bluuebunny/crossref_metadata_2025 huggingface dataset:
A note on horizontal-refraction-modal tomography
Authors: Voronovich A. G. , Shang E. C.
Published: October 2005

The use of horizontal antennas composed of long, mode-resolving, vertical arrays is potentially useful in ocean acoustics. A scheme for acoustic tomography of the ocean based on measurements of the horizontal refraction of horizontal rays, which are related to different acoustic modes, is discussed. The horizontal refraction angle of a given mode is equal to the transverse gradient of the refraction index averaged over the depth interval embraced by this mode and integrated over the acoustic path. The effect of internal waves is estimated. It is shown that internal waves do not significantly blur the angular distribution of the received field. An experiment that involves two pairs of long, vertical arrays and a towed tonal source is proposed for the reconstruction of a 3-D picture of the ocean’s inner structure over a 1000-×1000-km area.
Theoretical description of possible detection of swimbladdered fish in forward scatter
Authors: Ye Z.
Published: October 2005

This paper presents a possible theory for acoustic detection of swimbladder fish in forward scatter. A major application of this theory lies in counting fish in rivers. First, the calculation of the forward scattering cross section of gas-filled fish swimbladders with various shapes is presented. Then useful formulas for fish detection in the forward scatter are derived. It is shown that in a nonturbulent medium the fish moving speed may be calculated from the signal amplitude auto-correlation function, which may also be used to estimate the size of fish if the fish speed can be determined by other means. In a turbulent medium, the signal correlation functions are calculated incorporating both sound scattering from fish and turbulence and it is shown that the scattering from the fish may have distinctive features compared to that from the turbulence. An explicit example shows to what degree the fish is countable. Application to an actual measurement is also briefly discussed.
Detection of acoustic second harmonics in solids using a heterodyne laser interferometer
Authors: Moreau A.
Published: October 2005

Acoustic second harmonic generation in solids is difficult to measure and often requires careful sample preparation. In this paper, a heterodyne interferometer modified to measure acoustic fundamental and second harmonics is presented. It requires relatively little sample preparation and it provides noncontact, wideband, absolute, and pointlike measurements. It is shown that the output of an ideal heterodyne interferometer does not contain any even harmonics of a single-frequency acoustic signal. Odd harmonics, however, are produced in calculable amounts. A detailed model of the interferometer is introduced to account for various sources of spurious second harmonics and the model is experimentally verified. Three methods of calibration for the absolute measurement of surface displacement are presented. Measurements of the nonlinearity parameter, β, of a fused quartz sample are shown to agree with literature values.
Nonlinear standing waves: Theory and experiments
Authors: Maa Dah-You , Liu Ke
Published: October 2005

The theoretical treatments of nonlinear standing waves had been hampered for years by the simultaneous nonlinear partial differential equations of Riemann. It is suggested that the situation may become encouraging if attention is concentrated on the motion of a particle at a point fixed in space, or on the waveform of the standing wave with fixed alternating values of the particle velocities. It is shown that the motion of a particle at a point fixed on the waveform of a standing wave is readily soluble from the Riemann equations, and an exact, stable solution of the nonlinear standing wave is obtained, which differs from that in linear acoustics only in containing an additional term proportional to the particle displacements in the arguments of the time and space functions. These implicit functions are readily developed into explicit power series, and the field parameters of the standing wave result in terms representing the harmonics. The properties of the nonlinear standing waves thus obtained have been confirmed by experiments. A standing-wave tube has been built and equipped with a high power loudspeaker driver as the source of excitation. The gradual spectral variation of the standing wave with increasing excitation has been observed. Experimental results agree well with the theoretical predictions and further uncover a number of interesting phenomena. Under certain conditions, saturation and bifurcation appear at a high sound level.
Effects of thermal conduction on bubble dynamics near the sonoluminescence threshold
Authors: Yasui Kyuichi
Published: October 2005

A simple model of bubble dynamics is constructed in which effects of thermal conduction and those of evaporation and condensation of water vapor are included. Results of numerical calculations when a bubble is irradiated by an ultrasonic wave reveal that the effect of thermal conduction is considerable. The calculated results fit with the experimental data of the radius–time curve much more satisfactorily than those by a model without thermal conduction. It is also concluded that a bubble transduces the energy of the acoustic wave into heat. Numerical calculations also reveal that the partial pressure of water vapor in a bubble differs considerably from the saturated vapor pressure especially at collapse of the bubble. Connection with sonoluminescence is also discussed.
Spherical coordinate Green’s functions for ring tractions in a solid unbounded medium
Authors: Kapoor Tarun K. , Schmidt Henrik
Published: October 2005

