• Journal of the Korean School Mathematics Society
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• v.12 no.2
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• pp.151-170
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• 2009

The purpose of the study is to analyze the sixth graders' understanding of concepts and operation about fraction. The test was administered and analyzed to 707 sixth graders' performance on fractions after the fraction instructions in elementary schools in Seoul, Korea. The participants are asked to answer two sets of questions for 40 minutes. First, they are asked to answer to 16 problems about the concepts of fraction with respect to part-whole, ratio, operator, measure, quotient, equivalent, and operations. Second, specially, to investigate sixth graders' ability of drawing and describing the situation of division including fraction, the descriptive problem asked students (1) to describe $3\;{\div}\;\frac{1}{2}$ into pictorial representation and (2) to write the solving process. The participants of this study didn't show deep understandings about the concepts and operation of fraction. The degree of understanding of subconstructs of fraction shows that their knowledge of ratio concept with respect to fraction was highest while their understanding of measure with respect to fraction was lowest. Considering their wrong answers, about 59% of participants showed misconception to the question of naming one fraction that appears between $\frac{1}{5}$ and $\frac{1}{6}$. Further, they didn't explain their understanding with drawing about the division of fraction ($3\;{\div}\;\frac{1}{2}$).

• Journal of Elementary Mathematics Education in Korea
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• v.15 no.1
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• pp.1-18
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• 2011

The purpose of this study was to investigate the effects of estimation strategy on placing decimal point in multiplication and division of decimals. To examine the effects of improving calculation ability and reducing decimal point errors with this estimation strategy, the experimental research on operation with decimal was conducted. The operation group conducted the decimal point estimation strategy for operating decimal fractions, whereas the control group used the traditional method with the same test paper. The results obtained in this research are as follows; First, the estimation strategy with understanding a basic meaning of decimals was much more effective in calculation improvement than the algorithm study with repeated calculations. Second, the mathematical problem solving ability - including the whole procedure for solving the mathematical question - had no effects since the decimal point estimation strategy is normally performed after finishing problem solving strategy. Third, the estimation strategy showed positive effects on the calculation ability. Th Memorizing algorithm doesn't last long to the students, but the estimation strategy based on the concept and the position of decimal fraction affects continually to the students. Finally, the estimation strategy assisted the students in understanding the connection of the position of decimal points in the product with that in the multiplicand or the multiplier. Moreover, this strategy suggested to the students that there was relation between the placing decimal point of the quotient and that of the dividend.

• Journal of Periodontal and Implant Science
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• v.50 no.3
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• pp.197-206
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• 2020

Purpose: The aim of this study was to determine the impact of different compressive forces on deproteinized bovine bone mineral (DBBM) particles covered by native bilayer collagen membrane (NBCM) during alveolar ridge preservation (ARP) in the molar area, and to identify any histomorphometric and clinical differences according to the compressive force applied. Methods: Sockets were filled with DBBM after tooth extraction, and different compressive forces (30 N and 5 N, respectively) were applied to the graft material in the test (30 N) and control (5 N) groups. The DBBM in both groups was covered with NBCM in a double-layered fashion. A crossed horizontal mattress suture (hidden X) was then made. A core biopsy was performed using a trephine bur without flap elevation at the implant placement site for histomorphometric evaluations after 4 months. The change of the marginal bone level was measured using radiography. Results: Twelve patients completed the study. The histomorphometric analysis demonstrated that the mean ratios of the areas of new bone, residual graft material, and soft tissue and the implant stability quotient did not differ significantly between the groups (P>0.05). However, the mean size of the residual graft material showed a significant intergroup difference (P<0.05). Conclusions: The application of 2 compressive forces (5 N, 30 N) on particulate DBBM grafts during open-healing ARP in the posterior area led to comparable new bone formation, implant feasibility and peri-implant bone level.

• Journal of the Economic Geographical Society of Korea
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• v.17 no.2
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• pp.335-348
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• 2014

This study investigates the technical level and industrial structure for the case of the Gazelle industry in Chungnam Province. As a results of the empirical study, the Gazelle industry of Chungnam Province shows a competitive position in terms of scale and growth capacity, which. in turn, provides income and tax collection effects due to the high level of industrial efficiency. Among the Gazelle industry of Chungnam Province, low-level technology industry, compared to high and middle-level technology industries, accelerates higher level of agglomeration and industrial growth, which provides a rapid change of industrial structure of the province. Theses research results imply that research and development investment in the Gazelle industry is essential and industrial development strategy should be conducted via step-by-step with business scale quotient (BQ) and industrial growth rate (IG). Meanwhile, there should be a serious policy review whether low-level technology industry is better off for the province compared to high and middle-level technology industries. This study expects that regional industrial policy applying the concept of Gazelle industry can accelerate regional development since the Gazelle industry contributes to the high level of income growth and employment creation.

• Communications of Mathematical Education
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• v.23 no.1
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• pp.145-174
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• 2009

Based on the thinking that people can understand more clearly when the problem is related with their prior knowledge, the Purpose of this study was to analysis students' informal knowledge, which is constructed through their mathematical experience in the context of real-world situations. According to this purpose, the following research questions were. 1) What is the characteristics of students' informal knowledge about fraction before formal fraction instruction in school? 2) What is the difference of informal knowledge of fraction according to reasoning ability and grade. To investigate these questions, 18 children of first, second and third grade(6 children per each grade) in C elementary school were selected. Among the various concept of fraction, part-whole fraction, quotient fraction, ratio fraction and measure fraction were selected for the interview. I recorded the interview on digital camera, drew up a protocol about interview contents, and analyzed and discussed them after numbering and comment. The conclusions are as follows: First, students already constructed informal knowledge before they learned formal knowledge about fraction. Among students' informal knowledge they knew correct concepts based on formal knowledge, but they also have ideas that would lead to misconceptions. Second, the informal knowledge constructed by children were different according to grade. This is because the informal knowledge is influenced by various experience on learning and everyday life. And the students having higher reasoning ability represented higher levels of knowledge. Third, because children are using informal knowledge from everyday life to learn formal knowledge, we should use these informal knowledge to instruct more efficiently.