• The Korean Journal of Ecology
• /
• 제14권3호
• /
• pp.327-343
• /
• 1991

Clonal growth and rhizome architecture of calmagrostis epigeios, were studied in a 15-year old coastal reclamed land. As c. epigeios patch grew from center to margin radially over time, concentric annuli were added. the radial increases of the mature patch were 80~130cm/yr. the patch ages of c. epigeios estimated by relationships between the diameter and is radial increament, were 1~6year old. There were the marked variations of density, phytomass, shoot height and inflorecence frequency with increasing age of rhizome system within the patch. the maximum performance occurred at 2-year-old concentric annuli of the patch. The growth phasic continuum with aging was divided into 5 grwth phases ; pioneer, building, matyre, senile and degenerate. The rhizome aging had a more significant effect on the inflorescence frequency than on the other attributes. new rhizomes tended to diverge from the direction of the parent ramet by sympodial growth. in a 1-year-old patch, average length of rhizome segment was 7cm, average number of internode was 6, and the tillering frequency was 27%. The tillering in the early stage resultd in the increase of shoot density and the producation of multibranching rhizome. as the result of that, circular patchwas formed in a year. The branching structure based on such facts was represented graphically in branching degree of 60 and 100. therefore, c. epigeios with clonal growth may establish and grow vigorously earlier than other glycophytes in high salt conditions such as the coastal reclaimed land.

• Journal of Electrical Engineering and Technology
• /
• 제8권6호
• /
• pp.1468-1473
• /
• 2013

This paper dealt with the propagation characteristics of acoustic signals produced by partial discharges and the positioning of PD origin in insulation oil to develop insulation diagnostic techniques of oil-immerged transformers. Electrode systems such as needle to plane, plane to plane, and particle electrodes were fabricated to simulate some defects of power transformers. In addition, the frequency spectrum and propagation characteristics of acoustic signals with partial discharge (PD) in insulation oil were analyzed. Although there were differences based on the type of defect, the frequency spectra of the acoustic signals measured by wide and narrow band acoustic emission (AE) sensors were distributed in the range of 50 kHz-400 kHz. Therefore, a narrowband AE sensor is suitable for the diagnosis of oil-immersed power transformers. We could find the position of the PD source with an error margin of 10% in the experiments by calculating the position of the PD occurrence using the time difference of arrival measured by five AE sensors.

• 한국항공운항학회지
• /
• 제25권3호
• /
• pp.74-80
• /
• 2017

As for A rotary wing aircraft, the configuration change about split yaw swaged rod was executed to improve hit treat capability for dealing with a long rod. The purpose of this study was to analyze if or not the quality of the split yaw swaged rod was obtained, and so the flight safety was ensured or not. Buckling analysis, Coupling Thread Strength Analysis, Thermal Stress analysis and Rod Natural Frequency Analysis were executed for structural analysis. The results of the analysis were presented that the split rod had the sufficient margin of safety and so there were no anomalies in the limit load and no failures in the ultimate load. And there were no resonances in result of natural frequency analysis. In conclusion, this study showed that the split yaw swaged rod had structural safety, so flight safety of rotary wing aircraft was secured and there was no problem in aircraft operation. It is certain that the technology of splitting the yaw swage rod will contribute to the operational Safety of the rotary wing aircraft in the future.

• 한국우주과학회:학술대회논문집(한국우주과학회보)
• /
• 한국우주과학회 2008년도 한국우주과학회보 제17권2호
• /
• pp.28.4-29
• /
• 2008

