bluuebunny/crossref_metadata_2025 huggingface dataset:
Radial extrapolation of wave fields from synthetic measurements of the nearfield
Authors: Blacodon Daniel , Candel Sébastien M. , Elias Georges
Published: October 2005

Wave extrapolation methods are commonly used to evaluate the farfield radiation pattern of a complex source from nearfield measurements. The nearfield data are usually collected with transducer arrays or matrices. This standard procedure poses problems of signal conditioning, calibration, and recording that may be avoided by performing a synthetic detection of the nearfield. This alternate procedure, which borrows its principle from the field of synthetic aperture radar (SAR), is explored and illustrated in this article. The problem of radial wave extrapolation in a layered configuration is also analyzed. Acoustic wave radiation from a uniform stream to a region at rest is specifically considered. Exact and approximate wave extrapolators are derived. Comparisons between experimental measurements and wave extrapolation results indicate that the combination of synthetic nearfield detection and radial wave extrapolation is reliable and that extrapolation in layered situations may be carried out with little additional effort.
Preliminary observations on the use of duration as a cue to syllable-initial fricative consonant voicing in English
Authors: Baum Shari R. , Blumstein Sheila E.
Published: October 2005

Acoustic analyses were undertaken to explore the durational characteristics of the fricatives [f,θ,s,v,F,z] as cues to initial consonant voicing in English. Based on reports on the perception of voiced–voiceless fricatives, it was expected that there would be clear-cut duration differences distinguishing voiced and voiceless fricatives. Preliminary results for three speakers indicate that, although differences emerged in the overall mean duration of voiced and voiceless fricatives, contrary to expectations, there was a great deal of overlap in the duration distribution of voiced and voiceless fricative tokens. Further research is needed to examine the role of duration as a cue to syllable-initial fricative consonant voicing in English.
Calculated B/A parameters for n-alkane liquids
Authors: Hartmann Bruce , Balizer Edward
Published: October 2005

An analytic PVT equation of state, supplemented with experimental heat capacity data, was used to calculate the acoustic nonlinearity parameter B/A as a function of temperature and pressure for a series of n-alkane liquids (including polyethylene melt as a limiting case). It was found that this method generally predicts B/A values in agreement with experimental results from the literature to within the experimental uncertainty of the results, 5%. It is predicted that B/A has a maximum as a function of temperature, and this prediction is confirmed by the experimental results. A minimum as a function of pressure is also predicted and borne out by the data. The n-alkane chain length dependence of B/A is not straightforward but tends to decrease as the chain length increases. The higher-order nonlinearity parameter C/A was found to be independent of chain length.
Diffraction of a plane acoustic wave by two equal circular infinite soft strips
Authors: Jain Sarita , Jain D. L.
Published: October 2005

This article deals with the solution of the problem of diffraction of a time-harmonic obliquely incident plane acoustic wave by two equal infinite coaxial soft circular strips. A simple integral equation technique is presented to solve this two-dimensional problem by the perturbation method when the wavelength of the incident plane wave is much larger than the radius of the circular strips. Approximate expressions for the farfield amplitude and the scattering cross section are derived.
Comments on the applicability of the Kuster–Toksöz method to the derivation of the dynamic material parameters of inhomogeneous media
Authors: Scharnhorst Kurt P.
Published: October 2005

The Kuster–Toksöz method for predicting the quasistatic elastic properties of microinhomogeneous materials with low concentrations of inclusions and neglecting multiple scattering was extended by Gaunaurd and Überall to predict the dynamic effective material properties of bubbles in water, air-filled cavities in solids, and solid inclusions in solids. Excellent agreement with previously published theoretical results was obtained in the limiting cases of low concentrations of bubbles in water and air-filled cavities in rubbery solids. The purpose here is to present three areas of concern pertaining to the results of this theoretical treatment. These concerns apply to: (1) the numerical significance of a certain term (the X term) in the relationship derived by Gaunaurd and Überall, (2) the significance of multiple scattering; and (3) the existence of an anomalous wave amplification phenomenon predicted by their theory. It is believed that these areas of concern are of sufficient significance to warrant careful consideration by those who wish to apply the Gaunaurd and Überall relationships.
A new theory for the radiation from a concave piston source
Authors: Hasegawa Takahi , Inoue Naoki , Matsuzawa Kiichiro
Published: October 2005

The exact theory for the radiation of a circular concave piston surrounded by an infinite rigid baffle is presented. The Rayleigh surface integral, giving the velocity potential for a circular concave piston source, reduces to an infinite series of the simplest form when the origin of a system of spherical coordinates is taken at an arbitrary point on the acoustic axis. The theoretical framework has the advantages that it includes neither approximations nor numerical integrations and that it has application in solving other boundary-value problems such as the sound scattering by a sphere whose center coincides with the origin in the field of a concave piston source.
A higher-order parabolic wave equation
Authors: Knightly George H. , Lee Ding , St. Mary Donald F.
Published: October 2005

