bluuebunny/crossref_metadata_2025 huggingface dataset:
A model for wave propagation in a porous medium saturated by a two-phase fluid
Authors: Santos Juan E. , Douglas Jim , Corberó Jaime , Lovera Oscar M.
Published: October 2005

A theory to describe the propagation of elastic waves in a porous medium saturated by a mixture of two immiscible, viscous, compressible fluids is presented. First, using the principle of virtual complementary work, the stress–strain relations are obtained for both anisotropic and isotropic media. Then the forms of the kinetic and dissipative energy density functions are derived under the assumption that the relative flow within the porous medium is of laminar type and obeys Darcy’s law for two-phase flow in porous media. The equations of motion are derived, and a discussion of the different kinds of body waves that propagate in this type of medium is given. A theorem on the existence, uniqueness, and regularity of the solution of the equations of motion under appropriate initial and boundary conditions is stated.
The calculation of acoustic fields in solids for transient normal surface force sources of arbitrary geometry and apodization
Authors: McNab A. , Cochran A. , Campbell M. A.
Published: October 2005

Methods used to calculate the radiated acoustic field of transient normal surface force sources applied to elastic solids have previously included significant approximations or have constrained the surface force distribution in practically restrictive ways. In this paper, a theoretically exact, quantitative, numerical solution to the problem is described. The only constraint on the applied suface force in this solution is that it is cophased. Nevertheless, by efficient numerical construction, the computational expense required is not inconveniently large. Theoretical results are presented and compared with results in the literature.
The interaction of Helmholtz resonators in a row when excited by a turbulent boundary layer
Authors: Flynn Kevin P. , Panton Ronald L.
Published: October 2005

The interaction between individual Helmholtz resonators when arranged in a row and excited by a turbulent boundary layer was explored experimentally. A wind tunnel wall, which had a turbulent boundary layer, provided the test region for the resonators that were placed across the span. Ten resonator orifices were flush mounted on the wall and the cylindrical resonator cavities were behind the orifice plate. In a series of tests, the effect of resonator spacing upon the response level, frequency, and the coherence and phase between resonators was determined. When two resonators were paired the oscillating cavity pressure level increased by 1 dB (at orifice spacings of one boundary layer thickness). This effect decreased with increased spacing. The same trend occurred for the correlation between resonator signals. When a row of several resonators was tested, the coherence and response level enhancement were less than that for two paired resonators. In both row and paired configurations, the oscillation between adjacent cavities was out of phase: the angle varied from 150 to 180 deg. This antiphase behavior was attributed to a fluid mechanic coupling as contrasted to acoustic coupling. The frequency of a single resonator’s response was seen to be an almost linear function of air speed. This behavior was also observed when interacting with other resonators, although the frequencies were increased by about 1%. Estimates were made of the appropriate outside end-correction factor that would be associated with these frequency changes.
Numerical implementation of a modal solution to a range-dependent benchmark problem
Authors: Thomson David J. , Brooke Gary H. , DeSanto John A.
Published: October 2005

Numerical results are presented for a modal representation of sound propagation in a range-dependent waveguide with plane-parallel, perfectly reflecting boundaries. Range dependence in the waveguide is embedded in the sound speed that varies sinusoidally with depth and exponentially with range. The modal expansion is based on a conformal mapping technique, whereby the solution to the Helmholtz equation in a range-dependent waveguide is expressed in terms of a solution to a parabolic equation in a corresponding waveguide whose sound speed is constant in the mapped coordinates.
Reply to ‘‘Comment on ‘Thermal noise in a fiber optic sensor’ ’’ [J. Acoust. Soc. Am. 8
4, 471–475 (1988)]
Authors: Hofler Thomas J. , Garrett Steven L.
Published: October 2005

This Letter is a reply to the comment by M. D. Mermelstein [J. Acoust. Soc. Am. 87, XXX–XXX (1990)].
Acoustic tracking from closest point of approach time, amplitude, and frequency at spatially distributed sensors
Authors: Milios Evangelos E. , Nawab S. Hamid
Published: October 2005

This paper addresses the problem of passive acoustic tracking from closest point of approach (CPA) time, amplitude, and frequency data at spatially distributed sensors in the case of finite sound-propagation delay. A novel method is presented for the computation of source velocity (speed and direction) from the CPA times at three noncollinear sensors that lie on the same side of the source path. The method reduces the problem to the solution of a linear trigonometric equation. The method is used as the basis for determining the qualitative location of a straight source path with respect to a square grid of calibrated sensors, assuming that the amplitude of the sensor signal at CPA varies monotonically with the distance between source and sensor. In the case of a maneuvering source, qualitative relations are stated between the local shape of the source path, its relative position with respect to an acoustic sensor, and whether amplitude and frequency increase or decrease monotonically with (source) time at that sensor. These qualitative relations from multiple sensors are then used to segment the source path into straight and maneuvering segments (under negligible propagation delay). Experimental results with real data are presented for the source-velocity computation, together with a sensitivity analysis.
Two models for the spatially covariant field scattered by randomly rough pressure-release surfaces with Gaussian spectra
Authors: Restrepo Juan Mario , McDaniel Suzanne T.
Published: October 2005