The aim of the test is to provide an experimental basis to validate the prediction of the FEM for high frequency jitter analysis due to reaction wheel. The principle is to measure structural transfer functions between the input disturbances at RWA base plate and the accelerations near the end tips of payload, in a configuration close to the operational model. The spacecraft shall have to be suspended, in order to be representative of on-orbit boundary conditions. The results of the test shall be compared to the output of the FEM analysis, and if needed, local upgrades of the FEM and/or margin policy shall be defined in order to guarantee a good test/FEM consistency. Test results were compared with the transfer functions of the FEM, which is globally tuned based on the results of vibration test and consequently have lower damping coefficients values than 1% in the frequency range of 60~200Hz. The damping coefficients estimated from the figures of FRF test results are different from the theoretical FEM, but the magnitude trend of FRF of the test results is somewhat similar with the analytical, it is expected that the overall jitter effect of final estimation is nearly same with the preliminary analysis result in which the damping coefficients were assumed to be 1% for all modes in FEM.

• JSTS:Journal of Semiconductor Technology and Science
• /
• 제7권1호
• /
• pp.20-27
• /
• 2007

An analytic design guide was formulated for the design of 3-stage CMOS OP amp with the nested Gm-C(NGCC) frequency compensation. The proposed design guide generates straight-forwardly the design parameters such as the W/L ratio and current of each transistor from the given design specifications, such as, gain-bandwidth, phase margin, the ratio of compensation capacitance to load capacitance. The applications of this design guide to the two cases of 10pF and 100pF load capacitances, shows that the designed OP amp work with a reasonable performance in both cases, for the range of compensation capacitance from 10% to 100% of load capacitance.

• 한국전자파학회논문지
• /
• 제7권4호
• /
• pp.288-299
• /
• 1996

무선 중계시스템을 통한 전파 전송방식중 동일 채널 중계방식은 현재 보면적으로 사용중인 인터리브드방식에 비하여 특히 주파수 이용 효율변에서 커다란 장점을 자기고 있으므로, 한정된 주파수 자원의 효율적 운용을 위하여 이바한 동일 채널 중계방식의 개발 및 적용에 대한 연구는 매우 중요한 의미를 지닌다. 본 논문에서는 lOGHz 이하 대역에서 동일 채널 무선 중계방식을 사용하는 디지탈 시스템의 성능 및 페이드마진 계산 방안을 제시하였으며 시뮬레이션을 통해 실제 상황에의 적용방안을 다루었다.

• 항공우주시스템공학회지
• /
• 제15권5호
• /
• pp.8-15
• /
• 2021

본 논문은 고기동 제트항공기의 종축 비행성 요구도를 만족하기 위해 최적화 기법을 이용한 설계 방법에 관해 기술한다. 대상 항공기는 모델 역변환 기법이 적용되었으며, 제어이득 최적화로 종축 단주기 비행성 요구도를 만족하지만, 안정성 여유 항목이 고려되지 않았다. 안정성 여유를 만족하지 못하는 경우 개선을 위해 시행 착오법 등을 통한 이득의 직접 재조정이 필요하며, 이를 개선하기 위해 추가적인 보상기와 최적화 구속조건을 추가한 제어이득 최적화 방안을 제시하였다. 또한, 최적화 결과에 대한 비행성 만족도를 재평가하였으며, 최적화 구속조건으로 설정된 비행성 요구도가 반영하지 못하는 시간 반응의 수렴성과 정상상태 오차에 대한 추가적인 제어법칙 평가 기준 설정 및 그 결과에 관해 기술한다.

