• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1997년도 한국자동제어학술회의논문집; 한국전력공사 서울연수원; 17-18 Oct. 1997
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• pp.1844-1847
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• 1997

Assuming that EEG(electroencephalogram), which is generated by a nonlinear electrical of billions of neurons in the brain, has chaotic characteristics, it is confirmend by frequency spectrum analysis, log frequency spectrum analysis, correlation dimension analysis and Lyapunov exponents analysis. Some chaotic characteristics are related to the degree of brain activity. The slope of log frequency spectrum increases and the correlation dimension decreasess with respect to the activities, while the largest Lyapunov exponent has only a rough correlation.

• 한국항공운항학회지
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• 제15권2호
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• pp.1-8
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• 2007

In this research, algorithm and software for the medium frequency signal analysis of DGPS(Differential Global Positioning System) station were developed. Based on new MF(Medium Frequency) algorithm, the software of NDGPS(National DGPS) signal analysis was developed for coverage analysis. Predicted MF propagation data from this software was compared to the measurement data for the verification of a developed MF algorithm. GIS(Geographic Information System) techniques including digital map with elevation data were used because MF propagation is closely related to ground conductivity, mountains, building intensity.

• Interaction and multiscale mechanics
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• 제5권3호
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• pp.169-185
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• 2012

The concrete bridge is likely to produce fatigue cracks during long period of service due to the moving vehicular loads and the degeneration of materials. This paper deals with the time-frequency analysis of a coupled bridge-vehicle system. The bridge is modeled as an Euler beam with breathing cracks. The vehicle is represented by a two-axle vehicle model. The equation of motion of the coupled bridge-vehicle system is established using the finite element method, and the Newmark direct integration method is adopted to calculate the dynamic responses of the system. The effect of breathing cracks on the dynamic responses of the bridge is investigated. The time-frequency characteristics of the responses are analyzed using both the Hilbert-Huang transform and wavelet transform. The results of time-frequency analysis indicate that complicated non-linear and non-stationary features will appear due to the breathing effect of the cracks.

• 셀메드
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• 제14권2호
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• pp.2.1-2.10
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• 2024

Through big data analysis of the 'Joseonwangjosilok', this study examines the perception of ginseng among the ruling class and its utilization during the Joseon era. It aims to provide foundational data for the development of ginseng into a high-value cultural commodity. The focus of this research, the Joseonwangjosilok, comprises 1,968 volumes in 948 books, spanning a record of 518 years. Data was collected through web crawling on the website of the National Institute of Korean History, followed by frequency analysis of significant words. To assess the interest in ginseng across the reigns of 27 kings during the Joseon era, ginseng frequency records were adjusted based on years in power and the number of articles, creating an interest index for comparative rankings across reigns. Analysis revealed higher interest in ginseng during the reigns of King Jeongjo and King Yeongjo in the 18th century, King Sunjo in the 19th century, King Sejong in the 15th century, King Sukjong in the 17th century, and King Gojong in the 19th century. Examining the temporal emergence and changes in ginseng during the Joseon era, general ginseng types like insam and sansam had the highest frequency in the 15th century. It appears that Korea adeptly utilized ceremonial goods in diplomatic relations with China and Japan, meeting the demand for ginseng from their royal and aristocratic societies. Processed ginseng varieties such as hongsam and posam, along with traded and taxed ginseng, showed peak frequency in the 18th century. This coincided with increased cultivation, allowing a higher supply and fostering the development of ginseng processing technologies like hongsam.

• Geomechanics and Engineering
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• 제7권2호
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• pp.149-164
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• 2014

One of the most advanced classes of techniques for ground response analysis is based on the use of Transfer Functions. They represent the ratio of Fourier spectrum of amplitude motion at the free surface to the corresponding spectrum of the bedrock motion and they are applied in frequency domain usually by FFT method. However, Fourier spectrum only shows the dominant frequency in each time step and is unable to represent all frequency contents in every time step and this drawback leads to inaccurate results. In this research, this process is optimized by decomposing the input motion into different frequency sub-bands using Wavelet Multi-level Decomposition. Each component is then processed with transfer Function relating to the corresponding component frequency. Taking inverse FFT from all components, the ground motion can be recovered by summing up the results. The nonlinear behavior is approximated using an iterative procedure with nonlinear soil properties. The results of this procedure show better accuracy with respect to field observations than does the Conventional method. The proposed method can also be applied to other engineering disciplines with similar procedure.

