• Journal of Powder Materials
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• v.19 no.2
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• pp.105-109
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• 2012

Magnetic properties and the microstructures of magnets prepared by spark plasma sintering were investigated in order to enhance magnetic properties by grain size control. Nd-Fe-B magnets were fabricated by the spark plasma sintering under 30 MPa at various temperatures. The grain size was effectively controlled by the spark plasma sintering and it was possible to make Nd-Fe-B magnets with grain size of 5.9 ${\mu}m$.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2008.05a
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• pp.305-308
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• 2008

This paper presents characteristics of soil ionization when high currents such as lightning and switching surge currents are injected into a grounding rod. Soil ionization phenomena are investigated by using both voltage and current signals recorded by oscilloscope. As a result, a critical electric field intensity($E_C$) for ionization is decreased with reduction of grain size. The pre-ionization resistance($R_1$) and post-ionization resistance($R_2$) at the sand with fine grain size are getting lower with increasing current magnitude. Finally, the time to ionization($t_1$) and ionization current peak($t_2$) of fine grain size are significantly shorter than those of medium grain size.

• Proceedings of the KSRS Conference
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• 2007.10a
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• pp.225-228
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• 2007

This paper presents a geostatistical methodology to model local uncertainty in spatial estimation of sediment grain size with high-resolution remote sensing imagery. Within a multi-Gaussian framework, the IKONOS imagery is used as local means both to estimate the grain size values and to model local uncertainty at unsample locations. A conditional cumulative distribution function (ccdf) at any locations is defined by mean and variance values which can be estimated by multi-Gaussian kriging with local means. Two ccdf statistics including condition variance and interquartile range are used here as measures of local uncertainty and are compared through a cross validation analysis. In addition to local uncertainty measures, the probabilities of not exceeding or exceeding any grain size value at any locations are retrieved and mapped from the local ccdf models. A case study of Baramarae beach, Korea is carried out to illustrate the potential of geostatistical uncertainty modeling.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2005.04a
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• pp.446-450
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• 2005

Hydraulic conductivity of unconsolidated media can be determined by aquifer tests, laboratory tests and empirical equations based on grain size analysis. Commonly, the different methods give different hydraulic conductivities. Grain size measurements were done to determine hydraulic conductivity, using 184 soil samples collected from eight boreholes in a riverbank filtration area, Daesan-Myeon, Changwon City, Korea, Pumping tests were conducted at the riverbank filtration area. The average hydraulic conductivity by the empirical relations from grain size measurements comes out around $10^{-2}m/s$, 22 to 55 times higher than by the pumping test analyses. The hydraulic conductivity obtained from the empirical equations is interpreted to have a relationship with steady-state condition while that obtained from the pumping tests is interpreted to have a relationship with unsteady-state condition. Thus, hydraulic conductivity obtained from various methods should be critically analyzed for reasonable management of groundwater development.

• Transactions of Materials Processing
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• v.8 no.6
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• pp.620-625
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• 1999

A finite element analysis is performed to predict the recrystallized volume fraction and the mean grain size in hot compression of Al-5wt%Mg alloy. In the analysis, a modeling equation of flow stress is assumed as a function of strain, strain rate, and temperature. And the influence of above varibles on flow stress is quantified by using Zener-Hollomon Parameter. In the modeling equation, effects of strain hardening and dynamic recrystallization on microstructure of Al-5wt%Mg alloy are investigated. The predicted results of recrystallized volume fraction and mean grain size are in good agreement with those of microstructures obtained from hot compression tests.

• Journal of the Korean Ceramic Society
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• v.26 no.2
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• pp.258-266
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• 1989

The effects of grain size and dopant ZnO on the photoelectrochemical conversion in TiO2 ceramic electrodes have been investigated. The photocurrent increases with increasing grain size in the undoped TiO2 ceramic electrode. In ZnO-doped TiO2 electrodes, the photocurrent decreases with increasing ZnO up to 0.4 wt% due to decrease of donor concentration, and then with further addition of ZnO, photocurrent increases according to the formation of second phase. However, the photoresponse appears at wavelength of 420nm, which is very close to the energy band gap of TiO2, regardless of grain size and amount of ZnO.

• 한국정보디스플레이학회:학술대회논문집
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• 2007.08a
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• pp.972-973
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• 2007

Relationships between field effect mobility and grain size on pentacene thin-film transistors with $polyimide/SiO_2$ gate dielectrics have been studied. 6 kinds of polyimide were used as surface treatment gate dielectric layer. Grain size of the pentacene thin film were between 5 and $30\;{\mu}m$ and depended on the polyimide. The field effect mobility were also depended on the polyimide and the those values were from 0.027 to $0.69\;cm^2/(Vs)$. The field effect mobility tends to increase with increasing the grain size. Precursor type polyimide containing polyamic acid show better mobility of $0.69\;cm^2/(Vs)$ than soluble type polyimide. Bias stress characteristics in air are discussed in the basis of the grain size.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2007.11a
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• pp.79-82
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• 2007

Recently, the use of ALC has became increasingly popular. ALC is a unique building material. Because of its cellular nature, it is lightweight, self-insulating, sound and fireproof, as well as insect and mold resistant. Furthermore, ALC is free of VOCs and various fibers associated with wood and glass wool construction. However, ALC have high water absorption, low compressive strength and popout the origin of the low surface strength in its properties. These properties make troubles under construction such as cracking and popout. Thus, this study is to improve the fundamental strength by controls of increasing of admixtures, and grain size. Admixtures make use of metakaolin, silica fume, sodium silicate and sodium hydroxide. From the test result, the ALC using admixture have a good fundamental properties compared with plain specimen. Compressive strength, specific strength and abrasion's ratio were improved depending on increasing admixtures ratio's, and grain size.

• Economic and Environmental Geology
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• v.8 no.4
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• pp.203-210
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• 1975

The engineering properties of some Gyeongsang sedimentary rocks with respect to the grain size and the orientation of bedding planes were studied. The suitability of the rocks for civil and architectural construction was also investigated. The porosity of the rocks increases in proportion to the grain size. The ratio of the strain due to stress perpendicular to the bedding planes to the strain resulting from stress parallel to the bedding planes increases as the grain size decreases. The study indicates however, that the ratio of Young's modulus due to stress perpendicular to the bedding planes to Young's modulus resulting from stress parallel to the bedding planes increases in proportion to the grain size. The compressive strength of the sandstones studied is much greater than the strength of the conglomerate or shale. Only the coarse grained sandstone can be used for civil and architectural construction, regardless of the orientation of bedding planes. The relationships between compressive strength and density, elasticity and porosity, and compressive strength and mineral content were also studied.

• Journal of The Geomorphological Association of Korea
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• v.27 no.4
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• pp.1-11
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• 2020

Coastal dunes play an important role in coastal defense. The Moraeul dune in Daecheongdo Island is representative in this regard. However, there is little knowledge, concerning the morphology, grain size, and formation timing of the dune. This study investigated the geomorphological characteristics of the Moraeul dune using topographic surveys, grain size analyses, and OSL dating. The dune was classified as 'single accreted foredune', which was developed under dense vegetation cover and efficient sand trapping. The dune consisted of fine to medium sand with 1.6Φ of mean grain size, and was covered with pine trees (> 100 years old). The samples from the upper part of the dune yielded quartz OSL ages ranging 0.5 ~ 0.7 ka. Therefore, it is likely that the dune developed at least before the Little Ice Age and became what it is today about one century ago.