bluuebunny/crossref_metadata_2025 huggingface dataset:
Inverse problems in two-dimensional acoustic media: A linear imaging model
Authors: Goutsias John I. , Mendel Jerry M.
Published: October 2005

A fundamental problem in reflection seismology and ultrasound medicine is to identify the spatially variant parameters of the Earth or human tissue (e.g., the density and velocity profiles) from reflection and transmission wave-field data. This is known as the inverse scattering problem, or the diffraction tomography problem. Computer technology, and especially the development of supercomputing capabilities, revolutionized seismic and medical imaging. Various techniques have been developed for imaging the Earth’s interior, as well as obtaining tomographic images of the interior of the human body, from measured backscattered wave-field data. Although these techniques try first to model the underlying forward scattering mechanisms, an accurate model for these mechanisms has not been available yet. The main contribution of this article is the development of a linear image formation system for modeling the traveling of waves through, and the scattering of waves from, a two-dimensional acoustic medium, that allows us to view the medium identification problem as an image restoration problem. A two-dimensional imaging model, characterizing the wave motion inside an inhomogeneous, isotropic, acoustic medium is described. A Born-series expansion of the wave field is employed and a linear two- dimensional imaging system is obtained. The higher-order scattering terms are incorporated in this model by approximating them, thus resulting in a more accurate scattering model. A variable background reference medium is used. It is argued that accurate acoustic imaging can be performed by developing a recursive downward continuation/image restoration procedure. The properties of this procedure are examined.
Synchrony suppression in complex stimulus responses of a biophysical model of the cochlea
Authors: Shamma Shihab A. , Morrish Kathleen A.
Published: October 2005

A minimal biophysical model of the cochlea is used to investigate the validity of the hypothesis that a single compressive nonlinearity at the hair cell level can explain some of the suppression phenomena in cochlear responses to complex stimuli. The dependencies of the model responses on the amplitudes and frequencies of two-tone stimuli resemble in many respects the behavior of the experimental data, and can be traced to explicit biophysical parameters in the model. Most discrepancies between theory and experiment stem from simplifications in parameters of the minimal model that play no direct role in the hypothesis. The analysis and simulations predict further results which, pending experimental verification, may provide a more direct test of the influence of the compressive nonlinearity on the relative amplitudes of the synchronous response components, and hence of its role in synchrony suppression. For instance, regardless of the overall absolute levels of a two-tone stimulus applied to this type of model, the ratio of the amplitudes at the input and the ratio of the corresponding responses at the output remain approximately constant and equal (the output ratio changes by at most 6 dB in favor of the stronger tone).

Other nonlinear responses to multitonal stimuli can also be reproduced, such as ‘‘spectral edge enhancement’’ [Horst et al., Peripheral Auditory Mechanisms (Springer, Berlin, 1985)] and some aspects of three-tone suppression [Javel et al., Mechanisms of Hearing (Monash U. P., Australia, 1983)]. In contrast to the complex behavior of suppression with increasing sound intensity and the drastic influence of the compressive nonlinearity on the absolute response measures on the auditory nerve (e.g., average rate and synchrony profiles), the percepts of complex sounds are relatively stable. This suggests that the invariant relative response measures are more likely used in the encoding and CNS extraction of the spectrum of complex stimuli such as speech.
Minimum stimulus levels for temporal gap resolution in listeners with sensorineural hearing loss
Authors: Fitzgibbons Peter J. , Gordon-Salant Sandra
Published: October 2005

The minimum sensation levels required for optimal temporal gap resolution were measured in five listeners with moderately severe degrees of sensorineural hearing loss. The stimuli were three continuous octave-band noises centered at 0.5, 2.0, and 4.0 kHz. Subjects used a Békésy tracking procedure to determine the minimum signal levels needed to resolve periodic temporal gaps of fixed durations. Analysis of data across subjects and signal revealed only a weak correlation between this minimum SL and the corresponding HLs; most listeners resolved threshold gaps at minimum levels of 25–35 dB SL, independent of degree of hearing loss. The results differ from those of normal subjects with masking-induced hearing loss, [Fitzgibbons, Percept. Psychophys. 35, 446–450 (1984)], which showed an inverse relationship between HL and the SLs required for gap threshold. The findings indicate that assessment of optimal gap resolution in listeners with cochlear impairment requires stimulus presentation levels of at least 25–35 dB SL. Even with sufficient stimulus intensity, each of the hearing-impaired listeners exhibited abnormal gap resolution for each octave-band signal.
Gap detection and masking in hearing-impaired and normal-hearing subjects
Authors: Glasberg Brian R. , Moore Brian C. J. , Bacon Sid P.
Published: October 2005

