bluuebunny/crossref_metadata_2025 huggingface dataset:
Acoustic scattering in the ocean from velocity and density fluctuations in the sediments
Authors: Yamamoto Tokuo
Published: October 2005

According to spectral analyses of many crosswell acoustic tomograms and cores collected from ten seabed locations [Yamamoto, J. Acoust. Soc. Am. 98, 2235–2248 (1995)], the 3-D power spectra of velocity and density fluctuations in the seabed sediments are strongly anisotropic and dipping in general. Anisotropy, dip, and spectral properties of the fluctuations vary greatly depending on the sediment type and the geographical location. Based on the Born approximation and the Wood sediment model, an analytical solution has been obtained for the acoustic wave field scattered from the velocity and density fluctuations within sediment volume having arbitrary 3-D power spectra. Relative density fluctuations are proportional to relative velocity fluctuations in the sediment. The proportionality constant varies from over ten for soft sediments to one for dense sediments. Thus density fluctuation is the dominant mechanism for scattering from a sediment volume. The grazing angle dependence of acoustic backscattering is strongly affected by the fluctuation anisotropy. Dip in the 3-D power spectra of fluctuations causes azimuthal dependence of acoustic backscattering. The model agrees excellently with the backscattering data reported by Jackson and Briggs [J. Acoust. Soc. Am. 92, 962–977 (1992)] and Mourad and Jackson [J. Acoust. Soc. Am. 94, 344–358 (1993)]. Model-data comparisons confirmed the three theoretical findings: The dominant volume scattering of density fluctuations in soft sediments, the anisotropy-grazing angle relationship and the dip-azimuthal angle relationship of acoustic backscattering. In addition, the model predicts that the moderate frequency dependence of acoustic volume scattering is affected by a power low spectra of velocity and density fluctuations and attenuation within the sediments.
Deterministic and stochastic analyses of acoustic plane-wave reflection from inhomogeneous porous seafloor
Authors: Badiey Mohsen , Cheng Alexander H-D. , Jaya Indra
Published: October 2005

The propagator matrix technique for the acoustic plane-wave reflection in layered, porous, anisotropic seafloor is combined with Monte Carlo simulation to investigate the layering effect of the sediment. Statistical data from a geologically known site are processed and used as a benchmark. Realizations of sediment property profiles are generated using a spectral technique. A deterministic analysis demonstrates that the amplitude and phase of reflection coefficient is highly dependent on the variation of porosity. In a stochastic analysis, the effect of randomness is examined. It is found that the fluctuation of the sediment physical properties around a mean profile has a significant influence on the seabed reflectivity, particularly for the incident angles near and above the critical value. Frequency behavior of reflectivity is strongly dependent on the correlation length of medium inhomogeneities. This behavior is attributed to the interaction among different waves that propagate in the porous sediment layers, suggesting the possibility of obtaining the properties using the reflection loss data.
Investigation of parametric drive of a longitudinal gas-filled resonance tube
Authors: Raspet Richard , Denardo Bruce , Bass H. E. , Brewster James , Kordomenos John
Published: October 2005

High power drives for thermoacoustic refrigerators are being investigated by several groups. Theoretical calculations have been performed of the feasibility of parametrically driving a longitudinal resonance tube by uniformly modulating the temperature of the gas with a high-power laser. Parametric drives are promising since the drive mechanism is distributed over the entire volume of gas and because the response may become large before saturation occurs. Although it is demonstrated that laser drive is not a practical means of high-power drive for longitudinal resonators, much interesting physics has been considered in the analysis of the proposed system and is discussed.
Forward coupled-mode propagation modeling for coastal acoustic tomography
Authors: Chiu Ching-Sang , Miller James H. , Lynch James F.
Published: October 2005

A coupled normal-mode approach for the prediction of pulse propagation in a complex coastal environment is presented. In this broadband approach, the received time-domain sound-pressure signal is generated by Fourier synthesis using the product of the source signal spectrum and the source-to-receiver ocean transfer function. For a given frequency, the basic formulation involves decomposing the acoustic pressure into slowly varying complex envelopes that modulate (mode by mode) analytic, rapidly varying, adiabatic-mode solutions. A coupled set of differential equations governing these complex modal envelopes is derived and the numerical solution techniques used are discussed. This coupled-mode approach has been used to model the modal arrival structure in the 1992 Barents Sea Coastal Acoustic Tomography Test. Model results and comparison to the data measured by a vertical hydrophone array are discussed.
Experimental study of enhanced backscattering from a highly irregular, acoustic–elastic interface
Authors: Schultz Craig A. , Toksöz M. Nafi
Published: October 2005

