• Nuclear Engineering and Technology
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• 제56권5호
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• pp.1932-1940
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• 2024

The current work deals with investigation of the gamma ray shielding properties for various natural stones from Vietnam to be applied in the radiation shielding applications. The physical and chemical properties affecting the γ-ray shielding performance were examined. The MH-300A density meter was utilized to measure the density (ρ, g/cm³) of stone samples, as well as the chemical composition of Vietnamese natural stones was measured using the X-ray fluorescence analyzer (Olympus X-5000). The study shows that the increase in Fe + Ca concentrations within the stone samples increases their density (from 2.48 to 2.86 g/cm³) accompanied with a reduction in the porosity (Φ, %) (from 8.23 to 0.15%) and water absorption (K, %) (from 3.42 to 0.05%) factors. Additionally, the increase in Fe + Ca concentrations increases the linear attenuation coefficient (μ, cm^-1) of the studied stones, where the Vietnamese marble stone (M 3.1) with the highest Fe + Ca concentration (65.97 wt%) has the highest linear attenuation coefficient which varied between 3.781 and 0.155 cm^-1 with raising the gamma ray energy between 0.040 and 1.332 MeV.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2009년도 춘계학술대회 논문집
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• pp.379-381
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• 2009

The simulation model for metal-supported Solid Oxide Fuel Cell(SOFC) is developed in this study. Open circuit voltage is calculated using Nernst equation and Gibbs free energy is required by thermodynamic. The exchange current densities are compared with experimental results since exchange current density is most effective factor for the activation loss. Liu's study is used for the exchange current density of cathode, BSCF, and Koide's result is applied for the exchange current density of anode, Ni/YSZ. For the ohmic loss, ionic conductivity of YSZ is described from Kilner's mode and the data are compared with Wanzenberg's experimental data. Diffusivity is an important factor for the mass transfer through the porous medium. Both binary diffusion and Knudsen diffusion are considered as the diffusion mechanism. For validation, simulation results at this work are compared with our experimental results.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2011년도 제37회 추계학술대회논문집
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• pp.702-704
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• 2011

대표적인 낮은 성능의 액체 연료(Jet A-1)에 고밀도 고에너지특성을 갖는 첨가제를 혼합하였을 때 연료의 물성 미치는 영향을 조사하였다. 액체 연료의 주요 인자인 밀도, 점도, 발열량을 중심으로 첨가제혼합에 따른 혼합연료의 물성을 비교 분석하여, 액체 연료(Jet A-1)의 성능향상과 같은 특성변화의 가능성이 있음을 파악하였다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2002년도 하계학술대회 논문집
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• pp.58-61
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• 2002

SBT thin films were etched at different content of Cl$_2$in Cl$_2$/Ar plasma. We obtained the maximum etch rate of 883 ${\AA}$/min at Cl$_2$(20%)/Ar(80%). As Cl$_2$ gas increased in Cl$_2$/Ar plasma, the etch rate decreased. The maximum etch rate may be explained by variation of volume density for Cl atoms and by the concurrence of two etching mechanisms such as physical sputtering and chemical reaction with formation of low-volatile products, which can be desorbed only by ion bombardment. The variation of volume density for Cl, F and Ar atoms and ion current density were measured by the optical emission spectroscopy and Langmuir probe. To evaluate the physical damage due to plasma, X-ray diffraction and atomic force microscopy analysis carried out. After etching process, P-E hysteresis loops were measured by ferroelectric workstation.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2001년도 The 6th International Symposium of East Asian Resources Recycling Technology
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• pp.638-643
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• 2001

Macroporous pellets were prepared from industrial waste flyash by foaming method. The surface and inside of flyash pellets, the shape was almost spherical and the average size was about 3 mm, were composed of the spherical pores interconnected through windows. The controlling of pellet size was conducted with solid loading. The flyash pellets with different relative density were characterized for porosity, average pore size, and specific surface area. As results, most physical properties had a tendency to increase as relative density decreased - extension ratio increased. The correlation between relative density and other properties was inspected through microstructural features evaluated by SEM. As a result, high porosity and high specific surface area were estimated to result from the superior connectivity between pores.

• Journal of the Korean Wood Science and Technology
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• 제31권3호
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• pp.17-23
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• 2003

As a fundamental study of developing sawdust board from thinning softwood logs from three species (Pinus densiflora S. et Z., Larix leptolepis G. and Pinus koraiensis S. et Z.), this study examined the effect of board density and resin content on physical and mechanical properties of sawdust board. As the board density increase, thickness swelling, bending strength, and Brinell hardness increased while water absorption decreased. With increasing the resin content, the bending strength and hardness increased while water absorption and thickness swelling decreased. The board made of L. leptolepis was slightly low in its water absorption, and the one made of P. koraiensis was a little high in its bending strength, while there was no definite difference between each kind of trees in their hardness values.

