• The Mathematical Education
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• v.50 no.1
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• pp.103-118
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• 2011

The study examined whether the relation between mathematics self-efficacy and mathematics achievement was partially mediated by the learning strategies, using latent growth model analyses. It was also examined the auto-regressive, cross-lagged (ARCL) panel model for testing the stability and change in the relation of mathematics self-efficacy and learning strategy over time. The study analyzed the first-year to the third-year data of the Korean Educational Longitudinal Survey (KELS). The result of ARCL panel model analysis showed that earlier mathematics self-efficacy could predict later learning strategy use. There were linear trends in mathematics self-efficacy, learning strategy, and mathematics achievement. Specifically, mathematics achievement was increased over the three time points, whereas mathematics self-efficacy and learning strategies were significantly decreased. In the analyses of latent growth models, the mediating effects of learning strategies were overall supported. That is, both of initial status and change rate of rehearsal strategy partially mediated the relation of mathematics self-efficacy and mathematics achievement. However, in elaboration and meta-cognitive strategies, only the initial status of each variable showed the indirect relationship.

• Communications of Mathematical Education
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• v.23 no.3
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• pp.583-597
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• 2009

The purposes of this study are to analyze error that the students in science and engineering show in the process of thinking a extremum value. First, in view of examples of incorrect answers that appeared in a test by students in science and engineering, it has been found that the most frequent incorrect answers were due to a lack of understanding about necessary matters and concepts. In this regard, it is necessary to use various examples and pictures(graphs) to teach students in science and engineering. In addition, it has been found that it is more effective to use questions asking why it happens and why they think that way to help those having difficulties in understanding various concepts and principles.

• Management Science and Financial Engineering
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• v.16 no.3
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• pp.49-70
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• 2010

Customer population management models can be classified into three categories: the first category includes the models that analyze the customer population at cohort level; the second one deals with the customer population at aggregate level; the third one has interest in the interactions among the customer populations in the competitive market. Our study proposes a model that can analyze the dynamics of customer population in consumer-durables market at aggregate level. The dynamics of customer population includes the retention curves from the purchase or at a specific duration time, the duration time expectancy at a specific duration time, and customer population growth or decline including net replacement rate, intrinsic rate of increase, and the generation time of customer population. For this study, we adopt mathematical ecology models, redefine them, and restructure interdisciplinary models to analyze the dynamics of customer population at aggregate level. We use the data of previous research on dynamic customer population management at cohort level to compare its results with those of ours and to demonstrate the useful analytical effects which the precious research cannot provide for marketers.

• Journal of Power Electronics
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• v.18 no.2
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• pp.547-557
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• 2018

This work proposes a control method of frequency stabilization for grid integration of large-scale wind farms via the voltage source converter-based high-voltage direct current (VSC-HVDC) technology. First, the topology of grid integration of a large-scale wind farm via the VSC-HVDC link is provided, and simple control strategies for wind turbines, wind farm side VSC (WFVSC), and grid side VSC are presented. Second, a mathematical model between the phase angle of WFVSC and the frequency of the wind farm is established. The control principle of the large-scale wind power integrated system is analyzed in theory in accordance with the mathematical model. Third, frequency and AC voltage controllers of WFVSC are designed based on the mathematical model of the relationships between the phase angle of WFVSC and the frequency of the wind farm, and between the modulation index of WFVSC and the voltage of the wind farm. Corresponding controller structures are established by deriving a transfer function, and an optimization method for selecting the parameters of the frequency controller is presented. Finally, a case study is performed under different operating conditions by using the DIgSILENT/PowerFactory software. Results show that the proposed control method has good performance in the frequency stabilization of the large-scale wind power integrated system via the VSC-HVDC technology.

• The Mathematical Education
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• v.37 no.1
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• pp.87-99
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• 1998

Mathematics education is very important in future because mathematics is the basis of every study, for example, natural and social science, etc. Our nation wide curriculum has been revised six times since 1948. In 1992, the sixth revision was enforced and we are using the revised textbook now. This study aims at helping of continuous investigation for educational curriculum and textbook, and aims at efficient teaching by preventing unnecessary repetition and excessive gap in real field by analyzing the articulation of Analytics part in school textbook from elementary to high school. This thesis consists of the followings. 1.Investigation of the principles and natures of articulation along with curriculum course and notice the articulation based on the analysing tools. 2.Importance of learning functions. 3.To get the propriety, formation of 8 judging group and classification of content materials in function chapters by the judges based on the analyzing tools. 4.Analysis of presentation method and terminologies in the first concepts, suggestion teaching method to reduce gap and help of understanding on first concepts in the study of function. As a result 'development' consists of 55.8% of the total and it is higher than 'duplication' and 'gap'. To be specific in periods, between elementary school and middle school 'development' takes 64.5% and this shows an acceptable articulation in the period. While 39.4% of 'gap' in articulation between middle school and high school looks high compared with 'gap' between the previous periods. The item suggested with the 'gap' is the 'definition of function', 'value of function', 'parallel translation', 'exponential and logarithmic function'. It is observed that these materials is suddenly appeared in high school.

