• Journal of the Korean Geosynthetics Society
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• v.23 no.2
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• pp.53-62
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• 2024

Recently, development of non-traditional energy such as oil sands has been actively conducted in the cold region such as Canada. Frozen soil has different thermal and mechanical characteristics from general soil due to its high organic contents. This study evaluated the impact of organic matter content on the thermal and mechanical behavior of frozen soil samples collected from Alberta, Canada, and Gangwon Province, South Korea. As the organic content increases, the maximum dry unit weight decreases and the optimum moisture content increases in compaction tests. In uniaxial compression tests under frozen conditions, the strength of the frozen specimens increased as the temperature decreased. The strength of Canada soil sample increased with higher organic matter content at low temperatures. However, the strength of frozen soil was not significantly affected by organic matter content due to the complex behavior and unfrozen water content. Thermal conductivity tests showed higher thermal conductivity in frozen conditions compared to unfrozen conditions, due to the higher thermal conductivity of ice compared to water. These findings provide essential data for geotechnical design and construction in large-scale projects such as oil sands development in cold regions. Further research is needed to explore the impact of organic matter content on different types of frozen soils.

• Journal of Aerospace System Engineering
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• v.18 no.3
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• pp.70-75
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• 2024

The insulation performance of a common bulkhead propellant tank for small launch vehicles with variations in insulation thickness was analyzed. The common bulkhead propellant tank composed of a single part allows for lightweight design, as it eliminates the need for tank connections. However, problems such as propellant loss and ignition delay due to heat transfer caused by temperature differences between oxidizer and fuel may arise. Therefore, it is essential to verify the insulation performance of the common bulkhead structure that separates the oxidizer tank and fuel tank. In this study, transient heat transfer analysis was conducted for propellant tanks with insulation thicknesses of (50, 55, 60, 65, and 70) mm to analyze the insulation performance using boil-off mass. Subsequently, the boil-off mass of the oxidizer generated during the first-stage flight time of the propellant tank was determined. The results confirmed that increasing the insulation thickness reduces the boil-off mass, thereby improving the insulation performance.

• Journal of Radiation Protection and Research
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• v.40 no.1
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• pp.10-16
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• 2015

Bone changes are common sequela of irradiation in growing animal. The purpose of this study was to establish an experimental model of radiation-induced bone loss in growing mice using micro-computed tomography (${\mu}CT$). The extent of changes following 2 Gy gamma irradiation ($2Gy{\cdot}min^{-1}$) was studied at 4, 8 or 12 weeks after exposure. Mice that received 0.5, 1.0, 2.0 or 4.0 Gy of gamma-rays were examined 8 weeks after irradiation. Tibiae were analyzed using ${\mu}CT$. Serum alkaline phosphatase (ALP) and biomechanical properties were measured and the osteoclast surface was examined. A significant loss of trabecular bone in tibiae was evident 8 weeks after exposure. Measurements performed after irradiation showed a dose-related decrease in trabecular bone volume fraction (BV/TV) and bone mineral density (BMD), respectively. The best-fitting dose-response curves were linear-quadratic. Taking the controls into accounts, the lines of best fit were as follows: BV/TV (%) = $0.9584D^2-6.0168D+20.377$ ($r^2$ = 0.946, D = dose in Gy) and BMD ($mg{\cdot}cm^{-3}$) = $8.8115D^2-56.197D+194.41$ ($r^2$ = 0.999, D = dose in Gy). Body weight did not differ among the groups. No dose-dependent differences were apparent among the groups with regard to mechanical and anatomical properties of tibia, serum ALP and osteoclast activity. The findings provide the basis required for better understanding of the results that will be obtained in any further studies of radiation-induced bone responses.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.49 no.12
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• pp.654-664
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• 2000

