• Korean Journal of Materials Research
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• v.28 no.11
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• pp.640-645
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• 2018

The design of non-precious electrocatalysts with low-cost, good stability, and an improved oxygen reduction reaction(ORR) to replace the platinium-based electrocatalyst is significant for application of fuel cells and metal-air batteries with high energy density. In this study, we synthesize iron-carbide($Fe_3C$) embedded nitrogen(N) doped carbon nanofiber(CNF) as electrocatalysts for ORRs using electrospinning, precursor deposition, and carbonization. To optimize electrochemical performance, we study the three stages according to different amounts of iron precursor. Among them, $Fe_3C$-embedded N doped CNF-1 exhibits the most improved electrochemical performance with a high onset potential of -0.18 V, a high $E_{1/2}$ of -0.29 V, and a nearly four-electron pathway (n = 3.77). In addition, $Fe_3C$-embedded N doped CNF-1 displays exellent long-term stabillity with the lowest ${\Delta}E_{1/2}=8mV$ compared to the other electrocatalysts. The improved electrochemical properties are attributed to synergestic effect of N-doping and well-dispersed iron carbide embedded in CNF. Consequently, $Fe_3C$-embedded N doped CNF is a promising candidate for non-precious electrocatalysts for high-performance ORRs.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.39 no.1
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• pp.227-237
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• 2019

In terms of the concept of space in urban planning and design, the modern city approaches from the perspective that all spaces are made up of different places based on identity. In this study, we analyzed disparate image by paying attention to the difference between the individual spaces that form the city. And the physical and behavioral factors that respond to the disparate spatial images are derived through legibility measurement. As a result, the urban space in Busan has disparate images such as closure, openness, dynamic + closure, dynamic + openness, quiet space. The following are the legibility factors that make each image stronger. The elements of closure are high-density and high-rise buildings, residence, work, openness appeared as a factor of water space, walking and viewing. Dynamic & Closure is the element of industrial activity, dynamic & openness is open space, water space, swimming element, quiet space image is green space, walking, stay factor.

• Journal of radiological science and technology
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• v.41 no.6
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• pp.595-602
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• 2018

Quality control (QC) of Computed Tomography (CT) devices is based on image quality measurement on AAPM CT phantom which is a standard phantom. Although it is possible to control the accuracy of the CT apparatus, it is expensive and has a disadvantage of low penetration rate. Therefore, in this study, we make image quality measurement phantom at low cost using FFF (Fused Filament Fabrication) type three-dimensional printer and try to analyze the usefulness, compare it with existing standard phantom. To print a phantom, We used three-dimensional printer of the FFF system and PLA (Poly Lactic Acid, density: $1.24g/cm^3$) filament, and the CT device of 64 MDCT (Aquilion CX, Toshiba, Japan). In addition, we printed a phantom using three-dimensional printer after design using various tool based on existing standard phantom. For image quality evaluation, AAPM CT phantom and self-generated phantom were measured 10 times for each block. The measured data were analyzed for significance using the Mannwhiteney U-test of SPSS (Version 22.0, SPSS, Chicago, IL, USA). As a result of the analysis, phantom fabricated with three-dimensional printer and standard phantom showed no significant difference (p>0.05). Furthermore, we confirmed that image quality measurement performance of a phantom using three-dimensional printer is similar to the existing standard phantom. In conclusion, we confirmed the possibility of low cost phantom fabrication using three dimensional printer.

• Journal of IKEEE
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• v.23 no.2
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• pp.425-430
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• 2019

This work describes the design and characterization of a X-band power amplifier (PA) monolithic microwave integrated circuit (MMIC) using a $0.25{\mu}m$ gate length gallium nitride (GaN) high electron mobility transistor (HEMT) technology. The developed X-band power amplifier MMIC has small signal gain of over 22.7 dB and saturated output power of 43.02 dBm (20.04 W) over the entire band of 9 to 10 GHz. Maximum saturated output power is a 43.84 dBm (24.21 W) at 9.5 GHz. Its power added efficiency (PAE) is 41.0~51.24% and the chip dimensions are $3.7mm{\times}2.3mm$, generating the output power density of $2.84W/mm^2$. The developed GaN power amplifier MMIC is expected to be applied in a variety of X-band radar applications.

• Geomechanics and Engineering
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• v.17 no.1
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• pp.81-95
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• 2019

Due to the importance of soil reinforcement using geotextiles in geotechnical engineering, study and investigation into long-term performance, design life and survivability of geotextiles, especially due to installation damage are necessary and will affect their economy. During installation, spreading and compaction of backfill materials, geotextiles may encounter severe stresses which can be higher than they will experience in-service. This paper aims to investigate the installation damage of geotextiles, in order to obtain a good approach to the estimation of the material's strength reduction factor. A series of full-scale tests were conducted to simulate the installation process. The study includes four deliberately poorly-graded backfill materials, two kinds of subgrades with different CBR values, three nonwoven needle-punched geotextiles of classes 1, 2 and 3 (according to AASHTO M288-08) and two different relative densities for the backfill materials. Also, to determine how well or how poorly the geotextiles tolerated the imposed construction stresses, grab tensile tests and visual inspections were carried out on geotextile specimens (before and after installation). Visual inspections of the geotextiles revealed sedimentation of fine-grained particles in all specimens and local stretching of geotextiles by larger soil particles which exerted some damage. A regression model is proposed to reliably predict the installation damage reduction factor. The results, obtained by grab tensile tests and via the proposed models, indicated that the strength reduction factor due to installation damage was reduced as the median grain size and relative density of the backfill decreases, stress transferred to the geotextiles' level decreases and as the as-received grab tensile strength of geotextile and the subgrades' CBR value increase.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.18 no.1
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• pp.24-30
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• 2019

