bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamic mechanical and acoustic characterization of a PVC-based commercial damping elastomer.
Authors: Szabo Jeffrey P. , Guigne Jacques Y. , Chin Voon H.
Published: October 2005

Experiments carried out on a PVC-based commercial damping elastomer, Isodamp C-1002, are used to illustrate a forced vibration, nonresonant method for the determination of complex modulus in the frequency range 10 Hz–10 kHz, using tensile and compressive excitation. For tensile excitation, a simple model was successful in interpreting the data up to the resonance frequency of the sample. Compressive excitation, on the other hand, required a model that incorporated the inertial mass acting on the force transducer; however, interference from sample resonance was excluded. Sources of error in both cases could be traced to the phase angle, which is sensitive to resonance phenomena, and low signal to noise ratio. Transmission loss and echo reduction measurements were carried out on immersed 1-×1-ft samples in the frequency range 4–100 kHz using a narrow beam parametric array source to minimize edge diffraction and tank reverberation effects.
The development of consonant and vowel differentiation.
Authors: MacNeilage Peter F.
Published: October 2005

This paper focuses on the results of an investigation of the differentiation of consonants and vowels in infancy. The theoretical model upon which the study is based seeks to account for fundamental properties of speech systems and their motoric organization.
Vocal development in hearing-impaired infants.
Authors: Carney Arlene E.
Published: October 2005

Vocal development in infants has been analyzed in a variety of ways−acoustically phonetically, and linguistically. An important milestone of vocal development is the onset of canonical babbling, during which the infant produces utterances with the syllabic characteristics of adultlike speech. Infants with profound hearing losses have been observed to develop canonical babbling significantly later than infants with normal hearing [D. K. Oller and R. E. Eilers, Child Develop. 59, 441–449 (1988)]. The purpose of this study was to investigate vocalization behavior in four infants, with hearing losses ranging from moderate to profound degree, from early vocalizations through first words or those vocalizations accompanying first signs. Vocalizations were analyzed with reduced aspect feature transcription (RAFT) [A. E. Carney, J. Acoust. Soc. Am. Suppl. 1 87, S89 (1990)] to describe the range of articulatory behaviors observed. Results were compared to those obtained from a control group of four infants with normal hearing. Onset of canonical babbling and RAFT patterns were analyzed as function of degree of hearing loss, age of identification of hearing loss, and age of amplification and intervention. Results are discussed with regard to the role of auditory feedback in early vocal development. [Work supported by NIH-NIDCD.]
Speech categorization in infants.
Authors: Walton Gail E. , Shoup-Pacenka Angela G. , Bower T. G. R.
Published: October 2005

Kuhl has demonstrated that infants of 6 months can identify a phoneme across changes in talkers. Twenty-four newborns participated in a speech categorization task involving the phonemes /u/ and /i/. Twelve subjects were presented with computer-synthesized speech sounds /u/ and /i/ in low-, mid-, and high-frequency bands. The other 12 subjects were presented with a male, a female, and a child talker uttering /u/ and /i/. Babies indicated discrimination between the phonemes by sucking on a pacifier connected to a computer via a pressure transducer in an operant choice sucking procedure which presented the phonemes through a speaker. This study showed that human newborns also detect the identity of a phoneme across changes in talker. For newborns, the phoneme change from /u/ to /i/ is much more salient than changes in talker (child versus adult female versus adult male). The effect holds for natural and synthesized speech sounds, and may be stronger for the latter.
Development of an arctic ray model.
Authors: Stotts Steven A. , Bedford Nancy R.
Published: October 2005

Recent additions to a previously developed ray model [E. K. Westwood and P. J. Vidmar, J. Acoust. Soc. Am. 81, 912–924 (1987); E. K. Westwood and C. T. Tindle, ibid. 81, 1752–1761 (1987)] have been completed. The inclusion of top layering above the user-specified ocean and bottom layer environment makes the updated model (ICERAY) applicable to ice-covered regions. Sources are specified in the ocean, while receivers may be located in either the ocean or top layers. The implementation consisted of the calculation of several ray types, and energy contributions from the various ray paths were analyzed independently. Compressional and shear rays were included in the ice. The analysis of evanescent waves showed them to be the most important for propagation to receivers in the ice from sources at longer ranges. The evanescent contribution was implemented by calculating an eigenray to a receiver just below the ice–water interface at the location of the actual ice-embedded receiver and including an appropriate transmission coefficient and exponential decay factor. Comparisons to the full-wave model SAFARI [H. Schmidt, SafariUser’sGuide, SACLANTCEN SR-113, NATO SACLANT Undersea Research Centre, La Spezia, Italy (1989)] demonstrated the accuracy of the ray model for various source and receiver geometries starting with simple environments and evolving to a realistic arctic environment. [Work supported by the Office of Naval Research and the Internal Research and Development Program of the Applied Research Laboratories, The University of Texas.]
Benchmarking the wedge assemblage method for sinusoidal surfaces.
Authors: Keiffer Richard S.
Published: October 2005

The wedge assemblage (WA) approach uses the exact solution of Biot and Tolstoy for an infinite impenetrable wedge as a building block to approximate the impulse response of sinusoidal surfaces. For 1-D surfaces, this is accomplished by generating an assemblage of finite wedges from rectangular facets to approximate the surface of interest, calculating the diffracted response (no reflections are calculated) from each wedge apex, and summing in the time domain. Of interest is how well this single-scatter, diffraction-only scattering model performs as a function of scattering geometry, kh (where k is the acoustic wave number and h is the amplitude of the sinusoid), and the maximum slope of the sinusoid. [Work supported by ONR.]
Wave theoretic seismic processing.
Authors: Weglein Arthur B.
Published: October 2005

The goal of seismic processing is to determine the character of the subsurface of the earth from wave-field measurements on the surface. In this inversion problem, both the target and the propagating medium are unknown. Also, the character of the energy source is not typically known. In this paper, the evolution of methods which address various aspects of the problem is described. Approximate linear inverse scattering approaches often can produce useful results. Nonlinear inversion approaches have the potential of providing certain important practical benefits not provided by linear approaches, although the former are typically less robust than the latter. Examples of linear and nonlinear inversion methods illustrate the strengths and weaknesses of each. Real data quality issues such as aperture, spatial sampling, and noise will impact what algorithm is appropriate and what goal level can be achieved with confidence. A recent wavelet estimation method [A. B. Weglein and B. G. Secrest, Geophysics 55, No. 7 (1990)] provides an approach for identifying the source signature and radiation pattern.
Passive synthetic acoustic arrays for ocean acoustics applications.
Authors: Yen Nai-chyuan
Published: October 2005

This paper gives a brief review, based on the concept of the inverse radiation problem, on the formulation of a synthetic virtual receiving array formed by scanning a single sensor following a designed locus in a stationary acoustic field. Both the beamforming method and the signal decomposition analysis are used to examine the parameters needed for determining the radiation sources’ locations. Studies show that considerable angular resolution can be achieved for observing distant sound sources through adaptive signal processing techniques. Applications in ocean acoustics for directional acoustic field measurement are discussed for two special types of synthetic arrays, linear and circular. Problems involved with the directionality ambiguity due to Doppler frequency shift, angular resolution degradation originated from array deformation, effects caused by instability of ocean conditions, and deployment feasibility are also addressed. The concluding results may be used to establish the guidelines for engineering design and deployment of passive synthetic arrays for ocean acoustics applications.
Quinine sulfate reduces otoacoustic emissions.
Authors: McFadden Dennis , Pasanen Edward G.
Published: October 2005

A moderate dose of quinine sulfate was given to a subject having three spontaneous otoacoustic emissions (OAEs). Approximately 3 h after the first dose (325 mg), two of these OAEs were nearly eliminated and the middle one was unaffected. All were eliminated following the fifth dose (22 h after the first dose). Recovery was almost complete for two of the three OAEs about 28 h after the last dose. These effects were more rapid than the similar effects previously demonstrated for aspirin. At the 22-h point, the levels of two primary tones used to produce an emitted 2f1-f2 distortion product (DP) located just above the middle spontaneous OAE had to be raised about 10 dB re: the pre-drug condition, the DP obtained saturated at an SPL about 15 dB lower than before the drug, and the slope of the DP gain function was approximately halved under the drug. Hearing loss was 10–15 dB across test frequencies at the 22-h point and had fully recovered about 28 h after the last dose. [Work supported by NIDCD grant.]
Relations between dc and ac mechanical responses of the outer hair cell.
Authors: Santos-Sacchi J.
Published: October 2005

Whole cell voltage clamp and displacement measuring photodiode techniques were used to study electrophysiological and mechanical properties of the guinea pig OHC. OHCs demonstrate a voltage-to-movement (V-M) function which can be fit by a two-state Boltzmann relation, where the cell normally rests near the hyperpolarizing saturation region (−70 to −90 mV). The voltage at half-maximal length change (Vh;−40 to −20 mV) is depolarized relative to the resting potential. Mechanical responses can be as large as 30 nm/mV. The form of the V–M function ensures that for symmetrical sinusoidal voltage stimulation about the resting potential, ac and dc mechanical responses will be produced. Analysis of OHC motility using pure tone voltage bursts from 11 to 3200 Hz demonstrates both ac and dc mechanical responses; ac responses can be as large as 3–4 μm, and decrease in magnitude roughly linearly with voltage. However, dc mechanical responses which can be as large as 1/4 of the ac response with large ac voltage stimuli, decrease nonlinearly with ac voltage. The net effect is that the mechanical dc/ac ratio approaches zero for small ac voltages. This is predicted from the form of the V–M function, whose nonlinearity is a consequence of the resting potential being displaced from Vh. Invivo, an ac receptor potential at auditory threshold at 15 μV, would produce a dc mechanical response 2500 times smaller than the ac response. Measures of the ac mechanical frequency response have shown 3-dB break points approaching 1 kHz, with the phase of the fundamental component (obtained by FFT) corresponding to the phase of the transmembrane voltage and not that of current, as would be expected for a voltage driven process. Maximum velocity induced by voltage step is 6.5 mm/s. The invivo speed of OHC motility will be limited by the cell’s RC time constant, which itself is dynamic due to voltage dependent conductances and capacitance in the OHC membrane. [Work supported by NIDCD DC00273.]
Excitatory/inhibitory mechanisms in lateral superior olive units.
Authors: Zacksenhouse M. , Johnson D. H. , Tsuchitani C.
Published: October 2005

The binaural responses of lateral superior olivary (LSO) units, involved in extracting high-frequency cues for sound localization, are studied using a general point process approach. Previously reported results indicated that the contralateral input does not inhibit by attenuating the excitatory ipsilateral drive [Tsuchitani, J. Neurophysiol. 59, 184–210 (1988)]. Statistical analyses revealed that inhibition operates by scaling the recovery function−the post-spike instantaneous discharge rate. Thus the inhibitory process can be summarized by a single variable: the scaling factor. The variations of the scaling factor with the interaural level difference (ILD) demonstrate that LSO units are spatially tuned. In contrast, the effect of the excitatory stimulus on LSO unit discharges is more evolved: Excitation operates by both shifting and amplifying the unit recovery function. Thus the excitatory process affects also the unit refractory period. A specific point process model describing the effects of both the ipsilateral and contralateral stimulus levels on the statistical structure of all LSO unit discharges is presented. [Work supported by NIDCD grants.]
Improved information transfer of phoneme features with a multiple-electrode cochlear implant.
Authors: McDermott Hugh J. , McKay Colette M.
Published: October 2005

The spectral maxima sound processor (SMSP), recently developed at the University of Melbourne, has been shown to provide improved speech discrimination in quiet and in noise for subjects using the Mini System 22 cochlear implant when compared with commercially available speech processors, including the Mini Speech Processor (MSP) [C. M. McKay and H. J. McDermott, J. Acoust. Soc. Am. 89, 1959 (1991)]. The ability of five subjects to perceive phoneme features using the SMSP has been compared with their ability using the MSP. Information transfer analysis has been applied to the results of open-set CNC word tests and closed-set vowel and consonant recognition tests. Phoneme features studied were consonant manner and place of articulation and voicing, vowel duration, formant frequencies, and formant transitions. The results show an overall improvement in the perception of all phoneme features, with large improvements seen in perception of consonant place of articulation. This consonant feature has been perceived poorly relative to other consonant features with all previous speech processors used with this implant. Further development of the SMSP is being guided by the results of this analysis.
Discrete speech information for cochlear implants: First results.
Authors: Ouayoun Michel , Frachet Bruno , Eskénazi Maxine
Published: October 2005

Cochlear implants give hearing disabled patients links to the hearing world: detecting danger and understanding speech when lipreading. In the best cases, patients understand without lipreading. For other cases, another speech processing approach must be found to free them from lipreading. The method experimented here associates the continuous speech signal with a discrete series of signals, using an automatic speech recognition system as a preprocessor. The 100-ms discrete signal approximately corresponds to the duration of the syllable for average speed speech. However, there are too many syllables (signals to be learned) if an everyday vocabulary is to be attained (2500 syllables). The number of syllables has been compacted by grouping sets of syllables which are usually confused during lipreading. Using the same, instead of complementary information, and relying on patients’ higher-level knowledge to complete the message, the signals alone should provide fluent speech understanding without lipreading. Results of preliminary tests designed to prove that patients can associate signals to syllables in real time for well-known mono- and disyllable-French word test lists will be shown. The use of specially developed training methods is essential to the success of the approach.
Electrophonic excitation from electrical stimulation of the hearing-impaired cochlea of the cat.
Authors: McAnally K. I. , Clark G. M.
Published: October 2005

Electrophonic excitation from electrical stimulation of the cochlea was investigated in seven cats by examining the forward masking of the compound action potential (CAP) to acoustic probes using pulsatile and sinusoidal electrical maskers. Monopolar electrical stimulation of the round window or bipolar stimulation of the basal turn of the scala tympani elicited electrophonic excitation at regions of the cochlea acoustically tuned to the frequency of electrical stimulation (i.e., remote from the electrodes). This was true for a cat with no organ of Corti in the region of the stimulating electrodes. CAP tuning curves for electrophonic excitation appeared similar to those measured with acoustic stimulation. Masking was measured for electrical stimulus frequencies as high as 20 kHz (the highest tested). The spatial profile of excitation along the length of the cochlea was estimated by variation of the probe frequency. This showed peaks of excitation at cochlear locations acoustically tuned to the electrical stimulus frequency and its harmonics. The results suggest that a traveling wave along the basilar membrane, in part, explains electrophonic hearing.
Central auditory dysfunction: qEEG correlates of individual differences in ear advantages and REP/ABR results.
Authors: Lauter Judith L.
Published: October 2005

A new test battery for central-auditory diagnostics, supplementing standard audiometry with MacCAD (a Macintosh-based program for central auditory diagnostics), and the ABR version of our repeated-evoked potentials (REPs) protocol, was described to the Spring 1991 meeting of this Society. As reported then, preliminary results distinguished among a variety of patients, with some details predictive of individual patterns of supra-brainstem involvement. Subsequent testing of the same subjects using quantitative EEG provides initial support for these predictions. For example, in one subject originally diagnosed as ‘‘central auditory,’’ previous findings such as ‘‘polar-opposite’’ ear advantages and ‘‘release signs’’ in ABR stability profiles, were accompanied by qEEG characteristics such as reduced beta power over auditory cortex bilaterally, and diminished interhemispheric coherence. Similar findings in other subjects suggest that by exploiting the sensitivity of repeated-measures test designs to individual characteristics, it may be possible to generate more detailed physiological and behavioral profiles of central auditory function.
Bottom scattering in the adiabatic normal mode framework.
Authors: Dacol Dalcio K.
Published: October 2005

The adiabatic normal mode model is a full wave propagation model that is computationally efficient in the modeling of long distance propagation in range-dependent environments. Its usual formulation does not include bottom backscattering, thus precluding its use in reverberation modeling. How to include such effects in the adiabatic normal mode model is the subject of this presentation; both theoretical developments and numerical examples will be presented. In particular it is shown that there can be significant backscattering even in situations where mode coupling is a minor effect. A modification of the usual adiabatic normal mode model allows for the inclusion of some backscattering effects without mode coupling. [Work supported by ONR.]
Recent results regarding turbulent wall pressure and shear stress in boundary-layer flow and the role of the viscous wall condition.
Authors: Chase David M.
Published: October 2005

Recently, the relation between fluctuating wall pressure and shear stress at low streamwise (subconvective) wave numbers, and between these and their fluctuating Reynolds-stress ‘‘sources,’’ has been examined analytically for nominally homogeneous, slightly compressible turbulent boundary-layer flow. At low-wave-vector magnitude (but within the incompressive domain), the contributions to the wall pressure and to the wave-vector-directed component of shear stress associated with imposition of the viscous wall condition prove to be equal, perfectly coherent, and differing in phase by π/2. Assuming apparently plausible source scaling and properties, this viscous contribution is then expected to be nearly wave-vector-white and of such magnitude as to dominate the low-wave-number spectrum of wall pressure as well as shear stress and account for currently measured levels. The lack of experimental evidence for the decrease in the spectrum of turbulent wall pressure toward low wave numbers that would be expected if the Kraichnan–Phillips theorem applies as in inviscid flow might thereby be accounted for. Likewise, the level of turbulent wall-shear stress at low wave numbers obtained by model-based extrapolation of measured sublayer velocity spectra is comparable with the level of wall pressure, as predicted. But a recent treatment seems to imply that the spectrum of wall pressure vanishes toward low wave numbers even for real, viscous flow. This result is suggested to relate only to wave numbers on the order of the reciprocal streamwise extent of the turbulent boundary layer, not to wave numbers which, though perhaps smaller than the reciprocal boundary-layer thickness, are great enough to lie in the domain of interest where the condition of streamwise homogeneity is met. Controversy and conflicting views of the role of the viscous wall condition in determining turbulent boundary-layer pressure at low wave numbers thus endure. [Work supported by ONR, Code 1132F.]
Effective forces and wave-number domain analysis of piezoactuators.
Authors: Kim S. J. , Sonti V. R. , Jones J. D.
Published: October 2005

The use of piezoelectric materials as actuators for structures in active structural acoustic control has drawn much attention in recent times because of the ability to vary their geometry, location, and material properties in order to obtain the desired modal coupling. Investigations on the effect of shaping [Bailey and Hubbard] and varying the polarization profile of the piezoactuator [Lee] have been done and it was shown that selective modal coupling is possible by carefully varying the moment distribution function over the surface of the actuator. This essentially is effected by shaping the actuator, by varying the polarization profile, by varying the thickness of the actuator over the surface and by varying the electrode resistivity. In order to understand the full potential of distributed actuators, existing actuator models need to be viewed in terms of the equivalent moments and forces which they exert on the structure and also analyzed in terms of their spatial frequency (wave-number) components to determine the modal excitation characteristics. In this investigation, which is essentially the two-dimensional extension of the aforementioned studies, distributed actuators with different elementary shapes (rectangular, circular, triangular) surface bonded to flat plates are chosen and are analyzed in terms of the equivalent forces and moments they exert on the substructure. Also, the wave-number transforms of the spatial coordinates of these distributed piezoactuators are studied to ascertain their modal response characteristics. The elementary shapes are chosen without any apriori knowledge. The motivation is to design an actuator which has low shell mode coupling behavior and hence alleviates the control spillover problem and to better understand the influence of shape and moment profile of the piezoactuator on the substructure. Closed form solutions are given wherever possible and in other cases numerical integration results are presented.
Optimal placement of piezoelectric actuators and polyvinylidene fluoride (PVDF) error sensors in active structural acoustic control approaches (ASAC).
Authors: Clark Robert L. , Fuller Chris R.
Published: October 2005

Optimization of the location of a rectangular piezoelectric actuator and both the size and location of a rectangular surface strain error sensor constructed from polvinylidene fluoride (PVDF) for active structural acoustic control (ASAC) is studied in this work. An algorithm is proposed for choosing the optimal actuator/sensor configuration for controlling sound from a baffled simply supported plate excited harmonically, and the resulting acoustic response is predicted from analytical models. These results are compared to those measured in the lab on a test rig duplicating the appropriate boundary conditions and situated in an anechoic chamber. Results from a single optimally located control actuator are compared to those from control with a nonoptimally positioned actuator as well as multiple control actuators. In addition, either microphones are used to provide error information in the test cases or a single optimally located and dimensioned PVDF error sensor is implemented as the cost function. Results from this study indicate that optimization of control actuators and error sensors provided a method for realizing ‘‘smart’’ structures for active structural acoustic control (ASAC), rivaling in importance the performance increase gain when acoustic control is achieved with microphone error sensors and multiple control actuators. [Work supported by ONR /DARPA.]
Training a structured neural network with graded targets.
Authors: Burr D. J.
Published: October 2005

Two neural networks and a Gaussian classifier were compared on a phoneme labeling task. They consisted of (1) a fully connected two layer neural network, (2) a partially connected neural network, and (3) a nearest neighbor Gaussian classifier. Networks were trained using a novel coarticulated target model. Instead of quantizing targets to 0 and 1, they were graded in proportion to the number of input frames represented by the pattern in the input window. Labeled training data from 146 male speakers were obtained from the TIMIT database. Input features consisted of a sequence of 30 16-ms Hamming-windowed DFTs stepped at 8-ms intervals and reduced to 16 frequency bins. The partially connected network had ten groups of three adjacent input frames fully connected to 30 separate hidden neurons each, and a fully connected output layer of 39 phoneme categories. Consecutive three-frame groups shared the same weights. Classification accuracy was highest (55.0%) for the partially connected network, 51.1% for the fully connected network and 28.2% for the Gaussian classifier.
Speech processing using an auditory model and neural networks: A preprocessing comparison.
Authors: Anderson Timothy R.
Published: October 2005

A neural network that employs unsupervised learning was used on the output of a neurophysiologically based model of the auditory periphery [K. L. Payton, J. Acoust. Soc. Am. 83, 145–162 (1988)] to perform phoneme recognition [T. R. Anderson, J. Acoust. Soc. Am. Suppl. 1 87, S107 (1990)]. Continuous speech from ten speakers (three female and seven male) taken from the TIMIT database [W. Fisher, V. Zue, J. Bernstein, and D. Pallet, J. Acoust. Soc. Am. Suppl. 1 81, S92 (1987)] was processed through the auditory model and through an FFT based filter bank for this experiment. Each representation used a window length of 16 ms with an 8-ms overlap. The average firing rate of 20 channels from the auditory model and the FFT filter-bank output was used to train two separate Kohonen self-organizing feature maps. Results indicate that the auditory model performs significantly better than the FFT. However, the two representations make different types of broad class errors. Results in the form of average recognition, substitution, deletion, and insertion rates, codebook distortion, and codebook entropy, as well as broad class recognition rates, will be presented for each preprocessing method. [Work supported by AFOSR.]
Influence of an internal reference system and cross-modality matching the subjective rating of speech synthesizers.
Authors: Pavlovic Chaslav V. , Rossi Mario , Espesser Robert
Published: October 2005

In previous studies the present authors have concluded that contextual invariance and subject invariance of categorical and magnitude estimates of speech quality could be improved by introducing a reference system and by normalizing the results with respect to it. The reference signal used in the previous studies was natural speech. The use of such a reference system may present problems for applications where cross-language comparisons of synthesizers are made. In particular, this refers to the difficulty of ensuring equal subjective quality of different talkers in different languages. In this study the possibility of substituting an actual reference signal with an ‘‘internal’’ reference defined to the subject as the system of optimal quality is investigated. Another objective of this study is to explore whether the occasionally difficult task of free number production, required in magnitude estimations, could be replaced by cross-modality matches using lines of various lengths produced by subjects on a computer screen. The main concern here was related to the unknown effects of the limited width of the computer screen on the magnitude estimation task. [This research was made possible by Grant No. 2589 from the EEC Esprit SAM project.] a)Also at University of Iowa, Iowa City, IA.
Quantizing formants for speech compression using an auditory model.
Authors: Carnegie Dale , Holmes Geoff , Smith Lloyd
Published: October 2005

An auditory model has been implemented that produces as output an in synchrony bands spectrum (SBS) [O. Ghitza, IEEE Acoust. Speech Signal Process ASSP-35, 736–740 (1987)]. To reconstruct speech from this output it is necessary to use the amplitudes and phases of the input speech as determined by an FFT earlier in the process. The model dramatically reduces (by up to 70%) the number of frequency components in the signal. The data rate of the resulting speech is determined by the number of frequency components and the number of bits used to quantize the frequencies, amplitudes, and phases. Experiments are currently being run to determine the number of bits necessary to maintain intelligibility. This paper will report the results of these experiments.
Stochastic modeling of seafloor morphology.
Authors: Goff John A.
Published: October 2005

One of the basic requirements for modeling ocean bottom scattering and acoustic reverberation is a realistic quantitative description of the seafloor. Because of the small scales usually required (say ∼1 m or smaller) for such modeling, deterministic descriptions of the seafloor are often prohibitive. Fortunately, the gap between what is needed by acoustic modelers and what can be delivered by seafloor mappers can be narrowed or eliminated through the application of stochastic modeling. In the methodology presented here, the statistical characteristics of abyssal hill morphology (the predominant ocean bottom morphology) are modeled using parametrized forms of the topographic moments to order four. The first moment, or mean, is considered known and removable. The model for the second moment, or covariance function, contains parameters describing the rms height, characteristic length and width, azimuthal orientation, and fractal dimension. Parametrization of the third and fourth moments provides information regarding the vertical and lateral asymmetry and the degree of peakiness. The ability of the model to interpolate stochastic behavior to scales smaller than the instrument resolution is investigated using coregistered bathymetry from surface and deep-tow instruments.
Slowness-time spectra of backscattering using vertical arrays.
Authors: Baggeroer Arthur B. , Fricke J. Robert , Schmidt Henrik
Published: October 2005

Acoustic backscattering of 2-D reverberation from the seafloor was synthesized using both finite differences and a boundary integral element method. The seafloor was represented by a ‘‘single slice’’ from the Goff–Jordan Atlantic data set. The signals generated were for a vertical array with a low grazing angle source similar to the ones proposed for the ONR Acoustic Reverberation Special Research Program. Center frequencies up to 100 Hz have been simulated. Slowness-time spectra of the array data indicate that the backscattering is ‘‘discrete’’ where there are regions of relatively high levels associated with local slopes that dominate the data. [Work supported by ONR.]
Analytical evaluation of flush-mounted hydrophone array response to the Corcos turbulent wall pressure spectrum
Authors: Ko Sung H. , Nuttall Albert H.
Published: October 2005

An analytical development for determination of the frequency spectral density that gives the response of a hydrophone array mounted on a rigid surface to turbulent boundary layer pressure fluctuations is presented. Two approaches are given for the evaluation of the integral that represents the frequency spectral density. The first approach is the contour integral (residue method), and the second is the employment of Parseval’s theorem. Numerically integrated results compare favorably with the results calculated using the exact expressions presented here.
Acoustic interactions in arrays of spherical elastic shells
Authors: Scandrett C. L. , Canright D. R.
Published: October 2005

The acoustical performance of a submerged linear array of spherical transducers is examined by combining the T-matrix method of solving for multiple acoustic interactions among separate bodies with a model for transducers as thin spherical elastic shells. This approach solves the fully coupled problem of the response of the array to internal forcing. The results show that the assumptions giving rise to the Chebyshev criteria for optimal arrays of point sources appear to apply well even for large spheres at low frequencies. However, at frequencies near or above the lowest resonant frequency, the directional pattern may be degraded, depending on the material of the shells.
The robust design of active noise control systems based on relative stability measures
Authors: Tokhi Mohammad O. , Leitch Roy R.
Published: October 2005

This paper presents a design method for active noise control (ANC) systems operating in a three-dimensional nondispersive propagation medium based on an analysis of the relative stability of the inherent feedback loop. For practical systems the use of absolute stability is not useful; a system having an extremely long oscillatory response is unlikely to be accepted and would be liable to instability under small parameter variations. In this respect, a measure of the relative stability can provide a more acceptable design criterion. This procedure results in a robust design able to operate under changing operating conditions, with guaranteed system stability under stationary and slowly varying conditions. The frequency domain stability conditions are interpreted as spatial conditions on the geometry of the ANC system. Practical limitations in the design of the controller owing to the geometric configuration of the system are also discussed.
Piezoelectric modal sensor/actuator pairs for critical active damping vibration control
Authors: Lee C. -K. , Chiang W. -W. , O’Sullivan T. C.
Published: October 2005

