• Korea-Australia Rheology Journal
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• 제14권2호
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• pp.87-90
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• 2002

The measurement of the storage and loss moduli (G' and G" respectively) of materials as functions of frequency is now commonplace and is of wide utility. Yet il is not easy to trace the history of such measurements. and so this article discusses the genesis of this important experimental technique. We find that the technique grew out of a parallel technique for dielectric measurements (ca. 1900) and was developed in the mid-1930s by Philippoff and others. Important breakthroughs due to digital circuitry have occurred only in the last 20 years or so.r so.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2002년도 추계학술대회 논문집(II)
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• pp.1086-1093
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• 2002

In Korea mid chord offset method has been used to measure the track irregularities. This method has been also used all over the world widely because of its accessibility and the operational excellence for measured data. But it has been pointed out recently that track irregularities reconstructed from measured data have unexpected noise in the high frequency area as the defect of this way. This study shows the cause of noise which occurs during reconstructing process and mentions the solutions briefly.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2005년도 전력전자학술대회 논문집
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• pp.45-47
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• 2005

A digital controller of stepping motors is designed for removing mid-range resonance. Rotor oscillation is detected from motor currents and the microprocessor generates frequency modulation taking into account rotor oscillation. ATmega16 is employed and the controller drives stepping motors up to 3000[rpm] at micro stepping.

• The Journal of the Acoustical Society of Korea
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• 제21권1E호
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• pp.12-17
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• 2002

Two improvements are discussed in measurement of the complex Young's modulus of the acoustic materials by using the transfer function method. It is found that the accelerometer misalignment might result in the severe measurement error, particularly in high frequency range. The supporting structure is modified to attach the upper and lower accelerometers along the vertical axis. Secondly, the method fur solving the equation associated with wave model is described. The solution of the lumped mass-spring model is chosen as the starting value for low frequency range, while in the mid and high frequency, the solution to the previous frequency step is used as the initial values. Measurements are done for hard and soft rubber specimens. It is shown that the erroneous peaks in the transfer function, due to the measurement error, cause highly incorrect Young's modulus and loss factors.

• 한국항해학회지
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• 제18권3호
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• pp.19-30
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• 1994

By use of the recent tropical cyclones' data in the Northwest Pacific Ocean, the occurrence frequency and region of typhoon as well as the features of the monthly mean track were analyzed. As the result of this study, (1) mean occurrence frequency of typhoon per year is 27.5, and 68% of total typhoons were formed in July to October and shown the highest frequency in August. (2) The ave-rage duration of typhoons is 8.5 days, and super typhoon which maximum sustained surface wind speeds is more than 130 knots occurs most frequently in October and November. (3) The highest frequency ap-pears around the Caroline, Mariana and Marshall Islands, and in wintertime, typhoon occurs in lower lati-tude comparing with those in summertime. (4) The typhoon track depends upon the distribution of pres-sure system and steering current in neighbouring areas. The mean track of typhoon can be classified into three types such as westward-moving type, northward-moving type and abnormally moving type. The west-ward-moving typhoons make landfall on the southern China by way of the South China Sea in June and July, on mid-part of China in August and September, and on Indo-china Peninsula in October and Novem-ber. The northward-moving typhoons approximately move on north~northwestward track to $20~30^{\circ}N$ from the occurrence region, then recurve to the East Sea through Korean Peninsula and Kyushu Island in June and July, to the Noth Pacific Ocean along the Japanese Islands in August and September and to the North Pacific Ocean through the seas far south off the Japan in October and November.

