bluuebunny/crossref_metadata_2025 huggingface dataset:
Modes of noncircular fluid-filled boreholes in elastic formations
Authors: Randall C. J.
Published: October 2005

Dispersion curves for4 the modes of noncircular fluid-filled boreholes in homogeneous elastic formations are calculated with a boundary integral formulation. Results are displayed for the propagatory modes of several borehole shapes in both fast and slow formations. Any departure from circularity reduces the tube wave speed. Agreement with exact analytical results is obtained for elliptical boreholes, while a simple approximate relation involving borehole perimeter and area is verified for arbitrary cross sections. Higher-order surface modes such as the flexural and screw modes split into two distinct branches distinguished by their orientation with respect to the principal axes of the borehole cross section. Modal dispersion characteristics in elliptical boreholes may be approximately by scaled circular borehole results. In fast formations the effective scaled radii are related to transverse dimensions of the borehole, but in slow formations they are more closely related to local radii of curvature of the borehole. For more complex cross sections with a single axis of symmetry, dispersion of the flexural mode is well modeled by that in elliptical boreholes of similar dimensions, while that of Stoneley and screw modes is not. In asymmetrical boreholes, significant torsional and out-of-phase motion may occur.
Effects of boundary conditions on the nonlinear interaction of sound beams
Authors: Tjo/tta Jacqueline Naze , TenCate James A. , Tjo/tta Sigve
Published: October 2005

Weak nonlinearity in the propagation and interaction of real sound beams in a lossless fluid is considered. Special emphasis is given to the effects produced by various boundary conditions at the sound sources and other bounding surfaces. Asymptotic formulas and numerical results are presented for the second harmonic, and for the scattered sum and difference frequency sound generated by two harmonic beams that intersect at an arbitrary angle. The results are derived from a general theory presented earlier [Naze Tjo/tta and Tjo/tta, J. Acoust. Soc. Am. 83, 487–495 (1988)], which is valid for any source separation and amplitude distribution. In situations where the parabolic approximation is not legitimate (large angles, broad beams), properly accounting for the boundary conditions may be crucial. Also discussed are implications for the parametric emitting and receiving arrays.
A higher-order energy-conserving parabolic equqation for range-dependent ocean depth, sound speed, and density
Authors: Collins Michael D. , Westwood Evan K.
Published: October 2005

Outgoing solutions of the wave equation, including parabolic equation (PE) and normal-mode solutions, are usually formulated so that pressure is continuous with range for range-dependent problems. The accuracy of normal-mode solutions has been improved by conserving energy rather than maintaining continuity of pressure [Porter et al., “The problem of energy conservation in one-way equations,” J. Acoust. Soc. Am. 89, 1058–1067 (1991)]. This approach is applied to derive a higher-order energy-conserving PE that provides improved accuracy for problems involving large ocean bottom slopes and large range and depth variations in sound speed and density. A special numerical approach and complex Padé coefficients are applied to suppress Gibbs’ oscillations. The back-propagated half-space field, an improved PE starter, is applied to handle wide propagation angles. Reference solutions generated with a complex ray model and with the rotated PE are used for comparison.
Theoretical and measured underwater noise from surface wave orbital motion
Authors: Cato Douglas H.
Published: October 2005

This paper develops a theory of sound generation by orbital motion of sea surface waves (as distinct from motion directly resulting from wave breaking such as bubble oscillation) and compares the noise predictions with measurements in a carefully controlled experiment. Theory and measurement were found to agree within the experimental errors. The mechanism is also known as the nonlinear interaction of surface waves and has been addressed by a number of authors. The approach of this paper differs from other models in that it avoids the use of the commonly applied perturbation expansion, and calculates the total noise field whereas others have limited their estimates to sound production from standing waves and waves that closely approximate standing waves. It is shown that while standing waves result in distributed dipoles with vertical axes, other wave interactions result in dipoles with axes inclined to the vertical so that there are components with both horizontal and vertical axes. The relative contribution of the horizontal dipole components to the noise field is of the same order of magnitude as that of the vertical dipole components. This paper therefore predicts higher noise levels and different directionalities, and also determines the contribution from the evanescent or near field that dominates for receiver depths less than several hundred meters (depending on frequency) resulting in substantially higher noise levels at shallow receivers. On the basis of this and previous work there seems little doubt that this mechanism is a significant source of noise in the ocean, usually dominant from about 0.2 to 5 Hz.
Dynamic interaction of a poroelastic layer and a half-space
Authors: Tajuddin M. , Ahmed Syed Iqbal
Published: October 2005

The dynamic interaction of a poroelastic layer and a half-space is investigated using the analytical model based on Biot’s theory of wave propagation in fluid-saturated porous media. The wave velocity equations are derived and discussed in the case of welded and smooth contacts, each for pervious and impervious surfaces. In the limiting case of wave number, the problem reduces to more simplified forms discussed in previous works.
Threshold and suprathreshold temporal integration effects in the crossed and uncrossed human acoustic stapedius reflex
Authors: Cacace Anthony T. , Margolis Robert H. , Relkin Evan M.
Published: October 2005

Threshold and suprathreshold temporal integration (TI) effects were studied in the crossed and uncrossed human acoustic stapedius reflex. Changes in reflex threshold were compared at four stimulus durations and for six threshold response criteria; suprathreshold effects were similarly compared at four stimulus durations and at five stimulus sound-pressure levels. Our results showed that reflex thresholds were significantly lower for the uncrossed condition and for longer duration stimuli. Both effects were dependent on threshold response criteria. Threshold Ti measurements in both crossed and uncrossed conditions were equivalent at low criterion levels (0%–4%, p>0.05) but were significantly larger in the crossed condition at higher criterion levels (5%–6%, p<0.05). Prominent suprathreshold effects also occurred. The main effect was characterized by significantly larger reflex magnitudes in the uncrossed condition. Duration dependent slope differences in magnitude intensity functions (MIFs) were also observed and were characterized by steeper slopes for longer duration stimuli. Saturation effects and/or intensity-dependent slope decelerations in MIFs were predominant in the uncrossed condition and for stimulus durations exceeding 20 ms. These data provide further quantitative evidence for asymmetric threshold and suprathreshold response properties of the crossed and uncrossed human acoustic stapedius reflex and demonstrate the dependence of these effects on stimuli of different durations.
Polydisperse scattering theory and comparisons with data for red blood cells
Authors: Berger N. E. , Lucas R. J. , Twersky V.
Published: October 2005

Recent results for low-frequency scattering by polydisperse distributions of correlated low-refracting particles averaged over orientation are analyzed numerically. The roles of shape and correlations (parameterized by c) and polydispersity (specified by the normalized variance d in size governed by the gamma probability density) are investigated. The key variable is the net volume fraction w occupied by the particles. The incoherent scattering is determined by Δ=PS(c,d;w) with P as a particle population factor that is independent of w, and S as the fluctuation-correlation function of w. Earlier applications of monodisperse (d=0) theory emphasized the influence of c on the peak Δ=Δ∧ and its location w=w∧ in order to invert ultrasonic scattering data of Shung and his associates for red blood cell suspensions under different flow conditions. For d>0, comparable curves for Δ(w) decrease more gradually with w increasing past w∧ (because of additional scattering arising from polydispersity) and thereby provide better fits to data for the more controlled flows over broader ranges of hematocrit.
The effect of an adjacent viscous fluid on the transmission of torsional stress waves in a submerged waveguide
Authors: Kim Jin O. , Wang Yuzhou , Bau Haim H.
Published: October 2005

The effects of an adjacent fluid’s viscosity and density on the characteristics of torsional stress waves transmitted in a waveguide with a circular cross section are studied theoretically and experimentally. Expressions for the torsional wave speed, dispersion relations, and attenuation are obtained as functions of the adjacent fluid’s viscosity and density. The theoretical results are compared with experimental observations. It is demonstrated that a device similar to the one described herein can be used as a rugged, real-time, on-line sensor for measuring the viscosity of a fluid with a known density. Such a sensor can measure the viscosity of fluids with a density viscosity product (ρfμ) greater than 100 kg2/m4 s to a precision of 1% or better.
Some aspects of acoustic interactions in sonar transducer arrays
Authors: Audoly Christian
Published: October 2005

To calculate the transmitting characteristicsof sonar arrays, taking into account the acoustic interactions between the transducers and the finite size of the array, a computer model has been developed. The method applies to arbitrary-shaped arrays with piston transducers. The acoustic mutual impedance matrix between the transducers is first computed, and comparison with analytical results in a special case is presented. Then, some results on arrays containing 8 and 32 transducers are shown. For a densely packed array of circular pistons with diameter equal to λ/4 at the resonance, the acoustic interactions may have large effects on the pressure and velocity distributions on the surface of the array.
Sonic properties of rocks under confining pressure using the resonant bar technique
Authors: Lucet Nathalie , Rasolofosaon Patrick N. J. , Zinszner Bernard
Published: October 2005

This paper presents in detail the resonant bar technique used to measure acoustic properties of materials in the sonic frequency range (≃5–20 kHz). Measurements are corrected for the effects of added mass and jacketing; extrinsic effects such as the sample diameter or the dispersion at higher frequencies can mask intrinsic properties of material and are analyzed here. When this technique is used on porous saturated media such as rocks, it is important to avoid the “Biot–Gardner–White” effect; this intrinsic effect can lead to erroneous high attenuations in unjacketed saturated samples. Experimental evidence of its occurrence on water-saturated rods is presented. Experimental results of velocity and attenuation obtained on various rock types such as limestones and sandstones show the drastic sensitivity of these measurements to effective pressure. Hertz’s theory can be applied to describe the behavior of under-consolidated sandstones. Under high confining pressure, sonic attenuation in water-saturated limestone samples is found to be very low (Q⩾100); attenuation in sandstones is always low (Q⩾50), except for some shaly sandstones.
Higher-order Padé approximations for accurate and stable elastic parabolic equations with application to interface wave propagation
Authors: Collins Michael D.
Published: October 2005