A higher-order paraboliclike approximation to the wave equation is presented. An implicit finite-difference discretization of the equation is implemented and its stability is discussed. The accuracy of the treatment of wide-angle propagation is examined by comparing computed solutions with exact solutions. Comparisons with other approaches are made to investigate the wide-angle capability of the method.
Form invariant constitutive relations for transversely isotropic piezoelectric materials
Authors: Varadan Vasundara V. , Jeng Jiann-Hwa , Varadan Vijay K.
Published: October 2005

Using the concept of isotropic integrity bases to describe the free energy of a system described by several tensor, vector, and scalar fields that are consistent with the symmetries of the material, the constitutive equations for the material can be derived in a form invariant manner, i.e., invariant under a coordinate transformation. This method of deriving the constitutive relations also immediately yields the minimum number of material parameters that is needed consistent with the symmetry of the material. Form invariant constitutive relations are necessary in scattering problems where the geometry of the scatterer may be inconsistent with material symmetries, so that it is not possible to choose a convenient coordinate system with respect to both. In this article, form invariant constitutive relations are derived for transversely isotropic piezoelectric materials in which the elastic stress and strain fields are coupled to the electric displacement fields. The material parameters derived are related to the better known elastic stiffness coefficients, dielectric constants, and piezolelectric coupling coefficients when the constitutive relations are written in indicial notation in Cartesian coordinates. In many problems, it is appropriate to make the quasistatic approximation for the electromagnetic field. In this limit, a form invariant stress–strain relation is derived which includes the piezoelectric coupling but not explicitly the electric field.
Frequency dependence of the speed of sound in air
Authors: Howell G. P. , Morfey C. L.
Published: October 2005

Recent papers demonstrate some confusion over the frequency dependence of the speed of sound in air. The aim here is to correct the misunderstandings that have arisen.
Stimulus intensity and loudness recruitment: Neural correlates
Authors: Phillips D. P.
Published: October 2005

An abnormally rapid rate of loudness growth for given increments in stimulus intensity is seen both in patients with cochlear pathology and in normal listeners under conditions of wide-spectrum noise masking. The phenomenological similarity between these psychophysical observations raises the question of whether a single mechanism, or set of mechanisms, underlies them. Recent neurophysiological studies in animals have addressed the effects of cochlear pathology and noise masking on the neural correlates of stimulus intensity in the central auditory nervous system. A comparison of the data presented in those studies reveals that there are sequelae of cochlear pathology seen in the discharges of auditory-nerve fibers that might reasonably be expected to contribute to a steepened loudness function. These sequelae are not seen at the same locus in normal animals studied with noise masking paradigms. Noise masking, however, may have effects on the tonal sensitivity of more central neurons that mimic some of the sequelae of cochlear pathology seen in the auditory nerve. These data suggest that the mechanisms underlying the two manifestations of recruitment may be quite different, one having a uniquely cochlear site, while the other reflects purely central processes.
A method for predicting acoustic signal fluctuations using a distribution of Gaussian correlation functions
Authors: Chotiros N. P. , Culbertson C. R.
Published: October 2005

The autocorrelation function of the refractive index inhomogeneities in a turbulent medium was modeled as a continuous distribution of Gaussian functions. The advantage of this approach lies in the simplicity of the solutions of the wave scattering integral for a weakly inhomogeneous medium with a Gaussian spatial correlation function. The density function of the distribution for the case of a turbulent medium was constructed. Convolution of the solution of the wave scattering integral for a unit Gaussian function with the density function yields the solution for the turbulent medium. The results are identical with those obtained by Tatarskii [Wave Propagation in a Turbulent Medium (McGraw-Hill, New York, 1961 and Dover, New York, 1967); and The Effects of the Turbulent Atmosphere on Wave Propagation, translated by the Israel Program of Scientific Translations Ltd., available as TT-68-50464 from the U.S. Dept. of Commerce] by the more complicated approach of using the wavenumber spectrum and the structure function.
Psychophysical studies relevant to the design of a digital electrotactile speech processor
Authors: Blamey P. J. , Clark G. M.
Published: October 2005