Two models for the spatial covariance of scalar waves scattered by randomly rough pressure-release surfaces are presented. The first model is based on partial integration of the Helmholtz–Kirchhoff integral. The second employs potential theory to solve the radiation problem from a surface that is thought of as a dipole source distribution. In-plane and out-of-plane intensity and coherence from both models are compared using flat surfaces and surfaces with a Gaussian spectrum. Comparisons of intensity show good agreement if the surface is very rough and/or the direction is specular, and that for directions far from the specular one the second model is more accurate. Comparisons of coherence, on the other hand, show good agreement under all circumstances.
Resonance scattering in waveguides: Acoustic scatterers
Authors: Carrion Philip M. , de Brito Marco Antonio P.
Published: October 2005

In this paper, acoustic scattering in shallow and deep inhomogeneous waveguides is analyzed. The full acoustic wave equation that describes the scattered and reflected wave fields, as well as all multipathing within the scatterer and the waveguide, is employed. The explicit finite difference time integration and the k–w transform in the space domain (pseudospectral method) were utilized. Properly chosen boundary conditions enabled the authors to model both shallow and deep oceans. The pseudospectral method was compared with the explicit finite difference technique (see Appendix). The pseudospectral method can be valuable for modeling different underwater wave phenomena: It is characterized by much smaller numerical dispersion than the conventional finite difference method. The results show that in shallow ocean, strong resonance coupling between the underwater scatterer and the waveguide may occur. An important conclusion of this paper is that in a limited aperture experiment when the acoustic reflections are beyond the recording aperture (due to the finite length of the recording cable), the measured data are mainly represented by the primary diffraction arrivals and ‘‘diffraction resonances.’’ In this paper, a detailed discussion will be given on the acoustic scattering in an inhomogeneous waveguide. (For the sake of simplicity, an acoustic scatterer of the rectangular shape was considered.) Different complexities (elastic scatterers, more complicated structures of the index of refraction in the water, etc.) will be compounded in the original model and reported elsewhere.
Environmental signal processing: Three-dimensional matched-field processing with a vertical array
Authors: Perkins John S. , Kuperman W. A.
Published: October 2005

Matched-field processing in a three-dimensional (range and azimuthal dependent) environment provides the possibility of localizing a source in bearing, as well as in range and depth, with a purely vertical array since the environment itself breaks the azimuthal symmetry of the vertical array. This added dimension in aperture is a result of including environmental complexity in the matched-field process. The processing is referred to here as environmental signal processing (ESP) and is demonstrated by simulation. A Gulf Stream environment where sound speed and bathymetry vary in three dimensions is selected for this simulation.
On estimating the amplitude of harmonic vibration from the Doppler spectrum of reflected signals
Authors: Huang Sung-Rung , Lerner Robert M. , Parker Kevin J.
Published: October 2005

The Doppler spectrum of echoes from a sinusoidally vibrating scatterer has discrete spectral lines weighted by Bessel functions of the first kind. Because the signal and spectrum are complicated functions of the vibration amplitude, a number of different approaches have been tried in the past to estimate the vibration amplitude, given a received signal. Here, a new and simple relationship between the spread (or variance) of the Doppler spectrum and the vibration amplitude is derived. A method of estimating the vibration amplitude is proposed based on this relation and a noise compensation procedure is also demonstrated. The performance of the estimators is studied through simulations. High accuracy is predicted under proper sampling conditions even when the signal-to-noise ratio is poor. Slight deviations from single-frequency oscillation, as would be caused by nonlinear or nonideal medium or source effects, are found to have little contribution to the total estimation error.
Recovery of acoustic source extent by Fourier phase analysis of emitted signals
Authors: Sachse Wolfgang , Pierce Wilbur F.
Published: October 2005

This paper considers an algorithm for recovery of the size of an extended, finite source of elastic waves in a plate from the Fourier phase function of the signals it emits. In the forward problem, an extended source is modeled as an assemblage of point sources of variable strength arranged along a straight line. The Fourier phase spectrum of the first arrival signal from such a source is determined. It is shown that this phase function contains information related to the spacial extent of the source and that it can be processed, along with the phase function of a single point source, to recover the extent of the extended acoustic source. Applications of the algorithm to process synthetic signals from extended sources with three spatial distributions in the interior of the plate are given.
Radiation efficiency of acoustic guitars
Authors: Lai J. C. S. , Burgess M. A.
Published: October 2005

