• Journal of the Korean School Mathematics Society
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• v.15 no.2
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• pp.331-348
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• 2012

With a gradual increase in research on teaching and learning calculus, there have been various studies about students' thinking about the derivative. This paper reviews the results of the existing empirical studies published in Korean and English. These studies mainly have shown that how students think about the derivative is related to their understanding of the related concepts and the representations of the derivative. There are also recent studies that emphasize the importance of how students learn the derivative including different applications of the derivative in different disciplines. However, the current literature rarely addressed how students think about the derivative in terms of the language differences, e.g., in Korean and English. The different terms for the derivative at a point and the derivative of a function, which shows the relation between concepts, may be closely related to students' thinking of the derivative as a function. Future study on this topic may expand our understanding on the role language-specific terms play in students' learning of mathematical concepts.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.6
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• pp.783-790
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• 2013

Circular path generation for ball bar measurement using the simultaneous movement of two axes with at least one rotary axis requires the execution of CAM software. However, a change in the machine type or measurement condition requires a new execution of the CAM software, which is cumbersome. This paper presents a circular path generation technique that does not require CAM software and is applicable to different types of driving axes with an arbitrary structural configuration of machine tools and any ball bar setup condition. Mathematical equations are derived for three cases using the proposed technique. In addition, to inspect the measurement feasibility for avoiding physical interference among the ball bar parts, a tilting angle calculation is proposed. The validity of the proposed technique was verified by performing a ball bar experiment with A and C as the simultaneous axes of a five-axis machine tool.

• Journal of the Korean Institute of Intelligent Systems
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• v.24 no.3
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• pp.245-250
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• 2014

Addiction can be largely divided into two categories. One is called medium addiction in which medium itself causes an addiction. Another is called cause addiction that brings addiction through combination of sensitive self and latent personal action. The medium addiction involves addiction phenomena directly caused by illegal drugs, alcohol and various other chemicals. The cause addiction is dependent on personal sensitivities as a sensitive problem of personal and includes cyber addictions such as shopping, work, game, internet, TV, and gambling. In this paper we propose two-dimensional addiction model that are equivalent to using an R-L-C series circuit of Electrical circuit and a Spring-Damper-mass of mechanical system. We also organize a Duffing equation that is added a nonlinear term in the proposed two-dimensional addiction model. We represent periodic motion and chaotic motion as time series and phase portrait according to parameter's variation. We confirm that among parameters chaotic motion had addicted state and periodic motion caused by change in control coefficient had pre-addiction state.

• Journal of Energy Engineering
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• v.6 no.1
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• pp.41-51
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• 1997

A dynamic mathematical model of a thermal power plant with a single drum-type boiler is described with the base on modular concept. The present process model, which is including full scope of the components and high load changes, is based on physical approach through lumped parameters. The module, which means a component of the power plant and must essentially depict the characteristics of the component well, might be interconnected using pressure nodal method in a arrangement determined by users. With the results of the load changes of 75 MW to 95 MW and 95MW to 75 MW with the rate of 3 MW/min, the applicability of the process model is examined connecting to DCS(Dispersion Control System), which has a real running logic of 100 MW real power plant.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.5
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• pp.535-543
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• 2014

In the robust optimization field, the robustness of the objective function emphasizes an insensitive design. In general, the robustness of the objective function can be achieved by reducing the change of the objective function with respect to the variation of the design variables and parameters. However, in conventional methods, when an insensitive design is emphasized, the performance of the objective function can be deteriorated. Besides, if the numbers of the design variables are increased, the numerical cost is quite high in robust optimization for nonlinear programming problems. In this research, the robustness index for the objective function and a process of robust optimization are proposed. Moreover, a method using the supremum of linearized functions is also proposed to reduce the computational cost. Mathematical examples are solved for the verification of the proposed method and the results are compared with those from the conventional methods. The proposed approach improves the performance of the objective function and its efficiency.