In this study, experimental and numerical statistical models are developed for the scattering of an acoustic P wave which is incident on a highly irregular, random acoustic–elastic interface to determine the general nature of reflected energy. It is then elucidated whether or not enhanced backscattering, already identified numerically for acoustic (SH) and fully elastic media (P-SV), occurs. Experimentally, a glass etching process using photoresist templates with Gaussian statistics allowed for the generation of characterized interface irregularities. Experiments were performed on a glass surface with an ‘‘rms’’ slope of 30 deg, for the case of an incident wavelength with a size on the same order as the interface irregularities. The numerical models predict an enhancement of energy diffracted back toward the source, and results obtained in our ultrasonic laboratory strongly support the presence of this retroreflective energy. In terms of general scattering, it is found that, at smaller incident angles (relative to vertical), the 2-D numerical results can give insight into the 3-D experimentally observed scattering over most scattering angles. However, at larger incident angles, fundamental differences between 2-D and 3-D scattering may exist.
Binaural beats at high frequencies: Listeners’ use of envelope-based interaural temporal and intensitive disparities
Authors: Bernstein Leslie R. , Trahiotis Constantine
Published: October 2005

Two experiments were conducted in order to assess listeners’ ability to utilize interaural disparities within interaurally ‘‘mistuned’’ envelopes of two-tone complexes centered at 3500 Hz. In the first experiment, listeners were required to distinguish between rightward or leftward directions of intracranial movement produced by the beat. The stimuli and experimental paradigm were designed so that such judgments would be made on the basis of the dynamically varying, envelope-based interaural temporal disparities (ITDs). In the second experiment, listeners were required only to distinguish between the presence or absence of an envelope-based binaural beat in a paradigm similar to that employed by McFadden and Pasanen [Science 190, 394–396 (1975)]. For both experiments, monaural envelope (beat) rates of between 10 and 640 Hz were employed with interaural beat rates of 0.25, 0.5, and 1.0 Hz. The data indicate that listeners are indeed capable of discriminating the direction of intracranial movement based on time-varying ITDs conveyed by the envelopes of high-frequency two-tone complexes. Changes in sensitivity produced by altering the rate of change of the ITD and/or its extent appear to be accounted for by assuming that there is a relatively simple trade-off between these two parameters. When the task is changed to one that is similar to that employed by McFadden and Pasanen [Science 190, 394–396 (1975)] such that listeners are merely required to discriminate between the presence and absence of an envelope-based interaural beat, the data appear to be accounted for quite parsimoniously by assuming that listeners base their decisions upon the presence or absence of dynamically varying interaural intensitive disparities.
Introduction to papers on speech recognition and perception from an articulatory point of view
Authors: McGowan Richard S. , Faber Alice
Published: October 2005

The following group of papers resulted from a special session entitled Speech Recognition and Perception from an Articulatory Point of View that was held during the spring 1994 meeting of the Acoustical Society of America in Cambridge, Massachusetts. Organization of the session began when Richard McGowan, Terry Nearey, and Juergen Schroeter invited speakers to give papers and critiques on the role of articulation in human perception and machine recognition. Presentations were invited from three speakers or groups of speakers who were representative of the three speech areas in the Society: production, perception, and processing. One talk was given by Björn Lindblom, another was given by John Ohala, and the third by Rick Rose, Juergen Schroeter, Mohan Sondhi, and Oded Ghitza. The invited critiquers for the Lindblom paper were Ken Stevens, Robert Remez, and Bishnu Atal; for the Rose et al. paper, Roger Moore, Joe Perkell, and Terry Nearey; and for the Ohala paper, Mary Beckman, Douglas O’Shaughnessy, and Carol Fowler. These people created a very interesting and provocative session. Robert Fox, associate editor of the speech perception section of the Journal, initiated publication of and edited the papers that appear here. Written versions of the invited papers are included here, as well as the critiques by Stevens, Remez, Nearey, Moore, and O’Shaughnessy. Because it was felt that Carol Fowler’s view of the importance of articulation in speech perception was not sufficiently aired in a short critique, she was asked to present her views in a longer paper.
Critique: Phonological contrast and articulatory properties
Authors: Nearey Terrance M.
Published: October 2005

The use of articulatory modeling in automatic speech recognition has the greatest relevance for phonetic theory if aspects of articulation define linguistic symbols (such as distinctive features, or phonemes.) Although the use of descriptive articulatory labels for phonetic dimensions is standard practice, there is heated debate within the speech science community concerning the strength of the relation between articulations and symbols. However, it is argued that research of the type reviewed by Rose et al. [J. Acoust. Soc. Am. 99, 1699–1709 (1996)] on the incorporation of speech production models into automatic speech recognition may have important benefits for speech science as well as for technological applications even if only relatively weak symbol-to-articulation relations obtain in nature.
Critique: Speech perception: Acoustic or articulatory?
Authors: O’Shaughnessy Douglas
Published: October 2005

