• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.2-2
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• 2011

Single-walled carbon nanotubes (SWNTs) have been considered as a promising candidate for nextgeneration electronics due to its extraordinary electrical properties associated with one-dimensional structure. Since diversity in electronic structure depends on geometrical features, the major concern has been focused on obtaining the diameter, chirality, and density controlled SWNTs. Despite huge efforts, the controlled synthesis of SWNTs has not been achieved. There have been various approaches to synthesize controlled SWNTs by preparation of homogeneously sized catalyst because the SWNTs diameter highly depends on catalyst nanoparticles size. In this study, geometrically controlled SWNTs were synthesized using designed catalytic layers: (a) morphologically modified Al2O3 supporting layer (Fe/Al2O3/Si), (b) Mo capping layer (Mo/Fe/Al/Si), and (c) heat-driven diffusion and subsequent evaporation process of Fe catalytic nanoparticles (Al2O3/Fe/Al2O3/Si). These results clearly revealed that (a) the grain diameter and RMS roughness of Al2O3 supporting layer play a key role as a diffusion barrier for obtaining Fe nanoparticles with a uniform and small size, (b) a density and diameter of SWNTs can be simultaneously controlled by adjusting a thickness of Mo capping layer on Fe catalytic layer, and (c) SWNTs diameter was successfully controlled within a few A scale even with its fine distribution. This precise control results in bandgap manipulation of the semiconducting SWNTs, determined by direct comparison of Raman spectra and theory of extended tight binding Kataura plot. We suggest that these results provide a simple and possible way for the direct growth of diameter, density, and bandgap controlled SWNTs by precise controlling the formation of catalytic films, which will be in demand for future electronic applications.

• Journal of Soil and Groundwater Environment
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• v.15 no.6
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• pp.91-98
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• 2010

The effective thermal conductivity of porous materials is usually determined by porosity, water content, and the conductivity of the matrix. In addition, it is also affected by the internal structure of the materials such as the size, arrangement, and connectivity of the matrix-forming grains. Based on the structural models for multi-phase materials, thermal conductivities of soils and sands measured with varying the water content were analyzed. Thermal conductivities of dry samples were likely to fall in the region between the Maxwell-Eucken model with air as the continuous phase and the matrix as the dispersed phase ($ME_{air}$) and the co-continuous (CC) model. However, water-saturated samples moved down to the region between the $ME_{wat}$ model and the series model. The predictive inconsistency of the structural models for dry and water-saturated samples may be caused by the increase of porosity for water-saturated samples, which leads to decrease of connectivity among the grains of matrix. In cases of variably saturated samples with a uniform grain size, the thermal conductivity showed progressive changes of the structural models from the $ME_{air}$ model to the $ME_{wat}$ model depending on the water content. Especially, an abrupt increase found in 0-20% of the water content, showing transition from the $ME_{air}$ model to the CC model, can be attributed to change of water from the dispersed to continuous phase. On the contrary, the undisturbed soil samples with various sizes of grains showed a gradual increase of conductivity during the transition from the $ME_{air}$ model to the CC model.

• Applied Chemistry for Engineering
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• v.32 no.1
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• pp.91-96
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• 2021

This study was conducted to improve the operating conditions of an adsorption tower filled with potassium impregnated activated carbon for high hydrogen sulfide capture capacity. Heat treatment modified the surface properties of activated carbon, and ultimately determined its adsorption capacity. The activated carbon doped with potassium showed 57 times more adsorption at room temperature than that of using the raw adsorbent. It is believed that uniform pore formation and strong bonding of the potassium on the surface of carbon contributed to the chemical and physical absorption of hydrogen sulfide. The SEM analysis on the surface structure of various commercial carbons showed that the modification of surface properties through the heat treatment generated the destruction of pore structures resulted in the decrease of the absorption performance. The pressure drop across the activated carbon bed was closely related with the grain size and shape. The optimum size of irregularly shaped activated carbon granules was 2~4 mesh indicating economical feasibility.

• Journal of the Korean Ceramic Society
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• v.41 no.5
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• pp.375-380
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• 2004

Pb(Ni$\_$1/3/Nb$\_$2/3/)O$_3$-PbZrO$_3$-PbTiO$_3$ thick films were screen-printed on platinized alumina substrates and fired at 800-1000$^{\circ}C$. Two kinds of powders with different particle size were prepared by attrition and ball milling methods. Effects of particle size of starting material on the microstructure and electrical properties of the thick films were investigated. Average particle size of attrition milled-powder (0.44 ${\mu}$m) was much smaller than that of ball milled-powder (2.87 ${\mu}$m). Average grain size of the thick film prepared from attrition-milled powder was smaller than that of the thick film prepared from ball-milled powder at the sintering temperature of 800$^{\circ}C$. However, the difference in average particle size became smaller with increasing the sintering temperature. Thick films prepared from attrition-milled powders showed more uniform and denser microstructures at all firing temperatures. Thick films prepared from attrition-milled powders had better electrical properties at the firing temperature above 900$^{\circ}C$ than thick films prepared from ball-milled powders. Dielectric constant, remanent polarization and coercive field of the thick film prepared from attrition-milled powders and fired at 900$^{\circ}C$ were 559, 16.3 ${\mu}$C/cm$^2$, and 51.3 kV/cm, respectively.

