• Journal of the Society of Disaster Information
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• v.10 no.1
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• pp.61-70
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• 2014

Synthetic fiber reinforced concrete is applicable to many applications for construction material. In general, synthetic fibers have low tensile strength and elastic modulus, but they have many advantages such as high crack resistance, impact resistance, chemical resistance, flexural behavior and corrosion free in fiber reinforced concrete. Recently, fiber reinforced concrete with macro synthetic fibers has been used to improve performance of structures in tunnel shotcrete, precast segmental lining and bridge slab and precast concrete structures. This study investigated the influence of bundled type polyamide fiber reinforced concrete on the flexural behavior in accordance with ASTM C 1609 and KS F 2566 standards.

• Journal of Korea Foundry Society
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• v.4 no.2
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• pp.96-101
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• 1984

The morphologies of eutectic cell formed during solidification affect on the mechanical properties in high Cr cast iron. In order to investigate the influence of Si on the structure, five kinds of specimen containing 16.42% Cr with varying amount of Si (0.51%, 1.17%, 2.22%, 2.71%, 3.56%) were poured into shell mould preheated $330^{\circ}C$ at $1510^{\circ}C$. The effect of Si on matrix in hypo-eutctic Cr cast iron (2.48% C, 16.42%) were studied through its mechanical tests and observation of microstructure using of metallurgical microscope, EPMA, SEM and Image analyzer systematically. The results obtained from the above studies are as follows: 1. Because of ${\Delta}T$ decreasing with increasing Si content, the morpologies of colony change into uniform bar-type carbide from plate-type ones, moreover eutectic colony size (Ew) becomes narrow and spacing of carbide wider. 2. As Si content increases, the amount of carbides also increases and most of Cr were dissolved in carbides while Si in matrix. 3. The hardness, tensile strength and wear resistance were increasing while impact value decreased with increasing Si content. 4. In fracture section, small amount of dimple pattern was observed in less than 1.17% Si but more than 2.22% Si river pattern was presented.

• International Journal of Naval Architecture and Ocean Engineering
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• v.6 no.4
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• pp.922-934
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• 2014

In casting steels for offshore construction, manufacturing integral casted structures to prevent fatigue cracks in the stress raisers is superior to using welded structures. Here, mold design and casting analysis were conducted for integral casting steel. The laminar flow of molten metal was analyzed and distributions of hot spots and porosities were studied. A prototype was subsequently produced, and air vents were designed to improve the surface defects caused by the release of gas. A radiographic test revealed no internal defects inside the casted steel. Evaluating the chemical and mechanical properties of specimens sampled from the product revealed that target values were quantitatively satisfied. To assess weldability in consideration of repair welding, the product was machined with grooves and welded, after which the mechanical properties of hardness as well as tensile, impact, and bending strengths were evaluated. No substantive differences were found in the mechanical properties before and after welding.

• Journal of Power System Engineering
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• v.16 no.5
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• pp.76-82
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• 2012

Duplex stainless steels have the dual microstructure of austenite and ferrite phases. This steel exhibits generally a high corrosion resistance and higher mechanical strength compared with austenitic stainless steels. The steels used in the investigation have the chemical composition of Fe-22Cr-xNi-yMn-0.2N in which the contents of Ni and Mn were varied with maintaining the equal [Ni/Cr] equivalent. The fraction of ferrite phase was increased with the increase of annealing temperature. The impact factor of Mn element on the [Ni] equivalent was amended on the basis of the results of the investigation. 4Mn-2Ni alloy showed the highest pitting corrosion resistance. The fraction ratio, grain size and misorientation angle between grains were measured, and the correlation with pitting potential was investigated.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2015.05a
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• pp.185-186
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• 2015

The use of non-bearing lightweight wall has increased recently due to the increase of high-rise buildings and supply of long-life housing. Lightweight wall has advantages such as reducing the self-weight of the building, convenience in installation, and shortening construction period, however, must have a sufficient strength to external force. This study standardized the stiffness (static horizontal load resistance) test method for lightweight walls by using the actual impact load obtained through the load analysis test conducted in the previous studies. The size of specimen was set up as height 2.4m and width 3.0m. Test apparatus and test methods were referred to BS 5234-2:1992. However, the loading level applied to the specimen was divided into 3 steps (3000N, 1000N, 500N) that can be applied selectively depending on the purpose of the wall. The deformation characteristics according to the same loading level were vary depending on the specimen's type, and the evaluation criteria for functional damage may vary depending on the material, method of construction, and purpose of wall. Therefore, we did not suggest unified evaluation criteria of the stiffness to the test results.