In this review of John Ohala’s paper (‘‘Speech perception is hearing sounds, not tongues’’), we are sympathetic to his position that acoustic properties have largely driven the selection of sounds found in speech production. It is very reasonable that listeners need not refer to articulation during speech perception. However, like many human perception theories, it is difficult (if not impossible) to verify experimentally. The arguments Ohala uses to attack the articulatory theories of speech perception do not really disprove them; instead, they simply argue that an acoustically based theory is more plausible. When dealing with plausibility arguments, one must be careful to ponder the evidence for different positions. Thus this paper comments on the weight of Ohala’s arguments and notes whether any theory of the fundamental basis of speech perception can actually be proven or disproven. It also discusses speech perception from the communication point of view.
Comments on ‘‘Design of active structural acoustic control systems by eigenproperty assignment’’ [J. Acoust. Soc. Am. 96, 1582–1591 (1994)]
Authors: Cunefare Kenneth A.
Published: October 2005

The recent article by Burdisso and Fuller [‘‘Design of active structural acoustic control systems by eigenproperty assignment,’’ J. Acoust. Soc. Am. 96, 1582–1591 (1994)] does not fully illuminate the contributions of a number of prior authors for a crucial part of the work, that is, the development of weak radiator modes. This comment places the subject development of Burdisso and Fuller in context with the prior art. Further, it demonstrates the similarities of the subject development to prior work published by K. A. Cunefare [‘‘The minimum multimodal radiation efficiency of baffled finite beams,’’ J. Acoust. Soc. Am. 90, 2521–2529 (1991)]. The authors recognize and acknowledge that Burdisso and Fuller’s implementation of the concept, through eigenproperty assignment, is unique and valuable.
Response to ‘‘Comments on ‘Design of active structural acoustic control systems by eigenproperty assignment’ ’’ [J. Acoust. Soc. Am. 99, 1785–1788 (1996)]
Authors: Burdisso R. A. , Fuller C. R.
Published: October 2005

The authors thank Professor Cunefare for his interest in our paper on the design of active structural acoustic control systems. This Letter is to clarify questions raised in his Comments.
Acoustic field in unsteady moving media
Authors: Bauer F. , Maestrello L. , Ting L.
Published: October 2005

In the interaction of an acoustic field with a moving airframe, a canonical initial value problem for an acoustic field induced by an unsteady source distribution q(t,x) with q≡0 for t≤0, in a medium moving with a uniform unsteady velocity U(t)î in the coordinate system x fixed on the airframe, is encountered. Signals issued from a source point S in the domain of dependence 𝒟 of an observation point P at time t will arrive at point P more than once corresponding to different retarded times τ in the interval [0,t]. The number of arrivals is called the multiplicity of the point S. The multiplicity equals one if the velocity U remains subsonic and can be greater when U becomes supersonic. For an unsteady uniform flow U(t)î, rules are formulated for defining the smallest number of I subdomains Vi of 𝒟 with the union of Vi equal to 𝒟. Each subdomain has multiplicity 1 and a formula for the corresponding retarded time. The number of subdomains Vi with nonempty intersection is the multiplicity m of the intersection. The multiplicity is at most I. Examples demonstrating these rules are presented for media at accelerating and/or decelerating supersonic speed.
Ultrasound wave propagation through rough interfaces: Iterative methods
Authors: Berkhoff Arthur P. , Thijssen Johan M. , van den Berg Peter M.
Published: October 2005

Two iterative methods for the calculation of acoustic transmission through a rough interface between two media are compared. The methods employ a continuous version of the conjugate gradient technique. One method is based on plane-wave expansions and the other on boundary integral equations and Green’s functions. A preconditioner is presented which improves the convergence for spectra that include evanescent modes. The methods are compared with regard to computational efficiency, rate of convergence, and residual error. The sound field differences are determined for a focused ultrasound beam distorted by surfaces having a Gaussian roughness spectrum. The differences are evaluated from the root-mean-square differences on the rough surface and in the focal plane.
Acoustic characterization of rigid-frame air-filled porous media using both reflection and transmission measurements
Authors: Frederickson Carl K. , Sabatier James M. , Raspet Richard
Published: October 2005

Acoustic measurements in and above porous materials (500-μm-diam glass beads) have been used to determine rigid-frame porous medium parameters. The propagation constant for the acoustic signal propagating through the air in the pores was calculated from probe microphone measurements made inside the porous medium. Reflection measurements have been used to calculate the characteristic impedance of a thick porous medium. A model relating porous medium properties to the propagation constant and impedance was used to analyze the data from both the reflection and transmission measurements. Both reflection and transmission measurements are needed to determine the rigid-frame porous medium parameters. Porous medium parameters can be calculated using the model and the data. The calculated porous medium parameters from the transmission and reflection measurements are compared. Some possible explanations for the discrepancy and suggestions for further work are presented.
Analysis of the numerically implemented angular spectrum approach based on the evaluation of two-dimensional acoustic fields. Part II. Characteristics as a function of angular range
Authors: Wu Ping , Kazys Rymantas , Stepinski Tadeusz
Published: October 2005