Higher-order Padé approximations are applied to derive accurate and stable parabolic equations for sound propagation in oceans bounded below by an elastic bottom or bounded above by ice cover. Accuracy is achieved by placing constraints on the derivatives of the Padé approximations at the point corresponding to the reference wave number. Stability is achieved by requiring that the Padé approximations map part of the lower-left quadrant of the complex plane into the upper half of the complex plane. Elastic parabolic equations based on these Padé series can handle problems involving compressional, shear, and interface waves, very wide propagation angles, and large depth variations and weak range variations in the seismoacoustic parameters. A finite-difference spectral solution is developed for generating reference solutions and starting fields. The rotated elastic parabolic equation is used to investigate the accuracy of the elastic parabolic equation for range-dependent problems.
A comparison of three classical concert halls
Authors: Bradley J. S.
Published: October 2005

Values of newer auditorium acoustics quantities are presented for measurements in three well-known classical concert halls: the Amsterdam Concertgebouw, the Vienna Grosser Musikvereinssaal, and the Boston Symphony Hall. The measured octave band quantities included reverberation time, early decay time, sound strength or level, early/late sound ratios, and lateral energy fractions. Hall average values from the measured unoccupied conditions are presented as well as estimated occupied values. The variation of parameters with both source and receiver position is examined in detail. The results help to define the range of conditions that are to be expected in good concert halls, and reveal some of the detailed differences among these halls.
Spectral interference in a binaural detection task
Authors: Bernstein Leslie R.
Published: October 2005

Several investigations suggest that sensitivity to changes in interaural disparities within select spectral regions may be degraded by the presence of energy at other, even remote, spectral regions. This study assessed whether similar degradations would be observed in an MLD paradigm. Detection thresholds were measured for NoSo and NoSπ. The signal, an 800-Hz tone (100-ms), was presented in continuous, broadband noise. Thresholds were also measured in the presence of a 400-Hz tone (the interferer) presented with an interaural phase disparity of 180° and gated simultaneously with the signal or presented continuously. NoSπ thresholds increased by about 7 dB with the gated interferer at 80 dB SPL. Smaller increases were observed with lower levels of the interferer. Presenting the interferer continuously reduced substantially its effect. NoSo thresholds were affected only slightly by the interferer. Reversing the roles of the signal and interferer (400-Hz signal, 800-Hz interferer) led to smaller, but reliable degradations in performance. Diotic interferers had, in general, smaller effects on performance. The possible relation between the mechanisms that produce interference and those that foster an ability to segregate sources of sound is discussed.
The effect of masker spectral asymmetry on overshoot in simultaneous masking
Authors: Schmidt Sabine , Zwicker Eberhard
Published: October 2005

“Overshoot” is a simultaneous masking phenomenon: Thresholds for short high-frequency tone bursts presented shortly after the onset of a broadband masker are raised compared to thresholds in the presence of a continuous masker. Overshoot for 2-ms bursts of a 5000-Hz test tone is described for four subjects as a function of the spectral composition and level of the masker. First, it was verified that overshoot is largely independent of masker duration. Second, overshoot was determined for a variety of 10-ms masker bursts composed of differently filtered uniform masking noise with an overall level of 60 dB SPL: unfiltered, high-pass (cutoff at 3700 Hz), low-pass (cutoffs at 5700 Hz), and third-octave-band-(centered at 5000 Hz) filtered uniform masking noises presented separately or combined with different bandpass maskers (5700–16000 Hz, 5700–9500 Hz, 8400–16000 Hz) were used. Third, masked thresholds were measured for maskers composed of an upper or lower octave band adjacent to the third-octave-band masker as a function of the level of the octave band. All maskers containing components above the critical band of the test tone led to overshoot; no additional overshoot was produced by masker components below it. Typical values of overshoot were on the order of 12 dB. Overshoot saturated when masker levels were above 60 dB SPL for the upper octave-band masker. The standard neurophysiological explanation of overshoot accounts only partially for these data. Details that must be accommodated by any full explanation of overshoot are discussed.
Binaural modulation masking
Authors: Grantham D. Wesley , Bacon Sid P.
Published: October 2005

Modulation thresholds were measured in three subjects for a sinusoidalloy amplitude-modulated (SAM) wideband noise (the signal) in the presence of a second amplitude-modulated wideband noise (the masker). In monaural conditions (Mm-Sm) masker and signal were presented to only one ear; in binaural conditions (M0-Sπ) the masker was presented diotically while the phase of modulation of the SAM noise signal was inverted in one ear relative to the other. In experiment 1 masker modulation frequency (fm) was fixed at 16 Hz, and signal modulation frequency (fs) was varied from 2–512 Hz. For monaural presentation, masking generally decreased as fs diverged from fm, although there was a secondary increase in masking for very low signal modulation frequencies, as reported previously [Bacon and Grantham, J. Acoust. Soc. Am. 85, 2575–2580 (1989)]. The binaural masking patterns did not show this low-frequency upturn: binaural thresholds continued to improve as fs decreased from 16 to 2 Hz. Thus, comparing masked monaural and masked binaural thresholds, there was an average binaural advantage, or masking-level difference (MLD) of 9.4 dB at fs=2 Hz and 5.3 dB at fs=4 Hz. In addition, there were positive MLDs for the on-frequency condition (fm=fs=16 Hz: average MLD=4.4 dB) and for the highest signal frequency tested (fs=512 Hz: average MLD=7.3 dB). In experiment 2 the signal was a SAM noise (fs=16 Hz), and the masker was a wideband noise, amplitude-modulated by a narrow band of noise centered at fs. There was no effect on monaural or binaural thresholds as masker modulator bandwidth was varied from 4 to 20 Hz (the average MLD remained constant at 8.0 dB), which suggests that the observed “tuning” for modulation may be based on temporal pattern discrimination and not on a critical-band-like filtering mechanism. In a final condition the masker modulator was a 10-Hz-wide band of noise centered at the 64-Hz signal modulation frequency. The average MLD in this case was 7.4 dB. The results are discussed in terms of various binaural capacities that probably play a role in binaural release from modulation masking, including detection of varying interaural intensity differences (IIDs) and discrimination of interaural correlation.
Energetics of the deep ocean’s infrasonic sound field
Authors: D’Spain G. L. , Hodgkiss W. S. , Edmonds G. L.
Published: October 2005

Simultaneous measurements of infrasonic (0.5–20 Hz) acoustic particle velocity and acoustic pressure made by the Marine Physical Laboratory’s set of freely drifting Swallow floats are analyzed in terms of the energetics of acoustic fields. Results from a recent deep-ocean deployment indicate that the midwater column’s acoustic potential and kinetic energy density spectra are equal above 1.7 Hz since, away from the ocean boundaries, the sound field is locally spatially homogeneous. Near the ocean bottom, the vertical spatial inhomogeneity is statistically significant between 0.6–1.4 Hz and 7–20 Hz. In the lower band, the pressure autospectrum decreases with increasing distance from the ocean bottom, whereas in the upper band, it increases due to the deep sound channel’s ability to trap acoustic energy at the higher infrasonic frequencies. For ship signals, the signal-to-noise ratio in the active intensity magnitude spectrum is 3–6 dB greater than in either of the two energy density spectra due to the vector nature of acoustic intensity. Although smaller than the net horizontal flux above a few hertz, a statistically significant net vertical flux density of energy occurs across the whole frequency band, from the ocean surface into the bottom. The direction of the net horizontal flux density for various discrete sources, e.g., a magnitude 4.1 earthquake, a blue whale, and commercial ships, is discussed. The net horizontal flux density of the background sound field between 5 and 12 Hz may have been determined by the surrounding ocean bottom topography in one experiment; its direction approximately coincides with the center of a topographic window. However, it also matches the heading toward a 4000-km-distant hurricane. A third possibility of an unknown, broadband source cannot be eliminated with the available data.
Characterization of Terfenol-D for magnetostrictive transducers
Authors: Moffett Mark B. , Clark Arthur E. , Wun-Fogle Marilyn , Linberg Jan , Teter Joseph P. , McLaughlin Elizabeth A.
Published: October 2005

Measurements were made of the piezomagnetic d33 coefficient, the free permeability, μ33T, and the open-circuit elastic compliance coefficient, s33H, of grain-oriented Terfenol-D, Tb0.3Dy0.7Fe1.93, produced by a modified Bridgman technique. Prestress levels to 9500 psi (65 MPa) and magnetic bias fields up to 2200 Oe (175 kA/m) were applied with a laboratory electromagnetic modified so that one pole piece served as a hydraulically actuated piston. The results indicate that d33, μ33T, and s33H are dependent on stress and magnetic field, so that proper mechanical prestress and magnetic bias conditions are critical to the successful use of Terfenol-D in transducers and actuators. Radiated-power limits for underwater acoustic projectors are estimated and compared with those for projectors having lead zirconate titanate (PZT-4) piezoelectric drivers. Terfenol-D based transducers can be as much as 8 dB superior to PZT-4 under low-Q, field-limited conditions (Q=mechanical quality factor).
Acoustic scattering from submerged cylinders. MIIR Im/Re: Experimental and theoretical study
Authors: Maze Gérard
Published: October 2005

To recognize a target submerged in water, a spectroscopy based on the backscattering spectrum or on the resonance spectrum can be used. These spectra are experimentally obtained from the quasiharmonic or short pulse method of isolation and identification of resonances (MIIR). They show sharp amplitude variations that are related to the scatterer’s resonances. These resonances are related to the surface waves that propagate around the target. The backscattering spectrum and the resonance spectrum are power spectra. They are obtained from the computation of the modulus of the Fourier transform of the signal scattered by the target. In this paper, the computation of the phase tangent of the Fourier transform is presented. The spectra obtained are called the Im/Re spectra. The experimental results are compared with the computation of the ratio of the imaginary part over the real part of the complex pressure observed at a large distance from the target center. It is shown that the Im/Re spectra are highly useful for distinguishing resonances in scatterers with large absorptivity, where conventional backscattering or resonance spectra prove insensitive.
Reflection and transmission of acoustic plane waves on an immersed orthotropic and viscoelastic solid layer
Authors: Hosten Bernard
Published: October 2005