Thin films of ZnO are deposited by using an RF magnetron sputtering with varying the substrate temperature(RT~39$0^{\circ}C$) and RF power(50~250W). Cu-doped ZnO(denoted by ZnO:Cu) films have also been prepared by co-spputtering of a ZnO target on which some Cu-chips are attached. Different substrate materials, such as Si, $SiO_{2}/Si$, sapphire, DLC/Si, and poly-diamond/Si, are employed to compare the c-axial growth features of deposited ZnO films. Texture coefficient(TC) values for the (002)-preferential growth are estimated from the XRD spectra of deposited films. Optimal ranges of RF powers and substrate temperatures for obtaining high TC values are determined. Effects of Cu-doping conditions, such as relative Cu-chip sputtering areas, $O_{2}/(Ar+O_{2})$ mixing ratios, and reactor pressures, on TC values, electrical resistivities, and relative Cu-compositions of deposited ZnO:Cu films have been systematically investigated. XPS study shows that the relative densities of metallic $Cu(Cu^{0})$ atoms and $CuO(Cu^{2+})$-phases within deposited films may play an important role of determining their electrical resistivities. It should be noted from the experimental results that highly resistive(> $10^{10}{\Omega}cm$ ZnO films with high TC values(> 80%) can be achieved by Cu-doping. SAW devices with ZnO(or Zn):Cu)/IDT/$SiO_{2}$/Si configuration are also fabricated to estimate the effective electric-mechanical coupling coefficient($k_{eff}^{2}$) and the insertion loss. It is observed that the devices using the Cu-doped ZnO films have a higher $k_{eff}^{2}$ and a lower insertion loss, compared with those using the undoped films.

• Journal of Korean Tunnelling and Underground Space Association
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• v.16 no.3
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• pp.311-320
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• 2014

High strength concrete is not only vulnerable to the occurrence of spalling which generates the loss of cross-section in concrete structures but produces faster degradation in its mechanical properties than normal strength concrete in the event of fire. This study aims to evaluate fire resistance of high strength segment concrete with PET fibers mixed to prevent spalling under ISO834 (2hr) and RABT fire curve. As results, the samples without PET fibers show the concrete loss up to the depth of about 8 cm and 9.5 cm from the surface exposed to fire under ISO834 and RABT fire curve respectively. The samples mixed with PET fiber of 0.1% show no spalling under ISO834 fire curve and the spalled thickness of 6.5 cm under RABT fire curve after the fire tests. Finally, the sample mixed with PET fiber of 0.2% shows no spalling under RABT fire curve. The results indicate that the suitable amounts of PET fiber for securing fire resistance performance of this high strength segment concrete are 0.1% under ISO834 fire curve and 0.2% under RABT fire curve. However, even though spalling does not occur, it is necessary to repair the deterioration of concrete up to 4 cm from the surface exposed to fire after fire.

• Korean Journal of Agricultural Science
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• v.31 no.2
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• pp.105-114
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• 2004

This study was performed to examine the physical and mechanical properties of eco-concrete using soil, natural coarse aggregate, soil compound and polypropylen fiber. The mass loss ratio was decreased with increasing the content of coarse aggregate and soil compound. The compressive strength, flexural strength, ultrasonic pulse velocity and dynamic modulus of elasticity were increased with increasing the content of coarse aggregate, soil compound and polypropylene fiber. The compressive and flexural strengths were showed in 8.07 MPa and 2.641 MPa at the curing age 28 days, respectively. The coefficient of permeability was decreased with increasing the content of coarse aggregate and soil compound, but it was increased with increasing the content of polypropylene fiber. The lowest coefficent of permeability was showed in $5.066{\times}10^{-9}cm/s$.

• Journal of Conservation Science
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• v.26 no.3
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• pp.295-310
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• 2010

Since wall paintings in Maitreya Hall of Geumsan-sa temple had displayed a serious state of damage and deterioration, a detailed examination such as structural analysis of the wall, cause of damage, and the state of deterioration have been thoroughly conducted before the conservation treatment has commenced. The most seriously deteriorated part of the wall paintings was the south wall of the building in particular in its painted and surface layer. The painted layer had formed its own layer of thick, which has been separation from the surface layer. As such problem developed the whole surface layer has been separated from the wall. The problem has been caused by two reasons: 1. the heavy weight of the roof section and it caused cracks and damage on the wall; 2. the loss of function of consolidating material and it caused discolouring and the separation of surface layer from the wall. The cause of damage on the painted and surface layers can be assumed in two ways: 1. its surrounding environment such as the change of temperature and humidity level and ultraviolet rays ; 2. the loss of mechanical function of consolidating material, synthetic resin which had been applied in the past conservation treatment. The separation of layers from the wall and cracks was caused by the mistake in choosing an applicable consolidating material and dismantling technique which had ignored a different characteristic of the wall painting of Korean buddhist temples.

