• Journal of Korean Academy of Nursing
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• v.35 no.3
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• pp.621-630
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• 2005

Purpose: The purpose of this study was to -retrospectively describe the childhood sports activity level of Korean adult men and women and to determine whether a higher level of childhood sports activity was positively associated with adult bone mineral density. Methods: A cross-sectional study of 100 Korean men (n=40) and women (n=60) was completed. Participants completed a detailed lifetime sports activity questionnaire and had their bone mineral density of the femur and lumbar spine measured using dual energy x-ray densitometry (DEXA). All sports activities were classified into four categories of peak strain score on the basis of ground reaction forces (GRF). Results: During the age of high school, women and men who participated in a high intensity sports activity demonstrated higher bone density in the femur site after adjustment for the effects of body weight, fat body mass, lean body mass, the level of calcium intake, and breast feeding period than those who did not participate in sports activity at all. Conclusion: These results highlight the need to participate in high intensity sports activity during high school age as a means of increasing peak bone mass in the femur site.

• Journal of Nutrition and Health
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• v.29 no.6
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• pp.590-593
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• 1996

This study was done to evaluate the effect of dietary calcium level (a diet which met 100% or twice the calcium level in AIN-76 diet) on preventing bone loss in ovariectomized rats. Forty Sprauge-Dawley female rats(body weight 200$\pm$5g)were divided into two groups. One group were ovariecotomized (Ovx) while the others received sham operation(Sham). Thereafter, each rat group was further divided into normal calcium diet(0.52%) and high calcium diet(1.04%) subgroups. All rats were fed on experimental diet and deionized water ad libitum for 8 weeks. The total body, spine and femur bone mineral densities and bone mineral contents were measured by Dual Energy X-ray Absorptiometry, Eight weeks following operation, ovariectomized rats fed a high calcium diet had a significantly higher total bone mineral content, total bone calcium content, spine bone mineral density, spine bone mineral content and femur bone mineral content than ovariectomized rats fed control calcium diet. The correlation between dietary calcium intake level and spine bone mineral density were positive, but there was no correlation between dietary calcium intake and femur bone mineral density. The findings from the present study demonstrated that bone loss due to ovarian hormonal deficiency can be partially prevented by a high calcium diet. Futhermore, these findings support the strategy of the use of a high calcium diet in the prevention of estrogen depleted bone loss(postmenopausal osteoporosis)

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.20 no.8
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• pp.42-51
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• 2021

Investigations of process parameters are essential when fabricating high-quality parts using additive manufacturing. This study investigates the change in the mechanical characteristics of a SUS316L specimen fabricated using selective laser melting based on the energy density and bead overlap ratio. The SUS316L powder particles were spherical and 35 ㎛ in size. Single-bead and hexahedral shape deposition experiments were performed sequentially. A single bead experiment was performed to obtain the bead overlap ratios for different laser parameters utilizing laser power and scan speed as experimental parameters. A hexahedral shape deposition experiment was also performed to observe the difference in mechanical properties, such as the internal porosity, surface roughness, and hardness, based on the energy density and bead overlap ratio of the three-dimensional printed part. Laser power, scan speed, overlap ratio, and layer thickness were chosen as parameters for the hexahedral shape deposition experiment. Accordingly, the energy density applied for three-dimensional printing, and the experimental parameters were calculated, and the energy density and bead overlap ratio for fabricating parts with good properties have been suggested.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 1989.10a
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• pp.19-24
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• 1989

The electron energy distribution function in mercury discharge positive columns are calculated numerically from the Boltzmann eqation under a set of parameters, such as the electron temperature to. the atomic temperature Tw. the electron number density no. and the electric field E. Especially, using the approximation that collision cross sections only depend on the energy, the calculated electron energy distribution function was shown that it falls off rapidly in the high energy tail.

• Nuclear Engineering and Technology
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• v.47 no.3
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• pp.380-387
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• 2015

A lead slowing-down spectrometer (LSDS) system is a promising nondestructive assay technique that enables a quantitative measurement of the isotopic contents of major fissile isotopes in spent nuclear fuel and its pyroprocessing counterparts, such as $^{235}U$, $^{239}Pu$, $^{241}Pu$, and, potentially, minor actinides. The LSDS system currently under development at the Korea Atomic Energy Research Institute (Daejeon, Korea) is planned to utilize a high-flux ($>10^{12}n/cm^2{\cdot}s$) neutron source comprised of a high-energy (30 MeV)/high-current (~2 A) electron beam and a heavy metal target, which results in a very intense and complex radiation field for the facility, thus demanding structural shielding to guarantee the safety. Optimization of the structural shielding design was conducted using MCNPX for neutron dose rate evaluation of several representative hypothetical designs. In order to satisfy the construction cost and neutron attenuation capability of the facility, while simultaneously achieving the aimed dose rate limit (< $0.06{\mu}Sv/h$), a few shielding materials [high-density polyethylene (HDPE)eBorax, $B_4C$, and $Li_2CO_3$] were considered for the main neutron absorber layer, which is encapsulated within the double-sided concrete wall. The MCNP simulation indicated that HDPE-Borax is the most efficient among the aforementioned candidate materials, and the combined thickness of the shielding layers should exceed 100 cm to satisfy the dose limit on the outside surface of the shielding wall of the facility when limiting the thickness of the HDPE-Borax intermediate layer to below 5 cm. However, the shielding wall must include the instrumentation and installation holes for the LSDS system. The radiation leakage through the holes was substantially mitigated by adopting a zigzag-shape with concrete covers on both sides. The suggested optimized design of the shielding structure satisfies the dose rate limit and can be used for the construction of a facility in the near future.