This paper presents a method of characterizing orthotropic and viscoelastic behavior of some composite materials. The purpose is to measure the nine coefficients of the complex stiffness matrix, by using ultrasonic waves transmitted through a plate-shaped sample immersed in water. From a study or propagation in principal planes that has been reported in a previous publication [B. Hosten et al., J. Acoust. Soc. Am. 82, 1763–1770 (1987)], this paper emphasizes heterogeneous mode conversion and propagation through a nonprincipal plane, inside the composite. A numerical method is proposed for computing reflection and transmission coefficients of plane waves for any incidence plane through an orthotropic, lossy solid layer. Numerical calculations of reflection and transmission are compared to experimental data: Amplitudes, wave vectors, and damping vectors are given for a unidirectional graphite/epoxy composite.
Vibrational relaxation in gaseous SiF4 by Ar and Ne at 304 K
Authors: Amme Robert C. , Jacobs Bradley , Olson John R.
Published: October 2005

A computer-controlled ultrasonic interferometer has been utilized for exploring room-temperature relaxation of gaseous SiF4–Ar and SiF4–Ne mixtures. A single relaxation process was observed for all mixtures, and the relaxation rates, 1/pτ, were found to vary linearly with the mole fraction of added argon or neon. Analysis of the mixture relaxation data shows that collisions between SiF4 molecules and either Ar or Ne atoms are less efficient for V−T transfer than are SiF4 self-collisions. This result can be explained within the Schwartz–Slawsky–Herzfeld formulation if it is assumed that a steep repulsive potential (i.e., the 7:28 function) is operative for SiF4–SiF4 collisions, while the repulsive interaction for SiF4–noble gas collisions is treated as being between a molecule obeying a 7:28 law and an atom characterized by a 6:12 function.
Ray synthesis of the form function for backscattering from an elastic spherical shell: Leaky Lamb waves and longitudinal resonances
Authors: Kargl Steven G. , Marston Philip L.
Published: October 2005

An acoustic ray analysis is employed in synthesizing the form function for backscattering, f(θ=π,ka), from a fluid-loaded evacuated elastic spherical shell where k is the wave number of the incident plane wave and a is the outer radius of the shell. The synthesis contains a component associated with a specular reflection, fsp, and contributions from leaky Lamb waves. The contribution fl of the lth leaky Lamb wave is expressible in a Fabry–Pérot resonator form [P. L. Marston, J. Acoust. Soc. Am. 83, 25–37 (1988)]. A comparison of the ray synthesis for f(ka) with the exact partial-wave series representation for a 440c stainless-steel shell verifies the usefulness of the ray synthesis for the present case of a shell. The present synthesis is also new in that it includes the effects of longitudinal resonances on fsp. A novel ray synthesis of fsp indicates a significant resonance effect near the condition kLh=nπ (n=1,2,…). The thickness of the shell is h, and kL=ω/cL is the longitudinal wave number where cL is the longitudinal speed of sound in the elastic material. The ray synthesis demonstrates that the curvature of the shell is essential to the modeling of longitudinal resonances. Although acoustic ray modeling is generally a high-frequency technique, the ray synthesis of f(ka) for a 440c stainless-steel shell appears to be applicable for ka as small as 7. Certain anomalies in the synthesis are investigated to better understand the limitations of the present ray model.
Characterization of fiber-matrix interface by guided waves: Axisymmetric case
Authors: Xu P.-C. , Datta S. K.
Published: October 2005

A hybrid method combining the finite-element and eigenfunction expansions is proposed to study the guided waves in composite cylinders. This method is shown to be flexible in modeling generally anisotropic cylinders and computationally efficient. However, most of the analysis is confined to the case of a transversely isotropic cylindrical core surrounded by coaxial isotropic cylinders. The object is to model uniaxial fiber-reinforced materials with interface zones between the fiber (which is anisotropic) and the matrix (which is isotropic). Numerical results are presented for the axisymmetric case for a graphite fiber in magnesium and epoxy matrices. In particular, the measurable and analyzable effects of imperfect bonding are investigated. The reduction of bond stiffness is found to have significant effect on the leaky waves.
Propagation of Love waves in an initially stressed medium consisting of a slow elastic layer lying over a liquid-saturated porous solid half-space
Authors: Sharma M. D. , Gogna M. L.
Published: October 2005

The dispersion equation, for Love wave propagation in a slow elastic layer overlying a liquid saturated porous solid half-space, is derived. Both the media are assumed to be under initial stress. The effect of porosity and initial stress on the phase velocity of Love waves has been discussed. Dispersion curves for the phase velocity have been plotted, both with the presence and absence of prestress, for different values of the sandiness parameter. Some special cases have also been deduced.
Numerical errors associated with the method of superposition for computing acoustic fields
Authors: Song Limin , Koopmann Gary H. , Fahnline John B.
Published: October 2005