• Journal of Wetlands Research
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• v.13 no.2
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• pp.243-263
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• 2011

In order to understand the sedimentary environment of the southern intertidal zone of Shihwa Lake, west coast of Gyeonggi-do, 10 surface and 2 core sediment samples were analysed for grain size, water content, AVS (Acid Volatile Sulfide), TOC (Total Organic Carbon), concentrations of metals (Al, Fe, Mn, Cu, As, Pb, Zn, Ni, Cd, and Cr). The surface sediments are generally poorly sorted (0.60~2.31 ${\phi}$) sandy Silt, slightly gravelly muddy Sand, silty Sand, Sand with mean grain size of 2.95 to 6.00 ${\phi}$. The sediments contain Al (1.54%), Fe (1.75%), Cu (9.1ppm), As (1.1ppm), Pb (18.8 ppm), Ni (11.0 ppm), Cd (0.02 ppm), and Cr (30.1 ppm) on the average. Heavy metals are concentrated less than ERL (Effect Range-Low), verified by NOAA (National Oceanic and Atmospheric Administration). In the core sediments, they are also less than the ERL. Based on the uniform vertical distribution of excess radioactivity of $^{210}Pb$, the core sediments seen to have been actively mixed biologically or rapidly deposited after the construction of Shi-Hwa Seawall. The 'enrichment factor' of metals, normalized to Al, shows that the upper sediments of 35 cm in depth are more polluted. infect was significant in 2 core sediment samples in 35 cm below layer.

• Journal of the Korean Ceramic Society
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• v.39 no.7
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• pp.649-656
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• 2002

In situ patterned zinc oxide thin films were prepared by precipitation of Zn(NO$_3$)$_2$ aqueous solution containing urea and by microcontact printing using Self-Assembled Monolayers(SAMs) on A1/SiO$_2$/Si substrates. The visible precipitation of Zn(OH)$_2$ that was formed in the Zn(NO$_3$)$_2$ aqueous solution containing urea was enhanced with an increase of the reaction temperature and the amount of urea. As the reaction time of Zn(NO$_3$)$_2$ with urea was prolonged, the thickness and grain size of Zn(OH)$_2$ thin layers were increased, respectively. The optimum precipitation condition was at 80$\^{C}$ for 1 h for the solution with the ratio of Zn(NO$_3$)$_2$ to urea of 1 : 8. Homogeneous ZnO thin films were fabricated by the heat treatment of 600$\^{C}$ for 1 h of Zn(OH)$_2$ precipitation on Al/SiO$_2$/Si substrate. This was available to the in-situ patterned ZnO thin films with uniform grain size. Hydrophobic SAM, Octadecylphosphonic Acid(OPA) and hydrophilic SAM, 2-Carboxyethylphosphonic Acid(CPA) were applied on the Al/SiO$_2$/Si substrate by microcontact printing method. In situ patterned ZnO thin film was successfully prepared by the heat treatment of Zn(OH)$_2$ precipitated on the surface of hydrophilic SAM, CPA.

• Journal of Technologic Dentistry
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• v.35 no.1
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• pp.57-64
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• 2013

Purpose: Waste parts of zirconia blocks and powders were remained after CAD/CAM process. In order to make these residual zirconia fit for practical use, zirconia single cores were produced by drain casting process. Methods: Remained zirconia blocks were reduced to powders with zirconia mortar, and screened with 180 mesh sieve. Zirconia slip was prepared from waste parts of zirconia by ball milling. Plaster molds for forming cores by slip casting were also prepared. Formed cores were removed from mold after partial drying. Dried cores were biscuit fired at $1,100^{\circ}C$ for 1hour. Biscuit fired cores were treated with tools to control the fitness and thickness. Finished cores were $2^{nd}$ fired at $1,500^{\circ}C$ for 1hour. Microstructure of cross section of core was observed by SEM. Results: When mill pot was filled with 100g of zirconia and alumina mixed powder, 300g of zirconia ball, and 180g of distilled water, the optimum slip for drain casting was obtained. Gypsum plaster for ceramic forming was more suitable then yellow stone plaster for casting process. SEM photograph showed the microstructure of fully dense with uniform grain size of zirconia and well dispersed alumina grains into the zirconia matrix. Conclusion: Zirconia single cores were produced by drain casting process. Drain casting is useful process to make these residual zirconia fit for practical use. Further study will be focused on the preparation of the bridge type cores by casting.