• Elastomers and Composites
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• v.55 no.1
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• pp.46-50
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• 2020

Material extrusion (ME)-type 3D printing is the most popular among the 3D printing processes. In this study, the cross-section morphologies of ME-type 3D printing manufactured specimens were observed with respect to the thermal properties of the material. The cross-section morphology of a specimen is related to the deposition strength, and the outside profile of the cross-section is related to the surface roughness. The filaments used in this study, with different thermal conductivities, were the acrylonitrile-butadiene-styrene (ABS), the high impact polystyrene (HIPS), the glycol-modified polyethylene terephthalate (PETG), and the polylactic acid (PLA). The cross-sections and the surfaces of the 3D manufactured specimens were examined. In ME-type 3D printing, the filaments are extruded through a nozzle and they form a layer. These layers rapidly solidify and as a result, they become a product. The thermal conductivity of the material influences the cooling and solidification of the layers, and subsequently the cross-section morphology and the surface roughness.

• Journal of Aerospace System Engineering
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• v.11 no.6
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• pp.1-9
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• 2017

The ICS, Intercom is the equipment which mixes and distributes the audio signal from other LRUs and plays the Voice Messages. Henceforth, it is of immense contributory importance to the pilots. Especially, the audio routing, which controls On/Off mode of each audio channel, is significant in executing a pilots' mission. But the audio routing process is quite complicated as it has the interface combination of many control signals. Underthecondition, the exceptional handling becomes difficult, which decreases maintainability and productivity. In the present work, to prevent such a situation, the author suggests amethodology,whichwillhavealower impact when the software is changed and provides high maintainability and productivity for audio routing processing.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.21 no.3
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• pp.27-40
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• 2013

Rotorcraft operating in the domestic aviation safety techniques are applied CRM training is conducted but, aircraft accidents caused by human factors has not shown a declining trend. Thus, knowledge of aviation safety and human factors for the spread of awareness of improved rotorcraft flight operations department managers to understand the complexity of nature and culture, and to perform high-risk mission helicopter pilot study of local activation and enhance safety awareness research was conducted in order to. In this study, the development direction of CRM training studies in order to identify the leading NOTECHS (Non-Technical Skills; non-technical pilot skills) of the four categories as the independent variable and the dependent variable corresponding to the resulting effect on the key variables awareness of the differences were studied. In addition, the direction and strength of the relationship were analyzed to determine the relationship of each independent variable to assess the impact on the dependent variable regression analysis was performed. Pilot training and evaluation of non-technical skills related to the teaching reflected in the CRM training and assessment must be carried out with 5 star rating scale was preferred. Therefore, to meet our country rotorcraft operating environment 'NOTECHS' aviation safety by developing training programs reflected in the educational process, implementation, and periodic training and assessment is done in future research on this analysis and feedback is done to reflect the specific performance expect.

• The Korean Journal of Physiology and Pharmacology
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• v.19 no.4
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• pp.341-347
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• 2015

This study analyzed the effect of regular Taekwondo training for 16 weeks on physical fitness and growth index depending on different IGF-1 gene polymorphisms. The subjects of the study were 44 male students who were 8 year years old. The IGF-1 gene showed the highest frequency of 18 CA repeat (190 bp) in 50% of subjects, and was found in the homozygote (n=11), heterozygote (n=22) and non-carriers (n=11). The results of the physical fitness and growth index among the gene polymorphism groups indicated no significant differences but the expected height of the non-carrier group was significantly high (p<0.05). After Taekwondo training, the homozygote group and the non-carrier groups demonstrated significant (p<0.05) increase in grip strength and in time in the standing with one leg while closing eyes test, respectively. Only the homozygote group had a significant (p<0.05) increase in thigh circumference. IGF-1 concentration significantly (p<0.05) increased in the heterozygote group, while HOMA-IR significantly (p<0.05) decreased in the homozygote group. Furthermore, there was a significant (p<0.05) decrease in glucose in both the homozygote and the non-carriers groups. The difference between physical fitness and growth index depending on the IGF-1 gene polymorphism after Taekwondo training did not show consistent impact.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.05a
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• pp.321-324
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• 2005

The main purpose of the present study has been placed on investigating the effects of controlled rolling and cooling on the microstructures and mechanical properties of C-Si-Mn-V steels for cold forming. The steels were manufactured in vacuum induction melting(VIM) furnace and casted to 1.1ton Ingots and the ingots were forged to $\Box150$ billet. The forged billets were reheated in walking beam furnace and rolled to coil, the stocks were rolled by Controlled Rolling and Cooling Technology (CRCT), so rolled at low temperature by water spraying applied in rolling stage and acceleratly cooled before coiling. Rolled coils were cold drawed to the degree of $27\%$ of area reduction without heat treatment. Microstructual observation, tensile test, compression test and charpy impact tests were conducted. The mechanical properties of the steels were changed by area reduction of cold drawing and it is founded that there are optimum level of cold drawing to minimize compression stress for these steels. From the result of this study, it is conformed that mechanical properties and microstructure of C-Si-Mn-V steels for cold forming were enhanced by accelerated cooling and founded optimum level of cold drawing.