• 한국전자파학회논문지
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• 제8권4호
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• pp.403-414
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• 1997

각종 원인에 기인하는 궤도별 우주폐기물의 분포는 우주환경에 있어서 위성통신 방송 및 통신신호의 전파전파 에 방해요소로 작용하게 된다. 본 논문에서는 수치해석적 접근에 의해 우주폐기물의 공간분포밀도와 사용 주파 수의 변화에 따른 EM파의 정규화 산란계수를 계산하고 우주폐기물에 의한 감쇠도 및 위상변화를 구하였다. 그 결과 우주폐기물에 의한 위성통신 방송선호 전파에 었어서 감쇠도는 베셀함수에 의해 표현된 전계 요소의 진폭 함수의 실수부에 의해 가장 큰 영향을 받게 되고 위상 변화량은 허수부에 의해 주로 결정됨을 분석하였다. 본 논 문의 결과는 우주폐기물의 기하급수적 증가에 따른 우주환경의 새로운 인식과 우주폐기물을 고려한 위성통신망 의 링크버짓 설계의 활용에 적합하다.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제48권1호
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• pp.42-47
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• 1999

This paper presents the information transmission between on-board and ground-site in MAGLEV. considering safety and high speed operation and density operation, information transmission between them is necessary. Therefore it is necessary for transmission system to ensure high speed transmission, low error rate, massive information, and reliability of information. To provide above conditions, 1.1km signal line assembly was constructed and Frequency Shift Keying(FSK) modulation and Open System Interconnection(OSI) based high-level data link control(HDLC) protocol are applied. To modulate digital signal for transmission from ground-site to on-board, carrier frequency of 70kHz is used and 90khz is used for transmission from on-board to ground-site. Transmission speed is 2400bps for consideration of train speed, quantity of information, and data error rate. And this paper introduces information monitoring considering user interface and presents the method for an effective data transmission in MAGLEV which is now being tested and intends to provide for an intelligent train operation system in future.

• 국제초고층학회논문집
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• 제5권2호
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• pp.87-94
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• 2016

High-rise as a building typology is gaining popularity in Asian mega-cities, due to its advantages in increasing volumetric density with limited land resources. Numerous factors contribute to the formation of high-rise urban form, from economical and institutional, environmental to socio-political. Environmental concerns over the impact of rapid urbanization in developing economies demand new thought on the link between urban environment and urban form. Outdoor and indoor climate, pedestrian comfort, and building energy consumption are all related to and impacted by urban form and building morphology. There are many studies and practices on designing individual "green" high-rise buildings, but far fewer studies on designing high-rise building clusters from the perspective of environmental performance optimization.. This paper focuses on the environmental perspective, and its correlation with the evolution of the high-rise urban form. Previous studies on urban morphology in terms of environmental and energy performance are reviewed. Studies on "parameterizing" urban morphology to estimate its environmental performance are reviewed, and the possible urban design implications of the study are demonstrated in by the author, by way of a microclimate map of the iconic Shanghai Xiao Lujiazui CBD. The study formulates the best-practice design guidelines for creating walkable and comfortable outdoor space in a high-rise urban setting, including proper sizing of street blocks and building footprint, provision of shading, and facilitating urban ventilation.

• 디지털콘텐츠학회 논문지
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• 제13권2호
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• pp.247-254
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• 2012

정보체계 개발 시 사용자 요구사항의 관리는 핵심요소이다. 그동안 요구사항의 관리와 관련하여 추적 테이블을 이용한 추적 모델이나 SOA 등 특정 방법론을 기반으로 한 추적 기법은 연구된 바 있다. 그러나 IT비전문가인 사업담당자를 위한 객관적이며 정량화된 평가 방법과 판정 기준을 제시한 사례는 없었다. 이에, 본 연구자는 선행 사례 연구를 통해 공공분야의 정보시스템을 구축하는 과정에서 요구사항 반영의 적정성을 판단하는데 있어 비전문가도 접근하기 쉽고 객관적이며 정량화된 평가 방법과 판정 기준을 제시한 바 있다. 본 연구에서는 선행 연구의 한계점을 고찰하여 요구사항 반영에 대한 평가 산식을 개선하고 다양한 사업 사례 분석을 통해 사업 특성 별 판정기준을 도출, 제시하였다.

• International Journal of Ocean System Engineering
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• 제3권2호
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• pp.102-110
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• 2013

The purpose of this study was to improve the properties of epoxy resin using titanium oxide nanoparticles. The effects of particle weight fraction, dispersion agent, and curing agents with different molecular weights on the thermal and mechanical properties of titanium-oxide-reinforced epoxy resin were investigated. In addition, the effect of the particle dispersion condition on the mechanical properties of nanocomposites was studied. As a result, it was found that the glass transition temperature of film-shaped nanocomposites decreased with an in-crease in the nanoparticle content. Because nanoparticles interrupted the cross linkage between the epoxy resin and the amine curing agent, the cross-link density of the epoxy became lower and led to a decrease in $T_g$ in the nanocompo-sites. The tensile strength and modulus in film-shaped nanocomposites also increased with the particles content. But in the case of dog-bone-shaped nanocomposites, the values were not similar to the trend for the film-shaped nanocompo-sites. This was probably a result of the different nanoparticles dispersions in the epoxy resins resulting from the respective-thicknesses of the film and dog-bone-shaped samples.

