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Study on the PMD impairment of optical multilevel DPSK systems and its mitigation methods
Yoon, Hosung,Kim, Na Young,Park, Namkyoo IEEE 2005 Photonics Technology Letters Vol.17 No.12
We examine the polarization-mode dispersion (PMD) impairment of optical multilevel differential phase-shift keying systems, and also its mitigation method by comparing the electrical equalization technique and the receiver bandwidth optimization. Analysis has been carried out with 40-Gb/s systems experiencing 0∼60 ps of instantaneous differential group delay, corresponding up to 240%/80% of bit/symbol transmission rate. Results show considerable improvement in the PMD tolerance for return-to-zero format for the optimized receiver bandwidth either with or without the electrical equalization. For nonreturn-to-zero, the bandwidth optimization alone does not significantly improve the system's PMD tolerances.
The Change in Rolling Resistance of Bearing Surgaces Coated by a Soft Metallic Film
Kong, Hosung,Yoon, Eui-Sung,Yoon, Eui-Sung ENGINEERING TRIBOLOGY RESEARCH INSTITUTE KYUNGPOOK 1998 INTERNATIONAL SYMPOSIUM ON HIGH PERFORMANCE OF TRI Vol.1998 No.-
An experimental study was performed to discover the effect of a soft metallic film on the behavior of rolling resistance. Pure silver was coated on AII 52100 bearing steel by a thermal evaporation method, where the coating thickness ranged from 100 nm to 20,000 nm. A thrust ball bearing-typed test rig was used and the rolling resistance was measured with the contact cycles under various environmental conditions such as ambient air, vacuum, dry air and controlled humidity conditions. In order to find out the changes occurred at the contact surfaces, analyses were performed by using SEM and EPMA. Results showed that minimum rolling resistance was rather obtained after the initial coating failure where the fluctuation of rolling resistance ceased to remain stable. The rease of rolling resistance was resulted mainly from shakedown phenomena occurred at the contact patches which were agglomerated by transferred coating films. It was also found that rolling resistance was strongly affected by environmental conditions. Results suggested that humidity is related closely to the agglomeration of particles which affects the rolling resistance.
윤원재(Wonjae Yoon),안종현(Jonghyeon Ahn),안규복(Kyubok Ahn),윤호성(Hosung Yoon) 한국추진공학회 2021 한국추진공학회지 Vol.25 No.3
An experimental study was conducted on the spray characteristics of the pintle injector by opening distance. The discharge coefficient of the pintle injector was investigated and the spray angle was measured by taking the spray image by test conditions. As a result of the measurement of the discharge coefficient, it was confirmed that the change in the discharge coefficient of the outer injector was not significant over the experimental conditions, but the change in the discharge coefficient of the inner injector was decreased as the flow rate increased. Measurement of the spray angle showed that the change in the spray angle was not significant in the conditions under which the spray was fully developed, but the spray was not fully developed at low flow rates. This confirmed the possibility of thrust control using the pintle injector.
윤원재(Wonjae Yoon),안종현(Jonghyeon Ahn),안규복(Kyubok Ahn),윤호성(Hosung Yoon) 한국추진공학회 2020 한국추진공학회 학술대회논문집 Vol.2020 No.11
개도에 따른 핀틀 분사기의 분무특성에 대한 실험적 연구를 수행하였다. 분사조건에 따른 핀틀 분사기의 유량계수를 확인하였으며, 분무 이미지 촬영을 통해 분무각을 측정하였다. 유량계수 측정 결과 바깥쪽 분사기는 실험조건에 걸쳐 유량계수 변화가 크지 않았지만 안쪽 분사기는 유량에 따른 유량계수 변화가 큰 것을 확인하였다. 분무각 측정결과 분무가 완전 발달되는 조건에서는 분무각의 변화가 크지 않았으나 낮은 유량에서 분무가 완전 발달되지 않는 경우가 있었다. 이를 통해 핀틀 분사기의 추력조절 가능성을 확인하였다. An experimental study was conducted on the spray characteristics of the pintle injector by opening distance. The discharge coefficient of the pintle injector was investigated and the spray angle was measured by taking the spray image by test conditions. As a result of the measurement of the discharge coefficient, it was confirmed that the change in the discharge coefficient of the outer injector was not significant over the experimental conditions, but the change in the discharge coefficient of the inner injector was decreased as the flow rate increased. Measurement of the spray angle showed that the change in the spray angle was not significant in the conditions under which the spray was fully developed, but the spray was not fully developed at low flow rates. This confirmed the possibility of thrust control using the pintle injector.