bluuebunny/crossref_metadata_2025 huggingface dataset:
On the Lynch variational method for scattering of waves by randomly rough surfaces
Authors: Yordanov O. I. , Ivanova K. , Michalev M. A.
Published: October 2005

A modification of the physical optics surface source density based on the Lynch variational approach is proposed for the case of scattering by one-dimensional pressure-release Gaussian random rough surfaces. Rather than the local radius of curvature, it involves the surface correlation length and introduces new criteria validating the physical optics evaluation of the coherent and incoherent scattering intensities. Closed expressions for the coherent reflection coefficient and the incoherent scattering cross section are derived without resorting to high-frequency approximation techniques. Numerical data based on these expressions and conventional geometrical optics shadowing theory are presented and shown to be in very good agreement with recently published exact Monte Carlo simulation results.
GLORIA interference patterns with modes akin to surface-duct modes
Authors: Weston David E. , Somers Michael L. , Revie Jack
Published: October 2005

Observations with the GLORIA sonar in coastal waters have shown regular patterns in the reverberation. These are interpreted as due to the interference between the first two normal modes, having characteristics similar to those in the surface duct, but with insonification below the thermocline. Up to four peaks have been seen at a spacing of about 3 km, in good agreement with expectation for the 6.4-kHz frequency. The main scatterers appear to be shallow biological targets such as fish, probably located close to the thermocline.
Horizontal spatial correlation of bottom reverberation for normal incidence
Authors: Smith Brian V. , Atkins Philip R.
Published: October 2005

The spatial correlation in the backscattered field for waves incident normally on a random boundary is derived using Kirchhoff–Helmholtz scattering theory in which the effects of both boundary heights and slopes are included. The acoustically rough case is considered and it is shown that the scattering process may be interpreted in terms of a deep, random phase screen; the influence of the boundary slopes is interpreted as diffraction at the screen. For a directive source, it is shown that the spatial correlation distance of the field is determined by the correlation of the source shading for a wide variety of boundary conditions; limited experimental data supports this result. For an omnidirectional source, the spatial correlation coefficient is 2J1(kg)/kg.
Bubble noise and wavelet spills recorded 1 m below the ocean surface
Authors: Updegraff Garr E. , Anderson Victor C.
Published: October 2005

A remote instrument has been used to record the sound and environment of small surface spills in light winds from a depth of approximately 1 m in the open ocean. Recordings from the instrument indicate that these small breaks have no correlation with the amplitude or phase of long-period swells moving faster than prevailing winds. The sound from the spills, which is composed of a number of distinct resonant bubble oscillations, is very similar to that described by Medwin and Beaky [J. Acoust. Soc. Am. 86, 1124–1130 (1989)] for windless artificial wave breaks. Peak oscillation source pressures range up to 1.2 Pa. The average of several acoustic spectra from a single energetic spill has shown a slope of −5 dB per octave over the frequency range of the instrument, roughly 500–8000 Hz. The unique frequency for each oscillating bubble within a spill indicates that bubbles are “rung” as they are formed during entrainment, die out exponentially within milliseconds, and then no longer contribute actively to the acoustic record. Analysis of the acoustic energy generated by a number of bubbles versus frequency suggests that the −5 dB per octave wind-dependent ambient noise slopes of the Knudsen curves [J. Mar. Res. 7, 410–429 (1948)] are caused by the shorter lifetimes of high-frequency bubbles, rather than significantly lower peak pressures.
The annoyance caused by simultaneous noise and vibration from railways
Authors: Howarth Henrietta V. C. , Griffin Michael J.
Published: October 2005

A study has been conducted to determine a method of predicting subjective response to simultaneous noise and vibration produced in buildings near railways. The method of magnitude estimation was used by 20 subjects to indicate the annoyance produced by vibration and noise in houses during the passage of six trains. The subjects were exposed to 90 stimuli consisting of 15 paired combinations of four levels of noise and four magnitudes of vibration for each of the six trains. The influence of duration, magnitude, and frequency of vibration and the effect of simultaneous noise were combined to provide a method of predicting the relative annoyance for different combinations of noise and vibration. The resulting relation, which involved the summation of the individual effects of the two stimuli in terms of the vibration dose value and the sound exposure level, was shown to provide a more accurate means of predicting the overall reaction from simultaneous noise and vibration than a method based on either noise or vibration alone. It may also be employed to indicate the relative importance of the two stimuli. The findings suggest that the vibration dose value and the sound exposure level are sufficient to provide useful approximations to subjective reactions to short duration exposures to railway vibration and noise.
Current status of Peterson–Barney vowel formant data
Authors: Watrous Raymond L.
Published: October 2005

A question concerning the status of the Peterson–Barney vowel formant data is raised. Two machine-readable copies of the data were located, compared, and found to contain minor discrepancies. These discrepancies were resolved by comparison with a listing of the original data.
A comparison between the boundary element method and the wave superposition approach for the analysis of the scattered fields from rigid bodies and elastic shells
Authors: Miller Russel D. , Moyer E. Thomas , Huang Hanson , Überall Herbert
Published: October 2005

