• Journal of Astronomy and Space Sciences
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• 제29권2호
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• pp.97-101
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• 2012

Monitoring sunspots consistently is the most basic step required to study various aspects of solar activity. To achieve this goal, the observers must regularly calculate their own correction factor $k$ and keep it stable. Relatively recently, two observing teams in South Korea have presented interesting papers which claim that revisions that take the yearly-basis $k$ into account lead to a better agreement with the international relative sunspot number $R_i$, and that yearly $k$ apparently varies with the solar cycle. In this paper, using artificial data sets we have modeled the sunspot numbers as a superposition of random noise and a slowly varying background function, and attempted to investigate whether the variation in the correction factor is coupled with the solar cycle. Regardless of the statistical distributions of the random noise, we have found the correction factor increases as sunspot numbers increase, as claimed in the reports mentioned above. The degree of dependence of correction factor $k$ on the sunspot number is subject to the signal-to-noise ratio. Therefore, we conclude that apparent dependence of the value of the correction factor $k$ on the phase of the solar cycle is not due to a physical property, but a statistical property of the data.

• 한국해양공학회지
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• 제37권6호
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• pp.238-246
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• 2023

This paper proposes an effective inertia coefficient (EIC) in the Morison equation for better wave-force calculations. The OC4 semi-submersible floating offshore wind turbine (FOWT) platform was considered to test the feasibility. Large diffraction at large Keulegan-Carpenter (KC) numbers and the interaction between columns can result in errors in estimating the wave force using the Morison equation with a theoretical inertia coefficient, which can be corrected by the EIC as a function of the wave period and direction. The horizontal and vertical wave forces were calculated using the Morison equation and potential theory at each column, wave period, and wave direction. The EICs of each column were then obtained, resulting in a minimal difference between the Morison inertia force and the wave excitation force by the potential theory. The EICs, wave forces, phase angles, and dynamic motions were compared to confirm the feasibility of an EIC concept under regular and random waves.

• 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.

• 대한전자공학회논문지SD
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• 제46권3호
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• pp.10-19
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• 2009

본 논문에서는 다중위상래핑과 실수값 함수를 이용하는 효율적인 광 워터마킹을 제안하였다. 원 영상 삽입 과정에서 숨겨야 될 두 원 영상을 제로 패딩 시켜서 입력 평면의 두 개의 사분면에 하나씩 위치시킨 후 푸리에 변환을 수행하고 다중위상래핑을 적용하여 무작위 정 실수 값을 가지는 패턴을 생성시킨 후 하나의 실수부를 취하여 복호화 키를, 두 패턴 모두의 허수부의 합을 취하여 은닉영상을 생성시킨다. 위에서 생성된 은닉영상을 인간 시각으로는 감지 할 수 없도록 감쇄화 시킨 후 커버 영상과 일차 선형 변환 시켜서 배포영상을 제작한다. 복호화 과정에서는 배포영상과 복호화 키가 곱해져서 광학적인 역 푸리에 변환을 수행하고 출력 평면에서 원점에 대하여 대칭인 원영상이 간단히 복원된다. 컴퓨터 모의 실험과 광실험을 통하여 제안된 워터마킹이 광학적인 시스템에 적용 가능함을 확인하였다.

• 전산구조공학
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• 제10권3호
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• pp.175-184
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• 1997

본 논문의 목적은 부등침하를 받는 회전 쉘의 최대 응답과 표준편차와의 관계를 규명하는 것이다. 이를 위해 표준편차에 대한 최대응답의 비(.eta.)및 그 개략값(.eta./sub apr/)를 통계적 수법으로 조사하였다. 또한 탁월차수(predoninant harmonic number)의 함수로 표현되는 .eta./sub apr/을 구하기 위한 식을 제안하였다. 한편 침하는 Fourier급수로 표시하였다. 이때 각 항은 2개의 계수를 포함하게 되는데 하나는 진폭 스펙트럼이고 다른 하나는 위상각이다. 여기서는 위상각은 확률변수로, 진폭은 확정값으로 가정하였다. 해석에서는 .eta., .eta./sub apr/의 특성을 조사하기 위해 2가지 type의 진폭 스펙트럼을 실측데이터를 근거로 설정한 후, 각 type에 대해 100 sample씩의 위상각을 가정하여 사용하였다. .eta.,.eta./sub apr/은 응답의 종류, 쉘의 위치 그리고 진폭 스텍트럼의 type에 상관없이 거의 일정한 값으로 분포하며 그 값은 2.0에서 2.5사이의 값이 된다. 또한 .eta./sub apr/의 값은 .eta.의 값과 거의 비슷하지만 약간 큰 값으로 나타났다. 결론으로 부등침하를 받는 회전 쉘의 최대 응답은 표준편차의 .eta./sub apr/(약 2.5)배 임을 밝히고 있다.