Subjects with cochlear impairments often show reduced temporal resolution as measured in gap-detection tasks. The primary goals of these experiments were: (1) to assess the extent to which the enlarged gap thresholds can be explained by elevations in absolute threshold; and (2) to determine whether the large gap thresholds can be explained by the same processes that lead to a slower-than-normal recovery from forward masking. In experiment I gap thresholds were measured for nine unilaterally and eight bilaterally impaired subjects, using bandlimited noise stimuli centered at 0.5, 1.0, and 2.0 kHz. Gap thresholds were usually larger for the impaired ears, even when the comparisons were made at equal sensation levels (SLs). Gap thresholds tended to increase with increasing absolute threshold, but the scatter of gap thresholds was large for a given degree of hearing loss. In experiment II threshold was measured as a function of the delay between the onset of a 210-ms masker and the onset of a 10-ms signal in both simultaneous- and forward-masking conditions. The signal frequency was equal to the center frequency of the bandlimited noise masker, which was 0.5, 1.0, or 2.0 kHz. Five subjects with unilateral cochlear impairments, two subjects with bilateral impairments, and two normal subjects were tested. The rate of recovery from forward masking, particularly the initial rate, was usually slower for the impaired ears, even when the maskers were presented at equal SLs. Large gap thresholds tended to be associated with slow rates of recovery from forward masking.
Relations among temporal acuity, hearing loss, and the perception of speech distorted by noise and reverberation
Authors: Irwin R. J. , McAuley S. F.
Published: October 2005

Eight normal listeners and eight listeners with sensorineural hearing losses were compared on a gap-detection task and on a speech perception task. The minimum detectable gap (71% correct) was determined as a function of noise level, and a time constant was computed from these data for each listener. The time constants of the hearing-impaired listeners were significantly longer than those of the normal listeners. The speech consisted of sentences that were mixed with two levels of noise and subjected to two kinds of reverberation (real or simulated). The speech thresholds (minimum signal-to-noise ratio for 50% correct) were significantly higher for the hearing-impaired listeners than for the normal listeners for both kinds of reverberation. The longer reverberation times produced significantly higher thresholds than the shorter times. The time constant was significantly correlated with all the speech threshold measures (r=−0.58 to −0.74) and a measure of hearing threshold loss also correlated significantly with all the speech thresholds (r=0.53 to 0.95). A principal components analysis yielded two factors that accounted for the intercorrelations. The factor loadings for the time constant were similar to those on the speech thresholds for real reverberation and the loadings for hearing loss were similar to those of the thresholds for simulated reverberation.
Low-frequency scattering by correlated distributions of randomly oriented particles
Authors: Twersky Victor
Published: October 2005

Random distributions of correlated scatterers averaged over orientation are considered, corresponding to isotropic fluids of statistical mechanics particles (with volume v, number concentration ρ, and volume fraction w=ρv). For minimum separation of centers small compared to wavelength and acoustic particle parameters close to the embedding medium’s, the incoherent differential scattering from unit volume and the corresponding attenuation coefficient are proportional to the fluctuations (variance) in number concentration. For arbitrary convex hard particles (e.g., ovals or simple polyhedra, repulsive at contact) with shape parameter c≥3, the variance is expressed in terms of a quotient S(c;w) of polynomials in w that has a maximum S■(c) at w■(c). Spheres (c=3) were considered earlier. For c>3, the fluctuations and S■ and w■ are smaller than for spheres; for c<3 (which we consider formally), they are larger than for spheres. The results are interpreted by comparing leading terms with the second virial coefficients for more general statistical mechanics models. Scattering data for suspensions of discoidal red blood cells versus w under different flow conditions can be fitted adequately by S(c;w) for different values of c<3. The low values of c suggest weaker repulsion between deformable cells, and attractive interparticle forces mediated by flow and aggregative trends.
Nonuniformly poled spherical shell piezoelectric transducers
Authors: Hazony Dov
Published: October 2005

Elastic and electric properties of the radial mode spherical shell piezoelectric transducer are studied in detail. It is shown that impedance matrices may be associated with these properties and electrical networks identified with these matrices.
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o B/A determination in a mammalian organ
Authors: Zhang Jian , Dunn Floyd
Published: October 2005

Investigations of the ultrasonic nonlinearity parameter B/A have been restricted previously to in vitro preparations. The parameter B/A has now been determined in vivo in cat liver and found to have the same value as in vitro determinations. The finite amplitude method was used, with a substitutional procedure to improve accuracy.
Sample boundary effect in acoustic attenuation of fluid-saturated porous cylinders
Authors: Dunn Keh-Jim
Published: October 2005

It was shown previously, by using Biot theory, that there exists an attenuation in the low-frequency elastic modulus measurement on fluid-saturated porous rock cylinders caused by the open-pore boundary condition. This attenuation is associated with the energy dissipation of the viscous flow of the pore fluid in and out of an open-pore boundary of a fluid-saturated rock sample. For the extensional mode, the relaxation frequency of this attenuation is directly proportional to the permeability of the rock and inversely proportional to the viscosity of the pore fluid and the square of the sample radius. In this article, experimental studies that support the theoretical prediction of this sample boundary effect are reported. Experiments of varying saturation, sample radius, pore fluid viscosity, and rock permeability were carried out. The results, though consistent with the theoretical prediction, are not satisfactory in a quantitative sense because of the lack of an idealized sample. It was found, however, the procedure of jacketing the sample with an aluminum sleeve and measuring it at ambient pressure condition is not sufficient to remove the attenuation caused by the boundary effect completely.
Analysis of liquid-core cylindrical acoustic waveguides
Authors: Safaai-Jazi A. , Jen C. K. , Farnell G. W. , Cheeke J. D. N.
Published: October 2005

