• Journal of Nutrition and Health
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• 제36권2호
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• pp.167-174
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• 2003

This study investigated associations between nutrient intake, lumbar bone mineral density (BMD) , and bone mineral content (BMC) among 33 ovariectomized women (mean age =47.2 y) . Forty-five premenopausal women participated as a control group. The BMD and BMC of the lumbar spine (L$_2$-L$_4$) were measured by dual energy x-ray absorptiometry. Nutrient intake was estimated by the convenient method and a quantitative food frequency questionnaire was designed for this study that included the most commonly consumed foods sources of calcium. Participants were asked to identify all daily physical activities, and the number of hours per activity. The participants were also grouped by calcium intake. The total calcium intake of all participants was estimated by dietary calcium intake and then the subjects were divided into quartiles to assess the lumbar BMD and BMC of the highest quartile and the lowest quartile of calcium intake. The ovariectomized women consumed 602 mg/d of calcium which is 86% of RDA. There were significant differences in lumbar BMD and BMC between control and ovariectomized group. Within ovariectomized group the highest quartile calcium intake group had significantly greater lumbar bone mineral density and bone mineral content than the lowest quartile calcium intake group. Correlation analysis revealed that the ALP was positively associated with calcium index in control women, while ALP was positively associated with energy intake in ovariectomized women. And body weight was positively correlated with the spinal BMD and BMC in all women. The spinal BMD was negatively associated with menarche age, number of child, and the age of last child delivery, and age in control women. However, neither menarche age nor the age of last child delivery were associated with both spinal BMD in ovariectomized women. These results confirmed that ovariectomized and low calcium intake is associated with poor bone mineral density. Energy and calcium intake and adequate body weight should be recommended in ovariectomized women to prevent osteoporosis.

• 한국재료학회지
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• 제22권11호
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• pp.604-608
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• 2012

Recently, inorganic-organic hybrid materials have attracted much attention not only for their excellent thermal conductivity but also for their flame retardant properties. In this study, the properties of organic-inorganic hybrid insulating materials using inorganic fillers and polyurethane foam with different foaming conditions have been investigated. The addition of 1.5 wt% water to polyurethane as foaming agent shows the best foaming properties. The pore size was decreased in the foaming body with increasing of the $CaCO_3$ addition. The apparent density and thermal conductivity were increased by increasing the $CaCO_3$ addition. With an increasing amount of $CaCO_3$ powder, the flame retardant property is improved, but the properties of thermal conductivity and apparent density tend to decrease. When the addition of fine particles of $CaCO_3$, the apparent density and thermal conductivity were increased and, also, with the addition of coarse particles over $45{\mu}m$ in size, the apparent density and thermal conductivity were increased as well. In this study, the adding of $CaCO_3$ with average particle size of $27{\mu}m$ led to the lowest thermal conductivity and apparent density. After evaluation with different inorganic fillers, $Mg(OH)_2$ showed the highest thermal conductivity; on the other hand, $CaCO_3$ showed the lowest thermal conductivity.

• 한국해양공학회지
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• 제36권5호
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• pp.326-339
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• 2022

Recently, not only Korea but also the world has been suffering from problems related to coastal erosion. The hard defense method has been primarily used as a countermeasure against erosion. However, this method is expensive and has environmental implications. Hence, interest in other alternative methods, such as the eco-friendly vegetation method, is increasing. In this study, we aim to analyze the hydraulic characteristic of submerged rigid vegetation according to the cross-sectional change through a hydraulic experiment and numerical simulation. From the hydraulic experiment, the reflection coefficient, transmission coefficient, and energy dissipation coefficient were analyzed according to the density, width, and multi-row arrangement of the vegetation zone. From numerical simulations, the flow field, vorticity distribution, turbulence distribution, and wave distribution around the vegetation zone were analyzed according to the crest depth, width, density, and multi-row arrangement distance of the vegetation zone. The hydraulic experiment results suggest that the transmission coefficient decreased as the density and width of the vegetation zone increased, and the multi-row arrangement condition did not affect the hydraulic characteristics significantly. Moreover, the numerical simulations showed that as the crest depth decreased, the width and density of vegetation increased along with vorticity and turbulence intensity, resulting in increased wave height attenuation performance. Additionally, there was no significant difference in vorticity, turbulence intensity, and wave height attenuation performance based on the multi-row arrangement distance. Overall, in the case of submerged rigid vegetation, the wave energy attenuation performance increased as the density and width of the vegetation zone increased and crest depth decreased. However, the multi-row arrangement condition did not affect the wave energy attenuation performance significantly.

