• 대한조선학회지
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• 제24권2호
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• pp.36-46
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• 1987

This paper presents the results of seakeeping tests in a container ship model in irregular head waves. A time domain signal generating procedure is devised so that the wave maker behaves in accordance with the specified wave spectrum. The surface elevation of generated waves is measured and analysed to render the recorded wave spectrum for comparison with the specified one. Correction is made to the time domain signal until the differences between the two spectra become negligible. The motion responses and vertical acceleration of the self-propelled ship model are measured and analysed by both the spectral and the double amplitude methods. The two methods give nearly same statistical values. Finally the recorded spectra are compared with those calculated from the frequency domain motion analysis to show the credibility of the experimental results.

• 동력기계공학회지
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• 제8권4호
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• pp.11-16
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• 2004

In this study, to investigate the effects of omitting low-amplitude cycles from a flight-simulation loading, crack growth tests were conducted on 2124-T851 aluminum alloy specimens. Three test spectra were generated by omitting small load ranges as counted by the rain-flow count method. The crack growth test results were compared with the data obtained from the flight-simulation loading. The experimental results show that the ranges equal to or smaller than 5% of the maximum load do not contribute to crack growth behavior because these are below the initial stress intensity factor range. Omitting these from the flight-simulation loading, test time can be reduced by 54%. However, in the case of omitting the load ranges below 15% of the maximum load, crack growth rates decreased, and crack growth curve deviated from the crack growth data under the flight-simulation loading because loading cycles above fatigue fracture toughness were omitted.

• 천문학회보
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• 제39권2호
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• pp.76.1-76.1
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• 2014

We present near-infrared spectroscopic and photometric observations of the nova V2468 Cyg taken from 2008 March 14 till 2008 November 11 following its outburst on 2008 March 7. The JHK spectra of the nova have been taken from the Mount Abu Infrared Observatory using the Near-Infrared Imager/Spectrometer. The early spectra are dominated by strong H I lines from the Brackett and Paschen series, Fe II, O I and C I lines, typical of Fe II type novae but after 46 days from outburst there is significant reduction in the strength of the C I lines and the spectra are dominated by He I lines. The FWHM of the Pa-beta and Br-gamma lines change from 2200-2300 km s-1 to 1700-1800 km s-1 after 12 days from outburst. Three additional small amplitude outbursts are seen near 110, 185 and 240 days in the V band light curve after the discovery. The upper limit for the ejecta mass for V2468 Cyg is estimated to be $5.2{\times}10-6Msun$.

• Nuclear Engineering and Technology
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• 제55권3호
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• pp.968-980
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• 2023

The dynamic structural responses are sensitive to the time-frequency content of seismic waves, and seismic input motions in time-history analysis are usually required to be compatible with design response spectra according to nuclear codes. In order to generate spectra-compatible input motions while maintaining the intrinsic non-stationarity of seismic waves, an improved time-domain approach is proposed in this paper. To maintain the nonstationary characteristics of the given seismic waves, a new time-frequency envelope function is constructed using the Hilbert amplitude spectrum. Based on the intrinsic mode functions (IMFs) obtained from given seismic waves through variational mode decomposition, a new corrective time history is constructed to locally modify the given seismic waves. The proposed corrective time history and time-frequency envelope function are unique for each earthquake records as they are extracted from the given seismic waves. In addition, a dimension reduction iterative technique is presented herein to simultaneously superimpose corrective time histories of all the damping ratios at a specific frequency in the time domain according to optimal weights, which are found by the genetic algorithm (GA). Examples are presented to show the capability of the proposed approach in generating spectra-compatible time histories, especially in maintaining the nonstationary characteristics of seismic records. And numerical results reveal that the modified time histories generated by the proposed method can obtain similar dynamic behaviors of AP1000 nuclear power plant with the natural seismic records. Thus, the proposed method can be efficiently used in the design practices.