Psychophysical tests were carried out to investigate the perception of electrocutaneous stimuli delivered to the digital nerve bundles. The tests provided data for defining the operating range of a tactile aid for patients with profound-to-total hearing loss, as well as the individual differences between subjects and the information that could be transmitted. Monopolar biphasic constant current pulses with variable pulse widths were used. Threshold pulse widths varied widely between subjects and between fingers for the same subject. Thresholds were reasonably stable, but maximum comfortable levels increased with time. Perceived intensity was weakly dependent on pulse rate. Absolute identification of stimuli differing in pulse width gave information transmissions from 1.3–2.1 bits, limited by the dynamic ranges of the stimuli (3–17 dB). Stimuli from electrodes placed on either side of each finger were identified easily by all subjects. Absolute identification of stimuli differing in pulse rate gave information transmissions from 0.5–2.0 bits. Difference limens for pulse rate varied between subjects and were generally poor above 100 pps. On the basis of the results, an electrotactile speech processor is proposed, which codes the speech amplitude as pulse width, the fundamental frequency as pulse rate, and the second formant frequency as electrode position. Variable performances on tasks relying on amplitude and fundamental frequency cues are expected to arise from the intersubject differences in dynamic range and pulse rate discrimination. The psychophysical results for electrotactile stimulation are compared with previously published results for electroauditory stimulation with a multiple-channel cochlear implant.
One-dimensional implosions under gravity-induced hydrostatic pressure
Authors: Marzetta Thomas L. , Burridge Robert , Stickler David C.
Published: October 2005

An imploding cavity in a fluid-filled borehole is potentially attractive as a powerful source of acoustic energy for borehole seismic experiments. It is reasonable to model the fluid pressure response due to the implosion as purely one-dimensional. A simple analysis based on the assumption that the fluid behaves elastically, with a linear pressure/strain relation, predicts that the fluid pressure response becomes negative at depths less than that of the source. This is an untenable prediction since a fluid cavitates under negative pressure. It is more realistic to assume that the fluid behaves in a linear elastic fashion for negative strains (and positive pressures), and that the fluid pressure is zero for positive strains. This leads to a nonlinear, free-boundary problem in acoustic wave propagation, which surprisingly has a closed-form analytical solution. The analysis predicts the existence of several unexpected phenomena which could complicate the interpretation of data taken in borehole seismic experiments utilizing this type of source.
Transmit–receive mode responses from finite-sized targets in fluid media
Authors: McLaren Stephen , Weight John P.
Published: October 2005

Detailed calculations are made of the transmit–receive mode echo responses arising from solid targets of various size interrogated by short pulses of ultrasound propagating in a fluid medium. The theoretically predicted results are in good agreement with experimentally measured results obtained using transducers typical of those used in nondestructive evaluation. The effects of target size, field position, and material on both the amplitude and shape of the echo responses are investigated. The structure of the responses is explained in terms of the plane and edge waves radiated by the source. Implications for the use of ultrasonic pulse-echo techniques to characterize real defects are considered.
Model for the quadrupole oscillations of drops for determining interfacial tension
Authors: Hsu Chaur-Jian , Apfel Robert E.
Published: October 2005

A simplified model is developed for describing the free and forced oscillations of the quadrupole mode of a liquid drop freely suspended in a liquid host. The decay rate of the free oscillations and the phase-frequency relation for the forced oscillations are derived and compared with previous theories. A parameter, interfacial viscosity, is included as an example to demonstrate the versatility of this simplified model. The application of this model in determining the interfacial tension between two liquids is discussed. The experimental technique and some results for different liquids are briefly reviewed.
Vortex modes in rooms
Authors: Waterhouse Richard V.
Published: October 2005

The existence of a circulation of sound energy in an enclosure of square cross section was demonstrated on theoretical grounds by Preston Smith [Smith et al., ‘‘Intensity measurements in near fields and reverberant spaces,’’ Bolt Beranek and Newman Report No. 1135 (1964)]. Recent work has confirmed experimentally the flow of sound energy in a vortex pattern in various sound fields. Here it is shown that for any rectangular enclosure (e.g., a room or duct) having reflecting walls with two dimensions in the ratio of any two integers, there exists an infinite set of vortex modes, whose frequencies form a harmonic series. Also, for an enclosure in the form of a right circular cylinder, there exist infinite sets of vortex modes whose frequencies depend on the extrema of the Bessel functions Jm. Energy streamlines are given for some of the above modes. The practical significance of these sound vortices is discussed, with regard to vehicles, musical instruments, and the playing and recording of music in rooms.
Sharp mechanical tuning in a cochlear model without negative damping
Authors: Kolston Paul J.
Published: October 2005

It is possible for a cochlear model without active negative damping to exhibit a mechanical response peak that is arbitrarily high and arbitrarily wide. Conventional active models rely on external energy inputs to the cochlea to produce the required peak shape. The new model proposed here produces very similar response profiles by assuming that outer hair cell stereocilia stiffness suppresses the mechanical motion in all regions basal of the response peak. Therefore, the model is not active in the usual sense of adding energy to the cochlea. The model suggests a reason for the differing basilar membrane structure in the arcuate and pectinate zones and simulates in vivo and postmortem responses similar to those measured in the real cochlea.
Segmental durations in connected-speech signals: Current results
Authors: Crystal Thomas H. , House Arthur S.
Published: October 2005

