• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.1
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• pp.384-389
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• 2011

This article presents an ultra broadband resistive power divider circuit for smart grid applications. Since the future smart grid system is expected to deploy high speed power line communication, the frequency response of the resitive power divider circuit is naturally of significance. Employing a thin film technology, the resistive power divider was designed, measured, and fabricated. For the circuit design, the conductor-backed coplanar waveguide line was firstly designed and measured. The 3 dB cutoff frequency was 72 GHz and S11 remains <-20 dB upto 70 GHz. The fabricated resistive power divider shows the 3 dB cutoff frequency of 50 GHz. It was experimentally verified that the resistive power divider circuit shows the insertion loss of 6 dB for high-speed input signal (40 Gb/s).

• KSCE Journal of Civil and Environmental Engineering Research
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• v.40 no.6
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• pp.633-641
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• 2020

Residential complexes offer a sense of community and convenience, but making closed and privated space have been criticized.Closed urban spaces have issues encouraging residential segregation.large apartment complexes over 1,000 households,the most poular housing type in Korea, seems to make urban space more closed and privated than ever before. Our study puts forward and tests the hypothesis that large apartment complexes with over 1,000 households are linked to residential segregation. First of all, we examined the degree of residential segregation of metropolitan cities in Korea over a nine-year period (2011-2019). The dissimilarity index and the delta index were used for determining the extent of residential segregation. Next, we tested our hypothesis by Spearman's rank correlation analysis. Spearman's rank correlation analysis was performed on the residential segregation index per administrative division ("dong") and the number of large apartment complexes per administrative division ("dong").

• Journal of computational fluids engineering
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• v.13 no.2
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• pp.1-7
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• 2008

For Aerodynamic analysis of vehicle at altitude, 100km, the validity of governing equations based on continuum model, was reviewed. Also, as the preliminary study for the sub-orbital space plane development, a candidate geometry was suggested and computational fluid dynamic(CFD) analysis was performed for various angles of attack in subsonic and supersonic flow regimes to analyze the aerodynamic characteristics and performance. The inviscid flow analyses showed that the stall starts at angle of attack above $20^{\circ}$, the maximum drag is generated at angle of attack, $87^{\circ}$ and the maximum lift to drag ratio is about 8 in subsonic flow. In supersonic, the stall angle is about $40^{\circ}$ and the maximum drag is generated at angle of attack, $90^{\circ}$. Also, mach number distribution of re-entry vehicle was computed versus altitudes.

• Proceedings of the KIEE Conference
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• 1994.07a
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• pp.400-402
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• 1994

This paper presents a digital implementation of delta modulation Technique for Active Power Filters. Delta modulated scheme is to control the harmonic-compensating current indirectly by adjusting the capacitor voltage to be sinusoidal. The overall control system has two feedback loops. One is the outer propotional feedback for loop regulating the dc current of active filters and the other is the inner feedback loop for maintaining the ac current waveform to be sinusoidal, and have zero power factor angle(i.e. unity power factor). The characteristics of the proposed is investigated by digital simulation using ACSL and experimental results are obtained by TMS370C756 Single-Chip Microprocessor relative to analog delta modulation technique.

• Journal of Welding and Joining
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• v.14 no.3
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• pp.75-85
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• 1996

In this paper the influence of postweld heat treatment on mechanical properties of SMAW and FCAW stainless steel weldments was examined and the obtained results are as follows ; (1) The amount of $\delta$-ferrite formed by SMAW and FCAW process decreased with increasing holding temperature and time in post weld heat treatment(PWHT), and it was found that the reduced ferrite was transformed into sigma phase after $800^{circ}C{\times}50hr$ PWHT. This sigma phase, even though it was very small, resulted in brittleness of dissimilar weldment between carbon steel and stainless steel in bending test, however in similar weldment between stainless steel and stainless steel was not occured. (2) The chemical composition of sigma phase was measured to 28-30%Cr, 7-9%Mo, 4-6Ni in 316L weldment, and also 35-37%Cr, 0.9-1.0Mo, 6-8%Ni in 309L weldment by EDS analysis.