The numerically implemented angular spectrum approach (ASA) is investigated in terms of the characteristics of the ASA as a function of angular range over which the angular spectrally decomposed plane waves are superimposed to construct an acoustic field radiated by a source. The investigation is based on the evaluation of the 2-D fields radiated by striplike planar sources and 1-D linear phased arrays with different aperture sizes and on the comparison with those obtained by using the analytical solution derived with the point spread function method. The convergence and the spatial aliasing of the ASA’s results are systematically dealt with. A region well converging to the analytical solution as the angular range increases is found to exist before the aliasing comes up. Analytical formulas to determine the boundaries of this region are given. Based on the instantaneous frequency concept, an analytical expression for optimal selection of the angular range used is derived. Hence the sampling frequency can be chosen to be optimal and adaptive to the discretization size of the source plane without worrying that the number of the samples for the discretization size should be chosen to be a power of two that the fast Fourier transform (FFT) usually needs. An excellent agreement of the ASA’s results with the analytical solution is demonstrated when using the optimal selection of the angular range for the specified parameters. The analysis made in this paper can be extended to the case of 3-D fields.
Comparison of linear and nonlinear elastic moduli for reservoir rock by use of a granular medium model
Authors: Belyaeva I. Yu. , Ostrovsky L. A. , Zaitsev V. Yu. , Stefan V. , Sutin A. M.
Published: October 2005

The variations of linear and nonlinear elastic parameters as a function of initial stress and material structure are considered using a model of a granular medium with fluid pore filling. Examples of such variations for some geological conditions interesting for seismoprospecting are presented. It is demonstrated that the nonlinear parameter may be used in exploration seismology as a much more sensitive characteristic compared with conventionally exploited linear moduli.
Asymptotic phase errors in parabolic approximations to the one-way Helmholtz equation
Authors: Tappert F. D. , Brown Michael G.
Published: October 2005

Asymptotic (in the geometric limit) phase errors associated with parabolic approximations to the one-way Helmholtz equation are investigated. In order to estimate the phase accuracy of various parabolic approximations, the canonical Hamiltonian formalism is used to derive ray equations. It is shown that among the class of parabolic approximations that allow the split-step Fourier algorithm to be used, the wide-angle c0-insensitive approximation [Tappert et al., J. Acoust. Soc. Am. 97, 2771–2782 (1995)] has full second-order accuracy. Other approximations in this class, such as the Thomson–Chapman and the Berman–Wright–Baer approximations, are shown to have second-order errors, as does the standard first-order parabolic approximation. Numerical calculations support the expectation that among this class of parabolic approximations the wide angle c0-insensitive approximation is superior.
Acoustic radiation of an unbaffled vibrating plate with general elastic boundary conditions
Authors: Atalla Noureddine , Nicolas Jean , Gauthier Carol
Published: October 2005

If the simulations of the radiated field of a baffled plane structure has been deeply studied, the unbaffled case, although more realistic, has retained little attention. The proposed work investigates the radiation, in light fluid, of a plane unbaffled thin structure of finite dimensions and general elastic boundary conditions. The approach used is based on a variational formulation for the plate’s displacement and the pressure jump through the structure. A Rayleigh–Ritz approximation with a polynomial set of trial functions is used for both variables. A good agreement is found with a numerical approach based on a boundary element method. Acoustic radiation of unbaffled rectangular plates will be discussed and compared to the baffled case. This will show in particular that the effect of the baffle is very important at low frequencies but there are no simple tendencies. Precise measurements confirm the validity of the simulations.
The effect of noise exposure on the details of distortion product otoacoustic emissions in humans
Authors: Engdahl Bo , Kemp David T.
Published: October 2005

The effect of noise exposure on amplitude and phase of distortion product otoacoustic emissions (DPOAEs) was examined by five different paradigms: across a wideband of frequency, microstructure, input/output function, primary frequency ratio tuning curve, and group delay. The aim was to investigate the vulnerability of these different features to moderate levels of noise exposure. Nine subjects were exposed to third-octave-band noise. The DPOAE amplitude was reduced frequency specifically with the greatest reduction approximately half an octave above the frequency of the noise. The degree of amplitude reduction was greatest at low stimulus levels. There were no observed effects on the shape of the primary ratio tuning curve. A weak tendency to a decrease was seen in group delays. Distinct microstructure was seen in the amplitude against frequency of five out of seven subjects. The maximum to minimum ratio of the microstructure decreased, and the whole pattern shifted toward lower frequencies after noise exposure. Evidence of multiple internal reflection or interference was seen in the periodicity of the microstructure. Using a simple model of the microstructure based on multiple reflections, the noise-induced changes were reevaluated. A reduction in maximum to minimum microstructure ratio could be interpreted as a decrease in the internal reflection coefficient. The implications of these observations for the interpretation of the DPOAE measurements are considered.
Frequency correlation functions for the detection of a tone added to modulated noise maskers
Authors: Richards Virginia M. , Buss Emily
Published: October 2005

