bluuebunny/crossref_metadata_2025 huggingface dataset:
Shallow-water high-frequency bottom scattering off Panama City, Florida
Authors: Stanic S. , Briggs K. B. , Fleischer P. , Ray R. I. , Sawyer W. B.
Published: October 2005

A series of bottom backscattering measurements was made in a flat, uniform, and isotropic area 19 miles south of Panama City, FL. Sidescan sonar, underwater television, stereo photography, high-resolution bathymetry, and sediment core analysis were used to locate and classify the experimental site. A sidescan sonar areal mosaic was contructed detailing the relationship between the experimental area and the surrounding topography. Bottom backscattering measurements were made as a function of frequency (20–180 kHz), grazing angle (5°–30°), azimuthal angle, and environmental conditions. Backscattering strengths were found to follow Lambert’s law with little frequency dependence or measurable anisotropy. For this particular site, scattering strengths at 90 kHz were found to agree with predictions made using the Applied Physics Laboratory—University of Washington (APL—UW) model.
An experimental study of acoustic waves in saturated glass beads
Authors: Costley R. D. , Bedford A.
Published: October 2005

The Biot–Stoll theory describes the propagation of acoustic waves in a saturated granular material. Expressions for the phase velocity and attenuation derived from the theory depend explicitly on the viscosity, density, and bulk modulus of the pore fluid. The results of an experiment designed to measure the dependence of the phase velocity and attenuation of compressional waves on these properties of the fluid are reported. The measurements were made in a laboratory tank containing glass beads saturated with a mixture of water and glycerin. To compare theory to data, the parameters of the theory were chosen so that they agreed with the measurements for the case of pure water. The values of the parameters were then kept constant and the theory was compared with the measurements obtained for various proportions of glycerin. It was shown that, within the estimates of the accuracy of the measurements, the Biot–Stoll theory predicts the effect of the fluid properties on the phase velocity and attenuation of compressional waves.
Effects of water-depth mismatch on matched-field localization in shallow water
Authors: Del Balzo Donald R. , Feuillade Christopher , Rowe Mary M.
Published: October 2005

This article discusses the impact of incorrect estimates of the water column depth on matched-field source localization in a shallow water environment. Computer calculations were performed for the case of a nominal 100-m depth water column subject to water-depth variations of up to ±3.5 m, which would be caused by long-period ocean swell or by tidal changes. The environment was assumed to be range independent (by proper choice of the geometry); thus the question of rough surface scattering was not an issue. The calculations incorporated source depths of 25, 50, and 75 m, a propagation distance of 4 km, an acoustic frequency of 150 Hz, and a linear vertical receiving array. The array consisted of 21 hydrophones with an interelement spacing of 2.5 m, and it spanned the center one-half of the water column (25- to 75-m depth). The matched-field algorithm utilized in this study is the high-resolution maximum-likelihood estimator. A primary result of the work is that, as the output of the matched-field processor degrades due to water-depth mismatch, the apparent source location varies in a systematic way; i.e., the source appears closer and deeper for increasing water depth and, conversely, the source appears farther and shallower for decreasing water depths. Another significant observation is that, as acoustic modes are stripped from the waveguide due to reduced channel depth, instabilities in the solution of the processor cause random variations in localization estimates.
Sidelobe suppression in annular array and axicon imaging systems
Authors: Moshfeghi Mehran
Published: October 2005

The equations describing the focal depth two-way cw beam patterns of an annular array, which is focused on transmit and receive, are analyzed. The approach of using different size apertures on transmit and receive, in order to place the minima of one beam pattern near the sidelobe of the other for sidelobe suppression, is investigated. The optimum sidelobe response occurs when the transmit aperture is about 0.76 (or 1/0.76) of the receive aperture. A similar analysis is carried out for J20 synthesis in axicon imaging. The effects of pulsed mode operation, aperture apodization, and the shape of the beam pattern outside of the focal depth are investigated with computer simulations for the beam pattern of a 5-MHz annular array.
Prediction of rectified diffusion during nonlinear bubble pulsations at biomedical frequencies
Authors: Church Charles C.
Published: October 2005

A computer study of rectified diffusion was made over the biomedical frequency range (1–10 MHz). Solutions of the Gilmore–Akulichev [E. Cramer, in Cavitation and Inhomogeneities in Underwater Acoustics, edited by W. Lauterborn (Springer, New York, 1980), pp. 54–63] formulation for bubble dynamics were combined with the Eller–Flynn [A. Eller and H. G. Flynn, J. Acoust. Soc. Am. 37, 493–503 (1965)] approach to rectified diffusion in order to calculate thresholds and growth rates. It is found that: (1) for frequencies above 1 MHz, the widely held view that small bubbles grow by rectified diffusion to ‘‘resonance size’’ and then collapse violently is true only for narrow ranges of bubbles; (2) growth rates in the low megahertz range can be quite high for medically relevant pressures, ∼20 μm/s at 1 MHz, 1 bar; (3) thresholds derived analytically are accurate for low frequencies over a wide range of bubble radii but, for high frequencies, only near the fundamental resonance radius; and (4) thresholds are quite sensitive to dissolved gas concentration at low frequencies.
Attenuation of sound mufflers with absorption and lateral resonances
Authors: Tarnow Viggo , Pommer Christian
Published: October 2005

