bluuebunny/crossref_metadata_2025 huggingface dataset:
An integral equation method for coupled fluid/fluid scattering in three dimensions
Authors: Seybert A. F. , Casey D. K.
Published: October 2005

In this article, the time-harmonic, three-dimensional fluid/fluid scattering problem is reformulated using an integral equation method. In this method, the fluid/fluid boundary value problem leads to a pair of boundary integral equations, one for the exterior fluid medium and the other for the interior fluid medium. The two integral equations are coupled by the continuity relationships at the interface between the two media. The coupled integral equations are reduced to algebraic equations by using a quadratic isoparametric representation for the geometry and variables of the problem. As an example, the scattering of a plane sound wave by an air bubble in water is studied. Of special interest here is the ability of the integral equation method to predict accurately the giant monopole resonance of the bubble. A half-space, fluid/fluid scattering problem is formulated using modified kernels in the basic integral equations. The use of the half-space formulation is illustrated for the scattering of a plane sound wave by an air bubble in water and in proximity to a hard wall.
An iterative solution to acoustic scattering by rigid objects
Authors: Kleinman R. E. , Roach G. F. , Schuetz L. S. , Shirron J.
Published: October 2005

The scattering problem is formulated as a boundary integral equation over the scattering surface that, through the use of a modified Green’s function, is uniquely solvable for all wavenumbers of interest. This integral equation is further transformed, by operating with the adjoint, into a self-adjoint equation into which a parameter has been introduced by adding and subtracting multiples of the identity. This equation is discretized and is solved in a Neumann series that has been shown to converge, with a suitable choice of the parameter, with no restriction on the wavenumber. Numerical results from several examples—spheres, spheroids, and finite cylinders—are presented and shown to be in complete agreement with those obtained using T-matrix methods. Results of a numerical experiment are presented that show how the parameter choice affects the rate of convergence.
Statistical evaluation of backscattered ultrasonic grain signals
Authors: Saniie Jafar , Wang Tao , Bilgutay Nihat M.
Published: October 2005

Insonification of the microstructure of materials results in a backscattered signal consisting of multiple interfering echoes with random amplitudes and phases. Information pertaining to grain scattering cross section and grain size distribution is an inherent property of the backscattered signal. A statistical model of grain signals is developed that describes the spatial and time averaged data, and their relationship to signal attenuation caused by scattering and absorption. Both spatial and temporal averaging permits the estimation of the attenuation coefficient, which has been found to be position dependent. Furthermore, it has been shown experimentally and theoretically that the performance of spatial and time averaging is governed by correlation properties of the grain signal.
Low-frequency scattering by mixtures of correlated nonspherical particles
Authors: Twersky Victor
Published: October 2005

Earlier results for scattering by correlated distributions of randomly oriented particles (with minimum separation small compared to wavelength, and acoustic particle parameters close to the embedding medium’s) are generalized to mixtures of similarly shaped but differently sized particles. The development for these large-scale fluids is based on scaled particle statistical mechanics for mixtures of convex particles (with nonsphericity parameter c). The scattering depends on fluctuations (S) in number concentration, and simple forms of S in terms of the volume fraction (w) are derived for multicomponent mixtures and continuum analogs. Continuous size distributions governed by Poisson probability functions whose skewness depends on the variance (d) lead to simple two-parameter fluctuation functions S(c,d;w). The original discussion of the one-component case (d=0) emphasized the influence of c on the curve peak and its location in w; the primary effects of d are to increase the values of both, and to reduce the falloff of S with increasing w (increasing packing).
Diffraction of plate waves at a fixed point
Authors: Waterhouse R. V. , Archibald F. S.
Published: October 2005

Rectilinear bending waves at a fixed frequency travel along an infinite thin plate in vacuo. One point on the plate is fixed: its displacement is zero, but the plate rotates about the point. Waves are scattered from the fixed point, and contours of the rms displacement near the fixed point are given. Next the fluid-loaded case is computed by evaluating numerically a complicated integral. The energy scattered to the farfield is calculated from the real part of the driving point impedance at various frequencies below coincidence for a steel plate, 1 cm thick, loaded with water on one side. The impedance in vacuo is real and independent of frequency, but, for the fluid-loaded plate, it is complex and frequency dependent. Charts of the pressure contours are given for the nearfield, both on the plate and in the water.
Reply to ‘‘Comment on ‘Air absorption of motor vehicle noise’ ’’ [J. Acoust. Soc. Am. 8
4, 437–439 (1988)]
Authors: Makarewicz Rufin
Published: October 2005

This letter rebuts the foundations of Verhas’ comments.
Comments on radiation from a concave piston source
Authors: Ginsberg J. H. , Rogers Peter H. , Van Buren A. L.
Published: October 2005

