• 한국안전학회지
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• 제13권4호
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• pp.162-171
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• 1998

This paper presents the harmonics obstacle analysis and countermeasure of electrical consumption a place. Harmonics that can be cosidered as a environmental pollution of the power systems become the cause of the accidents and damages. The responsibility of eliminating the harmonics firstly lies on the generating side. But the original characteristics of the system sush as the harmonic transfer characteristics and the impedance of the system affect each other in the process of the generation and transmission of the harmonic. Therefore it is very difficult to specify clearly the harmonic controlling responsibility, because electric machinery generating harmonics are various in the industrial fields. The output of a inverter has a high harmonic content. There are several ways of minimizing the output harmonic content. One way is to use pulse width modulation techniques within inverter. An alternative method is to combine a number of square-wave inverters. In this research, we measure the harmonic of the countermeasure of electrical consumption a place. The paper present the problem of new harmonic elimination method of PWM inverter fed induction motor system using W-FT series. In the future, the proposed PWM pattern by W-FT series is effective not only to the induction motor but also to the electromagnetic machine such as voltage reglator, UPS.

• 한국정밀공학회지
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• 제30권1호
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• pp.32-38
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• 2013

Small mobile robots which use round wheels are suitable for driving on a flat surface, but it cannot climb the obstacle whose height is greater than the radius of wheels. As an alternative, legged-wheels have been proposed by many researchers due to its better climbing performance. However, driving and climbing performances have a trade-off relationship so that their driving performance should be sacrificed. In this study, in order to achieve both driving and climbing performances, a new transformable wheel was developed. The developed transformable wheel can have a round shape on a flat surface and change its shape into legged-wheel when it makes a contact with an obstacle. For design of the transformable wheel, the performance of legged-wheel was analyzed with respect to the number and curvature of the leg, and then the new transformable wheel was designed based on the analysis. Contrary to the existing transformable wheels that contain additional actuators for the transformation, the developed transformable wheel can be unfolded without any additional actuator. In this study, in order to validate the transformable wheel, a simple robot platform was fabricated. Consequently, it climbed the obstacle whose height is 2.6 times greater than the wheel radius.

• 제어로봇시스템학회논문지
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• 제17권2호
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• pp.176-182
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• 2011

Industrial network, often referred to as fieldbus, becomes an indispensable component for intelligent manufacturing systems. Thus, in order to satisfy the real-time requirements of field devices such as sensors, actuators, and controllers, numerous fieldbus protocols have been developed. But, the application of fieldbus has been limited due to the high cost of hardware and the difficulty in interfacing with multi-vendor products. As an alternative to fieldbus, the Ethernet (IEEE 802.3) technology is being adapted to the industrial environment. However, the crucial technical obstacle of Ethernet is its non-deterministic behavior that cannot satisfy the real-time requirements. Recently, the EtherCAT protocol becomes a very promising alternative for real-time industrial application due to the elimination of uncertainties in Ethernet. This paper focuses on the implementation of the IEC 61800 based real-time EtherCAT network for multi-axis smart driver. To demonstrate the feasibility of the implemented EtherCAT slave module, its synchronization performance is evaluated on the experimental EtherCAT testbed with a single axis smart driver.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 추계학술대회
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• pp.1166-1171
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• 2004

The combustion instability acts as a serious obstacle for the lean premixed combustion of gas turbine and even causes the fatal damage to the combustor and whole system. In this experiment, the pressure fluctuation is highly related to the stabilizing position of flame and fuel injection location. The fuel injection location is connected with the convection time of the fresh mixture, which is important time scale to refresh the mixtures near the flame stabilization location. The flame is extremely unstable when the alternative stabilization occurs and bulk mode frequency (${\sim}10Hz$) of pressure fluctuation is observed in this condition. It was found that the convection time scale of the fresh reactant coincided with the time scale of the bulk mode fluctuation. Hence this phenomenon results from the local equivalence ratio change caused by the pressure fluctuation induced by thermo-acoustic effects.

• 대한수학교육학회지:수학교육학연구
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• 제11권1호
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• pp.89-102
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• 2001

Computer has been regarded as an alternative that could overcome the difficulties in the teaching and learning of mathematics. But the didactical problems of the computer-based environment for mathematics education could give us new obstacles. In this paper, first of all, we examined the application of the learning theories of mathematics to the computer environment. If the feedbacks of the computer are too immediate, students would have less opportunity to reflect on their thinking and focus their attention on the visual aspects, which leads to the simple abstraction rather than the reflective abstraction. We also examined some other Problems related to cognitive obstacle to learn the concepts of geometric figure and the geometric knowledge. Based on the analysis on the problems related to the computer-based environment of mathematics teaching and learning, we tried to find out the direction to use computer more adequately in teaching and learning geometry.

