• ETRI Journal
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• v.27 no.2
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• pp.227-230
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• 2005

A specific anthropomorphic mannequin (SAM) model was used to investigate the relation between local specific absorption rate (SAR) and head size. The model was scaled to 80 to 100% sized models at intervals of 5%. We assumed that the shell of the SAM model has the same properties as the head-equivalent tissue. Five handsets with a monopole antenna operating at 835 MHz were placed in the approximate cheek position against the scaled SAM models. The handsets had different antenna lengths, antenna positions, body sizes, and external materials. SAR distributions in the scaled SAM models were computed using the finite-difference time-domain method. We found that a larger head causes a distinct increase in the spatial peak 1-voxel SAR, while head size did not significantly change the peak 1-g averaged-SAR and 10-g averaged-SAR values for the same power level delivered to the antenna.

• The Journal of the Acoustical Society of Korea
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• v.15 no.4E
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• pp.3-8
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• 1996

The bubble size distribution is critical information to understand sound propagation and ambient noise in the ocean. To estimate the bubble size distribution in a bubbly water, the sound attenuation has been only in the conventional acoustic bubble sizing method without considering the sound speed variation. However, the effect of the sound speed variation in bubbly water cannot be neglected because of its compressibility variation. The sound attenuation is also affected by the sound speed variation. In this paper, a coherent acoustic bubble sizing inverse technique is introduced as a new bubble sizing technique with considering sound speed variation as well as the sound attenuation. This coherent sizing method is theoretically verified with the bubble distribution functions of single-size, Gaussian, and power-law functions. Its numerical test results with the coherent acoustic bubble sizing method show good agreement with the given bubble distributions.

• Steel and Composite Structures
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• v.35 no.1
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• pp.147-157
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• 2020

In the present research, thermo-elastic buckling of small scale functionally graded material (FGM) nano-size plates with clamped edge conditions rested on an elastic substrate exposed to uniformly, linearly and non-linearly temperature distributions has been investigated employing a secant function based refined theory. Material properties of the FGM nano-size plate have exponential gradation across the plate thickness. Using Hamilton's rule and non-local elasticity of Eringen, the non-local governing equations have been stablished in the context of refined four-unknown plate theory and then solved via an analytical method which captures clamped boundary conditions. Buckling results are provided to show the effects of different thermal loadings, non-locality, gradient index, shear deformation, aspect and length-to-thickness ratios on critical buckling temperature of clamped exponential graded nano-size plates.

• Journal of Power System Engineering
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• v.21 no.2
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• pp.57-63
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• 2017

The large-eddy simulation(LES) was carried out to evaluate the drag and static pressure acting on the blade surface of a small-size axial fan(SSAF) under the condition of unsteady-state, incompressible fluid and three-dimensional coordination. The axial component of drag coefficient increases with the increase of operating load, but the radial components have negligible sizes regardless of operating loads. Otherwise, the static pressures acting on the blade surfaces of SSAF show different distributions around the operating point of D equivalent to the stall. Also, with the increase of operating load, the static pressures acting on the pressure and suction surfaces of blade concentrate at the tips and leading-edges as a whole.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2003.04a
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• pp.169-172
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• 2003

Manufacturing process for autonomic microcapsules was introduced and autonomic microcapsules were manufactured by varying with various manufacturing process variables. Urea-formaldehyde resin was used for the wall of microcapsules and DCPD (dicyclopentadiene) was used for the self-healing agent. The characteristics of these microcapsules was evaluated through a particle size analyaer, an optical microscope, and a TGA. The various manufacturing process variables, such as pH and agitation speed of the emulsified solution, were considered to focus in this study. According to the results, the particle size distributions were affected on the agitation speed of the emulsified solution, and the thermal stability was influenced by pH of the emulsified solution.