The steady state analysis of the scattering of plane acoustic waves from submerged rigid and elastic bodies using two approaches is presented. The first approach uses a combined finite element/boundary element (FE/BE) methodology. The NASA structural analysis (NASTRAN) program is used to formulate the structural matrices based on the finite element method (FEM). The surface integral equation radiation and scattering (SIERRAS) program creates the fluid matrices based on the boundary element method (BEM) and solves the coupled fluid-structure interaction problem. A superparametric boundary element (BE) with nine nodes is employed. The combined Helmholtz integral equation formulation (CHIEF) is employed to provide a unique solution for all frequencies. In the second approach, the superposition method (SUP) is used for modeling the fluid. The SUP method is an off-boundary approach that employs a number of point sources moved inside the body to represent the fluid response at the surface. This allows the fluid matrices to be formed without surface integration. Formulations for the SUP method are introduced for both the radiation and scattering problems. The program SUPER reads the NASTRAN structural matrices and solves the combined FE/SUP fluid-structure equations. The FE/BEM and FE/SUP methods are applied to the scattering of an infinite set of plane waves from a submerged rigid sphere, rigid prolate spheroid, right cylinder, and from an elastic cylindrical shell with hemispherical endcaps. The SUP method is found to be easier to implement and to provide an accurate result at internal resonance frequencies where the BEM requires additional equations to ensure an accurate solution.
The emission pattern of vocalizations and directionality of the sonar system in the echolocating bat, Pteronotus parnelli
Authors: Henze Darrell , O'Neill William E.
Published: October 2005

The radiation patterns of the first three harmonics (approx. 30, 60, 90 kHz) of the mustached bat biosonar signal were measured from vocalizations elicited by cortical microstimulation. The primary foci of the acoustic beam patterns were in front of the mouth but somewhat below the horizontal plane. The prominent second and third harmonics showed sharp cutoffs between 20° and 30° lateral to the midline. Sidelobes were found, suggesting the influence of some vocal tract interference. When compared with previously measured estimates of the directionality of the auditory system, the vocal emission patterns are roughly complementary: Regions of maximum auditory sensitivity are found in areas of submaximal power for the sonar pulse beam pattern. The result is that, for the two most important harmonics, the “biosonar system” (i.e., vocal beam pattern plus receiver directionality) has a broader and more uniform directionality than either component alone. Therefore, within a limited region of space, echo amplitude will vary less as a function of angular displacement. This reduces the confounding influences of absolute sound pressure level on interaural intensity differences.
Structural intensity in thin cylindrical shells
Authors: Williams Earl G.
Published: October 2005

A rigorous derivation of the structural intensity vector for a thin cylindrical shell is provided based on Flügge’s equations of motion and expressions for the total energy density in the shell. The shell is assumed driven by normal forces, loaded externally by a fluid, and to have no internal loss. It is confirmed that the structural intensity vector is composed of five terms, and simple physical interpretations of these terms are provided. The relationship between the structural intensity and the normal acoustic intensity is derived. The five structural intensity terms are investigated in some detail using results from a numerical experiment. The numerical model was a simply supported, point-driven cylindrical shell with external fluid loading, assumed to exist in an infinite rigid baffle. A sum over in vacuo modes was used to solve the equations of motion. The results show, in the frequency range below the ring resonance of a steel shell with h/a=0.01, that the divergence of the extensional power flow term dominates over the other four terms in the transfer of power to the fluid and, equivalently, into the far field.
A boundary element approach to ocean seismoacoustic facet reverberation
Authors: Gerstoft Peter , Schmidt Henrik
Published: October 2005

A numerically efficient, hybrid method is introduced for modeling of short and long range seismoacoustic facet reverberation in the ocean environment. The method combines the global matrix approach to the solution of the wave equation in horizontally stratified media with a boundary element formulation of the boundary conditions at a contour surrounding the facet. The present paper describes a two-dimensional formulation for facets within an elastic seabed or an elastic ice cover, but allows for simulation of the reverberant field within the water column as well. The approach is directly extendable to treat reverberation from seabed-penetrating facets as well as three-dimensional elastic facets. In contrast to discrete methods such as the finite element and finite difference approaches, the solution obtained with the present hybrid approach is not only efficient for short- as well as long-range reverberation, but inherently decomposes the total solution in the temporal and spatial spectral components, of importance to the basic physical understanding of the factors affecting seismoacoustic facet reverberation.
Reflection of a plane wave from a fluid layer with continuously varying density and sound speed
Authors: Robins Alvin J.
Published: October 2005