The need for Green’s functions for excitation of a solid elastic medium by ring traction loads arises when modeling the interaction between a spherical boundary and a cylindrical boundary using the full three-dimensional elastodynamic equations of motion. Here, the explicit analytical solutions for the Green’s functions for excitation of a solid unbounded elastic medium by ring loads acting in the radial (r), polar (θ), and azimuthal (φ) directions using spherical coordinates are developed. As an extension, the Green’s function for a ring bending moment acting in the azimuthal (φ) direction is also derived. The Green’s functions are obtained by expanding the potentials in terms of spherical harmonic waves (SHW) and it is demonstrated how the Green’s functions for excitation by a point load may be synthesized by summing the appropriately phased ring load solutions. It is shown that explicit analytical solutions may be obtained by implementing a linear transformation of the tangential displacements and stresses.
Fast converging binomial series for radiation field calculation
Authors: Lawu Tjundewo , Tabei Makoto , Ueda Mitsuhiro
Published: October 2005

An analytical description for the radiation field of a planar source by fast converging binomial series expansion is derived. The terms of the series correspond to the Fresnel solution and its derivatives. Consequently, if the Fresnel solution of the diffraction integral is expressed by differential functions, the radiation field can be obtained by calculating the series. As a result of the expansion, this method can be applied to any region except the points on the surface of transducer. The results are compared with the correct computations and those obtained by conventional Fresnel approximation.
Diffracted effects due to guided modes on finite (truncated) structure elements
Authors: Lu I.-Tai , Bertoni H. , Yao Y. Q.
Published: October 2005

This paper considers a uniform asymptotic method for computing radiation into the surrounding water due to guided waves on a finite (truncated) structure. The effect due to two radiation mechanisms (leaky or trapped mode radiation and end-point diffraction) is discussed and quantified using numerical examples.
Relationships between speech production and speech perception skills in young cochlear-implant users
Authors: Tye-Murray Nancy , Spencer Linda , Gilbert-Bedia Elizabeth
Published: October 2005

The purpose of this investigation was to examine the relationships between young cochlear-implant users’ abilities to produce the speech features of nasality, voicing, duration, frication, and place of articulation and their abilities to utilize the features in three different perceptual conditions: audition-only, vision-only, and audition-plus-vision. Subjects were 23 prelingually deafened children who had at least 2 years of experience with a Cochlear Corporation Nucleus cochlear implant, and an average of 34 months. They completed both the production and perception version of the Children’s Audio–visual Feature Test, which is comprised of ten consonant–vowel syllables. An information transmission analysis performed on the confusion matrices revealed that children produced the place of articulation fairly accurately and voicing, duration, and frication less accurately. Acoustic analysis indicated that voiced sounds were not distinguished from unvoiced sounds on the basis of voice onset time or syllabic duration. Subjects who were more likely to produce the place feature correctly were likely to have worn their cochlear implants for a greater length of time. Pearson correlations revealed that subjects who were most likely to hear the place of articulation, nasality, and voicing features in an audition-only condition were also most likely to speak these features correctly. Comparisons of test results collected longitudinally also revealed improvements in production of the features, probably as a result of cochlear-implant experience and/or maturation.
Floquet analysis of guided waves in periodically layered composites
Authors: Safaeinili A. , Chimenti D. E.
Published: October 2005

In this paper analytical and numerical calculations, together with experimental measurements, are presented on the propagation of elastic guided waves in a composite plate composed of periodic layers. The guided waves are constructed by superposing obliquely traveling Floquet partial wave solutions in such a way that they satisfy a standing-wave resonance condition through the thickness of the periodic composite. It is demonstrated that transverse resonance can be established only in the Floquet passbands of the periodic composite. The predicted reflection spectra are compared with experimental observations in the Lamb wave case for an aluminum/aramid-epoxy composite and demonstrate excellent detailed agreement. This study offers an opportunity to gain new insight into the technologically important problem of plates with periodic structures.
The splitting of dispersion curves for the fluid-loaded plate
Authors: Dickey J. , Maidanik G. , Überall H.
Published: October 2005

The splitting of the free-wave dispersion curve for a fluid-loaded plate into sub- and supersonic branches, and the apparent ‘‘repulsion’’ of these two branches, is discussed.
Benchmarking an acoustic coupling theory for elastic shells of arbitrary shape
Authors: Rebinsky Douglas A. , Norris Andrew N.
Published: October 2005

Coupling coefficients for thin shells of arbitrary curvature based upon a ray-theoretic approach devised by the authors are benchmarked against exact and high-frequency results for canonical geometries, i.e., the spherical and infinite circular cylindrical shells. The well-known high-frequency approximations of the coupling coefficients are found to describe their magnitude accurately but not the phase for midfrequencies (between ring and coincidence) when compared with results obtained by applying the Sommerfeld–Watson transformation to the exact modal series. The coupling coefficients characterize both the magnitude and the phase accurately and simply in terms of fundamental physical parameters.
Influence of viscosity on the reflection coefficient at a fluid–solid interface
Authors: Bianco Bruno , Tommasi Tullio
Published: October 2005

A viscous fluid can carry both an attenuated longitudinal wave and an attenuated shear wave. The presence of a shear wave makes it necessary to satisfy the boundary conditions for a solid–solid interface when calculating the reflection coefficient at a lossy-liquid/solid interface. Numerical results are presented which point out the influence of viscosity on reflection coefficients.
Frequency discrimination of bandlimited harmonic complexes related to vowel formants
Authors: Lyzenga Johannes , Horst J. Wiebe
Published: October 2005

Just-noticeable differences (jnd’s) in the center frequency of bandlimited harmonic complexes were measured for normal hearing subjects. A triangular and a trapezoidal spectral envelope were used. The center frequency ranged from 2000 to 2100 Hz for the triangular envelope and from 2000 to 2200 Hz for the trapezoidal envelope. For both envelope shapes the values 100, 200, and 400 dB/oct were used for the slope. The fundamental frequency was 100 Hz for all complexes. A three-interval, three-alternative forced-choice task was used. All measurements were performed with and without roving of the signal level. Without roving, the jnd’s were in most cases about a factor of 1.5 smaller than with roving. The bandwidth and the center frequency were factors having the major influence on the jnd’s. For the triangular envelope, the jnd’s were smallest for center frequencies that were halfway between two signal components. For the trapezoidal envelope, the jnd’s were smallest for center frequencies that coincided with a signal component. For the triangular envelope, the smallest jnd’s for each slope were about half the value of those for the trapezoidal envelope. In the case of the smallest jnd’s for each spectral envelope shape, the jnd’s were smaller when the spectral slope was steeper. Part of the data for the triangular envelope can be explained by modulation depth discrimination data. The data for the trapezoidal envelope can be interpreted in terms of a spectral profile comparison. The remaining part might be interpreted either in terms of a temporal mechanism, or of the mentioned spectral profile comparison. It is argued that, for this spectral comparison, the ear probably combines information over a limited frequency range by comparing the spectral profiles of the two presented stimuli, rather than comparing individual component levels.
Critical bandwidth for phase discrimination in hearing-impaired listeners
Authors: Nelson David A. , Schroder Anna C.
Published: October 2005

Monaural phase discrimination was evaluated in normal-hearing and hearing-impaired listeners as a function of the frequency separation among components in three-tone complexes. The phases of the center components of 100% sinusoidal amplitude-modulated (SAM) waveforms were shifted by 90° to yield quasi-frequency-modulated (QFM) waveforms that had identical long-term spectra but different envelopes and temporal fine structure. Normal-hearing listeners can distinguish QFM waveforms from SAM waveforms as long as the modulation frequency (frequency separation between components) is less than about 40% of the carrier frequency (center component). Phase discrimination performance (d′) was measured as a function of modulation frequency, and critical bandwidths for phase discrimination (CBphs) were specified as the modulation frequency corresponding to a performance index (d′) of 1.0. In normal-hearing ears, CBphs increased with stimulus SPL. In hearing-impaired ears, CBphs estimates were equal to or narrower than normal when comparisons were made at the same SPLs; CBphs estimates from hearing-impaired ears were broader (better) than normal only when comparisons were made at equivalent SLs. Differences between CBphs estimates in normal-hearing and hearing-impaired ears are explained by level-dependent auditory filtering and the sensation levels at which comparisons are made, without the necessity to postulate abnormal tuning in hearing-impaired ears.
The origin of periodicity in the spectrum of evoked otoacoustic emissions
Authors: Zweig George , Shera Christopher A.
Published: October 2005

Current models of evoked otoacoustic emissions explain the striking periodicity in their frequency spectra by suggesting that it originates through the reflection of forward-traveling waves by a corresponding spatial corrugation in the mechanics of the cochlea. Although measurements of primate cochlear anatomy find no such corrugation, they do indicate a considerable irregularity in the arrangement of outer hair cells. It is suggested that evoked emissions originate through a novel reflection mechanism, representing an analogue of Bragg scattering in nonuniform, disordered media. Forward-traveling waves reflect off random irregularities in the micromechanics of the organ of Corti. The tall, broad peak of the traveling wave defines a localized region of coherent reflection that sweeps along the organ of Corti as the frequency is varied monotonically. Coherent scattering occurs off irregularities within the peak with spatial period equal to half the wavelength of the traveling wave. The phase of the net reflected wave rotates uniformly with frequency at a rate determined by the wavelength of the traveling wave in the region of its peak. Interference between the backward-traveling wave and the stimulus tone creates the observed spectral periodicity. Ear-canal measurements are related to cochlear mechanics by assuming that the transfer characteristics of the middle ear vary slowly with frequency compared to oscillations in the emission spectrum. The relationship between cochlear mechanics at low sound levels and the frequency dependence of evoked emissions is made precise for one-dimensional models of cochlear mechanics. Measurements of basilar-membrane motion in the squirrel monkey are used to predict the spectral characteristics of their emissions. And conversely, noninvasive measurements of evoked otoacoustic emissions are used to predict the width and wavelength of the peak of the traveling wave in humans.
Filtering and spectral characteristics of averaged auditory brain-stem response and background noise in infants
Authors: Sininger Yvonne Satterblom
Published: October 2005