• Journal of Chest Surgery
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• 제47권6호
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• pp.548-551
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• 2014

Type II chronic dissecting thoracoabdominal aortic aneurysms are a surgically challenging disease. The conventional thoracoabdominal aortic aneurysm repair technique using cardiopulmonary bypass is a high-risk procedure. However, a recently developed endovascular technique may be an alternative treatment for the disease, but faces the obstacle of lesional restriction. This new technique uses a hybrid strategy to overcome the limits of endovascular thoracoabdominal aortic aneurysm repair. Herein, we report on a successful outcome after performing the hybrid visceral debranching procedure.

• 한국결정성장학회지
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• 제23권3호
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• pp.119-123
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• 2013

Most of the world's solar cells in photovoltaic industry are currently fabricated using crystalline silicon. Czochralski-grown silicon crystals are more expensive than multicrystalline silicon crystals. The future of solar-grade Czochralski-grown silicon crystals crucially depends on whether it is usable for the mass-production of high-efficiency solar cells or not. It is generally believed that the main obstacle for making solar-grade Czochralski-grown silicon crystals a perfect high-efficiency solar cell material is presently light-induced degradation problem. In this work, the substitution of boron with gallium in p-type silicon single crystal is studied as an alternative to reduce the extent of lifetime degradation. The diamond-wire sawing technology is employed to slice the silicon ingot. In this paper, the quality of the diamond wire-sawn gallium-doped silicon wafers is studied from the chemical, electrical and structural points of view. It is found that the characteristic of gallium-doped silicon wafers including texturing behavior and surface metallic impurities are same as that of conventional boron-doped Czochralski crystals.

• 제어로봇시스템학회논문지
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• 제14권5호
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• pp.489-495
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• 2008

This paper offers a practical control scheme for driving mode transformation of a rescue robot already developed. The rescue robot, VSTR(Variable Single-Tracked Robot), has two driving modes, so can traverse untidy terrain and overcome obstacles such as stairs easily by use of timely driving mode transformation. Classical PI control scheme was used firstly for driving mode transformation, but stationary phenomenon, which might have a bad effect on the performance in real situation, came into existence. Therefore, we suggest a new controller, PI-based feedforward controller, which should be a good alternative for the problem, and compare it with other nonlinear control scheme.

• International journal of advanced smart convergence
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• 제8권2호
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• pp.30-38
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• 2019

Recently, the spread of personal mobility has been rapidly increasing due to the development of environmentally friendly alternative transportation means. In addition, the level of battery technology is also rapidly developing, accelerating the popularization of personal mobility. Such personal mobility has convenience of location transfer, amusement, and high portability compared to other transportation devices. Most personal mobility, however, is made up of small wheels, which cannot overcome obstacles such as rugged roads or obstacles on the road. In this paper, to solve these problems, we tried to devise a device that can easily overcome obstacles by combining wheels with small moving means. The wheel size can be mounted on the front wheel of the small moving means in a protruding manner so that obstacles can be encountered before the front wheels and the safety and ride comfort of the running can be improved.

• 한국정보처리학회논문지
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• 제5권11호
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• pp.2897-2907
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• 1998

학습 예(training examples)로 부터 규칙을 생성하는 문제는 큰 탐색 공간상에서 많은 지역최소치를 가지고 있는 최적화 문제로 귀결되므로 복잡하고 어려운 문제로 알려져 있다. 이러한 생성규칙을 만들기 위한 여러 가지 학습방법들이 제안되었으며, 그 중 한가지 학습방법이 유전자알고리즘을 연산모델로 사용하는 것이다. 그러나 전통적인 유전자알고리즘은 전역해 부근에서 수렴속도가 떨어지고, 추출된 규칙의 효율성에 문제가 있다. 본 논문에서는 유전자알고리즘의 학습과정에서 포착되는 염색체의 스키마를 분석하여 탐색공간을 부분해(subsolution)를 구할 수 있는 공간들로 분할함으로써, 보다 일반화된 분류 규칙집합을 찾는 방법을 제안하였다. 또한, 실험을 통하여 기존의 기계학습 방법을 사용한 경우와 효율을 상호 비교하여 제안한 방법을 타당성을 입증하였다.