Incorporating the piezoelectric effect into classical laminate plate theory, distributed sensors and actuators capable of sensing and controlling the modal vibration of a one-dimensional cantilever plate are derived theoretically and verified experimentally. It is shown that critical damping of a particular mode can be achieved using such a modal sensor/actuator combination as long as the vibrational amplitude of the controlled structure does not saturate the modal actuator. Since the sensor signal is proportional to the modal coordinate time derivative, velocity feedback control can be employed without using any element tuned to the resonant frequency in the feedback controller. Therefore, the sensitivity of the closed-loop performance and stability to resonant frequency variations is minimized. By eliminating electromagnetic interference and ground loop noise, critical damping is experimentally demonstrated for the first mode of a one-dimensional cantilever plate using PVF2 as the sensor/actuator material.
Symmetric multilayer structures and their use in the design and fabrication of Chebyshev acoustic antireflection coatings
Authors: Cheng Z. Y. , Martin B. G.
Published: October 2005

As discussed in a previous paper [B. G. Martin et al., J. Acoust. Soc. Am. 87, 193–200 (1990)], Chebyshev theory can be used in designing wideband acoustic multilayer antireflection (ar) coatings. For some situations, however, the required Chebyshev layer impedances may be difficult to match with commonly available materials. In such cases, the Chebyshev layer can be replaced by an acoustic symmetric multilayer (ASM) with equivalent properties. ASM dispersion effects, however, somewhat degrade the originally designed ar behavior. To explore this problem, an experimental investigation was made by using ASMs as layer replacements in the fabrication of Chebyshev ar coatings for normally incident ultrasonic waves. It is concluded from this investigation that the ar properties of the Chebyshev coating is only moderately degraded by the use of optimized ASM replacements.
A generalized impedance method for application of the parabolic approximation to underwater acoustics
Authors: Marcus Sherman W.
Published: October 2005

The parabolic equation (PE) has become an important computational tool for approximating underwater acoustic path losses in inhomogeneous environments. The numerical solution of this equation is performed on a grid over the propagation medium which includes the water column, and has also included a homogeneous ‘‘false bottom’’ below the actual ocean bottom. This situation is viewed as one in which the propagation medium can be divided into a horizontally inhomogeneous upper layer and a horizontally homogeneous lower layer. The pressure field in the latter layer is found using standard techniques valid for homogeneous media, and in the former layer is found using an implicit finite difference scheme. These fields and their normal derivatives are matched along the interface between the layers. The result is referred to as a generalized impedance boundary condition (GIBC), which serves to eliminate the need for a false bottom. Predictions obtained using the standard parabolic equation and a completely homogeneous bottom medium indicate improved numerical efficiency, and excellent agreement with other methods. The improved efficiency can be potentially significant for three-dimensional propagation problems.
Acoustic scattering from ocean microbubble plumes in the 100 Hz to 2 kHz region
Authors: Henyey Frank S.
Published: October 2005

The observed levels of high sea-state surface-related reverberation are modeled as scattering from plumes of microbubbles. The plume model is constrained as much as possible by existing microbubble data, particularly the average bubble content as a function of depth measured by Farmer and Vagle [J. Acoust. Soc. Am. 86, 1897–1908 (1989)]. The Chapman–Harris [J. Acoust. Soc. Am. 34, 1592–1597 (1962)] and Chapman–Scott [J. Acoust. Soc. Am. 36, 1735–1737 (1964)] experimental levels are fit with reasonable parameter choices. Frequency and grazing angle dependence are predicted by the model. Wind speed dependence is not addressed in this paper.
Acoustic backscatter cross sections for rough sea surface excited from above and below the air–water interface
Authors: Bahar Ezekiel
Published: October 2005

Acoustic backscatter cross sections (normalized scattered pressure intensities) are evaluated for rough seas using a unified full-wave approach that accounts for specular point scatter and Bragg scatter in a self-consistent manner. Thus the two-scale model of the sea surface is not used in these investigations. Different surface wind speeds are considered. The full-wave cross sections are shown to be significantly different for excitations from above or below the air–water interface. The full-wave solutions are compared with the corresponding physical-acoustic and small-perturbation solutions.
Summary of marine sedimentary shear modulus and acoustic speed profile results using a gravity wave inversion technique
Authors: Trevorrow Mark V. , Yamamoto Tokuo
Published: October 2005

Experimental techniques and inverse methods have been established to extract marine sediment shear modulus with depth profiles from measurements of wave-induced seabed motion on the shallow continental shelf. Seabed sediments are modeled as a quasistatic, incompressible, layered elastic medium in response to wave-induced pressures. An iterative eigenvalue expansion technique is used to extract the inverse. Under typical continental shelf conditions, this inversion method is found to have a depth resolution limit of approximately 3 m, with a maximum penetration of 200 m. Using semiempirical sediment models, it is possible to deduce sediment porosity, bulk density, and shear and compressional wave speeds from the shear modulus profile. One representative result from the New Jersey Shelf is examined in detail, and favorably compared with independent sediment profiling methods. A summary of experimentally determined sediment profiles from four other sites on the Eastern U.S. continental shelf is given.
Automatic extraction of spring-time Arctic ambient noise transients
Authors: Zakarauskas Pierre , Parfitt Carlton J. , Thorleifson Jon M.
Published: October 2005