Filtering of electrode-recorded activity before averaging is used in evoked-potential measurements to reduce background noise under the assumption that unwanted spectral components will be suppressed without substantially altering neural activity. Desired filter characteristics depend on signal and noise spectra and filter choice can affect the validity and efficiency of ABR measurement. Spectral characteristics of the human auditory brain-stem response (ABR) change with subject age and state and with the level and spectrum of the stimulus. Brain-stem evoked potentials from infants comprise greater low-frequency spectral components than do adult ABRs. Physiologic noise can also change with age of the subject. This study compares the effects of 30- and 100-Hz high-pass filters on ABR amplitude and response Fsp in full-term infants. Stimuli used to elicit ABRs are moderate- and low-level clicks and 500-Hz tone bursts. Spectral characteristics of the averaged ABR and the no-stimulus background noise from full-term infants are also characterized. Results indicate that (1) energy in the infant ABR is concentrated below 100 Hz and (2) a high-pass recording filter of 30 Hz reveals a larger-amplitude ABR and enhances the overall signal-to-noise ratio as measured by Fsp as compared to a 100-Hz high pass.
Sound equalization in enclosures using modal reconstruction
Authors: Asano Futoshi , Swanson David C.
Published: October 2005

The equalization of complex sound pressure in an enclosure is investigated in this paper. The sound field in the enclosure is modeled with the sum of a series of modes. This sound field is controlled by multiple sources distributed in the enclosure so that a certain region in the enclosure has a desired complex sound pressure. First, the optimum solution which minimizes the average potential energy of the error pressure over the region is derived, where the error is defined as the difference between the desired sound pressure and the sound pressure caused by the sources. By using the optimum solution, the achievable best performance can be known for the given region and the source distribution. The optimum solution can also be a useful tool for finding an effective source distribution since the performance of the optimum solution depends only on the source distribution. Furthermore, the eigenvalues of the source coupling matrix, which appears in the derivation of the optimum solution, indicates the effectiveness of the source distribution. The effectiveness of source distribution is discussed with nine examples of source distributions in a two-dimensional enclosure. The multipoint equalization method to approximate the optimum solution is also discussed for the practical use.
Minimization of bias error due to windows in planar acoustic holography using a minimum error window
Authors: Kwon Hyu-Sang , Kim Yang-Hann
Published: October 2005

Bias errors in the prediction of a sound field using planar acoustic holography are due to aliasing and window effects. It is noteworthy that aliasing is negligible in the forward predictions if the sampling space is less than a quarter wavelength. However, bias error induced by a window is the major concern for accurate holographic prediction because of the small number of measurement points in the planar acoustic holography. For the reduction of this error, a new class of window, the MEW, is proposed and compared with Hann, Gaussian, and Kaiser–Bessel windows. It is built by modifying the method that Papoulis proposed by minimizing the second-order moment of the window spectrum. The characteristics of the MEW vary with the number of weighting values and the number of higher-order moment terms to be eliminated. The applicability of the MEW on planar acoustic holography is demonstrated.
Acoustic scattering of a plane wave by two spherical elastic shells
Authors: Huang H. , Gaunaurd G. C.
Published: October 2005

The acoustic scattering by two spherical elastic shells in close proximity insonified by plane waves at arbitrary angles of incidence is analyzed exactly in the low- and intermediate-frequency ranges. The incident and scattering wave fields are expanded in terms of the classical modal series and the addition theorem for the spherical wave functions facilitates the exact expression of the sound fields scattered by each spherical elastic shell in the presence of the other, referred to coordinate systems at the centers of either spherical shell. The solution to the scattering problem is obtained by simultaneously solving the Helmholtz equation governing the wave motion in the fluid medium in which the two shells are submerged and the two sets of equations of motion of the two elastic shells satisfying the boundary conditions at all fluid–shell interfaces and the far-field radiation condition. Numerical computation of the scattered wave pressure involves the solution of the truncation of an ill-conditioned complex matrix system the size of which depends on how many terms of the modal series are required for convergence. This in turn depends on the value of the frequency, and on the proximity of the two spherical elastic shells. The ill-conditioned matrix equation is solved using the Gauss–Seidel iteration method and Twersky’s method of successive iteration double checking each other. Backscattered echoes from two identical spherical elastic shells are extensively calculated. The result also demonstrates that the large amplitude low-frequency resonances of the echoes of the neighboring elastic shells shift downward with proximity to each other. This can be attributed to the increase of added mass for the vibration of the shells.
Effects of 1-Hz and 2-Hz transient vertical vibration on discomfort
Authors: Ruffell Catherine M. , Griffin Michael J.
Published: October 2005