• 한국항공우주학회지
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• 제44권2호
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• pp.131-138
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• 2016

본 논문에서는 SAR (Synthetic Aperture Radar)에 사용되는 광대역 첩 신호에 대한 IRF(Impulse Response Function) 성능을 분석하였다. 영상 레이더의 첩 신호에서 영상품질에 크게 영향을 주는 인자는 진폭과 위상으로 크게 분류할 수 있다. 이 값들을 2차 다항식 커브 피팅을 사용하여 선형, 직교, 랜덤 그리고 리플 이득으로 구분할 수 있다. 본 연구에서는 이러한 인자들에 의한 IRF 영향을 분석하고, PSLR(Peak Side Lobe Ratio) 및 ISLR(Integrated Side Lobe Ratio)의 규격을 만족하기 위한 RF 비선형성에 의한 오차 값들의 최소치를 제안하였다.

• 한국항행학회논문지
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• 제21권2호
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• pp.187-192
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• 2017

단일 모드 광섬유 (SMF; single mode fiber)의 길이와 중계 구간 당 잉여 분산 (RDPS; residual dispersion per span)이 랜덤하게 분포하는 광 위상 공액과 결합된 분산 제어 (DM; dispersion management)가 적용된 장거리 (50 fiber spans ${\times}80km$) 전송 링크에서 SMF와 분산 보상 광섬유 (DCF; dispersion compensating fiber) 배열과 전체 잉여 분산 (NRD; net residual dispersion)을 조절하는 위치에 따른 왜곡된 WDM 채널의 보상 특성을 수치적으로 분석해 보았다. NRD 조절 위치는 중계 구간을 구성하는 SMF와 DCF의 배열과 관계되어 있지만, NRD 조절의 구체적 위치보다 중계 구간을 이루는 SMF와 DCF의 배열이 WDM 채널의 수신 성능에 영향을 미치는 것을 확인하였다.

• 대한물리의학회지
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• 제18권2호
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• pp.1-11
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• 2023

PURPOSE: This study examined the immediate effects of applying ankle eversion taping using kinesiology tape in chronic stroke patients-design: a randomized cross-over trial. METHODS: Seventeen stroke patients underwent three interventions in random order. The subjects were initially assigned randomly to an ankle eversion taping, placebo taping, or no taping for each intervention. Ankle eversion taping was used for mechanical correction and was involved in ankle dorsiflexion and eversion. The tape was stretched by 30-40%. Placebo tapping was applied in the same form as eversion tapping but was not stretched. The balance ability was assessed using the Y-balance test. The gait ability was assessed by maximum foot pressure and time of stance phase, and gait speed was assessed using a 10 m walk test (10MWT). All measurements were performed immediately after the intervention. RESULTS: The results showed that the dynamic balance and stance phase time in chronic stroke patients was improved after ankle eversion taping. The ankle eversion taping conditions increased significantly (p < .05) compared to the placebo and no taping conditions. CONCLUSION: The application of ankle eversion taping that uses kinesiology tape instantly increased the gait ability of chronic stroke patients. On the other hand, more research will be needed to identify the long-term effects of ankle eversion taping.

• Journal of the Optical Society of Korea
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• 제7권4호
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• pp.211-215
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• 2003

Statistical characteristics of the backscattered light from turbid tissues obtained by polarizationsensitive optical coherence tomography are investigated. The amplitude of the backscattered light is found to faithfully follow the Rayleigh distribution predicted by the scattering theory of electromagnetic waves in random media. The probability density function of the phase difference between the two orthogonal polarization components of the backscattered light is explicitly derived and then verified in comparison with the experimental data measured from in-vitro tissues of porcine ligament.

• 한국원자력학회:학술대회논문집
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• 한국원자력학회 1996년도 춘계학술발표회논문집(2)
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• pp.227-232
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• 1996

The one-third calibrating relation by steady solution can cause large error when applied to an unsteady flow with large amplitude waves. Extended calibrating method, which can treat the normal convective contribution, is developed. The normal mass convective term is included into the 2-D mass transport equation by means of rms value and random function. The unknown shear rate is numerically determined by solving the 2-D mass transport equation inversely. This recovery method which predicts the unknown shear rate is constructed. It is found that it works very well without distortion. The inclusion of the normal convective term has a negligible effect on the mass transfer coefficient.