• Journal of Korea Foundry Society
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• v.19 no.1
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• pp.71-76
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• 1999

Eutectic and off-eutectic Al-Fe alloys were unidirectionally solidified at the solidification rate of $1{\sim}50\;mm/min$ under the temperature gradients $75{\sim}80^{\circ}C/cm$. The investigation has been carried out for the microstructural variation, phase transition, mechanical properties by means of detailed analyses of stress-strain, micro-Vickers hardness and scanning electron micrography. The thermal stability at elevated temperature has been studied on $Al-Al_6Fe$ eutectic alloy held at $600^{\circ}C$ for $0{\sim}150$ hours. When the solidification rate was less than 10mm/min, the X-ray diffraction and EDS analysis showed the presence of $Al_3Fe$ compound. As the solidification rate more than 20 mm/min, $Al-Al_3Fe$ eutectic phase was transfered into $Al-Al_6Fe$ eutectic phase. The mechanical properties of unidirectionally solidified off-eutectic Al-Fe alloy is better than those of unidirectionally solidified eutecic Al-Fe alloy Maximum ultimate tensile strength was obtained in Al-2.25% Fe alloy which was unidirectionally solidified at the solidification rate of 20 mm/min. The metastable $Al-Al_6Fe$ phase was transferred into stable $Al-Al_3Fe$ phase at $600^{\circ}C$ held for 150 hours.

• Animal cells and systems
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• v.1 no.3
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• pp.483-489
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• 1997

This study was performed to investigate the differentiation and distribution of choline acetyltransferase (ChAT}-immunoreactive cells in the magnacellular preoptic nucleus (MCPO) of the postnatal and adult rat forebrains, utilizing techniques of immunocytochemistry. According to the cell shape and the ratio of long axis versus short axis of cell soma, the ChATimmunoreactive nerve cells in the MCPO were classified into six types: 1) round, 2) oval, 3) elongated, 4) fusiform, 5) triangular, and 6) polygonal types. Frequency distributions of the oval and round nerve cells on the postnatal day (PND) 0 were observed to be high. But in the adult, frequency distributions of the same cells were shown to decrease. Compared to those of the postnatal rats, frequency distributions of elongated, fusiform, triangular, and polygonal nerve cells in the adult were increased. The total mean volumes of ChAT-immunoreactive cell somata in the MCPO of PND 0 rat were the lowest, while those in the PND 17 rat were shown to be the highest and decreased in the adult. The soma volumes of the immunoreactive cells at the PND 17 were evenly distributed, but those in the other developmental stages (e.g. PND 7 and adult) appeared to exhibit unimodal distributions. On the electron micrography, the free ribosomes, polysomes, and rough endoplasmic reticula (RER) of the nerve cells in the MCPO of PND 21 rat forebrains were immunoreactive to ChAT in the tissues untreated with triton X-100. According to the observations in the present study, it is considered that the ChAT-immunoreactive nerve cells in the MCPO of the rat forebrains are differentiated throughout the following processes during the postnatal development: 1) increase in cell soma volumes, 2) development of neurites, 3) increase in the frequency of differentiated cell types, and 4) decrease in cell soma volumes. The ribosomes, polysomes, and RER are considered to be closely related to the intracellular localization and biosynthesis of the ChAT but not Golgi complex.

• Journal of the Korean Chemical Society
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• v.10 no.2
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• pp.67-75
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• 1966

Four kinds of clays from Sinyewon mine which is located in Chungchoungnam-Do district and two kinds of Japanese clays (Gairome, Kibushi) were selected and studied on the fundamental properties of these clays and those which are refined by the elutriation method. Chemical analysis, grading analysis such as refractoriness, specific gravity, color, fired color and plasticity, particle size distribution, various thermal tests, X-ray diffraction analysis and electron microscopic survey were carried out on these clays. The comparison of domestic clays with Japanese clays was made. 1. In chemical composition and physical properties, these four kinds of Sinyewon clays are almost similar to each other and also to Gairome and Kibushi clays. In refractoriness, Gairome and Kibushi clays have relatively high value such as SK 34 and 35, while Sinyewon clays have the value of about SK 32. Especially Sinyewon clay B has the low refractoriness (SK 18) and plasticity. Refined clays have the tendency of somewhat higher value than crude ones in refractoriness. 2. When burnt up to $900^{\circ}C$, the coefficients of contraction of Sinyewon clays were under 1.5%, Gairome under 1.3%, Kibushi under 3.0%. Only Sinyewon clay B showed expansion (1.0%) instead of contraction. 3. X-ray diffraction analysis and electron micrography showed that all of four Sinyewon clays and two Japanese clays are mainly composed of poorly crystallized kaolin, containing small amount of halloysite, sericite and considerable amount of quartz and feldspar. Sinyewon clay B contains especially large amount of quartz and feldspar. In general, it has been found out that the refined clays were free from large amount of iron oxide, quartz and feldspar.

