• Nuclear Engineering and Technology
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• v.47 no.6
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• pp.678-699
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• 2015

Although the harsh space environment imposes many severe challenges to space pioneers, space exploration is a realistic and profitable goal for long-term humanity survival. One of the viable and promising options to overcome the harsh environment of space is nuclear propulsion. Particularly, the Nuclear Thermal Rocket (NTR) is a leading candidate for nearterm human missions to Mars and beyond due to its relatively high thrust and efficiency. Traditional NTR designs use typically high power reactors with fast or epithermal neutron spectrums to simplify core design and to maximize thrust. In parallel there are a series of new NTR designs with lower thrust and higher efficiency, designed to enhance mission versatility and safety through the use of redundant engines (when used in a clustered engine arrangement) for future commercialization. This paper proposes a new NTR design of the second design philosophy, Korea Advanced NUclear Thermal Engine Rocket (KANUTER), for future space applications. The KANUTER consists of an Extremely High Temperature Gas cooled Reactor (EHTGR) utilizing hydrogen propellant, a propulsion system, and an optional electricity generation system to provide propulsion as well as electricity generation. The innovatively small engine has the characteristics of high efficiency, being compact and lightweight, and bimodal capability. The notable characteristics result from the moderated EHTGR design, uniquely utilizing the integrated fuel element with an ultra heat-resistant carbide fuel, an efficient metal hydride moderator, protectively cooling channels and an individual pressure tube in an all-in-one package. The EHTGR can be bimodally operated in a propulsion mode of $100MW_{th}$ and an electricity generation mode of $100MW_{th}$, equipped with a dynamic energy conversion system. To investigate the design features of the new reactor and to estimate referential engine performance, a preliminary design study in terms of neutronics and thermohydraulics was carried out. The result indicates that the innovative design has great potential for high propellant efficiency and thrust-to-weight of engine ratio, compared with the existing NTR designs. However, the build-up of fission products in fuel has a significant impact on the bimodal operation of the moderated reactor such as xenon-induced dead time. This issue can be overcome by building in excess reactivity and control margin for the reactor design.

• Journal of the Korean Geotechnical Society
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• v.33 no.11
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• pp.73-82
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• 2017

Recently, offshore bucket cut-off walls were developed to solve several problems in conventional offshore cut-off walls. In this study, a numerical analysis was carried out to investigate the seepage stability of offshore bucket cut-off walls. The ground was assumed as uniform homogeneous sand and steady state flow conditions were applied. The flow condition was compared among 2-dimensional flow (2-D), 2-dimensional concentrated flow (2-DC), and axisymmetric flow. The analysis results showed that the seepage velocities in axisymmetric flow were about 1.5 and 2 times larger than those of 2-DC and 2-D flow conditions, respectively. Thereafter, the axisymmetric flow condition was applied because the seepage flow was concentrated toward the center of the circular-shaped wall. A parametric study was performed varying bucket radius, penetration depth, total head difference between in and outside of the wall. The exit gradient, which used for the calculation of piping stability, decreased with increase of the penetration depth and bucket radius. Design charts were proposed to estimate the factor of safety and the exit gradient at various analysis conditions. Finally, the design equation was proposed to calculate the exit gradient for the preliminary design of the bucket cut-off wall.

• Korean Journal of Comparative Education
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• v.27 no.3
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• pp.129-159
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• 2017

