• 한국광학회지
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• 제17권2호
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• pp.113-119
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• 2006

망막검사를 위한 검안경용 망막 카메라를 개발하기 위한 광학계 설계를 연구하였다. 이에 앞서 사람의 눈에 대한 광학계 제원은 김상기와 박성찬이 발표한 정밀모형안을 채택하였다. 이를 토대로 하여 광학계를 4개의 렌즈 군으로 구성하였고 제 1군으로 모든 시야각에 대한 광을 중심으로 모았다가 제2, 제3, 제4군에 의해 결상하도록 하였다. 결상된 망막의 상은 CCD 광검출기에 의해 모니터로 전시한다. 제 1군을 단일 렌즈로 하고 나머지 광학계를 triplet로 하여 최적화를 통해 설계하였다. 광선수차, spot diagram, 회절을 고려한 point spread function 및 MTF를 계산하여 분석한 결과, 좋은 성능을 가진 광학계 설계가 가능하였다. 본 연구 결과에서 얻은 광학계로서 양질의 망막 카메라를 개발할 순 있을 것으로 믿는다.

• 한국융합학회논문지
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• 제12권4호
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• pp.43-50
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• 2021

최근 포항시를 비롯한 일부 지역의 지진 발생 빈도가 증가함에 따라, 대한민국 내에서 발생한 지진에 대한 대응책에 대한 필요성이 여러 가지 측면으로 요구되고 있다. 지진 발생 이후 액상화 현상이 발생하였고, 지진에 대한 사전대비와 대처에 대한 미흡함으로 인해, 지역 주민의 불안감이 가중 되었다. 이러한 현상에 대한 대처와 지역 주민에 대한 불안감을 해소하기 위해, 우리는 기존 지진 대응에 대한 시스템에 대한 한계를 분석하고, 그것을 해결하기 위한 하나의 방법을 마련하고자 한다. 이에 우리는 재난 상황에 적극적으로 대처할 수 있는 평가 기반의 지진 정보를 표출하고 확산할 수 있는 원스톱 모바일 지원 확산 시스템을 제안하고, 구현하여, 그 가능성을 증명한다.

• 대기
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• 제34권2호
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• pp.217-231
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• 2024

The Korea Integrated Model (KIM)-based real-time volcanic ash dispersion prediction system, which employs the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model, has been developed to quantitatively predict volcanic ash dispersion in East Asia and the Northwest Pacific airspace. This system, known as KIM-HYSPLIT, automatically generates forecasts for the vertical and horizontal spread of volcanic ash up to 72 hours. These forecasts are initiated upon the receipt of a Volcanic Ash Advisory (VAA) from the Tokyo Volcanic Ash Advisory Center by the server at the Korea Meteorological Administration (KMA). This system equips KMA forecasters with diverse volcanic ash prediction information, complemented by the Unified Model (UM)-based HYSPLIT (UM-HYSPLIT) system. Extensive experiments have been conducted using KIM-HYSPLIT across 128 different volcanic scenarios, along with qualitative comparisons with UM-HYSPLIT. The results indicate that the ash direction predictions from KIM-HYSPLIT are consistent with those from UM-HYSPLIT. However, there are slight differences in the horizontal extent and movement speed of the volcanic ash. Additionally, quantitative verifications of the KIM-HYSPLIT forecasts have been performed, including threat score evaluations, based on recent eruption cases. On average, the KIMHYSPLIT forecasts for 6 and 12 hours show better quantitative alignment with the VAA forecasts compared to UM-HYSPLIT. Nevertheless, both models tend to predict a broader horizontal spread of the ash cloud than indicated in the VAA forecasts, particularly noticeable in the 6-hour forecast period.

• 정보통신설비학회논문지
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• 제11권1호
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• pp.10-15
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• 2012

Ultra wideband (UWB) technologies have been developed to exploit a new spectrum resource in substances and to realize ultra-high-speed communication, high precision geo-location, and other applications. The energy of UWB signal is extremely spread from near DC (Direct Current) to a few GHz. This means that the interference between conventional narrowband systems and UWB systems is inevitable. However, the interference effects had not previously been studied from UWB wireless systems to conventional wireless systems sharing the frequency bands such as broadcasting system. This paper experimentally evaluates the interference from two kinds of UWB sources, namely an orthogonal frequency division multiplex UWB source and an impulse radio UWB source, to a broadcasting transmission system. The S/N ratio degradation of broadcasting system is presented. From these experimental results, we show that in all practical cases UWB system can be coexisted 35m distance in-band broadcasting network.

