• Transactions of the Korean Society of Automotive Engineers
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• v.19 no.1
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• pp.1-8
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• 2011

In recent years, there has been an interest in early-injection diesel engines as it has the potential of achieving a more homogeneous and leaner mixture close to TDC compared to standard diesel engine. The more homogeneous mixture may result in reduced NOx and soot emissions and higher efficiency in homogeneous charge compression ignition engines. While earlier studies have shown that a reduction in NOx emissions from HCCI engine is possible, there are some significant problems including the control of ignition timing and combustion rate. In order to investigate the effect of EGR and hydrogen enriched gas on combustion characteristics and emissions, an experiments with single cylinder CRDi engine were carried out concerning the formation of various premixed charge, which can achieved by early injection, EGR and hydrogen enriched gas. EGR was not effective to further reduce NOx and PM emissions. It was found that NOx emissions were decreased with an introduction of hydrogen enriched gas and an adequate diesel fuel amount.

• Transactions of the Korean Society of Automotive Engineers
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• v.14 no.4
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• pp.20-25
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• 2006

Recently, there has been an interest in premixed diesel engines as it has the potential of achieving a more homogeneous and leaner mixture close to TDC compared to conventional diesel engines. Early studies are shown that in a HCCI(Homogeneous Charge Compression Ignition) engine, the fuel injection timing and injection angle affects the mixture formations. Thus the purpose of this study was to investigate relationship of combustion and mixture formations according to injection timing and injection angle in a common rail direct injection type HCCI engine using a early injection method called the PCCI(Premixed Charge Compression Ignition). From this study, we found that the fuel. injection timing and injection angle affect the mixture formations and in turn affects combustion in the PCCI engine.

• Transactions of the Korean Society of Automotive Engineers
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• v.10 no.3
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• pp.93-100
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• 2002

For natural gas and LPG fuel, measurements on the concentrations of individual exhaust hydrocarbon species have been made as a function of air-fuel ratio in a 2-liter four-cylinder engine using a gas chromatography. NMHC in addition to the species of HC, other emissions such as CO$_2$, CO and NOx were examined for natural gas and LPG at 1800rpm far two compression ratios (8.6 and 10.6). Fuel conversion efficiencies were also investigated together with emissions to study the effect of engine parameters on the combustion performances in gas engines especially under the lean bum conditions. It was found that CO$_2$ emission decreased with smaller C value of fuel, leaner mixture strength and the higher compression ratio. HC emissions from LPG engine consisted primarily of propane (larger 60%), ethylene and propylene, while main emissions from natural gas were mothane (larger than 60%), ethane, ethylene and propane on the average. The natural gas was proved to give the less ozone formation than LPG fuel. This was accomplished by reducing the emissions of propylene, which has relatively high MIR factor, and propane that originally has large portion of LPG. In addition, natural gas shows a benefit in other emissions (i.e. NMHC,NOx, CO$_2$and CO), SR and BSR values except fuel conversion efficiency.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.466-471
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• 2004

In gas turbines, excess air for combustion is available and therefore lean premixed combustion is the most promising approach to the significant reduction of thermal NOx emissions. At lean conditions, however, flame stability is inherently worse and hence combustion tends to be incomplete. Efforts have been devoted toward extending the operating range of complete combustion at leaner conditions. One of them is the lean-lean two-stage combustion where lean to ultra-lean secondary mixtures are mixed with the hot burned gas from the primary stage. Conventional flame combustion or flameless reaction are initiated depending on the conditions of the secondary zone. In the first part of the present study, the effects of fuel injection on the emissions and flame stability were investigated for a single tubular flame, In the second part, the emissions and flame stability were studied for a two-stage combustor with secondary mixture injected through the tangential slots on a cylindrical combustor wall. The effects of the ratio of air flow rates to the primary and secondary zones on the emissions and combustion characteristics were investigate.

• Journal of the Korean earth science society
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• v.25 no.8
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• pp.739-747
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• 2004

This study was to promote meaning ways of leaning and observe the influence of concept maps on middle school students' conceptual formation with regards to the topic of the 'sea water'. Concept map is one way to examine a leaner's conceptual formation process. The subjects of this study consisted of four classes within the first grade students of a Busan middle school, which were divided into two groups: the experimental group which applied concept map teaching and the ordinary teaching group. This study was carried out before and after class, examining the science leaning achievement, self-directed leaning characteristics, and awareness change on the concept maps. The result of this study was as follows: First, the leaning achievement of middle school students was positively affected by the use of concept maps. Second, the teaching method with concept map was more effective self-directed leaning characteristics compared to the ordinary one. Third, concept map teaching was a positive reaction to conceptual formation.