Transmission properties of guided modes in liquid-core cylindrical acoustic waveguides are investigated. It is observed that for each value of the circumferential order n the first mode becomes of Stoneley-type above a certain frequency. There are two modes without cutoff frequencies, in contrast to only one mode in solid-core waveguides. They are the first modes with n=0 and 1. The application of liquid-core waveguides in sensor devices is pointed out and some preliminary experimental results are reported.
Nearfield acoustic holography (NAH) II. Holographic reconstruction algorithms and computer implementation
Authors: Veronesi W. A. , Maynard J. D.
Published: October 2005

The basic theory treating steady-state acoustic radiation problems in the nearfield has been presented in several articles on nearfield acoustic holography. In this article, the approximations and assumptions necessary to reduce the infinite and continuous convolution integrals encountered in these problems to a finite and discrete form, suitable for high-speed numerical processing, are illuminated theoretically and tested numerically. To evaluate the convolution integrals two assumptions are made: First, the boundary field may be replaced with a patchwise constant field for reasonably small patches; and, second, the field is negligible outside of a finite region. With these two assumptions, the problem reduces to one of representing the Green’s functions. Six methods of sampling or representing the Green’s functions are developed, and these are compared theoretically and numerically.
A criterion for an energy vortex in a sound field
Authors: Waterhouse R. V. , Crighton D. G. , Ffowcs-Williams J. E.
Published: October 2005

Measurements with intensity meters have shown that energy vortices exist in certain sound fields. In these vortices, sound energy flows around closed paths, in the steady state. Vortices occur in some sound fields (e.g., that of a point source near a reflecting edge), but not in others (e.g., that of a plane rigid piston in a plane rigid baffle). It is shown that in a two-dimensional or axisymmetric sound field, a necessary and sufficient condition for a vortex to exist is the presence of an isolated maximum or minimum in the stream function. Two examples are given for a vortex in (a) a duct of square cross section, and (b) the field of two monopole sources, one of which just extinguishes the other. Some relations for the interaction between two monopole sources are also given.
Acoustic radiation force on a particle in a temperature gradient
Authors: Collas P. , Barmatz M.
Published: October 2005

A general expression is derived for the acoustic radiation force on a small spherical particle of radius R in a standing wave field in a temperature gradient.The case of a particle inside a long tube chamber with a temperature gradient along the axis of symmetry is examined in more detail. The analysis is considerably simplified by the introduction of the mass flux density potential ψ. Assuming kR≪1, and neglecting convection, acoustic streaming, heat conduction, and viscosity effects, an expression is obtained for the force that consists of a ‘‘local’’ version of Gor’kov’s result as well as correction terms of order β/k, where β∼(1/T)(dT/dz).
The reflection of radiation from randomly irregular surfaces
Authors: Frankenthal Shimshon
Published: October 2005

Surface interactions of radiation propagating in a nonuniform, scattering medium are treated using the strength and diffraction parameters, which currently serve to describe volume scattering in the application of the path-integral formalism. A procedure for tracing the volume diffraction parameter through specular surface reflections is outlined and illustrated. Subsequently, a phase screen model is used to account for scattering by surface irregularities. The statistics of these irregularities take up the role of the statistics of the refractivity fluctuations, and the Rayleigh roughness parameter replaces the strength parameter. The diffraction parameter is defined using the correlation length of the surface irregularities and an appropriate surface phase curvature. The application is illustrated by the computation of the two-point, two-frequency correlation for a surface-to-surface multipath in a linear sound-speed channel.
Time domain formulation for pulse propagation including nonlinear behavior at a caustic
Authors: McDonald B. Edward , Kuperman W. A.
Published: October 2005

This paper derives a simple three-dimensional time domain formulation for small angle propagation of finite amplitude acoustic pulses and weak shocks in a medium that can be range dependent. The formulation is closely related to a full wave model, and does not contain the artificial singularities of ray-based models at caustics. The simplicity of the formulation suggests that it may be of value for broadband linear as well as nonlinear propagation. Two derivations are given: one heuristic and the other a formal series expansion from the fluid equations. The result is a first-order nonlinear progressive wave equation (NPE) cast in a wave-following frame of reference.The NPE is shown to be the nonlinear time domain counterpart of the frequency domain parabolic wave equation (PE). The NPE gives a natural separation of terms governing refraction, spreading, and nonlinear steepening. Numerical calculations (not involving Fourier synthesis) are presented using the NPE to simulate the following cases: (a) broadband linear pulse propagation in a waveguide; (b) the development of an initially smooth nonlinear pulse into an N wave; and (c) the behavior of a weak shock at a caustic. Cases (a) and (b) are compared with analytic solutions.
Critical behavior of the ultrasonic attenuation for the binary mixture: Nitrobenzene and n-heptane
Authors: Fast Steven J. , Yun S. S.
Published: October 2005

