• Korean Journal of Materials Research
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• v.16 no.2
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• pp.137-143
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• 2006

The effects of Cu and Fe additions on the thermal stability, microstructure and mechanical properties of $Al_{85}-Ni_{8.5}-Mm_{6.5},\;Al_{84}-Ni_{8.5}-Mm_{6.5}Cu_1,\;Al_{84}-Ni_{8.5}-M_{m6.5}Fe_1$ alloys, manufactured by gas atomization, degassing and hot-extrusion were investigated. Gas atomization, with a wide super-cooled liquid region, allowed the alloy powders to exhibit varying microstructure depending primarily on the powder size and composition. Al hotextruded alloys consisted of homogeneously-distributed fine-grained fcc-Al matrix and intermetallic compounds. A substitution of 1 at.% Al by Cu increased the thermal stability of the amorphous phase and produced alloy microstructure with smaller fcc-Al grains. On the other hand, the same substitution of 1 at.% Al by Fe decreased the stability of the amorphous phase and produced larger fcc-Al grains. The formation of intermetallic compounds such as $Al_3Ni,\;Al_{11}Ce_3\;and\;Al_{11}La_3$ was suppressed by the addition of Cu or Fe. Among the three alloys examined, the highest Vickers hardness and compressive strength were obtained for $Al_{84}-Ni_{8.5}-M_{m6.5}Cu_1$ alloy, and related to the finest fcc-Al grain size attained from increased thermal stability with Cu addition.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2019.05a
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• pp.27-28
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• 2019

Recently, a bed company detected a radon more than Red Politics and became a hot topic of conversation. This has led to increased interest in radon, and a number of free-of-charge bodies have also been established to recognize the dangers of radon. In addition, the Korean Institute of Geological and Resource Research is planning to assist the installation of radon alarm systems in 10,000 households nationwide, free of charge. Since radon is a colorless, odorless and tasteless gas that causes lung cancer, it aims to reduce lung cancer incidence by absorbing radon using bamboo activated carbon as a way to reduce it. Due to the use of bamboo activated carbon, radon concentration per hour tends to decrease as substitution rate increases, and table flow tends to decrease as substitution rate increases. Through this experiment, 30% of the replacement rate of bamboo activated carbon is judged to be the most suitable replacement rate.

• The Korean Journal of Zoology
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• v.35 no.1
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• pp.80-86
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• 1992

The nucleotide sequences of 185 rRNAs of the five Korean decapods were partially determined by the direct sequencing method using the reverse transcriptase. ne average GC content of five species was 51.1% which is higher than that of yeast(45.0%) and lower than those of frog (53.0%) and rat (55.6%). This result follows the general patterns of the GC content in the nucleotides of the nucleic acid shown among the various phylogenetic groups. The average ratio of transrional/transversional nucleotide substitution of pairwise comparison among six species (including Anemia salina) was 1.200 $\pm$ 0.310 when whole region alas examined. However, the ratio showed some differences when the conservative regions and variable regions frere separatelv examined. The molecular phylogenies of the five species were constructed by using two different tree making methods. In general the results support the previously reported molecular phylogeny of the decapod crustaceans. However, our results indicate thats in the analysis of the sequence dat3, the UPGMA clustering method of the distance matrix method should be carefully employed after considering the rate of nucneotide substitution in the different regions of the molecule.

• Journal of Ocean Engineering and Technology
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• v.27 no.2
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• pp.75-79
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• 2013

This study was carried out to investigate the precipitation behavior of the ${\chi}$ phase and the impact toughness of 25%Cr-7%Ni-2%Mo-4%W super duplex stainless steel. The ${\chi}$ phase was precipitated in the early stage of aging, and with the increasing aging time. However, after reaching a maximum value, the number decreased as a result of the gradual transformation of the ${\chi}$ phase into the ${\sigma}$-phase. It was proved that the ${\chi}$ phase was an intermetallic compound, which represented a lower nickel concentration, higher chromium and molybdenum concentrations, and very higher tungsten concentration compared to the matrix phases. It also showed higher molybdenum and tungsten concentrations than the ${\sigma}$ phase. The decomposition of the ferrite phase into the ${\gamma}_2$ and ${\sigma}$ phases was retarded by W substitution for Mo. Thus, the number of ${\chi}$ phases increased. The impact value was decreased by the substitution of W for Mo. The impact toughness rapidly decreased with time when the ${\chi}$ phase began to precipitate in the initial stage of aging. The impact toughness was, therefore, greatly influenced for the precipitation of the ${\chi}$ phase.

• Korean Journal of Materials Research
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• v.20 no.2
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• pp.65-71
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• 2010

In this study, the effect of Sn and Mg on microstructure and mechanical properties of Cu-Fe-P alloy were investigated by using scanning electron microscope, transmission electron microscope, tensile strength, electrical conductivity, thermal softening, size and distribution of the precipitation phases in order to satisfy characteristic for lead frame material. It was observed that Cu-0.14wt%Fe-0.03wt%P-0.05wt%Si-0.1wt%Zn with Sn and Mg indicates increasing tensile strength compare with PMC90 since Sn restrained the growth of the Fe-P precipitation phase on the matrix. However, the electrical conductivity was decreased by adding addition of Sn and Mg because Sn was dispersed on the matrix and restrained the growth of the Fe-P precipitation. The size of 100 nm $Mg_3P_2$ precipitation phase was observed having lattice parameter $a:12.01{\AA}$ such that [111] zone axis. According to the results of the study, the tensile strength and the electrical conductivity satisfied the requirements of lead frame; so, there is the possibility of application as a substitution material for lead frame of Cu alloy.