• 한국분말재료학회지
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• 제29권5호
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• pp.390-398
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• 2022

Recently, considerable attention has been given to nickel-based superalloys used in additive manufacturing. However, additive manufacturing is limited by a slow build rate in obtaining optimal densities. In this study, optimal volumetric energy density (VED) was calculated using optimal process parameters of IN718 provided by additive manufacturing of laser powder-bed fusion. The laser power and scan speed were controlled using the same ratio to maintain the optimal VED and achieve a fast build rate. Cube samples were manufactured using seven process parameters, including an optimal process parameter. Analysis was conducted based on changes in density and melt-pool morphology. At a low laser power and scan speed, the energy applied to the powder bed was proportional to ${\frac{P}{\sqrt{V}}}$ and not ${\frac{P}{V}}$. At a high laser power and scan speed, a curved track was formed due to Plateau-Rayleigh instability. However, a wide melt-pool shape and continuous track were formed, which did not significantly affect the density. We were able to verify the validity of the VED formula and succeeded in achieving a 75% higher build rate than that of the optimal parameter, with a slight decrease in density and hardness.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2001년도 하계학술대회 논문집 C
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• pp.1427-1429
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• 2001

Polycrystalline silicon(poly-Si) films are deposited on low temperature glass substrate by Hot-Wire CVD(HWCVD). The structural properties of the poly-Si films are strongly dependent on the wire temperature($T_w$). The films deposited at high $T_w$ of 2000$^{\circ}C$ have superior crystalline properties; average lateral grain sizes are larger than $1{\mu}m$ and there at·e no vertical grain boundaries. The surface of the high $T_w$ samples are naturally textured like pyramid shape. These large grain size and textured surface are believed to give high current density when applied to solar cells. However, the poly-si films are structurally porous and contains high defect density, by which high concentration of C and O resulted within the films by air-penetration after removed from chamber.

• Nuclear Engineering and Technology
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• 제32권4호
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• pp.361-371
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• 2000

The 123Te(p,n)123I, 124Te(p,n)124I and 124Te(p,2n)123I reactions, among the many reaction channels opened, are the major reactions under consideration from a diagnostic purpose because reaction residuals as the gamma emitters are used for most radiophamaceutical applications involving radioiodine. Based on the available experimental data, the absorption cross sections and elastic scattering angular distributions of the proton-induced nuclear reaction on Te isotopes below 60 MeV are calculated using the optical model code APMNK. The transmission coefficients of neutron, proton, deuteron, trition and alpha particles are calculated by CUNF code and are fed into the GNASH code. By adjusting level density parameters and the pair correction values of some reaction channels, as well as the composite nucleus state density constants of the pre-equilibrium model, the production cross sections and energy-angle correlated spectra of the secondary light particles, as well as production cross sections and energy distributions of heavy recoils and gamma rays are calculated by the statistical plus pre-equilibrium model code GNASH. The calculated results are analysed and compared with the experimental data taken from the EXFOR. The optimized global optical model parameters give overall agreement with the experimental data over both the entire energy range and all tellurium isotopes.