The ultrasonic attenuation of the binary mixture nitrobenzene and n-heptane was measured at 5 and 15 MHz and compared with the dynamic scaling theory of Ferrell and Bhattacharjee [Phys. Rev. A 31, 1788 (1985); 24, 1643 (1981); Phys. Rev. B 24, 4095 (1981); Phys. Lett. A 86, 109 (1981); 88, 77 (1981)]. The values of α/f 2 vs f −1.06 yield a straight line as predicted by theory. The experimental values of α/αc are also compared to the scaling function F(ω*).
Circumferential propagation of S
H waves in hollow cylinders
Authors: Brun Yves , Candel Sébastien M.
Published: October 2005

This paper concerns the circumferential propagation of shear horizontally polarized waves in hollow, infinite, elastic cylinders. The exact solution of this classical problem expressed in terms of Bessel and Hankel functions gives rise to serious numerical difficulties when the circumferential wavenumber takes large values. A different method is developed to treat such cases. The method is based on a direct integration of the problem cast in the Sturm–Liouville form. Calculations performed with the Sturm–Liouville solver of Bailey et al. [ACM Trans. Math. Software 4, 193–208 (1978)] allow accurate determinations of SH modes for a wide range of geometrical parameters, reduced frequencies, and circumferential wavenumbers. This direct approach may be extended to other modal problems which are amenable to a standard Sturm–Liouville formulation.
Transient acoustic waves in a fluid-filled borehole with a horizontal bed boundary separating two solid formations
Authors: Tsang Leung
Published: October 2005

In a previous paper the acoustic logging problem of a pulsed point source in a fluid-filled borehole with a horizontal bed boundary separating two fluid formations was solved with the hybrid method. In this paper the method is extended to treat the case when there are two elastic solid formations outside the borehole that are separated by the horizontal bed boundary. The equations of the hybrid method for elastic formations are derived and are more complicated than the fluid case. The steps of the implementation of the numerical procedure are also discussed. Based on the method, the sonic waveforms, including the compressional and shear head waves and the normal mode arrivals, are calculated. Transmission coefficients of the head waves across the bed boundary are also calculated.
Stability of a Stokes boundary layer
Authors: Thompson Charles
Published: October 2005

The stability of the Stokes boundary layer generated by an acoustic disturbance in a two-dimensional waveguide is examined. Special attention is given to waveguides which have slowly varying cross sections. It is shown that the stability of the Stokes layer to three-dimensional vortical disturbances is governed by the value of three small parameters: ε, 1/R, and 1/S, where ε is the wall slope of the duct, 1/R is the ratio of the oscillatory boundary layer thickness to the typical duct height, and 1/S is the ratio of the oscillatory particle displacement to the duct height. A stability analysis is presented for the amplitude range ε2R/S2=O(R1/2). It is shown that instability occurs when ‖h″‖ε2R1/2/S2 is greater than 4.23. Attention is also given to the weakly nonlinear evolution of 3-D vortical disturbances. It is found that the Reynolds stress causes the solution for the disturbance field to bifurcate supercritically from that obtained by linear stability theory. The disturbance amplitude is shown to be governed by the solution of the nonlinear Schrödinger equation.
A numerical model for nonlinear and attenuative propagation and reflection of an ultrasonic bounded beam
Authors: Ngoc Tran D. K. , King Keith R. , Mayer Walter G.
Published: October 2005

Based on a numerical solution to the Burger’s equation, a computational model is developed to describe the propagation of an initially sinusoidal ultrasonic bounded beam. The propagation algorithm fully describes the combined effects of nonlinearity and attenuation mechanisms, which are responsible for the predicted growth and depletion of higher harmonics in a liquid medium. The model also incorporates reflection of the bounded beam from a solid plate immersed in the liquid and continues the propagation description after reflection. The important features of the computer model are presented and representative results are given for a 2.98-MHz, 2.0-cm-diam beam.
Eigenray finding and time series simulation in a layered-bottom ocean
Authors: Westwood Evan K. , Vidmar Paul J.
Published: October 2005

A ray theory approach for simulating the propagation of broadband signals interacting with a layered ocean bottom is presented. The range-invariant environment consists of the ocean and an arbitrary number of bottom layers. Each bottom layer has profiles of compressional and shear wave velocity, attenuation, and density. Eigenrays, including those with multiple interactions and refractions in the ocean and bottom layering, are found using a thorough and efficient algorithm based on an analysis of the sound velocity profile and the dependence of ray path geometry on the Snell invariant. The time series at a receiver due to an arbitrary source waveform is obtained by constructing a frequency domain transfer function from the eigenray characteristics. Several example applications demonstrate the potential use of this approach and show that reflection from relatively simple layering can severely distort a received time series.
The effect of impulse intensity and the number of impulses on hearing and cochlear pathology in the chinchilla
Authors: Hamernik Roger P. , Patterson James H. , Salvi Richard J.
Published: October 2005

