• 디지털산업정보학회논문지
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• 제8권3호
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• pp.133-145
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• 2012

This paper describes the high density discrete wavelet transformation which is one that expands an N point signal to M transform coefficients with M > N. The double-density discrete wavelet transform is one of the high density discrete wavelet transformation. This transformation employs one scaling function and two distinct wavelets, which are designed to be offset from one another by one half. And it is nearly shift-invariant. Similarly, triple-density discrete wavelet transformation is a new set of dyadic wavelet transformation with two generators. The construction provides a higher sampling in both time and frequency. Specifically, the spectrum of the first wavelet is concentrated halfway between the spectrum of the second wavelet and the spectrum of its dilated version. In addition, the second wavelet is translated by half-integers rather than whole-integers in the frame construction. This arrangement leads to high density wavelet transformation. But this new transform is approximately shift-invariant and has intermediate scales. In two dimensions, this transform outperforms the standard and double-density discrete wavelet transformation in terms of multiple directions. Resultingly, the proposed wavelet transformation services good performance in image and video processing fields.

• 한국세라믹학회지
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• 제21권2호
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• pp.121-126
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• 1984

The dielectric properties of $BaTiO_3$ containing 0~0.3mol% and ZnO respectively as additives were investigated as a function of temperature from $25^{\circ}C$ to 14$0^{\circ}C$ and frequency from 24 KHz to 15MHz. The density of sintered $BaTiO_3$ was increased with addition of increasing to 0.15mol% amounts of $Sb_2O_3$ and the dielectric constant was also increased. This is due to space charge polarization with Ba vacancies. Above 0.15mol% $Sb_2O_3$ the density was decreased and the dielectric constant was also decreased due to occuring the discharge through voids. The density of sintered $BaTiO_3$ was decreased with addition of increasing to 0.15mol% amounts of ZnO and the dielectric constant was decreased due to occuring the discharge through voids. Above 0.15mol% ZnO the density was increased and the dielectric constant was also increased.

• 한국전자파학회논문지
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• 제13권7호
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• pp.679-686
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• 2002

본 논문에서는 PSK 변조 신호에 대한 위상 잡음 성능 특성을 무한 급수로 전개하여 위상 잡음 분포 함수인 Tikhonov 함수와 Gaussian 함수에 대한 오율 특성을 평가하였으며, 위상 잡음에 의한 성능 손실 분석을 통하여 Tikhonov 함수와 Gaussian 함수에 의한 위상 잡음 영향이 일치하는 복원 반송파 신호대 잡음비 범위를 고찰하였다. 그리고, 주파수 변조 신호의 변조 지수와 위상 잡음의 상관 정의에 의해 1/f$^2$특성을 갖는 위상 잡음 신호를 발생하였으며, 발생된 위상 잡음 신호를 디지털 위성통신시스템 수신기에 적용하여 측정한 위상 잡음에 의한 성능 손실과 위상 잡음 분포 함수에 의해 분석된 성능 열화를 평가하였다

• 한국음향학회지
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• 제24권2호
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• pp.97-102
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• 2005

해저 경계면에 서식하는 거머리말 (Zostera marina : 잘피)의 후방산란 특성을 연구하기 위하여 음향 실험을 실시하였다. 해상실험은 남해 동대만에서 거머리말의 광합성 시 발생되는 산소 공기방울의 영향을 파악하기 위해 주간과 야간에 실시하였다. 다중 주파수 (30$\~$120 kHz)에 대한 주파수 응답특성을 측정하였고 단일 주파수 (120 kHz)를 이용하여 거머리말의 움직임에 따라 변화하는 후방산란강도의 분포를 확률밀도함수 (probability density function)로 나타내었다. 실험결과 다중 주파수에 대한 주파수 의존성과 주$\cdot$야간 산란강도의 차이를 확인하였고 거머리말 움직인에 대한 산란강도의 분포 양상은 가우시안 확률밀도 함수 (Gaussian PDF)로 특성을 나타냈다 주$\cdot$야간 산란강도의 차이는 광합성에 의해 생성된 산소 공기방울에 의한 영향으로 추정되었다.

• 한국측량학회지
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• 제25권3호
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• pp.257-266
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• 2007

적조에 관한 조사는 육안과 샘플링에 의한 현지조사에 의해 일반적으로 진행되고 있다. 이와 같은 기존의 조사, 분석방법은 적조의 발생과 소멸까지의 경로를 정확하게 예측하기 곤란하였다. 이에 좀더 객관적이고 과학적인 방법으로 적조의 발생과 그 이동경로 등 시 공간적인 환경인자를 분석해 볼 필요성이 대두되고 있다. 본 연구에서는 지리정보시스템을 적용하여 적조의 공간특성을 분석하고자 Arc/Info를 활용하여 자료를 구축한 후 적조발생해역에서의 적조밀도분포를 추정하기 위해 IDW 보간법을 적용하였다. 그 후 GRID 모듈의 CON 및 SUM Function을 이용하여 밀도 1,000cells/ml이상 발생된 해역을 추출하였으며, 추출된 해역을 기준으로 날짜별로 밀도를 누적하였다. 본 연구를 통하여 적조가 발생되는 해역을 지리정보시스템에 의해 적조의 분포 현황을 시 공간적으로 판단할 수 있었으며, 적조발생지의 공간별 밀도와 누적빈도를 GIS를 적용하여 분석한 결과 최대밀도 발생해역과 최대 빈도 발생해역 모두 남해도 남면일대 해역으로서 최대 누적빈도는 49회임을 알 수 있었다. 이를 근거로 차 후 발생되는 적조발생해역에 대한 자료의 보완이 이뤄질 경우 적조 발생과 소멸까지의 이동경로를 예측 할 수 있으리라 판단된다.

• 한국원자력학회:학술대회논문집
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• 한국원자력학회 1997년도 춘계학술발표회논문집(1)
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• pp.90-95
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• 1997

In this work, linear dynamics of a circulating fluid-fueled subcritical reactor system with temperature feedback and external neutron source was modeled and examined. In a circulating fluid-fuel system, the stable region is slightly moved by a circulation fluid effect. The effects of subcriticality and temperature feedback coefficient on the reactor stability were tested by calculating frequency response of neutron density originated from reactivity perturbation or external source oscillation of system. The amplitude transfer function has a different shape near subcritical region due to the exponential term in the transfer function. The results of the study show that at a slightly subcritical region, low frequency oscillation in accelerator current or reactivity can be amplified depending on the temperature feedback. However, as the subcriticality increases, the oscillation becomes negligible regardless of the magnitude of the temperature feedback coefficient.

• 대한전자공학회논문지SP
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• 제48권6호
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• pp.124-132
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• 2011

현대 전자전에서 레이더 신호 환경은 매우 복잡하고 고밀도화 되어 가고 있다. 이러한 신호로부터 원래의 방사체로 각각 분리하여 분석하고 식별하기 위한 전자전지원을 위해서는 신뢰성있는 신호분석 기법이 요구된다. 본 논문에서는 전자전지원의 신호분석 단계에서 신뢰성을 보장하며 신호처리 비용을 줄일 수 있는 새로운 레이더 신호 그룹화 알고리즘을 제안하였다. 제안된 기법은 주파수 변조 특성에 대한 통계적 분포 특성을 활용하여 수신 신호로부터 커널 밀도 추정 방식을 이용하여 신호 그룹화한다. 제안된 기법에 대해 실험 결과를 통해 우수한 성능을 보유함을 확인하였다.

• Structural Engineering and Mechanics
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• 제75권4호
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• pp.425-434
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• 2020

Practical non-synoptic fluctuating wind often exhibits nonstationary features and should be modeled as nonstationary random processes. Generally, the coherence function of the fluctuating wind field has time-varying characteristics. Some studies have shown that there is a big difference between the fluctuating wind field of the coherent function model with and without time variability. Therefore, it is of significance to simulate nonstationary fluctuating wind field with time-varying coherent function. However, current studies on the numerical simulation of nonstationary fluctuating wind field with time-varying coherence are very limited, and the proposed approaches are usually based on the traditional spectral representation method with low simulation efficiency. Especially, for the simulation of multi-variable wind field of large span structures such as transmission tower-line, not only the simulation is inefficient but also the matrix decomposition may have singularity problem. In this paper, it is proposed to conduct the numerical simulation of nonstationary fluctuating wind field in one-spatial dimension with time-varying coherence based on the wavenumber-frequency spectrum. The simulated multivariable nonstationary wind field with time-varying coherence is transformed into one-dimensional nonstationary random waves in the simulated spatial domain, and the simulation by wavenumber frequency spectrum is derived. So, the proposed simulation method can avoid the complicated Cholesky decomposition. Then, the proper orthogonal decomposition is employed to decompose the time-space dependent evolutionary power spectral density and the Fourier transform of time-varying coherent function, simultaneously, so that the two-dimensional Fast Fourier transform can be applied to further improve the simulation efficiency. Finally, the proposed method is applied to simulate the longitudinal nonstationary fluctuating wind velocity field along the transmission line to illustrate its performances.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2008년도 춘계학술대회논문집
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• pp.534-538
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• 2008

The vehicle system is exposed to random source in service. Therefore, it is important to consider dynamic effect of the system. But, fatigue analysis is traditionally performed by using time signal of loading. To obtain dynamic effect of resonance, we carried out resonance durability analysis with frequency response and the dynamic load on frequency domain. The study shows that the damage considering resonant frequency of fuel tank system can be effectively estimated.

• Structural Engineering and Mechanics
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• 제54권2호
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• pp.257-289
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• 2015

Shear connectors are generally used to link the slab and girders together in slab-on-girder bridge structures. Damage of shear connectors in such structures will result in shear slippage between the slab and girders, which significantly reduces the load-carrying capacity of the bridge. Because shear connectors are buried inside the structure, routine visual inspection is not able to detect conditions of shear connectors. A few methods have been proposed in the literature to detect the condition of shear connectors based on vibration measurements. This paper proposes a different dynamic condition assessment approach to identify the damage of shear connectors in slab-on-girder bridge structures based on power spectral density transmissibility (PSDT). PSDT formulates the relationship between the auto-spectral densities of two responses in the frequency domain. It can be used to identify shear connector conditions with or without reference data of the undamaged structure (or the baseline). Measured impact force and acceleration responses from hammer tests are analyzed to obtain the frequency response functions at sensor locations by experimental modal analysis. PSDT from the slab response to the girder response is derived with the obtained frequency response functions. PSDT vectors in the undamaged and damaged states can be compared to identify the damage of shear connectors. When the baseline is not available, as in most practical cases, PSDT vectors from the measured response at a reference sensor to those of the slab and girder in the damaged state can be used to detect the damage of shear connectors. Numerical and experimental studies on a concrete slab supported by two steel girders are conducted to investigate the accuracy and efficiency of the proposed approach. Identification results demonstrate that damages of shear connectors are identified accurately and efficiently with and without the baseline. The proposed method is also used to evaluate the conditions of shear connectors in a real composite bridge with in-field testing data.