The method of “wave superposition” is based on the idea that an acoustic radiator can be approximately represented by the sum of the fields due to a finite number of interior point sources. The accuracy of this representation depends upon how well the velocity boundary condition on the surface of the body is approximated. The ultimate objective of this study, then, is to provide some guidelines for improving the accuracy of the surface velocity reconstruction and, consequently, the accuracy of the superposition solutions. In general, this is dependent upon the particular surface velocity distribution to be reconstructed, as well as other formulation factors such as the acoustic wave number, the number and locations of the surface nodes, and the number and locations of the point sources. Velocity interpolation functions are introduced as a means of quantifying the dependence of reconstruction errors on the acoustic wave number and the placement of the surface nodes and point sources. Numerical experiments on cylindrical radiators with different velocity distributions are performed to further illustrate how the solution accuracy depends on the surface velocity boundary conditions as well as the other formulation factors.
Plane sound waves of finite amplitude for intermediate Gol’dberg numbers
Authors: Coulouvrat François Y.
Published: October 2005

Burgers equation provides a good description of the propagation of plane sound waves of finite amplitude for which nonlinear effects are important. Although an exact solution is known, simple asymptotic approximations are useful since they may provide starting points in the case of more general situations for which no exact solution is known. Approximation solutions of Burgers equation are sought by means of a “mixed asymptotic method” involving both the method of multiple scales and the method of strained coordinates. The main point is the introduction of a new slow variable binding the solution in the region before shock formation with the solution in the old age region. For an emitted monochromatic wave, the method yields a simple and complete description for Gol’dberg numbers up to 20, as it is shown by comparison to exact or other approximated solutions. For higher Gol’dberg numbers, the solution is valid up to the shock formation distance and it can be connected with Fay solution beyond.
Similarities between various Lamb waves in submerged spherical shells, and Rayleigh waves in elastic spheres and flat half-spaces
Authors: Gaunaurd G. C. , Werby M. F.
Published: October 2005

A variety of resonance features are studied in the back-scattering cross sections (BSCS) of an air-filled metal spherical shell submerged in water and insonified by a plane cw sound wave. Rayleigh (R) and whispering gallery (WG) waves were originally investigated for vibrational purposes for (flat) half-spaces in contact with vacuum. Lamb waves were originally studied in flat plates also in contact with vacuum. These old findings are generalized to the cases of an elastic spherical shell (o.d./i.d.=2a/2b) fluid-loaded on both surfaces, and excited by an incident plane wave. The various (leaky-type) Lamb waves present in the shell are shown to reduce to the earlier R/WG waves as a≫1≫b and ρf→0. The manner in which each one of these various shell waves manifests itself in the various frequency bands of the shell’s BSCS as perceived by a remote sensor is also studied. Dispersion plots for the various phase velocities of the various waves are displayed in very wide (i.e., 0<ka<500) bands, and a number of analogies between Lamb and R/WG waves are obtained as the submerged shell becomes a solid sphere (b≪a), and vice versa (b≲a). The fluid loadings, the finite shell thickness, and the curvatures of the structure all generate novel types of waves in the shell (that manifest their effects in its BSCS) that could have never emerged from earlier models that ignored these effects, and which are analyzed here.
Acoustic generation of bubbles in excised canine urinary bladders
Authors: Fowlkes J. B. , Carson P. L. , Chiang E. H. , Rubin J. M.
Published: October 2005

A high-intensity, 555-kHz acoustic field was used to generate bubbles within urinary bladders excised from dogs. Following the exposure, bubbles were visualized on a diagnostic ultrasound scanner with a 5-MHz in-line mechanical sector scanhead. Scattering of the high-intensity ultrasound by the bubbles was also observed during the exposure as high-amplitude scan lines. The bladders used had been surgically removed after tying off the ureters and urethra to prevent urine loss and exposure to external contaminants. Each bladder was sealed in a plastic bag filled with a degassed saline solution. The bladder was centered in a sealed degassed water path at the common focus of a 7-cm-diam transducer and a 10-cm-diam brass reflector. The 555-kHz transducer and reflector were both focused at 10 cm and were aligned coaxially. Using various acoustic pressure amplitudes, two, 10-s low-frequency exposures, separated by ∼30 s, occurred at approximately 2-min intervals. Experiments on a single bladder lasted as long as 45 min. The sizes of the largest bubbles, which were easily imaged, were estimated from rise velocity measurements as 50–70 μm in radius, and pressure amplitudes used to generate those large bubbles were estimated as 10–20 bars. The detection of smaller bubbles was limited by the inability to clearly distinguish bubble echoes from artifacts caused by the reverberant field within the bladder. Visual inspection of the exterior and interior bladder wall showed no significant discoloration within the high intensity beam path. Results of this study indicate that bubbles might be generated in vivo from external sources for possible use as echo contrast agents and for studying the bioeffects of acoustic cavitation.
A Fourier transform solution for the acoustic radiation from a source near an elastic cylinder
Authors: Butler John L. , Porter David T.
Published: October 2005

A Fourier transform solution for a small source on or in the vicinity of an elastic cylinder is developed. The case of acoustic radiation from the source and cylinder and, also, the direct mechanical coupling to an elastic shell are treated in a consistent manner that allows coupling through the transducer. Numerical results are given for a sample case of a thin-walled elastic tube and these results are compared with the limiting cases of a rigid and soft cylinder.
Effective attenuation of signals in noise under focused attention
Authors: Dai Huanping , Scharf Bertram , Buus So/ren
Published: October 2005