• 한국조명전기설비학회:학술대회논문집
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• 한국조명전기설비학회 2005년도 학술대회 논문집
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• pp.377-382
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• 2005

This paper presents two new circuit topologies of DC bus lineside active edge resonant snubber assisted soft-switching PWM full-bridge DC-DC converter acceptable for either utility AC 200V-rms or AC 400V-rms input voltage source. One topology of proposed DC-DC converters is composed of a typical voltage source-fed full-bridge high frequency PWM inverter using DC busline side series power semiconductor switching devices with the aid of a parallel capacitive lossless snubber. All the active power switches in the full-bridge arms and DC busline can achieve ZCS turn-on and ZVS turn-off commutations and the total turn-off switching power losses of all active switches can be reduced for high-frequency switching action. It is proved that the more the switching frequency of full-bridge soft switching inverter increases, the more soft-switching PWM DC-DC converter with a hish frequency transformer link has remarkable advantages for its efficiency and power density as compared with the conventional hard-switching PWM inverter type DC-DC converter

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제11권8호
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• pp.4061-4076
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• 2017

With the development of high-speed railway technologies, train velocities can now reach speeds up to 350 km/h, and higher in the future. In high-speed railway systems (HSRs), loss of communication can result in serious accidents, especially when the train is controlled through wireless communications. For to this reason, operators of Long Term Evolution for Railway (LTE-R) communication systems install eNodeBs (eNBs) with high density to achieve highly reliable communications. However, densely located eNBs can result in unnecessary frequent handovers (HOs) resulting in instability because, during every HO process, there is a period of time in which the communication link is disconnected. To solve this problem, in this paper, an HO scheme based on the maximum cell residence time (CRT) and adaptive time to trigger (aTTT), which are collectively called CaT, is proposed to reduce unnecessary HOs (using CRT estimations) and decrease HO failures by improving the handover command transmission point (HCTP) in LTE-R HSR communications.

• 대한원격탐사학회지
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• 제26권6호
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• pp.617-627
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• 2010

Although many researches for heat island study have been developed, there is little attempt to link the findings to actual and hypothetical scenarios of urban developments which would help to mitigate the Urban Heat Island (UHI) in cities. The aim of this paper is to analyze the UHI at urban area with different geometries, land use, and environmental factors, and emphasis on the influence of different geometric and environmental parameters on ambient air temperature. In order to evaluate these effects, the parameters of (i) Air pollution (i.e. Aerosol Optical Thickness (AOT)), (ii) Green space Normalized Difference Vegetation Index (NDVI), (iii) Anthropogenic heat (AH) (iv) Building density (BD), (v) Building height (BH), and (vi) Air temperature (Ta) were mapped. The optimum operational scales between Heat Island Intensity (HII) and above parameters were evaluated by testing the strength of the correlations for every resolution. The best compromised scale for all parameters is 275m resolution. Thus, the measurements of these parameters contributing to heat island formation over the study areas of Hong Kong were established from mathematical relationships between them and in combination at 275m resolution. The mathematical models were then tabulated to show the impact of different percentages of parameters on HII. These tables are useful to predict the probable climatic implications of future planning decisions.

• Journal of Power Electronics
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• 제19권6호
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• pp.1536-1543
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• 2019

This paper presents an improved torque predictive control (TPC) for permanent magnet synchronous motors (PMSMs) using an indirect matrix converter (IMC). The IMC has characteristics such as a high power density and sinusoidal waveforms of the input-output currents. Additionally, this configuration does not have any DC-link capacitors. Due to these advantages of the IMC, it is used in various application field such as electric vehicles and railway cars. Recently, research on various torque control methods for PMSM drives using an IMC is being actively pursued. In this paper, an improved TPC method for PMSM drives using an IMC is proposed. In the improved TPC method, the magnitudes of the voltage vectors applied to control the torque and flux of the PMSM are adjusted depending on the PMSM torque control such as the steady state and transient response. Therefore, it is able to reduce the ripples of the output current and torque in the low-speed and high-speed load ranges. Additionally, the improved TPC can improve the dynamic torque response when compared with the conventional TPC. The effectiveness of the improved TPC method is verified by experimental results.

• 환경생물
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• 제36권3호
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• pp.370-376
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• 2018

It is important to consider interaction between species in understanding structure and function of the biological community. Current ecological issues such as climate change and habitat loss emphasize the significance of the concept of species interaction in that varying species' interaction across environmental gradients may lead to altered ecological function and services. However, most community studies have focused on species diversity through analysis of quantitative indices based on species composition and abundance data without considering species interactions in the community. 'Ecological network analysis' based on network theory enables exploration of structural and functional properties of ecosystems composed of various species and their interactions. In this paper, network analysis of Cheonggye stream as a case study was presented to promote uses of network analysis on ecological studies in Korea. Cheonggye stream has a simple biological structure with link density of 1.48, connectance 0.07, generality 4.43, and vulnerability 1.94. The ecological network analysis can be used to provide ecological interpretations of domestic long-term monitoring data and can contribute to conserving and managing species diversity in ecosystems.