• Journal of the Korean Wood Science and Technology
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• 제26권1호
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• pp.38-50
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• 1998

Laser cutting tests were conducted to investigate the laser cutting characteristics of solid woods such as 25mm-thick white oak(Quercus acutissima) and maple(Acer mono), and wood-based panels such as 15mm-thick medium density fiberboard and particleboard. Test variables were laser power, cutting speed, grain direction, and moisture content. Specific cutting energy was measured and the qualities of cut surface were estimated in constant laser power. Specific cutting energy of white oak was larger than that of maple, and specific cutting energy of medium density fiberboard was smaller than that of particleboard. For both white oak and maple, specific cutting energy of green wood was smaller than that of air-dried wood because weight loss of moisture evaporation in green wood was larger than that in air-dried wood. In laser-cut surface, wood cells were not deformed and damaged, but in circular saw-cut surface fibers were pushed out and cut, and wood cells were deformed severely. However, mechanical surface roughness of saw-cut surface was smoother than that of laser-cut surface because of the existence of undeformed cell cavity in laser-cut surface.

• Nuclear Engineering and Technology
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• 제3권1호
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• pp.21-31
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• 1971

금속의 소성변형에 필요한 일의 일부는 전표면자유에너지 (Total Surface Free Energy)의 변화에 소모된다. 전표면자유에너지 변화는 비표면 자유에너지 (Specific Surface Free Energy)에 의해 변화하며 비표면자유에너지는 분위기에 따라 달라 진다. 열역학적규명, 체적불변율과 흡착으로 인한 두 개의 판이하게 다른 강화 혹은 약화를 초래하는 전위(Dislocation) 상호작용기구를 기반으로 금속의 소성변형으로 인한 가공경화, 응력 및 에너지에 미치는 분위기의 영향을 이론식으로 도출했다. 이론식은 진공중금속표면장력 (${\gamma}$$_{s}$), 개면장력 (${\gamma}$$_{se}$ ), 포면전위밀도($\rho$$_{s}$), 내부전위 밀도($\rho$$_{i}$)와 표면노출율(f)의 함수로 표시할 수 있었다. 이론식을 이용하여 각기 다른 분위기내에서의 금속의 기계특성을 예측 비교해봤다.다.다.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2006년도 춘계학술대회
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• pp.478-481
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• 2006

Energy is vital to global prosperity, yet dependence on fossil fuels as our primary energy source contributes to global climate change environmental degradation, and health problems. Hydrogen $(H_2)$ offers tremendous potential as a clean renewable energy currency. Hydrogen has the highest gravimetric energy density of any known fuel and is compatible with electrochemical and combustion processes for energy conversion without producing carbon-based emission that contribute to environmental pollution and climate change. Numerous methodologies have been developed for effective hydrogen production. Among them, the biological hydrogen production has gained attention, because hydrogen can be produced by cellular metabolismunder the presence of water and sunlight. The green alga Chlamydomonas reinhardtii is capable of sustained $H_2$ photoproduction when grown under sulfur deprived condition. Under sulfur deprived conditions, PSII and photosynthetic $O_2$ evolution are inactivated, resulting in shift from aerobic to anaerobic condition in the culture. After anaerobiosis, sulfur deprived algal cells induce a reversible hydrogenase and start to evolve $H_2$ gas in the light. According to above principle, we investigated the effect of induction parameters such as cell age, cell density. light intensity, and sulfate concentration under sulfur deprived condition We also developed continuous hydrogen production system by sulfate re-addition under sulfur deprived condition.

• 반도체디스플레이기술학회지
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• 제17권4호
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• pp.1-5
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• 2018

Atomic force microscopy (AFM) simulation for Si (001) surface defects was conducted by using density functional theory (DFT). Three major defects on the Si (001) surface are difficult to analyze due to external noises that are always present in the images obtained by AFM. Noise-free surface defects obtained by simulation can help identify the real surface defects on AFM images. The surface defects were first optimized by using a DFT code. The AFM tip was designed by using five carbon atoms and positioned on the surface to calculate the system's energy. Forces between tip and surface were calculated from the energy data and converted into an AFM image. The simulated AFM images are noise-free and, therefore, can help evaluate the real surface defects present on the measured AFM images.