When attending to a tone at a given frequency, listeners are most sensitive to that tone and others within a restricted band of frequencies surrounding it. This region of enhanced sensitivity defines the attention band that was measured in two experiments using a modified version of the probe-signal method of Greenberg and Larkin [J. Acoust. Soc. Am. 44, 1513–1523 (1968)]. Experiment 1 showed that at five center frequencies, from 0.25 to 4.0 kHz, the shape of the attention band resembles that of the auditory filter as inferred from notched-noise masking experiments by other investigators. The width of the attention band is close to the critical band at higher frequencies, but only half as wide at 0.25 and 0.5 kHz. Experiment 2 produced psychometric functions for unattended probe tones at least 0.23 kHz away from a fully attended, 1-kHz target tone. From these functions, the effective attenuation, measured as the threshold difference between the 1-kHz target and the probes, was estimated to be 7 dB; the amount of attenuation appeared to be about the same regardless of how far the probe frequency was from the attended band. One interpretation of these results is that bands centered on the unattended tones contribute to the decision process with some small but measurable weight and are not entirely ignored.
The effects of attenuating returning echolocation signals at the lower jaw of a dolphin (Tursiops truncatus)
Authors: Brill Randall L. , Harder Patrick J.
Published: October 2005

Recordings were made duringan echolocation experiment in order to observe any changes in the parameters of outgoing signals as a function of the deliberate attenuation of returning signals at the lower jaw of a dolphin (Tursiops truncatus). A dolphin was conditioned to perform a discrimination task while wearing either of two rubber hoods covering its lower jaw in addition to performing the same task while wearing no hood. A control hood, made of gasless neoprene, allowed returning acoustic signals to pass to the lower jaw. An experimental hood, made of closed-cell neoprene, significantly attenuated such signals. As previously reported (Brill et al., 1988), the dolphin’s ability to echolocate was significantly hindered while wearing the experimental hood. The acoustical data we recorded during that experiment suggest that the use of the hoods did not affect the dolphin’s ability to emit useful echolocation signals. The dolphin appeared to vary the temporal parameters of its emitted signals in terms of lower click repetition rates in both the control and experimental conditions and interclick intervals (ICIs) of shorter duration in the experimental condition. The lower repetition rates and shorter ICI’s in the latter condition are attributed to the attenuation of returning echoes at the dolphin’s lower jaw. The results support the theory that returning echolocation signals are best received along the lateral sides of the dolphin’s lower jaw.
Effects of signal-to-noise ratio on the frequency discrimination of complex tones with overlapping or nonoverlapping harmonics
Authors: Moore Brian C. J. , Glasberg Brian R.
Published: October 2005

Frequency difference limens for multiple-component complex tones (DLCs) were measured using an adaptive two-interval, two-alternative forced-choice task. The tones were presented either in quiet or in pink noise at various noise levels. The tones to be discriminated either had all harmonics in common, or no common harmonics. DLCs for the tones with no common harmonics were generally, but not always, larger than those for complex tones with common harmonics. For the former, performance did not worsen monotonically with increasing noise level, but tended either to stay constant or improve at first, only worsening when the tones were almost completely masked by the noise. For the latter, performance tended to worsen monotically with increasing noise level, although, again, large changes only occurred when the tones were almost completely masked by the noise. Even at the highest noise level used, DLCs for complex tones with no common harmonics were usually larger than DLCs for tones with common harmonics. The results suggest that the worse performance for tones with no common harmonics does not result from internal noise in the channels conveying information from the periphery to the mechanism determining residue pitch. Rather, spectral differences between tones with noncoincident harmonics appear to have a distracting effect that impairs pitch discrimination.
Virtual pitch and phase sensitivity of a computer model of the auditory periphery. I: Pitch identification
Authors: Meddis Ray , Hewitt Michael J.
Published: October 2005

Licklider [Experientia 7, 128–133 (1951)] presented a theory of pitch highlighting the role of auditory-nerve interspike-interval timing information in the process of pitch extraction. His theory is simplified and amended and presented here as a computer implementation. This implementation has been successfully tested using simulations of a wide range of classical demonstrations of pitch phenomena including the missing fundamental, ambiguous pitch, pitch shift of equally spaced, inharmonic components, musical chords, repetition pitch, the pitch of interrupted noise, the existence region, and the dominance region for pitch. The theory is compared with a number of alternative theories and the physiological plausibility of a temporal model is considered.
Effect of silence duration in intervocalic velar plosive on voicing perception for normal and hearing-impaired subjects
Authors: Cazals Yves , Palis Lionel
Published: October 2005

