• International Journal of Control, Automation, and Systems
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• v.5 no.6
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• pp.652-662
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• 2007

This paper presents a new and simple method for sensorless operation of matrix converter drives using a constant air-gap flux and the imaginary power flowing to the motor. To improve low-speed sensorless performance, the non-linearities of a matrix converter drive such as commutation delays, turn-on and turn-off times of switching devices, and on-state switching device voltage drop are modeled using PQR transformation and compensated using a reference current control scheme. The proposed compensation method is applied for high performance induction motor drives using a 3 kW matrix converter system. Experimental results are shown to illustrate the feasibility of the proposed strategy.

• Proceedings of the IEEK Conference
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• 2000.06b
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• pp.103-106
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• 2000

The electronic properties of carbon nanotube are currently the focus of considerable interest. In this paper, the electronic properties of finite length effect in carbon nanotube for cabon nanoscale device is presented. To calculate the electronic properties of carbon nanotube, Empirical potential method (Brenner' hydrocarbon potential) for carbon and Tight binding molecular dynamic (TBMD) simulation are used. As a result of study, we have known that the value of the band gap decreases with increasing the length of the tube. The energy band gap of (6, 6) armchair carbon nanotube have the ranges between 0.3 eV and 2.5 eV. Also, our results were compared with the results of the other computational techniques. As that result, our results are very well united.

• Journal of the Korean Society for Precision Engineering
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• v.15 no.12
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• pp.55-61
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• 1998

Recently, the needs of machining technologies of very small parts have been increasing with advent of micro-revolution. These technologies have mostly used the method applied to semi-conductor production process such as LIGA, etc. But they have serious difficulties to settle down in terms of workpiece materials, machining thickness, 3-dimensional structure. Therefore. mciro-machining technology using EDM(Electrical Discharge Machining) was proposed. It is very difficult to machine the micro-parts (microshaft, microhole) using conventional machining. Micro-machining using BDM can machine the micro-parts easily because it requires little machining force. This MEDM(Micro-EDM) need the capabilities to move a electrode and control a discharge energy precisely, and the gap control strategy to maintain the optimal discharge condition is necessary. Therefore, in this study, the new EDM machine with high precision motion stage and high-performance EDM device was developed. Using this MEDM machine, we have machined microshaft and microhole with various shapes and sizes.

• Proceedings of the Korea Society of Information Technology Applications Conference
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• 2005.11a
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• pp.233-235
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• 2005

Non-contact power supply (NCPS), as a clean and safe energy supply concept has been applying wildly. Comparing with the conventional transformer the non-contact transformer has a large air gap between the long primary winding and the secondary winding. Due to it, the non-contact transformer has increased leakage inductance and reduced magnetizing inductance. So the high frequency series resonant converter has been widly used on the non-contact power supply system for transferring the primary power to the secondary one, from what a high influence voltage can be gained on the secondry coil even though the large air gap exists. However, it still has the disadvantages of the load sensitive voltage gain characteristics when load is changing. In this paper, we propose a fuzzy logic controller to adjust the frequency of the inverter to track the resonat which is changing when the load is change.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1996.10a
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• pp.202-206
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• 1996

An experimental study of the characteristics of the repulsiveytype magnetic bearing using high Tc superconductor is presented. In field cooling superconductor has the position-stability due to a flux pinning effect and the strong damping due to hysterisis, while in zero field cooling it has the only strong repulsive force due to Meissner effect. Lift force in superconducting levitation has a hysterisis characteristics, and it is the dissipation of energy, the mechanism of damping. As the relative linear velocity between a magnet and a superconductor increases, the area of the hysterisis loop becomes smaller. It means the decrease of damping. In field cooling, the static stiffness is very nonlinear in smaller than initial gap, but almost linear in larger than initial gap.

• Journal of Magnetics
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• v.17 no.2
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• pp.115-123
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• 2012

Contactless electrical power transfer through an air gap is a revived technology for supplying energy to many movable applications including Maglev. In this paper, magnetic equivalent circuits and analytical models of contactless electrical power transfer systems are developed and evaluated through experiment. Overall coupling coefficient and overall efficiency are introduced as means for evaluating the systems' performance. Compensating capacitors in primary and secondary sides of the systems improve the overall coupling coefficient and overall efficiency. Using the analytical models, the effects of different parameters and variables such as air gap and load current are analyzed to give a high coupling coefficient and an improved efficiency of power transfer for different compensation structures.

• Nuclear Engineering and Technology
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• v.52 no.8
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• pp.1742-1748
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• 2020

TSSD, TSSP, and TSSP2 of hydrogen for optimized-Zirlo (Zirlo™) alloy were measured by DSC in the range of 53-457 wppm. Solvus curves of the TSSs are derived and proposed in this study. The results show that the temperature gap between TSSD and TSSP solvus lines of Zirlo™ are similar to those of other zirconium alloys, but another gap between the TSSD and TSSP2 line differs significantly. In particular, the TSSP2 solvus line becomes closer to the TSSD solvus line than to TSSP unlike Zircaloy-4, so ΔT_TSSD-TSSP2 of Zirlo™ decreases with decreasing temperature. This implies that hydride reorientation can take place more significantly in Zirlo™ than in Zircaloy-4, and the limited temperature variation of 65 ℃ during the vacuum drying and the cooling-down process may not be sufficient to prevent the triggering of hydride reorientation in Zirlo™ cladding under long-term dry storage.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2010.06a
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• pp.151-151
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• 2010

본 연구에서는 배위자로 공액계 벤젠고리로 연결된 중심금속이 이리듐인 착물화합물과 합성하여 인광재료로서의 가능성을 실험하였다. 새로운 이리듐착물화합물의 화학적 구조를 알아보기 위해 $^1H$-NMR, $^{13}C$-NMR, UV-vis, spectrophotometer를 사용하였으며, 광 물리학적, 전기화학적 특성에 대한 측정은 spectrofluorometer, cyclic voltammetry를 통하여 측정하였다. 이리듐 단핵 및 이핵착체는 589~598nm의 영역에서 발광파장이 확인되었으며, DMSO[$5{\times}10^{-5}$]용액에서 양자효율이 단핵 착물화합물의 경우 0.1, 이핵착물화합물의 경우 0.13으로 나타났다. 이핵 이리듐착물화합물의 전기화학적 특성은 energy gap은 2.45eV, optical band gap은 2.58eV로 계산되었다.

• Journal of the Korean Ceramic Society
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• v.35 no.5
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• pp.493-498
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• 1998

ZnS doped borosilicate glass for nonlinear optical application was prepared by melting and precipitation process. The optical band gap of the precipitated ZnS particles ranged from 3.83 to 3.96 eV compared with the bulk ZnS energy gap of 3.53 eV. This result was interpreted in terms of a quantum confinement effect due to small crystal size. ZnS partilcle size estimated by effective mass approximation ranged from about 39 to 83 $\AA$ It increased wtih the increase of heat tratment time and temperature.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.21 no.10
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• pp.905-915
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• 2011

The free flexural vibration of a hanged clamped-free cylindrical shell partially submerged in water with gap from bottom is investigated. The fluid is assumed to be inviscid and irrotational. The cylindrical shell is modeled by using the Rayleigh-Ritz method based on the Sanders shell theory. The kinetic energy of the fluid is derived by solving the boundary-value problem related to the fluid motion. The natural vibration characteristics of the partially submerged cylindrical shell are discussed with respect to the added virtual mass approach. In this study, experiments were carried out to confirm theoretical results. It was found that theoretical prediction is in good agreement with experimental results.