This paper considers the transmission of an acoustic plane wave through a horizontally stratified fluid layer whose density and sound speed both vary continuously with depth. The stratified layer is of finite thickness and lies between two semi-infinite homogeneous fluids. The situation modeled is intended to be representative of an inhomogeneous marine sediment overlying a uniform substrate. Exact solutions of the Helmholtz equation, valid in the stratified layer, are derived for a class of density profiles and a number of classes of sound-speed profile. These include profiles that closely resemble measured density and sound speed variation in marine sediments. The solutions in the stratified layer are matched with solutions in the homogeneous upper and lower layers, to derive analytical expressions for the reflection coefficient of a plane wave, incident from the upper medium. Internal losses are modeled in both the substrate and the sediment layer. The solutions enable assessments to be made of the dependence of reflection coefficient on wavenumber and grazing angle for different shapes of density and sound speed profile in the sediment. The limiting cases of very low and very high frequency are examined, and both limits are shown to give reflection coefficients independent of the shape of the density or sound speed profile in the sediment layer. A number of numerical results are presented, and comparison is made with computed results from a general propagation model.
Reverberant phase in a room and zeros in the complex frequency plane
Authors: Tohyama Mikio , Lyon Richard H. , Koike Tsunehiko
Published: October 2005

Transfer function (TF) phase of finite-damped systems can be estimated from the distribution of poles and zeros in the complex frequency domain. This paper investigates the distribution of nonminimum phase zeros of TFs from impulse response data measured in a reverberant space for which the modal overlap is large. The number of nonminimum phase zeros is found to be inversely proportional to the damping of the system. This result is shown to be consistent with earlier work on the relation between phase and energy decay. The distribution of zeros and the phase of transfer function are also changed by windowing the impulse response. An exponential window is recommended in order to reduce the effect of truncation on the zeros, although such a window will have the effect of added damping.
Receiver-transmitter optimization for detection in doubly spread channels
Authors: Drumheller David Mark , Ricker Dennis W.
Published: October 2005

The problem addressed in this paper is the maximization of the expected matched filter receiver response to a signal which has been propagated through an acoustic channel whose average scattering properties may be expressed in terms of a scattering function. The channel is assumed to be doubly spread; i.e., a signal propagating through it will experience both time delay and frequency spreading. For this model, the expected receiver response is given by the two-dimensional convolution of the channel scattering function and the cross-ambiguity function defined by the transmitted and processing waveforms. It is shown that the response may be maximized by iteratively altering either one or both of the waveforms so that the volume distribution of the cross-ambiguity function approaches that of the scattering function. It is shown that under specific conditions, convergence can be guaranteed.
Evidence for the influence of aging on distortion-product otoacoustic emissions in humans
Authors: Lonsbury-Martin Brenda L. , Cutler Wayne M. , Martin Glen K.
Published: October 2005

Previous measures of distortion-product otoacoustic emissions (DPOAEs) in young adults suggested that these responses were capable of detecting the functional effects of auditory aging. The primary goal of the present study was to provide more detailed evidence for the influence of aging processes on the ability of healthy, older ears to generate DPOAEs. Toward this end, DPOAEs were examined in a series of human subjects, with clinically normal hearing, ranging in age from 31 to 60 years. Acoustic-distortion products were measured in two basic forms consisting of “audiograms” and response/growth or input/output functions. Distortion-product “audiograms” depicted the detailed frequency pattern of DPOAE amplitudes in response to constant-level stimuli, whereas the growth functions described the detection “threshold” and suprathreshold aspects of DPOAE activity, at specific frequencies, in response to primary tones that were systematically increased in level. The principal finding was that, when compared to emissions in young ears, DPOAEs accurately tracked the systematic deterioration of high-frequency hearing in aging individuals.
Ipsilateral, contralateral, and binaural masking effects on the human brain-stem auditory-evoked responses to click stimuli
Authors: Owen G. A. , Burkard R.
Published: October 2005

Two experiments concerning the effects of continuous broadband noise on wave V of the click-evoked human BAER are reported. Experiment I compared the effects of broadband masking noise presented ipsilaterally, contralaterally, and binaurally on the BAER to 100-dB pSPL monaurally presented clicks. For noise levels up to 75 dB SPL, contralateral masking had no effect on either the latency or the amplitude of wave V. Ipsilateral and binaural noise levels above 35–45 dB SPL increased wave V latency and decreased its amplitude, and the magnitudes of these effects were similar for ipsilateral and binaural noise conditions. Experiment II compared the effects of broadband masking noise on wave V to 100-dB pSPL clicks presented monaurally to each ear, and binaurally, with the noise being presented to the ear(s) of click presentation. In agreement with experiment I, noise levels above 35–45 dB SPL increased wave V latency and decreased wave V amplitude. There were no significant differences for right versus left ear. Wave V latency did not vary significantly for monaural versus binaural presentation, while wave V amplitude was larger for binaural than monaural presentation modes for all noise-level conditions.
Stimulated ultrasound absorption in aqueous solutions of biomolecules
Authors: Barnes C. , Lewis T. J.
Published: October 2005