A new method of calculating the effect of damping material placed in a sound muffler without flow and with arbitrary geometry is presented. The sound field in the muffler is calculated by constructing the Green’s function for the muffler chamber. This Green’s function is then expanded in a series consisting of the orthogonal eigenfunctions of the empty muffler. By using this expansion the impedance matrix is calculated for a single chamber muffler with circular cylindrical geometry lined with damping material. Using plane-wave theory for the inlet and outlet tube, the damping effect of the muffler is calculated for two different fiber absorbers. Taking into account the first lateral resonance in the series expansion, good agreement between experiments and calculated values is achieved for all experimental values.
A diffusion model of the transient response of the cochlear inner hair cell synapse
Authors: Westerman Larry A. , Smith Robert L.
Published: October 2005

One class of models of hair cell synaptic function that has been investigated in recent years consists of one or more reservoirs of synaptic material connected to other reservoirs and/or the synaptic cleft by means of diffusion paths. One such general model is considered here, comprising two reservoirs and a global source of synaptic material connected in series and releasing material into the synaptic cleft by a diffusion path characterized by an intensity-dependent permeability. The explicit form of the solution of the model for a sudden onset of stimulation is derived: The solution comprises two exponentially decaying terms plus a constant. This solution is shown to have a unique inverse. This allows the determination of the parameters of the model directly from experimental data from auditory-nerve fibers in the Mongolian gerbil. The behavior of the derived model parameters with variation of stimulus intensity is demonstrated, and implications for synaptic function are discussed.
Noise power fluctuations and the masking of sine signals
Authors: Hartmann W. M. , Pumplin Jon
Published: October 2005

This article is concerned with fluctuations in noise power and with the role that such fluctuations play in the masking of sine signals by noise. Several measures of noise fluctuations are discussed: the fourth moment of the waveform, the fourth moment of the envelope, and the crest factor. Relationships among these quantities are found for cases of equal-amplitude random-phase noise and Rayleigh-distributed-amplitude noise. Of particular interest is a special non-Gaussian noise called low-noise noise in which the fluctuations are small by any of our measures. The results of frozen-noise masking experiments are reported where the noise waveform was fixed for all stimulus presentations. In separate experiments, equal-amplitude random-phase Gaussian noise, with typical fluctuations, and low-noise noise, with almost no fluctuations were used. The data show that for a noise bandwidth less than the critical bandwidth, the masked threshold is about 5 dB lower for low-noise noise than for Gaussian noise. When the noise bandwidth is larger than the critical bandwidth, the masked threshold is the same for both kinds of noise. It is concluded that noise power fluctuations increase masked threshold by about 5 dB and that filtering by the auditory system reintroduces fluctuations into broadband low-noise noise.
Failure to obtain comodulation masking release with frequency-modulated maskers
Authors: Schooneveldt Gregory P. , Moore Brian C. J.
Published: October 2005

These experiments were intended to determine whether comodulation masking release (CMR) occurs for maskers that are modulated in frequency rather than in amplitude. In experiment I, thresholds for a sinusoidal signal were measured in the presence of two continuous sinusoidal maskers: one was centered at the signal frequency (1.0 kHz), and the other was positioned at flanking frequencies ranging from 0.5 to 2.0 kHz. The two maskers were frequency modulated (FM) by the same low-pass-noise modulator (correlated condition) or by independent noise modulators (uncorrelated condition). Thresholds were the same for the correlated and uncorrelated maskers, i.e., no CMR occurred. This was also true when the flanking band was presented in the ear opposite to that containing the signal and the on-frequency masking band. In experiment II, 25-Hz-wide noise maskers were used. The on-frequency band was sinusoidally frequency modulated, while the off-frequency band either had the same FM or no FM. Thresholds were similar for the two conditions, again indicating that no CMR occurred. The results suggest that, unlike amplitude modulation, correlated FM of the masker in different frequency bands does not give rise to a release from masking.
Excess masking among listeners with a sensorineural hearing loss
Authors: Gagné Jean-Pierre
Published: October 2005

Three experiments were conducted to determine whether listeners with a sensorineural hearing loss exhibited greater than normal amounts of masking at frequencies above the frequency of the masker. Excess masking was defined as the difference (in dB) between the masked thresholds actually obtained from a hearing-impaired listener and the expected thresholds calculated for the same individual. The expected thresholds were the power sum of the listener’s thresholds in quiet and the average masked thresholds obtained from a group of normal-hearing subjects at the test frequency. Hearing-impaired listeners, with thresholds in quiet ranging from approximately 35–70 dB SPL (at test frequencies between 500–3000 Hz), displayed approximately 12–15 dB of maximum excess masking. The maximum amount of excess masking occurred in the region where the threshold in quiet of the hearing-impaired listener and the average normal masked threshold were equal. These findings indicate that listeners with a sensorineural hearing loss display one form of reduced frequency selectivity (i.e., abnormal upward spread of masking) even when their thresholds in quiet are taken into account.
The negative effect of amplitude compression in multichannel hearing aids in the light of the modulation-transfer function
Authors: Plomp Reinier
Published: October 2005