The analysis of the circular concave piston source in two recent articles by Hasegawa et al. [J. Acoust. Soc. Am. 79, 927–931 (1986); 82, 706–708 (1987)] is incorrect. The authors express the velocity potential as a surface integral of the normal velocity using the Green’s function for a plane surface. This Green’s function does not satisfy the condition of zero normal velocity on the concave surface of the piston and hence cannot be used for this problem.
Sensory threshold estimation from a continuously graded response produced by reflex modification audiometry
Authors: Fechter Laurence D. , Sheppard Lianne , Young John S. , Zeger Scott
Published: October 2005

This article describes the use of reflex modification to determine sensory detection thresholds. The method is based upon the finding that low-intensity sensory stimuli presented shortly before a reflex eliciting stimulus are able to modify the amplitude of the reflex. The extent of such modification is related to the intensity of the initial low-intensity stimulus. In contrast to earlier reported procedures for threshold estimation, the method described in this article consists of fitting a smooth function to the relationship between startle response amplitude and the intensity of the inhibiting stimulus. The method entails fitting a cubic spline function to the medians of the square-root reflex amplitude at each prestimulus intensity. The resulting audiometric curves closely approximate audiometric data obtained from traditional operant methods both in sensitivity and shape. Parametric data are also presented that allow for optimizing stimulus presentation so as to obtain reliable thresholds using a minimal number of test trials. The procedures developed in this article may prove useful in other situations involving the estimation of a threshold effect from a continuously graded response.
Electromechanical modeling of distortionless piezoelectric transducers with nonuniform parameters
Authors: Hazony Dov , Raya Justo
Published: October 2005

Ample analytical and experimental evidence shows that a nonuniformly poled piezoelectric medium may offer much advantage in transducer work. For example, ideal coupling sections may be matched between media of different impedance levels and transducers may be made with ideal pressure impulse response. However, the medium may interfere with sound transmission causing dispersion and spurious signals. These problems are avoided when the nonuniformity of the medium is controlled so as to render sound transmission distortionless. Properties of such media are studied. It is shown that it is possible to associate impedance matrices with these properties and electrical networks with these matrices.
Partial dissociation of spontaneous otoacoustic emissions and distortion products during aspirin use in humans
Authors: Wier Craig C. , Pasanen Edward G. , McFadden Dennis
Published: October 2005

Otoacoustic emissions (OAEs) of two types—spontaneous and evoked distortion products—were studied before, during, and following a period of aspirin use. As previously reported, aspirin consumption uniformly reduced the spontaneous OAEs (SOAEs) to unmeasurable or extremely low levels. Aspirin consumption also reduced the amplitude of the evoked distortion products (EDPs) but did not eliminate them entirely. The amplitude of the EDP and its change with aspirin consumption were related to both the proximity of the EDP to the frequency of the SOAE and to the level of the primaries producing the EDP. At low primary levels, even with the SOAE absent (due to aspirin consumption, or suppression), EDPs near the SOAE frequency were 10–20 dB higher than when they were 100 Hz away from the SOAE frequency.
On the prediction of sound fields in large empty rooms
Authors: Hodgson Murray
Published: October 2005

This article discusses the prediction of sound propagation and sound decay in large nominally empty rooms of parallelepipedic shapes. The results of sound propagation and sound decay measurements made in an empty 1:50 scale model in 12 shape configurations, and in 14 parallelepipedic, nominally empty, full-size gymnasiums and factories, are compared with predictions by the Eyring and method-of-image models. The Eyring model is shown only to be accurate for quasicubic rooms; the method of images is shown to account for arbitrary shape. Using method-of-image prediction, the diffuse-field absorption coefficient or that derived from the measured sound decay using the Eyring formula, is found to give, within the limitations of the prediction model and experimental uncertainties, a best fit with the experimental results. In the case of the scale model, improved prediction accuracy is obtained when the angular variation of the surface absorption, this due to the surface boundary layer and porosity, is considered. The results further suggest that significant volume and/or surface scattering occurred in the test rooms, and that this must be considered in prediction. It is alternatively hypothesized that it may be necessary to consider wave sphericity in order to obtain accurate predictions.
Enhancement of the sound power of a component of a complex noise source by sound from other nearby components
Authors: Hickling Robert , Marin Samuel P.
Published: October 2005

In determining the sound power of the components of a complex noise source, such as an engine or a piece of machinery, the interaction between the sound fields of the components has usually been considered to be unimportant. Existing experimental evidence for heavy-duty diesel engines shows, however, that there is an enhancement of the sound power of individual components by sound from the rest of the engine. This enhancement effect is analyzed here in a theoretical study using a simple spherical model whose surface undergoes random vibrations similar to those of engines and machinery. Computations were also performed with a sphere pulsating like a monopole or oscillating like a dipole. The study shows that, for wavelengths greater than the radius of the sphere, the enhancement is due to an augmentation of the acoustical pressure on the surface of the component by correlated sound diffracted from regions of the surface immediately adjacent to the component. Essentially, in this low-frequency range, correlated sound from adjacent surfaces increases the radiation efficiency of the component. For sources as large as heavy-duty diesel engines, the enhancement is relatively small, roughly 20% to 60% over the audible frequency range, as indicated both by the theoretical model and the experimental data. The model predicts, however, that the magnitude of the enhancement increases significantly as the size of the source, or the maximum frequency of interest, decreases. Thus the enhancement should be greater for passenger car engines and greater still for smaller sources. The model also indicates that introducing correlation or phase changes between adjacent parts of the surface of a structure can provide a means of noise reduction, although this may be difficult to achieve in practice.
Mathematical treatment of context effects in phoneme and word recognition
Authors: Boothroyd Arthur , Nittrouer Susan
Published: October 2005