• Membrane Journal
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• v.12 no.3
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• pp.171-181
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• 2002

The parameter which determines the plateau length of current-voltage curve for ion- exchange membranes was studied at various concentrations of NaCl and different flow rates. Moreover, the feasibility of the electrodialytic removal of 0.1 M NaCl solution at various current densities was tested by assessing the electrodialysis performance parameters such as salt removal efficiency, current efficiency, energy consumption and water dissociation. The diffusion boundary layer (DBL) thickness decreased with the NaCl concentration and flow rate of fled solution and it was observed that the plateau length of current-voltage curves was related with the DBL thickness. The removal efficiency and current efficiency were not affected significantly by the current densities even at the overlimiting current region indicating that most current were passed by electrolyte, and water dissociations are not responsible for the overlimiting current. Energy consumption increased when the current density supplied exceeded the limiting current density (LCD) values, because additional energy was necessary to overcome the plateau potential. Beyond the LCD values the energy consumption required to get a certain removal efficiency was not affected by the current density applied. The result suggests that it is allowed to operate electrodialysis processes at as high as possible current density unless water-splitting does not occur.

• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
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• v.5B no.2
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• pp.181-188
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• 2005

In this paper, a DC smoothing filterless soft switching pulse modulated high frequency AC power conversion circuit connected to utility. frequency AC power source is proposed for consumer induction heating hot water producer, steamer and super heated steamer. The operating principle of DC link filterless utility frequency AC-high frequency AC (HF AC) power conversion circuit defined as high frequency cycloinverter is described, which can operate under a principle of ZVS/AVT and power regulation based on alternate asymmetrical PWM in synchronization with the utility frequency single phase AC positive or negative half wave voltage. The dual mode modulation control scheme based on high frequency PWM and commercial frequency AC voltage PDM for the proposed high frequency cycloinverter are discussed to enlarge its soft switching commutation operating range for wide HF AC power regulation. This high frequency cycloinverter is developed for high frequency IH Dual Packs Heater (DPH) type boiler used in consumer and industrial fluid pipeline systems. Based on the experiment and simulation results, this high frequency cycloinverter is proved to be suitable for the consumer use IH-DPH boiler and hot water producers. The cycloinverter power regulation and power conversion efficiency characteristics are evaluated and discussed.

• Proceedings of the Materials Research Society of Korea Conference
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• 1998.11a
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• pp.125-125
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• 1998

No Abstract.see full/text

• Nuclear Engineering and Technology
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• v.55 no.5
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• pp.1742-1756
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• 2023

The hydrogen behavior in a nuclear containment vessel is a significant issue when discussing the potential of hydrogen combustion during a severe accident. After the Fukushima-Daiichi accident in Japan, we have investigated in-depth the hydrogen transport mechanisms by utilizing experimental and numerical approaches. Computational fluid dynamics is a powerful tool for better understanding the transport behavior of gas mixtures, including hydrogen. This paper describes a Large-eddy simulation of gas mixing driven by a high-buoyancy flow. We focused on the interaction behavior of heat and mass transfers driven by the horizontal high-buoyant flow during density stratification. For validation, the experimental data of the Containment InteGral effects Measurement Apparatus (CIGMA) facility were used. With a high-power heater for the gas-injection line in the CIGMA facility, a high-temperature flow of approximately 390 ℃ was injected into the test vessel. By using the CIGMA facility, we can extend the experimental data to the high-temperature region. The phenomenological discussion in this paper helps understand the heat and mass transfer induced by the high-buoyancy flow in the containment vessel during a severe accident.

• Journal of Electrochemical Science and Technology
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• v.14 no.3
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• pp.293-300
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• 2023

The global energy storage markets have gravitated to high-energy-density and low cost of lithium-ion batteries (LIBs) as the predominant system for energy storage such as electric vehicles (EVs). High-Ni layered oxides are considered promising next-generation cathode materials for LIBs owing to their significant advantages in terms of high energy density. However, the practical application of high-Ni cathodes remains challenging, because of their structural and surface instability. Although extensive studies have been conducted to mitigate these inherent instabilities, a two-step process involving the synthesis of the cathode and a dry/wet coating is essential. This study evaluates a one-step β-Li₂SnO₃ layer coating on the surface of LiNi_0.8Co_0.2O₂ (NC82) via the thermal segregation of Sn owing to the solubility limit with respect to the synthesis temperature. The doping, segregation, and phase transition of Sn were systematically revealed by structural analyses. Moreover, surface-engineered 5 mol% Sn-coated LiNi_0.8Co_0.2O₂ (NC82_Sn5%) exhibited superior capacity retention compared to bare NC82 owing to the stable surface coating layer. Thus, the developed one-step coating method is suitable for improving the properties of high-Ni layered oxide cathode materials for application in LIBs.