• 한국전자파학회논문지
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• 제14권2호
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• pp.133-138
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• 2003

본 논문에서는 비가시거리(NLOS) 전파환경에서 원형편파를 송신하고 수직, 수평편파 안테나로 수신하는 원형편파 다이버시티(CV-CH)방식에 대하여 이론적 모델을 제시하고 이의 우수성을 확인하였다. 원형편파 다이버 시티에 대한 간단한 이론적 모델을 통하여 XPD에 대한 상관계수 평가식을 유도하였으며, 비가시거리 전파환경에서 원형편파다이버시티 경우 직선편파다이버시티(VV-VH) 경우보다 교차편파분리도(XPD)가 약 6~7 dB 정도 낮게 됨을 알 수 있었다. 그 결과 원형편파 다이버시티 경우의 상관계수는 기존의 직선 편파다이버시티보다 더 낮은 상관계수 값을 나타내는 이론적 모델을 제시하였고 측정된 결과로부터 이의 성능을 확인하였다.

• 대한기계학회논문집B
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• 제23권9호
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• pp.1113-1120
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• 1999

Leakage vortices fonned near the blade tip cause an increase of total pressure loss near the casing endwall region and as a result, the efficiency of rotor decreases. The reduction of rotor efficiency is related to the size of tip clearance. In this study, the three-dimensional flow fields in an axial flow rotor were calculated with varying tip clearance under various flow rates, and the numerical results were compared with experimental ones. The effects of tip clearance and the of attack on the leakage vortex and overall performance, and the los9 distributions were investigated through numerical calculations. In this study, tip leakage flow rate and total pressure loss due to the tip clearance were evaluated using numerical results and approximate equations were presented to evaluate the reduction of rotor efficiency due to the tip leakage flow.

• 한국측량학회지
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• 제29권2호
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• pp.165-173
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• 2011

일반적으로 표적에 대한 탐지는 감시장비의 성능과 지형지물의 차폐 여부가 가장 큰 영향을 준다. 본 논문은 DEM과 DSM을 활용하였을 경우, 적외선 감시장비를 이용하여 탐지확률을 비교 분석하였다. 일차적으로 DEM과 DSM으로부터 가시선분석을 수행하여 가시영역과 비가시영역으로 구분하였고, 가시영역에 대해서 ACQUIRE모델을 사용하였다. DSM은 DEM의 탐지확률보다 매우 낮았으며, 관측지점의 고도를 높일수록 탐지 확률이 상승함을 알 수 있었다.

• 한국대기환경학회지
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• 제8권1호
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• pp.1-6
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• 1992

Using data measured in 1989, a study on variations of visibility and air pollution observed in Seoul, Chongju and Choopoongryong is carried out. Analysis includes on low visibility (< 10km) and smog occurring in the Metropolitan Seoul. It was observed that number of days of visibility less than 10km during 1989 was 56.7% (207 days) for Seoul, 45.7%(167 days) for Chongju and 5.8% (21 days) for Choopoongryong. Chongju is a medium size city (population : a half million) and Choopoongryong is a rural site. In the urban are as, however, the number of low visibility days was relatively large during the winter but with little seasonal variations. In each month these cities recorded more than 10 days of low visibility. The visibility reduction due to mist, fog and haze been occurred with air pollution. In particular, the reduction in a cold season related with an increase in high concentrations of $SO_x$ and aerosols. This type of low visibility occurring in Seoul is a similar type that is occurring in London, U.K. On the other hand, the visibility reduction during in a warm season is related with high concentrations of NOx and other photochemical precursors. The visibility reduction in Seoul during summer is the same type occurring in Los Angeles, U.S.A.

• 한국위성정보통신학회논문지
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• 제8권3호
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• pp.20-24
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• 2013

본 논문에서는 HEMP의 개념을 소개하고, 안테나 요소의 배치 변화에 따른 방호 효율성을 분석한다. 높은 주파수의 EMP를 맥스웰 방정식을 이용하여 LOS에서 근사한다. 전자기파 감쇄의 영향을 분석하기 위하여, 차폐룸을 구성하여 측정 데이타를 얻는데 이용한다. 수신 안테나의 거리와 주파수를 변화시켜 차폐 정도를 측정한다. 기준이 되는 미국 규격문서와 측정값을 비교하고 측정방법을 간소화해본다. 차폐룸 내부를 3가지 조건으로 만들어 변화를 차폐 정도를 측정한다. 정방향 측정과 역방향 측정의 차이를 살펴보고 차폐룸 측정에 영향을 미치는 요소를 찾는다.

