• The Korean Journal of Applied Statistics
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• v.22 no.3
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• pp.499-513
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• 2009

An economic signal in the real world usually reflects complex phenomena. One may have difficulty both extracting and interpreting information embedded in such a signal. A natural way to reduce complexity is to decompose the original signal into several simple components, and then analyze each component. Spectral analysis (Priestley, 1981) provides a tool to analyze such signals under the assumption that the time series is stationary. However when the signal is subject to non-stationary and nonlinear characteristics such as amplitude and frequency modulation along time scale, spectral analysis is not suitable. Huang et al. (1998b, 1999) proposed a data-adaptive decomposition method called empirical mode decomposition and then applied Hilbert spectral analysis to decomposed signals called intrinsic mode function. Huang et al. (1998b, 1999) named this two step procedure the Hilbert-Huang transform(HHT). Because of its robustness in the presence of nonlinearity and non-stationarity, HHT has been used in various fields. In this paper, we discuss the applications of the HHT and demonstrate its promising potential for non-stationary financial time series data provided through a Korean stock price index.

• Journal of Biomedical Engineering Research
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• v.26 no.1
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• pp.55-63
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• 2005

A novel imaging system for High-resolution Ultrasonic Transmission Tomography (HUTT) and soft tissue differentiation methodology for the HUTT system are presented. The critical innovation of the HUTT system includes the use of sub-millimeter transducer elements for both transmitter and receiver arrays and multi-band analysis of the first-arrival pulse. The first-arrival pulse is detected and extracted from the received signal (i.e., snippet) at each azimuthal and angular location of a mechanical tomographic scanner in transmission mode. Each extracted snippet is processed to yield a multi-spectral vector of attenuation values at multiple frequency bands. These vectors form a 3-D sinogram representing a multi-spectral augmentation of the conventional 2-D sinogram. A filtered backprojection algorithm is used to reconstruct a stack of multi-spectral images for each 2-D tomographic slice that allow tissue characterization. A novel methodology for soft tissue differentiation using spectral target detection is presented. The representative 2-D and 3-D HUTT images formed at various frequency bands demonstrate the high-resolution capability of the system. It is shown that spherical objects with diameter down to 0.3㎜ can be detected. In addition, the results of soft tissue differentiation and characterization demonstrate the feasibility of quantitative soft tissue analysis for possible detection of lesions or cancerous tissue.

• Journal of the Earthquake Engineering Society of Korea
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• v.1 no.2
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• pp.17-29
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• 1997

Single-mode spectral analysis method is usually applied to a small-scale bridges with the simple geometric shape and uses only fundamental period to estimate the elastic earthquake forces and the displacements of the substructure. On the other hand, multi-mode spectral analysis method may be used instead if the possibilities of potential damage are developed when considering significance, scale, and geometric shape of briages. Since the dynamic responses of bridge can be significantly different depending on the modeling techniques for the restraint and support conditions etc, it may be misled to the unexpected results. In this study the dynamic analysis program which can model and analyze the bridge as a two- or three-dimensional framed structure is developed and verified with the results of other reliable program. Using this program together with the post processor, the designer can easily and readily obtain the reponses(moments, base shears, and displacements)of bridges necessary to design purpose. And further from the analysis results according to the variations of type, scale, and restraint and supprot conditions of bridges including sectional properties, applications of the effective and desirable seismic design are presented.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1999.04a
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• pp.159-168
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• 1999

In seismic analysis, there are two main ways - uniform load method and dynamic analysis, dynamic analysis can be divided into response spectrum analysis and time history analysis. In case of which get the complexion of the vibration with 3-axis of coordinate direction in each mode of free vibration mode happened owing to complication of the shape, 3-dimensional dynamic analysis is recommended to perform as multi-mode spectral analysis in standard specification for highway bridge. The purpose of this study is to understand the dynamic behavior by performing multi-mode seismic analysis according to responses analysis and time history anal)'sis in using record of earthquake. In accordance with the criterion of seismic design as defined in standard specification for highway bridge by using modified records of the El Centre and Coyote Lake earthquake, response spectrum was constructed by using the tripartite logarithmic plot. The 3-span continuous space truss bridge was selected as model of numerical analysis. As the result performed time history analysis and analysis of response spectrum for the model of numerical analysis, the result of time history analysis was slightly larger than that of response spectrum analysis. This coincide with the tendency of the result came from the analysis when using a jagged response spectrum analysis, This coincide with the tendency of the result came from the analysis when using a jagged response spectrum for a single excitation. In the Process of performing these two analysis. response spectrum analysis is more effective than time history analysis in saving times in analyzing data.

• Journal of the Korean Society of Safety
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• v.31 no.4
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• pp.104-110
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• 2016

The effect of a partially earth anchored cable system on the structural safety of a long span cable-stayed bridge under seismic and wind loads are examined during construction process. By assuming the FCM (free cantilever method) construction stages with structural vulnerability, a multi-mode spectral analysis and a multi-mode buffeting analysis are performed for specific seismic load and wind load, respectively. Results show that the wind load dominates the structural safety of a cable-stayed bridge during construction. And, the application of a partially earth anchored cable system can enhance structural safety under wind load since the maximum pylon moment in the model with partially earth anchored cable system is reduced by 49% under wind load. In contrast, the maximum pylon moment occurred by seismic load is only decreased by 8%.