The ultrasonic absorption of a range of amino acids and of bovine serum albumin in aqueous solution has been measured in the frequency range 200 kHz to 1 MHz as a function of pH and of the concentration of an added denaturant, guanidine hydrochloride, using spherical resonators. In all cases conditions could be established in which the absorption was not relaxational in form but had a much sharper frequency dependence. In the case of glutamic acid with certain concentrations of guanidine hydrochloride, it was possible to obtain an absorption for the solution which was less than that of water. These unusual results are considered in terms of a theoretical model of stimulated, combination frequency, three-wave interactions in which the presence in the solution of molecular clusters with a large second-order compressibility factor is an essential part. Molecular association brought about by changes in hydrogen bonding is proposed as the mechanism for cluster formation. It is concluded that stimulated parametric nonlinear effects might be readily established in aqueous solutions of biomolecules.
Ambient noise in the ocean as an analogy of daylight.
Authors: Pumphrey Hugh C. , Ruskell L.
Published: October 2005

Current methods of underwater acoustic imaging and detection tend to fall into two classes: active sonar and passive sonar. The former consists of sending out a pulse of sound and listening for the echoes that return from the object, while the latter involves listening for noises that are made by the target itself. If an analogy is made with vision, active sonar would correspond to seeing objects in a dark room by shining a torch at them, while passive sonar would correspond to seeing an object because it was glowing. Of course, the majority of the seeing that one does falls into neither category: things are seen because they scatter, reflect, and absorb the wash of daylight that surrounds them. In the ocean, the ambient noise is a remarkable acoustic analog of daylight, especially the daylight of a cloudy day. It is broadband, but with the long wavelengths more intense than the short. It comes from all over the ‘‘sky,’’ i.e., the water surface. The question is, can we use it in a similar way to daylight, to form images of the underwater scene? This paper will examine the possibilities and limitations of this idea. It will also show the preliminary results of laboratory experiments.
On the use of a split-beam array for tracking a moving talker.
Authors: Lobo Arthur P. , Champagne Benoit , Kabal Peter
Published: October 2005

Microphone arrays have been used in an audio-teleconferencing environment to pick up the speech signal from a known direction in the presence of noise and reverberation. In current algorithms, the direction of interest is obtained by measuring the output of a beamformer at a finite set of look directions and comparing it to a threshold. Unless the set of look directions is made sufficiently large, this method is not well suited to track a moving talker. In this paper a split-beam array configuration is used for the tracking problem. The time delay between the two halves of the array is obtained by a generalized cross-correlation method. A one-step Kalman predictor is then used to predict the delay for the next frame. This value is used to steer the beamformer. The system has been tested on computer-simulated data which modeled a talker moving along a linear trajectory in a reverberant room. Results indicate that this method can provide reliable estimates of the talker bearing angle in highly reverberant environments. [Work supported by Bell Northern Research.]
Finite element modeling of active periodic structures.
Authors: Hladky-Hennion A.-C. , Decarpigny J.-N. , Hamonic B.
Published: October 2005

The finite element approach has been previously used, with the help of the ATILA code, to model the scattering of acoustic waves by single passive periodic structures, such as compliant tube gratings [A.-C. Hennion etal., J. Acoust. Soc. Am. 87, 1861–1870 (1990)], or by doubly passive periodic structures, such as Alberich anechoic coatings [A.-C. Hennion etal., J. Acoust. Soc. Am. Suppl. 1 88, S115 (1990)]. Within this approach, only the unit cell of the structure, including a small part of the surrounding fluid domain, has to be meshed, while the acoustic field on both sides of this mesh is described by a plane wave expansion, with progressive as well as evanescent contributions. Internal losses and anisotropy of the materials as well as normal or oblique incidence of the wave can be described in the model. This technique has been extended to active periodic structures, such as composite piezoelectric materials, parallel piezoelectric connecting strips in a passive matrix, for example, or large high frequency arrays. In this communication, the general method is first presented, particularly the aspects related to the piezoelectric elements. Then, several examples are given, for which analytical models exist. Finally, finite element results are compared with experiments in the case of the free-field voltage sensitivity or the transmitting voltage response of 1–3 piezocomposites and demonstrate the accuracy of the whole approach.
Determination of surface geometry for beam expansion.
Authors: Hamidzada Wali A. , Nassef Ahmed M.
Published: October 2005

Some applications, for example, large area acoustic imaging, require ultrasonic beams of 8- to 12-cm diameter with a uniform intensity distribution in a plane normal to the beam axis. Expansion of the far field of a 1-in.-diam disk-type transducer by means of reflection from a surface with a specific geometry has been investigated. Using a reflecting surface minimizes energy loss due to attenuation common in beam expansion by acoustic lenses. For an energy flux angle variation not exceeding 4 deg from the reflected beam axis, the reflecting surface geometry is calculated. It is found that the expanded beam cross section after reflection is quite uniform. Uniformity of the intensity distribution across the reflected beam depends on the angle between the incident beam axis and the axis of the reflecting surface.
A model for nonlinear oscillations of a gas bubble in liquids.
Authors: Ryu Jei-Cheong , Kwak Ho-Young
Published: October 2005

It is well known that the damped bubble oscillation due to finite heat exchange with surrounding liquid displays an available power loss where there is entropy production. However, the nonlinear bubble analysis using a polytropic relation of the form, PVn=const (P is the pressure inside the bubble, V is the bubble volume, and n is the polytropic exponent) fails to account for such thermal damping. In this study, a self-consistent model for the dynamics of a spherical bubble driven into oscillation in a liquid by employing the energy equation and the equation of state for a vapor inside a bubble, and the momentum and energy equations for the surrounding liquid is formulated. The heat transfer between vapor inside the bubble and the surrounding liquid is assumed to occur through the thin boundary layer adjacent to the bubble wall. The heat transfer due to an instantaneous temperature distribution inside the bubble is also considered in this analysis. The calculated frequency response curves for the forced oscillation of a bubble are quite different from the ones obtained by the analysis using the polytropic relation. Calculation results show that the amplitude peak corresponding to the fundamental resonance during a steady oscillation for a 10∼25-μm-diam bubble is 20% less than the value obtained by the polytropic model.
Sound velocity measurements in a bubble cloud.
Authors: Cheyne Stanley A. , Roy Ronald A.
Published: October 2005

Sound velocity and attenuation measurements have been made in bubble clouds comprised of water and air. It has been known for some time that the sound velocity in a bubbly liquid is less than that of either the gas or liquid phase (e.g., 70 m/s at 2% void fraction for air bubbles in water). Standing-wave and time-of-flight methods in cylindrical tubes were used. A standing-wave technique patterned after Silberman [J. Acoust. Soc. Am. 29, 925 (1957)] was used to measure sound velocity at low void fractions (<2%). In this work, more attention was given to the problem of obtaining a more uniform bubble size distribution which was not present in Silberman’s experiment. To achieve this, hypodermic needles were used to produce a reasonably nondispersive bubble size distribution within the cloud. Also, time-of-flight measurements were made at pulse frequencies well below the bubble resonance to observe the dependence of high void fraction (≳10%) on sound velocity and attenuation. [Work supported by ONR.]
Psychoacoustic benefits of aircraft noise barriers.
Authors: Murphy Deborah W.
Published: October 2005

Annoyance is the most common reaction to aircraft noise. Over the years, residents of the communities adjacent to the Sarasota–Bradenton Airport have registered a substantial number of noise complaints. The nature of complaints suggests that community annoyance arises from three distinct sources: aircraft flying directly overhead, aircraft building up to full power immediately before and during their takeoff roll, and the thrust reversal associated with aircraft arrivals. In response to these complaints, a study was undertaken to determine the feasibility of constructing noise barriers to mitigate the impact of airport operations on the neighboring communities. The empirical decibel reductions predicted in the study may not justify the cost of constructing the recommended barriers [V. R. Desai, Wyle Res. Rep. WR 91-12, 24–25 (June 1991)]. The psychoacoustic benefits, however, may far outweigh the purely analytical conclusion. The construction of noise barriers may influence the community’s subjective response, by affecting their attitude toward the parties producing the noise. Community perception of reduced annoyance is as valuable to the Airport as any measurable reduction in noise level.
Flow noise induced in large arrays via the flexure of the support.
Authors: Dubus B. , Montgomery R. E.
Published: October 2005

The noise induced by the turbulent boundary layer in sonar arrays is usually split into a direct path where the fluctuating pressures excite directly the hydrophones after traveling through an elastomer layer backed by a rigid surface, and the indirect path where the excitation of the support by the turbulent boundary layer induces the noise in the array. To describe this last phenomena, the force-modal transform method [M. C. Junger and D. Feit, Sound, Structures, andtheirInteraction (MIT, Cambridge, MA)] has been extended to describe the flexure of a submerged multilayered plate and the wave-number spectrum of the noise sensed by the array. Several configurations are analyzed showing the effect of the stiffness and the damping of the support and of the distribution of the hydrophones. From these results, some solutions to reduce the noise level are proposed. [Work partially supported by direction des Recerches Etudes et Techniques, Paris.]
Scattering by a mass inhomogeneity on a fluid-loaded elastic plate.
Authors: Feit D. , Johnson S.
Published: October 2005

The scattering of acoustic waves by a finite length mass distribution attached to an infinite fluid-loaded elastic plate is investigated. The scattered field is made up of two parts, one the specularly reflected wave proportional to the plane wave reflection coefficient, and the other represents the wave scattered by the mass inhomogeneity. The first-order approximation to the latter wave is obtained by a Born-type approximation to the wave-number space integral equation for the plate velocity transform. This is examined to reveal the sensitivity of the scattered field to the magnitude of the mass perturbation, the spatial extent over which the mass is distributed and the degree of continuity of the distribution function, especially at the end points. Three specific distributions are examined, each having the same total mass distributed over a constant length L. For low frequencies, i.e., acoustic wavelength comparable to L, the constant mass distribution is acoustically better than the others, but for higher frequencies, the distribution having the highest degree of continuity at the end points is found to be superior.
Time functions for elemental articulatory events.
Authors: Fujimura Osamu , Wilhelms Reiner
Published: October 2005