Two types of analyses have been performed on the measured durations of recordings produced by six talkers reading two scripts of approximately 300 words each. The texts, the combined visual–auditory marking technique, and preliminary results were reported earlier by Crystal and House [J. Acoust. Soc. Am. 72, 705–716 (1982)]. The average durations and standard deviations of various classes of speech sounds, as well as individual speech sounds, have been determined and segmental measurements are compared to earlier data and to various pertinent published reports. The histograms of the measured durations of various sounds and categories have been fitted with distributions which are, equivalently, the exit-probability sequence for a Markov chain or the impulse response of an IIR digital-filter network.
Piano string excitation V: Spectra for real hammers and strings
Authors: Hall Donald E. , Askenfelt Anders
Published: October 2005

New measurements of piano hammer properties are reported, as well as hammer accelerations during impact and resulting string motion on a grand piano. Comparison with extant theory on string–hammer interaction requires discussion of limitations due to: (1) nonlinear mode coupling for finite amplitude, (2) string stiffness and the resulting dispersion, (3) soundboard admittance, (4) finite hammer width, and (5) nonlinearity in the hammer. Items (1) and (4) are shown to be relatively unimportant for measurements made promptly after striking, while (3) is significant mainly for the uppermost treble octave. Item (2) becomes important above roughly 1 kHz for notes at the bass end, 5 kHz in midrange, and 10 kHz at the treble end. Item (5) is the most important limitation, and leads us to consider either using an ‘‘effective compliance’’ to obtain an approximate spectrum or performing numerical integrations to handle the nonlinearity. With these limitations in mind, an examination is made of how well the theory can explain the measured string vibration spectra. The agreement is moderately good in the bass and midrange while, at the treble end, the measured spectra fall off significantly faster than the predictions. Further progress apparently requires methods capable of fully integrating the nonlinear hammer compliance into the theory.
Electrical excitation of flexural mechanical resonances in symmetrically electroded piezoelectric and ferroelectric specimens
Authors: Blue Joseph E. , Chen Peter J. , Henriquez Theodore A. , Ting Robert Y.
Published: October 2005

A clear understanding of the relationship of mechanical and acoustical excitation to electrical output of piezoelectric materials is important in the design of large-area acoustic sensors. Chen [Il Nuovo Cimento 2 D, 1145–1155 (1983)] has reported on electrical excitation of flexural mechanical resonances that are not accompanied by detectable electrical disturbances in the ac drive circuits in a number of different specimens such as X- and Z-cut quartz, Z-cut LiNbO3, ADP, PZTs, BaTiO3, and PLZTs. These observations have raised questions about the understanding of electromechanical interactions. Speculations about the cause of the resonances include the possibility of incompleteness of the constitutive equations of piezoelectricity, surface polarization phenomena, and simple couplings due to slight structural asymmetries. In the latter regard, the objective was to see if the flexural resonances could be easily excited in a Ca-doped PbTiO3 disk having a very small lateral piezoelectric constant (d31≊0.03d33) which would tend to minimize the couplings due to slight structural asymmetries. These resonances were also excited in this material.
Acoustic radiation force on a heated sphere including effects of heat transfer and acoustic streaming
Authors: Lee Chun P. , Wang Taylor G.
Published: October 2005

In this investigation, our previous theoretical result on the subject of the acoustic radiation force on a heated sphere [Lee and Wang, J. Acoust. Soc. Am. 75, 88–96 (1984)] is reexamined. For a more complete understanding, effects of heat transfer and acoustic streaming are taken into consideration. Essentially, it was found that at high sound-pressure levels in a steady situation, the force is not affected significantly by the temperature profile, consistent with the result of an experimental work [Leung and Wang, J. Acoust. Soc. Am. 77, 1686–1691 (1985)]. This resolves the earlier apparent contradiction between the theory and the experiment. But our previous result is reaffirmed that, if excessive hot air is accumulated around the sphere, which can happen in transient situations, the force can be weakened or reversed in sign. As a by-product of our study, a heat transfer model due to acoustic streaming was also found.
Combined integral equation formulation and null-field method for the exterior acoustic problem
Authors: Stupfel B. , Lavie A. , Decarpigny J. N.
Published: October 2005

The numerical implementation of a combined integral equation and null-field method used to solve the exterior Neumann problem [D. S. Jones, Q. J. Mech. Appl. Math. XXVII, 129 (1974)] is presented here. The exterior Helmholtz integral equation is solved on the radiating or scattering surface, and the irregular frequencies are eliminated up to a given irregular frequency fM through the use of M additional null-field equations. An impedance matrix, defined on the object surface, is then obtained that can be used as an exact radiation condition in a finite-element code. The program and the numerical examples presented here are specialized to axisymmetrical problems. A purely null-field method is implemented and simple rules are defined that display its failure when applied to high aspect-ratio objects and (or) in the high-frequency range. Similar, but less restricting rules are used to specify the numerical limitations of Jones’ technique. Besides, a few theoretical considerations clarify the role played by the additional null-field equations in the elimination of the irregular frequencies and help in performing accurate high-frequency computations for surfaces such as the circular cone and the finite circular cylinder.
The effect of windowing on spectral estimation of echoes scattered by a random medium
Authors: Akita Masahiko , Ueda Mitsuhiro
Published: October 2005