Percent recognition of phonemes and whole syllables, measured in both consonant–vowel–consonant (CVC) words and CVC nonsense syllables, is reported for normal young adults listening at four signal-to-noise (S/N) ratios. Similar data are reported for the recognition of words and whole sentences in three types of sentence: high predictability (HP) sentences, with both semantic and syntactic constraints; low predictability (LP) sentences, with primarily syntactic constraints; and zero predictability (ZP) sentences, with neither semantic nor syntactic constraints. The probability of recognition of speech units in context (pc) is shown to be related to the probability of recognition without context (pi) by the equation pc=1−(1−pi)k, where k is a constant. The factor k is interpreted as the amount by which the channels of statistically independent information are effectively multiplied when contextual constraints are added. Empirical values of k are approximately 1.3 and 2.7 for word and sentence context, respectively. In a second analysis, the probability of recognition of wholes (pw) is shown to be related to the probability of recognition of the constituent parts (pp) by the equation pw=pjp, where j represents the effective number of statistically independent parts within a whole. The empirically determined mean values of j for nonsense materials are not significantly different from the number of parts in a whole, as predicted by the underlying theory. In CVC words, the value of j is constant at approximately 2.5. In the four-word HP sentences, it falls from approximately 2.5 to approximately 1.6 as the inherent recognition probability for words falls from 100% to 0%, demonstrating an increasing tendency to perceive HP sentences either as wholes, or not at all, as S/N ratio deteriorates.
Statistical analysis of word-initial voiceless obstruents: Preliminary data
Authors: Forrest Karen , Weismer Gary , Milenkovic Paul , Dougall Ronald N.
Published: October 2005

A statistical procedure for classifying word-initial voiceless obstruents is described. The data set to which the analysis was applied consisted of monosyllabic words starting with a voiceless obstruent. Each word was repeated six times in the carrier phrase ‘‘I can say —— , again’’ by each of ten speakers. Fast Fourier transforms (FFTs), using a 20-ms Hamming window, were calculated every 10 ms from the onset of the obstruent through the third cycle of the following vowel. Each FFT was treated as a random probability distribution from which the first four moments (mean, variance, skewness, and kurtosis) were computed. Moments were calculated from linear and Bark transformed spectra. Data were pooled across vowel contexts for speakers of a given gender and input to a discriminant analysis. Using the moments calculated from the linear spectra, 92% of the voiceless stops were classified correctly when dynamic aspects of the stop were included. Even more important, the model constructed from the males’ data correctly classified about 94% of the voiceless stops produced by the female speakers. Classification of the voiceless fricatives when all places of articulation were included in the analysis did not exceed 80% correct when the moments from either the linear or Bark transformed scales were used. However, classification of only the voiceless sibilants was 98% correct when the moments from the Bark transformed spectra were used. As with the stops, the classification model held across gender.
Evidence for sensory-trace comparisons in spectral shape discrimination
Authors: Kidd Gerald , Mason Christine R. , Hanna Thomas E.
Published: October 2005

The ability of experienced observers to discriminate changes in the shapes of complex sound spectra was studied for three conditions. In one condition, the reference spectrum or ‘‘background’’ was fixed in spectral shape across each block of trials; in a second condition, the reference spectrum differed in spectral shape from trial to trial within each block of trials but was the same for the two presentations within a trial; and, in a third condition, the reference spectrum differed in spectral shape on every stimulus presentation. The variation in the reference spectrum was a random perturbation in the amplitudes of the tonal components comprising the complex sounds. The signal was an intensity increment to the center component (1000 Hz) of the complex and was present in one interval of each two-interval, two-alternative, forced-choice trial. The principal experimental manipulations were the degree of amplitude perturbation of the reference spectrum and the interval of time between the two stimulus presentations of each trial (interstimulus interval, ISI). The theory proposed by Durlach and Braida [J. Acoust. Soc. Am. 46, 372–383 (1969)] describing memory processes involved in the perception of sound intensity was used to explain the experimental results. As that theory was applied in this study, only the condition in which the stimuli were perturbed between trials showed evidence for comparisons based on ‘‘sensory traces,’’ while the conditions in which the stimuli were fixed or were perturbed within trials were best explained by comparisons based on judgments relative to the stimulus context.
Laboratory measurements of backscattering from marine sediments
Authors: Thorne Peter D. , Pace Nicholas G. , Al-Hamdani Zyad K. S.
Published: October 2005