For normally hearing subjects shortening the silence duration of an intervocalic voiceless plosive induces a misperception of voicing. The time boundary for this effect is about 60 ms, which corresponds to a possible forward masking effect at the frequency of voicing. If recovery from masking is indeed involved, hearing-impaired subjects, who may have prolonged forward masking, can be expected to show abnormally long time boundary for voicing misperception. This study investigated the perception of voicing of an intervocalic plosive for a natural speech sample “aka” as a function of occlusive silence duration for normally hearing and hearing-impaired subjects. To investigate a correlation with forward masking, a second test was performed on the subjects. The same first a of the “aka” was selected and at its end was concatenated a voice murmur taken from an “aga” elocution from the same speaker, and the minimum duration of the voiced murmur necessary for it to be perceived was measured. About half of the hearing-impaired subjects needed an abnormally long silence duration to avoid voicing misperception. The data indicate a significant correlation between the results of the two tests with a slope of regression line close to unity, and thus support the hypothesis of a voicing perception ruled by recovery from forward masking. Increase in silence duration of voiceless plosives might then be a beneficial acoustical processing for some hearing-impaired subjects.
The influence of extraneous sounds on the perceptual estimation of first-formant frequency in vowels under conditions of asynchrony
Authors: Roberts Brian , Moore Brian C. J.
Published: October 2005

The presence of an extraneous sound in the first formant (F1) region of a voiced vowel has been shown to influence its perceived phonetic quality when the vowel and the extraneous sound begin and end in synchrony. These experiments examine whether this effect, produced here by a pair of extraneous tones not harmonically related to the vowel’s fundamental frequency, depends on the degree of synchrony of the vowel and the tones. The phonetic effects of the tones were measured as a change in the position of the phoneme boundary on a continuum of vowels, perceived as changing from /ɪ/ to /ɛ/ as F1 was increased. Experiment 1 demonstrated that the boundary shift resulting from the addition of the tones declined when the tones began prior to the vowel. This effect might be due to adaptation or to perceptual grouping. In experiment 2, a sequence of “captor” tones was used in an attempt to reinstate the phonetic effects of these tones, by “grouping out” the portions that were not simultaneous with the vowel. This did not provide any evidence for perceptual grouping. Experiment 3 demonstrated that offset asynchronies could also reduce the phonetic effects of the extraneous tones, although not to the same extent as could onset asynchronies. This indicated that perceptual grouping mechanisms were at least partly responsible for the effects of asynchronies. The boundary shift induced by the extraneous tones was significant even for the longest onset and offset asynchronies used, indicating that the phonetic effects of these tones are not limited to cases where vowels and tones are precisely synchronized.
Cross-language speech perception in adults: Phonemic, phonetic, and acoustic contributions
Authors: Polka Linda
Published: October 2005

Cross-language studies have shown that foreign consonant contrasts vary in the degree of perceptual difficulty which they present adult non-native listeners. Phonemic, phonetic, and acoustic factors have been considered important in accounting for this variability. These factors were examined by comparing English listeners’ perception of the Hindi retroflex versus dental place-of-articulation constant in four different voicing contexts: voiceless unaspirated, breathy voiced, voiceless aspirated, and prevoiced. Differences in perceptual difficulty of the four contrasts were predicted based on (1) phonemic status (the functional status of the contrast in the listeners’ native phonology), (2) phonetic experience (as allophones or free variants), and (3) differences in acoustic salience related to voicing. Performance was not “nativelike” for any of the four contrasts; however, significant differences in perceptual difficulty among the four contrasts were evident. Perceptual differences were correlated with both acoustic salience of place cues and subjects’ descriptions of their assimilation strategies.
A note on the cell length of noncircular supersonic jets
Authors: Powell Alan
Published: October 2005

Prandtl in 1904 [L. Prandtl, Phys. Z. 5, 599–601 (1904)] determined the cell length of a supersonic jet issuing from a circular exit; less well known is Rayleigh’s treatment of 1916 [Lord Rayleigh, Philos. Mag. 32, 177–187 (1916)] in which the cell structure was considered to be composed of standing sound waves in the jet. He also pointed out the analogy with the fundamental vibration of a taut membrane having the shape of the jet orifice, so that membrane solutions (e.g., for rectangular, semicircular, and elliptic shapes) can be applied directly to the estimation of cell length (corresponding to the periodic time of the membrane). Moreover, Rayleigh’s principle may be applied to obtain simple approximation for “roundish” shapes. The notion of “comparable constraint” is introduced, annular shapes being given as an example.
Comodulation masking release and the masking-level difference
Authors: Cohen Marion F. , Schubert Earl D.
Published: October 2005

An experiment was performed to determine if the mechanism that mediates comodulation masking release (CMR) is associated with that used to improve detection by the masking-level difference (MLD). The experiment consisted of first improving detectability of a masked diotic tone burst by adding a synchronous noise band at another frequency region (CMR), and then measuring an MLD in the usual manner, by inverting the tone-burst signal to one ear. Results indicate that a substantial MLD can be measured for a signal whose detectability has already been improved by CMR. However, that MLD (9 dB) is smaller than that measured in random noise (14 dB). Put another way, a small CMR (4 dB) can be produced even when the detectability of a stimulus has already been improved due to the MLD. These data are in general agreement with those of Hall et al. [J. Acoust. Soc. Am. 83, 1839–1845 (1988)] and Schooneveldt and Moore [J. Acoust. Soc. Am. 85, 262–272 (1989)].