The deck floor of a the cargo truck becomesis damaged and aged due to the continuous loading of the loading cargo and external environmental factors. Floor boards made of wood and metal are often used. In the case of wood, the cost is high due to the use of imported wood, and the strength is easily deterioratesd due to environmental factors. In the case of metal materials, the durability is higher than that of wood, but problems are raised due to the effect of major factors that hinder the weight reduction, and the effects of corrosion. In order to replace this stucturestructural design, this study proposed a wood fiber composite using natural raw materials. Woody composites are being used as environmentally and friendly exterior materials with the combined advantages of plastic, and wood,; low cost and low density. However, due to the nature of the woody composites, the properties are differentdiffer depending on the contents of the matrix, reinforcing agent, additives, compatibilizer, etc. In this study, we investigate these problems through analysis of the microstructure and mechanical properties according to proper content and injection molding conditions. As a result, it is considered that the wood deck composite can replaced the current Deck Floor Boardreplace current deck floor boards through continuous continued research and results of this study.

• Journal of Korean Society for Quality Management
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• v.46 no.4
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• pp.899-910
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• 2018

Purpose: Generally, since the population density is lower in suburban areas, the distance to school is inevitably long. Therefore, schools in suburban areas often operate school buses to improve student welfare. However, since school buses are usually used only during going to and from school, the utilization rates are relatively low. Therefore, this study aims to establish integrated operation plan of public school bus covering all schools. Methods: It is necessary to decide which school buses will serve the specific demand node which want to go to certain school in order to design an integrated operation plan for school buses. Therefore, a mathematical model is developed for minimizing the total number of vehicles and the distance of transportation by reflecting the characteristics of school buses and students as constraints. To solve the proposed mathematical model, CPLEX, a commercial solver, is applied. Results: To validate and to confirm the proposed process, numerical example is designed with the comparison between before and after integrated operations of school buses in terms of total operation cost. The result shows that the integrated operation can lead the reduction of the number of school buses as well as the decreasing of the fuel cost. Conclusion: This study provides the quantitative method to perform the integrated operation of school buses in suburban areas. The optimal operation strategy is required because there are more complex decision-making elements considering the integrated operation. It is expected to apply this research result at real situation to expand this services based on an optimal operation.

• Journal of the Architectural Institute of Korea Planning & Design
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• v.34 no.6
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• pp.57-66
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• 2018

In Japan, apartment housing occupies a great proportion of residence due to high population density like Korea. Although Korea and Japan are similar in big proportions of apartment housing, and apartment housing management systems and utilization behaviors, there are considerable differences. This paper examined Japanese public facilities and the status of public facility management and utilization, which differ from those in Korea. In order to analyze the status of public facilities from a perspective of management companies, a preliminary survey was conducted targeting apartment management companies in the top 100 and a field study on public facilities was conducted targeting chief directors and managers of individual housing facilities to look into public facility utilization methods, problems with public facility management, demands of residents, and utilization situations. Also, the present state of facility utilization and utilization promotion plans were investigated, based on the drawings of facilities collected. As the result, results were found in three respects; 'elements, related to building plans', 'elements, related to utilization promotion', and 'elements, related to facility remodeling, including changes of uses'. In relation to the use of public facilities in the future, a more active communication between managers and users would be needed for planning. Also, there would be a need to provide public facilities for visitors when there are events for both occupants and visitors in order to promote the use of facilities and management companies would have to share information of excellent facility models.

• Journal of the Architectural Institute of Korea Planning & Design
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• v.35 no.2
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• pp.127-137
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• 2019

Low-rise residential community is the most popular type (51%) of residential neighborhoods in Seoul. Currently, there is a shortage of public facilities needed for living conditions and the quality of life in low-rise residential areas. This study defines 'public facility' as infrastructure to improve the living environment and used by residents jointly in low-rise residential areas. In this regard, this study analyzes current legal and institutional standards, latest trends in public facility of apartments, and residents' demand and satisfaction level in order to find out the criteria for installation of priority public facilities. As a result, the essential facility basically conforms to the number of household which is the standard of the facility supply in apartment. However, considering the limitations on the accessibility due to low density, it should consider two standards at the same time: the number of household and distance (radius of neighborhood). In conclusion, it is necessary to install legally prescribed facilities according to the number of household and distance: 500 households facilities in 250m radius neighborhood and 1,000 households facilities in 400m radius neighborhood. Also, considering the reality of low-rise residential area, it is necessary to integrate some facilities that can be functionally linked to improve level of utility and efficiency of operation and management. It is expected that the output of this study can be applied to institutionalize of the legal basis for the public facility of low-rise residential community.

• Journal of the Architectural Institute of Korea Planning & Design
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• v.36 no.1
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• pp.49-60
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• 2020

Although the number of child loss in commercial facilities has been growing recently, the prevention method for child loss are still lacking in the environmental aspect. This research examines the causes of lost child in behavioral aspects in order to develop a guideline to prevent child loss in U.E.C. The observational study on the behaviors of guardians and children was conducted in the U.E.C that is visited by many customers accompanied with children. Then the results of the observational study were marked on the behavioral maps. After analyzing the behavioral maps, the causes of child loss were determined by classifying into behaviors by age and behaviors by functional space. As a result, when guardian is unable to pay attention to child by doing something else such as making a purchase, or an inquiry, child may lose guardian by going towards the interesting factors or playing around. Moreover, if the spaces related to children are located at the node with high pedestrian density and open structure or the environment that is hard for the guardians to watch over their children, it will be easy for guardians to be inattentive to their children, and get separated from each other.