In executing spectral analysis of echoes scattered by a random medium, a window is generally applied to an echo signal. Spatial resolving power to characterize the random medium is improved by shortening the window length. But it is difficult to shorten the window length arbitrarily since, in the conventional method, the shorter the window length, the more severely the spectrum is distorted. This article shows that the spectrum distorted by the window can be expressed as a convolution of the spectrum of echoes that would be obtained from a spatially truncated thin layer of the random medium with the spectrum of the window function. Consequently, it can be corrected by a deconvolution operation, and by the fact that the spectral estimation over a wide frequency range can be carried out even using a window of shorter length. The effects of the deconvolution are first demonstrated by computer simulation where a random signal is used as the echo signal. The effects can be seen more clearly in the measurement of attenuation coefficient slope obtained by the ratio of two spectra that are subjected to different attenuation. Finally, the applicability of this method is shown by the experiments where the attenuation coefficient slope of an agar block is measured using the window of various lengths.
Calculation of integrals which occur in the analysis of circular stretched membrane sound radiation
Authors: Streng J. H.
Published: October 2005

The fundamental analysis of the vibrational behavior of circular stretched membranes in free space yields a number of integrals that may be calculated numerically. It will be shown in this letter that numerical integration procedures can be avoided by means of power series expansions of the integrands of the said integrals.
Masked cochlear whole-nerve response intensity functions altered by electrical stimulation of the crossed olivocochlear bundle
Authors: Dolan David F. , Nuttall Alfred L.
Published: October 2005

Cochlear whole-nerve response (CAP) intensity functions were recorded from the guinea pig round window. The intensity functions were obtained in the presence of masking noise, with electrical stimulation of the crossed olivocochlear bundle (COCB), and the combination of masking noise and COCB stimulation. Electrical stimulation of the COCB produced the expected reduction of CAP magnitude for low- to moderate-intensity tone bursts. Masking noise produced reductions in CAP magnitude over the whole signal intensity range used in this study. The combination of electrical stimulation of the COCB with the masking noise produced CAP magnitude changes graded between reduction and enhancement dependent on signal and masker levels. In general, at low signal levels, the masked CAP magnitude is reduced compared to the masked alone condition. At high signal levels, the masked CAP is increased in magnitude. These results confirm and extend the earlier observations of Nieder and Nieder [Exp. Neurol. 28, 174–188 (1970); also, Nature 227, 184–185 (1970)].
Gap detection with sinusoids and noise in normal, impaired, and electrically stimulated ears
Authors: Moore Brian C. J. , Glasberg Brian R.
Published: October 2005

Thresholds for the detection of temporal gaps were measured using two types of signals to mark the gaps: bandpass-filtered noises and sinusoids. The first experiment used seven subjects with relatively flat unilateral moderate cochlear hearing loss. The normal ear of each subject was tested both at the same sound-pressure level (SPL) as the impaired ear, and at the same sensation level (SL). Background noise was used to mask spectral ‘‘splatter’’ associated with the gap. For the noise markers, gap thresholds tended to be larger for the impaired ears than for the normal ears when the comparison was made at equal SPL; the difference was reduced, but not eliminated, when the comparison was made at equal SL. Gap thresholds for both the normal and impaired ears decreased as the center frequency increased from 0.5 to 2.0 kHz. For the sinusoidal markers, gap thresholds were often similar for the normal and impaired ears when tested at equal SPL, and were larger for the normal ears when tested at equal SL. Gap thresholds did not change systematically with frequency. Gap thresholds using sinusoidal markers were smaller than those using noise markers. In the second experiment, three subjects with single-channel cochlear implants were tested. Gap thresholds for noise bands tended to increase with increasing center frequency when the noise bandwidth was fixed, and to decrease with increasing bandwidth when the center frequency was fixed. Gap thresholds for sinusoids did not change with center frequency, but decreased markedly with increasing level. Gap thresholds for sinusoids were considerably smaller than those for noise bands. The pattern of results is consistent with the idea that the inherent fluctuations in noise bands can limit gap thresholds; ‘‘dips’’ in the noise may be confused with the gap. This effect is more marked in subjects with cochlear hearing loss or cochlear implants owing to the presence of loudness recruitment, which makes the dips more prominent. The results suggest that temporal resolution per se is not necessarily adversely affected by cochlear hearing loss or in patients with cochlear implants.
A technique for the study of acoustic scattering from microparticles
Authors: Roos Mark S.
Published: October 2005

A technique for observing acoustic scattering from individual particles with volumes on the order of 100 μm3 is described. The apparatus consists of an array of focused acoustic transducers, a fluid jet to position the particles, and electronics incorporating quadrature detection. A maximum likelihood estimator is developed for the scattering amplitude that combines the data received from a series of pulses as a particle is carried through the focal zone of the transducers. A calibration method and performance of the apparatus are discussed.
Transient and harmonic fluid loading on vibrating plates in a uniform flow field via a wave-vector/time domain method
Authors: Li Dong-Jye , Stepanishen Peter R.
Published: October 2005