A series of measurements is presented of the backscattering coefficient from marine sediments between 10° and 90° grazing angle. The observations were taken, using a side-scan arrangement in a laboratory test tank under well-defined conditions, on three surfaces composed of different mean sediment sizes. The surface statistics were measured in detail for each case, and both a numerical and analytical representation were established. Utilizing the statistical descriptions, expressions for the backscattering coefficient are obtained using the Helmholtz–Kirchhoff integral applied to a side-scan configuration, and comparisons are made with the data. For each of the sediment surfaces, moderate agreement is obtained over the measurement region; however, there are discrepancies and these are considered.
Matched mode localization
Authors: Wilson Gary R. , Koch Robert A. , Vidmar Paul J.
Published: October 2005

In this article, a method of passively localizing a narrow-band source in range and depth in a waveguide is presented based on ‘‘matching’’ predicted normal mode amplitudes to measured mode amplitudes. The modes are measured by using a vertical array of hydrophones and performing mode filtering. Previous studies of mode filtering have considered only the overdetermined case, i.e., where there are more hydrophones than discrete modes present in the waveguide. In this study, mode filtering is considered for the underdetermined case, i.e., where there are fewer hydrophones than the total number of discrete modes in the waveguide, but only a subset of the total number of modes is to be estimated. Previous studies of matched field localization have been based on matching the entire pressure field. In this study, the pressure field is expressed in terms of normal modes, and only a subset of the total number of modes is used for localization. Using a subset of modes allows trade-offs to be made between localization accuracy, computational complexity, and sensitivity to environmental mismatch. In this article, the matched mode localization method is presented, and the dependence of its localization accuracy on the number of modes used and environmental conditions is demonstrated.

The effects of array length and hydrophone spacing on mode estimation error, and hence on localization accuracy, are also demonstrated for the particular method of mode estimation used here. Other methods of mode estimation may produce different results. Finally, the effects of mismatch between the assumed and actual environment due to water depth variation are explored. It is shown that localization accuracy in range is proportional to the mode interference distance between the lowest and highest modes used to localize, and that as few as six modes can be used for ranging. It is also shown that the array length need not be any longer than the depth extent of the highest mode to be estimated, and that the hydrophone spacing must be no greater than half the vertical wavelength of the highest mode that contributes significantly to the sound field (not just the highest mode to be estimated). Localization is most sensitive to environmental mismatch effects that contribute to changes in the phase of the horizontal component of the mode amplitudes. Because a subset of modes is used for localization instead of the entire pressure field, this method of localization can be fairly insensitive to certain kinds of environmental mismatch.
Shear wave logging in elastic formations
Authors: Schmitt D. P.
Published: October 2005

The analysis of the dispersion and attenuation of the modes generated both by a dipole and a quadrupole source in a fluid-filled borehole surrounded by a (multilayered) elastic formation is performed. The displacement-stress vectors are propagated through the layers using the Thomson–Haskell method. Only the well-bonded configuration is investigated. In the time domain, the effects of the source center frequency on synthetic full waveform microseismograms computed using the discrete wavenumber method are investigated. Whatever the formation (fast or slow) and the configuration, the low-frequency part of both the flexural and screw modes follows the virgin formation shear wave characteristics. Their high-frequency parts behave like that of the Stoneley wave excited by a monopole source. As a result, the fundamental modes are very sensitive to the properties of the inner layers at intermediate and high frequencies. In the presence of an invaded zone, the internal dynamics of the waveforms can be significantly modified, while the useful starting energy of the fundamental modes is shifted toward lower frequencies. The reverse phenomenon occurs when the borehole is cased. For this last configuration, it is only with low source center frequencies that multipole sources can log a slow formation shear wave due to the leaky character of the fundamental modes. Such behaviors emphasize the need for useful low-frequency energy for the actual logging tools.
Low-frequency underwater hearing sensitivity in belugas, D
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Authors: Awbrey Frank T. , Thomas Jeanette A. , Kastelein Ronald A.
Published: October 2005

The underwater hearing sensitivity of three captive belugas (Delphinapterus leucas) was measured at octave intervals between 125 Hz and 8 kHz. The average threshold of the three animals was 65 dB re:1 μPa at 8 kHz, which is in excellent agreement with previously published data [White et al., HSWRI Tech. Rep. No. 78-109, Sea World Research Institute, San Diego, CA (1978)]. Below 8 kHz, sensitivity decreased at approximately 11 dB per octave, and was 120.6 dB at 125 Hz.
Comments on recent criticism of the T-matrix method
Authors: Varadan V. V. , Lakhtakia A. , Varadan V. K.
Published: October 2005

Recently, the T-matrix method has been criticized in this Journal. This letter will point out that such criticisms are invalid since they involve comparison with data computed using older versions of the T-matrix method. Furthermore, through an extensive bibliography, attention is drawn to the wide variety of problems that have been solved using this method.
A search for a word-beginning superiority effect
Authors: Nooteboom S. G. , van der Vlugt M. J.
Published: October 2005

