• Transactions of the Korean Society of Machine Tool Engineers
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• v.11 no.3
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• pp.102-109
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• 2002

The fatigue crack growth under mixed mode condition has been discussed within the scope of linear fracture mechanics such as maximum tangential stress, maximum tangential principal stress and minimum strain energy density. The purpose of this study is to investigate the characteristics of fatigue test crack growth in 304 stainless steel under mixed node. The fatigue test results carried out by using inclined pre-crack specimens was compared to both of the theoretical predictions of the criteria, maximum tangential stress and stain energy density. As difference from theoretical analysis, the transition region from mixed mode to mode I appeared in the fatigue test. There is deep relationship between the angle of slanted pre-crack and transition. Therefore, as applying the different stress intensity factor to each node I+II and mode I, the directions and rates of fatigue crack growth are evaluated more accurately under mixed mode.

• Transactions of the Korean hydrogen and new energy society
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• v.19 no.4
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• pp.276-282
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• 2008

The effects of hydrogen enrichment to methane have been investigated with swirl-stabilized premixed hydrogen-enriched methane flame in a laboratory-scale pre-mixed combustor. The hydrogen-enriched methane fuel and air were mixed in a pre-mixer and introduced to the combustor through different degrees of swirl vanes. The flame characteristics were examined for different amount of hydrogen addition to the methane fuel and different swirl strengths. The hydrogen addition effects and swirl intensity on the combustion characteristics of pre-mixed methane flames were examined using micro-thermocouple, particle image velocity meter (PIV) and chemiluminescence techniques to provide information about flow field. The results show that the flame area increases at upstream of reaction zone because of increase in ignition energy from recirculation flow for increase in swirl intensity. The flame area is also increased at the downstream zone by recirculation flow because of increase in swirl intensity which results in higher centrifugal force. The higher combustibility of hydrogen makes reaction faster, raises the temperature of reaction zone and expands the reaction zone, consequently recirculation flow to reaction zone is reduced. The temperature of reaction zone increases with hydrogen addition even though the adiabatic flame temperature of the mixture gas decreases with increase in the amount of hydrogen addition in this experiment condition because the higher combustibility of hydrogen reduces the cooler recirculation flow to the reaction zone.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.43 no.1
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• pp.83-91
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• 2011

Hemicelluloses are useful materials for papermaking and other biotechnological applications. To recover and further utilize the hemicelluloses, this study carried out the pre-extraction of the hemicelluloses from Korean mixed hardwoods chips using hot water and sodium hydroxide solution at various temperature and time conditions. Through the hot water pre-extraction, the wood components of 22% was extracted and the 35% of the hemicelluloses which were contained in the original wood chips were dissolved into the pre-extractives. The yield of the pre-extractives was more significantly influenced by the pre-extraction temperature than the time. The pre-extractives with the yield of 30% could be obtained by alkali pre-extraction and alkali concentration was the most important factor. It had lower hemicellulose content but high molecular weight, compared with the hot water pre-extractives.

• Asian-Australasian Journal of Animal Sciences
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• v.23 no.1
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• pp.52-60
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• 2010

This experiment was conducted on 60 Hanwoo calves comprising five feed additive groups, with 12 calves in each group, to determine the effects of additives at pre- and post-weaning on growth performance and blood profile. The groups were control, antibiotic (Neomycin 110 ppm), illite (2%), fermented green tea probiotics (FGTP, 0.5%), and mixed additives (FGTP 0.25%, illite 1% and licorice 0.1%). The calves were offered experimental pellet feeds ad libitum and after one month were supplied with imported timothy hay. They moved freely within the group and suckled their mother' milk during the pre-weaning stage (birth to 3 months) and were separated from their dam during the post-weaning stage (4-5 months). During the pre-weaning stage, the highest average daily gain (ADG) was recorded in the antibiotic- and mixed additive-fed groups followed by FGTP, control and illite groups. In the post-weaning stage, significantly higher total weight gain and ADG were recorded in both the FGTP and mixed additive groups compared to the other groups (p<0.05). Feed efficiency of mixed additive- and illite-fed calves were almost similar with antibiotic-fed calves compared to the other two groups, but the ADG was lowest in illite-fed calves during the pre-weaning stage. In contrast, post-weaning calves fed FGTP and mixed additives showed better feed efficiency. The values of hematological indices, differential leukocyte count, blood proteins and immunoglobulin among the additive-fed calves were not significantly different (p>0.05), although hemoglobin and hematocrit values were lower in FGTP compared to control, but similar in mixed additive and antibiotic groups. These results indicate no detrimental effects of feed additives on the blood profile of calves at both pre- and post-weaning age. Serum albumin in post-weaning calves of all feed additive groups were similar but significantly lower (p<0.05) than in the control group. Post-weaning, IgM was significantly lower (p<0.05) in illite-fed calves compared to other treatment groups, but there was no difference at pre-weaning. Considering all factors, the mixed feed additives and FGTP can be the replacement feed formula for antibiotic for Hanwoo beef calf production, especially when used post- weaning.

