• Journal of Elementary Mathematics Education in Korea
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• v.23 no.4
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• pp.481-506
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• 2019

Perpendicularity and parallelity are important concepts in Mathematics as well as real-life contexts. However, those concepts are rather reduced in 2015 revised curriculum compared to previous 2009 revised curriculum. This study firstly analyzed teaching method related to perpendicularity and parallelity in a series of mathematics textbooks of Korea, Singapore and Japan. Moreover, the unit of perpendicularity and parallel was redesigned in a way to understand the concepts meaningfully and to give opportunities for students to explore how to make perpendicular and parallel lines. The results showed that noticeable changes has been as the curriculum was revised in Korea. Also, three countries showed some differences in concepts definition and learning activities. This study is expected to suggest implications for how to teach perpendicularity and parallelity in elementary school mathematics.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.12
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• pp.3909-3916
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• 1996

Magnetic bearing is the machine element that supports the shaft without mechanical contact using the magnetic force induced by permanent magnet of electromagnet. Active magnetic bearing system is composed of sensor, controller, power amplifier, and electromagnet. If all the elements were dieal, shaft position could be controlled to sensor resolution, Because each elements inreal system have mechanical and electricla losses and nonlinearity, it is impossible to attain the desired performance using general control algorithm. So far it has been studied on improvement of the control algorithm of the electric characteristics of each elements. Another factors to affect shaft behavior are the manufacturing errors due to machine work, and assembling errors due to accumulate manufacturing errors of the radial magnetic bearing. This paper describes that the shaft behavior due to accumulate manufacturing errors and asymmetric bolting. This paper describes that the shaft behavior due to assembling errors of the radial bearings donot affect the rotaitonal accuracy of the shaft. But when the amplitude of the assembling errors increasees over the certain value, the bearing can not support the shaft properly.