Forty-one chinchillas, divided into seven groups, were exposed to 1, 10, or 100 noise impulses (one every 3 s) having peak intensities of 131, 135, 139, or 147 dB. Hearing thresholds were measured in each animal before and after exposure using an avoidance conditioning procedure; a surface preparation of the cochlear sensory epithelia was performed approximately 90 days after exposure. There was generally an orderly relation between the amount of permanent threshold shift and the severity of exposure, and a general agreement between averaged histological data and the audiometric data. For the impulses used in this study, there is a range of intensities which is bounded on the high side by the intensity which just produces injury with single impulse exposures and bounded on the low side by a critical intensity below which the injury potential drops precipitously with a reduction of impulse intensity. This region is only about 10–15 dB wide for the exposure conditions of this experiment. Within this region, the threshold of injury is a constant total energy; i.e., 10-dB change of intensity implies a tenfold change in the number of impulses for threshold injury. Detailed relations between temporary and permanent threshold shift, cochlear pathology, and exposure variables are discussed, as are the implications of these data to the development of exposure criteria.
Spectral transition dynamics of voiceless stop consonants
Authors: Kobatake Hidefumi , Ohtani Shigeko
Published: October 2005

This article presents dynamic characteristics of spectra of the voiceless stop consonants /p/, /t/, and /k/ in a feature space. The feature variables used in this article are the principal components of spectra of the voiceless stops. They characterize the gross spectral shape, such as a prominent midfrequency spectral peak, a diffuse-rising spectrum, and a diffuse-falling one. The invariability of the transition patterns of each consonant after the burst is evaluated quantitatively, and it is found that each consonant shows its own transition pattern in the majority of cases. Time history of the distance between the three consonants in the feature space is also shown. It shows that the gross spectral shape which characterizes /t/ and /p/ fades out very quickly and the time duration in which distinct spectral differences between them can be observed is as short as 5 ms, at most, after the burst. These spectral transition dynamics are confirmed by supplementary classification experiments.
Survey of impedance methods and a new piezo-disk-driven impedance head for air columns
Authors: Benade A. H. , Ibisi M. I.
Published: October 2005

The six major techniques used heretofore for the swept-sinusoid measurement of air column input impedances are first reviewed, after which the basic theory of a new, impedance head design that requires no servo mechanism is outlined. In this simple device, a low-cost piezoelectric disk is used as the primary flow excitation source, and the resulting response pressure is detected by a similarly inexpensive miniature electret microphone. Detailed experimental tests of the device are presented. Analysis of these tests shows that, up to about 5000 Hz, essentially no calibration corrections are needed; furthermore, the driver impedance is so high that its perturbations of the air column are experimentally negligible. A detailed mathematical analysis of the major finite-impedance, displaced-microphone, and higher-mode perturbations associated with the driving disk itself are set forth, and an outline of general procedures for obtaining the absolute calibration of any air column impedance head is given.
An acoustic impedance sensor with two reciprocal transducers
Authors: Bruneau Anne-Marie
Published: October 2005

A sensor has been built with two capacitive reciprocal transducers, one used to emit sound, the other acting as a microphone. Since the theoretical impedance functions of tubes are easily obtained, the calibration and the control of the functioning of the sensor are realized by taking detailed measurements of the input impedance of such tubes. This apparatus allows a variety of acoustical impedances to be measured with facility over a frequency range from 0.2–7 kHz.
Ray linking for computed tomography by rebinning of projection data
Authors: Andersen Anders Hvid
Published: October 2005

This paper presents a novel approach to geometrical acoustics ray linking for computed tomography. The complicated solutions to boundary value problems are replaced by much simpler initial value problems. As a result, a rebinning of projection data is performed.
Comments on the infrasonic noise theory of Isakovich and Kur’yanov and its modification by Wilson
Authors: Adair Richard G.
Published: October 2005

The infrasonic noise theory of Isakovich and Kur’yanov and its modification by Wilson are reviewed and evaluated. The tractability of the theory’s formulation depends upon two assumptions. The most crucial assumption is that the turbulent wind field, acting normally at the sea surface, linearly excites acoustic waves and wind waves in identical manners. This assumption is physically unreasonable. The second assumption is that the wind waves attenuate. Isakovich and Kur’yanov assume viscous attenuation, while Wilson incorporates the recent conjecture of Hasselmann that above a critical wind speed the attenuation is due to whitecapping and is quadratic in frequency. It is shown that, due to incorrect implementation of Hasselmann’s attenuation term, Wilson’s expressions for the noise source and pressure levels are too low by a factor of (2π)−2, or −16 dB.
Response to ‘‘Comments on the infrasonic noise theory of Isakovich and Kur’yanov and its modification by Wilson’’ [J. Acoust. Soc. Am. 8
1, 1192–1195 (1987)]
Authors: Wilson James H.
Published: October 2005