A new approach is presented to evaluate the fluid loading on vibrating elastic vibrators with specified time-dependent velocities in uniform flows. An in vacuo eigenfunction expansion with time-dependent coefficients is used to describe the specified normal velocity of the plate. Acoustic fluid loading on the plate is expressed as an eigenfunction expansion in which each modal coefficient is expressed as a summation of convolution integrals involving fluid/modal impulse responses and the modal velocity coefficients. Wave-vector/time domain methods are used to develop expressions for the fluid modal impulse responses. Numerical results are presented to illustrate the characteristics of the fluid/modal impulse responses and fluid loading for various modes of simply supported plates and Mach numbers.
Geoacoustic parameters and the depth-dependent Green’s function for a silty sediment at 100 Hz in shallow water
Authors: Mercer J. A.
Published: October 2005

A technique for inferring geoacoustic sediment parameters from the depth-dependent Green’s function is examined using elements of discrete inverse theory. Acoustic data for transmissions at 100 Hz, in a simple shallow-water environment with a horizontally stratified silty sediment, are simulated using a fast-field method of solving the Helmholtz equation. The basic data consist of the amplitudes and wavenumbers of the peaks and nulls of the depth-dependent Green’s function. The Frechet matrix, i.e., the derivative of the artificial data with respect to the sediment model parameters, is determined numerically and used to represent the data kernel of the linearized inverse problem. This kernel allows the computation of the model parameter resolution matrix which provides a formal evaluation of the ability to predict the model parameters from the data. The resolution matrix is difficult to interpret directly, but an evaluation is provided based on the condition numbers of its submatrices. Results for this particular environment and acoustic frequency suggest that the water–sediment sound-speed ratio is the only geoacoustic parameter that can be reliably inferred. From another point of view, this ratio is the only sediment parameter that need be determined to predict long-range propagation in this scenario.
Interpretation of a few ice event transients
Authors: Stein Peter J.
Published: October 2005

This article discusses some of the observables important to the study of sound radiated into the water by ice fracturing events. Such studies are important in order to understand the mechanisms of Arctic Ocean ambient noise generation. Theoretical work for a homogeneous ice plate indicates that there are three important paths of elastic wave propagation over which energy travels away from an ice event source. These are the flexural wave in the ice, the longitudinal wave in the ice, and the acoustic wave in the water. Each has a distinctive propagation speed, attenuation, and associated pressure field in the water. The experimental work, consisting of the interpretation of four ice events, supports the theoretical description. In each case the event is located and the contributing wave paths identified. In all cases the acoustic wave dominates. The work also demonstrates how event analysis can be used to determine ice properties.
On the coefficient of nonlinearity β in nonlinear acoustics
Authors: Hamilton Mark F. , Blackstock David T.
Published: October 2005

An analysis valid to second order in the acoustic variables is used to investigate the origin and form of the coefficient of nonlinearity β. Two cases are considered. First, for progressive plane waves, the well-known formula is β=1+B/2A, where B/2A is the coefficient of the quadratic term in the isentropic pressure–density relation. It is shown that the component 1, which is associated with convection, comes solely from nonlinear terms in the equation of continuity. The second component comes from a quadratic term in the equation of state. The momentum equation is linear for this type of wave motion and therefore contributes nothing to the expression for β. Second, for noncollinear interaction of two plane waves, quasilinear analysis shows that the expression for β appropriate for the sum and difference frequency waves has three components. In this case, the momentum equation does contribute to the formula. For most practical problems the three-component formula reduces to β=cos θ +B/2A, where θ is the angle of interaction. The factor cos θ represents the combination of contributions cos2(θ/2) and −sin2(θ/2) from the continuity and momentum equations, respectively.
The validity of the Kirchhoff approximation for rough surface scattering using a Gaussian roughness spectrum
Authors: Thorsos Eric I.
Published: October 2005

The validity of the Kirchhoff approximation for rough surface scattering is examined by comparison with exact results obtained by solving an integral equation. The pressure release boundary condition is assumed. The field quantity calculated is the bistatic scattering cross section, which is obtained with a Monte Carlo technique. The accuracy of correcting the Kirchhoff scattering cross section for shadowing is also addressed. The surface realizations used are randomly rough with a Gaussian roughness spectrum and have height variations in only one direction. The surface correlation length is found to be the most important parameter in defining the valid region of the Kirchhoff approximation away from the low grazing angle region. A procedure is given that provides a quantitative measure of the accuracy of the shadow-corrected approximation when the root-mean-square (rms) slope angle of the surface γ is ≲20° and when the incident grazing angle θ is ≳2γ. Examples with θ≲2γ are also discussed.
Biological effects of the hand–arm vibration syndrome: Historical perspective and current research
Authors: Taylor William
Published: October 2005