• 한국해양공학회지
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• 제17권3호
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• pp.46-51
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• 2003

Acoustic emission (AE) signals, emanated during local failure of aluminum alloys, have been the subject of numerous investigations. It is well known that the characteristics of AE are strongly influenced by the previous thermal and mechanical treatment of the sample. Possible sources of AE during deformation have been suggested as the avalanche motion of dislocations, fracture of brittle particles, and debonding of these particles from the alloy matrix. The goal of the present study is to determine if AE occurring as the result of fatigue crack propagation could be evaluated by the joint time-frequency analysis method, short time Fourier transform (STFT), and Wigner-Ville distribution (WVD). The time-frequency analysis methods can be used to analyze non-stationary AE more effectively than conventional techniques. STFT is more effective than WVD in analyzing AE signals. Noise and frequency characteristics of crack openings and closures could be separated using STFT. The influence of various fatigue parameters on the frequency characteristics of AE signals was investigated.

• 한국철도학회논문집
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• 제9권2호
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• pp.187-192
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• 2006

The regularity of railway track alignment is a crucial component fur maintaining travel safety and the smoothness of passenger ride. The conventional spectral analysis has been considered to estimate the severity of the track irregularity from measured data. The time domain data used to be changed into the frequency domain by Fourier transform. Because the measuring points can be regarded as the time points, the spatial-frequency can be introduced instead of the time-frequency. Although FFT(Fast Fourier Transform) and/or PSD(Power Spectral Density) function could provide fairly localized information within frequency domain, but chronical configurations of data could be missed. In this study, we attempt to apply the Morlet wavelet transform for the purpose of a frequency-time-domain analysis rather than a frequency-domain analysis. The applicability of wavelet transform is examined for the estimation of the track irregularity with real measured track data on the section of Kyoung-bu line by EM-120 measuring vehicle. It is shown that the wavelet transform can be an effective tool to manage the track irregularity.

• Journal of the Optical Society of Korea
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• 제18권5호
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• pp.558-563
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• 2014

Sum-frequency generation spectra of a Langmuir monolayer on water surface at varying surface areas were studied with two-dimensional correlation analysis. Upon enlarging the area/molecule of the Langmuir monolayer, the sum-frequency spectra changed reflecting the conformation change of the alkyl chains of the molecules in the monolayer. These changes stood out more clearly by employing two-dimensional correlation analysis of the above sum-frequency spectra. Features not very pronounced in the original spectra such as closely-spaced spectral bands can also be easily distinguished in the two-dimensional correlation spectra.

• 대한의용생체공학회:의공학회지
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• 제17권2호
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• pp.155-164
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• 1996

In the clinical environment, measurements of some characteristics of the skeletal muscle are currently used to assess the severity of a neuromuscular disease or in some cases to assist in making a diagnosis. But a quantitative method of evaluation has not yet been introduced satisfactorily. In this paper, the skeletal EMG(biceps muscle, masseter muscle) analysis has been processed both in the time and in the frequency domain by designing the digital signal processing system based on pentium PC and transputer (IMS 7805). The experiment have been performed in five normal subjects, and various parameters have been statistically tested and compare4 As a results, the effective parameters obtained for the evaluation of skeletal EMG electrical activity are turn analysis, MiTi, MiTa, IEMG, PDF in the time domain, and are mean frequency, median frequency, skewness, kurtosis, muscle fatigue slope in the frequency domain. The designed H/W and S/W in this study can be used effectively for the establishment of EMG data base and for clinical research.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2002년도 proceedings of the second asia international conference on tribology
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• pp.273-274
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• 2002

In order to evaluate the flying characteristics of slider, the acoustic emission (AE) as well as friction signals are typically utilized. In this work the frequency spectrum analysis is performed using the AE signal obtained during the head/disk interaction such as load/unload mechanism using ramp, impact situation in the presence of a bump on disk surface and other contact phenomena including particle interaction. It was shown that the influence of impact can be characterized effectively in the AE frequency spectrum. As a result of this work, frequency spectrum analysis will be utilized with better understanding for studying the head/disk interface (HDI) characteristics and monitoring the particle interaction in HDI effectively.