Psychophysical experiments using reproducible stimuli were completed for the detection of a 1000-Hz tone added to a masker. The noise masker was either sinusoidally amplitude modulated or not, and masker bandwidths of 100, 300, and 900 Hz were tested. The masker was centered at 1000 Hz and the rate of amplitude modulation, when present, was 29 Hz. On average, comodulation masking release values of 10 and 16 dB were obtained for the 300- and 900-Hz-wide maskers, respectively. No release from masking was obtained for the 100-Hz-wide maskers. Data analysis consisted of computing the correlation coefficient between the level of each spectral component of each stimulus token and the observers’ responses to that token. The resulting correlation functions estimate the relative contribution or weight of different frequency regions to the observers’ responses. While the correlation functions for the modulated and unmodulated maskers share some features, differences in both the pattern and quality of fit are apparent for wideband maskers. For two of the observers, however, restricting the region of comparison to the region surrounding the signal frequency led to increased similarity of the correlation functions.
Profile analysis with amplitude-modulated nontarget components
Authors: Bacon Sid P. , Smith Michael A.
Published: October 2005

This study was concerned with why amplitude modulation of nontarget components disrupts profile analysis. The 1-kHz target component was unmodulated whereas the nontarget components were unmodulated or sinusoidally amplitude modulated at a rate of 10 Hz. In experiment 1, thresholds were measured as a function of the modulation depth of the nontarget components for four different targets: One consisted of a long-duration tone and three consisted of multiple short-duration tones located at the peaks, valleys, or leading edges of the modulation cycles of the nontarget components. Although there were differences across the three subjects, thresholds typically increased with increasing modulation depth for all four targets, indicating that restricting profile analysis to particular points in the modulation cycle does not alleviate the effect of amplitude modulation. In experiment 2, the signal consisted of multiple short-duration tones; the nontarget components were unmodulated and presented at levels below or above the level of the target component (i.e., positive and negative pedestals were created). Although thresholds generally were worse when the target and nontarget components were unequal in level than when they were equal, the results suggest that this pedestal effect cannot account entirely for the effect of amplitude modulation on profile analysis. This conclusion was further substantiated by a supplemental experiment that used square-wave modulation. For the single subject tested, thresholds increased as modulation depth increased, regardless of whether or not the target and nontarget components were equal in level at the time of signal occurrence.
Compressibility of air in fibrous materials
Authors: Tarnow Viggo
Published: October 2005

The dynamic compressibility of air in fibrous materials has been computed for two assumed configurations of fibers which are close to the geometry of real fiber materials. Models with parallel cylinders placed in a regular square lattice and placed randomly are treated. For these models the compressibility is computed approximately from the diameter and mean distances between cylinders. This requires calculation of the air temperature, which is calculated for cylinders in a regular lattice by the Wigner–Seitz cell approximation. In the case of random placement, the calculation is done by a summation over thermal waves from all fibers, and by a self-consistent procedure. Figures of the compressibility in the frequency range 10–100 000 Hz, are given for diameter of the cylinders of 6.8 μm, and mean distances between them from 50 to 110 μm, which corresponds to glass wool with a density of 40 to 16 kg/m3. When the theoretical values for random placement were compared with measurements, it turned out that the random model could not describe the experimental data. However, they could be described accurately by assuming that the fibers have a tendency to form pairs.
Transient detection using the nonstationary bispectrum
Authors: Barlett Martin L. , Baugh Kevin W. , Wilson Gary R.
Published: October 2005

A detection statistic is described which exploits features in the three-dimensional response of the nonstationary bispectrum (third-order cumulant spectrum) for an assumed class of transient signals. The detection performance of the proposed detector is investigated for transients of this class in the presence of additive white stationary interference. The results are presented relative to the performance of a conventional power spectrum detector and a detection statistic based on the spectral correlation (second-order cumulant spectrum). The merits of the nonstationary bispectral detector relative to other transient detection approaches are also discussed.
Reconstruction of fluid motion in acoustic diffraction tomography
Authors: Rychagov Michael N. , Ermert Helmut
Published: October 2005

This paper shows how the technique of diffraction tomography can be applied for reconstructing the magnitudes and the directions of the velocity vectors as well as stationary sound-speed perturbation in a fluid flow. The analysis is based on the wave equation describing the propagation of the sound in an inhomogeneous moving fluid medium. For plane-wave irradiation and scattered field detection by a linear array of receivers, the Fourier diffraction theorem for the fluid vorticity has been obtained. Similar to the scalar case, the theorem relates the Fourier transform of the measured forward scattered data to the spatial spectrum of the vorticity and leads to the values of the two-dimensional transform of the velocity vector curl along a semicircular arc in the frequency domain. Utilizing the nonreciprocity of sound scattering from moving fluid (as opposed to the reciprocity of the elastic scattering on the scalar potential), a procedure for the separation of scalar and moving components of the flow has been proposed. It has been shown that nonreciprocity of the sound scattering by flow offers additional information which can be used to separate two independent components of the velocity vector and thus to solve the vector reconstruction problem uniquely for an arbitrary 2-D vector field without any additional constraints concerned with the flow model, what was impossible in previous algorithms based on the time-of-flight measured data. The results offer independent confirmation of those derived by Rouseff and Winters [D. Rouseff and K. B. Winters, ‘‘Two-dimensional vector flow inversion by diffraction tomography,’’ Inverse Problems 10, 687–697 (1994)].
Two-tone suppression in cochlear mechanics
Authors: Cooper Nigel P.
Published: October 2005

