• Journal of the Korea Institute of Information and Communication Engineering
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• v.14 no.5
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• pp.1085-1092
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• 2010

This paper describes the development of estimating equation for under 16 aged children's exposure to habitat's magnetic field for 24 hours by using particle swarm optimization(PSO) algorithm, which was carried out by using the measured database collected from the exposure survey to Korean habitat's magnetic field as to under 16 aged Korean students such as preschooler, children in elementary school, and children in middle school. Sex, age, residence type, size of habitation site, distance from power line, and power transmission voltage are used as the input data of estimating 24 hour's personal exposure to magnetic field. And distribution of 24 hour's personal exposure to magnetic field, exposure characteristic to magnetic field, and exposure characteristic to magnetic field according to special conditions, are analyzed for under 16 aged children.

• Elastomers and Composites
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• v.58 no.4
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• pp.179-190
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• 2023

The effect of the particle size and silica structure on the wear behavior of Silica/Styrene-Butadiene Rubber (SBR) compounds was investigated using a blade-type abrader and the findings were compared with those obtained with an Akron abrader. The compensated characteristic parameter (Ψ_c), which was the contributory factor of the combined effect of the particle size and filler structure, was introduced. This parameter was found to exhibit a linear relationship with the Young's modulus. The Young's modulus correlated more with Ψ_c than the uncompensated characteristic parameter (Ψ) modeled for carbon black. The wear rate and volume loss measured using a blade-type abrader and Akron abrader were respectively observed to be inversely proportional to Ψ_c, that is, the wear resistance of Silica/SBR compound improved as the particle size became smaller and the silica structure became intricate. The coefficient of determination (R²) obtained from the linear relationship between Ψ_c and wear rate was higher than those between Ψ_c and volume loss for the Silica/SBR compound. Thus, the blade-type abrader exhibited high potential to be used for accurately evaluating the effect of particle size and structural properties of silica on the wear behavior of SBR compounds.

• Journal of Soil and Groundwater Environment
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• v.7 no.3
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• pp.103-114
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• 2002

Knowledge of soil water retention characteristic is essential for many problems involving water flow and organic solute transport in unsaturated soils. A physico-empirical approach based on the translation of the particle-size distribution (PSD) into a corresponding water retention curve has been accomplished by others using the concept that the pore-size distribution is directly related to PSD. This approach implies that details of a PSD curve may affect the estimation of water retention characteristic (WRC). To determine whether the WRC estimation using the Arya-Paris model could be affected by the selection of a PSD model, four PSD models with one to four fitting parameters were used. The Jaky model with only one fitting parameter had greater WRC estimation ability than other models with greater number of fitting parameters. The better performance of the Jaky model may be explained by the effect of soil structure in field soils.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2044-2049
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• 2007

In order to predict the thermal radiation induced from alumina particle cloud in the plume of solid propellant motor, view factor method is applied to space shuttle SRB and the result is compared with that of monte carlo method. For this purpose, radiative characteristics, such as particle cloud temperature distribution, effective emissivity or emissive power of particle cloud are studied. In the case of effective emissivity, inverse wavelength method is applied and plume reduction characteristic length is used for emissive power distribution. As a result, thermal radiation using view factor method gives more conservative results than that using monte carlo method. So it can be used for preliminary design of thermal protection system.

• Korean Journal of Materials Research
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• v.4 no.8
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• pp.927-933
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• 1994

The effect of particle shape and size on the settling characteristics in monodisperse suspensions of non-spherical particles was investigated. The slope index n values which was obtained from the plot of logarithm of settling rate vs. voidage were increased with the decrease of particle size because different amount of liquid could be adsorbed on irregular particle shape and/or size at same volume concentration. From the experimental results, an equation, $n_{i}=n(a+b/d_{v})$ where n is value of spherical particles, dv is minimum particle diameter and a, b are constants for characteristic of particles.

