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나정열,팽동국 漢陽大學校 環境科學硏究所 1995 環境科學論文集 Vol.16 No.-
Munk가 제안한 대양에서의 “표준해양(Canonical Ocean)”을 근거로 한국 동해의 표준해양 음속분포를 구했다. 이 때 음속은 국립 수산진흥원에서 27년(1961-1987)동안 격월로 관측한 수온과 염분자료로 Medwin(1975) 공식을 사용해서 계산하였으며 최소 음속층은 대양과는 달리 400m에 존재했다. 이러한 표준해양에 eddy로 인한 음속 변화를 준와도 방정식(Scully-Power, 1988)을 이용해서 이론적으로 계산한 값과 현장관측으로부터 구한 한국 동해에 출현하는 eddy 내의 음속분포를 비교하였다. 1979년 4월 수산진흥원 정선 102에서 관측된 eddy는 이론적으로 계산된 값과 표층을 제외하고는 약 5m/s 이내의 오차범위내에서 잘 일치하였다. 1988년 4월과 1992년 4월 인공위성에서 찍은 표층 수온 분포를 통해 음속의 수직 분포를 이론적으로 계산한 결과 관측값과 약 10m/s의 차이를 보였다. 또한 eddy 내의 해류를 계산했는데 수평적 분포는 시계방향의 순환을 하는 warm eddy의 특성을 잘 보여준다. 수직적으로는 표층에서 최대값을 가지며 수심에 따라 지수함수적으로 감소하여 800m 에서 2㎝/s 값을 갖는다. The canonical ocean sound speed profile of the East Sea of Korea was obtained by using the Munk's model(1974) in that, the sound speed was calculated by the Medwin(1975)'s formula from the bimonthly temperature and salinity data of the FRDA(Fisheries Research & Development Agency) for 27 years(1961-1987). The depth of sound channel axis exists at the 400m depth in the East Sea of Korea. The sound speed perturbed by eddies of the East Sea of Korea was theoretically calculated in three dimensions by using the quasi-geostrophic potential vorticity equation(Scully-Power, 1988). The observed sound speed profiles of eddies in the East Sea of Korea were compared with the ones calculated theoretically. The sound speed profiles of the eddy observed along the Line 102 in April 1979, except the surface, showed the same tendency and magnitude with the one calculated theoretically within 5m/s error range. The vertical sound speed profiles in April 1988 and 1992 were also calculated from the satellite images of the sea surface temperature and showed the error range of 10m/s. The calculated surface current velocity within the eddy was anti-cyclonic which is characteristic of the warm eddy. In vertical structures, it showed the maximum current speed at the surface and is exponentially decreased with depth to the magnitude of 2㎝/s in the 800m depth.
Dong-Guk Paeng,Kweon-Ho Nam,Min Choi,Shung, K.K. IEEE 2009 and Frequency Control Vol.56 No.4
<P>To investigate the echogenicity variation due to blood flow disturbance near a stenosis under pulsatile flow, a series of in vitro experiments were performed in a rigid tube with an eccentric stenosis of 70% area reduction in a mock flow loop. An ultrasonic B-mode with a Doppler spectrogram was used to correlate echogenicity with flow speed and stroke rate. This paper reports echogenicity variation upstream of a stenosis under pulsatile flow. The experimental results showed that blood flow disturbed by the stenosis affects echogenicity and red blood cell rouleaux upstream. A hypoechoic ldquoblack holerdquo was shown at the center of the stream at systole. During diastole, the ldquobright ringrdquo in cross-sectional images was observed as eddy-like or parabolic profiles in longitudinal images. These images could be reconstructed into a 3-dimensional animation, providing a better understanding of dynamic changes of the rouleaux distribution upstream of a stenosis under pulsatile flow.</P>
Computation of the Mutual Radiation Impedance in the Acoustic Transducer Array: A Literature Survey
Paeng, Dong-Guk,Bok, Tae-Hoon,Lee, Jong-Kil The Acoustical Society of Korea 2009 韓國音響學會誌 Vol.28 No.e2
Mutual radiation impedance becomes more important in the design and analysis of acoustic transducers for higher power, better beam pattern, and wider bandwidth at low frequency sonar systems. This review paper focused on literature survey about the researches of mutual radiation impedance in the acoustic transducer arrays over 60 years. The papers of mutual radiation impedance were summarized in terms of transducer array structures on various baffle geometries such as planar, cylindrical, spherical, conformal, spheroidal, and elliptic cylindrical arrays. Then the computation schemes of solving conventional quadruple integral in the definition of mutual radiation impedance were surveyed including spatial convolution method, which reduces the quadruple integral to a double integral for efficient computation.