In a syllable-based theory of phonetic implementation called the converter–distributor model [Fujimura etal., XIIth International Congress of Phonetic Sciences (in press)], articulatory gestures are evoked by an impulse representing each syllable in relevant articulators, roughly speaking as stored patterns of muscular contraction (but allowing certain parametric real-time modifications). Each event, such as closing and opening action of the tongue tip for apical stop consonants, in either the initial or final consonant clusters, is superimposed on a vowel-to-vowel base time function in each articulatory dimension. The event is approximated as an impulse response function in response to the syllable impulse, whose time and amplitude values are computed according to the phonological and other prosodic specifications of the utterance. Previous observations of temporal characteristics of articulatory gestures have been considered for assuming an appropriate family of functions with controllable parameters as viable elements of the converter–distributor model. Preliminary evaluation of microbeam pellet movement time functions using a simplified version of this theory will be presented and discussed.
Vocal tract area functions from magnetic resonance (MR) images.
Authors: Nye Patrick W.
Published: October 2005

MR equipment was used to obtain axial, coronal, and sagittal images of the vocal tracts of two male subjects during sustained vowel production. Spaced at 0.5-cm intervals, the MR image sections sampled the region from the larynx to the lips. A computer algorithm traced the air-tissue boundaries of the tract sections, and the boundaries of intermediate sections were interpolated at intervals of approximately 1 mm. These boundary data were used in 3-D digital reconstructions of the tract shape. Two methods for determining the area function from a 3-D tract model were applied and the results compared. Based on the assumption that the tract could be approximated by two straight tubes connected by a gradual right-angled bend, method 1 resectioned the model with a systematic combination of radial and parallel gridplanes designed to intersect the tract at equal intervals along its midline [cf. J. M. Heinz and K. N. Stevens, J. Acoust. Soc. Am. 36, 1037 (A) (1964); P. Mermelstein, J. Acoust. Soc. Am. 53, 1070–1082 (1974)]. Method 2 made no assumptions as to tract uniformity and traced the midline with an area minimization algorithm applied to the 3-D data. A sequence of equidistant points along the midline was then found and the area function derived. Several differences between the area functions are found, a major one being tract length which tends to be longer by method 2 than method 1. Also, the precision that can be gained by method 2 depends on the presence of many high definition MR images to ensure minimization stability. [Work supported by NIH Grant DC-00121.]
An average parabolic equation propagation method.
Authors: Oba Roger M.
Published: October 2005

Ensembles of velocity profiles are used as a model of a random ocean environment. These profiles are taken to be piecewise range independent (∂c/∂r=0) with common intervals of invariance. A parabolic wave equation, for example, may be solved analytically over each range interval using normal mode methods. This expression for the solution can then be averaged over each range interval to find mean properties. If the probability distribution of the profiles over each range interval are statistically independent, an averaged solution can be propagated from one interval to the next through the entire range. This single computation for the average solution can be compared to the average of many runs with different profile realizations of a deterministic model. Distinctions and similarities between these two methods and others are made, and their relative merits are discussed. [Work supported by ONR/NOARL and ONR Young Navy Scientist Program.]
A study of low-frequency sound propagation in shallow water ducts.
Authors: Monti Joseph M. , Herstein Peter D. , Sammis Jefferey H. , Browning David G.
Published: October 2005

An analysis is made of sound propagation conditions found in ten shallow water locations. It is found that on a yearly basis some form of ducting or channeling occurs in most locations a majority of the time. A modeling study is conducted to determine typical cutoff frequencies and the impact of in- and below-duct configurations. The results are compared to the previous works of Smith [P. W. Smith, Jr., J. Acoust. Soc. Am. 79, 71–75 (1986)] and Jensen and Kuperman [F. B. Jensen and W. A. Kuperman, J. Acoust. Soc. Am. 73, 813–819 (1983)].
The hydroacoustics of a raindrop impact and its contribution to the underwater sound generated by rain.
Authors: Ostwald Leo H. , Nystuen Jeffrey A.
Published: October 2005

The impact acoustic signature of rainfall needs to be assessed in developing acoustical techniques for measuring rainfall rates at sea. Laboratory experiments and numerical simulations of the impact of a water drop onto a water surface reveal three pressure components. The first is an acoustic water hammer as the bottom and sides of the drop strike the stationary underlying fluid. This produces an acoustically propagating wave with near-field (1/r2) and far-field (1/r) components and is responsible for broadband acoustic noise underwater. The second is a hydrodynamic effect associated with the opening of the splash cavity. This is modeled using Laplace’s Equation and the pressure effect is shown to decay with 1/r2. Finally, internal reflection of the acoustic water hammer effect from the top and sides of the drop produce observed oscillations from 90–115 kHz depending on drop size. The impact sound is the dominant sound source for raindrops of 1.1- to 2.2-mm diameter. Raindrops in this size range have not been observed to create acoustically active underwater bubbles. [Work supported by ONR.] a) Lt., USN.
Underwater sound energy from large terminal velocity raindrops as a function of drop volume, temperature, and salinity.
Authors: Jacobus Peter W. , Medwin Herman , Nystuen Jeffrey A.
Published: October 2005