The article deals with the question of why multichannel amplitude compression appears to have a negative rather than a positive effect on speech intelligibility by hearing-impaired listeners. It is argued that the small time constants of amplitude compression diminish the temporal as well as the spectral contrasts in the speech signal. According to the modulation-transfer function concept, this results in reduced intelligibility scores. Experimental evidence is reviewed indicating that the following two arguments in favor of amplitude compression in case of sensorineural hearing loss are not valid: (1) to compensate for the effects of loudness recruitment and (2) to get weak consonants above threshold. The author concludes that, in multichannel hearing aids, automatic gain control with time constants of 0.25–0.5 s should be given preference to amplitude compression.
Spectrum factors relevant to phonetogram measurement
Authors: Gramming Patricia , Sundberg Johan
Published: October 2005

Phonetograms showing the sound-pressure level (SPL) in loudest and softest possible phonation are frequently used in some voice clinics as an aid for describing the status of voice function. Spectrum analysis of the vowel /a/ produced by ten females and ten males with healthy, untrained voices revealed that the fundamental was mostly the strongest spectrum partial in soft phonation while the loudest partial in loud phonation was generally an overtone. Also, the first-formant frequency was generally lower in soft than in loud phonation. Measuring SPL in dB(A) rather than in dB lowered the phonetogram contour for soft phonation, an effect increasing with decreasing fundamental frequency. SPL measurements on a group of 22 females with healthy voices showed that the vowel /a/ gave higher SPL values than other vowels in loud phonation. The effect of using dB rather the dB(A) was great but similar for all vowels in soft phonation while, in loud phonation, the effect was small, particularly for /a/. In dB, the effect of using different vowels amounts to about ±5 dB, approximately. Interpretation of a phonetogram in terms of voice physiology is facilitated if SPL is given in dB and if a vowel with a high first-formant frequency is used.
Perception of aperiodicities in synthetically generated voices
Authors: Hillenbrand James
Published: October 2005

The purpose of this study was to investigate univariate relationships between perceived dysphonia and variation in pitch perturbation, amplitude perturbation, and additive noise. A time-domain, pitch-synchronous synthesis technique was used to generate sustained vowels varying in each of the three acoustic dimensions. A panel of trained listeners provided direct magnitude estimates of roughness in the case of the stimuli varying in pitch and amplitude perturbation, and breathiness in the case of the stimuli varying in additive noise. Very strong relationships were found between perceived roughness and either pitch or amplitude perturbation. However, unlike results reported previously for nonspeech stimuli, the subjective quality associated with pitch perturbation was quite different from that associated with amplitude perturbation. Results also showed that perceived roughness was affected not only by the amount of perturbation, but also by the degree of correlation between adjacent pitch or amplitude values. A strong relationship was found between perceived breathiness and signal-to-noise ratio. Contrary to previous findings, there was no interaction between signal-to-noise ratio and the amount of high-frequency energy in the periodic component of the stimulus: Stimuli with similar signal-to-noise ratios received similar ratings, regardless of differences in the spectral slope of the periodic component.
Wave propagation in laminated composite plates
Authors: Datta S. K. , Shah A. H. , Bratton R. L. , Chakraborty T.
Published: October 2005

A stiffness method has been used in this article to study dispersive wave propagation in a laminated anisotropic plate. The advantage of this method is in its usefulness in obtaining numerical results for the dispersion characteristics of waves propagating in a plate with an arbitrary number of arbitrarily anisotropic laminae. This method has been applied here, as a way of illustration, to a plate made up of transversely isotropic laminae with the axis of isotropy of each lamina lying in the plane of the lamina. Results thus obtained are shown to agree well with the exact solutions for isotropic and transversely isotropic single layered plates. Numerical results are presented for cross-ply (0°/90°/0°) laminated composite plates and show that the frequency spectrum in this case differs considerably from that for a single layered (0°) plate.
Wideband ambiguity function of broadband signals
Authors: Lin Zhen-biao
Published: October 2005

