摘要:

The intensity of the noise generated by snapping shrimp between 0.6 and 12.5 kHz was measured from Auckland Wharf to the end of the dredged channel leading into Gladstone, Queensland, Australia, and on a route out across to the edge of the Great Barrier Reef. The noise was recorded about every nautical mile within the channel and every 5 miles across the reef. Water depths varied between 11.5 and 58 m, with sites ranging from just a few meters from piers to 82 km from the mainland. Intense snapping shrimp noise was found at all sites and was the dominant source of ambient noise. Within the channel the noise exceeded that which would be expected from wind generated noise during sea state 7. Across the reef the noise levels were lower, but still exceeded that from sea state 3 wind generated noise. Comparison is made with other published snapping shrimp noise spectra which show differences in both level and shape.

ISSN:0001-4966    

DOI:10.1121/1.418153

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

The acoustic information used by bats is produced by a combination of the properties of the sound emission and the reception at the eardrum. The potential localization cues used by bats can only be fully revealed when the magnitude spectra of the emission and the external ear are convolved to produce the echolocation combination magnitude spectra. The spatially dependent changes in the magnitude spectra of the echolocation combination ofEptesicus fuscusare described. The emission and external ear magnitude spectra act together to enhance the potential localization cues. In the echolocation combination, the spectral peaks are sharpened and there is greater contrast in intensity between peaks and notches when compared to the spectra of the ear alone. The spectral localization cues in the echolocation combination appear to be restricted to a cone of space of approximately ±30°.

ISSN:0001-4966    

DOI:10.1121/1.418271

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

A theoretical study of penetration depth control in superficial hyperthermia utilizing parallel opposed linear ultrasound arrays and a double-faced (V-shaped) scanning reflector is presented. This is a dual array system (DAS), where one array operates at a low frequency and the other at a high frequency (1 and 5 MHz, respectively in this study). The arrays are positioned facing each other and both are aimed at a double-faced scanning reflector which distributes the energy over the scanned surface. Each reflecting surface is angled at 45° with respect to the sound propagation direction so that both beams are deflected in the same direction toward the treatment volume. The system was designed to be compatible for combined operation with a medical linear accelerator for the delivery of simultaneous thermoradiotherapy. It is demonstrated that by varying the excitation magnitude of one array relative to the other, it is possible to control the magnitude of absorbed energy as a function of depth, and thus improved control of the heating pattern in all three spatial dimensions is obtained. This improvement is demonstrated with bio-heat transfer simulations which show how penetration depth control translates into control of temperature distributions. The simulations also show that the DAS is able to produce more uniform temperature distributions in highly perfused tissue.

ISSN:0001-4966    

DOI:10.1121/1.418154

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

Because the variance parameter, σ, in a cumulative normal function is not the same as the spread parameter,S,of a logistic function, the subscripts of the four stimulus placements of Eq. (3), and thereafter, of Lam et al. [J. Acoust. Soc. Am.99, 3689–3693 (1996)] should beX12,X27,X73,andX88.

ISSN:0001-4966    

DOI:10.1121/1.418181

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

The scattering of sound waves by an empty, cylindrical, elastic shell in a fluid is considered in the resonance regime. A long-standing difficulty in the application of the resonance scattering theory is that an exact expression of the acoustical background has been elusive to find over the years. The exact expression, named theinherentbackground coefficient, is presented here. The coefficient is uniquely determined by the generalized fluid-loading-parameter and leads to the impenetrable background coefficient in appropriate limit. Numerical calculations show that it describes the background for a shell of arbitrary thickness and material correctly over the entire frequency range.

ISSN:0001-4966    

DOI:10.1121/1.418182

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.419482

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.419483

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.419484

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP