• Education of Primary School Mathematics
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• v.17 no.3
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• pp.231-251
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• 2014

The number and units are not apart from each other, especifically units clarifies number. Students often encounters many problems involving units, researcher found that students have difficulty in recognize the meaning of calculation results. These students recognizes units, just presented thing in the problem. And they could not connect units with the meaning of calculation results. With this results, this study researched limitation of pre serviced didactic transposition and found the effectness of using units to recognize the meaning of calculation results. Especially we discussed didactic transposition with permitting probability of unit calculation and suggested implications. So we accented the inevitability of change, and tried to offer substantial help.

• Journal of Educational Research in Mathematics
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• v.27 no.3
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• pp.391-410
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• 2017

This study aims to analyze mathematically gifted students' characteristics of generalization and justification for a given mathematical task and induce didactical implications for individual teaching methods by students' learning styles. To do this, we identified the learning styles of three mathematically gifted 6th graders and observed their processes in solving a given problem. Paper-pencil environment as well as dynamic geometrical environment using Geogebra were provided for three students respectively. We collected and analyzed qualitatively the research data such as the students' activity sheets, the students' records in Geogebra, our observation reports about the processes of generalization and justification, and the records of interview. The results of analysis show that the types of the students' generalization are various while the level of their justifications is identical. Futhermore, their preference of learning environment is also distinguished. Based on the results of analysis, we induced some implications for individual teaching for mathematically gifted students by learning styles.

• Journal of Educational Research in Mathematics
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• v.15 no.3
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• pp.335-352
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• 2005

In this paper, we consider a center of gravity of convex polygon which could be an enriched topic for the gifted in mathematics(7th grades) and suggested a case that the gifted experienced a center of gravity. Based on properties of Archimedes' center of mass, we define it as a point which make a polygon be in counterpoised with its area and explain how to find that point through using integral calculus or internal division. Then we consider that the gifted would experience various kinds of mathematical thinking and apply diverse ways of problem solving 3s searching for this topic. As this research, the teacher would be able to conduct the gifted with penetration into center of gravity and to let them participate in advanced learning courses which value ma-thematical thinking while they undergo similar experiences such as mathematicians.

• School Mathematics
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• v.6 no.4
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• pp.411-433
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• 2004

Many researchers have reported that 7th graders have severe difficulties in using letters and algebraic expressions. This study investigated the way Microsoft Excel contributes to student's understanding of letters and algebraic expressions. For six hours through two weeks, four 7th grade students experienced various activities with Excel after school and both before and after the experimentation, the interviews to check their understanding was conducted. The results were as follows; First, after the experimentation, students used various letters to express formulas and recognized that letters represent not only some objects but also changing objects. Also they accepted that same objects could be represented by different letters and different objects could be represented by the same letters. Second, Excel improved students' abilities to discriminate variables and invariables in the problem and to find mathematical relationships among variables. And with Excel students could divide the whole calculation procedure into several steps in order to handle it more easily. Also, Excel made immediate numerical feedback possible and it made students express the calculation in a more formalized way than a paper and pencil environment did.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.24 no.8
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• pp.583-591
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• 2014

The mathematical modeling on the free vibration and stability of a multi-stepped shaft of turbo compressor is performed in this study. The multi-stepped shaft is modeled as a non-uniform Timoshenko beam supported by anisotropic bearings. It is assumed that the shaft is spinning with constant speed about its longitudinal axis and subjected to a conservative axial force induced by front and rear impellers attached to the shaft. The structural model incorporates non-classical features such as transverse shear and rotary inertia. A structural coupling between vertical and lateral motions is induced by Coriolis acceleration terms. The governing equations are derived via Hamilton's variational principle and the equations are transformed to the standard form of an eigenvalue problem. The implications of combined gyroscopic effect, conservative axial force, bearing stiffness and damping are revealed and a number of pertinent conclusions are outlined. In this study analytical results are compared with those from ANSYS finite element analysis and experimental modal testing.