• Journal of the Korean Ceramic Society
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• v.36 no.11
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• pp.1198-1204
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• 1999

The effect of sintering atmosphere on the grain sizes and phase distributions in 3Y-ZrO2 and 8Y-ZrO2 was investigated O2 and N2 were used as sintering atmospheres. In the case of 3Y-ZrO2 the sintered density was higher in N2 than in O2 while in the case of 8Y-ZrO2 contrary results were obtained. The observation can be explained by the nitrogen solubility into the zirconia lattice. That is nitrogen gas can behave as a diffusive gas contrary to the behavior in other oxides depending on the amount of Y2O3. In 3Y-ZrO2 tetragonal phase was retained at room temperature irrespective of sintering atmospheres. Grain sizes of two specimens were below 2㎛ and larger in O2 thin in N2 Under a given stress the transformability of tetragonal phase into monoclinic phase was higher in O2 than N2. The results are discussed on the basis of an effect of the grain size and non-transformable ttragonal(t') phase.

• Journal of the Korean Ceramic Society
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• v.32 no.11
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• pp.1227-1232
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• 1995

Effect of heating rate on the microstructure of the silicon nitride ceramics has been investigated. The specimens with composition of 92Si3N4-6Y2O3-2Al2O3 (in wt%) were sintered at 176$0^{\circ}C$ under 127 kPa for 3h in N2 atmosphere at various heating rates from 1 to 10$0^{\circ}C$/min. The grain size of larger than 2${\mu}{\textrm}{m}$ and less than 1${\mu}{\textrm}{m}$ were measured and compared for the specimens. Regardless of heating rate, grain size of all the specimens showed bimodal distributions and the fracture toughness remained in the range of 5.53~5.72 MPa.m1/2. However, the aspect ratio of the grains of diameter above 2${\mu}{\textrm}{m}$ increased with the heating rate while their grain size and volume fraction decreased.

• Proceedings of the Korea Association of Crystal Growth Conference
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• 1998.09a
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• pp.117-121
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• 1998

The Rapid Expansion of supercritical fluid Solutions (RESS) process was applied to particles coating. Experiments were conducted in a fluidized bed with an internal nozzle in the center of the reaction tube. Microcapsules (mean particle size : 49$\mu\textrm{m}$) prepared by spray drying method were used as the core particles. Supercritical CO2 solutions of paraffin were expanded through the nozzle in to the bed that was fluidized by air. Surface morphology prepared particles was observed by SEM. For the inspection of particle size change, particle size distributions were measured before and after coating. The releasing behavior of Mg2+ ions inspected by AA.

• Journal of the Semiconductor & Display Technology
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• v.19 no.2
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• pp.37-44
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• 2020

In improving laser cutting of optical plastic films for mass production of optoelectronics display units, it is important to understand particle contamination over optical film surface due to fume particle generation and dispersion. This numerical study investigates the effects of downward and upward air flow motions on fume particle dispersion around laser cut line. The simulations employ random particle sampling of up to one million fume particles by probabilistic distributions of particle size, ejection velocity and angle, and fume particle dispersion and surface landing are predicted using Basset-Boussinesq-Oseen model of low Reynolds number flows. The numerical results show that downward air flow scatters fume particles of a certain size range farther away from laser cut line and aggravate surface contamination. However, upward air flow pushes fume particles of this size range back toward laser cut line or sucks them up with rising air motion, thus significantly alleviating surface contamination.

• Journal of Environmental Health Sciences
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• v.22 no.4
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• pp.55-61
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• 1996

Measurements of the seasonal variations of concentration and size distribution of TSP, $SO_4^{2-}, NO_3^-, Cl^-, NH_4^+, Na^+, K^+, Ca^{2+}$ and $Mg^{2+}$ were made by Andersen air sampler from May 1995 to April 1996 in Seoul. The size distribution of these ions was divided into four patterns. 1) Distribution was concentrated on fine particles over a year such as $NO_3^-$ component, 2) Distribution was predominated in coarse particles fraction over a year such as $Mg^{2+}$ and $Ca^{2+}$ components, 3) Distribution was differerent from various seasons such as $NH_4^+, SO_4^{2-}, Cl^-$ and $K^+$ components, 4) Distribution was bi-modal such as $Na^+$.