The principal underwater sound energy radiated by terminal velocity raindrops at sea is due to the bubble oscillations which occur for drops of diameter 0.8 to 1.1 mm (type I) and 2.2 to 4.6 mm (type II). In the absence of bubbles, between 1.1 and 2.2 mm, the impact sound radiation is significant. The type I bubbles radiate at frequencies close to 15 kHz, whereas type II bubbles radiate between 2 and 10 kHz, depending on drop diameter. Therefore type II bubbles, which are common in moderate to heavy rainfall, offer the opportunity to determine rainfall drop distribution and total rainfall rate by remote underwater listening. Type II bubbles radiate almost twice as much energy when the drop and surface temperatures differ by 10 °C. Type II bubbles radiate 45% as much energy in saline water (35 ppt) as in fresh water. The distinctive sound spectral shape for a particular diameter raindrop does not change appreciably with extreme differences of temperature (0 to 22 °C) or salinity (0 to 35 ppt). It is possible, therefore, to condense the data from hundreds of drops acquired in our laboratory into a single relation which gives the average energy radiated by a type II raindrop as a function of drop volume, temperature, and salinity. Using this relation, good agreement is found between measurements at sea and the predicted sound spectrum for a given drop-size distribution. Also, the total rainfall rate and drop-size distribution from sound spectra measured at sea (the inverse problem) are calculated. These early successes lay the groundwork for real-time measurements of total rainfall rate and drop-size distributions in moderate to heavy rainfalls by remote underwater listening. [Work supported by ONR.] a) Lt., USN.
Predicted geoacoustic properties of gas hydrate saturated marine sediments.
Authors: Curtis William R. , Anderson Aubrey L.
Published: October 2005

Natural gas hydrates are clathrates, a class of compounds in which an expanded crystalline structure of water forms about a host gas molecule. Gas hydrates found in the marine environment are generally composed of methane combined with varying amounts of other hydrocarbon gases such as ethane and propane. The occurrence of gas hydrates within the seafloor may significantly alter elastic properties of the bulk sediment resulting in the possibility of identifying hydrated sediments by acoustic remote sensing. The Biot poroelastic theory [R. D. Stoll, Geophysics 42, 715–725 (1977)] is used to gain insight into the acoustic response of an unconsolidated marine sediment with included gas hydrates. Available geoacoustic parameter measurements for hydrated sediments, and their constituents, are of limited extent. Therefore, physical sediment model parameters are estimated both theoretically and empirically for varying concentrations of gas hydrate saturation within the sediment. These geoacoustic modeling results, together with simulations of acoustic profiler response, indicate that discernable returns for a hydrated marine sediment should be present under certain conditions. [Work supported by the NSF Eng. Res. Ctr. Grant CDR-8721512.]
Wind-wave modeling and the scattering problem.
Authors: Mellen R. H. , Leykin I. A.
Published: October 2005

Wind-wave modeling appears to be the weakest link in the surface-scattering modeling problem. Wave models are based mainly on early ocean measurements at very low frequencies, which showed strong dispersion effects and frequency spectra with F−5 asymptotes for fully developed sea conditions. Analysis indicated that this is consistent with irrotational wave theory, wherein first-order nonlinear interactions are negligible. Flume measurements at higher frequencies and shorter fetch, on the other hand, show dispersionless propagation and spectra with F−3 asymptotes. Analysis shows that this is consistent with the observed asymmetric steepening of wave fronts, which appears to be due to combined effects of dispersion and first-order nonlinearity. The proposed mechanism for first-order nonlinear interactions is vortical wave motion induced by wind stress. Azimuthal dependence of scattering strength associated with waveform asymmetry/skewness has already been observed in microwave radar experiments.
A thermoacoustic refrigerator for space applications.
Authors: Adeff Jay A. , Hofler Thomas J. , Garrett Steven L.
Published: October 2005

A thermoacoustic refrigerator has been designed, tested, and certified by NASA to be flown aboard the space-shuttle get-away-special (GAS) payload program on STS-42 in January 1992. This thermoacoustic heat pump uses acoustic power to pump heat from a low-temperature source to a high-temperature sink. It has only 15 g of moving mass operating at 400 Hz, is entirely self-contained, and operates autonomously. Using an inert gas mixture of helium and xenon, a temperature ratio of Tcold/Thot=0.74 has been achieved while a maximum coefficient of performance relative to Carnot of 16% was observed while pumping a load of 3.3 W at a temperature ratio of 0.85. The greatest observed temperature span with no external heat load was ΔT=76 °C.
Constitutive laws in time and frequency domains for linear viscoelastic materials.
Authors: Szumski Rick , Green Itzhak
Published: October 2005

