• School Mathematics
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• v.18 no.1
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• pp.215-229
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• 2016

This study aims to identify Archimedes' idea used while proving proposition 23 in 'Quadrature of the Parabola' and to provide an alternative way for finding the sum of geometric series without applying the concept of limit by extending the idea though metaphor. This metaphorical model is characterized as static and thus can be complimentary to the dynamic aspect of limit concept adopted in Korean high school mathematics textbooks. In addition, middle school students can understand $0.999{\cdots}=1$ with this model in a structural way differently from the operative one suggested in Korean middle school mathematics textbooks. In this respect, I argue that the metaphorical model can be an useful educational tool for Korean secondary students to overcome epistemological obstacles inherent in the concepts of infinity and limit by making it possible to transfer from geometrical context to algebraic context.

• Journal of the Korean Institute of Gas
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• v.16 no.2
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• pp.60-66
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• 2012

With diversification of research and development activity according to fusion of state-of-the-art technology, potential hazard and risk factors in new forms have been increased in the laboratories. Also, as there are many cases where the experimental condition is extremely high/low temperature and pressure, many many accidents producing loss of life and/or injuries occur due to the extreme condition. In this study, The common fact questionnaire as the survey tool for the establishment of the accident prevention countermeasure in laboratory have been developed to safety security of the laboratory workers. The current status of chemical materials and the realization of important on laboratory safety management using the questionnaire investigated by an electronic mail and visiting survey in the laboratories and universities. The collected data was analyzed with Excel program and it can be utilized as basic data for accident prevention in laboratories.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.942-944
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• 2017

High-speed vehicles are subjected to complex loads, such as acoustic pressure from the engine at launch and aerodynamic heating and aerodynamic pressure during flight. A thermal protection system panel is required to protect internal systems such as the fuel tank of the vehicle from the external environment. This study defines analytical models for heat transfer and thermal structure characteristics of the thermal protection system panel. Furthermore, the study performed parameters analysis to achieve the thermal structural integrity and to make it lighter.

• Journal of the Mineralogical Society of Korea
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• v.23 no.4
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• pp.315-329
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• 2010

Characteristics of thermophilic bacteria and secondary materials on the pyrrhotite surface were investigated by using scanning electron microscopy (SEM). The thermophilic bacteria from an acid hot spring in Japan were incubated with pyrrhotite at $42^{\circ}C$, $52^{\circ}C$, and $62^{\circ}C$ respectively. SEM analysis of the reacted pyrrhotite showed that indigenous rod-shaped bacteria ranging from $0.4{\times}1.5{\mu}m$ to $0.3{\times}11.9{\mu}m$ in size were attached to the pyrrhotite surface at these temperatures with formation of secondary materials. Extracellular polymer substances were formed on the bacterial surface. We suggest that these polymers functioned as a capsule protecting bacteria from the extreme environment. Secondary materials such as elemental sulfur, Fe-hydroxide, S-Fe and O-P-Fe compounds were found on the pyrrhotite surface.

• Journal of the Korean Geotechnical Society
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• v.19 no.2
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• pp.237-246
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• 2003

The driven pile has environmental problems such as vibration and noise. Especially, if the site consists of gravel, cobble and weather rock, the driven pile can not be applied. Therefore, the application of the drilled shafts is increasing in Korea. However, the bearing capacity values by the suggested theoretical formulas are generally considered too conservative. In this paper, static load tests for the rock socketed drilled shaft at Gwangandaero and Suyeong3hogyo are performed and in order to estimate the side friction of the shaft, strain gauges are applied. The bearing capacities from the field test data and the bearing capacity values by the theoretical formula are compared. Even the static load tests didn't reach to the ultimate bearing capacity condition, and all the measured bearing capacity values were higher than those by the theoretical formulas. The field data also showed that the major bearing capacities were not due to end bearings but side friction resistances. Based on the above results, several suggestions are proposed for the drilled shaft design.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.21 no.7
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• pp.842-849
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• 2010

This paper deals with a TT&C circularly polarized turnstile antenna for LEO satellites. The turnstile antenna consists of radiator for radiating power to free-space and power divider for generating circularly polarized wave. we presents a radiator to tolerate in space environments and a power divider to provide flat phase difference at wide bandwidth. The bandwidth of the proposed antenna covers the frequency bands of up- and down-link. The antenna shows wide beamwidth and enhanced axial ratio for unfavorable space environments.

• Microbiology and Biotechnology Letters
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• v.40 no.3
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• pp.268-273
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• 2012

Microbial diversity analyses were performed in several geothermal areas in Indonesia using a culture-independent approach with 16S rRNA gene sequencing. All areas and the majority of samples were noted as being affiliated with Proteobacteria. In addition, unclassified bacteria with no phylum affiliation were detected at an incidence rate of 20.0-26.5% in every location. The majority groupings in the geothermal hot stream in Cisolok belonged to ${\beta}$-Proteobacteria (27.1%) and Cyanobacteria (11.0%), whereas the majority from the volcanic area in Kamojang was ${\gamma}$-Proteobacteria (51.5%) followed by Aquificales (12.9%). The predominant groups around an underwater thermal vent in the sea at Likupang were ${\gamma}$-Proteobacteria (33.3%) and then Bacteroidetes (27.6%). This detailed microbial community analyses of each area strongly support a possible association with plausible community groups and environmental habitats, such as extremely geothermal or marine habitats. This study has significantly contributed to the expansion of scientific knowledge of the microbial community in Indonesia.

• Journal of the Korean Institute of Gas
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• v.13 no.6
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• pp.15-20
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• 2009

The number of compressed natural gas (CNG) vehicles have increased gradually by virtue of korea government's urban air quality improvement policy since 1998. Although the use of CNG as transportation fuel gives environmental benefits, there is a possibility of huge accidents from unexpected fire. Therefore, needs for the guarantee of safety are indispensible for the reliable operation of CNG vehicles. A check valve is a safety device which prevents leakage of the pressurized fuel charged in a fuel tank. Durability of this component should be guaranteed in spite of repeated operation. This research has performed durability tests of a CNG check valve regarding the repeated usage, extreme chattering, and the effect of compressor oil.Although a check valve used for CNG vehicle satisfies validation requirements in the test results, it has been found that problem in the function of leakage prevention in a check valve could take place in the case of prolonged exposure to compressor oil.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.12
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• pp.1567-1572
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• 2013

To supply electric power in certain extreme environments such as a spacecraft or in military applications, a radioisotope thermoelectric generator has been highlighted as a useful energy source owing to its high energy density, long lifetime, and high reliability. A radioisotope thermoelectric generator generates electric power by using the heat energy converted from the radioactive energy of a radioisotope. In this study, FE analyses such as radiation shield analysis, heat transfer analysis, and power recovery rate analysis have been carried out to achieve an optimal design for a radioisotope thermoelectric generator using $SrTiO_2$.

• Journal of the Korean Society for Nondestructive Testing
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• v.36 no.3
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• pp.202-210
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• 2016

A thermal barrier coating (TBC) has been widely applied to machine components working under high temperature as a thermal insulator owing to its critical financial and safety benefits to the industry. However, the nondestructive evaluation of TBC damage is not easy since sensing of the microscopic change that occurs on the TBC is required during an evaluation. We designed an eddy current probe for evaluating damage on a TBC based on the finite element method (FEM) and validated its performance through an experiment. An FEM analysis predicted the sensitivity of the probe, showing that impedance change increases as the TBC thermally degrades. In addition, the effect of the magnetic shield concentrating magnetic flux density was also observed. Finally, experimental validation showed good agreement with the simulation result.