Broadband signal analysis and design for radar and sonar systems require the use of a wideband ambiguity function (WAF) to estimate their performance. The properties of WAF for FM signals are studied and the results of numerical computation are compared with the theoretical expressions. The main findings presented here include the following. (a) A broadband LFM signal is not a Doppler tolerant one. At high velocity, the magnitude of WAF is similar to the signal envelope, and its range resolution decreases obviously. (b) an LPM signal exhibits a fairly good range resolution, even at very high velocity. The performances of Doppler tolerant signals for three models are described and compared. The different envelopes for the LPM case have little influence on the behavior of WAF. (c) The unbiased delay estimation for both LFM and LPM signals, with bandwidth B= f max− f min and duration T, can be obtained by a special shift in time, which is such that t ∈ ( f minT/B,  f maxT/B). An approximate method for derivation of WAF, based on the Doppler cross-power spectrum and the stationary phase principle, is proposed. Such an analysis is applied to a bat’s sonar signal.
Analysis of acoustic scattering from fluid cylinders using a multifilament source model
Authors: Boag Amir , Leviatan Yehuda , Boag Alona
Published: October 2005

A solution is presented for the problem of two-dimensional acoustic scattering from homogeneous fluid cylinders. The solution uses fictitious filamentary isotropic sources to simulate both the field scattered by the cylinder and the field inside the cylinder and, in turn, point-matches the continuity conditions for the normal component of the velocity and for the pressure across the cylinder surface. The procedure is simple to execute and is general in that cylinders of arbitrary shape can be handled effectively. Perfectly rigid cylinders are treated as reduced cases of the general procedure. Results are given and compared with available analytic solutions, which demonstrate the very good performance of the procedure.
Investigation of Lamb waves having a negative group velocity
Authors: Wolf J. , Ngoc T. D. K. , Kille R. , Mayer W. G.
Published: October 2005

The propagation characteristics of Lamb waves in a solid plate are typically represented by a set of dispersion curves, which describe the Lamb-wave phase velocity as a function of the product fd, where f is the acoustic frequency and d is the plate thickness. For certain modes, within a range of phase velocity and fd, it has been theoretically predicted that the associated group velocity could be negative, i.e., the energy transport is in the opposite direction to the phase velocity. In the present study, Lamb waves are generated via mode conversion from a water-borne sound beam incident onto a flat brass plate. Measurement of the phase and group velocities of the Lamb waves of the S1 mode is performed for the fd range of 2.0–2.3 MHz-mm. Comparison of the measured and computed values of phase and group velocities shows good agreement and clearly demonstrates that S1-mode Lamb waves have a negative group velocity for fd=2.08–2.24 MHz-mm.
Frequency selectivity in loudness adaptation and auditory fatigue
Authors: Charron Sylvie , Botte Marie-Claire
Published: October 2005

An intermittent monaural tone may induce a decline in the loudness of a continuous tone presented to the same ear [Canévet et al., Br. J. Audiol. 17, 49–57 (1983)]. Two experiments studied the frequency selectivity of loudness adaptation induced in this manner. The method of successive magnitude estimations was used to measure the loudness of a monaural 84-s test tone before and after a single presentation of a 24-s inducer tone in the same ear. The first experiment shows that, for an inducing tone (500, 1000, or 3000 Hz) approximately 15 dB more intense than a test tone set to one of 21 different frequencies, adaptation is greatest when the two tones have the same frequency; with increasing difference between the test-tone and inducer frequencies, adaptation progressively declines. The second experiment measured frequency selectivity in the loudness reduction caused by a 1000-Hz inducer as a function of its level. As inducer level went from 75 to 95 dB (with test tone constant at 60 phons), selectivity passes progressively from the type seen in short-term or low-level fatigue (maximal for the 1000-Hz test tone) to a type seen in long-term or high-level fatigue (maximal at frequencies higher than that of the inducer or fatiguing tone). A common cochlear origin and a continuity between the mechanisms of ipsilaterally induced adaptation and high-level fatigue are suggested by the data.
Processing of acoustic signals in the auditory system of bony fish
Authors: Rogers Peter H. , Popper Arthur N. , Hastings Mardi C. , Saidel William M.
Published: October 2005

In order to determine unambiguously the bearing of a sound source, a fish must be able to resolve acoustic pressure and the components of the acoustic displacement vector from the signals detected by the otolithic organs. A new hypothesis for the processing of acoustical information by bony fish is presented. It is demonstrated that much of the processing required to do this may be implicit in the structure of the ear and its associated neural innervation. Possible algorithms are presented that the central nervous system might use to further process the derived information to localize a sound source and discriminate frequency and range. The hypothesis is shown to be consistent with much of what is known of the morphology and physiology of the auditory system of bony fishes.
Mutual interaction effects between array elements at different wavelengths in a coaxial circular array
Authors: Chakraborty Bishwajit
Published: October 2005

An analysis of the input impedances as well as excitation velocities of the 24 radiators in a coaxial circular array was carried out at different operating wavelengths suitable for underwater transducer application. Values of mutual impedances and excitation velocities were plotted against radiator number. From the present studies, it is established that, except at the operating wavelength of 7.5 λ, the values of mutual impedance and radiation resistance are higher. The highest values of excitation velocities are obtained at the operating wavelength of 7.5 λ and compared with others.
Synchronized videostroboscopic and electroglottographic examination of glottal opening
Authors: Anastaplo Sara , Karnell Michael P.
Published: October 2005