• Journal of Welding and Joining
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• v.2 no.1
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• pp.4-17
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• 1984

Overlaid weld metals of austenitic stainless steel in a pressure vessel of power reactor are usually post-weld heated for a long period of time after welding. The PWHT is considered as a kind of sensitizing and it is important to check the soundness of the weld metal after PWHT, especially about the precipitation of carbides. The purpose of this report is to obtain information on the relation between the change of microstructure and Post-Weld Heat Treatment in the overlaid weld metals. Metallurgical aspects of the problem on austenitic stainless steel heated at $625^{\circ}C$, $670^{\circ}C$, $720^{\circ}C$ and $760^{\circ}C$ for 3, 10, 30, 100 and 300 hours have been investigated by means of optical-micrography, micro-hardness measurement, scanning electron microscope and electron-probe micro analysis. From the results obtained, the following conclusions are drawn; 1) The PWHT above $625^{\circ}C$ for a long time causes a diffusion of carbon atoms from low alloy steel into stainless steel, and consequently carbon is highly concentrated at the boundary layer of stainless steel. 2) C in ferritic steel migrated to austenitic steel and carbides precipitated in austenitic steel along fusion line. At higher temperatures, the ferrite grains coarsened in the decarburized zone. 3) In the change of microstructure of stainless steel overlaid weld metal, the width of carbides precipitated zone and decarburized zone increased with increase of PWHT temperature and time. 4) At about $625^{\circ}C$ to $760^{\circ}C$, chromium carbides, mainly $M_{23} C_6$, precipitate very closely in the carburized layer with remarkable hardening. 5) Precipitation of delta ferrite from molten weld metal depends on solidification phenomenon. There was a small of ferrite near the bond in which the local solidification time was short, comparing with after parts of weld metal. Shape and amount of ferrite were not changed by Post-Weld Heat Treatment after solidification.

• Journal of Welding and Joining
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• v.16 no.4
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• pp.55-62
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• 1998

While excellent joint quality has been obtained using dry chamber underwater welding methods, the size limitations imposed by this process restrict its use for underwater construction work. The wet underwater shielded metal-arc welding eliminates this restriction but suffers from poor weld properties by the 1-pass bead-on-plate welding due to the excessive diffusible hydrogen. On the other hand, in the wet underwater welding, it is well known that the quantity of diffusible hydrogen in multi-pass welded parts reduce to less than that in 1-pass welded parts. Therefore, in this paper, welding experiments are made the 3-pass bead-on-plate welds by using TMCP and normalized steel plates and E4301 and cellulose coated electrode. After that, The amounts of the hydrogen absorbed into the 3-pass welded area were measured according to the JIS Z 3118 specification. The microstructural changes as well as the microhardness distribution after the underwater 3-pass welding were also investigated using Vickers microhardness tester and S.E.M and O.M. The results indicated that the quantity of diffusible hydrogen in 3-pass welded areas was reduced little less than a half of one of that in 1-pass welded areas at the specific welding condition. As a result, the cold cracking of 3-pass welded areas decreased by reduced effect of diffusible hydrogen. In the underwater 3-pass welding, the micrography of cold cracking fracture surface showed mainly the cleavage of hydrogen embrittlement.

• Journal of Periodontal and Implant Science
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• v.36 no.3
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• pp.757-765
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• 2006

Human periodontal ligament fibroblasts (hPDLF) are very important for curing the periodontal tissue because they can be differentiated into various cells. A tissue engineering approach using a cell-scaffold is essential for comprehending today's periodontal tissue regeneration procedure. This study examined the possibility of using an acellular dermal matrix as a scaffold for human periodontalligament fibroblast (hPDLF). The hPDLF was isolated from the middle third of the root of periodontally healthy teeth extracted for orthodontic reasons. The cells were cultured in a medium containing Dulbecco's modified Eagle medium supplemented with 10% fetal bovine serum at $37^{\circ}C$ in humidified air with 5% $CO_2$. The acellular dermal matrix(ADM) was provided by the US tissue banks(USA). Second passage cells were used in this study. The hPDLF cells were cultured with the acellular dermal matrix for 2 days, and the dermal matrix cultured by the hPDLF was transferred to a new petri dish and used as the experimental group. The control group was cultured without the acellular dermal matrix, The control and experimental cells were cultured for six weeks. The hPDLF cultured on the acellular dermal matrix was observed by Transmission Electron microscopy (TEM). Electron micrography shows that the hPDLF was proliferated on the acellular dermal matrix. This study suggests that the acellular dermal matrix can be used as a scaffold for hPDLF.