There have been numerous phenomenological approaches to the characterization of linear isothermal viscoelastic material behavior. The particular form of the relaxation function has an impact not only upon how well it can be fit to data from a simple relaxation test but also upon how amenable it is to the integral transform techniques commonly used to solve problems of linear viscoelasticity. A new viscoelastic constitutive law is proposed and compared to the fractional calculus model in the context of a particular problem. The solution procedures for each law demonstrate that the new constitutive law requires less computation. Comparison of the actual results themselves, however, is not meaningful since conclusions drawn would depend upon the particular material being modeled and how well each law can be fit to the particular material. The problem is solved once more using a relaxation modulus defined in terms of a Prony series. Significant computational advantages over the previous two are demonstrated for this constitutive law. The results indicate that the particular constitutive law used for a linear viscoelasticity problem can be chosen based upon a trade-off between material property presentation and computational ease. [Work supported by ONR.]
Influence of data accuracy on characterization of polymer damping behavior.
Authors: Jones David I. G.
Published: October 2005

Data accuracy is an issue of major current importance, impacting test techniques for measuring complex modulus properties of polymeric damping materials and their temperature-frequency characterization. Wicket plot analysis of data sets, namely plots of log loss factor versus log modulus, clearly display possible errors and areas where data are lacking. These factors, in turn, influence conclusions. Examples of such impacts are discussed, including (i) Polyisobutylene [E. R. Fitzgerald etal., J. Appl. Phys. 24, 650–655 (1953)]; (ii) a commercial damping polymer [D. I. G. Jones, Proc. DAMPING ’91, San Diego, CA (13–15 Feb. 1991)]; and (iii) Poly (-alkyl L-glutamates)s [Y. Yamashita etal., Polymer J. 12, 439–445 (1980)]. In the first case, it is shown that sparse data in the glassy region make it difficult to differentiate between a Williams–Landel–Ferry (WLF) and an Arrhenius shift factor relationship. In the second case, a variety of error sources are identified. And, in the third case, it is shown to be at least probable that a ‘‘vertical shift,’’ invoked by the authors to characterize the material behavior, can instead be ascribed to errors arising from thermally induced stresses in the specimen. The need for great care in conducting tests and reporting test results is strongly demonstrated.
The emergence of phonological organization.
Authors: Vihman Marilyn May , Roug-Hellichius Liselotte
Published: October 2005

The first unit of phonological organization is the word, with emergent control of component phonetic gestures. Long before the segment functions in speech production, the child must find a systematic way to maximize output while using a minimum of gestural schemata. The emergence of such organization may promote lexical expansion, or, instead, the pressure of accumulating word storage may trigger the initial organization. This study focuses on the origins of systematization in early word phonology. Analysis of the first 30–50 words of children acquiring five languages reveals the following two strategies. I. Controlled expansion: Constraints on production patterns are gradually relaxed, with a parallel broadening of attempted adult word shapes. Relational rules emerge when the relaxation of selection constraints outpaces the relaxation of production constraints. II. Crystallization: A variety of production patterns are explored; controlled selection of adult words becomes evident as the range of production patterns is reduced, combining elements of early vocal motor schemes to achieve a relatively complex production routine.
Young infants’ sensitivity to formant transitions.
Authors: Lacerda Francisco
Published: October 2005

Infant discrimination of pairs of vowels, CV and VC syllables was studied with Swedish subjects whose mean age was about 100 days. The data were obtained using the high-amplitude sucking paradigm. Eighty-seven subjects were tested in four different sessions, during which the following contrasts were studied: [ɑ ] vs [a], [bɑ ] vs [dɑ ], [ba] vs [bɑ ], and [ɑ b] vs [ɑ d]. The contrasts were obtained by a 2-Bark shift of the F2 frequency. When applied to the vowel’s F2, this shift resulted in two distinct vowels. When applied to the onset (or offset) of F2 transitions, it generates a /b/ vs /d/ contrast. To control for learning effects due to the repeated measures procedure, the overall experiment is counterbalanced. Each subject was randomly assigned to one of the possible 24 permutations of the four experimental conditions. The results indicate a more reliable discrimination for stimuli in which the relevant information was carried by initial or final formant transitions.
Age-related auditory discrimination of short-duration steady-state, and frequency glides signals.
Authors: MacNeil J. F. , Slawinski E. B.
Published: October 2005

Evidence indicates a developmental component to the ability of the auditory system to resolve rapid frequency changes: Both young children and elderly listeners require larger acoustic differences in order to be able to differentiate signals, and this occurs in the absence of any reduced pure-tone sensitivity. The present study examined auditory sensitivity of school-aged children, young adults, and elderly listeners in the discrimination of both frequency glides and steady-state signals corresponding to the frequency range of the second formant of speech. Frequency glides had a constant onset frequency and diverged to varying offset frequencies; steady state signals corresponded to the offset frequencies of the gliding signals. Stimuli were presented monaurally and just noticeable differences were calculated using a two-cue, two-alternative, forced-choice paradigm. Significant differences were noted as a function of age and signal type, and a shift in the psychometric functions suggesting a greater sensitivity for the young adults. Results are discussed in terms of the maturation and efficiency of auditory processes.