• Transactions of the Society of Information Storage Systems
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• v.3 no.1
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• pp.17-22
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• 2007

[ $TiO_2$ ] nanoparticles are added into UV curable resin to increase the refractive index of the cover-layer which is laminated on the media for cover-layer incident NFR. High refractive index is required for the cover-layer operating for the solid immersion lens optics with high effective numerical aperture. The eyepattern could be achieved from the cover-layer coated 20 GB ROM disc in which the refractive index of the cover-layer was 1.75, but the gap servo was unstable due to the rough surface of the cover-layer. Even though the light loss due to the nanoparticles is not serious, the rough microstructure is developed by adding the nanoparticles in the organic binder material. To achieve smooth surface for the stable gap servo, some special techniques should be added, for example the solubility of the nanoparticles should be enhanced by the optimization of the surface of the nanoparticles.

• Transactions of the Society of Information Storage Systems
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• v.4 no.1
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• pp.13-18
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• 2008

Scratches are observed on a polymer cover-layer of near-field recording (NFR) media after a servo test with rotating disc. The scratches are formed by the collision of a solid immersion lens (SIL)-media. One of the possible ways to avoid the scratch problem is to coat a dielectric protective film on the polymer cover-layer which enhances the hardness of the surface. The surface with hard characteristics in the surface reduces the scratch problem in the cover-layer. Not only the mechanical properties but also the optical properties should be controlled. Specifically, the refractive index of the dielectric protective film should be matched with the polymer cover-layer not to lose light at the interface due to the difference of the refractive index. The refractive index of the dielectric film can be tailored by controlling process parameters during sputtering and matched with that of the polymer cover-layer.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.7 no.3
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• pp.35-47
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• 2004

In order to study changes in vegetation pursuant to rooftop revegetation plantation methods, plantation methods for rooftop revegetation were divided into two types through an analysis of recent trends. Then, Planted plants and invasive plants on sites where the planting methods were introduced were monitored. Planting methods were divided into mono-layer meadow cover type and multi-layer planting cover type. They showed some differences in terms of the availability of wetland, the structure of vegetation layers, the planted species, and the material of mulching. According to the results of monitoring the two sample sites for different plantation methods, the number of invasive plants was higher in multi-layer planting cover type and the ratio of naturalized plants was higher by 30% in average in mono-layer meadow cover type. The main reason for such a result is that the natural soil used in the multi-layer planting cover type likely contained some seeds. Moreover, it's harder for invasive plant seeds to germinate in volcanic rocks than in natural soil. Also, it is attributable to wetlands available in multi-layer planting cover type and diverse living environments created by multi-layer planting. The reason of the ratio of naturalized plants being higher by at least 10% in mono-layer meadow cover type is the character of naturalized plants being stronger in unfavorable conditions than nature plants are. Accordingly, the germination rate in the volcanic rock mulching has likely contributed in raising the introduction and germination of naturalized plants. The results showed that multi-layer planting cover type using wetland creation and nature soil can increase the number of invasive plants and lower the ratio of naturalized plants. However, since seeds contained in the natural soil can affect the growth of planted plants, this needs to be clarified, It was judged that mono-layer meadow cover type may affect more greatly on the germination and growth of invasive plants than on those of planted plants, Its potential adoption in highly urbanized areas was examined. By complementing with the mutual benefits of each plantation method, it appeared possible to shift to a rooftop revegetation system suitable to the site.

• Journal of The Korean Society of Agricultural Engineers
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• v.48 no.5
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• pp.73-80
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• 2006

The mono-layer cover system is composed of soils only as a filling material and various plants are planted on the surface to control the water balance in the cover system. In this paper, the mono-layer cover system was considered as an alternative landfill final cover system and developed a model that could utilize industrial by-product (especially, coal ash & phosphogypsum) as additive filling materials. The mixture of granite soil, coal ash, and phosphogypsum was placed as a cover material in a box constructed with cement. Laboratory tests were carried out to investigate the environmental effect on the utilization of coal ash & phosphogypsum and to determine the mxing ratio of each materials. In the leaching test, all materials showed lower heavy metal concentration than the threshold values of regulation. The optimum mixing ratio of materials which was applied to field model test was determined to soil (4) : coal ash (1) : phosphogypsum (1) on the volume base. Field model tests were continued from February to July, 2004 in the soil box that was constructed with cement block. It was verified that coal ash and phospogypsum mixed with soil was to be safe environmentally and the water balance of mono-layer cover system was reasonable.