• The Mathematical Education
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• v.58 no.2
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• pp.299-317
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• 2019

In this study, we analyzed the change of teacher knowledge through task design in the teacher-researcher community focused on knowledge of students in the area of derivatives application. The following subjects were studied. First, we have analyzed the focus of the discussion related to teacher knowledge of students within the teacher-researcher community. Second, we have analyzed the change of teacher knowledge of students according to the focus. The results of this study are as follows. First, community member' different knowledge of students led the discussion on the task solving paths. The main focus of the discussion was the possibility in inducing responses and motivation. Second, the process of reviewing and evaluating task solving paths and reaching consensus led the improvement of teacher knowledge. Teachers and researchers led changes of teacher knowledge by sharing the knowledge based on previous research and experience, respectively. This ultimately shows the necessity of co-learning between teachers and researchers in teacher education.

• Communications of Mathematical Education
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• v.33 no.2
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• pp.47-66
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• 2019

The purpose of this study is followings. First, we develop and apply teaching and learning methods for conducting team projects in flipped calculus class. Second we collect data such as team reports, individual reviews, and surveys during class activities. Third we survey the impacts on participation in student team activities, advanced studying, communication and collaboration. A total of 120 engineering and science majoring students participated in the 16-week long class study administered in team project learning styles in Spring 2018. There were two characteristics of this class. First students studied concepts and examples with video in pre-class and did the team project learning in the classroom. Second we used Google Drive to record team project progress, and to make sure the instructor to intervene appropriately in team activities. We conducted a team project inside and outside the classroom. This could lead the instructor to advise students and so their participation in team activity increased. As a result, it not only had a good effect on communication and cooperation, but also had an effect on advanced learning.

• Korean Journal of Poultry Science
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• v.7 no.2
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• pp.28-36
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• 1980

This study was carried out to estimate combining abilitie or economic traits in layer chickens. The data used in this study were the record of 10 single crosses produced by half diallel cross of 5 lines of Single Comb White Leghorns, such as A, B, C, K and S lines. Total 720 progenies of the crosses were reared at the Poultry Breeding Farm, College of Agriculture, Seoul National University from Feb. 1979 to August, 1980. Combining abilities were estimated by Grilling's mathematical model for the traits; age the first egg, total egg number, egg weight and body weight. The results attained from the studies were summarized as follows; In estimate of combining ability, an age at first egg of BS cross was largely due to significiantly higher general combining ability (G. C. A.) effect of B and S strains than Cand K strains in G. C. A. effect, and to specific combining ability (S. C. A) effect of B and S-trains. AB and BS crosses showed the highest egg Production. AB cross performance was result from high G.C.A. effect of A ana B strains. BS cross performance was result from high G. C. A. effect of B and high S. C. A. effect of BS cross. Specific combining ability effect in egg. weight was not statiscally significiant, but S strain showed high G. C. A. effect. A and B strains in body weight showed significantly low C. C. A. effect. From the above results, BS cross in an age at first egg, AB and BS crosses in egg Production, S strain in egg weight and AB cross in body weight were superior to other strains or crosses.

• Journal of the Korean Society for Nondestructive Testing
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• v.23 no.6
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• pp.622-634
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• 2003

This paper is concerned with a computational method for recovering a crack shape of steam generator tubes of nuclear plants. Problems on the shape identification are discussed arising in the characterization of a structural defect in a conductor using data of eddy current inspection. A surface defect on the generator tube ran be detected as a probe impedance trajectory by scanning a pancake type coil. First, a mathematical model of the inspection process is derived from the Maxwell's equation. Second, the input and output relation is given by the approximate model by virtue of the hybrid use of the finite element and boundary element method. In that model, the crack shape is characterized by the unknown coefficients of the B-spline function which approximates the crack shape geometry. Finally, a parameter estimation technique is proposed for recovering the crack shape using data from the probe coil. The computational experiments were successfully tested with the laboratory data.

• Journal of Korean Society of Rural Planning
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• v.16 no.3
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• pp.173-184
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• 2010

The objectives of this study are to quantitatively analyze problems and improvement directions of the comprehensive rural village development projects through DEMATEL and contents analysis. Contents analysis was conducted for 15 existing researches and 28 problems were deducted at the stage of the comprehensive rural village development projects. The Decision Making Trial and Evaluation Laboratory(DEMATEL), a mathematical computation method, was utilized as an objective method to handle the inner dependences within a set of problems. The results of this research are summarized as follows. First, insufficient education and publicity of project was the most considerable cause problem. Second, lack of participation, will, and ability of residents was the most considerable effect problem. Finally, several improvements of the comprehensive rural village development projects were deducted by cause and effect relationship of problems.