This article reports two experiments examining whether or not auditory word recognition is more sensitive to word-initial than to word-final stimulus information. In the first experiment the contributions of prefixes and suffixes to word recognition were compared. These affixes carried widely varying amounts of lexical information and were added to somewhat degraded monomorphematic word stems in Dutch synthetic speech. Although there was a strong effect of lexical information on word recognition, no difference was found between the contributions of prefixes and suffixes. In the second experiment the effects of masking with noise of either initial or final parts of polysyllabic and monomorphematic synthesized Dutch words were compared. The amount of lexical redundancy carried by initial and final parts of words was the same. Again no difference was found. We conclude that the process of lexical activation during spoken-word recognition is equally sensitive to word-initial and word-final stimulus information. A special role of word onsets remains because the onsets can ensure proper temporal alignment between stimulus and candidate word forms.
Discrimination of interaural differences of time in the envelopes of high-frequency signals: Integration times
Authors: Buell Thomas N. , Hafter Ervin R.
Published: October 2005

Listeners detected interaural differences of time in trains of high-frequency clicks. The manipulated variables were the number of clicks in the train and the period between clicks. Thresholds were compared to an optimal integrator, where the binaural information accrued from each click in the stimulus train is equivalent. In agreement with data reported in the past, integration is optimal only when the period between clicks exceeds approximately 10 ms and when the duration of the entire stimulus train is less than about 250 ms. The first constraint represents a limitation due to a form of ‘‘binaural adaptation’’ and the second is due to a limited ‘‘integration period.’’
Acoustical absorption and scattering cross sections of spherical bubble clouds
Authors: d’Agostino Luca , Brennen Christopher E.
Published: October 2005

The present work investigates the acoustical absorption and scattering cross sections of spherical bubble clouds subject to harmonic farfield pressure excitation. Bubble dynamics effects and energy dissipation due to viscosity, heat transfer, liquid compressibility, and relative motion of the two phases are included. The equations of motion for the average flow and for the bubble radius are linearized and a closed-form solution is obtained. Due to the presence of natural oscillatory modes and frequencies, the acoustical cross sections of the cloud are very different from those of each individual bubble in the cloud, as well as from the acoustical cross sections of a single large bubble with the same volume of vapor and gas. In general, the acoustical properties of any given volume of the dispersed phase depend strongly on the degree of dispersion because of the complex interactions of the dynamics of the bubbles with the whole flow.
Generation of underwater sound by colliding spheres
Authors: Thorne Peter D. , Foden Derek J.
Published: October 2005

A laboratory examination of the acoustic field generated by spheres impacting underwater has been carried out. Records of the sound arising from collisions were taken and analyzed in the time and frequency domain. The transient radiated had the approximate form of a 1 1/2 -cycle sinusoid that, in some cases, had superimposed a high-frequency ripple. A theoretical analysis of the signal in terms of rigid body radiation has been conducted. For such cases the sphere is treated as rigid and the motion of the sphere itself during impact generates a pressure wave that propagates out into the fluid. Using the Hertz law of contact to describe the acceleration time history of the spheres during impact, predictions for the underwater rigid body radiation were obtained and comparisons made with laboratory data. Also the natural modes of vibration of the sphere are considered to explain the high-frequency component of the signal.
Estimation of surface noise source level from low-frequency seismoacoustic ambient noise measurements
Authors: Schmidt Henrik , Kuperman W. A.
Published: October 2005

The waveguide nature of a shallow water environment bounded below by a viscoelastic medium permits noise to couple into seismic waves. Geophone and hydrophone measurements have shown that below a threshold frequency of about 10 Hz in 100 m of water, there is a large increase in the measured noise levels, with a peak at approximately 0.25 Hz. A previously developed wave theory of distributed noise in a waveguide has been combined with a full wave solution technique for stratified elastic media and used for numerical modeling and analysis of this phenomenon. It is demonstrated that this low-frequency increase in noise level is only partly due to an increase in the source spectral level. At these frequencies, seismic interface waves become important propagation paths for the ambient noise, leading to a significant magnification of the observed noise levels. This strongly suggests that propagation effects have to be accounted for when evaluating source theories by comparison to experimental data.
Reexamination of dynamic problems of elasticity for negative Poisson’s ratio
Authors: Lipsett A. William , Beltzer Abraham I.
Published: October 2005

Recently, isotropic elastic materials with a negative Poisson’s ratio have been manufactured. Since most of the theoretical results of linear elasticity focus on a positive Poisson’s ratio, the need arises for their extension and reexamination. The above materials may have a variety of technological applications so the motivation for this study is not purely academic. The article deals first with some of the limit cases arising when Poisson’s ratio takes on an extreme value. For models represented by these limit cases, the material and structure responses may not be treated independently from each other. Then such basic dynamic elasticity problems as reflection from a free surface, propagation of Rayleigh waves, and lateral vibrations of beams and plates are reconsidered for the case of a negative Poisson’s ratio. It is shown, in particular, that the static definition of the shear factor in Timoshenko beam theory may not be satisfactory in all cases. Extensive numerical results are also given.
Active control of low-frequency harmonic sound radiated by a finite panel
Authors: Deffayet C. , Nelson P. A.
Published: October 2005