• The Mathematical Education
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• v.55 no.2
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• pp.171-192
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• 2016

As teachers' competency is evaluated based on their teaching performance. pre-service teachers need to have an opportunity to reflect on themselves by systematically analyzing and evaluating their own lesson planning and teaching performance through self-assessment. In this study, we aimed to examine what evaluation criteria for lesson planning and teaching performance pre-service mathematics teachers consider in the process of self-assessment. This study used a mixed-methods research design. To draw the self-evaluation criteria for lesson planning and teaching performance, pre-service self-reported assessments were analyzed using qualitative analyses. In addition, descriptive statistics were used to investigate the pre-service teachers' distribution across the criteria and check the ratio of pre-service mathematics teachers for each element. As a result, it was disclosed that pre-service mathematics teachers considered eight elements in self evaluating their own lesson planning and teaching performance. In addition, we found that pre-service mathematics teachers tended to consider Pedagogical Content Knowledge (PCK) more than Subject-Matter Knowledge (SMK). Moreover, the results of this study provide educational implications for the curriculum in the pre-service teacher's education program.

• 한국연소학회:학술대회논문집
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• 2003.05a
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• pp.103-108
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• 2003

The control of flame shapes in a laminar pre-mixed flame has been experimentally investigated for propane/air pre-mixed laminar flames. Flames of different size and shapes are observed with heated wires or by controlling the equivalence ratio and flow rate of a mixture. The characteristics of the partitioning of a flame or the merge of flames are analyzed and explained by considering the balance between laminar flame speed and upstream mixture velocity. A combustor might be sized down while maintaining its heat production rate the same by partitioning a flame established in it. When the equivalence ratio of mixture is decreased, individual flames are merged together and the upstream mixture velocity can be practically decreased on a nozzle having opening ratio less than unity. As a result, the flame shape is to he adjusted until the newly established balanced condition is satisfied, and then. the stable combustion can be achieved again.

• Transactions of the Korean Society of Automotive Engineers
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• v.3 no.6
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• pp.112-122
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• 1995

As an alternative fuel producing less exhaust emissions, natural gas is of interest for use both in SI and CI engines. The potential of natural gas fuelled dual-fuel engine is considered high enough. However, much effort has to be made so that gaseous fuel is used efficiently with simultaneous minimum use of pilot oil. Hence, a simplified three-dimensional model, using a finite volume method in cylindrical coordinates, has been developed to facilitate an understanding of the dual-fuel combustion phenomena and to predict the complex interactions between the pilot distillate and natural gas. The computer model was calibrated by comparing it with the experimental results obtained from diesel engine like combustion bomb tests. In the pre-mixed natural gas combustion, the fuel burning was highly reliant on the injection condition and subsequent burning nature of the pilot distillate.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2022.04a
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• pp.192-193
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• 2022

In this study, concrete durability was reviewed before CGS, a by-product generated from IGCC, was used as a fine aggregate for concrete. The characteristics of concrete and effect on carbonization according to the type of pre-mixed cement and the CGS substitution rate were analyzed. As a result of the analysis, the depth of carbonation according to the pre-mixed cement types increased by up to 52%, and the carbonation resistance tended to be similar overall when CGS was used as a fine aggregate.

• Educational Technology International
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• v.12 no.1
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• pp.1-20
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• 2011

The study described in this paper examined the effectiveness of a multimedia case-based learning environment to teach technology integration to Korean pre-service teachers. The structure and philosophy behind the use of embedded video in an online, multimedia system and the data collected from 103 pre-service teachers are presented and discussed. The overall finding shows that there was no significant difference from pre- to posttest among the lecture, the case-based, and the mixed environment groups. However, low prior knowledge students improved more when they learned about technology integration with the mixed method than with the case-based method alone. Discussion about this result and its educational implications conclude the paper.

• Journal of Korean Society on Water Environment
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• v.35 no.4
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• pp.362-369
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• 2019

In this study, biodegradation efficiency improvement of mixed sludge for the anaerobic digestion process in wastewater treatment plant was investigated. In order to release the organic material contained in the sludge cell and promote the hydrolysis step, mixed sludge of 7% TS (Total Solids) was physically shear-treated at a shear strength of 1,000 ~ 4,000 rpm and a maximum of 120 mins. As a result of the comparison between mixed sludge before and after the treatment, the concentration of $SCOD_{Cr}$(Soluble Chemical Oxygen Demand-chromium method) was increased through the conversion of granular organic matter into dissolved organic matter as shear strength and treatment time increases. The solubilization efficiency increased rapidly after 30 min of solubilization application time, and they were 11.23 %, 20.10 %, 22.52 % and 25.43% at 120 min for each shear strength conditions, respectively. Additionally, the BMP(Biochemical Methane Potential) test was conducted with the optimized samples to determine the increase of methane production by the shear pre-treatment. Consequently, methane production of each samples were 0.275, 0.310, 0.323 and $0.335m^3/kg\;VS_{add}$, which indicates that methane production was increased to a maximum of 21.28% compared to the control without the solubilization process ($0.262m^3/kg\;VS_{add}$). As a result, the physical shear-treatment is a promising process for sewage sludge pre-treatment to reduce the organic waste and increase the energy production.