This study examines the social recognition of teachers' treatment and teaching profession through the comparison and analysis of the teachers' remuneration systems in the Republic of Korea(hereafter, Korea) and Canada. For this purpose, literature review and qualitative research were conducted. As a result of comparing and analyzing the orientation of teachers' remuneration systems in both countries and perception of teachers, the following differences were found. First, in terms of the management philosophy of the remuneration system, Korea emphasized the efficiency of the national competitiveness dimension, while Canada focused on the interrelationship with development of individual-oriented competency. Second, although the remuneration systems for teachers in both countries are quite different, they have aimed at establishing a reasonable remuneration system, which considers equality in common. But the position on equality was different between the two countries. In the case of Korea, equity was considered by comparing the pay scale with those of other government employees, while equity in Canada mainly had to do with gender equality. Third, the teachers of both countries regarded the sense of duty and ethics as important qualities of the teaching profession, and they recognized the social safety net as an indicator of their social status. However, there was a difference in attitude toward the teaching profession. In Korea, it was deemed to be a stable and socially desirable profession, but the entry barriers were quite high and the remuneration system was relatively rigid. In Canada, on the other hand, it was easy to enter the teaching profession and the remuneration system was far less rigid. But teachers were more likely to quit or take a second job, and their social status fluctuated.

• Nuclear Engineering and Technology
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• v.53 no.10
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• pp.3217-3228
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• 2021

Flow blockage of the fuel assembly in the lead-based fast reactor (LFR) may produce critical local spots, which will result in cladding failure and threaten reactor safety. In this study, the flow blockage characteristics were analyzed with the sub-channel analysis method, and the circumferentially-varied method was employed for considering the non-uniform distribution of circumferential temperature. The developed sub-channel analysis code SACOS-PB was validated by a heat transfer experiment in a blocked 19-rod bundle cooled by lead-bismuth eutectic. The deviations between the predicted coolant temperature and experimental values are within ±5%, including small and large flow blockage scenarios. And the temperature distributions of the fuel rod could be better simulated by the circumferentially-varied method for the small blockage scenario. Based on the validated code, the analysis of blockage characteristics was conducted. It could be seen from the temperature and flow distributions that a large blockage accident is more destructive compared with a small one. The sensitivity analysis shows that the closer the blockage location is to the exit, the more dangerous the accident is. Similarly, a larger blockage length will lead to a more serious case. And a higher exit temperature will be generated resulting from a higher peak coolant temperature of the blocked region. This work could provide a reference for the future design and development of the LFR.

• Journal of Bio-Environment Control
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• v.30 no.4
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• pp.377-382
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• 2021

Oriental melon (Cucumis melo L.) is generally cultivated on the ground by creeping culture. A farmer has a higher workload for training stems. This study was conducted to find out a new cultivation of oriental melon to reduce a workload and improve the quality of fruit. There were three treatments for training stem of oriental melon; upward stem growing, downward stem growing, control (creeping stem growing). The results of the plant growth and the net photosynthesis showed higher in upward stem growing. The root activity was higher in downward stem attract. The yield was not significant as 4,055kg/10a in upward stem attract and 3,983kg/10a in downward stem attract. According to the results of the ergonomic agricultural workload evaluation, in the case of the working posture, the working posture of creeping cultivation methods (squatting, bending) showed a higher risk level than the upward and downward cultivation methods. Therefore, it is recommended the upward stem attract of oriental melon is a new cultivation as well as an alternative method for creeping stem attract in terms of improving the plant growth and yield, and reducing the workload.

• Nuclear Engineering and Technology
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• v.53 no.6
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• pp.1942-1946
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• 2021

Gadolinium oxysulfide (GOS) is regarded as a novel scintillator for the realization of ultra-high spatial resolution in neutron imaging. Monte Carlo simulations of GOS scintillator show that the capability of its spatial resolution is towards the micron level. Through the time-of-flight method, the light output of a GOS scintillator was measured to be 217 photons per captured neutron, ~100 times lower than that of a ZnS/LiF:Ag scintillator. A detector prototype has been developed to evaluate the imaging solution with the GOS scintillator by neutron beam tests. The measured spatial resolution is ~36 ㎛ (28 line pairs/mm) at the modulation transfer function (MTF) of 10%, mainly limited by the low experimental collimation ratio of the beamline. The weak light output of the GOS scintillator requires an enormous increase in the neutron flux to reduce the exposure time for practical applications.