The transfer functions between acceleration and force (‘‘accelerance’’) at the driving point and radiation efficiencies for the top plates of guitars have been investigated. A vibration exciter was used for driving the guitar at the bridge and the transfer functions and cross-power spectra were measured at the driving point with the aid of an impedance head. The frequency spectrum of the accelerance function determined in this manner showed good agreement with those reported for the same guitar using a different excitation and measurement method. The output acoustic intensity was measured with a sound-intensity probe and the radiated sound power from the top plate was determined. The radiation efficiency, determined from the ratio of the top plate radiated sound power and the input power, is presented for different guitars and for a guitar with a modified top plate.
Speech feature recognition by profoundly hearing impaired children using a multiple-channel electrotactile speech processor and aided residual hearing
Authors: Alcántara Joseph I. , Whitford L. A. , Blamey P. J. , Cowan R. S. C. , Clark G. M.
Published: October 2005

A group of prelinguistically profoundly hearing impaired children, between 7 and 11 years of age, were trained in the perception of vowel duration and place, the fricative /s/, and manner of articulation (/m/ vs /b/ and /s/ vs /t/) distinctions, using information provided by a multiple-channel electrotactile aid (Tickle Talker), and through aided hearing. Training was provided in the tactile-plus-aided hearing (TA) and tactile (T) conditions. Speech feature recognition tests were conducted in the TA, T, and aided hearing (A) conditions, during pre-training, training, and post-training phases. Test scores in the TA and T conditions were significantly greater than scores in the A condition for all tests, suggesting that perception of these features was improved when the tactile aid was worn. Test scores in the training and post-training phases were significantly greater than in the pretraining phase, suggesting that the training provided was responsible for the improvement in feature perception. Statistical analyses demonstrated a significant interaction between the main effects of condition and phase, suggesting that training improved perception in the TA and T conditions, but not in the A condition. Post-training and training test scores were similar suggesting that the perceptual skills acquired during training were retained after the removal of training. Recognition of trained features improved for trained, as well as for untrained words.
On the dependence of ( f2−f1) difference tones on subject and on additional masker
Authors: Zwicker Eberhard , Martner Otto
Published: October 2005

For a group of eight subjects showing stronger than usual irregularities in the level dependence of the quadratic distortion product, the level and phase of the (f2−f1) difference tone were measured using the method of cancellation for three sets of primary frequencies as a function of the primary levels. An additional masker seems to ‘‘linearize’’ the level dependence toward regular behavior. Using data sets produced with and without the additional masker, it is possible to separate two sources of quadratic nonlinearity, one with regular behavior presumably located in the middle ear and another with irregular behavior (similar to that of cubic distortion) presumably located in the characteristics of outer hair cells. Through the ‘‘subtraction’’ of empirically determined patterns from idealized patterns, it is possible to approximate patterns stemming from the inner-ear source alone.
Perceived sound quality of reproductions with different frequency responses and sound levels
Authors: Gabrielsson Alf , Hagerman Björn , Bech-Kristensen Tommy , Lundberg Göran
Published: October 2005

Three programs (female voice, jazz music, and pink noise) were reproduced using four different frequency responses and two different sound levels. Fourteen normal hearing subjects listened to the reproductions via earphones and judged the sound quality on seven perceptual scales (loudness, clarity, fullness, spaciousness, brightness, softness/gentleness, and nearness) and a fidelity scale. Significant differences among the reproductions appeared in all scales and could be attributed to the differences in frequency response or sound level or both. Interactions between the reproductions and the programs could be explained by the relations between the spectrum of the programs and the frequency responses used. The results for the noise program were similar to those for the jazz music program.
Perception of sentences, words, and speech features by profoundly hearing-impaired children using a multichannel electrotactile speech processor
Authors: Cowan R. S. C. , Blamey P. J. , Galvin K. L. , Sarant J. Z. , Alcántara J. I. , Clark G. M.
Published: October 2005

Fourteen prelinguistically profoundly hearing-impaired children were fitted with the multichannel electrotactile speech processor (Tickle Talker) developed by Cochlear Pty. Ltd. and the University of Melbourne. Each child participated in an ongoing training and evaluation program, which included measures of speech perception and production. Results of speech perception testing demonstrate clear benefits for children fitted with the device. Thresholds for detection of pure tones were lower for the Tickle Talker than for hearing aids across the frequency range 250–4000 Hz, with the greatest tactual advantage in the high-frequency consonant range (above 2000 Hz). Individual and mean speech detection thresholds for the Ling 5-sound test confirmed that speech sounds were detected by the electrotactile device at levels consistent with normal conversational speech. Results for three speech feature tests showed significant improvement when the Tickle Talker was used in combination with hearing aids (TA) as compared with hearing aids along (A). Mean scores in the TA condition increased by 11% for vowel duration, 20% for vowel formant, and 25% for consonant manner as compared with hearing aids alone. Mean TA score on a closed-set word test (WIPI) was 48%, as compared with 32% for hearing aids alone. Similarly, mean WIPI score for the combination of Tickle Talker, lipreading, and hearing aids (TLA) increased by 6% as compared with combined lipreading and hearing aid (LA) scores. Mean scores on open-set sentences (BKB) showed a significant increase of 21% for the tactually aided condition (TLA) as compared with unaided (LA). These results indicate that, given sufficient training, children can utilize speech feature information provided through the Tickle Talker to improve discrimination of words and sentences. These results indicate that, given sufficient training, children can utilize speech feature information provided through the Tickle Talker to improve discrimination of words and sentences. These results are consistent with improvement in speech discrimination previously reported for normally hearing and hearing-impaired adults using the device. Anecdotal evidence also indicates some improvements in speech production for children fitted with the Tickle Talker.
Time-domain analysis of auditory-nerve-fiber firing rates
Authors: Secker-Walker Hugh E. , Searle Campbell L.
Published: October 2005