The discomfort caused by 1-Hz and 2-Hz vertical sinusoidal vibration has been studied with 20 seated subjects, using the method of magnitude estimation. The sinusoidal transients were superimposed on an 80-s background vibration which consisted of a 1-oct band of random vibration, centered on 1 Hz, with a magnitude of 0.63 m s−2 rms. The transients were added at five magnitudes (0.63–1.6 m s−2 rms) and seven durations (1–60 s). Male and female subjects produced comparable results and similar discomfort was produced by the two frequencies of vibration. Discomfort increased when the magnitudes or the durations of the transients were increased. Of alternative methods of predicting the discomfort, the overall vibration dose values gave the highest correlations with subject estimates, followed by the overall root-mean-square accelerations. A lower correlation was found with peak acceleration and the lowest correlation was with a running rms measurement, using a 1-s window.
A theoretical study on the influence of some constituent material properties on the behavior of 1-3 connectivity composite transducers
Authors: Hayward Gordon , Bennett Jeremy , Hamilton Robin
Published: October 2005

The influence of constituent material properties on the behavior of doubly periodic, 1-3 connectivity composite transducers is described using constrained unidimensional theory, supplemented by finite element analysis. Two functional situations are discussed, corresponding to thickness drive and quasihydrostatic operation. In each case the active ceramic and inert filler phases are varied as functions of ceramic-filler volume fraction. For the composite dimensions under consideration, there is general good agreement between the constrained theory and finite element modelling, although where this is not the case, differences are highlighted and reasons provided for their occurrence. A strong practical emphasis is placed throughout, with a view towards providing useful guidelines for the transducer design engineer.
Impulse-response method to predict echo responses from defects in solids. Part I. Theory
Authors: Lhémery Alain
Published: October 2005

A model is proposed to predict the echo response from a defect of complex geometry at arbitrary position in a solid medium in the field of an arbitrary transducer. Isotropic media and scatterers with homogeneous (free) boundary conditions are assumed. The radiated field incident on the defect is calculated by using a recent model based on the impulse response approach [A. Lhémery, ‘‘A model for the transient ultrasonic field radiated by an arbitrary loading in a solid,’’ J. Acoust. Soc. Am. 96, 3776–3786 (1994)]. The present model (elastic model) treats the scattering by the defect under the Kirchhoff approximation. The derivation of an expression for the overall impulse response essentially follows that of a previously proposed model (acoustic model) to predict echo responses from targets immersed in a fluid [A. Lhémery, ‘‘Impulse response method to predict echo-responses from targets of complex geometry—Part I: Theory,’’ J. Acoust. Soc. Am. 90, 2799–2807 (1991)]. The transient reception by the receiver is treated under the same approximation as that made for the transient radiation. An explicit integral formulation for the overall impulse response is obtained in a general form. To illustrate the applicability of the new formulation, the case of flat-bottomed holes interrogated by a disk compression wave transducer is treated. In this case, a semianalytic solution is derived. Results predicted by the present elastic model and the existing acoustic model are compared.
Heat transfer from a cylinder in an acoustic standing wave
Authors: Mozurkewich George
Published: October 2005

Heat transfer was measured from wires of various diameters located at a velocity antinode in an acoustic standing wave. A transient method was used, in which the rate of heat transfer was deduced from the rate of change of temperature after heating was turned off. For fixed wire diameter and acoustic frequency, the dimensionless heat-transfer coefficient (Nusselt number) Nu shows a distinctive variation with acoustic amplitude. At high amplitude, Nu follows the well-known, steady-flow, forced-convection correlation, time averaged over an acoustic cycle, while at low amplitude, Nu has a constant value determined by natural convection. The transition between these regimes, which occurs rather abruptly when the streaming Reynolds number (based on wire diameter and acoustic velocity amplitude) equals 88, is discussed in terms of a heat-transfer bottleneck that is opened by acoustic streaming. An empirical correlation is presented. Applicability to heat exchangers for thermoacoustic heat engines is considered.
Mean and variance of the ultrasonic signal from a scatterer beneath a rough surface: Theory
Authors: Bilgen Mehmet , Rose James H.
Published: October 2005

A simple model is presented that predicts the ultrasonic signal from a weakly scattering inclusion beneath a randomly rough water–solid interface that is insonified by a normally oriented phase-sensitive transducer. The rough surface is modeled by a spatially uniform, normally distributed random process with a Gaussian autocorrelation function. The effects of roughness are introduced via the phase-screen approximation. Analytic series solutions are derived and presented for the mean, mean square, and mean absolute square of the pulse-echo signal. Rough surface effects are shown to depend on the depth of the scatterer beneath the surface. The depth dependence of the rough-surface effects is shown to arise from the statistical dependence of the phase shifts that arise due to the entry and exit of the ultrasound through the rough surface. The roughness-induced loss of the average signal is found to be greatest for scatterers immediately below the surface. The average roughness-induced signal loss is least for scatterers that are farthest from the surface for unfocused transducers or at the focal point for focused transducers and can be modeled by a simple frequency-dependent transmission coefficient in these cases. The variance in the signal increases with the frequency and is relatively large for scatterers immediately below the surface. The variance is smallest at the focal point, and in the far field for unfocused transducers. The variance is greatest for the scatterers with the smallest lateral extent and least for scatterers with the largest lateral extent. Finally, it is found that the power backscattered from a small near-surface scatterer is actually increased on the average by the rough surface.
Calculation of turbulent boundary layer wall pressure spectra
Authors: Capone Dean E. , Lauchle Gerald C.
Published: October 2005

