• Elastomers and Composites
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• v.33 no.3
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• pp.193-200
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• 1998

It is well known that EPDM(ethylene propylene diene monomer) rubber has inherently excellent resistance to the weathering, ozone, heat, cold and moisture, whereas crosslinked IIR (isobutylene isoprene divlnyl benzene terpolymer) shows proper resistance to the water and gas permeation. Various characteristics of EPDM blend with crosslinked IIR such as curing characteristics, mechanical properties, dispersion of minor component and gas impermeability were explored. The optimum curing time $(t_{90})$ examined with peroxide was decreased by adding small amount of crosslinked IIR to the EPDM rubber. Mechanical properties of blends such as tensile strength, hardness and elongation at break were enhanced by increasing EPDM content. These results might be explained with the affinity of carbon black to the EPDM rubber. On the other hand, the physical properties were not changed significantly after aging, and the increase of crosslinked IIR fraction caused the decrease of compression set to small rate. EPDM rubber shows different behavior with crosslinked IIR in oxygen permeability. By adding 30wt.% crosslinked IIR to the EPDM rubber, the resistance to the oxygen permeation was improved up to three times than that of pure EPDM rubber. Conclusively, EPDM blend containing 30wt.% crosslinked IIR might be commercially applied to the o-ring and electric parts because of its proper resistance to the weathering, ozone and oxygen permeability.

• Elastomers and Composites
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• v.47 no.1
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• pp.75-81
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• 2012

Acrylic rubber was synthesized using ethyl acrylate. butyl acrylate, methoxyethyl acrylate as main monomers and glycidyl methacrylate as cure site monomer by emulsion polymerization. Rubber compound was made by adding 2,2-bis[4-(4-aminophenoxy)phenyl]propane as crosslinking agent. Increase of ethyl acrylate content in the main monomer ratio resulted in enhancement of heat resistance due to decrease of glass transition temperature in acrylic rubber. And also oil resistance was increased with increasing content of ethyl acrylate because ethyl acrylate has the highest ester concentration in the three main monomers. With content of 2,2-bis[4-(4-aminophenoxy)phenyl]propane, both tensile strength and elongation were increased until 2 phr, but in higher content than that, they decreased owing to reduction of viscosity and elongation by increase of crosslinking density.

• Journal of Korean Society for Quality Management
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• v.40 no.3
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• pp.245-258
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• 2012

Purpose: Recently, many quality issues are aroused in military forces, such as failures in K-series weapons, combat boots defects and 40mm ammunition explosion accident. To address these problems, the one and only government defense quality assurance agency, DTaQ(Defense Agency for Technology & Quality) tried to improve many quality assurance procedures and introduced new systems such as MRA(Manufacturing Readiness Assessment), TRA(Technology Readiness Assessment), and etc. However, as the amount of war supplies increasing every year, the resource(budget and manpower) for quality assurance is limited. Therefore, DTaQ had difficulty to handle the issue efficiently and effectively, and we propose the method to address this problem. Methods: The most popular quality assurance technique is a sampling method, in this research, we first review the many sampling techniques and compare the strength and weakness of each method. After then, we selected the most appropriate sampling techniques and applied the procedures in combat force support material and ammunition areas. Results: We can reduce the number of samples dramatically, thus the required amount of labor time and money can be saved. Also, the new sampling technique enforces the supplier to produce the product which meets the target value(desirable value). Conclusion: We can reduce the number of samples dramatically, thus the required amount of labor time and money can be saved. Also, the new sampling technique enforces the supplier to produce the product which meets the target value(desirable value). Lastly, since the new sampling method requires many numerical calculations, we developed a simple android OS smart-phone application which can be used easily in field.

