• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2006.05a
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• pp.172-175
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• 2006

Effects of deformation at austenite non-recrystallization region and cooling rate on the microstructure and mechanical properties of low carbon (0.06 wt. %) high strength low alloy steels have been investigated. Average grain size decreased and polygonal ferrite transformation promoted with increasing deformation amount due to increase of ferrite nucleation site. As cooling rate increased, the major microstructure changed from polygonal ferrite to acicular ferrite and the fraction of M/A constituents gradually increased. Discontinuous yielding occurred in highly deformed specimen due to the formation of polygonal ferrite. However, small grain size of highly deformed specimen caused lower ductile-to-brittle transition temperature than slightly deformed specimen.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.03a
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• pp.181-188
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• 2008

In this study, estimation of behavioral characteristics between twin tunnels was performed through the series of laboratory experiment on the small scale tunnel model. In the model test, the experimental parameters were geological conditions, center to center distance between twin tunnels, application of discontinuous inclination. To estimated behavior of pillar and load-displacement relationship by model tests and numerical analyses.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.04a
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• pp.756-761
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• 1999

The objective of this study is to develop finite element analysis technique to predict the strength reduction of deteriorated reinforced concrete beams and their strengthening capacity. In order to consider the effect of rebar corrosion, a tension stiffening model is proposed and area reduction of rebars due to corrosion is considered. For the analysis of strengthened deteriorated RC beams, one dimensional truss element and an interface element are introduced for models of the strengthening composite and the interface between concrete and composite to simulate delamination or discontinuous behavior at the interface. Then, analyses for deteriorated RC beams strengthened with glass fiber reinforced epoxy panel (GFREP) are carried out to predict both flexural failure and plate-end delamination failure. Finally, analysis results are verified with experimental results.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.04a
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• pp.443-448
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• 1999

Tests have been carried out on four concrete containing different levels of silica fume to measure their permeability coefficient using water and oxygen, chloride ion. The total cementitious content was 351kg/㎥, and the water/cementitious materials ratio was 0.55. The results show that a dramatic reduction in permeability of concrete containing silica fume occurs due to formation of a discontinuous macro-pore system which inhibits flow. Porosity estimates from mercury-intrusion porosimetry are used to develop an explanations for the water and air permeability reduction. And, results of the rapid permeability test showed that the resistance of concrete to the penetration of chloride ions increases significantly as a contents of silica-fume is increased. The current intensity passing through the concrete containing silica fume is presented from 664C to 2166C.

• Proceedings of the Korea Concrete Institute Conference
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• 2000.10a
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• pp.769-774
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• 2000

The first thing in developing precast post-tensioned concrete frame system verify the shear resistance capacity of the beam-column connection at which the transfer of member forces become discontinuous. Complying with the necessity of such experimental research, shear tests have been performed for six test specimens which were cast and cured at Dong-Ah Concrete Manufacturing Company and post-tensioning at Concrete Laboratory of Inha University. Shear key and magnitude of post-tensioned force are taken test variables. From the test results, it has been observed that the shear resistance of the specimens attained to higher values than those of theoritical calculations based on the shear friction with shear friction coefficient being 0.6.

• 한국정보통신설비학회:학술대회논문집
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• 2004.08a
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• pp.386-389
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• 2004

This thesis complemented the weak points that the existing theses did not represented a phase characteristic as the equivalent circuit by applying 4-port simulation to DGS (Defected Ground Structure) characteristic and an equivalent circuit, which are the transmission line structure that has the defect made in the ground surface. We used a distribute device and a lumped device, obtained the equivalent circuit by applying the structure of balun to a discontinuous part. An indicated DGS (Defected Ground structure) is a dumbbells-shaped single defect, we indicated satisfying a magnitude and phase characteristics by applying this equivalent circuit.

• Korean Journal of Child Studies
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• v.28 no.4
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• pp.73-95
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• 2007

Causal relationships of kindergarteners' phonological awareness and processing to their ability to read words was investigated with the participation of 289 4- to 6-year-old children attending three kindergartens in Busan. Results showed gradual growth in reading ability with age. Children performed best in reading words and poorest in reading low frequency letters. They showed continuous development in skills of syllable deletion, phoneme substitution, phoneme insertion, phonological memory and naming. Discontinuous development was found in counting syllables. Longer syllables were difficult to count, and middle syllables of 3 syllable words were hard to delete. Children had poor perception of final consonants of Consonant-Vowel-Consonant syllables. Children's phonological awareness and processing were latent variables strongly related to ability to read words written in Hangul.

• Proceedings of the KIPE Conference
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• 1999.07a
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• pp.278-281
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• 1999

In a utility interactive photovoltaic system, a PWM inverter is used for the connection between the photovoltaic arrays and the utility. The DC current becomes pulsated causes the distortion of the AC current waveform. This paper presents the reduced pulsation of DC input current by operating the inverter with buck-boost chopper in the discontinuous conduction mode. The DC current with contains harmonics component is analyzed by means of separating into two terms of a ripple component and a direct component. The constant DC current without pulsation is supplied from photovoltaic array to the inverter. The proposed inverter system provide a sinusoidal AC current for domestic loads and the utility line with unity power factor.

• Proceedings of the KIPE Conference
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• 1999.07a
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• pp.639-642
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• 1999

An integrated zero current switching(ZCS) quasi-resonant converter(QRC) for power factor correction and high efficiency with single switch is proposed in this thesis. Boost integrated circuit operating discontinuous conduction mode(DCM) and QRC are used for power factor correction and reducing switching loss, respectively. A prototype converter has been designed and experimented. At rated condition, the THD in the input current waveform of this prototype has approximately 18%. The efficiency is obtained about 70%, the power factor is about 0.985 as well. Therefore, the proposed converter is suitable for a low power level converter with operating switching frequency above several hundred KHz.

• Proceedings of the KIPE Conference
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• 1999.07a
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• pp.663-666
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• 1999

This paper describes a three-phase converter with high power factor using a scheme of discontinuous current mode(DCM). The proposed system can replace the conventional diode bridge with step-up chopper which is used as a converter for adjustable speed drive. In this system, the current of reactor is zero at turn-on instance because of operation in DCM, while the switch turns off at the instance of maximum current. A soft-switching scheme with lossless snubber was proposed. Therefore, a zero-voltage switching at turn off can be achived by lossless snubber and zero-current switching at turn on can be obtained by operating under DCM. A theoretical analysis and computer simulations with PSpice were done to verify the operation of the proposed system. Also a prototype of hardware system was built and tested for verifying the feasibility of proposed system.