• Journal of the Korean Mathematical Society
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• v.35 no.3
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• pp.793-802
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• 1998

We apply the generalization of Levy's infinitesimal equation $\delta$X(t) = $\psi$(X(s), s $\leq$ t, $Y_{t}$, t, dt), $t\in R^1$, for a random field X (C) indexed by a contour C or by a more general set. Assume that the X(C) is homogeneous in x, say of degree n, then we can appeal to the classical theory of variational calculus and to the modern theory of white noise analysis in order to discuss the innovation for the X (C.)

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1994.10a
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• pp.121-125
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• 1994

본 논문에서는 Hu에 의해 고안된 random 탐색법과 조합된 tabu 탐색법(radnom tabu 탐색법)을 결합계수를 구하는 학습 알고리즘으로 직접 사용하여 국소적 최적해에 수렴하는 것을 방지하고, 수렴정도를 개선하는 새로운 방법을 제안한다. 이 방법을 배타적 논리합 문제에 적용하여 역전파법 및 tabu 탐색법을 이용한 오차역전파법과 비교한다. 그리고, 각 파라메터가 오차함수의 수렴에 미치는 영향을 조사한다.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1996.10a
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• pp.301-306
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• 1996

A torsional damper is generally used to reduce the torsional vibration which occurs at a crankshaft of a multi-cylinder high speed diesel engine. Vibration amplitude should be estimate by the appropriate simulation model to determine the optimum specifications of damper. In this paper a new method which was based on the random tabu search method(RTSM) would be introduced for the viscous damper design to optimize the damping performance. The result was ascertained by comparing with conventional rubber damper.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.51 no.7
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• pp.387-398
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• 2002

In this paper, a new Three-Phase Lead-Lag Random Pulse Position PWM(LL-RPWM) scheme is proposed and implemented for decreasing audible acoustic noise of motor drives. In the proposed RPWM(Random PWM), each of three phase pulses is located randomly in each switching interval. Based on the space vector modulation technique, the duty ratio of the pulses is calculated. Along with the randomization of the PWM pulses, we can obtain the effects of spread spectra of voltage, current as in the case of randomly changed switching frequency. To verify the validity of the proposed LL-RPWM, the simulation and experimental study was tried. Along with the randomization PWM pulses, the space vector modulation is also executed in the C167 micro-controller. The simulation and experimental results show that the voltage and current harmonics are spread to a wide band area and that the audible acoustic noise is reduced by the proposed RPWM method.

• Journal of Institute of Control, Robotics and Systems
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• v.22 no.11
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• pp.977-983
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• 2016

This paper proposes a novel code-tracking scheme to track the fine code synchronization for BOC (pn,n)-modulated global navigation satellite system signals in a repeat-back jamming environment. The correlation function of BOC (pn,n)-modulated signals has several peaks. The correlation function in the advanced offset region remains almost unchanged due to the repeat-back signals being received later than a line-of-sight signal in the same multipath signal receiving case. Additionally, the combined pseudo-random noise signal can be treated as repeat-back jamming signals, like multipath signals. In this paper, we propose a novel code-tracking scheme utilizing the advantages of using a combined pseudo-random noise signal in the advanced offset region and verify its performance through simulation.

• Publications of The Korean Astronomical Society
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• v.30 no.2
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• pp.433-437
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• 2015

We show the results of a time series analysis of the long-term light curves of four blazars. 3C 279, 3C 345, 3C 446, and BL Lacertae. We used densely sampled light curves spanning 32 years at three frequency bands (4.8, 8, 14.5 GHz), provided by the University of Michigan Radio Astronomy Observatory monitoring program. The spectral indices of our sources are mostly flat or inverted (-0.5 < ${\alpha}$ < 0), which is consistent with optically thick emission. Strong variability was seen in all light curves on various time scales. From the analyses of time lags between the light curves from different frequency bands and the evolution of the spectral indices with time, we find that we can distinguish high-peaking flares and low-peaking flares according to the Valtaoja et al. classification. The periodograms (temporal power spectra) of the light curves are in good agreement with random-walk power-law noise without any indication of (quasi-)periodic variability. We note that random-walk noise light curves can originate from multiple shocks in jets. The fact that all our sources are in agreement with being random-walk noise emitters at radio wavelengths suggests that such behavior is a general property of blazars. We are going to generalize our approach by applying our methodology to a much larger blazar sample in the near future.