Interpretation of electroglottography (EGG) as an index of glottal contact area has been complicated by difficulty obtaining independent validation measures. The purpose of this research was to implement a new simultaneous EGG/videostroboscopic technique for the evaluation of the relationship between a discontinuity in the opening phase of the EGG waveform with the onset of glottal opening viewed via videostroboscopy. The results support previous suggestions that this EGG discontinuity, when observed in nonpathologic individuals, usually marks the onset of glottal opening along the superior surface of the vocal folds.
Similarities of vowels in nonreverberant and reverberant fields
Authors: Nábělek Anna K. , Letowski Tomasz R.
Published: October 2005

Perceptual distances among single tokens of American English vowels were established for nonreverberant and reverberant conditions. Fifteen vowels in the phonetic context /b–t/, embedded in the sentence ‘‘Mark the /b–t/again’’ were recorded by a male talker. For the reverberant condition, the sentences were played through a room with a reverberation time of 1.2 s. The CVC syllables were removed from the sentences and presented in pairs to ten subjects with audiometrically normal hearing, who judged the similarity of the syllable pairs separately for the nonreverberant and reverberant conditions. The results were analyzed by multidimensional scaling procedures, which showed that the perceptual data were accounted for by a three-dimensional vowel space. Correlations were obtained between the coordinates of the vowels along each dimension and selected acoustic parameters. For both conditions, dimensions 1 and 2 were highly correlated with formant frequencies F2 and F1, respectively, and dimension 3 was correlated with the product of the duration of the vowels and the difference between F3 and F1 expressed on the Bark scale. These observations are discussed in terms of the influence of reverberation on speech perception.
Simulation of a player–clarinet system
Authors: Sommerfeldt Scott D. , Strong William J.
Published: October 2005

A time-domain simulation model has been developed for investigating the player–clarinet system. The three components that constitute the simulation model consist of the player’s air column, reed, and the clarinet. The player’s air column is represented in terms of an analogous circuit model to obtain the mouth pressure. The reed is represented as a damped, driven, nonuniform bar. The clarinet is represented in terms of a scaled version of its input impedance impulse response. A convolution of the impulse response with the volume velocity determines the mouthpiece pressure. Use of the model is valid for both small- and large-amplitude reed oscillations. Many of the nonlinearities associated with the clarinet are incorporated in the model in a rather natural way. Several vocal tract configurations are investigated to determine the influence of the vocal tract on the player’s air column impedance and the concomitant effect on the clarinet tone.
A note on the use of intensity vector maps for source identification
Authors: Juvé Daniel
Published: October 2005

A procedure to identify noise sources from intensity vector maps is presented. It is based on the minimization, in a mean-squares sense, of the difference between the measured intensity field and an estimated one. The sensitivity of this inversion scheme to small random errors in the data is then studied by numerical simulations. It is shown that good estimates of the positions and strengths of the noise sources are obtained only when the measurements are made in the close vicinity of the source region.
Residue series solution of impulse noise propagation into a shadow zone
Authors: Raspet Richard , Franke Steven J.
Published: October 2005

Previously published calculations of impulse noise propagation into a shadow zone have been performed using expressions that are only valid above the creeping wave layer [C. G. Don and A. J. Cramond, J. Acoust. Soc. Am. 80, 302–305 (1986)]. In this letter the results of a calculation accurate within the creeping wave layer will be described.
User evaluation of major new performing arts halls
Authors: Engle Donald L.
Published: October 2005

The evaluations of individuals who respond to, and live with, the acoustics of recently completed performance arts spaces have been surveyed. The views surveyed are those of performers, media critics, reporters, facility managers, and patrons. The ways in which such evaluations are used in selecting an acoustical consultant for a new or renovated facility are discussed.
Exercises in acoustical measurement and signal analysis: A real world approach
Authors: Hixson Elmer L.
Published: October 2005

A laboratory course in acoustics for senior engineering or physics students is described. Learning basic measurements and analysis, followed by significant engineering oriented projects, is the recommended format. The area of environmental acoustics is chosen to minimize expense, yet provide measurement experience applicable to other fields. A list of the minimum required facilities and equipment is presented. A brief description of the basic measurement part of the course is followed by a set of shopping lists of projects. It is intended that the students learn project planning, execution, and documentation in addition to the subject material.
Note on the wave propagation across the boundary separating two elastic diatomic media
Authors: Nowinski J. L.
Published: October 2005

After establishing the equations of motion and the constitutive equations of the diatomic media, the solution of the resulting system of two coupled field equations is given. The relations between the wave amplitude coefficients are determined by appeal to the boundary conditions and an illustrative example involving relaxed bonds between the constitutive media is solved in some detail and illustrated by a graph.
Ultrasonic scattering by two concentric cylinders
Authors: Sinai Julian , Waag Robert C.
Published: October 2005