• 한국노년학
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• v.38 no.3
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• pp.627-643
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• 2018

This study aims to analyze gender differences in the prevalence of and risk factors for self-neglect among the elderly in South Korea. In order to investigate the differences between male and female elderly group, we compared 793 elderly men and 1,089 women from the data "Research on the Healthy Aging and Well-being of the Elderly" conducted in 2018. First, t-test and ${\chi}^2$-test and multiple regression analysis identified that gender differences in the prevalence of elder self-neglect was not statistically significant. Second, There are differences in risk factors affecting self-neglect between genders. age and class(perception) are the factors only affecting men. Income(monthly), having-religion, living-alone, satisfaction with life, social network are the ones only affecting women. Third, the risk factors for both men and women are depression and social support(public support). It is notable that we verify the empirical evidence supporting the hypothesis that risk factors for elder self-neglect may exist differently according to gender. In particular, gender characteristics revealed in this study can be reasonably explained through exchange theory and feminist theory. Therefore, we emphasize that the policy approach should be done depending on the gender of the elderly, and that the social safety net more paying attention to the depression of the elderly should be strengthened.

• Journal of Navigation and Port Research
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• v.43 no.4
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• pp.264-272
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• 2019

In this study, the rate of return on investment used as a proxy variable for the entity's value and financial structure (liability ratio) is related to positive balance. This is consistent with the Static Tradeoff Theory (STT) that the entity's value and financial structure are related to a positive balance because the capital expense of a debt (tax-saving effects) that is less than its equity cost before it is in financial difficulty. Also, operating profitability (EBITDA/Sales), investment safety, total asset growth, net working capital and depreciation expenses are related to negative (-) with financial structure (liability ratio). This is the result of an analysis consistent with the Pecking Order Theory (POT). Fuel costs, borrowing, total asset turnover, financial costs, and tangible asset ratios have a significant positive relationship with the debt ratio. This is consistent with the agency theory and confirms that excessive chartering expenses, such as the bankrupt H company, are the main factors that pressure the financial structure of Korean ocean carriers.

• 한국노년학
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• v.37 no.4
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• pp.853-870
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• 2017

This study examined the changes of depression and life satisfaction among the elderly living together in group-home and congregate housing. And in this course, it was to verify the practical effects of the recent government and local authority community life of elderly people by comparing them with the groups of elders living alone. The study was divided into Time 1 and Time 2, and 205 person's data were used for the final analysis. PASW Statistics 18.0 was utilized to analysis the data of this study, because it is difficult to explain the results of this analysis, secondary qualitative research has been used to identify additional contextual information. The major results of this study are as follows. First, the depression of the subjects was significantly improved in the case of living in group-home and congregate housing, and it was significantly worse in the group of elders living alone. Second, the life satisfaction of survey subjects was significantly improved when living in congregate housing, group-home was significantly worse, and the group of elders living alone were not statistically significant but slightly worse. Third, mixed research methods were applied to make accurate interpretation of changes of life satisfaction of the elderly living in group-home. Based on the results of this study, it is possible to establish appropriate measures for the elderly to improve early adjustment and quality of life in community life. And the community life of the elderly can contribute to a real social safety net by solving the blind spot of welfare. At the national level, it can be utilized as a standard reference to improve and strengthen existing policies by providing data that can simultaneously examine the performances and problems of various policies related to housing or the welfare of the elderly.

• Journal of Digital Convergence
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• v.16 no.12
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• pp.635-640
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• 2018

The study conducted a Focus Group Interview (FGI) on college students to identify single-person households and Solitary Deaths of single-person households recognized by college students. This can be provided as basic data to address problems in single-person households and social problems such as future youth solitary death and will contribute to building a social safety net. This study conducted FGI to analyze data for five fourth graders majoring in social welfare. In the case of involuntary independent living, the high poverty and unemployment rate of single-person households was cited as the cause of economic instability, housing problems and emotional relationship formation. He said that he thinks about young loneliness because he has vague fears about what happens in the media and what can happen to them. As the number of young single-person households will inevitably increase in the coming months and economic difficulties are the biggest problem and the biggest cause of young solitude, institutional support is needed first, especially for housing costs.