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Mar 2000

Volume 107, Issue 3, pp. 1077-L18

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Rheo-acoustical study of the shear disruption of reversible aggregates. Ultrasound scattering from concentrated suspensions of red cell aggregates

L. Haider, P. Snabre, and M. Boynard

J. Acoust. Soc. Am. Volume 107, Issue 3, pp. 1715-1726 (2000); (12 pages) | Cited 1 time

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Shear-induced disruption of reversible aggregates or clusters in a concentrated suspension is investigated by ultrasound backscattering in the low shear regime. Fractal aggregates are considered as non-Brownian scatterers much smaller than the wavelength with acoustic properties close to those of the surrounding liquid, so that the attenuation of the coherent field is weak and multiple scattering can be neglected. The concept of variance in local particle volume fraction is used to deduce a first-order expression of the ultrasound scattering cross section per unit volume for Rayleigh scatterers in a dense suspension. On the basis of a scaling law for the shear-induced disruption of aggregates, the shear stress dependence of the ultrasonic scattered intensity from a dense suspension of clusters is derived. In a second part, the shear breakup of hardened red blood cell aggregates is investigated in plane–plane flow geometry by ultrasound scattering. Rheo-acoustical experiments are analyzed within the framework of the self-consistent field approximation and the scaling laws currently used in microrheological models. Finally, the ability of ultrasonic, light reflectometry and viscometry methods to provide quantitative information about red blood cell aggregation and membrane adhesiveness is discussed. © 2000 Acoustical Society of America.
Show PACS
43.80.Gx Mechanisms of action of acoustic energy on biological systems: physical processes, sites of action
43.80.Ev Acoustical measurement methods in biological systems and media
43.35.Bf Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in liquids, liquid crystals, suspensions, and emulsions

Ultrasound sensitivity in the cricket, Eunemobius carolinus (Gryllidae, Nemobiinae)

Hamilton E. Farris and Ronald R. Hoy

J. Acoust. Soc. Am. Volume 107, Issue 3, pp. 1727-1736 (2000); (10 pages) | Cited 1 time

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Extracellular recordings from the cervical connectives in both long- and short-winged E. carolinus reveal auditory units that are sensitive to frequencies >15 kHz with best sensitivity at 35 kHz (79 dB SPL threshold). Stimuli in this frequency range also elicit a startle response in long-winged individuals flying on a tether. For single-pulse stimuli, startle and neck connective thresholds decrease with increasing ultrasound duration, consistent with the operation of an exponential integrator with a ∼32.5-ms time constant. There is evidence for adaptation to long duration pulses (>20 ms) in the neck connectives, however, as it is more difficult to elicit responses to the later stimuli of a series. For paired-pulse stimuli consisting of 1-ms pulses of 40 kHz, temporal integration was demonstrated for pulse separations <5 ms. For longer pulse separations, startle thresholds were elevated by 3 dB and appear to be optimally combined. Startle thresholds to 5 ms frequency modulated (FM) sweeps (60–30 kHz) and pure tone pulses (40 kHz) did not differ. The characteristics and sensitivity of this ultrasound-induced startle response did not differ between males and females. As in some other tympanate insects, ultrasound sensitivity in E. carolinus presumably functions in the context of predation from echolocating bats. © 2000 Acoustical Society of America.
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43.80.Lb Sound reception by animals: anatomy, physiology, auditory capacities, processing

Masking by harmonic complexes in budgerigars (Melopsittacus undulatus)

Marjorie R. Leek, Micheal L. Dent, and Robert J. Dooling

J. Acoust. Soc. Am. Volume 107, Issue 3, pp. 1737-1744 (2000); (8 pages) | Cited 5 times

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In humans, masking by harmonic complexes is dependent not only on the frequency content of the masker, but also its phase spectrum. Complexes that have highly modulated temporal waveforms due to the selection of their component phases usually provide less masking than those with flatter temporal envelopes. Moreover, harmonic complexes that are created with negative Schroeder phases (component phases monotonically decreasing with increasing harmonic frequency) may provide more masking than those created with positive Schroeder phases (monotonically increasing phase), even though both temporal envelopes are equally flat. To date, there has been little comparative work on the masking effectiveness of harmonic complexes. Using operant conditioning and the method of constant stimuli, masking of pure tones by harmonic complexes was examined in budgerigars at several different masker levels for complexes constructed with two different fundamental frequencies. In contrast to humans, thresholds in budgerigars differed very little for the two Schroeder-phase waveforms. Moreover, when there was a difference in masking by these two waveforms, the positive Schroeder was the more effective masker—the reverse of that described for humans. Control experiments showed that phase selection was relevant to the masking ability of harmonic complexes in budgerigars. Release from masking occurred when the components were in coherent phase, compared with a complex with random phases selected for each component. It is suggested that these psychoacoustic differences may emerge from structural and functional differences between the avian and mammalian peripheral auditory systems involving traveling wave mechanics and spectral tuning characteristics. © 2000 Acoustical Society of America.
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43.80.Lb Sound reception by animals: anatomy, physiology, auditory capacities, processing
43.66.Gf Detection and discrimination of sound by animals

A dual passive cavitation detector for localized detection of lithotripsy-induced cavitation in vitro

Robin O. Cleveland, Oleg A. Sapozhnikov, Michael R. Bailey, and Lawrence A. Crum

J. Acoust. Soc. Am. Volume 107, Issue 3, pp. 1745-1758 (2000); (14 pages) | Cited 15 times

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A passive cavitation detector (PCD) identifies cavitation events by sensing acoustic emissions generated by the collapse of bubbles. In this work, a dual passive cavitation detector (dual PCD), consisting of a pair of orthogonal confocal receivers, is described for use in shock wave lithotripsy. Cavitation events are detected by both receivers and can be localized to within 5 mm by the nature of the small intersecting volume of the focal areas of the two receivers in association with a coincidence detection algorithm. A calibration technique, based on the impulse response of the transducer, was employed to estimate radiated pressures at collapse near the bubble. Results are presented for the in vitro cavitation fields of both a clinical and a research electrohydraulic lithotripter. The measured lifetime of the primary growth-and-collapse of the cavitation bubbles increased from 180 to 420 μs as the power setting was increased from 12 to 24 kV. The measured lifetime compared well with calculations based on the Gilmore–Akulichev formulation for bubble dynamics. The radiated acoustic pressure 10 mm from the collapsing cavitation bubble was measured to vary from 4 to 16 MPa with increasing power setting; although the trends agreed with calculations, the predicted values were four times larger than measured values. The axial length of the cavitation field correlated well with the 6-dB region of the acoustic field. However, the width of the cavitation field (10 mm) was significantly narrower than the acoustic field (25 mm) as bubbles appeared to be drawn to the acoustic axis during the collapse. The dual PCD also detected signals from “rebounds,” secondary and tertiary growth-and-collapse cycles. The measured rebound time did not agree with calculations from the single-bubble model. The rebounds could be fitted to a Rayleigh collapse model by considering the entire bubble cloud as an effective single bubble. The results from the dual PCD agreed well with images from high-speed photography. The results indicate that single-bubble theory is sufficient to model lithotripsy cavitation dynamics up to time of the main collapse, but that upon collapse bubble cloud dynamics becomes important. © 2000 Acoustical Society of America.  
Show PACS
43.80.Sh Medical use of ultrasonics for tissue modification (permanent and temporary)
43.25.Yw Nonlinear acoustics of bubbly liquids
43.35.Ei Acoustic cavitation in liquids
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