• Journal of the Korea Institute of Information and Communication Engineering
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• v.10 no.10
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• pp.1796-1803
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• 2006

This Paper describes a systematic method for designing the $H_{\infty}$ controller for the inverted pendulum which is a nonlinear and single-input double-outputs system. In particular, the open-loop system is conbined with a pre-filter to shape the open-loop transfer function for the sensitivity function ind the complementary sensitivity function to be kept the desirable frequency characteristics. Consequently, the loop shaping technique of the open-loop transfer function reduces the impacts of the model uncertainties, measurement noises and exogenous disterbances on the dynamic characteristics of the inverted pendulum. The results of simulation and experiment show the efficiency of the proposed control method comparing with conventional PID control method.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.7
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• pp.97-104
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• 2006

The spray and breakup characteristics of swirling liquid sheet were investigated by measuring the spray angle and breakup length as the axial Weber number Wel was increased up to 1554 and the ambient gas pressure up to 4.0MPa. As Wel and ambient gas density increased, the disturbances on the annular liquid sheet surface were amplified by the increase of the aerodynamic forces, and thus the liquid sheet disintegrated near from the injector exit. The measured spray angles according to the ambient gas density were different before and after the sheet breaks. Before the liquid sheet breaks, the spray angle was almost constant, but once the liquid sheet started to breakup, the spray angle decreased. And the breakup length decreased because of the increase of the aerodynamic force as the ambient gas density and Wel increased. Lastly, the measured breakup length according to the ambient gas density and Wel was compared with the result by the linear instability theory. We found that the corrected linear instability theory considering the attenuation of sheet thickness agrees well with our experimental results.

• Journal of Aerospace System Engineering
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• v.13 no.3
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• pp.1-8
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• 2019

The electromagnetic forces generate a torque on the gimbal motor, and changes in the coil current causes torque ripple. This affects the gimbals' speed and results to unstable satellite attitude. It is therefore essential to reduce the torque ripple of the gimble motor with the aim of improving the attitude control accuracy of the satellite. This paper theoretically analyzes the torque generated from the modeling of a motor for general concentrated winding and distributed winding. The prototype was designed and fabricated through selection of the winding that reduces the torque ripple through simulation results. The results of the magnetic fields' theoretical analysis and the back electromotive force of the prototype were compared with the calibrated results for verification of conformity and manufacture of the design. The low-speed test proved that the torque ripple is reduced by improving the speed stability.

• Economic and Environmental Geology
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• v.38 no.3 s.172
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• pp.305-317
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• 2005

This study addresses the preliminary results of rock slope stability analyses including hazard assessments for slope failure conducted on the selected sections of rural road cut slope which are about 4 km long. The study area is located in the Mt. Chuntae northeast of Busan and mainly composed of Cretaceous rhyolitic ash-flow tuff', fallout tuff, rhyolitc and andesite. The volcanic rock mass in the area has a number of discontinuities that produce a potentially unstable slope, as the present cut slope is more than 70 degrees in most of the slope sections. Discontinuity geometry data were collected at selected 8 scanline sections and analyzed to estimate important discontinuity geometry parameters to perform rock slope kinematic and block theory analyses. Kinematic analysis for plane sliding has resulted in maximum safe slope angles greater than $65^{\circ}$ for most of the discontinuities. For most of the wedges, maximum safe cut slope angles greater than $45^{\circ}$ were obtained. Maximum safe slope angles greater than 80" were obtained fur most of the discontinuities in the toppling case. The block theory analysis resulted in the identification of potential key blocks (type II) in the SL4, SL5, SL6 and SL8 sections. The chance of sliding taking place through a type ll block under a combined gravitational and external loading is quite high in the investigated area. The results support in-field observations of a potentially unstable slope that could become hazardous under external forces. The results obtained through limit equilibrium slope stability analyses show how a stable slope can become an unstable slope as the water pressure acting on joints increases and how a stable slope under Barton's shear strength criterion can fail as the worst case scenario of using Mohr-Coulomb criterion.

