• Journal of the Korean Statistical Society
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• 제33권4호
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• pp.459-470
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• 2004

We study the approximation of the solution of linear stochastic evolution equations driven by infinite-dimensional fractional Brownian motion with Hurst parameter H > 1/2 through discretization of space and time. The rate of convergence of an approximation for Euler scheme is established.

• 한국지진공학회논문집
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• 제23권5호
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• pp.269-277
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• 2019

In a seismic design, a structural demand by an earthquake load is determined by design response spectra. The ground motion is a three-dimensional movement; therefore, the design response spectra in each direction need to be assigned. However, in most design codes, an identical design response spectrum is used in two horizontal directions. Unlike these design criteria, a realistic seismic input motion should be applied for a seismic evaluation of structures. In this study, the definition of horizontal spectral acceleration representing the two-horizontal spectral acceleration is reviewed. Based on these methodologies, the horizontal responses of observed ground motions are calculated. The data used in the analysis are recorded accelerograms at the stations near the epicenters of recent earthquakes which are the 2007 Odeasan earthquake, 2016 Gyeongju earthquake, and 2017 Pohang earthquake. Geometric mean-based horizontal response spectra and maximum directional response spectrum are evaluated and their differences are compared over the period range. Statistical representation of the relations between geometric mean and maximum directional spectral acceleration for horizontal direction and spectral acceleration for vertical direction are also evaluated. Finally, discussions and suggestions to consider these different two horizontal directional spectral accelerations in the seismic performance evaluation are presented.

• Wind and Structures
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• 제18권6호
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• pp.693-715
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• 2014

Stochastic processes are used to represent phenomena in many diverse fields. Numerical simulation method is widely applied for the solution to stochastic problems of complex structures when alternative analytical methods are not applicable. In some practical applications the stochastic processes show non-Gaussian properties. When the stochastic processes deviate significantly from Gaussian, techniques for their accurate simulation must be available. The various existing simulation methods of non-Gaussian stochastic processes generally can only simulate super-Gaussian stochastic processes with the high-peak characteristics. And these methodologies are usually complicated and time consuming, not sufficiently intuitive. By revealing the inherent coupling effect of the phase and amplitude part of discrete Fourier representation of random time series on the non-Gaussian features (such as skewness and kurtosis) through theoretical analysis and simulation experiments, this paper presents a novel approach for the simulation of non-Gaussian stochastic processes with the prescribed amplitude probability density function (PDF) and power spectral density (PSD) by amplitude modulation and phase reconstruction. As compared to previous spectral representation method using phase modulation to obtain a non-Gaussian amplitude distribution, this non-Gaussian phase reconstruction strategy is more straightforward and efficient, capable of simulating both super-Gaussian and sub-Gaussian stochastic processes. Another attractive feature of the method is that the whole process can be implemented efficiently using the Fast Fourier Transform. Cases studies demonstrate the efficiency and accuracy of the proposed algorithm.

• 대한원격탐사학회지
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• 제10권2호
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• pp.37-48
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• 1994

In spatial information processing, particularly in non-renewable resource exploration, the spatial data sets, including remote sensing, geophysical and geochemical data, have to be geocoded onto a reference map and integrated for the final analysis and interpretation. Application of a computer based GIS(Geographical Information System of Geological Information System) at some point of the spatial data integration/fusion processing is now a logical and essential step. It should, however, be pointed out that the basic concepts of the GIS based spatial data fusion were developed with insufficient mathematical understanding of spatial characteristics or quantitative modeling framwork of the data. Furthermore many remote sensing and geological data sets, available for many exploration projects, are spatially incomplete in coverage and interduce spatially uneven information distribution. In addition, spectral information of many spatial data sets is often imprecise due to digital rescaling. Direct applications of GIS systems to spatial data fusion can therefore result in seriously erroneous final results. To resolve this problem, some of the important mathematical information representation techniques are briefly reviewed and discussed in this paper with condideration of spatial and spectral characteristics of the common remote sensing and exploration data. They include the basic probabilistic approach, the evidential belief function approach (Dempster-Shafer method) and the fuzzy logic approach. Even though the basic concepts of these three approaches are different, proper application of the techniques and careful interpretation of the final results are expected to yield acceptable conclusions in cach case. Actual tests with real data (Moon, 1990a; An etal., 1991, 1992, 1993) have shown that implementation and application of the methods discussed in this paper consistently provide more accurate final results than most direct applications of GIS techniques.

• Bulletin of the Korean Chemical Society
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• 제14권1호
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• pp.21-29
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• 1993

For the study of relaxation processes in complex spin system, a general master equation, which can be used to simulate a vast range of pulse experiments, has been formulated using the Liouville representation of quantum mechanics. The state of a nonequilibrium spin system in magnetic field is described by a density vector in Liouville space and the time evolution of the system is followed by the application of a linear master operator to the density vector in this Liouville space. In this master equation the nuclear spin relaxation due to intramolecular dipolar interaction or randomly fluctuating field interaction is explicitly implemented as a relaxation supermatrix for a strong coupled two-spin (1/2) system. The whole dynamic information inherent in the spin system is thus contained in the density vector and the master operator. The radiofrequency pulses are applied in the same space by corresponding unitary rotational supertransformations of the density vector. If the resulting FID is analytically Fourier transformed, it is possible to represent the final nonstationary spectrum using a frequency dependent spectral vector and intensity determining shape vector. The overall algorithm including relaxation interactions is then translated into an ANSIFORTRAN computer program, which can simulate a variety of two dimensional spectra. Furthermore a new strategy is tested by simulation of multiple quantum signals to differentiate the two relaxation interaction types.