• Transactions of the Society of Information Storage Systems
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• v.1 no.1
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• pp.58-66
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• 2005

Pseudo-Near Field Recording (Pseudo-NFR) system is proposed to prevent contamination and oxidation of media surface occurred in conventional NFR systems. To solve these critical problems of the NFR systems, we investigate the optimal thickness of cover layer for Pseudo NFR. This paper presents the theoretical analysis for cover layer thickness based on the measured length of dust particle and numerical simulation for the temperature distribution using Finite Difference Time Domain (FDTD) method and heat conduction equation. To verify the simulation results, we conduct and compare simulation results in case of far field MO recording and near field MO recording. A measured dust particle length in general environment was mostly less than $20{\mu}m$, and the optimal thickness of cover layer is $30{\mu}m$ in this case. Based on the designed optimal cover layer thickness, temperature distribution is simulated to have $800{\~}850^{\circ}C$.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.05a
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• pp.113-116
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• 2005

In this paper, a computational and experimental analysis about the flow behavior of thin polymer film in the spin coating process for stable cover layer coating of a blu-ray disc is described. The blu-ray disc, a next-generation optical disc format over 25GB, consists of a 1.1mm thick substrate and a 0.1mm tick cover layer. Generally, cover layer on the blu-ray disc is made by the polymer spin coating process. However, it is hard to secure sufficient coating uniformity around the rim on the cover layer. In order to get the uniform thickness deviation and to minimize the bead around the rim, the edge of the disc substrate can be modified into various shapes around the rim on the disc and analyzed with various parameters, such as surface tension, viscosity, and rotation speed, etc. The optimal shape of the rim was tried to get by 3 dimensional computer simulation of the polymer expulsion process.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.2 no.1
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• pp.23-34
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• 2004

To validate the previous conceptual design of cover system, construction of the engineered barrier test facility is completed and the performance tests of the disposal cover system are conducted. The disposal test facility is composed of the multi-purpose working space, the six test cells and the disposal information space for the PR center. The dedicated detection system measures the water content, the temperature, the matric potential of each cover layer and the accumulated water volume of lateral drainage. Short-term experiments on the disposal cover layer using the artificial rainfall system are implemented. The sand drainage layer shows the satisfactory performance as intended in the design stage. The artificial rainfall does not affect the temperature of cover layers. It is investigated that high water infiltration of the artificial rainfall changes the matric potential in each cover layer. This facility is expected to increase the public information about the national radioactive waste disposal program and the effort for the safety of the planned disposal facility.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.10a
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• pp.467-471
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• 2005

In this paper, experimental methods about the flow behavior of thin polymer film by various edge patterns in the spin coating process for stable cover layer coating of a blu-ray disc is described. The blu-ray disc, a next-generation optical disc format over 25GB, consists of a 1.1m thick substrate and a 0.1mm tick cover layer. Generally, cover layer on the blu-ray disc is made by the polymer spin coating process. However, it is hard to secure sufficient coating uniformity around the rim on the cover layer. In order to get the uniform thickness deviation and to minimize the bead around the rim, the edge of the disc substrate can be modified into various patterns, such as normal plain, trench, step and chamfer pattern, etc, around the rim on the disc and experimented with various parameters, such as surface tension, viscosity, coating time, temperature and rotation speed, etc. And the optimal shape of the rim was tried to get by 3 dimensional computer simulation of the polymer expulsion process.

• Transactions of the Society of Information Storage Systems
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• v.2 no.3
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• pp.178-183
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• 2006

A Blu-ray disc, which has a more than 25GB optical capacity, has been known as a promising next-generation optical disc format. It commonly has a 1.1 mm thick substrate and a 0.1 mm thick cover layer for beam transmitting and the protection of the reflecting surface. The cover layer is generally formed by the spin coating process. However, in conventional spin coating, small bumps are formed along the rim of the disc, which results in the fatal reading error. Numerical simulation of the thin film flow behaviors during spin coating with the commercial solver and optimal spinning conditions was obtained. Thickness distribution of the cover layer according to the variation of substrate's edge shape could be calculated as well. By modifying the shape of the substrate edge shape, the bumps along the disc rim could be minimized, and it was proved that the chamfered edge, around $5{\sim}10$ degree, is the simplest and most effective way to minimize the bumps.

• Journal of the Korean institute of surface engineering
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• v.52 no.6
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• pp.310-315
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• 2019

The use of a silicon carbide (SiC)-based composite ceramic layer for the mold of a curved cover glass was demonstrated. The stress of SiC/VDR/graphite-based mold structure was evaluated via finite element analysis. The results revealed that the maximum tensile stress primarly occured at the edge region. Moreover, the stress can be reduced by employing a relatively thick SiC coating layer and, therefore, layers of various thicknesses were deposited by means of chemical vapor deposition. During growth of the layer, the orientation of the facets comprising the SiC grain became dominant with additional intense SiC(220) and SiC(004). However, the roughness of the SiC layer increased with increasing thickness of the layer and. Hence, the thickness of the SiC layer needs to be adjusted by values lower than the tolerance band of the curved cover glass mold.