• Korean journal of communication and information
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• v.81
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• pp.75-121
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• 2017

Maeul Community Media is community media practice that media education combine with community activism based on the region. Maeul Community Media appeared with Seoul city's supporting policy in 2012 and is now enlarging on a national scale beyond Seoul. This study is aimed at understanding and investigating Maeul Community Media activists' practice process by using a grouned theory approach. In-depth interviews were carried out of study participants who worked on as activists based on visual and radio field since 2012. By open coding based on grounded theory, 16 categories and 59 subcategories were discovered. The outcome of axial coding showed the centeral phenomena that can be called 'sustainable desire for Maeul Community Media act'. On the condition of the instability of public support and the absence of a village channel, the strategic practices were discovered, which are diversification of participants recruitment and modes of participation, invention of space-media, seeking multilateral distribution methodologies and the collective action plans of networks to stabilize the management and to empower Maeul Community Media networks. As a result, Maeul Community Media and civil society were networked by discovering and agenda-setting pending issues. And we could find that the desire and expectation for the role as a village's public sphere were enlarging.

• Proceedings of the KIEE Conference
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• 2008.04a
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• pp.244-245
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• 2008

본 논문은 관성센서를 이용한 무인 항공체의 자세 제어에 관한 연구를 다루었다. 항공계의 종류는 크게 고정익기와 회선익기로 나뉘는데 본 연구에서는 회전익기의 형태를 가진 Quarter Vehicle을 사통하였다. Quarter Vehicle은 4개의 프로펠러에 의한 양력과 회전 반발력으로 비행을 한다. 이때의 양력은 수평면에 대해 수직으로 추력을 발생시키므로 다른 비행체보다 불안정하며 이를 안정하게 제어하기 위해 관성 센서를 적용하여 균형을 유지한다. 본 연구에서는 관성센서를 이용하여 UAV의 자세와 균형을 안정적으로 유지하여 안정적인 비행이 가능하도록 하였다. 또한 상호 의존적인 항법 시스템으로 환경변화에 영향을 받지 않으며, 정확한 위치정보를 제공하는 GPS를 사용하여 3개 이상의 위성으로부터 정보를 받아 좌표를 계산하고 위치, 속도 및 방향을 결정하여 자율 비행이 가능하도록 설계하였다. 본 논문에서는 Quarter Vehicle의 구조와 이론적 배경을 통한 설계, 그리고 관성센서와 GPS의 적용을 위한 방법을 제시 한다.

• Journal of the Korean Home Economics Association
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• v.38 no.5
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• pp.91-106
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• 2000

대부분의 갈등해소에 관한 연구들은 갈등해소방법 사용의 상황에 따른 일관성을 미리 가정하고 있다. 그러나 몇몇 연구에서 갈등해소방법에 있어 성격의 효과와 함께 상황적 효과가 있음을 보고하고 있다. 아직까지는 갈등의 쟁점, 감정, 관련 인물과 이들의 상호작용을 고려한 갈등해소방법의 일관성에 관한 연구가 부재한 실정이다. 본 연구는 상황에 따른 갈등해소 방법 선택의 일관성의 수준과 결혼 적응도에 있어서의 이들의 영향을 조사하였다. 나아가, 갈등해소의 과정 및 절차를 관찰하였다. 350쌍의 한국 부부들에게 설문조사(1차연구)를 실시하였으며, 이를 바탕으로 50쌍을 선발하여 갈등해소 과정을 관찰하였다(2차연구). 설문조사 결과에 의하면, 쟁점의 종류나 관련 대상에 따라서는 비교적 일관성 있는 방법을 사용하였으나, 감정상태에 따라서는 비 일관적인 해소방법을 사용하였다. 안정형 애착유형자는 건설적 해소 방법을 사용하는 반면, 불안정 애착유형자는 파괴적 또는 회피적 해소방법을 사용하는 경향을 보였다. 관찰 연구 결과에 의하면, 건설형 및 회피형 사용자는 설문조사와 관찰연구에서 일관성 있는 행동을 보였으며, 파괴형 해소방법 사용자는 설문조사와 관찰연구에 있어 일관성이 결여되어 있었다. 갈등해소의 과정, 즉 시작, 진행, 종료에 있어 유의한 타이가 발견되었으며, 이것이 결혼 적응도에 영향을 주었다. 연구결과들은 갈등해소와 결혼 적응에 관한 이론과 연계되어 논의되었다.