• Korean Journal of Food Science and Technology
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• v.31 no.1
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• pp.91-98
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• 1999

Plums (Prunus salicina L.) were coated with calcium-treated methylcellulose (CaMC) and hydroxypropylmethylcellulose-15 (CaHPMC-15). Respiration rate, weight loss, pH and titratable acidity, texture, and sensory characteristics were compared during 8-day storage period at $30^{\circ}C$. Weight loss and respiration rate of plums coated with CaMC and CaHPMC-15 were lower than those of control plums during storage while pH increased and titratable acidity slowly deceased during storage. Mechanical firmness was significantly deceased during storage, in which CaMC and CaHPMC-15-coated plums were harder than the control. Amount of soluble pectin, and pectin esterase and polygalacturonase activities as the markers of softening commonly increased with storage, but both CaMC and CaHPMC-15-coated plums were not found those increases. Sensory evaluation showed that the flesh softening of plums decreased during storage, and that in the coated plums exhibited the harder flesh. In conclusion, introduction of CaMC and CaHPMC-15 coatings on plums decreased respiration rate and contributed to delay of flesh softening, and the significant difference in postharvest storage quality of the both plums were not found between CaMC and CaHPMC-15 coatings.

• Journal of Electrical Engineering and Technology
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• v.12 no.5
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• pp.2021-2030
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• 2017

In this paper, the unipolar corona-needle charger was developed and its capabilities were both numerically and experimentally investigated. The experimental corona discharges and particle losses in the charger were obtained at different corona voltage, aerosol flow rate and particle diameter for positive and negative coronas. Inside the charger, the electric field and charge distribution and the transport behavior of the charged particle were predicted by a numerical simulation. The experimental results yielded the highest ion number concentrations of about $1.087{\times}10^{15}ions/m^3$ for a positive corona voltage of about 3.2 kV, and $1.247{\times}10^{16}ions/m^3$ for a negative corona voltage of about 2.9 kV, and the highest $N_it$ product for positive and negative coronas was found to about $7.53{\times}10^{13}$ and $8.65{\times}10^{14}ions/m^3$ s was occurred at the positive and negative corona voltages of about 3.2 and 2.9 kV, respectively, and the flow rate of 0.3 L/min. The highest diffusion loss was found to occur at particles with diameter of 30 nm to be about 62.50 and 19.33 % for the aerosol flow rate of 0.3 and 1.5 L/min, respectively, and the highest electrostatic loss was found to occur at particles with diameters of 75 and 50 nm to be about 86.29 and 72.92 % for positive and negative corona voltages of about 2.9 and 2.5 kV, respectively. The numerical results for the electric field distribution and the charged particles migration inside the charger were used to guide the description of the electric field and the behavior of charged particle trajectories to improve the design and refinement of a unipolar corona-needle charger that otherwise could not be seen from the experimental data.

• Journal of Korean Tunnelling and Underground Space Association
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• v.16 no.2
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• pp.213-224
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• 2014

Recently, tunnelling with TBM is getting popular for the construction of cable tunnel in urban area. Mechanized tunnelling method using shield TBM has various advantages such as minimization of ground settlement and prevention of vibration induced by blasting that should be accompanied by conventional tunnelling. In Korea, earth pressure balance (EPB) type shield TBM has been mainly used. Despite the popularity of EPB shield TBM for cable tunnel construction, study on the mechanical behavior of cable tunnel driven by shield TBM is insufficient. Especially, the effect of backfill grout injection on the behavior of cable tunnel driven by shield TBM is investigated in this study. Tunnelling with shield TBM is simulated using 3D FEM. The distance of backfill grout injection from the end of shield skin varies. Sectional forces such as axial force, shear force and bending moment are monitored. Vertical displacement at the ground surface is measured. Futhermore, the relation between volume loss and the distance of backfill grout injection from the end of skin plate is derived. Based on the stability analysis with the results obtained from the numerical analysis, the most appropriate injection distance can be obtained.