• Korean Journal of Metals and Materials
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• v.46 no.8
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• pp.524-537
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• 2008

Zr-based amorphous alloy matrix composites reinforced with metallic continuous fibers were fabricated by liquid pressing process, and their fracture properties were investigated by directly observing microfracture process using an in situ loading stage installed inside a scanning electron microscope chamber. About 60 vol.% of metallic fibers were homogeneously distributed inside the amorphous matrix. Apparent fracture toughness of the stainless-steel- and tungsten-fiber-reinforced composites was lower than that of monolithic amorphous alloy, while that of the Ta-fiber-reinforced composite was higher. According to the microfracture observation, shear bands or cracks were initiated at the amorphous matrix, and the propagation of the initiated shear bands or cracks was effectively blocked by fibers, thereby resulting in stable crack growth which could be confirmed by the fracture resistance curve (R-curve) behavior. This increase in fracture resistance with increasing crack length improved fracture properties of the fiber-reinforced composites, and could be explained by mechanisms of formation of multiple shear bands or multiple cracks at the amorphous matrix and blocking of crack or shear band propagation and multiple necking at metallic fibers.

• Proceedings of the KIEE Conference
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• 2007.07a
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• pp.218-219
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• 2007

Silicon feed stock shortage have acted as major restraints for growth of photovoltaic industry. Concentrating photovoltaic (CPV) system will reduce the use of silicon PV materials. This paper presents the application possibility of mono-crystalline silicon solar cell, which has increased in market share, for PV concentrator. We measured the power of solar cell using sun simulator and I-V curve tracer and compared the results. The comparison of results showed that the concentrated solar cell generated the power more approximately 7 times than without concentration in spite of non-heat sink. If CPV technology included heat sink combines already developed PV tracking system, it will have a merit economically.

• Journal of the Korean institute of surface engineering
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• v.55 no.5
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• pp.292-298
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• 2022

In this study, PEO (plasma electrolytic oxidation) film formation behavior of AZ31 Mg alloy under application of 300 Hz pulse current was studied by the analyses of V-t curve, arc generation behavior, PEO film thickness and morphology of PEO films with treatment time in 0.05 M NaOH + 0.05 M Na₂SiO₃ + 0.1 M NaF solution. PEO films was observed to grow after 10 s of application of pulse current together with generation of micro-arcs. PEO film grew linearly with treatment time at a growth rate of about 5.58 ㎛/min at 200 mA/cm² of pulse current but increasing rate of film formation voltage became lowered largely with increasing treatment time after passing about 250 V, suggesting that resistivity of PEO films during micro-arc generation decreases with increasing film formation voltage at more than 250 V.

• Journal of Information Technology Services
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• v.13 no.4
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• pp.255-273
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• 2014

The widespread use of smart phones and smart pads has given rise to the use of eBook services based on these smart devices. Consequently, the size of eBook services has exploded both in the domestic as well as overseas market. However, the growth curve becomes flatter than before, and the adoption rate is still not high in Korea. Hence, this study explores the factors affecting the intention to use eBook services based on smart devices, and their relationships. Finally, we propose an eBook adoption model, which extends the Technology Adoption Model. An online survey was conducted to validate the research model. By applying Partial Least Squares, we found that there are strong relationships among perceived usefulness, perceived ease of use, perceived playfulness, social influence, and intention to use. In addition, we found that smart devices enjoyment positively affects the perceived playfulness of eBooks, and that personal innovativeness positively affects perceived ease of use. Our findings shed some light on how to design eBook services based on smart devices.

• Journal of Korean Institute of Industrial Engineers
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• v.40 no.3
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• pp.333-341
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• 2014

The purpose of this study is to forecast the penetration rate of renewable energy and a reasonable scale for the R&D investment plan in Korea based on the relationship between the diffusion and R&D investments drawn by analogy from empirical cases of advanced countries. Among numerous candidate developed countries, the German market was chosen based on the similarity of the diffusion patterns to those of the Korean plan. We then figured out how the investment triggers the growth of technology from the selected benchmark, and applied the technology S-curve relation formula to derive the desirable investment plan for Korea. The present paper is a pioneering attempt to forecast the diffusion process of renewable energy technology in Korea using the comparative analogy from cases of advanced countries.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.43 no.6
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• pp.715-722
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• 2010