• International Journal of Industrial Entomology and Biomaterials
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• v.13 no.1
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• pp.7-14
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• 2006

A breeding programme was initiated during 2001 to introduce sex-limited larval markings to a productive multivoltine breed - BL67 from an inbred sex-limited line, MY1 (SL) maintained at Central Sericultural Research and Training Institute, Mysore. Introgressive hybridization, recurrent backcrossing for six generations followed by sib-mating resulted in synthesis of a new multivoltine silkworm breed BL67 (SL) with sex-limited larval markings. The new breed was studied for combining ability by crossing with eight bivoltine breeds viz., $NB_4D_2,\;CSR_2,\;CSR_2 (SL),\;CSR_2,\;CSR_4,\;CSR_8,\;CSR_{18}\;and\;CSR_{19}$. General combining ability effects of the new breed showed its superiority over the popular Pure Mysore by expressing significant GCA effects for six out of twelve characters whereas the results are on par with the original multivoltine breed. The hybrid $BL67(SL){\times}CSR2(SL)$ excelled in several quantitative characters such as pupation rate (90.2%), cocoon weight (1.97 g), cocoon shell weight (40 cg), cocoon shell ratio (20.3%), filament length (918 m), denier (2.96), raw silk percentage (14.96%) and neatness (90 p). Studies on cocoon size variability revealed that the cocoons of $BL67(SL){\times}CSR2(SL)$ were found comparatively uniform showing less standard deviation of 6.55 and co-efficient of variation of 3.91 %. The suitability of newly developed breed for easy grain age operation and commercial exploitation with promising hybrid have been discussed.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.28 no.10
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• pp.82-88
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• 2014

This paper presents the results of model tests for the attachment process of lightning leader to ground which is one of poorly understood processes of cloud-to-ground lightning discharges. In order to simulate the attachment process of lightning leader to ground, we investigated the discharge characteristics of air gap between the tip of needle-shaped electrode and the soil surface as a parameter of moisture content in soils when the positive and negative $1.2/50{\mu}s$ lightning impulse voltages are applied. The breakdown voltage and the discharge light were observed. As a result, the attachment processes of lightning leader to ground are strongly dependent on the grain size and the moisture content of soils. The time to breakdown was shortened with increasing the magnitude of incident impulse voltages. The delay time from application of the highest voltage to breakdown in sand is shortened with increasing the moisture content. The delay time from application of the voltage to breakdown in gravel varied from about $0.5{\mu}s$ to several ${\mu}s$. As the moisture content in soil increases, the breakdown voltages are decreased and the breakdown voltage versus time to breakdown curves are shifted toward the lower side. The results obtained in this work are similar to those for non-uniform air gap stressed by lightning impulse voltages.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 1997.10a
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• pp.7-7
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• 1997

During sintering of very porous green bodies, as obtained by compaction of hard powders - such as tungsten carbide or ceramics - or by injection moulding, important shrinkage occurs. Due to heterogeneous green density field, gravity effects, friction on the support, thermal gradients, etc., this shrinkage is often non-uniform, which' may induce significant shape changes. As the ratio of compact dimension to powder size is very high, the mechanics of continuum is relevant to model such phenomena. Thus numerical techniques, such as the finite element method can be used to simulate the sintering process and predict the final shape of the sintered part. Such type of simulation has much been developed in the last decade firstly for hot isostatic pressing and next for die compaction. Finite element modelling has been recently applied to free sintering. The simulation of sintering should be based on constitutive equations describing the thermo-mechanical behaviour of the material under any state of stress and any temperature which may arise within the sintering body. These equations can be drawn either from experimental data or from micromechanical models. The experiments usually consist in free sintering and sinter-forging tests. Indeed applying more complex loading conditions at high temperature under controlled atmosphere is delicate. Micromechanical models describe the constitutive behaviour of aggregates of spheres from the deformation of two-sphere contact either by viscous flow or grain boundary diffusion. Such models are not able to describe complex microstructure and mechanisms as observed in real materials but they can give some basic information on the formulation of constitutive equations. Practically both experimental and theoretical approaches can be coupled to identify the constitutive equations. Such procedure has been performed for modelling the sintering of compacts obtained by die pressing of a mixture of tungsten carbide and cobalt powders. The constitutive behaviour of this material during sintering has been described by a linear viscous constitutive model, whose functions have been fitted from results of free sintering and sinter-forging experiments. This model has next been introduced in ABAQUS finite element code to simulate the sintering of heterogeneous green compacts of various geometries at constant temperature. Examples of simulations are shown and compared with experiments.