• Education of Primary School Mathematics
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• v.23 no.4
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• pp.191-206
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• 2020

The purpose of this study was to find an implication for a direction to improve professional development in mathematics by exploring elementary school teachers' perception of the need for professional development in mathematics. To this end, 4 elementary school teachers were organized into one focus group, and group discussion materials were collected and analyzed based on cases of mathematics professional development needs. As a result of the study, the elementary school teachers' perception that the need for professional development in mathematics is both unnecessary and necessary. The perception of unnecessary was influenced by the easy level of elementary school mathematics content and the ease of teaching. Also, the perception of necessary factors were considering various aspects of mathematics teaching, changing the accumulation of failures in mathematics classes, maintaining authority of students, demand for class improvement due to social change, the impact of school work, the influence of the community of professional development and peers in school, and efforts to grow as teachers. Based on these results, the author discussed ways to promote teachers' participation in mathematics professional development by considering elementary school teachers' perceptions of the need of mathematics professional development.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.05a
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• pp.1334-1337
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• 2006

System identification is the field of modeling dynamic systems from experimental data. As a modeling technique, we can mention finite element method (FEM). In addition, we are able to measure modal data as the experimental data. The system can be generally categorized into a gray box and black box. In the gray box, we know mathematical model of a system, but we don't know structural parameters exactly, so we need to estimate structural parameters. In the black box, we don't know a system completely, so we need to identify system from nothing. To date, various system identification methods have been developed. Among them, we introduce system realization theory which uses Hankel matrix and Eigensystem Realization Algorithm (ERA) that enable us to identify modal parameters from noisy measurement data. Although we obtain noise-free data, however, we are likely to face difficulties in identifying a structure with hidden modes. Hidden modes can be occurred when the input or output position comes to a nodal point. If we change a system using a mode decoupling controller, the hidden modes can be revealed. Because we know the perturbation quantities in a closed loop system with the controller, we can realize an original system by subtracting perturbation quantities from the closed loop system. In this paper, we propose a novel method to identify a structure with hidden modes using the mode decoupling controller and the associated example is given for illustration.

• Journal of Korea Water Resources Association
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• v.31 no.1
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• pp.95-103
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• 1998

Dam sediment can be predicted from the two methods: the one is a physical analysis based on the hydrjulic mechanism and the other is an empirical approach using observed data as a design factor. The former can be used to estimate short-term phenomena by mathematical methods. the latter can be used for deriving long-term design parameters such as dead storage calculation. Monthly reservoir operation is possible with the sluicing efficiency curve based on empirical data. The optimal sediment management can be carried out using the information variable which traces deposit sediments corresponding to the reservoir storage. The idea can provide an optimal operation strategy to save effective storage varying with time. This study presents a methodology for the long-term sediment prediction using sluicing efficiency curve. An application is conducted for estimating accumulated sedment deposit and water supply capability ofr the Fenhe dam in the Yellow rever of China.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.18 no.2
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• pp.97-111
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• 2006

Using the eigenfunction expansion method, a mathematical model has been developed to calculate the reflection and transmission of regular waves from a multiple-row curtainwall-pile breakwater. In addition, hydraulic model experiments have been conducted with different values of porosities between the piles, drafts of the curtain walls, and distances between the rows of the breakwater. It is found that the reflection and transmission coefficients decrease and increase, respectively, with decreasing relative water depth, but they bounce to increase and decrease, respectively, as the relative water depth decreases further. When either the porosity between the piles or the draft of the curtain wall is changed with other parameters fixed, the relative magnitudes of the reflection and transmission coefficients have been changed, but the general trend remained the same. When the wavelength is the same as the distance between the rows of the breakwater, a rapid change was observed for the reflection and transmission coefficients. A good agreement between the measurement and prediction was also founded for three-row breakwaters.

• Journal of Elementary Mathematics Education in Korea
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• v.20 no.2
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• pp.259-281
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• 2016

Teaching practicum plays a significant role in teacher education program because it provides pre-service teachers with an opportunity to apply what they have learned to the actual teaching contexts. As such, it needs to be conducted in terms of close collaboration between university and school. Given that, in a mathematics methods course the prospective teachers in this study had an opportunity to discuss mathematics lessons they had implemented during their teaching practicum. This paper analyzed in what ways prospective teachers' comments on elementary mathematics instruction were changed through this experience. The results of this study showed that in late comment the teachers tended to focus more on mathematical discourse, consider not only the teacher of the lesson but also students, and suggest alternative approaches on the classroom events they had noticed. It is noticeable that the results analyzed by researchers were consistent with prospective teachers' self-assessment. Building on these results, this paper provides implications of teacher preparation programs to enhance prospective teachers' ability to analyze elementary mathematics lessons.