Mechanical responses to one- and two-tone stimuli were recorded from the basilar membrane (BM) in the hook region of the guinea-pig cochlea. The most sensitive or ‘‘best’’ frequencies (BFs) for the sites studied were ∼25–30 kHz. Two-tone suppression (2TS) of the responses to near BF probe tones was noted using suppressor tones either above or below the BF. Rates of growth of 2TS were highest (∼1 dB/dB) when the suppressor tones were presented below the BF. Below-BF suppression thresholds (the suppressor intensities causing ∼10% reduction in the probe-evoked responses) corresponded to BM displacements of ∼1–5 nm. Above-BF suppression thresholds corresponded to much smaller displacements at the location studied. Both above- and below-BF suppressor tones changed the phase of the probe tone responses in the same way that increases in the probe tone intensity did (they evoked small phase-lags for below-BF probes, and small phase-leads for near- and above-BF probes). Low-frequency suppressor tones (<∼7 kHz) evoked a frequency- and intensity-dependent mixture of phasic (ac) and tonic (dc) suppression. Peak (ac) suppression was observed around the times of peak BM displacement (not velocity). These findings are discussed in relation to those of other workers.
The effects of static indentation on vibrotactile threshold
Authors: Makous James C. , Gescheider George A. , Bolanowski Stanley J.
Published: October 2005

Vibrotactile thresholds were measured on the thenar eminence and the volar forearm at different static depths of skin indentation. Three stimulus frequencies (1, 20, and 200 Hz) were delivered through either a 0.008- or a 2.9-cm2 contactor. The indentation depths ranged from 0 to 1 mm (0.25-mm steps) relative to the point of skin contact with the stimulator. There was a significant effect of indentation in all stimulus combinations of contactor size, location, and frequency. These results resolve an apparent discrepancy in the literature regarding threshold reduction with increasing contactor size observed on the forearm at low frequencies.
Young children’s production of syllable stress: An acoustic analysis
Authors: Schwartz Richard G. , Petinou Kakia , Goffman Lisa , Lazowski Gerri , Cartusciello Christine
Published: October 2005

The acoustic characteristics of stress were examined in young children’s productions of minimal pairs of novel words (e.g., sofi versus so’fi). Fourteen 2-year-olds participated as subjects. Their productions were analyzed in terms of vowel duration, syllable duration, peak amplitude, and peak fundamental frequency. The analyses revealed that children produced stressed and unstressed syllables distinctly along each of the dimensions examined. The absolute and relative (unstressed/stressed) values of the children’s productions were compared to those of the single adult experimenter, who modeled the novel words, permitting a unique comparison of input to children’s productions. One systematic difference was the relative values; the children’s stressed and unstressed syllables were less distinct than the adults along each of the acoustic correlates. Furthermore, the acoustic features of both stressed and unstressed syllables appear to be subject to developmental change. The results are discussed in terms of their implications for young children’s production capabilities and for the relationship between input and children’s production characteristics.
Acoustic radiation force and streaming induced by focused nonlinear ultrasound in a dissipative medium
Authors: Rudenko O. V. , Sarvazyan A. P. , Emelianov S. Y.
Published: October 2005

Based on asymptotic methods recently developed in nonlinear acoustics, analytical solutions of the equations for the radiation force induced by nonlinear focused ultrasound in a dissipative medium are considered. Equations describing spatial structure of the radiation force field in the paraxial region of the ultrasound beam and the spatial–temporal behavior of the induced nonlinear streaming are derived. The equations enable analytical investigation of dependencies of radiation pressure and resulting streaming on the acoustic field and medium parameters. Estimates have shown that nonlinearity of medium can significantly enhance radiation force in the focal region at the intensities lower than those used in ultrasound devices for medical imaging. The initiation of acoustical streaming by radiation force is considered, and the spatial and temporal characteristics of induced flow are discussed. Both acoustic and hydrodynamic nonlinearities are taken into account. The paper concludes by discussing possible medical and industrial applications of ultrasound radiation force and induced acoustical streaming.
Scattering of sound by a fluid-loaded plate with a distributed mass inhomogeneity
Authors: Feit D. , Cuschieri J. M.
Published: October 2005

