• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.26 no.6
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• pp.555-563
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• 2015

This paper presents signal processing algorithms of a frequency-modulated continuous-wave(FMCW) radar altimeter and provides a practical assessment technique. The radar altimeter is initially operated in search mode, when the radar altimeter detects a valid altitude, search mode is switched to track mode and a altitude being tracked is displayed. The sweep bandwidth in each mode is a function of altitude to narrow the beat frequency bandwidth. In addition, transmit power and receiver gain in each mode are controlled to compensate for the dynamic range of wide altitude range. To assess more realistic operation, the radar altimeter was tested using the crane setup. The crane test demonstrated that signal processing algorithms described in this paper resulted in a reduced measurement error rate.

• Geophysics and Geophysical Exploration
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• v.20 no.3
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• pp.163-175
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• 2017

In land seismic exploration, irregular surface topography and weathering layer in near surface distorts the reflected signals of data. Therefore, typical land seismic data should be compensated for this distortion by static correction. To perform the static correction, near-surface velocity is required, which can be obtained by seismic refraction survey. However, land seismic data is often acquired in a limited form of geometry depending on the equipment availability, accessibility condition, and permission for the survey site. In this situation, refraction analysis should be performed using reflection data because it is impossible to acquire refraction-oriented data due to limited source and receiver geometry. In this study, we aimed to analyze the reliability of the results obtained by refraction traveltime tomography when using reflection data with a limited number of sources and receivers from irregular surface topography. By comparing the inversion result from irregular topography with that from flat surface, we found that the surface topography affects the reliability of the inversion results to some degree. We also found that the number of sources has little effect on the inversion results unless the number of sources are very small. On the other hand, we observed that velocity distortion occurred in the overlapped part of receiver arrays when using a limited number of receivers, and therefore suggested the size of the least overlapping ratio to avoid the velocity distortion. Finally, we performed numerical tests for the model which simulates the surface topography and acquisition geometry of the survey region and verified the reliability analysis of inversion results. We identified reliable areas and suspicious area of the inverted velocity model by applying the analysis results to field data.

• The Korean Journal of Air & Space Law and Policy
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• v.19 no.1
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• pp.79-107
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• 2004

Shielding theory is to allow the construction of a structure that would be shielded by existing permanent structures even thought such structure extends above the height limits prescribed for such zones. This theory is mentioned as recommended practices in ICAO Annex, and is adopted, with modification, in the current Military Airbase Law, amended in August 26th 2002. However, the Military Airbase Law adopts shielding standard allowing 45 meters uniformly, which is a unique standard compared to other countries shielding guideline. The basic principle in applying the shielding theory is, after considering the circumstances of location of shielded structure, whether such structure has physical effect on aeronautical operations. Based upon the basic principle of shielding theory, the uniform application of shielding standard in the Military Airbase Law would undermine the safety of aeronautical operations. This article is to review subsection 2 of section 8 of the Military Airbase Law, which adopts modified shielding theory, and is to suggest better guideline. From a comparative analysis perspective, shielding guidelines of ICAO and other countries will be discussed. Based upon this discussion, the general problems of shielding theory and the specific problems in the Military Airbase Law will be examined. Finally, this article suggests the case-by-case application of shielding theory, considering circumstances of location, for the purpose of ensuring aviation safety.

• 한국노년학
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• v.30 no.4
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• pp.1311-1327
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• 2010

This study was conducted to identify the relationship between depression and subjective/objective health status, and to examine predicting factors on depression in the elderly in Korea. This study was a secondary analysis using the data of Korea National Health and Nutrition Examination Survey(VI-1) 2007. A total of 939 data from the subjects ≥60 years who completed health-related survey were used for analysis. Data were analyzed using SAS (version 9.1) PC program. Depression was identified in the 20.3% of the older subjects. Multiple logistic regression analysis showed that women (OR=2.04), senior high school graduation (OR=0.27) and lowermiddle household income (OR=2.83) were significant associating factors(p<0.05). After adjustment for socio-demographic factors, hypertension (OR=1.93) and asthma (OR=3.32) as objective health status, and stress (OR=7.27), limited activity in daily living due to fracture or joint injury (OR=6.59) and poor self-rate health (OR=1.64) as subjective health status were found as factors predicting depression in the elderly(p<0.05). According to the type of health status, the subjects who had chronic disease or perceived poor physical health were 5.94 times more likely to have disposition to depression than the subjects who had no chronic disease or perceived good physical health (p=0.001). These findings suggest that preventive education and intervention focus on preventing and managing chronic diseases such as hypertension, asthma, fracture and joint injury should be needed to decrease depression in the elderly.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.37 no.1
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• pp.1-9
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• 2000

In this paper, we design a robust output feedback controller for robot manipulators with bounded parametric uncertainties using high-gain observer. The proposed control scheme with integral action improves tracking error due to limit of the robust feedback gains. High-gain observer is used to solve the noise problem with the joint velocity measurement. This controller avoids the limitation on the variation of unknown parameters and guarantees the uniformly ultimate boundedness of the closed-loop system. The performance of the proposed method is demonstrated by simulation on a 2-link manipulator.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.1
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• pp.94-98
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• 2010

The auxiliary power supply for satellite should make the power safe and support it for subsystems during its operational lifetime. Several contstraints should be required to get high reliability. In this paper, the auxiliary power supply was satisifed and designed to be satisified with some contstraints. Control circuits for the auxiliary power supply used majority voter circuits to remove the single point failure. To verify majority voter circuits, proto-type auxiliary power supply was manufactured and tested.

