• Journal of Astronomy and Space Sciences
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• 제6권1호
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• pp.41-47
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• 1989

RS CVn형 변광성 Hㅇ 8358을 1987년 10우러부터 1988년 12월까지 총 15일간 소백산천문대의 61cm 반사망원경으로 UBV 광전관측을 하여 새로운 광도 곡선을 얻었다. 우리의 광도곡선에서는 두 개의 극대광도가 보였다. 한편, 극대광도가 관측된 날들의 극대 시각들을 조사한 결과, 그때의 위상이 계속 변함을 알았다. 또한 1987년 10월 -1988년 1월의 관측 값에 비해서, 1988년 11월 -12월의 관측 값이 $\Delta(b-\upsilon)$는 청색화해졌으나 $\Delta(u-b)$는 적생화해졌다.

• Journal of Astronomy and Space Sciences
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• 제14권1호
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• pp.18-23
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• 1997

We present X-ray light curves and the energy spectra for two contact binaries SW Lac and W UMa, which are obtained from the ASCA(Advanced Satellite for Cosmology and Astrophysics) observations. We find that both sources show appreciable flux variations during the observatoins, and the variations are erratic and are not orbital-phase dependent. From a spectral analysis, we also find that the W UMa spectrum can be reproduced by a variable-abundance plasma model with a single temperature of $T_1=6.8{\times}10^6K$, while the SW Lac spectrum requires two different temperatures $T_1=6.5{\times}10^6K$ and $T_2=1.4{\times}10^7K$.

• 제어로봇시스템학회논문지
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• 제7권2호
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• pp.173-182
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• 2001

Ascent trajectory optimization and optimal explicit guidance problems for a satellite launch vehicle in a 2-dimensional pitch plane are studied. The trajectory optimization problem with boundary conditions is formulated as a nonlinear programming problem by parameterizing the pitch attitude control variable, and is solved by using the SQP algorithm. The flight constraints such as gravity-turn are imposed. An optimal explicit guidance algorithm in the exoatmospheric phase is also presented, the guidance algorithm provides steering command and time-to-go value directly using the current states of the vehicle and the desired orbit insertion conditions. To verify the optimality and accuracy of the algorithm simulations are performed.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2006년도 하계종합학술대회
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• pp.215-216
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• 2006

In this paper, the antenna the with linear active phased array of $1{\times}16$ operated in DBS band was designed. The antenna was composed of sixteen radiating elements, sixteen active channels and five Wilkinson power combiners with 4-channel inputs, a digital control board and a stabilizing DC bias board. The radiating element of the array has the structure of a microstrip stack patch with a left-hand circular polarization. And, each active channel consists of a low noise ampilifier, a 3-bit digital phase shifter and a variable analog attenuator. The breadboard of linear active phased array antenna was also fabricated to test the electrical performances. The radiation patterns of the antenna were measured after correcting initial phases of each active channel in aechoic chamber. And also, the beam scanning chracteristcs of $10^{\circ}$, $20^{\circ}$, $30^{\circ}$ were measured.

• JSTS:Journal of Semiconductor Technology and Science
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• 제16권4호
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• pp.520-527
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• 2016

A new dual-loop digital delay-locked loop (DLL) using a hybrid (binary + sequential) search algorithm is presented to achieve both wide-range operation and high delay resolution. A new phase-interpolation range selector (PIRS) and a variable successive approximation register (VSAR) algorithm are adopted to resolve the boundary switching and harmonic locking problems of conventional digital DLLs. The proposed digital DLL, implemented in a $0.18-{\mu}m$ CMOS process, occupies an active area of $0.19mm^2$ and operates over a wide frequency range of 0.15-1.5 GHz. The DLL dissipates a power of 11.3 mW from a 1.8 V supply at 1 GHz. The measured peak-to-peak output clock jitter is 24 ps (effective pk-pk jitter = 16.5 ps) with an input clock jitter of 7.5 ps at 1.5 GHz. The delay resolution is only 2.2 ps.

• 한국군사과학기술학회지
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• 제13권6호
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• pp.1043-1050
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• 2010

This paper examined the probabilistic load analysis for the tailplane during pitching maneuvering in the conceptual aircraft design phase. The flight load analysis based on the probabilistic distribution of design variables are compared with the results of the deterministic analysis. Two forms of variable distribution are used in this paper. One is standard normal distribution, the other distribution is calculated from the results of short-period longitudinal equation of aircraft motion. The influence of the distribution parameter on the probabilistic load analysis was investigated and the significant design variables that have an impact on the mean and variance of probabilistic load were identified. The comparison indicates that probabilistic load analysis provides more reliable probabilistic load distribution for the structural design than the traditional deterministic analysis.

• 전기학회논문지
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• 제61권12호
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• pp.1959-1963
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• 2012

Since electric railway load is variable largely due to starting and braking characteristics as well as various operation patterns, load modeling is not easy but complicated. For this reason, a simple technique for modeling of electric railway load of is required to analyze the AC substation system of electric railway. In this paper, a modeling technique of converter-based electric railway load is proposed and is tested using nonlinear loads on Matlab/Simulink.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1998년도 하계학술대회 논문집 C
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• pp.1244-1246
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• 1998

This paper present a variety fault problem brought out with the multifunctional Battery Energy Storage System [MBESS] expected to be practical in the short future interconnected to power distribution system. Multifunctional BESS model and interconnection model to power system is simply configured, the problems of protection coordination and operation is studied. A line fault in the power distribution system are discussed such as line to ground and three phase fault in order to show the impact on power utilities, demand-side and BESS-side. In order to simulate a variable transient phenomenon due to 2 the BESS interconnection operation to power distribution system, in this paper, PSCAD/EMTDC simulation tools is used.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1995년도 하계학술대회 논문집 B
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• pp.784-786
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• 1995

Variable Structure Control(VSC) scheme with sliding mode is widely used to keep a control system insensitive to parameter variations and disturbances. However, the conventional sliding mode control has the undesired phenomenon of chattering which may become a serious problem. Also the restriction of the sliding mode regime cannot guarantee the insensitivity throughout an entire response. In this paper, the sliding surfaces, which are composed of three-line segments, are used to remove the reaching phase. Also, the concept of fuzzy logic is incorporated with the sliding mode control in order to control the unknown or partially known systems effectively. The proposed method is applied to a Double-Sided MM Type LDM to show its usefulness.

• 한국추진공학회지
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• 제2권3호
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• pp.90-98
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• 1998

본 연구에서 개발한 고압증발 모델을 이용하여 고압 연소장에서의 액체연료추진제의 증발 과정을 수치적으로 해석하였다. 고압상태에서 액적의 증발 특성에 중요한 영향을 미치는 실제 기체의 거동, 온도 및 압력에 따른 가변물성치의 영향, 주위기체의 용해현상을 고려하였고 일반적인 상평형 관계식을 이용하였다. 실험치와 비교하여 고압증발모델의 예측능력을 체계적으로 검증하였고 로켓엔진의 고온 고압 연소실조건에서 LOX 액적의 증발 특성을 상세하게 논의하였다.