• The Transactions of the Korean Institute of Power Electronics
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• v.22 no.5
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• pp.449-456
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• 2017

This study proposes a method for compensating for the commutation torque ripple of delta-connected brushless DC motors with low inductance based on a current predictions. At the commutation instant, a phase current at the next sampling period is predicted and compared with the reference phase current to determine whether torque ripples will occur or not. If the predicted current cannot reach the reference phase current, the reference current is modified and the relevant voltage reference is produced to reduce the torque ripple. The validity of the proposed method has been verified by simulation and experimental results. The commutation torque ripple has been decreased by 17.7% at 1,000 rpm and 80% load conditions.

• Proceedings of the KIEE Conference
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• 2003.07b
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• pp.1250-1252
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• 2003

This Paper presents Sigma-Delta Modulation(SDM) schemes to generate switching waveform for a high-power factor boost-type rectifier. The SDM scheme can be implemented by simple digital algorithm unlike conventional PWM schemes with several hardware, and has the characteristics of spectrum-spreading and noise-shaping effects, which are profitable in harmonic reduction of input current in the boost-type rectifier. The comparison results of their spectrum performances shows that the 1st-order SDM has better harmonic suppression effect than conventional PWM scheme and Dithered SDM scheme.

• Proceedings of the KIEE Conference
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• 1993.07b
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• pp.736-738
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• 1993

The problems of he plentiful harmonics and low power factor have occured to the increase of semiconductor power conversion equipments. These problems should be improved by the active power filters which have been studied recently. This paper described the appliaction of delta modulation technique to current-fed filter and control performance. Through digital simulation the output characteristics of delta modulator are investigated theoretically.

• Proceedings of the Korea Water Resources Association Conference
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• 2017.05a
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• pp.125-125
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• 2017

우리나라는 도시의 집중화 현상이 점차 심화되고 있으며, 기후변화에 따른 기상 수문학적 영향으로 인해 집중호우, 홍수 등 수재해 증가, 가뭄으로 인한 물 부족 및 물 자급율 저하로 도시의 수원 다원화 및 재활용에 대한 관심이 증가하고 있다. 최근들어 이러한 문제점을 인식하고 각 지자체 별 도시의 건전한 물순환을 회복시키기 위한 노력이 이루어지고 있다. 서울시는 서울특별시 빗물관리 기본계획을 수립하였으며, 수원시는 2013년부터 레인시티를 본격적으로 도입하였고, 환경부는 5곳의 물순환 선도도시를 공모하여 선정하였다. 또한 한국토지주택공사에서는 LID 분산형 빗물관리 기준을 수립하여 지구단위계획지침에 토지이용별 빗물관리 기준을 명시 하였으며, K-water는 에코델타시티와 송산그린시티 개발사업을 수행하면서 도시개발부터 건전한 물순환체계를 유지하기 위하여 저영향개발 기법을 적극 활용하기 위한 연구를 수행하고 있다. 본 연구에서는 수변도시 및 물순환 도시에 대하여 소개하고 수변도시, 물순환도시를 정의할 수 있는 여러 방향에 대한 고려사항을 제시하여 물순환 도시에서 검토되어야 할 사항을 확인하고자 하였다.

• Korean journal of applied entomology
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• v.46 no.3
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• pp.349-356
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• 2007

Three active components (Z8-12:Ac, E8-12:Ac, and Z8-12:OH) are known in sex pheromone of the oriental fruit moth, Grapholita molesta, and have been commercially available to apply for population monitoring and mating disruption. However, there have been variation among commercial products in pheromone composition and amount impregnated in each pheromone releaser. This study was performed to optimize factors influencing on pheromone monitoring of G. molesta by analyzing pheromone composition/amount, effective period of releaser, and trap type/placement in apple trees. High purity of Z8-12:Ac component was effective to attract males, in which 96% or more of cis acetate isomer component appeared to be optimal composition. Pheromone amounts ($0.01-1\;{\mu}g$) impregnated in each rubber dispenser did not give significant effect on monitoring during 90 days from June to August. "Delta" trap was much more efficient than "cone" trap to collect males. Trap installation was another factor, in which placing traps at canopy level was much efficient than at trunk or ground levels. Pheromone trap monitoring with these optimal factors indicated three to four adult peaks from June to September in addition to high overwintering population from April to May in pesticide-applied orchards in Andong, Korea.