• Proceedings of the Korea Concrete Institute Conference
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• 2001.05a
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• pp.231-236
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• 2001

In this paper, tests are carried out in order to investigate the validities of anti-freeze agent, which is developed using waste coolant and existing anti-freeze agent through previous study, under various W/C and contents. According to test results, adequate dosage of developed anti-freeze agent shows positive performance in slump, air content and chloride contents in the mixture of 40% and 50% of W/C, accelerates setting time and drops the freezing temperature of concrete. Meanwhile, in the region of 30% of W/C, followings can be indicated that increasing the contents of anti-freeze agent leads to reduce fluidity, rapid setting and excessive chloride contents. Improved strength gain is shown when anti-freeze agent is used with in 8%.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2001.10a
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• pp.57-60
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• 2001

In order to extend the life time of building and civil infra-structure, nowadays, patch type fibrous composite materials are widely used. Retrofitted concrete columns and beams gain the stiffness and strength, but they lose toughness and show brittle failure. Usually, the cracks of concrete structures are visible with naked eyes and the status of the structure in the life cycle is estimated with visible inspection. After retrofitting of the structure, crack visibility is blocked by retrofitted composite materials. Therefore, structural monitoring after retrofitting is indispensible and self diagnosis method with optical fiber sensor is very useful. In this paper, We try to detect peel out effect and find the strain difference between main structure and retrofitting patch material when they separate each other.

• Journal of Mechanical Science and Technology
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• v.17 no.10
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• pp.1543-1551
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• 2003

The present study investigates turbulent flows subject to strong wall injection in a channel through a Direct Numerical Simulation technique. These flows are pertinent to internal flows inside the hybrid rocket motors. A simplified model problem where a regression process at the wall is idealized by the wall blowing has been studied to gain a better understanding of how the near-wall turbulent structures are modified. As the strength of wall blowing increases, the turbulence intensities and Reynolds shear stress increase rapidly and this is thought to result from the shear instability induced by the injected flows at the wall. Also, turbulent viscosity grows rapidly as the flow moves downstream. Thus, the effect of wall-blowing modifies the state of turbulence significantly and more sophisticated turbulence modeling would be required to predict this type of flows accurately.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.31 no.5
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• pp.18-23
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• 1999

This study examined the effects of multiple recycling on deinkability and properties of recycled paper from laser computer printout(LCPO). First, alkaline paper with a 20% printed area was disintegrated by TAPPI standard disintegrator. After dewatering , the pulp was followed by flotation, handsheet making, and drying at room temperature, in order. A sequence of printing , disintegrating, flotating , handsheet making and drying was one recycling cycle and this cyclic treatment was repeateed from zero to five times. The residual ink content in recycled handsheets by SEM-EDXA and Py-GC analyseswas increased slightly as recycling number increase. After five cycles of recycling the ISO brightness of recycled handsheets dropped to about 90% of the original brightness. However, it had a gain of 10% in opacity. The most of physical properties of recycled handsheets were decreased as recycling numbers increase except of for tear strength.

• Bulletin of the Korean Space Science Society
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• 2008.10a
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• pp.36.2-36.2
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• 2008

This paper presents the impact of Japanese radio source on the S-Band communication between KOMPSAT-2 satellite and TT&C ground system. Major specifications such as transmitting EIRP (Effective Isotropic Radiated Power) and location of Japanese terrestrial station were informed from Radio Research Laboratory in Korea Communication Commission. To estimate path loss in S-Band, the distance between Japanese station and TT&C ground system was obtained by using COTS (Commercial Off-The-Shelf) software. After that the signal strength of Japanese radio source placed at the TT&C ground system was calculated from link parameters such as transmitting EIRP, path loss, and receiving antenna gain. Consequently, this paper shows that the degradation caused by Japanese radio source is acceptable to TT&C ground system for satellite operation.

• Tribology and Lubricants
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• v.8 no.1
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• pp.63-69
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• 1992

In order to gain better understanding of wear behaviors of TiN-coated boron cast iron, tests and analyses were conducted with block-on disc type tribometer. TiN layer of thickness $2 \mu m$ and $4 \mu m$, coated by cathodic arc evaporation process, were experimentally investigated with the variation of applied load and sliding speed under dry sliding condition. Wear characteristics were expressed in terms of the three-dimentional wear map as well as the wear rate vs sliding speed and load. Comparisons of wear and friction characteristics between coated cast irons and uncoated cast irns were also made. Wear mechanism of TiN layer was explained in view of surface interaction between the mating surfaces. The thicker coating exhibited higher hardness and adhesion strength. the significance of stresses at the surface and in the subsurface was briefly discussed in relation to the wear behavior.

• Proceedings of the IEEK Conference
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• 1998.06a
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• pp.165-168
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• 1998

This paper describes the characteristics of CT-2 radio wave propagation at 900MHz range. Typical cell coverage of CT-2 based on picocellular design provides a 200m radius. The five sites of urban regions of Kwang Ju city were chosen to characterize propagation in various environments. On the basis of cell coverage data measured with field strength meter, average 75% of telepoint service was retained and it was lack 25% of overall gain. In some sites telepoint service was limited to two of four directions around a station. If specially designed collinear antenna with specific directivities are used in these shadow area, improved results will be acquired.

• Journal of the Korean Academy of Esthetic Dentistry
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• v.11 no.2
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• pp.33-36
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• 2002

As patients have concerned the esthetics of dental restorations, the porcelain fused to metal restorations have gain their popularity due to their strength and esthetic appearance for many years. However, metal collar in subgingival level of porcelain fused to metal restoration often causes black shadows. Inadequately positioned metal collar causes plaque depositions, gingival inflammations, black shadows, and discolorations of margin area. Those problems can be avoided by a clear finishing line, well-fabricated provisional restorations with precise margin and fine polishing, collarless porcelain fused to metal restoration, and all ceramic restoration. In this case report, collarless porcelain fused to metal restoration was used to treat cervical discoloration from old restorations.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2001.04a
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• pp.930-933
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• 2001

Titanium Alloys used in this experiment has an good corrosion resistance and specific strength, and is the new material developed for medical supplies living goods. In this study the rolled titanium alloy is done by annealing, solution heat-treatment and aging and then is worked by wire EDM. With changing the process conditions, the process properties of surface hardness, surface roughness, shape of process surface and the analysis of ingredients are measured through experiment repeating main cut and finish cut. It is confirmed to gain good measure values as increasing the number of processing of wire EDM. In this experiment the phenomena of processing is studied and the appropriate process condition is proposed.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.24 no.6A
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• pp.767-774
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• 1999

In this paper, we compare the performance of asynchronous W-CDMA system with different bandwidth. We take into consideration of wideband multipath channel environment which consists of discrete multipath components whose strength is Rayleigh distributed. Each CDMA system different bandwidth experience different effects of multipath because there are different number of multipath within one chip duration according to the spreading bandwidth. We derive the average error probability versus the capacity, and compare the capacity of W-CDMA systems using the RAKE receiver with EGC diversity.