• The Journal of the Korea Contents Association
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• v.11 no.3
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• pp.128-136
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• 2011

Although learners learn with the same educational games, they show differences in successes. This is because they do not share the same individual characteristics. Currently, there are various studies conducted on effective education according to gender among other characteristics of learners off-line. When this effective educational method according to gender is applied to educational games, it will create more effective outcomes. In addition, this study observed the effective educational method according to gender and learning styles. Through the observation, the considering factors for educational game designs according to the learners' gender was defined. These considering factors were categorized into cognitive and perceptive factors, with each definitions reflected on the characteristics of each gender. This study has its meanings in that it has conducted theoretical results of the considering factors for educational game designs based on reference studies. This study will be utilized as a reference study when designing various games.

• Transactions of the Korean Society of Automotive Engineers
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• v.21 no.2
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• pp.146-153
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• 2013

CNG buses has contributed to improve air quality in cities. But it is difficult to meet the next emission regulations such as EURO-VI without the help of additional post-processing device. Hydorgen has higher flame speed and lower combustion temperature that make it thermal efficiency increase with leaner operation. Using hydrogen natural gas blend (HCNG) fuel is promising technology which can reduce $NO_x$ and $CO_2$ emissions for a natural gas vehicle. However, fuel flow rate of HCNG should be increased since hydrogen's energy density per volume is much smaller than natural gas. In the present study, the characteristics of fuel supply system and its applicability were evaluated in a heavy duty natural gas engine. The results showed that the potential of fuel pressure regulator and fuel metering valve had enough capacity with HCNG. Employed mixer did not affect the distribution characteristics of mixture.

• Education of Primary School Mathematics
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• v.17 no.3
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• pp.205-230
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• 2014

New teaching and learning theory on various aspects about class is needed to implement education which reflects constructivism, ideally. For an ideal learner-centered mathematics class, tangible and intangible elements related to education(view of knowledge, view of leaner, teacher's role, evaluation, the form of class, learning, teaching material, etc.) should be integrated from a constructive perspective and especially, teaching material has to be premised on that learners have intellectual abilities to construct knowledge themselves, and reflect integrity of knowledge, diversity and others, and contain open attributes. In addition to this, teaching material should have characteristics different from those when objective epistemology applies, so there is a need to analyze whether teaching material has those characteristics. For this, this study compared and analyzed <1. Three-Digit Numbers> which belongs to the domain of numbers and operations out of the units of mathematics(3) textbook of the 2009 revised curriculum for the first and second grade that first introduced story-telling, and <3. Understanding of Place Values> for the second grade of constructive math class used in the U.S.

• Journal of the Korean Society of Clothing and Textiles
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• v.19 no.3
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• pp.397-415
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• 1995

The purpose of this study was to identify the change and characteristics of 20th men's fashion. The result of the Study as follows; 1 In the period 1890's-World War I there was a display of opulence and extravagance Therefore men's fashion pursued with elegance and grace. The rise of sports and an erosion of rules of Victorian society were evident influences before 1914. So men's silhouette resembled athletic appearance and less formality was shown in masculine attire. 2. During the period World War I-1920's the new equality of social relations between the sexes had an influence in fashion. Unisex look evolved so boyish shaped became the feminine ideal, men wanted to boyish fitted leaner stylings and natural shoulder suits. In the twenties youth, who seemed to have a social dominance, asserted their own testes in fashion. New style of men's fashion such as oxford bags and Ivy League Look appeared. After World War I "comfort" is the aim of fashion so casualness was reflected in fashion: vests often were discarded and man wore a soft, detachable collars. 3. In the thirties depression marked a shift in mood from gaiety and progressivism of the twenties to the conservative, even reactionary values. The role of men and women returned to more traditional attitudes, Every men's general appearance was bold and manly: his chest was broad and well-built, his shoulders square and muscular. The effects of World War ll were not on style but on textiles and clothing construction: lighter weight fabrics appeared and construction was simplified 4. Men's dress changed only in detail and not in essence. But there was a continued increase in the variety of clothes and color in men's fashion.

• The Journal of the Korea Contents Association
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• v.20 no.11
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• pp.402-410
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• 2020

It is very important for Academic purpose Korean leaner to understand main ideas and overall context of texts. In order to understand the overall context and mail ideas of text, learners need output task, ways to perform what they are learning, such as retelling. That would help them to realize that there is a gap between what they have understood and what they can actually speak or write. These out activities help learners comprehend the text more efficiently, while at the same time raising their confidence level. The purpose of this study was to develop an education plan to improve reading comprehension ability by using retelling activity. To achieve the purpose of the study, retelling activity, which makes it easier to take an integrated approach to language function and is considered to be relatively effective, was utilized because of the characteristics of retelling activity education instead of teacher-centered education methods.