• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.6D
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• pp.663-671
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• 2012

The demand of CWR is rapidly increasing because of the adaptation of concrete track, the need for rapid and comfortable ride, and the reduction of maintenance cost. Because of short applying period of the concrete track, there is not a case of CWR fracture in Korea caused by repeated load of the train, which makes it difficult to calculate replacement period of rail based on rail fatigue life using an actual field data. This study thus inspected the bending stress at rail bottom through analyzing the vehicle/track interaction, performed multiple regression analysis on the data, deducted the bending stress prediction equations by the speed and the surface irregularity. Finally, the fatigue life of CWR on the concrete track was predicted based on the prediction equations for bending stress at rail bottom.

• Korean Journal of Optics and Photonics
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• v.12 no.1
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• pp.17-24
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• 2001

Two-dimensional binary-phase diffraction gratings which can be employed to fabricate two- and three-dimensional periodic structures are designed and analyzed using rigorous coupled-wave analysis. These gratings serve as phase-masks which generate several diffracted waves from a normally incident beam and thus can produce a periodic interference pattern in space via nearfield holography. The properties of the diffracted beams can be controlled by varying the polarization and wavelength of the incident beam, surface-profile, groove depth and duty cycle of the mask. For the two-dimensional structure, optimum results can be obtained when the diffraction efficiency of the zero-order beam is minimized while that of the first-order maximized. On the other hand, when the diffraction efficiency of the zero-order is appreciable or even greater than other orders, we can obtain a variety of three-dimensional interference patterns which may be used to fabricate photonic crystals of tetragonal-body-centered and hexagonal structures in a submicron scale. scale.

• Journal of Sensor Science and Technology
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• v.29 no.4
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• pp.255-260
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• 2020

In this study, we developed a method of improving the surface-enhanced Raman spectroscopy (SERS) response characteristics by depositing a nanoporous Ag metal thin film through cluster source sputtering after forming a pyramidal texture structure on the Si substrate surface. A reactive ion etching (RIE) system with a metal mesh inside the system was used to form a pyramidal texture structure on the Si surface without following a complicated photolithography process, unlike in case of the conventional RIE system. The size of the texture structure increased with the RIE process time. However, after a process time of 60 min, the size of the structure did not increase but tended to saturate. When the RF power increased from 200 to 250 W, the size of the pyramidal texture structure increased from 0.45 to 0.8 ㎛. The SERS response characteristics were measured by depositing approximately 1.5 ㎛ of nanoporous Ag metal thin film through cluster sputtering on the formed texture structure by varying the RIE process conditions. The Raman signal strength of the nanoporous Ag metal thin film deposited on the Si substrate with the texture structure was higher than that deposited on the general silicon substrate by up to 19%. The Raman response characteristics were influenced by the pyramid size and the number of pyramids per unit area but appeared to be influenced more by the number of pyramids per unit area. Therefore, further studies are required in this regard.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.1
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• pp.329-332
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• 2012

LEDs are using widely in a field of illumination, LCD LED backlight, mobile signals because they have several merits, such as low power consumption, long lifetime, high brightness, fast response, environment friendly. To achieve high performance LEDs, one needs to enhance output power, reduce operation voltage, and improve device reliability. In this paper, we have proposed that the optimum design and specialized process could improve the performance of LED chip. It was showed an output power of 7cd and input supplied voltage of 3.2V by the insertion technique of current blocking layer. In this paper, GaN-based LED chip which is built on the sapphire epi-wafer by selective MOCVD were designed and developed. After that, their performances were measured. It showed the output power of 7cd more than conventional GaN-based chip. It will be used the lighting source of a medical equipment and LCD LED TV with GaN-based LED chip.

• Korean Journal of Materials Research
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• v.22 no.11
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• pp.636-641
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• 2012

In this study, we have investigated highly efficient nanoscale surface corrugated light emitting diodes (LEDs) for the enhancement of light extraction efficiency (LEE) of nitride semiconductor LEDs. Nanoscale indium tin oxide (ITO) surface corrugations are fabricated by using the conformal nanoimprint technique; it was possible to observe an enhancement of LEE for the ITO surface corrugated LEDs. By incorporating this novel method, we determined that the total output power of the surface corrugated LEDs were enhanced by 45.6% for patterned sapphire substrate LEDs and by 41.9% for flat c-plane substrate LEDs. The enhancement of LEE through nanoscale surface corrugations was studied using 3-dimensional Finite Different Time Domain (FDTD) calculation. From the FDTD calculations, we were able to separate the light extraction from the top and bottom sides of device. This process revealed that light extraction from the top and bottom sides of a device strongly depends on the substrate and the surface corrugation. We found that enhanced LEE could be understood through the mechanism of enhanced light transmission due to refractive index matching and the increase of light scattering from the corrugated surface. LEE calculations for the encapsulated LEDs devices also revealed that low LEE enhancement is expected after encapsulation due to the reduction of the refractive index contrast.