• 대한전자공학회논문지TC
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• 제41권12호
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• pp.93-102
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• 2004

본 논문은 개구면 결합 공진기 급전 마이크로스트립 패치 안테나에 대하여 간결하면서도 정확한 등가회로 모델을 추출하기 위한 일반적인 전자기 이론을 제안하였다. 그리고 등가회로는 이상적인 트랜스, 어드미턴스, 그리고 전송선으로 구성된다. 관련소자들의 값은 복소전력 개념, Fourier 변환, Fourier 급수, 그리고 spectral-domain immittance-approach를 적용하여 계산된다. 본 논문에서는 이 방법을 이용하여 안테나의 입력 임피던스를 구하고, 기존 논문에서 발표된 계산값, 그리고 측정값들과 비교하였다. 기존의 연구 결과와의 정확한 일치는 본 논문이 제안한 등가회로 모델의 간결성과 정확성을 입증해 준다.

• 음성과학
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• 제12권4호
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• pp.53-70
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• 2005

A Vowel of speech signals are multicomponent signals composed of AM-FM components whose instantaneous frequency and instantaneous amplitude are time-varying. The changes of emotion states cause the variation of the instantaneous frequencies and the instantaneous amplitudes of AM-FM components. Therefore, it is important to estimate exactly the instantaneous frequencies and the instantaneous amplitudes of AM-FM components for the extraction of key information representing emotion states and changes in speech signals. In tills paper, firstly a method decomposing speech signals into AM - FM components is addressed. Secondly, the fundamental frequency of vowel sound is estimated by the simple method based on the spectrogram. The estimate of the fundamental frequency is used for decomposing speech signals into AM-FM components. Thirdly, an estimation method is suggested for separation of the instantaneous frequencies and the instantaneous amplitudes of the decomposed AM - FM components, based on Hilbert transform and the demodulation property of the extended Fourier transform. The estimates of the instantaneous frequencies and the instantaneous amplitudes can be used for modification of the spectral distribution and smooth connection of two words in the speech synthesis systems based on a corpus.

• 한국전자파학회논문지
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• 제15권10호
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• pp.1005-1010
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• 2004

슬롯 결한 마이크로스트립라인-도파관 천이기에 대해 간략하지만 정확한 등가 회로 모델을 추출하기 위한 해석 방법을 제안한다. 이 등가회로는 이상적 변압기, 마이크로스트립 개방 스터브, 그리고 슬롯 중심에서 도파관 쪽과 급전선 쪽 반평면으로 바라보는 각각의 어드미턴스들로 구성된다. 관련된 회로 변수 값들은 가역 정리 (Reciprocity theorem), 푸리에 변환과 푸리에 급수(Fourier transform and series), 복소 전력 개념(Complex power concept), 파스발 정리(Parceval's theorem), 그리고 스펙트럼 영역 이미턴스 접근법(Spectral-domain immittance approach)에 의해 계산된다. 계산된 산란계수 값을 측정된 값과 비교하였으며 이들 사이의 상당한 일치도는 제안된 등가회로 모델의 간편성과 정확성을 뒷받침한다.

• 전자공학회논문지D
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• 제36D권11호
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• pp.1-11
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• 1999

원통형 쌍이방성 기판위에 부착된 다이폴의 방사특성이 덮개층에 의해서 받는 영향에 대해 연구하였다. 매질의 특성을 나타내기 위해 특별한 구성관계식이 사용되었고, 이 관계식을 그린함수로 유도하였다. 주파수 영역에서의 전자장과 경계조건을 이용하여 주파수 표현 형태의 그린 함수를 구한 다음 주파수 영역에서의 전계를 무한 원점에서의 근사식을 이용하여 퓨리에 역변환을 통해 공간 영역에서의 전계를 구하였다. 이 전계로부터, 원통형 쌍이방성 기파나위에 덮개층을 갖는 다이폴의 방사특성을 구하였다. 빔 주사, 지향성 향상, 후방지역 방사 그리고 수평면 방사를 포함한 방사 특성에 대해 쌍이방성 덮개층의 영향을 논의하였다.

• 한국측량학회:학술대회논문집
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• 한국측량학회 2004년도 춘계학술발표회논문집
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• pp.239-243
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• 2004

It does not exist almost that Most satellite image has both high spectral and spatial resolution. In order to apply the satellite image for to be actual, we need numerical and analytical technique development to improve the resolution. Specially in the function of solid illustration, we represent the solid image through the image generation to solid screen. The main function includes magnification, reduction, screen center movement, Panning, territory magnification. The method to process the image includes histogram and contrast modulation. Afterwards, we will develop the function includes 3-dimension cursor to control the elevation position and calculate the ground coordination automatically. There is the layer control includes the representation and the edition of 3D vector, extraction the Z value by On the Ground and digital elevation.