This letter is in response to comments made by R. Adair on previous work by Wilson.
Fundamental frequency stability characteristics of elderly women’s voices
Authors: Linville Sue Ellen , Korabic Edward W.
Published: October 2005

The purpose of this investigation was to gather information on how much variability on measures of jitter and fundamental frequency standard deviation (F0 s.d.) can be expected within individual elderly women when phonating sustained vowels ‘‘as steadily as possible.’’ Fifteen repeat productions of the vowels /i/, /a/, and /u/ from 18 elderly women (69–90 years) were analyzed for F0 s.d. and jitter. Results indicate that intraspeaker variability on jitter and F0 s.d. measures in elderly women’s sustained vowel productions can be quite considerable in some cases. This is a factor which needs to be considered in establishing normative data on elderly speakers’ vocal capabilities.
Estimation of arbitrary time delays of multichannel synthetic data
Authors: Callison J. Douglas , Riemer Terry E. , Trahan Russell E.
Published: October 2005

A new method for computing arbitrary time delays between multichannel data is introduced based on the idea of using the ordinary cross-correlation technique. It is shown that, by windowing the data record, events can be isolated and identified between channels. This new technique, called the window-correlation technique (WCT), is capable of determining arbitrary delays, very accurately, down to a signal-to-noise ratio of 0 dB. Finally, results of the WCT are compared to those of the ordinary cross correlation for Gaussian signals corrupted by additive Gaussian white noise.
Alternative approach for the formulation of the optimal image reconstruction algorithm for finite-size objects
Authors: Lee Hua
Published: October 2005

In a recent paper, the formulation of the optimal image reconstruction algorithm for finite-size objects with discrete data acquisition systems was introduced [J. Acoust. Soc. Am. 80, 195–198 (1986)]. The construction of the algorithm included the use of dual vector spaces and an inner product pair, and the formation of the adjoint operator of the linear continuous-discrete mapping associated with the wave propagation and data acquisition. In this article, an alternative derivation for the formulation of the optimal algorithm is provided. This approach bypasses the formation of the adjoint operator and therefore significantly reduces the complexity of the derivation. This method performs the entire derivation in a single inner product space and achieves the same optimal filter structure.
Randomized arrays
Authors: Lockwood J. C.
Published: October 2005

In acoustics, many arrays of practical interest are neither totally random, nor are their positions completely deterministic. Such arrays may be described as randomized arrays, wherein each element position is the sum of a deterministic design position and a random component. Expressions for the ensemble average and variance of the array factor are derived for randomized arrays of arbitrary design with five different randomization geometries. It is shown that the variance of the array factor is greatest far from its mainlobe. There is a low variance region centered at the steering direction, the size of which depends on the size of the randomization regions. Calculated examples are presented including applications to linear and planar arrays of various element design distributions. It is concluded that, in situations of limited randomization, the choice of design element distribution can determine whether or not an array will have repeatable, high sidelobes.
Performance comparison of the Wagstaff–Berrou and maximum entropy method beamformers
Authors: Meredith Roger W. , Ramsdale Dan J.
Published: October 2005

The performances of the maximum entropy method (MEM) and Wagstaff–Berrou broadband (WB2) high-resolution spatial processing techniques are compared with each other and with the conventional fast Fourier transform (FFT) beamformer. The comparisons are based on the analysis of three sets of measurements acquired at sea during two different environmental acoustics field exercises. Chosen for comparison are the effects of signal-to-noise ratio (SNR) on beamwidth and the effect of the number of array elements on the bearing estimation accuracy and beamwidth of the spatial processors. Results from these data indicate that both of the high-resolution methods yield smaller beamwidths than the conventional FFT processor, and that the high-resolution beamwidths show little dependence on SNR for values greater than 8 dB at the hydrophone input. Also, MEM beamwidths are generally slightly smaller than WB2 beamwidths and show less dependence on aperture. Measured MEM beamwidths show the same general trend as theoretical calculations for sensitivity to SNR, and the average arrival angles of all three beamformers show the same general dependence on the aperture.
The effect of broadband noise on the human brain-stem auditory evoked response. III. Anatomic locus
Authors: Burkard Robert , Hecox Kurt E.
Published: October 2005

The effects of broadband noise on the brain-stem auditory evoked response (BAER) are reported for two experiments. Experiment 1 used a high-pass subtractive-masking technique and covaried derived bandwidth and continuous broadband noise level. Comparisons of responses to half-octave wide derived bands in the presence of within-band noise showed that wave V latency changes were greater than could be explained on the basis of shifts in the cochlear region responsible for generating the response. The magnitude of within-band noise-induced wave V latency shift was independent of the frequency separation of the masker cutoffs. In experiment 2 the effects of noise level and rate on waves I, III, and V of the BAER were evaluated. Peak latencies increased and peak amplitudes decreased with increasing noise level and rate. Higher noise levels and rates produced an increased central (I–V) conduction time in which the wave III–V increase was greater than the wave I–III increase. Together, these results are most consistent with the hypothesis that a nonplace, central auditory mechanism produces most of the noise-induced latency shifts in normal-hearing adults.
The effect of broadband noise on the human brain-stem auditory evoked response. IV. Additivity of forward-masking and rate-induced wave V latency shifts
Authors: Burkard Robert , Hecox Kurt E.
Published: October 2005