• 지구물리와물리탐사
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• 제7권1호
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• pp.45-50
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• 2004

This paper describes a method of detecting formation boundaries, and permeable fractures, from frequency-domain Stoneley wave logs. Field data sets were collected between the depths of 330 and 360 m in well EE-4 in the Higashi-Hachimantai geothermal field, using a monopole acoustic logging tool with a source central frequency of 15 kHz. Stoneley wave amplitude spectra were calculated by performing a fast Fourier transform on the waveforms, and the spectra were then collected into a frequency-depth distribution of Stoneley wave amplitudes. The frequency-domain Stoneley wave log shows four main characteristic peaks at frequencies 6.5, 8.8, 12, and 13.3 kHz. The magnitudes of the Stoneley wave at these four frequencies are affected by formation properties. The Stoneley wave at higher frequencies (12 and 13.3 kHz) has higher amplitudes in hard formations than in soft formations, while the wave at lower frequencies (6.5 and 8.8 kHz) has higher amplitudes in soft formations than in hard formations. The correlation of the frequency-domain Stoneley wave log with the logs of lithology, degree of welding, and P-wave velocity is excellent, with all of them showing similar discontinuities at the depths of formation boundaries. It is obvious from these facts that the frequency-domain Stoneley wave log provides useful clues for detecting formation boundaries. The frequency-domain Stoneley wave logs are also applicable to the detection of a single permeable fracture. The procedure uses the Stoneley wave spectral amplitude logs at the four frequencies, and weighting functions. The optimally weighted sum of the four Stoneley wave spectral amplitudes becomes almost constant at all depths, except at the depth of a permeable fracture. The assumptions that underlie this procedure are that the energy of the Stoneley wave is conserved in continuous media, but that attenuation of the Stoneley wave may occur at a permeable fracture. This attenuation may take place at anyone of the four characteristic Stoneley wave frequencies. We think our multispectral approach is the only reliable method for the detection of permeable fractures.

• 한국의학물리학회지:의학물리
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• 제6권2호
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• pp.61-70
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• 1995

헤마토포르피린 유도체는 광역학 치료를 위한 활성감응제로 이용되고 있다. 본 연구는 헤마토포르피린 유도체 분자의 암세포와의 에너지 전달과정을 조사하기 위하여 동시 모드록킹된 색소 레이저와 ~70 피코초 ($10^{-12}$ sec) 시산 분해능을 갖는 단일광자 계수장치 장치를 이용하여 용액에서와 암세포에서 각각 시간분해 형광 스펙트럼을 측정 분석하였다. 측정된 스펙트럼은 deconvolution 방법으로 곡선맞춤되었는데 단량체의 느린 소멸 ($\tau$$_1$=6.3 ㎱)과 이량체의 빠른 소멸 ($\tau$$_1$= 250 ㎰)로 분석되었으며 정상상태에서의 흡수 및 형과 스펙트럼의 결과와 일치하였다. 농도를 일정하게 하고 극성 분자를 5%에서 95%까치 증가시키면서 형광 소멸 곡선을 측정하여 곡선 맞춤과 결과 빠른 소멸성분 ( $A_2$) 값이 증가하였으며 그 증가 폭이 비극성 분자인 메탄올에서 보다 현저하게 나타났다. 헤마토포르피린 유도체 용액에 암세포를 자연 부유시켜 형광 소멸 곡선을 비교 분석한 결과 암세포에 흡착되었을 때 유효 형광 수명 시간이 감소하였다. 이것은 단량체에 비하여 이량체가 암세포의 흡착에 관여하고 있다는 증거로 분석되었다.

