• Communications of Mathematical Education
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• v.28 no.1
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• pp.1-17
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• 2014

Recently a student's mathematical thinking and problem-solving skills are emphasized. Nevertheless, the students solved the problem associated with a given type of problem solving using mechanical algorithms. With this algorithm, It's hard to achieve the goal that are recently emphasized. Furthermore It may be formed error or misconception. However, consistent errors have positive aspects to identify of the current cognitive state of the learner and to provide information about the cause of the error. Thus, this study tried to analyze the error happening in the process of solving gearwheel-involved problem and to propose the correct teaching method. The result of student's error analysis, the student tends to solve the gear-wheel problem with proportional expression only. And the student did not check for the proportional expression whether they are right or wrong. This may be occurred by textbook and curriculum which suggests only best possible conditioned problems. This paper close with implications on the discussion and revision of the concepts presented in the curriculum and sequence related to the gearwheel-involved problem as well as methodological suggested of textbook.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.2
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• pp.503-510
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• 2020

Eco-friendly mountain railways operate on concrete rack tracks embedded on existing sharp curved and steep roads to preserve the environment in mountainous areas. Owing to the narrow roads, single lines are inevitable, and many branches are required. In branches, previous switchers and heating devices cannot be applied, because of the limited spacing for the rack and the slow removal of thick ice. To solve these problems, a switch and a heating device have been developed. The switcher changes the line by moving the block of concrete track with hydraulic actuators. The lack of discontinuity reduces the derailment risk and makes locking simple. The heating device uses high frequency induction coils to increase the efficiency and melt the thick ice rapidly. The prototype switcher and heating device were produced and operated to prove their performance. The heating device yielded a 10 times greater efficiency than the previous one. The switcher and heating device are the essential core technologies for the operation of mountain trams in winter and contribute to the spread of mountain railways to domestic or foreign resort areas by enhancing safety and efficiency. In addition, they can provide transportation rights to local residents in poor winter traffic, and bring about tourism and local economic growth.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2010.03b
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• pp.39-39
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• 2010

낮은 에너지를 이용하여 상대론적 영역에서 동작하는 마이크로파 출력장치를 연구하였다 그에 따른 후진파 발진기는 대전력 마이크로파를 발생시키는 장치로서 연구하였으며 관내에 전자빔을 입사시킴으로서 발진이 일어나 출력을 발생 시킨다.

• Proceedings of the IEEK Conference
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• 2001.06e
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• pp.177-180
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• 2001

A saw-tooth waveform generator with current-controllable frequency is described. The generator utilizes operational transconductance amplifiers as switching element. It features simple and wide sweep capability. The circuit built with commercially avaliable components exhibits good linearity of current to frequency and relatively low temperature sensitivity.

• 주택과사람들
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• s.205
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• pp.82-85
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• 2007

길을 걷다 발길을 멈출 때가 있다. 향긋한 여인네의 향취나 포르쉐의 매끈한 보디라인 때문이 아니다. 낯설고도 새롭게 느껴지는 건축물 때문이다. 그 옛날 동굴에서 거푸집으로, 또는 벽돌집에서 미끈한 콘크리트 건물로, 다시 거대한 글래스 타워까지 건축의 역사는 인류의 발전 과정과 톱니바퀴처럼 맞물려오지 않았나. 예술과 철학, 패션과 직.간접적으로 영향을 주고받으면서 성장해온 건축은 시대를 반영하고, 때로는 그 시대의 문화를 이끌기도 한다.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2010.11a
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• pp.245-246
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• 2010

• Journal of the Korea Academia-Industrial cooperation Society
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• v.10 no.12
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• pp.3688-3693
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• 2009

In this paper the design methode of a separated composition state machine based on the compositive map with connecting two chaotic maps together - sawtooth map $S_2(x)$ and tent map $T_2(x)$ and the result of that is proposed. this paper gives a graph of the chaotic states generated by the composition state machine using the compositive logic of two different chaotic maps - sawtooth map and tent map and also shows that the period of pseudo-random states has the length according to the precision of the discreet truth table.

• Journal of Advanced Marine Engineering and Technology
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• v.29 no.6
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• pp.685-691
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• 2005

In this study, high performance waste heat recovery heat exchanger was developed using the bayonet tube with spiral serrated fins. Especially, heat exchanger of the bayonet tube type was operated well because of double water passes mechanism and characteristics. A cooling water Passes down inner tubes to thimble-form tubes, then flows back up as it boils. The heat exchanger of bayonet tube type was composed of steel tube with 7channels$(I.D_1\;14mm.\;I.D_2\;31.6mm)$ and spiral serrated fins. The performance tests were conducted under the following conditions A cooling water flow rate was 273kg/h and engine l·pm was varied from 750rpm to 3500 rpm. From the experimental result. waste heat recovery was 9.21kW when engine rpm was 3500. and pressure drop was $15\~260mmHg/m^3$ The effectiveness of heat exchanger was about /$0.7\~0.9$. The performance of heat exchanger was evaluated by using the $\varepsilon-NTU$ method. In the study the NTU of the heat exchanger was $1.57\~2.33$.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.3
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• pp.357-366
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• 2003

An experimental study is performed to investigate characteristics of near of wakes of circular cylinders with serrated fins using a hot-wire anemometer for various freestream velocities. The main focus of this paper is to investigate a reason why a vortex formation length is increased suddenly. Velocity of the fluid which flow through fins decreases as fin's height and freestream velocity increases and fin pitch decreases, and a thickness of boundary layer increases. The finned tube has a lower velocity gradient when the higher boundary layer grows. This velocity gradient on finned tube makes a weak shear force in the wake and moves to downstream in a state of lower momentum transfer between the freestream and the wake. The phenomenon makes a vortex formation length increased suddenly. The fluctuations of the velocity distributions on the finned tube and (equation omitted) = 1.0 contour line in the vortex formation region decreases when the fin height increases and the pitch decreases.

• New & Renewable Energy
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• v.16 no.2
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• pp.1-13
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• 2020

The reduction of noise from wind turbines has been studied using various methods. Some examples include controlling wind turbine blades, designing low-noise-emitting wind turbine blades, and using trailing-edge serrations. Among these methods, serration is considered an effective noise reduction method. Various studies have aimed to understand the effects of trailing-edge serration parameters. Most studies, however, have focused on fixed-wing concepts, and few have analyzed noise reduction or developed a prediction method for rotor-type blades. Herein, a noise prediction method, composed of two noise prediction methods for a wind turbine with trailing-edge serrations, is proposed. From the flow information obtained by an in-house program (WINFAS), the noise from non-serrated blades is calculated by turbulent ingestion noise and airfoil self-noise prediction methods. The degree of noise reduction caused by the trailing-edge serrations is predicted in the frequency domain by Lyu's method. The amount of noise reduction is subtracted from the predicted result of the non-serrated blade and the total reduction of the noise from the rotor blades is calculated.