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초내열 합금 Alloy718의 저주기 피로시험에서 반복연화 및 R=X (X=0,-1)효과
최병학,신수근,신정근,김선화,윤기봉,염종택,박노광 국립7개대학공동논문집간행위원회 2005 공업기술연구 Vol.5 No.-
The LCF properties for R=0 as tension-tension and R=-1 as tension-compression were examined in DA alloy718. While the hysteresis loops composed of ?ε_(t), ?ε_(p) and ?σ were figured with similaity in both of R=0 and R=-1, the loops of R=0 were continuely going down along the stress axis during cyclic fatigue progressing. It was caused by Bauschinger effect, which includes a tendancy for stress recovering as an amount of compression stress. The phenomena of cyclic softening in both of R=0 and R=1 seem to be caused by planar slip of dislocations, which was accompanied by shearing the γ'/γ" precipitates during the cyclic fatigue test.
Performance analysis of satellite and terrestrial spectrum-shared networks with directional antenna
Yeom, Jeong Seon,Noh, Gosan,Chung, Heesang,Kim, Ilgyu,Jung, Bang Chul Electronics and Telecommunications Research Instit 2020 ETRI Journal Vol.42 No.5
Recently, to make the best use of limited and precious spectrum resources, spectrum sharing between satellite and cellular networks has received much interest. In this study, we mathematically analyze the success probability of a fixed (satellite) earth station (FES) based on a stochastic geometry framework. Both the FES and base stations (BSs) are assumed to be equipped with a directional antenna, and the location and the number of BSs are modeled based on the Poisson point process. Furthermore, an exclusion zone is considered, in which the BSs are prohibited from locating in a circular zone with a certain radius around the FES to protect it from severe interference from the cellular BSs. We validate the analytical results on the success probability of the cognitive satellite-terrestrial network with directional antennas by comparing it using extensive computer simulations and show the effect of the exclusion zone on the success probability at the FES. It is shown that the exclusion zone-based interference mitigation technique significantly improves the success probability as the exclusion zone increases.
6G 이동통신시스템을 위한 주파수 공유형 초지향성 네트워크의 성능분석
염정선(Jeong Seon Yeom),정방철(Bang Chul Jung) 한국통신학회 2021 한국통신학회 학술대회논문집 Vol.2021 No.2
본 논문은 동일 주파수 대역을 사용하는 1차 네트워크와 2차 네트워크가 공존하며 모든 송수신단이 지향성 안테나를 사용하는 주파수 공유형 지향성 네트워크의 전송 성공 확률 (coverage probability)을 수학적으로 분석한다. 구체적으로 확률 기하를 기반으로 시스템을 모델링하며 1차 네트워크 주변에 2차 네트워크의 송신단이 존재하지 못하는 배타지역을 설정하여 1차 네트워크에 미치는 간섭량을 감소시킨다. 안테나 방사 이득은 실제 uniform linear array 안테나를 고려하되 수학적 분석을 위해서 계단형 근사법으로 근사화하며 열린 형태의 함수의 하한을 고려하여 1차 네트워크의 전송 성공 확률을 닫힌 형태의 수식으로 유도한다. 시뮬레이션 결과를 통해 본 논문에서 수학적으로 유도한 전송 성공 확률이 거의 정확함을 보인다.