• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.23 no.4
• /
• pp.865-872
• /
• 1998

This paper proposes a multiuse detection system in a multi-cell M-ary Frequency Shift Keying(MFSK)/frequency hopping(FH)-Code Division Multiple Access(CDMA) environment, in which the channel model is an OR-channel and in the reverse link. We have proposed a multiuse detection system in a single cell. However, this sitye is not adequate to detect multiuser in a multi-cell environment. Therefore, we propose a multiuser detection system based on 3 level OR decision with two threholds. The proposed detection system can delete interference as well as intra-cell interference, receive the weakened desired signal and reject the false alarm. computer simulation shows the performance improvement.

• Journal of the Optical Society of Korea
• /
• v.13 no.3
• /
• pp.386-391
• /
• 2009

PSPICE circuit parameters of the blue laser diodes grown on wurtzite AlGaInN multiple quantum well structures were extracted directly from the three level rate equations. The relevant optical gain parameters were separately calculated from the self-consistent multiband Hamiltonian. The resulting equivalent circuit model for a blue laser diode was schematically presented, and its modulation characteristics, including the pulse response and the frequency response, have been demonstrated by using a conventional PSPICE.

• Journal of The Korean Astronomical Society
• /
• v.23 no.1
• /
• pp.71-82
• /
• 1990

Theoretical calculations of the combined radiative transfer and statistical equilibrium equation including the charge-particle conservations have been earned out for a multilevel hydrogen atom in quiescent prominences. Cool and dense models show the steep changes of population and radiation field in the vicinity of the surface, while these physical quantities remain unchanged for models with temperature of 7,300K, regardless of total densities. Ionization rate of hydrogen atom related with metallic line formation varies in considerable amounts from the surface to the center of model prominences cooler than 6,300K. However, such cool models cannot release enough hydrogen line emissions to explain observed intensities. Prominence models with a temperature higher than 8,000K can yield the centrally reversed Lyman line profiles confirmed by satellite EUV observations. We find that queiscent prominence with a density between $2{\times}10^{11}$ and $10^{12}cm^{-3}$ should be in temperature range between 6,300K and 8,300K, in order to explain consistently observed H alpha, beta line emissions and $n_p/n_l$ ratio.

• Proceedings of the KIPE Conference
• /
• 2018.07a
• /
• pp.372-373
• /
• 2018

HVDC(High Voltage Direct Current)전력망은 발전소에서 생산한 교류를 직류로 변환한 이후 송전하여 부하에 가까운 전력변환기를 이용하여 교류로 변환한 후에 사용하는 방식이며, 전압형 HVDC에 MMC(Modular Multilevel Converter)가 널리 사용되고 있다. 본 논문에서는 MMC가 적용된 HVDC를 이용한 해상 풍력 계통 제어 성능을 테스트하기 위해 실시간 시뮬레이션 툴인 RT-Lab에 적용한 모델에 대해 설명하고자 한다.

• Proceedings of the KIPE Conference
• /
• 2017.07a
• /
• pp.12-13
• /
• 2017

최근 멀티레벨 인버터가 high power and medium voltage에서 많이 사용되면서 레벨 증가가 비교적 쉬운 CHB 구조가 많이 사용되고 있다. 멀티레벨 인버터에서 모델 예측 제어를 사용하면 빠른 동특성을 얻을 수 있지만 레벨 증가에 따른 계산량이 급격하게 증가하는 단점을 갖는다. 그래서 본 연구에서는 정상상태에서 기준 전압 벡터의 인근 벡터만 고려하여 계산량을 감소시키고 과도상태에서 최적화 기법을 통한 빠른 동특성을 유지하는 최적 모델 예측 제어를 제안한다. 본 논문에서는 5-level CHB 인버터를 이용하여 시뮬레이션을 진행하고 기존 모델 예측 제어와 제안하는 알고리즘의 성능을 비교한다.