Quadratic optimization theory is applied to determine the minimum sound power output of a simply supported panel in a baffle when the radiation is controlled with additional ‘‘secondary’’ monopole sources. The theory presented produces analytical results for the optimal complex strengths of the secondary sources and the resulting value of minimum power output. The results are valid in the low-frequency limit when the panel dimensions are much smaller than the wavelength of the radiated sound. The results demonstrate the importance of matching the secondary source distribution to the type of panel mode and can be explained using Maidanik’s modal radiation classification scheme.
Generating direct starting fields for parabolic equations
Authors: Robinson E. Richard , Wood David H.
Published: October 2005

It is well known that parabolic equation models require the user to provide a starting field. Although the correct starting field involves normal modes, alternative approximations are often used because they are more readily computed. This article presents a new approach to computing the correct starting field. It is not necessary to compute the normal modes individually. Instead, a matrix equation is derived governing the special combination of normal modes that gives the starting field.
Time-domain reciprocity theorems for acoustic wave fields in fluids with relaxation
Authors: de Hoop Adrianus T.
Published: October 2005

Time-domain reciprocity theorems of the time-convolution and the time-correlation type for acoustic wave fields in linear, time-invariant, and locally reacting fluids are discussed. Inhomogeneity, inertial anisotropy, and arbitrary relaxation effects in inertia and compressibility properties, both of the active and the passive type, are included. The theorems also apply to the ‘‘equivalent fluid model’’ of a solid in which only compressional waves are considered and shear is neglected. The analysis is entirely carried out in space-time, without intermediate recourse to the frequency or the wave vector domains. The application to inverse source and inverse constituency (or inverse profiling/scattering, or imaging) problems is briefly indicated.
The k-space formulation of the acoustic scattering problem
Authors: Koshigoe Shozo , Bojarski Norbert N.
Published: October 2005

The k-space formulation of the scattering problem was applied to a one-dimensional acoustic slab. Good results were obtained with the conjugate gradient method of iteration.
Alternatives to the impulse response h(t) to describe the acoustical behavior of conical ducts
Authors: Agulló Joaquim , Barjau Ana , Martínez Jordi
Published: October 2005

In unidimensional acoustical systems, the impulse response h(t) at the input section, which describes the pressure evolution originated at this section by the introduction of a flow unit impulse through it, relates pressure p(t) and flow u(t) at the input section by means of the convolution product p=h*u. If damping and radiation are small, it is interesting to find other functions of faster decay than h(t) in order to improve the convolution convergence. As alternatives to h(t), this article studies the impulse responses h′(t) and h″(t), which correspond to the modified systems that result when coupling the original acoustical system input section to a cylindrical anechoic termination and a conical anechoic termination, respectively. These functions h′(t) and h″(t) are related to the plane-wave reflection function Rp−(t) and spherical-wave reflection function Rs−(t), respectively. The comparison of these three impulse responses shows that the use of h′(t) and h″(t), though of faster decay than h(t) in principle, is not always advisable. For conical bores with small truncation, the convolution with h′(t) may lead to numerical instability more easily than that with h(t). On the other hand, the impulse response h″(t) turns out to be divergent for certain geometrical duct configurations, and thus it is useless as a kernel function in a convolution in these cases.
Analysis of vocal tract parameters in Parkinsonian speech
Authors: Gath I. , Yair E.
Published: October 2005

A method for the analysis of vocal tract parameters is developed, aimed to perform quantitative analysis of rigidity from speech signals of Parkinsonian patients. The cross-sectional area function of the vocal tract is calculated using pitch synchronous autoregressive moving average (ARMA) analysis. The changes in Parkinsonian subjects of the cross-sectional area during the utterance of sustained sounds are attributed to both Parkinsonian tremor and rigidity. In order to isolate the effects of the rigidity on the vocal tract from those of the tremor, an adaptive tremor cancellation (ATC) algorithm is developed, based on the correlation of tremor signals extracted from different locations of the speech production system.
Patterns of interarticulator phasing and their relation to linguistic structure
Authors: Nittrouer Susan , Munhall Kevin , Kelso J. A. Scott , Tuller Betty , Harris Katherine S.
Published: October 2005

Work by Tuller and Kelso [J. Acoust. Soc. Am. 76, 1030–1036 (1984)] and Kelso et al. [J. Phon. 14, 29–59 (1986)] has demonstrated stable relations between jaw and lip movements in /bV♯CVb/ utterances across rate and stress conditions. Specifically, the onset of lip movement toward the intervocalic consonant was found to be constant with respect to the vowel-to-vowel jaw cycle in both time and relative phasing. An attempt was made to replicate and extend this work by investigating interarticulator phase relations for utterances having a broader range of linguistic organization: In addition to rate and stress, syllable structure (open versus closed syllables) and identity of the intervocalic consonant (/p/ vs /m/) were manipulated. Results showed that the upper lip’s lowering onset varied systematically with respect to the jaw vowel cycle as a function of both rate and stress. In addition, syllable structure and consonant identity influenced the relation of lip and jaw gestures. There was a general tendency for any condition that shortened the first vowel to produce earlier onsets of the upper lip relative to the jaw. However, the within-condition jaw cycle duration variability did not correlate with the within-condition variability in phase. Thus it seems that stable interarticulator phase relations maintain not only the integrity of phonological structure, as suggested by Kelso et al., but structural integrity at other levels of linguistic organization as well.
Four channels mediate the mechanical aspects of touch
Authors: Bolanowski S. J. , Gescheider G. A. , Verrillo R. T. , Checkosky C. M.
Published: October 2005

Although previous physiological and anatomical experiments have identified four afferent fiber types (PC, RA, SA II, and SA I) in glabrous (nonhairy) skin of the human somatosensory periphery, only three have been shown to mediate tactile (mechanoreceptive) sensation. Psychophysical evidence that four channels (P, NP I, NP II, and NP III) do, indeed, participate in the perceptual process is presented. In a series of experiments involving selective masking of the various channels, modification of the skin-surface temperature, and testing cutaneous sensitivity down to very low-vibratory frequencies, the fourth psychophysical channel (NP III) is defined. Based on these experiments and previous work from our laboratory, it is concluded that the four channels work in conjunction at threshold to create an operating range for the perception of vibration that extends from at least 0.4 to greater than 500 Hz. Each of the four channels appears to mediate specific portions of the overall threshold-frequency characteristic. Selection of appropriate neural-response criteria from previously published physiological data and correlation of their derived frequency characteristics with the four psychophysical channels indicates that each channel has its own physiological substrate: P channel and PC fibers, NP I channel and RA fibers, NP II channel and SA II fibers, and NP III channel and SA I fibers. These channels partially overlap in their absolute sensitivities, making it likely that suprathreshold stimuli may activate two or more of the channels at the same time. Thus the perceptual qualities of touch may be determined by the combined inputs from four channels.
The radiation impedance of the external ear of cat: Measurements and applications
Authors: Rosowski J. J. , Carney L. H. , Peake W. T.
Published: October 2005

The configuration of external ears varies dramatically among mammalian species. In order to relate these structural differences to acoustic performance, it is useful to determine the ‘‘output’’ (radiation) impedance of the external ear. Measurements were made of the radiation impedance ZE of the cat external ear looking out from the location of the tympanic membrane. Freshly excised external ears were coupled to a calibrated sound source at the tympanic ring, and the resulting sound pressure at the source was measured. The ZE calculated from these measurements is masslike at frequencies below 2 kHz and approximately resistive above 4 kHz. The contributions of anatomically distinct sections of the external ear to ZE were assessed by measuring the impedance before and after surgical removal of the pinna flange and of the concha. Mean measurements of the lengths and cross-sectional areas of components of the external ear are used in a simple model that consists of a uniform tube and an exponential horn; the radiation impedance of the model shows many of the features of the measured ZE’s. Measurements of the input impedance of the middle ear are combined with ZE to infer the diffuse-field absorption cross section ADF, which is a measure of the ear’s performance as a coupler of acoustic power. It is suggested that ADF is useful for across-species comparisons of the performance of external and middle ears.
An exact solution to a modified wide-angle parabolic equation
Authors: Robertson J. S.
Published: October 2005

A modified wide-angle parabolic equation (MWAPE) [St. Mary et al., J. Comput. Phys. 71, 304–315 (1987)] is studied for a uniform plane-parallel waveguide with pressure-release surface and rigid bottom. In this situation, the MWAPE is separable, and the resulting fourth-order boundary value problem is obtained and solved, which leads to an exact solution of the MWAPE. It is shown that the depth-dependent eigenfunctions in this instance are identical to those resulting from both the standard parabolic equation and Helmholtz equation in the same channel. Modal wavenumbers for the MWAPE are shown to be equivalent to the first three terms of the Taylor expansion for the Helmholtz wavenumbers, which is one term better than the standard PE wavenumbers. This exact solution can serve as an accuracy benchmark for numerical implementations of the MWAPE.
Duration discrimination of steady and gliding tones: A new method for estimating sensitivity to rate of change
Authors: Dooley Gary J. , Moore Brian C. J.
Published: October 2005