Time domain analysis of firing-rate data from over 200 fibers from the auditory nerve of cat has been used to estimate the formats of the synthetic-syllable stimuli. Distinct groups of fibers are identified based on intervals between peaks in the fiber firing rates. The large extent of some of these groups—over an octave in terms of characteristic frequency—and the lack of short intervals in the longer-interval groups suggest that the behavior of the nonlinear cochlear filters for these signals is effectively wideband with steep high-frequency cutoffs. The measured intervals within each group are very similar, and correspond to the period of the format that dominates the group’s response. These intervals are used to estimate the dynamic speech formants. The overall formant estimates are better than those of the previous spectral analyses of the neural data, and the details of lower-formant dynamics are tracked more precisely. The direct temporal representation of the formant is contrasted with the diffuse spectral representation, the dependence of spectral peaks on nonformant parameters, and the distortion of the spectrum by rectification. It is concluded that a time-domain analysis of the responses to complex stimuli can be an important addition to frequency-domain analysis for neural data, cochlear models, and machine processing of speech.
The effect of a semicircular diffuser on the sound field in a rectangular room
Authors: Pan Jie , Bies David Alan
Published: October 2005

Previous experimental work has shown the influence of a rotating diffuser upon the diffusion of a reverberant field, upon the radiation impedance of a sound source in a reverberation room, and upon the boundary absorption. Some interesting results of the latter work require a quantitative interpretation, while others suggest a need for further investigation to obtain a detailed physical insight. In an effort to gain insight into and an interpretation of the latter work, a finite-element approach is presented. This paper is an interim report on continuing research, and it reviews an investigation of the effect of a semicircular diffuser upon a two-dimensional sound field in a rectangular room. A numerical relationship between the resonance frequencies of the acoustical modes in the room and the diffuser orientation is given. The sound-pressure distributions of the acoustical modes are also given as the function of the diffuser orientation. A three-dimensional cavity is used for experimental verification. In this cavity, only the sound waves in the horizontal plane will be affected by the diffuser. The experimental and numerical results agree closely.
Auditory temporal integration in the normal-hearing and hearing-impaired cat
Authors: Solecki Janet M. , Gerken George M.
Published: October 2005

Temporal integration functions obtained from human subjects with sensorineural hearing loss have shallower slopes than the functions obtained from normal-hearing subjects. The present investigation was designed to explore this relation in animals in order to compare normal-hearing cats and humans. Auditory temporal integration functions were measured for five cats before and after they were exposed to a 2-kHz tone at 110 dB SPL for 48 h. To measure the temporal integration functions, ten stimuli were used that had overall durations from 8.32 to 275 ms and that were configured either as single or multiple tone bursts of 6.25 kHz. Twelve thresholds for each stimulus were obtained from each animal before and after the sound exposure. Pre- and postexposure audiograms were also obtained and the mean permanent threshold shift at 6.25 kHz was 32.5 dB. Exponential and power function models were used to describe the data. The exponential model (with grand-mean data) yielded a pre-exposure time constant (τ) of 188 ms [mean absolute residual (MAR) of 1.5 dB] and a postexposure τ of 21 ms (MAR of 1.4 dB). For the power function model with grand-mean data, the pre-exposure slope was 6.6 dB per decade of duration (MAR of 1.4 dB) and a postexposure slope of 3.8 dB per decade of duration (MAR of 0.7 dB). The results indicated that the slope of the temporal integration function was less steep after sensorineural hearing loss of cochlear origin, and that the power function model was more effective in describing temporal integration data for the range of stimulus durations employed. It is concluded that the temporal integration functions for cat and human are similar.
The role of single-channel cues in synchrony perception: The summed waveform
Authors: Richards Virginia M.
Published: October 2005

Human observers are able to discriminate between simultaneously presented bands of noise having envelopes that are identical (synchronous) rather than statistically independent (asynchronous). The possibility that the detection of envelope synchrony is based on cues available in a single critical band, rather than on a simultaneous comparison of envelopes extracted via independent critical bands, is examined. Two potential single-channel cues were examined, both relying on the assumption that information present in the envelope of the summed bands is available to the listener. One such single-channel cue is the rms of the envelope of the summed waveform; the envelope is more deeply modulated for the summed synchronous bands than for the summed asynchronous bands. The second cue examined was envelope regularity; the envelope of the summed synchronous bands has periodic envelope minima, while the summed asynchronous bands exhibit aperiodic envelope minima. Psychophysical results suggest that such within-channel cues may be both available to, and utilized by, the listener when the component bands are separated by less than 1/3 of an octave.
Age changes in pure-tone hearing thresholds in a longitudinal study of normal human aging
Authors: Brant Larry J. , Fozard James L.
Published: October 2005