• Proceedings of the KIEE Conference
• /
• 1999.07h
• /
• pp.21-25
• /
• 1999

This paper proposes a novel control strategy of SVC(Static var compensator) using cascade multilevel inverter. To control the reactive power instantaneously, the dq-dynamic system model is described and analyzed. A single pulse pattern based on the SHE(Selective Harmonic Elimination) technique is determined from the look-up table to reduce the line current harmonics and a rotating fundamental frequency switching scheme is applied to adjust the DC capacitor voltage at the scheme level. From the simulation, it is verified that this proposed control scheme make the dynamic control response of SVC fast, the current harmonics low, and the DC capacitor voltage balanced.

• Journal of Power Electronics
• /
• v.19 no.6
• /
• pp.1486-1495
• /
• 2019

Dealing with the DC link fault poses a technical problem for an HVDC based on a modular multilevel converter. The fault suppressing mechanisms of several sub-module topologies with DC fault current blocking capacity are examined in this paper. An improved half-bridge sub-module topology with double direction control switch is also designed to address the additional power consumption problem, and a sub-module topology called hybrid double direction blocking sub module (HDDBSM) is proposed. The DC fault suppression characteristics and sub-module capacitor voltage balance problem is also analyzed, and a self-startup method is designed according to the number of capacitors. The simulation model in PSCAD/EMTDC is built to verify the self-startup process and the DC link fault suppression features.

• Safety and Health at Work
• /
• v.12 no.2
• /
• pp.277-281
• /
• 2021

Singapore's construction sector employs more than 450,000 workers. During the height of the COVID-19 pandemic in Singapore from April to June 2020, migrant workers were disproportionately affected, including many working in the construction sector. Shared accommodation and construction worksites emerged as nexuses for COVID-19 transmission. Official government resources, including COVID-19 epidemiological data, 43 advisories and 19 circulars by Singapore's Ministries of Health and Manpower, were reviewed over 8 month period from March to October 2020. From a peak COVID-19 incidence of 1,424.6/100,000 workers in May 2020, the incidence declined to 3.7/100,000 workers by October 2020. Multilevel safe management measures were implemented to enable the phased reopening of construction worksites from July 2020. Using the Swiss cheese risk management model, the authors described the various governmental, industry, supervisory and worker-specific interventions to prevent, detect and contain COVID-19 for safe resumption of work for the construction sector.

• International conference on construction engineering and project management
• /
• 2015.10a
• /
• pp.294-298
• /
• 2015

In the United States, the completion of Construction Work Zone (CWZ) impact assessments for all federally-funded highway infrastructure improvement projects is mandated, yet it is regarded as a daunting task for state transportation agencies, due to a lack of standardized analytical methods for developing sounder Transportation Management Plans (TMPs). To circumvent these issues, this study aims to create a spatiotemporal modeling framework, dubbed "SWAT" (Spatiotemporal Work zone Assessment for TMPs). This study drew a total of 43,795 traffic sensor reading data collected from heavily trafficked highways in U.S. metropolitan areas. A multilevel-cluster-driven analysis characterized traffic patterns, while being verified using a measurement system analysis. An artificial neural networks model was created to predict potential 24/7 traffic demand automatically, and its predictive power was statistically validated. It is proposed that the predicted traffic patterns will be then incorporated into a what-if scenario analysis that evaluates the impact of numerous alternative construction plans. This study will yield a breakthrough in automating CWZ impact assessments with the first view of a systematic estimation method.

• Health Policy and Management
• /
• v.25 no.1
• /
• pp.31-39
• /
• 2015

Background: The purpose of this study is comparison of the results between regression and multi-level analysis to find out factors influencing outcome indicators (in-hospital death, length of stay, and medical charges) of stroke patients. Methods: By using patient sample data of Health Insurance Review & Assessment Service, patients admitted with stroke were selected as survey target and 15,864 patients and 762 hospitals were surveyed. Results: For the results of existing regression analysis and multi-level analysis, models were assessed through model suitability index value and as a result, the value of results of multi-level analysis decreased compared to the results of regression, showing it is a better model. Conclusion: Factors influencing in-hospital death of stroke patients were analyzed and as a result, intra-class correlation (ICC) was 13.6%. In factors influencing length of stay, ICC was 11.4%, and medical charges, ICC was 17.7%. It was found that factors influencing the outcome indicators of stroke patients may vary in every hospital. This study could carry out more accurate analysis than existing research findings through analysis of reflecting structure at patient level and hospital level factors and analysis on random effect.