• International Journal of Computer Science & Network Security
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• 제21권9호
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• pp.303-316
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• 2021

Digital content protection has recently become an important requirement in biometrics-based authentication systems due to the challenges involved in designing a feasible and effective user authentication method. Biometric approaches are more effective than traditional methods, and simultaneously, they cannot be considered entirely reliable. This study develops a reliable and trustworthy method for verifying that the owner of the biometric traits is the actual user and not an impostor. Watermarking-based approaches are developed using a combination of a color face image of the user and a mobile equipment identifier (MEID). Employing watermark techniques that cannot be easily removed or destroyed, a blind image watermarking scheme based on fast discrete curvelet transform (FDCuT) and discrete cosine transform (DCT) is proposed. FDCuT is applied to the color face image to obtain various frequency coefficients of the image curvelet decomposition, and for high frequency curvelet coefficients DCT is applied to obtain various frequency coefficients. Furthermore, mid-band frequency coefficients are modified using two uncorrelated noise sequences with the MEID watermark bits to obtain a watermarked image. An analysis is carried out to verify the performance of the proposed schema using conventional performance metrics. Compared with an existing approach, the proposed approach is better able to protect multimedia data from unauthorized access and will effectively prevent anyone other than the actual user from using the identity or images.

• 한국음향학회지
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• 제21권2호
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• pp.150-159
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• 2002

광대역 소음저감을 위한 압전지능패널에 대한 실험적 연구를 수행하였다. 압전지능패널은 기본적으로 압전재료를 부착한 평판구조물에 션트회로를 연결하고 흡음재들을 부가한 구조물이다. 압전감쇠와 수동적 특성을 혼용하여 중 주파수영역에서 흡음재의 수동적 특성을 이용하고 저주파수 영역의 공진주파수에서는 압전감쇠를 적용하여 소음저감시키는 개념이다. 저주파수 공진에서의 소음저감을 위하여 측정한 전기적 임피던스 모델을 이용하는 압전감쇠를 적용하였다. 압전감쇠를 위한 공진 션트회로는 직렬로 연결된 저항과 인덕터로 구성되었으며, 저항과 인덕터는 회로에서 소산되는 에너지가 최대가 될 수 있는 값으로 최적설계하였다. 압전지능패널의 전달소음저감 성능은 음향터널을 사용하여 실험을 수행하였다. 음향터널은 사각단면 형태이며 소음원으로 터널의 한 쪽 끝에 스피커가 설치되었다. 패널들을 터널의 중앙에 설치하여 투과 음압을 측정하였다. 흡음재와 공기층을 갖는 압전이중지능패널은 수동적 특성에 의해 저주파수 영역의 공진주파수를 제외한 중주파수 영역에서 뚜렷한 소음저감 효과를 나타내었다. 압전감쇠를 통하여, 공진주파수에서의 좋은 소음저감을 얻었다. 압전감쇠와 수동적 방법을 혼용하는 압전지능 패널은 넓은 주파수 영역에서의 소음저감을 위한 유망한 기술이다.

• 음성과학
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• 제9권3호
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• pp.169-184
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• 2002

Korean has two types of voiceless alveolar fricatives: a non-tense fricative /$S^{h}$ and a tense fricative /s'/. Twenty native speakers of Korean produced five pairs of isolated words containing word initial $S^{h}V$ and /s'V/ sequences where V was any one of five (/a, e, i, o, u/) of Korean vowels. Acoustic measures such as duration, fricative noise prominent frequency, energy change of following vowel, and fundamental frequency at vowel onset were examined. Results showed that among the parameters, aspiration noise duration of /s'/ in mid and low vowel contexts was less than 21 ms. In a perception experiment, where only the aspiration noise interval of the /$S^{h}$/ tokens was incrementally reduced, some listeners shifted perception from /$S^{h}$/ to /s'/.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2008년도 하계종합학술대회
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• pp.825-826
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• 2008

Focusing is the principal factor that decides the image quality. In the low illuminance condition, captured images with a digital camera usually blurred because the autofocus system of the camera fail to detect the in-focus position. The failure of focusing is due to thermal noise in the captured image. In this paper, we propose a new focus detection algorithm. The proposed algorithm use the new focusing index which is weighted sum of the high-frequency energy and mid-frequency energy. The weight is determined by the local variance of the image. The proposed algorithm performs stable focusing detection with in the low illuminance condition.

• 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.