Hearing thresholds were obtained on 813 adult males (20–95 years) measured at 11 frequencies ranging from 0.125–8 kHz from pure-tone audiograms collected over a 20-year period from 1968 to 1987. Audiograms taken at two to six different ages spanning a maximum observation period of 15 years were obtained for each male belonging to one of seven different age groups (20,30,...,80 years) based on the age of initial observation. The males were participants in the Baltimore Longitudinal Study of Aging (BLSA), a multidisciplinary community-based study of nomal human aging. Changes in hearing thresholds occurred in all age groups during the 15-year follow-up period. For example, at 0.5 and 8 kHz for combined left and right ears there was an average longitudinal loss of 5.7–7.6 and 5.1–21.1 dB, respectively, for 20-year-olds, 10.0–12.7 and 35.2–53.0 dB for 50-year-olds, and 22.9–48.5 and 69.0–84.5 dB for 80-year-olds. As in results from previous cross-sectional studies, hearing loss in the males 70 years and older is greatest at the highest frequencies. The rate of change for these older males is faster in the speech-range frequencies 0.5–2 kHz than in the higher frequencies, since their hearing has already diminished at the high frequencies.
The behavior of the acoustic distortion product, 2f1−f2, from the human ear and its relation to auditory sensitivity
Authors: Gaskill Sally A. , Brown Ann M.
Published: October 2005

The acoustic intermodulation distortion product 2f1−f2 (ADP) was measured in human subjects to investigate (1) the dependence of ADP level on stimulus parameters and (2) the relationship between ADP level and auditory sensitivity. The frequency ratio ( f2/f1), at which ADP level is maximal, varies only slightly across frequency and subjects. The average optimal ratio is 1.225. Beyond the maximum, the ADP level declines with increasing f2/f1 ratio, at rates of up to 250 dB/oct. As the level of one stimulus is increased relative to the other, the ADP grows, saturates, and in most cases shows a bendover. Maximum distortion is generated when L1 exceeds L2. Growth rate and saturation point are dependent on which stimulus is incremented and on the level of the stationary stimulus. With optimal stimulus parameters (levels below 60 dB SPL; L1>L2 by 15 dB; f2/f1=1.225), ADP levels are commonly 30 dB below L2. Patterns of ADP level across frequency vary between subjects, but are repeatable within each subject. As the frequency of one or both of the stimuli is varied, changes in ADP level exhibit a broadly featured pattern with a fine structure superimposed upon it. This fine structure was compared with the features in the stimulus frequency emission spectrum in one subject. With appropriate stimulus parameters, half of our subjects show a statistically significant correlation across frequency, between ADP level and auditory sensitivity at the corresponding f1 frequency. Our results suggest that, with low levels of stimulation, ADP measurements could form the basis of an objective measure of cochlear function in human subjects.
Time course of adaptation and recovery from adaptation in the cat auditory-nerve neurophonic
Authors: Chimento Thomas C. , Schreiner Christoph E.
Published: October 2005

The auditory-nerve neurophonic (ANN) reflects the ensemble response of phase-locked firing in single auditory-nerve fibers to sustained signals. Consequently, neural response properties such as adaptation and recovery from adaptation can be observed. In this study, ANN responses to 800-Hz, 100-ms tones presented at 10–30-dB SL were recorded using bipolar platinum–iridium electrodes placed on the auditory nerve of the cat. The cat ANN adaptation properties were determined and fit to the equation: A(tp)=Yre(−tp/τAr) +Yse(−tp/τAs)+Ass. The rapid time constant of adaptation (τAr) was invariant across stimulus level, with a mean value of 4.8(±2.1) ms. The short-term time constant (τAs) decreased approximately 21 ms for each 10-dB increase in probe amplitude. The mean τAs was 116 ms at 10 dB SL, 83.2 ms at 20 dB SL, and 73.5 ms at 30 dB SL. The ANN recovery from adaptation data was analyzed and fit to the equation: A(Δt)=Amax−Yre(−Δt/τRr) −Yse(−Δt/τRs). Here, τRr, the rapid time constant of recovery, and τRs, the short-term time constant, were independent of masker intensity in the studied range, with values of 16.2(±9.8) and 125(±50.1) ms, respectively. The results of this study indicate that ANN time constants are comparable to those measured for single units and that the adaptation behavior of phase-locked and nonphase-locked activity appears to be similar.
Test of Sabine’s reverberation time in ergodic auditoriums within geometrical acoustics
Authors: Legrand Olivier , Sornette Didier
Published: October 2005