• Journal of Soil and Groundwater Environment
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• v.13 no.6
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• pp.50-61
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• 2008

In this study, new integrated particle tracking algorithm was developed to reduce the inherent problem of Eulerian- Lagrangian method, or adverse effect of particle tracking error on mass balance error. The new integrated particle tracking algorithm includes numerical method, semi-analytical method, and analytical method which consider both temporal and spatial changes of velocity field during time step. Detail of mathematical derivations is well illustrated and four examples are made to verify through the comparison of the new integrated particle tracking with analytical solution or Runge-Kutta method. Additionally, It was shown that the there is better superiority of the new integrated particle tracking algorithm over other existing particle tracking method such as Lu's method.

• The KIPS Transactions:PartB
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• v.9B no.3
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• pp.293-302
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• 2002

Gradual scene change detection is known as more difficult problem then abrupt scene change detection on video data analysis for contents based retrieval. In this paper, we present a new method for scene change detection far both abrupt and gradual change using the variable dynamic threshold arid cut frame difference (CFD). For this, We present the characteristics arid mathematical models of gradual transitions anti then, how can be detected by the CFD. And also we present new scene change detection algorithm based on cut frame difference. By the experimental result using real world video data indicate that the proposed method detect various scene changes both abrupt and gradual change efficiently without time-consuming computation and any dependency on a kind of gradual change effects.

• 대한공업교육학회지
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• v.32 no.2
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• pp.155-170
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• 2007

The purpose of this study was to estimate key competencies according to their levels in order to understand person's ability in automobile fields of school and workplace. For this study, key competencies consisting of mathematical skills, problem solving skills, communications skills, self management and development skills, resources recycling skills, interpersonal relationship skills, technological skills, information skills, organizational understanding skills were determined. We examined the related literatures to determine the level of key competencies and diverse opinions were accommodated with visits to workplace in order to enhance the validity of the results of this study. Based on the results of this study, it was concluded that the estimation of key competencies according to their levels was possible and valid.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2014.06a
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• pp.223-224
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• 2014

Along with container freights keep increasing globally, lots of containers used for inland distribution increase steadily too. In Korea, there are many modes to transfer container freights such as roadway, railroad, coastal shipment. The roadway transportation is the most common but it is considered as the most inefficient mode. This paper studies about reasons that affect to the inefficiency of roadway transport and finds solution to resolve the problem. First backhaul transportation is addressed and some suggested solutions are presented such as construction of inland inspection center or managing efficiently container management. Then mathematical model is used to show the quantitative evaluation of backhaul transport solution.

• Journal of Electrical Engineering and Technology
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• v.10 no.4
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• pp.1527-1539
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• 2015

In this paper the hardware implementation of the direct torque control based on the fuzzy logic technique of induction motor on the Field-Programmable Gate Array (FPGA) is presented. Due to its complexity, the fuzzy logic technique implemented on a digital system like the DSP (Digital Signal Processor) and microcontroller is characterized by a calculating delay. This delay is due to the processing speed which depends on the system complexity. The limitation of these solutions is inevitable. To solve this problem, an alternative digital solution is used, based on the FPGA, which is characterized by a fast processing speed, to take the advantage of the performances of the fuzzy logic technique in spite of its complex computation. The Conventional Direct Torque Control (CDTC) of the induction machine faces problems, like the high stator flux, electromagnetic torque ripples, and stator current distortions. To overcome the CDTC problems many methods are used such as the space vector modulation which is sensitive to the parameters variations of the machine, the increase in the switches inverter number which increases the cost of the inverter, and the artificial intelligence. In this paper an intelligent technique based on the fuzzy logic is used because it is allows controlling the systems without knowing the mathematical model. Also, we use a new method based on the Xilinx system generator for the hardware implementation of Direct Torque Fuzzy Control (DTFC) on the FPGA. The simulation results of the DTFC are compared to those of the CDTC. The comparison results illustrate the reduction in the torque and stator flux ripples of the DTFC and show the Xilinx Virtex V FPGA performances in terms of execution time.