• Korean Journal of Ichthyology
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• v.12 no.2
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• pp.111-117
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• 2000

There were observed the histomorphological alterations such as chloride cell hyperplasia, branchial lamellar epithelial separation, the increased cellular turnover of chloride cells, glomerular shrinkage and blood congestion in rainbow trout (Oncorhynchus mykiss) during the seawater adaptation. The ultrastructure by scanning electron microscope (SEM) indicated that the gill secondary lamella of rainbow trout exposed to seawater, were characterized by rough convoluted surfaces during the adaptation. There were observed a large number of mitochondria with the elongate and well-developed cristae in chloride cells exposed to seawater by transmission electron microscope (TEM). The presence of two mitochondria- rich cell types is discussed with regard to their possible role in the hypoosmoregulatory changes which occur during seawater-adaptation. Glomerulus shrinkage and blood congestion were occurred higher in nephrons of seawater-adapted fish than those living in freshwater. Our findings demonstrated that rainbow trout tolerated moderately saline environment and the increased body weight living in seawater was relatively higher than that living in freshwater in spite of histopathological changes.

• Journal of the Korean Vacuum Society
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• v.18 no.4
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• pp.310-317
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• 2009

Vertical wet equipment for the BGA develop process was newly developed substituted for conventional horizontal wet equipment. The benefits of vertical equipment are that the pattern damages generated by the collision between the patterns and transferring rollers can be eliminated because the direct contact between the equipment's transferring units and the soft dry film patterns does not occurs. Taguchi experiment was conducted to optimize the process characteristics for the vertical equipment. The experiment was organized as the smaller the better problem which includes adequate uncontrollable factor and controllable factors. The uncontrollable factors are the 4 sides of two panels which are loaded to the equipment at the same time. By the analysis of the experiment, temperature of the develop chemicals and develop spraying time are analyzed as the main controllable factors. Finally, line pattern's minimum width which is not damaged for the develop process was improved from $13.8{\mu}m$ for the horizontal equipment to $10.4{\mu}m$ for the vertical equipment. And dot pattern's minimum width is improved from $22.1{\mu}m$ to $16.3{\mu}m$.

• The Journal of the Convergence on Culture Technology
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• v.4 no.4
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• pp.413-418
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• 2018

The purpose of this study is to investigate the cause of rail corrugation and the track force for concrete track (STEDEF) in the urban transit. From the field measurements, the dynamic wheel load, vertical displacement of sleeper and rail bending stress were measured and it was evaluated by regarding to the rail corrugation. As a result of the study, the causes of rail corrugation was experimentally proved by frequency analysis using measured dynamic wheel load data. The influence of corrugation on dynamic wheel load, rail bending stress and sleeper displacement was evaluated that the periodic irregularities of rail corrugation on the rail surface amplified the dynamic track force such as the dynamic wheel load, and thus the rail bending stress and the vertical displacement of sleeper could be increased by a maximum of 1.7 times.

• Korean Journal of Metals and Materials
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• v.50 no.12
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• pp.913-920
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• 2012

In spite of some problems in processability and bondability, Au wires in the microelectronics industry are gradually being replaced by copper wires to reduce the cost of raw material. In this article, the effects of surface roughness enhanced capillaries on thermosonic Cu wire bonding were evaluated. The roughness-enhanced zirconia toughened alumina (ZTA) capillaries were fabricated via a thermal grooving technique. As a result, the shear bond strength of first bonds (ball bonds) bonded using the roughness-enhanced capillary was enhanced by 15% as compared with that of normal bonds due to more effective plastic deformation and flow of a Cu ball. In the pull-out test of second bonds (stitch bonds), processed at two limit conditions on combinations of process parameters, the bond strength of bonds formed using the roughness-enhanced capillary also resulted in values higher by 55.5% than that of normal bonds because of the increase in the bonding area, indicating the expansion of a processing window for Cu wire bonding. These results suggest that the adoption of roughness-enhanced capillaries is a promising approach for enhancing processability and bondability in Cu wire bonding.

• Journal of The Geomorphological Association of Korea
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• v.17 no.1
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• pp.1-14
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• 2010

This paper deals with the classification and distribution of geomorphic surfaces and analysis on effects of geomorphic processes on the landforms in the inaccessable DMZ (Demilitarized Zone) to Wonsan Bay of East Sea coast of Chugaryeong Rift Valley, Central Korea. DEM (Digital Elevation Model) and Landsat images are used for the above anlaysis. The geomorphic surfaces are classified by TPI (Topographical Position Index) for the analysis of the convexity and concavity calculated using topographical elements such as elevation, steepness, and relief. In the Chugayreong Valley, 10 geomorphic surfaces are classified as steep valley, shallow valley, upland drainage, U-shaped valley, plain, open slope, upper slope, local ridge, midslope ridge, and high ridge. Zonal Statistics presents average characteristics of geomorphological processes of surfaces by the relationships between bedrock and relief, surface and relief, and between surface and NDVI. So, these analysis can help to understand geomorphological process such as dissection of lava plateau and watershed divide evolution.