• Korean Journal of Crystallography
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• v.8 no.2
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• pp.149-153
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• 1997

ZnO varistor based on ZnO-Bi2O3-Co3O4-MnCO3-Cr2-O3-Sb2O3 system with Sb2O3 contents were studied for grain size variation and microstructure properties. The composition of pure ZnO varistor was observed composition was inhibited owing to formation of Zn7Sb2O12 spinel phase and did not observed abnrmal grain growth. With Sb2O3 contents, the grain sizes of ZnO varistor were remarkably decreased and the microstructure had the distribution of dense and homogeneous grains.

• Interaction and multiscale mechanics
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• v.1 no.3
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• pp.369-379
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• 2008

A combined stochastic diffusion and mean-field model is developed for a systematic study of the grain growth in a pure single-phase polycrystalline material. A corresponding Fokker-Planck continuity equation is formulated, and the interplay/competition of stochastic and curvature-driven mechanisms is investigated. Finite difference results show that the stochastic diffusion coefficient has a strong effect on the growth of small grains in the early stage in both two-dimensional columnar and three-dimensional grain systems, and the corresponding growth exponents are ~0.33 and ~0.25, respectively. With the increase in grain size, the deterministic curvature-driven mechanism becomes dominant and the growth exponent is close to 0.5. The transition ranges between these two mechanisms are about 2-26 and 2-15 nm with boundary energy of 0.01-1 J $m^{-2}$ in two- and three-dimensional systems, respectively. The grain size distribution of a three-dimensional system changes dramatically with increasing time, while it changes a little in a two-dimensional system. The grain size distribution from the combined model is consistent with experimental data available.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2008.06a
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• pp.325-326
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• 2008

• Journal of The Geomorphological Association of Korea
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• v.26 no.1
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• pp.15-26
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• 2019

In this study, we investigated the grain size, lithological type, and shape of coarse bed materials in the upper and middle reaches of Gongneungcheon River. For this purpose, 11 sampling points were selected along the river. For 100 samples of the coarse bed materials at each point, three axes (long, intermediate, and short) of samples were measured, and their lithological types were also identified. By measuring grain size, the sphericity and flatness of samples were calculated. Finally, every particle was classified into four shape categories: sphere, disc, blade and rod. We found that the grain size in incised meandering reach is the largest. This is mainly due to the supply of coarse materials from steep valley sides along the meandering channel. According to the lithological analysis, all samples were identified as granite, gneiss and schist, and quartz. The proportion of granite decreased, whereas the proportion of gneiss and schist increased downstream. These patterns indicate that the bedrock distribution within the study area accounts for the downstream lithological variation of coarse bed materials. With regard to the grain shape, sphericity gradually decreased while flatness gradually increased downstream. In the case of the shape classification, unlike the general downstream pattern of grain shape, the proportion of the sphere type decreased and the proportion of the blade type increased downstream. Such a reversal change in the downstream direction turns out to be determined by the lithology (such as foliation, bedding and the pattern of weathering) of coarse bed materials.

• Journal of Environmental Science International
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• v.17 no.11
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• pp.1203-1210
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• 2008

Flow resistance in a natural stream is caused by complex factors, such as the grains on the bed, vegetation, and bed-form, reach profile. Flow resistance in a generally stable gravel bed stream is due to protrudent grains from bed. Therefore, the flow resistance can be calculated by equivalent roughness in gravel bed stream, but estimation of equivalent roughness is difficult because nonuniform size and irregular arrangement of distributed grain on natural stream bed. In previous study, equivalent roughness is empirically estimated using characteristic grain size. However, application of empirical equation have uncertainty in stream that stream bed characteristic differs. In this study, we developed a model using an analytical method considering grain diameter distribution characteristics of grains on the bed and also taking into account flow resistance acting on each grain. Also, the model consider the protrusion height of grain.