A series solution for scattering from two concentric, fluid cylinders of different speeds and densities has been employed to compute the scattered pressure for a range of frequencies, material parameters, and emitter and detector functions. This range includes the nominal parameters of measurements that were made at a frequency of 1.0 MHz and a radius of 150 mm on a gel model with an outer radius of 25.00 mm and an inner radius of 9.52 mm. The nominal parameters correspond to a ka of 626.2 for the measurement radius, a ka of 106.0 for the outer cylinder, and a ka of 39.8 for the inner cylinder. Scattering was calculated for frequencies for 10 kHz to 10 MHz which resulted in ka values from 6.26 to 6262 for the measurement radius, from 1.06 to 1060 for the outer cylinder, and from 0.398 to 398 for the inner cylinder. The effects on scattering of changes in speed and density parameters of the concentric cylinders are presented. First, the speed of the outer cylinder was raised by a factor of 10 from the nominal while the density of the outer cylinder and the speeds and densities of the inner cylinder and the surrounding medium were held fixed. Next, the density of the outer cylinder was raised while its speed was fixed at nominal, as were the speeds and densities of the inner cylinder and the medium. Finally, the speed first and then the density of the inner cylinder was raised while the parameters of the outer cylinder and of the medium were held fixed at nominal.

Plane-wave incidence as well as illumination from the one-dimensional versions of an ideal disk with a radius of 2.11 wavelengths at 1 MHz in water and an equivalent Gaussian aperture were considered, both modeled as an angular spectrum of plane waves. Detection at a point receiver and by a small Gaussian aperture equivalent to a disk radius of 0.498 wavelengths at 1 MHz was also investigated, as were increases by a factor of 10 in emitter and detector apertures while all other parameters were fixed at their nominal values. The combination of the wide range of parameters in this entire study required the development of accurate computational algorithms for Bessel and Neumann functions of arbitrary argument and arbitrary integer order. Measured results for the gel model and calculated results for the model parameters corroborate one another. Although agreement between measured and calculated magnitudes is better than that between measured and calculated phases, the results show that our model includes important effects.
Propagation of guided waves in fluid-coupled plates of fiber-reinforced composite
Authors: Nayfeh Adnan H. , Chimenti D. E.
Published: October 2005

Guided wave propagation in fluid-coupled plates of fiber-reinforced composites has been investigated by studying ultrasonic reflection in these structures. From measurements of ultrasonic reflection on unidirectional graphite-epoxy plates over a range of incident angles, experimental dispersion curves using a total-transmission criterion for leaky plate waves have been constructed. Theoretical calculations with no adjustable parameters demonstrate excellent agreement with the experimental data. Unusual behavior observed in the fundamental total-transmission curve led to a reexamination of the mode identification criteria. Both the total-transmission curves and the normal modes of the fluid-coupled plate differ significantly from the result expected on the basis of the widely used Cremer coincidence condition to identify propagating plate waves. It is found that these differences are particularly pronounced in cases where the ratio of fluid to solid densities is high, as for composite materials. The existence of such behavior is also demonstrated numerically in a fluid-coupled aluminum plate by arbitrarily increasing the density of the fluid.
Acoustic wave propagation through porous media with arbitrary pore size distributions
Authors: Yamamoto Tokuo , Turgut Altan
Published: October 2005

In the Biot [J. Acoust. Soc. Am. 28, 168–178 (1956); 28, 179–191 (1956)] theory, the effect of frequency on the viscous forces within a porous medium is treated by replacing the kinematic viscosity ν by an oscillatory viscosity νF, in which F is a function of angular frequency ω, the kinematic viscosity ν, and the single pore size a. The mathematical expression of F for arbitrary distribution of pore sizes that can be used in the Biot theory without modification is presented. It is shown that porous media with a given permeability and porosity may be represented by an infinite number of pore size distributions. The velocities and attenuation of acoustic waves through such porous media are independent of the pore size distribution at the low-frequency limit and at the high-frequency limit, while they are strongly dependent on the pore size distribution in the intermediate frequency range. Comparisons between Hamilton’s [Geophysics 37, 620–646 (1972)] data of attenuation coefficient of compressional waves through marine sediments and the prediction by our theory show good agreement.
A diffraction beam field expressed as the superposition of Gaussian beams
Authors: Wen J. J. , Breazeale M. A.
Published: October 2005

The diffraction field of a Gaussian planar velocity distribution is a Gaussian beam function under the condition (ka)2≫1. This property makes a series of Gaussian functions attractive as a possible base function set. The new approach presented enables one to express any axisymmetric beam field in a simple analytical form—the superposition of Gaussian beams about the same axis but with beam waists of different sizes located at different positions along the axis. A computer optimization is used to evaluate the coefficients, as well as the beam waists and their positions. The extreme case of a piston radiator is used to test the approach. Good agreement between a ten-term Gaussian beam solution and the results of numerical integration (or analytical solution on axis) is obtained throughout the beam field: in the farfield, the transition region, and the nearfield. Discrepancies exist only in the extreme nearfield (<0.1 times the Fresnel distance). For surface velocity distributions that are less discontinuous (smoother), the number of terms in the Gaussian beam solution is reduced. In the extreme case of a Gaussian radiator, only one term is needed. The approach, then, reduces the study of any axisymmetric beam field to the study of the much simpler Gaussian beam.
The response of planar elastic vibrators in a uniform flow field with broadband mechanical excitations
Authors: Li Dong-Jye , Stepanishen Peter R.
Published: October 2005

