摘要:

The paper ‘‘Overcoming ray chaos’’ [J. Acoust. Soc. Am.95, 3167–3170 (1994)] by Collins and Kuperman incorrectly suggests that ray chaos can be overcome by a suitable choice of numerical techniques. Chaos, when present, is a property of the ray equations, and not the numerical techniques used to solve these equations.

ISSN:0001-4966    

DOI:10.1121/1.415970

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP

摘要:

The comments by Brown and Tappert [J. Acoust. Soc. Am.100, 1234–1239 (1996)] are discussed. Their claim that the paper [J. Acoust. Soc. Am.95, 3167–3170 (1994)] contains ‘‘incorrect and/or unsubstantiated statements’’ is shown to be incorrect.

ISSN:0001-4966    

DOI:10.1121/1.415971

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP

摘要:

Modal impedances are found by solving the equations of motion of a thin spherical shell in terms of nonaxisymmetric modes of vibration. These mechanical impedances relate the modal expansion coefficients of the applied force per unit area and the velocity of the shell. The application and interpretation of these modal impedances require an awareness of the lack of orthogonality of certain modes. In proper combinations, the modal impedances in the nonaxisymmetric case are found to be identical to known modal impedances in the axisymmetric case. The analysis is restricted to extensional effects of a thin shell with radial forcing.

ISSN:0001-4966    

DOI:10.1121/1.415972

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP

摘要:

In the subject paper [Alku and Vilkman, J. Acoust. Soc. Am.98, 763–767 (1995); hence AV], AV describe the results of their research on the effect of bandwidth on estimated voice source parameters. They found that reducing the bandwidth (by low‐pass filtering the glottal flow signals) leads to a distortion of the estimated parameters. Although I do agree that low‐pass filtering influences the estimate of the voice source parameters, I do not agree with some of their conclusions, explanations, and recommendations. Furthermore, the method they used does not seem to be optimal for the purpose of their research. These matters are discussed in this Letter.

ISSN:0001-4966    

DOI:10.1121/1.415973

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP

摘要:

Deposition of heat as a result of loss in an ultrasonic wave may result in damage to biological tissues. The extensive use of ultrasound for diagnostic purposes during pregnancy necessitates the evaluation of thermal risk to a developing fetus during routine clinical exposures. Because of the small ultrasonic absorption coefficient in soft tissues at low megahertz frequencies, temperature elevations exceeding 1 °C are not expected from clinically employed ultrasound systems, and there is no evidence that such small temperature increases can result in deleterious effects. However, when the propagation path includes bone, which is known to be highly lossy, theoretical calculations and experimental work indicate that local heating might exceed 1 °C for realistic clinical conditions. Thus it is imperative to obtain reasonable estimates of the temperature elevation in and around fetal bone in order to assess risk. Because of a lack of measured data for the thermal and acoustic properties of fetal bone, which depend on gestational age, estimates of the temperature elevation resulting from exposure to ultrasound must be based on crude models. A measured quantity for a heat source resulting from conversion of acoustic to thermal energy in an ultrasound field is suggested. The heat source is developed from theoretical considerations, and can be used in the bioheat transfer equation to obtain better estimates of the temperature increase in fetal bone and the surrounding tissues as a result of exposure to ultrasound.

ISSN:0001-4966    

DOI:10.1121/1.415974

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.416307

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.416218

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.415980

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP