bluuebunny/crossref_metadata_2025 huggingface dataset:
Loudness growth in forward masking
Authors: Zeng Fan-Gang
Published: October 2005

The growth of loudness as a function of intensity was measured for a brief tone burst following a forward masker. The level of the forward-masked tone was adjusted to balance the loudness of a standard tone presented without a forward masker, using a 2AFC, double-staircase, tracking procedure. The forward masker was a 90 dB SPL, 100-ms, 1000-Hz pure tone. The standard and the balanced stimuli were 25-ms, 1000-Hz tones. The forward masker and the balanced tone were always presented in the first interval and the delay between them was 100 ms. In general, the masker caused the following tone to appear louder than it would if it had not been masked, a phenomenon termed ‘‘loudness enhancement’’ [Zwislocki and Sokolich, Percept. Psychophys. 16, 80–90 (1974); Elmasian and Galambos, J. Acoust. Soc. Am. 58, 229–234 (1975)]. In addition, the present results show a nonmonotonic function; a 10- to 20-dB enhancement effect for midlevel tones and no enhancement for low- and high-level tones. The loudness jnd’s derived from the upper and lower sequences, also show a similar nonmonotonic function. The present data indicate that loudness grows much steeper following a forward masker and there is a strong relationship between loudness and the jnd’s. [Work supported by NIDCD.]
Masker duration effects frequency resolution in simultaneous and nonsimultaneous masking
Authors: Wright Beverly A.
Published: October 2005

Frequency resolution was estimated as a function of masker duration in four masking conditions for three subjects. The signal was a 4-ms, 1000-Hz tone. The wideband masker (33-dB spectrum level) had a spectral notch of variable width centered on the signal. Masker duration was 6 (only in simultaneous masking), 62, or 412 ms. Rise/decay time was 2 ms for all stimuli. In two simultaneous-masking conditions, signal offset came 1 ms before masker offset (forward-fringe) or signal onset came 1 ms after masker onset (backward-fringe). In two nonsimultaneous-masking conditions, signal onset came immediately after masker offset (forward masking) or signal offset came immediately before masker onset (backward masking). In all conditions, threshold decreased as the width of the masker notch increased. However, the rate of the threshold decrease tended to increase with masker duration. Further, the threshold decrease was more marked in the two ‘‘forward’’ than in the two ‘‘backward’’ conditions. These data indicate that measured frequency resolution may dynamically change due to prior, or even subsequent, stimulation. [Work supported by the NIDCD.]
Forward- and backward-masked intensity discrimination measured using an adjustment procedure
Authors: Turner Christopher W. , Horwitz Amy R. , Souza Pamela E.
Published: October 2005

A ‘‘mid-level hump’’ in the intensity jnd has been reported for pure tones preceded [Zeng etal., Hearing Res. 55, 223–230 (1991)] or followed [Plack and Viemeister, J. Acoust. Soc. Am. 91, 2457 (A) (1992)] by an intense masker where the signal-masker interval was 100 ms. Both of these studies used forced-choice procedures, in which subjects heard two test signals and were required to indicate the more intense tone. The present experiment used the method of adjustment to obtain intensity jnd’s. Subjects listened to an alternating sequence of standard and variable tones, and adjusted the variable tone to the same loudness as the standard. The subject was allowed to listen to the sequence as long as desired before ending the sequence. The jnd was taken as the standard deviation of repeated adjustments. With this method, there was no difference between jnd’s obtained in unmasked conditions versus those obtained with forward or backward maskers. [Work supported by NIDCD.]
A modal hybridization method for vibroacoustic studies at medium frequencies
Authors: Morand H. J-P.
Published: October 2005

A general size reduction procedure of large modal models is set up by means of Ritz–Galerkin projection techniques based on a reduced set of hybrid modes defined in each frequency band by an appropriate linear combination of the eigenmode shapes of the modal reference model. This method applies in the case of ‘‘broadband excitation’’ such as transient or random forces and leads in this case to good estimates of the vibration energy and of response maxima. It appears that the present approach differs from the well-known SEA mainly by accounting for the specificity of the external (or coupling) loads−an appropriate space averaging of the MHM leading to equipartition of energy and therefore to the SEA results. In a first part, this method is introduced in the modal analysis of the response of a structure to external forces (resp. to a prescribed motion) imposed on its interaction surface. It is shown that the hybrid modes cumulate the modal excitabilities (resp. the effective modal masses) of the ‘‘component modes.’’ The second part is devoted to the coupled vibroacoustic problem viewed through the coupling of two sets of acoustic and structure oscillators. It is shown that the resonant coupling problem can be reduced−in each frequency band−to the coupling of N acoustic hybrid modes with N structure hybrid modes corresponding to the N predominant singular values of the (rectangular) coupling matrices (additional structure hybrid modes must be considered for accounting for the external loading). The explicit solution of this problem is given in the case of a frequency band in which a cluster of modes of one subsystem is coupled with a single mode or a pair of modes of the other subsystem.
The effect of substructures on the acoustic radiation from axisymmetric shells of finite length
Authors: Bjarnason J. , Igusa T. , Achenbach J. D.
Published: October 2005

A modal-based method is developed to analyze the acoustic radiation of shells of finite length with internal substructures subjected to time-harmonic loads. In this method, variational analysis is used to solve for the shell surface velocity and pressure, and Lagrange multipliers are used to determine the substructure motion. To gain insight into the physical characteristics of the fluid/shell/substructure system, a singularity decomposition is introduced. This decomposition is based on the response singularities of the system in complex wave-number space that are closest to the real axis. It is then shown how the decomposition leads to a frequency window method to reduce computational effort. The method is demonstrated for a cylindrical shell with hemispherical endcaps and an internal circular panel. The effects of the substructure are illustrated by comparing the response of the shell/substructure system with corresponding quantities for an empty shell. [Work supported by ONR.]
Iterative algebraic learning for language acquisition
Authors: Farrell K. , Mammone R. J. , Gorin A. L.
Published: October 2005

A new iterative approach to adaptive language acquisition is presented. Prior methods for adaptive language acquisition have used statistical associations to determine the connection between words and actions. However, the performance of these methods degrades when dealing with small-sample statistics. An alternative approach for language acquisition has been recently developed, which circumvents the problems of small-sample statistics. This alternative approach consists of modeling the language acquisition problem as a linear system of equations (i.e., algebraic learning), where each equation represents a sentence. The pseudoinverse solution for this linear system of equations, as obtained by a singular value decomposition (SVD), has been found to provide connection weights that are less subject to the effects of small-sample statistics. However, the batch-mode form and computational requirements of the SVD make it unsuitable for adaptive on-line language acquisition. A logical method for overcoming this limitation is to iteratively solve the linear system of equations. An iterative approach based on this concept is now presented. The iterative approach consists of solving for the connection weights on a ‘‘sentence-by-sentence’’ basis as opposed to requiring a block of sentences as in the SVD approach. The iterative approach is shown to converge to a pseudoinverse solution. The iterative approach provides significant improvement over the SVD approach due to the availability of on-line training and in addition provides improved generalization. Techniques for iterative training and simulation results are discussed.
Isolation of a negative pressure pulse by means of diffraction
Authors: Bailey Michael R. , Blackstock David T. , Carstensen Edwin L.
Published: October 2005

A unipolar negative pressure pulse would be a useful tool in research in biomedical ultrasound and cavitation. To the extent to which an underwater spark generates a unipolar positive pulse (the accompanying negative tail is often not very noticeable), diffraction from a circular aperture may be used to produce the desired negative pulse. If the spark and hydrophone are located on the axis of the aperture, the signal received by the hydrophone is the direct (positive) pulse followed by the edge or diffracted wave, which is an inverted replica of the direct pulse. The direct wave may be blocked out by inserting an irregularly shaped occlusion in the center of the aperture (irregularity causes the diffracted wave from the occlusion to be incoherent). The edge wave is then isolated as the desired (nearly) unipolar negative pulse. Experiments to demonstrate this effect have been done with an underwater spark that generates a 1.5-μs positive pulse, a corprene aperture 50 mm in diameter, a corprene occlusion, and a piezoceramic needle hydrophone. Theoretical work to assess sensitivity of the desired pulse to misalignment is in progress. [Work supported by ONR and NIH.]
Megahertz-frequency acoustic cavitation at high duty cycles and long pulse lengths
Authors: Calabrese Adam M. , Roy Ronald A.
Published: October 2005

The threshold pressure for the onset of transient acoustic cavitation due to high-frequency, pulsed ultrasound has been shown to be dependent on the frequency and initial nucleus size. Therefore, assuming that a range of optimally sized nuclei are present in a fluid, the amount of cavitation one gets depends on the applied acoustic pressure and the frequency. This idea has been incorporated into the concept of the ‘‘cavitation index’’ [Apfel and Holland, Ultrasound Med. Biol. 17, 179–185 (1991)], which specifies the conditions below which cavitation should not occur. However, the influence that time-averaged effects, such as rectified diffusion, have on the cavitation threshold has not been extensively studied yet. A set of laboratory experiments designed to study these effects has been performed. Clean water is seeded with polystyrene spheres (to act as nucleation sites), and the cavitation threshold is measured using a modified version of a passive detection technique [Atchley etal., Ultrasonics 26, 280–285 (1988)]. The dependence of the threshold pressure on duty cycle (0.1%–10%) and pulse length (about 3–100 cycles) is presented at frequencies of 1, 2.25, and 5 MHz. Results are interpreted in light of existing theories for bubble dynamics. [Work supported by the NIH.]
Effect of noise envelope coherence, modulation rate, and duration on the detection of a sinusoid in narrow-band noise
Authors: Divenyi Pierre L. , Algazi Alain
Published: October 2005

Signal-to-noise ratios (Es/N0) necessary to detect a 1-kHz tone presented in 100-Hz quasirandom noise were measured in trained young, normal-hearing subjects. The noise was generated by digital addition of random-phase sinusoids separated by 1 Hz. In one set of conditions, 20-Hz-wide spectral slices of the 100-Hz noise band were provided with envelopes either identical to or uncorrelated with the envelope of the 20-Hz wideband centered at 1 kHz, thus generating degrees of envelope coherence (r) between 0 and 1. The duration of the sinusoidal signal was 400 ms. In another set of conditions, the noise was divided into two to five equal-width slices, each having an identical envelope; signal duration was constant at 400 ms. In the final set of conditions, the duration of the signal varied between 25 and 400 ms, with the envelope being either random or maximally coherent in the five 20-Hz spectral slices. By regarding a fixed Es/N0 as an indicator of a fixed degree of envelope correlation detection [V. M. Richards, J. Acoust. Soc. Am. 82, 1621–1630 (1987)], a comparison of the results in the three sets of conditions allows one to specify some of the temporal constraints that limit the envelope following process. [Work supported by the National Institute on Aging and the Department of Veterans Affairs.]
Detection of an interaural delay of a reproducible target noise band in the presence of reproducible diotic noise bands
Authors: Stellmack M. A.
Published: October 2005

The purpose of this study was to examine the ability of listeners to detect an interaural delay of a target noise band in the presence of diotic noise bands when the target and distractors have identical or different temporal envelopes. The target noise band was centered at 750 Hz, while two flanking distractor bands were equally spaced in frequency around the target. In each block of trials, the target and distractors were of equal bandwidth. For 20-Hz-wide stimuli, spacings between target and distractor center frequencies of 50, 100, and 200 Hz were examined. For 10-Hz-wide stimuli, a 100-Hz spacing between the target and distractors was examined. On each trial, one of three envelopes was randomly chosen for the target and distractors. The two distractor bands always had identical envelopes, while there was a 1/3 probability of the target and distractors having the same envelopes. The target band was presented either diotically or with a fixed ongoing interaural delay. The target and distractors were synchronously gated. For the 20-Hz bandwidth conditions, detectability of the interaural delay of the target was poorest when the target and distractors had identical envelopes. For the 10-Hz bandwidth conditions, interaural delays of targets with certain envelopes proved more detectable than others, independent of the relationship between target and distractor envelopes. [Work supported by NIH.]
ASA and regulatory noise control
Authors: DiPolvere Edward J.
Published: October 2005

The enforcement of noise control regulations is an area of noise control engineering that deserves increased attention by the society. The society must assist the regulators in three specific ways: (1) Education of the public and particularly the decision makers that noise is a health hazard; (2) the design of regulations that are not only technically accurate but legally defensible and understandable by the public, particularly the regulated community; and (3) the design of test methods and procedures that are simple and straightforward since most local regulatory officials may not be engineers.
Harmonic interactions in plane and cylindrical nonlinear Rayleigh waves
Authors: Shull Davis J. , Hamilton Mark F. , Il’insky Yuri A. , Zabolotskaya Evgenia A.
Published: October 2005

In a recent article [E. A. Zabolotskaya, J. Acoust. Soc. Am. 91, 2569–2575 (1992)], a new theoretical model for nonlinear Rayleigh waves in isotropic solids was derived and used to generate numerical results that demonstrate the distortion of time waveforms. In the present paper, attention is focused on the predicted behavior of the spectral components. Quasilinear solutions are obtained for second harmonic generation in both plane and cylindrical Rayleigh waves. Following Merklinger’s analysis of finite amplitude sound in fluids [J. Acoust. Soc. Am. 54, 1760–1761 (1973)], the quasilinear solutions are used to develop taper functions that account for the finite amplitude loss of energy from the source frequency component. Numerical results are presented in the form of propagation and saturation curves for the first several harmonics, and ‘‘extra attenuation’’ (EXDB) curves for the source frequency. The analytical solutions for the taper functions are found to be in reasonable agreement with the numerical results. Time waveforms are also presented. [Work supported by the David and Lucile Packard Foundation and by ONR.]
On the existence of stationary nonlinear Rayleigh waves
Authors: Hamilton Mark F. , Il’insky Yuri A. , Zabolotskaya Evgenia A.
Published: October 2005

The existence of stationary nonlinear Rayleigh waves is investigated theoretically on the basis of a new model equation for the propagation of finite amplitude Rayleigh waves in isotropic solids [E. A. Zabolotskaya, J. Acoust. Soc. Am. 91, 2569–2575 (1992)]. The spectral components of the proposed stationary waveforms are governed by coupled quadratic algebraic equations that are similar in form to those used by Parker and Talbot [J. Elast. 15, 389–426 (1985)]. However, whereas the theoretical investigation of Parker and Talbot predicted the existence of stationary nonlinear Rayleigh waves, the present investigation does not, unless artificial constraints are imposed on the frequency spectrum. The constraints considered here consist of abrupt truncation or gradual amplitude shading of the spectrum. Examples of stationary waves that result from these constraints will be presented. Differences between nonlinearity in Rayleigh wave propagation in isotropic solids and nonlinearity in sound wave propagation in fluids will also be discussed. [Work supported by the David and Lucile Packard Foundation and by ONR.]
Acoustic daylight: Theory and numerical simulations for an imaging system using ambient noise in the ocean
Authors: Potter John R.
Published: October 2005

Following a successful pilot experiment for the acoustic daylight concept, it is planned to build a multibeam device to form real-time moving images. In support of this design, it is important to investigate the expected performance as a function of object shape, composition, apparent size and the degree and orientation of anisotropy in the illuminating ambient noise field. With such a large number of variables in the operating environment, a simple scattering model is required for the problem to remain tractable. This paper begins with the Helmholtz–Kirchhoff integral and uses the Fraunhoffer approximation, evaluating the integral by stational phase. This closely parallels the work of Funk and Williams [D. E. Funk and K. L. Williams, J. Acoust. Soc. Am. 91, 2606–2614 (1992)]. The analytic result is then summed numerically over ambient noise sources in a distributed field which result in specular scattering onto the receiver from a numerically specified surface. Some examples of simple analytic results and numerical simulations will be presented. [Work supported by the Office of Naval Research.]
Arctic ring eddies and acoustic ambient noise
Authors: Doolittle Richard D. , Schulkin Morris
Published: October 2005

It is postulated that ocean ring eddies produce hydrodynamic dipoles whose velocity fluctuations contribute to ambient noise. Arctic Ocean ring eddies are studied to relate existing flow data to ambient noise models on a yearly basis. The angular velocity of the ring flow shows annular regions of solid body rotation, irrotational flow and turbulence with transitions determined by maximum velocity and the Rayleigh–Taylor instability criterion. In decay, this rotating system, acting under vertical shear, produces Couette flow yielding horizontal dipoles with wave numbers that correspond to acoustic frequencies of 20 to 50 Hz. Using a dipole model and an estimated mechanoacoustic conversion efficiency, noise source levels are computed for the rings. Then, by the Ross formula for noise levels and the eddy areal density measured in AIDJEX (1975–1976), predicted ambient noise agrees with the Buck and Rosser model for low and moderate noise levels. This mechanism complements other noise sources, especially during times of quiet wind and ice. [Work supported by ONT.]
Microactuators of thin film shape memory alloy on silicon
Authors: Johnson A. David , Busch John D. , Ray Curtis A. , Sloan Charles
Published: October 2005

Microns-thick sputtered films of TiNi shape memory alloy deposited on silicon substrates have been capable of forceful electrical actuation. Present devices are made to millimeter scale. Research under way concentrates on reducing component size to hundreds of microns. Combined with springs, orifices, and ports, these devices made miniature valves for pneumatic and fluid control. Design, fabrication, and flow characteristics of a valve of 0.25 cm3 in size are discussed. Other applications for this technology will also be addressed, including microswitches and movable micromirrors.
Ultrasonically induced mixing and transport produced with flexural waves in a micromachined membrane
Authors: White Richard M.
Published: October 2005

Using 1-mW, 5-MHz flexural plate waves in 3-μm-thick membranes, mixing in liquids and transport of both liquids and of granular solids in air have been produced. In all cases, the plate-wave velocities are lower than the sound speeds in the adjacent fluids, so the elastic disturbances in the fluids are evanescent, with typical 1/e distances of only 16 μm. Mixing has been studied with an electrochemical cell, while the transport of solids and liquids has been observed directly via optical microscopy. Acoustic streaming theory accounts quantitatively for the observed features of the liquid pumping−square-law dependence on wave amplitude, and liquid-pumping velocities which range up to 300 μm/s. The approximate theory will be described, and the experimental observations will be presented and illustrated with a short video.
Monolithically integrated optically interrogated pressure microsensor
Authors: Kim Youngmin , Neikirk Dean P.
Published: October 2005

A new class of optically interrogated pressure microsensors with tailored dielectric film mirrors will be discussed. The sensors are based on the well-established combination of a pressure sensitive membrane serving as the sensing element with an optical fiber as the interconnect. The pressure sensitive element consists of a Fabry–Perot cavity monolithically built by etching a polysilicon sacrifical layer that lies between dielectric film stacks. The size of the cavity can be precisely adjusted by controlling the thickness of the sacrificial layer grown using LPCVD. Using LPCVD, multiple dielectric films (typically consisting of silicon dioxide and silicon nitride) can be deposited to form wavelength selective dielectric mirrors. This batch fabrication technique allows excellent alignment and parallelism of the two mirrors in the cavity, which has been a problem in devices using hybrid assembly. A guiding structure for the optical fiber can also be formed using anisotropic silicon etching. The structure allows accurate alignment between the pressure sensitive Fabry–Perot cavity and the fiber. Similar fabrication techniques can be applied to construct a tunable optical filter that allows the use of optical wavelength modulation detection techniques, which are much less sensitive to light loss during interrogation.
Fundamental noise limits in micromachined acoustic and vibration sensors
Authors: Gabrielson Thomas B.
Published: October 2005

Since the introduction of the micromachining process, wherein small mechanical structures are etched from blocks of silicon, a number of very small acoustic and vibration sensors have been built. This size reduction is attractive for many applications but the small moving parts are especially susceptible to mechanical noise resulting from molecular agitation. For sensors designed for small-signal applications (microphones and hydrophones, for example), this mechanical-thermal noise is often one of the limiting noise components. While often neglected in design and analysis, this component is relatively easy to estimate, since, like electrical-thermal noise, the magnitude of mechanical-thermal noise depends only on temperature and the magnitude of mechanical damping. This paper will review several techniques for evaluating noise in acoustic and vibration sensors in general and in micromachined sensors in particular: (1) addition of a white-noise force generator for each component of mechanical resistance; (2) distribution of the equipartition noise power according to the frequency response of the sensor; and (3) application of a software electronic-circuit simulator to the mechanical equivalent circuit of a device. In addition, the complementary relationship of shot noise (nonequilibrium) and thermal noise (equilibrium) will be discussed. Several case studies including capacitive and electron-tunneling micromachined sensors will be used to illustrate the analysis procedures and to unravel some of the misconceptions about noise limits in sensing systems. [Work supported by Office of Naval Technology.]
Low-frequency, high efficiency sources for acoustic monitoring of climatic temperature changes in ocean basins
Authors: Slavinsky Mark , Bogolubov Boris , Spiesberger John
Published: October 2005

The problems for creating low-frequency, high-efficiency sources for acoustic monitoring of climatic temperature changes in ocean basins are discussed. The properties of monopole, dipole, Helmholtz resonator, resonate 1/4 wavelength tube sources with wave parameter KA<1 are discussed where K is the acoustic wave number and A is the characteristic dimension of the source. Monopole resonant sources have the highest quality and can be realized with available deformation of existing materials in gas-filled interiors. It is shown how to overcome the main engineering problems for this source to provide (1) a uniform mode of oscillation of the radiation surfaces, (2) the highest bandwidth at maximum efficiency, and (3) the minimum strain in the radiating surfaces. The modeling data and the results of source tests show high efficiency over a bandwidth suitable for acoustic monitoring.
Evaluating the influence of directional scattering coefficients for reflection, absorption, and diffusion in the auralization of acoustic designs
Authors: D’Antonio Peter , Mochimaru Akira
Published: October 2005

Auralization of virtual spaces by convolution of anechoic music with the room’s impulse response, measured from either scale models or calculated for CAD image or ray-tracing models, is becoming popular as a design diagnostic. This process requires the use of directional scattering coefficients, as opposed to random incidence coefficients, to properly account for absorption, reflection, diffusion, and diffraction at the room’s boundaries. Since these polar coefficients, which take into account the direction and frequency of the incident sound, observation position and surface area, do not exist in the acoustical literature, D’Antonio has begun a systematic analysis using a new polar mapping measurement methodology. This paper describes the measurement methodology and initial attempts to incorporate them into the Acousta CADDR program and evaluate their effect. Implementation of the directional scattering coefficients involves attenuation of scattered rays as a function of the angle of incidence, observation and frequency and the introduction of the appropriate time spread of each surface into the time response. If computing power permits, the room’s impulse response will be evaluated by convolution of the impulse response of all incident rays, appropriately delayed and spherically attenuated by the travel path, with the respective impulse response of each surface. The polar response of each surface will define the solid angle irradiated and the level will be used to determine the reflection order.
Full-wave modeling of the transmission of sound over theater seats: Far-field investigation
Authors: Chéenne Dominique J. , Kubik Robert D. , Maher Robert C. , Bahar Ezekiel
Published: October 2005

The full-wave theory [E. Bahar, J. Acoust. Soc. Am. 89, 19–26 (1991)] is applied to a computer simulation of sound transmission over simplified rows of theater seats. The investigation is concerned with the acoustic response in the far field for variable angles of incidence. The model consists on 1, 3, 5, or 8 rows, both short and tall seats, with narrow and wide spacings, for a total of four seating configurations. The surface is described if terms of its adiabatic bulk modulus. The influence of seat spacing on the backscatter appears to be quite relevant for all angles of incidence regardless of the seat height. Widely spaced seats lead to more irregular responses than narrowly spaced seats. These results suggest the need for separation between the spectral and backscattered energy during future experiments. The near-field investigation of this problem is also under way and will include a comprehensive assessment of the model using experimental data obtained by others [J. S. Bradley, J. Acoust. Soc. Am. 90, 324–333 (1991)].
Comparative acoustic measurements of the ocean bubble layer
Authors: Dahl Peter H. , Trevorrow Mark , Jessup Andrew T.
Published: October 2005

During January 1992, the University of Washington, Applied Physics Laboratory (APL-UW) made acoustic surface scattering (20–50 kHz) and environmental measurements from the research platform FLIP, while the Institute of Ocean Sciences (IOS) measured the ocean surface bubble field using its SEASCAN sonar drifter, deployed from the USNS DeSteiguer operating nearby FLIP. The experiment took place 400 n.mi. off the southern California coastline. Its goal was to obtain coordinated acoustic surface scattering, bubble field, and environmental sea state measurements to contribute to the understanding of the ocean bubble field, e.g., its spatial distribution and depth scale, and the role of bubbles in near-surface acoustic scattering and propagation. Measurements of low-grazing angle surface forward scattering were made using an omnidirectional source (suspended from a spar buoy tethered to FLIP), and receivers mounted on FLIP’s hull. The portion of received signal scattered from the sea surface experienced variable pulse elongation and energy loss. The latter is attributed to the extinguishing effects of the ocean bubble field through which surface bounce paths must traverse, and can be related to the average bubble field density along the propagation path. The SEASCAN collected multifrequency (28–400 kHz) vertical incidence backscatter and horizontal-looking sidescan sonar measurements from the same bubble field, from which microbubble density versus radius distributions were derived. Results from these two complementary measurements of the bubble field, APL-UW attenuation based and IOS scattering based, will be discussed. [Work supported by ONT (APL-UW), and DREA (IOS).]
Stochastic scattering model predictions for reverberation from the near-surface oceanic bubble layer
Authors: Gilbert Kenneth E.
Published: October 2005

A stochastic bubble-layer scattering model has recently been developed that uses as input the horizontal wave-number spectrum of the sound-speed fluctuations in the bubble layer [K. E. Gilbert and L. Wang, J. Acoust. Soc. Am. 90, 2300 (A) (1991)]. The wave-number spectrum is of the form P(K)=AK−β, where β≊4 is a nearly universal constant that has been inferred from 11 different deep-ocean reverberation experiments. To determine the constant A, one needs to know the rms sound-speed fluctuation in the bubble layer and the horizontal scale of the largest inhomogeneities in the layer (‘‘outer scale’’). In the past year, oceanographic experiments have directly measured these parameters so that predictions with the stochastic scattering model can now be more reliably made. In this paper, the scattering model is briefly reviewed and predictions for backscatter from the bubble layer using measured oceanographic parameters as input are presented. It is shown that with oceanographically constrained parameters (i.e., no ‘‘adjustable’’ parameters) the stochastic scattering model gives a good account of the observed backscatter, as a function of both frequency and angle. [Work supported by ONR.]
Acoustic characteristics of laboratory breaking waves
Authors: Kolaini Ali R. , Crum Lawrence A.
Published: October 2005

Results of a laboratory experiment to characterize the underwater sound field radiated from breaking waves are described. Waves are generated by a computer controlled plunging-type wave maker that propagate along a 40-ft-long channel and break at the surface of 12×12×8-ft anechoic water tank. The wave-maker parameters are controlled to produce spilling-type breakers with different breaker intensity (i.e., bubble cloud size). At smaller wave-maker amplitudes, a ‘‘gentle’’ spilling breaker can be produced to create a discrete number of bubbles. The number of bubbles and the sounds emitted by them can be measured and their type can be identified [H. Medwin and A. C. Daniel, J. Acoust. Soc. Am. 88, 408–412 (1990)]. Increasing the amplitude of the wave maker causes the breaker intensity to increase. The evolution of the bubble cloud size and its acoustic emissions are monitored by a high-speed video camera. The acoustic noise emitted at different breaker intensities by individual bubbles and by bubble clouds is presented and scaled to ocean breakers. Backscattering from bubble clouds was also observed using a parametric source. The scattered signal level was measured in the presence and absence of breaking waves as the insonifying frequency approached the collective oscillation frequencies of the bubble clouds. [Work supported by ONR.]
High-frequency reflection coefficient of sea ice
Authors: Sammelmann Gary Steven
Published: October 2005

This article describes a simple one-parameter model of the high-frequency reflection coefficient of sea ice. Sea ice is modeled as a layered Biot Stoll medium over a viscoelastic half-space. The viscoelastic half-space represents the columnar zone of sea ice, and the layered Biot Stoll layer represents the dendritic layer of sea ice. The model uses APL/UW’s Biot model of the elastic moduli of sea ice to parametrize the sound velocity in the columnar zone as a function of the temperature and salinity of the sea ice in the columnar zone. The model also uses APL/UW’s Biot model of the elastic moduli of sea ice to parametrize the sound velocities in the dendritic layer as a function of the porosity of the dendritic layer. The dendritic layer is assumed to have a linear porosity profile. The model predicts that the sound velocity transitions from 1800 m/s at the ice water interface to 3700 m/s at the ice–ice interface at the columnar zone.
Inversion for shear speed in an Arctic underwater environment
Authors: Huston R. D. , Dosso S. E.
Published: October 2005

In situ shear speed measurements for ocean bottom sediments are especially difficult to obtain in the Arctic. A novel experiment was performed in a shallow water Arctic environment in April 1991 to determine shear speeds from measurements of the reflection coefficient at the ocean floor as a function of grazing angle. The receiver was composed of a vertical array of nine hydrophones spanning 210 m and suspended from the ice in 320 m of water. Imploding light bulbs were used as acoustic sources at various depths and ranges. Compressional speeds required for shear speed estimation were determined by a conventional refraction method using 1.1-oz explosive charges detonated on the ocean floor at various ranges and with an ocean bottom seismometer as the receiver. Estimates of shear speed were obtained by fitting the data to classical expressions for reflection coefficients from an elastic half-space.
Speech production skills of children with cochlear implants with congenital or acquired deafness
Authors: Osberger Mary Joe , Collins M. Jane
Published: October 2005

Earlier results [J. Acoust. Soc. Am. 88, S192 (1990)] showed that children with early acquired deafness demonstrated speech production skills superior to those of children with congenital deafness both before and after they had received cochlear implants. In the previous study, however, speech production changes were analyzed without regard for type of implant used by the child. This study examined changes in speech production in terms of age at onset of deafness (congenital or acquired before age 3) and type of implant (single-or multichannel). Speech samples were obtained in the pre-implant condition and at four, 6-month post-implant intervals. The subjects with acquired deafness produced phonetic features with greater accuracy than did the subjects with congenital deafness in the pre-implant condition. At all post-implant intervals, the subjects with acquired deafness who received the single-channel implant demonstrated better speech skills than those of the children with congenital deafness. In contrast, the speech skills of the children with congenital deafness who received multichannel cochlear implants appeared to approximate, over time, those of the children with acquired deafness over time. [Work supported by NIH-NIDCD.]
Individual speech-recognition susceptibility to noise in elderly listeners
Authors: Crandell Carl
Published: October 2005

A pervasive characteristic of aging is an inability to understand speech, particularly in adverse listening environments. The present investigation examined individual differences in speech recognition in 30 elderly listeners with similar degrees/configurations of sensorineural hearing loss (SNHL) and equivalent speech recognition in quiet. Speech recognition was assessed via the speech reception threshold procedure [R. Plomp and A. M. Mimpen, J. Acoust. Soc. Am. 66, 1333–1342 (1979)] utilizing the predictability-high sentences from the revised speech perception in noise (SPIN) test. The multi-talker babble derived from the SPIN test presented at a level of 75 dB SPL, served as the noise competition. Results indicated a nonsignificant correlation (r=−0.03, p<0.01) between speech-recognition ability in quiet and in noise. These data suggest that elderly individuals with similar audiometric configurations often demonstrate varying degrees of difficulty understanding speech in a background of noise. Theoretical and clinical implications for the development of rehabilitation procedures, such as digital amplification devices, for the elderly will be addressed.
Temporal and spectral characteristics of diadochokinetic utterances produced by speakers with ALS
Authors: Southwood M. Helen
Published: October 2005

Diadochokinesis (DDK), the rapid production of syllable sequences, is used when assessing motor speech disorders. The validity and reliability of DDK tasks has been questioned because of the variability in performance across and within speakers. The variability in the temporal and spectral characteristics of ten syllables extracted from the middle of the DDK utterances /pu/ and /ti/ produced by one normal and four ALS subjects was examined. Smaller coefficients of variation for the durations of /Λ/ (0.10–0.20) and /i/ (0.05–0.13) were observed for the ALS speakers. The coefficient for the duration of /p/ tended to be slightly higher for the ALS speakers (0.22–0.38), regardless of the severity of the speech impairment. Smaller coefficients of variation were observed for the mildly and severely dysarthric speakers for /t/, 0.11 and 0.12, respectively. Skewness and kurtosis measures were also computed. Evaluation of the averaged spectrum for both /Λ/ and /i/ revealed similar patterns across repetitions for each speaker, although minor variations were observed across the speakers. The findings suggest that ALS speakers consistently produce temporal and spectral characteristics of syllables in DDK sequences.
Prosodic marking in the error revision of apraxic speakers
Authors: Liss Julie M.
Published: October 2005

Speakers use certain cues to let listeners know when they are revising a speech production error. This marking of revisions−often prosodic or semantic in form−is related to the amount of contrast between error and repair, and may be driven by the speaker’s perception of how the error has affected the integrity of the intended message [W. J. M. Levelt and A. Cutler, J. Semantics 2, 205–217 (1983)]. The present study examined error revisions in the spontaneous speech of four men with apraxia of speech (AOS). Successive approximations of words, in which speakers eventually produced the intended target, were evaluated. Acoustic and perceptual analysis revealed that, as for normal speakers, these subjects often marked repair attempts through modifications of duration, intensity and fundamental frequency. However, interpretation of error revision in AOS is complicated by the observations that, (1) speakers did not always revise, even when words were severely distorted, and (2) the final ‘‘accepted’’ productions (i.e., those following successive approximations) were often distorted. Results will be discussed relative to theories of speech production and perception, and with regard to self-monitoring among disordered speakers.
The importance of phase in the perception of intervocalic stop consonants
Authors: Liu L. , He J. L. , Smit A. C.
Published: October 2005

Identification experiments were performed to assess the relative importance of phase information versus amplitude information of vowel–stop–consonant–vowel (VCV) utterances for intervocalic consonant perception. Three types of stimuli were constructed from the VCVs spoken by six German speakers: (1) swapped stimuli: synthesized from the phase spectrum of one VCV utterance and the amplitude spectrum of another; (2) amplitude-only stimuli: the original amplitude spectrum of a VCV utterance combined with a zero or random phase spectrum; (3) phase-only stimuli: original phase spectrum with zero or random amplitude spectrum. About 66% of intervocalic stop consonants in the phase-only stimuli could be correctly identified as compared to less than 25% for amplitude-only stimuli. Over 55% of type 1 stimuli were identified as the VCV utterances that had provided the phase information, and less than 22% as those that had provided the amplitude information. Consonant identification performance was seen to vary with voicing and place of articulation of the stops, as well as with vowel context. The results indicated that it was the phase spectrum, rather than the amplitude spectrum of a VCV utterance that conveys more important information for stop consonant perception.
An experimental analysis of spirantization in Spanish
Authors: Romero Joaquín
Published: October 2005

An experimental analysis is presented of the spirantization phenomenon in Spanish. Spirantization is a phonological rule of all dialects of Spanish by which underlying voiced obstruents /b/, /d/, and /g/ surface as voiced continuants /β/, /edh/, and /ṽ/ when preceded by other continuants. It is argued that spirantization can be explained as the result of the overlapping and blending of articulatory gestures. Gestures are specified in two main dimensions: constriction location and constriction degree [C. B. Browman and L. Goldstein, Phonology 6, 201–251 (1989)]. The overlap of underlying obstruents with the preceding continuants results in blending of the two constriction degrees, thus creating another continuant. An electromagnetic midsagittal articulometer was used to record movement of the jaw, lower and upper lip, tongue tip, tongue blade, and tongue body, together with the acoustic signal, during the production of /b/, /d/, and /g/ in a number of phonological contexts. Results show that the magnitude of the obstruent gesture is indeed affected by that of the preceding continuant in terms of duration, constriction degree, and articulator velocity, and that the relationship between gestures is consistent across points of articulation. [Work supported by NIH Grant Nos. DC-00121 and HD-01994 to Haskins Laboratories.]
Effect of a thin low-velocity layer underneath a floating plate on flexural waves
Authors: Chamuel Jacques R.
Published: October 2005

Time-domain pulsed broadband laboratory experimental results are presented demonstrating that a thin low velocity fluid layer (thickness <H/10) at the bottom of a floating plate (thickness H) drastically decreases the group velocity of flexural waves on the right side of the dispersion curve maximum Umax. The low Scholte wave velocity of the layer affects the Scholte wave branch dispersion curve and causes it to deviate towards a lower value. Hunkins’ seismic studies of sea-ice [J. Geophys. Res. 65(10) (1960)] revealed two discrepancies between measured and calculated flexural wave group velocity dispersion: (a) sea-ice thickness determined from flexural wave dispersion is generally lower than the actual thickness, and (b) flexural wave components on the right of Umax have considerable lower velocity than predicted. Ultrasonic modeling studies [J. R. Chamuel and G. H. Brooke, J. Acoust. Soc. Am. Suppl. 1 79, S57 (1986)] provided a possible explanation for the first discrepancy namely that the presence of a large number of small cracks in a floating plate reduces U and shifts the corresponding dispersion curves towards an ‘‘effective’’ thinner plate. The current paper provides an explanation for the second discrepancy in Hunkins’ results which cannot be compensated for by changing ‘‘H.’’ Bogorodskii [Sov. Phys. Acoust. 22, 158–159 (1976)] showed the existence of a ‘‘clear-ice’’ layer underneath the ice, during the rapid growth of the ice cover, which has a compressional wave velocity of about 1050 m/s substantially less than the velocity of sound in water. [Work supported by ONR.]
Experimental examination of growing and newly submerged sea ice including acoustic probing of the skeletal layer
Authors: Williams K. L. , Garrison G. R. , Mourad P. D.
Published: October 2005

Results of an in-situ experiment to examine acoustic parameters and scattering properties of growing and newly submerged arctic sea ice are presented. The primary emphasis is on the acoustic properties of highly porous sea ice. High resolution (to about 1 cm) vertical profiles of the longitudinal wave speed in growing and submerged sea ice are derived from the experimental data. The results indicate a skeletal layer about 3 cm thick at the bottom of the growing ice. The time dependence of the vertical sound-speed profile in a submerged block reveals a long time scale process of up to 80 h and a short process of a few hours. The former process is block warming, the latter is thought to be due to the disturbance of the hydrostatic equilibrium as the ice is submerged. Concurrently with the wave speed measurements, scattering from the underside of the ice was measured at several frequencies. A comparison with predictions based on the sound-speed data demonstrate the ability to predict normal incidence reflectivity from sound-speed profiles as well as the viability of using scattering data in inversions to obtain sound-speed profiles. The data were also used to calculate the absorption of a longitudinal wave propagating vertically. The peak absorption rate in the skeletal layer was between 2 and 5 dB/cm at 92 kHz. The temperature dependence of the absorption seen in the submerged ice suggests that the McCammon–McDaniel equation is useful away from the skeletal layer. [Work supported by the Office of Naval Research (N00014-91-J-1647).]
The effect of incomplete coating coverage on acoustic scattering from cylinders
Authors: Shaw Christopher E. , Ginsberg Jerry H.
Published: October 2005

Scattering of a plane wave at beamwise incidence to a cylinder whose flat ends are rigid and whose curved surface is coated with a pressure release material is considered. In comparison to previous studies of complete coating coverage, the present work uses a boundary element formulation to evaluate the effect of removing regions of coating, thereby converting those regions to rigid scatterers. The study explores the dependence of the amplitude of the far-field scattered signal on several factors: the percentage of uncovered area, the ratio of axial to circumferential dimension of the missing patch, the location of the uncoated region, proximity of missing patches, and frequency. In general, the following factors tend to increase the far-field backscatter: (1) large regions of missing coating, (2) impedance discontinuities near the end of a cylinder with rigid endcaps, (3) small regions of missing coating on the shadow side of the cylinder, and (4) higher driving frequencies. [This work was supported in part by ONR.]