• 조명전기설비학회논문지
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• 제26권6호
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• pp.94-101
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• 2012

In this paper, The Next Generation High Speed Railway inverter system based on IPMSM drives using Random Pulse Position Modulation is proposed to reduce electromagnetic noise. To verify the validity of study, the simulator for the proposed system is designed and impplemented. Simulation program is developed using Matlab/Simulink. The simulation results of the proposed system was compared with the system using conventional method. The results show that the voltage and current harmonics of the proposed Next Generation High Speed Railway Inverter system. significantly decrease and spread into wide band area by the proposed Random Pulse Position modulation technique based on Space Vector Modulation method.

• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
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• 제3B권2호
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• pp.103-110
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• 2003

With significant development of power electronics technology, the proliferation of nonlinear loads such as static power converters has deteriorated power quality in power transmission and distribution systems. Notably, voltage harmonics resulting from current harmonics produced by the nonlinear loads have become a serious problem in many countries. Many photovoltaic power generation systems installed in building systems have harmonics that are the worst object for distribution systems as a utility interactive system, and it tends to spread out continuously. Proposed and implemented in this paper is a multi-function inverter control strategy that allows a shunt active filter function to the power inverter of the photovoltaic power generation system established on a building system. The effectiveness of the proposed system is demonstrated through the simulation of a hypothetical power system using PSCAD/EMTDC.

• 한국항공운항학회지
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• 제7권1호
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• pp.7-18
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• 1999

The FAA, along with the ICAO and other members of the civil aviation community, has recognized that a GNSS will provide the primary stand-alone navigation system in the 21st Century. FAA has initiated plans to transition from its present ground-based navigation and landing system to satellite-based using signals generated by the GPS. In spite of some risks, GPS users are increasing rapidly. About 52 aircraft equipped with various GPS in their system and wide spread of GPS may be expected in Korea. However, the regulations concerning with CPS implementation were not established by the government. Another problem is GPS receiver's interface. The user interface, operating method and capability vary with GPS class and model. As a direct operator for the system, pilots have to ensure these limitations and rules for efficient adaptation and safety. The issues identified by the study are highly interrelated, and are evidence of aviation system problem. To treat one issue in isolation may improve certain aspects of the aviation system, but will ultimately fail to fundamentally increase the safety and efficiency for the system.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2000년도 ITC-CSCC -1
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• pp.497-500
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• 2000

In this paper, we compare the bit-error-rate performance of the fast-frequency-hopped spread-spectrum multiple-access (FFH/SSMA) and direct-sequence code-division multiple access (DS/CDMA) systems in a Rician fading channel. Each system has a same data rate, bandwidth and transmits over a Rician fading channel. The results illustrate tradoffs in performance between the FFH/SSMA and DS/CDMA systems as a function of the parameters such as average signal to noise ratio and processing gain. The performance of the FFH/SSMA system is shown to be less sensitive to the change of fading environments, while the change of processing gain and average signal to noise ratio gives considerable affect to the FFH/SSMA system compared with the DS/CDMA system. Without respect to the change of system parameters, for most of Rician fading channels (except non-fading channel), FFH/SSMA system gives better performance than DS/CDMA system in BBR < 10$\^$-3/.

• 조명전기설비학회논문지
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• 제28권11호
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• pp.100-105
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• 2014

In this paper, Uninterruptible Power Supply(UPS) Inverter system using Carrier Frequency Modulated PWM (CFM-PWM) is proposed to reduced harmonics and electromagnetic noise. Power conversion of UPS system is executed by the ON-OFF operation of semiconductor switching devices. However, this switching operation causes the surge and EMI which deteriorate the reliability of the UPS system. This Problems improved by Random PWM switching method. The simulation results of the proposed system was compared with the system using conventional method using Matlab/Simulink. The results show that the output voltage and current harmonics of the proposed UPS system significantly decreased and spread into wide band area by the proposed Carrier Frequency Modulated PWM(CFM-PWM) method based on the Space Vector Modulation.

• Journal of electromagnetic engineering and science
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• 제6권1호
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• pp.76-81
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• 2006

Ultra wideband(UWB) technologies have been developed to exploit a new spectrum resource in substances and to realize ultra-high-speed communication, high precision geo-location, and other applications. The energy of UWB signal is extremely spread from near DC to a few GHz. This means that the interference between conventional narrowband systems and UWB systems is inevitable. However, the interference effects had not previously been studied from UWB wireless systems to conventional wireless systems sharing the frequency bands such as Broadcasting system. This paper experimentally evaluates the interference from two kinds of UWB sources, namely a orthogonal frequency division Multiplex UWB source and an impulse radio UWB source, to a Broadcasting transmission system. The receive power degradations of broadcasting system are presented. From these experimental results, we show that in all practical cases UWB system can coexist 35 m distance in-band broadcasting network.