The additivity of forward masking and repetitive stimulation effects on wave V of the brain-stem auditory evoked response (BAER) was investigated. The effects of repetitive stimulation were evaluated for a stimulus train (called the adaptation series), with a 12.5-ms within-train interclick interval. The forward masker was a 100-ms, 80-dB SPL broadband noise with forward-masker intervals ranging from 12.5–87.5 ms. Forward masking and repetitive stimulation increased the latency of wave V of the BAER. The combined forward masking/adaptation series produced less wave V latency shift than the summed individual effects. Forward masking reduced wave V amplitude at brief forward masker intervals, while repetitive stimulation did not affect wave V amplitude. Wave V amplitude was decreased for the combined forward masking/adaptation series, and the time course of amplitude recovery of the combination was prolonged compared to the forward masking alone condition. The nonadditivity of forward masking and rate effects on wave V latency is similar to that found for repetitive stimulation and simultaneous masking [Burkard and Hecox, J. Acoust. Soc. Am. 74, 1204–1213 (1983)]. These findings are consistent with the position that forward masking and rate effects on wave V latency are produced by overlapping mechanisms.
The acoustic radiation damping of the modes of a rectangular panel
Authors: Wallace C. E.
Published: October 2005

The acoustic damping for single modes of a finite rectangular panel, simply supported in an infinite baffle, is theoretically determined from the ratio of the acoustic energy radiated per cycle to the vibratory energy of the panel. Asymptotic solutions for the low-frequency region are presented for a panel mode driven at an arbitrary frequency and for a panel mode vibrating at its natural frequency. Curves of acoustic damping for a panel mode vibrating at resonance, as a function of the panel thickness-to-length ratio, are presented for various panel aspect ratios. For panels vibrating below the critical frequency, the damping depends on the aspect ratio with square panels developing the smallest value. For panels vibrating above the critical frequency, the damping is nearly independent of the aspect ratio.
Free vibration of unsymmetrically joined shell structures with a closed member
Authors: Kobayashi Yukinori , Irie Toshihiro
Published: October 2005

Free vibration is analyzed for unsymmetrical joined plate or shell structures with a closed member by means of the transfer matrix method. For this purpose, the continuity and equilibrium relations for the displacements and forces at the joints are written with use of the joint matrices. The connection matrix between the closed member and other members at the joints is derived by introducing the structure matrix of the closed member, and the entire structure matrix is obtained by the product of the connection matrix of the closed member and the transfer matrices of other members. This method is applied to a plate structure with an unsymmetrically sited duct and a box-type structure with an aslant interior plate, and the natural frequencies are calculated numerically together with the mode shapes of vibration giving the results.
A fundamental problem with mobility analysis of vibration isolation systems
Authors: Busch-Vishniac Ilene J.
Published: October 2005

The standard approach to vibration isolation analysis represents the source, isolator, and receiver by their mobilities. However, the choice of appropriate descriptor for each element is not arbitrary. Causality arguments show that whether the isolator is treated as a one-port or a two-port element, at least one of the system components must be represented by its impedance.
Wheel/rail rolling noise, II: Validation of the theory
Authors: Remington Paul J.
Published: October 2005

An analytical model for the prediction of wheel/rail noise is validated through comparison with measurements made using the state-of-the art car (SOAC) on a test track. Predictions of wheel and rail vibrations and wayside noise are seen to agree reasonably well with measurements although areas of uncertainty remain. Model improvements to reduce discrepancies between theory and measurement are discussed.
On the damped frequency response of a finite-element model of the cat eardrum
Authors: Funnell W. Robert J. , Decraemer Willem F. , Khanna Shyam M.
Published: October 2005

This article presents frequency responses calculated using a three-dimensional finite-element model of the cat eardrum that includes damping. The damping is represented by both mass-proportional and stiffness-proportional terms. With light damping, the frequency responses of points on the eardrum away from the manubrium display numerous narrow minima and maxima, the frequencies and amplitudes of which are different for different positions on the eardrum. The frequency response on the manubrium is smoother than that on the eardrum away from the manubrium. Increasing the degree of damping smooths the frequency responses both on the manubrium and on the eardrum away from the manubrium. The overall displacement magnitudes are not significantly reduced even when the damping is heavy enough to smooth out all but the largest variations. Experimentally observed frequency responses of the cat eardrum are presented for comparison with the model results.
Measurements on a liquid state electromagnetic transducer
Authors: Ajisaka Hidemi , Hixson Elmer L.
Published: October 2005

