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[01.30.Tt, 43.10.Jk] The 1989 NTIS Published Search TM Master Catalog lists Published

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sound. Experimental measurements of cavitation thresholds are presented here that elucidate the importance of ultrasound host fluid and nuclei pa- rameters in determining these thresholds. These results are interpreted in the context of an approximate theory, included as an appendix, describing the relationship between these parameters and cavitation threshold pres- sures. An automated experimental apparatus has been developed to deter- mine thresholds for cavitation produced in a fluid by short tone bursts of ultrasound at 0.76, 0.99, and 2.30 MHz. A fluid jet was used to convect potential cavitation nuclei through the focal region of the insonifying trans- ducer. Potential nuclei tested included 1-/tm polystyrene spheres, micro- bubbles in the 1- to 10-/tm range that are stabilized with human serum albumin, and whole blood constituents. Cavitation was detected by a pas- sive acoustical technique that is sensitive to sound scattered from cavitation bubbles. Measurements of the transient cavitation threshold in water, in a

fluid of higher viscosity, and in diluted whole blood are presented. Results from these experiments, which permit the control of nuclei and host fluid properties, are compared with the approximate analytical theory for the prediction of the onset of cavitation.

Thesis advisor: Robert E. Apfel.

Micro-mechanics of granular fluid-saturated porous media using the finite element method [43.20.Bi, 43.30.Ma, 43.35.Bf, 47.55.Mh]-- B. Yavari, Engineering Mechanics Department, The University of Texas at Austin, Austin, TX, 78712, August 1988 (Ph.D.). Biot's equations have been used by many investigators to predict the acoustical behavior of fluid-satu- rated porous media. Since the coefficients in Biot's equations depend on the microstructure and frequency, an accurate comparison of experimental data with Biot's equations has not yet been established. Bedford et al. [J. Acoust. Soc. Am. 76, 1804-1809 (1984) ] suggested a method to evaluate the drag and virtual mass coefficients as functions of frequency. The method is based on a hypothetical experiment that requires solving for the motion of the fluid in the pores when the pore walls are subjected to an oscillatory motion. In this dissertation, the finite element method is used to solve for the motion of the fluid. The fluid is treated as a nearly incompressible, viscous material. The drag and virtual mass coefficients are determined for several two- and three-dimensional pore spaces. The qualitative behavior of these coefficients is shown to be independent of the pore geometry. It is concluded that the drag coefficient is insensitive to the pore geometry, while the virtual mass coefficient is very sensitive to the pore geometry. It is also shown that the results can be expressed in nondimensional forms which permit them to be determined for different values of a characteristic dimen- sion of the pore space. Calculations of wave velocity and attenuation of compressional waves based on these coefficients are compared with experi- mental data. [Work supported in part by the Office of Naval Research. ]

Thesis advisor: A. Bedford.

Copies of the dissertation ( same title) are available from U.M.I., 300 North Zeeb Road, Ann Arbor, MI 48106.

Advanced-degree dissertations in acoustics Editor• note: Abstracts of Doctoral and Master's degree theses will be

welcomed at any time. Please note that they must conform to the usual limit of 200 words, as for archival papers, must be double-spaced, and must bear the appropriate PACS classification numbers. It would be useful to provide the name of the thesis supervisor, and to indicate how a copy of the thesis may be obtained.

Thresholds of transient cavitation produced by pulsed ultrasound in a controlled nuclei environment [43.25.Yw, 43.80.Ev]--Christy Katherine Smith Holland, Engineering and Applied Sciences, Yale Universi- ty, Yale Station •t•215 9, New Haven, CT06520, May 1989 (Ph.D.J. Concern persists over the potential of damage at the cellular level due to transient cavitation produced by diagnostic and high-intensity therapeutic ultra-

Acoustic transmission in the respiratory system [43.80.Jz, 43.80.Qf]•George Robert Wodicka, Harvard-MIT Division of Health Sciences and Technology, Massachusetts Institute of Technology, Cam- bridge, MA 02139, May 1989 (Ph.D.). A model of sound transmission from within the respiratory tract to the chest wall, which accounts for the acous- tic coupling through the walls of the large airways, was developed. The respiratory tract is represented over the frequency range from 100-600 Hz by an equivalent acoustic circuit. The propagation of sound within the sur- rounding lung parenchyma is modeled as a cylindrical wave in a homoge- neous mixture of air bubbles in water with associated thermal losses, and the chest wall is considered to be a massive boundary to the wave propagation. Predicted spectral characteristics of transmission include two resonance peaks and an overall decrease in magnitude as frequency increases. The amplitude of sound transmission from mouth to chest wall was measured in adult subjects. The experimental observations agree favorably with the model predictions. The model suggests that the resonance peaks are deter-

844 J. Acoust. Soc. Am. 86(2), Aug. 1989 0001-4966/89/080844-02500.80 @ 1989 Acoustical Society of America 844

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mined by the properties of the respiratory tract and that the decreased amplitude of transmission at higher frequencies can be largely attributed to the absorption of sound in the surrounding lung parenchyma. The model provides a theoretical framework for further investigation into the effects of structural changes on sound transmission in both health and disease.

Thesis advisors: Daniel C. Shannon, Kenneth N. Stevens.

Sound propagation under the Arctic ice canopy [43.30.Ma]--David Glen Wegmann, Naval Postgraduate School, Monterey, C•4 93943, M.S., Engrg. •4coustics, M. $., Systems Technology, March 1989. Propagation in a shallow-water waveguide, covered by a layer of"ice," was studied in a lO- rn-long, 19-cm-deep laboratory facility that models both the scale and the

physical properties of the Arctic. Smooth ice measurements were compared with predictions of the Naval Research Laboratory computer model KEN, which includes the effects of elastic layers. Although the ice canopy thickness is only a small fraction of a wavelength, the sound field is distin- guishable from the usual Pekeris waveguide (no ice cover) behavior by the evidence of seismic-type plate modes. The observed effects are related to the stimulation of ice head waves, which has been reported previously for deep water regions [J. Acoust. $oc. Am. 83, 1794 (1988) and $uppl. 1 82, $31 (1987) ]. The autoregressive and Prony spectral estimation techniques were demonstrated to be effective in identifying the acoustic modes, but they were not as suitable as Fourier techniques for describing the mode coupling caused by a rough ice cover.

Thesis advisor: H. Medwin.

845 J. Acoust. Soc. Am., Vol. 86, No. 2, August 1989 Notes and Briefs 845

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