• Structural Engineering and Mechanics
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• 제66권2호
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• pp.185-193
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• 2018

In this study, low- and high-frequency structure behaviors were identified and a systematic analysis procedure was proposed using noisy GPS data from a 165-m-high tower in ${\dot{I}}stanbul$, Turkey. The raw GPS data contained long- and short-periodic position changes and noisy signals at different frequencies. To extract the significant results from this complex dataset, the general structure and components of the GPS signal were modeled and analyzed in the time and frequency domains. Uncontrolled jumps and deviations involving the signal in the time domain were pre-filtered. Then, the signal was converted to the frequency domain after applying low- and high-pass filters, and the frequency and periodic component values were calculated. The spectrum of the tower motion obtained from the filtered GPS data had dominant peaks at a low frequency of $1.15572{\times}10-4Hz$ and a high frequency of 0.16624 Hz, consistent with two equivalent GPS datasets. Then, the signal was reconstructed using inverse Fourier transform with the dominant low frequency values to obtain filtered and interpretable clean signals. With the proposed sequence, processing of noisy data collected from the GPS receivers mounted very close to the structure is effective in revealing the basic behaviors and features of buildings.

• 한국산학기술학회논문지
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• 제7권5호
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• pp.907-912
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• 2006

음성신호의 프리-엠퍼시스 과정은 고주파 영역의 약화된 성분을 보상하기 위해 사용되어진다. 프리-엠퍼시스 필터의 일반적인 형태는 y(n)=s(n)-A${\cdot}$s(n-1)이고, A 값은 유성음의 경우$0.9{\sim}1.0$ 사이의 값이다. 그리고, A 값은 프리-엠퍼시스의 기울기 값을 반영하고 기존의 방법에서는 R(1)/R(0)를 사용한다. 본 논문에서는 성문특성으로 인해 고주파 특성이 약화되는 것을 보상하기 위하여 새로운 평탄화 기법을 제안한다. 우선 신호 왜곡의 최소화를 위하여 QMF를 사용하였다. QMF를 사용한 후, 각 프레임별 자기상관계수를 사용하여 평탄화 과정을 수행하였다. 실험결과에서는 제안한 방법이 자기상관 방법보다 약화된 고주파 성분을 효과적으로 보상하는 평탄화 특성이 우수한 것으로 나타났다. 그러므로 평탄화 알고리즘은 음성 인식, 음성 분석 및 합성 등과 같은 음성 신호 처리 분야에 광범위하게 적용되어질 수 있다.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2005년도 추계종합학술대회
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• pp.427-430
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• 2005

In this paper, we propose a new post-processing method, based on the theory of the projection onto convex sets (POCS) to reduce the blocking artifacts in decoded images. We propose a new smoothness constraint set (SCS) and its projection operator in the wavelet transform (WT) domain to remove unnecessary high-frequency components caused by blocking artifacts. We also propose a new method to find and preserve the original high frequency components of the image edge. Experimental results show that the proposed method can not only achieve a significantly enhanced subjective quality, but also have the PSNR improvement in the output image.

• 대한음성학회:학술대회논문집
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• 대한음성학회 2006년도 춘계 학술대회 발표논문집
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• pp.131-134
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• 2006

The narrowband speech over the telephone network is lacking in the information from low-band (0-300 Hz) and high-band (3400-8000 Hz) that are found in wideband speech (0-8000 Hz). As a result, narrowband speech is characterized by the reduced intelligibility and muffled quality, and degraded speaker identification. Spectral folding is the easiest way to reconstruct the missing high-band; however, the reconstructed speech still brings the sense of band-limited characteristic because of the absence of low-band and mid-band frequency components. To compensate for the lack of the extended speech, we propose to combine the spectral folding method and GMM transformation method, which is a statistical method to reconstruct wideband speech. The reconstructed wideband speech showed that the absent frequency components was filled up with relatively low spectral mismatch. According to the subjective speech quality evaluations, the proposed method was preferred to other methods.