A new nonparametric transient detecting and extracting algorithm is described that was used to extract transients automatically from ambient noise time series. The advantage of this peak-thresholding algorithm over the more usual power-thresholding algorithm is that the beginning and end of transients can be found precisely. This new algorithm was applied to three 5-min-long ambient noise samples taken under the Arctic pack ice during the month of April. The samples cover a wide range of ambient noise conditions. One was associated with thermal ice cracking, another one to distant lead formation events, while the third had extremely low ambient noise levels. The data were bandpass filtered in order to study the transient content at different frequencies and improve detection performances. It was found that the relative duration and power of transients within the time series varied greatly with frequency. During noise periods, transients accounted for only 5%–25% of the power around 10 Hz, and 45%–80% of the power between 100 and 1000 Hz. On the other hand, during quiet periods, transients accounted for 35%–45% of the power around 10 Hz, and 80%–95% of the power between 100 and 1000 Hz.
New approaches to nonlinear diffractive field propagation
Authors: Christopher P. Ted , Parker Kevin J.
Published: October 2005

In many domains of acoustic field propagation, such as medical ultrasound imaging, lithotripsy shock treatment, and underwater sonar, a realistic calculation of beam patterns requires treatment of the effects of diffraction from finite sources. Also, the mechanisms of loss and nonlinear effects within the medium are typically nonnegligible. The combination of diffraction, attenuation, and nonlinear effects has been treated by a number of formulations and numerical techniques. A novel model that incrementally propagates the fields of baffled planar sources with substeps that account for the physics of diffraction, attenuation, and nonlinearity is presented. The model accounts for the effects of refraction and reflection (but not multiple reflections) in the case of propagation through multiple, parallel layers of fluid medium. An implementation of the model for axis symmetric sources has been developed. In one substep of the implementation, a new discrete Hankel transform is used with spatial transform techniques to propagate the field over a short distance with diffraction and attenuation. In the other substep, the temporal frequency domain solution to Burgers’ equation is implemented to account for the nonlinear accretion and depletion of harmonics. This approach yields a computationally efficient procedure for calculating beam patterns from a baffled planar, axially symmetric source under conditions ranging from quasilinear through shock. The model is not restricted by the usual parabolic wave approximation and the field’s directionality is explicitly accounted for at each point. Useage of a harmonic-limiting scheme allows the model to propagate some previously intractable high-intensity nonlinear fields. Results of the model are shown to be in excellent agreement with measurements performed on the nonlinear field of an unfocused 2.25-MHz piston source, even in the near field where the established parabolic wave approximation model fails. Next, the model is used to compare the water path and in situ fields of a medical ultrasound device. Finally, the model is used to calculate the spatial heating rate associated with a nonlinear field and to simulate the phenomenon of saturation-induced beam broadening.
Signal enhancement with ‘‘Mach–Čerenkov’’ waves
Authors: Ben-Menahem Ari
Published: October 2005

A novel tool is introduced into acoustic and seismic exploration, the primary aim of which is to enhance the amplitudes of seismic signals interacting with material discontinuities and structural contrasts in sedimentary formations. This is achieved by creating a moving source with supershear or even superdilatational velocity, and recording the ensuing Mach waves on arrays of sensors. The theory shows that the spectral enhancement factor of a single sensor equals kΔ, where k=ω/C0 and Δ is the horizontal separation of the moving-source line and the sensor line. For Δ=120 ft, f=100 Hz, and C0=8000 ft/s, this factor is about 10. This ratio can be further increased by summing the output of a sensor array. A number of field experiments are suggested to test the theory.
New approaches to the linear propagation of acoustic fields
Authors: Christopher P. Ted , Parker Kevin J.
Published: October 2005

New algorithms are described that provide insight into linear field propagation and offer significant reductions in computational complexity. The developments presented here include the usage of a recently developed discrete Hankel transform to implement two single step, planar propagation algorithms for baffled, radially symmetric, acoustic pressure or velocity fields; an update on the single step approaches that reduce computational complexity through geometrically determined spatial frequency limitations; and algorithms for extending to multistep propagation. Two equivalent means of introducing arbitrary medium attenuation into the above schemes are presented. Finally, a planar boundary crossing algorithm that accounts for refraction and reflection (but not multiple reflections) is added to one of the multistep propagating algorithms. The resulting algorithm is then used to examine the differences between the corresponding fields of a focused piston source operating in water and in a layered fat/liver (biomedical imaging) medium. The results yield computationally efficient algorithms that can be used for linear propagation of focused or unfocused beams in attenuating, multilayer media, and also provide the basis for a novel nonlinear propagation algorithm.