An electrically conducting fluid in a magnetic field generates forces as a result of the application of an electric current in the fluid, and a wave motion in the fluid generates an electromotive force. This effect has been applied to an underwater acoustic transducer: liquid state electromagnetic transducer. For the two acoustic ports and the electrical port, three-port equations have been presented whose coefficients are functions of such physical parameters as the duct size, fluid conductance, wave speed in the duct, and magnetic flux density. In this research, to examine the analytical model, salt water was used in a square duct of anodized aluminum, which has a pair of facing copper electrodes on the inside walls of the duct. A magnetic field was applied externally by an electromagnet. A series of measurements to evaluate every coefficient of the three-port equations was performed. Good experimental support for the model was obtained.
Diffraction of elastic waves by cracks or cavities using the discrete wavenumber method
Authors: Bouchon Michel
Published: October 2005

A new method to calculate the diffraction of elastic waves by cracks or cavities is presented. The method yields the complete diffracted wave field and is valid at any frequency. It is based on a discretization of the inclusion surface and on the assumption of a periodic repetition of the diffracting inclusion. Body forces are applied at the discretized points along the inclusion surface and the discrete wavenumber method is used to evaluate the resulting radiation. The application of the boundary conditions then leads to a linear system of equations, which is solved by matrix inversion. Examples of calculation and comparisons with results from other techniques are presented in the case of plane incident waves as well as in the case of a line source. The presence of a free surface is also considered.
The interior acoustic field of an automobile cabin
Authors: Succi George P.
Published: October 2005

The acoustic field in an automobile cabin can be calculated using a Green’s function method. A method for calculating the acoustic field of an arbitrary volume bounded by an arbitrary surface is shown. The eigenvalues of the system, including the effects of arbitrary shape and surface impedance, are found. Alternatively, the acoustic response is calculated when one or more of the surfaces is in vibration without first calculating the eigenvalues. The method works equally well in one, two, or three dimensions.
The effects of boundary surface inhomogeneities on acoustic scattering. I. Theory
Authors: Kuo Edward Y. T.
Published: October 2005

Analytical methods of Marsh [J. Acoust. Soc. Am. 33, 330–333 (1961)] and Kuo [J. Acoust. Soc. Am. 36, 2135–2142 (1964)] are applied to high-frequency acoustic wave scattering from an ocean bottom of roughness amplitude typically quite small in comparison with the acoustic wavelength of interest. The bottom surface variation in acoustic velocity is considered negligible but the bottom surface variation in density is considered appreciable and included in the model. The analytical result indicates the possibility of a new scattering effect in grazing incident directions due to correlated roughness and density variations. When there exists an identifiable dominant roughness wavenumber, the theory predicts discrete backscattering. This phenomenon was observed in an experiment reported by Roderick and Dullea (TD 7181, Naval Underwater Systems Center, 1984). When the dominant roughness wavenumber is zero, the result is that of Rayleigh’s flat boundary. When the dominant roughness wavenumber is low compared to acoustic wavenumber, the result is that of the Kirchhoff approximation.
Analysis of the amplification and convolution of reflected bulk acoustic waves in a piezoelectric/semiconductor structure
Authors: Josse Fabien
Published: October 2005

The amplification of reflected bulk acoustic waves (RBW) and the convolution of two oppositely traveling incident bulk acoustic waves is analyzed. The case of a normal field degenerate convolver is considered. It is shown, on an orientation of the bismuth germanium oxide (BGO) crystal in which only one mode is excited and in which no mode conversion occurs upon reflection, that RBWs can be amplified by the drifting carriers in a semiconductor. It is also shown that convolution resulting from the mixing of two incident bulk acoustic waves can be obtained. The overall behavior of the amplified RBW and of the convolver open-circuit voltage with the semiconductor parameters and the applied drift field and air gap is found to have some similarities to those of observed results in SAWs. A dependence of the acoustoelectric interactions on the angular distribution of the bulk wave radiation, hence the applied signal frequency, is shown. There may, however, exist some critical angles for the RBW for which no interaction exists due to the absence of an electric field in the gap. Results are presented for a BGO/Si structure and characteristics of the proposed RBW acoustoelectric devices are discussed.
Harmonic waves in a solid with a periodic distribution of spherical cavities
Authors: Achenbach J. D. , Kitahara M.
Published: October 2005

A dispersion relation has been obtained for the propagation of harmonic waves in an elastic solid containing a three-dimensional array of regularly spaced spherical cavities of equal radius. The general pattern of the frequency spectrum is one of passing and stopping bands. Results are presented for the lowest acoustic mode, the transition to the first optical mode, and for a segment of the first optical mode.
A multiscale analysis of nonlinear oscillations of gas bubbles in liquids
Authors: Samek L.
Published: October 2005

The nonlinear oscillations of a spherical gas bubble in a compressible viscous liquid subject to the action of a sound field are investigated by the multiscale perturbation method. Approximate analytical solutions for the transient oscillations in the regions of the main resonance, first and second harmonic, and first and second subharmonic, are obtained to second order in the expansion.