The suitability of various wave-vector–frequency spectral models for predicting the point wall pressure spectrum due to developed turbulent boundary layer flow over planar, rigid surfaces is investigated. The early Corcos model [G. Corcos, J. Fluid Mech. 18, 353–378 (1964)] along with the incompressible and compressible models developed by Chase [D. Chase, J. Sound Vib. 112, 124–147 (1987)] are given particular attention. The effect of finite-sized measurement transducers is included in the integration of the theoretical wave-vector–frequency spectrum over the in-plane wave numbers in order to arrive at an attenuated point pressure frequency spectrum that can be compared directly to existing experimental data obtained in air, water, and glycerine. The selected experiments cover a wide range of fluid properties and Reynolds numbers. It is found that the Corcos model does not predict the measured data as well as the Chase model. An optimum set of empirical constants needed to exercise the Chase models are presented, but found to depend on the experiment considered. The need to consider viscous effects in future modeling is borne out when dealing with viscous fluids like glycerine.
Shallow-water sediment layer structure and composition effects on range-dependent acoustic propagation at the Atlantic Generating Station (AGS) site
Authors: Bongiovanni K. P. , Badiey M. , Siegmann W. L.
Published: October 2005

Effects of shallow-water sediment layers on acoustic propagation over a broad band of frequencies are examined using simulations and measured experimental data. Accurate geoacoustic data from the New Jersey Shelf AGS site have provided profiles of compressional and shear sound speed, attenuation, and density. Along with the detailed bathymetry and CTD data, these profiles are used for input to transmission loss and wave-number calculations. In order to examine range-dependent effects of geoacoustic properties and geological structures in this region on acoustic wave propagation, parabolic equation (PE) models are employed for frequencies ranging from 75 to 1200 Hz. Sensitivities to variations in sediment structure and characteristics are determined to show their acoustic influences. Uncertainties in geoacoustic parameters and sensitivities to required vertical resolution of modeled geoacoustic data are displayed. Comparisons of elastic PE simulations illustrate the influence of shear effects. Discussion of sediment layering effects and range dependence on acoustic propagation are given in connection with broadband experimental data.
Constraining acoustic backscatter estimates of suspended sediment concentration profiles using the bed echo
Authors: Thorne Peter D. , Holdaway Glenn P. , Hardcastle Peter J.
Published: October 2005

The application of acoustic backscattering to the measurement of suspended sediment transport is being increasingly employed. This is due to the unique property of acoustics being able to measure profiles using a single instrument. Also the profiles can readily be obtained with a high spatial and temporal resolution, and this is beginning to provide detailed images of suspended sediments which have the potential to significantly advance our understanding of suspension processes. However, at periods of high concentration, when sound attenuation due to sediment scattering becomes significant, the inversion technique used to obtain the suspended sediment profiles, can, due to relatively small errors ∼5%–10%, generate unbounded concentration profiles which diverge to infinity or zero. Therefore at the periods of greatest scientific interest, the acoustic technique can encounter difficulties. In the present work the bed echo is utilized to identify the input errors, and constrain the calculated concentration profiles, and therefore enable acoustics to play a useful role at high concentration levels.
Spatial coherence of a sound field in a refractive shadow: Comparison of simulation and experiment
Authors: Havelock David I. , Di Xiao , Daigle Gilles A. , Stinson Michael R.
Published: October 2005

The coherence of a sound field in a refractive shadow near the ground has been examined for microphone separations which are transverse or longitudinal to the direction of propagation. Single tone test signals at 1 kHz, 500, and 100 Hz were measured at a range of 700 m by a microphone array, spanning 270 m longitudinally and 15 m transversely. Estimates of the spatial correlation, based on 10-minute averages, indicate transverse coherence lengths less than 2 m and longitudinal correlation lengths less than 7 m for moderately strong upward refraction conditions. Numerical simulations were done which emulate the experimental conditions. The Green’s-function method for the parabolic equation was used to generate two-dimensional sound fields within a refractive shadow. An upward refracting atmospheric model with homogeneous isotropic Gaussian turbulence was used. The coherence in the simulated sound fields compares well, qualitatively, with the experimentally measured coherence. Both simulation and experiment indicate that the longitudinal coherence length within a refractive shadow is dramatically less than is typically observed outside of a shadow. The reduced coherence will restrict the useful aperture size of beamforming arrays deployed in acoustical non-line-of-sight conditions.
Investigation of a high intensity sound beam from a plane transducer. Experimental and theoretical results
Authors: Nachef Sylvain , Cathignol Dominique , Tjo/tta Jacqueline Naze , Berg Aina M. , Tjo/tta Sigve
Published: October 2005