• Aerospace Engineering and Technology
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• v.9 no.1
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• pp.151-157
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• 2010

The tracking radars in NARO space center are precious, long-range tracking systems for tracking the launch vehicle (KSLV-1) and transmitting TSPI (Time, Space and Position Information) data to MCC (Mission Control Center). Because TSPI data from tracking radars to MCC are important information for the launch mission and flight safety control, TSPI data are required to be more accurate. In this paper, we analyzed theoretically the required specification of the random noise error in tracking radar and verified the real random noise error. In this analysis, we evaluated the TSPI data of several flight tests performed in NARO space center.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.24 no.11
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• pp.840-845
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• 2014

Vibration profiles consist of two kinds of pattern, random and harmonic, at general engineering problems and the detailed vibration test mode of a target system is decided by the spectral condition that is exposed under operation. In moving mobility, random responses come generally from road source; whereas the harmonic responses are triggered from rotating machinery parts, such as combustion engine or drive shaft. Different spectral input may accumulate different damage in frequency domain since the accumulated fatigue damage dependent on the pattern of input spectrum in high cyclic loading condition. To evaluate the sensitivity of spectral damage according to different loading conditions, a linear elastic system is introduced to conduct a uniaxial vibration testing. Measured data, acceleration and strain, is analyzed using energy isocline function and then, the calculated fatigue damage is compared by different loading cases, random and harmonic.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.8 no.8
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• pp.1713-1718
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• 2004

It has been known that 1/f noise of MOSFET is generated by the superposition of single random telelgraph signals (RTS). In this study, jitters caused by 1/f noise of MOSFET are analysed with RTS supplied to all of the nodes of the CMOS ring oscillator under investigation. Through the analysis of the variations of jitters and jitter ratios with varying values of the amplitude of RTS, it is found that the jitters and the jitter ratios are proportional to the amplitude of RTS. And the analysis of FFT of the outputs of the ring oscillator reveals that the jitters are closely related to the phase noise of the high order harmonics of the ring oscillator outputs.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.51 no.3
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• pp.120-125
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• 2002

The switching-mode power converter has been widely used because of its features of high efficiency and small weight and size. These features are brought by the ON-OFF operation of semiconductor switching devices. However, this switching operation causes the surge and EMI(Electromagnetic Interference) which deteriorate the reliability of the converter themselves and entire electronic systems. This problem on the surge and noise is one of the most serious difficulties in AC-to-DC converter. In the switching-mode power converter, the output voltage is generally controlled by varying the duty ratio of main switch. When a converter operates in steady state, duty ratio of the converter is kept constant. So the power of switching noise is concentrated in specific frequencies. Generally, to reduce the EMI and improve the immunity of converter system, the switching frequency of converter needs to be properly modulated during a rectified line period instead of being kept constant. Random Pulse Width Modulation (RPWM) is performed by adding a random perturbation to switching instant while output-voltage regulation of converter is performed. RPWM method for reducing conducted EMI in single switch three phase discontinuous conduction mode boost converter is presented. The more white noise is injected, the more conducted EMI is reduced. But output-voltage is not sufficiently regulated. This is the reason why carrier frequency selection topology is proposed. In the case of carrier frequency selection, output-voltage of steady state and transient state is fully regulated. A RPWM control method was proposed in order to smooth the switching noise spectrum and reduce it's level. Experimental results are verified by converter operating at 300V/1kW with 5%~30% white noise input. Spectrum analysis is performed on the Phase current and the CM noise voltage. The former is measured with Current Probe and the latter is achieved with LISN, which are connected to the spectrum analyzer respectively.