• Journal of Hydrogen and New Energy
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• v.23 no.2
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• pp.143-149
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• 2012

용융탄산염 연료전지 상용화를 위해서 40,000 시간이상 장기 운전이 가능해야 한다. 장기운전을 위해 크랙 발생이 적고 기계적 강도가 높은 강화 매트릭스의 개발이 절실히 요구되고 있다. 본 연구에서는 $LiAlO_2$에 알루미늄 나노입자를 첨가하여 매트릭스의 기계적 강도를 향상시키는 연구를 수행하였다. 나노 알루미늄 첨가 $LiAlO_2$ 그린 시트를 수소 분위기에서 열처리한 결과, 공기 분위기에서 열처리한 매트릭스에 비해 기계적 강도가 1.5배 증가함을 확인하였다. 이는 환원분위기에서 열처리를 할 경우, 알루미늄의 입자간의 소결으로 인한 neck이 형성 되어 $LiAlO_2$ 입자 간에 다리를 만들어주는 효과가 나타나 매트릭스의 기계적 강도가 크게 증진되었으리라 판단된다.

• Journal of Korea Foundry Society
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• v.25 no.1
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• pp.40-50
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• 2005

A series of heavy section ductile cast iron ingots with the cube length of 250mm were systematically investigated as functions of casting parameters of sand casting. Abnormal graphite formation was specially observed with the variation of Si content and Bi or Sb addition. Effects of chilling during casting and adaptation of riserless system were also examined, and proved to be effective for the prevention of both shrinkage and abnormal graphite such as chunky one. The formation of chunky graphite was effectively prevented by low Si content despite the promotion of pearlite matrix structure. The ferritic matrix was encouraged to form by high Si content and chunky graphite formation was effectively suppressed by the addition of Bi and Sb. Bi addition, however, was not good enough to control the microstructure owing to the sensitive cooling rate dependent inoculation behavior and relative low ability of nodulization. Sb addition, on the other hand, was proved to be effective for the microstructural control and enhancement of various mechanical properties such as strength, elongation, and impact energy. It may be suggested that optimized casting parameters should be applied to produce heavy section ductile cast iron with reliability.

• Journal of Navigation and Port Research
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• v.26 no.1
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• pp.15-21
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• 2002

Re Ministry of Maritime Affairs and Fisheries in Korea completed the installation of 8 maritime DGPS station mfd is to going install 3 additional Maritime DGPS station for the enhancement of dual coverage in Korean coasts until Oct. 2002. Moreover, Korean government decided to provide the NDGPS service over the whole Korean inland area, which will be schedule to complete until June. 2004. On this paper to evaluate the propagation characteristics of using maritime DGPS site as un element of NDGPS ann to evaluate the required number of additional NDGPS sites, the propagation characteristics of the radio waves of 300kHz bands on sea and land nth are studied With the result of study, the conceptional design of Korean NDGPS System is proposed, which consists of 5 NDGPS sites with modified antenna and tかee coverage monitoring sites.

• Journal of KIISE:Information Networking
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• v.32 no.2
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• pp.215-219
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• 2005

Generally, the mobile nodes in MANET have the limited power capacity available for actual communications. Thus, the power management is very important for packet routing or forwarding. Although MTPR, MBCR and MMBCR are proposed to treat the problem of power consumption, there have been few researches resolving the link breakdown that is occurred by the power exhaustion during transmission. In this sense, the reliable scheme should be required to ensure the routing connectivity. In this paper, we propose three schemes to enforce the routing connectivity. If the signal strength is dropped below a signal threshold, the candidate route is previously selected to prepare the link breakdown. Also, on multi-channel, we propose the lifetime increment scheme of a node that it manage its available power to the needed power of a new link. The simulation results show the enforcement of the link connectivity and the performance improvements of the delay time through the effective connection management.