• Proceedings of the KIPE Conference
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• 2013.07a
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• pp.303-304
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• 2013

기술이 발전함에 따라 전력변환기의 소형화 고효율화가 요구되어지고, 이를 위해 고주파 스위칭 전력변환기가 필요로 하게 된다. 하지만 스위칭 주파수와 비례적으로 스위칭 손실이 증가하기 때문에 시스템의 효율이 감소한다. 이러한 문제를 해결하기 위해 DCM방식이나 공진을 이용한 ZVZCS(Zero-Voltage Zero-Currrent) 컨버터가 제안되고 있으나 소자의 정격용량이 커지는 단점을 갖는다. 또한 ZVT(Zero-Voltage Transition)를 포함한 소프트 스위칭 기법을 적용하는 다양한 컨버터가 제안되고 있으나 공진전류의 첨두에서 보조스위치가 스위칭을 하게 되어 보조스위치 스위칭 손실이 큰 단점이 있다. 본 논문에서는 변압기로 공진인덕터의 전압을 제한시켜 보조 스위치가 영전압/영전류 스위칭을 하게 함으로서 스위칭 손실을 발생시키지 않는 소프트 스위칭 구조를 제안한다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.11a
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• pp.82-85
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• 2008

A Helmholtz resonator is applied to control high frequency combustion instability in liquid rocket engine. Damping characteristics of the Helmholtz resonator are investigated by the flow characteristic and its design. To simulate combustion instability, resonance in a test section(with fixed volume) is made by a pressure pulsator, and then damping characteristics are investigated. Its orifice length and diameter are selected as the design parameters and flow rates are varied to reveal the effect on damping characteristics. The experimental results show that a Helmholtz resonator is also working with flows. When length and diameter of an orifice are small, the tuning frequency increases as the flow velocity increases.

• Proceedings of the Korea Water Resources Association Conference
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• 2020.06a
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• pp.38-38
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• 2020

SPI지수는 강수량이 감소하기 시작하면 필요한 물수요에 비해서 상대적으로 물부족을 유발하게 되고, 가뭄발생의 발단이 된다는 것에 착안하여 개발된 지수이다. 하지만 다른 가뭄지수와 마찬가지로 강수량 또는 유출량 시계열을 상대적인 표준정규분포로 산정하였기 때문에 인근 지역에 비해 상대적으로 강수량이 많은 지역도 실제로 발생하지 않은 가뭄이 발생한다고 분석이 된다. 이러한 현상을 완화시키기 위해 수정된 가뭄분석 기법이 요구된다. 이에 Jeung et. al(2019)은 이런 현상을 완화시키기 위해 SPI지수 계산과정에서 해당지점의 시계열을 대상으로 계산되는 Gamma 분포를 전국으로 확장 시켜 산정 후 표준정규분포에 적용하여 가뭄지수를 산정하였다. 또한 과거 제한급수가 발생했던 지역을 대상으로 극한가뭄과 가뭄지속기간을 이용하여 M-SPI지수의 효용성을 확인한 결과, 제한급수 실시년도와 SPI, M-SPI 결과와의 비교결과 과거 가뭄을 정확하게 모사하는 것을 확인하였다. 하지만 M-SPI는 전국을 하나의 지역으로 가정하여 산정하였고, 증발산량과, 고도 등 지형의 특성을 고려하지 않았기 때문에 일부의 가뭄사상을 재현하지 못하였다. 이에 본 연구에서는 기상학적 인자와, 지형학적 인자를 고려하여 지역화를 하고, 각 지역별로 대표 확률분포를 산정하여 가뭄지수를 산정하고자 한다. 또한 한국 기상청에서 제공하고 있는 국가 표준기후변화 시나리오를 수집하여 M-SPI에 적용하여 미래 극한 가뭄빈도의 변화를 전망하고자 한다.

• The Journal of the Korea Contents Association
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• v.17 no.11
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• pp.435-445
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• 2017

This study was conducted to overcome the limitations of prior research on the equity of medical care performed by identifying simple differences in the use of medical care or using limited medical needs and medical utilization indicators. Specifically, we used activity limits, chronic diseases, and subjective health status as medical needs, and used outpatient, inpatient, and emergency services as medical uses. In addition, we used concentration index, concentration curve, and Le Grand factor to analyze the equity of medical use considering medical needs. The main results are as follows. First, the amount of medical care for the low-income class is higher than that of the high-income class when considering the concentration of medical use. In particular, the number of hospitalization days for low-income households and hospitalization fees were higher than the fees of outpatient medical consultation and emergency room usage. Second, medical needs were concentrated in the low income class. In other words, low-income group is not as healthy as the high-income group. Third, the Le Grand factor was calculated in order to confirm the fairness of the medical uses considering the medical needs. Even if medical needs are taken into consideration, the high-income earners will have a large amount of medical care. In addition, when considering the limitation of activity and the number of chronic diseases, the medical use of the high income class was more frequent. However, when the subjective health condition and the chronic illness were considered, medical use of the low income class was more frequent. This may be due to the underestimation of the medical needs of the low-income earners by neglecting their own health status and perception of chronic diseases.