• Korean Journal of Optics and Photonics
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• v.25 no.1
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• pp.1-7
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• 2014

Multiple scattering effects in cloud are important error sources of the Mie scattering Lidar inversion method, which should be measured to correct the Lidar equation in single wavelength Mie Lidar. We have calculated the multiple scattering effects in liquid water clouds by using a Monte Carlo method, and we have applied these multiple scattering effects in measuring water cloud effective size and LWC (Liquid Water Content). When cloud effective size is less than $2.5{\mu}m$, we can easily extract cloud effective size and LWC by using two wavelength Lidar such as extinction coefficients measured at 355nm and 1064nm. For a larger size cloud, we can find that saturated degree of linear polarization is strongly correlated with cloud effective size, LWC, and extinction coefficients. From these correlations we know that we can measure LWC and cloud effective size if we use single wavelength Rotational Raman Lidar and Mie scattering polarization Lidar.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2009.04a
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• pp.243-246
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• 2009

본 연구에서는 분자동역학 전산모사와 미시역학 모델을 이용하여 나노입자의 크기와 체적분율 변화가 나노복합재의 물성변화에 미치는 영향을 효과적으로 묘사할 수 있는 순차적 브리징 해석기법을 개발하였다. 나노 입자의 크기변화와 체적분율 변화에 따른 영률과 전단계수를 분자동역학 전산모사를 통해 예측한 후, 이를 연속체 모델에서 구현하기 위해 다중입자 모델을 적용하였다. 나노입자의 크기효과를 반영하기 위해 입자와 기지 사이에 유효계면을 추가적인 상으로 도입하였고, 체적분율 효과는 나노복합재를 둘러싸는 무한영역의 물성값을 통해 조절되도록 하였다. 유효계면과 무한영역의 물성을 입자의 반경과 체적분율의 함수로 근사한 후, 다양한 입자의 크기와 체적분율에서 나타나는 나노복합재의 물성변화를 예측하였다. 제안된 해석기법의 적용을 통해 분자동역학 전산모사 결과와 잘 일치하는 예측해를 효과적으로 얻을 수 있었다.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.25 no.4
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• pp.315-321
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• 2012

In this study, a sequential multiscale homogenization method to characterize the effective thermal conductivity of nano particulate polymer nanocomposites is proposed through a molecular dynamics(MD) simulations and a finite element-based homogenization method. The thermal conductivity of the nanocomposites embedding different-sized nanoparticles at a fixed volume fraction of 5.8% are obtained from MD simulations. Due to the Kapitza thermal resistance, the thermal conductivity of the nanocomposites decreases as the size of the embedded nanoparticle decreases. In order to describe the nanoparticle size effect using the homogenization method with accuracy, the Kapitza interface in which the temperature discontinuity condition appears and the effective interphase zone formed by highly densified matrix polymer are modeled as independent phases that constitutes the nanocomposites microstructure, thus, the overall nanocomposites domain is modeled as a four-phase structure consists of the nanoparticle, Kapitza interface, effective interphase, and polymer matrix. The thermal conductivity of the effective interphase is inversely predicted from the thermal conductivity of the nanocomposites through the multiscale homogenization method, then, exponentially fitted to a function of the particle radius. Using the multiscale homogenization method, the thermal conductivities of the nanocomposites at various particle radii and volume fractions are obtained, and parametric studies are conducted to examine the effect of the effective interphase on the overall thermal conductivity of the nanocomposites.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.22 no.4
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• pp.343-348
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• 2009

In this study, an efficient sequential bridging method to characterize both the particle size effect and concentration effect on the mechanical properties of nanocomposites at high volume fraction is suggested through a molecular dynamics(MD) simulations and micromechanics of composites materials. The Young's modulus and the shear modulus of the nanocomposites at various particle radius and at 12% volume fraction were obtained from MD simulations and multi-inclusion model was adopted to describe both modulus in continuum model. In order to describe the particle size effect, an additional phase, effective interface, was adopted as characteristic phase and the non-dilute concentration effect which appears at 12% volume fraction was describe via the variation of the elastic modulus of the infinite medium. Both the elastic modulus of the interface and infinite medium were fitted into functions of particle radius for the applicability of the present bridging method at various particle radii. Using the present bridging method the elastic modulus of the nanocomposites was efficiently obtained with accuracy. In addition, the effect of the interface thickness and modulus on the elastic modulus of the nanocomposite was investigated.

• Korean Chemical Engineering Research
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• v.49 no.6
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• pp.790-797
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• 2011

Hydrodynamic similarity was analyzed by employing scaling factor in three phase fluidized beds. The scaling factor was defined based on the holdups of gas, liquid and solid particles and effectivity volumetric flux of fluids between the two kinds of fluidized beds with different column diameter. The column diameter of one was 0.102 m and that of the other was 0.152 m. Filtered compressed air, tap water and glass bead of which density was 2,500 kg/$m^3$ were used as gas, liquid and solid phases, respectively. The individual phase holdups in three phase fluidized beds were determined by means of static pressure drop method. Effects of gas and liquid velocities and particle size on the scaling factors based on the holdups of each phase and effective volumetric flux of fluids were examined. The deviation of gas holdup between the two kinds of three phase fluidized beds decreased with increasing gas or liquid velocity but increased with increasing fluidized particle size. The deviation of liquid holdup between the two fluidized beds decreased with increasing gas or liquid velocity or size of fluidized solid particles. The deviation of solid holdup between the two fluidized beds increased with increasing gas velocity or particle size, however, decreased with increasing liquid velocity. The deviation of effective volumetric flux of fluids between the two fluidized beds decreased with increasing gas velocity or particle size, but increased with increasing liquid velocity. The scaling factor, which was defined in this study, could be effectively used to analyze the hydrodynamic similarity in three phase fluidized processes.