• Journal of the Korean Ceramic Society
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• v.34 no.11
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• pp.1173-1181
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• 1997

Effects of particle size distribution of alumina ceramics on behaviors of tape casting were investigated with emphases on the rheological characteristic of slurry, green density, green sheet strength, and sintering density. For the control of particle size distribution of alumina, the commercial grade low soda alumina, which had different mean particle size of 3.58 ${\mu}{\textrm}{m}$ and 0.42 ${\mu}{\textrm}{m}$, were chosen and blended together. As results, the mixing of 80 wt% fine powder and 20 wt% coarse powder(designated to FC20) led to the increase of packing density and strength of green sheet, and made it easy to handle during processing without lowering of sintering density. Besides, the pseudoplastic behavior of slurry decreased with increase of the fraction of coarse alumina powder.

• Bulletin of the Korean Chemical Society
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• v.25 no.6
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• pp.801-805
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• 2004

In this work, the fundamental study of on-line monitoring of $SiO_2$ particles in the size range of 40 nm to 725 nm was carried out using turbidimetry. The size of particle was measured using a field emission scanning electron microscope (FE-SEM). The factors affecting on the turbidity were discussed, for example, wavelength, size, and concentration. In order to observe the dependence of turbidity on the wavelength, a turbidimetric system equipped with charged coupled detector (CCD) was built. The shape of the transmitted peak was changed and the peak maximum was shifted to the red when the concentration of particle was increased. This result indicates that the turbidity is related to the wavelength, which corresponds to the characteristic of the Mie extinction coefficient, Q, that is a function of not only particle diameter and refractive index but also wavelength. It is clear that a linear calibration curve for each particle in different size can be obtained at an optimized wavelength.

• Proceedings of the Korean Geotechical Society Conference
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• 2002.03a
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• pp.743-750
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• 2002

Unsaturated soil has a possibility to induce a negative pore water pressure. Until now, saturated soil is mainly focused on the research of soil mechanics. Recently, soil mechanics is researched on two major parts such as saturated and unsaturated soil mechanics. Negative pore water pressure has a non-linear relationship with the water content changes. Soil-water characteristic curves of soil in Korea are not determined. There is no proper characteristic value such as air-entry value and residual water content. In this study, the characteristic curves of reclaimed soil, sand, and weathered granite soil were determined by laboratory tests. Air-entry value and residual water content were determined by fitting methods. Soil-water characteristic curves were estimated based on the particle-size distribution and compared with the laboratory test results. The results of soil-water characteristic curves estimation indicated that Fredlund and Wilson's model is excellent for sand and weathered granite soil. Arya and Paris's model is excellent for reclaimed soil.

• Journal of the Korean Geotechnical Society
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• v.25 no.10
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• pp.41-53
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• 2009

In order to analyze the influence of particle shape on evolution of particle crushing and characteristic of shear behavior of granular soil, direct shear test was simulated by using DEM (Discrete Element Method). Six particle shapes were generated by clump and cluster model built in PFC (Particle Flow Code). The results of direct shear test for six particle shapes were compared and analyzed with those for circular particle shape. The results of numerical tests showed a good agreement with those of experimental tests, thus the appropriateness of numerical modelling set in this study was proved. As for particle shape, more angular and rougher particle induced larger internal friction angle and more particle crushing than relatively round and smooth particle. When particles were crushed, crushing was concentrated on the shear band adjacent to the shear plane. Finally, it can be concluded that the numerical models suggested in this study can be used extensively for other studies concerning the shear behavior of granular soil including soil crushing.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.03a
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• pp.740-746
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• 2010

Most important characteristics of calcareous sand are the particle angularity and hollow structure. These characteristics lead to the different behavior of calcareous sand compared to siliceous sand. This study performs a series of dilatometer test using calibration chamber, in order to analyze the effect of particle characteristic of calcareous sand on DMT indices. From experimental test, it is observed that the horizontal stress index($K_D$) and dilatometer modulus($E_D$) of calcareous Jeju sand is underestimated compared to siliceous sand. This is because the particle crushing during penetration induces the less contraction of the dilatometer membrane. A slightly smaller influence of particle crushing is reflected in $E_D$ rather than $K_D$, because $P_1$ pressure reflects the deformation characteristics of un-crushed particle relatively well. It is also observed that $K_D$ of Jeju sand is differently influenced by the vertical effective stress compared with that of siliceous sand.