Results of a systematic investigation of a high intensity sound beam from a plane circular transducer are presented for a large range of excitation levels. The ratio of the shock formation distance to the Rayleigh distance ranges from 1.7 to 0.06. A detailed description of the experimental setup is given. Problems encountered when calibrating highly intense and highly directive sound sources are discussed, and a novel method of calibration is proposed. Experimental results for the case of cw excitation are presented and compared with a simulation using the Bergen Code, thus allowing to assert the usefulness of the model (Khokhlov–Zabolotskaya–Kuznetsov equation) and of the numerical algorithm (spectral decomposition and finite difference method of the transformed beam equation) for high intensity sound beams. A new effect, nonlinear defocusing of the beam, is uncovered.
Acoustic scattering from a rigid tapered finite parabolic cylinder
Authors: Partridge Chris , Smith Edgar R.
Published: October 2005

The deformed cylinder method is a very versatile model that can be used on a wide range of acoustic scattering problems. To date, it has been applied to axisymmetric bodies of circular cross section, whether it be rigid, an elastic solid, or a shell. In this paper, the method is applied to nonaxisymmetric bodies of parabolic cross section. Results are given for the backscattering from a tapered finite rigid parabolic cylinder and are found to be in good agreement with estimates obtained using the Kirchhoff (physical optics) method.
The acoustic trachea of Tettigoniids as an exponential horn: Theoretical calculations and bioacoustical measurements
Authors: Hoffmann Elke , Jatho Martin
Published: October 2005

The morphology and acoustic characteristics of the acoustic tracheal system were examined in certain tettigoniid species. Morphological measurements and statistical analysis reveal that in all species of bushcrickets investigated the shape of the acoustic trachea can be approximated by the equation of an exponential horn. Based on this approximation the transmission functions of the different tracheae were calculated theoretically. Because of its small size, the acoustic trachea must not be treated as an infinite exponential horn but its transmission function must be calculated by means of the equations for a finite-length horn. The finite horn amplifies sound from a certain frequency on (cutoff frequency) in a broad range of frequencies as the infinite horn does. But the broadbanded transmission is superposed by a few resonances which are caused by reflections inside the horn. Bioacoustical measurements were made with a probe microphone. As expected from the theoretical considerations the course of the measured transmission function corresponds much better with the one calculated for the finite exponential horn than with the one calculated for the infinite horn. The present results are discussed referring to the consequences of the transmission properties of the acoustic trachea for the hearing ability of Tettigoniids. Additionally, they are compared with other investigations concerning the function of the acoustic trachea in tettigoniid hearing.
Measurements of ultrasonic backscatter coefficients in human liver and kidney in vivo
Authors: Wear Keith A. , Garra Brian S. , Hall Timothy J.
Published: October 2005

Ultrasonic backscatter coefficients, in the range of 2.0–4.0 MHz, were measured in normal human livers and kidneys in vivo. In liver, data were acquired and analyzed from 15 normal volunteers and 19 patients with hepatitis. No significant difference between normal and chronic hepatitis was found. The power-law fit to the backscatter coefficient in normal liver as a function of frequency was η(f )=4.5×10−5 f1.6 cm−1 Str−1. This is comparable to that measured by other investigators in in vitro preparations of human and animal liver and to that measured by two other teams of investigators in in vivo human liver. In kidney, data were acquired from 11 normal volunteers. The power-law fit to the backscatter coefficient in normal kidney was η(f )=2.3×10−5 f2.1 cm−1 Str−1. This is in the range of that measured by other investigators in in vitro preparations of human and animal kidney. In order to assess the system dependence of in vivo abdominal organ backscatter coefficients, measurements were performed using two different ultrasonic data-acquisition systems. The two systems exhibited close agreement.
The time course of auditory segregation: Concurrent vowels that vary in duration
Authors: McKeown J. Denis , Patterson Roy D.
Published: October 2005

Human listeners perform well when identifying both members of simultaneous steady-state vowel pairs, even when the vowels start and stop at the same time, are presented monaurally, have approximately equal intensities, and have the same fundamental frequency (f0). The sensation described by listeners is of one dominant, vowel ‘‘colored’’ by the second, less easily identified, or nondominant vowel. Introducing a small separation in f0 between the vowels improves performance and listeners now report that there is a sensation of two voice sources rather than one. It has been suggested that listeners use an f0-guided segregation strategy in identifying two vowels that differ in f0. An experiment is reported in which four listeners attempted to identify both members of a pair of concurrent vowels which varied in duration from a single cycle of the stimulus waveform (one pitch period) up to eight cycles. A dominant vowel was identified with near 100% accuracy even in the single-cycle condition, whereas identification of the nondominant vowel showed a slow improvement up to eight cycles. A difference in f0 between the vowels improved identification of the nondominant vowel, but between three and four cycles of the vowels were necessary for this advantage. It is first concluded that the improvement in performance with stimulus duration is due to an improvement in identification of the nondominant vowel; and, second, a difference in f0 is not required for segregation of the dominant vowel which is available from stimuli which are too brief to provide a useful estimate of f0.
A gesture-based dynamic model describing articulatory movement data
Authors: Kröger Bernd J. , Schröder Georg , Opgen-Rhein Claudia
Published: October 2005