Flow-induced forces on structures can significantly affect their dynamic response. A new method is presented to evaluate the dynamic response of planar elastic vibrators in uniform fluid flow fields to broadband mechanical excitations. The approach is based on the use of an in vacuo eigenfunction expansion to solve the fluid-loaded problem. The time-dependent coefficients of the modal expansion for the velocity are shown to satisfy a set of coupled convolution integral equations that involve mode and Mach-number-dependent impulse responses. Pressures in the field are simply expressed as a summation of uncoupled convolution integrals. Numerical results are presented to illustrate the effects of Mach number on the transient response of a plate subjected to a broadband mechanical excitation.
Low-frequency backscatter from Arctic leads
Authors: Medwin Herman , Browne Michael J. , Johnson Kevin R. , Denny Patrick L.
Published: October 2005

Scale model experiments are used to demonstrate the significance of underwater low-frequency backscatter from Arctic leads, its relation to dipole radiation, and the difference between backscatter from a leading edge and a trailing edge. Application of the theory of impulse diffraction from a pressure-release wedge and its image is shown to successfully predict backscattering strength for a leading edge but to be inadequate for a trailing edge. The latter incorporates reradiation contributions from mode-converted waves in the plate, and head wave radiation, as well as diffraction. The dominant backscatter from a lineal element is due to mirrored diffraction from a single wavelength extent of the wedgelike scattering element at the least-time intercept. Backscattering strengths for point sources are given for a 3-octave range of frequencies over kI=0.5, where k is the wavenumber in water and I is the depth of immersion of the ice model.
Suppression tuning curves for spontaneous otoacoustic emissions in infants and adults
Authors: Bargones Jill Y. , Burns Edward M.
Published: October 2005

Suppression tuning curves (STCs) for spontaneous otoacoustic emissions (SOAEs) were longitudinally obtained in seven infants (at 3 weeks, 2 months, and 3, 4, or 6 months of age) and in five adults. Excellent reproducibility was obtained for adult STCs. Reproducibility for infant STCs was poorer, but the curves at each age resemble those of adults both qualitatively and quantitatively as measured by slopes of the lower and upper segments of the STCs and by Q10’s. Evidence from two subjects suggests that developmental changes in the fine tuning of the system may occur postnatally. Results are discussed with respect to the development of cochlear frequency selectivity.
Average discharge rate representation of voice onset time in the chinchilla auditory nerve
Authors: Sinex Donal G. , McDonald Lynn P.
Published: October 2005

Responses of chinchilla auditory-nerve fibers to synthesized stop consonants differing in voice onset time (VOT) were obtained. The syllables, heard as /ga/–/ka/ or /da/–/ta/, were similar to those previously used by others in psychophysical experiments with human and with chinchilla subjects. Average discharge rates of neurons tuned to the frequency region near the first formant generally increased at the onset of voicing, for VOTs longer than 20 ms. These rate increases were closely related to spectral amplitude changes associated with the onset of voicing and with the activation of the first formant; as a result, they provided accurate information about VOT. Neurons tuned to frequency regions near the second and third formants did not encode VOT in their average discharge rates. Modulations in the average rates of these neurons reflected spectral variations that were independent of VOT. The results are compared to other measurements of the peripheral encoding of speech sounds and to psychophysical observations suggesting that syllables with large variations in VOT are heard as belonging to one of only two phonemic categories.
Signal transmission in noisy environments: Auditory masking in the tympanic nerve of the bushcricket M
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Authors: Bailey Winston J. , Stephen Richard O. , Yeoh Paul
Published: October 2005

Physiological responses of the auditory leg nerve were recorded in the tettigoniid Metaballus litus to suprathreshold tone pulses of 12.45 kHz, which is close to the carrier frequency of the male’s call. This stimulus tone frequency was determined by characterizing the polar response of the foreleg. Physiological threshold of the receptors was calculated from intensity input/output curves, and the experimental stimulus was set at 40 dB above this threshold value. There was low variance in threshold values between preparations. Continuous octave filtered white noise centered on the stimulus frequency was presented at the same time as the tone pulse at increasing intensities. The summed action potentials (SAPs) of the whole leg nerve were averaged over 256 stimulus presentations and the magnitude of the response was calibrated to dB values. The range of noise levels was set between that inducing no decrease in the SAP response to the tone pulse stimulus, up to a masking intensity where the response to the tone pulse was only just observable. Decrement in SAP magnitude was linear, and complete masking occurred when the noise level was 20–25 dB above the initial level of zero masking. This final level was comparable in magnitude to the sound-pressure level of the tone pulse and within the natural range of the insect’s auditory behavior. Following the cessation of the noise signal, the SAPs were monitored over intervals of 2 min until the SAP asymptoted to the preexperimental condition. The reduction in SAP magnitude during noise presentation was attributed to a loss in synchrony from the individual tympanic receptors.
Effective properties of multicomponent simultaneous maskers under conditions of uncertainty
Authors: Neff Donna L. , Callaghan Brian P.
Published: October 2005

