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Pekeris 도파관에서 음선 접근법을 이용한 지면파 해석
최지웅,Choi, Jee-Woong 한국음향학회 2009 韓國音響學會誌 Vol.28 No.3
지면파는 해저면 음속이 깊이에 따라 일정할 경우 해저면 음속으로 진행하는 음파로 일반적으로 모드분산으로부터 설명된다. 모드분산은 도파관의 기하학적 구조에 의한 음파의 반사 및 굴절에 의해 발생되므로 본 논문에서는 지면파를 음선이론에 기초하여 모의하였다. 지면파는 일련의 선두파들의 조합으로써 해석될 수 있으므로 [Choi와 Dahl, J. Acoust. Soc. Am. 119, 3660-3668 (2006)], 음선 접근법을 이용하여 시간영역에서 여러 경로로 전파되는 선두파들의 채널 임펄스 응답과 선두파 신호의 컨볼루션을 취하여 지면파를 모의한다. 모의된 지면파는 광대역 시간영역 포물선 방정식 기법을 이용하여 모의된 지면파와 비교, 검증된다. Ground wave is an acoustic wave propagating at a sediment sound speed in the case that sediment sound speed is constant with depth, which is explained by modal dispersion effects. In this paper, the ground wave in time domain is simulated using the ray-based approach, which is possible because the modal dispersion can be explained by the guiding of energy caused by reflection and refraction in the waveguide geometry. For a Pekeris waveguide, the ground wave can be interpreted as a sequence of head waves, called a head wave sequence [Choi and Dahl, J. Acoust. Soc. Am. 119, 3660-3668 (2006)]. The ground wave is simulated by convolution of the source signal with a channel impulse response of the head wave sequence, which is compared with simulated signals obtained via a Fourier synthesis of a complex parabolic equation (PE) field.
박순식,최지웅,윤관섭,나정열 한양대학교 이학기술연구소 2002 이학기술연구지 Vol.5 No.-
During the last several decades, although there have been lots of efforts to develope the high-frequency bottom reflection loss model, the frequency dependence of bottom loss was not considered in most cases because the sea bottom was assumed to be generally much smoother and lower gradient than the sea surface. However, if the sea bottom is rougher than acoustic wavelength, the scattered field will be increased and the reflected field will be decreased. In this paper, the high-frequency bottom reflection losses were obtained through the measurement of reflected waves from the artificially-made-flat sandy bottom. The experimental data were compared with the values calculated by the forward loss model of Mourad & Jackson. Conseouently, we suggest the frequency dependence of bottom reflection loss. 기존 해저면 반사손실 모델들은 해저면을 해수면에 비해 거칠기와 경사도가 매우 평탄하거나 완만한 경계면으로 가정하므로 주파수에 따른변화를 고려하지 않거나 미약하다고 가정하였다. 그러나 고주파를 사용하는 소오나 시스템의 경우, 음파의 파장에 비해 해저면이 거칠다면 음파는 산란 영향이 증가하게 되므로 상대적으로 반사손실 또한 증가하게 된다. 따라서 본 논문에서는 임의로 모의된 사질 성분의 해저면에서 수십 ㎑ 이상의 고주파들을 사용하여 주파수별 반사손실을 계산하고, 이를 기존의 해저면 반사손실 모델과 비교하였으며, 해저면 반사손실의 주파수 종속성을 제시하고자 한다.
( Jee Woong Choi ),( Bo Ri Kim ),( Eunmi Seo ),( Sang Woong Youn ) 대한피부과학회 2017 Annals of Dermatology Vol.29 No.1
Background: The prevalence and clinical characteristics of psoriatic arthritis (PsA) in patients with psoriasis are not well described in Asian populations, including Koreans. Objective: The purpose of this study was to investigate the prevalence of PsA by using the classification of psoriatic arthritis (CASPAR) criteria on the basis of physical examination only, as well as its correlation with psoriasis severity and other medical conditions including nail psoriasis. Methods: A single- center, cross-sectional observational cohort study was conducted, and the included patients were evaluated for PsA according to the CASPAR criteria. The psoriasis area severity index (PASI) and the nail psoriasis severity index (NAPSI) were calculated. Results: The prevalence of PsA in patients with psoriasis in Korea was 13.5%. When performing logistic regression, hyperlipidemia and localized pustular psoriasis were found to be significant predictors of PsA. The PASI score was significantly higher in PsA patients than in those with psoriasis alone (p=0.014). Psoriatic nail involvement was found in 85.5% of the study population, and all PsA patients had nail psoriasis. The mean NAPSI score was higher in patients with PsA; however, the difference was not statistically significant. Conclusion: There was a close relation between psoriasis severity and PsA, although nail psoriasis severity was not related to PsA status. Dermatologists can diagnose PsA from current physical findings by using the CASPAR criteria. To validate the CASPAR criteria for PsA diagnosis, the definition of nail psoriasis clinical types and severity in the CASPAR criteria should be reviewed again. (Ann Dermatol 29(1) 48∼54, 2017)