects-based sediment quality guidelines, the potential for the biological effects on the marine organisms were expected to be very low. From the examinations of the four PAH origin indices, such as LMW /HMW (low molecular weight 2-3 ring PAHs over high molecular weight 4-6 ring PAHs), phenanthrene/anthracene ratio, fluoranthene/pyrene ratio, chrysene/benzo[a]anthracene ratio, it can be concluded that the sediment PAH contaminations were ascribed to both of pyrolytic and petrogenic origins.

• Korean Journal of Agricultural Science
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• v.44 no.3
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• pp.359-365
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• 2017

Biochar has the ability to mitigate climate change, improve crop productivity, and adsorb various contaminants. The aim of this work was to confirm the effect of biochar as a soil amendment on growth of Chinese cabbage (Brassica chinensis) using a pot experiment. Biochar was produced from residual-wood burnt at a pyrolytic temperature of $400^{\circ}C$ and consisted of 51.6 % carbon (C) by mass. The biochar was added to the soil at 0, 1, 3, and 5% by weight, which represent about 0, 18, 54, and $90t\;ha^{-1}$, respectively. The treatments were arranged in a randomized complete block design with 3 replications. The Chinese cabbage was grown for 49 days in a glasshouse in pots filled with sandy loam soil. Experimental results showed that the residual-wood biochar used for the experiment was slightly alkaline (pH 7.5). The fresh weights of Chinese cabbage were 86.22 g, 84.1 g, 63.23 g and 70.87 g, respectively, for biochar applications at 0, 18, 54, and $90t\;ha^{-1}$. Compared with the control (i.e., no biochar), biochar application increased soil pH and electrical conductivity (EC). Addition of biochar (54 and $90t\;ha^{-1}$) to sandy loam soil had no effect on growth of Chinese cabbage. This might be due to excessive increase of soil pH from the biochar application, leading to reduced availability of plant nutrients. Based on these results, the authors conclude that an excessive addition of biochar may have negative effects on the healthy growth of Chinese cabbage.