• 대한물리치료과학회지
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• 제13권3호
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• pp.7-14
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• 2006

Despite well-known benefits of physical activity for older adults, most older adults remain significantly underactive. The purpose of this study was to examine the effects of a physical activity on blood cholesterol in older adults with an inclusive, choice-based physical activity promotion program to increase lifetime physical activity levels of seniors. A six-month comparison-group trial was conducted with 14 older adults(experimental group = 8, control group = 6) in community senior center. Changes in self-reported physical activity and blood cholesterol were evaluated using paired t-test. The intervention group increased estimated caloric expenditure by 858 calories/week in physical activities of any intensity (p=.050), total cholesterol(p=0.049), high density lipoprotein cholesterol(p=0.045). Control group changes were also negligible. The program led to meaningful physical activity increase. Individually tailored programs to encourage lifestyle changes in seniors may be effective and applicable to health care and community settings.

• The Journal of the Acoustical Society of Korea
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• 제25권2E호
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• pp.49-55
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• 2006

Compressional wave velocity (Vp), shear wave velocity (Vs), elastic and physical properties, and electrical resistivity for two core sediments obtained from Southeastern Yellow Sea Mud (SEYSM) were measured and computed. The sediments consist of homogeneous mud (mostly silt and clay) with shells and shell fragments. As a result, the mean grain size is uniform ($7.5-8.5{\Phi}$ throughout the core sediments. However, physical properties such as wet bulk density and porosity show slightly increasing and decreasing patterns with depth, compared to the mean grain size. The compressional (about 1475 m/s in average) and shear wave (about 60 m/s in average) velocities with depth accurately reflect the pattern of wet bulk density and porosity. Electrical resistivity is more closely correlated with compressional wave velocity than physical properties. The computed Vp/Vs and Poisson's ratios are relatively higher (more than 10) and lower (approximately 0.002) than Hamilton's (1979) data, respectively, suggesting the typical characteristics of soft and fully water-saturated marine sediments. Thus, the Vp/Vs ratio in soft and unconsolidated sediments is not likely sufficient to examine lithology and sediment properties. Relationships between the elastic constant and physical properties are correlated well. The elastic constants (Poisson's ratio, bulk modulus, shear modulus) given in this paper can be used to characterize soft marine sediments saturated with seawater.

• 성인간호학회지
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• 제14권4호
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• pp.532-542
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• 2002

Purpose: This study were to investigate BMD of middle-aged women and to examine the relationships between BMD and Physical, Obstetric characteristics Method: The data was collected from 119 healthy women who were 40-60 years old. they were examined for BMD at 4 regions(forearm, lumbar, femur, whole body), %fat by DEXA and investigated physical, obstetric characteristics using scale, questionnaire from January to March, 2001. Result: 1) According to bone diagnostic results by WHO classification, 95.8% of forearm and whole body BMD were normal but 21.8-48.7% of lumbar and femur BMD(neck, trochanter, ward's triangle) were diagnosed osteoporosis or osteopnea. 2) The bones were significantly positive correlations of each other (r=.19-.69, p=.04-.00) and there were significant correlations between BMD and physical, obstetric characteristics such as age (r=-.22, p=.02), weight(r=.36~.48, p=.00), height(r=.22, p=.02), %fat(r=.19, p=.04) and age of first delivery(r=-.28, p=.00). Conclusion: Based on this study, healthy middle-aged women were also exposed to risk of osteoporosis related to aging, change of physical conditions or hormonal release. Further research to develop nursing interventions for the purpose of preventing osteoporosis by modifying risk factors is suggested.

• Journal of the Korean Wood Science and Technology
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• 제25권2호
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• pp.33-44
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• 1997

This study was executed to examine the effects of polypropylene fiber length and process variables of the composites made from wood fiber and nonwood fiber mixed formulations. As a nonwood fiber the polypropylene with 3 denier thickness of tow condition was selected and cut into each length of 0.5, 1.0, 1.5, 2.0 and 2.5cm to mix with wood fiber. And also western hemlock wood fiber for medium density fiberboard was prepared. First, to decide an adequate polypropylene mixing fiber length, the composites of 1.0g/$cm^3$ density were made from 10% polypropylene fiber by each of five lengths and 90% western hemlock fiber mixed formulations. Thereafter as the experiments of process variable, the composites applied with adequate polypropylene fiber length(1.5cm) were made from 4 density levels (0.6, 0.8, 1.0, 1.2g/$cm^3$). 3 mixed formulations of wood fiber to polypropylene fiber(95 : 5, 90 : 10, 85 : 15), and 3 mat moisture contents(5, 10, 20%). According to the results and discussions it was concluded as follows ; The physical and mechanical properties were shown improved tendency. as polypropylene fiber length was increased in the range from 0.5 to 1.5cm, but shown decreasing tendency from 2.0 to 2.5 cm. Accordingly, it was shown that polypropylene fiber length is limited to 1.5cm or less length in mixing wood fiber and polypropylene fiber by turbulent air mixing process. As the densities of wood fiber-polypropylene fiber composites were increased, the physical and mechanical properties were clearly improved. Also they were shown significantly increasement statistically between densities respectively. In the mixed formulations, physical and mechanical properties were shown only slightly improvement, as they changed from 95 : 5 to 85 : 15 in wood fiber to polypropylene fiber. Despite of increasement of mat moisture content, mechanical properties were not improved significantly but physical properties were improved somewhat in wood fiber-polypropylene fiber composites.