In room acoustics, Sabine’s formula for the reverberation time, as a function of its volume and effective surface absorption, is valid in the limit of a perfectly ‘‘diffuse’’ sound. In the spirit of the general discussion of Joyce [J. Acoust. Soc. Am. 58, 643 (1975)] in the geometrical acoustic limit, and as a paradigm of the complex three-dimensional problem, here a simple two-dimensional (2-D) room with the shape of a stadium with smooth boundaries is considered. In this system, it is known that almost all trajectories are chaotic in the strongest sense of the term, namely, ergodic, mixing, and K-complex. Numerical results are reported on the decay law of an impulse sound, and on its characteristic reverberation time as a function of room volume (in 2D, the stadium surface) and effective surface absorption (in 2D, effective perimeter absorption). In the limit of very small absorptions, Sabine’s law is verified with good accuracy. However, these results show that larger, but still small, absorptions lead to a departure from a pure exponential decay. This stems from the existence of finite time correlations that are important at short times.
Testing convergence schemes on the solution of two-dimensional boundary value problems in elasticity
Authors: Oakes Alexandria
Published: October 2005

This paper is the first of a three-part series in which solutions are given to two-dimensional and three-dimensional boundary value problems in elasticity. Using a new convergence technique developed here, the stress in the near zone for the case of a two-dimensional semi-infinite slab subject to static loading will be evaluated. In the next article this same technique will be applied in two ways to evaluate the dynamic response of a three-dimensional solid cylinder subject to time-dependent end loading. In addition, the third article will discuss a resonance phenomenon associated with the reflection of an infinite wave train off the free end of a semi-infinite cylindrical bar.
Unidimensional modeling of 1-3 composite transducers
Authors: Hayward Gordon , Hossack John A.
Published: October 2005

Composite transducers, utilizing the complementary properties of a piezoelectric ceramic and a polymer, often possess acoustic matching and electromechanical efficiency that are superior to conventional isotropic materials. The extent of the performance enhancement is a complex function involving composite design in conjunction with external electrical and mechanical loading conditions. This work uses an established modeling technique, supported by finite element analysis and experimental observation, to predict the mechanical, electrical, and piezoelectric properties of 1-3 composite structures. These parameters are then combined in a modified thickness-drive model to predict the performance of composite probe assemblies under realistic operating conditions. Accurate correlation between simulation and experimental results is demonstrated over an extensive range of ceramic-polymer volume fraction. Significantly, the results suggest that composites that possess relatively high-volume fractions of ceramic are superior to the lower volume fraction devices on which previous work has concentrated.
Parametrically driven variable-reluctance generator
Authors: Wright W. B. , Swift G. W.
Published: October 2005

In the parametrically driven variable-reluctance generator, the inductance of an iron-core inductor is varied at an acoustic frequency by an external force. Nonlinear effects thereby absorb mechanical power from the external force and deliver electrical power to a load connected to the inductor, with the electrical phenomena occurring at half the frequency of the mechanical phenomena. Both a theoretical description of this device and measurements in agreement with the theory are presented. Several interesting nonlinear dynamical phenomena can be observed with this simple system; it is also capable of highly efficient power transduction.
Perception of intraphonemic differences by phoneticians, musicians, and inexperienced listeners
Authors: Hillenbrand James , Canter Gerald J. , Smith Bruce L.
Published: October 2005

Several studies have shown that extensive training with synthetic speech sounds can result in substantial improvements in listeners’ perception of intraphonemic differences. The purpose of the present study was to investigate the effects of listening experience on the perception of intraphonemic differences in the absence of specific training with the synthetic speech sounds being tested. Phonetically trained listeners, musicians, and untrained listeners were tested on a two-choice identification task, a three-choice identification task, and an ABX discrimination task using a synthetic [bi]–[phi] continuum and a synthetic [wei]–[rei] continuum. The three-choice identification task included the identification of stimuli with an ‘‘indefinite’’ or ‘‘ambiguous’’ quality in addition to clear instances of the opposing phonetic categories. Results included: (1) All three subject groups showed some ability to identify ambiguous stimuli; (2) phonetically trained listeners were better at identifying ambiguous stimuli than musicians and untrained listeners; (3) phonetically trained listeners performed better on the discrimination task than musicians and untrained listeners; (4) musicians and untrained listeners did not differ on any of the listening tasks; and (5) participation by the inexperienced listeners in a 10-week introductory phonetics course did not result in improvements in either the three-choice identification task or the discrimination task.
An evaluation of an alternating magnetic field device for monitoring tongue movements
Authors: Tuller Betty , Shao Shuyong , Kelso J. A. Scott
Published: October 2005

Alternating magnetic field devices hold much promise for tracking movements of multiple articulators, including the tongue, in the midsagittal plane. Here, the accuracy, repeatability, and linearity of one such device, the Articulograph AG-100 (Carstens Medizinelektronik GmbH, Göttingen, West Germany) are evaluated. The results indicate that with proper precautions in transducer calibration and placement, the Articulograph can be a useful tool in speech production research.
Modeling the perception of concurrent vowels: Vowels with different fundamental frequencies
Authors: Assmann Peter F. , Summerfield Quentin
Published: October 2005

