Volume 104, Issue 4, October 1998
Index of content:
- BIOACOUSTICS 
Interrelation between proton transfer reactions and solvent structure studied by the ultrasonic absorption method104(1998); http://dx.doi.org/10.1121/1.423754View Description Hide Description
Ultrasonicabsorption coefficients in aqueous solutions of methanol at 1.00, 2.00, 3.00, 4.00, and 6.00 mol dm−3 and in those of ethanol at 1.00, 2.00, 3.00, 4.00, 5.00, and 6.00 mol dm−3 have been measured in the frequency range from 0.8–220 MHz at 25.0 °C. No excess absorption has been observed in any of these solutions except in the 5.00 and 6.00 mol dm−3ethanol solutions, for which a Debye-type single relaxational equation has been fitted. In order to see the effects of methanol and ethanol on the dynamic characteristics of aqueous amine solutions, the ultrasonic absorption measurements have been carried out in aqueous solutions of propylamine containing 1.00, 2.00, 3.00, 4.00, and 6.00 mol dm−3 methanol and 1.00, 2.00, 3.00, and 4.00 mol dm−3ethanol. The excess absorption has been observed, and the frequency dependence of the ultrasonicabsorption coefficients has been well described by the Debye-type single relaxational equation. The cause of the relaxation is due to a perturbation of equilibrium associated with a proton transferreaction. The rate constants have been determined from hydroxide ion concentration dependence of the relaxation frequency, and the standard volume change of the reaction has been calculated from the reactant concentration dependence of maximum absorption per wavelength. It has been found that the addition of methanol causes the decrease in the diffusion controlled rate constant and the trend of the decrease is more remarkable in the concentration range from 3.00–6.00 mol dm−3. On the other hand, the rate constant in the solution with ethanol has decreased linearly with an increase in the ethanol concentration. The reverse rate constant and the volume change of the reaction have not been affected by the addition of the two alcohols. Using a theoretical equation for the diffusion controlled reaction, a diffusion coefficient of the hydroxide ion has been determined at various concentrations of the additives. These results are discussed in relation to the effects of methanol and ethanol on water structure.
Frequency relationships for ultrasonic activation of free microbubbles, encapsulated microbubbles, and gas-filled micropores104(1998); http://dx.doi.org/10.1121/1.423755View Description Hide Description
The ultrasonic activation of free microbubbles, encapsulated microbubbles, and gas-filled micropores was explored using available linear theory. Encapsulated microbubbles, used in contrast agents for diagnosticultrasound, have relatively high resonance frequencies and damping. At 2 MHz the resonance radii are 1.75 μm for free microbubbles, 4.0 μm for encapsulated microbubbles, and 1.84 μm for gas-filled micropores. Higher-pressure amplitudes are needed to elicit equivalent subharmonic, fundamental, or second-harmonic responses from the encapsulated microbubbles, and this behavior increases for higher frequencies. If an encapsulated microbubble becomes destabilized during exposure, the resulting liberated microbubble would be about twice the linear resonance size, which would be likely to produce subharmonic signals. Scattered signals used for medical imaging purposes may be indicative of bioeffects potential: The second harmonic signal is proportional to local shear stress for a microbubble on a boundary, and a strong subharmonic signal may imply destabilization and nucleation of free-microbubble cavitation activity. The potential for bioeffects from contrast agent gas bodies decreases rapidly with increasing frequency. This information should be valuable for understanding of the etiology of bioeffects related to contrast agents and for developing exposure indices and risk management strategies for their use in diagnosticultrasound.
Playback of acoustic thermometry of ocean climate (ATOC) -like signal to bony fishes to evaluate phonotaxis104(1998); http://dx.doi.org/10.1121/1.423756View Description Hide Description
The aim of this study was to evaluate whether acoustic thermometry of ocean climate (ATOC) signals have a positive or negative phonotactic effect on the behavior of fish present near the sound source at Pioneer Seamount off Central California. We played back an ATOC-like signal to three species of rockfish kept within a 15×2-m field enclosure in Bodega Bay, California. Each subject was observed during a 25-min “silent” control period followed immediately by a test period comprised of a 5-min “ramp-up,” in which the sound level increased gradually to a peak level, and a 20-min period at constant peak level. The amount of time that each subject spent in 15 zones, each 1 m wide, at increasing distances from the sound transducer, was observed. It was suspended in midwater at the center of zone 1, the deepest portion of the enclosure. We observed little movement by fish in response to the playback of the ATOC signal. The subjects remained in zones 1 and 2, despite sound pressure levels present of 145.1–153.0 dB re: 1 μPa. Little difference existed in the behavior of fish during sound playback period and the “silent” control period. The median time interval that fishes occupied zone 1 was 100% of the experiment duration for both test and control periods (i.e., 6 of 11 subjects in the former remained exclusively within that zone versus 7 of 11 subjects in the latter).
Echolocation range of captive and free-ranging baiji (Lipotes vexillifer), finless porpoise (Neophocaena phocaenoides), and bottlenose dolphin (Tursiops truncatus)104(1998); http://dx.doi.org/10.1121/1.423757View Description Hide Description
The interclick intervals of captive dolphins are known to be longer than the two-way transit time between the dolphin and a target. In the present study, the interclick intervals of free-ranging baiji, finless porpoises, and bottlenose dolphins in the wild and in captivity were compared. The click intervals in open waters ranged up to 100–200 ms, whereas the click intervals in captivity were in the order of 4–28 ms. Echolocation of free-ranging dolphins appears to adapt to various distance in navigation or ranging, sometimes up to 140 m. Additionally, the difference of waveform characteristics of clicks between species was recognized in the frequency of maximum energy and the click duration.
Comparison of electrohydraulic lithotripters with rigid and pressure-release ellipsoidal reflectors. I. Acoustic fields104(1998); http://dx.doi.org/10.1121/1.423758View Description Hide Description
The most common lithotripter, a Dornier HM-3, utilizes an underwater spark to generate an acoustic pulse and a rigid ellipsoidal reflector to focus the pulse on the kidney stone to be comminuted. The pulse measured in water with a PVDF membrane hydrophone at the external focus of the ellipsoid was a 1-μs positive-pressure spike followed by a 3-μs negative-pressure trough. When we replaced the rigid reflector in our experimental lithotripter with a pressure-release reflector, the pulse was a 1.6-μs trough followed by a 0.6-μs positive spike. The waveforms are nearly time inverses (i.e., their spikes and troughs are reversed). The frequency spectra, the maximum peak positive pressures (42 MPa, rigid and 43 MPa, pressure-release), and the maximum peak negative pressures (−12 MPa and −14 MPa) are comparable. The maximum occurred 20 mm closer to the reflector than did the maximum for both reflectors. However, the spatial maxima of the peak pressures and produced by the pressure-release reflector were located 20 mm nearer to the reflector than those produced by the rigid reflector. Qualitative explanation of the waveforms and the location of pressure maxima as well as comparison to previous theoretical and experimental results is given. The alternate waveform produced by the pressure-release reflector may be a tool in determining the role of cavitation in lithotripsy because cavitation is highly sensitive to waveform.