The effects of temperature, salinity and irradiance on the growth of the harmful red tide dinoflagellate Cochlodinium polykrikoides Margelef isolated from the South Sea of Korea were examined in the laboratory. Growth was examined under the following combinations of temperature and salinity: 15, 20, 25 and $30^{\circ}C$, and 15, 20, 25, 30 and 35 psu at a constant irradiance of $180\;{\mu}mol/m^2/s$. No growth was observed with a temperature of $15^{\circ}C$ and a salinitiy of 15 psu. Moderate growth rates of more than 0.30 /day were obtained at $25^{\circ}C$ with salinities of 25.35 psu. These values are similar to in situ observations for this species. The maximum growth rate, 0.35 /day, was obtained at $25^{\circ}C$ and 30 psu. In light experiments, cell growth of C. polykrikoides was conducted with constant temperature ($20^{\circ}C$) and salinity (30 psu) under light photon flux densities (PFD) of 10, 25, 50, 70, 100, 150, 250 and $350\;{\mu}mol/m^2/s$. C. polykrikoides did not grow at $10\;{\mu}mol/m^2/s$. Cell growth was observed at irradiance values of $25\;{\mu}mol/m^2/s$ and above. The irradiance-growth curve was described as ${\mu}=0.30{\cdot}(I-15.27)/(I+27.22)$, (r=0.99). This suggests a compensation PFD of $15.27\;{\mu}mol/m^2/s$ and a maximum growth rate of 0.30 /day. In conclusion, C. polykrikoides prefers high salinity, temperature and irradiance in summer in Korea. These results provide important information for understanding the mechanism of C. polykrikoides blooms and developing technology to predict blooms of this organism in the field.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.33 no.6
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• pp.268-275
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• 2023

This paper delves into the crucial realm of support structures in metal additive manufacturing (AM) processes and their direct impact on the stiffness of printed components. With the continuous evolution of AM technologies, optimizing support structures has become imperative to enhance the overall quality and performance of manufactured metal parts. Therefore, in this study, tensile specimens were manufactured using various representative support design variables such as support type, spacing, and penetration depth, and the differences in displacement-load curve were analyzed though tensile test. Using additively manufactured support shaped tensile specimen, the paper presents a comprehensive examination of the effect of support parameters on their stiffness. The findings contribute to advancing the understanding how to design supports to suppress thermal deformation of metal parts during AM process, thereby paving the way for enhanced design freedom and functional performance in the ever-expanding field of AM.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.24 no.3
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• pp.89-93
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• 2014

In this study, effects of the V/III ratio on a-plane GaN epitaxial on r-plane grown by HVPE have been investigated. According to increasing of V/III ratio, the value of FWHM of a-plane (11-20) GaN and the value of surface roughness (Ra) were decreased. Growth rate of a-plane GaN epitaxial layer were increased until V/III ratio = 7 as the increasing of V/III ratio, but it was reduced at V/III ratio = 10. At V/III ratio = 10, the FWHM of a-plane (11-20) GaN RC and the surface roughness (Ra) were 829 arcsec and 1.58 nm, respectively, as the lowest value in this study. Also for V/III ratio = 10, cracks under surface or voids were observed the lowest values in images of optical microscope. An M-shaped azimuthal dependence over $360^{\circ}$ angle range was observed for all samples. At V/III ratio = 10, the difference of FWHM of a-plane GaN between $0^{\circ}$ and $90^{\circ}$ was 439 arcsec revealed as the lowest value in the 4 samples.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.17 no.4
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• pp.69-79
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• 2014

Coastal wetlands are among the most productive biomes in the Earth. The economic values include the direct use of a coastal wetland's ecosystem services, such as food, raw materials, recreation, and tourism. Other values comprise the indirect use of a coastal wetland's ecosystem services, such as carbon sequestration, waste-water treatment, and erosion prevention. In particular, Suncheon Bay is recently attracting attention as the most successful case of the preservation and restoration. This study applies Travel Cost Method (TCM) to estimate the economic value by drawing the demand curve for trips to Suncheon Bay. The TCM is an approach used for economic valuation of non-market goods and services. Based on the results of TCM, this study shows that the economic benefit from recreational uses of the site adds up to \174.7 billion per year. It is also significant in the sense that monetary information is suggested to help local policy makers evaluate the realistic values of coastal wetlands.

• Proceedings of the PSK Conference
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• 2002.10a
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• pp.316.3-317
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• 2002

In previous reports, we exhibited that acteoside showed significant cytotoxicity against various cancer cells. In this study we investigated that acteoside is capable of inducing differentiation in HL -60 human leukemia cell line. After being treated with acteoside, the growth curve was decreased remakably in a dose- and time-dependent manner, and cell doubling time was delayed. Exposure of cells to 20 $\mu\textrm{g}$/m$\ell$ acteoside induced differentiation of HL-60 cells to monocyte/macrophage-like cells by cell surface antigen expression. The percentage of NBT reducing activity was increased in a time-dependent manner. In addition. the protein lever of p21 and p16 increased and ppRb decreased in western biot analysis. Theas results suggest that acleoside possess the activity of inducing differentiation in HL-60 cells.