A quantitative dynamic model for the description of speech movements using a critically damped linear second-order system is proposed. This six-parameter model is able to fit natural movement data with high accuracy. Since in this approach the actual location of gestural onset and gestural offset, i.e., the location and duration of gestural activation, results from the fitting procedure, no advance sectioning of movement traces is necessary. The model parameters are target position, eigenperiod, and four time parameters describing the temporal location of gestural onset and offset. The fitting algorithm is tested on simulated and natural data in order to evaluate the accuracy of the fits and the repeatability of the dynamic parameters extracted.
Additivity of masking in normally hearing and hearing-impaired subjects
Authors: Oxenham Andrew J. , Moore Brian C. J.
Published: October 2005

The effects of combining two equally effective maskers were studied in normally hearing and elderly hearing-impaired subjects. The additivity of nonsimultaneous masking was investigated by measuring thresholds for a brief 4-kHz signal in the presence of a broadband-noise forward masker, a backward masker, and a combination of both. For the normally hearing subjects, combining two equally effective nonsimultaneous maskers resulted in up to a 15-dB greater increase in threshold than the 3 dB predicted by an energy-summation model (‘‘excess masking’’). However, the hearing-impaired subjects showed little or no excess masking. The difference between the two groups is consistent with a theory linking excess masking to the compressive transfer function measured on the basilar membrane (BM). In the hearing-impaired subjects the transfer function is more linear, accounting for the lack of excess masking. The additivity of simultaneous masking was investigated by measuring thresholds for a 100-ms 4-kHz signal in the presence of either a 400-ms broadband noise masker or a 400-ms sinusoidal masker at the same frequency as the signal, and then combining two equally effective maskers, a noise and a tone. The maximum amount of excess masking (3 to 4 dB) was similar across the two groups of subjects, consistent with an explanation based on the use of different detection cues for the tonal and noise maskers. It is argued that, while peripheral compression may underlie excess masking for pairs of nonsimultaneous maskers, it is unlikely that in simultaneous masking, where the maskers are close in frequency to the signal, the two maskers are compressed individually before their effects are combined. It is further suggested that BM nonlinearity may underlie the effects of the upward spread of masking and the nonlinear growth of forward masking, as well as accounting for the additivity of simultaneous masking when the masker frequencies are well below that of the signal.
Effect of mean flow on responses of a fluid-loaded plate
Authors: Wu Sean F. , Zhu Jinshuo
Published: October 2005

Asymptotic solutions to the dynamic and acoustic responses of a fluid-loaded infinite plate subject to a time-dependent line force excitation in mean flow are obtained. Results show that mean flow has a significant effect on the plate traveling waves, the modification factor being α2(1∓M)8 when the excitation frequency is above the plate coincidence frequency, where α is the fluid-loading factor, M is the mean flow Mach number, and minus and plus signs indicate upstream and downstream propagating waves, respectively. At the coincidence frequency, the amplitudes of traveling waves are modified by mean flow by (c0+c1M+c2M2), where cj, j=0, 1, and 2 are α-dependent constants. For light fluid loading, for example, an air/steel interface, α≊6.5×10−4, the leading term of the traveling wave is proportional to α−4/3M2. For heavy fluid loading, for example, a water/steel interface, α≊0.133, the leading term is proportional to α−2/3M. Below the coincidence frequency, the effect of mean flow on plate traveling waves is insignificant. Mean flow also changes the radiated acoustic pressures. In particular, the amplitudes of the leaky waves are modified by mean flow, to the leading order of a small value of α, by (√Ω±M)2[4Ω√(Ω±M)2−1]−1, where Ω is the ratio of the excitation frequency to the plate coincidence frequency. The effect of mean flow on the cylindrical waves depends on Ω. When Ω≳1, the peak amplitudes of the cylindrical waves are modified by mean flow by √(1−Ω−1)±2Ω−1/2M−M2, and the beam angles are rotated by θb=sin−1(M∓Ω−1/2). When Ω<1, the effect of mean flow on the cylindrical waves is greatly decreased. Mean flow modifies the wave numbers of the traveling waves and acoustic waves as well. As a result, the waves propagating in the upstream direction are squeezed and those in the downstream direction are relaxed in space.
Speech intelligibility in noise: Relative contribution of speech elements above and below the noise level
Authors: Drullman Rob
Published: October 2005

In a previous study [R. Drullman, J. Acoust. Soc. Am. 97, 585–592 (1995)], the relative contribution of temporal modulations and fine structure to sentence intelligibility was investigated. This Letter reports additional listening experiments to assess in more detail the effect of masking noise on the peaks and troughs of the speech signal. For this purpose, the signal structure of each 1/4-oct band in a 24-band filterbank (100–6400 Hz) was altered by manipulating the distribution of speech and noise over the sentences. Results for 12 normal-hearing subjects indicate that removing noise from the peaks has no effect on intelligibility; removing the speech signal from the noisy troughs, however, yields a 2-dB increase of the speech-reception threshold. So, it appears that, even below the noise level, weak speech elements do contribute to intelligibility.