• 한국지구과학회지
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• 제28권2호
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• pp.179-186
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• 2007

응답스펙트럼은 내진설계에 있어서 중요한 기초자료의 하나이다. 응답스펙트럼을 얻기 위하여, 한반도에서 발생하는 지진들의 지진원 특성에 근거하여 다수의 강진동을 Boore(2005)에 의해 개발된 컴퓨터 프로그램 SMSIM을 사용하여 모사하였다. 여러 연구결과들에 대한 충분한 검토를 통하여, 모사에 필요한 입력자료들을 선정하였다. 모사된 강진동으로부터 얻은 응답스펙트럼은 가속도 1.0 g에 대하여 정규화하여 미국 원자력위원회(1973)의 표준응답스펙트럼과 비교하였다. 이 연구에서 얻어진 응답스펙트럼의 스펙트럼 진폭은 대략 10 Hz 이상의 고주파 대역에서 표준 응답스펙트럼 값에 비하여 큰 것으로 나타났다. 또한 응력강하량의 변화에 따른 응답스펙트럼의 변화를 평가하였다. 그 결과 큰 응력강하량에 대한 응답스펙트럼의 스펙트럼 진폭은 저주파 범위내에서 큰 값을 나타냄을 제시하였다.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2000년도 춘계 학술발표회 논문집 Proceedings of EESK Conference-Spring
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• pp.44-48
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• 2000

Several parameters to represent the characteristics of the observed at the domestic networks from several earthquakes occurred in the Korean Peninsula. Parameters to fit most the multiple Fourier amplitude spectra of the observed accelerations are estimated. This study adopts the stochastic ground motion model referred to the BLWN mode in which the energy is distributed randomly over the duration of the source and which has proven to be very effective in modeling a wide range of ground motion observations. The stochastic ground motion model employed here uses an omega-squared ({{{{ omega ^2 }}) Brune source model with a single corner frequency and a constant stress drop,. The {{{{ omega ^2 }} source model has become a seismological standard because of its simplicity an ability to predict spectral amplitudes and shapes over an extremely broad ranges of magnitudes distances and from the inversion show very unstable based on the fact of high values of mean/median. These results may imply that more observed data and more precise site classification including accurate preparation analysis of data such as more accurate scaling from counts to kine are needed for more stable are effective inversion of Fourier amplitude spectrum of the observed ground motions.

• Journal of Power Electronics
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• 제17권2호
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• pp.380-388
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• 2017

Since the carrier sequence is not reproducible in a period of the random carrier pulse width modulation (RCPWM) and a higher harmonic spectrum amplitude is likely to affect the quality of the power supply. In addition, electromagnetic interference (EMI) and mechanical vibration will appear. To solve these problems, this paper has proposed an optimal RCPWM based on a genetic algorithm (GA). In the optimal modulation, the range of the random carrier frequency is taken as a constraint and the reciprocal of the maximum harmonic spectrum amplitude is used as a fitness function to decrease the EMI and mechanical vibration caused by the harmonics concentrated at the carrier frequency and its multiples. Since the problems of the hardware make it difficult to use in practical engineering, this paper has presented a hardware system. Simulations and experiments show that the RCPWM is effective. Studies show that the harmonic spectrum is distributed more uniformly in the frequency domain and that there is no obvious peak in the wave spectra. The proposed method is of great value to research on RCPWM and integrated power systems (IPS).

• 한국전기전자재료학회논문지
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• 제23권3호
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• pp.228-233
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• 2010

We studied the optical characteristics correlated with low dielectric constants of low-k SiOCH thin films through ellipsometry. The low-k SiOCH thin films were prepared by CCP-PECVD method using BTMSM(Bis-trimethylsilylmethane) precursors deposited on p-Si wafer. The Si-O-CHx, Si-O-Si, Si-CHx, CHx and Si-H bonding groups were specified by FTIR spectroscopic spectra, and the groups coupled with the nano-porous structural organic/inorganic hybrid-type of SiOCH thin films which has extremely low dielectric constant close to 2.0. The structural groups includes highly dense pore as well as ions in SiOCH thin films affecting to complex refraction characteristics of single layer on the p-Si wafer. The structural complexity originate the complex refractive constants of the films, and resulted the elliptical polarization of the incident linearly polarized light source of Xe-light source in the range from 190 nm to 2100 nm. Phase difference and amplitude ratio between s wave and p wave propagating through SiOCH thin film was studied. After annealing, the amplitude of p wave was reduced more than s wave, and phase difference between p and s wave was also reduced.