• The Journal of the Korea Contents Association
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• v.21 no.12
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• pp.517-535
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• 2021

The development of digital technology has not only brought many changes to our lives, but also many changes to the online education environment. The emergence of micro-learning is to meet the needs of individual learners who hopes to receive personalized learning content immediately when they need it. Therefore, Micro-learning can be said to be 'adaptive' education. This research attempts to explore the development principles of adaptive micro-learning through literature research and case analysis. The results of the research draw four aspects of the development principles, including adaptive learning environment, adaptive learning content, adaptive learning sequence and adaptive learning evaluation, as well as detailed elements of each aspect. Micro-learning is a new form of e-learning that reflects the needs of the current society. As exploratory research, this research attempts to point out the direction for future follow-up research.

• Journal of the Microelectronics and Packaging Society
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• v.10 no.2
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• pp.55-59
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• 2003

In this study, $Al_xTa_{1-x}$(x=0.0∼1.0) alloy thin films were grown by RF-Magnetron sputtering system, and the structural, mechanical and electrical properties of samples were examined by 4-point probe, XRD, AFM and micro-Vickers hardness profiler. The electrical resistivity was maximum and the crystal quality was optimum for the samples with Al content x=0.245 (Al 24.5 at.%). Regarding the surface hillock formation, the hillock density decreased with an increase of Al content for the low Al content range, and the hillock was eliminated for the sample with Al=24.5 at.%. The hillock density increased with the further increase of Al content. The high values of micro-Vickers hardness were obtained for the samples with x=0.2∼0.45. The results obtained demonstrate that the crystal quality, electrical resistivity, surface morphology and micro-hardness are closely inter-related, and that the optimum physical properties are obtained for the sample with x=0.245.

• International Journal of Oral Biology
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• v.42 no.4
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• pp.155-161
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• 2017

Teeth and bones are highly mineralized tissues containing inorganic minerals such as calcium phosphate, and a growing number of evidences show that their mineral content is associated with many diseases. Although the quantification of mineral contents by micro-computed tomography(micro- CT) has been used in diagnosis and evaluation for treating bone diseases, its application for teeth diseases has not been well established. In this study, we attempted to estimate a usefulness of a high-resolution micro-CT in analysis of human teeth. The teeth were scanned by using the Skyscan 1172 micro-CT. In order to measure tooth mineral content, beam hardening effect of the machine was corrected with a radiopaque iodine-containing substance, iodoacetamide. Under the maximum resolution of $6.6{\mu}m$, X-ray densities in teeth and hydroxyapatite standards were obtained with Hounsfield unit (HU), and they were then converted to an absolute mineral concentration by a CT Analyzer software. In enamel layer of cusp area, the mean mineral concentration was about $2.14mg/mm^3$ and there was a constant mineral concentration gradient from the enamel surface to the dentinoenamel junction. In the dentin of middle 1/3 of tooth, the mean mineral concentration was approximately $1.27mg/mm^3$ and there was a constant mineral concentration gradient from the outer of root to the pulp side, ranging from 1.3 to $1.06mg/mm^3$. In decay region of dentin, the mineral content was gradually decreased from the intact inner side to the decayed surface. These results suggest that high-resolution micro-CT can be as a useful tool for non-invasive measurement of mineral concentration in teeth.

• Macromolecular Research
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• v.15 no.1
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• pp.22-30
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• 2007

High water vapor permeable coating materials were prepared by blending aqueous poly(vinyl alcohol) (PVA) solution with waterborne polyurethane-urea (WBPU) dispersions synthesized by prepolymer mixing process. Stable WBPU/PVA dispersions were achieved at PVA content below 30 wt%. As the water soluble polymer PVA content increased, the number and density of total micro-pores (tunnel-like/isolated micro-pores) formed after the dissolution of PVA in water increased, and the water vapor permeability of coated Nylon fabric also increased significantly. Using WBPU/water soluble polymer PVA blends as a coating material and then dissolving PVA in water was confirmed to be an effective method to obtain prominent breathable fabrics.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.67 no.9
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• pp.1189-1196
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• 2018

7 type composites (40, 45, 50, 55, 60, 65, and 70 wt.%)were prepared for the environmentally friendly GIS Spacer. Five kinds of samples were prepared for optimization of the filler content ratio (MS: MA = 1: 9, 3: 7, 5: 5, 7: 3, 9: 1) of epoxy / microsilica and microalumina. As a result of evaluation of the partial discharge resistance characteristic, surface erosion is generally slowed down as the fill amount of micro silica is increased. Also, partial discharge resistance characteristics for the development of insulating materials with optimal mixing ratios of heterologous showed a higher partial resistance of discharge and a decrease in erosion, as the filler content ratio of micro silica was larger. In the future, various researches such as electrical, mechanical, and thermal studies will be needed to develop insulating materials that can commercialize power devices in environmentally friendly insulating gas.