• Journal of the Optical Society of Korea
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• 제19권5호
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• pp.456-466
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• 2015

We investigated an anti-aliasing (AA) filter for digital camera photography by which the excessively high-frequency components of the image signal are suppressed to avoid the aliasing effect. Our optomechanical AA filter was implemented by applying rapid relative motions to the imaging sensor. By the engineered motion blur of the mechanical dithers, the effective point-spread function (PSF) of the imaging system could be tailored to reject the unwanted high-frequency components of the image. For optimal operations, we developed a spiral filter motion protocol that could produce a Gaussian-like PSF. We experimentally demonstrated that our AA filter provides an improved filtering characteristic with a better compromise of the rejection performance and the signal loss. We also found that the pass band characteristic can be enhanced further by a color-differential acquisition mode. Our filter scheme provides a useful method of digital photography for low-error image measurements as well as for ordinary photographic applications where annoying $moir{\acute{e}}$ patterns must be suppressed efficiently.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1992년도 하계학술대회 논문집 B
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• pp.1100-1103
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• 1992

Two different resonance inverters used as fluorescent lamp ballast are based on the self oscillation at the series resonance of the circuit components. Each circuit is simulated on a computer in order to explain its function and the variation of the circuit variables for each of the circuit elements. Experimental results have bean carried out on the unsymmetrical scheme to indicate the voltage and current of the fluorescent lamp operation at the high frequency.

• 한국경영과학회:학술대회논문집
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• 한국경영과학회 2004년도 추계학술대회 및 정기총회
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• pp.582-586
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• 2004

The purpose of this study is to examine the lead-lag relationship between volatility and returns in high frequency stock market data to see the validity of two hypotheses that explain volatility asymmetry. Specifically, wavelet analysis is applied to decompose the volatility process into permanent and transitory components and then each component is investigated in conjunction with returns. The results from cross-correlation analysis between volatility and returns support the leverage effect hypothesis rather than the volatility feedback hypothesis in all cases.

• International Journal of Safety
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• 제5권1호
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• pp.1-4
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• 2006

The safety performance of the current collection system is evaluated by conducting a test run in which accelerometer and load cell signals are analyzed. It has been found that the current collection performance is strongly influenced by the train speed, with the major frequency components arising from the train traversing the span spacing and the 8.5 Hz component originating from the panhead resonance. The train acceleration is found to have significant influence on the span passing frequency but negligible effect on the resonant response.

• Wind and Structures
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• 제18권4호
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• pp.457-471
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• 2014

A summary of the main results from an international comparative study for the high-frequency base balance is given. Two buildings were specified - a 'basic' and an 'advanced' building. The latter had more complex dynamic response with coupled modes of vibration. The predicted base moments generally showed good agreement amongst the participating groups, but less good agreement was found for the roof accelerations which are dominated by the resonant response, and subject to measurement errors for the generalized force spectra, to varying mode shape correction techniques, and different methods used for combining acceleration components.

• 한국음향학회지
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• 제21권6호
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• pp.566-575
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• 2002

이동통신망과 같이 제한된 대역폭에서 실시간 멀티미디어 스트리밍 서비스를 제공하기 위해서는 보다 낮은 비트율로 비디오와 오디오 데이터를 압축하여야 한다. 또한 대부분의 대역이 비디오 데이터를 위해 할당되어 있으므로 제한된 대역폭만이 오디오에 할당되게 된다. 오디오 데이터를 낮은 비트율로 압축하기 위해서는 압축율이 높은 알고리즘을 사용하거나, 표본화 주파수 (sampling frequency)를 낮춤으로써 데이터 양을 줄여 낮은 비트율로 부호화하여야 한다. 본 논문에서는 이러한 문제점을 극복하기 위해서 낮은 표본화 주파수로 오디오 신호를 압축하고, 낮은 표본화주파수를 사용함으로서 발생하는 대역폭의 손실은 소량의 부가정보를 이용하여 복원해 줌으로써 음질을 향상시키는 알고리즘을 제안한다. 높은 주파수의 스펙트럼을 복원하기 위하여 부호화단에서 낮은 주파수 대역과 다운 샘플링 과정 중에 손실되는 높은 주파수 대역간의 에너지비를 바크밴드에 구한 후 이를 부호화하여 복호화 단으로 전달하고 이를 이용하여 높은 주파수 성분을 복원하는 방법을 제안하였다. 제안된 방법을 이용하면 10%∼20% 정도의 추가적인 비트를 사용하면서 기존의 방식보다 세그멘탈 신호대 잡음비는 1㏈∼3㏈의 성능 개선을 보였으며, 주관적인 MOS 듣기 평가를 수행한 결과 기존의 방식보다 음질이 향상됨을 확인하였다. 또한 본 논문에서 제안한 방법은 주파수 영역에서 압축을 수행하는 모든 오디오 부호화 방식에도 적용이 가능하다.