• 대한방사선치료학회지
• /
• 제33권
• /
• pp.117-125
• /
• 2021

목 적: 본 연구는 뇌 정위 방사선수술에서 비 동일 면빔 사용 시 couch 회전에 따른 Set-up 오차에 대한 상관관계를 알아보고 선량 학적 차이 평가를 통해 치료 용적의 추가적인 margin 설정을 제안하고자 한다. 대상 및 방법: 4개의 Arc beam을 사용하였으며 전체 beam 중에 non coplanar beam의 빈도 수를 달리하는 각각의 시나리오 치료 계획을 만들었다. 이후 couch를 회전한 후 Exact system을 이용하여 couch Setup 오차 값을 측정하였다. 이를 적용하여 재 치료 계획을 만들어 선량적 정확성을 평가하였다. 결 과 : Couch가 30°, 45°, 60°, 90°로 회전하였을 시 X축 이동 값의 평균은 각 0.29 mm, 0.26 mm, 0.51 mm, 0.08 mm으로 측정되었다. Y축 이동 값의 평균은 각 0.75 mm, 0.5mm, 0.35 mm, 0.29 mm 으로 측정되었다. Z축 이동 값의 평균은 각 0.5 mm, 0.28 mm, 0.22 mm, 0.1 mm으로 측정되었다. 선량 학적 결과로는 1-NC VMAT, 2-NC VMAT, 3-NC VMAT 모두 각 initial plan 대비 D99에서 0.1%, 3.1%, 1.9% 선량 감소하였고 1-NC VMAT의 GTV의 CI(Conformity Index)는 0.8이며 2-NC VMAT는 0.79, 3-NC VMAT는 0.75이다. 결 론 : NC-VMAT의 뇌 정위 방사선수술 시 전체 beam의 개수 중 50% 이상의 non coplanar beam을 사용하여 치료하는 경우 couch 회전 시 image verification 이 각각 필요하다. 그러나 선형가속기 장비 특성상 couch가 회전된 상태에서 image verification이 가능하지 않다면 GTV에 couch 회전으로 인한 최대 오차 값을 포함하는 1.5 mm margin을 추가하여 치료 계획을 수립하는 것이 유용할 것으로 사료된다.

• 한국전자파학회논문지
• /
• 제14권5호
• /
• pp.489-498
• /
• 2003

최근 초고속 무선접속 및 3세대 이동통신 이후 시스템의 신규 서비스 도입을 위해 5 GHz 대역에 대한 관심이 고조되고 있다. 이러한 주파수 확보를 위해 수요감소와 경제성이 낮은 6 GHz 이하의 마이크로웨이브 중계주파수 이전을 6 GHz 이상의 대역으로 고려하고 있다. 본 논문에서는 주파수 이전을 대비한 마이크로웨이브 링크설계의 품질분석 수단으로 Vigants & Barnett의 불가동 예측 모델을 검토하였다. 불가동 및 가용율 계산에대한 실례를 보이기 위해 4 GHz 운용 국소를 분석하였으며, 6.7 및 8 GHz 대역으로 이전시의 고려사항과 다이버시티 종류, 비트 오율 및 가용율에 대해 수치 계산한 결과를 제시하였다. 계산 결과에의하면 공간 다이버시티 또는 공간 및 주파수 다이버시티를 혼용하는 경우에만 주파수 이전에 상관없이 년간 목표 가용율을 만족하는 것으로 나타났다.

• Journal of Electrical Engineering and Technology
• /
• 제11권1호
• /
• pp.86-92
• /
• 2016

Upon detecting a frequency event in a power system, the stepwise inertial control (SIC) of a wind turbine generator (WTG) instantly increases the power output for a preset period so as to arrest the frequency drop. Afterwards, SIC rapidly reduces the WTG output to avert over-deceleration (OD). However, such a rapid output reduction may act as a power deficit in the power system, and thereby cause a second frequency dip. In this paper, a hybrid reference function for the stable SIC of a doubly-fed induction generator is proposed to prevent OD while improving the frequency nadir (FN). To achieve this objective, a reference function is separately defined prior to and after the FN. In order to improve the FN when an event is detected, the reference is instantly increased by a constant and then maintained until the FN. This constant is determined by considering the power margin and available kinetic energy. To prevent OD, the reference decays with the rotor speed after the FN. The performance of the proposed scheme was validated under various wind speed conditions and wind power penetration levels using an EMTP-RV simulator. The results clearly demonstrate that the scheme successfully prevents OD while improving the FN at different wind conditions and wind power penetration levels. Furthermore, the scheme is adaptive to the size of a frequency event.