• Industrial Engineering and Management Systems
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• v.9 no.3
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• pp.227-241
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• 2010

A memory module industry's supply chain usually consists of multiple manufacturing sites and multiple distribution centers. In order to fulfill the variety of demands from downstream customers, production planners need not only to decide the order allocation among multiple manufacturing sites but also to consider memory module industrial characteristics and supply chain constraints, such as multiple material substitution relationships, capacity, and transportation lead time, fluctuation of component purchasing prices and available supply quantities of critical materials (e.g., DRAM, chip), based on human experience. In this research, a directed graph-based supply network planning (DGSNP) model is developed for memory module industry. In addition to multi-site order allocation, the DGSNP model explicitly considers production planning for each manufacturing site, and purchasing planning from each supplier. First, the research formulates the supply network's structure and constraints in a directed-graph form. Then, a proposed genetic algorithm (GA) solves the matrix form which is transformed from the directed-graph model. Finally, the final matrix, with a calculated maximum profit, can be transformed back to a directed-graph based supply network plan as a reference for planners. The results of the illustrative experiments show that the DGSNP model, compared to current memory module industry practices, determines a convincing supply network planning solution, as measured by total profit.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2019.11a
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• pp.174-175
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• 2019

Recently, due to air pollution caused by fine dust, it is considered as a social problem. Increasing fine dust has intensified air pollution, causing many diseases and damages. This year, Seoul, South Korea, reached a severe level of fine dust pollution worldwide. The Ministry of Environment has strengthened the environmental standard for fine dust (PM2.5) from $50{\mu}g/m^3$ to $35{\mu}g/m^3$ since March 2018. When fine dust enters the human body, it causes bronchial or skin elongation such as respiratory allergies, irritable pneumonia, asthma and atopy. In this study, $TiO_2$ rutile with photocatalytic activity was used, and materials prepared by rutile sulfuric acid method were used. The photocatalytic activity rate is 95% or more and the density is $4.1g/cm^3$. The matrix was based on cement, and the substitution rate of $TiO_2$ was 0, 5, 10, 15, 20 (%). The test item is flexural strength and compressive strength.

• Advances in concrete construction
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• v.16 no.5
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• pp.269-276
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• 2023

In order to study the effect of rubber particle size and admixture on the frost resistance of self-compacting concrete, three self-compacting concrete specimens with equal volume replacement of fine aggregate by rubber particles of different particle sizes were prepared, while conventional self-compacting concrete was made as a comparison specimen. The degradation law of rubber aggregate self-compacted concrete under freeze-thaw cycles was investigated by fast-freezing method test. The results show that the rubber aggregate has some influence on the mechanical properties and freeze-thaw durability of the self-compacting concrete. With the increase of rubber aggregate, the compressive strength of self-compacting concrete gradually decreases, and the smaller the rubber aggregate particle size is, the smaller the effect on the compressive strength of the matrix; rubber aggregate can improve the frost resistance of self-compacting concrete, and the smaller the rubber particle size is, the more obvious the effect on the improvement of the frost resistance of the matrix under the same dosage. Through the research of this paper, it is recommended to use 60~80 purpose rubber aggregate and the substitution rate of 10% is chosen as the best effect.

• Journal of the Korean Magnetics Society
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• v.18 no.4
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• pp.136-141
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• 2008

In this study, the magnetic(static and high-frequency) and microwave absorbing properties have been investigated in Ru-Co substituted M-hexaferrites($BaFe_{12-2x}Ru_xCo_xO_{19}$). The powders and sintered specimens were prepared by conventional ceramic processing technique. With the calcined powders, the composite specimens were prepared using the silicone rubber as a matrix material. The substitution ratio of Ru-Co to obtain in-plane magnetic anisotropy, thus having the minimum coercivity, is much smaller (about x=0.3) than the previously reported Ti-Co substituted specimen. Owing to this low substitution, the specimen has a large value of saturation magnetization($M_s$=65 emu/g). Ferromagnetic resonance behavior and microwave absorbing frequency band is strongly influnced by the coercvity which can be controlled by Ru-Co substitution ratio. It is found that the M-hexaferrites with planar magnetic anisotropy by doping Ru-Co in both sintered and composite form have superior microwave absorbing properties in GHz frequency range.

• Journal of Pharmaceutical Investigation
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• v.25 no.2
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• pp.109-116
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• 1995

For the administration of narcotic antagonist with short half-life and low patient compliance, the sustained release system using biodegradable matrix is effective. Polyphosphazenes are of considerable interest as biodegradable matrix systems for controlled release of drugs. In this study, biodegradable polyphosphazenes available for the sustained release implantable device were synthesized, and their application was examined. Poly[dichlorophosphazene] was synthesized by solution polymerization method and confirmed with IR spectrum. Poly[bis(ethyl glycinate) phosphazene] and poly[ (diethyl glutamate)-co-(ethyl glycinate)phosphazene] were then produced by substitution of amino acid alkyl esters for chloride side groups. Using these polymers, the implantable devices of 1 mm thickness and $10{\times}10\;mm$ size containing naloxone hydrochloride were prepared and their release and degradation profiles were measured. In the case of poly[bis(ethyl glycinate)phosphazene] with swelling characteristics, degradation rate was slower than the release rate, showing that the release rate is partly dependent on the swelling rate. In contrast, the degradation rate of polyl[(diethyl glutamate)-co-(ethyl glycinate)phosphazene] matrix was identical with release rate of naloxone hydrochloride. On the basis of these results, it is expected that these polymers can be applied to sustained release implantable systems delivering narcotic antagonist.