Dong-Guk Paeng,Jin Ho Chang,Ruimin Chen,Humayun, M.S.,Shung, K.K. IEEE 2009 and Frequency Control Vol.56 No.3
<P>High frequency ultrasound over 40 MHz has been used to image the anterior segment of the eye, but it is not suitable for the posterior segment due to the frequency-dependent attenuation of ultrasound and thus the limitation of penetration depth. This paper proposes a novel scan method to image the posterior segment of the eye with an angled high frequency (beyond 40 MHz) ultrasound needle transducer. In this method, the needle transducer is inserted into the eye through a small incision hole (~1 mm in diameter) and rotated around the axial direction to form a cone-shaped imaging plane, allowing the spatial information of retinal vessels and diagnosis of their occlusion to be displayed. The feasibility of this novel technique was tested with images of a wire phantom, a polyimide tube, and an excised pig eye obtained by manually rotating a 40 MHz PMN-PT needle transducer with a beveled tip of 45deg. From the results, we believe that rotational scan imaging will help expand the minimally invasive applications of high frequency ultrasound to other areas due to the capability of increased closeness of an angled needle transducer to structures of interest buried in other tissues.</P>
웨이브렛 패킷 기반 캡스트럼 계수를 이용한 수중 천이신호 특징 추출 알고리즘
김주호(Juho Kim),팽동국(Dong-Guk Paeng),이종현(Chong Hyun Lee),이승우(Seung Woo Lee) 한국해양공학회 2014 韓國海洋工學會誌 Vol.28 No.6
In general, the number of underwater transient signals is very limited for research on automatic recognition. Data-dependent feature extraction is one of the most effective methods in this case. Therefore, we suggest WPCC (Wavelet packet ceptsral coefficient) as a feature extraction method. A wavelet packet best tree for each data set is formed using an entropy-based cost function. Then, every terminal node of the best trees is counted to build a common wavelet best tree. It corresponds to flexible and non-uniform filter bank reflecting characteristics for the data set. A GMM (Gaussian mixture model) is used to classify five classes of underwater transient data sets. The error rate of the WPCC is compared using MFCC (MeI-frequency ceptsral coefficients). The error rates of WPCC-db20, db40, and MFCC are 0.4%, 0%, and 0.4%, respectively, when the training data consist of six out of the nine pieces of data in each class. However, WPCC-db20 and db40 show rates of 2.98% and 1.20%, respectively, while MFCC shows a rate of 7.14% when the training data consists of only three pieces. This shows that WPCC is less sensitive to the number of training data pieces than MFCC. Thus, it could be a more appropriate method for underwater transient recognition. These results may be helpful to develop an automatic recognition system for an underwater transient signal.
Nam, Kweon-Ho,Paeng, Dong-Guk,Choi, Min-Joo The Acoustical Society of Korea 2006 韓國音響學會誌 Vol.25 No.e4
Human, horse and rat bloods in a cylindrical chamber where flow was controlled by a stirring magnet were used for studying red blood cell aggregation. Ultrasound backscattered powers from blood were obtained from the backscattered signals measured by a 5 MHz focused transducer in a pulse-echo setup. The experimental results showed the differences in red blood cell (RBC) aggregation tendency among the three mammalian species with an order of horse > human > rat. The ultrasound backscattered power decreased with stirring speed in human and horse blood, but no variations were observed in rat blood. Sudden flow stoppage led to the slow increase of the backscattered power for human and horse blood. There was no self-aggregation tendency in rat blood. The enveloped echo images showed the spatial and temporal variations of RBC aggregations in the cylindrical chamber. These observations from the different mammalian species may give a better understanding of the mechanism of RBC aggregation.