• Proceedings of the Korea Water Resources Association Conference
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• 2006.05a
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• pp.1450-1454
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• 2006

Empirical mode decomposition (EMD) is applied to analyze time series characterized with nonlinearity and nonstationarity. This decomposition could be utilized to construct finite and small number intrinsic mode functions (IMF) that describe complicated time series, while admitting the Hilbert transformation properties. EMD has the capability of being adaptive, capture local characteristics, and applicable to nonlinear and nonstationary processes. Unlike discrete wavelet transform (DWT), IMF eliminates spurious harmonics and retains meaningful instantaneous frequencies. Examples based on data representing natural phenomena are given to demonstrate highlight the power of this method in contrast and comparison of other ones. A presentation of the energy-frequency-time distribution of these signals found to be more informative and intuitive when based on Hilbert transformation.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2000.10a
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• pp.341-347
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• 2000

Even for the same structure, the analysis results as well as design values might have differences depending on the selected analysis model. Therefore it is desirable to determin model considering the required accuracy of the analysis results, the given time restried economy. " Standard Specification for Roadway Bridges" Division V, Seismic Design prove "Single Mode Spectral Analysis Method" as the basic analysis method for the earthquake design of roadway bridges classified as "regular". In this study a 5 span steel box girl selected which satisfies the regularity and the applicability of the provided analysis simplified model in checked. For the comparision of the analysis results, "Multi-Mode Spect Method" is used with a detailed model.hod" is used with a detailed model.odel.

• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.3
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• pp.16-22
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• 2013

A general characterization procedure based on the extraction of a 2n-port admittance matrix corresponding to n uniform coupled lines on the multi-layered substrate using the Finite-Difference Time-Domain (FDTD) technique is presented. In this paper, the frequency-dependent normal mode parameters are obtained from the 2n-port admittance matrix to analyze multi-layered asymmetric coupled line structure, which in turn provides the frequency-dependent propagation constant, effective dielectric constant, and line-mode characteristic impedances. To illustrate the technique, several practical coupled line structures on multi-layered substrate have been simulated. Especially, embedded conductor structures have been simulated. Comparisons with Spectral Domain Method are given, and their results agree well. It is shown that the FDTD based time domain characterization procedure is an excellent broadband simulation tool for the design of multiconductor coupled lines on multilayered PCBs as well as thick or thin hybrid structures.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 1998.04a
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• pp.89-97
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• 1998

This study is intended to investigate the seismic responses of bridge structures considering site effects. The site effects in the seismic analysis of bridge structures were classified into two parts. At first, the seismic responses of the structures on each "soil profile types" of the code were evaluated in accordance with code-specified method and compared with results of time-history analysis method. And next, as a second stage of the study, the responses of the two different soil with considerably different soil properties, even though they are classified to the same "soil profile types" of the code, were evaluated and compared each other. The first part of study is purposed to evaluate the applicability of code-specified method, while the other part is purposed to find the variance of the seismic responses from the different soil sites in the same soil profile types of the code. For the analysis, two major methods of the code, single-mode spectral anaysis and multi-mode spectral analysis, were used and the time-history analysis method which is expected to give more accurate responses was also used for the comparison purposes. For the time-history analysis, time-domain analysis technique of the lumped-mass model with frequency-independent soil springs and dampers was adopted and artificially generated spectra of the code was used as input motion. As the results of the study, the code specified methods for the seismic responses considering the site effects were verified to give the results in conservative side for the most of the cases. However, for the structures on the site with considerable flexibility, the responses of the bridge girders or deckplates by the code methods both in section forces and horizontal movement responses, may have much smaller values than the actual responses. Therefore, more detailed analysis considering the flexibility of the base soil may be required to have more reasonable results in girder responses.in girder responses.

• Wind and Structures
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• v.12 no.3
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• pp.259-279
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• 2009

The paper is concerned with the numerical study of the cross-wind response of the 295 m-tall six-flue industrial chimney, located in the power station of Belchatow, Poland. The response of the chimney due to turbulent wind flow is caused by the lateral turbulence component and vortex excitation with taking into account motion-induced wind forces. The cross-wind response has been estimated by means of the random vibration approach. Three power spectral density functions suggested by Kaimal, Tieleman and Solari for the evaluation of the lateral turbulence component response are taken into account. The vortex excitation response has been calculated by means of the Vickery and Basu's model including some complements. Motion-induced wind forces acting on a vibrating chimney have been modeled as a nonlinear aerodynamic damping force. The influence of three components mentioned above on the total cross-wind response of the chimney has been investigated. Moreover, the influence of damping ratios, evaluated by Multi-mode Random Decrement Technique, and number of mode shapes of the chimney have been examined. Computer programmes have been developed to obtain responses of the chimney. The numerical results and their comparison are presented.