• Journal of Physiology & Pathology in Korean Medicine
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• v.31 no.4
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• pp.238-245
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• 2017

This retrospective observational study was aimed to evaluate that Daoyin Exercise therapy improves the symptoms related to lumbar disc herniation. We analyzed the medical records of 7 patients, who satisfied with inclusion and exclusion criteria. The subjects of the study were the patients who were prescribed Daoyin Exercise Therapy and Korean medical treatments for lumbar intervertebral disc herniation at Dunsan Korean Medicine Hospital of Daejeon University from July 25th, 2016 to March 31th, 2017. The effects of Daoyin Exercise Therapy was evaluated by comparing before and after taking Daoyin Exercise Therapy through 0-10 Numeric Rating Scale(NRS), Roland & Morris Disability Questionnaire(RMDQ), Trunk Extension Flexion(TEF) Program, EuroQol five Demension Questionnaire(EQ-5D, EQVAS) of the symptoms including lower back pain. The Daoyin Exercise Therapy combined with Korean medicine treatment reduced NRS($3.357{\pm}3.038$) and RMDQ($9.50{\pm}6.364$), and improved Muscle endurance($44.429{\pm}45.136$), EQ-5D($0.09{\pm}0.12$) and EQVAS($6.571{\pm}19.260$) of the 7 patients without side effects. These results implied that Daoyin Exercise Therapy might helps to improve symptoms of patients with lumbar disc herniation by reducing the symptoms of lower back pain and improving muscle endurance, quality of life, strength enhancement and core muscles.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.5
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• pp.47-54
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• 2018

Concrete undergoes various deterioration on surface. Impregnant with silicate is usually applied to concrete surface and forms insoluble hydrates, which can provide many engineering advantages. In the work, concrete impregnated with colloidal silicate is used for durability enhancement in surface and self-clearing performance is evaluated with photocatalyst-$TiO_2$ spraying. For the work, various tests are performed both for strength evaluation and durability evaluation such as absorption ratio, drying shrinkage, chloride penetration, sulfate resistance, and freezing/ thawing action. Furthermore, removal and self-clearing performance are evaluated with Acetaldehyde decomposition and Methylene blue decolorization. Through silicate impregnation and photocatalyst spraying, the impregnated concrete can have not only durability enhance but also self-clearing performance.

• The Korean Journal of Physiology and Pharmacology
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• v.2 no.4
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• pp.529-539
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• 1998

The effects of membrane surface charge originated from lipid head groups on ion channels were tested by analyzing the activity of single large conductance $Ca^{2+}-activated\;K^+$ (maxi K) channel from rat skeletal muscle. The conductances and open-state probability ($P_o$) of single maxi K channels were compared in three types of planar lipid bilayers formed from a neutral phosphatidylethanolamine (PE) or two negatively-charged phospholipids, phosphatidylserine (PS) and phosphatidylinositol (PI). Under symmetrical KCl concentrations $(3{\sim}1,000\;mM)$, single channel conductances of maxi K channels in charged membranes were $1.1{\sim}1.7$ times larger than those in PE membranes, and the differences were more pronounced at the lower ionic strength. The average slope conductances at 100 mM KCl were $251{\pm}9.9$, $360{\pm}8.7$ and $356{\pm}12.4$ $(mean{\pm}SEM)$ pS in PE, PS and PI membranes respectively. The potentials at which $P_o$ was 1/2, appeared to have shifted left by 40 mV along voltage axis in the membranes formed with PS or PI. Such shift was consistently seen at pCa 5, 4.5, 4 and 3.5. Estimation of the effect of surface charge from these data indicated that maxi K channels sensed the surface potentials at a distance of $8{\sim}9\;{\AA}$ from the membrane surface. In addition, similar insulation distance ($7{\sim}9\;{\AA}$) of channel mouth from the bilayer surface charge was predicted by a 3-barrier-2-site model of energy profile for the permeation of $K^+$ ions. In conclusion, despite the differences in structure and fluidity of phospholipids in bilayers, the activities of maxi K channels in two charged membranes composed of PS or PI were strikingly similar and larger than those in bilayers of PE. These results suggest that the enhancement of conductance and $P_o$ of maxi channels is mostly due to negative charges in the phospholipid head groups.