When more than one sinusoid is used as a masker, more masking is observed than would be predicted by a simple combination of their individual effects. This masking is dramatically increased when the masker components vary in frequency and intensity with each presentation. These studies manipulated several masker parameters under conditions of high masker uncertainty, examining the effect of excluding critical-band components, fixing or randomizing component amplitudes and frequencies, and narrowing the frequency range of the components. The signal was always a 200-ms, 1000-Hz sinusoid, presented simultaneously with the 200-ms masker. Removing critical-band components reduced the amount of masking, but considerable masking remained that appears to be nonperipheral in origin. Fixing masker frequencies across the two intervals of a trial greatly reduced the masking observed, whereas fixing masker amplitudes had no effect. Reducing the frequency range from 5000 to 2700 Hz generally increased the masking observed, but appeared to depend on other masker parameters. Summaries across ten listeners show individual differences that are resistant to extensive training. It is difficult to account for most of the masking observed in terms of masker energy falling near the region of the signal.
Adaptive staircase techniques in psychoacoustics: A comparison of human data and a mathematical model
Authors: Kollmeier Birger , Gilkey Robert H. , Sieben Ulrich K.
Published: October 2005

Data from a simple tone-in-noise simultaneous masking task were used to evaluate each of two common adaptive staircase rules (a ‘‘1 up 2 down’’ rule and a ‘‘1 up 3 down’’ rule) and the parameter estimation by sequential testing (PEST) technique in combination with each of two psychophysical procedures [a two-alternative forced-choice (2AFC) and a three-alternative forced-choice (3AFC) procedure]. These human data were compared to predictions generated by a mathematical model based on Markov theory. The model predicts that threshold estimates obtained with the adaptive techniques should be equal to those derived with equivalent ‘‘fixed signal level’’ techniques. However, the human data indicate that the adaptive techniques tend to yield lower thresholds. The model predicts that the standard error of a threshold estimate obtained from an adaptive technique will decrease and approach zero as the number of trials used to compute the estimate increases. The human data show greater variability than predicted and approach a nonzero value as the number of trials increases. The predictions of the model suggest that the commonly used combination of the 2AFC procedure and the 1 up 2 down rule is the least efficient method of estimating a threshold and that the 3AFC procedure in combination with the 1 up 3 down rule is the most efficient method. The human data are less consistent, but generally show the combination of the 2AFC procedure and the 1 up 2 down rule to be one of the least efficient methods. Possible explanations for the differences between the model’s predictions and the human data, as well as suggestions for laboratory practice, are discussed.
Community response to noise: A review of factors influencing the relationship between noise exposure and reaction
Authors: Job R. F. S.
Published: October 2005

Social surveys of the relationship between noise exposure and the subjective reactions to it were reviewed. This review indicated that remarkably similar results have been obtained across different nationalities with different measurement techniques. Only a small percentage (typically less than 20%) of the variation in individual reaction is accounted for by noise exposure. Analysis of potential errors in both measurement of noise and reaction suggests that elimination of errors would only slightly increase the observed correlations. Variables, such as attitude to the noise source and sensitivity to noise, account for more variation in reaction than does noise exposure. The weaker relationship between noise exposure and attitude than between reaction and attitude suggests that the attitude/reaction relationship is not entirely due to noise exposure causing a change in attitude itself. Noise/reaction correlations based on individual data are significantly lower in studies of impulsive noise than nonimpulsive noise. This may be caused, in part, by the restricted range of noise exposure studied in some socioacoustic investigations of impulsive noise. However, the significantly higher correlations of attitude and reaction in impulsive noise studies suggest that attitude plays an even larger part, while noise exposure plays a lesser part in determining reaction to impulsive noise, relative to nonimpulsive noise.
The role of glycogen and phosphate in ultrasonic attenuation of liver
Authors: Parker K. J. , Tuthill T. A. , Baggs R. B.
Published: October 2005

The excess ultrasonic attenuation caused by adding glycogen and inorganic phosphate to liver homogenates has been studied to determine the underlying differences between attenuation coefficients of normal and diffusely diseased livers. Results show that glycogen has a higher than average specific absorption coefficient compared to other large molecular weight biomolecules. Since the glycogen content of liver can vary from 1%–10% of wet weight, this compound may have a major time-varying effect on the liver ultrasonic attenuation coefficient, even in normal subjects. In contrast, the excess attenuation of liver homogenate resulting from addition of inorganic phosphate was not significant at presumed physiological levels. The implications of these findings are discussed relative to tissue characterization efforts based on in vivo measurements of ultrasonic attenuation coefficients of liver.