• Journal of Korea Foundry Society
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• v.33 no.2
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• pp.55-62
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• 2013

Effect of Fe and Mn contents on the castability of Al-4wt%Mg-0.9wt%Si system alloy has been studied. According to the analysis of cooling curve for Al-4wt%Mg-0.9wt%Si-0.3wt%Fe-0.3/0.5wt%Mn alloy, ${\alpha}-Al_{15}(Fe,Mn)_3Si_2$ and ${\beta}-Al_5FeSi$ phases crystallized above eutectic temperature of $Mg_2Si$. Therefore, these phases affected both the fluidity and shrinkage behaviors of the alloy during solidification. As Fe and Mn contents of Al-4wt%Mg-0.9wt%Si system alloy increased from 0.1 wt% to 0.4 wt% and from 0.3 wt% to 0.5 wt% respectively, the fluidity of the alloy decreased by 26% and 33%. When Fe content of the alloy increased from 0.1 wt% to 0.4 wt%, 23% decrease of macro shrinkage and 19% increase of micro shrinkage appeared. Similarly, Mn content of the alloy increased from 0.3 wt% to 0.5 wt%, 11% decrease of macro shrinkage and 14% increase of micro shrinkage appeared. Judging from the castability of the alloy, Al-4wt%Mg-0.9wt%Si alloy with low content of Fe and Mn, 0.1 wt% Fe and 0.3 wt% Mn, is recommendable.

• Transactions of the Korean Society of Automotive Engineers
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• v.20 no.3
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• pp.1-6
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• 2012

This paper developed the chassis part as micro-alloyed steel with high toughness. The performance of micro-alloy steels are superior to similar heat treated steels. The strengthening effects of vanadium make micro-alloyed steels particularly suited for high-strength-steel applications. The disadvantages are that ductility and toughness are not as good as quenched and tempered (Q&T) steels. Precipitation hardening increases strength but may contribute to brittleness. Toughness can be improved by reducing carbon content and titanium additions. dispersed titanium nitrides (TiN) formed by titanium additions effectively prevents grain coarsening. Grain refinement increases strength but also improves toughness. For the chassis parts using high toughness micro-alloy steel, it had proven superior to a plain steel forging by static strength test and endurance test.

• YAKHAK HOEJI
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• v.5 no.1
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• pp.24-26
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• 1960

Micro-determination of Lead by Dithizone Method was studied as follows: 1) Max. absorption wave length of Dithizone-pb complex in CC $l_{4}$ soln. is 510m.mu., 2) at the range of 5.gamma.-120.gamma. pb content, Bourguer-Beer's law hold good, 3) co-existence of F $e^{++}$ Z $n^{++}$, and C $u^{++}$ interfere.rfere.

• Nuclear Engineering and Technology
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• v.52 no.3
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• pp.589-596
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• 2020

Many components in the assembly section of Sodium-cooled Fast Reactor are made of good corrosionresistant 316 LN Stainless Steel material. To avoid self-welding of the components with the coolant sodium at elevated temperature, hardfacing is inevitable. Ni-based colmonoy-5 is used for hardfacing due to its lower dose rate by Plasma Transferred Arc process due to its low dilution. Since Ni-Cr-B-Si alloy becomes very fluidic while depositing, the major height of the weld overlay rests inside the groove. Hardfacing is also done over the plain surface where grooving is not possible. Therefore, grooved and ungrooved hardfaced specimens were prepared at different travel speeds. Fe content at every 100 ㎛ of the weld overlay was studied by Energy Dispersive Spectroscopy and also the micro hardness was determined at those locations. A correlation between iron dilution from the base metal and the micro hardness was established. Therefore, if the Fe content of the weld overlay is known, the hardness at that location can be obtained using the correlation and vice-versa. A new correlation between micro hardness and dilution coefficient is obtained at different locations. A comparative study between those specimens is carried out to recommend the optimum travel speed for lower dilution.

• Advances in concrete construction
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• v.10 no.3
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• pp.257-269
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• 2020

The aim of this study is to investigate the flexural performance of hybrid fiber reinforced self-compacting concrete (HFRSCC) having different ratio of micro and macro steel fiber. A total of five mixtures are prepared. In all mixtures, the sum of the steel fiber content is 1% and also water/binder ratio is kept constant. The amount of high range water reducer admixture (HRWRA) is arranged to satisfy the workability criteria of self-compacting concrete. Four-point bending test is carried out to analyze the flexural performance of the mixtures at 28 and 56 curing days. From the obtained load-deflection curves, the load carrying capacity, deflection and toughness values are investigated according to ASTM C1609, ASTM C1018 and JSCE standards. The mixtures containing higher ratio of macro steel fiber exhibit numerous micro-cracks and, thus, deflection-hardening response is observed. The mixture containing 1% micro steel fiber shows worst performance in the view of all flexural parameters. An improvement is observed in the aspect of toughness and load carrying capacity as the macro steel fiber content increases. The test results based on the standards are also compared taking account of abovementioned standards.