Thresholds for the detection of differences in duration were measured in a two-alternative, forced-choice task for four types of signals, all centered at 2000 Hz: (1) sinusoids fixed in frequency and level; (2) sinusoids of fixed frequency whose level was swept up or down by 5 or 10 dB; (3) sinusoids of fixed level whose frequency was swept up or down by 100 Hz; and (4) sinusoids whose level was swept up or down by 10 dB and whose frequency was swept up or down by 100 Hz. For types (2)–(4), the direction of the sweeps was fixed within a run. The duration of the standard was either fixed at 750 ms or was varied randomly from trial to trial by up to ±7% about 750 ms. The duration of the comparison signal was initially 100 ms greater than that of the standard and was varied adaptively to determine threshold. The pattern of results was similar for all four subjects tested. Duration-discrimination thresholds for the signals that were swept in level and/or frequency were lower than those for the fixed signal, typically by 15–20 ms. This indicates that subjects were sensitive to the rate of change of frequency and/or level and could use this as a cue for duration discrimination. The Weber fraction for rate of change was estimated to be about 0.05–0.06 and was similar for changes in level and in frequency.
Generalized thermoelastic waves in anisotropic media
Authors: Sharma Jagan Nath , Singh Harinder
Published: October 2005

In this article, the propagation of generalized thermoelastic plane harmonic waves in homogeneous anisotropic media has been investigated. Four types of waves, namely a quasilongitudinal, two quasitransverse, and a thermal wave, are found to exist. The thermal mode, which was diffusive in nature in the nonthermal relaxation case, now becomes wavelike with a finite, though large, wave speed. The results obtained theoretically have been verified numerically and are represented graphically for a single crystal of magnesium.
Effects of scattering due to seafloor microrelief on a multifrequency- sonar seabed profiler
Authors: Chakraborty Bishwajit
Published: October 2005

A theoretical study of the interaction effect of circular beams generated by coaxial circular array operated at useful frequencies with different beam widths is carried out for different types of seabed ripples. Analysis, by means of calculation of the probability density function (PDF) of the echo amplitude, echo waveform structure, and reflected echo energy density, shows that the fluctuation effects are prominent even at the most narrow beam width at an operating frequency of 20 kHz for rippled bottoms of different sediment type. In this article, the operating frequencies and ripple parameters are more responsive toward scattering effects than narrow beam widths, generated by the coaxial circular array.
Underwater sound produced by individual drop impacts and rainfall
Authors: Pumphrey Hugh C. , Crum L. A. , Bjo/rno/ L.
Published: October 2005

An experimental study of the underwater sound produced by water drop impacts on the surface is described. It is found that sound may be produced in two ways: first when the drop strikes the surface and, second, when a bubble is created in the water. The first process occurs for every drop; the second occurs for some impacts but not others. A range of conditions is described in which a bubble is produced for every drop impact, and it is shown that these conditions are likely to be met by a significant fraction of the raindrops in a typical shower. Underwater sound produced by artificial as well as real rain is reported. A comparison between artificial and real rain noise power spectra shows some deviations due to different drop-size distributions. Addition of surface tension reducing liquids to the water in the test tank caused a disappearance of the characteristic spectral peaks in the frequency range 14–16 kHz. These peaks have been observed by several scientists during measurements of real rain. Our findings provide evidence for the theory that the 14- to 16-kHz spectral peak is caused by the ringing of bubbles entrained in the water by the drop impact process.
Ocean acoustic tomography based on adiabatic mode theory
Authors: Shang E. C.
Published: October 2005

A new method of ocean acoustic tomography is developed on the basis of adiabatic normal-mode theory. It is a full-wave method suitable for low frequency in a slowly varying range-dependent waveguide. The modal phase difference perturbations are proposed as data for inverting the sound-speed profile perturbation for a continuous-wave (cw) source. The modal travel time perturbations are proposed as data for a pulse source. It is shown that the ‘‘normalized depth structure,’’ as well as the ‘‘range-averaged strength parameter’’ (defined as the product of the effective horizontal scale and the maximum sound-speed perturbation), can be retrieved from the vertical slice modal tomography. A simulation example of inversion is presented to verify the basic ideas.
Numerical integration methods in gas-bubble dynamics
Authors: Kamath Vinod , Prosperetti Andrea
Published: October 2005

A recent detailed formulation of the dynamics of a gas bubble requires the numerical integration of a nonlinear heat equation in the bubble. In this article, a variety of numerical methods for this purpose are studied. The most efficient technique is found to be an adaptive Galerkin–Chebyshev spectral method, which is explained in detail. Examples of oscillations at high forcing and chaotic response are also given. These results differ very considerably from those obtained by use of the simpler models used by previous investigators.
Calculation of a ‘‘narrowed’’ autocorrelation function
Authors: Brown Judith C. , Puckette Miller S.
Published: October 2005

A method of calculating an autocorrelation function with extremely narrow peaks is described. This is done by including terms in the autocorrelation expression corresponding to delays at 2τ, 3τ, etc., in addition to the usual term with delay τ. Implications in the frequency domain are explored. Graphs of this autocorrelation function for a number of violin sound samples, including a two-octave scale, vibrato, and glissando, are presented. Graphs of the autocorrelation function for some synthetic sound samples are also included.