If two vowels with different fundamental frequencies ( f0’s) are presented simultaneously and monaurally, listeners often hear two talkers producing different vowels on different pitches. This paper describes the evaluation of four computational models of the auditory and perceptual processes which may underlie this ability. Each model involves four stages: (i) frequency analysis using an ‘‘auditory’’ filter bank, (ii) determination of the pitches present in the stimulus, (iii) segregation of the competing speech sources by grouping energy associated with each pitch to create two derived spectral patterns, and (iv) classification of the derived spectral patterns to predict the probabilities of listeners’ vowel-identification responses. The ‘‘place’’ models carry out the operations of pitch determination and spectral segregation by analyzing the distribution of rms levels across the channels of the filter bank. The ‘‘place–time’’ models carry out these operations by analyzing the periodicities in the waveforms in each channel. In their ‘‘linear’’ versions, the place and place–time models operate directly on the waveforms emerging from the filters. In their ‘‘nonlinear’’ versions, analogous operations are applied to the output of an additional stage which applied a compressive nonlinearity to the filtered waveforms. Compared to the other three models, the nonlinear place–time model provides the most accurate estimates of the f0’s of pairs of concurrent synthetic vowels and comes closest to predicting the identification responses of listeners to such stimuli. Although the model has several limitations, the results are compatible with the idea that a place–time analysis is used to segregate competing sound sources.
Loudness growth in 1/2-octave bands (LGOB)—A procedure for the assessment of loudness
Authors: Allen Jont B. , Hall J. L. , Jeng P. S.
Published: October 2005

In this paper, a method that has been developed for the assessment and quantification of loudness perception in normal-hearing and hearing-impaired persons is described. The method has been named LGOB, which stands for loudness growth in 1/2-octave bands. The method uses 1/2-octave bands of noise, centered at 0.25, 0.5, 1.0, 2.0, and 4.0 kHz, with subjective levels between a subject’s threshold of hearing and the ‘‘too loud’’ level. The noise bands are presented to the subject, randomized over frequency and level, and the subject is asked to respond with a loudness rating (one of: VERY SOFT, SOFT, OK, LOUD, VERY LOUD, TOO LOUD). Subject responses (normal and hearing-impaired) are then compared to the average responses of a group of normal-hearing subjects. This procedure allows one to estimate the subject’s loudness growth relative to normals, as a function of frequency and level. The results may be displayed either as isoloudness contours or as recruitment curves. In its present form, the measurements take less than 30 min. The signal presentation and analysis is done using a PC and a PC plug-in board having a digital to analog converter.
Coherence theory in volume scattering and structural acoustics
Authors: Beran Mark J. , McCoy John J.
Published: October 2005

This paper considers the use of the two-point coherence function, defined for arbitrarily positioned points, to study wide-angle, volume-scattering problems in the ocean and wave propagation in shells subject to random forcing. Although the basic equations of the two phenomena are different, it will be shown that the basic approach developed 30 years ago in optics is a useful way to study these and similar problems. First, a review is presented of the theory of partial coherence developed in optics for free-space propagation from random sources. Then it is shown how this theory has been simplified and used to treat variable index-of-refraction and narrow-angle volume-scattering problems in the atmosphere and ocean. Next, an approximation is considered that may be used to treat wide-angle scattering problems. In the last sections, the coherence equations are formulated for the shell-propagation case and methods of solution are discussed. Finally, the equations needed to solve statistical wave-propagation problems in an elastic plate with random parameters are derived.
Transient high-order ultrasonic scattering
Authors: Cavicchi Thomas J.
Published: October 2005

To improve the reliability of diagnosis of tissue pathologies (e.g., cancers) based on ultrasonic imaging, quantitative images of physiological parameters such as speed of sound and/or absorption coefficient can in theory be obtained by inverse scattering procedures. Previous studies [Cavicchi et al., IEEE Trans. Ultrason. Ferroelec. Freq. Control UFFC-35, 22–33 (1988)] employed a moment-method matrix formulation under a monofrequency assumption. Periodicities of the field phasors caused a uniqueness problem in the inverse scattering solution for scatterers with phase shift magnitudes greater than π; in practical medical imaging, the phase shift would be hundreds of π. A reformulation of the method in the time domain appears more promising because the phase shifts are now merely time delays. The moment-method formulation is presented for forward scattering. A preliminary numerical study has verified the expansion using the moment-method equation and the internal field calculated by the inverse discrete Fourier transform of the well-known monofrequency solution solved at many frequencies. Future studies will address the more difficult problems of time-domain field inversion and inverse scattering.
Acoustic fields of concave cylindrical transducers
Authors: Theumann J.-F. , Arditi M. , Meister J.-J. , Jaques E.
Published: October 2005

The calculation of ultrasonic beam profiles from concave cylindrical sources is carried out, using the diffraction impulse response approach. Both transient and continuous wave radiation and receiving patterns can be derived with this method. Analytic expressions are given for the impulse response, in certain conditions, and numerical integration methods are applied for solving the problem at points of divergence. Experimental results obtained in water are presented for comparison.
Reply to ‘‘Comment on ‘Near-grazing propagation above a soft ground’ ’’ [J. Acoust. Soc. Am. 8
8, 1170–1172 (1990)]
Authors: Makarewicz R.
Published: October 2005