The objective of this paper is to highlight gaps of information regarding mechanisms of vascular, neurological, and musculo-skeletal damage caused by vibration. Also addressed is evidence that high noise level may act synergistically to the development of vibration syndrome of the hand and arm. Areas of research currently active in psychophysical and neurophysiological investigations to increase our understanding of tactile and spatial discrimination are discussed. Although the importance of sensory loss or ‘‘fine touch’’ is understood, there is neither a proven objective scientific test with which the syndrome can be diagnosed nor is there a scale of damage assessment. Determining the exact role of the central nervous system in assessing damage from vibration is difficult in view of nonspecific symptoms reported from eastern Europe and from Japan. To complicate matters still further, there is the possibility that repeated, rapid mechanical movements of the hand and arm associated with handling heavy tools produce carpal tunnel syndrome but that the injury is not directly attributed to vibration. Therefore, it follows that there could exist an element of carpal tunnel syndrome in many vibration syndrome cases.
Biomolecular absorption of ultrasound. III. Solvent interactions
Authors: Kremkau Frederick W.
Published: October 2005

Absorption coefficients for several biomolecules have been measured to determine the role of solvent interactions in the absorption characteristics of biomolecules at neutral pH. The presence of phosphate buffer ions in aqueous solvent dramatically increases the absorption of small biomolecules (sugars and amino acids). These increases suggest the importance of solvent interactions in absorption. For large molecules (proteins and polysaccharides), buffer ion effects are lessened and the role of solvent interactions is not as clear. Absorptions of hemoglobin are essentially the same in each of five aqueous solvents and are greater in nonaqueous solvents. Solvation interactions may be inhibited by the tertiary structure of globular proteins. Solvation apparently does contribute to absorption in biomolecules along with other physicochemical processes.
Electronic system for the measurement of flow resistance
Authors: Stinson Michael R. , Daigle Gilles A.
Published: October 2005

A measurement system has been developed that can determine flow resistances quickly and accurately and can be used to complement acoustical measurements on the same samples. The use of electronic components permits measurements to be made 20–50 times faster than with the commonly used Leonard apparatus. Variable-capacitance pressure transducers are used to measure pressure differences across both the test sample and a laminar flow element with known flow resistance (these two in series): For steady nonpulsating flow, the ratio of flow resistances equals the ratio of measured pressure differences. The rate of air flow through the sample is adjusted using a mass flow controller; flows of 10−3–1 cm3 s−1 can be controlled to better than 1%. Flow resistances between 1 and 105 g cm−4 s−1 can be determined with an accuracy of better than 1.6%. The corresponding range of flow resistivities of porous materials that can be determined with the present sample holder is 1–106 cgs-rayl cm−1. Initial measurements have been made using small circular orifices and samples of porous material.
Evidence for different types of mechanoreceptors from measurements of the psychophysical threshold for vibrations under different stimulation conditions
Authors: Lamoré P. J. J. , Keemink C. J.
Published: October 2005

The shape of the psychophysical frequency threshold curve for vibrations presented to the skin in the frequency region 5–1000 Hz is strongly dependent on the static force that the vibrator exerts on the skin and on whether there is a rigid surround around the vibrating contactor (presence of contrast). Where there is no rigid surround, an increase in static force reduces the threshold in the high-frequency region and increases it at low frequencies. When the static forces are sufficiently large, the thresholds reach a minimum value above 30 Hz and a maximum one below 30 Hz, this being the crossover frequency. Under these conditions in the frequency region around 200 Hz, where the threshold is determined by the Pacini receptor system, the vibration sensitivities of finger pad and thenar eminence (glabrous skin) are equal, while the value for the inner side of the forearm p (hairy skin) is 12 dB higher. However, when a rigid surround is used, the threshold increases above 30 Hz and decreases below 30 Hz. The latter increase in sensitivity, which is introduced by the presence of contrast cues, amounts to about 20 dB and is sharply tuned at 18 Hz for the glabrous skin of the finger. It is argued that in this case the threshold is determined by the Meissner receptor system. This increase in sensitivity is less pronounced (about 10 dB) and less sharply tuned for the other sites. Finally, when the contact of the vibrating surface to the skin is at a minimum, the vibration threshold has the same displacement value (about 3 μm) over the whole frequency region independent of the site of stimulation and whether or not a rigid surround is present.
Superresonant systems of scatterers. II
Authors: Tolstoy I. , Tolstoy A.
Published: October 2005