• The Korean Journal of Financial Studies
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• v.6 no.1
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• pp.223-247
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• 2000

본 연구에서는 유로커런시와 외환시장의 초과수익률을 설명하는 여러 가지 모형을 검증하였다. 비록 Campbell-Clarida(1987)와 Lewis(1990,1991)는 이 시장에서 3개월물의 초과수익률에 대한 단일잠재변수모형을 기각할 수 없었지만 본 연구에서는 이 모형이 여러 포트폴리오에 대하여 기각되고 있음을 보여준다. 그러나 이 모형의 검증은 결합가정을 필요로 하기 때문에 모형의 기각원인을 찾는다는 것은 어려운 일이다. 기각의 가능성으로 세계 경제에 하나 이상의 위험요인이 존재할 수 있다는 것이 될 수도 있고 불안정한 상수가 원인일 수가 있다. 상수의 안정성검증에서 1979년 12월을 전후한 기간에 상수가 변하지 않는다는 귀무가설이 모든 포트폴리오에서 기각되었다. 따라서 양기간에 단일잠재변수모형과 두잠재변수모형을 검증하였다. 모든 포트폴리오에 대하여 1979년 12월 이전에는 단일변수모형이 기각되지 않았지만, 1979년 이후에는 체계적으로 기각되었다. 한편 두잠재변수모형은 양기간 모두에서 기각되지 않았다 따라서 위험요인에 변화를 주는 연방준비은행의 운영절차의 변화가 단일변수모형의 기각의 원인일 수 있다고 유추할 수 있다. 마지막으로 시간 가변적인 베타가 단일변수모형의 기각의 원인이 될 수 있는지를 검증하기 위하여 Harvey(1989,1991)에 의해서 개발된 모형을 적용해 보았지만 모형이 기각되었다. 따라서 유로커런시와 외화자산의 3개월물의 초과수익률에 두 잠재변수모형이 자료를 비교적 잘 설명한다고 볼 수 있다. 그러나 잠재변수모형의 검증은 자산가격결정의 일반균형이론의 검증도 아니고 검증력도 강하지 않기 때문에, 위험프리미엄을 설명해주는 단순한 실증분석으로 보아야 한다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.7
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• pp.779-784
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• 2014

This study provided the analytical model describing the friction-induced noise in the ball joint system under the edge loading condition. The frictional and conformal contact kinematics between the spherical bearing and the hemispherical socket was derived and the dynamic equations of the perturbed motion were established. The numerical results revealed that the bending modes of the ball joint system can become unstable due to friction, and the axial load and contact stiffness strongly influenced the dynamic instability. In contrast, the tilting angle of the socket was not found to significantly contribute to the dynamic instability of the ball joint.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.10
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• pp.875-883
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• 2007

The objective of this research was to develop a coaxial rotor MAV which is suitable for a indoor reconnaissance mission. Preliminary design parameters were determined, based on the dimensions of other reference MAVs. The designed rotor performance was estimated by Blade Element Momentum Theory, and the analyses were compared against the measurements. Stability and vibration issues of the prototype were circumvented by making parts of vehicle with NC machine, as well as equipped with teetering rotor and stabilizer. The designed coaxial rotor MAV showed successfully flight equipped with video camera. However, it was founded that further research activities should be focused on efficient rotor design to obtain better performance.