• Structural Engineering and Mechanics
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• 제59권4호
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• pp.653-669
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• 2016

Recent earthquakes worldwide show that a significant portion of the earthquake shaking happens in the vertical direction. This phenomenon has raised significant interests to consider the vertical ground motion during the seismic design and assessment of the structures. Strong vertical ground motions can alter the axial forces in the columns, which might affect the shear capacity of reinforced concrete (RC) members. This is particularly important for non-ductile RC frames, which are very vulnerable to earthquake-induced collapse. This paper presents the detailed nonlinear dynamic analysis to quantify the collapse risk of non-ductile RC frame structures with varying heights. An array of non-ductile RC frame architype buildings located in Los Angeles, California were designed according to the 1967 uniform building code. The seismic responses of the architype buildings subjected to concurrent horizontal and vertical ground motions were analyzed. A comprehensive array of ground motions was selected from the PEER NGA-WEST2 and Iran Strong Motions Network database. Detailed nonlinear dynamic analyses were performed to quantify the collapse fragility curves and collapse margin ratios (CMRs) of the architype buildings. The results show that the vertical ground motions have significant impact on both the local and global responses of non-ductile RC moment frames. Hence, it is crucial to include the combined vertical and horizontal shaking during the seismic design and assessment of non-ductile RC moment frames.

• 한국정보통신학회논문지
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• 제7권5호
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• pp.872-878
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• 2003

본 논문에서는 3D-Ray Tracing 기법을 이용한 옥내 무선통신용 편파발생 시뮬레이터를 개발하고, 실내 무선전파환경에서 실제 측정한 데이터와의 비교를 통하여 검증하였다. 개발된 시뮬레이터를 이용하여 Line-Of-Sight(LOS)와 Non-Line-Of-Sight(NLOS) 무선전파 환경에서 수직, 수평, 원편파에 대한 채널특성과 편파 다이버시티 수신특성을 해석하였다. 그 결과 원편파의 경우 기수회 반사파를 억제 수신하는 특성 때문에 수직 및 수평편파의 경우와 비교하여 다중경로 페이딩이 현저하게 경감됨을 알 수 있었다.

• Journal of Communications and Networks
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• 제3권4호
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• pp.342-350
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• 2001

The Internet routing instability, or the rapid fluctuation of network reachability information, is an important problem currently facing the Internet engineering community. High levels of network instability can lead to packet loss, increased network latency, and delayed routing convergence. At the extreme, high levels of routing instability can lead to the loss of internal connectivity in wide-area networks. In this paper, we investigate the variation of domain degree and domain count of the inter-domain network over time by using linear regression model in order to analyze the topology variation of inter-domain network. We Also propose an efficient policy management model to reduce the instability in the inter-domain routing system. The proposed model can be used to identify whether a routing policy is adequate to reduce convergence time that is required to return to a normal state when BGP routing instability happens. Experimental analysis shows that the proposed model can be used to set up routing policy in domains for the purpose of minimizing the effects and the propagation of BGP routing instability.

• 한국통신학회논문지
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• 제30권8C호
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• pp.754-761
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• 2005

본 논문에서는 나카가미-n(라이시안) 페이딩 채널 상에서 그레이 부호화된 직사각 QAM(Rectangular-QAM) 신호를 최대비 합성(maximal ratio combining) 다이버시티로 수신하는 경우 비트노율(Bit Error Rate, BER)을 계산하는 수식을 다양한 채널에 적용할 수 있도록 일반적 형태로 유도하고 그 성능 분석을 실시한다. 유도된 BER 수식은 휘태커 함수)Whittaker function)와 초기하 함수(confluent hypergeometric)로 표현된다. 또한 M-PSK와의 성능 비교를 통하여 나카가미-n 페이딩 채널의 특성을 확인한다. BER 수식이 일반적인 형태로 유도되었기 때문에 가시 경로(line-of-sight)를 가지는 통신채널이나 위성통신 채널의 성능분석에 본 논문에서 유도한 BER 수식을 쉽게 적용할 수 있다.

• 전자공학회논문지A
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• 제33A권6호
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• pp.81-89
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• 1996

Quantum RF impedance of SIS (superconductor insulator superconductor) junction has been analyzed by using through on tucker's quantum mixer theory in the frequency range form 80 GHz to 120 GHz. The embedding impedance of waveguide-type mixer mount and its equivalent circuit have been evaluated. From these evaluated results, the impedance matching efficiency between mixer mount embedding impedance and mixer port impedance of upper-side band and IF which were determined by augmented admittance matrix with given backshort position has been discussed in detail. It is found that the mixer with fixed backshort mount ahs a impedance matching efficiency about 80% at each port of mixer within 85GHz to 115GHz, which implys a conversion los of mixer would be good enough to be operated such a wide band frequency range. Therefore, the theoretical evaluated results show that our method can be used ot design the mixer mount without any mechanical tuning elements such a backshort or an E-plane tunners for wide band operation.