• Polymer(Korea)
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• v.26 no.4
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• pp.445-451
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• 2002

In this work, the adsorption characteristics and mechanical interfacial properties of treated silicas by silane coupling agents, such as, ${\gamma}$-methacryloxy propyl trimethoxy silane (MPS), ${\gamma}$-glycidoxy propyl trimethoxy silane (GPS), and ${\gamma}$-mercapto propyl trimethoxy silane (MCPS), were investigated. The equilibrium spreading pressure ($pi_e$), surface free energy ($gamma_s$ s/), and specific surface area ($S_{BET}$) were studied by the BET method with $N_2$/77 K adsorption. The developments of nonpolar functional groups of the silica surfaces treated by silane coupling agents led to the increase in the $S_{BET}$, $pi_e$, and $gamma_s$, resulting in the improved tearing energy ($G_{mc}$)of the silica/rubber composites. The composites treated by MPS showed the superior mechanical interfacial properties in these systems. These results explained by changing of crystalline size, dispersion, agglomerate, and surface functional group of silica/rubber composites.

• Journal of Ocean Engineering and Technology
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• v.27 no.5
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• pp.99-104
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• 2013

Recently, various nanoparticles have been used for filler in polymer matrices. The particles of nano size are whether high or not cross-link density in polymer affects the thermal and mechanical properties of one. The properties change as a result of chemical reactions between the nanoparticles and the surface of the polymer. There are two models for nanocomposites: "repulsive interaction" and "attractive interaction" between the nanoparticles and matrix. In this study, the variation in the curing mechanism was examined when nano-size $TiO_2$ was dispersed into an epoxy (Bisphenol A, YD-128) with different curing agents. The results of this study showed that the exothermic temperature and Tg in the case of the nanoparticles used (Jeffamine) (D-180) at room temperature were reduced by an increase in the $TiO_2$ contents because of the "repulsive interaction" between the nanoparticles and the matrix. The tensile strengths were increased by increasing amounts of $TiO_2$ until 3 wt% because of a dispersion strengthening effect caused by the nanoparticles, because of the repulsive interaction. However, such tensile properties decreased at 5 wt% of $TiO_2$, because the $TiO_2$ was agglomerated in the epoxy. In contrast, in the case of the nanoparticles that used NMA and BDMA, the exothermic temperature and Tg tended to rise with increasing amounts of $TiO_2$ as a result of the "attractive interaction." This was because the same amounts of $TiO_2$ were well dispersed in the epoxy. The tensile strength decreased with an increase in the $TiO_2$ contents. In the general attractive interaction model, however, the cross-link density was higher, and tensile strength tended to increase. Therefore, for the nanoparticles that used NMA, it was difficult to conclude that the result was caused by the "attractive model."

• Resources Recycling
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• v.9 no.6
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• pp.36-44
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• 2000

Fly ash was composed of the unburned carbon and mineral particles. The former was able to attach on the bubbles, while the latter was not. Therefore, it was possible to separate the unburned carbon and the mineral from fly ash using the froth flotation process. This study was carried out to evaluate the separation efficiency as a function of the ny ash particle properties in the column flotation. Separation efficiency was analyzed for various size fraction of -38 fm,38~125 fm and 1125 W, and for various fly ash samples containing 7, 11, and 20 wt% unburned carbon. For the size fractions of -38 fm containing 7 wt% unburned carbon, separation efficiency was 86ft, whereas separation efficiency was found to be 74% for the size fraction of +125$\mu\textrm{m}$ containing 20 wt% unburned carbon. The results indicated that separation efficiency increased with the decrease in the particle size and the unburned carbon content of the fly ash.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.3A
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• pp.513-521
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• 2006

Many studies have been conducted on the high tension bolt friction connection in the view of the field practice. Those effort, however, unfortunately have not been appropriately applied in the design specifications. Recently, particularly for steel bridges, rationalization of design takes greater attention from designers and hence, demand on rationalization of high tension connection becomes more significant. The purpose of this study is to suggest direction for the rationalization of high tension bolt connection and to also provide fundamental information for the improvement of the design specifications. In order to accomplish the purposes, the design specifications in Korea was analyzed and compared with other specification from abroad, and was studied one of the most important factors including slip coefficient, and the specifications on the size of bolt holes. The effect of over-sized bolt hole and the reduction of axial force on bolt was evaluated through the experimental studies on the slippage of the high tension bolt connections. Other research topics included herein includes the difference of slip coefficients, the effect of over-sized bolt holes and the gap distance of members, and the application of filler plate and corrosion protected bolts. From the research results, it is known that the specifications in Korea apply a constant slip coefficient with respect to the contacted surface conditions while various coefficients are available depending on the contacted surface conditions. Therefore, it is recommended that the specifications in Korea also develop and detail the slip coefficient which can appropriately take account of the variation of the contacted surface conditions. It is also suggested that the limitation abroad on the over-sized bolt hole may be applied for enhancing the effectiveness of construction.

• The Journal of the Acoustical Society of Korea
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• v.18 no.3
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• pp.3-9
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• 1999

This paper presents the study on the rejection capability based on anti-phone modeling for vocabulary independent speech recognition system. The rejection system detects and rejects out-of-vocabulary words which were not included in candidate words which are defined while the speech recognizer is made. The rejection system can be classified into two categories by their implementation methods, keyword spotting method and utterance verification method. The keyword spotting method uses an extra filler model as a candidate word as well as keyword models. The utterance verification method uses the anti-models for each phoneme for the calculation of confidence score after it has constructed the anti-models for all phonemes. We implemented an utterance verification algorithm which can be used for vocabulary independent speech recognizer. We also compared three kinds of means for the calculation of confidence score, and found out that the geometric mean had shown the best result. For the normalization of confidence score, usually Sigmoid function is used. On using it, we compared the effect of the weight constant for Sigmoid function and determined the optimal value. And we compared the effects of the size of cohort set, the results showed that the larger set gave the better results. And finally we found out optimal confidence score threshold value. In case of using the threshold value, the overall recognition rate including rejection errors was about 76%. This results are going to be adapted for stock information system based on speech recognizer which is currently provided as an experimental service by Korea Telecom.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.33 no.2
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• pp.54-60
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• 2023

In this study, microstructure and basic property analysis of DG (Desulfurization gypsum) and CCMs (Carbondioxide conversion capture materials) made by reacting CO₂ with DG were conducted to analyze applicability as a cement admixture. The main crystalline phases of DG were CaO and CaSO₄, and CCMs were CaSO₄, CaCO₃, Ca(OH)₂ and CaSO₄·H₂O. As a result of particle size analysis, the difference in average particle sizes between the two materials was about 7 ㎛. No major heavy metals were detected in the CCMs, and as a result o f TGA, the CO₂ decomposition of CCMs was more than twice as high as that of DG. Therefore, it was judged that CCMs could be used as a cement admixture through optimization of manufacturing conditions. As a results of measuring the strength behavior of DG and CCMs mixture ratios, the long-term strength of CCMs-mixed mortar was higher, and this is due to the filler effect of CaCO₃ in CCMs.