• Polymer(Korea)
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• v.35 no.5
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• pp.375-377
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• 2011

$PbTiO_3$/P(VDF/TrFE) 0~3 composites thin films with 0.10 and 0.13 of ceramic volume fraction factor have been fabricated by two-step spin coating technique and analyzed. 0~3 connectivity of $PbTiO_3$/P(VDF/TrFE) composites film was observed successfully by SEM micrography. The SEM picture confirmed 0~3 connectivity. And, in all the properties, 0~3 $PbTiO_3$/P(VDF/TrFE) composites film was superior to P(VDF/TrFE) copolymer. Therefore, with a good low-dielectric constant and a high pyroelectric coefficient, the composite thin films can be used for a new pyroelectric infrared sensor of higher performance.

• Food Science and Preservation
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• v.16 no.6
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• pp.985-990
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• 2009

Fatty acid composition, protein content, and shape change of Listeria monocytogenes treated with ethanol extracts from Schizandra chinensis were examined. Transmission electron micrography of cells treated with ethanolic S. chinensis extracts showed development of morphological changes. Cell surfaces were irregular, swollen, or even disrupted after treatment with ethanol extracts, compared with the smooth surfaces of normal cells. Interestingly, cell protein content was decreased by ethanol extract treatment. Cell fatty acid composition was also changed after treatment with ethanol extracts. The levels of 13-methylpentadecanoic acid (i-15:0), 12-methylpentadecanoic acid (a-15:0) and 15-methylpentadecanoic acid (i-17:0) of L. monocytogenes Scott A and L. monocytogenes ATCC 19111 were decreased, but the concentrations of Cis-9,12 octadecanoic acid ($18:2^{9,12}$) and cis-9-octadecanoic acid ($18:1^9$) were increased. 13-methylpentadecanoic acid (i-15:0) and 12-methylpentadecanoic acid (a-15:0) levels in L. monocytogenes Brie I were decreased but the concentrations of Cis-9,12 octadecanoic acid ($18:2^{9,12}$) and cis-9-octadecanoic acid ($18:1^9$) were increased after treatment with ethanolic extracts. Notably, the levels of 12-methylpentadecanoic acid (a-15:0) significantly were decreased but those of cis-9,12 octadecanoic acid ($18:2^{9,12}$) significantly were increased in all tested microorganisms.

• The Korean Journal of Ecology
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• v.4 no.3_4
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• pp.114-123
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• 1981

Diurnal acid fluctuations, stomatal resistance, and morphology and anatomy were investigated in leaves and stems P. oleracea L. growing under the natural environmental condition. A CAM-like pattern of acid fluctuation was exhibited not in leaves of the young purslane but in its stems. Defoliated stems showed a decreased in diurnal changes of total acidity as compared with normal stems. Excised stems stored in continuous darkness exhibited diurnal acid rhythms, and they showed light deacidifications for three days. Kranz-type arrangement was observed in leaves, but not in stems. Micrography of cross sections of stems showed cells with relatively large vaculoles and a few chloroplasts. The number of stomata was 3,275cm-2 in leaves, while the stomata could not be observed in stems. Stomatal resistance was high at night and low in daytime in leaves of the young purslane, and the range of its value was 5~40 sec.$\textrm{cm}^{-1}$. But stomatal resistance in leaves of the water-stressed plant was comparratively high in day time, and its value was 30 sec.$\textrm{cm}^{-1}$. The result of these studies showed the possibility that the stem of P.oleracea L. possesses CAM under certain stressed conditions.

• Journal of the Korean Wood Science and Technology
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• v.40 no.4
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• pp.268-275
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• 2012

This study was carried out to understand the anatomical characteristics of Korean mistletoe (Viscum album var. coloratum) and host tree of Mongolian oak (Quercus mongolica) by the aid of light and scanning electron microscopy. The branch diameter of host tree at the parasitic part by mistletoe is larger than that of non-parasitic part. In the mistletoe, phloem consists of bast fiber and parenchyma cell and xylem is composed of fiber, ray and axial parenchyma cell, and vascular tracheid. The volume of ray parenchyma cell is higher than common wood species and is heterocellular made up of procumbent, upright, and square cells in the mistletoe. In the vascular tracheid of mistletoe, coarse spiral thickenings and bordered pit are present. Due to the insertion of the mistletoe haustorium, some deformed vessels but no tylosis are observed in the mistletoe. The shapes of mistletoe haustorium are sharp, and the destruction of the host tree cells due to the insertion of the mistletoe haustorium are not identified.