The author agrees with comments made by Li et al. [J. Acoust. Soc. Am. 88, 1170–1172 (1990)] and generalizes their results based on the two-parameter variable porosity model.
Moving load on a Timoshenko beam
Authors: Mackertich Seroj
Published: October 2005

This letter presents the dynamic response of a simply supported beam excited by moving loads based on the Timoshenko beam theory with corrections for the shear-deformation and rotatory inertia effects. Numerical results for various velocities of moving loads are given, and results are compared with response of a Bernoulli–Euler beam theory.
Comments on resonant systems of scatterers
Authors: Twersky Victor
Published: October 2005

Details are provided for aspects of scattering by resonant systems.
Matched-field processing in a range-dependent environment
Authors: Zala Cedric A. , Ozard John M.
Published: October 2005

Matched-field processing (MFP) is being considered increasingly for three-dimensional (3-D) localization of an acoustic source in a noisy ocean environment. MFP consists of comparing the measured acoustic field to the full field computed using a geophysical and a propagation model. Most MFP implementations have involved only range-independent propagation models, and many have been restricted to vertical arrays. However, many realistic environments cannot be adequately described by range-independent models, and the problem of localization using more general arrays is of increasing interest. In this paper, a technique is described for range-dependent MFP with arbitrary arrays, where the field is computed using a parabolic equation (PE) approximation. Using PE, two-dimensional (2-D) field values are computed for each sensor in the array for a set of possible source ranges, depths, and (N) bearings to form an N×2-D field model. Discrete estimates of the position of the source are obtained by applying MFP, with this range-dependent model providing field values at the sensors for possible source positions. Using simulated data, source localization in a noisy range-dependent environment is illustrated for several arrays. For the particular cases studied, a lower level of ambiguity was observed for range-dependent MFP than for a related range-independent problem. The use of range-dependent models in MFP should significantly improve array design and analysis of real data from many locations.
The discovery of a second kind of rotational wave in a fluid-filled porous material
Authors: Liu Qing-Rui , Katsube Noriko
Published: October 2005

The existence of a second kind of shear wave in an infinite fluid-filled porous material is theoretically predicted in the low-frequency range. This wave exists due to the interaction torque between fluid and solid constituents. The constitutive equation for the interaction torque that appears in the mixture theory by Crochet and Naghdi was used, and the material coefficient for the interaction torque was estimated from steady-state boundary-value problems. The second kind of shear wave is the counterpart of the well-known Biot’s second kind of dilatational wave. It exists due to solid–fluid constituent interactions and has such great attenuation that it is difficult to observe. If the second kind of shear wave indeed exists, however, it can describe additional energy-loss mechanisms operating in various wave phenomena.
Frequency discrimination of single-, double-, and triple-cycle sinusoidal acoustic signals
Authors: Mark Hermann E. , Rattay Frank
Published: October 2005

Very short acoustic signals in the frequency range from 256–2048 Hz consisting of only one, two, or three sinusoidal cycles are examined. Although they are recognized as clicks, they can be distinguished by pitch. Frequency difference limens of these signals are in the order of 1–2 semitones. A tonal character of these short tones appears only with a longer signal, and is linked closer with the duration than with the number of periods.
A Note on ‘‘The effective depth of a Pekeris ocean waveguide, including shear wave effects’’ [Chapman e
t a
l., J. Acoust. Soc. Am. 8
5, 648–653 (1989)]
Authors: Balasubramanian P. , Muni M. M.
Published: October 2005

Chapman et al. [J. Acoust. Soc. Am. 85, 648–653 (1989)] considered a constant effective depth for all modes in a Pekeris channel, and this resulted in inaccurate estimates of mode phase speeds in the case of higher-order modes. It is reported that angle-dependent effective depth leads to highly accurate estimates of mode phase speeds for all normal modes without much effort.
Transient radiation and scattering from fluid-loaded oscillators, membranes, and plates
Authors: Stepanishen Peter R.
Published: October 2005

Transient radiation and scattering from fluid-loaded mechanical oscillators, membranes, and plates is addressed using time domain methods. The pressure field is expressed as a sum of convolution integrals that involve appropriately defined space and time-dependent modal impulse responses and modal velocities. A general set of coupled convolution integral equations is developed to relate the time-dependent modal coefficients of the velocity to the modal forces for the vibrators of interest. The form of the coupled convolution integral equations is noted to be the same for the case of spatially discrete or continuous vibrators, and the equations are readily solved by a ‘‘marching forward in time’’ procedure. Some numerical results for the special case of a planar-baffled single-degree-of-freedom oscillator and a plate or membrane are presented. These results clearly illustrate the effects of time-dependent radiation-induced forces on the response of the vibrators. In general, a decrease in the in vacuo natural frequency and a change in the quality factors are clearly observed in the low- and midfrequency regions for a vibrator. In the high-frequency region, decreased quality factor and settling time are observed due to radiation damping.