The scattering of a plane acoustic wave by a fluid-loaded, thin, elastic plate, of infinite extent, with a distributed mass inhomogeneity is investigated. Two approaches are presented, an iterative approach valid when a measure of the distributed impedance is much lower than that of the uniform fluid-loaded plate, and a full numerical solution which while having no restricting assumptions is somewhat demanding computationally. For the iterative solution a set of correction terms is evaluated and applied to the response of the uniform plate with no inhomogeneities. The number of correction terms required is dependent on the relative magnitude of the inhomogeneity. In the full numerical solution, the presence of the distributed inhomogeneity in the equation of motion, when expressed in the wave-number domain, results in a Fredholm integral equation of the third kind. By substituting for the product of the response and the plate characteristic equation (impedance), the Fredholm integral of the third kind is reduced to a Fredholm integral of the second kind. The plate response in the spectral wave-number domain is obtained from the solution of the Fredholm integral. Inverse Fourier transforming the wave-number domain response function gives the spatial domain solution for the response. The hybrid numerical analytical approach [J. Acoust. Soc. Am. 95, 1998–2005 (1994)] is used to perform the inverse Fourier transform. The far-field scattered pressure is obtained from the spectral domain solution of the response. Response and scattered pressure results for distributed mass inhomogeneities, with different distribution functions, are presented and compared to the results for a line inhomogeneity.
Acoustic point source scattering by a spherical elastic shell submerged beneath a free surface
Authors: Huang H. , Gaunaurd G. C.
Published: October 2005

The scattering of incident acoustic plane waves by a submerged spherical elastic shell near a free surface has previously been analyzed in detail using an exact, classical separation of variables solution. The problem is studied here again for cases where the incident waves are emitted from point sources at arbitrary positions in space. The result demonstrates that for a nearby point source, the scattered wave field is significantly different from that due to a plane incident wave, and that when the distance from the point source to the shell is more than 20 shell radii, the backscattered echo can be closely approximated by that of a plane incident wave. The scattered field due to an array of point sources can also be obtained by linear superpositions of the solution developed here.
Scintillating shallow-water waveguides
Authors: Creamer Dennis B.
Published: October 2005

An analysis of acoustic wave propagation in a random shallow-water waveguide with an energy absorbing sub-bottom is presented, in which deviations of the index of refraction are a stochastic process. The specific model studied is motivated by the oceanic waveguide in shallow waters, in which the sub-bottom sediment leads to energy loss from the acoustic field, and the stochastic process results from internal (i.e., density) waves. In terms of the normal modes of the waveguide, the randomness leads to mode coupling while the energy loss results from different attenuation rates for the various modes (i.e., mode stripping). The distinction in shallow water is that there exists a competition between the mode-coupling terms, which redistribute the modal energies, and mode stripping, which results in an irreversible loss of energy. Theoretically, averaged equations are formulated for both the modal intensities and fluctuations (the second and fourth moments of acoustic pressure, respectively), similar to previous formulations which, however, did not include the effects of sub-bottom absorption of acoustic energy. The theory developed here predicts that there is a mismatch between decay rates between the second and fourth moments, implying that the scintillation index (which is a measure of the strength of the random scattering) grows exponentially in range. Thus the usual concept of equilibrium or saturated statistics must be modified. This theoretical prediction is generally valid and depends only on assuming the forward scattering approximation, the Markov approximation (i.e., the short-range nature of the correlations between sound-speed fluctuations) and neglecting the cross-modal coherences. In order to assess the importance of these assumptions Monte Carlo simulations of stochastic coupled-mode equations are presented. For these simulations, models of internal-wave processes, deterministic shallow-water acoustic environments, and sub-bottom attenuation that simplify the numerical computation were chosen. While these models are unrealistic they illustrate the theoretically predicted behavior.
Lamb and shear-horizontal wave production by interdigital transducers deposited on both sides of a piezoelectric plate
Authors: Laurent T. , Bastien F.
Published: October 2005

Interdigital transducers (IDT) deposited on one side of a sample are commonly used to generate and detect acoustic plate modes. The electromechanical coupling coefficient can be calculated to find the relative efficiency of mode generation by IDT. However, experimental observations have shown that some modes are difficult to excite with IDT deposited on only one side of the plate. In this paper it is shown that the shape of the tranducer and its electrical connections can be adjusted for each mode, A0, S0, and SH0, in order to achieve an electromechanical conversion in good agreement with theoretical predictions. Some experiments have been performed on quartz plates with different kinds of transducers in order to check the validity of this approach. The electrostatic potential generated by these transducers has been compared with the electrical potential associated with a plate mode already excited. It appears that when the electrostatic field generated by the excitation device has the same symmetry as the electric field associated with a piezoelectrically coupled plate mode, excitation and detection of this particular mode are possible.
A finite element model for sound transmission through foam-lined double-panel structures
Authors: Kang Yeon June , Bolton J. Stuart
Published: October 2005

In this paper, methods for coupling both elastic porous material (i.e., foam) and structural finite elements with either modal or finite element representations of acoustical system are presented. In addition, interface conditions are described for coupling elastic porous material finite elements with acoustical and structural finite elements in various configurations. The foam finite element is based on the elastic porous material theory of Biot. By considering sound transmission through layered systems placed in a waveguide, the accuracy of the coupled acoustical-structural-foam finite element model has been verified by comparing its transmission loss predictions with analytical solutions for the matching cases of infinite lateral extent. The constraint conditions at the edges of both the foam lining and the facing panels were found to have a significant effect on the normal incidence sound transmission loss of the double panel system at low frequencies.
The interaction of a single laser-generated cavity in water with a solid surface
Authors: Shaw S. J. , Jin Y. H. , Schiffers W. P. , Emmony D. C.
Published: October 2005