• The Korean Journal of Ceramics
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• v.6 no.3
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• pp.262-266
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• 2000

We investigated the effect of the grain size on the photovoltaic current in (Pb$_{1-x}$La$_x$)TiO$_3$ceramics, and the photoinduced domain switching in (Pb$_{0.85}$La$_{0.15}$)TiO$_3$and BaTiO$_3$ceramics. These behaviors in ferroelectric ceramics were attributed to the grain boundary at which photoexcited electrons were trapped. As the charged grain boundary acted as an electro-potential barrier which impeded the movement of electrons, the photovoltaic current showed a peak at a critical grain size. The space charge field built by the electrons trapped at the grain bound-aries was accounted for the photoinduced domain switching, and AE experimental results support well this account.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.336-337
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• 2006

During sintering of cemented carbides abnormal grain growth is often observed but cannot be understood from the classical LSW-theory. A model based on 2-D nucleation of new crystalline layers and a grain-size distribution function is formulated and the equations are solved numerically. Experimental studies and computer simulations show that the initial grain size distribution has a strong effect on the grain growth behavior. For example, a fine-grained powder can grow past a coarser powder.

• Journal of Korea Water Resources Association
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• v.57 no.5
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• pp.347-357
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• 2024

Numerous prior studies have delineated the size distribution of noncohesive sediment in suspension, focusing on mean size and standard deviation. However, suspensions comprise a heterogeneous mixture of sediment particles of varying sizes. The transport dynamics of suspended sediment in turbulent flow are intimately tied to settling velocities calculated based on size and density. Consequently, understanding the grain size distribution becomes paramount in comprehending sediment transport phenomena for noncohesive sediment. This study aims to introduce a straightforward modeling approach for simulating the grain size distribution of suspended sediment amidst turbulence. Leveraging insights into the contrast between cohesive and noncohesive sediment, we have meticulously revised a stochastic flocculation model originally designed for cohesive sediment to aptly simulate the grain size distribution of noncohesive sediment in suspension. The efficacy of our approach is corroborated through a meticulous comparison between experimental data and the grain size distribution simulated by our newly proposed model. Through numerical simulations, we unveil that the modulation of grain size distribution of suspended sediment is contingent upon the sediment transport capacity of the carrier fluid. Hence, we deduce that our simplified approach to simulating the grain size distribution of suspended sediment, integrated with a sediment transport model, serves as a robust framework for elucidating the pivotal bulk properties of sediment transport.

• Korean Journal of Materials Research
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• v.24 no.10
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• pp.520-525
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• 2014

Effects of Cu and B on effective grain size and low-temperature toughness of thermo-mechanically processed high-strength bainitic steels were investigated in this study. The microstructure of the steel specimens was analyzed using optical, scanning, and transmission electron microscopy; their effective grain size was also characterized by electron back-scattered diffraction. To evaluate the strength and low-temperature toughness, tensile and Charpy impact tests were carried out. The specimens were composed of various low-temperature transformation products such as granular bainite (GB), degenerated upper bainite (DUB), lower bainite (LB), and lath marteniste (LM), dependent on the addition of Cu and B. The addition of Cu slightly increased the yield and tensile strength, but substantially deteriorated the low-temperature toughness because of the higher volume fraction of DUB with a large effective grain size. The specimen containing both Cu and B had the highest strength, but showed worse low-temperature toughness of higher ductile-brittle transition temperature (DBTT) and lower absorbed energy because it mostly consisted of LB and LM. In the B-added specimen, on the other hand, it was possible to obtain the best combination of high strength and good low-temperature toughness by decreasing the overall effective grain size via the appropriate formation of different low-temperature transformation products containing GB, DUB, and LB/LM.

• Journal of The Korean Society of Agricultural Engineers
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• v.58 no.1
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• pp.11-17
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• 2016

Dredging and land reclamation works has actively carried out for the efficient use of land and secure of agricultural and industrial site. During the reclamation, a portion of landfills are lost from the desired location due to a variety of causes. However, these causes has been rarely studied, and water flow velocity has a great influence on the movement of landfills. For the economical and efficient reclamation, it is important to predict the movement of landfills in water. In this paper, an experimental study was carried out to investigate the deposition distance according to the flow velocity and soil grain size. We have made a large open-channel apparatus that can reproduce a laminar flow, and the deposition test was carried out on the four grain size (0.638, 1.425, 3.375, 7.125 mm) and four flow velocity (0.1, 0.3, 0.5, 0.67 m/s) with high definition video recording. As a results, average deposition distance increased with the flow velocity, and its relationship is shown linearly. For the grain size, the average deposition distance were drastically increased as the grain size becomes smaller.