S y s t e m s of identical monopole scatterers interacting through multiple scatter will, under certain conditions, develop normal modes, i.e., bonafide resonant behavior at certain frequencies (corresponding to poles of the multiple scatter coefficients). This occurs when the monopole scattering cross sections are large enough to give significant interaction; this happens for highly tuned scatterers, e.g., gas-filled bubbles/balloons/shells in water, insonified at frequencies near their characteristic resonant frequencies. This phenomenon has been called superresonance (SR) and has been discussed mostly in the case when the primary energy transport mechanism between scatterers is a cylindrically spreading boundary wave, like the flexure mode of a thin elastic plate [I. Tolstoy, J. Acoust. Soc. Am. 80, 282–294 (1986)]. The singularity of the field at the scatterer is removed by introducing the finite radius of the scatterers. The present article investigates the effect of the plate material on the SR phenomenon, showing that for a steel plate and a pair of bubbles/balloons (doublet) the acoustic amplitudes on the scatterer surfaces may be 3×103 times the free-field value, i.e., one has an amplitude amplification factor μ≊3×103, where μ decreases as the plate rigidity decreases. On the other hand, in a homogeneous acoustic full space SR does not, strictly speaking, occur:

The scatterer system does not become fully resonant (the theory does not indicate the existence of poles) since spherically spreading acoustic modes are less efficient transporters of energy between scatterers than the cylindrically spreading boundary modes. Nevertheless, simple symmetrical systems of bubbles/balloons/shells can still demonstrate a tendency to resonate, i.e., produce sharp peaks on the μ curve. Plane and polyhedral configurations may still yield μ≊102 at each scatterer. To distinguish this from bonafide SRs near a plate, we call these quasiresonances (QRs). It is shown, however, that partial shielding between selected pairs of scatterers in such configurations affects the phase relationships in the system in such a way as to allow the appearance of true SRs.
Experimental confirmation of horizontal refraction of cw acoustic radiation from a point source in a wedge-shaped ocean environment
Authors: Doolittle R. , Tolstoy A. , Buckingham M.
Published: October 2005

Analysis of experimental data obtained in the region of the East Australian Continental Slope has been found to be consistent with theoretical predictions of energetic horizontal refraction due to multiple reflections from a sloping bottom. The observed azimuthal characteristics are in accordance with both normal mode and ray theoretical solutions. The experiment, conducted with two ships (one towing a source and the other an array), started in water ≊400 to 500 m deep with an initial separation of 34 km and proceeded to deeper water on a diverging but constant line of bearing course. Bearing shifts deduced from beamformed data show changes of tens of degrees in as little as half an hour. These bearing shifts demonstrate the dominance of horizontally refracted arrivals for the geometry. A combination of source–array positions and critical angle effects served to limit both the azimuthal extent of energy received and the total number of modes arriving at any one position.
Modeling sensorineural hearing loss. I. Model and retrospective evaluation
Authors: Humes Larry E. , Espinoza-Varas Blas , Watson Charles S.
Published: October 2005

The present article describes an approach to the evaluation of psychoacoustic data from the hearing impaired. The results obtained from the hearing impaired in several studies of frequency resolution, temporal resolution, and speech recognition are compared to the results expected for noise-masked normal listeners. It is presumed in this approach that the hypothetical noise-masked normal listeners have masked thresholds that agree perfectly with the quiet thresholds of the hearing-impaired subjects. Using this approach, most of the results obtained from impaired ears on spectral-resolution and speech-recognition tasks could be accurately predicted, an exception being results from spectral-resolution paradigms using fixed-level signals. Some of the data from hearing-impaired listeners on temporal-resolution tasks, on the other hand, could not be adequately described with this approach. The latter data, however, were much more limited. Additional data are needed to better evaluate the adequacy of this approach in describing the performance of the hearing impaired on temporal-resolution tasks.
On the nonspecular reflection of bounded acoustic beams
Authors: Kundu Tribikram
Published: October 2005

In this article, a comprehensive study of the reflection phenomenon of bounded acoustic beams by uniform and layered half-spaces and plates is carried out. The incident beam strength is assumed to have a Gaussian variation with different widths and frequencies. The Thomson–Haskell matrix method with delta matrix modification is adopted to solve this problem. Different types of reflectors only change the boundary and continuity conditions but the basic formulation remains unchanged. Several interesting and new features of reflected beam profiles are observed.
Intensity–time tradeoff for constant hearing loss with high sound levels
Authors: Oftedal Gunnhild , Nivison Mary Ellen , Jinze Zheng
Published: October 2005

The tradeoff relation between exposure intensity and duration for constant hearing loss was investigated in two series of experiments using Mongolian gerbils. The gerbils were exposed to a 1/3 octave band of noise at 2.5 kHz. In the first series animals were exposed to 120 dB SPL for 1 h, to 126 dB SPL for 15 min, and to 126 dB SPL for 3.75 min. In the second series, shorter durations were used: 120 dB SPL for 15 min, 126 dB SPL for 3.75 min, and 126 dB SPL for 56 s. The hearing thresholds were determined behaviorally immediately before exposure and 6 weeks after exposure. The results suggest that the intensity–time tradeoff for the investigated intensity interval is between 1.5 and 3 dB per halving of the duration.