This paper reexamines the collapse of a cavity in water and its role in possible damage processes. Laser-generated cavities were formed near to a water–solid boundary and simultaneous observations made of the collapse processes and stresses on the solid surface. Using schlieren photography and a thin film transducer on the solid, the importance of fluid flow to induced material stress was determined. The stresses in the solid were also observed using dynamic photoelasticity. The cavity deformation in the collapse phase was observed with high spatial and temporal resolution. Two distinct surface stresses were observed associated with bubble collapse near the boundary. The results indicate that one was due to a shock wave. It is postulated that the second stress was associated with fluid flow through the bubble, set up by the so-called ‘‘liquid jet’’ as opposed to jet impact on its own.
Modeling approach for two-dimensional distributed transducers of arbitrary spatial distribution
Authors: Sullivan Jeanne M. , Hubbard James E. , Burke Shawn E.
Published: October 2005

A new modeling method for two-dimensional distributed transducers with arbitrary spatial distribution is presented. The spatial weighting of a distributed transducer is defined using multidimensional distributions with composite functions as arguments. A differentiation theorem is derived for one-dimensional distributions of composite functions and is extended to multidimensions through the use of partial distributional derivatives and the product rule. The resulting theory is used to determine the differential operator describing the distributed transducer’s spatial dynamics. The methodology, which is valid for both uniaxial and biaxial transducers, is applied to several two-dimensional problems.
Optimal placement of microphones and piezoelectric transducer actuators for far-field sound radiation control
Authors: Wang Bor-Tsuen
Published: October 2005

This paper presents an optimization solution technique to determine the optimal locations of piezoelectric transducer (PZT) actuators and far-field microphone sensors for active structural acoustic control in conjunction with the use of least-mean-square (LMS) feedforward control algorithm. A simply supported beam in an infinite rigid baffle subject to an harmonically excited point force is considered. The piezoceramic patches are adhered to the beam and act as control transducers, while microphones located in the far field are used as error sensors. The objective function is first defined as the total radiated sound power. The design variables which are the locations of PZT actuators and microphone sensors are then identified and determined. The genetic algorithm (GA) incorporated with the use of linear quadratic optimal control theory (LQOCT) to calculate the control voltages to the actuators is adopted to solve the optimization problem. Results show that the optimally placed PZT actuators and microphone sensors can perform better sound radiation control than the arbitrarily selected ones. In particular, for off-resonance excitation cases the optimized PZT actuators and microphone sensors can efficiently control the sound radiation and eliminate the control spillover. The control mechanisms of PZT actuators and microphone sensors are demonstrated through the studies of radiation directivity patterns and beam displacement distributions as well as the wave-number analysis. The effect of the number of microphone sensors are also presented. The use of optimally positioned PZT actuators and microphone sensors can efficiently achieve structural sound radiation control.
Experimental study of a rapidly convergent adaptive controller applied to suppression of random noise transmission
Authors: Koshigoe S. , Gordon A. A. , Ndefo E. D. , Tsay Ching-Hsu , Teagle Allen
Published: October 2005

In this letter, an efficient, rapid-convergent, control algorithm will be developed and compared with finite impulse response (FIR), filtered-x, LMS [Widrow et al., Proc. IEEE 63, 1692–1711 (1975)], and a modified version of Godard’s algorithm [D. Godard, IBM J. Res. Develop., pp. 267–273 (1974)]. The experiments will be performed on an active noise control (ANC) system. Comparisons of the random noise attenuation capability, transient and convergence performance, and computational requirements of each algorithm will be made as the order of the controller and relevant convergence parameters are varied. The ANC system used for these experiments is a test bed of noise suppression technology for expendable launch vehicles. It consists of a flexible plate backed by a rigid cavity. Piezoelectric actuators are mounted on the plate and polyvinylidene fluoride (PVDF) microphones are used to sense the reference and error signals. The plate is bombarded with an amplified random noise signal, and the control system is used to suppress the cavity noise generated by the sound source.
Simulation of lower-lip motor unit activity and movements in speech
Authors: McClean Michael D. , Clay John L.
Published: October 2005

A computer model is described which is intended to aid in the interpretation of electromyographic-kinematic studies of lower-lip movements for speech. The model consists of three muscles having forcing functions which act to produce displacements of a common point. Each muscle is represented as a set of single motor units. The results of parametric analyses indicate (1) linear associations between parameters of motor unit discharge and movement, (2) a strong dependence of velocity-displacement ratios on spike-burst duration, and (3) variations in movement direction with changes in the relative timing of different muscles.