• Journal of Radiation Protection and Research
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• v.28 no.4
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• pp.321-325
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• 2003

The effects of AMAD, absorption type, and intake pattern were compared and analysed for the internal dose evaluation of workers who chronically inhale uranium. The committed effective doses$(E_{50})$ based on AMAD, absorption type, and intake pattern were evaluated using 3 monthly lung predicted monitoring data due to a chronic intake of uranium for 5 years. The relative error ranges of $E_{50}$ evaluated with each AMAD$(0.1{\sim}10{\mu}m)\;to\;E_{50}$ evaluated with $5{\mu}m$ AMAD were $-37.0{\sim}49.8%$, and the relative error ranges of En evaluated with Type M to $E_{50}$ evaluated with Type S were $15.9{\sim}56.6%$, and the relative error ranges of $E_{50}$ evaluated with an acute intake to $E_{50}$ evaluated with a chronic intake were $0.55{\sim}4.52%$. Thus AMAD and the absorption type affected the results of $E_{50}$, but the intake pattern didn't really affect the results of $E_{50}$.

• Journal of the Korean Society for Marine Environment & Energy
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• v.2 no.1
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• pp.26-33
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• 1999

Coastal sediments in polluted areas adsorb many hydrophobic pollutants such as PCBs. During environmental remediation projects like dredging, they can be resuspended and transported to less polluted areas. To assess the environmental impact, the author previously developed a mathematical model that can simulate the changes of particle size distribution (PSD) due to sedimentation, vortical dispersion and coagulation. In this research, the simulation results using this model were presented in conjunction with observed PSDs from a 2-m settling column simulating coastal environments. The simulations showed that the model predictions were in fairly good agreement with the observed data (changes of PSDs in terms of depths and times), and that the resuspended sediments coagulated during the vertical transport. So, this study showed that the developed model has a good ability to describe the very complicated phenomena of real aggregation and vortical transport dynamics of coastal sediments with various particle sizes.

• Journal of the Korean Geotechnical Society
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• v.19 no.2
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• pp.199-206
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• 2003

Particle-size distribution in soils is one of the most fundamental physical properties of soils. One of the latest developments in the study of particle-size distributions has focused on the use of fractal theories. In this study, the fragmentation fractals were used for determining the characteristics of the particle-size distribution curve. It was shown that the mass-size distribution method was more practical than the cumulative number-size distribution method. From the co-relation between fractal dimensions($D_{tot}$) and the coefficient of uniformity($C_{u}$), there was a sharp increase in fractal dimensions for $C_{u}$<4, but fractal dimension converged the single value for $D_{u}$$\geq$6. Fractal dimensions were affected by small sized particles for $C_{c}$$\geq$3 and large sized particles for $C_{c}$/<3. As a result of the analysis of the influence of the effective size($D_{10}$), it was observed that the changes of $D_{tot}$/ were nominal beyond the effective size.

• Economic and Environmental Geology
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• v.44 no.2
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• pp.171-180
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• 2011

For 21 rock samples consisting of granite, sandstone and the effective thermal conductivity (TC) was measured with the LFA-447 Nanoflash, and mineralogical compositions were also determined from XRD analysis. The structural models were used to examine the effects of quartz content and the size of minerals on TC of rocks. The experimental results showed that TC of rocks was strongly related to quartz content with $R^2$ value of 0.75. Therefore, the proposed regression model can be a useful tool for an approximate estimation of TC only from quartz content. Some samples with similar values of quartz content, however, illustrated great differences in TC, presumably caused by differences in the size of minerals. An analysis from structural models showed that TC of rocks with fine-grained minerals was likely to fall in the region between Series and EMT model, and it moved up to ME and Parallel model as the size of minerals increased. This progressive change of structural models implies that change of TC depending on the size of minerals is possibly related to the scale of experiments; TC was measured from a disk sample with a thickness of 3 mm. Therefore, in case of measurements with a thin sample, TC can be overestimated as compared to the real value in the field scale. The experimental data illustrated that the scale effect was more pronounced for rocks with bigger size of minerals. Thus, it is worthwhile to remember that using a measured TC as a representative value for the real field can be misleading when applied to many geothermal problems.

• Journal of the Korean Geotechnical Society
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• v.22 no.11
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• pp.47-54
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• 2006

Shear wave velocity of uncemented soil can be expressed as the function of effective stresses when capillary phenomena are negligible. However, the terms of effective stresses are divided into the direction of wave propagation and polarization because stress states are generally anisotropy. The shear wave velocities are affected by ${\alpha}$ parameters and ${\beta}$ exponents that are experimentally determined. The ${\beta}$ exponents are controlled by contact effects of particulate materials (sizes, shapes, and structures of particles) and the ${\alpha}$ parameters are changed by contact behaviors among particles, material properties of particles, and type of packing (i.e., void ratio and coordination number). In this study, consolidation tests are performed by using clay, mica and sand specimens. Shear wave velocities are measured during consolidation tests to investigate the stress-induced and inherent anisotropies by using bender elements. Results show the shear wave velocity depends on the stress-induced anisotropy for round particles. Furthermore, the shear wave velocity is dependent on particle alignment under the constant evvective stress. This study suggests that the shear wave velocity and the shear modulus should be carefully estimated and used for the design and construction of geotechnical structures.